JPH0736257A - Image forming device - Google Patents

Abstract

PURPOSE:To abut rollers on an image carrier with low pressure for suppressing the deformation and abrasion of the rollers, to increase the durability of each roller and to obtain a stable image over a long period by disposing flanges whose diameters are larger than the elastic main body parts of the rollers, so as to abut them on the image carrier in a degree that they are not elastically deformed, in positions out of image forming regions in the vicinities of both ends of each roller. CONSTITUTION:A primary electrifying roller 23 and a transfer roller 4 are made of conductive foamed rubber whose volume resistivity is suitable adjusted and the flanges 24 and 10 are disposed on both ends of a primary electrifying roller 23 and on the transfer roller 4, respectively. Each diameter of respective flanges is made a little larger than that of the elastic main body parts of the primary electrifying roller 23 and the transfer roller 4. Thus, constitution that the flanges 24 and 10 of the larger diameter are arranged on both ends of respective rollers and made to abut on the image carrier 3 is adopted. Consequently, the elastic main body parts of the primary electrifying roller 23 and the transfer roller 4 can be made to about on the image carrier 3 with the low pressure.

Description

Detailed Description of the Invention

[0001]

[Object of the Invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using electrostatic recording means such as an electrostatic copying machine and a printer.

In the known image forming apparatus as described above, the surface of the running image carrier is uniformly charged by the charging means,
Toner is applied to the electrostatic latent image formed by applying an image signal to the charged surface to form a toner image, and then the toner image is transferred onto a transfer material such as paper by a transfer charging unit. The existing ones are widely used.

As a charging means of such a device, conventionally, a corona discharger in which a discharge wire is extended is disposed in the vicinity of a surface to be charged, and a high voltage is applied to the corona discharger to perform corona discharge, thereby charging the charged surface. Those configured to give an electric charge have been put into practical use.

However, such a device has a problem that a high-voltage power source is required to generate discharge, ozone is generated by the discharge, and the structure of the discharger and the transfer conditions are maintained. For this reason, a large number of high-precision parts are required, and there are inevitable disadvantages in terms of parts cost and assembly cost. Further, in this type, since the discharge wire is exposed in the transfer material passage, there is a risk of occurrence of jam, disconnection of the discharge wire, etc., formation of an oxide film on the surface of the wire, and adhesion of floating toner. However, there is a problem that the charging function is deteriorated due to the above.

In order to avoid the problem in the charging means using such a discharge wire, a roller made of an elastic material such as rubber adjusted to an appropriate volume resistivity is brought into contact with the image carrier. Rollers and transfer rollers are being used more and more.

Since such a charging means does not require a high voltage power source, generates very little ozone, and has a simple structure, it can be said that it is most suitable for a low-priced apparatus.

At the same time, contact type charging means such as a charging roller and a transfer roller are not without problems.
For example, this type of charging means is usually in contact with the image carrier at all times, so depending on its material, the photosensitive layer of the image carrier may be chemically damaged or contacted for a long period of time.
The roundness of the roller made of an elastic material is impaired, and the contact pressure or peripheral speed on the image carrier or transfer material changes in the circumferential direction, resulting in image expansion or contraction, periodic image blurring, or other image quality fluctuations. There is a problem that causes deterioration.

When the hardness of the transfer roller is increased, excessive pressure is applied to the toner of the toner image on the image carrier at the nip portion at the time of transfer, and the toner may adhere to the image carrier to cause transfer failure. . In order to avoid this, if the pressure contact force of the roller is weakened and the deformation of the roller is also prevented, the holding force of the transfer material in the nip portion becomes weak, and the elastic force due to the curl of the thick transfer material or the apparatus itself The rollers tend to float due to vibrations and the like, and the transfer performance is reduced, which may lead to deterioration of image quality. Further, the reduction of the pressure contact force causes the transfer material to slip at the transfer site, which also causes an image defect.

Problems with the transfer roller will be further described. The transfer roller is normally pressed against the shaft of the roller by a spring in the direction of the image carrier, but due to the pressure at this time, the toner forming the toner image on the image carrier is pressed against the image carrier. May cause blocking. Such toner cannot be removed by voltage application during transfer. When copying is performed under such a situation, in the case of a black solid mark having a diameter of 4 mm, for example, a phenomenon occurs in which the toner in the central portion comes off in a donut shape and remains on the image carrier.

