US3162763A - Thermographic reproduction paper, method of making and method of using - Google Patents

Description

Dec. 22, 19 4 G c. HUETT ETAL THERMOGRAPHIIEC REPRODUCTION PAPER, METHOD OF MAKING AND METHOD OF USING Filed April 5, 1962 HEA r SENSITIVE 00A mva co/vrm/w/va (/1 4010, AND

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Y GEORG c. HUETT HARTWELL L. BRIGGS CORN ELIUS B. AWYER BY MW ATT'YS United States Patent Ofifice 3,152,763 Patented Dec. 22, 1964 3,162,763 THERMOGRAPHIC REPRODUCTION PAPER, WTHOD (IF MAKING AND METHOD OF USING George C. Huett, Hartwell L. Briggs, and Cornelius B. Lawyer, Chicago, Ill., assignors to Eugene Dietzgen Co., Chicago, Ill., a corporation of Delaware Filed Apr. 5, 1962, Ser. No. 185,347 7 Claims. (Cl. 250-65) The subject invention relates to the production of thermographic paper. More particularly, the present invention is directed to improved copying materials which are capable of producing a facsimile copy by means of radiant energy.

In the past several years, various types of copy paper have been developed which produce a facsimile copy when exposed to radiant energy such as infrared light beneath graphic subject matter set forth on an original. A typical thermographic process is described in the patent to Miller, US. 2,740,896. As is disclosed in this patent, carbon inks and certain other marking means absorb radiant energy from infrared bulbs creating heat. This energy is transferred to a sensitized sheet of copy paper in contact with the original causing the formation of duplicate characters.

A wide variety of materials have been used as color producing bodies in coating the copy paper. In heat developable diazotype reproduction systems, for example, the copy paper is coated with a diazo compound, a coupler, and a compound which produces an alkaline reaction when heated. In other systems such materials as nickel acetate, silver nitrate, sodium behenate, ferric stearate, etc., have been used as components of the color producing coating.

It has been found that compositions of the above type often have disadvantages, especially where the copy paper is to be used on a commercial basis. Such materials, for example, often tend to be unstable both prior to development and subsequent to the formation of the facsimile, which facsimiles cannot be used as intermediates for producing other copies. Additionally, many of the known coating compositions are relatively expensive and are difiicult to handle on a commercial scale.

A novel thermographic method is described in copending application Serial No. 181,091, which was filed on March 20, 1962. In this application, a process is disclosed in which either the cellulose in paper or carbohydrates coated on a suitable base are treated in such a manner that a color image is produced by means of radiant energy transferred from the characters of the original to a copy sheet. If the cellulose of the paper is to be transformed into the color forming body, it is only necessary to coat the sheet with an aqueous solution containing particular amounts of particular acids preferably along with certain stabilizing agents. In the second embodiment of the invention, paper or another base is coated with a solution of a carbohydrate such as lactose, glucose, mannose, etc., along with particular amounts of particular acids, preferably again with certain stabilizing agents.

It is an object of the present invention to provide an improvement in the above described thermographic process.

Another object of the invention is to provide thermographic reproduction paper which can produce images of originals having black characters as well as characters of certain other colors.

Still another object of the invention is to provide copy paper which will produce accurate and clear facsimiles.

Still another object is to provide copy paper which can produce facsimiles of originals which are printed on both sides.

Another object is to provide copy material which can be used to produce read out copies or intermediates regardless of whether the copy material is coated on one or both sides.

Still another object is to provide copy paper which can be used to produce facsimiles having well defined characters and without causing the blurring of surrounding background areas.

Other objects will become apparent to those skilled in the art from the following detailed description of the invention.

In general, the present invention comprises the discovery that an improved thermographic process is obtained by coating a suitable base with a particular composition containing an organic acid and an organic aromatic polyhydroxy or polyamine compound. In embodiments two and three of the invention, an aldehyde, a ketone, or an aldehyde-forming compound is included in the composition. Under the infiuence of heat and a catalyst a reaction takes place between the components of the composition forming color bodies which duplicate the characters of an original. The aldehyde (1) can be derived from the cellulose of a paper base, (2) can be derived from a carbohydrate such as lactose, glucose, mannose, etc., or (3) an aliphatic or aromatic aldehyde can be added to the composition. Compounds which convert to aldehydes under the reaction conditions can also be used in the process as can ketones. In all instances, it is advantageous to add certain stabilizing agents to the treating solutions.

