Process for the formation of a polyolefin coating layer onto a metal surface

Abstract

A process for forming a polyolefin coating layer onto a surface of a metal which comprises coating an uncured epoxy resin layer onto the surface of a metal and melt-bonding a polyolefin modified with an unsaturated carboxylic acid or an anhydride thereof onto the uncured epoxy resin layer coated onto said metal surface. The coating layer has a high bonding strength and excellent water resistance, especially resistance against brine.

What is claimed is: 
     
       1. A process for coating a metal surface with a polyolefin comprising: I. coating a metal surface with a first layer consisting essentially of an uncured epoxy resin and least one curing agent; and   Ii. melt-bonding onto the first uncured layer, a second layer which is:   A. a first polyolefin modified by copolymerization with one member of the group consisting of: i. an unsaturated dicarboxylic acid having the carboxylic groups attached to adjacent carbon atoms,   ii. an anhydride of the acid of (i); or     B. a blend of polyolefins consisting essentially of: i. a second polyolefin, and   ii. the modified first polyolefin of (A),   the polyolefin of (B) (i) and (B) (ii) being the same or different, with the provisos that: (1) for (A), the weight percentage of the repeating units of (A) (i) or (A) (ii) is from 10 -4  to 10% of the modified polyolefin; and (2) for (B), the weight percentage of the repeating units of (B) (ii) is from 10 -4  to 10% of the polyolefin blend.       
     
     
       2. The process of claim 1, wherein the second layer is (A). 
     
     
       3. The process of claim 2, wherein (A) (i) is present, and is selected from the group consisting of: maleic acid; citraconic acid; fumaric acid; 5-norbornene-2,3-dicarboxylic acid; and 1-pentene-4,5-dicarboxylic acid. 
     
     
       4. The process of claim 2, wherein (A) (ii) is present and is selected from the group consisting of anhydrides of: maleic acid; citraconic acid; fumaric acid; 5-norbornene-2,3-dicarboxylic acid; and 1-pentene-4,5-dicarboxylic acid. 
     
     
       5. The process of claim 2 wherein the polyolefin is selected from at least one of the group consisting of polyethylene and polypropylene. 
     
     
       6. The process of claim 1, wherein the second layer is (B). 
     
     
       7. The process of claim 6, wherein (B) (ii) is modified by copolymerization with a member of the group consisting of: maleic acid; citraconic acid; fumaric acid; 5-norbornene-2,3-dicarboxylic acid; and 1-pentene-4,5-dicarboxylic aicd; and 1-pentene-4,5-dicarboxylic acid. 
     
     
       8. The process of claim 6, wherein (B) (ii) is modified by copolymerization with the anhydride of an acid selected from the group consisting of: maleic acid; citraconic acid; fumaric acid 5-norbornene-2,3-dicarboxylic acid; and 1-pentene-4,5-dicarboxylic acid. 
     
     
       9. The process of claim 6 wherein the first and second polyolefins are selected from at least one of the group consisting of polyethylene and polypropylene. 
     
     
       10. The process of claim 5, wherein the polyolefin is modified by graft copolymerization with maleic anhydride. 
     
     
       11. The process of claim 9 wherein the polyolefin is modified by graft copolymerization with maleic anhydride. 
     
     
       12. The process of claim 1 wherein the uncured epoxy resin has a molecular weight of from 500 to 200,000. 
     
     
       13. The process of claim 1 wherein the uncured epoxy resin has a curing temperature of from 100° to 300° C. 
     
     
       14. The process of claim 1 wherein the weight percentage of proviso (1) is from 0.01 to 5. 
     
     
       15. The process of claim 1 wherein the weight percentage of proviso (2) is from 0.01 to 5. 
     
     
       16. The process of claim 1 including the additional step of heat-curing the first layer after the second layer has been applied, the curing temperature being from 80° to 300° C. 
     
     
       17. The process of claim 16 wherein the curing temperature is from 100° to 300° C. 
     
     
       18. The process of claim 16 wherein the second layer is (A), the polyolefin is selected from at least one of the group consisting of polyethylene and polypropylene and is modified by graft copolymerization with maleic anhydride. 
     
     
       19. The process of claim 16 wherein the second layer is (B), the polyolefin is selected from at least one of the group consisting of polyethylene and polypropylene and is modified by graft copolymerization with maleic anhydride. .Iadd. 20. A process for coating a metal surface with a polyolefin comprising: I. coating a metal surface with a first layer consisting essentially of an uncured epoxy resin; and   II. melt-bonding onto the first uncured layer, a second layer which is: A. a first polyolefin modified by copolymerization with one member of the group consisting of: i. an unsaturated dicarboxylic acid having the carboxylic groups attached to adjacent carbon atoms, and   ii. an anhydride of the acid of (i); or     B. a blend of polyolefins consisting essentially of: i. a second polyolefin, and   ii. the modified first polyolefin of (A), the polyolefin of (B) (i) and (B) (ii) being the same or different, with the provisos that: (1) for (A), the weight percentage of the repeating units of (A) (i) or (A) (ii) is from 10.sup. -4 to 10% of the modified polyolefin; and (2) for (B), the weight percentage of the repeating units of (B) (ii) is from 10 -4  to 10% of the polyolefin blend. .Iaddend..Iadd. 21. The process of claim 20, in which the uncured epoxy resin is an epoxy resin which does not contain a curing agent and which has a molecular weight of not less than 10,000. .Iaddend..Iadd. 22. The process of claim 21, wherein the second layer is melt-bonded to the first layer at a temperature of at least 200° C. .Iaddend..Iadd. 23. The process of claim 21, wherein the second layer is (A). .Iaddend. .Iadd. 24. The process of claim 23, wherein (A) (i) is present and is selected from the group consisting of: maleic acid; citraconic acid; fumaric acid; 5-norbornene-2,3-dicarboxylic acid; and 1-pentene-4,5-dicarboxylic acid. .Iaddend..Iadd. 25. The process of claim 23, wherein (A) (ii) is present and is selected from the group consisting of anhydrides of: maleic acid; citraconic acid; fumaric acid; 5-norbornene-2,3-dicarboxylic acid; and 1-pentene-4,5-dicarboxylic acid. .Iaddend..Iadd. 26. The process of claim 23, wherein the polyolefin is selected from at least one of the group consisting of polyethylene and polypropylene. .Iaddend..Iadd. 27. The process of claim 21, wherein the second layer is (B). .Iaddend..Iadd. 28. The process of claim 27, wherein (B) (ii) is modified by copolymerization with a member of the group consisting of: maleic acid; citraconic acid; fumaric acid; 5-norbornene-2,3-dicarboxylic acid; and 1-pentene-4,5-dicarboxylic acid. .Iaddend..Iadd. 29. The process of claim 27, wherein (B) (ii) is modified by copolymerization with the anhydride of an acid selected from the group consisting of: maleic acid; citraconic acid; fumaric acid; 5-norbornene-2,3-dicarboxylic acid; and 1-pentene-4,5-dicarboxylic acid. .Iaddend..Iadd. 30. The process of claim 27, wherein the first and second polyolefins are selected from at least one of the group consisting of polyethylene and polypropylene. .Iaddend..Iadd. 31. The process of claim 26, wherein the polyolefin is modified by graft copolymerization with maleic anhydride. .Iaddend..Iadd. 32. The process of claim 29, wherein the polyolefin is modified by graft copolymerization with maleic anhydride. .Iaddend. .Iadd. 33. The process of claim 21, wherein the uncured epoxy resin has a molecular weight of from 30,000 to 200,000..Iaddend.