Conducting member

Abstract

A conductive member of the present invention includes: a metallic conductive base material including a joining region to be joined to another conductive member when the conductive member is used; and a conductive-auxiliary-coating-agent layer for imparting conductivity and an oxidation preventing property to a joining section between the joining region and another conductive member when the conductive member is used, the conductive-auxiliary-coating-agent layer being formed by applying a conductive auxiliary coating agent to the joining region of the conductive base material, in which the joining region of the conductive base material has a surface roughness of 0.6 μm or less in terms of an arithmetic mean roughness Ra specified in JISB0601 (1994).

Claims

1. A bus bar, comprising: a metallic conductive base material including a joining region to be joined to another conductive member when the bus bar is used; and an electrically conductive-auxiliary-coating-agent layer for imparting conductivity and an oxidation preventing property to a joining section between the joining region and the another conductive member when the bus bar is used, the electrically conductive-auxiliary-coating-agent layer being formed by applying an electrically conductive auxiliary coating agent to the joining region of the conductive base material, wherein the joining region of the conductive base material is subjected to oxide film removing treatment before the electrically conductive-auxiliary-coating-agent layer is formed and has a surface roughness of 0.6 μm or less in terms of an arithmetic mean roughness Ra specified in JISB0601 (1994), wherein the electrically conductive auxiliary coating agent comprises conductive auxiliary grease containing one or two or more powders selected from the group consisting of chromium oxide, zinc, silicon carbide, and a bismuth-tin alloy, and wherein the bus bar has a bolt fastening hole at the joining region of the metallic conductive base material so that the bus bar is joined to said another conductive member.

2. The bus bar according to claim 1, wherein the electrically conductive-auxiliary-coating-agent layer has a thickness of 100 μm or less.

3. The bus bar according to claim 2, wherein the electrically conductive-auxiliary-coating-agent layer has a thickness of from 10 μm to 40 μm.

4. The bus bar according to claim 1, further comprising a removable protective cover disposed on the electrically conductive-auxiliary-coating-agent layer so that the removable protective cover covers and protects the electrically conductive-auxiliary-coating-agent layer and is removed when the bus bar is used.

5. The bus bar according to claim 4, wherein the removable protective cover comprises a release sheet formed into a film shape or a sheet shape to be releasably bonded to the electrically conductive-auxiliary-coating-agent layer.

6. The bus bar according to claim 5, wherein the removable protective cover covers an entire surface of a joining surface and a side surface of the electrically conductive-auxiliary-coating-agent layer.

7. The bus bar according to claim 4, wherein the removable protective cover comprises a guarding sheet for covering and protecting the joining region of the conductive base material and the electrically conductive-auxiliary-coating-agent layer formed on the joining region, the guarding sheet being formed into a tubular shape opened at both ends or a bag shape opened at one end.

8. The bus bar according to claim 4, wherein the removable protective cover comprises a guarding cover including a covering section for covering an entire surface of the electrically conductive-auxiliary-coating-agent layer and a locking section for detachably locking the covering section to the conductive base material.

9. The bus bar according to claim 1, wherein a material for the conductive base material comprises aluminum or an aluminum alloy.

10. The bus bar according to claim 1, wherein the oxide film removing treatment is chemical etching or mechanical processing.

11. The bus bar according to claim 1, wherein the electrically conductive-auxiliary-coating-agent layer has a thickness of from 11 μm to 33 μm.

12. The bus bar according to claim 1, wherein the joining region of the conductive base material has a surface roughness of 0.5 μm or less.

13. A bus bar joint structure, comprising: the bus bar according to claim 1; said another conductive member; and a bolt and a nut; wherein the joining region of the bus is joined to said another conductive member by the nut and the bolt so that the electrically conductive-auxiliary-coating-agent layer is placed between the bus bar and another conductive member.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A is an explanatory view for illustrating a conductive member in which a release sheet (protective cover) is bonded to only a joining surface of conductive-auxiliary-coating-agent layer.

