JP5271924B2 - Drum unit and image forming apparatus equipped with the drum unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drum unit for achieving long life of a photoreceptor drum, and an image forming apparatus having the drum unit. <P>SOLUTION: This drum unit includes the photoreceptor drum (18) where a photosensitive layer (67) by an organic photosensitizing agent is formed on a base material (60) and a toner image is formed in the photosensitive layer through electrostatic charge by rotation driving thereof, a charging apparatus (20) that comes into contact with the photosensitive layer to charge it, a circumferential groove (62) formed by reducing the outer diameter of the base material in a region that is outside a paper feeding width and inside a charging width in the view of the rotation axis direction of the photoreceptor drum comparing with the inside region of the paper feeding width, and an end photosensitive layer (68) formed by filling the circumferential groove with the organic photosensitizing agent and making the outer diameter of the photosensitive layer in the region that is outside the paper feeding width and inside the charging width substantially equivalent to the inside region of the paper feeding width. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a drum unit having a photosensitive drum charged by a contact charging type charger and an image forming apparatus equipped with the drum unit.

  In this type of image forming apparatus, an electrophotographic system is used. When the charger precharges the photosensitive drum and the exposure device irradiates the photosensitive layer of the photosensitive drum with light, the photosensitive layer of the photosensitive drum is applied to the photosensitive drum. An electrostatic latent image is formed. Further, the developing device carries toner, and this toner adheres to the electrostatic latent image, and the toner image is developed on the photosensitive layer of the photosensitive drum. The visualized toner image is transferred and fixed on the paper.

Here, in the photosensitive drum, a technique in which a photosensitive layer is immersed (dipped) in a cylindrical base material is known (for example, see Patent Document 1), and a liquid organic photosensitive agent is applied on the base material. Thus, a photosensitive layer is formed.
On the other hand, when the photosensitive layer made of the organic photosensitive agent is in direct contact with the contact charging type charger, the photosensitive layer near the end of the charger is easily deteriorated by discharge. Therefore, a structure in which the film thickness at both ends of the photosensitive layer is made thicker than the center film thickness is disclosed (for example, see Patent Document 2).

JP-A-4-451 JP-A-8-137115

  However, the technique of Patent Document 2 still has a problem that the life of the photosensitive drum is shortened. If the film thickness at both ends of the photosensitive layer is simply made thicker than the film thickness at the center, the film thickness of the photosensitive drum changes abruptly in the region where the charger contacts, and a step is generated on the surface of the photosensitive drum. . In the portion where the level difference is generated, the contact between the charger and the photosensitive drum is incomplete and abnormal discharge occurs, and on the contrary, the deterioration of the photosensitive layer on the surface of the photosensitive drum is promoted.

  Here, even if the technique of Patent Document 1 is combined with the technique of Patent Document 2, deterioration due to discharge is promoted at both ends of the photosensitive layer. This is because the grooves described in Patent Document 1 are stabilized quickly by applying a liquid organic photosensitive agent, and are arranged on the outer side (near the end of the photosensitive layer) of the photosensitive layer used for image formation. ing. In other words, even in this combined configuration, the outer side of both ends of the photosensitive layer is buried in the groove, but the thickness of the photosensitive drum changes abruptly in the region where the charger contacts, and a step is left on the surface of the photosensitive drum. That's why.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a drum unit that can solve the above-mentioned problems and achieve a long life of the photosensitive drum, and an image forming apparatus equipped with the drum unit.

  A first invention for achieving the above object is a photosensitive drum in which a photosensitive layer made of an organic photosensitive agent is formed on a substrate, and a toner image is formed by charging the photosensitive layer by rotation of the photosensitive layer. A charger for contacting and charging the photosensitive layer, and an outer region of the sheet passing width in the rotational axis direction of the photosensitive drum, and an outer diameter of the substrate in the inner region of the charging width is set to the inner region of the sheet passing width. The circumferential groove formed smaller than the circumferential groove and the circumferential groove is filled with an organic photosensitive agent, and the outer diameter of the photosensitive layer in the outer region of the sheet passing width and in the inner region of the charging width is passed through this groove. And an end photosensitive layer formed substantially equal to the inner region of the paper width.

