Patent Publication Number: US-7899376-B2

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

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2007-144063 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, a photoconductor as an example of an image bearing member for bearing a latent image, and a developing device for developing the latent image borne on the photoconductor. In the case where image signals etc. are sent out from an external device such as a host computer, the image forming apparatus positions the developing device at a developing position which is in opposition to the photoconductor. The latent image borne on the photoconductor is then developed with toner contained in the developing device, and a toner image is formed on the photoconductor. The image forming apparatus then transfers the toner image onto a medium, to ultimately form an image on the medium. 
     In order to achieve the above-mentioned function of developing the latent image borne on the photoconductor and other functions, the developing device has: a rotatable toner bearing roller that bears the toner and develops the latent image with the toner; and a regulation blade that abuts, with a predetermined width, against the circumferential surface of the toner bearing roller in its circumferential direction in such a manner that the longitudinal direction of the blade is along the direction of a rotation axis of the toner bearing roller, and that regulates the amount of toner borne on the toner bearing roller. The toner bearing roller develops the latent image borne on the photoconductor with the toner that is borne on the toner bearing roller and that has been regulated in amount by the regulation blade. 
     Further, among such toner bearing rollers, there are those that have projections and depressions (projecting sections and non-projecting sections) arranged regularly on its surface. (See, for example, JP-A-2006-259384 and JP-A-2003-57940.) 
     As regards the style (mode) according to which the above-mentioned regulation blade performs regulation, the so-called non-edge regulation (or flat-region-abutment regulation; a regulation style in which the tip edge, in the lateral direction and the thickness direction, of the regulation blade is not located within an abutting section having the above-mentioned predetermined width) is well known. There are cases, however, in which it is effective to adopt the so-called edge regulation (a regulation style in which the tip edge, in the lateral direction and the thickness direction, of the regulation blade is located within the abutting section having the above-mentioned predetermined width), from the viewpoint of curbing occurrence of development memory (development hysteresis), for example. 
     However, in cases where edge regulation is adopted, there is a possibility that, at the time the regulation blade regulates the amount of toner borne on the toner bearing roller, the tip edge of the regulation blade may enter into and collide against the non-projecting section of the toner bearing roller, thereby causing the tip edge to curl up or chip away. Such a problem is a cause of impairing the functionality of the regulation blade. 
     SUMMARY 
     An advantage achieved by some aspects of the present invention is that it is possible to curb functionality impairment of the regulation blade. 
     A primary aspect of the invention is a developing device including: a rotatable toner bearing roller that has regularly-arranged projecting sections and non-projecting sections, that bears toner whose volume average particle diameter is smaller than a depth of the non-projecting section relative to the projecting section, and that develops a latent image borne on an image bearing member with the toner borne on the toner bearing roller; and a regulation blade that is for regulating an amount of the toner borne on the toner bearing roller and that abuts, with a predetermined width, against a circumferential surface of the toner bearing roller in a circumferential direction thereof in such a manner that a longitudinal direction of the regulation blade is along a direction of a rotation axis of the toner bearing roller, a tip edge of the regulation blade in a lateral direction and a thickness direction thereof being located within an abutting section having the predetermined width, the predetermined width being larger than a maximum width, in the circumferential direction, of the non-projecting section. 
     Other features of this invention will be made clear through the description of the present specification with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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  of  FIG. 1 . 
         FIG. 3  is a conceptual diagram of a developing device. 
         FIG. 4  is a sectional view showing main structural components of the developing device. 
         FIG. 5  is a schematic perspective view of a developing roller  510 . 
         FIG. 6  is a schematic front view of the developing roller  510 . 
         FIG. 7  is a schematic diagram showing the shapes of projecting sections  512 , depressed sections  515 , etc. 
         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 around the periphery of a tip edge  560   b  of the regulation blade  560  abutting against the developing roller  510 . 
         FIG. 10  is a schematic diagram showing a relative positional relationship between an abutment nip  560   a  of the regulation blade  560  and the projecting sections  512  and non-projecting sections  513  of the developing roller  510 . 
         FIG. 11  is a perspective view of a holder  526 . 
         FIG. 12  is a perspective view showing how an upper seal  520 , the developing roller  510 , the regulation blade  560 , and the blade-supporting member  564  are assembled onto the holder  526 . 
         FIG. 13  is a perspective view showing how the holder  526  is mounted onto a housing  540 . 
         FIG. 14  is an explanatory diagram for describing a mechanism according to which development memory occurs. 
         FIG. 15  is a diagram showing a state, at a developing position, of toner borne on the projecting section  512  and the depressed section  515 . 
         FIGS. 16A and 16B  are explanatory diagrams for describing the effectiveness of the developing device according to one embodiment. 
         FIGS. 17A to 17E  are schematic diagrams showing the transformation of the developing roller  510  during a process of manufacturing the developing roller  510 . 
         FIG. 18  is an explanatory diagram for describing a rolling process for the developing roller  510 . 
         FIG. 19  is a flowchart for describing a method of assembling a yellow developing device  54 . 
         FIG. 20  is an enlarged schematic diagram showing a state around the periphery of the tip edge  560   b  of a developing device according to another embodiment. 
         FIG. 21  is an explanatory diagram showing the external structure of an image forming system. 
         FIG. 22  is a block diagram showing the configuration of the image forming system shown in  FIG. 21 . 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     At least the following matters will be made clear by the present specification and the accompanying drawings. 
     A developing device includes: a rotatable toner bearing roller that has regularly-arranged projecting sections and non-projecting sections, that bears toner whose volume average particle diameter is smaller than a depth of the non-projecting section relative to the projecting section, and that develops a latent image borne on an image bearing member with the toner borne on the toner bearing roller; and a regulation blade that is for regulating an amount of the toner borne on the toner bearing roller and that abuts, with a predetermined width, against a circumferential surface of the toner bearing roller in a circumferential direction thereof in such a manner that a longitudinal direction of the regulation blade is along a direction of a rotation axis of the toner bearing roller, a tip edge of the regulation blade in a lateral direction and a thickness direction thereof being located within an abutting section having the predetermined width, the predetermined width being larger than a maximum width, in the circumferential direction, of the non-projecting section. 
     With this developing device, functionality impairment of the regulation blade is appropriately curbed. 
     Further, the predetermined width may be larger than a sum of a width, in the circumferential direction, of the non-projecting section and a value twice a width, in the circumferential direction, of the projecting section, over a range extending from one end to another end, in the longitudinal direction, of the regulation blade. 
     In this case, functionality impairment of the regulation blade is curbed even more appropriately. 
     Further, the predetermined width may be larger than a sum of a value twice a width, in the circumferential direction, of the non-projecting section and a width, in the circumferential direction, of the projecting section, over a range extending from one end to another end, in the longitudinal direction, of the regulation blade. 
     In this case, functionality impairment of the regulation blade is curbed even more appropriately. 
     Further, of a first surface of the regulation blade along the lateral direction and a second surface of the regulation blade along the thickness direction, the abutting section having the predetermined width may be provided on the first surface; and the tip edge may be located at one end, in the lateral direction, of the abutting section. 
     In this case, it is possible to easily achieve a developing device in which the predetermined width is larger than the maximum width, in the circumferential direction, of the non-projecting section. 
     Further, the non-projecting section may include a depressed section and a side section that connects the projecting section and the depressed section; and a boundary between the side section and a section of the projecting section located downstream in a rotating direction of the toner bearing roller may be rounded off. 
     In this case, functionality impairment of the regulation blade is appropriately curbed, even if the tip edge enters into the non-projecting section. 
     It is also possible to achieve an image forming apparatus including: an image bearing member for bearing a latent image; and a developing device having a rotatable toner bearing roller that has regularly-arranged projecting sections and non-projecting sections, that bears toner whose volume average particle diameter is smaller than a depth of the non-projecting section relative to the projecting section, and that develops the latent image borne on the image bearing member with the toner borne on the toner bearing roller, and a regulation blade that is for regulating an amount of the toner borne on the toner bearing roller and that abuts, with a predetermined width, against a circumferential surface of the toner bearing roller in a circumferential direction thereof in such a manner that a longitudinal direction of the regulation blade is along a direction of a rotation axis of the toner bearing roller, a tip edge of the regulation blade in a lateral direction and a thickness direction thereof being located within an abutting section having the predetermined width, the predetermined width being larger than a maximum width, in the circumferential direction, of the non-projecting section. 
     With this image forming apparatus, functionality impairment of the regulation blade is appropriately curbed. 
     It is also possible to achieve an image forming system including: a computer; and an image forming apparatus connectable to the computer, the image forming apparatus having: an image bearing member for bearing a latent image; and a developing device having a rotatable toner bearing roller that has regularly-arranged projecting sections and non-projecting sections, that bears toner whose volume average particle diameter is smaller than a depth of the non-projecting section relative to the projecting section, and that develops the latent image borne on the image bearing member with the toner borne on the toner bearing roller, and a regulation blade that is for regulating an amount of the toner borne on the toner bearing roller and that abuts, with a predetermined width, against a circumferential surface of the toner bearing roller in a circumferential direction thereof in such a manner that a longitudinal direction of the regulation blade is along a direction of a rotation axis of the toner bearing roller, a tip edge of the regulation blade in a lateral direction and a thickness direction thereof being located within an abutting section having the predetermined width, the predetermined width being larger than a maximum width, in the circumferential direction, of the non-projecting section. 
     With this image forming system, functionality impairment of the regulation blade is appropriately curbed. 
