US3310401A

US3310401A - Electrophotographic member and process utilizing polyarylmethane dye intermediates

Info

Publication number: US3310401A
Application number: US305206A
Authority: US
Inventors: Greig Harold Grey
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1963-08-28
Filing date: 1963-08-28
Publication date: 1967-03-21
Anticipated expiration: 1984-03-21
Also published as: BE652332A; NL6409932A; DE1497083A1; GB1078731A; CH450464A; DE1497083B2; SE321148B

Description

3,310,461 Retest! 94st- 2 ;?6

3,310,401 ELECTROPHOTOGRAPHIU MEMBER AND PROC- ESS UTILIZING POLYARYLMETHANE DYE IN- This invention relates to improved photoconductive elements and more specifically to improved organic electrophotographic elements as well as methods of preparing such elements and methods of record-ing thereon.

Generally speaking, electrophotographic recording members presently in commercial use have high contrast characteristics. For this reason, it is desirable, in commercial recording elements, such as those which include a photoconductive insulating layer of selenium or zinc oxide dispersed in a resinous binder, to improve the faithfulness with which continuous tone originals are reproduced. In high contrast reproductions, the full gray scale of the original may be compressed into a limited number or less) gray scale steps in the reproduction. In addition, an improvement in electrophotography is desired in reproducing large solid-colored areas. Efforts have been made to achieve the desired improved characteristics by employing screening techniques during the reproduction process. However, "heretofore, screening techniques have used additional equipment at the point of reproduction, have'rnade less efiicient' use of light sources and/ or have reduced the maximum image density which can be achieved.

It is a general object of this invention to provide improved electrophotographic recording elements.

Another object of this invention is to provide an improved electrophotographic recording element having a I Yet another object of this invention is to provide im- A still further object is to provide improved electro photographic methods of graphic reproduction.

Yet another object of: this invention is to provide improved electropho-tographic methods of preparing screened reproductions of, continuous tone originals.

These and other objects and advantages are accomplished in accordance with this invention by preparing a composition comprising one or more certain colorless dye intermediates dissolved in an organic resinous binder material. The composition may be coated on a suitable substrate and allowed to dry or it may be cast into a self-supporting film. The resinous material in the composition not only functions as a binder but also reacts, in thesolid state, with the dye intermediate to form a third material which acts as a photoconductive sensitizer. The sensitizer is a dye formed in situ from the dye in termediate. The formation of this sensitizer results from exposure of the solid solution to actinic radiation such as, for example, radiant heat, visible and/or ultraviolet light. 1

An important step in the preparation of a recording element, in accordance with this invention, involves formation of dye in selected portions of a solid solution coating or film thereby providing a substantially uniform geometric pattern of'discrete areas on the coating or film which are photoconductively sensitized. This is accomplished by exposing the coating or film to a pattern of actinic radiation.

For example, the coating may be l exposed for a short time to ultraviolet light passing through a photographic half-tone contact screen; In this way a dot (or line) screen structure is built into the coatingv or film. lnthe exposedareas, actinic radiation produces dye formation and photoconductive sensitization. The unexposed center of adot (or line) contains little or no'sensitizer and is least sensitive in anelectrophotographic process. Outwardly from the center of the dot (or line) increased amounts "of sensitizer are formed; Thus, in direct electrophotographic printing, exposure to image high-lights produces maximum discharge of dots and exposure to half tones produces agraded discharge of the dots. The photoconductive coatings or films, being solid solutions, are grainless so that .the dot resolution may be almost unlimited, limited only by diffusion of the actinicradiation in the thickness of the coating or film.",'

In most cases, considerably less than one percent of the colorless dye intermediate need by converted to the sensitizer to provide maximum sensitivity. Formation of more sensitizer increases the amount of color in the coating or film without any apparent increase in photoconductive'sensitivity. With only trace amounts of-sensitizer, photoconductive layers are formed which are substantially transparent to light within the visible spectrum, which have a dark resistivity of 'at least 10 ohm-centimeters, and which, in sensitized areas, have a resistivity of at least two orders of magnitude (10 less when irradiated.

An unsensitized recording element may be supplied to the ultimate, user into which he may build a screen pattern of his own choosing. For example,-a film -or plate including a coating of a suitable resinous material having dissolved therein a selected dye intermediate may be provided. Care should be taken to prevent accidental exposure of the coated film or plate prior to use. When ready to make a halftone reproduction, or, if desired, at anytime before, the user may selected a suitablehalf tone line or dot screentransparency and, by exposureto actinic radiation through'the transparency, build into the coating a half tone screen by dye formation in a screen pattern. Thereafter, the coating is electrostatically charged and exposed to a continuous tone image to form an'electrostatic latent image which is developed into a visible image.

As mentioned heretofore, the compositions for the element are prepared by dissolving in a suitable resinous material a selected dye intermediate. For satisfactory results, organic resinous materials are employed which have a volume resistivity of at least 10 ohm-centimeters and in which the selected dye intermediate is soluble. The photoconductive sensitizer'is formed in situ byactinic radiation, formation 'ofthe sensitizer'being indicated by formation of a dye from the selected dye intermediate. Thus a resinous material is selected with which the dye intermediate can react'to form a dye or the resinous material is admixed with at least a trace amount of a material with which the dye intermediate can react.

