GB2137905A - Electrophotographic Developing Head - Google Patents

Abstract

In a developing head (2) in which liquid developer is applied to the photosensitive surface of electrophotographic material the outer peripheral surface of the head is shaped to prevent leakage of the developer by capillarity from the gap (2k) between the photosensitive surface (3a) and the framed opening (2a) of the developing head. A supply of gas for squeezing off residual developer from the photosensitive surface after development is provided via passage (19). A valve (17) closes the passage when developer is supplied via passage (18). A pressure plate (12) can be provided to press the photosensitive surface against the framed opening (2a) during developing and squeezing. A suction pump (25) can apply reduced pressure to the gap (2k) when the electrophotographic material is forwarded by one frame. <IMAGE>

Description

SPECIFICATION Developing Head for Electrophotographic Apparatus The present invention relates to a developing head for electrophotographic apparatus which is capable of effectively supplying a liquid developing agent by a liquid feeding means.

Unlike conventional photographic film which uses silver halide photographic as the photosensitive member, electrophotographic material has a feature that it becomes photosensitive only after it is electrically charged. For this characteristics, a roll of elongated film is used as the electrophotographic material for microfilm which is charged, exposed, developed and fixed in part for recording an image, and serviced for projection of the thus obtained images together with unrecorded portions and images which are newly added to the unrecorded portions thereof.

So-called wet type electrophotographic apparatus which employs microfilm such as mentioned above develops electrostatic latent images by using a liquid developer and by charging, exposing, developing, drying and fixing the electrophotographic material frame by frame.

It is therefore desirable that the liquid developer should not overflow from or leak into regions on the electrophotographic material other than where it should be treated for developing. It is also preferabie that the excess liquid developer be removed as quickly as possible before the electrophotographic material is detached from the developing head and forwarded to subsequent processing sections.

Fig. 1 (a) is a schematic view to show the structure of the developing head according to the prior art. As is shown in the figure, a developing head 1 is provided with a developing mask means 2. The developing mask means 2 has an opening with a frame 2a which is identical in size to one frame of an electrophotographic material 3 for an electrophotographic apparatus. The mouth 2b of the framed opening is in contact with the electrophotographic material 3. The outer frame surface 2c of the developing mask means 2 opposes the electrophotographic material 3 via an interval. The inlet port 2d for liquid developer in the developing mask means 2 connects with the top of a passageway 4. The base of the passageway is immersed in the liquid developer 5 pooled in a toner tank 7.The top of a passageway 8 interposed with a pump 6 is connected to the outlet port 2e in the developing mask means 2, and the base thereof is located in the upper space of the toner tank 7. The inlet port 2d and the outlet port 2e for the liquid developer communicate via a passageway 2f. As the vacuum pump 6 is actuated, the pressure inside the chamber passageway 2f becomes negative, so that the liquid developer 5 is introduced into the chamber passageway 2f via the passageway 4 to come in contact with the electrophotographic material 3 which is formed with electrostatic latent images for developing in the developing chamber 2g which is an opening defined by the frame 2a. The liquid developer 5 after developing is sucked and returned to the toner tank 7 by the vacuum pump 6.

Fig. 2 is a schematic view to show the structure of another prior art developing head which is so structured as to remove the liquid developer 5 from the photosensitive surface 3a (hereinafter termed as squeezing).

As is shown in this figure, the developing head 1 of this type is provided with a developing mask means 2, which has an opening with a frame 2a identical in size with one frame of the electrophotographic material 3. The mouth 2b of the framed opening is in contact with the electrophotographic material 3. Thus, the photosensitive surface 3a which is one frame of the electrophotographic material 3 faces the developing chamber 2g. The liquid developer 5 is applied to the photosensitive surface 3a via the developing chamber 2g to obtain a predetermined latent image. In this case, the liquid developer 5 on the photosensitive surface 3a is then squeezed off from the surface 3a by injecting, for example, gas such as air onto the surface 3a. In order to do this, it is necessary to send the liquid developer 5 and the gas (in this case, air) into the developing chamber 2g.This is done by pumping up the liquid developer 5 pooled in the toner tank by means of the vacuum pump 6, which also draws the air in from the atmosphere as the valve 9 opens. In other words, there are provided passageways 4 and 8 which extend from the toner tank 7 into the developing mask means 2 and return to the toner tank 7 via the developing chamber 2g and the vacuum pump 6, and another passageway 10 which has its end portion opening into the atmosphere and extends into the developing mask means 2 via the valve 9 to join the passageway 4 at the upstream from the developing chamber 2g. A pressing plate 12 abuts against the electrophotographic material 3 at its back to press the same toward the mouth 2b of the framed opening during developing and subsequent squeezing of the liquid developer 5.

Its pressing is released when the electrophotographic material is forwarded for one frame for the next processing step.

On the other hand, the developing head 1 as shown in Figs. 1 (a) and 2 utilizes the vacuum pump 6 for feeding the liquid developer 5 or the liquid developer 5 and the gas for squeezing said agent. Because the vacuum pump 6 is expensive, the developing head 1 becomes costly and difficult to reduce in size as well as in price.

