JPH0511636A - Roller transfer device - Google Patents

Abstract

PURPOSE:To make the quality of a transfer image excellent and simultaneously to obtain an inexpensive transfer roller by forming the transfer roller with a high polymer porous body having a micropore. CONSTITUTION:A transfer roller 5 is constituted by lining a core metal 5a made of stainless steel, etc., with a conductive high polymer porous body having the micropore, as an elastic layer 5b. As the high polymer porous body, a polyurethane sponge is used, and a conductivity applying agent such as carbon black, is added to apply conductivity. On the other hand, the pore of the high polymer porous body has a small diameter enough to prevent an influence to transfer image quality. This pore diameter can be easily adjusted by changing the grain diameter of a pore producing agent used for producing the high polymer porous body. Thus, the porous body lowers its actual hardness, but toner and a toner image carrier do not have the influences of a plasticizer and a low molecular weight component, and a defect in a pin hole does not exist, as well, so that the image quality is made excellent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roller transfer device used in an image recording device utilizing an electrostatic transfer process such as a laser printer and an electrostatic copying machine.

[0002]

2. Description of the Related Art Corona transfer system and bias roller transfer system have been well known as a device for transferring a toner image formed on a toner image carrier onto a transfer medium by an electrophotographic image forming method such as the so-called Carlson method. ing. The corona transfer method has a simple structure and is widely used in printers, copiers, etc., but when the humidity is high, the recording paper absorbs moisture and has low resistance, which causes transfer failure, and ozone that is harmful to the human body is generated. However, when the recording paper is separated from the image carrier, the toner is scattered and a sharp image cannot be obtained. On the other hand, in the roller transfer method, the toner is transferred by pressure, so that it is less affected by the moisture absorption state of the paper and a stable transfer image is obtained even at high humidity, and a sharp image with less toner scattering is obtained. Further, since no ozone is generated by corona discharge, the roller transfer method can be said to be a transfer method that compensates for the above-mentioned drawbacks of the corona transfer method.

[0003]

The conventional roller transfer method has the following problems and has been an obstacle to its practical use. Generally, the transfer roller used in the roller transfer method is a cored bar made of stainless steel or the like and a conductive rubber or sponge lined. When a rubber material is used, a plasticizer is usually added to reduce the hardness in order to provide an appropriate contact width in the contact area between the toner image carrier and the transfer roller. However, this plasticizer migrates to the surface of the toner or the toner image bearing member, causing a blocking phenomenon or a filming phenomenon of the toner, or adversely affecting the characteristics of the toner image bearing member to cause a problem that the image density is lowered. Was. As a rubber material, it is possible to use a material whose hardness can be reduced without adding a plasticizer such as silicone rubber, but low molecular weight components such as oil are placed inside the rubber to reduce the crosslink density and hardness. However, there is a problem in that the low molecular weight component leaches out to the surface and adheres to the toner image bearing member to reduce the image density like the plasticizer. Such leaching of the plasticizer and the low molecular weight component is likely to occur in a high temperature environment, and also tends to occur when the transfer roller is left in contact with the toner image carrier for a long period of time. When a sponge, which is a foam, is used, the hardness can be substantially reduced as compared with rubber because of the voids, so the amount of the plasticizer is reduced and the above problems can be avoided. However, in the process of manufacturing a sponge, an abnormally large foam diameter of 1 mm or more, that is, a so-called pinhole defect occurs, so that several pinholes are present on the roller surface. When transfer is performed by a roller having such a pinhole on the surface, transfer voltage and pressure do not act on the pinhole, so that transfer omission occurs at that portion. Although it is possible to manufacture the transfer roller in a portion having no pinhole defect, it is not practical because the yield becomes extremely low.

Therefore, an object of the present invention is to provide a roller transfer device which can improve the quality of a transferred image and has an inexpensive transfer roller.

[0005]

In view of the above object, the present invention provides a roller transfer device including a transfer roller for transferring a toner image formed on a toner image bearing member onto a transfer medium, in which the transfer roller is minute. Provided is a roller transfer device characterized by being formed of a polymer porous body having various pores.

