JP5000384B2 - Conductor roll for continuous electroplating equipment, continuous electroplating equipment for metal steel strip, electroplated metal steel strip, and surface-treated steel sheet - Google Patents

Description

  The present invention relates to a conductor roll for a continuous electroplating apparatus, a continuous electroplating apparatus for a metal steel strip, an electroplated metal steel strip, and a surface-treated steel sheet, and the conductor roll of the present invention is used in an electroplating process. Continuous electroplating that forms fine irregularities on the surface of the plating plate that becomes the surface-treated steel sheet, improves the conductivity of the surface-treated steel sheet that is the product, and achieves high levels of corrosion resistance, fingerprint resistance, and conductivity. The present invention relates to a conductor roll for an apparatus.

  A surface-treated steel sheet for exterior materials used in electronic devices such as home appliances and personal computers is required to have corrosion resistance and so-called fingerprint resistance in which fingerprint residue is not noticeable. In addition, the exterior surface-treated steel sheet is also required to have electrical conductivity on the surface of the steel sheet for energizing the ground terminal of the internal device to ensure grounding in order to stabilize the operation of the electronic device and to block noise (electromagnetic wave shielding). This is an important characteristic. Further, there is a case where conductivity for assembling the member by current welding such as spot welding or seam welding is required.

  In general, in order to improve corrosion resistance and fingerprint resistance, a coating made of an organic or inorganic component is applied to cover the surface-treated steel sheet, but since these coatings are often insulators, Are difficult to balance. Therefore, conventionally, in order to ensure the conductivity of the surface-treated steel sheet, a technique for appropriately controlling the coverage by the film has been found. For example, a technique for controlling the coverage of a metal surface with a film as in Patent Document 1, and a film with a specific thickness according to the roughness of the metal surface as in Patent Document 2, Patent Document 3, and Patent Document 4 Techniques for coating and the like are disclosed. Further, Patent Document 5 discloses a surface treatment that improves conductivity by forming a minute convex portion on the surface of a metal steel strip that is an original plate of a surface-treated steel sheet, and forming a corrosion-resistant film on the top of the convex portion. An invention for a steel sheet is disclosed.

  As for a conductor roll for continuous electroplating (also referred to as an energizing roll), for example, Patent Document 6 discloses an invention relating to a conductor roll provided with a groove for removing deposits on the surface of the conductor roll.

Japanese Unexamined Patent Publication No. 7-41961 Japanese Patent Laid-Open No. 10-16128 Japanese Patent Laid-Open No. 10-330954 JP 2002-363766 A JP 2005-139551 A Japanese Patent Laid-Open No. 10-88388

  According to the detailed examination of the inventor, in the surface-treated steel sheet used for the exterior of the electronic device described above, the fine uneven structure existing on the surface of the plating original plate before applying the corrosion-resistant coating is important for the expression of conductivity. is there. This fine concavo-convex structure is formed in the electroplating process due to micro variation in the deposition rate of the plating crystal, and the arrangement pitch of the concavo-convex is about 1 μm or less. As a result of careful study of the continuous electroplating process, the inventors have found the following.

  That is, when performing electroplating on the cold-rolled steel strip that is the original plate of the plated steel strip, a metal conductor roll is pressed against the cold-rolled original plate in order to apply a voltage to the cold-rolled steel strip. The surface of a normal conductor roll is a cylindrical surface. At this time, the pressing force by the conductor roll is applied to the surface of the cold rolled steel strip. Alternatively, friction is generated by rubbing the surface of the conductor roll and the cold-rolled steel strip. As a result, the fine concavo-convex structure formed by the plating crystal deposited on the surface of the cold rolled original plate is crushed and smoothed.

  That is, in the plated steel sheet by the conventional manufacturing apparatus and manufacturing method, the surface of the plated steel sheet is smoothed and the roughness is lowered. Therefore, the roughness described in Patent Documents 1 to 5 (the roughness of the plated original sheet before the corrosion-resistant coating is applied) Is difficult to obtain and does not have excellent conductive properties.

