Heat aging resistant ethylene vinyl acetate copolymer composition and process for its production

Abstract

Polyamide-filled EVA copolymer compositions comprising a continuous EVA copolymer phase and a discontinuous polyamide phase are produced by a melt mixing process. When crosslinked with peroxide curatives the polyamide-filled EVA copolymer compositions exhibit enhanced resistance to heat aging compared to EVA elastomer compositions reinforced with carbon black or other inorganic fillers.

1 . A polymer blend comprising a polyamide-filled EVA copolymer composition, said polyamide-filled EVA copolymer composition consisting essentially of
 (a) about 40 wt % to about 95 wt % of an EVA copolymer component comprising one or more EVA copolymers wherein the EVA copolymer comprises at least 40% by weight copolymerized vinyl acetate monomer units; and   (b) about 5 wt % to about 60 wt % of a polyamide component comprising one or more polyamides having a melting peak temperature of at least 160° C.,   wherein i) the polyamide-filled EVA copolymer composition has a Mooney viscosity (ML 1+4, 100° C.) determined according to ASTM D1646 of 5 to 200, and ii) the weight percentages of the EVA copolymer and polyamide components are based on the combined weight of the EVA copolymers and polyamides in the polyamide-filled EVA copolymer composition.   
     
     
         2 . The polymer blend of  claim 1  wherein the EVA copolymer composition consists essentially of from about 60 wt % to about 90 wt % of the EVA component and 10 wt % to 40 wt % of the polyamide component. 
     
     
         3 . The polymer blend of  claim 1  wherein the Mooney viscosity of the polyamide-filled EVA copolymer composition is from about 10 to about 150. 
     
     
         4 . A curable polyamide-filled EVA copolymer composition comprising
 (a) a polyamide-filled EVA copolymer composition comprising
 (i) 40 to 95 wt % of an EVA copolymer component comprising one or more EVA copolymers wherein the EVA copolymer comprises at least 40% by weight copolymerized vinyl acetate units; and 
 (ii) 5-60 wt % of a polyamide component comprising one or more polyamides having a melting peak temperature of at least 160° C., wherein i) the polyamide-filled EVA copolymer composition has a Mooney viscosity (ML 1+4, 100° C.) of 5-200, as determined according to ASTM D1646, and ii) the weight percentages of the EVA copolymer and polyamide components are based on the combined weight of the EVA copolymers and polyamides in the polyamide-filled EVA copolymer composition; and 
   (b) a peroxide curative.   
     
     
         5 . The curable composition of  claim 4  wherein the polyamide has a melting peak temperature from about 180° C. to 260° C. 
     
     
         6 . The curable composition of  claim 4  wherein the composition has an increase in torque (MH−ML) when tested in a rotorless cure meter per ASTM D5289-07a at conditions of 177° C. for 24 minutes of at least 2.5 dN-m. 
     
     
         7 . The curable composition of  claim 4  comprising from about 60 wt % to 90 wt % of the EVA component and from about 10 wt % to 40 wt % of the polyamide component. 
     
     
         8 . A process for production of a polyamide-filled EVA copolymer composition, the process comprising the steps
 (a) providing one or more EVA copolymers consisting essentially of EVA copolymers comprising at least 40% by weight vinyl acetate monomer, and one or more polyamides having a melting peak temperature of at least 160° C.;   (b) mixing the one or more EVA copolymers and the one or more polyamides at a temperature above the melting peak temperatures of the one or more polyamides to disperse the one or more polyamides within the one or more EVA copolymers, the one or more EVA copolymers and one or more polyamides being present in sufficient amounts to form a polyamide-filled EVA copolymer composition comprising 5-60 wt % polyamide based on the total amount of EVA copolymers and polyamides in the blend; and   (c) cooling the polyamide-filled EVA copolymer composition to a temperature below the crystallization peak temperatures of the one or more polyamides, thereby forming a polyamide-filled EVA copolymer composition having a Mooney viscosity (ML 1+4, 100° C.) of 5 to 200, as determined according to ASTM D1646.   
     
     
         9 . The process of  claim 8 , additionally comprising the step of adding a peroxide curative to the polyamide-filled EVA copolymer composition after said copolymer composition has been cooled below the crystallization peak temperatures of the one or more polyamides, the addition taking place at a temperature of less than 160° C. 
     
     
         10 . The process of  claim 9 , in which the polyamide has a melting peak temperature from about 180° C. to 260° C. 
     
