Polyimide film and method for producing same
The present invention relates to a polyimide film and a preparation method thereof. According to the present invention, a polyamic acid solution having a high weight-average molecular weight may be obtained by adjusting viscosity and solid content of the polyamic acid solution, and thus, a desired polyimide film may be prepared therefrom. Furthermore, since a length of carbon chains rearranged during graphitization is increased, a graphite sheet having excellent thermal conductivity can be prepared from the polyimide film of the present invention. Also, since the polyimide film has improved windability by further including inorganic particles as a filler, it may facilitate the wind operation.
1. A method of preparing a polyimide film for graphite sheet, the method comprising:
(a) preparing a polyamic acid solution by reaction of a diamine monomer with an acid dianhydride monomer in a solvent;
(b) mixing the polyamic acid solution with an imidization solution to prepare a gel film; and
(c) imidizing the gel film by performing a heat treatment,
wherein, a solid content (β1) of the polyamic acid solution is in a range of 15% to 20% where the solid content (β1) of the polyamic acid solution denotes a weight percentage of the monomers based on a total weight of the solvent and the monomers used in the reaction; the polyamic acid solution has a viscosity (β2) of 55,000 cps to 900,000 cps at 23° C.; and the solid content (β1) and viscosity (β2) of the polyamic acid solution satisfy Equation 1:
Equation 1
−0.87≤−1.46 log 10(β1)+0.18 log 10(β2)
wherein the graphite sheet has a thermal conductivity of 402−477.4 W/(m·K),
wherein the diamine monomer comprises one or more selected from the group consisting of para-phenylenediamine (pPDA), diaminophenyl ether, o-phenylenediamine, m-phenylenediamine, 4,4-diaminodiphenyl ether (ODA), 3,4-diaminodiphenyl ether, and 2,4-diaminodiphenyl ether, and
wherein the acid dianhydride monomer comprises one or more selected from the group consisting of biphenyltetracarboxylic acid dianhydride or a derivative thereof, pyromellitic dianhydride (PMDA), 3,3′,4,4′-benzophenone tetracarboxylic acid anhydride, and p-phenylene-bis trimellitic dianhydride.
2. The method of claim 1 , wherein the imidization solution comprises a filler, and the filler comprises one or more inorganic particle selected from the group consisting of silicon, silicon dioxide, silicon nitride, aluminum, alumina, titanium, titanium oxide, phosphorus, calcium phosphate, calcium hydrogen phosphate (dicalcium phosphate), calcium, potassium, and a mixture thereof.
3. The method of claim 1 , wherein the imidization solution comprises a filler, and the filler is included in an amount of 500 ppm to 5,000 ppm based on a total weight of the polyimide film.