  In addition, when a conductor roll having a plurality of grooves described in Patent Document 6 is used, there is no contact between the conductor roll and the surface of the cold-rolled steel sheet immediately below the groove part, and plating formed on the surface of the cold-rolled steel strip Although the fine roughness due to crystals is not smoothed, the plating formation state differs between the groove part and non-groove part of the conductor roll, and there is a problem that a linear striped pattern is generated on the manufactured plated steel sheet and the appearance is impaired. is there.

  In the continuous electroplating process, the present invention smooths the fine plated crystal uneven structure by pressing the conductor roll, or smoothes the fine plated crystal uneven structure by friction between the surface of the cold rolled steel strip and the conductor roll surface. This is to prevent the change. By providing a method for producing an electroplated steel sheet that is formed in the electroplating process and maintains the fine roughness roughness due to the plated crystals, the electroplated steel sheet is coated with an anticorrosive film and has good conductivity after the so-called surface coating treatment. An object of the present invention is to provide a surface-treated steel sheet that has both excellent corrosion resistance, fingerprint resistance, and conductivity.

That is, the gist of the present invention is as follows.
(1) A conductor roll of a continuous electroplating apparatus metals steel strip, to the conductor roll surface having a small surface roughness than the surface roughness of the plating crystals precipitated on the surface of the metal steel strip, the conductor roll have a plurality of discrete recess each other with respect to the axial direction and the circumferential direction in both directions, the recess is defined by the following formula (I) with the opening area S and the circular constant π of depressions viewed portion circle equivalent diameter D being is at 10μm or 0.5mm or less, and is not less 5μm or more depths, and the total sum of the areas of the recess opening Ru 50% der less than 10% of the conductor roll surface area A conductor roll characterized by that.
D = √ (4 × S / π) (I)

Also,
( 2 ) A continuous electroplating device for a metal steel strip, characterized by having at least one conductor roll having a depression on the surface,
( 3 ) A continuous electroplating apparatus for metal steel strip, wherein one or more conductor rolls having depressions on the surface are used in order from the conductor roll of the last electroplating tank.

Moreover,
( 4 ) An electroplated metal steel strip, characterized by being manufactured using the above-described conductor roll, and
( 5 ) A surface-treated steel sheet having conductivity and corrosion resistance using the electroplated metal steel strip as an original sheet.

  By using the conductor roll of the present invention, it is possible to provide surface-treated metal materials and metal parts that are excellent in fingerprint resistance and corrosion resistance, and are excellent in grounding property and current-weldability when used in home appliances, particularly electronic devices. .

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  The relationship between the grounding property and the current-welding property required for a surface-treated metal material for an exterior casing of an electronic device such as a personal computer or an AV home appliance and the surface roughness of the surface-treated metal material will be described.

  In a personal computer casing or the like, electrical conductivity for grounding is often secured by contact between a metal material and a spring-type ground terminal. In addition, conductivity in welding by energization heating such as spot welding or seam welding is ensured by press contact between the metal material, the welding electrode, and the metal material.

  In this case, the requirement for ensuring the conductivity of the surface-treated metal material with a coating used for the application is that there is no insulating film on the surface of the metal material that contacts the ground terminal or the welding electrode, or the film on the surface of the surface-treated metal material. Is easily broken by contact with the ground terminal or electrode terminal. Therefore, in order to ensure conductivity, it is essential that the surface unevenness of the surface-treated metal material, which has many opportunities to contact the ground terminal, is not covered with a coating or the coating on the top of the projection is extremely thin. The more such convex portions exist per unit area of the steel sheet, the more advantageous is the expression of the conductivity.

  On the other hand, the requirements for improving the corrosion resistance of a metal material by coating with a coating are that the contact between the corrosive environment and the metal material is blocked, and that the rust preventive pigment contained in the coating is uniformly disposed on the metal surface. . The requirement for improving fingerprint resistance is to prevent the mixture of oil and corrosive components adhering to the fingertip from adhering to the metal surface or the coating itself, and to suppress discoloration when adhering, thereby making it inconspicuous. All of these are advantageous when the coating rate of the metal surface by the coating is high and the coating is thick.

