Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-01-20
2003-02-18
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S414000, C428S461000, C428S462000, C428S463000
Reexamination Certificate
active
06521687
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an autodepositable adhesive, particularly an adhesive for bonding an elastomeric material to a metallic material.
It is generally known that the corrosion resistance of metal substrates can be improved by coating the substrate with an autodeposition composition that generally comprise an aqueous solution of an acid, an oxidizing agent and a dispersed resin. Immersion of a metallic surface in an autodeposition composition produces what is said to be a self-limiting protective coating on a metal substrate. The general principles and advantages of autodeposition are explained in a multitude of patents assigned to Parker Amchem and/or Henkel (see, for example, U.S. Pat. Nos. 4,414,350; 4,994,521; 5,427,863; 5,061,523 and 5,500,460). However, to the best of the inventors' knowledge these autodeposition compositions have not been successfully used as one coat adhesives or covercoat adhesives.
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 increasingly exposed to 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. Current aqueous adhesives suffer from user drawbacks. Application of an adhesive by dipping the adherend in a bath of the adhesive is frequently preferred by the user due to its simplicity. However, dipping of aqueous adhesives leads to problems with controlling the film thickness and dripping.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method for bonding two substrates comprising applying an autodepositable adhesive to one of the substrates and then bonding the substrates together. This method is especially useful for bonding elastomers to metals.
According to a first embodiment, the autodepositable adhesive is a one coat adhesive having a low pH (approximately 1-3) and including (A) a flexibilizer or film-former, (B) optionally, 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 (C) an acid. According to a more particular embodiment of a one coat adhesive, the adhesive further includes a control agent that improves the, uniformity of the film thickness formed by the adhesive. Organic nitro compounds are the preferred control agents. According to another particular embodiment of a one coat adhesive, the adhesive further includes a crosslinker that improves the adhesive performance. The crosslinker can be an aromatic nitroso compound or aromatic nitroso compound precursor.
According to a second embodiment, the autodepositable adhesive is a covercoat adhesive that includes a flexibilizer or film-former that is a latex that coagulates when exposed to metallic ions generated from the metallic substrate upon which the covercoat is applied. The covercoat preferably also includes a crosslinker as described above in connection with the one coat embodiment.
The one coat autodepositable adhesive can be autodeposited on a metal substrate and then an elastomeric substrate is contacted to the metal substrate to effect bonding of the metal substrate to the elastomeric substrate. The covercoat autodepositable adhesive preferably is applied onto a metal substrate that has been previously treated or coated with an autodepositable metal treatment composition or primer. The autodepositable metal treatment or primer provides the acidic environment that generates metal ions thereby activating the autodeposition characteristic of the autodepositable covercoat adhesive.
An autodepositable adhesive provides for easier film thickness control, increased film thickness uniformity and substantially eliminates dripping. The autodepositable adhesive also is substantially free of volatile organic compounds.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Unless otherwise indicated, description of components in chemical nomenclature refers to the components at the time of addition to any combination specified in the description, but does not necessarily preclude chemical interactions among the components of a mixture once mixed.
Certain terms used in this document are defined below.
“Phenolic compound” means a compound that includes at least one hydroxy functional group attached to a carbon atom of an aromatic ring. Illustrative phenolic compounds include unsubstituted phenol per se, substituted phenols such as alkylated phenols and multi-hydroxy phenols, and hydroxy-substituted multi-ring aromatics. Illustrative alkylated phenols include methylphenol (also known as cresol), dimethylphenol (also known as xylenol), 2-ethylphenol, pentylphenol and tert-butyl phenol. “Multi-hydroxy phenolic compound” means a compound that includes more than one hydroxy group on each aromatic ring. Illustrative multi-hydroxy phenols include 1,3-benzenediol (also known as resorcinol), 1,2-benzenediol (also known as pyrocatechol), 1,4-benzenediol (also known as hydroquinone), 1,2,3-benzenetriol (also known as pyrogallol), 1,3,5-benzenetriol and 4-tert-butyl-1,2-benzenediol (also known as tert-butyl catechol). Illustrative hydroxy-substituted multi-ring aromatics include 4,4′-isopropylidenebisphenol (also known as bisphenol A), 4,4′methylidenebisphenol (also known as bisphenol F) and naphthol.
“Aldehyde compound” means a compound having the generic formula RCHO. Illustrative aldehyde compounds include formaldehyde, acetaldehyde, propionaldehyde, n-butylaldehyde, n-valeraldehyde, caproaldehyde, heptaldehyde and other straight-chain aldehydes having up to 8 carbon atoms, as well as compounds that decompose to formaldehyde such as paraformaldehyde, trioxane, furfural, hexamethylenetriamine, acetals that liberate formaldehyde on heating, and benzaldehyde.
“Phenolic resin” generally means the reaction product of a phenolic compound with an aldehyde compound. The molar ratio of the aldehyde compound (for example, formaldehyde) reacted with the phenolic compound is referred to herein as the “F/P ratio”. The FJP ratio is calculated on a per hydroxy-substituted aromatic ring basis.
“Phenolic resin precursor” means an unmodified or conventional phenolic resin that is reacted with the aromatic modifying agent to produce the phenolic resin that is dispersed in an aqueous phase.
As described above, there are two embodiments of the invention—one coat and covercoat. “One coat adhesive” means a composition that by itself adheres together two substrate surfaces without the need for a primer. For example, a one coat adhesive according to the invention can be directly applied to a metal surface that has been simply conventionally treated or converted such as by phosphatizing, degreasing/descaling or grit blasting. “Covercoat adhesive” means a composition that is applied over a primer or autodepositable metal treatment composition to enable the bonding of two substrate surfaces.
The flexibilizer or film-former can be any ingredient that forms a film and/or any material that contributes flexibility and/or toughness to the film formed from the composition. The toughness pr
Cowles Rebecca S.
Kucera Helmut W.
Mowrey Douglas H.
Cain Edward J.
Dearth Miles B.
Lord Corporation
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