JPH03233481A - Image forming device - Google Patents

Abstract

PURPOSE:To miniaturize a device, to reduce the cost thereof, to prevent ozone from being evolved and to improve image quality by providing a conductive member to which a power source is connected and which comes in contact with the back surface of a transfer material carrying member at least at the time of transfer in an electric field generating means for generating electric field and specifying the volume resistivity of the transfer material carrying member. CONSTITUTION:The electric field generating means 19-21 for generating the electric field are provided with the conductive member 21 which is connected to the power source and comes in contact with the back surface of the transfer material carrying member 9 at least at the time of transfer. The volume resistivity of the transfer material carrying member 9 is 10<8>-10<16>OMEGA.cm. Therefore, a discharger for transfer is not necessitated and the power source having large voltage and current capacity and a wiring whose breakdown strength is high are made needless. Thus, the device is miniaturized, the cost thereof is reduced, the ozone is prevented from being evolved and the image quality is improved.

Description

[Detailed Description of the Invention] No. 1 The present invention generally relates to an image forming apparatus,
In particular, an image obtained by transferring a toner image formed on an image carrier by an electrophotographic method or an electrostatic recording method to a transfer material supported on a transfer carrier member by applying a transfer electric field. The present invention relates to a forming device. Such image forming apparatuses include black-and-white, monochrome, or full-color electrophotographic copying apparatuses, printers, and various other recording devices.

For example, various multicolor (full color) image forming apparatuses have been proposed in the past, but the multicolor electronic image forming apparatus equipped with a developing device called a so-called rotary developing device, as shown in FIG. A photocopying apparatus is illustrated.

To briefly explain with reference to FIG. 5, the multicolor electrophotographic copying apparatus includes an image bearing member, that is, a photosensitive drum 3, which is rotatably supported on a shaft and rotates in the direction of the arrow, and an image forming means is provided on the outer periphery of the image bearing member, that is, a photosensitive drum 3. is placed. The image forming means may be any means, but in this example, a primary charger 4 that uniformly charges the photosensitive drum 3 and a color-separated light image or a light image equivalent thereto are irradiated to form an image on the photosensitive drum 3. The photosensitive drum 3 includes an exposure means 8 formed of, for example, a laser beam exposure device, which forms an electrostatic latent image on the photosensitive drum 3, and a rotary developing device 1, which converts the electrostatic layer image on the photosensitive drum 3 into a visible image.

The rotary developing device 1 includes four developing devices 4Y, 4M, and 4C14 each housing four color developers: yellow developer, magenta developer, cyan developer, and black developer.
8, these four developing devices 4Y, 4M, 4C148K
It consists of a substantially cylindrical casing that holds and is rotatably supported. The rotary developing device 1 conveys a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 3 by rotating the housing, develops a latent image on the photosensitive drum, and develops a latent image for four colors. It is configured to allow full color development.

The visible image, that is, the toner image, on the photosensitive drum is transferred onto a transfer material P carried by a transfer device 9 and conveyed. In this example, the transfer device 9 is a rotatably supported transfer drum, and as understood with reference to FIG. It has a connecting portion 9C that connects both cylinders 9a and 9b, and a transfer material carrying member 93 is stretched over the opening area of the outer peripheral surface of the cylinders 9a and 9b. The transfer material carrying member 93 is usually a film-like dielectric sheet such as polyethylene terephthalate or polyvinylidene fluoride resin film. Further, the connecting portion 9c includes a transfer material gripper 7 that grips the transfer material P fed from the paper feeding device. Further, on the inside and outside of the transfer drum 5, there are a transfer discharger 10 and an inner charge-eliminating discharger 13 constituting a charge-eliminating means.
and outer static elimination dischargers 11.14 are arranged.

A brief explanation of the process of forming a full-color image using the multicolor electrophotographic copying apparatus configured as described above is as follows.

