Hydrolysis resistant polyester films

Abstract

A biaxially oriented polyester film comprising polyester and at least one hydrolysis stabiliser selected from a glycidyl ester of a branched monocarboxylic acid, wherein the monocarboxylic acid has from 5 to 50 carbon atoms, wherein said hydrolysis stabiliser is present in the film in the form of its reaction product with at least some of the end-groups of said polyester, and wherein said reaction product is obtained by the reaction of the hydrolysis stabiliser with the end-groups of the polyester in the presence of a metal cation selected from the group consisting of Group I and Group II metal cations.

1 . A process for the manufacture of a biaxially oriented polyester film, wherein the process comprises:
 (i) extruding a layer of molten polyester and at least one hydrolysis stabiliser selected from a glycidyl ester of a branched monocarboxylic acid, wherein the monocarboxylic acid has from 5 to 50 carbon atoms, wherein said hydrolysis stabiliser is present in the extrudate in the form of its reaction product with at least some of the end-groups of said polyester, and wherein said reaction product is obtained by reaction of the hydrolysis stabiliser with the end-groups of the polyester in the presence of a metal cation selected from the group consisting of Group I and Group II metal cations, wherein the extrusion temperature is within the range of from about 280 to about 300° C.;   (ii) quenching the extrudate;   (iii) stretching the quenched extrudate in two mutually perpendicular directions to effect orientation; and   (iv) heat-setting the film.   
     
     
         2 . The process according to  claim 1 , wherein the metal cation is selected from the group consisting of Group I metal cations. 
     
     
         3 . The process according to  claim 1 , wherein said polyester is polyethylene terephthalate. 
     
     
         4 . The process according to  claim 1 , wherein the process comprises the further step of manufacturing said hydrolysis stabiliser by reaction of epichlorohydrin with said branched monocarboxylic acid. 
     
     
         5 . The process according to  claim 1 , wherein the hydrolysis stabiliser is reacted with the polyester by injecting the hydrolysis stabiliser into the polyester prior to or during introduction of the polyester into the extruder. 
     
     
         6 . The process according to  claim 1 , wherein the film has one or more additional layer(s) disposed on one or both surfaces thereof to form a composite structure and wherein the process comprises co-extrusion of the respective layers. 
     
     
         7 . The process according to  claim 1 , wherein said orientation is sequential orientation effected by stretching the quenched extrudate in a first, longitudinal direction and then in a transverse direction, wherein stretching in said transverse direction is effected in a stenter apparatus. 
     
     
         8 . The process according to  claim 1 , wherein stretching is effected at temperatures higher than the Tg of the polyester. 
     
     
         9 . The process according to  claim 8 , wherein stretching is effected at temperatures about 15° C. higher than the Tg of the polyester. 
     
     
         10 . The process according to  claim 1 , wherein the heat-set temperature is within the range of from about 200° C. to about 225° C. 
     
     
         11 . The process according to  claim 1 , wherein the biaxially oriented polyester film comprises at least one hydrolysis stabiliser selected from a glycidyl ester of a branched monocarboxylic acid, wherein the monocarboxylic acid has from 5 to 50 carbon atoms, wherein said hydrolysis stabiliser is present in the film in the form of its reaction product with at least some of the end-groups of said polyester and wherein said reaction product is obtained by the reaction of the hydrolysis stabiliser with the end-groups of the polyester in the presence of a metal cation selected from the group consisting of Group I and Group II metal cations. 
     
     
         12 . The process according to  claim 2 , wherein the biaxially oriented polyester film comprises polyester and at least one hydrolysis stabiliser selected from a glycidyl ester of a branched monocarboxylic acid, wherein the monocarboxylic acid has from 5 to 50 carbon atoms, wherein said hydrolysis stabiliser is present in the film in the form of its reaction product with at least some of the end-groups of said polyester, and wherein the polyester film further comprises a metal cation selected from the group consisting of Group I metal cations. 
     
     
         13 . The process according to  claim 1 , wherein the metal cation is sodium cation. 
     
     
         14 . The process according to  claim 1 , wherein the amount of the metal cation present in the film, and/or present in the reaction mixture during the reaction of the hydrolysis stabiliser with the end-groups of the polyester, is at least 45 ppm by weight, relative to the amount of polyester. 
     
     
         15 . The process according to  claim 1 , wherein the intrinsic viscosity of the polyester in the polyester film is at least about 0.65 as measured according to ASTM D5225-98(2003). 
     
     
         16 . The process according to  claim 1 , wherein the hydrolysis stabiliser is present in an amount in the range from 0.1% to 2.0%, relative to the total weight of the layer. 
     
     
         17 . The process according to  claim 1 , wherein the hydrolysis stabiliser(s) in the polyester film consist(s) essentially of said at least one glycidyl ester of a branched monocarboxylic acid. 
     
     
         18 . The process according to  claim 1 , wherein said branched monocarboxylic acid has from 5 to 15 carbon atoms, and/or wherein said branched monocarboxylic acid is saturated, and/or said branched monocarboxylic acid is a synthetic material. 
     
