Low surface energy adhesive

Abstract

Adhesives suitable for use with low surface energy materials are described. The adhesive contain an acrylic copolymer, a high glass transition temperature tackifier and a low glass transition temperature tackifier. The acrylic copolymer is the reaction product of a first alkyl(meth)acrylate having at least 5 carbon atoms in the alkyl group, a second alkyl(meth)acrylate having 1 to 4 carbon atoms in the alkyl group, and a vinyl carboxylic acid. Both tackifiers have a Tg greater than the Tg of the acrylic copolymer. The high glass transition temperature tackifier has a Tg of at least 20° C. and the low glass transition temperature tackifier has a Tg of less than 0° C.

1 . An adhesive comprising:
 a) an acrylic copolymer comprising the reaction product of   i) a first alkyl (meth)acrylate, wherein the alkyl group of the first alkyl (meth)acrylate comprises at least 5 carbon atoms;   ii) a second alkyl(meth)acrylate, wherein the alkyl group of the second alkyl (meth)acrylate comprises 1 to 4 carbon atoms; and   iii) a vinyl carboxylic acid; and   b) a high Tg tackifier having a glass transition temperature of at least 20° C.; and   c) a low Tg tackifier having a glass transition temperature of no greater than 0° C., wherein the glass transition temperatures of the high Tg tackifier and the low Tg tackifier are greater than the glass transition temperature of the acrylic copolymer.   
     
     
         2 . The adhesive according to  claim 1 , wherein the weight ratio of the first alkyl (meth)acrylate to the second alkyl (meth)acrylate is between 3:1 and 1:3. 
     
     
         3 . The adhesive according to  claim 1 , wherein the acrylic copolymer comprises at least 3% by weight and no greater than 8% by weight of the vinyl carboxylic acid. 
     
     
         4 . The adhesive according to  claim 1 , wherein the adhesive comprises 40 to 60% by weight total tackifier content based on the total weight of the acrylic copolymer, the high Tg tackifier and the low Tg tackifier. 
     
     
         5 . The adhesive according to  claim 1 , wherein the adhesive comprises 35 to 45% by weight of the high Tg tackifier based on the total weight of the acrylic copolymer, the high Tg tackifier and the low Tg tackifier. 
     
     
         6 . The adhesive according to  claim 1 , wherein the adhesive comprises 2 to 13% by weight of the low Tg tackifier based on the total weight of the acrylic copolymer, the high Tg tackifier and the low Tg tackifier. 
     
     
         7 . The adhesive according to claim, further comprising a crosslinker. 
     
     
         8 . The adhesive of  claim 7 , wherein the crosslinker is a covalent crosslinker selected from the group consisting of bisamides, epoxies, and melamines. 
     
     
         9 . The adhesive of  claim 7 , wherein the crosslinker is an ionic crosslinking agent, wherein the ionic crosslinking agent is selected from the group consisting of multifunctional amines, metal oxides, and organo-metallic chelating agents. 
     
     
         10 . The adhesive according to  claim 1 , further comprising an additional component selected from the group consisting of fillers, dyes, pigments, antioxidants, UV-stabilizers, fumed silica, nanoparticles, and surface-modified nanoparticles. 
     
     
         11 . The adhesive according to  claim 1 , wherein the glass transition temperature of the adhesive is no greater than 260 K, as calculated using the Fox Equation. 
     
     
         12 . An adhesive article comprising a first substrate and an adhesive according to  claim 1  bonded to the substrate. 
     
     
         13 . The adhesive article of  claim 12 , wherein the adhesive is directly bonded to the first substrate. 
     
     
         14 . The adhesive article of  claim 12 , wherein the adhesive is bonded to a second substrate. 
     
     
         15 . The adhesive article of  claim 12 , wherein the first substrate is a low surface energy substrate having a surface energy of no greater than 35 millinewtons per meter. 
     
     
         16 . The adhesive of  claim 1 , wherein
 (a) the weight ratio of the first alkyl (meth)acrylate to the second alkyl (meth)acrylate is between 3:1 and 1:3; and   (b) the acrylic copolymer comprises at least 3% by weight and no greater than 8% by weight of the vinyl carboxylic acid.   
     
     
         17 . The adhesive of  claim 16 , wherein the adhesive comprises
 (c) 40 to 60% by weight total tackifier content based on the total weight of the acrylic copolymer, the high Tg tackifier and the low Tg tackifiers;   (d) 35 to 45% by weight of the high Tg tackifier based on the total weight of the acrylic copolymer, the high Tg tackifier and the low Tg tackifiers; and   (e) 2 to 13% by weight of the low Tg tackifier based on the total weight of the acrylic copolymer, the high Tg tackifier and the low Tg tackifiers.   
     
     
         18 . The adhesive of  claim 17 , wherein the adhesive further comprises a crosslinker. 
     
     
         19 . An adhesive article comprising a first substrate and the adhesive according to  claim 17  bonded to the substrate. 
     
     
         20 . The adhesive article of  claim 19 , wherein the first substrate is a low surface energy substrate having a surface energy of no greater than 35 millinewtons per meter.