Extrusion coating compositions and method

Abstract

Solid extrusion coating compositions for metal substrates, a method of extrusion coating a metal substrate, and a metal article are disclosed. The extrusion coating composition is a thermoplastic material and comprises: (a) a polyester having a weight average molecular weight of about 10,000 to about 50,000, and optionally, (b) a modifying resin, such as an epoxy resin having an epoxy equivalent weight of about 500 to about 15,000. The extrusion coating composition is applied to a metal substrate in an extrusion process to provide a composition film having a thickness of about 1 to about 40 microns.

1 . A composition comprising: 
 (a) about 50% to about 95%, by total weight of the composition, of a polyester having a weight average molecular weight of about 10,000 to about 50,000, a glass transition temperature of about −30° C. to about 120° C., a melt viscosity of about 10 to about 100 Pa·s at 200° C. or about 25 to about 200 Pa·s at 240° C., a melt flow index of about 20 to about 800 g/10 min at 200° C., and a softening point of about 120° C. to about 200° C., and    (b) 0% to about 25%, by total weight of the composition, of a modifying resin selected from the group consisting of an epoxy or phenoxy resin having an epoxy equivalent weight of about 500 to about 15,000, an acrylic resin having a weight average molecular weight of about 15,000 to about 100,000, a polyolefin resin having a weight average molecular weight of about 15,000 to about 1,000,000 and mixtures thereof;    (c) 0% to about 50%, by total weight of the composition, of an inorganic filler; and    (d) 0% to about 4%, by total weight of the composition, of a flow control agent; and    (e) 0% to about 50%, by total weight of the composition, of a second modifying polymer,    said composition in the form of an extruded film.    
   
   
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       3 . A method of coating a metal substrate comprising: 
 (a) heating the metal substrate to a temperature of about 120° C. to about 250° C. to provide a preheated metal substrate;    (b) heating a solid, thermoplastic coating composition to a sufficient temperature to melt the coating composition and provide a molten coating composition, said coating composition comprising: 
 (i) about 50% to about 100%, by total weight of the composition, of a polyester having a weight average molecular weight of about 10,000 to about 50,000, a glass transition temperature of about −30° C. to about 120° C., a melt viscosity of about 10 to about 100 Pa·s at 200° C. or about 25 to about 200 Pa·s at 240° C., a melt flow index of about 20 to about 800 g/10 min at 200° C., and a softening point of about 120° C. to about 200° C., and  
 (ii) 0% to about 25%, by total weight of the composition, of a modifying resin selected from the group consisting of an epoxy or phenoxy resin having an epoxy equivalent weight of about 500 to about 15,000, an acrylic resin having a weight average molecular weight of about 15,000 to about 100,000, a polyolefin resin having a weight average molecular weight of about 15,000 to about 1,000,000, and mixtures thereof;  
   (c) extruding the molten coating composition onto a surface of the preheated metal substrate to provide a layer of molten coating composition about one to about 40 microns thick on the preheated metal substrate and provide a coated metal substrate; and    (d) allowing the coated metal substrate to cool.    
   
   
       4 . The method of  claim 3  further comprising the stop of heating the cooled coated metal substrate of step (d) at a temperature of about 250° C. to about 550° C. for about 5 to about 30 seconds.  
   
   
       5 . the method of  claim 3  wherein the thermoplastic coating composition further comprises: 
 (iii) 0% to about 50%, by total weight of the composition, of an inorganic filler; and    (iv) 0% to about 4%, by total weight of the composition, of a flow control agent.    
   
   
       6 . The method of  claim 3  wherein the thermoplastic coating composition further comprises 0% to about 50%, by total weight of the composition, of a second modifying polymer.  
   
   
       7 . The method of  claim 6  wherein the second modifying polymer is a thermoplastic polymer.  
   
   
       8 . The method of  claim 6  wherein the second modifying polymer is a thermoset polymer.  
   
   
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       17 . The method of  claim 3  wherein the coating composition comprises two or more polyesters.  
   
   
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