Biaxially oriented multi-layer laminated film and method for manufacture thereof

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 . A biaxially drawn multilayer laminated film composed of the 1st layers and the 2nd layers alternately laminated to a total layer number of 11 or more and subjected to biaxial drawing provided that each layer has a thickness of 0.05 to 0.5 μm, the 1st layer is made of a crystalline thermoplastic resin, the 2nd layer is made of a crystalline thermoplastic resin having a composition different from the composition of the resin constituting the 1st layer, the maximum reflectance of light within the wavelength range of 350 to 2,000 nm is higher than the base line reflectance obtained from the light reflection curve within the wavelength range of 350 to 2,000 nm by 20% or more, the film has plural melting points measured by differential scanning calorimetry, the temperature difference between the melting points is 5° C. or over and the film has at least one crystallization peak measured by differential scanning calorimetry.  
     
     
         2 . A biaxially drawn multilayer laminated film described in the  claim 1  wherein both of the crystalline thermoplastic resins of the 1st layers and the 2nd layers are polyester compositions.  
     
     
         3 . A biaxially drawn multilayer laminated film composed of the 1st layers and the 2nd layers alternately laminated to a total layer number of 11 or more and subjected to biaxial drawing provided that each layer has a thickness of 0.05 to 0.5 μm, the 1st layer is made of a polyester composition, the 2nd layer is made of a polyester composition having a composition different from the composition of the resin constituting the 1st layer, the maximum reflectance of light within the wavelength range of 350 to 2,000 nm is higher than the base line reflectance obtained by the light reflection curve within the wavelength range of 350 to 2,000 nm by 20% or more, and the ratio of the ethylene terephthalate component in the film is 80 mol % or more based on the total repeating units of the polyester.  
     
     
         4 . A biaxially drawn multilayer laminated film described in the  claim 3  wherein the film has plural melting points measured by differential scanning calorimetry and the temperature difference between the melting points is 5° C. or over.  
     
     
         5 . A biaxially drawn multilayer laminated film described in the  claim 3  wherein the crystallization peak measured by differential scanning calorimetry is within the range of 100 to 190° C.  
     
     
         6 . A biaxially drawn multilayer laminated film described in the  claim 3  wherein 1.5 to 20 mol % of the total repeating units is isophthalic acid component or 2,6-naphthalenedicarboxylic acid component.  
     
     
         7 . A biaxially drawn multilayer laminated film described in the  claim 3  wherein the polyester constituting the 1st layer is a crystalline polyester and at least 90 mol % of the total repeating units is ethylene terephthalate component.  
     
     
         8 . A biaxially drawn multilayer laminated film described in the  claim 3  wherein the polyester constituting the 2nd layer is a crystalline polyester and 75 to 97 mol % of the total repeating units is ethylene terephthalate component.  
     
     
         9 . A biaxially drawn multilayer laminated film described in the  claim 3  wherein the breaking strengths of the film in both film-forming direction and lateral direction are 50 MPa or over.  
     
     
         10 . A biaxially drawn multilayer laminated film composed of the 1st layers and the 2nd layers alternately laminated to a total layer number of 11 or more provided that each layer has a thickness of 0.05 to 0.5 μm, the 1st layer is made of a polyester composition, the 2nd layer is made of a polyester composition having a composition different from the composition of the polyester constituting the 1st layer, the maximum reflectance of light within the wavelength range of 350 to 2,000 nm is higher than the base line reflectance obtained from the light reflection curve within the wavelength range of 350 to 2,000 nm by 20% or more, and the ratio of ethylene 2,6-naphthalenedicarboxylate component in the film is 80 mol % or over based on the total repeating units of the polyester.  
     
     
         11 . A biaxially drawn multilayer laminated film described in the  claim 10  wherein the film has plural melting points measured by differential scanning calorimetry and the temperature difference between the melting points is 5° C. or over.  
     
     
         12 . A biaxially drawn multilayer laminated film described in the  claim 10  wherein the crystallization peak measured by differential scanning calorimetry is within the range of 150 to 220° C.  
     
     
         13 . A biaxially drawn multilayer laminated film described in the  claim 10  wherein 1.5 to 20 mol % of the total repeating units is terephthalic acid component or isophthalic acid component.  
     
     
         14 . A biaxially drawn multilayer laminated film described in the  claim 10  wherein the polyester constituting the 1st layer is a crystalline polyester and at least 90 mol % of the total repeating units is ethylene 2,6-naphthalene dicarboxylate component.  
     
     
         15 . A biaxially drawn multilayer laminated film described in the  claim 10  wherein the polyester constituting the 2nd layer is a crystalline polyester and 75 to 97 mol % of the total repeating units is ethylene 2,6-naphthalenedicarboxylate component.  
     
     
         16 . A biaxially drawn multilayer laminated film described in the  claim 10  wherein the breaking strengths of the film in both film-forming direction and lateral direction are 100 MPa or over.  
     
     
         17 . A biaxially drawn multilayer laminated film described in the  claim 10  wherein the thermal shrinkage of the film at 200° C.×10 min is 3% or below in both film-forming direction and lateral direction.  
     
     
         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.