The organic polyhydroxy and polyamine compounds that are used in the subject invention include compounds such as hydroquinone, resorcinol, catechol, phloroglucinol, diresorcinol, pyrogallol, hydroanthraquinone, naphthols, and polyamines such as ortho-, meta-, and para-phenylene diamine, and benzidine. The polyhydroxy compounds are capable of being oxidized to compounds having a quinonic type chemical structure.

In the first embodiment of the invention, a paper base itself is treated so as to produce the aldehyde reaction component of the system. In the process a coating composition consisting of a suitable aromatic polyhydroxy or polyamine compound along with an acid such as metabenzene-disulfonic acid and a stabilizing agent is applied to the paper. When the paper is heated by the transfer of energy from the characters of the original to the copy sheet, the cellulose in the paper appears to break down forming a reducing type carbohydrate. The carbohydrate gives up water to form a cyclic aldehyde compound such as hydroxymethyl furfural. Under the conditions prevailing during the heating step, this cyclic aldehyde polymerizes and reacts with the aromatic polyhydroxy or polyamine and the acid to form a colored character. The color of the character depends upon the particular hydroxy or amine compound that is used in the formulation.

In the second embodiment of the invention, the carbohydrate compound in the coating solution takes the place of the cellulose in the paper. The combined action of the acid and the heat converts the carbohydrate into a cyclic aldehyde such as hydroxymethyl furfural. This material then polymerizes and reacts with the aromatic polyhydroxy or polyamine compound and the acid to form the colored characters.

In the third embodiment, the aliphatic or aromatic aldehyde, aldehyde-forming component, or ketone reacts with the aromatic polyhydroxy or polyamine compound and the acid to form the colored characters.

The invention is illustrated in the attached schematic drawing in which:

FIGURE 1 is an enlarged fragmentary cross-section .amine compound, and preferably a stabilizing agent.

of a sheet of reproduction paper embodying the invention and shown in print making relation to a cross-section of the original to be copied; and

FIGURE 2 is an enlarged fragmentary cross-section of a sheet of reproduction material which illustrates a modified process which may be practiced in carrying out thesubject invention.

The reproduction or copy material 1 illustrated in the drawing is composed of a sensitive layer 2 on a base 3. In the first embodiment of the invention, the sensitive layer 2 consists of paper which has been treated with a particular aqueous acid solution and an organic polyhydroxy or polyamine compounnd, preferably along with a stabilizing agent such as urea. In the second embodiment of the invention, thesensitive layer 2 contains a carbohydrate such as mannose, glucose. etc., a particular acid, an organic polyhydroxy or polyamine compound, and preferably a stabilizing agent. In the third embodiment, the sensitive layer 2 contains an organic, aliphatic, or aromatic aldehyde, or aldehyde-forming compound, or ketone, a particular acid, an organic polyhydroxy or poly- In the second or third embodiment of the invention, base 3 can either be paper or another material such as clear plastic, glass cloth, etc. The base, of course, should be capable of transmitting radiant energy.

FIG. 1 illustrates a front printing process which constitutes a preferred embodiment of the invention. In this process, the sheet of reproduction material 1 containing sensitized layer 2 on base 3 is superimposed on master or original 4 forming an exposure sandwich S. The master consists of a sheet or base layer 5 of paper or graphically markable sheet material containing a design, drawing, w'ritten or typed character 6 to be copied. As is indicated in the figure, character 6 can be on both sides of the sheet in the front printing system. R-adiations Re such as visible light in the orange and red spectral zones as well as invisible infrared radiation is produced by radiation source 7. The radiations Re pass through the copy material 1 and strike the face surface 8 of original 4. Radiation striking character 6 of master 4 are converted to heat which is conducted as indicated at H to the sensitive layer 2 of the reproduction material. An image 6" is produced which duplicates original character 6. Radiations that are not absorbed either are reflected as shown at 9 or are transmitted through the materials. Where the original is printed on both sides, the unabsorbed radiations are reflected by adjusting radiations Re. The radiations are focused on the surface of the copy paper in an elongated zone normal to the face of the sandwich, while the sandwich moves with respect to said zone in the direction of the arrow. If it is desired, the base 3 can be coated or synthesized on both sides. Under these circumstances, the print would appear both on the front and the back of the copy sheet.

