JPH0995789A - Organic coated zinc-chromium-ferrous element-alumina plated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an organic coated zinc-chromium-ferrous element-alumina plated steel sheet capable of producing with reduced equipment at a low cost and having corrosion resistance and adhesion in addition for coating material. SOLUTION: This steel sheet has a compsn. contg., by weight, 0.1 to 14% chromium, 0.01 to 3% ferrous elements and alumina by 0.01 to 1 % expressed in terms of aluminum, and the balance zinc with inevitable impurities and has a dispersed plating layer of 5 to 30g/m<2> . The upper layer of the above dispersed plating layer is provided with an organic film formed by electrolytic polymerization by 0.01 to 3g/m<2> to obtain the objective organic coated zinc-chromium- ferrous elementalumina composite dispersed plated steel sheet.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an organic coated zinc-chromium-iron group element-alumina composite dispersion-plated steel sheet,
In particular, an organic coating zinc-chromium-iron group element-which has both corrosion resistance and paint adhesion, can be manufactured with less equipment and cost lower than conventional methods, and is mainly suitable as a steel sheet for automobile bodies- Alumina composite dispersion-plated steel sheet.

[0002]

2. Description of the Related Art In recent years, the application of various surface-treated steel sheets has been expanding year by year in response to the social demand for high corrosion resistance of automobile bodies. As such a surface-treated steel sheet, a galvanized steel sheet, a zinc-based alloy plated steel sheet, etc. are used.
However, in the coating performed after assembly of the car body, the paint is not sufficiently spread, and the bag structure part and the bent product (hemming part) on the inner surface of the car body exposed to a high-humidity atmosphere are more difficult than conventional surface-treated steel sheets. A high degree of corrosion resistance is required. In response to such demands, for example, an organic composite-coated steel sheet was proposed in which a chromate layer and an organic polymer resin layer containing silica (several μm or less) were formed on a zinc or zinc-based alloy plated steel sheet ( JP-A-3-130141
Japanese Patent Laid-Open No. 2-258335). Since this organic composite coated steel sheet has very good corrosion resistance even in the unpainted state, it is often used for the inner surface of the vehicle body.

However, in recent years, along with the deterioration of the economic environment and the like, further cost reduction is required in the manufacture of automobiles. And, in the production of conventional organic composite coated steel sheet, since a chromate film formation and an organic film formation are performed after plating, a coating coater and a baking furnace facility are required for each process, and both the facility and the operation are considerable. This is a cause of cost increase. In addition, there is a problem that the mechanical property value is lowered due to the heating process at the time of baking.

As a method for forming an organic film on the surface of a steel sheet, a method using electrodeposition coating is used. This electrodeposition coating is a method in which an aqueous solution containing an aqueous or emulsified resin (polymer) and a pigment is charged to migrate and deposit the polymer and the pigment. Compared with coater coating, this electrodeposition coating has poor uniformity of the obtained coating film,
It is difficult to uniformly coat the surface with a thin film of several μm. Also, it is necessary to bake after electrodeposition coating,
Since high voltage electrolysis is required, high cost is also required.

Furthermore, there is an electrolytic polymerization method as another means for forming an organic film by electrolysis. This electrolytic polymerization method is a method in which a monomer is polymerized on the surface of a material to be treated by electrolysis to form an organic film on the surface of the material to be treated. This electrolytic polymerization method has been rapidly used in recent years mainly in the fields of capacitors and electromics (for example, Japanese Examined Patent Publication No. 3-65008,
JP-B-3-61314 and JP-B-4-7521). The property required for the coating film in this field is mainly electroconductivity, and its contribution to the corrosion resistance of the material to be treated has not been studied at all.

Further, as a method of directly forming an electrolytic polymerized film on the surface of a metal to treat the surface of the metal body, Japanese Patent Publication No. 50-15485 and Japanese Patent Laid-Open No. 55-16075.
Although there is a method described in the publication, these methods are for forming an electrolytic polymerized film on an aluminum plate or an iron plate, and are not sufficient to improve the corrosion resistance of the poorly thrown part of the electrodeposition paint. Is. Further, if the amount of formed film is too large, the spot weldability deteriorates, but this is not taken into consideration at all, and it cannot be put to practical use as a steel sheet for automobiles.

