Hot melt pressure sensitive adhesive for paper labels

Abstract

A HMPSA is provided that preferably includes at least a) from 30 to 50% of a mixture of triblock and diblock styrenic copolymers having an overall styrene content comprised between 14 and 40%, b) from 40 to 55% of a tackifying resin with a softening temperature comprised between 70 and 150° C. obtainable by hydrogenating, polymerizing or copolymerizing mixtures of aliphatic unsaturated hydrocarbons having about 5, 9 or 10 carbon atoms; c) from 4 to 20% of a hydrocarbon oil with an aromatic content less than 15%; d) from 1 to 6% of a filler selected among calcium carbonate or a low molecular weight homopolymer or copolymer of polyethylene. A laminated system is also provided that includes at least an adhesive layer utilizing the HMPSA and paper facestock. Also included are PSA labels obtainable from the laminated system with a reduced tendency to discolor after storage.

1 . A hot melt pressure sensitive adhesive (HMPSA) composition comprising:
 a) from 30 to 50% of a mixture of styrenic block copolymers including:
 10 to 70% of at least one SX 1 S triblock copolymer, and 
 30 to 90% of at least one SX 2  diblock copolymer; 
 wherein:
 S represents a polymerized segment of a styrene monomer, 
 X 1  and X 2 , identical or different, represent each an elastomeric polymerized segment of one or two monomers including isoprene, butadiene, or their respective hydrogenated derivatives; 
 
 and wherein the overall styrene monomer content in said mixture is between 14 and 40%; 
   b) from 40 to 55% of one or more tackifying resin(s) with a softening temperature between 70 and 150° C. and comprising a tackifying resin (i) that includes hydrogenated, polymerized or copolymerized mixtures of aliphatic unsaturated hydrocarbons having from about 5 to 10 carbon atoms;   c) from 4 to 20% of a hydrocarbon oil with an aromatic content less than 15%; and   d) from 1 to 6% of a filler comprising calcium carbonate or a low molecular weight homopolymer or copolymer of polyethylene.   
     
     
         2 . The HMPSA composition according to  claim 1 , wherein the mixture of styrenic block copolymers includes 10 to 30% of SX 1 S triblocks and 70 to 90% of SX 2  diblocks. 
     
     
         3 . The HMPSA composition according to  claim 1 , wherein the elastomeric polymerized segments X 1  and X 2  are the same monomer. 
     
     
         4 . The HMPSA composition according to  claim 1 , wherein the overall styrene monomer content is from 15 to 30%. 
     
     
         5 . The HMPSA composition according to  claim 1 , wherein X 1  and X 2  represent a polymerized segment of isoprene or a polymerized segment of butadiene. 
     
     
         6 . The HMPSA composition according to  claim 1 , wherein the tackifying resin(s) (i) are in admixture with up to 50% of one or more tackifying resin(s) comprising:
 a tackifying resin (ii) comprising a natural or chemically modified rosin;   a tackifying resin (iii) comprising a terpenic resin, optionally modified by action of phenols; or   a tackifying resin (iv) comprising a copolymer based on a natural terpene.   
     
     
         7 . The HMPSA composition according to  claim 6 , wherein the admixture comprises about 50% of resin (i) and about 50% of resin (ii), (iii) or (iv). 
     
     
         8 . The HMPSA composition according to  claim 1 , wherein the softening temperature of the tackifying resin(s) is between 80 and 140° C. 
     
     
         9 . The HMPSA composition according to  claim 1 , wherein the hydrocarbon oil has an aromatic content which is less than 7%. 
     
     
         10 . The HMPSA composition according to  claim 1 , wherein the filler is a homopolymer or copolymer of polyethylene with an average number molecular weight comprised between 1 and 5 kDa. 
     
     
         11 . The HMPSA composition according to  claim 1 , further comprising:
 from 32 to 40% of component a);   from 45 to 50% of component b);   from 10 to 20% of component c); and   from 3 to 5% of component d).   
     
     
         12 . The HMPSA composition according to  claim 1 , further comprising 0.5 to 2% of one or more stabilizer or antioxidant. 
     
     
         13 . A laminated system comprising:
 an adhesive layer comprising the HMPSA composition as defined in  claim 1 ,   a paper facestock in contact with said adhesive layer, and   a release liner in contact with the adhesive layer.   
     
     
         14 . The laminated system according to  claim 13 , wherein the paper is a white paper comprising a grammage of between 60 and 100 g/m 2 . 
     
     
         15 . A self-adhesive label obtainable by conversion of the laminated system such as defined in  claim 13 . 
     
     
         16 . The HMPSA composition according to  claim 1 , wherein the softening temperature of the tackifying resin is between 85 and 110° C.