Method Of Recording And Reproducing Information

Abstract

A heat-sensitive recording material of the type covered by U.S. Pat. No. 3,476,937 and including a recording layer formed of a dispersion of solid hydrophobic thermoplastic polymer particles in a water-soluble hydrophilic binder is modified to include a diffusion-resistant colorant material and a visible finely divided material absorbing radiation and converting the same into heat, such material being either chemically bleachable or soluble in an aqueous liquid. The resultant heat-sensitive material is exposed to radiation pattern and then contacted with at least one liquid to bleach or dissolve the radiation absorbing and converting material and to remove by washing the water-soluble portions of the recording layer, the portions corresponding to the radiation pattern having been rendered water-insoluble by the exposure step but remain water-permeable to permit the radiation absorbing and converting material to be bleached or dissolved by penetration of the liquid.

Description

The present invention relates to methods for recording and reproducing information and to materials for use in said methods. The invention more particularly but not exclusively relates to a method for recording imagewise or recordwise modulated light energy, which is transformed into heat in a heat-sensitive recording material.

It has been proposed to record information by informationwise heating a recording layer composed so that under the action of such heating it undergoes a change in water-permeability. In consequence of the informationwise heating the information is therefore recorded in terms of a difference in the water-permeabilities of different areas of the recording layer.

Certain recording materials for use in that way, and recording processes using such materials, are described and claimed, inter alia, in Belgian Pat. specification No. 656,713 and in the published Dutch Pat. application No. 6,606,719 corresponding to U.S. Pat. No. 3,476,937. Such recording materials have recording layers comprising a network of hydrophobic thermoplastic polymer particles, solid, at room temperature, or comprising hydrophobic thermoplastic polymer particles dispersed in a continuous phase hydrophilic binder medium.

Other recording materials in which information can be recorded in terms of a differential water-permeability by informationwise heating a recording layer are described and claimed in Belgian Pat. specification Nos. 682,767 and 683,054. In such recording materials the recording layer is composed wholly or mainly of gelatin which becomes more water-soluble and consequently more water-permeable, when sufficiently heated.

An interesting development of this principle of recording information is the use of a recording material which contains one or more distributed substances capable of absorbing electromagnetic radiation, e.g., infrared radiation and/or visible light, and in which the recording layer becomes heated by virtue of radiation absorption by such substance(s) when the recording material is irradiated. The aforesaid earlier patent specifications include descriptions of recording materials useful in that way, and further such materials are described in Belgian Pat. specification No. 681,138. When a radiation-absorbing substance is distributed in the recording layer, the informationwise heating of the recording layer which brings about the water-permeability or water-solubility differentiation can be achieved by informationwise exposing the recording material to sufficient radiation of the appropriate type.

The presence of the radiation-absorbing substance(s) in the aforesaid recording materials makes the record visible, provided the recording material is treated, following the informationwise heating, to remove the recording layer selectively in dependence on the water-permeability pattern. It will be apparent however that the result of forming a visible record in that way is that the color and optical density of the record is determined by the substance(s) used for absorbing the electromagnetic radiation. It is also possible, following the informationwise heating of the layer to allow a colored substance to penetrate differentially into the layer according to the water-permeability pattern, but the still present radiation absorbing substance(s) impair the color and contrast of the developed record.

The present invention provides an improved process, according to which radiation-absorbing substance(s) used for heat generation in the recording layer is or are entirely or substantially entirely removed from the recording layer after a record in terms of a water-permeability differentiation has been formed.

The present invention includes any information recording process wherein a recording layer which is composed so that it undergoes a change of water-permeability under the action of heat and which contains a substance or substances which can absorb certain electromagnetic radiation, is informationwise heated by irradiation of such layer with electromagnetic radiation which is absorbed by said substance(s) so that said information is recorded in terms of a difference in the water-permeabilities of different areas of such layer, and the said radiation-absorbing substance(s) is or are then bleached in or leached out of said layer without destroying the water-permeability differentiation.

The invention also includes, by way of modification, any information-recording process as above defined but wherein following the informationwise heating which establishes the record in terms of a water-permeability differentiation, selected parts of the recording layer are removed depending on their water-permeability, and the radiation-absorbing substance(s) in the remaining portions of the layer is or are bleached in or leached out from such remaining portions.

