Image forming apparatus

Abstract

To provide an image forming apparatus that extends a free length of an end of a blade to prevent turn-up of the blade, and effectively prevents the occurrence of passing of toner occurring due to the extension of the free length of the blade.SOLUTION: A free length of an end of a blade in a blade width direction is made longer than that at a center part of the blade, and the surface roughness of a photoconductor drum is reduced at a position facing a development area in an area where the free length of the blade is set longer.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with a cleaning device that cleans toner with a cleaning blade. [Background technology]

[0002] As image forming devices become faster, the mainstream full-color image forming device is a configuration in which multiple image forming units are arranged in parallel corresponding to the belt member, and the image creation process for each color is performed in parallel. For example, in electrophotographic image forming devices, there is a full-color tandem system using an intermediate transfer belt.

[0003] The full-color tandem method is an image forming method in which a full-color image is obtained on a recording medium by using a plurality of image forming units arranged in an array.

[0004] This type of full-color image forming apparatus is equipped with a photoconductor cleaning device that removes residual toner remaining on the photoconductor drum after the primary transfer, and an intermediate transfer body cleaning device that removes residual toner remaining on the intermediate transfer belt after the secondary transfer.

[0005] For these cleaning devices, a cleaning blade in which an elastic material such as rubber is bonded to a supporting metal plate is widely used. In particular, the counter type, in which the cleaning blade is brought into contact with the photosensitive drum or intermediate transfer belt in the driving direction opposite to the photosensitive drum or intermediate transfer belt, is generally adopted because of its high cleaning performance.

[0006] However, in this counter type blade cleaning, it is known that when the frictional force between the cleaning blade and the photosensitive drum or intermediate transfer belt becomes large, a problem such as blade curling occurs.

[0007] Therefore, Patent Document 1 discloses a configuration in which the free length of the cleaning blade at its longitudinal ends is made longer than the free length at its longitudinal center, thereby suppressing the occurrence of blade curling. Note that the "free length" of a cleaning blade refers to the length in the short direction of the part that protrudes from a support member or a regulating member that is in contact with or opposite to the surface of the cleaning blade and regulates deformation of the free end side of the cleaning blade. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2006-259394 A Summary of the Invention [Problem to be solved by the invention]

[0009] In this way, by appropriately setting the free length of the cleaning blade, the occurrence of blade curling can be stably suppressed. At the end of the cleaning blade, there is an area (hereinafter referred to as a high μ area) where the toner or developer serving as a lubricant is hardly supplied. In such an area, the frictional force is high, and therefore blade curling is particularly likely to occur. Therefore, in order to reduce the frictional force between the photosensitive drum and the cleaning blade, it is considered to set the width of the area where the free length of the cleaning blade is set to be long to be larger than the width of the high μ area. On the other hand, if the free length is set to be long, the contact pressure of the cleaning blade may decrease, which may cause cleaning defects, so it is considered preferable to set the width of the area where the free length is set to be long so that it does not overlap the area where the toner image is formed.

[0010] However, even outside the toner image forming area, minute fog toner continues to be supplied onto the photosensitive drum at a position facing the area (developing area) where the developing device is coated with toner. That is, minute fog toner continues to be supplied to the area outside the toner image forming area and inside the high μ area. If the free length of the cleaning blade in this area is long, the minute fog toner is not sufficiently collected by the cleaning blade and adheres to the charging roller located downstream. If such fog toner continues to be supplied to the charging roller for a long period of time, the accumulated toner becomes a resistor, causing charging failure and vertical streaks to appear on the edge of the paper.

[0011] The present invention has been made in consideration of these problems, and aims to provide an image forming apparatus that can effectively suppress the occurrence of fog toner slip-through at the ends of the development area while suppressing blade curling in high μ areas. [Means for solving the problem]

