JPH04335683A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 process in a copying machine, a printer, etc., and more particularly to a transfer apparatus using an electrostatic transfer process.

0002

2. Description of the Related Art A printing device using a transfer roller for an electrophotographic process uses a transfer roller having a conductive member arranged around its shaft and a bias in order to transfer a toner image formed on an image carrier to a recording medium. The transfer device includes a bias control device for applying bias.

The transfer roller of such a transfer device is made of an elastic material such as rubber, and is connected to a drive source.

According to such a device, when transferring the toner image formed on the image carrier, the transfer roller is elastically deformed due to its elasticity to ensure a contact area with the recording carrier and transfer the toner image. Transfer can be performed by supplying the necessary electric field between the toner image surface and the recording carrier.

[0005] Furthermore, since a conveying force can be applied to the recording medium by driving the transfer roller, the recording medium can be conveyed stably.

[0006]

However, when the transfer roller applies a bias between the toner image on the image bearing member and the recording medium, if the elastic portion of the transfer roller has high hardness, the central portion of the toner image is pressed strongly. If the pressure is too high, the problem of image omission occurs, so a common method is to reduce the hardness of the transfer roller and increase the contact area without increasing the pressure.

[0007] As an effective means for this purpose, it is known to use a foam member. This foamed member is usually formed by a reaction injection molding method in which a stock solution of foamed material is injected into a mold and reacted, so the density increases approximately parabolically near the surface, and at least the foamed part is formed on the surface of the foamed member. A solid surface layer with almost no foam cells is formed of the same material. When the transfer roller with such a surface rotates in contact with the image carrier between sheets during continuous paper feeding, residual toner due to cleaning residue on the image carrier and Coulomb force from the developing roller to the image carrier may be generated. Also, toner that adheres due to mirror image force or the like will adhere to the surface of the transfer roller. Furthermore, the adhered residual toner adheres to the back surface of the next page of the recording carrier, causing a problem of back staining. Furthermore, in order to improve the cleaning performance of the transfer roller, a transfer roller in which cells of a foamed member are exposed on the surface is known, but since the surface of such a transfer roller has a uniform cell shape, the cell openings on the surface The shape and the bottom shape of the cell recess tend to be the same shape,
It becomes a bag shape. Therefore, toner easily enters the recesses of the cells, and a large amount of toner easily enters. Furthermore, there is a problem in that the toner is difficult to fall from the bag-shaped cells due to the rotation of the transfer roller.

The present invention has been made in view of the above circumstances, and provides a novel image forming apparatus in which the elastic portion of the transfer roller is formed of a foamed member, in which the back surface of the recording carrier is not stained. It's there. Yet another object is to provide a transfer roller that is easy to manufacture and low cost.

[0009]

[Means for Solving the Problems] In order to solve these problems, the present invention includes an image carrier and an elastic transfer roller that comes into pressure contact with the image carrier, and provides a recording medium between the image carrier and the transfer roller. In an image forming apparatus that transfers images by passing through a carrier, the elastic portion of the transfer roller is formed of a foamed member, and the size of the foamed cells is maximized on the surface of the foamed member of the transfer roller.

Further, the image forming apparatus of the present invention includes an image carrier and an elastic transfer roller that is in pressure contact with the image carrier, and forms an image by passing a recording carrier between the image carrier and the transfer roller to transfer the image. In the apparatus, the elastic portion of the transfer roller is formed of a foamed member, and the foamed member is electrically conductive.

Furthermore, in the image forming apparatus of the present invention, the foam member is made of flexible foam, and is any one of polyurethane foam, polystyrene foam, polyethylene foam, elastomer foam, and rubber foam.

0012

【Example】

(Embodiment 1) The details of the present invention will be explained below based on the illustrated embodiment. FIG. 1 is a schematic sectional view showing the main parts of an electrophotographic printing apparatus using a transfer roller of the present invention, and reference numeral 6 in the figure represents a recording carrier such as paper. Reference numeral 1 denotes a photoreceptor drum which is an image carrier, and rotates in the direction of arrow D in the figure, that is, in the direction of moving the record carrier 6 to the left side, and an optical signal generator 2 that generates a light beam is mounted on the upper part. It is arranged.

A charging unit 3, a developing device 4, and an erase unit 5 are arranged around the photosensitive drum 1. A transfer device 7, which is a feature of the present invention, is arranged below the photosensitive drum 1 to transfer a toner image onto a recording medium 6.

