Optical compensation film, and polarizing plate and liquid crystal display employing the same

Abstract

The present invention provides an optical compensation film, which has excellent visibility such as light leakage, uneven color tone and front contrast, and can simultaneously realize retardation and wavelength dispersion. The optical compensation film is characterized by containing a cellulose ester, the following polymer (a), and the following compound (b). (a) A polymer produced by copolymerizing an ethylenically unsaturated monomer having in its molecule a partial structure represented by Formula (1) with at least one ethylenically unsaturated monomer. (b) An esterified compound produced by esterifying all or a part of OH groups in a compound (A) having one furanose structure or one pyranose structure, or an esterified compound produced by esterifying all of or a part of OH groups in a compound (B) containing nor less than 2 and not more than 12 structures of at least one of a furanose structure or a pyranose structure.

1 . An optical compensation film characterized by comprising Polymer (a) and Compound (b), wherein
 Polymer (a): A polymer produced by copolymerizing an ethylenically unsaturated monomer having a partial structure represented by Formula (1) in its molecule with at least one ethylenically unsaturated monomer,   
       
         
           
           
               
               
           
         
         
           wherein, R 1 , R 2  and R 3  each independently represent an aliphatic group which may have a substituent, an aromatic group which may have a substituent, or a heterocycle group which may have a substituent, provided that any two of R 1 , R 2  and R 3  are combined with each other to form a 5 to 7 member ring structure together with a nitrogen atom to which the two of R 1 , R 2  and R 3  are bonded or together with the nitrogen atom and a carbon atom, and 
         
         Compound (b): An esterified compound in which all or a part of OH groups in Compound (A) having one furanose or pyranose structure are esterified, or an esterified compound in which all or a part of OH groups in Compound (B), in which 2 to 12 structures of at least one of furanose or pyranose structure are bonded, are esterified. 
       
     
     
         2 . The optical compensation film of  claim 1 , characterized by satisfying Formulas (i), (ii) and (iii),
   20≦ Ro≦ 100(nm)  (i)     70≦ Rt≦ 200(nm)  (ii)     0.82≦ Ro (480)/ Ro (630)≦0.96  (iii)   wherein,
 Ro=(nx−ny)×d 
 Rt=((nx+ny)/2−nz)×d 
   in the formulas, nx represents a refractive index in retarded phase axis direction in a plane of the optical compensation film, ny represents a refractive index in a direction perpendicular to the retarded phase axis direction in a plane, nz represents a refractive index in a thickness direction and d represents a thickness (nm) of the optical compensation film respectively, the measuring wavelength for the refractive index being 590 nm, and Ro (480) and Ro (630) represent Ro measured with the wavelength of 480 nm and Ro measured with the wavelength of 630 nm, respectively.   
     
     
         3 . The optical compensation film of  claim 1 , characterized by that weight average molecular weight (Mw) of the Polymer (a) is within a range of 1,000 to 70,000. 
     
     
         4 . The optical compensation film of  claim 1 , characterized by that ethylenically unsaturated monomer having a substructure represented by Formula (1) in a molecule is N-vinyl pyrrolidone, N-acryloyl morpholine, N-vinyl piperidone, N-vinyl caprolactam, or a mixture thereof. 
     
     
         5 . The optical compensation film of  claim 1 , characterized by that the esterified compound is benzoate of monosaccharide (□-glucose, □-fructose) or benzoate of polysaccharide prepared by dehydration condensation of arbitrary two or more parts of
 —OR 12 , —OR 15 , —OR 22  and —OR 25  in monosaccharide represented by Formula (2), in which m+n=2 to 12.   
       
         
           
           
               
               
           
         
       
     
     
         6 . A polarizing plate characterized by employing the optical compensation film of any one of above described  claim 1  on at least one surface of a polarizing plate. 
     
     
         7 . A liquid crystal display characterized by employing the polarizing plate of above described  claim 6  on at least one surface of a liquid crystal cell.