JP2816559B2 - Manufacturing method of black galvanized steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a black galvanized steel sheet used for building materials, home appliances, and automobiles.

(Prior art) Black-coated galvanized steel sheets are generally pre-coated steel sheets coated with black paint, but in recent years inorganic materials with excellent weldability, scratch resistance and fingerprint resistance that overcome the drawbacks of painted steel sheets. Black plated steel sheet having a black coating is used. These methods are obtained by etching a zinc alloy-plated steel sheet containing nickel, cobalt, or the like with an oxidizing acid or by anodic electrolytic oxidation. These methods have the disadvantage that they are limited to certain zinc alloy platings. In particular, there is no technology for blackening hot-dip coated steel sheets. The present invention is a technique for blackening zinc plating and zinc alloy plating at high speed. The prior art related to the present invention includes a method of forming a coating on the surface of zinc or a zinc alloy disclosed in Published Japanese Patent Application No. 52-22618, and a summary of the 74th Annual Meeting of the Metal Surface Technology Association (October 14, 1986). There is a blackening treatment of the electrogalvanized steel sheet of 16C-1). In any case, a chemical conversion aqueous solution containing nickel-ion and antimony ions is brought into contact with a zinc-based metal to form a coating. The former is not for the purpose of obtaining a black color, but the latter is for the purpose of black electrogalvanizing.

(Problem to be Solved by the Invention) By using the latter conventional technique described above, a black film is deposited. However, the black-plated steel sheet required by the present invention and the like is a wide-width steel sheet used in all fields, and is required to have excellent performance. In particular, corrosion resistance, adhesion workability, and weldability are essential performances that are indispensable.
With conventional technology, this performance is contrary to the black appearance,
You can't get anything for practical use. That is, in order to obtain a black appearance, it is necessary to increase the reaction amount and increase the amount of nickel and antimony deposited. Because of the displacement plating, the coating is loosened due to the dissolution of zinc in the lower layer of the deposited coating in proportion to the amount of deposition, and the adhesion is deteriorated. In addition, even if the chromate and the resin of the thin film are coated because a metal precious than zinc precipitates, the salt water environment (generally evaluated by the salt spray test specified in JIS-Z-2371) because of the potential difference between zinc and the deposited metal ) Has a problem that zinc is selectively corroded by the microcell and white rust is generated. Therefore, if a black coating is intended, a high adhesion amount is required, and these two problems must be solved.

(Means for Solving the Problems) The present invention is a black-plated steel sheet which solves the above-mentioned problems by the following method.

(1) Nickel, iron,
Metal ions selected from cobalt are 2 to 100 g / l and metal ions selected from antimony, bismuth, silver, copper, lead and tin are 0.1 to 5 g / l, and borofluoride ions as fluorine complex ions are 1 g / fluorine ions. chemical in the chemical treatment bath containing more than l, or electrolytic treatment was then Cr ³⁺ / Cr ⁶⁺ ratio 1/9
A method for producing a black galvanized steel sheet, comprising applying a chromate treatment of about 7/3 and coating an organic or inorganic polymer film.

(2) Nickel, iron,
Metal ions selected from cobalt are 2 to 100 g / l and metal ions selected from antimony, bismuth, silver, copper, lead and tin are 0.1 to 5 g / l, and borofluoride ions as fluorine complex ions are 1 g / fluorine ions. l ^{3 +} / C after chemical or electrolytic treatment in a chemical conversion bath containing organic acid
a method for producing a black galvanized steel sheet, characterized by coating chromate treatment with an r ⁶⁺ ratio of 1/9 to 7/3 and coating an organic or inorganic polymer film.

(Function) In the present invention, in order to obtain a black-plated steel sheet having excellent adhesion and corrosion resistance, the blackened steel sheet is blackened with a specific blackening treatment bath composition, and then has a three-layer structure in which a coating chromate and a polymer film are coated. Achieved. The coated steel sheets treated according to the present invention include hot-dip galvanized and zinc alloy coated steel sheets, electric zinc and zinc alloy coated steel sheets, sprayed zinc and zinc alloy plated steel sheets, vacuum zinc and zinc alloy coated steel sheets. As the type of alloy plating, zinc alloy plating containing aluminum, magnesium, iron, nickel, cobalt, copper, tin, etc. is possible, but the most effective plating by the method of the present invention is a high melting weight plating system. And aluminum-zinc alloy-plated steel sheet. In particular, an excellent black coating can be obtained at a high speed on a hot-dip aluminum / zinc alloy-plated steel sheet. Hereinafter, the blackening chemical treatment bath will be described in detail.

