ELECTROSTATIC SEPARATOR FIELD OF THE INVENTION The present invention relates to electrostatic imaging generally and more particularly to liquid toner electrostatic imaging. BACKGROUND OF THE INVENTION Separation of toner particles from carrier liquid is important in various applications of electrophotography. Various types of separation apparatus are known in the patent literature. For example, there is described in U.S. Patent 4,737,268 apparatus for electrostatically separating particles in a liquid stream. The technique of U.S. Patent 4,737,268 is essentially a plating operation and thus requires periodic deplating in order to operate. There is described in U.S. Patent 4,504,138 a method and apparatus for developing electrostatic latent images wherein a thin highly viscous layer of concentrated toner particles is defined on a roller, portions of the layer being transferred to an image bearing surface by electrostatic means. SUMMARY OF THE INVENTION The present invention seeks to provide improved apparatus for separating toner particles from a carrier liquid and for creating a layer of concentrated toner particles on a roller. There is thus provided in accordance with a preferred embodiment of the present invention electrostatic separator apparatus for the separation of particles from a liquid including a drum having a drum surface, means for supplying a particle dispersion including particles dispersed in a liquid to the drum surface, electrostatic means for causing at least some of the particles to adhere to the drum surface in a non-i agewise configuration, resilient blade means, downstream of the electrostatic means, for operative engagement with the drum surface for retaining a layer of particle rich material on the drum surface, and layer removal means for layerwise removing substantially all of the layer from the drum surface.

Further in accordance with a preferred embodiment of the present invention, the blade is maintained at an electrical potential different from the electrical potential of the drum surface. Still further in accordance with a preferred embodiment of the present invention, the particles are charged and the blade means is maintained at an electrical potential which is operative to repel the particles toward the drum surface. There is also provided in accordance with a further preferred embodiment of the present invention, apparatus for the separation of particles from a liquid including a drum having a drum surface, means for supplying a particle dispersion including particles dispersed in a liquid to the drum surface, electrostatic means for causing at least some of the particles to adhere to the drum surface in a non- imagewise configuration, retaining means downstream of the electrostatic means for operative engagement with the drum surface for retaining a layer of particle rich material on the drum surface, the retaining means maintained at an electrical potential different from that of the drum surface, and layer removal means for layerwise removing of substantially all of the layer from the drum surface. Further in accordance with a preferred embodiment of the present invention, the retaining means includes a blade. Still further in accordance with a preferred embodiment of the present invention, the retaining means includes a squeegee roller. Additionally in accordance with a preferred embodiment of the present invention, the particles are charged and the retaining means is operative to repel the particles toward the drum surface. Further in accordance with a preferred embodiment of the present invention, the means for supplying includes a bath through which the drum surface travels. There is also provided in accordance with yet a further embodiment of the present invention apparatus for separation of toner particles from a carrier liquid including a surface, means for repeatedly supplying a layer of material

relatively rich in toner particles and containing carrier liquid to the surface and for subsequently concentrating the layer and removing therefrom a substantial portion of the carrier liquid, and means for supplying additional material rich in toner particles and containing liquid carrier to the surface and further concentrating the new material to increase the thickness of the layer. Further in accordance with a preferred embodiment of the present invention, the toner material is charged and the means for repeatedly supplying and concentrating includes concentrating means maintained at a potential of the same sign as the charge on the toner particles. Still further in accordance with a preferred embodiment of the present invention, the means for repeatedly supplying and concentrating includes concentrating means including a blade. Additionally in accordance with a preferred embodiment of the present invention, the means for repeatedly supplying and concentrating includes concentrating means including a squeegee roller. There is further provided in accordance with yet a further preferred embodiment of the present invention apparatus for the separation of particles from a liquid including a drum having a resilient drum surface, means for supplying a particle dispersion including particles to the drum surface, means for causing at least some of the particles to adhere to the drum surface, and retaining means for operative engagement with the drum surface for retaining a layer of particle rich material on the drum surface in a non-imagewise configuration. According to still a further preferred embodiment of the present invention there is provided a method for separation of particles from a liquid including the steps of supplying a particle dispersion including particles in a carrier liquid to a surface, causing at least some of the particles in the dispersion to adhere to the surface in a non-imagewise configuration, contacting.the surface with a resilient blade for retaining a layer of particle rich

material on the surface, and layerwise removing of substantially all of the layer from the surface. According to an additional preferred embodiment of the present invention there is provided a method for separation of particles from a liquid including the steps of supplying a layer of material relatively rich in toner and containing carrier liquid to a surface, further concentrating the layer and removing therefrom a substantial portion of the carrier liquid, and repeating the steps of supplying and further concentrating to increase the thickness of the layer. According to still a further preferred embodiment of the present invention there is provided a method for the separation of particles from a liquid including the steps of supplying.a layer of material relatively rich in toner and containing carrier liquid to a surface, supplying a particle dispersion in a liquid to the surface, causing at least some of the particles to adhere to the surface in a non-imagewise configuration, causing operative engagement of an electrified member with the surface for retaining a layer of particle rich material on the surface, and layerwise removing of substantially all of the layer from the surface. Further in accordance with a preferred embodiment of the present invention, the apparatus also includes layerwise removal means for removing the thicker layer from the drum . surface. Still further in accordance with a preferred embodiment of the present invention, the- eans for supplying supplies the layer in a non-imagewise configuration. Additionally in accordance with a preferred embodiment of the present invention, the apparatus also includes layer removal means for layerwise removing of the layer from the drum surface. Further in accordance with a preferred embodiment of the present invention, the method further includes the step of layerwise removal of the layer from the drum surface. There is further provided in accordance with yet a further preferred embodiment of the present invention

