US3414410A - Recording process - Google Patents

Description

1963 R. F. BARTLETT ETAL 3,414,410

RECORDING PROCESS Filed April 15, 1964 2 Sheets-Sheet 1 lNvENToRs RICHARD E BARTLETT CARL FW. E/(MAN JUL/ETTE I. P/A BY M, 7 1mm 1 ATTORNEY Dec. 3, 1968 RECORDING PROCESS Filed April 15, 1964 R. F. BARTLETT ET AL 2 Sheets-Sheet Z I I! I QED 1 RICHARD E BARTLETT CARL E W. EKMA/V UL/ETTE E R/AN 4mm MW ATTZRNEYS United States Patent 3,414,410 RECORDING PROCESS Richard F. Bartlett, Lexington, Carl F. W. Ekman, Bedford, and Juliette F. Plan, Burlington, Mass., assignors to Itek Corporation, Lexington, Mass., a corporation of Delaware Filed Apr. 15, 1964, Ser. No. 359,956 14 Claims. (Cl. 96-27) ABSTRACT OF THE DISCLOSURE A dye-sensitized copy medium comprising a photosensitive semiconductor is exposed to an image pattern of radiation which desensitizes the dye-sensitized medium to activating radiation in those portions which are struck by this desensitizing radiation. This thus-imaged copy medium is then uniformly exposed to activating radiation to activate those portions of the copy medium which remain sensitive to this radiation. The activated portions of the copy medium are then developed by contacting with suitable image-forming materials.

The present invention relates to data reproduction, and relates in particular to methods and apparatus for directly making positive prints of images to be reproduced.

Commonly owned copending application Ser. No. 199,211, filed May 14, 1962 by Berman et al. and incorporated herein by reference discloses methods for producing images in a copy medium comprising photoconductive materials by exposure of the copy medium to an image pattern of activating radiation to render chemically reactive those portions of the photoconductor medium which are struck by the activating radiation. The activated irradiated medium is next contacted with a developer to effect a chemical redox reaction between the developer and the activated chemically reactive portions of said medium on such contact.

For example, according to the invention of the copending application, a copy medium comprising finely-divided titanium dioxide, such as a TiO filled or coated paper, may be exposed to light through an image pattern to be reproduced. .Where light strikes the photosensitive oxide coating, the oxide becomes activated, i.e. chemically reactive. The medium is subsequently contacted with a developer system, for example including a solution of silver ion, which reacts at the chemically reactive portions of the activated medium. Thus, for instance, silver ion reacts to precipitate metallic silver. The exposed medium may be developed by contacting it with a developer system which tends to deposit solids where solids are already present on the medium. Such systems amplify faint or invisible images and render them visible. A typical developer system for image amplification, for example, is one in which a metal ion such as silver or mercury is present together with a material forming a redox system, such as hydroquinone. With such a developer system, relatively heavy deposits of metal will be formed on the medium in those portions which have been illuminated and which comprise chemically reactive activated TiO resulting in the direct formation of a visible image in the copy medium on contact with the developer system.

Images formed according to the technique just described will be negative images, that is opaque portions will form in the print in lightstruck areas, i.e. those corresponding with translucent areas in the image pattern to be reproduced. Thus, unless a negative of the image desired to be reproduced is first made and employed as the image pattern through which the copy medium is exposed, prints obtained according to the process just described will be negatives of the desired image.

3,414,410 Patented Dec. 3, 1968 According to the present invention, certain dyes known to the art and commonly used as sensitizers in silver halide photography are used for the treatment of photoconductive materials in preparing copy media for a process which permits the direct production of positive prints of good quality. In particular, the dyes play a dual role as both sensitizers and desensitizers for the photoconductive mateirals treated.

According to the present invention, positive prints are made employing a copy medium in which one or more sensitizing dyes are present in at least a monomolecular layer atthe surface of a photoconductive material present in said copy medium. Suitable photosensitive materials include elements and compounds such as Ge, TiO ZnO, ZI'Og, S1102, Bl2O B60, $13205, T3205, T602, B203, ZnS, and SnS for example. Many of these materials are photoconductive compounds of metals with non-metals of group VI-A of the Periodic Table, for example metallic oxides and sulfides.

