JP2007286229A - Image processing device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing device capable of both prolonging the lifetimes of image processing units and preventing the occurrence of cleaning failures, and to provide an image forming apparatus having the image processing units. <P>SOLUTION: The image processing device includes the plurality of image processing units 110Y, each having an image carrier 111Y for holding a toner image thereon and a cleaning blade 165Y for cleaning off the toner on the image carrier 111Y that is abutted against the image carriers 111Y, 110M and 110K; and an intermediate transfer belt 131, on which toner images formed by the image processing units, are transferred in the order. The contact pressure of the cleaning blade 165K of at least one of the image processing units, which is located farthest downstream, in the order of transfer of a toner image to the intermediate transfer belt 131, is lower than the contact pressure of the cleaning blade 165Y of the image processing unit, located on the upstream side of the intermediate transfer belt 131. This enables both the prevention of the occurrence of cleaning failure, and the prolongation of the lifetimes of the image processing units. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus capable of forming a full-color or black-and-white image using an electrophotographic method, and an image forming apparatus including the same.

  In recent years, full-color image forming apparatuses (for example, fax machines, printers, copiers, etc.) instead of monochrome are becoming widespread, and so-called tandem-structured image forming apparatuses are widely used in order to achieve high image quality and high speed. Yes.

  In general tandem structure, image processing units that form toner images of each color such as yellow (Y), magenta (M), cyan (C), and black (K) are arranged in parallel and contacted with these image processing units. The toner images are sequentially superimposed one by one on the intermediate transfer member arranged in this manner to obtain a color image.

  Each image process unit includes a photosensitive drum as an image carrier, a charger that uniformly charges the surface of the photosensitive drum, an exposure device that performs image exposure on the surface of the photosensitive drum according to image information of each color, and exposure. The developing device is configured to supply toner to the electrostatic latent image formed by the above, and to visualize the toner image, and the cleaning device to remove the transfer residual toner on the photosensitive drum.

  As a cleaning device for an image process unit, a type in which toner is scraped by bringing the edge of a cleaning blade made of urethane rubber or the like as an elastic body into contact with the surface of a rotating photosensitive drum with pressure is the mainstream. The cleaning blade of the elastic body is bonded to the holding sheet metal and fixed by screwing both ends of the holding plate to the cleaning container. Generally, the setting angle of the cleaning blade, the amount of biting, the cleaning blade material and shape, etc. are all the same.

  By the way, the lubricity between the cleaning blade and the photosensitive drum is kept constant as the toner external additive, which is fine particles externally added to the toner, passes between the cleaning blade and the photosensitive drum. However, in actuality, there are cases where the toner scraped off by the cleaning blade is insufficient and the lubricity is deteriorated. For example, if image formation using only yellow (Y), magenta (M), and cyan (C) is repeated, no toner is supplied to the cleaning blade of the black (K) image process unit. As a result, the frictional force increases due to the lack of external toner additives, and the cleaning blade suddenly wears and the behavior of the cleaning blade becomes unstable, causing squealing, toner slipping, edge breakage, turning, etc. The original cleaning action is not performed.

  Therefore, even if the supply of toner to the image processing unit is insufficient and the cleaning blade suddenly wears out, the cleaning blade is brought into contact with the photosensitive drum in order to exert a stable cleaning action. A method of setting the pressure larger than usual is generally employed. Such a phenomenon of insufficient toner external additives is considered to occur in any image processing unit, and the contact pressure of the cleaning blade to the photosensitive drum is set to be higher than usual for all the image processing units. .

  In addition, in the case of small particle size toners that have been widely used in recent years for high image quality, cleaning defects due to slipping occur compared to toners with large particle size regardless of toner shortage due to the difference in usage frequency. In order to prevent this, it is necessary to set the contact pressure of the cleaning blade to the photosensitive drum larger.

  However, in any of the above cases, if the contact pressure of the cleaning blade to the photosensitive drum is increased, the frictional force between the cleaning blade and the photosensitive drum surface is maintained high. Increase in wear becomes severe. Of course, the increase in wear of the cleaning blade edge is even greater. For this reason, there is a problem that image defects are likely to occur, and as a result, the durable life of the photosensitive drum and the cleaning blade is shortened.