  Therefore, appropriate roughness is formed on the surface of the original metal plate before the corrosion-resistant coating is applied, electrical conductivity is ensured by exposure from the local coating, and most of the steel sheet is covered with the corrosion-resistant coating. This is necessary for a surface-treated steel sheet that achieves a high level of compatible properties such as corrosion resistance or fingerprint resistance and conductivity.

  A film for corrosion resistance and fingerprint resistance is a method of forming a final film by adding a rust-preventive pigment to an organic resin or an inorganic solvent and applying it to the surface of the steel sheet, followed by heating and drying to volatilize and remove the solvent. It is common. At this time, due to the viscosity of the coating, if the surface roughness of the metal steel sheet is formed with fine irregularities having an arrangement pitch of irregularities of 1 μm or less, the coating cannot follow the fine irregularities. In the uneven convex part, a thin part of the film or a part where the apex of the convex part is exposed from the film is likely to be formed.

  The cold-rolled steel strip, which is the original sheet of the normal surface-treated steel sheet, is rolled with a so-called dull roll for the purpose of improving the luster and workability of the steel sheet, resulting in irregular irregularities with an average roughness Ra of about 1 μm on the surface. A pattern is formed. However, the roughness of the cold-rolled steel strip is not maintained as it is in the process of plating. The unevenness on the surface of the cold-rolled steel strip acts as a nucleus for forming the plating crystal, whereby the terrace-shaped convex structure 11 shown in FIG. 4 is formed on the surface of the steel strip after plating. According to the measurement results of the inventors, the size of the terrace-shaped convex portion 11 is about 10 to 100 μm in diameter, and the average height of the terrace-shaped convex portion 11 is about 1 to 5 μm. When a surface-treated steel plate is used for an exterior casing of an electronic device and a contact ground is formed by a spring-type terminal, a portion that comes into contact with the spring-type terminal is an upper surface portion of the terrace-like convex portion 11 having a convex structure. . Therefore, the roughness of the upper surface of the terrace-shaped convex portion 11 shown in FIG. 4 is particularly important in the surface roughness of the surface-treated steel sheet.

  In the electroplating process, in addition to the terrace-like macro convex structure 11, a fine concavo-convex structure 12 (FIG. 6) having a height of about 1 μm or less due to variation in the growth rate of the plating crystal is formed. That is, the surface of the electroplated steel sheet is formed by mixing two concavo-convex structures of a large convex structure having a diameter of 10 to 100 μm and a height of 1 to 5 μm and a micro concavo-convex structure having a height of 1 μm or less. The As described above, (1) the portion in contact with the ground terminal is the upper surface of the terrace-like macro convex portion. (2) If fine irregularities with an arrangement pitch of 1 μm or less are formed, the coating cannot follow the fine irregularities, and in the convex portions of the fine irregularities, the thin portion of the coating or the vicinity of the apex of the convex portion For the two reasons that a portion exposed from the film is likely to be formed, the fine uneven structure 12 formed by plating crystals formed on the upper surface of the terrace-shaped protrusion 11 becomes a portion of the surface-treated steel sheet that exhibits electrical conductivity. Proper placement on the steel sheet surface at an appropriate density is an important requirement for obtaining a surface-treated steel sheet having excellent conductivity.

  The inventors have discovered that in the continuous electroplating line, the plating crystal on the top surface of the terrace-like convex is smoothed, and the fine uneven structure necessary for obtaining conductivity disappears in the continuous electroplating line. did.

  A widely known apparatus for continuously electroplating the surface of a metal strip is a horizontal continuous electroplating cell as shown in FIG. The mechanism of plating in such a horizontal continuous electroplating cell is as follows.

  The cold-rolled steel strip 20 is guided and fed while the surface of the cold-rolled steel strip (metal strip) 20 is brought into contact with a plurality of conductor rolls 1 serving as cathodes arranged in a plating tank 21 filled with a plating solution 22. Let it run. In the illustrated example, one conductor roll 1 is arranged, and the metal strip 20 that has entered the left end of the plating tank 21 from above is guided by the left end transport roll 25 and turned to the horizontal right, After passing through the conductor roll 1, the direction is again changed by the right-side transport roll 25 and advanced upward.

