Patent Publication Number: US-7907877-B2

Title: Developing device, image forming apparatus, and image forming system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Japanese Patent Application No. 2007-144066 filed on May 30, 2007, which is herein incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to developing devices, image forming apparatuses, and image forming systems. 
     2. Related Art 
     Image forming apparatuses such as laser beam printers are well known. Such image forming apparatuses include, for example, an image bearing member that bears a latent image, and a developing device that develops the latent image borne on the image bearing member using toner. In the case where an image signal or the like is sent from an external device such as a computer, the image forming apparatus forms a toner image on the image bearing member by developing the latent image borne on the image bearing member using the developing device. Then, the image forming apparatus transfers the toner image to a medium and finally the image is formed on the medium. 
     The developing device is provided with a toner bearing member that bears toner and develops the latent image borne on the image bearing member using toner, and a regulation member that comes into contact with a contact section on a surface of the toner bearing member to regulate an amount of toner borne on that surface. The toner bearing member is provided with projecting sections that are arranged in a regular manner on its surface, and bears toner on the projecting sections and in portions of its surface other than the projecting sections. The regulation member is arranged so that a longitudinal direction of the regulation member runs along an axial direction of the toner bearing member, and so that a leading edge of the regulation member in a lateral direction and a thickness direction faces an upstream side of the toner bearing member in a rotating direction. In this developing device, after the toner borne on the toner bearing member is regulated by the regulation member, the toner is supplied for the development of the latent image on the image bearing member.
     Patent document 1: JP-A-2006-259384   Patent document 2: JP-A-2003-57940   

     By the way, there are cases where a toner having a slow charging rise (toner that takes time for its charging amount to reach a saturated charge amount) is used as the toner in this image forming apparatus. And a phenomenon called development memory can occur due to the slowness of the charging rise when the latent image is to be developed using this toner. And occurrences of this phenomenon are a cause of deterioration of image quality in images. 
     Accordingly, to inhibit the aforementioned development memory, a system is conceivable in which the latent image is developed using toner borne on portions other than the projecting sections on the surface of the toner bearing member. And this system is achievable by bringing the regulation member into contact with the toner bearing member so that a distance between the leading edge and the projecting sections in the case where the leading edge of the regulation member faces the projecting sections of the toner bearing member is smaller than a volume mean particle size of the toner. 
     However, in regard to the above description, it becomes difficult for the toner to be borne on the projecting sections, and the contact section of the regulation member may come into direct contact with the projecting sections without toner interposed therebetween. In the case where the contact section comes into direct contact with the projecting sections, the contact section adheres closely to the projecting sections undesirably, and due to this, problems such as unusual sounds may occur between the toner bearing member and the contact section during rotation. 
     SUMMARY 
     The invention is devised in light of these issues, and it is an advantage thereof to appropriately prevent deterioration in image quality of images and to cause the regulation member to come into contact with the toner bearing member appropriately. 
     A primary aspect of the invention for addressing these issues involves:
         a developing device, provided with:   a toner bearing member that bears toner that has core particles and a particulate external additive externally added to the core particles, and that develops a latent image borne on an image bearing member using the toner, the toner bearing member being rotatable and having projecting sections arranged in a regular manner on a surface of the toner bearing member; and   a regulation member that regulates an amount of toner borne on a surface of the toner bearing member by coming into contact with that surface at a contact section, the regulation member being arranged so that a longitudinal direction of the regulation member runs along an axial direction of the toner bearing member, and so that a leading edge of the regulation member in a lateral direction and a thickness direction faces an upstream side in a rotating direction of the toner bearing member,   wherein in the case where a volume mean particle size of the toner is set to a toner particle size A, a volume mean particle size of the external additive is set to an external additive particle size B, a ten-point average roughness of the projecting sections is set to a protrusion roughness C, and a distance between the leading edge and the projecting sections in the case where the leading edge of the regulation member faces the projecting sections is set to a distance D,   a relationship among sizes of the toner particle size A, the external additive particle size B, the protrusion roughness C, and the distance D is so that the protrusion roughness C&lt;the external additive particle size B&lt;the distance D&lt;the toner particle size A.       

     Other features of the invention will be made clear by reading the description of the present specification with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings wherein: 
         FIG. 1  is a diagram showing main structural components constituting a printer  10 ; 
         FIG. 2  is a block diagram showing a control unit of the printer  10  in  FIG. 1 ; 
         FIG. 3  is a schematic diagram of a developing device; 
         FIG. 4  a cross-sectional view showing main structural components of the developing device; 
         FIG. 5  is a perspective schematic diagram of a developing roller  510 ; 
         FIG. 6  is a front schematic diagram of the developing roller  510 ; 
         FIG. 7  is a schematic diagram showing shapes including projecting sections  512  and depressed sections  515 ; 
         FIG. 8  is a perspective view of a regulation blade  560  and a blade-supporting member  564 ; 
         FIG. 9  is an enlarged schematic diagram showing a state near a contact section  560   a  of the regulation blade  560  that comes into contact with the developing roller  510 ; 
         FIG. 10  is a perspective view of a holder  526 ; 
         FIG. 11  is a perspective view illustrating the holder  526  to which an upper seal  520 , the developing roller  510 , the regulation blade  560 , and the blade-supporting member  564  are attached in an assembled manner; 
         FIG. 12  is a perspective view illustrating the holder  526  attached to a housing  540 ; 
         FIG. 13  is an explanatory diagram for describing a mechanism of development memory occurrences; 
         FIG. 14  is a schematic diagram for describing a condition in which the contact section  560   a  comes into direct contact with the projecting sections  512  without toner being interposed therebetween; 
         FIG. 15  is a diagram for illustrating the projecting sections  512  being rough; 
         FIG. 16  is a schematic diagram that shows a state in which the contact section  560   a  comes into contact with the projecting sections  512  through the external additives; 
         FIGS. 17A and 17B  are schematic diagrams for describing a condition in which the toner borne on the projecting sections  512  roll; 
         FIG. 18  is a schematic diagram for describing a comparative example; 
         FIGS. 19A to 19E  are schematic diagrams showing transitional states of the developing roller  510  during the manufacturing process thereof; 
         FIG. 20  is an explanatory diagram for describing the rolling process of the developing roller  510 ; 
         FIG. 21  is a flowchart for describing an assembly method for a yellow developing device  54 ; 
         FIG. 22  is an explanatory diagram showing an external configuration of an image forming system; and 
         FIG. 23  is a block diagram showing the configuration of the image forming system shown in  FIG. 22 . 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     At least the following matters will be made clear by the present specification and the accompanying drawings. 
     A developing device, provided with:
         a toner bearing member that bears toner that has core particles and a particulate external additive externally added to the core particles, and that develops a latent image borne on an image bearing member using the toner, the toner bearing member being rotatable and having projecting sections arranged in a regular manner on a surface of the toner bearing member; and   a regulation member that regulates an amount of toner borne on a surface of the toner bearing member by coming into contact with that surface at a contact section, the regulation member being arranged so that a longitudinal direction of the regulation member runs along an axial direction of the toner bearing member, and so that a leading edge of the regulation member in a lateral direction and a thickness direction faces an upstream side in a rotating direction of the toner bearing member,   wherein in the case where a volume mean particle size of the toner is set to a toner particle size A, a volume mean particle size of the external additive is set to an external additive particle size B, a ten-point average roughness of the projecting sections is set to a protrusion roughness C, and a distance between the leading edge and the projecting sections in the case where the leading edge of the regulation member faces the projecting sections is set to a distance D,   a relationship among sizes of the toner particle size A, the external additive particle size B, the protrusion roughness C, and the distance D is so that the protrusion roughness C&lt;the external additive particle size B&lt;the distance D&lt;the toner particle size A. With this development apparatus, it is possible to appropriately prevent deterioration in image quality of images and to cause the regulating member to come into contact with the toner bearing member appropriately.       

     Furthermore, in the developing device, it is preferable that:
         the projecting sections and depressed sections that bear the toner are arranged in a regular manner on a surface of the toner bearing member,   the depressed sections are bottom portions of two types of spiral groove portions having different inclination angles with respect to a circumferential direction of the toner bearing member,   the two types of spiral groove portions mutually intersect so as to form a grid pattern,   the projecting sections are a square top surface surrounded by the two types of spiral groove portions, and   one of two diagonal lines of the square top surface runs along the circumferential direction.       

     Furthermore, in the developing device, it is preferable that:
         a small groove that is formed during processing of the toner bearing member and that runs along the circumferential direction of the toner bearing member is provided on the projecting sections. In this case, the contact section of the regulation member can be effectively prevented from adhering closely to the toner bearing member.       

     Furthermore, in the developing device, it is preferable that:
         the small groove is provided so as to not connect from one end to another end in the circumferential direction of the protrusion on which the small groove is provided. In this case, the contact section of the regulation member can be more effectively prevented from adhering closely to the toner bearing member.       

     Furthermore, in the developing device, it is preferable that:
         the toner is provided with a plurality of types of the external additives that are externally added to the core particles, and   the external additive particle size B is a volume mean particle size of an external additive having a largest volume mean particle size among the plurality of types of external additives. In this case, the contact section of the regulation member can be more effectively prevented from adhering closely to the toner bearing member.       

     Furthermore, in the developing device, it is preferable that:
         the regulation member is constituted by a rubber elastic member. In this case, the effect of appropriately bringing the projecting sections into contact with the contact section is achieved more effectively.       

     Furthermore, an image forming apparatus provided with a developing device can be achieved, the developing device including
         (a) an image bearing member for bearing a latent image,   (b) a toner bearing member that bears toner that has core particles and a particulate external additive externally added to the core particles, and that develops the latent image borne on the image bearing member using the toner, the toner bearing member being rotatable and having projecting sections arranged in a regular manner on a surface of the toner bearing member, and   (c) a regulation member that regulates an amount of toner borne on a surface of the toner bearing member by coming into contact with that surface of the toner bearing member at a contact section, the regulation member being arranged so that a longitudinal direction of the regulation member runs along an axial direction of the toner bearing member, and so that a leading edge of the regulation member in a lateral direction and a thickness direction faces an upstream side in a rotating direction of the toner bearing member,   wherein when a volume mean particle size of the toner is set to a toner particle size A, a volume mean particle size of the external additive is set to an external additive particle size B, a ten-point average roughness of the projecting sections is set to a protrusion roughness C, and a distance between the leading edge and the projecting sections when the leading edge of the regulation member faces the projecting sections is set to a distance D,   the developing device is so that a relationship among sizes of the toner particle size A, the external additive particle size B, the protrusion roughness C, and the distance D is so that the protrusion roughness C&lt;the external additive particle size B&lt;the distance D&lt;the toner particle size A. With this image forming apparatus, it is possible to appropriately prevent deterioration in image quality of images and to cause the regulating member to come into contact with the toner bearing member appropriately.       