The photosensitive drum 3 is uniformly charged by the primary charger 4, and the exposure means 8 irradiates the photosensitive drum 3 with a light image E according to image information, thereby forming an electrostatic latent image on the photosensitive drum 3. The electrostatic latent image is visualized as a toner image on the photosensitive drum 3 by the rotary developing device 1 using a resin-based toner having an average particle size of 8 to 10 μm.

On the other hand, the transfer material P is sent to the transfer drum 9 through the paper feed guide 18 by the registration roller 6 in synchronization with the image, and its tip is gripped by the gripper 7 or the like. conveyed in the direction.

Next, the transfer material carrying member of the transfer drum 9, i.e., the dielectric sheet 93, is subjected to a corona discharge of opposite polarity to the toner by the transfer discharger 10 from the back side of the transfer material carrying member of the transfer drum 9 in the area in contact with the photosensitive drum 3. The toner image is transferred onto the transfer material P.

After the transfer process has been performed the necessary number of times, the transfer material P is subjected to static elimination by the static elimination dischargers 11, 13.
The conveyor belt 16 is peeled off from the transfer drum 9 due to the action of
The image is conveyed to the fixing device 17 by the image forming apparatus. After being fixed by heat in the fixing device 17, it is discharged outside the machine.

On the other hand, after the residual toner on the surface of the photosensitive drum 3 is cleaned by a cleaning device 12, the photosensitive drum 3 is subjected to the image forming process again.

Further, the surface of the dielectric sheet of the transfer drum 9 is similarly cleaned by the action of the cleaning device 5 consisting of a fur brush or the like and the cleaning auxiliary means 8, and then subjected to the image forming process again.

However, since the conventional example described above uses a discharger for transfer, it has the following drawbacks.

That is, it is necessary to apply a high voltage of usually 6 to SKV to the wire of the discharger, and furthermore, only a part of the corona current flows toward the photosensitive drum, and the rest flows to the shield of the discharger, which is grounded. , a current greater than that flowing through the transfer corona 1 that actually contributes to transfer is required. Therefore, t# with large voltage and current capacity! In addition, wiring insulation needs to have a higher withstand voltage, leading to an increase in the size and cost of the device.

Furthermore, since a discharger is used, corona discharge is generated and ozone is generated, which adversely affects the photosensitive drum and the human body.

Therefore, an object of the present invention is to eliminate the need for a transfer discharger,
Therefore, there is no need for a large voltage or current capacity, and wiring with a higher withstand voltage, thereby reducing the size of the device.
An object of the present invention is to provide an image forming apparatus that can reduce costs, eliminate ozone generation, and obtain images of good quality.

for The above object is achieved by an image forming apparatus according to the present invention.

In summary, the present invention provides a transfer method that includes an image carrier on which a toner image is formed and a transfer material carrier member that carries and conveys a transfer material, and in which the toner image on the image carrier is transferred to the transfer material by an electric field. In the image forming apparatus, the electric field generating means for generating the electric field has a conductive member that is connected to a power source and comes into contact with the back surface of the transfer material carrying member at least during transfer; The image forming apparatus is characterized in that the material supporting member has a volume resistivity of 10 6 to 10 8 Ω·cm. Preferably, the transfer material supporting member is a dielectric sheet, and the volume resistivity thereof is lOg.
~1OΩ·cm, and its relative permittivity is 4 or more.

According to the present invention, as described above, the transfer material carrier, that is,
The dielectric sheet has a volume resistivity of 10' to 1016Ω・c
m, preferably lo9 to l o12 Ω·cm, enables good transfer. The reason is as follows.

In other words, when the volume resistivity is large, for example, in the case of a multicolor image forming apparatus that performs multiple transfer, the dielectric sheet surface has a polarity opposite to that of the bias voltage applied to the conductive member that is the electric field forming means during the first color transfer. After being charged, it takes a long time for the potential to attenuate, and when transferring the second and subsequent colors, the effective electric field that contributes to transfer becomes weaker, resulting in lower transfer efficiency. Furthermore, if the volume resistivity is large, a larger bias voltage is required to obtain the same image density, which not only increases the size of the power supply but also reduces the initial charging potential of the dielectric sheet during transfer. Since it becomes high, it also causes a decrease in transfer efficiency.

