JP2005077539A - Transfer roller and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a transfer roller which is used in an image forming apparatus using an electrophotographic process and is made inexpensive and easily prevents a transfer memory phenomenon. <P>SOLUTION: The transfer roller 14 is equipped with a roller part 22 abutting on a photoreceptor drum 11, and a core shaft body 21 inserted along the center shaft of the roller part. The core shaft body has a large-diameter part 21a extended in a longitudinal direction and a small-diameter parts 21b integrally formed at both ends of the large-diameter part, extended in the longitudinal direction and having a smaller outside diameter than the large-diameter part. A hollow part, in which the core shaft body is inserted and which is extended in the longitudinal direction, is formed at the roller part, and the diameter of the hollow part is smaller than the outside diameter of the small-diameter part. Thus, a tapered surface 22a inclined to the inside in a radial direction is defined at the end of the conductive roller part in the case of inserting the conductive core shaft body in the hollow part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is used to transfer a toner image formed on an image carrier in contact with an image carrier such as a photosensitive drum to a recording sheet in an image forming apparatus such as a copying machine, a printer, or a facsimile machine. The present invention relates to a transfer roller and a manufacturing method thereof.

  In general, in an image forming apparatus, after the surface of a photosensitive drum as an image carrier is uniformly charged, the photosensitive drum is exposed in accordance with image data to form an electrostatic latent image on the photosensitive drum. . Thereafter, the electrostatic latent image is developed with toner to form a toner image, and the toner image formed on the photosensitive drum is transferred onto a recording sheet by a transfer roller. Then, the recording paper is conveyed to the fixing unit, and the toner image is fixed on the recording paper.

  During the above transfer, a bias current is applied to the transfer roller, and the toner image on the photosensitive drum is transferred to the recording paper. When the photosensitive drum and the transfer roller are in direct contact, so-called transfer is performed. This may cause a memory phenomenon, and this transfer memory phenomenon may cause a serious defect in the image (for example, a charging potential may decrease due to the transfer memory phenomenon, and so-called fogging may occur).

  For example, when an A4 paper (210 mm × 297 mm) is used for vertical feeding in an image forming apparatus capable of longitudinal feeding of letter size paper (216 mm × 279 mm), the width of the transfer roller in the paper transport direction is the width of the letter size paper (216 mm). ), The portion where the transfer roller is in direct contact with the photosensitive drum is very small at 3 mm at both ends of the transfer roller, and the contact area (non-image forming area) is an area where the recording paper exists (image forming area). Since the resistance value is lower than the resistance value of), the current is concentrated in the contact region, and the transfer memory phenomenon appears remarkably. Then, if image formation is performed using letter-size paper immediately after using A4-size paper, there is a risk that tension memory will occur. When the photosensitive member is charged in the reverse direction by the charging roller, particularly in the case of a positively charged single layer organic photosensitive member, it is difficult to remove the charged charge by static elimination, and therefore, a transfer memory phenomenon occurs during charging. The surface potential of the part is lower than usual. As a result, fog occurs corresponding to the portion of the photoreceptor where the transfer memory phenomenon has occurred, or a change in image density occurs.

  In order to prevent such a problem, a small-diameter portion that does not contact the surface of the photosensitive drum over a predetermined width is formed at each of both ends of the roller portion, and an annular groove orthogonal to the axis is formed on the peripheral surface portion of the small-diameter portion. It is known that the width of the small-diameter portion is set so that the width of the region other than the small-diameter portion at the center of the roller portion is larger by a predetermined amount than the width of the effective image region. Is increased, the distance (creeping distance) of the path from the exposed end of the metal shaft to the end of the contact portion along the surface of the roller portion is increased, and leakage due to creeping discharge is prevented (see Patent Document 1).

  Furthermore, in order to prevent direct contact between the photosensitive drum and the transfer roller, there is a type in which the diameter of the end portion that directly contacts the photosensitive drum can be changed when the recording paper is sandwiched. A plurality of open / close rods that can rotate in the radial direction are provided at both ends of the roller, and the ends of the open / close rods are free ends. When the open / close wire of the mechanism is connected to the drive plate via the link rod inside the transfer roller and the open / close wire connected to the torsion prevention link inserted into the drive plate is wound around the pulley, the drive plate and open / close ring move. Then, the open / close bar is opened, and the diameter of the end portion of the transfer roller is changed according to the paper size (see Patent Document 2).