According to the first aspect of the present invention, a toner image is formed on the surface of the photosensitive drum, that is, the photosensitive layer, by the rotational driving of the photosensitive drum.
The contact charging type charger is charged in contact with the photosensitive layer of the photosensitive drum, and ozone and nitrogen oxides are not generated compared to the case of using a corona discharge type charging device. Can be achieved.

  Here, when the voltage from the charger is applied in direct contact with the photosensitive layer, the outer area of the photosensitive layer and the inner area of the charging width of the photosensitive layer are rapidly worn. Since this area faces the vicinity of the edge of the charger, the discharge range is wide. In this area, the current flowing from the charger to the photosensitive layer increases compared to the inner area of the sheet passing width, and the amount of discharge during discharge (discharge) This is because the surface deterioration of the photosensitive drum due to energy) is accelerated.

  However, according to the present invention, in the photosensitive drum, a circumferential groove is provided in the outer region of the sheet passing width and the inner region of the charging width, so that the photosensitive layer is formed thicker than the photosensitive drum. The outer diameter of the material is reduced in advance, and this circumferential groove is filled with an organic photosensitive agent. Thus, if the photosensitive layer in the area is made thicker than the photosensitive layer in the inner area of the paper width, the apparent capacitance increases, the current discharged from the charger to the photosensitive drum decreases, and the generation of discharge energy occurs. It is possible to delay the progress of surface deterioration of the photosensitive drum due to the above.

Furthermore, the outer diameter of the photosensitive layer in the region is formed to be approximately the same as the outer diameter of the photosensitive layer in the inner region of the sheet passing width, and the continuous photosensitive layer is substantially flush with no step. The discharge to the body drum is stable, and the abrasion of the photosensitive layer in the region can be reliably suppressed as compared with the case where the film thickness of the region outside the sheet passing width and the region inside the charging width is simply increased.
As a result, the life of the photosensitive drum can be extended.

According to a second aspect of the present invention, in the configuration of the first aspect, in the photosensitive drum, a latent image formed through charging on the photosensitive layer is developed with toner containing an external additive to form a toner image. The partial photosensitive layer is characterized in that an inner durable layer in which circumferential grooves are filled with an organic photosensitive agent is formed.
According to the second aspect of the invention, in addition to the action of the first aspect, even when a developing bias voltage is applied, the toner itself in the outer region of the sheet passing width and the inner region of the developing width is applied to the photosensitive layer. Does not adhere. On the other hand, the external additive itself is detached from the toner and left behind in this portion to improve the polishing performance, and the inner region of the development width is polished more than the inner region of the paper width, and the amount of wear of the photosensitive drum in this portion However, the life of the photosensitive drum is particularly shortened.

  However, the photosensitive layer in the outer region of the sheet passing width and the inner region of the developing width described above has a photosensitive layer in the inner region of the sheet passing width by the thickness of the inner durable layer in which the circumferential groove is filled with the organic photosensitive agent. Since it becomes thicker than the layer, in addition to delaying the surface deterioration of the photosensitive drum due to the generation of the discharge energy described above, it is possible to delay the progress of wear of the photosensitive layer due to polishing of the external additive.

According to a third invention, in the configuration of the first or second invention, the difference between the outer diameter of the base material having the circumferential groove and the outer diameter of the base material in the inner region of the sheet passing width is 10 × 10 ⁻⁶ m. It is the above.
According to the third aspect of the invention, in addition to the effects of the first and second aspects, the outer diameter of the substrate in the outer region of the sheet passing width and in the inner region of the charging width is the base in the inner region of the sheet passing width. The depth is 10 × 10 ⁻⁶ m or more smaller than the outer diameter of the material, and the depth of the circumferential groove is 5.0 × 10 ⁻⁶ m or more than the inner region of the sheet passing width. In other words, the photosensitive layer in which the circumferential groove is filled with an organic photosensitive agent is clearly formed to have a size larger than the degree of variation in coating, and the wear of the photosensitive layer due to discharge and external additives is further ensured. Can be suppressed.

