JP2012027242A - Color image forming device and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device in which production yield is improved while maintaining an image quality required for a color image, by effectively utilizing a development roller having relatively large color spot level caused by projections on the development roller, and to provide a manufacturing method of the same.SOLUTION: The development rollers 23 are ranked based on magnitudes of the coating projections 41 produced on the surfaces of the development rollers 23, a development roller 23 in which at least one of maximum diameter or height H of the coating projections 41 is large is mounted on a development device for forming a yellow image whose visual sensitivity is weakest, and a development roller 23 in which at least one of maximum diameter or height H of the coating projections 41 is small is mounted on each of development devices for forming cyan and Magenta images whose visual sensitivities are relatively strong and a development device for forming a black image whose visual sensitivity is strongest.

Description

  The present invention relates to a color image forming apparatus in which a plurality of developing devices are mounted for each color and a manufacturing method thereof.

  In recent years, in an image forming apparatus using an electrophotographic method, a toner having a small particle diameter tends to be used for high image quality and high definition. This small-diameter toner has a problem that since the surface area is large and the surface charge tends to be large, a so-called charge-up phenomenon occurs and the toner is easily fixed to the developing roller (developer carrier).

  If the toner adheres to the developing roller, the toner supplied to the electrostatic latent image formed on the photosensitive member may be insufficient and the image density may be reduced (density following failure). Further, when a new toner thin layer is formed on the developing roller, the toner layer thickness is thinner in the developing area in the immediately preceding development than in the non-consuming area where the small diameter toner remains. When a full-color image or a halftone image is developed in this state, the amount of toner that moves from the immediately preceding development area to the photoconductor side is small, and thus the immediately preceding developed image emerges as an afterimage (history development).

  Therefore, in order to prevent the toner from being overcharged during the development process and to suppress the adhesion of the toner to the developing roller, for example, in Patent Document 1, a resin coating layer (coat layer) such as a urethane resin is provided on the outer peripheral surface of the developing roller. There has been proposed a method for forming the.

  In addition, when an image forming technique based on electrophotography is applied to full-color image formation, a plurality of sets of photosensitive drums and developing devices (for example, 4 when cyan, magenta, yellow, and black are used for full-color image formation) Set) to form a primary color image. Here, since the toner of each color used in the color image forming apparatus has different adhesion to the developing roller for each toner color, Patent Documents 2 and 3 describe the surface roughness of the developing roller depending on the color of the toner used. A method is disclosed in which the amount of toner of each color adhered to the developing roller is made uniform by changing.

Japanese Patent Laid-Open No. 11-249414 JP-A-11-102112 JP 2004-29603 A

  When the coating layer is formed on the outer peripheral surface of the developing roller as in Patent Document 1, spray coating or dipping coating is mainly used. However, the protrusion on the surface of the sleeve base tube that forms the coating layer or the coating layer is used. Occurrence of protrusions (hereinafter referred to as film protrusions) due to contamination of foreign matters such as dust and resin particle aggregates in the coating liquid forming the film is inevitable.

  When the size and height of the film projections exceed a certain level, the toner is developed in a non-image area (white background) on the photoreceptor, and a color point is generated on the image. For this reason, the generation of color points caused by film projections on the surface of the developing roller is also strictly defined, and after the developing roller is manufactured, sufficient inspection is performed and only those satisfying the standards are mounted on the developing device.

  However, in the color image forming apparatus, when the standard for the generation of color points caused by film projections on the surface of the developing roller is the same as that for monochrome, the number of color points generated is four times that for monochrome because the number of developing rollers used is four. End up. For this reason, in order to obtain an image level similar to that of monochrome, it is necessary to use a developing roller with a stricter standard, which causes a problem that the yield of the developing roller is greatly reduced and the apparatus cost is increased.

  On the other hand, the techniques disclosed in Patent Documents 2 and 3 make uniform the amount of toner of each color by adjusting the surface roughness of the entire developing roller, and the coating protrusions irregularly occur on the surface of the developing roller. It was not a technique for dealing with adverse effects.

  Here, the problem caused by the coating protrusion of the developing roller having a coating layer formed on the surface has been described. However, the sleeve base tube is also applicable to the developing roller in which the surface of the aluminum sleeve base tube is anodized. A similar problem occurred due to the irregular protrusions.

  In the present invention, in view of the above problems, in a plurality of developing rollers used in a color image forming apparatus, by determining the specifications of the developing roller for each color, the color point level generated by the protrusion on the surface of the developing roller is relatively low. An object is to effectively utilize a large developing roller to improve the yield of the developing roller to reduce the apparatus cost in color image formation and to maintain the image quality required for the color image.