     Overall Configuration Example of Image Forming Apparatus 
     Next, with reference to  FIG. 1 , an outline of an image forming apparatus will be described, taking a laser-beam printer  10  (hereinafter referred to also as a printer) as an example.  FIG. 1  is a diagram showing main structural components constructing the printer  10 . Note that in  FIG. 1 , the vertical direction is shown by the arrow, and, for example, a paper supply tray  92  is arranged in a lower section of the printer  10 , and a fusing unit  90  is arranged in an upper section of the printer  10 . 
     As shown in  FIG. 1 , the printer  10  according to this embodiment has 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 components are arranged along the direction of rotation of a photoconductor  20  as an example of an image bearing member. The printer  10  is further provided with a second transferring unit  80 , a fusing unit  90 , a displaying unit  95  constructed of a liquid-crystal panel and serving as means for making notifications to a user, and a control unit  100  for controlling these units etc. and managing the operations as a printer. 
     The photoconductor  20  has a cylindrical electrically-conductive base and a photoconductive layer formed on the outer circumferential surface of the base, and it is rotatable about its central axis. In this embodiment, the photoconductor  20  rotates clockwise, as shown by the arrow in  FIG. 1 . 
     The charging unit  30  is a device for electrically charging the photoconductor  20 . The exposing unit  40  is a device for forming a latent image on the charged photoconductor  20  by radiating a laser beam thereon. The exposing unit  40  has, for example, a semiconductor laser, a polygon mirror, and an F-θ lens, and radiates a modulated laser beam onto the charged photoconductor  20  in accordance with image signals having been input from a not-shown host computer such as a personal computer or a word processor. 
     The YMCK developing unit  50  is a device for developing the latent image formed on the photoconductor  20  using toner contained in each developing device, that is, black (K) toner contained in ablack developing device  51 , magenta (M) toner contained in a magenta developing device  52 , cyan (C) toner contained in a cyan developing device  53 , and yellow (Y) toner contained in a yellow developing device  54 . 
     The YMCK developing unit  50  can move the positions of the four developing devices  51 ,  52 ,  53 , and  54  by rotating while the four developing devices  51 ,  52 ,  53 , and  54  are in an attached state. More specifically, the YMCK developing unit  50  holds the four developing devices  51 ,  52 ,  53 , and  54  respectively with four holding sections  55   a ,  55   b ,  55   c , and  55   d . The four developing devices  51 ,  52 ,  53 , and  54  can be rotated about a central shaft  50   a  while maintaining their relative positions. Every time image formation for one page is finished, each of the developing devices selectively opposes the photoconductor  20 , to thereby successively develop the latent image formed on the photoconductor  20  using the toner contained in each of the developing devices  51 ,  52 ,  53 , and  54 . Note that each of the four developing devices  51 ,  52 ,  53 , and  54  described above is attachable to and detachable from the respective holding sections of the YMCK developing unit  50 . Further, details on the developing devices will be described further below. 
     The first transferring unit  60  is a device for transferring, onto the intermediate transferring member  70 , a single-color toner image formed on the photoconductor  20 . In the case where the toners of all four colors are successively transferred in a superimposing manner, a full-color toner image will be formed on the intermediate transferring member  70 . 
     The intermediate transferring member  70  is a laminated endless belt that is made by providing a vapor-deposited tin layer on the surface of a PET film, and then further applying semiconducting coating on the outer layer thereof. 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 member  70  onto a medium such as paper, film, and cloth. 
     The fusing unit  90  is a device for fusing the single-color toner image or the full-color toner image, which has been transferred onto the medium, to the medium to make 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  made to abut against the surface of the photoconductor  20 , and that is for removing the toner 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  is made up of a main controller  101  and a unit controller  102  as shown in  FIG. 2 . Image signals and control signals are input to the main controller  101 , and according to instructions based on the image signals and control signals, the unit controller  102  controls each of the above-mentioned units etc. to form an image. 
     Next, operations of the printer  10  structured as above will be described. 
     First, in cases where image signals and control signals are input from the not-shown host computer to the main controller  101  of the printer  10  through an interface (I/F)  112 , the photoconductor  20  and the intermediate transferring member  70  rotate under the control of the unit controller  102  based on the instructions from the main controller  101 . While being rotated, the photoconductor  20  is successively charged by the charging unit  30  at a charging position. 
     With the rotation of the photoconductor  20 , the charged area of the photoconductor  20  reaches an exposing position. A latent image according to image information about the first color, for example, yellow Y, is formed in that area by the exposing unit  40 . Further, the YMCK developing unit  50  positions the yellow developing device  54 , which contains yellow (Y) toner, at the developing position, which is in opposition to the photoconductor  20 . 
     With the rotation of the photoconductor  20 , the latent image formed on the photoconductor  20  reaches the developing position, and is developed with the yellow toner by the yellow developing device  54 . Thus, a yellow toner image is formed on the photoconductor  20 . 
     With the rotation of the photoconductor  20 , the yellow toner image formed on the photoconductor  20  reaches a first transferring position, and is transferred onto the intermediate transferring member  70  by the first transferring unit  60 . At this time, a first transferring voltage, which is in an opposite polarity from the polarity to which the toner has been charged, is applied to the first transferring unit  60 . Note that, during this process, the photoconductor  20  and the intermediate transferring member  70  are placed in contact with each other, but the second transferring unit  80  is kept separated from the intermediate transferring member  70 . 
     By subsequently performing the above-mentioned processes for the second, the third, and the fourth colors using each of the developing devices, toner images in four colors corresponding to the respective image signals are transferred onto the intermediate transferring member  70  in a superimposed manner. As a result, 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 a medium by the second transferring unit  80 . Note that the medium is transported from the paper supply tray  92  to the second transferring unit  80  via a paper-feed roller  94  and resisting rollers  96 . Further, during transferring operations, a second transferring voltage is applied to the second transferring unit  80  and also the unit  80  is pressed against the intermediate transferring member  70 . 
     The full-color toner image transferred onto the medium is heated and pressurized by the fusing unit  90  and fused to the medium. 
     On the other hand, after the photoconductor  20  passes the first transferring position, the toner adhering to the surface of the photoconductor  20  is scraped off by the cleaning blade  76  that is supported on the cleaning unit  75 , and the photoconductor  20  is prepared for electrical charging for forming the next latent image. The scraped-off toner is collected in a remaining-toner collector of the cleaning unit  75 . 
     Overview of Control Unit 
     Next, a configuration of the control unit  100  is described with reference to  FIG. 2 . The main controller  101  of the control unit  100  is electrically connected to a host computer via the interface  112 , and is provided with an image memory  113  for storing the image signals that have been input from the host computer. The unit controller  102  is electrically connected to the units in the body of the apparatus (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 fusing unit  90 , and the displaying unit  95 ), and it detects the state of each unit by receiving signals from sensors provided in those units, and controls the units based on the signals that are input from the main controller  101 . 
     Configuration Example of Developing Device 
     Next, a configuration example of the developing device is described with reference to  FIGS. 3 to 13 .  FIG. 3  is a conceptual diagram of a developing device.  FIG. 4  is a sectional view showing main structural components of the developing device.  FIG. 5  is a schematic perspective view of a developing roller  510 .  FIG. 6  is a schematic front view of the developing roller  510 .  FIG. 7  is a schematic diagram showing the shapes of projecting sections  512 , depressed sections  515 , etc., wherein the lower diagram of  FIG. 7  shows the sectional shape along the cross-section A-A of 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 (conceptual diagram) showing a state around the periphery of a tip edge  560   b  of the regulation blade  560  abutting against the developing roller  510 .  FIG. 10  is a schematic diagram (conceptual diagram) showing the relative positional relationship between an abutment nip  560   a  of the regulation blade  560  and the projecting sections  512  and non-projecting sections  513  of the developing roller  510 .  FIG. 11  is a perspective view of a holder  526 .  FIG. 12  is a perspective view showing how an upper seal  520 , the developing roller  510 , the regulation blade  560 , and the blade-supporting member  564  are assembled onto the holder  526 .  FIG. 13  is a perspective view showing how the holder  526  is mounted onto a housing  540 . Note that the sectional view of  FIG. 4  shows a cross-section of the developing device cut away along a plane perpendicular to the longitudinal direction shown in  FIG. 3 . Further, in  FIG. 4 , the vertical direction is shown by the arrow as in  FIG. 1 , and for example, the central axis of the developing roller  510  is below the central axis of the photoconductor  20 . Furthermore, in  FIG. 4 , the yellow developing device  54  is shown to be in a state where it is positioned at the developing position in opposition to the photoconductor  20 . Further,  FIG. 9  corresponds to cross-section B-B of  FIG. 10 . Furthermore, in  FIGS. 5 to 7 ,  9 , and  10 , the scale of the projecting sections  512  etc. differs from the actual scale for the sake of clarity of the figures. Further, the arrows in  FIG. 8  respectively indicate the longitudinal and lateral directions of the regulation blade  560 , and the arrows in  FIG. 9  respectively indicate the lateral and thickness directions of the regulation blade  560 . 
     The YMCK developing unit  50  is provided with a black developing device  51  containing black (K) toner, a magenta developing device  52  containing magenta (M) toner, a cyan developing device  53  containing cyan (C) toner, and a yellow developing device  54  containing yellow (Y) toner. Since the configuration of each developing device is the same, the yellow developing device  54  will be described below. 
     The yellow developing device  54  has, for example, a developing roller  510  as an example of a toner bearing roller, an upper seal  520 , a toner containing member  530 , a housing  540 , a toner supplying roller  550 , a regulation blade  560 , and a holder  526 . 
