US3336906A - Apparatus for immersion development - Google Patents

Description

Aug. 22, 1967 M. MICHALCHIK APPARATUS FOR IMMERSION DEVELOPMENT Filed June 9, 1965 K 3 mm V W m H M 6%25 p5? 477 A/EVS United States Patent 3,336,906 APPARATUS FOR IMMERSION DEVELOPMENT Michael Michalchik, Bethpage, N.Y., assiguor to Fairchild Camera & Instrument Corporation, Syosset, N.Y., a corporation of New York Filed June 9, 1965, Ser. No. 462,483 9 Claims. (Cl. 118637) This invention relates toapparatus for immersion development and more particularly to apparatus designed for the liquid development of electrostatic images in which conductive particles are suspended in the insulating carrier fluid thereby dispensing with the need of a fixed electrode and eliminating the criticality of the spacing of the electrode from the base material on which the image is being printed.

It is well-known in the prior art that solid areas cannot be satisfactorily reproduced by the liquid development of electrostatic or electrophotographic images where development is attempted by immersing the electrostatic or electrophotographic image in insulating fluid which has suspended therein only a toner or developer. If development is attempted in this manner it generally results in deposition of toner or developer material around the edges of large letters and similar solid areas. In accordance with prior art teaching one of the methods for overcoming this problem is to maintain an electrode or grounded conductor in close proximity to the surface bearing the electrostatic or electrophotographic image while such image is in contact with the insulating fluid having suspended therein the toner or developer. The electrode has the effect of filling in the center of solid images by changing the electrostatic lines of force which normally bend between the charged and uncharged portions of the insulations. It is now Wellknown that by positioning a conductive element near the charged surface to be printed that the lines of force or flux from the electrostatic image are formed into lines of force perpendicular to the surface to be printed and the electrostatic field from the image is strengthened and thereby attracts additional toner or developer particles. It has therefore become common practice in the printing of large electrostatic or electrophotographic areas to immerse a fixed conductor in the liquid developer and to maintain the fixed or rigid conductor a predetermined distance from the electrostatic or electrophotographic image.

The disadvantage with this prior art method of printing solid electrostatic and electrophotographic areas is that the spacing between the electrode and the base material on which the image is to be printed is critical. This problem is particularly acute in such applications as the printing of billboards where large irregularities frequently appear in the surface to be printed. Since any irregularity in the surface to be printed varies the spacing of the electrode from the surface to be printed, inferior results with poor resolution have been obtained where printing is attempted on surfaces which have any degree of irregularities.

In view of the prior art problems which have been encountered by the use of a fixed rigid electrode in liquid development a method has been described wherein the rigid electrode is replaced by a plurality of floating electrodes which are suspended in'the liquid carrier. These fluidized electrodes or conductors are metallic powders' which are suspended in the liquid carrier. This method is described in patent application Ser. No. 462,718, which is being filed concurrently with this patent application.

In accordance with such method the fluidized conductors consist of conductive particles such as iron filings which are suspended in the carrier liquid. These conductive particles function essentially as a shield for the electrostatic image, thus dispensing with the criticality of the ice spacing of the fixed electrode from the surface to be printed.

The present invention is directed to an apparatus for the immersion development of electrostatic or electrophotographic images in accordance with the method described in patent application Ser. No. 462,718 filed on even date herewith. The apparatus of the present invention basically includes a gravity settling bed and a flow arrangement to fluidize the heavy particles in the liquid developer. The apparatus of the present invention directs the insulating carrier fluid into a pattern of flow which results in the suspension of the fluidized conductive particles within an enclosure in which the electrostatic or electrophotographic image is immersed in order to be developed.

In view of the foregoing the primary object of the present invention is to provide an apparatus for the immersion development of electrostatic or electrophotographic images in which the apparatus maintains'in suspension in the liquid developer fluidized conductive particles which eliminates the necessity for a fixed conductor or electrode.

