JPH08286519A - Electrophotographic method and device - Google Patents

Abstract

PURPOSE: To obtain an electrophotograph excellent in color reproducibility of a color image by previously setting at least one of a developing bias voltage and a developer concentration in each developer. CONSTITUTION: A developing means 20 arranged on the right of a photoreceptor drum 11 is horizontally moved to the side of the photoreceptor drum 11 by a driving means, so that a yellow toner image is developed by a first developing unit 21, a magenta toner image is developed by a second developing unit 22 and cyan and black toner images are successively developed similarly. At this time, the concentrations of the developers of each color and the developing bias voltages applied to developing rollers in the developing units 21-24 are previously set at prescribed values respectively. Therefore, the color balance of each developed electrostatic latent image is suitably kept. Thus, the toner images developed by each developing unit are successively transferred to an intermediate transfer drum 31 and a multicolor toner image obtained by the laminating of the toner images of four colors is formed on the drum 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic method and an electrophotographic apparatus.

[0002]

2. Description of the Related Art In a color electrophotographic method using a plurality of developers, the color reproducibility of each developer determines the quality of an image. Therefore, as a method for improving the color reproducibility, for example, JP-A-50-99333 and JP-A-5-99333.
No. 0-137138 or JP-A No. 54-28139 discloses a color electrophotographic method and the like.

The first method disclosed in Japanese Patent Laid-Open No. 50-99333 is to control the potential of the electrostatic latent image for each color. Also, JP-A-50-137138
The second method disclosed in the publication is to control the post-charge amount given to the developed color image for each developed color image when the developed color image is transferred onto the transfer member. Furthermore, JP-A-54
According to the third method disclosed in Japanese Patent Publication No. 28139, the developing speed is adjusted so that the moving speed of the means for supplying the developer of each color and the moving speed of the photoconductor are different from each other.

[0004]

In the color electrophotographic method, although the color reproducibility in a color image is improved by various methods as described above, satisfactory results have not been obtained yet. is the current situation. The present invention has been made in view of the above points, and an object thereof is to provide an electrophotographic method and an electrophotographic apparatus that are excellent in color reproducibility in a color image.

[0005]

In order to achieve the above object, according to the invention of claim 1, an electrostatic latent image for each color is formed on a latent image bearing medium and each of these electrostatic latent images is developed. In the electrophotographic method of developing with a developer of a corresponding color while applying a bias voltage, at least one of the developing bias voltage and the density of the developer is set in advance for each developer. is there.

In order to achieve the above object, according to the invention of claim 2, an electrostatic latent image for each color is formed on the latent image bearing medium, and each of these electrostatic latent images is a liquid of a corresponding color. In the electrophotographic method of developing with a developer, the conductivity of the developer is set for each developer. Furthermore,
In order to achieve the above object, according to the invention of claim 3, an electrostatic latent image of each color is formed on the latent image bearing medium, and each of these electrostatic latent images is formed into a corresponding color while applying a developing bias voltage. In the electrophotographic method of developing with the liquid developer, the developing bias voltage so as to obtain the same developing density for each color,
At least one of the concentration of the developer and the conductivity of the developer is set for each developer.

Preferably, in the electrophotographic method according to each of the above claims, halftones are reproduced in area gradation. On the other hand, in order to achieve the above object, according to the invention of claim 5, a latent image carrying medium and a developing means are provided, and electrostatic latent images of different colors are formed on the latent image carrying medium. In an electrophotographic apparatus for developing a latent electrostatic image with a developer of a corresponding color while applying a developing bias voltage between the latent image bearing medium and the developing means, the developing bias voltage, the concentration of the developer, the developing At least one of the conductivity of the developer is set in advance for each developer.

Preferably, the developing bias voltage is applied by a bias power supply capable of generating a voltage corresponding to each color at least when developing each color. By setting at least one of the developing bias voltage and the developer concentration for each developer in advance, you can set the optimum developing conditions for each color when developing each electrostatic latent image, and you can set the white background stain for each color. Can be suppressed and almost the same reflection density (printing density) can be realized, and the color balance between the developers can be preferably maintained.