[0012] The image forming apparatus according to the present invention includes an image carrier, a developer carrier that carries a developer to be supplied to a surface of the image carrier, a cleaning member for removing developer from the surface of the image carrier, the cleaning member including: an elastic blade whose free end abuts against the surface of the image carrier along a width direction substantially perpendicular to a moving direction of the surface of the image carrier; and a regulating portion for regulating a free length of the elastic blade on a base end side opposite to the free end in a direction intersecting the width direction of the elastic blade; and at both ends in the width direction, an end of a development area, which is an area where the developer carrier can carry a developer, is located outside an end of an image forming area, where an image can be formed with the developer on the image carrier, and an end of a cleaning area, which is an area where the elastic blade comes into contact with the image carrier, is located outside the end of the development area, and a free length of the blade outside the image forming area in the width direction is longer than a free length of the blade in the image forming area, The surface roughness of the image carrier in a first region, which is outer than the image forming region and inner than the end of the development region, in the width direction is smaller than the surface roughness of the image carrier in a second region, which is the image forming region, and smaller than the surface roughness of the image carrier in a third region, which is outer than the end of the development region. Effect of the Invention

[0013] According to the present invention, it is possible to provide an image forming apparatus capable of effectively suppressing the occurrence of fogging toner passing through at the end of the development area, while suppressing blade curling in the high μ area. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention; [Diagram 2] 5A and 5B are explanatory diagrams of the shape of recesses on the surface of the photosensitive drum according to the present embodiment. [Diagram 3] FIG. 2 is an explanatory diagram of a longitudinal arrangement of the image forming apparatus according to the present embodiment. [Figure 4] FIG. 2A is a plan view illustrating a schematic configuration of a cleaning blade according to the present embodiment, and FIG. 2B is a perspective view illustrating the schematic configuration of a cleaning blade according to the present embodiment. [Diagram 5] 11 is an explanatory diagram showing the frictional force between a photosensitive drum and a cleaning blade at a longitudinal end of a conventional image forming apparatus. [Figure 6] 5A and 5B are explanatory diagrams showing surface roughness adjustment positions at the longitudinal ends of the photosensitive drum according to the present embodiment. [Figure 7] 5 is a plan view illustrating the frictional force between the photosensitive drum and the cleaning blade at the longitudinal end of the image forming apparatus according to the present embodiment. FIG. [Figure 8] 1A is a plan view of the longitudinal center portion of the surface of a photosensitive drum according to this embodiment, and FIG. 1B is a plan view of a region with small surface roughness at a longitudinal end portion. [Figure 9] FIG. 2 is a plan view illustrating a schematic configuration of a photosensitive drum in the first embodiment. [Figure 10]5A to 5C are explanatory diagrams of the occurrence of poor cleaning and blade curling in the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, only the main parts related to the formation / transfer of a toner image will be described, but the present invention can be embodied in various applications such as printers, various printing machines, copiers, FAX machines, and multifunction machines by adding necessary devices, equipment, and housing structures.

[0016] <Image forming device> Fig. 1 is an explanatory diagram of the configuration of an image forming apparatus. As shown in Fig. 1, image forming apparatus 100 is a tandem type intermediate transfer type full-color printer in which image forming units 109Y, 109M, 109C, and 109Bk for yellow, magenta, cyan, and black are arranged along intermediate transfer belt (ITB) 101.

[0017] In image forming unit 109Y, a yellow toner image is formed on a photosensitive drum serving as an image carrier and transferred to intermediate transfer belt 101. In image forming unit 109M, a magenta toner image is formed in a similar procedure to image forming unit 109Y and transferred and superimposed on the yellow toner image on intermediate transfer belt 101. In image forming units 109C and 109Bk, a cyan toner image and a black toner image are formed in a similar procedure to image forming unit 109Y and transferred and superimposed in order to intermediate transfer belt 101.

[0018] The four-color toner images carried on the intermediate transfer belt 101 are transported to a secondary transfer section T2 and are collectively (secondarily) transferred onto a recording material P. The recording material P onto which the four-color toner images have been (secondarily) transferred is separated from the intermediate transfer belt 101 by curvature and sent to a fixing device 112. The fixing device 112 heats and presses the recording material P with a fixing roller 112a and a pressure roller 112b to melt the toner and fix the image onto the surface. Thereafter, the recording material P is discharged outside the apparatus body.

[0019] The image forming units 109Y, 109M, 109C, and 109Bk are substantially identical in configuration, except that the colors of toner used in the respective developing devices are different: yellow, magenta, cyan, and black. In the following, the toner image forming process of the black image forming unit 109Bk will be described, and duplicated descriptions of the other image forming units 109Y, 109M, and 109C will be omitted. Also, the symbols Y, M, C, and Bk representing the toner colors yellow, magenta, cyan, and black will be omitted as appropriate.

