Liquid developing device for electrophotography

Abstract

A liquid developing device for use in multicolor electrophotographic copying machines is provided with a plurality of feed pipes for supplying different liquid color developers to a developing station, which feed pipes are connected to a common developer supply pipe. Valves are provided in the feed pipes wherein each of the valves are actuated by an electrical signal to supply only a selected liquid color developer to a developing station at a time. The liquid developing device is also provided with a belt for removing residual liquid developer remaining on an image bearing member after development and with a plurality of blades for scraping and collecting the thus removed liquid developer, which are actuated in correspondence with a selected color.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a liquid developing device for electrophotography, and more particularly to an improved liquid developing device adapted for use in a multicolor electrophotographic copying machine, said system being small-sized and compact in mechanism and capable of reproducing color images of high quality.

2. Description of the Prior Art

In the conventional multicolor electrophotograhic copying machines, multicolor images have been formed by using many different types of developer in superposed relationship, that is, by placing them one on the other in layers. According to this method, unnecessary developer could be mixed at the developing electrode to reduce the copying performance, making it impossible to accurately reproduce the designated colors.

As a solution to this problem, it was attempted to provide separate developing units corresponding to the respective colors and to perform development by selectively moving these independent developing units to the developing station in accordance with the designated color. According to this method, however, the developing units and the mechanism for moving them are complicated and also the copying machine itself becomes bulky. Further, the developer may be scattered or may run out in droplets as the developing units move, and such developer droplets may adhere to the developing unit moving mechanism thereby impeding its operation.

Also, if one tries to dispose the developing units in regular arrangement in the developing section so as to accomplish the color by color developing operation successively in every copying cycle, there is required an even larger space for the developing section, and also, since the time required from formation of latent image to its development and the time from development to transfer are varied according to the position of the developing units for respective colors, it is hardly possible to develop all the colors under the optimum conditions, and poor color reproducibility results.

SUMMARY OF THE INVENTION

A principal object of the present invention, therefore, is to provide an improved liquid developing device for electrophotography whereby it is possible to develop the color images with high quality.

Another object of the present invention is to provide a small-sized and compact liquid developing device for electrophotography.

It is still another object of the present invention to provide a liquid developing device of the type described which includes additional improvements whereby the developing solution which flows out during development is collected for reuse.

It is yet another object of the present invention to provide a liquid developing device of the type recited whereby the developing solution of each color is recovered separately from developing solutions of other colors.

A further object of the present invention is to provide a liquid developing device for electrophotography incorporating the various improvements which are described in detail hereinbelow.

According to the present invention, development is practised under the same conditions for each color with no need of moving any developing unit for development of any designated color, that is, the latent images on a sensitive medium are developed by selectively supplying the developing solution of a designated color to a common developing electrode and the portion of the developing solution of each color which flows down from said electrode is carried out by a carriage means and collected separately from the developing solutions of other colors. There is thus obtained according to the present invention a high-performance developing system which is small-sized and compact and has very excellent reproducibility of any designated color as compared with the conventional devices.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings show embodiments of the developing system adapted in a multicolor electrophotographic copying machine according to the present invention. In the drawings,

FIG. 1 is a side view of the device with the developer recovering means being shown in a declining position,

FIG. 2 is a similar view to FIG. 1 but shows the developer recovering means arranged in a vertical position,

FIG. 3 is also a similar view of the system where a squeeze roller is disposed between the sensitive member and the developer recovering means,

FIG. 4 is a side elevation of the system as it was adapted to a copying machine using an endless belt-like sensitive member,

FIG. 5 is a side elevation of the system adapted to a copying machine in which the endless belt-like sensitive member is arranged vertically,

FIG. 6 is a side view of the system adapted to a copying machine using a reciprocating flat plate-like sensitive member, and

FIG. 7 is a perspective view of a part of the developing electrode assembly .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described below in detail by way of some preferred embodiments thereof with reference to the accompanying drawings.

Reference numeral 1 designates a sensitive member which may be drum-shaped (FIGS. 1 to 3), belt-shaped (FIGS. 4 and 5) or reciprocative flat plate-shaped (FIG. 6). This sensitive member may be of a type having a photoconductive layer and an electroconductive layer or a type having an insulating layer, a photoconductive layer and an electroconductive layer. Along the course of movement of said sensitive member are arranged a charger, a light image exposure means (or a light image exposing opposite-polarity secondary charger or light image exposing AC corona discharger), a developing means, a transfer means and a cleaning means, but these means, except for the developing means, are not shown here as they may be of the types known in the art and may be adapted in any suitable way. The charging, exposing and developing steps in said electrophotographic process are repeated for reproducing each color upon one rotation or one reciprocation of the sensitive member, in the same way as known in the art.