It has been found that a contact pressure of about 20 g or less is suitable when the pressure is reduced to prevent the occurrence of such a phenomenon. At the same time, if the driving force is transmitted to the transfer roller with this level of pressure, in the case of this type of device, the gear attached to the image carrier is engaged with the gear attached to the transfer roller shaft to drive the drive. Since the meshing of the gears is loosened, vibrations are generated to hinder the smooth rotation of the transfer roller, or the pressure applied to the transfer roller itself fluctuates, resulting in deterioration of image quality.

On the contrary, when the pressure is increased, the width of the nip becomes large, and the electric field is generated at two points, that is, the point where the nip starts and the point where the nip ends. In such a situation, part of the toner on the image carrier flies in the air, and high-voltage electrons draw a curve, so the toner may scatter before it reaches the transfer material, or the toner once attached to the transfer material may be removed again. The phenomenon that the image is scattered and the image is blurred occurs.

Further, a filming phenomenon may occur in which components mixed in the toner are strongly coated on the surface of the image carrier, and further, dirt adheres to the surface of the transfer roller to contaminate the back surface of the transfer material, or the surface of the transfer roller. There is a problem that the surface resistance becomes high and the transfer performance deteriorates.

Since the transfer roller and the image bearing member constantly rub against each other at the nip portion, the surface of the image bearing member is damaged, or the diameter of the transfer roller is reduced due to the wear of the transfer roller and the image after the transfer is formed. A phenomenon occurs such that it shrinks in the traveling direction.

In this type of apparatus, an image carrier that rotates and runs,
Although it is unavoidable that an air flow is generated in the advancing direction in the vicinity of the transfer material which is in contact with the transfer material, this air flow is blocked at the nip portion between the image carrier and the transfer roller. At this time, the blocked airflow flows backward on the upstream side of the nip portion. Due to the air flow in the opposite direction, a part of the untransferred toner on the image bearing member may be blown off, which may contaminate the image portion at the subsequent position.

As has been outlined above, the reality is that contact-type charging means also suffer from various problems. The present invention has been made in view of the current situation as described above,
In an image forming apparatus using a contact type charging means such as a charging roller and a transfer roller, a large-diameter flange member is arranged on these rollers to make the contact pressure between the roller body and the image carrier a light pressure. As a result, an image forming apparatus that prevents wear of the image carrier and the roller, which is the charging unit that contacts the image carrier, as much as possible and allows the roller to always contact the image carrier with the optimum contact pressure. It is intended to be provided.

[0016]

[Constitution of the invention]

In order to achieve the above-mentioned object, the present invention provides an image forming apparatus including a primary charging roller and a transfer roller which are in contact with an image carrier.
At a position outside the image region near both ends of each roller, the elastic main body portion of each roller is concentric with the elastic main body portion and has a larger diameter than this so that the elastic main body portion abuts on the image carrier without elastically deforming. It is characterized in that it is provided with a flange.

With this configuration, charging,
It is possible to effectively prevent deformation of each transfer roller, damage to the image carrier, and each roller, and maintain good charging and transfer functions for a long period of time.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS "FIG. 1" is a side sectional view showing an essential part of an image forming apparatus showing an embodiment of the present invention, which extends in a direction perpendicular to the plane of the drawing and rotates in a direction indicated by an arrow A. The surface photosensitive layer of the image carrier 3 is uniformly charged by the primary charging roller 23, and the image signal E is projected on this charging surface to form an electrostatic latent image.

When the latent image reaches the developing portion where the latent image and the developing device 2 face each other as the image carrier 3 rotates,
The latent image is visualized by the toner supplied from the developing device 2 into a toner image.

When the image carrier 3 further rotates and the toner image arrives at the transfer position facing the transfer roller 4 on the image carrier 3, the transfer material P passes through the registration roller 18 at the same timing. Is transferred to the transfer portion, and a transfer bias is applied to the transfer roller 4 together with the transfer portion, so that the toner image on the image carrier side is transferred to the transfer material by the action of the electric field formed.

After that, the transfer material P that electrostatically carries the toner image is separated from the image carrier and is conveyed to a fixing portion (not shown). On the other hand, a part of the toner that has not transferred to the transfer material at the transfer site reaches the cleaning device 5 and is removed by the cleaning blade 25 so that the next image forming process can be performed.
To the position of. Although the illustrated apparatus is an apparatus in which the image carrier 3, the primary charging roller 23, the developing device 2 and the cleaning device 5 are integrally formed in a cartridge, the present invention is not limited to such an apparatus. Of course.

The image forming apparatus having the above-mentioned structure is characterized in that it has the following structure. 2 is an end view of the main part as seen in the X-X direction of FIG. 1, in which the primary charging roller 23 is above the image carrier 3 and the transfer roller 3 is below. They are arranged respectively.