     Furthermore, an image forming system can be achieved equipped with:
         (A) a computer; and   (B) an image forming apparatus that is connectable to the computer,       

     the image forming apparatus including a developing device provided with
             (a) an image bearing member for bearing a latent image,   (b) a toner bearing member that bears toner that has core particles and a particulate external additive externally added to the core particles, and that develops the latent image borne on the image bearing member using the toner, the toner bearing member being rotatable and having projecting sections arranged in a regular manner on a surface of the toner bearing member, and   (c) a regulation member regulates an amount of toner borne on a surface of the toner bearing member by coming into contact with that surface of the toner bearing member at a contact section and, the regulation member being arranged so that a longitudinal direction of the regulation member runs along an axial direction of the toner bearing member, and so that a leading edge of the regulation member in a lateral direction and a thickness direction faces an upstream side in a rotating direction of the toner bearing member,       wherein when a volume mean particle size of the toner is set to a toner particle size A, a volume mean particle size of the external additive is set to an external additive particle size B, a ten-point average roughness of the projecting sections is set to a protrusion roughness C, and a distance between the leading edge and the projecting sections in the case where the leading edge of the regulation member faces the projecting sections is set to a distance D,   the developing device is so that a relationship among sizes of the toner particle size A, the external additive particle size B, the protrusion roughness C, and the distance D is so that the protrusion roughness C&lt;the external additive particle size B&lt;the distance D&lt;the toner particle size A. With this image forming system, it is possible to appropriately prevent deterioration in image quality of images and to cause the regulation member to come into contact with the toner bearing member appropriately.
 
Example of Overall Configuration of Image Forming Apparatus
       

     Next, using  FIG. 1 , an outline of a laser beam printer (hereinafter, also referred to as “printer”)  10  serving as an example of an image forming apparatus is described.  FIG. 1  is a diagram showing the main structural components constituting the printer  10 . It should be noted that in  FIG. 1 , the vertical direction is indicated by the arrows, and, for example, a paper supply tray  92  is arranged at a lower section of the printer  10  and a fixing unit  90  is arranged at an upper section of the printer  10 . 
     As shown in  FIG. 1 , the printer  10  according to the present embodiment includes a charging unit  30 , an exposing unit  40 , a YMCK developing unit  50 , a first transferring unit  60 , an intermediate transferring member  70 , and a cleaning unit  75 , these units being arranged along the direction of rotation of a photoconductor  20 , which serves as an example of an image bearing member, and the printer  10  further includes a second transferring unit  80 , a fixing unit  90 , a display unit  95  constituted by a liquid crystal panel and serving as a means for making notifications to the user, and a control unit  100  for controlling these units and the like and managing operations of the printer. 
     The photoconductor  20  has a cylindrical conductive base and a photoconductive layer formed on the outer peripheral surface of the conductive base, and it is rotatable about its central axis. In the present embodiment, the photoconductor  20  rotates clockwise, as shown by the arrow in  FIG. 1 . 
     The charging unit  30  is a device for charging the photoconductor  20 , and the exposing unit  40  is a device that irradiates a laser beam to form a latent image on the charged photoconductor  20 . The exposing unit  40  includes, for example, a semiconductor laser, a polygon mirror, and an F-θ lens, and irradiates a modulated laser beam onto the charged photoconductor  20  in accordance with image signals that have been inputted from a host computer, not shown in the drawings, such as a personal computer or a word processor. 
     The YMCK developing unit  50  is a device that uses a toner T contained in the developing device to develop the latent image formed on the photoconductor  20 , the toner T being a black (K) toner contained in a black developing device  51 , a magenta (M) toner contained in a magenta developing device  52 , a cyan (C) toner contained in a cyan developing device  53 , and a yellow (Y) toner contained in a yellow developing device  54 . 
     By rotating the YMCK developing unit  50  in a state in which the four developing devices  51 ,  52 ,  53 , and  54  are mounted, it is possible to move the positions of these four developing devices  51 ,  52 ,  53 , and  54 . More specifically, the YMCK developing unit  50  holds the four developing devices  51 ,  52 ,  53 , and  54  with four holding sections  55   a ,  55   b ,  55   c , and  55   d , and the four developing devices  51 ,  52 ,  53 , and  54  can be rotated around a central shaft  50   a  while maintaining their relative positions. Every time the image forming corresponding to one page is finished, the developing devices are caused to selectively oppose the photoconductor  20 , thereby successively developing the latent image formed on the photoconductor  20  using the toner T contained in the developing devices  51 ,  52 ,  53 , and  54 . It should be noted that each of the four developing devices  51 ,  52 ,  53 , and  54  can be removed from the holding sections of the YMCK developing unit  50 . The developing devices are described in detail further below. 
     The first transferring unit  60  is a device for transferring a single color toner image formed on the photoconductor  20  to the intermediate transferring member  70 , and when the four toner colors are successively transferred over one another, a full color toner image is formed on the intermediate transferring member  70 . 
     The intermediate transferring member  70  is an endless belt made by providing a tin vapor deposition layer on the surface of a PET film and forming in a layered manner a semiconductive coating on its surface, and the intermediate transferring member  70  is driven to rotate at substantially the same circumferential speed as the photoconductor  20 . 
     The second transferring unit  80  is a device for transferring the single-color toner image or the full-color toner image formed on the intermediate transferring body  70  onto a medium such as paper, film, or cloth. 
     The fixing unit  90  is a device for fusing the single-color toner image or the full-color toner image, which has been transferred to the medium, onto the medium to turn it into a permanent image. 
     The cleaning unit  75  is a device that is provided between the first transferring unit  60  and the charging unit  30 , that has a rubber cleaning blade  76  that comes into contact with the surface of the photoconductor  20 , and that is for removing the toner T remaining on the photoconductor  20  by scraping it off with the cleaning blade  76  after the toner image has been transferred onto the intermediate transferring member  70  by the first transferring unit  60 . 
     The control unit  100  includes a main controller  101  and a unit controller  102  as shown in  FIG. 2 . An image signal and a control signal are inputted into the main controller  101 , and in accordance with a command based on the image signal and the control signal, the unit controller  102  controls the various units, for example, to form the image. 
     Next, description will be given regarding the operation of the printer  10  configured as above. 
     First, when image signals and control signals from a host computer (not shown) are inputted to the main controller  101  of the printer  10  via an interface (I/F)  112 , the photoconductor  20  and the intermediate transferring member  70  are rotated under the control of the unit controller  102  in accordance with a command from the main controller  101 . While rotating, the photoconductor  20  is successively charged by the charging unit  30  at a charging position. 
     The region of the photoconductor  20  that has been charged is brought to an exposure position through rotation of the photoconductor  20 , and a latent image corresponding to image information of a first color, for example yellow Y, is formed in that region by the exposing unit  40 . The YMCK developing unit  50  positions the yellow developing device  54 , which contains yellow (Y) toner, at the developing position opposing the photoconductor  20 . 
     The latent image formed on the photoconductor  20  is brought to the developing position by the rotation of the photoconductor  20 , and is developed with yellow toner by the yellow developing device  54 . Thus, a yellow toner image is formed on the photoconductor  20 . 
     The yellow toner image that is formed on the photoconductor  20  is brought to the first transferring position through rotation of the photoconductor  20  and is transferred to the intermediate transferring member  70  by the first transferring unit  60 . At this time, a first transferring voltage, which has an opposite polarity to the polarity to which the toner T is charged, is applied to the first transferring unit  60 . It should be noted that, during this process, the photoconductor  20  and the intermediate transferring member  70  are in contact, whereas the second transferring unit  80  is kept apart from the intermediate transferring member  70 . 
     By sequentially repeating the above-described processes with each of the developing devices for the second, the third, and the fourth color, toner images in four colors corresponding to the respective image signals are transferred to the intermediate transferring member  70  in a superimposed manner. Thus, a full color toner image is formed on the intermediate transferring member  70 . 
     With the rotation of the intermediate transferring member  70 , the full-color toner image formed on the intermediate transferring member  70  reaches a second transferring position, and is transferred onto the medium by the second transferring unit  80 . It should be noted that the medium is transported from the paper supply tray  92  to the second transferring unit  80  via a paper supply roller  94  and registration rollers  96 . Also, when performing the image transfer operation, the second transferring unit  80  is pressed against the intermediate transferring member  70  while applying a secondary transferring voltage to it. 
     The full-color toner image transferred onto the medium is heated and pressurized by the fixing unit  90  and thus fused to the medium. 
     On the other hand, after the photoconductor  20  has passed the first transferring position, the toner T adhering to the surface of the photoconductor  20  is scraped off by the cleaning blade  76  that is supported by the cleaning unit  75 , and the photoconductor  20  is prepared for charging in order to form the next latent image. The scraped-off toner T is collected in a remaining-toner collector of the cleaning unit  75 . 
     Overview of the Control Unit 
     Next, description is given regarding the configuration of the control unit  100  with reference to  FIG. 2 . The main controller  101  of the control unit  100  is electrically connected to the host computer via the interface  112 , and is provided with an image memory  113  for storing image signals inputted into it from the host computer. The unit controller  102  is electrically connected to each of the units of the apparatus body (i.e., the charging unit  30 , the exposing unit  40 , the YMCK developing unit  50 , the first transferring unit  60 , the cleaning unit  75 , the second transferring unit  80 , the fixing unit  90 , and the display unit  95 ), detects the state of the units by receiving signals from sensors provided in those units, and controls each of the units in accordance with the signals that are inputted from the main controller  101 . 