Such problems can be overcome if a compression-feeding means such as a liquid feeding pump is used instead of the vacuum pump 6, but this again entails other problems such as: a) As the liquid developer 5 is introduced into the developing chamber 2g under pressure applied by the compression means, there is danger that the liquid developer 5 might leak through the interstice between the mouth 2b of the framed opening and the photosensitive surface 3a.Such leakage would cause the liquid developer 5 to disperse over the entire area of said interstice by the capillarity since the interstice between the outer peripheral surface 2c and the electrophotographic material 3 is very narrow and the angle between the two is very small (ca. 5 ). The liquid developer 5 would eventually spread over the other areas of the electrophotographic that are not yet to be contacted with the liquid developer. Or, it may even flow into other parts of the electrophotographic apparatus. This is particularly marked in the developing head 1 shown in Fig.

1(a), the portion A thereof shown as an enlarged view in Fig. 1(b).

A developing head which is free from leakage of the liquid developer has been proposed, such as disclosed in Japanese Patent Publication No.

Sho-51-1341 5, in which the mounth of the framed opening to be contacted with the electrophotographic material is made of resilient member such as rubber. However, the use of a rubber mask at the mouth of the framed opening will involve an extra manufacturing process of pasting the rubber with adhesive. This will lead to a cost increase as well as troubie due to a stagnant liquid developer in the bonded portion and an inferior durability of the rubber mask. Also, if the developing head is made integral with the charging/exposing head, the use of a resilient member in the developing mask means results in unstable positioning of the electrophotographic material with respect to the developing head. This then affects the positioning of the lens with respect to the electrophotographic material which requires precision in reproduction.

b) With the developing head 1 in which the liquid developer 5 is squeezed after developing such as shown in Fig. 2, the distance between the photosensitive surface 3a in the developing region and the developing electrode 11 is generally very narrow, whereby the liquid developer is likely to enter into the passageway 10 for feeding the gas because of the liquid resistance caused by the viscosity of the liquid developer. If the liquid developer enters into the pump, it would cause various problems, and the liquid developer entering into the passageway 10 would be jetted into the developing chamber 2g to reduce the squeezing efficiency when the pump is activated.

c) Moreover, although the liquid developer 5 is squeezed by applying the gas to the photosensitive surface 3a, this is not sufficient.

Squeezing may become adequate if sufficient time is allowed, but this too would cause another problem of reduced processing efficiency per unit time.

US Pat. 3,916,828 and US Pat. 4,141,647 are referred to as the prior art in relation to Fig. 1 or 2.

In view of the defects found in the prior art, the present invention aims to provide a developing head for an electrophotographic apparatus capable of satisfactory developing even with the use of the feeding means for supplying the liquid developer alone or for supplying the liquid developer with squeezing gas. The second object of the present invention is to provide a developing head which is inexpensive and free from the leakage of the liquid developer. The third object of the present invention is to provide a developing head with a squeezing process which is capable of preventing the liquid developer from coming into a piping for squeezing gas. The fourth object of the present invention is to provide a developing head which is capable of squeezing the liquid developer effectively and more quickly in the squeezing process.

In the developing head for electrophotographic apparatus according to the present invention which comprises a developing mask having a developing chamber defined by a framed opening facing the photosensitive surface of an electrophotographic material for an electrophotography, the mouth of said opening abutting on said photosensitive surface, and the outer peripheral surface of said developing mask opposing the photosensitive surface, which is contacted with the liquid developer supplied from a liquid feeding means via said developing chamber to achieve development of the electrophotographic material via an interval the developing head is characterized in that:: a bent or curved portion is formed near the mouth of the framed opening to assume an angle greater than that formed between the rest of the outer peripheral surface of the developing mask and said electrophotographic material so that an interval can be formed to prevent the liquid developer from leaking between said bent portion and the electrophotographic material by capillarity; a first passageway is provided exclusively for supplying the liquid developer; a feeding means for supplying gas onto the photosensitive surface in order to squeeze the liquid developer therefrom after it contacted with te;surface.

a second passageway is provided exclusively for supplying the gas; a valve is provided to close said second passageway when the liquid developer is supplied; a pressing mechanism is provided to press the electrophotographic material against said mouth of the framed opening during the developing process to apply the liquid developer and during the squeezing process to apply the gas to remove the liquid developer, said press being released when the electrophotographic material is forwarded for one frame, a reduction means is provided to apply a negative pressure to the interval between the photosensitive surface and at least a portion of the mouth of the frame opening of the developing mask means.

In the accompanying drawings, Fig. 1 (a) is a schematic view to show the structure of the developing head according to the prior art. Fig.

1 (b) is an enlarged view of the portion A in Fig.

1(a).

Fig. 2 is a schematic view to show the structure of another developing head according to the prior art.

Fig. 3(a) is a schematic view to show the structure of one embodiment according to the present invention, Fig. 3(b) is an enlarged view of the portion B in Fig. 3(a).

