JPH0711454A - Method for chromating metal by coating - Google Patents

Abstract

PURPOSE:To produce various metals excellent in corrosion resistance and coating adhesion by chromating the metals by coating. CONSTITUTION:A chromating bath obtained by incorporating 2-20 pts.wt. of a long-chain colloidal silca having 2-20nm thickness and 25-250nm length, 7-35 pts.wt. of phosphoric acid and 3-10 pts.wt. of MgO into a bath where Cr(III)/(Cr(III)+Cr(V1))=0.4 to 1.0 and contg. 5-30 pts.wt. of total chromic acid is applied on various metals or alloys to remarkably improve their corrosion resistance. These effects are produced by the synergistic effect of the five components, and an excellent characteristic is not obtained even when one component is absent. The chromate film thus obtained is highly adhesive to a coating material, and hence the film is optimum as the backing of a coated steel sheet or further as the backing of various org. composite plated steel sheets.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a surface of a metal, and particularly to improve the corrosion resistance of a metal and the adhesion to an organic film. The surface-treated steel sheet obtained by this treatment method has excellent corrosion resistance and adhesion to an organic film, and thus can be used as a corrosion-resistant material for various home appliances, building materials, and automobiles.

[0002]

As is well known, electrogalvanized steel sheets, hot-dip galvanized steel sheets, and various alloy-plated steel sheets are widely used in automobiles, home appliances, building materials and the like. Under these circumstances, the demand for surface-treated steel sheets having particularly excellent corrosion resistance has become stronger in recent years, and the demand for such steel sheets tends to increase in the future. For example, in the home electric appliance industry, there is a demand for a steel sheet having excellent corrosion resistance that can be used without a coating, from the viewpoint of process saving and cost saving. Also in the automobile industry, environmental changes in recent years, such as corrosion by rock salt sprayed to prevent freezing of winter roads in North America and Northern Europe,
Further, there is a strong demand for a surface-treated steel sheet having excellent corrosion resistance from the viewpoint of safety because the vehicle body is exposed to a severe corrosive environment such as corrosion due to acid rain due to generation of SO ₂ gas in an industrial area. Various studies have been made to solve these problems, and many products have been developed.

Up to now, galvanizing has been carried out in order to improve the corrosion resistance of steel sheets. The galvanized steel sheet prevents corrosion of the steel sheet by the sacrificial anticorrosive action of zinc, and the zinc adhesion amount must be increased to obtain corrosion resistance. Therefore, there are some problems such as an increase in the cost of the required zinc amount, a reduction in workability, weldability, and productivity. In addition, galvanized steel sheets generally have poor paint adhesion.

Various alloy-plated steel sheets have been developed as a method for improving the corrosion resistance of such galvanized steel sheets. As these alloy-plated steel sheets, for example, Zn-Ni
System, Zn-Ni-Co system, Zn-Ni-Cr system, Zn-
Examples thereof include Fe-based, Zn-Co-based, Zn-Cr-based, Zn-Mn-based, and the like. It is recognized that these alloy platings improve the bare corrosion resistance by about 3 to 5 times as compared with normal galvanized steel sheets. However, even if it is left outdoors for a long time or sprayed with water or salt water, there is a problem that white rust or red rust easily occurs.

On the other hand, a method of performing chromate treatment in order to improve the corrosion resistance can be considered. In addition, as a recent tendency, in order to further improve the corrosion resistance, a zinc-based plated steel sheet is chromated and various resins are applied thereon.
A so-called simple pre-coated steel sheet (hereinafter referred to as an organic plated steel sheet) has been developed and is partially commercially available. As a matter of course, the chromate film used as a base for such an organic composite plated steel sheet must have excellent adhesion to an organic resin. Many chromate treatments for various plated steel sheets are already known, and various chromate treatment methods have been developed and made proper.

The chromate treatment is roughly classified into electrolytic type and coating type chromate. Examples of the electrolytic chromate include, for example, chromic acid as a main component and sulfuric acid added thereto (Japanese Patent Publication No. 39-7461) and phosphoric acid added (Japanese Patent Publication Nos. 30-3514 and 35-8917).
Japanese Patent Publication No. 36-9559, Japanese Patent Publication No. 36-9
560), to which boric acid is added (US Pat. No. 2)
No. 733199, No. 2780592), and halogen (Cl ⁻ , F ⁻ ) added (Japanese Patent Publication No. 39-143).
63) and the like, using a bath to which various anions are added,
Cathodic electrolytic treatment of steel sheets has been performed.