     Configuration Example of the Developing device 
     Next, description is given regarding a configuration example of the developing devices using  FIG. 3  to  FIG. 12 .  FIG. 3  is a schematic diagram of the developing device.  FIG. 4  is a cross-sectional view showing the main structural components of this developing device.  FIG. 5  is a perspective schematic diagram of a developing roller  510 .  FIG. 6  is a front schematic diagram of the developing roller  510 .  FIG. 7  is a schematic diagram showing shapes including projecting sections  512  and depressed sections  515 , and the lower diagram in  FIG. 7  shows a cross-sectional shape of an A-A cross section in the upper diagram of  FIG. 7 .  FIG. 8  is a perspective view of a regulation blade  560  and a blade-supporting member  564 .  FIG. 9  is an enlarged schematic diagram showing a state near a leading edge  560   b  of the regulation blade  560  that comes into contact with the developing roller  510 .  FIG. 10  is a perspective view of a holder  526 .  FIG. 11  is a perspective view illustrating the holder  526  to which an upper seal  520 , the developing roller  510 , the regulation blade  560 , and the blade-supporting member  564  are attached in an assembled manner.  FIG. 12  is a perspective view illustrating the holder  526  attached to a housing  540 . It should be noted that the cross-sectional view shown in  FIG. 4  shows a cross section of the developing device taken along a plane perpendicular to the longitudinal direction shown in  FIG. 3 . Moreover, in  FIG. 4 , as in  FIG. 1 , the vertical direction is indicated by arrows, and for example the central shaft of the developing roller  510  is in a lower position than the central shaft of the photoconductor  20 . Also, in  FIG. 4 , the yellow developing device  54  is shown positioned at the developing position, which is in opposition to the photoconductor  20 . Furthermore, in  FIG. 5  to  FIG. 7 , and  FIG. 9 , the projecting sections  512  and the like are not to scale in order to make the diagrams easier to understand. Furthermore, the longitudinal direction and the lateral direction of the regulation blade  560  in  FIG. 8  and the lateral direction and the thickness direction of the regulation blade  560  in  FIG. 9  are shown with arrows respectively. 
     The YMCK developing unit  50  is provided with the black developing device  51  containing black (K) toner, the magenta developing device  52  containing magenta (M) toner, the cyan developing device  53  containing cyan (C) toner, and the yellow developing device  54  containing yellow (Y) toner. However, since the configuration of each of the developing devices is the same, only the yellow developing device  54  is described below. 
     The yellow developing device  54  includes the developing roller  510 , which is an example of a toner bearing member, the upper seal  520 , a toner container  530 , the housing  540 , a toner supply roller  550 , the regulation blade  560 , which is an example of a regulation member, the holder  526 , and the like. 
     The developing roller  510  bears toner T and transports it by rotating to the developing position opposite the photoconductor  20 , and develops the latent image borne on the photoconductor  20  using the toner T (the toner T that is borne on the developing roller  510 ). The developing roller  510  is a member made of an aluminum alloy or iron alloy or the like. The developing roller  510  includes the projecting sections  512  and non-projecting sections  513  on a surface of its central area  510   a , and the non-projecting sections  513  are provided with lateral sections  514  and the depressed sections  515 . As shown in  FIG. 5  to  FIG. 7 , these are arranged regularly on the surface of the developing roller  510 . It should be noted that in the present embodiment, each of the projecting sections  512  and the non-projecting sections  513  (the lateral sections  514  and the depressed sections  515 ) functions as a toner bearing member for bearing the toner T. And the developing roller  510  develops the latent image that is borne on the photoconductor  20  using the toner T borne on the projecting sections  512 , the lateral sections  514 , and the depressed sections  515 . 
     The projecting sections  512  are the highest area within the central area  510   a , and are a top surface in a square planar shape as shown in the upper diagram of  FIG. 7 . A length L 1  of one side of the square projecting sections  512  (see lower diagram in  FIG. 7 ) is approximately 50 μm. The two diagonals of the square shapes of the projecting sections  512  are formed on the surface of the central area  510   a  so as to align along a rotation-axis direction and a circumferential direction of the developing roller  510  respectively. 
     In the present embodiment, the non-projecting sections  513  are constituted by a first groove portion  516  and a second groove portion  518  that wind around the developing roller in different directions. Here, the first groove portion  516  is a spiral groove whose longitudinal direction runs along a direction shown by symbol X in  FIG. 6 , and the second groove portion  518  is a spiral groove whose longitudinal direction runs along a direction shown by symbol Y in  FIG. 6 . Thus, the first groove portions  516  and the second groove portions  518  intersect each other to form a grid shape and the projecting sections  512  are surrounded by the first groove portions  516  and the second groove portions  518 . It should be noted in regard to both the groove portions that the acute angles formed by their longitudinal direction and the rotation-axis direction of the developing roller  510  are approximately 45 degrees (see  FIG. 6 ). Furthermore, a groove width L 2  of the groove portions (in other words, the distance between projecting sections  512  adjacent to each other, see the lower diagram in  FIG. 7 ) is equivalent to the length L 1  of one side of the projecting sections  512 , which is approximately 50 μm. 
     The lateral sections  514  are slanted surfaces connecting the projecting sections  512  and the depressed sections  515 , and as shown in the upper diagram of  FIG. 7 , four lateral sections  514  are provided in correspondence with the four sides of the above-described square projecting sections  512 . And as shown in  FIG. 5  to  FIG. 7 , many instances of (groups of) the protrusion  512  and the four lateral sections  514  are arranged regularly in a meshed manner on the surface of the central area  510   a  of the developing roller  510 . 
     The depressed sections  515  correspond to the bottom portions of the non-projecting sections  513  (namely, the first groove portions  516  and the second groove portion  518 ), and are the lowest areas of the central area  510   a . As shown in  FIG. 5  to  FIG. 7 , the depressed sections  515  are formed regularly in a meshed manner surrounding the projecting sections  512  and the four lateral sections  514  on all four sides. It should be noted that, as shown in  FIG. 7 , a depth d of the depressed sections  515  (the non-projecting sections  513 ) with reference to the projecting sections  512  (a length from the projecting sections  512  to the depressed sections  515  in the diameter direction of the developing roller  510 ) is approximately 8 μm. In the developing roller  510 , the projecting sections  512  and the depressed sections  515  are formed so that the depth d is uniform between all the depressed sections  515  provided in the developing roller  510 . In the present embodiment, the toner T is granular (particulate) and the volume mean particle size of the toner T is approximately 4.6 μm, and therefore the size of the volume mean particle size of the toner T is smaller than the depth d of the depressed sections  515 . 
     Further still, the surface of the central area  510   a , which is provided with the above-described projecting sections  512 , lateral sections  514 , and depressed sections  515 , is subjected to electroless Ni—P plating. 
     Furthermore, the developing roller  510  is provided with a shaft section  510   b , and the developing roller  510  is rotatably supported as a result of the shaft section  510   b  being supported via bearings  576  with developing roller supporting sections  526   b  of the holder  526 , which are described later ( FIG. 11 ). As shown in  FIG. 4 , the developing roller  510  rotates in a direction (the counterclockwise direction in  FIG. 4 ) that is opposite to the rotating direction of the photoconductor  20  (the clockwise direction in  FIG. 4 ). 
     Moreover, in the state in which the yellow developing device  54  opposes the photoconductor  20 , there is a gap between the developing roller  510  and the photoconductor  20 . That is, the yellow developing device  54  develops the latent image that has been formed on the photoconductor  20  in a non-contact state in which the toner T borne on the developing roller  510  is not contacting the photoconductor  20 . 
     The housing  540  is manufactured by welding together a plurality of integrally-molded housing sections made of resin, namely, an upper housing section  542  and a lower housing section  544 . A toner containing member  530  for containing toner T is formed inside the housing  540 . The toner containing member  530  is divided by a partitioning wall  545  for partitioning the toner T, which protrudes inwards (in the vertical direction of  FIG. 4 ) from the inner wall, into two toner containing sections, namely, a first toner containing section  530   a  and a second toner containing section  530   b . The first toner containing section  530   a  and the second toner containing section  530   b  are in communication at the upper sections, and in the state shown in  FIG. 4 , the movement of toner T is regulated by the partitioning wall  545 . Moreover, as shown in  FIG. 4 , the housing  540  (that is, the first toner containing section  530   a ) has an opening  572  at its lower section, and the developing roller  510  is arranged so that it faces this opening  572 . 
     The toner supply roller  550  is disposed on the above-mentioned first toner containing section  530   a  and supplies the toner T contained in the first toner containing section  530   a  to the developing roller  510 . The toner supply roller  550  is made of polyurethane foam, for example, and comes into contact with the developing roller  510  in an elastically deformed state. The toner supply roller  550  is rotatable around its center axis, and by rotating, it transports the toner T to the contact position where it comes into contact with the developing roller  510 . Then, at the contact position, the toner T is frictionally charged due to the toner supply roller  550  and the developing roller  510 , and the thus-charged toner T adheres to the developing roller  510  and is appropriately borne on the developing roller  510 . In this manner, the toner supply roller  550  supplies the toner T to the developing roller  510 . 
     It should be noted that the toner supply roller  550  rotates in a direction (the clockwise direction in  FIG. 4 ) that is opposite the rotating direction of the developing roller  510  (the counterclockwise direction in  FIG. 4 ). Furthermore, the toner supply roller  550  not only has the function to supply the toner T to the developing roller  510 , but also the function to scrape off the toner T that has remained on the developing roller  510  after the development from the developing roller  510 . 
     The upper seal  520 , which comes into contact with the developing roller  510  along its rotation-axis direction, allows the movement of toner T that has remained on the developing roller  510  after passing the developing position into the housing  540  and restricts the movement of toner T inside the housing  540  from moving out of the housing  540 . This upper seal  520  is a seal made of polyethylene film or the like. The upper seal  520  is supported by an upper seal supporting section  526   a  of the holder  526  described later, and is disposed so that its longitudinal direction runs along the rotation-axis direction of the developing roller  510  ( FIG. 11 ). 
     Furthermore, an upper seal urging member  524  made of an elastic member such as Moltopren is provided in a compressed state between the upper seal support section  526   a  and the surface of the upper seal  520  that is on the opposite side to a contact surface  520   b  contacting the developing roller  510  (this surface is also referred to as “opposite surface  520   c ”). The upper seal urging member  524  presses the upper seal  520  against the developing roller  510  by urging the upper seal  520  toward the developing roller  510  with its urging force. 