  In addition, a groove in the rotation direction of the transfer roller is provided on the end surface portion of the semiconductive layer of the transfer roller, and a leak path from the core metal is lengthened in the outer portion of the groove close to the photosensitive drum, so that the transfer roller There is a battery whose surface voltage is small to prevent discharge in the air with the photosensitive drum (see Patent Document 3).

JP-A-6-51656 (paragraph (0007) to paragraph (0012), FIG. 1) JP-A-8-54793 (paragraph (0019) to paragraph (0022), FIGS. 1 and 7) Japanese Unexamined Patent Publication No. 2000-39883 (paragraph (0006) to paragraph (0007), FIG. 1)

  By the way, in general, the transfer roller has a metal shaft (rotary shaft) and a rubber roller portion into which the shaft body is inserted. If a small-diameter portion that does not come into contact with each other is formed and an annular groove perpendicular to the axis is formed on the peripheral surface portion of this small-diameter portion, there is a problem that the molding process of the roller portion becomes complicated and the cost increases.

  Also, as in Patent Document 2, when the diameter of the transfer roller end is changed according to the paper size, the mechanism and control for that change are complicated, which also increases the cost. .

  On the other hand, in Patent Document 3, there is a problem in that the forming process of the roller part is complicated and the cost is increased due to the formation of the groove extending in the axial direction in the semiconductive layer (conductive rubber roller part). is there. For example, a complicated mold must be prepared when forming the roller portion.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a transfer roller that is inexpensive and can easily prevent a transfer memory phenomenon, and a method for manufacturing the transfer roller, in view of the problems of the prior art.

  Therefore, in order to solve such a problem, the present invention provides a transfer roller used for transferring the toner image as a transfer image onto a transfer material in contact with an image carrier on which a toner image is formed. A roller portion formed with a hollow portion that is in contact with the body and extending in the longitudinal direction; and a core shaft body that extends along the hollow portion of the roller portion and supports the roller portion, the core shaft body including the roller An inclined surface defining portion for defining an inclined surface inclined inward in the radial direction is formed at the longitudinal end of the portion.

  In the present invention, the core shaft body includes a large-diameter portion extending in the longitudinal direction, and a small-diameter portion formed at both ends of the large-diameter portion and having a smaller outer diameter than the large-diameter portion extending in the longitudinal direction. The diameter of the hollow part formed in the roller part is smaller than the outer diameter of the small diameter part, and the slope defining part is defined by the step part defined by the large diameter part and the small diameter part.

  According to the present invention, in the transfer roller used when contacting the image carrier on which the toner image is formed and transferring the toner image to the transfer material as a transfer image, the roller contacting the image carrier And a core shaft body that is inserted along the central axis of the roller section and supports the roller section, the core shaft body including a large-diameter portion extending in the longitudinal direction, and both ends of the large-diameter portion. A small-diameter portion that extends in the longitudinal direction and has a smaller outer diameter than the large-diameter portion, and a hollow portion that extends in the longitudinal direction into which the core shaft body is inserted is formed in the roller portion, The transfer roller is characterized in that the diameter of the hollow portion is larger than the outer diameter of the small diameter portion and smaller than the diameter of the large diameter portion.

  Further, according to the present invention, in a manufacturing method for manufacturing a transfer roller that is used to transfer a toner image as a transfer image onto a transfer material in contact with an image carrier on which a toner image is formed, a hollow extending in the longitudinal direction is used. A first step of forming a roller member having a portion, a large diameter portion extending in the longitudinal direction, and a small diameter portion formed at both ends of the large diameter portion and extending in the longitudinal direction and having an outer diameter smaller than the diameter of the hollow portion A second step of forming a core shaft body, and a third step of attaching a spacer having a diameter smaller than the diameter of the hollow portion to at least one of the small diameter portions; and A transfer roller comprising: a fourth step of inserting from one end side of the hollow portion until a part of the spacer protrudes from the other end side of the hollow portion; and a fifth step of removing the spacer. Production method can be obtained.

  And in this invention, the outer diameter of the spacer main body part except the front-end | tip part of the said spacer is the same as the outer diameter of the said large diameter part, and when performing the said 4th step, a part of said spacer main body part Is located in the hollow portion, and after the fourth step, the fifth step is preferably performed after the sixth step of polishing the outer peripheral surface of the roller portion.