  In order to achieve the above object, the present invention provides an electrostatic image sensor corresponding to one or more image carriers and cyan, magenta, yellow and black which are four primary colors for image formation formed on the image carrier. A color image forming apparatus including four developing devices for developing a latent image into a toner image of each color, wherein each of the developing devices includes a developing roller for carrying cyan, magenta, yellow, and black toners, respectively. In the developing roller carrying yellow toner, at least one of the maximum diameter or height of the protrusions generated on the outer peripheral surface of the developing roller is higher than that of the developing roller carrying cyan, magenta and black toner. It is characterized by being large.

  According to the present invention, in the color image forming apparatus having the above-described configuration, the developing roller carrying yellow toner has projections generated on the outer peripheral surface of the developing roller having a maximum diameter and height of cyan, magenta, and black. It is larger than the developing roller carrying toner.

  According to the present invention, in the color image forming apparatus configured as described above, the developing roller has a coating layer made of a resin material on an outer peripheral surface, and the protrusion is a film protrusion generated in the coating layer forming step. It is characterized by being a thing.

  According to the present invention, in the color image forming apparatus having the above-described configuration, the maximum diameter of the protrusion of the developing roller carrying yellow toner is 0.5 mm or more and less than 0.75 mm and carrying cyan, magenta and black toners. The maximum diameter of the protrusion of the developing roller is less than 0.5 mm.

  According to the present invention, in the color image forming apparatus configured as described above, the height of the protrusion of the developing roller carrying yellow toner is 40 μm or more and less than 50 μm, and the developing roller carrying cyan, magenta and black toners. The height of the protrusion is less than 40 μm.

  The present invention also provides an electrostatic latent image corresponding to four primary colors cyan, magenta, yellow, and black for image formation formed on the image carrier and toner of each color. In a method of manufacturing a color image forming apparatus including four developing devices for developing an image, a developing roller for carrying cyan, magenta, yellow, and black toners used in each of the developing devices. A first rank in which at least one of the maximum diameter or height of the protrusions generated on the outer peripheral surface is a predetermined level or less, and a second rank in which at least one of the maximum diameter or height of the protrusions is greater than the first rank; In order to form cyan, magenta and black images, the second-rank developing roller is selected and used as the developing roller carrying yellow toner. It is characterized in that to produce a color image forming apparatus wherein the first rank developing roller selection adopted by serving as a developing roller.

  According to the present invention, in the method for manufacturing a color image forming apparatus having the above-described configuration, the developing roller ranked in the first rank has a maximum diameter and height of the protrusions that are equal to or lower than a predetermined level. The developing roller ranked in the rank is characterized in that the maximum diameter and height of the protrusions are larger than the first rank.

  According to the present invention, in the method for manufacturing a color image forming apparatus having the above-described configuration, the maximum diameter of the protrusion of the developing roller ranked in the first rank is less than 0.5 mm, and is ranked in the second rank. The maximum diameter of the protrusion of the developing roller is 0.5 mm or more and less than 0.75 mm.

  According to the present invention, in the manufacturing method of the color image forming apparatus having the above-described configuration, the height of the protrusion of the developing roller ranked to the first rank is less than 40 μm, and the development ranked to the second rank. The height of the protrusion of the roller is 40 μm or more and less than 50 μm.

  According to the first configuration of the present invention, all of the plurality of developing rollers used in the color image forming apparatus do not employ the developing roller having a small maximum diameter and height of the protrusion on the roller surface, and carry yellow toner. By adopting a developing roller in which at least one of the maximum diameter or height of the film projections is relatively large, it is possible to improve the yield of the developing roller while maintaining a practically acceptable image quality.

  Further, according to the second configuration of the present invention, in the color image forming apparatus of the first configuration, as the developing roller carrying yellow toner, the maximum diameter and height of the projections are both cyan, magenta, and magenta. By adopting a roller larger than the developing roller carrying black toner, the image quality is further improved without reducing the yield of the developing roller and more effectively preventing the occurrence of color points due to protrusions. Can be made.

  According to the third configuration of the present invention, in the color image forming apparatus having the first or second configuration, the color resulting from the coating protrusion generated in the coating layer forming step on the outer peripheral surface of the developing roller. It is possible to effectively prevent the generation of dots and to suppress the decrease in the yield of the developing roller due to the generation of the coating protrusions.

  According to the fourth configuration of the present invention, in the color image forming apparatus having any one of the first to third configurations, the maximum diameter of the protrusion of the developing roller carrying yellow toner is 0.5 mm or more. The maximum diameter of the protrusions of the developing roller carrying cyan, magenta and black toners of less than 0.75 mm was set to less than 0.5 mm, so that the drum-roller gap was used in an image forming apparatus having a gap of 100 to 150 μm. In this case, it is possible to form a high-quality full-color image in which the color points of the respective colors resulting from the film projections are hardly visible on the image.

