Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-05-23
2002-02-26
Jagannathan, Vasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06350799
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to primer compositions that are useful for bonding elastomers to various substrates, such as metals, ceramics, fiberglass, and organic polymers. The primer compositions of the invention contain organic-functional silane compounds.
BACKGROUND OF THE INVENTION
Since the late 1980's, elastomer coated stainless steel coils have been used to design multi-layered steel engine head gaskets. In particular, these stainless steel coils have been coated with elastomers such as nitrile butadiene rubber or fluoroelastomer. Application of a thin primer between the rubber coating and stainless steel surface is a common industrial practice since an elastomer coating alone does not provide the desired wet adhesion on stainless steels. Generally speaking, the resistance of the primer to the surrounding media, such as engine oil, coolant, fuel and heat, in a great degree, decides the performance and durability of the gasket.
Numerous silane adhesive compositions have previously been developed for the purpose of bonding elastomeric materials to various substrates. For example, U.S. Pat. Nos. 5,532,314 and 5,907,015 relate to silane adhesive compositions which have various organic-functional silanes as a bonding agent. Primers based on silanes generally show good dry adhesion in bonding organic coatings to steel or other metal substrates. However, some of the silane based primers have been found to not have the desired durability in hot coolant immersion.
Phenolic resoles toughed by elastomers or flexible organic resins are widely used as primers or structural adhesives to bond metals. The adhesion between the phenolic resole based primers and the metal surface can be enhanced by addition of organic silanes. In many applications, satisfactory adhesion is achieved using a phenolic/silane based primer. However, the adhesion is gradually lost under aggressive wet environments such as boiling water exposure or hot coolant immersion.
Thus, there is a need in the art for a primer or adhesive composition for bonding elastomers to substrates which exhibits good adhesion in both dry and wet applications. There further is a need in the art for a primer or adhesive composition which shows robust dry and wet adhesion to metallic or other surfaces under harsh environments such as hot oil, hot coolant and thermal aging. Additionally, there is a need in the art for a coolant resistant primer or adhesive for bonding elastomers to substrates which also is thermally stable. Moreover, there is a need in the art for a primer composition which can bond elastomers to substrates without surface treatment of the substrate. This invention provides such a primer and a method for bonding an elastomer to a substrate with the primer of the invention.
SUMMARY OF THE INVENTION
The present invention provides primer compositions which bond elastomers to substrates such as metals, ceramics, fiberglass, or organic polymers. In particular, the invention is directed to a primer composition which includes an organic-functional silane adduct. In one embodiment, the organic-functional silane adduct is prepared by reacting at least one amino-functional silane with at least one isocyanato-functional silane. In another embodiment, the primer composition comprises a phenolic resin, a phenoxy resin, and an organic-functional silane adduct, preferably an organic-functional silane adduct wherein the silane adduct is prepared by reacting at least one amino-functional silane with at least one isocyanato-functional silane. In a preferred embodiment, the primer composition further comprises talc.
The invention further is directed to a method of bonding an elastomer to a metal comprising coating the metal with a primer composition comprising a phenolic resin, a phenoxy resin, and an organic-functional silane adduct, drying the primer composition coating, applying an elastomer coating to the primer composition coating, and curing the elastomer coating with heat.
It has been found that the primer compositions of the present invention containing an organic-functional silane adduct provides robust dry and wet adhesion, particularly of elastomers to substrates such as metals, when these adducts are used in compositions as primers, adhesives or as a protective coating on metals.
DETAILED DESCRIPTION OF THE INVENTION
The silane adducts used in accordance with the present invention are organic-functional silane compounds. An organic-functional silane adduct as used herein is a reaction product of two or more organic functional silane compounds. Preferably, the silane adducts are prepared by reacting at least one amino-functional silane with at least one isocyanato-functional silane. It has unexpectedly been found that the reaction products of these types of organic-functional silanes provide good adhesion in both wet and dry applications. The reaction of an amino-functional silane and an isocyanato-functional silane results in a hexaalkoxylsilane bonded through a urethane or substituted urea linkage. The resulting adduct provides excellent properties when used as a primer, even in aggressive wet environments.
Silanes previously have been used as adhesion promoters for organic coatings. However, it is known that the siloxane bond formed after silane crosslinking can be hydrolyzed with water. Consequently, most of the silane based primers have good dry adhesion but poor wet adhesion. The primer composition of the present invention has overcome this deficiency of the art by utilizing an organic-functional silane adduct, preferably synthesized by the reaction of an amino-functional silane with an isocyanato-functional silane. While not wishing to be bound by any theory, it is believed that this adduct provides superior wet adhesion for a number of reasons. First, this adduct has a higher molecular weight than that of the individual silane and that of silanes known in the art. The higher molecular weight of the silane adduct is believed to reduce the evaporation rate during the cure of the coating in hot air. Thus, this silane adduct is more effectively involved in the metal and coating adhesion. Secondly, this silane adduct becomes a more effective crosslinker by doubling the methoxy or ethoxy groups of the individual silanes through the reaction. Thus, this silane adduct should have higher crosslinking density at the primer to substrate interface under water attack.
Amino-functional silanes useful in the present invention may be any amino-functional silane capable of reacting with an isocyanato-functional silane. In one embodiment, the amino-functional silane is an aminoalkyl silane. In another embodiment, the amino-functional silane is a secondary amino-functional silane. In a preferred embodiment, the amino-functional silane is a phenyl-substituted amino-functional silane. Examples of amino-functional silanes which are useful in the present invention include those available under the tradename Silquest™. Examples of useful Silquest™ amino-functional silanes include Silquest™ Y-9669, N-phenyl-gamma-aminopropyltrimethoxysilane, Silquest™ A1170, bis-(gamma-trimethoxysilylpropyl)amine, Silquest™ A1100, gamma-aminopropyltriethoxysilane, Silquest™ A1110, gamma-aminopropyltrimethoxysilane, and Silquest™ A1120, N-(beta-aminoethyl)-gamma-aminopropyltrimethoxysilane. The preferred amino-functional silane for use in the present invention is Silquest™ Y-9669.
The isocyanato-functional silane used in the primer composition of the present invention may be any isocyanato-functional silane which can react with an amino-functional silane. Generally, the isocyanato-functional silane has at least one isocyanate group. In a preferred embodiment, the isocyanato-functional silane is an isocyanatoalkylalkoxysilane, wherein the alkyl and alkoxy groups have 1-5 carbon atoms. An example of an isocyanato-functional silane useful in the present invention is Silquest™ A-1310, which is ganima-isocyanatopropyltriethoxysilane.
The relative proportion of amino-functional silane to isocyanato-functional silane present in the composition of
Dearth Miles B.
Jagannathan Vasu
Lord Corporation
Shosho Callie E.
LandOfFree
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