Trivalent chromium is mainly used as the coating type chromate.
Water-soluble chromium compounds, inorganic colloid compounds and
And acidic aqueous solution containing inorganic anion
(JP-A-63-218279), Cr⁶⁺Part of
Mixing colloidal silica with trivalent reduced chromic acid
What is processed (Japanese Patent Laid-Open No. 63-243279),
Chromic acid with a constant reduction rate and a specific proportion of colloidal compound and no
For treating a liquid mixed with organic anions (JP-A-63-
188373), Cr⁶⁺/ (Cr³⁺+ Cr ⁶⁺)ratio
Chromic Acid and Inorganic Colloidal Compounds and Inorganic
What is treated with a liquid containing anions, SiO₂And PO_Four
^2-Water containing chromic acid containing trivalent / total Cr molar ratio
One that processes a solution (Japanese Patent Laid-Open No. 1-65272),
Hexavalent and trivalent chromium containing a specific amount of trivalent chromium ions
Specific amount of silicofluoride and fluoride
Treating a liquid containing thorium salt (Japanese Patent Laid-Open No. 1-5
6879), containing a specific amount of trivalent chromium ions.
Specific amount of SiO2 for hexavalent and trivalent chromium ions₂
Which treats an aqueous solution containing (JP-A-1-568)
77), hexavalent containing a specific amount of trivalent chromium ions
And a specific amount of trifluorochromium ion
Treat the liquid containing monium and silane coupling agent
(Japanese Patent Laid-Open No. 1-56878), chrome and siri
Contains a specific proportion of kasol, Cr⁶⁺Amount and particle size of silica sol
Which treats the liquid specified in Japanese Patent Application Laid-Open No. 2-104672
Gazette), specific ratio of chromium ion, phosphoric acid, silicic acid sol
Hexavalent chromium ion in total chromium ion containing
Which treats the liquid specified in Japanese Patent Application Laid-Open No. 2-85372
Gazette), chromic acid, anhydrous colloidal compound, silane cup
Treatment of a liquid containing a ring agent in a specific ratio
3 to 146676 gazette) Trivalent Cr / 6 Hexavalent Cr specified
And treat the solution containing silica gel, phosphoric acid, and Zn.
(Japanese Patent Laid-Open No. 3-67883) and the like.
it can. All of these ensure a certain degree of corrosion resistance
However, the paint adhesion is not always sufficient.
There is no.

[0008]

Generally, when a Zn-based alloy-plated steel sheet is subjected to coating chromate treatment, Zn
Zn ions in the chromate film 6 due to the elution of ions
The trivalent Cr is changed to trivalent and a trivalent rich chromate film is formed. When the chromate film becomes trivalent rich, the corrosion resistance is slightly lowered but the paint adhesion tends to be improved. However, when alloys with excellent corrosion resistance or various metals are treated with coating type chromate, the corrosion resistance is good and the elution of Zn ions from the base is small, so the ratio of hexavalent Cr becoming trivalent is small, which is excellent. It tends to be difficult to secure paint adhesion. An object of the present invention is to provide a chromate treatment method which can solve the above-mentioned drawbacks of the conventional techniques, remarkably improve the corrosion resistance of metals, and can secure extremely excellent adhesion to an organic film or a coating material. It is a thing.

[0009]

That is, the present invention provides 6
Add special amounts of special colloidal silica, phosphoric acid and MgO to a special chromic acid bath where trivalent Cr is reduced to a specific ratio of trivalent and apply it to metal to form a special chromate film to improve corrosion resistance. In particular, the product value is remarkably enhanced by remarkably improving the adhesion to the organic film. This excellent property is obtained when only a colloidal silica is contained in a special chromic acid bath in which hexavalent Cr is reduced to a specific ratio of trivalent, or when only phosphoric acid is added, or when only MgO is contained. It is not possible to obtain, and it is extremely excellent in corrosion resistance and adhesion to organic film only when special colloidal silica, phosphoric acid and MgO are simultaneously added to a special chromic acid bath in which hexavalent Cr is reduced to a specific ratio of trivalent. It was found that the property can be obtained. Generally, a low-grade organic resin or a low temperature baking type or a room temperature drying type paint does not have good adhesion with a known chromate film, but even with these organic resins or paints, excellent adhesion can be secured. The characteristics of each component will be described below.

