JP2785982B2 - High corrosion resistance hot-dip galvanized steel sheet with excellent blackening resistance - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot-dip zinc- or zinc-alloy-plated steel sheet having excellent corrosion resistance which does not discolor with time and is used for building materials, civil engineering, electric appliances, automobiles and the like.

(Prior art) Hot-dip galvanized steel sheets are diversified in use with increasing demand, and are required to have excellent appearance, workability, chemical conversion, and excellent corrosion resistance. In recent years, in particular, the appearance of products tends to be regarded as important, and there is a strong demand for a solution to the problem that conventional hot-dip galvanized steel sheets, particularly hot-dip galvanized steel containing Al, turn black over time (hereinafter, blackening over time). . As a technique for preventing temporal blackening of a hot-dip zinc or zinc alloy coated steel sheet, a method of treating a coated steel sheet with an aqueous solution containing Ni ions or Co ions has been disclosed in Japanese Patent Application Laid-Open No. 59-177381. However, in this method, zinc tends to selectively corrode due to a different corrosion cell formed between Ni and Co and the underlying zinc, which is not preferable for white rust resistance. It is difficult to prevent blackening over time for a long time. Further, in the construction material field, when a flaw is formed by a roll former process or the like, the flawed part is likely to be blackened, and the conventional technique requires practical improvement.

(Problems to be Solved by the Invention) As described above, the prior art is not always sufficient for the current multipurpose use, and the following problems must be developed for hot-dip coated steel sheets.

Plated steel sheet with excellent corrosion resistance without blackening for a long time Plated steel sheet with rust-proof coating that is not easily scratched in the forming process Processing method.

An object of the present invention is to provide a hot-dip galvanized steel sheet in which the above-mentioned problems have been solved by a post-treatment film.

(Means for Solving the Problems) The present invention has solved the above-mentioned problems, and the gist of the present invention is to provide: 1 zinc or a zinc alloy on a surface of a hot-dip coated steel sheet;
Either Co, or a composite plating having 0.5-50 mg / m ² in terms of metal, including some oxides and hydroxides of these both metals or the metal, Cr deposition amount thereon is 10-100m
g / m ² and ratio of silica to CrO ₃ conversion (SiO ₂ / CrO ₃ ratio)
1. A highly corrosion-resistant hot-dip galvanized steel sheet having excellent blackening resistance, characterized by having a silica-containing chromate film containing 0.5 to 3.0 and a resin film of 0.3 to 3.0 g / m ^{2 on} the upper layer.

2. The highly corrosion-resistant hot-dip galvanized steel sheet according to claim 1, wherein the chromate film contains a compound of Co or Ni.

3. The highly corrosion-resistant hot-dip galvanized steel sheet according to claim 1, wherein the resin film layer contains at least one of a cobalt complex, a nickel complex, silica, carbon black, and a chromic acid pigment. .

4. The composite plating layer containing one of Ni and Co, or both of these metals, or a partial oxide and a hydroxide in the metal, further comprises Mo oxide, Cr oxide, Fe oxide, and Ba oxide. The highly corrosion-resistant hot-dip galvanized steel sheet having excellent blackening resistance according to claim 1, comprising one or more of Mg oxide, Ca oxide, Zn oxide and metallic Zn.

It is.

(Action) The highly corrosion-resistant hot-dip galvanized steel sheet having excellent blackening resistance of the present invention is one in which three treatment layers are formed by three-stage treatment.

First, Ni, C
o, or both of these metals or a composite plating containing a part of oxide and hydroxide in the metal is formed in an amount of 0.5 to 50 mg / m ^{2 in} terms of metal. Ni and Co improve the blackening resistance over time in proportion to the adhesion amount, but decrease the white rust resistance.
White rust resistance is improved by coexisting Zn. From the viewpoint of the black modified with lapse requires 0.5 mg / m ² or more, in order to ensure corrosion resistance in the corrosion resistance in particular salt water atmosphere, 50
mg / m ² or less. The most preferred coverage range is 1 to 10 mg /
a m ^2. Also, by coexisting Ni and Co, corrosion resistance and blackening over time can be further improved, and the Ni / Co ratio is desirably 0.2 to 1.0 / 1.

