JPH08248789A - Color image forming device provided with transfer means - Google Patents

Abstract

PURPOSE: To effectively perform the cleaning of color toner stuck on a transfer roller, by holding transfer means in press contact with an image carrier by a specified pressure, for a specified time on an occasion of non transfer operation, and alternately applying the positive and negative transfer voltage. CONSTITUTION: The pressure transfer roller 18 is composed in attachably and detachably, so as to be held in contact with respect to a photoreceptor drum 10 through an elastic member, kept in a distant position at the time of forming a color image, and brought in press contact only on the occasion of transferring. While, at the time of transferring, a transfer power source is switched to positive/negative transfer voltage applying means, and the positive/negative transfer voltage, whose positive transfer voltage is at 8μA and negative is at -1.2 KV, is applied to the pressure transfer roller 18. At the time of transferring the color image formed on the photoreceptor drum 10 to a recording paper P, the color image is transferred by applying the transfer voltage of the positive and the negative, and moreover the transfer is efficiently performed by holding the pressure transfer roller 18 in press contact with the photoreceptor drum 10 across the recording paper P with a pressing force 100 to 700g/cm<2> , while shifting the toner stuck on the roller part outer periphery to the photoreceptor drum 10 surface and cleaning the outer periphery part.

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 utilizing electrostatic transfer such as an electrostatic copying machine, an electrostatic printer, etc. The present invention relates to a color image forming apparatus that transfers an image and further superimposes at least two or more monochromatic toner images on an image carrier.

[0002]

2. Description of the Related Art In electrostatic copying machines and electrostatic printers using electrophotography, corona dischargers have been widely used as a charging / transferring device. However, the corona discharger requires a high voltage of 5 to 10 KV and has problems such as generation of ozone due to discharge. Therefore, in recent years, a contact charging method and a transfer roller method aiming at low voltage and ozoneless have been attracting attention as alternative technologies.

The transfer roller method has been put into practical use in recent years because it has the advantages that the amount of ozone generated is smaller than that in the conventional transfer by corona discharge and there is no transfer unevenness due to dirt on the discharge wire. .

Known techniques for controlling the current and voltage in the transfer roller system include Japanese Patent Publication No. 52-33494 and Japanese Patent Application Laid-Open No. 50-19456.
JP-A-52-45344 and JP-A-2-123385.

Further, as a transfer roller system, an image carrier and
When there is recording paper between the transfer rollers, a transfer bias having a polarity opposite to that of the toner to be transferred to the recording paper is applied to the transfer roller, and when there is no recording paper on the transfer roller, a bias having the same polarity as the toner is applied to the transfer roller. Japanese Patent Application Laid-Open No. 2-244081 is disclosed as a means for applying a voltage.

Further, as a transfer roller system, Japanese Patent Application Laid-Open No. 5-27605 discloses a system in which the positive and negative polarity of a cleaning bias is alternately switched when cleaning the transfer roller.

Further, as a transfer roller method, a method of switching the polarity of the cleaning bias between positive and negative in accordance with the passing condition of the recording medium between the image carrier and the transfer roller at the time of cleaning the transfer roller is disclosed in Japanese Patent Laid-Open No. No. 51654 is disclosed.

As a transfer roller system, when a predetermined transfer voltage is applied to the transfer roller to transfer an image onto a recording paper and a cleaning operation for moving the toner adhering to the surface of the transfer roller to the surface of the image carrier is performed. Japanese Patent Laid-Open No. 5-119646 discloses a means for applying a voltage of the same polarity as the transfer voltage to the transfer roller after applying a voltage of the opposite polarity to that at the time of transfer.

[0009]

As described above, conventionally, there are many known means for transferring an image formed on an image carrier using a transfer roller to a recording paper.

In particular, it is necessary to improve the transfer efficiency and the cleaning efficiency of the transfer roller by switching positive and negative polarities of the voltage with respect to the transfer roller.

