Low temperature hot melt adhesives for disposable articles with high creep resistance
View Patent ↗The present invention is directed to adhesives suitable for application using a hot melt process at a relatively low temperature in the range of about 110° C. to about 130° C. Such adhesives exhibit desirable viscoelastic properties and are suitable for bonding an elastic attachment in the manufacture of disposable articles, such as disposable diapers.
1. A low application temperature hot melt adhesive consisting essentially of:
(a) 5 to 20 wt % of the styrenic block copolymer that (i) has a melt flow index greater than 33, measured in accordance with ASTM D 1238, and (ii) has a styrene content greater than 40%;
(b) 0.5 to 5% wt % of the wax;
(c) 30-70 wt % of a tackifier that has a ring and ball softening point less than about 105° C.;
(d) 0.1-2 wt % of an antioxidant; and
(e) optionally, up to 30 wt % of an oil
wherein the adhesive has a viscosity less than about 8,500 centipoises at 120° C.; and
wherein the adhesive has a creep performance of less than about 25% after 300% strain applied at 38° C. for four hours.
2. The low application temperature hot melt adhesive of claim 1 wherein the tackifier is selected from the group consisting of aliphatic C5 resins, aliphatic resins, dicyclopentadiene resins, C5/C9 blended resins and mixtures thereof.
3. The low application temperature hot melt adhesive of claim 1 wherein the adhesive has a crossover temperature greater than 60° C.
4. The low application temperature hot melt adhesive of claim 3 wherein the crossover temperature, measured as the point where tan d=1, is greater than 65° C.
5. The low application temperature hot melt adhesive of claim 1 wherein the adhesive has a yield stress of greater than 50 psi.
6. The low application temperature hot melt adhesive of claim 5 wherein the yield stress is greater than 75 psi.
7. The low application temperature hot melt adhesive of claim 1 wherein the styrenic block copolymer is a styrene-isoprene-styrene, styrene-butadiene-styrene or mixtures thereof.
8. The low application temperature hot melt adhesive of claim 1 wherein the wax is selected from the group consisting of paraffin waxes, microcrystalline waxes, polyethylene waxes, polypropylene waxes, by-product polyethylene waxes, Fischer-Tropsch waxes, oxidized Fischer-Tropsch waxes, functionalized waxes, and mixtures thereof.
9. An article comprising the low application temperature hot melt adhesive of claim 1 .
10. The article of claim 9 which is a disposable article.
11. The article of claim 10 which is an elastic attachment.