Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-06-06
2003-12-09
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S304400, C428S317100, C428S317300, C428S317700, C428S319300, C428S346000, C528S048000, C528S052000, C528S053000, C528S067000, C528S219000, C528S368000, C525S452000, C525S453000, C525S457000, C525S458000
Reexamination Certificate
active
06660376
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hot melt moisture cure adhesive composition well suited for bonding porous substrates such as fabric, methods of adhesively bonding substrates and corresponding articles. The adhesive composition exhibits a combination of flexibility, high green strength, low molten viscosity and high heat resistance. In view of these properties, the adhesive is particularly amendable to hot melt adhesive application techniques wherein small individual discrete deposits of adhesive are applied to a substrate. The adhesive composition prepolymer is preferably the reaction product of at least one polyol, at least one polyisocyanate and at least one high molecular weight thermoplastic polyurethane lacking hard segments.
BACKGROUND OF THE INVENTION
Reischle et al., U.S. Pat. No. 4,585,819 issued Apr. 29, 1986 and DE-A-32 36 313 relate to an adhesive comprising an isocyanate prepolymer, a low molecular weight ketone resins, and optionally a thermoplastic polyurethane or polyester. Exemplified is a thermoplastic polyurethane formed from 404 grams of polyester diol based on adipic acid 1,4 butane diol and ethylene glycol with an OH-number of about 55 and a molecular weight of about 2,000, 20 grams of 1,4-butane diol and 109.5 g of 4,4′-diisocyanatodiphenyl methane. The inclusion of 1,4-butane diol contributes hard segments in the thermoplastic urethane component.
Brauer et al., U.S. Pat. No. 5,036,143 issued Jul. 30, 1991 teaches a high green strength curable urethane adhesive composition of a polyol, an organic isocyanate compound, a thermoplastic polyurethane which is soluble in methyl ethyl ketone, and optionally a solvent for controlling the percent solids and viscosity of the composition. The most preferred TPU is Millathane E-34. Other suitable TPU's are described in U.S. Pat. No. 3,043,807 issued Jul. 10, 1962, incorporated therein by reference. The 100% solids urethane adhesives are prepared from liquid reactants. The compositions are 100% solids in that the compositions do not contain solvents. However, due to the low melting point of the reactants, such compositions are flowable at room temperature. The adhesive compositions have a relatively high green strength for a liquid, per se. However, the compositions have relatively low green strength in comparison to thermoplastic solids wherein the initial green strength is obtained by the increase in modulus obtained by cooling the composition from a liquid state to a solid state. Further, in the case of bonding fabrics, liquid adhesive composition have a tendency to penetrate too far into the fabric resulting in poor bond strengths, undesirable stiffening of the fabric upon subsequent cure of the adhesive, or penetration through the fabric resulting in adhesive build-up on the equipment.
Takada et al., U.S. Pat. No. 5,115,180 issued Oct. 13, 1992 teaches a moisture curing hot melt adhesive comprising a blend of urethane prepolymers. The first urethane prepolymer comprising hard and soft segments as well as other specific properties, whereas the second urethane prepolymer comprises a soft segment moiety and terminal isocyanate group which is prepared in a specific manner. The exemplified adhesive compositions have a relatively high viscosity, greater than 1×10
6
cps at 120° C.
More recently, Krebs, U.S. Pat. No. 5,994,493 issued Nov. 30, 1999 stated that, “For formulations which are intended to have high initial strengths and to be applied to porous materials, 5 to 40% by weight of the thermoplastic polyurethane has to be added. Unfortunately, this increases the melt viscosity with the result that these adhesive can only be applied by spraying at very high temperatures.” Krebs describes reactive hot melt adhesives having a viscosity of less than about 8000 mPas at 150° C. consisting of a polyurethane prepolymer terminated by reactive isocyante groups which is the reactive product of based on liquid polyether or polyester polyol having certain properties, certain polyol alkoxylation products having a molecular weight below 1000 and at least one diisocyanate.
Although low in viscosity, the compositions of Krebs et al. tend to be stiff and exhibit short open times. Accordingly, industry would find advantage in hot melt moisture curing adhesive compositions having an improved balance of properties, particularly for fabric bonding.
SUMMARY OF THE INVENTION
The applicants have discovered a hot melt moisture cure adhesive composition exhibiting a synergistic combination of low viscosity and high green strength that is particularly useful for fabric bonding. The present invention relates to an article comprising a permeable or porous substrate bonded to at least one substrate with a hot melt moisture cure adhesive composition having a viscosity of less than about 60,000 cps and preferably less than about 30,000 cps at 250° F. The low viscosity property of the adhesive composition is advantageously combined with high green strength, as reflected by the peel resistance and/or storage modulus, G′. The storage modulus (G′) of the adhesive composition after about 100 seconds of cooling ranges from about 1×10
4
dynes/cm
2
to about 1×10
6
dynes/cm
2
. Further, the adhesive composition typically resists a bond displacement of about 20 mm for at least about 1 minute, and preferably for 10 minutes or longer. Advantageously, the composition of the present invention exhibits a higher storage modulus, (G′) in comparison to other hot melt moisture cure adhesive composition having about the same complex modulus or stiffness. The composition is flexible, having a complex modulus (G*) ranging from about 100 seconds of cooling ranges from about 1×10
4
dynes/cm
2
to about 1×10
7
dynes/cm Additionally, the composition preferably exhibits high heat resistance, having a peel adhesion failure temperature greater than 250° F.
The hot melt moisture cure polyurethane composition is prepared from about 40 wt-% to about 80 wt-% of at least one polyol, from about 5 wt-% to about 50 wt-% of at least one thermoplastic polyurethane that is substantially free of hard segments and having a molecular weight (Mn) of greater than about 10,000 g/mole, and at least one polyisocyanate present at an equivalent ratio of isocyanate to hydroxyl ranging from about 1.2 to about 10. The polyol component is relatively low in molecular weight and in the case of fabric bonding, preferably amorphous.
In another embodiment, the present invention relates to a method of bonding a permeable or porous substrate, such as fabric, comprising coating the low viscosity, high green strength hot melt moisture curing adhesive composition. The adhesive composition can advantageously be applied at low application temperatures ranging from about 200° F. to about 300° F. The adhesive composition is well suited for gravure roll coating, pattern coating, and particularly porous coating hot melt adhesive application techniques, wherein small individual discrete deposits of the adhesive are applied to a substrate. Particularly in the case of porous coating, adhesive build-up on the die, known as “roll up” does not occur.
Thermoplastic polyurethane is preferably prepared in situ during preparation of the hot melt moisture cure adhesive composition. At least one polyol is polymerized with at least one polyisocyanate such that a thermoplastic polyurethane having terminal OH groups and a molecular weight greater than 10,000 g/mole is formed. A second polyol having a molecular weight of less than about 5000 g/mole is added followed by a second addition of polyisocyanate. In preferred embodiments, the second polyol is the same polyol as employed in the preparation of the high molecular weight thermoplastic polyurethane.
DETAILED DESCRIPTION OF THE INVENTION
The adhesive composition is particularly useful for hot melt application techniques that apply discrete individual deposits of adhesive to a substrate such as engraved roll coating, pattern coating and in particular the Nordson Porous Coat™ System, as de
Bunnelle William L.
Kryzer Brendon J.
Zimmel John M.
H. B. Fuller Licensing & Financing Inc.
Ribar Travis B
Seidleck James J.
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