Patent Publication Number: US-7917067-B2

Title: Magnetic field generating member and manufacturing method thereof, magnetic particle support body, image development device, process cartridge and image forming apparatus

Description:
PRIORITY CLAIM 
     This application claims priority from Japanese Patent Application No. 2008-000749, filed with the Japanese Patent Office on Jan. 7, 2008, the contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetic field generating member used in a copier, facsimile, printer or the like as well as a magnetic particle support body, an image development device, a process cartridge and an image forming apparatus. For example, the present invention relates to a magnetic particle support body that forms a toner image by image developing an electrostatic latent image on an electrostatic latent image support body using a developer agent constituted from toners and magnetic particles. The present invention also relates to a magnetic field generating member used in such a magnetic particle support body and an image development device that includes such a magnetic particle support body. In addition, the present invention relates to a process cartridge and an image forming apparatus having such an image development device. 
     2. Description of the Related Art 
     A variety of image development devices that form an image using a so called binary developer agent including toners and magnetic carriers (described as developer agent hereinbelow) are used in an image forming apparatus of a copier, a facsimile and a printer or the like. This kind of image development device delivers the developer agent to an image development area facing a photosensitive drum (that is, the electrostatic latent image support body) and includes an image development roller (that is, the magnetic particle support body) that forms a toner image by image developing the electrostatic latent image formed on the photosensitive drum using the delivered developer agent. 
     The image development roller includes a cylindrical shaped image development sleeve constituted from non-magnetic materials and a magnet roller (that is, the magnetic field generating member) held inside the image development sleeve that generates magnetic force so that the developer agent is spike erected on the surface of the image development sleeve. In the image development roller, magnetic carriers contained in the developer agent spike erect on the image development sleeve along the magnetic lines (magnetic force) generated by the magnet roller and toners become attached to the spike erected magnetic carriers, that is, the developer agent is spike erected. 
     In recent years, electronic copiers and printers are increasingly colorized. These color image forming apparatuses require an image development device generally corresponding to 4 colors (yellow, magenta, cyan and black). In order for these image forming apparatuses to become smaller sized, the image development device also needs to be down-sized, which naturally leads to the down-sizing of the image development roller used in the image development device. 
     A smaller sized image development roller is realized by a magnet roller of a smaller diameter. However, when the diameter of the magnet roller becomes smaller, the volume of the magnet is reduced and magnetic force generated by the magnet roller is impaired. Therefore, when image development is performed using an image development roller with the magnet roller of a smaller diameter, deteriorations in quality of development images become problematic. Propositions to solve this problem are made in JP 2000-243620A. 
     The main body part of a magnet roller proposed in JP 2000-243620A includes a cylindrical column-like shaped ferrite resin magnetic body and a rare-earth resin magnetized body fixed in a concave groove disposed along an axial direction of the cylindrical column-like body in the external circumference surface of the cylindrical column-like body. The main body part of this magnet roller is shaped by magnetic materials and includes the rare-earth resin magnetized body having high magnetic force so that a magnet roller of small diameter but high magnetic force can be obtained. 
     However, the main body part (including the axial part) of the magnet roller proposed in JP 2000-243620A is shaped by a ferrite resin magnetic body of an inferior strength. Furthermore, the concave groove is disposed in the external circumference surface of the main body part. Therefore, stiffness of the magnet roller becomes insufficient and the magnet roller is subject to easy flexure. Thereby deformation due to time lapse or warpage and deflection of the magnet roller or the like is inevitably generated at times. Therefore, magnetic force on the surface of the image development roller becomes non-uniform during image development operations so that irregularities are generated to the spike erections of the developer agent and quality of development images deteriorates problematically. 
     In addition, because of the flexure of the magnet roller due to insufficient stiffness, there is a possibility that the rare-earth resin magnetized body fixed to the magnet roller might be bent and damaged so that during usage of the magnet roller, malfunction of the image development device or the like is triggered and during storage of the magnet roller, defective products are yielded despite their not even being in-use. Therefore, reliability and product quality deteriorates problematically. 
     SUMMARY OF THE INVENTION 
     The present invention is made to solve the above-described problems. An object of the present invention is to provide a magnetic field generating member of high stiffness and small size, an image development device including such a magnetic field generating member, a process cartridge and an image forming apparatus as well as the manufacturing method of the magnetic field generating member. 
     To accomplish the above object, the present invention includes a magnetic field generating member having a cylindrical column-like shaped main body part, a groove of the main body part with a rectangular shaped cross-sectional surface disposed in the external circumference surface of the cylindrical column-like shaped main body part along an axial direction and a long magnetic compact fixed in the groove of the main body part in which an interposition member with a “U” character shaped cross-sectional surface is fixed in the groove of the main body part and the long magnetic compact is fixed in the concave portion of the interposition member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an enlarged cross-sectional diagram (along the II-II line of  FIG. 18 ) that illustrates a first embodiment of a magnet roller according to the present invention. 
         FIG. 2  is a cross-sectional diagram that illustrates an assembly method of the magnet roller of  FIG. 1 . 
         FIG. 3  is a diagram that illustrates an oriented direction of magnetic anisotropy in a main body part of the magnet roller of  FIG. 1 . 
         FIG. 4  is a diagram that illustrates in a frame format the strength of the magnetic force on the external surface of the magnet roller of  FIG. 1 . 
         FIG. 5  is a cross-sectional diagram that illustrates an approximate structure of a metal mold that shapes the main body part of the magnet roller of  FIG. 1 . 
         FIG. 6  is an enlarged cross-sectional diagram that illustrates a second embodiment of the magnet roller according to the present invention. 
         FIG. 7  is a cross-sectional diagram that illustrates an assembly method of the magnet roller of  FIG. 6 . 
         FIG. 8  is an enlarged cross-sectional diagram that illustrates a third embodiment of the magnet roller according to the present invention. 
         FIG. 9  is a cross-sectional diagram that illustrates an assembly method of the magnet roller of  FIG. 8 . 
         FIG. 10  is a cross-sectional diagram that illustrates a first shape of an interposition member in the magnet roller of  FIG. 8 . 
         FIG. 11  is a cross-sectional diagram that illustrates a second shape of the interposition member in the magnet roller of  FIG. 8 . 
         FIG. 12  is a cross-sectional diagram that illustrates a third shape of the interposition member in the magnet roller of  FIG. 8 . 
         FIG. 13  is a cross-sectional diagram that illustrates a fourth shape of the interposition member in the magnet roller of  FIG. 8 . 
         FIG. 14  is a cross-sectional diagram that illustrates an approximate structure of a metal mold that shapes the main body part of the magnet roller of  FIG. 8 . 
         FIG. 15  is a cross-sectional diagram that illustrates a first part of the approximate operations of when the metal mold of  FIG. 14  is detached from the mold. 
         FIG. 16  is a cross-sectional diagram that illustrates a second part of the approximate operations of when the metal mold of  FIG. 14  is detached from the mold. 
         FIG. 17  is a cross-sectional diagram of magnetic carriers contained in a developer agent. 
         FIG. 18  is a cross-sectional diagram that illustrates an embodiment of an image development roller according to the present invention. 
         FIG. 19  is a cross-sectional diagram that illustrates an embodiment of a process cartridge and an image development device according to the present invention. 
         FIG. 20  is a cross-sectional diagram that illustrates an embodiment of an image forming apparatus according to the present invention. 
         FIG. 21  is a graph that illustrates a relationship between the amount of displacement (flexure amount) and load against the magnet roller. 
         FIG. 22  is a graph that illustrates a relationship between the deflection variation ratio and storage time of the magnet roller. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A First Embodiment of a Magnetic Field Generating Member 
       FIG. 1  is an enlarged cross-sectional diagram that illustrates a first embodiment of a magnet roller according to the present invention.  FIG. 2  is a cross-sectional diagram that illustrates an assembly method of the magnet roller of  FIG. 1 .  FIG. 3  is a diagram that illustrates an oriented direction of magnetic anisotropy in a main body part of the magnet roller of  FIG. 1 .  FIG. 4  is a diagram that illustrates in a frame format the strength of the magnetic force on the external surface of the magnet roller of  FIG. 1 .  FIG. 5  is a cross-sectional diagram that illustrates an approximate structure of a metal mold that shapes the main body part of the magnet roller of  FIG. 1 . 
     A magnet roller  133 A of the present embodiment includes a cylindrical image development sleeve  132  (illustrated in  FIG. 18 ) shaped so that the magnet roller  133 A becomes an internal capsule and an image development roller  115  as a magnetic particle support body. The magnet roller  133 A is a magnetic field generating member that generates magnetic force on an external surface of the image development roller  115  to support a so called binary developer agent (described as developer agent hereinbelow) including toners and magnetic carriers  135  (illustrated in  FIG. 17 ). 
     The magnet roller  133 A, as illustrated in  FIG. 1 , includes a main body part (main body)  140 , an interposition member  142  and a magnetic member, for example, a rare earth magnet block  141  as a long magnetic compact. 
     The main body part  140  is shaped into a cylindrical column-like body using magnetic materials. The so-called plastic magnet or rubber magnet that mixes magnetic powders with high polymer compounds can be used as the magnetic materials. Sr ferrite or Ba ferrite is used as the magnetic powders. PA (polyamide) series materials of 6 PA or 12 PA or the like, ethylene series compounds of EEA (ethylene ethyl copolymer) or EVA (ethylene vinyl copolymer) or the like, chlorine series materials of CPE (chlorinated polyethylene) or the like and rubber materials of NBR or the like can be used as the high polymer compounds. A linear main body groove  144  is disposed along the longitudinal direction on the external surface of the main body part  140 . In addition, an axial part protruding from both end surfaces of the main body part  140  in the same axial direction is shaped in integration. In addition, in the main body part  140 , a portion of the cylindrical column-like body can be cut along the axial direction so that a portion of the external surface is in plane shape. 
     The main body groove  144  is equal to the groove provided in the main body described in the claims. A cross-section (lateral cross-section) of the main body groove  144  orthogonal to the axial direction of the main body part  140  is concave and approximately rectangular shaped in the external circumference surface of the main body part  140 . The main body groove  144  is extended linearly along the longitudinal direction of the main body part  140  and disposed across the whole length of the main body part  140 . In addition, the main body groove  144  is disposed to oppose a later-described photosensitive drum  108  (that is, in a position of an image development magnetic pole) when the magnet roller  133 A is incorporated into a later-described image development device  113  (illustrated in  FIG. 19 ). 
     The main body groove  144 , as illustrated in  FIG. 2 , includes a pair of side surfaces  1441  and a bottom surface  1442 . 
     The pair of side surfaces  1441  respectively include a pair of straight surfaces  1441   a  and a pair of tapered surfaces  1441   b  disposed thereof. 
     The pair of straight surfaces  1441   a  are rectangular plane surface parts disposed mutually parallel and mutually opposed in the vicinity of an opening part of the main body groove  144  along the longitudinal direction and orthogonal to the width direction of the opening part. The width (short side direction) of the pair of straight surfaces  1441   a  has differing adequate values according to the shape of the groove. If the width of the straight surface  1441   a  is too short, sufficient effects that prevent the drop off of the interposition member  142  can not be obtained. In addition, if the width of the straight surface  1441   a  is too long, a placed piece  148  ( FIG. 5 ) that constitutes the metal mold for shaping the main body groove  144  can not be pulled out from the main body part  140  during shaping of the main body part  140 . 
     The pair of tapered surfaces  1441   b  are rectangular plane surface parts shaped so that mutual intervals between the pair  1441   b  gradually narrow from lower ends of the straight surfaces  1441   a  (long sides) towards a bottom surface  1442  the closer to the bottom surface  1442 . The pair of tapered surfaces  1441   b  is shaped to form an angle against the pair of straight surfaces  1441   a  with a direction in which the two come mutually closer by 3 to 10 degrees (that is, an angle, tapered angle hereinbelow, against a direction orthogonal to the width direction of the opening part of the main body groove  140 ). The pair of tapered surfaces  1441   b  are constituted so that the above-described placed piece  148  of the metal mold can be easily pulled out. 
     Each of the long sides of the pair of tapered surfaces  1441   b  is respectively connected to the bottom surface  1442 . The bottom surface  1442  is shaped parallel to the width direction of the opening part of the main body groove  144 . The width L 2  of the bottom surface  1442  is shaped to be narrower than the width L 1  of the opening part of the main body groove  144 . Depth from the opening part of the main body groove  144  to the bottom surface  1442  (that is, depth of the main body groove  144 ) is determined according to specific constitutions but if the depth is too shallow, the height (the length of the short side direction) of a pair of wall sections  1421  of the later described interposition member  142  becomes insufficient. Therefore, stiffening effects by the interposition member  142  cannot be obtained sufficiently. 
     The main body part  140  uses a metal mold of a structure illustrated in  FIG. 5  and is manufactured by injection and magnetic field molding. The metal mold shapes the main body part  140 . The main body groove  144  is shaped by disposing the placed piece  148  at the position of the metal mold. In order for the placed piece  148  to be detached (pulled out) easily from the main body part  140 , a so-called pull out gradient (tapered angle) of about 3 to 10 degrees is applied. The pair of tapered surfaces  1441   b  is tapered shaped due to the pull out gradient. Desired shapes of the main body groove can be obtained according to the shape of the placed piece  148 . 
     When injection molding of the main body part  140  is complete, a nesting  150 A and a nesting  150 B of the fixed side do not move. A nesting  150 C and a nesting  150 D of the movable side together with the placed piece  148 , the EJ (ejection) pin  149  and the main body part  140  move in the right direction inside  FIG. 5  (mold opening). Next, the EJ pin  149  pushes out the main body part  140  and the placed piece  148  (eject). Next, the placed piece  148  is detached from the main body part  140  so that the main body part  140  can be obtained. 
     An orientated direction  143  of magnetic field (magnetic anisotropy) of the main body part  140 , as illustrated in  FIG. 3 , in the case of one direction, is approximately parallel to the bottom surface  1442  of the main body groove  144  and approximately orthogonal to the axial direction. In the case of 4 equally divided poles also, one direction should desirably be parallel to the bottom surface  1442  of the main body groove  144  and orthogonal to the axial direction, but it is not limited to such. 
     The interposition member  142  is obtained by shaping general plastic materials. The interposition member  142  can be also obtained by applying bending work to metal materials. Non-magnetic materials should be preferably used for either the plastic materials or the metal materials used for the interposition member  142 . The rare earth magnet block  141  as the internal capsule has magnetic poles. When the interposition member  142  using non-magnetic materials is fixed in the main body groove  144 , with regard to the magnetic poles, peak magnetic flux density on the external surface of the main body part  140  becomes higher so that the attachment of a magnetic carrier  135  contained in the developer agent becomes advantageous. 
     In order to improve stiffness property of the magnet roller  133 A by the interposition member  142 , usage of the metal materials is comparatively advantageous. Within non-magnetic metal materials, spring materials of SUS301 are further advantageous from the viewpoints of property and cost. Within spring materials of SUS301, ½H (more than 310 HV) or ¾H (more than 370 HV) or H (more than 430 HV) or EH (more than 490 HV) is further desirable but the higher the hardness, the easier a crack can be generated to bent sections or the like during bending work so that attention is necessary. 
     The interposition member  142  is shaped to the same length as the main body groove  144 . A cross-section of the short side direction of the interposition member  142  (that is, lateral cross section) is “U” character shaped. The interposition member  142  includes a floor part  1422  and a pair of wall sections  1421 . The rare earth magnet block  141  is fixed in a concave portion  1423  of the interposition member  142  by press-fitting. In addition, the concave portion  1423  is shaped by the floor part  1422  and the pair of wall sections  1421 . The concave portion  1423  is equal to the concave portion of an interposition member described in the claims. 
     The floor part  1422  is a rectangular flat plate shaped so that its width (short side direction) matches with the width of the bottom surface  1442  of the main body groove  144  so that the two widths cross over. The floor part  1422  is disposed so that when the interposition member  142  is fixed in the main body groove  144  by press-fitting, its lower surface  1422   b  comes into contact with the bottom surface  1442 . 
     The pair of wall sections  1421  is rectangular flat plates disposed uprightly and forming two approximate right angles. The angles are formed from a pair of mutually opposing long sides of the floor part  1422  against the floor part  1422 . The length (that is, height) from an upper end  1421   a  to a lower end  1421   b  of the pair of wall sections  1421  is preferably shaped to equal the width of the tapered surface  1441   b  of the main body groove  144 . When the interposition member  142  is press-fitted into the main body groove  144 , an external surface  1421   c  of the pair of wall sections  1421  comes into contact with the tapered surface  1441   b  and the upper end  1421   a  is positioned in a boundary  1441   c  between the straight surface  1441   a  and the tapered surface  1441   b . Thereby the upper end  1421   a  is caught in the boundary  1441   c  (that is, the straight surface  1441   a ) so that drop off of the interposition member  142  from the main body groove  144  can be prevented. 
     The thickness of the floor part  1422  and the pair of wall sections  1421  of the interposition member  142  has differing adequate values according to the shape of the main body part. The floor part  1422  and the pair of wall sections  1421  should be advantageously thickened in order to improve stiffness property. But desired magnetic forces (for example, the Ba illustrated in  FIG. 4 ) by the rare earth magnetic block  141  become difficult to obtain if the floor part  1422  and the pair of wall sections  1421  become too thick. 
     The rare earth magnetic block  141  is equal to a long magnetic compact described in the claims and has the same length as the interposition member  142 . A cross-section (lateral cross-section) of the short side direction of the rare earth magnet block  141  is rectangular shaped fitting into the shape of the cross-section of the concave portion  1423  of the interposition member  142 . The rare earth magnetic block  141  as a whole is in the shape of a long rod and is fixed in the concave portion  1423  of the interposition member  142  by press-fitting. Then the rare earth magnetic block  141 , together with the interposition member  142 , is fixed in the main body groove  144  by press-fitting. Thereafter the main body part  140  (that is, the image development roller  115 ) is disposed so that the rare earth magnet block  141  and the photosensitive drum  108  mutually oppose. The rare earth magnet block  141  forms an image development magnetic pole and generates magnetic forces on the external surface of the image development sleeve  132 , that is, the image development roller  115  so that a magnetic field is formed between the image development sleeve  132  and the photosensitive drum  108 . The rare earth magnet block  141  forms magnetic brushes by the magnetic field so that toners of the developer agent adsorbed to the external surface of the image development sleeve  132  are transferred to the photosensitive drum  108 . In such a way, the rare earth magnet block  141  forms on the external surface of the image development sleeve  132  an image development area  131  ( FIG. 19 ) that transfers the toners of the developer agent attached to the above-described external surface of the image development sleeve  132  to the photosensitive drum  108 . 
     Magnetic particles are constituted from a rare earth magnetic body. A magnet compound including magnetic powders constituted from the magnetic particles is filled into the pressed metal mold inside a magnetic field and compression molded to obtain the rare earth magnet block  141 . In compression molding, only a small quantity of binding resin is necessary for possible molding so that the compounding ratio of magnetic powders can be heightened. In addition, the molding density of the rare earth magnet block  141  can be heightened by the compression molding so that the compression molding is an excellent method for obtaining higher magnetic force. However, because the quantity of the binding resin is small, there is a tendency for a lack of strength. 
     The magnet compound used for compression molding is constituted from minute resin particles having thermal plasticity as well as rounded off magnetic powders of an average particle diameter of 80 to 150 μm and a powder density of 3.3 g/cm 3  to 4.0 g/cm 3 . The compression molded magnet compound is heated thereafter so that binding forces with the magnetic powders increases because the minute resin particles having thermal plasticity are melted-through. 
     The compounding ratio of the magnetic powders in the magnet compound is preferably 90 to 99 wt % and further preferably, 92 to 97 wt %. If contained amount of the magnetic powders is too small, improvement of magnetic property cannot be realized. In addition, if the contained amount of the magnetic powders is too great, the contained amount of the binding resin becomes small so that moldability of the magnet block deteriorates (generation of cracks or the like). 
     The rare earth magnet block  141  can also be obtained by injection molding the magnet compound inside a magnetic field. The quantity of binding resins needed for the injection molding is more than that of the compression molding so that the compounding ratio of magnetic powders becomes difficult to be heightened. In addition, the magnetic force of the magnetic powders including a rare earth element is reduced by heat because the binding resins are melted-through at a high temperature. Therefore, injection molding is inferior to compression molding from a viewpoint of obtaining a high magnetic force. However, since the quantity of the binding resins is large and the binding resins are solidified after melt-through, the binding force is strong. Therefore, injection molding is an excellent method for increasing strength. 
