JPH0686668B2 - Metal surface treatment composition and surface treatment method using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a metal surface treatment composition and a surface treatment method using the same, and more particularly to a coating-coated metal object having excellent corrosion resistance, scratch resistance and coating property. The present invention relates to a metal surface treatment composition capable of imparting film adhesion and a surface treatment method using the same.

[Problems to be Solved by Conventional Techniques and Inventions] Coating is generally performed for the purpose of decorating metal and preventing corrosion. In this step, so-called surface treatment such as zinc phosphate, iron phosphate, chromate, and anodizing treatment is carried out for the purpose of increasing the affinity between the metal and the coating film and imparting corrosion resistance and coating film adhesion. In recent years, in the field of metal painting, labor saving of painting process, reduction of manufacturing cost,
Aiming to be pollution-free for environmental protection, a coating / anhydrous wash-type chromate treatment was developed in which the formation of a chemical conversion treatment film by a conventional chemical reaction with a metal and subsequent washing work was omitted, and a precoat It is practiced in the field of plates (painted metal plates obtained by coil coating a metal plate in advance). As the coating type chromate treatment agent, the main agent is chromic chromate, which is a complex compound of trivalent chromium and hexavalent chromium,
Further, a composition has been proposed in which various additives are used together for the purpose of imparting corrosion resistance, scratch resistance, and film-forming property. For example, those using silica particles as an additive in addition to the main agent (Japanese Patent Publication No. 42-14050, Japanese Patent Publication No. 45-38891), those using organic polymer resins (Japanese Patent Publication No. 56-15790, Japanese Patent Laid-Open No. 50790). -1
03437), those using silica and organic polymer resin (Japanese Patent Publication No. 56-39393), those using organic polymer resin and heavy metal ions (Japanese Patent Publication No. 59-14552), organic polymer resin and oritriic acid (JP-A-59-123775) and the like have been proposed.

In general, there is a process in which a precoated plate is processed into a desired container at the customer. For example, household appliances such as refrigerators and washing machines, office furniture such as lockers and cabinets,
Molding processing such as roll forming, lock forming, bend forming, press forming, etc. is performed in various fields such as building materials such as roofing materials, interior and exterior wall materials, automobile parts such as doors, hoods, and fenders. . In this case, the coated plate may be scratched or squeezed by a mold or tools in the forming process, and the coating film may be peeled off to expose the metal base. Such a state not only impairs the appearance of the coated plate, but also significantly deteriorates the performance and loses its value as a product (hereinafter, this phenomenon is referred to as "scratch property"). As means for avoiding such a phenomenon, a strong coating film is applied, adhesion between the coating film and a metal is improved, and the surface morphology of the metal material or the surface-treated film is adjusted.

In particular, the scratch resistance correlates with the surface roughness of the metal or the surface-treated film, and in the surface treatment, a zinc phosphate film which forms a film having a depth of 1 to several microns is generally preferable. On the other hand, however, the coating type chromate that has been put into practical use has a film thickness of
Since it is 0.1 micron or less, it is pointed out that the scratch resistance is inferior when the metal material is relatively smooth. As a measure for compensating for such a defect, the above Japanese Patent Publication No.
The technique of using silica, which is an inorganic particulate substance having high hardness, as described in JP-A-38891, or the technique of using a fine-particle organic resin, as described in JP-A-58-213064, Proposed.

However, the specific gravity of this type of treatment agent that is generally put into practical use is around 1 to 1.2, and the dispersion stability of silica particles (2.3) with a large specific gravity is 0.3 micron or less and the particle size is 0.3 micron or less. Those having a particle size of 8 will be rapidly sedimented and separated in the treated liquid. Furthermore, it tends to become an unredispersible aggregate over time. Therefore, in the method of continuous coating at a high speed such as roll coating, the particle size of silica is limited, so that the target surface roughness cannot be obtained and scratch resistance is insufficient. Similarly, it is known that when a fine particle organic resin is used, a completely similar behavior is exhibited.

On the other hand, as a method for preventing the precipitation of the particulate matter, for example, a method of using an organic resin such as an acrylic emulsion as a thickener has been proposed, but since these organic resins cover the particles during the film formation process, The effect is diminished. Moreover, since most of the thickeners generally used in the water system are hydrophilic, the water resistance of the formed film is not sufficient, and therefore, the corrosion resistance of the precoated plate,
There is a problem that the weather resistance is not sufficient. Further, since a composition in which silica is used in combination is generally anionic, a method in which a cationic alumina sol or a zirconia sol is used in combination with this to adjust the charge in the composition to increase the viscosity is also considered. Is not a practical method because it becomes a gel.

