JPH11231692A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excellently perform the transfer of a toner image from an image forming body to an intermediate transfer body and the retransfer of the toner image from an intermediate transfer body to a transfer member by impressing intermediate transfer bias by a constant-voltage power source on the intermediate transfer body and impressing transfer bias by a constant-current power source on the transfer member. SOLUTION: An intermediate transfer roller 140 being a drum-type intermediate transfer body abuts on a photoreceptor drum 10 at a 1st transfer position T1. A transfer roll 150 being the transfer member abuts on the roller 140 at a 2nd transfer position T2. Voltage as the intermediate transfer bias having an opposite polarity to toner is impressed on the roller 140 at the position T1 by the constant-voltage power source E1, and the toner image is transferred to the peripheral surface of the roller 140. Current by the transfer bias having the opposite polarity to the toner is impressed on the roller 150 at the position T2 by the constant-current power source E2, and the toner image on the roller 140 is transferred to recording paper P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile or the like. The color toner image is formed by superimposing the toner images during one rotation of the image forming body to form a color toner image. After the image is transferred to the intermediate transfer body, the color toner image on the intermediate transfer body is transferred by a transfer member such as a transfer roller. The present invention relates to an electrophotographic color image forming apparatus for re-transferring to an image.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a multi-color image, a single color image formed on each image forming body is provided with the same number of image forming bodies, charging means, developing means and the like as the number of colors required for image formation. Color image forming apparatus that forms a color image by superimposing the toner image on a transfer material, or a color image forming apparatus that rotates the image forming body a plurality of times and repeats charging, image exposure, and development for each color to form a color image Alternatively, there is known a color image forming apparatus which forms a color image by sequentially performing charging, image exposure, and development for each color within one rotation of the image forming body.

However, each of the above image forming apparatuses is provided with the same number of image forming bodies, charging means, developing means, etc. as the number of colors required for image formation, and superposes a single color toner image formed on each image forming body on a transfer material. A color image forming apparatus that forms a color image together has a drawback that the volume of the apparatus is increased due to the necessity of transporting a plurality of image forming bodies and a transfer material. A color image forming apparatus that forms a color image by repeating charging, image exposure, and development has a limitation that although the volume is reduced, the size of the formed image is limited to the surface area of the image forming body or less. .

In this regard, a color image forming apparatus which forms a color image by sequentially performing charging, image exposure and development for each color within one rotation of the image forming body has no restriction on the size of the image and has a high speed image. There are advantages such as enabling formation. Further, an apparatus in which a light-transmitting substrate is used as a substrate of an image forming body and an image exposing means is arranged inside the image forming body to reduce the size of the apparatus has been proposed, for example, in Japanese Patent Application Laid-Open No. 5-307307. .

Further, a color toner image is formed by superimposing a plurality of toner images on the peripheral surface of the image forming body by the above-described image forming method, and the color toner image is formed by using a belt-like intermediate transfer member. A color image forming apparatus for retransferring a color toner image on an intermediate transfer member to a transfer material by a transfer roller as a transfer member after transfer to a transfer member is disclosed in Japanese Patent Application No. 8-7 / 1996.
No. 6560.

[0006]

In the color image forming apparatus proposed above, as shown in FIG. 3, a color toner image on a photosensitive drum 510 (image forming body) is transferred to an intermediate transfer belt 540 (intermediate transfer body). ), And a bias from the constant current power supplies E51 and E52 is applied as a transfer bias when the color toner image on the intermediate transfer belt 540 is re-transferred to the transfer material by the intermediate transfer roller 550. However, since the intermediate transfer belt 540, which is a belt-shaped intermediate transfer member, is used as the intermediate transfer member, the first transfer position T51 for transferring the color toner image on the photosensitive drum 10 to the intermediate transfer belt 540, At the second transfer position T52 where the color toner image on the intermediate transfer belt 540 is retransferred to the transfer material, the two transfer positions are separated by a belt-shaped member. Therefore, there was no interference between the intermediate transfer bias and the transfer bias.

However, if a roller-shaped member is used as the intermediate transfer member, an intermediate transfer bias using a constant current power supply is used at the second transfer position when the color toner image on the intermediate transfer member is re-transferred to the transfer material. Current flows into the transfer roller to change the transfer conditions, which causes a problem that a good transfer of the color toner image to the transfer material is not performed. In addition, the transfer current at the first transfer position when the color toner image on the image forming body is transferred to the intermediate transfer body also changes, so that there is a problem that a good transfer of the color toner image to the intermediate transfer body is not performed. . Further, the transfer conditions change depending on the type of the transfer material, and the transfer conditions change even in the case of monochrome image formation and color image formation, so that good transfer of the toner image to the transfer material is not performed. .