  As described above, the transfer roller according to the present invention has an inclined surface that defines an inclined surface that is inclined radially inward at the longitudinal end portion of the roller portion when the core shaft body is inserted into the roller portion. Since the defining portion is formed, the phenomenon that current is concentrated on the end of the transfer roller can be prevented with a simple configuration, and as a result, the transfer memory phenomenon is prevented and image defects do not occur. effective.

  In the present invention, the core shaft body has a large-diameter portion extending in the longitudinal direction, and a small-diameter portion integrally formed at both ends of the large-diameter portion and extending in the longitudinal direction and having an outer diameter smaller than that of the large-diameter portion. Since the hollow portion extending in the longitudinal direction in which the core shaft body is inserted is formed and the diameter of the hollow portion is made smaller than the outer diameter of the small diameter portion, the roller can be obtained by inserting the core shaft body into the hollow portion of the roller portion. An inclined surface (tapered surface) inclined radially inward is formed at the end portion in the longitudinal direction of the portion, so that an inclined surface can be formed extremely easily at the end portion of the roller portion. Further, if the diameter of the hollow portion is larger than the outer diameter of the small diameter portion and smaller than the diameter of the large diameter portion, the core shaft body does not contact the roller portion in the small diameter portion and protrudes from the paper. It is possible to suppress the transfer memory phenomenon by concentrating current at the end of the roller portion.

  Furthermore, in the present invention, since the spacer having the tip portion smaller than the hollow portion diameter of the roller portion is mounted on the small diameter portion and the spacer is inserted from one end side of the hollow portion, the core shaft is very easily There is an effect that the body can be inserted into the roller portion.

  Also, in the present invention, when the outer diameter of the spacer main body excluding the tip of the spacer is the same as the outer diameter of the large diameter portion of the core shaft body, when the core shaft body is inserted into the roller portion, Since the outer peripheral surface of the roller portion is polished by positioning the portion in the hollow portion, the outer peripheral surface of the roller portion is defined as a cylindrical outer peripheral surface until the spacer is pulled out, and the polishing can be performed very easily. There is.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  First, an example of an image forming apparatus using a transfer roller according to the present invention will be described with reference to FIG. In the illustrated image forming apparatus, a charger 12, a developing device 13, a transfer roller 14, a cleaning roller 15, and a static eliminator 18 are arranged around the photosensitive drum 11 along the rotation direction of the photosensitive drum 11. When image formation is performed, the surface of the photosensitive drum 11 is uniformly charged by the charger 12, and then the surface of the photosensitive drum 11 is irradiated with laser light 16 according to image data. As a result of exposure, an electrostatic latent image is formed on the photosensitive drum 11.

  Thereafter, the electrostatic latent image on the photosensitive drum 11 is developed by the developing device 13 into a toner image, and the toner image formed on the photosensitive drum 11 is transferred to a transfer material (for example, recording paper (for example, recording paper ( Hereinafter simply referred to as paper))) transferred to P. At this time, a current flows between the photosensitive drum 11 and the transfer roller 14 due to the movement of the charged toner. This current is controlled to a predetermined value (constant current control), and the amount of toner adhering to the paper P is controlled. Stabilize.

  After the transfer, the toner remaining on the photosensitive drum 11 is collected by the cleaning roller 15, and the residual potential on the photosensitive drum 11 is erased by the static eliminator 18, and the surface of the photosensitive drum 11 is again recharged by the charger 12. The process of uniformly charging is repeated. On the other hand, the paper P is sent to the fixing unit 17 where the toner image on the paper P is fixed by the fixing unit 17 and then discharged to a paper discharge tray (not shown) through a paper discharge path. .

  By the way, because the paper P acts as an electric resistance, the current (the non-image forming area) where the paper P does not exist becomes easier to flow than the portion (image forming area) where the paper P exists. May concentrate on a non-image forming region having a low resistance value, and the transfer memory phenomenon described above may occur, resulting in an image defect.

