JPH05224536A - Wet type electrophotographic developing device - Google Patents

Abstract

PURPOSE:To attain uniform development by stable sticking of toner together with the stability of a developing bias voltage, by circulating a liquid excellent in renewal with a reduced quantity of developing liquid to be sent. CONSTITUTION:Developing room sidewalls 50 made of resin are provided on both sides of a rear guide 10, developing gap side surfaces under developing electrodes 32 and 36 are sealed with a part of the sidewalls, and the other parts of the sidewalls 50 have the same height as that of the conveying surface of a printing plate. At this time, it is necessary that a developing gap is always filled with a liquid, and when a developing liquid flows out from the side surface, the quantity of the liquid to be sent is required to be increased by the quantity of the outflow, so that the developing room sidewalls 50 are provided to prevent the outflow of the developing liquid. When a photosensitive material intrudes into a developing room whose side surfaces are sealed, an apparent developing gap is made small, and the quantity of the liquid to be sent, required before the intrusion, becomes excessive. The excessive developing liquid can be discharged from the parts of the developing room sidewalls 50 on almost a level with the rear guide 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a developing electrode and a developing chamber of a wet electrophotographic developing device for developing an electrophotographic photosensitive material on which an electrostatic latent image is formed with a developing solution (toner solution).

[0002]

2. Description of the Related Art FIG. 8 shows the structure of a conventional general wet electrophotographic developing apparatus, which is a rear guide 1 made of an insulating material.
00 is inclined by a predetermined angle, and the back guide 1
00, a developing electrode 101 is provided with a predetermined developing gap. The developing electrode 101 is biased to 150 [V] to 200 [V] by the bias power source 102, and the electrophotographic photosensitive material 120 on which the electrostatic latent image is formed in the exposure section (not shown) is back-guided together with the developing solution 110. It is designed to be conveyed in the developing gap above 100 for development. The electrophotographic photosensitive material 120 includes a support layer 121 made of a conductive material such as aluminum and an OPC (O
The photosensitive layer 122 is made of an organic photoconductor (organic photoconductor) and is formed into a plate shape, and the support layer 121 is grounded and developed.

In the reversal development method, toner adheres to the exposed portion (image portion) of the photosensitive layer 122, and the portion of the photosensitive layer 122 charged with positive charges (non-image portion) is chemically etched to form an image. To be done. In reversal development, in order to prevent fogging, the developing bias voltage value must be set lower than the surface potential of the non-image area of the photosensitive material. Therefore, the developing bias voltage is selected between the surface potential of the non-image portion and the surface potential of the image portion (actually, not zero but a little potential remains, which is referred to as residual potential), and the bias voltage and the non-image portion are selected. Alternatively, it is usual that there is a sufficient potential difference between both potentials in the image area. Therefore, in the developing section, the photosensitive material 1
When the non-image area of 20 is positioned below the developing electrode 101 for a long time, the surface potential of the photosensitive layer 122 becomes higher than the bias voltage, so that the surface of the developing electrode 101 on the opposite surface of the photosensitive layer 122 is exposed.
The toner 111 adheres and accumulates as shown in FIG.
The adhered toner 111 gradually disappears after the plate passes through the developing electrode 101 due to the electrical repulsion between the developing electrode 101 and the toner 111 and the liquid flow of the developing solution 110, but before the toner disappears, the electrophotographic photosensitive material 120 is removed. Is conveyed to the developing unit, the bias voltage apparently becomes higher than the bias voltage of the bias power source 102 due to the charge of the toner 111, and the image is crushed. Such a phenomenon appears remarkably in the case of developing a long plate such as a two-page vertical newspaper plate (about 1100 mm), which is a serious problem. Further, the time required for toner disappearance becomes smaller and smaller as the plate-making repeating cycle (multi-plate) is speeded up, so it is important to keep the bias voltage stable.