The present invention relates to the improvements in the developing means in the above-said steps. The liquid developer, from a developer supply pump (not shown) flows out from a supply pipe 3 at the ends of the developer feed pipes 3.sub.1 - 3.sub.4 (each feed pipe being designed to feed developer of a designated color) so that said developer will be spread over the entire width of the sensitive member 1 through the associated branch pipes 4.sub.1 - 4.sub.4 by the operation of the associated solenoid valves 5.sub.1 - 5.sub.4 which are operated by a designated color signal. The liquid developer which has flown out from said supply pipe 3 is provided as a uniform layer of liquid by a developer receiving plate 6 and further flows onto a developing electrode 7 such as shown in FIG. 7. The latent image on the sensitive member 1 is developed by the developer on said electrode 7. The belt 10 turns in a direction opposite to the movement of the sensitive member 1 by a driving shaft 11 while approaching to said member to such an extent as will not damage the image on said member when passing around a guide roller 9.sub.1.

The developer which has been used for developing the latent image on the sensitive member 1 further flows along the surfaces of the developing electrode 7 and a developer guide plate 8 and falls onto the belt 10 whereby said used developer, adhering to the belt, is carried downwardly and scraped away from the belt by one of the recovery blades 13. Said recovery blades are provided one for each color and arranged such that each of them is contacted with or separated from the belt 10 by rotation of a retainer belt 14 and blade shaft 15. Their operation is selectively controlled such that when recovering the developer of a first color, the recovery blade at the first stage will be in its operative position, and when recovering the developer of a second color, the recovery blade at the second stage will be in its operative position, etc. On the backside of said belt 10 is provided a flat receiving plate 12 designed such that any recovery blade 13, when operated, will be pressed against the belt 10 with uniform pressure.

The developer which was scraped down by the blades 13 is first collected in tanks 16 and then recovered in a developing tank (not shown). The belt 10 is cleaned by a cleaning brush 17 so that said belt is cleared of any residual developer and again performs said transport of used developer for recovery. The developer removed from the belt by the brush 17 is collected in a tank 18 and then discharged out therefrom through a pipe 19. It is desirable to fill the tank 18 with a cleaning liquid. The belt 10 is larger in width than the sensitive member 1 and is provided with ridges along both edges thereof so that the developer will not be scattered off of the belt when the developer flowing down from the developing means 7 is received on the belt and when residual developer is scraped off by the blades 13. In order to increase the developing effect, the belt 10 is made of a conductive material such as metal, conductive rubber or conductive resin so that a bias voltage may be applied thereto, but the belt is insulated from the body portion of the device. When the bias voltage applied to the belt 10 is of the same polarity as the toner in the developer, an electrostatic repulsive force acts between the belt and toner to enhance the developing effect, while when said bias voltage is of the opposite polarity to the toner, an electrostatic suction force is produced to effect defogging at the non-image portion on the sensitive member.

For the best developing effect, the clearance between the developing electrode 7 and sensitive member 1 should be 0.2 to 2.0 mm. In the multicolor developing method of the present invention, one needs to supply the developing solutions of different colors successively to the same developing electrode 7 in such a way that the developing solutions of different colors are not mixed with each other. Therefore, if the abovesaid clearance is enlarged, such much greater amount of developer is fed and, in this case, the developer may fail to flow down uniformly to the electrode 7, causing a reduction of the developing effect. On the other hand, if said clearance is diminished, although the developing effect is improved, there arises a possibility that the sensitive member 1 would be damaged if any foreign matter entered the developer and stayed on the developing electrode 7. Therefore, said clearance should preferably be within the above-said range. However, such small clearance proves insufficient to permit smooth flow-down of the developer staying on the electrode 7 after going through the developing step, and this may cause the developer to remain and deposit in the developing section.

To avoid this, arrangement may be made such that a cam 26 is turned clockwise by a spring 27 during development so as to let the developing electrode 7 turn upwardly about the shaft 25.sub.1 through a movable side plate 25 to thereby maintain said clearance. Then, during the period when development with developer of a certain color has been completed and; development is temporarily suspended until starting the development for the next color, power is connected to a solenoid 28 to energize it so as to let said cam 26 turn counterclockwise through a plunger 29 and a pin 29.sub.1 integral therewith, causing downward movement of the electrode 7 to thereby expand the space between it and the sensitive member 1. After completion of development, any residual developer on the surface of the sensitive member is squeezed off by the action of corona discharge effected by a corona discharger 20.

FIG. 2 shows an embodiment where, instead of applying a bias voltage to the belt 10, said belt is turned in the same direction as the sensitive member 1 and a squeeze roller 21 applied with a bias voltage is disposed on the side where said belt separates away from the sensitive member 1. Said squeeze roller 21 is made of a conductive material such as metal, conductive rubber or conductive resin and is rotated at high speed in a direction opposite to the direction of rotation of the sensitive member so as to allow the residual developer to deposit on the belt 10 while yet further improving said developing effect.

FIG. 3 shows still another embodiment where a squeeze roller 21, the same as shown in FIG. 2, is disposed between the sensitive member 1 and the belt 10 such that said squeeze roller is positioned adjacent the sensitive member 1 and in contact with the belt 10. According to this arrangement, any developer depositing on the squeeze roller 21 is wiped off by the belt 10 and recovered in its entirety, so that the squeeze roller contacts the sensitive member always in a cleaned state.

