JPH03233577A - Multicolor image forming device - Google Patents

Abstract

PURPOSE:To prevent transfer efficiency in transfer from decreasing by setting bias voltage, which is applied to an electric field generating means, equal to or larger than that in last-color transfer in transfer of 2nd and succeeding colors, and setting the volume resistivity of a transfer material carrying member to 10<8> - 10<16>OMEGA.cm. CONSTITUTION:The electric field generating means which generates an electric field has a conductive member 21 which is connected to a power source 30 and also contacts the reverse surface of the transfer material carrying member 9 at least in transfer operation. Then the bias voltage applied to the electric field generating means is made equal to or larger than that in the last-color transfer in the transfer of 2nd and succeeding colors and made larger than that in first-color transfer in final-color transfer. Further, the volume resistivity of the transfer material carrying member 9 is set to 10<8> - 10<16>OMEGA.cm. Consequently, a dielectric sheet which constitutes the transfer material carrying member is prevented from decreasing in transfer efficiency owing to electrostatic charging and a multicolor image of good quality is obtained.

Description

[Detailed Description of the Invention] No. 1 The present invention generally relates to an image forming apparatus,
In particular, a multicolor image can be created 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 multicolor image forming apparatus. Such multicolor image forming devices include full-color electrophotographic copying devices, printers, and various other recording devices.

Conventionally, for example, various multicolor (full color) image forming apparatuses have been proposed, and FIG. 1 shows, as an example, a multicolor electrophotographic copying apparatus equipped with a developing device called a so-called rotary developing device. is illustrated.

Briefly explained with reference to FIG. 1, 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. 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 latent image on the photosensitive drum 3 into a visible image.

The rotary developing device 1 has four developing units IY, LM, IC, and I, which respectively store four color developers: yellow developer, magenta developer, cyan developer, and black developer.
BK and these four developing devices lY, IM, IC1IBK
It consists of a substantially cylindrical casing that holds and is rotatably supported. The rotary developing device 1 transports a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 3 by rotating the housing, develops the electrostatic latent image on the photosensitive drum, and develops the electrostatic 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 the transfer drum 9 has cylinders 9a and 9b arranged at both ends, as understood with reference to FIG.
and a connecting portion 9c that connects the two cylinders 9a, 9b, and a transfer material carrying member 93 is stretched over the opening area of the outer peripheral surface of the cylinders 9a, 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.

Inside the transfer drum 9, as shown in FIG.
(not shown).

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 etc. It is transported in the direction of the arrow.

Next, the toner image on the photosensitive drum 3 is transferred by receiving a transfer electric field from the conductive sheet 21 to which a bias is applied from the back side of the transfer material carrying member of the transfer drum 9, that is, the dielectric sheet 93, in the area in contact with the photosensitive drum 3. is transferred onto the transfer material P.

The transfer material P is transferred to the separating claw 1 after the necessary number of transfer processes have been performed.
5, the toner is peeled off from the transfer drum 9 and conveyed to the fixing device 17 by the conveyor belt 16. 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, the above conventional example has the following drawbacks. That is, when the transfer material after receiving the first color developable image transferred from the photosensitive drum 3 is peeled off from the photosensitive drum, it ionizes the air in the vicinity. At this time, for example, if the toner of the developer is charged with negative polarity and the polarity of the bias applied to the conductive sheet 21 is set to positive, the transfer material is Of the air ionized by the peeling, negatively charged air adheres to the surface of the transfer material, and positively charged air adheres to the outer peripheral surface of the photosensitive drum. As a result,
The negative charges attached to the transfer material act to weaken the transfer electric field caused by the bias voltage applied to the conductive sheet 21 that is in contact with the back surface of the dielectric sheet 93.

On the other hand, since the toner itself transferred from the photosensitive drum 3 to the transfer material is negative, the transfer electric field is weakened similarly to the development described above. As a result, the current flowing from the power supply through the conductive sheet also decreases, resulting in a decrease in transfer efficiency for the second and subsequent colors. Conventionally, in such cases, there is a dielectric sheet placed close to the dielectric sheet inside or outside the transfer drum. In some cases, there is a method of discharging the static electricity by disposing an AC corona discharger with a superimposed DC component, or using a static elimination brush or the like to eliminate static electricity from the dielectric sheet.

However, when removing static electricity using a corona discharger, a high voltage is required, and ozone is generated which is harmful to the photosensitive drum and the human body, and the device configuration becomes complicated, reducing reliability and durability. There are problems such as rising costs. or,
The static elimination method using a static elimination brush may not be sufficiently effective, and furthermore, there are similar problems such as a decrease in reliability and durability, and an increase in cost.

