GB1167670A - Microporous Sheet Structures - Google Patents

Abstract

1,167,670. Microporous coatings. FARBENFABRIKEN BAYER A.G. 29 April, 1968 [28 April, 1967], No. 20294/68. Heading B2E. [Also in Divisions B5 and C3] Microporous coatings which are permeable to water vapour are prepared by subjecting to elevated temperature with concomitant shaping sedimenting and redispersible aqueous polyurethane (urea) dispersions or pastes obtained therefrom which cointain at least the following components in solid form, (A) 65 to 99% by weight of polyurethane (urea) microgel particles which are insoluble in methyl ethyl ketone and cannot on their own form homogeneous films at temperatures below 60‹C, which particles have an average minimum diameter of 2 to 500 Á and which contain on their surface reactive groups that are capable of reacting with a component B, (B) to 35% by weight of a polyfunctional, thermoplastic polymer containing at least two groups reactive with groups at the surface of A, for every 2000 molecular weight units, and/or a compound of M.W. of not more than 2000, which compound contains at least two groups reactive with group at the surface of A. The suspensions or pastes are advantageously applied to porous supports to form coated articles or alternatively they may be applied to non-porous supports from which they may be detached. The polyurethane (urea) microgel particles (A) may be made generally by the following three methods, by cross-linking latex particles (a) after dispersion, (b) simultaneously with dispersion thereof and (c) before dispersion. Particular details of all three methods are specified. The reactive component B may be a water-soluble thermoplastic polyurethane, a water dispersible polyurethane or polyurea, derivatives of formaldehyde or a substance that reacts in a similar manner as formaldehyde, a polyfunctional alkylating agent and/or a polyacid, a polyamine or polysulphide, a polyfunctional base, or a compound containing groups reactive with olefinic double bonds. The suspensions or pastes may be applied to porous or non porous supports and solidifies at 50 to 180‹C when the particles at the same time, sinter and intermesh mechanically or undergo partial fusion of the boundary surfaces, and a chemical cross-linking reaction takes place between the boundary surfaces of the particles. The porous support, which may be a woven or non-woven textile, fibre mat, felt or fleeces including paper fleeces, foam plastic sheetings or split leather, remain as part of the finished product. The microporous sheet is usually stripped from the non-porous support which may be of metal, glass, paper, cardboard, ceramic material, sheet steel, silicone rubber or aluminium foil.