  In particular, in a situation where the frequency of use of monochromatic image formation (for example, monochrome mode) is high, the replacement cycle is accelerated only for a specific image process unit, so that the problem of increasing the frequency of maintenance is significant.

In order to extend the life of the photosensitive drum and the cleaning blade, for example, only the cleaning blade of the black (K) image process unit, which is frequently used in the monochrome mode, is coated with nylon. A method of reducing the wear of the cleaning blade of the black (K) image processing unit, which has higher durability and higher use frequency than the cleaning blade of the image processing unit (for example, see Patent Document 1), or only black (K) There has been proposed a method of extending the life of the photosensitive drum by increasing the diameter of the photosensitive drum (for example, see Patent Document 2).
JP-A-6-195010 (FIGS. 1 and 2) Japanese Patent Laid-Open No. 2000-242057 (FIG. 2)

  However, in the apparatus using a highly durable blade disclosed in Patent Document 1, although the wear resistance of the cleaning blade is improved, the photosensitive drum has the same conditions as the units of other colors. The lifespan is not improved.

  Further, the method of increasing the diameter of the photosensitive drum disclosed in Patent Document 2 is not efficient from the viewpoint of sharing the image process unit as a consumable part.

  The present invention has been made to solve the technical problems as described above, reduces the wear of the photosensitive drum, prevents the cleaning blade from being defectively cleaned, and provides a stable image over a long period of time. An image processing apparatus that can be used and an image forming apparatus including the image processing apparatus are provided.

  An image processing apparatus of the present invention is formed by an image carrier that carries a toner image, a plurality of image process units that have a cleaning blade that contacts the image carrier and cleans the toner on the image carrier, and the image process unit. An intermediate transfer member to which toner images are sequentially transferred, and the contact pressure of at least one cleaning blade of an image process unit located downstream in the order of toner image transfer to the intermediate transfer member In this configuration, the pressure is smaller than the contact pressure of the cleaning blade of the image process unit located on the upstream side.

  With this configuration, the behavior of the cleaning blade can be maintained in a stable state, and the wear of the photosensitive drum is suppressed and the life of the image processing unit is effectively extended while preventing damage to the cleaning blade and occurrence of poor cleaning. be able to.

  In the image processing apparatus of the present invention, the image process unit that frequently forms a toner image is disposed downstream of the image process unit that does not frequently form a toner image in the order of transferring the toner image to the intermediate transfer member. It is the composition to do.

  With this configuration, it is possible to effectively suppress the wear of the photosensitive drum in the downstream image process unit, prevent a cleaning failure, and effectively extend the life of the image process unit. As a result, the image process apparatus The overall life can be optimized.

  The image processing apparatus of the present invention has a configuration in which the contact pressure is defined by the amount of biting of the cleaning blade into the image carrier.

  With this configuration, the contact pressure can be defined by adjusting the mounting position while keeping the cleaning blade the same.

  The image processing apparatus of the present invention has a configuration in which the contact pressure is defined by the Young's modulus of the cleaning blade.

  With this configuration, it is possible to define the contact pressure by using a cleaning blade having a different Young's modulus of the elastic body while maintaining the same mounting position.

  The image processing apparatus of the present invention has a configuration in which the contact pressure is defined by the thickness of the cleaning blade. With this configuration, it is possible to define the contact pressure by using cleaning blades having different thicknesses of elastic bodies while keeping the mounting position the same.

  The image processing apparatus of the present invention has a configuration in which the contact pressure is defined by the free length of the cleaning blade.

  With this configuration, the contact pressure can be defined by using cleaning blades having different free lengths while maintaining the same composition of the elastic body.

  The image forming apparatus of the present invention has a configuration using any one of the image processing apparatuses described above.

  With this configuration, an image forming apparatus that effectively extends the life of the image processing unit can be obtained.