As described above, the function of transferring the image formed of the toner formed on the image bearing member onto the recording paper is that when the electrostatic latent image formed on the image bearing member is first developed by the developing device, the electrostatic latent image is formed. The toner has a polarity opposite to that of the image and is strongly attracted to each other to form a good image. However, when the toner image is transferred onto the recording paper, it is necessary to weaken the attraction force of the toner image to the electrostatic latent image, and the attraction force is weakened by means such as pre-transfer exposure. Then, an electric charge having a polarity opposite to that of the toner is applied to the transfer roller so that the toner image is sufficiently transferred to the recording paper, and the toner is strongly attracted toward the recording paper. Therefore, the transfer toner inevitably adheres to the transfer roller after the recording paper is transferred, and the problem is to efficiently clean the adhered toner. Therefore, as disclosed in the above-mentioned prior art, cleaning is performed by transferring the toner adhering to the transfer roller to the image carrier, and the toner adhering to the transfer roller during the cleaning operation. It is preferable that the adsorbing power of the toner is weak and that the toner is strongly adsorbed to the image carrier. In this way, the image carrier and transfer roller
At the time of transfer and at the time of cleaning, the opposite actions are performed.

In particular, a color image is formed on an image bearing member by using full-color toners of four colors, which have become popular recently. The developing order of the four color toners is yellow (Y), magenta (M), cyan (C), and black (BK) in this order. Particularly, the four color toners are superposed on the image carrier. When formed together, the yellow (Y) toner that is developed first and the black (BK) toner that is developed last have a large time difference after development, and the attraction force to the image carrier is different, and the four color toners are also used. The adsorption force to the image bearing member is slightly different depending on the type of the. Therefore, the adhesion force of the toner to the transfer roller to which a constant positive and negative bias voltage is applied is also different, and a part of the color toner strongly adheres to the transfer roller, and if the transfer roller is simply pressed against the image carrier, The toner adhering to the transfer roller cannot be transferred to the image carrier, and a good cleaning action cannot be performed. Such a situation also applies to the process of transferring an image from a photosensitive drum to a recording sheet via an intermediate transfer member.

The present invention has been particularly conceived in order to remedy the above drawbacks. That is, in the image forming apparatus,
Multicolor (4 colors) color toners formed on the image carrier are superposed to form a color image, and the color image is transferred from the image carrier to the recording paper by the transfer roller, and then adhered particularly to the transfer roller. The purpose is to efficiently clean color toner.

[0014]

To achieve the above object, the present invention provides an image forming means for forming a toner image, which is obtained by superposing toners of two or more colors, on an image carrier in claim 1. Then, the toner image on the image bearing member is electrostatically transferred onto the recording sheet by passing the recording sheet while keeping the pressure contact state between the image bearing member having the toner image and the transfer unit. In a color image forming apparatus for batch transfer, the transfer means is pressed against the image carrier for at least a fixed time during non-transfer operation, and biases of the same polarity and reverse polarity as those during transfer operation are applied. And the pressing force of the transfer means against the image carrier is 100 to 700 g / cm ² . The transfer means according to claim 2, wherein the transfer means is a pressure transfer roller. The pressure transfer roller according to claim 3, wherein the pressure transfer roller is formed of a foamed resin material. The image carrier according to claim 4, wherein the image carrier is a photosensitive drum or a photosensitive belt. 6. The developing device according to claim 5, wherein the developing means superimposes a direct current component and an alternating current component on the surface of the image carrier on which an electrostatic latent image is formed and on the developing area of the developing means which holds a two-component developer. Being a component developing means. The developing device according to claim 6, wherein the developing device is a non-contact developing device. 8. The developing device according to claim 7, wherein the developing device is a reversal developing device.
In claim 8, it is achieved by the image carrier having a radius of curvature of 40 mm or more at least at the transfer or separation position with respect to the recording paper.

