JPH0748678A - Surface coating method - Google Patents

Abstract

PURPOSE:To form a corrosion preventive coating film having excellent corrosion resistance with reduced man-hour at a low cost by pretreating a substrate. CONSTITUTION:A metallic substrate coated with a baking metal corrosion preventive composition contg. a water-soluble chromic acid compd. and powder zinc is dipped immediately after baking and heating in a liq. composition contg. a chromic acid compd. and/or a single resin to coat the substrate surface. Thus, a corrosion preventive coating film excellent in corrosion resistance is formed with reduced man-hour at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface coating method, and more particularly to a method for forming a coating film having a high degree of corrosion resistance on a metal surface.

[0002]

2. Description of the Related Art Various compositions are known as coating compositions used for corrosion protection of metals mainly composed of steel. As a coating composition having an excellent effect, there is a metal anticorrosion coating composition containing chromic anhydride and a metal powder such as zinc and aluminum, which is described in JP-B-60-50228. As one of them, Dacrodip (registered trademark) is commercially available.

This Daclodip (registered trademark) is usually a first component containing chromic anhydride and water as main components, a second component containing a metal powder and an oxohydroxy low molecular weight ether such as propylene glycol, and a thickening agent. Provided to the user as a combination with the agent. The user mixes the first component, the second component, and the thickener at the time of use, and applies a certain amount to the surface of the metal base material on which the coating film is to be provided. The coating amount is usually the amount necessary to finally form a coating layer of several microns or more. Then, the coated metal can be heated at a temperature of about 300 ° C. for a predetermined time to form a coating film on the metal substrate.

This coating film exerts an excellent effect of preventing corrosion of iron and steel against salt water, but recently, an anticorrosion film having higher corrosion resistance is required. In order to meet this demand, after the above-mentioned coating treatment (hereinafter referred to as "first coating treatment"), further coating treatment such as chromate treatment or coating treatment (hereinafter referred to as "second coating treatment") ) Is often applied. As described above, by performing the second coating treatment after the first coating treatment, it becomes possible to satisfy the requirement for the corrosion resistance. However, since coating, baking, and cooling are performed in the first coating processing step, and then coating, baking, and cooling are performed again in the second coating processing step, the processing man-hour is almost doubled, and processing time and processing cost are increased. The big increase was a problem.

An object of the present invention is to solve the above problems. That is, it is an object of the present invention to provide a surface treatment method capable of forming an anticorrosion coating having excellent corrosion resistance at a low cost with a reduced number of treatment steps.

[0006]

The invention according to claim 1 for solving the above-mentioned problems is a metal base coated with a baking type metal anticorrosion composition containing a water-soluble chromic acid compound and zinc powder. The material is a surface coating treatment method characterized by immersing the material in a liquid composition containing a chromic acid compound and / or a resin immediately after the baking and heating treatment in the coating treatment, and the invention according to claim 2 is The surface coating treatment method according to claim 1, wherein the metal base material maintained at 50 ° C. or higher after the baking heat treatment is immersed in the liquid composition, and the invention according to claim 3,
The surface coating method according to claim 1 or 2, wherein the metal after the baking and heating treatment is immersed in the liquid composition for 30 minutes or less.

The present invention will be described in detail below.

The bake-type metal anticorrosive composition is not particularly limited as long as it contains a water-soluble chromic acid compound and zinc powder.

The water-soluble chromic acid compound is not particularly limited, and known compounds can be used,
For example, water-soluble metal salts of chromic acid such as chromic anhydride, calcium chromate and magnesium chromate, and heavy metal salts such as zinc dichromate, potassium dichromate, sodium dichromate, magnesium dichromate and calcium dichromate. Chromates may be mentioned.

Although the zinc powder may have any shape, it is preferable that it has a flake shape. In particular, the zinc powder has a thickness of 0.1 to 0.5 μm and a longest length of 15 μm or less. It is preferably flake. The zinc powder may be used together with the aluminum powder.

The content ratio of the water-soluble chromic acid compound is
It is 1 to 12% by weight, preferably 2 to 8% by weight, based on the composition finally obtained. The content ratio of the zinc powder is 10 to 4 with respect to the finally obtained composition.
It is 0% by weight, preferably 15 to 30% by weight.

The bake-type metal anticorrosive composition comprises the zinc powder, the water-soluble chromic acid compound, and boric acid or boron oxide, oxohydroxy low-molecular weight etal and a pH adjusting agent, and a wetting agent which are added as necessary. , Water and /
Alternatively, it contains an organic solvent.