In FIG. 2 a back printing method is described in which reproduction material 1 is beneath master or original 4. Once again, the master consists of a sheet or base layer 5 of paper or graphically markable sheet material containing a design, drawing, written or typed character 6 to be copied. The master is superimposed on the sheet of reproduction material 1 to form an exposure sandwich S. Radiations Re such as visible light in the orange and red spectral zones as well as invisible infrared radiation is produced by radiation source 7. The radiant energy source 7 preferably is arranged so as to scan the original and copy materials. Radiations Re are concentrated and focused on the face surface 8 of the original in an elongated zone normal to the face of the drawing, while the sandwich moves with respect to said zone in the direction of the arrow. As each portion of the sandwich passes through the focal zone, radiations are absorbed by the design area 6 and are converted to heat, which, as shown at H, is conducted through the base 5 of the original 4, to the sensitive layer 2 of the copy material. In embodiment one of the invention, this heat converts the cellulose of the paper, the acid, and the aromatic polyhydroxy or polyamine compound into duplicate character 6". In embodiment two of the invention, the heat converts the reducing carbohydrate, the acid, and the aromatic polyhydroxy or polyamine compound into duplicate character 6". In embodiment three, the heat converts the organic, aliphatic or aromatic aldehyde, the aldehydeforming compound, or the ketone, the acid, and the aromatic polyhydroxy or polyamine compound into duplicate character 6".

The radiations which are not absorbed by character 6 are reflected as is illustrated at 9, or they may be transmitted through base 5 of the original depending upon the materials used. These rays normally do not affect the reproduction if the original contains a design only on its face surface.

As was pointed out above, it is essential that the reproduction paper or coated base be treated with particular solutions of particular organic acids. In embodiment one of the invention, the following organic acids have been found to be satisfactory: I

Meta-benzene disulfonic acid Benzene sulfonic acid p-Toluene sulfonic acid Benzene trisulfonic acid Citric acid Sulfanilic acid In general, organic acids having dissociation constants varying from that of citric acid to that of benzene sulfonic acid are satisfactory. In other words, the acid should not be stronger than benzene sulfonic acid nor weaker than citric acid.

The reducing carbohydrates which can be used in the second embodiment of the invention include monosaccharides such as galactose, glucose, mannose, gulose, dextrose, etc.; oligosaccharides such as maltose, lactose, cellobiose, etc.; polysaccharides, cellulose, starch, dextrin, pentoses such as arabinose, ribose, xylose, and lyxose, etc., and ketose sugars such as fructose. These carbohydrates act in much the same manner as the cellulose of the paper when treated with the particular acid solution and when heated by radiant energy in the manner described above once it has been broken down to a saccharide. The carbohydrates form cyclic aldehyde compounds which polymerize and react with the acid and the organic aromatic polyhydroxy or polyamine compound to form color bodies. Additionally, certain oxidation side reactions take place producing other color bodies such as humines.

Both aliphatic and aromatic aldehydes and ketones can be used in the third embodiment of the invention. It is essential however, that the aldehydes and ketones have a boiling point of 50 C. or higher. Among the suitable aliphatic aldehydes are those containing from 3 to 8 carbon atoms, such as glyoxal, adipaldehyde, a-hydroxyadipaldehyde, n-butyraldchyde, isobutyraldehyde, valeraldehyde, isovaleraldehyde, trirnethylacetaldehyde, ncaproic aldehyde, heptaldehyde, and n-capyrylic aldehyde. Suitable aliphatic ketones would include those containing from 4 to 11 carbon atoms, such as dihydroxy acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl n-butyl ketone, methyl isobutyl ketone, methyl sec-butyl ketone, ethyl propyl ketone, ethyl isopropyl ketone, dipropyl ketone, methyl amyl ketone, dibutyl ketone, and diamyl ketone. Suitable aromatic aldehydes and ketones would include benzaldehyde, ortho-, metaand para-toluic aldehyde, ortho-, metaand parahydroxy benzaldehyde, ortho-, meta-, and para-chlorobenzaldehyde, orthoand metanitrobenzaldehyde, a-naphthaldehyde, phenylacetaldehyde, vanillin, anisaldehyde, salicylic aldehyde, acetophenone and benzophenone. Among the compounds which form aldehydes under the conditions of the reaction which can be used in the process are eugenol, isoeugenol, anethole, and safrole.

In addition to urea and biuret, the following stabilizing agents can be used in the process: triphenylphosphate, tributylphosphate, tricresylphcsphate, symmetrical dimethyl urea, symmetrical diphenyl urea, thiourea, allyl thiourea, dithiobiuret, and dimethylol urea.

