JPH02282485A - Production of black zinc plated steel sheet - Google Patents

Abstract

PURPOSE:To obtain a black Zn plated steel sheet having superior blackness, satisfactory corrosion resistance and adhesion by blackening a Zn (alloy) plated steel sheet by chemical or electrolytic treatment with a chemical treating bath having a specified compsn., carrying out chromating by application and coating with a polymer coating film. CONSTITUTION:A steel sheet plated with Zn (alloy) by hot dip plating or other method is blackened by chemical or electrolytic treatment with a chemical treating bath contg. 2-100g/l metal ions of Ni, Fe or Co, 0.1-5g/l metal ions of Sb, Bi, Ag, Cu, Pb or Sn and >=1g/l (expressed in terms of fluorine) fluorine complex ions. Chromating by application with a chromating bath having 1/9-7/3 ratio of Cr<3+>/Cr<6+> and coating with a coating film of an org. polymer such as acrylic resin dispersed in water or an inorg. polymer such as a water soluble silicate compd. are then carried out. Borofluoride ions are preferably used as the fluorine complex ions.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing black galvanized steel sheets used for building materials, home appliances, and automobiles.

(Prior art) Black galvanized steel sheets were generally pre-coated steel sheets coated with black paint, but in recent years, inorganic galvanized steel sheets have been developed that overcome the drawbacks of painted steel sheets and have excellent weldability, scratch resistance, and fingerprint resistance. A black plated steel sheet with a black coating is used. These methods are obtained by etching a zinc alloy plated steel sheet containing nickel, cobalt, etc. with an oxidizing acid or by anodic electrolytic oxidation. These methods have the disadvantage of being limited to specific zinc alloy plating.

In particular, there is no technology available for blackening hot-dip galvanized steel sheets. The present invention is a technology for blackening zinc plating and zinc alloy plating at high speed. Prior art related to the present invention includes a method for forming a film on the surface of zinc or zinc alloy as disclosed in Japanese Patent Publication No. 52-22618, and Abstracts of the 74th Lecture Conference of the Metal Surface Technology Association (October 14, 1986). 16C-1) is a blackening treatment for electrogalvanized steel sheets. In both cases, a film is formed by bringing a zinc-based metal into contact with a chemical aqueous solution containing nickel ions and antimony ions. The former is not intended for obtaining black color, but the latter is for black electrogalvanizing.

(Problems 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 is a wide steel sheet used in all fields, and is required to have excellent performance. In particular, corrosion resistance, adhesion workability, and weldability are essential basic performances. In the conventional technology, this performance is in a contradictory relationship with the black appearance, and it is impossible to obtain a product that can be put to practical use. That is, in order to obtain a black appearance, it is necessary to increase the amount of reaction and the amount of nickel and antimony deposited. Due to displacement plating, the coating becomes loose and its adhesion deteriorates in proportion to the amount of deposited zinc due to dissolution of the lower layer of the deposited coating. In addition, since metals more responsible than zinc precipitate, even if coated with chromate and a thin film of resin, there is a potential difference between the zinc and the precipitated metal in a saltwater environment (for boat fishing, evaluation is carried out using the salt spray test specified by JIS-Z-2371). ), there is a problem that zinc selectively corrodes due to microcells and white rust occurs. therefore,
If a black film is intended, a high coating amount is required, so these two problems must be solved.

(Means for Solving the Problems) The present invention is a black-plated steel sheet in which the above-mentioned problems are solved by the method described below.

(1) Zinc or zinc alloy coated steel sheet with nickel, iron,
Contains 2 to 100 g/l of metal ions selected from cobalt, 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 fluorine complex ions as fluorine. Black zinc characterized by being chemically or electrolytically treated in a chemical conversion treatment bath, followed by coating chromate treatment with a Cr'/Cr' ratio of 1/9 to 7/3 and coating with an organic or inorganic polymer film. Method of manufacturing plated steel sheets.

(2) Nickel or zinc alloy coated steel sheet.

2-100g/metal ion selected from iron and cobalt
chemically in a chemical conversion bath containing an organic acid and a metal ion selected from antimony, bismuth, silver, copper, lead, and tin at 0.1 to 5 g/l and a fluorine complex ion at 1 g/f1 or more as fluorine. Or Cr3+/C after electrolytic treatment
A method for producing a black galvanized steel sheet, characterized by coating with a coating chromate treatment having an r6+ ratio of 1/9 to 7/3 and coating with an organic or inorganic polymer film.