The composition of the recording layer may be such that after the bleaching or leaching operation the recording layer is substantially colorless. The latent record can be subsequently developed by allowing a colored developer, e.g., a dye solution, to penetrate into the layer or the remaining portions thereof. Obviously a wide choice of developer is available since the only function of the developer is to provide the required color in the developed record.

According to preferred embodiments however the recording layer initially contains not only the necessary radiation-absorbing substance(s) but also a colored ingredient or ingredients providing the final record color or colors, the nature of such ingredient(s) being such that the radiation-absorbing substance(s) can be bleached in or leached out of the recording layer without affecting the said colored ingredient(s).

The present invention also includes any recording material having a recording layer which is composed so that it undergoes a change of water-permeability under the action of heat and which contains (a) at least one distributed substance capable of absorbing certain electromagnetic radiation and thereby yielding heat to bring about a said change in water-permeability, and (b) at least one coloring ingredient or color-former of such nature that it can remain in the layer substantially unaffected if the latter is treated with an appropriately selected liquid composition which bleaches or leaches said radiation-absorbing substance in or from the layer. The expression "color former" includes a mixture of components capable of entering into a color-forming reaction in the layer when heated or subjected to other conditions.

Heat-sensitive recording materials useful in carrying out the present invention include materials containing a hydrophilic colloid and which in itself or by the action of substances dispersed or dissolved therein become less water-permeable, as described e.g., in the Belgian Pat. specification Nos. 656,713, 676,329, 674,218, 681,138, 683,053 and 705,529 and in the published Dutch Pat. application No. 6,705,963.

Other heat-sensitive recording materials useful in carrying out the present invention include materials containing a hydrophilic colloid, more particularly gelatin and preferably gelatin of the type described in the United Kingdom Pat. specification No. 985,933, which by the action of heat becomes more water-soluble and consequently more water-permeable, as described in the Belgian Pat. specification No. 682,767.

According to a preferred embodiment a recording material is used comprising at least one heat-sensitive layer undergoing a decrease in permeability to water when heated, and incorporating particles composed wholly or mainly of a hydrophobic thermoplastic polymer. Said layer contains preferably a major part by volume of a dispersion of said particles in a hydrophilic binder in a weight ratio greater than 1:1 as well as an amount of a colored substance which absorbs infrared radiation and/or visible light and converts a substantial part thereof into heat, said substance being capable of being bleached or leached out from the portions of the recording layer having a reduced permeability to an aqueous liquid penetrating the imagewise heated recording layer all over its surface.

Suitable hydrophilic binders and thermoplastic polymers for preparing such a recording material are described in the Belgian Pat. specification Nos. 656,713 and 681,138.

Preferably, the heat-sensitive layer used in the present invention, at room temperature incorporates solid particles of hydrophobic thermoplastic polymeric material, which has been dispersed in an aqueous medium by means of a dispersing agent. The sensitivity of the recording layers depends on the concentration of the said thermoplastic hydrophobic polymer particles in the hydrophilic binder and preferred compositions contain these particles in a weight ratio of at least 3:2. The said recording layer for reason of sensitivity preferably consists for at least 50 percent by volume of the dispersion of said hydrophobic polymer particles in the hydrophilic binder. As a matter of course the sensitivity of the recording layer also depends on the concentration of the light-absorbing heat-generating substance(s) and its (their) absorption spectrum. Preference is given to dark substances, which absorb electromagnetic radiation in a visible part of the electromagnetic spectrum as large as possible, and preferably in the infrared region (wavelength beyond 700 nm.). If the recording material is to be used in a reflex exposure, the concentration of heat-generating substances should be such that the optical density to applying light preferably is comprised between 0.2 and 0.8. Recording materials applied in direct exposure preferably possess an optical density of at least 1. The sensitivity of the preferred heat-sensitive layers is such that an exposure energy of only 0.3 watt.sec./sq.cm. is required for producing a practical useful differentiation in water-permeability.