[0010]

FIG. 1 shows the corrosion resistance of a steel sheet when hexavalent Cr of chromic acid is reduced to trivalent, and FIG. 2 shows the adhesion with a coating film. That is, a Zn-Ni alloy plated steel sheet (basis weight: 20 g / m ² , Ni = 13.1%) has a thickness of 8 to
10 parts of long-chain colloidal silica having a length of 10 nm and a length of 100 to 120 nm (hereinafter referred to as parts by weight), phosphoric acid 20 parts,
Corrosion resistance when changing the trivalent Cr / (total chromic acid = trivalent Cr + hexavalent Cr) with 20 parts of total chromic acid in a bath of 3 parts of MgO is shown in Fig. 1, and on the obtained chromate film FIG. 2 shows the paint adhesion when the melamine-based paint is spray-coated so as to have a thickness of 20 μ after baking. FIG. 3 shows the corrosion resistance of the steel sheet when the concentration of chromic acid was changed, and FIG. 4 shows the adhesion with the coating film.

That is, 10 parts of long-chain colloidal silica having a thickness of 8 to 10 nm and a length of 100 to 120 nm on a Zn-Ni alloy plated steel sheet (basis weight: 20 g / m ² , Ni = 13.1%). (Parts by weight hereinafter) phosphoric acid 20 parts, Mg
Corrosion resistance obtained by fixing trivalent Cr / (total chromic acid = trivalent Cr + hexavalent Cr) = 0.5 in a bath of O3 and changing total chromic acid at various ratios is shown in FIG. FIG. 4 shows the paint adhesion when the melamine-based paint was baked on the chromate film and spray-coated so as to have a thickness of 20 μm. FIG. 5 shows the corrosion resistance of the steel sheet when the concentration of the long-chain colloidal silica was changed, and FIG. 6 shows the adhesion with the coating film.

That is, 20 parts of total chromic acid on Zn-Ni alloy plated steel sheet (weight per unit area: 20 g / m ² , Ni = 13.1%), trivalent Cr / (total chromic acid = trivalent Cr + hexavalent Cr) = 0.5, phosphoric acid 20 parts, and MgO 3 parts in a case where a long-chain colloidal silica having a thickness of 8 to 10 nm and a length of 100 to 120 nm is added in various proportions by coating with a roll. FIG. 5 shows the corrosion resistance, and FIG. 6 shows the paint adhesion when the resulting chromate film is spray-coated so as to have a thickness of 20 μm after baking. FIG. 7 shows the corrosion resistance of the steel sheet when the length of the long-chain colloidal silica was changed, and FIG. 8 shows the adhesion with the coating film.

That is, total chromic acid 20 parts, trivalent Cr / (total chromic acid = trivalent Cr + hexavalent Cr) on Zn-Ni alloy plated steel sheet (basis weight: 20 g / m ² , Ni = 13.1%). = 0.5, phosphoric acid 20 parts, MgO 3 parts bath with 10 to 10 parts of long-chain colloidal silica having a thickness of 8 to 10 nm and various lengths is applied. 7 shows the adhesiveness of the paint when a melamine-based paint was baked on the obtained chromate film and then spray-coated so as to have a thickness of 20 μm. FIG. 9 shows the corrosion resistance of the steel plate when the thickness of the long-chain colloidal silica is changed, and FIG.
Indicates the adhesion to the coating film.

That is, 20 parts of total chromic acid on Zn-Ni alloy plated steel sheet (weight per unit area: 20 g / m ² , Ni = 13.1%), trivalent Cr / (total chromic acid = trivalent Cr + hexavalent Cr) = 0.5, phosphoric acid 20 parts, MgO 3 parts bath with a length of 100 to 120 nm and 10 parts of long-chain colloidal silica with various thicknesses added, and the corrosion resistance when applied by a roll. 9 shows the adhesion of the paint when a melamine-based paint was baked on the obtained chromate film and then spray-painted to a thickness of 20 μm. FIG. 11 shows the corrosion resistance of the steel sheet when the particle size of the granular colloidal silica was changed, and FIG. 12 shows the adhesion with the coating film.