As the boric acid, commercially available orthoboric acid is suitable, and if necessary, metaboric acid or tetraboric acid may be used instead of or together with the orthoboric acid. When boric acid and / or boron oxide is used, its content in the baking-type metal anticorrosive composition is usually 10 to 75% by weight based on the total weight of boric acid and / or boron oxide and the water-soluble chromic acid compound. %, And preferably 15 to 50% by weight. When the content of boric acid and / or boron oxide is within the above range, it is possible to obtain a composition exhibiting an excellent anticorrosion action against both environments of salt water and fresh water.

As the oxohydroxy low molecular weight ether, glycol and its low molecular weight ether type polymer can be used, and specifically, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene. Mention may be made of glycols, diacetone alcohol and close homologues and mixtures thereof.
These ethers can act as a reducing agent for the water-soluble chromic acid compound to convert it into a chromic acid compound, and moreover, the baking-type metal anticorrosive composition is applied to the surface of the metal substrate and then heated. At the time of forming the coating film, it is possible to prevent boiling evaporation of the solvent and the like by gradually volatilizing during formation of the coating film, and to facilitate formation of a uniform anticorrosion coating.

The pH adjuster is effective when used when the water-soluble chromic acid compound is strongly acidic. This pH
The adjusting agent is used to adjust the pH of the mixed solution between 3.0 and 6.0, and is usually lithium, strontium, calcium, barium, magnesium, zinc, cadmium or lithium and IIA. It is selected from oxides and hydroxides of metals that belong to the group or higher-valued groups. This pH adjuster adjusts the pH of the bake-type metal anticorrosive composition to a value between 3 and 6, keeps the storage stability of the bake-type metal anticorrosive composition in the optimum state, and prevents the zinc powder and the acids in the liquid. It is possible to prevent a rapid reaction and deterioration of the adhesiveness of the coating layer or darkening of the appearance.

The wetting agent is used to assist in the suspension and dispersion of the zinc powder. Examples of the wetting agent include nonionic surfactants, particularly alkylphenol polyethoxy addition compounds such as "Nobco 1592" (registered trademark) manufactured by Diamond Shamrock, USA.

The baking type metal anticorrosion composition of the present invention comprises:
The components can be prepared by a known method, for example, by mixing them using a high speed stirrer or the like.

Preferred baking-type metal anticorrosion compositions are disclosed in Japanese Patent Publication No. 60-50228, which include chromic anhydride, metals such as zinc and aluminum, and pH adjusters such as metal oxides and hydroxides. Examples thereof include a composition containing oxohydroxy low molecular weight ether such as polyglycols and a solvent (commercially available as Daclodip (registered trademark)).

This bake-type metal anticorrosion composition usually comprises a first component containing chromic anhydride and water as main components,
Provided to the user as a combination with a metal powder and a second component containing an oxohydroxy low molecular weight ether and a thickener.

The user mixes the first component, the second component and the thickener at the time of use and applies a fixed amount on the surface of the metal base material on which the coating film is to be provided. The coating amount is usually the amount necessary to finally form a coating layer of several microns or more. Then, the coated metal can be heated at a temperature of about 300 ° C. for a predetermined time to form a coating film on the metal substrate.

The metal base material is not particularly limited in size, shape, etc., and a known metal base material can be used. Since the method of the present invention exerts an excellent effect particularly on the corrosion protection of steel, a steel base material is often used. However, in this method, it is preferable to remove dust and oils and fats on the surface of the metal base material to be coated with an alkaline cleaner or a chlorine-based vapor cleaning solvent.

The coating treatment of the baking type metal anticorrosion composition on the metal substrate includes coating and baking.

The above-mentioned coating is known, for example, brush coating, tampo coating, spray coating, hot spray coating, air spray coating, electrostatic coating, roller coating, curtain flow coating, flow coating, dip coating, electrodeposition coating, spatula coating, etc. Can be performed by the method of. When using dip coating,
After the immersion, the extra droplets may be removed by centrifugal shaking off or vibration.

In the baking, a metal substrate coated with the baking type metal anticorrosion composition is heated in a hot air circulating furnace (IDG combustion furnace or electric furnace), far infrared heating furnace, infrared heating furnace, high frequency induction heating furnace, or the like. It is carried out by heating by a method selected from the combination. The heating is performed at a temperature of 180 ° C. or higher for at least 0.2 seconds or longer, preferably 20 seconds.
0.5 seconds or more at a temperature of 0 ° C. or more, more preferably 26
It is performed at a temperature of 0 ° C. or higher for 0.5 seconds or longer.

