US3352671A - Activated photoconductors and recording element therewith - Google Patents

Description

United States Patent 3,352,671 ACTEVATED PHOTOC'QNDUCTORS AND RECORDHNG ELEMENT THEREWITH Michael Michalchik, Bethpage, N.Y., assignor to Fairchild Camera and instrument Corporation, Syosset, N.Y., a

corporation of New York No Drawing. Filed Dec. 28, 1964, Ser. No. 421,631

17 Claims. (Cl. 961.8)

This invention relates to electrophotography. More particularly, it relates to electrophotographic compositions used for coating a base material such as paper or metal, and the recording elements thus produced. It rclates also to amine activated photoconductors.

The art of electrophotography depends principally on the photoconductive properties of metals and metallic compounds. These include, for example, the oxides, sulfides, iodides, selenides and tellurides of zinc, mercury, aluminum, antimony, bismuth, cadmium and molybdenum; metallic lead and selenium; arsenic trisulfide, lead chromate and cadium arsenide. By far the most widely employed photoconductive substance is zinc oxide.

Electrophotography has been applied to many purposes. Dry reproduction of originals in ofiice copying by the well known electrofax process is one example. Lithography, photoengraving and production of electrical printed circuits are others.

For convenience this invention will be principally described as applied to the production of lithographic plates. Those skilled in the art will recognize that it is also applicable to other electrophotographic processes such as those mentioned above. Accordingly, the invention is not limited to the production of lithographic plates.

In the preparation of a lithographic plate, a recording element is first produced by coating 21 plate of zinc, magnesium or other etchable metal with a coating com position comprising an electrically insulating film in which a photoconductive substance such as zinc oxide is suspended. Photoconductive zinc oxide is well known. It generally has a surface photoconductivity of at least about ohms /square/watt/cm. when exposed to a wave length of 3900 A.

" The coating is then made sensitive to light by substantially covering the surface with an electrostatic charge in the dark. One convenient method of charging is to expose the surface to be charged to a corona discharge produced by connecting one or more fine wires to a direct circuit source, e.g., a direct circuit source of 3-10 kilovolts negative. The atmosphere surrounding the wires is ionized and the ion flow establishes the charge density on the surface. The charge decays slowly in the dark over a period of minutes or hours depending upon the nature of the coating.

The recording element now sensitive to light, is exposed by any of the conventional photographic processes and the electrostatic charge is selectively leaked from the surface. The degree of charge decay on a particular element is directly proportional to the amount of light to which the area is exposed. If light is projected through a photographic negative onto the charged surface, the largest amount of charge decay will be in the area of the recording element corresponding to the most transparent areas of the film. Charge decay in other areas will be correspondingly less depending upon the transparency of the corresponding areas of the film. There is thus produced an electrostatic image on the surface of the recording element which accurately reproduces the negative image on the film.

It is, of course, possible to effect selective charge decay by other procedures. For example, a contact print or drawing may be focused onto the charged surface of the recording element with the aid of an optical system using light from one or more incandescent lamps.

In one method of producing a lithographic plate, the insulating film in which the photoconductive material is suspended is a polymeric substance which is capable of further polymerization by the action of a catalyst or by actinic light to produce a polymer of higher molecular weight.

In the next step of the process, the electrostatic image is converted to a polymeric image by controlled polym erization of the areas which have retained a charge. This is often accomplished by depositing a polymerization catalyst such as finely divided aluminum octoate on the areas of the recording element bearing the electrostatic charge. Deposition may be effected, for example, by immersing the recording element in a developer bath comprising a liquid carrier in which the catalyst is suspended. The liquid is characterized by a high electric resistivity and is usually an aliphatic hydrocarbon or a mixture of aliphatic hydrocarbons including heptane and homologues thereof. Halogenated hydrocarbons may also be employed. The catalyst particles, by a process which is not completely understood, but is probably a triboelectric phenomenon, acquire a positive charge relative to the surface of the recording element and are, therefore, attracted to the electrostatic image and deposited on it.

The recording element with the catalyst selectively deposited on its surface is removed from the developer bath and rinsed to remove any catalyst particles which may have been deposited on the surface of the recording element in areas other than those bearing the electrostatic image.

After rinsing, the recording element is'placed in a curing oven where heat polymerization of the catalyzed areas takes place with the result that a polymeric image is produced corresponding to the original electrostatic image. The polymeric image comprises areas of high molecular weight solvent resistant polymers surrounded by areas of low molecular weight solvent sensitive polymers. The background areas are selectively dissolved to expose the metal surface which may be etched according to standard procedures after cleaning or descumming to produce a photoengraving resist.