  According to the fifth configuration of the present invention, in the color image forming apparatus having any one of the first to fourth configurations, the height of the protrusion of the developing roller carrying the yellow toner is 40 μm or more and less than 50 μm. The height of the protrusions on the developing roller carrying cyan, magenta and black toners is less than 40 μm, so that the film protrusions can be formed when used in an image forming apparatus having a drum-roller gap of 100 to 150 μm. It is possible to form a high-quality full-color image in which the resulting color point of each color is hardly visible on the image.

  Further, according to the sixth configuration of the present invention, even if a second-rank developing roller having a relatively large maximum diameter or height of the film projection is used as the developing roller carrying yellow toner, It is possible to manufacture a color image forming apparatus in which the color point is not conspicuous and has no practical problem, and the yield of the photosensitive drum can be improved and the cost of the apparatus can be reduced.

  Further, according to the seventh configuration of the present invention, in the method of manufacturing the color image forming apparatus of the sixth configuration, as the first rank developing roller, both the maximum diameter and the height of the protrusions are below a predetermined level. No. 2 was ranked as the developing roller of the second rank, and both the maximum diameter and height of the protrusion were larger than the first rank, so that the protrusion without reducing the yield of the developing roller. It is possible to more effectively prevent the occurrence of color points due to the above, and it is possible to manufacture a color image forming apparatus with higher image quality at a low cost.

  According to the eighth configuration of the present invention, in the method for manufacturing a color image forming apparatus having the sixth or seventh configuration, the maximum diameter of the protrusions of the developing roller ranked in the first rank is set to 0. By setting the maximum diameter of the protrusions of the developing roller ranked in the second rank to be less than 5 mm and less than 0.5 mm to less than 0.75 mm, the drum-roller gap was used in an image forming apparatus having a diameter of 100 to 150 μm. In this case, it is possible to manufacture a high-quality color image forming apparatus in which the color points of the respective colors resulting from the protrusions are hardly visible on the image.

  According to the ninth configuration of the present invention, in the method for manufacturing a color image forming apparatus having any one of the sixth to eighth configurations, the height of the protrusion of the developing roller ranked in the first rank. Is less than 40 μm, and the height of the protrusions of the developing roller ranked in the second rank is 40 μm or more and less than 50 μm, so that the protrusion is used when used in an image forming apparatus having a drum-roller gap of 100 to 150 μm. It is possible to manufacture a high-quality color image forming apparatus in which the color point of each color caused by an object is hardly visible on the image.

Schematic configuration diagram showing a color image forming apparatus of the present invention Side surface sectional view of the developing device mounted in the color image forming apparatus of the present invention Enlarged photo of film protrusions on the developing roller surface Cross-sectional view of the surface of the developing roller including film protrusions The figure which shows an example of the gauge used for the measurement of the maximum diameter of a film projection

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus equipped with the developing device of the present invention. Here, a tandem color image forming apparatus is shown. In the main body of the color printer 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  The image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors, and are further driven by a driving unit (not shown). The intermediate transfer belt 8 that rotates clockwise is provided adjacent to the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially primary-transferred and superimposed on the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1a to 1d, and then the secondary transfer roller. 9 is secondarily transferred onto a transfer paper P as an example of a recording medium, and further fixed on the transfer paper P in the fixing unit 13 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and drives a secondary transfer roller 9 and an intermediate transfer belt 8 described later via a paper feed roller 12a and a registration roller pair 12b. It is conveyed to the nip portion with the roller 11. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt having no seam is mainly used. A blade-like belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed downstream of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure device 5 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning parts 7a, 7b, 7c and 7d are provided.

  When image data is input from a host device such as a personal computer connected to the color printer 100, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then the light is irradiated by the exposure device 5. Beams are irradiated on the surfaces of the photosensitive drums 1a to 1d according to image data, and electrostatic latent images corresponding to the image data are formed on the photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of a two-component developer containing toner of each color of cyan, magenta, yellow, and black. In addition, when the ratio of the toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described later, each developing device 3a to 3d is transferred from the toner container 4a to 4d. Toner is replenished. The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically adheres to the electrostatic latent image formed by the exposure from the exposure device 5. A toner image is formed.

  The primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and cyan, magenta, yellow, and yellow on the photosensitive drums 1a to 1d. A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, in preparation for the subsequent formation of a new electrostatic latent image, the toner remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer is removed by the cleaning units 7a to 7d.

