JPH10312112A - Wet type image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent the surface staining of a non-image part at the time of making an electrostatic latent image visualizable with a liquid developer whose concentration and viscosity are high by applying an alternating voltage to a developer carrier, so as to develop the electrostatic latent image on a photoreceptor. SOLUTION: A developing means 5 is provided with a developing belt 51 which is wound on plural rotary rollers 52-54 and moved counterclockwise at the same surface moving speed as that of a photoreceptor drum 1, a developer coating roller group 57 for coating the developing belt 51 with the liquid developer 56 in a developer puddle 55, to form a thin layer of the liquid developer 56 and a belt cleaning blade 58. As a developing bias, the alternating voltage is applied to the developing belt 51 by an alternating-bias applying means 59. Thus, the alternating voltage in a mixed state of DC and AC components is applied to the belt 51, to prevent toner from sticking to the non-image part, at the time of developing the electrostatic latent image on the drum 1, so that the surface staining can be prevented.

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 for visualizing an electrostatic latent image formed by an electrophotographic method using a liquid developer, and more particularly, to the prevention of background contamination in a non-image area. is there.

[0002]

2. Description of the Related Art An image forming apparatus for visualizing an electrostatic latent image using a high-viscosity, high-concentration liquid developer is disclosed in, for example, Japanese Patent Application Laid-Open No.
No. 209922 and JP-A-7-239615. In this image forming apparatus, as shown in FIG. 6, the photosensitive drum 1 is uniformly positively charged by the charging roller 2 and then the pre-wet liquid reservoir 31 of the pre-wet liquid applying means 3
A pre-wet liquid 32 such as dimethylpolysiloxane oil or the like having a releasability and a chemical inertness stored in the photosensitive drum 1 is applied to the photoreceptor drum 1 by a pre-wet liquid application roller group 33 on the photosensitive drum 1. The photosensitive drum 1 coated with a uniform thickness and coated with the pre-wet liquid 32 is exposed to writing light 4 to form an electrostatic latent image. When this electrostatic latent image is formed, the portion of the surface of the photosensitive drum 1 that has been exposed to light loses its charge, and the portion of the surface that has not been exposed to light remains as an electrostatic latent image. This electrostatic latent image is visualized by the developing means 5.

The developing means 5 is a high-viscosity liquid developer in which toner, which is visualized particles, is dispersed at a high concentration in a developer solvent made of an insulating liquid such as dimethylpolysiloxane oil. A liquid developer 56 in a developer reservoir 55 is applied to a developing belt 51 wound around a plurality of rotating rollers 52, 53, 54 by a developer applying roller group 57 to visualize the image. To form a thin layer of the liquid developer 56. A DC bias is applied to the developing belt 51 by a bias applying unit (not shown). The surface moving speed of the developing belt 51 is set to be equal to the surface moving speed of the photosensitive drum 1 so that a normal image is formed in the developing area. The thin layer of the liquid developer on the developing belt 51
When the toner passes through the developing area in close proximity to the photosensitive drum 1, the charged toner contained in the liquid developer layer is moved to the image portion of the photosensitive drum 1 by electrostatic force and adheres to the toner to visualize the toner. Also, no electrostatic force acts on the toner contained in the liquid developer layer that comes into contact with the non-image portion where the charge on the surface of the photosensitive drum 1 has disappeared,
In addition, since the surface of the photosensitive drum 1 and the liquid developer layer are separated by the pre-wet liquid layer, toner does not adhere to the non-image portion, and the background is prevented from being stained to prevent the image from being deteriorated. The toner image formed on the photosensitive drum 1 is transferred onto the transfer paper 7 conveyed by the transfer roller 6 to which a bias is applied. After the transfer step, the residual toner on the photosensitive drum 1 is removed by the cleaning blade 8, and the residual potential on the photosensitive drum 1 is erased by the discharging lamp 9.
The residual toner on the developing belt 51 that has passed through the developing area is removed by a belt cleaning blade 58.

