US3120446A - Method of transferring a developed solid particulate image - Google Patents

Description

H. H. HUNTER Feb. 4, 1964 METHOD OF TRANSFERRING A DEVELOPED SOLID PARTICULATE IMAGE Filed Feb. 1, 1961 INVENTOR HARVEY H. HUNTER 15 A 7' TORNE V United States Patent Ofitice 3,2l2%,44t3 Feb. 4 1%4 l, No. 85,524 :Cl. ill-17.5)

Thi invention relates to Xerography, and more par ticularly to the trans-iv of Xerographic image ln a; or" Xerog a 1y it is conventional to form an electrostatic latent age on a Xerographic plate ineluding a photocon uc ve insulating layer and to develop the latent image on xerographic plate by the selective electrostatic attraction thereto of suitable finely divided particles. Some development techniques, known to the art and in commercial use, which share the common characteristic that he particles and applied in a dry condi n, involve divided powder materials either by themselves or in conjunction with other particles. Another form of Xerographic development is known as liquid ism development and is accomplished by irnrnersi r image bearing member in a suspension of linel marking al suspended in a volatile insulat w ,uid. This develo c tent method is particularly tive for many applications, since it involves Ol tively si apparatus and since it h of developing of extremely hag" resolution with a minimum of apparent iness.

In most, 'lthough not all ns of Xerography, it is desired to transfer the eveloper powder pattern from the Xerographic plate to some other more suitable support member, such as a sheet of paper. arious methods of accomplishing image transfer are known and include the use of specially coated papers or the like which have adhesive properties toward powder image, the use of electrostatic holds to transfer the powder pattern, and the like. These transfer procedures are uite ol'lective when used with images produced by conventional dry development processes nd such transfer methods enjoy wide commercial use. It been found, however, that these methods applied to images produced by liquid immersion development effect only incomplete transfer result. :1 images which are low in density, blotchy in appearance and of low resolution. The reasons for such low on transier are rally l nown, but it is believed that the dry development methods deposit on the Xerographic plate particles which are effectively surrounded by a thin air film and thus are readily removable from the plate. ln liquid immersion development, however, the liquid of the developer evapo rates as t e plate is w thdrawn from the developer, appar ently causing the p? 11d cles to adhere to one another to the plate in a very intimate manner. In addition, it is both possible and advantageous to use unusually fine developer particles in the liquid immersion process, and these tend to adhere more tenaciously to a Xerographic plate than the somewhat larger particles generally used in dry developing processes.

Now, in accordance with the present invention, there is provided an improved method for transferring images. The novel method or" transfer of this invention is particularly applicable to developed images formed by a liquid process, and it is accordingly a principal objective of the present invention to provide improved Xerographic transfer methods to transfer liquid developed images. Also, in accordance with the present invention, there is provided an improved method of producing more con plete transfers than has heretofore been possible when transferring images developed using, dry development techniques. Accordingly it is a further objective of this invention to define novel and improved transfer methods for dry developed images. These, as well as subsidiary objectives, will become apparent from the following specification and from the drawing which represents a partially schematic view of mage transfer being carried out accordin to the invention.

The starting point of a Xerographic process is generally the formation of an electrostatic latent image. Methods are known whereby such images may be formed on ordinary insulatins materials, and such images may be utilized in conjunction with the present invention. A more common Xerographic method involves the use of a Xerographic plate including a photoconductive insulati layer as the latent image bearing member. The photoconductive insulating material may comprise a vit ous material, such as vitreous selenium, which may onal y be formed on a conductive or other support Other forms of photoconductive insulating mate- 13 are including dispersions of photoconductive as zinc oxide in an insulating resin binder. h layers may also be formed on suitable supports which n Depending upon e nature of the photoconductor and 'ograpnic plates may be either rigid or flexible. if ri d, they may be in the form of flat plates, cylir crs or other sh pes, and ii" flexible, they may be in the form of she webs or the like. The present plate in of these forms.

be formed on a e by uniiorr ly electrostatically charging g layer by any of the known then selectively dissipating charge oy exposing the Xerographic plate to a pattern or l ht and shadow as The latent electros age may be developed or made visible by numerous methods, but since transfer according to the present invention is particularly valuable in connection with n ersion method 0 developrne 0 g the latent image emplo iliquid immersion development will be describe However, it is to be recalled that tlr principles of transfer are also applicable to an ima e developed g dry evelopment tech .iques, and it is intended to encompass such transfers within the scope of thi invei ion. In all applications the liquid employed should, of course, not be a solvent for the developed image.

