Alloys or metallic compositions – Magnesium base – Aluminum containing
Reexamination Certificate
2001-12-06
2003-12-30
Jenkins, Daniel J. (Department: 1742)
Alloys or metallic compositions
Magnesium base
Aluminum containing
C428S689000
Reexamination Certificate
active
06669900
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of manufacturing a magnesium alloy molded product, a painted structure thereof, a method of painting the same, and casings using the same.
BACKGROUND OF THE INVENTION
In recent years, magnesium alloys have attracted public attention for their ease of recycling, low specific gravities, and good heat dissipating properties. As the products using magnesium alloys, the casings for household electrical appliances, such as television receivers, notebook-type personal computers, and portable minidisk players, or wheels of vehicles have been practically used. Magnesium alloys used in these products are mainly of AZ91 series for casting and AD31 series for sheet metal processing, and most of these are materials for casting, which are formed into molded products by the die-casting method or the thixo molding method.
On the surface of a metal molded product such as a magnesium alloy molded product, an anticorrosive film is normally formed for preventing the occurrence of rust, as well as providing an aesthetic appearance. Since flow marks produced during molding, or voids in which gas is trapped are present in the surface of magnesium alloy molded products, putty as well as layers of painting are applied to the surface of the molded products in order to hide flow marks and to prevent the gas trapped in voids from expanding and foaming.
For example, painting of middle to large size molded products, such as the housings of television receivers and notebook-type personal computers comprising a step (S
1
) of forming an anticorrosive film on the surface of a molded product; and a step (S
2
) of forming a painted film on the surface of the anticorrosive film. In the anticorrosive-film forming step (S
1
), dewaxing (S
1
-
1
) and activation (S
1
-
2
) are performed, and an anticorrosive film is formed (S
1
-
3
). Next, in the painted film forming step (S
2
), a primer is applied onto the surface of the anticorrosive film to form a painted film (S
2
-
1
), which is baked for curing (S
2
-
2
), then putty is applied (S
2
-
3
), the putty is baked for curing (S
2
-
4
), the putty overflown around the molded product is removed (S
2
-
5
), a primer is further applied (S
2
-
6
), and this primer is baked for curing (S
2
-
7
). Finally, top coating is applied (S
2
-
8
), and this is baked for curing (S
2
-
9
). This application of top coating is repeated twice or more as required.
In such conventional painting methods, however, a large number of process steps are required, and because of putty applying, the painting process is interrupted, and it is impossible to process the parts continuously. Therefore, there are problems that the efficiency of processing is limited, and the processing costs are high.
Therefore, the object of the present invention is to provide a painted structure of a magnesium alloy molded product having an aesthetic appearance, a method of manufacturing a molded product that can obtain a painted structure of a magnesium alloy molded product having an aesthetic appearance in a few process steps, a method of painting such a molded product, and a casing using such a molded product.
DISCLOSURE OF THE INVENTION
The present inventors paid attention to the fact that application of putty in a process of forming a painted film was the largest cause that complicated the coating step, that is, the number of process steps was increased and the processes could not be performed continuously. The inventors have devised to omit the application of putty, and to form the painted film by a single application of a powder paint and a single baking-for-curing treatment. As a result of studying the appearance of a magnesium alloy molded product completed in this painting process from various view points, it was known that an aesthetic appearance can be secured by setting the thickness of a painted film to a certain ratio or more relative to flow marks normally appearing in a magnesium alloy molded product, and by specifying the surface roughness of the molded product, such that flow marks can be sufficiently hidden in a single layer painted film in which application of putty is omitted.
A painted structure of a magnesium alloy molded product of the present invention comprises at least a magnesium alloy molded product having flow marks of a depth D, and a painted film of a thickness T formed on a surface of the magnesium alloy molded product, wherein the thickness of the painted film is 80% or more of the depth of the flow marks. Here, the thickness of the molded product is 0.3 mm to 5.0 mm. Also, the painted film contains no putty-filled regions.
Further, the painted structure of a magnesium alloy molded product has flow marks of which maximum depth is 100 &mgr;m and maximum opening width is 0.5 mm, wherein an anticorrosive film is formed on the surface of the magnesium alloy molded product, and a painted film having an average surface roughness of 10 &mgr;m or more and a thickness of 80 &mgr;m or more is formed on the surface of the anticorrosive film.
According to this configuration, since the painted film having an average surface roughness of 10 &mgr;m or more has been formed on the surface of the magnesium alloy molded product having flow marks as described above, light beams radiated onto the surface of the painted film can be irregularly reflected. Also, since the painted film has a thickness of 80 &mgr;m or more, it is enough to hide flow marks in cooperation with the irregular reflection. Therefore, a single layer of the painted film can hide flow marks, securing an aesthetic appearance without using putty as in conventional methods. Further, the anticorrosive film prevents occurrence of rust on the molded product.
When the painted film has an average roughness of less than 10 &mgr;m and a thickness of less than 80 &mgr;m, flow marks may be insufficiently hidden in a magnesium alloy molded product having flow marks of which maximum depth is 100 &mgr;m and of which maximum opening width is 0.5 mm.
In the painted structure according to the present invention, the painted film may be formed from a powder paint. According to this configuration, the particles of the powder paint ensure the average surface roughness of the painted film.
Also, in the painted structure according to the present invention, the painted film may contain an aluminum powder. According to this, the irregular reflection on the surface of the painted film is promoted by the aluminum powder.
Also, in the painted structure according to the present invention, the painted film may be formed from the film of the oxide of magnesium constituting the magnesium alloy molded product. According to this configuration, the magnesium oxide film prevents the occurrence of rust on the molded product, and ensured the adhesion of the painted film.
Furthermore, a method of manufacturing a magnesium alloy molded product according to the present invention comprises the steps of: melting all or a part of a magnesium-aluminum alloy containing 4 to 12% aluminum; heating a mold to which a release agent is applied to a temperature between 200° C. and 300° C.; injection-molding the magnesium alloy; and removing flow parts other than the product part from the obtained molded body. The thickness of the molded product is 0.3 mm to 5.0 mm.
According to this manufacturing method, a molded product that can hide flow marks with the painted film can be obtained, and such a thickness of the molded can be ensured that gives a large hiding effect.
Furthermore, the method of painting a magnesium alloy molded product according to the present invention comprises the steps of: forming an anticorrosive film on the surface of a magnesium alloy molded product; applying a powder paint on the surface of the anticorrosive film, a curing start temperature of which powder paint is 140° C. or lower; and bake-curing the applied powder paint.
According to the above-described configuration, since the powder paint is applied, the curing-start temperature of which powder paint is 140° C. or lower, in the step of base
Kamikawaji Mitsuharu
Matsumura Keizou
Matsunaga Koji
Nishikawa Yukio
Shikata Naohiro
Jenkins Daniel J.
Parkhurst & Wendel L.L.P.
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