JPH0830123A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which is equipped with a transfer roller capable of carrying a transfer material at regular speed without being influenced by the kind of the transfer material and being inexpensively and easily produced and where the deterioration of an image such as transfer deviation is eliminated. CONSTITUTION:Transfer bias is applied to the transfer roller 2 consisting of an elastic roller which comes into contact and rotates with an image carrier, so that a toner image formed on the image carrier is transferred on the transfer material carried to a nip part between the image carrier and the transfer roller 2. The length (h) of the transfer roller 2 in an axial direction is made longer than the maximum width of the transfer material which can pass through the nip part and at least the outside diameter Da of one part other than a transfer material passing part of the transfer roller 2 is formed to be a little larger than the outside diameter Db of the transfer material passing part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system.

[0002]

2. Description of the Related Art Conventionally, transfer bias is applied to a transfer roller that rotates in contact with an image carrier (photoconductor), and the transfer material (transfer paper) is conveyed to a nip portion between the image carrier and the transfer roller. , A recording medium), a roller transfer type image forming apparatus is known which transfers the toner image formed on the image carrier.

The prior art relating to this roller transfer type image forming apparatus is as follows: (1) The axial length of the transfer roller is made longer than that of the recording medium, and the thickness of the recording medium is provided at both outer ends of the recording medium. By integrally forming a protrusion having a height smaller than the entire circumference over the entire circumference, the adhesion between the image carrier and the recording medium is secured and at the same time the transfer roller is prevented from being soiled (JP-A-63-7).
"Structure of transfer member" described in Japanese Patent No. 5773). (2) By making the outer diameter of the transfer roller or the core metal into a crown shape, a uniform nip width can be obtained over the entire length of the transfer roller ("Image forming apparatus" described in JP-A-2-24685). . (3) By processing the outer diameter of the transfer roller into an inverted crown shape, the occurrence of slack and wrinkles on the transfer paper is suppressed, and
An image having no unevenness is obtained (“image forming apparatus” described in JP-A-4-321082). (4) A transfer roller having an elastic region at the center, which is substantially the same as the maximum lateral dimension of the transfer material used, and regions that are not substantially elastically deformed at both ends on the outer side in the axial direction. By using a member having a large friction coefficient or a member having a relatively high resistance, a light pressure and a uniform pressure are applied to the transfer material to provide an image free from transfer marks and transfer deviations (Japanese Patent Laid-Open No. 4-215680). "Transfer roller"). Etc. are known.

[0004]

By the way, as shown in FIGS. 8 and 9, the image carrier 1 is not driven by an external drive.
In the image forming apparatus using the transfer roller 2 which is rotated together by contact with the elastic layer 2 of the transfer roller 2.
When the axial width h _{2 of a} is substantially the same as the maximum width h ₃ of the transfer material 3 that can be passed, when the maximum width of the transfer material 3 that can be passed is passed, the transfer roller 2 Since the contact surface between the surface of the image carrier 1 and the image carrier 1 is almost eliminated only at the portions A at both ends of the elastic layer 2a, the rotation of the transfer roller 2 is reduced.
The area due to the frictional force between the non-transfer surface (back surface) and the surface of the transfer roller 2 becomes large.

Therefore, in this type of image forming apparatus, O
When the transfer speed of the transfer material deviates from the linear speed of the image carrier 1 for some reason when a transfer material having a maximum width such as a HP sheet or a thick paper that can be passed through is passed. The deviation cannot be completely absorbed by the bending of the transfer material, resulting in a change in the linear velocity at the transfer portion.

This is because an anti-conveying force due to the stiffness of the transfer material 3 is applied to the transfer material 3, and this anti-conveying force tries to convey the transfer material 3 at a constant speed with the image carrier 1. The transfer material 3 overcomes the transport force (the combined force of the electrostatic transport force with the image carrier 1 and the transport force applied from the transfer roller 2) to transfer the transfer material 3 to the surface of the transfer roller 2 and the image carrier 1. Slip or transfer material 3
Is caused to slip on the surface of the image carrier 1 while dragging the transfer roller 2.

