Hot melt positioning adhesive
A hot melt adhesive composed of a styrene-butadiene-styrene polymer having a relatively high diblock content and styrene content, a second styrenic block copolymer having a lower diblock content than the styrene-butadiene-styrene polymer, which is preferably a styrene-isoprene-styrene polymer, together with tackifying resin, and liquid plasticizer. The preferred styrene-butadiene-styrene polymer contains a styrene content of greater than 30 percent and a diblock content greater than 30 percent by weight. When used in conjunction with a styrene-isoprene-styrene polymer, the hot melt composition provides improved peel strength at 5° C., and when used as a pad attachment positioning adhesive, did not exhibit adhesive transfer at 40° C.
1. A hot melt adhesive composition, comprising a mixture of the following components:
(a) about 2% to about 25% by weight of a first styrenic block copolymer, based on the total adhesive composition, comprising a styrene-butadiene-styrene block polymer having a styrene content greater than 35% by weight and up to about 50% by weight and a styrene-butadiene diblock content greater than 30% by weight and less than 70% by weight;
(b) about 2% to about 25% by weight of a second styrenic block copolymer, based on the total adhesive composition, comprising a styrene-isoprene-styrene block copolymer or a styrene-butadiene/isoprene-styrene block copolymer, each said block copolymer having a styrene content from 15% to 30% by weight and a styrene-isoprene or styrene-butadiene/isoprene diblock content present in the second styrenic block copolymer and lower than the first styrenic block copolymer and less than 40% by weight;
(c) about 25% to about 60% by weight of a tackifying resin, based on the total adhesive composition, said tackifying resin present in an amount greater than the combined amount of the first and second styrenic block copolymers and having a Ring and Ball softening point of at least 115° C.;
(d) about 0% to about 15% by weight of an aromatic endblock reinforcing resin based on the total adhesive composition;
(e) a liquid plasticizer in an amount of greater than 25% to about 50% by weight based on the total adhesive composition; and
(f) about 0% to about 5% by weight of a stabilizer or antioxidant based on the total adhesive composition.
2. The hot melt adhesive composition of claim 1 wherein the styrene-butadiene diblock content of said first styrenic block copolymer is greater than 45% by weight.
3. The hot melt adhesive composition of claim 1 wherein the styrene-butadiene diblock content of said first styrenic block copolymer is greater than 60% by weight.
4. The hot melt adhesive composition of claim 1 wherein said first styrenic block copolymer is present in an amount of from about 5% to about 20% by weight based on the total adhesive composition.
5. The hot melt adhesive composition of claim 1 wherein said first styrenic block copolymer is present in an amount of from about 8% to about 16% by weight based on the total adhesive composition.
6. The hot melt adhesive composition of claim 1 wherein said second styrenic block copolymer has styrene content from 15% to 25% by weight.
7. The hot melt adhesive composition of claim 1 wherein said second styrenic block copolymer has styrene content from 15% to 20% by weight.
8. The hot melt adhesive composition of claim 1 wherein the styrene-isoprene or styrene-butadiene/isoprene diblock content of said second styrenic block copolymer is less than 30% by weight.
9. The hot melt adhesive composition of claim 1 wherein said second styrenic block copolymer is present in an amount of from about 5% to about 20% by weight based on the total adhesive composition.
10. The hot melt adhesive composition of claim 1 wherein said second styrenic block copolymer is present in an amount of from about 8% to about 16% by weight based on the total adhesive composition.
11. The hot melt adhesive composition of claim 1 , wherein said second styrenic block copolymer is the styrene-isoprene-styrene polymer.
12. The hot melt adhesive composition of claim 1 wherein said plasticizer is present in an amount of from greater than 25% to about 45% by weight based on the total adhesive composition.
13. The hot melt adhesive composition of claim 1 wherein said plasticizer is present in an amount of from greater than 25% to about 40% by weight based on the total adhesive composition.
14. The hot melt adhesive composition of claim 1 wherein said composition has a glass transition temperature at or below about 15° C.
15. The hot melt adhesive composition of claim 1 wherein said first styrenic block copolymer has a solution viscosity (25% by weight in toluene) less than about 500 centipoise.
16. The hot melt adhesive composition of claim 1 wherein said first styrenic block copolymer has a solution viscosity (25% by weight in toluene) less than about 400 centipoise.
17. The hot melt adhesive composition of claim 1 wherein said first styrenic block copolymer has a solution viscosity (25% by weight in toluene) less than about 200 centipoise.
18. The hot melt adhesive composition of claim 1 wherein the triblock of said second styrenic block copolymer consists of a styrene-isoprene-styrene polymer.
19. The hot melt adhesive composition of claim 1 , wherein the amount of liquid plasticizer is at least 32% by weight based on the total adhesive composition.
20. The hot melt adhesive composition of claim 1 , wherein the amount of liquid plasticizer is at least 32.6% by weight based on the total adhesive composition.
21. The hot melt adhesive composition of claim 1 , wherein said first styrenic block copolymer is linear.
22. The hot melt adhesive composition of claim 1 , wherein said second styrenic block copolymer is linear.
23. The melt adhesive composition of claim 1 , wherein both said first styrenic block copolymer and said second styrenic block copolymer are linear.
24. The melt adhesive composition of claim 1 , wherein the Ring and Ball softening point of the tackifying resin is at most 142° C.
25. The melt adhesive composition of claim 24 , wherein the Ring and Ball softening point of the tackifying resin is at least 130° C.