JP4011932B2 - Full color electrophotographic transfer voltage control method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transfer voltage control method and apparatus for full-color electrophotography in which toner images of a plurality of colors developed on a photoreceptor are transferred based on a transfer potential.
[0002]
[Prior art]
A conventional tandem liquid developing type electrophotographic apparatus has a structure as shown in FIG. A photosensitive member having a developing unit is provided around the intermediate transfer member in association with each color of yellow, magenta, cyan, and black. On each color photoconductor, a charger (not shown) for charging the photoconductor to about 700 V, and an exposure device for exposing the charged photoconductor using laser light having a wavelength of, for example, 780 nm based on image data. (Not shown) or the like is provided, and an electrostatic latent image is formed on the photosensitive member so that the potential of the exposed portion is about 100V. Further, a static elimination device (not shown) is provided to neutralize the remaining potential on the photoconductor.
[0003]
A developing unit including a developing roller is provided on each color photoconductor. The developing roller is biased to a predetermined voltage such as about 400 V to 600 V, and supplies the positively charged toner to the photosensitive member according to the electric field between the developing roller and the developing roller. As a result, toner is deposited on the exposed portion of the photosensitive member charged to about 100 V, the electrostatic latent image on the photosensitive member is developed, and an image is formed. On the developing roller, from a toner supply roller (not shown), for example, a liquid toner having a toner viscosity of 100 to 4000 mPa · S and a carrier viscosity of 20 to 500 cSt, preferably 100 cSt, is thinly extended from the toner reservoir. The liquid toner is applied with a predetermined layer thickness (for example, 4 to 10 μm) on the developing roller by being conveyed.
[0004]
An intermediate transfer roller as an intermediate transfer member is biased to about −800 V, and transfers toner adhered to the photosensitive member according to an electric field between the photosensitive members. The intermediate transfer roller first transfers, for example, yellow toner attached to the first photosensitive member, and subsequently transfers, for example, magenta toner attached to the second photosensitive member. For example, cyan toner attached to the third photosensitive member is transferred, and finally, black toner attached to the fourth photosensitive member is transferred. Thus, the four color toner images developed on the first to fourth photoconductors are sequentially superimposed on the intermediate transfer roller to form a color image. In this way, usually, the toner images of four colors are transferred onto the intermediate transfer roller and superimposed while the intermediate transfer roller is rotated once.
[0005]
Thereafter, the toner image transferred onto the intermediate transfer roller is heated and melted at a contact portion with the print medium under pressure from the backup roller, and is melted and transferred to the print medium.
[0006]
FIG. 5 is a diagram showing a conventional multi-pass liquid developing type electrophotographic apparatus. In this multi-pass method, the only photoconductor used in common for each color is in contact with the intermediate transfer member. Therefore, a charging device (not shown) for charging the photosensitive member, an exposure device (not shown), a charge eliminating device (not shown), and the like are also common to the four colors. A developing unit including a developing roller provided for each color is in contact with the photosensitive member.
[0007]
The intermediate transfer member transfers the toner attached to the photosensitive member one by one in the order of yellow, magenta, cyan, and black in accordance with the electric field between the photosensitive member and the four-color toner image on the intermediate transfer member. Are superimposed. The four-color toner image superimposed on the intermediate transfer member is transferred and fixed on the print medium.
[0008]
In such a conventional electrophotographic apparatus using a high-viscosity liquid toner, density unevenness is likely to occur due to destructive separation of the liquid toner at the roller nip exit of the development and transfer section, and the image quality tends to deteriorate.
[0009]
The problem is that the force that the liquid tries to adhere to the object is strong (wetting) and the liquid holds the coloring material particles (pigments) strongly, so the coloring material particles are affected by this force. By meandering. In order to prevent such a phenomenon, in general, what is called wet electrophotography in which development is performed using liquid toner, the toner viscosity is lowered to reduce the mechanical viscosity of the toner, or a reverse rotation roller is used. To create a state without destructive separation.
[0010]
However, in the wet development method using a high-concentration and high-viscosity liquid developer, the viscosity of the toner is high, so that the viscous force becomes larger than the electric field force due to the bias. Cheap.
[0011]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve such problems and to perform bias control for improving the quality of an image without causing image deterioration in a transfer portion even when a high viscosity liquid toner is used. .
[0012]
[Means for Solving the Problems]
Transfer voltage control method and apparatus for full-color electrophotography of the present invention, transfer based toner images of a plurality of colors developed on the photoreceptor to a transfer voltage.