  In order to suppress such a transfer memory phenomenon, the transfer roller 14 shown in FIG. 2 is used here. Referring to FIGS. 2A and 2B, the illustrated transfer roller 14 includes a metal shaft (core shaft body: hereinafter simply referred to as a shaft) 21. The shaft 21 includes a large-diameter portion 21a. The large-diameter portion 21a has a small-diameter portion 21b formed integrally with the large-diameter portion 21a coaxially with the central axis of the large-diameter portion 21a at both ends. The outer diameter of 0 mm and the small diameter portion 21b is 5.0 mm. The shaft 21 is inserted along the central axis of a rubber roller portion (hereinafter simply referred to as a roller portion) 22, and the roller portion 22 is supported by the shaft 21.

  The roller part 22 is a tube-like body in which a hollow part 221 extending along the central axis is formed, and the inner diameter (4.5 mm) of the roller part 22 is smaller than the outer diameter of the small diameter part 21b. The shaft 21 is inserted into the hollow portion 221 of the roller portion 22. As shown in FIG. 2, the large-diameter portion 21a of the shaft 21 is inserted into the roller portion 22, and the small-diameter portions 21b located at both ends of the large-diameter portion 21a are part of them (part on the large-diameter portion 21a side). ) Is located in the roller portion 22, and the remaining portion of the small diameter portion 21 b protrudes from the roller portion 22.

  As described above, the outer diameter of the small diameter portion 21b is smaller than the inner diameter of the roller portion 22 (naturally, the outer diameter of the small diameter portion 21b is smaller than the outer diameter of the large diameter portion 21a). In addition, when the shaft 21 is inserted into the roller portion 22, as shown in FIG. 2, the roller portion 22 has an inclined circumferential surface (inclined radially inward) starting from a step portion 21 c between the small diameter portion 21 b and the large diameter portion 21 a. Tapered surface) 22a is formed. That is, just by inserting the shaft 21 into the roller portion 22, tapered surfaces 22 a that are inclined inward in the radial direction are formed at both ends of the roller portion 22 toward the outer side in the axial direction.

  At this time, as shown in the figure, a space 21d is formed in the vicinity of the stepped portion 21c, and the roller portion 22 and the shaft 21 are not in direct contact with each other by the space 21d.

  As shown in FIG. 2B, the length in the direction perpendicular to the sheet conveyance direction of the sheet having the maximum length in the direction perpendicular to the sheet conveyance direction (letter size in this embodiment) is the axial length of the roller portion 22. As a result, the photosensitive drum 11 (FIG. 1) is not in contact with the roller portion 22 at both ends thereof. In the example shown in the drawing, a length (indicated by a symbol L in FIG. 2) defined between the starting points of the tapered surfaces 22a formed at both ends of the roller portion 22 and a sheet that is a target for preventing the generation of the transfer memory (this embodiment) In the example, the length in the direction perpendicular to the sheet conveyance direction (A4 size) is set to be the same.

  In this way, even when image formation is performed using A4 size paper, it is possible to prevent the roller portion 22 protruding from both ends of the paper from directly contacting the surface of the photosensitive member. The concentration of current is suppressed, and the transfer memory phenomenon can be prevented.

Here, the formation (manufacturing) of the transfer roller 14 will be described. First, the roller portion 22 is manufactured by a normal method to obtain a conductive foam rubber tube (roller portion) (here, for example, The inner diameter of the rubber tube is 4.5 mm and the outer diameter is 16.0 mm). The volume specific resistance value of the conductive foam rubber tube is preferably 10 ⁵ Ω · cm to 10 ¹⁰ Ω · cm, and in the above example, the conductive foam having a volume resistance value of 2.6 × 10 ⁷ Ω · cm. A rubber tube was used. If the volume resistivity is 10 ⁵ Ω · cm or less, the resistance value is too low, and thus the above-mentioned effect cannot be obtained. If the volume resistivity is 10 ¹⁰ Ω · cm or more, the transfer current is Since it becomes difficult to flow through the roller portion, there is a possibility that transfer defects are likely to occur. The volume resistance value is a value measured at an applied voltage of 1000 V in the volume resistivity test described in JIS K6911.

  Next, a shaft member is prepared, and both end sides of the shaft member are ground to form the small diameter portion 21b as described above (the remaining portion excluding both end sides becomes the large diameter portion 21a). Obtained. In the illustrated example, the outer diameter 21a of the large diameter portion is 6.0 mm, and the outer diameter of the small diameter portion 21b is 5.0 mm. The rubber tube has an inner diameter of 4.5 mm and an outer diameter of 16.0 mm.

