JP2000056594A - Transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device of simple constitution, capable of preventing stains at the ends of an image carrier. SOLUTION: This transfer device includes a contact transfer member 21 having a contact part 21 a making contact with the surface of an image carrier 11, and a toner image on the surface of the image carrier 11 is transferred onto a transfer material 18 by means of a charge applied to the contact transfer member 21 and having an opposite polarity to that of charge on the surface of the image carrier 11. The width D1 of the contact part 21a in a direction perpendicular to the conveying direction of the transfer material 18 is set to be not less than a maximum image area width D2 that is the maximum value of a size in a direction perpendicular to the conveying direction of the area of the transfer material 18 on which the image is transferred and not more than a maximum paper passing width D3 that is the maximum value of a size in a direction perpendicular to the conveying direction of the transfer material 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, an electrostatic latent image is formed by exposing the surface of an image carrier uniformly charged by a charging device to an image by an exposure device to partially attenuate the potential. The electrostatic latent image is visualized by toner supplied from the developing device. The toner image on the surface of the image carrier is transferred to a transfer material by a voltage applied from a transfer device and having a polarity opposite to the charging polarity of the surface of the image carrier.

[0003] Among the above-mentioned transfer devices, there is a contact-type transfer device provided with a contact transfer member such as a transfer roller, a transfer belt, or a transfer drum that comes into contact with the surface of the image carrier. In a conventional contact-type transfer device, the dimension (width) of the contact transfer member in the direction orthogonal to the transfer material transport direction is larger than the maximum value (maximum paper passing width) of the dimension (width) of the transfer material in the transfer material transport direction. It was set large.

For example, a contact type transfer device 1 shown in FIGS. 8 and 9 has a conductive elastic member 3 on the outer periphery of a metal core 2.
And a transfer roller 4 provided with the conductive elastic member 3.
Contacts the transfer paper 6 supplied to the outer periphery of the photosensitive drum 5 as an image carrier. The width D1 of the conductive elastic member 3 is:
The maximum value (maximum image area width D) of the area on the transfer paper 6 where the image is formed in the direction perpendicular to the transfer direction of the transfer paper 6
2) and larger than the maximum sheet passing width D3.

The surface of the photosensitive drum 5 and the toner 7 are negatively charged, and the surface of the photosensitive drum 5 is charged by a positive charge applied from the power source 8 to the conductive elastic member 3 via the metal core 2. The toner 7 is transferred to the transfer paper 6. At this time, since the width D1 of the conductive elastic member 3 is set as described above, the end 3a of the conductive elastic member 3 in the width direction is set.
Protrudes from the widthwise end 6a of the transfer paper 6, and a portion (non-sheet passing portion 5a) of the surface of the photosensitive drum 5 outside the widthwise end 6a of the transfer paper 6 (non-sheet passing portion 5a). Elastic member 3
Are in direct contact with the surface of the photosensitive drum 5. Therefore,
A positive charge is applied from the conductive elastic member 3 to the non-sheet passing portion 5a. This positive charge is injected into the photosensitive drum 5, and a part of the positive charge is neutralized by the negative charge that charges the photosensitive drum 5, but the rest remains inside the photosensitive drum 5. . The remaining positive charges are gradually neutralized by the negative charges on the surface of the photosensitive drum 5, and as a result, the charged potential on the surface of the photosensitive drum 5 decreases with time.

When the width of the transfer paper 6 is the maximum paper passage width D3, as shown by a one-dot chain line L1 in FIG. The surface potential V _O of the body drum 5 drops significantly, and a position (developing position) facing a developing device (not shown)
, The charge potential of the toner supplied from the developing device is lower than the developing potential (developing potential V _b ). As a result, toner adheres to the non-paper passing portion 5a from the developing device, and so-called edge stains occur.

On the other hand, the width of the transfer paper 6 is the maximum paper passing width D3.
10 is sufficiently smaller than the dashed line L2 in FIG.
As shown by the arrow, the decrease rate of the potential V _O of the non-sheet passing portion 5a due to the positive charge applied from the transfer device 1 is small.
Therefore, the surface potential V of the non-sheet passing portion 5a at the developing position
_O does not fall below the development potential _Vb, and toner does not easily adhere to the non-sheet passing portion 5a.

