Retardation film and optical device employing it

Abstract

A retardation film comprised of a single oriented polymer film, characterized in that the retardation at wavelengths of 450 nm and 550 nm satisfies the following formulae (1) and/or (2), and the water absorption is no greater than 1%. R(450)/R(550)<1   (1) K(450)/K(550)<1   (2) where R(450) and R(550) represent the in-plane retardation of the oriented polymer film at wavelengths of 450 nm and 550 nm, respectively, and K(450) and K(550) are the values calculated by K=[n z −(n x +n y )/2]×d (where n x , n y and n z represent the three-dimensional refractive indexes of the oriented polymer film as the refractive indexes in the direction of the x-axis, y-axis and z-axis, respectively, and d represents the thickness of the film) for the oriented polymer film at a wavelength of 450 nm and 550 nm, respectively. There are provided laminated retardation films and liquid crystal display devices employing the retardation film.

1. A retardation film, characterized in that said retardation film is a single oriented film, the retardation at wavelengths of 450 nm and 550 nm of said retardation film satisfies the following formulae (1) and/or (2), and the water absorption of said retardation film is no greater than 1%:
   R(450)/R(550)<1   (1)  
   K(450)/K(550)<1   (2)  
 
       where R(450) and R(550) represent the in-plane retardation of the oriented polymer film at wavelengths of 450 nm and 550 nm, respectively, and 450 nm and 550 nm, respectively,  and K(450) and K(550) are the values calculated by K=[n z −(n x +n y )/2]×d (where n x , n y  and n z  represent the three-dimensional refractive indexes of the oriented polymer film as the refractive indexes in the direction of the x-axis, y-axis and z-axis, respectively, and d represents the thickness of the film) for the oriented polymer film at a wavelength of 450 nm an  and 550 nm, respectively, wherein the absolute value of R(   550   )  is  20  nm or more and/or K (   550  nm )  is  20  nm or more . 
     
     
       2. A retardation film according to  claim 1 , wherein the retardation at wavelengths of 450 nm, 550 nm and 650 nm satisfies the following formulae (3) and (4):
   0.6<R(450)/R(550)<0.97   (3)  
   1.01<R(650)/R(550)<1.4   (4)  
 
       where R(650) represents the in-plane retardation of the oriented polymer film at a wavelength of 650 nm. 
     
     
       3. A retardation film according to  claim 1  or  2 , wherein the retardation is smaller with a shorter wavelength in the wavelength range of 400-700 nm. 
     
     
       4. A retardation film according to  claim 1 , which comprises an oriented polymer film wherein
 (1) the film is composed of a polymer comprising a monomer unit of a polymer with positive refractive index anisotropy (hereunder referred to as “first monomer unit”) and a monomer unit of a polymer with negative refractive index anisotropy (hereunder referred to as “second monomer unit”),  
 (2) R(450)/R(550) for the polymer based on said first monomer unit is smaller than R(450)/R(550) for the polymer based on the second monomer unit, and  
 (3) the film has positive refractive index anisotropy.  
 
     
     
       5. A retardation film according to  claim 1 , which comprises an oriented polymer film wherein
 (1) the film is composed of a polymer comprising a monomer unit that forms a polymer with positive refractive index anisotropy (hereunder referred to as “first monomer unit”) and a monomer unit that forms a polymer with negative refractive index anisotropy (hereunder referred to as “second monomer unit”),  
 (2) R(450)/R(550) for the polymer based on said first monomer unit is larger than R(450)/R(550) for the polymer based on the second monomer unit, and  
 (3) the film has negative refractive index anisotropy.  
 
     
     
       6. A retardation film according to  claim 1 , wherein said oriented polymer film is made of a polymer material with a glass transition temperature of 120° C. or higher. 
     
     
       7. A retardation film according to  claim 1 , wherein said oriented polymer film contains a polycarbonate with a fluorene skeleton. 
     
