JP3479461B2 - Electrophotographic equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus using a liquid developer.

[0002]

2. Description of the Related Art As a developing method adopted for image formation in an electrophotographic apparatus, a dry developing method and a wet developing method are generally known.

In an electrophotographic apparatus using a wet development method, an electrostatic latent image is formed on a liquid developer prepared by dispersing toner particles made of carbon black coated with a resin in a solvent made of a petroleum solvent. Charged toner in the liquid developer by supplying the liquid developer to the surface of the latent image carrier by supplying the liquid developer between the surface of the formed latent image carrier and a counter electrode arranged at a constant distance from the surface. It is generally practiced to visualize an electrostatic latent image by utilizing the electrophoretic phenomenon of particles and then transfer the image onto an image carrier such as paper to form an image.

Compared with the dry developing method, such a wet developing method can use a very fine toner particle having a submicron size, so that high image quality can be realized and a sufficient image density can be obtained with a small amount of toner particles. Therefore, there are advantages that it is economical, that a texture equivalent to that of printing (for example, offset printing) can be realized, and that energy saving can be realized because toner particles can be fixed on paper at a relatively low temperature.

However, the conventional wet development method has some problems.

One of these problems is deterioration of image quality in the transfer process. That is, conventionally, the toner particles adhering to the latent image holding member are transferred by electric field directly to the paper in the transfer step, so that the transfer unevenness is caused by the electric field fluctuation according to the unevenness of the paper surface. In addition, transfer defects are apt to occur due to variations in electrical characteristics of paper and environmental dependence.

The second problem in the wet development method is an environmental problem due to the solvent adhering to the paper in the transfer process. In the electric field transfer of a liquid developer, toner particles, which are charged particles, move in a solvent by an electrophoretic phenomenon and are transferred onto a sheet. Therefore it is necessary to supply a substantial amount of solvent during the latent image holding member and the paper is in a field transfer. As a result, a large amount of solvent adheres to the paper after transfer. A part of this solvent volatilizes during the fixing process due to heat and is released to the outside of the machine, which causes a problem such as bad influence on the human body due to inhalation of odor and vapor.

[0008]

As described above, in the electrophotographic apparatus using the conventional wet developing method, the toner particles adhering to the latent image carrier are adhered to the paper by the method without using the intermediate transfer medium. Since the electric field was transferred directly, the transfer unevenness was caused by the electric field fluctuation according to the unevenness of the paper surface. In addition, transfer defects are apt to occur due to variations in electrical characteristics of paper and environmental dependence. There is also a problem that a large amount of the solvent contained in the liquid developer adheres to the paper and is easily discharged outside the apparatus.

It is an object of the present invention to provide an electrophotographic apparatus capable of suppressing the release of the solvent to the outside of the machine to a minimum, always having good transfer characteristics, and capable of realizing high-quality image output.

[0010]

The present invention SUMMARY OF THE INVENTION are provided a latent image forming means for forming an electrostatic latent image on the latent image bearing member, a liquid developer containing toner particles and a solvent to the electrostatic latent image Then, in an electrophotographic apparatus having a developing means for forming a toner image on the latent image holding member and a transfer means for transferring the toner image onto the image carrier by pressure, the electrophotographic device is provided at a position facing the transferring means. Of a cylindrical roller that comes into contact with the surface of the latent image holder on the side where the electrostatic latent image is not formed and absorbs the heat of the latent image holder
It is an electrophotographic apparatus having a heat absorbing roller having a cooling medium flowing inside a hollow .

In the electrophotographic apparatus of the present invention, since the toner image is transferred from the latent image carrier to the image carrier by pressure, unlike the conventional electric field transfer system, the transfer unevenness due to the electric field fluctuation according to the unevenness of the paper is caused. Does not occur. Further, unlike the electric field transfer method, it is not necessary to supply a solvent at the time of transfer, and a large amount of solvent does not adhere to the image carrier after the transfer is completed.

Further, as in the present invention, a cooling means is provided for providing a temperature difference between the surface of the latent image carrier and the surface of the image carrier to cool the surface temperature of the latent image carrier 1 below the surface temperature of the image carrier. By installing it, the adhesive force between the surface of the image carrier and the toner particles can be made relatively high, and the toner image is transferred from the surface of the latent image carrier to the image carrier when the transfer is performed by pressure. And the image quality after transfer is improved. This is because the toner particles contain a resin component and are in a higher temperature state, so that the toner particles have higher tackiness.

Regarding one toner particle on the latent image carrier, the solvent adhering to the image carrier side volatilizes, and a very small amount of solvent is present only at the interface between the latent image carrier and the toner particle. It is possible to easily create a state in which there remains.
The slight residual solvent assists the peeling of the toner particles, and when pressure is applied, the toner image is easily transferred from the surface of the latent image carrier 1 to the image carrier, and the image quality after transfer is improved.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to FIG. FIG. 1 is a schematic view showing an example of the electrophotographic apparatus of the present invention.

