JPS6388582A - Transfer device - Google Patents

Abstract

PURPOSE:To increase transfer efficiency and to reduce image fogging by providing an applying means which applies a transfer voltage to a pressure conductive layer which is applied with pressure by a pressure applying means. CONSTITUTION:A developing or fogging sheet 125 on a photosensitive body 91 is pressed by as conductive rubber roller 93 for transfer and applied with a transfer voltage 127 through the pressure conductive sheet to perform transfer to the pressure conductive sheet. In a retransfer process which is entered automatically at a restart after misconveyance, the transfer voltage applied to the conductive rubber becomes a voltage 128 having the opposite polarity, so toner 126 which is transferred is retransferred onto the photosensitive body 91 again at a transfer part, so that toner is cleaned by the cleaning process of a transfer drum and can be reused. Namely, the toner 129 which is retransferred onto the photosensitive body is removed cleanly from the photosensitive body by a sweeping device for the photosensitive device. Consequently, the transfer efficiency is improved and image defogging is eliminated.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention relates to a transfer system in electrophotography, and in particular to electrostatic transfer of a toner image formed on a photoreceptor while applying an electric field to a transfer material. The present invention relates to a transfer device for transferring images.

(Prior art) Conventional transfer mounting methods include a method using a corona charger,
There is a method in which a roller is used and a voltage is applied to the roller from the outside. Also, the method of using a corona charger differs between monochrome and color. The transfer method using a corona charger, which has been put into practice by Xerox Corporation in the United States for a long time and is widely used in general monochrome copying machines, is a method in which voltage is applied directly from the back of the transfer material using the corona charger. The disadvantage of this method is that since the transfer material is directly irradiated with corona ions, toner re-transfer occurs when the conductivity of the plain paper used as the transfer material increases due to the influence of environmental temperature. It is directly affected by the conductivity of the material, and the image is easily distorted because discharge occurs easily when the transfer material is carried into and out of the photoreceptor section.1
Lowering the transfer voltage to suppress discharge has disadvantages such as lower transfer efficiency. However, since this system has a simple configuration, it is adopted in most monochrome copying machines, which can be sufficiently effective as long as it has a certain level of transfer efficiency.

On the other hand, for colors that overlap each color, the transfer efficiency of each color must be constant, the transfer efficiency of each color must be stable even when the conductivity of the transfer material changes due to environmental changes, and the image on the transfer material must be stable. Since the transfer material is overlapped three times, conditions are required such as being able to include a mechanism that can transport the transfer material accurately and with high precision. In order to satisfy this condition, an insulating sheet is pasted on a hollow drum, the transfer material is conveyed onto the photoreceptor by this drum, the photoreceptor and the transfer material are brought into soft contact, and the back side of the insulating sheet is There is a method of performing flea transfer by irradiating corona ions (Japanese Patent Laid-Open No. 54-19751).

This method is based on the same principle as the belt transfer method, and each time a color toner image is overlaid multiple times, charge accumulates on the insulating belt and the transfer efficiency decreases. Therefore, when performing overlapping transfer of color images, it is necessary to set the color density taking into account the gradual decrease in transfer efficiency. Another drawback is that image disturbances occur due to discharge when the transfer material is carried into and out of the photoreceptor.

Another color transfer method using a corona charger is a method using a transfer drum in which an insulating mesh is attached to a hollow drum (Japanese Patent Application Laid-open No. 164370/1983).

In this method, in order to eliminate the discharge that occurs when the transfer material is carried into and out of the photoreceptor, the mesh is coated with a conductive organic material that has an appropriate time constant. The blur of the image is reduced. However, the corona ions that pass through the mesh gap and directly irradiate the transfer material have the disadvantage that image blurring remains due to the discharge that occurs when the transfer material is carried in and out between the photoreceptors.

Transfer methods using conductive rollers include methods using hard rollers and creating a gap between the photoreceptor and the roller;
There is a method in which a soft conductive rubber roller is used to bring the transfer material and the photoreceptor into close contact. In the method using these conductive rollers, a thin insulating layer is provided on the surface so that stable transfer efficiency can be exhibited in an environment of 19 degrees Celsius. Methods using hard rollers require maintaining a precise gap between the photoreceptor and the roller, transfer efficiency varies when the thickness of the transfer material differs, and when using a conventional two-component developer, iron This method has not been put to practical use because if the powder carrier adheres to the photoreceptor, the photoreceptor will be damaged in the transfer area.

On the other hand, there is a method using a conductive soft roller (Japanese Unexamined Patent Publication No. 50-22640). This soft roller uses a foamable conductive rubber roller. This method allows the transfer material to come into soft contact with the photoreceptor, and the pressure of contacting the transfer material with the photoreceptor causes the foam rubber to shrink, increasing the conductivity of the foam rubber in the transfer area, and applying high voltage only to the transfer area. The conductive rubber roller has high resistance at the transfer section, which allows the transfer material to be transferred to and from the photoconductor without applying pressure, and has the advantage of eliminating electrical discharge and eliminating image blurring.

However, with this technology, the necessary resistance change (from 1010 ΩclTl to 104 Ω
cm) is obtained. The optimal thickness of the foam layer at this time is shown to be 0.8 cm to 2 cm, and 1
When compressed to /3, the thickness goes from 0.2 cm to 0.7 c.
It becomes m. This variation in the diameter of the transfer roller that also transports the transfer material is achieved with high precision (0.01 (to) or less).
Not suitable for color transfer mechanisms that require transfer material transportation. Furthermore, this foamable conductive rubber roller is repeatedly compressed and stretched, and each time the internal conductive rubber structures come into contact or separate under high voltage, causing discharge, which destroys the conductive rubber structures.

In order to prevent this, it has been proposed to impregnate the roller with insulating oil, but in order to create a structure that does not allow this insulating oil to leak, the structure of the foamable conductive rubber roller is complicated and requires many manufacturing steps, making it expensive. The product also lacked stability.