A further object of the present invention is to provide an apparatus for the immersion development of electrostatic or electrophotographic images which permits the printing of large, solid electrostatic or electrophotographic areas with good resolution regardless of irregularities in the surface of the area to be printed.

These and further objects and features of the present invention will appear from a reading of the following detailed description of one embodiment of the invention which is to be read in conjunction with the drawing which level 24' with any conventional insulating carrier, liquid is a vertical cross-section through a'machine illustrating the features of the present invention. A

The apparatus of the present invention is designed to develop electrostatic or electrophotographic images formed in any well-known manner. It is essential, however, to the operation of the apparatus of the present invention that the surface of the base material that is opposite to the surface on which the electrostatic or electrophotographic image is formed, be electrically conductive. As a typical example, a conductive base material, such as tinfoil, can be coated on one surface thereof with a photoconductive insulating material which is then subjected to a corona discharge. A portion of the charge is then discharged such, for example, as by exposure to a light forming image in order to form an electrostatic or electrophotographic image. As another example a conductive base material such as tinfoil can be coated on one surface with an insulating material which is not photoconductive. A point charge is. then used to trace on the insulating surface an electrostatic image which it is desired to print. These examples are merely illustrative of manners in which the electrostatic or electrophotographic images are formed and which it is desired to print. As stated above, the apparatus of the present invention is designed to develop any electrostatic or electrophotographic image with the limitation that the surface of the base material that is opposite to that containing the image to be printed must be conductive for a purpose to be presently described.

Referring now to the figure the apparatus of the present invention includes a tank 10 which must be made of a conductive material such as iron, steel, aluminum, etc. The tank 10 as illustrated is grounded for a purpose to be presently described. The tank 10 is filled to a desired 11, such as kerosene, heptane, or a halogenated or nonhalogenated hydrocarbon, particularly fluorinated hydrocarbons such as Freon TF available from E. I. du Pont de Nemours.

The interior of the tank 10 is divided into a plurality of compartments such as 12 and 13 by means of partitions such as 14 and 15. The compartments are generally funnel shaped and have a neck portion 16 adjacent the bottom 18 of the tank 10, and tapering walls 17 which extend divergently from the neck 16 such that the mouth portion of the funnel i directed toward the surface 24 of the liquid carrier 11.

The compartments such as 12 and 13 are formed by the partitions such as 14 and 15 which are cone shaped in order to form the funnel shaped compartments. The partitions 14 and 15 have walls 17 which correspond to the walls of the compartments 12 and 13, the walls of the partitions 14 and 15, however, extending from the neck portions 16 upwardly and in a convergent manner such that the walls 17 slope toward the necks 16.

As illustrated in the figure, the neck 16 of the various compartments such as 12 and 13 are interconnected with each other by means of the passageway 19 which is adjacent the bottom 18 of the tank 10. At one end of the tank 10 the passageway 19 communicates with a vertical shaft 20 which opens into the interior of the tank 10 adjacent to but below the level 24 of the liquid carrier 11 and approximately at the level of the tops of the partitions 14 and 15.

The insulating liquid carrier 11 is adapted to flow from the compartments 12 and 13 through the shaft 20 into the passageway 19 and then through the neck portion 16 back into the compartments 12 and 13, the flow being in the direction of the arrows as shown in the figure. The liquid carrier 11 is circulated continuously in this closed cycle by means of the pump 21 or by any other well-known means. The velocity of the liquid carrier flow is regulated by controlling the speed of the pump 21.

The toner or developer material is suspended in the liquid carrier 11. The particle size of the toner or developer used is preferably less than microns. The volume of toner or developer in the liquid carrier 11 is maintained by replenishing the supply of developer or toner from a source not illustrated. A metered quantity of toner or developer is added to the liquid carrier 11 depending upon the speed and quantity of developing.

