JP3456916B2 - Wet 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 a wet electrophotographic apparatus using a non-volatile, high-viscosity and high-concentration liquid toner, and more particularly to a developing roller capable of applying a uniform developing solution over the entire printing width. A wet electrophotographic apparatus.

[0002]

2. Description of the Related Art Electrophotographic devices that produce an electrostatic latent image on a photoconductor (photosensitive drum), attach toner to it, and then transfer and fix it on paper or the like are generally dry type using powder toner. It is used.

However, the powder toner has a problem that the toner is scattered, and the toner particles are 7 to 10 μm.
Since it is as large as m, there is a problem that the resolution is poor.

Therefore, when high resolution is required, a wet type using liquid toner is used. Liquid toner has small toner particles of about 1 μm,
Due to the large amount of charge, the toner image is less likely to be disturbed,
This is because a high resolution can be realized.

In a conventional wet electrophotographic apparatus, a low-viscosity liquid toner prepared by mixing a toner with an organic solvent at a ratio of 1 to 2% is used as a developing solution. However, since such a developing solution uses an organic solvent that is harmful to the human body and uses a large amount of it due to its low toner concentration, it has a serious problem of causing environmental problems.

Against this background, in International Publication No. "WO95 / 08792", a wet method using a high-viscosity and high-concentration developer formed by dispersing a high-concentration toner in silicone oil or the like is used. The invention of an electrophotographic apparatus has been disclosed. The use of this liquid toner has the advantages that it does not pose a problem of harming the human body and that it does not require the use of a large amount of developer because the toner concentration is high.

As disclosed in "International Publication No. WO95 / 08792", even when a developer of such a high-viscosity and high-concentration liquid toner is used, the same idea as in the case of using powder toner has been conventionally used. According to the above, a configuration is adopted in which the developing solution is applied to the developing roller or the developing belt, and the developing roller or the like is brought into contact with the photoconductor to adhere the toner to the photoconductor on which the electrostatic latent image is formed. Is taking.

As described above, the liquid toner developing solution is applied to the developing roller or the developing belt, and the electrostatic latent image on the photoconductor is developed using the developing roller or the developing belt. Has a problem that it is difficult to make uniform and apply it to the developing roller.

FIG. 8 shows an example of high-viscosity, high-concentration characteristics of the liquid toner usable in the present invention. In the figure, the horizontal axis represents the shear rate [1 / S], the vertical axis represents the shear stress [Pa] in the upper figure, and the viscosity [mPaS] in the lower figure.

A high-viscosity and high-concentration liquid toner has solid particles dispersed in a liquid carrier, and its viscous characteristics are complicated. The liquid toner shown as an example in FIG. 8 has an extremely high toner viscosity in a region where the shear rate is low. The viscosity was as high as 10000 [mPaS] in the low shear rate region, but decreased to 100 [mPaS] in the high shear rate region. This means that it looks stiff until a certain level of force is applied, but it suddenly begins to flow beyond that. It can be said that the yield point is high and the flow is bad.

The difficulty of supplying the liquid toner having such characteristics will be described with reference to FIG. Considering a case where the toner is to be spread in a certain range (span), for example, A4 width or A3 width, when the liquid toner advances inside the tube, the inside of the tube is as shown in FIG. A velocity profile has been formed. The velocity is 0 on the wall surface of the pipe, and the maximum velocity is at the center. What is shear rate?
Since it is the gradient in the lateral direction (y direction) of the velocity profile, in the case of the example, the shear velocity near the wall surface is large,
Moreover, the central portion is small, and a portion with a shear rate of 0 exists in the central portion. When a high-viscosity and high-concentration liquid toner is flown through such a pipe, the central portion is integrated because the shearing speed is low, resulting in a "plug flow" state in which only the wall surface flows.

In order to uniformly supply the liquid toner in such a state over a certain span, it is conceivable to form holes in the pipe at equal intervals as shown in FIG.
As shown in (a), in the case of a Newtonian fluid, its pressure distribution becomes higher as it gets closer to the pump, but becomes uniform. Therefore, by adjusting the size of the hole, it is possible to supply it uniformly over a span. Is possible. However, in the case of a fluid having high non-Newtonian fluid characteristics (high viscosity and high shear rate dependence) such as a high-viscosity and high-concentration liquid toner, as shown in FIG. There is a problem that the amount of toner that comes in becomes uneven. It is thought that this is because the pressure distribution in the pipe becomes non-uniform due to the toner flow.