(Problems to be Solved by the Invention) As described above, although the transfer device using a foamed conductive rubber roller has various advantages, it has disadvantages such as lack of conveyance accuracy, structural complexity, and device stability. was there.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to further enhance the advantages of increasing transfer efficiency and reducing image blurring, increase conveyance accuracy, and provide a transfer device with a simple structure.

[Structure of the Invention] (Means for Solving the Problems) This invention is characterized in that a pressurized conductive material is used in a transfer device that transfers an image on a photoreceptor to a transfer material. . That is, pressure is applied to a layer made of a pressurized conductive material and a transfer voltage is applied at a position where the transfer material and the photoreceptor come into contact.

(Function) First, the inventor of the present invention found that the conventional transfer device using a foamed conductive rubber roller had the above-mentioned drawbacks because it attempted to achieve the following three functions with one roller. I focused on this.

That is, (1) The roller resistance values at the conveyance/export portion of the transfer material to the photoconductor and the transfer portion are changed to obtain a highly efficient and high quality transferred image.

(2) Bring the transfer material into soft contact with the photoreceptor.

(3) Convey the transfer material.

This is the function.

In contrast, the present invention uses a pressurized conductive sheet, and in the transfer section, soft pressure is applied from the back side of the pressurized conductive sheet with a conductive roller to bring the photoreceptor and the transfer material into contact. With this method, a high voltage can be applied only to the transfer portion, thereby increasing the transfer efficiency. On the other hand, in the portion where the transfer material is carried in and out of the photoreceptor, no pressure is applied and the pressure conductive sheet has a high resistance, so that no discharge occurs between the transfer material and the photoreceptor. As a result, there is no image blurring during transfer, and highly efficient transfer is possible. Furthermore, by using a hollow cylinder to which a pressurized conductive sheet is attached to support the transfer material during color transfer, a transfer drum mechanism for color is possible.

(Example) Next, one embodiment of the present invention will be described in detail using the drawings.

FIG. 1 is a schematic cross-sectional view of a transfer section according to the present invention. The toner image (2) formed on the photosensitive drum (1) is indicated by arrow A.
move in the direction. At this time, the transfer material (3) is conveyed together with the pressurized conductive sheet (4) in the direction of arrow B at the same speed as the photosensitive drum, and the pressurized conductive sheet is transported near the point (5) where it is in contact with the photosensitive drum. A soft conductive rubber roller (6) with a hardness of 40" from the back shows conductivity at a low pressure of about 3009/cJ, and the value reaches its maximum near the center of the contact area (5), resulting in a high transfer voltage. (7) is applied through a conductive rubber roller.As a result, highly efficient transfer is possible.Meanwhile, the transfer material is transferred to the photosensitive drum (8),
In the unloading section (9), there is no pressure and the pressurized conductive sheet has a high resistance, so no voltage is applied and no air discharge occurs. Therefore, it is possible to transfer images without blurring, and there is no damage to the photoreceptor on the photoreceptor drum due to discharge.

The relationship between the pressure and the conductivity of this pressurized conductive sheet is shown in FIG. 2(a). 300 suitable for transcription! ? When a pressure of about /cd is applied, the conductivity increases from 1010ΩCII+ to 1
It changes to about 0.04Ωcan. Appropriately, the pressure applied during this transfer is about 3009/cd; if the pressure is too high, the toner will stick to the photoreceptor, resulting in a transferred image with white spots. On the other hand, if the pressure is lower than this, the resistance value of the pressed conductive sheet will increase and the transfer efficiency will decrease. As described above, the pressurized conductive sheet in the pressurized portion of the transfer section exhibits resistance, and exhibits contact at the transfer section where the transfer material is carried into the photosensitive drum (7) and at the transfer section (8). Therefore, if the following conditions are satisfied, no discharge occurs between the transfer material and the photoreceptor, and a high transfer voltage can be applied. As a result, transfer efficiency increases and image blur due to discharge is eliminated. The conditions are shown below.

The gap distance between the photoreceptor on which the toner image is formed and the transfer material is 2, the thickness of the photoreceptor on the photoreceptor drum (1) is Ls, the thickness of the transfer material (3) is Lp, and the pressure conductivity is Sheet (
4), let the thickness be Ld, and let the relative dielectric constants be Ks, , K
When p, , Kd, the voltage applied to the gap between the photoreceptor and the transfer material is given by the following equation. Here, the unit of length is all expressed as μ.

Further, Va is a bias voltage applied to the conductive roller from the outside, and VC is a surface potential on the photoreceptor.

The above formula indicates that the transfer material is dry when the humidity is low and can be treated as a dielectric, and when the humidity is high it becomes resistive and becomes Lp-0. Moreover, Lo indicates the thickness of the insulating coating coated on the conductive roller or pressurized conductive sheet. KO is the dielectric constant of the coating.

Next, the state where there is no coating at Lo-0 will be explained. The photoconductor thickness Ls is 10μ, the transfer material thickness is 100μ, the pressure conductive sheet is 11m, and the relative permittivity Ks of each is
When Kp is set to 3, Kd is set to 3, Kd is set to 6, and Ko is set to 3, the gap voltage with respect to the gap distance is calculated and shown superimposed on the Paschen curve as shown in FIG. 2(b). As is clear from this figure, when the difference between the photoreceptor surface potential and the roller applied voltage is about 3000 V or less, no discharge occurs between the transfer material and the photoreceptor. In addition, the transfer material becomes resistant at high humidity and Lp-0
In addition, even when an insulating coating is provided on the transfer roller to prevent direct injection of electric charge into the transfer material, the pressure conductive sheet is thick enough that its curve hardly changes, which is necessary for transfer. The electric field acting on the toner between the gaps is given by the following equation.

Next, the value of the electric field with respect to the gap distance when the value of (V'a+Vc) is 3000V is shown by curve (11) in FIG.

