Patent GB-1061655-A (GB)
Title: Water vapour permeable polyurethane films
IPC: B29C44/00
Filed: 1963-12-18
Abstract: Microporous polyurethane film permeable to water vapour is made by forming a film between 2 and 15 mils. in thickness from an intimate uniform mixture of 100 parts by weight of a polyesterurethane prepared as described in Specification 849,136 or a polyalkyleneether-urethane prepared as described in Specification 852,357 and 100 to 300 parts by weight of a finely divided solid chemical compound stable at atmospheric temperatures but capable of becoming completely decomposed at temperatures below 130 DEG  C. with formation of one or more gases to which the film is permeable without damage or the formation of pores visible to the naked eye, and heating the film at a temperature above the decomposition temperature of the compound at but not above 130 DEG C. until evolution of the gas or gases has ceased.  The gas-forming substance may be ammonium carbonate or ammonium bicarbonate passing through a 270 mesh A.S.T.M. screen. The mixture may contain a volatile organic solvent for the polyurethane.  The polyesterurethane films employed in the invention are permeable, in thicknesses from 4-15 mils., to gaseous ammonia, hydrogen and carbon dioxide, but impermeable to air, oxygen and nitrogen.  In an example, a 25% by weight solution of a polyesterurethane in tetrahydrofuran is made up and 100 parts of finely divided ammonium carbonate per 100 parts of polymer are uniformly mixed into the solution.  The solution is extruded through a 2 mil. gap slot on to cellophane to form a film 2 mils. thick which is then stripped from the cellophane.  In another example the solution is spread in a layer on a non-woven fabric 18 mils. thick made by the conventional wet paper process, and the solvent evaporated off, leaving a film coating 6 mils. thick in the non-woven fabric.  The lower side of the latter is mounted in a non-woven layer of polypropylene, 3 denier, random web, cross-laid and needled, 72 mils. thick to give an over-all sheet thickness of 78 mils.  Four sample portions of the composite fabric are heated at temperatures ranging from 100 DEG  to 130 DEG  C. to drive off the ammonium bicarbonate and render the polyurethane film portion of the composite fabric permeable to water vapour.  Films made microporous by the process of the invention are readily combined with various non-woven fabric base stratums to form leather substitutes for shoe uppers and other articles of wearing apparel.ALSO:Microporous polyurethane film permeable to water vapour is made by forming a film between 2 and 15 mls. in thickness from an intimate mixture of 100 parts by weight of a polyesterurethane or a polyalkylemetheurethane and 100 to 300 parts by weight of a finely divided solid chemical compound stable at atmospheric temperatures but capable of becoming completely decomposed at temperatures below 130 DEG C. with formation of one or more gases to which the film is permeable without damage or the formation of pores visible to the naked eye, and heating the film at a temperature above the decomposition temperature of the chemical compound but not above 130 DEG C. until evolution of the gas or gases has ceased.  The gas-forming substance may be ammonium carbonate or ammonium bicarbonate passing through a 270 mesh ASTM screen. The mixture may contain a volatile polyurethane solvent.  The preparation of the particular polyesterurethanes employed is described in Specification 849,136 and the preparation of the particular polyalkyleneetherurethane which may alternatively be employed is described in Specification 852,357.  The polyesterurethane films employed in the invention are permeable, in thicknesses from 4-15 mils, to gaseous ammonia, hydrogen and carbon dioxide, but impermeable to air, oxygen and nitrogen.  In an example, a 25% by weight solution of a polyesterurethane in tetrahydrofuran is made up and 100 parts of finely divided ammonium carbonate per 100 parts of polymer are uniformly mixed into the solution.  The solution is extruded on to cellophane to form a film 2 mil. thick which is then stripped from the cellophane.  In another example the solution spread in a layer on a non-woven cellulose fabric 18 mils. thick made by the conventional wet paper process, and the solvent evaporated off, leaving a film coating 6 mils. thick in the non-woven fabric.  The lower side of the latter is mounted in a non-woven layer of polypropylene, 3 denier, random web, cross laid and needled, 72 mils. thick to give an over-all sheet thickness of 78 mils.  Four sample portions of the composite fabric are heated at temperatures ranging from 100 to 130 DEG C. to drive off the ammonium bicarbonate and render the polyurethane film portion of the composite fabric permeable to water vapour.  Films made microporous by the process of the invention are readily combined with various non-woven fabric base stratums to form leather substitutes for shoe uppers and other articles of wearing apparel.