The medium comprising a dye-sensitized photoconductor is exposed to an image pattern of activating radiation for a period of time dependent on the type of dye used and the light source but commonly averaging about three or more minutes in length, for example, when a low inten sity incandescent source is employed. During earlier portions of this exposure, the dye may act as a photosensitizer for the photoconductive material, facilitating transfer of the incident radiant energy to the material in a manner known in the arts relating to the dye sensitization of lightsensitive pigments of this type, thereby activating the material in exposed portions. However, on extended ex posure to radiation according to the methods of the present invention, the dye-treated material becomes increasingly insensitive to further irradiation and becomes relatively less activated.

This desensitization or deactivation effect is shown in FIG. 1 of the accompanying drawings. In FIG. 1, the printability or degree of activation of a copy medium comprising a typical dye-sensitized photoconductive material is plotted in arbitrary units on the ordinate as a function of the time of exposure to an activating light source plotted on the abscissa. The printability of the medium rapidly reaches a maximum, then typically decreases in a manner not heretofore recognized by those skilled in the art.

The relatively long image exposure mentioned above as a first step in the method of the invention should preferably be of such length as reduces the printability of the activated or lightstruck portions of the medium to at least one half of its maximum value on a plot similar to that shown in FIG. 1. The photoconductivity in air of a dyetreated copy medium is one measure of its printability, and will typically follow a curve like that shown in FIG. 1.

After the image exposure resulting in a deactivation rand desensitization of light-exposed areas, the dye-treated printing medium is next uniformly illuminated by exposure to a light source for a short time period, commonly averaging about three seconds when a low intensity incandescent source is employed, for example, so that the medium is in the range of maximum printability as shown in the typical plot of FIG. 1. Those portions of the printing medium not previously struck by light during said first exposure to an image pattern of desensitizing radiation are relatively more light sensitive, and the dye coating in these areas assists in the activation of the sensitive photoconductor to render it reactive with oxidizing and reducing agents used as developers. On the other hand, those portions of the printing medium which have previously been exposed to an image pattern of radiation for a long period of time have become desensitized, and are not activated to a great degree by the short uniform second exposure.

Thus, it will be seen that those portions of the twiceexposed printing medium which remain activated, i.e. are left chemical-1y reactive by the two exposures just described, correspond with opaque portions of the image to be reproduced. On development, these activated portions of the printing medium can be rendered opaque, for example by contact with silver ion to form visible deposits of metallic silver, so that a positive print of the original image results.

A number of developing techniques suitable for use in the present invention are disclosed in copending application Ser. No. 199,211. For example, development may occur in a single step by first contacting the twice-exposed medium with a developer such as a solution containing a metal ion reducible to free metal on such contact, e.g. silver ion or mercury ion, which are respectively reduced to free silver and mercury on contact with activated portions of the medium. However, a high degree of surface activation is generally required for production of a visible image in this manner. It is more convenient to develop the exposed medium using an image-amplifying developer system of the type discussed earlier herein. In one such process, a developer is first employed to form a latent developed image in the medium. That is, the twiceexposed medium is developed (e.g. by contact with silver ion) to produce an invisible image (e.g. a fine invisible deposit-of metallic silver) therein. In a later second step, the developed image invisibly present on the medium may be made visible by contact with a developer bringing about image amplification. Such developers, as known in the art of silver halide photography for example, suitably comprise a metallic ion combined with a redox system such as of hydroquinonequinone and are formulated to tend to deposit a metal such as silver on sites where silver is already present. Thus, a latent developed silver image produced according to the positive printing process of the present invention can be made visible by such development with amplification.

More simply, such an amplifying developer system may be used to produce a visible image directly in the exposed medium in a single step, without prior development of a latent developed image.

In general activation of the photoconductive materials contained in the copy media of the invention makes the materials chemically reactive with oxidizing agents which are at least as easily reduced as copper ions, e.g., copper, mercury, silver, gold and other noble metals, as well as organic materials such as methylene blue.