Therefore, an object of the present invention is to prevent a decrease in transfer efficiency during transfer of the second and subsequent colors due to charging of a dielectric sheet constituting a transfer material carrying member, and to obtain a multicolor image of good quality. An object of the present invention is to provide a multicolor image forming apparatus.

The above object is achieved by a multicolor image forming apparatus according to the present invention. In summary, the present invention includes an image carrier on which a toner image is formed, a transfer material carrying member that carries and conveys a transfer material,
A multicolor image forming apparatus including a transfer device that transfers the toner image on the image carrier to the transfer material using an electric field,
The electric field forming means for generating the electric field has a conductive member that is connected to a power source and contacts the back surface of the transfer material carrying member at least during transfer, and the bias voltage applied to the electric field forming means is When transferring the second and subsequent colors, the size is the same as or larger than when transferring the previous color, and at least when transferring the final color, it is larger than when transferring the first color,
Furthermore, the volume resistivity of the transfer material supporting member is 10' to 10
This is a multicolor image forming apparatus characterized by 16Ω:C, m. Preferably, the transfer material supporting member is a dielectric sheet and has a volume resistivity of 10''-10''Ω·c.
m, and the dielectric sheet has a dielectric constant of 4 or more.

In this way, the volume resistivity of the transfer material carrying member, that is, the dielectric sheet is set to 10' to 1016 Ω·cm, preferably IQ
Good transfer is possible by setting it to 11 to 1016 Ω·cm. The reason is as follows.

In other words, if the volume resistivity is large, for example, in the case of a multi-color image forming apparatus that performs multiple transfer, after the dielectric sheet is charged during the first color transfer, it takes a long time for the potential to decay, as described above. During transfer of the second and subsequent colors, the effective electric field contributing to transfer becomes weaker, resulting in lower transfer efficiency.

Furthermore, if the volume resistivity is large, a higher bias voltage is required to obtain the same image density, which not only increases the size of the power supply but also increases the initial charging potential of the dielectric sheet during transfer. This results in 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, a discharge pattern occurs 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 stop working at all.

Furthermore, even if the injected current is small and the potentials of the dielectric sheet and the transfer material are of opposite polarity, the volume resistivity of the dielectric sheet is small, so the charge decays quickly over time, and the adsorption force also weakens accordingly. (It turns out.

Here, if the transfer device, that is, the transfer drum is provided with a transfer material gripper, even if there is no adsorption force between the dielectric sheet and the transfer material (but the leading edge of the transfer material is held by the transfer drum), , make sure the holding force of the gripper is quite strong (otherwise, the position of the transfer material may shift slightly, causing color misalignment or color unevenness, or it may come off completely, causing a jam. Also, make sure that the tip of the transfer material is not completely attached to the gripper). Even if the transfer material is held at the rear edge, the curvature of the photosensitive drum causes the transfer material to separate from the dielectric sheet, resulting in color misregistration, color unevenness, and reduced transfer efficiency. The separation from the body sheet is caused by the transfer material being thick or hard, the so-called "stiffness".
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.

View 1 Next, one embodiment of the image forming apparatus according to the present invention will be described in detail with reference to the drawings.

The present invention may be preferably 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 assumed to be embodied in the multicolor electrophotographic copying apparatus shown in FIG. 1, and is equipped with a transfer device, that is, a transfer drum 9, shown in FIG. Since the structure and operation of the multicolor electrophotographic copying apparatus and transfer drum 9 are as described above, a detailed explanation of the overall structure and operation of the multicolor electrophotographic copying apparatus and transfer drum 9 will be omitted.

As described above, the transfer drum 9 includes two cylinders 9a.
, 9b, a transfer material carrying member, that is, a dielectric sheet 93
It is constructed by stretching. In this example, the dielectric sheet has a volume resistivity of approximately lOI' to 1016Ω''.
A polyvinylidene fluoride resin (PVdF) having a dielectric constant of about 8 cm and a thickness of about 100 μm was used. Dielectric sheet 9
The front and rear end portions of the transfer drum 3 are fixed on a connecting portion 9C that connects the 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 photosensitive drums, etc., is 160 m.
m/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 explained below with reference to FIG. 4. do.

The electric field forming means includes an elastic sheet 20 made of an elastic synthetic resin film, in this embodiment polyethylene terephthalate (PET), provided on a support base 19 made of a rigid body such as metal, and a It is constructed by providing a conductive metal sheet 21 at the tip. 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. 3, 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 other 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 3 was then transferred to a transfer material by the transfer device having the above-mentioned configuration. Next, the transfer material was separated from the transfer drum 9 and fixed in the fixing device 17.