According to a fourth invention, in the configuration of the first or second invention, the film thickness of the edge photosensitive layer is 5.0 × 10 ⁻⁶ m or more thicker than the film thickness of the photosensitive layer in the inner region of the sheet passing width. It is characterized by.
According to the fourth invention in addition to the operation of the first and second invention, the end thickness of the photosensitive layer, passage width of 5.0 × than the thickness of the photosensitive layer in the inner region 10 ^{- The} thickness is ⁶ m or more, which corresponds to the thickness of the inner durable layer in which the circumferential groove is filled with an organic photosensitive agent. As described above, since the inner durable layer is intentionally formed with a size equal to or larger than the variation in coating, the abrasion of the photosensitive layer based on the discharge and the external additive can be further reliably suppressed.

According to a fifth invention, in any one of the first to fourth inventions, the photosensitive layer is constituted by a single layer.
According to the fifth invention, in addition to the effects of the first to fourth inventions, the single photosensitive layer is affected by the variation in film thickness as compared with the case where the charge generation layer and the charge transport layer are laminated. It is difficult to receive and contributes to the long life of the photosensitive drum. On the other hand, since it is particularly easy to scrape, there is a concern that abrasion of the photosensitive layer has a great influence on the photosensitive drum. However, if the circumferential groove and the end photosensitive layer are formed, the characteristics of the photosensitive drum can be improved for a long time. It can be maintained over a period of time, and has a particularly remarkable effect.

A sixth invention is an image forming apparatus in which any one of the first to fifth drum units is mounted and the toner image is transferred to a transfer material.
According to the sixth invention, in addition to the effects of the first to fifth inventions, if the above-described drum unit is mounted, good image formation is performed over a long period of time. Contributes to improvement.

  According to the present invention, it is possible to provide a drum unit in which the outer diameter of a base material is reduced by an amount corresponding to the formation of a thick photosensitive layer, and the progress of deterioration due to discharge is delayed, and an image forming apparatus equipped with the drum unit. it can.

1 is a schematic configuration diagram of a printer according to an embodiment. It is sectional drawing of the drum unit periphery of FIG. FIG. 3 is an explanatory diagram of widths of a photosensitive drum, a charging roller, and a developing roller in FIG. 2. FIG. 3 is an external perspective view of the photosensitive drum in FIG. 2. It is arrow sectional drawing seen from the VV line | wire of FIG. It is a fragmentary sectional view of the photoconductive drum of a comparative example.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
FIG. 1 schematically shows the structure of a printer 1 capable of color printing, which is an example of an image forming apparatus. The cross section shown in the figure is seen from the left side of the printer 1. For this reason, the front surface of the printer 1 is positioned on the right side and the rear surface of the printer 1 is positioned on the left side.

As shown in the figure, a paper discharge tray 36 is provided above the apparatus main body 2 of the printer 1, and a plurality of operation keys used for various operations by the user are provided near the paper discharge tray 36. A front cover 5 on which a screen for displaying various types of information is arranged is provided.
Further, a sheet feeding cassette 4 is disposed below the apparatus main body 2, and sheets of sheets are stored in the storage unit 40 in a stacked state. As shown in the figure, a paper feed roller 46 is provided on the upper right side of the accommodating portion 40.

Then, the sheet is sent toward the upper right of the sheet feeding cassette 4 in the figure, and the sent sheet is conveyed upward along the front surface of the printer 1 inside the apparatus main body 2.
Further, the paper feed cassette 4 is configured to be able to be pulled out to the front side of the printer 1, that is, in the right direction in FIG. 1, and in this pulled out state, a new sheet can be replenished to the storage section 40. The paper can be replaced with another type of paper.

Inside the apparatus main body 2, a transport roller 10, a registration roller 14, an image forming unit 16, and a secondary transfer unit 30 are sequentially arranged on the downstream side in the paper transport direction from the paper feed cassette 4.
Four drum units 17 are arranged side by side in the image forming unit 16, and each drum unit 17 is provided with a photosensitive drum 18 (FIGS. 1 and 2). The photosensitive drum 18 is rotatably installed and is driven clockwise in FIGS. 1 and 2 by a driving motor (not shown).

