JP2001134102A - Wet type image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wet type image forming device which is constituted so that the best image quality is maintained by transferring the sufficient quantity of developing grains to a developer supporting body as for respective liquid developer having different properties and enhancing image density and whose cost can be reduced by sharing a coating device. SOLUTION: Bias obtained by superimposing DC on AC is applied to a coating roller 24 by a high-voltage power source 61 and a developing belt 31 is grounded by a pair of rotary rollers 33 and 34. By giving a jumping effect or a loosening effect to the developing grains included in the liquid developer with which the belt 31 is coated from the roller 24, the transferring quantity of the developing grains is increased and the image density is enhanced. Thus, the best image quality can be maintained. Besides, coating nip width is constituted so that the optimum overlapping coating nip passing time is obtained as for the liquid developer having different properties. Moreover, the cost is reduced by sharing the coating device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet image forming apparatus such as a copying machine, a facsimile, a printer and the like, and more particularly, to visualize a latent image formed on a latent image carrier using a liquid developer. The present invention relates to a wet image forming apparatus including a developing unit, a coating unit for applying a liquid developer to a thin layer of a developer support of the developing unit, and a bias applying unit for applying a bias to the coating unit.

[0002]

2. Description of the Related Art In a wet image forming apparatus using a liquid developer, a developing means transfers a developing particle contained in the liquid developer from a developer support onto a latent image carrier disposed opposite to the developer support. The latent image is visualized by the transfer. The developing means electrostatically attracts the visualized particles onto the latent image carrier by an electric action acting between the latent image carrier previously charged by the charge applying device and the developer support. At this time, by applying a bias to the developer support, the movement of the visualized particles attached to the image area is optimized, and as a result, a high-quality image can be obtained.

[0003] Further, in the means for applying the liquid developer,
When a bias is applied to one of the coating member and the developer support to form a potential difference between the coating member and the developer support, the image density can be improved and the image quality can be improved. The reason is that, for example, when a liquid developer containing positively charged visualized particles is used, a positive bias is applied to, for example, an application roller as an application member, and the developer support is grounded. This is because a sufficient amount of the visualized particles can be transferred from the application roller to the developer support by the potential difference.

[0004]

The liquid developer contains other than visualized particles such as a charge control agent and a developer dispersant in view of the electrical properties of the developer and the dispersibility of the visualized particles. The liquid developer has different properties depending on the ratio of the charge control agent or the developer dispersant to the entire liquid developer.
In addition, the liquid developer has different properties depending on the difference in the concentration of toner particles (solid content) and the viscosity of the liquid developer in addition to the ratio of these agents. However, among the liquid developers having different properties, there is a liquid developer in which an image becomes worse when a bias is applied by an application unit. This is because the visualized particles contained in the liquid developer having the different properties are transferred to the developer support,
This is because each has an optimum coating nip passage time.
Therefore, if the time is shorter or longer than the optimum coating nip passage time, the desired amount of transfer of the visualized particles to the developer support cannot be obtained.

Accordingly, the present applicant has filed Japanese Patent Application No. 11-2089.
No. 57, it is possible to obtain the optimum image quality by selectively extracting the effect that the visualized particles contained in each liquid developer are attracted to the surface of the developer support for the liquid developers having the different properties. We proposed a wet image forming apparatus that can be used. In this wet image forming apparatus, a bias is applied by a coating unit, and the time for applying the developer, that is, the application nip passing time is changed according to the properties of each liquid developer. For this purpose, for example, a structure is used in which the coating nip width is made different.

For example, when a liquid developer having a high solid content is used and a DC bias is applied by a coating means,
If the transit time is longer than the optimal coating nip transit time, the charges are injected into the visualized particles toward the developer support and move away from the developer support again. There is a tendency that a desired amount of transition of the activated particles cannot be obtained.
In this case, the coating nip width is set to be short so that electric charges are not injected into the visualized particles, so that an optimum coating nip passage time can be obtained. On the other hand, for example, when a liquid developer having a high ratio of the developer dispersant or the charge control agent is used and a DC bias is applied by the application unit, the developer dispersant surrounding the visualized particles, the charge The ionic layer formed by the control agent moves faster than the visualized particles,
The movement of the visualized particles that should originally be transferred is prevented. The visualized particles whose movement has been blocked are agglomerated on the opposite side of the developer support to form a thin layer, and are apparently larger than the original visualized particles have, making it difficult to move in the carrier,
Transfer to the developer support becomes difficult. In this case, the width of the coating nip is set to be longer so that the optimum coating nip passage time is obtained so that the visualized particles are sufficiently transferred.

