Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1997-06-10
2002-12-17
Gallagher, John J. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S306900, C156S315000, C156S331400, C521S159000, C521S160000, C521S174000
Reexamination Certificate
active
06494977
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improved adherence of decorative parts to vehicles, such as body side moldings and exterior ornamentation on automobiles and aluminum skins on truck trailers. More particularly, the present invention relates to adhering such decorative parts by means of a polyurethane foam especially designed to have sufficient adhesive capacity, suitable high and low temperature physical properties, stress-relieving properties and other functional characteristics previously achieved only with a combination of acrylic adhesive and sealing foam.
Polyurethane foam sealants have traditionally been prepared using a polyol precursor material having 100% diol content, or a mixture of diols and triols and less than 1% monol content. This polyol material is reacted with an isocyanate precursor material to form a variety of polyurethanes. See, “Optimizing Properties of Urethane Sealants,”
Adhesives
&
Sealants Industry,
June/July 1994, pp. 38-42. Such polyurethane sealants have essentially no tack or resistance to peel and are not useful for adhering decorative parts to vehicles.
Polyurethane adhesives of various types are well known and typical compositions are disclosed in U.S. Pat. Nos. 3,779,794, 4,624,996, 4,625,012, 5,102,714, and 5,227,409. However, while these products may exhibit good adhesiveness and other desirable physical properties for use in attaching automotive and decorative parts, none have also been found to have completely suitable stress-relieving capability and low temperature properties. In an attempt to overcome these problems of polyurethane adhesives, adhesive and foam combinations have been suggested. For example, EP-A-0,601,582 teaches the use of a foam elastomer substrate in combination with a pressure-sensitive adhesive to provide high adhesion to rough surfaces.
Current commercially available adhesive foam combinations, while having improved stress-relieving capability, have not had an adequate overall combination of adhesiveness, peel strengths on multiple surfaces, resistance to degradation at low temperature, elongation, and the like to meet the demands of the marketplace. These deficiencies are particularly notable in the demanding systems existing in the automotive industry. Painted steel or fiber reinforced plastic composite vehicle surfaces and decorative trim manufactured from thermoplastic polymers, such as olefins and polyvinylchloride, having poor wettability characteristics are widely used in the industry.
As a result, much of the adherence of automotive parts today is accomplished by coating both sides of a foam strip with expensive acrylic pressure sensitive adhesive layers so adhesive contacts the vehicle and the decorative trim or part. In view of the ongoing desire to both simplify and reduce the cost of the manufacture of automobiles, trucks, boats, trailers, trains and other vehicles, research and development continues to seek improved adhesive systems. The present invention is a result of that ongoing research.
SUMMARY OF THE INVENTION
This invention provides a method for adhering a decorative part to a vehicle, comprising the steps of:
(a) applying a pressure sensitive adhesive consisting of a polyurethane foam having a density of about 20 to 55 lbs/cu ft to an inner surface of the decorative part; and
(b) joining the decorative part to the vehicle by means of a bond formed by the polyurethane foam, wherein the bond between the decorative part and the vehicle is substantially free of any adhesive other than the polyurethane foam and the bond has an ASTM D-1000-87 peel test strength of at least 2 lbs/inch.
The polyurethane foam of the invention comprises a reaction mixture of:
(a) 100 parts of a substantially linear polyether polyol having a monol molecule content greater than about 3 weight %, a functionality of less than 2, a functional molecular weight of about 3,000 to 5,000 and a viscosity of about 700 to 1,500 centipoise at 25° C.;
(b) 12-18 parts of a modified polyisocyanate, comprising about 40-50 weight % 4,4′-diphenylmethane diisocyanate, about 15-25 weight % 2,2- and 2,4-diphenylmethane diisocyanates, about 10-20 weight % oligomers of the diphenylmethane diisocyanates, and less than about 2 weight % phenyl isocyanate, and having an isocyanate molecule content of about 25-30 weight %, a viscosity at 25° C. of about 100-200 mPa, and an equivalent weight of about 140-170;
(c) 0.1-1 parts of a thermal urethane catalyst;
(d) 1-5 parts of a silicone surfactant; and
(e) 8-15 parts of a foam generator, wherein sufficient gas is introduced into the mixture by the foam generator to yield a density of 20 to 55 lbs/cu ft.
The polyurethane foam may also comprise at least one component selected from the group consisting of 1-5 parts of chain extender, 0.03-3 parts of pigment, and 0.1-1 parts of epoxy stabilizer. In a preferred composition, the urethane catalyst is an organo-tin catalyst, the chain extender is a dialkylene-glycol and the epoxy stabilizer is a Bisphenyl A epichlorohydrin.
If the decorative part comprises an annodized aluminum surface and the polyurethane foam is adhered to the annondized aluminum surface, then the bond between the vehicle and the decorative part has an ASTM D-1000-87 peel test of at least 6 lbs/inch, without the use of an added layer of a pressure sensitive adhesive or a primer.
If the decorative part consists of a thermoplastic olefin polymer, or otherwise is difficult to wet with the polyurethane foam, then the method of the invention includes the further step of adding an interlayer composition, such as an acrylic adhesive, or an acrylic polymer primer, or a primer blend of acrylic polymer/hydroxy terminated polyvinyl chloride or a silane coupling agent, between the polyurethane foam and the vehicle part to provide a bond between the vehicle and the decorative part having a peel test strength of at least 6 lbs/inch. However, the amount of adhesive required in combination with the polyurethane foam of the invention is about 10-60% less than the amount required by prior art combinations.
DETAILED DESCRIPTION OF THE INVENTION
The polyurethane foam used in the present invention is the reaction product of a reaction mixture containing a hydroxyl-terminated polyurethane prepolymer, a modified polyisocyanate, a urethane catalyst, a surfactant, and optionally, a chain extender, an epoxy stabilizer and a pigment, wherein components are reacted in the presence of glass microbubbles or some other foam generator or with a process which creates a foam in the polyurethane product.
In a preferred aspect, the present invention utilizes a hydroxyl-terminated polyurethane prepolymer. The prepolymer is prepared from a substantially linear polyether polyol having a high monofunctional molecule (monol) content, i.e greater than about 3 weight %, a functionality less than 2, and preferably a molecular weight of about 3,000 to 5,000 and a viscosity of about 1,200 to 1,800 centipoise. A suitable polyether polyol is sold by Bayer, Inc., under the Multranol 9111 tradename. The polyol is reacted with a small amount of modified polyisocyanate to yield the prepolymer.
The modified polyisocyanate is preferably an isocyanate mixture such as one containing about 40-50 wt % 4,4′-diphenylmethane diisocyanate (MDI), about 15-25 wt % 2,2- and 2,4-diphenylmethane diisocyanates, about 10-20 wt % higher oligomers of these MDIs, and less than about 2 wt % phenyl isocyanate, and having an isocyanate molecule (NCO) content of about 25-30%, a viscosity at 25° C. of about 100-200 mPa, and an equivalent weight of about 140-170. Those skilled in the art will recognize that other isocyanates such as toluene diisocyanates (TDI) or various isocyanate terminated prepolymers can also be used.
The urethane catalyst is a thermal or other delayed action urethane catalyst, (i.e. activated by heat), preferably a tin catalyst, more preferably an organo-tin, such as stannous dioctoate which is optionally dissolved in an organic solvent such as dioctylphthalate, or polyglycols, or various polyether o
Smith Charles A.
Waldenberger Dean A.
Gallagher John J.
Lew Jeffrey C.
Norton Performance Plastics Corporation
Porter Mary E.
Ulbrich Volker R.
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