GB1162215A - Improvements in Compositions and Process for Making Micriporous Bodies - Google Patents

Abstract

1,162,215. Microporous polyurethane coatings. U.S.M. CORPORATION. 20 Oct., 1966 [21 Oct., 1965], 'No. 46980/66. Heading B2E. [Also in Division C3] Substrates may be coated with. microporous polyurethanes prepared by forming an emulsion composition comprising fine droplets of a liquid dispersed in a continuous (phase which comprises reactive material readable to form a polyurethane, the liquid being substantially non-solvent for the reactive material and immiscible in the continuous phase and being present in amount from 25% to 300% by weight based on the weight of the reactive material, causing the reactive material to react at a temperature below the b.p. 'of the liquid so that the emulsion gels and solidifies, the droplets being held in the material until it solidifies sufficiently not to collapse upon removal of the droplets, and removing the liquid to leave pores and discontinuities in the solidified polyurethane. The emulsion composition may suitably be cast as a film on a surface from which it is readily strippable after solidification or alternatively a sheet of fibrous material may be laid over the cast film while the film is wet, the solidified film on being stripped from the surface forming a watervapour permeable coating adhered to the fibrous material. The emulsion composition may be spread directly to a sheet of fibrous material to form a similar coated product. The reactive material suitably comprises an organic compound containing at least two reactive -NCO groups per molecule (including a prepolymer) together with an organic compound containing at least two active hydrogen atoms, which is suitably a polyether or polyester polyol or when the prepolymer method is employed, a diamine or polyol. The continuous phase may be in the form of a solution in an organic solvent. Preferably the pore-forming liquid has a bp. of at least 100‹C and may be a liquid aliphatic hydrocarbon including petroleum hydrocarbon fractions, a liquid alkyl ether or water. Dispersion of the liquid is achieved by vigorous agitation, optionally in the presence of an emulsifying agent. The liquid is finally removed by evaporation or extraction by solvents. Surfaces which may be coated are casting surfaces e.g. glass or silicone treated paper, porous bases such as woven or non-woven fibrous sheet material, paper or felt and particularly a needled non woven fibre fabric (e.g. polypropylene) with a collagen fibre structure therein. The base may be coated with a natural or synthetic rubber or resin to control the absorption of the emulsion composition.