US3382068A - Photocopying method - Google Patents

Description

United States Patent 3,382,068 PHOTOCOPYING METHOD Robert M. Gold, Brooklyn, N.Y., assignor to Itek Corporation, Lexington, Mass, a corporation of Delaware No Drawing. Continuation-impart of abandoned application fier. No. 137,476, Sept. 7, 1961. This application June 22, 1966, Ser. No. 559,386

11 Claims. (Cl. 96--27) ABSTRACT OF THE DISSLOSURE A method of recording an image pattern of activating radiation comprising exposing imagewise a copy medium comprising at least one photosensitive semiconductor pigment which becomes activated upon exposure to activating radiation and the first of two components of a colorforming oxidation-reduction reaction composition, and then applying to at least exposed portions of the copy medium the second component of the oxidation-reduction reaction composition, whereby the reaction products of the first and second components of the oxidation-reduction reaction composition form a permanent, irreversible image.

This application is a continuation-impart of patent application Ser. No. 137,476 filed Sept. 7, 1961, now abandoned.

The present invention relates to a process of photoimaging and more particularly to a method of photocopying employin semi-conductor materials.

Various types of photographic and reproduction materials and methods are known, a number of which employ semi-conductor and photo-conductive materials. One popular imaging method is the electrophotographic process which employs a coating of photoconductive pigments on a carrier sheet material of electroconductive properties. Applying to the photoconductive layer a uniform electrostatic charge and exposing the layer to a light image results in an imagewise distribution of differentially charged areas on the sheet material. The charge distribution is then developed to a visible image by application of a suitable finely divided toner material which adheres selectively to the electrostatically charged portions of the coated base sheet. Although the electrophotographic method has found wide use, it remains particularly expensive in view of the equipment requirements and the preparation of highly specialized base sheet materials.

A method related to electrophotography is the photocondnctographic process which employs the photoconductive activity associated with semi-conductor pigment materials similar to those used in electrophotography and by photo-imaging creates an imagewise distribution of current-conducting pathways through the copy material. Such areas of selective conductivity are employed, with current application and developer compositions including electroplating materials, to produce visible images corresponding to the imagewise distribution of the conductive pattern. As With the electrophotographic process, the base sheet materials are generally required to be conductive and copying equipment is expensive and particularly complicated.

According to the present invention, a copying method is provided which makes use of the electrophotographic 3,382,068 Patented May 7, 1968 properties of semi-conductor pigment materials, but which may be accomplished inexpensively without the use of complicated equipment and which further makes use of less expensive, non-conducting base sheet materials.

Photocopying processes have previously been described, for example by Levinos in US. Patent 3,052,541, which employ a combination of semi-conductor pigments and solutions of reducible ions. Imagewise light exposure of the pigment/ ion combination results in the reduction of the ion to form an immediately visible image. A particular disadvantage of such photo-imaging methods has been the requirement that the photo-reactive composition be in a fluid condition or at least under the influence of a fluid medium during the moment of photo exposure. The capability of such methods to provide constant density images is greatly dependent upon the uniformity of conditions of fluidity or moisture content over the whole of the copy sheet surface during photo exposure. Particularly expensive equipment and close operative attention to material manipulation are therefore particularly important, and represent significant disadvantages.

It has now been found according to the present invention that constant-density images may be prepared through the use of photolytically-initiated oxidation-reduction color-forming reaction, but without the attendant disadvantages of maintaining moist reaction media, as previously noted. The invention generally provides a photocopying method in which a copy sheet comprising a uniform coating of a semi-conductor pigment on a carrier sheet is sensitized to actinic radiation by the application of one component of an oxidation-reduction colorforming reaction, for example, readily reducible noble metal ions, such as from a coating of a solution of silver nitrate. The sensitizing coating is dried, thereby eliminating the uneven reaction densities experienced with earlier photolytic reduction copying methods dependent upon moist sensitized surfaces. The dried, sensitized photocopying material is then imagewise exposed to actinic radiation and a visible image is subsequently developed by application of a second component of the oxidationreduction color-forming reaction. Materials useful as cooperative color progenitors with readily reducible metal ion sensitizing compositions include normally colorless oxidizable secondary polyamine color formers such as derivatives of paraphenylene diamine, dimethyl aniline, and

orthotolidine.