For the production of printed copper circuits the recording element comprises a photoconductive layer which is deposited on the copper surface of a copper laminate and an electrostatic image corresponding to the desired circuit formed thereon. The polymer image is formed and the background area dissolved as described above to leave the bare copper. This copper is then removed by etching, for example, with ferric chloride or ammonium persulfate solution. The polymer image which covers the circuit is then removed with a solvent to leave bare copper in the desired configuration for the electrical circuit.

In the electrostatic printing process the photoconductive substance, preferably finely divided zinc oxide in a polymeric film is coated on paper. The electrostatic image is then produced by any convenient procedure and a developer or toner, generally comprising a pigmented, low

melting resin powder on a carrier of iron particles, applied to the paper in the charged areas with a magnetic brush. The resin particles adhere to the charged areas by triboelectric deposition and the iron powder remains on the magnetic brush. The paper is then heated to fuse the resin and produce the image.

All of these processes have the common element that a low molecular Weight polymer film containing a dispersed photoconductive material is formed on a base. The base may be either a metal such as zinc, magnesium or copper, or it may be a fibrous substance especially cellulosic fibers as in a paper; The polymeric electric insulator is generally referred to as the binder and will be so identified hereinafter. The film is deposited as a liquid photoconductive composition which contains the binder in solution and the photoconductive substance in suspension. It may also contain other special purpose ingredients such as dyes to increase the spectral range of the photoconductive material. The composition is evenly distributed on the base, for example by spraying or swirling, and the solvent evaporated to produce a recording element.

There are a number of problems which are common to these processes. It has been found that the binder film is susceptible to localized breakdown under theinfiuence of corona discharge. The result is that pinholes are produced in the binder film and catalyst or toner are not deposited, with the result that the ultimate image is marred.

Another problem is the problem of top voltage. The maximum voltage of the charge applied to the binder surface should be as reproducible as possible to insure consistent printing density. With silicone binders, this so called top voltage is of the order of 400-600 volts. With other binders it it somewhat less. In any event as the recording element ages by storage before use, this top voltage changes.

Still another, is the apparently reduced charge capacity of the recording element under conditions of low relative humidity. The result of this reduction is that the attainable print density may be reduced to only 75% of the normal print density expected from the recording element at 50% relative humidity.

It has been found that these problems are substantially alleviated by preparing recording elements in accordance with this invention in which an N-alkanol amine containing an aryl moiety is absorbed on the surface of the photoconductive substance. N-alkanol amines containing a phenyl substituent are useful and of these tertiary-N- benzyl-N-alkanol amines are particularly suitable. An especially preferred class of amines is represented by the formula (CH2) OH CuH CHgN wherein n is an integer from 1 to 3, Y is C H CH and alkyl group containing from 1 to 3 carbon atoms or (CH OH wherein n is an integer from 1 to 3. For reasons of commercial availability the preferred compounds within the scope of the above formula are N,N- dibenzylethanol amine; N-methyl-N-benzylethanol amine and N,N-diethanol-benzyl amine.

The selected amine is preferably at least partially soluble in the solvent for the binder so as to permit uniform absorption on the photoconductor surface from solution. This is not essential, however, since the photoconductor can be independently activated. In one method the photoconductor is exposed to an atmosphere containing vapors of the selected amine. In another the photoconductor is suspended in a solution of the amine and the solvent evaporated. The thus activated photoconductor is then resuspended in the binder solution.

If the wet development procedure is employed, i.e. if the developer is deposited on the electrostatic image from a liquid medium, the amine should, of course, be insolument technique utilizing a magnetic brush, for example is employed.

Any of the binder materials generally used in electrophotography are applicable to the process of this invention although silicone resins are preferred. Satisfactory binder materials include, forexample, polystyrene; acrylic and methacrylic ester polymers such as Acryloid A10 and B72, polymerized ester derivatives of acrylic and methacrylic acids, both supplied by Rohm & Haas Company; Lucite 44, Lucite 45 and Lucite 46, polymerized butyl methacrylates supplied by E. I. duPont de Nemours & Company; chlorinated rubber such as Parlon supplied by The Hercules Powder Company; vinyl polymers and copolymers such as polyvinyl'chloride, polyvinyl acetate, etc. including Vinylite VYHH and VMCH manufactured by the Bakelite Corporation; cellulose esters and others such as ethyl cellulose nitrocellulose, etc.; alkyd resins such as Glyptal 2469 manufactured by The General Elec-v tric Company; Rezyl 869, a linseed oil-glycerol alkyd provided by American Cyanamid Company; silicone resins such as DC 801, 804 and 996, all manufactured by the Dow Corning Corp. or SR82 a methyl phenyl polysiloxane mixture available from General Electric Company. This latter silicone resin is especially effective in admixture with ethoxylated phenyl siloxanes, for example R 830, available from Union Carbide Corp. Other binder mixtures containing one or more of the above mentioned binders, or other, may also be employed.