However, in the above-mentioned wet image forming apparatus, since the coating nip width is changed in accordance with the properties of each liquid developer, it is difficult to use a common coating apparatus, which may increase the manufacturing cost of the coating apparatus. is there. In particular, in the case of a full-color wet image forming apparatus, an image is formed by superposing four color liquid developers having different properties, but in order to change the coating nip width, the configuration of the coating apparatus itself must be changed for each color. Therefore, there is a possibility that the cost may be increased in terms of common use of the developing device.

The present invention has been made in view of the above background, and it is an object of the present invention to transfer a sufficient amount of visualized particles to a developer support for each liquid developer having different properties. It is an object of the present invention to provide a wet image forming apparatus capable of improving the density to keep the image quality at the best, and using the same coating apparatus to reduce the cost.

[0009]

In order to achieve the above object, the present invention is directed to a developing means for visualizing a latent image formed on a latent image carrier using a liquid developer; In a wet image forming apparatus comprising: a coating unit for applying a liquid developer to a thin layer on a developer support of a developing unit; and a bias applying unit for applying a bias to the coating unit, the bias applying unit is configured to switch between AC and DC. And a power supply capable of superimposing and applying a voltage.

In the wet image forming apparatus according to the first aspect, the bias is applied to the coating unit by superimposing a direct current on an alternating current by the bias applying unit. By applying the bias, by providing a jumping or loosening effect on the visualized particles in the liquid developer applied to the developer support, to improve the transfer amount of the visualized particles, The image quality can be kept at the best by improving the image density. In addition, in the case of bias application of DC only, if the coating nip passage time is longer than the above-described optimal coating nip passage time,
For a liquid developer in which electric charges are injected into the visualized particles and a desired transfer amount cannot be obtained, a bias in which a direct current is superimposed on an alternating current is applied by the bias applying unit. Then, even if the transit time is longer than the optimal coating nip transit time, by giving a jumping or loosening effect to the visualized particles, it is possible to prevent a decrease in the transfer amount due to the injection of the electric charge and to achieve a desired transfer. You can get the quantity. Thereby, the range of the optimal coating nip passage time of the liquid developer can be widened. On the other hand, in the case of applying only DC bias, if the coating nip transit time is shorter than the above-described optimal coating nip transit time, the visualized particles aggregate on the opposite side to the developer support to form a thin layer and a desired transition. For the liquid developer whose amount cannot be obtained, a bias in which DC is superimposed on AC is applied by the bias applying means. Then, even if the transit time is shorter than the optimal coating nip transit time, the visualized particles aggregated into a thin layer are loosened, the dispersibility of the visualized particles is increased, and the visualized particles move. Can be given an optimal condition. Thereby, the range of the optimal coating nip passage time of the liquid developer can be widened. As described above, for the liquid developers having the above-described different properties, the range of the respective optimum coating nip passing times is expanded, so that the overlapping range of the respective optimum coating nip passing times can be obtained. . Therefore, by configuring the application nip passage time of the application unit to be the overlapped optimal application nip passage time, the same configuration of the application unit can be used for liquid developers having different properties. Costs can be reduced.

According to a second aspect of the present invention, in the wet image forming apparatus of the first aspect, the developing means includes a plurality of liquid developers, and at least two or more of the plurality of liquid developers. The bias application conditions applied by the power supply are different from each other.

In the wet image forming apparatus of the second aspect, the conditions for applying the bias applied by the power supply are different from each other for at least two or more of the liquid developers of the plurality of colors. Each color liquid developer has a different transfer state of the visualized particles to the developer support in the coating nip due to a difference in properties. Therefore, by setting the bias application conditions for each color liquid developer, a sufficient amount of the visualized particles can be transferred to the developer support, the image density can be improved, and the image quality can be improved. Become.