FIGS. 4 and 5 show a form or adaptation of the present invention to the developing system in a copying machine where the flexible sensitive member 1 is turned like an endless belt. In this case, too, it is possible to adapt modified forms of squeeze rollers such as shown in FIGS. 2 and 3.

FIG. 6 illustrates application of the developing device of the present invention to a copying machine using a flat plate-shaped sensitive member.

In FIGS. 1 to 6, like reference numerals are used to indicate like parts throughout.

Claims

We claim:

1. A liquid developing device for electrophotography comprising:

a selective developing solution supply means whereby a developing solution of any designated color is selected from developing solutions of different colors and supplied to an electrophotographic sensitive member in successive relation with the developing solutions of other colors;

a common developing means disposed in a developing position to retain sequentially each said supplied developing solution on the surface of said sensitive member;

movable means separate from said common developing means for transporting excess developing solution flowing out from said developing means; and

means for recovering the developing solutions of respective colors separately from each other during transportation by said movable transporting means.

2. The liquid developing device according to claim 1, wherein said developing means includes a developing electrode plate disposed at a given distance from the surface of the sensitive member.

3. The liquid developing device according to claim 2, wherein said developing electrode plate is movably mounted for movement away from said developing position upon completion of a developing operation.

4. The liquid developing device according to claim 1, wherein said excess developing solution transport means is an endless rotative structure.

5. The liquid developing device according to claim 4, wherein said endless rotative structure is an endless belt.

6. The liquid developing device according to claim 4, wherein the sensitive member is movable and the direction of rotation of said endless rotative structure is opposite to the direction of movement of the sensitive member.

7. The liquid developing device according to claim 4, wherein sensitive member is movable and the direction of rotation of said endless rotative structure is same as the direction of movement of the sensitive member.

8. The liquid developing device according to claim 4, wherein said developing solution recovering means has a plurality of blades corresponding in number to the respective colors of developing solutions and mounted to be selectively contacted with the surface of said endless rotative structure such that the selected blade will recover the developing solution of the designated color, and reservoirs for collecting the respective developing solutions recovered by said respective blades.

9. The liquid developing device according to claim 8, wherein a receiving plate is provided at the backside of the portion of said endless rotative structure contacted with said blades.

10. A liquid developing device for electrophotography comprising:

selective developing solution supply means whereby a developing solution of any designated color is selected from developing solutions of different colors and supplied to an electrophotographic sensitive member in a successive relation with the developing solutions of other colors;

a common developing means for sequentially retaining each said supplied developing solution on the surface of said sensitive member;

means separate from said common developing means for transporting excess developing solution flowing out from said developing means;

means for recovering the developing solutions separately in a color by color way during transportion by said transporting menas;

and means for cleaning said transporting means after recovery of each different developing solution.

11. The liquid developing device according to claim 10, wherein said cleaning means includes a cleaning fluid.

12. The liquid developing device according to claim 1, wherein said excess solution transporting means is provided adjacent the surface of the sensitive member and a bias voltage is applied thereto.

13. The liquid developing device according to claim 12, wherein said developing solution includes a charged toner, and wherein said bias voltage is of the same polarity as that of toner in the developing solution.

14. The liquid developing device according to claim 12, wherein said developing solution includes a charged toner, and wherein said bias voltage is of opposite polarity to that of the toner in the developing solution.

15. A liquid developing device for electrophotography comprising:

selective developing solution supply means whereby a developing solution of any designated color is selected from developing solutions of different colors and supplied to an electrophotographic sensitive member in a successive relation with the developing solutions of other colors;

a common developing means whereby each said supplied developing solution is retained on the surface of said sensitive member;

means separate from said developing means for transporting excess developing solution flowing out from said developing means;

means for recovering the developing solutions separately in a color by color way during transportation by said transporting means; and

a developing solution squeeze roller provided between said developing means and said excess solution transport means.

16. A liquid developing device for electrophotography comprising:

selective developing solution supply means whereby a developing solution of any designated color is selected from a plurality of developing solutions of different colors and supplied to an electrophotographic sensitive member in a successive relation with the developing solutions of other colors;

a common developing means for retaining each said supplied developing solution is retained on the surface of said sensitive member;

means separate from said common developing means for transporting excess developing solution flowing out from said developing means;

means for recovering the developing solutions separately in a color by color way during transportation by said transport means; and

means for squeezing off unnecessary developing solution from the surface of the sensitive member after said excess solution has been transported away therefrom.

17. The liquid developing device according to claim 16, wherein said developing solution squeezing-off means is a corona discharger.

18. The liquid developing device according to claim 16, wherein said developing solution squeezing-off means comprises a squeeze roller and a corona discharger both of which are disposed adjacent the surface of the sensitive member.

19. The liquid developing device according to claim 4, wherein said endless rotative structure is provided with solution flow-out preventive ridges along both edges thereof.