     The developing roller  510  bears toner T, transports the toner by rotating to the developing position which is in opposition to the photoconductor  20 , and develops the latent image borne on the photoconductor  20  with the toner T (the toner T borne on the developing roller  510 ). The developing roller  510  is a component made, for example, of aluminum alloy or iron alloy. 
     The developing roller  510  has projecting sections  512  and non-projecting sections  513  on the surface of its central section  510   a . The non-projecting sections  513  include side sections  514  and depressed sections  515 . As shown in  FIGS. 5 to 7 , the projecting and non-projecting sections are arranged regularly on the surface of the developing roller  510 . 
     The projecting sections  512  are the highest sections within the central section  510   a , and as shown in the upper diagram of  FIG. 7 , each has a flat, square-shaped top surface. The length L 1  of each side of the square-shaped projecting section  512  (refer to the lower diagram of  FIG. 7 ) is approximately 50 μm. The projecting section  512  is formed on the surface of the central section  510   a  in such a manner that the two diagonals of the square are along the rotation-axis direction and the circumferential direction of the developing roller  510 , respectively. 
     In this embodiment, the non-projecting sections  513  are made of first groove sections  516  and second groove sections  518  whose winding directions differ from one another. The first groove section  516  is a helical groove whose longitudinal direction is along the direction indicated by the symbol X in  FIG. 6 , whereas the second groove section  518  is a helical groove whose longitudinal direction is along the direction indicated by the symbol Y in  FIG. 6 . Note that, for either of the groove sections, the acute angle formed between the longitudinal direction of the groove section and the rotation-axis direction of the developing roller  510  is approximately 45° (refer to  FIG. 6 ). Further, the groove width L 2  of the groove section (in other words, the distance between adjacent projecting sections  512 ; refer to the lower diagram of  FIG. 7 ) is approximately 50 μm, as with the length L 1  of each side of the projecting section  512 . 
     The side section  514  is a slanted surface that connects the projecting section  512  and the depressed section  515 , and as shown in the upper diagram of  FIG. 7 , there are four side sections  514  respectively corresponding to the sides of the square-shaped projecting section  512  described above. Further, as shown in  FIGS. 5 to 7 , a multitude of (sets of) the projecting section  512  and the four side sections  514  are arranged regularly in a meshed manner on the surface of the central section  510   a  of the developing roller  510 . 
     The depressed section  515  corresponds to the bottom section of the non-projecting section  513  (i.e., the first groove section  516  or the second groove section  518 ), and is the lowest section within the central section  510   a . As shown in  FIGS. 5 to 7 , the depressed sections  515  are formed regularly in a net-like manner so as to surround the four sides of the projecting section  512  and the four side sections  514 . Note that, as shown in  FIG. 7 , the depth d of the depressed section  515  (non-projecting section  513 ) relative to the projecting section  512  (i.e., the length from the projecting section  512  to the depressed section  515  in the radial direction of the developing roller  510 ) is approximately 8 μm. The developing roller  510  has the projecting sections  512  and the depressed sections  515  formed thereon in such a manner that the depth d is uniform among all of the depressed sections  515  provided in the developing roller  510 . In this embodiment, the toner T is granular (particulate), and the volume average particle diameter of the toner T is approximately 4.6 μm. Thus, the size of the volume average particle diameter of the toner T is smaller than the depth d of the depressed section  515 . 
     Furthermore, the surface of the central section  510   a , which is provided with the projecting sections  512 , the side sections  514 , and the depressed sections  515 , is plated with electroless Ni—P plating. 
     Further, the developing roller  510  has a shaft section  510   b , and the developing roller  510  is rotatably supported due to the shaft section  510   b  being supported, via bearings  576 , by developing-roller supporting sections  526   b  of a holder  526  described further below (see  FIG. 12 ). As shown in  FIG. 4 , the developing roller  510  rotates in a direction (the counterclockwise direction in  FIG. 4 ) opposite from the rotating direction of the photoconductor  20  (the clockwise direction in  FIG. 4 ). 
     Further, there is a gap between the developing roller  510  and the photoconductor  20  in a state where the yellow developing device  54  is in opposition to the photoconductor  20 . That is, the yellow developing device  54  develops the latent image formed on the photoconductor  20  in a contactless state in which the toner T borne on the developing roller  510  is not in contact with the photoconductor  20 . 
     The housing  540  is manufactured by welding together a plurality of integrally-molded housing sections made of resin—that is, an upper housing section  542  and a lower housing section  544 . In the housing  540 , a toner containing member  530  is formed for containing the toner T. The toner containing member  530  is divided into two toner containing sections, namely, the first toner containing section  530   a  and the second toner containing section  530   b , by a partitioning wall  545  that is for partitioning the toner T and that protrudes inward (in the up/down direction of  FIG. 4 ) from the inner wall. The first toner containing section  530   a  and the second toner containing section  530   b  are connected at their upper sections, and in the state shown in  FIG. 4 , movement of the toner T is restricted by the partitioning wall  545 . Further, as shown in  FIG. 4 , the housing  540  (more specifically, the first toner containing section  530   a ) has an opening  572  in its lower section, and the developing roller  510  is provided facing the opening  572 . 
     The toner supplying roller  550  is provided in the first toner containing section  530   a  described above and supplies the toner T contained in the first toner containing section  530   a  to the developing roller  510 . The toner supplying roller  550  is made, for example, of polyurethane foam, and abuts against the developing roller  510  in an elastically deformed state. The toner supplying roller  550  is rotatable about its central axis, and by rotating, it transports the toner T to an abutting position where the roller  550  abuts against the developing roller  510 . Then, at the abutting position, the toner T is frictionally charged by the toner supplying roller  550  and the developing roller  510 , and the electrically-charged toner T adheres to the developing roller  510  and is appropriately borne on the developing roller  510 . In this way, the toner supplying roller  550  supplies the toner T to the developing roller  510 . 
     Note that the toner supplying roller  550  rotates in a direction (clockwise in  FIG. 4 ) opposite from the rotating direction of the developing roller  510  (counterclockwise in  FIG. 4 ). Further, the toner supplying roller  550  not only serves to supply the toner T to the developing roller  510 , but it also serves to strip off, from the developing roller  510 , the toner T remaining on the developing roller  510  after development. 
     The upper seal  520  abuts against the developing roller  510  along the rotation-axis direction thereof to allow the toner T remaining on the developing roller  510  after passing the developing position to move into the housing  540  and also to restrict the toner T in the housing  540  from moving outside therefrom. The upper seal  520  is a seal made, for example, of polyethylene film. The upper seal  520  is supported by an upper-seal supporting section  526   a  of the holder  526  described below, and it is arranged in such a manner that its longitudinal direction is along the rotation-axis direction of the developing roller  510  (see  FIG. 12 ). 
     Further, in between the upper-seal supporting section  526   a  and a surface of the upper seal  520  (which is also referred to as the opposite surface  520   c ) on the opposite side from the abutting surface  520   b  of the upper seal  520  with which it abuts against the developing roller  510 , there is provided an upper-seal urging member  524  made of an elastic body, such as Moltoprene, in a compressed state. 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  abuts against the developing roller  510  in such a manner that the longitudinal direction of the regulation blade  560  is along the rotation-axis direction of the developing roller  510  over the range extending from one end to the other end, in the rotation-axis direction, of the developing roller  510 , and regulates the amount of toner T borne on the developing roller  510  (the projecting sections  512  and the non-projecting sections  513 ) as well as applies electrical charge to the toner T borne on the developing roller  510 . 
     The regulation blade  560  has a thickness of approximately 2 mm, is made, for example, of silicone rubber or urethane rubber having a rubber hardness of approximately 65 degrees according to JIS-A, and is supported by a blade-supporting member  564  as shown in  FIGS. 4 and 8 . The blade-supporting member  564  is made up of a thin plate  564   a  and a thin-plate supporting section  564   b , and supports the regulation blade  560  with one end  564   d  thereof in the lateral direction (i.e., the end on the side of the thin plate  564   a ). The thin plate  564   a  is made, for example, of phosphor bronze or stainless steel having a thickness of approximately 0.15 mm, and has a spring-like characteristic. The thin plate  564   a  directly supports the regulation blade  560 , and presses the regulation blade  560  against the developing roller  510  with its urging force. (The linear pressure of the regulation load of the regulation blade  560  is approximately 2.33 g/mm.) The thin-plate supporting section  564   b  is a plate made of metal arranged on the other end  564   e , in the lateral direction, of the blade-supporting member  564 . The thin-plate supporting section  564   b  is attached to the thin plate  564   a  in a state where the section  564   b  supports an end of the thin plate  564   a  on the opposite side from the side supporting the regulation blade  560 . Further, the regulation blade  560  and the blade-supporting member  564  are attached to the regulation-blade supporting sections  526   c  of the holder  526  described below in a state where both ends  564   c , in the longitudinal direction, of the thin-plate supporting section  564   b  are supported by the regulation-blade supporting sections  526   c.    
     As shown in  FIG. 9 , the regulation blade  560  abuts, with a predetermined width, against the circumferential surface of the developing roller  510  in the circumferential direction. In other words, the regulation blade  560  has formed thereon an abutting section (also referred to below as an abutment nip  560   a ) having a predetermined width (also referred to below as a regulation nip width). 
     Further, the tip edge  560   b , in the lateral direction and the thickness direction, of the regulation blade  560  is located within the abutment nip  560   a  having the above-mentioned predetermined width. That is, the tip edge  560   b  abuts against the developing roller  510 . This regulation style of the regulation blade  560  is the so-called edge regulation. 
