Microcellular closed cell foams and their method of manufacture
AssigneeMassachusetts Institute of Technology
InventorsJane E. Martini-Vvedensky, Nam P. Suh, Francis A. Waldman
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Abstract
Microcellular foam materials having void fractions of about 5 to 30 percent and uniform void sizes on the order of 2 to 25 microns are produced by pre-saturating the material to be processed with a uniform concentration of a gas while controlling temperature and pressure to avoid cell nucleation. Processing is also done under pressure to avoid nucleation. After processing, pressure is released and cell nucleation occurs at or near the glass transition temperature of the material; it is then cooled quickly to preserve the microcellular structure.
Claims25
A method for producing closed cell, microcellular-foamed structures in pre-formed polymeric materials, the method comprising:
- (a) saturating the material at an elevated pressure between about 1 cc (STP)/gram and about 4 cc (STP)/gram with a uniform concentration of a non-reactive gas;
- (b) heating the material to its glass transition temperature;
- (c) reducing the pressure to a state where the material is super-saturated with gas and a very large number of cells are nucleated;
- and
- (d) rapidly dropping the temperature of the material to prevent cell growth, whereby a foamed polymeric material having voids on the order of about 2 to 25 microns is produced.
A microcellular foam material formed by saturating a polymeric material at about its glass transition temperature with a uniform concentration of a gas, reducing the pressure, and then cooling the material, thereby controlling the nucleation of cells within the material, the material being characterized by uniformaly packed, closed cells ranging in size from about 2 microns to 25 microns and having a void fraction of about 5 to 30 percent.
A method of processing polymeric materials to produce closed cell, microcellular foams, the method comprising:
- (a) saturating the material at an elevated pressure and at a temperature below the glass transition temperature of the material with a uniform concentration of gas;
- (b) heating the material to a molten state to render it processable;
- (c) shaping the material at an elevated pressure sufficiently high to prevent cell nucleation within the material
- (d) reducing the temperature and pressure to a state where the material is super-saturated with gas and a very large number of cells are nucleated;
- and
- (e) rapidly dropping the temperature of the material after nucleation has occurred to prevent cell growth, whereby a foamed polymeric material having voids on the order of about 2 to to 25 microns is produced.
Dependencies are inferred from the claim text.