The light-absorbing substances wherein by exposure to visible and/or infrared light heat is generated are preferably bleachable substances e.g., bleachable metals or dyes or dyes of the water-soluble type, e.g., dyestuff salts, or are easily soluble in aqueous compositions containing a certain amount of a water-miscible organic solvent, e.g., ethanol, an acid which improves the removal of basic dyestuffs, or a base which can improve the removal of acid dyes.

Light-absorbing heat-generating substances which are suited to be used according to the present invention are preferably colored ionic substances with a high rate of diffusion in gelatin coatings swollen in water. The measurement of dye diffusion rates in swollen gelatin coatings has been described by R. B. Pontius and I. A. Wenrich in Phot. Sci. and Eng., Vol. 2, No. 3, Oct. 1958, p. 131-135. Preferably anionic or cationic nondiffusion resistant organic dyes containing water-solubilizing salt or acid groups are used, e.g., acid or neutralized acid dyes used in the hydrotype printing process for the production of imbibition prints. Examples of such dyes can be found in the U.S. Pat. specification No. 2,892,822. It is to be understood that mixtures of such dyes can be used too.

In the recording, preference is given to a short-duration high-intensity imagewise exposure. An advantage of this type of exposure is that it yields a reproduction with great image sharpness, since the lateral diffusion of heat is limited here to a minimum value. Thus, it i preferred in carrying out the exposure step to apply an imagewise or informationwise exposure lasting no longer than 10.sup.-.sup.1 sec. The exposure must be sufficiently intense in order to effect the desired decrease in water-permeability in the exposed areas.

Suitable radiation sources for producing copying light of high intensity in a rather short period of time are so-called flash-lamps. Good results are obtained with xenon gas discharge lamps with an exposure time of 10.sup.-.sup.5 to 10.sup.-.sup.2. These flash lamps emit a larger part of visible light than of infrared radiation. Details on a copying device containing such a discharge lamp can be found in the Belgian Patent Specification 664,868 and in the published Dutch Pat. application No. 6,808,648.

If the emitted energy is focused onto a relatively small heat-sensitive area, e.g., of the size of one picture of a motion picture film a gas discharge lamp with a relatively low energy output can be used. E.g., for copying on an area of 19 mm. .times. 35 mm. a flash lamp with an energy output of 40 watt.sec. will suffice.

Self-evidently, the heat-sensitive surface layer before or during the imagewise exposure to heat-generating radiation can be subjected to an overall heating to a certain temperature below the temperature at which a substantial decrease in permeability to water takes place. In this way, less imagewise supplied heat-generating electromagnetic radiation is required to produce the desired reduction in water-permeability.

The technique of the integral removal by bleaching or leaching out of colored heat-generating substances from the heat-exposed recording layer opens up the possibility to produce colored or black prints without having to selectively remove the nonheated portions of the recording layer.

According to a particular embodiment the light absorbing heat generating substances are integrally removed after the imagewise light exposure and relying on the difference in water-permeability between the exposed and nonexposed portions of the recording layer a positive color print i obtained by differential penetration of a dye solution. The density of the color print is directly proportional to the degree of water-permeability of the nonheated portions of the recording layer. The disturbing effect of a dark image background which would have been present if the heat-generating substances had not been removed is completely excluded here.

In this connection reference is made to the published Dutch Pat. application No. 6,806,658, wherein the production of positive images by imagewise water-permeability differentiation is described. According to an embodiment of the invention described therein the heat-sensitive layer containing light absorbing pigments has to be removed integrally from an image containing layer. The present method is especially interesting in such a case wherein it is interesting to maintain the heat-sensitive layer on top of the image containing layer avoiding damaging of the underlying layer.

According to an important embodiment pigments that are fast to light, e.g., yellow, cyan or magenta diffusion-resistant pigment dyes, are incorporated into the heat-sensitive layer together with the light-absorbing and heat-generating substances which can be washed away. After imagewise exposure the heat-generating substances are integrally leached out, e.g., by means of tap water, and the heat-sensitive layer is washed away in accordance with the nonexposed areas, so that a spectrally pure pigment dye image of high fastness to light is left. By applying the latter embodiment of the present invention it is possible to obtain yellow dye images by heat-generating exposure e.g., infrared exposure and subsequent selective removal of the recording layer by washing away. In order to understand the advantage associated with said technique, it has to be noted that by means of yellow dyes as the sole light-absorbing colored component in the heat-sensitive layer this was practically impossible so far, as yellow dyes absorb only a minor part of the visible light and none of infrared light so that by exposure little or no heat is generated in said dyes.