FIG. 2 of the accompanying drawing shows a system for producing positive prints according to the present invention. FIG. 2 shows imaging means 11 comprising activating radiation source 12, image object 13 such as a photographic transparency, and conventional optical means 14 for focusing an image pattern of radiation on copy medium 15, which latter is dye sensitized according to the present invention. In the apparatus, copy medium 15 is suitably transported by conveying means 16 shown in FIG. 2 as a belt and roller system, though other suitable conveying means will be apparent to those skilled in the art. After exposure to an image pattern of radiation, copy medium 15 is next uniformly illuminated by exposure to radiation source 17 (shown with the medium f in position 15a). Conveying means 16a by which copy medium 15a is transported to and from source 17 may be the same as means 16, or may be distinct therefrom,

aqueous solution of silver nitrate. On emergence from bath 18, the medium will have formed thereon a latent (i.e. invisible) silver image which is suitably amplified by further development in bath 19 (position comprising, for example, a solution of quinone-hydroquinone. The presence of the redox system furnished by bath 19 causes further ionic silver, adhering to copy medium 15b on emergence from bath 18, to deposit as metallic silver on those portions of the medium where :a latent image comprising invisible deposits of metallic silver priorly existed. Bath 19, thus, effects an amplification of the latent image, and renders the latent image visible. Finally, copy medium 15d having a visible silver image therein is transported to bath 20, suitably comprising water for washing, and/or other fixing and stopping agents. In FIG. 2, as for conveying means 16 and 16a, conveying means 21 for transporting copy medium 15a-15d through baths 18, 19, and 20 may comprise a single continuous con veying system, or two or more individually controllable and regulable conveying means.

The dyes employed for treating the photoconductive insulating pigments of the invention are, in general, those heretofore used in the photograhic arts for sensitizing silver halides (cf. The Theory of the Photographic Process by C. E. Kenneth Mees, the Macmillan Publishing Co., New York, Revised Edition, 1954) or materials such as zinc oxide, to render them sensitive to and activatable by light of Wavelengths other than those to which the untreated material would be sensitive. Normally, dye sensitization extends the usual ultraviolet sensitivity of the untreated photoconducting substrate to longer wavelengths such as those in the visible. The dyes include acridine dyes such as Acridine Orange, thiazine dyes such as Methylene Blue, phthaline dyes such as Rose Bengal and Eosin Y, triphenylmethane dyes such as Malachite Green, or Crystal Violet, and cyanine dyes such as kryptocyanine, neocyanine, dicyanine, and pinacyanol.

The dyes may be used in solution to treat the Photoconductive materials prior to their incorporation into a copy medium. The dyed pigments can be simply deposited on a substrate, or can be incorporated into a substrate such as the fibrousweb of paper. Alternatively, the dye can be combined with the photoconductive materials in the copy medium, for example by dispersion of the dye in the same resin commonly used to bind photosensitive pigments to a suitable insulating or conductive backing such as wood, glass, paper, or metal.

The cyanine dyes, including the simple cyanines, carbocyanines, :and higher cyanines, are particularly preferred for use in the present invention since they promote maximum differences in activity between those areas of the copy medium in which the photoconductive material has been desensitized by a first extended exposure to an image pattern of radiation and those portions containing photoconductive material which is first activated by the later uniform exposure.

Another technique for improving discrimination in the print is dark adaption of the copy medium after the first imaging exposure. This is particularly desirable where the imaging radiation tends to activate the photoconductive insulating pigment even in the absence of sensitizing dyes. For example, the exposure of dye-sensitized titanium dioxide to imaging light from a tungsten lamp causes the printability of a copy medium containing the same to behave in a manner suggested by FIG. 1 of the drawings. The insensitivity of exposed portions of the TiO to subsequent radiation is consistent with a destruction of the sensitizing dye where extended exposure to light has taken place, or with some other interference with the capacity of the dye to transfer energy to the pigment. The underlying titanium dioxide pigment, once the dye is incapacitated by the imaging exposure, cannot be activated to a significant extent by a second exposure to a tungsten source, since it is now substantially insensitive to the incident radiation in those lightstruck areas where the sensitizing dye no longer sensitizes.

On the other hand, if ultraviolet light is used for the imaging exposure, to which light the titanium dioxide pigment under consideration is sensitive even in the absence of sensitizing dye, the underlying pigment tends to become activated and to remain activated for some time after exposure, even though dye may be destroyed or otherwise incapacitated by the exposure employed. In the latter case, it is desirable to dark adapt the copy medium after the first exposure in order further to deactivate the medium.

