US3849171A

US3849171A - Method for cleaning background areas from developed recording surfaces

Info

Publication number: US3849171A
Application number: US00093313A
Authority: US
Inventors: I Takahashi; M Sato
Original assignee: Rank Xerox Ltd
Current assignee: Xerox Ltd
Priority date: 1969-12-02
Filing date: 1970-11-27
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19
Also published as: DE2059397A1; CA931618A

Abstract

Method and apparatus for forming images by providing an electrostatographic imaging member bearing an electrostatic latent image on a recording surface, developing the electrostatic latent image with a liquid developer comprising an insulating carrier liquid and suspended toner particles whereby at least a portion of the toner particles deposit on the recording surface to form an imaged recording surface having image areas and background areas, and contacting the imaged recording surface with a film of cleaning liquid carried on the surface of an applicator member to remove toner particles deposited in the background areas.

Description

United States Patent [191 Takahashi et al.

[ METHOD FOR CLEANING BACKGROUND AREAS FROM DEVELOPED RECORDING SURFACES lsoji Takahashi; Masamichi Sato, both of Asaka, Japan Assignee: Rank Xerox, Ltd., London, England Filed: Nov. 27, 1970 Appl. No.: 93,313

Inventors:

[30] Foreign Application Priority Data Dec. 2, 1969 Japan 44-96397 U.S. Cl. 117/37 LE, 96/1 LY, 134/122, 355/10, 355/15 Int. Cl. G03g 13/10, 603g 13/22 Field of Search 117/37 LE; 96]] LY; 118/637, DIG. 23; 355/10, 15; 134/122 References Cited UNlTED STATES PATENTS 6/1959 Bolton 117/37 LE 5/1960 Bolton et a1...

6/1962 Johnson 118/637 [451 Nov. 19, 1974 3,247,007 4/1966 Oliphant 117/37 LE 3,276,896 10/1966 Fisher 117/37 LE 3,356,498 12/1967 Moe et a1... 117/37 LE 3,367,791 2/1968 Lein 117/37 LE 3,368,526 2/1968 Matsumoto et a1 117/37 LE 3,372,027 3/1968 Gundlach et al. 117/37 LE 3,384,051 5/1968 Hunstiger 117/37 LE 3,419,411 12/1958 Wright 117/37 LE 3,577,259 5/1971 Sato et a1 117/37 LE Primary Examiner-Michael Sofocleous [5 7] ABSTRACT Method and apparatus for forming images by providing an electrostatographic imaging member bearing an electrostatic latent image on a recording surface, developing the electrostatic latent image with a liquid developer comprising an insulating carrier liquid and suspended toner particles whereby at least a portion of the toner particles deposit on the recording surface to form an imaged recording surface having image areas and background areas, and contacting the imaged recording surface with a film of cleaning liquid carried on the surface of an applicator member to remove toner particles deposited in the background areas.

19 Claims, 3 Drawing Figures PATENIUV 191914 INVENTORS ISOJI TAKAHASHI MASAMICHI SATO ATTORNEY METHOD FOR CLEANING BACKGROUND AREAS FROM DEVELOPED RECORDING SURFACES BACKGROUND OF THE INVENTION This invention relates to imaging systems, and more particularly, to an improved method and apparatus for developing electrostatic latent images with a liquid developer.

Processes for the formation and the development of images on the surface of photoconductive materials by electrostatic means are well known. These processes include dry techniques such as cascade, powder cloud and magnetic brush processes and wet techniques such as the liquid development process. One conventional liquid development process involves placing a uniform electrostatic charge on a photoconductive insulating layer comprising zinc oxide power and a resinous binder carried on a conductive paper substrate, exposing the layer to a light and shadow image to dissipate the charge on the areas of the layer exposed to the light and developing the electrostatic latent image by depositing on the image a charged toner which is dispersed in an insulating liquid. The charged toner may be suitably colored and may have a polarity of charge identical with or opposite to that of the latent image to be developed. If the polarity or charge of the toner is identical to that of the latent image, reversal development will occur whereas a toner having a charge opposite to that of the latent image will be attracted to the latent image.

Although considered a highly desirable technique for the formation of images, difficulties are encountered with attempts to form high quality images with the liquid development process. Generally, liquid development is effected by either immersing the electrostatic latent image bearing surface into the liquid developer or contacting the image bearing surface with a uniform film of liquid developer carried on an applicator surface. The liquid developer adhering to the imaging surface is thereafter dried by mere exposure to ambient air at room temperature, circulating heated air, infrared heating, pressure from squeegee rollers or the like. Unfortunately, the liquid developer adhering to the background areas of the imaging surface contain toner particles which remain on the imaging surface after drying. These undesirable background deposits are particularly acute in high speed continuous tone development systems employing a liquid developer containing high concentrations of toner particles.