[0004]

As described above, when an electrostatic latent image on a photosensitive drum is visualized with a high-viscosity liquid developer in which toner is dispersed at a high concentration, background contamination of a non-image portion is caused. Although the pre-wet liquid is applied to the photoreceptor drum in order to prevent the occurrence of the contamination, the background contamination may not be reliably prevented even if the pre-wet is applied.

SUMMARY OF THE INVENTION The present invention has been made to solve such a disadvantage, and it is an object of the present invention to surely prevent background contamination of a non-image portion when an electrostatic latent image is visualized with a high-density, high-viscosity liquid developer. It is an object of the present invention to obtain a wet type image forming apparatus capable of performing the following.

[0006]

SUMMARY OF THE INVENTION A wet image forming apparatus according to the present invention applies a transparent pre-wet liquid having a dielectric property to a photosensitive member before visualizing an electrostatic latent image formed on the photosensitive member. Then, in a wet image forming apparatus for developing an electrostatic latent image of a photoconductor with a charged toner contained in a high-concentration liquid developer applied in a thin layer on a developer carrier, and transferring the electrostatic latent image to a recording medium, An alternating voltage is applied to the agent carrier to develop an electrostatic latent image on the photoconductor.

It is desirable that the time average voltage of the alternating voltage applied to the developer carrying member has a polarity such that the toner moves to the image area of the electrostatic latent image on the photosensitive member.

[0008] The amplitude voltage, which is the range of change between the minimum voltage and the maximum voltage of the alternating voltage applied to the developer carrying member, is at least equal to or more than, preferably, about twice the charging potential difference between the image area and the non-image area of the photosensitive member. Good to be.

The alternating frequency f (Hz) of the alternating voltage applied to the developer carrier and the developing speed V (mm / sec)
Is desirably f / V ≧ 1 and the alternating frequency f is 1 kHz or less.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A wet image forming apparatus according to the present invention comprises:
After the photosensitive drum is uniformly charged by the charging roller, the pre-wet liquid is applied with a uniform thickness by a pre-wet liquid applying unit. The photosensitive drum coated with the pre-wet liquid is exposed to form an electrostatic latent image, and the electrostatic latent image is visualized by developing means to form a toner image. The formed toner image is transferred to a transfer sheet by a transfer roller, the residual toner on the photosensitive drum is removed by a cleaning blade, and the residual potential on the photosensitive drum is erased by a discharge lamp.

The developing means has a developing belt which is wound around a plurality of rotating rollers and moves at the same surface moving speed as the surface moving speed of the photosensitive drum. A thin layer of a developer is formed, and toner is adhered to the electrostatic latent image on the photosensitive drum with a liquid developer for development. An alternating voltage obtained by combining an AC voltage component and a DC voltage component that does not fluctuate with time is applied to the developing belt as a developing bias. The AC component of the alternating voltage applied to the developing belt prevents toner from adhering to the non-image portion of the electrostatic latent image on the photosensitive drum, thereby reducing background contamination.

As described above, when the alternating bias is applied to the developing belt, the DC component has a polarity such that the toner moves to the image portion of the photosensitive drum, so that the image may be disturbed when the alternating bias is applied. Prevents image density from decreasing.

Further, by making the amplitude of the AC component of the alternating bias applied to the developing belt equal to or greater than the potential difference between the image portion and the non-image portion of the electrostatic latent image on the photosensitive drum, toner attached to the non-image portion can be reduced. To reduce background fouling. By setting the amplitude of the AC component to about twice the potential difference between the image portion and the non-image portion of the electrostatic latent image on the photosensitive drum, it is possible to form a stable image with less background contamination.

Further, if the frequency of the AC component of the alternating bias applied to the developing belt is less than the developing speed, density unevenness occurs. Therefore, the frequency f (Hz) of the AC component is set to f / V ≧ 1 with respect to the developing speed V (mm / sec). Also,
If the frequency of the AC component is too high, the effect of the AC component is lost. Therefore, the alternating frequency is set to 1 kHz or less to obtain a good image free from background contamination.

