Patent GB-752171-A (GB)
Title: Improvements in method of making articles by dipping
IPC: B29C41/14
Filed: 1954-08-17
Abstract: An intermediate product obtained by reacting a linear hydroxy terminated polyester with a 20-250 per cent molar excess of a diisocyanate is cured by reaction with a diprimary diamine.  The modified polyester is applied in solution in an inert volatile solvent to a moulding former (see Group V) and the diamine applied subse quently as previously or both.  The resulting polyurethane is insoluble and the solvent evaporates.  In an example a former was dipped at room temperature in a solution of polyester - diisocyanate intermediate derived from a polyester made by heating, at 220-230 DEG C., a mixture of propylene glycol (11 mols.), ethylene glycol (4.25 mols.) and adipic acid (11.25 mols.). Unreacted glycol was removed by vacuum distillation.  The resulting alkyd was mixed at a temperature of 85 DEG C. with an excess of p,p1-diphenylmethane diisocyanate in the proportions of 80 parts polyester to 20 parts diisocyanate resulting in a polyurethane intermediate characterized by the presence of unreacted isocyanate groups.  A former was dipped in a solution of the polyester-diisocyanate intermediate in acetone.  The former, covered with a film of the solution, was then dipped in a 5 per cent solution of 4,41-diamino diphenylmethane in methyl isobutyl ketone, and when the former was removed the diprimary diamine had cured the polyester-diisocyanate to a nontacky state.  The dipping cycle was repeated until a thickness of 0.002 in. had been deposited. In this example the former was subsequently partly dipped in a solution of polyester-diisocyanate intermediate coloured with molybdate orange pigment paste.ALSO:A method of making a dipped article of polymethane elastomer comprises the steps of (i) dipping a moulding former into a normally tacky liquid polyester-diisocyanate intermediate reaction product (see Group IV(a)) containing unreacted isocyanate groups to deposit a thin film of the intermediate reaction product on the former (ii) treating the film on the former with a diprimary diamine to convert the film into a solid non-tacky cured condition (iii) stripping the resulting polymethane article from the former.  Any suitable inert, volatile, organic liquid may be used as a solvent for the materials, e.g. the polyester-diisocyanate may be dissolved in acetone and the diprimary diamine in methyl isobutyl ketone.  The polyurethane formed at the end of the dipping process is insoluble in the solvent which therefore evaporates.  The former may be dipped first in the polyester-diisocyanate solution and then in the diamine, or in the reverse order; advantageously there are several alternate dippings.  Further partial dippings result in a product with a greater thickness in one part, which may be coloured if a pigment paste is added to the polyester-diisocyanate solution. The surface of the dipping former must be of a material uniformly wet by the polyester-diisocyanate solution; polished chromium is suitable, but the preferred material is plasticized polyvinyl chloride, of which the whole core may consist or which may be deposited on a core of e.g. aluminium by applying a fluid plastisol and heating.  The former is preferably pre-heated if the solution of the polyester-diisocyanate is concentrated.  By regulating the temperature and degree of concentration the thickness of the deposited film may be controlled.  For a single dip it is of the order .001-.002 in.  A thickness of .002 in. is sufficient for the material of an overshoe, if the lower area of the shoe is given a thickness of .012-.014 in. by further partial dipping.  The curing may be accelerated by placing the former, after dipping in the solution of diprimary diamine, in a heated chamber.  An air jet may be used to assist in stripping the article from the former, and the article may then be left for ageing for about seven days.  Gloves and easily-portable overshoes are readily produced by the invention, and the amount of material may be so small that the articles are cheap enough to be used once only.