Dar-k adaption may be effected in a literal manner by permitting the copy medium to remain in the dark, for example, for periods of from 1224 hours, at room temperature. With increasing periods of time, the first exposed portions of the medium become less and less apt to react with developing agents after the second uniform exposure to which the medium is next to be subjected. Hence, maximum contrast is obtained between the portions of the medium activated by such a later uniform exposure and those portions exposed and deactivated during the prior imaging exposure.

Alternatively, dar-k adaption may be effected more rapidly by heating of the exposed copy medium at temperatures below the decomposition temperature of the dyes present. Forjexample, the copy medium can be heated gently in the dark in an oven arrangement at about 250 C. for periods up to a minute or more, for example. It may be convenient to subject the exposed medium to hot air from a blower. Temperatures of about 300C. are commonly generated by such blowers, and exposures to such temperatures for as little as seconds will help speed desensitization of the medium.

Finally, the exposed copy medium can be dark adapted by exposure to a corona discharge, for example by passing the spark from a Tesla coil over the surface of the medium. This technique has the disadvantage that dye remaining in unexposed portions of the copy medium may be adversely affected by the corona discharge, perhaps by oxidation.

FIG. 3 shows another embodiment of apparatus according to the present invention in which dye-sensitized copy medium 31 prepared according to the invention is exposed to radiation source 32 through image object 33 and appropriate conventional optical means 34. Medium 31, conveyed by suitable conveying means 35 is next transported to means 36 for dark adapting the exposed medium. Means 35, for example, comprises infrared source 37, shown as an electric resistance heater. With its movement controlled by conveying means 35a, copy medium 31a is dark adapted for an appropriate time period. Next (position 31b) said copy medium is uniformly exposed to radiation source 38, and then developed. Medium 31c, for example, can be directly contracted with bath 39 comprising a developer such as a metal ion in combination with a redox system immediately to produce a visible image on print 310 on contact with the developer. Developed print 31d is next suitably contacted with bath 40 comprising a fixing agent for silver ion, such as a soluble thiosulfate salt. After fixing, p-rint 31e is water washed in bath 41. As for FIG. 2, conveying means 43 transporting the prints through the developing stage may comprise a single conveying system, or two or more independently regulable and controllable conveying means.

Maximum discrimination in the prints produced by the techniques of the invention is obtained when cyanine dyes are employed, and when some form of dark adaption is used to further desensitize those portions of the coply medium struck by activating radiation during the first exposure to an image pattern of such radiation. However, the use of these dyes alone, or of some form of dark adaption alone, will also tend to give better prints.

For the second uniform exposure prior to developing, the copy medium is suitably exposed to a light source which will activate only those portions of the medium where dye is still present and which will leave substantially unaffected those portions of the medium where dye has been destroyed or which have otherwise been rendered insensitive. Conveniently, the medium is exposed to visible light, which will activate the previously unexposed dye sensitized portions, but will not affect those portions of the medium where dye may have been destroyed by the prior imaging exposure.

For both exposures, the time-intensity relationships well known in the photographic arts are applicable, and specific exposure conditions can readily be determined by anyone skilled in the photographic arts.

A better understanding of the present invention and of its many advantages will be had by referring to the following specific examples, given by way of illustration.

Example 1 A mixture of 4 parts by weight of titanium dioxide and 1 part by weight of an emulsion of Rhoplex acrylate resin containing about 50 percent of solids in water was used to coat paper sheets.

A sheet of the coated paper was sensitized by dipping into a solution containing 10 milligrams of neocyanine in ml. of methanol, and then dried.

The sensitized paper was exposed at a distance of about 4 inches to imaging light from a 25 watt tungsten bulb filtered to remove wavelengths less than 460 millimicrons for periods of time between about 3 minutes and 15 minutes.

The exposed sheets were immediately uniformly exposed to the same source of light for short time periods, of the order of 5 seconds.

The exposed prints were then dipped in a saturated solution of silver nitrate in methanol, and then in a solution comprising 1 gm. of phenidone, 8 gm. of citric acid monohydrate, and 100 ml. of methanol. A positive copy of the exposure image was obtained.