  The present invention relates to an image carrier that carries a toner image, a plurality of image process units that are in contact with the image carrier and have a cleaning blade that cleans the toner on the image carrier, and a toner image formed by the image process unit. And an intermediate transfer body that is sequentially transferred, and the contact pressure of at least one cleaning blade of the image process unit positioned downstream in the order of toner image transfer to the intermediate transfer body is positioned upstream. By adopting a configuration that is smaller than the contact pressure of the cleaning blade, it is possible to provide an image processing apparatus that can provide a stable image over a long period of time.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

(Embodiment)
FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus to which the present embodiment is applied, and shows a so-called tandem digital color printer.

  In FIG. 1, an image forming apparatus 100 according to the present embodiment includes image processing units 110Y (yellow), 110M (magenta), 110C (cyan), 110K (black), and image processing units that form toner images of respective colors. Photoconductor drums (111Y, 111M, 111C, 111K), a laser scan unit (LSU) 120 that forms a latent image by irradiating laser light, an intermediate transfer unit 130 that superimposes the toner images of the above colors, and paper 180 are supplied. A paper feed unit 150 for fixing the toner transferred to the paper 180, and a fixing unit 140 for fixing the toner.

  For example, the image process unit 110Y is a drum-like rotating body, and a photosensitive drum 111Y as an image carrier, a charging roller 112Y as a device for uniformly charging the photosensitive drum 111Y, and a developing device 113Y as a toner supply device. And a primary transfer roller 114Y as a toner transfer device to the intermediate transfer member, and a photoconductor cleaner 115Y as a device having a cleaning blade and scraping off the toner remaining on the surface of the photoconductor drum. In response to the supply, a yellow (Y) toner image is formed on the photosensitive drum 111Y.

  The developing device 113Y is filled with a two-component developer composed of toner and carrier, and includes a developing roller 116 and a stirring screw 117. The image processing units 110M, 110C, and 110K for other colors are configured in the same manner as the image processing unit 110Y, and include photoconductor cleaners 115M, 115C, and 115K. Each developing device 113Y, 113M, 113C, 113K is filled with toner of each color (yellow (Y), magenta (M), cyan (C), black (K)).

  The laser scanning unit 120 passes each laser beam (white triangular arrow in the figure) separated into four colors through a polygon mirror, an f-θ lens, a reflection mirror, an imaging lens, etc. (not shown) to each image processing unit 110Y. , 110M, 110C, and 110K photosensitive drums 111Y, 111M, 111C, and 111K.

  The intermediate transfer unit 130 includes an intermediate transfer belt 131 as an intermediate transfer member, a driving roller 132, and a driven roller 133. The intermediate transfer belt 131 is rotatably suspended by a driving roller 132 and a driven roller 133, and is driven by the driving roller 132 to rotate in the direction of the arrow.

  In addition to the fixing roller 141 and the pressure roller 142, the fixing unit 140 includes a heat source (not shown) and the like, and heats the surface of the fixing roller 141 to a predetermined temperature. The fixing roller 141 and the pressure roller 142 are pressed against each other to melt and fix the unfixed toner on the paper 180 conveyed between the rollers by heat and pressure.

  The paper feeding unit 150 is disposed in the lower part of the apparatus main body 101, and the paper 180 is separated and fed one by one from the paper cassette 151 by a pick roller and a separation roller (not shown).

  In FIG. 1, the photosensitive drums 111Y, 111M, 111C, and 111K of the image processing units 110Y, 110M, 110C, and 110K are rotated in a predetermined direction by a driving system (not shown) at a predetermined timing, and charging rollers 112Y, 112M, and 112C are rotated. , 112K, the surface is sequentially charged to a predetermined potential.

  The surfaces of the charged photosensitive drums 111Y, 111M, 111C, and 111K are sequentially exposed to each laser beam emitted from the laser scan unit 120. Thereby, electrostatic latent images of the respective colors are formed on the surfaces of the photosensitive drums 111Y, 111M, 111C, and 111K.

  The electrostatic latent images of the respective colors formed on the surfaces of the photosensitive drums 111Y, 111M, 111C, and 111K are agitated by the agitating screws 117 of the developing devices 113Y, 113M, 113C, and 113K and supplied by the developing roller 116. Thin-layered yellow (Y), magenta (M), cyan (C), and black (K) toners are sequentially developed and visualized as four-color toner images.