The photosensitive drum 18 of the present embodiment is a single-layer OPC drum formed with a diameter of, for example, 30 mm and having an organic photosensitive layer on a cylindrical base material (OPC: Organic Photoconductor).
Specifically, this base material is composed of an aluminum base tube 60 having a thickness of 1 to 2 mm (FIGS. 4 and 5), and a liquid organic photosensitive agent is applied onto the base tube 60 to form photosensitive layers 67 and 68. Has been. The photosensitive layers 67 and 68 of this embodiment are a single layer in which the charge generation layer and the charge transport layer are integrated.

  An exposure unit 15 is provided between the photosensitive drum 18 and the paper feed cassette 4 (FIG. 1), and laser light is irradiated from the exposure unit 15 toward the photosensitive drums 18 respectively. Is done. As shown in FIGS. 1 and 2, a charger 20, a developing device 24, an intermediate transfer roller 13, and a cleaning unit 50 are provided at appropriate positions around each photosensitive drum 18.

  As shown in FIG. 2, the charger 20 is located below the drum unit 17 and has a charging roller 21 in contact with the photosensitive drum 18 and a slide provided with a brush for cleaning the surface of the charging roller 21 by polishing rubbing. A rubbing roller 22 is provided to charge the photosensitive layers 67 and 68 of the photosensitive drum 18. The charging roller 21 is made of, for example, epichlorohydrin rubber, and has a diameter of, for example, φ12 mm.

The developing device 24 is disposed on the left side of the drum unit 17 and includes a developing roller 25 that faces the photosensitive drum 18. The developing roller 25 is driven counterclockwise in the figure by a driving motor (not shown).
The reference numeral 26 in FIG. 2 is a gap regulating roller. The gap regulating rollers 26 are provided at both ends of the developing roller 25 (FIG. 3), and the gap between the developing roller 25 and the photosensitive drum 18 is set with the photosensitive drum 18.

  The image forming unit 16 includes a rubber intermediate transfer belt (transfer material) 12, and the intermediate transfer belt 12 is disposed above each photosensitive drum 18, and between the intermediate transfer belt 12 and the paper discharge tray 36. There are four toner containers 23 (FIG. 1). These toner containers 23 are arranged in the order of magenta, cyan, yellow, and black from the back side to the front side of the printer 1, and the toner container for black has the largest capacity. Is done.

The secondary transfer unit 30 includes a secondary transfer roller 31, and the secondary transfer roller 31 is configured to be able to press against the intermediate transfer belt 12 from obliquely below. The intermediate transfer belt 12 and the secondary transfer roller 31 form a nip portion for transferring a toner image onto a sheet.
A fixing unit 32, a discharge branching unit 34, and a paper discharge tray 36 are sequentially arranged on the downstream side of the secondary transfer unit 30 in the paper transport direction.

In this embodiment, a duplex printing conveyance path 38 is formed between the secondary transfer unit 30 and the manual feed tray 3. The duplex printing conveyance path 38 branches from the discharge branching portion 34 on the front side of the apparatus main body 2 and extends downward, and is connected to the upstream side of the registration roller 14.
Here, a small amount of external additives (titanium oxide, silica, alumina, etc.) are added to the toner of this embodiment. As shown in FIG. 2, the cleaning unit 50 has a housing 51 that opens toward the photosensitive drum 18 on the downstream side of the transfer position with the intermediate transfer roller 13 as viewed in the rotational direction of the photosensitive drum 18. And a cleaning blade 52 and a toner recovery unit 80 are provided at appropriate positions of the housing 51.

  Specifically, the cleaning blade 52 includes a main body of a galvanized steel plate fixed to the lower end of the housing 51, and a polyurethane rubber blade portion welded to the main body. It extends along the rotation axis. Then, the edge touches in the counter direction at a position lower than the rotational axis of the photosensitive drum 18, and scrapes residual toner and discharge products including external additives attached to the photosensitive layers 67 and 68 of the photosensitive drum 18. taking it.

Residual toner and the like scraped from the photosensitive layers 67 and 68 of the photosensitive drum 18 by the cleaning blade 52 are collected from the toner collecting unit 80.
Specifically, the toner recovery unit 80 has a screw 88 near the bottom surface of the housing 51. The screw 88 is installed on the right side of the cleaning blade 52 as viewed in FIG. 2, extends along the rotational axis direction of the photosensitive drum 18, and has a tip connected to a drive motor (not shown). When the drive motor is driven, residual toner and the like in the housing 51 are collected in a collection container via the screw 88.