  And the above-mentioned shaft 21 was inserted into the central hole (hollow part) of the conductive foam rubber tube (in addition, when inserting the shaft 21, the shaft 21 is made conductive while the conductive foam tube is inflated by air. Inserted into foam rubber tube). Thereafter, the surface (outer peripheral surface) of the conductive foamed rubber tube (roller portion) 22 was polished to obtain a transfer roller 14. As a result, as described above, tapered surfaces 22 a that are inclined inward in the radial direction are formed at both ends of the roller portion 22. In the illustrated example, the distance L between the starting points of the tapered surface 22a is 210 mm, and the total length of the roller portion 22 is 216 mm.

The transfer roller 14 described above was installed in the image forming apparatus described with reference to FIG. 1 to perform image formation. In the image formation, the charging potential of the photosensitive drum 11 was 475 volts (V), the wavelength of the laser beam was 780 nm, and the laser exposure amount was 0.9 μJ / cm ² . Further, the developing bias was a direct current (DC) + alternating current (AC) rectangular wave, a DC voltage of 350 V, an AC frequency of 2.4 kHz, an AC amplitude of 1.6 kV, and a duty ratio of 50 percent. Further, the transfer forward bias was set to -10 μA constant current control, and the transfer reverse bias was set to 550 V constant voltage control (transfer bias is applied to the shaft 21). In cleaning, the linear pressure was set to 15 g / cm, the neutralization using an LED was used for slow power, the LED wavelength was 630 nm, and the LED exposure amount was 4.0 μJ / cm ² .

  In this way, when the toner image on the photosensitive drum 11 was transferred to the paper P and an image was formed, no image defect occurred and good transfer performance was obtained. As described above, if the shaft 21 having the small diameter portion 21b at both ends of the large diameter portion 21a is inserted into the roller portion 22 having a hollow portion having a diameter smaller than the outer diameter of the small diameter portion 21b, both end portions of the roller portion 22 are obtained. As a result of forming the tapered surface inclined radially inward, the manufacturing cost can be reduced and the phenomenon of current concentration at the end of the roller portion 22 can be prevented. That is, the current does not concentrate in the non-image forming area, and the transfer memory phenomenon can be satisfactorily prevented.

  In the first embodiment, the small diameter portion 21b may be formed at both ends of the shaft 21, and the roller portion 22 does not need to be processed at all. In addition, when the small diameter portion 21b is formed on the shaft 21, both end portions of the shaft 21 can be cut using a cutting machine or the like to form the small diameter portion 21b, and the transfer roller itself can be easily manufactured. In this way, it is possible to obtain a transfer roller that is inexpensive and can satisfactorily prevent the transfer memory phenomenon.

  In addition, in Example 1, although the example using the shaft 21 by which the level | step-difference part 21c was prescribed | regulated by the small diameter part 21b and the large diameter part 21a was demonstrated, the small diameter part 21b and the large diameter part 21a incline in radial direction inner side. You may make it form integrally in a taper part. Further, the boundary between the large diameter portion 21a and the small diameter portion 21b may be formed in an arc shape so that the tapered portion 22a formed at both ends of the roller portion 22 and the shaft 21 do not directly contact each other. In any case, when the shaft 21 is inserted into the hollow portion of the roller portion 22, both ends of the shaft 21 are formed so that tapered surfaces inclined radially inward are defined at both ends of the roller portion 22. (That is, a tapered surface defining portion that defines a tapered surface at both ends of the roller portion 22 when the shaft 21 is inserted into the roller portion 22 may be formed at both ends of the shaft 21.) Even if the tapered portion as in the present invention is formed, only the width of the transfer nip formed between the photosensitive drum 11 and the roller portion 22 is reduced, and the transfer performance is not greatly affected. Since 3 mm from the end of the sheet is outside the image forming area, there is no problem even if letter size paper is used in this respect. Since the transfer nip is reduced in this way, even if the photosensitive drum 11 and the roller portion 22 are in direct contact with each other, an excessive current does not flow, so that the generation of a transfer memory can be prevented.

  Here, with reference to FIG. 3, another example of manufacturing the transfer roller 14 by inserting the shaft 21 into the roller portion 22 will be described. As shown in FIG. 3A, a cylindrical spacer 31 is attached to the tip (insertion side) of the shaft 21, and this spacer 31 has an inner diameter slightly larger than the outer diameter of the small diameter portion 21b. An insertion space 31a is formed, and one end side (the right end in FIG. 3C) of the insertion space 31a is open. Furthermore, the axial length of the insertion space 31a is the same as the axial length of the small diameter portion 21b, and one of the small diameter portions 21b is inserted into the insertion space 31a.

