Polymer Film, Optically-Compensatory Film, Process for Producing the Same, Polarizing Plate and Liquid-Crystal Display Device

Abstract

A polymer film that has: a ratio R (VT/VM) of a sound velocity in a transverse direction VT to a sound velocity in a machine direction VM of from 1.05 to 1.50; and an in-plane retardation Re(λ) and a thickness-direction retardation Rth(λ) satisfying formula (I): (I) 0≦Re(630)≦10, and |Rth(630)|≦25, wherein Re(λ) represents an in-plane retardation at a wavelength of λ (nm); and Rth(λ) represents a thickness-direction retardation at a wavelength of λ (nm).

1 . A polymer film that has: a ratio R (VT/VM) of a sound velocity in a transverse direction VT to a sound velocity in a machine direction VM of from 1.05 to 1.50; and an in-plane retardation Re(λ) and a thickness-direction retardation Rth(λ) satisfying formula (I):
   0 ≦Re (630)≦10, and | Rth (630)|≦25  (I)   wherein Re(λ) represents an in-plane retardation at a wavelength of λ (nm);   and Rth(λ) represents a thickness-direction retardation at a wavelength of λ (nm).   
     
     
         2 . A polymer film that has: a tensile modulus in a transverse direction of from 240 to 600 kgf/mm 2  (2.35 GPa to 5.88 GPa); a tensile modulus in the machine direction of from 230 to 480 kgf/mm 2  (2.25 GPa to 4.70 GPa); a ratio of a tensile modulus in a transverse direction to a tensile modulus in a machine direction of from 1.15 to 1.80; and an in-plane retardation Re(λ) and a thickness-direction retardation Rth(λ) satisfying formula (I):
   0 ≦Re (630)≦10, and | Rth (630)|≦25;  (I)   wherein Re(λ) represents an in-plane retardation at a wavelength of k (nm);   and Rth(λ) represents a thickness-direction retardation at a wavelength of λ (nm).   
     
     
         3 . The polymer film according to  claim 1 , which has at least one surface having a surface energy of 50 mN/m or more but not more than 80 mN/m. 
     
     
         4 . The polymer film according to  claim 3 , which has at least one surface-treated surface,
 wherein the at least one surface-treated surface has a surface energy of 30 mN/m or more but not more than 50 mN/m before a surface treatment, and has a surface energy of 50 mN/m or more but not more than 80 mN/m after a surface treatment.   
     
     
         5 . The polymer film according to  claim 1 , which has an in-plane retardation Re(λ) and a thickness-direction retardation Rth(λ) satisfying formula (II):
   | Re (400)− Re (700)|≦10, and | Rth (400)− Rth (700)|≦35;  (II)   wherein Re(λ) represents an in-plane retardation at a wavelength of λ (nm);   and Rth(λ) represents a thickness-direction retardation at a wavelength of λ (nm).   
     
     
         6 . The polymer film according to  claim 1 , which is a polymer film comprising at least a cellulose acylate and a compound having a molecular weight of not more than 3000. 
     
     
         7 . The polymer film according to  claim 6 ,
 wherein an acyl substituent in the cellulose acylate is substantially an acetyl group alone, a total degree of substitution thereof is from 2.80 to 2.99, and a mean degree of polymerization of the cellulose acylate is from 180 to 550.   
     
     
         8 . The polymer film according to  claim 6 ,
 wherein an acylate group in the cellulose acylate comprises at least one of acetate, propionate and butylate, and a total degree of substitution thereof is from 2.50 to 3.00.   
     
     
         9 . The polymer film according to  claim 1 , which has a photoelasticity coefficient of not more than 25×10 −13  cm 2 /dne (2.5×10 −13  N/m 2 ). 
     
     
         10 . An optically-compensatory film comprising:
 a polymer film according to  claim 1 ; and   an optically-anisotropic layer formed on the polymer film,   wherein the optically-anisotropic layer satisfies formulae: Re(630)=0 to 200 (nm), and |Rth(630)|=0 to 400 (nm).   
     
     
         11 . The optically-compensatory film according to  claim 10 ,
 wherein the optically-anisotropic layer comprises a polymer film.   
     
     
         12 . The optically-compensatory film according to  claim 11  that is obtained by a method comprising:
 spreading a polymer having been dissolved in a solvent and thus liquefied on a polymer film; and   subjecting the thus obtained laminate to a stretching treatment, a shrinking treatment or both of them to thereby orient polymer molecules in the plane.   
     
     
         13 . The optically-compensatory film according to  claim 11 ,
 wherein the polymer film comprises at least one polymer selected from the group consisting of polyamide, polyimide, polyester, polyetherketone, polyaryl-ether ketone, polyamidimde and polyesterimide.   
     
     
         14 . A process for producing a polymer film according to  claim 1 , which comprises stretching a film in a transverse direction. 
     
     
         15 . A process for producing a polymer film according to  claim 1 , which comprises shrinking a film in a machine direction. 
     
     
         16 . A process for producing an optically-compensatory film according to  claim 10 , which comprises:
 spreading a polymer having been dissolved in a solvent and thus liquefied on a polymer film; and   stretching the thus obtained laminate in a transverse direction.   
     
     
         17 . A process for producing an optically-compensatory film according to  claim 10 , which comprises:
 spreading a polymer having been dissolved in a solvent and thus liquefied on a polymer film; and   shrinking the thus obtained laminate in a machine direction.   
     
     
         18 . A process for producing the optically-compensatory film according to  claim 10 , which comprises:
 layering a polymer having been dissolved in a solvent and thus liquefied on a polymer film by a co-casting method; and   stretching the thus obtained laminate in a transverse direction.   
     
     
         19 . A polarizing plate comprising a polymer film according to  claim 1  as a protecting film for a polarization film. 
     
     
         20 . The polarizing plate according to  claim 19 , which has at least one layer selected from the group consisting of a hard coat layer, an antiglare layer and an antireflection layer provided on a surface of the polarizing plate. 
     
     
         21 . A liquid-crystal display device, which comprises a polymer film according to  claim 1 . 
     
     
         22 . The liquid-crystal display device according to  claim 21 , which is a VA or IPS liquid-crystal display device.