     The injection molded magnet compound is constituted from thermal plastic resins as well as rounded off magnetic powders of an average particle diameter of 80 to 150 μm and a powder density of 3.3 g/cm 3  to 4.0 g/cm 3 . In the injection molding, magnetic powders including rare earth element are shaped in a dispersed state within melted-through thermal plastic resins and cooled for solidifying. Therefore, a rare earth magnet block of a higher strength than that by compression molding can be obtained. 
     The compounding ratio of the magnetic powders in the magnet compound is preferably 80 to 95 wt % and further preferably, 87 to 93 wt %. If the amount of the magnetic powders contained is too small, no improvement in the magnetic property can be realized. In addition, if the amount of the magnetic powders contained is too great, the fluidity decreases and injection molding becomes difficult. 
     The magnetic powders are constituted from magnetic particles. The magnetic particles are constituted from rare earth magnetic bodies capable of realizing a high magnetic force (more than 13 MGOe). The rare earth magnetic bodies are preferably the following (i) to (iii) constituted from alloy including rare earth elements and transition metals, but most preferably, the following (i). 
     (i) An alloy with B and transition metals of mainly R (however, R is at least one kind of rare earth element including Y) and Fe as the basic components (the so-called R—Fe—B series alloy). Representative alloys of this kind are Nd—Fe—B series alloy, Pr—Fe—B series alloy, Nd—Pr—Fe—B series alloy, Ce—Nd—Fe—B series alloy, Ce—Pr—Nd—Fe—B series alloy, as well as other alloys substituting a portion of the Fe within these alloys to other transition metals of Co and Ni or the like. 
     (ii) An alloy with rare earth elements of mainly Sm and transition metals of mainly Co as the basic components (the so-called Sm—Co series alloy). SmCo5 and Sm2TM17 (TM is a transition metal) can be cited as representative alloys of this kind. 
     (iii) An alloy with rare earth elements of mainly Sm, transition metals of mainly Fe and interstitial elements of mainly N as the basic components (the so-called Sm—Fe—N series alloy). Sm2Fe17N3 prepared by azotizing Sm2TM17 alloy can be cited as a representative alloy of this kind. 
     Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and misch metal or the like can be included as the rare earth elements. One kind or two kinds or more of these rare earth elements can be included in the alloy. In addition, Fe, Co and Ni or the like can be included as the transition metals. One kind or two kinds or more of these transition metals can be included in the alloy. In addition, in order to improve the magnetic property, B, Al, Mo, Cu, Ga, Si, Ti, Ta, Zr, Hf, Ag and Zn or the like can be included in the alloy as magnetic powders according to necessity. 
     The average particle diameter of a volume of magnetic particles that constitutes the magnetic powders is preferably 80 to 150 μm and further preferably, 90 to 140 μm. The average particle diameter is measured by a DRY unit of a Mastersizer 2000 made by Sysmex Corp. 
     The average particle diameter of the minute resin particles having thermal plasticity is preferably not over one tenth ( 1/10) of the average particle diameter of the magnetic particles of the magnetic powder. As stated above, the average particle diameter in such a way is not over one tenth ( 1/10) of the magnetic particles of the magnetic powders. Therefore, the molding density of the magnet compact can possibly be heightened and the magnetic property can be improved. 
     The minute resin particles having thermal plasticity are preferably minute particles of a spherical shape manufactured by an emulsion polymerization method or a suspension polymerization method. As stated above, the minute resin particles of thermal plasticity in such a way are spherical shaped minute particles manufactured by the emulsion polymerization method or the suspension polymerization method. Therefore, a compression molded product of high density can possibly be obtained. Thereby the magnetic property can be further improved. In addition, when spherical minute particles as such are used, areas covering the magnetic powders are improvingly increased so that areas in which the magnetic powders are exposed on the surface of the magnet compact can be decreased and effects that prevent corrosion are generated. 
     For example, styrene series compounds of polystyrene, polychloroethylene and polyvinyltoluene or the like and mono-polymers constituted from their substitution products as well as styrene series copolymers of styrene-p-chlorostyrene, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-methyl chlormethacrylate copolymer, styrene-acrylic nitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylic nitrile-indene copolymer, styrene-maleic acid copolymer and styrene-maleic acid ester copolymer or the like can be cited as the thermal plastic resin that constitutes the minute resin particles of thermal plasticity. In addition, the thermal plastic resin can be resins of polymethylmethacrylate, polybutylmethacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyvinyl butyl butyral, polyacrylate resin, rosin, denatured rosin, terpene resin, phenol resin and epoxy-polyol series resin or the like. One kind of these resins can be used. In addition, two kinds or more of these resins can be mixed for usage. 
     The minute resin particles having thermal plasticity, as described above, are used as the binding resin (binder). For example, a charged control agent (CCA), a colorant and a material of low softening point (wax) are dispersed in and mixed with the thermal plastic resins of polyester, polyol or the like. Materials of silica, oxidized titanium or the like are added externally as an external addition agent to the periphery thereof so that fluidity is heightened. The added quantity of the colorant is 1 to 20 wt % and preferably, 5 to 10 wt %. The charged control agent is added to improve dispersing quality of magnet particles and the minute resin particles having thermal plasticity. The added quantity of the charged control agent is 1 to 20 wt % and preferably, 0.5 to 10 wt %. A mold release agent is added to improve mold release properties after molding. The added quantity of the mold release agent is 1 to 20 wt % and preferably, 2 to 10 wt %. The minute resin particles  153  having thermal plasticity are excellent in fluidity and easily charged to negative. Therefore, the minute resin particles  153  having thermal plasticity have superior electrostatic attachment force with the magnetic powders so that gaps between the magnet particles can be filled sufficiently. 
     For example, oxidized aluminum, oxidized titanium, strontium titanate, oxidized cerium, magnesium oxide, chrome oxide, tin oxide, metal oxide of zinc oxide or the like, nitride of silicon nitride or the like, carbide of silicon carbide or the like, calcium sulfate, barium sulfate, metallic salt of calcium carbonate or the like, fatty acid metal salt of zinc stearate, calcium stearate or the like, carbon black and silica can be cited as the external addition agent for the minute resin particles having thermal plasticity. Particle diameter of the external addition agent is normally in a range of 0.1 to 1.5 μm. If the quantity before addition of the external addition agent is 100 parts by weight, the added quantity of the external addition agent is preferably 0.01 to 10 parts by weight and further preferably 0.05 to 5 parts by weight. These external addition agents can be used singly or in combination of two or more. In addition, these external addition agents are preferably applied hydrophobized processing. 
     For example carbon black, lampblack, magnetite, titan black, chrome yellow, ultramarine blue, aniline blue, phthalocyanine blue, phthalocyanine green, hansa yellow G, rhodamine 6G, chalco oil blue, quinacridone, benzidine yellow, rose bengal, malachite green lake, quinoline yellow, C.I. Pigment Red 48:1, C.I. Pigment Red 122, C.I. Pigment Red 57:1, C.I. Pigment Red 184, C.I. Pigment Yellow 12, C.I. Pigment Yellow 17, C.I. Pigment Yellow 97, C.I. Pigment Yellow 180, C.I. Solvent Yellow 162, C.I. Pigment Blue 5:1, C.I. Pigment Blue 15:3 and carmine or the like can be cited as the colorant. 
     In addition, the material having low softening point can be added internally to the internal parts of the minute resin particles having thermal plasticity. Paraffin wax, polyolefin wax, Fischer-Tropsch wax, amide wax, higher fatty acid, ester wax and derivative of these or graft/block compound of these can be cited as the materials of low softening point as such. In the case the material having low softening point as such is added, about 5 to 30 mass % should preferably be added. 
     The rare earth magnet block  141  has a maximum magnetic flux density of 100 to 130 mT and therefore, higher magnetic force (13 to 16 MGOe) than a conventional plastic magnet having a maximum magnetic flux density of 80 to 120 mT. The rare earth magnet block  141  can be press-fitted into the concave portion  1423  of the interposition member after magnetization or alternatively, magnetized after being press-fitted into the concave portion  1423  of the interposition member. In addition, in the present embodiment, the magnet block used includes rare earth elements but the materials used for the magnet block are not limited to such and can be randomly selected if the necessary magnetic force can be obtained. 
     A plurality of fixed magnetic poles that generates magnetic force (illustrated in a frame format in  FIG. 4  and includes the rare earth magnet block  141  as the image development magnetic pole with other components not illustrated) are disposed in the magnet roller  133 A. Line B illustrated in  FIG. 4  shows in a frame format the size of the magnetic forces (magnetic flux density) generated by each magnetic pole. The magnetic forces head towards normal directions in the external circumference surface of the magnet roller  133 A.  FIG. 4  illustrates that the farther the line B is away from the external surface of the magnet roller  133 A, the larger the magnetic force. In particular, line Ba illustrates the size of the magnetic force (magnetic flux density) generated by the rare earth magnet block  141 . 
     Fixed magnetic poles disposed in the magnet roller  133 A except the image development magnetic pole are formed with a portion of the main body part  140  corrected to north pole (N) or south pole (S). Fixed magnetic poles are extended along the longitudinal direction of the magnet roller  133 A and disposed across the whole length of the magnet roller  133 A. 
     The image development device  113  includes a stirring screw  118 . One of the fixed magnetic poles is disposed opposed to the stirring screw  118 . The one fixed magnetic pole forms a pumping magnetic pole and generates magnetic force on the external surface of the image development sleeve  132 , that is, the image development roller  115  so that the developer agent is adsorbed to the external surface of the image development sleeve  132 . 
     At least one fixed magnetic pole is disposed between the above described pumping magnetic pole and the main body groove  144 . The at least one fixed magnetic pole generates magnetic force on the external surface of the image development sleeve  132 , that is, the image development roller  115  and delivers the before image development developer agent towards the photosensitive drum  108 . 
     These fixed magnetic poles generate magnetic forces on the external surface of the image development sleeve  132 . Then magnetic carriers  135  contained in the developer agent mutually overlap along magnetic lines generated by the fixed magnetic poles and are arranged in an erect manner (spike erect) on the external surface of the image development sleeve  132 . As just described, the state in which a plurality of magnetic carriers  135  overlap along the magnetic lines and are arranged in an erect manner on the external surface of the image development sleeve  132  is termed the magnetic carriers  135  spike erects on the external surface of the image development sleeve  132 . Then, the above-described toners are adsorbed to the spike erected magnetic carriers  135 . That is, the image development sleeve  132  adsorbs the developer agent to its external surface by the magnetic force of the magnet roller  133 A. 
     In addition, an agent severance pole (not illustrated) that weakens the magnetic force generated on the external surface of the image development roller  115  so that the developer agent drops off from the external surface of the image development roller  115  is disposed in the magnet roller  133 A at an approximately opposed position against the above-described image development magnetic pole. The agent severance pole is extended along the longitudinal direction of the magnet roller  133 A and disposed across the whole length of the magnet roller  133 A. 
     Next, an assembly method of the magnet roller  133 A is described. First, the rare earth magnet block  141  is press-fitted into the concave portion  1423  of the interposition member  142  in a direction of an arrow R 1  of  FIG. 2  to be fixed thereof. At this moment, a bottom surface  141   b  and side surfaces  141   c  of the rare earth magnet block  141  are press-fitted to respectively come into contact with an upper surface  1422   a  and inner surfaces  1421   d  of the interposition member  142 . 
     Next, the interposition member  142  press-fitted with the rare earth magnet block  141  is press-fitted into the main body groove  144  in a direction of an arrow R 2  of  FIG. 2  to be fixed thereof. At this moment, the press-fitting is performed so that the lower surface  1422   b  of the interposition member  142  comes into contact with the bottom surface  1442  of the main body groove  144  and the external surface  1421   c  of the interposition member  142  comes into contact with the tapered surface  1441   b  of the main body groove  144  and furthermore, the upper end  1421   a  of the pair of wall sections  1421  of the interposition member  142  is positioned in a boundary  1441   c  of the main body groove  144 . 
     Finally, fixed magnetic poles necessary for the image development roller  115  are magnetized by an electromagnet type magnetizing yoke. Thereby the magnet roller  133 A is completed. In addition, in the present embodiment, each member is press-fitted to be fixed but it is not limited to such. For example, each member can be mutually fixed using an adhesive agent. 
     In the above-described assembly method (manufacturing method) of the magnet roller  133 A, the interposition member  142  is press-fitted into the main body groove  144  after the rare earth magnet block  141  is press-fitted into the concave portion  1423  of the interposition member  142  so that the rare earth magnet block  141  is reinforced by the interposition member  142 . Therefore, bending and damages generated when the rare earth magnet block  141  is press-fitted into the main body groove  144  can be prevented. Consequently, the assembly workability of the magnet roller  133 A and the yield ratio of the rare earth magnet block  141  can be improved so that productivity can be heightened. 
     In addition, in  FIG. 1 , there seemingly is a gap between the rare earth magnet block  141  and the interposition member  142  but actually, only an extremely minute gap exists between the two members. 
     In addition, in the present embodiment, the main body part  140  is shaped to have an external diameter of 8.5 mm and an overall length of 313 mm. The main body groove  144  is shaped to have a length of 313 mm. In the main body groove, the bottom surface  1442  is shaped to have a width of 2.7 mm, the pair of straight surfaces  1441   a  in the pair of side surfaces  1441  is shaped to have a width of 0.17 mm and the pair of tapered surfaces  1441   b  in the pair of side surfaces  1441  is shaped to have a width of 2.2 mm. The tapered surfaces are shaped to have a 5 degree angle against the straight surfaces. In addition, the interposition member  142  is shaped to have a length of 313 mm and a thickness of 0.3 mm. In the interposition member  142 , the width of the floor part  1422  is shaped to 2.6 mm and the height of the pair of wall sections  1421  is shaped to 2.3 mm. The pair of wall sections  1421  is shaped to have a 95 degree angle against the floor part  1422 . The rare earth magnet block  141  is shaped to have a width of 2.0 mm, a height of 2.4 mm and a length of 313 mm. Each of these dimensions is only an example and can be adequately determined according to constitutions or the like. 
     As described above, according to the present invention, the interposition member  142  with a “U” character shaped cross-sectional surface is fixed in the main body groove  144  of the cylindrical column-like shaped main body part  140 . The rare earth magnet block  141  is fixed to the concave portion  1423  of the interposition member  142  so that the main body part  140  is reinforced by the interposition member  142  and stiffness property of the main body part  140  can be heightened. Therefore, even in the case the main body part  140  is shifted to a smaller diameter (that is, smaller size), the stiffness property of the main body part  140  can be secured. Consequently, the magnet roller  133 A can be provided with heightened stiffness property and smaller size. 
     In addition, the interposition member  142  is fixed in the main body groove  144  by press-fitting so that it is not necessary to use an adhesive agent for the fixture of the two members. Therefore, the interposition member  142  can be detached easily from the main body groove  144 . Consequently, reuse of the interposition member  142  becomes possible and the magnet roller  133 A can be provided at a cheap price. In addition, because an adhesive agent is not used for the fixture of the interposition member  142  and the main body groove  144 , positional displacements of these members generated by the thickness of the adhesive agent or due to the drying of the adhesive agent can be avoided. Therefore, high precision assembly is possible. 
     In addition, the rare earth magnet block  141  is fixed in the concave portion  1423  of the interposition member  142  by press-fitting so that it is not necessary to use an adhesive agent for the fixture of the two members. Therefore, the rare earth magnet block  141  can be detached easily from the interposition member  142 . Consequently, reuse of the expensive rare earth magnet block  141  becomes possible and the magnet roller  133 A can be provided at a cheap price. In addition, because an adhesive agent is not used for the fixture of the interposition member  142  and the rare earth magnet block  141 , positional displacements of these members generated by the thickness of the adhesive agent or due to the drying of the adhesive agent can be avoided. Therefore, high precision assembly is possible. 
     In addition, the pair of side surfaces  1441  of the main body groove  144  includes the pair of straight surfaces  1441   a  shaped mutually parallel in the vicinity of the opening part of the main body groove  144  and the pair of tapered surfaces  1441   b  shaped so that mutual intervals between the pair  1441   b  gradually narrow from lower ends of the straight surfaces  1441   a  towards the bottom surface  1442  the closer to the bottom surface  1442 . Therefore, when the interposition member  142  is press-fitted into the main body groove  144 , the pair of straight surfaces  1441   a  serves as stoppers and drop off of the interposition member  142  from the main body groove  144  can be prevented. The image development device or the like breaks down due to the drop off of the interposition member  142 . Consequently, the magnet roller  133 A with high reliability that can prevent such breakdowns is provided. 
     In addition, an external surface  1421   c  of the pair of wall sections  1421  in the interposition member  142  respectively comes into close contact with the pair of tapered surfaces  1441   b  in the main body groove  144 . The upper end  1421   a  of the pair of wall sections  1421  is respectively shaped to be positioned in the boundary  1441   c  between the straight surface  1441   a  and the tapered surface  1441   b . Therefore, when the interposition member  142  is press-fitted into the main body groove  144 , the upper end  1421   a  of the pair of wall sections  1421  is caught in the boundary  1441   c  so that the two members are mutually fixed more reliably. Consequently, drop off of the interposition member  142  from the main body groove  144  can be prevented more reliably. The image development device or the like breaks down due to the drop off of the interposition member  142 . Hence the magnet roller  133 A with high reliability that can prevent such breakdowns is provided. 
     In addition, the interposition member  142  is shaped using non-magnetic materials. In comparison to a case in which magnetic materials are used for the interposition member  142 , peak magnetic flux density on the external surface of the image development roller  115  (a part of the external surface of the image development roller  115  corresponds to the position of the interposition member  142 ) can be heightened (that is, the highest point of the line Ba illustrated in  FIG. 4  can be set farther apart from the external surface of the magnet roller  133 A). Therefore, the developer agent can be more reliably supported on the external surface of the image development roller  115  and attachment of the developer agent to the photosensitive drum  108  or the like can be prevented. 
     In addition, non-magnetic metals are used for the interposition member  142  so that stiffness property of the magnet roller  133 A can be further heightened. 
     In addition, by applying magnetic force (magnetic field) in a direction approximately parallel to the bottom surface  1442  of the groove  144  of the main body part and approximately orthogonal to the axial direction of the main body part, magnetic anisotropy is provided. Therefore, a point that shifts magnetic poles of the magnetic force (pole shift point) can be generated in the vicinity of the opening part of the groove so that magnetic force at this position can be lessened. Hence the developer agent attached to the magnetic particle support body can be cut at this position so that the developer agent drops off from the external surface of the image development roller  115 . Consequently, rotations under a state in which the developer agent is ceaselessly adhering to the external surface of the image development roller  115  due to the magnetic particle support body can be prevented. 
     In addition, the magnet roller  133 A includes the rare earth magnet block  141  that contains rare earth elements so that high magnetic force can be realized. 
     A Second Embodiment of the Magnetic Field Generating Member 
       FIG. 6  is an enlarged cross-sectional diagram that illustrates a second embodiment of the magnet roller according to the present invention.  FIG. 7  is a cross-sectional diagram that illustrates an assembly method of the magnet roller of  FIG. 6 . In  FIG. 6  and  FIG. 7 , the same reference numbers are assigned to parts with the same constitutions to the first embodiment and descriptions of which are abbreviated hereby. 
     A magnet roller  133 B of the present embodiment, as illustrated in  FIG. 6 , includes a main body part (main body)  240 , an interposition member  242  and a magnetic member, for example, the rare earth magnet block  141  as the long magnetic compact. 
     The main body part  240  uses magnetic materials and is cylindrical column-like shaped. The same magnetic materials as the first embodiment, that is, plastic magnet or rubber magnet can be used. A linear groove  244  provided in the main body  240  is disposed along a longitudinal direction on the external surface of the main body part  240 . In addition, an axial part protruding from both end surfaces of the main body part  240  in the direction of the same axial is shaped in integration. In addition, in the main body part  240 , a portion of the cylindrical column-like body can be cut along the axial direction so that a portion of the external surface is in plane shape. 
     The main body groove  244  is equal to the groove of the main body part described in the claims. A cross-section (lateral cross-section) of the main body groove  244  orthogonal to the axial direction of the main body part  240  is concave and approximately rectangular shaped in the external circumference surface of the main body part  240 . The main body groove  244  is extended linearly along the longitudinal direction of the main body part  240  and disposed across the whole length of the main body part  240 . In addition, the main body groove  244  is disposed to oppose a later-described photosensitive drum  108  (that is, in a position of an image development magnetic pole) when the magnet roller  133 B is incorporated into a later-described image development device  113  (illustrated in  FIG. 19 ). 
     The main body groove  244 , as illustrated in  FIG. 7 , includes a pair of side surfaces  2441  and a bottom surface  2442 . 
     The pair of side surfaces  2441  is two opposing plane parts shaped along the longitudinal direction of the main body groove  244  and to be approximately orthogonal against a width direction of an opening part. Each long side of the pair of side surfaces  2441  is respectively connected with the bottom surface  2442 . The bottom surface  2442  is a plane part shaped along the longitudinal direction of the main body groove  244  and to be approximately parallel against the width direction of the opening part. An angle formed by the pair of side surfaces  2441  and the bottom surface  2442  is preferably above 90 degrees and below 100 degrees. That is, the pair of side surfaces  2441  is tapered shaped so that a width M 2  of the bottom surface  2442  is slightly smaller than the width M 1  of the opening part of the main body groove  244 . The pair of side surfaces  2441  is shaped as such so that the placed piece  148  ( FIG. 5 ) that shapes the main body groove  244  can be detached (pulled out) easily. Depth from the opening part of the main body groove  244  to the bottom surface  2442  (that is, depth of the main body groove  244 ) is determined according to specific constitutions but if the depth is too shallow, the height (the length of the short side direction) of a pair of wall sections  2421  of the later described interposition member  242  becomes insufficient. Therefore, stiffening effects by the interposition member  242  cannot be obtained sufficiently. 
