US3185584A - Heat responsive marking sheets - Google Patents

Description

May 25, 1965 CO-CRYSTAL ADDUCT OF AN AMINE AND A HYDROXYPHENOL COMPOUND A PHENOL 0 NITROPHENOL AN OXIDANT SUPPORT v INVENTORS MICHAEL E BAUMANN BYWILLIAM R. LAWTON ATTORNEYS United States Patent "ice 3,185,584 1 HEAT RESPONSIVE MARKING SHEETS Michael F. Baumann, Hudson, and, William R. Lawton, Nashua, N.H., assignors to Nashua Corporation, Nashua, N.H., a corporation of Delaware Filed Nov.19, 1962, Ser. No. 238,712

4 Claims. (Cl. 117-36.8)

This invention relates to thermographic copying sheets and is particularly concerned with a copy sheet which is characterized by its ability to form a colored image of a color contrasting to the background; wherever the sheet is exposed to heat.

The exposure may be made through a master copy which is exposed to radiant energy. That energy is converted to sensible heat in the indi-cia appearing on the master sheet. Consequently the copy sheet is subjected to selective, localized heating under theindica and a colored image of the original indica appears. In recording apparatus, the sheet is heated directly by a hot stylus.

For brevity, both such modes of heating will be referred to as the thermographic process.

The present invention is a continuation of work begun in the applications of. William R. Lawton and Eugene F. Lopez, Serial No. 808,012, =filed April 22, 1959, now US. Patent No. 3,076,707, and the application of William R. Lawton (sole) Serial No. 206,186, filed June 29,

1962, both of which are assigned to the assignee of this invention. The entire disclosure of both above identi fied applications is herein incorporated by reference.

The above applications disclosed that the co-crystal adducts of a bisphenol and an amine, or a hydroxyphenol substituted chroman and an amine can be coated on a copy sheet wherethey remain inert and non-reactive. When heated to between 50 and 150 C. however, these complex crystals dissociate; releasing the amine which thereupon can react with materials with which it is in intimate contact. In the two applications mentioned above onesuch material is an azo compound which is developed or changed in color by the amine which has beenreleased by the heat of the thermographic process.

We have now discovered that when the amine is heatreleased from a cocrystal adduct in the presenceof an oxidizing agent and a substance which gives rise to a color change upon oxidation, a good, intense, and highly responsive color change occurs. When a sheet coated with a composition including thesevari-ous materials is used in a .thermographic copying process a satisfactory reproduction of the original indica results.

The color change is not entirely due to a change in color of the oxidant when it is reduced, but is evidently due in great part to the ability of the oxidant to promote a change in colorin the substance which is oxidized.

Among the substances capable of acting as oxidants in tbis envir'onment are compounds such as copper nitroprusside (CuFe(CN )NO), nickel nitroprusside (NiFe(CN )NO) sodium nitroprusside (Na Fe(CN )NO.), copperoxalate, potassium ferricyanide, and the eerie salts. Sodium nitroprusside is preferred because ofits ability not only to act as an oxidizingagent (the complexed iron goes from plus three to plus two), but because it apparently also forms a complexed material with the resulting product, especially with oxidized oxygen, nitrogen or sulfo linkages. i

Compounds which are capable of being oxidized in this reaction include compounds with the grouping HO- aromat-ic-OH, HO-aromatic-arornatic, HO-aromatic-NH The comounds having the groupings tri-OH-arOmflfiiCQ HO- a-romatic-S, and H Naromatic (s)-NH give superior performance. V x

Patented May 25, 1965 Among the oxidizable materials which give good results are gallic acid, phloroglucinol, P-phenylenediamine, benzidene, tannic acid, pyrogallal, hydroq-uinone, and O- phenylenediamine. Of these pyrogallol and its derivatives,

.benzidene and the phenylenediamines are preferred.

found to be operative. Among such carriers may be mentioned tetrachloro-bisphenol A, tetrabromobisphenol A, 2,2-thiobisnaphol, and the hydroxyphenol substituted ohromans. As a class, the co-crystal adducts of amines bisphenols are well known. Many are described in US. Patent 2,829,175. The hyd-roxyphenol substituted chroman :co-crysta-l adducts are described by Cramer, EIN- SCHLUSSVERBINDUNGEN, (published by Springer- Verlag, Berlin, 1954).

