JPH0922196A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record an image of high quality at a high transfer rate and to enable stable separating and feeding by providing an exposure means for exposing an image carrier surface in a region from a transfer part to the separating part. SOLUTION: An exposure device 30 as the exposure means for exposing a photoreceptor surface with a transfer material is installed in the region between the transfer part and the separating part. on the periphery of a photoreceptor drum 10. When the transfer material is fed in accordance with the movement of the images of a single color or plural colors actualized on the drum 10 and the press-contact of a transfer roller 18 is attained to perform a transfer, the drum 10 is exposed with the transfer material by the exposure device 30 at the same time when the leading edge of the transfer material arrives at the exposing position of the exposure device 30 or prior to the arrival. The photoreceptor of a toner image part reelectrified by the exposure and a white surface part, is destaticized and separation conditions for the respective parts and a nonreelectrified toner image part are set. Proper conditions for separating can be expanded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a color toner image by superimposing at least two or more color toner images on the surface of an image carrier by an electrostatic recording method, and the color toner image is formed on a transfer material. The present invention relates to a color image forming apparatus of a type that is transferred and recorded on a sheet.

[0002]

2. Description of the Related Art As an apparatus for recording a multicolor image, for example, a plurality of developing means containing yellow, magenta, cyan, and black developers necessary for forming a color image are provided, and an image carrier is provided. Each time rotation is performed, charging, image exposure and development corresponding to each color are repeated on the peripheral surface to form a toner image of each color on the image carrier by superimposing toner images of each color, and this is collectively transferred to a transfer material. A color image forming apparatus for recording is known.

[0003]

In such a color image forming apparatus, the image quality of an image to be recorded is influenced by the accuracy of superimposing toner images, that is, the registration accuracy, as well as the transfer rate of the toner image of each color to the transfer material. However, it is big.

As a method for improving the transfer rate, generally, a so-called pre-transfer entire surface exposure means for exposing the entire surface of the image carrier before the toner image transfer to make the potential uniform and constant, is used. When applied to the color image forming apparatus described above, the toner of the superposed toner images may scatter around the image before transfer and disturb the image.

In order to solve this problem, the applicant of the present invention has proposed a pre-transfer image exposure system in which the image is re-exposed only in the image area of the image carrier according to Japanese Patent Laid-Open No. 4-352183.

According to this pre-transfer image exposure system, the potential of the image carrier is made uniform and constant, and at the same time, a wide range of toner layers from a multicolor toner image layer to a monochromatic toner image layer is superimposed. It is possible to obtain good transfer performance without image repelling or insufficient transfer.

However, in order to realize such a system, it is necessary to have a memory for recording each image unit for forming an image of image exposure corresponding to each color even at the end of development, and to re-record after superimposing toner images. Since it is necessary to further rotate the image carrier for the exposure, the speed of the printing process is reduced, and the transferred image is distorted if the resist accuracy with respect to the previously formed toner image at the time of re-exposure is low. There are some problems left to be solved. Further, in the method in which the image is formed on the photoconductor a plurality of times, the diameter of the photoconductor becomes large, so that it becomes difficult to separate the transfer material from the photoconductor, and the reliability is lowered.

The present invention solves this problem and improves the result.
It is an object of the present invention to provide a color image forming apparatus capable of recording a high quality image with a high transfer rate and stably separating and feeding without causing the above-mentioned problems.

[0009]

The above object is to form a toner image on the surface of the image carrier by superposing the toner image on the peripheral surface of the image carrier by repeating charging, image exposure and development a plurality of times. In a color image forming apparatus for collectively transferring a toner image onto a transfer material by a transfer means, the surface of the image carrier is transferred from the transfer part of the transfer means to a separation part between the transfer material and the surface of the image carrier. This is achieved by a color image forming apparatus characterized in that an exposure means for exposing through a transfer material is provided.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, the structure and operation of the color image forming apparatus of the present invention will be described with reference to FIG.

