JP2002309387A - Organic substance coated steel sheet having excellent black rust resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic substance coated steel sheet which has excellent black rust resistance. SOLUTION: In the organic substance coated steel sheet in which a galvanizing film, a chromate film and an organic resin film are formed on the surface of a cold rolled steel sheet in order from the lower layer side. The average roughness Ra measured by the method in JISB0601 of the surface of the cold rolled steel sheet as the base material is <1.2 μm, or the number of the crests of the roughness is <100 peak/inch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organically coated steel sheet having excellent black spot rust resistance for suppressing spot corrosion of zinc, which is a particular phenomenon in a high-temperature and high-humidity environment.

[0002]

2. Description of the Related Art Among surface-treated steel sheets, a surface of a galvanized steel sheet is subjected to a chromate treatment, and a film thickness of 1 μm is further formed on an upper layer.
Organic composite coated steel sheets coated with a thin organic resin film of about m are widely used for materials such as AV / OA equipment and home electric appliances. This steel sheet is excellent in white rust resistance, fingerprint resistance, and conductivity, and has been developed to have multi-functions such as paintability and lubricity, and has reached the mainstream of galvanized steel sheets. For example, Japanese Patent Publication No. 5-54823 is mentioned.

[0003] Japanese Patent Publication No. 5-54823 discloses a technique in which a resin coating containing an ethylene copolymer resin and silica is formed on the surface of a steel sheet to improve the coating properties and corrosion resistance.

[0004] Recently, manufacturers of AV / OA equipment and home electric appliances have moved their production bases to Southeast Asia in order to reduce production costs. Therefore, galvanized steel sheet,
Demand for organic coated steel sheets is also growing in Southeast Asia, and exports from domestic blast furnace manufacturers to Southeast Asia are increasing rapidly.At the same time, we export hot rolled steel sheets, which are raw materials from Japan, and manufacture cold-rolled and surface-treated steel sheets in Southeast Asia. Local procurement is also progressing.

[0005]

However, in Southeast Asia,
Especially in hot and humid areas like South China, the rainy season is one.
It accounts for 80% of the year and is in a different corrosive environment than in Japan. Therefore, in such an area, during the transportation and storage of surface-treated steel sheets including organic coated steel sheets, a phenomenon called local spot corrosion of zinc (hereinafter referred to as black spot rust) occurred, and the commercial value The problem of spoiling is occurring. That is, when an organic-coated steel sheet developed for domestic use is directly exported to Southeast Asia or manufactured locally, there is a problem that black spot rust occurs.

[0006] The technique disclosed in Japanese Patent Publication No. 5-54823 also has the above-mentioned problem.
It is not sufficient in terms of black spot rust resistance. The present invention has been made in view of such circumstances, and provides an organic-coated steel sheet excellent in black spot rust resistance, in which generation of a unique black spot rust under a high-temperature and high-humidity environment such as Southeast Asia is appropriately suppressed. The purpose is to:

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by controlling the surface roughness of the base material cold-rolled steel sheet to a specific range, the black spot rust is reduced. It has been found that the occurrence of cracks is remarkably reduced and an organically coated steel sheet having excellent rust resistance can be obtained.

[0008] The present invention has been made based on such knowledge, and has the following configuration.

[1] An organic-coated steel sheet having a zinc-based plating film, a chromate film, and an organic resin film formed on the surface of a cold-rolled steel sheet in order from the lower layer side.
The average roughness Ra measured by the method of B0601 is 1.2
An organic-coated steel sheet having excellent black spot rust resistance, which is less than μm.

[2] In an organic coated steel sheet formed on a cold-rolled steel sheet surface in the order of a zinc-based plating film, a chromate film and an organic resin film from the lower layer side, the peak count number RPVC of the roughness of the base material cold-rolled steel sheet surface is as follows. An organic-coated steel sheet having excellent black spot rust resistance, which is less than 100 peaks / inch.

[3] In an organic coated steel sheet having a zinc-based plating film, a chromate film, and an organic resin film formed on the surface of the cold-rolled steel sheet in order from the lower layer, the wavelength of the surface of the base material cold-rolled steel sheet is 1
The peak count number RPVC of 100 to 150 μm is 100 pe.
An organic-coated steel sheet having excellent black spot rust resistance, which is less than ak / inch.