A high-viscosity, high-concentration liquid toner has a very high dependence of viscosity on the shear rate. When such toner is introduced into the dynamic conveyance path, the movement of the toner affects the pressure distribution inside the conveyance path as described above, resulting in a local difference in the toner discharge amount, and It becomes unstable. This is because the kinetic energy due to the toner discharge exchanges energy with the pressure, and as a result, the pressure at the outflow temporarily drops sharply and then recovers to form a kind of stick-slip vibration system. Conceivable.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and there is a case where a liquid toner having a high viscosity and a high concentration, which is non-volatile, is used.
It is an object of the present invention to provide a new wet electrophotographic apparatus that allows a uniform developing solution to be applied to a developing roller over the entire printing width.

[0015]

The wet electrophotographic apparatus of the present invention uses a non-volatile, high-viscosity, high-concentration liquid toner as a liquid developer. This wet electrophotographic apparatus responds to a photoconductor 10 on which an electrostatic latent image is formed, a liquid developing solution which is brought into contact with the photoconductor 10 and which is generated between the photoconductor 10 and the photoconductor 10. The developing roller 25 for adhering the toner particles of the liquid developing solution to the photoconductor 10 and the two applicator rollers 26, 27 which are in contact with each other are used to supply the liquid developing solution to the two applicator rollers. A developing solution applying means for applying a film of a liquid developing solution to the developing roller 25 by applying the film to the developing roller 25 by applying one of the applicator rollers 27 to the developing roller 25 while extending the surface with 26 and 27. . This developing solution applying means is 2
The guide frames 28 to 30 for forming a substantially closed space having a predetermined width in the axial direction in cooperation with the two applicator rollers 26 and 27 are provided to the two applicator rollers 2.
6, 27, and the liquid developer is supplied into the closed space from a supply source at a substantially constant pressure.

According to the present invention, even a high-viscosity and high-concentration liquid toner (liquid having poor flow) is uniformly supplied over the entire printing width. This basic idea was obtained by analyzing the characteristics of a toner having a complicated viscoelastic behavior such as a high-viscosity and high-concentration liquid toner in detail and verifying it experimentally. . To solve this problem, the toner is statically confined and the pressure is evenly distributed over the toner so that the toner is spread and spread over the entire printing area. Therefore, it is possible to provide a special container for confining the toner and a means for filling the inside of the toner with a constant pressure and stopping the supply when a certain pressure is reached. As a result, it becomes possible to reliably supply the toner to the entire region even if the toner has a viscosity that extremely changes depending on the shear rate.

Further, in order to incorporate such a container structure that defines a closed space in the roller array, extremely high dimensional accuracy is required. The present invention enables control that requires as little accuracy as possible by devising the rotation of the roller and the drive timing of the pump.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail according to embodiments. FIG. 1 shows the overall structure of a wet electrophotographic apparatus on which the present invention is based.

As shown in this figure, the wet electrophotographic apparatus includes a photoconductor 10, a charging device 11, an exposure device 12, and
Pre-wetting device 13, developing device 14, intermediate transfer member 15, blade 16, charge eliminating device 17, and heating device 1
8 and a pressure roller 19.

The charging device 11 uses the photosensitive member 10 at about 700V.
To charge. The exposure device 12 forms an electrostatic latent image on the photoconductor 10 by exposing the photoconductor 10 with a laser beam having a wavelength of 780 nm so that the potential of the exposed portion becomes about 100V.

The pre-wetting device 13 is 2.5 cSt-2.
Silicone oil with a viscosity of 0 cSt is 4-5μ
The thickness of m is applied to the surface of the photoconductor 10. Here, the pre-wetting device 13 may perform the pre-wetting process before the exposure process performed by the exposure device 12, but may also perform the pre-wetting process after the exposure process.