The use of removable heat-generating substances thus makes it possible according to the present invention to record an image of any color in a photothermographic way of combining said removable heat-generating dyes with one or more colored substances which are fast to diffusion, e.g., pigments conferring the desired color to the image.

By means of this technique it is possible to produce color images for color proofing. Color-proofing materials serve to form a proof for submission to the printer to give an idea of a multicolor reproduction as will be produced by imagewise overprinting with four inks (yellow, magenta, cyan and black) printed at the strength normally used in practice. The proof obtained wit a color proofing material enables to determine the necessary corrections of the intermediate negatives used in preparing the etching resists and to adapt the exposure conditions. In an already existing method for preparing such a colorproof use is made of a multicolor silver halide photographic material which is exposed through the screened black-and-white selection negatives corresponding respectively with the yellow, magenta, cyan and black separation images of a multicolor original. The difficulty associated with said method resides in finding the right color couplers for forming dyes having an absorption spectrum practically identical t that of the printing dyes or pigments used. The method of the present invention provides a solution of that problem in that previously prepared dyestuffs or pigments with the right absorption spectrum can be applied in nonmigratory state.

According to one technique a multicolor proof is obtained by successively coating, exposing and developing four heat-sensitive hydrophilic water-permeability differentiable layers which contain a black, a cyan, a magenta and a yellow pigment dye respectively through the corresponding black-and-white selection negatives of the multicolor original to be reproduced by printing. The said heat-sensitive layers are separately coated on one and the same support. Following its coating, each of the four heat-sensitive layers is exposed to light through the proper black-and-white selection negative, and the development carried out by washing away the nonexposed portions of the exposed recording layer removing at the same time the nondiffusion resistant light-absorbing heat-generating dyes in the exposed portions.

According to another technique the pigment coatings are applied to four separate transparent supports. After exposure and processing the images were brought in register and examined by means of transmitted light, e.g., in a diascope, or overhead projector.

According to said techniques the colored heat-sensitive layers contain in addition to dark heat-generating bleachable or removable substances, a dye, a pigment or a mixture of both, which resists diffusion and which dye or pigment has an absorption spectrum as conform as possible to that of the color of the printing dye for each printing step (cyan, magenta, yellow).

As is known the magenta ink pigments have unwanted absorptions in the blue region of the spectrum, and to a much less extent in the red one, the magenta ink prints as if it were a true magenta ink containing some yellow and a little cyan. Normally sufficient correction is obtained by reducing the amount of yellow in proportion t the amount of magenta printed.

The cyan ink pigments have unwanted absorptions in the blue and green regions of the spectrum; the cyan ink prints as if it were a true cyan ink containing magenta and yellow.

The yellow ink pigments normally approaches the ideal way of absorbing blue light and no correction is necessary unless it is a special "warm-ink" (orange-yellow) in which case it may be desirable to reduce the strength of the magenta printed in the yellow areas.

The black toner being preferably present in the first exposed layer can be a black or grey pigment, e.g., carbon black or dark metal particles, their sulphides and oxides, e.g., nickel, lead, silver, bismuth, lead(IV) oxide, copper(II) oxide and copper(II) sulphide. The black-toned material preferably contains carbon black in the heat-sensitive layer, which preferably is applied to a subbing or interlayer of the type described in the Belgian Pat. specification No. 692,422.

Nonmigratory pigments suitable for use in the "color proofing" system of the invention are known under the trade name "Pigmosol" dyes. "Pigmosol" is a registered trademark of Badische Anilin- & Soda-Fabrik A.G., Ludwigshafen/Rh., W.-Germany, for organic pigment dyes which are mixed with a dispersing agent for aqueous medium. These pigment dyes are very resistant to light, heat, acids and bases. They are insoluble in hydrophilic colloids, e.g., gelatin and poly-N-vinylpyrrolidone which colloids are preferably used in heat-sensitive layers intended for use in the washing away technique.

The following examples illustrate the present invention.