     The same as the main body part  140  of the first embodiment, the main body part  240  uses a metal mold of a structure illustrated in  FIG. 5  and is manufactured by injection and magnetic field molding. The metal mold shapes the main body part  240 . The main body groove  244  is shaped by disposing the placed piece  148  at the position of the metal mold. In order for the placed piece  148  to be detached (pulled out) easily from the main body part  240 , a so-called pull out gradient (tapered angle) is applied. The pair of side surfaces  2441  is tapered shaped due to the pull out gradient. Desired shapes of the main body groove can be obtained according to the shape of the placed piece  148 . 
     When injection molding of the main body part  240  is complete, a nesting  150 A and a nesting  150 B of the fixed side do not move. A nesting  150 C and a nesting  150 D of the movable side together with the placed piece  148 , the EJ (ejection) pin  149  and the main body part  240  move in the right direction inside  FIG. 5  (mold opening). Next, the EJ pin  149  pushes out the main body part  240  and the placed piece  148  (eject). Next, the placed piece  148  is detached from the main body part  240  so that the main body part  240  can be obtained. 
     An orientated direction  143  of magnetic field (magnetic anisotropy) of the main body part  240 , as illustrated in  FIG. 3 , in the case of one direction, is approximately parallel to the bottom surface  2442  of the main body groove  244  and approximately orthogonal to the axial direction. In the case of 4 equally divided poles also, one direction should desirably be parallel to the bottom surface  2442  of the main body groove  244  and orthogonal to the axial direction but it is not limited to such. 
     The interposition member  242  is obtained, for example, by applying bending work to flat plate shaped non magnetic metal materials of a same length as the main body groove  244  so that a cross-section (lateral cross-section) of a short side direction of the non magnetic metal materials becomes “U” character shaped. The rare earth magnet block  141  as the internal capsule has magnetic poles. By using non magnetic materials for the interposition member  242 , when the interposition member  242  is fixed in the main body groove  244 , with regard to the magnetic poles, peak magnetic flux density on the external surface of the main body part  240  becomes higher so that the attachment of magnetic carrier  135  contained in the developer agent becomes advantageous. 
     The interposition member  242  can be shaped using resin materials. But in order to improve the stiffness property of the magnet roller  133 B by the interposition member  142 , usage of the metal materials is comparatively advantageous. Within non-magnetic metal materials, spring materials of SUS301 are further advantageous from the viewpoints of property and cost. Within spring materials of SUS301, ½H (more than 310 HV) or ¾H (more than 370 HV) or H (more than 430 HV) or EH (more than 490 HV) is further desirable but the higher the hardness, the easier a crack can be generated to bent sections or the like during bending work so that attention is necessary. 
     The interposition member  242  includes a floor part  2422  and a pair of wall sections  2421 . The rare earth magnet block  141  is fixed in a concave portion  2423  of the interposition member  242  by press-fitting. The concave portion  2423  of the interposition member  242  is shaped by the floor part  2422  and the pair of wall sections  2421 . The concave portion  2423  is equal to a concave portion of an interposition member described in the claims. 
     The floor part  2422  is rectangular flat plate shaped so that its width (short side direction) matches with the width of the bottom surface  2442  of the main body groove  244  so that the two widths cross over. The floor part  2422  is disposed so that when the interposition member  242  is fixed in the main body groove  244  by press-fitting, its lower surface  2422   b  comes into contact with the bottom surface  2442 . 
     The pair of wall sections  2421  is rectangular flat plates disposed uprightly and forming angles (θ of  FIG. 7 ) larger than 90 degrees. The angles are formed from a pair of mutually opposing long sides of the floor part  2422  against the floor part  2422 . The length (that is, height of the pair of wall sections  2421 ) from an upper end  2421   a  to a lower end  2421   b  of the pair of wall sections  2421  is shaped to be less or equal to the width (height) of the pair of side surfaces  2441  of the main body groove  244  and preferably, to equal the width (height) of the pair of side surfaces  2441  of the main body groove  244 . 
     In an external surfaces  2421   c  of the pair of wall sections  2421 , a plurality of wedge grooves  2421   e  of the external surface directed from the upper end  2421   a  towards the lower end  2421   b  of the pair of wall sections  2421  (downward direction in  FIG. 7 ) are disposed across the whole length of the pair of wall sections  2421  along the longitudinal direction. In addition, external surface wedges  2421   g  are shaped by disposing the plurality of wedge grooves  2421   e  of the external surface. 
     In an internal surfaces  2421   d  of the pair of wall sections  2421 , a plurality of wedge grooves  2421   f  of the internal surface directed from the lower end  2421   b  towards the upper end  2421   a  of the pair of wall sections  2421  (upward direction in  FIG. 7 ) are disposed across the whole length of the pair of wall sections  2421  along the longitudinal direction. In addition, internal surface wedges  2421   h  are shaped by disposing the plurality of wedge grooves  2421   f  of the internal surface. 
     The external surface  2421   c  of the pair of wall sections  2421  is shaped to come into contact with the pair of side surfaces  2441  of the main body groove  244  when the interposition member  242  is press-fitted into the main body groove  244 . Because the wedge grooves  2421   e  of the external surface are disposed in the external surface  2421   c , when the interposition member is press-fitted into the main body groove  244 , areas in contact between the pair of side surfaces  2441  and the external surface  2421   c  decrease so that large force is not necessary for the press-fitting and assembly property is improved. In addition, after the press-fitting, the external surface wedges  2421   g  are caught by the pair of side surfaces  2441  of the main body groove  244 . Therefore, drop off of the interposition member  242  from the main body groove  244  can be prevented more reliably. 
     In addition, the internal surface  2421   d  of the pair of wall sections  2421  is shaped to come into contact with the side surfaces  141   c  of the rare earth magnet block  141  when the rare earth magnet block  141  is press-fitted into the concave portion  2423  of the interposition member  242 . Because the wedge grooves  2421   f  of the internal surface are disposed in the internal surface  2421   d , when the rare earth magnet block  141  is press-fitted into the concave portion  2423  of the interposition member  242 , areas in contact between side surfaces  141   c  of the rare earth magnet block  141  and the internal surface  2421   d  decrease so that large force is not necessary for the press-fitting and assembly property is improved. In addition, after the press-fitting, the internal surface wedges  2421   h  are caught by side surfaces  141   c . Therefore, drop off of the rare earth magnet block  141  from the interposition member  242  can be prevented more reliably. 
     In addition, the wedge grooves  2421   f  of the internal surface are preferably shaped before bending work is applied to the interposition member  242 . Because the shaping of the wedge grooves  2421   f  of the internal surface towards the vicinity of the floor part  2422  becomes difficult if performed after the bending work. 
     In addition, the length or the interval of the external surface wedge  2421   g  and the internal surface wedge  2421   h  differ according to the thickness of the interposition member  242  and the height of the pair of wall sections  2421  (that is, deepness of the concave portion  2423  of the interposition member  242 ). The deepness of the external surface wedge  2421   g  and the internal surface wedge  2421   h  is preferably one third of the thickness of the interposition member  242  or below in consideration to cracks of the interposition member  242  generated when bending work is applied or due to slit ups during usage. 
     The wedge grooves  2421   e  of the external surface and the wedge grooves  2421   f  of the internal surface should at least be disposed in the following three positions. The positions are the vicinity of the upper end  2421   a , the vicinity of the lower end  2421   b  and the vicinity of an intermediate part between the upper end  2421   a  and the lower end  2421   b . In particular, in the case the angle formed by the pair of wall sections  2421  of the interposition member  242  against the floor part  2422  is larger than 90 degrees, effects to prevent positional displacements of each member and effects to prevent drop off are largely dependent upon the wedge grooves  2421   e  of the external surface and the wedge grooves  2421   f  of the internal surface disposed in the vicinity of the lower end  2421   b.    
     The wedge grooves  2421   e  of the external surface and the wedge grooves  2421   f  of the internal surface should desirably be disposed so that they remain mutually misaligned. A constitution as such can prevent cracks or the like generated to the interposition member  242  during usage or bending work. 
     The length of the external surface wedge  2421   g  and the internal surface wedge  2421   h  is preferably 0.1 mm and below. Furthermore, in consideration of abrasion, the length is further preferably set to 0.07 mm and above. In addition, the interval between the external surface wedges  2421   g  and the interval between the internal surface wedges  2421   h  is set to 1 mm and below. The wedge grooves  2421   e  of the external surface are desirably misaligned for 0.3 mm and above against the wedge grooves  2421   f  of the internal surface. The wedge grooves  2421   e  of the external surface and the wedge grooves  2421   f  of the internal surface are preferably disposed in more than three positions. 
     The thickness of the pair of wall sections  2421  and the floor part  2422  of the interposition member  242  has differing adequate values according to the shape of the main body part  240 . Increased thickness is advantageous for improving stiffness property, but desired magnetic force (for example, Ba illustrated in  FIG. 4 ) by the rare earth magnet block  141  becomes difficult to be obtained if the thickness becomes too thick. 
     The same as the first embodiment, a plurality of fixed magnetic poles that generates magnetic force (illustrated in a frame format in  FIG. 4  and includes the rare earth magnet block  141  as the image development magnetic pole with other components not illustrated) and an agent severance pole are disposed in the magnet roller  133 B. 
     Next, an assembly method of the magnet roller  133 B is described. First, the rare earth magnet block  141  is press-fitted into the concave portion  2423  of the interposition member  242  in a direction of an arrow S 1  of  FIG. 7  to be fixed thereof. At this moment, a bottom surface  141   b  and side surfaces  141   c  of the rare earth magnet block  141  are press-fitted to respectively come into contact with an upper surface  2422   a  and internal surfaces  2421   d  of the interposition member  242 . 
     Next, the interposition member  242  press-fitted with the rare earth magnet block  141  is press-fitted into the main body groove  244  in a direction of an arrow S 2  of  FIG. 7  to be fixed thereof. At this moment, the press-fitting is performed so that the lower surface  2422   b  of the interposition member  242  comes into contact with the bottom surface  2442  of the main body groove  244  and the external surfaces  2421   c  of the interposition member  242  respectively come into contact with the pair of side surfaces  2441  of the main body groove  244 . 
     Finally, fixed magnetic poles necessary for the image development roller  115  are magnetized by an electromagnet type magnetizing yoke. Thereby the magnet roller  133 B is completed. In addition, in the present embodiment, each member is press-fitted to be fixed but it is not limited to such. For example, each member can be mutually fixed more strongly by combining use of an adhesive agent. 
     In the above-described assembly method (manufacturing method) of the magnet roller  133 B, the interposition member  242  is press-fitted into the main body groove  244  after the rare earth magnet block  141  is press-fitted into the groove  2423  of the interposition member  242  so that the rare earth magnet block  141  is reinforced by the interposition member  242 . Therefore, bending and damages generated when the rare earth magnet block  141  is press-fitted into the main body groove  244  can be prevented. Consequently, the assembly workability of the magnet roller  133 B and the yield ratio of the rare earth magnet block  141  can be improved so that productivity can be heightened. 
     In addition, in the present embodiment, the main body part  240  is shaped to have an external diameter of 8.5 mm and an overall length of 313 mm. The main body groove  244  is shaped to have a length of 313 mm. In the main body groove, the bottom surface  2442  is shaped to have a width of 2.7 mm, the pair of side surfaces  2441  is shaped to have a height of 2.4 mm. In addition, the interposition member  242  is shaped to have a length of 313 mm and a thickness of 0.3 mm. In the interposition member  242 , the width of the floor part  2422  is shaped to 2.6 mm and the height of the pair of wall sections  2421  is shaped to 2.3 mm. The pair of wall sections  2421  is shaped to have a 90 degree angle against the floor part  2422 . The external surface wedge  2421   g  and the internal surface wedge  2421   h  are shaped to have a length of 0.1 mm. The interval of the external surface wedge  2421   g  and the interval of the internal surface wedge  2421   h  are shaped to 0.6 mm. Positional displacements (misalignment) between the wedge groove  2421   e  of the external surface and the wedge groove  2421   f  of the internal surface are shaped to 0.3 mm. The rare earth magnet block  141  is shaped to have a width of 2.0 mm, a height of 2.4 mm and a length of 313 mm. Each of these dimensions is only an example and can be adequately determined according to constitutions or the like. 
     As described above, according to the present invention, the interposition member  242  with a “U” character shaped cross-sectional surface is fixed in the main body groove  244  of the cylindrical column-like shaped main body part  240 . The rare earth magnet block  141  is fixed to the concave portion  2423  of the interposition member  242  so that the main body part  240  is reinforced by the interposition member  242  and stiffness property of the main body part  240  can be heightened. Therefore, even in the case the main body part  240  is shifted to a smaller diameter (that is, smaller size), the stiffness property of the main body part  240  can be secured. Consequently, the magnet roller  133 B can be provided with heightened stiffness property and smaller size. 
     In addition, the interposition member  242  is fixed in the main body groove  244  by press-fitting so that it is not necessary to use an adhesive agent for the fixture of the two members. Therefore, the interposition member  242  can be detached easily from the main body groove  244 . Consequently, reuse of the interposition member  242  becomes possible and the magnet roller  133 B can be provided at a cheap price. In addition, because an adhesive agent is not used for the fixture of the interposition member  242  and the main body groove  244 , positional displacements of these members generated by the thickness of the adhesive agent or due to the drying of the adhesive agent can be avoided. Therefore, high precision assembly is possible. 
     In addition, the rare earth magnet block  141  is fixed in the groove  2423  of the interposition member  242  by press-fitting so that it is not necessary to use an adhesive agent for the fixture of the two members. Therefore, the rare earth magnet block  141  can be detached easily from the interposition member  242 . Consequently, reuse of the expensive rare earth magnet block  141  becomes possible and the magnet roller  133 B can be provided at a cheap price. In addition, because an adhesive agent is not used for the fixture of the interposition member  242  and the rare earth magnet block  141 , positional displacements of these members generated by the thickness of the adhesive agent or due to the drying of the adhesive agent can be avoided. Therefore, high precision assembly is possible. 
     In addition, the interposition member  242  includes, in the external surface  2421   c  of the pair of wall sections  2421 , wedge grooves  2421   e  of the external surface directed from the upper end  2421   a  towards the lower end  2421   b  and shaped to form an acute angle thereof. Besides, external surfaces  2421   c  of the pair of wall sections  2421  are respectively shaped to closely contact the pair of side surfaces  2441  of the main body groove  244 . By disposing the wedge grooves  2421   e  of the external surface, the external surface wedges  2421   g  directed from the lower end  2421   b  towards the upper end  2421   a  of the pair of wall sections  2421  are shaped. Consequently, when the interposition member  242  is press-fitted into the main body groove  244 , without the external surface wedges  2421   g , the interposition member  242  is likely to drop off from the main body groove  242  in a direction. However, with the external surface wedges  2421   g , the external surface wedges  2421   g  are caught by the pair of side surfaces  2441  of the main body groove  244  against the drop off direction so that each of these members is fixed more reliably. Therefore, drop off of the interposition member  242  from the main body groove  244  and positional displacements thereof can be prevented more reliably. The image development device or the like breaks down due to the drop off of the interposition member  242 . Hence the magnet roller  133 B with high reliability that can prevent such breakdowns is provided. 
     In addition, the pair of wall sections  2421  in the interposition member  242  is shaped to form an angle larger than 90 degrees against the floor part  2422  in the interposition member  242 . Therefore, when the interposition member  242  is press-fitted into the main body groove  244 , without the external surface wedges  2421   g , the interposition member  242  is likely to drop off from the main body groove  242  in a direction. However, with the external surface wedges  2421   g  and the larger than 90 degrees angle formed by the pair of wall sections  2421 , the external surface wedges  2421   g  are further strongly caught by the pair of side surfaces  2441  of the main body groove  244  against the drop off direction so that each of these members is fixed more reliably. Therefore, drop off of the interposition member  242  from the main body groove  244  and positional displacements thereof can be prevented more reliably. The image development device or the like breaks down due to the drop off of the interposition member  242 . Hence the magnet roller  133 B with high reliability that can prevent such breakdowns is provided. 
     In addition, the interposition member  242  includes, in the internal surface  2421   d  of the pair of wall sections  2421 , wedge grooves  2421   f  of the internal surface directed from the lower end  2421   b  towards the upper end  2421   a  and shaped to form an acute angle thereof. Besides, internal surfaces  2421   d  of the pair of wall sections  2421  are respectively shaped to closely contact the side surfaces  141   c  of the rare earth magnet block  141 . By disposing the wedge grooves  2421   f  of the internal surface, the internal surface wedges  2421   h  directed from the upper end  2421   a  towards the lower end  2421   b  of the pair of wall sections  2421  are shaped. Consequently, when the rare earth magnet block  141  is press-fitted into the interposition member  242 , without the internal surface wedges  2421   h , the rare earth magnet block  141  is likely to drop off from the interposition member  242  in a direction. However, with the internal surface wedges  2421   h , the internal surface wedges  2421   h  are caught by the side surfaces  141   c  of the rare earth magnet block  141  against the drop off direction so that each of these members is fixed more reliably. Therefore, drop off of the rare earth magnet block  141  from the interposition member  242  and positional displacements thereof can be prevented more reliably. The image development device or the like breaks down due to the drop off of the rare earth magnet block  141 . Hence the magnet roller  133 B with high reliability that can prevent such breakdowns is provided. 
     In addition, the interposition member  242  is shaped using non-magnetic materials. In comparison to a case in which magnetic materials are used for the interposition member  242 , peak magnetic flux density on the external surface of the image development roller  115  (a part of the external surface of the image development roller  115  corresponds to the position of the interposition member  242 ) can be heightened. Therefore, the developer agent can be more reliably supported on the external surface of the image development roller  115  and attachment of the developer agent to the photosensitive drum  108  or the like can be prevented. 
     In addition, non-magnetic metals are used for the interposition member  242  so that stiffness property of the magnet roller  133 B can be further heightened. 
     In addition, by applying magnetic force (magnetic field) in a direction approximately parallel to the bottom surface  2442  of the groove  244  of the main body part and approximately orthogonal to the axial direction of the main body part, magnetic anisotropy is provided. Therefore, a point that shifts magnetic poles of the magnetic force (pole shift point) can be generated in the vicinity of the opening part of the groove so that magnetic force at this position can be lessened. Hence the developer agent attached to the magnetic particle support body can be cut at this position so that the developer agent drops off from the external surface of the image development roller  115 . Consequently, rotations under a state in which the developer agent is ceaselessly adhering to the external surface of the image development roller  115  due to the magnetic particle support body can be prevented. 
     In addition, the magnet roller  133 B includes the rare earth magnet block  141  that contains rare earth elements so that high magnetic force can be realized. 
     A Third Embodiment of the Magnetic Field Generating Member 
       FIG. 8  is an enlarged cross-sectional diagram that illustrates a third embodiment of a magnet roller according to the present invention.  FIG. 9  is a cross-sectional diagram that illustrates an assembly method of the magnet roller of  FIG. 8 .  FIG. 10  is a cross-sectional diagram that illustrates a first shape of an interposition member in the magnet roller of  FIG. 8 .  FIG. 11  is a cross-sectional diagram that illustrates a second shape of the interposition member in the magnet roller of  FIG. 8 .  FIG. 12  is a cross-sectional diagram that illustrates a third shape of the interposition member in the magnet roller of  FIG. 8 .  FIG. 13  is a cross-sectional diagram that illustrates a fourth shape of the interposition member in the magnet roller of  FIG. 8 .  FIG. 14  is a cross-sectional diagram that illustrates an approximate structure of a metal mold that shapes the main body part of the magnet roller of  FIG. 8 .  FIG. 15  is a cross-sectional diagram that illustrates a first part of the approximate operations of when the metal mold of  FIG. 14  is detached from the mold.  FIG. 16  is a cross-sectional diagram that illustrates a second part of the approximate operations of when the metal mold of  FIG. 14  is detached from the mold. Same reference numbers are assigned to parts with the same constitutions to the above-described first and second embodiments and descriptions of which are abbreviated hereby. 
     A magnet roller  133 C of the present embodiment, as illustrated in  FIG. 8 , includes a main body part (main body)  340 , an interposition member  342  and a magnetic member, for example, the rare earth magnet block  141  as the long magnetic compact. 
