Patent GB-962545-A (GB)
Title: Improved thermographic copy-sheets
IPC: G03C1/54
Filed: 1960-08-08
Abstract: 962, 545. Thermographic copy sheets. MINNESOTA MINING & MANUFACTURING CO. Aug. 8, 1960 [Aug. 7, 1959], No. 27414/60. Heading G2C. A thermographic copy sheet includes a visibly heat-sensitive layer containing in intimate association (1) weakly coloured solid non-hygroscopic non-volatile inter-reactant formers of intensely coloured organic compounds containing as an essential chromophore doubly bonded nitrogen, one of the inter-reactants being convertible by acid conditions to a modification which under acid conditions rapidly and visibly reacts irreversibly with another of the reactants, and (2) an acidcondition producing substance stable under normal storage which liberates a Lewis acid on being heated to 90 to 150‹C. Specific classes of acid-producing substances are diazonium salts such as fluoborates and hexafluorophosphates, several examples of which are given, and organic halogen compounds which react with aqueous alcoholic silver nitrate to form silver halide. Examples 1, 2, 3 relate to the formation of oxazine dyes. Example 4 involves forming azo dyes from azenes, while Example 5 is concerned with the formation of a Schiff's base colour body. In Example 1, a transparent polyester support is coated with a ball milled mixture of polystyrene and p-N-methylacetylamino-benzene diaxonium fluoborate in acetone and over the dried coating is applied a coating of a mixture of two separately ball milled dispersions in dioxane of a polycarbonate resin and respectively 3-methyl-4-nitrosophenol and gallic acid. To provide an off white background for the greenish black image formed by exposure to heat, an overcoat of butadienestyrene copolymer containing titanium dioxide may be used. Alternative reactants are 2-hydroxy- 3-methyl-5-nitrosobenzoic acid and gallic acid or resorcinol; nitrosothymol and gallic acid, 3- hydroxy-2-naphthoic acid or #-naphthol; andpnitrosobenzoic acid and gallic acid. In Example 2, tracing paper is given a single coating of a mixture of separately ball milled n-butyl methylacrylate resin in acetone dispersions respectively of N-carbethoxy-p-nitrosodiphenylamine and of gallic acid or 3-hydroxy-2-naphthoic acid and (3-chlorophenyl) benzene. In Example 3, a similar dark blue or blue-black image forming sheet is produced by coating tracing paper with a blended mixture of separate dispersions in ethyl cellulose in an acetone-heptane solvent mixture of N-nitrosodiphenylamine or N-nitrosophenylbenzylamine and of protocatechuic acid and α-naphthoyl chloride. In Example 4, a transparent polyester support is first coated with a dispersion of p-aminoacetanilide benzenediazonium fluoborate in a methylcyclohexane solution of an isobutylene-styrene resin and the dried coating is overcoated with a mixture of polystyrene in acetone dispersions of 3: 3<SP>1</SP>-dimethoxy-4 : 4<SP>1</SP>-diphenylene-bis-(3<SP>11</SP>- methyl-3<SP>11</SP>-phenyl-1<SP>11</SP>-triazene) and of Napthol AS-Supra, an arylamide of 3-hydroxy-2-naphthoic acid. A large number of other triazenes are mentioned as suitable reactants, as are also 3- phenyl-4-oxo-3 : 4-dihydro-1: 2: 3-benzotriazine and 4-hydroxy-1 : 2: 3-naphthotriazine, while aromatic amine and active methylene group azo couplers may also be used. In Example 5 the acetal binder serves also as one of the reactants. A transparent web is coated with an ethanol dispersion of α-chlorophenylacetate, polyvinyl formal or butyral, and p-aminoacetanilide, p -amino-N-methylacetanilide, dodecylamine, or p-phenylenediamine. An opacifying overcoat of a butadiene-styrene copolymer containing titanium dioxide may be applied The Specification also states without giving examples that the polymeric binder may be applied in monomeric or incompletely polymerized form and polymerized in situ and that the heat-sensitive reactants may be incorporated into the body of the supporting web.