Zn, Ni, and Co precipitate preferentially over the activity of the plating surface, and do not necessarily need to cover the plating surface uniformly.

The structure of the deposited Zn, Ni, Co is a composite plating structure containing a metal or a partial oxide and a hydroxide as a result of examination by XPS (photoelectron spectroscopy).

Co, Ni treatment coating, by immersion and spray contact with acidic aqueous solution containing these metal ions, alkaline aqueous solution and hot-dip zinc or zinc alloy coated steel plate, displacement plating, chemical plating, or by electroplating can get.

In addition, other metal ions (Mo ⁶⁺ , Cr ³⁺ , Fe ²⁺ , Ba ⁺⁺ , Mg ⁺⁺ , Ca ⁺⁺ , Zn ⁺⁺ ) are contained in an acidic aqueous solution containing Ni ²⁺ or Co ²⁺ . As a result, a treated film having more excellent blackening resistance can be obtained. The addition amount of these ions is 0.1 to 0.1% in proportion to Ni ²⁺ and Co ^2+.
0.5% / l is preferable, and the adhesion amount is 0.01 to
0.1 / l is preferred.

In particular, when Zn ²⁺ is present in the bath, the Zn oxide or Zn metal coexists in the coating together with the Ni or Co metal or the composite plating partially containing an oxide and a hydroxide on the metal, and Ni, Co and It has the effect of reducing the deterioration of corrosion resistance due to galvanized corrosion cells, and greatly contributes to the improvement of corrosion resistance.

According to XPS analysis, Zn coexists in the form of oxide in chemical plating, but is a metal in electroplating. Zn ²⁺ / (Ni ²⁺ ＋ Co
The ratio of ²⁺ ) is determined by chemical plating in the bath because Zn is likely to precipitate.
For a 0.1 to 1.0 / l electroplating bath, 0.01 to 0.2 / l is preferred.

A coating type chromate treatment containing silica is performed on the surface on which Ni and Co are deposited. Deposition amount of chromate is chromium compound is 10-100 mg / m ² of Cr in terms of the silica is composed of 0.5 to 3.0 at a ratio of CrO ₃ in terms (SiO ₂ / CrO ₃ ratio). Silica-free chromate is not effective against blackening because of its small barrier effect against oxygen and water. Moreover, it is inferior to corrosion resistance. The chromium compound stabilizes the chromate film when the Cr ³⁺ / Cr ⁶⁺ ratio in the treatment bath is 2/8 to 5/5, and forms a film excellent in corrosion resistance and blackening.

If the total chromium coating amount of the chromate film is less than 10 mg / m ^2, it is insufficient for corrosion resistance and blackening. Also, 100m
If it exceeds g / m ^2, it is advantageous for corrosion resistance and blackening, but it is not preferable because defects such as adhesion workability and color unevenness are likely to occur.

For the above reasons, the chromium deposition amount is desirably ²⁰ to 50 mg / m ² . Silica is preferably a silica sol which is stable when mixed with chromic acid having a fine particle diameter, and a granular or secondary-agglomerated acidic sol having a particle diameter of 5 to 50 nm can be used. If the ratio to chromic acid is less than 0.5, the effect of blocking the corrosion ions of the silica sol, that is, the improvement in corrosion resistance and blackening is insufficient, and the silanol groups on the silica surface that participate in bonding with the organic resin are insufficient. Quality cannot be obtained. silica/
When the chromic acid ratio is more than 3.0, cohesive failure occurs due to too much silica component, and it is difficult to secure performance after processing. SiO ₂ / CrO
A coating having a ratio of ₃ to 2 is desirable.

In the present invention, for the purpose of improving the quality of the chromate film, high quality can be obtained by further adding Co or Ni to a metal oxide.

These compounds can be added to the chromate solution in the form of a solution or dispersion, and can be contained in the chromate film by baking after coating. The addition amount is desirably 0.01 to 0.1 in terms of CrO ₃ conversion.

 Hereinafter, the organic resin film will be described.