     The main body part  340  uses magnetic materials and is cylindrical column-like shaped. The same magnetic materials as the first and the second embodiments, that is, plastic magnet or rubber magnet can be used. A linear groove  344  provided in the main body  340  is disposed along a longitudinal direction on the external surface of the main body part  340 . In addition, an axial part protruding from both end surfaces of the main body part  340  in the direction of the same axial is shaped in integration. In addition, in the main body part  340 , a portion of the cylindrical column-like body can be cut along the axial direction so that a portion of the external surface is in plane shape. 
     The main body groove  344  is equal to the groove of the main body part described in the claims. A cross-section (lateral cross-section) of the main body groove  344  orthogonal to the axial direction of the main body part  340  is concave and approximately rectangular shaped in the external circumference surface of the main body part  340 . The main body groove  344  is extended linearly along the longitudinal direction of the main body part  340  and disposed across the whole length of the main body part  340 . In addition, the main body groove  344  is disposed to oppose a later described photosensitive drum  108  (that is, in a position of an image development magnetic pole) when the magnet roller  133 C is incorporated into a later described image development device  113  (illustrated in  FIG. 19 ). 
     The main body groove  344 , as illustrated in  FIG. 9 , includes a pair of side surfaces  3441  and a bottom surface  3442 . 
     The pair of side surfaces  3441  is two opposing plane parts shaped along the longitudinal direction of the main body groove  344  and to be approximately orthogonal against a width direction of an opening part. Each long side of the pair of side surfaces  3441  is respectively connected with the bottom surface  3442 . The bottom surface  3442  is a plane part shaped along the longitudinal direction of the main body groove  344  and to be approximately parallel against the width direction of the opening part. An angle formed by the pair of side surfaces  3441  and the bottom surface  3442  is shaped to be smaller than 90 degrees. That is, the pair of side surfaces  3441  is reverse tapered shaped (undercut) so that a width N 2  of the bottom surface  3442  is slightly larger than the width N 1  of the opening part of the main body groove  344 . That is, the main body groove  344  is dovetail joint shaped in which the width of the bottom surface  3442  is larger than the width of the opening part. Depth from the opening part of the main body groove  344  to the bottom surface  3442  (that is, depth of the main body groove  344 ) is determined according to specific constitutions but if the depth is too shallow, the height (the length of the short side direction) of a pair of wall sections  3421  of the later-described interposition member  342  becomes insufficient. Therefore, stiffening effects by the interposition member  342  cannot be obtained sufficiently. 
     The main body part  340  uses a metal mold of a structure illustrated in  FIG. 14  and is manufactured by injection and magnetic field molding. The metal mold shapes the main body part  340 . The main body groove  344  is shaped by disposing a slide piece  148 A, a slide piece  148 B and a slide piece  148 C at the position of the metal mold. The slide piece  148 A, the slide piece  148 B and the slide piece  148 C are constituted by a not illustrated “T” letter shaped groove structure. When injection molding is complete, the slide piece  148 C, as illustrated in  FIG. 15 , moves in an upper direction. The slide piece  148 A and the slide piece  148 B movably assembled by the “T” letter shaped groove respectively move until a predetermined position in which the undercut of the main body groove  344  can be avoided. Thereafter, as illustrated in  FIG. 16 , the slide piece  148 A, the slide piece  148 B and the slide piece  148 C in their entity move in the upper direction and shape the main body groove  344 . Next, a nesting  150 C and a nesting  150 D of the movable side together with the slide piece  148 A, the slide piece  148 B and the slide piece  148 C, the EJ (ejection) pin  149  and the main body part  340  move in the right direction inside  FIG. 16  (mold opening). Next, the EJ pin  149  pushes out the main body part  340  (eject). Next, the EJ pin  149  is detached from the main body part  340  so that the main body part  340  can be obtained. 
     An orientated direction  143  of magnetic field (magnetic anisotropy) of the main body part  340 , as illustrated in  FIG. 3 , in the case of one direction, is approximately parallel to the bottom surface  3442  of the main body groove  344  and approximately orthogonal to the axial direction. In the case of 4 equally divided poles also, one direction should desirably be parallel to the bottom surface  3442  of the main body groove  344  and orthogonal to the axial direction but it is not limited to such. 
     The interposition member  342  is obtained, for example, by shaping general plastic materials or by applying bending work to metal materials. Non-magnetic materials should be preferably used for either the plastic materials or the metal materials used for the interposition member  342 . The rare earth magnet block  141  as the internal capsule has magnetic poles. When the interposition member  342  using non-magnetic materials is fixed in the main body groove  344 , with regard to the magnetic poles, peak magnetic flux density on the external surface of the main body part  340  becomes higher so that the attachment of magnetic carrier  135  contained in the developer agent becomes advantageous. 
     In order to improve the stiffness property of the magnet roller  133 C by the interposition member  342 , the metal materials can be comparatively advantageously used for the interposition member  342 . Within non-magnetic metal materials, spring materials of SUS301 are further advantageous from the viewpoints of property and cost. Within spring materials of SUS301, ½H (more than 310 HV) or ¾H (more than 370 HV) or H (more than 430 HV) or EH (more than 490 HV) is further desirable but the higher the hardness, the easier a crack can be generated to bent sections or the like during bending work so that attention is necessary. 
     The interposition member  342  is shaped to the same length as the main body groove  344 . A cross-section of the short side direction of the interposition member  342  (that is, lateral cross-section) is “U” character shaped. The interposition member  342  includes a floor part  3422  and a pair of wall sections  3421 . The rare earth magnet block  141  is fixed in a concave portion  3423  of the interposition member  342  by press-fitting. The concave portion  3423  of the interposition member  342  is shaped by the floor part  3422  and the pair of wall sections  3421 . The concave portion  3423  is equal to a concave portion of an interposition member described in the claims. 
     Before the interposition member  342  is press-fitted into the main body groove  344 , the width of the lower surface  3422   b  of the floor part  3422  is shaped to be smaller than the width of the opening part of the main body groove  344 . After the interposition member  342  is press-fitted into the main body groove  344 , the floor part  3422  is shaped to match the bottom surface  3442  of the main body groove  344  so that the two members cross over. Then, when the interposition member  342  is press-fitted into the main body groove  344  to be fixed thereof, the interposition member  342  is disposed so that its lower surface  3422   b  comes into contact with the bottom surface  3442  of the main body groove  344 . Under such a constitution, the width of the floor part  3422  of the interposition member  342  becomes larger than the width of the opening part of the main body groove  344  after the press-fitting so that the interposition member  342  is caught by the pair of side surfaces  3441  (serves as stoppers) of the main body groove  344  and drop off of the interposition member  342  from the main body groove  344  can be prevented. 
     In addition, the kinds of shapes of the floor part  3422  can be various. For example, the lateral cross sectional surface of the floor part  3422  can be a concave “R” shaped floor part  3422  illustrated in  FIG. 10 , a convex “R” shaped floor part  3422 A illustrated in  FIG. 11 , a “V” letter shaped floor part  3422 B illustrated in  FIG. 12  and a reverse “V” letter shaped floor part  3422 C illustrated in  FIG. 13  or the like. However, shapes of the floor part  3422  are not limited to these. 
     The pair of wall sections  3421  is rectangular flat plates disposed uprightly originating from a pair of mutually opposed long sides of the floor part  3422 . The length (that is, height of the pair of wall sections  3421 ) from an upper end  3421   a  to a lower end  3421   b  of the pair of wall sections  3421  is shaped to be less or equal to the width of the pair of side surfaces  3441  of the main body groove  344  and preferably, to equal the width of the pair of side surfaces  3441  of the main body groove  344 . When the interposition member  342  is press-fitted into the main body groove  344 , external surfaces  3421   c  of the pair of wall sections  3421  are shaped to come into contact with the pair of side surfaces  3441 . 
     The thickness of the floor part  3422  and the pair of wall sections  3421  of the interposition member  342  has differing adequate values according to the shape of the main body part  340 . The floor part  3422  and the pair of wall sections  3421  should be advantageously thickened in order to improve stiffness property. But desired magnetic forces (for example, the Ba illustrated in  FIG. 4 ) by the rare earth magnetic block  141  become difficult to obtain if the floor part  3422  and the pair of wall sections  3421  become too thick. 
     The same as the first and the second embodiments, a plurality of fixed magnetic poles that generates magnetic force (illustrated in a frame format in  FIG. 4  and includes the rare earth magnet block  141  as the image development magnetic pole with other components not illustrated) and an agent severance pole are disposed in the magnet roller  133 C. 
     Next, an assembly method of the magnet roller  133 C is described. The rare earth magnet block  141  is press-fitted into the concave portion  3423  of the interposition member  342  in a direction of an arrow T 1  of  FIG. 9  while simultaneously the interposition member  342  is press-fitted into the main body groove  344  in a direction of an arrow T 2  of  FIG. 9 . Then the floor part  3422  of the interposition member  342  reaches the bottom surface  3442  of the main body groove  344 . Furthermore, the bottom surface  141   b  of the rare earth magnet block  141  is pressed against the floor part  3422 . The floor part  3422  is extended in a flat plate shape along the bottom surface  3442  and the two respectively match and cross over. In addition, the external surface  3421   c  of the pair of wall sections  3421  of the interposition member  342  come into contact with the pair of side surfaces  3441  of the main body groove  344 . The rare earth magnet block  141 , the interposition member  342  and the main body part  340  are mutually fixed under a state in which the width of the floor part  3422  is larger than the width of the opening part of the main body groove  344 . 
     Finally, fixed magnetic poles necessary for the image development roller  115  are magnetized by an electromagnet type magnetizing yoke. Thereby the magnet roller  133 C is completed. In addition, in the present embodiment, each member is press-fitted to be fixed but it is not limited to such. For example, each member can be mutually fixed more strongly by combining use of an adhesive agent. 
     In the above-described assembly method (manufacturing method) of the magnet roller  133 C, the rare earth magnet block  141  is press-fitted into the concave portion  3423  of the interposition member  342  while simultaneously the interposition member  342  is press-fitted into the main body groove  344  so that the rare earth magnet block  141  is reinforced by the interposition member  342 . Therefore, bending and damages generated when the rare earth magnet block  141  is press-fitted into the main body groove  344  can be prevented. Consequently, the assembly workability of the magnet roller  133 C and the yield ratio of the rare earth magnet block  141  can be improved so that productivity can be heightened. 
     In addition, in  FIG. 8 , there seemingly is a gap between the rare earth magnet block  141  and the interposition member  342  but actually, only an extremely minute gap exists between the two members. 
     In addition, in the present embodiment, the main body part  340  is shaped to have an external diameter of 8.5 mm and an overall length of 313 mm. The main body groove  344  is shaped to have a length of 313 mm. In the main body groove, the bottom surface  3442  is shaped to have a width of 2.7 mm, a distance from an axial center to the bottom surface  3442  is 1.85 mm, the width of the opening part of the main body groove  344  is 2.31 mm and angles formed between the bottom surface  3442  and the pair of side surfaces  3441  are shaped to 85 degrees. In addition, the interposition member  342  is shaped to have a length of 313 mm and a thickness of 0.3 mm. In the interposition member  342 , the width of the side of the upper surface  3422   a  of the floor part  3422  is shaped to 1.6 mm and the height of the side of the internal surface  3421   d  of the pair of wall sections  3421  is shaped to 1.92 mm. The floor part  3422  is concave “R” shaped ( FIG. 10 ). The rare earth magnet block  141  is shaped to have a width of 2.0 mm, a height of 2.4 mm and a length of 313 mm. Each of these dimensions is only an example and can be adequately determined according to constitutions or the like. 
     As described above, according to the present invention, the interposition member  342  with a “U” character shaped cross sectional surface is fixed in the main body groove  344  of the cylindrical column-like shaped main body part  340 . The rare earth magnet block  141  is fixed in the groove  3423  of the interposition member  342  so that the main body part  340  is reinforced by the interposition member  342  and stiffness property of the main body part  340  can be heightened. Therefore, even in the case the main body part  340  is shifted to a smaller diameter (that is, smaller size), the stiffness property of the main body part  340  can be secured. Consequently, the magnet roller  133 C can be provided with heightened stiffness property and smaller size. 
     In addition, the interposition member  342  is fixed in the main body groove  344  by press-fitting so that it is not necessary to use an adhesive agent for the fixture of the two members. Therefore, the interposition member  342  can be detached easily from the main body groove  344 . Consequently, reuse of the interposition member  342  becomes possible and the magnet roller  133 C can be provided at a cheap price. In addition, because an adhesive agent is not used for the fixture of the interposition member  342  and the main body groove  344 , positional displacements of these members generated by the thickness of the adhesive agent or due to the drying of the adhesive agent can be avoided. Therefore, high precision assembly is possible. 
     In addition, the rare earth magnet block  141  is fixed in the concave portion  3423  of the interposition member  342  by press-fitting so that it is not necessary to use an adhesive agent for the fixture of the two members. Therefore, the rare earth magnet block  141  can be detached easily from the interposition member  342 . Consequently, reuse of the expensive rare earth magnet block  141  becomes possible and the magnet roller  133 C can be provided at a cheap price. In addition, because an adhesive agent is not used for the fixture of the interposition member  342  and the rare earth magnet block  141 , positional displacements of these members generated by the thickness of the adhesive agent or due to the drying of the adhesive agent can be avoided. Therefore, high precision assembly is possible. 
     In addition, the main body groove  344  is reverse tapered shaped (dovetail joint shaped) in which the width of the bottom surface  3422  is larger than the width of the opening part. When the interposition member  342  is press fitted into the main body groove  344 , because the width of the lower surface  3422   b  of the interposition member  342  is shaped to be larger than the width of the opening part of the main body groove  344 , the interposition member  342  is caught by the opening part of the main body groove  344  so that the interposition member  342  can be fastened within the main body groove  344  to be fixed thereof. Therefore, drop off of the interposition member  342  from the main body groove  344  can be prevented more reliably. The image development device or the like breaks down due to the drop off of the interposition member  342 . Hence the magnet roller  133 C with high reliability that can prevent such breakdowns is provided. 
     In addition, the interposition member  342  is shaped using non-magnetic materials. In comparison to a case in which magnetic materials are used for the interposition member  342 , peak magnetic flux density on the external surface of the image development roller  115  (a part of the external surface of the image development roller  115  corresponds to the position of the interposition member  342 ) can be heightened. Therefore, the developer agent can be more certainly supported on the external surface of the image development roller  115  and attachment of the developer agent to the photosensitive drum  108  or the like can be prevented. 
     In addition, non-magnetic metals are used for the interposition member  342  so that stiffness property of the magnet roller  133 C can be further heightened. 
     In addition, by applying magnetic force (magnetic field) in a direction approximately parallel to the bottom surface  3442  of the groove  344  of the main body part and approximately orthogonal to the axial direction of the main body part, magnetic anisotropy is provided. Therefore, a point that shifts magnetic poles of the magnetic force (pole shift point) can be generated in the vicinity of the opening part of the groove so that magnetic force at this position can be lessened. Hence the developer agent attached to the magnetic particle support body can be cut at this position so that the developer agent drops off from the external surface of the image development roller  115 . Consequently, rotations under a state in which the developer agent is ceaselessly adhering to the external surface of the image development roller  115  due to the magnetic particle support body can be prevented. 
     In addition, the magnet roller  133 C includes the rare earth magnet block  141  that contains rare earth elements so that high magnetic force can be realized. 
     An Embodiment of a Magnetic Particle Support Body 
       FIG. 18  is a cross-sectional diagram that illustrates an embodiment of an image development roller as a magnetic particle support body according to the present invention. 
     The later-described image forming apparatus  101  (illustrated in  FIG. 20 ) includes an image development device  113  (illustrated in  FIG. 19 ). The image development roller  115  of the present embodiment is incorporated in the image development device  113 . The image development roller  115  supports developer agent on its external surface and delivers the developer agent to an image development area  131 . A photosensitive drum  108  has electrostatic images formed on its surface. The image development area  131  opposes the photosensitive drum  108 . 
     The image development roller  115 , as illustrated in  FIG. 18 , includes one of the magnet rollers  133 A,  133 B and  133 C (magnet roller  133  hereinbelow) illustrated in the above described first, second and third embodiments as a magnetic field generating member. The image development roller  115  also includes a cylindrical shaped image development sleeve  132  shaped so that the magnet roller  133  becomes an internal capsule. In addition, in the image development roller  115 , a cored bar conventionally present is not illustrated but it is not problematic even the cored bar is present. However, magnet volumes of the magnet roller  133  decrease due to the cored bar and magnetic force thereof is weakened. Therefore, countermeasures that compensate this phenomenon are necessary. 
     The image development sleeve  132  is equal to a hollow body described in the claims. The image development sleeve  132  is shaped so that the magnet roller  133  becomes an internal capsule (contained within). The image development sleeve  132  is disposed freely rotatable around an axial core. The image development sleeve  132  is rotated so that its internal circumference surface opposes fixed magnetic poles in a sequence. The external surface of the image development sleeve  132  is applied roughen processing (SWB) so that many concavities are disposed thereon. The plane shape of the concavities is ellipsoidal. A plurality of (many) concavities (the concavities just described) are disposed randomly on the external surface of the image development sleeve  132 . Needless to say, the concavities include those whose longitudinal direction is along the axial direction of the image development sleeve  132  and those whose longitudinal direction is along the circumference direction of the image development sleeve  132 . The concavities whose longitudinal direction is along the axial direction of the image development sleeve  132  are more than the concavities whose longitudinal direction is along the circumference direction of the image development sleeve  132 . Furthermore, the length (long diameter) of the longitudinal direction of the concavities is greater or equal to 0.05 mm and less or equal to 0.3 mm. The width (diameter at end) of the width direction is greater or equal to 0.02 mm and less or equal to 0.1 mm. 
     Aluminum, SUS (stainless) or the like can be used as the materials for the image development sleeve  132 . Aluminum is used more often from the viewpoints of workability and lightness. In the case of aluminum, A6063, A5056 and A3003 or the like can be used. In the case of SUS, 303, 304 and 316 or the like can be used. 
     As described above, the present invention includes one of the magnet rollers  133 A,  133 B and  133 C illustrated in the above described first, second and third embodiments as the magnetic field generating member so that the image development roller  115  of a smaller size can be provided. 
     An Embodiment of an Image Development Device 
       FIG. 19  is a cross-sectional diagram that illustrates an embodiment of a process cartridge and an image development device according to the present invention. 
     The image development device  113  of the present embodiment, as illustrated in  FIG. 19 , includes at least a developer agent supply part  114 , a case  125 , the above described image development roller  115  and a developer agent control blade  116  as a developer agent control member. 
     The developer agent supply part  114  includes a holding tank  117  and a pair of stirring screws  118  as a stirring member. The holding tank  117  is box shaped with an approximate same length to the photosensitive drum  108 . In addition, a partition  119  extended along the longitudinal direction of the holding tank  117  is disposed within the holding tank  117 . The partition  119  compartments the space within the holding tank  117  into a first space  120  and a second space  121 . In addition, both end parts of the first space  120  and the second space  121  are mutually connected. 
     The holding tank  117  contains developer agent in both the first space  120  and the second space  121 . The developer agent includes magnetic carrier  135  and toner. The toner is adequately supplied to one end part of the first space  120 . The first space  120  is situated at a side remote from the image development roller  115  in comparison to the second space  121 . The toner is spherical minute particles manufactured by the emulsion polymerization method or the suspension polymerization method. In addition, the toner can be obtained by crushing a lump constituted from synthetic resin in which various dye compounds or colorants are mixed and dispersed. The average particle diameter of the toner is greater or equal to 3 μm and less or equal to 7 μm. In addition, the toner can be shaped by a crush processing. 
     The magnetic carrier  135  is contained in both the first space  120  and the second space  121 . The average particle diameter of the magnetic carrier  135  is greater or equal to 20 μm and less or equal to 50 μm. The magnetic carrier, as illustrated in  FIG. 17 , includes a wicking  136  as the material for the core, a resin coating membrane  137  covering the external surface of the wicking  136  and a plurality of alumina particle  138  dispersed by the resin coating membrane  137 . 
     Ferrite is a magnetic material. The spherical shaped wicking  136  is constituted from ferrite. The external surface of the wicking  136  is covered by the resin coating membrane  137  in its entirety. The resin coating membrane  137  contains an electrical-charged adjustment agent and a resin component obtained by cross-linking thermal plastic resins of acryl or the like with melamine resin. The resin coating membrane  137  has elasticity and strong adhesive force. The alumina particles  138  are spherical shaped with an external diameter larger than the thickness of the resin coating membrane  137 . The alumina particles  138  are held by the strong adhesive force of the resin coating membrane  137 . The alumina particles  138  are protruding more towards the external circumference side of the magnet carrier  135  in comparison to the resin coating membrane  137 . 