[0008] As described above, when the width of the transfer paper 6 is large, the end portion is easily stained.
It is presumed that this is because the area of the non-sheet passing portion 5a is reduced, and positive electric charges are intensively applied from the conductive elastic member 3 to the non-sheet passing portion 5a.

Conventionally, a charging device is provided between the transfer device and the charging device in order to prevent the above-described end portion contamination, and the surface of the image carrier after the transfer process is once uniformly charged to a predetermined polarity by the charging device. 2. Description of the Related Art There is known an image forming apparatus configured to perform such an operation. To reduce the size of this type of charging device,
Some include a thin conductive sheet that comes into contact with the surface of the image carrier. Further, in order to enhance the effect of uniformly charging the surface of the image carrier, to remove the charge on the surface of the image carrier substantially at the same position as the charging device or on the downstream side in the moving direction of the surface of the image carrier from the charging device. An image forming apparatus provided with a light neutralizing device is also known.

[0010]

However, in the case where a charging device or a light neutralizing device for making the potential of the surface of the image carrier uniform is provided as described above, the size of the image forming apparatus increases, the number of parts increases, and so on. This leads to complicated control and the like, leading to an increase in cost.

In the charging device provided with the conductive sheet, the toner and the post-treatment agent of the toner are easily deposited on the contact portion between the conductive sheet and the image carrier, and the dirt reduces the charging capability in a short time. The end portion is stained again.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems in the conventional transfer device, and provides a transfer device capable of reliably preventing the end portion of the image carrier from being stained with a simple configuration. That is the task.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention comprises a contact transfer member having a contact portion that comes into contact with the surface of an image bearing member. In a transfer device for transferring a toner image on the surface of the image carrier to a transfer material inserted between the contact portion and the surface of the image carrier by the charge of the opposite polarity to the charging polarity, the transfer material of the contact portion is The width that is the dimension in the direction orthogonal to the transport direction is equal to or greater than the maximum image area width that is the maximum value of the dimension in the direction orthogonal to the transport direction of the area where the image of the transfer material is transferred, and It is an object of the present invention to provide a transfer apparatus characterized in that the transfer material is set to be equal to or less than a maximum sheet passing width which is a maximum value of a dimension of a transfer material in a direction orthogonal to the transport direction.

In the transfer device of the present invention, the width of the contact portion of the contact transfer member is set to be equal to or greater than the maximum image area width and equal to or less than the maximum paper passing width, so that the contact portion protrudes from the transfer material and directly contacts the surface of the image carrier. Never do. Therefore, it is possible to prevent the charge having the opposite polarity to the charge polarity of the image carrier from being applied from the contact transfer member to the image carrier surface, and the toner adheres to the image carrier surface to cause edge stains. Can be prevented.

The contact transfer member includes a non-contact portion at both ends in the width direction of the contact portion opposed to the surface of the image carrier with a space therebetween, and the non-contact portion is provided with an image toward an end in the width direction. The distance from the non-contact portion to the surface of the image carrier at the position corresponding to both ends of the transfer material with the maximum paper passing width is continuously increased from the contact transfer member to the image carrier. In the portion from the connection between the contact portion and the non-contact portion to the position corresponding to both ends of the transfer material having the maximum paper passing width, the distance from the non-contact portion to the surface of the image carrier is set so that no charge is applied. Alternatively, the contact transfer member may be set so that charges of opposite polarity are applied to the transfer material.

With this configuration, even if the position of the toner image on the surface of the image carrier relative to the contact transfer member in the width direction is displaced, in the image area, the polarity is opposite to that of the surface of the image carrier from the contact transfer member to the transfer material. Is reliably applied, so that loss of an image can be prevented.

As the contact transfer member, a transfer roller,
There are a transfer drum and a transfer belt.

When a transfer roller is employed as the contact transfer member, it is preferable to provide a rotary drive mechanism for rotating the transfer roller synchronously with the image carrier.

[0019]

Next, the present invention will be described in detail based on an embodiment shown in the drawings.

