STRUCTURAL ADHESIVE RESIN COMPOSITION
Field and Background of the Invention
The present invention relates to structural adhesive resin compositions, and more particularly structural adhesives for bonding various substrates together. In various industries, there is a strong desire for a product that will bond plastics to the same or different plastics, metal to metal, and fiber reinforced plastic (FRP) to metal or to other like or dissimilar substrates. For example, in the automotive, truck, recreation vehicle, marine and personal watercraft industries, repair of various plastic and metal body panels and parts has become a critical issue. This is particularly relevant to the automotive industry wherein many metal side and body panels have been replaced with molded plastics such as sheet molding compound (SMC). The need to formulate adhesives for bonding and repairing those plastics has dramatically increased.
It is known to repair the dented or gauged metal surfaces by applying a thermosetting resin (e.g., unsaturated polyester resin or epoxy vinyl resin) to the damaged metal surfaces. For example, U.S. Patent No. 4,525,427 to Bayha proposes polyester compositions capable of forming a thin film that adheres to metal and plastic substrates, such as steel, and are particularly useful in repairing automobile bodies. These compositions are referred to as "body putty primers". Bayha also discloses that the metallic surface may also be chemically etched to maximize adhesion of surfacing materials to the metal surface.
It is also known to utilize polyurethene, epoxy and polymerizable acrylate or methacrylate based adhesives to bond plastic substrates together. See, for example, U.S. Patent No. 4,959,405 to Briggs et al.
There, however, remains a need for a structured adhesive that exhibits improved adhesion characteristics but also should be non-staining particularly when painted, have excellent sandability, have extended shelf life and have sufficient impact strength, durability and thermal cycling as compared to conventional adhesives.
Summary of the Invention With the foregoing objects, features and advantages in mind, the adhesive resin composition of the present invention meets the above-identified criteria. The adhesive resin composition is crosslinkable and comprises an unsaturated polyester, a graft copolymer, optionally a non-aromatic unsaturated monocarboxylic ester monomer, optionally a saturated mono- or dicarboxylic acid monomer and an amine activator. Preferably, the unsaturated polyester comprises a first polyester derived from dicylopentadiene, a second polyester derived from a dibasic acid or anhydride, and a third polyester derived from a polyhydric alcohol and an α,β-un saturated dicarboxylic acid or its anhydride. The resin composition is crosslinkable by the end user using a catalyst, preferably a peroxide that will form free radicals, and most preferably benzoyl peroxide. The adhesive composition can be used for bonding a plurality of substrates to each other. The adhesive composition is particularly useful in the repair of automotive SMC body panels and as a structural adhesive for SMC body panels.
Detailed Description of the Invention
The present invention will be described more fully hereinafter. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein; rather, this embodiment
is provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
In accordance with the present invention, a crosslinkable adhesive resin composition useful as a structural adhesive is provided. The adhesive resin composition is useful for bonding like and dissimilar substrates together. The composition has excellent adhesion properties, is sandable, is non-staining, has extended shelf life and has sufficient impact strength, durability, and thermal cycling as compared to conventional adhesives.
As summarized above the crosslinkable adhesive resin composition comprises a unsaturated resin blend of preferably three polyesters, a graft copolymer, a optionally non-aromatic unsaturated monocarboxylic ester monomer, optionally an unsaturated mono-or dicarboxylic acid monomer; and an amine activator. The unsaturated polyester blend comprises a first polyester derived from dicyclopentadiene, a second polyester derived from a saturated or unsaturated dibasic acid or anhydride and a third polyester derived from a polyhydric alcohol and an α,β-unsatu rated dicarboxylic acid or its anyhdride.
The preparation of polyesters derived from dicyclopentadiene is well known. See, for example, U.S. Patent No. 3,347,804 to Zimmerman, the disclosure of which is incorporated herein by reference in its entirety. Derivatives of dicyclopentadiene can also be used such as dicyclopentadiene alcohols.
The second polyester is derived from a saturated or unsaturated dibasic acid or anhydride. Suitable dibasic acids or anhydrides include orthophthalic, isophthalic, terephthalic, tetrahydrophthalic, tetrachlorophthalic, nadic acid, maleic, fumaric, adipic and cyclohexane dicarboxylic acids and mixtures thereof. A particularly preferred second polyester is isophthalic derived polyester. The third polyester is derived from a polyhydric alcohol and an ,β- unsaturated dicarboxylic acid or its anhydride. Suitable polyhydric alcohols include ethylene glycol diethylene glycol, propylene glycol, dipropylene glycol,
1 ,3-butanediol, 1 ,4-butanediol, 1 ,3 hexanediol, neopentyl glycol, 2-methyl-1 ,3- propanediol, 1 ,3-butylene glycol, 1 ,6-hexanediol, neopentyl glycol, ethylene oxide adduct of bisphenol, and propylene oxide adduct of bisphenol, and mixtures thereof and the α,β unsaturated acid and mixtures thereof. Suitable α,β- unsaturated acids include maleic, fumaric, itaconic, chloromaleic and citraconic acids, and mixtures thereof. A particularly preferred third polyester is a polyethylene glycol/maleic acid derived polyester.
The graft copolymer can be acrylonitrile-butadiene-styrene (ABS), acrylonitrile-butadiene-acrylonitrile (ABA), methacrylate-butadiene-styrene (MBS), methacrylate-acrylonitrile, butadiene-styrene (MABS), styrene-butadiene, styrene- butadiene-styrene, methacrylate-butyl acrylate, styrene-isoprene-styrene, acrylonitrile-butyl acrylate and the like blends thereof. A particularly preferred graft copolymer is MABS sold under the trademark Terlux® by BASF, Mount Olive, New Jersey. Suitable non-aromatic unsaturated monocarboxylic ester monomers are acrylates and methacrylates which may include functional groups such as amino groups, hydroxy groups, epoxy groups and the like. Exemplary acrylates and methacrylates include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, glycidyl acrylate, glycidyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxybutyl methacrylate and the like, and combinations and blends thereof. Particularly preferred is methyl methacrylate (MMA). Suitable unsaturated mono- or dicarboxylic acid monomers are acrylic acid, methacrylic acid and itaconic acid. Particularly preferred is methacrylic acid (MAA).
Suitable amine activators include tertiary amines, and aldehyde reaction products, for example, N,N-dimethylanaline, N,N-dimethyltoluidene, N,N-
diethylanaline, N,N-diethyltoluidene, p-toly diethanolamine, butyraldehyde- analine, butyraldehyde-butylamine, phenyl diethynolamine and the like, and combinations and blends thereof. These may be incorporated into the polyester backbone via esterfication or can be mixed into the resin composition in a manner known to those skilled in the art.
The curing of resin composition can be catalyzed by free radical peroxide initators such as benzoyl peroxide, methyl ethyl ketone peroxide, t-butyl hydroperoxide, t-butyl perbenzoate, and others known in the art. Those skilled in the art will recognize that certain peroxide initiators will require that a metallic salt such as cobalt octoate/napthenate could be blended into the composition to effect cure. Various types and concentrations of quinone and other types of inhibitors may be used to obtain the required gel time with free radical peroxide initiators.
The adhesive resin composition can further include fillers, pigments and dyes, stabilizers, thixotropic additives and other additives familiar to one skilled in the art. Suitable fillers include calcium carbonate, clay, talc, alumina trihydrate, kaolin, silica sand, glass, silica and polymeric microspheres, mica, wood flour, barytes and the like. Reinforcing materials can also be included. A wide variety of reinforcing materials are available and include glass fibers, glass microbal loons, carbon fibers, sisal fibers, Kevlar® fibers, asbestos fibers, cotton fibers, steel fibers, and the like.
In a preferred embodiment, the adhesive resin composition comprises about 40 to 60 percent by weight of a polyester comprising about 50 to 70 percent by weight of the polyester of the first polyester derived from dicyclopentadiene, about 15 to 35 percent by weight of the polyester of a second polyester derived from a dibasic acid or anhydride; and 10 to 15 percent by weight of the polyester of the third polyester resin derived from a polyhydric alcohol and an α,β-unsaturated dicarboxylic acid or its anhydride; about 10 to 15 percent by weight of the composition of a graft copolymer; about 35 to 40
percent by weight of the composition of the non-aromatic unsaturated monocarboxylic ester monomer; about 1 to 10 percent by weight of the composition of the unsaturated mono-or dicarboxylic acid, about 2 to 4 percent by weight of the composition of dibutylphthalate stabilizer and 0.50 to 1 .50 percent by weight of the composition of an amine activator
The following examples are illustrative of the present invention, and are not to be construed as limiting thereof.
EXAMPLES Example 1 An exemplary composition is as follows-
Component % bv Weight
Poly te® 323861 50.0
Terlux KR28122 preblended in
16% by weight MMA3 10.0
MMA3 18.0
MA3 2.5
Dibutylphthalate 1 .9
Paraflint Spray 304 predissolved in
1.0% by weight MMA 0.1
NaEDTA 0.03
N,N-dιmethyl-p-toluιdιne5 1 .30
Isopropyl alcohol 0.285
Distilled water 0.285
' Available from Reichhold, Research Triangle Park, N.C. and is a dicylopentadiene/isophthalic polyester.
2 Available from BASF, Mount Olive, N.J.
3 Available from Rohm and Haas, Philadelphia, Pa
4 Available from Moore and Munger, Shelton, Ct
5 Available from First Chemical, Pascagoula, Ms
Example 2
?r exemplary composition is as follows:
Component % bv Weight
Polylite® 44285-006 27.20
Polylite® 44393-007 1 1 .70
Polylite® 44286-008 9.71
Terlux KR2812 preblended in 9.72
16% by weight MMA
MMA3 33.9
MA 2.44
Paraflint Spray 30 predissolved in
1 .0% by weight MMA 0.82
5%EDTA/IPA:H20 0.60
N,N-dimethyl-p-toluidine 0.50
1 ,4 Naphthaquinone 0.02 tolyl diethenolamine 0.50
Ethanox A-7039 0.05
Comparative Testing
Comparative Example 1 is Reichhold 32386, a standard polyester body filler.
Comparative Example 2 is Reichhold 371 51/37640 (3: 1 ) epoxy resin.
Comparative Example 3 is Pliogrip, a urethane adhesive available from Ashland Chemicals.
6 Available from Reichhold, Research Triangle Park, N.C. and is a dicylopentadiene polyester.
7 Available from Reichhold, Research Triangle Park, N.C. and is a isophthalic polyester.
8 Available from Reichhold, Research Triangle Park, N.C. and is a propylene glycol/maleic acid polyester
9 Available from Albemarle Corporation, Baton Rouge, LA.
Table 1
Lapshear testing was conducted on Samples A-l by bonding a SMC substrate to itself. The data is given as lapshear (psi)/fiber tear (%) using a Instron with 20,000 pound load at 0.10 in/min, a temperature of 73°F and a 24 hour latent period prior to testing. The data is in Table 2.
Table 2
*Epoxy cured only for 24 hours.
This data illustrates that samples C, D and E of the invention provide comparable, if not better, adhesion as compared to Samples A, B and F, namely, the comparative examples.
Sample E was also tested for adhesion between the SMC substrate and other materials as detailed in Table 3.
Table 3
Material Lapshear(psi)/fiber tear(%)
Different SMC 590/45
Same SMC but alon a seam 800/100
Aluminum 1386/NA
Steel 760/NA
Galvanized steel 1370/NA
ABS 443/**
Polycarbonate 543/**
* *Coupon material broke
This demonstrates that the present invention can provide excellent adhesion properties for SMC to other substrates. The present invention has been described in detail above. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein above; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.