Figs. 4 through 7 are enlarged views of the portion B in various modifications of the present invention.

Fig. 8 is a schematic view to show the structure of the second embodiment according to the present invention.

Figs. 9(a) through 9(c) are sectional views of the present invention to show the detaiis of the valves shown in Figs. 8 and 10.

Fig. 10 is a schematic view to show the structure of the third embodiment according to the present invention.

Fig. 11 is a schematic view to show the structure of the fourth embodiment according to the present invention.

Fig. 12 is an explanatory view to show the parts of the processing head shown in Fig. 11 when viewed from the front.

Fig. 13 is a partial sectional view of the processing head according to the prior art.

Figs. 14 and 1 5 show the pressing plate of the processing head; Fig. 14(a) is a front view of the processing head; Fig. 1 4(b) is a sectional side view of pressing plate. Fig. 1 5 is a partial sectional view of still another embodiment of the pressing plate of the present invention.

The preferred embodiments of the present invention will now be described in detail referring to the accompanying drawings. The parts identical with the prior art head are given identical reference numerals.

Fig. 3(a) shows the first embodiment according to the present invention, with its portion B shown in enlarged view in Fig. 3(b). As shown in these figures, a bent portion 2h is formed on the framed opening near the mouth 2b thereof. The angle a between the outer surface 2c near the mouth 2b of the framed opening and the electrophotographic material 3 is 900 and the angle,3 between the rest of the outer surface 2c and the electrophotographic material 3 is about 5 . The outer surface 2c is spaced from the electrophotographic material 3 with an interval I of about 1 mm at the bent portion. Thus, a relatively large interval 13 is made between the outer surface 2c of the developing mask means and the electrophotographic material 3 to prevent leakage.In other words, even if the liquid developer 5 supplied by means of a compression pump 14 seeps through the interval between the mouth 2b of the framed opening and the electrophotographic material 3, there occurs no capillarity because the interval 13 for preventing the leakage is quite large. Instead, the liquid developer 5 will be prevented from dispersing any further.

Referring to Fig. 3(b), an interstice is generally present to a certain extent between the electrophotographic material 3 and the mouth 2b of the framed opening of the developing mask means which abuts against the electrophotographic material 3 due to limited manufacturing precision and the planar deviation caused by the pressing plate. With the head in this embodiment as well as in all the other embodiments hereinafter, the interstice can be reduced to 25 tjm or less over the entire mouth 2b. This permits the liquid developer to be applied to the developing head for a longer period of time without leaking.

Observation of liquid behavior in terms of dynamics at the developing head reveals that the force F (per unit length) acting on the liquid present in between the electrophotographic material 3 and the mouth 2b of the framed opening in the outward direction can be expressed as: F=t P+a(1 +cos a)28 =t p-( p--S(11-cos a) wherein: t represents the interstice between the electrophotographic material 3 and the mouth 2b of the framed opening; P, the pressure within the developing head; 8, surface tension (shown in Table 1) of the liquid developer 5; and a, the angle formed by the electrophotographic material 3 and the outer surface 2c of the mask as shown in Fig. 3(b).

TABLE 1

cyclohexane 25 dyn/cm decane 23.9 dyn/cm dodecane 25.4 dyn/cm toluene 28.4 dyn/cm As is seen in Table 1, the surface tension of the liquid developer 5 is in the range of between 20 and 30 dyn/cm. Suppose the pressure within the developing head 1 is several ten grams weight/cm2, the force F assumes a negative value if the angle a is in the proximity of 900, whereby leakage of the liquid developer 5 can be prevented. It is preferable that the mouth 2b of the framed opening be spaced from the electrophotographic material 3 by a distance within 0.3 mm in order to prevent a large amount of the liquid developer 5 from overflowing even if the pressure of the pump which feeds the liquid developer 5 temporarily increases and the surface tension of the agent fails to prevent flowing.The viscosity of the liquid developer 5 would in this case prevent its flowing.

Referring now to Figs. 4 through 7 which show the essential parts of modified embodiments in enlargement. The embodiment shown in Fig. 4 comprises the developing mask means 2 with its surface facing the passageway 2f being made flat so that the liquid developer 5 can easily make contact with the electrophotographic material 3.

The modified embodiment shown in Fig. 5 is formed with a bent portion 2h which is so curved as to satisfy the relation, which is the angle a > the angle /3, in order to form the interval 13 for leakage prevention. Further, the angle a of the embodiment shown in Fig. 6 is made still greater, so that the capillarity of the liquid becomes less likely to occur. In Fig. 7, an annular groove profiling the shape of the framed opening 2a is made on the outer surface 2c of the developing mask means near its mouth 2b to provide the modified interval 13. This interval 13 is also effective in preventing leakage as mentioned in the foregoing embodiments.

