GB1483453A - Water vapour permeable sheet materials - Google Patents

Abstract

1483453 Porous composite elastomer sheet PORVAIR Ltd 25 July 1974 [25 July 1973] 35469/73 Heading B2E [Also in Division C3] A water-vapour-permeable soft flexible sheet #0.8 mm thick, has #3 superimposed porous layers of elastomeric polymer; is free from fibrous reinforcement and has elongation at break >200%; and comprises, in order, a flesh-coat layer (a), a strength-imparting substrate layer (b), and a topcoat layer (c), (b) having greater density than (a) and (c), the combined thickness of (a) and (c) being 30- 175% of the thickness of (b). (a) and (c) may adhere integrally to (b). The sheet may be made by: successively depositing coagulable elastomeric polymer composition layers (A), (B) and (C) respectively, containing removable particulate filler (F A ), (F B ), and (F C ) respectively; layer (A) being deposited on a porous support to form (a), then, prior to coagulation of (A), layer (B) is deposited on (A), and then, prior to coagulation of (A) and (B), layer (C) is deposited; the composite material is then coagulated. (F A ) and (F' C ) have mean particle size smaller than (F B ). The coagulation may be performed by contact with a non-solvent, e.g. water, and the fillers may be leached out. The filler may be NaCl or other inorganic salt. The non-solvent may comprise 0-30% solvent and 0-15% of the filler substance. Composition (B) may comprise a 25-40% wt solution of a polyurethane in a polar organic solvent (S B ) with filler (F B ) dispersed therethrough, (F B ) being insoluble in (S B ), (F B ) having average particle size 20-200 Ám, where (F B )/(F B ) polyurethane polyurethane weight ratio is from 1.8 to 2.7; and where (F A ) and (F B ) have average particles size <20 Ám. Each layer (a), (b) and (c) may be microporous, having randomlydistributed compact voids intercommunicating via pores penetrating the walls between the voids, the thickness of these walls being greater in (b) than in (a) or (c). Layer (b) may be 0.5-1.5 mm thick, have a total void volume or porosity 50-65% where #50% of the porosity is due to interconnecting pores and voids, the pores having diameter 5-100 Ám; non-interconnecting pores may have diameter 1-30 Ám, being 1-10 Ám apart, and may occur in regions the majority of which are 30-100 Ám thick between adjacent voids. Layers (a) and (c) may have voids 5-75 Ám wide, separated by walls 1-5 Ám thick having pores passing through. The polymer may be: in (b), a polyester-polyurethane, and in (a) and (c), a polyester-urethane or polyether-urethane having lower Shore hardness than that of (b): or the same polyurethane may be used for all 3 layers. The cut tear strength may be #1.5 kg, and (cut-tear strength)/stiffness may be >4.2. Topcoat (c) may be finished to form a thin densified permeable layer, #30 Ám thick, at the outer surface of (c).