The developing device 14 is provided in association with yellow / magenta / cyan / black, is biased to about 400 V, and has a toner viscosity of 400 to 4000 mPa · s.
S, a liquid toner having a carrier viscosity of 20 cSt,
By using a plurality of applicator rollers to convey the toner from the toner reservoir while spreading it thinly
A toner layer having a thickness of μm is formed. The developing roller supplies the toner particles, which are positively charged, to the photoconductor 10 according to an electric field between the photoconductor 10 and the developing roller, so that the exposed or unexposed portion of the photoconductor 10 charged to about 100 V is charged. Adhere toner particles. At that time, the pre-wetting device 1
According to the pre-wet layer 3 applied, toner particles can be prevented from adhering to the non-exposed portion of the photoreceptor 10.

The intermediate transfer member 15 is biased to about −800 V and follows the electric field between the intermediate transfer member 15 and the photosensitive member 10.
The toner attached to 0 is transferred. This intermediate transfer member 15
First, the yellow toner attached to the photoconductor 10 is transferred, the magenta toner attached to the photoconductor 10 is transferred, and the cyan toner attached to the photoconductor 10 is subsequently transferred. Is transferred, and subsequently, the black toner attached to the photoconductor 10 is transferred.

The blade 16 removes the toner and the prewetting liquid remaining on the photoconductor 10. The static eliminator 17 removes static electricity from the photoconductor 10.

The heating device 18 heats the surface of the intermediate transfer member 15 to melt the toner attached to the intermediate transfer member 15. The pressure roller 19 fixes the toner of the intermediate transfer body 15 melted by the heating device 18 to the print medium.
In this way, using the heating device 18 and the pressure roller 19,
Since the toner attached to the intermediate transfer body 15 is melted and fixed to the print medium without heating the print medium, print media other than paper can be handled.

FIGS. 2 and 3 show a first example of the toner supply structure, and FIG. 2 shows a developing roller 25 in contact with the photoconductor 10 and two applicator rollers 26, 27 for supplying a developing solution thereto. And FIG. 3 is a view for explaining the toner supply between the applicator rollers 26 and 27.

The developing roller 25 is in contact with the photoconductor 10 so as to maintain a two-layer structure with the prewetting liquid film on the photoconductor (photosensitive drum structure) 10, and supplies the liquid developer. Further, it is a roller that adheres the positively charged toner particles of the liquid developer to the surface of the photoconductor 10 according to the electric field between the photoconductor 10 and the photoconductor 10. Last stage applicator roller 2
7 cooperates with an applicator roller 26 that is rotationally driven from a motor through a gear to widely spread the developing solution introduced from the toner supply port 31 between both rollers to form a thin layer.
It is further applied to the surface of the developing roller 25.

Although the guide frames 28 to 30 are illustrated as being divided into three parts, the guide frames 28 and 30 on both sides in the axial direction of the roller have the same shape, and are arranged above the two applicator rollers 26 and 27. The projections 32 are provided on the lower surfaces of the guide frames 28 and 30 while being in contact with each other. The protrusion 32 is long in the roller axial direction and conforms to the shape of the nip between the rollers, and has a shape that fills the upper gap between the rollers 26 and 27.
Further, the central guide frame 29 is a plate-shaped member, and therefore, the guide frame 29 is formed by the rollers 26,
Both rollers 2 when installed on top of 27
A space is formed between 6 and 27. The axial length of the guide frame 29 corresponds to the printing width such as A4 width or A3 width. Note that the illustrated guide frames 28, 29, and 30 are configured to be divided into three and are integrally coupled, but they may be configured to be integrated. In short, the guide frame can be formed in any shape as long as it has a space for confining the toner limited to a predetermined width in the axial direction and the toner does not leak from both sides in the axial direction. .

The liquid toner is supplied from the toner container 36 into the toner supply port 31 by the tube pump 35 and into the space formed by the two applicator rollers 26, 27 and the guide frames 28, 29, 30 described above. It is introduced to fill the space there with liquid toner. The tube pump 35 is known per se, and the projection formed on the surface of the rotating cylindrical body deforms the liquid in the elastic resin tube from the outside of the tube to the tube so as to squeeze out the liquid. By adding it, it is sent forward.

With such a structure, the liquid toner is statically confined, and the toner can be spread and spread over the entire printing area while the pressure is uniformly applied to the entire toner. Thus, the liquid toner pressure must be high enough to spread throughout the print area, but not so high that liquid toner leaks between the guide frame and the rollers. Therefore, the present invention is provided with a means for stopping or controlling the supply by filling the inside of the toner with a constant pressure and stopping the supply pump when a certain pressure is reached. For that purpose, a pressure sensor for detecting that the pressure has reached a constant value is provided.