According to a third aspect of the present invention, in the wet image forming apparatus of the second aspect, two or more liquid developers having different average particle diameters of visualized particles contained in the liquid developer are controlled by the power supply. The present invention is characterized in that the application conditions of the applied bias are different from each other.

In the wet image forming apparatus according to the third aspect, a bias application condition applied by the power supply is applied to two or more liquid developers having different average particle diameters of visualized particles contained in the liquid developer. Are different from each other. For example, when the average particle size of the visualized particles is relatively large, the visualized particles are difficult to move, and as an application condition for strengthening the AC component, the effect of loosening the aggregated visualized particles is enhanced. Make it easy to move. On the other hand, when the average diameter of the visualized particles is relatively small, the visualized particles are likely to move, so the application condition is set so as to weaken the AC component. As described above, by changing the bias application condition based on the average particle size of the visualized particles, an optimal state for applying each visualized particle is provided, and the developer support of the visualized particles is provided. It is possible to optimize the transfer onto the body and optimize the image quality on the final recording medium.

According to a fourth aspect of the present invention, in the wet image forming apparatus of the first aspect, the bias applying means has an adjusting means capable of changing a bias applying condition applied by the power supply. Things.

In the wet image forming apparatus of the fourth aspect, it is possible to change the bias application condition by the adjusting means so that the transfer amount of the visualized particles contained in the liquid developer is maximized. Become.

According to a fifth aspect of the present invention, in the wet image forming apparatus according to the fourth aspect, the bias applying means includes at least one of a DC voltage, an AC peak-to-peak voltage, or an AC frequency applied by the power supply. Can be changed.

In the wet image forming apparatus according to the fifth aspect, at least one of the DC voltage, the AC peak-to-peak voltage, or the AC frequency is changed for the various liquid developers having the different properties. Thus, more effective bias application conditions can be set, and the transfer amount of the visualized particles contained in the liquid developer can be maximized.

The invention according to claim 6 is the invention according to claims 1, 2, 3, and 4.
Alternatively, in the wet image forming apparatus of 5, the frequency of the AC component of the bias applying means is set to 5 Hz or more and 400 Hz or less.

According to the experimental results, when the frequency of the AC component of the bias applying means is less than 5 Hz, no jumping or loosening effect of the visualized particles in the liquid developer occurs.
By setting the frequency to 5 Hz or more, these effects occur, and the amount of the visualized particles transferred onto the developer support is improved. On the other hand, when the frequency exceeds 400 Hz, the effect of improving the transfer amount of the visualized particles onto the developer support decreases. In the wet image forming apparatus according to the sixth aspect, the frequency of the AC component of the bias applying unit is 5 Hz or more,
Since the frequency is 400 Hz or less, a jumping or loosening effect of the visualized particles occurs, and the transfer amount of the visualized particles onto the developer support can be improved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] An embodiment in which the present invention is applied to a wet electrophotographic copying machine (hereinafter simply referred to as "copier") will be described below. FIG. 1 is a schematic diagram of a main part of a copying machine according to the present embodiment. FIG. 2 shows FIG.
FIG. 4 is an enlarged view of the vicinity of an application roller 24 in the inside.

First, a schematic configuration of the copying machine will be described. As shown in FIG. 1, a charging roller 2, a developing unit 3, an intermediate transfer member 4, a discharging lamp 5, a photosensitive drum cleaning unit 6, and the like are arranged around a photosensitive drum 1 as a latent image carrier. I have. Further, a transfer roller 7 and an intermediate transfer body cleaning unit 8 are provided as transfer means for transferring the developed image to a transfer sheet P as a final transfer material, facing the intermediate transfer body 4.

The developer support of the developing unit 3 includes a developing belt 31 and six rotating rollers 32, 33, 3 for rotating the developing belt 31 while keeping the tension of the developing belt 31.
4, 35, 36, and 37,
2 is a drive roller. Among these rotating rollers, a pair of rotating rollers 33 and 34 are opposed to an application roller described later, and are arranged so as to form a certain nip. When speeding up image formation by increasing the speed of the developing belt 31, in order to stably form a normal image, the above-mentioned six rotating rollers 32, 33, 34, and 3 are required.
It is preferable that at least two or more of 5, 36, and 37 are drive rollers. The pair of rotating rollers 35 and 36 among these rotating rollers are the photosensitive drum 1.
And a developing roller for applying a developing bias between the developing belt 31. Here, in order to form a normal image in the developing section, the surface moving speed of the developing belt 31 is set to be equal to the surface moving speed of the photosensitive drum 1.

