Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-06-11
2003-05-13
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C526S298000, C526S299000
Reexamination Certificate
active
06562181
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to adhesives and coatings that include a free radical polymerizable component wherein the free radical polymerizable component includes a trifunctional olefinic monomer.
Reactive acrylic adhesives that cure by free radical polymerization of (meth)acrylic esters (i.e., acrylates) are known, but suffer from certain drawbacks. Commercially important acrylic adhesives tend to have an offensive odor, particularly those that are made from methyl methacrylate. Methyl methacrylate-based acrylic adhesives also have low flash points (approximately 59° F.). Low flash points are particularly an issue during storage and transportation of the adhesives. If the flash point is 141° F. or lower, the U.S. Department of Transportation classifies the product as “Flammable” and requires marking and special storage and transportation conditions.
Another problem with reactive, two-part, acrylic adhesives utilizing a benzoyl peroxide/tertiary amine free radical initiator system is that the volume mix ratio of one part with the other part is not 1:1—it is typically 4:1 or 10:1. Obviously, this requires more careful measurement calculation during application of the adhesive and causes packaging problems. The mix ratio problem results largely from the instability of mixtures of free radical initiators such as benzoyl peroxide with (meth)acrylic monomers at room temperature. The free radical initiators generate a sufficient amount of free radical to gel the monomers over a short time period.
Styrenic monomers such as styrene and vinyl toluene have been suggested as alternatives to (meth)acrylic adhesives (see, e.g., U.S. Pat. No. 2,981,650), but these have at least two drawbacks. The film formed from styrenic monomers is too brittle and the cure rate of styrenic monomers is too slow to be useful as a structural adhesive.
A two part reactive adhesive with reduced odor and flammability that could be mixed at a 1:1 volume ratio without comprising shelf life stability or adhesive performance would be very desirable.
SUMMARY OF THE INVENTION
The composition of the invention is a reactive adhesive or coating that includes two parts or sides that are mixed together at the time of use. The reaction of the two parts acts to cure the adhesive or coating. It has been discovered that a certain copolymerization system provides a reactive adhesive or coating composition that has very useful characteristics.
In particular, a trifunctional olefinic first monomer and an olefinic second monomer copolymerize when mixed together with a free radical initiator system. If the initiator and monomer mixture is applied to a substrate, the copolymerization process acts to form a highly crosslinked composition that is strongly adhesively bonded to the substrate.
Thus, according to a first embodiment of the invention there is provided a method for bonding together two substrates that includes applying to a first substrate an adhesive composition that includes (a) a trifunctional olefinic first monomer, (b) an olefinic second monomer that is copolymerizable with the first monomer and (c) a free radical initiator and then contacting a second substrate to the composition-applied first substrate so that the first and second substrate adhesively bond together.
According to a second embodiment of the invention there is provided a method for providing a coating on a substrate that includes applying to the substrate a composition that includes (a) a trifunctional olefinic first monomer, (b) an olefinic second monomer that is copolymerizable with the first monomer and (c) a free radical initiator and then allowing the composition to cure.
According to a further embodiment of the invention there is provided a bonded assembly that includes a first substrate, a second substrate and an adhesive composition between the first and second substrates wherein the adhesive composition is the cured product of a reaction mixture comprising (a) a trifunctional olefinic first monomer, (b) an olefinic second monomer that is copolymerizable with the first monomer and (c) a free radical initiator.
According to another embodiment of the invention there is provided an adhesive composition comprising (a) a free radical polymerizable monomer component that includes a trifunctional olefinic first monomer and an olefinic second monomer that is copolymerizable with the first monomer and (b) a redox initiator system, wherein the adhesive composition is a liquid at room temperature and is curable at room temperature.
One advantage of trifunctional olefinic monomers is that they do not homopolymerize in the presence of a free radical initiator. Thus, in a two-part reactive composition the trifunctional olefinic monomer can be included in the same part as the free radical initiator. This more easily allows for the formulation of 1:1 equal mix ratio between the two parts since the trifunctional olefinic monomer can be used as a reactive diluent for the initiator-containing part thus allowing adjustability of the volume and mole ratio relative to the other part. Additional advantages of the reactive adhesive system according to the invention is lower odor and lower flammability, particularly a flash point of 141° F. or higher. A further advantage is that certain trifunctional olefinic monomer/copolymerizable olefinic monomer systems exhibit low viscosity allowing for compounding with inexpensive fillers. In addition, the reactivity of the trifunctional olefinic monomers with stryenic monomers allows for commercially practical use of styrenic monomers in adhesives.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Unless otherwise indicated, description of components in chemical nomenclature refers to the components at the time of addition to any combination specified in the description, but does not necessarily preclude chemical interactions among the components of a mixture once mixed.
As used herein, the following terms have certain meanings.
“Flash point” is the temperature at which a substance evolves sufficient flammable vapor to give a visible flash on the introduction of a spark or a small flame.
“Room temperature” means ambient workplace (manufacturing or assembly plant, laboratory, etc.) temperature range, typically 10-40° C., more typically 20-30° C.
The trifunctional olefinic monomers are monomers that include olefinic or ethylenic unsaturation and at least three functional groups that are each bonded directly to the unsaturated carbon atoms. As used in the context of “trifunctional”, “functional group” includes alkyl as well as the various functional groups conventionally referred to in the organic chemical art. The trifunctional olefinic monomers are electrophilic.
Useful trifunctional olefinic monomers typically have a generic structure represented by formula A
wherein each X is the same or different and is an electron withdrawing group such as —SO
2
R
1
, —CN, SO
2
Ar, —(C═O)R
2
, or halogen (wherein R
1
is alkyl, alkoxy, alkyl ether, amino, alkylamino, alkylimino, or alkylamimidoyl; Ar is an aryl or substituted aryl group; R
2
is R
1
, —OR
1
, —N(H)R
1
, or —NH
2
); Y is —R
1
, —Ar or an electron withdrawing group as identified for X; and Z is a moiety selected from the first or second row elements of the Periodic Chart in the form of either a single element (such as —H or —F) or linearly bonded multiple elements (such as —CN). The two X groups or the X and Y groups also could form a fused ring system such as a lactone, anhydride or imide. Both unsaturated carbon atoms of the trifunctional olefinic monomer are sterically hindered by the functional groups. Preferably, X is —CN or —COOR
1
; Y is —CN, —COOR
1
or —Ar; Z is hydrogen; and R
1
is a primary or secondary linear or branched alkyl having 1 to 18 carbon atoms. “Primary” alkyl means that the carbon atom of R
1
bonded to —OOC— is also bonded to only one non-hydrogen atom (thus, it is bonded to two hydrogen atoms). “Secondary” alkyl means that the carbon atom of R
1
bonded to —OOC— is also bonded to two non-hydrogen atoms (thus, it is bonded
Aftergut Jeff H.
Dearth Miles B.
Lord Corporation
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