US3384051A - Electrostatic liquid developer system - Google Patents

Description

y 1968 F. HUNSTIGER 3,384,051

ELECTROSTATIC LIQUID DEVELOPER SYSTEM Filed Sept. 21, 1966 INVENTOR. FRANCIS HUNSTIGER M WM 7M? ATTORNEYS United States Patent 0 3,384,051 ELECTRDdTATlC LIQUH) DEVELOPER SYSTEM Francis Hunstlger, Parma Heights, Ohio, assignor to Harris-lntertype Corporation, Cleveland, Ohio, :1 corporation of Delaware Filed Sept. 21, 1966, Ser. No. 581,064

3 Claims. (Cl, 118637) AESTRACT Gil THE DISCLOSURE A liquid electrostatic developer includes a drum roll for submerging the image side of the Web while maintaining the non-image side free of liquid developer in which the drum roll is formed with a blanket of polyurethane elastomer which is relatively unaffected by the developer liquid, and a hard squeegee roll engaging the image side of the web, confining slippage to the non-image side of the web.

This invention relates to electrostatic photography and more particularly to an improved developer apparatus in which an image bearing member having an electrostatic image is developed by bringing the member directly into contact with a liquid developer.

This invention relates primarily to an improved developer system in which the electrostatic image bearing member is supported on a drum roll for movement through a tank containing a liquid developer, and in which a squeegee roll is applied against the member on the drum roll to remove excess developer liquid. When such an image bearing member, such as a web of electrophotographic paper, is pulled through a nip formed between a hard drum roll surface and a resilient surface on the squeegee roll, there is some slippage at the nip. If this slippage occurs against the newly developed image, it may cause elongation or smearing of small detail such as elongation of dots, fine lines, and the like. While such elongation may not be readily noticeable, it does have the effect of reducing the sharpness of the smaller detail and, in systems for making multiple-color images, this distortion may be repeated from developer station to developer sta tion to the point where it could become objectionable, if it is not eliminated at each developer station.

The above disadvantages are eliminated in the developer system of this invention by providing the resilient surface on the drum roll and supporting the image bearing member with its non-image side against the resilient material, The squeegee roll forming the pressure nip may then preferably be formed of a suitable hard material.

By placing the resilient material on the drum roll, it is possible to form the squeegee roll with a relatively hard surface which lends itself to easy cleaning. The back of the image bearing material remains dry against the surface of the drum roll. Since the squeegee roll is in direct contact with the image, in the absence of constant cleaning, some ghosting or offsetting of the image may occur onto the squeegee roll, which must be removed. Hard squeegee rolls such as made of polished aluminum, chrome plated, or metal coated with polytetrafluoroethylene, can be easily cleaned and wiped in a continuous operation.

It is important that the resilient material on the drum roll be resistant to the solvent component of the developer liquid. This is particularly important where the sheet material has a width less than that of the drum roll, so that the edges of the roll and the exposed ends are wetted by the solvent or thinner, while the portion of the drum roll which is wrapped by the sheet material remains dry. Under such circumstances, it is important that no swelling or other dimensional instability occur within the resilient material on the drum roll. If such swelling should occur,

Ce Patented May the web wou d tend to ride toward the high side of the roll and accordingly would become unstable in alignlent, as it would tend to move from the center toward either end of the roll after such swelling occurred.

It is therefore an important object of this invention to provide an improved liquid developer system, as outlined above, in which a resilient material is carried on a drum roll for movement at least partially within a developer tank for supporting the movement of image bearing member through said tank in contact with a liquid developer therein, and in which at least a portion of the drum roll at the resilient covering thereon is in contact with the developer liquid, and in which a further portion thereof supporting the image bearing member remains dry.

A further object of this invention is the provision of an electrostatic liquid developer system, as outlined above, in which a drum roll is mounted for movement with a portion thereof normally submerged below the liquid surface of a developer tank, and in which a resilient coating is formed on the drum roll of a material having a high resistance to swelling in hydrocarbon liquids.

A still further object of this invention is the provision of an electrostatic liquid developer system in which a drum roll is positioned with its periphery at least partially submerged or positioned below the liquid level of a developer tank, an elastomeric surface formed on the drum roll of material highly resistant to such developer liquid for supporting the non image bearing side of an image bearing member, and a relatively hard squeegee roll forming a pressure nip with the drum roll which is relatively easily wiped or cleaned.

