Pressure sensitive adhesive material and method of preparation

A process for preparing a water vapor permeable, pressure sensitive adhesive material, said process comprising:

• (A) forming on a silicone surface a continuous coating of an aqueous emulsion consisting essentially of a hydrophobic, acrylic, pressure sensitive adhesive copolymer and absorbed in the dispersed phase of said emulsion a water immiscible petroleum ether, which is more volatile than water and which does not break the emulsion;
• (B) maintaining said coating at a first temperature not above about 40.degree. C. to cause said petroleum ether to evaporate, thereby forming pores substantially uniformly distributed throughout said coating, and wherein said silicone surface is sufficiently non-wettable or sufficiently poorly wettable by said emulsion to thereby result in an increase in size of said pores to about 100-600 microns during said evaporation;
• (C) raising the temperature of said coating to a second temperature of at least about 60.degree. C. to dry said coating and to substantially prevent further increase in said pore size;
• and
• (D) transferring the resulting adhesive mass to a water vapor permeable backing material;
• wherein said coating, when dry, has a water vapor permeability of from 2,000 to 10,000 units.

A process for preparing a water vapor permeable, pressure sensitive adhesive material, said process comprising:

• (A) forming on a surface a continuous coating of an aqueous emulsion-based pressure sensitive adhesive having dispersed therein a water immiscible organic liquid, which is more volatile than water and which does not break the emulsion;
• (B) maintaining said coating at a first temperature not above about 40.degree. C. to cause said organic liquid to evaporate, thereby forming pores in said coating, and wherein said surface is sufficiently nonwettable or sufficiently poorly wettable by said emulsion to thereby result in an increase in size of said pores to about 30-600 microns during said evaporation;
• (C) raising the temperature of said coating to a second temperature of at least about 60.degree. C. to dry said coating and to substantially prevent further increase in said pore size;
• and
• (D) transferring the resulting adhesive mass to a water vapor permeable backing material;
• wherein said coating, when dry, has a water vapor permeability of from 2,000 to 10,000 units.