In this color printer, after each color toner image sequentially formed on an image carrier is superimposed, the color image is formed on a recording sheet by a transfer unit once, and then the image is formed by a separating unit. This is a color image forming apparatus of a method of peeling off from a surface of a carrier.

In FIG. 1, reference numeral 10 denotes a photosensitive drum which is an image bearing member, and is an OPC photosensitive member (organic photosensitive member) formed by coating on a drum substrate, which is grounded and driven and rotated clockwise in the drawing. 12 is a scorotron charger, provided by a corona discharge by a grid and the corona discharge wire which uniform charging has been potential held in the V _G of the V _H the photosensitive drum 10 peripheral surface. Prior to the charging by the scorotron charger 12, a PCL (pre-charging static eliminator) using a light emitting diode or the like in order to eliminate the history of the photosensitive member until the previous printing.
The peripheral surface of the photoconductor is neutralized by exposure with 11.

After the photosensitive drum 10 is uniformly charged, the image exposure means 13 performs image exposure based on the image signal. The image exposure means 13 is a means for performing a main scan in which an optical path is bent by a reflection mirror 134 through a polygon mirror 131, an fθ lens 132, and a cylindrical lens 133 which rotate using a laser diode (not shown) as a light emitting source.
A latent image is formed by rotation (sub-scanning) of the photosensitive drum 10. In this embodiment, the character portion is exposed to form a reversal latent image such that the character portion has a lower potential _VL .

At the peripheral edge of the photosensitive drum 10, a developing device 14 (14Y) in which a developer including toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a carrier is incorporated. , 14M, 14C, 14K), and the developing sleeve 14 for rotating the first color yellow developing roller has a built-in magnet and holds a developer.
1 is performed. The developer consists of a carrier in which ferrite is used as a core and is coated with an insulating resin around it, and a toner whose main component is polyester and pigments according to the color and charge control agents, silica, titanium oxide, etc. are added. The developer is a developing sleeve 1 by means of a layer forming means.
The layer 41 is regulated to have a layer thickness (developer) of 100 to 600 μm and is conveyed to the developing area.

[0015] As 0.2~1.0mm gap is greater than the layer thickness (developer) to the developing sleeve 141 in the developing zone between the photosensitive drum 10, the DC bias of the AC bias and V _DC of V _AC during which The signals are superimposed and applied. V _DC and V _H, for charging the toner are the same polarity, the toner given the opportunity to leave from the carrier by V _AC and V
_It does not adhere to the _VH portion having a higher potential than _DC, but adheres to the _VL portion having a lower potential than _VDC , and visualization (reversal development) is performed.

After the visualization of the first color is completed, the second color magenta image forming process is performed, and the scorotron charger 1 is again used.
The uniform charging by 2 is performed, and the latent image based on the image data of the second color is formed by the image exposure unit 13. At this time 1
The charge elimination by the PCL 11 performed in the color image forming process is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image portion.

The latent image similar to that of the first color is formed on the portion of the photoconductor having the potential of _VH which is again at the potential of _VH over the entire peripheral surface of the photoconductor drum 10 and the image is not developed. is carried out, 1 again part for developing image to the portion where there is the color, the latent image of V _M 'by the charge possessed by the shading of the toner itself by the toner adhering the first color is formed, V
Developing in response to the potential difference between the _DC and V _M 'is performed. In the overlapping portion of the first color image and the second color image, development of the first color is performed by V
_When the latent image of _L is formed, the balance between the first color and the second color is lost, so that the exposure amount of the first color is reduced and V _H > V _M >
In some cases, the intermediate potential may be V _L.

An image forming process similar to that of the magenta of the second color is performed for the cyan of the third color and the black of the fourth color, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 10.

On the other hand, a half moon roller 16
One sheet of transfer material (recording paper) P that has been conveyed through is temporarily stopped, and when the transfer timing is adjusted, it is fed to the transfer area by the rotational operation of the registration roller 17.