Also, in the transfer area, the pressure conductive sheet is pressed,
The electric field applied to the toner when it becomes conductive (104 Ωcm) is given by the following equation.

The state of the electric field when the value of (Va + Vc) in the above equation is 3000V is shown by curve (12) in FIG. As described above, when pressure is applied to the pressurized conductive sheet, the electric field strength is several times that when no pressure is applied to the pressurized conductive sheet. Further, it can be predicted that when the toner layer becomes thick and the gap distance 2 during transfer increases, the electric field strength weakens and the transfer efficiency decreases. Generally, the toner layer consists of several layers and has a thickness of 50 to 60 μm.
is the value of

This gap can provide a sufficient electric field for transfer. By bringing the transfer material into pressure contact with the toner as described above, highly efficient and high-definition transfer is possible.

On the other hand, at the part where the photoconductor and transfer material are separated after transfer, the pressure of the conductive sheet is removed and its resistance increases, and no discharge occurs between the gaps, causing blurring of the transferred toner image. There isn't. Next, the case where the transfer material becomes resistant during high humidity will be described. At this time, since the transfer material is resistive, it becomes Lp-O, and the electric field applied to the gap is expressed by the following equation.

The state of this electric field is shown by curve (13) in FIG. 2(C).

In this case, the electric field applied to the toner is higher and the transfer efficiency increases, but charges are directly injected into the toner through the transfer material, which may conversely reduce the transfer efficiency. To prevent this, as shown in FIG. 3, an insulating sheet (15) is provided on the conductive soft rubber roller (6) or the pressurized conductive sheet (4). The thickness of this insulating sheet is preferably thin in order to increase the electric field during transfer, but it is preferably in the range of 50 to 10 .mu.m considering mechanical strength.

Next, as another embodiment, a copying machine using the present invention for belt transfer will be described with reference to FIG. The reflected light (18) of the original (17) illuminated by the original (16) is reflected by the lens (19).
passes through and forms an image on the photoreceptor (1). On the other hand, the photoreceptor rotating in the direction of the arrow is charged by a main charger (20) and irradiated with the light to form an electrostatic latent image.

This electrostatic latent image is developed with toner by a developing device (21) and becomes visible. The toner image formed on this photoreceptor is transferred to a transfer material (23) on a transfer belt (22) using the pressurized conductive sheet of the present invention. This transfer belt made of a pressurized conductive sheet is pressurized from the back side by a conductive rubber roller (6) to which a transfer voltage is applied, increasing the contact area with the photoreceptor (1) to ensure sufficient transfer. . The transfer material onto which this toner image has been transferred is conveyed to a heat roller (24) and fixed thereon.

On the other hand, the photoreceptor after the transfer is irradiated with light from a light source (25) to erase the surface charge. Thereafter, residual toner is cleaned with a wiping blade (26) and the toner is reused.

Next, an embodiment in which the transfer device of the present invention is applied to a color copying machine will be described with reference to FIG. As shown in FIG. 5(a), a pressurized conductive sheet (4) is provided on a hollow support (27), and pressure is applied from the back side of the sheet with a conductive rubber roller (6>). A claw (29) for fixing the transfer material is provided on the support part (28) of the body, making it possible to fix the transfer material on the photoreceptor and convey it three times. In the copying machine, reflected light (18) from a document (17) illuminated by a light source (1G) passes through a lens (19) and forms an image on the photoreceptor (1). During the irradiation, it passes through a switchable color filter (3o) and is separated into the three primary colors (R, G, B), or a black and white light image, which irradiates the photoreceptor.On the other hand, in the direction of the arrow The rotating photoreceptor (1) is a main charger (20)
and is exposed to the color-separated light to form an electrostatic latent image. When forming a black and white image, the filter (30) is switched to an achromatic filter to expose the photoreceptor. The electrostatic latent image corresponding to this black and white image is developed and visualized in a black and white dedicated developer (21) which has a large developer container fixed around the photoreceptor. The toner image formed on the photoconductor is transferred to a transfer material (23) conveyed by a transfer drum (31) to which a pressure conductive sheet is attached.
Transfer is performed using a transfer voltage applied to a conductive soft roller. The transfer material to which this toner image has been transferred is peeled off from the transfer drum by a peeling claw (32), and then removed by a heat roller (24).
The toner image is fixed. After the transfer, the photoreceptor is irradiated with light by a light source (25) to erase the surface charge, and the remaining toner is wiped off with a wiping blade (2G) to be reused.

On the other hand, when forming a color image, the reflected light from the original passes through a color filter (30) that can be switched to each color.
The photoreceptor (1) is exposed to light separated into the three primary colors of R, G, and B. When the R (red) filter is selected and an electrostatic latent image is formed, the R (red) and complementary color C (cyan) developer of the rotationally movable developer (33) is selected, and the image is formed on the photoreceptor. Develop the electrostatic latent image. This rotationally movable developing device has R
There are color developers for C (cyan), 1M (magenta), and Y (yellow), which are complementary colors of (red), G (green), and B (blue). Each developer is for a non-magnetic component, consisting of a developer transport sleeve (34) and a developer container (35). Each developing device is rotated in the direction of arrow C to select the developing device of the required color, and the developing device is fixed so that its developing sleeve (37) is in contact with the photoreceptor. In this way, it is possible to develop the required color. The monochromatic toner image formed on the photoreceptor is transferred onto a transfer material conveyed by a transfer drum (31) according to the present invention. At the time of this transfer, a transfer voltage is applied to the conductive soft roller (6) in the transfer drum. This process is repeated three times, and the color toner images are superimposed on the transfer material to form a full-color image. During this color image formation, the fixed developing device (21) containing black toner is at rest, but a black image for undercolor processing may be further added as necessary. The color image thus formed is fixed by a fixing device (24) and fixed onto the transfer material.

Next, as another example, an example in which contact at the transfer portion can be realized more softly will be described.

