Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention provides anaerobic adhesive compositions, reaction products of which demonstrate controlled-strength at ambient temperature conditions and enhanced resistance to thermal degradation at elevated temperature conditions. The compositions are (meth)acrylate- and/or polyorganosiloxane-based and may include one or more of a variety of other components, such as certain coreactants, a maleimide component, a diluent component reactive at elevated temperature conditions, mono- or poly-hydroxyalkane components, and other components.
2. Brief Description of the Technology
Anaerobic adhesive compositions generally are well-known. See e.g., R. D. Rich, “Anaerobic Adhesives” in
Handbook of Adhesive Technology,
29, 467-79, A. Pizzi and K. L. Mittal, eds., Marcel Dekker. Inc., New York (1994) and references cited therein. Their uses are legion and new applications continue to be developed.
Anaerobic adhesive compositions may be classified as ones having high strength, medium strength or low strength. Controlling the strength of anaerobic adhesive compositions to render them having medium or low strength has ordinarily been achieved through the inclusion of a plasticizer or non-reactive diluent component into a high strength anaerobic adhesive composition, with the amount of such component influencing the degree of strength of the cured composition. While apparently satisfactory to provide an anaerobic adhesive composition with the properties desired, such an approach typically provides only a temporary solution to an immediate need and does little to advance the knowledge base of controlling the strength of anaerobic adhesive compositions.
Moreover, the inclusion of a non-reactive diluent in a high strength anaerobic adhesive composition by trapping the diluent in the polymeric matrix which forms upon curing, effectively limits the cross-link density which can form in the cured composition. This reduces the overall strength of the cured compositions.
More specifically, in use at ambient temperature conditions, the cured composition retains the non-reactive diluent. However, as the temperature of the environment in which the cured composition increases, the non-reactive diluent either evaporates or otherwise escapes from the polymeric matrix due to its decreased viscosity in view of the increased temperature. In either event, at increased temperatures (e.g., about 250° F. and greater) the so-formed polymeric matrix becomes little more than a shell resulting in virtually no strength retention.
The patent literature points out examples of related anaerobic adhesives:
U.S. Pat. No. 4,107,109 (Kassal) (composition for making graft copolymers under anaerobic conditions at elevated temperatures, including a solution of certain uncured elastomers in a polymerizable vinyl monomer and a thermally activatable modified peroxide initiator, which form a continuous phase with the resulting vinyl polymer forming a separate and discrete phase); U.S. Pat. No. 4,216,134 (Brenner) (one-component anaerobic adhesive compositions which include ethylenically unsaturated diluent monomers, prepolymers and triallyl cyanurate or triallyl isocyanurate as reaction components); U.S. Pat. No. 4,269,953 (Brand) (certain biphenylene additives as reactive plasticizers which are said to render easier working, molding, extruding and the like, of the polymer and react to cross link certain aromatic thermoplastic polymers); U.S. Pat. No. 4,302,570 (Werber) (the purported use of reactive non-terminal hydroxydiesters of unsaturated organic dicarboxylic acids or anhydrides as plasticizers for anaerobic adhesives); U.S. Pat. No. 4,384,101 (Kovacs) (thermosetting resin mixtures which contain epoxide components, isocyanate components, latent-hardening components and triallyl cyanurate as a cross-linking compound); U.S. Pat. No. 4,431,787 (Werber) (polymerizable acrylic monomers, depicted with internal chain unsaturation as well as acrylic unsaturation, which cross-polymerize through the sites of internal chain unsaturation to furnish the reaction product); U.S. Pat. No. 4,524,176 (Pike) (anaerobic adhesive which includes the reaction product of an hydroxyl-containing polyester and a glycidyl acrylate) and the addition of a modifier—i.e., triallyl cyanurate—to alter flexibility and bond strength of the cured adhesive); U.S. Pat. No. 4,600,738 (Lamm) and U.S. Pat. No. 4,624,725 (Lamm) (two-component acrylic modified polyester adhesives of (a) the acrylic modified polyester reaction product of a glycidyl acrylate and a hydroxyl containing polyester and (b) an organometallic acid salt containing a polymerizable monomer).
Also of interest are:
U.S. Pat. No. 5,567,741 (Casey) (in the context of foaming applications, acrylate anaerobic compositions, certain of which include ethylene glycol); U.S. Pat. No. 3,794,610 (Bachmann) (plasticized anaerobic compositions including a polymerizable acrylate ester monomer (a non-silicone based acrylate monomer), a peroxy polymerization initiator and a polymeric plasticizer); U.S. Pat. No. 4,267,330 (Rich) (certain diaza accelerators for curable adhesive and sealant compositions); U.S. Pat. No. 3,988,299 (Malofsky) (heat curable composition having improved thermal properties, which includes certain acrylate monomers and maleimide compounds); and U.S. Pat. No. 5,302,679 (Maandi) (anaerobic compositions which expand when post cured).
In addition, L. J. Baccei and B. M. Malofsky, “Anaerobic Adhesives Containing Maleimides Having Improved Thermal Resistance” in
589-601, L-H, Lee, ed., Plenum Publishing Corp. (1984) reports the use of maleimides—specifically, N-phenyl maleimide, m-phenylene dimaleimide and a reaction product of methylene dianiline and methylene dianiline bismaleimide—to increase the thermal resistance of anaerobic adhesives which are fully cured at temperatures of at least 150° C.
And, F. J. Campbell, “Electron Beam Curing Improves High Temperature Strength of Vinyl Ester Adhesives”, Nat'l SAMPE Symp. Exh., 59-63 (1977) speaks to radiation curing of acrylic-modified epoxies together in formulations with vinyl functional monomers (i.e., divinyl benzene, trialkyl cyanurate and styrene) to form cured resins of higher level (cross-linking and superior ambient and elevated temperature performance.
Silicones (or polyorganosiloxanes), because of their excellent thermal stability, have been used for many sealant, adhesive and coating applications. However, because of large amounts of dissolved oxygen and high permeability to oxygen, conventional wisdom generally believed until recently that silicones would not be anaerobically curable.
For instance, U.S. Pat. No. 4,035,355 (Baney) teaches anaerobically curing sealant compositions of acrylate-containing polyorganosiloxanes and a hydroperoxy polymerization initiator. These compositions require relatively long cure times—i.e., about 24 hours—and therefore would have limited commercial acceptance.
U.S. Pat. No. 5,391,593 (Inoue) is directed to a silicone rubber sealant composition of an organopolysiloxane, organic peroxide and carbon black which is said to cure under anaerobic conditions into silicone rubber having improved physical properties. These silicones require about 2 to 3 days after removal of oxygen to fully cure. Such a cure profile again would meet with poor commercial acceptance.
Japanese Patent Document JP 04-268,315 appears to be directed to an anaerobically and ultraviolet curable polyorganosiloxane composition for adhesive purposes that is reported to have good heat resistance.
Recently, Loctite Corporation made an advance in the field of anaerobically-curable silicone formulations by teaching an anaerobic composition including (a) a silicone fluid formed as the reaction product of a first silane having at least one hydrolyzable functional group, and a second silane having a (meth)acrylic functional group and at least one hydrolyzable functional group; (b) a (meth)acrylate monomer; and (c) polymerization initiator. See U.S. Pat. No. 5,60
Bennington Lester D.
Konarski Mark M.
Levandoski Susan L.
Bauman Steven C.
Mulcahy Peter D.
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