Cellulose acylate film, its production method, polarizer and liquid crystal display device

A method for producing a cellulose acylate film, comprising:

• forming a polymer solution that comprises a cellulose acylate and a sugar ester compound comprising from 1 to 12 pyranose structures or furanose structures in which at least one hydroxyl group is esterified, into a film,
• stretching the film, and
• processing the stretched film in high temperature and high humidity environments under a condition satisfying the following formulae (7) and (8):
• 70° C.≦temperature of the treatment≦140° C. (7)
• 250 g/m3≦volumetric humidity of the treatment≦400 g/m3 (8)

A cellulose acylate film produced by the method for producing a cellulose acylate film of comprising:

• forming a polymer solution that comprises a cellulose acylate and a sugar ester compound comprising from 1 to 12 pyranose structures or furanose structures in which at least one hydroxyl group is esterified, into a film,
• stretching the film, and
• processing the stretched film in high temperature and high humidity environments under a condition satisfying the following formulae (7) and (8):
• 70° C.≦temperature of the treatment≦140° C. (7)
• 250 g/m3≦volumetric humidity of the treatment≦400 g/m3 (8)

A polarizer comprising a polarizing element and the cellulose acylate film comprising:

• a cellulose acylate and a sugar ester compound, wherein the sugar ester comprises from 1 to 12 pyranose structures or furanose structures in which at east one hydroxyl group is esterified,
• wherein the film has an in-plane retardation at a wavelength of 550 nm satisfying the following formula (1):
• 40 nm≦Re(550)≦60 nm (1)
• wherein RE(550) means the in-plane retardation of the film at a wavelength of 550 nm,
• wherein the film has a thickness-direction retardation at a wavelength of 550 nm satisfying the following formula (2):
• 100 nm≦Rth(550)≦140 nm (2)
• wherein Rth(550) means the thickness-direction retardation of the film at a wavelength of 550 nm,
• the film has a dimensional change before and after 24 hours at 60° C. and at a relative humidity of 90% satisfying the following formula (3) in the film conveying direction and in the direction perpendicular thereto,
• −0.5%≦{(L′−L0))/L0}×100≦0.5% (3)
• wherein L0 means the length (unit:
• mm) of the film before aged for 24 hours at 60° C. and at a relative humidity of 90%;
• and L′ means the length (units:
• mm) of the film after aged for 24 hours at 60° C. and at a relative humidity 90% and further after conditioned for 2 hours,
• and wherein the film has an internal haze of at most 0.1% on at least one side of the polarizing element.

A liquid crystal display device comprising a polarizing element and the cellulose acylate film comprising a cellulose acylate and a sugar ester compound

• wherein the sugar ester comprises from 1 to 12 pyranose structures or furanose structures in which at least one hydroxyl group is esterified,
• wherein the film has an in-plane retardation at a wavelength of 550 nm satisfying the following formula (1):
• 40 nm≦Re(550)≦60 nm (1)
• wherein RE(550) means the in-plane retardation of the film at a wavelength of 550 nm, wherein the film has a thickness-direction retardation at a wavelength of 550 nm satisfying the following formula (2):
• 100 nm≦Rth(550)≦140 nm (2)
• wherein Rth(550) means the thickness-direction retardation of the film at a wavelength of 550 nm,
• the film has a dimensional change before and after 24 hours at 60° C. and at a relative humidity of 90% satisfying the following formula (3) in the film conveying direction and in the direction perpendicular thereto,
• −0.5%≦{(L′−L0)/L0}×100≦0.5% (3)
• wherein L0 means the length (unit:
• mm) of the film before aged for 24 hours at 60° C. and at a relative humidity of 90%;
• and L′ means the length (unit:
• mm) of the film after aged for 24 hours at 60° C. and at a relative humidity of 90% and further after conditioned for 2 hours,
• and wherein the film has an internal haze of at most 0.1% on at least one side of the polarizing element.