Contrast in the print was increased by permitting the copy medium to stand at room temperature in the dark for 24 hours after the imaging exposure and prior to the uniform exposure. Better contrast was also observed if the copy medium was gently heated after the first exposure.

Alternatively, filled paper sheets containing about 20 percent of photoconductive ZnO or TiO pigment were prepared in conventional paper making apparatus by addition of an aqueous slurry of the pigment to the beater.

Finely divided water insoluble photoconductive pigments were also dye sensitized by contacting the pigments with dilute solutions of sensitizing dyes. Excess dye solution was decanted, and the treated pigments were dried. The pigments can suitably be deposited without a binder on a substrate such as glass, or can be incorporated into a plastic or the fibrous web of a paper, or can be dispersed in a binder such as sodium silicate or polyvinyl alcohol and used to coat rigid or flexible electrically insulating or conducting substrates.

Example 2 A number of TiO coated copy sheets like those of Example 1 were treated by contacting them respectively with methanol solution of the dyes indicated below. After drying of the sheets, they were each first exposed for 15 minutes to an image pattern of light from a tungsten lamp as in Example 1, and then were given a 2 minute uniform second exposure. In each case, a positive copy of the image pattern was obtained.

The dyes used were:

(1) Fuchsia-basic (pararosaniline chloride) (2) Orthochrome T (l,1'-diethyl-6,6-dimethyl-2,4-cyanine iodide) (3) Quinaldine Red (4) Diethyl thiocarbocyanine iodide (5) 3,3-diethyl-9methyl-thiocarbocyanine iodide (ll) ltttlplaayanine (l2) Dicyanine Although specific embodiments have been shown and described, it is to be understood that they are illustrative, and are not to be construed as limiting on the scope and spirit of the invention.

What is claimed is:

1. A process for recording an image pattern of activating radiation comprising (1) exposing a uniformly dyesensitized copy medium, said copy medium comprising a photosensitive semiconductor, to an image pattern of radiation which at least partially desensitizes said dye-sensitized medium to activating radiation in those portions thereof which are struck by this desensitizing radiation, and (2) then uniformly exposing the selectively desensitized medium to activating radiation to activate those portions of the medium which were not desensitized by the first imagewise exposure, thereby making these portions capable of causing chemical reactions.

2. A process as in claim 1 comprising the additional step of contacting said copy medium with image-forming materials to produce a permanent, irreversible image in the portions of the copy medium activated by the second uniform exposure to activating radiation.

3. A process as in claim 2 wherein the image-forming materials comprise a liquid redox developer system.

4. A process as in claim 1 wherein the photosensitive semiconductor compound is at least one compound of a metal with a non-metal of Group VI-A.

5. A process as in claim 4 comprising the additional step of contacting at least the activated portions of the copy medium with a developer system comprising silver ions.

diamino-S-phenyl phenazinium treg-te'g filergethod as in claim 1 mm is desensitized b P mgn of visible light.

e met is a yanis d e. n Clam 6 Wherem cyanme y The method as in claim 1 wherein said dye-treated medium 15 desensitized by exposure to an image pattern of light destructive of said dye.

9. The method as in claim 1 wherein those portions of the medium struck by radiation during said first exposure to said image pattern of radiation are deactivated prior to said uniform exposure to activating radiation.

10. The method as in claim 9 wherein those portions of the medium struck by radiation during said first exposure are deactivated by storing the medium after said first exposure with the exclusion of activating radiation.

11. The method as in claim 9 wherein those portions of the medium struck by radiation during said first exposure are deactivated by heating the medium at a temperature below the decomposition temperature of the sensitizing dye.

12. The method as in claim 1 wherein said medium comprises finely divided particles of a solid photoconductive material insoluble in said liquid redox system.

13. The method as in claim 12 wherein said photoconductive material is a member selected from the group consisting of semiconducting oxides and sulfides.

14. The method as in claim 1 wherein said photoconductive material is titanium dioxide.

wherein a cyanine dyey extended exposure to References Cited UNITED STATES PATENTS 5/1967 Hanson et al. 96-49 7/1967 Oliver 88-24

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