In this example, a transfer belt having a conductive layer and a pressed conductive sheet provided on a plastic support is used, and the recording medium on the transfer belt is applied from behind to the photoreceptor with a soft pressure of about 3009/C-. It consists of a rubber roller with low hardness ('20 to 40') that is brought into contact, or a mechanism that applies tension to the transfer belt and brings the photoreceptor into soft contact. In an embodiment different from the method in which the conductive sheet is pressed directly at the transfer section using a conductive rubber roller with limited softness, the transfer voltage is supplied from a place other than the transfer section. Therefore, pressure is applied with a conductive roller from the surface of the transfer belt that is different from the transfer area, and the pressure is guided through the pressure conductive sheet and the conductive layer to the transfer area, and pressure is applied by the soft pressure applied by a soft rubber roller at the transfer area. The voltage is applied through a conductive sheet. Furthermore, by providing this transfer belt on a hollow support and providing fixed claws for conveying the recording medium on this hollow support, a color transfer drum can be obtained.

In the embodiment having the above configuration, a transfer belt having a conductive layer and a pressurized conductive sheet provided on a plastic support is used, and a soft rubber roller (hardness: 20" to 40"'), or a mechanism that applies tension to the transfer belt and a mechanism that brings the belt into soft contact with the photoreceptor. It is a soft touch. The transfer voltage is applied by applying pressure with a conductive roller at a portion different from the transfer portion. This method using a pressurized conductive sheet makes it possible to apply a high voltage at the center of the transfer area, which is necessary for transfer, and since pressure is not applied to the area where the recording medium is carried in and out of the photoreceptor, pressure is applied. The conductive sheet has high resistance and can prevent gas discharge. In this way, highly efficient transfer without image blurring is possible. This allows for softer contact than with transfer equipment that uses a conductive rubber roller or conductive rubber sheet, which has a lower hardness limit (~40'), and enables stable transfer without toner sticking to the photoreceptor. becomes. For color printing, a transfer drum is used in which the transfer belt is provided on a hollow cylindrical support including a recording medium conveyance mechanism.

Next, a more detailed explanation will be given using the drawings. FIG. 6 is a schematic cross-sectional view of the transfer section according to this embodiment. The toner image (62> formed on the photosensitive drum (61) moves in the direction of the arrow. At this time, the recording medium (63) is conveyed together with the transfer belt (64) in the direction of arrow B at the same speed as the photosensitive drum. This transfer belt (64) is a support (65) made of a polyester film with low plastic elongation.
) on which a conductive layer (66) and a pressurized conductive sheet (67) are provided.

At the transfer section (68) where the transfer belt and the photoreceptor come into contact, soft pressure is applied from the back side of the transfer belt by a softening rubber roller (69) with a hardness of 40" or less at a low pressure of about 300 g/c. This pressure The pressurized conductive sheet (67) exhibits conductivity, and its value is maximum near the center of the contact area (68), and the value of the transfer voltage (70) applied through the conductive layer (66) is also maximum. This transfer voltage (70) is supplied through a pressurized conductive sheet exhibiting conductivity by pressure applied to a closed conductive roller (71) at a location different from the transfer section, and is applied through a conductive layer (6B). In this way, a high transfer voltage is applied to the transfer section, enabling highly efficient transfer.In addition, there is no pressure at the location where the recording medium (63) is carried in and out of the photoreceptor drum (81). As a result, the resistance value of the pressurized conductive sheet (67) increases, no voltage is applied, and gas discharge can be prevented.

Therefore, highly efficient transfer without image blurring is possible. The relationship between the applied Calorie pressure and the conductivity of this pressurized conductive sheet is
As shown in the figure. 300g/no toner sticking on the photoconductor
The conductivity changes from 101oΩσ to 104 due to a pressure of about ej.
ΩcI decreases to about 11. At a pressure lower than this pressure, the resistance value of the pressurized conductive sheet will be high and it will exhibit 80% resistance, and as a result, a substantial transfer voltage will not be applied at the locations where there is no pressure when the recording medium is carried into and out of the photoreceptor. First, gas discharge is prevented and image blur due to toner scattering is eliminated.

Next, the transfer equipment of this embodiment will be explained with reference to FIG. FIG. 5A is a diagram showing the structure of the transfer drum. A transfer belt (64) is provided on a hollow support (72) constituting a transfer drum, and both ends (73) of the hollow support (72) are attached from the back side of the belt (64).
(74) and a softer rubber roller (69)
) to apply pressure. Both ends (7) of this hollow support (72)
3) (74) Upper Transfer Bell) A rigid conductive roller (71) is brought into pressure contact with (64), and a transfer voltage is applied. Further, the support portion (75) of the hollow support (74) is provided with a recording medium fixing claw (7G) that enables conveyance of the recording medium (63). The recording medium fixed by the claws (76) is conveyed three times over the photoreceptor (61) with high precision, thereby forming a high-quality color image.

FIG. 7(b) is a sectional view of a portion where a photoreceptor and a transfer drum are in contact using a soft rubber roller. The outer diameter of the support (72) of the transfer drum moves along a trajectory indicated by a dotted line (77). Transfer belt (84) and recording medium (6
3) is in close contact with the photoreceptor and moves on the outer periphery of the transfer drum support (72). This value is set in advance so that the image does not stretch.

FIG. 7(e) shows another transfer mechanism that realizes the contact method between the photoreceptor and the transfer drum. A photoconductor (61) is placed between rollers (78) and (79) that apply tension to the transfer belt (64).
The photoreceptor and the recording medium (3) can come into soft contact without using a soft rubber roller.

FIG. 8 is a schematic diagram of a color copying machine using the apparatus of this embodiment. Light from the light source (81) illuminates the original (82), passes through the optical path (83), passes through the lens (84), and illuminates the photoreceptor (61). This light is filtered into three primary colors (R, G) by a color filter (85) that can be switched midway.

B) is decomposed into Also, if it is a black and white image, leave it as is:t:
Irradiate the photoreceptor. The photoreceptor rotates in the direction of arrow A (
1) is charged by a main charger (86) and exposed to the color-separated light to form an electrostatic latent image.

