Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Patent
1996-12-03
1999-11-30
Gorr, Rachel
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
528905, 1563314, 525440, 525460, C08G 1848
Patent
active
059944935
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a quick-setting, moisture-curing polyurethane hotmelt adhesive, to its production and to its use.
DISCUSSION OF RELATED ART
Moisture-curing or moisture-crosslinking polyurethane hotmelt adhesives are adhesives which are solid at room temperature and which are applied in the form of a melt, their polymeric constituents containing urethane groups and reactive isocyanate groups. Cooling of the melt results initially in rapid physical setting of the adhesive followed by a chemical reaction of the isocyanate groups still present with moisture to form a crosslinked, infusible adhesive. It is only after this chemical curing with moisture, accompanied by an increase in the size of the molecule or crosslinking, that the adhesive acquires its final properties. Polyurethane hotmelt adhesives in the narrower sense are solventless adhesives.
The main advantages of hotmelt adhesives over other adhesive systems lies in their very quick setting and in the absence of water and solvents.
Corresponding moisture-curing polyurethane hotmelt adhesives for bonding various substrates are known.
Thus, DE-A-32 36 313 describes a hotmelt adhesive containing a prepolymeric isocyanate, a thermoplastic polymer and a low molecular weight synthetic resin. The prepolymeric isocyanate is a reactive polyurethane prepolymer of an aromatic diisocyanate and/or a prepolymer of this diisocyanate with a short-chain diol and of a polyether or a polyester containing OH groups and a short-chain diol.
This hotmelt adhesive is suitable for the bonding of thermoplastics and thermosets, foams, painted surfaces, rubber, textiles, nonwoven materials, leather, wood, metal and paper. 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 adhesives can only be applied by spraying at very high temperatures.
GB-A-2,234,516 describes a moisture-curing hotmelt adhesive consisting of a polyurethane prepolymer A with hard and soft chain segments and terminal isocyanate groups and a urethane prepolymer B with soft chain segments and terminal isocyanate groups. The prepolymer A is prepared in steps from a thermoplastic saturated polyester polyol with a molecular weight of 1,000 to 6,000 and a melting point of 50.degree. C. or higher, a polyol with a molecular weight of not more than 8,000 and a diisocyanate. The prepolymer B is prepared from a polyol with a molecular weight of not more than 8,000 and a diisocyanate. This polyol may be liquid at room temperature or may have a melting point below 50.degree. C. 4,4'-diphenyl methane diisocyanate or toluenediisocyanate is said to be particularly preferred as the diisocyanate. Unfortunately, these hotmelt adhesives require an elaborate production process. Either the prepolymer A and the prepolymer B are prepared in a three-stage process or the polymers have to be prepared in separate two-stage or one-stage processes and subsequently mixed. The melt viscosity of these adhesives at 120.degree. C. is very high (>1 million mPas) so that not only are these adhesives expensive to produce, they are also unsuitable for spray application.
EP-A-340 906 describes a quick-setting polyurethane hotmelt adhesive consisting of a mixture of at least two amorphous polyurethane prepolymers, the two prepolymers having different glass transition temperatures. The first polyurethane prepolymer preferably has a glass transition temperature above room temperature while the second polyurethane prepolymer has a glass transition temperature below room temperature. The polyurethane prepolymer with the higher glass transition temperature preferably consists of a polyester diol and a polyisocyanate while the polyurethane prepolymer with the lower glass transition temperature preferably consists of a linear or lightly branched polyester or of a polyether. Aromatic diisocyanates, such as 4,4'-diphenyl me
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Chemical Dictionary, 5th edt., Grant & Hackh's, p. 287 ; 1987.
Gorr Rachel
Harper Stephen D.
Henkel Kommanditgeesellschaft auf Aktien
Jaeschke Wayne C.
Szoke Ernest G.
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