In order to accomplish liquid development, the Xerographic plate bearing the la.ent image is immersed in rwise contacted wi h a liquid developer material comprising a dispersion of finely ided particles in a liquid carrier. The carrier liquid must be a hi hly insu lating material in order to avoid discharge of the electrostatic latent image. Additionally, it should not be excessively viscous and should b; at least moderately volatile, since the desired result of the development process is a dry image. This is most readily achieved by allowing the liquid to evaporate from a developed image leaving only the dry particles behind. Many different liquids are suitable for use as carrier liquids in liquid develop- A particularly useful class of materials comprises refined petroleum hydrocarbons having a volatility at least about as great as hat of kerosene, and preferably not more than about that of gasoline. Such materials -y or may not be highly electrically conductive.

invention operates with a A latent electrostatic nic o a technique of develmay be employed as the solid component of the developer mixture. One useful class of materials comprises finely divided mineral pigments including fine metallic powders. Another useful class of materials comprises pigmented or unpigmented resin particles similar to toners which are widely used in conventional xerographic practice. These resinous materials may be ground to a fine particle size, or, where particularly fine particles are desired, they may be formed by spray drying a solvent solution of the resin material. In general, particles used in liquid development have a particle size of a few microns at most. When dispersed in the carrier liquid, the particles acquire either positive or negative electrostatic charge, depending upon the particular choice of powder and liquid materials. In accordance with conventional xerographic principles, a powder having a polarity, when mixed in the carrier liquid, opposite to that of the latent image pattern is employed when it is desired to develop the charged areas of the latent image and particles of like polarity, when mixed in the carrier liquid, are selected when unchanged area development is desired. A further component in the form of a soluble film forming materials, such as linseed oil, is sometimes included in the developer mixture to increase the permanence of the developed image. For general information on liquid development, reference may be had to British Patent 755,486, US. Patent 2,899,335 and US. Patent 2,913,353.

In carrying out the present invention the first step is the formation of an electrostatic latent image. This is generally carried out by electrostatically charging a xerographic plate and exposing it to a pattern of light and shadow. The latent image is then developed by immersing or otherwise wetting it with a liquid developer material of the type already described. In accordance with conventional techniques, the xerographic plate would then be removed from the developer material and evaporation of the carrier liquid would soon leave a dry powder image on the plate. Such an image is useful for many purposes but, as already pointed out, cannot be readily transferred to a further support.

In accordance with an improved form of transfer, however, and as illustrated in the drawnig, the developed xerographic plate is reimmersed into the liquid carrier of the developer dispersion and while so immersed is contacted with a sheet of paper or other transfer member. In the drawing, there is shown a tray which is partly filled with carrier liquid 11 and is which is immersed a xerographic plate 12 including a photoconductive insulating layer 13 overlying a support layer 14. A transfer member 15 such as paper or the like is shown being rolled into contact with plate 12 by a roller 16. Roller 16 includes an insulating handle 17 and a conductive rubber cylindrical element 18 overlying a conductive core 9. The operative portion of the roller 16 is maintained at a potential in the range of from 1,000 to 3,000 volts DC. through a connection to a power supply 19. The support layer 14 of plate 12 is simultaneously maintained at zero potential through its contact with tray 10 which in this embodiment is both electrically conductive and electrically grounded. The electrical field established between paper 15 and plate 12 causes the developer particles on plate 12 to transfer to paper 15. Since these developer particles are wetted by the liquid of carrier liquid 11, they are not tightly bonded to plate 12 except by electrostatic forces which are readily overcome by the potential applied to roller 16. After roller 16 has passed over paper 15, the paper may be separated from plate 12 and upon evaporation of the carrier liquid from the paper, there is formed a dry developed image on the paper. It is desirable, but not essential, to maintain an image bearing plate in darkness through the transfer process, and this is particularly so when transferring following uncharged area type development. Of course, if the image bearing member is not light sensitive, precautions need not be taken against exposure to light.

