Pressure sensitive compositions based on a modified rubber polymer aqueous dispersion

Abstract

The invention relates to an aqueous polymer dispersion which comprises: a) an aqueous polymer dispersion comprising grafted rubber polymeric particles from rubber polymer being selected from natural or synthetic rubber, b) an aqueous polymer dispersion with polymeric particles of a second polymer comprising monomeric units derived from a monomeric composition b) comprising: b1) a (meth)acrylate of a linear or branched alcohol in C 4 to C 10 or a mixture of such (meth)acrylates, said (meth)acrylate having Tg b1 lower than −30° C., b2) optionally, at least one comonomer having Tg b2 higher than −30° C., with said grafted rubber polymeric particles being grafted in an aqueous dispersion by a part of said monomeric composition b) as defined above. The invention covers also a specific process of preparation of said dispersion, an adhesive composition comprising said dispersion, the use of said dispersion in pressure sensitive adhesives and the resulting adhesive.

1 . An aqueous polymer dispersion comprising a mixture of two aqueous polymer dispersions a) and b) which are different from each other, aqueous polymer dispersion a) comprising grafted rubber polymeric particles a) and aqueous polymer dispersion b) comprising ungrafted polymeric particles b):
 a) an aqueous polymer dispersion comprising grafted rubber polymeric particles from rubber polymer being selected from natural or synthetic rubber,   b) an aqueous polymer dispersion with polymeric particles of a second polymer comprising monomeric units derived from a monomeric composition b) comprising:
 b1) a (meth)acrylate of a linear or branched alcohol in C 4  to C 10  or a mixture of such (meth)acrylates, said (meth)acrylate having Tg b1  lower than −30° C., and 
 b2) at least one comonomer having Tg b2  higher than −30° C., of Tg b2  higher than −10° C. 
   with said grafted rubber polymeric particles being grafted in an aqueous dispersion by a part of said monomeric composition b) as defined above and with said grafted part of monomeric composition b) on said rubber polymer a) representing from 25 to 50% w/w of the total weight of said monomeric composition b) involved in both grafted polymer particles a) and in ungrafted polymer particles b),   wherein b1) is selected from n-butyl acrylate, 2-ethyl hexyl (meth)acrylate, 2-octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl(meth)acrylate or decyl (meth)acrylate or a mixture of at least two or of at least three of these monomers.   
     
     
         2 . The aqueous polymer dispersion according to  claim 1 , wherein said rubber polymer a) is natural rubber. 
     
     
         3 . The aqueous polymer dispersion according to  claim 1 , wherein said rubber polymer a) is synthetic rubber and selected from: polyisoprene and their copolymers, polybutadiene and their copolymers, isoprene-butadiene, and from other copolymers of isoprene and butadiene. 
     
     
         4 . The aqueous polymer dispersion according to  claim 1 , wherein the weight proportion of said rubber polymer a), without grafted monomers, with respect to the global weight of a)+b), represents from 5 to 45% 
     
     
         5 . The aqueous polymer dispersion according to  claim 1 , wherein b1) is 2-ethyl hexyl acrylate. 
     
     
         6 . The aqueous polymer dispersion according to  claim 1 , wherein said polymer b) comprises monomeric units derived from a comonomer b2) selected from: functional and/or non-functional ethylenically unsaturated monomers, with said functional monomers being selected from monomers bearing at least one carboxy (—CO 2 H), hydroxyl (—OH), acetoacetoxy, amine or nitrile (—CN) functional group, and with said non-functional monomers being selected from C 1  to C 6  esters of (meth)acrylic acid, vinyl aromatic monomers, and esters of vinyl alcohol with C 2  to C 18  carboxylic acids. 
     
     
         7 . The aqueous polymer dispersion according to  claim 6 , wherein the weight content of b2) in said polymer b) varies from 0.1 to 30%. 
     