The application of the cooperating color progenitors may be reversed with the same advantageous effectthat is, the oxidizable polyamine may be applied and dried prior to exposure, and the reducible metal ion solution applied after exposure as the image-developing composition.

The semi-conductor pigments useful in the materials of the present invention include the zinc oxide, titanium dioxide, lead chromate and lead molybdate normally employed in the aforementioned photoconductographic, electrophotographic, and photochemical copying methods. The variations in response of these semiconductor pigments in different actinic radiation spectra bands is well known and these differences in properties may be advantageously employed in the method of the present invention in the manner similar to their use in the abovementioned prior copying methods. Thus, for example, zinc oxide may be used as the semiconductor pigment when radiations in the near ultraviolet range are anticipated, or others of the noted pigment materials may be used where response to longer wave lengths of light is desired. Advantageously, mixtures of the various pigments may be used and a resulting broader spectrum response is obtained.

Supporting sheet materials may be selected from any of the large number of available paper and plastic films. Such selection need depend only upon the preference of the manufacturer, since no special properties, such as electroconductivity, need be provided. The application of the semiconductor pigment coatings to selected base materials is accomplished by means of normal coating techniques and coating compositions will preferably include up to about 25% of a relatively inert insulating binder resin material. Where the natural surface of a selected base sheet material normally resists the application of coatings, for example when a plastic film such as polyethylene terephthalate is used, priming or subbing coatings are advantageously applied.

The amounts of sensitizing and developing compositions applied in accordance with the present copying process may vary over a substantial range depending upon the base sheet material, pigment composition, coating conditions, and intended conditions of use such as exposure intensities, temperatures, and the like. It is anticipated that such procedural details may be readily determined in the light of operating conditions selected according to the preference of the particular operator.

It has been generally found, however, that sensitizing and developing compositions of less than about 5% of reactive material in a suitable solvent will be fully effective for most applications when applied by a non-metering method such as dip-coating with removal of excess solution and subsequent drying.

The present invention will be more apparent with reference to the following examples setting forth some preferred embodiments of the present photo-imaging process.

Example 1 A coating composition of about 75 parts of titanium dioxide dispersed in a resinous solution binder containing about 25 parts of a styrene-butadiene polymer is applied in a uniform coating on a paper base sheet. After drying, the pigment coated sheet is dipped in an alcoholic 3% solution of silver nitrate. The excess solution is wiped off and the sheet dried. The sheet material thus sensitized is exposed to light through a master transparency in an ordinary photoproj'ection device. Subsequent to exposure, a 1% alcohol solution of 2,2'-dinaphthyl-para-phenylenediamine is applied to the photo-exposed surface, and the excess developer solution is wiped from the surface when a sufficiently dense image is obtained. Similar dense images are obtained with polyarnine developer solutions containing about 1% 4,4,4"-methylidyne tris (N,N') dimethyl-aniline, or orthotolidine.

Example 2 The semi-conductor pigment coating of Example 1 is dip-coated with a 1% alcohol solution of N,N'-dinaphthyl para-phenylene diamine, the excess wiped from the surface, and the coated material dried. The surface thus sensitized is light-exposed through a master transparency by ordinary contact exposure means and is then developed with a solution of 3% silver nitrate in alcohol to obtain a dense image in the light-struck areas. The developed copy material is washed and dried to provide a fixed image. Fixing may also be accomplished by contacting the developed surface with thiourea, preferably in an alcohol solution. While the inclusion of a solvent such as alcohol is preferred as a means of improving penetration with higher binder content compositions, aqueous vehicles are fully satisfactory when lower binder proportions are used.

