U.S. Pat. No. 5,037,411 disclosed the use of a hot melt adhesive composition for the multiline construction of disposable laminates, such as disposable diapers and feminine pads, said adhesive composition comprising:
(a) 5 to 15% by weight of a radial copolymer having three or four (AB) arms, wherein polymer blocks A are poly(styrene) blocks and polymer blocks B are poly(butadiene) or hydrogenated poly(butadiene) blocks having a molecular weight greater than 140,000 and containing at least 15 parts styrene per 100 parts of block copolymer, PA1 (b) 40 to 80% by weight of a compatible tackifying resin, PA1 (c) 5 to 30% by weight of a plasticizing oil, PA1 (d) 0 to 5% by weight of petroleum derived wax, and PA1 (e) 0.1 to 2% by weight of a stabiliser. PA1 (a) 10 to 40% by weight of a substantially radial styrene-butadiene block copolymer having a styrene content greater than 35% by weight, such as KRATON DX-1122, SOL-T162 LW/1 and SOL-T162 LW/2, PA1 (b) 20 to 65% by weight of at least one compatible tackifying resin, PA1 (c) 0.1 to 4% by weight of stabiliser, and PA1 (d) the remainder up to about 60% by weight, comprising at least one oil diluent. PA1 (a) a radial multiarmed block copolymer (AB).sub.n X, wherein A is a block predominantly derived from a monovinylaromatic compound, B is a block predominantly derived from butadiene and which optionally has been partially or completely hydrogenated, X is the residue of a multifunctional coupling agent, and n is in the range of from 3 to 6; PA1 (b) a linear block copolymer AB, the components (a)+(b) being present in an amount of 100 parts by weight; PA1 (c) a tackifying resin which is compatible with the blocks B in an amount of from 100 to 500 parts by weight; PA1 (d) a plasticizer in an amount of from 100 to 300 parts by weight; and PA1 (e) an antioxidant -UV stabiliser in an amount from 0.1 to 5 parts by weight.
A preferred block copolymer to be used as component (a) was mentioned to be KRATON 1184, having a styrene content of 30%, but having a low vinyl content (&lt;5%).
European patent application No. 0358900 teaches hot melt adhesive compositions suitable for disposable constructions, comprising:
"New Modified TPE Polymers" by D. J. Dougherty, Firestone Synthetic Rubber and Latex Company, Akron, USA (TAPPI Proceedings 1994 Hot Melt Symposium, 115-123, described the effect of vinyl modification in the range of from 30 to 50% on the relevant adhesive compositions containing styrene-butadiene block copolymers as compared to the properties of adhesive compositions containing the commercial block copolymer grade STEREON 840A, a linear multiblock copolymer. The Quick Stick property was found to be relatively unaffected by vinyl content up to 49%. 180.degree. polyethylene peel was relatively constant up to 39% vinyl and then underwent a deterioration. 180.degree. peel from stainless steel was fairly erratic, but generally increased with vinyl content. Polyken Tack was basically unaffected by vinyl content up to 49%, but was poor at 58% vinyl. The low adhesive viscosity was significantly improved by an increased in vinyl level. The adhesive tensile strength increased as the vinyl content was increased. However, no teaching at all was provided as to the interrelation of the adhesive properties and additional block copolymer manufacturing parameters such as styrene content, coupling agent, coupling efficiency, and molecular weights of the respective block constituents.
It will be appreciated that from an economical viewpoint there is still a need for further improvement of hot melt adhesive compositions to be used for disposable articles which composed of polymer film layers which are as thin as possible. Such hot melt adhesive compositions must, on the one hand, show a melt viscosity which is low enough for an efficient application on the substrate layers at the maximum processing temperature, governed by the thinner gauge polymer substrates, such as poly(ethylene) or poly(propylene), and, on the other hand, exhibit sufficiently high standard adhesive properties as prescribed by the consumer requirements and/or processing requirements.
An object of the present invention is therefore to provide such improved hot melt adhesive compositions for multiline construction or multidot construction of disposables by selection of block copolymers and tackifying resins and plasticizers as main ingredients for said adhesive compositions. As a result of extensive research and experimentation, said hot melt adhesive compositions surprisingly have been found.