     
       8. A retardation film according to  claim 1 , which is an oriented polymer film comprising copolymer and/or blend of polycarbonates in which 30-90 mole percent of the total consists of a repeating unit represented by the following general formula (I): 
                 
 where R 1 -R 8  are each independently selected from among hydrogen, halogen atoms and hydrocarbon groups of 1-6 carbon atoms, and X is 
                 
 
  and 70-10 mole percent of the total consists of a repeating unit represented by the following general formula (II): 
                 
 
 where R 9 -R 16  are each independently selected from among hydrogen, halogen atoms and hydrocarbon groups of 1-22 carbon atoms, and Y is 
                 
 
  or —R 23 —,  
 where in Y, R 17 -R19, R 21  and R 22  are each independently selected from among hydrogen, halogen atoms and hydrocarbon groups of 1-22 carbon atoms, R 20  and R 23  are selected from among hydrocarbon groups of 1-20 carbon atoms, and Ar is selected from among aryl groups of 6-10 carbon atoms.  
 
     
     
       9. A retardation film according to  claim 8 , which is an oriented polymer film comprising copolymer and/or blend of polycarbonates in which 35-85 mole percent of the total consists of a repeating unit represented by the following general formula (III): 
                 
 where R 24  and R 25  are each independently selected from among hydrogen and methyl,  
 and 65-15 mole percent of the total consists of a repeating unit represented by the following general formula (IV): 
                 
 
 where R 26  and R 27 , are each independently selected from among hydrogen and methyl,  
 and Z is selected from among 
                 
 
 
     
     
       10. A retardation film according to  claim 5 , which is a blended oriented polymer film in which said polymer with positive refractive index anisotropy is poly(2,6-dimethyl-1,4-phenyleneoxide) and said polymer with negative refractive index anisotropy is polystyrene, wherein the polystyrene content is from 67 wt % to 75 wt %. 
     
     
       11. A retardation film according to  claim 1 , wherein the b* value representing the object color is 1.3 or smaller. 
     
     
       12. A retardation film according to  claim 1 , which is a λ/4 plate. 
     
     
       13. A retardation film according to  claim 1 , which is a λ/2 plate. 
     
     
       14. A retardation film according to  claim 12  or  13 , wherein R(550)≧90 nm. 
     
     
       15. A laminated retardation film prepared by laminating a λ/4 plate and a λ/2 plate, wherein both the λ/4 plate and λ/2 plate are a retardation film according to  claim 1 . 
     
     
       16. A laminated retardation film according to  claim 15 , wherein the angle formed between the optical axes of the λ/4 plate and λ/2 plate is in the range of 50°-70°. 
     
     
       17. A circular polarizing plate or elliptical polarizing plate prepared by laminating a polarizing plate with a retardation film according to  claim 1 . 
     
     
       18. A circular polarizing plate or elliptical polarizing plate prepared by laminating a reflective polarizing plate with a retardation film according to  claim 1 . 
     
     
       19. A circular polarizing plate or elliptical polarizing plate prepared by laminating a polarizing plate with a retardation film according to  claim 1  and a reflective polarizing plate. 
     
     
       20. A circular polarizing plate or elliptical polarizing plate according to  claim 18  or  19 , wherein said reflective polarizing plate has a function of reflecting only circularly polarized light rotated in one direction. 
     
     
       21. A circular polarizing plate or elliptical polarizing plate according to  claim 20 , wherein said reflective polarizing plate is composed of a cholesteric liquid crystal polymer. 
     
     
       22. A liquid crystal display device provided with a retardation film according to  claim 1 . 
     
     
       23. A liquid crystal display device according to  claim 22 , which is a reflective liquid crystal display device. 
     
     
       24. A liquid crystal display device according to  claim 22 , wherein said retardation film is a viewing angle compensating plate. 
     
     
       25. A retardation film which is a retardation film comprised of a single polycarbonate oriented film, wherein the retardation at wavelengths of 450 nm and 550 nm satisfies the following formula (1):
   R(450)/R(550)<1   (1)  
 
       where R(450) and R(550) represent the in-plane retardation of the oriented polymer film at wavelengths of 450 nm and 550 nm, respectively, and R(550) is at least 50 nm. 
     
     
       26. A reflective liquid crystal display device provided with a polarizing plate, a λ/4 plate and a liquid crystal cell containing a liquid crystal layer between two substrates each with an electrode with at least one of the electrodes being a transparent electrode in that order, the reflective liquid crystal display device employing as the λ/4 plate a retardation film comprising a single oriented polycarbonate film, wherein the retardation at wavelengths of 450 nm and 550 nm satisfies the following formula (1):
   R(450)/R(550)<1  
 
       where R(450) and R(550) represent the in-plane retardation of the oriented polymer film at wavelengths of 450 nm and 550 nm, respectively, and R(550) is 100-180 nm.