[0020] The image forming unit 109Bk includes a photosensitive drum 103, a charging roller 104, an exposure device 105, a developing device 106, a primary transfer roller 107, and a photosensitive drum cleaning blade 108 arranged around the photosensitive drum 103.

[0021] The photosensitive drum 103 has a photosensitive layer with a negative charge polarity formed on the surface of an aluminum tube, and is driven by a motor (not shown) in the direction of the arrow at a process speed of 0.3 m / s. The photosensitive drum 103 has a plurality of independent recesses on its circumferential surface. FIG. 2 shows an example of the shape of the recesses. The maximum width of the contour of the opening of the recess in the axial direction is 20 μm to 80 μm, and the depth is 0.5 μm to 8 μm. The contour of the opening of the recess has an apex at an angle of 0° to 90° at least on the upstream side in the rotation direction of the photosensitive drum 103, and the width of the contour of the opening of the recess becomes smaller from the part where the width of the contour of the opening of the recess is the maximum width toward the apex. The depth of the recess becomes shallower from the deepest point toward the apex as viewed in the axial direction. For example, the recesses can be formed by pressing a mold having a convex portion corresponding to the recess to be formed against the circumferential surface of the photosensitive drum to transfer the shape. Examples of the material of the mold include metal, metal oxide, plastic, and glass. Among these, stainless steel (SUS) is preferable from the viewpoints of mechanical strength, dimensional accuracy, and durability.

[0022] A negative DC voltage is applied to the charging roller 104, which negatively charges the surface of the photosensitive drum 103. The exposure device 105 writes an electrostatic image of an image on the surface of the photosensitive drum 103 by scanning a laser beam that is ON-OFF modulated based on scanning line image data obtained by developing a black separated color image, using a rotating mirror.

[0023] The developing device 106 frictionally charges a two-component developer containing a negatively charged non-magnetic toner and a magnetic carrier using an agitating member. The developer is transported by a transport member and carried on a developing sleeve as a developer carrier. The developer carried on the developing sleeve has its thickness regulated by a regulating blade, and is then transported to a portion facing the photosensitive drum 103. The developing sleeve is held at a predetermined distance from the photosensitive drum 103. By applying an oscillating voltage, which is an AC voltage superimposed on a negative DC voltage, to the developing sleeve, the negatively charged toner is transferred to the exposed portion of the photosensitive drum 103, which has become relatively positive, and the electrostatic image is reversed and developed.

[0024] The toner used in this embodiment may be a known toner in which a coloring material, a charge control material, etc., is added to a binder resin. The toner may preferably have a volume average particle size of 5 μm or more and 15 μm or less. In this embodiment, toner with a volume average particle size of 6 μm is used for all colors of yellow, magenta, cyan, and black.

[0025] The primary transfer roller 107 forms a primary transfer portion T1 between the photosensitive drum 103 and the intermediate transfer belt 101. By applying a positive DC voltage to the primary transfer roller 107, the toner image carried on the photosensitive drum 103 is primarily transferred to the intermediate transfer belt 101.

[0026] The photoconductor cleaning blade 108 abuts against the photoconductor drum 103 in the driving direction thereof, and collects residual toner remaining on the photoconductor drum 103. The photoconductor cleaning blade 108 is composed of a plate-shaped elastic member and a supporting metal plate, and the elastic member is made of, for example, urethane rubber having a hardness of 77° (JIS-A) and a thickness of 2 mm. The contact edge of the elastic member of the photoconductor cleaning blade 108 abuts against the photoconductor drum 103 at an angle of 22° with a linear pressure of 30 N / m. This linear pressure is the average value over the entire area in the longitudinal direction.

[0027] The secondary transfer roller 111 comes into contact with the outer surface of the intermediate transfer belt 101 between the image forming unit 109Bk and the intermediate transfer body cleaning blade 102 in the toner image transport direction. The secondary transfer roller 111 comes into contact with the intermediate transfer belt 101, the inner surface of which is supported by an opposing roller (drive roller) 110, to form a secondary transfer portion T2. ​​By applying a positive DC voltage to the secondary transfer roller 111, the full-color toner image carried on the intermediate transfer belt 101 is secondarily transferred to the recording material P.

