Source: {"pile_set_name": "USPTO Backgrounds"}

The present invention relates to an aqueous primer or coating, particularly a primer for use in polymeric material-to-metal adhesive bonding and a coating for protecting metallic surfaces.
Primers are often used as an undercoat in combination with a covercoat adhesive in order to achieve superior bonding between two substrates made from different materials. One particular application for such primers is in bonding metal surfaces to elastomeric surfaces. Elastomer-to-metal bonding is subjected to severe environmental conditions in many industrial and automotive assemblies. For example, many engine mounting assemblies that employ elastomer-to-metal bonding contain fluids in order to assist in damping of vibration of the engine. These fluid-filled engine mounting devices are being exposed to increasingly high temperatures such that the elastomer-to-metal adhesive bonds within the mounts are being exposed to very high temperature fluid environments. Many elastomer-to-metal assemblies, particularly those utilized in automobile applications, are routinely exposed to materials that contain corrosive salts or other corrosive materials that may act to degrade the elastomer-to-metal adhesive bond.
In light of the increasing regulations regarding volatile organic compounds (VOC), the use of traditional solvent-borne adhesives is becoming more problematic. Consequently, there is significant ongoing work to develop water-borne replacements. For example, U.S. Pat. No. 4,167,500 describes an aqueous adhesive composition that includes a water-dispersible novolak resin, a methylene donor and water. Aqueous or water-borne primers are known and described in U.S. Pat. Nos. 5,200,455 and 5,162,156, but they have various shortcomings compared to solvent-borne primers. For example, it is desirable to improve the environmental resistance performance of aqueous elastomer-to-metal adhesion primers that include polyvinyl alcohol-stabilized phenolic resin dispersions (see U.S. Pat. No. 5,200,455) when used with certain important adhesive covercoats. Elastomer-to-metal primers that include phenolic resins derived from water soluble phenolic precursors are also known (see U.S. Pat. No. 5,162,156) but these suffer from drawbacks that prevent their use to form robust, environmentally resistant films. Before being thermoset, films formed from water soluble phenolic resins tend to re-solvate when exposed to water. The source of the water can be an aqueous covercoat applied to the film. Application of the aqueous covercoat essentially washes away the film formed from the water soluble phenolic resin. In addition, such films exhibit very limited resistance to corrosive fluids.
Another problem associated with the bonding of elastomer to metal relates to pre-heating or pre-baking of the dried adhesive prior to bonding. The metal substrate typically is coated with the adhesive, the adhesive is dried and then the adhesive-coated metal substrate is placed in a mold. Elastomer then is introduced into the mold and bonded to the metal substrate during vulcanization of the elastomer. The bonded part is removed from the mold and the next metal substrate is placed in the mold. When this subsequent metal substrate is placed in the mold it is subjected to the heat retained in the mold from the previous molding operation. The dried adhesive must be able to withstand this retained heat (referred to herein as xe2x80x9cpre-heatingxe2x80x9d) prior to bonding.
Consequently, there exists a continuing need for an aqueous primer that provides robust adhesive bonding in hot, corrosive environments, has an affinity for a broad range of covercoats, and forms a flexible film that is resistant to pre-heating conditions and exhibits superior shelf-life stability and resistance to resolvation. It would be especially advantageous if such a primer could also be used as a coating for protecting a metallic surface.
At present, there are two commonly-used metal coating methods electrodeposition and autodepositionxe2x80x94that are typically used subsequent to, or as a substitute for, phosphatizing of the metallic surface. Electrodeposition (frequently referred to as xe2x80x9cE-coatxe2x80x9d) involves immersing a metal surface in a composition then applying a voltage through the composition so that a coating will deposit on the metal surface. An autodeposition coating is commercially available from Henkel and its subsidiary Parker Amchem under the trademark AUTOPHORETIC(copyright).
According to the patents and commercial literature, immersion of a metallic surface in an autodeposition composition produces what is said to be a self-limiting protective coating on a metal substrate. Autodeposition compositions are known to generally include water, resin solids dispersed in the aqueous medium, and an activator. For example, the aqueous autodeposition solution in one commercial embodiment contains 3-5 percent solids of a latex (polyvinylidene chloride or acrylic) and carbon black, ferric fluoride and a low concentration of hydrofluoric acid to provide a solution pH of 2.5-3.0. According to the commercialized multi-stage process, a clean degreased steel panel is immersed in an autodeposition solution for one to two minutes, the resulting xe2x80x9cgreenxe2x80x9d film is rinsed in a reaction rinse solution and then dried at 100xc2x0 C. The reactive rinse solution can include a diphosphonic acid.
