JPH0564349B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a prevention device for preventing distortion of a copied image in an electrophotographic copying apparatus.

Conventional Structure and Problems Generally, an electrophotographic copying apparatus charges a drum-shaped or belt-shaped photoreceptor with a charger and exposes it to form an electrostatic latent image. This is developed with toner, and with the transfer paper in contact with the developing surface of the photoreceptor surface, a transfer charger applies corona discharge of opposite polarity to the charge held by the toner to the transfer paper, and the developed toner image is Transfer it to transfer paper. Next, in order to separate the transferred transfer paper from the photoconductor, a separation charger is used to apply an AC corona discharge to remove the electric charge of the transfer paper and toner itself, which has been charged by the transfer. It separates naturally from the photoreceptor due to its own weight. This transfer paper is guided to the fixing device by the fixing guide,
The toner image is fixed on the transfer paper.

The configuration described above is a common electrophotographic copying device, but there is an increasing trend to simplify the configuration of copiers and commercialize smaller, cheaper products. A copying machine has been devised in which charging and transfer are performed with a single charger, the separate charger is removed, and the AC high voltage power source is also removed. FIG. 1 shows these conventional examples. As shown in FIG. 1, a transfer paper 2 guided by a transfer guide 3 to a belt-shaped photoreceptor 1 attached to a photoreceptor driving drum 1a and a photoreceptor driven roller 1b is transferred to a belt-shaped photoreceptor by an image forming means. The toner image formed on the surface of the body 1 is transferred by a charger 4 which serves both charging and transfer. Next, the transfer paper 2 and the belt-shaped photoreceptor 1 advance at the same speed, and when the leading edge of the transfer paper 2 reaches the photoreceptor driven roller 1b, the curvature of the photoreceptor driven roller 1b is increased, so that the transfer paper 2 moves at the same speed. Due to this curvature, the transfer paper 2 moves straight due to its rigidity, and the transfer paper 2 separates from the belt-shaped photoreceptor at this curvature. As the transfer paper 2 and the belt-shaped photoreceptor 1 further advance, the leading edge of the transfer paper 2 advances downward due to its own weight, contacts the fixing guide 5, and advances further, and is then moved to the fixing device 6. The toner image is guided onto the transfer paper 2
It is something that will be established in the future. However, when performing so-called double-sided copying in which a certain number of copies have been made on a transfer paper, which is then turned over and copied again, the toner image on the belt-shaped photoreceptor 1 is transferred to the transfer paper 2 at the moment it contacts the fixing guide, as shown in FIG. There has been a problem that so-called image disturbance occurs in which the transferred unfixed toner image is scattered. Therefore, at present, double-sided copying is not possible. This development does not occur in the conventional copying machine configuration, which uses a separate charger to eliminate the charge on the transfer paper and toner after transfer. In addition, common components of copying machines that cause these image disturbances are those that separate the transfer paper from the photoreceptor without using a separation charger, such as separation belts, separation claws, and the photoreceptor described in the above conventional example. Increase the curvature of some parts of the body,
There is a method of naturally separating the transfer paper at that part.
The common point between these methods is that the transfer paper is separated from the photoconductor without static electricity removal, so the transfer paper itself is charged with electricity due to the transfer. When the transfer paper comes into contact with the fixing guide, the unfixed toner image on the transfer paper scatters, causing image disturbance, which has the disadvantage that high-quality screen copying cannot be performed.