[0028] The intermediate transfer member cleaning blade 102 comes into contact with the intermediate transfer belt 101 in the driving direction opposite the tension roller 115, and collects the residual toner remaining on the intermediate transfer belt 101. The intermediate transfer member cleaning blade 102 is composed of a plate-shaped elastic member and a supporting metal plate, and the elastic member is made of, for example, urethane rubber with a hardness of 77° (JIS-A) and a thickness of 2 mm. The contact edge of the elastic member of the intermediate transfer member cleaning blade 102 comes into contact with the intermediate transfer belt 101 at an angle of 25° with a linear pressure of 35 N / m. This linear pressure is the average value over the entire area in the longitudinal direction.

[0029] The intermediate transfer belt 101 is a belt member that is driven to be transported in the direction of the arrow R, and is tensioned by a drive roller 110 that is a drive member, tension rollers 113 and 114 that are tension members, and a tension roller 115 that applies a predetermined tension to the intermediate transfer belt 101. The drive roller 110 also functions as a secondary transfer inner roller disposed in the secondary transfer portion T2. ​​However, the number of rollers that tension the intermediate transfer belt 101 is not limited to the configuration in FIG. 1.

[0030] <Explanation of toner slippage> FIG. 3 is an explanatory diagram of the longitudinal arrangement of the main elements of the image forming apparatus 100. In consideration of the development stability at the longitudinal end, the longitudinal width of the developing device 106 is set to be larger than the longitudinal width of the required toner image (longitudinal width of the maximum image forming area). Also, in order to clean toner scattered from the longitudinal end of the developing device 106, the longitudinal width of the photoconductor cleaning blade 108 is set to be larger than the longitudinal width of the developing device 106. Furthermore, the following length relationship is set so that the toner on the intermediate transfer belt 101 can be cleaned even if a longitudinal positional deviation occurs due to meandering of the intermediate transfer belt 101. That is, the longitudinal width of the intermediate transfer body cleaning blade 102 is set to be larger than the longitudinal width of the photoconductor cleaning blade 108.

[0031] In such a longitudinal arrangement, there are regions (hereinafter referred to as high μ regions) at the longitudinal ends of the photoconductor cleaning blade 108 and the intermediate transfer member cleaning blade 102 where little toner or external additives serving as lubricants are supplied. Here, the "high μ region" refers to a region of the cleaning region, which is the region of the photoconductor drum where the photoconductor cleaning blade 108 contacts the photoconductor drum 103, that is outside the development region, which is the region carrying the developer on the developing sleeve. Since not even fog toner is supplied from the developing device to this region, the coefficient of friction between the photoconductor drum 103 and the photoconductor cleaning blade 108 becomes extremely high.

[0032] FIG. 4 is an explanatory view of the schematic configuration of the cleaning blade according to the present embodiment. The cleaning blade is composed of an elastic member 1 as an elastic blade and a support sheet metal 2. In the present embodiment, the support sheet metal 2 functions as a regulating portion that regulates the free length of the elastic member 1. In the present embodiment, the free length is changed in the longitudinal direction according to the shape of the support sheet metal 2. Specifically, the length from the adhesion surface of the elastic member 201 and the support sheet metal 202 at the central portion in the longitudinal direction of the elastic member 1 to the free end of the elastic member 201 (hereinafter referred to as the free length) is set as L1 [mm]. Further, when the free length in the region of the width w at the longitudinal end portion is set as L2 [mm], the following formula, the relationship of L1 < L2 is set to be satisfied. In the present embodiment, the free length in the image forming region is substantially constant. Further, at both end portions in the width direction of the cleaning blade, the free length in the region of the width w, that is, the region outside the developing region is set to be substantially constant.

[0033] Here, the free length L1 [mm] is the average value of the free length L1 [mm] of the cleaning blade in the image forming region. Further, the free length L2 [mm] is the average value of the free length L2 [mm] of the cleaning blade outside the developing region in the width direction of the cleaning blade.

[0034] By setting the width w to be larger than the width of the high μ region, the load applied to the elastic member 1 in the high μ region can be released. In the present embodiment, a configuration for further releasing the load is adopted by setting the relationship of 1.2 × L1 ≤ L2. Note that the detailed shape of the support sheet metal 2 is not limited to the configuration of FIG. 4.

[0035] When the free length is set long, the contact pressure of the elastic member 1 against the photosensitive drum 103 decreases. Therefore, when the width w is large as it is applied to the toner image forming region, there is a possibility of occurrence of cleaning failure. Therefore, it is desirable to set the width w to be larger than the width of the high μ region and not to be applied to the toner image forming region.