     The regulation blade  560  comes into contact with the developing roller  510  at a contact section  560   a  so that the longitudinal direction of the regulation blade  560  runs along the rotation-axis direction of the developing roller  510  from one end portion to the other end portion in the rotation-axis direction of the developing roller  510 , and regulates the amount of the toner T borne on the developing roller  510  (the projecting sections  512  and the non-projecting sections  513 ), and moreover, it applies a charge to the toner T borne on the developing roller  510 . 
     The regulation blade  560  is constituted by a silicone rubber or a urethane rubber or the like, which are examples of a rubber elastic body, and as shown in  FIG. 4  and  FIG. 8 , it is supported by the blade-supporting member  564 . The blade-supporting member  564  is made of a thin plate  564   a  and a thin-plate supporting section  564   b , and supports the regulation blade  560  at its one end  564   d  in its lateral direction (that is, at the end on the side of the thin plate  564   a ). The thin plate  564   a  is made of phosphor bronze or stainless steel or the like and has spring properties. The thin plate  564   a  directly supports the regulation blade  560  and presses the regulation blade  560  with its urging force against the developing roller  510 . The thin-plate supporting section  564   b  is a metal plate that is arranged on the other end  564   e  in the lateral direction of the blade-supporting member  564 , and this thin-plate supporting section  564   b  is attached to the thin plate  564   a  in a state in which it is supported at the end of the thin plate  564   a  that is opposite from the side that supports the regulation blade  560 . The regulation blade  560  and the blade-supporting member  564  are attached to a regulation blade support sections  526   c  with longitudinal direction end portions  564   c  of the thin-plate supporting section  564   b  being supported by the regulation blade support sections  526   c  of the holder  526  described later. 
     Furthermore, as shown in  FIG. 9 , the regulation blade  560  is disposed so that its leading edge  560   b  in the lateral direction and thickness direction of the regulation blade  560  faces the upstream side of the developing roller  510  in the rotating direction. That is, the regulation blade  560  is in so-called counter contact. 
     Furthermore, as shown in  FIG. 9 , the leading edge  560   b  does not come into contact with the developing roller  510 , and the contact section  560   a  that comes into contact with the developing roller  510  is positioned at a position apart from the leading edge  560   b.  Further still, in the present embodiment, a distance g from the leading edge  560   b  to the projecting sections  512  in the case where the leading edge  560   b  is in opposition to the projecting sections  512  among the projecting sections  512  and the depressed sections  515  of the rotating developing roller  510  ( FIG. 9  shows this state, that is, a state in which the developing roller  510  rotates and the leading edge  560   b  becomes in opposition to the projecting sections  512 , and the area in opposition to the top of the projecting sections  512  is indicated with the symbol  512   a ) is extremely small (in other words, when a virtual line is drawn from the leading edge  560   b  toward the cross-sectional center of the developing roller  510  shown in  FIG. 4  with the symbol C, the distance g corresponds to a length of the virtual line from an intersection of the virtual line and the projecting sections  512  to the leading edge  560   b ). More specifically, the distance g is approximately 2 μm, which is a value smaller than the volume mean particle size of the toner T (approximately 4.6 μm). 
     Furthermore, as shown in  FIG. 11 , end seals  574  are provided on the outer sides in the longitudinal direction of the regulation blade  560 . The end seals  574  are made of nonwoven fabric, and contact the developing roller  510  along the circumferential surface thereof at the end portions in the rotation-axis direction thereof along the circumferential surface thereof, so as to perform a function to prevent leakage of the toner T from a space between the circumferential surface and the housing  540 . 
     The holder  526  is a metal member on which various members such as the developing roller  510  are assembled. As shown in  FIG. 10 , it includes the upper seal support section  526   a  disposed along the longitudinal direction of the holder  526  (namely, the rotation-axis direction of the developing roller  510 ), the developing roller support sections  526   b  that are provided on the outside in the longitudinal direction (the rotation-axis direction) of the upper seal support section  526   a  and intersect the longitudinal direction (the rotation-axis direction), and the regulation blade support sections  526   c  that intersect the developing roller support sections  526   b  and face the end portion in the longitudinal direction of the upper seal support section  526   a.    
     As shown in  FIG. 11 , the upper seal  520  is supported by the upper seal support section  526   a  at a lateral direction end portion  520   a  thereof ( FIG. 4 ), and the developing roller  510  is supported by the developing roller support sections  526   b  at its ends. Further still, the regulation blade  560  and the blade-supporting member  564  are supported by the regulation blade support sections  526   c  at the longitudinal direction end portions  564   c  of the blade-supporting member  564 . The regulation blade  560  and the blade-supporting member  564  are secured to the holder  526  by being screwed into the regulation blade support sections  526   c . In this manner, the holder  526  on which the upper seal  520 , the developing roller  510 , the regulation blade  560 , and the blade-supporting member  564  are attached in an assembled manner, is attached to the above-described housing  540  via a housing seal  546  ( FIG. 4 ) for preventing leakage of the toner T from between the holder  526  and the housing  540 , as shown in  FIG. 12 . 
     In the yellow developing device  54  configured in this manner, the toner supply roller  550  supplies the toner T contained in the toner container  530  to the developing roller  510 . During supply the toner T is frictionally charged due to the toner supply roller  550  and the developing roller  510 , and the thus-charged toner T adheres to the developing roller  510  and is appropriately borne on the developing roller  510 . The toner T borne on the developing roller  510  reaches the regulation blade  560  along with rotation of the developing roller  510 , then the amount of the toner T is regulated by the regulation blade  560  and the toner T is further frictionally charged. The toner T on developing roller  510  is brought to the developing position in opposition to the photoconductor  20  due to further rotation of the developing roller  510 , and is supplied for developing the latent image formed on the photoconductor  20  in an alternating electric field at the developing position. The toner T on the developing roller  510  that has passed the developing position due to further rotation of the developing roller  510  passes the upper seal  520  and is collected in the developing device without being scraped off by the upper seal  520 . Moreover, the toner T that is still remaining on the developing roller  510  is scraped off by the toner supply roller  550 . 
     Mechanism of Development Memory Occurrences 
     As described in the section “Problems to be Solved by the Invention”, in the case where toner having a slow charge buildup (toner that takes time for its charging amount to reach a saturated charge amount) is used in the printer  10 , a phenomenon known as a so-called development memory can occur due to the slowness of the charge build-up. Here, description is given regarding a mechanism of development memory occurrences using  FIG. 13 .  FIG. 13  is an explanatory diagram for describing a mechanism of development memory occurrences. 
     As described earlier, the toner is frictionally charged due to the toner supply roller  550  and the developing roller  510 , and the thus-charged toner adheres to the developing roller  510  and is borne on the developing roller  510 . Then, the toner borne on the developing roller  510  reaches the developing position that opposes the photoconductor  20  after being further frictionally charged by the regulation blade  560 , and is supplied for the development of the latent image at the developing position. That is, the following processes that are executed when the developing roller  510  performs one revolution, namely a process of charging and supplying toner using the toner supply roller  550  (causing toner to be borne on the developing roller  510 ), a process of charging the toner using the regulation blade  560 , and a process of developing the latent image on the photoconductor  20 , are executed a plurality of times by the developing roller  510  performing a plurality of revolutions. Then, for example, a toner image formed on the photoconductor  20  by executing the aforementioned series of processes in an n-th revolution of the developing roller  510 , and a toner image formed on the photoconductor  20  by executing the aforementioned series of processes in an (n+1)-th revolution of the developing roller  510 , become lined up in the circumferential direction of the photoconductor  20 . 
     Here, in the present section we will examine the aforementioned processing of the developing roller  510  in a case involving a latent image expressing the alphabet letter “O” being developed and a toner image expressing the alphabet letter “O” being formed on the photoconductor  20  by executing the aforementioned series of processes in the n-th revolution of the developing roller  510 , and a halftone image being formed on an entire surface of the photoconductor  20  by developing a latent image as a result of executing the aforementioned series of processes in the (n+1)-th revolution of the developing roller  510 . And by examining this, a mechanism of development memory occurrences will be clarified. 
     When developing the latent image that expresses the alphabet letter “O” in the aforementioned development processing in the n-th revolution of the developing roller  510 , of the toner borne on the developing roller  510 , it is the toner borne on the developing roller  510  in the portions facing the latent image that is consumed so as to form a toner image. For this reason, after the completion of the development processing in the n-th revolution of the developing roller  510 , this facing portion no longer bears toner. On the other hand, toner that is borne on the developing roller  510  in portions not facing the latent image are not consumed, and therefore toner is still borne on these non-facing portions after the completion of the development processing. When the aforementioned series of processes in the n-th revolution of the developing roller  510  finishes in this manner, a first region in which toner is not borne (this first region is shaped as the letter “O”) and a second region in which toner is borne are produced on the developing roller  510 . 
     Then, due to the developing roller  510  rotating, the first region and the second region eventually reach the contact position that is in contact with the toner supply roller  550 , and the aforementioned series of processes in the (n+1)-th revolution of the developing roller  510  commences. In other words, at the contact position, the process of charging and supplying toner is executed using the (n+1)-th revolution of the toner supply roller  550 . 
     Here, toner is already borne on the second region, and this toner is in a sufficiently charged state due to the execution of the process of charging and supplying toner using the toner supply roller  550  in the n-th revolution and the process of charging the toner using the regulation blade  560  in the n-th revolution. Then, (without being scraped off by the toner supply roller  550 ) this toner is even further charged by executing this processing, and therefore the adhesiveness by which the toner adheres to the developing roller  510  is further increased. Consequently, while continuing to be borne on the developing roller  510 , this toner is transported toward the regulation blade  560  so as to execute the next processing. 
     On the other hand, since toner is not borne on the first region, toner that is contained in the toner container  530  is freshly supplied to the first region. The toner here is different from the second region toner, which is sufficiently charged due to the execution of the toner charging process in the n-th revolution, and its charge is insufficient. Then, in this processing, the toner is frictionally charged by the toner supply roller  550  and the developing roller  510 , but in the case where the toner has a property of a slow charge build-up (where it takes time for the charging amount of the toner to reach a saturated charge amount), toner will not be appropriately borne on the developing roller  510  during the frictional charging (it can also be said that the supply of toner by the toner supply roller  550  in the first region is not executed sufficiently). 