Preferred reactive resinous materials include the following:

(1) Chlorinate paraffins, such as Chlorowax 70.

(2) Polyvinylidene chloride.

(3) Polyvinylidene chloride copolymers, such as Saran (4) Vinyl chloride copolymers, VAG'H, VYCM' or VMQH.-

Other resinous materials including the following may also be employed when mixed with the above listed masuch as Vinylite terials' (1 to 4)-or with'othernon-volatil'e halogenated ganic materials r -(5) Polystyrene and styrene copolymers,

wherein R and R are selected from the class consisting of monoalkylamin-o, di-alkylamino, mono-arylamino and alkylarylamino; and, X is selected from the class consisting of H and wherein R is selected from the class consisting of H, CH3, OCH3, R1 and wherein R and R are selected from the class consisting of H, CH and OCH These dye intermediates may be leuco bases from which dyes may be prepared. As employed herein, leuco base is defined as a colorless intermediate from which the dye may be prepared by oxidation in the presence of a suitable anion. The anion is, in this case, supplied by the resin or other halogen containing material, oxidation being accomplished by actinic radiation.

Dye intermediates may be employed to provide photoconductive materials having selected spectral response and selected degrees of transparency. Some dye intermediates are more readily available and less costly than others. Because of such considerations, two specific dye intermediates are presently preferred. These are:

(1) The leuco base of malachite green, bis-(4,4'-dimethylaminophenyl) phenyl methane (4,4-tetramethyldiaminotriphenyl methane) (2) The leuco base of crystal violet, tris-(4,4,4"-dimethylaminophenyl) methane, (4,4',4 hexamethyltriamion-triphenyl methane) In addition to the foregoinng examples of dye intermediates, the following Will provide advantageous results:

(3) Bis-(4,4' dimethylaminophenyl) 4" methoxyphenyl methane, (4.4 tetramethyl-diarnino-4"-rnethoxy triphenyl methane) OCH;

(4) Bis-(4,4' -dimethylaminopllenyl}4"-tolyl methane, (4,4-tetramethyl diarnino-4-methyl-triphenyl methane) (5) Bis (4,4 ethyl-benzylaminopheny'l) phenyl methane, 4,4'-benzylidenebis (N,N ethyl-benzyl aniline) (7) Tris-(4,4',4"-phenylaminophenyl) methane Q Q Q- -Q (8) Bis (4,4'-ethy1phenylam-ino phenyl) phenyl methane (9) Bis (4,4- ethylaminophenyl) 4-tolyl methane (10) Bis (4,4/ dimethylaminophenyl) 2",4" dimethoxyphenyl methane OCH! OCH;;

(11) Bis (4,4 dimlethylamiinophenyl) 2",4" xylyl methane CHr CHI

H -Q-t-Q- (13) Bis (4,4' methylamimophenyD-4"-methoxyphenyl methane (14) Bis (4,4 methylarninophenyl) 4" tolyl methane (llHa H H CH3lLTOC-IL'-OH:

(15 Bis (4,4' methylaminophenyl)-2",4"-dimethoxyphenyl methane 6 (16) Bis (4,4-methylaminophenyl)-2,4"-xylyl methane -CHa t i (17) Tris (4,4',4" ethylphenylaminophenyl) phenyl methane Photoconductive compositions are conveniently prepared, for example, by dissolving a quantity of the resinous material in a suitable solvent such as, for example, methyl ethyl ketone, toluene or mixtures thereof and, when the resinous material is completely dissolved, adding to the solution a quantity of the dye intermediate. The proportion of dye intermediate to resinous material may vary over a wide range depending on the end use that is contemplated. The choice of resinous material as Well as the dye intermediate can change the optimum ratio for a given use. In many instances, it is desirable that a photoconductive layer or coating be as transparent as possible. For such purposes 1 /3 parts by weight or less of dye intermediate for each 10 parts by weight of resinous material can be employed. For other purposes, the color or capacity of a photocondu-ctive film or coating is of no concern. For such purposes, 1% parts by weight or more of dye intermediate for each 1.0 part by weight of resinous material may be employed. The solubility of a particular dye intermediate in a particular resin should also be taken into consideration. In some instances if a. solution is prepared containing too much dye intermediate, the excess thereof, upon drying, crystallizes out of solution and a photoconductive surface so produced is, for most purposes, unsatisfactory.

Various modifying agents may be added to the foregoing compositions to vary the physical properties or appearance thereof provided they do not interfere With the electrical properties. For example, when such compositions are to be coated on flexible substrates or formed into self-supporting flexible films, flexibility can be enhanced by including in the compositions small amounts of a plasticizer, such as, for example, tricresyl phosphate, butyl aphthalyl-butyl-glycolate, tris-(2,3=dibromo-propyl) phosphate, and di-(Z-ethylhexyl) phthalate.

Enhanced flexibility can also be provided by employing combinations of resinous materials in coating or film forming compositions. For example, mixtures of polyvinyl chloride with chlorinated paraflins or hydrocarbon terpene resins can provide highly flexible coatings or films.

When a composition is preparedwherein a dye intermediate is dissolved in a non-halogenated resin, enhanced results can often be obtained by including in the composition at least a trace amount of a compatible non-volatile halogenated compound such as, for example, tris-(2,3-dibromopropyl) phosphate or any compatible chlorinated paraffin.

