Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
1999-08-19
2001-05-15
Boykin, Terressa M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
Reexamination Certificate
active
06232431
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an anaerobic curable sealant composition and more particularly to an anaerobic curable sealant composition useful as a fluid gasket for forming a seal between two surfaces of flanges which are large in the amount of displacement. The anaerobic curable sealant composition of the present invention is employable usefully especially as a fluid gasket for preventing the leakage of a lubricating oil in various industrial machines and devices such as internal combustion engines and drive units.
PRIOR ART
Heretofore, in the fields of automobile parts, electric parts and various mechanical parts, as a method for bonding and sealing components to be sealed on an assembly line there has been adopted a method wherein sealing surfaces are pressure-welded through a molded gasket or a method wherein sealing surfaces are sealed through a fluid gasket. Particularly, as to the latter method using a fluid gasket, an FIPG (Formed In Place Gaskets) method, in which sealing surfaces are sealed under automatic application of a liquid sealant using a robot or the like on an assembly line, is most popular because of high productivity, low cost and highly reliable sealing performance. As an FIPG there mainly is used an anaerobic gasket containing as main components a room temperature curing type silicone material (silicone RTV) which reacts with moisture contained in the air and cures and a urethane (meth)acrylate which cures in a short time upon contact with metallic surfaces after shutting out oxygen by sandwiching a sealant in between flange surfaces. Particularly, silicone RTV is presently in use most widely because of its high heat resistance and excellent workability and adaptability to coated flange surfaces.
In the FIPG using silicone RTV, however, with upgrading of various oils, including engine oil, the damage to silicone rubber caused by oils has been becoming more and more serious and the attainment of a high resistance to oil is now a problem to be solved.
Particularly, as to oils used in automobiles or the like, an acrylic anaerobic curable sealant has come to be used. This sealant, because of an acrylic type, involves the drawback that it is poor in flexibility as compared with silicone compositions. The sealant is required to possess flexibility sufficient to cope with vibrations and stresses in a sealing portion including flanges or the like and also possess a repulsive force sufficient to retain sealability. It is difficult to consider that the acrylic anaerobic curable sealant satisfies these characteristics required. Thus, this sealant is unsatisfactory in actual use, and it is the actual situation that silicone RTV is used in most applications.
The flange of an oil pan is in many cases formed by combining different materials such as iron and aluminum. Therefore, a large lateral displacement is apt to occur at the flange surface due to a difference in thermal expansion coefficient between both materials which is caused by a change in temperature of the engine portion. The sealant layer is required to exhibit a high follow-up performance for coping with such displacement. This problem is serious especially in large-sized engines. The lateral displacement of the flange surface can be diminished by increasing the thickness of the gasket, but this attempt gives rise to an extremely serious drawback that an anaerobic curing does not take place.
In view of this point, methods have been proposed to impart flexibility to an anaerobic curable polymeric composition as an acrylic composition, such as a method of imparting flexibility to the composition itself by using an urethane acrylate as acryl material and a high molecular prepolymer prepared by polymerizing a monomer which is a soft segment of, say, a polyether in the main chain, and a method of imparting flexibility to the entire composition by adding a plasticizer or synthetic rubber particles such as acryl rubber or butyl rubber particles to an acryl polymerizable compound.
However, in the case of using a soft segment-containing high-molecular prepolymer, the flexibility of the composition is deteriorated when the composition is used in an atmosphere held at 120° C. or so, that is, when subjected to heat history. At a portion which becomes high in temperature the flexibility of sealant is lost with the lapse of time. In the synthetic rubber particles-added type, although flexibility is retained, there occurs a marked deterioration of solubility during production, thus requiring a long time in the manufacturing process. Moreover, if the sealant is stored in a liquid state, the rubber particles may be precipitated or agglomerated and clogged in the nozzle of an applicator. The use of a plasticizer gives rise to the drawback that the plasticizer oozes out from the sealant after curing.
In the conventional anaerobic curable fluid gasket, if engine oil, auto transmission fluid, or gear oil, is adhered to sealant bonding surfaces, there occurs a marked deterioration of bonding force. Usually, a mold release agent or an abrasive oil is adhered to the bonding surfaces and therefore it is necessary to perform degreasing and washing with use of an organic solvent or a detergent.
An anaerobic curable sealant composition is applied in an appropriate amount to sealing surfaces of flanges or the like, and when the sealing surfaces are clamped, an oxygen-shut out portion polymerizes and cures to form a seal layer. However, when the amount of the composition to be applied cannot be controlled precisely or when it is used in an excess amount for attaining a reliable sealing performance, the composition may be forced out from the flange surfaces. The thus-exposed portion of the anaerobic curable sealant composition, which portion is in contact with air, does not cure. Therefore, it is necessary that the composition should possess a property not exerting a bad influence on the surrounding materials.
Particularly when the anaerobic sealant composition is used in the engine and transmission of an automobile or the like, it is required in practical use that the composition exposed from the flange bonding surfaces and before curing should have a property of being dispersed uniformly in the oils used. The anaerobic curable composition containing synthetic rubber particles as a flexibility imparting agent is deficient in such dispersibility.
OBJECTS OF THE INVENTION
It is an object of the present invention to solve the above-mentioned problems of the prior art and provide an anaerobic curable sealant composition superior in all of oil resistance, flexibility and sealability and capable of retaining excellent felxibility even after subjected to heat history.
SUMMARY OF THE INVENTION
The present invention resides in an anaerobic curable sealant composition comprising an urethane (meth)acrylate prepolymer, a radical polymerizable monomer, an organic peroxide, and core-shell fine particles comprising a core of a rubbery polymer and a shell of a glassy polymer.
DETAILED DESCRIPTION OF THE INVENTION
An anaerobic curable sealant composition comprising an urethane (meth)acrylate prepolymer, a radical-polymerizable monomer and an organic peroxide is already publicly known. The present invention is characterized by adding specific fine particles to the said composition to improve the performance of the composition.
The urethane (meth)acrylate used in the present invention is a prepolymer having a urethane structure in its main chain and having (meth)acryloyloxy groups at its ends. This prepolymer is prepared by reacting a compound having two or more hydroxyl groups as functional groups with an organic compound having two or more isocyanate groups as functional groups to prepare a polyurethane prepolymer and introducing (meth)acryloyloxy groups into its molecular ends.
For example, the prepolymer in question is obtained by reacting a urethane prepolymer, which results from mixing and reacting a polyether polyol and an organic diisocyanate at a molar ratio in the range from 1:1 to 1:2 in a diluting solvent, with a (
Boykin Terressa M.
Dilsworth & Barrese, LLP
Three Bond Co. Ltd.
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