In accordance with the present invention a volume of dense and conductive particles 22 is added to the insulating liquid carrier 11 and maintained in suspension in the liquid carrier by means of the pump 21. Thus, the conductive particles 22 are maintained in suspension by rapid agitation of the liquid carrier 11. The conductive particles are preferably metal spheroids of metals such as steel filings, iron filings, or powders of metal such as copper, zinc, lead, aluminum, etc. The conductive particles 22 are preferably maintained between 50 and 325 mesh in size. In this size range the conductive particles 22 are small enough to be suspended in the liquid carrier 11 and are too large to adhere to the electrostatic image to be printed.

In the apparatus illustrated it is, of course, desirable only to recirculate the liquid carrier 11 in order to maintain the conductive particles 22 in suspension. For this reason the entrances to the necks 16 and to the shaft 20 are provided with perforated closures 23 in order to permit recirculation of the liquid carrier 11 but which will prevent the powders or the conductive particles 22 from entering the shaft 20.

The configuration of the compartments 12 and 13 and correspondingly of the partitions 14 and 15 serves a twofold purpose. Since the walls 17 of the compartments 12 and 13 converge toward the neck 16 through which the liquid carrier 11 is discharged into the compartments 12 and 13, the conductive particles 22 will be concentrated adjacent the entrance to the neck 16 at which the velocity of the liquid carrier 11 is greatest. Due to this high velocity of the liquid carrier 11 as it leaves the neck 16 the conductive particles 22 will be constantly maintained in agitation and therefore in suspension in the liquid carrier 11. The liquid carrier 11 will accordingly be in a condition of turbulent flow adjacent the outlet of the neck 16. Since the walls 17 of compartments 12 and 13 rapidly diverge or flare apart as they extend away from the neck 16 the flow of the liquid carrier 11 will rapidly become laminar, such that a laminar flow is issued at the surface 24 of the liquid carrier 11.

In developing electrostatic or electrophotogaphic images with the apparatus of the present invention, it is essential that the conductive particles 22 be suspended in the liquid carrier 11 and that the velocity of the liquid fiow be laminar and low at the image surface 24. The electrophotographic or electrostatic image is developed by immersion of the image bearing surface in the liquid carrier 11 which contains in suspension the conductive particles 22 and the toner or developer. In the form illustrated in the figure the electrostatic image is formed by coating a conductive base material 25, such as tinfoil, with a photoconductive material 26. The photoconductive surface 26 is then charged in any desired manner with a portion thereof being discharged such as by exposure to a light forming image such that what remains on the photoconductive surface 26 is an electrostatic charge 27 corresponding to the image to be printed.

The base material 25 is then moved past or through the tank 10 by means not illustrated in such manner that the electrostatic image 27 is immersed in the liquid carrier 11 preferably slightly below the image surface 24. In the preferred embodiment of the invention the surface 28 of the base material 25 which does not contain the electrostatic image 27 is not immersed in the liquid carrier 11 such that it remains dry.

In order for the apparatus of the present invention to properly develop electrostatic or electrophotographic images it is necessary that the tank 10 and the conductive base material 25 be of the same electrical potential. In order to avoid any physical interconnection between the base material 25 and the tank 10 these components are electrically interconnected by grounding both the tank 10 and the conductive base material 25. In the case of the moving base material 25 this can be done by means of a flexible contact (not illustrated) which maintains contact with the side 28 of the base material 25 opposite the image 27, regardless of the variations in the movement of the base material 25.

As the image 27 is going through the liquid carrier 11 the image is developed by deposition from the liquid carrier 11 onto the image 27 of the developer or toner suspended in the liquid carrier 11. This carrier is subsequently fixed to the surface of the base material 25 by any well-known means, such, for example, as by the application of heat which fuses the developer to the surface of the base material. During development the conductive particles 22 function as a floating or fluid electrode which therefore obviates any criticality between the spacing of the electrode from the surface to be printed. The level of the liquid carrier 11, i.e. the imaging surface 24, must be so related to the quantity of conductive particles 22 maintained in suspension in the liquid carrier 11 that the conductive particles 22 effectively function as an electrode. Thus, if the concentration of conductive particles 22 in suspension in the liquid carrier 11 is too small the result will be as if no electrode were present, whereas if the concentration is too great the result is the same as if the electrode were held too close to the surface to be printed. It has been found that optimum results can be obtained if the volume of conductive particles such as iron in the compartments 12 and 13 is approximately 68 percent and the insulating liquid carrier 11 such as Freon is approximately 31.7 percent with the toner or developer representing about 0.3 percent of the volume.