[0013]
Then , a relationship between the development current and the surface potential on the photoconductor after development is obtained in advance, and based on this relationship, the surface potential is set from the development current value read at the time of development. An optimum transfer voltage value is set for each color so as to keep the potential difference between the two colors. The potential difference between the toner layer potential on the photoreceptor after development and the potential of the transfer target is controlled to be equal to the optimum transfer voltage value for each color.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
If the charge amounts of the respective color toners used in the liquid developing electrophotographic apparatus are different, the toner layer potential on the photoreceptor after development also differs for each color. That is, even when the same amount of toner for each color is developed on the photoconductor, the surface potential of the photoconductor becomes higher for a color having a large charge amount of the toner alone.
[0015]
On the other hand, there is an optimum value for the transfer potential difference for transferring from the photosensitive member to the intermediate transfer member (or print medium). In a color printer, since the charge amount differs among the four color toners, the toner layer potential on the photoreceptor after development differs between the colors. At the time of transfer, image degradation can be reduced most by controlling the potential of the intermediate transfer member according to the toner layer potential of the photosensitive member and controlling the potential difference to an optimum value.
[0016]
FIG. 3 is a diagram for explaining the optimum transfer voltage in the case where development is performed after exposure based on each color information of magenta, cyan, and black. This figure shows the photosensitive member surface potentials when exposed and developed based on color information of magenta, cyan, and black in the direction from left to right. As shown in the figure, there is no difference for each color between the exposure potentials on the photoconductor when exposed based on each color information. This is shown as one horizontal line as the exposure potential in the figure. However, after the toner is attached and developed, the surface potential of the photoreceptor rises from the exposure potential. This increase in potential depends on the difference in charge amount of each color toner as described above. That is, the photoreceptor surface potential is different for each toner color. This is illustrated as different for each color of magenta, cyan, and black in the drawing. If the illustrated example is a solid image, the amount of developed toner is small in the case of halftone, and therefore the potential increase on the photosensitive member is small.
[0017]
In this way, the present invention reads the surface potential on the photoconductor after development, which differs for each color, and controls the optimum transfer voltage for each color on the basis of the read surface potential. Is reduced. Each color optimum transfer voltage ΔVm, ΔVc, ΔVk shown in the figure represents a potential difference from the surface potential of the photoreceptor. The values of the optimum transfer voltages ΔVm, ΔVc, ΔVk themselves can be obtained in advance experimentally and empirically. As a transfer bias voltage (voltage value based on the ground potential) applied to the intermediate transfer member, it is necessary to apply a voltage obtained by adding this optimum transfer voltage to the surface potential of the photosensitive member. The present invention can be applied not only to a transfer from a photoreceptor to an intermediate transfer member and then to a print medium, but also to an electrophotographic apparatus that directly transfers from a photoreceptor to a print medium. Therefore, in the present specification, as an upper concept including an intermediate transfer body or a printing medium to be transferred from the photoconductor, it may be broadly referred to as a “transfer object”.
[0018]
FIG. 1 is a diagram for explaining transfer voltage control according to the present invention. Here, the transfer bias voltage applied to the intermediate transfer member is controlled based on the detection of the development current. The developing roller of the developing unit is biased to a predetermined voltage and supplies the positively charged toner to the photoconductor in accordance with the electric field between the photoconductor and the developing current and the photoconductor after development. There is a certain correlation with the upper surface potential.
[0019]
The current detector measures the development current (for each color). If the development current is measured, a surface potential having a predetermined relationship with the development current can be obtained. A value obtained by adding a constant value as the optimum transfer voltage to the surface potential value is the bias voltage to be applied to the intermediate transfer member. In other words, the applied bias voltage value is determined so that the transfer voltage becomes an optimum value.
[0020]
Alternatively, the fact that there is a predetermined relationship between the developing current and the surface potential also means that there is a certain relationship between the developing current and the optimum transfer bias voltage. Can be determined for each color, and the optimum value of the transfer bias voltage can be set directly from the development current value read during development by the current detection unit. This transfer bias voltage value is applied to the intermediate transfer member.
[0021]
In this way, by setting the transfer bias voltage to an appropriate value, the optimum transfer voltage, that is, the potential difference ΔV between the transfer bias voltage and the developed toner layer potential on the photosensitive member is controlled to an optimum value for each color. It becomes possible to do.
[0022]
When such a bias voltage control technique based on the present invention is applied to a tandem apparatus as described with reference to FIG. 4, the intermediate transfer member is set to a reference potential (for example, ground potential), and the intermediate transfer member is The respective transfer potentials of the respective colors can be set to the optimum values by manipulating the respective potentials of the photoconductors arranged corresponding to the respective colors. That is, the transfer bias controller in FIG. 1 controls the bias voltage applied to the photosensitive member, not the intermediate transfer member.