The useful amines include ethanolamine, diethanolamine, triethanolamine, N-methylethanolamine, phenyl ethanolamine, propyleneamine, polyglycolamine, tetramethylguanidine, and ethylenediamine. The alcohol amines are preferred.

All combinations of these carriers and the amines heatdecompose within the range of heats which are practicable in the thermographic process, namely 50 to 150 C. and, upon thermographic heating, provide a favorable medium for reactivity.

Copy sheets are prepared by dispersing 10 parts of each of the active materials in parts of a 2.5% solution of a resinous binder dissolved in a suitable solvent. When the desired particle size of each ingredient has been reached, the dispersions are combined by simple mixing. The dispersion mixture is then coated on a suitable supporting sheet, e.g. glassine. A coating weight of approxi mately 5 lbs. per ream of 24" x 36" x 500 sheets is effective. The accompanying drawing illustrates schematically a heat sensitive sheet corresponding to this invention. The sheet is represented as being in cross section.

PREPARATION OF THE BISPHENOL/AMINE ADDUCT Example 1 The solid molecular complex adduct of Tetrachlorobisphenol A and Diethanolamine is prepared in the following manner. 1 mole (366 grams) of Tetrachlorobisphenol A is dissolved in 1098 grams of toluol with heat. To this solution is added 2 moles (210 grams) of Diethanolamine with constant agitation. A fine crystalline precipitate is obtained and the crystals are collected by filtering and are washed three times with norm-a1 hexane and allowed to dry. The product is the ad-duct-Tetradhlorobisphenol A/Dietho-nalamine (TCBA/ DEA) In the foregoing example, the bisphenol used was tetrachlorobisphenol A (4,4'-isopropylidene-bis-(2,6-dichlorophenol). We have found that this material is efifective in the formation of numerous of the co-crystal adducts which dissociate at temperatures within the range of about 50+150 C., but other bisphenols are available and are useful. These other bisphenol compounds may be employed in the preparation of solid heat-dissociable co-crystal adducts with amines. Compounds which are preferred include tetrabromobisphenol A; 4,4'-isopropylidene-bisphenol; 2,2 methylene bis (4-methyl-6-butylphenol); 4,4'-thio-bis-(6-tert. butyl-m-cresol); 4,4-,butylidene-bis-(G-tert. butyl-m-cresol); 2,2-thio-bis-(4,6-dichlorophenol) 2,2 methyl-4,4'-bis-(3,4,6-trichlorophen01), and 2,2-thiobisnaphthol. Other bisphenol compounds which may be used in this manner are set forth in the previously mentioned Patent, 2,829,175.

PREPARATION OF THE CHROMAN ADDUCTS Example 2 A hydroxyphenol substituted chroman, namely 2'-hydroxy-2,4,4,7,4-phentamethylflavan is prepared according to a procedure described by Baker and Besley in J. Chem. 80., 1951, 1102-6. A mixture of m-cresol (440 g.) and acetone is saturated with gaseous HCl without cooling and kept at 40 C. for two days with the exclusion of water. The dark product is added to an excess of 20% sodium hydroxide solution, a layer of ether is poured on the surface, and the mixture is vigorously stirred causing the ether addition product of the dimeride to crystallize. After standing overnight in an open vessel the solid is collected, washed thoroughly with water, dissolved in hexane, and dried with calcium chloride. The solution is filtered and a small amount of 'ether is added to the solution. The ether complex of the flaven compound separates in large, colorless, thick 'rhombic prisms having a melting point of 7677 C. A fiaven co-crystal adduct is prepared by mixing fifteen parts of a 10% hexane solution of the flavan ether complex with 7.5 parts of dicyclohexylamine, chilling the mixture overnight, and filtering the solid crystalline adduct product, M.P. 103-105 C.