     Note that, as shown in  FIGS. 4 and 9 , the regulation blade  560  has a rectangular sectional shape and is provided with a first surface  560   c  along the lateral direction and a second surface  560   d  along the thickness direction. In this embodiment, the abutment nip  560   a  is provided on the first surface  560   c  of the two surfaces, and the tip edge  560   b  is located at one end, in the lateral direction, of the abutment nip  560   a . Further, the regulation blade  560  is arranged in such a manner that its tip edge  560   b  faces toward the upstream side in the rotating direction of the developing roller  510 . That is, the regulation blade  560  makes a so-called counter-abutment with respect to the roller  510 . 
     Further, in the case of considering the size of the regulation nip width of the abutment nip  560   a  (in the circumferential direction) as compared to the size of the width of the non-projecting section  513  etc. in the circumferential direction, the regulation nip width (indicated by the symbol L 3  in  FIG. 10 ) is larger than the maximum width, in the circumferential direction, of the non-projecting section  513 , as shown in  FIG. 10 . 
     As shown in  FIG. 10 , the width, in the circumferential direction, of the non-projecting section  513  differs depending on the position of the non-projecting section  513  in the rotation-axis direction. (For example, the width indicated by the symbol L 4  and the width indicated by the symbol L 5  are different.) The regulation nip width is larger than the largest width among the various widths that differ from one another, i.e., the maximum width. In other words, in this embodiment, the regulation nip width is larger than the width, in the circumferential direction, of the non-projecting section  513  over the range extending from one end to the other end, in the longitudinal direction, of the regulation blade  560 . In this embodiment, the regulation nip width is approximately 300 μm, whereas the maximum width, in the circumferential direction, of the non-projecting section  513  is the width indicated by the symbol L 4  and is approximately 141.4 μm (twice the value obtained by multiplying fifty by the square root of two). (Note that the width indicated by the symbol L 4  is not the length of a line segment from the right end of the projecting section  512  indicated by the symbol M 1  to the right end of the projecting section  512  indicated by the symbol M 3  passing the left end of the projecting section  512  indicated by the symbol M 2 , but is the length of a line segment  1  which is slightly to the left of the above-mentioned line segment. That is, the line segment  1  is not on the left end of the projecting section  512  indicated by the symbol M 2 .) Incidentally, the width indicated by the symbol L 5  is the minimum width, in the circumferential direction, of the non-projecting section  513  and is approximately 70.7 μm (a value obtained by multiplying fifty by the square root of two). 
     Furthermore, the regulation nip width according to this embodiment is sufficiently larger than the width, in the circumferential direction, of the non-projecting section  513 . More specifically, the regulation nip width is larger than the sum of the width, in the circumferential direction, of the non-projecting section  513  and a value twice the width, in the circumferential direction, of the projecting section  512  over the range extending from one end to the other end, in the longitudinal direction, of the regulation blade  560 . (This sum is also referred to below as a first sum.) The magnitude of the first sum also differs depending on the position in the rotation-axis direction. (For example, the first sum indicated by the symbol L 6  and the first sum indicated by the symbol L 7  are different.) However, regardless of the position, the regulation nip width is larger than the first sum. (Note that the maximum first sum is the sum indicated by the symbol L 6  and is approximately 212.1 μm.) Further, the regulation nip width is larger than the sum of a value twice the width, in the circumferential direction, of the non-projecting section  513  and the width, in the circumferential direction, of the projecting section  512  over the range extending from one end to the other end, in the longitudinal direction, of the regulation blade  560 . (This sum is also referred to below as a second sum.) The magnitude of the second sum also differs depending on the position in the rotation-axis direction. (For example, the second sum indicated by the symbol L 8  and the second sum indicated by the symbol L 9  are different.) However, regardless of the position, the regulation nip width is larger than the second sum. (Note that the maximum second sum is the sum indicated by the symbol L 8  and is approximately 282.8 μm.) 
     Further, as shown in  FIG. 12 , 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 contacts with the ends, in the rotation-axis direction, of the developing roller  510  along the circumferential surface of the developing roller  510 , to thereby serve to prevent the toner T from spilling from between the circumferential surface of the roller and the housing  540 . 
     The holder  526  is a component made of metal for assembling thereon various components such as the developing roller  510 . As shown in  FIG. 11 , the holder  526  has: an upper-seal supporting section  526   a  along the longitudinal direction (i.e., the rotation-axis direction of the developing roller  510 ); developing-roller supporting sections  526   b  that are provided on the outer sides of the upper-seal supporting section  526   a  in the longitudinal direction (the rotation-axis direction) and that intersect with the longitudinal direction (the rotation-axis direction); and regulation-blade supporting sections  526   c  that intersect with the developing-roller supporting sections  526   b  and that are located in opposition to the ends, in the longitudinal direction, of the upper-seal supporting section  526   a.    
     As shown in  FIG. 12 , the upper seal  520  is supported by the upper-seal supporting section  526   a  at its end  520   a  in the lateral direction (see  FIG. 4 ), and the developing roller  510  is supported by the developing-roller supporting sections  526   b  at its ends. 
     Furthermore, the regulation blade  560  and the blade-supporting member  564  are supported by the regulation-blade supporting sections  526   c  at both ends  564   c , in the longitudinal direction, of the blade-supporting member  564 . The regulation blade  560  and the blade-supporting member  564  are fixed to the holder  526  by being screwed onto the regulation-blade supporting sections  526   c.    
     The holder  526  having the upper seal  520 , the developing roller  510 , the regulation blade  560 , and the blade-supporting member  564  assembled thereto in this way is attached to the above-mentioned housing  540  via a housing seal  546  (see  FIG. 4 ) for preventing the toner T from spilling from between the holder  526  and the housing  540 , as shown in  FIG. 13 . 
     In the yellow developing device  54  structured as described above, the toner supplying roller  550  supplies the toner T contained in the toner containing member  530  to the developing roller  510 . At the time of being supplied, the toner T is frictionally charged by the toner supplying roller  550  and the developing roller  510 , and the electrically-charged toner T adheres to the developing roller  510  and is appropriately borne on the developing roller  510 . With the rotation of the developing roller  510 , the toner T borne on the developing roller  510  reaches the regulation blade  560 , and the regulation blade  560  regulates the amount of the toner T and also frictionally charges the toner T even further. With further rotation of the developing roller  510 , the toner T on the developing roller  510  reaches the developing position opposing the photoconductor  20 . Then, under the alternating field, the toner T is used at the developing position for developing the latent image formed on the photoconductor  20 . With further rotation of the developing roller  510 , the toner T on the developing roller  510 , which has passed the developing position, passes the upper seal  520  and is collected into the developing device by the upper seal  520  without being scraped off. Further, the toner T that still remains on the developing roller  510  can be stripped off by the toner supplying roller  550 . 
     Reason for Adopting Edge Regulation in Printer  10  According to Present Embodiment 
     As described in the “Related Art” section above, the so-called non-edge regulation (or flat-region-abutment regulation; a regulation style in which the tip edge  560   b , in the lateral direction and the thickness direction, of the regulation blade  560  is not located within the abutment nip  560   a  having the above-mentioned predetermined width) is well known as the style (mode) according to which the regulation blade  560  performs regulation. There are cases, however, in which it is effective to adopt the so-called edge regulation (a regulation style in which the tip edge  560   b , in the lateral direction and the thickness direction, of the regulation blade  560  is located within the abutment nip  560   a  having the above-mentioned predetermined width) from the viewpoint of curbing occurrence of development memory (development hysteresis), for example. Further, there is a certain relationship between the constitution of the toner and the degree at which development memory occurs, and therefore, the degree at which development memory occurs differs depending on the constitution of the toner used in the printer  10 . Therefore, in cases where toner having characteristics that significantly cause development memory is used, it is desirable to curb the occurrence of development memory by adopting edge regulation. 
     The toner according to this embodiment has such characteristics that significantly cause development memory, and therefore, in this embodiment, edge regulation is adopted in order to curb the occurrence of development memory. 
     Below, a mechanism according to which development memory occurs is described first. Next, the constitution of the toner according to this embodiment is described, and then the reason why such toner significantly causes development memory is described. Further, the reason why it is possible to curb the occurrence of development memory by adopting edge regulation is described next. These descriptions will reveal the reason for adopting edge regulation in the printer  10  according to this embodiment. 
     Mechanism According to which Development Memory Occurs 
     In this section, a mechanism according to which development memory occurs is described with reference to  FIG. 14 .  FIG. 14  is an explanatory diagram for describing a mechanism according to which development memory occurs. 
     As described above, toner is frictionally charged by the toner supplying roller  550  and the developing roller  510 , and the electrically-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  is frictionally charged even further by the regulation blade  560 , and then reaches the developing position in opposition to the photoconductor  20  and is used for developing a latent image at the developing position. That is, in the case where the developing roller  510  makes one revolution, the following processes are executed: a process of charging and supplying the toner by the toner supplying roller  550  (a process of causing the toner to be borne on the developing roller  510 ); a process of charging the toner by the regulation blade  560 ; and a process of developing the latent image on the photoconductor  20 . This series of processes is executed a plurality of times as the developing roller  510  makes a plurality of times of revolutions. Further, for example, a toner image formed on the photoconductor  20  by executing the above-mentioned series of processes for the n th  revolution of the developing roller  510  and a toner image formed on the photoconductor  20  by executing the above-mentioned series of processes for the n+1 st  revolution of the developing roller  510  will be in such a state that the toner images are located side-by-side in the circumferential direction on the photoconductor  20 . 