- Manyof the compositions contemplated herein, when coated on a substrate or formed into a film, may have a tendency to form so much color as to be undesirable under some circumstances. Color formation in a film or coating can be substantially controlled or retarded by including in the compositions a small amount of an antioxidant to stabilize the dye intermediate therein. A specific example of a suitable stabilizer is one having the formula Other materials such as solid unreacted epoxy resins may be used. Some compositions including such a stabilizer will remain substantially colorless for a considerable time unless subjected to intense ultra-violet radiation.

ELECTROPHOTOGRAPHIC RECORDING ELEMENTS The recording elements may comprise self-supporting films or, in the alternative, coatings may be formed on suitable substrates to provide such recording elements. Specific examples of such recording elements include the following:

Example I v A coating formulation is prepared which includes:

1.5 parts by weight of a vinyl chloride copolymer (Vinylite VAGH) 1.0 part by weight leuco base, bis-(4,4'-dimethylaminophenyl) phenyl methane 15.5 parts by weight methyl ethyl ketone The vinyl chloride copolymer is dissolved in the ketone and when the solution is complete the leuco base is dissolved in the solution. A suitable substrate such as, for example, an aluminum plate, is coated with the combined solution which is then dried to produce a thin uniform layer on the substrate. The coated substrate may be moderately heated to accelerate drying. Excessive heating will cause dye formation. For example, continued heating of the dried coating for from two to three minutes at a temperature of 180 to 200 C. causes the entire coating to take on a faint but visible green tint. Formation of dye throughout the coating would detract from the usefulness of the coating for the present purposes. In fact, if an excessive amount of dye were so formed, the coating could become useless for present purposes. The risk of producing undesired dye formation can bereduced by drying the coating in vacuum or under reduced pressure in the absence of artificial heating.

A built-in screen is readily produced in the dry coating by exposure to ultraviolet light. For example, a contact halftone line (or dot) transparency is placed on the surface of the coating. One type of suitable transparency is a Caprock 60-line positive gray scale screen. With the transparency firmly held on the coating, the coating is exposed to actinic radiation passing through the transparency. Suitable exposure can be made in from to minutes to a 4-watt ultraviolet lamp held about six inches from the transparency. Exposure times can be considerably reduced by using high pressure mercury vapor lamps or mercury arc lamps as sources of ultraviolet radiation.

A recording element, prepared as described, with a line screen photographic transparency, has a built-in half-tone screen consisting of a pattern of lines or bands having a graded sensitivity. Along the center of each such hand, there is little or no sensitivity, substantially no dye hav ing been there formed. Toward both edges of each such band, sensitivity and dye formation are both gradually increased to a maximum, dye formation being evidenced by a faint green tint in the otherwise clear coating. Had a positive dot screen been employed, the coating would contain a pattern of sensitized dots each having minimum sensitivity at the center and. maximum sensitivity at a maximum distance from the dot center.

8 Example 11 An electrophotographic transparency is prepared with the following:

16.8 parts by weight of a vinyl chloride copolymer (Vinylite VAGH) 5.6 parts by weight of a solid uncured epoxy resin (Epon 16.5 parts by weight leuco base, bis-(4,4'-dimethylamino phenyl) phenyl methane The above materials, in a suitable solvent such as methyl ethyl ketone, are coated on a glass slide or transparent film in the manner described in Example I. Here, actinic (U.V.) radiation passing through a half-tone screen produces a built in screen which is practically colorless, having only a very pale greenish-yellow tint.

Example III In a similar manner to that of Example I, one part by weight of a vinyl chloride copolymer consisting essentially of 91% vinyl chloride and 9% vinyl acetate is dissolved in about 20 parts by weight of methyl ethyl ketone. In this instance, heating of the solution aids in dissolving the copolymer. When the solution is complete and cooled to room temperature, about 0.75 part by weight of bis- (4,4-dimethylaminophenyl) phenyl methane is dissolved therein. This formulation is particularly adapted for making a self-supporting electrophotographic transparency. A mirror finish aluminum plate is coated with the formulation and the solvent evaporated therefrom. Thereafter, the coating is physically stripped from the aluminum plate to provide a self-supporting electrophotographic film having the same response as in Example I. A built-in screen is produced by U.V. exposure as in Example I, exposure being made either before or after the coating is physically stripped from the aluminum plate.

Example IV As in Example I, a suitable substrate is coated with a formulation of:

10 parts by weight of a vinyl chloride-acetate copolymer (Vinylite VAGH) solution (15% solids in methyl ethyl ketone) 0.20 part by Weight of bis (4,4'-dimethylaminophenyl)- 4" methoxyphenyl methane 5 parts by Weight of toluene After U.V. exposure through a screen transparency, the coatmg has a response slightly different from the coating of either Example I or II and the built-in half-tone screen has a greenish-blue tint.

Example V When a relatively strong color of a dot or line pattern Is not ob ectionable, a layer may be produced in accordance with the procedure of Example II with the following materials:

After U.V. exposure through a screen transparency, this layer has a wider spectral response than any of Examples I through IV and the built-in half-tone screen has a reddish-blue tint.

