Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-04-26
2003-11-11
Dawson, Robert (Department: 1712)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C427S387000, C427S515000, C428S447000, C428S448000, C428S450000, C524S425000, C524S430000, C524S433000, C524S588000, C528S034000, C528S038000
Reexamination Certificate
active
06645339
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to compositions for sealing and adhering magnesium-based substrates. More particularly, the present invention relates to compositions which demonstrate excellent resistance to fluid solvents, particularly automotive fluids, while maintaining excellent adherence to magnesium-based substrates.
BACKGROUND OF RELATED TECHNOLOGY
Room temperature vulcanizable (RTV) silicones posses an interesting combination of properties that make them very desirable for a large number of applications. These properties include a viscosity range that allows for use as flowable liquids or soft pastes, excellent thermal stability characteristics of high-consistency silicone rubber, good adhesion to many surfaces without requiring pressure, and curing without the need for heating, as their name implies. However, RTV silicones have not been used for sealing and bonding magnesium-based substrates, such as magnesium alloy substrates.
It is known to add viscosity-modifying filler materials to RTV silicones to improve their resistance to fluid solvents. For example, the addition of certain grades of metal oxides to silicone elastomers is known to result in silicone rubber compositions having a certain degree of oil resistance. European Patent Publication No. 572 148, assigned to General Electric Company, discloses the incorporation of mixed metal oxides into heat cured silicone elastomeric compositions containing MQ resins (M=R
3
SiO
1/2
monofunctional groups; Q=SiO
2
quadri- functional groups). In the '148 publication, such compositions are formed into engine gaskets which are reported to display a certain degree of oil resistance.
It is further known to add silane compounds to silicone elastomers to improve the adhesive properties of RTV silicone compositions. For example, U.S. Pat. No. 5,569,750 to Knepper et al. discloses a silicone rubber composition including an aminohydrocarbyl-substituted ketoximinosilane which reportedly possesses improved adhesive properties.
Silicone elastomers are commonly used as adhesives and sealants in automotive applications. For instance, U.S. Pat. Nos. 4,847,396 and 4,735,979, both assigned to Loctite Corporation, disclose RTV silicone compositions as automotive sealants. These patents disclose the use of adhesion promoters in silicone compositions to improve the adhesive strength of the silicone compositions to ferrous and aluminum substrates, even when these substrates have motor oil coated on their surfaces. Further, U.S. Pat. No. 5,434,214, also assigned to Loctite Corporation, discloses hydrosilation cured silicone formulations which cure at room temperature and, after a subsequent heat cure cycle, provide good primerless adhesion to aluminum and titanium substrates.
Magnesium alloys, typically alloys which include magnesium, aluminum and, to a lesser degree, zinc and manganese, have traditionally been used in aeronautic applications. They are characterized as being light in weight, offering high strength, being easily molded, having the ability to withstand high tolerances, and having the ability to withstand high temperatures. As a result of these properties, magnesium alloys are finding increased utility in other areas, such as automotive applications.
Magnesium alloys have traditionally been joined by riveting or welding. It is desirable, however, to bond and seal magnesium alloys using adhesives, as adhesive bonding and sealing offers advantages in weight saving, fatigue strength, and corrosion resistance. Attempts at such bonding and sealing, however, have proven generally commercially unacceptable for many applications, particularly automotive applications where the adhesives are exposed to automotive fluids, such as engine oils and coolants, at temperatures observed during operation of an automobile engine. These fluids tend to degrade the adhesives, thereby destroying their ability to seal and bond the substrates. Further, oxidation on the surface of magnesium alloys results in the formation of a layer of magnesium oxide which prevents bonding of adhesive materials to the underlying magnesium alloy.
Therefore, there exists a need for an elastomeric composition which exhibits improved adherence to magnesium-based substrates such as magnesium alloys, maintains structural integrity upon exposure to fluid solvents, and exhibits flexibility when subjected to thermal and mechanical stresses. The current invention is directed towards meeting these and other needs.
SUMMARY OF THE INVENTION
The present invention is directed to compositions which are suitable for use as sealants and adhesives on magnesium-based substrates such as magnesium alloy substrates. Particularly, the present invention is directed to a silicone composition, the reaction products of which demonstrate improved adhesion to magnesium-based substrates, which includes at least one polymerizable silicone component, at least one amino-containing silane adhesion promoter, and at least one filler. These compositions demonstrate excellent resistance to fluids, such as automotive fluids, while maintaining their enhanced adherence to magnesium-based substrates. Additionally, these compositions maintain their structural integrity when subjected to thermal and mechanical stresses. Desirably, the compositions include one or more polymerizable silicone polymers, such as RTV silicones, at least one amino-containing silane compound which serves as a magnesium alloy adhesion promoter, and at least one filler which serves to provide fluid resistance to the compositions. The present compositions can be used to seal interfaces between magnesium-based substrates, bond magnesium-based substrates together, and bond magnesium-based substrates to non-magnesium-based substrates. The present invention is also directed to a method for providing enhanced adhesion to magnesium-based substrates by disposing a composition of the present invention between two substrates and then curing the composition. Additionally, the present invention is directed to an article of manufacture including a composition of the present invention.
Compositions of the present invention can be dispensed on magnesium-based substrates in a liquid phase and allowed to cure at room temperature or can be cured prior to application to form automotive sealant devices, such as gaskets and o-rings. Methods of making these compositions and their use are also disclosed.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to compositions which are curable to an elastomeric state and which exhibit improved adherence to magnesium-based substrates such as magnesium alloys and enhanced resistance to fluids, such as those commonly used in and around automotive engines. Compositions of the present invention include polymerizable silicone compounds, such as reactive polysiloxanes, at least one amino-containing silane compounds, and at least one filler.
Any conventional polysiloxane may be used in compositions of the present invention and may be present in any amount, provided the resulting compositions effectively bond to magnesium-based substrates, form effective seals when cured, and are rendered substantially insoluble or resistant to automotive fluid solvents. For example, room temperature curing, actinic radiation curing, heat curing or silicones which cure by more than one of these mechanisms may be used. Desirably, the polysiloxane is an RTV compound. RTV compounds are typically low-consistency silicone elastomers that can be easily extruded from a tube or other dispenser and subsequently cured. Silicones which cure at room temperature may exist in one-part systems or in two-part systems.
In a one-part system, the silicones are typically organosiloxane compounds which may include hydrolyzable groups on their ends. They are stored in a noncrosslinked state in a moisture-impermeable container until they are to be used. When they are removed from the container and exposed to moisture, the hydrolyzable groups react with the moisture in a condensation reaction, resu
Bauman Steven C.
Dawson Robert
Henkel Loctite Corporation
Zimmer Marc S.
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