Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-08-06
2003-11-11
Dawson, Robert (Department: 1712)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S331600, C156S332000, C156S335000, C428S413000, C523S466000, C525S065000, C525S099000, C525S109000, C525S113000, C525S122000, C525S132000, C525S533000
Reexamination Certificate
active
06645341
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions used as adhesives, and in particular to two-part epoxide adhesive compositions having improved peel and shear strength.
BACKGROUND OF THE INVENTION
Epoxy-based adhesives are utilized for providing high quality, permanent bonding in many different commercial and industrial settings. Epoxy-based adhesives are especially useful for their ability to strongly adhere to a variety of materials, including metal, glass, plastic, wood and fiber. Consequently, these adhesives are often used to bond dissimilar materials together. Epoxy-based adhesives also provide the benefit of excellent resistance to attack by many corrosive chemicals. Because of these properties, these adhesives are often utilized in place of metal solder which, in contrast to epoxy, may contain toxic metals and require fluxing.
Two forms of epoxy-based adhesive compositions are commonly commercially available. The first form, one-component adhesives, are available as rigid epoxy adhesives, frozen pre-mix flexible epoxy adhesives, and room-temperature stable flexible epoxy adhesives. While one-component compositions provide the convenience of storage as a single component, they also require elevated curing temperatures. The second form of adhesive, two-component adhesives, are stored as two separate components that are mixed prior to application on the surfaces to be bonded together. Two-component adhesives overcome the often inconvenient curing requirements of one-component adhesives in that two-component adhesives are curable at room temperature.
Two critical measurements of adhesives are peel strength and shear strength. Generally, epoxy adhesives are brittle materials that fail when subjected to peel forces. Thus, epoxy adhesives are unsuitable for applications that require the adhesives to be subjected to damaging external forces. Consequently, there is a need in the art for the development of an epoxy adhesive having improved peel and shear strength which would provide resilient bonds when subjected to external forces. Such adhesives would advantageously include additives to provide the adhesive with the ability to withstand peel forces and increase the shear strength of the adhesive, but would not require the adhesive to be cured at high temperatures.
SUMMARY OF THE INVENTION
The present invention discloses a two-component epoxy-based adhesive comprising a resin component and a curing agent component. The resin component comprises an epoxy resin, a toughener that is preferably a polymer polyol and, optionally, fumed silica. The curing agent comprises a polyoxyalkyleneamine, an amine terminated butadiene-acrylonitrile polymer, tertiary amine, polyamide resin, silane and fumed silica. The adhesive composition is particularly useful for bonding of metals, plastics and composites and for functions such as laminating, honeycomb bonding, automotive assembly and construction assembly.
Another embodiment of the invention is directed to a method for bonding materials together which comprises applying the adhesive composition of the invention in a liquid or paste form to a first substrate, bringing a second substrate in contact with the composition applied to the first substrate, and subjecting the applied composition to conditions which will allow the composition to cure to an irreversible solid form. Still another aspect of the invention is directed to an article of manufacture comprising the adhesive of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The two-component epoxy-based adhesive of the present invention comprises resin and curing agent components. The resin component comprises an epoxy component, one or more polymer polyols and, optionally, fumed silica.
Examples of epoxy resins suitable for use in the present adhesive composition include monofunctional and multifunctional glycidyl ethers of Bisphenol-A and Bisphenol-F, and cycloaliphatic epoxy resins or a combination thereof. The cycloaliphatic epoxides are preferably selected from non-glycidyl ether epoxides containing more than one 1.2 epoxy group per molecule. These epoxides are characterized by a ring structure wherein the epoxide group may be part of the ring or may be attached to the ring structure. Examples of non-glycidyl ether epoxides include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, which contains two epoxide groups that are part of the ring structures and an ester linkage, vinylcyclohexene dioxide, which contains two epoxide groups and one of which is part of the ring structure, 3,4-epoxy-6-methyl cyclohexyl methyl-3,4-epoxycyclohexane carboxylate and dicyclopentadiene dioxide.
Glycidyl ether epoxides are preferred in the invention, either separately or in combination with the non-glycidyl ether epoxides. These resins are selected from glycidyl ether epoxides containing more than one 1.2 epoxy group per molecule. A preferred epoxy resin of this type is Bisphenol A resin. Preferred Bisphenol A type resin includes 2,2-bis(4-hydroxyphenyl) propane-epichlorohydrin copolymer. A further preferred epoxy resin is Bisphenol F type resin. These resins are generally prepared by the reaction of one mole of bisphenol F resin and two moles of epichlorohydrin. A further preferred type of epoxy resin is epoxy novolac resin. Epoxy novolac resin is commonly prepared by the reaction of phenolic resin and epichlorohydrin. A preferred epoxy novolac resin is poly(phenyl glycidyl ether)-co-formaldehyde. Biphenyl type epoxy resin may also be utilized in the present invention. This type of resin is commonly prepared by the reaction of biphenyl resin and epichlorohydrin. Dicyclopentadiene-phenol epoxy resin, naphthalene resins, epoxy functional butadiene acrylonitrile copolymers, epoxy functional polydimethyl siloxane and mixtures thereof are additional types of epoxy resins which may be employed. The preferred epoxy for the adhesive of the present invention is a blend of Bisphenol F type resin and Bisphenol A type resin, commercially available from Vantico as ARALDITE PY720. Other suitable Bisphenol A/F blends commercially available include EPIKOTE 235, 234 and 238 (Shell), NPEF 185, 198 and 187 (Whyte Chemicals), DER 351, 356 and 352 (Dow), or RUTAPOX 0169 or 0166 (Bakelite). Bisphenol F type resin is available from CVC Specialty Chemicals under the designation 8230E, EPIKOTE 862 (Resolution), or Whyte Chemicals as NPEF 170. Bisphenol-A type resin is commercially available from Resolution Technology as EPON 828, 828EL or 828XA. The epoxy resin component of the resin comprises from about 50 to about 90 weight percent of the resin component and, preferably, about 75 to about 85 weight percent of the resin component.
The toughener segment of the resin component is preferably a polyol and most preferably a polyester or polyether polyol. Examples of polyether polyols include a linear and/or branched polyether having plural numbers of ether bondings and at least two hydroxyl groups, and contain substantially no functional group other than the hydroxyl groups. Examples of the polyether polyol may include polyoxyalkylene polyol such as polyethylene glycol, polypropylene glycol, polybutylene glycol and the like. Further, a homopolymer and a copolymer of the polyoxyalkylene polyols may also be employed. Particularly preferable copolymers of the polyoxyalkylene polyols may include an adduct at least one compound selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, 2-ethylhexanediol-1,3,glycerin, 1,2,6-hexane triol, trimethylol propane, trimethylol ethane, tris(hydroxyphenyl)propane, triethanolamine, triisopropanolamine, ethylenediamine and ethanolamine; with at least one compound selected from the group consisting of ethylene oxide, propylene oxide and butylene oxide.
A number of suitable polyols are commercially available. Non-limiting examples include CP4701 (Dow Chemicals), NIAX 11-34 (Union Carbide Corp), Desmophen 3900 (Bayer), Propylan M12 (Lankro Chemicals), Highflex 303 (Daiichi Kogyo Seiyaku K.K.) and D
Almer Charles W.
Aylward D.
Dawson Robert
National Starch and Chemical Investment Holding Corporation
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