The application of the liquid developer to the developing belt 31
This is performed by thinning the liquid developer stored in the developer reservoir 22 of the coating device 20 via three coating rollers 23, 24, and 25. Coating roller 2 in coating device 20
Reference numeral 5 denotes a roller arranged to regulate the amount of the liquid developer supplied from the developer reservoir 22. Developing belt 31
Is set to 140 mm / sec.

As shown in FIG. 2, a bias of a predetermined value is applied to the coating roller 24 from the high voltage power supply 61, and at a position 101 where the rotating roller 33 and the coating roller 24 are in contact with each other with the developing belt 31 interposed therebetween. A bias is applied to the developing belt 31. The distance from the position 101 to the position 102 where the developing belt 31 and the application roller 24 are separated, that is, the contact distance (nip width) was 10 mm. This position 101
1 where the developing belt 31 and the application roller 24 are separated from
The distance up to 02 is the distance at which the bias effectively acts on the visualized particles.

The high-voltage power supply 61 is a power supply capable of superimposing direct current on alternating current, and is also capable of separately outputting alternating current and direct current. This high voltage power supply 6
Reference numeral 1 is electrically connected to the control device 60 so that the control device 60 can adjust the bias application condition. As the bias application condition, for example, the magnitude of the DC component and the magnitude and frequency of the peak-to-peak voltage of the AC component are adjusted.

Next, the operation of forming an image in the copying machine having the above configuration will be described. As shown in FIG. 1, the photosensitive drum 1 is driven to rotate at a constant speed in the direction of arrow B at the time of image formation by driving means such as a motor (not shown). Then, after being uniformly positively charged in the dark by the charging roller 2, the writing exposure 9 is irradiated and imaged based on the image information, and an electrostatic latent image is formed on the photosensitive drum 1. Then, the developing belt 31 on which the liquid developer is applied with a uniform film thickness by the applying device 20 having the applying roller comes into contact with the photosensitive drum 1 in the developing section.

In the developing section, a potential between the minimum value and the maximum value of the latent image potential on the photosensitive drum 1 is applied to the developing belt 31 by a high voltage power supply 38 via a pair of rotating rollers 35 and 36. ing. For example, a developing bias of +300 V is applied. The liquid developer on the developing belt 31 is transferred to the photosensitive drum 1 in a region where the potential of the electrostatic latent image on the photosensitive drum 1 is higher than the developing belt bias potential. In the low region, the toner does not transfer to the photosensitive drum 1 and remains on the developing belt 31. Thus, an image is formed on the photosensitive drum 1 by applying a developing bias to the developing belt 31 in the developing unit.

The image formed on the photosensitive drum 1 is transferred onto an intermediate transfer member 4 driven at the same speed as the photosensitive drum 1. The image transferred onto the intermediate transfer body 4 is transferred onto a transfer sheet P conveyed from a paper feed cassette (not shown) to a transfer unit.
The image is transferred by the transfer roller 7. And after the transfer is completed,
The transfer sheet P is fixed by a fixing unit (not shown) and is discharged to a discharge tray (not shown).

[Embodiment 1] Next, a description will be given of an embodiment in which the conditions for applying the bias output from the high-voltage power supply 61 are changed in the copying machine having the above configuration. The liquid developer used had a solid content of 15%, a developer dispersant content of 5%, a charge control agent content of 0.5%, and a carrier viscosity of 100 cSt based on the total weight. Alternating voltage output from high voltage power supply 61
(Hereinafter, referred to as “AC”) and direct current (hereinafter, referred to as “DC”) components: AC: DC = 1000V: 0V, 750
V: 250V, 500V: 500V, 250V: 750
V, 0 V: The transfer rate of the visualized particles corresponding to the optical density of the output image was measured while changing to 1000 V. If only the output of the high-voltage power supply 61 related to coating is changed and other conditions are the same, if the transfer rate of the visualized particles is high, many of the particles that develop color move on the paper, and as a result, the optical density of the image is reduced. This increases the image quality. Note that AC:
DC = 0V: 1000V corresponds to the result when only the DC power supply is used. The potential of each component was set to a maximum of 1000 V in consideration of the durability of the device itself against the voltage. The frequency of the AC component was 100 Hz, and only the magnitude of the potential was changed.

