Heat-resistant polymer foam, process for producing the same, and foam substrate

Abstract

A heat-resistant polymer foam is disclosed which has excellent heat resistance, a fine cellular structure, and a low apparent density. The heat-resistant polymer foam comprises a heat-resistant polymer having a glass transition point of 120° C. or higher, e.g., a polyimide or polyether imide, and has an average cell diameter of from 0.01 μm to less than 10 μm. This heat-resistant polymer foam can be produced by, for example, impregnating a heat-resistant polymer under pressure with an non-reactive gas such as carbon dioxide, which is in, e.g., a supercritical state, reducing the pressure, and then heating the polymer at a temperature exceeding 120° C. to foam the polymer.

What is claimed is:  
     
         1 . A heat-resistant polymer foam comprising a heat-resistant polymer, said foam having an average cell diameter of from 0.01 μm to less than 10 μm.  
     
     
         2 . The heat-resistant polymer foam as claimed in    claim 1   , wherein the heat-resistant polymer has a glass transition point of 120° C. or higher.  
     
     
         3 . The heat-resistant polymer foam as claimed in    claim 1   , wherein the heat-resistant polymer is a polymer selected from the group consisting of polyimides and polyether imides.  
     
     
         4 . A process for producing a heat-resistant polymer foam which comprises impregnating a heat-resistant polymer with a non-reactive gas under pressure, reducing the pressure, and then heating the impregnated polymer at a temperature exceeding 120° C. to foam the polymer.  
     
     
         5 . The process for producing a heat-resistant polymer foam as claimed in    claim 4   , wherein the heating for foaming is conducted at a temperature at which the heat-resistant polymer in an unfoamed state has a modulus of elasticity of ×10 7  Pa or higher.  
     
     
         6 . The process for producing a heat-resistant polymer foam as claimed in    claim 4   , wherein the heat-resistant polymer has a glass transition point of 120° C. or higher.  
     
     
         7 . The process for producing a heat-resistant polymer foam as claimed in    claim 4   , wherein the heat-resistant polymer is a polymer selected from the group consisting of polyimides, polyimide precursors and polyether imides.  
     
     
         8 . The process for producing a heat-resistant polymer foam as claimed in    claim 4   , wherein the non-reactive gas is carbon dioxide.  
     
     
         9 . The process for producing a heat-resistant polymer foam as claimed in    claim 4   , wherein the non-reactive gas with which the heat-resistant polymer is impregnated is used in a supercritical state.  
     
     
         10 . A foam substrate comprising: 
 a foamed resin layer comprising a heat-resistant polymer foam comprising a heat-resistant polymer, said foam having an average cell diameter of from 0.01 μm to less than 10 μm, and a metal foil layer formed on at least one side of the resin layer.