EXAMPLE 1

A polyethylene terephthalate support of 0.1 mm. thickness was coated with the following composition pro rata of 17 g. per sq.m.:

20% aqueous dispersion of copoly (vinylidene-chloride/N-butylmaleimide/ itaconic acid) (88/10/2) with an average particle size of 0.1.mu. 40 g.

40% aqueous dispersion of polyethylene having a particle size of less than 0.1.mu. and an average molecular weight comprises between 15,000 and 30,000 40 g.

30% aqueous dispersion of silica with an average particle size of 0.025.mu. 40 ml. water 780 ml.

ethanol 100 ml.

The subbing layer thus obtained was dried at 30.degree. C. A heat-sensitive layer, for use in a washing-away-development by rubbing with a cotton pad soaked with water at 20.degree. C., was coated on this subbing layer pro rata of 15 g. per sq.m. from the following composition:

10% aqueous solution of poly-N- vinyl pyrrolidone 170 ml. 40% aqueous dispersion of polyethylene as described above 195 g.

water 120 ml. aqueous carbon dispersion containing per 100 g. 16 g. of carbon (average particle size 0.1.mu. ) and 2 g. of poly-N-vinyl pyrro- lidone 450 ml.

3% aqueous dispersion of the sodium salt of tetradecyl sulphate 65 ml.

The heat-sensitive layer was dried at 30.degree. C. While in contact with a black-and-white selection negative corresponding with those parts of an original that had to be printed in black, the heat-sensitive material was exposed for 1/2000 sec. through said selection negative by means of a xenon gas discharge lamp of 1,000 watt.sec. Subsequently, the unexposed portions of the recording layer were washed away with water so that a positive image was obtained in accordance with those parts of the original that have to be printed in black.

The layer comprising the black image was then coated with a second thermosensitive layer comprising a cyan pigment for the formation of the cyan image areas. The black image layer was therefor mounted horizontally in a centrifuge rotating at 100 revolutions per min. at a temperature of 43.degree. C. The following composition was poured onto the black image layer to form a coating which, on drying comprises 30 g. per sq.m.

40% aqueous dispersion of polyethylene as described above 100 g. 20% aqueous dispersion of poly-N-vinyl pyrrolidone 20 ml.

Heliogen blau B Colanyl Teig (a cyan pigment insoluble in water, sold by Badische Anilin- & Soda-Fabrik A.G., Ludwigshafen/Rh., W-Germany) 22 g.

10% aqueous solution of a compound corresponding to the following struc- tural formula: ##SPC1## 7% aqueous solution of a compound corresponding to the following structural formula: ##SPC2## 3% aqueous solution of sodium tetradecylsulphate 20 ml.

After having been dried the material obtained was exposed, while in register contact with a black-and-white selection negative corresponding with those parts of the original that had to be printed in cyan, the exposure being effected through the said selection negative by means of a xenon gas discharge lamp of 1,000 watt.sec. for 1/2000 sec.

Subsequently the unexposed portions of the recording layer were washed away with water, the water-soluble dyes in the exposed areas being rinsed away immediately. The black image already present remained intact. The image obtained consisted of black and cyan parts. The material was then coated again with a thermosensitive layer comprising a yellow pigment for the formation of a yellow image. The composition was analogous to that of the preceding thermosensitive layer, but instead of 22 g. of Heliogen Blau B Colanyl Teig use was made of 15 g. of Permanent Gelb HR Colanyl Teig (a yellow pigment insoluble in water, sold by Farbwerke Hochst A.G. Frankfurt(M) - Hochst, W.-Germany).

The resulting material was then exposed through a black-and-white negative corresponding with those parts of the original that had to be printed in yellow.

After having been washed the material was coated again with a composition analogous to that of the preceding layer, with the exception, however, that 20 g. of Permanentcarmin FBB Colanyl Teig (a magenta pigment insoluble in water, sold by Farbwerke Hochst A.G. Frankfurt(M) - Hochst, W-Germany) was used therein instead of the 22 g. of Heliogen Blau B Colanyl Teig.

After having been dried the resulting material was exposed now through a black-and-white selection negative corresponding with those parts of the original that had to be printed in magenta.

