US 6,080,798 AGranted

Manufacturing foams by stress-induced nucleation

OwnerPaul Handa, Zhiyi Zhanginventors

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Abstract

The invention disclosed provides a method for inducing nucleation in a polymer by subjecting the polymer containing dissolved gas to an external stress generated, for example, by applying hydrostatic or mechanical pressure. The applied stress restricts the bubble growth so that the foamed materials have small cells and high cell density. Such microcellular foams can be produced over a wide low temperature range, i.e. from the temperature at which the polymer is conditioned with the blowing agent up to about the glass transition temperature of the polymer-blowing agent system. Stress induced nucleation can also be conducted at higher temperatures i.e. up to about the T.sub.g of the neat polymer, leading to foams with larger cells. A variety of homogeneous and heterogeneous foams can be produced by this technique.

Claims17

Dependent claims

A method for producing a closed cell polymer foam, comprising

(a) selecting a suitable polymer and inert blowing agent combination, wherein the polymer is in a solid or melt state, and the blowing agent is in the form of a gas or a volatile liquid,
(b) exposing the polymer to the blowing agent in the gas or liquid state at a conditioning temperature, pressure and exposure time, selected according to the thermodynamic properties of the polymer/blowing agent combination to provide a polymer/blowing agent solution having a desired solubility up to a maximum of saturation solubility of the blowing agent in the polymer,
(c) slowly depressurizing the polymer/blowing agent solution to ambient pressure to prevent premature foam formation,
(d) applying an external compressive stress to the polymer-blowing agent solution at a temperature at which the polymer is conditioned with the blowing agent up to about the T.sub.g of the neat polymer, wherein the amount of stress applied is dependent upon the thermodynamic properties of the polymer/blowing agent combination and the amount of blowing agent dissolved in the polymer, to induce cell nucleation and foam formation, and
(e) quenching the foam by rapid cooling to a lower temperature.

2 more elements

Dependencies are inferred from the claim text.