When forming a black and white image, the filter (85) is switched to an achromatic filter and the photoreceptor is exposed. When forming this black and white image, the toner is developed and visualized using a developing device (88) having a large developer container (87) fixed around the photoreceptor. On the other hand, the recording medium (90) conveyed by the transfer drum (89) using a pressurized conductive sheet is
A soft rubber roller (69) makes contact with a photoreceptor (61) having a toner image. A transfer voltage is applied to the transfer belt having a pressurized conductive sheet provided on the transfer drum from a rigid conductive roller (71), and the toner image on the photoreceptor is transferred onto the recording medium. The recording medium to which this toner image has been transferred and a visible image has been formed is peeled off and conveyed from the transfer drum (89) by a peeling claw (91), and fixed by a heat roller (92) to fix the toner image on the recording medium. Ru.

When forming a color image, the reflected light from the original passes through a switchable color filter (85) and is separated into three primary colors, RlG, B, and No, and exposes the photoreceptor (61). When the R (red) filter is selected and an electrostatic latent image is formed on the photoconductor, the color rotary developing device (93) rotates one rotation.
7. A developing device having a C (cyan) developer, which is a complementary color to R (red), is selected and developed. In this way, a visible image of color toner is formed on the photoreceptor. The rotary developing device used at this time is C (cyan), which is the complementary color of R (red), G (green), and B (blue).

Contains M (magenta) and Y (yellow) color developers. Further, these color developing devices are small and lightweight ones for non-magnetic components, and have a simple structure consisting of a conveying sleeve (94) and a developer container (95). This rotationally movable developing device (93) moves in the direction of arrow C, and the developing sleeve is fixed so that the developing device of the required color is selected and comes into contact with the photoreceptor. In this way, the necessary colors are developed. This monochromatic toner image on the photoreceptor is transferred to the recording medium on the transfer drum (89) according to the present invention, and by repeating this process three times, the color toner images are superimposed to form a full-color image. During this color image formation, the fixed developing device (87) containing black toner is inactive, but a black image may be added for undercolor processing if necessary. The color image thus formed on the recording medium is fixed and fixed by a fixing device (92).

According to the apparatuses of the two embodiments, the recording medium and the photoreceptor can be brought into softer contact during transfer, and stable transfer is possible without toner sticking to the photoreceptor. Further, even if the transfer efficiency is increased by increasing the transfer voltage, gas discharge can be prevented when the recording medium is carried into and out of the photoreceptor, and a high-quality image without image deterioration can be formed. In this way, it is possible to achieve high image quality transfer, which is an advantage of the transfer device using a conductive rubber roller, and to achieve less dependence on humidity, as well as higher transfer efficiency.

Furthermore, in the case of color recording, by configuring a transfer drum that also serves to convey the recording medium, it is possible to align the color toner images with high precision and form a good color image.

Next, it can be applied to recording media of various sizes,
Further, an embodiment will be described in which the transfer drum is not contaminated even with toner images or fog on a photoreceptor of any size, and a transfer drum wiping device is not required.

In a transfer device using a pressurized conductive sheet as a transfer drum, the length of the pressure roller can be adjusted to the size of the recording medium by utilizing the fact that only the portion of the pressurized conductive sheet that is applied pressure from the back side becomes conductive. The transfer area on the photoreceptor is set by switching according to the change.

Further, the image length in the rotational direction on the photoreceptor can be set by detecting the leading edge of the recording medium for the transfer voltage application time. In addition, if toner adheres to the transfer drum due to a recording medium transport error, etc., the transfer voltage is reversed, the pressure roller length is switched to the maximum length, and the toner is retransferred to the photoreceptor -F. This makes it possible to clean all the toner adhering to the transfer drum. On the other hand, the adhered toner on the photoconductor is removed by a wiping device for the photoconductor. This method of retransferring onto the photoreceptor is not possible with other transfer drum systems using a corona charger.

With the above (1N composition), a toner image can be recorded on the entire recording medium, and no backside stains occur. Even if the toner image is transferred, it is retransferred onto the photoreceptor, eliminating the need for a wiping device for the transfer drum. Maintenance is improved. Figure 9 is a schematic cross-sectional view of a transfer device having the above characteristics. Figure (a) shows a method using a pressurized conductive sheet and a soft (approximately 40 degrees or less) conductive rubber roller. The photosensitive drum (91) on which the toner image has been formed moves in the direction of the arrow and comes into contact with a recording medium (not shown) conveyed together with a transfer drum consisting of a pressurized conductive sheet (92). .

This contact is softly pressed (approximately 300 g/c#) by conductive rubber rollers (93), (94), and (95) having a hardness of approximately 40 degrees. Further, a transfer voltage (99) necessary for transfer is supplied to the conductive rubber rollers (93), (94), and (95). This conductive rubber roller (93).

A plurality of (94) and (95) exist in the transfer drum (three in the figure), and each length corresponds to the width of a different recording medium. This group of conductive rubber rollers rotates in the direction of arrow B depending on the size of the recording medium, is selected and fixed.

The same figure (b) shows the conductive layer (9B) on the plastic support (9B).
97>, a transfer belt made of a pressurized conductive sheet (92), and softer rubber rollers (100), (101)
, (102), which enables softer transfer.

In general, conductive rubber rollers have carbon particles doweled inside them, so there is a lower limit to their hardness, which makes them somewhat unstable for use in transfers that require soft contact. This method allows the use of softer rubber rollers than usual, allowing for softer and more stable contact between the recording medium and the photoreceptor. Therefore, the transfer voltage is supplied by a rigid conductive roller (LO3) that contacts and presses the pressurized conductive sheet, passes through the conductive layer (97), is supplied to the transfer section, and passes through the pressurized conductive sheet (92) that is pressurized. Given. Inside this transfer drum, there are a plurality of (three in the figure) soft pressure rubber rollers corresponding to 111 of different recording media, as in FIG. 2A. A roller corresponding to the width of the recording medium is selected from the plurality of rubber rollers and used in a fixed manner.