  The four color toner images formed on the surfaces of the photosensitive drums 111Y, 111M, 111C, and 111K are respectively transferred to the primary transfer rollers 114Y, 114M, and 114C on the image transfer surface (outer peripheral surface) of the rotating intermediate transfer belt 131, respectively. , 114K are sequentially superimposed and primarily transferred. As a result, a full color image is formed on the image transfer surface of the intermediate transfer belt 131.

  Untransferred toner and toner external additives remain on the photosensitive drums 111Y, 111M, 111C, and 111K after the toner image is transferred. These are scraped off by the photoconductor cleaners 115Y, 115M, 115C, and 115K.

  The sheet 180 fed from the sheet feeding unit 150 is transported to the secondary transfer roller 102 under the control of a registration roller 152 that controls the transport timing. The full color image primarily transferred onto the intermediate transfer belt 131 is secondarily transferred onto the sheet 180 by the secondary transfer roller 102. The full-color image to be secondarily transferred is always transferred from a predetermined position of the paper 180 by the conveyance control of the paper 180 by the registration roller 152.

  The sheet 180 on which the full color image has been secondarily transferred is fixed on the full color image by the fixing unit 140, and then discharged onto a discharge tray provided on the upper portion of the apparatus main body 101 by the discharge roller 103.

  However, when a multicolor image is formed, a phenomenon in which toner is transferred in the reverse direction from the intermediate transfer belt 131 to the photosensitive drum (eg, 111K), so-called retransfer toner, occurs.

  This will be described with reference to FIG. 1 and a layout diagram showing the relationship between the toner image on the intermediate transfer belt 131 shown in FIG. 2 and the photosensitive drum of each color.

  That is, when a multicolor image is formed, when transferring a toner image from a photosensitive drum (eg, 111K) located on the downstream side of the intermediate transfer unit 130, the intermediate transfer belt 131 has an upstream side. Since the transferred toner image (for example, yellow (Y), magenta (M), cyan (C)) is already carried, it is necessary to transfer, for example, a black (K) toner image again. .

  However, at this time, the toner is transferred from the intermediate transfer belt 131 to the photosensitive drum (eg, 111K) in the reverse direction, and a retransfer toner phenomenon occurs.

  Since the retransfer toner amount is proportional to the toner amount carried on the intermediate transfer belt 131, the photosensitive drums 111Y, 111M, 111C, and 111K that are in contact with the same intermediate transfer member are downstream of the intermediate transfer belt 131 in the traveling direction. Therefore, the amount of retransfer toner can be increased as compared with the case where the toner is disposed on the upstream side.

  Therefore, by arranging an image process unit (for example, 111K) that frequently forms a toner image on the most downstream side, the retransfer toner of the image process unit at this position can be increased. Eliminates poor cleaning due to cleaning blade damage due to lack of toner. That is, even if the contact pressure of the cleaning blade 165K of the image process unit at this position is set smaller than the contact pressure of the other cleaning blades 165Y, 165M, 165C, the retransfer toner increases, so that the cleaning blade is damaged. In this case, it is possible to suppress defective cleaning and simultaneously reduce the contact pressure, thereby effectively reducing the wear amount of the photosensitive drum (eg, 111K) and providing a stable image over a long period of time. . Furthermore, maintenance costs can be reduced by reducing the replacement frequency of consumables such as cleaning blades and photosensitive drums.

  FIG. 3 is a schematic side view of a process unit used in the image processing apparatus of the present invention. FIG. 4 shows a photosensitive drum 111Y, a back plate 163Y, and a cleaning blade 165Y of the process unit used in the image processing apparatus of the present invention. It is a principal part perspective view which shows the relationship.

  3 and 4 show the yellow process unit, but the other colors have the same configuration.

