Compositions: coating or plastic – Coating or plastic compositions – Corrosion inhibiting coating composition
Reexamination Certificate
2000-12-13
2002-09-10
Dawson, Robert (Department: 1712)
Compositions: coating or plastic
Coating or plastic compositions
Corrosion inhibiting coating composition
C106S014140, C523S401000, C523S402000, C524S492000, C524S556000, C524S589000, C524S591000, C524S601000, C524S804000, C524S832000, C524S837000, C524S839000, C524S907000
Reexamination Certificate
active
06447589
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of producing a water-base resin composition for the non-chromate rust-preventive coating of metallic substrates, particularly for galvanized steel panels.
PRIOR ART
As the metallic surface treating agent, a chromium-containing surface treating agent such as a chromate system or a phosphate-chromate system has heretofore been used broadly and still in use today. However, in view of the recent trend toward more stringent regulatory control for environmental protection, it is likely that the use of such coating systems will be restricted for fear of the toxicity, particularly carcinogenicity, of chromium. Therefore, development of a rust-preventing agent not containing chromium and yet as effective as the chromium-containing treating agent in imparting corrosion resistance has been awaited. As disclosed in Japanese Kokai Publication Hei-11-29724, the inventors of the present invention previously developed a nonchromate rust-preventing agent comprising a water-base resin and, as incorporated therein, a thiocarbonyl group-containing compound, a phosphate ion, and water-dispersible silica. Regrettably, however, this system was found to be deficient in storage stability and somewhat poor in corrosion resistance at thin coating thickness, although it provides corrosion resistance equivalent to that afforded by a chromium-containing treating agent.
Meanwhile, with regard to the use of silane coupling agents in surface treating agents, an acidic surface treating agent containing two dissimilar silane coupling agents is disclosed in Japanese Kokai Publication Hei-8-73775. However, this system is intended to improve finger-print resistance and coating adhesion and is quite deficient in corrosion resistance for use in applications where high corrosion resistance is required after application of a rust-preventing agent as in the present invention.
Moreover, Japanese Kokai Publication Hei-10-60315 discloses a steel structure surface treating agent containing a silane coupling agent having a certain functional group reactive with an aqueous emulsion but the corrosion resistance required here is only that of a degree satisfying comparatively mild test requirements such as those of a wet test and as far as corrosion resistance is concerned, the system is a far cry from a rust-preventing agent meeting the highly critical corrosion resistance requirements, such as those of a salt spray test at thin film thicknesses, as provided by the present invention. With the above state of the art by way of background, there has been a standing demand for development of a nonchromate rust-preventing agent expressing sufficient corrosion resistance at thin coating thickness.
SUMMARY OF THE INVENTION
The present invention has for its object to provide a method of producing a water-base resin composition for rust-preventive coating which is suited for metal-coated steel panels, particularly galvanized steel panels, and despite the absence of chromium therein, is capable of imparting high corrosion resistance to coated metals, with the additional advantage of improved storage stability, and to a water-base resin composition as obtained by the above production method.
The production technology according to the present invention is a method of producing a water-base resin composition for rust-preventive coating which comprises reacting a water-base resin composition containing, in each liter thereof, 10 to 500 g of water-dispersible silica and 0.02 to 20 g of a silane coupling agent and/or a hydrolytic condensation product thereof at a temperature of not less than 50° C. and not over the boiling temperature thereof. The water-dispersible silica mentioned above is preferably one member or a mixture of two or more members selected from the group consisting of spherical silica, chainlike silica and aluminum-modified silica.
The water-base resin composition according to the present invention is a water-base resin composition for rust-preventive coating as obtainable by the above production method.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the water-base resin composition contains water, which serves as a solvent, and a water-base resin. The water-base resin includes not only water-soluble resins but also resins which are intrinsically insoluble in water but are provided as finely dispersed in water, for example as emulsions or suspensions. The resin usable as such water-base resin includes polyolefin resin, polyurethane resin, acrylic resin, polycarbonate resin, epoxy resin, polyester resin, alkyd resin, phenol resin, and other thermosetting resins, and these can be used as a suitable mixture. The more preferred are crosslinkable resins which have functional groups, such as either carboxyl or hydroxyl, or both. Particularly preferred is a polyolefin resin, a polyurethane resin or a system comprising those two kinds of resins.
In the water-base resin composition of the invention, the water-base resin accounts for 1 to 80 weight parts, in terms of nonvolatile matter, and water accounts for 99 to 20 weight parts, in each 100 weight parts of the water-base resin and water combined. If the proportion of resin solids is less than 1 weight part, the corrosion resistance and top coat adhesion will not be sufficient. On the other hand, if the proportion exceeds 80 weight parts, the composition will be liable to undergo the undesirable gelation.
In the production method of the invention, a silane coupling agent and/or a hydrolytic condensation product thereof is used as the silane compound. The hydrolytic condensation product of a silane coupling agent means an oligomer obtainable by hydrolytic polymerization of the silane coupling agent.
The silane coupling agent which can be used as above in the present invention is not particularly restricted but includes the following, among others: vinylmethoxysilane, vinyltrimethoxysilane, vinylethoxysilane, vinyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, N- (1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, N,N′-bis[3-(trimethoxysilyl)propyl]ethylenediamine, N-(&bgr;-aminoethyl)-&ggr;-aminopropylmethyldimethoxysilane, N-(&bgr;-aminoethyl)-&ggr;-aminopropyltrimethoxysilane, &ggr;-aminopropyltrimethoxysilane, &ggr;-aminopropyltriethoxysilane, &ggr;-glycidoxypropyltrimethoxysilane, &ggr;-glycidoxypropyltriethoxysilane, &ggr;-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, &ggr;-methacryloxypropyltrimethoxysilane, &ggr;-methacryloxypropyltriethoxysilane, &ggr;-mercaptopropyltrimethoxysilane, &ggr;-mercaptopropyltriethoxysilane and N-[2-(vinylbenzylamino)ethyl]-3- aminopropyltrimethoxysilane.
The particularly preferred silane coupling agent includes vinylmethoxysilane, vinylethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine and N,N′-bis[3-(trimethoxysilyl)propyl]ethylenediamine. These silane coupling agents can be used each alone or in a suitable combination.
In the present invention, said silane compound is used in an amount of 0.02 to 20 g (silica solids: ca 0.04 to 40 wt. %), preferably 0.1 to 2.5 g (silica solids: ca 0.2 to 5 wt. %), in each liter of the water-base resin composition. If the amount of the silane compound is less than 0.02 g, the contribution to corrosion resistance and top coat adhesion will be insufficient. On the other hand, if the limit of 20 g is exceeded, the shelf-life of the composition will be sacrificed.
In the method of producing a water-base resin composition according to the invention, water-dispersible silica is further employed. The water-dispersible silica which can be used is not particularly restricted but is preferably a spherical silica, chainlike silica or aluminum-modified silica which is weakly basic and lean in sod
Sasaki Motohiro
Shimakura Toshiaki
Yamasoe Katsuyoshi
Connolly Bove & Lodge & Hutz LLP
Dawson Robert
Nippon Paint Co. Ltd.
Zimmer Marc S
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