The following examples are illustrative of the subject invention.

Example I In this example, reproduction paper was treated with a composition made up with the following ingredients:

Water 50.00

mBDSA 14.25 Triethanol amine 4.50 Pyrogallol 5.00

1 Meta-Benzene disulfonic acid.

The solution was applied to paper with a solution-wet roller, although other suitable means could be used such as spraying, kiss coating, slot fountain, etc. After the excess was removed the paper was dried for about two minutes in a drying oven held at 6080 C. and was superimposed on an original containing typed graphic characters. The sandwich was placed beneath an infrared bulb whereby the characters on the original were reproduced on the copy paper by a front printing system such as is illustrated in FIG. 1 of the drawing. An excellent reproduction of an original was obtained by this method. The characters of the facsimile were black-brown in color.

Example 11 In this example, cellulosic reproduction paper was treated with a composition made up of the following ingredients:

Water 30.00 Solvent 20.00 mBDSA 10.00

Biuret 1.10 Hydroquino-ne 5.00

In this test the solution again was applied to paper with a solution-wet roller. After the excess had been removed and the paper dried it was placed in sandwich relationship with a superimposed original containing typed graphic characters. The sandwich was' placed beneath an infrared bulb whereby radiation from the radiation source was absorbed by the graphic characters on the original. Heat was transferred to the copy paper which caused a polymerization reaction to occur forming brown-black characters which duplicated the characters of the original.

Example III In this example, cellulosic reproduction paper was treated'with a composition made up of the following ingredients:

Water 4.50 mBDSA 2.00 Biuret 0.31 Ethyl alcohol 45.50 Pyrogallic acid (Pyrogallol) 5.00

Once again the solution was applied to paper with a solution-wet roller. After the excess had been removed and the paper dried, it was superimposed on an original containing typed graphic characters. The sandwich was placed beneath an infrared bulb whereby the characters on the original were reproduced on the copy paper by a front printing system such as is illustrated in FIG. 1 of the drawing. Inasmuch as an organic solvent was used in the composition, the amount of acid required was considerably lessened. An excellent reproduction of an original was obtained by the method. The characters of the facsimile were blaclobrown in color. The printing temperature in this example was about 280320 F. The drying time of the paper in the oven was about two minutes, and the oven temperature was about 60 80 C. The paper had excellent shelf life properties.

In a modification of the process, one gram of bleached cane sugar was added to the composition set forth in Example 111. This composition was then coated on a paper base in the manner described above. Development of the paper in the front printing system described in Example III produced an excellent reproduction of the original. The characters of the facsimile again were brown-black in color. The coated paper also had excellent shelf life properties.

Example IV This example illustrates the third embodiment of the Cellulosic paper was treated with the above solution and placed in sandwich relationship with an original in a manner described in Example III. An excellent reproduction of the original was obtained by the method. Characters of the facsimile were black-brown in color. The printing temperature in this example was about 280- 320 F. The paper had excellent shelf life properties.

The amount of acid used in the invention can vary from about 10 to about ,35 grams per 100 grams of water. If an organic solvent such as ethyl alcohol, isopropanol, butanol, ethyl cellosolve (or other low molecular weight alcohols) or benzene or toluene, etc., is used rather than water, the amount of acid can vary from about 2 to about 35 grams per 100 grams of solvent. The amount of urea or other stabilizing agent can vary from 0 gram to about 20 grams, preferably 210 grams, per 100 grams of water. If alcohol is used as the solvent from 0.4 to 4.0 grams of stabilizer is preferred. If it i desired, a metal sulfate such as cadmium sulfate, nickel sulfate, and cobalt sulfate can be added to the treating solution as an additional tabilizing agent. The amount of the metal sulfate can vary from 0 to about 15 grams per 100 grams of water.

The amount of carbohydrate, aldehyde or ketone that is used in the coating solution can vary widely. It has been found that from about 0.5 gram to about 20 grams of carbohydrate, aldehyde or ketone per 100 grams of water or organic solvent is satisfactory in most instances. The preferred range is from about 2 to about 10 grams per 100 grams of solvent.

In the second and third embodiments of the invention, the coating solution is applied to the base in an amount varying from 5 to 30 grams, preferably 8 to 14 grams, per square meter. The drying time for the paper generally will be from about 1 to about 3 minutes depending upon the temperature of the drying oven. A suitable oven temperature would be between about 60 C. and about C.