The organic resin is preferably a coating obtained from a water-dilutable emulsion, but a coating obtained from an organic solvent-soluble clear coating can also be used. The structure of the resin used in the present invention is acrylic or its copolymer, epoxy or its copolymer, olefin copolymer, polyester resin, alkyd resin, fluororesin, urethane resin, phenol resin and the like. Water-dispersible emulsion resins such as olefin acrylics, epoxy acrylics, and acrylic esters are characterized by excellent blackening resistance and corrosion resistance even at low temperature baking. Those which are hardly blackened are urethane-based coating films and fluororesins.

Furthermore, from the viewpoint of corrosion resistance and blackening resistance, a melamine compound, an amine compound, an N-containing organic compound of an amide compound, a sulfonic acid group, It is desirable to contain an S-containing organic compound having a group or an oxide sol such as silica, alumina, zirconia, or titania.

Addition of a Co or Ni compound, particularly an ionizable complex, to the organic coating can significantly improve body blackening. As the complex, an organic acid salt of an oxycarboxylic acid, such as citric acid or tartaric acid, or an EDTA complex is effective, and the amount of addition is 0.01 to 10% in terms of Co and Ni relative to the resin. If it exceeds 10%, the water resistance of the resin film itself deteriorates, and the corrosion resistance decreases, which is not preferable. If less than 0.01%, the effect is unknown. 0.1 to 2% is the most preferable range with good balance.

Silica (SiO ₂ ), alumina (Al
The content of fine particles such as ₂ O ₃ ), zirconia (ZrO ₂ ), and titania (TiO ₂ ) is preferably 10 to 40% by weight. If it is less than 10%, the improvement effect by the fine particles is not remarkably recognized, and 40%
If it is excessively high, the corrosion resistance deteriorates.

In addition, when a coating obtained by adding 1 to 30% by weight of carbon black to an organic resin is used in the present invention, a high-quality appearance with a light gray tone is exhibited, the color tone of the appearance is stabilized, and blackening is not conspicuous. 1-30% by weight of carbon black is desirable. 1%
If it is less than 30%, the coloring is insufficient, and if it exceeds 30%, the abrasion resistance is deteriorated due to the falling off of carbon. Chromate compounds such as zinc chromate, calcium chromate, barium chromate, strontium chromate,
By including a rust preventive pigment such as magnesium chromate, corrosion resistance can be improved without adversely affecting blackening. The content is desirably 0.1 to 10%. 1
If it exceeds 0%, the resin film is greatly deteriorated by chromic acid, the adhesion is lowered, and the abrasion property is deteriorated. The adhesion amount of the third layer resin coating is 0.3 ~
3.0 g / m ² is within the scope of the present invention. Blackening resistance in proportion to the adhesion amount, the corrosion resistance is improved but not observed effect on耐黒variable is less than 0.3 g / m ^2, as a performance balance with 3 g / m ^2, greater than cost can not welded But not preferred.

The hot-dip galvanized steel sheet used in the present invention is a general hot-dip galvanized steel sheet containing 0.1 to 0.5% of aluminum.
Zinc aluminum alloy coated steel sheet containing ~ 55% aluminum, zinc magnesium alloy coated steel sheet containing 0.01 to 1% magnesium, and zinc iron alloy coated steel sheet containing 0.2 to 12% iron, especially Pb in the plating layer Is 0.05
% Or less is effective for a substantially lead-free hot-dip galvanized steel sheet.

(Examples) Example 1 Table 1 shows a 5% aluminum zinc alloy coated steel sheet (with a basis weight of 40 g / m ² and a skin pass) manufactured by a continuous hot-dip galvanized steel sheet line using a normal non-chlorination furnace method. 50 g of cobalt sulfate and nickel sulfate / zinc sulfate 25 at pH = 2
Spray Ni, Co or Ni + Co with an aqueous solution of g / g to deposit the required amount of Ni and Co, then apply an aqueous solution of 10g / of chromic acid with a reduction rate of 38% and 30g / of silica sol to reach the plate. After drying at a temperature of 80 ° C., a urethane / polyester emulsion to which melamine was added was applied in a dry adhesion amount of 0.3 to 3.0 g / m ^{2, and} baked to an ultimate plate temperature of 150 ° C. to prepare a sample.

After cutting the sample to 100 × 150 mm, it was left in a wet box (humidity test) at a temperature of 70 ° C. and a relative humidity of 98% for 14 days to evaluate blackening, and was subjected to outdoor exposure for 1 year.
Value) was measured with a color difference meter, and the change was evaluated. The corrosion resistance is evaluated by the salt spray test specified in JIS Z 2371 (continuous method).
For 200 hours, and the white rust generation state (area ratio) was visually evaluated.

