Polycarbonate resin film, and transparent film and process for producing the same
View Patent ↗Disclosed herein is a process for producing a transparent film, including the step of stretching a film in at least one direction under a condition(s) that satisfies an expression (5): 200%/min≤[stretching speed(strain rate)]≤1,200%/min (5), wherein the film comprises a polycarbonate resin containing at least a constitutional unit derived from a dihydroxy compound (A) that has a bonded structure represented by a structural formula (1): in which no hydrogen atom is bonded to the oxygen atom contained in the structural formula (1).
1. A process for producing a transparent film, the process comprising:
stretching a film in at least one direction under a condition(s) that satisfies an expression (5):
200%/min≤[stretching speed(strain rate)]≤1,200%/min (5),
wherein:
the film comprises a polycarbonate resin which contains at least a constitutional unit derived from a dihydroxy compound (A) that has a bonded structure represented by a structural formula (1):
no hydrogen atom is bonded to the oxygen atom contained in the structural formula (1);
a thickness of the transparent film is from 10 μm to 54 μm;
a thickness unevenness of the transparent film is from 7.1 μm to 15.4 μm; and
a birefringence of the transparent film is 0.0026 or more; wherein:
an upper yield stress in tension and a lower yield stress in tension of the transparent film satisfy the following expression (2):
0.9≤[(lower yield stress in tension)/(upper yield stress in tension)]≤1 (2);
the upper yield stress in tension and a breaking stress in tension of the transparent film satisfy the following expression (3):
[(breaking stress in tension)/(upper yield stress in tension)]≥1 (3);
and a storage modulus at 40° C. of the polycarbonate resin is 2.7 GPa or less.
2. The process for producing a transparent film according to claim 1 , wherein the dihydroxy compound (A) is a dihydroxy compound having a cyclic ether structure.
3. The process for producing a transparent film according to claim 1 , wherein the polycarbonate resin further comprises a structural unit derived from a dihydroxy compound (B).
4. The process for producing a transparent film according to claim 3 , wherein the dihydroxy compound (B) is alicyclic dihydroxy compound.
5. The process for producing a transparent film according to claim 1 , wherein a stretching temperature of the transparent film is from (glass transitional temperature of the polycarbonate resin)−20° C. to (glass transitional temperature of the polycarbonate resin)+40° C.
6. The process for producing a transparent film according to claim 1 , wherein the polycarbonate resin is stretched by uniaxial stretching.
7. The process for producing a transparent film according to claim 1 , wherein stretch ratio is 1.05 to 4 times.