As shown in FIG. 3, the applicator rollers 26 and 27 are rotated in such a direction that both roller surfaces move downward at the abutting portions of both rollers.
At the contact portion between each of the rollers 26 and 27 and the central guide frame 29, the roller surface moves from the outside toward the internal space. For this reason, when the roller is rotating, the liquid toner trapped in the internal space is not supported by the roller and the central guide frame 29.
The structure is such that it does not easily leak from the abutting part with. In other words, when the liquid toner is supplied by the tube pump, the applicator rollers 26 and 27 are controlled to rotate, so that the accuracy of the member for confining the liquid toner such as the guide frame 29 is not increased.
It becomes possible to confine it with sufficient certainty. As the applicator roller, a rubber roller having a hardness of JISA 25 to 30 degrees can be used.

When the tube pump is stopped, it is desirable that the applicator rollers 26 and 27 are further rotated at least once and then stopped. As a result, the liquid toner, which is still maintained at a high pressure when the tube pump is stopped, is discharged from the roller and the guide frame 2.
It does not leak from the contact part with 9.

FIG. 4 shows a second example having the same structure as that of FIG. 3 but provided with a toner regenerating port. Excess liquid toner in the space surrounded by the guide frame and the two applicator rollers 26 and 27 can be returned to the toner container 36 by providing the regeneration port 33. As a result, it is possible to maintain the toner pressure at a predetermined value without providing a special configuration for detecting and controlling the pressure of the liquid toner in the enclosed space.

FIG. 5 shows an example of a pressure sensor for detecting the pressure of the liquid toner in the enclosed space. The left side of the figure is a view seen from the end portion in the axial direction of the applicator roller, and the right side of the figure is a cross-sectional view taken at the center of the pressure sensor. The actuator 38 tends to move downward due to its gravity, but moves upward according to the pressure of the liquid toner filled in the space surrounded by the guide frame and the two applicator rollers. The movement of the actuator can be detected by an optical detector including, for example, a light emitting diode and a photodiode.

FIG. 6 is a sectional view similar to FIG. 5, but showing the actuator mounted laterally. In this case, it is not the gravity of the actuator 38 that opposes the pressure of the liquid toner, but the flexible elastic member 39.
Is. Similar to the case of FIG. 5, by combining with an optical detector or the like, it becomes possible to detect the pressure of the liquid toner regardless of the arrangement posture of the applicator roller.

FIG. 7 is a third example showing the same configuration as the first and second examples except for the toner supply means.
Liquid toner from the toner container 36 is transferred to the applicator rollers 26 and 27 and the guide rollers 28 to 30 as in the above-described example.
In this example, a gravitational driving force such as the weight 40 is used to supply the toner. This makes it possible to keep the toner pressure constant with a simple structure.

[0037]

According to the present invention, since the toner is statically confined and the pressure is evenly applied to the entire toner, the toner is spread and spread over the entire printing area. As for the toner, the liquid toner can be uniformly supplied over the entire printing width.

Further, by providing a means for filling the toner at a constant pressure in the confined space and stopping the supply when a certain pressure is reached, the toner whose viscosity changes extremely depending on the shear rate Even in this case, it becomes possible to reliably supply the toner to the entire area.

Further, in order to incorporate the structure of the container forming such a space into the roller array, usually, extremely high dimensional accuracy is required. However, according to the present invention, the rotation of the roller or the pump is used. By devising the drive timing,
It is possible to enable control that does not require much precision.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a wet electrophotographic apparatus of the present invention.

FIG. 2 is a diagram illustrating a first example of a toner supply configuration, showing a developing roller that contacts a photoconductor and two applicator rollers that supply a developing solution to the developing roller.

FIG. 3 is a diagram for explaining toner supply between two applicator rollers in the first example shown in FIG.

FIG. 4 is a diagram illustrating a second example illustrating toner supply similar to that of FIG.

FIG. 5 is a diagram showing an example of a pressure sensor for detecting the pressure of the liquid toner in the enclosed space.

FIG. 6 is a diagram showing another example of the pressure sensor when the actuator is mounted in the lateral direction.

FIG. 7 is a diagram showing a third example showing a toner supply configuration similar to the first and second examples except for the toner supply unit.

