Patent GB-682677-A (GB)
Title: Urea-aldehyde type resin compositions containing latent curing catalysts
IPC: C08K5/00
Filed: 1949-09-02
Abstract: A thermosetting condensation product of the urea-aldehyde type which contains a latent curing catalyst is prepared by adding to a primary condensation solution of the components one or more substances which upon dissolution produce at least two protolytic systems of conjugate pairs of acids and bases, one of which systems has hydrogen peroxidisulphate ion as conjugate acid and the other at least one conjugate base capable of being decomposed and/or condensed into the resin composition when exposed to heat reaching or surpassing the melting temperature of the resin, said or another conjugate base having a pka value exceeding 9, and said substance or substances being of such kind as to regulate the pH value of the solution to between 5 and 12, and thereupon evaporating the resin solution at a temperature below the melting point of the resin until a dried product is obtained.  Specified ureas are urea itself, thiourea, dicyandiamide, and urethanes. The protolytic systems may be introduced in the form of salts of ammonium, hexamethylenetetramine, guanidine, diphenyl-biguanide, guanyl urea, tolylbiguanide and benzyl-trimethyl-ammonium-hydroxide.  Specified substances having a pka value above 9 are guanidine carbonate, guanidine formate, diphenyl guanidine, tolyl biguanide, guanyl urea, benzyl - trimethyl-ammonium-hydroxide, diethylamine, 2,3-diaminonaphthalene, methyl benzylamine, and alpha - gamma - diaminopyridine.  If desired, buffering substances having a pka value of 5 to 8.5 may be added to the condensation solution, of which the following are specified: 1,4-diaminonaphthalene; alpha - phenyl - propanol-gamma - amine; N - ethylaniline; amido - dimethylaniline; alpha - aminopyridine; betaaminopyridine; hexamethylenetetramine; paraanisidine; benzidene; l-histidine; diguanidine mono - hydrophosphate; diphenyl - guanidine - mono-hydrophosphate and benzyl-trimethyl-ammonium oleate.  The condensation products may be modified with alcohols, e.g. ethanol, propanol, butanol, glycols, glycerine and pentaerythritol.  In examples: (1) urea and formaldehyde are heated in presence of sodium hydroxide, ammonia is added to pH 8, guanidine persulphate and then alpha-cellulose added and the mixture dried; (2) urea, formaldehyde and diphenyl-guanidine are heated, diphenyl guanidine added to pH 5.0-5.2, guanidine persulphate, alpha-aminopyridine and alpha-cellulose added and the mixture dried; (3) urea and formaldehyde are heated in presence of sodium hydroxide, urea added and the mixture neutralized with ammonia.  Then sodium hydroxide, ammonium persulphate and ammonium hydroxide are added and the solution evaporated; (4) a mixture of urea, formaldehyde, alcohol, ammonium hydroxide, diphenylguanidine and urea is heated, then further urea and sulphuric acid added, the mixture heated and further diphenyl guanidine added.  Then benzyl-trimethyl-ammonium-hydroxide, diguanidine phosphate and diphenyl-guanidine persulphate are added and the solution used to impregnate paper; (5) a mixture of formaldehyde, alcohol, ammonium hydroxide and diphenyl-guanidine are heated, further urea, then formic acid and then diphenyl guanidine are added.  To this solution is added guanidine carbonate, hexamethylene tetramine and ammonium persulphate and the solution is used to impregnate paper; (6) a condensation solution is prepared as in example (5) except that the further urea is replaced by guanyl urea.  To this solution is added diphenyl-guanidine, guanidine persulphate and hexamethylene tetramine and the solution used to impregnate paper; (7) a mixture of formaldehyde, glycol, ammonium hydroxide, diphenyl-guanidine and urea are heated, sulphuric acid is added to pH 3.0-3.5, heating continued and guanidine carbonate added to pH 7.0-8.0.  To this solution is added guanidine carbonate, ammonium persulphate and alpha- or heta-aminopyridine and paper is impregnated therewith.  Specifications 545,081, 551,950, [both in Group IV (b)], and 613,957 are referred to.  The Specification as open to inspection under Sect. 91 refers to the use of sodium and potassium persulphate as latent curing catalysts and mentions acetaldehyde, benzaldehyde and furfural as suitable aldehydes.  It contains the following additional examples: (a) urea, formalin and triethanolamine are heated, hexamethylene tetramine persulphate added and the solution used to impregnate paper; (b) urea, formaldehyde and diphenyl-guanidine are heated and further diphenyl-guanidine added. To the solution is added alpha-cellulose, diphenyl-guanidine, guanidine persulphate and hexamethylene tetramine; (c) urea, formaldehyde and sodium hydroxide are heated, sulphuric acid added and the solution spray dried.  To the powder is added guanidine carbonate, ammonium carbonate and ammonium persulphate.  This subject-matter does not appear in the Specification as accepted.