Polymeric piezoelectric material, and process for producing the same

Abstract

The invention provides a polymeric piezoelectric material including a helical chiral polymer having a weight-average molecular weight of from 50,000 to 1,000,000 and having optical activity, wherein a crystallinity of the material measured by a DSC method is from 20% to 80%, and a product of a standardized molecular orientation MORc measured by a microwave transmission type molecular orientation meter based on a reference thickness of 50 μm and the crystallinity is from 25 to 250.

1 . A polymeric piezoelectric material comprising a helical chiral polymer having a weight-average molecular weight of from 50,000 to 1,000,000 and having optical activity,
 wherein a crystallinity of the material measured by a DSC method is from 20% to 80%, and a product of a standardized molecular orientation MORc measured by a microwave transmission type molecular orientation meter based on a reference thickness of 50 μm and the crystallinity is from 25 to 250.   
     
     
         2 . The polymeric piezoelectric material according to  claim 1 , wherein the crystallinity is 40.8% or less. 
     
     
         3 . The polymeric piezoelectric material according to  claim 1 , wherein an internal haze with respect to visible light is 40% or less. 
     
     
         4 . The polymeric piezoelectric material according to  claim 1 , wherein the standardized molecular orientation MORc is from 1.0 to 15.0. 
     
     
         5 . The polymeric piezoelectric material according to  claim 1 , wherein a piezoelectric constant d 14  measured by a displacement method at 25° C. is 1 pm/V or higher. 
     
     
         6 . The polymeric piezoelectric material according to  claim 1 , wherein the helical chiral polymer is a polylactic acid-type polymer having a main chain comprising a repeating unit represented by the following formula (1): 
       
         
           
           
               
               
           
         
       
     
     
         7 . The polymeric piezoelectric material according to  claim 1 , wherein an optical purity of the helical chiral polymer is 95.00% ee or higher. 
     
     
         8 . The polymeric piezoelectric material according to  claim 1 , wherein a content of the helical chiral polymer is 80 mass % or more. 
     
     
         9 . The polymeric piezoelectric material according to  claim 1 , wherein an internal haze with respect to visible light is 1.0% or less. 
     
     
         10 . A process for producing the polymeric piezoelectric material according to  claim 1 , comprising a first step of heating a sheet in an amorphous state containing the helical chiral polymer to obtain a pre-crystallized sheet, and a second step of stretching the pre-crystallized sheet simultaneously in biaxial directions. 
     
     
         11 . The process for producing the polymeric piezoelectric material according to  claim 10 , wherein, in the first step for obtaining the pre-crystallized sheet, the sheet in an amorphous state is heated at a temperature T satisfying the following formula until the crystallinity becomes between 1% and 70%:
   Tg−40° C.≦T≦Tg+40° C.
   
       wherein Tg represents a glass transition temperature of the helical chiral polymer. 
     
     
         12 . The process for producing the polymeric piezoelectric material according to  claim 10 , wherein, in the first step for obtaining the pre-crystallized sheet, the sheet in an amorphous state containing polylactic acid as the helical chiral polymer is heated at from 20° C. to 170° C. for from 5 sec to 60 min. 
     
     
         13 . The process for producing the polymeric piezoelectric material according to  claim 10 , wherein an annealing treatment is conducted after the second step.