It is necessary for a chemical conversion bath to contain two groups of metal ions. The first group is nickel,
One or more ion sources selected from cobalt and iron; the second group is antimony, bismuth,
One or more metal ions selected from silver, copper, lead, and tin. In addition, zinc ions as dissolved ions of the metal to be treated are present in the bath in a wide range of concentrations. Zinc plating is treated in a bath containing a normal inorganic acid or organic acid such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid, acetic acid, citric acid, tartaric acid or malic acid in a bath containing these metal ions. Then, when the deposition amount is low, excellent adhesion and performance with little deterioration of corrosion resistance can be obtained. However, it is used as a base coat for painting because of a half-tone non-uniform appearance.

As a result of various studies, the inventors of the present invention have found that a high-adhesion coating film is deposited and blackened in a chemical conversion bath obtained by adding a fluorine complex ion to the above-mentioned two groups of metal ion treatment baths, and immediately thereafter, a chromate treatment described later is performed. The solution was applied and dried, and then a polymer compound was coated and cured by heating. As a result, a deposited film having a high adhesion amount and excellent adhesion and corrosion resistance was successfully obtained. Boron fluoride ions (B
F ₄ ⁻ ) is a fluorine complex ion that gives the best results in black appearance and adhesion. Other fluorine complex ions useful in the present invention include aluminum fluoride ion (AlF ₄
^-), zirconium fluoride ion (ZrF ₆ ^2-), titanium fluoride ion (TiF ₆ ^2-), there is a fluorosilicate ions (SiF ₆ ^2-). Fluorine complex ions have a pH buffering effect on the chemical conversion bath, not in proportion to the concentration of the solution, which greatly contributes to the etching.The pH of the chemical conversion bath can be maintained stably even when the concentration is high. Stable etching action and uniformly dissolves plating surface. Hereinafter, the conditions will be described in detail.

The concentration of the first metal ion group is 2 to 100 g /, preferably 5 to 20 g / as metal ions. If it is less than 2 g /, the black appearance and particularly the adhesion are poor. 100g /
If the content is more than the solubility, the dissolution of zinc plating becomes insufficient because of exceeding the solubility, so that it is difficult to obtain a black appearance. In addition, problems such as easy generation of scratches due to pushing during production due to the precipitation product are likely to occur. For these reasons, 5 to 20 g / is the most preferable range. A black appearance cannot be obtained with only the first metal ion group. The concentration of metal ions in the second group is 0.
It is 1-5 g / preferably 0.5-1 g /. If it is less than 0.1 g /, a black appearance cannot be obtained. On the other hand, if it is more than 5 g / ml, the solubility is low, so that precipitation occurs and the entire chemical conversion bath becomes cloudy. These metal ions can be added in the form of sulfates, chlorides, nitrates, carbonates, oxides, hydroxides, phosphates, sulfamate organic acid salts.

The concentration of the fluorinated complex ion is 1 g / or more in terms of fluorine. If it is less than 1 g /, the effect of the present invention is insufficient. The upper limit is not particularly limited from the above-mentioned characteristics, but is limited by the solubility of the compound, the amount of corrosion of the plating, and the like. In the case of borofluoride ions, a concentration of 20 g / or less is preferred.

In the present invention, excellent effects can be obtained by adding an organic acid in addition to the above components. The organic acid is preferably an oxycarboxylic acid or a polyvalent carboxylic acid acting as a complex salt ion.
Specifically, the former includes citric acid, tartaric acid, malic acid and the like, and the latter includes oxalic acid, phthalic acid, maleic acid, EDTA and the like. These compounds have an effect of preventing precipitation of metal ions, particularly zinc eluted in a wide pH range, as well as pH buffering agents and uniform etching. As the concentration, 1 to 50 g / is within the range of the present invention. If it is less than 1 g /, the effect of the present invention is insufficient. If the amount is more than 50 g / mol, complex metal ionization of effective metal ions is required in view of solubility and the reaction rate is reduced.

