JPH01177063A - Transfer device for image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent quality image whose back is not tainted by specifying the hardness of a transfer roller and the press-contact force that a roller applies to an image carrier. CONSTITUTION:As the transfer roller, an inner layer made of conductive sponge is formed on a metallic core, and an outer layer made of solid, conductive rubber is placed on the outside of the inner layer. The hardness of the transfer roller is set at 30 deg. (JIS A) or below, and the press-contact force that the roller applies to the image carrier is set at 300gr/cm<2> or below. Thus, the adhesion of toner to the transfer roller and taint of transfer material due to the adhesion can be effectively prevented without needing a special mechanism such as a cleaning blade.

Description

Detailed Description of the Invention (1) Purpose of the Invention (Field of Industrial Application) The present invention relates to image forming apparatuses that utilize an electrostatic transfer process, such as electrostatic copying machines and printers, and in particular to transfer mounting thereof. be.

(Prior art and problem to be solved 8) In an image forming apparatus including a step of electrostatically transferring a transferable toner image formed on a photosensitive layer on the surface of an image carrier to a sheet-like transfer material mainly composed of two papers. An image carrier that runs in an endless shape such as a cylinder or an endless belt is used for one revolution, and a transfer roller to which a bias is applied is pressed against the image carrier, and a transfer material is passed between the two to form a toner image on the image carrier side. A device configured to transfer the image onto a transfer material has already been proposed.

Compared to transfer means that utilize corona discharge, which has been widely used in the past, such a device adjusts the pressure force of the transfer roller against the image carrier to increase the adsorption area of the transfer material to the image carrier. Since the transfer material is actively pressed and supported at the transfer site, there is less risk of transfer misalignment due to poor synchronization by the transfer material conveying means or loops or curls existing in the transfer material. It is easy to meet the demands of shortening the transfer material conveyance path and reducing the diameter of the image carrier due to the miniaturization of image forming devices, but on the other hand, if a jam occurs at the transfer site, the photosensitive layer on the surface of the image carrier If you use a transfer material that is easy to damage the surface of the transfer roller and is small compared to the size of the original image, the toner on the image carrier side will transfer to the transfer roller in an area where no transfer material is present, and this will cause the next toner to arrive. There were drawbacks such as staining on the back of the transfer material.

In order to avoid such drawbacks, for example, there is a method of cleaning the transfer roller with a cleaning blade or the like, and an electric field is created between the transfer roller and the image carrier during non-transfer in a direction in which the toner is displaced toward the image carrier. However, in the former method, since the transfer roller has a relatively low hardness, it is difficult to sufficiently apply the scraping action of the cleaning blade, and the scraping action of the cleaning blade causes This was not practical because the rollers would be damaged and the rotational torque would increase.

In addition, in the latter method, the transfer roller comes into pressure contact with the image carrier and is compressed and deformed into a concave shape, so the adhering toner tends to aggregate, and therefore a high electric field is required for sufficient cleaning. It was not suitable.

The present invention was made in view of the current situation, and
To provide a transfer device that can effectively transfer toner in a non-image area to an image bearing member in an image forming device using a transfer roller, and can obtain a high-quality image without smudging. The purpose is to

(2) Structure of the Invention In order to achieve the above object, the present invention comprises an image carrier and a transfer roller that is in pressure contact with the image carrier, and a transfer material is passed between the two to form a toner image on the image carrier. In an image forming apparatus that transfers toner to a transfer material and also transfers toner to an image carrier during non-transfer, the hardness of the transfer roller is set to 300 (JISA) or less, and the hardness of the roller to the image carrier is It is characterized by a pressure contact force of 300 gr/cm2 or less.

With this configuration, it is possible to effectively prevent toner from adhering to the transfer roller and contamination of the transfer material caused by this, without requiring any special additional mechanism such as a cleaning blade.

(Description of Embodiments) FIG. ffi1 is a side view of essential parts showing an embodiment in which the present invention is applied to an image forming apparatus equipped with a rotating cylindrical image bearing member.

An elastic transfer roller 2 is in pressure contact with an image carrier 1 extending perpendicularly to the plane of the paper and rotating in the direction of arrow A so as to form a nip N.

When the toner image formed on the surface of the image carrier l reaches the nip N, which is the transfer site, a transfer material (not shown) is supplied from the conveyance path 4 at the same timing and reaches the nip N, It is assumed that the toner image on the image carrier is transferred to a transfer material by the action of the transfer bias applied by the power source 3, and then this transfer material is separated from the image carrier and conveyed to a fixing site (not shown).

On the other hand, after the transfer is completed, an electric field is applied to the power source 3 to transfer the toner to the image carrier during non-transfer when the next transfer material does not pass through.
Switch the polarity of : $, : :.

