Method of making water vapor permeable polymer sheet material

Claim 1

A method of making a water vapor permeable polymer sheet material which comprises forming an initial mixture comprising elastomeric thermoplastic polyurethane dissolved in dimethylformamide with microscopic water soluble inorganic salt particles dispersed through the mixture, forming a layer at least 0.5 mm thick of the initial mixture in adherence with an endless porous fabric belt, passing the layer in adherence with said belt into contact with a body of coagulating liquid which is a solvent for said salt while the free surface of said layer is uppermost and has coagulating liquid on and over it and while said layer and belt are so supported as to prevent said layer adhered to said belt from assuming a concave transverse configuration, said layer being in contact with said body for a time sufficient to partially coagulate said layer, said layer adhering to and becoming keyed to said belt, bringing said partially coagulated layer on said belt into contact, with said free surface lowermost, with a second body of coagulating liquid non-solvent which is a solvent for said salt, said belt and layer passing through said second body until said layer is coagulated to self-supporting condition, and then stripping said self-supporting layer in sheet form from said belt, said second body of liquid being situated under said first body of liquid, said layer and belt being transferred from said first body to said second body by leading said belt carrying said adhering layer around guide means in a manner such that said free surface is held out of contact with said guide means and is prevented from assuming a concave transverse configuration.

Claim 2

A method of making a water vapor permeable polymer sheet material which comprises forming an initial mixture comprising elastomeric thermoplastic polyurethane dissolved in dimethylformamide with microscopic water soluble inorganic salt particles dispersed through the mixture, forming a layer at least 0.5 mm thick of the initial mixture in adherence with an endless porous fabric belt, passing the layer in adherence with said belt into contact with a body of coagulating liquid which is a solvent for said salt while the free surface of said layer is uppermost and has coagulating liquid on and over it and while said layer and belt are so supported as to prevent said layer adhered to said belt from assuming a concave transverse configuration, said layer being in contact with said body for a time sufficient to partially coagulate said layer, said layer adhering to and becoming keyed to said belt, bringing said partially coagulated layer on said belt into contact, with said free surface lowermost, with a second body of coagulating liquid non-solvent which is a solvent for said salt, said belt and layer passing through said second body until said layer is coagulated to self-supporting condition, and then stripping said self-supporting layer in sheet form from said belt, said second body of liquid being situated under said first body of liquid, said layer and belt being transferred from said first body to said second body by leading said belt carrying said adhering layer around guide means in a manner such that said free surface is held out of contact with said guide means and is prevented from assuming a concave transverse configuration.