  A tapered portion 31 b that is inclined radially inward is formed at the distal end portion of the spacer 31, and the distal end diameter of the spacer 31 is smaller than the inner diameter of the roller portion 22. In the illustrated example, the tip of the spacer 31 has a truncated cone shape. In the spacer 31, the outer diameter of the portion excluding the tapered portion 31 b (hereinafter referred to as the spacer main body portion 31 c) is the same as the outer diameter of the large diameter portion 21 a of the shaft 21.

  Now, as shown in FIG. 3A, the shaft 21 is inserted into the hollow portion of the roller portion 22 from the tip end side of the spacer 31 as shown by a thick arrow from one end side of the roller portion 22. As described above, the distal end diameter of the spacer 31 is smaller than the inner diameter of the roller portion 22, and the tapered portion 31 b is formed at the distal end portion of the spacer 31, so that the spacer 31 can be easily formed into the hollow portion of the roller portion 22. Can be inserted. Then, after inserting the spacer 31 into the roller portion 22, the shaft 21 is press-fitted into the roller portion 22 (since the roller portion 22 is made of rubber, air is supplied from the side opposite to the insertion side of the roller portion 22 as described above. If the tip of the shaft 21 (that is, the spacer 31) is inserted into the roller portion 22 while blowing and inflating the roller portion 22, it is easy to insert the shaft 21 itself into the roller portion 22).

  The shaft 21 is inserted into the roller portion 22, and the tip of the spacer 31 is protruded from the other end side of the roller portion 22 to the state shown in FIG. In the state shown in FIG. 3B, the stepped portion 21 c is located in the roller portion 22, and the tapered portion 31 b is out of the roller portion 22. Thereafter, as indicated by a thick arrow in FIG. 3B, the outer peripheral surface of the roller portion 22 is polished while the shaft 21 is rotated. At the time of polishing, the polishing jig 41 is moved in the axial direction as indicated by a thick arrow to perform polishing. When the spacer 31 is pulled out after the polishing is finished, as shown by a thick arrow in FIG. 3C, the peripheral surface of the roller portion 22 is inclined radially inward at the portion corresponding to the small diameter portion 21b, and the tapered surface 22a. Will be specified.

  By the way, it is preferable to attach the spacer 31 to the rear end side of the shaft 21 in consideration of polishing. That is, it is desirable to attach the spacer 31 to both ends of the shaft 21. If it does in this way, it will be in the state where a part of spacer main part 31c of spacer 31 located in both ends of large diameter part 21a and shaft 21 is located in roller part 22, and the outside diameter of large diameter part 21a Since the outer diameter of the spacer main body 31c is the same, the outer peripheral surface of the roller part 22 becomes a cylindrical peripheral surface shape. As a result, polishing becomes extremely easy. Also in this case, if the spacers 31 at both ends are pulled out from the roller portion 22 after the polishing is finished, the tapered surfaces 22 a are defined at both ends of the roller portion 22.

  In Example 2, as shown in FIGS. 4A and 4B, the inner diameter of the roller portion 22 (the diameter of the hollow portion 221) is set to 5.5 mm, and the diameter of the hollow portion 221 is made smaller than that of the small diameter portion 21 b of the shaft 21. By enlarging (the shaft 21 is the same as that of the first embodiment), the end portion of the roller portion 22 is in a floating state without being in contact with the small diameter portion 21b of the shaft 21 as illustrated. The portion 22d that floats in the air at the end of the roller portion 22 has a length of 3 mm in the second embodiment, and therefore is kept horizontal by the strength of the roller portion 22 and does not contact the shaft 21. For this reason, when an image is formed using A4 size paper, it is possible to suppress the occurrence of a transfer memory phenomenon on the photosensitive drum 11 due to current concentration at the end 22d of the roller portion 22 protruding from the paper. The The transfer roller used in the second embodiment can be manufactured in the same manner as in the first embodiment.