In multicolor processes, where the development process is repeated with different colored developers corresponding to the primary colors to form a colored print on a single photosensitive surface, it is highly desirable that the charging and discharging properties of the photosensitive layer remain substantially unaffected by the presence of a toner image previously formed on the photosensitive layer. Generally, with conventional liquid development processes, the fixing agent, stabilizer, electric charge regulator and the like which are employed in liquid developer remain on the photosensitive layer after development and tend to deteriorate the photoreceptor properties thereby inhibiting the proper formation of subsequently developed images.

It has been found that uniform photoreceptor properties can be maintained and background toner deposits can be reduced by immersing the imaging surface immediately after development in a rinsing liquid which contains little or no toner particles or other contaminants. However, the rinsing liquid rapidly becomes ineffective due to the accumulation of toner particles and other undesirable materials found in liquid developers. In addition, a rinsing step presents additional problems in high speed development systems because treatment time and equipment complexity is increased. In addition, as a result of increasing toner contaminants in the rinsing liquid, additional equipment is required to remove these contaminants.

In addition to mere dipping of a developed imaging surface into a toner free cleaning liquid, one could attempt to remove toner from the background areas of a developed surface by injecting a cleaning liquid against the developed surface. This method comprises drawing up a cleaning liquid with means such as a pump and projecting it against the developed surface so as to wash away the liquid developer adhering to the developed surface. Although this washing method is effective, it is deficient in that equipment complexity and the space required for its installation are increased. In addition, this method requires the use of a hoze, nozzle, and a liquid pump further complicating the washing operation. Also, maintenance of the washing equipment proves to be particularly troublesome. Since most liquid development techniques are deficient in one or more of the above areas, there is a continuing need for improving imaging processes.

SUMMARY OF THE INVENTIO It is therefore an object of this invention to provide an imaging system overcoming the above noted deficiencies.

It is another object of this invention to provide an imaging technique which improves electrostatographic image quality.

It is a further object of this invention to provide images having reduced background deposits.

It is still another object of this invention to provide an imaging system which removes contaminants more effectively from imaging surfaces.

It is another object of this invention to provide an imaging system superior to those of known systems.

The above objects and others are accomplished in accordance with this invention, generally speaking, by providing an electrostatographic imaging member bearing an electrostatic latent image on a recording surface, developing the electrostatic latent image with a liquid developer comprising an insulating carrier liquid and suspended toner particles whereby at least a portion of the toner particles deposit on the recording surface to form an imaged recording surface having image areas and background areas, and contacting the imaged recording surface with a film of cleaning liquid carried on the surface of an applicator member to remove toner particles deposited in the background areas. Mechanically, only the cleaning liquid film is permitted to come into contact with the developed surface. Accordingly, the developed image will not be damaged or destroyed. Further, the cleaning can be accomplished in a very short period of time because the cleaning liquid film may be contacted with the developed surface at a high rate of speed.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of the improved electrostatographic imaging systems will become further apparent upon consideration of the following disclosure of the invention, particularly when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic sectional view in which an electrostatographic image is cleaned by immersion in a cleaning liquid.

FIG. 2 is a schematic sectional view of an electrophotographic imaging apparatus employing an embodiment of the cleaning system of this invention.

FIG. 3 is a schematic sectional view of an alternative form of the apparatus shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The conventional technique to remove toner parti cles from the background areas of a developed electrostatographic recording member by immersion in a toner-free cleaning liquid is illustrated in FIG. ll. Reference character designates a toner image formed by conventional liquid development techniques on a photoreceptor sheet 11. Removal of excess toner particles 12 deposited on the front and rear surfaces of the photoreceptor sheet 11 is effected by immersing the photoreceptor sheet 11 in cleaning liquid 13. During immersion, various components such as fixing agents, stabilizers and electric charge regulators originating from the liquid developer are also removed from the photoreceptor sheet 11 by cleaning liquid 13. It is apparent, that the cleaning liquid employed in this cleaning system is most efficient when fresh uncontaminated cleaning liquid is employed. Obviously, the cleaning liquid should be selected from liquids which will not destroy the toner image or dissolve and swell the photorecepter sheet 11. It is further apparent, that the cleaning liquid is preferably a liquid which is highly insulating and has a low dielectric constant. Although the cleaning process described with reference to FIG. 1 reduces background deposits in developed images, it requires a time consuming operation and is difficult to automate.