It is.

(Function) In order to obtain a black-plated steel sheet with excellent adhesion and corrosion resistance, the present invention has a three-layer structure in which the steel sheet is blackened with a specific blackening treatment bath composition and then coated with a coated chromate and polymer film. Achieved. The coated steel sheets treated according to the present invention include hot dip galvanized and zinc alloy coated steel sheets, electrolytic zinc and zinc alloy coated steel sheets, thermal sprayed zinc and zinc alloy coated steel sheets, vacuum zinc and zinc alloy coated steel sheets. As for the type of alloy plating, zinc alloy plating containing aluminum, magnesium, iron, nickel, cobalt, copper, tin, etc. is possible, but the plating that is most effective in the method of the present invention is molten metal plating with a high basis weight. galvanized steel sheets, and aluminum/zinc alloy plated steel sheets. especially.

Excellent black coating can be obtained at high speed on hot-dip aluminum/zinc alloy coated steel sheets. below.

The blackening chemical conversion treatment bath will be described in detail.

The chemical conversion bath must contain two groups of metal ions.The 61st group contains one or more ions selected from nickel, cobalt, and iron, and the second group contains antimony. , bismuth, silver,
One or more metal ions selected from copper, lead, and tin. Zinc ions are present in the bath in a wide range of concentrations as dissolved ions of the ground treatment metal. Zinc plating is treated in a bath containing these metal ions with addition of ordinary inorganic acids or organic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid, acetic acid, citric acid, tartaric acid, and malic acid. Then, when the amount of precipitation is low, excellent adhesion and performance with less deterioration of corrosion resistance can be obtained.

However, it is used as a base coating for painting because of its uneven appearance and half-baked color tone.

As a result of various studies, the present inventors added fluorine complex ions to the above-mentioned two groups of metal ion treatment baths, deposited a coating with a high amount of coating in the chemical conversion treatment bath, and then immediately after blackening the coating, described below. By applying a chromate solution and drying it, and then coating it with a polymer compound and curing it by heating, we succeeded in obtaining a deposited coating with excellent adhesion and corrosion resistance and a high coating weight. As a fluorine complex ion, borofluoride ion (BF4
-) is the fluorine complex ion that gives the best results in terms of black appearance and adhesion. In addition, aluminum fluoride ion (Afl
F, →, zirconium fluoride ion (ZrF6''), titanium fluoride ion (TiFs''-)-fluorosilicate ion (SiFG2-). Fluorine complex ions have a pH buffering effect on the chemical conversion treatment bath, without having a proportional relationship with the concentration of the pH of the bath, which greatly contributes to etching, and the p)l of the chemical conversion treatment bath can be maintained stably even if the concentration is increased. Therefore, it always has a stable etching action and uniformly dissolves the plating surface. The conditions will be explained in detail below.

The concentration of the first metal ion group is 2 as metal ions.
~100 g/Q, preferably 5-20 g/l. If it is less than 2 g/2, the black appearance and especially the adhesion are poor. If it exceeds 100 g/l, the solubility will be exceeded and the zinc plating will not be sufficiently dissolved, making it difficult to obtain a black appearance. In addition, problems such as press marks and abrasions are likely to occur during production due to precipitation products. For these reasons, the most preferred range is 5 to 20 g/l. A black appearance cannot be obtained with the first metal ion group alone. Second
The concentration of metal ions of the group is between 0.1 and 5 g/l, preferably between 0.5 and 1 g/II. If it is less than 0.1 g/l, a black appearance cannot be obtained. Moreover, if it exceeds 5 g#l, the solubility is low, so that precipitation occurs and the entire chemical conversion treatment 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 fluorine complex ions is 1 g/Q or more in terms of fluorine. If it is less than Ig/Ω, the effect of the present invention is insufficient. There is no particular upper limit due to the above-mentioned characteristics, but it is limited by the solubility of the compound, the amount of corrosion of the plating, etc. In the case of borofluoride ions, a concentration of 20 g/l 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 polyhydric carboxylic acid that acts as a complex ion. Specifically, the former uses citric acid, tartaric acid, malic acid, etc., and the latter uses oxalic acid, phthalic acid, maleic acid, EDTA, etc.
It is Nato. These compounds prevent the precipitation of metal ions, especially eluted zinc, over a wide pH range, and act as pH buffers to make etching uniform. The concentration range of the present invention is 1 to 50 g/l.