     In this section, consideration is made regarding the above-mentioned processes of the developing roller  510 , assuming that a latent image representing the alphabet “O” is developed and a toner image representing the alphabet “O” is formed on the photoconductor  20  by executing the above-mentioned series of processes for the n th  revolution of the developing roller  510 , and a latent image is developed and a halftone image is formed on the entire surface of the photoconductor  20  by executing the above-mentioned series of processes for the n+1 st  revolution of the developing roller  510 . Through this consideration, the mechanism according to which development memory occurs is revealed. 
     When the latent image representing the alphabet “O” is developed in the development process for the n th  revolution of the developing roller  510 , the toner—among all the toner borne on the developing roller  510 —that is borne on a section of the developing roller  510  opposing the latent image is consumed for forming the toner image. Thus, after the development process for the n th  revolution of the developing roller  510  is finished, the opposing section will be in such a state that no toner is borne thereon. On the other hand, the toner that is borne on a section of the developing roller  510  not opposing the latent image is not consumed. Therefore, even after the development process is finished, the toner will still be borne on the non-opposing section. In this way, after the above-mentioned series of processes for the n th  revolution of the developing roller  510  is finished, a first region having no toner borne thereon (this first region will be in the shape of the letter “O”) and a second region having toner borne thereon will be created on the developing roller  510 . 
     Then, as the developing roller  510  rotates, the first and second regions eventually reach the abutting position where the roller  510  abuts against the toner supplying roller  550 , and the above-mentioned series of processes for the n+1 st  revolution of the developing roller  510  is started. More specifically, at the abutting position, the process of charging and supplying the toner by the toner supplying roller  550  for the n+1 st  revolution is executed. 
     It should be noted here that the second region already has toner borne thereon, and the toner is in a sufficiently-charged state due to execution of the process of charging and supplying the toner by the toner supplying roller  550  for the n th  revolution and the process of charging the toner by the regulation blade  560  for the n th  revolution. Further, since the toner is charged even further by execution of the present process, the adhesive force with which the toner adheres to the developing roller  510  is enhanced even further. Thus, the toner is transported toward the regulation blade  560  for execution of the subsequent process while being kept borne on the developing roller  510 . 
     On the other hand, the first region has no toner borne thereon, and therefore, toner contained in the toner containing member  530  is supplied anew to the first region. It should be noted here that the electrical charge of this toner is still in an insufficient state, in contrast to the toner in the second region which has been sufficiently charged by execution of the processes of charging the toner for the n th  revolution. Further, the toner is frictionally charged by the toner supplying roller  550  and the developing roller  510  in the present process, but in cases where the toner has characteristics in which the buildup of the electrical charge of the toner is slow (it takes time for the electrical-charge amount to reach the saturation electrical-charge amount), the toner is not appropriately borne on the developing roller  510  at the time frictional charging is carried out (in other words, the toner is not sufficiently supplied by the toner supplying roller  550  in the first region). 
     Then, the first region on which the toner is not borne appropriately and the second region on which the toner is borne appropriately first reach the regulation blade  560  for execution of the process of charging the toner by the regulation blade  560  for the n+1 st  revolution, and then reach the developing position in opposition to the photoconductor  20 . Here, the development process for the n+1 st  revolution is executed and the latent image is developed, and thus a halftone image is formed on the entire surface of the photoconductor  20 . However, the first region does not bear the toner appropriately, even though the second region bears the toner appropriately. Therefore, the darkness of the halftone image formed by developing the latent image in opposition to the first region becomes lighter than the darkness of the halftone image formed by developing the latent image in opposition to the second region. 
     This state (in which there is difference between the darkness of the two images) is shown in  FIG. 14 .  FIG. 14  shows the toner image representing the alphabet “O” formed on the photoconductor  20  by executing the above-mentioned series of processes for the n th  revolution of the developing roller  510 , and the halftone image formed on the photoconductor  20  by executing the above-mentioned series of processes for the n+1 st  revolution of the developing roller  510 . This figure shows the toner images, which are formed on the photoconductor  20 , on the circumferential surface of a schematically-developed photoconductor  20 , and indicates the circumferential direction and the axial direction of the photoconductor  20  with the respective arrows. The length L shown in the figure corresponds to the length of one revolution of the circumferential surface of the developing roller  510 . 
     Further,  FIG. 14  shows a state in which the darkness of the halftone image formed by developing the latent image in opposition to the first region (indicated by the character A 1  in the figure) is lighter than the darkness of the halftone image formed by developing the latent image in opposition to the second region (indicated by the character A 2  in the figure). Further, as described above, since the first region has the shape of the letter “O”, the halftone image lighter in darkness—which is formed by developing the latent image in opposition to the first region—also has the shape of the letter “O”. That is, a phenomenon, i.e., development memory, occurs in which the shape of the toner image formed on the photoconductor  20  by executing the above-mentioned series of processes for the n th  revolution appears in the halftone image formed on the photoconductor  20  by executing the above-mentioned series of processes for the n+1 st  revolution. 
     In this way, in cases where toner having a slow electrical-charge buildup is used in the printer  10 , development memory may occur significantly due to this slow electrical-charge buildup. 
     Conversely, in cases where toner having a fast electrical-charge buildup is used, the developing roller  510  will appropriately bear the toner also in the first region at the time the toner is frictionally charged by the toner supplying roller  550  and the developing roller  510  during the process of charging and supplying the toner for the n+1 st  revolution. Thus, the darkness of the halftone image formed by developing the latent image in opposition to the first region will substantially be the same as the darkness of the halftone image formed by developing the latent image in opposition to the second region. Therefore, in this case, occurrence of development memory is curbed. 
     Toner According to Present Embodiment 
     This section describes the constitution of the toner according to this embodiment, that is, the toner used in the printer  10  according to this embodiment, and the reason why the toner significantly causes development memory. 
     Toner Constitution 
     (1) Particle Diameter of Toner 
     The toner used in the printer  10  according to this embodiment has a smaller toner particle diameter (volume average particle diameter of 5 μm or less) than the particle diameter of toner generally used heretofore (volume average particle diameter of above 5 μm), for placing high importance on achieving superior image quality in finally-obtained images (achieving good reproducibility of dots). More specifically, as described above, the volume average particle diameter Ave thereof is approximately 4.6 μm. Note that the 3σ values—that is, σ value obtained by subtracting a value three times the standard deviation σ in the toner-particle-diameter distribution from the volume average particle diameter Ave (referred to below as “−3σ value” for convenience), and a value obtained by adding a value three times the standard deviation σ in the toner-particle-diameter distribution to the volume average particle diameter (referred to below as “+3σ value” for convenience)—are approximately 2.3 μm and approximately 6.9 μm, respectively. 
     It should be noted here that the volume average particle diameter is a value calculated as the sum total from i=1 to n of the product of Ri and Pi, in cases where the volume occupancy rate of toner having a particle diameter of Ri (i=1 . . . , n) is Pi (i=1 . . . , n; the sum total from P 1  to Pn is one). Further, the above-mentioned standard deviation σ is the square root of the variance, and the variance is a value calculated as the sum total from i=1 to n of the product of Pi and the square of the difference between Ri (i=1 . . . , n) and Ave. 
     (2) Degree of Circularity of Toner 
     The toner used in the printer  10  according to this embodiment has a larger degree of circularity (which is close to a perfect circle; degree of circularity of 0.950 or greater) than the degree of circularity of toner generally used heretofore (degree of circularity of less than 0.950), for placing high importance on transferability during the first transfer and the second transfer. More specifically, the degree of circularity thereof is approximately 0.960 to 0.985. 
     (3) Charge Control Agent (CCA) 
     The toner used in the printer  10  according to this embodiment does not include any charge control agents (CCA). 
     Typical methods for manufacturing toner include the pulverization method and the polymerization method. The toner according to this embodiment, however, is manufactured through the polymerization method, because the polymerization method is suitable for manufacturing toner having a small particle diameter and toner having a high degree of circularity. In cases where the polymerization method is employed as the toner manufacturing method, there is a possibility that disadvantages may occur by mixing charge control agents (CCA). Therefore, in this embodiment, no charge control agent (CCA) is included in the toner. 
     Note that the suspension polymerization method and the emulsion polymerization method, for example, may be given as examples of polymerization methods. With the suspension polymerization method, it is possible to form colored toner particles having a desired particle size by, for example, adding, while stirring, a monomer composition having dissolved/dispersed therein polymerizable monomers, coloring agents (coloring pigments), and mold-release agents as well as other additives—such as dyes, polymerization initiators, and cross-linking agents—as necessary into an aqueous phase including suspension stabilizers (water-soluble high polymers and poorly water-soluble inorganic substances), to thereby form the composition into particles and cause polymerization. With the emulsion polymerization method, it is possible to form colored toner particles having a desired particle size by, for example, dispersing monomers and mold-release agents as well as other agents—such as polymerization initiators and emulsifiers (surfactants)—as necessary into water to thereby cause polymerization, and then adding coloring agents (coloring pigments), flocculants (electrolytes), etc. during the flocculation process. 
     The toner according to this embodiment is manufactured through the emulsion polymerization method. Described below is a method of manufacturing cyan toner—among the above-mentioned four colors of toners (black toner, magenta toner, cyan toner, and yellow toner)—through the emulsion polymerization method. 
     First, a monomer mixture including 80 parts by mass of styrene monomer as the monomer, 20 parts by mass of butyl acrylate, and 5 parts by mass of acrylic acid was added into an aqueous solution mixture including 105 parts by mass of water, 1 part by mass of a nonionic emulsifier (“Emulgen 950” from Dai-Ichi Kogyo Seiyaku Co., Ltd.), 1.5 parts by mass of an anionic emulsifier (“Neogen R” from Dai-Ichi Kogyo Seiyaku Co., Ltd.), and 0.55 parts by mass of potassium persulfate as a polymerization initiator, and polymerization was carried out for eight hours at 70° C. while stirring the mixture under a nitrogen gas stream. After the polymerization reaction, the mixture was cooled, and a milk-white resin emulsion having a particle diameter of 0.25 μm was obtained. 