(2) FIG. 1B is an explanatory view for illustrating a conductive member in which an entire surface of the joining surface and a side surface of the conductive-auxiliary-coating-agent layer is covered with the release sheet (protective cover).

(3) FIG. 2A is an explanatory view for illustrating a conductive member in which the conductive-auxiliary-coating-agent layer is covered with a guarding sheet having a tubular shape opened at both ends.

(4) FIG. 2B is an explanatory view for illustrating a conductive member in which the conductive-auxiliary-coating-agent layer is covered with a guarding sheet having a bag shape opened at one end.

(5) FIG. 3A is a perspective view for illustrating a conductive member in which the conductive-auxiliary-coating-agent layer is covered with a guarding cover.

(6) FIG. 3B is a sectional view of the conductive member of FIG. 3A when viewed from a direction denoted by a white arrow.

DESCRIPTION OF EMBODIMENTS

(7) Now, preferred embodiments of the present invention are described specifically.

(8) In the present invention, a conductive base material serving as a basis material is a metal having conductivity, which is impaired due to the formation of an oxide film on a surface in various environments, and examples thereof include but are not limited to an aluminum material formed of aluminum or an aluminum alloy, a copper material formed of copper or a copper alloy, and an iron material formed of iron or an iron alloy. The conductive base material can be selected based on the application of a conductive member to be formed through use of the conductive base material, and various physical properties such as conductivity, strength, corrosion resistance, and processability required in the application. In the case of using an aluminum material, a 1,000-series (pure Al series) excellent in conductivity or a 6,000-series (Al—Mg—Si series) that is inferior in conductivity to the 1,000-series but that has high strength and is also excellent in formability is preferred. The conductive base material can be manufactured by, for example, a method involving casting, extrusion, rolling, or forging.

(9) Further, according the present invention, in a joining region that is formed on a surface of the conductive base material and is joined to another conductive member, it is preferred that an oxide film formed on the joining region be removed in advance. The removing treatment of the oxide film can be appropriately selected based on the kind, thickness, and the like of the oxide film, and for example, there may be given chemical etching treatment or mechanical processing treatment. When the oxide film that inhibits electric resistance is removed, the passage of an electric current between the conductive member and another conductive member when the conductive member is used becomes satisfactory. Further, the amount of oxygen remaining in a void section of a contact surface between the conductive base material and a conductive auxiliary coating agent to be described later can be reduced by smoothening the joining region to the extent possible to improve the adhesiveness of the joining region with respect to the conductive auxiliary coating agent. Thus, the oxide film is not formed easily even when the conductive member is used, and an increase in electric resistance caused by the formation of the oxide film is less liable to occur. As the chemical etching, for example, there may be given alkaline treatment and alkali phosphate treatment using an alkaline solution. Specifically, in the case of the alkaline treatment, at least one kind of alkaline aqueous solution selected from sodium hydroxide, potassium hydroxide, and lithium hydroxide having a concentration of from 30 g/L to 200 g/L can be used. Further, in the case of the alkali phosphate treatment, at least one kind of alkali phosphate aqueous solution selected from sodium hydroxide, sodium phosphate, and potassium hydroxide having a concentration of from 30 g/L to 100 g/L can be used. Further, as the mechanical processing treatment, a method such as polishing, grinding, cutting, shotblasting, or wet blasting can be used. It should be noted that in the case where a smut is formed on a surface of the base material by the chemical etching treatment, for example, desmutting treatment may be performed by acid treatment using an acid aqueous solution.