Alternatively, by setting the conductivity of the developer for each color, the developing characteristics can be controlled, and the color balance between the developers can be maintained appropriately. In particular,
In an area gradation type electrophotographic printer that reproduces halftones by changing the area ratio of the printing area, the reflection density of the printing area is important. The color reproduction is good.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an electrophotographic method of the present invention will be described below in detail with reference to FIG. 1 by taking an electrophotographic printer for color printing as an example. As shown in FIG. 1, the electrophotographic printer 1 includes a photosensitive unit 10, a developing unit 20, an intermediate transfer unit 30, a cleaning unit 40, a transfer / fixing unit 50, a pre-transfer charger 60, and an auxiliary squeeze unit 70. The exposure means (not shown) irradiates the photosensitive means 10 with exposure light.

The photosensitive means 10 has a photosensitive drum 11, a charge eliminating lamp 12 and a primary charger 13. The photosensitive drum 11 has a cleaning means 4 prior to removing residual charges.
0 cleans the surface. In the photosensitive drum 11, a photosensitive layer made of a photoelectric material is formed on the surface of a cylindrical drum, and an electrostatic latent image is formed by the light emitted from the exposing unit. The static elimination lamp 12 is a small incandescent lamp,
The surface of the photosensitive drum 11 is irradiated with light to remove residual charges. The primary charger 13 is a corona charger that uniformly charges the surface of the photosensitive drum 11 with ions generated by corona discharge.

The developing means 20 includes the first developing units 21 to 21.
The fourth developing unit 24 is provided, and these are integrally moved in a horizontal direction indicated by an arrow in the drawing, which is a tangential direction of the photosensitive drum 11, by a driving unit (not shown). Further, a toner cartridge (not shown) containing each of yellow, magenta, cyan, and black developing solutions is detachably attached to each developing unit. The developer used is one in which toner particles such as yellow, magenta, and cyan are dispersed in a liquid carrier.

Here, each developer has a solid content concentration (wt%) indicating the ratio of the toner particles to the carrier and a pigment concentration (wt%) indicating the ratio of the pigment weight to the weight of the synthetic resin forming the toner particles. The two types of densities are defined as predetermined values. For example, solid content concentration (wt%)
Is 2% for yellow, 2.3% for magenta, and 1.8 for cyan.
% And black were set to 3%, respectively. The pigment concentration (wt%) was set to 15% for cyan and 20% for the others. In the present embodiment, the two types of densities are changed for each color, but of course, only one of the densities may be specified for each color. Here, the pigment concentration is 5
Is preferably in the range of 30 to 30% by weight, more preferably in the range of 9 to 25% by weight, and the solid content concentration is in the range of 0.5 to 5% by weight, and further preferably in the range of 1 to 4% by weight. Choose the optimum value.

Alternatively, the conductivity of the developer can be changed for each color by setting the average toner particle diameter of the liquid developer or the concentration of the charge control agent generally used for each color separately. As a result, the electrical characteristics of the toner particles, that is, the so-called development characteristics can be controlled, and the color reproducibility can be improved. Here, the average toner particle size is
It is preferably in the range of 0.2 to 5 μm, and more preferably in the range of 0.3 to 4 μm, the optimum value is selected for each color.

As the conductivity measuring method, for example, a method based on AC conductivity by applying an AC electric field between the measuring electrodes and a method based on DC conductivity by applying a DC voltage between the measuring electrodes. Can be given. Although the conductivity by any of the measuring methods is an index of the developing characteristics, specifically, for example, as a measuring method by the AC conductivity, Scient
Model 627 from i-fica (USA), Kawaguchi Electrics Works (Japan,
Model P618 cell electrode from Tokyo) and high resistance meter from Takeda Riken (current name Advantest, Tokyo, Japan)
It can be measured by combining Model PR8601 etc. As a parameter of the DC conductivity, there are a peak current value immediately after voltage application and a base current value after stabilization, but the development characteristics change regardless of which one. Even if the peak value or the base value of AC conductivity or DC conductivity is changed, the developing characteristics can be controlled and the color reproducibility can be improved.

