JP2005062746A - Transfer roller and method for manufacturing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate the prevention of transfer memory phenomena at low costs, in a transfer roller used in an image forming apparatus using an electrophotographic process. <P>SOLUTION: The transfer roller 14 transfers a toner image to a transfer medium as a transfer image by contact with a photoreceptor drum 11 having the toner image formed thereon. The transfer roller includes a roller section 22 disposed in contact with the photoreceptor drum, and a conductive core shaft 21 which extends along the axis of the roller section and supports the roller section. Grooves 23 are formed in the periphery of the conductive core shaft so as to correspond with the longitudinal ends of the roller section. Thus, the area of the contact of the roller section and conductive core shaft at each of the longitudinal ends of the roller section is reduced. <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 feed in an image forming apparatus capable of vertical feed of letter size paper (216 mm × 279 mm), the width of the transfer roller in the paper transport direction is the same as that of the letter size paper. When the width is equal to 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 recording paper exists ( Since the resistance value is lower than the resistance value of the image forming area), current is concentrated in the contact area, and the transfer memory phenomenon appears remarkably. If an image is formed using a letter size paper immediately after the A4 size paper is used, there is a possibility that a tension memory is generated. When the photosensitive member is charged in the reverse direction by the charging roller, in particular, in the case of a positively charged single layer organic photosensitive member, the charged charge is difficult to be removed by static elimination. The surface potential of the portion where the occurrence is reduced is lower than usual. As a result, fogging or a change in image density occurs corresponding to the portion of the photoreceptor where the transfer memory phenomenon has occurred.

  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, generally, the transfer roller has a metal shaft (rotary shaft) and a conductive rubber roller portion into which the shaft is inserted. When a small diameter portion that does not contact the drum surface is formed and an annular groove perpendicular to the axis is formed on the peripheral surface portion of the small diameter portion, the molding process of the roller portion becomes complicated and the cost increases. is there.

  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. In general, the mold is very expensive, which increases the cost.

  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.

  Accordingly, in order to solve the above-described problems, the present invention provides a transfer roller for use in transferring a toner image as a transfer image onto a transfer material in contact with an image carrier on which a toner image is formed. And a core shaft body that extends along the central axis of the roller section and supports the roller section, and a contact area between the roller section and the core shaft body at a longitudinal end portion of the roller section. It has the contact area reduction part which reduces this.

  In the present invention, in a transfer roller used when the toner image is transferred to a transfer material as a transfer image by contacting an image carrier on which a toner image is formed, a roller portion that contacts the image carrier; A core shaft body that extends along the central axis of the roller portion and supports the roller portion, and a groove portion is formed on a peripheral surface of the core shaft body corresponding to a longitudinal end portion of the roller portion, A transfer roller is obtained in which a contact area between the roller portion and the core shaft body is reduced at an end portion in the longitudinal direction of the roller portion.

  And it is desirable to form the said groove part in the surrounding surface of the said core shaft body so that it may cross | intersect the axial center of the said core shaft body.

  Further, in the present invention, a plurality of groove portions are formed in the core shaft body as groove patterns at a predetermined pitch in the axial direction of the core shaft body, corresponding to the longitudinal ends of the roller portions, and the roller It is preferable that an end face of the portion is positioned on a selected one of the plurality of groove portions so that a part of the plurality of groove portions is covered with the roller portion.

  In the present invention, the core shaft body is formed with a plurality of groove portions corresponding to the end portions in the longitudinal direction of the roller portion as a groove pattern in the axial direction of the core shaft body. One of them is formed as a wide groove whose groove width is wider than the other groove width, the end surface of the roller part is positioned on the wide groove, and a part of the plurality of groove parts is covered with the roller part. Also good. In addition, you may make it form the said groove part helically in the surrounding surface of the said core shaft body.

  In addition, according to the present invention, in a manufacturing method for manufacturing a transfer roller used for transferring 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, and a groove portion is formed on the peripheral surface of the shaft member so as to intersect the shaft center of the shaft member at both ends of the shaft member whose outer diameter is larger than the inner diameter of the roller member And a third step of inserting the core shaft body into the roller member and positioning the groove portion at a longitudinal end portion of the roller member. A transfer roller manufacturing method is obtained.

  As described above, the transfer roller according to the present invention has the contact area reducing portion that reduces the contact area between the roller portion and the core shaft at the longitudinal end portion of the roller portion. It is possible to prevent the phenomenon that current is concentrated on the end portion, and as a result, the transfer memory phenomenon is prevented and the image defect does not occur.

