Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2000-09-22
2002-06-11
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S413000, C428S304400, C428S313300, C521S076000, C521S082000, C521S098000, C521S099000, C521S128000, C523S400000, C523S465000
Reexamination Certificate
active
06403222
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a thermosettable composition useful for protecting a metallic surface against corrosion.
2. Discussion of the Related Art
It is known that a number of industries, e.g., the automobile industry, require parts that are both strong and lightweight. One attempt to achieve this balance between strength and minimal weight utilizes hollow parts constructed of relatively thin sheet metal. However, hollow metal parts are easily distorted. Accordingly, it is also known that the presence of structural foam in the cavities of the hollow parts can improve the strength and stiffness of such parts.
Generally, such foams are prepared from formulations comprising a thermosettable resin such as an epoxy resin, a blowing agent and fillers and reinforcing agents such as hollow glass microspheres. Preferably, these foams have a density of about 20-40 lb/ft
3
(about 0.30-0.65 g/cc) and are able to withstand heat in excess of 175° C., most preferably in excess of 200° C. Optional ingredients include curatives, processing aids, stabilizers, colorants, and UV absorbers.
Composites comprised of a metal substrate and a structural foam must be capable of withstanding prolonged exposure to moisture (e.g., through water immersion or high humidity conditions) with minimal corrosion of the surface of the metal, which is in contact with the structural foam. The structural foam component contains cells, which can trap moisture. The trapped moisture (particularly when dissolved salts are present) corrodes the metal surface; the resulting corrosion degrades the ability of the structural foam to adhere to the metal surface. Eventually, full or partial adhesive bond failure can occur wherein the structural foam separates from the metal substrate, thereby weakening the composite. It would therefore be highly desirable to develop methods of retaining the desirable reinforcing properties of the composite when the composite is used in a water-containing environment.
SUMMARY OF THE INVENTION
It has now been found that the addition of a relatively minor amount of wax to thermosettable compositions used to form composites with metal parts greatly improves the resistance of the composite to moisture, salt spray and the like. The wax-modified thermosettable composition provides composites such as structural foam -reinforced hollow metal parts wherein the metal surface in contact with the cured thermosettable composition exhibits significantly reduced corrosion as compared to composites prepared using analogous wax-free thermosettable compositions. Corrosion of the metal surface is even greatly reduced at the isolated areas at the interface of the thermoset and the metal surface where the thermoset is not bonded tightly to the metal surface, which normally are sites of attack by moisture. Retention of compressive strength and modulus upon prolonged environmental exposure is also greatly improved. The presence of the wax at low levels does not interfere with the adhesive bond between the cured thermosettable composition and the metal substrate. This result was quite surprising, as waxes are commonly used in industry as mold release agents.
DETAILED DESCRIPTION OF THE INVENTION
Waxes are water-insoluble substances which are solid at ambient temperatures with a relatively low melting point and which are capable of softening when heated and hardening when cooled. Petroleum waxes (essentially saturated hydrocarbon mixtures obtained by the refining of petroleum) are preferred for use in the present invention, with paraffinic and microcrystalline waxes being especially preferred. Such materials are well-known in the art (see, for example, the chapter entitled “Waxes” in Vol. 17 of the Encyclopedia of Polymer Science and Engineering, Second Edition) and are readily available from a number of commercial sources. For example, the AKROWAX petroleum waxes sold by Akrochem Corporation of Akron, Ohio may be utilized in the present invention (including AKROWAX 5030, AKROWAX 5031 and AKROWAX 5032). Mixtures and blends of different waxes may be employed.
An amount of wax is incorporated into the thermosettable composition, which is effective to improve the corrosion and moisture resistance of a composite comprised of a metal substrate and a thermoset derived by curing the thermosettable composition. Such amounts may vary depending upon the particular thermosettable composition, metal substrate, and wax selected, but typically will be at least about 0.05% by weight, more preferably at least about 0.1% by weight, of the thermosettable composition. At the same time, however, the wax concentration should not be so great that the properties of the composite, such as the adhesion of the thermoset to the surface of the metal substrate, are significantly compromised. Generally speaking, no more than about 2% by weight, more preferably no more than about 1% by weight, of wax is present in the thermosettable composition. The optimum amount of wax for a particular end-use application may be readily determined by standard experimental techniques.
While in principle any of the thermosettable resins known in the art may be employed, including, for example, vinyl esters, thermoset polyesters, urethanes, phenolic resins, and the like, the present invention is especially well-suited for use with epoxy resin-based systems.
Any of the thermosettable resins having an average of more than one (preferably about two or more) epoxy groups per molecule known or referred to in the art may be utilized as the epoxy resin component of the present invention.
Epoxy resins are described, for example, in the chapter entitled “Epoxy Resins” in the Second Edition of the
Encyclopedia of Polymer Science and Engineering,
Volume 6, pp. 322-382 (1986). Exemplary epoxy resins include polyglycidyl ethers obtained by reacting polyhydric phenols such as bisphenol A, bisphenol F, bisphenol AD, catechol, resorcinol, or polyhydric alcohols such as glycerin and polyethylene glycol with haloepoxides such as epichlorohydrin; glycidylether esters obtained by reacting hydroxycarboxylic acids such as p-hydroxybenzoic acid or beta-hydroxy naphthoic acid with epichlorohydrin or the like; polyglycidyl esters obtained by reacting polycarboxylic acids such as phthalic acid, tetrahydrophthalic acid or terephthalic acid with epichlorohydrin or the like; epoxidated phenolic-novolac resins (sometimes also referred to as polyglycidyl ethers of phenolic novolac compounds); epoxidated polyolefins; glycidylated aminoalcohol compounds and aminophenol compounds, hydantoin diepoxides and urethane-modified epoxy resins. Mixtures of epoxy resins may be used if so desired; for example, mixtures of liquid (at room temperature), semi-solid, and/or solid epoxy resins can be employed. Any of the epoxy resins available from commercial sources are suitable for use in the present invention. Preferably, the epoxy resin has an epoxide equivalent molecular weight of from about 150 to 1000.
The use of epoxy resins based on glycidyl ethers of bisphenol A is especially advantageous. The epoxy resin preferably contains an average of about 2 epoxy groups per molecule and should be selected so as to provide the desired combination of properties in both the thermosettable composition and the final cured thermoset and composite prepared therefrom.
The hardening of the thermosettable resins utilized in the present invention may be accomplished by the addition of any of the chemical materials known in the art for curing such resins. Such materials are referred to herein as “curatives”, but also include the substances known to workers in the field as curing agents, hardeners, activators, catalysts or accelerators. While certain curatives promote curing by catalytic action, others participate directly in the reaction of the resin and are incorporated into the thermoset polymeric network formed by condensation, chain-extension and/or crosslinking of the resin. Where the thermosettable resin is an epoxy resin, it is particularly desirable to employ at l
Dawson Robert
Feely Michael J
Harper Stephen D.
Henkel Corporation
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