As a result, in this type of image forming apparatus, the transfer material cannot be conveyed at a regular speed, which may cause image deterioration such as transfer deviation.

As a method for solving such a problem,
Among the above-mentioned conventional techniques, like the "transfer roller" described in Japanese Patent Laid-Open No. 4-215680, the transfer material passing portion of the transfer roller is formed of an elastic member, and the outer portion thereof is formed of a member that is not elastically deformed. Therefore, the method of ensuring the driving force of the transfer roller is effective.

However, in the image forming apparatus using this method, since the constituent material is different between the central portion and both end portions of the transfer roller, the manufacturing process of the transfer roller and the used material increase, and the cost increases. There is.

The present invention has been made in view of the above points, and an object thereof is to convey a transfer material at a regular speed without being influenced by the type of the transfer material, and to easily and inexpensively manufacture the transfer material. An object of the present invention is to provide an image forming apparatus equipped with a transfer roller capable of eliminating image deterioration such as transfer deviation.

[0011]

According to the present invention, in order to solve the above-mentioned problems, in claim 1, a transfer bias is applied to a transfer roller composed of an elastic roller which rotates in contact with an image carrier. In the image forming apparatus for transferring the toner image formed on the image carrier to the transfer material conveyed to the nip portion between the image carrier and the transfer roller, the axial length of the transfer roller. Is formed to be longer than the maximum width of the transfer material that can be passed through the nip portion, and the outer diameter of at least one of the portions other than the transfer material passing portion of the transfer roller is set to the outer diameter of the transfer material passing portion. The configuration is slightly larger than the above.

According to a second aspect of the present invention, the surface of the large diameter portion of the transfer roller that comes into contact with the image carrier is coated with a material having a resistance higher than the specific resistance of the transfer roller.

According to a third aspect of the present invention, the coefficient of static friction of the surface of the large diameter portion of the transfer roller that comes into contact with the image carrier with respect to the surface of the image carrier is defined as the static friction coefficient of the transfer material sheet passing portion of the transfer roller. The configuration is set to be larger than the coefficient of static friction with respect to the surface of the image carrier.

Further, in the present invention, when the large diameter portion of the transfer roller is formed only on one side of the transfer roller, the pressing force Fa applied to the rotary shaft on the side where the large diameter portion of the transfer roller is not formed is Fa. And the pressing force Fb applied to the rotary shaft on the side where the large diameter portion of the transfer roller is formed is Fa <
The transfer roller is brought into pressure contact with the image carrier so as to be Fb.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings. Transfer roller 2 in the image forming apparatus of the present invention
As shown in FIG. 1, is a core metal member 2b made of metal, conductive ceramic, hard plastic, or the like.
And an elastic layer 2a formed of a conductive elastic member such as a conductive rubber formed so as to cover the periphery of the core metal member 2b, and the axial length h thereof is the image carrier. 1 and with is formed longer than the maximum width h ₃ of the transfer material 3 that can be sheet passing the nip portion between the transfer roller 2, at least one of the outer portions of the non-sheet passing portion of the transfer material 3 of the transfer roller 2 The diameter Da is formed to be slightly larger than the outer diameter Db of the sheet passing portion of the transfer material 3.

Further, in the transfer roller 2 of this embodiment, as shown in FIGS. 1 and 2, the width a of the paper passing portion 2c passes through the nip portion between the image carrier 1 and the transfer roller 2. Transfer material 3
Is longer than the maximum width h _{3 of} the same and the width b of the large diameter portion 2d
However, it is set large enough.

Therefore, according to the image forming apparatus equipped with this transfer roller, even when a transfer material having a strong elasticity such as an OHP sheet or a thick paper is passed, as shown in FIG. However, since it is pressed against the surface of the image carrier 1 with a sufficient width b, the rotational force of the transfer roller 2 to be driven at the same speed as the image carrier 1 can be increased, and the transfer material 3 It is possible to suppress the effect of changing the transport speed.