That is, 20 parts of total chromic acid on Zn-Ni alloy plated steel sheet (weight per unit area: 20 g / m ² , Ni = 13.1%), trivalent Cr / (total chromic acid = trivalent Cr + hexavalent Cr) = 0.5, phosphoric acid 20 parts, and MgO 3 parts, the corrosion resistance of a bath in which 10 parts of granular colloidal silica having different particle diameters are added by a roll is shown in FIG. Fig. 12 shows the paint adhesion when spray coating the melamine-based paint to 20μ after baking.
Shown in. FIG. 13 shows the corrosion resistance of the steel sheet when the concentration of phosphoric acid was changed, and FIG. 14 shows the adhesion with the coating film.

That is, 20 parts of total chromic acid on Zn-Ni alloy plated steel sheet (basis weight: 20 g / m ² , Ni = 13.1%), trivalent Cr / (total chromic acid = trivalent Cr + hexavalent Cr) = 0.5, the thickness is 8 to 10 nm, and the length is 100 to
10 parts of long-chain colloidal silica of 120 nm, MgO3
Fig. 13 shows the corrosion resistance of a bath fixed with various concentrations of phosphoric acid at various ratios applied by a roll, and after the melamine-based paint was baked on the obtained chromate film, 2
FIG. 14 shows the paint adhesion when spray coating is performed so as to obtain 0 μ. FIG. 15 shows the corrosion resistance of the steel sheet when the concentration of MgO was changed, and FIG. 16 shows the adhesion with the coating film.

That is, 20 parts of total chromic acid on Zn-Ni alloy-plated steel sheet (basis weight: 20 g / m ² , Ni = 13.1%), trivalent Cr / (total chromic acid = trivalent Cr + hexavalent Cr) = 0.5, the thickness is 8 to 10 nm, and the length is 100 to
10 parts of 120 nm long-chain colloidal silica, phosphoric acid 2
FIG. 15 shows the corrosion resistance in the case where a bath having various concentrations of MgO added to a bath fixed at 0 part was coated with a roll,
FIG. 16 shows the paint adhesion when a melamine-based paint is baked on the obtained chromate film and then spray-painted to a thickness of 20 μm.

Here, the corrosion resistance indicates a rusting condition after 1000 hours by a salt spray test according to JIS-Z-2371 standard (concentration of salt solution 5%, bath temperature 35 ° C., spray pressure 20 psi). , ○, △, ×, XX is evaluated in 5 stages, and ◎ is the best. ◎: Red rust occurrence rate 0% ○: 〃 more than 0 to 1% △: 〃 more than 1 to 10% ×: 〃 more than 10 to 50% XX: more than 50%

Adhesion with the paint was spray-coated with a low-temperature baking type (baking temperature: 110 ° C.) melamine-based paint on the obtained chromate film so as to be 20 μm after baking,
Thereafter, the film was immersed in boiling water for 1 h, the film was cut on a 2 mm goggle, the tape was peeled off, and the peeled area was evaluated. ◎: Peeling area 0% ○: 〃 more than 0 to 1% △: 〃 more than 1 to 10% ×: 〃 more than 10 to 50% XX: more than 50%

As is apparent from FIG. 1, the value of trivalent Cr / (trivalent Cr + hexavalent Cr) does not directly affect the corrosion resistance. As is clear from FIG. 2, trivalent Cr / (trivalent Cr + 6
The value of (valent Cr) affects the adhesiveness of the paint, and the value of trivalent Cr /
When the value of (trivalent Cr + hexavalent Cr) is 0.4 or more and 1.0 or less, excellent paint adhesion is exhibited. Here, 1.0 is hexavalent C
This means that r is 0 (zero). On the other hand, 0.4
If it is less than 100%, the paint adhesion tends to decrease. As is clear from FIG. 3, the concentration of chromic acid affects the corrosion resistance, and excellent corrosion resistance is obtained at 5 parts or more and 30 parts or less, and the corrosion resistance decreases at less than 5 parts or more than 30 parts.

