Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-10-08
2001-09-11
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S292000, C524S306000, C524S394000, C524S396000
Reexamination Certificate
active
06288149
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to increasing surface tension.
Hot melt adhesive compositions are used in a variety of applications and on a variety of substrates including nonwoven webs, including tissue. Nonwoven webs are used commercially in a variety of applications including insulation, packaging, household wipes, surgical drapes, medical dressings, and disposable articles, e.g., diapers, adult incontinent products and sanitary napkins.
When hot melt adhesives are applied to nonwoven webs it is desirable that the adhesive possess good flexibility (i.e., hand) and be free from bleed through. When used in applications such as disposable diapers, sanitary napkins and bed pad constructions, it is also desirable for the hot melt adhesive to be capable of transmitting liquid or moisture from the nonwoven fibers into the superabsorbent or fluff core substrates that are common in such applications. This property is known as wicking and is used to draw moisture away from the body and into the adsorbent core as quickly as possible after the nonwoven is wetted. Some hot melt adhesives are hydrophobic and repel moisture, rather than drawing moisture through the adhesive layer.
SUMMARY
In one aspect, the invention features an adhesive composition that includes: a) a block copolymer comprising monomers selected from the group consisting of styrene isoprene, butadiene, and combinations thereof, b) from about 0.5% to about 10% by weight surfactant, and a tackifying agent. The adhesive composition has a surface tension of at least about 34 dynes/cm
2
. In one embodiment, the block copolymer is styrene-isoprene-styrene.
In another embodiment, the surfactant is nonionic. In some embodiments, the surfactant is selected from the group consisting of fatty acid esters. The surfactant can be glycerol monostearate.
In one embodiment, the composition includes from about 10% by weight to about 80% by weight of the polymer, from about 0.5% by weight to about 10% by weight of the surfactant, and from about 20% by weight to about 50% by weight of the tackifying agent.
In some embodiments, the composition further includes a plasticizer. In one embodiment, the plasticizer includes a crystallizing plasticizer.
In another aspect, the invention features an article that includes a nonwoven substrate and an adhesive composition disposed on the substrate, where the adhesive composition has a surface tension of at least about 34 dynes/cm
2
.
In other aspects, the invention features an article that includes adhesive fibers that include an above-described adhesive composition.
The adhesive composition provides a durable bond to a nonwoven article, including tissue articles, and exhibits flexibility, non-staining, and a viscosity sufficient to enable mass production. The adhesive also possesses exceptional thermal stability relative to moisture sensitive hot melt adhesive compositions. The hydrophilic nature of the adhesive composition facilitates transmission of fluids throughout nonwoven and porous articles that include the adhesive composition.
Other features of the invention will be apparent from the following description of preferred embodiments thereof, and from the claims.
DETAILED DESCRIPTION
The hot melt adhesive composition exhibits a surface tension of at least about 34 dynes/cm
2
, more preferably at least about 40 dynes/cm
2
, most preferably at least about 44 dynes/cm
2
. The adhesive composition, when present on substrate or incorporated in a substrate, provides an increase in the surface tension of the substrate such that the substrate can be more easily wet by a fluid, e.g., water, body fluid (e.g., blood, urine, and combinations thereof) and combinations thereof (i.e., the adhesive improves the wettability of the substrate). The adhesive composition includes a polymer and a surfactant.
The polymer of the composition can be a block copolymer, an olefin-containing polymer, or a combination thereof. Preferably the polymer is a block copolymer.
A wide variety of block copolymers are useful in the hot melt adhesive of the resent invention including A-B-A triblock polymers, A-B diblock structures, star block copolymers, (A-B)
n
radial block copolymer, comb polymers, as well as branched and grafted versions of such, wherein the A endblock is a non-elastomeric polymer block, typically comprising polystyrene and/or vinyl, and the B block is an unsaturated conjugated diene or hydrogenated version thereof. In general, the B block is typically isoprene, butadiene, ethylene/butylene (hydrogenated butadiene), ethylene/propylene (hydrogenated isoprene), and mixtures thereof.
In general, block copolymers range in A block (styrene or vinyl) content from 0, as in the case of multi-arm (EP)n
8
100% diblock polymers to about 50 wt-%. Typically, the non-elastomeric A block concentration ranges from about 10 wt-% to about 45 wt-% with respect to the weight of the block copolymer. Block copolymers also range in diblock contents from 0, wherein the block copolymer is 100% coupled, to 100% diblock, as previously mentioned. Further, the molecular weight of block copolymer is related to the solution viscosity at 77° F. (25° C.) of a given weight of polymer in toluene. The amount of block copolymer employed for determining the solution viscosity depends on the molecular weight. For relatively high molecular weight block copolymers, the solution viscosity is typically expressed as a function of a 10 wt-% block copolymer solution, whereas for more conventional and lower molecular weight block copolymers, a 25 wt-% block copolymer solution is employed. A preferred high molecular weight block copolymer is a substantially saturated A-B-A block copolymer, wherein the A block is polystyrene or vinyl and the B block is ethylene-butylene, ethylene-propylene or mixtures thereof, such as Kraton™ G-1651.
Useful commercially available polymers include, e.g., Kraton® D and G series block copolymers, available from Shell Chemical Company (Houston, Tex.), Europrene® Sol T block copolymers, e.g., SIS and SBS block copolymers, available from EniChem (Houston, Tex., Vector® block copolymers, e.g., SIS and SBS block copolymers, available from Exxon (Dexco) (Houston, Tex.), as well as others. Branched versions such as Kraton® TKG-101 having a styrene-ethylene/butylene-styrene backbone with isoprene side chains as well Kraton® G-1730, an S-EP-S-EP block copolymer having a terminal ethylene-propylene block rather than terminal polystyrene, are also useful for increasing tack.
Preferably the block copolymer is present in the adhesive composition in an amount of from about 10% by weight to about 50% by weight, more preferably from about 15% by weight to about 40% by weight.
Suitable olefin-containing polymers are those in which ethylene is polymerized with 15 to 45% by weight of copolymerizable monomers such as vinyl acetate, N-butyl acrylate, propylene, methyl acrylate, methyl acrylic acid, acrylic acid, metallocene catalyzed ethylene based polymers and the like, as well as any mixtures thereof.
Additional suitable polymers are pure homopolymers or copolymers of the following monomers: olefins, such as ethylene, propylene, butene, hexene octene, or other alpha-olefins; vinyl monomers, such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl hexanoate; acrylic monomers, such as acrylic acid and methacrylic acid, methacrylic acid esters, hydroxy ethyl acrylate, and the like. Preferred polymers are ethylene/vinyl acetate copolymers such as those obtainable from Dupont under the Elvax tradename. The preferred range for the vinyl acetate will be in the range of 18%-40% by weight, with 33% most preferred.
Other adhesive compositions may be prepared according to the invention using, as a base polymer, amorphous polyolefins or blends thereof. Amorphous polyolefins are made by the atactic polymerization of polypropylene. Polymerization occurs in the presence of a catalyst comprising a coordination complex of a transition metal halide with an organometallic compound. The solid amorphous polypropylene has a softening point of abou
H. B. Fuller Licensing & Financing Inc.
Harlan R.
Quan Nancy
Wu David W.
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