FIG. 8 is an example of a high-viscosity and high-concentration characteristic of the liquid toner usable in the present invention.

FIG. 9 is a diagram showing a velocity profile inside a tube.

FIG. 10 is a diagram for explaining a state of fluid being blown out from a hole formed in a pipe.

[Explanation of symbols]

10 Photoconductor (drum) 11 Charging device 12 Exposure equipment 13 Prewetting device 14 Developing device 15 Intermediate transfer body (roller) 16 blades 17 Static eliminator 18 heating device 19 Pressure roller 25 developing roller 26 Applicator Roller 27 Applicator Roller 28 Guide frame 29 Guide frame 30 guide frame 31 Toner supply port 32 protrusion 33rd birth mouth 35 tube pump 36 toner container 38 Actuator 39 Elastic member 40 weight

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Uno-nu, 98, Unoki-cho, Hebei-gun, Kawakita-gun 2 PIE Co., Ltd. (72) Inventor Masahisa Takahata 98 Uno-nu, Unoku-cho, Hebei-gun, Ishikawa Prefecture No. 2 No. 2 Inoue, PFU Co., Ltd. (72) Genji Ichida Unoki Nu, character, Unoki-cho, Hebei-gun, Ishikawa Prefecture 98 No. 2 No. Nu-Inu, P 72, Inc. Inventor, Shigeharu Okano, Unoki-nu, Heki-gun, Ishikawa Prefecture No. 98 No. 2 PFI Co., Ltd. (72) Inventor, Yasukazu Takeda Uno-nu, Unoku-cho, Hebei-gun, Ishikawa Prefecture No. 98 No. 2 PFU Co., Ltd. (56) Reference JP-A-7-271195 (JP, A) JP-A-8-110741 (JP, A) Special table HEI 7-500679 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/10

Claims (9)

(57) [Claims] 1. A wet electrophotographic apparatus using a non-volatile, high-viscosity, high-concentration liquid toner as a liquid developer, comprising: an image support on which an electrostatic latent image is formed; and an image support on the image support. A developing roller which supplies liquid developer in contact with the image carrier and adheres toner particles of the liquid developer to the image carrier in accordance with an electric field generated between the liquid carrier and the image carrier; It is composed of two rotating rollers, and the liquid developing solution supplied is applied to the surface while being stretched by the two rotating rollers, and one of the rotating rollers is brought into contact with the developing roller to form a film of the liquid developing solution. A developing device for applying a developing solution to the developing roller, wherein the developing solution applying device cooperates with the two rotating rollers to form a guide frame for forming a virtually closed space having a predetermined width in the axial direction. , The two above Brought into contact with the rotating roller, for supplying the liquid developer to the closed space in the substantially constant pressure from a supply source, liquid electrophotography apparatus characterized by. Wherein providing a pressure sensor for detecting the pressure of the liquid developer of the closed space, it is detected that the pressure reaches a certain value, according to claim 1 for preventing excessive supply of the liquid developer The wet electrophotographic apparatus according to 1. 3. The supply of liquid developer to the closed space,
The wet electrophotographic apparatus according to claim 1 , wherein the wet electrophotographic apparatus is performed using a pump. 4. performs using a pump supplying the liquid developer to said closed space, when it is supplied by the pump is controlled to rotate the two rotating rollers 請
Wet electrophotographic apparatus according to Motomeko 1. 5. The wet electrophotographic apparatus according to claim 4 , wherein when the supply by the pump is stopped, the two rotating rollers are stopped after further rotating at least once. 6. The wet electrophotographic apparatus according to claim 1 , further comprising means for returning excess liquid developer in the closed space to the supply source to maintain the pressure in the closed space substantially constant. . 7. The wet electrophotographic apparatus according to claim 2 , wherein the pressure sensor includes an actuator that moves according to pressure and an optical sensor that detects the movement of the actuator. 8. The actuator comprises an elastic member,
The wet electrophotographic apparatus according to claim 7 , wherein the wet electrophotographic apparatus moves according to the pressure of the liquid developer and the elastic force of the elastic member that opposes the pressure. 9. The liquid developer supply to the closed space,
The wet electrophotographic apparatus according to claim 1 , wherein the wet electrophotographic apparatus is performed by using a gravitational driving force such as a weight.