JP2007286522A - Transfer member, image forming apparatus, and manufacturing method for the transfer member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer member and an image forming apparatus that can perform image formation with edge fogging suppressed. <P>SOLUTION: A transfer roll 23 used for the image forming apparatus is constituted with a foamed rubber layer 23r formed around a shaft 23s to a predetermined thickness. Its external shape is a barrel-shaped crown shape which gradually decreases in diameter, going from axial center part to both ends, and the foamed rubber layer 23r has larger voidage (volume rate of foam gaps), at both the axial ends than at the center part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile, and more particularly to an image forming apparatus using a contact transfer method.

  An image forming apparatus using an electrophotographic method forms an electrostatic latent image in which the charge is reduced by exposure by an exposure device after the photoreceptor on the surface of the photosensitive drum as an image carrier is charged by a charging device. Then, the toner charged by the developing device is attached to the electrostatic latent image to form a toner image. Then, the toner image on the photosensitive drum is transferred to a recording medium such as a recording paper by a transfer device, and the recording paper on which the toner image has been transferred is heated and pressed by a fixing device to fix the toner image and then discharged.

  In such an image forming apparatus, a transfer device that applies a transfer voltage to a recording sheet to transfer a toner image from the photosensitive drum to the recording sheet includes a non-contact method using a corona charger and the like, and a contact with the photosensitive drum. And a contact method using a transfer roll and a transfer conveyance belt. Recently, a contact method that can reduce the generation amount of ozone and suppress blurring of a transferred image is often used.

The contact-type transfer device includes a transfer roll pressed against the photosensitive drum and a bias power source that applies a transfer voltage to the transfer roll, and applies a transfer voltage (bias) between the photosensitive drum and the transfer roll. By doing so, a transfer electric field is formed between the transfer roll and the photosensitive drum. The toner image formed on the photosensitive drum is electrostatically transferred onto the recording paper by the formed transfer electric field.
For example, the photosensitive drum of the photosensitive drum is negatively charged, the toner charged negatively by the developing device is attached to the electrostatic latent image whose charge has been reduced by exposure by the exposure device, and the recording paper is positively charged. Let

By the way, in such a contact-type transfer device, when continuous recording paper is shifted in the width direction with respect to the feeding direction in continuous image formation, transfer with the photosensitive drum in the image forming area is performed. Direct contact with the roll.
In this way, when the photosensitive drum and the transfer roll come into direct contact within the image forming area, electric charges are directly injected from the transfer roll to the photosensitive drum, and the potential of the photosensitive member on the surface of the photosensitive drum is lowered. . In the above-described example, a positive charge is injected from the transfer roll to the negatively charged photosensitive drum, and the negative potential of the photosensitive drum is lowered.
Even if there is no deviation in the recording paper, the transfer roll is always in direct contact with the photosensitive drum outside the side edge of the recording paper, where charge is injected, and a large number of images are continuously formed. When the formation is performed, the charge injection here gradually reaches the image forming area.

When the potential of the photosensitive member decreases and the amount of decrease increases in this way, it becomes difficult to charge to a predetermined potential by the charging device. When the charging potential is insufficient, toner adheres to the area by the developing action, and this is transferred to the recording paper and causes smudges such as wrinkles. Since this occurs at the edge of the recording paper, it is generally called edge fog.
Edge fog is particularly likely to occur when the transfer voltage is high or when the electrical resistance value of the recording paper is high, because current concentrates on the contact portion between the transfer roll and the photosensitive drum.
This is a problem particularly in an image forming apparatus that requires a high transfer voltage for image formation at high speed.
This also causes a problem in the double-sided image forming apparatus in which the resistance value of the recording paper is high. This is because, in a double-sided image forming apparatus, the recording paper is dried by heating by the fixing device when forming an image on one side, and the recording paper becomes high resistance when forming an image on the other side. It depends.