In addition, as a workability evaluation, 20 x 20 mm with a load of 500 g
The surface of the plating was rubbed 50 times with a sheet of paper, and the sample was subjected to a wet test (processing wet test) to evaluate blackening.

Examples Nos. 1, 2 and 3 were prepared by spraying metal Ni
After adhering, chromate and remove urethane resin
It is an example of the present invention coated with 1 g / m ² . All have good blackening and good corrosion resistance. Higher Ni deposition yields better results. In Examples Nos. 4, 5, and 6, the same post-treatment was performed after depositing metal Co, and the same performance as Ni was obtained in the examples of the present invention. Examples Nos. 7, 8 and 9 are examples of the present invention in which metals Ni and Co were co-deposited, and a blackening performance excellent particularly in a wet test was obtained. In Examples Nos. 10, 11 and 12, 13 of the present invention in which a large amount of Co and Ni were precipitated, excellent blackening resistance was obtained.

Comparative Example No. 1 is only chromate Comparative Example No. 2 is an example of two-step treatment of chromate and resin, and Comparative Examples No. 3 and No. 4 are examples of chromate treatment after precipitation of Ni or Co. In each case, blackening was apt to occur when exposed outdoors, and those in which Ni and Co were precipitated had insufficient corrosion resistance.

Example-2 5% aluminum zinc alloy plated steel sheet (basis weight 40 g / m ²
50g of cobalt sulfate / 20g of zinc sulfate /
Aqueous solution of pH ≒ 2 to which 5 g / molar of chromium sulfate, molybdenum sulfate and calcium sulfate were added respectively at 50 ° C. to deposit the adhering amount shown in Table 2, and then 10 g of chromic anhydride and silica sol 20g / and nickel hydroxide 0.1,0.5,1.0g / in terms of Ni, cobalt hydroxide as Co
0.1,0.5,1.0 g / Chromate solution added was applied and the chromate solution was applied and dried at the ultimate plate temperature of 80 ° C., and then the urethane polyester, fluororesin and olefin acrylic copolymer were dried at 1 g / m ^2.
Fluororesins were applied at 0.5 and 1.0 g / m ^{2 and} baked at a plate temperature of 150 ° C. to prepare samples. The evaluation was performed according to Example 1.

Example No. 14 is the present invention example in which the lowermost layer was made of eutectoid metal Co and Cr oxide, and then coated with chromate and urethane polyester resin.No. 15, 16 were metal Co and Mo oxide, Ca In the example in which the oxide was eutectoid, a good and well-balanced result was obtained with respect to corrosion resistance and blackening. Example No. 17-19
After depositing metal Co on the zinc alloy plating, the present invention example of applying a urethane polyester resin after performing coating chromate with addition of Ni ions, No. 20, 21 and 22
Is an example of the present invention in which a coating chromate to which Co ions are added is performed and then a urethane polyester resin is coated. N
Blackening was improved by i, Co-added chromate.
Nos. 23 to 25 use olefin acrylic for the resin composition of the top layer,
In the examples of the present invention using a fluororesin, the fluororesin showed excellent characteristics.

Example 3 A 5% aluminum zinc alloy-plated steel sheet was treated with N in Example 1.
After performing chromate treatment by attaching Co under the conditions of o.5, 1 g of an amino crosslinking agent and 20 g of silica were added to 100 g of an olefin acrylic resin, and further, an EDTA-2Co complex and EDTA-
An emulsion resin containing 2Ni complex, conart citrate, cobalt tartrate carbon black, and zinc chromate as shown in Table 3 was applied as a dry coating weight, and the sheet temperature was adjusted to 15
Samples were prepared by baking at 0 ° C. The evaluation was in accordance with Example 1.

In Examples Nos. 26 to 28, the effect of the film thickness was recognized in the examples of the present invention in which the resin composition of the uppermost layer was coated by changing the film thickness using an olefin acrylic resin to which silica was added.