In the transfer area, a transfer roller 18, which is a transfer means, is pressed against the peripheral surface of the photosensitive drum 10 in synchronization with the transfer timing, and the supplied recording paper P is nipped and a multicolor image is collectively formed. Is transcribed.

Then, the recording paper P is destaticized by the separation pole 19 and separated from the peripheral surface of the photosensitive drum 10 to be fixed to the fixing device 20.
The toner is melted by being heated and pressed by a heat roller (upper roller) 201 and a pressure roller (lower roller) 202, and then discharged to the outside of the apparatus through a paper discharge roller 21. The transfer roller 18 is retracted and separated from the peripheral surface of the photoconductor drum 10 after the recording paper P has passed, to prepare for the next toner image formation.

On the other hand, the photosensitive drum 10 from which the recording paper P is separated
Removes and cleans the residual toner by pressing the blade 221 of the cleaning device 22, and again receives the charge removal by the PCL 11 and the charge by the scorotron charger 12 to start the next image forming process. The blade 221
Moves to the photosensitive drum 10 after cleaning the photosensitive surface.
Retreat from the peripheral surface.

The features of the functions and performances of the respective equipments constituting the image forming section of the above apparatus will be described below.

(Photosensitive member) The photosensitive drum 10 is stably rotated so that the OPC photosensitive member on the peripheral surface is uniformly charged by the scorotron charger 12. At the time of charging, the grid potential is controlled to stabilize the charging potential. The specifications of the photoreceptor and the charging conditions thereof are set as follows as an example. In particular, JP-A 64-17066
JP-A-2-183258, JP-A-2-18326
OPC using Y-type titanyl phthalocyanine or polycrystalline titanyl phthalocyanine described in JP-A-3-128973 and JP-A-3-128973 is preferable.

Photosensitizer: OPC, diameter 120 mm, linear velocity 100 mm / sec, negative charging Charging conditions: Charging wire: Platinum wire (clad or alloy) is preferably used. _VH- 850V, _VL- 50
V (image exposure) The OPC photoconductor on the peripheral surface of the photoconductor drum 10 is negatively charged by the scorotron charger 12, and then exposed by the light emission of the semiconductor laser unit 135 of the image exposure means 13 to form an electrostatic latent image. .

Image data is a laser diode (LD)
The LD of the semiconductor laser unit emits light by the modulated image signal sent to the modulation circuit, and the polygon mirror 131
Is projected to

The polygon mirror 131 reflects the beam light on its polyhedron for scanning, and the scanning light is fθ lens 13
2. After the beam shape is corrected by the cylindrical lens 133, the photoconductor is exposed through the reflection mirror 134 and main scanning is performed to form an electrostatic image. At this time, a part of the scanning light is received by a sensor provided outside the image area, and each scanning is synchronized.

The beam system of the laser beam is narrowed down to an equivalent of 600 DPI by the optical system. Therefore, in order to obtain a high quality image, it is necessary to reduce the particle size of the toner. In this embodiment, a toner having a size of 8 μm is used for each color. However, the black character quality is most important to the user, and the black toner is preferably a small particle size toner (7 μm to 11 μm).

As the optical system for image exposure, for example, the one having the construction described below is used.

Polygon mirror: 6 faces, rotation speed 2360
0 rpm, air bearing adopted Lens focal length: f = 140 mm Dot clock: 20 MHz beam diameter: Approx. 60 × 80 μm (Development) The toner supplied from the toner replenishment box is dropped to the right end of the developing unit and in opposite directions. A pair of rotating stirring screws 142 stir and mix with the carrier to set a predetermined charge amount (Q / M).

On the other hand, the toner density is detected by the magnetic permeability detection method (L detection method), and the toner supply amount is controlled based on this output frequency to set and control the toner density value to about 7 to 9%.

