US3442682A - Heat-sensitive copy-sheet - Google Patents

Description

United States Patent 2,682 HEAT-SENSITIVE COPY-SHEET Kaneo Fukawa, Moriguchi-shi, Osaka-fu, Japan, assignor to General Co., Ltd., Osaka-shi, Japan, a corporation of Japan No Drawing. Filed July 7, 1965, Ser. No. 470,212 Claims priority, application Japan, July 17, 1964, 39/ 40,150; June 18, 1965, 40/286,016 Int. .Cl. B41m 5/22 U.S. Cl. ll736.8 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a heat-sensitive copy-sheet with a novel coating composition. More particularly, this invention relates to a heat-sensitive copy-sheet having a support with a heat-sensitive layer coated on the support, the coating containing component A and component B, which both participate in a color-developing reaction, the component A being at least one component selected from the group consisting of diphenylcarbazide and derivatives thereof, diphenylcarbazone and derivatives thereof, and diphenylthiooarbazide and derivatives thereof, the component B being selected from metal salts of organic acids, and if desired, an inhibitor of unusual color-development, and additionally, if desired, a White pigment and a heat melting material.

In the prior art, among copying sheets giving a copied image by a thermgraphic process, there is, for example, a copying sheet which comprises a relatively deeply colored paper, coated with a white or a light color (similar to white) material having an appropriate melting point, the

surface being thereby made white or light color, and thematerial is subjected to heat to be melted and rendered transparent, cooled and again solidified, but the resulting solid matter having a different crystalline form so that the ground color appears. There is also another thermocopying sheet, similar to the above mentioned one, lWhlCh comprises a material appearing white and having an appropriate melting point coated on the back face of an semi-transparent sheet, such as tracing paper, or a transparent sheet, such as polyester film, the coating being further coated with a colored material. When this sheet is looked at from the front side, it appears white, or of light color. The surface of coating of such copy-sheet is very weak and the ground color appears on only a slight rubbing, and, moreover, the coating disadvantageously adheres to the original sheet during the thermocopying operation. Also, the possible support is limited to a transparent or semi-transparent material, that is, relatively transparent material, and further it is unsightly owing to the colored back face.

Furthermore, there are other heat-sensitive copying sheets based on a principle of color development completely different from those mentioned above, for example, based on formation of an inorganic pigment, or the formation of diazonium dye, color development by chemical reaction of light color metal salts caused by heat 3,442,682 Patented May 6, 1969 "ice melting, and others. In some of them the chemical reaction proceeds gradually, during storage, to develop color. Some of them are very sensitive to perspiration of hands and fingers and slight rubbing, and lack in enough lightproof against the sun light or ultra violet rays from luminescent lamps, and require fixing after the printing. Also, the copying sheet is originally unfavorably colored, and the color of the formed image is not preferable. Thus, conventional heat-sensitive copying sheets have many disadvantages depending on the type of the heat sensitive composition constituting the copying layer.

By way of contrast, the heat-sensitive copy-sheet according to the present invention is an excellent one which solves all the (above-mentioned various difficulties. The color of the copied image can be any of various colors, such as, for example, dark purple. The main feature of the present invention distinguishable over the prior art resides in the principle of color development, that is, the heat-sensitive composition comprises at least one component selected from the group consisting of diphenylcarbazide and derivatives thereof, diphenylcarbazone and derivatives thereof, and diphenylthiocarbazide and derivatives thereof, that is, component A, and one or more metal salts of organic acid, that is, component B.

Diphenylcarbazide and its derivatives according to the present invention are compounds having the general formula:

where Ar is an aryl group which may be nuclearly substituted or unsubstituted, and such aryl groups may be the same as, or different from each other.

Also, diphenylcarbazone and its derivatives according to the present invention are compounds having the general formula:

Furthermore diphen-ylthiocarbazide and its derivatives are compounds having the general formula:

Ar-NHNHCNHNHAr where the Ars are as defined above.