These and other objects and advantages of the present invention will be apparent from the following description, the accompanying drawings and the appended claims.

In the drawings:

FIG. 1 is a somewhat diagrammatic vertical section of an electrostatic liquid developing apparatus constructed according to this invention;

FIG. 2 is a further vertical section of a developer apparatus which is slightly modified in that the squeegee roll is positioned above the liquid level of the developer tank; and

FIG. 3 is a somewhat diagrammatic end view, with the squeegee roll removed, showing a typical relationship between the sheet material and the drum roll in the developer tank.

Referring to the figures of the drawings which illustrate preferred embodiments of the invention, an electrostatic liquid developing apparatus is shown in FIG. 1 as comprising a tank 10 formed with a semi-cylindrical bottom 11, an inlet side 12, and a forwardly and upwardly extending portion 13 at the outlet side 14 thereof. A drum roll 15 having a core 16 is rotatably positioned within the semi-cylindrical portion ll of the tank it), with a portion thereof received within the tank 10 and normally submerged below the surface of liquid developer 13 carried within the tank i The developer 18 may be formulated according to the application of Fauser, Ser. No. 762,756, filed Sept. 23, 19-58, now Pat. No. 3,311,490, and Ser. No. 420,449, filled Dec. 22, 1964, now abandoned, and generally may consist of charged particles of toner each of which includes a pigment and resin binder, the toner being suspended in an electrically insulating carrier liquid and maintained in dispersed condition throughout the carrier liquid.

The drum roll 15 supports the image bearing member il for movement through the developer tank 10 from the inlet side 12 to the outlet side 14-. The member 19 has previously been charged and an electrostatic image formed on its outer or exposed surface. This outer surface is submerged below the level of the developer liquid 18 as the member moves through the tank for development of the electrostatic image. The back or inner surface of the member 19 is maintained dry against the drum roll since the drum roll 15 is only partially submerged within the developer tank and since the degree of wrap exceeds the depth of submersion within the tank 10.

The outer covering of the drum roll which is in contact with the sheet material is formed as a layer of elastomeric material 20. The material 20 may be formed by casting thereon an elastomer which has good resilience, toughness, and resistance to abrasion. Particularly, this material must have good resistance to the hydrocarbon carrier liquid of the developer 18.

As shown in FIG. 3, the member 19 will frequently have a width which is less than the overall width of the drum roll 15, leaving end portions 23 and 24 of the drum roll 15 thereof exposed directly to the developer 18. In addition, the submerged vertical edges of the drum roll 15 are similarly exposed. It is important that the elastomeric coating material 20 be highly resistant to the solvents in the developer liquid 18 to prevent differential swelling or dimensional instability which would otherwise occur at the exposed ends 23 and 24 in relation to the relatively dry center section of the roll.

A suitable material for this purpose has been found to be cast solid polyurethane elastomer. Such a polyurethane elastomer is a reaction product of a polyester and a diisocyanate having a Durometer hardness from 10 on the Shore A scale to 70 on the Shore scale. The preferred range in accordance with the present invention is between 20 to 50 on the Shore A scale. A polyurethane elastomer which has been used in accordance with this invention is a reaction product of a polyester having a Hydroxyl Number of 57-63, an Acid Number of 0.8 to 1.5, a viscosity of between 1000 and 1100 cps. at 73 C. and a specific gravity (ZS/15.5 C.) of 1.19; and a diisocyanate mixture of the 2,4 and 2,6 isomers in the ratio of 801296 and 20:2%, respectively. Between 7 and parts by weight of polyester per 100 parts of diisocyanate are used depending on the hardness required. Typical commercially available polyester and diisocyanate materials are available under the trademark designation of Multithrane R 26 and Mondue TD80 of Mobay Chemical Co.

The invention further includes a hard surfaced squeegee roll 25 which is positioned to form a pressure nip at 26 with the resilient surface or covering on the roll 15 with the member 19 passing therebetween. The squeegee roll is preferably formed with a hard surface and thus my be formed of solid polished aluminum, or chromium or Teflon coated metal, such as steel, or formed of any other hard material which is easily wiped.

The use of a metal squeegee roll 25 is of particular advantage since it permits the grounding of this roll and the removal of any electrostatic charges which may tend to otherwise build up on the surface of the roll.