In the multicolor electrophotographic copying apparatus having the above configuration, the dielectric sheet serving as the transfer material carrying member has a volume resistivity of about 10' to
Various changes were made within the range of 10'' Ω·am, and in each case, the bias voltage was further changed to output a color image. Some of the results are shown in Table 1.

Table 1 In Table 1, the volume resistivity of the dielectric sheet is 10''''
Ω'cm and 1O11Ω"cm, and the density of the first color was the same at bias voltages of 1.2 KV and 0.8 KV, respectively. Four color images were transferred under these constant bias voltages. However, as shown in Figure 5, the image in this case did not overlap two or more colors in the same area.In Figure 5, M (magenta) is the first color, C (cyan) ) is the portion transferred to the second color, Y (yellow) is the portion transferred to the third color, and BK (black) is the portion transferred to the fourth color.

As shown in Table 1, the image density of the second and subsequent colors gradually decreases, and this tendency is more pronounced as the volume resistivity of the dielectric sheet increases. This is because when the volume resistivity is large, the decay of the charged potential is slow. Therefore, if the volume resistivity is reduced, the charge-up of the dielectric sheet can be reduced, but as mentioned above, this will weaken the adhesion force between the dielectric sheet and the transfer material, which is disadvantageous for a stiff transfer material.

Therefore, if an attempt is made to maintain the dielectric sheet and the transfer material with an attractive force, chassis and lumps of the dielectric sheet are unavoidable.

Therefore, by applying the present invention, the bias voltage was increased for the second and subsequent colors to strengthen the effective transfer electric field. The results are shown in Table 2. In Table 2, the values of the bias voltages for the second and subsequent colors are shown in parentheses.

Table 2 In this way, even when using a dielectric sheet with a large volume resistivity and slow decay of charged potential, by increasing the pie-sumi pressure sequentially from the second color onwards, a decrease in image density can be prevented and a good image can be obtained. Obtained.

FIGS. 6 and 7 show other embodiments of electric field forming means that can be suitably used in the present invention.

In FIG. 6, 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. 7, 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.

By applying a bias voltage to the conductive member of the roller 22, a transfer electric field is formed, and by rotating the roller 22 in the same direction and at the same speed as the dielectric sheet, friction with the dielectric sheet is eliminated (the electric field is formed). Durability of both the means and the dielectric sheet, and changes over time in position and stacking are small (reliability is improved).

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, a multicolor image can be created 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 invention relates to a multicolor image forming apparatus that obtains
The present invention can be applied to full-color (multicolor) electrophotographic copying devices, printers, and various other recording devices as image forming devices.

The image forming apparatus according to the present invention configured as described above has the following features:
This has the effect of preventing a decrease in transfer efficiency due to charging of the dielectric sheet constituting the transfer material carrying member, and making it possible to obtain a multicolor image of good quality.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a multicolor electrophotographic copying apparatus in which the present invention can be preferably implemented. FIG. 2 is a perspective view of the transfer device. FIG. 3 is a schematic cross-sectional view of the multicolor electrophotographic copying apparatus showing electric field forming means. FIG. 4 is a sectional view showing the electric field forming means. FIG. 5 was used for evaluation of the present invention. FIG. 2 is a diagram showing an image sample produced by a multicolor electrophotographic copying device. 6 and 7 are cross-sectional views showing other embodiments of the electric field forming means. 3: Image carrier (photosensitive drum) 9: Transfer device 9a, 9b Niji cylinder 9C connection part 19: Support stand 20: Elastic sheet 21: Metal sheet 22 Two transfer bias openings - Engraving of drawing (no change in content) Fig. Figure 4 9 Figure 5 6 Figure 19 Figure 7 Procedural amendment (method) Display of the case 1990 Patent Application No. 29898 Name of the invention Person who corrects multicolor image forming device Relationship to the case

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 multicolor image forming apparatus having a transfer device, the electric field generating means for generating the electric field has a conductive member connected to a power source and in contact with the back surface of the transfer material carrying member at least during transfer, Further, the bias voltage applied to the electric field forming means is set to be the same or larger when transferring the second and subsequent colors than when transferring the previous color, and at least 1 when transferring the final color.
A multicolor image forming apparatus characterized in that the volume resistivity of the transfer material carrying member is greater than that during color transfer, and further characterized in that the volume resistivity of the transfer material carrying member is 10^8 to 10^1^6 Ω·cm. 2) The multicolor image forming apparatus according to claim 1, wherein the transfer material carrying member is a dielectric sheet and has a volume resistivity of 10^1^1 to 10^1^6 Ω·cm. 3) The multicolor 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.