(10) In addition, after the removing treatment of the oxide film is performed, a conductive auxiliary coating agent for imparting required conductivity and a required oxidation preventing property to a joining section between the joining region and another conductive member is applied to the joining region to form a conductive-auxiliary-coating-agent layer on the joining region. As the conductive auxiliary coating agent, for example, there may be given grease containing one or two or more conductive powders or conductive auxiliary powders selected from the group consisting of chromium oxide, zinc, silicon carbide, and a bismuth-tin alloy in grease serving as a base (for example, trade name “NIKKEI JOINTAL” manufactured by Shizuoka Kosan Co., Ltd.) and a conductive auxiliary coating agent obtained by adding a conductive filler and as required an oxidation preventing agent or the like to a binder resin, followed by mixing (see, for example, JP 2005-26187 A, JP 2007-317489 A, or JP 2010-539650 A). Further, as preferred characteristics of the conductive auxiliary coating agent, it is preferred that the consistency specified in JIS-K2220 be from 290 to 340 from the viewpoint of a discharging property from the joining section. Further, it is preferred that the flash point specified in JIS-K2220 be 200° C. or more, and the dropping point fall within a range of from 160° C. to 210° C., from the viewpoint of aging degradation.

(11) Herein, in the present invention, the surface roughness of a coated surface (joining region) of the conductive base material to which the conductive auxiliary coating agent is applied is 0.6 μm or less, preferably 0.2 μm or less in terms of an arithmetic mean roughness Ra specified in JISB0601 (1994). In the present invention, as described above, in order to obtain a conductive member that can be used also as, for example, a small bus bar for an automobile or the like, it is necessary to decrease the thickness of the conductive-auxiliary-coating-agent layer to be formed so as to reduce the contact resistance even in the case where the contact surface pressure is relatively low (for example, contact surface pressure: 52.4 kgf/cm.sup.2 or less). Therefore, when the surface roughness (arithmetic mean roughness Ra) of the coated surface (joining region) of the conductive base material to which the conductive auxiliary coating agent is applied is set within the above-mentioned range, even in the case where the contact surface pressure is relatively low, the conductive auxiliary coating agent can be discharged properly from between the joined members in the case where the conductive member of the present invention is joined to another conductive member, and thus the thickness of the conductive auxiliary coating agent can be decreased to reduce the contact resistance. In the case where the surface roughness is more than 0.6 μm, the discharging property of the applied conductive auxiliary coating agent is not sufficient, and the contact resistance increases, with the result that sufficient conductivity and sustainability thereof cannot be obtained. It should be noted that the joining surface of another conductive member or the like to be joined to the conductive member of the present invention preferably satisfies the above-mentioned surface roughness. Although the absolute value of the contact resistance varies depending on the size and contact surface pressure of the conductive member, it is preferred that a resistance ratio obtained by dividing the contact resistance value of the conductive member after the application of the conductive auxiliary coating agent by the contact resistance value of only the conductive base material before the application of the coating agent be less than 2.5 (more preferably less than 2.0).

(12) In addition, as a method of setting the surface roughness (arithmetic mean roughness Ra) of the coated surface (joining region) of the conductive base material to which the conductive auxiliary coating agent is applied as described above, for example, there may be given rolling processing using a roll having its roughness adjusted, extrusion processing, or cutting processing.

(13) Further, the thickness of the conductive-auxiliary-coating-agent layer formed by applying the conductive auxiliary coating agent is preferably 100 μm or less, more preferably from 10 μm to 40 μm. It is not preferred that the thickness be more than 100 μm because the distance between the conductive members to be joined through intermediation of the conductive-auxiliary-coating-agent layer increases, and a large contact surface pressure is required for obtaining sufficient conductivity. On the other hand, it is not preferred that the thickness be less than 10 μm for the following reason. The amount of the conductive auxiliary coating agent to be held when the conductive member is joined to another member becomes small, and hence water-tightness and air-tightness of the joining section become insufficient. As a result, there is a risk in that moisture and oxygen enter the joining section (joining surface of the conductive member) to form an oxide film when the conductive member is used, thereby decreasing conductivity, and irregularities are liable to occur in the thickness of the conductive-auxiliary-coating-agent layer to cause variation in conductivity. It should be noted that it is more preferred that the conductive auxiliary coating agent be applied also to a counterpart member for joining, and the total thickness including the applied conductive auxiliary coating agent be 100 μm or less.