[0015]

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

In the color printer, the toner images of respective colors sequentially formed on the image carrier are superposed, and then transferred at one time on the recording paper at the transfer portion to form a color image, and thereafter the image is separated by the separating means. It is a color image forming apparatus of the type that is peeled from the surface of a carrier.

In FIG. 1, reference numeral 10 denotes an image bearing member, which is a photosensitive drum or a photosensitive belt. As the photosensitive drum here, Se, As ₂ , Se ₃ , a-Si, OPC.
Material such as is used. The OP used here
As C, Y-type titanyl phthalocyanine or polycrystalline titanyl phthalocyanine described in JP-A-64-17066, JP-A-2-183258, JP-A-2-183265 and JP-A-3-128973 can be used. The one used is preferred. The OP
A C photoconductor (organic photoconductor) is formed by coating on a drum base, and is grounded and driven and rotated clockwise in the drawing.
Reference numeral 12 denotes a scorotron charger, which applies a uniform charge of V _{H to} the peripheral surface of the photosensitive drum 10 by corona discharge by a grid and a corona discharge wire whose potential is held at V _G. Prior to the charging by the scorotron charger 12, exposure is performed by a PCL (pre-charging static eliminator) 11 using a light emitting diode or the like to eliminate the history of the photoconductor until the previous printing, and the peripheral surface of the photoconductor is neutralized. deep.

After the photosensitive drum 10 is uniformly charged, the image exposing means 13 performs image exposure based on the image signal. The image exposure means 13 uses a laser diode (not shown) as a light emitting source, and has a rotating polygon mirror 131 and an fθ lens 13
2. The optical path is bent by the reflection mirror 134 through the cylindrical lens 133 to perform the main scanning, and the latent image is formed by the rotation (sub-scanning) of the photosensitive drum 10. In this embodiment, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential V _L.

Around the periphery of the photosensitive drum 10, a developing device 14 (14Y) containing a developer containing toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a carrier is incorporated. , 14M, 14C, 14K), and first, the development of the first color yellow is carried out by the developing sleeve 141 which has a magnet built therein and rotates while holding the developer. The developer is a two-component developer consisting of a carrier in which ferrite is used as a core and an insulating resin is coated around the core, and a toner containing polyester as a main material and a pigment according to a color and a charge control agent, silica, titanium oxide The developer is regulated to a layer thickness (developer) of 100 to 600 μm on the developing sleeve 141 by the layer forming means, and is conveyed to the developing area.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.2 to larger than the layer thickness (developer).
As 1.0mm, D of the AC bias and V _DC of V _AC during this time
The C bias is superimposed and applied. Since V _DC and the electrostatic potential V _H have the same polarity as the toner charge, the toner that is triggered by the V _AC to leave the carrier is V
_It does not adhere to the V _H portion having a potential higher than _DC, but adheres to the V _L portion having a potential lower than V _DC to perform visualization (reversal development).

After the visualization of the first color is completed, the process proceeds to the magenta image forming step of the second color, and the scorotron charger 12 again.
Uniform charging is performed, and a latent image based on the image data of the second color is formed by the image exposure unit 13. At this time, the charge elimination by the PCL 11 performed in the image forming process for the first color is not performed because the toner attached to the image portion for the first color scatters due to the sudden decrease in the potential around the image.

Again, V is applied over the entire surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and the image of the first color is not developed, but development is performed again on the portion having the image of the first color. In the portion to be performed, the latent image of V _M ′ is formed due to the light shielding by the toner of the first color and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference of V _M ′. At the overlapping portion of the images of the first and second colors, the development of the first color is V
_When a latent image of _L is formed, the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and V _H > V _M >.
It may be an intermediate potential that becomes V _L.

An image forming process similar to that for 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, the recording paper P pushed up by the push-up plate 152 in the paper feed cassette 15 is carried out via the half-moon roller 16, and separated by the separating claw 151 into one recording paper P and conveyed. The paper feed roller 17 is temporarily stopped, and when the transfer timing is adjusted, the paper feed roller 17 is rotated to feed the paper to the transfer area.