If it is less than 1 g/l, the effect of the present invention is insufficient.

If it exceeds 50 g/l, the reaction rate will be low from the viewpoint of solubility and because a large amount of effective metal ions will be ionized into complex salts.

In addition to the above, boric acid, phosphoric acid, etc. can also be added as additives.

The pH of the chemical conversion treatment bath varies depending on the treatment method. In the present invention, chemical treatments such as spraying or dipping, and electrolytic treatments such as anodic electrolysis or alternating current electrolysis can be employed as the blackening treatment method. In the case of chemical treatment, the pH of the chemical conversion bath is 4 or less, preferably 1-3. The temperature of the bath is 20 to 80°C, and if the pH is 2 or higher, the temperature is 60°C.
A temperature higher than that is desirable. In the case of electrolytic treatment, the bath temperature is preferably 40 to 60°C.The pH of the chemical conversion treatment bath is adjusted with various acids and metal oxides, hydroxides, and carbonates.

It is desirable that the black film is mainly composed of hydrated oxides of the metals of the first group, and the metals of the second group are precipitated at a rate of 50 to 500 .mu./m@2 in terms of metal, and 5 to 50 .mu./.mu.d in terms of metal. In the present invention, the degree of blackness is enhanced by the applied chromate and polymer coating, which will be described below, so that a good black appearance can be obtained even if the degree of blackness is not sufficient with only the black chemical conversion treatment.

After the blackened plated steel sheet is washed with water, the chromate treatment is immediately applied. The chromate treatment of the present invention is a bake-hardening coating type chromate treatment.

The chromate film of the present invention passivates the black film and penetrates into the film to fix the black film.

The chromate treatment solution is a bath having a composition of partially reduced chromic acid, in which a part of the chromic acid (Cry) in the bath is reduced to trivalent chromium through reduction treatment. The reason for using an aqueous solution of partially reduced chromic acid is to make the chromate film colored to strengthen its blackness, and to improve its adhesion by impregnating and curing the underlying black layer.

The ratio of trivalent chromium (Cr”)/hexavalent chromium (Cr”) is 1
/9 to 7/3. In addition to chromic acid, the treatment bath can contain phosphoric acid, a fluorine compound, silica sol, and a water-soluble or water-dispersible resin.

After spraying the chromate treatment bath on the black-treated plating surface, apply 20 to 200 μ/Po in terms of chromium using an air knife, roll coating, electrostatic coating, etc., and then reach a plate temperature of 4.
Dry at o~120°C. For chromate treatment, the best results are likely to be obtained with the air knife method, which is applied at a low concentration.

The reason for this is that the chromate bath permeates into the black film and dries it, thereby strongly bonding the black film and suppressing the direct reaction between the polymer and the black film, which will be described later.

Although chromate treatment may be used as the final treatment, perfect quality can be obtained by further coating the film with an organic or inorganic polymer compound described below to a thickness of 0.2 to 3.0 μm. The organic polymer compound includes all organic resins, but the most preferred resins are water-dispersed acrylic resins, such as olefin acrylic acid copolymer, ethyleneimine acrylic acid copolymer, epoxy acrylic acid copolymer, and urethane acrylic acid. It is a clear paint made by combining copolymer resin or resin with fine particles such as silica sol or carbon black. These resins not only have excellent fingerprint resistance, corrosion resistance, and scratch resistance, but also can be cured at low temperatures. Examples of the inorganic polymer compound include water-soluble silicate compounds such as lithium silicate, potassium silicate, sodium silicate, ammonium silicate or ammonium carbonate zirconate, and condensed phosphoric acid compounds.

The coating method can be obtained by applying by existing methods such as roll coating, air knife, electrostatic coating, etc., and then heating the plate to an ultimate temperature of 80°C or higher, preferably 80 to 200°C.

