Coating processes – Applying superposed diverse coating or coating a coated base
Reexamination Certificate
2003-02-06
2004-09-07
Barr, Michael (Department: 1762)
Coating processes
Applying superposed diverse coating or coating a coated base
C427S327000, C427S376100, C427S337000, C427S343000, C427S600000, C148S275000, C148S420000
Reexamination Certificate
active
06787192
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for preparing magnesium and/or magnesium alloy component or part.
BACKGROUND ART
Magnesium is the most lightweight of all the metals for use as practically useful structural materials, has a high specific strength, is easy to machine and therefore has found wide use for motor vehicle components, electric products such as computers and acoustic devices, aircraft components, etc. Generally, magnesium and magnesium alloys are made into shaped articles mainly by die casting, extrusion or rolling, while the so-called thixomolding process with use of an injection molding machine has been established technically in recent years. This process assures the freedom of shape of moldings, the productivity thereof and improved properties, rendering the moldings useful for wider application.
Conventionally, castings or molding obtained by die casting or thixomolding are made into magnesium alloy products generally by the following steps.
1. Mechanical Treating Step
Polishing step with use of a polishing belt, abrasive paper or brush or by barrel finishing, buffing, blasting or the like for removing surface roughness or extraneous matter such as burrs, tough oxides, extrusion lubricant, mold releasing agent, casting sand or common soil.
2. Degreasing Step
(1) Degreasing with solvent: Preliminary degreasing or cleaning for removing cutting oil, grease or the like with a petroleum, aromatic, hydrocarbon or chlorine solvent.
(2) Degreasing with alkali: Degreasing or cleaning with use of caustic soda or like alkali solution for removing common soil, scorched graphite lubricant or cutting oil, etc.
(3) Degreasing with emulsion: Cleaning for removing soil from the metal surface by emulsification.
3. Pickling Step
The step of cleaning with a solution of single acid such as hydrofluoric acid, nitric acid, sulfuric acid, phosphoric acid or chromic acid or a solution of a mixture of such acids for removing oxide film, corrosion product, scorched lubricant, lodged abrasive agent, shot, casting sand or other soil which remains unremoved by the degreasing step, activating the surface of the casting or molding, or removing segregated layer.
4. Step of Treatment with Chromic Acid
The step of forming a chromate film over the surface of the casting or molding generally with use of a chromic acid agent to give corrosion resistance.
5. Cleaning Step
The step of cleaning with alkali and water or the like for removing the above chromate coating.
6. Drying Step
7. Coating or Plating Step
8. Assembling Step
In the above step 4, magnesium alloy components are generally treated with chromates (for example, JP-B-17911/1986, etc.). The chromate treatment nevertheless involves difficulty in setting the conditions for the treatment, so that it has been desired to provide more convenient corrosion inhibiting processes. Furthermore, the chromate treatment has the drawback that when conducted, the treatment discolors the surface of the metal, depriving the metal of its luster. In view of recent environmental protection, chrome compound is restricted or prohibited in use and processes are more desirable which are less likely to burden the environment.
Some of treating methods are proposed as a substitute for chromate treatment. For example, proposed are method using potassium permanganate under alkaline condition and method using manganese phosphate under acid condition. However, although these methods obtain corrosion effect by coating manganese on magnesium surface, insufficient effect is achieved.
An object of the present invention is to provide a process for preparing magnesium and/or magnesium alloy component which is excellent in corrosion resistance, coating adhesiveness and property of shielding electromagnetic waves.
DISCLOSURE OF THE INVENTION
(1) The present invention provides a process for preparing a treated magnesium and/or magnesium alloy component comprising (A) treating the magnesium and/or magnesium alloy component with a surface treating agent containing a phosphate, and thereafter (B) treating the component with a pre-treating agent used before a corrosion inhibition treatment.
(2) The present invention provides a process for preparing a treated magnesium and/or magnesium alloy component comprising (A) treating the magnesium and/or magnesium alloy component with a surface treating agent containing a phosphate,
(B) treating the component with a pre-treating agent used before a corrosion inhibition treatment, and thereafter
(D) treating the component with a corrosion inhibitor for magnesium.
(3) The present invention provides a process for preparing a treated magnesium and/or magnesium alloy component comprising (A) treating the magnesium and/or magnesium alloy component with a surface treating agent containing a phosphate,
(B) treating the component with a pre-treating agent used before a corrosion inhibition treatment,
(C) treating the component with a cleaning agent containing surfactant and at least one compound selected from among aromatic carboxylic acids and salts thereof, and thereafter
(D) treating the component with a corrosion inhibitor for magnesium.
(4) The present invention provides a process as defined in the above (1) to (3) wherein as the treating agent (A) is used an agent containing a phosphate and at least one compound selected from among aromatic carboxylic acids and salts thereof, and further as required at least one compound selected from among pyrazole compounds and triazole compounds.
(5) The present invention provides a process as defined in the above (1) to (4) wherein as the treating agent (D) is used an agent containing at least one compound selected from among aromatic carboxylic acids and salts thereof, and further as required at least one compound selected from among pyrazole compounds and triazole compounds.
(6) The present invention provides a process as defined in the above (1) to (5) wherein at least one step of (A), (B), (C) and (D) is conducted under ultrasonic wave.
(7) The present invention provides a process as defined in the above (1) to (6) wherein washing with water is added in a next step of each of at least one step of (A), (B), (C) and (D).
Further, the present invention provides a process for preparing a treated magnesium and/or magnesium alloy component comprising (1) deburring the magnesium and/or magnesium alloy component when required, (2) treating the component with a surface treating agent containing a phosphate, (3) treating the component with a pre-treating agent used before a corrosion inhibition treatment, (4) treating the component with a corrosion inhibitor for magnesium, (5) drying the component, (6) coating or plating the component, and (7) thereafter assembling the component.
The present inventors have investigated various substitutes for chromate treating agent. During the investigation, it is revealed that a treatment prior to corrosion inhibitory step is one of factors which contribute to improvement in corrosion resistance, coating adhesiveness and property of shielding electromagnetic waves.
The present inventors have proposed in PCT/JP00/00019 a surface treating agent which is useful for moldings of magnesium and/or magnesium alloys and contains a phosphate and at least one compound selected from among aromatic carboxylic acids and salts thereof. The present inventors have further investigated to obtain more excellent corrosion resistance, coating adhesiveness and property of shielding electromagnetic waves using the above surface treating agent. As the result, it is found that effects in corrosion, coating and plating are greatly enhanced by using a pre-treating agent for corrosion inhibition after treating moldings of magnesium and/or magnesium alloys with a surface treating agent containing a phosphate, or at least one compound selected from among aromatic carboxylic acids and salts thereof together with the phosphate. The present invention has been accomplished by this finding. The similar effect was obtained by use of the above phosphate, at least one compound selected from a
Fukumura Kazunori
Sakane Koji
Barr Michael
Kubovcik & kubovcik
Otsuka Kagaku Kabushiki Kaisha
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