  The backup roll 23 disposed on the lower surface side of the cold-rolled steel strip 20 facing the central conductor roll 1 presses the cold-rolled steel strip 20 against the central conductor roll 1 so that a good electrical property is obtained at the contact portion between the two. It is designed to ensure contact. Although no backup roll is arranged on the conductor rolls 1 at both ends, good electrical contact is ensured by the tension applied to the cold-rolled steel strip 20.

  Further, a plurality of pairs of electrode plates 24 serving as anodes are arranged facing both the upper and lower sides across the cold-rolled steel strip 20. A plating tank is formed by connecting an anode of a DC power source (not shown) to the electrode plate 24 and a cathode to the conductor roll 1, and applying an appropriate voltage to the electrode plate 24 and the cold-rolled steel strip 20. While the cold-rolled steel strip 20 passes through the inside 21, the surface is continuously plated. Further, it is generally performed to perform plating by arranging a plurality of plating tanks shown in FIG. A plurality of conductor rolls 1 may be arranged in one plating tank.

  In the electroplating method as described above, if a gap is generated between the conductor roll 1 and the cold-rolled steel strip 20, a spark is generated due to the voltage, so that a flaw is generated on the surface of the cold-rolled steel strip. The roll 1 is pressed against the cold-rolled steel strip 20 with an appropriate pressure. Therefore, when the conductor roll 1 is a normal conductor roll, in the continuous electroplating apparatus of FIG. 5, the fine concavo-convex structure of about 1 μm or less due to the plated crystal to be deposited on the surface of the cold rolled steel strip is crushed by the conductor roll. Will be smoothed. In addition, since the surface speeds of the conductor roll and the metal strip cannot be completely matched, the cold-rolled steel strip 20 passes through the plating tank 21 while rubbing against the surface of the conductor roll. Also at this time, the plated crystal is smoothed.

  In particular, in the crushing process of the plated crystal by the above-described conductor roll, the top of the above-mentioned macro terrace-shaped convex portion is highly likely to touch the conductor roll, and as a result, the fine uneven structure by the plated crystal on the terrace-shaped surface disappears. The surface becomes smooth (SEM cross-sectional photograph in FIG. 7).

  In this way, the surface of the plated steel strip formed by a continuous electroplating apparatus using a normal conductor roll has a terrace-like convex structure in a smooth state in which the fine uneven structure of the plated crystal is smoothed by crushing. Become. When a corrosion-resistant coating or fingerprint-resistant coating is applied to this plated steel strip, the upper surface portion of the terrace-shaped projection is smooth, so that exposure from the corrosion-resistant coating of the plated steel strip to ensure conductivity is unlikely to occur, and the conductive properties Will result in a bad surface-treated steel sheet.

  On the other hand, the conductor roll of this invention has the hollow 2 on the roll surface, as shown in FIG. In the present invention, as shown in FIG. 2, the opening shape of the recess itself may be (a) a circle, (b) a rectangle, (c) a triangle, or a more complex (d) a shape close to a polygon. The essence of the present invention is that the depressions 2 having an appropriate size (opening area) and depth are arranged at an appropriate number density on the surface of the conductor roll. Further, FIG. 2 shows a state in which the depressions 2 on the surface of the conductor roll are regularly arranged at an equal pitch. Of course, the depressions 2 do not have to be arranged in an orderly manner, and the number density suitable for the purpose of the present invention. It is sufficient if it is disposed on the surface of the conductor roll.

As an index representing the size of the depression on the surface of the conductor roll of the present invention, it is represented by the opening diameter D of the circular opening depression, and the opening diameter of the circular opening depression having the same area S is expressed as follows. Is defined as a circle equivalent diameter D as follows.

