Breathable, waterproof sheet materials and methods for making the same

A method of making a unitary sheet material from a polymeric material and a filler material, the method comprising the steps of:

• preparing a sheet of polymeric material, said preparing step comprising:
• melt blending to form a solution comprising a crystallizable thermoplastic polymer and a compound with which said thermoplastic polymer is miscible and in which said thermoplastic polymer will dissolve at the melting temperature of said thermoplastic polymer but which will phase separate on cooling to a temperature at or below the crystallization temperature of said thermoplastic polymer;
• forming a sheet from the melt blended solution;
• and
• cooling said sheet to a temperature at which said thermoplastic polymer crystallizes to cause phase separation to occur between said compound and said polymer, thereby providing said sheet with an aggregate of a first phase comprising particles of crystallized thermoplastic polymer in a second phase comprising said compound with adjacent thermoplastic polymer particles being distinct but having a plurality of zones of continuity;
• stretching said polymeric sheet in a first direction so as to render said sheet more microporous;
• coating said polymeric sheet, after said polymeric sheet has been stretched in the first direction, with a liquid filler material which is capable of infiltrating the micropores of said polymeric sheet;
• stretching said coated polymeric sheet, after said coating step, in a second direction so as to render said polymeric sheet more microporous, said stretching of said polymeric sheet in the second direction serving to enhance infiltration of said liquid filler material into the micropores of said polymeric sheet;
• and
• converting said liquid filler material from a liquid state to a relatively solid state.

A method of preparing a breathable, waterproof material, the method comprising the steps of:

• preparing a sheet of polymeric material, said preparing step comprising:
• melt blending to form a solution comprising a crystallizable thermoplastic polymer and a compound with which said thermoplastic polymer is miscible and in which said thermoplastic polymer will dissolve at the melting temperature of said thermoplastic polymer but which will phase separate on cooling to a temperature at or below the crystallization temperature of said thermoplastic polymer;
• forming a sheet from the melt blended solution;
• and
• cooling said sheet to a temperature at which said thermoplastic polymer crystallizes to cause phase separation to occur between said compound and said polymer, thereby providing said sheet with an aggregate of a first phase comprising particles of crystallized thermoplastic polymer in a second phase comprising said compound with adjacent thermoplastic polymer particles being distinct but having a plurality of zones of continuity;
• stretching said polymeric sheet from about 100% to about 400% in the lengthwise direction so as to render said sheet more microporous;
• coating said polymeric sheet, after said polymeric sheet has been stretched in the lengthwise direction, with a liquid filler material which can be cured to form a solid hydrophilic material which is water vapor permeable and liquid water impermeable, said liquid filler material being capable of substantially filling the micropores of said polymeric sheet;
• stretching said coated polymeric sheet, after said coating step, from about 100% to about 400% in the transverse direction so as to render said polymeric sheet more microporous, said stretching of said polymeric sheet in the transverse direction serving to significantly enhance infiltration of said liquid filler material into the micropores of said polymeric sheet;
• and
• converting said liquid filler material into said solid hydrophilic material by heating said infiltrated polymeric sheet to a temperature and for a period of time sufficient to completely cure said filler material.