Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-08-07
2004-03-23
Short, Patricia A. (Department: 1712)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S331400, C524S445000, C524S590000, C524S507000, C525S09200D, C525S130000, C525S131000, C525S452000, C525S458000, C528S060000, C528S077000, C528S081000
Reexamination Certificate
active
06709539
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates to a one-part polyurethane based adhesive useful in bonding porous and nonporous materials. The adhesive is especially useful in bonding glass into window frames, for example windshields and other window glass into automobiles.
Polyurethane adhesive compositions typically comprise at least one urethane prepolymer. Adhesives useful for bonding to nonporous substrates, such as glass, to metal, are well-known. When glass is installed in automobiles on a production line, a one-part moisture curable polyurethane adhesive is preferably used, as the equipment needed for the application of such an adhesive in an automobile assembly plant is less expensive than the equipment needed to apply a two-part adhesive. One part polyurethane adhesives are disclosed in U.S. Pat. Nos. 4,374,237 and 4,687,533 incorporated herein by reference.
U.S. Pat. No. 5,922,809 discloses a one-part polyurethane adhesive comprising a prepolymer comprising the reaction product of A) one or more polyisocyanates; B) one or more compounds containing an average of more than one isocyanate reactive moieties; preferably a mixture of a polyether diol and a polyether triol; and C) a dispersion triol containing from about 10 to about 60 percent by weight based on the dispersion of particles of an organic polymer having a particle size of from about 5 to about 50 microns, preferably comprising a polymer derived from styrene, halo or alkyl styrene; or a rubber modified polymer derived from styrene, or halo or alkyl substituted styrene; wherein the prepolymer has an isocyanate content of from about 0.8 to about 2.2 percent by weight; and D) a catalyst for the reaction of a polyisocyanate with water, incorporated herein by reference.
In the automotive after-market replacement industry, glass is often bound into automobiles through the use of two-part moisture curable polyurethane adhesives. Two-part polyurethane adhesives are used because they offer rapid initial cure allowing for rapid drive-away times. Two-part adhesives require special applicators which mix the two parts in specific proportions immediately prior to application. These applicators are more difficult to and costly to use than applicators used for one-part adhesives. Further, the improper application or mixing of two-part adhesives can result in poor adhesion. Two-part polyurethane adhesives are well known, see U.S. Pat. Nos. 4,835,012, and 5,603,798, both incorporated herein by reference, and DE 4,210,277.
The market demands simpler application systems and faster curing adhesives which allow even faster drive-away times. If the adhesive cures too rapidly, then the window installer loses the necessary time to install and properly place the glass into the frame before the adhesive becomes too intractable to work with. Working time is defined as the period from application of adhesive until the adhesive becomes too intractable to work with.
Regulations in the U.S. require dual airbags for the front seat of vehicles. During crashes the airbags inflate and exert additional pressure on the windshield. Federal Transportation Agency regulations require that windshield remain in place at crashes of up to 30 mph (48 KPH). This requires adhesives which have enhanced strength at the drive-away time. To meet such a standard, the lap shear strengths of the adhesive should be preferably 150 psi (1033 kPa) or greater as determined according to ASTM D-3163 and demonstrate impact energy strength of 9 ft-lbs (12.2 Joules) or greater at 23° C./50% RH.
There is a need for a one-part adhesive which can survive such a crash two hours after application of the adhesive at 15° F. (−9.4° C.). Survive a crash means that the windshield remains bonded in the automobile during and after the crash.
SUMMARY OF THE INVENTION
The present invention is a polyurethane prepolymer comprising the reaction product of
A) one or more polyisocyanates;
B) one or more diols and one or more triols;
C) one or more dispersion triols containing from about 10 to about 60 percent by weight based on the dispersion of particles of an organic polymer having a particle size of from about 5 to about 50 microns;
wherein the prepolymer has a free isocyanate content of from about 0.8 to about 2.2 percent and the weight ratio of diol to triol and dispersion triol is from about 0.8 to about 1.2. The free isocyanate content referred to here is measured 24 hours after prepolymer production.
In another embodiment the invention is a one-part adhesive composition comprising the polyurethane prepolymer of the invention and a catalyst capable of catalyzing the reaction of isocyanate moieties with water.
In another embodiment the invention is a process for bonding two substrates together which comprises contacting the two substrates together with the adhesive composition of the invention disposed between the two substrates and allowing the adhesive to cure and bond the substrates together.
The adhesive of this invention is capable of bonding primed glass into an automobile such that glass will not delaminate from the window frame in a crash at 35 mph at 35° F. (1.7° C.) and 45 percent relative humidity 2.5 hours after adhesive application and at 30 mph at 15° F. (−9.4° C.) two hours after adhesive application. The adhesive of the invention also provides reasonable working times, preferably about 6 to about 15 minutes, and more preferably about 8 to about 10 minutes. Additionally, many of the problems associated with two-part adhesives described before are eliminated.
DETAILED DESCRIPTION OF THE INVENTION
The urethane prepolymers have an average isocyanate functionality sufficient to allow the preparation of a crosslinked polyurethane upon cure and not so high that the polymers are unstable. Stability in this context means that the prepolymer or adhesive prepared from the prepolymer has a shelf life of at least 6 months at ambient temperatures, in that it does not demonstrate an increase in viscosity during such period which prevents its application or use. Preferably the prepolymer or adhesive prepared therefrom does not undergo an increase in viscosity of more than about 50 percent during the stated period. Preferably, the average isocyanate functionality is at least about 2.2 and preferably at least about 2.4. Below about 2.2 the ability of the prepolymer to crosslink sufficiently to achieve the desired strength of the cured adhesive is compromised. Preferably the average isocyanate functionality of the prepolymer is 3.0 or less and more preferably 2.8 or less. Above 3.0 average isocyanate functionality the prepolymer and adhesives prepared from the prepolymer may exhibit unacceptable stability. The prepolymer preferably has a free isocyanate content which facilitates acceptable strength in adhesives prepared from the prepolymers after 60 minutes and stability of the prepolymer. Preferably, the free isocyanate content is about 0.8 percent by weight or greater based on the weight of the prepolymer and more preferably about 0.9 percent by weight or greater, and preferably about 2.2 percent by weight or less, more preferably about 2.0 or less, even more preferably about 1.4 percent by weight or less and even more preferably about 1.1 percent by weight or less and most preferably about 1.0 percent by weight or less. Above about 2.2 percent by weight the adhesives prepared from the prepolymer may demonstrate lap shear strengths after 60 minutes which are too low for the intended use and foaming during cure of the adhesive prepared from the prepolymer may occur. Below about 0.8 percent by weight the prepolymer viscosity is too high to handle and the working time is too short.
The free isocyanate content changes with time as the free isocyanate groups react with moisture. Primary free isocyanate content means the isocyanate content measured within a short period of time, less than 1 hour, after production of the prepolymer. Secondary free isocyanate content means the weight percent of isocyanate groups present in the prepolymer about 24 hours after production of the
Dow Global Technologies Inc.
Sims Norman L
LandOfFree
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