FIG. 3 is a graph showing the relationship between the change in the AC and DC components in the image formation performed under the above conditions and the transfer rate of the visualized particles. As shown in FIG.
From C: DC = 0V: 1000V to 600V: 400V, the transition rate is higher than when only the DC component is applied, and there is an effect of superimposing the AC component. However, AC: D
C = 600V: When the AC component after 400V is increased, the transition rate decreases. This is considered as follows.

As shown in FIG.
4 to the developing belt 31, the coating device 20
, A potential difference is applied from the high-voltage power supply 61 to the electric field, and the electric field forms a DC electric field in one direction, thereby moving the charged visualized particles.
In the Japanese Patent Application No. 11-208957, when the electric field forms a one-way DC electric field, the developer formed by the developer dispersant surrounding the visualized particles and the ion formed by the charge control agent. If the layer moves faster than the visualized particles, the movement of the visualized particles, which should originally be transferred, is prevented, and unless the coating time is increased, the visualized particles cannot be transferred sufficiently. It is known that the specified image density is not reached. The blocked visualized particles agglomerate on the application roller 24 in the opposite direction to the developing belt 31, that is, form a thin layer, and appear to be larger than the original visualized particles, and consequently move in the carrier. It becomes difficult.

By superimposing the potential difference of the AC component on the uniformly formed DC electric field, the visualized particles aggregated in a thin layer are loosened, and the particles are reduced to the size of the visualized particles themselves. It is considered that the movement of the developing belt 31 is increased as a result of the movement. Here, the potential difference of the DC component has an effect of forming an electric field necessary for the visualized particles to move from the application roller 24 to the developing belt 31. AC
The component has the effect of loosening the aggregates of the visualized particles formed by inhibiting the migration by the addition of the charge control agent or the developer dispersant, and increasing the transfer rate by making the transferable state. However, when AC: DC = 600V: 400V or higher, if the AC component is increased more than the DC component, the movement (repetitive movement) of loosening the aggregated thin layer rather than the movement in the direction in which the visualized particles should originally transfer. It is thought that the metastasis rate decreases as a result.

Embodiment 2 Next, an embodiment in which the frequency of the AC component is changed will be described. As in the case of Example 1 above, the solid content of the liquid developer was 15% of the total weight.
%, The developer dispersant fraction is 5%, and the charge control agent fraction is 0.5
% And a carrier viscosity of 100 cSt were used. FIG.
Means that the AC and DC components have the highest transfer ratio of the visualized particles from the results of Example 1 above: AC: DC = 250V: 75
It is a graph which shows the result of having set it to 0V and changing the frequency of the AC component, and measuring the transition rate. In the example of FIG. 4, the frequency of the AC component is 1 Hz, 5 Hz, 10 Hz, 50 Hz, 10 Hz,
The measurement was performed at 0 Hz, 250 Hz, and 400 Hz. FIG. 5 shows that AC and DC components are AC: DC = 500V:
It is a graph which shows the result of having set it to 500V and changing the frequency of the AC component, and measuring the transition rate. Further, FIG.
It is a graph which shows the result of having set the C and DC components to AC: DC = 200V: 800V, and changing the frequency of the AC components and measuring the transition rate.