In addition to the above, boric acid, phosphoric acid and the like can be added as additives.

The pH of the chemical conversion bath varies depending on the treatment method. In the present invention, a chemical treatment such as spraying or immersion, and an electrolytic treatment of anodic electrolysis or alternating current can be adopted as the blackening method. In the case of chemical treatment,
The pH is 4 or less, preferably 1-3. The temperature of the bath is 20 to 80 ° C, and when the pH is 2 or more, the temperature is preferably 60 ° C or more. In the case of electrolytic treatment, the bath temperature is 40-60
C is preferred. The pH of the chemical conversion bath is adjusted with various acids and metal oxides, hydroxides and carbonates.

Black coating metal 50 to 500 mg / m ² the second group based on metal conversion hydrated oxide is the main component of the first group metal is preferably be 5 to 50 mg / m ² deposited on metal conversion. In the present invention, since the blackness is enhanced by the coating chromate and the polymer coating described below, there is a feature that a good black appearance can be obtained even if the blackness is not sufficient only by the black chemical conversion treatment.

The blackened treated plated steel sheet is immediately subjected to chromate treatment after washing with water. The chromate treatment of the present invention is a bake-hardening coating chromate. The chromate coatings of the present invention passivate the black coating and penetrate into the coating to immobilize the black coating.

The chromate treatment liquid is a bath having a configuration of partially reduced chromic acid in which a part of chromic acid (CrO ₃ ) in the bath is reduced to trivalent chromium by a reduction treatment in advance. The reason for using the aqueous solution of partially reduced chromic acid is to enhance the degree of blackness by coloring the chromate film, and to improve the adhesion by impregnating and curing the lower black layer. The ratio of trivalent chromium (Cr ³⁺ ) / hexavalent chromium (Cr ⁶⁺ )
1/9 to 7/3. The treatment bath may contain phosphoric acid, a fluorine compound, a silica sol, and a water-soluble or water-dispersible resin in addition to chromic acid. After spraying the chromate treatment bath on the black plating surface, air knife, roll coat,
After applying 20 to 200 mg / m ^{2 in} terms of chromium by electrostatic coating or the like, the coating is dried at 40 to 120 ° C. as the ultimate plate temperature. As a chromate treatment, a coating obtained by an air knife method of applying a low concentration is most likely to obtain the best results.

The reason is that the chromate bath penetrates into the black coating and is dried, so that the black coating is firmly bonded and a direct reaction between the polymer and the black coating described later is suppressed.

Although the chromate treatment may be the final treatment,
Perfect quality can be obtained by coating a film of an organic or inorganic polymer compound described below with a film thickness of 02 to 3.0 μm. The organic polymer compound includes all organic resins, but the most preferred resin is an aqueous acrylic resin such as olefin acrylic acid copolymer, ethylene imine acrylic acid copolymer, epoxy acrylic acid copolymer, urethane acrylic acid. This is a clear coating in which a resin of a copolymer or a resin is combined with fine particles such as silica sol and carbon black. These resins are not only excellent in fingerprint resistance, corrosion resistance and scratch resistance but also can be cured at low temperatures. As an inorganic polymer compound, a water-soluble silicate compound such as lithium silicate, potassium silicate,
These are sodium silicate, ammonium silicate or ammonium zirconate carbonate, and condensed phosphate compounds.

The coating method can be obtained by applying by a conventional method such as roll coating, air knife, electrostatic coating, etc., and then heating to a plate temperature of at least 80 ° C or more, preferably 80 to 200 ° C.

