Microporous materials and methods of making the same
Assignee3M Innovative Properties Company
InventorsShannon Kay Hughes, Robert Steven Kody, James Stephen Mrozinski, Myles Lee Brostrom
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Abstract
Microporous materials and articles are disclosed. The microporous materials contain a crystallizable propylene-containing polymer, a beta-nucleating agent, and a diluent that is miscible with the polymer at a temperature above the melting temperature of the polymer and that phase separates from the polymer at a temperature below the polymer crystallization temperature. The invention is also directed to methods of forming the microporous material using thermal induced phase separation and subsequent processing.
Claims18
A microporous material comprising:
- a crystallizable propylene-containing polymer;
- a beta-nucleating agent;
- and
- a diluent that is miscible with the polymer at a temperature above the melting temperature of the polymer and that phase separates from the polymer at a temperature below the polymer crystallization temperature.
A microporous polymeric material, the material prepared by:
- (a) forming a melt solution comprising a crystallizable propylene-containing polymer, a beta-nucleating agent, and a diluent;
- wherein the diluent is miscible with the polymer at a temperature above the melt temperature of the polymer but phase separates from the polymer when cooled below the crystallization temperature of the polymer;
- (b) cooling the melt solution to a temperature where phase separation occurs by crystallization precipitation of the polymer component to form a phase comprising network of polymer particles connected to each other by tie fibrils and a diluent phase;
- and
- (c) creating interconnected micropores by either orienting the material in at least one direction to separate adjacent crystallized polymer particles from one another, or by removing at least a portion of the diluent from the material.
A method of making a microporous article, comprising the steps of:
- (a) melt blending to form a mixture comprising:
- (i) about 30 to about 80 parts by weight of crystallizable propylene-containing polymer,
- (ii) a sufficient amount of a beta-nucleating agent to initiate subsequent nucleation of crystals of the propylene-containing polymer at a significantly greater number of crystallization sites as compared to crystallization without a nucleating agent, and
- (iii) about 20 to about 70 parts by weight of a diluent with which the propylene-containing polymer is miscible and into which the propylene-containing polymer will dissolve at the melting temperature of the propylene-containing polymer but from which the propylene-containing polymer will phase separate on cooling to a temperature at or below the crystallization temperature of the propylene-containing polymer;
- (b) shaping the melt blended mixture;
- (c) cooling the shaped mixture to a temperature at which the beta-nucleating agent initiates crystallization within the propylene-containing polymer so as to cause phase separation between the diluent and polymer particles connected to each other by tie fibrils, thereby providing an article comprising an aggregate of crystallized propylene-containing polymer in the diluent;
- and
- (d) increasing the porosity of the article by one or both of stretching the shaped article in at least one direction and removing at least a part of the diluent.
A microporous article comprising:
- a microporous material containing a crystallizable propylene-containing polymer, a beta-nucleating agent, and a diluent that is miscible with the polymer at a temperature above the melting temperature of the polymer and that phase separates from the polymer at a temperature below the polymer crystallization temperature;
- and
- a substrate on which the microporous material is deposited.
Dependencies are inferred from the claim text.