The latent image carrier 1 has a drum shape.
This is a photosensitive drum in which an organic or amorphous silicon photosensitive layer is provided on a conductive substrate. First, the latent image carrier 1 is uniformly charged by the charger 21. A corona charger, a scorotron charger, or the like can be used as the charger.

Further, the image-modulated laser beam 3
An electrostatic latent image is formed on the surface by the exposure of 1.

After that, the electrostatic latent image is visualized by the first developing device 41 containing the liquid developer. In the first developing device 41, a liquid developer in which toner particles are dispersed in a solvent is disposed on the surface of the latent image holding member 1 on which an electrostatic latent image is formed and at a constant distance from the surface. The liquid developer is supplied between the counter electrode and the liquid developer to bring it into contact with the surface of the latent image carrier, and the electrostatic latent image is visualized by utilizing the electrophoretic phenomenon of the charged toner particles in the liquid developer.

As materials for the toner particles, ethylene vinyl acetate copolymer, polyester resin, epoxy resin, rosin modified resin, paraffin wax, polyolefin,
Examples thereof include those containing a resin component such as a styrene-butadiene resin or an acrylic ester-based graft resin. Examples of the solvent include organic solvents such as isoparaffin-based isoper (Nixon Chemical), isododecane (British petroleum), IP solvent (Idemitsu Petroleum), and normal paraffin-based norper (Exxon Chemical).

The toner particles adhering to the electrostatic latent image may be directly transferred to the transfer step and transferred onto the image carrier such as paper by the pressure roller 8. However, here, the second charger 22 and the second charger 22 continue. Similar to the first developing device, the second developing device 42 that forms the second electrostatic latent image with the laser beam 32 and stores the second liquid developer of a color different from that of the first developing device 41 is used. To develop this.

Therefore, after the second development, two color toner images are formed on the latent image carrier 1. Similarly, the third and fourth developments are performed, and a full-color toner image is formed on the latent image holder 1. This toner image is transferred onto the image carrier 10 such as paper by the pressure of the pressure roller 8.

An electric field in the direction in which the toner image is transferred may be applied between the pressure roller 8 and the latent image carrier 1. Specifically, an electric field having a polarity opposite to that of the toner is applied from the latent image carrier to the pressure roller. By applying an electric field in the transfer direction, the solvent remaining at the interface between the slightly remaining toner particles and the latent image holding member has a function of assisting separation of the toner particles. In the present invention, the latent image holding member after transfer is cleaned by the cleaner 9, but the cleaner used at this time may have a blade shape or a roller shape.

In the electrophotographic apparatus of the present invention, the surface temperature on the latent image carrier 1 must be lower than the surface temperature of the image carrier 10. As a concrete means therefor, a means for cooling the latent image holder (latent image holder cooling means) may be provided. Further, a means for heating the image carrier may be further added.

As the latent image holding member cooling means, for example, FIG.
The solvent suction nozzle 12 is installed on the surface of the latent image holding member as shown in (3), and the gas near the surface of the latent image holding member is sucked to cool the solvent of the liquid developer remaining on the surface by evaporation heat.

As another means for cooling the latent image holding member, for example, as shown in FIG. 1, a heat absorbing roller 11 is installed at a position in contact with the inside of the latent image holding member 1 and facing the pressure roller 8. Means for cooling by absorbing the heat of the surface of the holding body can be mentioned. As the heat absorbing roller 11, it is preferable to use a metal having a large heat capacity. Also shown in FIG.
The figure which shows an example of 1 is given. In FIG. 2, (a) shows a side surface of the heat absorbing roller, and (b) shows a cross section of the heat absorbing roller. The heat absorbing roller 11 has a cylindrical shape, and a through hole 13 is provided inside thereof. Moreover, the efficiency of heat absorption can be improved by providing unevenness 14 on the cross section of the hole to increase the surface area. Further, the efficiency of heat absorption can be further increased by passing the cooling solvent or the cooling gas through the through holes. At this time, as the cooling solvent, the solvent removed by the cleaner 9 or the like may be reused or a liquid such as water may be used. The cooling gas may be air or a cooling medium such as CFC.

As another means for cooling the latent image carrier, a method may be used in which holes are provided on the side surface of the latent image carrier so that air can circulate between the inside and the outside of the latent image carrier.

As a means for heating the image carrier, for example,
This can be performed by providing means for heating the pressure roller 8.

The temperature of the surface of the latent image carrier varies depending on the composition of the liquid developer, but is preferably in the range of room temperature (20 ° C.) to 120 ° C. The temperature of the surface of the image carrier varies depending on the composition of the liquid developer, but is preferably in the range of room temperature (20 ° C.) to 150 ° C. Latent image holder 1
The temperature difference between the upper surface temperature and the surface temperature of the image carrier 10 varies depending on the composition of the liquid developer, but is preferably 5 ° C. or higher in order to stably develop the change in the adhesiveness of the resin.