  The intermediate transfer belt 8 is stretched between an upstream conveying roller 10 and a downstream driving roller 11, and the intermediate transfer belt 8 is rotated as the driving roller 11 is rotated by a driving motor (not shown). , The transfer paper P is transferred from the registration roller 12b to the nip portion (secondary transfer nip portion) between the driving roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. The full color toner image (hereinafter abbreviated as toner image) on the intermediate transfer belt 8 is transferred onto the transfer paper P. The transfer paper P onto which the toner image has been transferred is conveyed to the fixing unit 13.

  The transfer paper P conveyed to the fixing unit 13 is heated and pressed by the fixing roller pair 13 a to fix the toner image on the surface of the transfer paper P. The transfer paper P on which the toner image is formed is distributed in the transport direction by a branching section 14 that branches in a plurality of directions. When an image is formed only on one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when forming images on both sides of the transfer paper P, the transfer paper P that has passed through the fixing unit 13 is once transported in the direction of the discharge roller 15, and the discharge roller after the rear end of the transfer paper P has passed through the branching unit 14. 15 is rotated in the reverse direction and the conveyance direction of the branching portion 14 is switched, so that the paper is distributed from the rear end of the transfer paper P to the paper conveyance path 18 and re-conveyed to the secondary transfer nip portion with the image surface reversed. . Then, after the next image formed on the intermediate transfer belt 8 is transferred by the secondary transfer roller 9 to the surface of the transfer paper P where the image is not formed and conveyed to the fixing unit 13 and the toner image is fixed. , And discharged to the discharge tray 17.

  FIG. 2 is a side sectional view showing the structure of the developing device of the present invention. Here, the developing device 3a disposed in the image forming unit Pa of FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter simply referred to as a developer) is accommodated, and the developing container 20 is divided into a first wall and a second wall by a partition wall 20a. The first and second stirring chambers 20b and 20c are divided into stirring chambers 20b and 20c, and the toner (positively charged toner) supplied from the toner container 4a (see FIG. 1) is mixed with the carrier and stirred to be charged. A first agitation screw 21a and a second agitation screw 21b are provided for rotation.

  The developer is conveyed in the axial direction while being stirred by the first stirring screw 21a and the second stirring screw 21b, and passes through the developer formed at both ends in the longitudinal direction of the partition wall 20a (the front and back direction in FIG. 2). It circulates between the 1st and 2nd stirring chambers 20b and 20c via a path (not shown). In the illustrated example, the developing container 3 a extends obliquely upward to the left, a magnetic roller 22 is disposed above the second stirring screw 21 b in the developing container 20, and the developing is performed obliquely upward to the left of the magnetic roller 22. Rollers 23 are arranged opposite to each other. The developing roller 23 faces the photosensitive drum 1a on the opening side (left side in FIG. 2) of the developing container 20, and the magnetic roller 22 and the developing roller 23 rotate clockwise in FIG.

  Note that a toner sensor (not shown) is disposed in the developing container 20 so as to face the first stirring screw 21a, and the toner replenishing port 35 is opened from the toner container 4a according to the toner concentration detected by the toner sensor. Thus, the toner is supplied into the developing container 20.

  The magnetic roller 22 includes a non-magnetic rotating sleeve 22a and a fixed magnet roller 22b having a plurality of magnetic poles enclosed in the rotating sleeve 22a. In the example shown in FIG. 2, the fixed magnet roller 22b has five magnetic poles composed of three N poles (N1 pole to N3 pole) and two S poles (S1 pole and S2 pole). In the rotation direction, the S1 pole is disposed between the N1 pole and the N2 pole, and the S2 pole is disposed between the N3 pole and the N1 pole.

  The developing roller 23 is formed of a non-magnetic rotating sleeve, and is opposed to the rotating sleeve 22a of the magnetic roller 22 at a facing position (facing position) with a predetermined gap G1 between the rollers. That is, the developing roller 23 faces the N1 pole with a predetermined gap interposed therebetween. The inter-roller gap G1 is maintained at 0.3 to 1.5 mm.

  In addition, a spike cutting blade 25 is attached to the developing container 20 along the longitudinal direction of the rotary sleeve 22a (the front and back direction in FIG. 2), and the spike cutting blade 25 is rotated in the rotational direction of the rotary sleeve 22a (in FIG. 2). In the clockwise direction), the developing roller 23 and the magnetic roller 22 are positioned upstream of the facing position. A slight gap (roller-blade gap) G2 is formed on the surface of the tip of the ear cutting blade 25 and the rotary sleeve 22a. The roller-blade gap G2 is set to about 0.3 to 1.5 mm, similar to the above-mentioned roller gap G1.