(First Embodiment) FIG. 1 shows an electrophotographic image forming apparatus provided with a transfer device 10 according to a first embodiment of the present invention. Photoconductor drum 1 as image carrier
1 is driven to rotate in the direction of arrow A by a drive mechanism (not shown), and a charging device 12, an exposure device 13, a developing device 14, a transfer device 10 and a cleaning device 15 are arranged around the device in the direction of rotation.

The photosensitive drum 11 uniformly charged to a predetermined polarity (minus in this embodiment) by the charging device 12
Is exposed to light from the exposure device 13 to form an electrostatic latent image. This electrostatic latent image is visualized by toner supplied from the developing device 14.

On the other hand, the transfer paper 18, which is a transfer material supplied from a paper supply unit (not shown), is provided with registration rollers 19A, 19A.
B and the transfer device 1 in synchronization with the rotation of the photosensitive drum 11
Transported to zero. In the transfer device 10, the photosensitive drum 1
The transfer paper 18 to which the toner image on one surface has been transferred is guided by a transport guide 19 and discharged to a discharge tray (not shown) via a fixing device (not shown). A plurality of types of transfer papers 10 having different sizes are accumulated in the paper supply unit, and transfer papers of a predetermined size are supplied according to an input from an operation switch (not shown).

As shown in FIGS. 2 and 3, the transfer device 10 has a cylindrical core 20 made of a conductive metal.
Is provided with a transfer roller 22 having a columnar conductive elastic member 21 having a constant outer diameter formed of a conductive sponge made of urethane foam. A gear 24 fixed to one end of the cored bar 20 is engaged with a gear 26 fixed to one end of a rotating shaft 25 of the photosensitive drum 11, and the transfer roller 22 is synchronized with the photosensitive drum 11. It is designed to rotate.

The transfer paper 18 of the conductive elastic member 21
Is set to be equal to or larger than the maximum image area width D2. The width D1 of the conductive elastic member 21 is set to be equal to or less than the maximum sheet passing width D3.

The operation of the transfer device 10 will be described.
The transfer paper 18 conveyed by the registration rollers 19A and 19B is synchronized with the arrival of the toner image formed on the surface of the photosensitive drum 11 in the area facing the transfer roller 22 by the transfer roller 18. And transfer roller 22
Of the conductive elastic member 21 of FIG.

Further, a charge having a polarity opposite to the charge polarity on the surface of the photosensitive drum 11 (positive in this embodiment) is applied to the conductive elastic member 21 from the power supply 28 via the core 20.

As described above, the width D1 of the conductive elastic member 21
Is set to be larger than the maximum image area width D2, so that the toner image on the surface of the photosensitive drum 11 has a positive charge applied to the conductive elastic member 21 even when the width of the transfer paper 18 is large. Is transferred to the transfer paper 18 reliably.

On the other hand, since the width D1 of the conductive elastic member 21 is set to be equal to or less than the maximum sheet passing width D3, even if the width of the transfer paper 18 is large, the end 21a of the conductive elastic member 21 is
As shown in FIGS. 2 and 3, the widthwise end of the conductive elastic member 21 is located outside the widthwise end 18 a of the maximum image area and inside the widthwise end 18 b of the transfer paper 18. The portion 21a does not protrude from the end 18b in the width direction of the transfer paper 18. Therefore, the conductive elastic member 21 is
Paper contact portion 11 on the surface of the photosensitive drum 11
A positive charge is not directly applied to a from the conductive elastic member 21. Therefore, as shown by the solid line L3 in FIG. 4, the rate of decrease in the charging potential of the non-sheet passing portion 11a is small, and does not fall below the developing voltage _Vb even when the non-sheet passing portion 11a reaches the developing position. No toner 7 is supplied.

As described above, in the transfer device 22 of the present embodiment, the width D1 of the conductive elastic member 21 is set to the maximum image area width D2.
By setting the width to be equal to or less than the maximum paper passing width D3, it is possible to reliably prevent the end portion of the photosensitive drum 11 from being stained without providing a charging device or a light removing device.

(Second Embodiment) In a second embodiment of the present invention shown in FIGS. 5 and 6, the conductive elastic member 21 of the transfer roller 22 has a cylindrical shape with a constant outer diameter, and
A contact portion 21a that contacts the surface, and a tapered non-contact portion 21 that is provided continuously at both ends in the width direction of the central portion 21a.
b, 21b.