(14) As a method of applying the conductive auxiliary coating agent, a known method can be adopted, and means such as a roll coating method, a bar coating method, a spraying method, or an immersion method can be used. More simply, a roller to be used in a general coating operation can be used.

(15) Further, in the present invention, it is preferred that, after the conductive-auxiliary-coating-agent layer is formed on a surface of the conductive base material, the conductive-auxiliary-coating-agent layer be protected by being covered with a protective cover. As the protective cover, any cover may be used as long as the cover can prevent the conductive-auxiliary-coating-agent layer from being contaminated or broken during storage or distribution and can be easily removed when the conductive member is used. For example, there may be given a film-shaped or sheet-shaped release sheet that can be detachably bonded to the conductive-auxiliary-coating-agent layer, a guarding cover for covering an entire surface of the conductive-auxiliary-coating-agent layer, and other forms of protective covers. There is no particular limitation on the material for the protective cover, and a resin, a metal, ceramics, paper, or the like can be used.

(16) As the manner of mounting of the protective cover on the conductive-auxiliary-coating-agent layer in the case where the protective cover is the above-mentioned release sheet, there may be given a case where the protective cover is merely releasably bonded only the joining surface of the conductive-auxiliary-coating-agent layer as illustrated in FIG. 1A, and a case where an entire surface of the joining surface and a side surface of the conductive-auxiliary-coating-agent layer is covered with the protective cover as illustrated in FIG. 1B. It is more preferred that the entire surface of the joining surface and the side surface of the conductive-auxiliary-coating-agent layer be covered with the protective cover as illustrated in FIG. 1B because the water-tightness and air-tightness of the joining section of the conductive-auxiliary-coating-agent layer during storage become more sufficient.

(17) Further, as the manner of mounting of the release sheet, the release sheet can also be a guarding sheet having a tubular shape opened at both ends as illustrated in FIG. 2A or a bag shape opened at one end as illustrated in FIG. 2B. The above-mentioned manner of mounting of the release sheet is preferred because the entire joining region of the conductive base material and the entire conductive-auxiliary-coating-agent layer can be covered with the guarding sheet, and hence the water-tightness and air-tightness of the joining section of the conductive-auxiliary-coating-agent layer during storage can be further maintained. It should be noted that an opening of the guarding sheet can be closed by a method such as bonding with an adhesive, or thermal welding.

(18) Further, in the case where the protective cover is the above-mentioned guarding cover, the guarding cover can be configured to include a covering section for covering the entire surface of the conductive-auxiliary-coating-agent layer and a locking section for detachably locking the covering section to the conductive base material, for example, as illustrated in FIG. 3.

(19) Further, as a method of joining the conductive member of the present invention to another conductive member or the like, the conductive-auxiliary-coating-agent layer can be joined to a joining surface of another conductive member or the like to be joined to the conductive-auxiliary-coating-agent layer by a method such as ultrasonic joining, vibration welding, or caulking after the protective cover is removed. More simply, the conductive-auxiliary-coating-agent layer can be joined to another conductive member or the like by fastening with a bolt through a bolt fastening hole (4) as illustrated in FIG. 1A, FIG. 1B, FIG. 2A, and FIG. 2B. The contact surface pressure is preferably 76.8 kgf/cm.sup.2 or less, more preferably from 26.4 kgf/cm.sup.2 to 52.4 kgf/cm.sup.2 in the case of a small conductive member.

EXAMPLES

(20) The embodiments of the present invention are described based on the following test examples.