     Then, the first region, in which toner is not appropriately borne on, and the second region, in which toner is being appropriately borne on, reach the regulation blade  560  so as to execute the process of charging the toner using the regulation blade  560  in the (n+1)-th revolution, after which they arrive at the developing position facing the photoconductor  20 . Here, a halftone image is formed on the entire surface of the photoconductor  20  by executing the development processing of the (n+1)-th revolution and developing the latent image, but although the toner is borne appropriately on the second region, the toner is not borne appropriately on the first region, and therefore the density of the halftone image formed by developing the latent image facing the first region is lighter than the density of the halftone image formed by developing the latent image facing the second region. 
     This condition (a difference between the two densities) is shown in  FIG. 13 .  FIG. 13  shows a toner image expressing the alphabet letter “O” formed on the photoconductor  20  by executing the aforementioned series of processes in the n-th revolution of the developing roller  510 , and a halftone image formed on the photoconductor  20  by executing the aforementioned series of processes in the (n+1)-th revolution of the developing roller  510 . In  FIG. 13 , the toner images formed on the photoconductor  20  are shown on the circumferential surface of the photoconductor  20 , which is schematically extended, and the circumferential direction and the axial direction of the photoconductor  20  are indicated with arrows. The length L indicated in  FIG. 13  corresponds to a length of one revolution of the circumferential surface of the developing roller  510 . 
     And  FIG. 13  shows a condition in which the density of the halftone image formed by developing the latent image facing the first region (indicated in  FIG. 13  with the reference symbol A 1 ) is lighter than the density of the halftone image formed by developing the latent image facing the second region (indicated in  FIG. 13  with the reference symbol A 2 ). Also, since the first region is shaped as the letter “O” as mentioned earlier, the lighter density halftone image that is formed by developing the latent image facing the first region is also shaped as the letter “O”. That is, a phenomenon, namely, development memory, occurs in which a form of the toner image, which has been formed on the photoconductor  20  by executing the aforementioned series of processes in the n-th revolution, appears on the halftone image that is formed on the photoconductor  20  by executing the aforementioned series of processes in the (n+1)-th revolution. 
     In the case where toner having a slow charge build-up is used in the printer  10  in this manner, development memory caused by this slowness of the charge build-up can occur conspicuously. 
     Conversely, in the case where toner having a fast charge build-up is used, toner is appropriately borne on the developing roller  510  in the first region also while the toner is frictionally charged by the toner supply roller  550  and the developing roller  510  in the process of charging and supplying toner in the (n+1)-th revolution, and therefore the density of the halftone image formed by developing the latent image facing the first region and the density of the halftone image formed by developing the latent image facing the second region are substantially equivalent. Thus, in this case, occurrences of development memory are inhibited. 
     Regarding the Toner Structure According to the Present Embodiment and the Relationship between the Toner Structure and Extent of Development Memory Occurrences 
     As mentioned earlier, in the case where toner having a slow charge build-up is used in the printer  10 , development memory caused by this slowness of the charge build-up can occur conspicuously. And since the speed of the toner charge build-up is linked to the structure of the toner, there is a regular relationship between the toner structure and the extent of development memory occurrences. 
     Here, description is given first regarding the structure of the toner according to this embodiment, that is, the toner used in the printer  10  according to the present embodiment. Then, following this, the relationship between the structure of the toner according to the present embodiment and the extent of development memory occurrences is examined. 
     Regarding the Structure of Toner According to the Present Embodiment 
     1) Regarding Toner Particle Size 
     In regard to the toner used in the printer  10  according to this embodiment, in giving importance to achieving excellent image quality for the images to be finally obtained (improving dot reproducibility), the toner particle size is set smaller than the toner particle size (larger than a volume mean particle size of 5 μm) that has been used in general conventionally (that is, the volume mean particle size here is not greater than 5 μm). More specifically, as mentioned earlier, its volume mean particle size Ave is approximately 4.6 μm. Furthermore, a 3σ value, namely a value obtained by subtracting 3 times a standard deviation σ in the toner particle size distribution from the volume mean particle size Ave, and a value obtained by adding 3 times the standard deviation σ in the toner particle size distribution to the volume mean particle size are approximately 2.3 μm and approximately 6.9 μm respectively. 
     It should be noted that the volume mean particle size is a value calculated by a sum total of the products of Ri and Pi from i=1 to n under a condition in which volume occupation rates of toner of particle sizes Ri (i=1 to n) are respectively Pi (i=1 to n, the sum total from P 1  to Pn is 1). Furthermore, the standard deviation σ is a square root of dispersion, and the dispersion is a value calculated by a sum total of the products of the square values of a difference between Ri (i=1 to n) and Ave, and Pi from i=1 to n. 
     2) Regarding the Degree of Circularity of the Toner 
     In giving importance to transferability in first transferring and secondary transferring for the toner used in the printer  10  according to this embodiment, the degree of circularity of the toner is greater (approaching a perfect circle, and where the degree of circularity is not less than 0.950) than the degree of circularity of toner that is used in general conventionally (where the degree of circularity is less than 0.950). More specifically, the degree of circularity is approximately 0.960 to 0.985. 
     3) Regarding the Charge Control Agent (CCA) 
     The toner used in the printer  10  according to this embodiment does not contain a charge control agent (CCA). 
     Typical toner manufacturing methods include pulverization techniques and polymerization techniques, but since the polymerization techniques are more suited to the manufacture of small particle size toner and to the manufacture of toner having a high degree of circularity, the toner according to the present embodiment is manufactured using a polymerization technique. And since there is a possibility of difficulties occurring if a charge control agent (CCA) is included in the case where a polymerization technique is used as the toner manufacturing method, in this embodiment, the toner does not contain a charge control agent (CCA). 
     It should be noted that examples of polymerization techniques that can be put forth include suspension polymerization and emulsion polymerization. In the suspension polymerization technique, a colored toner particle (core particle) having a desired particle size can be formed by adding while agitating a monomer composite, in which a polymerizable monomer, a coloring agent (coloring pigment), a release agent, and further as required, a dye, a polymerization initiator, a cross-linking agent, and other additives have been dissolved or dispersed, to an aqueous phase containing a suspension stabilizer (a water-soluble macromolecule and a poorly water-soluble inorganic substance), then causing granulation and polymerization. In the emulsion polymerization technique, a coloring toner particle (core particle) having a desired particle size can be formed by dispersing a monomer and a release agent, and further as required, a polymerization initiator, an emulsifying agent (a surface-active agent) or the like, in water and carrying out polymerization, then adding a coloring agent (coloring pigment) and an agglutination agent (an electrolyte) or the like in an agglutination process. 
     The toner according to this embodiment is manufactured using an emulsion polymerization technique, and hereinafter description is given regarding a manufacturing method based on an emulsion polymerization technique for the cyan toner of the aforementioned toners of four colors (black toner, magenta toner, cyan toner, and yellow toner). 
     First, a monomer mixture, which is constituted by 80 parts by mass styrene monomer, which is a monomer, 20 parts by mass butyl acrylate, and 5 parts by mass acrylic acid, is added to an aqueous mixture of 105 parts by mass water, 1 part by mass nonionic emulsifying agent (Emulgen 950 produced by Dai-ichi Kogyo Seiyaku), 1.5 parts by mass anionic emulsifying agent (Neogen R produced by Dai-ichi Kogyo Seiyaku), and 0.55 parts by mass potassium persulfate, which is a polymerization initiator, then, while this is agitated in a nitrogen gas stream, it is subjected to polymerization for 8 hours at 70° C. Cooling is performed after the polymerization reaction, thereby obtaining a milk-white resin emulsion having a particle size of 0.25 μm. 
     Next, 200 parts by mass of the resin emulsion, 20 parts by mass of a polyethylene wax emulsion (produced by Sanyo Chemical Industries Ltd.), which is a release agent, and 25 parts by mass phthalocyanine blue, which is a coloring agent, are dispersed into 0.2 liters of water containing 0.2 parts by mass sodium dodecylbenzenesulfonate, which is a surface-active agent, then diethylamine is added and the pH is adjusted to 5.5, after which 0.3 parts by mass aluminum sulfate, which is an electrolyte, is added while agitating the mixture, and following this, dispersion is carried out by performing high speed agitation using an agitation device (T.K. HOMO Mixer). 
     Further still, 40 parts by mass styrene monomer, 10 parts by mass butyl acrylate, and 5 parts by mass zinc salicylate are added along with 40 parts by mass water, and this is heated to 90° C. in a similar manner while being agitated in a nitrogen gas stream, then hydrogen peroxide water is added and polymerization is performed for 3 hours, thereby growing the particles. After polymerization has stopped, the temperature is raised to 95° C. while adjusting the pH to 5 or greater and held there for 5 hours so as to increase the bond strength of the associating particles. After this, the particles obtained are rinsed then subjected to vacuum drying for 10 hours at 45° C., thereby obtaining a cyan toner core particle (coloring toner particle). 
     By admixing the thus-obtained coloring toner particle and an external additive (specifically, silica and titania, which are described later), the external additive becomes externally added to the coloring toner particle, and thus obtaining a cyan toner having a volume mean particle size of 4.6 μm. 
     4) Regarding the Coloring Agent (Coloring Pigment) 
     Taking into account that the particle size of the toner is small for the toner used in the printer  10  according to this embodiment, the amount of coloring agent (coloring pigment) contained in the toner is greater (namely, not less than 10 wt %) than the amount of coloring agent (coloring pigment) contained in toner that is used in general conventionally (which is less than 10 wt %). That is, in the case where the toner particle size is small, the amount of toner that finally adheres to the medium such as paper is small, and therefore there is a tendency for the density of the image to become lighter. Accordingly, more coloring agent (coloring pigment) is included in the present embodiment in order to compensate for this. 
     Regarding the Relationship between the Toner Structure and Extent of Development Memory Occurrences 
     The toner according to this embodiment has properties that were described in numbered sections 1 to 4 above. And due to the toner having these properties, development memory tends to occur easily in the printer  10  according to the present embodiment in which this toner is used. 
     That is, when the toner particle size becomes smaller, the saturated charge amount of the toner becomes higher, and therefore the toner charge build-up becomes slower. Furthermore, since the toner does not contain a charge control agent (CCA), charge control for increasing the speed of the toner charge build-up cannot be implemented. Furthermore, the toner charge build-up will be slow regardless since there is a large amount of coloring agent (coloring pigment). 
     Thus, in the printer  10  according to this embodiment, the toner charge build-up is slow, and therefore development memory tends to occur easily. 
