RETARDATION FILM, AND CIRCULARLY POLARIZING PLATE AND IMAGE DISPLAY DEVICE EACH USING THE SAME
A retardation film insusceptible to color dropout or color shift even under environment of severe temperature or humidity conditions and capable of being produced by a melt film-forming method. The retardation film is obtained by molding at least one polymer selected from polycarbonate and polyester carbonate each having a glass transition temperature of 110 to 180° C. and satisfies the relationships of the following formulae (A) and (B): 0.7<R 1 (450)/R 1 (550)<1 Formula (A): |R 2 (450)/R 2 (550)−R 1 (450)/R 1 (550)|<0.020. Formula (B):
1 . A retardation film, obtained by a process comprising molding at least one polymer selected from the group consisting of polycarbonate and polyester carbonate each having a glass transition temperature of 110 to 180° C., the retardation film satisfying formulae (A) and (B):
0.7<R 1 (450)/R 1 (550)<1; and Formula (A):
|R 2 (450)/R 2 (550)−R 1 (450)/R 1 (550)|< 0 . 020 , Formula (B):
wherein R 1 (450) and R 1 (550) represent a retardation value in film plane at respective wavelengths of 450 nm and 550 nm, and R 2 (450) and R 2 (550) represent a retardation value in film plane at respective wavelengths of 450 nm and 550 nm after leaving the retardation film to stand at a temperature of 90° C. for 48 hours.
2 . The retardation film according to claim 1 , satisfying formulae (C) and (D):
1<R 1 (650)/R 1 (550)<1.2; and Formula (C):
|R 2 (650)/R 2 (550)−R 1 (650)/R 1 (550)1<0.010, Formula (D):
wherein R 1 (650) represents a retardation value in film plane at a wavelength of 650 nm, and R 2 (650) represents a retardation value in film plane at a wavelength of 650 nm after leaving the retardation film to stand at a temperature of 90° C. for 48 hours.
3 . The retardation film according to claim 1 , wherein the at least one polymer comprises a structural unit derived from a dihydroxy compound represented by formula (1):
wherein each of R 1 to R 4 independently represents a hydrogen atom, a substituted or unsubstituted alkyl group having a carbon number of 1 to 20, a substituted or unsubstituted cycloalkyl group having a carbon number of 6 to 20, or a substituted or unsubstituted aryl group having a carbon number of 6 to 20, and the same or different groups are substituted as respective substituents on four benzene rings; each of X 1 and X 2 independently represents a substituted or unsubstituted alkylene group having a carbon number of 2 to 10, a substituted or unsubstituted cycloalkylene group having a carbon number of 6 to 20, or a substituted or unsubstituted arylene group having a carbon number of 6 to 20; and each of m and n independently represents an integer of 0 to 5.
4 . The retardation film according to claim 3 , wherein the at least one polymer comprises a structural unit derived from a dicarboxylic acid compound.
5 . The retardation film according to claim 3 , wherein the at least one polymer comprises a structural unit derived from a dihydroxy compound different from the dihydroxy compound represented by formula (1).
6 . The retardation film according to claim 5 , wherein the dihydroxy compound is a dihydroxy compound having an etheric oxygen atom on at least one β- or γ-position of the hydroxy group.
7 . The retardation film according to claim 6 , wherein in the at least one polymer, a content of the structural unit derived from a dihydroxy compound having an acetal structure is 10 mol % or less based on all dihydroxy compound-derived structural units.
8 . The retardation film according to claim 6 , wherein the dihydroxy compound having an etheric oxygen atom on at least one β- or γ-position of the hydroxy group is at least one compound selected from compounds represented by the following formula (2) or (3):
wherein in formula (3), R 5 represents a substituted or unsubstituted alkylene group having a carbon number of 2 to 10, and p represents an integer of 2 to 50.
9 . The retardation film according to claim 5 , wherein the dihydroxy compound is an aromatic dihydroxy compound.
10 . The retardation film according to claim 9 , wherein the aromatic dihydroxy compound is 2,2-bis(4-hydroxyphenyl)propane.
11 . The retardation film according to claim 1 , wherein a chlorine content is 50 ppm by weight or less in terms of the weight of chlorine atom.
12 . The retardation film according to claim 1 , wherein a content of a monohydroxy compound is 2,000 ppm by weight or less.
13 . The retardation film according to claim 1 , wherein a photoelastic coefficient of the at least one polymer is 45×10 −12 Pa· −1 or less.
14 . The retardation film according to claim 1 , wherein a glass transition temperature of the at least one polymer is from 125 to 150° C.
15 . A circularly polarizing plate, comprising the retardation film according to claim 1 and a polarizing plate.
16 . An image display device, comprising the circularly polarizing plate according to claim 15 .
17 . The image display device according to claim 16 , wherein the image display device uses an organic EL.