D = √ (4 × S / π) (I)

Therefore, when the opening areas of the depressions in FIGS. 2A to 2D are all the same So (mm ² ), the depression size is defined by D in the formula (I) and defined as the same depression. The

  Now, FIG. 3A shows a state of contact in the electroplating process of the cold rolled steel strip and the conductor roll having a depression on the surface of the present invention. The upper side represents the cross section of the conductor roll, and the lower side represents the cross section of the cold-rolled steel strip. The size of the recess on the surface of the conductor roll has an equivalent circle diameter of 10 μm or more, and the recess 2 on the surface of the conductor roll is larger than the terrace-shaped convex portion 11 formed on the plated steel plate surface 10. For this reason, in the electroplating process, the terrace-shaped convex portion 11 enters the recessed portion 2 of the conductor roll, and the upper surface of the terrace-shaped convex portion is not in direct contact with the conductor roll (A1, A2, A3 part). As a result, the fine concavo-convex structure 12 of the plated crystal formed on the upper surface of the terrace-shaped protrusion 11 remains on the surface of the plated steel sheet without being smoothed by the conductor roll (A1, surrounded by a dotted line in FIG. 3B). A2, A3 part). The fine concavo-convex structure of the plating crystal formed on the upper surface of the terrace-shaped convex part is formed by locally exposing the surface of the film or locally forming a thin part of the film when applying the corrosion resistance or anti-fingerprint film. It exhibits excellent conductivity as a surface-treated steel sheet after application of a corrosion-resistant or fingerprint-resistant film.

  On the other hand, B1 and B2 part of Fig.3 (a) show the states which parts other than the hollow part of a conductor roll are contacting with the cold-rolled steel strip. In this case, since the plating crystal deposited on the surface of the cold-rolled steel strip and the conductor roll are in direct contact with each other, the top surface of the terrace-like convex 11 is finely formed by the plating crystal as shown by B1 and B2 surrounded by a dotted line in FIG. The uneven structure is crushed and smoothed.

  In the present invention, the upper surface of the terrace-shaped convex portion 11 is plated by setting the area ratio of the depression 2 on the surface of the conductor roll (the ratio of the total area of all depression openings to the surface area of the conductor roll) to an appropriate value. It is possible to manufacture a plated steel sheet in which portions such as A1, A2, and A3 where the fine concavo-convex structure 12 of crystals is formed are present on the surface at an appropriate ratio. Then, the portions such as A1, A2, and A3 in FIG. 3B are such that after the corrosion-resistant coating is applied, the fine uneven structure 12 of the plated crystal is locally exposed from the coating as shown in the SEM image of FIG. It acts as a conduction point necessary for grounding, and improves the conductivity of the surface-treated steel sheet.

  In the present invention, the size of the recess has a circle equivalent diameter of 0.5 mm or less. Because the plating roughness just below the dent and the non-dent is different, if the diameter of the dent is larger than 0.5 mm, a mottled pattern that can be visually confirmed on the surface of the plated steel sheet will occur and the surface quality will be impaired. is there.

  In the present invention, the depth of the recess is 5 μm or more. The height of the terrace-shaped protrusion formed on the surface of the plated steel sheet is about 1 to 5 μm, and the depth of the recess is required to be 5 μm or more so that the upper surface of the terrace-shaped protrusion does not contact the recess bottom. If there is no contact with the bottom surface of the dent, the fine concavo-convex structure 12 formed by the plating crystal formed on the upper surface of the terrace-like convex portion 11 of the plated steel plate surface 10 is not crushed and smoothed.

  In this invention, the total area of the opening part of a hollow is 10% or more of the area of the conductor roll surface. The site | part used as the energization point of a surface treatment steel plate is a site | part in which the terrace-shaped convex part of the plating steel plate surface and the hollow of the roll surface corresponded in the plating process. These are dominated by stochastic factors. As a result of evaluating the conductivity of the surface-treated steel sheet using a conductor roll in which the inventors actually changed the area ratio of the depression opening, the total area of the depression portion was determined to be sufficient to obtain sufficient conductivity. It was necessary to be about 10% or more.

  Moreover, in this invention, when the total area of the dent opening part on the surface of a conductor roll is too large, the area of the site | part exposed from the corrosion-resistant film surface will become large by fine unevenness | corrugation, and corrosion resistance will deteriorate. According to the study by the inventors, in order not to deteriorate the corrosion resistance, it is desirable that the total area of the opening of the recess is 50% or less of the area of the surface of the conductor roll.