Example VI The coating composition having a relatively low softenmg point is advantageous for some applications. With such a coating on a suitable substrate, an electrostatic image can be produced thereon and developed with a toner powder having a high melting point such as, for example, finely-divided carbon black to provide high resolution. Fixing of an image so developed is then conveniently accomplished by heating to soften the coating and cause the toner powder tosink into and become fixedto the coating. A suitable coating composition is produced following the procedure of Example II with the following materials: 2 parts by weight of achlorinated paraffin (Chlorowax 7O) 10 parts by weight of solvent (equal parts of methyl ethyl ketone and toluene) 0.75 part by Weight of his (4,4'-dirnet-hylaminophenyl) phenyl methane A coating of this composition has a much lower softening point (95 to 110 C.) than any of the previous examples. After exposure through a screen transparency, the builtin half-tone screen has a dark green color.

Example VII Very thin transparent coatings can be prepared in the manner described in Example 11 from the following materials:

1.5 parts by weight of a styrene butadiene copolymer (Pliolite S-D) 1 part by Weight bis (4,4'-dimethylaminophenyl) phenyl methane 2.0 parts solvent (equal parts of methyl ethyl ketone and toluene) When coated on conductive glass and exposed to 'U.V. passing through a screen transparency this composition provides an excellent transparency, the built-inscreen exhibiting little color.

ELECTROPHOTOGRAPHIC HALF-TONE REPRODUCTION One field in which the improved electrophotographic elements described in the foregoing examples are useful is in the electrophotographic reproduction of continuous tone images. Usually a uniform electrostatic charge is deposited on a photoconductive surface of the element and the element is then exposed to a continuous tone light image which causes reduction in or removal of charge from areas exposed to light, thereby resulting in the formation of an electrostatic image on the coating. The electrostatic image can then be made visible by applying thereto finely-divided electroscopic developer particles by any known methods. Alternatively, the electrostatic image may be produced by first exposing the photoconductive coating to a light image and thereafter applying a uniform electrostatic charge to the coating. Areas which have been previously exposed to light are rendered conductive and the charges on the surface drain off from those areas. The charges remain on the coating in unexposed areas forming an electrostatic image.

When' an elefctrophotographic element has been prepared in accordance with one of Examples I-VII, including in the element a built-in dot screen, the center of a dot in the element has the least amount of sensitizer and is the least sensitive portion of the dot in the electrophotographic process. As the distance from the center of the dot increases so does the amount of sensitizer. With such a recording element the electnophotog-raphic procedure .described in the preceding paragraph can be carried out to produce thereon an electrostatic image.

After development of the electrostatic image to produce a visible image on the element, the effect of the builtin .dotscreen becomes apparent. Exposure to the highlight areas of an original continuous tone image produces the smallest developed dots on the element wherea exposure to the dense areas of the original produces the largest developed dots on the element. ,Since the coatings described are thin and grainless, dot resolution can producing such charges on coated paper or on self supportnig tfilms it is frequently convenient to employ a double corona charging unit. Such a unit is described in US. Patent No. 2,922,883 to E. C. Giaimo, Jr. With such a unit, electrostatic charges of one polarity are applied to one side of the recording element while at the same time electrostatic charges of opposite polarity are applied to the other side of the recording element.

COLOR PRINTING Methods of producing composite color images are also possible with the prescreened recording elements described herein. For example, the prescreened element can be charged and exposed (through appropriate'color filters) to produce thereon an electrostatic image corresponding to one color component of an original color image. This electrostatic image is then developed with a colored developer substance corresponding to that one color. Charging and exposure are repeated for another color to produce a second electrostatic image on the same recording element. This second electrostatic image is then developed into its appropriate color with a proper color developer material. This procedure is repeated as many times as needed toreproduce all the color components of the original image. When all color images are developed on the recording element they can then be heated to the softening temperature of the coating to fix all colors thereon and provide a screened reproduction of the original continuous tone image.

Another method of producing composite color images employs a plurality of prescreened self-supporting films such as in Example III. In this case, each film has produced thereon 'a developed and fused image of a single color corresponding to one color of the original continuous tone image. For example, one film mayhave produced thereon a red image, another a blue image and a third a yellow image. The separate films bearing different color images are then laminated into a unitary structure. This is accomplished by placing on film on another with the images thereof in registry and then compressing the whole while heating to fuse all the films together.

ELECTROSTATIC THERMOPLASTIC RECORDING The electrophotographic layers or elements also possess properties which make them particularly useful for preparing slides or films by electrostaticthermoplastic techniques. Such techniques are employed to'produce surface modulations on a thermoplastic photoconductive layer. One such method of reproduction includes the steps of producing a substantially uniform electrostatic charge on a surface of the layer and then exposing it to a light image to reduce or remove the charge in the exposed areas. Thereafter the layer is heated to at'least the softening temperature of the thermoplastic layer. In areas on the layer which were not exposed or only partly exposed, electrostatic charges remain. These remaining charges provide electrostatic forces which, as the layer is softened, produce depressions in the layer surface. The

entire layer surface thus becomes physically modulated in a configuration corresponding to the original light image. When the layer is cooled the surface modulations are frozen into the layer surface.