[4] An organic-coated steel sheet having a zinc-based plating film, a chromate film, and an organic resin film formed on the surface of the cold-rolled steel sheet in this order from the lower layer side.
The average roughness Ra measured by the method of B0601 is 1.2
An organic-coated steel sheet excellent in black spot rust resistance, characterized in that the peak count number RPVC having a wavelength of 100 to 150 μm is less than 100 peak / inch.

[5] In the above items [1] to [4], the chromate film adhesion amount is 1 to 100 mg / m ^{2 in} terms of metal chromium,
An organic-coated steel sheet having excellent black spot rust resistance, characterized in that an organic resin film adhesion amount is 0.1 to 5 g / m ² .

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below together with the reasons for limiting them. As a result of investigating the cause of black spot rust, if there is a local thin portion (hereinafter referred to as a thin film portion) in the organic resin film on the surface of the organically coated steel sheet, this thin film portion becomes the starting point of corrosion and black spot rust occurs. And that the thin-film portion is formed under the influence of the roughness of the steel sheet surface because the average thickness of the organic resin film of the organic-coated steel sheet is extremely small (generally about 1 μm). I understood.

First, the organic resin film, chromate, and zinc plating of the organic coated steel sheet on which black spot rust is generated and the organic coated steel sheet on which black spot rust is not generated are etched and removed with dilute hydrochloric acid so that the steel sheet surface is not dissolved. The roughness curve of the surface of the cold rolled steel sheet was measured by a non-contact type roughness meter, and the surface was arranged in an average roughness distribution for a specific wavelength region. The average roughness distribution for the specific wavelength region indicates the average roughness when the wavelength region is limited by a specific pitch, and the average roughness Ra (hereinafter, referred to as “JIS B0601”) which is generally specified. JIS-Ra ”). The results obtained are shown in FIG. According to FIG. 1, the average roughness distribution does not vary depending on the wavelength of the steel sheet without black spot rust, and the distribution is low at any wavelength. On the other hand, the steel sheet with black spot rust has the average roughness distribution of black spot rust. It can be seen that the average roughness distribution is extremely high in a specific wavelength range of 100 to 150 μm, in addition to the overall roughness of the steel sheet in which no generation occurs.

Next, in order to examine the surface roughness of the base material cold-rolled steel sheet, which forms a thin film portion of the organic film and affects the occurrence of black spot rust, cold-rolling which has been subjected to temper rolling by a roll of an electric discharge machining finish. Regarding steel sheets, JIS B0601-199
Average roughness Ra of the surface measured in accordance with No. 4 (“JIS
-Ra "), the peak count number RPVC and the occurrence of black spot rust were investigated. FIG. 2 shows the obtained results. Here, JIS-Ra is JIS by a contact type surface roughness meter.
It measured according to the method of B0601. The peak count number RPVC is obtained by measuring a roughness curve with a non-contact type surface roughness meter, filtering the data with a high-frequency cutoff value by a low-frequency filter and a low-frequency cutoff value by a high-frequency filter, The peak count number in the range of 100 to 150 μm was extracted. In addition, the condition of black spot rust occurrence is high temperature and high humidity environment (average temperature 26 to 31 ° C, average relative humidity 70 to 85 RH).
% Carried out by generating the number of four months sunspots rust storage steel plate under the conditions of), passed 105cm number of black spot rust per ² area is the number of black spot rust per 105cm ² area 2 or less, 105cm ² area Three or more black spot rusts were evaluated as rejected.

From FIG. 2, the JIS-Ra of the base material cold rolled steel sheet is less than 1.2, or the peak count number RPVC is 100 p.
It can be seen that black spot rust does not occur in a region less than eak / inch. As described above, in the present invention, the surface roughness of the base material cold-rolled steel sheet is determined such that JIS-Ra is less than 1.2 μm or the peak count number RPVC of the roughness is 100 peaks.
/ Inch. By defining the surface roughness of the cold-rolled steel sheet within the above range, the formation of a local thin film portion can be suppressed, and the occurrence of black spot rust can be suppressed. Further, in the present invention, the surface roughness of the base material cold-rolled steel sheet is determined according to JIS-Ra
Is less than 1.2 μm and the peak count number RPVC of the roughness
Is less than 100 peaks / inch, an organic coated steel sheet having further excellent black spot rust resistance can be obtained.

There is no particular lower limit for JIS-Ra. There is no particular lower limit on the peak count number RPVC of a specific wavelength.