In the transfer area, the transfer roller 18 is pressed against the peripheral surface of the photosensitive drum 10 in synchronization with the transfer timing,
The supplied recording paper P is sandwiched and the multicolor image is transferred at once.

Next, the recording paper P is de-charged by the separating brush 19 which is brought into a pressed contact state almost at the same time, and the recording paper P is separated by the separating power source 190 from the separating power source 190 by the peripheral surface of the photosensitive drum 10. Separate P. In addition, with the transfer,
The radius of curvature of the photosensitive drum 10 at the separation position is set to 40 mm or more. Next, the recording paper P is separated and fixed.
After being conveyed to 20, the heat roller (upper roller) 211 and the pressure roller (lower roller) 212 are heated and pressed to fuse the toner, and then the toner is ejected to the outside of the apparatus through the paper ejection roller 22.
The transfer roller 18 and the separating means 19 are retracted and separated from the peripheral surface of the photosensitive drum 10 after the recording paper P has passed therethrough 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 231 of the cleaning device 23, and again receives the charge removal by the PCL 11 and the charge by the charger 12 to start the next image forming process. The blade 231 moves immediately after cleaning the surface of the photoconductor and retracts from the peripheral surface of the photoconductor drum 10. Reference numeral 153 denotes a manual paper feeding device for the recording paper P, which is carried out by a paper feeding roller 154, separated into one recording paper P and conveyed, and then temporarily stopped by the second paper feeding roller 17, and the transfer timing is set. When the above condition is satisfied, the paper is fed to the transfer area by the rotation operation of the paper feeding roller 17.

FIG. 2 is a sectional view showing the structure of the developing device 14.
The toner supplied from the toner replenishing box is dropped to the right end portion of the developing device 14, and is agitated and mixed with the carrier by a pair of agitating screws 142 rotating in opposite directions 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 the detected frequency to set the toner density value to about 5 to 7%.

The agitated two-component developer is supplied to the supply roller 14
3 is conveyed to the developing sleeve 141 through the layer thickness regulating member 14
It is made a thin layer by 4 and conveyed to the developing area of the photoconductor drum 10, and the electrostatic latent image is reversely developed under the developing conditions described below. In this development method, the developer spikes and the photoconductor drum 10
And non-contact two-component reversal development is performed by a developing electric field in which an alternating current component is superposed on a direct current component.

Development interval: 0.5 mm Toner conveyance amount: 20 to 30 mg / cm ² Development bias (AC): ² kV, 8 KHZ (DC): -750 V Rotation direction of developing sleeve: Normal rotation with respect to photoconductor drum: Image density adjustment: L Detection Method The pressing transfer roller 18 described in FIG. 1 will be described with reference to FIG.

The pressure transfer roller 18 has a variable position with respect to the peripheral surface of the photoconductor drum 10, and is placed in pressure contact with the photoconductor drum 10 at the time of printing a single color image, but retracts during the formation of a color image. It is kept in a separated position, and is pressed into contact only during transfer. After the color image is transferred onto the recording paper P, the pressure transfer roller 18 is pressed against the peripheral surface of the photosensitive drum 10 to perform cleaning.

The pressure transfer roller 18 includes a shaft body (core bar) 181 made of a stainless steel rod, and a roller portion 182 made of foamed silicone resin, foamed polyurethane resin, or EPDM resin (used by Bridgestone Corporation). Has been done. It is composed of a roller portion 182 described below.

