US2954291A - Method for preparing a spirit duplicating master - Google Patents

Description

United States Patent ice METHOD FOR PREPARING A SPIRIT D'UPLICATING MASTER I-Iarold E. Clark, Pen'field, N.Y., assignor to Haloid gzierfix Inc., Rochester, N.Y., a corporation of New No Drawing. Filed Jan. 4, 1957, Ser. No. 632,421

1 Claim. (CI. 96- 1) This invention relates in general to xerography and in particular to a sensitive plate therefor. More specifically the invention relates to a new xerographic member comprising a conductive backing having on at least one surface thereof a mixture of crystal violet in an insulating binder which member is known as a xerographic plate.

In xerography it is usual to form an electrostatic latent image on a surface. One method of doing this is to charge a photoconductive insulating surface and then dissipate the charge selectively by exposure to a pattern of activating radiation. The-resulting electrostatic charge pattern is Patented Sept. 27, 1960 or solution onto a suitable conductive surface in a layer utilized by the deposition of electroscopic particles thereon through electrostatic attraction whereby there is formed a .visible image of electroscopic particles corresponding to the electrostatic latent image. Alternatively, the electrostatic charge pattern may be transferred to an insulating film and the electroscopic particles deposited thereon to form the visible image. In any case this visible image in'turn may be transferred to a second surface to form a xerographic print or may be fixed directly to the photoconductive surface. i

The member bearing the photoconductive insulating surface in this process is called a xerographic plate and indeed its unique properties make the process possible. A xerographic plate comprises a photoconductive insulating layer on a conductive backing. Hereto-fore, it has been found that vitreous selenium has been the most satisfactory photoconductive insulating material and, therefore, prior plates have consisted of conductive backing members with coatings of vitreous selenium thereon.

Now, in accordance with this invention, it has been found that a xerographic plate can be prepared with crystal violet distributed in an insulating binder to form the photoconductive layer on the plate. In general, the measured vapparent resistivity of the composite, layer should be at least 10 ohms-cm.

The binder material which is employed in cooperation with this crystal violet is a material which is an insulator to the extent that an electrostatic charge placed on the layer is not conducted by the binder at a rate to prevent the formation and retention of an electrostatic latent image or charge thereon. Among the various binder materials which have been found satisfactory are the following: polystyrene resins, silicone resins, acrylic polymers such as acrylic and methacrylic ester polymers and the like, vinyl polymers, cellulose esters and ethers, chlorinated hydrocarbons, such as, for example, chlorinated rubber, alkyd resins, and mixtures of these and other resin binders.

The conductive backing member on which the photoconductive insulator is coated is any suitable support member having suflicient electrical conductivity to dissipate electrical charges. Such support members include metal surfaces such as iron, aluminum, brass, chromium, zinc and the like, glass with a conductive layer thereon as of tin oxide, indium oxide and the like, conductive plastics, paper and other conductive surfaces in flat, spherical, cylindrical or other conformations as desired.

In the preparation of the xerographic plate, according between about 10 and 200 microns thick. In general, the ratio between binder and crystal violet is from about one part binder and ten parts crystal violet to about two binder and one part'crystal violet by volume. The actual proportions will, of course, depend on the particular binders and the properties and characteristics desired.

The general nature of the invention having been set forth, the following example is presented as illustrative but not limiting of the meansof carrying out the invention.

Example. A crystal violet commercially available from National Aniline Division of Allied Chemical and Dye Corporation was mixed with an adhesive binder which was a silicone resin commercially known under the name DC-804 (Dow Corning Company). The crystal violet had a particle size of about 3 microns. The crystal violet and the binder were mixed together in equal parts by weight together with toluene in an amount equal to the binder material. The crystal violet was not appreciably soluble in the toluene and the crystals were dispersed throughout the binder. The resulting mixture was coated on the surface of a sulfide pulp paper and was allowed to The product was a xerographic plate comprising a paper backing and a photoconductive insulating layer thereon. A piece of the paper was placed in darkness and charged by means of corona discharge as described in co-pending application Serial No. 154,295, filed April 6, 1950, by Lewis E. Walkup. A potential of about 600 volts, positive, was placed on the electrode grille or grid while about 7,000 volts, positive, were placed on the corona wires. The charged paper was then exposed to a positive transparency using a No. 1 photoflood lamp. After exposure, with the paper still in the dark, it was contacted with a magnetic brush formed by mixing finely-divided thermoplastic resin particles with iron filings and contacting the mixture with a permanent magnet. The resin particles used were prepared as described in co-pending application Serial No. 373,431, filed on July 29, 1953, by John I. Rheinfrank et al. The mixture of iron filings and thermoplastic particles adhere -to the magnet forming long brushlike streamers. The brush was placed over the plate bearing the electrostatic image so that the streamers contacted the photoconductive insulating surface of the paperand the brush was moved in a sweeping motion several times across .the photoconductive insulating surface.

" Asa result, resin particles deposited on the photoconductive surface in accordance with the electrostatic latent image thereon to give an exact reproduction of the original positive transparency. A sheet of paper was then placed on top of the resin particles resting in turn on the photoconductive insulating surface to form a sandwich and the combined assembly was placed in a chamber saturated with trichloroethylene vapors such as described in copending application Serial No. 299,673, filed on July 18, 1952, by C. F. Carlson. After remaining in the chamber for :about 60 seconds the sandwich was removed, care being taken to preserve the face-to-face relationship of the paper and the paper-backed plate.

