Patent GB-1103833-A (GB)
Title: Improvements in and relating to the production of supported or unsupported flexible microporous films
Inventor: CHEZAUD JEAN CLAUDE
IPC: C09D175/04
Filed: 1965-05-13
Abstract: Polyurethane polymer powders containing a minor proportion of a blocked isocyanate, and useful for making microporous polyurethane films, may be formed by mixing the polymer and blocked isocyanate in powder form, or adding the blocked isocyanate to a polyurethane solution and precipitating the polyurethane. Alternatively a compound containing an active hydrogen atom may be added to a solution containing a polyurethane comprising terminal, isocyanate groups in an amount such as to form, after reaction, a polyurethane containing a minor proportion of a blocked isocyanate.  In the examples powders comprising a polyester polyurethane prepared from ethylene glycol polyadipate, 1,4 - bis - (hydroxymethyl cyclohexane, and n-hexane-1,6-diisocyanate and (2) tolylene diisocyanate blocked with e -caprolactam, (3) diphenylmethane-4,41-diisocyanate blocked with phenol are prepared.  The powders may be deposited on a support as a continuous layer which is sintered under heat and pressure to liberate the isocyanate and convert the layer into a porous film which may then be removed from the support.ALSO:Supported or unsupported flexible microporous film permeable to air and water vapour but impermeable to liquid water is produced by depositing on a support a layer of a powder comprising a major proportion of a powdered thermoplastic linear polyurethane having a modulus of elasticity less than 5kg/mm2.  The a minor proportion of a blocked isocyanate, and sintering the said layer by the action of heat and pressure under conditions such as to liberate the blocked isocyanate. The support may be a microporous sheet, e.g. a non-woven fibrous layer made from fibres shrunk in situ and impregnated with a binder having a modulus of elasticity less than 5Kg/mm2.  The support may be non-adherent to the sintered powder layer, e.g. a non-adherent textile, polished metal, or glass, in which case the sintered layer is removed from the support and, preferably, then bonded to a non-woven fibrous layer.  The support may be first coated with a swelling agent for the binder and the polymer in the powder.  The preparation of polyurethane polymer powders containing blocked isocyanate is described (see Division C3).  A minor proportion of a powder of another synthetic linear polymer with a modulus of elasticity less than 5 Kg/mm2 may be added, e.g. polyvinyl chloride powder to improve the mechanical properties of the sintered layer, such as resistance to abrasion.  The powder may be doctored or sprinkled through a screen on to the support, and agglomerated with a calender or a press, the rollers or plates of which are heated, or the heat and pressure may be applied separately.  The sintered layer may be further coated with a microporous film, e.g. by applying a prepared microporous film to the powder layer and uniting the assembly by heat and pressure. In the Examples (1) a polyurethane powder C is applied to a sheet A of non-woven polyethylene terephthalate fibres shrunk in situ and impregnated with a polyester polyurethane B, the sheet being abraded on both faces; (2) a mixture of C and tolylene diiocyanate blocked with e -caprolactam is applied to A; (3) a mixture of C and diphenylmethane-4,4\sv-diisocyanate blocked with phenol is applied to an abraded face of A previously sprayed with a solution of triphenylmethane triisocyanato; (4) the aforesaid mixture is applied to a cotton fibre and the sintered film stripped off and applied to A the surface of which is coated with an adhesive mixture comprising a polyurethane elastomer consisting of an isocyanate-modified polyester precondensate, and a condensate of tolylene diisocyanate and trimethylolpropane, the assembly being calendered.  The products can be used as replacements for leather and may be subjected to finishing treatments such as dyeing, brushing, varnishing.  They may be used to manufacture shoe uppers.