While the above flavan material is one which we have found to be effective in the formation of numerous cocrystal adducts which exhibit dissociation temperatures within the range of about 50-l50 C. it is not the only available or useful hydroxyphenol substituted chroman. Numerous other hydroxyphenol substituted chromans may be used and among these which we prefer are 7,4'-diethyl-2'-hydroxy-2,4,4-trimethyl flavan; cyclohexanespiro-4-(2'-hydroxy-7,4-dimethyl 2,3 tetramethylene) flavan; 2' hydroxy 2,4,4,6,7,4,5 heptarnethyl flavan; 2-hydroxy-2,4,6,5'-pentamethyl flavan; 4-p-hydroxyphenol-2,2,4trimethyl chroman. As in the case of the bisphenols, many amines are suitable, the most effective being the alcohol amines. The chroman adducts can normally be prepared by simple mixing of the selected chroman and amine in the manner shown above.

7 These adducts are incorporated in a coating composition as follows:

Example 3 (A) Ten parts of sodium nitroprusside is added to 90 parts of a 2 /z% solution of polyvinyl butyral (Butvar B-76) in trichloroethylene and ground in a ball mill until the nitroprusside is reduced to fine particle size.

(B) Ten parts of pyrogallol is added to 90 parts of a 2 /2 solution of polyvinyl butyral in trichloroethylene and ground in the same manner.

(C) Similarly, 10 parts of the co-crystalline adduct of tetrachlorobisphenol-A and diethanolamine is added to 90 parts of a 2' /2% solution of polyvinyl butyral in trichloroethylene and ball milled as above.

When the desired particle size is reached, the three dispersions are combined in the ratios of solid ingredients as follows:

Parts (A) Sodium nitroprusside 2 (B) Pyrogallol 2 (C) TCBA/diethanolamine 4 After thorough stirring, the combined dispersions then form the coating composition which is spread by conventional coating machinery on a suitable supporting sheet, e.g. thin paper having a ream weight of 22 lbs. per ream of 500 sheets, 24" x 26". The dry Weight of the coating is approximately 5 lbs. per ream. After the volatile suspending medium has evaporated, the sheet will produce a deep purple image when exposed in thermographic apparatus.

4 The following coating compositions all prepared as set forth in Example 3 were combined in the ratios of solid ingredients as follows.

(Imageblack-brown.)

The hydroxyphenol substituted chroman adducts may be substituted for the bisphenol adducts of the preceding examples with substantially the same result, but because of their water insensitivity it is convenient, at times, to apply a first coat containing only the chroman adduct suspended in a water solution of a water-soluble binder, e.g. polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, or gums. In such cases, the aqueous first coat which is applied to the supporting sheet at the dry weight of approximately 4 lbs. per ream of 24" x 26" x 500 sheets may be as follows.

Example 8 Parts 2-hydroxy-2,4,4,7,4-pentamethyl flavan/ethylenediamine '20 Polyvinyl alcohol 2 Water 98 When the coating is dry it is overcoated to a dry weight of about 2 lbs. per ream of the following coating composition.

Ratios of solid ingredients:

Parts Sodium nitroprusside (dispersed in trichloroethylene as in Ex. 3) 4 Pyrogallol (dispersed in trichloroethylene as in Ex. 3) 4 When the second coat is dry, this sheet, when exposed to heat in thermographic apparatus, will produce a deep purple image.

Sodium aminopentacyanoferroate (Na Fe(CN) -NH and Gallic acid under these conditions will produce a purple image on a yellow background. When phloroglucinol is the oxidizable substance, the image is black. Ceric sulfate, or ceric ammonium sulfate with gallic acid will produce a deep brown image. Copper Oxalate and p-phenylenediamine or benzidine form coatings having excellent heat response and produce strong, green images. The combination of sodium nitroprusside and 1,5-naphthalenediol produces a brown-black image. With 1,1- thiobisnaphthol, the image is violet; with benzidene, black. Copper nitroprusside and nickel nitroprusside give results similar to those of the sodium salt, but copper produces brown colors. With nickel, the colors are blacker.