     Also, in the case where the degree of circularity of the toner is small, the toner more easily sticks to the developing roller  510 , and therefore even if the toner charge build-up is slow, the aforementioned inappropriateness relating to bearing of toner in the first region is slightly alleviated. For this reason, the difference between the density of the halftone image formed by developing the latent image facing the first region and the density of the halftone image formed by developing the latent image facing the second region becomes very small, thereby somewhat inhibiting occurrences of development memory. However, this can not be expected to help in this situation since the toner according to the present embodiment has a high degree of circularity and consequently occurrences of development memory become more conspicuous in this embodiment. 
     Overview of the External Additive 
     Next, description is given regarding an overview of the external additive that is externally added to the core particle of the toner. 
     External additives are externally added to the core particles mainly with an object of improving fluidity of the toner and charge stabilization. In the present embodiment, four types of external additives are externally added to the core particle (coloring toner particle). The four types of external additives are external additives having different volume mean particle sizes respectively, specifically, a silica having a volume mean particle size of 15 nm (nanometers) (hereinafter also referred to as 15 nm silica), a titania having a volume mean particle size of 30 nm, a silica having a volume mean particle size of 50 nm (hereinafter also referred to as 50 nm silica), and a silica having a volume mean particle size of 500 nm (hereinafter also referred to as 500 nm silica). And an amount (externally added amount) of the 15 nm silica that is externally added to the core particle is 1.0 wt %, the externally added amount of titania is 1.0 wt %, the externally added amount of 50 nm silica is 1.0 wt %, and the externally added amount of the 500 nm silica is 0.5 wt %. 
     The four types of external additives are externally added to the core particles by being admixed with the core particles, in a mixing vat such as a Henschel mixer. A stirring blade or the like is arranged in the mixing vat to admix the core particles and the external additives, and the external additives are externally added to the core particles by rotating the stirring blade for a predetermined time only. In this embodiment, the four types of external additives are admixed to the core particles in the following sequence. Initially, the 50 nm silica (1.0 wt %) is injected to the mixing vat and is admixed with the core particles for 20 seconds (that is, the stirring blade is rotated for 20 seconds). Next, the 15 nm silica (1.5 wt %) and the titania (1.0 wt %) are injected to the mixing vat and admixed for a further 30 seconds (during this 30 seconds, the previously injected 50 nm silica is also admixed). Finally, the 500 nm silica (0.5 wt %) is injected to the mixing vat and admixed for a further 10 seconds. 
     In regard to toner having external additives that are externally added to the core particles, sometimes the external additives separate from the core particles during usage of the developing devices  51 ,  52 ,  53 , and  54 . And separation of the external additives from the core particles tends to occur more easily for external additives having larger volume mean particle sizes. Thus, of the four types of external additives, the 500 nm silica, which has the largest volume mean particle size, tends to separate easily. Furthermore, separation of the external additives from the core particles also has a relationship with the mixing time of the external additives and the core particles in the mixing vat, and external additives having shorter mixing times tend to separate more easily from the core particles. And as mentioned earlier, it is the 500 nm silica of the four types of external additives that is last to be admixed with the core particles and its mixing time is also shorter compared to the mixing times of the other external additives. For this reason, compared to the other external additives, the 500 nm silica tends to separate more easily from the core particles. 
     Inhibiting Effect on Development Memory Due to Regulation State of Regulation Blade  560   
     As shown in  FIG. 9 , the regulation state of the regulation blade  560  according to this embodiment is set so that the leading edge  560   b  of the regulation blade  560  faces the upstream side in the rotating direction of the developing roller  510 , and so that a distance g (approximately 2 μm) from the leading edge  560   b  to the projecting sections  512  at the time the leading edge  560   b  faces the projecting sections  512  of the developing roller  510  is smaller than the toner volume mean particle size (approximately 4.6 μm). In this way, occurrences of the aforementioned development memory can be effectively inhibited. This point is described in greater detail below. 
     As described earlier, the toner that is frictionally charged by the toner supply roller  550  and the developing roller  510  and that is borne on the developing roller  510  reaches the regulation blade  560  along with rotation of the developing roller  510 , then the amount of the toner is regulated by the regulation blade  560  and the toner is further frictionally charged. 
     Here, in the case where the distance g (approximately 2 μm) is smaller than the toner volume mean particle size (approximately 4.6 μm), in the case where the toner that has been borne on the projecting sections  512  of the developing roller  510  has reached the regulation blade  560  in accordance with rotation of the developing roller  510 , the toner that is borne on the projecting sections  512  having this volume mean particle size is unable to pass through the (2 μm) gap between the leading edge  560   b  and the opposing area  512   a  (rebounds after hitting the leading edge  560   b ), and cannot reach the developing position facing the photoconductor  20 . 
     On the other hand, when focusing on the toner borne on the depressed sections  515 , the toner volume mean particle size (approximately 4.6 μm) is smaller than the depth d of the depressed sections  515  (approximately 8 μm), and therefore the toner that is borne on the depressed sections  515  and has this volume mean particle size is able to pass through the (2 μm) gap between the leading edge  560   b  and the opposing area  512   a  and reaches the developing position facing the photoconductor  20 . 
     As a result, the condition of the toner borne on the projecting sections  512  and the depressed sections  515  at the developing position facing the photoconductor  20  is as follows. Namely, the extremely small particle size toner (the amount of this toner is small) that was able to pass through the (2 μm) gap between the leading edge  560   b  and the opposing area  512   a  is borne on the projecting sections  512 . On the other hand, toner of various particle sizes (mainly toner having the above-described volume mean particle sizes) is borne on the depressed sections  515 . And a large amount of toner is borne on the depressed sections  515  so that the entirety of the depressed sections  515  is covered. 
     Next, description is given regarding why occurrences of development memory are inhibited and deterioration of image quality of images is appropriately prevented when the regulation blade  560  performs regulation as described above. 
     In the first region where toner is not being borne, which occurs when the development processing of the n-th revolution of the developing roller  510  has finished, toner contained in the toner container  530  is freshly supplied in the process of charging and supplying toner using the toner supply roller  550  in the (n+1)-th revolution. And description has been given regarding a point above that in the case where the toner freshly supplied to the first region is toner having a property of being a toner whose charge build-up is slow, the toner will not be borne appropriately on the first region of the developing roller  510  in the case where frictional charging has been carried out by the toner supply roller  550  and the developing roller  510 . 
     Here, the projecting sections  512  and the depressed sections  515  are present within the first region, but the extent of inappropriateness relating to bearing of toner in the first region varies depending on which among the projecting sections  512  and the depressed sections  515  of the first region the toner is borne on. That is, the non-projecting sections  513  including the depressed sections  515  are cupped so as to easily accommodate toner, and therefore toner readily enters the non-projecting sections  513 . And the toner that has entered the non-projecting sections  513  is subjected to packing within the non-projecting sections  513 , and an agglutinative force produced at this time provides an effect of bearing the toner in the depressed sections  515 . Consequently, in the depressed sections  515 , even if the toner charge build-up is slow, the aforementioned inappropriateness relating to bearing of toner in the first region is alleviated. In contrast to this, this effect is not obtained for the projecting sections  512 , and the extent of inappropriateness is smaller in the depressed sections  515  than the projecting sections  512 . 
     For this reason, during the development processing of the (n+1)-th revolution, a difference between the density of the halftone image formed by developing the latent image facing the depressed sections  515  of the first region and the density of the halftone image formed by developing the latent image facing the depressed sections  515  of the second region is smaller than a difference between the density of the halftone image formed by developing the latent image facing the projecting sections  512  of the first region and the density of the halftone image formed by developing the latent image facing the projecting sections  512  of the second region. In other words, in inhibiting occurrences of development memory, it is better to as much as possible develop the latent image using toner borne on the depressed sections  515 , of the projecting sections  512  and the depressed sections  515 . 
     In light of these facts, in this embodiment, the distance g is smaller than the volume mean particle size of the toner (approximately 4.6 nm). In this way, as described above, at the developing position, in contrast to the slight amount of toner borne on the projecting sections  512 , a large amount of toner is borne on the depressed sections  515 . And by developing the latent image under these conditions, the difference between the density of the halftone image formed by developing the latent image facing the first region and the density of the halftone image formed by developing the latent image facing the second region becomes very small compared to a case where for example the latent image is developed in a condition in which the amount of toner borne on the projecting sections  512  is equivalent to the amount of toner borne on the depressed sections  515 . As a result, occurrences of development memory can be inhibited and deterioration in image quality of the finally obtained image is appropriately prevented. 
     Regarding Unusual Sounds Produced Between the Developing Roller  510  and the Regulation Blade  560   
     As described earlier, the regulation blade  560  comes into contact with the contact section  560   a  at the surface of the developing roller  510  that rotates. In this regard, there is a risk that the contact section  560   a  will adhere closely to the projecting sections  512  when it comes into contact with projecting sections  512  that are not bearing toner. And when the developing roller  510  further rotates while the contact section  560   a  is closely adhering to the projecting sections  512 , there is a risk that problems such as unusual sounds will be produced. In particular, in the case where the distance g is smaller than the toner volume mean particle size, unusual sounds, which are described later, tend to be more easily produced. 
     To address these problems, in the printer  10  according to this embodiment, a relationship among sizes of the volume mean particle size of the external additives constituting the toner (hereinafter also referred to as external additive particle size B), a ten-point average roughness Rz of the projecting sections  512  (hereinafter also referred to as protrusion roughness C), and the distance g from the leading edge  560   b  to the projecting sections  512  at the time the leading edge  560   b  faces the projecting sections  512  (hereinafter also referred to as distance D) is set so that the protrusion roughness C&lt;the external additive particle size B&lt;the distance D (note that below the toner volume mean particle size is also referred to as toner particle size A). 
     Hereinafter, first description is given regarding a mechanism by which unusual sound is produced between the contact section  560   a  and the projecting sections  512  in the case where the distance g is smaller than the toner volume mean particle size, and following this description is given regarding why occurrences of unusual sounds are inhibited when a relationship of the protrusion roughness C&lt;the external additive particle size B&lt;the distance D is implemented. 
     Mechanism Producing Unusual Sounds 
     As described above, the amount of toner borne on the projecting sections  512  is very small in the case where the distance g (approximately 2 μm) is smaller than the toner volume mean particle size (approximately 4.6 μm) (namely, where there is a relationship of distance D&lt;the toner particle size A). 
