Biaxially drawn multilayer laminated film and method for producing the same

Abstract

A film composed of a number of layers having different refractive indices and alternately laminated one upon another has characteristic optical properties by light interference. Conventional films having such structure have problems of poor interlaminar adhesivity and low tear strength. The problems are solved by a film having the following constitution. A biaxially drawn multilayer laminated film composed of alternately laminated 1st layers and 2nd layers at a total layer number of 11 or more. Each layer has a thickness of 0.05 to 0.5 μm. The 1st layer is made of a crystalline thermoplastic resin and the 2nd layer is made of a crystalline thermoplastic resin having a composition different from that of the resin constituting the 1st layer. The maximum light reflectance of the film within the wavelength range of 350 to 2,000 nm is higher than the base line reflectance obtained from a light reflectance curve within the wavelength range of 350 to 2,000 nm by 20% or over.

1 - 17 . (canceled)  
   
   
       18 . A method for producing a biaxially drawn multilayer laminated film comprising 
 a film-forming process for forming a sheet composed of alternately laminated crystalline thermoplastic resin for the 1st layer and crystalline thermoplastic resin for the 2nd layer having a melting point lower than that of the crystalline thermoplastic resin for the 1st layer by 15° C. or over at a total layer number of 11 or more,    a process for drawing the obtained sheet in the film-forming direction and the lateral direction at a draw ratio of 2 to 50 each, and    a process for heat-setting the product at a temperature within a range from a temperature lower than the melting point of the crystalline thermoplastic resin for the 2nd layer by 10° C. to a temperature lower than the melting point of the crystalline thermoplastic resin for the 1st layer by 15° C.    
   
   
       19 . A method for producing a biaxially drawn multilayer laminated film comprising 
 a film-forming process for forming a sheet composed of alternately laminated polyester for the 1st layer containing ethylene terephthalate as a main component and having a melting point of 250 to 260° C. and polyester for the 2nd layer having a melting point lower than that of the polyester for the 1st layer by 15° C. or over at a total layer number of 11 or more,    a process for drawing the obtained sheet in the film-forming direction and the lateral direction at a draw ratio of 2 to 50 each, and    a process for heat-setting the product at a temperature within a range from a temperature lower than the melting point of the polyester for the 2nd layer by 10° C. to a temperature lower than the melting point of the polyester for the 1st layer by 15° C.    
   
   
       20 . A method for producing a biaxially drawn multilayer laminated film comprising 
 a film-forming process for forming a sheet composed of alternately laminated polyester for the 1st layer containing ethylene 2,6-naphthalenedicarboxylate as a main component and having a melting point of 260 to 270° C. and polyester for the 2nd layer having a melting point lower than that of the polyester for the 1st layer by 15° C. or over at a total layer number of 11 or more,    a process for drawing the obtained sheet in the film-forming direction and the lateral direction at a draw ratio of 2 to 50 each, and    a process for heat-setting the product at a temperature within a range from a temperature lower than the melting point of the polyester for the 2nd layer by 10° C. to a temperature lower than the melting point of the polyester for the 1st layer by 15° C.