By the way, in the drum unit 17 of the present embodiment, when the rotation axes are arranged, the widths of the developing roller 25, the charging roller 21, the photosensitive drum 18, and the like are not the same.
Specifically, as shown in FIG. 3 explaining the relationship between the widths of these components, the substrate width of the photosensitive drum 18 shown by a broken line in FIG. 3 is larger than the charging width shown by the solid line in FIG. Is also widely set. Note that the width of the transfer belt 12 described above is set between the base material width of the photosensitive drum 18 and the charging width, or equal to the charging width.

Further, this charging width is set wider or equal to the developing width shown by the two-dot chain line in FIG. This is because if the charge width is narrower than the development width, the toner continues to adhere to the outer region of the charge width.
Further, the development width is always set wider than the sheet passing width indicated by the one-dot chain line in FIG. This is because a toner image can be formed on both right and left ends of the sheet.

  That is, the photosensitive layer 67 of the photosensitive drum 18 corresponds to an inner region of the sheet passing width as viewed in the rotation axis direction of the photosensitive drum 18 (central photosensitive layer). On the other hand, the photosensitive layer 68 of the photosensitive drum 18 corresponds to an outer region of the sheet passing width as viewed in the rotation axis direction of the photosensitive drum 18 (edge photosensitive layer), and also contacts the sheet on the transfer surface of the transfer belt 12. Therefore, the image is not formed.

  That is, the latter photosensitive layer 68 is an outer region of the sheet passing width indicated by a one-dot chain line in FIG. 3, and an inner region of the charging width indicated by a solid line in FIG. Corresponds to the non-image area 76 indicated by the hatched line, and faces the vicinity of the edge of the charging roller 21, so that the current flowing from the charging roller 21 to the photosensitive layer 68 increases as compared to the photosensitive layer 67.

Further, the toner containing the external additive as in this embodiment is directed to the inner region of the developing width indicated by the two-dot chain line in FIG. 3 in the non-image region 76 by the application of the developing bias voltage.
The toner itself does not adhere to the photosensitive layer 68 of the photosensitive drum 18 and returns to the developing unit 24. This is because the non-image area 76 corresponds to the inner area of the charging width.

  On the other hand, the external additive itself is detached from the toner and left in the inward portion of the non-image area 76, and then only this external additive is transferred from the photosensitive layer 68 of the photosensitive drum 18 to the transfer surface of the transfer belt 12. Then, the inward portion of the non-image area 76 of the photosensitive drum 18 that comes into contact next time is polished with the external additive. The inward portion of the non-image area 76 is formed on all the photosensitive drums 18 for magenta, cyan, yellow, and black.

Therefore, the outer diameter of the raw tube 60 of the photosensitive drum 18 is partially reduced so that the film thickness of the photosensitive layer 68 corresponding to the non-image area 76 is larger than the film thickness of the photosensitive layer 67.
Specifically, one non-image region 76 among the non-image regions 76 and 76 shown in FIGS. 3 and 4 will be described. As shown in FIG. 5 as seen from the line VV in FIG. The outer diameter of the raw tube 60 corresponding to the region 76 is formed to be, for example, 10 μm (10 × 10 ⁻⁶ m) or more smaller than the outer diameter of the raw tube 60 corresponding to the inner region of the sheet passing width. A constricted groove (circumferential groove) 62 is provided in the element tube 60 corresponding to 76.

The constriction groove 62 has a depth of 5.0 μm (5.0 × 10 ⁻⁶ m) or more, a bottom 63 formed over the entire circumference of the photosensitive drum 18, and rotation of the photosensitive drum 18. It has the expansion slope part 64 each connected with the bottom part 63 in an axial direction. Then, when the liquid organic photosensitive agent is applied to the base tube 60, first, the inner durable layer 70 in which the constricted groove 62 is filled with the organic photosensitive agent is formed, and the film thickness becomes 5.0 μm or more and the inner side of the sheet passing width. It is substantially flush with the raw tube 60 corresponding to the region. In addition, since the expanded slope portion 64 extends toward the outer diameter of the raw tube 60, it is difficult for air to enter the inner durable layer 70 even if an organic photosensitive agent is applied to the raw tube 60.