A particularly useful roller 16, used in connection with the above method and the improved methods of the present invention, included an electrically conductive silicone rubber cylindrical element 2 inches in diameter over a l-inch diameter metal core. The roll had a durometer hardness of 42 and the electrical resistance was of the order of 10 ohms for a 6-inch long member measured between the metal core and a fiat metal plate in contact with the outside of the roll while the roll was under an applied force of 10 pounds.

The figure represents only a specific embodiment of image transfer with respect to both methods and material. Thus, transfer member 15 is generally representative of a class of transfer materials which are characterized as having at least an insulating surface or substantially insulating surface. Ordinary paper is sufficiently insulating for use with this transfer method. In addition to ordinary paper, one can employ either paper or metals coated with insulating plastics or the like. Such coatings are chosen to be insoluble in the carrier liquid to avoid image deterioration which otherwise results. The transfer material should also have a smooth surface to permit intimate contact with the surface of plate 12. A particularly suitable paper has been found to be Kromekote cast-coated paper manufactured by the Champion Paper and Fiber Company, Hamilton, Ohio. Sheets of Mylar polyester film have also been used successfully. While plate 12 is shown as being immersed in the developer tray, it is only necessary in carrying out this transfer method that the developed image and area of its contact with the plate be wet, and thus, transfer may, for example, be effected outside of the developer after wetting the image and before the liquid has evaporated.

The illustrated and described conductive rubber roller in conjunction with a conductive tray is merely one way in which intimate contact can be established between transfer member 15 and plate 12 while establishing a strong electric field between them. Other forms of rollers or even flat, conductive plates may be substituted for roller 16, and a variety of means may be used to maintain support layer 14 at a different potential from that of roller 16 or its equivalent. In accordance with conventional xerographic practice, transfer can also be effected by passing a corona charging device adjacent to paper 15 while it is in contact with plate 12. This can be accomplished while plate 12 is moist, but cannot readily be carried out where the plate and transfer member are actually immersed beneath the surface of a liquid bath at the time of transfer.

Particle transfer from the xerographic plate to the transfer material is carried out in the foregoing procedure through the agency of an electric field which is maintained between the plate and transfer material through potentials applied to external rollers, electrodes, or the like. It is, however, also possible to effect transfer in accordance with the present invention by electric fields generated internally of the plate-transfer member combination rather than externally thereof. In accordance with this further embodiment, the developed xerographic plate is removed from the developer bath and is uniformly electrostatically charged. Such charging may be performed by any conventional form of corona charging apparatus or the like, but is most conveniently per-formed in the same apparatus previously used to charge the plate in connection with the described process of electrostatic latent image formation. The potential to which the plate and the image thereon are charged is not critical and may be on the order of several hundred volts. Since this is the same range of potentials generally used in connection with charging a plate for image formation, the same charging apparatus as previously used may be employed for this second charging without any readjustment thereof. The plate is then contactedwith a sheet of paper or other transfer material in the same general manner as described above and shown in the drawing. If the plate bearing the developed image Was wetted prior to this charging operation transfer may be carried out without further wetting. However, if the surface of the Xerographic plate is not very wet appearing, it may be desirable to reiminerse the plate and transfer member in a bath of dielectric liquid. With this embodiment it is however, not necessary to apply a potential to roller 16 from power supply 19, and it is instead only required that the xerographic plate and the transfer material be brought into contact and that the backs or outer surfaces of the plate and paper or other transfer member be brought to about the same electrical potential. This may conveniently be accomplished by the same apparatus shown in the drawing. In this embodiment the developer particles are transferred from the plate to the paper by the electric fields resulting from the uniform charge layer previously deposited on the Xerographic plate. It is also permissible to apply a potential to roller 16 or to deposit uniform charge on the outer surface of the transfer member as through the use of a corona discharge electrode or the like in connection with this embodiment of the invention. It has been found that slightly superior or slightly inferior results are obtained with the added roller potential, depending upon the particular developer materials em ployed, the potential applied and the like. Best results to date in connection with this invention have resulted following chargin of the developed plate and then immersed transfer employing a grounded roller.

