Catalysts for thermal cure silicone release coatings

Abstract

An environmentally acceptable catalyst, coating system, and methods for thermal cure silicone release coatings that utilize bismuth (“Bi”) catalyst to retain properties of tin (“Sn”)-catalyzed systems but do not have the toxicity and environmental hazards associated therewith. The coating systems and methods also provide a laminate that shows reduced orange peel distortion over time compared with tin (“Sn”)-catalyzed systems and methods.

1 . An environmentally acceptable reaction system for use in forming thermal cure silicone release coatings, said reaction system comprising:
 (a) a hydroxyl-terminated polysiloxane, a silanol prepolymer, or a combination thereof;   (b) a silane cross-linking agent having a Si—H functionality of at least 2; and   (c) a catalyst component consisting essentially of a bismuth-containing carboxylate catalyst comprising in the range of from 8 weight percent to 28 weight percent bismuth, based on the total weight of said bismuth-containing carboxylate catalyst,   wherein, when combined, said hydroxyl-terminated polysiloxane, silanol prepolymer, or combination thereof reacts with said silane cross-linking agent in the presence of said catalyst component via a dehydrogenative condensation reaction to thereby form a cross-linked polysiloxane.   
     
     
         2 . The reaction system of  claim 1 , wherein said bismuth-containing carboxylate catalyst further comprises at least one additional metal selected from the group consisting of zinc, zirconium, titanium, palladium, and aluminum. 
     
     
         3 . The reaction system of  claim 1 , wherein said bismuth-containing carboxylate catalyst is selected from the group consisting of a bismuth-zinc neodecanoate catalyst, a bismuth 2-ethylhexanoate catalyst, a metal carboxylate catalyst of bismuth and zinc, and a metal carboxylate catalyst of bismuth and zirconium. 
     
     
         4 . The reaction system of  claim 1 , wherein said catalyst component consists of said bismuth-containing carboxylate catalyst. 
     
     
         5 . The reaction system of  claim 1 , wherein said catalyst component is present in said reaction system in an amount of 2 to 14 weight percent, based on the total weight of said hydroxyl-terminated polysiloxane, silanol prepolymer, or combination thereof. 
     
     
         6 . The reaction system of  claim 1 , further comprising at least one amino silicone. 
     
     
         7 . The reaction system of  claim 1 , wherein said silane cross-linking agent has a lower molecular weight than said hydroxyl-terminated polysiloxane, silanol prepolymer, or combination thereof. 
     
     
         8 . The reaction system of  claim 1 , further comprising an inhibitor. 
     
     
         9 . A release liner comprising a liner and coating layer formed on at least one surface of said liner, wherein said coating layer comprises said reaction system of  claim 1 . 
     
     
         10 . An environmentally acceptable reaction system for use in forming thermal cure silicone release coatings, said reaction system comprising:
 (a) a hydroxyl-terminated polysiloxane, silanol prepolymer, or combination thereof;   (b) a silane cross-linking agent having a Si—H functionality of at least 2;   (c) a bismuth-containing carboxylate catalyst; and   (d) at least one amino silicone.   
     
     
         11 . The reaction system of  claim 10 , wherein said bismuth-containing carboxylate catalyst comprises in the range of from 8 weight percent to 28 weight percent bismuth, based on the total weight of said bismuth-containing carboxylate catalyst, and wherein said bismuth-containing carboxylate catalyst is present in said reaction system in an amount of 2 to 14 weight percent, based on the total weight of said hydroxyl-terminated polysiloxane, silanol prepolymer, or combination thereof. 
     
     
         12 . The reaction system of  claim 10 , wherein said bismuth-containing carboxylate catalyst further comprises at least one additional metal selected from the group consisting of zinc, zirconium, titanium, palladium, and aluminum. 
     
     
         13 . The reaction system of  claim 10 , wherein said bismuth-containing carboxylate catalyst is selected from the group consisting of a bismuth-zinc neodecanoate catalyst, a bismuth 2-ethylhexanoate catalyst, a metal carboxylate catalyst of bismuth and zinc, and a metal carboxylate catalyst of bismuth and zirconium. 
     
     
         14 . The reaction system of  claim 10 , wherein said amino silicone is present in said reaction system in an amount of 1.5 weight percent or less, based on the total weight of said reaction system. 
     
     
         15 . The reaction system of  claim 10 , wherein said silane cross-linking agent has a lower molecular weight than said hydroxyl-terminated polysiloxane, silanol prepolymer, or mixture thereof, and wherein, when combined, said hydroxyl-terminated polysiloxane, silanol prepolymer, or combination thereof reacts with said silane cross-linking agent in the presence of said bismuth-containing carboxylate catalyst via a dehydrogenative condensation reaction to thereby form a cross-linked polysiloxane. 
     
     
         16 . A release liner comprising:
 (a) a coating layer formed from a reaction system, said reaction system comprising—
 (i) a silicone diol; 
 (ii) a silane prepolymer cross-linking agent; and 
 (iii) a bismuth-containing carboxylate catalyst; and 
   (b) a liner, wherein said coating layer is formed on at least one surface of said liner,   wherein said release liner has a peel release value (PRV) that is statistically the same as the PRV obtained from a comparative release liner identical to said release liner but including a comparative coating layer that uses a dibutyltin dilaurate catalyst in place of said bismuth-containing carboxylate catalyst, wherein the amount of said dibutyltin dilaurate catalyst in said comparative coating layer is at least four times higher than the amount of said bismuth-containing carboxylate catalyst in said coating layer.   
     
     
         17 . The liner of  claim 16 , wherein said bismuth-containing carboxylate catalyst is present in said reaction system in an amount in the range of from 2 to 14 weight percent, based on the total weight of said silicone diol. 
     
     
         18 . The liner of  claim 16 , wherein said bismuth-containing carboxylate catalyst comprises bismuth or a combination of bismuth and zinc. 
     
     
         19 . The liner of  claim 16 , wherein said reaction system further comprises at least one solvent selected from the group consisting of heptane, toluene, and combinations thereof. 
     
     
         20 . The liner of  claim 16 , wherein the degree of cure measured by extraction in n-heptane is statistically the same for said release liner and said comparative release liner.