  In summary, the conductor roll surface is equivalent to (1) yen as a condition to prevent the appearance quality from being visually deteriorated and to prevent the fine irregularities due to the plating crystals on the plated steel plate surface from being smoothed by friction or pressing during the plating process. It is most effective that recesses having a diameter of 10 μm to 0.5 mm and (2) a depth of 5 μm or more are formed at a ratio of (3) 10% to 50% of the surface area of the conductor roll.

  In a normal continuous electroplating apparatus, the plating tank shown in FIG. 5 is installed in about 10 stages and electroplating is performed. In each plating tank, the thickness of the plating crystal is formed by about 0.2 μm, and finally a plating layer of about 2 to 3 μm is formed on the surface of the cold rolled steel strip. The roll of the present invention is intended to prevent the fine concavo-convex structure of the grown plating crystal from being crushed and smoothed by a conductor roll. Therefore, in the plating process in which a plurality of plating tanks as described above are arranged in series, if the last-stage conductor roll is the conductor roll with a recess according to the present invention, then the plated crystal is not crushed and a fine uneven structure is obtained. Is maintained.

  In addition, by using a plurality of conductor rolls of the present invention continuously from the last stage, the plating crystal fine uneven structure is not crushed during the growth of the plating crystal having a thickness of about 1 μm. A fine concavo-convex structure can be formed on the surface of the metal steel strip, which is effective in expressing the conductive properties of the surface-treated steel sheet as a product. Further, although FIG. 5 has been described with reference to a schematic view of a horizontal electroplating apparatus, it is clear that the same effect can be obtained even if the conductor roll of the present invention is used for the conductor roll of the vertical electroplating apparatus. It is.

  As a means for providing a concave portion on the surface of the conductor roll, for example, a method of performing fine recess processing by locally irradiating the surface of the conductor roll with a high energy beam such as a laser, a method of dissolving the surface of the conductor roll with a chemical after masking, etc. Is mentioned.

  In order to obtain a conductor roll having a depression according to the present invention, a fine hole was formed on the surface of the conductor roll using a pulse YAG laser device (a state of the roll surface is shown in FIG. 1C). As the conductor roll, a roll having the following three types of depressions was manufactured. C4 is a roll prepared for comparison, in which the number density of the provided surface depressions is outside the range of the present invention. C5 is a normal conductor roll prepared for comparison, which is not subjected to surface recessing by a laser.

Using the C1 to C5 conductor rolls in Table 1 above, electrogalvanizing was performed on the metal steel strip under the following conditions. For the galvanization, a horizontal continuous electroplating apparatus having 10 plating baths as shown in FIG. 5 was used. The average roughness Ra of the surface of the cold-rolled steel strip used as the original plate is 1.5 μm, and the thickness of the steel strip is 0.8 mm. The amount of zinc plating attached to the cold-rolled steel strip was 20 g / m ² . A corrosion resistant coating was applied to the electrogalvanized steel strip after the continuous electrogalvanization by a coater device. As the corrosion resistant coating, three types of coatings shown in Table 2 were applied. The coating thickness was 1 μm.

  The organic resin that is the corrosion-resistant coating component of the present invention is not particularly limited as long as it can act as a binder for particles, and any of water-soluble organic resins, emulsion-type organic resins, and solvent-based organic resins can be used. is there. For example, olefin resins, acrylic resins, ionomer resins, epoxy resins, urethane resins, polyester resins, phenol resins, vinyl acetate resins, fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride, or polystyrene And polyethersulfone, polyphenylene ether, polyphenyl sulfide, polyamideimide, cycloolefin polymer, liquid crystal polymer and the like. These may be used alone or in combination of two or more, or may be a copolymer (for example, ethylene- (meth) acrylic acid copolymer, (meth) acrylic acid- (meth) acrylic acid). Ester copolymer), modified with each other (for example, epoxy-modified urethane resin, acrylic-modified ionomer resin, etc.), or modified with another organic substance (for example, amine-modified epoxy resin) may be used. In this example, acrylic resin, polyester resin, and epoxy resin were used as the organic resin as shown in Table 2 below.

  The film thickness is calculated from the mass fraction and film specific gravity of silica sol contained as a pigment in the film by measuring the amount of Si detected from the film surface within a diameter of 35 mm by the fluorescent X-ray method. From the measurement result with CMA, the method described above was used.