The agitated two-component developer is supplied to the supply roller 14
3, and is conveyed to the developing area of the photosensitive drum 10 in a thin layer by the layer thickness regulating member 144, and performs reversal development of the electrostatic latent image under the following developing conditions. In this developing method, the developing process is carried out in a non-contact state between the developer spike and the drum, and non-contact two-component reversal development is carried out by a developing electric field in which an alternating current component is superposed on a direct current component.

Current image gap: 0.5 mm Developer transport amount: 20 to 30 mg / cm ² Development bias (AC): 2 KV, 8 KHz (DC): -750 V Rotation direction of developing sleeve: Normal image with respect to photosensitive drum Density adjustment: Development sleeve rotation speed control or development bias control (a standard printing plate is formed on the photoconductor by a laser beam, the reflection density is measured after development to adjust the image density) Toner density control: L detection method (paper feed) The recording paper P is stored in the paper feed cassette 15 on the basis of one side. Therefore, the separating claw 151 is provided only on the reference surface side of the recording paper P, and the half-moon roller 16 is also a cantilever structure. It is located on one side of the plane.

The paper feeding section has a dedicated motor, and the half-moon roller 16 rotates in the direction of the arrow to pick up the recording paper P stacked on the push-up plate 152 by the action of the separating claw 151 and the uppermost layer thereof. Carry out only one.

The recording paper P carried out from the paper feed cassette 15
Enters the transport path, makes a U-turn, and immediately after the leading edge passes the registration roller 17, the motor is temporarily stopped by the detection of a paper feed sensor (not shown), and then the motor starts to rotate again when the transfer timing is adjusted. , Is fed to the transfer area while maintaining a predetermined angle with respect to the surface of the photoconductor.

On the other hand, manual feeding is performed by rotating the manual feeding table 153 located on the front surface of the apparatus main body from the position shown by the one-dot chain line in FIG. 1 to the position shown by the solid line.

The manually fed paper is the pickup roller 15
It is conveyed by the rotation of 4, and is fed to the transfer area via the registration roller 17.

Papers to be fed by manual feeding include general recording paper P of 16 lbs to 24 lbs which is usually used, thick paper of 36 lbs, transparency sheet for OHP and the like. Also, remove the manual feed tray 153,
You can also feed envelopes by installing a dedicated feeder as an option.

(Transfer) The transfer roller 18, which is a transfer unit, can be brought into contact with and separated from the peripheral surface of the photosensitive drum 10, and is always in a pressure contact state as shown in FIG. 2 when printing (transferring) a single color image. However, during color image formation, they are retracted and kept at separated positions, and are pressed against each other only during transfer. Further, even when a single-color image is formed, if there is any inconvenience in the pressure contact state, such as when the image density is adjusted between prints, they are placed at separated positions.

In the apparatus of this embodiment, a transfer power source capable of constant current control is used in order to reduce the influence of the use environment. Further, a separating power supply 190 for applying a bias voltage in which DC and AC are superposed is used for the separating pole 19.

(Fixing) As shown in FIG. 3, the fixing device 20 provided in the apparatus of the present embodiment is a so-called heat roller type fixing device including a pair of rollers, and has a fixing heater built therein and is driven and rotated clockwise. The recording paper P is heated and conveyed by the nip portion formed between the upper roller 201 and the lower roller 202 which is pressed against the upper roller 201 and is driven to rotate, so that the toner image is fused.

The upper and lower rollers 201 and 202 are both covered with a heat-resistant tube, and the nip portion is formed in a substantially linear shape by pressure contact, so that wrinkles on the paper surface which are likely to occur when an envelope or the like is conveyed are prevented. To be done.

The temperature of the peripheral surface of the upper roller 201 is controlled by being detected by a temperature sensor 205 such as a thermistor to be kept within a predetermined temperature range, and dirt adhering to the toner by welding is pressed against the cleaning roller 203. Removed and cleaned by. This cleaning roller 20
3 is replaced with a new one when the number of prints is about 40,000. When the time during which the fixing heater is not used exceeds a predetermined time, a SLEEP mode is set, and energy saving control is performed.