     Next, 200 parts by mass of the resin emulsion, 20 parts by mass of a polyethylene wax emulsion (from Sanyo Chemical Industries, Ltd.) as a mold-release agent, and 25 parts by mass of phthalocyanine blue as a coloring agent were dispersed into 0.2 l of water including 0.2 parts by mass of sodium dodecylbenzenesulfonate as a surfactant. After adding diethylamine and adjusting the pH to 5.5, 0.3 parts by mass of aluminum sulfate as an electrolyte was added to the mixture while stirring, and then dispersion was carried out by stirring at high speed with a stirring device (“TK homomixer”). 
     Furthermore, 40 parts by mass of styrene monomer, 10 parts by mass of butyl acrylate, and 5 parts by mass of zinc salicylate were added along with 40 parts by mass of water. The mixture was heated to 90° C. while stirring under a nitrogen gas stream as above, hydrogen peroxide solution was added to the mixture, and polymerization was carried out for three hours, to thereby let the particles grow. After termination of the polymerization, the temperature of the mixture was raised to 95° C. while adjusting the pH to 5 or above and the mixture was held in this state for five hours, in order to increase the bonding strength of the aggregated particles. Then, the obtained particles were washed with water and vacuum-dried at 45° C. for ten hours, to thereby obtain cyan-toner core particles (colored toner particles). 
     The colored toner particles obtained in this way were mixed with external additives (specifically, silica and titania) and thus the external additives were added to the exterior of the colored toner particles, to thereby obtain cyan toner having a volume average particle diameter of approximately 4.6 μm. 
     (4) Coloring Agents (Coloring Pigments) 
     As regards the toner used in the printer  10  according to this embodiment, the amount of coloring agent (coloring pigment) included in the toner is larger (i.e., 10 wt % or greater) than the amount of coloring agent (coloring pigment) included in toner generally used heretofore (i.e., less than 10 wt %), in consideration of the fact that the toner particle diameter is small. That is, in cases where the toner particle diameter is small, the amount of toner that ultimately adheres to the medium such as paper becomes small, and therefore, the darkness of the image tends to be light. Therefore, in order to compensate for this, a larger amount of coloring agent (coloring pigment) is included in this embodiment. 
     Reason why Toner According to Present Embodiment Significantly Causes Development Memory 
     The toner according to this embodiment has the characteristics as described in (1) to (4) above. Due to the fact that the toner has such characteristics, development memory is prone to occur in the printer  10  according to this embodiment in which the above-mentioned toner is used. 
     More specifically, as the toner particle diameter becomes small, the saturation electrical-charge amount of the toner increases, and thus the electrical-charge buildup of the toner becomes slow. Further, since the toner does not include any charge control agents (CCA), it is not possible to employ charge control for accelerating the electrical-charge buildup of the toner. Further, since the amount of coloring agent (coloring pigment) is large, the electrical-charge buildup of the toner inevitably becomes slow. 
     Thus, due to the electrical-charge buildup of the toner being slow, development memory is prone to occur in the printer  10  according to this embodiment. 
     Further, in cases where the degree of circularity of the toner is small, it is likely that the toner will get caught by the developing roller  510 , and therefore, the above-mentioned inappropriateness regarding the toner borne in the first region is somewhat reduced, even if the electrical-charge buildup of the toner is slow. Thus, the difference between the darkness of the halftone image formed by developing the latent image in opposition to the first region and the darkness of the halftone image formed by developing the latent image in opposition to the second region is further reduced, and thereby the occurrence of development memory is somewhat curbed. However, since the degree of circularity of the toner according to this embodiment is high, it is not possible to expect such an effect. Therefore, the occurrence of development memory is more significant in this embodiment. 
     Effect of Curbing Development Memory by Edge Regulation 
     As described above, the toner according to this embodiment has characteristics that significantly cause development memory. Therefore, the printer  10  according to this embodiment adopts edge regulation in order to curb the occurrence of development memory. 
     This section describes the reason why the occurrence of development memory is appropriately curbed in the printer  10  according to this embodiment—that is, the reason why the occurrence of development memory is appropriately curbed by adopting edge regulation as the regulation style of the regulation blade  560 . 
     As described above, the toner is frictionally charged by the toner supplying roller  550  and the developing roller  510 , and the electrically-charged toner adheres to the developing roller  510  and is borne on the developing roller  510 . Then, with the rotation of the developing roller  510 , the toner borne on the developing roller  510  reaches the regulation blade  560 , and the regulation blade  560  regulates the amount of the toner and also frictionally charges the toner even further. 
     It should be noted here that in this embodiment, edge regulation is employed as the regulation style of the regulation blade  560 . More specifically, as shown in  FIG. 9 , the tip edge  560   b , in the lateral direction and the thickness direction, of the regulation blade  560  is located within the abutment nip  560   a  having the above-mentioned predetermined width (i.e., the tip edge  560   b  abuts against the developing roller  510 ). Therefore, at the time the toner borne on the projecting sections  512  reaches the regulation blade  560  with the rotation of the developing roller  510 , the toner on the projecting sections  512  is struck by the tip edge  560   b  and is flicked off, and therefore cannot reach the developing position in opposition to the photoconductor  20 . 
     Now, attention is focused on the toner borne on the depressed sections  515 . The volume average particle diameter of the toner (approximately 4.6 μm) is smaller than the depth d (approximately 8 μm) of the depressed section  515  (the non-projecting section  513 ). Therefore, the toner borne on the depressed sections  515  is appropriately prevented from being struck by the tip edge  560   b , and can thus reach the developing position in opposition to the photoconductor  20 . 
     As a result, at the developing position in opposition to the photoconductor  20 , the toner borne on the projecting section  512  and the depressed section  515  is in such a state that, as shown in  FIG. 15 , the projecting-section covering rate at which the toner in contact with the projecting section  512  (indicated by the symbol AT in  FIG. 15 ) covers the projecting section  512  is smaller than the depressed-section covering rate at which the toner in contact with the depressed section  515  (indicated by the symbol BT in  FIG. 15 ) covers the depressed section  515 . The developing roller  510  develops the latent image in a state where the projecting-section covering rate is smaller than the depressed-section covering rate. 
     Note that  FIG. 15  is a diagram showing a state, at the developing position, of the toner borne on the projecting section  512  and the depressed section  515 .  FIG. 15  shows the toner being borne not only on the depressed section  515  but also on the projecting section  512 . The reason to this is as follows. That is, after passing the regulation blade  560 , the toner borne on the depressed section  515  reaches the developing position with the rotation of the developing roller  510 . In the course of passing the regulation blade  560  and reaching the developing position, there are instances where a portion of the toner (albeit an extremely small amount) borne on the depressed section  515  moves onto the projecting section  512 . 
     In cases where the developing roller  510  develops the latent image in a state where the projecting-section covering rate is smaller than the depressed-section covering rate, the occurrence of development memory is curbed according to the reason described below. 
     That is, during the process of charging and supplying the toner by the toner supplying roller  550  for the n+1 st  revolution, the toner contained in the toner containing member  530  is supplied anew to the first region which appears at the end of the development process for the n h revolution of the developing roller  510  and on which no toner is borne. Further, the sections hereinabove described the fact that, in cases where the toner has a slow electrical-charge buildup characteristic, the toner supplied anew to the first region of the developing roller  510  is not appropriately borne on the first region at the time frictional charging by the toner supplying roller  550  and the developing roller  510  is carried out. 
     It should be noted here that there are projecting sections  512  and depressed sections  515  within the first region, and the extent of inappropriateness regarding the toner borne in the first region differs depending on whether the toner is borne on the projecting section  512  or the depressed section  515  of the first region. More specifically, the non-projecting section  513  having the depressed section  51 S has a wide-mouthed structure that allows the toner to be easily received therein, and therefore, the toner can easily enter into the non-projecting section  513 . Further, in cases where the toner enters into the non-projecting section  513 , it is packed within the non-projecting section  513 , and the cohesion force generated at this time brings about an effect of causing the toner to be borne on the depressed section  515 . Thus, as for the depressed section  515 , the above-mentioned inappropriateness regarding the toner borne in the first region is reduced, even if the electrical-charge buildup of the toner is slow. On the contrary, such an effect is not obtained for the projecting section  512 . Therefore, the extent of inappropriateness is smaller for the depressed section  515  than the projecting section  512 . 
     Therefore, at the time of the development process for the n+1 st  revolution, the difference between the darkness of the halftone image formed by developing the latent image in opposition to the depressed sections  515  of the first region and the darkness of the halftone image formed by developing the latent image in opposition to the depressed sections  515  of the second region becomes smaller than the difference between the darkness of the halftone image formed by developing the latent image in opposition to the projecting sections  512  of the first region and the darkness of the halftone image formed by developing the latent image in opposition to the projecting sections  512  of the second region. In other words, of the toner on the projecting sections  512  and the depressed sections  515 , it is more preferable, to the extent possible, to develop the latent image using the toner borne on the depressed sections  515  in order to curb the occurrence of development memory. 
     It can be said from the above that, in cases where the developing roller  510  develops the latent image in a state where the projecting-section covering rate is smaller than the depressed-section covering rate, the difference between the darkness of the halftone image formed by developing the latent image in opposition to the first region and the darkness of the halftone image formed by developing the latent image in opposition to the second region is reduced, compared to a case in which the latent image is developed in a state where the projecting-section covering rate is equal to the depressed-section covering rate, for example. Therefore, the occurrence of development memory can be curbed. 