For the reasons described above, in order to obtain an organic-coated steel sheet having even more excellent rust resistance, J is generally specified.
In addition to making the IS-Ra less than 1.2 μm, for the same reason as above, to obtain an organic-coated steel sheet having further excellent black spot rust resistance, the peak count number RPVC of the roughness is 10
In addition to making it less than 0 peak / inch, it is preferable to control the roughness of the surface of the cold-rolled steel sheet at a specific wavelength of 100 to 150 μm.

The specific wavelength of 100 to 150 μm generally corresponds to the roughness wavelength of the temper roll (finished by discharge dull roll). Therefore, by managing the roughness after the temper rolling, that is, by controlling the temper rolling conditions (surface roughness of the rolling roll, pressure regulation rate), the JIS-R
a less than 1.2 μm or a specific wavelength of 100 to 150 μ
m peak count number RPVC is 100 peak / inch
And the occurrence of black spot rust can be suppressed.

In the organic coated steel sheet of the present invention, a zinc-based plating is formed on the surface of a cold-rolled steel sheet, and a chromate film and an organic resin film are further formed thereon. The zinc-based plating is not particularly limited, and a zinc-coated steel sheet, a Zn-Ni-plated steel sheet, Zn
-Fe plated steel sheet (electroplating, galvannealed), Zn-Cr plated steel sheet, Zn-Mn plated steel sheet,
Zn-Co plated steel sheet, Zn-Co-Cr alloy plated steel sheet, Zn-Cr-Ni plated steel sheet, Zn-Cr-Fe plated steel sheet, Zn-Al plated steel sheet (for example, Zn-5%
Al alloy-plated steel sheet, Zn-55% Al alloy-plated steel sheet), Zn-Mg-plated steel sheet, Zn-Al-Mg-plated steel sheet, and zinc-based composite coated steel sheet in which metal oxides, polymers, etc. are dispersed in these platings ( For example, Zn-
SiO2 dispersion plating) can be used. Further, among the above platings, a multi-layer plated steel sheet obtained by plating two or more layers of the same or different types can be used.
As the aluminum-based plated steel sheet, an aluminum-plated steel sheet or an Al-Si plated steel sheet can be used.
Further, between the above plating and the steel plate, a thin plating such as Ni may be applied in advance. As a plating method, any practicable method among an electrolysis method (electrolysis in an aqueous solution, electrolysis in a non-aqueous solvent), a melting method, and a gas phase method can be adopted.

Further, when a chromate film is formed on these plating surfaces by coating, if necessary, any alkali degreasing, solvent degreasing, surface conditioning treatment (alkaline Surface conditioning treatment, acidic surface conditioning treatment). In addition, in order to prevent the steel sheet coated with the coating of the present invention from being blackened (a kind of oxidation phenomenon on the plating surface) in the use environment, the iron surface metal ions (Ni ion, Ni ion, An acidic or alkaline surface conditioning treatment containing (Co ions, Fe ions) can also be performed.
When electrogalvanizing is used as a base, iron group metal ions (Ni ions,
These metals can be contained in the plating film in an amount of 1 ppm or more by containing Co ions and Fe ions).
In this case, the upper limit of the iron group metal concentration in the plating film is not particularly limited.

Examples of the chromate film include a reaction type, an electrolytic type and a coating type. The amount of Cr attached is 1 to 100 mg / m ² , preferably 5 to 60 mg in terms of metal chromium.
mg / m ² . If the amount of Cr attached is less than 1 mg / m ² , the corrosion resistance becomes insufficient, which is not preferable. In addition, 100 mg /
m appearance color tone yellowish ^two at greater than, unfavorably uneven.

Examples of the organic resin film include resins such as epoxy resin, ethylene resin, urethane resin, acrylic resin and polyester resin. These may be solvent-based, water-dispersible, or water-soluble. Also, in the organic resin film,
As rust preventive additives, metal oxide fine particles such as silica and alumina, phosphates such as condensed phosphate Al and condensed phosphate Ca, Mo salts such as Al molybdate, Ca-exchanged silica, and organics such as thiol and thiuram A system inhibitor can be added. Further, a lubricant such as polyethylene wax or PTFE can be added to the organic resin film. Organic resin film adhesion amount is 0.1-5g / m
² , preferably 0.5 to 3 g / m ² . If the amount of the organic resin adhered is less than 0.1 g / m ² , the corrosion resistance becomes insufficient, which is not preferable. On the other hand, if it exceeds 5 g / m ^2, it is not economical, and the conductivity is undesirably reduced.