Here, there is a configuration as disclosed in Patent Document 1 as an attempt to suppress end fogging.
This is because a plurality of sheets are sequentially fed to a transfer portion formed between the photosensitive drum and a transfer roll to which a bias voltage is applied, and the toner image formed on the photosensitive drum is transferred to the sheet by the transfer roll. In the image forming apparatus, the feeding interval of the sheet to the transfer unit is made longer than the circumferential length of the photosensitive drum.
As a result, the toner adhering area on the photosensitive drum that causes end fogging does not overlap the second sheet and does not appear as end fog on the sheet.

JP 09-251245 A

  However, in the technique described in Patent Document 1 as described above, the gap between the sheets on which images are continuously formed must be set longer than the circumference of the photosensitive drum. The problem is that it is difficult and inefficient.

The present invention has been made to solve the technical problems as described above, and an object of the present invention is to provide a transfer member and an image forming apparatus capable of forming an image while suppressing the occurrence of end fogging. Is to provide.
Another object of the present invention is to provide a method for manufacturing a transfer member that enables image formation while suppressing the occurrence of end fogging.

For this purpose, the transfer member of the present invention is disposed adjacent to an image carrier that carries a toner image, and a transfer voltage is applied to transfer the toner image to a recording medium interposed between the transfer member and the image carrier. The member is made of a foam material having a large number of voids, and the volume ratio of the voids is set larger than the central portion at both side edges corresponding to both side edges in the width direction perpendicular to the moving direction of the recording medium. It is characterized by being.
Here, the transfer member can be characterized in that it is formed in a roll shape with a foam material layer made of a foam material on the outer periphery of the conductive core material.
In addition, the transfer member may be characterized in that a roll-shaped outer shape is formed in a barrel-shaped crown shape having a thicker central portion than both side end portions.

  An image forming apparatus according to the present invention includes an image carrier that carries an electrostatic latent image, a developing device that converts the electrostatic latent image into a toner image, a transfer voltage that is disposed adjacent to the image carrier, A transfer member that transfers a toner image to a recording medium interposed between the recording medium and the transfer member. The transfer member is formed of a foam material having a large number of voids, and the volume ratio of the voids is orthogonal to the moving direction of the recording medium. The side end portions corresponding to both side edges in the width direction are set larger than the central portion.

Here, the image forming apparatus may further include a transfer conveyance belt member that conveys the recording medium and electrostatically transfers the toner image to the recording medium between the image carrier and the transfer member.
The transfer member may be a roller having a foam layer made of a foam material on the outer periphery of a conductive core material.
Furthermore, the outer shape of the transfer member can be characterized in that it is formed in a barrel-shaped crown shape with a thicker central portion than both side end portions.

  The transfer member manufacturing method according to the present invention is formed by a foam material having a large number of voids so that the volume ratio of the voids differs in the axial direction, and is disposed adjacent to an image carrier that carries a toner image. A manufacturing method for manufacturing a transfer member for transferring a toner image to a recording medium interposed between a body and a foam material kneaded with a foaming agent so that the outer diameter in the axial direction is different, After forming a roll-shaped material having different foaming ratios in directions, the outer surface of the roll-shaped material is processed into a predetermined columnar shape.

  Here, in order to make foaming so that the outer diameters in the axial direction are different, the roll raw material is inserted into a mold member that is molded into different outer diameters in the axial direction and foamed, and the roll shape has a different foaming rate in the axial direction. It can be characterized by molding the material. For example, the roll raw material is inserted into a mold member that is formed with a large diameter compared to the central portion at both axial ends, and the foaming rate at both axial ends is large compared to the central portion. be able to.

