Patent Application
20090255824
1. Field of the Invention
The present invention relates to a method for surface treating a substrate.
2. Discussion of the Related Art
Mobile devices, such as mobile telephones, personal digital assistants, or MP3 players, enable consumers to enjoy the convenience of high technology services, almost anytime and at virtually any location. These mobile devices often employ a variety of decorative housings to attract consumers. Electroplating is an attractive and effective process for improving corrosion resistance and metallic appearance of the housings. Many housings for mobile devices are processed to form metal coatings on surfaces thereof by electroplating.
However, electroplated housings can be excessively bright and cause discomfort to the users.
Therefore, there is room for improvement within the art.
Many aspects of the method for surface treating a substrate can be better understood with reference to the following drawing. The components in the drawing are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the method for surface treating a substrate.
The FIGURE is a flow chart of an exemplary embodiment of a method for surface treating a substrate.
Referring to the FIGURE, a method for surface treating a substrate may include the steps S100 to S600.
In step S100, a substrate is provided. The substrate includes a metallic surface capable of being electroplated with a metal coating.
According to the exemplary embodiment, the substrate is made of plastic selected from a group consisting of acrylonitrile butadiene styrene (ABS), poly methyl methacrylate (PMMA), and polycarbonate (PC). The substrate is metalized by wet chemical deposition. During wet chemical deposition, a surface of the substrate to be metalized is firstly etched so that the surface is roughened. The etching of the substrate allows an activating layer in a subsequent process to be attached to the roughened surface. The etching process may be carried out, for example, in chromic acid, chromosulfuric acid, or potassium permanganate etching solution. An associated cleaning step is then carried out for cleaning the substrate. Subsequently, the surface of the substrate is activated in such manner that active metal particles, i.e., noble metal particles, are deposited on the surface of the substrate when being immersed into an activating solution containing hydrochloric acid, polyamide acid, and noble metal salt. During activation, the noble metal particles are separated out from the activating solution, dispersed, and deposited on the surface of the substrate. The noble metal salt may include palladium salt. After being activated, the substrate is rinsed with water and then metalized with chemical plating in a copper electrolyte containing copper salt and sulfuric acid, thereby depositing a chemical copper coating on the substrate. As such, the surface of the substrate is metalized. It should be understood that the substrate can instead be made of metal selected from a group consisting of steel, aluminum, titanium, magnesium, and alloys thereof.
In step S200, a first electroplated metal coating is deposited onto the metalized surface of the plastic substrate by electroplating. The first electroplated metal coating may include copper. The electroplating may be carried out by immersing the substrate into an electrolyte including at least one of copper sulfate and copper pyrophosphate, with the metalized surface of the plastic substrate being a cathode, and a copper anode being provided and immersed in the electrolyte. The thickness of the first electroplated metal coating is in a range from about 10 to about 50 microns.
In step S300, the first electroplated metal coating is passivated (i.e., has its chemical reactivity reduced) in an oxidizing agent containing chromic acid or chromate salt. That is, the first electroplated metal coating is oxidized to form an oxidized metal film coated thereon, which may protect the first electroplated metal coating from moisture corrosion.
In step S400, the passiviated first electroplated metal coating then undergoes sand blasting. During the sand blasting process, a mixture of quartz sand and water in an air sand blower strike the passiviated first electroplated metal coating, to put a plurality of dispersed and distributed dents in the passiviated first electroplated metal coating. The dents cause the first electroplated metal coating to possess a dull frosted appearance, which may be more attractive to consumers. The oxidized metal film is partially struck away from the first electroplated metal coating by sand blasting, thereby partially exposing the first electroplated metal coating.
In step S500, the first electroplated metal coating is repeatedly passivated in the oxidizing agent so as to passiviate the exposed portion thereof.
In step S600, the first electroplated metal coating is activated to remove the oxidized metal film that covers the first electroplated metal coating. The activation is carried out in an electrolyte including sodium hydroxide by an electric current.
In step S700, the substrate is immersed into hydrofluoric acid to remove the residual quartz sand on the first electroplated metal coating.
In step S800, a second electroplated metal coating is electroplated onto the first electroplated metal coating. The second electroplated metal coating may be made one of palladium and alloys of tin and copper. The thickness of the second electroplated metal coating is in a range from about 2 to about 8 microns and less than that of the first electroplated metal coating. It should be understood that, the second electroplated metal coating can be further coated with a decorative coating made of chrome, which has a thickness in a range from about 0.1 to about 2 microns and less than that of the second electroplated metal coating. The first electroplated metal coating and the second electroplated metal coating may give the substrate a dull frosted appearance attractive to consumers.
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200810301065.4 | Apr 2008 | CN | national |