The invention has thus far been described in terms of a developed image formed using liquid immersion developing techniques. All embodiments discussed, however, have been employed starting with an image developed using dry development techniques such as cascade, powder cloud and the like. In such cases it is found that more complete transfers result when compared to dry transfer techniques.

The above procedures have been found to create transferred images of high density, a high degree of uniformity and very high resolution when used with a wide variety of Xerographic plates, carrier liquids and powder materials. There is, however, a tendency with the above methods to deposit background, i.e., a uniform deposition of powder, in addition to the powder corresponding to the electrostatic latent image if the carrier liquid becomes dirty with developer particles. This background problem can be avoided or overcome by refreshing the carrier liquid or by using a clean batch free of developer particles. Since a clean carrier bath is free of particles, the only particles which transfer are those particles electrostatically adherent on the Xero-graphic plate, and there results a background-free transferred image.

a .e invention has been described in terms of certain physical forms of apparatus, but it is to be understood that such description was for illustrative purposes only rather than by Way of limitation. Transfer according to the present invention may be carried out with various forms of development apparatus, various forms of Xerographic plates, various means for contacting the xerographic plate with the transfer material and various means for applying electric fields therebetween. While the invention has been described in terms of a manual operation, it is apparent that it can be adapted to various forms of automatic processing equipment. These and various other modifications lie within the scope of the invention and are intended to be encompassed within the appended claims.

What is claimed is:

l. The method of transferring a developed solid particulate image from an image bearing surface comprising contacting the developed image and the image bearing surface with a developer-free, electrically insulating iquid incapable of dissolving said image, positioning a transfer web across the developed image and image bearing surface while said image continues to be Wet with said insulating liquid, and applying electrostatic field between said developed image and said transfer web to cause movement of said still wet developed image to said transfer Web.

2. The method of claim 1 in which said electrostatic field is applied by rolling a roller at a raised potential across the rear surface of said transfer web.

3. The method of claim 1 in which said electrostatic field is applied by depositing charge on the rear surface of said transfer web from a corona discharge electrode.

4-. The method of claim 1 in which the developed image comprises a dry developed image.

5. The method of claim 4 in which said dry developed image is developed employing a dry development techni ue.

6. The method of claim 1 in which said electrostatic field is applied by first corona chargin the image bearing surface prior to positioning the transfer Web across the image bearing surface and then applying a uniform electrostatic potential across the rear surface of said tra sfer web while said transfer web is across said image bear' surface.

7. The method of claim 6 in which said uniform electrostatic potential is applied across said transfer web by corona discharge.

8. The method of claim 6 in which said uniform electrostatic potential is applied across said transfer web by a contacting electrode at a bias potential.

9. The method of transferring a developed solid particulate image from an image bearing surface to a transfer Web comprising contacting the developed particulate image and the image bearing surface with a patti lofree, volatile, electrically insulating liquid in which said imag said surface and said web are each insoluble, positioning a transfer web across the developed image and irnage bearing surface while said image continues to be wet with said insulating liquid, appling an electrostatic field between said developed image and said transfer web to cause movement of said still wet developed image to said transfer Web, then separating said transfer Web from said image bearing surface with said transfer web bearing said developed image, and allowing said volatile liquid to evaporate from the transferred developed image.