     The first space  120  and the second space  121  respectively contain the stirring screw  118 . The longitudinal direction of the stirring screw  118  is parallel to the longitudinal direction of the holding tank  117 , the image development roller  115  and the photosensitive drum  108 . The stirring screw  118  is disposed freely rotatable around the axial core. The stirring screw  118  stirs the magnetic carrier  135  and the toner by rotating around the axial core and delivers the developer agent along the axial core. 
     In the illustrated example, the stirring screw  118  within the first space  120  delivers the developer agent from the above described one end part towards the other end part. The stirring screw  118  within the second space  121  delivers the developer agent from the other end part towards the one end part. 
     According to the above-described constitution, the developer agent supply part  114  stirs the toner supplied to the one end part of the first space  120  with the magnetic carrier  135  and delivers the toner to the other end part. The developer agent is then delivered from the other end part of the first space  120  to the other end part of the second space  121 . Then the developer agent supply part  114  stirs the toner and the magnetic carrier  135  within the second space  121 . The developer agent supply part  114  then delivers the developer agent in the axial core direction and supplies the developer agent to the external surface of the image development roller  115 . 
     The box shaped case  125  is fixed on the holding tank  117  of the above described developer agent supply part  114  and covers the image development roller  115  or the like together with the holding tank  117 . In addition, an opening part  125   a  is disposed in a part of the case  125 . The part opposes the photosensitive drum  108 . 
     The above-described image development roller  115  is disposed in the vicinity of the above-described opening part  125   a  and also between the second space  121  and the photosensitive drum  108 . The image development roller  115  is parallel to both the photosensitive drum  108  and the holding tank  117 . The image development roller  115  is disposed having an interval with the photosensitive drum  108 . 
     The developer agent control blade  116  is disposed in an end part of the image development device  113  close to the photosensitive drum  108 . The developer agent control blade  116  is fixed on the above-described case  125  in a state having an interval with the external surface of the image development sleeve  132 . The developer agent control blade  116  trim off the developer agent on the external surface of the image development sleeve  132  exceeding the desired thickness into the holding tank  117  so that the developer agent on the external surface of the image development sleeve  132  is delivered to the image development area  131  in desired thickness. 
     In the image development device  113 , the toner and the magnetic carrier  135  are sufficiently stirred by the developer agent supply part  114 . The stirred developer agent is adsorbed onto the external surface of the image development sleeve  132  by the fixed magnetic poles. Then the image development sleeve  132  is rotated so that the developer agent adsorbed by the plurality of fixed magnetic poles is delivered towards the image development area  131 . Then the developer agent shifted into the desired thickness by the developer agent control blade  116  is adsorbed onto the photosensitive drum  108  by the image development device  113 . In such a way, the image development device  113  supports the developer agent to the image development roller  115  and delivers the developer agent to the image development area  131 . Then an electrostatic latent image on the photosensitive drum  108  is developed by the image development device  113  so that a toner image is formed. 
     Then the after image development developer agent is detached towards the holding tank  117  by the image development device  113 . Then the after image development developer agent held in the holding tank  117  is again sufficiently stirred with other developer agent within the second space  121  to be used for development of an electrostatic latent image of the photosensitive drum  108 . 
     As described above, the present invention includes the above described image development roller  115  so that the image development device  113  of a smaller size can be provided. 
     An Embodiment of a Process Cartridge 
       FIG. 19  is a cross-sectional diagram that illustrates an embodiment of a process cartridge and an image development device according to the present invention.  FIG. 20  is a cross-sectional diagram that illustrates an embodiment of an image forming apparatus according to the present invention. 
     A process cartridge  106  of the present embodiment, as illustrated in  FIG. 19 , includes a cartridge case  111 , an electrical-charged device such as an electrical-charged roller  109 , an electrostatic latent image support body such as a photosensitive drum  108 , a cleaning device such as a cleaning blade  112  and the above described image development device  113 . Therefore, the image forming apparatus  101  includes at least the electrical-charged roller  109 , the photosensitive drum  108 , the cleaning blade  112  and the image development device  113 . 
     The cartridge case  111  is freely detachable from an apparatus main body  102  of the image forming apparatus  101 . The electrical-charged roller  109 , the photosensitive drum  108 , the cleaning blade  112  and the image development device  113  are held in the cartridge case  111 . The external surface of the photosensitive drum  108  is electrically charged uniformly by the electrical-charged roller  109 . The image development device  113  includes the above-described image development roller  115 . The photosensitive drum  108  is disposed having an interval with the image development roller  115 . The photosensitive drum  108  is cylindrical column-like shaped or cylindrical shaped. The photosensitive drum is freely rotatable with an axial core as the center. Electrostatic latent images are formed on the external surface of the photosensitive drum  108  by corresponding laser writing units of  122 Y,  122 M,  122 C and  122 K. The electrostatic latent images are also supported by the photosensitive drum  108 . Toner is adsorbed onto the electrostatic latent images so that the electrostatic latent images are developed. A toner image obtained as such is transferred onto a piece of recording paper  107 . The recording paper  107  is positioned between the photosensitive drum  108  and a delivery belt  129 . The cleaning blade  112  removes residual toners remaining on the external surface of the photosensitive drum  108  after the toner image is transferred onto the recording paper  107 . 
     As described above, the present invention includes the above-described image development device  113  so that the process cartridge  106  of a smaller size can be provided. 
     An Embodiment of an Image Forming Apparatus 
       FIG. 20  is a cross-sectional diagram that illustrates an embodiment of an image forming apparatus according to the present invention. 
     The image forming apparatus  101  forms on a piece of the recording paper  107  as a transfer material color images, that is, images of each color of yellow (Y), magenta (M), cyan (C) and black (K). In addition, units or the like corresponding to each color of yellow (Y), magenta (M), cyan (C) and black (K) are illustrated hereinbelow with Y, M, C and K attached to the end of the respective reference numbers. 
     The image forming apparatus  101 , as illustrated in  FIG. 20 , includes at least the apparatus main body  102 , a paper feeding unit  103 , a pair of resist roller  110 , a transfer unit  104 , a fixing unit  105 , a plurality of laser writing units  122 Y,  122 M,  122 C and  122 K as well as a plurality of process cartridges  106 Y,  106 M,  106 C and  106 K. 
     The apparatus main body  102  is for example, box shaped and can be disposed on a floor or the like. The paper feeding unit  103 , the pair of resist roller  110 , the transfer unit  104 , the fixing unit  105 , the plurality of laser writing units  122 Y,  122 M,  122 C and  122 K as well as the plurality of process cartridges  106 Y,  106 M,  106 C and  106 K are held in the apparatus main body  102 . 
     The above-described process cartridges  106 Y,  106 M,  106 C and  106 K correspond to each color respectively and are disposed between the transfer unit  104  and the laser writing units  122 Y,  122 M,  122 C and  122 K. The process cartridges  106 Y,  106 M,  106 C and  106 K are freely detachable from the apparatus main body  102 . The process cartridges  106 Y,  106 M,  106 C and  106 K are disposed in parallel along the delivery direction of the recording paper  107 . 
     A plurality of the paper feeding unit  103  is disposed in the lower part of the apparatus main body  102 . The above-described recording paper  107  is held and stacked in layers in the paper feeding unit  103 . The paper feeding unit  103  includes a plurality of paper feeding cassette  123  and a plurality of paper feeding roller  124 . The paper feeding cassette  123  can be taken freely in and out of the apparatus main body  102 . The paper feeding roller  124  is pressed against the uppermost piece of recording paper  107  within the paper feeding cassette  123 . The paper feeding roller  124  sends out the above-described uppermost piece of recording paper  107  into a delivery path between the photosensitive drum  108  and a later described delivery belt  129 . The transfer unit  104  includes the later-described delivery belt  129 . The process cartridges  106 Y,  106 M,  106 C and  106 K include the photosensitive drum  108 . 
     The recording paper  107  is delivered from the paper feeding unit  103  to the transfer unit  104 . The pair of resist rollers  110  is disposed in the delivery path of the recording paper  107 . The pair of resist rollers  110  includes a pair of rollers  110   a  and  110   b . The recording paper  107  is interleaved between the pair of rollers  110   a  and  110   b . The interleaved recording paper  107  is then sent out into the delivery path between the transfer unit  104  and the process cartridges  106 Y,  106 M,  106 C and  106 K by the pair of resist roller  110  in a timing that can be superimposed with a toner image. 
     The transfer unit  104  is disposed above the paper feeding unit  103 . The transfer unit  104  includes a drive roller  127 , a driven roller  128 , the delivery belt  129 , transfer rollers  130 Y,  130 M,  130 C and  130 K. The drive roller  127  is disposed in a downstream side of the delivery direction of the recording paper  107 . The drive roller  127  is rotary driven by a drive source such as a motor or the like. The driven roller  128  is supported by the apparatus main body  102 . The driven roller  128  is freely rotatable and is disposed in an upstream side of the delivery direction of the recording paper  107 . The delivery belt  129  is circularly shaped with no end and encircles both the above described drive roller  127  and the driven roller  128 . The delivery belt  129  is rotary driven by the drive roller  127  and circulates around the above described drive roller  127  and the driven roller  128  in a counter clock-wise direction in the figure (run with no end). 
     The delivery belt  129  and the recording paper  107  on the delivery belt  129  are interleaved between the photosensitive drum  108  of the process cartridges  106 Y,  106 M,  106 C and  106 K and the respective transfer rollers  130 Y,  130 M,  130 C and  130 K. The transfer rollers  130 Y,  130 M,  130 C and  130 K press the recording paper  107  sent out from the paper feeding unit  103  onto the external surface of the photosensitive drum  108  of each of the process cartridges  106 Y,  106 M,  106 C and  106 K so that the toner image on the photosensitive drum  108  is transferred to the recording paper  107 . The transfer unit  104  sends out the recording paper  107  transferred with the toner image towards the fixing unit  105 . 
     The fixing unit  105  is disposed downstream in the delivery direction of the recording paper  107  delivered by the transfer unit  104 . The fixing unit  105  includes a pair of rollers  105   a  and  105   b . The recording paper  107  is interleaved between the pair of rollers  105   a  and  105   b . The fixing unit  105  presses and heats the recording paper  107  sent out from the transfer unit  104  between the pair of rollers  105   a  and  105   b  so that the toner image transferred onto the recording paper  107  from the photosensitive drum  108  is fixed on the recording paper  107 . 
     The laser writing units  122 Y,  122 M,  122 C and  122 K are respectively fixed on the upper part of the apparatus main body  102 . Each of the laser writing units  122 Y,  122 M,  122 C and  122 K respectively corresponds to one of the process cartridges  106 Y,  106 M,  106 C and  106 K. The process cartridges  106 Y,  106 M,  106 C and  106 K include the electrical-charged roller  109 . The photosensitive drum  108  is electrical-charged uniformly by the electrical-charged roller  109 . The laser writing units  122 Y,  122 M,  122 C and  122 K irradiate (project) laser beams onto the external surface of the photosensitive drum  108  to form an electrostatic latent image. 
     The image forming apparatus  101 , as illustrated hereinbelow, forms an image on the recording paper  107 . First, the image forming apparatus  101  rotates the photosensitive drum  108  so that the external surface of the photosensitive drum  108  is electrical-charged uniformly by the electrical-charged roller  109 . Next, laser beams are irradiated (projected) onto the external surface of the photosensitive drum  108  so that an electrostatic latent image is formed on the external surface of the photosensitive drum  108 . Then when the electrostatic latent image is positioned in the image development area  131 , the developer agent adsorbed onto the external surface of the image development sleeve  132  of the image development device  113  is adsorbed onto the external surface of the photosensitive drum  108  so that the electrostatic latent image is developed and a toner image is formed on the external surface of the photosensitive drum  108 . 
     Then when the recording paper  107  delivered by the paper feeding roller  124  or the like of the paper feeding unit  103  is positioned between the delivery belt  129  of the transfer unit  104  and the photosensitive drum  108  of the process cartridges  106 Y,  106 M,  106 C and  106 K, the image forming apparatus  101  transfers the toner image formed on the external surface of the photosensitive drum  108  to the recording paper  107 . The image forming apparatus  101  fixes the toner image onto the recording paper  107  by the fixing unit  105 . In such a way, the image forming apparatus  101  forms a color image on the recording paper  107 . 
     As described above, the present invention includes the above described process cartridges  106 Y,  106 M,  106 C and  106 K so that the image forming apparatus  101  of a smaller size can be provided. 
     (Evaluation Test A) 
     The inventors of the present invention implemented a stiffness property test, a change of form test, an assembly property test, a drop off prevention test, a magnetic carrier attachment test and an agent severance property test using a magnet roller illustrated in the first embodiment (embodiment A1 through A4) and another magnet roller as the target of comparison (comparison example D1 through D4). 
     Embodiment A1 
     A compound of anisotropic Sr ferrite and PA12 (manufactured by Toda Kogyo Corp.) is used for the main body part  140 . The main body part  140  is injection molded at a resin temperature of 300° C. while a magnetic field of 0.6 T is simultaneously applied in a direction approximately parallel to the bottom surface  1442  of the main body groove  144 . Thereafter a magnetic field of 0.1 T is applied in a reverse direction to the direction during injection to demagnetize. Consequently, the main body part  140  of an external diameter φ of 8.5 mm and an overall length of 313 mm is obtained. In the main body groove  144  of the main body part  140 , the bottom surface  1442  is shaped to have a width of 2.7 mm, a tapered angle of 5 degrees is formed, the pair of tapered surfaces  1441   b  is shaped to have a width of 2.2 mm, the pair of straight surfaces  1441   a  is shaped to have a width of 0.17 mm. The groove shape of the main body groove is realized by the shape of a placed piece disposed orthogonal to the direction of the oriented magnetic field. 
     SUS301-¾H, that is, a spring material of non magnetic metal with a width of 6.0 mm, a length of 313 mm and a thickness of 0.3 mm is applied bending work to obtain the interposition member  142 . In the interposition member  142 , the floor part  1422  is shaped to have an outermost width of 2.6 mm, the pair of wall sections  1421  is shaped to have an outermost height of 2.3 mm, a 5 degrees spread angle (that is, an angle against the direction orthogonal to the width direction of the floor part) is formed. 
     For the rare earth magnet block  141 , 950 g of anisotropic Nd—Fe—B magnetic powders (Magfine MF-P13 manufactured by Aichi Steel Corp.) and 50 g of minute resin particles of thermal plasticity (against 100 parts by weight of polyester resin, 1.5 parts by weight of quaternary ammonium salt (charged control agent), 1.5 parts by weight of styrene acryl resin (low softening point material) and 2.0 parts by weight of carbon black are added internally, 1.5 parts by weight of silica (H2000) is added externally) are kneaded in a tumbler mixer to be filled into the metal mold thereafter. The rare earth magnet block  141  is then compression molded within the magnetic field under a pressed pressure of 400 kN while an oriented current of 100 A is applied in a 90 degrees direction against the pressed direction. Thereafter the metal mold and the magnet block are demagnetized at a pulse voltage of 3500V, demolded and burned at 100° C. for 60 minutes. Consequently, the rare earth magnet block  141  of a width of 2.0 mm, a height of 2.4 mm, a length of 313 mm and a “R” shaped upper surface (reverse to the side of press-fitting) is obtained. 
     The rare earth magnet block  141  is magnetized. Next, the rare earth magnet block  141  is press-fitted into the concave portion  1423  of the interposition member  142 . Then the interposition member  142  is press-fitted into the main body groove  144  of the main body part  140 . Thereby the magnet roller  133 A of the embodiment A1 is obtained. 
     Embodiment A2 
     The embodiment A2 is the same as the embodiment A1 except that the material for the interposition member  142  is changed to a spring material of SUS301-H. 
     Embodiment A3 
     The embodiment A3 is the same as the embodiment A1 except that the rare earth magnet block  141  is first press-fitted into the interposition member  142 . Then the rare earth magnet block  141  is magnetized. Thereafter the interposition member  142  is press-fitted into the main body groove  144  of the main body part  140 . 
     Embodiment A4 
     The embodiment A4 is the same as the embodiment A2 except that the rare earth magnet block  141  is first press-fitted into the interposition member  142 . Then the rare earth magnet block  141  is magnetized. Thereafter the interposition member  142  is press-fitted into the main body groove  144  of the main body part  140 . 
     Comparison Example D1 
     A compound of anisotropic Sr ferrite and PA12 (manufactured by Toda Kogyo Corp.) is used for a magnet roller main body part having a groove shape. The magnet roller main body part is injection molded at a resin temperature of 300° C. while a magnetic field of 0.6 T is simultaneously applied in a direction parallel to a bottom surface of the groove of the magnet roller main body part. Thereafter a magnetic field of 0.1 T is applied in a reverse direction to the direction during injection to demagnetize. Consequently, the magnet roller main body part of an axial integrated type is obtained having an external diameter φ of 8.5 mm and an overall length of 313 mm. The groove of the magnet roller main body part is shaped so that the bottom surface has a width of 2.1 mm, a tapered angle of 5 degrees is formed, a pair of tapered surfaces has a width of 1.9 mm and a pair of straight surfaces has a width of 0.17 mm. The groove shape of the magnet roller main body part is realized by the shape of a placed piece disposed orthogonal to the direction of the oriented magnetic field. 
     For a rare earth magnet block, 950 g of anisotropic Nd—Fe—B magnetic powders (Magfine MF-P13 manufactured by Aichi Steel Corp.) and 50 g of minute resin particles of thermal plasticity (against 100 parts by weight of polyester resin, 1.5 parts by weight of quaternary ammonium salt (charged control agent), 1.5 parts by weight of styrene acryl resin (low softening point material) and 2.0 parts by weight of carbon black are added internally, 1.5 parts by weight of silica (H2000) is added externally) are kneaded in a tumbler mixer to be filled into the metal mold thereafter. The rare earth magnet block is then compression molded within the magnetic field under a pressed pressure of 400 kN while an oriented current of 100 A is applied in a 90 degrees direction against the pressed direction. Thereafter the metal mold and the magnet block are demagnetized at a pulse voltage of 3500V, demolded and burned at 100° C. for 60 minutes. Consequently, the rare earth magnet block of a width of 2.0 mm, a height of 2.4 mm, a length of 313 mm and an “R” shaped side reverse to the side of press-fitting is obtained. 
     The rare earth magnet block is magnetized. Next, the rare earth magnet block is press-fitted into the axial integrated type magnet roller main body having the groove shape. Thereby the magnet roller of the comparison example D1 is obtained. 
     Comparison Example D2 
     The comparison example D2 is the same as the embodiment A1 except that the shape of the placed piece is changed to obtain an axial integrated type magnet roller in which a main body groove  144  includes a bottom surface  1442  shaped to have a width of 2.7 mm, a tapered angle of 5 degrees, a pair of tapered surfaces  1441   b  shaped to have a width of 2.4 mm, a pair of straight surfaces  1441   a  shaped to have no width (0 mm). 
     Comparison Example D3 
     The comparison example D3 is the same as the embodiment A1 except that the material used for the interposition member  142  is changed to a spring material of SUS420J2 having magnetic property. 
     Comparison Example D4 
     The comparison example D4 is the same as the embodiment A1 except that the oriented magnetic field is applied in a direction approximately orthogonal to the bottom surface  1442  of the main body groove  144 . 
     Each of the constitutions of the above-described embodiment A1 through A4 and comparison example D1 through D4 is illustrated in table 1. 
                                         TABLE 1                       groove           relationship           shape of       assembly   between the           the   material of the   sequence of the   oriented magnetic           magnet   interposition   rare earth magnet   field and the main           roller   member   block   body groove                                                        Embodiment   straight   SUS301-3/4H   magnetize →   approximately       A1   part and   (non   press-fitted into the   parallel to the           tapered   magnetic)   interpostition   bottom surface of           part       member →   the main body                   press-fitted into the magnet   groove                   roller       Embodiment   straight   SUS301-H   magnetize →   approximately       A2   part and   (non   press-fitted into the   parallel to the           tapered   magnetic)   interpostition   bottom surface of           part       member →   the main body                   press-fitted into the   groove                   magnet roller       Embodiment   straight   SUS301-3/4H   press-fitted into   approximately       A3   part and   (non   the interposition   parallel to the           tapered   magnetic)   member →   bottom surface of           part       magnetize →   the main body                   press-fitted into the   groove                   magnet roller       Embodiment   straight   SUS301-H   press-fitted into   approximately       A4   part and   (non   the interposition   parallel to the           tapered   magnetic)   member →   bottom surface of           part       magnetize →   the main body                   press-fitted into the   groove                   magnet roller       Comparison   straight   none   magnetize →   approximately       ExampleD1   part and       press-fitted into   parallel to the           tapered       the magnet roller   bottom surface of           part           the main body                       groove       Comparison   without   SUS301-3/4H   magnetize →   approximately       ExampleD2   straight   (non   press-fitted into the   parallel to the           part   magnetic)   interpostition   bottom surface of                   member →   the main body                   press-fitted into the   groove                   magnet roller       Comparison   straight   SUS402J2   magnetize →   approximately       ExampleD3   part and   (magnetic)   press-fitted into the   parallel to the           tapered       interpostition   bottom surface of           part       member →   the main body                   press-fitted into the   groove                   magnet roller       Comparison   straight   SUS301-3/4H   magnetize →   approximately       ExampleD4   part and   (non   press-fitted into the   orthogonal to the           tapered   magnetic)   interpostition   bottom surface of           part       member →   the main body                   press-fitted into the   groove                   magnet roller                    
(Test Method)
 