The present invention solves the above-mentioned problems and improves the transfer of a color toner image from an image forming member to an intermediate transfer member and the re-transfer of a color toner image from an intermediate transfer member to a transfer material. Another object of the present invention is to provide a color image forming apparatus capable of performing both transfer satisfactorily irrespective of monochrome image formation or color image formation.

[0009]

The object of the present invention is to provide a plurality of sets of a plurality of charging means, developing means, and a plurality of image exposing means on the outer peripheral surface of an image forming member, and to rotate the image forming member during one rotation. The charging of the image forming body by the charging unit and the formation of a latent image by image exposure by the image exposing unit and the development of the latent image by the developing unit are repeated, and a plurality of latent images are formed on the peripheral surface of the image forming body. A color in which a color toner image is formed by superimposing toner images, the color toner image on the image forming body is transferred to an intermediate transfer body, and then the color toner image on the intermediate transfer body is re-transferred to a transfer material by a transfer member. In the image forming apparatus, a drum-shaped intermediate transfer body is used as the intermediate transfer body, an intermediate transfer bias is applied to the drum-shaped intermediate transfer body by a constant voltage power supply, and a transfer bias is applied to the transfer member by a constant current power supply. Apply It is accomplished by a color image forming apparatus characterized by.

[0010]

Embodiments of the present invention will be described below. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope.

FIG. 1 shows an image forming process and each mechanism of an embodiment of a color image forming apparatus according to the present invention.
This will be described with reference to FIG. FIG. 1 is a cross-sectional configuration diagram showing one embodiment of a color image forming apparatus according to the present invention, and FIG. 2 is an enlarged view of the intermediate transfer member of FIG. An intermediate transfer roller composed of a roller-shaped member is used as the intermediate transfer member of the present embodiment.

According to FIG. 1 or FIG. 2, a photosensitive drum 10 as an image forming body is provided with a transparent conductive material around a cylindrical base formed of a transparent member such as optical glass or transparent acrylic resin. A photosensitive layer such as a layer, an a-Si layer or an organic photosensitive layer (OPC) is formed, and is rotated clockwise as indicated by an arrow in FIG. 1 with the conductive layer grounded.

According to the present invention, in the photoconductor layer of the photosensitive drum, which is the image forming point of the exposure beam for image exposure, an appropriate contrast is provided to the light attenuation characteristic (photocarrier generation) of the photoconductor layer. It is sufficient that the exposure light amount has a wavelength that can be obtained. Therefore, the light transmittance of the light-transmitting substrate of the photosensitive drum in the present embodiment does not need to be 100%, but may be such that a certain amount of light is absorbed when the exposure beam is transmitted. Should just provide an appropriate contrast. Acrylic resin,
In particular, those obtained by polymerization using a methacrylic acid methyl ester monomer are preferably used because they are excellent in light transmission, strength, precision, surface properties, etc., but are used for other general optical members such as acrylic, fluorine, polyester, polycarbonate, Various translucent resins such as polyethylene terephthalate can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. As the light-transmitting conductive layer, indium tin oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, Au, Ag, N
A light-transmissive metal thin film made of i, Al, or the like is used. As a film forming method, a vacuum deposition method, an active reactive deposition method,
Various sputtering methods, various CVD methods, dip coating methods, spray coating methods, and the like are used. Various organic photosensitive layers (OPC) are used as the photoconductor layer.

A scorotron charger 11 serving as a charging unit for each color, an exposure optical system 12 serving as an image exposing unit for each color, and a developing unit 13 serving as a developing unit for each color constitute a set of these components, and the yellow (Y) , Magenta (M), cyan (C)
4 for the image forming process of each color of black and black (K)
A set is provided and arranged in the order of Y, M, C, and K with respect to the rotation direction of the photosensitive drum 10 indicated by the arrow in FIG.

The scorotron charger 11, which is a charging means for each color, has a control grid maintained at a predetermined potential and a discharge electrode 11a composed of, for example, a sawtooth electrode, and faces the photosensitive layer of the photosensitive drum 10. And installed
The charging operation (in the present embodiment, negative charging) is performed by corona discharge having the same polarity as that of the toner.
A uniform potential is given to 0. As the discharge electrode 11a, a wire electrode or a needle electrode may be used.

