JPH10158854A - Organic composite plated steel sheet excellent in conductivity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an org. composite plated steel sheet excellent in conductivity and corrosion resistance, mainly for such members as house appliances which is grounded for antistaticization. SOLUTION: A chromate coating film is provided on the surface of a zinc or zinc alloy-plated steel sheet as a first layer at >=10mg/m<2> , expressed in terms of Cr, and an org. coating film with polyaniline and dopant as the essential components is furnished thereon as a second layer at 0.5-5.0g/m<2> . One or >=2 kinds among general resin, wax and silica sol can be incorporated into the org. coating film by 70 parts in total to improve adhesion, lubricity, appearance, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an organic composite plated steel sheet having excellent conductivity. More specifically,
The present invention relates to an organic composite plated steel sheet having excellent grounding properties, which can be mainly used for home appliances and the like.

[0002]

2. Description of the Related Art Chromate treatment is widely used as a treatment for preventing white rust on a Zn-based plated steel sheet and as a coating base treatment. More recently, an organic composite steel sheet having an organic film formed on a chromate-treated layer has been widely used for the purpose of further improving the corrosion resistance of the chromate-treated steel sheet. By coating with an organic film, not only corrosion resistance is improved, but also unevenness is prevented by suppressing elution of Cr and fingerprint resistance is improved (for example, JP-A-63-69986). However, since such organic composite steel sheets have poor conductivity of the organic coating itself, it is necessary to improve conductivity as much as chromate material for parts that require antistatic such as computer parts. Is desired.

As an attempt to improve the conductivity of an organic composite steel sheet, for example, Japanese Unexamined Patent Publication No. 2-145774 discloses a method in which the roughness of the plating surface is controlled and a portion having a small film thickness is provided so as to provide a current-carrying point. Have been. However, although this method has improved conductivity, it is not sufficient when compared with a chromate material, and there is a fundamental problem that deterioration of corrosion resistance in a thin portion of the coating is inevitable. .

[0004] In order to impart conductivity without reducing the film thickness, it is conceivable to add a substance having conductivity to the organic coating or to apply a polymer having conductivity to the organic itself. In this case, there is a concern that the corrosion resistance may be deteriorated. That is, electrons can easily be transferred between an anode reaction (emission of electrons due to dissolution of a metal or the like) which is an elementary reaction of a corrosion reaction and a cathode reaction (reduction of oxygen or generation of hydrogen), which may promote corrosion. Because.

[0005]

SUMMARY OF THE INVENTION In view of the above, the present invention provides
An object of the present invention is to provide an organic composite plated steel sheet which is based on a zinc-based plated steel sheet, has excellent conductivity, and has good corrosion resistance, fingerprint resistance, and the like.

[0006]

Means for Solving the Problems The present inventors have conducted various studies on the above problems, and as a result, have performed a chromate treatment on a galvanized steel sheet, and further formed an organic film containing polyaniline and a dopant thereon. By doing so, it has been found that good conductivity can be imparted, and that the corrosion resistance is remarkably improved by the combined effect of the chromate and the organic film, and the present invention has been achieved.

That is, according to the present invention, a chromate film is formed as a first layer on the surface of a galvanized steel sheet, and a second layer is coated with 0.5 to 5 g of an organic film containing polyaniline and a dopant as essential components. / M ² coating, or furthermore, an organic coating containing at least one of general-purpose resin, wax and silica sol in addition to the essential components, and having a total solid content of 70 parts or less. The present invention provides an organic composite plated steel sheet having excellent conductivity.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The galvanized steel sheet according to the present invention is made of pure Zn or Zn-N
i, any of normal zinc alloy plated steel sheets such as Zn-Fe may be used. There is no particular requirement for the roughness of the original sheet.

It is essential to subject these plating surface layers to chromate treatment. The corrosion resistance is greatly improved by the chromate treatment. The chromate treatment includes a reaction type, a coating type, and an electrolytic type, and any of them can be used. However, what is characteristic of the present technology is that the corrosion resistance of the chromate itself after being combined with a polyaniline-based organic film, whether it is good or poor, is equally good. It is to become.

That is, the corrosion resistance of the chromate itself is not so important, and a treatment advantageous in other characteristics may be selected. Specifically, for example, a chromate treatment in which phosphoric acid and silica are combined (for example,
18751, JP-A-52-68036, etc.)
Has excellent corrosion resistance, but is not preferred because the conductivity is deteriorated by the presence of silica. Considering this point and the chromate appearance and operability, electrolytic chromate treatment (for example, Japanese Patent Publication No. Sho 47-44417).
However, although the corrosion resistance itself is inferior, it is optimal for use in the present invention.

The amount of attached chromate is 1 in terms of Cr.
0 mg / m ² or more is required. Below this, the corrosion resistance is insufficient. Even if the amount of Cr is increased, the corrosion resistance is not significantly improved. Therefore, an amount of about 10 to 50 mg / m ² is desirable.