The electrophotographic compositions of this invention comprise dissolved binder which may be partially polymerized as in the production of a lithographic plate or substantially completely polymerized, as in the electrofax process in a solvent containing dispersed photoconductor and from about 0.02 to about 0.08% of the selected amine which in the composition may be absorbed on the surface of the photoconductor. Suitable solvents include aliphatic or aromatic hydrocarbon solvents containing, for example, up to eight carbon atoms. Benzene, toluene, methylene dichloride, ethylene dichloride, ethylene trichloride, carbon tetrachloride, hexane, heptane and isooctane may be mentioned by way of example. The choice of solvents is not critical. Mixed solvents may be employed.

The amount of zinc oxide or other photoconductor present in the liquid may vary between rather wide limits. It may vary, for example, from about 7% to about 50% by weight based on the total weight of the composition. The total solids in the composition may vary from about 10% to about 60% and this will be substantially all binder and photoconductor plus, in some cases minor amounts of other additives such as dyes. The ratio of photoconductor to binder in the composition and in the recording element is accordingly, from about 1.5/1 to 9/ 1.

A recording element of this invention comprises a base member, with a surface coating comprising aphotoconductor activated by absorbed amine dispersed in an electrically insulating binder. The percent by weight of photoconductor in the film is from about 50% to about by weight. The ratio of photoconductor to binder is from about 1.5/1 to about 9/1 and the amine content is from about 0.02% to about 0.08% by weight based on the weight of photoconductor.

The binder films on the base which are obtained using the compositions of this invention are superior to previously known products in several respects. The. principal improvements are that the original charge may be more uniformly dispersed on the surface coat and the changes in the coated base due to aging are minimized.

The following examples are given by way of illustration only and are not to be construed as limitations of this invention, many apparent variations of which are possible without departing from the spirit and scope thereof.

EXAMPLE 1 The photo-resist composition is prepared containing the following ingredients and parts.

Ingredients: Parts SR-SZ 1 milliliters 630 Xylene do 900 Toluene do 100 N,N-diethanolbenzyl amine do 0.3 Photoconductive zinc oxide (0.35 micron particles size) grams 700 Uranine dye (1% in methanol) milliliters 18 1A silicone binder available from the General Electric Company.

The amine is added to the binder and solvent composition before the addition of the zinc oxide. The Zinc oxide is added to the mixture gradually and dispersed by high speed stirring for approximately two minutes. The dye is added drop-wise in 30 milliliters of toluene. The mixture is then stirred rapidly for approximately 3 minutes. It is used to prepare a photoengraving or lithographic plate.

EXAMPLE II Part A The composition is prepared containing the following ingredients and parts.

Ingredients: Parts Pliolite S-7 grams 100 Toluene milliliters 150 Activated hotoconductive zinc oxide grarns 100 I A styrene-butadiene copolymer available from Goodyear Tire 8; Rubber Company.

Part B The composition is a preparation of activated zinc oxide composed of the following ingredients and parts.

Ingredients: Parts Photoconductive zinc oxide grams 100 3 USP N0. 12 available from New Jersey Zinc.

and is taken up in 200 milliliters of acetone containing 0.15 gram of dissolved N,N-dibenzylethanol amine and the composition thoroughly mixed by high speed stirring. The acetone is evaporated and the zinc oxide heated for two hours at 250 F. until thoroughly dry.

I The mixture of Part A containing activated Zinc oxide from Part B is ball-milled for six hours to produce an electrophotographic composition suitable for coating a base member to prepare a recording element.

EXAMPLE III The following components are mixed together in a high speed blender and applied to a roughened metal surface to provide the recording element.

Ingredients: Parts Methyl isobutyl ketone milliliters 500 Triphenyl phosphate grams 1O N,N-diet-hanolbenzyl amine milliliters.. 0.05 SR-184 4 do 18 Cellulose acetate butyrate (Eastman Grade Eab 500-1) grams 80 Photoconductive zinc oxide do 250 4 A silicone binder available from General Electric Company.

EXAMPLE IV The following components are mixed in a high speed blender to provide an electrophotographic composition which is useful for the preparation of recording elements with an extremely smooth surface coating.