Exposure optical system 12 as image exposure means for each color
Indicates that the exposure position on the photosensitive drum 10 is different from that of the scorotron charger 11 for each color described above.
Photosensitive drum 1 so as to be located on the downstream side in the rotation direction of
0. Each exposure optical system 12
A linear exposure element in which a plurality of LEDs (light emitting diodes) as light emitting elements of image exposure light arranged in the main scanning direction in parallel with the drum axis are arranged, and a light converging light transmission as an imaging element. An exposure unit including a body (trade name: Selfoc lens array), which is attached to the holding member 20. The exposure optical system 12 for each color performs image exposure of the photosensitive layer of the photosensitive drum 10 from the back side in accordance with image data of each color read by a separate image reading device and stored in the memory, and electrostatically exposes the photosensitive layer on the photosensitive drum 10. Form a latent image. As the exposure element, in addition to an LED, an element in which a plurality of light emitting elements such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array can be used. The emission wavelength of the image exposure light emitting element is usually 7 that is highly transparent to Y, M, and C toners.
Although a wavelength in the range of 80 to 900 nm is used, in this embodiment, since the image is exposed from the back surface, a shorter wavelength of 400 to 780 nm, which does not have sufficient transparency to the color toner, may be used.

A developing device 13 as a developing means for each color keeps a predetermined gap with respect to the peripheral surface of the photosensitive drum 10 and rotates in the forward direction with respect to the rotating direction of the photosensitive drum 10, for example, 0.5 to 1 mm in thickness. A developing sleeve 131 formed of a non-magnetic stainless steel or aluminum material having an outer diameter of 15 to 25 mm, and a developing casing 138. Inside the developing casing 138, yellow (Y) and magenta are provided, respectively. (M), one-component or two-component developer of cyan (C) and black (K). Each developing unit 1
Reference numeral 3 denotes a developing bias in which a DC voltage and an AC voltage are superimposed on the developing sleeve 131 and is kept in non-contact with the photosensitive drum 10 by a contact roller (not shown) with a predetermined gap, for example, 100 to 500 μm. When applied, non-contact reversal development is performed, and a toner image is formed on the photosensitive drum 10.

The fixing device 17 as a fixing means is composed of two roller-shaped fixing members, a fixing roller 17a and a pressure roller 17b, and includes a fixing roller 17a and a pressure roller 17b.
By applying heat and pressure at the nip between the two, the toner image on the recording paper P is fixed.

An intermediate transfer roller 140, which is a drum-shaped intermediate transfer member, is provided in contact with the photosensitive drum 10 at a first transfer position T1, and is made of a conductive material such as an aluminum material or a stainless steel material. A volume resistivity of 10 ⁶ to 1 is formed as an elastic layer on the outer periphery of the metal roller 141 as a base.
Silicon rubber of 0 ¹² Ω · cm is provided with a thickness of 1 to 5 mm, and the surface thereof has a thickness of 1 to 10 μm and a volume resistivity of 10 ¹²
It is a soft roller provided with a dielectric layer 142 of, for example, a fluororesin tube or a fluororesin coat of 10 ¹⁶ Ω · cm.

An intermediate transfer member cleaning device 114, which is an intermediate transfer member cleaning means, is provided in contact with the photosensitive drum 10, and has an intermediate transfer member cleaning blade 114a whose leading end is always in contact with the intermediate transfer roller 140. The transfer residual toner on the intermediate transfer roller 140 is cleaned by the intermediate transfer body cleaning blade 114a.

A transfer roller 150, which is a transfer member, is provided in contact with the intermediate transfer roller 140 at a second transfer position T2. For example, a metal roller 151 as a conductive base using a metal member such as an aluminum material or a stainless steel material is used. Has a volume resistivity of 10 ⁶ to 10 ¹² Ω
cm, for example, a hard roller provided with a dielectric layer 152 using a silicon tube or a fluororesin coat.

Next, the image forming process will be described.

By starting a photoconductor driving motor (not shown) at the start of image recording, the photoconductor drum 10 is rotated clockwise as shown by an arrow in FIG. Body drum 1
Application of a potential to 0 starts.

The latent image is reversely developed in a non-contact state by a Y developing unit 13, and a yellow (Y) toner image is formed on the photosensitive drum 10.

