1. Field of the Invention
The present invention relates to an electrical apparatus connected to a commercial power source and a method of manufacturing the electrical apparatus.
2. Description of the Related Art
An electrical apparatus of this type, for example, an AC adapter has a metal plug, and the plug is connected to a commercial power source. The plug is made up of a set of blades and is insert-molded in a waterproof resin case. Such a plug is disclosed in a pamphlet of International Publication WO 07/116791.
This adapter converts alternating-current power to direct-current power, and during this conversion, heat is generated in the adapter. This heat causes gaps between the case and the blades due to a difference in shrinkage percentage between the case and the blades, which will be a cause of lowering airtightness of the case.
Under such circumstances, Japanese Patent Publication No. 3815733 (Japanese Patent Application Laid-open No. 2004-265748) discloses an example of a technique for enhancing airtightness of the case by filling a sealing resin material in the case. However, this resin material is generally expensive, and in addition, the time for drying the resin material is required in addition to the time for solidifying the resin forming the case, resulting in a longer manufacturing period.
Further, Japanese Patent Application Laid-open No. Hei 9-306578 and Japanese Utility Model Registration Publication No. 3075008 disclose techniques for coating outer peripheries of the blades by injection molding. These techniques can fill the gap between the case and the blades.
However, the techniques disclosed in Japanese Patent Application Laid-open No. Hei 9-306578 and Japanese Utility Model Registration Publication No. 3075008 apply an insulation layer for coating in order to prevent tracking and are not intended to ensure airtightness of the case. Further, in these techniques, a groove and a through hole are formed in an exposed part of each of the blades connected to a receptacle in order to facilitate the application of the insulation layers, which is not preferable in view of regulations regarding safety of electrical appliances.
Further, in these techniques, the groove is formed in part of each of the blades, and therefore, part of the blade where no groove is formed is not fully in close contact with the insulation layer, which poses a problem that airtightness of the case cannot be ensured. Another problem to be noted in these techniques is that the through hole is formed in the blade. This hole has a function of guiding the insulation layer to a rear side of the blade, but the injection pressure may possibly separate the insulation layer and the blade all the more.
As described above, the aforesaid techniques of coating the outer periphery of the blade still have a problem to be solved with respect to ensuring waterproofness of the case.