     And in the case where the a very small amount of toner is borne on the projecting sections  512 , the contact section  560   a  comes into direct contact with the projecting sections  512  where toner is not being borne on as shown in  FIG. 14 . Here, the projecting sections  512  are the top surface (in  FIG. 14  the top surface is a border surface), and the contact section  560   a  is configured to contact the protrusion  512  along its width, and therefore when the contact section  560   a  comes into direct contact with the projecting sections  512 , the contact section  560   a  sometimes adheres closely to the projecting sections  512 . In particular, since the regulation blade  560  is a urethane rubber or the like, the surface area of the contact section  560   a  that comes into contact with the projecting sections  512  tends to be large due to the contact section  560   a  undergoing elastic deformation to come into contact with the projecting sections  512 , and the contact section  560   a  tends to adhere closely to the projecting sections  512 . And when the developing roller  510  further rotates (moves the projecting sections  512 ) from the state shown in  FIG. 14  (a state in which the contact section  560   a  is closely adhering to the projecting sections  512 ), there is a risk that an unusual sound will be produced between the contact section  560   a  and the projecting sections  512  during this rotation. It should be noted that  FIG. 14  is a schematic diagram for describing a condition in which the contact section  560   a  comes into direct contact with the projecting sections  512  without toner being interposed therebetween. 
     It should be noted that in the case where the contact section  560   a  adheres closely to the projecting sections  512 , there is not only the aforementioned unusual sounds, but there is also a problem in that the torque required for rotating the developing roller  510  greatly increases. 
     Advantages of the Developing device According to the Present Embodiment 
     In contrast to this, the developing devices  51 ,  52 ,  53 , and  54  according to this embodiment are configured such that a relationship among the volume mean particle size of the external additives (external additive particle size B), a ten-point average roughness Rz of the projecting sections  512  (protrusion roughness C), and the distance g (distance D) is the protrusion roughness C&lt;the external additive particle size B&lt;the distance D. In this case, occurrences of unusual sounds are inhibited by the contact section  560   a  coming into contact with the projecting sections  512  via the external additives that rotatively move on the projecting sections  512  (the external additives have separated from the toner) Detailed description is given regarding this point below. 
     The toner according to this embodiment is provided with core particles and four types of external additives that are externally added to the core particles (namely, 15 nm silica, 50 nm silica, 500 nm silica, and titania). And although these external additives can be made to separate from the core particles during use of the developing devices  51 ,  52 ,  53 , and  54 , as described earlier it is the 500 nm silica, which has the largest volume mean particle size among the four types of external additives, that readily separates from the core particles. 
     External additive (500 nm silica) that has separated from the core particles is borne on the developing roller  510  (the projecting sections  512  and the depressed sections  515 ) in a same manner as the toner. In this regard, the projecting sections  512  are rough as shown in  FIG. 15 , and in this embodiment, a ten-point average roughness Rz of the projecting sections  512  is smaller than the volume mean particle size (500 nm) of the 500 nm silica (protrusion roughness C&lt;external additive particle size B). For this reason, a portion of the 500 nm silica that has separated from the core particles becomes sandwiched in a jumped-out manner (see  FIG. 17B ) at areas where the projecting sections  512  are rough (specifically, small grooves  512   b  shown in  FIG. 15 ). Here, the small grooves  512   b  are provided along the circumferential direction of the developing roller  510  and are formed at the time of processing the developing roller  510  (cutting processing and rolling processing). It should be noted that  FIG. 15  is a diagram for illustrating the projecting sections  512  being rough. 
     Unlike the toner, the external additive (500 nm silica) borne on the projecting sections  512  (small grooves  512   b ) passes through the gap between the leading edge  560   b  of the regulation blade  560  and the opposing area  512   a  during rotation of the developing roller  510 . This is because the volume mean particle size (500 nm) of the 500 nm silica is smaller than the distance g (approximately 2 μm) (the external additive particle size B&lt;the distance D). It should be noted that in this embodiment, the external additive particle size B refers to the volume mean particle size of the 500 nm silica, which has the largest volume mean particle size among the four types of external additives. 
     The 500 nm silica that has passed between the leading edge  560   b  and the opposing area  512   a , and that is borne on the projecting sections  512  (some of this 500 nm silica has jumped out from the projecting sections  512 ) moves along with the rotation of the developing roller  510  and makes contact with the contact section  560   a  of the regulation blade  560 . Then, the 500 nm silica that is in contact with the contact section  560   a  is rotatively moved along with further rotation of the developing roller  510  while maintaining its state of contacting the contact section  560   a . Thus, as shown in  FIG. 16 , while the 500 nm silica rolls, the contact section  560   a  comes into contact with the projecting sections  512  through the 500 nm silica (indicated by circles in  FIG. 16 ). In this way, the surface area of the contact section  560   a  that comes into contact with the projecting sections  512  is decreased and it becomes more difficult for the contact section  560   a  to closely adhere to the projecting sections  512 , and therefore occurrences of unusual sounds can be inhibited in the case where the developing roller  510  rotates. It should be noted that  FIG. 16  is a schematic diagram that shows a state in which the contact section  560   a  comes into contact with the projecting sections  512  through the external additive. 
     Here, as shown in  FIG. 17A  and  FIG. 17B , the external additive (500 nm silica) rolls along the small grooves  512   b  formed in the projecting sections  512  on which the external additive has been borne. Specifically, the 500 nm silica rolls from the bottom toward the top in  FIG. 17A . In this regard, as shown in  FIG. 17A , the small grooves  512   b  are formed so that they do not connect from one end to the other end in the circumferential direction of the developing roller  510  across the projecting sections  512  on which the small grooves  512   b  are provided (in other words, the small grooves  512   b  do not connect to the lateral sections  514 ). In this case, the 500 nm silica, which is borne on the small grooves  512   b  and makes contact with the contact section  560   a , rolls on the projecting sections  512  along with rotation of the developing roller  510  so that it runs up from the small grooves  512   b  ( FIG. 17B ). Then, along with these rolling movements of the 500 nm silica, the contact section  560   a  that makes contact with the 500 nm silica is shifted vertically up and down, and the contact section  560   a  is even more effectively prevented from adhering closely to the projecting sections  512 . It should be noted that  FIGS. 17A and 17B  are schematic diagrams for describing a condition in which the toner borne on the projecting sections  512  rolls. Also note that  FIG. 17B  is a cross-sectional view taken along a line C-C of  FIG. 17A . 
     In the above description, when a relationship of the protrusion roughness C&lt;the external additive particle size B&lt;the distance D is established, the external additive (500 nm silica) that has separated from the toner is borne on the roughened portions of the projecting sections  512  (namely, the small grooves  512   b ) and passes through the gap between the leading edge  560   b  and the opposing area  512   a . Then, since the contact section  560   a  of the regulation blade  560  comes into contact with the projecting sections  512  through the external additives that roll on the small grooves  512   b , the regulation blade  560  can be prevented from closely adhering to the projecting sections  512  and occurrences of the aforementioned unusual sounds can be inhibited. 
     Furthermore, the external additives work as a lubricant between the contact section  560   a  and the projecting sections  512 , and due to the external additives, friction is reduced between the contact section  560   a  and the projecting sections  512  when the developing roller  510  rotates. For this reason, the load on the motor during rotation of the developing roller  510  is reduced and it is possible to prevent the torque required in rotating the developing roller  510  from increasing greatly. 
     In the description above, by establishing a relationship in which the protrusion roughness C&lt;the external additive particle size B, the external additive (500 nm silica) is borne on the small grooves  512   b  of the projecting sections  512 , but as shown in  FIG. 18 , in the case where the protrusion roughness C&gt;the external additive particle size B, the external additives (also shown using circles in  FIG. 18  as in  FIG. 16 ) are borne on the small grooves  512   b  of the projecting sections  512 . However, in this case, the external additives enter into the small grooves  512   b  and it is difficult for them to roll. And when the external additives enter into the small grooves  512   b , the contact section  560   a  comes into direct contact with the projecting sections  512  without the external additives interposed therebetween, and occurrences of unusual sounds cannot be suppressed.  FIG. 18  is a schematic diagram for describing a comparative example. 
     It should be noted that as described in the section “Inhibiting Effect on Development Memory Due to Regulation State Of Regulation Blade  560 ,” when the distance D&lt;the toner particle size A, occurrences of the development memory can be inhibited effectively and as a result, deterioration in the image quality of images is appropriately prevented. Accordingly, with the developing devices  51 ,  52 ,  53 , and  54  according to this embodiment, by establishing a relationship in which the protrusion roughness C&lt;the external additive particle size B&lt;distance D&lt;the toner particle size A, it is possible to appropriately prevent deterioration in image quality of images and to appropriately bring the regulation blade  560  into contact with the developing roller  510 . 
     Developing device Manufacturing Method 
     Next, description is given regarding a method for manufacturing the developing devices with reference to  FIGS. 19A to 21 .  FIGS. 19A to 19E  are schematic diagrams showing transitional states of the developing roller  510  during the manufacturing process thereof.  FIG. 20  is an explanatory diagram for describing the rolling process of the developing roller  510 .  FIG. 21  is a flowchart for describing an assembly method for the yellow developing device  54 . It should be noted that in manufacturing the developing device, the above-described housing  540 , holder  526 , developing roller  510 , toner supplying roller  550 , regulation blade  560  and the like are manufactured first. Then, the developing device is manufactured by assembling these members. Now, among manufacturing methods for these members, the method for manufacturing the developing roller  510  is described first, and thereafter the method for assembling the developing device is described. In the following description, the yellow developing device  54  is taken as an example from among the black developing device  51 , the magenta developing device  52 , the cyan developing device  53 , and the yellow developing device  54 . 
     Method for Manufacturing the Developing Roller  510   
     The method for manufacturing the developing roller  510  is described with reference to  FIG. 19A  to  FIG. 20 . 