As was indicated above, the temperature of the paper in the areas of the polymerization reaction will vary from about 240 F. to about 360 F. The temperature required to produce a satisfactory print, of course, will depend upon the printing speed, the voltage across the lamp source, etc. In most instances, the paper need be exposed to the radiation for only a brief period of time, for example, from 0.05 second up to about 3 seconds, and preferably from 0.1 to 0.5 second.

In carrying out the subject process, it is not necessary to use binder resins to hold the applied coatings to the surface of the base. If it is desired, however, water-soluble or water-emulsifiable polymers can be used such as polyvinyl acetates, acrylic type polymers, polyvinyl acetates-acrylic type copolymers, water-soluble alkyd resins, water-soluble polyesters, water-soluble alkydcopolymers, etc.

In addition to ethanol, other solvents can be used in place of water such as isopropanol, butanol, butyl cellosolve, etc. As was pointed out above, less acid is re quired where alcohol is used as a solvent rather than water.

It is believed that the color producing reaction of the subject process proceeds as follows: cellulose molecules of the paper or the molecules of other reducing type polysaccharides are split under the influence of acid and heat to form monomeric reducing-type carbohydrates. The monomeric carbohydrates are then dehydrated and cyclicized to form cyclic aldehydes of the furan type such as furfural and hydroxymethyl furfural. Under the heat and acid conditions produced in the copy sheet, the aldehyde aut'opolymerizes, reacts with the organic polyh'ydroxy or polyamine compound, and with the acid forming characters of a particular color. The color of the character depends largely upon the organic polyhydroxy or polyamine compound that is used in the formula. As was pointed out above, the carbohydrate that is applied to the base sheet in embodiment two of the invention can be a monosaccharide such as glucose, mannose, galactose, fructose, etc., a reducing disaccharide such as maltose, succrose, lactose, and cellobiose, or a polysaccharide such as starch or cellulose.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for gnaphically reproducing an original which comprises: placing an original having preferentially radiation absorbing areas in contact with a cellulosic paper base coated with \a visibly heat-sensitive composition, said composition comprising (1) an organic acid, said acid having a dissociation constant varying from that .of citric acid to that of metabenzene 'disulfonic acid, and

.which comprises: placing an original having preferentially nadiation absorbing areas in contact with a cellulosic paper base coated with a visibly heatcensitive composition, said composition comprising (1) :a compound selected from the group consisting of an aldehyde, a ketone, eugenol, isoeugenol, anethole, and safrole, said compound having a boiling point of at least about 50 C., (2) an organic acid, said acid having a dissociation constant varying from that of citric acid to that of meta-benzene disulfonic acid, and (3) an organic compound selected from the group consisting of hydroquinone, resorcinol, catechol, phloroglucinol, pyrogallol, hydroanthaquinone, a naphthol, ortho, meta-, and para-phenylene diamine, and benzidine, and irradiating said original with heat producing radiations to increase the temperature of the supported layer in the areas of said supported layer registering with said radiation absorbing areas to a temperature of from about 240 F. to about 360 F., whereby a reaction occurs in said radiation absorbing areas and said original is visibly reproduced.

3. A process for graphically reproducing an original which comprises: a placing an original having preferentially radiation absorbing areas in contact with a paper base coated with a visibly heat-sensitive composition, said composition comprising (1) a reducing carbohydrate, said carbohydrate being selected from the group consisting of glucose, mannose, galactose, maltose, lactose, fructose, arabinose, xylose, lyxose, ribose, cellobiose, starch, dextrin, and cellulose, (2) an organic acid, said acid having a dissociation constant varying from that of citric acid to that of meta-benzene disulfonic acid, and (3) an organic compound selected from the group consisting of hydroquinone, resorcinol, oatechol, phloroglucinol, pyrogallol, hydroanthraquinone, a naphthol, ortho-, meta, and p'araphenylene di-amine, and benzidine, and irradiating said original with heat producing radiations to increase the temperature of the supported layer in the areas of said supported layer registering with said radiation labsorbing areas to a temperature of from about 240 F. to about 360 F., whereby a reaction occurs in said radiation absorbing areas and said original is visibly reproduced.