As shown in section -F, the pressed conductive sheet becomes conductive in the area pressed by the conductive rubber roller or the pressure roller, and transfer voltage (99) is applied to the recording medium to perform the transfer. Since the pressurized conductive sheet in the non-pressurized portion is insulative, no transfer voltage is applied and no transfer is performed. In this way, one of the pressurized conductive sheets in the transfer drum is
The toner image or fog on the photoreceptor is not transferred to a large unnecessary portion in the 11 direction, and the stain on the transfer drum is significantly reduced. In addition, unnecessary toner images or fog in the length direction (circumferential direction) of the pressurized conductive sheet can be removed by applying a transfer voltage L2 according to the size of the recording medium, and transferring the image to the recording medium according to the length of the recording medium. By performing the transfer, it is possible to remove the transfer to the extra parts.

Next, a method for removing toner when the recording medium is not conveyed to the transfer drum 2 due to a conveyance error or the like and toner adheres to the transfer drum will be described with reference to FIG. Figure (a)
1 shows how toner is directly transferred to the pressurized conductive sheet of the transfer drum L due to an error in conveyance of the recording medium. The development or fog toner (125) on the photoreceptor (91) is transferred to a transfer voltage (12
7) is added and transferred onto the pressure conductive sheet. In the retransfer process that automatically starts when restarting after a conveyance error, the transfer voltage applied to the conductive rubber roller becomes a voltage of opposite polarity (128), so the transferred toner (1
2G) is re-transferred onto the photoreceptor ('91) in the transfer section, and its toner is cleaned off in the transfer drum cleaning process, making it possible to reuse it. In other words, the toner (129) retransferred onto the photoreceptor is cleanly removed from the photoreceptor by the photoreceptor wiping device.

FIG. 11 is a schematic diagram of a color copying machine using the apparatus of the above embodiment. Light from the light source (81) illuminates the original (82), passes through the optical path (83), passes through the lens (84), and forms an image on the photosensitive drum (61). This light passes through a color filter (85) that can be switched midway through R (red) 2 G
It is separated into three primary colors: (green) and B (blue). R
When the filter is selected and an electrostatic latent image is formed on the photoconductor, the rotary color developing device (93) rotates, and the developing device having the developer of C (cyan), which is its complementary color, is selected. Development is performed. This developed toner image is transferred to a transfer drum (89) using a pressurized conductive sheet according to the present invention.
The image is transferred onto the recording medium that is transported by the printer. This recording medium is conveyed from the tray, guided to a transfer drum (89), and wound around the transfer drum by a fixed claw on the transfer drum.

On the other hand, as is well known in known copying machines,
Information about the size of the recording medium is sent to a CPU (not shown) which controls the entire copying machine by selecting the size of the recording medium tray. Therefore, this CPU
selects the size of the pressure conductive rubber roller in the transfer drum according to this information.

This prevents images larger than the recording medium from being transferred. Also, a recording medium leading edge detection device (110
), the time of the transfer voltage applied to the conductive rubber roller is set so that an image that is longer than the recording medium is not transferred.In this way, a toner image of the same size as the recording medium is transferred to the recording medium. The toner image or fog toner is not transferred to unnecessary portions of the transfer belt.

After the cyan toner image on the photoconductor is transferred in this way, the remaining toner on the photoconductor is removed by a wiping device (11G
) and then reused. By repeating this process three times, a color toner image is formed on the recording medium. This color image is subjected to undercolor processing using black toner, if necessary. The recording medium on which this color image has been formed is separated from the transfer drum by a release claw (91) and fixed by a fixing device (92) to fix the toner image.

On the other hand, when forming a black and white image, filter (8
5) is switched to an achromatic filter and the photoreceptor (61) is exposed. To develop this black and white image, a developing device (83) having a large developer container (87) fixed around the photoreceptor is used. A color image or a monochrome image can be obtained as described below.

Next, a toner cleaning process will be described when toner is transferred onto the transfer drum due to a conveyance error of the recording medium (90). The detector (110) detects whether the recording medium (90) or the transfer drum is being conveyed to the correct position, and if it is not conveyed or is conveyed diagonally, the device automatically stops image recording and starts the cleaning process. enter. In this cleaning step, the transfer voltage applied to the conductive rubber roller is switched to the opposite polarity by the above-mentioned CPO, and the toner adhering to the transfer drum L is transferred to the photoreceptor (61). It is more effective to apply a surface potential to this photoreceptor (61) by turning the main charger (86) on (J [7), and then transport it to the transfer section without developing it and reverse transfer the toner on the transfer drum. The toner on the transfer drum is cleaned automatically.

The toner adhering to the photoreceptor (61) in this manner is wiped off by the wiping device (36). By including such a process in the recovery process when a recording medium is conveyed incorrectly, a color copying apparatus that is easier to maintain and does not require a toner wiping device on the transfer drum can be realized.

According to this example, it is possible to prevent a toner image or toner fog in an area larger than the recording medium on the photoreceptor from being directly transferred onto the transfer drum. Furthermore, even if the toner is directly transferred onto the photoreceptor onto the transfer drum due to an error in conveyance of the recording medium, the toner is re-transferred onto the photoreceptor, so the transfer drum is not smeared. In this way, the transfer drum wiping device, which was conventionally necessary for color recording using a transfer drum, becomes unnecessary, and the maintenance of the color electrophotographic apparatus increases. Furthermore, the backside stains on the recording medium, which occur due to transfer drum stains in conventional color electrophotographic devices, are also significantly reduced.

Furthermore, unlike conventional devices, there is no need to make the recorded image smaller than the recording medium in order to prevent staining of the transfer drum, and it is possible to gradually record the entire surface of the recording medium at the leading edge of the recording medium conveyance portion.