[0036] However, even outside the toner image forming area, minute fog toner continues to be supplied onto the photosensitive drum 103 at a position facing the area where the developing device 106 is coated with toner. If the free length of the cleaning blade 108 in this area is long (the contact pressure with the photosensitive drum 103 is low), the minute fog toner is not sufficiently collected by the cleaning blade 108 and adheres to the charging roller 104 located downstream. The fog toner that has slipped through the cleaning blade 108 does not appear as an image defect in the short term, but if it continues to be supplied to the charging roller 104 for a long period of time, the accumulated toner becomes a resistor, causing charging defects and resulting in vertical streaks on the edge of the paper.

[0037] The mechanism by which toner slippage occurs in the conventional configuration will be described with reference to FIG. 5. In a cleaning blade with a long free length at the end, the blade pressure is low in the region with the long free length relative to the image forming region. The friction coefficient of the surface of the photosensitive drum 103 is small at the position facing the developing device 106 because toner and external additives are supplied. On the other hand, the friction coefficient is large in the outer region where toner and external additives are not supplied. As a result, the friction force between the photosensitive drum 103 and the cleaning blade 108 has a profile as shown in FIG. 5. If the friction force is too large, the blade will be turned over, while if the friction force is too small, sufficient cleaning performance cannot be obtained, and there is a risk of cleaning failure (toner slippage). The dotted line a in FIG. 5 represents the threshold value for cleaning failure, and if the friction force falls below the wavy line a, cleaning failure occurs. In the conventional configuration, the friction force is below the dotted line a at the longitudinal position where the region with the long free length of the cleaning blade 108 faces the developing device 106, and cleaning failure occurs. (Hereinafter, this longitudinal position will be referred to as the toner slip-through area.) EXAMPLES

[0038] <Free blade length> 6 is an explanatory diagram of the longitudinal relationship of the main elements of the image forming apparatus 100 in this embodiment. As described above, the free length of the cleaning blade 108 in the image forming area (maximum image forming area) where a toner image can be formed is a first length. In addition, the free length of the cleaning blade 108 outside the maximum image forming area in the width direction of the cleaning blade 108 is a second length longer than the first length. That is, by lengthening the free length of the end of the cleaning blade 108 in the area outside the maximum image forming area in the width direction of the cleaning blade 108, it is possible to suppress blade curling in the area where developer is difficult to supply.

[0039] <Surface roughness of photosensitive drum> As described above, toner slip-through is likely to occur in the region of the cleaning blade 108 with a long free length facing the developing device 106 (developing region). That is, toner slip-through is likely to occur in the region of the photosensitive drum 103 that is outside the image forming region (maximum image forming region) where a toner image can be formed and inside the developing region where the developing sleeve of the developing device can carry developer (the region where toner slip-through is likely to occur is also called the cleaning failure occurrence region).

[0040] Therefore, in this embodiment, the surface roughness of the photosensitive drum in the region where cleaning defects occur is set to be smaller than that of other longitudinal positions (other cleaning regions).

[0041] The surface roughness of the photosensitive drum can be observed using a microscope such as a laser microscope, an optical microscope, an electron microscope, or an atomic force microscope. For example, the following instruments can be used as the laser microscope. Ultra-deep shape measuring microscope VK-8550, ultra-deep shape measuring microscope VK-9000, ultra-deep shape measuring microscope VK-9500, VK-X200, and VK-X100 manufactured by Keyence Corporation can be used. In addition, a scanning confocal laser microscope OLS3000 manufactured by Olympus Corporation and a real color confocal microscope Oplitex C130 manufactured by Lasertec Corporation can also be used. In this embodiment, a laser microscope (VK-X110) was used as a measuring instrument, and the arithmetic mean surface roughness (Sa) was measured with a 20x objective lens. Under the above measurement conditions, it is possible to detect the uneven shape of the photosensitive drum surface.

[0042] The effect of the countermeasure against poor cleaning in the configuration of this embodiment will be explained with reference to Fig. 7. In the configuration of this embodiment, the cleaning blade pressure is low in the area with a long free length relative to the image forming area, as in the conventional configuration. This makes it possible to effectively suppress blade curling that occurs at the blade end.