The developing mask means 2 to be used in the embodiments according to the present invention must be made from a material which would not deform when the electrophotographic material 3 is pressed against the mouth 2b of the framed opening, or even if it should deform, the positional displacement of the electrophotographic material due to deformation at the charging/exposing head should fall within the optically permissible tolerance. More specifically, various resins such as acryl, polystyrene, vinyl chloride, epoxy polycarbonate, phenol, olyphenylene oxide, polyacetal, diaryl phtalate, nylon, urea, unsaturated polyester resins; metal such as alumium alloys, iron alloys, copper alloys; or ceramics having alumina as the principal ingredient can be used to achieve the objective.

According to the present embodiment, the liquid developer can be supplied free of leak even if the pressure inside the developing chamber is equivalent to or slighly higher than the pressure outside. The present embodiment, therefore, can achieve cost reduction since conventional pumps can be used as the feeding means to supply liquid developer. Presence of the interval between the outer surface of the developing mask means and the electrophotographic material is quite effective in preventing the liquid developer from leaking.

Needless to say, this invention is effectively applicable for the case where a pressure reducing pump is utilized as the feeding means for the liquid developer.

Referring now to Fig. 8 which is a schematic view to show the structure of the second embodiment according to the present invention, the developing head 1 is provided with the developing mask means 2 of the prior art as mentioned above. The developing mask means 2 has a framed opening 2a with an area corresponding to that of one frame of the electrophotographic material to be developed. The mouth 2b of the framed opening 2a abuts against the electrophotographic material 3. As a result, the photosensitive surface 3a, or one frame of the electrophotographic material 3 is exposed to the developing chamber 2g. By applying the liquid developer 5 via the developing chamber 2g, a predetermined latent image can be developed on the surface 3a.

After developing, air can be introduced to squeeze off the residual liquid developer 5. The first passageway 1 8 has its one end opening into the toner tank 7 where the liquid developer is pooled and functions as the exclusive passageway for the liquid developer 5 by means of a compression pump 14 interposed in the midway. Various pumps known in the art such as the Emperor type pump, gear pump, and vane pump can be used as the compression-feeding pump 14. The second passageway 1 9 has its one end opening into the atmosphere and exclusively feeds the air which is sucked by the air pump 20 interposed in the midway of the passageway.The other ends of the passageways 18 and 19 respectively are connected to a valve 1 7. The valve 1 7 is also connected to the inlet port of the third passageway 21 which communicates with the developing chamber 2g. The valve 17 closes the connection between the second passageway 19 and the third passageway 21 when the liquid developer 5 is fed under pressure. The valve 1 7 opens the connection between the second passageway 19 and the third passageway 21 when the liquid developer 5 is not fed. The valve 1 7 prevents the liquid developer 5 from flowing into the second passageway 1 9 which is a passage for feeding the gas, whereby effective squeezing of the liquid developer as well as developing can be achieved.

A valve 1 7 may be a solenoid valve which is structured to be actuated in sequence aligned with the developing process. As shown in Figs.

9(a) through (c), if an automatic valve is used, the apparatus can further be reduced in size and cost.

The valve 1 7 shown in Fig. 9(a) comprises a housing 17a, a cavity 1 7b formed in said housing 17a, and a ball 1 7c contained in said cavity 17b.

The valve 1 7 is three-directional, communicating with passageways 18, 19 and 21 via the cavity 17b. Thus, while the liquid developer is supplied, or when the compressive feeding pump 14 is operating, the liquid developer 5 presses the ball 1 7c to move toward the right in the drawing and close the second passageway 1 9. As the feeding is suspended, or when the air pump 20 is actuated to supply the air, the air presses the ball 1 7c toward the left in the drawing to open the second passageway 1 9 and concurrently close the first passageway 18..The valve 1 7 shown in Fig. 9(b) comprises a housing 17d, a cavity 1 7e formed therein and a thin plate valve member 1 7f provided at the mouth of the second passageway 1 9. This valve is also three-directional, communicating with the passageways 1 8, 1 9 and 21, via the cavity 17e. Thus, when the liquid developer is introduced, the liquid developer presses the valve member 1 7f upward in the drawing to close the second passageway 1 9.

When the air is supplied, the air presses the valve 1 7f downward in the drawing to open the second passageway 1 9. With the valve 1 7 as mentioned above, the first passageway 1 8 is open at all times. The valve 17 shown in Fig. 9(c) comprises a housing 1 7g, a cavity 1 7h formed therein and a ball 1 7i contained in said cavity 17h, and the passageways 18, 19 and 21 are communicating with the cavity 1 7h. Because of the projections 1 7j provided in the cavity 17h, the ball 1 7i will not drop of its own weight.With this arrangement, the air coming into the cavity 1 7h via the second passageway 1 9 will be guided to the third passageway 21 via the groove 1 7k provided on the inner wall of the housing 17g. On the other hand, when the liquid developer 5 is introduced, the ball moves upward in the drawing to close the second passageway 1 9. In other words, the width of the cavity 1 7h, the weight and the diameter of the ball 1 7i and the diameter of the second passageway at the mouth are so selected so as to prevent the liquid developer 5 from flowing into the second passageway 19 when the ball 1 7i moves upward and the ball 1 7i is lighter in weight than the liquid developer 5.