     Effectiveness of Developing Device According to Present Embodiment 
     The developing device according to this embodiment includes: a rotatable developing roller  510  that has regularly-arranged projecting sections  512  and non-projecting sections  513 , that bears toner whose volume average particle diameter is smaller than a depth of the non-projecting section  513  relative to the projecting section  512 , and that develops a latent image borne on a photoconductor  20  with the toner borne on the developing roller  510 ; and a regulation blade  560  that is for regulating an amount of the toner borne on the developing roller  510  and that abuts, with a predetermined width, against a circumferential surface of the developing roller  510  in a circumferential direction thereof in such a manner that a longitudinal direction of the regulation blade  560  is along a direction of a rotation axis of the developing roller  510 , a tip edge  560   b  of the regulation blade  560  in a lateral direction and a thickness direction thereof being located within an abutment nip  560   a  having the predetermined width, the predetermined width being larger than a maximum width, in the circumferential direction, of the non-projecting section  513 . With this structure, functionality impairment of the regulation blade  560  is appropriately curbed. 
     The above fact is described by comparing the developing device according to this embodiment (present example) with a developing device according to a comparative example (heretofore example), with reference to  FIGS. 16A and 16B .  FIGS. 16A and 16B  are explanatory diagrams for describing the effectiveness of the developing device according to this embodiment, and are enlarged schematic diagrams (conceptual diagrams) showing a state around the periphery of the tip edge  560   b  of the regulation blade  560  abutting against the developing roller  510 .  FIG. 16A  is a diagram regarding the comparative example, and  FIG. 16B  is a diagram regarding the present example. The left diagram of  FIG. 16B  is the same diagram as  FIG. 9 , and the right diagram of  FIG. 16B  is a diagram in which the developing device according to the present example has transitioned from a state shown in the left diagram of  FIG. 16B  (or  FIG. 9 ) (a state in which the tip edge  560   b  is located at a position in opposition to the projecting section  512 ) to a state in which the tip edge  560   b  is located at a position in opposition to the non-projecting section  513  as a result of rotation of the developing roller  510 . On the other hand, the left and right diagrams of  FIG. 16A  are diagrams that respectively correspond to the left and right diagrams of  FIG. 16B . More specifically, the right diagram of  FIG. 16A  is a diagram in which the developing device according to the comparative example has transitioned from a state shown in the left diagram of  FIG. 16A  (a state in which the tip edge  560   b  is located at a position in opposition to the projecting section  512 ) to a state in which the tip edge  560   b  is located at a position in opposition to the non-projecting section  513  as a result of rotation of the developing roller  510 . Note that the developing device according to the comparative example is similar to the present example in terms that it includes: a rotatable developing roller  510  that has regularly-arranged projecting sections  512  and non-projecting sections  513  and that bears toner whose volume average particle diameter is smaller than a depth of the non-projecting section  513  relative to the projecting section  512 ; and a regulation blade  560  that abuts, with a predetermined width, against a circumferential surface of the developing roller  510  in a circumferential direction thereof and whose tip edge  560   b  is located within an abutment nip  560   a  having the predetermined width. The comparative example, however, is different from the present example in terms that the predetermined width (regulation nip width) is smaller than the maximum width, in the circumferential direction, of the non-projecting section  513 . 
     As described above, edge regulation is effective in situations where development memory is prone to occur. However, as shown in the right diagram of  FIG. 16A  (the comparative example), in cases where edge regulation is adopted, there is a possibility that, when the tip edge  560   b  is located at a position in opposition to the non-projecting section  513  at the time the regulation blade  560  regulates the amount of toner borne on the developing roller  510 , the tip edge  560   b  may enter into the non-projecting section  513 . This may cause the tip edge  560   b  to collide against the non-projecting section  513  (in particular, near the boundary of the side section  514  with respect to the projecting section  512 ), and thereby curl up or chip away. Such a problem is a cause of impairing the functionality of the regulation blade  560 . (If this functionality is impaired, image-quality deterioration, such as appearance of image streaks, will occur in the finally-obtained image.) 
     On the contrary, according to the present example, such a problem is appropriately kept from occurring, because the regulation nip width is larger than the maximum width, in the circumferential direction, of the non-projecting section  513 , as shown in  FIGS. 9 ,  10 , and  16 B. More specifically, in cases where the regulation nip width is larger than the width, in the circumferential direction, of the non-projecting section  513 , at least one of the projecting sections  512  is always included within the abutment nip  560   a  having the regulation nip width, regardless of the relative positional relationship between the developing roller  510  (the projecting sections  512  and the non-projecting sections  513  thereof) and the regulation blade  560 . In other words, a state in which at least one of the projecting sections  512  is in contact with the regulation blade  560  is always ensured. Furthermore, in cases where the regulation nip width is larger than the maximum width, in the circumferential direction, of the non-projecting section  513 —more specifically, in cases where the regulation nip width is larger than the width, in the circumferential direction, of the non-projecting section  513  over a range extending from one end to the other end, in the longitudinal direction, of the regulation blade  560 —a state in which at least some of the projecting sections  512  are in contact with the regulation blade  560  is always ensured over the range extending from one end to the other end, in the longitudinal direction, of the regulation blade  560 . Thus, even in cases where the above-mentioned relative positional relationship enters a positional relationship in which the tip edge  560   b  is in opposition to the non-projecting sections  513  (refer to the right diagram of  FIG. 16B ) at the time the regulation blade  560  regulates the amount of toner borne on the developing roller  510 , the tip edge  560   b  is appropriately kept from entering into the non-projecting section  513 , because at least one projecting section  512  in contact with the regulation blade  560  (for example, the section indicated by the symbol M 4  in the right diagram of  FIG. 16B ) receives (supports) the regulation blade  560 . In this way, the tip edge  560   b  is prevented from colliding against the non-projecting section  513  and curling up or chipping away, and thus, functionality impairment of the regulation blade  560  is appropriately curbed. 
     Further, in order to keep the tip edge  560   b  from entering into the non-projecting section  513  and curb functionality impairment of the regulation blade  560 , it is desirable that the entire projecting section  512  (i.e., the area extending from one end to the other end, in the circumferential direction, of the projecting section  512 ) is always included within the abutment nip  560   a  having the regulation nip width (and not just a portion of the projecting section  512 ), regardless of the above-mentioned relative positional relationship. The present example is configured in this way, as shown in  FIGS. 9 ,  10 , and  16 B. More specifically, the condition to be met in order for the entire projecting section  512  to always be included within the abutment nip  560   a  regardless of the above-mentioned relative positional relationship is as follows: the regulation nip width is larger than the above-mentioned first sum, that is, the sum of the width, in the circumferential direction, of the non-projecting section  513  and a value twice the width, in the circumferential direction, of the projecting section  512 . (On the contrary, if this condition is not met, there may be instances in which the entire projecting section  512  is not included within the abutment nip  560   a  depending on the above-mentioned relative positional relationship.) As described above, in the present example, this condition is met over the range extending from one end to the other end, in the longitudinal direction, of the regulation blade  560 , and therefore, a state in which the entire projecting section  512  is in contact with the regulation blade  560  is always ensured over the range extending from one end to the other end, in the longitudinal direction, of the regulation blade  560 . Thus, even in cases where the above-mentioned relative positional relationship enters a positional relationship in which the tip edge  560   b  is in opposition to the non-projecting sections  513  (refer to the right diagram of  FIG. 16B ) at the time the regulation blade  560  regulates the amount of toner borne on the developing roller  510 , the tip edge  560   b  is more appropriately kept from entering into the non-projecting section  513  compared to a case where, for example, only a portion of the projecting section  512  receives the regulation blade  560 , because the entire projecting section  512  in contact with the regulation blade  560  (for example, the section indicated by the symbol M 5  in the right diagram of  FIG. 16B ) receives (supports) the regulation blade  560 . Thus, functionality impairment of the regulation blade  560  is curbed even more appropriately. 
     Further, in order to keep the tip edge  560   b  from entering into the non-projecting section  513  and curb functionality impairment of the regulation blade  560 , it is desirable that a plurality of projecting sections  512  (in the circumferential direction) are always included within the abutment nip  560   a  having the regulation nip width, regardless of the above-mentioned relative positional relationship. The present example is configured in this way, as shown in  FIGS. 9 ,  10 , and  16 B. More specifically, the condition to be met in order for a plurality of projecting sections  512  to always be included within the abutment nip  560   a  regardless of the above-mentioned relative positional relationship is as follows: the regulation nip width is larger than the above-mentioned second sum, that is, the sum of a value twice the width, in the circumferential direction, of the non-projecting section  513  and the width, in the circumferential direction, of the projecting section  512 . (On the contrary, if this condition is not met, there may be instances in which a plurality of projecting sections  512  are not included within the abutment nip  560   a  depending on the above-mentioned relative positional relationship.) As described above, in the present example, this condition is met over the range extending from one end to the other end, in the longitudinal direction, of the regulation blade  560 , and therefore, a state in which a plurality of projecting sections  512  are in contact with the regulation blade  560  is always ensured over the range extending from one end to the other end, in the longitudinal direction, of the regulation blade  560 . Thus, even in cases where the above-mentioned relative positional relationship enters a positional relationship in which the tip edge  560   b  is in opposition to the non-projecting sections  513  (refer to the right diagram of  FIG. 16B ) at the time the regulation blade  560  regulates the amount of toner borne on the developing roller  510 , the tip edge  560   b  is more appropriately kept from entering into the non-projecting section  513  compared to a case where, for example, only a single projecting section  512  receives the regulation blade  560 , because a plurality of projecting sections  512  in contact with the regulation blade  560  (for example, the section indicated by the symbol M 4  and the section indicated by the symbol M 6  in the right diagram of  FIG. 16B ) receive (support) the regulation blade  560 . Thus, functionality impairment of the regulation blade  560  is curbed even more appropriately. 