[0007]

Therefore, an object of the present invention is to have both corrosion resistance and paint adhesion, and moreover, it can be manufactured with less equipment and cost as compared with the conventional method. An object of the present invention is to provide an organic coated zinc-chromium-iron group element-alumina composite dispersion-plated steel sheet suitable as.

[0008]

In order to solve the above-mentioned problems, the present invention provides, as a first aspect, chromium of 0.1 to 1
4 to 30% by weight, iron group element 0.01 to 3% by weight, alumina 0.01 to 1% by weight in terms of aluminum, balance plating layer containing zinc and unavoidable impurities 5 to 30 g / m 2.
² has, organic coated zinc excellent organic coating by upper layer electrolytic polymerization of the dispersion plating layer in corrosion resistance having 0.01 to 3 g / m ² - chromium - iron group element - intended to provide an alumina composite dispersion plating steel sheet is there.

In a second aspect of the present invention, chromium is 0.1 to 14% by weight, iron group element is 0.01 to 3% by weight, and alumina is 0.01 to 1% by weight in terms of aluminum. It has a dispersed plating layer containing the balance zinc and unavoidable impurities in an amount of 5 to 30 g / m ² , and C is added to the upper layer of the dispersed plating layer.
An organic-coated zinc-chromium-iron group element-alumina composite dispersion-plated steel sheet having a chromate layer of 10 to 500 mg / m ^{2 in} terms of r and an organic coating of 0.01 to 3 g / m ² by electrolytic polymerization and having excellent corrosion resistance. It is provided.

Hereinafter, the zinc-chromium-iron group element of the present invention-
Alumina composite dispersion-plated steel sheet 8 (hereinafter referred to as "plated steel sheet of the present invention") will be described in detail.

The plated steel sheet of the present invention has a zinc-chromium-iron group element-alumina composite dispersed plating layer (hereinafter referred to as "dispersed plating layer") on a base steel sheet. The base steel sheet is not particularly limited, and for example, SPCC,
SPCD, SPCE, SPFC (JIS G3141)
Any of these steel plates may be used.

The dispersed plated layer in the plated steel sheet of the present invention is one in which zinc, chromium and an iron group element such as Fe, Ni and Co form an alloy, and alumina is dispersed in the plated layer as oxide fine particles. Is. Zinc in the dispersed plating layer is an essential component for obtaining a plated steel sheet that exhibits sacrificial corrosion resistance to the base steel sheet and has excellent corrosion resistance.

In the present invention, the chromium content in the dispersed plating layer is 0.1 to 14% by weight, preferably 5 to 11% by weight. Chromium content 0.1% by weight
If it is less than the above range, the corrosion resistance becomes insufficient, and if it exceeds 14% by weight, the effect of the content rate on the corrosion resistance becomes small, which is disadvantageous in cost.

The content of the iron group element in the dispersed plating layer is 0.01 to 3% by weight, preferably 0.1 to
It is 1.5% by weight. If the content of the iron group element in the plated layer is less than 0.01% by weight, the corrosion resistance is insufficient, and if it exceeds 3% by weight, the effect of the content on the corrosion resistance becomes small, which is disadvantageous in terms of cost.

The content of aluminum in the dispersed plating layer is 0.01 to 1% by weight, preferably 0.1 to 1%.
% By weight. The content of aluminum in the plating layer is 0.01
If it is less than 1% by weight, the effect of alumina on the corrosion resistance does not appear, and if it exceeds 1% by weight, the plating adhesion is deteriorated.

The coating amount of the dispersed plating layer is 5 to 30.
g / m ² . If the amount of the dispersed plating layer deposited is less than 5 g / m ² , sufficient corrosion resistance cannot be obtained. Also 30 g / m ²
Even if it exceeds, the effect of contributing to the corrosion resistance due to the increase in the coating amount becomes small, which is disadvantageous in terms of cost.