As is clear from FIG. 4, the concentration of chromic acid also affects the coating adhesion and shows excellent coating adhesion at 5 parts or more and 30 parts or less, and decreases at less than 5 parts or more than 30 parts. . As is apparent from FIG. 5, the amount of long-chain colloidal silica added affects the corrosion resistance, and excellent corrosion resistance is exhibited at 2 parts or more and 20 parts or less, and the corrosion resistance decreases at less than 2 parts or more than 20 parts. Tend to do. As is clear from FIG. 6, the amount of long-chain colloidal silica added affects the paint adhesion.
When the amount is from 1 part to 20 parts, excellent paint adhesion is exhibited, and when it is less than 2 parts and more than 20 parts, it tends to decrease.

As is clear from FIG. 7, the length of the long-chain colloidal silica affects the corrosion resistance, and is 25 nm or more to 2 or more.
When the thickness is 50 nm or less, excellent corrosion resistance is exhibited, and when it is less than 25 nm or more than 250 nm, the corrosion resistance tends to decrease. Figure 8
As is clear from the above, the length of the long-chain colloidal silica has an influence on the coating adhesion, and shows excellent coating adhesion at 25 nm or more and 250 nm or less, less than 25 nm and 250 n.
If it exceeds m, it tends to decrease. As is clear from FIG. 9, the thickness of the long-chain colloidal silica also affects the corrosion resistance,
Excellent corrosion resistance is exhibited at 2 nm or more and 20 nm or less.
When the thickness is less than 20 nm and exceeds 20 nm, the corrosion resistance gradually decreases.

As is apparent from FIG. 10, the thickness of the long-chain colloidal silica has an influence on the coating adhesion and shows excellent coating adhesion at 2 nm to 20 nm, and decreases at less than 2 nm and more than 20 nm. As is clear from FIG. 11, the particle size of the spherical colloidal silica affects the corrosion resistance and the smaller the particle size, the more the corrosion resistance tends to improve, but the corrosion resistance is lower than that of the long chain colloidal silica as a whole. As is clear from FIG. 12, the particle size of the spherical colloidal silica also affects the paint adhesion, and the smaller the particle size, the better the paint adhesion, but the paint adhesion is generally lower than that of the long-chain colloidal silica. .

As is clear from FIG. 13, the amount of phosphoric acid added affects the corrosion resistance, showing excellent corrosion resistance at 7 parts or more and 35 parts or less, and decreasing corrosion resistance at less than 7 parts or more than 35 parts. To do. As is clear from FIG. 14, the addition amount of phosphoric acid also influences the paint adhesion, showing excellent paint adhesion at 7 parts or more and 35 parts or less, and the paint adhesion at less than 7 parts or more than 35 parts. descend. As is clear from FIG. 15, the added amount of MgO affects the corrosion resistance, and excellent corrosion resistance is exhibited at 2 parts or more.
As is clear from FIG. 16, the addition amount of MgO also affects the paint adhesion, and shows excellent paint adhesion at 1 part or more.
As a result of the above, the optimum addition amount of MgO is at least 2 which satisfies the corrosion resistance and the adhesion of the organic film at the same time, and the upper limit is not particularly limited but is 10 parts or less from the economical viewpoint.

As is clear from the above results, the optimum components are as follows. Chromic acid 5 to 30 parts by weight Trivalent Cr / (trivalent Cr + hexavalent Cr) 0.4 to 1.0 Long chain colloidal silica (thickness: 2 to 20 nm, 2 to 20 parts by weight Length: 25 to 250 nm) Phosphoric acid 7 to 35 〃 MgO 2 to 10 parts by weight

By appropriately diluting the bath of the present bath composition and applying it to various metals, extremely excellent corrosion resistance can be secured, and particularly low-grade organic resin or low-grade dry type and normal temperature dry type It is possible to secure remarkably excellent paint adhesion to paints. Here, the excellent corrosion resistance can be ensured by this treatment because of the dense passivation film formed of chromic acid, colloidal silica and M.
It is presumed that it is ensured by the passivation effect of stabilizing the corrosive substance by gO and forming the barrier layer, and the strong film-forming property of the long-chain colloidal silica.