The other com-ponent which takes part in the colordevelopin-g reaction is a metal salt of an organic acid. There are many metallic elements which react with the above-mentioned components A, and form coordination compounds to develop color. Among them, metals which elfect the desirable color development upon copying and give good image as a copy to attain the purpose of the present invention, are, for example, strontium, magnesium, calcium, zinc, aluminium, mercury, cadmium, lead, tin, copper, iron, cobalt, nickel, manganese, molybdenum, bismuth, barium, etc. Organic acid salts of those metals each have a particular crystalline form and color depending upon the metal. Some of them are white, some of them are of light color slightly colored, and some are relatively deeply colored. However, as far as they are used in a thin layer for the copying sheet, the appearance often becomes light colored and the contrast is not lowered there by when a fairly deeply colored one is coated on a support as a thin layer, such as 1-10 thick. There fore, color of the salt does not restrict the metals to be used in the present invention.

The organic acid used in the present invention is preferably that having a melting point ranging from about 50 C. to about C. as a metal salt of the organic acid. As is known, the melting point is not only affected by the kind of organic acid, but also largely by the metal.

In view of such purpose, preferable organic acids which form metal salts are, for example, aliphatic carboxylic acids having about 8 to about 24 carbon atoms. They are, for example, caprylic, pelargonic, capric, lauric, myristic, palmitic, stearic, margaric, arachic, behenic, lignoceric, oleic, elaidic, erucic and cetoleic acids etc.

Metal salts of organic acids are prepared from the above-mentioned metals and organic acids as follows. For example, to an organic acid is added caustic soda in an amount enough to neutralize the organic acid, and sufficient water to dissolve them, and then the mixture is heated to a temperature near the melting point of the organic acid to form an aqueous solution. To the resulting aqueous solution is added an aqueous solution of an inorganic salt of the metal in an amount equivalent to the organic acid to react each other, and a vmetal salt of the organic acid is obtained which is insoluble in water. The particles of metal salt of an organic acid show different colors, depending upon the type of metal as mentioned previously, and also different melting points, depending upon the type of metal and the type of organic acid. As described previously, the color of the particles of such metal salts of organic acids is preferably white or of a light color near white in view of the practice in heat-sensitive copy-sheets at the present time. However, even if the inherent color of a particle is fairly deep, it can be used without any trouble, provided that the contrast between the color of the metal salt when coated to form a copysheet and the color developed by the reaction with component A is enough to distinguish them from each other. As to the melting point of metal salts of organic acids, the melting point is changed depending upon the combination of the type of metallic element and the type of organic acid. Consequently, the only problem is to produce combinations to give a melting point of from about 50 C. to about 170 C., which is a preferable temperature range for color-development for heat-sensitive copysheets. Therefore, the type of metallic element and the type of organic acid are not particularly limited in the production of a preferable combination except in respect of the problem of the melting point. Also, if it is desirable to lower the melting point of a metal salt of an organic acid, one or more of free organic acids having appropriate melting points, for example, which are the same as, or different from, the organic acid forming said metal salt, is selected and added to the metal salt in an appropriate amount to lower the melting point according to the principle of depression of melting points of mixtures. Thus, it is possible to effect color-development of heat-sensitive copy-sheets at relatively lower temperatures and the sensitivity will be enhanced thereby.