The dispersed resin solid typically is derived from ethylenically unsaturated monomers. Polyvinylidene chloride is the preferred resin. Polyethylene, polyacrylic, styrene-butadiene and epoxy resins are mentioned as possible resin particles that are dispersed or emulsified in water (see U.S. Pat. Nos. 4,414,350; 4,994,521; 5,427,863; 5,061,523; and 5,500,460). According to U.S. Pat. No. 5,486,414, AUTOPHORETIC(copyright) 800 Series compositions are based on polyvinylidene chloride and AUTOPHORETIC(copyright) 700 Series compositions are based on acrylic resins.
The activator is an ingredient or ingredients that convert the composition into one which will form a self-limiting resinous coating on a metallic surface. The activating system generally comprises an acidic oxidizing system, for example: hydrogen peroxide and HF; HNO3; a ferric-containing compound and HF; and other soluble metal-containing compounds, for example, silver fluoride, ferrous oxide, cupric sulfate, cobaltous nitrate, silver acetate, ferrous phosphate, chromium fluoride, cadmium flouride, stannous flouride, lead dioxide, and silver nitrate in an amount of 0.025 to 50 g/l and an acid, which can be used alone or in combination with hydrofluoric acid, and including, for example, sulfuric, hydrochloric, nitric and phosphoric acid, and organic acids, including, for example, acetic, chloroacetic and trichloroacetic acids.
In the case of treating zinciferous surfaces (e.g., galvanized steel), PCT International Patent Application Publication No. WO 97/09127 discloses treating the surface prior to autodeposition with a composition consisting of water, dissolved phosphonate (for example, diethylene triaminepenta(methylene phosphonic acid) or aminotri(methylene phosphonic acid)), aromatic sulfonate surfactant (for example, disulfonated derivative of dodecyl ether (DOWFAX 2A1 or 2A0)), and dissolved non-oxidizing acid (for example, hydrochloric acid).
Autodeposition coatings are recognized as being very distinct from coatings formed by immersing metallic surfaces in compositions simply comprising solid resin particles dispersed in water (in other words, conventional latices) and coatings formed from acidic aqueous coating compositions that contain dispersed solid resin particles and relatively high amounts of water soluble corrosion inhibitors such as hexavalent chromium compounds (see U.S. Pat. No. 4,242,379). In both instances, the thickness of the resulting coating is not determined by the amount of time in which the metallic surface is immersed in the composition.
According to the present invention there is provided a composition useful as a primer or a coating that includes (A) an aqueous dispersion of a phenolic resin that includes water and a reaction product of a phenolic resin precursor, a modifying agent and, optionally, a multi-hydroxy phenolic compound wherein the modifying agent includes at least one functional moiety that enables the modifying agent to react with the phenolic resin precursor and at least one ionic moiety, and (B) a flexibilizer. According to one embodiment the modifying agent is an aromatic compound. According to another embodiment the ionic moiety of the modifying agent is sulfate, sulfonate, sulfinate, sulfenate or oxysulfonate and the dispersed phenolic resin reaction product has a carbon/sulfur atom ratio of 20:1 to 200:1.
One preferred embodiment of the composition is particularly useful as a primer for bonding a metallic surface to a polymeric surface and includes a novolak version of the phenolic resin dispersion (A), the flexibilizer (B), and (C) an aldehyde, preferably formaldehyde, donor compound. According to another preferred embodiment the composition is a coating for a metallic surface that includes a resole version of the phenolic resin dispersion (A) and the flexibilizer (B).
When applied to a substrate surface, particularly a metal surface, and thermoset the composition forms a flexible film that protects the surface from high temperatures, corrosive conditions and chemical attack or degradation. In addition, when used as a primer in combination with an adhesive covercoat, the primer has improved adhesion to a broad range of covercoats and exhibits superior resistance to resolvation and chemically aggressive environments. The aqueous composition also has more than adequate shelf-life stability.
A unique advantage