     First of all, as shown in  FIG. 19A , a pipe member  600  is prepared, which is used as the base member of the developing roller  510 . The wall thickness of this pipe member  600  is 0.5 to 3 mm. Then, as shown in  FIG. 19B , flange press-fitting sections  602  are formed at the both ends in the longitudinal direction of the pipe member  600 . The flange press-fitting sections  602  are made by a cutting process. Next, as shown in  FIG. 19C , a flange  604  is injected to the flange press-fitting sections  602 . In order to reliably fasten the flanges  604  to the pipe member  600 , it is also possible to glue or weld the flanges  604  to the pipe member  600  after press-fitting the flanges  604 . Next, as shown in  FIG. 19D , the surface of the pipe member  600  to which the flanges  604  are injected is subjected to centerless grinding. This centerless grinding is performed on the entire surface, and the ten-point average roughness Rz of the surface after the centerless grinding is not equal to or less than 1.0 μm. Next, as shown in  FIG. 19E , the pipe member  600  with the flanges  604  injected thereto is subjected to a rolling process. In this embodiment, a so-called through-feed rolling process (also referred to as “continuous rolling”) using two round dies  650 ,  652  is performed. 
     That is, as shown in  FIG. 20 , the two round dies  650 ,  652  arranged so that they sandwich the pipe member  600  serving as the workpiece are rotated in the same direction (see  FIG. 20 ) while being pressed with a predetermined pressure (the direction of this pressure is marked with the reference symbol P in  FIG. 20 ) against the pipe member  600 . In the through feed rolling, due to rotation of the round dies  650  and  652 , the pipe member  600  moves in the direction indicated by the reference symbol H in  FIG. 20  while rotating in the direction opposite to the rotating direction of the round dies  650  and  652  (see  FIG. 20 ). Convex sections  650   a  and  652   a  for forming a groove  680  are provided respectively on the surface of the round dies  650  and  652 . The convex sections  650   a  and  652   a  deform the pipe member  600  to form the groove  680  on the pipe member  600  (here the groove  680  corresponds to the first groove portion  516  and the second groove portion  518 ). 
     After completion of the rolling process, plating is performed on the surface of the central area  510   a . In this embodiment, electroless Ni—P plating is employed. However, there is no limitation to this, and hard chrome plating or electroplating may be employed for example. 
     In the thus-manufactured developing roller  510 , a size of a ten-point average roughness Rz of the projecting sections  512  is smaller than 500 nm (which is the volume mean particle size of the external additive 500 nm silica). 
     Method for Assembling the Yellow Developing Device  54   
     A method for assembling the yellow developing device  54  is described next with reference to  FIG. 21 . 
     First, the above-described housing  540 , holder  526 , developing roller  510 , regulation blade  560 , blade-supporting member  564 , and the like are prepared (step S 2 ). 
     Next, the regulation blade  560  and the blade-supporting member  564  are secured to the holder  526  as a result of the regulation blade  560  and the blade-supporting member  564  being fixed to the regulation blade support sections  526   c  of the holder  526  with screws (step S 4 ). It should be noted that the aforementioned end seal  574  is attached to the regulation blade  560  ahead of this step S 4 . 
     Next, the developing roller  510  is attached to the holder  526  to which the regulation blade  560  and the blade-supporting member  564  have been secured (step S 6 ). At this time, the developing roller  510  is attached to the holder  526  so that the regulation blade  560  comes into contact with the developing roller  510  through one end to the other end in the rotation-axis direction of the developing roller  510 . The aforementioned upper seal  520  is attached to the holder  526  ahead of this step S 6 . 
     Then, the holder  526  to which the developing roller  510 , regulation blade  560  and the like have been attached, is attached to the housing  540  via the housing seal  546  (step S 8 ), thereby completing assembly of the yellow developing device  54 . It should be noted that the aforementioned toner supply roller  550  is attached to the housing  540  ahead of this step S 8 . 
     Other Embodiments 
     A developing device or the like according to the invention was described by way of the foregoing embodiment, but the foregoing embodiment of the invention is merely for the purpose of elucidating the invention and is not to be interpreted as limiting the invention. The invention can of course be altered and improved without departing from the gist thereof and equivalents are intended to be embraced therein. 
     In the foregoing embodiment, an intermediate transferring type full-color laser beam printer was described as an example of the image forming apparatus, but the invention can also be applied to various other types of image forming apparatuses, such as full-color laser beam printers that are not of the intermediate transferring type, monochrome laser beam printers, copying machines, and facsimile machines. 
     Moreover, the photoconductor is not limited to a so-called photosensitive roller, which is configured by providing a photoconductive layer on the outer circumferential surface of a cylindrical conductive base, and can also be a so-called photoconductive belt, which is configured by providing a photoconductive layer on the surface of a belt-shaped conductive base. 
     Furthermore, in the foregoing embodiment, the projecting sections  512  and the depressed sections  515 , which bear the toner, were arranged in a regular manner on the surface of the developing roller  510 . Furthermore, the depressed sections  515  were bottom portions of two types of spiral groove portions (the first groove portion  516  and the second groove portion  518 ) having different inclination angles with respect to the circumferential direction of the developing roller  510 , and the two types of spiral groove portions mutually intersected so as to form a grid pattern. Further still, the projecting sections  512  were square top surfaces surrounded by the two types of spiral groove portions, and one of two diagonal lines of the square top surface runs along the circumferential direction. However, there is no limitation to this. For example, the projecting sections  512  maybe rhomboid top surfaces or circular top surfaces or the like. 
     Furthermore, in the foregoing embodiment, the small grooves  512   b  were provided that were formed in the projecting sections  512  during processing of the developing roller  510  as shown in  FIG. 15  and that runs along the circumferential direction of the developing roller  510 , but there is not limitation to this. For example, the small grooves  512   b  may be provided so as to run along the rotation-axis direction. 
     However, in the case where the small grooves  512   b  are provided running along the circumferential direction, the external additives borne on the small grooves  512   b  and that makes contact with the contact section  560   a  at the time the developing roller  510  rotates are more easily caused to roll along the small grooves  512   b , thereby enabling effective prevention of the contact section  560   a  adhering closely to the projecting sections  512 , and in regard to this point the above-described embodiment is more preferable. 
     Furthermore, in the foregoing embodiment, the small grooves  512   b  were provided as shown in  FIG. 17A  so as to not connect from one end to the other end in the circumferential direction of the developing roller  510  across the projecting sections  512  on which the small grooves  512   b  are provided, but there is no limitation to this. For example, the small grooves  512   b  may be provided connecting from one end to the other end of the projecting sections  512 . 
     However, in the case where the small grooves  512   b  are provided so as to not connect from the one end to the other end, when the external additives borne on the small grooves  512   b  and that makes contact with the contact section  560   a  roll so as to run up from the small grooves  512   b  (see  FIG. 17B ), the contact section  560   a  shifts vertically up and down, thereby enabling the contact section  560   a  to be prevented more effectively from closely adhering to the projecting sections  512 , and in regard to this point the above-described embodiment is more preferable. 
     Furthermore, in the foregoing embodiment, the toner had four types of external additives that were externally added to the core particles, and the external additive particle size B was set as the volume mean particle size of the external additive (500 nm silica) having the largest volume mean particle size among the four types of external additives, but there is no limitation to this. For example, the external additive particle size B may be the volume mean particle size of an external additive other than the 500 nm silica of the four types of the external additives. 
     However, in the case where the external additive particle size B is the volume mean particle size of 500 nm silica, the 500 nm silica, which is most easily separated among the four types of external additives, is borne on the small grooves  512   b  and rolls in the small grooves  512   b , thereby enabling more effective prevention of the contact section  560   a  adhering closely to the projecting sections  512 , and in regard to this point the above-described embodiment is more preferable. 
     Furthermore, in the foregoing embodiment, the regulation blade  560  was constituted by a rubber elastic member (urethane rubber or the like), but there is no limitation to this. For example, the regulation blade  560  may be constituted by a sheet metal. 
     However, as is described below, the effect of causing the regulation blade  560  to appropriately come into contact with the projecting sections  512  is more effectively achieved, and in regard to this point, the above-described embodiment is more preferable. Compared to sheet metal, a rubber elastic member more readily has a larger surface area for coming into contact with the projecting sections  512 , and therefore tends to easily adhere closely to the developing roller  510 . For this reason, in the case where the regulation blade  560  is constituted by a rubber elastic member, the effect due to establishing a relationship in which the protrusion roughness C&lt;the external additive particle size B&lt;the distance D, that is, the effect of appropriately bringing the contact section  560   a  into contact with the projecting sections  512  is more effectively achieved. 
     Configuration of the Image Forming System, etc. 
     Next, an embodiment of an image forming system serving as an example of an embodiment of the invention is described with reference to the drawings. 
       FIG. 22  is an explanatory diagram showing an external configuration of an image forming system. An image forming system  700  is provided with a computer  702 , a display device  704 , a printer  706 , input devices  708 , and reading devices  710 . In this embodiment, the computer  702  is contained within a mini-tower type housing, but there is no limitation to this. A CRT (cathode ray tube), a plasma display, or a liquid crystal display device, for example, is generally used as the display device  704 , but there is no limitation to these. The printer described above is used as the printer  706 . In this embodiment, the input devices  708  are a keyboard  708 A and a mouse  708 B, but there is no limitation to these. In this embodiment, a flexible disk drive device  710 A and a CD-ROM drive device  710 B are used as the reading device  710 , but the reading device  710  is not limited to these, and it may also be an MO (magnet optical) disk drive device or a DVD (digital versatile disk), for example. 
       FIG. 23  is a block diagram showing the configuration of the image forming system shown in  FIG. 22 . An internal memory  802  such as a RAM is provided within the casing containing the computer  702 , and furthermore an external memory such as a hard disk drive unit  804  is provided. 
     In the above explanations, an example was given in which the image forming system is constituted by connecting the printer  706  to the computer  702 , the display device  704 , the input devices  708  and the reading devices  710 , but there is no limitation to this. For example, the image forming system may also be made of the computer  702  and the printer  706 , and the image forming system does not have to be provided with any of the display device  704 , the input devices  708 , and the reading devices  710 . 
     It is also possible that the printer  706  for example has some of the functions or mechanisms of the computer  702 , the display device  704 , the input devices  708 , and the reading devices  710 . For example, the printer  706  may be configured so as to have an image processing section for carrying out image processing, a display section for carrying out various types of displays, and a recording media mount/dismount section into and from which recording media storing image data captured by a digital camera or the like are inserted and taken out. 
     As an overall system, the image forming system that is thus achieved is superior to conventional systems. 
     Although the preferred embodiment of the invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from spirit and scope of the inventions as defined by the appended claims.