[0006]

For example, polyurethane or the like belongs to a polymeric porous body. These porous bodies reduce the hardness substantially, but there is no influence of the plasticizer and the low molecular weight component on the toner and the toner image bearing member, Since there are no hole defects, the image quality is good.

[0007]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an embodiment of an electrophotographic apparatus using the present invention. In the figure, 1 is a photosensitive drum, 2 is a charging device, 3 is an exposing device, 4 is a developing device, 5 is a transfer roller, 6 is a bearing, 7 is a spring, 8 is a bias power supply,
9 is a cleaner and 10 is a recording paper. In the figure, the transfer roller 5 receives the pressure applied to the photosensitive drum 1 via a bearing 6 by a spring 7. This pressure affects the transfer characteristics, especially the transfer efficiency, so 1 to 500 × 10 ^-3 kg
It is adjusted by changing the amount of displacement of the spring 7 so that the pressure can obtain good transfer characteristics in the range of w / cm. Further, the bias power source 8 applies a bias voltage to the transfer roller 5, and the bias power source 8 moves from the photosensitive drum 1 to the recording paper.
When the toner is transferred to 10, a voltage having a polarity opposite to the charging polarity of the toner is generated. Like the pressure, the bias voltage has a great influence on the transfer characteristics. Therefore, in consideration of the resistivity of the transfer roller 5, the resistivity of the transfer medium, etc., good transfer characteristics can be obtained in the range of 0.1 to 4 kV during transfer. Always regulated to voltage.

The transfer roller used in the present invention is shown in FIG.
As shown in the sectional view of FIG.
Has fine pores as the elastic layer 5b on (outer diameter 8 mm)
The conductive polymer porous body is lined.
In the present example, Toyo Polymer is used as the polymer porous material.
Made of Polyurethane sponge, Rubicell (registered trademark)
Conductivity such as carbon black to impart conductivity
A sex-providing agent is added. The pores of the polymer porous body are
The diameter is small enough not to affect the image quality. This
Pore size of porosity used in the production of porous polymer
Can be easily adjusted by changing the particle size of the formulation
In this example, the pore diameter was 10 to 20 μm. Bullet
The volume resistivity of the material layer 5b greatly affects the transfer characteristics.
So 10 ²~Ten¹³Is adjusted in the range of Ωcm, and in this embodiment
Ten⁶~Ten⁹Ωcm. Also, the hardness is the same as the recording paper at the time of transfer.
It affects the transfer characteristics in relation to the adhesion with the toner image.
Therefore, the hardness that ensures sufficient adhesion is 10-40 degrees (ASK
ER-C), which is adjusted to a relatively low hardness, and is 30
(ASKER-C). The thickness of the elastic layer 5b is the hardness
Similar to the above, it is involved in the adhesion between the recording paper and the toner image
Therefore, it is appropriately determined in the range of about 1 to 15 mm.
Then, it was set to 6 mm.

In the apparatus having the above structure, the photosensitive drum 1 is first uniformly charged by the charger 2. Next, an electrostatic latent image is formed by the exposure device 3 and visualized by the developing device 4 to form a toner image which is a visible image. When the toner image on the photoconductor reaches the contact area with the transfer roller 5, the toner image is pressed against the recording paper 10 conveyed in synchronization with it, and at the same time, a voltage is applied from the bias power source 8 to the transfer roller 5. The toner image is transferred from the photosensitive drum 1 to the recording paper side. The toner remaining on the photosensitive drum 1 without being transferred is cleaned by the cleaner 9 to prepare for the next cycle starting from charging.

When a printing test was conducted in this apparatus in the above-mentioned process, the toner blocking phenomenon and the filming phenomenon did not occur, and there was no effect on the photosensitive drum, so that the image density declined. I couldn't do it. Further, even when a black solid image was printed, no transfer omission occurred. A similar printing test was conducted in a high temperature environment of 40 ° C, but no problem occurred. further,
Printing was carried out after leaving for 4 weeks in a high temperature environment of 40 ° C., but there was no effect on the photoconductor and no decrease in image density was observed.

