DE2338487A1 - DEVICE FOR APPLYING A LIQUID DEVELOPER TO A LATENT ELECTROSTATIC IMAGE - Google Patents

Description

OR.-ΙΝβ. ΟΙΜ ^ -ΙΝβ. Μ. SC. OIPL.-i'HYS. OR. HÖGER - LEGAL RIGHTS - GRIESSBACH - HAECKER A 4O259 h PATENTANWÄLTE IN STUTTGART

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July 24, 1973

U.S.Ser.No. 287 693

Savin Business Machines Corporation, Valhalla, N.Y., U.S.A ..

Device for applying a liquid developer to a latent electrostatic Image.

The invention relates to a device for applying a liquid developer onto the image surface of a latent electrostatic image present on a carrier a frame and with a conveying device for supplying developer liquid to an application device, the is attached to the frame.

There are already various methods known to apply a liquid developer to surfaces, the electrostatic Bear pictures. Liquid developers as used in the well-known "Elektrofax" process have several

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characteristic features that determine to a large extent the design of the application systems, as they are in the case of electrostatic Copying machines are used. Liquid developers generally contain finely divided toner particles that are in a relatively non-conductive, light hydrocarbon carrier fluid are suspended. In the case of sticky liquid developers, the fine particles are emulsified into a paste that is, a mixture of a sticky resin and a developer toner contained in a volatile carrier liquid is emulsified. In order to get a good reproduction, it is necessary that the developer liquid before use is mixed well and the application is done evenly. The application of a liquid developer in which the toner particles are not evenly distributed, undesirable contrasts and uneven development can result. The application of a liquid developer in an uneven manner may result in streaking and uneven development to have.

Attempts are already known to avoid these disadvantages. Known developer systems generally have a trough which is filled with developer liquid, and an application device, which transfers the developer liquid to the photoconductive image areas. In one procedure, the Developer liquid thrown by movable members against the surface to be developed, for example by rollers, which are partially immersed in the developer trough and which are used in pairs in such a way that a standing wave is generated above the rollers which the surface to be developed contacts when the surface passes through the developer zone passes through.

In another known application method, the developer liquid is stirred underneath the surface and

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then essentially against the surface to be developed evenly sprayed on.

According to a further method, the developer liquid is applied to a roller, which the developer on the Surface distributed by contacting and rolling on the surface. The developer liquid will play the role in the Manner supplied that a considerable amount of liquid is available at the front nip of the roll, so as to ensure that a sufficient amount of developer for a full developed image is present.

Method using moving belts as a transfer device or a direct partial immersion of the image-bearing surface in the developer trough are also possible known.

In all of the above-mentioned methods, the excess developer liquid is removed from the image-bearing surface removed and then fed back to a storage tank, where toner or carrier liquid is controlled and automatically added. When the copying machine is working, the developer liquid constantly circulated between the supply tank and the developer distribution apparatus. This circulation system also serves to prevent clumping and settling of toner particles to some extent. the However, ensuring the correct development characteristics does not only depend on maintaining an even distribution of toner particles in the developer liquid, but separate also from the contact of the surface bearing the image with the developer liquid in such a way that the attraction from suspended toner particles to the charged areas of the surface represents an optimum. The latter task can be solved by the formation of eddies in the developer liquid layer is reduced when this is reduced to the

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moving surface. The systems of known type achieve however, no satisfactory uniform toner particle distribution or no optimal toner particle attraction. These disadvantages occur in particular in application systems that use a mechanical transfer, for example by rollers, for the developer application. The toner particles cling often adhere to the transmission mechanism, whereby the uniformity of the application of the liquid and also the Mixture will be affected. The spray method is not a favorable method to ensure a high level of uniformity to achieve.

The problem of achieving a uniform and appropriate development on the image-bearing surface is in the Even more difficult to solve in cases where a rapid developer action is required, for example when that is too developing medium through the development zone with a relative moving at high speed.

The invention is now based on the object of the developer liquid both to mix well and to apply evenly. This task is carried out in the aforementioned

of the invention
direction according to ^ solved in that the application device

is designed in such a way that the liquid can be dispensed in a multiplicity of planar, preferably laminar liquid flows which are directed towards the image surface and which combine to form a common stream when they are spent. With the help of the liquid streams a steady one becomes Mixing and uniform application to the image-bearing surface is achieved. It also causes clumping reduced by subjecting the liquid developer to shear forces which create laminar flow layers, whereby the toner particles are mixed in suspension in the liquid. This system according to the invention is used

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furthermore no cumbersome mechanical transmission devices. It is particularly suitable for high speed application of the developer, but by no means limited to this.

In a particular embodiment, the has to distribute a liquid developer serving means a grid of horizontally spaced parallel guide plates. The developer liquid flows upwards from the base of the Setup through narrow spaces between the guide plates. The separate developer flows then emerge from the Rooms in the development zone at the top of the facility the end. The streams combine and then form a very well mixed layer of developer fluid that mixes with the Moved photoconductive image surface and contacted them when this surface moves through the development zone. This novel system distributes the. Developer liquid on the entire exposed area of the photoconductive surface in such a way that a high uniformity and a rapid order is ensured. The developer liquid must pass up through the spaces in the grid made of metal plates before this layer of liquid is formed / which then contacts the photoconductive surface. The flow in these spaces is due to the viscous shear forces, that arise between the panel walls, laminar. The liquid laminar layers help mix the toner in suspension, ensuring that the developer fluid is in the best possible condition prior to contacting the photoconductive surface.

