Solvent casting process, polarizing plate protective film, optically functional film and polarizing plate

Abstract

A process for solvent casting which comprises, casting a dope from a casting die onto a casting support, drying the cast dope on the casting support to form film, stripping off the film from the casting support, and further drying the film, wherein the dope has a solid matter content of from 17 mass % to 30 mass %, and a mean drying rate between the casting of the dope and the stripping off is more than 300 mass %/minute and not more than 1000 mass %/minute is proposed. The process for solvent casting for producing a film comprising the steps of casting a dope from a casting die to a casting support, forming the film by drying the dope to some extent, stripping off the film from the casting support and further drying the film while conveying the film with carrying it at both side edges of the film by a tenter under a specified condition is also proposed. The high-speed solution film forming methods enable to produce the film having good quality with stable conveying and with stable drying especially in the conveying of the film by the tenter machine in the drying steps after stripping off from the casting support.

1 . A process for solvent casting which comprises, casting a dope from a casting die onto a casting support, drying the cast dope on the casting support to form film, stripping off the film from the casting support, and further drying die film, wherein the dope has a solid matter content of from 17 mass % to 30 mass %, and a mean drying rate between the casting of the dope and the stripping off is more than 300 mass %/minute and not more than 1000 mass %/minute.  
     
     
         2 . A process for solvent casting which comprises, casting a dope from a casting die onto a casting support, drying the cast dope on the casting support to form film, stripping off the film from the casting support, and further drying the film, wherein the dope has a solid matter content of from 17 mass % to 30 mass %, and a mean drying rate within 15 m from die casting point of the dope is more than 300 mass %/minute and not more than 1000 mass %/minute.  
     
     
         3 . A process for solvent casting which comprises, casting a dope from a casting die onto a casting support, drying the cast dope on the casting support to form film, stripping off the film from the casting support, and further drying the film, wherein the dope has a solid matter content of from 17 mass % to 30 mass %, and the mean drying rate between 3 seconds and 20 seconds after the casting of the dope is more than 300 mass %/minute and not more than 1000 mass %/minute.  
     
     
         4 . The process for solvent casting of  claim 1 , wherein the casting support has a surface temperature of 10° C. or less, and temperature difference between arbitrary two points in the area on the surface of the casting support where the dope is cast is 5° C. or less.  
     
     
         5 . The process for solvent casting of  claim 1 , wherein the dope on the casting support is dried by streaming drying wind having an oxygen concentration of 10 vol. % or less, and a dew-point of the solvent contained in the drying wind is lower than the surface temperature of the casting support by 5° C. or more.  
     
     
         6 . The process for solvent casting of  claim 1 , wherein drying of said film stripped off from the casting support is started after 0.1-10 seconds from the stripping off, awhile adding tension to the film by a tenter.  
     
     
         7 . The process for solvent casting of  claim 1 , wherein drying of said film stripped off from the casting support is started in the range from 0.1 m to 10 m as conveyed distance from the stripping off, while adding tension to the film by a tenter.  
     
     
         8 . The process for solvent casting of  claim 1 , wherein said film stripped off from the casting support is conveyed by a cooling roller before being carried by a tenter and the surface temperature of the cooling roller is made lower than gelation temperature of the dope by 1-20° C.  
     
     
         9 . The process for solvent casting of  claim 1 , wherein said dope is cellulose acylate solution containing a plasticizer in an amount of from 0.1 mass % to 20 mass % of the cellulose acylate.  
     
     
         10 . The process for solvent casting of  claim 1 , wherein said dope is cellulose acylate solution containing a fluorine-containing surfactant in an amount of from 0.002 mass % to 2 mass % of the cellulose acylate.  
     
     
         11 . A polarizing plate protective film produced by the process for solvent casting of  claim 1 .  
     
     
         12 . An optically functional film produced by the process of solvent casting of  claim 1 .  
     
     
         13 . A polarizing plate comprising the polarizing plate protective film according to  claim 11  and/or the optically functional film according to  claim 12 .  
     
     
         14 . A process for solvent casting which comprises casting a dope from a casting die onto a casting support, drying the cast dope on the casting support form film, stripping off the film from the casting support, and further drying the film while conveying the film with carrying it at both side edges of the film by a tenter, wherein dry thickness (X μm) of the both side edges and mean dry thickness (T μm) of product portion of the film have following relationship: in the case that the tenter is a pin tenter, 
 in the range of T≦60,  
 40≦X≦200  (1) 
 in the case of 60<T≦120,  
 40+( T− 60)×0.2≦ X≦ 300  (2) 
 in the case of 120<T,  
 52+( T− 120)×0.2≦ X≦ 400  (3) 
 in the case that the tenter is a clip tenter,  
 in the range of T≦40,  
 5≦ X≦T+ 50  (4) 
 in the case of 40<T≦120,  
 20 ≦X≦T+ 100  (5) 
 in the case of T>120,  
 60≦ X≦T+ 200  (6) 
 
     
     
         15 . The process for solvent casting of  claim 14 , wherein the tenter is a pin tenter.  
     