The object of the present invention is to solve the above-mentioned conventional problems, that is, to form a surface treatment film having excellent corrosion resistance, scratch resistance, and coating adhesion, and to provide a stable surface treatment composition free from sedimentation and separation. And providing a surface treatment method using the same.

[Means for Solving Problems] The inventors of the present invention have conducted extensive studies based on the above-mentioned findings in order to achieve the above object, and as a result, have found that a chromic chromate compound composed of hexavalent chromium and trivalent chromium. (Less than,
A water-swellable layered silicate compound (hereinafter referred to as "layered silicate") is added to a composition consisting of "chromate") and a particulate silicon oxide compound (hereinafter referred to as "silica"). The present invention completes the present invention by discovering that the composition composed of the composition forms a film that greatly improves the scratch resistance of the coating film, and forms a stable water-dispersible composition in which sedimentation and separation of silica is suppressed. Came to.

That is, the present invention is characterized by containing (A) a chromic chromate compound composed of hexavalent chromium and trivalent chromium (B) a particulate silicon oxide compound and (C) a water-swellable layered silicate compound. The present invention relates to a metal surface treatment composition and a surface treatment method using the composition.

The chromate compound of the component (A) used in the present invention is a complex compound composed of hexavalent chromium and trivalent chromium compounds. The method for producing this chromate is not particularly limited, but it can be obtained, for example, by partially reducing a hexavalent chromium compound such as chromic anhydride, a water-soluble chromate or a dichromate. Examples of the reducing agent include polysaccharides such as sucrose and starch, alcohols such as methanol, ethanol, isopropyl alcohol, cellosolve, and ethylene glycol, and compounds such as hydroquinone, formaldehyde, and amines or chromic acid in the molecule. A substance containing a functional group that undergoes an oxidation-reduction reaction can be used. Hydrogen peroxide is preferred as the inorganic substance. To obtain partially reduced chromate, hexavalent chromium and 3
The reducing agent is added by a stoichiometric calculation to carry out the reaction so that the ratio of valent chromium is within a predetermined range. It is preferable to heat for the purpose of completing the reduction reaction.

The ratio of hexavalent chromium in the chromate in the present invention is in the range of 20 to 80% by weight (converted to CrO ₃ ) with respect to the total amount of chromium, and preferably 40 to 70% by weight. When the amount of hexavalent chromium is less than 20%, the corrosion resistance of the metal is insufficient, and the trivalent chromium in the metal surface treatment composition aggregates, resulting in poor liquid stability. On the other hand, if it exceeds 80% by weight, the water-soluble hexavalent chromium compound in the metal surface treatment film is large, so that the water resistance of the coated plate becomes insufficient and blister easily occurs.

Further, the stability of the chromate solution is preferably in the range of pH 1.5 to 3.5, and in the partial reduction reaction of the chromic acid compound and the reducing agent, it is necessary to adjust the pH within a predetermined pH range with an acid or an alkali. Is. That is, the pH
If it exceeds 3.5, the trivalent chromium in the chromate agglomerates and gels, making it unsuitable as a treatment liquid. Also pH 1.5
If it becomes lower, corrosion of the metal to be coated occurs and the function as a surface treatment agent disappears. The pH adjuster is not particularly limited as long as it is a compound or concentration range that does not affect the intended performance even if it remains in the metal surface treatment film. Preferably, the acid component is selected from phosphoric acid having a metal anticorrosive function, and the alkali component is selected from potassium hydroxide and potassium carbonate having a film forming auxiliary function. The chromate solution of the present invention is not limited to the method of partial reduction using a chromic acid compound as a starting material as described above, but the existing water-soluble trivalent chromium compound and the water-soluble chromic acid compound are mixed at a predetermined mixing ratio. They can also be mixed and manufactured.

The silica as the component (B) in the present invention is a main component for forming a scratch resistant film. The silica that can be used for such a purpose is classified into the following two types depending on the supply form to the market, and both can be used in the present invention.