Thus, when the liquid developer is introduced, it presses the ball 1 7i upward to close the second passageway 1 9. When the air is introduced, or at the suspension of liquid developer feeding, the ball 1 7i comes down by its own weight to reach the projections 1 7j to open the second passageway 1 9. The first passageway 1 8 stays open at all times with this valve.

In the second embodiment of the present invention, the valve 1 7 closes the second passageway 1 9 as the compression-feeding pump is actuated to feed the liquid developer 5 and prevents the liquid developer from flowing into the passageway. The liquid developer 5 will be applied to the photosensitive surface 3a via the third passageway 21 and the developing chamber 2g. One might conceive of modifying the feeding systems for liquid developer and the air in the developing head shown in Fig. 2 into a compression type as obtained in the foregoing embodiment. However, the liquid developer 5 will flow and stay in the section of the passageway 10 between the valve 9 and the junction where the passageways 10 and 4 meet.The stagnant liquid developer 5 will then be mixed with the air in the subsequent squeezing process and blown over the photosensitive surface 3a to either smear itor reduce the squeezing efficiency. In the squeezing process following the developing, the valve 1 7 opens the second passageway 1 9 as the air pump 20 is actuated for squeezing and introduced the air onto the photosensitive surface 3a via the third passageway 21 and the developing chamber 2g.

With the valve 1 7 shown in Figs. 9(b) and 9(c), the first passageway 1 8 is open at the same time, so that a portion of the air will flow into the passageway 1 8 but this gives no adverse influence.

The third embodiment of the present invention is shown in Fig. 10. In this embodiment, the valve 1 7 is provided in the second passageway 1 9 on the side of the developing head. The liquid developer 5 is supplied directly to the developing mask means 2 via the first passageway 18. The valve 1 7 may be one-directional that allows the liquid developer 5 to flow from the passageway 1 9 to the developing mask means. This reduces the cost and simplifies the operation. Moreover, because the air is present in the passageway 22 as the valve 17 is closed by the actuation of the pump 14, the liquid developer 5 will not reach the valve 17, protecting more area in the piping from the liquid developer.This further prevents the photosensitive surface 3a from being soiled at the time of squeezing.

In the embodiments shown in Figs. 8 and 10, the air pump 20 is employed as a compressionfeeding means for the gas. Similar effect and action can be obtained by connecting the passageway 1 9 with a bomb containing compressed gas or liquified gas. In this case, gasses such as carbon oxide, fluorcarbon, propane and butane can be used as the squeezing gas other than air. Liquid content of the liquid developer will drop by its weight toward the lower part of the photosensitive surface 3a because the surface 3a is positioned to be vertical or substantially vertical a shown in Figs. 8 and 10. It may therefore be more effective to spray the squeezing gas against said lower portion of the surface 3a.

Thus, according to the second and third embodiments, the compression-feeding system of the liquid developer and the squeezing gas not only results in simplified structure but also prevents the flow of the liquid developer into the second passageway which is exclusively for feeding the gas.

Fig. 11 is a schematic view of the fourth embodiment to show its structure. As shown in the drawing, the developing head 1 is provided with a mask means 2 having an opening with a frame 2a which is identical in area with one frame of the electrophotographic material 3 and in abutment therewith. One frame of the photosensitive surface 3a of the electro-photographic material 3 therefore faces the developing chamber 2g. By applying the liquid developer 5 via the chamber 2g while pressing the electrophotographic material against the developing mask means 2, an electrostatic latent image is developed. Air is then applied to the photosensitive surface 3a for squeezing. More specifically, the liquid developer 5 is pumped out from the toner tank 7 where the liquid developer is pooled and supplied via the first passageway 1 8. The air for squeezing is supplied via the second passageway 1 9 which opens into the atmosphere at one end and is provided with the air pump 20 at its midway which acts as a compressive gas feeding means.

In other words, the liquid developer 5 and the squeezing air are both supplied by compressive means instead of suction means as employed in the prior art. The valve 17 is therefore provided in the second passageway 1 9 to prevent the flow of the liquid developer 5 into the passageway 19 or the air pump 20. The excessive liquid developer 5 after developing on the surface 3a and the air after squeezing return to the toner tank 7 through the outlet port 2e which is formed in the developing chamber 2g to communicate with the fourth passageway 23 for discharging the liquid developer. In this way, the liquid developer 5 pumped out from the toner tank by the compressive pump 14 is applied to the photosensitive surface 3a to develop a given latent image and then squeezed off by the air sucked in by the air pump 20.After developing and squeezing, the pressing plate 12 on the electrophotographic material 3 is released and the electrophotographic material 3 is forwarded by one frame.

The developing mask means 2 of this embodiment is further formed with a suction channel 2i. One end of the suction channel 2i opens into the atmosphere via the suction port 2j.