According to the transfer member and the image forming apparatus of the present invention, it is possible to form an image while suppressing the occurrence of end fogging.
In addition, according to the transfer member manufacturing method, it is possible to manufacture a transfer member that enables image formation with the occurrence of end fogging suppressed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to the present embodiment. Although not shown in detail, the image forming apparatus 1 can form an image on one side of a recording sheet P as a recording medium and then reversely convey it to form an image on the back side of the same recording sheet P. It is.
The image forming apparatus 1 includes a charger 11, a laser exposure device 12, and a developing device around a photosensitive drum 10 as an example of an image carrier that rotates in a direction indicated by an arrow A in FIG. The developing device 13, the pre-transfer charger 14, the transfer unit 20 constituting the transfer unit 15, the pre-cleaning charger 16, the drum cleaner 17, and the like are arranged.
In addition, the image forming apparatus 1 includes a recording paper transport mechanism 40 that transports the recording paper P, a fixing device 50 that fixes an unfixed toner image transferred to the recording paper P, and a control unit that controls the operation of each operation unit. 30.

In the photosensitive drum 10, an organic photosensitive layer made of a negatively charged material is formed on the surface of a metal thin cylindrical drum. In the present embodiment, the photoconductor has a diameter of 84 mm and the surface layer is an organic photoreceptor having sensitivity in an infrared region composed of a polymer resin having a polycarbonate binder and a triphenylamine-based charge transport agent. And it is rotationally driven by a drum drive motor (not shown).
The charger 11 is a scorotron charger in which two charging wires are stretched in a shield case that opens toward the photosensitive drum 10 and a grid is provided in the opening, and is charged from a high-voltage power source (not shown). A constant current of −650 μA is applied to the wires, and a DC voltage of −800 V to −850 V is applied to the grid at a constant voltage to charge the photoreceptor surface to −750 V.

The laser exposure device 12 irradiates the photosensitive drum 10 with, for example, an exposure beam Bm emitted from a semiconductor laser according to the input image data, and forms an electrostatic latent image on the photosensitive member on the peripheral surface.
The developing device 13 develops the electrostatic latent image on the photosensitive drum 10 by using a toner and a reversal developing method. Therefore, the toner is of a negative charge type, and for example, a toner prepared by a polymerization method and having a shape factor SF1 of 110 to 140 is used.
The pre-transfer charger 14 is constituted by a corotron charger disposed in a non-contact manner with respect to the photosensitive drum 10, and performs a negative discharge to form a toner image on the photosensitive drum 10. Is adjusted before transfer.

The transfer unit 20 includes a transfer conveyance belt 21A as a transfer conveyance belt member, and a transfer roll 23 as a transfer member disposed inside the transfer conveyance belt 21A.
The transfer roll 23 presses the transfer conveyance belt 21 </ b> A from the inner side toward the photosensitive drum 10 to be in pressure contact therewith. Further, a high voltage power source (not shown) is connected to the transfer roll 23 so that a charge having a polarity opposite to the toner charging polarity on the photosensitive drum 10 is applied to the transfer conveyance belt 21A.
A pressure contact portion of the transfer conveyance belt 21 </ b> A to the photosensitive drum 10 by the transfer roll 23 is a transfer portion 15 that transfers the toner image formed on the photosensitive drum 10 to the recording paper P.
The transfer unit 20 will be described in detail later.

The pre-cleaning charger 16 is constituted by a corotron charger disposed in a non-contact manner with respect to the photosensitive drum 10, and performs a negative discharge and charges (transfer electric field) remaining on the photosensitive drum 10 after transfer. Is removed).
The drum cleaner 17 includes a cleaning blade 17A that is disposed in pressure contact with the photosensitive drum 10 in the counter direction. The cleaning blade 17A scrapes and removes toner remaining on the surface of the photosensitive drum 10.
The recording paper transport mechanism 40 includes a paper tray 41 that stores the recording paper P, and a plurality of transport rolls 42 that send out the recording paper P stored in the paper tray 41 and transport the recording paper P along a predetermined path.
The fixing device 50 includes a heating roll 51 having a heating source therein and a pressure roll 52 disposed in pressure contact with the heating roll 51, and a toner image is transferred between the heating roll 51 and the pressure roll 52. The toner image is fixed to the recording paper P by heating and pressurizing the recording paper P.