     Method of Manufacturing Developing Device 
     Next, a method of manufacturing a developing device is described with reference to  FIGS. 17A to 19 .  FIGS. 17A to 17E  are schematic diagrams showing the transformation of the developing roller  510  during a process of manufacturing the developing roller  510 .  FIG. 18  is an explanatory diagram for describing a rolling process for the developing roller  510 .  FIG. 19  is a flowchart for describing a method of assembling the yellow developing device  54 . Note that in manufacturing the developing device, the above-mentioned housing  540 , the holder  526 , the developing roller  510 , the toner supplying roller  550 , the regulation blade  560 , etc. are manufactured separately, and then these components are used to assemble the developing device. The present section first describes the method of manufacturing the developing roller  510 , among the methods of manufacturing each of the above-mentioned components, and then describes the method of assembling the developing device. Note that the following description takes the yellow developing device  54  as an example, among the black developing device  51 , the magenta developing device  52 , the cyan developing device  53 , and the yellow developing device  54 . 
     Method of Manufacturing Developing Roller  510   
     This section describes the method of manufacturing the developing roller  510 , with reference to  FIGS. 17A to 18 . 
     First, as shown in  FIG. 17A , a pipe member  600  is provided as the base material of the developing roller  510 . The wall thickness of this pipe member  600  is 0.5 to 3 mm. 
     Next, as shown in  FIG. 17B , flange press-fitting sections  602  are formed on 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. 17C , flanges  604  are respectively press-fitted into the flange press-fitting sections  602 . In order to reliably fasten the flanges  604  to the pipe member  600 , the flanges  604  may be bonded or welded to the pipe member  600  after press-fitting the flanges  604 . 
     Next, as shown in  FIG. 17D , the surface of the pipe member  600  to which the flanges  604  have been press-fitted 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 centerless grinding is 1.0 μm or less. 
     Next, as shown in  FIG. 17E , a rolling process is performed on the pipe member  600  to which the flanges  604  have been press-fitted. In this embodiment, the so-called through-feed rolling process (also referred to as continuous rolling) using two round dies  650 ,  652  is performed. 
     More specifically, as shown in  FIG. 18 , the two round dies  650 ,  652  arranged in such a manner that they sandwich the pipe member  600  serving as a workpiece are rotated in the same direction (see  FIG. 18 ) while being pressed with a predetermined pressure (the direction of this pressure is indicated by the symbol P in  FIG. 18 ) against the pipe member  600 . In the through-feed rolling, as the round dies  650 ,  652  rotate, the pipe member  600  moves in the direction indicated by the symbol H in  FIG. 18  while rotating in the opposite direction (see  FIG. 18 ) from the rotating direction of the round dies  650 ,  652 . The surfaces of the round dies  650 ,  652  have projecting sections  650   a ,  652   a  for forming grooves  680 , and these grooves  680  are formed in the pipe member  600  as a result of the projecting sections  650   a ,  652   a  deforming the pipe member  600 . 
     After termination of the rolling process, the surface of the central section  510   a  is plated. In this embodiment, electroless Ni—P plating is employed as the plating. This, however, is not a limitation, and hard chromium plating or electroplating, for example, may be employed. 
     Method of Assembling Yellow Developing Device  54   
     Next, the method of assembling the yellow developing device  54  is described with reference to  FIG. 19 . 
     First, the above-mentioned housing  540 , the holder  526 , the developing roller  510 , the regulation blade  560 , the blade-supporting member  564 , etc. are prepared (step S 2 ). 
     Next, the regulation blade  560  and the blade-supporting member  564  are fixed to the holder  526  by screwing the regulation blade  560  and the blade-supporting member  564  onto the regulation-blade supporting sections  526   c  of the holder  526  (step S 4 ). Note that the above-mentioned end seals  574  are attached to the regulation blade  560  in advance before 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 fixed (step  56 ). At this time, the developing roller  510  is attached to the holder  526  in such a manner that the regulation blade  560  abuts against the developing roller  510  over a range extending from one end to the other end, in the rotation-axis direction, of the roller  510 . Note that the above-mentioned upper seal  520  is attached to the holder  526  in advance before step S 6 . 
     Finally, the holder  526 , which has the developing roller  510 , the regulation blade  560 , etc. attached thereto, is attached to the housing  540  via the housing seal  546  (step S 8 ), and accordingly, the assembly of the yellow developing device  54  is completed. Note that the above-mentioned toner supplying roller  550  is attached to the housing  540  in advance before step S 8 . 
     Other Embodiments 
     In the foregoing, a developing device etc. of this invention was described according to the above-mentioned embodiment thereof. However, the foregoing embodiment of the invention is for the purpose of elucidating this invention and is not to be interpreted as limiting the invention. The invention can be altered and improved without departing from the gist thereof, and needless to say, the invention includes its equivalents. 
     In the foregoing embodiment, an intermediate transferring type full-color laser beam printer was described as an example of the image forming apparatus, but this invention is also applicable to various 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 facsimiles. 
     Further, the photoconductor is not limited to a so-called photoconductive roller having a structure in which a photoconductive layer is provided on the outer circumferential surface of a cylindrical, electrically-conductive base. The photoconductor may be a so-called photoconductive belt structured by providing a photoconductive layer on a surface of a belt-like electrically-conductive base. 
     Further, the shapes of the projecting sections  512  and the non-projecting sections  513  (the side sections  514  and the depressed sections  515 ) of the developing roller  510  are not limited to the above. 
     Further, in the foregoing embodiment, of the first surface  560   c  of the regulation blade  560  along the lateral direction and the second surface  560   d  of the regulation blade  560  along the thickness direction, the abutment nip  560   a  having the predetermined width was provided on the first surface  560   c ; and the tip edge  560   b  was located at one end, in the lateral direction, of the abutment nip  560   a . This, however, is not a limitation. For example, the abutment nip  560   a  may be provided extending across both the first surface  560   c  and the second surface  560   d , and the tip edge  560   b  may be located in a central section of the abutment nip  560   a  (i.e., between the first surface  560   c  and the second surface  560   d ). 
     The foregoing embodiment, however, is more desirable because it is easier to achieve an abutment nip  560   a  having a large regulation nip width and is thus possible to easily achieve a developing device in which the regulation nip width is larger than the maximum width, in the circumferential direction, of the non-projecting section  513 . 
     Further, as shown in  FIG. 20 , a boundary  584  between the side section  514  and a section  582  of the projecting section  512  located downstream in the rotating direction of the developing roller  510  may be rounded off. In this way, even if the tip edge  560   b  enters into the non-projecting section  513 , the tip edge  560   b  is prevented from colliding against the non-projecting section  513  and curling up or chipping away, and thus, functionality impairment of the regulation blade  560  is appropriately curbed. Note that  FIG. 20  is an enlarged schematic diagram (conceptual diagram) showing a state around the periphery of the tip edge  560   b  of a developing device according to another embodiment. Further, this roundness may, for example, be obtained by grinding the developing roller  510  with a grindstone after termination of the rolling process of the developing roller  510  in such a manner that the grindstone comes into contact with the boundary  584  of the developing roller  510 . 
     Furthermore, in the foregoing embodiment, edge regulation was carried out for the purpose of curbing the occurrence of development memory. This invention, however, is not limited to being applied to edge regulation carried out for the above-mentioned purpose, but is also applicable to edge regulation carried out for other purposes. Therefore, although the toner used in the printer  10  according to the foregoing embodiment was described as having characteristics that significantly cause development memory as described in (1) to (4) above, the toner is not limited thereto, and it does not have to possess such characteristics. 
     Configuration of Image Forming System Etc. 
     Next, an embodiment of an image forming system, which serves as an example of an embodiment of this invention, is described with reference to the drawings. 
       FIG. 21  is an explanatory drawing showing an external structure of an image forming system. The image forming system  700  includes a computer  702 , a display device  704 , a printer  706 , an input device  708 , and a reading device  710 . In this embodiment, the computer  702  is accommodated in a mini-tower type housing, but this is not a limitation. 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 this is not a limitation. The printer described above is used as the printer  706 . In this embodiment, a keyboard  708 A and a mouse  708 B are used as the input device  708 , but this is not a limitation. 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 is not limited thereto, and other devices such as an MO (magneto optical) disk drive device or a DVD (digital versatile disk) may be used. 
       FIG. 22  is a block diagram showing a configuration of the image forming system shown in  FIG. 21 . Further provided are an internal memory  802 , such as a RAM inside the housing accommodating the computer  702 , and an external memory such as a hard disk drive unit  804 . 
     Note that in the above description, an example in which the image forming system is structured by connecting the printer  706  to the computer  702 , the display device  704 , the input device  708 , and the reading device  710  was described, but this is not a limitation. For example, the image forming system may be made of the computer  702  and the printer  706 , and the image forming system does not have to be provided with one of the display device  704 , the input device  708 , and the reading device  710 . 
     Further, for example, the printer  706  may have some of the functions or mechanisms of the computer  702 , the display device  704 , the input device  708 , and the reading device  710 . As an example, the printer  706  may be configured so as to have an image processing section for carrying out image processing, a displaying section for carrying out various types of displays, and a recording media attach/detach section to 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 achieved in this way is superior to heretofore systems.