  A predetermined DC voltage and an AC voltage are applied to the magnetic roller 22 and the developing roller 23, respectively. As described above, the first stirring screw 21a and the second stirring screw 21b circulate in the developing container 20 while the developer is being stirred to charge the toner, and the second stirring screw 21b causes the developer to move to the magnetic roller 22. Be transported. Then, a magnetic brush (not shown) is formed on the magnetic roller 22, and the layer thickness of the magnetic brush on the magnetic roller 22 is regulated by the ear-cutting blade 25, and the potential difference between the magnetic roller 22 and the developing roller 23 and A thin toner layer is formed on the developing roller 23 by a magnetic field between the N1 pole and the developing roller 23. Then, the electrostatic latent image on the photosensitive drum 1 a is developed by the toner thin layer on the developing roller 23. A slight gap (roller-drum gap) G3 is formed between the surface of the developing roller 23 and the surface of the photosensitive drum 1a. The roller-drum gap G3 is set to about 100 to 150 μm.

  A method for regulating the amount of toner on the magnetic roller 22 will be described in detail with reference to FIG. As shown in FIG. 2, since the S2 pole (the magnetic pole for spike cutting) is opposed to the spike cutting blade 25, the tip and the rotation of the spike cutting blade 25 are rotated by using a non-magnetic material or a magnetic material as the spike cutting blade 25. A magnetic field is generated in a direction attracting the gap with the sleeve 22a.

  This magnetic field forms a so-called magnetic brush in which the toner and the carrier stand up like a brush between the spike cutting blade 25 and the rotating sleeve 22a. When the rotating sleeve 22a rotates clockwise and the magnetic brush moves to a position facing the developing roller 23, a magnetic field attracting between the N1 pole and the developing roller 23 is applied. A thin toner layer is formed in contact with the surface.

  When the rotating sleeve 22a further rotates clockwise, the magnetic brush is now separated from the surface of the developing roller 23 by the horizontal (roller circumferential direction) magnetic field generated between the N1 pole and the S1 pole, thereby forming a toner image. The toner that has not been used in the process is collected from the surface of the developing roller 23 onto the rotating sleeve 22a. When the rotating sleeve 22a further rotates, a magnetic field repelled by the N2 pole and the N3 pole is applied, so that the toner and the carrier are detached from the rotating sleeve 22a in the developing container 20. Then, after being stirred and transported by the second stirring screw 21b, a magnetic brush is again formed on the rotating sleeve 22a by the magnetic field of the S2 pole. That is, not only the roller-blade gap G2 but also the amount of toner attached to the magnetic roller 22 is strictly controlled by the magnetic field generated there.

  Next, the developing roller 23 will be described in detail. The developing roller 23 is formed by forming a coat layer made of silicon-modified polyurethane on the outer peripheral surface of an aluminum or aluminum alloy sleeve body. The coat layer suppresses the adhesion of the toner supplied on the developing roller 23 so that the toner can be relatively easily supplied from the developing roller 23 to the surface of the photosensitive drum 1a. Further, since the mechanical stress applied to the developer by the coat layer is less than that on the metal surface, both improvement in toner recoverability from the developing roller 23 and prevention of developer deterioration when the developer transport amount is increased are achieved. Can be achieved.

  Examples of the material of the coating layer include urethane-modified resin, acrylic resin, melamine resin, silicone resin, fluorine resin, etc. in addition to silicone-modified polyurethane. Good urethane resin and acrylic resin are preferable. Among these, the use of a silicon-modified polyurethane resin in which a part of carbon of the urethane resin is replaced with silicon is preferable because the hygroscopic property of the urethane resin is improved and the change in charging characteristics of the coat layer with respect to environmental changes is suppressed.

In addition, the coating layer contains a conductive material having a dielectric constant of 10 or more as a resistance adjusting agent, thereby adjusting the volume resistance value of the coating layer and suppressing resistance unevenness. Examples of the resistance adjusting agent include carbon black, acetylene black, and fiber-shaped potassium titanate. As a result, it is possible to stabilize the charged state of the toner layer and improve the releasability during toner recovery. The volume resistance value is preferably about 10 ⁴ to 10 ⁸ Ω that can appropriately retain the residual charge on the surface of the developing roller 23.

The surface roughness (arithmetic mean roughness) Ra of the coating layer is the surface roughness normally obtained when the coating agent is applied by spraying, dipping, roll coating, or the like, or the surface roughness of urethane beads or the like is adjusted. It is prepared to 0.4 to 1.5 μm by applying an agent. Further, the surface free energy of the silicon-modified polyurethane is 15 to 25 mJ / cm ² .

  Moreover, before forming the coat layer, the outer peripheral surface of the sleeve body may be anodized to form the anodized layer. According to this configuration, since the alumite layer formed on the surface has a function as a charge barrier layer, it is possible to prevent the occurrence of leakage when a developing bias is applied to the developing roller 23.