The image forming apparatus 1 configured as described above performs image formation by acting as follows.
That is, the photosensitive drum 10 is rotationally driven, the photosensitive member on the surface thereof is charged by the charger 11, and the charged photosensitive drum 10 is scanned by the exposure beam Bm of the laser exposure unit 12 to electrostatically charge the photosensitive drum 10. A latent image is formed. Next, the electrostatic latent image formed on the photosensitive drum 10 is developed by the developing device 13 to be visualized (toner image), and the charging polarity of the toner image is made uniform by the pre-transfer charger 14.
In the transfer unit 15, the recording paper P transported by the recording paper transport mechanism 40 is a toner image formed on the photosensitive drum 10 by a transfer bias applied between the photoconductor drum 10 and the transfer roll 23. Transcript to.
Residual toner remaining on the photosensitive drum 10 after the transfer is charged by the pre-cleaning charger 16 and then removed by the drum cleaner 17.
On the other hand, the recording paper P to which the toner image is transferred is conveyed to the fixing device 50 by the transfer conveying belt 21A, and the toner image is fixed by the fixing device 50 and discharged.

Next, the transfer unit 20 will be described in detail.
The transfer unit 20 includes a transfer conveyance unit 21 and a cleaning unit 22. The transfer unit 15 transfers the toner image on the photosensitive drum 10 to the recording paper P conveyed and supplied by the recording paper conveyance mechanism 40. In addition, the recording paper P having the toner image transferred thereon has a function of conveying it to the fixing device 50.
The transfer / conveying unit 21 has a transfer / conveying belt 21 </ b> A having a predetermined circumferential length wound around a driving roll 21 </ b> B and a driven roll 21 </ b> C disposed in parallel with the photosensitive drum 10, and the above-described inside of the circulation path In this manner, a transfer roll 23 for transferring a toner image onto the recording paper P by forming a transfer electric field with the photosensitive drum 10 is provided. A high voltage power source is connected to each of the driven roll 21C and the transfer roll 23, and a bias can be applied independently.

The transfer / conveying belt 21A is formed to have a thickness of 450 to 500 μm by applying an overcoat of 3 to 7 μm in thickness with a urethane resin in which PTFE (polytetrafluoroethylene) is dispersed on the surface of a rubber layer made of chloroprene rubber, for example. Semiconductive endless belt. The volume resistivity is set to 7.5 to 10 log Ωcm (measured at 22 ° C./55% RH, 500 V applied with ADVANTEST R8340A / HR probe).
The drive roll 21B is rotationally driven by a drive motor (not shown), thereby driving the transfer / conveying belt 21A in a direction indicated by an arrow B in the drawing at a predetermined speed.

As will be described in detail later, the transfer roll 23 is configured to have a predetermined resistance value (for example, 5.0 to 7.0 logΩ) by forming a foam rubber layer of foam rubber on a metal shaft to a predetermined thickness.
A transfer bias having a polarity (positive polarity) opposite to the toner charging polarity (negative polarity) is stably applied to the transfer roll 23 from a high voltage power source (not shown), and the toner on the photosensitive drum 10 is charged to the transfer conveyance belt 21A. A charge having a polarity opposite to the polarity is applied. In this embodiment, the transfer bias is applied by a constant current method. The optimum value of the transfer current varies depending on the process speed, environment, paper type, and the like. When the process speed is fast, the transfer current needs to be increased, but is generally 60 μA to 120 μA.