The reason why image disturbance occurs when double-sided copying is performed is that moisture is removed from the transfer paper after the transfer due to heat from the first fixing, and the resistance value of the transfer paper itself increases, resulting in an increase in the amount of charge. Therefore, if this transfer paper is used as double-sided copy paper, the amount of charge accumulated on the transfer paper due to the second transfer will be significantly increased compared to the first transfer, so this transfer paper may not be used as a photoreceptor. When the transfer paper is separated from the transfer paper and comes into contact with the fixing guide, the charge on the transfer paper is rapidly removed, and at that moment unfixed toner on the transfer paper scatters, causing image disturbance. Therefore, image distortion does not occur in the first copy, but image distortion occurs in the second copy (double-sided copying) because of the amount of charge that the transfer paper has after it is separated from the photoconductor, in other words, the amount of charge on the fixing guide. This is because the amount of change in charge that is removed when the transfer paper comes into contact with it is large. In addition, although image disturbance occurs under normal conditions during double-sided copying, when a polyester sheet with a high resistance value is used as the transfer paper, image disturbance occurs even during the first copying. Therefore, in conventional copying machines, it is necessary to take measures such as limiting the resistance value of the transfer paper used. This method has disadvantages such as high production cost of transfer paper.

The image disturbance as described above occurs due to an increase in resistance value due to drying of the transfer paper. Meanwhile, environmental tests are being conducted to put the copying machine into practical use, but in high humidity environments (for example, 30°C, 90% RH), copying machines with conventional configurations experience transfer defects. The reason for this is that if the resistance value of the transfer paper drops significantly due to high humidity, even if you try to transfer it with the transfer charger, the electric potential applied to the transfer paper will pass through the fixing guide because the resistance value of the transfer paper has become low. It will leak. As a result, only a low potential is applied to the transfer paper, and most of the toner image formed on the surface of the photoreceptor remains. So-called transfer defects occur. To solve this problem, there is a method to completely insulate the fixing guide or to make the distance between the fixing guide and the transfer charger sufficiently large. However, if the fixing guide is completely insulated, the charge of the transfer paper itself after being transferred to the fixing guide will accumulate due to contact with the transfer paper, causing image disturbance that disturbs the unfixed toner image on the transfer paper, and The electric charge may increase and cause spark discharge, which has the disadvantage that this spark discharge becomes noise and may cause the electric circuit to malfunction. Furthermore, if the distance between the fixing guide and the transfer charger is sufficiently increased, the size of the copying machine will be increased, which is contrary to the desire to make a small and inexpensive product.

OBJECTS OF THE INVENTION The purpose of the present invention is to prevent disturbance of unfixed toner images in a copying machine configured to separate transfer paper from a photoreceptor without using a separation charger, and to solve the problem of transfer defects at high humidity. A turbulence prevention device is provided.

Structure of the Invention The image disturbance prevention device of the present invention connects a varistor element to a conductive fixing guide located in an intermediate area between the point where the transfer paper separates from the photoreceptor after transfer and the fixing device, and grounds the fixing guide. This configuration prevents image distortion, sufficiently withstands environmental tests, and provides a compact and inexpensive copying machine.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows the configuration of a copying machine to which the image disturbance prevention device of the present invention is applied. In Fig. 2, 1 is an OPC belt-shaped photoconductor (hereinafter referred to as photoconductor), 1a is a photoconductor driving drum, 1b is a photoconductor driven roller, 2 is transfer paper, 3 is a transfer guide, 4 is charging and transfer A dual-purpose charger (hereinafter referred to as a charger), 5 a fixing guide, 7 a varistor element connected to the fixing guide and grounded, 6 a fixing device, 8 a cassette containing transfer paper 2,
9 is a sending roller, 10 is a pair of conveying rollers,
11 is a developing device; 12 is an exposure device including an optical system including a glass fiber lens 12a and a lamp 12b; 13;
14 is a cleaning device, 14 is a photoreceptor static elimination lamp,
15 is a paper discharge tray.

The operation of the image distortion prevention device of this embodiment configured as described above will be described below.