Roller portion 182 diameter: 16φ, shaft body (core metal) 181 diameter: 8φ Hardness: 30 ° (JIS-K6301 Asuka-C scale hardness) Resistance value: 3.0 × 10 ⁷ Ω (20 ° C, 50% measurement ) Pressing force of the pressing transfer roller 18: 230 g / cm ² Pressing force measurement: Measured with a nip tester (using a nip width sensor manufactured by Toshiba Silicone Co., Ltd.) Then, a positive / negative transfer voltage is applied to the pressing transfer roller 18 A changeover switch 186 is provided for the voltage application unit 184 and the negative transfer voltage application unit 185 for applying only the negative transfer voltage.

In the image forming apparatus 1 configured as described above, a process of feeding the recording paper P and performing color image transfer and separation will be described with reference to FIG.

As shown in FIG. 1, one sheet of recording paper P discharged from the paper feed cassette 15 via the half-moon roller 16 is temporarily stopped, and when the transfer timing is adjusted, the paper feed roller 17
The paper is fed to the transfer area by the rotation operation of.

The pressure transfer roller 18 is capable of coming into contact with and separating from the photoconductor drum 10, and via the elastic member 183, the photoconductor drum 1
It is configured to contact 0. Single color image on recording paper P
When the color image is formed on the photoconductor drum 10, the photoconductor drum 10 is held at a position separated from the surface of the photoconductor drum 10 and is separated from the surface of the photoconductor drum 10, and is brought into pressure contact only during the transfer. To configure. As the pressure contact and retracting means of the pressure transfer roller 18, for example, a cam mechanism, a mechanism in which a cam and a lever are combined, a motor, or the like can be used.

During the transfer, the transfer power source 180 is switched to the positive / negative transfer voltage applying means 184 by the changeover switch 186 as shown in FIG. 3, and the positive / negative transfer voltage shown in FIG. A positive (+) voltage is applied to 18 with a transfer voltage of 8 μA and a negative (−) 1.2 KV.

When the change-over switch 186 shown in FIG. 3 is changed to negative (-), (-) 1.4 KV or 2. as shown in FIG. 5 (b).
A transfer voltage of 0 KV is applied.

Next, the pressing force of the pressing transfer roller 18 will be described.

When the color image formed on the photoconductor drum 10 is transferred onto the recording paper P, the transfer voltage is applied to transfer the color image onto the recording paper P as described above. As described above, the pressing force of 230 g / cm ² is applied to the recording paper P.
Is pressed against the photoconductor drum 10 to efficiently perform transfer.
Further, the roller portion 182 of the pressure transfer roller 18 is brought into contact with the surface of the photoconductor drum 10 and pressed with the pressing force of 230 g / cm ² , whereby the color toner adhered to the outer periphery of the roller portion 182 is transferred to the surface of the photoconductor drum 10. Then, the outer peripheral surface of the roller portion 182 is cleaned.

Table 1 below shows the pressing force and the cleaning efficiency when the roller portion 182 of the pressure transfer roller 18 is brought into contact with the surface of the photosensitive drum 10 on the photosensitive drum 10.

[0043]

[Table 1]

As shown in Table 1 above, the pressure transfer roller 18
, The pressing force when positive and negative transfer voltages are alternately applied,
In Examples 1 to 4, when the photosensitive drum 10 is cleaned using a pressing force of 200, 300, 400, 600 g / cm ² , 95% of cleaning is performed from the initial stage to completion of copying 80 sheets. . In the fifth embodiment, the roller portion 182 having a hardness of 40 is used, and the pressing force of the pressing transfer roller is 300 g /
Even when it is set to cm ² , 95% of cleaning is performed at the stage when 80 copies are completed from the initial stage.