  As evaluation items, fingerprint resistance, corrosion resistance as fog spray corrosion resistance, and conductivity as interlayer resistance and current weldability were investigated. Fingerprint resistance was evaluated by pressing a real finger against a surface-treated metal material for 3 seconds, and visually observing the degree of conspicuous fingerprint marks. Table 3 shows ○ when the fingerprint mark is not noticeable and can be put to practical use as a member of household appliances, and × (none in Table 3) shows that the fingerprint mark is noticeable and not suitable for use as a member of household appliances It was written in.

For the interlayer resistance value, the interlayer resistance value (Ω · cm ² ) was measured in accordance with JIS C 2550 for each surface-treated metal material.

  The current weldability was evaluated by a continuous weldability test by spot welding. An appropriate welding current range was determined, and the limit continuous welding spot number at a predetermined welding current value obtained from the result was determined. The appropriate current range was determined by the following procedure.

Plate assembly: Two sets of the same kind of surface-treated steel sheets shown in the examples Welding electrode: T-16D (Material symbol DHOM)
Pressure between electrodes: 1960N
Welding pattern: Pressurization start → Hold for 0.5 seconds → Apply predetermined current (0.2 seconds) → Release pressure

  When welding with the above pattern, the lowest current value that can ensure a nugget diameter of 4 mm or more is the lower limit current value, and the lowest current value that causes strong welding between the test piece and the electrode is the upper limit current value. The appropriate current range was set between.

  The limit continuous welding spot number is the upper limit of the continuous welding spot number that can secure the necessary nugget diameter, and was determined by the following procedure.

Plate assembly: Two sets of the same kind of surface-treated steel sheets shown in the examples. Welding electrode: Obara Corporation T-16D (material symbol DHOM)
Pressure between electrodes: 1960N
Welding pattern: Pressurization start → Hold for 0.5 seconds → Apply predetermined current (0.2 seconds) → Release pressure Welding current value: Intermediate value of the appropriate welding current range obtained previously (lower limit current value + upper limit current value) ) / 2

Under the welding conditions described above, the striking speed was 1 point / 3 seconds, and the maximum number of continuous striking points that ensured the diameter of the nugget formed on the test piece to be 4 mm or more was defined as the limit continuous welding striking number. The scoring indicators were as follows. In the case of a rating of 2, it is recognized that the electric current weldability is good.
Grade 2: The number of continuous hits is 500 points or more

Corrosion resistance was measured on the following criteria by performing salt spray on the flat plate of each surface-treated metal material according to JIS Z 2371, measuring the area ratio of white rust and red rust after 168 hours of salt spray. A rating of 3 or 4 is desirable for practical use as a member of home appliances.
Score 4: No rust generation Score 3: Although rust generation is observed, the area ratio is less than 5%. Score 2: The area ratio of rust generation is 5% or more and less than 20%. Score 1: The area ratio of rust generation is 20% or more.

  Table 3 shows the evaluation results of the inventive examples and comparative examples in the present invention.

Since the corrosion-resistant film was thickly applied, the scores of fingerprint resistance and corrosion resistance are all acceptable in Example 1 to Comparative Example 15. The interlayer resistance value is preferably 2.5 (Ω · cm ² ) or less in order to secure the ground by the spring contact, and the first to the fifth examples using the conductor roll of the present invention are preferred. No. 9 is 0.2 (Ω · cm ² ) or less, and shows good conductivity. On the other hand, the steel sheets of Comparative Example 10 to Comparative Example 15 have an interlayer resistance value of 5.0 (Ω · cm ² ) or more and lack of conductivity. Also, with respect to the current weldability, Examples 1 to 9 were good, but Comparative Examples 10 to 15 had poor weldability.

  FIG. 6A is an SEM image of the plated steel sheet of Example 1 in Table 3. On the upper surface of the terrace-like convex portion 11, a fine concavo-convex structure 12 made of a galvanized crystal of about 0.5 μm can be confirmed, and it can be seen that it is rough. FIG. 6B is a cross-sectional SEM image of the plated steel sheet of Example 1 as well, and the convex portions of the fine concavo-convex structure 12 on the top surface of the terrace-shaped convex portion are exposed from the film 13.