Further, excellent paint adhesion can be ensured by adjusting the trivalent Cr and the hexavalent Cr to a specific ratio so that the OH group of the trivalent Cr becomes an optimum ratio and that the long chain colloidal silica has It is considered that this is due to the fact that it has a synergistic effect with the OH group and that it has an interaction with the PO ₄ ²⁻ group. Here, as the alloy-plated steel sheet, for example, Zn-Ni system, Zn
-Ni-Co system, Zn-Ni-Cr system, Zn-Fe system,
Examples thereof include Zn-Co type, Zn-Cr type, Zn-Mn type and the like, and they can also be directly used for quasi metals such as Zn, Ni, Sn and Cu.

Further, as a coating method, any method such as roll coating or spraying and then squeezing with a roll may be used. In this result, the result of melamine-based paint was shown as an example, but it is also possible to apply various resins after this chromate treatment and use it as a base for organic composite steel sheet because of its excellent adhesion to organic resin. Is.

That is, after this chromate treatment, polyacrylic acid ester, olefin / acrylic acid copolymer resin,
Polymethacrylic acid and its copolymer resin, polymethacrylic acid ester and its copolymer resin, polyacrylic acid and its copolymer resin, polyacrylic acid ester and its copolymer resin, acrylic modified epoxy resin, ester modified epoxy Resin, acrylic modified epoxy ester resin,
Excellent adhesion is secured with any organic resin such as ester resin, epoxy resin, urethane-modified epoxy resin, and various water-based and solvent-based resins such as melamine resin.
Therefore, it is possible to form an organic composite plated steel sheet by forming the above organic film on the present chromate film because of its excellent adhesion to the organic resin, and it is also possible to directly form E
Since it has excellent adhesion to the coating film when it is D-painted or spray-painted, it is also most suitable as a base for coated steel sheets.

[0030]

EXAMPLES Examples of the present invention will be shown below together with comparative examples. Example 1 Zn-Ni alloy plated steel sheet (Basis weight: 20 g / m ² ,
Ni = 13.5%) was roll-coated with the following bath components and treated so that the Cr adhesion amount was 43 mg / m ² . Bath component Chromic acid 10 parts by weight Trivalent Cr / (trivalent Cr + hexavalent Cr) 0.6 Long chain colloidal silica (thickness: 8 to 10 nm, 5 parts by weight Length: 100 to 120 nm) Phosphoric acid 15 parts by weight MgO 3 parts by weight

Example 2 Zn-Fe alloy plated steel sheet (Basis weight: 20 g / m ² ,
(Fe = 12.2%) was roll-coated with the following bath components and treated so that the Cr deposition amount was 48 mg / m ² . Bath component Chromic acid 20 parts by weight Trivalent Cr / (trivalent Cr + hexavalent Cr) 0.9 Long chain colloidal silica (thickness: 8 to 10 nm, 18 parts by weight Length: 150 to 170 nm) Phosphoric acid 30 parts by weight MgO 4 parts by weight

Example 3 Zn-Al alloy plated steel sheet (Basis weight: 35 g / m ² ,
Al = 4.9%) was roll-coated with the following bath components, and treated so that the Cr adhesion amount was 55 mg / m ² . Bath component Chromic acid 25 parts by weight Trivalent Cr / (trivalent Cr + hexavalent Cr) 0.45 Long chain colloidal silica (thickness: 14 to 16 nm, 10 parts by weight Length: 230 to 250 nm) Phosphoric acid 32 parts by weight MgO 3 parts by weight

Example 4 Zn-Cr alloy-plated steel sheet (weight per unit area: 20 g / m ² ,
(Cr = 11.5%) was roll-coated with the following bath components and treated so that the Cr adhesion amount was 51 mg / m ² . Bath component Chromic acid 10 parts by weight Trivalent Cr / (trivalent Cr + hexavalent Cr) 0.95 Long chain colloidal silica (thickness: 4 to 6 nm, 15 parts by weight Length: 60 to 80 nm) Phosphoric acid 10 parts by weight MgO 3 parts by weight

Example 5 Zn-Mn alloy plated steel sheet (Basis weight: 20 g / m ² ,
(Mn = 40.8%) was roll-coated with the following bath components and treated so that the Cr deposition amount was 58 mg / m ² . Bath component Chromic acid 15 parts by weight Trivalent Cr / (trivalent Cr + hexavalent Cr) 0.60 Long chain colloidal silica (thickness: 16 to 18 nm, 18 parts by weight Length: 150 to 170 nm) Phosphoric acid 15 parts by weight MgO 5 parts by weight