Furthermore, if the charged potential of the dielectric sheet is high, the transfer material will adhere excessively to the surface of the dielectric sheet during transfer, and the gap between the two will be pinched, which is coupled with the fact that the charged potential of the dielectric sheet is high. Therefore, when the dielectric sheet and the transfer material are separated after the toner image transfer, electric discharge is likely to occur due to dielectric breakdown of the air. As a result, discharge patterns occur in the transferred image and toner scatters, resulting in a significant deterioration in image quality.

As a countermeasure to this problem, there are methods such as installing a self-discharge static eliminator or the like at the separation part between the dielectric sheet and the transfer material to alleviate the discharge during separation, or eliminating static electricity using an AC corona discharge device. However, each method has drawbacks such as insufficient effectiveness, ozone generation from the corona charger, complicated device configuration, and increased cost.

On the other hand, if the volume resistivity is small, current is injected into the dielectric sheet from the metal sheet that is the bias electrode, and the potentials of the dielectric sheet and the transfer material become the same polarity, which weakens the adsorption force between them. Or it won't move at all.

Here, if the transfer device, that is, the transfer drum is provided with a transfer material gripper, the leading edge of the transfer material will be held on the transfer drum even if no adsorption force acts between the dielectric sheet and the transfer material. If the holding force of the gripper is not strong enough, the position of the transfer material may shift slightly, causing color misalignment or color unevenness, or it may come off completely, causing a jam. Furthermore, even if the leading edge of the transfer material is completely held by the gripper, the curvature of the photosensitive drum causes the transfer material to separate from the dielectric sheet at the rear end, which is still a cause of color misregistration, color unevenness, and reduced transfer efficiency. becomes. This separation between the trailing edge of the transfer material and the dielectric sheet is caused by the so-called "stiffness" when the transfer material is thick or hard.
This is more noticeable when the

By the way, the thinner the dielectric sheet is, the stronger the effective electric field that contributes to the transfer will be, even when the same bias voltage is applied, which is convenient for transfer, but in reality, from the perspective of supporting the transfer material, requires mechanical strength, so there is a limit to how thin it can be. Therefore, in order to compensate for the decrease in the transfer electric field due to the thickness of the dielectric sheet, it is preferable that the dielectric sheet has a high dielectric constant, and by setting the dielectric constant to 4 or more, sufficient transfer efficiency can be obtained.

Next, one embodiment of an image forming apparatus according to the present invention will be described in detail with reference to the drawings.

The present invention may be practiced in a multicolor electrophotographic reproduction machine having a rotary development device as previously described in connection with FIG. Therefore, in this embodiment, the image forming apparatus is the multicolor electrophotographic copying apparatus shown in FIG. 5, and only the transfer electric field forming means in the transfer apparatus is improved according to the present invention. In addition, the transfer device is
The transfer drum 9 shown in FIG. 6 is provided, and its structure and operation are as described above. Therefore, the overall structure and operation of the multicolor electrophotographic copying apparatus and the transfer drum 9 will be omitted except for the electric field forming means.

FIG. 1 is a drawing that best represents the characteristic parts of the present invention, and shows the vicinity of the transfer section of the multicolor electrophotographic copying apparatus shown in FIG. 5, and other parts are omitted. The electric field generation means constructed according to the drawings are illustrated in particular detail.

The transfer device, ie, the transfer drum 9, is constructed by stretching a transfer material carrying member, ie, a dielectric sheet 93, between two cylinders 9a and 9b, as described in connection with FIG. In this example, the dielectric sheet is a polyvinylidene fluoride resin (PVdF) with a volume resistivity of approximately 10@~1O16 Ωcm, a relative permittivity of approximately 8, and a thickness of approximately 1100 tt.
) was used. The front and rear ends of the dielectric sheet 93 are fixed on a connecting portion 9C that connects two cylinders 9a and 9b that constitute the transfer drum 9.

