US3161770A - Thermographic reproduction paper and method of using - Google Patents

Description

Dec. 15; 1964 G. c. HUETT ETAL 3,161,770

THERMOGRAPHIC REPRODUCTION PAPER AND METHOD OF USING Filed March 20, 1962 FIG. I

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' REDUCING CARBOHYDRATE flfAC/D 3 2 GEORGE C. HUETT HZERTWELLGL.

BY 44 W ATT'YS United States Patent 3,161,770 THERMOGRAPHIC REPRODUCTION PAPER AND METHOD OF USING George C. Huett and Hartwell L. Briggs, Chicago, and Ken G. Prohst, Northlake, Ill., assignors to Eugene Dietzgen Co., Chicago, 11]., a corporation of Delaware Filed Mar. 20, 1962, Ser. No. 181,091 4 Claims. ((Il. 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, U.S. 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 conpler, 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, especiallywhere 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 asintermediates for producing other copies of the original. Additionally, many of the known coating compositions are relatively expensive and are diflicult to handle on a commercial scale. a t

It is an object of the present invention to provide improved copy paper for thermographic reproduction systems.

Another object of the invention is to provide thermographic paper which can be produced inexpensively and without difficulty.

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 original 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 side or both sides.

Another object is to provide copy paper which in addition to black characters will reproduce characters of certain other colors to a readable degree.

Still another object is to provide copy paper which can be used to produce facsimiles having well defined char- "ice acters 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 invention comprises the discovery of a process by which either the cellulose in paper or carbohydrates coated on a suitable base can be treated so that a color image will be produced by means of radiant energy transferred from the characters of the original to the 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.

If the paper itself is to produce the color forming body, the coating composition consists of an aqueous solution of an acid such as meta-benzene disulfonic acid along with a stabilizing agent such as urea. When the paper is heated by the transfer of energy from the characters of the original to the copy sheet, the cellulose appears to break down forming a reducing type carbohydrate. The carbohydrate gives up water to form a cyclic aldehyde compound of the furan type such as hydroxymethyl furfural. Under the conditions prevailing during the heating step, the cyclic aldehyde polymerizes forming a brown character. The color of the character can be modified by adding co-reacting components to the coating solution.

In the second embodiment of the invention, the carbohydrate contained in the coating solution takes the place of the cellulose of the paper. The combined action of the acid and the heat converts the carbohydrate into a cyclic aldehyde compound of the furan type such as hydroxymethyl furfural or furfural. This material polymerizes to form a colored character corresponding to the characters of the original.

The invention is illustrated in theattached schematic drawing in which:

FIGURE 1 is an enlarged fragmentary cross-section 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 the subject 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, preferably along with a stabilizing agent such as urea. In the second embodiment of the invention, the sensitive layer 2 contains a carbohydrate such as mannose, glucose, etc., a particular acid, and preferably a stabilizing agent. In the second embodiment of the inventiombase 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, written 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. 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 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 or paper into a color producing polymer producing duplieating character 6". In embodiment two of the invention, the heat converts the reducing carbohydrate into a color producing polymer to produce duplicate character 6".

The radiations which are not absorbed by character 6 are re flected as is illustrated at 9, or they may be transmitted through base 5 of the original depending upon the materials used. These rays normally donot afiect the face surface. 1

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:

reproduction if the original contains a design only on its In' general, .organic acids, having dissociation constants varyiii'g from that ofcitr'ic acid to that of benzene .sul-

fonic 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 monosac charides such as galactose, glucose, mannose, gulose, etc.; oligosaccharides such as maltose, lactose, cellobiose, etc.; polysaccharides, cellulose, starch, 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 carbohydrate forms cyclic aldehyde compounds which polymerize to form color bodies. Additionally, certain oxidation side reactions take place producing other color bodies such as humines.

The following examples are illustrative of the subject invention.

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

Water -n 100.00 'mBDSA 28.50 Urea 14.40 Thiourea 0.50 CdSO 8H O 10.50

The solution Was applied to the paper with a solutionwet roller, although other suitable means could be employed 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 70 C. and 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 colored areas which duplicated the characters of the original. The temperature of the paper in the polymerization areas was about 360 F. An excellent reproduction of the original was obtained by this method. The characters of the facsimile were brown in color.

In the preferred embodiment of the invention, the copy paper is superimposed on the original, in which case a front printing system is used as is illustrated in FIG. 1 of the drawing.

3 Example llf In this illustrative experiment, cellulosic reproduction paper was treated with the following solutions:

Meta- Bleached Water, g. benzene Urea, g. can

disulfonic sugar, g.

acid, g.

sults. In all of the above tests, the front printing system.

disclosed in FIG. 1 of the drawing can be used in place of the direct energy transfer method shown in FIG. 2 of the drawing.

It has been found that the subject process has little, if any, detrimental effect on the strength of the copy paper. In the first embodiment of the invention, for example, the degradation of the paper cellulose is relatively slight. The same is true of the coated papers of the second embodiment of the invention. As was pointed out above, the addition of copolymerizable compounds to the aqueous acid treating solution produces varying colors. This fact, among others, makes it clear that in the first embodiment of the invention the combined action of the acid and the heat does not produce charring of the paper.

The amount of acid used in both embodiments of the invention can vary from about 20 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 gram to about 20 grams, preferebly 2-l0 grams, per 100 grams of Water. If it is desired, a metal sulfate such as cadmium sulfate, nickel sulfate, and cobalt sulfate can be added to the treating solution as an additional stabilizing agent. The amount of the metal sulfate can vary from 0 to about 15 grams per 100 grams of water.

The amount of carbohydrate 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 per 100 grams of Water or organic solvent is satisfactory in most instances. The preferred carbohydrate range is from about 2 to about 10 grams per 100 grams of water.