In addition, in the electrophotographic apparatus, when the recording paper is not conveyed to the transfer portion due to a paper jam or the like, the toner image on the toner image carrier comes into direct contact with the transfer roller, and thus the surface of the transfer roller. Was contaminated, and as a result, the resistivity of the transfer roller was changed, the transfer efficiency was lowered, and the back surface of the recording paper was stained. In addition, after the recording paper passes through the transfer area and before the next recording paper is conveyed to the transfer area, the transfer roller remains in direct contact with the image carrier, so that the transfer roller remains on the image carrier. The adhered toner adheres to the surface of the transfer roller. Although this adhesion amount is very small, the adhesion amount increases during long-term use, and the resistivity of the transfer roller changes accordingly, which causes deterioration of transfer characteristics.

In order to avoid such a problem, a method of cleaning the transfer roller by providing a cleaning means such as a blade or a fur brush, or a method in which toner is carried on the toner image between the transfer roller and the image carrier at the time of non-transfer A method of forming an electric field in the direction of redeposition on the body side has been proposed.

As an example of the former method, Japanese Patent Laid-Open No. 1-18
5572, there is disclosed a method in which a roller having a skin layer on its surface is used as a transfer roller, and a cleaning blade is brought into contact with the transfer roller for cleaning. By forming the skin layer, it is possible to obtain a roller having small surface irregularities and a low friction coefficient, and it is said that the cleaning property is good. In this method, the skin layer has the property of not easily adhering the toner (releasing property), and therefore exhibits excellent cleaning characteristics as compared with the case where the skin layer is not provided. However, since the toner adhered to the surface of the transfer roller under pressure is relatively firmly attached, the toner firmly adhered to the surface of the transfer roller cannot be completely scraped off by the blade or the fur brush. On the contrary, the residual toner is liable to adhere to the recording paper due to the good releasability of the skin layer, and the back stain is likely to occur. Further, when a blade is used, the cleaning effect is higher than that of a fur brush, but since the friction with the transfer roller is large, the rotating torque is extremely increased, which is not practical. Furthermore, since the skin layer is slippery, the transportability of the recording paper is poor, and when transferring to a recording medium having a small friction coefficient such as an OHP sheet, there is a problem that the transferred image shrinks.

The latter method of forming an electric field between the transfer roller and the image bearing member in the direction of re-adhesion of the toner to the toner image bearing member side in the non-transferring method is also applicable to the toner adhered to the surface of the transfer roller. Since the adhesive force is larger than the electrostatic force, it was difficult to reattach the toner image bearing member.

In order to solve such a problem, according to the present invention, the skin layer formed at the time of forming the elastic layer 5b made of the polymer porous body of the transfer roller 5 shown in FIG. From the inside to the inside, the size is 5
It is composed of an elastic layer with continuous pores of about 150 micrometers. The pore diameter is determined in consideration of the particle diameter of the toner to be used, and since the toner having the average particle diameter of 10 μm is used in the embodiment of the present invention, the diameter that allows the toner to enter the pores is 10 to 120 μm. did. Also in this case, as in the case described above, the volume resistivity of the elastic layer largely influences the transfer characteristics, so that it is adjusted in the range of 10 ² to 10 ¹³ Ωcm, and in this example, 10 ⁶ to 10 ⁹ Ωcm. And Also, the hardness affects the transfer characteristics in relation to the adhesiveness between the paper and the toner image at the time of transfer, so a hardness of 10 to 40 degrees (ASK
ER-C), which is adjusted to a relatively low hardness, and is 30
(ASKER-C). Since the thickness of the elastic layer is related to the adhesion between the paper and the toner image at the time of transfer, like the hardness,
It is appropriately determined within the range of about 1 to 15 mm, and in this embodiment, it is 6 mm.
And

In the apparatus having the above construction shown in FIG. 1, the photosensitive drum 1 is first uniformly charged by the charger 2 as in the case described above. Next, an electrostatic latent image is formed by the exposure device 3 and visualized by the developing device 4 to form a toner image. When the toner image on the photoconductor reaches the contact area with the transfer roller 5, the recording paper 10 is conveyed in synchronization with it.
The toner image is pressed onto the transfer roller 5, and at the same time, a voltage is applied to the transfer roller 5 from the bias power source 8, so that the toner image is transferred onto the photosensitive drum 1.
Is transferred to the recording paper side. The toner that has not been transferred and remains on the photosensitive drum 1 is almost cleaned by the cleaner 9 to prepare for the next cycle starting from charging.