  In the present invention, a groove portion is formed on the peripheral surface of the core shaft body in correspondence with the longitudinal end portion of the roller portion so as to reduce the contact area between the roller portion and the core shaft body at the longitudinal end portion of the roller portion. Therefore, it is only necessary to cut the core shaft body, and the core shaft body is extremely easy to cut. Therefore, there is an effect that the transfer memory phenomenon can be easily prevented by reducing the cost.

  Furthermore, in the present invention, since the groove portion is formed on the peripheral surface of the core shaft body so as to intersect the axis of the core shaft body, there is an effect that the leakage current can be reduced and the transfer memory phenomenon can be surely prevented.

  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, and a cleaning roller 15 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. 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 FIG. 2, the illustrated transfer roller 14 includes a metal shaft (conductive core shaft: hereinafter simply referred to as a shaft) 21, and this shaft 21 is referred to as a conductive rubber roller portion (hereinafter simply referred to as a roller portion). ) 22 is inserted along the central axis of the roller 22, and the roller portion 22 is supported by the shaft 21. As shown in the drawing, a plurality of groove portions 23 are formed on both end portions of the shaft 21, and in the illustrated example, the groove portions 23 are formed on the circumferential surface of the shaft 21 so as to be orthogonal (intersect) with the extending direction of the shaft 21. (Hereinafter, the plurality of groove portions 23 will be referred to as groove patterns 24). That is, the groove portion 23 is formed on the peripheral surface of the shaft 21 corresponding to the longitudinal end portion of the roller portion 22, and the contact area between the roller portion 22 and the shaft 21 is reduced at the longitudinal end portion of the roller portion 22. The

  Here, referring also to FIG. 3, FIG. 3 is a cross-sectional view showing a part of the transfer roller 14, and the end surface of the roller portion 22 is located on the groove pattern 24. That is, the end surface of the roller portion 22 is positioned between one end side and the other end side of the groove pattern 24, and preferably, the end surface of the roller portion 22 is positioned on one of the groove portions 23 in the groove pattern 24 (FIG. 3). reference). A part of the plurality of groove portions 23 is covered with the roller portion 22, and the groove portion 23 is associated with the end portion of the roller portion 22. Thus, by positioning the end surface of the roller portion 22 on one of the groove portions 23 in the groove pattern 24, the leak path becomes longer and the leakage current can be reduced (along the end surface of the roller portion 22). The creeping current flowing in the photoconductor drum 11 is greatly reduced to suppress the occurrence of the transfer memory phenomenon on the photosensitive drum 11).

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 resistivity value is a volume resistivity value measured at an applied voltage of 1000 V in a volume resistivity test described in JIS K6911.

  Next, a shaft member was prepared, and a plurality of groove portions 23 were processed and formed on both peripheral sides of the shaft member at the both ends of the shaft member so as to be orthogonal to the longitudinal direction of the shaft member. In the illustrated example, the distance between the centers of the groove portions 23 of the groove pattern is 1.0 mm, the width of the groove portions 23 is 0.5 mm, the depth of each groove portion 23 is 1.0 mm, and the outer diameter of the shaft 21 is 6.0 mm. The shaft member is made of stainless steel.

  Then, the shaft 21 is inserted into the central hole of the conductive foam rubber tube so that the groove pattern is located on the end face of the conductive foam rubber tube. The shaft 21 was inserted into the conductive foam rubber tube while inflating the foam tube). Thereafter, the surface (outer peripheral surface) of the conductive foamed rubber tube (roller portion) 22 was polished to obtain a transfer roller 14. In the illustrated example, the length of the roller portion 22 in the longitudinal direction is 216 mm, but the length of the roller portion 22 is set to the maximum sheet width used in the image forming apparatus.

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). The linear pressure was 15 g / cm for cleaning, the LED wavelength was 630 nm, and the LED exposure was 4.0 μJ / cm ² during slow charging.

  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 groove pattern 24 is formed on the shaft 21 so that the end portion of the roller portion 22 is positioned on the groove pattern 24, the shaft 21 and the roller portion 22 are at the end portion of the roller portion 22. It is possible to prevent a phenomenon in which the contact area is reduced (that is, the degree of adhesion between the end portion of the roller portion 22 and the shaft 21 is reduced) and current is concentrated on the end portion of the roller portion 22. 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 groove pattern 24 is formed on the shaft 21, and the groove pattern 24 is positioned on the end surface of the roller portion 22. Since the contact area is reduced, current concentration at the end of the roller portion 22 is prevented (the groove portion 23 formed in the shaft 21 functions as a contact area reduction portion).