[0025]

EXAMPLE On a cold-rolled steel sheet surface, various organic-coated steel sheets formed in the order of a zinc-based plating film, a chromate film, and an organic resin film from the lower side in an environment of high temperature and high humidity (average air temperature of 26 to 31).
(C, average relative humidity 70 to 85 RH%) for 4 months and stored indoors to investigate the occurrence of black spot rust. Here, the zinc-based plating film was electrogalvanized at 20 g / m ² , the chromate film was 40 mg / m ^{2 in} terms of metallic chromium by reactive chromate, and the organic resin film was a film mainly composed of an ethylene-based resin and silica. . Furthermore, the organic resin film, chromate, and zinc plating of the above various organic coated steel sheets were removed by etching with dilute hydrochloric acid. Each was measured with a scale. The peak count number was set to a cutoff value between 100 and 150 μm. Table 1 shows the measured results together with the evaluation of black spot rust generation. In Table 1, the evaluation of black spot rust was performed based on the number of black spot rusts generated on steel sheets stored for 4 months under conditions of high temperature and high humidity (average temperature 26 to 31 ° C., average relative humidity 70 to 85 RH%). The number of black spot rusts per 105 cm ² area was evaluated according to the following criteria.

Pass: The number of black spot rusts per 105 cm ² area is 2 or less Fail: The number of black spot rusts per 105 cm ² area is 3 or more

[0027]

[Table 1]

As shown in Table 1, in the examples of the present invention, an organic-coated steel sheet which does not generate black spot rust and has excellent rust resistance is obtained.

On the other hand, in the comparative example, it can be seen that black spot rust occurs and the rust resistance is poor.

[0030]

As described above, according to the present invention, an organically coated steel sheet having excellent rust resistance can be obtained. Further, the organic coated steel sheet obtained by the present invention does not generate black spot rust and has excellent rust resistance, so that it can withstand use in a high-temperature and high-humidity environment, and is ideal for home appliances, building materials, and automotive applications. It is.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a wavelength, an average roughness distribution with respect to a wavelength region, and a black spot rust occurrence state.

FIG. 2 shows the average roughness JIS-Ra and a specific wavelength of 100 to 15
The figure which shows the relationship between the peak count number RPVC of 0 micrometer, and a black spot rust generation situation.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukio Kimura 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Japan Co., Ltd. Inside (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan F-term (reference) in this steel pipe Co., Ltd. CA18 CA42 CA53

Claims (5)

[Claims] 1. An organic-coated steel sheet having a zinc-based plating film, a chromate film, and an organic resin film formed on the surface of a cold-rolled steel sheet in order from the lower layer side.
The average roughness Ra measured by the method of B0601 is 1.2 μm.
m, an organic-coated steel sheet having excellent black spot rust resistance. 2. An organic-coated steel sheet having a zinc-based plating film, a chromate film, and an organic resin film formed on the surface of the cold-rolled steel sheet in order from the lower layer, and the peak count number RPVC of the surface roughness of the base material cold-rolled steel sheet is 100 peaks. An organic-coated steel sheet having excellent black spot rust resistance, which is less than / inch. 3. An organic-coated steel sheet having a zinc-based plating film, a chromate film, and an organic resin film formed on the surface of the cold-rolled steel sheet in order from the lower layer.
Mountain count number RPVC of 0 to 150 μm is 100pea
An organic-coated steel sheet having excellent black spot rust resistance, which is less than k / inch. 4. An organic-coated steel sheet having a zinc-based plating film, a chromate film, and an organic resin film formed on the surface of a cold-rolled steel sheet in this order from the lower layer side.
The average roughness Ra measured by the method of B0601 is 1.2 μm.
m, and a peak count number RPVC having a wavelength of 100 to 150 μm is less than 100 peaks / inch. An organic-coated steel sheet having excellent black spot rust resistance. 5. The method according to claim 1, wherein the amount of chromate film adhered is 1 to 100 mg / m ^{2 in} terms of chromium metal, and the amount of organic resin film adhered is 0.1 to 5 g / m ^2. Organic coated steel sheet excellent in black spot rust resistance described in Crab.