Transparent Substrate

Abstract

The present invention provides a formed article, or more specifically a transparent substrate, which effectively utilizes a natural stuff and which has a low linear expansion coefficient, a high light transmittance and an appropriate level of moisture permeability. The transparent substrate includes at least an oxidized polysaccharide and has a linear expansion coefficient of 50 ppm/° C. or less at 30-150° C. and a light transmittance of 70% or more at 660 nm. Its manufacturing method includes an oxidation process in which cellulose reacts with TEMPO or its derivatives as a catalyst to be oxidized in water under the presence of a co-oxidant, along with a fiberizing process in which the oxidized cellulose is fiberized in water to form a cellulose fiber, and a substrate-forming process in which a transparent substrate is formed from a cellulose dispersion liquid containing the cellulose fiber.

What is claimed is: 
     
         1 . A transparent substrate comprising a polysaccharide, said polysaccharide being oxidized and said transparent substrate having a linear expansion coefficient of 50 ppm/° C. or less at a temperature in the range of 30-150° C. and a light transmittance of 70% or more at 660 nm. 
     
     
         2 . The transparent substrate according to  claim 1 , further comprising a polymer including a plurality of functional groups in a single molecule, and wherein said functional groups are one or both of an oxazoline group and an isocyanate group. 
     
     
         3 . The transparent substrate according to  claim 2 , wherein said polysaccharide is a cellulose fiber having a crystal structure of cellulose I, and wherein said cellulose fiber has a fiber width in the range of 1 nm to 200 nm. 
     
     
         4 . The transparent substrate according to  claim 3 , wherein an aldehyde group amount contained in said cellulose fiber is 0.2 mmol/g or less. 
     
     
         5 . The transparent substrate according to  claim 4 , wherein a carboxy group amount contained in said cellulose fiber is in the range of 0.1-2.5 mmol/g. 
     
     
         6 . The transparent substrate according to  claim 5 , wherein said cellulose fiber has a degree of polymerization in the range of 100-1000. 
     
     
         7 . The transparent substrate according to  claim 5 , wherein said transparent substrate contains said cellulose fiber at a ratio in the range of 1-99.9%. 
     
     
         8 . The transparent substrate according to  claim 5 , further comprising a UV absorber, a degradation inhibitor and a hydrophobic additive. 
     
     
         9 . The transparent substrate according to  claim 1 , wherein a light transmittance of said transparent substrate at 450 nm after heating at 100° C. for 3 hours is 70% or more. 
     
     
         10 . The transparent substrate according to  claim 1 , wherein said transparent substrate has a moisture permeability of 1-99 g/m 2 /24 hr. 
     
     
         11 . The transparent substrate according to  claim 2 , wherein a YI value of said transparent substrate after heating at 150° C. for 1.5 hours is 2 or less. 
     
     
         12 . The transparent substrate according to  claim 2 , wherein water absorption of said transparent substrate after immersing in water for an hour is 50% or less. 
     
     
         13 . The transparent substrate according to  claim 5 , wherein said transparent substrate has a thickness in the range of 10-200 μm. 
     
     
         14 . A protection film for a polarizing plate comprising the transparent substrate according to  claim 5 .