The image carrier 3 is rotatably supported by shaft portions 3a, 3a, which are press-fitted at both ends thereof, in the apparatus main body, and in the case of the cartridge type, a fixed portion such as a casing of the image bearing body, and one shaft portion 3a (shown in the figure). A gear 3b is arranged on the right side in the case of (1) to obtain a driving force from a driving source (not shown).

A gear 3c is attached to the shaft portion 3a, and the gear 3c is attached to the shaft 4a of the transfer roller 4 and the gear 12 'attached to the shaft 22 of the primary charging roller 23. Meshes with.

The shaft 4a of the transfer roller 4 has bearings 13, 13
The shaft 22 of the primary charging roller 23 has bearings 13 ', 13'.
Respectively, and each bearing 13, 13 'is
1 and 26 are elastically biased toward the image carrier 3 respectively. Each of the shafts 4a and 22 is formed of a conductive member such as metal, and a transfer bias is applied to the transfer roller 4 from a high voltage power source through the spring 11, the bearing 13, and the shaft 4a. The charging roller 23 is also configured to be applied with a charging bias by the same method.

The primary charging roller 23 and the transfer roller 4
Is formed of conductive foamed rubber whose volume resistivity is appropriately adjusted. Flange 24 and 24 are arranged at both ends of the primary charging roller 23, and flanges 10 and 10 are arranged at the transfer roller 4. All the flange diameters are slightly larger than the elastic main body portions of the primary charging roller and the transfer roller. Thus, by arranging large-diameter flanges at both ends of each roller and abutting them on the image carrier, the elastic main body portions of the primary charging roller 23 and the transfer roller 4 are attached to the image carrier. It is possible to make a contact with light pressure.

The dimensional difference between the flange of each roller and the elastic body portion is such that the body portion is deformed as little as possible with a small pressure so that the desired nip width and charge amount can be obtained. It should be appropriately set according to the characteristics of the constituent materials, the hardness, the required bias voltage, and the like.

When the material of the flange is a conductive material, the current when a bias is applied is concentrated in this portion to be charged,
Due to insufficient electric field formation for transfer, charging and transfer failure occur. Even if a non-conductive coating is applied to the surface of the flange in order to avoid this, the flange itself is always in contact with the image carrier, so that the wear is large and there is a problem in durability.

Therefore, the flange material is required to be a non-conductive substance. In this case as well, in the case of an image near the flange in the case of transfer, in which the surface of the surface to be charged is poorly charged in the case of primary charging due to charging due to friction. It is necessary to take into consideration the characteristics of the flange material so as not to adversely affect the above. In manufacturing the above-mentioned quantity roller, the elastic main body portion of the roller is ground to a predetermined size with the shafts 4a and 22 as a reference, and then the flanges 10 and 24 are processed with the same reference, so that the roller main body portion and the flange portion are processed. It is possible to minimize the eccentricity between and.

[0030]

As described above, according to the present invention, the image forming apparatus is provided with the primary charging roller and the transfer roller which are in contact with the image carrier, but in the image forming apparatus, the large system flanges are provided at both ends of each roller. Therefore, since these rollers can be brought into contact with the image carrier with a light pressure, deformation and wear of the rollers due to the contact pressure can be suppressed as much as possible, and filming on the image carrier and contamination of the transfer roller can be prevented. Further, since it is possible to prevent the toner from scattering near the transfer nip portion, the durability of the image carrier, the charging roller, and the transfer roller is increased, which contributes to obtaining a stable and good image for a long period of time.

[Brief description of drawings]

FIG. 1 is a side sectional view of a main part of an image forming apparatus showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line X-X of the same as above. 1 image forming apparatus main body 2 developing device 3 image carrier 3b, 3c, 12 gear 4 transfer roller 5 cleaning device 10, 24 flange 11, 26 spring 13, 13 'bearing

Claims (4)

[Claims] 1. An image forming apparatus comprising a primary charging roller and a transfer roller which are in contact with an image carrier, and elastic main body portions of the respective rollers are not elastically deformed at positions outside the image areas near both ends of the respective rollers. An image forming apparatus characterized in that an abutting member is arranged so as to come into contact with the image carrier in a certain degree. 2. The image forming apparatus according to claim 1, wherein each of the abutting members is a flange that is concentric with the elastic main body portion of each roller and has a diameter larger than that. 3. The image forming apparatus according to claim 2, wherein the flange is made of a non-conductive material. 4. The image forming apparatus according to claim 2, wherein the flange is made of a non-magnetic material.