     
         11 . A process for preparing an EVA elastomer composition comprising the steps of
 (a) providing a polyamide-filled EVA copolymer composition that has been prepared by a process comprising the steps:
 (i) providing i) one or more EVA copolymers comprising at least 40% by weight copolymerized vinyl acetate monomer units, and ii) one or more polyamides having a melting peak temperature of at least 160° C.; 
 (ii) mixing the one or more EVA copolymers and one or more polyamides at a temperature above the melting peak temperatures of the one or more polyamides to disperse the one or more polyamides within the one or more EVA copolymers, the one or more EVA copolymers and one or more polyamides being present in sufficient amounts to form a polyamide-filled EVA copolymer composition comprising 5-60 wt % of one or more polyamides based on the total weight of EVA copolymers and polyamides in the polyamide-filled EVA copolymer composition; and 
 (iii) cooling the polyamide-filled EVA copolymer composition to a temperature below the crystallization peak temperatures of the one or more polyamides, thereby forming a polyamide-filled EVA copolymer composition that has a Mooney viscosity (ML 1+4, 100° C.) of 5 to 200, as determined according to ASTM D1646; 
   (b) adding a peroxide curative to the cooled polyamide-filled EVA copolymer composition at a temperature less than 160° C. to form a curable polyamide-filled EVA copolymer composition; and   (c) curing the curable polyamide-filled EVA copolymer composition by exposing the curable polyamide-filled EVA copolymer composition to a temperature of about 160° C. to about 220° C. for about 2 to 60 minutes to form an EVA elastomer composition having a Shore A hardness greater than 40, as determined according to ASTM D 2240-06, reading after 1 second.   
     
     
         12 . The process of  claim 11  in which the polyamide has a melting peak temperature from about 180° C. to 260° C. 
     
     
         13 . The process of  claim 12  in which the EVA component comprises 60 to 90 weight percent and the polyamide component comprises 10 to 40 weight percent of the sum of the EVA copolymer and polyamide components. 
     
     
         14 . A curable EVA copolymer composition comprising:
 (a) a polymer blend composition comprising
 (i) 40 to 95 wt % of an EVA copolymer component comprising one or more EVA copolymers comprising at least 40% by weight copolymerized vinyl acetate monomer units; and 
 (ii) 5-60 wt % of a polyamide component comprising one or more polyamides having a melting peak temperature of at least 160° C., 
   wherein the polymer blend has a Mooney viscosity (ML 1+4, 100° C.) of 5 to 200, as determined according to ASTM D1646, and the weight percentages of the EVA copolymer and polyamide components are based on the combined weight of the EVA copolymers and polyamides in the blend composition;   (b) a peroxide curative; and   (c) a reinforcing filler, the reinforcing filler being present in the curable EVA copolymer composition in an amount that causes an increase in the Shore A hardness of the cured EVA copolymer composition of no more than about 20 points as compared to the Shore A hardness of a control composition that is of identical composition but for the absence of the reinforcing filler, wherein i) the curable EVA copolymer composition and control composition are formed into test specimens of 1 mm to 2.5 mm thickness, the test specimens are cured by exposure to a temperature of 175° C. for 10 minutes in a closed mold at a pressure of at least 10 MPa, then removed from the mold and post cured in a hot air oven at a temperature of 175° C. for 30 minutes, ii) Shore A hardness of the post cured EVA copolymer composition and the post cured control composition is determined according to ASTM D 2240-06 (1 second reading), and iii) the cured EVA copolymer composition has a Shore A hardness greater than 40.   
     
     
         15 . The composition of  claim 14  wherein the reinforcing filler is carbon black. 
     
     
         16 . The composition of  claim 4  additionally comprising a compatibilizer. 
     
     
         17 . The composition of  claim 14  wherein the reinforcing filler is present in the curable EVA copolymer composition in an amount that causes an increase in the Shore A hardness of the cured EVA copolymer composition of no more than about 10 points as compared to the Shore A hardness of a control composition that is of identical composition but for the absence of the reinforcing filler, wherein i) the curable EVA copolymer composition and control composition are formed into test specimens of 1 mm to 2.5 mm thickness, the test specimens are cured by exposure to a temperature of 175° C. for 10 minutes in a closed mold at a pressure of at least 10 MPa, then removed from the mold and post cured in a hot air oven at a temperature of 175° C. for 30 minutes, ii) Shore A hardness of the post cured EVA copolymer composition and the post cured control composition is determined according to ASTM D 2240-06 (1 second reading), and iii) the cured EVA copolymer composition has a Shore A hardness greater than 40. 
     
     
         18 . A composition of  claim 6  in which the EVA component comprises at least 45 weight percent vinyl acetate. 
     
     
         19 . A composition of  claim 6  in which the EVA component comprises at least 50 weight percent vinyl acetate. 
     
     
         20 . A composition of  claim 14  having a Shore A hardness of equal to or less than about 80.