Example 1 The surfaces of hot-dip galvanizing (GI) with a basis weight of 60 g/m and 5% aluminum-zinc hot alloy plating (AG) were blackened by spraying using the chemical conversion treatment bath and treatment conditions shown in Table 1. Afterwards, it was washed with water and immediately treated with trivalent chromium (Cr3+) at a concentration of 10 g/Q in terms of chromic acid.
After spraying a chromic acid aqueous solution with a hexavalent chromium (Cr”) ratio of 4/6, use an air knife to 50 μ/rt in terms of chromium.
(After coating, the board was heated for a short time with hot air to a temperature of 60'C. Next, an olefin acrylic resin paint with 20% silica sol dispersed in the resin was applied to a dry film thickness of 1 μm.
After coating, the plate was baked to a temperature of 120°C and then cooled with water to produce a black plated steel plate. The obtained steel plate was evaluated as follows.

(1) Appearance The brightness (L value: the lower the number, the blacker) was measured using a dichroic meter and the target was 20 or less.

(2) Corrosion resistance: Area ratio (%) of white rust generated after 72 hours of salt spray test according to JIS-Z-2371
was visually evaluated.

(3) Adhesion: After pressing the sample at 90 degrees between a punch and die with a tip diameter of 51Tll+, a peeling test was performed using adhesive tape, and the peeling area ratio (%)
was visually evaluated.

Sample Nα1 is aluminum/zinc alloy plating.
This is an example of the present invention in which a chromate and organic resin were coated after blackening by spraying with an acidic chemical conversion treatment bath of pH 1 containing fluorinated ions, antimony ions, and borofluoride ions. Good results were obtained in terms of appearance, corrosion resistance, and adhesion. Sample Nα2 is an example of the present invention in which hot-dip galvanizing and sample Nu3 are aluminum-zinc alloy plating compared under the same conditions. Sample Nn 3 obtained a uniform black appearance with a lower L value. Sample Nα4 with increased nickel ion concentration also obtained good performance. Sample Nα5 contains antimony at 0.5g/
Although the inventive example was lowered to 12, it was still good. Sample Nα6°7.8 was an example of the present invention in which the borofluoride ion concentration was changed, and a black appearance was obtained. Under the same spray conditions, the lower the concentration, the higher the brightness. Sample Ha 7 had a low borofluoride ion content and some white rust occurred. Sample Nα9, p
The quality is insufficient in the comparative example in which H was adjusted.

Moreover, sample Nα10 was an example in which antimony was excluded and no black appearance was obtained. Samples Nα11, 12, 13゜14 are examples of the present invention with different types of fluorine complex ions, and sample Nα15
is a comparative example using hydrogen fluoride ions. It had a slightly reddish appearance compared to borofluoride ion. The comparative example had insufficient corrosion resistance and adhesion.

Example 2 The surface of 5% aluminum/zinc hot alloy plating (AG) with a basis weight of 60 g/rrf was sprayed to blacken it using the chemical conversion treatment bath and treatment conditions shown in Table 2, and then washed with water.
Immediately after spraying a chromate treatment solution containing 10 g/Q of chromic acid and phosphoric acid with a trivalent chromium (Cr3”)/hexavalent chromium (crG + ) ratio of 476 at a concentration of Log/l in terms of chromic acid. It was reduced to 50 mg/m in terms of chromium using an air knife, and heated for a short time with hot air to a board temperature of 60°C.Next, a urethane acrylic resin paint containing 20% silica sol and 20% carbon black dispersed in the resin was applied. Dry coating thickness is 1μm
After coating, the plate was baked to a temperature of 120°C, and then cooled with water to produce a black plated steel plate. The obtained steel plate was evaluated as in Example 1.

Example 3 The surface of 5% aluminum/zinc hot alloy plating (AG) with a basis weight of 60 g/m was sprayed or electrolytically treated (current density 20
A/di for 3 seconds), then rinsed with water and immediately treated with trivalent chromium (Cr3")/ at a concentration of Log/l in terms of chromic acid.
After spraying a chromate treatment solution containing 10 g/l of chromic acid and phosphoric acid with a hexavalent chromium (Cr") ratio of 476, the solution was reduced to 50 mg/m in terms of chromium using an air knife, and the plate was heated with hot air at 60°C. was heated for a short period of time.
An olefin acrylic resin paint containing 20% silica sol dispersed in the resin was applied to a dry film thickness of 0.5 μm, baked to a board temperature of 120°C, and cooled with water to produce a black plated steel sheet. The obtained steel plate was evaluated as in Example 1.

