Coated flexible sheet materials

Abstract

Abstract A coating for a flexible sheet material comprises a blown layer of a polyisocyanate-modified polyester. The polyester, which may be prepared from adipic acid, hexane-triol, and butylene glycol in various molar proportions, may be reacted with toluylene or hexamethylene diisocyanate or a triisocyanate obtained by reacting one of these with hexane-triol. The blown layer of polyisocyanate-modified polyester is formed from a mixture containing the polyester, the polyisocyanate, and a small amount of water, or of a material which will deliver its water content when a certain temperature is reached, e.g. silica gel or crystallized organic or inorganic salts containing water, e.g. aluminium sulphate. The silica gel or the crystals may be coated with paraffin, dodecyl amine, or synthetic wax to inhibit premature release of water. The velocity of the reaction between the polyester and the polyisocyanate may be retarded by adding plasticized polyvinyl chloride. Pigments such as titanium dioxide, cadmium or iron oxides and solvents such as ethyl and butyl acetate may be added. Examples 5 and 6 describe further porous layers made from a polyisocyanate-modified polyester composition in which finely-ground sodium chloride or sulphate has been incorporated. The soluble salt is removed by washing with water after the layer has dried. Example 6 describes a coating of polyvinyl chloride plasticized with dioctyl phthalate made porous by the addition, and subsequent reaction on heating, of a mixture of equal parts of tetramethylene dinitroso dimethyl urethane and dicyano diamide oxalate.

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