Here, when the transfer roller 2 is provided with the large diameter portions 2d as shown in FIG. 1A, the pressing force F applied to both ends of the transfer roller 2 as shown in FIG. Are set to be equal to each other. However, as shown in FIG. 1B, when the large diameter portion 2d is provided only on one side of the transfer roller 2, the same pressing force F is applied to both ends of the transfer roller 2 as in the example shown in FIG. When applied, the nip width of the paper passing portion 2c of the transfer roller 2 with respect to the image carrier 1 becomes as shown in FIG.
As indicated by N1, the transfer roller 2 is extremely uneven on the left and right sides, and the transferability and the transportability are different between the left and right sides, which causes problems such as uneven transfer and wrinkles on the transfer material 3.

Therefore, when the large diameter portion 2d of the transfer roller 2 is formed only on one side of the transfer roller 2 as described above,
Pressurizing force Fa applied to the rotary shaft of the transfer roller 2 on the side where the large diameter portion 2d is not formed, and pressurizing force Fb applied to the rotary shaft of the transfer roller 2 on the side where the large diameter portion 2d is formed.
The relationship is set so that Fa <Fb, and the transfer roller 2 is brought into pressure contact with the image carrier 1. In this way, by changing the pressing force at each end of the transfer roller 2 to optimize it,
As indicated by N2 in FIG. 3, the nip width of the sheet passing portion 2c of the transfer roller 2 with respect to the image carrier 1 can be made substantially uniform to the extent that the transferability and the transportability thereof do not occur.

On the other hand, in the transfer roller in the image forming apparatus of the present invention, the surface of the large-diameter portion 2d which is in contact with the image carrier 1 of the transfer roller 2 is unique to the elastic layer 2a, as shown by the diagonal lines in FIG. It may be configured to be coated with a material having a higher resistance than the resistance.

As a method of manufacturing the transfer roller 2, for example, as shown in FIG. 5, first, a roller having an elastic layer 2 having a uniform outer diameter over the entire width in the axial direction is formed (step 1), and then, this A coating material having a resistance higher than the specific resistance of the elastic layer 2a is applied to the surface of the roller (step 2), and finally, the paper passing portion 2c and the large diameter portion are formed so as to leave only the both ends where the coating material is applied. The part 2d is cut out (step 3).

As described above, since the transfer roller 2 can be manufactured only by adding a relatively simple step of applying the coating material in the manufacturing process, a large increase in cost can be avoided.

As shown in FIG. 6, the transfer roller in the image forming apparatus of the present invention has a coefficient of static friction of the surface of the large diameter portion 2d of the transfer roller 2 which is in contact with the image carrier 1 with respect to the surface of the image carrier. May be set to be larger than the static friction coefficient of the transfer material of the transfer roller 2 with respect to the surface of the image carrier of the sheet passing portion 2c.

As a method of manufacturing the transfer roller 2, for example, as shown in FIG. 7, first, a urethane roller in which the elastic layer 2 made of foaming urethane is carved out slightly larger than the regular outer diameter is formed. (Step 1) Next, a flange-shaped roller 4 having the same outer diameter Da as the outer diameter Da of the large diameter portion 2d of the regular transfer roller 2 is provided on both support shaft portions of the urethane roller.
Is mounted, and the heated heat roller 5 is brought into contact with the surface of the urethane roller while rotating, and the outer diameter of the urethane roller is the outer diameter D of the large diameter portion 2d of the regular transfer roller 2.
The surface of the urethane roller is heated to melt the surface layer until the outer diameter becomes the same as that of a (that is, until the heat roller 5 comes into sliding contact with each roller 4) (step 2), and then the outer diameter Da is formed. Both ends of the urethane roller (large diameter part 2
Except for d), the sheet passing portion 2c is carved out until the outer diameter Db is obtained (step 3).

In this manner, the coefficient of static friction of the surface of the large-diameter portion 2d with respect to the surface of the image carrier is formed to be larger than the coefficient of static friction with respect to the surface of the image carrier of the paper passing portion 2c. In the case of this transfer roller 2 as well as the above-mentioned transfer roller, since it can be manufactured only by adding a relatively simple process of heating the surface of the urethane roller by the heat roller 5 in the manufacturing process, a significant cost is increased. It does not invite up.