Films or slides prepared in this manner can be used in a schlieren projection system for viewing on a projection screen. When so used, the films or slides generally possess one inherent disadvantage. In a schlieren system an area which appears white on the projection screen is produced when light passing through a film (or slide) encounters a distorted or modulated portion of the film surface. The amount of light which falls on the viewing screen is proportional to the gradient or slope of an impression in the film surface. A fully exposed area on the film surface will have been substantially fully discharged so that heat development will produce no modulation of the surface in such an area. A similar result occurs in an area on the film which has not been exposed. In this case, no discharge of the area occurs during the exposure step. Heat development of an undischarged area produces no modulation of the area except at the edges thereof because of substantially uniform force acts over the entire area and whatever compression of the layer is produced it is produced uniformly to leave a flat surface. When light passes through any portion of the film having a flat surface, it is intercepted in the schlieren system and does not reach the the viewing screen. Thus, the known schlieren system is incapable of distinguishing between flat surfaces produced by full exposure and those produced by no exposure, both types of surfaces producing black areas on 'the viewing screen.

With a thermoplastic photoconductive layer havinga built-in half-tone screen, the aforementioned inherent dis advantage is overcome. For this purpose, the built-in pattern need not 'be a graded half-tone screen. It can, instead, be any pattern capable of breaking up a large area into discrete elements. For example, the layer can be exposed to U.V. through a silk screen or a pattern of fine lines to build into the layer a geometric pattern of discretely sensitized areas. An area on the surface of the screened layer, when exposed to a light image, includes discrete portions which are light sensitive and, hence, discharged by light and adjacent discrete portions which are not light sensitive and, hence, are not discharged. Areas on which no light fall during exposure retain charge. Heat development, as a result, causes exposed surface areas on the layer to become surface modulated in proportion to the amount of light striking the surface. With schlieren projection, then, these surface modulated areas produce white areas on a projection screen while unexposed areas on the layer, which remain flat during heat development, produce black areas on the viewing screen.

For use in schlieren projection systems, it is preferred that a thermoplastic photoconductive insulating layer be used which has a high degree of light transmissivity and which has a narrow temperature range over which transi tion occurs from the solid to a softened state and vice versa. An improved device may be prepared, for example, from the following materials:

Example VIII 7 parts by weight of a polystyrene such as Styron PS-2 7 parts by weight of the leuco base of malachite green,

bis-(4,4'-dimethylaminophenyl) phenyl methane v 1 part by weight of a vinyl chloride copolymer such as Vinylite VAGH 20 parts by weight methyl ethyl ketone 35 parts by weight of toluene The -7 parts leuco base are dissolved in a solution of the polystyrene and VAGH in the above solvents. The resulting solution is coated in any convenient manner, on a suitable substrate, such as conductive glass or metallized transparent film, and the coating is dried. A built-in half-tone screen is produced in the coating by exposure to actinic radiation as described in connection with Example I.

Charging and exposing of the coated substrate of Example VIII are accomplished in the usual manner. A visible surface modulated image can be heat developed on the coating in from 3 to 15 seconds by heating the coating and substrate at about 140 centigrade which raises the temperature of the coating to at least 50 C. Time and temperature are not critical so long as temperature and/or time are not sufficient to discharge the coating. Heat development can be accomplished in a simple way by placing the coated substrate on a hot plate (140 C.) and observing the coating while it is illuminated with low-angle safe-light (yellow). As soon as ripples or dimples are seen to form in the sunface, the coated substrate is removed and allowed to cool and thereby freeze the surface modulations in place. Excellent slides for schlieren projection can be prepared in this manner in a few seconds.

Another method of electrostatic thermoplastic recording produces, on a specially prepared slide or film, a light scattering image having much the same appearance as frosted glass. These prepared slides or films have the advantage that no special projection system, such as a schlieren system, is needed for viewing, an ordinary projector being quite suitable.

The slides of films employed can again include a suitable substrate such as conductive glass or metallized film coated with a prescreened layer of thermoplastic material in accordance with any of the preceding examples. Once the photoconductive coating is dried it is overcoated with a thin film of up to 500 Angstrom units in thickness of a material which is insoluble, i.e., incompatible with the thermoplastic photoconductive material. Reproductions are made on such a slide or film by applying a uniform charge to the film surface, exposing to a light image and then heating to at least the softening temperature of the photoconductive coating. Heat development causes the thin film to break up, in the charged and unexposed areas, and distort the surface of the photoconductive coating to produce a light scattering (frosted) image.

Suitable thin films can be overcoated on the thermoplastic layers using various materials and techniques. For example, a slide coated with thermoplastic photoconductive material can be overcoated by immersion in a water solution of polyvinyl alcohol. The slide is then flushed with deionized water and allowed to dry. In this way, the photoconductive coating is overcoated with a thin film of polyvinyl alcohol having a thickness of less than 500 Angstrom units. Prescreening using U.V. exposure, as described heretofore, can be performed before or after the thermoplastic layer is overcoated with polyvinyl alcohol.

Alternatively, the photoconductive coating can be overcoated with a thin film of gelatin by immersion in a solution containing one part by weight of gelatin in parts of water and thereafter flushing with distilled water. Other suitable thin films can be prepared by discharge deposition of styrene in vacuo to provide a thin crosslinked polystyrene film or by vacuum evaporation of metals such as gold or aluminum.