  The photoreceptor cleaner 115Y has a cleaning container 162Y, a back plate 163Y fixed to the cleaning container 162Y with a fixing screw 164Y, and a cleaning blade 165Y as a cleaning member held by the back plate 163Y. As shown in FIG. 4, long holes 166Y and 167Y through which the fixing screws 164Y are inserted are formed at both ends of the back plate 163Y, and the fixing position of the back plate 163Y with respect to the cleaning container 162Y is set up and down in FIG. It can be adjusted in the direction. The photosensitive drum 111Y is irradiated with the laser light 190Y from the laser scan unit 120.

  The cleaning blade 165Y is an elastic blade using, for example, urethane as an elastic body, and is held in contact with the photosensitive drum 111Y with pressure. The back plate 163Y is a stainless steel sheet metal member having a thickness of 1 mm.

  The other photoconductor cleaners 115M, 115C, and 115K are basically configured similarly to the photoconductor cleaner 115Y.

  FIG. 5 is a view showing the relationship between the photosensitive drum 111Y and the cleaning blade 165Y.

  In FIG. 5, the amount of biting δ is the amount of displacement of the leading edge of the cleaning blade 165Y by attaching the photosensitive drum 111Y. The thickness t is a thickness in the contact direction of the cleaning blade 165Y with the photosensitive drum 111Y. The free length L is a protruding amount of the cleaning blade 165Y from the back plate 163Y.

The contact pressure of the cleaning blade to the photosensitive drum can be generally calculated using the following equation.
F = δ × 3E × t ³ / (12 × L ³ )
F: Contact pressure (gf / cm)
δ: biting amount (cm)
E: Young's modulus (kg / cm ² )
t: thickness (cm)
L: Free end length (cm)
As shown in the above formula, the contact pressure increases as the biting amount δ, Young's modulus E, and thickness t of the cleaning blade 165Y increase, and the contact pressure decreases as the free length L increases.

  The amount of biting δ of the cleaning blade 165Y is adjusted by adjusting the attachment position of the back plate 163Y to the cleaning container 162Y in the range of the long holes 166Y and 167Y in FIG. Can be changed. The amount of biting δ is usually 0.6 to 1.5 mm.

  When the amount of biting δ is larger than 1.5 mm, a very high frictional force is applied to the photosensitive drum 111Y, so that the edge of the cleaning blade 165Y is easily chipped and squealed, and the wear of the photosensitive drum 111Y increases.

  If the amount of biting δ is smaller than 0.6 mm, not only the operation of the cleaning blade 165Y becomes unstable, but also the adhesion between the photosensitive drum 111Y and the cleaning blade 165Y is lost, and the toner easily slips through. It causes a defect.

The Young's modulus E of the cleaning blade 165Y is usually 30 to 100 kg / cm ² , and if it is larger than 100 kg / cm ² , the wear of the photosensitive drum 111Y becomes large, and if it is smaller than 30 kg / cm ² , it adheres to the surface of the photosensitive drum 111Y. And the toner becomes easy to slip through, resulting in an image defect.

  The thickness t of the cleaning blade 165Y is normally 1.5 mm to 2.5 mm. If the thickness t is less than 1.5 mm, the strength of the cleaning blade 165Y is turned over and the toner easily slips through and causes image defects. If the thickness is greater than 2.5 mm, the contact pressure tends to be non-uniform in the longitudinal direction, and uneven wear of the photosensitive drum 111Y tends to increase.

  The length of the portion protruding from the back plate 163Y of the cleaning blade 165Y, the so-called free length L, is usually 5 to 10 mm. If it is smaller than 5 mm, the contact pressure tends to be non-uniform in the longitudinal direction, and uneven wear of the photosensitive drum 111Y tends to occur. If it is larger than 10 mm, turning over or permanent deformation of the cleaning blade 165Y may be caused.

  As the color toner used in this embodiment, a mixture of a polymerized toner prepared by an emulsion polymerization aggregation method and a magnetic carrier was used as a two-component developer. The toner weight (T / D ratio) with respect to the total weight of the developer thus obtained was 8%.