In practice, the main components of the heat-sensitive copy-sheet according to the present invention are component T and component B, as previously stated. In preparing a coating agent to be coated on a support, such as paper and film, the following careful procedure serves to give better copy-sheets. Since component A, one of the color-developing agents, is soluble in organic solvents such as alcohols and the like, the partly or wholly dissolved component A causes partly or wholly color-development even if the metal salt of an organic acid (component B) is insoluble. This is, so-called, unusual colordevelopment. There are avrious methods for preventing unusual color-development; one of which is to form separate layers containing component A and component B, respectively, on a support. In this case, a binder dispersion liquid of component B is first coated on a support and dried. Then, a binder dispersion liquid of component A is coated on the previously coated layer, binder used for component A being different from that used for component B. Such binder is desirably a binder which does not affect or hardly affects the previously coated binder, protecting the layer of component B; that is, it is desired to use a solvent having a solvent property different from that of component B layer and a binder soluble in the solvent and is suitable for a heat-sensitive copy sheet (i.e. relatively high melting point or softening point and high transmission of infrared rays). A binder solution satisfying the above-mentioned conditions is used as the dispersion agent for component A, coated on the previously coated layer and dried. As the result, a metal salt of an organic acid (component B) is present in the lower layer and component A in the upper layer, so that white or light colored, nearly white, heat-sensitive copy-sheets can be produced without unusual color-development. When these heat-sensitive copy-sheets are used for copying, using an infrared ray copying apparatus, the partial heating at parts of letters in the original sheet by the infrared rays causes, firstly, melting of component B in the lower layer of the copy-sheet placed in intimate contact with the original sheet, and then the resulting molten component B contacts with particles of component A in the upper layer immediately to effect the color-developing reaction and produces sharp images of good contrast.

The formation of the layers may be effected in the opposite manner, that is, component A is coated first and component B is then coated thereon. The resulting copysheet is almost similar to the copy-sheet produced by the method immediately above described. As mentioned above, some of the metal salts of organic acids are relatively deeply colored. Therefore, it is preferable that one component having a lighter color than the other, in components A and B, is coated as the outer layer to result in copy-sheets of light color and excellent appearance.

Further, since the color-developing occurs at the melting point of the metal salt of the organic acid, it is preferable to place the metal salt of the organic acid in the lower layer for the purpose of keeping the holders and machines used for copying clean. Also, a heat-sensitive copy-sheet having a layer of metal salt of an organic acid nearer to the original paper, that is, contacting with the support, is preferable in view of the direction of heat transfer in the case of often used reflecting printing. However, when tracing paper and transparent film, etc., are used as the support, the relation of the front side and rear side of a copy sheet may become just opposite to the above-mentioned relation so that the above-mentioned matter is not always applicable. When a protective coating is applied, the situation is also the same as above.

According to another feature of the present invention, an inhibitor of unusual color-development is used together with other components, thereby component A and the metal salt of the organic acid can be made into a single coating agent to simplify the construction of the copysheet. The inhibitor of unusual color-development acts to check completely the reaction between component A and component B except when heated, or to delay it for long time. According to the present invention, the following materials have been found to be effective as an inhibitor of unusual color-development. For example, metal chelating agent, that is, a material forming a chelate compound by reacting with a metallic ion, is preferred. As the metal chelating agent, a material which easily reacts with a metal to form a chelate compound, elfective examples are amino carboxylic acids such as EDTA, nitrilotriacetic acid, (di(hydroxyethyl) glycine, (hydroxyethyl) ethylenediamine tetracetic acid, hydroxy carbonylic acids and their salts such as gluconic acid, citric acid, tartaric acid, malic acid, saccharic acid, sodium citrate, sodium tartarate, potassium citrate, potassium tartarate, ammonium malate, sodium malate, (carboxylmethylthio) succinic acid, Shiff bases, organic phosphates, (2-thenoyl)-trifluoroacetone (TTA), (Z-thienyl) -4,4,4-trifiuoro-L3-butadione, amino acids etc. These can be used singly or in combination of two or more.

When the above-mentioned chelating agents are used as an inhibitor to unusual color-development, some coating agents are allowed to stand for about one week after their preparation with only very slight color change occuring. Thus, it has been found that there is no trouble in the preparation of the coating agent. As to the prevention of unusual color-development, an appropriate selection of solvent for the coating agent other than above-mentioned two methods, is effective to prevent unusual color-development. As solvents of the binder employed for the purpose of preventing unusual color-development, there are, for example, aliphatic hydrocarbons, and n-heptane, n-hexane, petroleum benzine etc., which are very effective for such purpose.

The preparation of the coating agents is the same as mentioned above. The main components A and B are separately ground in separate ball-mills together with a binder solution and an inhibitor of unusual color-development, until they become fine particles, to produce a homogeneous dispersion solution. They are immediately combined before coating to prepare a coating agent and are coated preferably on an appropriate support. According to such procedure, unusual color-development is extremely little and the resulting copy-sheet has an excellent appearance. Particularly, a copy-sheet, obtained by coating on paper followed by drying, is hardly distinguishable from a general business paper in appearance.