4. Reproduction material which comprises: a layer of a visibly heat-sensitive composition coated on a cellulosic paper base, said composition including (1) a compound selected from the group consisting of an aldehyde, a ketone, eugenol, isoeugenol, anethole, and safrole, said compound having a boiling point of at least about 50 C., (2) an organic acid, said acid having a dissociation constant varying from that of citric acid to that of metabenzene disulfonic acid, and (3) an organic compound selected from the group consisting of hydroquinone, resorcinol, catechol, phloroglucinol, pyrogallol, hydroanthraquinone, a naphthol, ort-ho-, meta-, and para-phenylene diamine, and benzidine.

5. Reproduction material which comprises: a supported layer of a visibly heat-sensitive composition, said composition including (1) :a reducing carbohydrate selected from the group consisting of glucose, mannose, galactose, maltose, lactose, fructose, arabinose, xylose, lyxose, ribose, cellobiose, starch, dextrin, and cellulose, (2) an organic acid, said acid having a dissociation constant varying from that of citric acid to that of meta-benzene disulfonic acid, and (3) an organic compound selected from the group consisting of hydroquinone, resorcinol, catechol, phloroglucinol, pyrogallol, hydroanthnaquinone, a naph-thol, ortho, meta-, and paraphenylene diamine, and benzidine.

6. A process for producing a thermally developable copy sheet which comprises: applying a solvent solution o f an organic acid and an organic compound selected from the group consisting of hydroquinone, resorcinol, catechol, phloroglucinol, pyrogallol, hydroanthraquinone, a naphthol, ortho, meta-, and par a-phenylene diamine, and benzidine to a base layer containing a reducing carbohydrate, said organic acid having a dissociation constant varying from that of citric acid to that of meta-benzene disulfonic acid, said coating being applied in an amount varying from 5 to 30 grams per square meter of said base layer, and the amount of acid in said solvent solution being from about 2 to 35 grams per grams of solvent.

7. A process for producing a thermally developable copy sheet Which comprises: applying a solvent solution of (l) a reducing carbohydrate selected from the group cgnsisting of glucose, mannose, galactose, maltose, lactose, fructose, arabinose, xylose, lyxose, ribose, cellobiose, starch, deX-trin, and cellulose, (2) an organic acid having a dissociation constant varying from that of citric acid to that of meta-benzene disulfonic acid, and 3) an aromatic compound selected from the group consisting of hydroquinone, resorcinol, catechol, phloroglucinol, pyrogallol, hydroanthr'aquinone, a naphthol, ortho, meta-, and para- 9 16 phenylene di am ine, and benzidine 10 -a base layer in an References Cited in the file of this patent amount Varying from about 5 to 30 grams solution pear UNITED STATES PATENTS square M16161 of said base layer, the amount f reduc ng 1,844,199 Bicknell et a1. Feb. 9, 1932 carbohydrate in said solution being from about 0.5 $0 20 g i3 omson an. gnams per 100 grams of solvent (and the amount of ac d 2,844,733 Miner at a1 y 22, 1958 being firom about 110 about grams P61 grams of 10 377 Owen o 27 1959 selvent. 3,024,362 Sus et a1. Mar. 6, 1962

Claims (1)

1. A PROCESS FOR GRAPHICALLY REPRODUCING AN ORIGINAL WHICH COMPRISES: PLACING AN ORIGINAL HAVING PREFERENTIALLY RADIATION ABSORBING AREAS IN CONTACT WITH A CELLULOSIC PAPER BASE COATED WITH A VISIBLY HEAT-SENSITIVE COMPOSITION, SAID COMPOSITION COMPRISING (1) AN ORGANIC ACID, SAID ACID HAVING A DISSOCIATION CONSTANT VARYING FROM THAT OF CITRIC ACID TO THAT OF METABENZENE DISULFONIC ACID, AND (2) AN ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF HYDROQUINONE, RESORCINOL, CATECHOL, PHLOROGLUCINOL, PYROGALLOL, HYDROANTHAQUINONE, A NAPHTHOL, ORTHO-, META,- AND PARA-PHENYLENE DIAMINE, AND BENZIDINE, AND IRRADIATING SAID ORIGINAL WITH HEAT PRODUCING RADIATIONS TO INCREASE THE TEMPERATURE OF THE SUPPORTED LAYER IN THE AREAS OF SAID SUPPORTED LAYER REGISTERING WITH SAID RADIATION ABSORBING AREAS TO A TEMPERATURE OF FROM ABOUT 240* F. TO ABOUT 360*F., WHEREBY A REACTION OCCURS IN SAID RADIATION ABSORBING AREAS AND SAID ORIGINAL IS VISIBLY REPRODUCED.

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