(I) Silica powder: Fine particle silica synthesized by a gas phase method using a silicon tetrachloride compound as a starting material. So-called amorphous and porous synthetic silica such as silica obtained by finely pulverizing silica gel produced by gelation of silicic acid or silica obtained by dehydration drying of colloidal silica can be used. For example, Aerosil 200, OX50, TT600 pure silica and MOX80, MOX17 under the trade name "Aerosil"
Examples thereof include silica-alumina-modified products such as 0 and COK84, hydrophobic silica of R972, and siloids 244, 266, 7265, 978 represented by trade name "Syloid", or hydrophobically treated 162.

(Ii) Water-dispersible silica: produced by sodium removal of water glass, which was so-called colloidal silica. This is usually supplied as an aqueous dispersion. The form of colloidal silica that can be used in the present invention is effectively an acidic dispersion system or a dispersion system of particles in which the silica surface is modified with aluminum, and is shown, for example, under the trade name "Snowtex",
Snowtex O, OL, C, etc. are illustrated.

The particle size of silica effective in the present invention is in the range of 0.01 to 5 microns, preferably 0.1 to 1 micron. Particle size is
If it is less than 0.01 micron, the functions of scratch resistance, coating adhesion and corrosion resistance cannot be fully exerted. On the other hand, if it exceeds 5 microns, even if an inorganic thickener, which will be described later, is used, sedimentation occurs and the stability of the metal surface treatment liquid deteriorates. In addition, the formed metal surface treatment film becomes weak and the adhesion of the paint is deteriorated.

The amount of silica in the composition is in the range of 10/90 to 70/30 by weight ratio of silica / chromate, preferably 30/70.
~ 50/50. If the amount of silica is less than 10% or the amount of chromate is more than 90%, the functions of scratch resistance, coating adhesion and corrosion resistance deteriorate. On the other hand, if it exceeds 70%, the formed film becomes weak and the adhesion of the coating film deteriorates.

The water-swellable layered silicate of the component (C) in the present invention is the most featured material of the present invention that acts to prevent the silica component of the composition from settling. Further, since this material itself is hard fine particles, it can contribute to scratch resistance.

This layered silicate forms stable colloids in polar solvents such as water, alcohols, amines, etc., and changes from the sol state to the gel state depending on its concentration, and its dispersion exhibits thixotropic properties. Therefore, by using an appropriate amount of the water-swellable layered silicate, it is possible to uniformly disperse the inorganic granular material having a large specific gravity and prevent sedimentation separation. Further, due to the thixotropic property, the viscosity becomes low due to the shear stress during roll coating, and a predetermined amount of uniform film can be formed.

The water-swellable layered silicate having such a function is
A group of so-called montmorillonite minerals having a 2-octahedral structure and a 3-octahedral structure belonging to a phyllosilicate, and a cation-type ion having a small ionic radius such as Li, Na, and Ca and having high hydration property is coordinated between layers. What has been done is suitable.
Examples of such a substance include montmorillonite [(OH) ₄ Si ₃ (Al _3.34 · Mg _0.66 ) O ₂₀ · Na _0.66 ] beidellite [(OH) ₄ (Si _6.34 · Al _1.66 ) Al _4.34 O ₂₀ · Na _0.66 ] non- Tronite [(OH) ₄ (Si _7.34・ Al _0.66 ) Fe ³⁺ ₄ ▼ O ₂₀・ Na _0.66 ] Hectorite [(OH) ₄ Si ₈ (Mg _5.34・ Li _0.66 ) O ₂₀・ Na _0.66 ] Saponite [ (OH) ₄ (Si _7.34・ Al _0.66 ) Mg ₆ O ₂₀・ Na _0.66 ]. Further, as synthetic minerals having these forms, there are those synthesized by hydrothermal reaction or melting reaction by compositional composition of desired minerals. For example, JP-B-44-813, hectorite-like structure compounds described in JP-A-48-96499, saponite-like structure compounds described in JP-A-58-181718 {[(Si _7.20 Al _0.80 ) (Mg _5.97 Al _0.03 ). O
₂₀ (OH) ₄ ] ^-0.77 (Na _0.49 Mg _0.14 ) ^+0.77 } compound, fluorine tetrasilicon mica described in JP-A-52-150344 as a mica mineral group, for example, [NaMg _2.5 (Si ₄ O ₁₀ ). F ₂ ], [Ca _0.5 Mg _2.5 (Si ₄ O ₁₀ ) F ₂ ], [HMg _2.5 (Si ₄ O ₁₀ ) F ₂ ], [Al _0.3 Mg _2.5 (Si ₄ O ₁₀ ) F ₂ ], [Ba _0.5 Mg _2.5 (Si ₄ O ₁₀ ) F ₂ ], teniolites such as [NaMg ₂ Li (Si ₄ O ₁₀ ) F ₂ ], [LiMg ₂ Li (Si ₄ O ₁₀ ) F ₂ ], fluorine hectorites, For example, [Na _1/3 Mg _{2 (2/3)} Li _1/3 (Si ₄ O ₁₀ ) F ₂ ] and [Li _1/3 Mg _{2 (2/3)} Li _1/3 (Si ₄ O ₁₀ ). F ₂ ], etc. are valid.