The polymer toner used in the present invention has a shape factor SF of 100 to 140 represented by SF = (M ² π / 4A) × 100, where M is the maximum perimeter of toner particles and A is the projected area of the particles. In order to maintain high transfer efficiency, a substantially spherical toner that falls within the above range is preferable. Further, as the particle diameter of the toner, those having a weight average particle diameter in the range of 5 to 10 μm are preferable from the viewpoint of image quality because a good image can be obtained.

  The photosensitive drum 111Y is obtained by applying an organic photosensitive layer of about 20 μm on the outer peripheral surface of an aluminum tube having a diameter of 30 mm, and is driven to rotate in the direction of the arrow at a predetermined peripheral speed V = 105 mm / s.

  The charging roller 112Y is a roller having a diameter of 14 mm, which is manufactured by winding a rubber mainly composed of epichlorohydrin whose resistance is adjusted so as to have a predetermined resistance value with a metal shaft having a diameter of 8 mm as an axis, and grinding it into a cylindrical shape. It is.

  FIG. 6 shows experimental results of the following specific examples and comparative examples by the image forming apparatus of the present embodiment having the structure shown in FIGS.

(Comparative Example 1)
In the image forming apparatus having a tandem configuration in which image processing units are arranged in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side of the intermediate transfer belt 131, each image process The photosensitive drum cleaner of the unit was the same, and the setting of the cleaning blade was biting amount δ = 1.3 mm, Young's modulus E = 80 kgf / cm ² , thickness t = 2.0 mm, and free length L = 8 mm.

  Using this image forming apparatus, a four-sheet intermittent copy test of A4 plain paper was performed at an image coverage of 5%, which is the ratio of the image forming area to the entire area of the paper, and whether or not an image defect occurred due to a cleaning failure and photosensitivity The number of printable copies was measured before an image defect occurred due to wear of the body drum. The result is shown in FIG.

  As can be seen from the evaluation results in FIG. 6, in Comparative Example 1, no image defect occurred due to a cleaning defect. Further, the number of printable photoconductor drums was about 30,000 for each color.

Example 1
In the image forming apparatus having the same configuration as that of Comparative Example 1 described above, only the amount of biting δ in the cleaning blade of the black (K) image process unit located on the most downstream side of the intermediate transfer belt 131 is set to 0.8 mm. did. As a result, in this example, the contact pressure of the cleaning blade to the photosensitive drum was lower than that of Comparative Example 1 (bite amount δ = 1.3 mm).

  Using this image forming apparatus, a test of four intermittent copies of A4 plain paper at an image coverage of 5% is performed until image defects occur due to defective cleaning, and image defects occur due to photoconductor drum wear. The number of copies that can be printed on was measured. The result is shown in FIG.

  In Example 1, no defective image due to defective cleaning occurred. Further, the number of printable sheets of the photosensitive drum was about 30,000 for yellow (Y), magenta (M), and cyan (C), but about 36,000 for black (K). By reducing the amount of biting δ of the blade, it was possible to effectively suppress the wear of the photosensitive drum.

(Example 2)
In the image forming apparatus having the same configuration as that of Comparative Example 1 described above, only the Young's modulus E of the cleaning blade in the black (K) image process unit located on the most downstream side of the intermediate transfer belt 131 is set to 50 kgf / cm ² . Set. As a result, in this example, the contact pressure of the cleaning blade to the photosensitive drum was lower than in Comparative Example 1 (Young's modulus E = 80 kgf / cm ² ).

  Using this image forming apparatus, a test of four intermittent copies of A4 plain paper at an image coverage of 5% is performed until image defects occur due to defective cleaning, and image defects occur due to photoconductor drum wear. The number of copies that can be printed on was measured. The result is shown in FIG.

  In Example 2, there was no image failure due to cleaning failure. Further, the number of printable drums of the photosensitive drum was about 30,000 for yellow (Y) and magenta (M) cyan (C), but about 37,000 for black (K). By reducing the Young's modulus E, the wear of the photosensitive drum can be effectively suppressed.

(Example 3)
In the image forming apparatus having the same configuration as that of Comparative Example 1 described above, only the thickness t of the cleaning blade in the black (K) image process unit located on the most downstream side of the intermediate transfer belt 131 is set to 1.8 mm. did. As a result, in this example, the contact pressure of the cleaning blade to the photosensitive drum was lower than in Comparative Example 1 (thickness t = 2.0 mm).