  FIG. 3 is an enlarged photograph of the film protrusions generated on the surface of the developing roller 23, and FIG. 4 is a cross-sectional view of the surface of the developing roller 23 including the film protrusions. When the coating layer 40 is formed on the developing roller 23, foreign matter such as dust or resin particle agglomerates are mixed in the coating agent, so that the surface of the coating layer 40 is partially raised or bubbles in the coating agent are generated. The film protrusion 41 is generated by rupturing and rising like a crater. Since the roller-drum gap G3 (see FIG. 2) becomes small at the position where the film projection 41 is generated, if the maximum diameter R or height H of the film projection 41 becomes a certain value or more, the non-image on the photoconductor. The toner is developed in the region (white background), and a color point is generated on the image.

  On the other hand, since the recording medium such as transfer paper is usually white, the visual sensitivity to human image quality is the strongest for black having the highest contrast to white among the four primary colors of cyan, magenta, yellow and black. It is considered that the contrast with white is the weakest for yellow and the middle for cyan and magenta.

  Therefore, in the present invention, the developing roller 23 is ranked according to the size of the coating protrusion 41 generated on the surface of the developing roller 23, and the tolerance of the magnitude of the color point generation level corresponding to the visual sensitivity of each color. The developing rollers 23 of the respective ranks are combined in a range that does not exceed, and are mounted on the developing devices 3a to 3d. Specifically, the developing device 3c that forms the yellow image with the weakest visual sensitivity is equipped with a developing roller 23 having at least one of the maximum diameter R or the height H of the film projection 41, and the visual sensitivity is relatively low. Development devices 3a, 3b, and 3d that form strong cyan, magenta, and black images with the highest visual sensitivity have development in which at least one of the maximum diameter R or height H of the film projection 41 is smaller than that of the development device 3c. A roller 23 is mounted.

  As a result, the range of the developing roller 23 that can be used without expanding the image quality required for the color image can be expanded, and the number of developing rollers 23 that are not employed can be reduced. Therefore, the yield of the developing roller 23 can be improved and the cost of the color printer 100 can be reduced.

  The color printer 100 of the present invention can be manufactured as follows, for example. First, the developing roller 23 in which the coat layer 40 is formed on the surface is manufactured in advance, and the maximum diameter R and the height H of the film projection 41 are measured for each.

  As a measuring method of the maximum diameter R, for example, as shown in FIG. 5, by using a gauge 50 in which a black circle whose diameter changes stepwise is formed on a transparent sheet, by comparing the size of the film projection 41 with the black circle. The maximum diameter R of the film projection 41 is measured visually. As a method for measuring the height H, for example, the developing roller 23 is mounted on a height measuring jig, and the projection on the surface of the roller is photographed with a CCD camera while rotating, and the amount of protrusion from the flat portion is measured.

  Next, each developing roller 23 is attached to a test machine for evaluation, and the size of the color point generated on the image when white solid printing is performed is measured. Here, a developing roller having a diameter of 20 mm is used, the linear speed ratio of the developing roller to the photosensitive member is 1.5, the roller-drum gap G3 is 100 μm, and the peak-to-peak value of the AC bias applied to the developing roller 23 is 1. White solid printing was performed using black toner at a frequency of 5 kV and a frequency of 5 kHz, and the size of black spots generated on the image was visually measured.

  Table 1 shows the relationship between the maximum diameter R and height H of the film projection 41 and the size (mm) of the image color point. Table 2 shows the results of measuring the maximum diameter R and the height H of the film projections 41 for the 107 developing rollers 23 manufactured.

  As shown in Table 1, if the developing roller 23 has a maximum diameter R of the coating projection 41 of less than 0.5 mm and a height H of less than 40 μm, it can be used as any developing roller of the developing devices 3a to 3d. It can be seen that no color point is generated. Further, as shown in Table 2, there are 78 developing roller 23 (dot areas in Table 2) having a maximum diameter R of the coating projection 41 of less than 0.5 mm and a height H of less than 40 μm (about 73% of the whole). )It can be seen that it is. Therefore, conventionally, only about 70% of the manufactured developing roller 23 can be used.

  On the other hand, since the human visual sensitivity is the weakest with respect to yellow as described above, the relationship between the size of the yellow image color point and the visibility was investigated. Specifically, white solid printing was performed using yellow toner under the same conditions as described above, and the size of yellow spots generated on the image was measured. The results shown in Table 3 were obtained.