In FIG. 2, a photoreceptor sheet 14 bearing a developed surface on the lower side thereof is delivered by means of a guide roller 15 for advancing the photoreceptor sheet 14 in a fixed path. Reference character 16 denotes a roller adapted to rotate at a high rate of speed, with the lower part thereof submerged in fresh, clear cleaning liquid 17 which is contained in reservoir 18. Obviously, cleaning liquid 17 should contain little or no toner particles or other contaminants and should have a lower concentration of developer particles than the liquid developer employed to develop photoreceptor sheet 14 and should preferably be substantially free of any developer particles for most efficient cleaning results. Cleaning liquid 17, of course, also should be selected from those materials which will not swell or dissolve the photoreceptor sheet 14 or the toner image. For example, if photosensitive paper comprising zinc oxide and an insulating binder layer is employed, cyclohexane, hexane, heptane, or petroleum solvents such as isoparaffin or gasoline may be used. If desired, a suitable amount of chlorinated hydrocarbon or fluorinated hydrocarbon may be added to the cleaning liquid to render the cleaning mixture less flammable. As roller 16 rotates at a high rate of speed, a film of cleaning liquid 19 is formed on the peripheral surface thereof. Once this film of liquid is formed, it acquires a constant rate of rotation and rotates in conjunction with the roller. Upon contact of cleaning liquid film 19 with photorecepter sheet 14, cleaning liquid film 19 thereby washes away excess toner particles along with it. However, as a consequence, the same film of cleaning liquid remains around the roller and soiling of the cleaning liquid film becomes intensive. Therefore, a baffle plate 20 is disposed below roller 16 so as to insure desirable circulation of the cleaning liquid film in the cleaning liquid vessel. This circulation serves to permit all of the cleaning liquid in reservoir 18 to become soiled uniformly, with the aforementioned drawback eliminated thereby. The circulation of the cleaning liquid need not always be accomplished by means of such baffle plate or blade. Other suitable circulation methods, such as agitation with a stirrer, may be used for the purpose. Since photoreceptor sheet 14 is cleaned with a substantially uncontaminated cleaning liquid, maximum removal of excess toner particles and other undesirable developer components is effected. Further, it is apparent that cleaning liquid 17 can be repeatedly employed to clean photoreceptor sheet 14 because the film is continuously replenished from the cleaning liquid containing a very low concentration of developer components.

The cleaning step of this invention should be carried out before the developed photoreceptor sheet 14 is allowed to dry. Poor results are obtained when removal of background toner deposits is attempted after the developed photoreceptor sheet 14 is permitted to dry completely.

The thickness of film 19 of cleaning liquid 17 varies with the viscosity of cleaning liquid 17 and the peripheral speed of roller 16. The film thickness increases with increasing viscosity of the cleaning liquid and generally with an increasing rate of rotational speed of roller 16. Satisfactory results are achieved with a film thickness in the range of from about Va millimeter to about 3 millimeters.

The cleaning effect of film 19 is decreased where the thickness of film 19 is too small. To increase the cleaning speed, it is generally sufficient to increase the rotational speed of roller 16. However, if the rotational speed of roller 16 is increased excessively, film 19 adhering to roller 16 may be drawn away from roller 16 by virtue of centrifugal force, also the developed toner image may consequently be damaged or destroyed. Therefore, the upper limit of the rotational speed of roller 16 is determined by the nature of the developed image. Where there is firm adhesion between the developed toner image and the photoreceptor surface, safe cleaning can be accomplished if the relative speed of the developed surface and the film of cleaning liquid increases to a level of about 30 meters per second. Thus, safe cleaning may be accomplished where the film of cleaning liquid contacts the developed surface at a relative rate of speed greater than that of the developed surface. Where the adhesive force of the toner image to the photoreceptor surface is small, there may be cases in which the relative speed is preferably limited to a level of about 30 centimeters per second. It

should be apparent that when contact is made if there I is substantially no difference in the rate of speed between the film of cleaning liquid and the developed surface less efficient cleaning of the developed surface is obtained. For example, if both the film of cleaning liquid and the developed surface are traveling in the same direction and at substantially the same rate of speed,

cleaning efficiency decreases. Cleaning efficiency increases where the developed surface is moving slowly in one direction, for example, clockwise, and the film of cleaning liquid is moving in another direction, for example, counterclockwise, Maximum cleaning efficiency is obtained as the rate of speed of the developed surface is increased in one direction, for example, clockwise, with the rate of speed of the film of cleaning liquid increased in another direction for example, counterclockwise.