The other end thereof is connected to a passageway 26 for suction which opens into the atmosphere and which is interposed with a trap 24 and a reduction means such as a suction pump 25. The suction port 2j of the suction channel 2i communicates with the bottom end 2k of the developing chamber 2g via the interval between the developing mask means 2 and the electrophotographic material 3. When the suction pump 25 is in operation and the electrophotographic material is pressed against the developing mask means 2, the liquid which has leaked through the interstice between the side of the frame 2b and the photosensitive surface 3a is sucked out via a suction member 2i. After the excess liquid is squeezed off by air, the pressing plate 12 is released from the electrophotographic material 3 for forwarding the same by one frame.As the interval between the lower end of the developing chamber 2g and the electrophotographic material 3 is widened, air flows into the suction member 2j via the expanded interval to blow off the liquid developer which still remains on the lower end of the photosensitive surface 3a.

As the pressing plate 1 2 is released from the electrophotographic material 3 for forwarding the same by one frame after developing and subsequent squeezing processes, the suction force of the suction pump 25 will act on the interval made between the electrophotographic material 3 and the developing mask means 2 to suck the liquid developer dripping from the bottom end 2k due to squeezing and discharge the same from the passageway 26 via the trap 24 which acts as a filter. The developing head of this construction is capable of adequately squeezing off the excessive liquid developer from the photosensitive surface 3a. The structure mentioned above contributes to satisfactory squeezing of the residual liquid developer 5 on the surface 3a. In the prior art, there were about 1 to 2 mg of residual liquid developer per 1 cm2 on the surface 3a.This was reduced to about 0.3 mg/cm2 in the present invention, The present invention further allows the various parts with the dimension of t1 =0.1 to 0.5 mm and t2=0.3 to 0.5 mm. The suction pump 25 may be any inexpensive reduction means such as a vane pump, and electromagnetic pump, a diaphragm pump or a gear pump of about -50 mm h2O.

Although the trap 24 is provided in front of the suction pump 25 to separate the dripping liquid and the gas and to thereby prevent the liquid from flowing into the suction pump 25, said trap 24 may be omitted if a solvent-resistant pump is employed to return the liquid directly into the toner tank 7.

Fig. 12 shows the portions of the processing head that can be seen from the front. The processing head integrates various processing sections. In the figure, the reference numeral 31 denotes the charging/exposing chamber; 2g the developing/squeezing chamber; 32 the drying chamber; and 33 the fixing chamber, at their openings respectively. The construction of this embodiment allows the liquid developer and the squeezing gas to flow from the upper toward the lower portion of the developing chamber 2g. The suction port 2j is therefore located at downstream of the developing chamber 2g and extends as far as to the charging/exposing chamber in order to protect the chamber from the seeping liquid developer. It is also possible to locate the suction port 2j on the side of the drying chamber.When the squeezing gas is introduced from the side instead of from the upper portion, it is more effective to locate the suction port 2j at the farthermost downstream of the gas flow. As has been mentioned, it is more effective to locate the suction port 2j either at the lower portion of the developing cell 2g or at the farthermost downstream of the gas flow. It is still more effective to locate the suction port 2j at other peripheral portions of the developing cell 2g to suck the liquid developer 5 remaining on the edge of the mouth 2b of the framed opening which is in abutment with the electrophotographic material 3.

In principle, the suction sump 25 is actuated to act on said interval only when the pressing plate is released for forwarding the electrophotographic material by one frame. However, it may be operated continuously during the developing process as well.

Further in the embodiments shown in Figs.

3(a), 8, 10, and 11, although a compression pump is employed to feed the liquid developer, a conventional suction means such as a suction pump may be used for such a purpose and the suction means according to this invention may be used exclusively for sucking the dripping liquid remaining after the squeezing process.

Another embodiment of the means to feed the liquid developer into the developing chamber 2g may be a system including an auxiliary toner tank for the liquid developer provided above the chamber 2g wherein the liquid developer is cycled constantly between the auxiliary toner tank and the toner tank 7, and at the time of developing, the liquid developer stored in the auxiliary toner tank is supplied to the chamber 2g by opening the stop valve. As the surface of the liquid developer is maintained constant so that the liquid developer drips into the developing chamber by its own weight in the above system, the liquid developer can be fed to the chamber 2g at a constant pressure, a constant flow rate and free of influence of the pulsation of the pump, thereby enhancing the effect of this invention.

This embodiment enables thorough and quick squeezing of the residual liquid developer stagnant at the bottom of the developing head by sucking through the interval between the electrophotographic material and the developing mask means which appears when material is forwarded by one frame.

An integral processing head of Fig. 12 which is capable of charging, exposing, developing and fixing may be constructed as shown in Fig. 1 3.

Fig. 1 3 shows the processing head at its charging/exposing section 34 and the developing section 35. Corona ions from the discharge electrode 38 in the charging/exposing section 34 are uniformly discharged onto the electrophotographic material 3 where the light from the lens 39 is focused for exposing to form a pattern of residual charges or the latent image. The electrophotographic material 3 is then sent for one frame so that the exposed frame would fit in the opening frame 2a in the developing section 35 and the liquid developer 5 is applied on the surface of the electrophotographic material 3 for developing.A pressing plate 1 2 is provided to press the electrophotographic material 3 against the processing head in order to precisely position the electrophotographic material 3 with respect to the processing head as well as to maintain the same as flat as possible at the charging/exposing section 34. The pressing plate 12 also functions to prevent the developer containing the liquid developer 5 from leaking into the developing section 35. In the chargingiexposing section 34, a condensor lens 40 and a projection lamp 41 for projecting the images recorded on the electrophotographic material 3 are located the opposite side of explosure lens 39 with respect to the pressing plate 12.