Thus, a four-color image suitable for color proofing was obtained. By means of this four-color image the quality of the selection negatives and the future print was judged of easily.

EXAMPLE 2

A polyethylene terephthalate support having a thickness of 0.075 mm. was coated with a subbing layer as described in Example 1. The subbing layer itself was coated pro rata of 18 g./sq.m. with a black heat-sensitive layer comprising:

an aqueous dispersion of polyethylene comprising per 100 g. 18 g. of poly- ethylene (the polyethylene dispersion was prepared by dispersing polyethylene in water at 160.degree. C.) with 2.5 g. of nonyl- phenyl poly(ethyleneoxyde)n (the average value of n= 9-10), 2.5 g. of nonylphenyl- poly(ethyleneoxyde).sub.m ethanol (the average value of m= 7) and 0.4 g. of potassium hydroxide 175 ml.

water 465 ml. an aqueous carbon dispersion comprising per 100 g. 16 g. of carbon particles having a size of 0.1.mu. and 2 g. of poly- N-vinyl pyrrolidone 400 ml.

3% aqueous solution of sodium tetra- decyl sulphate 50 ml. 10% aqueous solution of animal glue 120 ml.

After having been dried the resulting material was exposed as described in Example 1, while in contact with a black-and-white selection negative corresponding with those parts of the original that had to be printed in black. The further treatments were analogous to those described in Example 1, with the proviso, however, that the following three differently colored heat-sensitive layers were coated successively pro rata of 40 g./sq.m.:

1. A thermosensitive layer comprising a cyan pigment:

aqueous dispersion of polyethylene comprising 18% of polyethylene prepared as described above 200 ml.

water 300 ml. 20% aqueous dispersion of poly-N-vinyl pyrrolidone 20 ml. Heliogen blau B Colanyl Teig (see Example 1) 50 g.

5% aqueous solution of a diffusible dye corresponding to the structural formula: ##SPC3## 7% aqueous solution of a diffusible dye corresponding to the structural formula: ##SPC4## ethanol 75 ml.

2. A thermosensitive layer comprising a yellow pigment, the composition of the layer being analogous to that of the preceding one, wit the proviso, however, that the 50 g. of Heliogen blau B Colanyl Teig were replaced by 100 g. of Paliogengelb RT Colanyl Teig (a pigment paste) sold by Badische Anilin- & Soda-Fabrik A.G. Ludwigshafen/Rh., W-Germany).

3. A thermosensitive layer comprising a magenta pigment, said layer having a composition analogous to that of the preceding one, but wherein the 50 g. of Heliogen Blau B Colanyl Teig were replaced by 100 g. of Helioechtrot ITR Feinteig (a pigment dispersion sold by Farbenfabriken Bayer A.G., Leverkusen, W.-Germany).

EXAMPLE 3

A heat-sensitive material consisting of a polyethylene terephthalate support, a subbing layer, and a black heat-sensitive layer as described in Example 1, was exposed through a selection negative while in contact therewith, said selection negative corresponding with those parts of the original that had to be printed in black, and the exposure being effected with the aid of a xenon gas discharge lamp of 1,000 watt.sec. in 2/1000 sec. After washing away of the unexposed areas with water, the material mounted horizontally in a centrifuge rotating at 100 revolutions per min. was coated therein at a temperature of 45.degree. C. pro rata of 40 g./sq.m. with a composition comprising the following ingredients:

40% aqueous dispersion of polyethylene (see Example 1) 100 ml. water 200 ml.

Heliogen blau B Colanyl Teig (see Example 1) 25 g. 20% aqueous dispersion of poly-N- vinyl pyrrolidone 20 ml.

10% aqueous dispersion of black silver particles 400 ml. 3% aqueous solution of sodium tetradecyl sulphate 20 ml.

After having been dried the material was exposed through a black-and-white selection negative corresponding with those parts of an original that had to be printed in cyan, the selection negative being brought in register contact with said material. After washing away of the unexposed portions of the recording layer, the material was coated again with a composition analogous to that of the preceding layer, with the proviso, however, that the 25 g. of Heliogen Blau B Colanyl Teig were replaced by 15 g. of Permanent Gelb HR Colanyl Teig sold by Hochst.

