Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-02-03
2003-03-11
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S270000, C524S271000, C523S105000, C523S111000
Reexamination Certificate
active
06531544
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to using certain block copolymer based hot melt adhesive compositions for the assembly of disposable absorbent articles such as disposable diapers wherein the adhesive is in contact with an oil-based skin care ingredient, and the resulting disposable absorbent article. The adhesive is particularly useful for adhesively bonding elastic to nonwoven, and exhibits good stress resistance in the presence of lotion.
BACKGROUND OF THE INVENTION
Hot melt pressure sensitive adhesives based on styrene-isoprene-styrene and/or styrene-butadiene-styrene, tackifying resin(s) and relatively high concentrations of plasticizing oil have been used extensively for the construction of disposable diapers. Block copolymer based adhesives are generally preferred, particularly for elastic attachment, due to the ability of such adhesive compositions to resist creep.
A recent trend in the disposable absorbent product industry has been to introduce certain oil-based skin care ingredients such as baby oil, lotions, ointments, petroleum jellies, sunscreens, etc. into such absorbent products. Typically, such ingredients are coated onto the topsheet that contacts the skin during use of the absorbent products. This trend has made it increasingly difficult to maintain adequate bond strengths in disposable absorbent products throughout the entire product life-cycle, particularly for elastic attachment bonds.
WO 97/39075, published Oct. 23, 1997, teaches an oil resistant polybutylene based hot melt adhesive having a variety of end uses, particularly in the construction and elastic attachment application of nonwoven disposable articles. The composition includes polybutylene copolymer or a mixture of polybutylene and polyolefin polymers, a tackifier resin, plasticizer, a wax, and a stabilizer. According to this reference, hot melt adhesives based on styrene-isoprene-styrene or styrene-butadiene-styrene lose most of their bond strengths upon exposure to mineral oil or other oil based ointments.
Likewise, WO 97/38739 published Oct. 23, 1997 discloses an adhesive that exhibits desired oil-resistance and processing properties. The adhesive is claimed to have a certain elastic modulus and viscosity. An adhesive material comprising styrene-isoprene-styrene rubber block copolymer, hydrocarbon tackifying resins, and mineral oil, is depicted as having a loss of peel from 693 to 196 grams, and a 72% loss of energy upon oil insult.
U.S. Pat. No. 5,948,709 issued to Paul et al. Sep. 7, 1999 is directed to oil resistant compositions and nonwoven articles comprising an adhesive prepared from polymeric dimer fatty acid polyamide resins which are especially suited for use in the elastic attachment of disposable nonwoven products and particularly for leg or waist bond closures for disposable products such as diapers. This reference also states that “block copolymer based adhesives lose most of their bond strength, resulting in adhesive bond failure upon exposure to mineral oil or other oil based ointments which are often used on infants to treat skin rashes. As a result, the elastic leg bands may actually come loose from the diaper resulting in a break down of the inner leg cuff.”
SUMMARY OF THE INVENTION
Surprisingly, the present inventors have found that certain block copolymer based hot melt adhesive compositions maintain their bond strength upon exposure to oil-based skin care ingredients such as lotion.
The adhesive composition comprises from about 10 wt-% to about 45 wt-% of a block copolymer component, from about 50 wt-% to about 80 wt-% of at least one tackifying resin, and from 0 to about 10 wt-% of a liquid plasticizer. The Applicants surmise that the low concentration of liquid plasticizer is critical to the ability of the adhesives to maintain adequate bond strength in the presence of oil-based skin care ingredients.
Preferably, the block copolymer component concentration is greater than about 20 wt-% and the tackifying resin concentration ranges from 70 wt-% to 80 wt-%. More preferably, the block copolymer component is a blend of a first, relatively soft lock copolymer and a second, relatively hard block copolymer. The first block copolymer is typically one or more styrene-isoprene-styrene (SIS) block copolymers having a diblock content of at least about 20 wt-%. The second block copolymer is preferably a styrene-butadiene-styrene (SBS) block copolymer having a melt flow rate of less than 10 g/10 minutes. For reduced viscosity and improved processability, one or more of the block copolymers are preferably radial.
The adhesive is useful for bonding a variety of substrates that contain or are coated with oil-based ingredients. The adhesive is particularly useful in the assembly of disposable absorbent articles for adhesively bonding nonwoven, film, and particularly elastic and elastomeric films and substrates.
In one embodiment, the present invention is a disposable article having at least one substrate bonded with a hot melt adhesive wherein said adhesive comprises:
(a) from about 15 wt-% to about 45 wt-% of a block copolymer component;
(b) from about 50 wt-% to about 80 wt-% of at least one tackifying resin; and
(c) from 0 to about 10 wt-% of an oil plasticizer;
wherein said adhesive is in contact with an oil-based skin care ingredient.
In another embodiment, the present invention is a method of using a hot melt adhesive composition in the assembly of disposable absorbent articles comprising the steps of:
(a) providing a molten hot melt adhesive composition comprising:
(i) from about 15 wt-% to about 45 wt-% of block copolymer component;
(ii) from about 50 wt-% to about 80 wt-% of at least one tackifying resin; and
(iii) from 0 to about 10 wt-% of an oil plasticizer;
(b) applying said adhesive to a substrate wherein said adhesive contacts an oil-based skin care ingredient.
DETAILED DESCRIPTION OF THE INVENTION
The adhesive composition contains a block copolymer component that contains one or more block copolymers in an amount ranging from about 10 wt-% to about 45 wt-%, preferably from about 15 wt-% to about 30 wt-% and most preferably from about 20 wt-% to about 30 wt-%.
A wide variety of block copolymers are useful in the present invention including A-B-A triblock structures, A-B diblock structures, (A-B)
n
radial block copolymer structures, as well as branched and grafted versions of such, wherein the A endblock is a non-elastomeric polymer block, typically comprising polystyrene, 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. The block copolymers comprising an unsaturated conjugated diene such as styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS) and mixtures thereof are preferred due to their increased tack and reduced cost. Commercial embodiments include the Kraton® D series block copolymers, available from Shell Chemical Company (Houston, Tex.), Europrene® Sol T block copolymers available from EniChem (Houston, Tex.), Vector® block copolymers available from Exxon (Dexco) (Houston, Tex.), Solprene® block copolymers from Housmex® (Houston, Tex.) as well as others.
In addition to the block configuration, block copolymers are typically characterized according to their reported styrene content, diblock content, and in terms of their melt flow rate (MFR, Condition G) or solution viscosity, which relates to the molecular weight of the block copolymer.
Typically, the non-elastomeric A block (styrene) concentration ranges from about 5 wt-% to about 45 wt-% with respect to the total weight of the block copolymer. The styrene portion is less susceptible to heat degradation. Accordingly, hot melt adhesive compositions based on higher styrene content block copolymers generally exhibit enhanced heat stability relative to hot melt adhesive compositions based on block copolymer having a lower styrene content. However, high styrene content (>30%) are typica
Flanagan Larry S.
Van Lith Greg J.
Vaughan Steve R.
Cain Edward J.
H.B. Fuller Licensing & Financing Inc.
Lee Katarzyna W.
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