GB809180A - Improvements in the manufacture of polyurethane foam sheets - Google Patents

Abstract

A method of making a sheet of polyurethane foam of substantially open-cell structure from a liquid mixture which forms such a foam by gas expansion to a fluid foam and subsequent gelation to a solid foam, comprises supporting said mixture during at least a part of the expansion while the mixture is fluid and during gelation on the surface of a carrier liquid while confining the mixture to a predetermined area on the surface. The materials for forming the foam comprise a polyetherglycol or an alkyd polyester having predominantly alcoholic end groups and an acid number less than 3.0 and a liquid organic diisocyanate together with water, foam stabilizer and a catalytic amount of a tertiary amine. The carrier liquid must not be a solvent or a swelling agent for the foam-forming mixture or the polyurethane, and the foam must spread on the surface of the liquid (i.e. the surface tension of the carrier liquid must be greater than the sum of the surface tension of the foam-forming mixture and the interfacial tension between the carrier liquid and the foamforming mixture). The density of the carrier may be greater or less than that of the foamforming mixture. The liquid preferably is volatile enough to evaporate rapidly below 100 DEG C. The preferred carrier liquid is water. Glycerine, fluid silicones, glycol and mineral oil are also suitable. In examples (1) and (2) a mixture of diisocyanate-polyether adduct (from 4.4 mols. of tolylene diisocyanate and one mol. of polypropylene ether glycol of m. wt. 2000), polydimethylsiloxane (foam stabilizer), diethyl cyclohexylamine and water, is stirred and run into a body of water in a tray. The mixture which at first sinks, rises when expansion begins to cover the surface of water with foam which gels and cures on standing; (3) a similar process is applied to a mixture of an adipic acid/diethylene glycol/trimethylolethane polyester, tolylene diisocyanate, polyoxyethylated vegetable oil, N-methylmorpholine and water; (4) glycerine and (5) silicone fluid are used as carrier liquids for the reaction mixture such as is used in Example (3).