In the second embodiment of the invention the coating solution is applied to the base in an amount varying from 5 to 30 grams, preferably 8 to 20 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 80 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, watersoluble 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 alkyd-copolymers type, etc.

The degree of print strength depends upon (1) temperature, (2) time, and (3) the degree of polymerization which takes place. The degree of polymerization is determined by the type of organic acid that is used in the sensitizing step and its concentration. Acids that are weaker than citric acid do not produce distinctive prints, while inorganic acids which are oxidizing in nature often cause carbonization of the carbohydrate. For these reasons only organic acids should be used having an ionization constant varying from that of citric acid to that of meta-benzene disulfonic acid.

In the second embodiment of the invention a number of materials can be used in addition to paper. Clear plastic materials, such as Mylar, as well as glass cloth of suitable thickness have been found to be satisfactory in most instances.

In general, the color producing reaction proceeds as follows: cellulose molecules of the paper or the molecules of other reducing type polysaccharides are split under the influence of the 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 polymerizes forming characters which are dark black to brown in color depending upon the particular formula that is used. As was pointed out above, the carbohydrate that is applied to the base sheet in embodiment two of the invention can be monosaccharide such as glucose, mannose, galactose, fructose, etc., a reducing disaccharide such as maltose, sucrose, lactose, and cellobiose, or polysaccharides such as starch and cellulose.

The sensitizing solution can also contain compounds which are able to inactivate the acids to a partial degree by complexing and/or partially neutralizing the acid. Compounds of this type would include urea, thiourea, triethanolamine, biuret, etc. These compounds tend to stabilize the formulation and prevent background discoloration. Further stabilization of the reproduction paper can be obtained by adding a metal sulfate to the composition in the manner described above.

Obviously many modifications and variations of the in vention 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 graphically reproducing an original which comprises: placing an original having preferentially radiation absorbing areas in contact with a visibly heat-sensitive composition coated on a base support, said composition comprising a reducing carbohydrate selected from the group consisting of glucose, mannose, galactose, maltose, lactose, fructose, arabinose, xylose, lyxose, ribose, cellobiose, and starch and an organic acid, said acid having an ionization constant varying from that of citric acid to that of meta-benzene disulfonic acid, and irradiating said original with heat producing radiations to increase the temperature of the composition in the areas of said supported layer registering with said radiation absorbing areas to from about 240 F. to about 360 F., whereby said original is visibly reproduced.

2. A process for graphically reproducing an original which comprises: placing an original having preferentially radiation absorbing areas in contact with a visibly heat-sensitive composition coated on a base support, said composition comprising a reducing carbohydrate, said carbohydrate being selected from the group consisting of glucose, mannose, galactose, maltose, lactose, fructose, arabinose, Xylose, lyxose, ribose, cellobiose, and starch, and an organic acid, said acid being selected from the group consisting of meta-benzene disulfonic acid, benzene sulfonic acid, p-toluene sulfonic acid, benzene trisulfonic acid, citric acid, and sulfanilic acid, and irradiating said original With heat producing radiations to increase the temperature of the composition in the areas of said supported layer registering with said radiation absorbing areas to from about 240 F. to about 360 F., whereby said original is visibly reproduced.

3. Reproduction material which comprises: a base support and a visibly heat-sensitive coating on said support, said coating comprising a mixture of a reducing carbohydrate selected from the group consisting of glucose, mannose, galactose, maltose, lactose, fructose, arabinose, xylose, lyxose, ribose, cellobiose, and starch, and an organic acid, said acid having an ionization constant vary- 1g from that of citric acid to that of meta-benzene diulfonic acid. 4. Reproduction material which comprises: a base upport and a visibly heat-sensitive coating on said supvort, said coating comprising a mixture of a reducing :arbohydrate selected from the group consisting of glucose, mannose, galactose, maltose, lactose, fructose, trabinose, xylosc, lyxose, ribose, cellobiose, and starch, 1nd an organic acid, said acid being selected from the group consisting of meta-benzene disulfonic acid, ben- :ene sulfonic acid, p-toluene sulfonic acid, benzene triaulfonic acid, citric acid, and sulfanilic acid, and a stabilizing agent selected from the group consisting of urea, thiourea, biuret, and ethanolamine.

References Cited in the file of this patent UNITED STATES PATENTS Bicknell et a1. Feb. 9, 1932 Martinez Jan. 23, 1934 Morrison 1 Jan. 13, 1953 Miller et July 22, 1958 Owen Oct. 27, 1959 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 VISIBLY HEAT-SENSITIVE COMPOSITION COATED ON A BASE SUPPORT, SAID COMPOSITION COMPRISING A REDUCING CARBOHYDRATE SELECTED FROM THE GROUP CONSISTING OF GLUCOSE, MANNOSE, GALACTOSE, MALTOSE, LACTOSE, FRUCTOSE, ARABINOSE, XYLOSE, LYXOSE, RIBOSE, CELLOBIOSE, AND STARCH AND AN ORGANIC ACID, SAID ACID HAVING AN IONIZATION CONSTANT VARYING FROM THAT OF CITRIC ACID TO THAT OF META-BENZENE DISULFONIC ACID, AND IRRADIATING SAID ORIGINAL WITH HEAT PRODUCING RADIATIONS TO INCREASE THE TEMPERATURE OF THE COMPOSITION IN THE AREAS OF SAID SUPPORTED LAYER REGISTERING WITH SAID RADIATION ABSORBING AREAS TO FROM ABOUT 240*F. TO ABOUT 360*F., WHEREBY SAID ORIGINAL IS VISIBLY REPRODUCED.

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