[0026]

According to the present invention, in claim 1, the OHP
Even if a strong transfer material such as a sheet or thick paper is passed through, the driving force necessary to rotate the image carrier can be secured, thus preventing uneven transfer and transfer deviation. Moreover, such an effect can be realized with a simple structure, and the manufacturing cost can be suppressed.

In the second aspect, since the portion of the transfer roller which is in contact with the image carrier is coated with the high resistance material, it is possible to prevent the transfer current from flowing from the contact portion to the image carrier side. It is possible to suppress a decrease in transferability and to manufacture this transfer roller at a low cost with a simple structure.

In the third aspect, since the friction coefficient of the portion of the transfer roller which is in contact with the image carrier is larger than the friction coefficient of the paper passing portion, no matter what kind of transfer material is passed, The driving force required to rotate the image carrier can be secured, uneven transfer and transfer deviation can be prevented, and the transfer roller can be manufactured at a low cost with a simple structure.

According to the present invention, since the large diameter portion is formed only on one side of the transfer roller, the axial length of the transfer roller can be shortened, the apparatus can be downsized, and the large diameter portion can be realized. Since the pressing force on one side is set to be larger than the pressing force on the other side, the nip width with respect to the image carrier can be optimized substantially uniformly, and good transferability and transportability can be secured.

[Brief description of drawings]

FIG. 1 is a schematic side view showing a configuration of a transfer roller in an image forming apparatus of the present invention.

FIG. 2 is a schematic side view showing the configuration of the embodiment of the image forming apparatus of the present invention.

FIG. 3 is a schematic side view showing the configuration of another embodiment of the image forming apparatus of the invention.

FIG. 4 is a schematic side view showing the configuration of another transfer roller in the image forming apparatus of the present invention.

FIG. 5 is a schematic side view showing a manufacturing process of another transfer roller in the image forming apparatus of the present invention.

FIG. 6 is a schematic side view showing the configuration of still another transfer roller in the image forming apparatus of the present invention.

FIG. 7 is a schematic side view showing still another transfer roller manufacturing process in the image forming apparatus of the present invention.

FIG. 8 is a perspective view of a transfer roller in a conventional image forming apparatus.

FIG. 9 is a schematic side view showing a configuration of a transfer unit of a conventional image forming apparatus.

[Explanation of symbols]

1 image carrier 2 transfer roller 2a elastic layer 2b core metal member 2c transfer roller sheet passing portion 2d transfer roller large diameter portion 3 transfer material a sheet passing portion width b large diameter portion h transfer roller axial direction Width h ₃ Transfer material width Da Large diameter outer diameter Db Paper passing outer diameter F, Fa, Fb Applied pressure

Claims (4)

[Claims] 1. A transfer roller, which is an elastic roller rotating in contact with an image carrier and rotating together, applies a transfer bias to the transfer material conveyed to the nip portion between the image carrier and the transfer roller. In the image forming apparatus for transferring the toner image formed on the image carrier, the axial length of the transfer roller is formed longer than the maximum width of the transfer material which can be passed through the nip portion. An image forming apparatus, wherein an outer diameter of at least one portion of the transfer roller other than the transfer material sheet passing portion is formed to be slightly larger than the outer diameter of the transfer material sheet passing portion. 2. The surface of a large diameter portion of the transfer roller which comes into contact with the image carrier is coated with a material having a resistance higher than the specific resistance of the transfer roller.
The image forming apparatus described. 3. The coefficient of static friction of the surface of the large diameter portion of the transfer roller that comes into contact with the image carrier with respect to the surface of the image carrier is defined as the surface of the image carrier of the transfer material sheet passing portion of the transfer roller. 3. The image forming apparatus according to claim 1, wherein the coefficient of static friction is larger than the coefficient of static friction. 4. When the large diameter portion of the transfer roller is formed only on one side of the transfer roller, the pressing force Fa applied to the rotary shaft on the side where the large diameter portion of the transfer roller is not formed, and the transfer roller. 7. The transfer roller is brought into pressure contact with the image carrier so that the relationship with the pressing force Fb applied to the rotating shaft on the side where the large diameter portion of the image is formed is Fa <Fb. The image forming apparatus according to any one of claims 1 to 3.