Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-04-10
2001-02-27
Osele, Mark A. (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C428S625000, C428S629000, C428S632000, C428S701000
Reexamination Certificate
active
06193835
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing a rubber-based composite material which has good adhesion between a rubber layer and a substrate.
Rubber-metal composite materials have been widely used as, for example, rubber vibration insulators. They need firm rubber-to-metal bonding.
In view of the foregoing, the present applicant proposed in Japanese Patent Laid-open Nos. 87311/1987 and 246278/1987 a process for producing a rubber composite material which is characterized by coating the substrate with a thin film of cobalt or cobalt alloy by “dry plating”, thereby achieving firm bonding between rubber and substrate at the time of vulcanization. In addition, the present applicant disclosed in Japanese Patent Laid-open No. 290342/1989 that the rubber composite material is improved in durability (resistance to wet heat deterioration) if the cobalt is oxidized when the cobalt film is formed or after the cobalt film has been formed.
Moreover, the present applicant proposed in Japanese Patent Laid-open No. 296032/1996 corresponding to the U.S. patent application Ser. No. 08/634,792 a method for preparing a rubber composite material comprising the steps of forming a thin film of cobalt oxide on a substrate, forming a rubber composition on the thin film, and vulcanizing the rubber composition, said step of forming a thin film of cobalt oxide comprising sputtering a target of cobalt in the presence of an inert gas and a gas having molecular oxygen with an input power which is at least the transition point at which an input voltage between the target and the substrate abruptly rises when an input power is supplied to the target from a DC supply.
This process yields a rubber-based composite material which exhibits good adhesion under the wet heat condition owing to the cobalt oxide (CoOx) film formed in the oxygen gas stream.
In the meantime, a rubber-based composite material (such as rubber vibration insulator) often has its bonding interface exposed, and there is a possibility of the bonding interface coming into direct contact with water. In anticipation of such incidences, the composite material undergoes test for adhesive failure under a wet condition.
The rubber-based composite material having a cobalt oxide film on a metal substrate experiences peeling in the test for adhesive failure as soon as the bonding interface is given water, although it exhibits good adhesion (with rupture occurring always only in rubber) in the ordinary test for adhesive failure. There has been a demand for solution to this problem.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a process for producing a rubber-based composite material which exhibits good adhesion even in the case where the bonding interface comes into contact with water.
In order to achieve the above-mentioned object, the present inventors carried out a series of research efforts, which led to the following finding. That is, a rubber-based composite material which is formed by laminating a layer of rubber compound onto a substrate, with a bonding layer of metal or metal compound interposed between them and subsequently vulcanizing the rubber compound, exhibits firm bonding between the rubber layer and the substrate if a prime coating film is interposed between the substrate and the bonding layer. The firm bonding is such that failure occurs solely in rubber in the wet bond test. When used as a rubber vibration insulator, the rubber-based composite material exhibits good adhesion even when the bonding interface comes into contact with water. The prime coating film produces its profound effect when it is formed on a metal surface with phosphating treatment or any other conversion treatment. The present invention is based on this finding.
Accordingly, the present invention provides a process for producing a rubber-based composite material comprising steps of laminating a rubber compound onto a substrate, with a bonding layer of metal or metal compound interposed therebetween, and subsequently vulcanizing the rubber compound, characterized in that a prime-coating film is interposed between the substrate and the bonding film of metal or metal compound.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The rubber-based composite material of the present invention is not specifically restricted in its substrate, which may be made of metal, ceramics, or plastics. Metal includes, for example, steel, stainless steel, titanium alloy, aluminum, aluminum alloy, copper, copper alloy, zinc, zinc alloy, and amorphous alloy. The choices of these materials such as metal, ceramics and plastics and the size and shape of the substrate depend on the intended use of the composite material.
The process of the present invention should preferably be applied to a steel substrate with zinc phosphating treatment or any other chemical conversion treatment.
The rubber compound to be laminated onto the substrate according to the present invention should be based on one or more than one kind of natural rubber (NR) or synthetic rubber having carbon-carbon double bonds in the structural formula.
Examples of the synthetic rubber include the following.
(1) Homopolymers of conjugated diene compound such as isoprene, butadiene, and chloroprene. Examples include polyisoprene rubber (IR), polybutadiene rubber (BR), and polychloroprene rubber.
(2) Copolymers of said conjugated diene compound with a vinyl compound such as styrene, acrylonitrile, vinylpyridine, acrylic acid, methacrylic acid, alkyl acrylate, and alkyl methacrylate. Examples include styrene-butadiene copolymer rubber (SBR), vinylpyridine butadiene styrene copolymer rubber, acrylonitrile butadiene copolymer rubber, acrylic acid butadiene copolymer rubber, methacrylic acid butadiene copolymer rubber, methyl acrylate butadiene copolymer rubber, and methyl methacrylate butadiene copolymer rubber.
(3) Copolymers of olefin (such as ethylene, propylene, and isobutylene) with diene compound. Examples include isobutylene-isoprene copolymer rubber (IIR).
(4) Copolymers (EPDM) of olefin with non-conjugated diene. Examples include ethylene-propylene-cyclopentadiene terpolymer, ethylene-propylene-5-ethylidene-2-norbornene terpolymer, and ethylene-propylene-1,4-hexadiene terpolymer.
(5) Polyalkenamer obtained by ring opening polymerization of cycloolefin. Examples include polypentenamer.
(6) Rubber obtained by ring opening polymerization of oxirane. Examples include polyepichlorohydrin rubber vulcanizable with sulfur.
(7) Polypropylene oxide rubber.
Additional examples include their halides, such as chlorinated isobutylene-isoprene copolymer rubber (Cl-IIR) and brominated isobutylene-isoprene copolymer rubber (Br-IIR). Other examples include polymers obtained by ring opening polymerization of norbornane. The above-mentioned rubber may be blended with a saturated elastomer such as epichlorohydrin rubber, polypropylene oxide rubber, and chlorosulfonated polyethylene.
The rubber compound used in the present invention should be incorporated with a vulcanizing agent such as sulfur, organic sulfur compound and the other crosslinking agents in an amount of 0.01-10 parts by weight, preferably 0.1-6 parts by weight, and a vulcanization accelerator in an amount of 0.01-10 parts by weight, preferably 0.1-5 parts by weight, for 100 parts by weight of the above-mentioned rubber component. A preferred example of the vulcanization accelerator is N-cyclohexyl-2-benzothiazylsulphenamide (CZ). It reduces the vulcanizing time.
The rubber compound used in the present invention should preferably be incorporated with process oil, mineral oil, or vegetable oil. Process oil includes paraffinic process oil, naphthenic process oil, and aromatic process oil. Mineral oil includes ethylene-&agr;-olefin cooligomer, paraffin wax, and liquid paraffin. Vegetable oil includes castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, and peanut oil. These oils improve the bonding under wet heat conditions of the rubber to the cobalt oxide thin film in the case
Kato Nobuko
Yoshikawa Masato
Bridgestone Corporation
Osele Mark A.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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