  Using this image forming apparatus, a test of four intermittent copies of A4 plain paper at an image coverage of 5% is performed until image defects occur due to defective cleaning, and image defects occur due to photoconductor drum wear. The number of copies that can be printed on was measured. The result is shown in FIG.

  In Example 3, no image defect occurred due to a cleaning defect. Further, the number of printable drums of the photosensitive drum was about 30,000 for yellow (Y), magenta (M), and cyan (C), but about 35,000 for black (K). By reducing the thickness t of the blade, it was possible to effectively suppress the wear of the photosensitive drum.

Example 4
In the image forming apparatus having the same configuration as that of Comparative Example 1 described above, only the free length L of the cleaning blade in the black (K) image process unit located on the most downstream side of the intermediate transfer belt 131 is set to 9 mm. As a result, in this example, the contact pressure of the cleaning blade to the photosensitive drum was lower than in Comparative Example 1 (free length L = 8 mm).

  Using this image forming apparatus, a test of four intermittent copies of A4 plain paper at an image coverage of 5% is performed until image defects occur due to defective cleaning, and image defects occur due to photoconductor drum wear. The number of copies that can be printed on was measured. The result is shown in FIG.

  In Example 4, there was no image defect due to poor cleaning. Further, the number of printable drums of the photosensitive drum was about 30,000 for yellow (Y), magenta (M), and cyan (C), but about 35,000 for black (K). By reducing the free length L of the blade, it was possible to effectively suppress the wear of the photosensitive drum.

(Example 5)
In the image forming apparatus having the same configuration as that of Comparative Example 1 described above, the amount δ of the cleaning blade in each color image process unit is 1.3 mm for yellow (Y), 1.2 mm for magenta (M), cyan ( C) was set to 1.1 mm, and black (K) was set to 0.8 mm. Thus, in this embodiment, the contact pressure of the cleaning blade to the photosensitive drum is the same for yellow (Y), magenta (M), cyan (compared to Comparative Example 1 (biting amount δ = 1.3 mm)). C), black (K), and the process units arranged downstream are configured to gradually become smaller.

  Using this image forming apparatus, a test of four intermittent copies of A4 plain paper at an image coverage of 5% is performed until image defects occur due to defective cleaning, and image defects occur due to photoconductor drum wear. The number of copies that can be printed on was measured. The result is shown in FIG.

  In Example 5, the image defect due to the cleaning defect did not occur. Further, the number of printable sheets of the photosensitive drum is about 30,000 for yellow (Y), about 31,000 for magenta (M), about 33,000 for cyan (C), and 36 for black (K). The photosensitive drum was effectively prevented from being worn by reducing the biting amount δ of the cleaning blade.

(Comparative Example 2)
In the image forming apparatus having the same configuration as that of Comparative Example 1 described above, the amount of biting of the cleaning blade of the yellow (Y), magenta (M), and cyan (C) image process unit δ = 0.8 mm, black (K) The image processing unit cleaning blade was set to bite amount δ = 1.3 mm. As a result, in this comparative example 2, the contact pressure of the cleaning blade to the photosensitive drum is yellow (Y), magenta (M), cyan (C) compared to comparative example 1 (bite-in amount δ = 1.3 mm). ) Is small, and black (K) is equivalent.

  Using this image forming apparatus, an A4 plain paper four-sheet intermittent copy test was performed at an image coverage of 5%, until there was an image defect due to a cleaning failure and an image defect due to photoconductor drum wear. The number of copies that can be printed on was measured. The result is shown in FIG.

  In Comparative Example 2, an image defect due to a cleaning defect occurred in the image process units of yellow (Y), magenta (M), and cyan (C). Further, the number of printable sheets of the photosensitive drum was about 33,000 for cyan (C) and about 30,000 for black (K), but image defects were observed with yellow (Y) and magenta (M). It was impossible to measure due to the violence, resulting in a significant reduction in the life of the image processing unit.