Another specific embodiment of the cleaning system of this invention is illustrated in FIG. 3. In this embodiment, shielding

plates

21 and 22 are disposed for the purpose of preventing cleaning liquid film 19 from being dispersed randomly by virtue of centrifugal force when roller 16 rotates at a high rate of speed.

Shielding plates

21 and 22 consequently prevent the cleaning liquid from being dispersed randomly and permit the selection of a suitable opening with roller 16 so as to control the thickness of liquid film being rotated since liquid film adhering to the roller may be sent flying by virtue of centrifugal force and the developed toner image may be damaged or destroyed. Although the rotational direction of roller 16 carrying the cleaning liquid thereon is opposite to that of roller carrying the photoreceptor sheet in the description of FIG. 2 and FIG. 3, it can be in the same direction. Higher relative speeds, however, and consequently higher cleaning rates are achieved with countercurrent contact.

After repeated use, the cleaning liquid becomes increasingly soiled. However, suitable recovery techniques can be used. For example, the toner material can be removed electrically, and the resinous component dissolved therein can be removed such as by means ofa desorbent. Thus, in the system of this invention, the background toner deposits and soluble liquid developer components which adhere to the surface of an electrostatographic imaging member are washed away by substantially fresh clean cleaning liquid. It is apparent from the foregoing description that consumption of cleaning liquid is reduced to a minimum and contamination of the cleaning liquid does not significantly impede cleaning effectiveness. Further, the

equipment required is quite simple and compact, the space necessary for its installation is small and both operation and maintenance are minimal.

Any suitable material, such as conventional binder plates, may be employed in the photoreceptor sheet of this invention. Preferably, the material should resist dissolving or swelling when contacted with the liquid developer and the cleaning liquid. For example, while photosensitive paper comprising zinc oxide and an insulating binder layer are discussed above, it is to be understood that other imaging members may be employed and that the choice of particular imaging member and particular development system may be readily determined by one skilled in the art. For example, cadmium sulfide, zinc sulfide, zinc selenide, cadmium selenide, titanium dioxide, phthalocyanine and polyvinyl carbazole may be employed as a photoconductive material. in addition, other suitable electrostatographic imaging members may be employed.

Any suitable conventional insulating liquid developer may be employed in the system of this invention. Typical liquid developers contain electroscopic marking particles dispersed in an insulating liquid vehicle and may also contain control agents and suspending agents for their well known functions. The electroscopic marking particles are conventionally dispersed and suspended in the liquid by stirring or agitation and where a highly uniform and stable suspension is desired, the suspension may be passed through a colloid mill. For optimum results, toner particles having an average diameter of less than about 1 micron are preferred because higher resolution images and more stable developer mixtures are achieved.

Although specific materials and conditions are set forth in the foregoing examples, these are merely intended as illustrations of the present invention. Various other suitable electrostatographic imaging members, developers, cleaning liquids and cleaning system configurations including those listed above may be substituted for those in the specific examples with similar results. For example, various other suitable applicator members such as an endless belt of metal, rubber, plastic, cloth, or paper may be used. Other materials may also be added to the imaging member, developer, or cleaning liquid to sensitize, synergize or otherwise improve the imaging properties or desirable properties of the system.

Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

l. A method of forming images comprising providing an electrostatographic imaging member bearing an electrostatic latent image on a recording surface, developing said electrostatic latent image with a liquid developer comprising an insulating carrier liquid and suspended toner particles whereby at least a portion of said toner particles deposit on said recording surface to form an imaged recording surface having image areas and background areas, rotating an applicator member in a cleaning liquid to form a film of said cleaning liquid on the surface of said applicator member, maintaining said applicator member free from contact with said imaged recording surface, and contacting said imaged recording surface with said film of cleaning liquid carried on the surface of said applicator member to remove toner particles deposited in said background areas.

2. A method according to claim 1 including removing said film of cleaning liquid contaminated with said toner particles from said surface of said applicator member.

3. A method according to claim 2 including recovering said film of cleaning liquid contaminated with said toner particles removed from said surface of said applicator member.

4. A method according to claim 3 including dispersing said film of cleaning liquid contaminated with said toner particles in a cleaning liquid bath to circulate at least a portion of said contaminated film and forming a new film of cleaning liquid on said surface of said applicator from substantially uncontaminated cleaning liquid for further treatment of imaged recording surfaces.

5. A method according to claim 4 including stirring said film of cleaning liquid contaminated with said toner particles in a cleaning liquid bath to circulate at least a portion of said contaminated film and forming a new film of cleaning liquid on said surface of said applicator from substantially uncontaminated cleaning liquid for further treatment of imaged recording surfaces.