Further, when a transparency sheet used for OHP is used as a transfer material, the periphery of the upper roller 201 is smoothed for the purpose of smoothing the toner image surface to prevent irregular reflection in order to improve the transmittance of the color toner image. Silicon oil is applied to the roller surface by the oil pad 204 on the surface.

Therefore, in the apparatus of this embodiment, the transfer material conveying speed is 100 mm / sec, 50 mm / sec and 12.
By switching to three stages of 5 mm / sec,
It has a mode that can use three types of transfer materials: plain paper, envelopes, and transparency sheets, and is used for a wide range of applications.

The set temperature of the upper roller 201 can be lowered to about 180 ° C. by using a toner that melts at a low temperature, and the oil pad 20 can be used.
By using a sponge material (porous PTFE coating) for 4, uneven pressing is eliminated and uniform oil application is realized.

(Transfer Roller) Next, the structure of the above-mentioned transfer roller 18 will be described.

FIG. 4A shows a single-layer type transfer roller 18.
FIG. In the figure, the transfer roller 18 includes a shaft body (core bar) 181 made of a stainless steel rod, and a resin material such as polyurethane rubber, silicone rubber, styrene-butadiene copolymer elastomer, and olefin-based elastomer on the outer periphery of the shaft body 181. A conductive elastic portion 182 which is formed by a foaming type or an open-cell type of about 100 μm and further contains an inorganic substance such as carbon black and / or an organic conductive agent as a conductivity-imparting agent mixed in the above resin material and capable of supplying electric charge. It consists of and. As an example of the elastic part 182, a polyurethane resin rubycell roller (manufactured by Nitto Kogyo Co., Ltd.) was used.

FIG. 4B shows a coating type transfer roller 1
It is sectional drawing which shows 8.

The transfer roller 18 comprises polyvinylidene fluoride (PVDF), polyamide 6 (nylon 6), and the outer peripheral surface of the elastic portion 182 of the single-layer type transfer roller.
A surface coating layer portion 183 made of polyamide 66 (nylon 66), polyethylene terephthalate (PET), perfluoroacrylate resin (PFA), polyester resin or the like is provided with a film thickness of 5 to 100 μm. By providing the coating layer portion 183, the surface of the transfer roller 18 can be easily and reliably cleaned, and the maintainability is improved.

FIG. 4C shows a coating type transfer roller 1.
It is sectional drawing which shows the other Example of 8th.

The transfer roller 18 has a medium resistance layer portion 184 as an outer layer of an elastic portion 182 provided on the outer peripheral surface of the shaft body 181, and the coating layer portion 183 formed on the outer peripheral surface thereof. is there. For the intermediate resistance layer portion 184, a material capable of optimally controlling electric resistance can be selected. As a result, the elastic portion 182 can have a required elasticity, and the middle resistance layer portion 184 can be a function separation type having a required conductivity imparting property. As a method of measuring the electric resistance, for example, both ends of the roller shaft are pressed against a conductive plate such as aluminum with a predetermined force (for example, 500 g weight), and the resistance value of the conductive plate and the roller shaft in Ω is measured.

The electric resistance of the transfer roller 18 is as follows.
In the above measuring method, a roller having a width of 210 mm is used for 10 ⁵
It is preferably from 10 to ^{11 11} Ω, more preferably from 10 ⁷ to 10 ⁸ Ω.

The rubber hardness of the transfer roller 18 is
Measured with a rubber hardness tester at 60 ° or less (JIS-K630
1 Asuka-C scale hardness) is preferred.

Roller transfer by the transfer roller 18 is
Transfer is performed by bringing the transfer roller 18 into direct contact with the back surface of the recording paper P, pressing the toner against it, and applying an electric charge having a polarity opposite to that of the toner.

