I PLUG BLADE BACKGROUND The present invention relates to a plug blade and, more particularly, to a conductive plug blade having an insulating layer protecting a user. 5 Electric appliances or equipment utilized in daily lives or industries generally a plug for coupling with a socket for electrical connection. A typical plug includes two or two blades and an optional grounding prong or blade. The blades are fixed on an inner frame and then placed in a mold so that a housing can be formed around the inner frame by molding injection. Exposed portions of 10 the blades can be inserted into a socket for electrical connection. To avoid the risk of electric shock, covering the exposed section of each blade with an insulating layer is mandatory in many counties. FIG. 1 shows a conventional cylindrical plug blade 1 that has not been covered by an insulating layer. The plug blade 1 is cylindrical in the longitudinal 15 direction. To allow easy molding injection, the outer diameter of the plug blade 1 is made as small as possible so that a larger flow path for molten plastic material is provided in the mold during formation of the housing. However, the plug blade 1 often fails to pass safety tests due to insufficient rigidity resulting from small outer diameter. On the other hand, the thickness of the insulating layer covered 20 on a section of the plug blade 1 is too thin and, thus, causes difficulty in molding injection if the outer diameter of the plug blade 1 is maintained. Specifically, molten plastic material can not reach the molding area distant to the injection port of the mold such that the resultant insulating layer is too thin and, thus, exposes the section of the plug blade 1 that should be covered for insulating 25 purposes.
2 FIGS. 2A and 2B show a conventional flat plug blade 1A that is also flat in a longitudinal direction thereof. A section of the plug blade 1 A is covered by an insulating layer 11 for insulating purposes. However, such a flat plug blade 1 A suffers the same problems as the round plug blade 1 shown in FIG. 1A. 5 SUMMARY A plug blade device according to the preferred teachings of the present invention includes a blade having a main section that has an outer periphery tapering from forward. An insulating layer is mounted around the main section and has a thickness tapering rearward such that an outer periphery of the 10 insulating layer is substantially rectilinear throughout a longitudinal direction of the combined main section/insulating layer. The plug blade according to the preferred teachings of the present invention meets both requirements of the insulating layer and the rigidity of the plug blade and can pass the safety rests of plug blades. 15 The blade can be a solid cylindrical blade, a solid flat blade, a hollow cylindrical blade, a hollow flat blade, or a blade of other shapes. The present invention will become clearer in light of the following detailed description of illustrative embodiments of this invention described in connection with the drawings. 20 DETAILED DESCRIPTION OF THE INVENTION The illustrative embodiments may best be described by reference to the accompanying drawings where: FIG. 1 shows a cross-sectional view of a conventional plug blade. FIG. 2A shows a partly-sectioned elevational view of another 25 conventional plug blade.
3 FIG. 2B shows a partly-sectioned side view of the conventional plug blade of FIG. 2A. FIG. 3 shows a perspective view of a plug blade of an embodiment according to the preferred teachings of the present invention with an insulating 5 layer removed. FIG. 4 shows a cross-sectional view of the plug blade of FIG. 3. FIG. 5 shows a partly-sectioned elevational view of an inner frame and two plug blades of FIG. 3 with an insulating layer formed on a section of each plug blade. 10 FIG. 6A shows an elevational view of a plug blade of another embodiment according to the preferred teachings of the present invention with an insulating layer removed. FIG. 6B shows a side view of the plug blade of FIG. 6A. FIG. 7A shows a partly-sectioned elevational view of the plug blade of 15 FIG. 6A with a section of the plug blade covered by an insulating layer. FIG. 7B shows a partly-sectioned side view of the plug blade of FIG. 7A. FIG. 8A shows an elevational view of the plug blade of FIG. 7A. FIG. 8B shows a side view of the plug blade of FIG. 8A. FIG. 9 shows an elevational view of the inner frame and the plug blades 20 of FIG. 5. All figures are drawn for ease of explanation of the basic teachings of the present invention only; the extensions of the Figures with respect to number, position, relationship, and dimensions of the parts to form the preferred embodiment will be explained or will be within the skill of the art after the 25 following teachings of the present invention have been read and understood. Further, the exact dimensions and dimensional proportions to conform to specific 4 force, weight, strength, and similar requirements will likewise be within the skill of the art after the following teachings of the present invention have been read and understood. Where used in the various figures of the drawings, the same numerals 5 designate the same or similar parts. Furthermore, when the terms "portion", "section", "front", "rear", "longitudinal", "forward", "rearward", "width", "thickness", and similar terms are used herein, it should be understood that these terms have reference only to the structure shown in the drawings as it would appear to a person viewing the drawings and are utilized only to facilitate describing the 10 invention. FIGS. 3-5 and 9 show a plug blade 2 of an embodiment according to the preferred teachings of the present invention and generally designated 2, wherein FIG. 3 shows a perspective view of the plug blade 2 without an insulating layer 24, FIG. 4 shows a cross-sectional view of the plug blade 2 of FIG. 3, FIG. 5 15 shows a partly-sectioned elevational view of an inner frame 3 and two plug blades 2 of FIG. 3 with an insulating layer 24 formed on a section 23 of each plug blade 2, and FIG. 9 shows an elevational view of the inner frame 3 and the plug blades 2 of FIG. 5. The plug blade 2 includes, from rear to front, a wire coupling section 21, 20 a rolled portion 22, a main section 23, and an insertion section 25. Conductive wires are coupled with the wire coupling portion 21 for electrical connection. The rolled portion 22 includes a pattern formed by rolling such that the plastic material forming a housing of the plug blade 2 can reliably "catch" the plug blade 2 when the plug blade 2 is mounted on an inner frame 3 and placed in a mold for 25 molding injection for forming the housing. The insertion section 25 can be inserted into a socket or the like for electrical connection.