The binder solution as mentioned above is not particularly critical, but well known binders can be used. Among them, for example, gelatin, polyvinyl alcohol, polyvinyl butyral, polyacrylic acid ester, polyacrylamide, polyvinylacetate, polyvinyl chloride, polystyrol, methylcellulose, ethylcellulose, acetylcellulose, polyamide resin, petroleum resin, terpene resin, and silicon resin, are particularly suitable for the purposes of the present invention. These binders may be used by dissolving them in appropriate solvents, for example, water, alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol and the like, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and the like, esters such as ethyl acetate and the like, aliphatic hydrocarbons such as hexane, heptane, petroleum benzine, halogenated compounds such as methylene chloride, benzyl chloride, and the like, aromatic hydrocarbons such as benzene, toluene, xylene and the like.

When the coating prepared according to the above procedure is coated on paper as a thin layer, an excellent copy-sheet is obtained which is hardly different from uncoated paper, has of easy handling properties, and is of good appearance and touch. As supports, other sheets, for example, of cellophane, film such as polyester film, polycarbonate film, polystyrol film, cellulose acetate film, polyvinyl chloride -film and the like, may be used to obtain heat-sensitive copy-sheets having such features.

According to further feature of the present invention, white pigment and heat melting material are used together with above-mentioned component A and component B, or component A, component B and an inhibitor of unusual color-development, for the purpose of suppressing aging to give heat-sensitive copy sheets which are highly stable for a long period, and also for the purpose of enhancing the contrast of copied images to solve the difliculty in reading the copied images owing to low contrast between the image and the background when the later is highly transparent or of high transmission.

Conventional heat-sensitive copy-sheets are very unstable and subjected to aging during usual use or storage,

. and particularly, after long periods serious deterioration of the copy-sheet occurs. For example, the appearance of the copy sheet is white or of a light color nearly white, but when exposed directly to sunlight or during the thermo copying operation, spontaneous color-development occurs to change the appearance of the copy sheets.

Heretofore, the support of heat-sensitive copy-sheets used in thermocopying systems is required having a background of high infrared ray transmission and of a color having high contrast with the heat-image, in view of the characteristics of the copying system. Therefore, there are the disadvantages that highly transparent and relatively thin white paper, for example tracing paper and tissue paper, are practically used, and a white layer should be formed on the back face thereof. According to the present invention, white pigment is used in an extremely large amount (for example, 250 parts by weight of white pigment per part of the color-developing compounds) to make the coating agent itself opaque. Therefore, even when a highly transparent support such as a completely transparent film and a semi-transparent tracing paper is used, the product after coating has a white ground to distinctly print the heat-image. The most important effect of the addition of white pigment is that a large amount of white pigment can hide the color developed spontaneously. Thus, the present invention has succeeded in improving conventional heat-sensitive copy-sheets which are subject to spontaneous color-development (discoloration) in background when stored for long periods. The combination of color of the background, the depth of the copied image, and the degree of spontaneous color-development, or the contrast among them, makes reading of the copied image easier and the vision feeling is also very natural. The color appearing as the result of spontaneous colordevelopment is not felt.

White pigments used in the present invention are, for example, zinc white, white lead, titanium oxide, lithopone, alumina white, calcium carbonate, white carbon, antimony white, basic lead sulfate, lead silicate, zirconium oxide, tin oxide, barium sulfate, barium carbonate, etc.