The resulting material was exposed through a black-and-white selection negative corresponding with those parts of the original that had to be printed in yellow. After washing away of the unexposed areas, the material was again coated with a solution analogous to the first described, with the exception, however, that the 25 g. of Heliogen Blau B Colanyl Teig were replaced by 20 g. of Permanentcarmin FBB Colanyl Teig (see Example 1).

After exposure through a black-and-white selection negative corresponding with those parts of the original that had to be printed in magenta and after washing away the nonexposed portions the material was immersed for 60 sec. in a common bleaching bath (Farmer's reducer), whereby the black residual silver in the three-color layer material was bleached away. The material was then rinsed and dried. A three-color transparency was obtained finally. The said transparency was used in a projection technique known as "overhead projection."

Claims

We claim:

1. A method of reproducing information comprising exposing to an electromagnetic radiation pattern according to said information a heat-sensitive recording material including a water-permeable recording layer formed by a dispersion of hydrophobic thermoplastic polymer particles in a continuous phase of a water-soluble hydrophilic binder in a ratio by weight of at least 1:1, said hydrophilic binder continuous phase also having distributed therethrough a water-insoluble colorant material resistant to diffusion from said continuous phase and a water-soluble visible finely divided material absorbing radiation and converting the same into heat, said recording layer after said exposure being water-insoluble but permeable to aqueous liquids, and after said exposure contacting said exposed recording layer with at least one aqueous liquid to dissolve said water-soluble radiation absorbing and converting material and to remove by washing the water-soluble portions of said layer, whereby the remaining portions form a colored relief image corresponding to said radiation pattern.

2. A method of reproducing information according to claim 1, wherein the dispersion consisting of hydrophobic polymer particles in the hydrophilic binder medium i present in the recording layer for at least 50 percent by volume.

3. A method of reproducing information according to claim 1, wherein the hydrophobic polymer particles are latex particles solid at room temperature and are present in said continuous hydrophilic binder medium in an amount by weight of at least 3:2.

4. A method of reproducing information according to claim 1, wherein said water-soluble colorant material is a diffusible anionic or cationic organic dye containing water-solubilizing salt or acid groups.

5. A method of reproducing information according to claim 1, wherein the exposure is a short-duration high-intensity imagewise exposure.

6. A method of reproducing information according to claim 5, wherein the exposure lasts no longer than 10.sup.-.sup.1 sec.

7. A method of producing information as a multicolor print according to claim 1, wherein said recording material includes four of said heat-sensitive recording layers applied thereon separately, said layers respectively contain a black, a cyan, a magenta, a yellow pigment, each layer containing a water-soluble dark colored substance which absorbs at least a part of the copying light and transforms it into heat and each layer is separately exposed in turn to light through a proper black-and-white screened selection negative of the color original to be reproduced and each layer following its exposure and before application to the next layer is treated with an aqueous liquid to remove the nonexposed portions and dissolve out the dark colored substance.

8. The process of claim 1 wherein the same aqueous liquid serves to dissolve said water-soluble radiation absorbing and converting material and to remove said water-soluble portions of said layer.

9. The process of claim 1 wherein the water-soluble portions of said exposed recording layer are first washed away with water and said water-soluble radiation absorbing and converting material in the remaining water-insoluble portions of said layer is then dissolved by contact with an aqueous solution.

10. The process of claim 1 wherein said colorant material is a diffusion-resistant colored or black pigment or dye.

11. A method of reproducing information comprising exposing to an electromagnetic radiation pattern according to said information a heat-sensitive recording material including a water-permeable recording layer formed by a dispersion of hydrophobic thermoplastic polymer particles in a continuous phase of a water-soluble hydrophilic binder in a ratio by weight of at least 1:1, said hydrophilic binder continuous phase also having distributed therethrough a colorant material resistant to diffusion from said continuous phase and a finely divided particles of visible silver metal absorbing said radiation and converting the same into heat, said recording layer after said exposure being water-insoluble but permeable to aqueous liquids, and after said exposure contacting said exposed recording layer with an bleaching solution for said silver converting the same to a water-soluble form and with a liquid to remove by washing the water-soluble portions of said layer, whereby the remaining portions form a colored relief image corresponding to said radiation pattern.