It is important that the squeegee roll 25 be easily wiped or cleaned since both the rolls 15 and 25 are preferably driven by the member 19, and hard rubbing contact with the squeegee roll 25 should be avoided. For the purpose of cleaning the squeegee roll, a brush, chamois cloth, or wiper 28 may be used as shown in FIG. 1, in which the cleaner 28 is positioned out of the liquid 18 and engages the surface of the roll 25 along its length. Also, to assist in cleaning, the surface of the roll 25, or the cleaner 28 may be moistened with thinner, such as shown diagrammatically by the shower head 29 applying a very small quantity of substantially toner-free carrier to the surface of the roll 25.

The embodiment shown in FIG. 2 differs from the embodiment shown in FIG. 1 in that the squeegee roll 25 is positioned above the surface of the liquid developer 18. A tray 30 containing clear thinner may be provided just under the roll 25 and above the tank 10 for constantly wetting the surface of the roll 25. This provides an arrangement in which the squeegee nip 26 remains close to the liquid to prevent drying of the solvent and ink. This arrangement may have some advantage where it is desired to cause a minimum of agitation of the developer 18. Again, a suitable cleaner 28 is positioned in running engagement with the surface of the roll 25 and is moistened by a shower 29 of toner-free carrier or thinner, for removing accumulated particles of toner from the roll 25.

In the operation of the invention, the image bearing member 19 which may have a Width less than the width of the drum roll 15, is supported for movement through the developer liquid 18 within the tank 10 supported on the surface of roll 15 defined by the elastomeric material 20. As the member 19 moves through the pressure nip 26 formed between the hard outer surface of the squeegee roll 25 and the resilient surface of the drum roll 15 formed by the drum roll covering 20, adhering carrier liquid of the developer is removed from the image side of the member 19. The non-image side is supported on the surface of the drum roll and is maintained relatively dry. Further, any slippage which occurs in the pressure nip is confined to the non-image side of the member 19 and will accordingly have no adverse affect upon the quality of the image. The cleaning apparatus 28 operates constantaly to maintain the hard outer surface of the squeegee roll 25 clean and free of image transfer and offsetting. Thus, a high quality image may be formed free of distortion due to slippage at the nip. While the areas 23 and 24 of the covering 20 are wetted by the developer, no differential swelling will result which would cause instability in the running of a web member through the developer apparatus.

The fact that the apparatus of this invention maintains one side of the image bearing material essentially dry during development, makes it particularly useful in systems for perfecting, that is in systems which print and develop on each side of a sheet of material. Thus, following the electrophotographic forming and developing of an image on one side of the image bearing material, while maintaining the obverse side essentially dry as described herein, this side can then be formed with an electrostatic image and developed by the apparatus of this invention while the first side is maintained essentially dry against the drum roll 15.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that this invention is not limited to this precise form of apparatus and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In an electrostatic liquid developer apparatus in which suspended toner particles are carried in an electrically insulating carrier liquid making up a developer liquid and applied to a flexible image bearing member having an electrostatic image on one side thereof for the development of such image, the improvement for reducing smearing and improving the image quality, comprising a developer tank adapted to contain a quantity of liquid developer to a predetermined level, a drum roll at least partially received in said tank with a peripheral supporting surface thereof in normally submerged relation below said liquid level and adapted to support and guide such image bearing member on said surface into and out of said tank with said one side thereof positioned outwardly of said roll in contact with developer liquid in said tank while maintaining the opposite side of said image bearing member essentially free of said developer liquid, said drum roll normally having a width which exceds the width of said image bearing member there being a portion of said drum roll surface in contact with said developer liquid, the portion of said drum roll surface in contact with said developer liquid, the portion of said drum roll defining said outer surface being a blanket of polyurethane elastomer relatively unaffected by and impervious to said insulating carrier liquid, and a relatively hard squeegee roll forming a pressure nip with said drum roll with said image bearing member therebetween With said nip thereof being positioned above said liquid level for removing excess carrier liquid from the developed surface of such image bearing member as it leaves the tank and confining substantially all slippage at said nip with the non-image side of the image bearing member.

2. The apparatus of claim 1 in which said polyurethane elastomer blanket has a hardness in the range of 20 to 50 on the Shore A scale.

3. The apparatus of claim 1 in which said squeegee roll is positioned above and out of contact with said developer liquid and further comprising a pan positioned beneath said squeegee roll and adapted to receive carrier liquid free of toner particles with said squeegee roll running in contact with said carrier liquid.

References Cited UNITED STATES PATENTS CHARLES A. WILLMUTH, Primary Examiner.

PETER FELDMAN, Examiner.

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