Example 1 The surfaces of hot-dip galvanized (GI) and 5% aluminum-zinc hot-dip alloy (AG) having a basis weight of 60 g / m ² were sprayed and blackened by a chemical treatment bath and treatment conditions shown in Table 1. After washing with water, the ratio of trivalent chromium (Cr ³⁺ ) / hexavalent chromium (Cr ⁶⁺ ) at a concentration of 10 g / chromic acid is immediately 4/6.
After spraying with a chromic acid aqueous solution, 50 mg / m ^{2 in} terms of chromium was applied using an air knife, and the plate temperature was briefly heated to 60 ° C. with hot air. Subsequently, silica sol was added to the resin at 20%
The dispersed olefin acrylic resin paint was applied at a dry film thickness of 1 μm, baked at a sheet temperature of 120 ° C., and then cooled with water to produce a black plated steel sheet. The obtained steel sheet was evaluated as follows.

(1) Appearance: The lightness (L value: the lower the number, the blacker) was measured with a color difference meter, and the target was 20 or less.

(2) Corrosion resistance: A salt spray test specified in JIS-Z-2371 was conducted for 72 hours, and the area ratio (%) of white rust generated was visually evaluated.

(3) Adhesion: The sample was sandwiched between a punch and a die having a diameter of 5 mm at the tip and pressed at 90 °. After that, a peeling test was performed with an adhesive tape, and the peeling area ratio (%) was visually evaluated.

Sample No. 1 is an example of the present invention in which aluminum-zinc alloy plating was blackened by spraying in an acidic chemical conversion treatment bath containing nickel ions, antimony ions and borofluoride ions at pH 1 and then coated with chromate and an organic resin.
Good results were obtained in appearance, corrosion resistance and adhesion. Sample N
Sample No. 3 is an example of the present invention in which hot-dip galvanizing is applied to sample No. 3 and aluminum-zinc alloy plating is compared under the same conditions. sample
No. 3 obtained a uniform black appearance with a lower L value. Sample No. 4 with an increased nickel ion concentration also obtained good performance. Sample No. 5 was an example of the present invention in which antimony was reduced to 0.5 g /, but was good. Samples Nos. 6, 7, and 8 had a black appearance in the examples of the present invention in which the borofluoride ion concentration was changed. Under the same spray conditions, the lower the density, the higher the brightness. Sample No.7
Had low borofluoride ion and slightly white rust occurred. Sample N
o.9 is a comparative example in which the pH was adjusted with hydrochloric acid, and the quality was insufficient. Sample No. 10 had no black appearance in the case where antimony was removed. Samples Nos. 11, 12, 13, and 14 are examples of the present invention in which the type of fluorine complex ion was changed, and sample No. 15 is a comparative example using hydrogen fluoride ions. Appeared slightly reddish in comparison to borofluoride ions. Comparative examples were insufficient in corrosion resistance and adhesion.

Example 2 A surface of a 5% aluminum-zinc hot-dip alloy (AG) having a basis weight of 60 g / m ² was sprayed and blackened by a chemical conversion bath and processing conditions shown in Table 2 and then washed with water and immediately chromium-containing. Chromic acid and phosphoric acid with a ratio of trivalent chromium (Cr ³⁺ ) / hexavalent chromium (Cr ⁶⁺ ) of 4 g at a concentration of 10 g / acid as ^1/6
Aperture 50 mg / m ² in terms of chromium and 0 g / including chromating liquid by a spray coating after air knife, sheet temperature in the hot air to 6
Heated briefly to 0 ° C. Subsequently, a urethane acrylic resin coating material in which silica sol was dispersed in 20% of the resin and carbon black in a concentration of 20% was applied in a dry film thickness of 1 μm, baked at a sheet temperature of 120 ° C., and cooled with water to produce a black plated steel sheet. The obtained steel sheet was evaluated as in Example 1.

Example 3 Spraying or electrolytic treatment (at a current density of 20 A / dm ² for 3 seconds) on the surface of a 5% aluminum-zinc hot-dip alloy plating (AG) with a basis weight of 60 g / m ² under the chemical conversion bath and treatment conditions shown in Table 3. ) And then washed with water. Immediately, the ratio of trivalent chromium (Cr ³⁺ ) / hexavalent chromium (Cr ⁶⁺ ) at a concentration of 10 g / chromic acid
Spray a chromate treatment solution containing 4 g of chromic acid and phosphoric acid at a rate of 10 g /
mg / m ^2, and the plate temperature was briefly heated to 60 ° C. with hot air.
Subsequently, an olefin acrylic resin paint in which silica sol was dispersed by 20% with respect to the resin was applied in a thickness of 0.5 μm on a dry film basis, baked at a sheet temperature of 120 ° C., and cooled with water to produce a black plated steel sheet. The obtained steel sheet was evaluated as in Example 1.