Example 4 In the treatment process of sample Nα24 of Example 3, 20% silica sol was dispersed instead of the final resin, resulting in a film thickness of 0.3μ.
m lithium silicate (sample NQ32) - ammonium zirconate carbonate (sample N (133) condensed sodium phosphate (
Sample Nα34) An inorganic polymer film was applied and hardened by baking at a plate temperature of 150°C. All the samples had an L value of 20 or less, and black plated steel sheets with good corrosion resistance and adhesion were obtained. Also, sample N
Sample Nα35, in which α33 was coated with an inorganic polymer film containing 20% carbon black dispersed therein, exhibited a good appearance with an L value of 14.

Example 5 Electrogalvanizing with a basis weight of 50 g/m' (sample Nα36) and a basis weight of 50 g/m' under the conditions of sample Nα24 of Example 3
rd galvanized zinc alloy plating (sample Nα37)
A black plated steel sheet was created.

The former has an L value of 17 and the latter has a blackness of 20, and has excellent corrosion resistance.
A quality with excellent adhesion was obtained.

Example 6 After blackening under the conditions of sample Xα4 of Example 1, washing with water,
Immediately, the ratio of trivalent chromium (Cr”)/hexavalent chromium (Cr”) with a concentration of 10 g/Q in terms of chromic acid becomes 1.
79 (sample Nα38), 515 (sample Nα39), 7
After spraying an aqueous solution of chromic acid of /3 (sample Nα40), the plate was coated with an air knife at a rate of 50 μ/i in terms of chromium, and then heated with hot air to a plate temperature of 60° C. for a short time.

Subsequently, an olefin acrylic resin paint in which 20% of silica sol was dispersed in the resin was applied to a dry coating thickness of 1 μm, and the plate was baked to a temperature of 120° C. and cooled with water to produce a black plated steel sheet. Sample Nα38 had a slightly high L value of 21, sample Nn39 had good results, and sample Nα4o had corrosion resistance with 5% white rust. Adhesion was good in all cases.

(Effects of the Invention) According to the present invention, the problems of black steel plates that are blackened by conventional paints are solved, and steel plates that are blackened before processing can be used. The black color of hot-dip galvanized steel allows for new applications in the building materials sector. Molten aluminum/zinc alloy plating has excellent corrosion resistance, but because a stable oxide film is formed on the surface, chemical conversion treatment tends to be uneven.Fluorine is used to blacken molten aluminum/zinc alloy plated steel sheets. The advantage of the present invention, which uses a chemical conversion bath containing complex ions, is of practical importance. Since the present invention can be blackened if it is a zinc-based surface, aluminum plated wire,
Black color such as zinc alloy die-casting is also possible.

Claims (4)

[Claims] (1) Zinc or zinc alloy coated steel sheet with nickel, iron,
A chemical compound containing 2 to 100 g/l of metal ions selected from cobalt, 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 fluorine complex ions as fluorine. It is characterized by chemical or electrolytic treatment in a treatment bath, followed by coating chromate treatment with a Cr^3^+/Cr^6^+ ratio of 1/9 to 7/3 and coating with an organic or inorganic polymer film. A method for producing black galvanized steel sheet. (2) Zinc or zinc alloy coated steel sheet with nickel, iron,
2 to 100 g/l of metal ions selected from cobalt, 0.1 to 5 g/l of metal ions selected from antimony, bismuth, silver, copper, lead, and tin, 1 g/l or more of fluorine complex ions as fluorine, and organic After chemical or electrolytic treatment in a chemical conversion treatment bath containing acid, Cr^3^+/Cr^
6^+ A method for producing a black galvanized steel sheet, characterized by coating with a coating chromate treatment and an organic or inorganic polymer coating with a ratio of 1/9 to 7/3. (3) In claim (1), after a zinc or zinc alloy plated steel sheet is chemically or electrolytically treated in a chemical conversion bath containing 1 g/l or more of borofluoride ions as fluorine complex ions, Cr^3^+/ Cr^6^+ ratio is 1
A method for producing a black galvanized steel sheet, characterized by applying a coating chromate treatment of /9 to 7/3 and coating with an organic or inorganic polymer film. (4) In claim (2), after chemically or electrolytically treating a zinc or zinc alloy plated steel sheet in a chemical conversion bath containing 1 g/l or more of borofluoride ions as fluorine complex ions, Cr^3^+/ Cr^6^+ ratio is 1
A method for producing a black galvanized steel sheet, characterized by applying a coating chromate treatment of /9 to 7/3 and coating with an organic or inorganic polymer film.