The streams of liquid that emerge from the interstices form a layer above the output surface of the grille, which then contacts the photoconductive surface and moves with it. The attraction of toner particles by the

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charged areas of the surface is increased because of the movement of the liquid, surface-contacting layer is relatively vortex-free and the toner particles are not stirred.

Further advantages and features of the invention emerge from the following description in connection with the drawing, includes embodiments of the invention. In the drawing show:

Fig. 1 is a schematic view of a first embodiment of an electrostatic copying machine below Use of the application device according to the invention for applying developer,

2 shows a plan view of the first embodiment of the application device,

3 shows a section according to. Line 3-3 of Fig. 2,

4 shows a partial side view of this first application device,

5 shows a plan view of a second embodiment of the application device according to the invention ,

6 shows a side view according to FIG. 5, with individual Parts broken off and others shown in section.

In Fig. 1, an embodiment of an electrostatic copying machine is designated as a whole with 1o. This copier has an application device according to the invention which is used to apply developer. The copier has furthermore a drum 12 which is carried by a shaft 15 so that the drum now rotates in the direction of arrow A can. The drum 12 carries on the surface a film of photoconductive material having a surface 14. In operation, that is, when the drum 12 rotates, the surface 14 of the for moves on an exposure source 16

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which removes any charge left on the drum as a result of previous actuation. The drum 12 then moves the surface 14 past a corona discharge station 18, which is known per se and which now has a electrostatic charge is applied to the photoconductive surface. After this charge, the photoconductive moves Surface past an exposure station 2o where the surface is exposed to the image of the original to be copied so that an electrostatic latent image is now formed on the photoconductive surface.

After exposure of the surface, which is now the latent electrostatic Carrying image, it moves past the developer station, at which the as a whole is designated with 6 Applicator is located. There a liquid developer is applied to the photoconductive surface 14 to so to develop the electrostatic image. The developer applied by the applicator 6 has a sticky one Toner suspended in a suitable carrier. Paper or other material that comes off a roll 22, moves through a heater 24 and then around a guide roller 26 and is then in contact with the photoconductive surface 14 brought by a pressure roller 28. While the developed photoconductive surface is the development station leaves the sticky toner present on the surface in contact with that against surface 14 attached paper. Because the sticky toner has a greater affinity for the surface of the paper than for the photoconductive one Film is on the drum 12, the image is now on the paper transfer. This then moves around guide rollers 3o and 32, which then pass on the copy.

Furthermore, a pump 34 feeds developer from a storage tank 36 via a line 38 to a distributor 4o which supplies the liquid

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distributed in the developing device in a manner as will be further described below. Furthermore, there is an overflow developer from a distributor device 42 in an overflow trough 44 collected, from which the liquid then flows via line 46 to tank 36. There is also a monitoring device 48 known type provided to determine the concentration of the developer. By controlling with the help of the monitor 48, when the concentration of the toner falls below a predetermined level, more toner is released Carrier liquid is supplied via line 5o from a storage system (not shown). Similarly, if "the If the carrier liquid in the storage tank 36 falls below a predetermined height, then more carrier liquid is supplied via a level sensor 52 supplied via line 5o.

The copying machine 1o serves as an example of the application the invention. The application device according to the invention can however, they can also be used in other electrostatic copying machines that employ liquid developers.

In Figs. 2 to 4, a first embodiment is a Applicator shown, which has a group of preferably formed of metal guide plates 54, which by Ü-members 56 are held at a distance so that narrow spaces 58 are formed, each approximately 0.368 mm wide The developer fluid then flows through these spaces. The guide plates are arranged at an angle to the direction of movement of the drum 12 in order to achieve greater evenness the developer application to the image surface 14 to achieve. The entire plate assembly of guide plates 54 and U-glasses 56 is held together between end plates 6o by screw connections 62. The guide plates 54 have openings 64 in the Proximity of the bottom of the spaces 58, so that after assembly of the guide plates a group of aligned openings 64 is present is.

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The distributor 4o now guides liquid developer through the group of openings 64 and the spaces 58 between the Guide plates too. This liquid developer flows up into the intermediate spaces towards the run-off edges 66 of the guide plates. During this upward movement of the liquid, it becomes Subjected to shear forces created by the walls of the guide plates. The run-off edges are around the axis of the drum 12 curved so that they define an arcuate drainage surface, which corresponds to the curvature of the drum 12. The currents liquid developer now flows out of their spaces and unite in a developer zone above the drainage area and below the photoconductive image area 14. Sealing strips 68 are on the longitudinal edges of the developer zone provided and prevent the liquid developer from flowing out of the spaces 58 over the longitudinal edges of the Front plates 6o away.