FIG. 2 shows an embodiment of the transfer device of the present invention, in which reference numeral 8 is a transfer roller, 14 is a bias control device for applying a bias to the transfer roller,
It is connected to the transfer roller shaft 9. Further, the transfer roller 8 is held by a bearing 15, and a pressure spring 16 is disposed so as to press the transfer roller 8 against the photosensitive drum 1 via the bearing 15. Further, the transfer roller 8 is connected to the drive gear 1
It is configured to be connected to a drive source via 7.

Next, the foamed member constituting the transfer roller will be explained. An elastic body 10 made of a foamed material is arranged around the transfer roller shaft 9, and the elastic body 10 is formed so that the foamed cells 18 are maximized on the surface B.

FIG. 3 is a diagram showing the density distribution, which also serves as a guideline for the size of the foam cells in the elastic portion of the transfer roller, in the image forming apparatus of the present invention. In the transfer roller elastic portion of the present invention, a foamed member is formed on the shaft by means such as vulcanization adhesion or by integral molding with the shaft, and the foamed portion has continuous foamed cells,
It has sufficient flexibility. Further, the density increases in a substantially parabolic manner near the outer periphery of the shaft and near the surface of the elastic part, and at least a solid surface layer C, which is made of the same material as the foamed part and has almost no foam cells, is formed on the outer periphery of the shaft A and the surface of the elastic part. ing. By polishing the solid surface layer C on the surface of the elastic part under appropriate conditions, the solid surface layer C is removed, and the cell walls expand or break due to stress release due to removal or polishing heat and polishing force. However, the density of the surface B becomes smaller and the cell diameter becomes larger. This state is shown by the broken line in FIG. As shown in FIG. 5, this cell shape is wide on the transfer roller surface and narrow on the transfer roller shaft 9 side. Such an elastic part can be formed by a reaction injection molding method or the like in which a stock solution of the foaming material is injected into a mold and reacted, and the solid surface layer part can be formed on the outer peripheral part of the shaft to improve the fixing strength. In addition, a transfer roller with high mechanical precision can be formed by the subsequent outer periphery polishing process.

[0017] The foamed portion can be used in either a single cell or open cell form, but open cells are preferable because single cells have a large dimensional change due to temperature. Furthermore, by setting the wall thickness of the foamed portion to about 2 to 10 mm, it is possible to secure a large amount of nip with very low pressure, which has been difficult with conventional rubber. Further, as the foam material, a flexible foam material is suitable, and polyurethane foam, polystyrene foam, polyethylene foam, elastomer foam, rubber foam, etc. can be used. Furthermore, as a manufacturing method for the foamed member, in addition to the reaction injection molding method, a gas mixing method, a blowing agent decomposition method, a solvent aeration method, a chemical reaction method, a sintering method, an elution method, etc. can be used. With either manufacturing method, a lightweight and low-cost transfer roller can be manufactured.

[0018] The foamed member can also be made from 1011 to 1 by dispersing conductive fine powder such as carbon black or metal.
0.012 Ωcm or less, preferably 10
A resistance of about 3 to 1010 Ωcm is preferable in terms of transfer function.

In this embodiment, when a print command is input, the record carrier 6 is sent to the photosensitive drum 1 from a stacker (not shown). A toner image is formed on the photoreceptor drum 1 through charging by the charging unit 3, formation of an electrostatic latent image by the optical signal generating device 2, and adhesion of toner to the electrostatic latent image by the developing device 4, in this order. The toner image on the photosensitive drum 1 and the recording medium 6 fed from the stacker move to a nip formed by the transfer roller 8 and the photosensitive drum 1.

Next, the bias control device 14 applies an electric field necessary for transfer to the transfer roller shaft 9 between the toner image and the recording medium 6.
A bias is applied to form a gap between the two. The applied bias is applied from the transfer roller shaft 9 to the contact surface A with the elastic body 10 made of a conductive member. At this time, since the contact surface A is formed by the solid surface layer, there is no gap between the transfer roller shaft 9 and the solid surface layer, and a uniform bias can be applied in the axial direction. A bias is then applied to surface B through the center.

[0021] At this time, surface B can be formed without losing the elasticity of the foamed member by polishing the solid surface layer, which has a higher hardness than the foamed part. Therefore, a large number of nips can be secured with low pressure, and the bias can be applied. becomes more stable.