In this example, the diameter of the transfer drum was set to 160 mm, and the moving speed was set to 160 mm/sec. At the same time, the process speed, which is the moving speed of the photosensitive drum 3, etc., is also 1.
The speed was set at 60 mm/sec. An electric field forming means for generating a transfer electric field is provided in the portion of the transfer drum 9 where the transfer drum 9 and the photosensitive drum 3 are in contact with each other, and the details of the electric field forming means will be described below with reference to FIG. explain.

The electric field forming means is provided with an elastic sheet 20 made of an elastic synthetic resin film, in this embodiment polyethylene terephthalate (PET), on a support base 19 made of a rigid body such as metal, and further provided with a tip of the elastic sheet 20. A conductive metal sheet 21 is provided in the section. A power source (not shown) is connected to the conductive metal sheet 21 serving as an electrode of the electric field forming means.

As shown in FIG. 1, the electric field forming means including the support base 19, the elastic sheet 20, and the metal sheet 21 includes the introduction of a dielectric sheet 93 in which the elastic sheet 20 and the metal sheet 21 are transfer material supporting members. The metal sheet 21 extends from the side toward the downstream side in the moving direction, and further corresponds to the position where the transfer material P finishes contacting the photosensitive drum 3, the position where the contact starts, or the position where the metal sheet 21 is as close as possible. It is positioned so as to press the dielectric sheet 93.

In this embodiment, the present inventors formed a latent image on the negatively charged photosensitive drum 3, and the average particle size was approximately 8 to 1.
A toner image was obtained by reversal development using a 0 μm toner. At this time, toner is composed of resin, coloring material, and minute amounts of additives to improve charge controllability and lubricity, and is triboelectrically charged with carrier particles in a developing device to become negatively charged. Met.

The toner image on the photosensitive drum was then transferred to a transfer material by a transfer device having the above configuration. Next, the transfer material was separated from the transfer drum 9 and fixed in a fixing device.

Even if the dielectric sheet 93 of the transfer drum 9 has a volume resistivity within the range of approximately 10 11 to 10 16 Ω·cm, the bias voltage applied to the metal sheet 21 for forming the transfer electric field is +0. It was possible to set the voltage to about .7 to 1.5 KV. This voltage is lower than the voltage of 6 to 8 KV required for conventional transfer using a corona current using a discharge device, but it was still possible to obtain transfer efficiency equivalent to transfer using a corona current. .

Further, when a conventional discharger is used, a current that does not directly contribute to transfer is generated, such as a current flowing to a shield, but according to the present invention, no current is generated.

Therefore, according to the present invention, a power supply with a small voltage and current capacity is required, and the dielectric strength of the wiring is also lower, making it possible to miniaturize the device and reduce costs.

Also, as a result of experiments with various volume resistivities of the dielectric sheet, approximately lO6 to 10'6 Ωcm, preferably 10'' to
By using a dielectric sheet of 1012Ω・cm,
As mentioned above, there is no deterioration in image quality due to the discharge that occurs when the dielectric sheet and transfer material are separated, or there is no color shift or color unevenness due to insufficient adhesion between the dielectric sheet and the transfer material, and the transfer efficiency is also reduced. A sufficient image was obtained.

Furthermore, if a dielectric sheet with a volume resistivity of 108 Ω·cm or less is used, the potential decay after charging during transfer is rapid, making it difficult to transfer during multiple transfer of the second to fourth colors or during continuous copying. There was no decrease in efficiency, or it was so small as to pose no practical problem.

Therefore, devices such as a corona charger for eliminating static electricity are no longer necessary, making it possible to further downsize the device, lower costs, and reduce the amount of ozone generated.

In addition, even if the volume resistivity of the dielectric sheet is relatively large, approximately IQ + 6 Ω・cm, by using a dielectric sheet with a relative dielectric constant of 4 or more, the bias voltage is 10 to 1.5 KV, which is necessary for transfer by corona current. Sufficient transfer efficiency was obtained with a low voltage, compared to a typical bias voltage of 6 to 8 KV.

FIGS. 3 and 4 show other embodiments of electric field forming means that can be suitably used in the present invention.

