Polyester film, use thereof and metal laminated sheet made of said film, and metal can and metal lid made of the sheet

Abstract

A polyester film made from two kinds of polyester resins and having a specific DSC (and a specific glass transition point) is provided, (i) which is superior in mechanical property, capable of thermocompression bonding with a metal sheet, despite a high degree of crystallization of the film, reduces quality change of plastic film laminated on the metal sheet even if faced with variation of conditions of thermocompression bonding with the metal sheet, and which is capable of thermocompression bonding even at a relatively low temperature, (ii) which is superior in formability, (iii) which is superior in flavoring property and impact resistance, and which obliterates occurrence of whitening or delamination of the film, or microcracks on the film, even if the film in the metal laminated sheet obtained by thermocompression bonding of the film on the metal sheet or on the surface of a metal can obtained by subjecting the metal laminated sheet to various form processings is crystallized, and (iv) which satisfies productivity at an industrial scale.

What is claimed is:  
     
         1 . A polyester film comprising a polyester resin composition comprising a polyethylene terephthalate resin (A) (10-70 wt %) and a polybutylene terephthalate resin (B) (90-30 wt %), 
 wherein the film after melting or softening to allow adhesion to an aluminum plate, followed by standing in a 270° C. atmosphere for 10 minutes, has 2 or more melting peaks in an area corresponding to not less than 180° C. and less than 280° C. of differential scanning calorimetry (DSC).    
     
     
         2 . The polyester film of  claim 1 , wherein the film has 2 or more melting peaks in an area of not less than 180° C. and less than 280° C. of differential scanning calorimetry (DSC) after standing in a 280° C. atmosphere for 10 minutes, and a glass transition point of not less than 20° C. and less than 60° C.  
     
     
         3 . A polyester film comprising a polyester resin composition comprising a polyethylene terephthalate resin (A) (10-70 wt %) a nd a polybutylene terephthalate resin (B) (90-30 wt %), 
 wherein the film has 2 or more melting peaks in an area corresponding to not less than 180° C. and less than 280° C. of differential scanning calorimetry (DSC) after standing in a 280° C. atmosphere for 10 minutes, and a glass transition point of not less than 20° C. and less than 60° C.    
     
     
         4 . The polyester film of  claim 3 , wherein the glass transition point is not less than 20° C. and less than 50° C.  
     
     
         5 . The polyester film of  claim 1  or  4 , which is to be laminated on a metal sheet.  
     
     
         6 . A metal laminated sheet comprising a metal sheet and the polyester film of  claim 1  or  4  laminated on the plate.  
     
     
         7 . A metal can or a lid of a metal can, which comprises the metal laminated sheet of claim  6 .