[0023]
In addition, the bias voltage control technique based on the present invention is applied to a multi-pass apparatus as described with reference to FIG. When applied, the photosensitive member is set to a reference potential (for example, ground potential), and the bias voltage applied to the intermediate transfer member can be set to the optimum value for each color by operating at the time of each transfer.
[0024]
Alternatively, the transfer potential can be set to an optimum value for each color when the image is directly transferred from the photosensitive member to the printing medium without an intermediate transfer member by the electrostatic transfer method.
[0025]
FIG. 2 is a diagram for explaining transfer voltage control different from FIG. 1 according to the present invention. The bias voltage applied to the intermediate transfer member is controlled based on the detection of the surface potential. In the illustrated example, the surface potential on the photoconductor after development is directly detected using a surface potential meter or the like. Similar to the above-described example, once the surface potential is obtained, a value obtained by adding a certain value (usually a different value for each color) to the optimum transfer voltage can be applied to the intermediate transfer member as a bias voltage. Alternatively, a predetermined relationship between the surface potential on the photoconductor and the optimum transfer bias voltage is obtained in advance for each color, and the transfer bias control unit reads the photoconductor based on the preliminarily obtained relationship. The optimum value of the transfer bias voltage is converted from the above surface potential and set, and applied to the intermediate transfer member as the transfer bias voltage value. As in the example shown in FIG. 1, the potential difference ΔV (optimum transfer voltage) between the applied bias voltage and the developed toner layer potential on the photoreceptor can be controlled to an optimum value for each color. In addition, as in the example of FIG. 1, the present invention can be applied to either a tandem system or a multipath system.
[0026]
In addition, the normal printing mode of this apparatus is provided with another adjustment mode. In this adjustment mode, a predetermined image pattern is printed, and based on this print image, the read photoreceptor surface potential and development current are read. It can be configured to optimize the transfer voltage from the value.
[0027]
In addition, these relationships can be obtained based on the printed image obtained by printing a pattern determined outside the image area immediately before printing. This makes it possible to cope with environmental changes and deterioration of consumables such as photoconductors.
[0028]
【Example】
When the photoreceptor surface potential after development was 260V and 300V, the potential of the intermediate transfer member was set to -400V and -300V, respectively, and this potential difference was controlled to 650V. .
[0029]
【The invention's effect】
The present invention obtains the surface potential from the current image current value, and, since it is used to control the transfer voltage on the basis of the surface potential, even with a liquid toner of a high viscosity, causing image deterioration in the transfer section In addition, it is possible to perform bias control for improving the quality of an image.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining transfer voltage control according to the present invention.
FIG. 2 is a diagram for explaining transfer voltage control different from FIG. 1 according to the present invention.
FIG. 3 is a diagram for explaining an optimum transfer potential in the case where development is performed after exposure based on color information of magenta, cyan, and black.
FIG. 4 is a diagram illustrating a conventional tandem liquid developing type electrophotographic apparatus.
FIG. 5 is a view showing a conventional multi-pass liquid developing type electrophotographic apparatus.

Claims (5)

In a full color electrophotographic transfer voltage control method for transferring a plurality of color toner images developed on a photoreceptor based on a transfer voltage,
Based on a predetermined relationship obtained in advance, the surface potential is set from the development current value read during development, and an optimum transfer voltage value is set for each color so as to keep the potential difference from the surface potential at a predetermined value. And
A transfer voltage control method for full-color electrophotography, comprising: controlling a potential difference between a toner layer potential on a photosensitive member after development and a transfer target potential to be equal to the optimum transfer voltage value for each color.   2. The full color electrophotographic transfer voltage control method according to claim 1, wherein a predetermined image pattern is printed and the transfer voltage is optimized during the adjustment mode operation of the apparatus.   3. The transfer voltage control method for full-color electrophotography according to claim 2, wherein the predetermined image pattern is printed outside the image area immediately before printing, and the transfer voltage is optimized for each printing from the read surface potential or current value.   The transfer target is an intermediate transfer drum, and is a device that sequentially superimposes each color from a common photosensitive member to an intermediate transfer member by a multi-pass method. 4. The transfer voltage control method for full-color electrophotography according to claim 1, wherein the transfer voltage for each color is set to an optimum value by operating at the time of transfer. In a full-color electrophotographic transfer voltage control device for transferring a plurality of color toner images developed on a photoreceptor based on a transfer voltage,
Based on the relationship obtained in advance, the surface potential is set for each color from the development current value read at the time of development, and the optimum transfer voltage value for keeping the potential difference from the surface potential at a predetermined value is set for each color. Means for setting;
Means for controlling the potential difference between the toner layer potential on the photoreceptor after development and the potential of the transferred body to be equal to the optimum transfer voltage value for each color;
A full color electrophotographic transfer voltage control device comprising:

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