Specifically speaking, in the case of regular development using an image bearing member that is negatively charged, the charge polarity of the toner is positive, and during transfer, a negative polarity bias opposite to that of the toner is applied to the transfer roller. However, when not transferring, a positive bias is applied to the roller.

In addition, when performing reversal development using an image bearing member that is negatively charged, the charging polarity of the toner is negative, and a positive bias is applied to the transfer roller during transfer, and during non-transfer, the image carrier is The charge on the body is turned off or the charge is removed using an image information providing means, and a negative bias is applied to the transfer roller.

It goes without saying that the main charger, image information providing means, developing device, cleaning device, and other members necessary for forming fine images are arranged around the image carrier 1, but these are not covered by the present invention. Since they are not directly related, they are all omitted.

It has been confirmed that when transfer is performed using the above-mentioned device, the amount of toner that is once transferred to the transfer roller and transferred again to the image carrier varies greatly depending on the contact pressure of the transfer roller against the image carrier. Ta.

As shown in FIG. 3A, the transfer roller is formed by the apparatus shown in FIG. FIG. 2 shows the change in cleaning efficiency with respect to the contact pressure of the transfer roller 2 against the image carrier using the one provided with the outer layer 2a. The cleaning efficiency in this case indicates the rate at which the toner is transferred back to the image carrier when the transfer roller to which the toner is attached rotates three times.

As can be seen from Figure 2, the contact pressure to the image carrier was 300
It can be seen that the cleaning efficiency is significantly improved when it is less than gr/cm2.

Using the transfer roller described above, the contact pressure to the image carrier was set to 200
gr/cm2, a nip width of 2 mm was removed, and there were no problems with transferability or conveyance.

Furthermore, the cleaning properties were good, and no staining on the back side of the transfer material was observed.

In this case, if the contact pressure is reduced, the nip N will not be sufficient, which may result in poor transfer or image blurring, so the hardness of the transfer roller should be 30' (JIS A
) or less, and like the roller above, 2
As for the layer structure, the outer layer surface is formed smoothly and has a slightly higher hardness to prevent the toner from strongly digging into the roller surface and increase durability, and the inner layer has a lower hardness to improve the overall hardness. I tried to keep it within the above range.

The transfer method in the case of the above device is a reversal development method using a negatively charged image bearing member, and the transfer bias is +500V when transferring the toner to the transfer material, and when not transferring,
The main charger is turned off and/or the image information imparting means is operated to eliminate static electricity from the image carrier, and the transfer roller
Good results were obtained with a relatively low bias such as applying a reverse bias of 0V.

3B and 3C respectively show other examples of the transfer roller, the former being made of a sponge-like conductive urethane 2d made of microporous material with a pore diameter of about 10 l, and the latter It is made of conductive rubber with a plurality of hollow parts formed inside. When these were applied to the above-mentioned apparatus, exactly the same results were obtained.

As explained above, in an image forming apparatus that presses an elastic transfer roller against an image carrier and passes a transfer material between the two to transfer a toner image on the image carrier to the transfer material, the hardness of the transfer roller is set to 30'. (JISA) or less, and by setting the pressure contact force to the image carrier to be 300 gr/C152 or less, it is possible to clean the transfer roller with a low bias without separately providing a special cleaning means.

(3) Effects of the Invention As can be seen from the above description, the present invention does not use additional means in an image forming apparatus equipped with a transfer roller that comes into pressure contact with an image bearing member, so the transfer roller is not damaged. Moreover, with a low bias, it is possible to stably obtain high-quality images without surface stains over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a side view of essential parts of an image forming apparatus showing an embodiment of the present invention, FIG. 2 is a graph showing the relationship between transfer roller contact pressure and cleaning efficiency, and FIGS. 3A to 3C are respectively FIG. 2 is a cross-sectional view showing the configuration of a transfer roller that can be used in the present invention. 1... Image carrier, 2... Transfer roller, 3... Bias power supply. Purification of Drawings No. 1 Drawing Am-381fU Procedural Amendment (released) May 1985, Commissioner of the Japan Patent Office Kunio Ogawa (1) Name Transfer device of image forming device (3) Person making the amendment Relationship to case Applicant address Name Canon Co., Ltd. (4) Agent

Claims (1)

[Scope of Claims] An image bearing member and a transfer roller in pressure contact with the image bearing member are provided, and a transfer material is passed between the two to transfer the toner image on the image bearing member to the transfer material, and when the toner image is not transferred, the toner image is transferred to the transfer material. In the image forming apparatus, the hardness of the transfer roller is set to 30° (JISA) or less, and the pressing force of the roller to the image carrier is set to 300 gr.
/cm^2 or less.