(Separation Means) With respect to the belt photoreceptor and the small-diameter drum photoreceptor, the small radius of curvature of the separation portion can be used to separate the recording paper only by the steel property, but the shape of the photoreceptor is restricted. In addition, stable high-speed separation is achieved by using it in combination with AC static elimination separation in high-speed machines and the like. In the AC charge elimination separation, the recording paper is eliminated by AC corona discharge immediately after the transfer to reduce the electrostatic attraction force of the recording paper to the photoconductor, and the separation is performed by utilizing the rigidity and self weight of the paper. But AC
If the charge removal is too strong, transfer defects such as missing images tend to occur,
If the recording paper is weak, it becomes more difficult to separate it as it is thinner and less rigid. Therefore, it is necessary to set the charge removal amount in a well-balanced manner in consideration of the recording paper type and environment. Various embodiments of the separation means by static elimination are shown in FIGS. 5 (A) to 5 (E).

FIGS. 5A and 5B show a separation pole 19 in which a conductive brush body 191 made of a thin metal wire (filament) such as a stainless steel wire or an aluminum wire is arranged in one row or a plurality of rows on a holding member 192. 5 is a perspective view of FIG.
(A) shows a dense array type, and (B) shows a sparse array type. The diameter of the conductive brush body 191 is 0.01 to 0.1 mm,
The protruding length of the metal wire from the holding member 192 is 2 to 20 mm.
It is. In the sparse array type shown in FIG. 5 (B), it is possible to obtain a preferable result as the separation effect when the conductive brush bodies 191 are arranged at intervals of 0.5 to 5 mm for each bundle. As the conductive brush body 191, it is also possible to form the separation electrode 19 by using a conductive fiber body 191A in which a conductivity imparting agent is added to rayon or the like, instead of the metal thin wire.

In FIG. 5C, instead of the metal fine wire or the conductive fiber body 191A, a metal needle 193 having a small spherical shape with a radius of curvature of the tip of 100 μm is implanted in the holding member 192.

In FIG. 5D, the tip of the conductive static elimination tape 194 is formed in a sawtooth shape and is sandwiched by the holding members 192. Examples of the conductive static elimination tape 194 include Teijin Metallian static elimination tape (manufactured by Teijin Ltd.) and Syntron 9
212 (manufactured by Shintron Fabric) and the like. Further, a similar sawtooth electrode may be formed by etching or pressing a metal plate such as stainless steel.

FIG. 5 (E) is a front view of FIG. 5 (B). In the figure, the conductive brush body 191 has a diameter of 0.1.
mm bundled into a bundle, the holding member 192 has a protruding length (hair length) L (2 to 20 mm), and a pitch p between each bundle (0.5 to
5 mm). The conductive brush body 1
Examples of 91 include fine metal wires (metal fibers) and conductive fibers.

The fine metal wire has ordinary conductivity and rigidity, and is made of stainless steel, iron, copper, aluminum, tungsten, chromium, nickel, nickel chrome steel, silver,
It is selected from lead, tin, zinc and alloys containing these or amorphous metals.

As the conductive fiber, resin (plastic) such as rayon, nylon or polyester containing an inorganic conductive material such as carbon or an organic conductive material is used. What is the conductivity of the conductive brush body 191?
It is preferably 10 ⁵ Ω · cm or less.

An exposure device 30 as an exposure means for exposing the surface of the photoconductor drum through the transfer material is installed in a region between the transfer portion and the separation portion on the peripheral surface of the photoconductor drum 10. The transfer section referred to here is an area where the transfer material sent from the paper feeding section is placed in the transfer electric field formed between the transfer roller and the photoconductor.
Actually, it is the nip portion between the transfer roller and the photoconductor and its immediate vicinity (2 to 3 mm before and after the nip portion although it depends on the diameter of the photoconductor or the transfer roller, the pressure contact force, and the hardness of the transfer roller).
The separating portion is a region from a position where the transfer material adsorbed to the photoconductor begins to receive the discharging current from the removing electrode to a position where the transfer material starts to separate from the photoconductor.