(21) [Confirmation Test of Contact Resistance based on Surface Roughness of Conductive Base Material]

(22) In order to confiuin the effect of a surface roughness (arithmetic mean roughness Ra) on contact resistance, the following test was conducted. An aluminum member having an oxide film formed on a surface was subjected to cold rolling processing so as to have a surface roughness Ra of 0.15 μm. After that, the resultant was subjected to cutting processing to prepare an aluminum conductive base material formed of a 6101-T6 aluminum (Al) material measuring 3 mm×50 mm×100 mm. Then, a conductive auxiliary coating agent (trade name“NIKKEI JOINTAL Z” manufactured by Shizuoka Kosan Co., Ltd.) was applied to a portion of the aluminum conductive base material corresponding to a joining region with respect to another conductive member (6101-T6 Al material), and the conductive auxiliary coating agent was rubbed with cotton waste to remove the surface oxide film. Then, the conductive auxiliary coating agent was again applied to the joining region to a thickness of 11 μm to obtain a conductive member. It should be noted that the surface roughness Ra after the surface oxide film was removed was 0.15 μm. Further, as another conductive member, a conductive member was also prepared by polishing a surface of a base material with emery paper so as to have a surface roughness Ra of from 0.4 μm to 1.0 μm.

(23) Another conductive member (conductive member under the same condition) was joined to the obtained conductive member through intermediation of the conductive auxiliary coating agent, followed by fastening so as to obtain a contact surface pressure of 52.4 kgf/cm.sup.2, to obtain aluminum test pieces according to Test Examples 1 to 5. A contact resistance ratio was measured under the following measurement conditions.

(24) <Measurement Conditions of Contact Resistance Ratio>

(25) Method: Four-terminal method Electric current: 1 A
A voltage between the conductive member and another conductive member joined to the conductive member was measured twice each for different directions of the passage of an electric current. Measurement values of a total of four measurements were averaged to calculate a contact resistance ratio. It should be noted that the case where the measurement was conducted with the 6101-T6 Al material alone was set to 1.

(26) TABLE-US-00001 TABLE 1 Surface Contact Coating thickness Resis- rough- surface of conductive tance ness pressure auxiliary coating ratio (μm) (kgf/cm.sup.2) agent (μm) (—) Remark Test 0.15 52.4 11 (22) ⊚ Corresponding Exam- to Example ple 1 Test 0.3 52.4 11 (22) Δ Corresponding Exam- to Example ple 2 Test 0.4 52.4 11 (22) Δ Corresponding Exam- to Example ple 3 Test 0.5 52.4 11 (22) Δ Corresponding Exam- to Example ple 4 Test 1.0 52.4 11 (22) X Corresponding Exam- to Comparative ple 5 Example *It should be noted that the numerical values in parentheses of the coating thickness indicate the total coating thickness of the conductive auxiliary coating agents of the two conductive members to be joined to each other.

(27) [Determination Criterion of Resistance Ratio] ⊚: The resistance ratio is less than 2, and conductivity is satisfactory. ∘: The resistance ratio is 2 or more and less than 2.5, and conductivity is sufficient. Δ: Although the resistance ratio is 2.5 or more and less than 3.0, and conductivity is slightly insufficient, there is no significant problem for use. x: The resistance ratio is 3.0 or more, and conductivity is insufficient.

(28) As shown in Table 1, it is understood that, in the conductive member according to Test Example 1 having a surface roughness Ra of 0.15 μm, the resistance ratio was less than 2, and thus satisfactory conductivity was obtained. Further, it is understood that, in each of the conductive members according to Test Examples 2 to 4 having a surface roughness Ra of more than 0.2 μm and 0.6 μm or less, the resistance ratio was less than 3.0, and thus sufficient conductivity was obtained. In contrast, it is understood that, in Test Example 5 having a surface roughness Ra of 1.0 μm corresponding to a Comparative Example, the resistance ratio was 3.0 or more, and thus sufficient conductivity was not obtained.