In order to prevent such inconvenience, the developing electrode 1 facing the photosensitive layer 122 of the electrophotographic photosensitive material 120.
No. 01-262980 to roughen the surface of No. 01
Proposed by the applicant in this issue. The principle is as follows. As a means for roughening the surface of the developing electrode, the electrode surface may be provided with irregularities such as grooves and holes,
A porous metal body such as Celmet (trade name) may be used. The material of the porous metal body is Al, Cu, Ni, A
A conductor such as g is desirable, and a metal having a higher conductivity has a better effect. FIG. 5 shows the difference in the surface roughness of the developing electrode and the state of toner adhesion. FIG. 5A shows the toner 2 on the surface of the developing electrode 1 having a flat surface roughness (hereinafter referred to as “specific surface area”) 1. Indicate that they adhere to each other, the distance between the toner and the electrode is the largest as compared with the roughened electrode, and the surface area of the electrode that attracts the electric charge of the toner is the smallest. The synergistic effect of these causes an apparent increase in bias voltage. This is the relationship between the conventional general developing electrode and toner adhesion. FIG. 5B shows a state in which the toner 2 adheres to the surface of the developing electrode 3 having a grooved specific surface area of about 70 to 100, and the toner adhesion consistency is higher than that in the case of FIG. Is deteriorated, the distance between the toner 2 and the developing electrode 3 is reduced, and the electrode surface area is increased, so that a synergistic effect can be obtained. Further, FIG. 5C shows a specific surface area of 2500 to
The case where the porous metal body 4 of about 3,000 is used as the developing electrode, the consistency of adhesion of the toner 2 is completely lost, and the toner 2
The distance between the developing electrode 4 and the developing electrode 4 is infinitely short, and the increase in the bias voltage can be suppressed to be extremely small in accordance with the size of the surface area. In this way, by improving the relative positional relationship between the toner and the developing electrode when the toner is attached, the developing bias is prevented from rising abnormally due to the toner attachment.

FIG. 6 shows a developing device in that case.
The electrophotographic photosensitive material 20 on which the electrostatic latent image is formed is conveyed at a predetermined speed on the back guide 10 inclined by a predetermined angle (for example, 7 °), and the electrophotographic photosensitive material 20 is supported. The layer is adapted to be grounded via ground terminals 21 and 22. The back guide 10 has minute protrusions for the purpose of reducing the contact resistance with the back surface of the photosensitive material for improving transportability and for suppressing the volume of the developing chamber so as not to unnecessarily increase the liquid transfer amount. It is composed of a glass plate. A developing electrode 30 having a predetermined developing gap is arranged above the back guide 10 and a developing electrode 30 having a structure shown in FIG. 7 is provided. A pair of aperture rollers 11 and 12 are provided at the outlet of the back guide 10. It is provided. The developed electrophotographic photosensitive material 20 is squeezed between the squeeze rollers 11 and 12 and then conveyed to a fixing unit (not shown) in the next stage. Further, a cleaning pad 13 for cleaning is attached to the squeezing roller 11 so that the squeezing rollers 11 and 12 are automatically cleaned.

The developing electrode 30 has two separated electrode supporting plates 31 and 32, and the electrode supporting plates 31 and 32 are provided.
Are connected by connecting plates 33, 34 at their ends. Further, on the lower surface side of the electrode support plates 31 and 32, Celmet (trade name: manufactured by Sumitomo Electric Industries, Ltd.) layers 35 and 36 as porous metal bodies are provided. The celmet layers 35 and 36 are electrically connected via a lead wire 37, and a bias voltage is applied to the celmet layers 35 and 36 by a bias power source 38.

On the other hand, the supporting plate 3 in which the developing electrode 30 is separated
A developer supply unit 40 is installed on the top of the supply pipe 1.
The developing solution supplied and stored from Nos. 1 and 42 is adapted to supply the developing solution 44 to the developing gap from a cylindrical ejection portion 43 having a porous or slit ejection port. The developing solution is pumped up from a developing solution tank (not shown) and stored in the developing solution supply section 40 through the supply pipes 41 and 42, and is supplied to the developing gap from the ejection section 43 of the developing solution supply section 40, thereby developing electrode. The developer overflowing from 30 is collected in the bath and returned to the developer tank. Such circulation of the developing solution is performed continuously or intermittently during the development and before and after the development.

[0008]

According to the above-mentioned developing device, the specific surface area due to the rough surface of the electrode is increased by using a porous metal body or the like to shorten the distance between the toner adhering to the electrode and the electrode. As a result of the synergistic effect of increasing the electrode surface area, it is possible to reduce the apparent increase in bias voltage due to the charge of the adhered toner. Therefore, the phenomenon that the developing bias voltage fluctuates depending on the image pattern is reduced,
Inconveniences such as image crushing can be eliminated.