The above examples have been presented for the purpose of illustration and should not be taken to limit the scope of the present invention. It would be apparent that the described examples are capable of many variations and modifications which are likewise to be included within the scope of the present invention as set forth in the appended claims.

What is claimed is:

1. A method of photo-imaging which comprises:

(a) providing a support having on a surface thereof a uniform coating comprising a semi-conductor pigment;

(b) uniformly applying to the surface of said coated support a fluid composition comprising the reducing agent component of a color-forming oxidation-reduction reaction composition;

(0) drying the coated surface of said support;

(d) imagewise exposing said coated surface to photoactinic radiation; and

(e) uniformly applying to said exposed surface a fluid composition comprising the oxidizing agent component of said oxidation-reduction reaction composition, whereby the reaction products of the reducing agent component and oxidizing agent component form a dense, visible image in the light-struck areas.

2. The method according to claim 1 wherein the reducing agent component is a normally colorless oxidizable secondary polyarnine color-former, and the oxidizing agent component is a readily reducible noble metal ion.

3. The method according to claim 1 wherein said support coating consists essentially of a uniform dispersion, in an insulating resinous binder material, of a semiconductor pigment selected from the group consisting of zinc oxide, titanium dioxide, lead chromate, lead molybdate, and mixtures of said pigments.

4. The method of recording an image pattern of acti vating radiation comprising exposing imagewise a copy medium comprising at least one semiconductor pigment which becomes activated upon exposure to activating radiation and a normally colorless oxidizable secondary polyarnine selected from the group consisting of N,N'- dinaphthyl-para-phenylene-diamine; 4,4,4 methylidynetris-(N,N')dimethyl-aniline; and orthotolidine and then applying to at least exposed portions of the copy medium the oxidizing agent component of the oxidation-reduction reaction, whereby the reaction product of the reducing agent component and the oxidizing agent component of the oxidation-reduction form a permanent, irreversible image in the exposed areas of the copy medium.

5. The method according to claim 4 wherein the semi conductor pigment is at least one member from the group consisting of zinc oxide, titanium dioxide, lead chromate, and lead molybdate.

6. A method of recording an image pattern of activating radiation comprising exposing imagewise a copy medium comprising at least one photosensitive semiconductor pigment which becomes activated upon exposure to activating radiation and a reducing agent component of a color-forming oxidation-reduction reaction composition and then applying to at least exposed portions of the copy medium the oxidizing agent component of the oxidation-reduction reaction composition, whereby the reaction products of the reducing agent component and the oxidizing agent component of the oxidation-reduction composition form a dense, visible image in the exposed areas of the copy medium.

7. The method according to claim 6 wherein the semiconductor pigment is at least one member of the group selected from metal oxides, metal chromates, and metal molybdates.

8. A method according to claim 6 wherein the semiconductor pigment is at least one member selected from the group consisting of zinc oxide, titanium dioxide, lead chromate and lead molybdate.

5 9. A method as in claim 8 wherein the oxidizing agent component of the oxidation-reduction reaction composition comprises silver ion.

10. The method according to claim 6 wherein the oxidizing agent component is a readily reducible noble metal 5 ion, and the reducing agent component is a normally colorless oxidizable secondary polyamine.

11. The method according to claim 10 wherein the polyamine is selected from the group consisting of N,N'- dinaphthyl-para-phenylene-diamine; 4,4,4" methylidynetris-(N,N')dimethylaniline; and orthotolidine.

6 References Cited UNITED STATES PATENTS 3,082,085 3/1963 Miller et a1. 96-1 3,152,903 10/1964 Shepard et a1. 96-64 NORMAN G. TORCHIN, Primary Examiner. J. TRAVIS BROWN, Examiner. C. E. VAN HORN, Assistant Examiner.