Example 6 Zn-Ni-Co alloy-plated steel sheet (weight per unit area: 20 g /
m² , Ni = 12.5%, Co = 0.9%)
Minute roll coating, Cr adhesion amount is 52mg / m ² Becomes
Was treated as Bath component Chromic acid 13 parts by weight Trivalent Cr / (trivalent Cr + hexavalent Cr) 0.75 Long chain colloidal silica (thickness: 10 to 12 nm, 17 parts by weight Length: 130 to 150 nm) Phosphoric acid 30 parts by weight MgO 3 parts by weight

Example 7 Zn-Ni-Cr alloy-plated steel sheet (Basis weight: 20 g /
m² , Ni = 0.7%, Cr = 12.3%)
Minute roll coating, Cr adhesion amount is 57mg / m ² Becomes
Was treated as Bath component Chromic acid 25 parts by weight Trivalent Cr / (trivalent Cr + hexavalent Cr) 0.50 Long chain colloidal silica (thickness: 2 to 4 nm, 10 parts by weight Length: 30 to 50 nm) Phosphoric acid 23 parts by weight MgO 3 parts by weight

Comparative Example 1 A Zn-Ni alloy-plated steel sheet (Ni = 11.8%) was coated with the following bath components by a roll, and the Cr deposition amount was 50 mg / m.
Processed to be ² . Bath components Chromic acid 15 parts by weight Phosphoric acid 20 parts by weight

Comparative Example 2 A Zn-Ni alloy-plated steel sheet (Ni = 13.4%) was coated with the following bath components by a roll, and the Cr deposition amount was 46 mg / m.
Processed to be ² . Bath component Chromic acid 25 parts by weight Granular colloidal silica (particle size: 8 to 10 μ) 15 parts by weight

Comparative Example 3 Zn-Ni-Co alloy plated steel sheet (Ni = 10.1)
%, Co = 1.5%) with the following bath components on a roll,
The treatment was performed so that the amount of deposited Cr was 46 mg / m ² . Bath components Chromic acid 20 parts by weight MgO 5 parts by weight

Comparative Example 4 A Zn-Ni alloy plated steel sheet (Ni = 13.8%) was coated with the following bath components by a roll, and the Cr deposition amount was 46 mg / m.
Processed to be ² . Bath components Chromic acid 20 parts by weight Phosphoric acid 15 parts by weight MgO 3 parts by weight

Comparative Example 5 Zn-Ni-Cr alloy plated steel sheet (Ni = 2.1%,
Cr = 10.8%) with the following bath components by a roll,
The treatment was performed so that the amount of r adhered was 46 mg / m ² . Bath component Chromic acid 20 parts by weight Phosphoric acid 10 parts by weight Long-chain colloidal silica (thickness: 10 to 12 nm, 10 parts by weight: 100 to 120 nm)

Comparative Example 6 Zn-Ni-Co alloy plated steel sheet (Ni = 12.9)
%, Co = 1.8%) with the following bath components on a roll,
The treatment was performed so that the amount of deposited Cr was 46 mg / m ² . Bath component Chromic acid 25 parts by weight Long chain colloidal silica (thickness: 4 to 6 nm, 10 parts by weight Length: 30 to 40 nm) MgO 3 parts by weight

Comparative Example 7 Zn-Ni-Co alloy plated steel sheet (Ni = 10.8)
%, Co = 1.7%) with the following bath components on a roll,
The treatment was performed so that the amount of deposited Cr was 46 mg / m ² . Bath component Chromic acid 25 parts by weight Phosphoric acid 30 parts by weight Granular colloidal silica (particle size: 12 to 15 nm) 10 parts by weight MgO 5 parts by weight

Comparative Example 8 Zn-Ni alloy-plated steel sheet (Ni = 13.2%) Coated with the following bath components by a roll, and the Cr deposition amount was 57 mg / m ^2.
It was processed so that Bath component Chromic acid 25 parts by weight Trivalent Cr / (trivalent Cr + hexavalent Cr) 0.2 Long chain colloidal silica (thickness: 4 to 6 nm) 15 parts by weight Length: 100 to 120 nm) Phosphoric acid 30 parts by weight MgO 2 parts by weight