In an electrophotographic apparatus having a processing head of this construction, exposure and projection can be conducted in the charging/exposing section 34. Because the light is irradiated from both sides of the pressing plate 12, the pressing plate 12 must be made lightpermeable. However, there will be an excess of light if the entire pressing plate 12 is made lightpermeable.

The illumination on the film surface at the time of projection is about 100,000 Lux, by far greater than the value at the time of exposure which is about 100 Lux. As a consequence, frames other than the one to be projected will also be exposed to extremely strong light, thereby causing fatigue or discoloration of the film and a decrease in film performance, especially so if the adjacent frames are not yet recorded.

Such defects can be overcome by providing a pressing plate 1 2 of the following construction.

That is, Fig. 14(a) shows the total front view of the processing head comprising charging/exposing section 34, the developing section 35, the drying section 36 for drying the liquid developer adherent to the photosensitive surface 3a, and the fixing section 35 where the liquid developer 5 is fixed by heat. The pressing member 1 2 which presses the electrophotographic material 3 against the processing head while the electrophotographic material 3 is processed for charging, exposing, developing and fixing at the head has the length and the width sufficient to cover the charging/exposing section 34 and the developing section 35. The pressing member 12 is necessary to accurately hold the electrophotographic material 3 in position at the charging/exposing section and to prevent the liquid developer from leaking at the developing section 35.

The pressing member 12 is a plate made of metal or plastic which is light-shielding and the portion thereof corresponding to the window of the charging/exposing section of the processing head for introducing the light is made open. The pressing member 12 can also be made of a transparent material 1 2a such as glass, as shown in Fig. 1 4(b), with the side facing the electrophotographic material 3 being plated with light-shielding metal 1 2b or coated with lightshielding paint. if a transparent material 1 2a is used as the pressing member 12, the portion corresponding to the light window must be made transparent without the metal plating or lightshielding paint.The transparent member 1 2a as shown in Fig. 14(b) is covered with light-shielding metal plating 1 2b or paint on the side facing the electrophotographic material 3 in order to prevent the light from filtering into the electrophotographic material 3 through the transparent member 12a.

The pressing plate 12 of Fig. 1 5 is made of a transparent member 1 2a such as glass at the portion which faces the light window of the charging/exposing section 34 and of a resilient member 42 such as rubber at the portion which faces the developing section 34 adjacent to the charging/exposing section 34. Both the transparent member 1 2 and the resilient member 42 are affixed to one base 43. The transparent member 1 2a is again covered with light-shielding film 44 at both ends to prevent the light from spreading. In case the resilient member 42 is light-shielding, the film 44 adjacent to the resilient member 42 can be omitted. The resilient member 42 is provided to press the electrophotographic material 3 firmly against the framed opening 2a so that the liquid developer 5 can be prevented from leaking during the developing.

The resilient member 42 is protruded slightly from the adjacent transparent member 1 2a and securely presses the electrophotographic material 3 against the framed opening 2a by its resilience.

The transparent member 1 2a also functions to securely press the electrophotographic material 3 against the framed opening 2a.

In the embodiments mentioned above, either a light-shielding metal or plastic member provided with an opening, or a transparent member 1 2a coated with light-shielding metal 1 2b or paint except for the transparent portion, or a transparent member 1 2a provided with lightshielding film at both ends and positioned adjacent to the resilient member 42 is employed as the pressing member 12. However, various modifications are possible if the opening or the transparent portion of the pressing member 12 is so constructed as to allow the light to pass while the rest of the member is made light-shielding to prevent the light from spreading onto the electrophotographic material 3.

The use of the pressing plate 12 which is capable of shielding the electrophotographic material 3 from the light except for one frame coming under the light window thereof is therefore effective, especially when the projection lamp 41 is switched on to irradiate the electrophotographic material 3 with very intensive light for one frame under the light window. Thus, even if the material surface adjacent to the surface being projected is not yet recorded, this surface will be shielded from the irradiation and there will be no fear for deteriorating the performance of the electrophotographic material 3.

After developing by applying the liquid developer 5 on the photosensitive surface 3a of the electrophotographic material 3, a rinsing liquid which is compatible with and dries more quickly than the solvent of the liquid developer 5 may be poured on said photosensitive surface, drained and then dried. Use of this quick-drying rinsing liquid after developing achieves quick drying of the photosensitive surface 3a.

The present invention encompasses the combinations of the four embodiments mentioned above.

The combinations include: a) the first embodiment with the second or third embodiment; b) the second or third embodiment with the fourth embodiment; c) the first embodiment with fourth embodiment; d) the first, second or third embodiment and fourth embodiment.