The cleaning unit 22 includes a cleaning blade 22A and a cleaning brush 22B.
The cleaning blade 22A is formed in a plate shape having a predetermined thickness with urethane rubber, and is disposed in pressure contact with the transfer conveyance belt 21A in the counter direction with respect to the moving direction thereof.
The cleaning brush 22B is a cylindrical brush formed by planting hair having a predetermined electric resistance value on a metal shaft, and is provided with the shaft grounded.
The bristles of the cleaning brush 22B are made of, for example, 10 denier polyester fibers in which carbon is dispersed, and the resistance value is set to 4.0 to 6.0 log Ωcm.
The cleaning brush 22B is more preferably provided, but is not necessarily provided.
By such a cleaning unit 22, fog toner transferred from the photosensitive drum 10 to the transfer conveyance belt 21 </ b> A is removed at a so-called inter-image unit between continuous recording sheets P, and these adhere to the back surface of the recording sheet P. To prevent it from becoming dirty.

Here, the transfer roll 23 of the transfer unit 20 is formed in a so-called barrel-shaped crown shape whose outer shape gradually decreases in diameter from the center in the axial direction toward both ends, and the porosity of the foamed rubber layer (foaming) The volume ratio of the voids is larger at both axial end portions than at the central portion.
Hereinafter, the transfer roll 23 will be described in detail.
FIG. 2 is a diagram conceptually showing the transfer roll 23, and FIG. 3 is a diagram conceptually showing a cross section thereof. In addition, the figure is exaggeratingly shown. In addition, refer to FIG. 1 for the reference numerals of each action mechanism in the description.

The transfer roll 23 is formed by forming a foam rubber layer 23r as a foam material layer with a predetermined thickness on the outer periphery of a metal shaft 23s as a core material, using a foam rubber of EP (ethylene-propylene) as a foam material. ing.
As shown in FIG. 2, the crown shape is formed in a barrel shape in which the outer diameter: φd at both ends in the axial direction is smaller than the outer diameter: φD at the center. As a result, as shown in FIG. 2A, the pressing force per unit area to the photosensitive drum 10 via the transfer conveyance belt 21A at both ends is smaller than that in the central portion. As a result, it is difficult for the current to flow to the photosensitive drum 10 from the central portion at both ends where the pressure contact force is small.

Further, as described above, the porosity of the foamed rubber layer 23r in the axial direction of the transfer roll 23 is set to be larger than that of the central portion at both ends in the axial direction, as shown in FIG. Thus, the resistance value is larger at both axial end portions than at the central portion.
Furthermore, as shown in FIG.3 (c), hardness is low compared with the center part in the axial direction both ends. As a result, the pressure contact force per unit area to the photosensitive drum 10 via the transfer conveyance belt 21A becomes small at both ends, and current hardly flows from the central portion to the photosensitive drum 10 at both ends.

That is, the transfer roll 23 is configured such that both ends in the axial direction have a larger resistance value than the central portion, and the pressure contact force to the photosensitive drum 10 via the transfer conveyance belt 21A is small. It is what.
By adopting such a transfer roll 23, charge injection from the transfer roll 23 to the photosensitive drum 10 (in the present embodiment, via the transfer conveyance belt 21 </ b> A) is performed at the central portion at both ends of the transfer roll 23. Less than As a result, the injection of charge from the both ends of the transfer roll 23 corresponding to the side edge of the recording paper P to the photosensitive drum 10 is reduced, and the potential of the photosensitive drum 10 caused by the injection of charge from the transfer roll 23 is reduced. Is suppressed, and end fogging caused by insufficient charging potential can be prevented.
In other words, when images are continuously formed, the recording paper P is displaced from the left and right with respect to the feeding direction, and charge is injected from the transfer roll 23 to the photosensitive drum 10 in the image forming area, and the side edge of the recording paper P is formed. It is possible to suppress the injection of electric charges from the transfer roll 23 to the photosensitive drum 10 that occurs outside, and to prevent edge fogging.