(1) Stiffness Property Test
 
     The magnet rollers of the embodiment A1 through A4 and the comparison example D1 are supported with a 300 mm distance between supporting points. When a load up to 3N is applied to the central part of the magnet rollers, amount of displacement (amount of flexure) is read by a lever type dial gauge. The slope of the load and the amount of flexure (in the unit of μm/N) is set as stiffness. The smaller is the slope, the higher is the stiffness (flexure is difficult to be generated). A graph summarizing the test result is illustrated in  FIG. 21 . 
     (2) Change of Form Test 
     The magnet rollers of the embodiment A1 through A4 and the comparison example D1 are disposed and stored for 72 hours in an environment of a temperature of 60° C. and a humidity of 80% RH. A laser end-measuring machine measures a deflection percentage change at the center of the body of the magnet rollers. The deflection percentage change is analyzed and a graph summarizing the test result is illustrated in  FIG. 22 . 
     (3) Assembly Property Test 
     When 1000 pieces of each of the magnet rollers of the embodiment A1 through A4 and the comparison example D1 are manufactured, the number of damaged rare earth magnet blocks when the rare earth magnet blocks are press-fitted is recorded. 
     (4) Drop Off Prevention Test 
     1000 pieces of each of the magnet rollers of the embodiment A1 through A4 and the comparison example D2 are manufactured. An image development sleeve of an external diameter of 10 mm, an internal diameter of 9.3 mm and a length of 325 mm is fixed on each of the magnet rollers so that image development rollers of an external diameter of 10 mm are obtained. Then a unit testing machine is mounted on each of the image development rollers. The image development rollers are then operated for 150 hours with the angular speed (rotation frequency) of the image development sleeves set to 400 RPM. Thereafter the number of interposition members dropped off (including positional displacements) is recorded. 
     (5) Magnetic Carrier Attachment Test 
     The magnet rollers of the embodiment A1 through A4 and the comparison example D3 are roller magnetized to obtain a final magnetic waveform. AL sleeves applied with SWB processing (external diameter φ 10 mm/internal diameter φ 9 mm) are fixed onto the magnet rollers so that image development rollers are obtained. An image development device is fixed on each of the image development rollers and a running test is performed. The number of carriers that passed over onto the photosensitive drum during the test is measured. 
     (6) Agent Severance Property Test 
     The magnet rollers of the embodiment A1 through A4 and the comparison example D4 are roller magnetized to obtain a final magnetic waveform. Image development sleeves made of aluminum and applied with SWB processing (external diameter φ 10 mm/internal diameter φ 9 mm) are fixed onto the magnet rollers so that image development rollers are obtained. The image development sleeve of the image development roller is rotated and the agent severance property of the developer agent is evaluated. 
     Each evaluation result is described by the following signs and summarized in Table 2. 
     ⊚: excellent 
     X: outside acceptable range (not suited for practical use) 
     ※1: with no interposition member 
     ※2: the same as the embodiment A1 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 (2) Change of form 
                 (3) Assembly 
                 (4) Drop off 
                   
                   
               
               
                   
                 (1) Stiffness 
                 test 
                 property test 
                 prevention test 
                 (5) Magnetic carrier 
                 (6) Agent severance 
               
               
                   
                 property test 
                 deflection 
                 number of 
                 number of dropped 
                 attachment test 
                 property test 
               
               
                   
                 stiffness 
                 percentage change 
                 damaged 
                 off interposition 
                 number of attached 
                 agent severance 
               
               
                   
                 [μm/N] 
                 [%] 
                 rare earth magnet 
                 member 
                 magnetic carriers 
                 property 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Embodiment A1 
                 ⊚: 81.2 
                 ⊚: below 17 
                 ⊚: 0/1000 piece 
                 ⊚: 0/1000 piece 
                 ⊚: below 10 
                 ⊚: with no ceaseless 
               
               
                   
                   
                   
                   
                   
                   
                 adhering of the developer 
               
               
                   
                   
                   
                   
                   
                   
                 agent 
               
               
                 Embodiment A2 
                 ⊚: 77.9 
                 ⊚: below 19 
                 ⊚: 0/1000 piece 
                 ⊚: 0/1000 piece 
                 ⊚: below 10 
                 ⊚: with no ceaseless 
               
               
                   
                   
                   
                   
                   
                   
                 adhering of the developer 
               
               
                   
                   
                   
                   
                   
                   
                 agent 
               
               
                 Embodiment A3 
                 ⊚: 81.7 
                 ⊚: below 18 
                 ⊚: 0/1000 piece 
                 ⊚: 0/1000 piece 
                 ⊚: below 10 
                 ⊚: with no ceaseless 
               
               
                   
                   
                   
                   
                   
                   
                 adhering of the developer 
               
               
                   
                   
                   
                   
                   
                   
                 agent 
               
               
                 Embodiment A4 
                 ⊚: 78.0 
                 ⊚: below 17 
                 ⊚: 0/1000 piece 
                 ⊚: 0/1000 piece 
                 ⊚: below 10 
                 ⊚: with no ceaseless 
               
               
                   
                   
                   
                   
                   
                   
                 adhering of the developer 
               
               
                   
                   
                   
                   
                   
                   
                 agent 
               
               
                 Comparison Example 
                 X: 139.2 
                 X: above 50 
                 X: 30/1000 pieces 
                 ※1 
                 ※2 
                 ※2 
               
               
                 D1 
               
               
                 Comparison Example 
                 ※2 
                 ※2 
                 ※2 
                 X: 20/1000 pieces 
                 ※2 
                 ※2 
               
               
                 D2 
               
               
                 Comparison Example 
                 ※2 
                 ※2 
                 ※2 
                 ※2 
                 X: above 50 
                 ※2 
               
               
                 D3 
               
               
                 Comparison Example 
                 ※2 
                 ※2 
                 ※2 
                 ※2 
                 ※2 
                 X: ceaseless adhering of the 
               
               
                 D4 
                   
                   
                   
                   
                   
                 developer agent is present 
               
               
                   
               
               
                 ⊚: excellent 
               
               
                 X: outside acceptable range (not suited for practical use) 
               
               
                 ※1: with no interposition member 
               
               
                 ※2 the same to the embodiment A1 
               
            
           
         
       