What is claimed is:

1. A recording element for electrostatic printing comprising:

a layer comprising a non-halogenated resinous material and at least a trace amount of a mixture of compatible non-volatile halogenated organic compounds;

at least one substantially colorless polyarylmethane dye intermediate dissolved in said layer;

said dye intermediate upon exposure to actinic radiation being reactive with said mixture of compounds to form a dye; and,

said layer having a substantially uniform geometric pattern of discrete areas the centers of which contain little or no amounts of said dye, and which contain increasing amounts of said dye outward from the centers thereof,

said layer having a resistivity in darkness of at least 10 ohm-centimeters and at least portions of said discrete areas having a resistivity, when irradiated,

of at least two orders of magnitude less than said resistivity in darkness. 2. A recording element for electrostatic printing comprising:

a layer of organic resinous material; at least one substantially colorless dye intermediate dissolved in said layer, said dye intermediate when exposed to actinic radiation being reactive with at least a portion of said organic resinous material to form a dye and having the general formula:

wherein R and R are selected from the class consisting of mono-alkylamino, di-alkylamino, mono-arylamino, and al-kylarylamino and X is selected from the class consisting of H and wherein R is selected from the class consisting of H, CH and OCH R and wherein R and R are selected from the class consisting of H, CH and OCH and,

.said layer having a substantially uniform geometric pattern of discrete areas the centers of which contain little or no amounts of said dye, and which contain increasing amounts of said dye outward from the centers thereof,

said layer having a resistivity in darkness of at least ohm-centimeters and at least portions of said discrete. areas having a resistivity, when irradiated,

of at least two orders of magnitude less than said resistivity in darkness.

3. A recording element according to claim 2 in which said pattern is a half-tone screen pattern.

4. A recording element for electrostatic printing comprising: v

a layer of organic resinous material comprising a nonvolatile halogenated material;

at least one substantially colorless dye intermediate dissolved in said layer, said dye intermediate when exposed to actinic radiation being reactive with said halogenatedmaterial to form a dye and having the general formula:

wherein R and R are selected from the class consisting of monoalkylamino, di-alkylamino, mono-arylarnino, and alkylarylamino and X is selected from the class consisting of H and wherein R is selected from the class consisting of H, CH3, OCH3, R1 and wherein R and R are selected from the class consisting H, CH3 and and,

said layer having a resistivity in darkness of at least 10 ohm-centimeters and at least portions of said discrete areas having a resistivity, when irradiated, of at least two orders of magnitude less than said resistivity in darkness.

5. A recording element for electrostatic printing comprising:

a layer comprising a non-halogenated resinous material and at least a trace amount of a compatible non-volatile halogenated organic material,

at least one substantially colorless dye intermediate dissolved in said layer, said dye intermediate when exposed to actinic radiation being reactive with said halogenated material to form a dye and having the general formula:

wherein R and R are selected from the class consisting of mono-alkylamino, di-alkylamino, mono-arylamino, and alkylarylamino and X is selected from the class consisting of H and wherein R is selected from the class consisting of H, CH3, OCH3, R1 and of at least two orders of magnitude less than said resistivity in darkness. 6. A self-supporting film for electrostatic printing comprising:

a layer of organic resinous material; at least one substantially colorless polyarylmethane dye intermediate dissolved in said layer, said dye intermediate upon exposure to actinic radiation being reactive with at least a portion of the material in said layer to form a dye; and,

7. An article according to claim 6 in which said film is substantially transparent and said resinous material is substantially colorless.

8. A recording element for electrostatic printing comprising:

at least one substantially colorless dye intermediate dissolved in said layer, said dye intermediate when exposed to actinic radiation being reactive with said halogenated material to form a dye and having the generalformular and alkylarylamino and X" is selected from the class consisting of Hand wherein R is selected from the class consisting of H, CH3, OCH3, R1 and wherein R and R are selected from the class consisting of H, CH and OCH and, I

said layer having av substantially uniform geometric pattern of discrete areas the centers of which contain little or no amounts of said dye, and which contain increasing amounts of said dye outward from the centers thereof,

said layer having a resistivity in darkness of at least ohm-centimeters and at least portions of said discrete areas having a resistivity, when irradiated, of at least two orders of magnitude less than said resistivity in darkness.

9. A recording element for electrostatic printing comprising:

a layer comprising a non-halogenated resinous mate rial and at least a trace amount of a compatible non-volatile halogenated organic material;

wherein R, and R are selected from the class consisting of mono-alkylamino, di-alkylamino, mono-arylarnino, and alkylarylamino and X is selected from the class consisting of H and Wherein- R is selected from the class consisting of H, CH3, R1 and 5 wherein R and R are selected from the class consisting of H, CH and OCH and,

said layer having a substantially uniform geometric pattern of discrete areas the centers of which contain little or no amounts ofsaid dye,.and,whichcontain increasing amounts of said dye outward from the centers thereof,

saidv layer having a resistivity in darkness of at least 10 ohm-centimeters and at least portions of said discrete areas having a resistivity, when irradiated, of at least two orders of magnitude less than said resistivity in darkness.

