Polycarbonate resin film, and transparent film and process for producing the same

1. A polycarbonate resin film for film stretching, comprising:

a polycarbonate resin which comprises at least a constitutional unit derived from a dihydroxy compound (A) that has a bonded structure represented by the structural formula (1) and a constitutional unit derived from at least one dihydroxy compound (B) selected from the group consisting of cyclohexanedimethanol, diethylene glycol and polyethylene glycol,

wherein said dihydroxyl compound (A) is a compound which has an aromatic group as a side chain and has, in a main chain, ether groups each bonded to an aromatic group,

said polycarbonate resin having a photoelastic coefficient of 30×10 −12 Pa −1 or lower, and

the polycarbonate resin film satisfies the expression (2) when subjected to a tensile test at a standard stretching temperature for the polycarbonate resin and at a pulling speed (strain rate) of 1,000%/min:

CH 2 —O   (1)

wherein no hydrogen atom is bonded to the oxygen atom contained in the structural formula (1); and

0.9≦[(lower yield stress in tension)/(upper yield stress in tension)]≦1  (2).

2. The polycarbonate resin film according to claim 1 , wherein the polycarbonate resin film satisfies the expression (3) when subjected to a tensile test at the standard stretching temperature for the polycarbonate resin and at a pulling speed (strain rate) of 1,000%/min:

[(Breaking stress in tension)/(upper yield stress in tension)]≧1  (3).

3. The polycarbonate resin film according to claim 1 , wherein said polycarbonate resin further comprises a compound represented by the structural formula (4)

4. The polycarbonate resin film according to claim 1 , wherein the polycarbonate resin has a storage modulus at 40° C. of 2.7 GPa or less.

5. The polycarbonate resin film according to claim 3 , wherein the polycarbonate resin is a copolymer which comprises a constitutional unit derived from a compound represented by the structural formula (4) and a constitutional unit derived from 1,4-cyclohexanedimethanol.

6. The polycarbonate resin film according to claim 1 , wherein the polycarbonate resin film has a birefringence of 0.001 or higher in the state of having been stretched in a free-end stretch ratio of 2.0 under the conditions of (standard stretching temperature for the polycarbonate resin)+5° C.

7. A transparent film formed by stretching the polycarbonate resin film according to claim 1 in at least one direction.

8. The transparent film according to claim 7 , wherein the transparent film has a refractive index as measured with sodium d-line (589 nm) of 1.57-1.62.

9. The transparent film according to claim 7 , wherein the transparent film has a birefringence of 0.001 or higher.

10. The transparent film according to claim 7 , wherein the transparent film has a retardation R450 measured at a wavelength of 450 nm and a retardation R550 measured at a wavelength of 550 nm, and the ratio of the R450 to the R550 satisfies an expression (6)

0.75≦ R 450/ R 550≦1.1  (6).

11. The transparent film according to claim 7 , wherein the transparent film has a photoelastic coefficient of 40×10 −12 Pa −1 or less.

12. The transparent film according to claim 7 , wherein the transparent film has a thickness of 150 μm or less.

13. The transparent film according to claim 7 , wherein the transparent film has refractive indexes, as measured respectively in two in-plane directions, of nx and ny and has a thickness-direction refractive index of nz, and the refractive indexes nx, ny, and nz have a relationship which satisfies any one of expressions (7) to (9)

nx>ny=nz   (7)

nx>ny>nz   (8)

nx>nz>ny   (9).

14. The transparent film according to claim 7 , wherein the transparent film has refractive indexes, as measured respectively in two in-plane directions, of nx and ny, a thickness-direction refractive index of nz, and a thickness of d, and the refractive indexes nx, ny, and nz and the thickness d have a relationship which satisfies expressions (10) and (11)

NZ coefficient=( nx−nz )/( nx−ny )=0.2 to 8  (10)

Δ nd =( nx−ny )· d= 30 to 400 nm  (11).

15. The transparent film according to claim 7 , wherein the transparent film has a water absorption of 0.5-2.0% by weight.

16. A polarizing plate which comprises the transparent film according to claim 7 and a polarizer thereon.

17. A process for producing the transparent film of claim 1 comprising:

stretching the film in at least one direction under a condition(s) that satisfies the expression (5):

200%/min≦[stretching speed(strain rate)]≦1,200%/min  (5).