Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
1998-12-08
2001-09-11
Copenheaver, Blaine (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S424200, C428S414000, C428S217000, C428S308400, C036S03000A
Reexamination Certificate
active
06287698
ABSTRACT:
BACKGROUND OF THE INVENTION
Polyurethane dispersion (PUD) adhesives have been developed in recent years as an alternative to solvent-based adhesives. Typically the dispersion is prepared by dispersing an isocyanate functional prepolymer in aqueous media, and chain extending the prepolymer after it is dispersed. Compatibility is conventionally provided by means of ionic groups such as carboxylate or sulfonate groups, or both, provided on the backbone of the polyurethane polymer. Addition of crosslinkers, such as isocyanates, aziridines, melamine resins, epoxies, oxazolines or carbodiimides at the time of use to improve bond strength is known and effective. However, substitution of polyurethane dispersion adhesives for solvent-based adhesives in specific applications often presents a potential user with special problems.
References describing polyurethane dispersion adhesives include U.S. Pat. No. 4,870,129; U.S. Pat. No. 5,334,690; U.S. Pat. No. 5,432,228; U.S. Pat. 5,494,960; U.S. Pat. No. 5,523,344; U.S. Pat. No. 5,532,058; U.S. Pat. No. 5,608,232; U.S. Pat. No. 5,610,232; U.S. application Ser. No. 08/561197 filed Nov. 21 1995, allowed (equivalent to WO97/19121); U.S. application Ser. No. 08/961,752, filed Oct. 31 1997; and DE 3930352, all incorporated herein by reference.
PUD adhesives offer several advantages over solvent based polyurethane adhesives such as low VOC, less odor, less hazard of fire, explosion or acute toxic reaction, greater acceptability from an environmental perspective and ease of handling. On the other hand PUD adhesives have drawbacks, such as lower water resistance, chemical resistance and heat resistance. To date the primary approach to overcoming these drawbacks is to use a polyisocyanate crosslinker.
In bonding rubbery materials to themselves, or to other substrates commonly found in footwear, it is conventional practice to apply a primer of a chlorinating compound, typically trichloroisocyanuric acid to the rubbery substrate(s). Application of the primer has been found to consistently provide bonds which fail by a substrate failure mode, rather than an adhesive failure mode. Use of this type of primer is conventional with solvent adhesives and provides similar benefits for polyurethane dispersion adhesives aged in limited humidity environments.
In bonding footwear rubber materials it has been found that isocyanate crosslinked PUDs made will give excellent T-peel bond strengths when aged in limited humidity (50%) environments, but that strength significantly deteriorates upon ageing in high humidity and high temperature environments. This problem is found with PUDs which contain carboxylate groups, sulfonate groups or mixtures of both as aqueous compatibilizing agents.
SUMMARY OF THE INVENTION
It has now been found that humidity resistance of bonded assemblies comprising a footwear rubber bonded with a polyurethane dispersion adhesive can be substantially improved when an epoxy functional compound is employed as the crosslinker.
In one aspect, therefore the invention is a method of bonding two substrates, at least one of which is a rubbery polymeric material having carbon-carbon double bonds on the polymer backbone, the method comprising:
a) applying an aqueous polyurethane dispersion adhesive composition to at least one of the substrates, the adhesive composition further comprising an epoxy resin;
b) allowing the composition to dry; and then
c) joining the substrates with heating to activate the adhesive.
The process is particularity advantageous when the rubbery material has been first primed with a chlorinating primer, especially when it is desired for the adhesive to be applied to the rubbery substrate promptly after the primer has dried.
In a further aspect, the invention is a bonded assembly comprising two substrates at least one of which is a rubbery polymeric material having carbon-carbon double bonds on the polymer backbone bonded by an adhesive therebetween, wherein the adhesive is a dried aqueous polyurethane dispersion adhesive composition, the adhesive composition further comprising an epoxy resin. Preferred bonded assemblies are laminates of molded rubbery material outer soles and molded foam midsoles for human footwear.