Examples Nos. 29 to 31 are examples of the present invention in which a Ni complex was added to a resin, and performance excellent in blackening resistance was obtained. Example No. 32
Nos. 34 to 34 showed good body blackening in the examples of the present invention in which a resin to which a Co complex resistor was added was applied. No. 35 and No. 36 also showed corrosion-resistant plated steel sheets having good blackening resistance in the inventive examples using Ni and Co complexes. Nos. 37 and 38 were examples in which carbon black was added to the resin, and a plated steel sheet with a grayish appearance and less discoloration was noticeable from the beginning. No. 39 is an example of the present invention to which zinc chromate which is a rust-preventive pigment is added, and has a small effect of improving blackening resistance to outdoor exposure, but good results were obtained in the accelerated test.

Example-4 Galvanized Steel Sheet Containing 0.2% Aluminum (Bass Weight 60g
/ m ² , skin pass) with cobalt sulfate 50g /, zinc sulfate 2
In a 5 g / containing acidic aqueous solution of pH = 3, current was passed at a current density of 5 A / dm ² for 2 seconds using a plated steel sheet as a cathode to precipitate 5 g / m ^{2 of} metallic nickel. Subsequently, a chromate solution containing 10 g of chromic anhydride with a reduction rate of 38% and silica sol at 20 g / SiO ₂ was applied at 20 mg / m ² with a Cr adhesion amount and baked at a plate temperature of 60 ° C. Then, a polyethyleneimine acrylic emulsion and silica were used. The resulting resin film was applied at a dry weight of 1 g / m ^{2 and} baked at a plate temperature of 150 ° C. to prepare a sample. Corrosion resistance is
No white rust was observed after 200 hours of salt spray. In addition, the change in blackening in the wet test was -1.0, and the change in the outdoor exposure was -3.0, which was good.

Co ⁺⁺ Example -5 Example -4 After 2.0 the pH of the Zn ⁺⁺ containing aqueous solution, after the Co deposition amount is 3 mg / m ² adhered by performing spray 3 seconds, like chromate, resin Was coated on a galvanized steel sheet containing 0.2% aluminum. The change in brightness in the wet test was -1.0, and the exposure outdoors -2.0 was good. Corrosion resistance is 20
No generation of white rust was observed at 0 hours.

(Effect of the Invention) By providing a hot-dip galvanized steel sheet having excellent corrosion resistance and blackening resistance, application to non-painting applications becomes possible. In particular, the effect of the present invention is great for aluminum zinc alloy plated steel sheets containing about 5% aluminum, which is weak against blackening, and is widely used for construction materials and home appliances. In particular, those coated with an organic resin are excellent in workability and hardly cause processing scratches,
In addition, the corrosion resistance is remarkably improved, and there is an excellent effect that it can be used for applications where painting is omitted.

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B32B 15/08 B05D 7/14 C23C 2/26 C23C 22/24 C23C 28/02

Claims (4)

(57) [Claims] A zinc or zinc alloy is coated on the surface of a hot-dip coated steel sheet by Ni or Co, or both of these metals, or a composite plating containing a part of oxide and hydroxide on said metal in 0.5% in terms of metal. -50mg / m ² has, is Cr deposition amount thereon
10-100 mg / m ² and the ratio of silica to CrO ₃ conversion (SiO ₂ / C
High corrosion-resistant hot-dip galvanized steel sheet with excellent blackening resistance, characterized by having a silica-containing chromate film containing 0.5 to 3.0 (rO ₃ ratio) and a resin film of 0.3 to 3.0 g / m ^{2 on} top of it. . 2. The hot-dip galvanized steel sheet according to claim 1, wherein the chromate film contains a compound of Co or Ni. 3. The high corrosion resistant melting excellent in blackening resistance according to claim 1, wherein the resin film layer contains at least one of a cobalt complex, a nickel complex, silica, carbon black and a chromic acid pigment. Galvanized steel sheet. 4. A composite plating layer containing one of Ni and Co, or both of these metals, or a metal partially containing an oxide and a hydroxide, further comprising a Mo oxide, a Cr oxide, and a Fe oxide. , Ba oxide, Mg oxide, Ca oxide, Zn oxide, Metal Zn
The hot-dip galvanized steel sheet having high corrosion resistance and excellent blackening resistance according to claim 1, comprising one or more of the following.