When AC: DC = 250V: 750V, as shown in FIG. 4, the transition rate is about 60% from 1 Hz to less than 5 Hz, which is almost the same as the result of only the DC component. On the other hand, it gradually increased in the range of 5 Hz or more and 100 Hz or less, and started decreasing after exceeding 100 Hz. At 400 Hz, the transition rate was about 80%.
When AC: DC = 500V: 500V, as shown in FIG. 5, the transition rate is about 50% at 1 Hz or more and less than 5 Hz, which is almost the same as the result of only the DC component. On the other hand, it gradually increased in the range of 5 Hz or more and 80 Hz or less, and started decreasing after exceeding 80 Hz.
Further, when AC: DC = 200V: 800V, as shown in FIG. 6, the transition rate is about 75% at 1 Hz or more and less than 5 Hz, which is almost the same as the result of only the DC component. On the other hand, it gradually increased in the range of 5 Hz or more and 50 Hz or less, and started decreasing after exceeding 50 Hz. When the DC component increases (DC = 800 V), the fluctuation range of the transition rate with respect to the frequency change of the AC component becomes smaller than that in the case shown in FIGS. This is probably because the contribution of the DC component increases. On the other hand, as shown in FIG. 5, when the AC component increases (AC = 500 V), the effect of the application of the AC component appears remarkably, and the fluctuation range of the transition rate with respect to the frequency change increases.

From the above results, the frequency of the AC component is 5 Hz.
It was found that when the voltage was applied as described above, the transition rate was higher than when only the DC component was applied. This is considered as follows.

The aggregated visualized particles in the liquid developer are
It is considered that the particles were not sufficiently loosened at a frequency lower than 5 Hz, which was almost the same as the result of only the DC component. In order to loosen the agglomerated particles, it is considered that there is no effect unless vibration is performed at a certain frequency. In the case of the jumping development method of dry developer, AC is DC
And the frequency of the AC component is 40
It is about 0 Hz. In a dry developer, loosening of the particles is the purpose of applying AC. In the jumping development method using a dry developer, a visualization process is realized by superimposing DC on AC. It is considered that the same effect occurs in the process of applying the liquid developer to the developing belt 31 from the applying roller 24 in the present embodiment.

On the other hand, when the frequency is 100 Hz or more, the transition rate becomes saturated or becomes lower than the maximum value. FIG. 4 above
Although not shown in FIG. 6 to FIG.
When z exceeds z, the effect of increasing the transition rate by applying an alternating current is reduced as compared with bias application of only a direct current component.

As described above, in the copying machine according to the present embodiment, the transfer rate of the visualized particles is optimized by applying the coating bias in which the DC is superimposed on the AC in the coating process,
The image quality can be kept best on the final recording medium.
Also, even when a common coating apparatus is used between different models using liquid developers having different properties, by changing the application conditions of the coating bias between the AC component and the DC component, development of the visualized particles can be performed. It is possible to optimize the transfer onto the agent support and reduce the cost while maintaining the best image quality on the final recording medium.

[Second Embodiment] In the first embodiment, a copying machine for forming an image using a single-color liquid developer has been described. However, a full-color copying machine for forming a color image using four different liquid developers. It can also be applied to
FIG. 7A is a schematic configuration diagram of a main part showing a state in which a yellow liquid developer is applied to a developing belt by a yellow applying device in the full-color copying machine according to the present embodiment. Similarly, FIG. 7B shows a magenta liquid developer, and FIG.
FIG. 3 is a schematic configuration diagram of main parts showing a state where a cyan liquid developer is applied to a developing belt, and a black liquid developer is applied to a developing belt. Members that are substantially the same as or correspond to those in the first embodiment will be described using the same reference numerals.

First, an outline of the full-color copying machine according to the present embodiment will be described with reference to FIG. Around a photosensitive drum 1 as a latent image carrier, a charging roller 2
A developing unit 300, an intermediate transfer member 4, a neutralization lamp 5, a photosensitive drum cleaning unit 6, and the like are provided. Further, a transfer roller 7 and an intermediate transfer body cleaning unit 8 are provided as transfer means for transferring the developed image to a transfer sheet P as a final transfer material, facing the intermediate transfer body 4.

Each coating device is provided on an installation table (not shown). The installation device includes a yellow coating device 310, a magenta coating device 320, a cyan coating device 330, and a black coating device 340. Has been established. These coating devices can be brought into contact with and separated from the developing belt 301 by driving means such as a solenoid (not shown).
As a configuration of the coating device, for example, a yellow coating device 310
Is mainly composed of a developer pool 311 for storing a liquid developer and three application rollers 312, 313, and 314. This configuration is the same for coating devices of other colors.

