Microcellular foams of semi-crystaline polymeric materials
AssigneeMassachusetts Institute of Technology
InventorsJonathan S. Colton, Nam P. Suh
Life of this patent
Estimating the term…
Abstract
A method for producing microcellular foam from a semi-crystalline polymeric material. The material is heated to its melting point at an elevated pressure and then saturated with a uniform concentration of a gas. The pressure is then lowered causing bubble nucleation and growth within the material. The material is then quenched to prevent further foaming. Bubbles on the order of 5 .mu.m in diameter are produced with a bubble density of approximately 10.sup.10 bubbles/cm.sup.3.
Claims11
A method of producing a foamed semi-crystalline polymeric material containing uniform closed-cell microcellular voids, comprising the steps, performed in the following sequence, of:
- a) first, heating a semi-crystalline polymeric material to a temperature at or above the melting temperature of the material to thereby melt the polymeric material;
- b) second, saturating the melted polymeric material at an elevated pressure at or above the melting temperature with a uniform concentration of gas;
- c) third, shaping the gas saturated polymeric material in a cavity, mold or die at an elevated pressure to substantially prevent cell nucleation within the material;
- d) fourth, initiating uniform bubble formation in the shaped polymeric material, in the absence of sonic vibrations, by reducing the pressure and supersaturating the shaped polymeric material with gas resulting in a uniform nucleated shaped polymeric material having closed-cell, microcellular voids of below about 100 microns in diameter in said polymeric material;
- and
- e) fifth, lowering the temperature below the melting point of said polymeric material to prevent further cell growth.
A method of producing a foamed semi-crystalline polymeric material containing uniform closed-cell microcellular voids, comprising the steps, performed in the following sequence, of:
- a) first, heating a semi-crystalline polymeric material selected from the group consisting of polyethylene, polypropylene and copolymers thereof, to a temperature at or above the melting temperature of the material to thereby melt the polymeric material;
- b) second, saturating the melted polymeric material with a uniform concentration of gas at an elevated pressure between approximately 750 psig and 2500 psig;
- c) third, shaping the gas saturated polymeric material in a cavity, mold or die at the elevated pressure to substantially prevent cell nucleation within the material;
- d) fourth, initiating uniform bubble formation in the shaped polymeric material, in the absence of sonic vibrations, by reducing the pressure and supersaturating the shaped polymeric material with gas resulting in a uniform nucleated shaped polymeric material having closed-cell, microcellular voids of below about 100 microns in diameter in said polymeric material;
- and
- e) fifth, lowering the temperature below the melting point of said polymeric material to prevent further cell growth.
Dependencies are inferred from the claim text.