As a specific product, for example, a product name “Osmos”, which is a purified natural bentonite belonging to montmorillonite,
Synthetic minerals include "Smecton", a trade name belonging to saponite, and "Dimonite", a trade name belonging to tetrafluorosilicon mica. Further, an organically modified layered silicate having an amine compound or the like inserted between layers of the swelling type layered silicate, or a water-swellable layered silicate (natural or synthetic) other than the above substances has the functions required for the present invention. If so, it can be applied to the present invention without any limitation.

The amount of the layered silicate effective in the present invention is 0.1 to 10% by weight as the solid content in the composition liquid. If the concentration is less than 0.1% by weight, the liquid viscosity effect sufficient to prevent the sedimentation of silica particles cannot be obtained. On the other hand, if it exceeds 10% by weight, the composition liquid will be completely gelled to form a hard cake, and will not exhibit fluidity even when subjected to shear stress, and cannot be used as a surface treatment agent.

The method for producing the composition of the present invention is as follows.
Chromate (B) silica is mixed in a predetermined amount, and both are sufficiently dispersed and mixed under stirring, and then (C) layered silicate is added under stirring to swell. Then the composition is appropriate
It can be carried out by adjusting the acid or alkali so that it falls within the pH range.

The metal surface treatment composition of the present invention has iron or iron alloy, aluminum or aluminum alloy, zinc or zinc alloy, copper or copper alloy, tin or tin alloy, or these metals as a multi-layer as an object to be coated. Metals and so-called surface-treated metals that have been subjected to acid treatment, chromate treatment, cobalt-iron composite oxide film treatment, electrolytic treatment, etc., to these metals are subjected to a predetermined degreasing treatment in advance to clean the metal surface. After that, it is applied by a method such as roll coating, spray coating, dip coating, and brush coating, and then dried to obtain a metal surface-treated film.

The above dry film amount is 10 to 1000 mg / m in terms of chromium atoms.
² , preferably in the range of 30 to 300 mg / m ² .
When the coating amount is less than 10 mg / m ² , the coating is too thin to obtain the surface shape required for scratch resistance, and the corrosion resistance is significantly poor. On the other hand, when the coating amount exceeds 1000 mg / m ² , the formed coating becomes brittle and the adhesion of the coating decreases. The drying conditions may be such that the water content in the chromate composition evaporates, but it is usually in the range of 60 to 250 ° C, preferably 100 to 200 ° C at the temperature of metals. When the film-forming temperature is lower than 60 ° C., for example, in a combination in which the overcoat film is a room-temperature dry type, the water-soluble hexavalent chromium in the metal surface-treated film may lower the water-resistant adhesion. Further, when the film forming temperature exceeds 250 ° C., hexavalent chromium decreases during film formation, and water-soluble hexavalent chromium in the film remarkably decreases, resulting in insufficient corrosion resistance of the coated article.

The surface-treated metals thus obtained can be coated for the purpose of imparting decorativeness, anticorrosion and functionality.
That is, any conventionally known organic solvent-based, water-based, solvent-free and powder-based coatings can be applied, and a single-layer coating or a multi-layer coating such as two or three layers depending on the purpose of coating. It is possible to These paints can be applied by any of the coating methods such as roll, spray, dip, brush, electrophoresis and electrostatic, and baking can be carried out from room temperature curing to heat curing, infrared curing, ultraviolet curing depending on the type of the top coating material. Any method such as curing or electron beam curing is possible. For example, electrodeposition for automobiles-intermediate coating-
Top coating system; Primer such as precoat metal for building materials-Top coat system; One coat system for electrical steel products etc .; Heavy anticorrosion coating system for ships, bridges, pipes, etc. and resin lining other than coating, laminating system etc. Is possible.