Next, the results of experiments using specific examples of the present invention will be described.
FIG. 4 shows the transfer roll 23 used in the experiment, in which (a) shows the foamed rubber layer 23r formed so that the porosity of the foamed rubber layer 23r gradually increases from the center toward both axial ends (example of the present application). 1) and (b) are examples in which the change in the porosity of the foamed rubber layer 23r is discontinuous, the porosity at both ends in the axial direction is large, and the porosity at the center is small (Example 2 of the present application). These were compared with a conventional product (comparative example) in which the porosity of the foamed rubber layer 23r was uniform in the axial direction.

  In the experiment, in a low-temperature and low-humidity environment (10 ° C., 15% RH) where edge fogging is likely to occur, a recording paper having a basis weight of 90 gsm and A3 is used, the process speed is 510 mm / s, and the entire halftone area 50 is formed. 10% images were continuously formed in the duplex mode. This is performed by changing the transfer current. At this time, the potential probe disposed between the laser exposure device 12 and the developing device 13 is placed 5 mm outside from both ends of the width of the recording paper P on the photoconductor of the photoconductor drum 10. The surface potential of the part was measured, and the decrease amount (ΔVh) of the charged potential on the photoreceptor due to charge injection was detected. Furthermore, the occurrence (concentration) of edge fogging with respect to the charge injection amount (amount of decrease in charging potential: equal to ΔVh) was evaluated.

The specifications of the transfer roll 23 of the present application example 1 and the present application example 2 are as follows:
External diameter φD: 14 mm
Length L: 325mm
Porosity: 30% at the center, 33-38% at both ends
Resistance value: 5.8 logΩ at the center, 6.3 logΩ at both ends
(Measured at 22 ° C / 55% RH, with 500V applied with ADVANTEST R8340A / HR probe)
Hardness: 38 to 42 degrees at the center, 32 to 36 degrees at both ends (Asuka C-type hardness meter, 500 g × 5 seconds value)
Core material: Material SUM (sulfur composite free cutting steel), Diameter: 8mm
It is.
The transfer roll 23 of the comparative example has the same specifications as the example of the present application except that the porosity and the resistance value are 30% and 5.8 logΩ in the entire axial direction, respectively.
In addition, the crown amount is the same condition that the central portion in the axial direction is +0.2 mm in the first and second examples and the comparative example.

Table 1 shows the experimental results. This table shows the worse of the measured values at both shaft ends. FIG. 5 is a graph of the experimental results.
FIG. 6 shows an output result of measurement data as an example of the experimental results, (a) is an example of the present application, and (b) is a comparative example. The horizontal axis represents the time required for image formation on ten sheets, and the vertical axis represents the measured potential.

  Further, Table 2 shows the results of evaluating the occurrence (concentration) of edge fog with respect to the charge injection amount. Edge fogging in Table 2: G is an index indicating the fog density, and no fog is observed at 0. Hereinafter, the fog density is higher as the numerical value is larger. From Table 2, it can be seen that end fog is not observed when the charge injection amount is 100 V or less, and therefore, end fog can be prevented by suppressing the charge injection amount to 100 V or less.

As a result of the experiment, in the comparative example, as shown in FIG. 6B, the surface potential (charging potential) decreases with the passage of time (increase in the number of continuously formed images), and as shown in Table 1 and FIG. When the current was 90 to 100 μA, the amount of decrease in charging potential: ΔVh exceeded 100V.
In contrast, in Examples 1 and 2 of the present application, the surface potential (charging potential) is stable over time as shown in FIG. 6A, and as shown in Table 1 and FIG. Even with a maximum transfer current of 120 μA, the amount of decrease in charging potential: ΔVh was 100 V or less.
Therefore, it was confirmed that the occurrence of end fogging can be suppressed by using the transfer roll 23 of the present invention.