[0043] On the other hand, the surface roughness of the photosensitive drum 103 is reduced in the longitudinal position where the region where the cleaning blade 108 has a long free length faces the developing device 106 (developing region). This makes it possible to increase the friction coefficient of the photosensitive drum surface in the region where toner slip-through is likely to occur, improve the cleaning performance of the cleaning blade 108, and effectively prevent toner slip-through. That is, in the region where the surface roughness is reduced, the contact area between the photosensitive drum 103 and the cleaning blade 108 increases, and the friction coefficient of the photosensitive drum surface increases. As a result, the friction force between the photosensitive drum 103 and the cleaning blade 108 exceeds the dotted line a, which is the threshold value for cleaning defects, over the entire longitudinal region, making it possible to prevent the occurrence of cleaning defects.

[0044] In order to confirm the effect of this embodiment, multiple photosensitive drums with reduced surface roughness in a portion of the longitudinal direction were fabricated, and were mounted on the image forming apparatus 100 to conduct a continuous paper feed test. In order to efficiently detect toner slip-through, an image with a print rate of 30% was used. In addition, in order to confirm the resistance to blade curling, a separate test was also conducted using an image with a print rate of 0%, which is prone to blade curling. The region with the long free length of the cleaning blade 108 was set to be larger than the width of the high μ region and not to overlap the toner image formation region.

[0045] 8 is a schematic diagram of the peripheral surface of the photosensitive drum 103 in this embodiment. The recesses on the peripheral surface of the photosensitive drum 103 are square regions with sides of 500 μm (area 250000 μm 2 ) is placed, the area of ​​the recess in that region is 100,000 μm 2 The surface roughness was adjusted by reducing the area ratio of the recesses in the square region mentioned above (Figure 8-b). 2 The surface roughness of the photosensitive drum 103 in the first region, which is the image forming region, and the surface roughness of the photosensitive drum 103 in the third region (high μ region) which is outside the end of the development region, are set to be the first surface roughness. The surface roughness of the photosensitive drum 103 in the second region (high μ region) which is outside the end of the development region, is set to be the second surface roughness which is smaller than the first roughness. In other words, the area ratio of the recesses formed per unit area in the first region (image forming region) and the third region (high μ region) of the surface of the photosensitive drum 103 is the first area ratio. Moreover, the area ratio of the recesses formed per unit area in the second region (region where toner slip-through occurs) is a second area ratio that is smaller than the first area ratio.

[0046] Fig. 9 shows schematic diagrams of four levels of photosensitive drums A to D used in the continuous paper feed test. Photosensitive drum A, which serves as a comparative example, has uniform surface roughness in the longitudinal direction, as in the past. Photosensitive drums B to D, which serve as the present embodiment, have a portion with small surface roughness in a part in the longitudinal direction, and the width of that region is changed.

[0047] FIG. 10 is an explanatory diagram of the occurrence of cleaning failure and blade curling in the continuous paper passing test in this embodiment. The number of continuous paper passing was 10,000, and when blade curling occurred during paper passing, paper passing was stopped at that point. In the conventional photosensitive drum A, blade curling did not occur, but cleaning failure occurred in the longitudinal position where the area where the cleaning blade 108 has a long free length and the developing device 106 face each other as described above. In the photosensitive drum B, the surface roughness of the entire area where toner slip-through occurs is set to be small, so cleaning failure did not occur. In addition, by lengthening the free length of the blade end, blade curling that occurs at the blade end can be suppressed. However, since the area where the surface roughness is small is provided to the inside of the area where the cleaning blade 108 has a long free length, the friction coefficient of the photosensitive drum 103 in this area becomes large. Therefore, there is a risk of blade curling depending on the environmental conditions. Therefore, it is preferable that the area where the surface roughness is small is not formed in the area inside the blade beyond the area where the cleaning blade 108 has a long free length. Photosensitive drum C was able to suppress blade curling at the blade end by lengthening the free length of the blade end. In addition, the surface roughness of at least a part of the area where toner slip-through occurs was set small. As a result, although minor cleaning failures occurred in some areas of the toner slip-through occurrence area, the occurrence of cleaning failures was suppressed. Photosensitive drum D did not experience either cleaning failures or blade curling.