  Subsequently, after the inner durable layer 70 is dried, when the same liquid organic photosensitive agent is further applied to the base tube 60, a photosensitive layer 68 integral with the inner durable layer 70 is formed outside the inner durable layer 70. Further, a photosensitive layer 67 is formed on the outside of the tube 60 corresponding to the inner region of the sheet passing width, and the outer diameter of the photosensitive layer 68 and the outer diameter of the photosensitive layer 67 are substantially equal. The line 68 is substantially flush with no step.

  Returning to FIG. 1 again, when the printer 1 equipped with the drum unit 17 performs printing, the paper is separated from the paper feed cassette 4 by the paper feed roller 46 and sent out one by one. The sent paper reaches the registration roller 14. The registration roller 14 corrects the oblique feeding of the paper and measures the image transfer timing with the toner image formed by the image forming unit 16, while feeding the paper to the secondary transfer unit 30 at a predetermined paper feed timing. Send it out.

On the other hand, a controller (not shown) is configured to be able to receive image data to be printed from the outside. This image data is data in which various images such as characters, codes, figures, symbols, diagrams, and patterns are converted into data. Based on this data, the controller controls light irradiation and the like.
Specifically, the eraser lamp 19 is turned on for each photosensitive drum 18 (FIG. 2), and then the charger 20 charges the photosensitive layers 67 and 68 of the photosensitive drum 18, respectively. Subsequently, when the exposure unit 15 irradiates the photosensitive layers 67 and 68 of the photosensitive drums 18 with laser beams, electrostatic latent images are formed on the photosensitive layers 67 and 68 of the photosensitive drums 18, respectively. A toner image of each color is formed from the image.

Each toner image is secondarily transferred onto a sheet by the secondary transfer unit 30. The toner remaining on the photosensitive layers 67 and 68 of the photosensitive drum 18 is removed by the cleaning unit 50.
Subsequently, the sheet is fed toward the fixing unit 32 with an unfixed toner image carried thereon, and is heated and pressed by the fixing unit 32 to fix the toner image. Thereafter, the sheet sent from the fixing unit 32 is discharged to the discharge tray 36 via the discharge roller 35 and stacked in the height direction.

  When double-sided printing is performed on this single-sided printing, the conveyance direction of the paper discharged from the fixing unit 32 is switched by the discharge branching unit 34. That is, the sheet printed on one side is pulled back into the apparatus main body 2 and conveyed to the duplex printing unit 38. Subsequently, the sheet is sent toward the upstream side of the registration roller 14 and is sent again toward the secondary transfer unit 30. As a result, the toner image is transferred to the side of the paper that has not been printed.

As described above, according to this embodiment, a toner image obtained by developing the latent image with toner is formed on the surface of the photosensitive drum 18, that is, on the photosensitive layers 67 and 68, by the rotational driving of the photosensitive drum 18. The toner image is transferred to the transfer belt 12.
The charger 20 is in direct contact with the photosensitive layers 67 and 68 to be charged, and ozone and nitrogen oxides are not generated as compared with the case of using a corona discharge type charger. Therefore, the image quality is improved. be able to.

  Here, the tube 60 corresponding to the photosensitive layer 68 is provided with a constriction groove 62. The photosensitive layer 68 has a sheet passing width corresponding to the thickness of the inner durable layer 70 in which the constriction groove 62 is filled with an organic photosensitive agent. Since it is thicker than the photosensitive layer 67 in the inner region, the surface deterioration of the photosensitive drum 18 due to the generation of discharge energy can be delayed, and the progress of wear of the photosensitive layer 68 due to the polishing of the external additive can also be delayed.