(29) [Confirmation Test of Contact Resistance based on Thickness of Conductive-auxiliary-coating-agent Layer]

(30) In order to confirm the effect of the thickness of a conductive-auxiliary-coating-agent layer on the contact resistance, the following test was conducted. An aluminum member having an oxide film formed on a surface was subjected to cold rolling processing so as to have a surface roughness Ra of 0.15 μm. After that, the resultant was subjected to cutting processing to prepare an aluminum conductive base material formed of a 6101-T6 aluminum (Al) material measuring 3 mm×50 mm×100 mm. Then, a conductive auxiliary coating agent (trade name “NIKKEI JOINTAL Z” manufactured by Shizuoka Kosan Co., Ltd.) was applied to a portion of the aluminum conductive base material corresponding to a joining region with respect to another conductive member (6101-T6 Al material), and the conductive auxiliary coating agent was rubbed with cotton waste to remove the surface oxide film. Then, the conductive auxiliary coating agent was again applied to the joining region to each thickness shown in Table 2 to obtain a conductive member. It should be noted that the surface roughness Ra after the surface oxide film was removed was 0.15 μm.

(31) Another conductive member (conductive member under the same condition) was joined to the obtained conductive member in the same way as above to obtain aluminum test pieces according to Test Examples 6 to 10. After that, a contact resistance ratio was measured under the same measurement conditions as above.

(32) TABLE-US-00002 TABLE 2 Coating thickness of Surface Contact conductive Resist- rough- surface auxiliary ance ness pressure coating ratio (μm) (kgf/cm.sup.2) agent (μm) (—) Remark Test 0.15 52.4 11 (22) ⊚ Corresponding Exam- to Example ple 6 Test 0.15 52.4 14 (28) ⊚ Corresponding Exam- to Example ple 7 Test 0.15 52.4 21 (42) ◯ Corresponding Exam- to Example ple 8 Test 0.15 52.4 33 (66) ◯ Corresponding Exam- to Example ple 9 Test 0.15 52.4  66 (132) Δ Corresponding Exam- to Example ple 10 *1 It should be noted that the numerical values in parentheses of the coating thickness indicate the total coating thickness of the conductive auxiliary coating agents of the two conductive members to be joined to each other. *2 The determination criterion of the resistance ratio is the same as that in the case of Table 1.

(33) As shown in Table 2, it is understood that, in each of the conductive members having a total coating thickness of the conductive auxiliary coating agents of 40 μm or less according to Test Examples 6 and 7, the resistance ratio was less than 2, and thus satisfactory conductivity was obtained. Further, it is understood that, in each of the conductive members having a total coating thickness of the conductive auxiliary coating agents of from 40 μm to 100 μm according to Test Examples 8 and 9, the resistance ratio was 2 or more and less than 2.5, and thus sufficient conductivity was obtained. Further, in the conductive member having a total coating thickness of the conductive auxiliary coating agents of 132 μm according to Test Example 10, although the resistance ratio was 2.5 or more and less than 3.0, and conductivity was slightly insufficient, there was no significant problem for use.

(34) [Confirmation Test of State and Conductivity of Conductive Auxiliary Coating Agent based on Protective Cover]

Test Example 11

(35) An aluminum member having an oxide film formed on a surface was subjected to cold rolling processing so as to have a surface roughness Ra of 0.15 μm. After that, the resultant was subjected to cutting processing to prepare an aluminum conductive base material formed of an A1050 aluminum (Al) material measuring 6 mm×50 mm×200 mm. Then, a conductive auxiliary coating agent (trade name “NIKKEI JOINTAL Z” manufactured by Shizuoka Kosan Co., Ltd.) was applied to a portion of the aluminum conductive base material corresponding to a joining region with respect to another conductive member (A1050 Al material), and the conductive auxiliary coating agent was rubbed with cotton waste to remove the surface oxide film. Then, the conductive auxiliary coating agent was again applied to the joining region to a thickness of 11 μm to obtain a conductive member. It should be noted that the surface roughness Ra after the surface oxide film was removed was 0.15 μm.

(36) Next, a release sheet (protective cover) formed of polyethylene terephthalate (PET) was bonded to a joining surface of the thus formed conductive-auxiliary-coating-agent layer so as to protect the joining surface, and thus a test piece (aluminum conductive member) was produced.