When the latent image carrier 1 is cooled, it is desirable that the temperature of the latent image carrier 1 be below the boiling point of the solvent. As a result, it becomes easier to create a state in which the solvent remains only at the interface between the latent image carrier and the toner particles, and the image quality can be further improved.

When the image carrier 10 is heated, it is desirable that the temperature of the image carrier 10 is equal to or higher than the melting point or Tg of the toner particles. Thereby, the adhesiveness of the toner particles can be further increased, and the image quality after transfer can be improved.

[0030]

Example 1 An image was transferred onto a sheet using the electrophotographic apparatus shown in FIG. A solvent suction nozzle 12 was installed on the surface of the latent image carrier as a means for cooling the latent image carrier, and gas near the surface of the latent image carrier was sucked. Further, the heat absorbing roller 11 was installed at a position in contact with the inside of the latent image holder 1 and facing the pressure roller 8. The heat absorbing roller 11 has a shape as shown in FIG.

First, the latent image carrier 1 was uniformly charged by the charger 21, and was exposed to the image-modulated laser beam 31 to form an electrostatic latent image on its surface. After that, the electrostatic latent image is converted into a toner image by the first developing device 41 containing the liquid developer.

The toner image formed by adhering toner particles to the electrostatic latent image is directly transferred to the transfer step and transferred onto the paper as the image carrier 10 by the pressure roller 8.

The surface temperature of the latent image carrier 1 was adjusted to 30 ° C. and the surface temperature of the paper was adjusted to 50 ° C. by the action of the latent image carrier cooling means. The weight of the pressure roller was set to be 5 kg per A4 sheet width. As the liquid developer, Isopar L manufactured by Exxon Co. was used as a solvent, and a charged liquid developer based on a methyl methacrylate-butyl acrylate copolymer (Tg: 30 ° C.) was used as the toner particles.

The transfer efficiency of the toner image from the latent image carrier to the paper was 100%, and the dots having a diameter of 40 μm were also transferred without being crushed. Further, the initial image quality was maintained even after the continuous output of 1000 images. (Embodiment 2) The voltage in the direction in which the image on the latent image carrier is transferred to the sheet between the latent image carrier and the pressure roller during transfer (DC 800
The same experiment as in Example 1 was carried out except that (V) was applied, and the transfer efficiency from the latent image carrier to the paper was 100%, and the dots having a diameter of 40 μm were also transferred without being crushed. Further, the initial image quality was maintained even after the continuous output of 1000 images. Similar results were obtained even when the weight of the pressure roller was 1 kg. (Comparative Example 1) When the same experiment as in Example 1 was carried out without using the latent image carrier cooling means, the latent image carrier surface temperature was 48 ° C. The paper surface temperature was 50 ° C. In the output image, the transfer failure was noticeable, and at the stage of outputting about 100 sheets, the solid image was not transferred at all. Further, the weight of the pressure roller is set to 10 kg, and the pressure is set to 800 as in the second embodiment.
No effect was observed even when a DC current of V was applied.

[0035]

According to the present invention, the release of the solvent to the outside of the apparatus can be suppressed to the minimum, and the excellent transfer characteristics can always be realized and the high-quality image output can be realized.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an electrophotographic apparatus of the present invention.

FIG. 2 is a diagram showing an example of a heat absorbing roller.

[Explanation of symbols]

1 ... Latent image holder 21, 22, 23, 24 ... Charger 31, 32, 33, 34 ... Laser beam 41, 42, 43, 44 ... Developing device 8 ... Pressure roller 9 ... Cleaner 10 ... Image carrier 11 ... Heat absorbing roller 12 ... Solvent suction nozzle 13 ... Through hole 14 ... unevenness

Continuation of front page (56) Reference JP-A-3-111873 (JP, A) JP-A-4-44073 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15 / 16 G03G 15/10

Claims (2)

(57) [Claims] 1. A latent image forming means for forming an electrostatic latent image on a latent image holding member, a liquid developer containing toner particles and a solvent prior to
In the electrophotographic apparatus, the electrophotographic apparatus has a developing unit that supplies the electrostatic latent image to form a toner image on the latent image holding member, and a transfer unit that transfers the toner image onto the image carrier with pressure. A cooling medium inside the hollow of a cylindrical roller that absorbs the heat of the latent image holder by contacting the surface of the latent image holder on the side where the electrostatic latent image is not formed.
An electrophotographic apparatus having a heat-absorbing roller in circulation . 2. The heat absorbing roller from the developing means.
It is installed between the two and sucks gas near the surface of the latent image carrier.
Further comprising a solvent suction nozzle for
Item 1. The electrophotographic apparatus according to Item 1.