When the toner image is transferred onto the transfer material P, a constant DC current is supplied from the voltage source 180 after the transfer roller 18 has been pressed against the drum surface, while the separation electrode 1
A high voltage obtained by superimposing a direct current and an alternating current is applied to the device 9 by the power source 190 before the front end of the transfer material enters the separating portion.

The exposure apparatus 30 shown in FIG. 2 includes a light source 30A composed of an LED array, a light guide guide member 30B for converging and guiding the light emitted from the light source 30A to the drum surface, and a light source 30A.
And a variable power source 300 that controls the amount of emitted light. When the transfer material is fed and the transfer roller 18 is pressed and transferred as the image of the single color or the plurality of colors visualized on the photosensitive drum 10 moves to the transfer portion, the transfer material is transferred. The same as when the tip of the exposure device comes to the exposure position of the exposure device 30, or by the exposure device 30 prior to that.
The photosensitive drum 10 is exposed through the transfer material. The photoconductor on the toner image area that has been recharged by this exposure and the photoconductor on the white background are neutralized, and these areas and the toner image area that has not been recharged (the image that was last developed, (Similar to the case where multiple latent images are formed and visualized by charging
It becomes possible to expand the proper separation conditions by aligning the separation conditions of.

The light guide member 30B is also effective in disposing the light source 30A at a position separated from the separation pole 19 to which a high voltage is applied, and by using it, the light source 30A is driven by a high voltage. It is possible to prevent damage and leakage current.

A control unit 400 drives the variable power source 300 to control the exposure amount of the light source 30A of the exposure device 30 and controls various conditions of the image forming process. In the control unit 400, 401 is an exposure amount table that stores exposure amount data for driving the variable power source 300 to control the exposure amount of the light source 30A, and 402 is the number of prints, the usage time of the photosensitive drum 10, the number of times of use, etc. It is a memory for storing.
An operation unit 403 inputs various data and commands to the control unit 400, and is composed of, for example, function keys and ten keys.

Reference numeral 40 is a light transmittance sensor for measuring the light transmittance of the transfer material P, and 500 is an environmental condition measuring unit for measuring the environmental conditions (for example, temperature, humidity, etc.) in which the apparatus operates.
The light transmittance sensor 40 and the environmental condition measuring unit 500
Is output to the control unit 400. The preferred operating conditions of the apparatus shown in FIG. 2 are as follows: the charging potential of the photosensitive drum surface is −750 V, the DC bias potential V _DC = −650 V, the AC bias potential V _AC = 1.7 kVpp, and the frequency is 8.0 kH.
z, developer transport amount 20 to 30 mg, image writing potential −10 to −50 V, image carrier line speed 100 m
m / sec, development sleeve line speed is 250mm
/ Sec.

In this configuration, the experimental results of the conditions such as the position of the removing electrode with respect to the photoconductor, the bias voltage, the exposure light amount, etc. will be illustrated.

The condition is that the photosensitive drum diameter is 120 m.
m, transfer roller diameter 18 mm, transfer roller resistance 10 ⁷ to 10 ⁸ Ω by the above measurement method, transfer material 16 lbs of plain paper, de-electrodes made of 0.1 mm thick stainless steel plate by etching in a sawtooth shape Was used. The sawtooth electrode has a sawtooth pitch of 2 mm, a sawtooth portion of a tooth height of 2 mm, and a tip of the sawtooth portion having a sharp angle of 13 °.

The transfer current I _T is 12 for a width of 214 mm.
~ 13μA, static elimination bias f _AC is 1.00KHz, 7K
A DC bias is superimposed on the AC V _{AC of} V _PP . The process speed is 97 mm / sec.