  As apparent from Table 3, it can be seen that a yellow spot having a diameter of about 0.2 mm is hardly visually confirmed. Therefore, the developing roller 23 having the maximum diameter R of the coating projection 41 of less than 0.5 mm and the height H of less than 40 μm is ranked first (dot region in Table 2), and the maximum diameter R of the coating projection 41 is 0.00. The developing roller 23 having a height of 5 mm or more and less than 0.75 mm and a height H of 40 μm or more and less than 50 μm is selected in the second rank (shaded area in Table 2). Then, the developing roller 23 ranked in the second rank is selectively adopted as the developing roller 23 used in the yellow developing device 3c.

  As shown in Table 2, the number of developing rollers 23 of the second rank is 16 (about 15% of the whole). Therefore, out of 107 manufactured developing rollers 23, 94 combined first rank and second ranked developing rollers 23, that is, about 90% of the manufactured developing rollers 23 can be used. Therefore, the yield at the time of manufacturing the developing roller 23 is significantly improved.

  In the above manufacturing example, the developing roller 23 in which both the maximum diameter R and the height H of the film projection 41 are not more than a predetermined level (here, the maximum diameter R is less than 0.5 mm and the height H is less than 40 μm) is used. The developing roller 23 having one rank and either one of the maximum diameter R and the height H being larger than the first rank is defined as the second rank, but either the maximum diameter R or the height H of the coating projection 41 is The developing roller 23 having a predetermined level or less may be set as the first rank.

  For example, in Table 2, when a developing roller having a maximum diameter R of the film projection 41 of less than 0.25 mm is ranked first and a developing roller having a maximum diameter R of 0.25 mm or more and less than 0.5 mm is ranked second, cyan Further, it is possible to prevent occurrence of a color point that can be visually recognized in each of the colors magenta, yellow, and black. Similarly, in Table 2, when a developing roller having a coating projection 41 having a height H of less than 30 μm is ranked first, and a developing roller having a maximum diameter R of 30 μm or more and less than 40 μm is ranked second, generation of a color point is prevented. can do. In particular, when ranking the developing roller 23 using only the maximum diameter R, the developing roller 23 can be ranked only by visual measurement, so that the manufacturing process can be simplified.

  On the other hand, when the developing roller 23 is ranked using only the maximum diameter R or the height H as described above, about 80% of the manufactured developing roller can be used, and the maximum diameter R and The yield is slightly reduced as compared with the case where the developing roller 23 is ranked using both of the heights H (about 90%). Therefore, a method of ranking the developing roller 23 using both the maximum diameter R and the height H of the film projection 41 is more preferable.

  Here, the developing roller 23 having the film projection 41 having the maximum diameter R of less than 0.5 mm and the height H of less than 40 μm is set as the first rank, the maximum diameter R is 0.5 mm or more and less than 0.75 mm, and the height. The developing roller 23 having the coating protrusion 41 having H of 40 μm or more and less than 50 μm is set as the second rank, but this is suitable for selective use in the developing devices 3a to 3d having a drum-roller gap G3 of 100 to 150 μm. This is an example of ranking. Therefore, the range of the maximum diameter R and the height H of the film projection 41 is not limited to this, and may be set as appropriate according to the drum-roller gap G3.

  In the above manufacturing example, white solid printing was performed using black toner and the size of black spots generated on the image was measured. However, black solid printing was performed and the size of white spots generated on the image was measured. You may do it. In addition, it is possible to use a toner of a color other than black, but when black having the highest contrast with the white transfer paper is used, the number and size of black spots or white spots can be easily measured. More preferred. Further, as a black spot or white spot measuring method, it is possible to adopt a method of automatically measuring using a detection means such as a line sensor in addition to a visual method.

  Further, it is not necessary to measure the size of the image color point every time the developing roller 23 is manufactured, and the relationship between the maximum diameter R and height H of the film projection 41 shown in Table 1 and the size of the image color point will be described next time. It can be used at the time of manufacturing.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, the developing roller 23 is selected and used based on at least one of the maximum diameter R or the height H of the coating projection 41 generated when the coating layer 40 is formed on the outer peripheral surface of the developing roller 23. In addition to the developing roller 23 having a coating layer formed on the outer peripheral surface, for example, the developing roller 23 in which the sleeve base tube is only anodized also has a maximum diameter R or a height of a projection on the surface generated during the anodizing process. By selectively using the developing roller 23 based on at least one of the lengths H, it is possible to obtain the same effect of preventing the deterioration of the image quality due to the generation of the color point while suppressing the decrease in the yield of the developing roller 23.

  In the above embodiment, the tandem color printer 100 as shown in FIG. 1 has been described as an example. However, the present invention is not limited to this. For example, four tandem color printers 100 are provided around one photosensitive drum. A developing device is disposed, a four-color image is sequentially formed on the photosensitive drum, and a single drum type that is superimposed on the intermediate transfer belt, or a rotary type color printer that sequentially switches the developing device facing the photosensitive drum, or The present invention can be applied to various color image forming apparatuses including four developing devices corresponding to four colors of cyan, magenta, yellow, and black, such as tandem, single drum, and rotary color copying machines.