The developer support comprises a developing belt 301, three rotating rollers 302, 303, and 304 for rotating the developing belt 301 while keeping the tension of the developing belt 301, and four sets each including a pair of rollers. Counter roller 305,
306, 307, and 308, and the rotating roller 304 is a driving roller. In the full-color copying machine according to the present embodiment, the surface moving speed of the developing belt 301 is kept constant. Further, the above four sets of opposed rollers 305, 306, 30 facing the application roller of each application device.
7, 308 (for example, 305a and 3)
05b), the coating nip widths are all the same.

Next, the operation of forming an image in the full-color copying machine having the above configuration will be described. As shown in FIG. 7A, the photosensitive drum 1 is driven to rotate in the direction of arrow B at a constant speed during image formation by a driving unit such as a motor (not shown). After being uniformly charged in the dark by the charging roller 2, an optical writing unit (not shown)
The writing light 9 is irradiated and imaged based on the image information, and an electrostatic latent image is formed on the photosensitive drum 1. This image information is monochromatic image information obtained by decomposing a desired full-color image into yellow, magenta, cyan, and black color information. And
A coating device of a desired color, which is disposed on a mounting table (not shown), comes into contact with the developing belt 301, and applies a liquid developer to the developing belt 30.
Apply to 1. The electrostatic latent image is developed with predetermined yellow, magenta, cyan, and black toners by the developing belt 301 rotating and abutting on the photosensitive drum 1 at the developing unit, and the electrostatic latent image is formed on the photosensitive drum 1. Each color image is formed.

Each color image formed on the photosensitive drum 1 is transferred to the intermediate transfer member 4 driven at the same speed as the photosensitive drum 1.
Above, for each single color of yellow, magenta, cyan, and black,
The images are sequentially transferred and superimposed. The yellow, magenta, cyan, and black images superimposed on the intermediate transfer member 4 correspond to the transfer paper P transported from a paper cassette (not shown) to the transfer unit.
Is collectively transferred by the transfer roller 7. After the transfer is completed, the transfer sheet P is fixed by a fixing unit (not shown) and is discharged to a discharge tray (not shown). In addition,
The liquid developer remaining on the photoconductor drum 1 that has not been transferred onto the intermediate transfer body 4 is removed by the cleaning blade 6 after the surface of the photoconductor drum 1 is removed of the residual potential by the charge removing lamp 5, and is then removed. For image formation. Further, the developer remaining on the developing belt 301 after passing through the developing unit is removed from the developing belt 301 by the cleaning blade 40.

Embodiment 3 Next, a more specific embodiment of the full-color copying machine according to the present embodiment will be described.
Developing device 3 configured to have the same coating nip width
Coating devices 310, 320, 330, 3
40, the application bias application conditions were made different for at least two or more liquid developers having different properties among the four color liquid developers, so that an optimum application bias was applied. Table 1 shows an example of the optimum coating bias for each color developer.

[0047]

[Table 1]

As a result of forming an image under the above conditions, as for the black developer, the average particle diameter of the visualized particles is relatively larger than that of the other colors, but using a coating apparatus having the same structure as the other colors. This is because, by changing the DC voltage, the AC peak-to-peak voltage, and the AC frequency, the best state can be given to the transfer of the visualized particles of the black developer. This makes it possible to control the final image density on the recording medium, and to make the machine relatively expensive without changing the coating apparatus in which each liquid developer having a different property is stored. By controlling the easily controllable bias, the image quality can be improved as a result.

In this embodiment, the bias application condition is changed according to the average particle size of the visualized particles. However, the image application is changed by changing the application condition according to the ratio of components other than the visualized particles such as the charge control agent. It is also possible to improve the quality.

[0050]

According to the first to sixth aspects of the present invention, a bias is applied to the liquid developer applied to the developer support by superimposing a direct current on an alternating current by the bias applying means. A jumping or loosening effect on the visualized particles in the liquid developer to improve the transfer amount of the visualized particles. Thereby, there is an excellent effect that the image density can be improved and the image quality can be kept at the best. Further, by configuring the coating means so as to obtain the above-mentioned overlapping optimal coating nip passage times for the liquid developers having the different properties, the coating means having the same configuration can be used, and the cost can be reduced. There is an excellent effect that reduction can be achieved.