     
         19 . The process according to  claim 1 , wherein said hydrolysis stabiliser has formula (I): 
       
         
           
           
               
               
           
         
         wherein: 
         R 1  and R 2  are independently selected from alkyl; R 3  is selected from hydrogen and alkyl; and 
         wherein the total number of carbon atoms in the alkyl groups R 1 , R 2  and R 3  is from 3 to 48. 
       
     
     
         20 . The process according to  claim 19 , wherein R 1  is methyl and R 2  and R 3  are independently selected from alkyl, wherein the total number of carbon atoms in the alkyl groups R 2  and R 3  is 7. 
     
     
         21 . The process according to  claim 1 , wherein said step of extruding said layer of molten polyester and said at least one hydrolysis stabiliser is the casting of said molten polyester and said at least one hydrolysis stabiliser into a film, and wherein said hydrolysis stabiliser is reacted with the polyester by injecting the hydrolysis stabiliser into the molten polyester prior to the polyester being cast into a film. 
     
     
         22 . The process according to  claim 1 , wherein the polyester film further comprises a UV-absorber. 
     
     
         23 . The process according to  claim 22 , wherein the amount of UV-absorber is in the range from 0.1% to 10% by weight, relative to the total weight of the layer. 
     
     
         24 . The process according to  claim 1 , wherein the polyester of the polyester film exhibits an endothermic high temperature peak at a temperature of (A)° C. and an endothermic low temperature peak at a temperature of (B)° C., both peaks being measured by differential scanning calorimetry (DSC), wherein the value of (A−B) is in the range from 15° C. to 50° C. 
     
     
         25 . The process according to  claim 1 , wherein the polyester film exhibits an elongation to break, measured according to ASTM D882, of at least 10% after at least 56 hours when aged at 121° C. and 1.2 bar pressure. 
     
     
         26 . The process according to  claim 1 , wherein the polyester film exhibits a haze of no more than 30% and/or a TLT of at least 50%. 
     
     
         27 . The process according to  claim 1 , wherein the polyester film is selected from the group consisting of a white film, a black film and an opaque film. 
     
     
         28 . The process according to  claim 1 , wherein the polyester film further comprises an anti-oxidant. 
     
     
         29 . The process according to  claim 1 , wherein the polyester film has disposed on a first surface thereof an additional polymeric layer, wherein said additional polymeric layer is a polyester layer optionally comprising one or more additives independently selected from hydrolysis stabiliser(s), UV-absorber(s), anti-oxidant(s) and particulate inorganic filler(s). 
     
     
         30 . The process according to  claim 1 , wherein the film has one or more additional layer(s) disposed on one or both surfaces thereof to form a composite structure. 
     
     
         31 . The process according to  claim 30 , wherein the one or more additional layer(s) is selected from PET and PET-based polyesters. 
     
     
         32 . The process according to  claim 30 , wherein any of the one or more additional layer(s) comprises at least one hydrolysis stabiliser. 
     
     
         33 . The process according to  claim 32 , wherein the one or more additional layer(s) is/are selected from PET and PET-based polyesters, and wherein the hydrolysis stabiliser in the one or more additional layer(s) is selected from a glycidyl ester of a branched monocarboxylic acid, wherein the monocarboxylic acid has from 5 to 50 carbon atoms, wherein said hydrolysis stabiliser is present in the one or more additional layer(s) in the form of its reaction product with at least some of the end-groups of the PET or the PET-based polyester. 
     
     
         34 . The process according to  claim 33 , wherein the hydrolysis stabiliser in the one or more additional layer(s) has formula (I): 
       
         
           
           
               
               
           
         
         wherein: 
         R 1  and R 2  are independently selected from alkyl; R 3  is selected from hydrogen and alkyl; and 
         wherein the total number of carbon atoms in the alkyl groups R 1 , R 2  and R 3  is from 3 to 48. 
       
     
     
         35 . A biaxially oriented polyester film obtained by the process of:
 (i) extruding a layer of molten polyester and at least one hydrolysis stabiliser selected from a glycidyl ester of a branched monocarboxylic acid, wherein the monocarboxylic acid has from 5 to 50 carbon atoms, wherein said hydrolysis stabiliser is present in the extrudate in the form of its reaction product with at least some of the end-groups of said polyester, and wherein said reaction product is obtained by reaction of the hydrolysis stabiliser with the end-groups of the polyester in the presence of a metal cation selected from the group consisting of Group I and Group II metal cations, wherein the extrusion temperature is within the range of from about 280° C. to about 300° C.;   (ii) quenching the extrudate;   (iii) stretching the quenched extrudate in two mutually perpendicular directions to effect orientation; and   (iv) heat-setting the film.   
     
     
         36 . The biaxially oriented polyester film according to  claim 35 , wherein the heat-set temperature is within the range of from about 200° C. to about 225° C. 
     
     
         37 . The biaxially oriented polyester film according to  claim 35 , wherein said orientation is sequential orientation effected by stretching the quenched extrudate in a first, longitudinal direction and then in a transverse direction, wherein stretching in said transverse direction is effected in a stenter apparatus. 
     
     
         38 . The polyester film according to  claim 35 , wherein the polyester of the polyester film exhibits an endothermic high temperature peak at a temperature of (A)° C. and an endothermic low temperature peak at a temperature of (B)° C., both peaks being measured by differential scanning calorimetry (DSC), wherein the value of (A−B) is in the range from 15° C. to 50° C.