For an organic film formed on the chromate treatment, the presence of polyaniline and a dopant is essential. As described above, the improvement in corrosion resistance due to the combined effect of the chromate treatment and the polyaniline-based organic film is not only due to the effect of physically protecting the chromate-treated layer by the organic film, but also due to the electrically active polyaniline film. It seems that the passivation film of the base has an effect of electrochemical protection.

The dopant used in the present invention is not particularly limited as long as it is a general electron-accepting dopant, but a protonic acid or a salt thereof is preferred because it is easy to handle. It is generally known that the conductivity of polyaniline changes depending on the characteristics of the dopant. However, from the viewpoint of the conductivity of a chromate material, which is the aim of the present invention, any dopant can be used to achieve the purpose. In the case where no dopant is present, conductivity does not appear, but there is a case where a substance serving as a dopant is inevitably mixed in the process of producing polyaniline, in which case it is not necessary to add a dopant. Needless to say.

As a method for preparing polyaniline, for example, as disclosed in JP-A-3-285953,
After the polymerization reaction, a polymer which has been dedoped and solubilized in a solvent can provide a uniform film, and is also preferable from the viewpoint of conductivity and corrosion resistance.

For the purpose of improving the organic film, a general polymer compound such as an epoxy resin, a urethane resin and an acrylic resin, a wax, and a silica sol can be mixed into the film. By mixing a general resin, a more uniform coating film having excellent corrosion resistance and appearance can be obtained. The physical properties (hardness etc.) of the film can be controlled by the resin to be added, and a film having the required characteristics can be obtained. The wax is polyethylene wax, Teflon wax or the like, and can be added for the purpose of improving the lubricity of the coating and improving the workability. Silica sol acts as a film thickening aid and is effective in improving the strength of the film.

Since these resins, waxes and silica sols are all non-conductive, when added in the present invention, the total amount of these must be 0 to 70 parts by solids. If it is further increased, conductivity cannot be imparted. When more importance is placed on conductivity, the range is preferably 0 to 50 parts.

The above polyaniline and dopant,
If necessary, a resin, a wax, and a silica sol are mixed with a solvent for dissolving them, applied on a chromate-treated steel sheet by means of roll coating, spraying, or the like, and baked under conditions in which the solvent is dried to form a film. I just need.
The thickness of the organic coating is desirably in the range of 0.5 to 5 g / m ² . If it is 0.5 g / m ² or less, the corrosion resistance is insufficient, and if it is 5 g / m ² or more, the workability deteriorates and the coloring with polyaniline becomes conspicuous.

The chromate / organic composite-treated plated steel sheet formed as described above exhibits excellent conductivity comparable to that of a chromate material, which cannot be achieved by a normal organic composite-plated steel sheet. It is suitable as a surface-treated steel sheet. Further, when compared with a normal chromate material, since it is covered with an organic film, the fingerprint resistance is good and the problem of elution of Cr does not occur. The corrosion resistance is also very good due to the combined effect of the chromate and the organic coating.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. 20g /
m ² Zn-plated steel sheet was used. The roughness of the original plate is R
max = 5.4 and PPI = 150. To form a chromate film to the plated steel sheet by cathodic electrolysis in CrO ₃ -SO ₄ ² system bath. Polyaniline was synthesized by the following method. 0.6 mol of aniline (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.) is dissolved in 1 liter (1 liter) of 1 M hydrochloric acid and kept at -3 ° C. Then, 1 L of 1 M hydrochloric acid in which 0.6 mol of ammonium persulfate is dissolved is slowly added dropwise with stirring at −3 ° C., followed by stirring. The precipitate is filtered off and water / acetone (1: 1)
After thoroughly washing with a solvent, the sample was undoped with 2M ammonia water, further washed with a water / acetone (1: 1) solvent, and dried. The polyaniline powder thus prepared and salicylic acid were dissolved in butyl cellosolve at a weight ratio of 2: 1 to obtain a base coating solution.

In this embodiment, the following evaluation methods are used unless otherwise specified. Conductivity (contact resistance): Two Cu cylinders (φ = 30 mm) with gold plating on the surface of a steel plate are placed at a distance of 5 cm, and a load of 20 g weight / cm ² is applied to each of them.
A V constant voltage was applied to measure the contact resistance. The results were shown in the following three stages. ；: 0.2 Ω or less in a stable state Δ: Intermediate of × ×: 2 Ω or more in a stable state Conductivity (interlayer resistance): According to the method of JISC2550. Bare corrosion resistance (SST): After sealing the edges and back of a 70 × 150 mm sample with tape, JISZ237
The evaluation was performed by the method of No. 1. The results were evaluated in terms of the time until the occurrence of 5% white rust, and represented by the following four levels. ；: 240 hours or more ；: 168 to 240 hours Δ; 72 to 168 hours ×: Less than 72 hours . The results are shown in the following three stages. ；; ΔE <1.0 Δ; 1 ≦ ΔE <2.0 ×; ΔE ≧ 2.0

