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US 4,539,256 AGranted
Microporous sheet material, method of making and articles made therewith
AssigneeMinnesota Mining and Manufacturing Company
InventorGene H. Shipman
Life of this patent
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AssigneeMinnesota Mining and Manufacturing Company
InventorGene H. Shipman
Estimating the term…
A method of making a microporous material is provided which comprises the steps of melt blending crystallizable thermoplastic polymer with a compound which is miscible with the thermoplastic polymer at the melting temperature of the polymer but phase separates on cooling at or below the crystallization temperature of the polymer, forming a shaped article of the melt blend, cooling the shaped article to a temperature at which the polymer crystallizes to cause phase separation to occur between the thermoplastic polymer and the compound to provide an article comprising a first phase comprising particles of crystallized thermoplastic polymer in a second phase of said compound, orienting the article in at least one direction to provide a network of interconnected micropores throughout. The microporous article comprises about 30 to 80 parts by weight crystallizable thermoplastic polymer and about 70 to 20 parts by weight of the compound. The oriented article has a microporous structure characterized by a multiplicity of spaced randomly dispersed, equiaxed, non-uniform shaped particles of the thermoplastic polymer which are coated with the compound. Adjacent thermoplastic particles within the article are connected to each other by a plurality of fibrils consisting of the thermoplastic polymer. The fibrils radiate in three dimensions from each particle. The compound may be removed from the sheet article. e.g., by solvent extraction. The preferred article is a sheet material.
A method of making a microporous article, comprising:
A microporous material comprising about 30 to 80 parts by weight of crystallizable thermoplastic polymer and about 70 to 20 parts by weight of 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 will phase separate on cooling to a temperature at or below the crystallization temperature of said thermoplastic polymer, said microporous material having an internal structure characterized by a multiplicity of spaced, randomly dispersed, non-uniform shaped, equiaxed particles of said thermoplastic polymer coated with said compound, adjacent coated particles throughout said material being separated from one another to provide said material with a network of interconnected micropores and said adjacent thermoplastic polymer particles being connected to each other by a plurality of fibrils consisting of said thermoplastic polymer.
A microporous material comprising crystallizable thermoplastic polymer, said microporous material having an internal structure characterized by a multiplicity of spaced, randomly disposed, non-uniform shaped, equiaxed particles of said thermoplastic polymer, adjacent particles throughout said material being separated from one another to provide said material with a network of interconnected micropores and being connected to each other by a plurality of fibrils consisting of said thermoplastic polymer.
A sheet material having a microporous structure extending to one major surface characterized by a multiplicity of spaced, randomly disposed, non-uniform shaped, equiaxed particles of thermoplastic polymer, adjacent particles throughout said microporous structure being separated from one another to provide said microporous structure with a network of interconnected micropores and being connected to each other by a plurality of fibrils consisting of said thermoplastic polymer and an opposite major surface comprised of said polymer but not having said microporous structure.
Dependencies are inferred from the claim text.