According to the present invention, a heat melting material is used together with white pigment, as mentioned above. The heat melting material inhibits a tendency to decrease in the color depth of the heat-image by the light scattering property of the heat image caused by the use of white pigment and makes the heat-image appear distinctly. That is, upon color-developing by heat, the heat melting material becomes a molten state, and the color-developing components dissolve therein and the color-developing reaction is accelerated thereby, and then the color-developed compound, produced from the color-developing components, dissolves therein to break the hiding of the white pigment to give the distinct heatimages. The heat melting material used in the present invention is an organic compound having a melting point of about 60 C. to about C., and miscible at the molten state with the color-developing components and the color-developed compound produced therefrom. The heat melting material satisfying such conditions is, for example, an organic compound having both hydrophilic group and alcoholphilic group (including a case one group having both properites).

The heat melting materials used in the present invention are preferably, for example, acetanilide, aceto-oanisidide, acetamide, o-anisidine, o-aminobenzylalcohol, p-aminobenzylalcohol, ethyl urea, fi-eleostearic acid, flhydroxyglutamic acid, o-hydroxybenzylalcohol, m-hydroxybenzylalcohol, cumarin, glycolic acid, diamino toluene, d-monoethyl tartarate, semicarbazide, desoxybenzoin, fl-m-tolylhydroxylamine, o-bis(hydroxymethyl) benzene, pimelic acid, phenyl acetic acid, fi-phenylhydroacrylic acid, benzylphenyl carbinol, p-benzylphenol, benzhydrol, benzoyl acetone, benzoyl formic acid, homocatechol, methyl urea, phthalic anhydride, stearic acid, ceryl alcohol, behenic acid, palmitic acid, margaric acid, guaiacol carbonate etc.

Of the above, one or more of the white pigments, arid also one or more of heat melting materials, can be used. The ratio of a white pigment and a heat melting material is not particularly restricted, but it is preferably 1:02 to 1.5.

Thus, the heat-sensitive copy-sheet according to the present invention can be stored both before and after copying without being subject to any series change for long periods under natural conditions.

The following examples will serve to illustrate but not to limit the invention. In the following examples all parts are by weight.

7 EXAMPLE 1 Suspension liquid A is prepared as follows. Petroleum rubber (product of Enjey Co. in U.S.A., of which the trade name is Vistanex) (1.9 parts) is dissolved in 94.3 parts of petroleum benzine to form a binder solution. The resulting binder solution is mixed with 1.9 parts of diphenylcarbazide and 1.9 parts of stearic acid and dispersed for about hours by using a porcelain ballmill. Then, suspension liquid B is prepared by dissolving 1.8 parts of petroleum rubber in 93.6 parts of petroleum benzine, adding 4.6 parts of mercurous laurate thereto and then dispersing for 10 hours by using a porcelain ball-mill. The resulting suspension liquids A and B are then mixed, coated on a white paper of about 40,4 thick, and dried at room temperature or at temperatures not higher thon 50 C. The sheet thus obtained is white and produces a dark purple color image upon thermotransferring by putting the sheet and an original sheet together.

The above-mentioned two compositions are treated in the same manner as in Example 1 to form suspension liquid A and suspension liquid B in which the fine particles are homogeneously dispersed. Then, the both suspension liquids are mixed, coated on a white paper of about 401/. thickness, and then dried at room temperature or at temperatures not higher than 50 C. The sheet thus obtained is light blue, but almost white. Upon thermocopying, a deep purple color image appears at a part corresponding to a drawn line on the original paper.

EXAMPLE 3 Formula for suspension liquid A:

Parts Diphenylcarbazone 1.9 Tartaric acid 0.9 Ethylcellulose 2.8 Methyl ethyl ketone 94.4

Formula for suspension liquid B:

Parts Zinc laurate 2.8 Ethylcellulose 2.8 Methyl ethyl ketone 94.4

The above-mentioned compositions are treated following the procedure in the previous examples. The sheet thus obtained gives a reddish purple color image upon thermocopying.

EXAMPLE 4 Formula for suspension liquid A:

Parts Diphenylthiocarbazide 1.8 Sodium tartarate 0.9 Polyvinyl butyral 8.9 Methyl alcohol 87.0

Formula for suspension liquid B:

Parts Calcium oleate 2.6 Stearic acid 1.7

Polyvinyl butyral 8.7 Methyl alcohol 87.0

A dark green color image is produced by heating a sheet obtained by treating it with the two compositions above, following the procedure of the previous examples.