In FIG. 3, by making the support base 19 from an insulating material, the metal sheet 21 serving as the electrode can be directly provided on the support base 19, which reduces the number of parts and improves reliability such as durability. It is possible to reduce manufacturing costs.

Alternatively, even if the support base 19 is conductive, the same effect as in the above embodiment can be achieved by using an insulating member to which the metal sheet 21 is attached.

In the embodiment shown in FIG. 4, the electric field forming means is
The transfer bias roller 22 is formed by covering the outer periphery of a cylindrical roller extending in the thrust direction with a conductive member.

The transfer bias roller 22 is installed so as to press a dielectric sheet, which is a transfer material carrying member, from the back surface thereof.

A transfer electric field is formed by applying a bias voltage to the conductive member of the roller 22, and by rotating the roller 22 in the same direction and at the same speed as the dielectric sheet, there is no friction with the dielectric sheet. , durability and positional accuracy of both dielectric sheets are less likely to change over time, improving reliability.

Furthermore, by using an elastic conductive member on the outer periphery of the transfer bias roller 22, the adhesion between the transfer bias roller and the dielectric sheet is increased, and the adhesion between the transfer material and the photosensitive drum is also increased. Better transfer is possible.

Although the above embodiments have been explained using a full-color electrophotographic copying apparatus as an example, the application of the present invention is not limited to this, and the shape of the conductive member constituting the electric field forming means may also be changed. The present invention is not limited to the above embodiments.

The present invention generally relates to an image forming apparatus,
In particular, an image obtained by transferring a toner image formed on an image carrier by an electrophotographic method or an electrostatic recording method to a transfer material supported on a transfer carrier member by applying a transfer electric field. The present invention relates to a forming device, and can be applied to black-and-white, monochrome, or full-color electrophotographic copying devices, printers, and various other recording devices as such image forming devices.

Incidentally, in the case of black and white or monochrome, it is effective when images are continuously output.

The image forming apparatus according to the present invention configured as described above is as follows:
There is no need for a transfer discharger, therefore, there is no need for a power supply with a large voltage or current capacity, or wiring with higher voltage resistance.
As a result, the device can be made smaller and lower in cost, and furthermore,
This has the effect of eliminating the generation of ozone and making it possible to obtain images of good quality.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a multicolor electrophotographic copying apparatus which is an embodiment of an image forming apparatus according to the present invention, and only the vicinity of the transfer section is shown in detail. FIG. 2 is a sectional view of the electric field forming means. 3 and 4 are cross-sectional views of other embodiments of the electric field forming means. FIG. 5 is a sectional view of a multicolor electrophotographic copying apparatus that can embody the present invention. FIG. 6 is a perspective view of the transfer device. 3: Image carrier (photosensitive drum) 9: Transfer device (transfer drum) 9a, 9b Niji cylinder 9c connection part 19: Support stand 20: Elastic sheet 21: Metal sheet 22: Transfer bias roller Engraving of drawing (no change in content) Figure 3 Figure 4 Figure 5 Procedure amendment (method) % formula % (100) Canon Co., Ltd. May 29, 1990 (Shipping mortar) (No change in content)

Claims (1)

[Scope of Claims] 1) An image bearing member on which a toner image is formed and a transfer material carrying member that supports and conveys a transfer material, and the toner image on the image carrier is transferred to the transfer material by an electric field. In the image forming apparatus having a transfer device, the electric field generating means for generating the electric field has a conductive member that is connected to a power source and comes into contact with the back surface of the transfer material carrying member at least during transfer; The volume resistivity of the transfer material supporting member is 10^
An image forming apparatus characterized in that the resistance is 8 to 10^1^5 Ω·cm. 2) The image forming apparatus according to claim 1, wherein the transfer material carrying member is a dielectric sheet and has a volume resistivity of 10^9 to 10^1^2 Ω·cm. 3) The image forming apparatus according to claim 1, wherein the transfer material carrying member is a dielectric sheet and has a dielectric constant of 4 or more.