[0015]

FIG. 1 is a block diagram of one embodiment of the present invention.
As shown in the figure, a charging roller 2, a pre-wet liquid coating unit 3, a developing unit 5, a set roller and a charging roller 2 arranged along a photosensitive drum 1 rotating clockwise in an image forming / transferring unit of a wet image forming apparatus. 1, a transfer roller 6, a cleaning blade 8, and a discharge lamp 9. Photoconductor drum 1
Is a liquid having releasability and chemically inert dielectric properties, which is uniformly charged, for example, by the charging roller 2 and then stored in the pre-wet liquid reservoir 31 by the pre-wet liquid applying means 3;
For example, dimethylpolysiloxane oil has a viscosity of 0.5 to 1
A pre-wet liquid 32 having a thickness of about 000 Pa · S and an electric resistance of 10 ¹² Ωcm or more is applied with a uniform thickness by a pre-wet liquid application roller group 33. The photosensitive drum 1 coated with the pre-wet liquid 32 is exposed to writing light 4 to form an electrostatic latent image. The electrostatic latent image is visualized by developing means 5 to form a toner image, and the formed toner image is electrically solidified by a set roller 10 to which a predetermined voltage is applied, and then transferred onto transfer paper 7 by transfer roller 6. Transcribe. The residual toner on the photosensitive drum 1 is removed by a cleaning blade 8, and the residual potential on the photosensitive drum 1 is erased by a charge removing lamp 9.

The developing means 5 includes a plurality of rotating rollers 52,5.
Developing belt 51 wound counterclockwise at the same surface moving speed as the surface moving speed of the photosensitive drum 1
And the liquid developer 56 in the developer pool 55 with the developing belt 5
1 and a developer cleaning roller group 57 for forming a thin layer of the liquid developer 56 and a belt cleaning blade 58. The developing belt 51 is provided with an alternating bias applying unit 5.
9, an alternating voltage is applied as a developing bias. Here, the alternating voltage refers to a voltage obtained by combining an AC voltage component and a DC voltage component that does not fluctuate with time. The alternating voltage applied to the developing belt 51 is not limited to a sine wave but may be a triangular wave, a sawtooth wave, a rectangular wave, or the like. Either is acceptable.

An alternating bias applying means 5 is applied to the developing belt 51.
As a method of applying the alternating voltage from the
In the case where a material having a low resistance value is used as 1, the effective voltage is hardly attenuated even when an alternating voltage is applied from a place a little distant from the development area in contact with the photosensitive drum 1, as shown in FIG. As described above, the rotating roller 53 around which the developing belt 51 is wound is formed of a conductive material, and an alternating voltage is applied to the axis of the rotating roller 53 by an alternating bias applying means 59, or as shown in FIG. An alternating voltage is applied by the bias roller 60 on the upstream side of the developing area of the developing belt 51. Further, the electric resistance of the developing belt 51 is large,
In the case where the alternating voltage is applied from the bias roller 60 on the upstream side of the developing region 3 or the developing region, the voltage loss increases.
As shown in (b), a bias roller 60 is provided on the back side of the developing belt 51 in the developing area to apply an alternating voltage.

By applying an alternating voltage in which a DC component and an AC component are mixed to the developing belt 51, toner is adhered to a non-image portion when an electrostatic latent image on the photosensitive drum 1 is developed. It has been confirmed that this can be prevented and the background dirt can be reduced.

