Retardation film, circularly-polarizing plate, and image-displaying device

1. A retardation film comprising a resin having positive refractive index anisotropy and comprising at least one bonding group of a carbonate bond and an ester bond and one or more structural units selected from the group consisting of a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2), wherein:

the value of wavelength dispersion (R450/R550) as a ratio of an in-plane retardation R450 at a wavelength of 450 nm to an in-plane retardation R550 at a wavelength of 550 nm is more than 0.5 and less than 1.0:

wherein in the general formula (1) and the general formula (2), each of R 1 to R 3 is independently a direct bond or an alkylene group having a carbon number of from 1 to 4, which may have a substituent, and each of R 4 to R 9 is independently hydrogen atom, an alkyl group having a carbon number of from 1 to 10, which may have a substituent, an aryl group having a carbon number of from 4 to 10, which may have a substituent, an acyl group having a carbon number of from 1 to 10, which may have a substituent, an alkoxy group having a carbon number of from 1 to 10, which may have a substituent, an aryloxy group having a carbon number of from 1 to 10, which may have a substituent, an acyloxy group having a carbon number of from 1 to 10, which may have a substituent, an amino group which may have a substituent, a vinyl group having a carbon number of from 1 to 10, which may have a substituent, an ethynyl group having a carbon number of from 1 to 10, which may have a substituent, a sulfur atom having a substituent, a silicon atom having a substituent, a halogen atom, a nitro group, or a cyano group, provided that at least two adjacent groups out of R 4 to R 9 may be linked to each other to form a ring and two substituents R 4 's, R 5 's, R 6 's, R 7 's, R 8 's, and R 9 's may be the same with or different from each other,

wherein in the resin, a content of an aromatic group-containing structural unit other than the structural unit represented by the general formula (1) and the structural unit represented by the general formula (2) is 5% by mass or less.

2. The retardation film according to claim 1 , which has a film thickness of 10 μm to 60 μm and a thickness accuracy of within ±5% and is composed of a single layer.

3. The retardation film according to claim 1 , wherein the resin has a refractive index at a sodium d line (wavelength: 589 nm) of from 1.49 to 1.56.

4. The retardation film according to claim 1 , wherein the resin contains 1% by mass or more and 40% by mass or less of one or more structural units selected from the group consisting of the structural unit represented by the general formula (1) and the structural unit represented by the general formula (2).

5. The retardation film according to claim 1 , wherein the resin has a glass transition temperature of 110° C. to 160° C.

6. The retardation film according to claim 1 , wherein the resin further comprises a structural unit represented by the following general formula (3):

7. The retardation film according to claim 1 , wherein the resin further comprises one or more structural units selected from the group consisting of structural units represented by the following general formulae (4) to (8):

wherein in the general formula (4), R 10 represents an alkylene group having a carbon number of from 2 to 20, which may be substituted;

wherein in the general formula (5), R 11 represents a cycloalkylene group having a carbon number of from 4 to 20, which may be substituted;

wherein in the general formula (6), R 12 represents a cycloalkylene group having a carbon number of from 4 to 20, which may be substituted;

wherein in the general formula (7), R 13 represents an alkylene group having a carbon number of from 2 to 10, which may be substituted, p is an integer of from 1 to 40, and two or more substituents R 13 's may be the same with or different from each other; and

wherein in the general formula (8), R 14 represents an acetal ring-containing group having a carbon number of from 2 to 20, which may be substituted.

8. An unstretched film, which is a long film and becomes the retardation film according to claim 1 by a stretching treatment.

9. A long retardation film obtained by stretching the unstretched film according to claim 8 at least in one direction.

10. A circularly polarizing plate comprising the retardation film according to claim 1 and a polarizer stacked on the retardation film.

11. An image display device comprising the circularly polarizing plate according to claim 10 .

12. An organic EL panel comprising the circularly polarizing plate according to claim 10 .

13. A retardation film comprising a resin having positive refractive index anisotropy and comprising at least one bonding group of a carbonate bond and an ester bond and one or more structural units selected from the group consisting of a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2), wherein:

the value of wavelength dispersion (R450/R550) as a ratio of an in-plane retardation R450 at a wavelength of 450 nm to an in-plane retardation R550 at a wavelength of 550 nm is more than 0.5 and less than 1.0:

wherein in the general formula (1) and the general formula (2), each of R 1 to R 3 is independently a direct bond or an alkylene group having a carbon number of from 1 to 4, which may have a substituent, and each of R 4 to R 9 is independently hydrogen atom, an alkyl group having a carbon number of from 1 to 10, which may have a substituent, an aryl group having a carbon number of from 4 to 10, which may have a substituent, an acyl group having a carbon number of from 1 to 10, which may have a substituent, an alkoxy group having a carbon number of from 1 to 10, which may have a substituent, an aryloxy group having a carbon number of from 1 to 10, which may have a substituent, an acyloxy group having a carbon number of from 1 to 10, which may have a substituent, an amino group which may have a substituent, a vinyl group having a carbon number of from 1 to 10, which may have a substituent, an ethynyl group having a carbon number of from 1 to 10, which may have a substituent, a sulfur atom having a substituent, a silicon atom having a substituent, a halogen atom, a nitro group, or a cyano group, provided that at least two adjacent groups out of R 4 to R 9 may be linked to each other to form a ring and two substituents R 4 's, R 5 's, R 6 's, R 7 's, R 8 's, and R 9 's may be the same with or different from each other; and

the retardation film has a film thickness of 10 μm to 60 μm and a thickness accuracy of within ±5% and is composed of a single layer.