(37) After the obtained test piece was stored for a while, the release sheet was removed so as to check the state of the conductive-auxiliary-coating-agent layer. Consequently, the breakage and the adhesion of foreign matters were not recognized. Further, the conductivity of a joining section, which was joined to another conductive member (A1050 Al material) having a conductive auxiliary coating agent with a coating thickness of 11 μm applied thereto in the same way as above through bolt fastening, was checked with a tester, and a satisfactory passage of an electric current was confirmed. The results are shown together in Table 3.

Test Example 12

(38) An aluminum member having an oxide film formed on a surface was subjected to cold rolling processing so as to have a surface roughness Ra of 0.15 μm. After that, the resultant was subjected to cutting processing to prepare an aluminum conductive base material formed of an A6101 Al material measuring 6 mm×50 mm×200 mm. Then, a portion of the aluminum conductive base material corresponding to a joining region with respect to another conductive member (copper material) was subjected to grinding treatment with a grinder to remove the oxide film. A conductive auxiliary coating agent (trade name “NIKKEI JOINTAL Z” manufactured by Shizuoka Kosan Co., Ltd.) was applied to the portion from which the oxide film had been removed, and the conductive auxiliary coating agent was rubbed with cotton waste to remove the surface oxide film. Then, the conductive auxiliary coating agent was again applied to the joining region to a thickness of 11 μm to obtain a conductive member. It should be noted that the surface roughness Ra after the surface oxide film was removed was 0.15 μm.

(39) Next, a release sheet (protective cover) formed of an aluminum foil was bonded to a joining surface of the thus formed conductive-auxiliary-coating-agent layer so as to protect the joining surface, and thus a test piece (aluminum conductive member) was produced.

(40) After the obtained test piece was stored for a while, the release sheet was removed so as to check the state of the conductive-auxiliary-coating-agent layer. Consequently, the breakage and the adhesion of foreign matters were not recognized. Further, the conductivity of a joining section, which was joined to another conductive member (copper material) having a conductive auxiliary coating agent with a coating thickness of 11 μm applied thereto through bolt fastening, was checked with a tester, and a satisfactory passage of an electric current was confirmed. The results are shown together in Table 3.

Test Example 13

(41) A test piece (aluminum conductive member) according to Test Example 13 was produced in the same way as in Test Example 11 except that the thickness of a conductive-auxiliary-coating-agent layer to be formed was set to 44 μm. Then, in the same way as in Test Example 11, after the obtained test piece was stored for a while, the release sheet was removed so as to check the state of the conductive-auxiliary-coating-agent layer. Consequently, the breakage and the adhesion of foreign matters were not recognized. Further, in the same way as in Test Example 11, the conductivity of a joining section, which was joined to another conductive member (A1050 Al material) through bolt fastening, was checked with a tester, and a satisfactory passage of an electric current was confirmed. The results are shown together in Table 3.

(42) TABLE-US-00003 TABLE 3 Thickness of conductive- Method of auxiliary- Conductive base Another removing coating- Protective Conductivity material conductive member oxide film agent layer cover after joining Test A1050 A1050 Alkali 11 (22) PET sheet Satisfactory Example Al Al etching μm 11 Test A6101 Cu Grinding 11 (22) Al foil Satisfactory Example Al with μm 12 grinder Test A1050 A1050 Alkali 44 (88) PET sheet Satisfactory Example Al Al etching μm 13 *It should be noted that the numerical values in parentheses of the coating thickness indicate the total coating thickness of the conductive auxiliary coating agents of the two conductive members to be joined to each other.

REFERENCE SIGNS LIST

(43) 1 . . . conductive base material, 2 . . . conductive-auxiliary-coating-agent layer, 3 . . . release sheet (protective cover), 4 . . . bolt fastening hole, 5 . . . guarding sheet (protective cover), 6 . . . opening, 7 . . . bonded portion, 8 . . . guarding cover, 8a . . . covering section, 8b . . . locking section