On the other hand, however, there remains a problem to be improved in the structure of the developing electrode and the developing chamber. That is,
In FIG. 6, the electrode 3 separated under the developer supply unit 40
Reference numerals 1 and 35 serve to adjust the liquid level of the developing solution in the developing solution inflow portion, but the developing solution front end portion 45 remains as a dead space in the circulating path of the developing solution, and renewability is not good. Therefore, at the liquid front end portion 45, the toner is not sufficiently replenished and the fixed portion is consumed by the development, so that the solid content concentration is lowered. When the surface layer is formed by a developing solution having a low solid content in the initial development, the toner hardly adheres in the subsequent development, which is called a pre-rinsing effect. From this, in the case of developing a long photosensitive material such as a newspaper two-page plate,
Since there is not enough toner adhered to the rear image portion, the toner is eluted in the elution step in the latter stage, resulting in a disorder in the image.

The present invention has been made under the above circumstances, and an object of the present invention is to use a developing electrode having a roughened surface so as to prevent toner adhesion to the electrode. (EN) Provided is a wet electrophotographic developing device which can eliminate the pre-rinsing effect by the leading end portion of the developing solution and perform reliable development with a small amount of solution fed.

..

SUMMARY OF THE INVENTION The present invention relates to a structure of an electrode and a developing chamber of a wet electrophotographic developing device. The above object of the present invention is to provide a side surface of an electrode having a roughened surface and a side surface of a back guide. A pair of insulating developer side walls are provided in contact with each other,
Downstream from the developer inflow portion, both sides of the developing gap are closed so that the developer does not flow out from the side surface, and upstream of the developer inflow portion, the height of the developing chamber side wall is substantially the same as the photosensitive material transport surface. This is achieved by a wet electrophotographic developing device in which the excess level of the developing solution overflowing when the photosensitive material enters the developing gap is discharged from both side surfaces.

Further, the height of the upper edge of the developing electrode downstream of the developing solution inflow portion is set to a position slightly lower than the developing solution discharge port, and the structure is such that the excess developing solution can overflow from the upper surface of the developing electrode. According to the above, the above-mentioned object can be achieved more effectively.

Further, by grading the developing gap composed of the developing electrode and the back surface guide from the upstream side to the downstream side, the required liquid feeding amount can be reduced.

[0014]

In the present invention, since the side wall of the developing chamber is provided and the side surface of the developing gap is closed, the inside of the developing cap can be filled with a small amount of liquid to be fed. This required liquid supply amount is further reduced by narrowing the outlet side of the developing gap. Further, when the photosensitive material enters the developing gap, the developing solution overflowing upward is caused to flow out from both side surfaces and the upper surface of the developing electrode, so that the tip portion of the developing solution, which is poor in renewability, does not rise.

[0015]

1 is a perspective view showing an embodiment of the present invention, and FIG. 2 is a plan view thereof. In the figure, a resin developer side wall 50 is provided on both sides of the back guide 10, and a part of the side wall 50 closes the side of the developing gap below the developing electrodes 32 and 36.
The other parts have the same height as the plate material conveying surface. Also,
FIG. 3 is a side sectional view of the developing device of the present invention.
In the figure, (B) shows a state where the photosensitive material is starting to enter and (B) is passing through the photosensitive material.

The plate material conveying surface has an inclination of about 7 ° with respect to the horizontal in the developing system, and serves as a developing electrode for the porous chamber metal member 3.
Ni cermet having a thickness of 2 mm was used as the electrodes 5, 36, and the electrode support plates 31, 32 were aluminum plates. The optimum value of the development gap formed by the Ni celmet layer and the back guide 10 is about 1 to 3 mm in view of the image quality. The developing gap must be filled with the liquid at all times, and if the developing liquid flows out from the side surface, it is necessary to increase the amount of liquid to be sent.
In the present invention, this is prevented by providing the side wall of the developing chamber. Next, when the photosensitive material enters the developing chamber whose side surface is blocked, the apparent developing gap is reduced in FIG. 3A, and the liquid feeding amount required before the entrance becomes excessive. The surplus developer is discharged from the side wall of the developer, which has substantially the same level as the back guide 10. The excess developing solution overflows the upper edges of the developing electrodes 32 and 36 as shown in FIG. 3B, and is discharged from the upper surfaces of the developing electrodes 32 and 36. Therefore, the height of the upper edges of the developing electrodes 32 and 36 is set to be slightly lower than the level of the developing solution ejecting portion 43. The height also determines the level of the developer tip 45 below the separated electrodes 31, 35.