The dispersion-plated steel sheet of the present invention is manufactured by using zinc,
In an acidic plating bath containing chromium and iron group element ions
Acetylene glycol, polyethylene glycol, etc.
0.1 to 10 g / l of the nonionic organic additive of
Current density 40-200A / dm ²Electrolysis with zinc,
A plating layer with an alloy of chromium and iron group element ions
It can be performed by the electroplating method that deposits on the steel plate.
Wear. At this time, the eutectoid of alumina in the plating layer
Alumina sol was suspended in the plating bath and co-deposited in the plating layer.
Method of dissolving, dissolving aluminum ions in the plating bath,
Due to the increase in pH due to the reduction reaction of hydrogen ions during electrolysis
And deposit as aluminum hydroxide at the cathode interface.
Either method such as eutectoid as alumina in the bed
You may go by law.

The plated steel sheet of the present invention has an organic film formed by electrolytic polymerization as an upper layer on the dispersion plated layer. This organic film can be formed by polymerizing the monomer by electrolysis to form a polymerized film. Examples of the monomer used include vinyl pyridine, acrylic acid, acrylonitrile, styrene,
Acetonitrile, methyl methacrylate, phenol, aniline, pyrrole, phenylene, thiophene and the like, and derivatives thereof and the like can be mentioned.

The electrolysis conditions are not particularly limited as long as a predetermined organic film is formed. Considering the productivity, it is preferable to carry out at a current density of 0.1 to 100 A / dm ² and a bath temperature of 20 to 80 ° C.

In the present invention, the amount of the organic film formed by electrolytic polymerization is 0.01 to 3 g / m ² , and preferably 0.1 to 3 g / m ^{2 from} the viewpoint of corrosion resistance and paint adhesion. When the amount of the organic coating is less than 0.01 g / m ² , sufficient corrosion resistance cannot be obtained, and even when it exceeds 3 g / m ² , the contribution to the corrosion resistance due to the increase in the amount of the organic coating becomes small, resulting in cost reduction. However, if the coating amount is large, the spot weldability becomes poor.

Further, in the plated steel sheet of the present invention, it is effective to provide a chromate layer as an intermediate layer between the dispersion plated layer and the organic film as an upper layer thereof, because further excellent corrosion resistance can be obtained. . Since the formation of the chromate film causes a cost increase, it is preferable to form the chromate layer depending on the required degree of corrosion resistance.
When a chromate layer is provided, the amount of chromium film is Cr
10 to 500 mg / m ^{2 in} terms of conversion, preferably 10 to 40
It is preferably 0 mg / m ² . The amount of chromate film is 1
If it is less than 0 mg / m ² , the effect of improving the corrosion resistance due to the formation of the chromate layer cannot be obtained. On the other hand, if it exceeds 500 mg / m ² , the effect of increasing the amount of the chromate film on the corrosion resistance becomes small, which is a cost disadvantage. When the amount of chromate film is large, spot weldability and electrodeposition coatability deteriorate.

The method for forming the chromate film is not particularly limited, and any method such as coating type chromate treatment, reactive type chromate treatment, electrolytic chromate treatment and vapor phase plating may be used, which is advantageous in terms of cost. In terms of
The most effective method is to form a chromate film by electrolytic treatment.

[0023]

In the plated steel sheet the present invention, chromium creates a passivation plating surface to inhibit corrosion of the plating and the base steel sheet, and a corrosion product of plating basic zinc chloride (ZnCl ₂ · 4Zn (OH) _It is believed that ₂ ) is thermodynamically stabilized.

Further, the iron group element suppresses the cathodic reaction on the plating surface, and stabilizes and conducts the thermodynamics of basic zinc chloride (ZnCl ₂ .4Zn (OH) ₂ ) which is a corrosion product of the plating. It is considered that it is responsible for suppressing the formation of highly resistant zinc oxide (ZnO).

Further, it is considered that alumina has an effect of mechanically retaining the corrosion product on the surface of the steel sheet.