In particular, according to the second aspect of the present invention, it is sufficient for at least two or more of the liquid developers of the plurality of colors to have different bias application conditions applied by the power supply. There is an excellent effect that an amount of the visualized particles can be transferred to the developer support to improve the image density and keep the image quality at the best.

In particular, according to the third aspect of the present invention, a bias application condition applied by the power source is applied to two or more liquid developers having different average particle diameters of visualized particles contained in the liquid developer. Are different from each other. This provides an optimum condition for applying each of the visualized particles, optimizes the transfer of the visualized particles onto the developer support, and optimizes the image quality on the final recording medium. There is an excellent effect that it becomes possible.

In particular, according to the fourth aspect of the present invention, it is possible to change the bias application condition by the adjusting means so that the transfer rate of the visualized particles contained in the liquid developer is maximized. Has an excellent effect.

In particular, according to the invention of claim 6, the frequency of the AC component of the bias applying means is 5 Hz or more and 40% or more.
Since the frequency is 0 Hz or less, a jumping or loosening effect of the visualized particles occurs, and the transfer amount of the visualized particles onto the developer support can be improved. This makes it possible to maintain the best image quality on the final recording medium.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a main part of a copying machine according to an embodiment.

FIG. 2 is an explanatory diagram of an enlarged main part of the developing device in FIG. 1;

FIG. 3 is a graph showing a relationship between a change in AC and DC components and a transition rate of a visualized particle.

FIG. 4 is a graph showing the relationship between the frequency of the AC component and the transition rate when AC: DC = 250V: 750V.

FIG. 5 is a graph showing the relationship between the frequency of the AC component and the transition rate when AC: DC = 500V: 500V.

FIG. 6 is a graph showing the relationship between the frequency of the AC component and the transition rate when AC: DC = 200V: 800V.

FIGS. 7A, 7B, 7C, and 7D are schematic diagrams of main parts of a full-color copying machine according to another embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 charging roller 3 developing unit 20 coating device 22 developer reservoir 23, 24 coating roller 25 developer amount regulating roller (coating roller) 31 developing belt 32, 33, 34, 35, 36, 37 rotating roller 40 Developing belt cleaning blade 60 Control device 61 High voltage power supply 300 Developing unit 301 Developing belt 310, 320, 330, 340 Coating device 305, 306, 307, 308 Opposing roller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AB02 AD16 AD19 BB02 BB23 BB27 BB34 BB42 BB44 BB54 BB71 2H073 AA02 BA04 BA09 BA13 BA41 BA45 CA22 CA32 2H074 AA03 AA04 AA41 AA44 BB02 BB50 BB54 CC28 EE07

Claims (6)

[Claims] 1. A developing means for visualizing a latent image formed on a latent image carrier using a liquid developer, and a coating means for applying a liquid developer in a thin layer on a developer support of the developing means. And a bias application unit for applying a bias to the coating unit, wherein the bias application unit has a power supply capable of applying a DC superimposed DC. Forming equipment. 2. The wet image forming apparatus according to claim 1, wherein said developing means includes liquid developers of a plurality of colors, and at least two or more of the plurality of liquid developers are applied by said power supply. A wet-type image forming apparatus, wherein the conditions for applying the bias are different from each other. 3. The wet image forming apparatus according to claim 2, wherein a bias applied by the power supply is applied to two or more liquid developers in which the visualized particles contained in the liquid developer have different average particle diameters. A wet image forming apparatus wherein conditions are different from each other. 4. The wet image forming apparatus according to claim 1, wherein said bias applying means has an adjusting means capable of changing a condition for applying a bias applied by said power supply. 5. The wet image forming apparatus according to claim 4, wherein said adjusting means comprises: a DC voltage applied by said power source;
A wet image forming apparatus, wherein at least one of an AC peak-to-peak voltage and an AC frequency can be changed. 6. A wet image forming apparatus according to claim 1, wherein the frequency of the AC component of said bias applying means is set to 5 Hz or more and 400 Hz or less. .