Example 4 In the treatment process of Sample No. 24 of Example 3, instead of the last resin, silica sol was dispersed by 20%, and lithium silicate having a thickness of 0.3 μm (Sample No. 32) and ammonium zirconate carbonate (Sample No. 24) were used. 33) Condensed sodium phosphate (Sample No. 34)
An inorganic polymer coating was applied and baked and cured at a plate temperature of 150 ° C. All samples had L values of 20 or less, and obtained black plated steel sheets having good corrosion resistance and adhesion. In addition, sample No. 33 was coated with an inorganic polymer film in which carbon black was dispersed by 20%.
o.35 showed a good appearance with an L value of 14.

Example 5 Under the conditions of Sample No. 24 of Example 3, electrogalvanized with a basis weight of 50 g / m ² (Sample No. 36) and galvanized zinc alloy plated with a basis weight of 50 g / m ² (Sample No. 37) After processing, a black plated steel sheet was prepared. The former had an L value of 17 and the latter had a blackness of 20, which was excellent in corrosion resistance and adhesion.

Example 6 After being blackened under the conditions of sample No. 4 of Example 1, it was washed with water,
Immediately, the concentration of trivalent chromium (Cr
³⁺ ) / hexavalent chromium (Cr ⁶⁺ ) ratio is 1/9 (Sample No. 38), 5 /
After spraying 5 (Sample No. 39) and 7/3 (Sample No. 40) chromic acid aqueous solution, apply 50 mg / m ^{2 in} chrome equivalent with an air knife and then heat to a plate temperature of 60 ° C. for a short time with hot air. . continue,
An olefin acrylic resin paint in which silica sol was dispersed in 20% with respect to the resin was applied at a dry film thickness of 1 μm, baked at a sheet temperature of 120 ° C., and cooled with water to produce a black plated steel sheet. Sample No. 38 had a slightly higher L value of 21 and Sample No. 39
Indicates that the sample No. 40 has corrosion resistance and 5% of white rust is generated. The adhesion was all good.

(Effect of the Invention) According to the present invention, the problem of the black steel plate blackened by the conventional paint is solved, and a blackened steel plate before processing can be used. The black color of the hot-dip coated steel sheet enables new use in the building materials sector. Hot-dip aluminum / zinc alloy plating has excellent corrosion resistance, but a stable oxide film is formed on the surface, which tends to cause non-uniform chemical conversion treatment. It is practically important that the present invention using a chemical conversion bath containing The present invention can be blackened as long as it is a zinc-based surface,
Black color such as zinc alloy die cast is also possible.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) C23C 22/00-22/86 C23C 28/00 B05D 3/10 C25D 11/34 303

Claims (2)

(57) [Claims] 1. A zinc or zinc alloy plated steel sheet is selected from nickel, iron and cobalt by 2 to 100 g / l.
Chemical or electrolysis in a chemical conversion bath containing 0.1 to 5 g / l of metal ions selected from antimony, bismuth, silver, copper, lead, and tin, and 1 g / l or more of borofluoride ions as fluorine complex ions as fluorine ions Cr ³⁺ / Cr after processing
^A method for producing a black galvanized steel sheet, characterized by coating chromate treatment with a ⁶⁺ ratio of 1/9 to 7/3 and coating an organic or inorganic polymer film. 2. A zinc or zinc alloy-plated steel sheet is coated with metal ions selected from nickel, iron and cobalt in an amount of 2 to 100 g / l.
0.1 to 5 g / l of metal ions selected from antimony, bismuth, silver, copper, lead, and tin, and 1 g / l or more of borofluoride ions as fluoride ions as fluorine complex ions, and chemically treated in a chemical treatment bath containing an organic acid. A method for producing a black galvanized steel sheet, comprising subjecting to electrolytic or electrolytic treatment and then applying a coating chromate treatment with a Cr ³⁺ / Cr ⁶⁺ ratio of 1/9 to 7/3 and coating an organic or inorganic polymer film. .