Example 1 A base coating solution was applied by a roll coater onto a chromate-plated steel sheet having a Cr adhesion amount of 10 mg / m ² and dried at 100 ° C.
An organic coating of 5 g / m ² was deposited. As shown in Table 1, the conductivity, corrosion resistance, and fingerprint resistance were all good results. (Example 2) A base coating solution was applied by a roll coater on a chromate-plated steel sheet having a Cr adhesion amount of 40 mg / m ² , dried at 100 ° C., and an organic film of 1.5 g / m ² was adhered. . As shown in Table 1, the conductivity, corrosion resistance, and fingerprint resistance were all good results. (Example 3) In Example 2, an acrylic resin (Almatec manufactured by Mitsui Toatsu Chemicals, Inc.) was used as a base coating solution in a solid content of 30 parts by weight, and a silica sol (OSCAL15 manufactured by Catalyst Kasei Kogyo) was used.
32) was added in the same manner as in the case of adding 10 parts in terms of the solid part number. As shown in Table 1, the conductivity, corrosion resistance, and fingerprint resistance were all good results. In particular, a uniform and beautiful appearance was obtained as compared with Example 2.

Example 4 The procedure of Example 3 was repeated except that the amount of the organic coating was 0.5 g / m ² . As shown in Table 1, the conductivity, corrosion resistance, and fingerprint resistance were all good results. (Example 5) In Example 3, the adhesion amount of the organic film was changed to 5
The adjustment was performed in the same manner except that g / m ² was used. As shown in Table 1, the conductivity, corrosion resistance, and fingerprint resistance were all good results. (Example 6) In Example 2, 5 parts by weight of Teflon wax (Rublon LDW10D manufactured by Daikin Industries, Ltd.) and 40 parts by weight of a urethane resin (Oyster manufactured by Mitsui Toatsu Chemicals) were added to the base coating solution. And adjusted similarly. As shown in Table 1, the conductivity, corrosion resistance, and fingerprint resistance were all good results. In particular, the dynamic friction coefficient (50 ° C.) was improved from 0.5 in Example 2 to 0.1.

(Comparative Example 1) The same evaluation was performed only for a chromate-treated steel sheet having a Cr adhesion amount of 40 mg / m ² . As shown in Table 1, the corrosion resistance and the fingerprint resistance were significantly deteriorated as compared with the examples. (Comparative Example 2) Organic coating was performed in the same manner as in Example 1 on a plated steel sheet that had not been subjected to chromate treatment. As shown in Table 1, the corrosion resistance was significantly deteriorated as compared with Example 1. (Comparative Example 3) The acrylic resin of Example 3 was replaced with 60
Parts, and 20 parts of silica sol.
5 g / m ^{2 was} adjusted. As shown in Table 1, the conductivity was significantly deteriorated.

(Comparative Example 4) A chromate-treated steel sheet having an adhesion amount of Cr of 40 mg / m ² was prepared according to JP-A-63-69986 by polyethylene resin: acrylic resin: silica sol =
An aqueous solution adjusted to a solid content weight ratio of 100: 20: 20 was applied and dried to form an organic film of 1.5 g / m ² . As shown in Table 1, the conductivity and the corrosion resistance were inferior to those of this example. (Comparative Example 5) According to an original sheet roughness condition for ensuring conductivity of an organic composite steel sheet disclosed in JP-A-2-145774, a plated original sheet having a roughness of Rmax = 23.1 and a PPI of 210 was used. Except for this, an organic film of 1.5 g / m ² was formed in the same manner as in Comparative Example 4. As shown in Table 1, although the conductivity was slightly improved, the conductivity and the corrosion resistance were inferior to those of this example.

[0025]

[Table 1]

[0026]

As described above, the organic composite plated steel sheet according to the present invention has both excellent conductivity, corrosion resistance, fingerprint resistance, and the like, and is particularly suitable for home appliances requiring antistatic. It is suitable as a surface-treated steel sheet.

Claims (2)

[Claims] 1. A chromate coating as a first layer on a surface of a zinc or zinc alloy-plated steel sheet in an amount of 10 mg / hr in terms of Cr.
m ² or more, and an organic film containing polyaniline and a dopant as essential components is further provided as a second layer thereon.
An organic composite plated steel sheet having excellent conductivity, which is provided in an amount of 5 to 5 g / m ² . 2. The method according to claim 1, wherein one or more of a general-purpose resin, a wax, and a silica sol are contained in addition to the polyaniline and the dopant in the organic coating, and the total solid content is 70 parts or less. Organic composite plated steel sheet with excellent conductivity.