Next, a manufacturing method for manufacturing the transfer roll 23 in which the porosity of the foamed rubber layer 23r is larger at both axial end portions than at the axial central portion will be described.
The manufacturing process of the transfer roll 23 includes kneading of raw materials, extrusion molding, vulcanization foaming, insertion of the shaft 23s, and polishing. That is, a rubber layer raw material obtained by blending and kneading a vulcanizing agent and a foaming agent into a resin is formed into a hollow roll-shaped roll raw material by extrusion molding, and after inserting the shaft 23s in the center of the roll raw material, Then, the roll raw material is vulcanized and foamed. Then, the outer peripheral surface of the roll after foaming is polished and finished to a predetermined diameter and accuracy.

Here, in the vulcanization and foaming step, the porosity is controlled by defining the outer diameter of the roll.
Specifically, foaming is suppressed and the porosity is reduced by restricting the diameter expansion of the part where the porosity is desired to be reduced.
In vulcanization foaming, there are compacted foam that defines the shape by the mold and free foaming that does not define the outer diameter, but in the case of compacted foam, a mold whose outer diameter is changed according to the site, In the case of free foaming, vulcanization foaming is performed by providing a member for restricting the diameter expansion at a site where the porosity is desired to be reduced.
FIG. 7 is an explanatory view of a manufacturing process by compaction foaming using a mold, and FIG. 8 is a diagram for explaining a manufacturing process by free foaming. FIG. 9 is a cross-sectional view of the transfer roll 23 formed by a different method.

In the case of compaction foaming using the mold shown in FIG. 7, a mold 60 is used as a mold member having a so-called pincushion-shaped cavity 61 in which the outer diameters at both ends in the axial direction gradually expand compared to the central part. Do it.
First, as shown to (a), the roll-form roll raw material 23A is inserted in the cavity 61 of the metal mold | die 60 by extrusion molding, and vulcanization foaming is performed.
Thereby, as shown in (b), an intermediate molded product 23B is obtained as a pincushion-shaped roll material corresponding to the cavity 61 of the mold 60. With such a shape, the intermediate molded product 23 </ b> B has a higher foaming ratio at both end portions than at the central portion. That is, the void ratio at both ends is increased. Next, the shaft 23s is inserted into the intermediate molded product 23B as shown in FIG. 5C, and the outer shape is polished into a predetermined crown shape to obtain the transfer roll 23.
By using the mold 60 having such a pincushion-shaped cavity 61, the porosity can be continuously increased gradually toward the end of the shaft, and the change rate of the porosity can be determined by setting the curvature shape of the cavity 61. Can be set as appropriate.

In the case of the free foaming shown in FIG. 8, a cylindrical foam regulating member 70 formed of PET (polyethylene terephthalate) resin or the like is removed from the central portion excluding both ends of the roll raw material 23A as shown in FIG. Then, as shown in (b), vulcanization foaming is performed by restricting the diameter expansion by the foam regulating member 70. As a result, foaming is restricted by the foam regulating member 70 in the central portion, resulting in partial consolidation foaming, and foaming proceeds without being regulated at both ends, so the foaming rate at both ends becomes higher than that in the central portion. . That is, an intermediate molded product 23B having a high porosity at both ends is obtained. The outer shape of the intermediate molded product 23B is polished to obtain a transfer roll 23 having a predetermined crown shape as shown in (c).
According to such a process, the transfer roll 23 in which the void ratio at both ends is discontinuously larger than that in the central portion is obtained as in the second application example in the experiment described above.

  Further, the transfer roll 23 shown in FIG. 9 is different from the above example in the manufacturing process, and is formed by extrapolating separately formed foamed rubber molded products having different foaming ratios to the shaft 23s. That is, the center member 23c formed of foamed rubber having a low foaming rate is inserted into the central part of the shaft 23s, and end members 23d formed of foamed rubber having a high foaming rate are inserted into both ends thereof. The center member 23c is formed by bonding and integration. Also by this, it is possible to form the transfer roll 23 in which the void ratio at both ends is discontinuously larger than that at the center.