The coating treatment can be repeated if necessary.

In this coating treatment, a metal substrate is usually coated with
A coating film having a thickness of 1 μm or more, preferably 3 μm or more is formed. When the thickness of the coating film is 3 μm or more, more stable corrosion resistance performance can be exhibited.

In the method of the present invention, the coating-treated metal substrate is immersed in a liquid composition containing a chromic acid compound and / or a resin immediately after the baking treatment in the coating treatment.

Here, "immediately after heat treatment" means that the metal base material after the heat treatment for baking addition is not completely cooled. Therefore, the dipping treatment is performed while the metal base material after the heat treatment for baking addition in the coating treatment is not completely cooled. The temperature of the metal substrate immersed in the liquid composition is preferably 50 ° C. or higher, and usually 50 to 350.
C., preferably 100 to 300.degree. When the temperature of the metal base material is 50 to 350 ° C., a coating film having a particularly beautiful appearance can be formed.

As the liquid composition containing a chromic acid compound and / or a simple substance of resin, generally used is a composition which forms a coating film by performing a drying treatment after coating.

The chromic acid compound contained in this liquid composition may be the same as the water-soluble chromic acid compound contained in the baking type metal anticorrosion composition used in the coating treatment. The type of chromic acid compound used in this dipping treatment and the type of water-soluble chromic acid compound used in the coating treatment may be the same or different. The chromic acid compounds used in this dipping treatment may be used alone or in combination of two or more.

Examples of the resin include a water-soluble resin, a resin dispersed in water as an emulsion, and a resin suspended in water. Specific examples of the resin include acrylic resin, polyester resin, polyethylene resin, polyvinyl resin, epoxy resin, butadiene resin, melamine resin, alkyd resin, and phenol resin. Among these, an acrylic resin can be mentioned as a preferable resin.

The liquid composition may contain a chromic acid compound without containing a resin, may contain a resin without containing a chromic acid compound, and may contain a chromic acid compound and a resin. It may be. In the method of the present invention, the liquid composition preferably contains both a chromic acid compound and a resin. In a liquid composition containing a chromic acid compound and a resin, the content of the chromic acid compound contained in the liquid composition is usually 0.1 to 50% by weight, preferably 0.5 to 30%. The resin content is usually 0.5 to 40% by weight, preferably 0.5 to 20% by weight.

Among the above-mentioned liquid compositions, preferred are chromate treatment liquid marketed as Dacromet # 100 (manufactured by Japan Dacro Shamrock Co., Ltd.) and resin coating marketed as Dacromet LTX (manufactured by the same company). An agent etc. can be mentioned.

When the liquid composition contains a solid content, the solid content concentration is preferably adjusted to 0.5 to 90% by weight, more preferably 1 to 50% by weight. When the solid content concentration is 0.5 to 90% by weight,
It is possible to obtain a coating film having a beautiful appearance and an appropriate film thickness.

In the surface treatment method according to the present invention, the temperature of the liquid composition may be important. If the temperature of the liquid composition is too low, the cooling effect may be too great to form a proper film. On the other hand, if the temperature of the liquid composition is too high, the liquid composition itself may deteriorate.
Although the temperature of the liquid composition varies depending on the temperature of the metal substrate to be dipped and the like, it is usually preferably adjusted to 5 to 95 ° C.

The immersion time of the metal base material that has been baked in the coating treatment in the liquid composition is preferably 20 minutes or less, but is usually 0.1 second to 30 minutes, preferably 0.5. Seconds to 5
Minutes. When the immersion time is 0.1 seconds to 30 minutes, a sufficient coating film is adhered to the metal base material, and the temperature of the base material does not drop too much, so that the heating and drying effect by baking in the coating treatment is effective. It will not be lost.

In the method according to the present invention, baking after the dipping treatment is usually unnecessary. It goes without saying that simple drying may be performed if necessary.

In the dipping treatment, usually, it is 0.
A coating film having a thickness of 1 μm or more, preferably 1 μm or more is formed. When the thickness of the coating film is 1 μm or more, it is possible to impart more stable corrosion resistance to the coating film formed by the first coating treatment, which is preferable.

[0039]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

The coating film formed in the examples was evaluated as follows.