FIGS. 6A and 6B show an appropriate separation DC bias for separating the transfer material from the drum and a separation DC for preventing the transfer omission when the distance between the drum and the removal electrode is changed. It is the result of the experiment for obtaining the bias.

From these results, the optimum condition was the distance between the drum removing electrodes (d _{DS in the} figure) of 4.6 mm and the DC bias of + 350V. This depends on the diameter of the photoconductor, the charging potential, the toner used, the transfer material, the process speed, and the difference in the transfer current due to the difference in these values.

[0074]

[Table 1]

Table 1 shows the results of the experiment which looked at the influence of the exposure light amount on the separation performance. The experiment of Table 1 was carried out at room temperature of 12 ° C. and 20% R
Under the condition of H, f _AC = 1.00 KHz, V _AC = 7.0 K
Transfer current I _T = + 12 μA at V _PP , V _DC = + 350 V
It is.

The amount of light is the amount of light exposed during the separation electrode having a separation area of 3 mm per 1 mm in the longitudinal direction of the removal electrode. The separation performance is easily affected by environmental changes and subtle changes in various conditions, and it is necessary to determine the conditions with a margin. In this embodiment, the required minimum light amount is 0.3 μm.
It was set to W / mm. Of course, this value also varies depending on various conditions.

As described above, proper exposure is performed on the photoconductor through the transfer material, so that the separation performance can be ensured and JP-A-4-35 can be used.
It is possible to simultaneously improve the transferability as shown in Japanese Patent No. 2183. (Without the exposure of the present invention, the exposure amount of the present experiment is equivalent to 0 μW / mm, and the separation performance is obviously inferior.) Further, in the present embodiment, the exposure is performed from outside the photoconductor drum via the transfer material. If the body is exposed, but the drum substrate is transparent to the exposure light, it is possible to expose from the inside of the photoconductor drum to the area in contact with the transfer material, and the effect is constant regardless of the type of transfer material. Can be obtained. Further, even when the curvature separation is performed using the belt photosensitive member, the exposure and the exposure can be performed in the same manner as in the drum embodiment of the present invention, so that more stable separation and transfer can be performed.

[0078]

According to the present invention, the photosensitive member is properly exposed to light through the transfer material in the area from the transfer portion of the transfer means to the separation portion between the transfer material and the photosensitive member surface. As a result, it becomes possible to secure stable separation performance of the transfer material and simultaneously realize good transfer performance.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus.

FIG. 2 is a configuration diagram of an image transfer unit and a separation unit.

FIG. 3 is a configuration diagram of a fixing device.

FIG. 4 is a cross-sectional configuration diagram of a transfer roller.

FIG. 5 is an external view of a separation brush.

FIG. 6 is an experimental result when the distance between the photoconductor and the removing electrode is changed.

[Explanation of symbols]

 10 Photoreceptor Drum 11 PCL 12 Scorotron Charger 13 Image Exposure Means 14 Developing Device 15 Paper Feed Cassette 16 Half Moon Roller 17 Registration Roller 18 Transfer Roller 19 Separation Electrode 20 Fixing Device 22 Cleaning Device 30 Exposure Device (Part) 30A Light Source 30B Light Guide Guide member 40 Optical transmittance sensor 180 Power source for transfer 190 Power source for separation 300 Variable power source 400 Control unit 401 Exposure amount table 402 Memory 403 Operation unit 500 Environmental condition measurement unit

Claims (2)

[Claims] 1. A toner image is superposed on the surface of the image carrier by repeating charging, image exposure and development a plurality of times on the surface of the image carrier, and the toner images are collectively formed on a transfer material by a transfer means. In the color image forming apparatus for transferring by means of the transfer means, an exposing means for exposing the surface of the image carrier through the transfer material is provided within a region from the transfer part of the transfer means to the separation part of the transfer material and the surface of the image carrier. A color image forming apparatus characterized by the above. 2. The color image forming apparatus according to claim 1, wherein the exposure unit changes the irradiation light amount according to the type of the transfer material.