JPH01185572A - 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 (1) Object of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus that uses an electrostatic transfer process, such as an electrostatic copying machine and a printer thereof.

(Prior Art and Issues to be Solved) In a well-known image forming apparatus that repeats the process of forming a transferable toner image on the surface of an image carrier and transferring it to a sheet-like transfer material mainly made of paper, toner A roller transfer type image forming apparatus configured to press an electrically conductive transfer roller to which a bias is applied to an image bearing member that carries an image, and to pass a transfer material between the two to transfer the toner image to the transfer material. has already been proposed.

This type of image forming apparatus achieves high transfer rates with a low bias compared to the conventionally widely used corona transfer method, in which a transfer material is brought into contact with a toner image and a corona discharge is applied from behind. It is efficient, is not affected by temperature and humidity, and can reliably hold the transfer material at the transfer site and provide strong conveyance force.
It is known that this method has various advantages, such as being able to more freely form the transfer material conveyance path and therefore the overall configuration of the device.

However, on the other hand, the roller transfer method has the following problems and has been difficult to put into practical use.

In other words, the transfer roller that comes into pressure contact with the image carrier first
It is common to add a plasticizer to rubber to give it appropriate elasticity, and add carbon black to give it conductivity, but this has an adverse effect on toner and the photosensitive layer on the surface of the image carrier. In order to avoid this, it is necessary to reduce the amount of plasticizer, and it is difficult to reduce the hardness of the roller due to the inclusion of carbon black or the like.

Therefore, in order to obtain a sufficient pressure nip between the transfer roller and the image carrier, the transfer roller must be strongly pressed against the image carrier.
In particular, there are problems with so-called hollow areas, where the center portion is pressed against the image carrier and is not transferred, and may cause damage to the photosensitive layer.

In order to reduce the hardness of the transfer roller and avoid the above situation, increasing the amount of plasticizer in the roller or decreasing the amount of conductive material such as carbon black will reduce the viscosity of the roller. In addition, the roller becomes difficult to clean, and this leads to contamination of the transfer material, which is undesirable.In the latter case, the roller cannot have the desired conductivity, so it is not practical. I can't stand it anymore.

In order to substantially reduce the hardness of the transfer roller, it may be possible to use a sponge-like material, but ordinary sponge materials have too many irregularities on one surface to prevent toner from firmly adhering to the recesses. Also, cleaning becomes difficult because the friction with the cleaning member is large.

The present invention has been made in view of the above situation, and an object of the present invention is to provide an image forming apparatus that uses a transfer roller, which achieves good transfer by rotation and has good cleaning/cleaning properties. That is.

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention includes a moving image bearing member and an elastic transfer roller that comes into pressure contact with the image bearing member. In an image forming apparatus that transfers a toner image on an image carrier to a transfer material by passing a transfer material between the two, the transfer roller is formed of fine continuous pores, and the pore diameter on the surface of the roller is It is characterized by having a smaller porosity than that inside.

With this configuration, the transfer roller can sufficiently form a nip portion necessary for transfer with a low pressing force, and the cleaning performance of the transfer roller can be improved.

(Description of Embodiments) FIG. 1 is a schematic side view showing the main parts of an embodiment in which the present invention is applied to a copying machine equipped with a rotating cylindrical photoreceptor.

An elastic transfer roller 2, which will be described below, is placed in pressure contact with a photoreceptor l extending perpendicularly to the plane of the paper and rotating in the direction of arrow A, so as to form a nip portion N of an appropriate amount.

When the transferable toner image formed on the surface of the photoreceptor 1 reaches the nip portion N as the photoreceptor rotates, a transfer material (not shown) is supplied by the conveyance path 3a at the same time as the photoreceptor. It is assumed that the toner image is brought into contact with the toner image on the body surface, and the toner image is transferred to the transfer material by the action of the bias applied thereto, and is then transported to a fixing site (not shown) via the transport path 3b.

As is well known, around the photoreceptor l,
The components necessary for image formation are provided, including a primary charger for charging the surface of the photoreceptor, an image signal applying means for forming a latent image thereon, a developing device for converting the latent image into a visible toner image, and a cleaning device. Of course, these are not directly related to the present invention, so they are all omitted.

Since the transfer roller 2 is always in pressure contact with the photoreceptor l, it is inevitable that toner will adhere to the transfer roller side, but for this reason, this toner will adhere to the back side of the transfer material that arrives from next time onwards. A cleaning blade 4 is brought into contact with the transfer roller to remove the toner so that the back side is not stained and the toner is not transferred to the photoreceptor and contaminates the screen.

The cleaning blade 4 has wear resistance, heat resistance, hardness,
Urethane is suitable from the viewpoint of reactivity with toner, and it is applied to the surface of the transfer roller 4 at a thickness of 20 to 50 g/cm.
shall be brought into elastic contact with a force of .

As the transfer roller 2, a polyurethane microporous sponge (trade name: Rubices, manufactured by Toyo Polymer Co., Ltd.), in which carbon was dispersed in a conductive fine open-pore material, was used.

In the case of the illustrated apparatus, the transfer roller was formed by unwinding 2b the material onto a metal core 2a with a diameter of 8φ to form a roller with an outer diameter of 16φ, and a bias was applied through the core.

The resistance of the porous material is 102~10"0cm, the bubble diameter is 10~50uLm inside, 1~5μLm on the surface, and the porosity (ratio of volume of bubbles contained in unit volume) is A skin layer was formed with a thickness of 80% or more on the surface and 70% or less on the surface.The appropriate thickness of the skin layer is 0.5 to lam.

With this structure, it has appropriate conductivity, has a small surface unevenness, has a low coefficient of friction, does not require a large amount of plasticizer, does not react with toner, has low viscosity, and has a hardness of 400 ( JISA) A flexible transfer roller was obtained.

By using the above-mentioned roller, a good image without voids was obtained, and the transfer roller was also easy to clean, and the photoreceptor was not damaged.

As a cleaning means for the transfer roller as described above, in addition to a cleaning blade, for example, as shown in FIG. A web cleaning method is constructed in which the web W is pressed against the transfer roller 2 and is sequentially removed in the direction of the arrow shown in the figure.As shown schematically in FIG. Of course, it is possible to use various types of one-stage leaning, such as a pad cleaning method in which the pad 5 is pressed against the pad 5 or a fur brush 6 as shown in FIG.

Further, although the present invention has been described above with respect to a case where it is applied to a copying machine, it is easy to understand that the present invention is not limited to this and can be applied to various image forming apparatuses, printers, etc. Probably.

(3) Effects of the Invention Since the present invention has the configuration described above, a sufficient nip width can be obtained by pressing the transfer roller against the image carrier with a relatively weak force. The transfer roller does not use plasticizer, so it has low viscosity, and the toner has good releasability and cleanability, so it can produce consistently high-quality images over a long period of time. It is very helpful to obtain the following.

[Brief explanation of the drawing]

FIG. 1 is a side view of a main part of an embodiment in which the present invention is applied to a copying machine, and FIGS. 2 to 4 are side views of main parts illustrating other configurations of the same cleaning device as above, respectively. . 1--Photoconductor, 2--Transfer roller, 3a. 3b--Conveyance path, 4.-Conveyance cleaning blade. Figure 1 b Figure 2

Claims (1)

[Claims] In an image forming apparatus that includes a moving image carrier and an elastic transfer roller that is in pressure contact with the image carrier, a transfer material is passed between the two to transfer a toner image on the image carrier to the transfer material. An image forming apparatus in which a transfer roller is formed of fine continuous pores, and the pore diameter and porosity of the surface of the roller are smaller than those of the inside.