10. A recording element for electrostatic printing comprising a substrate coated'with a photoconductive insulating material, said material comprising:

a layer of organic resinous material;

atleast one substantially colorless dye intermediate dissolved in said layer, said dye intermediate when exposed to actinic radiation being reactive with at least a portion of said organic resinous materialto form a dye and having the general formula:

wherein R andR are selected from the class consisting of mono-alkylarnino, di-alkylamino, mono-arylamino, and alkylarylamino and X is selected from the class consisting of H and wherein R is selectedfromthe classconsistingof H, CH

OCH R and wherein R and R are selected from the class consisting of H, CH and OCH and,

said layer having a resistivity in darkness of at least 10 ohm-centimetersand at least portions of'said discrete areas having a resistivity, when irradiated, of at least two orders of magnitude less than said resistivity in darkness;

11. A recording elementfor electrostatic printing comprising:

a substrate;

a-coating layer on said substrate comprising a thermoplastic resinous material having a softening point substantially less than a temperature at which saidsubstrate is deleteriously affected;

at least one substantiallycolorless polyarylmethane dye intermediate dissolvedin said coating layer, said dye intermediate upon exposure to actinic radiation being active at least a portion of the material in said layer to form a dye; and,

said layer having a substantially uniform geometric pattern of discreteareas the centers of which contain little or no amounts of said dye, and which contain increasing amounts of said dye outward from the centers thereof,

said layer having a resistivity in darkness of at least 10 ohm-centimeters and at least portions of said discrete areas having a, resistivity, when irradiated, of at least two orders of magnitude less than said resistivityin darkness.

12. A recording element for electrostatic printing comprising:

a substrate;

a coating layer on said substrate comprising a thermoplastic resinous material having a softening point substantially less than a temperature at which said substrate is deleteriously afi'ected;

at least one substantially colorless polyarylmethane dye intermediate dissolved in said coating layer, said dye intermediate upon exposure to actinic radiation being reactive with at least a portion of the material in said layer to form a dye;

said layer having a resistivity in darkness of at least least two orders of magnitude less than said resistivity in darkness; and,

a thin adherent film on said coating comprising a material which is insoluble in said resinous material and having a thickness of up to about 500 Angstrom units.

13. A method of reproducing a continuous tone image on an insulating layer comprising an organic resinous material having dissolved therein at least one substantially colorless dye intermediate which is reactive upon exposure to actinic radiation with at least a portion of the material in said layer to form a dye and to impart photoconductive properties to said layer, said method comprising:

exposing said layer to an actinic radiation pattern composed of discrete light and dark areas in a geometric pattern to form said dye in said layer in conformity with said pattern;

electrophotographically producing an electrostatic latent image on said layer in conformity with an original graphic image; and

developing said latent image into a visible reproduction of said original graphic image.

14. A method of reproducing a continuous tone image on an insulating layer comprising an organic resinous material having dissolved therein at least one substantially colorless dye intermediate which is reactive upon exposure to actinic radiation with at least a portion of the material in said layer to form a dye and to impart photoconductive properties to said layer said method comprising:

exposing said layer to an actinic radiation pattern comprising a half-tone screen pattern to form said dye in discrete areas of said layer in conformity with said screen pattern; 7

electrophotographically producing an electrostatic latent image on said layer in conformity with an original continuous tone image; and,

developing said latent image into a visible reproduction of said original continuous tone image.

15. A method of reproducing a continuous tone image on an insulating layer comprising an organic resinous material having dissolved therein at least one substantially colorless dye intermediate which is reactive upon exposure to actinic radiation with at least a portion of the material in said layer to form a dye and to impart photoconductive properties to said layer, said method comprismg:

exposing said layer to actinic radiation passing through a graded half-tone screen transparency to form a graded half-tone pattern of said dye in said layer;

applying a finely-divided developer material to the latent image on said layer to develop said latent image into a visible 'half-tone reproduction of said original continuous tone image.

16. A method of reproducing a continuous tone image on an insulating layer comprising a thermoplastic organic resinous material having dissolved therein at least one substantially colorless dye intermediate which is reactive upon exposure to actinic radiation with at least a portion of the material in said layer to form a dye and to impart photoconductive properties to said layer said method comprising:

exposing said layer to actinic radiation passing through a graded half-tone screen transparency to form a graded half-tone pattern of said dye in said layer; elect rophotographically producing an electrostatic latent image on an exposed surface of said layer in conformity with an original continuous tone image; and, heating said exposed surface to at least the softening temperature of said thermoplastic material to form a pattern of raised and depressed areas on said layer comprising a half-tone reproduction of said original continuous tone image. 17. A method of reproducing a continuous tone image on a recording element comprising an insulating layer of thermoplastic organic resinous material having dissolved therein at least one substantially colorless dye intermediate which is reactive upon exposure to actinic radiation with at least a portion of thetmaterial in said layer to form a dye and to impart photoconductive properties to said layer, said layer having one surface thereof a thin adherent film of material which is insoluble in the material which is insoluble in the material of said layer, said method comprising:

exposing said layer to actinic radiation passing through a graded half-tone screen transparency to form a graded half-tone pattern of said dye in said layer; electr-ophotographically producing an electrostatic latent image on said film in conformity with an original continuous tone image; and heating said film and at least the portion of said layer to which said film adheres to a temperature at least equal to the softening temperature of said thermo plastic material to disrupt said film and form a lightscattering image comprising a reproduction of said original continuous tone image.