Next, a potential is applied to the photosensitive drum 10 from above the Y toner image by the charging action of the magenta (M) scorotron charger 11, and the second color signal, that is, the M color signal, is applied by the M exposure optical system 12. Image writing is performed by an electric signal corresponding to the image data, and the magenta (M) toner image is superimposed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13. It is formed.

According to the same process, the cyan (C) toner image corresponding to the third color signal is further superimposed by the cyan (C) scorotron charger 11, the exposure optical system 12 of C, and the developing device 13 of C. The black (K) toner image corresponding to the fourth color signal is sequentially superimposed thereon by a black (K) scorotron charger 11, a K exposure optical system 12, and a K developing device 13. A superposed color toner image of four colors of yellow (Y), magenta (M), cyan (C), and black (K) is formed on the peripheral surface within one rotation of the photosensitive drum 10. .

These Y, M, C and K exposure optical systems 12
Image writing on the photosensitive layer of the photosensitive drum 10 is performed from the inside of the drum through the above-described translucent substrate. Therefore, the writing of the images corresponding to the second, third and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. Can be formed.

The color toner image formed on the peripheral surface of the photosensitive drum 10 is transferred to the intermediate transfer roller 1 in the form of a drum.
The image is temporarily transferred to the peripheral surface of the forty.

The drum-shaped intermediate transfer roller 140 is placed at a position where it comes into pressure contact with the peripheral surface of the photosensitive drum
And is driven in a counterclockwise direction so that the drum and the peripheral speed coincide with each other. At the first transfer position T1, the constant voltage power supply E1 has the opposite polarity (positive polarity in the present embodiment) to the toner. ), For example, 1000 to 2000 V
By applying the voltage V1 as the intermediate transfer bias to the intermediate transfer roller 140, the toner image is transferred to the peripheral surface thereof.

A material such as a transfer material whose thickness or resistance fluctuates according to monochrome image formation and color image formation does not pass between the image transfer member and the intermediate transfer member.
Therefore, good transfer can be performed by performing the constant voltage control. Control is performed such that the transfer voltage is set higher during color image formation than in the case of monochrome image formation.

The toner image transferred onto the peripheral surface of the drum-shaped intermediate transfer roller 140 is then transferred by a transfer roller 150 serving as a transfer member to a sheet feeding cassette 1 serving as a recording material storage means.
5, and is conveyed to a timing roller 15b, which is a recording material feeding means, by the driving of the timing roller 15b.
The recording paper P fed in synchronization with the toner image of No. 0,
The image is transferred from the intermediate transfer roller 15 onto the recording paper P.

That is, the transfer roller 150 is driven and rotated at the position in contact with the peripheral surface of the intermediate transfer roller 140 to form the above-described second transfer position T2, and the second transfer position T2
By applying a current I1 to the transfer roller 150 with a transfer bias of, for example, 5 to 50 μA having a polarity opposite to that of the toner (positive in the present embodiment) by the constant current power supply E2, the transfer roller 150 Transfer the toner image. At this time, the transfer voltage of the transfer roller 150 is 10 higher than the voltage of the intermediate transfer roller 140.
It is a value of 00 to 2000 V.

Since the transfer material of the transfer roller 150 has a different resistance value and a different thickness, an appropriate transfer voltage varies depending on the type of the transfer material. Therefore, it is preferable to perform constant current control by the constant current power supply E2. On the other hand, since the intermediate transfer roller 140 performs constant voltage control by the constant voltage power supply E1, even if there is a voltage fluctuation of the constant current power supply E2 performing the constant current control, the intermediate transfer roller 140 The transfer voltage is applied to the toner of the transfer roller 150 by the constant current power supply E2 effectively according to the type of the transfer material without causing the influence of the transfer on the toner. When the intermediate transfer roller 140 is controlled at a constant current, the transfer roller 150 performs a constant current control in consideration of the fluctuation. Further, when the transfer roller 150 is controlled at a constant current, the toner image is transferred from the photosensitive drum 10 to the intermediate transfer roller 140 by a change in current flowing into the intermediate transfer roller 140 in response to the passage of the recording paper P as a transfer material. Of the intermediate transfer roller 14
Using constant current control at zero is problematic. As in the present invention, the transfer of the toner image from the photosensitive drum 10 to the intermediate transfer roller 140 is performed without the recording paper P, and only the toner is used. The transfer condition to the intermediate transfer roller 140 is not affected.