  In the present embodiment, the transfer conveyance belt 21A is interposed between the transfer roll 23 and the photosensitive drum 10. However, the present invention is not limited to such a configuration, and the transfer conveyance belt 21A. The same effect can be obtained by applying to a configuration in which the transfer roller 23 is arranged in direct contact with the photosensitive drum 10 without the above.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an exemplary embodiment. It is a figure which shows a transfer roll notionally. It is a figure which shows notionally the cross section of a transfer roll. It is a figure which shows the transfer roll used for experiment. It is a graph which shows an experimental result. It is a graph which shows the output result of the measurement data of an example of an experimental result. It is explanatory drawing of the manufacturing process by the compaction foaming which uses a metal mold | die. It is a figure explaining the manufacturing process by free foaming. It is sectional drawing of the transfer roll formed by the different method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Photosensitive drum (image carrier), 13 ... Developing device (developing device), 20 ... Transfer unit, 21A ... Transfer conveyance belt (transfer conveyance belt member), 23 ... Transfer roll (transfer member) ), 23A ... roll material, 23B ... intermediate molded product (roll material), 23r ... foam rubber layer (foam material layer), 23s ... shaft (core material), 60 ... mold (mold member), P ... recording paper ( recoding media)

Claims (10)

A transfer member disposed adjacent to an image carrier carrying a toner image and transferring the toner image to a recording medium to which a transfer voltage is applied and interposed between the image carrier and
It is formed of a foam material having a large number of voids, and the volume ratio of the voids is set larger than the central portion at both side edges corresponding to both side edges in the width direction orthogonal to the moving direction of the recording medium. A transfer member characterized by that.   The transfer member according to claim 1, wherein the transfer member is formed in a roll shape including a foam material layer made of the foam material on an outer periphery of a conductive core material.   3. The transfer member according to claim 2, wherein the transfer member is formed in a barrel-shaped crown shape in which the central portion is thicker than the both side end portions. An image carrier for carrying an electrostatic latent image;
A developing device for converting the electrostatic latent image into a toner image;
A transfer member that is disposed adjacent to the image carrier, to which a transfer voltage is applied, and that transfers the toner image to a recording medium interposed between the image carrier and the image carrier.
The transfer member is
It is formed of a foam material having a large number of voids, and the volume ratio of the voids is set larger than the central portion at the side end corresponding to both side edges in the width direction orthogonal to the moving direction of the recording medium. An image forming apparatus.   5. The image forming apparatus according to claim 4, further comprising a transfer conveyance belt member that conveys the recording medium between the image carrier and the transfer member and electrostatically transfers the toner image to the recording medium. The image forming apparatus described.   The image forming apparatus according to claim 4, wherein the transfer member is a roller including a foam material layer made of the foam material on an outer periphery of a conductive core material.   The image forming apparatus according to claim 6, wherein an outer shape of the transfer member is formed in a barrel-shaped crown shape in which the central portion is thicker than the both side end portions. A recording medium which is formed by a foam material having a large number of voids so that the volume ratio of the voids is different in the axial direction, is disposed adjacent to the image carrier carrying a toner image, and is interposed between the image carrier. A manufacturing method for manufacturing a transfer member for transferring the toner image to
The roll raw material kneaded with the foaming agent is foamed so that the outer diameter in the axial direction is different, and after forming a roll-shaped material having a different foaming rate in the axial direction, the outer surface of the roll-shaped material is formed in a predetermined cylindrical shape. A process for producing a transfer member, characterized by comprising:   The roll raw material is inserted into a mold member that has different outer diameters in the axial direction to perform the foaming, and a roll-shaped material having a different foaming rate in the axial direction is formed. The manufacturing method of the transcription | transfer member of description.   The roll raw material is inserted into the mold member that is formed to have a large diameter compared to the central portion at both axial ends, and the foaming rate at both axial ends is large compared to the central portion. The method for producing a transfer member according to claim 9.

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