Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1998-07-21
2001-03-20
Lorin, Francis J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C427S372200
Reexamination Certificate
active
06203930
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rust preventive coating and a method for forming the same, and more particularly to a rust preventive coating having hydrophilic properties, air permeability and drying properties, and excellent in corrosion resistance, especially when scratches are developed. The coating is obtained by coating a surface mainly composed of iron with a metal baser or better in corrosion resistance than iron, and then, coating it with a specific paint composition, followed by drying at an ordinary temperature or heat drying at a low temperature.
Conventional rust preventing methods for iron include methods of lowering the electrode potential of iron, methods of coating the surface of iron to prevent the movement of ions, and methods of coating to prevent water and oxygen from passing through to iron, for preventing the anode reaction (formation of Fe
2+
) and the cathode reaction (formation of OH
−
) occurring on the surface of iron.
Specific examples of such rust preventing methods include coating methods with metals baser or better in corrosion resistance than iron, and coating methods by other coating means. However, in the case of only the former coating with metals, problems are encountered with regard to the durability and corrosion resistance of the metal. In the case of the latter coating with other coating means, problems arise in respect to the coating of edge portions, suppression of the occurrence of pin holes, maintenance of corrosion resistance and durability at the time when scratches are developed, and pursuing excellent processability and low cost.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a rust preventive coating having hydrophilic properties, air permeability and drying properties, and excellent in corrosion resistance, especially when scratches are developed, and a method for forming the same.
According to the present invention, there are provided a rust preventive coating formed on a surface of a substrate mainly composed of iron, which comprises an undercoat layer of the following (1) and an overcoat layer of the following (2):
(1) the undercoat layer obtained by coating the substrate with at least one metal selected from the group consisting of zinc, tin, lead, aluminum, chromium, nickel and copper by hot dipping, electroplating, penetration plating, thermal spraying or chemical plating, or a paint containing at least one rust preventive pigment selected from the group consisting of zinc dust, zinc chromate, minium, basic lead chromate, strontium chromate and lead chromate (hereinafter referred to as “undercoat paint”); and
(2) the overcoat layer obtained by coating the undercoat layer with a paint composition mainly composed of (a) 100 parts by weight of an inorganic filler, (b) 5 to 30 parts by weight of a binder in terms of solid content, and (c) 10 to 100 parts by weight of water and/or a hydrophilic organic solvent, and then, hardening the composition; and a method for forming the above-mentioned coating.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The rust preventive coating of the present invention is characterized in that the coating is formed of a corrosion-resistant metal layer or a rust preventive pigment-containing coat (undercoat layer) coating a surface of a substrate mainly composed of iron, and a hydrophilic, air-permeable protective coat (overcoat layer) for protecting the undercoat layer.
(1) Undercoat Layer
The undercoat layer is formed on the surface of the substrate mainly composed of iron as a metallic deposit layer having good corrosion resistance or a paint layer containing a rust preventive pigment mainly composed of a metal lower in ionization tendency than iron or a compound thereof.
The substrates mainly composed of iron which are used herein include flat plates, corrugated plates, steel products and bars formed of iron such as pure iron, steel iron or cast iron, and there is no particular limitation on the material and shape thereof.
In the above-mentioned plating, at least one metal selected from the group consisting of zinc, tin, lead, aluminum, chromium, nickel and copper is used, and particularly, zinc, tin or chromium is preferred.
Of the plating methods, the hot dipping is the method of dipping substrate in a bath of a melted metal such as zinc, tin, aluminum or a lead-tin alloy.
The electroplating is the method of electrolytically depositing, in an aqueous solution containing ions of the above-mentioned metal, cations of the metal such as zinc, tin, copper, nickel or chromium contained in the aqueous solution on the surface of substrate used as a cathode.
The penetration plating is the method of forming an alloy with chromium, aluminum or zinc on the surface of substrate by diffusion and penetration of the above-mentioned metal under an elevated temperature.
The thermal spraying is the method of spraying the metal such as zinc, aluminum, tin or lead melted with an arc on the surface of substrate to form a thick coating.
The chemical coating is the method of electrolessly depositing, from an aqueous solution containing ions of the above-mentioned metal, the metal such as nickel, chromium or copper on the surface of substrate with a reducing agent.
Specific examples of the undercoat layers formed by these plating methods include galvanized plates and tin plates.
There is no particular limitation on the thickness of the undercoat layers formed by these plating methods. Usually, however, the deposited amount of zinc is 50 to 300 g/m
2
for zinc hot dipping, that of tin is 20 to 30 g/m
2
for tin hot dipping, that of zinc is 10 to 55 g/m
2
for zinc electroplating, and that of tin is 5 to 20 g/m
2
for tin electroplating.
When the undercoat layer is formed with the paint containing the rust preventive pigment, at least one pigment selected from the group consisting of zinc dust, zinc chromate, minium, basic lead chromate, strontium chromate and lead chromate is used as the rust preventive pigment.
The paints include paints containing binders such as synthetic resins, alkoxysilanes and silicates, and rust preventive pigments such as zinc dust, zinc chromate, minium, basic lead chromate, strontium chromate, lead chromate and lead suboxide.
The amount of the rust preventive pigments contained in above-mentioned paints is usually 10 to 90% by weight, and preferably 50 to 85% by weight, in terms of solid content.
Specific examples of the paints containing the rust preventive pigments include Ceramica G1-720Z (manufactured by KABUSHIKI KAISHA NIPPANKENKYUSHO) and Ceramica MSA-800Z (manufactured by KABUSHIKI KAISHA NIPPANKENKYUSHO).
There is no particular limitation on the thickness of the undercoat layers formed of these rust preventive pigment-containing paints. However, the dried film thickness thereof is usually 5 to 400 &mgr;m, and preferably 15 to 160 &mgr;m.
When the undercoat layers are formed of the above-mentioned rust preventive pigment-containing paints, they are usually hardened at an ordinary temperature for 1 to 24 hours, or at a temperature of 100 to 150° C. for 10 to 60 minutes.
(2) Overcoat Layer
The overcoat layer used in the present invention acts as a protective coat which protects the above-mentioned undercoat layer, has hydrophilic properties and air permeability, is good in drying properties, suitably ionizes the metal or the rust preventive pigment of the undercoat layer, and forms no local electric cell in the substrate. Even if the substrate having the rust preventive coating of the present invention is damaged during or after the formation of the overcoat layer so that an iron portion of the substrate is exposed to the air, the surface of the exposed portion is subsequently converted to triiron tetraoxide (Fe
3
O
4
, black), and thereafter never changed to diiron trioxide (Fe
2
O
3
, red). Thus, a stable state of the substrate can be maintained. This is conceivably because the moisture in atmosphere is always kept in the overcoat layer due to the excellent hydrophilic properties and air permeability of the
Burgess, Ryan & Wayne
Kabushiki Kaisha Nippankenkyusho
Lorin Francis J.
Moran William R.
Wayne Milton J.
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