6 Ingredients Parts Freon TF milliliters 250 Lucite 46 grams 40 N,N-dibenzylethanol amine do 0.10 Photoconductive zinc oxide do 100 5 A halogenated hydrocarbon available from E. I. du Pont. 6 A mctliacrylic ester polymer available from E. I. du Pont.

EXAMPLE V An activated photoconductive zinc oxide is prepared by dispersing 100 grams of finely divided Zinc oxide in 190 milliliters of acetone containing 0.05 milliliter of N,N- diethanolbenzyl amine and evaporation of the solvent. The thus treated oxide is taken up in 100 milliliters of heptane containing 100 grams of Acryloid F-10 (available from Rohm & Haas, Inc.) and the mixture thoroughly blended in a high speed blender to provide an electrophotographic composition.

EXAMPLE VI An electrophotographic composition is prepared by thoroughly mixing the following components in a high speed blender.

Ingredients: Parts Photoconductive red mercuric oxide grams 100 R830 do 40 Toluene milliliters 40 N,N-diethanolbenzyl amine gram 0.25

TA silicone binder available from Union Carbide.

EXAMPLE VII An electrophotographic composition is prepared by stirring the following ingredients at high speed. Ingredients: Parts Photoconductive zinc sulfide grams R830 8 do 30 N,N-dibenzyl amine do 0.05 Toluene milliliters 5A silicone binder available from Union Carbide.

EXAMPLE VIII An elcctrophotographic composition is prepared by mixing the following ingredients in a high speed blender.

Lucite 46A methacrylic ester polymer available from E. I. du Pont.

The compositions of Examples VI, VII, and VIII are used to prepare recording elements using either zinc, magnesium or paper as the base member.

What is claimed is:

1. An electrophotographic composition comprising a binder dissolved in a volatile solvent containing a photoconductor and an amine selected from the group consisting of N,N-dibenzylethanol amine, N-rnethyl-N-benzylethanol amine, and N,N-diethanolbenzyl amine, the total solids in the composition being from about 10% to about 60% by weight based on total weight, the ratio of photoconductor to binder being from about 1.5/1 to about 9/1, and the total amine in the composition being from about 0.02% to about 0.08% by weight based on the weight of photoconductor.

2. An electrophotographic composition comprising a binder dissolved in a volatile solvent containing photoconductive zinc oxide and an amine selected from the group consisting of N,I I-dibenzylethanol amine, N-methyl- N-benzylethanol amine and N,N-diethanolbenzyl amine, the total solids in the composition being from about 10% to about 60% by weight based on the total weight, the ratio of zinc oxide to binder being from about 1.5/1 to 7 about 9/1, and the total amine in the composition being from about 0.02% to about 0.08% based on the weight of zinc oxide.

3. An electrophotographic composition comprising a binder dissolved in a volatile solvent containing photo.- conductive zinc oxide together with N,N-dibenzylethanol amine, the total solids in the composition being from about 10% to about 60% by weight based on the total weight, the ratio of zinc oxide to amine being from about 1.5 1 to about 9/ 1, and the total amine in the composition being from about 0.02% to about 0.08% based on the weight of zinc oxide.

4. An electrophotographic composition comprising a binder dissolved in a volatile solvent containing photoconductive zinc oxide together with N-methyl-N-benzylethanol amine, the total solids in the composition being from about 10% to about 60% by weight based on the total weight, the ratio of zinc oxide to amine being from about 1.5/ 1 to about 9/ 1, and the total amine in the composition being from about 0.02% to about 0.08% based on the Weight of zinc oxide.

5. An electrophotographic composition comprising a binder, dissolved in a volatile solvent containing photoconductive zinc oxide together with N,N-diethanolbenzyl amine, the total solids in the composition being from about 10% to about 60% by weight based on the total weight, the ratio of zinc oxide to amine being from about 1.5/1 to about 9/ 1, and the total amine in the composition being from about 0.02% to about 0.08% based on the Weight of zinc oxide.

6. A recording element comprising a base member having a surface coating comprising an insulating binder having dispersed therein from about 50% to about 90% by weight of a photoconductor, said photoconductor being activated by absorption of from about 0.02% to about 0.08% by weight of an amine selected from the group consisting of N,N-dibenzylethanol amine, N-methyl-N- benzylethanol amine and N,N-diethanolbenzyl amine based on the weight of photoconductor, the ratio of photoconductor to binder being from about 1.5/1 to about 9/ 1.

