Colorless and transparent polyamide-imide film, and manufacturing method therefor
Disclosed herein are a polyamide-imide film which is transparent and exhibits superior mechanical properties such as surface hardness, etc. and a method of preparing the same. The polyamide-imide film a copolymer of an aromatic diamine, an aromatic dianhydride, and an aromatic dicarbonyl compound, wherein the aromatic diamine and the aromatic dianhydride forms an imide unit; the aromatic diamine and the aromatic dicarbonyl compound forms an amide unit; and the amide unit accounts for 50-70 mol % of 100 mol % of the units of the copolymer, thereby exhibiting transparency and superior mechanical properties including surface hardness.
1. A polyamide-imide film which is a copolymer of an aromatic diamine, an aromatic dianhydride, a first aromatic dicarbonyl compound, and a second aromatic dicarbonyl compound,
wherein the aromatic diamine is 2,2′-bis(trifluoromethyl)-4,4′-diaminodiphenyl (TFDB),
wherein the aromatic dianhydride is 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA), wherein the first aromatic dicarbonyl compound is terephthaloyl chloride (TPC), and
wherein the second aromatic dicarbonyl compound is selected from a group consisting of 1,1-biphenyl-4,4-dicarbonyl dichloride (BPDC), 2,6-naphthalene dicarbonyl dichloride (NADOC), and a mixture thereof, and wherein the copolymer comprises:
an imide unit derived from the aromatic diamine and the aromatic dianhydride; and
an amide unit derived from the aromatic diamine and the first aromatic dicarbonyl compound or derived from the aromatic diamine and the second aromatic dicarbonyl compound,
wherein the amide unit accounts for 50 to 80 mol % of total 100 mol % of the units of the copolymer, and
wherein the amide unit of 100 mol % comprises 50 to 70 mol % of a unit derived from the second aromatic dicarbonyl compound.
2. The polyamide-imide film according to claim 1 , wherein the amide unit accounts for 60-70 mol % of 100 mol % of the units of the copolymer.
3. The polyamide-imide film according to claim 1 , wherein a surface hardness ranges from H to 4H based on a thickness of 20-100 μm.
4. The polyamide-imide film according to claim 3 , wherein a transmittance measured at 550 nm is 89% or higher and a haze is lower than 1% based on a thickness of 20-100 μm.
5. The polyamide-imide film according to claim 4 , wherein a yellowness index (YI) is 3 or lower based on a thickness of 20-100 μm.