While in the chamber the resinous particles absorb the vapors and are thereby tackified, i.e., reduced in viscosity and fused together in a mass that is internally cohesive and has a surface that is adhesive to both the photoconduot-ive surface and the paper superimposed on the resin image. When the sandwich is removed from the vapor chamber, the powder solvent evaporates and the pattern hardens firmly bonding the portion of the photoconductor corresponding to the resin pattern to the super-imposed paper. Thereafter the paper and the xerographic plate are separated and the adherent portion of the photoconductive layer isliterally pulled from the xerographic .plate and remains. affixed to the paper thereby rendering the paper a master sheet which may be used in the usual manner in the spirit duplicating process. The solvent used in the duplicating machine should be varied with the nature of the resin used in the xerographic plate. In the instant example, the master sheet so prepared was placed on a commercial spirit duplicating machine and several copies were run off. The solvent usedwas tri chloroethylene. The copies so produced were highly legible and comparable in quality to spirit duplicating copies produced by conventional procedures.

While in the example t-richloroethylene vapor was used, the vapor of any mutual solvent for the resin powder and the resin binder in the photoconduct-ive layer may be used. Alternatively heat and/or pressure may be used as alternative means of tackification and bonding or as assistants to solvent vapdr therefor. A suitable substrate maybe placed between the photoconductive layer and the conductive backing to permit better release of the photoconductive layer under the. tackified resin image. Other means of using the novel xero-graphic plates of the instant invention to prepare spirit duplicating masters will at time be apparent to those skilled in the art.

Paper is preferred as a backing for the photoconductor by reason of its cheapness which makes economically feasible the use of the xerographic plates of the invention as disposable plates. However, other backing materials may be used such as plastic films, zinc, steel, iron, brass, chromium, aluminum, conductive glass, etc. If it is desired to use as a backing material, a substance which is not itself conductive as a sheet of polystyrene or acrylic resin, a substitute for conductivity may be used. One method of doing this involves placing on the outer surface of the insulating backing electrostatic charges of opposite polarity to those used to sensitize the photoconlductive layer. Such a layer of electrostatic charges on the insulating backing acts much like a conductive layer and makes possible the use of the plate in the normal xerographic process as described.

The example illustrates magnetic brush development. However, any other development process known to those skilled in the art such as cascade development, as shown in U.S. 2,618,552, powder cloud development as shown in copending application Serial No. 185,387, filed September 18, 1950, by L. E. Walkup, etc. may be used. Similarly, any method of charging the photoconductive insulating surface such as corona discharge, etc. known to those skilled in the art may be used.

Correlation between particle size and picture quality or graininess may be observed. Thus, finer quality re sults with increasing subdivision or grinding of the crystal violet. However, the particle size is not critical.

While the xerographic plates of the instant invention are uniquely adapted for the preparation of spirit duplicating masters, they are not limited thereto but may be used in the normal xerographic pro'cess as set forth in U.S. 2,297,691 to C. F. Carlson.

I claim:

A method for preparing a spirit duplicating master comprising placing an electrostatic charge on the outer surface of a layer of crystal violet dispersed in an insulating organic resin binder which in turn is coated on a conductive support, exposing said surface to an optical image whereby the resulting changes in the electric field distribution will produce an electrostatic latent image on the said surface, contacting said suiface with finely-divided electrically charged resin marking particles Whereby said particles deposit on said surface in accordance with the electrostatic image configuration thereon, plac ing a master sheet in contact with said surface, mutually tackifying said powder image, and said binder for the crystal violet thereby bonding the finely-divided resin particles to both the master sheet and the said surface and separating the master sheet from the said surface whereby said resin binder containing the crystal violet is torn out from said surface in those areas which adhere to said finely-divided resin particles.

References Cited in the file of this patent UNITED STATES PATENTS 2,067,435 Chatfield et a1. Jan. 12, 1937 2,297,691 Carlson Oct. 6, 1942 2,305,799 Vierling Dec. 22, 1942 2,519,321 Newman Aug. 15, 1950 2,528,496 Chalkley Nov. 7, 1950 2,598,732 Walku-p June 3, 1952 2,663,636 Middleton Dec. 22, 1953 2,676,887 Chalkley Apr. 27, 1954 FOREIGN PATENTS 201,416 Australia Dec. 1, 1955 OTHER REFERENCES Vattanyan: Chem. Abstracts, vol. 41, page 2988 (1947).

Vartanian: Acta Physichimica URSS, vol. XXII, No. 2, pages 201-224 (1947).

The Condensed Chemical Dictionary, 5th ed., Reinhold, page 727, methyl violet (1950).

Color Index, 2nd ed. (1956), vol. 1, page 1634.

Color Index, 1st ed. (1924), page 174.

Simonds et al.: Handbook of Plastics, 2nd ed., Van Nostrand (1955), pages 360 377.

Petnikaln: 2 Phys. Chem, vol. 10B, pages 9-21.