In the present embodiment, a wet electrophotographic printer using a liquid developer has been described as an example, but also in a dry electrophotographic printer using a powder developer, in the case of a two-component developer, It is possible to change the developer concentration in the present invention by changing the ratio of the toner particles to the iron powder and the carrier. The first developing unit 21 is
A developing roller 21b and a squeeze roller 21c are arranged in a developer tank 21a. Liquid tank 21a
The developer is supplied from the toner cartridge arranged in the developing unit 21. The developing roller 21b and the squeeze roller 21c are arranged facing each other in parallel with the rotation axis of the photosensitive drum 11 with a predetermined distance in the vertical and horizontal directions when the developing means 20 is at the standby position on the right side of the photosensitive drum 11. There is. Both rollers 21b and 21c enable the developing means 20 to move in the horizontal direction, and therefore, the liquid tank 21a.
Is vertically movably arranged and is urged upward by a spring (not shown).

Here, the developing roller 21b is applied with a developing bias voltage preset to a predetermined value from an electrode plate (not shown). This developing bias voltage is -410V for the developing unit 21 for developing yellow, -350V for the developing unit 22 for developing magenta, -380V for the developing unit 23 for developing cyan, and -380V for the developing unit 23 for developing black. Each was set to -400V.

The setting of the bias voltage may be carried out by providing an individual power source for each color, the voltage dividing ratio or the like may be individually set from the same power source, and a common voltage capable of being dynamically set. It is also possible to connect the power source of No. 1 to apply the corresponding developing bias voltage when developing each color. The developing bias voltage is set between the image-exposed light portion surface potential and the unexposed dark portion surface potential of the photosensitive drum 11 in the developing area. For example, the dark portion potential −700V and the light portion potential −100V are set. In this case, the developing bias voltage is preferably in the range of -600 to -200V. More preferably, it is in the range of -550 to -250V. In order to achieve almost the same concentration within this range,
The developing bias voltage is set for each color. Of course, if there is no problem, the developing bias voltage for each color may be the same.

Since the other developing units 22 to 24 have the same structure as the first developing unit 21, detailed description thereof will be omitted. Here, the developing device 20 is arranged on the right side of the photosensitive drum 11 in the initial position before the start of development. Then, the developing units 21 to 24 are sequentially moved to the photosensitive unit 10 side in this order by the driving unit at the time of developing, and the electrostatic latent images formed based on the color-separated print information are sequentially developed. To be done.

Further, each developing solution is supplied to each developing unit from each toner cartridge only when the electrophotographic printer 1 is used, and normally, no developing solution is contained in the liquid tank of the developing unit. The intermediate transfer unit 30 includes an intermediate transfer drum 31, a charger 32, a heater 33, and the photosensitive drum 1.
1 is provided with a contact / separation mechanism (not shown).

The intermediate transfer drum 31 is brought into pressure contact with the photosensitive drum 11, and each time a toner image of each hue is developed by the developing units 21 to 24 of the developing means 20, the toner images are sequentially transferred in layers. The charger 32 charges the intermediate transfer drum 31 according to the same principle as that of the primary charger 13 of the photosensitive unit 10, and facilitates transfer of the next toner image having a different hue transferred from the photosensitive drum 11 to the front. At the same time as canceling the influence of the toner image, the toner image already transferred onto the intermediate transfer drum 31 is prevented from returning onto the photosensitive drum 11.

The heater 33 is a heater for heating the intermediate transfer drum 31 using a halogen lamp, an infrared lamp or the like. Then, in the intermediate transfer unit 30, the toner images developed on the photosensitive drum 11 are sequentially stacked and transferred to the intermediate transfer drum 31 while being charged by the charger 32. At the time of this transfer, a small amount of toner image and developer which have not been transferred to the intermediate transfer drum 31 remain on the photosensitive drum 11, but these are cleaned by the cleaning means 40.