For example, when the developing belt 51 is made of a polyimide resin mixed with carbon and having an electric resistance of 10 ¹ Ω · cm or less, a case where a DC voltage is applied to the rotating roller 53 and a case where an alternating voltage is applied are used. FIG. 3 shows a result obtained by developing the electrostatic latent image on the photosensitive drum 1 with the liquid developer 56 and examining changes in optical densities of the non-image portion and the image portion when the developed image is transferred to transfer paper. In FIG. 3, A is the optical density of the non-image area when only a DC bias is applied to the developing belt 51, and B is the optical density of the non-image area when an alternating bias obtained by combining a DC voltage and an AC voltage is applied to the developing belt 51. Optical density, C indicates the optical density of the image area when only a DC bias is applied to the developing belt 51, and D indicates the optical density of the image area when an alternating bias of DC voltage and AC voltage is applied to the developing belt 51. The non-image portion of the photosensitive drum 1 is approximately
The image portion was charged to about 700 V, and the image portion was charged to about 0 to 100 V. The alternating bias applied to the developing belt 51 was developed by changing the DC bias while keeping the amplitude of the AC component constant at 1500 V and the frequency at 100 Hz.

Normally, when only a DC bias is applied as a developing bias to the developing belt 51, development is started at a DC bias of about +150 V, and toner moves to an image portion on the photosensitive drum 1. At this time, the difference between the optical density of the non-image area when only the DC bias was applied and the optical density of the background of the transfer paper was about 0.04, whereas the difference when the alternating bias was applied was about 0.02. When the DC bias is increased, the optical density of the image portion does not change significantly as shown in FIGS. 3C and 3D, but as shown in A, the optical density of the non-image portion when only the DC bias is applied. Concentrations increase gradually, and background dirt increases. On the other hand, when the alternating bias is applied, the optical density of the non-image portion hardly changes even when the DC bias is increased to about 400 V, and the background contamination is greatly reduced as compared with the case where only the DC bias is applied. Was completed. As described above, when the alternating bias is applied to the developing belt 51, the DC component has a polarity such that the toner moves to the image portion of the photosensitive drum 1, so that when the alternating bias is applied, the DC bias is about 400V. No increase in the image density or image density was observed.

Next, the DC component of the alternating bias is set to +150 V
FIG. 4 shows the result of examining the change in the optical density of the non-image portion when developing the electrostatic latent image while changing the amplitude with the frequency of the AC component being 100 Hz while keeping the constant of the AC component. In FIG. 4, E is the optical density of the non-image portion when only the DC bias is applied, F is the optical density of the background of the transfer paper, and G is the optical density of the non-image portion when only the amplitude of the AC component is changed. As shown in FIG. 4, as the amplitude of the AC component is increased, the optical density of the non-image portion is reduced, and the background smear is reduced. The degree of the decrease in the optical density of the non-image portion decreases almost linearly when the amplitude of the AC component is reduced to approximately 700 V, gradually decreases when the amplitude of the AC component is increased from approximately 700 V to approximately 1500 V, and decreases when the amplitude increases to approximately 1500 V. Becomes almost constant. At this time, the potential difference between the image portion and the non-image portion of the electrostatic latent image on the photosensitive drum 1 is about 700
Since the voltage is V, the amplitude of the AC component is preferably equal to or larger than the potential difference between the image portion and the non-image portion of the electrostatic latent image on the photosensitive drum 1 in order to eliminate background contamination. Even if the amplitude of the AC component exceeds a certain limit, the optical density of the non-image portion becomes almost constant. It is about twice. Therefore, by setting the amplitude of the AC component to about twice the potential difference between the image portion and the non-image portion of the electrostatic latent image on the photosensitive drum 1, a stable image with little background contamination can be formed.