The metal surface treatment composition of the present invention can also be added with metal ions which are said to have a surface adjusting function for metals, such as cobalt, nickel, titanium, zirconium and the like. Further, it is possible to add an organic compound or an organic resin as a film forming reinforcing material.

[Examples] Examples and comparative examples will be described below. These examples illustrate the invention in more detail and do not limit the scope of the invention. Parts and% are parts by weight and% by weight
Indicates.

Example 1 150 parts of chromic anhydride (CrO ₃ ) was dissolved in 1000 parts of water, 13 parts of corn starch was added, and the mixture was heated and boiled for 3 hours to obtain a partially reduced chromate compound having a solid content of 16%. The amount of hexavalent chromium in this chromate compound was 63.2% by weight in terms of CrO _{3 with} respect to the total amount of chromium. Then silica powder (made by Nippon Aerosil Co., Ltd.,
Product name “Aerosil OX50” and water-swellable layered silicate powder (Kunimine Industry Co., Ltd., product name “Smecton”) are mixed so that the solid content is 12%, 12%, and 1%, respectively, and mixed by stirring. Thus, a metal surface treating agent having a high viscosity (Brookfield type rotational viscometer 6/60 rpm value 246/62 centipoise) was prepared.

Immediately after producing the above surface treatment agent, 200 g was taken in a 450 ml mayonnaise bottle, and the appearance after standing still at room temperature for 24 hours and stirring with a shaker (SA31 type manufactured by Yamato Scientific Co., Ltd.) 240 times / minute-10 minutes The subsequent appearance was observed and stability was examined. As a result, there was no abnormality and no precipitate was observed.

Next, on the minimum spun hot-dip galvanized steel sheet that has been degreased with a silicate-based alkaline cleaner (manufactured by Nippon CB Chemical Co., Ltd., trade name "CC561B"), the surface treatment agent of the above-mentioned formulation example 1 is applied in a dry film amount of chromium. Roll coat to a conversion of 50 mg / m ² and then peak metal temperature at 10
It was dried under the condition of reaching 0 ° C to prepare a yellowish brown chromate surface-treated plate. Then, on this treated plate, epoxy primer paint for precoat metal (manufactured by Kansai Paint Co., Ltd.,
Product name "KP Color 8470 Primer") is applied and 210 ℃
It was heated and cured for 50 seconds to prepare a coated plate having a film thickness of 5 μm. Then, a polyester-based topcoat material (manufactured by Kansai Paint Co., Ltd., trade name "KP Color 1470 Blue") was applied to the coated plate, and baked at 220 ° C for 50 seconds to prepare a coated plate having a total dry film thickness of 25 microns. The coated plate was tested for scratch resistance (coin scratch test, load shear test), folding adhesion, salt spray corrosion resistance, and wet resistance. As shown in Table 2, all the results are good. It was

Examples 2 to 10 Metal surface treating agents having the formulations shown in Table 1 were prepared in the same manner as in Example 1, and the stability thereof is shown in Table 2. Next, these metal surface treating agents were prepared in the same manner as in Example 1 to prepare a coated plate and perform a performance test. Table of the results
Shown in 2. All showed excellent performance.

Examples 11 to 21 In Example 1, the metal to be coated was a steel plate, a stainless plate,
Aluminum plate, chrome / magnesium / aluminum alloy plate, 5% aluminum / zinc plated steel plate, 55% aluminum / zinc plated steel plate, copper plate, tin plated steel plate, zinc phosphate treated hot dip galvanized steel plate, chromic acid electrolytic treated steel plate,
A coated plate was prepared and a performance test was carried out in the same manner as in Example 1 except that the cobalt-iron composite oxide film-treated galvanized steel plate was used. The results are shown in Table-3. All showed excellent performance.

Comparative Examples 1 to 6 Metal surface treatment agents were prepared with the formulations shown in Table-1. The stability of the treating agent is shown in Table-2. Next, using these treating agents in the same manner as in Example 1, a coated plate was prepared and a performance test was conducted. The results are shown in Table-2.

Comparative Examples 7 to 17 Using the metal surface treating agent of Comparative Example 5, the coated plate was prepared and the performance test was conducted in the same manner as in Examples 11 to 21. The results are shown in Table-3. All of them had poor scratch resistance.

* 10 Scratch resistance: Hold an unbroken 10-yen coin at 45 ° with respect to the coated surface and scratch the coated surface so strongly that it reaches the substrate. The length to scratch is about
Check the appearance of the painted surface by making it 50 mm and making scratches at a right angle into a cross.