The cleaning means 40 collects the toner image remaining on the photosensitive drum 11 after the toner image is transferred onto the intermediate transfer drum 31 and the residue of the developing solution.
It has two cleaning rollers 41 which are in contact with 1 and a squeeze blade 42 which is in contact with the photosensitive drum 11. The transfer / fixing unit 50 has heating rollers 51 and 52. The heating rollers 51, 52 are hollow metal pipes made of aluminum, stainless steel or the like, and an elastic layer made of silicone rubber, fluororubber or the like is formed on the outer peripheral surface thereof. Both rollers 51, 52 have a heater such as a halogen lamp in the hollow portion.
(Not shown) is built in and controlled to a constant temperature. As shown in FIG. 1, the heating rollers 51 and 52 are arranged in contact with the intermediate transfer drum 31 such that the heating roller 51 is on the upstream side in the conveyance direction of the recording sheet S and the heating roller 52 is on the downstream side. The peripheral speed of each rotation is the intermediate transfer drum 3.
It is set to be equal to the peripheral speed of 1. Here, the heating rollers 51 and 52 are normally arranged at positions apart from the intermediate transfer drum 31. And both rollers 51, 52
When the multicolor toner image is heated and fixed onto the recording sheet S, the multicolor toner image is integrally driven by a pressing mechanism (not shown) and brought into pressure contact with the intermediate transfer drum 31, and the multicolor toner images stacked and transferred onto the intermediate transfer drum 31 are transferred. It is heated and pressed to fix it on the recording paper S.

Here, the pressing mechanism is the photosensitive drum 11
When the toner image is transferred from the intermediate transfer drum 31 to the intermediate transfer drum 31, the heating rollers 51 and 52 are separated from the intermediate transfer drum 31. The pressing mechanism is used for the intermediate transfer drum 3
The heating rollers 51, 52 are pressed against the intermediate transfer drum 31 with a predetermined pressure contact force by the time the last toner image transferred portion of the four types of toner images 1 is reached. As a result, the heating rollers 51, 52 pressurize and heat the multicolor toner images laminated and transferred onto the intermediate transfer drum 31 to transfer and fix them onto the recording paper S.

The pre-transfer charger 60 is a corona charger that charges the surface of the photosensitive drum 11 on which the toner image is developed to the same polarity as the toner image, that is, the toner particles. Charger 60
Is the photosensitive drum 1 due to the ions generated by the corona discharge.
The surface on which the toner image No. 1 has been developed is charged to the same polarity as the toner particles, whereby a repulsive force is applied between the toner image surface and the toner particles, and the toner particles are aggregated on the surface of the photosensitive drum 11.

The auxiliary squeeze means 70 includes an auxiliary roller 71.
And a saucer 72. The auxiliary roller 71 rotates in the same direction as the photosensitive drum 11, and removes excess developer, especially liquid carrier, from the surface of the photosensitive drum 11 on which the toner image has been developed. The developer adhering to the auxiliary roller 71 is removed by the scraper and is collected in the waste liquid tank via the lower tray 72.

The electrophotographic printer 1 is configured as described above and produces a color image by the electrophotographic method described below. First, residual charge is removed from the surface of the photosensitive drum 11 cleaned by the cleaning unit 40 by the charge removal lamp 12, and the primary charger 13 uniformly charges the surface. Next, laser light is irradiated from the exposing means to sequentially form an electrostatic latent image based on the color-separated print information on the surface of the photosensitive drum 11. The electrostatic latent image produced by the irradiation of the laser light has a total of 4 corresponding to the hues of yellow, magenta, cyan and black.
Formed once.

Next, the developing means 20 arranged on the right side of the photosensitive drum 11 in the figure is horizontally moved to the photosensitive drum 11 side by the driving means (not shown), and the yellow toner image is generated by the first developing unit 21. Second developing unit 22
Then, the magenta toner image and the cyan and black toner images are successively developed in the same manner. At this time, in the method of the present invention, the concentration of the developer of each color and the developing unit 2
In each of 1 to 24, the developing bias voltage applied to the developing roller is set to a predetermined value in advance, so that the color balance of each electrostatic latent image to be developed is appropriately maintained.