In the non-contact portion 21b, the conductive elastic member 21
The outer diameter continuously decreases at a constant rate toward the end in the width direction, and the distance from the surface of the photosensitive drum 11 continuously increases at a constant rate. The reduction rate of the outer diameter of the non-contact portion 21b is determined by the distance t from the surface of the conductive elastic member 21 to the surface of the photosensitive drum 11 at the position P corresponding to the width end portion 18b of the transfer paper 18 having the maximum width. Is a conductive elastic member 2
The value is set to a value from 1 to such an extent that a positive charge is not applied to the surface of the photosensitive drum 11. Therefore, in the non-sheet passing portion 11a located on the end side in the width direction of the conductive elastic member 21 from the position P, a positive charge is not applied to the photosensitive drum 11 from the conductive elastic member 22.
It is possible to prevent the toner 7 from adhering to the non-sheet passing portion 11a due to the potential decay due to the charge.

On the other hand, in a portion Q from the connection between the contact portion 21a and the non-contact portion 21b to the position P, the distance from the surface of the conductive elastic member 22 to the surface of the photosensitive drum 11 is:
The value is set such that a positive charge is charged from the conductive elastic member 21 to the transfer paper 18. Therefore, even when the position of the toner image formed on the surface of the photosensitive drum 11 is shifted in the width direction of the conductive elastic member 22 as shown by the arrow B, the position shift of the toner image is not limited to the above-described portion. Within the range of Q, the entire toner image is reliably transferred to the transfer paper 18 by the positive charge applied from the conductive elastic member 22, and image defects can be prevented.

The other configuration and operation of the second embodiment are the same as those of the above-described first embodiment. Therefore, the same components are denoted by the same reference numerals and detailed description thereof will be omitted.

(Third Embodiment) FIG. 7 shows a transfer device according to a third embodiment of the present invention. In the third embodiment, the conductive elastic member 21 of the transfer roller 22 includes a non-contact portion 21b whose outer diameter decreases stepwise on both sides in the width direction of the contact portion 21a. As in the second embodiment, the distance t from the surface of the conductive elastic member 21 to the surface of the photosensitive drum 11 at the position P corresponding to the widthwise end portion 18b of the transfer paper 18 having the maximum paper passing width is equal to this position. P is set to a value at which a positive charge is not directly applied from the conductive elastic member 21 to the photosensitive drum 11. Therefore, the non-sheet passing portion 11
a, the conductive elastic member 21
, No positive charge is applied, and it is possible to prevent toner from adhering to the non-sheet passing portion 11a due to the potential decay due to the charge.

On the other hand, in a portion Q from the connection between the contact portion 21a and the non-contact portion 21b to the position P, the distance from the surface of the conductive elastic member 21 to the surface of the photosensitive drum 11 is:
The value is set such that a positive charge is charged from the conductive elastic member 21 to the transfer paper 18. Therefore, in the range of the portion Q, the position of the toner image is indicated by the arrow B in the conductive elastic member 2.
Even when the toner image is displaced in the width direction, the entire toner image is reliably transferred to the transfer paper 18, thereby preventing image loss.

The other configuration and operation of the third embodiment are the same as those of the above-described first embodiment. Therefore, the same components are denoted by the same reference numerals and detailed description is omitted.

The present invention is not limited to the above-described embodiment, but can be variously modified. The material of the conductive elastic member is not limited to the conductive sponge made of urethane foam, and the conductive and elastic members are not limited to the conductive sponge. Silicon, EP if the material has
Various materials such as DM can be used. Further, the conductive elastic member may be formed by a tube formed by laminating these materials.

The transfer roller may be driven to rotate with the photosensitive drum by contact pressure with the photosensitive drum, or may be driven to rotate by a drive mechanism different from the photosensitive drum. Good.

Further, the present invention is not limited to the transfer roller, but can be applied to a transfer device having another type of contact transfer member such as a transfer belt and a transfer drum.