1. Appearance The presence or absence of scale unevenness was visually observed.

The evaluation was carried out in the following three stages.

◎ ・ ・ ・ very good ○ ・ ・ ・ good ○ to △ ・ Slightly inferior but practically no problem △ ... inferior Corrosion resistance performance After carrying out the combined cycle corrosion test, the generation state of red rust was visually observed. The evaluation was performed in the following three stages.

◎ ・ ・ ・ Very good ○ ・ ・ ・ Good ○ ～ △ ・ Slightly inferior but practically no problem △ ... Inferior Required Treatment Time The time required for the treatment (man-hours) was relatively evaluated based on Comparative Example 1.

As the test base material, M10 mild steel bolts (total length: about 47 mm, weight: about 22 g) were used after being washed with solvent vapor and then dry-honed.

(Example 1) In the coating treatment, as a baking type metal anticorrosive composition, Dacrodip (registered trademark) was prepared by mixing by a predetermined method. In the immersion treatment, as a liquid composition containing a chromic acid compound (not containing a resin), Dacromet # 100BL (registered trademark,
A black chromate treatment liquid) was prepared. The composition of Dacrodip is as follows.

Chromic anhydride content: about 4% by weight Zinc powder content: about 20% by weight The test substrate was dipped in Dacrodip and centrifuged off. Then, put the test substrate in an electrically heated hot air circulation furnace,
After the temperature of the test base material reached 300 ° C. in the furnace, baking was performed by maintaining the same temperature for 5 minutes. When the temperature of the test substrate taken out of the furnace dropped to 290 ° C,
It was immersed in Dacromet # 100BL adjusted to 50 ° C., and after 1 second, it was pulled up and dried.

The coating weight of the coating film on the test substrate by the coating treatment was 100 mg / dm ² , and the same weight by the dipping treatment was 50 mg / dm ² . The test base material after the completion of the dipping treatment was evaluated by the above method. The results are shown in Table 1.

Example 2 The procedure of Example 1 was repeated except for the following points.

Dacromet LTX (registered trademark, clear) containing a resin (not containing a chromic acid compound) was prepared as a liquid composition used in the dipping treatment. After baking in the coating treatment, when the temperature of the test base material dropped to 250 ° C., it was immersed in Dacromet LTX (registered trademark, clear) adjusted to 40 ° C., and after 2 seconds, pulled up and dried.

The weight of the coating film deposited on the test substrate by the coating treatment was 100 mg / dm ² , and the same weight by the dipping treatment was 80 mg / dm ² . The test base material after the completion of the dipping treatment was evaluated by the above method. The results are shown in Table 1.

(Example 3) The same operation as in Example 1 was carried out except for the following points.

As a liquid composition used in the dipping treatment, Dachromet # 100 (registered trademark, chromate treatment liquid) containing a chromic acid compound (not containing a resin) was prepared. The immersion time in Dacromet # 100 was 5 seconds.

The weight of the coating film adhered to the test substrate by the coating treatment was 100 mg / dm ² , and the same weight by the dipping treatment was 50 mg / dm ² . The test base material after the completion of the dipping treatment was evaluated by the above method. The results are shown in Table 1.

Example 4 The same procedure as in Example 1 was carried out except for the following points.

In the baking of the coating treatment, after the temperature of the test base material reached 350 ° C. in the electrically heated hot air circulation furnace, it was held at the same temperature for 5 minutes. When the temperature of the test base material taken out from the furnace dropped to 300 ° C., it was immersed in the liquid composition adjusted to 95 ° C., and after 5 seconds, pulled up and dried.

The weight of the coating film deposited on the test substrate by the coating treatment was 100 mg / dm ² , and the same weight by the dipping treatment was 100 mg / dm ² . The test base material after the completion of the dipping treatment was evaluated by the above method. The results are shown in Table 1.

Example 5 The same procedure as in Example 1 was carried out except for the following points.

In the baking of the coating treatment, when the temperature of the test base material taken out from the electrically heated hot air circulation furnace dropped to 270 ° C., it was immersed in the liquid composition adjusted to 20 ° C.,
After 0.5 seconds, it was pulled up and dried.

The coating weight of the coating film on the test substrate by the coating treatment was 100 mg / dm ² , and the same weight by the dipping treatment was 30 mg / dm ² . The test base material after the completion of the dipping treatment was evaluated by the above method. The results are shown in Table 1.

Example 6 The same procedure as in Example 1 was carried out except that the dipping treatment was carried out after the coating treatment was repeated twice.