EXAMPLE 5 Formula for suspension liquid A:

Parts 2,2'-dimethylphenylthiocarbazide 1.9 Petroleum rubber 1.9 Petroleum benzine 96.2

Formula for suspension liquid B:

Parts Cadmium stearate 2.8 Stearic acid 1.8 Petroleum rubber 1.8 Petroleum benzine 93.6

An orange color image is produced by heating a sheet obtained by treating same with the above two compositions following the procedure in the previous examples.

EXAMPLE 6 In the present example, an inhibitor of unusual colordevelopment is not used, and the color-developing layer is formed in such a manner that it consists of two layers. Suspension liquid A is prepared by dissolving 2.8 parts of ethylcellulose in 93.6 parts of methyl alcohol to produce a binder solution, adding 1.8 parts of diphenylthiocarbazide and 1.8 parts of stearic acid, and ball-milling the mixture in a porcelain ball-mill for ten hours to form a homogeneous dispersion of fine particles. The suspension liquid A thus obtained is coated 011 a white paper, about 40 1. thick, and dried at temperatures not higher than 50 C. Then, suspension liquid B is separately prepared by dissolving 1.9 parts of petroleum rubber (a product of Enjey Co. in U.S.A., of which the trade name is Vistanex) in 94.4 parts of commercial petroleum benzine, adding 3.7 parts of bismuth palmitate thereto and grinding and admixing the resulting mixture for ten hours in a ballmill to form a dispersion of finely divided particles. The dispersion thus obtained is coated on a layer A previously produced with suspension liquid A and dried at temperatures not higher than 50 C. The color of the image produced by heating the resulting sheet is brown.

Upon heating, the color of the image of the sheet produced by following the procedure in the previous example from the above two compositions is purplish brown.

EXAMPLE 8 Formula of suspension liquid A:

Parts 2,2',4,4'-tetramethyldiphenylcarbazone 1.9 Stearic acid 1.9

9 Petroleum rubber 1.9 Petroleum benzine 94.3

Formula for suspension liquid B:

Parts Cobalt stearate 2.9 Petroleum rubber 1.9 Petroleum benzine 95.2

The color of the image formed on heating a sheet treated with the above compositions according to the previous examples is deep purple.

EXAMPLE 9 Formula of suspension liquid A:

The color of the image formed by heating a sheet produced by treatment with the above compositions following the procedure in the previous examples is blackish brown.

EXAMPLE 10 Formula of suspension liquid A:

Parts Diphenylthiocarbazide 1 .8 Citric acid 0.5 Sodium citrate 0.9 Polyvinyl butyral 8.8 Methyl alcohol 88.1

Formula for suspension liquid B:

Parts Aluminium stearate 4.4 Polyvinyl butyral 8.7 Methyl alcohol 86.9

The color of the image formed by heating a sheet treated with the above compositions following the procedure of the previous examples is dark green.

EXAMPLE 11 Formula of suspension liquid A:

Parts Diphenylthiocarbazide 1.9 Citric acid 0.5 Sodium citrate 0.9 Ethylcellulose 2.8 Methyl alcohol 93.9

Formula for suspension liquid B:

Parts Lead palmitate 2.8 Ethylcellulose 2.8 Methyl alcohol 94.4

The color of the image formed by heating a sheet treated with the above compositions following the procedure of the previous examples is crimson red.

EXAMPLE 12 Formula of suspension liquid A:

Parts Diphenylearbazide u -1 1.9 Methylcellulose 2.

Methyl alcohol 94.2

Formula for suspension liquid B:

Parts Mercurous palmitate 4.6 Methylcellulose 2.8 Methyl alcohol 92.5

Suspension liquid A is prepared by dissolving methylcellulose in methyl alcohol to form a binder solution, mixing the resulting binder solution with diphenylcarbazide and dispersing for ten hours in a ball-mill:

Then, suspension liquid B is prepared by dissolving methyl cellulose in methyl alcohol, adding mercurous palmitate anddispersing for ten hours in a ball-mill.