electrostatic separator apparatus for the separation of particles from a liquid including a drum having a drum surface, means for supplying a particle dispersion in a liquid to the drum surface, electrostatic means for causing at least some of the particles to adhere to the drum surface, resilient blade means, downstream of the means for causing, for operative engagement with the drum surface for retaining a layer of particle rich material on the drum surface, and removal means for non-imagewise removing of the layer from the drum surface, wherein an image is not formed in the layer. There is also provided in accordance with still a further preferred embodiment of the present invention apparatus for the separation of particles from a liquid including a drum having a drum surface, means for supplying a particle dispersion in a liquid to the drum surface, means for causing at least some of the particles to adhere to the drum surface a non-imagewise configuration, retaining means downstream of the means for causing for operative engagement with the drum surface for retaining a layer of particle rich material on the drum surface, the means maintained at a potential different from that of the drum surface, and removal means for non-imagewise removing of the layer from the drum surface, wherein an image is not formed in the layer. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: Fig. 1 is a schematic illustration of apparatus constructed and operative in accordance with a preferred embodiment of the present invention; and Fig. 2 is a schematic illustration of apparatus constructed and operative in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Fig. 1, which illustrates apparatus constructed and operative in accordance with a preferred embodiment of the invention including a drum 10, typically formed of metal and having a preferably cylindrical drum surface 12, also typically formed of metal. Preferably drum surface 12 is grounded. There is provided a liquid toner bath 14, typically defined by a negatively biased electrode, and which defines an inlet 16 for receipt of liquid toner and an outlet 18, typically disposed lower than inlet 16, for removal of carrier liquid which is relatively free of toner particles. Toner bath 14 is arranged preferably such that approximately one half of the drum diameter is immersed in the bath at the side of inlet 16 and less than one half of the drum diameter is immersed in the bath at the side of outlet 18. The toner located in bath 14 typically comprises negatively charged particles. If alternatively it is desired to employ positively charged toner particles, the electrode is accordingly positively biased. In the illustrated embodiment, the drum rotates in the direction of arrow 20 from the side adjacent outlet 18 through the bath 14 to the side adjacent inlet 16. Downstream of bath 14 there is provided a first blade 22, typically arranged at the upper, upward rotating quadrant of the drum surface 12, for operatively engaging the drum surface 12. According to a preferred embodiment of the invention, the first blade is operative to define on the drum surface a layer 24 of relatively viscous concentrated liquid toner. According to a preferred embodiment of the present invention, the first blade is typically formed of resilient polyurethane with a Shore A hardness of typically 20-60 and thickness 2 mm and is arranged to apply a total pressure of about 100 grams along a length of about 20 cm. Use of a resilient blade provides a generally uniform pressure to the layer of toner material notwithstanding variations in the relative positioning of the drum surface

thereto . According to a possible alternative embodiment of the invention the drum surface 12 is formed of relatively resilient material and the first blade 22 may be formed of relatively less resilient material. According to a preferred embodiment of the invention, the first blade may be maintained at a potential which is the same in sign as that of the charge on the toner particles, to compact the image and aid in liquid removal. For this embodiment the blade may be made of conductive resilient polymeric materials as described in either or both of U.S. Patents 3,959,574 and 3,863,603 which are incorporated herein by reference. In order to avoid the possibility of short circuits or arcing, as for example when there are no toner particles on the drum, current limitation may be added to the potential power supply. In accordance with an embodiment of the invention, the apparatus of the present invention may also include scraper blade apparatus 30, which typically operatively engages the drum surface 12 at the upper, downward rotating quadrant of the drum surface. Scraper blade apparatus 30 is operative to remove layer 24 and to direct the relatively viscous concentrated liquid toner of which layer 24 is composed to a concentrated dispersion tank 32. A tank 34 may be also provided for receipt of relatively clear carrier liquid from outlet 18. It is appreciated that scraper blade apparatus 30 may alternatively be eliminated. According to a preferred embodiment of the invention an inlet toner particle concentration of about 1.5% may be used with a bath electrode potential of approximately -800 to -1000 volts when the electrode is separated from the drum 10 by a distance of about 500 microns. For a typical drum diameter of 120 mm, a drum surface linear velocity of about 10 cm/sec may be employed. It is appreciated that when the scraper blade apparatus 30 is not used or is disengaged, the drum and the layer built up thereon may be rotated multiple times through the bath 14 and past the first blade to provide enhanced layer uniformity, thickness and

concentration. Three to four such rotations are preferred and provide a layer of typical thickness of about 5 microns. Should it be desired to remove the built up layer, the scraper blade apparatus 30 may be re-engaged. Reference is now made to Fig. 2, which illustrates apparatus which is substantially similar to the apparatus of Fig. 1, with the exception that the first blade 22 is replaced by a charged squeegee roller 40. Squeegee roller 40 is typically formed of resilient polymeric material such as that described in either or both U.S. Patent 3,959,574 and 3,863,603, having a hardness of typically 20 to 60 shore A and applies a pressure of to the layer 24 sufficient to form a nip, typically 0.5 to 1 cm. Where negatively charged toner particles are employed it is maintained at a typical voltage of -750 volts. In order to avoid the possibility of short circuits or arcing, as for example when there are no toner particles on the drum, current limitation may be added to the power supply. The present invention is especially useful when practiced with liquid toner materials of the type disclosed in U. S. Patent 4,794,651 which is incorporated herein by reference. It is also useful when practiced on a variety of other liquid toner types. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the invention is defined only by the following claims: