Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-02-26
2003-06-03
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S413000, C428S416000, C428S418000, C428S521000, C428S522000, C428S523000, C428S297400, C525S107000, C525S113000, C525S523000, C525S524000, C525S529000
Reexamination Certificate
active
06572971
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to structural engineering adhesives for bonding metal and fiber-reinforced composite parts (e.g. sheet molding compounds (SMC), fiberglass reinforced polyesters (FRP), structural reaction injected molded (SRIM), resin transfer moldings (RTM), and the like) to a variety of similar and dissimilar substrates, which find use in the manufacture of cars, trucks, boats, and a host of other products.
Sheet molding compound (SMC), for example, is defined (ASTM) as a molding compound in integral sheet form comprising a thermosetting resin, fibrous reinforcement, and additives required for processing or product performance, e.g., resin, catalyst, thickener, mold release agent, particulate filler, pigment, shrink control agent, etc. These materials and others generally are known as fiber-reinforced composites, reinforced composites, or simply composites. Metal may include, but not be limited to, hot dipped galvanized steel, electrogalvanized steel, e-coat steel, cold rolled steel, bare aluminum, anodized aluminum, etched aluminum, magnesium, etc.
One typical class of structural adhesives useful in adhering composite parts to the same and to different substrates is two-part polyurethane adhesives. Combining a prepolymer and a curative just before use makes these materials useful as adhesives. The ratio in which these materials are combined will vary depending upon the functionality of the prepolymer and the curative. Accurate combination of the materials requires a certain skill level of the worker and, unfortunately, there is substantial waste of adhesive during the mixing process even when using automatic pumping equipment. In addition, polyurethane adhesives generally have poor thermal properties and are not conducive to applications requiring high temperature ovens.
Another common class of structural adhesives useful in adhering metal parts to the same and to different substrates (e.g. composites) is epoxy adhesives. Epoxy adhesive compositions most often contain a polyfunctional epoxy resin and are cured by addition of a curative, which typically is provided in a separate package. The rate of cure and product characteristics are influenced by the choice of curing agent, which itself is influenced by the make-up of the adhesive composition, as dictated by the final properties desired by the user.
Structural adhesives are used by application to the surface of a part made of, e.g. metal, and positioning a surface of second part (of the same or different material) over the adhesive covered metal covered surface. Since the parts often have uneven surfaces, it is desirable that the adhesive possess the ability to fill the resulting voids of varying depth. It is important that the adhesive remain uncured and fluid for sufficient time to permit placing of the second substrate into contact with the adhesive. An adhesive, which hardens too quickly, does not permit flexibility in the assembly line process. Thus, the length of time the adhesive is fluid is measured and is referred to as “open time”. The adhesive may be cured by placing the adhered parts in an oven maintained at, e.g., 70°-190° C. for, e.g., 5 minutes or less to cure or harden the adhesive, or the adhesive may be cured by letting it stand at room temperature for one to several days, e.g., 3 days.
Representative epoxy structural adhesive compositions can be found in, for example, U.S. Pat. Nos. 5,385,990, 4,921,912, 4,661,539, 4,740,539, and 4,707,518, the disclosures of which are expressly incorporated herein by reference. Various combinations of epoxy resins, rubber modifiers, amine curing agents, amide curing agents, Lewis acids, mercaptan curing agents, etc. have been proposed for formulating high strength adhesive compositions. A major deficiency in these adhesives is that they often suffer from poor and/or limited adhesion, especially to SMC, SRIM, vinyl ester SMC, and other substrates. These same adhesives also require post-baking in order to obtain full cure and properties.
BROAD STATEMENT OF THE INVENTION
Broadly, the present invention embodies an adhesive composition, which comprises an epoxy resin, a coupling agent, filler, and an effective amount of an amine-curing agent or curative for said epoxy resin. Advantageously, tri-functional and/or tetrafunctional epoxy resins and/or acrylate monomers will be incorporated into the adhesive composition in order to reduce open time and enhance substrate adhesion. Advantageously, a mixture of amines will be used in the curative including aliphatic amines, which have low viscosities and efficiently wet the substrate for enhancing adhesion; polyamines, which can be used to manipulate open time and allow for improved ratio tolerance of the adhesive system; and amine-terminated rubbers (ATBN), which can improve impact resistance and the toughness of the cured adhesive. Preferred coupling agents are silanes. In addition, dicyandiamide may be incorporated in the amine side to react with any residual epoxy resin that may be present.
Advantages of the present invention include an adhesive composition, which does not need any post-baking to obtain full cure. Another advantage is excellent adhesion that the inventive adhesive composition retains without post-baking. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.
DETAILED DESCRIPTION OF THE INVENTION
Conventional two-component epoxy adhesives are extensively used in the automotive industry to bond SMC, SRIM (structural reaction injected molding), and other substrates. However, many of these epoxy systems, particularly polyamide-based systems, have undesirably long open times and require post-baking in order to achieve full cure of the adhesive composition. The inventive adhesive composition overcomes such problems by incorporation of a coupling agent with the epoxy resin and by using aliphatic amines as part of the curative.
Referring initially to the epoxy resin, a variety of monomeric and polymeric compounds or mixtures of compounds having an epoxy equivalency equal to or greater than 1 (i.e., wherein the average number of epoxy groups per molecule is 1 or more) can be used in formulating the inventive adhesives. Epoxy compounds are well-known as the art cited above details and which is expressly incorporated herein by reference. Useful epoxy compounds include, for example, polyglycidyl ethers of polyhydric polyols, such as ethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol, and 2,2-bis(4-hydroxy cyclohexyl)propane; polyglycidyl ethers of aliphatic and aromatic polycarboxylic acids, such as, for example, oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2,6-napthalene dicarboxylic acid, and dimerized linoleic acid; polyglycidyl ethers of polyphenols, such as, for example, bis-phenol A, bis-phenol F, 1,1-bis(4-hydroxyphenyl)ethane, 1,1-bis(4-hydroxyphenyl)isobutane, and 1,5-dihydroxy napthalene; modified epoxy resins with acrylate or urethane moieties; glycidlyamine epoxy resins; and novolak resins; and the like and mixtures thereof.
The foregoing epoxy resins may be augmented with modified epoxy resins in the form of epoxy-rubber adducts. Such adducts are well known and include epoxy compounds reacted with liquid or solid butadiene-(meth)acrylonitrile copolymers having at least two groups which are reactive with epoxy groups, including, for example, carboxyl, hydroxyl, mercapto, and amino. Such functional elastomeric copolymers having functional groups are well-known articles of commerce and need not be discussed in greater detail herein. It should be recognized additionally, that such rubber compounds also can be added to the curative pack of the two-pack structural adhesive of the present invention. Thus, the rubber modifier can be used neat or adducted with, for example, an epoxy; and included in one or more of the resin pack or the curative pack of the inventive adhesive composition. A preferred rubber is an amine terminated butadieneacr
Ashland Chemical
Dawson Robert
Feely Michael J
Mueller and Smith LPA
LandOfFree
Structural modified epoxy adhesive compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Structural modified epoxy adhesive compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Structural modified epoxy adhesive compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3124194