     
     Results of the evaluation test A are discussed hereinbelow. 
     From the results of embodiment A1 through A4 and the comparison example D1, in the embodiment A1 through A4 constituted to include the interposition member, high stiffness of the magnet roller is realized. As a result, deflection percentage change is suppressed to be less or equal to 20%. On the other hand, in the comparison example D1, the magnet roller has insufficient stiffness and deflection percentage change exceeds 50%. Therefore, it is clear that by including the interposition member, stiffness of the magnet roller can be heightened. In addition, in the embodiment A1 through A4, first, the rare earth magnet block is press-fitted into the interposition member  142 . Then the interposition member  142  press-fitted with the rare earth magnet block is press-fitted into the main body groove  144 . Consequently, damages generated to the rare earth magnet block during assembly can be avoided. On the other hand, in the comparison example D1, damages are generated to the rare earth magnet block. Therefore, it is clear that the rare earth magnet block can be reinforced by the interposition member and assembly property (productivity) of the magnet roller can be improved. 
     In addition, from the results of embodiment A1 through A4 and the comparison example D2, in the embodiment A1 through A4, the pair of straight surfaces is disposed in the pair of side surfaces of the main body groove so that the upper end of the interposition member is caught by the pair of straight surfaces. Consequently, it is clear that drop off of the interposition member from the main body groove can be prevented. On the other hand, in the comparison example D2, a pair of straight surfaces is not disposed so that it is clear that the interposition member easily drops off. Therefore, it is clear that by disposing the pair of straight surfaces in the pair of side surfaces of the main body groove, drop off of the interposition member can be prevented. 
     In addition, from the results of embodiment A1 through A4 and the comparison example D3, in the embodiment A1 through A4, it is clear that fly over of magnetic carriers onto the photosensitive drum can be suppressed and the magnetic carriers can be attracted to the external surface of the image development roller by the strong magnetic force generated. On the other hand, in the comparison example D3, fly over of magnetic carriers onto the photosensitive drum is generated. Consequently, it is clear that magnetic force generated on the external surface of the image development roller is weakened. Therefore, it is clear that by using non magnetic materials for the interposition member, strong magnetic force can be generated. 
     In addition, from the results of embodiment A1 through A4 and the comparison example D4, in the embodiment A1 through A4, it is clear that ceaseless adhering of the developer agent to the image development roller is not present. On the other hand, in the comparison example D4, it is clear that ceaseless adhering of the developer agent is generated. Consequently, it is clear that magnetic force of the pole shift point can be weakened when the oriented direction of magnetic anisotropy of the magnet roller (main body part) is set to be approximately parallel to the bottom surface of the main body groove and approximately orthogonal to the axial direction and the developer agent can be severed at this position. 
     In addition, from the results of embodiment A1 through A4, it is clear that no great difference is generated to the test result even if the materials used for the interposition member differ when the interposition member is shaped using non magnetic materials. In addition, it is also clear that the sequence of the magnetization of the rare earth magnet block does not have any influence on the test result. 
     (Evaluation Test B) 
     The inventors of the present invention implemented an evaluation test with regard to positional displacements or drop off of an interposition member generated when the interposition member is press-fitted into the main body groove and the state of contact between an operated magnet roller and an image development sleeve using a magnet roller illustrated in the second embodiment (embodiment B1 through B5) and another magnet roller as the target of comparison (comparison example E1). 
     Embodiment B1 
     A compound of anisotropic Sr ferrite and PA12 (manufactured by Toda Kogyo Corp.) is used for the main body part  240 . The main body part  240  is injection molded at a resin temperature of 300° C. while a magnetic field of 0.6 T is simultaneously applied in a direction approximately parallel to the bottom surface  2442  of the main body groove  244 . Thereafter a magnetic field of 0.1 T is applied in a reverse direction to the direction during injection to demagnetize. Consequently, the main body part  240  is obtained. The main body part  240  is shaped to have an external diameter φ of 8.5 mm and an overall length of 313 mm. In the main body groove  244  of the main body part  240 , the bottom surface  2442  is shaped to have a width of 2.7 mm, a pair of side surfaces  2421  is shaped to have a height (width) of 2.4 mm and a 0 degree tapered angle is formed. 
     An interposition member  242  is a “U” character shaped member of a thickness of 0.3 mm and a length of 313 mm in which the width of a floor part  2422  is shaped to 2.6 mm, the height of a pair of wall sections  2421  is shaped to 2.3 mm. In the interposition member  242 , external surface wedge  2421   g  of a length of 0.1 mm is disposed in an interval of 0.6 mm. Similarly, internal surface wedge  2421   h  of a length of 0.1 mm is disposed in an interval of 0.6 mm. Wedge grooves  2421   e  of the external surface are misaligned for 0.3 mm in position against wedge grooves  2421   f  of the internal surface. The wedge groove  2421   e  of the external surface is disposed at 4 positions of an external surface  2421   c . Similarly, the wedge groove  2421   f  of the internal surface is disposed at 4 positions of an internal surface  2421   d.    
     After each wedge groove is disposed in such a way, the pair of wall sections  2421  of the interposition member  242  is subjected to bending work so that the pair of wall sections forms a 90 degrees angle (that is, a 0 degree spread angle) against the floor part  2422  so that the interposition member  242  with a saw blade shaped pair of wall sections is obtained. 
     For the rare earth magnet block  141 , 950 g of anisotropic Nd—Fe—B magnetic powders (Magfine MF-P13 manufactured by Aichi Steel Corp.) and 50 g of minute resin particles of thermal plasticity (against 100 parts by weight of polyester resin, 1.5 parts by weight of quaternary ammonium salt (charged control agent), 1.5 parts by weight of styrene acryl resin (low softening point material) and 2.0 parts by weight of carbon black are added internally, 1.5 parts by weight of silica (H2000) is added externally) are kneaded in a tumbler mixer to be filled into the metal mold thereafter. The rare earth magnet block  141  is then compression molded within the magnetic field under a pressed pressure of 400 kN while an oriented current of 100 A is applied in a 90 degrees direction against the pressed direction. Thereafter the metal mold and the magnet block are demagnetized at a pulse voltage of 3500V, demolded and burned at 100° C. for 60 minutes. Consequently, the rare earth magnet block  141  of a width of 2.0 mm, a height of 2.4 mm, a length of 313 mm and an “R” shaped side reverse to the side of press-fitting is obtained. 
     The rare earth magnet block  141  is magnetized and then press-fitted into the interposition member  242 . Next, the interposition member is press-fitted into the main body groove  244  of the main body part  240 . Thereby the magnet roller  133 B of the embodiment B1 is obtained. 
     Embodiment B2 
     The embodiment B2 is the same as the embodiment B1 except the magnet roller  133 B is obtained by applying bending work to the interposition member  242  so that the pair of wall sections  2421  of the interposition member  242  forms a 95 degrees angle (that is, a 5 degree spread angle) against the floor part  2422 . 
     Embodiment B3 
     The embodiment B3 is the same as the embodiment B1 except the main body part  240  is shaped to have an external diameter φ of 8.5 mm and an overall length of 313 mm. In the main body groove  244  of the main body part  240 , the bottom surface  2442  is shaped to have a width of 2.7 mm, a pair of side surfaces  2421  is shaped to have a height (width) of 2.4 mm and a 5 degrees tapered angle is formed. The interposition member  242  is applied bending work so that the pair of wall sections  2421  of the interposition member  242  forms a 95 degrees angle (that is, a 5 degree spread angle) against the floor part  2422 . 
     Embodiment B4 
     The embodiment B4 is the same as the embodiment B1 except that in the interposition member  242 , external surface wedge  2421   g  of a length of 0.1 mm is disposed in an interval of 0.8 mm. Similarly, internal surface wedge  2421   h  of a length of 0.1 mm is disposed in an interval of 0.8 mm. Wedge grooves  2421   e  of the external surface are misaligned for 0.4 mm in position against wedge grooves  2421   f  of the internal surface. The wedge groove  2421   e  of the external surface is disposed at 3 positions of an external surface  2421   c . Similarly, the wedge groove  2421   f  of the internal surface is disposed at 3 positions of an internal surface  2421   d . The magnet roller  133 B is obtained under such a constitution. 
     Embodiment B5 
     The embodiment B5 is the same as the embodiment B1 except that in the interposition member  242 , external surface wedge  2421   g  of a length of 0.07 mm is disposed in an interval of 0.6 mm. Similarly, the internal surface wedge  2421   h  of a length of 0.07 mm is disposed in an interval of 0.6 mm. Wedge grooves  2421   e  of the external surface are misaligned for 0.3 mm in position against wedge grooves  2421   f  of the internal surface. The wedge groove  2421   e  of the external surface is disposed at 4 positions of an external surface  2421   c . Similarly, the wedge groove  2421   f  of the internal surface is disposed at 4 positions of an internal surface  2421   d . The magnet roller  133 B is obtained under such a constitution. 
     Comparison Example E1 
     A compound of anisotropic Sr ferrite and PA12 (manufactured by Toda Kogyo Corp.) is used for a magnet roller main body part having a groove shape. The magnet roller main body part is injection molded at a resin temperature of 300° C. while a magnetic field of 0.6 T is simultaneously applied in a direction parallel to a bottom surface of the groove of the magnet roller main body part. Thereafter a magnetic field of 0.1 T is applied in a reverse direction to the direction during injection to demagnetize. Consequently, the magnet roller main body part of an axial integrated type is obtained having an external diameter φ of 8.5 mm and an overall length of 313 mm. The groove of the magnet roller main body part is shaped so that the bottom surface has a width of 2.7 mm, a pair of side surfaces has a height (width) of 2.4 mm and a tapered angle of 0 degrees is formed. 
     An interposition member in the comparison example E1 is a “U” character shaped member of a thickness of 0.3 mm and a length of 313 mm in which the width of a floor part is shaped to 2.6 mm, the height (width) of a pair of wall sections is shaped to 2.3 mm. The interposition member includes no saw blade shaped parts. In addition, the angle formed by the pair of wall sections of the interposition member against the floor part is 90 degrees. 
     For a rare earth magnet block, 950 g of anisotropic Nd—Fe—B magnetic powders (Magfine MF-P13 manufactured by Aichi Steel Corp.) and 50 g of minute resin particles of thermal plasticity (against 100 parts by weight of polyester resin, 1.5 parts by weight of quaternary ammonium salt (charged control agent), 1.5 parts by weight of styrene acryl resin (low softening point material) and 2.0 parts by weight of carbon black are added internally, 1.5 parts by weight of silica (H2000) is added externally) are kneaded in a tumbler mixer to be filled into the metal mold thereafter. The rare earth magnet block is then compression molded within the magnetic field under a pressed pressure of 400 kN while an oriented current of 100 A is applied in a 90 degrees direction against the pressed direction. Thereafter the metal mold and the magnet block are demagnetized at a pulse voltage of 3500V, demolded and burned at 100° C. for 60 minutes. Consequently, the rare earth magnet block of a width of 2.0 mm, a height of 2.4 mm, a length of 313 mm and an “R” shaped side reverse to the side of press-fitting is obtained. 
     The rare earth magnet block is first magnetized and then press-fitted into the interposition member. Next, the interposition member together with the rare earth magnet block is press-fitted into the groove shaped axial integrated type magnet roller so that the magnet roller of the comparison example E1 is obtained. 
     (Test Method) 
     (7) Drop Off Prevention Test 
     1000 pieces of each of the magnet rollers of the embodiment B1 through B5 and the comparison example E2 are manufactured. An image development sleeve of an external diameter of 10 mm, an internal diameter of 9.3 mm and a length of 325 mm is fixed on each of the magnet rollers so that image development rollers of an external diameter of 10 mm are obtained. Then a unit testing machine is mounted on each of the image development rollers. The image development rollers are then operated for 150 hours with the angular speed (rotation frequency) of the image development sleeves set to 400 RPM. Thereafter the number of interposition members dropped off (including positional displacements) is recorded. Besides, rotational states of the image development sleeves during operation are also confirmed. 
     Evaluation results of each of the above described embodiments B1 through B5 and the comparison example E1 are described by the following signs and summarized in table 3. 
     ⊚: excellent 
     X: outside acceptable range (not suited for practical use) 
     ◯: the image development sleeve and the rare earth magnet block are not in contact and the image development sleeve maintains a constant angular velocity. 
     X: the image development sleeve and the rare earth magnet block are in contact and the image development sleeve is locked. 
     
       
         
           
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 (7) Drop off prevention test 
               
            
           
           
               
               
               
            
               
                   
                   
                 state of contact with 
               
               
                   
                 positional displacements 
                 the image 
               
               
                   
                 and drop offs after 
                 development sleeve 
               
               
                   
                 press-fitting 
                 during operation 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Embodiment B1 
                 ⊚: 0/1000 piece 
                 ◯ 
               
               
                 Embodiment B2 
                 ⊚: 0/1000 piece 
                 ◯ 
               
               
                 Embodiment B3 
                 ⊚: 0/1000 piece 
                 ◯ 
               
               
                 Embodiment B4 
                 ⊚: 0/1000 piece 
                 ◯ 
               
               
                 Embodiment B5 
                 ⊚: 0/1000 piece 
                 ◯ 
               
               
                 Comparison Example E1 
                 X: 20/1000 piece  
                 X 
               
               
                   
               
               
                 ⊚: excellent 
               
               
                 X: outside acceptable range (not suited for practical use) 
               
               
                 ◯: the image development sleeve and the rare earth magnet block are not in contact and the image development sleeve maintains a constant angular velocity. 
               
               
                 X: the image development sleeve and the rare earth magnet block are in contact and the image development sleeve is locked. 
               
            
           
         
       
     
     Results of the evaluation test B are discussed hereinbelow. 
     From the results of the embodiment B1 through B5 and the comparison example E1, in the embodiment B1 through B5, there are no positional displacements and drop offs of the interposition member during operation. On the other hand, in the comparison example E1, it is clear that the interposition member easily drops off. Therefore, it is clear that by disposing wedge grooves of the external surface and wedge grooves of the internal surface in the interposition member, positional displacements and drop offs of the interposition member can be prevented. 
     In addition, from the results of the embodiment B1 through B5, it is clear that positional displacements and drop offs of the interposition member can be prevented if at least the tapered angle of the main body groove  244  is 0 to 5 degrees and the spread angle of the pair of wall sections  2421  in the interposition member  242  is greater or equal to the tapered angle. In addition, it is clear that positional displacements and drop offs of the interposition member can be prevented if at least the length of the external surface wedges  2421   g  and the internal surface wedges  2421   h  is in the range of 0.07 to 0.1 mm, the interval of the external surface wedges  2421   g  and the interval of the internal surface wedges  2421   h  is in the range of 0.6 to 0.8 mm and the positional misalignment between the wedge grooves  2421   e  of the external surface and the wedge grooves  2421   f  of the internal surface is in the range of 0.3 to 0.4 mm. 
     (Evaluation Test C) 
     The inventors of the present invention implemented a stiffness property test, a change of form test, a drop off prevention test and an agent severance property test using a magnet roller illustrated in the third embodiment (embodiment C1 through C4) and another magnet roller as the target of comparison (comparison example F1 through F3). 
     Embodiment C1 
     A compound of anisotropic Sr ferrite and PA12 (manufactured by Toda Kogyo Corp.) is used for the main body part  340 . The main body part  340  is injection molded at a resin temperature of 300° C. while a magnetic field of 0.6 T is simultaneously applied in a direction approximately parallel to the bottom surface  3442  of the main body groove  344 . Thereafter a magnetic field of 0.1 T is applied in a reverse direction to the direction during injection to demagnetize. Consequently, the main body part  340  of an external diameter φ of 8.5 mm and an overall length of 313 mm is obtained. In the main body groove  344  of the main body part  340 , the bottom surface  3442  is shaped to have a width of 2.7 mm, a distance from the axial center to the bottom surface  3442  is shaped to 1.85 mm, the width of an opening part of the main body groove  344  is shaped to 2.31 mm, the angle formed by the bottom surface  3442  and a pair of side surfaces  3441  is shaped to 85 degrees (that is, reverse tapered shaped). The groove shape of the main body groove is realized by the shape of a placed piece disposed orthogonal to the direction of the oriented magnetic field. 
     SUS301-¾H, that is, a spring material of non magnetic metal with a thickness of 0.3 mm is applied bending work to obtain the interposition member  342 . In the interposition member  342 , the length (width) of the side of the upper surface  3422   a  of the floor part  3422  is shaped to 1.6 mm, the length (height) of the side of the internal surface  3421   d  of the pair of wall sections  3421  is shaped to 1.92 mm, the floor part  3422  is concave “R” shaped (refer to  FIG. 10 ) and a 3 degrees spread angle is formed. 
     For the rare earth magnet block  141 , 950 g of anisotropic Nd—Fe—B magnetic powders (Magfine MF-P13 manufactured by Aichi Steel Corp.) and 50 g of minute resin particles of thermal plasticity (against 100 parts by weight of polyester resin, 1.5 parts by weight of quaternary ammonium salt (charged control agent), 1.5 parts by weight of styrene acryl resin (low softening point material) and 2.0 parts by weight of carbon black are added internally, 1.5 parts by weight of silica (H2000) is added externally) are kneaded in a tumbler mixer to be filled into the metal mold thereafter. The rare earth magnet block  141  is then compression molded within the magnetic field under a pressed pressure of 400 kN while an oriented current of 100 A is applied in a 90 degrees direction against the pressed direction. Thereafter the metal mold and the magnet block are demagnetized at a pulse voltage of 3500V, demolded and burned at 100° C. for 60 minutes. Consequently, the rare earth magnet block  141  of a width of 1.76 mm, a height of 2.4 mm, a length of 313 mm and an “R” shaped side reverse to the side of press-fitting is obtained. 
     The rare earth magnet block  141  is first magnetized. Next, the rare earth magnet block  141  and the interposition member  342  are simultaneously press-fitted into the main body groove  344  of the main body part  340  so that the magnet roller  133 C of the embodiment C1 is obtained. 
     Embodiment C2 
     The embodiment C2 is the same as the embodiment C1 except that in the interposition member  342 , the length (width) of the side of the upper surface  3422   a  of the floor part  3422  is shaped to 1.6 mm, the length (height) of the side of the internal surface  3421   d  of the pair of wall sections  3421  is shaped to 1.92 mm, the floor part  3422  is convex “R” shaped (refer to  FIG. 11 ) and a 3 degrees spread angle is formed. 
     Embodiment C3 
     The embodiment C3 is the same as the embodiment C1 except that in the interposition member  342 , the length (width) of the side of the upper surface  3422   a  of the floor part  3422  is shaped to 1.6 mm, the length (height) of the side of the internal surface  3421   d  of the pair of wall sections  3421  is shaped to 1.92 mm, the floor part  3422  is “V” letter shaped (refer to  FIG. 12 ) and a 3 degrees spread angle is formed. 
     Embodiment C4 
     The embodiment C4 is the same as the embodiment C1 except that in the interposition member  342 , the length (width) of the side of the upper surface  3422   a  of the floor part  3422  is shaped to 1.6 mm, the length (height) of the side of the internal surface  3421   d  of the pair of wall sections  3421  is shaped to 1.92 mm, the floor part  3422  is reverse “V” letter shaped (refer to  FIG. 13 ) and a 3 degrees spread angle is formed. 
     Comparison Example F1 
     A compound of anisotropic Sr ferrite and PA12 (manufactured by Toda Kogyo Corp.) is used for a magnet roller main body part having a groove shape. The magnet roller main body part is injection molded at a resin temperature of 300° C. while a magnetic field of 0.6 T is simultaneously applied in a direction parallel to a bottom surface of the groove of the magnet roller main body part. Thereafter a magnetic field of 0.1 T is applied in a reverse direction to the direction during injection to demagnetize. Consequently, the magnet roller main body part of an axial integrated type is obtained having an external diameter φ of 8.5 mm and an overall length of 313 mm. The groove of the magnet roller main body part is shaped so that the bottom surface has a width of 2.1 mm, a pair of side surfaces has a height (width) of 2.4 mm and a tapered angle of 5 degrees is formed. The groove shape of the magnet roller main body part is realized by the shape of a placed piece disposed orthogonal to the direction of the oriented magnetic field. 
     For a rare earth magnet block, 950 g of anisotropic Nd—Fe—B magnetic powders (Magfine MF-P13 manufactured by Aichi Steel Corp.) and 50 g of minute resin particles of thermal plasticity (against 100 parts by weight of polyester resin, 1.5 parts by weight of quaternary ammonium salt (charged control agent), 1.5 parts by weight of styrene acryl resin (low softening point material) and 2.0 parts by weight of carbon black are added internally, 1.5 parts by weight of silica (H2000) is added externally) are kneaded in a tumbler mixer to be filled into the metal mold thereafter. The rare earth magnet block is then compression molded within the magnetic field under a pressed pressure of 400 kN while an oriented current of 100 A is applied in a 90 degrees direction against the pressed direction. Thereafter the metal mold and the magnet block are demagnetized at a pulse voltage of 3500V, demolded and burned at 100° C. for 60 minutes. Consequently, the rare earth magnet block of a width of 2.0 mm, a height of 2.4 mm, a length of 313 mm and an “R” shaped side reverse to the side of press-fitting is obtained. 
     The rare earth magnet block is first magnetized. Then the rare earth magnet block is press-fitted into the groove shaped axial integrated type magnet roller so that the magnet roller of the comparison example F1 is obtained. 
     Comparison Example F2 
     The comparison example F2 is the same as the embodiment C1 except the main body groove  344  of an axial integrated type magnet roller main body part is shaped so that the width of the bottom surface  3442  is 2.7 mm, the distance from the axial center to the bottom surface  3442  is 1.85 mm, the width of the opening part of the main body groove  344  is 2.31 mm and a tapered angle of 5 degrees is formed. Besides, an interposition member  342  is obtained in which the length (width) of the side of the upper surface  3422   a  of the floor part  3422  is shaped to 2.15 mm, the length (height) of the side of the internal surface  3421   d  of the pair of wall sections  3421  is shaped to 1.85 mm and the pair of wall sections  3421  forms a 5 degrees spread angle. 
     Comparison Example F3 
     The comparison example F3 is the same as the embodiment C1 except the applied direction of the oriented magnetic field is approximately orthogonal to the bottom surface  3442  of the main body groove  344 . 
     Each of the constitutions of the above-described embodiment C1 through C4 and the comparison example F1 through F3 is illustrated in table 4. 
                                         TABLE 4                               shape of the   relationship                   bottom   between the               material of   surface of   oriented               the   the   magnetic field           groove shape of the   interposition   interposition   and the           magnet roller   member   member   groove                                                        Embodiment   a reverse tapered angle   SUS301-3/4H   concave “R”   approximately       C1   of 85 degrees is formed   (non   shaped   parallel to the           between the bottom   magnetic)       bottom           surface of the main           surface of the           body groove and the           main body           pair of side surfaces           groove       Embodiment   a reverse tapered angle   SUS301-3/4H   convex “R”   approximately       C2   of 85 degrees is formed   (non   shaped   parallel to the           between the bottom   magnetic)       bottom           surface of the main           surface of the           body groove and the           main body           pair of side surfaces           groove       Embodiment   a reverse tapered angle   SUS301-3/4H   “V” letter   approximately       C3   of 85 degrees is formed   (non   shaped   parallel to the           between the bottom   magnetic)       bottom           surface of the main           surface of the           body groove and the           main body           pair of side surfaces           groove       Embodiment   a reverse tapered angle   SUS301-3/4H   reverse “V”   approximately       C4   of 85 degrees is formed   (non   letter   parallel to the           between the bottom   magnetic)   shaped   bottom           surface of the main           surface of the           body groove and the           main body           pair of side surfaces           groove       Comparison   a tapered angle of 95   none   none   approximately       ExampleF1   degrees is formed           parallel to the           between the bottom           bottom           surface of the main           surface of the           body groove and the           main body           pair of side surfaces           groove       Comparison   a tapered angle of 95   SUS301-3/4H   flat plane   approximately       ExampleF2   degrees is formed   (non   shaped   parallel to the           between the bottom   magnetic)       bottom           surface of the main           surface of the           body groove and the           main body           pair of side surfaces           groove       Comparison   a reverse tapered angle   SUS301-3/4H   concave “R”   approximately       ExampleF3   of 85 degrees is formed   (non   shaped   orthogonal to           between the bottom   magnetic)       the bottom           surface of the main           surface of the           body groove and the           main body           pair of side surfaces           groove                    
(Test Method)
 