     
         8 . The aqueous polymer dispersion according to  claim 1 , wherein said monomeric composition b) comprises 2-ethyl hexyl acrylate as monomer b1) and a comonomer b2) selected from at least one functional or non functional monomer, with said functional monomer selected from monomers bearing at least one carboxy (—CO 2 H), hydroxyl (—OH), acetoacetoxy, amine or nitrile (—CN) functional group, and with said non-functional monomers selected from C 1  to C 6  esters of (meth)acrylic acid, vinyl aromatic monomers, and esters of vinyl alcohol with C 2  to C 18  carboxylic acids, with a weight content of 2-ethyl hexyl acrylate as monomer b1) with respect to said monomeric composition b) varying from 70 to 99.9%, of said monomeric composition b) and said polymer b) is a copolymer of 2-ethyl hexyl acrylate as monomer b1) with a comonomer b2) selected from: at least one functional or non functional monomer, with said functional monomer selected from monomers bearing at least one carboxy (—CO 2 H), hydroxyl (—OH), acetoacetoxy, amine or nitrile (—CN) functional group, and with said non-functional monomer selected from C 1  to C 6  esters of (meth)acrylic acid, vinyl aromatic monomers, and esters of vinyl alcohol with C 2  to C 18  carboxylic acids, with a weight content of 2-ethyl hexyl acrylate as monomer b1) with respect to said polymer b) varying from 70 to 99.9%. 
     
     
         9 . The aqueous polymer dispersion according to  claim 1 , wherein said comonomer b2) is a functional monomer selected from a monomer bearing at least one carboxy group and/or a monomer bearing at least one hydroxyl group. 
     
     
         10 . A process of preparing an aqueous polymer dispersion as defined in  claim 1 , comprising the following successive steps:
 i) preparation of an aqueous dispersion of a polymer b) by emulsion polymerization with continuous constant rate feeding in a reactor, of a pre-emulsion of monomers b) comprising b1) and b2), as defined in  claim 1 ,   ii) before step iii) as defined below and during said continuous feeding of said pre-emulsion, adjusting of the pH of the reactor at a value higher than 7, by the feeding at a constant feeding rate of an aqueous solution of a basic agent, optionally with said feeding continuing up to the end of the following step iii) or by adding in a shot, an aqueous solution of said basic agent and   iii) when the quantity in the reactor of the said continuously fed pre-emulsion of monomers b) represents a prefixed value being from 50 to 85% w/w of said pre-emulsion, then starting a progressive addition at constant feeding rate of an aqueous dispersion of rubber polymer a) as defined according to  claim 1  with maintenance of the said continuous feeding at constant rate of the remaining pre-emulsion of monomers b), with a resulting chemical modification of said rubber polymer a) by the grafting reaction of said monomers b) on it,   with said emulsion polymerization and grafting reactions being conducted in the presence of an initiator which does not generate acidic decomposition products.   
     
     
         11 . The process according to  claim 10 , wherein the said initiator system is selected from redox initiator systems composed of an organic peroxide including hydroperoxides, and a reducing agent acting as a decomposition activator of said peroxide or from azo initiators. 
     
     
         12 . An adhesive composition comprising at least one aqueous dispersion defined according to  claim 1 . 
     
     
         13 . An adhesive composition comprising at least one aqueous dispersion obtained by a process according to  claim 10 . 
     
     
         14 . An adhesive composition according to  claim 12 , which is a pressure sensitive adhesive (PSA) composition. 
     
     
         15 . An adhesive composition according to  claim 12 , which is a two component composition, said composition further comprising a crosslinking agent selected from polyisocyanates for a comonomer b2) bearing hydroxyl groups and from polyaziridines if the comonomer b2) bears carboxy group. 
     
     
         16 . An adhesive composition according to  claim 12 , wherein it is a pressure sensitive adhesives (PSA) composition for labelling, packaging, assembling, construction and medical applications. 
     
     
         17 . An adhesive composition according to  claim 14 , wherein it is applied in the form of an adhesive tape, an adhesive plastic film, an adhesive label, an adhesive spray or an adhesive coating. 
     
     
         18 . An adhesive composition according to  claim 17  applied on a substrate selected from: paper, cardboard, wood, plywood, particleboard, metal, glass, plastic, plastic film, composite, textile, fibber, woven fabric, and non-woven fabric. 
     
     
         19 . The aqueous dispersion of  claim 1 , wherein Tg b1  is lower than −40° C. and Tg b2  is higher than −10° C. 
     
     
         20 . The aqueous dispersion of  claim 4 , wherein the weight proportion of said rubber polymer a), without grafted monomers, with respect to the global weight of a)+b), represents from 10 to 35%. 
     
     
         21 . The aqueous dispersion of  claim 8 , wherein said comonomer b2) is at least one functional monomer bearing at least one carboxy (—CO 2 H) or hydroxyl (—OH) functional group. 
     
     
         22 . The aqueous dispersion of  claim 8 , wherein the said weight content of 2-ethyl hexyl acrylate as monomer b1) with respect to said polymer b) varies from 80 to 98.5%.