10. The method of transferring a developed particulate image from a surface hearing such image comprising wetting the developed image and the image bearing surface with a p: ticle-free, electrically insulating liquid incapable of dissolving said image, uniformly electro statically charging said image and image bearing surface while said image and surface remain in a Wet condition, positioning a transfer web having an insulating surface across the developed image on said image bearing surface while said image and said surface continue to be wet with said insulating liquid, and separating said transfer web from said image bearing surface with said transfer web bea 'ng said developed image.

11. The method of claim it) including applying a grounded roller against the back surface of said transfer web prior to separating said transfer web from said image bearing surface.

12. The method of claim 10 including applying a uniform electrostatic potential from a corona discharge electrode to the back surface of said transfer web prior to separating said transfer Web from said image bearing surface.

13. in an image reproducing process wherein an electrostatic image bear ng surface is developed by the selective electrostatic deposition thereon in image configuration of a pattern of finely divided solid particles from a suspension of said particl s in a volatile, electrically insulating liquid, the improvement comprising removing the developed image bearing surface from said suspension into a bath of volatile, particle-free, electrically insulating liquid incapable of dissolving said particles, and electrostatically transferring said pattern of finely divided particles to a contacting transfer sheet while at least the image bearing member is wet by said volatile particle-free insulating liquid.

'14. The improvement in the process of claim 13 including using the same electrically insulating liquid as employed in the suspension of particles as the volatile insulating liquid in the both of volatile particle-free insulating liquid.

15. In an image reproducing process wherein an electrostatic image bearing surface is developed by the selective electrostatic deposition thereon in image configuration of a pattern of finely divided particles from a suspension of said particles in a volatile insulating liquid, the improvement comprising removing the image bearing suriace from said suspension to a bath of volatile, particlefree, electrically insulating liquid incapable of dissolving said particles, while maintaining the image bearing surface in a moistened condition contacting said pattern of finely divided particles on the image bearing surface with a transfer material including at least an insulating layer facing the image'bearing member, establishing an electric field between the image bearing member and the transfer material While at least the image bearing member is wet by said insulating liquid, and separating the transfer member from the image bearing member.

References Cited in the file of this patent UNITED STATES PATENTS 2,551,582 Carlson May 8, 1951 2,940,847 Kaprelian June 14, 1960 2,951,443 Byrne Sept. 6, 1960 2,959,153 Hider Nov. 8, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent New 3 IQO IMJ February 41 1964 I Harvey HO Hunter It is hereby certified that error appears in the above numbered natent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line .20 for "unchanged" read uncharged eolumn 7 line 6 for "both" read bath Signed and sealed this 8th day of September I964 (SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N09 3 120 446 February 4L 1964 Harvey H Hunter It is hereby certified, that error appears in the above numbered batent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 2O for "unchanged" read uncharged column 7 line 6 for "both" read bath Signed and sealed this 8th day of September 1964.,

(SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims (2)

1. THE METHOD OF TRANSFERRING A DEVELPED SOLID PARTICULATE IMAGE FROM AN IMAGE BEARING SURFACE COMPRISING CONTACTING THE DEVELOPED IMAGE AND THE IMAGE BEARING SURFACE WITH A DEVELOPER-FREE, ELECTRICALLY INSULATING LIQUID INCAPABLE OF DISSOLVING SAID IMAGE, POSITIONING A TRANSFER WEB ACROSS THE DEVELOPED IMAGE AND IMAGE BEARING SURFACE WHILE SAID IMAGE CONTINUES TO BE WET WITH SAID INSULATING LIQUID, AND APPLYING AN ELECTROSTATIC FIELD BETWEEN SAID DEVELOPED IMAGE AND SAID TRANSFER WEB TO CAUSE MOVEMENT OF SAID STILL WET DEVELOPED IMAGE TO SAID TRANSFER WEB.

4. THE METHOD OF CLAIM 1 IN WHICH THE DEVELOPED IMAGE COMPRISES A DRY DEVELOPED IMAGE.

Images