6. A method according to claim including reforming said film of cleaning liquid on said surface of said applicator member with recirculated cleaning liquid for further treatment of said imaged recording surfaces.

7. A method according to claim 1 including removing said toner particles deposited in said background areas substantially immediately after developing said electrostatic latent image.

8. A method according to claim 1 including transporting said film of cleaning liquid in an arcuate path to said imaged recording surface.

9. A method according to claim 1 including regulating the thickness of said film of cleaning liquid carried on said surface of said applicator member prior to contact with said imaged recording surface.

10. A method according to claim 9 including maintaining said thickness of said film of cleaning liquid carried on said surface of said applicator member prior to contact with said imaged recording surface in the range of from about 1% millimeter to about 3 millimeters.

11. A method according to claim 1 including reducing the thickness of said film of cleaning liquid carried on said surface of said applicator member prior to contact with said imaged recording surface.

12. A method according to claim 1 including contacting said imaged recording surface with a film of cleaning liquid carried on said surface of said applicator member sufficiently thick to remove at least a portion of said toner particles deposited in said background areas.

13. A method according to claim 1 including advancing an imaged recording surface in a fixed path and advancing said film of cleaning liquid carried on said surface of said applicator member in a direction countercurrent to said imaged recording surface.

14. A method according to claim 1 including contacting said imaged recording surface with said film of cleaning liquid carried on said surface of said applicator member and traveling at a relative rate of speed greater than said imaged recording surface.

15. A method according to claim 1 including contacting said imaged recording surface with said film of cleaning liquid carried on said surface of said applicator member and traveling at a relative rate of speed between about 30 centimeters per second and about 30 meters per second.

16. A method of surface cleaning developed electrostatographic recording surfaces comprising providing a recording member having an imaged recording surface bearing toner particles deposited in image areas and background areas, applying a film of cleaning liquid to the surface of an applicator member, transporting said imaged recording surface into a cleaning zone located outside a development zone, and contacting said imaged recording surface with said film of cleaning liquid carried on said surface of said applicator member to remove said toner particles deposited in said background areas.

17. A method according to claim 16 including contacting said imaged recording surface with said film of cleaning liquid carried on said surface of said applicator member and traveling at a relative rate of speed greater than said imaged recording surface.

18. A method according to claim 16 including disposing shielding plates adjacent to and spaced away from said applicator member and adapted to prevent said film of cleaning liquid from being dispersed randomly by virtue of centrifugal force when said applicator member rotates at a high rate of speed.

19. A method according to claim 16 including disposing shielding plates adjacent to and spaced away from said applicator member and adapted to control the thickness of said film of cleaning liquid being rotated. =i

Claims

1. A METHOD OF FORMING IMAGES COMPRISING PROVIDING AN ELECTROSTATOGRAPHIC IMAGINING MEMBER BEARING AN ELECTROSTATIC LATENT IMAGE ON A RECORDING SURFACE, DEVELOPING SAID ELECTROSTATIC LATENT IMAGE WITH A LIQUID DEVELOPER COMPRISING AN INSULATING CARRIER LIQUID AND SUSPENDED TONER PARTICLES WHEREBY AT LEAST A PORTION OF SAID TONER PARTICLES DEPOSIT ON SAID RECORDING SURFACE TO FORM AN IMAGES RECORDING SURFACE HAVING IMAGE AREAS AND BACKGROUND AREAS, ROTATING AN APPLICATOR MEMBER IN A CLEANING LIQUID TO FORM A FILM OF SAID CLEANING LIQUID ON THE SURFACE OF SAID APPLICATOR MEMBER, MAINTAINING SAID APPLICATOR MEMBER FREE FROM CONTACT WITH SAID IMAGED RECORDING SURFACE, AND CONTACTING SAID IMAGED RECORDING SURFACE WITH SAID FILM OF CLEANING LIQUID CARRIED ON THE SURFACE OF SAID APPLICATOR MEMBER TO REMOVE TONER PARTICLES DEPOSITED IN SAID BACKGROUND AREAS.

6. A method according to claim 5 including reforming said film of cleaning liquid on said surface of said applicator member with recirculated cleaning liquid for further treatment of said imaged recording surfaces.

10. A method according to claim 9 including maintaining said thickness of said film of cleaning liquid carried on said surface of said applicator member prior to contact with said imaged recording surface in the range of from about 1/3 millimeter to about 3 millimeters.

19. A method according to claim 16 including disposing shielding plates adjacent to and spaced away from said applicator member and adapted to control the thickness of said film of cleaning liquid being rotated.