Cellulose ester film and its manufacturing method

Abstract

Disclose is a cellulose ester film having a dry thickness of 20 to 60 μm, wherein the cellulose ester film is manufactured according to a solution cast film manufacture process comprising the step of providing a cellulose ester dope, casting the cellulose ester dope on a support to form a cellulose ester web, peeling the cellulose ester web at a peel position from the support, transporting the peeled web to a dryer, drying the peeled web therein to form a cellulose ester film, and winding the cellulose ester film around a spool, the residual solvent at the winding step of the cellulose ester film being not more than 0.05% by weight.

What is claimed is:  
     
         1 . A cellulose ester film having a dry thickness of 20 to 60 μm, wherein the cellulose ester film is manufactured according to a solution cast film manufacture process comprising the steps of providing a cellulose ester dope, casting the cellulose ester dope on a support to form a cellulose ester web, peeling the cellulose ester web at a peel position from the support, transporting the peeled web to a dryer, drying the peeled web therein to form a cellulose ester film, and winding the cellulose ester film around a spool, the residual solvent content at the winding step of the cellulose ester film being not more than 0.05% by weight.  
     
     
         2 . The cellulose ester film of  claim 1 , wherein the difference between the maximum residual solvent content and the minimum residual solvent content in the transverse direction of the cellulose ester film is not more than 0.02% by weight.  
     
     
         3 . A cellulose ester film having a dry thickness of 20 to 60 μm, the cellulose ester film being manufactured according to a solution cast film manufacture process comprising the steps of providing a cellulose ester dope, casing the cellulose ester dope on a support to form a cellulose ester web, peeling the cellulose ester web at a peel position from the support, transporting the peeled web to a dryer, drying the peeled web therein to form a cellulose ester film, and winding the cellulose ester film around a spool, wherein the peeled web is transported through a transport device from the peel position to a tension changing device nearest to the peel position at a tension of 10 to 100 N/m, the tension changing device being located between the peel position and the spool.  
     
     
         4 . The cellulose ester film of  claim 3 , wherein the tension is 10 to 80 N/m.  
     
     
         5 . The cellulose ester film of  claim 3 , wherein the tension is 10 to 50 N/m.  
     
     
         6 . The cellulose ester film of  claim 3 , wherein the distance between the peel position and the tension changing device is 2 to 90 m in terms of the web length.  
     
     
         7 . The cellulose ester film of  claim 3 , wherein the transport device uses guide rollers or an air float system.  
     
     
         8 . The cellulose ester film of  claim 7 , wherein some or all of the guide rollers are tendency rollers.  
     
     
         9 . A cellulose ester film having a dry thickness of 20 to 60 μm, the cellulose ester film being manufactured according to a solution cast film manufacture process comprising the steps of providing a cellulose ester dope, casting the cellulose ester dope on a support to form a cellulose ester web, peeling the cellulose ester web at a peel position from the support, transporting the peeled web to a dryer, drying the peeled web therein to form a cellulose ester film, and winding the cellulose ester film around a spool, wherein the cellulose ester dope is provided by a method comprising the steps of a) mixing a cellulose ester and one or more solvents comprising an organic solvent with a boiling point BP (° C.) as the main organic solvent in a tightly sealed pressure resistant vessel and heating the resulting mixture to around BP, b) unsealing the vessel at that temperature to allow it to stand for not less than 6 minutes, re-sealing the vessel and further heating the mixture to a temperature of from BP to BP+50 (° C.) to obtain a cellulose ester dope.  
     
     
         10 . The cellulose ester film of  claim 9 , wherein the cellulose ester film contains no air bubbles with a size of not less than 0.3 μm.  
     
     
         11 . The cellulose ester film of  claim 9 , wherein the method comprising the steps of after the re-sealing, c) further heating the mixture to a temperature of BP+20 to BP+50 (° C.) to be in a state of increased pressure, and d) maintaining the resulting mixture at that pressure to obtain a cellulose ester dope.  
     
     
         12 . The cellulose ester film of  claim 11 , wherein the cellulose ester film contains no air bubbles with a size of not less than 0.3 μm.  
     
     
         13 . The cellulose ester film of  claim 1 , wherein the residual solvent content is not more than 0.04% by weight.  
     
     
         14 . The cellulose ester film of  claim 1 , wherein the residual solvent content is not more than 0.02% by weight.