JP2001348672A - Galvanized steel sheet excellent in heat resistance, heating discoloration resistance and corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a galvanized steel sheet free from harmful hexavalent chromium at all, further free from the exhaust of hexavalent chromium at all even in the production process and excellent in heat resistance, heating discoloration resistance and corrosion resistance not only in red rust resistance but also in white rust resistance. SOLUTION: On this galvanized steel sheet excellent in heat resistance, heating discoloration resistance and corrosion resistance, a film layer of 0.1 to 2 g/m2 obtained by applying and drying an aqueous solution obtained by mixing colloidal silica of 10 to 100 pts.mass as solid content and a phosphonic compound of 1 to 50 pts.mass into magnesium biphosphate of 100 pts.mass as solid content is formed. It is also suitable that the film is further mixed with an aqueous resin of <=20 pts.mass as solid content. The temperature in the applying and drying is preferably controlled to >=150 deg.C. Moreover, as the phosphonic compound, 1-hydroxyethylidene-1,1'-diphosphonic acid is suitably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvanized steel sheet having excellent heat resistance, heat discoloration resistance and corrosion resistance. More specifically, the present invention relates to a zinc-free steel sheet containing no harmful hexavalent chromium. The present invention relates to a galvanized steel sheet having excellent heat resistance, heat discoloration resistance, and corrosion resistance in which hexavalent chromium is not discharged even in a process.

[0002]

2. Description of the Related Art Zinc-based plated steel sheets have excellent corrosion resistance.
Furthermore, it has been widely used for home appliances, building materials, and automobiles because it effectively protects the exposed iron portion of the cut surface from corrosion. Further, many steel plates having various functions by applying various post-treatments on zinc-based plating have been developed. Among the various functions, the most weak point of zinc-based plating is the heat-resistant function. Specifically, TV CRT shrink band,
It is used for stoves and the like.
It is heated to about 0 ° C, and in the latter case, 200 to 4
It is used for a long time at about 00 ° C. In such applications, stainless steel or aluminum-plated steel sheet is usually used, but both are disadvantageous in terms of cost as compared with zinc-based plated steel sheet, and in the latter, the corrosion resistance is insufficient in the processed part and the end face exposed part. There is a problem. For this reason,
It has been desired to provide a zinc-based plated steel sheet having a heat resistance function.

[0003] Japanese Patent Publication No. 6-2389 discloses a steel sheet having a plating layer and a treatment layer comprising a special organic-inorganic composite film on a plating, which is suitable for the above-mentioned applications such as a CRT shrink band and a stove. It can be used. However, as a recent new trend, there is a movement to eliminate environmentally harmful treatments containing harmful hexavalent chromium such as chromate from home appliance parts. There is a demand for the development of a galvanized steel sheet having excellent heat resistance that can be used for such applications.

For this purpose, Japanese Patent Application Laid-Open No. 2000-1574
No. 1 discloses a zinc-plated steel sheet on which a coating made of a straight silicone resin is formed, but the red rust resistance is sufficient, but the white rust resistance is insufficient before and after heating. Further, Japanese Patent Application Laid-Open No. 2000-793 by the present inventors
Even in the technique disclosed in Japanese Patent No. 70, the white rust resistance before heating was insufficient.

[0005]

According to the present invention, the harmful 6
It is an object of the present invention to provide a galvanized steel sheet which does not contain any valent chromium and does not emit hexavalent chromium even in the production process and is excellent in heat resistance, heat discoloration resistance and corrosion resistance. Further, with regard to corrosion resistance, it is another object of the present invention to provide a zinc-plated steel sheet which is excellent not only in red rust resistance but also in white rust resistance both before and after heating.

[0006]