Conventionally, an organic film formed by coating on a plated steel sheet requires a chromate film to be formed as an intermediate layer. This is because the coating is transferred to the metal plating surface using a coater and is bonded to the surface by baking, so the adhesion between the metal surface and the organic film is poor, and it is essential to form a chromate film as the intermediate layer. there were. In contrast, in the present invention,
By electropolymerization, the monomer is directly bonded to the metal surface,
The organic film formed by polymerizing them also has a strong binding force, and thus does not necessarily require the chromate treatment.

[0027]

EXAMPLES The present invention will be described more specifically below with reference to Examples and Comparative Examples of the present invention.

(Examples 1 to 18) In each of the examples, after cold-rolled steel sheet was degreased and pickled by a known method, the bath conditions were changed within the range shown below, and plating was performed at a current density of 40 to 200 A / dm ² . Then, zinc-chromium-iron group element-alumina dispersion plating having the coating amount and plating composition shown in Table 1 was performed. Bath composition Zinc sulfate heptahydrate 186 g / l 40% chromium sulfate aqueous solution 84 to 252 g / l Iron group element sulphate heptahydrate 3 to 36 g / l Aluminum sulphate 14-18 hydrate 35 to 100 g / l Sodium sulfate 45 g / l Acetylene glycol 1-10 g / l Bath pH 1.4-2.5

Furthermore, vinyl pyridine 0.5 mol /
1 and an electrolytic solution containing ammonium perchlorate 0.2 mol / l, electrolytic polymerization was carried out at a current density of 1 A / dm ² or more using a steel plate as a cathode to form an organic film of the type and the adhesion amount shown in Table 1. To obtain a plated steel sheet. At this time, in Examples 7 to 10, after performing the chromate treatment, the organic film formation was performed by electrolytic polymerization. The obtained plated steel sheet was subjected to a corrosion resistance test and a paint adhesion test.
Further, the coating amount and composition thereof, the amount of chromate film, the amount of organic film attached, and the corrosion resistance test and paint adhesion test were carried out according to the following methods.
The results are shown in Table 1.

(Amount of deposited plating and composition) After the plating layer was dissolved with an acid, the amount of each component of the plating layer eluted in the solution was measured by an atomic absorption method.

(Amount of Chromate Film) The amount of Cr deposited on the plated steel sheet before and after the chromate treatment was measured by a fluorescent X-ray analyzer and determined from the difference.

(Amount of Organic Coating Adhesion) The amount of the plated steel sheet before and after the electrolytic treatment was weighed and calculated from the difference.

(Corrosion resistance test) A cycle composite in which a plated steel sheet is subjected to salt water spraying at a concentration of 5% by weight (35 ° C, 4 hours), drying (60 ° C, 2 hours) and wet (50 ° C, 2 hours) as one cycle. The test (CCT) was performed, and the number of cycles until the occurrence of red rust was used as an index of corrosion resistance.

(Paint Adhesion Test) The surface of a plated steel sheet sample was subjected to electrodeposition coating using PTU-600 manufactured by Nippon Paint Co., Ltd. (film thickness 20 μm), and then the DuPont impact test shown below was performed to perform plating. The surface of the steel plate sample was peeled off with a tape and the adhesion was evaluated by the presence or absence of peeling of the organic film. DuPont Impact Test: 50 kg of 1 kg using 1/4 inch diameter
The sample was dropped from the height of cm to the back surface of the sample.

(Comparative Examples 1 to 13) In each of the examples, the cold rolled steel sheet was degreased and pickled by a known method in the same manner as in the example, and then zinc-chromium-iron group element-alumina dispersion plating was applied. . Next, an epoxy resin (bisphenol A type) was coated using a coating coater to obtain a surface-treated steel sheet. A corrosion resistance test and a paint adhesion test were performed on these surface-treated steel sheets. The results are shown in Table 1.