Next, the DC component of the alternating bias is increased by +150.
V, and the amplitude of the AC component of the alternating bias applied to the developing belt 51 is fixed at 1500 V, which is about twice the potential difference between the image portion and the non-image portion of the electrostatic latent image on the photosensitive drum 1, and the frequency is changed. FIG. 5 shows the result of examining the change in the optical density of the non-image area when the electro-latent image was developed. In FIG. 5, E is the optical density of the non-image portion when only the DC bias is applied, and H is the optical density of the non-image portion when only the frequency of the AC component is changed. In FIG. 5, the developing speed, that is, the moving speed of the photosensitive drum 1 was 100 mm / sec. However, when the frequency of the AC component was less than 100 Hz, density unevenness occurred in the formed image in proportion to the frequency of the AC component. When the frequency of the AC component became 100 Hz or more, the density unevenness of the formed image became a level that could not be confirmed with the naked eye. Also,
When the frequency of the AC component exceeds 1 kHz, the optical density of the non-image portion increases, and when the frequency becomes about 10 kHz, it is no different from the case where only a DC bias is applied to the developing belt 51. Therefore, the frequency f (Hz) of the AC component is determined by the developing speed V (mm / s).
ec), f / V ≧ 1 and the alternating frequency f is 1 k
Hz or less is desirable for obtaining a good image.

Although the above embodiment has been described with reference to the case where the developing belt 51 is used as the developing means 5, the present invention can be similarly applied to a developing means having a developing roller.

[0024]

As described above, according to the present invention, an alternating voltage obtained by synthesizing an AC voltage component and a DC voltage component that does not fluctuate with time is applied as a developing bias. Since the toner is prevented from adhering to the non-image portion of the latent image, it is possible to form a high-quality image without background contamination.

Further, when the alternating bias is applied as a developing bias, the DC component has a polarity such that the toner moves to the image portion of the photoreceptor. Can be prevented from becoming thin.

Further, by making the amplitude of the AC component of the alternating bias applied as the developing bias equal to or larger than the potential difference between the image portion and the non-image portion of the electrostatic latent image on the photosensitive member, toner attached to the non-image portion is reduced. As a result, background dirt can be reduced. Further, by setting the amplitude of the AC component to be about twice the potential difference between the image portion and the non-image portion of the electrostatic latent image on the photoconductor, a stable image with less background smear can be formed.

Further, the frequency f (Hz) of the AC component of the alternating bias applied as the developing bias is changed to the developing speed V (m).
By setting f / V ≧ 1 with respect to m / sec) and 1 kHz or less, it is possible to stably obtain a good image free from background contamination.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is another configuration diagram of a developing unit.

FIG. 3 is a graph showing optical density change characteristics of an image portion and a non-image portion with respect to a DC bias.

FIG. 4 is a graph showing an optical density change characteristic of an image portion and a non-image portion with respect to the amplitude of an AC component.

FIG. 5 is a graph showing optical density change characteristics of an image portion and a non-image portion with respect to the frequency of an AC component.

FIG. 6 is a configuration diagram of a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 charging roller 3 pre-wet liquid applying means 5 developing means 6 transfer roller 51 developing belt 59 alternating bias applying means

Claims (4)

[Claims] 1. A method for applying a transparent pre-wet liquid having a dielectric property on an image carrier before visualizing the electrostatic latent image formed on the photoconductor, and then applying a thin layer on the developer carrier. In a wet image forming apparatus that develops an electrostatic latent image on a photoreceptor with a charged toner contained in a high-concentration liquid developer and transfers the latent image to a recording medium, an alternating voltage is applied to a developer carrying member to form a photoreceptor. A wet image forming apparatus, which develops an electrostatic latent image. 2. The wet image forming method according to claim 1, wherein the time average voltage of the alternating voltage applied to the developer carrying member has a polarity such that the toner moves to the image area of the electrostatic latent image on the photosensitive member. apparatus. 3. An amplitude voltage, which is a change width between a minimum voltage and a maximum voltage of an alternating voltage applied to the developer carrying member, is at least equal to or more than twice as large as a charging potential difference between an image area and a non-image area of the photoconductor. 3. The wet image forming apparatus according to claim 2, wherein: 4. The relationship between an alternating frequency f (Hz) of an alternating voltage applied to the developer carrying member and a developing speed V (mm / sec) is f / V ≧ 1, and the alternating frequency f is 1 kHz or less. The wet image forming apparatus according to claim 3.