Evaluation point 5: Only scratches on the painted surface and no exposure of the base material.

〃 3: The exposure of the base material is recognized at a part such as the intersection of the crosses.

Evaluation point 1: Obviously, the exposure of the substrate is recognized.

* 11 Load shear resistance: Two 50 x 50 mm square coated plates (A, B) are put together and a load of 10 kg / cm ² is applied to rotate the B coated plate 90 ° relative to the A coated plate. After that, check the appearance of the painted surface.

Evaluation point 5: Only scratches on the painted surface and no exposure of the base material.

 〃 3: Slight exposure of the substrate is recognized.

 〃 1: Exposed body with a length of 10 mm or more is recognized.

* 12 Adhesion by folding: Bending about 180 ° around a rod with a diameter of 2 mm with the coated surface with a width of 50 mm outside, and sandwich a plate with the same thickness as the test piece in this part for a vise. Use to tighten. Then, press the cellophane adhesive tape firmly on the bent part with your hand to bring it into close contact, and then quickly peel it off and observe the degree of peeling.

Evaluation point 5: No peeling of coating film 〃 4: Length of peeling is 3 ± 1mm 〃 3: 〃 8 ± 2mm 〃 2: 〃 17 ± 3mm 〃 1: 〃 30 ± 4mm * 13 Salt spray corrosion resistance: According to JIS-Z-2371. A cross-cut is made with a knife so as to reach the base material on the coated surface, and after a lapse of a predetermined time, the peeling width on one side from the portion is evaluated.

* 14 Wet resistance: According to JIS-Z-0228. The coated plate is placed in a humidity test box at 50 ° C and 100% RH for 2000 hours and then taken out, and the state of the coated surface is observed.

[Effects of the Invention] As is clear from the above description, according to the present invention, since coarse silica powder can be uniformly dispersed in the chromate treatment agent without sedimentation and separation, coating such as roll coating is possible. It is possible to form a metal surface treatment film having a uniform surface property. Therefore, according to this method, it is possible to prevent the occurrence of scratches and ironing scratches on the coated plate, which was a difficulty in the conventional coating type chromate treatment in the precoat metal coating, and yet to provide excellent coating film adhesion and corrosion resistance. It is a composition.

Claims (10)

[Claims] 1. A composition containing (A) a chromic chromate compound composed of hexavalent chromium and trivalent chromium, (B) a particulate silicon oxide compound, and (C) a water-swellable layered silicate compound. A metal surface treatment composition, wherein the concentration of the water-swellable layered silicate compound (C) is 0.1 to 10% by weight as a solid content in the composition liquid. 2. A chromic chromate compound (A) containing 6
The amount of valent chromium is 20-80% by weight (CrO ₃
The metal surface treatment composition according to claim 1, wherein 3. The metal surface treatment composition according to claim 1, wherein the weight ratio of the chromic chromate compound (A) / the particulate silicon oxide compound (B) is 90/10 to 30/70. 4. The particle size of the particulate silicon oxide compound (B) is
The metal surface treatment composition according to claim 1, which is 0.01 to 5 microns. 5. The metal surface treatment composition according to claim 1, wherein the water-swellable layered silicate compound (C) is a synthetic mineral belonging to saponite. 6. A composition containing (A) a hexavalent chromium and trivalent chromium chromic chromate compound, (B) a particulate silicon oxide compound, and (C) a water-swellable layered silicate compound. A metal surface treatment composition in which the concentration of the water-swellable layered silicate compound (C) is 0.1 to 10% by weight as the solid content in the composition liquid is applied to the surface of a metal to be coated and dried. A surface treatment method characterized by densification. 7. The surface treatment method according to claim 6, wherein the coating amount of the metal surface treatment composition is in the range of 10 to 1000 mg / m ² in terms of chromium atoms. 8. The object to be coated is iron or an iron alloy, aluminum or an aluminum alloy, zinc or a zinc alloy, copper or a copper alloy, tin or a tin alloy, or a metal in which these metals are formed into a multilayer. The surface treatment method according to claim 6. 9. An article to be coated is a phosphate treatment, a chromate treatment,
The surface treatment method according to claim 6, which is a surface-treated metal subjected to a composite oxide film treatment or an electrolytic treatment. 10. The surface treatment method according to claim 6, wherein one or more paints selected from organic solvent-based, water-based, solvent-free and powder-based coatings are applied after the surface treatment. .