Next, an embodiment which is preferable in terms of structure and in which the I7 transfer drum is less contaminated will be described. The transfer arrangement according to this embodiment will be briefly explained as follows. That is, a conductive rubber having low hardness (20 to 50 degrees) and a pressurized conductive rubber layer are provided on the conductive drum as an upper layer to form an integrated structure. Furthermore, insulating guide rings are provided at both ends of the transfer drum so that the transfer drum and the guide rings are in contact with the photoreceptor on the same surface, and pressure corresponding to the thickness of the area where the recording medium passes is applied to the conductive rubber. join the layer,
The transfer voltage is applied by exhibiting the 2fX conductivity. On the other hand, no pressure is applied to the pressurized conductive comb layer in the portion through which the recording medium does not pass, and no transfer voltage is applied due to its high resistance value.

With this configuration, a high transfer voltage can be applied at the contact center where the photoreceptor and the recording medium are in contact and the contact pressure is highest. Further, in the area where the recording medium is carried into and out of the photoreceptor, the pressure applied conductive rubber layer has a high resistance, so that gas discharge does not occur and image blurring does not occur. Therefore, a high transfer voltage can be applied and highly efficient transfer is possible. In addition, by installing an insulating guide ring and making the surface of the photoconductor and transfer drum the same, pressure is applied in the area where the recording medium passes according to the amount of deformation relative to the thickness of the recording medium, making the pressurized conductive rubber layer conductive. Then, a transfer voltage is applied, and a guide ring prevents pressure from being applied to areas where there is no recording medium, so that no transfer voltage is applied.

For example, in the case of a 30φ transfer roller made of conductive rubber with a hardness of 40°, the nip width is 3 ml for a deformation amount of 100 microns in the thickness of the recording medium! +, and the pressure at this time shows a value of 400 g/ci. At this pressure, Figure 4
As shown in the figure, the pressurized conductive rubber layer becomes electrically conductive and the number is 9c.
Indicates a value of m or less. On the other hand, in the area where the recording medium does not pass, no pressure is applied by the guide ring, and the pressurized conductive rubber layer exhibits a value of 109ΩC11l or higher. In this way, only the image on the photoreceptor in the portion through which the recording medium passes is transferred to the recording medium, and the image in other portions is not transferred, and no stains occur on the transfer roller or drum.

Next, this embodiment will be explained in detail using the drawings.

FIG. 8 is a schematic diagram of the transfer drum according to this example. Figure (a) shows its cross-sectional view. The transfer drum (131) is placed on a drum (H2) made of aluminum.
The conductive rubber (133) of the 7Ωc button is baked on.

The hardness of this conductive rubber is in the range of 20 to 50''. Low hardness allows a wide range of pressure to be applied to the transfer drum, which is preferable in terms of mechanical design, but it has the disadvantage that the toner tends to stick due to the large amount of lactic acid it contains. If the hardness is too high, the pressure per unit area becomes large, and the toner on the photoreceptor tends to stick. Therefore, the optimum hardness range is only 30 to 40''. A pressurized conductive rubber layer (134) is baked and laminated on this F42B rubber (133). A schematic diagram of this transfer drum (131) is shown in FIG. Guide rings (135) made of freely rotating delrin having the same diameter as the transfer drum are fitted into both ends of the transfer drum (131). Further, this transfer drum <131) is smaller in width than the photoreceptor drum (13G), and the guide ring (135) and the pressurized conductive rubber layer (134) are in uniform contact with the photoreceptor surface. Further, the width of the photoreceptor (not shown) on the photoreceptor drum (13t3) may be the same as the width of the pressurized conductive rubber layer (H4) of the transfer drum. Further, the width of the recording medium (137) needs to be smaller than the width of the pressurized conductive rubber layer (134). Also, apply strong pressure to this guide ring. The pressure of 300 to 500 g/cd required for transfer is a small value as a mechanical spring pressure, and it is difficult to stably obtain this pressure with spring pressure alone in a device with a lot of mechanical vibration. Force fluctuations occur. As a result, the resistance value of the pressurized conductive rubber layer fluctuates, which changes the transfer efficiency and causes a striped pattern in the image that corresponds to the vibration. Therefore, by installing a guide ring as in this example, by applying strong pressure to the guide ring that is not affected by mechanical vibration, a stable pressure corresponding to the thickness of the medium is applied to the pressurized conductive rubber layer. Therefore, the transfer efficiency remains constant regardless of mechanical vibration. This aluminum drum (132) is designed so that a necessary voltage for transfer can be applied from the outside.

In FIG. 13, this transfer drum (131) is connected to the photoreceptor (13).
G) and a cross-sectional view of the transfer section in contact with the recording medium (137). In areas where there is no recording medium, the transfer drum (1
Since the pressurized conductive rubber layer (134) in 31) has a guide ring (135), it contacts the photoreceptor (13G) without receiving any pressure. Therefore, the specific resistance of the pressurized conductive rubber layer exhibits a large value of 10 9 Ωcm or more, as shown in the above-mentioned figure, and does not generate an electric field sufficient to move the toner (138) on the photoreceptor. On the other hand, when the recording medium (137) is carried into the transfer section, the conductive rubber (133) on the transfer drum is deformed by the thickness 140) of the recording medium (137) via the pressurized conductive rubber layer (134). , 3-4n nip l1l (
139). The thickness of this recording medium (137) is 1
40) is about 70 to 120 microns, but due to the deformation of the conductive rubber by this thickness, a pressure of about 400 g/c- is generated in the pressurized conductive rubber layer (134), and the specific resistance decreases to 104 Ωcm or less. . As a result, a transfer voltage is applied to the recording area (137) and transfer is performed. In this way, the toner (138) in the area where there is no recording medium is not transferred, and the transfer drum (31) is not covered by the toner image on the photoreceptor. Also, recording media (137
) is carried into the transcription department.