  As can be seen from the above embodiments, the process unit located on the downstream side of the intermediate transfer member increases the retransfer toner, increases the amount of toner supplied to the cleaning blade, and similarly increases the external toner additive. In addition, high lubricity can be maintained. For this reason, stable cleaning can be performed even if the contact pressure of the cleaning blade to the photosensitive drum is lowered, and the wear of both the cleaning blade and the photosensitive drum is reduced and the life is extended as the contact pressure decreases. Can do. In addition, by disposing black (K) that is frequently used in the most downstream, the replacement frequency of consumables such as the cleaning blade of the black process unit and the photosensitive drum is reduced, and the maintenance cycle can be extended. .

  In the above embodiment, an example using a non-magnetic polymerized toner is shown. However, the present invention is not limited to this, and for example, a pulverized toner may be used.

  In the above-described embodiment, an example in which an intermediate transfer belt is used as an intermediate transfer member has been described. However, the present invention is not limited to this. For example, a sheet is sucked and conveyed on the belt, and each color is transferred to the sheet. A configuration in which transfer is directly performed from the process unit may be employed.

  As described above, according to the present invention, it is possible to reduce the wear of the photosensitive drum and extend the life of the image processing unit while preventing the cleaning blade from being damaged or the occurrence of poor cleaning particularly in the frequently used photosensitive drum. Therefore, the present invention is useful as an image processing apparatus that can form full-color or black-and-white images using an electrophotographic method, an image forming apparatus including the image processing apparatus, and the like.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 5 is an arrangement diagram showing a relationship between a toner image on an intermediate transfer belt and a photosensitive drum of each color according to an embodiment of the present invention. 1 is a schematic side view of an image processing unit according to an embodiment of the present invention. 1 is a perspective view of a main part of an image processing unit according to an embodiment of the present invention. The figure which shows the relationship between the photosensitive drum of the image process unit which concerns on embodiment of this invention, and a cleaning blade. The figure which shows the image evaluation result of the form of the Example of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Apparatus main body 102 Secondary transfer roller 103 Paper discharge roller 110Y, 110M, 110C, 110K Image process unit 111Y, 111M, 111C, 111K Photosensitive drum 112Y, 112M, 112C, 112K Charging roller 113Y, 113M, 113C , 113K Developing device 114Y, 114M, 114C, 114K Primary transfer roller 115Y, 115M, 115C, 115K Photoconductor cleaner 116 Developing roller 117 Stirring screw 120 Laser scan unit 130 Intermediate transfer unit 131 Intermediate transfer belt 132 Drive roller 133 Driven roller 140 Fixing Unit 141 Fixing roller 142 Pressure roller 150 Paper feed unit 151 Paper cassette 152 Registration roller 162Y Clean Grayed container 163Y backplate 164Y fixing screws 165Y cleaning blade 166Y, 167Y slots 180 sheet 190Y laser beam

Claims (7)

A plurality of image processing units having an image carrier that carries a toner image, a cleaning blade that contacts the image carrier and cleans the toner on the image carrier, and the toner image formed by the image process unit includes: An intermediate transfer body that is sequentially transferred, and the contact pressure of at least one of the cleaning blades of the image process unit located downstream in the order of transfer of the toner image to the intermediate transfer body is the intermediate transfer body. An image processing apparatus, wherein the pressure is smaller than a contact pressure of the cleaning blade of the image processing unit located on the upstream side of the image processing unit. The image process unit that frequently forms the toner image is disposed downstream of the image process unit that does not frequently form the toner image in the order of transferring the toner image to the intermediate transfer member. The image processing apparatus according to claim 1. The image processing apparatus according to claim 1, wherein the contact pressure is defined by an amount of biting of the cleaning blade into the image carrier. The image processing apparatus according to claim 1, wherein the contact pressure is defined by a Young's modulus of the cleaning blade. The image processing apparatus according to claim 1, wherein the contact pressure is defined by a thickness of the cleaning blade. The image processing apparatus according to claim 1, wherein the contact pressure is defined by a free length of the cleaning blade. An image forming apparatus comprising the image processing apparatus according to claim 1.