  FIG. 7A is an SEM image of the plated steel sheet of Comparative Example 10 in Table 3. Although the same terrace-like convex part 11 as the steel plate of Example 1 shown in FIG. 6 exists, it is smooth | blunted by the contact with a conductor roll on the upper surface, and is a smooth state. FIG.7 (b) is the cross-sectional SEM image of the plated steel plate of Example 10 similarly. The upper surface of the terrace-shaped convex portion is smooth, and is entirely covered with the corrosion-resistant film 13, and there is no exposed portion.

  As described in the above examples, according to the present invention, the plating crystal on the surface of the electroplated steel sheet, which is the original plate, of the surface-treated metal material for exteriors used in OA electronic devices and the like that are required to have both grounding properties and corrosion resistance such as personal computers The fine concavo-convex structure is not smoothed by crushing. As a result, as a surface-treated steel sheet after coating with a corrosion-resistant film, the convex portions of the fine concavo-convex structure by the plating crystal are locally exposed from the corrosion-resistant coating, or the corrosion-resistant coating near the top of the convex portion becomes very thin. Thus, in the spring-type ground terminal or the base mounting process of the electronic component, the metal portion of the plating original plate secures conduction as a ground point, resulting in a surface-treated steel sheet having excellent conductivity.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

(A) is a schematic diagram of the conductor roll for electroplating of this invention. (B) is an enlarged view of the surface of a conductor roll for electroplating of the present invention. (C) is an optical microscope image of the surface of a conductor roll for electroplating of the present invention. (A), (b), (c), (d) is an example of the pattern of the hollow of the surface of the conductor roll of this invention, respectively. It is a schematic diagram of the cross section showing the contact state of the conductor roll and plated steel strip of this invention. It is a SEM image of the terrace-shaped convex structure 11 formed on the steel strip surface after plating. It is the schematic of a continuous electroplating apparatus. (A) is the SEM image of the terrace-shaped convex part vicinity formed in the plated steel plate surface manufactured with the electroplating apparatus using the conductor roll of this invention. (B) is the cross-sectional SEM image of the terrace-shaped convex part vicinity formed in the plated steel plate surface manufactured with the electroplating apparatus using the conductor roll of this invention. (A) is a SEM image near the terrace-shaped convex part formed in the surface of the plated steel plate produced using the normal conductor roll of the conventional method. (B) is the cross-sectional SEM image of the terrace-shaped convex part vicinity formed on the plated steel plate surface produced using the normal conductor roll of the conventional method.

Explanation of symbols

1: It is a conductor roll of the present invention 2: It is a hollow part given to the surface of the conductor roll of the present invention 10: Plated steel plate surface 11: Terrace-shaped convex part formed on the surface of the plated steel plate 12: Formed on the surface of the plated steel plate 13: Corrosion-resistant coating 20: Cold rolled steel strip 21: Plating tank 22: Plating solution 23: Backup roll 24: Electrode 25: Transport roll

Claims (5)

A conductor roll of a continuous electroplating device for a metal steel strip,
A plurality of dents discrete from each other in both the axial direction and the circumferential direction of the conductor roll on the surface of the conductor roll having a surface roughness smaller than the surface roughness of the plating crystal deposited on the surface of the metal steel strip. Department have a,
The indented portion has an equivalent circle diameter D defined by the following formula (I) using the opening area S and the circumference ratio π of the indented portion, which is 10 μm or more and 0.5 mm or less, and a depth of 5 μm or more. , and the and total area sum of the recess opening and wherein less than 50% der Rukoto 10% or more conductor roll surface area, conductor rolls.
D = √ (4 × S / π) (I) A continuous electroplating apparatus for metal steel strip, comprising at least one conductor roll according to claim 1 . Conductor roll according to claim 1, to the conductor roll of the electroplating bath of the last stage, characterized in that it is used one or more sequentially continuous electroplating apparatus metals steel strip according to claim 2. An electroplated metal steel strip manufactured using the conductor roll according to claim 1 . A surface-treated steel sheet having conductivity and corrosion resistance, wherein the electroplated metal steel strip according to claim 4 is used as a base plate.