The liquid developer in the developing zone now has the tendency i is mitzubewegen 14, as it moves through the Entwicklerζone, in the direction as indicated by the arrow B of FIG. In the direction of movement of the surface. Excess developer flows over the ends of the assembly consisting of guide plates 54 and U-members 56 through rooms 7o and 72 into an overflow trough 44. This excess developer is then pumped back from this trough to the overflow system, as described in connection with FIG. 1, whereupon this liquid is fed back to the distributor device.

The normal gap width between the run-off edges 66 of the applicator and the drum 12 is approximately 0.735 mm. Furthermore, an adjustment device is provided to adjust the distance of the application device relative to the drum 12. For this purpose, each shaft carries a pair of

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Shafts 74 rotatably mounted on the applicator, a pair of spaced eccentrics 76 contacting bearing blocks 78 mounted on the machine frame. By means of crank arms 8o on the shafts 74, the shafts can be rotated and thus the eccentrics 76 can be positioned on the bearing blocks 78 in such a way that the desired distance between the trailing edges of the guide plates 54 and the surface of the drum is set. Bolts 81 or the like on the crank arms 8o serve to fix the set positions along arcuate slots 82 by locking the crank arms 8o.

It is evident that the spaces can be arranged so that they form an angle to the direction of movement of the photoconductive image surface. A slight deviation from the parallel position to the direction of the surface movement corresponding to the gaps according to FIG. 2 is not essential, but this is advantageous because it improves the uniformity of the application of the liquid developer. It is possible that there may be some non-uniformity in the application near the longitudinal edges of the assembly when this interstitial plate arrangement is used. Such an unevenness of the application can now be avoided by using the application device according to FIGS. 5 and 6, in which the guide plates 84 are arranged essentially perpendicular to the direction of movement of the drum 12. Liquid developer is supplied to the interstices from a manifold 88 in the same manner as is described in connection with the arrangement of FIG. In either construction, the liquid developer in the development zone can be supplied to the entire area of the photoconductive surface.

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How the two embodiments of the developer system work is essentially the same. The liquid developer that is suspended in a carrier liquid 'There is toner particles, is via the pump 34 from a storage tank 36 to the distributor 4o according to FIGS. 1 to 4 or to the distributor 88 in the embodiment according to FIGS. 5 and 6. In both cases, the developer liquid is after above the drum 12 pushed through the narrow spaces between the guide plates, so that they now Shear forces through the panel walls is subjected. The mixing is also achieved by the reunification of the Improved currents that emanate from the spaces, open into the developer zone and there a layer of developer liquid form. The laminar arrangement of the guide plates also results in a highly uniform application of the liquid developer on the entire area of the photoconductive image surface, causing streaking and avoid uneven development, as occurs with other application systems of known type. The excess Developer flows .then over the ends of the aforementioned Assembly unit and is then fed back to the storage tank 36.

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Claims (11)

A 40 259 h - 12 - Claims Device for applying a liquid developer to the image surface of a latent carrier present electrostatic image with a frame and; with a conveying device for supplying developer liquid to an application device which is attached to the frame, characterized in that the application device (54, 56) is designed so that the liquid is in a variety of planar, preferably Laminar liquid flows can be output, which are directed towards the image surface (14) and which are dispensed when dispensing unite into a common stream. 2. Device according to claim 1, characterized in that the output device (54, 56) is provided so that on the supplied liquid shear forces are exerted. 3. Device according to claim 1 or 2, characterized in that the liquid flows have a small thickness and are relatively wide. 4. Device according to one of the preceding claims, characterized characterized in that the liquid streams are film-like. 5. Device according to one of the preceding claims, characterized in that the liquid flows parallel to one another are. 6. Device according to one of the preceding claims, characterized in that the position of the output device (54, 56) is adjustable relative to the image surface (14). 7. Device according to one of the preceding claims, characterized in that the output device (54, 56) a plurality of guide plates (54) which are held by spacing means (56) at a small distance, and that the - 13 - 4098 1 3 / 10A9 A 40 259 h '- 13 - Conveyor device (34) supplies liquid in spaces (58) between the guide plates. 8. Device according to claim 7, characterized in that ν the guide plates (54) have a plurality of parallel spaces (58) that are closed at the bottom and, if necessary, also at the sides. 9. Device according to claim 7 or 8, characterized in that that the guide plates (54) in the vicinity of the bottom have aligned openings (64) to which the conveying device (34) is connected. 10. Device with a movable carrier according to one of the preceding claims, characterized in that the liquid flows in the direction of width under one Angle to the direction of movement of the carrier (12) relative to the dispensing device (54, 56). 11. Device according to one of the preceding claims, characterized characterized in that the width direction of the liquid streams is substantially perpendicular to the movement of the Carrier (12) is relative to the output device (54, 56). 12 · Device with a carrier designed as a drum according to one of the preceding claims, characterized in that the dispensing device (54, 56) is arranged so that the liquid flows on a cylindrical Surface that corresponds to the curvature of the drum (12) 409813/10 Λ 9 Blank page