[0040]

As is apparent from the above description, in the transfer apparatus of the present invention, the width of the contact portion of the contact transfer member is set to be not less than the maximum image area width and not more than the maximum sheet passing width, and therefore, the transfer device has the maximum width. When the transfer material is used, it is possible to prevent the contact transfer member from coming into contact with the non-sheet passing portion on the surface of the image carrier, and to prevent the end portion from being stained due to the toner adhering to the non-sheet passing portion.

Further, the transfer device of the present invention can prevent the end portion from being stained only by setting the width of the contact portion within the above-mentioned range, has a simple structure, increases the size of the device, increases the number of parts, There is no complication of control.

Further, in the case where a non-contact portion whose distance from the surface of the image carrier increases continuously or stepwise toward both ends in the width direction of the contact transfer member at both ends of the contact portion, an image is formed. It is possible to prevent image defects due to a displacement of the toner image on the surface of the carrier in the width direction.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus including a transfer device according to a first embodiment of the present invention.

FIG. 2 is a schematic perspective view showing a transfer device according to the first embodiment of the present invention.

FIG. 3 is a partially enlarged sectional view taken along the line III-III of FIG. 2;

FIG. 4 is a diagram showing a change in a surface potential of a non-sheet passing portion.

FIG. 5 is a schematic perspective view illustrating a transfer device according to a second embodiment of the present invention.

6 is a partially enlarged sectional view taken along line VI-VI of FIG.

FIG. 7 is a partially enlarged cross-sectional view illustrating a transfer device according to a third embodiment of the present invention.

FIG. 8 is a schematic perspective view showing a conventional transfer device.

9 is a partially enlarged sectional view taken along line IX-IX in FIG.

FIG. 10 is a diagram illustrating a change in surface potential of a non-sheet passing portion.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 transfer device 11 photoreceptor drum (image carrier) 18 transfer paper (transfer material) 20 metal core 21 conductive elastic member 21a contact portion 21b non-contact portion 22 transfer roller (contact transfer member) 28 power supply D1 width D2 maximum image area Width D3 Maximum paper width

Claims (4)

[Claims] A contact transfer member having a contact portion which comes into contact with the surface of the image carrier, wherein the contact portion and the image carrier are charged by a charge applied to the contact transfer member having a polarity opposite to a charge polarity of the surface of the image carrier. In a transfer device for transferring a toner image on the surface of an image carrier onto a transfer material inserted between the transfer material and the body surface, a width of the contact portion in a direction perpendicular to a direction in which the transfer material is conveyed is set as a transfer material. Is larger than the maximum image area width which is the maximum value of the dimension of the area where the image is transferred in the direction orthogonal to the transport direction, and the dimension of the dimension in the direction orthogonal to the transport direction of the transfer material. A transfer apparatus characterized in that the transfer width is set to be equal to or less than a maximum value, that is, a maximum sheet passing width. 2. The contact transfer member includes a non-contact portion at both ends in the width direction of the contact portion, opposed to the surface of the image carrier with a space therebetween, and the non-contact portion faces an end in the width direction. The distance from the non-contact portion to the surface of the image carrier at the position corresponding to both ends of the transfer material with the maximum paper passing width is continuously increased from the contact transfer member to the image carrier. Set so that electric charge of opposite polarity is not applied, and in the part from the connecting part of the contact part and the non-contact part to the position corresponding to both ends of the transfer material of the maximum paper passing width, the part from the non-contact part to the image carrier surface 2. The transfer device according to claim 1, wherein the distance is set such that charges of opposite polarity are applied to the transfer material from the contact transfer member. 3. The contact transfer member includes a non-contact portion at both ends in the width direction of the contact portion opposed to the surface of the image carrier with a space therebetween, and the non-contact portion faces an end in the width direction. The distance from the non-contact portion to the surface of the image carrier at the position corresponding to both ends of the transfer material with the maximum paper passing width is gradually increased from the contact transfer member to the image carrier. Set so that electric charge of opposite polarity is not applied, and in the part from the connecting part of the contact part and the non-contact part to the position corresponding to both ends of the transfer material of the maximum paper passing width, the part from the non-contact part to the image carrier surface 2. The transfer device according to claim 1, wherein the distance is set such that charges of opposite polarity are applied to the transfer material from the contact transfer member. 4. The apparatus according to claim 1, wherein said contact transfer member comprises a transfer roller.
The transfer device according to Item.