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A porous insulating film comprising a highly heat resistant resin film having a fine porous structure with a mean pore size of 0.01-5 μm in at least the center of the film, and a porosity of 15-80%. A laminate is prepared by forming a heat resistant adhesive layer or a conductive metal layer or

A porous insulating film comprising a highly heat resistant resin film having a fine porous structure with a mean pore size of 0.01-5 μm in at least the center of the film, and a porosity of 15-80%. A laminate is prepared by forming a heat resistant adhesive layer or a conductive metal layer or an inorganic or metal substrate on one or both sides of the porous insulating film or by forming an inorganic or metal substrate on one side of the porous insulating film and a conductive metal layer on the other side.

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What is claimed is: 1. A porous insulating film consisting essentially of a highly heat resistant polyimide resin film having a fine porous structure wherein: a) fine continuous channels reaching to both surfaces of the insulating film in a nonlinear fashion have a mean pore size of 0.01-0.2 μ

What is claimed is: 1. A porous insulating film consisting essentially of a highly heat resistant polyimide resin film having a fine porous structure wherein: a) fine continuous channels reaching to both surfaces of the insulating film in a nonlinear fashion have a mean pore size of 0.01-0.2 μm in the center of the film and 0.4-0.9 μm at both surfaces of the film and a porosity of 15-80%; b) the polyimide resin film is prepared from a polyimide precursor solution and consists essentially of a polyimide obtained from the combination of at least one tetracarboxylic acid component and a diamine component; and c) the insulating film has a thickness of 5-150 μm, a resistance to passage of air of from 30 sec/100 cc to 2000 sec/100 cc, and a heat shrinkage of not greater than about 짹1% after being heat-treated at 105째 C. for 8 hours, and does not contain a dense layer on either of the surfaces. 2. The porous insulating film according to claim 1, wherein the porosity is 30-80%. 3. The porous insulating film according to claim 1, wherein the thickness is 5-100 μm. 4. The porous insulating film according to claim 1, which is fabricated by a film casting method. 5. The porous insulating film according to claim 1, which has a dielectric constant of no greater than 2.5. 6. The porous insulating film according to claim 1, wherein the pores in the porous structure are arranged in the film substantially parallel to the film surfaces. 7. A porous insulating film consisting essentially of a highly heat resistant polyimide resin film having a fine porous structure wherein: a) fine continuous channels reaching to both surfaces of the insulating film in a nonlinear fashion have a mean pore size of 0.01-0.2 μm in the center of the film and 0.4-0.9 μm at both surfaces of the film; and b) the polyimide resin film is prepared from a polyimide precursor solution and consists essentially of a polyimide obtained from the combination of at least one tetracarboxylic acid component and a diamine component; and c) the insulating film has a thickness of 5-100 μm, a resistance to passage of air of from 30 sec/100 cc to 2000 sec/100 cc, a heat resistance temperature of at least 200째 C., and a heat shrinkage of not greater than 짹1% after being heat-treated at 105째 C. for 8 hours, and does not contain a dense layer on either of the surfaces. 8. A battery separator comprising a porous insulating film according to claim 7. 9. The porous insulating film according to claim 7, wherein the pores in the porous structure are arranged in the film substantially parallel to the film surfaces. 10. The porous insulating film according to claim 1 or 7, wherein the tetracarboxylic acid component is selected from a biphenyltetracarboxylic dianhydride, pyromellitic dianhydride and a benzophenonetetracarboxylic dianhydride. 11. The porous insulating film according to claim 10, wherein the biphenyltetracarboxylic dianhydride is 3,3',4,4'-biphenyltetracarboxylic dianhydride. 12. The porous insulating film according to claim 1 or 7, wherein the diamine component is selected from a phenylenediamine or a diaminodiphenylether.