Next, after the recording medium 6 passes through the nip portion, the transfer roller 8 and the photosensitive drum 1 rotate in contact with each other. At this time,
Since there is residual toner on the photosensitive drum 1 due to cleaning residue, it tries to adhere to the transfer roller 8, but since the surface of the transfer roller 8 has a cell structure,
The toner tends to enter the concave portions of the cell portions or adhere to the convex portions of the cells. At this time, as shown in FIG. 5, since the transfer roller 8 of the present invention has the largest cell size on the surface, the cell recesses become narrower on the transfer roller shaft 9 side, and no one tries to enter the cell recesses. The toner 19 that has been removed is difficult to enter and is difficult to accumulate. Furthermore, the included toner 1
Since the surface opening of the transfer roller 9 is wide, the transfer roller 8 easily falls downward as it rotates. Furthermore, the toner 20 that attempts to adhere to the cell convex portion cannot adhere because the contact area with the cell convex portion is small, and falls as the transfer roller 8 rotates. Therefore, toner is less likely to adhere to the surface of the transfer roller 8, so that stains on the back of the recording medium can be reduced and the life of the transfer roller can be extended.

(Example 2) In general, when making an elastic body electrically conductive, in order to uniformly disperse conductive fine powder such as carbon black, it is necessary to optimize the selection of raw materials and the appropriate stirring conditions. It is necessary and has great difficulty. As a countermeasure, as shown in Fig. 4, the radial section is donut-shaped.
There is a method in which after forming the elastic body 10 made of a conductive member, a resistance value adjusting material 11 is coated around the transfer roller shaft 9 and then inserted into the elastic body 10 in a post-process. In this method, an elastic body 10 having a certain resistance value relative to a set resistance value is adjusted to a set value using a transfer roller shaft 9 coated with a resistance value adjusting material 11 having high resistance accuracy. Since the transfer roller 8 manufactured by this method is also manufactured by the same manufacturing method as the elastic body of the present invention, it is clear that it exhibits the same effect.

[0024]

[Effects of the Invention] As explained above, in the present invention,
In an image forming apparatus that includes an image carrier and an elastic transfer roller that is in pressure contact with the image carrier and transfers a recording carrier by passing the recording carrier between the image carrier and the transfer roller, the elastic portion of the transfer roller is formed of a foamed member. Since the size of the foamed cells is maximized on the surface of the foamed member of the transfer roller, there is no surface area on the surface of the foamed member of the transfer roller, and the convex portions of the cells make contact, so that the residual toner on the image carrier is The contact area becomes smaller, making it difficult for residual toner to adhere. Furthermore, since the concave shape of the cell is wide on the surface and narrow on the shaft side, toner is less likely to accumulate. Therefore, it is possible to extend the life of the transfer roller and reduce stains on the back surface of the recording medium.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an image forming apparatus of the present invention.

FIG. 2 is a front view and a sectional view of a transfer device in Example 1 of the present invention.

FIG. 3 is a density distribution diagram of the transfer roller of the present invention.

FIG. 4 is a sectional view of a transfer roller in Example 2 of the present invention.

FIG. 5 is a cross-sectional view of a transfer roller in implementation order 1 of the present invention.

[Explanation of symbols]

7 Transfer device 8 Transfer roller 9 Transfer roller shaft 10 Elastic body 14 Bias control device 15 Bearing 16 Pressure spring 18 Foam cell

Claims (3)

[Claims] 1. An image forming apparatus comprising an image carrier and an elastic transfer roller in pressure contact with the image carrier, and in which a recording carrier is passed between the image carrier and the transfer roller to transfer the image.
The elastic portion of the transfer roller is formed of a foamed member, and
An image forming apparatus characterized in that the foamed cells are formed to have a maximum size on the surface of the foamed member of the transfer roller. 2. An image forming apparatus comprising an image carrier and an elastic transfer roller that is in pressure contact with the image carrier, and in which a recording carrier is passed between the image carrier and the transfer roller to transfer the image.
The elastic portion of the transfer roller is formed of a foamed member, and
Claim 1, wherein the foam member is electrically conductive.
The image forming apparatus described in . 3. The foam member is made of flexible foam, and includes polyurethane foam, polystyrene foam,
Claim 1 characterized in that it is any one of polyethylene foam, elastomer foam, and rubber foam.
or the image forming apparatus according to 2.