  When the small diameter portion 21b is formed at both ends of the shaft 21 and the shaft 21 is inserted into the roller portion 22, for example, tapered ends inclined inward in the radial direction are defined at both ends of the roller portion 22, It can very easily prevent current concentration at both ends of the transfer roller 14 to prevent the transfer memory phenomenon, and can be used to prevent image defects in an image forming apparatus using an electrophotographic process such as a copying machine, a printer, or a facsimile machine. it can.

1 is a diagram schematically illustrating an image forming apparatus in which a first embodiment of a transfer roller according to the present invention is used. It is the schematic which shows Example 1 of the transfer roller by this invention, (a) is sectional drawing which shows the roller edge part before shaft insertion, (b) is sectional drawing which shows the transfer roller after shaft insertion. FIGS. 3A and 3B are diagrams illustrating an example when the transfer roller illustrated in FIG. 2 is manufactured, in which FIG. 3A is a cross-sectional view illustrating a state before a spacer is attached to the shaft and inserted into the roller portion, and FIG. Sectional drawing which shows the state grind | polished after inserting, (c) is sectional drawing which shows the state which pulled out the spacer after completion | finish of grinding | polishing. FIG. 5 is a schematic diagram illustrating a transfer roller according to a second embodiment of the present invention, where (a) is a cross-sectional view illustrating a roller end portion before shaft insertion, and (b) is a cross-sectional view illustrating the transfer roller after shaft insertion.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Photosensitive drum 12 Charging device 13 Developing device 14 Transfer roller 15 Cleaning roller 17 Fixing unit 18 Static eliminator 21 Metal shaft (conductive core shaft)
22 Conductive rubber roller portion 21a Large diameter portion 21b Small diameter portion 21c Stepped portion 22a Inclined peripheral surface (tapered surface)
31 Spacer

Claims (5)

In a transfer roller that is used to transfer the toner image as a transfer image onto a transfer material in contact with an image carrier on which a toner image is formed,
A roller part formed with a hollow part extending in the longitudinal direction in contact with the image carrier;
A core shaft body extending along the hollow portion of the roller portion and supporting the roller portion,
The transfer roller according to claim 1, wherein an inclined surface defining portion that defines an inclined surface inclined radially inward is formed at a longitudinal end portion of the roller portion on the core shaft body. The core shaft body has a large-diameter portion extending in the longitudinal direction, and a small-diameter portion having an outer diameter smaller than the large-diameter portion formed at both ends of the large-diameter portion and extending in the longitudinal direction,
The diameter of the hollow part formed in the roller part is smaller than the outer diameter of the small diameter part,
The transfer roller according to claim 1, wherein the slope defining portion is defined by a step portion defined by the large diameter portion and the small diameter portion. In a transfer roller that is used to transfer the toner image as a transfer image onto a transfer material in contact with an image carrier on which a toner image is formed,
A roller portion in contact with the image carrier;
A core shaft body inserted along the central axis of the roller portion and supporting the roller portion;
The core shaft body has a large-diameter portion extending in the longitudinal direction, and a small-diameter portion formed at both ends of the large-diameter portion and extending in the longitudinal direction and having a smaller outer diameter than the large-diameter portion,
A hollow portion extending in the longitudinal direction into which the core shaft body is inserted is formed in the roller portion, and the diameter of the hollow portion is larger than the outer diameter of the small diameter portion and smaller than the diameter of the large diameter portion. A transfer roller characterized by that. In a manufacturing method for manufacturing a transfer roller that is used to transfer a toner image as a transfer image onto a transfer material in contact with an image carrier on which a toner image is formed.
A first step of forming a roller member having a hollow portion extending in the longitudinal direction;
A second step of forming a core shaft body having a large-diameter portion extending in the longitudinal direction and a small-diameter portion formed at both ends of the large-diameter portion and extending in the longitudinal direction and having an outer diameter smaller than the diameter of the hollow portion; ,
A third step in which a spacer having a diameter smaller than the diameter of the hollow portion is attached to at least one of the small diameter portions;
A fourth step of inserting the spacer from one end side of the hollow portion until a part of the spacer protrudes from the other end side of the hollow portion;
And a fifth step of removing the spacer. The outer diameter of the spacer main body excluding the tip of the spacer is the same as the outer diameter of the large diameter portion,
When performing the fourth step, a part of the spacer main body is located in the hollow portion,
5. The transfer roller manufacturing method according to claim 4, wherein after the fourth step, after performing a sixth step of polishing an outer peripheral surface of the roller portion, the fifth step is performed. 6. Method.

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