Polyimide film
Disclosed is a polyimide film, which is colorless and transparent, and which prevents the distortion of an image and exhibits excellent color reproducibility.
1. A polyimide film, which is obtained by a process comprising: polymerizing a diamine and a dianhydride in presence of a first solvent to give a polyamic acid solution; imidizing the polyamic acid solution; adding the imidized solution to a second solvent; performing filtration and drying to give a solid polyimide resin; and dissolving the solid polyimide resin in the first solvent to prepare a polyimide solution, which is then subjected to a film forming process to obtain the polyimide film,
wherein the polyimide film has a refractive index of 1.60 or less and a birefringence of 0.10 or less when measured using a prism coupler; an average transmittance of 85% or more at 380-780 nm when measured using a UV spectrophotometer for a film thickness of 25-100 μm; a yellowness index of 5.0 or less and a whiteness index of 60 or more for the film thickness of 25-100 μm; and color coordinates in which L is 90 or more, a is 5 or less and b is 5 or less, when measured using a UV spectrophotometer for the film thickness of 25-100 μm.
2. The polyimide film according to claim 1 , which has a transmittance of 88% or more at 550 nm and a transmittance of 70% or more at 440 nm, when measured using a UV spectrophotometer for the film thickness of 25-100 μm.
3. The polyimide film according to claim 1 , which has a 50% cut-off wavelength of 400 nm or less when measured using a UV spectrophotometer.
4. The polyimide film according to claim 1 wherein the second solvent has a polarity lower than that of the first solvent.
5. The polyimide film according to claim 1 , wherein the first solvent comprises one or more selected from the group consisting of m-cresol, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetone, diethylacetate, a low boiling point solvent, and a low absorbing solvent, and the second solvent comprises one or more selected from among water, alcohols, ethers, and ketones.
6. The polyimide film according to claim 1 , wherein the dianhydride is an aromatic dianhydride which comprises one or more selected from the group consisting of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, 4,4′-(4,4′-isopropylidenediphenoxyl)bis(phthalic anhydride), 3,3′-(4,4′-oxydiphthalic dianhydride), and 3,4,3,4′-biphenyltetracarboxylic dianhydride.
7. The polyimide film according to claim 1 , wherein the diamine is an aromatic diamine which comprises one or more selected from the group consisting of 2,2-bis[4-(4-aminophenoxy)-phenyl]propane, 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl, 3,3′-bis(trifluoromethyl)-4,4′-diaminobiphenyl, 4,4′-bis(3-aminophenoxy)diphenylsulfone, bis(3-aminophenyl)sulfone, bis(4-aminophenyl)sulfone, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2′-bis[3 (3-aminophenoxy)phenyl]hexafluoropropane, 2,2′-bis[4(4-aminophenoxy)phenyl]hexafluoropropane, and oxydianiline.
8. An anti-reflective film, comprising the polyimide film of claim 1 .
9. A substrate for a display, comprising the polyimide film of claim 1 .
10. A protective film, comprising the polyimide film of claim 3 .