[0048] From the above results, as shown in FIG. 6, it was confirmed that by reducing the surface roughness of the photosensitive drum 103 at the position facing the toner slip-through occurrence region, the occurrence of toner slip-through can be suppressed while suppressing blade curling. In addition, in order to suppress blade curling caused by reducing the surface roughness of the photosensitive drum 103, it is preferable to set the area of ​​the photosensitive drum 103 with low surface roughness to a range that does not enter inside the area where the cleaning blade 108 has a long free length. In addition, in order to further enhance the effect of suppressing cleaning defects, it is more preferable to set the area of ​​the photosensitive drum 103 with low surface roughness to the entire area facing the toner slip-through occurrence region as much as possible. For example, the area of ​​the photosensitive drum 103 with low surface roughness can be set to 80% or more of the area facing the toner slip-through occurrence region. More preferably, it can be set to 90% or more of the area facing the toner slip-through occurrence region.

[0049] <Other> In this embodiment, the free length of the cleaning blade is configured to differ by one step between the blade center and the blade end, but is not limited to this. For example, the free length of the cleaning blade at the blade end may be changed in a stepwise or non-stepwise manner. The free length in the above-mentioned "toner slip-through occurrence area" may be set to be longer than the free length in the image forming area and shorter than the free length in the high μ area.

[0050] In addition, in this embodiment, the surface roughness of the first and third regions of the photosensitive drum is set to be the same, but it may be different between the third and first regions, and blade curling may be suppressed by making the surface roughness of the third region (high μ region) greater than that of the first region (image forming region).

[0051] As a means for increasing the frictional force between the photosensitive drum and the cleaning blade in the toner slip-through region, it is possible to gradually increase the free length of the cleaning blade from the toner slip-through region to the high μ region. However, the effect is small compared to the configuration of this embodiment. Even if the free length of the cleaning blade is abruptly changed from a certain longitudinal position as in this embodiment, the distribution of the cleaning blade pressure changes gradually before and after the free length change position as shown in FIG. 5. Therefore, even if the free length of the cleaning blade is gradually increased from the toner slip-through region to the high μ region, the distribution of the cleaning blade pressure is not significantly different from the distribution in this embodiment, and sufficient frictional force cannot be obtained in the toner slip-through region. [Explanation of symbols]

[0052] 1 Elastic member 2 Supporting plate 100 Image forming device 101 Intermediate transfer belt 102 Intermediate transfer member cleaning blade 103 Photosensitive drum 104 Charging roller 105 Exposure equipment 106 Developing device 107 Primary transfer roller 108 Photoconductor cleaning blade 109Y, 109M, 109C, 109Bk Image forming unit 110 Drive roller 111 Secondary transfer roller 112 Fixing device 113, 114 Tension roller 115 Tension roller

Claims

1. An image carrier; a developing device including a developer carrier that carries a developer and that develops an electrostatic image formed on a surface of the image carrier; a blade that comes into contact with a surface of the image carrier and removes developer from the surface of the image carrier; A restriction portion that restricts the free length of the blade; at both ends in the width direction, an end of a development area, which is an area where the developer carrier can carry a developer, is positioned outside an end of an image forming area that can be formed on the image carrier, and an end of a cleaning area, which is an area where the blade comes into contact with the image carrier, is positioned outside an end of the development area, a free length of the blade on an outer side of the image forming area in the width direction is longer than a free length of the blade in the image forming area, An image forming apparatus characterized in that in the width direction, the surface roughness of the image carrier in a first region which is outer than the image forming region and inner than the end of the development region is smaller than the surface roughness of the image carrier in a second region which is the image forming region, and smaller than the surface roughness of the image carrier in a third region which is the cleaning region which is located outer than the end of the development region.

2. When the average free length of the blade in the image forming area is L1 [mm], and the average free length of the blade in the width direction of the blade in the area outside the development area is L2 [mm], the following formula is obtained: L2≧1.2×L1, 2. The image forming apparatus according to claim 1, wherein the above-mentioned condition is satisfied.

3. 3. The image forming apparatus according to claim 1, wherein the image carrier has a plurality of recesses on its surface, and an area ratio of the recesses formed per unit area of ​​the first region is greater than an area ratio of the recesses formed per unit area of ​​the second region and the third region.

4. 4. The image forming apparatus according to claim 1, wherein a free length of the blade corresponding to the second region and the third region in the width direction is substantially constant.

5. 5. The image forming apparatus according to claim 1, wherein the maximum width of the opening of the recess in the width direction of the blade is 20 [mu]m to 80 [mu]m, and the depth of the recess is 0.5 [mu]m to 8 [mu]m.

Images