The gist of the present invention is that 10 to 100 parts by mass of a colloidal silica and 1 part by mass of a phosphonic acid compound are added to 100 parts by mass of a solid content of Mg biphosphate.
0.1 to 50 parts by weight of the mixed aqueous solution
A zinc-plated steel sheet having excellent heat resistance, heat discoloration resistance and corrosion resistance, characterized by having a coating layer of ² g / m ² formed thereon, wherein the coating further contains an aqueous resin at a solid content of 20 parts by mass or less. Mixing is also suitable. The temperature for coating and drying is preferably 150 ° C. or higher. As the phosphonic acid compound, 1-hydroxyethylidene-1,1′-diphosphonic acid is suitably used.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is to form an inorganic film or an inorganic-organic composite film having excellent heat resistance, heat discoloration resistance and corrosion resistance on a galvanized steel sheet, thereby significantly increasing the commercial value. As for corrosion resistance, white rust as well as red rust is effectively suppressed. Here, the zinc-based plated steel sheet is not limited to a plating means such as electroplating, hot-dip plating, vapor deposition plating, and even pure zinc plating, a metal other than zinc, for example, Ni, Co, A
Alloy plating with 1, Mg, Mn, or the like may be used. Also, a multi-layer plating may be used. The inorganic film formed on the plating is a point of the present invention, and an aqueous solution comprising Mg biphosphate (Mg dihydrogen phosphate, also referred to as Mg monophosphate), colloidal silica and a phosphonic acid compound was applied and dried. Things. By mixing these at a specific ratio, a film having excellent adhesion to zinc and excellent corrosion resistance can be obtained. In addition, it is considered that when heated, Mg biphosphate and colloidal silica in the film further react during heating, forming a denser film and blocking oxygen diffusion. Further, Mg in the film can stabilize the initial corrosion product of zinc, and therefore, by combining these effects, excellent corrosion resistance can be maintained even after heating. The phosphonic acid compound exhibits a white rust suppressing effect by a chelating action on Zn ions. The mixing ratio of the above-mentioned Mg biphosphate, colloidal silica and phosphonic acid compound is as follows:
g of the solid content of 100 parts by mass, the solid content of the colloidal silica is 10 to 100 parts by mass, and the phosphonic acid compound is 1 to
It must be 50 parts by mass. When the colloidal silica is less than 10 parts by mass, the water resistance of the obtained film,
Corrosion resistance may be reduced, causing a problem on primary rust prevention. On the other hand, if it exceeds 100 parts by mass, cracks of the film when heated are remarkable, discoloration is increased, and corrosion resistance is insufficient. When the amount of the phosphonic acid compound is less than 1 part by mass, the white rust resistance before heating deteriorates, and when it exceeds 50 parts by mass, the corrosion resistance after heating tends to deteriorate. In addition, as an example of a phosphonic acid compound, 1-hydroxy-ethylidene-1,1′-diphosphonic acid can be mentioned.

The coating of the present invention is prepared by adding an aqueous resin in an amount of not more than 20 parts by mass to 100 parts by mass of the solid content of Mg biphosphate in addition to the above-mentioned Mg biphosphate, colloidal silica and phosphonic acid compound. By using an organic composite film, the corrosion resistance of the sliding processed portion can be further improved. If it is added in excess of 20 parts by mass, the deterioration of the resin component during heating becomes severe, which is not preferable. The aqueous resin is particularly preferably a wax component.

The above-mentioned inorganic coating or inorganic-organic composite coating
Has a mass of 0.1 to 2 g / m^TwoMust be
If it is less than 0.1, sufficient heat resistance cannot be obtained. Also 2
g / m ^TwoBeyond that, the effect on heat resistance is saturated and uneconomical
As well as strict processing when the coating amount is too large
In some cases, the coating peels off when applied, which is counterproductive to corrosion resistance.
is there. In applications where welding is performed, the cause of poor welding
It is unsuitable because it can be. To form such a film
The method is not particularly limited.
It may be applied by a spray or the like and dried. Drying, moisture
Any temperature can be used as long as it can evaporate.
To deteriorate the primary rust prevention during storage
Bake at a temperature of at least about 80 ° C
Is desirable. In addition, the white rust resistance before heating is further improved.
For drying, it is desirable to dry at 150 ° C. or more.

[0010]

Examples of the present invention will be described below.

(1) Examples 1 to 11 and Comparative Examples 1 to 4 Sample preparation A Zn—Ni alloy electroplated steel sheet (sheet
7 mm, basis weight 20 g / m ² / one side, Ni 12.5%)
After degreasing with alkali spray, various treatment liquids were applied by a roll coater, and immediately afterwards, a plate temperature of 150 was applied in a hot air drying oven.
After heating to ℃, it was cooled with water. The coating solution used was a mixture of Mg biphosphate, colloidal silica, a phosphonic acid compound, and an aqueous resin at a solid content mass ratio shown in Table 1. Here, Mg biphosphate is an aqueous solution manufactured by Yoneyama Chemical Industry, colloidal silica is Snowtex-O manufactured by Nissan Chemical, and phosphonic acid compound is 1-hydroxy-ethylidene-1,1′-diphosphonic acid manufactured by Yokkaichi Gosei. A 60% aqueous solution was used.