(8) Stiffness Property Test
 
     The magnet rollers of the embodiment C1 through C4 and the comparison example F1 are supported with a 300 mm distance between supporting points. When a load up to 3N is applied to the central part of the magnet rollers, amount of displacement (amount of flexure) is read by a lever type dial gauge. The slope of the load and the amount of flexure (in the unit of μm/N) is set as stiffness. The smaller is the slope, the higher is the stiffness (flexure is difficult to be generated). 
     (9) Change of Form Test 
     The magnet rollers of the embodiment C1 through C4 and the comparison example F1 are disposed and stored for 72 hours in an environment of a temperature of 60° C. and a humidity of 80% RH. A laser end-measuring machine measures a deflection percentage change at the center of the body of the magnet rollers. The deflection percentage change is analyzed. 
     (10) Drop Off Prevention Test 
     1000 pieces of each of the magnet rollers of the embodiment C1 through C4 and the comparison example F2 are manufactured. An image development sleeve of an external diameter of 10 mm, an internal diameter of 9.3 mm and a length of 325 mm is fixed on each of the magnet rollers so that image development rollers of an external diameter of 10 mm are obtained. Then a unit testing machine is mounted on each of the image development rollers. The image development rollers are then operated for 150 hours with the angular speed (rotation frequency) of the image development sleeves set to 400 RPM. Thereafter the number of interposition members dropped off (including positional displacements) is recorded. 
     (11) Agent Severance Property Test 
     The magnet rollers of the embodiment C1 through C4 and the comparison example F3 are roller magnetized to obtain a final magnetic waveform. AL sleeves applied with SWB processing (external diameter φ 10 mm/internal diameter φ 9 mm) are fixed onto the magnet rollers so that image development rollers are obtained. The image development sleeve of the image development roller is rotated and the agent severance property of the developer agent is evaluated. 
     Each evaluation result is described by the following signs and summarized in table 5. 
     ⊚: excellent 
     X: outside acceptable range (not suited for practical use) 
     ※1: with no interposition member 
     ※2: the same to the embodiment C1 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                   
                   
                 (4) Drop off 
                   
               
               
                   
                   
                 (2) Change of 
                 prevention test 
               
               
                   
                 (1) Stiffness 
                 form test 
                 number of 
                 (6) Agent severance 
               
               
                   
                 property test 
                 deflection 
                 dropped off 
                 property test 
               
               
                   
                 stiffness 
                 percentage 
                 interposition 
                 agent severance 
               
               
                   
                 [μm/N] 
                 change [%] 
                 member 
                 property 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Embodiment 
                 ⊚: 81.2 
                 ⊚: below 17 
                 ⊚: 0/1000 piece 
                 ⊚: with no ceaseless 
               
               
                 C1 
                   
                   
                   
                 adhering of the 
               
               
                   
                   
                   
                   
                 developer agent 
               
               
                 Embodiment 
                 ⊚: 77.9 
                 ⊚: below 19 
                 ⊚: 0/1000 piece 
                 ⊚: with no ceaseless 
               
               
                 C2 
                   
                   
                   
                 adhering of the 
               
               
                   
                   
                   
                   
                 developer agent 
               
               
                 Embodiment 
                 ⊚: 81.7 
                 ⊚: below 18 
                 ⊚: 0/1000 piece 
                 ⊚: with no ceaseless 
               
               
                 C3 
                   
                   
                   
                 adhering of the 
               
               
                   
                   
                   
                   
                 developer agent 
               
               
                 Embodiment 
                 ⊚: 78.0 
                 ⊚: below 17 
                 ⊚: 0/1000 piece 
                 ⊚: with no ceaseless 
               
               
                 C4 
                   
                   
                   
                 adhering of the 
               
               
                   
                   
                   
                   
                 developer agent 
               
               
                 Comparison 
                 X: 139.2 
                 X: above 50 
                 ※1 
                 ※2 
               
               
                 Example F1 
               
               
                 Comparison 
                 ※2 
                 ※2 
                 X: 20/1000 
                 ※2 
               
               
                 Example F2 
                   
                   
                 pieces 
               
               
                 Comparison 
                 ※2 
                 ※2 
                 ※2 
                 X: ceaseless 
               
               
                 Example F3 
                   
                   
                   
                 adhering of the 
               
               
                   
                   
                   
                   
                 developer agent is 
               
               
                   
                   
                   
                   
                 present 
               
               
                   
               
               
                 ⊚: excellent 
               
               
                 X: outside acceptable range (not suited for practical use) 
               
               
                 ※1: with no interposition member 
               
               
                 ※2: the same to the embodiment C1 
               
            
           
         
       
     
     Results of the evaluation test C are discussed hereinbelow. 
     From the results of the embodiment C1 through C4 and the comparison example F1, in the embodiment C1 through C4 constituted to include the interposition member, high stiffness of the magnet roller is realized. As a result, deflection percentage change is suppressed to be less or equal to 20%. On the other hand, in the comparison example F1, the magnet roller has insufficient stiffness and deflection percentage change exceeds 50%. Therefore, it is clear that by including the interposition member, stiffness of the magnet roller can be heightened. 
     In addition, from the results of the embodiment C1 through C4 and the comparison example F2, in the embodiment C1 through C4, because the main body groove is reverse tapered shaped (dovetail joint shaped) and the width of the floor part of the interposition member after press-fitting is larger than the width of the opening part of the main body groove, the interposition member is caught by the pair of side surfaces of the main body groove so that it is clear drop off of the interposition member can be prevented. On the other hand, in the comparison example F2, because the main body groove is tapered shaped, it is clear that the interposition member easily drops off. Therefore, it is clear that drop off of the interposition member can be prevented if the main body groove is reverse tapered shaped and the width of the floor part of the interposition member after press-fitting is larger than the width of the opening part of the main body groove. 
     In addition, from the results of the embodiment C1 through C4 and the comparison example F3, in the embodiment C1 through C4, it is clear that ceaseless adhering of the developer agent to the image development roller is not present. On the other hand, in the comparison example F3, it is clear that ceaseless adhering of the developer agent is generated. Consequently, it is clear that magnetic force of the pole shift point can be weakened when the oriented direction of magnetic anisotropy of the magnet roller (main body part) is set to be approximately parallel to the bottom surface of the main body groove and approximately orthogonal to the axial direction and the developer agent can be severed at this position. 
     In addition, from the results of the embodiment C1 through C4, the shape of the floor part of the interposition member  342  can be concave “R” shaped, convex “R” shaped, “V” letter shaped and reverse “V” letter shaped. It is clear that drop off prevention effects of the interposition member do not change regardless of which shape. 
     Therefore, according to the present invention, an interposition member with a “U” character shaped cross-sectional surface is fixed in a groove of a cylindrical column-like shaped main body part. A long magnetic compact is fixed in a concave portion of the interposition member. The cylindrical column-like shaped main body part is reinforced by the interposition member so that stiffness property of the main body part can be heightened. Consequently, even in the case the cylindrical column-like shaped main body part is changed into a small diameter (that is, smaller size), stiffness property thereof can be secured. Therefore, a magnetic field generating member of high stiffness and a smaller size can be provided. 
     In addition, according to the present invention, the interposition member is press-fitted into the groove of the cylindrical column-like shaped main body part to be fixed thereof. Consequently, an adhesive agent is not used for fixture of these members. Hence the interposition member can be detached easily from the groove of the main body part. Therefore, reuse of the interposition member becomes possible and the magnet field generating member can be provided cheaply. In addition, because an adhesive agent is not used for the fixture of the interposition member and the groove of the main body part, positional displacements of these members generated due to the drying of the adhesive agent can be avoided. Therefore, high precision assembly is possible. 
     In addition, according to the present invention, the long magnetic compact is press-fitted into the concave portion of the interposition member to be fixed thereof. Consequently, an adhesive agent is not used for fixture of these members. Hence the long magnetic compact can be detached easily from the interposition member. Therefore, reuse of the long magnetic compact becomes possible and the magnet field generating member can be provided cheaply. In addition, because an adhesive agent is not used for the fixture of the interposition member and the long magnetic compact, positional displacements of these members generated due to the drying of the adhesive agent can be avoided. Therefore, high precision assembly is possible. 
     In addition, according to the present invention, the pair of side surfaces of the main body groove includes the pair of straight surfaces shaped mutually parallel in the vicinity of the opening part of the main body groove and the pair of tapered surfaces shaped so that mutual intervals between the pair of tapered surfaces gradually narrow from lower ends of the straight surfaces towards the bottom surface of the main body groove the closer to the bottom surface. Therefore, when the interposition member is press-fitted into the main body groove, the pair of straight surfaces serves as stoppers and drop off of the interposition member from the main body groove can be prevented. An image development device or the like breaks down due to the drop off of the interposition member. Consequently, the magnetic field generating member with high reliability that can prevent such breakdowns is provided. 
     In addition, according to the present invention, the external surface of the pair of wall sections in the interposition member respectively come into close contact with the pair of tapered surfaces in the main body groove. The upper end of the pair of wall sections is respectively shaped to be positioned in the boundary between the straight surface and the tapered surface. Therefore, when the interposition member is press-fitted into the main body groove, the upper end of the pair of wall sections is caught in the boundary so that the two members are mutually fixed more reliably. Consequently, drop off of the interposition member from the main body groove can be prevented more reliably. The image development device or the like breaks down due to the drop off of the interposition member. Hence the magnetic field generating member with high reliability that can prevent such breakdowns is provided. 
     In addition, according to the present invention, the interposition member includes, in the external surface of the pair of wall sections, wedge grooves of the external surface directed from the upper end towards the lower end and shaped to form an acute angle thereof. Besides, external surfaces of the pair of wall sections are respectively shaped to closely contact the pair of side surfaces of the main body groove. By disposing the wedge grooves of the external surface, the external surface wedges directed from the lower end towards the upper end of the pair of wall sections are shaped. Consequently, when the interposition member is press-fitted into the main body groove, without the external surface wedges, the interposition member is likely to drop off from the main body groove in a direction. However, with the external surface wedges, the external surface wedges are caught by the pair of side surfaces of the main body groove against the drop off direction so that each of these members are fixed more certainly. Therefore, drop off of the interposition member from the main body groove and positional displacements thereof can be prevented more reliably. The image development device or the like breaks down due to the drop off of the interposition member. Hence the magnetic field generating member with high reliability that can prevent such breakdowns is provided. 
     In addition, according to the present invention, the pair of wall sections in the interposition member is shaped to form an angle larger than 90 degrees against the floor part in the interposition member. Therefore, when the interposition member is press-fitted into the main body groove, without the external surface wedges, the interposition member is likely to drop off from the main body groove in a direction. However, with the external surface wedges and the larger than 90 degrees angle formed by the pair of wall sections, the external surface wedges are further strongly caught by the pair of side surfaces of the main body groove against the drop off direction so that each of these members is fixed more reliably. Therefore, drop off of the interposition member from the main body groove and positional displacements thereof can be prevented more reliably. The image development device or the like breaks down due to the drop off of the interposition member. Hence the magnetic field generating member with high reliability that can prevent such breakdowns is provided. 
     In addition, according to the present invention, the interposition member includes, in the internal surface of the pair of wall sections, wedge grooves of the internal surface directed from the lower end towards the upper end and shaped to form an acute angle thereof. Besides, internal surfaces of the pair of wall sections are respectively shaped to closely contact the surfaces of the long magnetic compact. By disposing the wedge grooves of the internal surface, the internal surface wedges directed from the upper end towards the lower end of the pair of wall sections are shaped. Consequently, when the long magnetic compact is press-fitted into the interposition member, without the internal surface wedges, the long magnetic compact is likely to drop off from the interposition member in a direction. However, with the internal surface wedges, the internal surface wedges are caught by the surfaces of the long magnetic compact against the drop off direction so that each of these members is fixed more reliably. Therefore, drop off of the long magnetic compact from the interposition member and positional displacements thereof can be prevented more reliably. The image development device or the like breaks down due to the drop off of the long magnetic compact. Hence the magnetic field generating member with high reliability that can prevent such breakdowns is provided. 
     In addition, according to the present invention, the main body groove is dovetail joint shaped in which the width of the bottom surface is larger than the width of the opening part. When the interposition member is press fitted into the main body groove, because the width of the lower surface of the interposition member is shaped to be larger than the width of the opening part of the main body groove, the interposition member is caught by the opening part of the main body groove so that the interposition member can be fastened within the main body groove to be fixed thereof. Therefore, drop off of the interposition member from the main body groove can be prevented more certainly. The image development device or the like breaks down due to the drop off of the interposition member. Hence the magnetic field generating member with high reliability that can prevent such breakdowns is provided. 
     In addition, according to the present invention, the interposition member is shaped using non-magnetic materials. In comparison to a case in which magnetic materials are used for the interposition member, peak magnetic flux density on the external surface of a magnetic particle support body (the magnetic particle support body corresponds to the position of the interposition member) can be heightened. Therefore, the support of the developer agent on the external surface of the magnetic particle support body becomes advantageous. 
     In addition, according to the present invention, the interposition member is shaped using non-magnetic materials. In comparison to a case in which magnetic materials are used for the interposition member, peak magnetic flux density on the external surface of the magnetic particle support body (the magnetic particle support body corresponds to the position of the interposition member) can be heightened so that stiffness property of the magnetic field generating member can be further heightened. 
     In addition, according to the present invention, by applying magnetic force (magnetic field) in a direction approximately parallel to the bottom surface of the groove of the main body part and approximately orthogonal to the axial direction of the main body part, magnetic anisotropy is provided. Therefore, a point that shifts magnetic poles of the magnetic force (pole shift point) can be generated in the vicinity of the opening part of the groove so that magnetic force at this position can be lessened. Hence the developer agent attached to the magnetic particle support body can be cut at this position so that the developer agent drops off from the external surface of the image development roller. Consequently, rotations under a state in which the developer agent is ceaselessly sticking to the external surface of the image development roller due to the magnetic particle support body can be prevented. 
     In addition, according to the present invention, the interposition member is press-fitted into the main body groove after the long magnetic compact is press-fitted into the concave portion of the interposition member so that the long magnetic compact is reinforced by the interposition member. Therefore, bending and damages generated to the long magnetic compact when the long magnetic compact is press-fitted into the main body groove can be prevented. Consequently, the assembly workability of the magnetic field generating member and the yield ratio of the long magnetic compact can be improved so that productivity can be heightened. 
     In addition, according to the present invention, the long magnetic compact is press-fitted into the concave portion of the interposition member while simultaneously the interposition member is press-fitted into the main body groove so that the long magnetic compact is reinforced by the interposition member. Therefore, bending and damages generated to the long magnetic compact when the long magnetic compact is press-fitted into the main body groove can be prevented. Consequently, the assembly workability of the magnetic field generating member and the yield ratio of the long magnetic compact can be improved so that productivity can be heightened. 
     In addition, the present invention includes the above-described magnetic field generating member so that a small sized magnetic particle support body can be provided. 
     In addition, the present invention includes the above-described magnetic particle support body so that a small sized image development device can be provided. 
     In addition, the present invention includes the above-described image development device so that a small sized process cartridge can be provided. 
     In addition, the present invention includes the above-described process cartridge so that a small sized image forming apparatus can be provided. 
     The above-described embodiment is only a representative embodiment of the present invention. The present invention is not limited to the above-described embodiment. That is, various modifications and changes can be made to the above embodiment within a range not deviating from the scope of the present invention.