  This point will be described in detail. First, as shown in FIG. 6A, when the photosensitive layers 67 and 98 having the same film thickness are formed on the substantially flat tube 60, the voltage from the charger 20 is changed to the photosensitive layers 67 and 98. When applied in direct contact with 98, the photosensitive layer 98 corresponding to the non-image area 76 in the photosensitive layers 67 and 98 progresses quickly. Since the photosensitive layer 98 faces the edge of the charging roller 21, the discharge range is wide. In the photosensitive layer 98, the inflow current from the charging roller 21 increases as compared with the photosensitive layer 67, and the photosensitive drum 18 due to the discharge energy. This is because the surface deterioration of the photosensitive member 18 is accelerated, and this shortens the life of the photosensitive drum 18.

Further, in the photosensitive layer 98 that has been worn out due to surface degradation, a leak that passes through the photosensitive layer 98 occurs without being able to withstand the voltage from the charger 20, and the current escapes outwardly to charge the photosensitive layer 67. Unusual images such as horizontal streaks are invited.
Further, even when a developing bias voltage is applied, the toner in the inner region of the developing width in the non-image region 76 does not adhere to the photosensitive layer 98. On the other hand, the external additive itself is detached from the toner and left in a part of the non-image area 76, and only this external additive is transferred from the photosensitive layer 98 to the transfer surface of the transfer belt 12. This phenomenon can also be seen from the appearance of a white band along the circumferential direction on the transfer surface. The portion appearing in the white band has high polishing performance, and a portion of the non-image region 76 is polished more than the inner region of the paper width, and the amount of wear of the photosensitive drum 18 in this portion is the photosensitive drum 18. Especially shortening the service life.

  However, according to the present embodiment, as shown in FIG. 5, the constricted groove 62 is provided in the non-image area 76, and the outer diameter of the element tube 60 is set in advance so as to increase the thickness of the photosensitive layer 68. The constricted groove 62 is filled with an organic photosensitive agent. Thus, if the photosensitive layer 68 in the non-image area 76 is made thicker than the photosensitive layer 67 in the inner area of the paper width, the apparent capacitance increases, and the current discharged from the charging roller 21 to the photosensitive drum 18 is also small. Therefore, as compared with the example of FIG. 6A, the progress of the surface deterioration of the photosensitive drum 18 due to the generation of discharge energy can be delayed, and the leakage through the photosensitive layer 68 can be reliably suppressed.

In addition, the thickness of the inner durable layer 70 in which the constricted groove 62 is filled with the organic photosensitive agent can also delay the progress of wear of the photosensitive layer 68 due to the polishing of the external additive.
Further, as shown in FIG. 6B, when the photosensitive layers 67 and 108 having a difference in film thickness are formed on the substantially flat tube 60, more specifically, the film of the photosensitive layer 108 at both ends. When the thickness is made thicker than the photosensitive layer 67 in the inner region of the sheet passing width by the thickness of the layer 110 protruding outward, a large step is generated in the photosensitive layers 67 and 108, and the photosensitive layer 108 in contact with the charging roller 21. The photosensitive layer 67 is not in contact with the photosensitive drum 67, and abnormal discharge occurs in the portion where the contact between the charging roller 21 and the photosensitive drum 18 is incomplete. Therefore, simply increasing the film thickness at both ends of the photosensitive layer 18 Surface degradation is encouraged.

However, according to the present embodiment, as shown in FIG. 5, the outer diameter of the photosensitive layer 68 corresponding to the non-image area 76 is formed substantially equal to the outer diameter of the photosensitive layer 67, and the continuous photosensitive layers 67 and 68. Since the currents flowing into the photosensitive layers 67 and 68 are substantially equal, the non-image area 76 as shown in FIG. 6B is simply thickened. In comparison, the wear of the photosensitive layer 68 in the non-image area 76 can be reliably suppressed.
As a result, the life of the photosensitive drum 18 can be extended.

  Further, the outer diameter of the raw tube 60 in the non-image region 76 is 10 μm or more smaller than the outer diameter of the raw tube 60 in the inner region of the sheet passing width, and the depth of the constricted groove 62 is smaller than the inner region of the sheet passing width. The size is deeper than 5.0 μm and less than the thickness of the raw tube 60. That is, the inner durable layer 70 in which the constricted groove 62 is filled with the organic photosensitive agent is clearly formed to have a size larger than the degree of variation in the application of the organic photosensitive agent, and this photosensitive layer 68 based on the discharge and the external additive. Can be more reliably suppressed.

