Microporous material having a coating of hydrophobic polymer

A method for forming a coated article which is substantially impermeable to liquid water and permeable to moisture vapor, said method comprising:

• (a) applying an aqueous emulsion comprising droplets of emulsified crosslinkable polymer to one side of a sheet of microporous material having generally opposing sides, said microporous material comprising:
• (1) a matrix consisting essentially of essentially linear ultrahigh molecular weight polyolefin which is essentially linear ultrahigh molecular weight polyethylene having an intrinsic viscosity of at least about 18 deciliters/gram, essentially linear ultrahigh molecular weight polypropylene having an intrinsic viscosity of at least about 6 deciliters/gram, or a mixture thereof;
• said matrix comprising regions of stretch-induced molecularly oriented ultrahigh molecular weight polyolefin distributed throughout said matrix,
• (2) finely divided particulate substantially water-insoluble filler, of which at least about 50 percent by weight is siliceous, distributed throughout said matrix, said filler constituting from about 50 percent to about 90 percent by weight of said microporous material, and
• (3) a network of interconnecting pores communicating throughout said microporous material, said pores on a coating-free and impregnant-free basis constituting more than 70 percent by volume of said microporous material;
• and
• (b) removing water from said applied emulsion to cause said droplets to coalesce and to form a substantially continuous coating of said crosslinkable polymer on said one side of said microporous material;
• and
• (c) crosslinking said polymer of said coating to provide a substantially continuous, moisture vapor permeable coating of hydrophobic network polymer joined to said one side of said microporous material, said substantially continuous, moisture vapor permeable coating being an elatomeric solid at ambient temperatures.

A coated article which is substantially impermeable to liquid water and permeable to moisture vapor, said article comprising:

• (a) a sheet of microporous material having generally opposing sides, said microporous material comprising:
• (1) a matrix consisting essentially of essentially linear ultrahigh molecular weight polyolefin which is essentially linear ultrahigh molecular weight polyethylene having an intrinsic viscosity of at least about 18 deciliters/gram, essentially linear ultrahigh molecular weight polypropylene having an intrinsic viscosity of at least about 6 deciliters/gram, or a mixture thereof,
• (2) finely divided particulate substantially water-insoluble filler, of which at least about 50 percent by weight is siliceous, distributed throughout said matrix, said filler constituting from about 50 percent to about 90 percent by weight of said microporous material, and
• (3) a network of interconnecting pores communicating throughout said microporous material, said pores on a coating-free and impregnant-free basis constituting from about 35 percent to about 80 percent by volume of said microporous material;
• and
• (b) a substantially continuous, moisture vapor permeable coating of hydrophobic polymer joined to one side of said microporous material, said coating being an elastomeric solid at ambient temperatures.