At the place where the transfer drum is carried out, the pressure on the transfer drum disappears, and the pressurized conductive rubber layer on the transfer drum has a high resistance, so that no transfer voltage is applied, preventing gas discharge from occurring and eliminating image blurring. As a result, it is possible to apply an even higher transfer voltage, and the transfer efficiency can be increased.

Next, a color copying machine to which the above example is applied will be explained using FIG. The configuration is almost the same as that shown in FIGS. 8, 11, etc., but the transfer drum (143) is different from the previous ones, and the one shown in FIG. 12 is applied.

Note that the transfer drum in this embodiment needs to have at least a conductive drum and a pressurized conductive rubber, and the number of layers is not limited to three.

According to this embodiment, the recording medium and the photoreceptor can be brought into softer contact during transfer, and stable transfer is possible without toner sticking to the photoreceptor. Also, increase the transfer voltage to <1. Even if the transfer rate is increased by 1, gas discharge can be prevented when the recording medium is carried into and out of the photoreceptor, and a high-quality image without image deterioration can be formed. In this way, it is possible to achieve high image quality transfer, which is an advantage of the transfer device using a conductive rubber roller, and to achieve less dependence on humidity, as well as higher transfer efficiency. Furthermore, in the case of color recording, by configuring a transfer drum that also serves to convey the recording medium, it is possible to align the color toner images with high precision and form a good color image. Further, the toner image on the photoreceptor in the independent portion of the recording medium is not transferred because no transfer voltage is applied because the pressure conductive rubber layer on the transfer drum has high resistance. As a result, the transfer drum is not contaminated. Furthermore, since the transfer drum is not stained, a color image can be printed over the entire surface of the recording medium.

In conventional electrophotographic color copying machines, images that are smaller than the recording medium are always formed to prevent the transfer drum from becoming dirty.

[Effects of the Invention] Several embodiments have been described above, but according to the present invention, it is possible to increase the transfer efficiency by 1 to 1 by applying a high transfer voltage during transfer. Further, unlike the conventional transfer method, electric discharge between the photoreceptor and the transfer material during loading and unloading of the transfer material to the photoreceptor can be suppressed, and there is no image blurring caused by electric discharge.

The transfer efficiency at this time was 80% compared to the conventional value of 70-80%.
It is possible to increase it to 90% or more. Further, the transfer material can be transported with high precision using a hollow support for transporting the transfer material provided with a pressurized conductive sheet, and is suitable for color image formation. Furthermore, by providing an insulating layer on the conductive rubber roller and the pressurized conductive sheet, there is no reduction in transfer efficiency in humid conditions, which is a drawback of conventional electrophotography.

[Brief explanation of the drawing]

1 is a schematic sectional view of a transfer device according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the transfer device shown in FIG. 1, and FIG. A diagram showing the relationship between the pressure and the resistance value of the piezoconductive sheet. Figure (b) shows the voltage applied to the gap between the photoreceptor and the transfer material and the Paschen curve (solid line). Figure (e) shows the relationship between the pressure and the resistance value of the piezoconductive sheet. Figure 3 is a diagram showing the electric field between the photoreceptor and the transfer material when the piezoconductive sheet is pressed, and Figure 4 is a diagram showing the pressure conductive sheet or conductive roller provided with an insulating coating. 1 is a schematic diagram of a copying machine using a transfer belt made of a pressurized conductive sheet, and FIGS. 5 to 14 are diagrams showing other embodiments. 1 Photoreceptor, 2 Toner image, 3 Transfer material, 4 Pressure conductive sheet, 9 Conductive roller, 16 Light source, 17 Original, 20 Main charger, 21 Developer, 22 Transfer belt, 6 Conductive rubber roller, 26 Wiping blade , 24 fixing device, 30 color filter, 33 rotary movable developing device.

Claims (13)

[Claims] (1) In a transfer device that transfers a toner image on a photoconductor to a transfer material, a transfer support including a pressure conductive layer and a pressure conductive layer are pressed at a position where the transfer material contacts the photoconductor. 1. A transfer apparatus comprising: a pressure means for applying pressure; and an application means for applying a transfer voltage to a pressure conductive layer to which pressure is applied by the pressure means. (2) The transfer device according to claim 1, wherein the pressurized conductive layer is formed of an endless belt-like sheet. (3) The transfer device according to claim 1, wherein the application means is provided at a pressure point by the pressure means, and the transfer voltage of the application means is applied to this point. (4) The transfer device according to claim 3, characterized in that the pressure conductive layer is provided on the surface of the hollow support, and pressure is applied from inside the hollow part of the hollow support with a conductive roller. (5) The transfer device according to claim 12, characterized in that an insulating layer is provided between the transfer material and the pressure conductive layer or between the pressure conduction layer and the application means. (6) The application means is arranged so that the transfer voltage is applied to the pressure conductive layer at a location different from the location where the pressure is applied to the pressure conductive layer by the pressure means. A transfer device according to claim 1. (7) The transfer device according to claim 1, wherein the pressurizing means selectively presses the pressurized conductive layer. (8) The transfer device according to claim 1, wherein the pressure means changes the pressure width according to the width of the recording medium. (9) The transfer device according to claim 1, wherein the pressure means includes a plurality of pressure rollers having different pressure widths. (10) The transfer device according to claim 1, wherein a reverse bias voltage is applied to the pressure conductive layer after being transferred to the transfer material. (11) The transfer device according to claim 1, wherein the transfer means has an integral structure consisting of a conductive drum and a pressurized conductive rubber provided on the drum. (12) The transfer support has an integral structure in which a conductive drum, a conductive rubber provided on the drum, and a pressurized conductive rubber provided on the conductive rubber are sequentially provided. A transfer device according to claim 1, characterized in that: (13) A claim characterized in that guide rings having a diameter approximately equal to the diameter of the pressurized conductive rubber are provided at both ends of the drum, and the guide rings are arranged so as to be in contact with the photoreceptor on the same surface. 13. The transfer device according to item 12.