A transfer paper 2 indicated by a broken line in FIG. 3 is sent to a transfer guide 3 by a pair of transport rollers 10. Next, the transfer paper 2 is guided to the photoreceptor 1 and is brought into close contact with the photoreceptor 1 electrostatically, and the toner image formed on the surface of the photoreceptor 1 is transferred by the charger 4 . Transfer paper 2
The leading edge of the transfer paper 2 reaches the photoconductor driven roller 1b, and due to the change in the curvature of the photoconductor 1 and the rigidity of the transfer paper 2, the transfer paper 2 moves at the same speed as the photoconductor 1. The tip of the transfer paper 2 is not able to follow the change in the photoconductor 1 at the photoconductor driven roller 1b.
It separates from and moves in a straight line. Furthermore, as the transfer paper 2 advances, the leading edge of the transfer paper 2 draws a descending line due to its own weight and the fixing guide 5
The transfer paper 2 advances while being in close electrostatic contact with the fixing guide 5 due to the electric charge that the transfer paper 2 has. At this time, the varistor voltage of 1000V is applied to the fixing guide 5.
Since the varistor element 7 (product name: ZNR) is connected and grounded, the fixing guide 5 is charged by the charge of the transfer paper 2 after transfer, but due to the characteristics of the varistor element, Even if a higher voltage is applied, it will absorb more than the varistor voltage of the element, so the potential of the fixing guide 5 is limited to 1000 V or less, and while the transfer paper 2 is passing through the fixing guide 5, the potential of 1000 V is always maintained. It can be assumed that there is. Therefore, when the varistor element is not connected to the fixing guide as in the past, the charge on the transfer paper itself is removed as soon as it contacts the fixing guide, so the amount of change in the charge on the transfer paper itself is large. Moreover, the sudden change affects the unfixed toner image on the transfer paper, resulting in image disturbance. but,
In the present invention, a varistor element with a varistor voltage of 1000V is connected, and as a result, the fixing guide
Since there is a potential of 1000V, there is little change in the charge on the transfer paper itself due to static elimination, and there is no effect on the final fixed toner image on the transfer paper, so image disturbance does not occur. In this manner, in FIG. 3, the transfer paper 2 separated from the photoreceptor 1 is guided to the fixing device 6 and fixed thereon with the fixing guide 5 preventing image disturbance. On the other hand, in high humidity conditions (30℃, 90% RH), the resistance value of the transfer paper decreases, and the potential applied to the transfer paper decreases because the potential caused by the transfer charge leaks from the transfer paper via the fixing guide. As a result, there was a shortage and a transfer failure occurred, but since the varistor element is connected to the fixing guide, the fixing guide ended up being insulated with a resistance value of 100MΩ or more, and it applied to the transfer paper. The potential defect was resolved and the transfer defect could be eliminated.

Note that although the embodiments of the present invention are limited to copying machines that use OPC belt-shaped photoreceptors, OPC
The present invention is not limited to the belt-shaped photoreceptor, and similar effects can be obtained in a copying machine using a selenium photoreceptor drum.

Furthermore, as a method for separating the transfer paper after transfer, the curvature of the photoreceptor driven roller section is increased, and the description is limited to copying machines that use a natural separation method that utilizes the straightness due to this curvature and the rigidity of the transfer paper. However, the present invention is not limited to this method; for example, a method using a separating claw or a copying machine using a separating belt can also be performed by connecting a varistor element to the fixing guide.
Image distortion can be prevented.

In addition, although a varistor element with a varistor voltage of 1000 V was used, if a varistor with a varistor voltage of 1000 to 2000 V is used, there will be no problem in practical tests such as environmental tests.

Effects of the Invention As is clear from the above description, the present invention is a device for preventing disturbances in a copied image. By connecting a varistor element to the fixing guide so that the fixing guide is grounded, it is possible to prevent image disturbances and eliminate transfer defects at times of high humidity.

[Brief explanation of drawings]

FIG. 1 is a side view of a conventional example, FIG. 2 is a side view of an embodiment of a copying machine to which the present invention is applied, and FIG.
It is a partially enlarged view of the figure. DESCRIPTION OF SYMBOLS 1... Belt-shaped photoreceptor, 2... Transfer paper, 5... Fixing guide, 7... Varistor element.

Claims (1)

[Claims] 1. An image disturbance prevention device configured to connect a varistor element to a conductive fixing guide located in an intermediate region between the point where the transfer paper separates from the photoreceptor after transfer and the fixing device, and to ground the fixing guide.