Next, FIGS. 4A and 4B show an example in which a gradient is provided from the upstream side to the downstream side of the developing gap. Figure 4
In (A), the separated electrode entrance gap is a, the development electrode 32, 36 entrance side gap is b, and the exit side gap is c, which are 2.65 mm, 2.35 mm, and 1.95 mm, respectively. By narrowing the outlet side in this way, the required liquid supply amount is reduced, and it is possible to fill the liquid in the developing gap with a liquid supply liquid supply amount of about 8 liters / min for a developing electrode having a width of about 400 mm. It was The taper gradient has a gap difference of 0.3 to 100 mm for an electrode length of 100 mm.
It is effective to set it to 0.8 mm. Also, FIG. 3 (B)
Is an example in which the separated electrodes 31 and 35 are not provided with a gradient and only the developing electrodes 32 and 36 are provided with a gradient. In this case as well, the effect of reducing the liquid transfer amount is the same, but comparing (A) and (B) of the same figure, in the case of FIG. And the solid content of the toner is reduced and the pre-rinsing effect is reduced even when the tip of the developer rises when the photosensitive material enters. Therefore, it is preferable to form a gradient including the separated electrodes.

[0018]

According to the developing device of the present invention, since a small amount of developer is sent and a liquid having good renewal property is circulated, it is possible to perform uniform development by stable adhesion of toner. High quality images can be obtained in combination with the stability of the developing bias voltage, which is an advantage of the roughened electrodes.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a plan view of FIG.

FIG. 3 is a side sectional view for explaining the operation of the present invention.

FIG. 4 is a side sectional view showing another embodiment of the present invention.

FIG. 5 is a diagram showing a difference in surface roughness of a developing electrode and a state of toner adhesion.

FIG. 6 is a side sectional view showing an example of a developing device using a roughened developing electrode.

FIG. 7 is a perspective view of FIG.

FIG. 8 is a side sectional view showing the structure of a conventional wet electrophotographic developing device.

FIG. 9 is a diagram illustrating a mechanism in which toner adheres to a developing electrode.

[Explanation of symbols]

 1 Flat Electrode 2 Toner 3 Electrode with Groove 4 Porous Body Electrode 10 Back Guide 11, 12 Squeeze Roller 13 Cleaning Pad 20 Electrophotographic Photosensitive Material 21, 22 Ground Terminal 30 Developing Electrode 31, 32 Electrode Support Plate 33, 34 Connecting plate 35,36 Celmet layer 37 Lead wire 38 Bias power supply 40 Developer supply part 41,42 Supply pipe 43 Discharge part 44 Developer 45 Developer tip 100 Back guide 101 Development electrode 102 Bias power supply 110 Developer 111 Toner 120 Electronic Photosensitive material 121 Support layer 122 Photosensitive layer

Claims (3)

[Claims] 1. An electrophotographic developing apparatus comprising: a developing electrode having a roughened surface; a back guide for guiding the transport of an electrophotographic photosensitive material; and a developer supply means for supplying a developer therebetween. A pair of insulating developing chamber side walls are provided in contact with the side surface of the developing electrode and the side surface of the back guide, the developing chamber side walls block both sides of the developing gap downstream from the developing solution inflow portion, and the developing solution inflow is provided. In the wet electrophotographic developing apparatus, the height of the side wall of the developing chamber is set to be substantially at the same level as the photosensitive material conveying surface upstream of the section. 2. The developing electrode downstream of the developing solution inflow portion is arranged such that the height of its upper edge is slightly lower than the developing solution discharge port, and excess developing solution is removed from the back surface of the developing electrode. The wet type electrophotographic developing apparatus according to claim 1, wherein the wet type electrophotographic developing apparatus is made to overflow. 3. The developing gap according to claim 1, wherein the developing gap has a gradient from upstream to downstream.
Wet electrophotographic developing device.