5 An insulating layer 24 is mounted around the main section 23 to protect a user from electric shock. The main section 23 has an outer periphery that tapers forward. According to the preferred form shown, the main section 23 includes a decreasing outer diameter toward the insertion section 25. 5 Furthermore, the insulating layer 24 has a thickness tapers rearward; namely, the insulating layer 24 is complementary to the main section 23 and includes an increasing thickness toward the insertion section 25. An outer periphery of the insulating layer 24 of the plug blade 2 is substantially rectilinear throughout a longitudinal direction of the main section 23, best shown in FIG. 5. Namely, the 10 plug blade 2 includes a substantially uniform outer diameter at the section of combined main section 23/insulating layer 24. The plug blade 2 shown in FIGS. 3-5 is a solid cylindrical blade. It can be appreciated that the plug blade 2 can be a solid flat blade, a hollow cylindrical blade, a hollow flat blade, or a blade of other shapes. FIG. 6A shows an 15 elevational view of a plug blade 2A in the form of a solid, flat blade according to the preferred teachings of the present invention with an insulating layer 24A removed. FIG. 6B shows a side view of the plug blade 2A of FIG. 6A. FIG. 7A shows a partly-sectioned elevational view of the plug blade 2A of FIG. 6A with a section 23A of the plug blade 2A covered by an insulating layer 24A. FIG. 7B 20 shows a partly-sectioned side view of the plug blade 2A of FIG. 7A. FIG. 8A shows an elevational view of the plug blade 2A of FIG. 7A. FIG. 8B shows a side view of the plug blade 2A of FIG. 8A. Specifically, the plug blade 2A includes, from rear to front, a wire coupling section 21A, a neck section 22A, a main section 23A, and an insertion 25 section 25A. Conductive wires are coupled with the wire coupling portion 21 A for electrical connection. An insulating layer 24A is mounted around the main 6 section 23A to protect the user from electric shock. The main section 23A has an outer periphery that tapers forward. According to the preferred form shown, the main section 23A includes a decreasing width toward the insertion section 25A (see FIG. 6A) and a decreasing thickness toward the insertion section 25A (see 5 FIG. 6B). Furthermore, the insulating layer 24A has a thickness tapers rearward; namely, the insulating layer 24A is complementary to the main section 23A and includes an increasing thickness toward the insertion section 25A (see FIGS. 7A and 7B). An outer periphery of the insulating layer 24A of the plug blade 2 is substantially rectilinear throughout a longitudinal direction of the section of 10 combined main section 23A/insulating layer 24A (see FIGS. 8A and 8B). Namely, the plug blade 2 includes a substantially uniform outer periphery at the section of combined main section 23A/insulating layer 24A. It can be appreciated that the plug blade 2, 2A according to the preferred teachings of the present invention meets both requirements of the insulating 15 layer 24, 24A and the rigidity of the plug blade 2, 2A and can pass the safety rests of plug blades. Thus since the invention disclosed herein may be embodied in other specific forms without departing from the spirit or general characteristics thereof, some of which forms have been indicated, the embodiments described herein 20 are to be considered in all respects illustrative and not restrictive. The scope of the invention is to be indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.