On the other hand, after the transfer is completed, a voltage having the same polarity as the charging polarity of the toner is applied to the transfer roller 5 until the next recording paper 10 is conveyed to the transfer area, and is applied to the photosensitive drum 1 side. Reattach toner and clean. In this example, the voltage during cleaning was set to 500V. In this device, when printing evaluation was performed by the above process,
Cleaning of the transfer roller 5 works well, and the recording paper 10
No back stain occurred, and the transfer efficiency did not change even if the transfer roller 5 was used for a long period of time.

FIG. 3 shows the cleaning efficiency and the backside stain of the paper when using the transfer roller 5 of Ruvicel whose skin layer was removed by polishing, and the conventional Ruvice transfer roller with the skin layer was used. FIG. 4 shows the cleaning efficiency and the stain on the back side of the paper in this case. Here, the cleaning efficiency is a percentage of the toner weight removed by the cleaning to the total toner weight attached to the roller, the removed toner weight is the difference between the roller weights before and after the cleaning, and the attached total toner weight is the cleaning weight. It can be measured by the difference between the weight of the roller before and the weight of the roller before use.

Comparing FIG. 3 and FIG. 4, the cleaning efficiency of the present invention is lower than that of the conventional case having a skin layer, but the back stain of the paper, which is a problem in practice, is reduced. I understand. This is because when the conventional skin layer is used, the toner tends to come off easily.
Therefore, it tends to adhere to the back surface of the paper instead, but in the present invention, the skin layer is removed, and a large number of fine holes for catching toner are present on the roller surface. Lines shown by broken lines in both figures show the limit of visual detection, and in the case of the present invention, it can be seen that by setting the cleaning voltage to about 500 V, it is effective enough that the back stain cannot be seen.

When a paper jam occurs, a voltage having the same polarity as the charging polarity of the toner is applied to the transfer roller at the time of recovery, and the toner is reattached to the photosensitive drum side, so that the transfer roller can be cleaned well. The backside of the recording paper could not be visually detected at the time of restart. Note that it is preferable to perform cleaning of the transfer roller by the same method when warming up the apparatus.
As a result, more reliable and stable cleaning can be realized. Further, the transfer roller of the present embodiment has a higher coefficient of friction than the case where there is a skin layer because the skin layer is polished and the surface is a sponge surface, and there is almost no slippage on the OHP sheet. The problem that the image after transfer shrinks did not occur.

As described above, according to the present embodiment, the transfer roller is formed by the continuous pores having the fine pores of 5 to 150 μm, and when the transfer is not performed, the transfer roller and the image carrier are
Since the transfer roller is cleaned by forming an electric field in the direction in which the toner reattaches to the image carrier side, the transfer roller can be cleaned satisfactorily. Therefore, the back surface of the recording paper is not stained, and the resistivity of the transfer roller does not change for a long period of time, so that stable image quality can be obtained.

[0022]

As is apparent from the above description, according to the present invention, since a low molecular weight component such as a plasticizer or oil is not used and it is not a foam, the image density at the time of transfer is lowered. A good transfer image can be obtained without causing transfer defects and transfer rollers, and the manufacturing cost of the transfer roller is low.

[Brief description of drawings]

FIG. 1 is a schematic view of a roller transfer device according to the present invention.

FIG. 2 is a sectional view of a transfer roller used in the apparatus of FIG.

FIG. 3 is an explanatory view of effects of the device of the present invention.

FIG. 4 is an explanatory diagram of effects of the conventional device.

[Explanation of symbols]

1 ... Photosensitive drum 5 ... Transfer roller 5a ... core metal 5b ... Elastic layer 8 ... Bias power supply 10 ... Recording paper

Claims (3)

[Claims] 1. A roller transfer device comprising a transfer roller (5) for transferring a toner image formed on a toner image carrier (1) onto a transfer medium (10), said transfer roller (5).
The roller transfer device is characterized in that the roller is formed by a polymer porous body having minute pores. 2. The roller transfer device according to claim 1, wherein the polymer material of the polymer porous body is polyurethane. 3. The roller transfer device according to claim 1, wherein the size of the fine pores is 5 to 150 micrometers, and the pores are continuous from the surface to the inside.