Retardation film and production method thereof

1. A retardation film, made of a material containing a component (A) and a component (B), wherein

the component (A) is cellulose acylate satisfying the following expression (1), and

the component (B) is cellulose acylate or cellulose ether which has a molecular weight different from a molecular weight of the component (A) and whose residual degree of hydroxyl group is 0.30 or more,

2.20 D Sac( A )+ D Say( A )≦2.90  (1)

where DSac(A) represents an acetyl substitution degree of the component (A),

DSay(A) represents a total substitution degree of acyl group which constitutes the component (A) and whose carbon number is three or four, and

wherein the component (A) satisfies the following expression (2),

D Say( A )/ D Sac( A )≧2  (2), and

wherein

the components (A) and (B) satisfy the following expression (10),

10,000≦Mn( A )−Mn( B )≦100,000  (10)

where Mn(A) represents a number average molecular weight of the component (A) on the basis of gel permeation chromatography and Mn(B) represents a number average molecular weight of the component (B) on the basis of the gel permeation chromatography,

Mn(A) and Mn(B) respectively satisfy the following expressions (11) and (12),

Mn( A )=30,000 to 150,000  (11)

Mn( B )=10,000 to 50,000  (12)

and wherein the amount of the component (A) is 30 to 40 wt %, and the amount of the component (B) is 70 to 60 wt %.

2. The retardation film as set forth in claim 1 , wherein

the component (B) is cellulose acylate satisfying the following expressions (3) and (4), and the components (A) and (B) satisfy the following expression (5),

2.00 D Sac( B )+ D Say( B )≦2.70  (3)

D Say( B )/ D Sac( B )≧2  (4)

( D Sac( A )+ D Say( A ))−0.05≧( D Sac( B )+ D Say( B ))  (5)

where DSac(B) represents an acetyl substitution degree of the component (B), and

DSay(B) represents a total substitution degree of acyl group which constitutes the component (B) and whose carbon number is three or four.

3. The retardation film as set forth in claim 1 , wherein

cellulose acylate of the component (A) is cellulose acetate propionate satisfying the following expressions (6) and (7), and

cellulose acylate of the component (B) is cellulose acetate propionate satisfying the following expressions (8) and (9),

2.20 ≦D Sac( A )+ D Spr( A )≦2.90  (6)

D Spr( A )/ D Sac( A )≧2  (7)

2.00 ≦D Sac( B )+ D Spr( B )≦2.70  (8)

D Spr( B )/ D Sac( B )≧2  (9)

where DSpr(A) represents a propionyl substitution degree of the component (A), and DSpr(B) represents a propionyl substitution degree of the component (B).

4. The retardation film as set forth in claim 1 , wherein

a molecular weight distribution (Mw(A)/Mn(A)) of the component (A) is 2.5 to 5.0, and a molecular weight distribution (Mw(B)/Mn(B)) of the component (B) is 1.5 to 4.0, and (Mw(A)/Mn(A))>(Mw(AB)/Mn(AB)),

where Mw(AB) represents a weight average molecular weight of a mixture of the components (A) and (B) present in the material of retardation film on the basis of the gel permeation chromatography and Mn(AB) represents a number average molecular weight of the mixture of the components (A) and (B) on the basis of the gel permeation chromatography.

5. The retardation film as set forth in claim 1 , wherein the following expressions (13) and (14) are satisfied,

Re(450)/Re(550)=0.80 to 0.95  (13)

Re(550)<Re(650)  (14)

where Re(450), Re(550), and Re(650) respectively represent retardation values at a wavelength of 450 nm, a wavelength of 550 nm, and a wavelength of 650 nm.

6. An optical compensation polarization plate, comprising the retardation film as set forth in claim 1 .

7. The optical compensation polarization plate as set forth in claim 6 , wherein the retardation film is laminated directly onto a polarizer.

8. A method for producing the retardation film as set forth in claim 1 ,

said method comprising the step of casting onto a support body a solution containing the components (A) and (B).

9. The method as set forth in claim 8 , wherein the solution contains methylene chloride.

10. The method as set forth in claim 8 , wherein a solvent contained in the solution includes 70 to 99 wt % of methylene chloride and 1 to 30 wt % of alcohol whose carbon number is three or less.

11. The method as set forth in claim 8 , wherein the retardation film is drawn at least in an uniaxial direction.

12. A method for producing an optical compensation polarization plate,

said method comprising the step of laminating the retardation film, obtained by the method as set forth in claim 8 , onto a polarizer with a protection film for polarizer, and/or other optical member.

13. A method for producing an optical compensation polarization plate,

said method comprising the step of laminating the retardation film, obtained by the method as set forth in claim 8 , directly onto a polarizer.