As the paragraph above indicates many permutations of the reactants are practicable and are, within the scope of this invention.

The process permits the manufacturer to have a substantial degree of flexibility. It permits copy sheets to be furnished which produce distinctively colored images-- often a great convenience when thesource of copied correspondence must be quickly identified.

What is claimed as the present invention is:

1. A heat-responsive copy sheet adapted to change visibly to a contrasting color wherever subjected to localized heating to a temperature between 50 and 150 C. comprising, in combination (a) a supporting sheet carrying on a surface thereof a coating comprising -a uniformly distributed intimate association of finely divided particles of (b) an oxidizable compound selected from the class consisting of phenols and nitrophenols,

(c) an oxidant selected from the class consisting of the nitroprussides of copper, nickel and sodium, copper oxalate, potassium ferricyanide, ceric sulfate, and ceric ammonium sulfate, and

(d) a solid, normally stable, co-crystal adduct comprising the reaction product of an amine and an hydroxyphenol compound selected from the class consisting of bisphenols and hydroxyphenol substituted chromans, and which is heat dissociable in the temperature range of 50 C. to 150 C.

2.. A heat-responsive copy sheet as claimed in claim 1 wherein the oxidant is sodium nitroprusside, the oxidizable compound is pyrogallol, and the co-crystal adduct is the adduct formed by tetrachlorobisphenol-A and di- ,ethanolarnine.

3. A heat-responsive copy sheet as claimed in claim 1 wherein the coating comprises a first layer comprising an hydroxy phenol substituted chroman adhered to the supporting sheet by a water-soluble binder, and a second layer co-extensive with said first layer comprising the oxidant and the oxidizable compound adhered to said first layer by a resinous binder.

4. A heat-responsive copy sheet as claimed in claim 1 wherein the co-crystal adduct is 2'-hydroxy-2,4,4,7,4'-

pentamethyl fiaven/ethy-lenediamine, the oxidant is sodium nitroprusside, and the oxidizable compound is pyrogallol.

References Cited by the Examiner UNITED STATES PATENTS 2,813,042 11/57 Gordon et a1. 4736.8 2,995,466 8/61 Sorensen 47-368 3,024,362 3/62 Su-s et al 4736.8 3,031,329 4/62 Winger-t 47--36.8 3,076,707 2/63 Lawton et a1. 4736.8

WILLIAM D. MARTIN, Primary Examiner.

RICHARD D. NEVIUS, MURRAY KATZ, Examiners.

Claims (1)

1. A HEAT-RESPONSIVE COPY SHEET ADAPTED TO CHANGE VISIBILY TO A CONTRASTING COLOR WHEREVER SUBJECTED TO LOCALIZED HEATING TO A TEMPERATURE BETWEEN 50* AND 150*C., COMPRISING, IN COMBINATION (A) A SUPPORTING SHEET CARRYING ON A SURFACE THEREOF A COATING COMPRISING A UNIFORMLY DISTRUBTED INITMATE ASSOCIATION OF FINELY DIVIDED PARTICLES OF (B) AN OXIDIZABLE COMPOUND SELECTED FROM THE CLASS CONSISTING OF PHENOLS AND NITROPHENOLS, (C) AN OXIDANT SELECTED FROM THE CLASS CONSISTING OF THE NITROPRUSSIDES OF COPPER, NICKEL AND SODIUM, COPPER OXALATE, POTASSIUM FERRICYANIDE, CERIC SULFATE, AND CERIC AMMONIUM SULFATE, AND (D) A SOLID, NORMALLY STABLE, CO-CRYSTAL ADDUCT COMPRISING THE REACTION PRODUCT OF AN AMINE AND AN HYDROXYPHENOL COMPOUND SELECTED FROM THE CLASS

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