Table 1 shows the corrosion resistance by the salt spray test of Examples, and Table 2 shows the corrosion resistance by the salt spray test of Comparative Examples.
Further, Table 3 shows the adhesion of the coating film when 20 μm of the melamine-based coating material of the example is applied. Table 4 shows the adhesion of the comparative example. The salt spray test method is shown in Figure 1, Figure 3, Figure 5, Figure 7,
This is the same as FIG. 9, FIG. 11, FIG. 13 and FIG. Also,
Evaluation of paint adhesion is shown in Figure 2, Figure 4, Figure 6, Figure 8, Figure 10,
This is the same as FIG. 12, FIG. 14 and FIG. As is clear from Table 1, when the present invention is applied to various alloy-plated steel sheets, the corrosion resistance hardly changes after 1200 hours and 1500 h.
There is a slight amount of red rust on the 1st part.

[0046]

[Table 1]

[0047]

[Table 2]

On the other hand, as is clear from Table 2, when treated with a known chromate bath (Comparative Example 1), SST
About 400% of white rust had already occurred after 400 hours, and 600 hours
There was considerable red rust. In addition, the corrosion resistance is considerably lowered when the composition is deviated from the optimum bath composition or an inappropriate composition is used. Further, the adhesiveness of the coating film is also the same, and as is clear from Table 3, when the present invention is carried out, even a melamine-based paint which is difficult to obtain paint adhesiveness shows extremely excellent adhesiveness, but as is clear from Table 4. There is evidence of delamination when treated in the baths known in US Pat.

[0049]

[Table 3]

[0050]

[Table 4]

[0051]

As described above, the chromate film obtained according to the present invention is remarkably excellent in adhesiveness with a coating material, and thus is most suitable as a base for coated steel sheets.
It is also optimal as a base for various organic composite plated steel sheets.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between trivalent Cr / (trivalent Cr + hexavalent Cr) in a chromate bath and corrosion resistance,

FIG. 2 is a diagram showing a relationship between trivalent Cr / (trivalent Cr + hexavalent Cr) in a chromate bath and paint adhesion,

FIG. 3 is a diagram showing the relationship between chromic acid concentration and corrosion resistance,

FIG. 4 is a diagram showing the relationship between chromic acid concentration and paint adhesion,

FIG. 5 is a diagram showing the relationship between the amount of long-chain colloidal silica added and corrosion resistance;

FIG. 6 is a graph showing the relationship between the amount of long-chain colloidal silica added and paint adhesion,

FIG. 7 is a diagram showing the relationship between the length of long-chain colloidal silica and corrosion resistance,

FIG. 8 is a diagram showing the relationship between the length of long-chain colloidal silica and paint adhesion,

FIG. 9 is a diagram showing the relationship between the thickness of long-chain colloidal silica and corrosion resistance,

FIG. 10 is a diagram showing the relationship between the thickness of long-chain colloidal silica and paint adhesion,

FIG. 11 is a diagram showing the relationship between the particle size of granular colloidal silica and corrosion resistance;

FIG. 12 is a diagram showing the relationship between the particle size of the granular colloidal silica and the adhesiveness of the paint,

FIG. 13 is a diagram showing the relationship between the amount of phosphoric acid added and corrosion resistance;

FIG. 14 is a diagram showing the relationship between the amount of phosphoric acid added and paint adhesion,

FIG. 15 is a diagram showing the relationship between the amount of MgO added and corrosion resistance;

FIG. 16 is a diagram showing the relationship between the amount of MgO added and coating adhesion.

Claims (1)

[Claims] 1. Trivalent Cr / (trivalent Cr + hexavalent Cr) =
In a bath of 0.4 to 1.0 and 5 to 30 parts by weight of total chromic acid, 1 to 20 parts by weight of long chain colloidal silica having a thickness of 2 to 20 nm and a length of 25 to 250 nm, and phosphoric acid of 10 to 35 parts by weight. A metal-applied chromate treatment method, characterized in that a bath containing 3 to 10 parts by weight of MgO is applied to various metals.