DETAILED DESCRIPTION OF THE INVENTION
Unless otherwise stated, references to percentages and parts herein are determined relative to the weight of the referenced composition.
Polyurethane dispersions which may be employed in the invention are typically formed by dispersing an isocyanate functional polyester polyurethane having ionic carboxylate and/or sulfonate groups, and then extending the polymer after dispersion by reaction of the isocyanate group with water or an amine. Such dispersions are described in U.S. Pat. No. 4,870,129; U.S. Pat. No. 5,334,690; U.S. Pat. No. 5,432,228; U.S. Pat. No. 5,494,960; U.S. Pat. No. 5,523,344; U.S. Pat. No. 5,532,058; U.S. Pat. No. 5,608,232; U.S. Pat. No. 5,610,232; U.S. application Ser. No. 08/561197 filed Nov. 21,1995, allowed (equivalent to WO97/19121); U.S. application Ser. No. 08/961,752, filed Oct. 31,1997; and DE 3930352. Commercial products include Dispercoll U KA-8464 sold by Bayer Corp. and FI-4000 and FI-4200 sold by H. B. Fuller Corp.
At least one of the substrates is a rubbery material, desireably a rubber having carbon-carbon double bonds in the polymer backbone. Suitable rubbery materials include styrene-butadicne rubber (SBR), styrene-butadience-styrene (SBS), and styrene-isoprene-styrene (SIS) rubbers. For footwear materials these materials will typically have a Shore A hardness value in the range of 50-90. The mating substrate may be the same, or same type, of material but will typically be a different type of polymer material. Specific examples include phylon, a lightly crosslinked EVA (ethylene vinyl acetate copolymer) foam which has been compression or injection molded. Shore A hardness values for these systems typically range from 25-75. Typically these substrate materials are compounded to a footwear manufacturer's specification, supplied as pellet or sheets, and then injection or compression molded by the footwear manufacturer.
The adhesives are particularly useful in sole bonding operations employing cup-sole, welt and stitch-down constructions and can be used for attaching direct injection molded soles.
A conventional chlorinating primer is typically used on the rubbery material substrate. A suitable such primer is trichloroisocyanuric acid. The primer is conventionally applied from solution and the substrate allowed to dry before the adhesive is applied. A commercial primer solution suitable for this purpose is Icortin C 27F, sold by H. B. Fuller Corp.
According to the inventive process an epoxy compound is mixed with the PUD at the time of use. The mixed adhesive is then applied onto the primed substrate and allowed to dry. Preferably the epoxy compound is added in the form of a dispersion or neat liquid resin. Use of a dispersion facilitates ease of blending. Furthermore the pot-life of the mixed adhesive is prolonged if the epoxy and polyurethane components remain in separate micelles, which do not substantially interact until the adhesive has dried and coalesced. However, the epoxy compound may also be directly dispersed in the PUD, for instance by means of a high speed mixer, without departing from the invention hereof.
Examples of epoxy compound which may be used in the invention include di or trifunctional liquid resins, such as DER 331 from Dow, or Epalloy 7190N75, Erisys GE-30, Erisys GE-35 and Erisys GE-36, all from CVC Specialty Chemical Company. Epoxy dispersions of difunctional resins such as EPI-REZ 3510 W-60 and EPI-REZ 3515 W-60, or trifunctional resins such as EPI-REZ 5003 W-60, all sold by Shell, may also be used.
The epoxy compound is suitably added to the PUD in the form of a dispersion or liquid resin in an amount of from about 1 to about 10%, preferably 2-8%, and more preferably about 4-6% by weight (epoxy solids basis) of the adhesive.
A conventional isocyanate crosslinker may also be incorporated into the adhesive formulatio
Duff Robert J.
Gottschalk Peter
Marty Brian L.
Zhu Yuduo
Binsu Nancy Quan
Copenheaver Blaine
H. B. Fuller Licensing & Financing Inc.
Paulraj Christopher
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