  In the above embodiment, the magnetic roller 22 and the developing roller 23 as shown in FIG. 2 are provided, and only the toner is moved from the magnetic roller 22 to the developing roller 23 to form a thin toner layer on the developing roller 23. However, the configuration of the developing device is not limited to this, and the developing device can be applied to a one-component developing type developing device having only a developing roller.

  INDUSTRIAL APPLICABILITY The present invention can be used in a color image forming apparatus having a developing device corresponding to four colors of cyan, magenta, yellow, and black, and the developing roller used in each developing device can be changed depending on the maximum diameter and height of the protrusion. A developing roller for forming at least one of the largest diameter or height is used as a developing roller for yellow image formation, and a developing roller for forming cyan, magenta, and black images having at least one of the largest diameter or height is small. It is used as

  By using the present invention, it is possible to provide a color image forming apparatus in which the color points on the image are hardly noticeable and have no practical problem without reducing the yield of the developing roller.

Pa to Pd Image forming section 1a to 1d Photosensitive drum (image carrier)
2a to 2d charger 3a to 3d developing device 5 exposure device 6a to 6d primary transfer roller 7a to 7d cleaning unit 8 intermediate transfer belt 9 secondary transfer roller 23 developing roller 40 coat layer 41 film projection 100 color printer (image forming apparatus) )

Claims (9)

One or more image carriers;
Four developing devices that develop electrostatic latent images corresponding to the four primary colors cyan, magenta, yellow and black for image formation formed on the image carrier into toner images of respective colors;
In a color image forming apparatus comprising:
Each of the developing devices has a developing roller that carries cyan, magenta, yellow, and black toners, and the developing roller that carries yellow toner has protrusions generated on the outer peripheral surface of the developing roller. A color image forming apparatus, wherein at least one of a maximum diameter and a height is larger than the developing roller carrying cyan, magenta and black toners.   The developing roller carrying yellow toner is characterized in that the maximum diameter and height of protrusions generated on the outer peripheral surface of the developing roller are larger than the developing roller carrying cyan, magenta and black toner. The color image forming apparatus according to claim 1.   2. The developing roller according to claim 1, wherein a coating layer made of a resin material is formed on an outer peripheral surface of the developing roller, and the protrusion is a film protrusion generated in the coating layer forming step. 2. A color image forming apparatus according to 2.   The maximum diameter of the protrusion on the developing roller carrying yellow toner is 0.5 mm or more and less than 0.75 mm, and the maximum diameter of the protrusion on the developing roller carrying cyan, magenta and black toner is 0.5 mm. The color image forming apparatus according to any one of claims 1 to 3, wherein the color image forming apparatus is less than or equal to.   The height of the protrusion of the developing roller carrying yellow toner is 40 μm or more and less than 50 μm, and the height of the protrusion of the developing roller carrying cyan, magenta or black toner is less than 40 μm. The color image forming apparatus according to claim 1. One or more image carriers;
Four developing devices that develop electrostatic latent images corresponding to the four primary colors cyan, magenta, yellow and black for image formation formed on the image carrier into toner images of respective colors;
In a method for manufacturing a color image forming apparatus comprising:
For the developing roller carrying cyan, magenta, yellow and black toners used in each of the developing devices, the first diameter or height of the protrusions generated on the outer peripheral surface of the developing roller is a first level not exceeding a predetermined level. The second rank developing roller is used as the developing roller that ranks at least one of the rank and the second rank in which at least one of the maximum diameter or height of the protrusions is larger than the first rank. A method of manufacturing a color image forming apparatus, wherein the first rank developing roller is selectively employed as the developing roller for forming cyan, magenta and black images.   The developing roller ranked in the first rank has a maximum diameter and height of the protrusions of a predetermined level or less, and the developing roller ranked in the second rank has a maximum diameter of the protrusions. The method for manufacturing a color image forming apparatus according to claim 6, wherein the height is higher than the first rank.   The maximum diameter of the protrusions of the developing roller ranked in the first rank is less than 0.5 mm, and the maximum diameter of the protrusions of the developing roller ranked in the second rank is 0.5 mm or more and 0.75 mm. 8. The method for manufacturing a color image forming apparatus according to claim 6, wherein the color image forming apparatus is less than the number.   The height of the protrusions of the developing roller ranked in the first rank is less than 40 μm, and the height of the protrusions of the developing roller ranked in the second rank is 40 μm or more and less than 50 μm. A method for manufacturing a color image forming apparatus according to any one of claims 6 to 8.

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