The weight of the coating film adhered to the test substrate by the coating treatment was 200 mg / dm ² , and the same weight by the dipping treatment was 100 mg / dm ² . The test base material after the completion of the dipping treatment was evaluated by the above method. The results are shown in Table 1.

Example 7 The procedure of Example 1 was repeated except for the following points.

As the liquid composition used in the dipping treatment, Dacromet # 100BL (registered trademark, chromate treatment liquid)
A 10% water-based acrylic acid ester (manufactured by Showa Highpolymer Co., Ltd.) was added and mixed as a resin.

The weight of the coating film adhered to the test substrate by the coating treatment was 100 mg / dm ² , and the same weight by the dipping treatment was 50 mg / dm ² . The test base material after the completion of the dipping treatment was evaluated by the above method. The results are shown in Table 1.

(Comparative Example 1) In the first coating treatment, as a baking type metal anticorrosive composition, a dacro dip prepared by mixing by a predetermined method was prepared. In the second coating treatment, dacromet # 100BL (black chromate treatment liquid) was prepared as a liquid composition containing a chromic acid compound and / or a simple substance of resin.

The test substrate was dipped in Dacrodip and spun off by centrifugation. Next, the test base material was put into an electrically heated hot air circulation furnace, and after the temperature of the test base material reached 300 ° C. in the furnace, the test base material was held at the same temperature for 5 minutes for baking.
The test substrate taken out from the furnace was naturally cooled to room temperature.

The test substrate was immersed in Dacromet # 100BL and centrifuged off in the same manner as the first coating treatment.
Again, the test base material was put into an electrically heated hot air circulation furnace, and after the temperature of the test base material reached 250 ° C. in the furnace, the test base material was held at the same temperature for 5 minutes for baking. The test base material taken out from the furnace was naturally cooled and returned to room temperature.

The weight of the coating film adhered to the test substrate by the first coating treatment was 100 mg / dm ² , and the same weight by the second coating treatment was 50 mg / dm ² . The coated test substrate was evaluated by the method described above. The results are shown in Table 1.

Comparative Example 2 The same procedure as in Comparative Example 1 was carried out except for the following points.

Dacromet LTX (clear) (resin coating agent) was prepared as a liquid composition used in the second coating treatment. The baking in the second coating treatment was performed by holding the test substrate at the same temperature for 5 minutes in the electrically heated hot air circulating furnace after the temperature of the test substrate reached 100 ° C. The test base material taken out from the furnace was naturally cooled and returned to room temperature.

The weight of the coating film adhered to the test substrate by the first coating treatment was 100 mg / dm ² , and the same weight by the second coating treatment was 80 mg / dm ² . The coated test substrate was evaluated by the method described above. The results are shown in Table 1.

Comparative Example 3 The first coating treatment was carried out in the same manner as in Example 1, but the second coating treatment was not carried out.

The weight of the coating film deposited on the test substrate was 100 m.
It was g / dm ² . The coated test substrate was evaluated by the method described above. The results are shown in Table 1.

(Comparative Example 4) As in Example 6, the first coating treatment was repeated twice and the second coating treatment was not performed.

The adhesion weight of the coating film on the test substrate is 200 m
It was g / dm ² . The coated test substrate was evaluated by the method described above. The results are shown in Table 1.

[0077]

[Table 1]

[0078]

According to the conventional method, a drying device is required in the dipping process step, which requires twice as many processing steps and processing time. On the other hand, the surface coating method according to the present invention,
The drying step in the coating process can be omitted by utilizing the fact that the temperature of the metal substrate is high due to the baking in the coating process. Therefore, the surface coating method according to the present invention can simplify the equipment and shorten the processing time, so that it is not only very industrially effective, but it can also contribute to effective use of energy and environmental protection. It is a thing.

Claims (3)

[Claims] 1. A metal substrate coated with a baking-type metal anticorrosive composition containing a water-soluble chromic acid compound and zinc powder is treated with a chromic acid compound and / or a resin immediately after the baking and heating treatment in the coating treatment. A method for surface coating treatment, which comprises subjecting the liquid composition to a dipping treatment. 2. The surface coating treatment method according to claim 1, wherein the metal base material maintained at 50 ° C. or higher after the baking heat treatment is dipped in the liquid composition. 3. The surface coating treatment method according to claim 1, wherein the metal after the baking and heating treatment is immersed in the liquid composition for 30 minutes or less.