As previously explained the tank 10 and the conductive backing plate 28 are grounded so as to be at the same potential. If desired a negative or positive voltage can be applied between the tank 10 and the backing plate 28 and will result in a variable contrast image or image reversal.

What has been described is an apparatus for developing electrostatic or electrophotographic images Without the use of a fixed electrode but through the use of a plurality of floating or fluidized electrodes. The fluidized or floating electrodes consist of conductive particles which are maintained in suspension in an insulating liquid carrier which also has in suspension the toner or developer.

I claim:

1. Apparatus for the immersion development of an electrostatic image formed on an insulating surface of a base material the other surface of which is conductive, said apparatus comprising a tank containing insulating carrier liquid, developer particles suspended in said liquid, a plurality of conductive particles in said liquid, means for immersing said image bearing surface in said liquid, and means for agitating said liquid such that said conductive particles are maintained in suspension in said liquid and function as a floating electrode whereby said developer is deposited uniformly over the area of said image regardless of irregularities in the surface of said base material containing said image.

2. Apparatus for the immersion development of an electrostatic image formed on an insulating surface of a base material the other surface of which is conductive, said apparatus comprising a tank containing insulating carrier liquid, developer particles suspended in said liquid, a plurality of conductive particles in said liquid, means for immersing said image bearing surface in said liquid, means for maintaining said conductive surface of said base material and said conductive particles at the same potential, and means for agitating said liquid such that said conductive particles are maintained in suspension in said liquid and function as a floating electrode whereby said developer is deposited uniformly over the area of said image regardless of irregularities in the surface of said base material containing said image.

3. Apparatus for the immersion development of an electrostatic image formed on an insulating surface of a base material the other surface of which is conductive, said apparatus comprising a tank containing insulating carrier liquid, developer particles suspended in said liquid, a plurality of conductive particles in said liquid, means for immersing said image bearing surface in said liquid, means for grounding said conductive surface of said base material and said conductive particles While said image bearing surface is immersed in said liquid, and means for agitating said liquid such that said conductive particles are maintained in suspension in said liquid and function as a floating electrode whereby said developer is deposited uniformly over the area of said image regardless of irregularities in the surface of said base material containing said image.

4. Apparatus for the immersion development of an electrostatic image formed on an insulating surface of a base material the other surface of which is conductive, said apparatus comprising a conductive grounded tank containing insulating carrier liquid, developer-particles suspended in said liquid, a plurality of conductive particles in said liquid, means for immersing said image bearing surface in said liquid, means for grounding said conductive surface of said base material while said image bearing surface is immersed in said liquid, and means for agitating said liquid such that said conductive particles are maintained in suspension in said liquid and function as a floating electrode whereby said developer is deposited uniformly over the area of said image regardless of irregularities in the surface of said base material containing said image.

5. Apparatus for the immersion development of an electrostatic image formed on an insulating surface of a base material the other surface of which is conductive, said apparatus comprising a conductive grounded tank containing insulating carrier liquid, developer particles suspended in said liquid, a plurality of conductive particles in said liquid, means for immersing said image bearing surface in said liquid, means for grounding said conductive surface of said base material while said image bearing surface is immersed in said liquid, and pump means for agitating said liquid such that said conductive particles are maintained in suspension in said liquid and function as a floating electrode whereby said developer is deposited uniformly over the area of said image regardless of irregularities in the surface of said base material containing said image.

6. Apparatus in accordance with claim 5 wherein said conductive surface of said base material is not immersed in said carrier liquid during development of said image.