Next, as shown in Table 1, with the pressure transfer roller 18,
Positive and negative transfer voltages are alternately applied, and in Comparative Examples 1 and 2, 100
When cleaned with 0,50g / cm the photosensitive drum 10 with a pressing force of ^2, the pressing force of 1000 g / cm ^2, but in the initial stages have been made 95% of the cleaning, the 80-sheet copying Cleaning at the completed stage has dropped to 65%. With a pressing force of 50 g / cm ² , 70% of the cleaning is performed in the initial stage, and the cleaning at the stage when 80 sheets have been copied is reduced to 40%, and the cleaning efficiency is halved. Then, a negative transfer voltage is applied by the pressing transfer roller 18, and when the photosensitive drum 10 is cleaned using the pressing force of 400,500 g / cm ² in Comparative Examples 3 to 4, the pressing force is
When the transfer voltage is 400 g / cm ² and the negative transfer voltage is −1.4 KV, 80% of the cleaning is performed in the initial stage, but the cleaning is 65% when 80 copies are completed.
Has fallen to. When a pressing force of 500 g / cm ² and a negative transfer voltage of −2.0 KV are applied, 80% of the cleaning is performed at the initial stage, and the cleaning at the stage when 80 copies are completed drops to 70%. ing.

[0046]

As described above, according to the present invention, the pressing force of the pressing transfer roller 18 against the photosensitive drum 10 is 200 to 600 g as described above.
/ Cm ² and when positive and negative transfer voltages are alternately applied, the pressure transfer roller 18 can achieve a cleaning efficiency of 95% on the photosensitive drum 10. Therefore, in particular, an image using four color toners such as yellow (Y), magenta (M), cyan (C), and black (K) is transferred onto the recording paper P and pressed using the photoconductor drum 10. When the transfer roller 18 is cleaned, the adherence of the color toner can be prevented for a long period of time.

[Brief description of drawings]

FIG. 1 is a sectional view of a color printer as an example of an image forming apparatus of the present invention.

FIG. 2 is a sectional view of a developing device.

FIG. 3 is a configuration diagram showing a pressing transfer roller of the present invention and switching of a transfer voltage.

FIG. 4 is a configuration diagram showing a pressure transfer roller of the present invention and a photosensitive drum.

FIG. 5 is an explanatory diagram showing positive and negative transfer voltages according to the present invention.

[Explanation of symbols]

 10 Photosensitive drum (image bearing member) 11 PCL (pre-charging static eliminator) 12 Scorotron charger 13 Image exposure means 14, 14Y, 14M, 14C, 14K Developing device 15 Paper feed cassette 18 Press transfer roller (transfer means) 182 Roller Part P Recording paper (transfer material)

Claims (8)

[Claims] 1. An image forming unit for forming a toner image on which two or more color toners are superposed on an image carrier, and the image carrier having the toner image and the transfer unit are pressure-bonded to each other. In a color image forming apparatus that electrostatically batch-transfers a toner image on the image carrier onto the recording paper by passing the recording paper while maintaining the state, at least non-transfer The transfer means is pressure-bonded to the image carrier for a certain period of time during operation, a bias having the same polarity as the transfer operation and a reverse polarity is applied, and the pressing force of the transfer means against the image carrier is 100 to 700 g / A color image forming apparatus having a transfer unit characterized by having a size of cm ² . 2. The color image forming apparatus having a transfer unit according to claim 1, wherein the transfer unit is a pressure transfer roller. 3. The color image forming apparatus having a transfer unit according to claim 2, wherein the pressure transfer roller is formed of a foamed resin material. 4. A color image forming apparatus having a transfer unit according to claim 1, wherein the image carrier is a photosensitive drum or a photosensitive belt. 5. The two-component developing device, wherein the developing device superimposes a direct current component and an alternating current component on a surface of the image carrier on which an electrostatic latent image is formed and a developing area of the developing device which holds a two-component developer. A color image forming apparatus having a transfer unit according to any one of claims 1 to 4, which is a unit. 6. A color image forming apparatus having a transfer unit according to claim 5, wherein the developing unit is a non-contact developing unit. 7. A color image forming apparatus having a transfer unit according to claim 5, wherein the developing unit is a reversal developing unit. 8. The transfer means according to claim 1, wherein the image carrier has a curvature radius of 40 mm or more at least at a transfer or separation position with respect to a recording paper. A color image forming apparatus having.