Claims (19)

1. A developing head for electrophotographic apparatus which comprises a developing mask means having a developing chamber defined by a framed opening facing the photosensitive surface of an electrophotographic material for electrophotography, the mouth of said opening abutting said photosensitive surface, the outer peripheral surface of said developing mask means facing the photosensitive surface and being shaped to inhibit the leakage of a liquid developer by capillary action outwardly between the mouth and the photosensitive surface.

2. A developing head according ot claim 1 in which a bent or curved portion is formed near the mouth of the framed opening to assume an angle greater than that formed between the rest of the outer peripheral surface of the developing mask means with said eiectrophotographic material so as to form a recess which inhibits leakage of the liquid developer past said bent portion by capillary action.

3. A developing head according to claim 1 or claim 2 wherein an annular groove is formed on the outer peripheral surface of the developing mask means near the mouth.

4. A developing head according to any of claims 1 to 3 wherein a liquid feeding means for said liquid developer comprises a toner tank, a liquid feeding pump and an auxiliary toner tank provided above the developing chamber.

5. A developing head according to any of claims 1 to 4 in which a gas applying means is provided to apply gas onto the photosensitive surface via the developing chamber to thereby squeeze off liquid developer after it contacts with the photosensitive surface.

6. A developing head according to claim 5 in which a pressing plate in abutment with the back of the electrophotographic material is arranged to press the same against the mouth of the framed opening when liquid developer is applied for developing and when the gas is applied to squeeze off the residual liquid developer and to release its pressing when the electrophotographic material is forwarded for one frame.

7. A developing head according to claim 5 or claim 6 in which a pressure reduction means is provided to apply a negative pressure to the interval made between the photosensitive surface and at least a portion of the mouth of the framed opening of the developing mask means.

8. A developing head according to claim 7 wherein said negative pressure is applied to the interval between the lower end of the mouth of the framed opening and the lower end of the photosensitive surface.

9. A developing head according to claim 7 or claim 8 wherein said pressure reduction means is a suction pump.

10. A developing head according to any of claims 5 to 9 in which: a first passageway is provided exclusively for supplying liquid developer; a second passageway is exclusively for supplying the gas; and a valve is provided to close said second passageway when the liquid developer is supplied.

11. A developing head according to claim 10 wherein said valve is located at the junction of a third passageway which communicates with the first and the second passageways and the developing chamber and where the liquid developer and the gas flow alternately.

12. A developing head according to claim 10 wherein said valve is located in the second passageway.

13. A developing head according to claim 6 or any of claims 7 to 12 taken with claim 6 which is characterized in that said electrophotographic material is pressed against said opening frame side surface so as to reduce the gap between said mouth and said electrophotographic material to 25 ym or less.

14. In a developing head for electrophotographic apparatus which comprises a developing mask means having a developing chamber defined by a framed opening facing the photosensitive surface of an electrophotographic material for electrophotography, the mouth of said opening abutting said photosensitive surface, an outer peripheral surface of said developing mask means facing and being spaced from the photosensitive surface, and wherein the photosensitive surface is contacted with the liquid developer supplied from a liquid feeding means via said developing chamber to achieve development of the electrophotographic material, said developing head is characterized in that: a gas applying means is provided to apply gas into the photosensitive surface via the developing chamber to thereby squeeze off the liquid developer after it contacted with the photosensitive surface.

a first passageway is provided exclusively for supplying the liquid developer; a second passageway is provided exclusively for supplying the gas; and a valve is provided to close said second passageway when the liquid developer is fed.

1 5. A developing head according to claim 14 wherein said valve is located at the junction of a third passageway where it communicates with the first and the second passageways and the developing chamber and where the liquid developer and the gas flow alternately.

1 6. A developing head according to claim 14 wherein said valve is located in the second passageway.

17. A developing head for electrophotographic apparatus which comprises a developing mask means having a developing chamber defined by a framed opening facing the photosensitive surface of an electrophotographic material for electrophotography, the mouth of said opening abutting on said photosensitive surface and the outer peripheral surface of said developing mask means facing and spaced from the photosensitive surface and wherein the photosensitive surface is contacted with the liquid developer supplied from a liquid feeding means via said developing chamber to achieve development of the electrophotographic material, for which head a gas applying means is provided to apply gas onto the photosensitive surface via the developing chamber to thereby squeeze off the liquid developer after it contacted with the photosensitive surface; ; a pressing plate is provided to press the electrophotographic material against said mouth of the framed opening during the developing process of applying the liquid developer and during the squeezing process of applying the gas to remove the liquid developer, said pressing being released when the electrophotographic material is forwarded for one frame; and a pressure reduction means is provided to apply a negative pressure to the interval between the photosensitive surface and at least a portion of the mouth of the framed opening of the developing mask means.

18. A developing head according to claim 17 wherein said negative pressure is applied to the interval made between the lower end of the mouth of the framed opening and the lower end of the photosensitive surface.

19. A developing head according to claim 17 wherein said pressure reduction means is a suction pump.