In this way, the toner image developed by each developing unit is sequentially transferred to the intermediate transfer drum 31,
On the intermediate transfer drum 31, a multicolor toner image in which toner images of four colors are stacked is formed. Then, the fourth developing unit 24
When the transfer of the toner image developed in step 1 to the intermediate transfer drum 31 is completed, the intermediate transfer drum 31 is separated from the photosensitive drum 11 by the contact / separation mechanism, and the intermediate transfer drum 31
The rotation speed of will decrease. After the rotation speed is reduced, the heating mechanism causes the heating rollers 51 and 52 to move to the intermediate transfer drum 3
Pressed to 1. As a result, the multicolor toner images stacked on the intermediate transfer drum 31 are heated and pressed, and are collectively transferred and fixed onto the conveyed recording paper S to complete the step of recording a color image. .

At this time, in the method of the present invention, each color is free from white background stains, the print density is in the range of 1.1 to 1.3, and the color balance is properly maintained. Therefore, a color image excellent in color reproducibility can be obtained. still,
The print density was measured using a reflection densitometer. When the recording of the multicolor toner image on the recording paper S is completed as described above,
The pressing mechanism releases the pressure contact of the heating rollers 51 and 52 to the intermediate transfer drum 31, and the developing unit 20 is moved to the initial position on the right side of the photosensitive drum 11 by the driving unit.

In the method of the present invention, the concentration of the developer of each color and the developing bias voltage applied to the developing roller in the developing units 21 to 24 are set to predetermined values in advance. However, according to environmental conditions such as temperature and humidity at the place where the electrophotographic printer 1 is installed, the developing conditions such as developing bias voltage and exposure power when developing each electrostatic latent image may be further adjusted. Needless to say.

[0032]

As is apparent from the above description, according to the electrophotographic method and the electrophotographic apparatus of the present invention, the color balance between the developers is appropriately maintained during the development of each electrostatic latent image. A color image with excellent color reproducibility can be obtained.
At this time, if the halftone is color-reproduced in the area gradation, the color balance can be maintained even in the halftone reproduction, and good color reproduction can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an electrophotographic printer to which an electrophotographic method of the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrophotographic printer 10 Photosensitive means 11 Photosensitive drum (latent image carrying medium) 12 Eliminating lamp 13 Primary charger 20 Developing means 21 First developing unit 21b Developing roller 21c Squeeze roller 22-24 Second to fourth developing unit 30 Intermediate transfer Means 31 Intermediate transfer drum 32 Charging device 33 Heater 40 Cleaning means 41 Cleaning roller 42 Squeeze blade 50 Transfer / fixing means 51,52 Heating roller 60 Pre-transfer charger 70 Auxiliary squeeze means 71 Auxiliary roller 72 Receiving tray S Recording paper

Claims (6)

[Claims] 1. An electrophotographic method for forming an electrostatic latent image for each color on a latent image bearing medium and developing each of these electrostatic latent images with a developer of a corresponding color while applying a developing bias voltage. An electrophotographic method, wherein at least one of the developing bias voltage and the concentration of the developer is set in advance for each developer. 2. An electrophotographic method for forming an electrostatic latent image for each color on a latent image bearing medium and developing each of these electrostatic latent images with a liquid developer of a corresponding color, wherein the conductive property of the developer is used. An electrophotographic method characterized in that the degree is set for each developer. 3. An electrophotographic method of forming an electrostatic latent image for each color on a latent image bearing medium and developing each of these electrostatic latent images with a liquid developer of a corresponding color while applying a developing bias voltage. In at least one of the developing bias voltage, the concentration of the developer, and the conductivity of the developer is set for each developer so that the same developing concentration can be obtained for each color. Photo method. 4. The halftone is reproduced in area gradation.
3 to 3 of the electrophotographic method. 5. A latent image carrying medium and a developing means are provided, electrostatic latent images of different colors are formed on the latent image carrying medium, and each of these electrostatic latent images is developed with the latent image carrying medium. In the electrophotographic apparatus for developing with the developer of the corresponding color while applying the developing bias voltage between the means and the means, at least one of the developing bias voltage, the concentration of the developer, and the conductivity of the developer is set in advance. An electrophotographic device characterized by being set for each developer. 6. The electrophotographic apparatus according to claim 5, wherein the developing bias voltage is applied by a bias power source capable of generating a voltage corresponding to each color at least when developing each color.