  Further, the thickness of the photosensitive layer 68 is 5.0 μm or more larger than the thickness of the photosensitive layer 67, and this corresponds to the thickness of the inner durable layer 70 that fills the constricted groove 62 with the organic photosensitive agent. As described above, since the inner durable layer 70 is intentionally formed to have a size larger than the variation in coating, the abrasion of the photosensitive layer 68 based on the discharge and the external additive can be further reliably suppressed. .

  Furthermore, the single photosensitive layers 67 and 68 are less susceptible to film thickness fluctuations compared to the case where, for example, an undercoat layer, a charge generation layer, and a charge transport layer are laminated on the raw tube 60 in this order. This contributes to extending the life of the drum 18. On the other hand, since it is particularly easy to scrape, there is a concern that the abrasion of the photosensitive layers 67 and 68 has a great influence on the photosensitive drum 18. However, if the constricted groove 62 and the photosensitive layer 68 are formed, The characteristics can be maintained over a long period of time, and there is a particularly remarkable effect.

Furthermore, if the above-described drum unit 17 is installed, good image formation is performed over a long period of time, which contributes to improving the reliability of the printer 1.
The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims.
For example, in the above embodiment, the toner image is transferred to the intermediate transfer belt above the photosensitive drum, but may be transferred to the belt below the photosensitive drum.

In the above-described embodiment, the printer 1 using the intermediate transfer belt is described. However, the present invention can also be applied to a case where the toner image on the photosensitive drum 18 is directly transferred to a sheet, and the transfer material of the present invention may be a sheet.
Further, although the photosensitive layers 67 and 68 in the above-described embodiments are composed of a single layer, the present invention can also be applied to a photosensitive drum in which a charge generation layer and a charge transport layer are laminated.

Furthermore, in this embodiment, an example in which the image forming apparatus is embodied in a printer is shown. However, the image forming apparatus of the present invention is naturally applicable to a multifunction machine, a copier, a facsimile machine, and the like.
In any of these cases, similarly to the above, there is an effect that the life of the photosensitive drum can be extended.

1 Printer (image forming device)
12 Intermediate transfer belt (transfer material)
17 Drum unit 18 Photosensitive drum 20 Charger 60 Element tube (base material)
62 Constriction groove (circumferential groove)
67 Photosensitive layer 68 Photosensitive layer (edge photosensitive layer)
70 inner durable layer 76 non-image area

Claims (6)

A photosensitive drum formed of an organic photosensitive agent on a substrate, and a toner image is formed by charging the photosensitive layer by rotation of the photosensitive drum;
A charger that contacts and charges the photosensitive layer;
A circumferential groove formed in the outer region of the sheet passing width as viewed in the rotation axis direction of the photosensitive drum and having the outer diameter of the base material in the inner region of the charging width smaller than the inner region of the sheet passing width. When,
The circumferential groove was filled with the organic photosensitive agent, and the outer diameter of the photosensitive layer in the outer region of the sheet passing width and the inner region of the charging width was made substantially equal to the inner region of the sheet passing width. A drum unit comprising an end photosensitive layer. The drum unit according to claim 1,
In the photosensitive drum, a latent image formed through charging on the photosensitive layer is developed with toner containing an external additive to form a toner image.
The drum unit, wherein the end photosensitive layer is formed with an inner durable layer in which the circumferential groove is filled with the organic photosensitive agent. The drum unit according to claim 1 or 2,
The drum unit, wherein a difference between an outer diameter of the base material having the circumferential groove and an outer diameter of the base material in an inner region of the sheet passing width is 10 × 10 ⁻⁶ m or more. The drum unit according to claim 1 or 2,
The drum unit, wherein the film thickness of the edge photosensitive layer is 5.0 × 10 ⁻⁶ m or more thicker than the film thickness of the photosensitive layer in the inner region of the sheet passing width. The drum unit according to any one of claims 1 to 4,
The drum unit, wherein the photosensitive layer is formed of a single layer.   An image forming apparatus comprising the drum unit according to claim 1 and transferring the toner image onto a transfer material.

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