  And the groove part 23 should just be formed in the shaft 21, and it is not necessary to give the roller part 22 any processing. Moreover, when the groove pattern 24 is formed on the shaft 21, the groove pattern 24 can be easily formed using a cutting machine or the like, so that 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 the example shown in FIGS. 2 and 3, the pitch of the groove portions 23 is set to a predetermined pitch. However, as shown in FIG. 4, the pitch of the groove portions 23 may be such that only one of the groove portions 23a is a wide groove. . In this way, when the shaft 21 is inserted into the roller portion 22 and the end surface of the roller portion 22 is associated with the groove portion 23, the positioning of the shaft 21 and the roller portion 22 can be easily performed using the wide groove 23a as the positioning groove. It can be performed. That is, if the pitch of the groove pattern 24 is changed, the shaft 21 and the roller portion 22 can be easily positioned. Furthermore, as described in FIGS. 2 and 3, it is not necessary to form the plurality of groove portions 23 at a predetermined pitch, and the grooves may be formed in a spiral shape on the peripheral surface of the shaft 21.

  In this way, the groove portion 23 is formed at both ends of the shaft 21, and the shaft 21 is inserted into the roller portion 22 so that the longitudinal end portion of the roller portion 22 corresponds to the groove portion 23, and the longitudinal direction of the roller portion 22 What is necessary is just to make it reduce the contact area of the shaft 21 and the roller part 22 in an edge part.

  In the above-described embodiment, the example in which the groove portion 23 (groove pattern 24) is formed at both end portions of the shaft 21 has been described. However, the groove portion 23 is formed on the inner peripheral surface at both end portions of the roller portion 22, and The contact area with the roller portion 22 may be reduced. Further, the groove portion 23 is formed at both end portions of the shaft 21, and the groove portion 23 is formed at the inner peripheral surface at both end portions of the roller portion 22. The contact area between the shaft 21 and the roller portion 22 may be reduced. In any case, a contact area reducing portion that reduces the contact area between the roller portion 22 and the shaft 21 may be provided at the longitudinal end portion of the roller portion 22. The outer peripheral surface of the shaft 21 and / or the inner peripheral surface of the roller portion 22 may be knurled to reduce the contact area.

  The groove portion 23 is formed at both ends of the shaft 21, and the shaft 21 is inserted into the roller portion 22 in association with the groove portion 23 at the end of the roller portion 22. Since the contact area with the shaft 21 is reduced, the transfer memory phenomenon can be prevented with a simple configuration, and it can be applied to the prevention of image defects in an image forming apparatus using an electrophotographic process such as a copying machine, a printer, or a facsimile machine.

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 a figure which cuts a roller part and shows Example 1 of the transfer roller by this invention. FIG. 3 is an enlarged sectional view showing a part of the transfer roller shown in FIG. 2. It is a figure for demonstrating the other example of the groove pattern formed in the shaft of a transfer roller.

Explanation of symbols

11 Photosensitive drum 12 Charger 13 Developing device 14 Transfer roller 15 Cleaning roller 17 Fixing unit 21 Metal shaft (conductive core shaft)
22 conductive rubber roller portion 23 groove portion 24 groove pattern

Claims (7)

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 extending along the central axis of the roller portion and supporting the roller portion,
A transfer roller having a contact area reducing unit that reduces a contact area between the roller unit and the core shaft body at an end portion in a longitudinal direction of the roller unit. 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 extending along the central axis of the roller portion and supporting the roller portion,
A groove portion is formed on the peripheral surface of the core shaft body so as to correspond to a longitudinal end portion of the roller portion,
A transfer roller characterized in that a contact area between the roller portion and the core shaft body is reduced at an end portion in a longitudinal direction of the roller portion.   The transfer roller according to claim 2, wherein the groove is formed on a peripheral surface of the core shaft body so as to intersect an axis of the core shaft body. In the core shaft body, a plurality of groove portions are formed as groove patterns at a predetermined pitch in the axial direction of the core shaft body, corresponding to the longitudinal ends of the roller portions,
The end surface of the roller portion is positioned on a selected one of the plurality of groove portions, and a part of the plurality of groove portions is covered with the roller portion. Transfer roller. In the core shaft body, a plurality of groove portions are formed as groove patterns in the axial direction of the core shaft body corresponding to the longitudinal ends of the roller portions, respectively.
One of the plurality of groove portions is formed as a wide groove whose groove width is wider than other groove widths,
The transfer roller according to claim 3, wherein an end surface of the roller portion is positioned on the wide groove, and a part of the plurality of groove portions is covered with the roller portion.   The transfer roller according to claim 3, wherein the groove is formed in a spiral shape on a peripheral surface of the core shaft body. 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 tubular roller member;
A second axial shaft member is formed by forming a groove on the peripheral surface of the shaft member so as to intersect the axial center of the shaft member at both ends of the shaft member having an outer diameter larger than the inner diameter of the roller member. Steps,
And a third step of positioning the groove at the longitudinal end of the roller member by inserting the core shaft body into the roller member.

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