18. A method of making an electrophotographic recording element comprising the steps of 2 forming a layer of a solid solution of at least one substantially colorless dye intermediate in a resinous material said dye intermediate being reactive upon exposure to actinic radiation with at least a portion of said resinous material to form a dye said dye intermediate having the general formula:

wherein R and R are selected from the class consisting of mono-alkylamino, di-alkylamino, mono-arylamino, and alkylarylarnino and X is selected from the class consisting of H and wherein R is selected from the class consisting of H, CH OCH R and wherein R and R are selected from the class consisting of H, CH and OCH and,

exposing said layer to an actinic radiation pattern composed of discrete light and dark areas in a geometric pattern to produce at least trace amounts of a dye from said dye intermediate in said solid solution. 19. A method of making an electrophotographic rec-ording element comp-rising the steps of:

dissolving a substantially colorless dye intermediate in a resinous material with which said dye intermediate is reactive upon exposure to actinic radiation to form a dye, said dye intermediate having the general formula:

wherein R and R are selected from the class consisting of mono-alkylamino, di-alkylamino, mono-arylamino, and alkylarylamino, and X is selected from the class consisting of H and wherein R is selected from the class consisting of H, CH OCH3, R1 and t wherein R and R are selected from the class consisting of H, CH and OCH forming said resinous material with said dye intermediate dissolved therein into a layer; and, exposing said layer to an actinic radiation pattern composed of discrete light and dark areas in a geometric pattern to form at least trace amounts of said dye in said layer. 20. A method of making an electrophoto graphic recording element comprising the steps of: Y

coating a substrate with a solid solution of a substan tially colorless dye intermediate dissolved in a resinous material with which the dye intermediate is reactive when exposed to actinic radiation to form a dye, said dye intermediate having the general formula:

wherein R and R are selected from the class consisting of mono-alkylamino, di-alkylamino, mono-arylamino, and alkylarylamino, and X is selected from the class consisting of H and wherein R is selected from the class consisting of H, CH OCH R and units.

References Cited by the Examiner UNITED STATES PATENTS 2,598,732 6/1952 Walkup 96l.4 3,003,870 10/1961 Jarvis et al. 961.7 3,046,209 7/ 1962 Sprague.

3,051,569 8/1962 Sugarman et al 96-1.7 3,052,540 9/1962 Greig 961.7 3,169,061 2/1965 Hudson 961.1 3,196,010 7/1965 Gofie et al 96--1.1 3,238,041 3/1966 Corrsin 96l.1

OTHER REFERENCES Greig II: An Organic Photoconductive System, RCA Review, September 1962.

NORMAN G. TORCHIN, Primary Examiner.

C. E. VANHORN, Assistant Examiner.

Claims

1. A RECORDING ELEMENT FOR ELECTROSTATIC PRINTING COMPRISING: A LAYER COMPRISING A NON-HALOGENATED RESIONOUS MATERAIL AND AT LEAST A TRACE AMOUNT OF A MIXTURE OF COMPATIBLE NON-VOLATILE HALOGENATED ORGANIC COMPOUNDS; AT LEAST ONE SUBSTANTIALLY COLORLESS POLYARYLMETHANE DYE INTERMEDIATE DISSOLVED IN SAID LAYER; SAID DYE INTERMEDIATE UPON EXPOSURE TO ACTINIC RADIATION BEING RECTIVE WITH SAID MIXTURE OF COMPOUNDS TO FORM A DYE; AND, SAID LAYER HAVING A SUBSTANTIALLY UNIFORM GEOMETRIC PATTERN OF DISCRETE AREAS THE CENTERS OF WHICH CONTAIN LITTLE OR NO AMOUNTS OF SAID DYE, AND WHICH CONTAIN INCREASING AMOUNTS OF SAID DYE OUTWARD FROM THE CENTERS THEREOF; SAID LAYER HAVING A RESISTIVITY IN DARKNESS OF AT LEAST 10**9 OHM-CENTIMETERS AND AT LEAST PORTIONS OF SAID DISCRETE AREAS HAVING A RESISTIVITY, WHEN IRRADIATED, OF AT LEAST TWO ORDERS OF MAGNITUDE LESS THAN SAID RESISTIVITY IN DARKNESS.

13. A METHOD OR REPRODUCING A CONTINUOUS TONE IMAGE ON A INSULATING LAYER COMPRISING AN ORGANIC RESINOUS MATERAIL HAVING DISSOLVED THEREIN AT LEAST ONE SUBSTANTIALLY COLORLESS DYE INTERMEDITE WHICH IS REACTIVE UPON EXPOSURE TO ACTINIC RADIATION WITH AT LEAST A PORTION OF THE MATERIAL IN SAID LAYER TO FORM A DYE AND TO IMPART PHOTOCONDUCTIVE PROPERITIES TO SAID LAYER, SAID METHOD COMPRISING: EXPOSING SAID LAYER TO AN ACTINIC RADIATION PATTERN COMPOSED OF DISCRETE LIGHT AND DARK AREAS IN A GEOMETRIC PATTERN TO FORM SAID DYE IN SAID LAYER IN CONFORMITY WITH SAID PATTERN; ELECTROPHOTOGRAPHICALLY PRODUCING AN ELECTROSTATIC LATENT IMAGE ON SAID LAYER IN CONFORMITY WITH AN ORGINIAL GRAPHIC IMAGE; AND DEVELOPING SAID LATENT IMAGE INTO A VISIBLE REPRODUCTION OF SAID ORIGINAL GRAPHIC IMAGE.