     
         16 . The process for solvent casting of  claim 14 , wherein the tenter is a clip tenter.  
     
     
         17 . A process for solvent casting which comprises casting a dope from a casting die onto a casting support, drying the cast dope on the casting support form film, stripping off the film from the casting support, and further drying the film while conveying the film with carrying it at both side edges of the film by a pin tenter, wherein residual volatile component content of both side edges of the film being carried by the pin tenter is from 30 mass % to 320 mass % of solid matter at the beginning of being carried by the pin tenter.  
     
     
         18 . A process for solvent casting of  claim 15 , wherein residual volatile component content of both side edges of the film being carried by the clip tenter is from 30 mass % to 320 mass % of solid matter at the beginning of being carried by the pin tenter.  
     
     
         19 . A process for solvent casting which comprises casting a dope from a casting die onto a casting support, drying the cast dope on the casting support form film, stripping off the film from the casting support, and further drying the film while conveying the film with carrying it at both side edges of the film by a clip tenter, wherein residual volatile component content of both side edges of the film being carried by the clip tenter is from 1 mass % to 200 mass % of solid matter at the beginning of being carried by the clip tenter.  
     
     
         20 . The process for solvent casitng of  claim 19 , wherein residual volatile component content of both side edges of the film being carried by the clip tenter is from 1 mass % to 200 mass % of solid matter at the beginning of being carried by the clip tenter.  
     
     
         21 . The process for solvent casting of  claim 14 , wherein the temperature of said tenter machine is lower than boiling point of residual solvent in the film, by 2-50° C.  
     
     
         22 . The process for solvent casting of  claim 14 , wherein said tenter is forced to be cooled by a cooling means.  
     
     
         23 . The process for solvent casting of  claim 14 , wherein a temperature elevation of the tenter is prevented by a drying wind shielding means.  
     
     
         24 . The process for solvent casting of  claim 14 , wherein said temperature of the film at both side edges carried by the tenter is lower than the boiling point of residual solvent by 2-50° C., but higher than dew-point of atmospheric gas by 2-50° C.  
     
     
         25 . The process for solvent casting of  claim 24 , wherein said temperature of the film at both side edges carried by the tenter is lower than gelation temperature of the film by 2-50° C.  
     
     
         26 . The process for solvent casting of  claim 14 , wherein the solvent evaporating from said film while being carried by said tenter is 50-99% of the solvent evaporating from the film between being stripped off from the casting support and being wound up after drying.  
     
     
         27 . The process for solvent casting of  claim 14 , wherein an oxygen concentration in the drying zone using the tenter is rendered 10% by volume or less, and wherein solvent gas generated in the drying zone is recovered by condensation water content of the recovered solvent is decreased to 2% by weight or less, and then reused as a part of raw material.  
     
     
         28 . The process for solvent casting of  claim 14 , wherein tension in a width direction given to said film by the tenter is 1960 N/m (200 kg/m) or less.  
     
     
         29 . The process for solvent casting of  claim 14 , wherein temperature distribution in width direction of the product portion of the film is 10° C. or less, while both side edges are carried by the tenter.  
     
     
         30 . The process for solvent casting of  claim 14 , wherein wind velocity distribution on the film surface in width direction of the product portion of the film is 10% or less, while both side edges are carried by the tenter.  
     
     
         31 . The process for solvent casting of  claim 14 , wherein an overall coefficient of heat transfer to the film by the drying wind is 5-300 kcal/m 2 ·hr·° C.  
     
     
         32 . The process for solvent casting of  claim 14 , wherein an overall coefficient of heat transfer of tenter cooled by the cooling means is 10-300 kcal/m 2 ·hr·° C.  
     
     
         33 . The process for solvent casting of  claim 14 , wherein said dope is a solution of a member selected from the group consisting of cellulose acylate, polycarbonate, aramid group polymers and norbornane group polymers.  
     
     
         34 . The process for solvent casting of  claim 14 , wherein said dope contains at least 10% by weight or more of cellulose acylate, wherein substitution ratio A of acyl groups at 6-position and substitution ratio B of remaining acyl groups satisfies formula (7) and formula (8).  
       A≧0.75  (7) 
       2.5 ≦A+B≦ 3.0  (8) 
     
     
         35 . The process for solvent casting according to  claim 34 , wherein the solvent of the dope comprises 50-90 mass % of methyl acetate, 0-40 mass % of acetone and 5-40 mass % of alcohol.  
     
     
         36 . The solution film forming method according to  claim 34 , wherein the dope contains a plasticizer in an amount of from 0.1 mass % to 20 mass % of the cellulose acylate.  
     
     
         37 . The process for solvent casting of  claim 34 , wherein said dope is cellulose acylate solution containing a fluorine-containing surfactant in an amount of from 0.002 mass % to 2 mass % of the cellulose acylate.  
     
     
         38 . A polarizing plate protective film produced by the process for solvent casting of  claim 14 .  
     
     
         39 . An optical by functional film produced by the process for solvent casting of  claim 14 .  
     
     
         40 . A polarizing plate comprising the polarizing plate protective film according to  claim 38  and/or the optically functional film according to  claim 39.