Process for producing graphite film and graphite film produced thereby

Abstract

In order to obtain a graphite film having an excellent thermal diffusivity, a high density, and excellent flatness without flaws, recesses and wrinkles on the surface, the process for producing a graphite film according to the present invention comprises the graphitization step for a raw material film made of a polymer film and/or a carbonized polymer film and/or the post-planar pressurization step for the film in this order to prepare a graphite film, wherein the graphitization step is a step of thermally treating two or more stacked raw material films at a highest temperature of 2,000° C. and includes a method of electrically heating the raw material films themselves and/or a method of thermally treating the films while applying pressure to the films planarly, and the post-planar pressurization step includes a method of planarly pressurizing the one raw material film or the multiple stacked raw material films after graphitization by single-plate press or vacuum press.

1 . A process for producing a graphite film comprising the step of graphitizing a raw material film made of a polymer film and/or a carbonized polymer film by retaining the film in and in contact with a container that can be directly electrified by application of voltage and electrifying the container electrified by application of voltage. 
   
   
       2 . The process for producing a graphite film according to  claim 1 , wherein the graphitization step includes thermal treatment at a temperature of 2,000° C. or more. 
   
   
       3 . The process for producing a graphite film according to  claim 1 , wherein the container that can be directly electrified by application of voltage is a graphite container. 
   
   
       4 . The process for producing a graphite film according to  claim 3 , wherein the graphitization step is carried out with carbon powder packed between the graphite container and the raw material film and/or around the outer periphery of the graphite container. 
   
   
       5 . The process for producing a graphite film according to  claim 1 , wherein the graphitization step is carried out with pressure applied to the raw material film planarly. 
   
   
       6 . The process for producing a graphite film according to  claim 5 , wherein the pressure is reduced in part of the graphitization step. 
   
   
       7 . The process for producing a graphite film according to  claim 1 , wherein the graphitization step is carried out in the state where the two or more raw material films are stacked. 
   
   
       8 . The process for producing a graphite film according to  claim 4 , wherein the number of the stacked films is 10 or more in the state where the two or more raw material films are stacked. 
   
   
       9 . The process for producing a graphite film according to  claim 7 , wherein the graphitization step is carried out in the state where the two or more raw material films are stacked and a carbon material having a height smaller than the height of the stacked films is present around the stacked films. 
   
   
       10 . The process for producing a graphite film according to  claim 1 , further comprising the post-planar pressurization step of pressurizing the graphitized raw material film planarly following the graphitization step. 
   
   
       11 . The process for producing a graphite film according to  claim 10 , wherein the pressurization is carried out by single-plate press in the post-planar pressurization step. 
   
   
       12 . The process for producing a graphite film according to  claim 10 , wherein the pressurization is carried out by vacuum press in the post-planar pressurization step. 
   
   
       13 . The process for producing a graphite film according to  claim 10 , wherein the graphitized raw material film is pressurized together with a film-like medium other than the graphitized raw material film in the post-planar pressurization step. 
   
   
       14 . The process for producing a graphite film according to  claim 10 , wherein the multiple graphitized raw material films are simultaneously pressurized in the post-planar pressurization step. 
   
   
       15 . The process for producing a graphite film according to  claim 10 , further comprising the independent recovery step of recovering the multiple graphitized raw material films planarly pressurized as independent graphite films after the post-planar pressurization step. 
   
   
       16 . The process for producing a graphite film according to  claim 1 , wherein the carbonized polymer film is obtained by a carbonization step of thermally treating a polymer film at a temperature of 600 to 1,800° C. 
   
   
       17 . The process for producing a graphite film according to  claim 1 , wherein the polymer film is made of one or more polymers selected from polyimide, polyamide, polyoxadiazole, polybenzothiazole, polybenzobisthiazole, polybenzoxazole, polybenzobisoxazole, poly(p-phenylene vinylene), polybenzimidazole, polybenzobisimidazole and polythiazole. 
   
   
       18 . The process for producing a graphite film according to  claim 17 , wherein the polymer film is a polyimide film. 
   
   
       19 . The process for producing a graphite film according to  claim 18 , wherein the polyimide film is a polyimide film having a birefringence of 0.08 or more. 
   
   
       20 . The process for producing a graphite film according to  claim 19 , wherein the polyimide film is a polyimide film having a birefringence of 0.12 or more. 
   
   
       21 . The process for producing a graphite film according to  claim 18 , wherein the polyimide film is prepared by imidizing a polyamide acid containing pyromellitic acid dianhydride and p-phenylenediamine using a dehydrating agent and an imidization promoter. 
   
   
       22 . The process for producing a graphite film according to  claim 18 , wherein the polyimide film is prepared by synthesizing a prepolymer having an acid dianhydride at each terminal from a diamine and the acid dianhydride; synthesizing a polyamide acid by reaction of the prepolymer with a diamine differing from the diamine; and imidizing the polyamide acid. 
   
   
       23 . A graphite film produced by the process for producing a graphite film according to  claim 1 , which has a coefficient of linear expansion of 0 ppm or less. 
   
   
       24 . The graphite film according to  claim 1 , which has a tensile modulus of elasticity of 1 GPa or more. 
   
   
       25 . The graphite film according to  claim 1 , which has a thermal conductivity in the contact thickness direction of 1.4 W/m·K or less measured by a thermal resistance measuring apparatus. 
   
   
       26 . The graphite film according to  claim 1 , which has a tensile strength of 25 MPa or more. 
   
   
       27 . The graphite film according to  claim 1 , which has a thermal diffusivity in the plane direction of 9.0×10 −4  m 2 /s or more. 
   
   
       28 . The graphite film according to  claim 1 , which has a density of 1.5 g/cm 3  or more. 
   
   
       29 . The graphite film according to  claim 1 , which has a variation in thickness of 10 μm or less. 
   
   
       30 . A graphite film produced by the process for producing a graphite film according to  claim 1 , which has a part with a surface layer and a layer other than the surface layer differing at least in cross-sectional pattern.