Evaluation method "White rust resistance before heating" After extruding a flat plate or Erichsen 7 mm (in each case, a tape seal is applied to the edge and the back), a salt spray test according to JIS-Z-2371 was conducted. The area ratio of the total white rust and discoloration after the day was measured. (XX; 100%, X; 60 to 99%, Δ; 2
0 to 60%, ；; 1 to 20%, ◎; 0%)

[0013] "Discoloration resistant" steel sheet samples from room temperature to about 1
Heating to a PMT of 600 ° C. at a heating rate of 0 ° C./sec,
Immediately after being taken out of the electric furnace, after being left for one day and night, the color difference (delta E value) before and after heating was measured with a color difference meter. (×; 4
Above, Δ; 2 to 4, O: 1-2, ２; 1 or less)

"Corrosion resistance after heating" A steel sheet sample was heated from room temperature to 600 ° C. at a heating rate of about 10 ° C./sec, immediately taken out of the electric furnace, left for a day and night, and the edges and the back were tape-sealed and JIS. The total area ratio of red rust and white rust after 3 days was measured by a salt spray test of -Z-2371. (XX; 100%, X; 60 to 99%, Δ; 20
６０60%, ；; 1-20%, ；; 0%)

[0015]

[Table 1]

(2) Examples 12-17 and Comparative Examples 5
8 Sample preparation The conditions were adjusted in the same manner as described above, but here, a water-based resin was added to form a film in order to evaluate a case involving more severe sliding in white rust resistance before processing. As the aqueous resin, an oxidized polyethylene wax emulsion (23% aqueous solution) was used. It was blended at the solid content mass ratio shown in Table 2. Other conditions were the same as those shown in Table 1.

Evaluation method Evaluation was made in the same manner as above, except for the evaluation of the processed portion of white rust resistance before heating. Regarding the evaluation of the processed part of the white rust resistance before heating, after sliding on a plane, the slidable part was cut out and edge-sealed, and JIS-Z
By the salt spray test of −2371, the area ratio of white rust and total discoloration after 12 hours was measured. (Xx; 100
%; ×; 60 to 99%; Δ; 20 to 60%;
0%, ；; 0%)

The plane sliding die is SKD-11, the crimping part 2
0 mm (r = 5 mm), holding load 100 kgf, 20
It slid at mm / sec.

[0019]

[Table 2]

Tables 1 and 2 show the results. In Examples of the present invention, zinc which is excellent in white rust resistance, heat resistance, heat discoloration resistance and corrosion resistance despite not using chromium at all. A system-plated steel sheet has been obtained. In the example of Table 2 in which the aqueous resin was blended, the white rust resistance of the severely processed portion was also improved. Those deviating from the scope of the present invention deteriorated some performance.

[0021]

Industrial Applicability According to the present invention, a zinc-based plated steel sheet which is excellent in heat resistance, heat discoloration resistance and corrosion resistance, does not contain any harmful hexavalent chromium, and does not emit hexavalent chromium even in the production process. Was obtained. The steel sheet of the present invention is excellent not only in red rust resistance but also in white rust resistance.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C09D 201/00 C09D 201/00 (72) Inventor Hidetoshi Moka 1 Fujimachi, Hirohata-ku, Himeji-shi Nippon Steel Corporation F-term in Hirohata Works (reference) 4D075 AE03 BB75X CA18 CA34 DA06 DB05 DC02 DC12 EA02 EA06 EA12 EC01 EC03 EC07 EC54 4F100 AA04B AA20B AB03A AB16 AB18 AB18A AB31 AH10B AK01B BA02 EH46 EH46BEJ32 GBH28 EH46BJ28 GBHH BA211 EA011 HA446 JC26 NA03 NA14 PC02 4K026 AA02 AA07 AA12 AA22 BA03 BB08 BB10 CA16 CA24 CA38 CA39 CA41 DA02 DA11 DA15 DA16

Claims (4)

[Claims] 1. A method according to claim 1, wherein the surface of the galvanized steel sheet is coated with
g of the solid content and 100 to 100 parts by mass of the solid content of colloidal silica and 1 to 5 parts by mass of the phosphonic acid compound.
0.1 to 2 g of 0 mass parts mixed aqueous solution applied and dried
/ M ² , a zinc-plated steel sheet having excellent heat resistance, heat discoloration resistance and corrosion resistance, characterized by having a coating layer of / m ² . 2. The surface of a galvanized steel sheet is coated with biphosphoric acid M
g of the solid content and 100 to 100 parts by mass of the solid content of colloidal silica and 1 to 5 parts by mass of the phosphonic acid compound.
Excellent heat resistance, heat discoloration resistance and corrosion resistance characterized by having a coating layer of 0.1 to ² g / m ² obtained by applying and drying an aqueous solution in which 0 parts by mass and a water-based resin are mixed in a solid content of 20 parts by mass or less. Galvanized steel sheet. 3. The galvanized steel sheet according to claim 1, wherein the temperature of the steel sheet at the time of forming a film by coating and drying is 150 ° C. or higher. 4. The galvanized steel sheet according to claim 1, wherein the phosphonic acid compound is 1-hydroxyethylidene-1,1′-diphosphonic acid.