As described above, the transfer of the color toner image from the image forming member to the intermediate transfer member and the retransfer of the color toner image from the intermediate transfer member to the transfer material are both performed favorably.

Further, since the transfer conditions are different between monochrome image formation and color image formation, it is necessary to change the transfer conditions for each image formation. That is, during the above-described color image formation, the application of the intermediate transfer bias to the intermediate transfer roller 140 at the voltage V1 and the transfer roller 1 at the current I1
In response to the application of the transfer bias to the transfer roller 50, the voltage V2 of the intermediate transfer bias to the intermediate transfer roller 140 and the current I2 of the transfer bias to the transfer roller 150 during monochrome image formation.
Are set low, and V2 = (0.6 to 0.9) ×
V1, I2 = (0.6 to 0.9) × I1.

As described above, regardless of whether a monochrome image or a color image is formed, the transfer of the toner image from the image forming body to the intermediate transfer member and the retransfer of the toner image from the intermediate transfer member to the transfer material are both excellent. Done.

The recording paper P to which the toner image has been transferred is discharged by the discharge needle 91 and is separated from the peripheral surface of the intermediate transfer roller 140, and is fixed via the transport belt 16 to the fixing device 17.
Roller 17 which is a roller-shaped fixing member
The toner image is fixed by applying heat and pressure at a nip portion between a and the pressure roller 17b. The recording paper P on which the toner image has been fixed is discharged to the outside of the apparatus by a discharge roller 18.

The toner remaining on the peripheral surface of the intermediate transfer roller 140 after the transfer is provided opposite to the intermediate transfer roller 140 and has an intermediate transfer member cleaning blade 114a which is always in contact with the intermediate transfer roller 140. Intermediate transfer member cleaning device 114 as a cleaning unit
Cleaning.

The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is transferred to a cleaning device 19 serving as an image forming member cleaning means, or a cleaning blade 19a made of a rubber material abutting on the photosensitive drum 10. And is collected by a screw 19b in a waste toner container (not shown). The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is charged by the Y scorotron charger 11, and enters the next image forming cycle.

Further, the transfer roller 150 is cleaned by the cleaning device 310 to remove stains due to toner adhesion or the like, thereby keeping the recording paper P clean.

[0041]

According to the first aspect, the transfer of the color toner image from the image forming member to the intermediate transfer member and the retransfer of the color toner image from the intermediate transfer member to the transfer material are both performed favorably.

According to the second aspect, regardless of whether a monochrome image or a color image is formed, the transfer of the toner image from the image forming member to the intermediate transfer member and the retransfer of the toner image from the intermediate transfer member to the transfer material. Are performed well together.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram illustrating an embodiment of a color image forming apparatus according to the present invention.

FIG. 2 is an enlarged view of the intermediate transfer member of FIG.

FIG. 3 is a diagram showing a conventional problem.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum 11 scorotron charger 12 exposure optical system 13 developing device 140 intermediate transfer roller 150 transfer roller E1 constant voltage power supply E2 constant current power supply T1 first transfer position T2 second transfer position P recording paper

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor ▲ Hama ▼ Shuta 2970-2, Ishikawacho, Hachioji-shi, Tokyo Konica Corporation (72) Inventor Toshihide Miura 5--14-14 Midoricho, Koganei-shi, Tokyo

Claims (3)

[Claims] A plurality of charging means, a plurality of developing means, and a plurality of image exposing means provided on an outer peripheral surface of the image forming body;
During one rotation of the image forming body, charging of the image forming body with the charging unit and formation of a latent image by image exposure by the image exposing unit and development of the latent image by the developing unit are repeated, A color toner image is formed by superimposing a plurality of toner images on the peripheral surface of the image forming body, and after transferring the color toner image on the image forming body to the intermediate transfer body, the color toner on the intermediate transfer body is transferred by a transfer member. In a color image forming apparatus for re-transferring an image to a transfer material, a drum-shaped intermediate transfer body is used as the intermediate transfer body, and an intermediate transfer bias is applied to the drum-shaped intermediate transfer body by a constant voltage power supply, and the transfer is performed. A color image forming apparatus, wherein a transfer bias is applied to a member by a constant current power supply. 2. The color image forming apparatus according to claim 1, wherein said transfer member is a transfer roller. 3. The method according to claim 1, wherein both the voltage value of the intermediate transfer bias by the constant voltage power supply and the current value of the transfer bias by the constant current power supply are changed in accordance with monochrome image formation or color image formation. 3. The color image forming apparatus according to 2.