Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1999-03-23
2001-11-06
Lovering, Richard D. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C252S182170, C522S056000, C525S212000, C525S523000, C525S535000, C568S062000
Reexamination Certificate
active
06313257
ABSTRACT:
POLY(MERCAPTOPROPYLARYL) CURATIVES
The present invention relates to mercapto-containing curing compounds and one and two part epoxy adhesive formulations including the compounds.
BACKGROUND OF THE INVENTION
Epoxy resins are often used as adhesives, especially for adhering metal parts. Epoxy resins are typically one part of two-part adhesive compositions. The epoxy resin and a curing agent are typically mixed immediately prior to use, and cure within a certain amount of time. Many curing agents are nucleophilic compounds, such as amines or thiols, with at least two nucleophilic groups. Amine-based curing agents often have a relatively long cure time at low temperatures. Thiol (mercaptan)-based curing agents tend to react more rapidly, and at lower temperatures, than amine-based curing agents. Accordingly, thiol-based curing agents are preferred for certain applications.
U.S. Pat. No. 3,310,527 to De Acetis discloses certain thiol-based curing agents. These compounds include three or more -RSH groups attached to one or more aromatic rings, where R is alkyl, oxyalkyl or thioalkyl. However, De Acetis does not disclose or suggest how the oxyalkyl or thioalkyl groups would be incorporated onto the aromatic rings.
There is a need for curing agents for epoxy resins which can be easily prepared and which provide a relatively fast cure for epoxy resins. The present application provides such curing agents.
SUMMARY OF THE INVENTION
Polyfunctional mercaptoalkyl-substituted aryl compounds, one and two-part adhesive compositions including the compounds, and methods of making and using the compounds are disclosed.
The compounds include one or more aromatic rings, wherein at least one, and in one embodiment, only one aromatic ring is substituted with one or more alkylthio groups and one or more oxyalkylthio groups. The aromatic rings are preferably phenyl, naphthyl or biphenyl rings, examples of which include novolak resins and polystyrenes, and can optionally be substituted with one or more groups selected from the group consisting of alkyl, aryl, substituted alkyl, substituted aryl, halo, —OH, amine, amide, and alkoxy. The alkyl moiety in the alkylthio and oxyalkylthio groups is a straight, branched or cyclic alkyl group which includes between one and ten carbon atoms, preferably three or more carbon atoms, and the thiol group can be present at any position on the alkyl group.
The compounds do not contain hydrolyzable linkages, as opposed to polymercaptans which include ester linkages. Because of the aromatic nucleus, these materials are capable of providing cured products with higher glass transition temperatures (T
g
's) than are available from most commercially available polymercaptans.
The compounds can be included in curing compositions which include one or more of the following optional elements: amine curatives, reinforcing elements, fillers, coupling agents, antioxidants, antioxidants, adhesion promoters, toughening agents, ambient temperature free radical reactive catalyst systems, accelerators/promoters, retardants, thixotropes, pigments, stabilizers, bondline spacers and mixtures thereof.
The compounds or curing compositions can be one part of a two-part adhesive system, where the second part includes an epoxy resin or other compounds such as terminal olefins which are known to react with thiols (polymerizable material), which preferably have a functionality greater than or equal to two, and optionally includes a reactive diluent, solvent, and any of the above optional elements which do not react with the polymerizable material.
In a preferred embodiment, the compounds are used in combination with amine curatives as a two-component curing system for epoxy resins. Since the compounds do not include hydrolyzable linkages, they are compatible with amine curatives. When properly formulated, this type of blended composition can yield a two-stage cure which enables very quick achievement of bonded parts with handleable strength at room temperature or below, or with relatively low bake temperatures (less than 120° C., preferably between 40 and 100° C.). The first reaction which partially cures the material involves the reaction of the resin with the thiol groups, and the second reaction which fixes the material involves reaction with the amine curatives.
De-roping (trimming excess adhesive, i.e., squeeze-out, after an intermediate cure) and other modifications can be made with relative ease after this initial cure. Finally, the part can be subjected to a second cure over a longer period of time or via heating to a higher temperature (i.e., between 100 and 200° C.).
The compounds can be prepared using known chemistry, for example, by directly forming ether linkages with hydroxy groups on an aromatic ring and directly alkylating the aromatic nucleus with a thiol containing moiety or with a group that is readily converted to a thiol group. In a preferred embodiment, the compounds are prepared by subjecting monofunctional phenolic materials to alkylation, oxy-Cope rearrangement, realkylation, and finally, thiolation.
When used as two-part adhesive formulations with epoxy resins, the epoxy resins preferably have a functionality greater than or equal to two. The compounds can also be combined with polyfunctional olefins in the presence of a free radical initiator to induce addition of the mercaptan groups across the olefinic bonds. The compounds can also be combined with polyfunctional acrylates, methacrylates, or other molecules capable of under going Michael additions in combination with the same catalysts useful with the epoxies. They can also be combined with an oxidizer to form a thermosetting composition via the formation of disulfide linkages. In all of these combinations, and others not listed, these materials can be used for coatings, adhesives, sealants, potting compounds, and the like.
When the compounds take part in a two-stage cure, the compositions can be shaped before, during, and after the initial cure, and are fixed in shape following the second cure. Methods for shaping the composition include laser ablation, compression molding, and the like.
DETAILED DESCRIPTION OF THE INVENTION
Polyfunctional mercaptoalkyl-substituted aryl compounds, curing compositions including the compounds, one and two-part adhesive compositions including the compounds or the compositions, and methods of making and using the compounds are disclosed.
Definitions
As used herein, cure is defined as an irreversible change in the properties of a thermosetting polymer by chemical reaction, that is, condensation, ring closure, or addition. Cure may be accomplished by addition of curing (cross-linking) agents with or without heat and pressure. A curing agent (also known as a hardener) is a catalytic or reactive agent that, when added to a polymer, causes polymerization. An example is a free radical polymerization initiator.
I. The Compounds
As used herein, the terms “thiol” and “mercaptan” are used interchangeably. The compounds include one or more aromatic rings, wherein at least one, and in one embodiment, only one aromatic ring is substituted with one or more alkylthio groups and one or more oxyalkylthio groups. The aromatic rings are preferably phenyl, naphthyl or biphenyl rings, examples of which include novolaks and polystyrenes (which preferably include ten or fewer styrene units) and can optionally be substituted with one or more groups selected from the group consisting of alkyl, aryl, substituted alkyl, substituted aryl, halo, —OH, amine, amide, and alkoxy. As used herein, substituted alkyl and substituted aryl mean substituents as listed above with respect to substituents on the aryl ring.
The alkyl moiety in the alkylthio and oxyalkylthio groups is a straight, branched or cyclic alkyl group which includes between one and ten carbon atoms, preferably three or more carbon atoms, and the thiol group can be present at any position on the alkyl group.
The compounds do not contain hydrolyzable linkages, as opposed to polymercaptans which include ester linkages. Because of the aromatic nucleus, thes
Dearth Miles B.
Lord Corporation
Lovering Richard D.
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