7. A recording element comprising a metallic base member having a surface coating comprising an insulating binder having dispersed therein from about 50% to about 90% by weight of a photoconductor, said photoconductor being activated by absorption of from about 0.02% to about 0.08% by weight of an amine selected from the group consisting of N,N-dibenzylethanol amine, N-methyl- N-benzylethanol amine and N,N-diethanolbenzyl amine based on the weight of photoconductor, the ratio of photoconductor to hinder being from about 1.5/ 1 to about 9/1.

8. A recording element comprising a paper base member having a surface coating comprising an insulating binder having dispersed therein from about 50% to about 90% by weight of a photoconductor, said photoconductor being activated by absorption of from about 0.02% to about 0.08% by weight of an amine selected from the group consisting of N,N-dibenzylethanol amine, N-methyl- N-benzylethanol amine and N,N-diethanolbenzyl amine based on the weight of photoconductor, the ratio of photoconductor to binder being from about 1.5/ 1 to about 9/ 1.

9. A recording element comprising a base member having a surface coating comprising an insulating binder having dispersed therein from about 50% to about 90% by weight of photoconductive zinc oxide activated by absorption of from about 0.02% to about 0.08% by weight of an amine selected from the group consisting of N,N-

zinc oxide, the ratio of zinc oxide to binder being from about 1.5/1 to about 9/1.

11. A recording element comprising a base member having a surface coating comprising an insulating binder having dispersed therein from about 50% to about by weight of photoconductive zinc oxide activated by absorption of from about 0.02% to about 0.08% by weight of N-methyl-N-benzylethanol amine based on the weight of zinc oxide, the ratio of zinc oxide to binder being from about 1.5/1 to about 9/1.

12. A recording element comprising a base member having a surface coating comprising an insulating binder having dispersed therein from about 50% to about 90% by weight of photoconductive zinc oxide activated by absorption of from about 0.02% to about 0.08% by weight 1 of N,N-diethanolbenzyl amine based on the weight of Zinc oxide, the ratio of zinc oxide to binder being from about 1.5/1 to about 9/1.

13. A photoconductor for use in the preparation of recording elements for electrophotography comprising a normally photoconductive material activated by absorption of from about 0.02% to about 0.08% by weight of an amine selected from the group consisting of N,N-dibenzylethanol amine, N-methyl-N-benzylethanol amine and N,N-diethanolbenzyl amine.

14. A photoconductor for use in the preparation of recording elements for electrophotography comprising a photoconductive zinc oxide activated by absorption of from about 0.02% to about 0.08% by weight of an amine selected from the group consisting of N,N-dibenzylethanol amine, N-methyl-N benzylethanol amine and N,N-diethanolbenzyl amine.

15. A photoconductor for use in the preparation of recording elements for electrophotography comprising a photoconductive zinc oxide activated by absorption of from about 0.02% to about 0.08% by weight of N,N-di' benzylethanol amine.

16. A photoconductor for use in the preparation of recording elements for electrophotography comprising a photoconductive zinc oxide activated by absorption of from about 0.02% to about 0.08% by weightof N-methyl- N-benzylethanol amine.

17. A photoconductor for use in the preparation of recording elements for electrophotography comprising a photoconductive zinc oxide activated by absorption of from about 0.02% to about 0.08% by weight of N,N-diethanolbenzyl amine.

References Cited UNITED STATES PATENTS 3,197,307 7/1965 Blakeet a1. 96-1.8 3,250,613 5/1966 Gramza et al 96l.8

NORMAN G. TORCHIN, Prihzary Examiner.

C. E. VAN HORN, Assistant Examiner,

Claims (1)

1. AN ELECTROPHOTOGRAPHIC COMPOSITION COMPRISING A BINDER DISSOLVED IN A VOLATILE SOLVENT CONTAINING A PHOTOCONDUCTOR AND AN AMINE SELECTED FROM THE GROUP CONSISTING OF N,N-DIBENZYLETHANOL AMINE, N-METHYL-N-BENZYLETHANOL AMINE, AND N,N-DIETHANOLBENZYL AMINE, THE TOTAL SOLIDS IN THE COMPOSITION BEING FROM ABOUT 10% TO ABOUT 60% BY WEIGHT BASED ON TOTAL WEIGHT, THE RATIO OF PHOTOCONDUCTOR TO BINDER BEING FROM ABOUT 1.5/1 TO ABOUT 9/1, AND THE TOTAL AMINE IN THE COMPOSITION BEING FROM ABOUT 0.02% TO ABOUT 0.08% BY WEIGHT BASED ON THE WEIGHT OF PHOTOCONDUCTOR.