These suspension liquids A and B are. stirred together to give a combined dispersion liquid, which is then mixed with the following suspension liquid C and coated as below stated.

Formula for suspension liquid C:

Parts Water 48.2 Titanium oxide 28.8 Palmitic acid 19.2 Citric acid 1.9 Sodium citrate 1.9

Suspension liquid C is prepared by agitating the abovementioned ingredients at 25 C. for 2 hours.

The above-mentioned suspension liquids A, B, and C are mixed to form a coating agent, which is coated on a support, such as a sheet, by any of various coating methods such as roll coating, kiss coating, air knife coating, reverse coating and the like, and then dried in air at room temperature or at temperatures not higher than 50 C. The sheet thus obtained is white or of light color, and the bluish purple image formed by heat copying of an original sheet is in marked contrast to the white or light colored background, being very distinct.

It is noted that a heat-sensitive copy-sheet obtained from only the suspension liquids A and B, without the suspension liquid C, according to the above-mentioned procedure (Example 12), is not satisfactory with respect to the points of long period storage stability and distinctness of the image on a highly transparent support.

EXAMPLE 13 The above ingredients are handled int he same manner as in Example 12. The color of the image formed by heating the resulting heat-sensitive copy-sheet is deep purple.

EXAMPLE 14 Formula for suspension liquid A:

Parts Diphenylcarbazide 3.7 Polyvinyl butyral 4.6 Methyl alcohol 91.7

Formula for suspension liquid B:

I Parts Cupric behenate 4.55 Polyvinyl butyral 4.55 Methyl alcohol 90.9

Formula for suspension liquid C:

Parts Polyvinyl butyral 4.2 Methyl alcohol 83.0 Titanium oxide 66.4 Behenic acid 2.4

Acetamide 41.4

Tartaric acid 1.8 Sodium citrate 0.8

The above ingredients are treated in the same manner as :in Example 12. The color of the image formed by heating the resultant heat-sensitive copy-sheet is deep purple.

EXAMPLE 15 Formula for suspension liquid A:

Parts Diphenylcarbazide 1.9

Petroleum rubber 2.9

Petroleum benzine 95.2

Formula for suspension liquid B:

Parts Mercurous palmitate 4.6

Petroleum rubber 2.8

Petroleum benzine 92.6

Formula for suspension liquid C:

Parts Petroleum rubber 6.6

Petroleum benzine 215.7 Titanium oxide 43.2 Stearic acid 34.5

The above ingredients are treated in the same manner as in Example 12. The color of the image formed by heating the resulting heat-sensitive copy-sheet is dark purple.

I claim:

1. A heat-sensitive copy sheet including a visibly heatsensitive, opaque layer comprising a uniform dispersion of particles of (1) at least one compound selected from the group consisting of diarylcarbazides, diarylthiocarbazides and diarylcarbazones,

(2) at least one organic acid metal salt reactive with said compound to form a colored reaction product,

(3) a white pigment component present in the amount of 2 to parts by weight per part of said compound and said metal salt together; and

(4) an inhibitor of unusual color development, in a fusible component having a melting point in the range of about to about C., said fusible component, when molten, being a solvent for said compound, said metal salt and said reaction product, the weight ratio of white pigment to said fusible component being in the range of 1:02 to 1:1.5.

2. A heat-sensitive copy-sheet according to claim 1 in which the inhibitor of unusual color-development are chelating agent.

3. A heat-sensitive copy sheet as set forth in claim 1, wherein the heat-sensitive layer is disposed on a translucent carrier sheet.

References Cited UNITED STATES PATENTS 2,663,656 12/1953 Millet et al. 117-36.8 2,897,090 7/1959 Van Dam 11736.8 2,910,377 10/ 1959 Owen 11736.8 2,916,395 12/1959 Owen 11736.8 3,111,423 11/1963 Ostie 11736.8 3,167,444 1/1965 Baumann et a1 117-36.8

,. a MURRAY KATZ, Primary Examiner.

US. Cl. X.R.