[0036]

[Table 1]

[0037]

[Table 2]

Examples 1 to 6 and Examples 11 to 18 are
1 shows the first aspect of the present invention, and a surface-treated steel sheet excellent in corrosion resistance and paint adhesion was obtained at a low cost which cannot be obtained by a conventional method. On the other hand, in Comparative Example 1, the amount of the organic coating film formed by electrolytic polymerization was as small as 0.005 g / m ^2, and therefore the effect of contributing to the corrosion resistance and the coating adhesion was not exhibited.
Further, in Comparative Example 2, the zinc-chromium-iron group element-alumina plating amount was as small as 3 g / m ^2, and therefore the plating covering was insufficient and the corrosion resistance was insufficient. Comparative Example 3
In No. 5, the content of any one of chromium, iron group elements and aluminum was out of the range of the present invention, and the corrosion resistance was insufficient. That is, in Comparative Example 4, chromium was
In the plating, the iron group element is contained beyond the claimed range. In this case, although the paint adhesion and corrosion resistance are good, there is a drawback that the production cost becomes high. Comparative Example 8
Had a dispersed plating layer with an aluminum content exceeding the range of the present invention, and peeled off from the plating layer during the DuPont test, resulting in poor plating adhesion. Comparative Examples 9 and 10 are zinc-chromium-iron group element-alumina-plated steel sheets alone, have no organic coating by electrolytic polymerization, and suffer from red rust and corrosion resistance in less than 50 cycles of the combined cycle test. Met. Further, it can be seen that, in the example having the organic film formed by electrolytic polymerization, the life of the steel sheet is considerably extended because the cycle exceeds 50 cycles until red rust occurs. In Comparative Examples 11 and 12, since the coating was formed by coater coating, the adhesion with zinc-chromium-iron group element-alumina plating was not sufficient, and therefore the contribution to corrosion resistance was insufficient. became.
Further, Examples 7 to 10 show the second aspect of the present invention, while Comparative Example 13 has a chromate film amount outside the range specified in the second aspect of the present invention. Therefore, the amount of the chromate film is small, and the effect of the chromate film on the corrosion resistance is not exhibited.

[0039]

The organic-coated zinc-chromium-iron group element-alumina composite dispersion-plated steel sheet of the present invention is a surface-treated steel sheet having both corrosion resistance and paint adhesion, and moreover requires less equipment than the conventional method. It can be manufactured at low cost. Therefore, the plated steel sheet of the present invention is excellent as a material for automobile bodies. In addition to having a great industrial effect, it can contribute to the improvement of the durability of the car body and eventually to the saving of global resources.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C23C 30/00 C23C 30/00 A C25D 3/22 C25D 3/22 9/02 9/02 15 / 02 15/02 F (72) Inventor Tomo Katahiri Katsura Tomokatsu 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Pref., Technical Research Institute, Kawasaki Steel Co., Ltd. (72) Inoue Nakakoji, 1 Kawasaki-cho, Chuo-ku, Chiba Address Kawasaki Iron & Steel Co., Ltd. Technical Research Laboratory (72) Inventor Kazuo Mochizuki 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Iron & Steel Co., Ltd. Technical Research Institute

Claims (2)

[Claims] 1. Dispersion plating containing 0.1 to 14% by weight of chromium, 0.01 to 3% by weight of iron group elements, 0.01 to 1% by weight of alumina in terms of aluminum, and the balance zinc and unavoidable impurities. Having a layer of 5 to 30 g / m ² , and an organic film formed by electrolytic polymerization of 0.01 to 3 g on the dispersion plating layer.
/ M ^{2 is} an organic coated zinc-chromium-iron group element-alumina composite dispersion-plated steel sheet having excellent corrosion resistance. 2. Dispersion plating containing 0.1 to 14% by weight of chromium, 0.01 to 3% by weight of iron group element, 0.01 to 1% by weight of alumina in terms of aluminum, and the balance zinc and unavoidable impurities. Having a layer of 5 to 30 g / m ² , and a chromate layer of 10 to 500 mg / m ^{2 in} terms of Cr and an organic film by electrolytic polymerization of 0.01 to 3 g on the dispersion plating layer.
/ M ² and an organic coated zinc-chromium-iron group element-alumina composite dispersion-plated steel sheet having excellent corrosion resistance.