7. Apparatus for the immersion development of an electrostatic image formed on an insulating surface of a base material the other surface of which is conductive, said apparatus comprising a conductive grounded tank containing insulating carrier liquid, said tank being longitudinally divided into a plurality of compartments, duct means adjacent the bottom of said tank and interconnecting said compartments, developer particles suspended in said liquid, a plurality of conductive particles in said liquid, means for immersing said image bearing surface in said liquid, means for grounding said conductive surface of said base material while said image bearing surface is immersed in said liquid, and pump means for recirculating carrier liquid from said compartments through said duct and back into said compartments, the velocity of said liquid into said compartments being of a magnitude such that said conductive particles are maintained in suspension in said liquid and function as a floating electrode whereby said developer is deposited uniformly over the area of said image regardless of irregularities in the surface of said base material containing said image.

8. Apparatus for the immersion development of an electrostatic image formed on an insulating surface of a base material the other surface of which is conductive, said apparatus comprising a conductive grounded tank containing insulating carrier liquid, said tank being longitudinally divided into a plurality of compartments, duct means adjacent the bottom of said tank and interconnecting said compartments, the walls of each of said compart ments extending divergently from said duct and terminating below the surface of the liquid in each compartment, developer particles suspended in said liquid, a pluralty of conductive particles in said liquid, means for immersing said image bearing surface in said liquid, means for grounding said conductive surface of said base material While said image bearing surface is immersed in said liquid, and pump means for recirculating carrier liquid from said compartments through said duct and back into said compartments, the velocity of said liquid into said compartments being of a magnitude such that said conductive particles are maintained in suspension in said liquid and function as a floating electrode whereby said developer is deposited uniformly over the area of said image regardless of irregularities in the surface of said base material containing said image.

9. Apparatus for the immersion development of an electrostatic image formed on an insulating surface of a base material the other surface of which is conductive, said apparatus comprising a conductive grounded tank containing insulating carrier liquid, said tank being longitudinally-divided into a plurality of compartments, duct means adjacent the bottom of said tank and interconnecting said compartments, the walls of each of said compartments extending divergently from said duct and terminating below the surface of the liquid in each compartment whereby liquid enters said compartments from said duct through a constricted opening resulting in turbulent flow of liquid adjacent said duct but laminar flow adjacent the surface of said liquid, developer particles suspended in said liquid, a plurality of conductive particles in said liquid, means for immersing said image bearing surface in said liquid, means for grounding said conductive surface of said'base material while said image bearing surface is immersed in said liquid, and pump means for recirculating carrier liquid from said compartments through said duct and back into said compartments, the velocity of said liquid into said compartments being of a magnitude such that said conductive particles are maintained in suspension in said liquid and function as a floating electrode whereby said developer is deposited uniformly over the area of said image regardless of irregularities in the surface of said base material containing said image.

References Cited UNITED STATES PATENTS Mayer 117---1.7 Jones 118429 X Metcalfe et a1. 11737 Thompson 118637 Gundlach 118637 X CHARLES A. WILLMUTH, Primary Examinen 10 PETER FELDMAN, Assistant Examiner.,

Claims (1)

1. APPARATUS FOR THE IMMERSION DEVELOPMENT OF AN ELECTROSTATIC IMAGE FORMED ON AN INSULATING SURFACE OF A BASE MATERIAL THE OTHER SURFACE OF WHICH IS CONDUCTIVE, SAID APPARATUS COMPRISING A TANK CONTAINING INSULATING CARRIER LIQUID, DEVELOPER PARTICLES SUSPENDED IN SAID LIQUID, A PLURALITY OF CONDUCTIVE PARTICLES IN SAID LIQUID, MEANS FOR IMMERSING SAID IMAGE BEARING SURFACE IN SAID LIQUID, AND MEANS FOR AGITATING SAID LIQUID SUCH THAT SAID CONDUCTIVE PARTICLES ARE MAINTAINED IN SUSPENSION IN SAID LIQUID AND FUNCTION AS A FLOATING ELECTRODE WHEREBY SAID DEVELOPER IS DEPOSITED UNIFORMLY OVER THE AREA OF SAID IMAGE RE-

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