JPH0442434B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating composition that inhibits filiform corrosion that often occurs when coated iron, aluminum, and magnesium articles are used at relative humidity of about 60 to 95%.

Filiform corrosion is one of the typical forms of corrosion in painted products such as containers, furniture, electrical appliances, and automobiles, and efforts are being made to suppress this corrosion. Methods currently in use include a method in which a so-called chemical conversion treatment is performed to crystallize iron phosphate or zinc phosphate on the surface of a steel sheet, and then painting is applied, and a method in which the surface of the steel sheet is coated with a metal that does not cause filiform corrosion.
That is, there is a method of plating with zinc, nickel chrome, etc., and then painting on top of this. However, although the former is effective when used in a mild environment such as in a dry room, it cannot sufficiently suppress filiform corrosion when used under high humidity. Although the latter can prevent filiform corrosion by plating sufficiently thickly, it poses problems in terms of resource conservation and manufacturing costs, and has not yet been commonly used as a paint base.

In view of these circumstances, the present invention proposes that if filiform corrosion can be suppressed by adding inexpensive additives to paints, it will be an extremely effective means to save resources and improve the commercial value of coated products at low cost. This was the result of various considerations.

That is, the present invention aims to provide a paint promoter that can suppress filiform corrosion.

The coating composition of the present invention contains a coating film-forming component containing a resin, and 0.5 to 20 parts by weight of the coating film-forming component, based on 0.00 parts by weight of the coating film-forming component.
It is characterized by containing part by weight of hydrotalcite.

According to the present invention, it is possible to provide an excellent coating composition that can suppress filiform corrosion.
Furthermore, this coating composition has excellent effects in the salt spray test described below, and there is no risk of impairing the smoothness of the coating film surface.

Next, the reason why the coating composition according to the present invention inhibits the progress of such filiform corrosion is considered as follows. That is, the hydrotalcite contained in the coating composition of the present invention reacts with the acid present at the tip of filamentous corrosion, which is considered to be the direct cause of filamentous corrosion.
Continuously neutralizes the acidity of filamentous corrosion tips. Therefore, the anion exchange ability of hydrotalcite traps monovalent inorganic anions, which are thought to play a catalytic role in the progression of filamentous corrosion. Immobilize ions.

In the present invention, the blending ratio of hydrotalcite is 0.5 to 2 parts by weight per 100 parts by weight of the coating film forming components. If the amount is less than 0.5 parts by weight, the effect of preventing filamentous corrosion will be weak, and if it exceeds 20 parts by weight, no further effect can be expected. A more preferable range is 1 to 100 parts by weight of the coating film forming component.
It is 10 parts by weight.

Furthermore, the hydrotalcite used in the present invention is
It is a double salt of Mg and Al, and its chemical formula is Mg ₄ Al ₂ (OH) ₁₂ CO ₃・3H ₂ O, Mg ₆ Al ₂
(OH) ₁₆ CO ₃・5H ₂ O or Mg ₆ Al ₄ (CH) ₁₆ CO ₃・
It is represented by 4H ₂ O and can be either a synthetic or natural product. The particle size of the hydrotalcite is preferably 1 μm or less in order to be uniformly dispersed and to obtain a smooth surface of the coated product.

As the coating film forming component, conventional coating film forming components can be used as they are. For example, paint film-forming components include paint resins, pigments, dyes, fillers, and various additives. Examples of resins for coatings include amino alkyd resins, baking-type acrylic resins, air-drying acrylic resins, boiled oil, phenolic resins, oil-modified butadiene resins, and epoxy resins. The form of the coating may be powder, oil-based, water-soluble, or electrodeposited. The coating composition of the present invention is effective when applied directly to the surface of a metal product. Therefore, when a multilayer coating including coating, intermediate coating, and top coating is formed, it is used as an undercoat paint.

Metal products coated with the coating composition of the present invention undergo filiform corrosion. It is a metal product made of iron, aluminum, and magnesium. Among these, iron and steel products are of practical importance. These metal products can be coated with the coating composition of the present invention on surfaces that have been normally cleaned. Note that it has been conventionally used as a pre-painting treatment. When the coating composition of the present invention is coated on a metal product that has been subjected to a so-called chemical conversion treatment in which iron phosphate or zinc phosphate is crystallized on the metal surface, the effect of preventing filiform corrosion becomes even more remarkable.

Examples will be described below, but first a test method for filamentous corrosion will be described.

Although filiform corrosion may be observed when painted products are used outdoors, its typical form is observed when used indoors. For this reason, it is most practical to evaluate the filamentous corrosion resistance by leaving the painted product indoors. However, since this test takes time to produce results, ASTMD-2803 is available as a filamentous corrosion evaluation method. This test method involves conducting a salt spray test (JISZ-2371) for 4 to 24 hours, and then exposing the product to an environment at a temperature of 25°C and a relative humidity of 85%. The evaluation method used in the present invention is this
This method complies with the ASTM method, where a cut is made in the paint film of a painted board that reaches the metal plate, and after intermittently contacting the cut with a 5% aqueous sodium chloride solution, the coating is heated at 40°C.
Five maximum lengths of thread-like corrosion generated from scratches are selected after exposure in an environment with relative humidity of 85%, and the evaluation is based on the average value.

Example 1 A paint composition was prepared by adding hydrotalcite to an aminoalkyd paint, and then this paint composition was applied to a steel plate treated with zinc phosphate,
The state of filamentous corrosion on the surface of the obtained coated plate was observed.

That is, hydrotalcite with a particle size of approximately 0.5 μm is uniformly dispersed in 20 times the amount of paint thinner whose main component is xylene using ultrasonic waves, and this is added to a commercially available amino alkyd paint by applying hydrogel to the film-forming components. Talcite was added in an amount of 3% by weight. Next, the viscosity was adjusted with thinner to a level suitable for spray painting, and spray painting was applied to a 0.8 mm thick steel plate (coating amount: 1.5 g/m ² ) that had been previously treated with zinc phosphate to a dry film thickness of approximately 30 μm.
Baking was performed at 140°C for 30 minutes. The obtained coated plate was subjected to the filamentous corrosion test described above. For comparison, a paint similar to the above without containing hydrotalcite was prepared, painted and baked in the same manner, and a filiform corrosion test was also conducted.

As shown in Figure 1, filamentous corrosion occurs on plate A coated with paint that does not contain hydrotalcite.
When it reaches 6.2mm, add 3 hydrotalcites.
The coated plate B of the paint to which % by weight was added was 2.4 mm or less.

Example 2 Using an aminoalkyd paint with the same paint composition as that prepared in Example 1, a dry film thickness of approximately 30 μm was applied to a 0.8 mm thick steel plate that had not been subjected to zinc phosphate treatment.
It was spray painted and baked at 140℃ for 30 minutes. The obtained coated plate was subjected to the filamentous corrosion test described above. Similarly, a painted board was made using a paint that did not contain hydrotalcite, and a filiform corrosion test was conducted.

As shown in FIG. 2, when the filamentous corrosion reached 6.0 mm on coated plate C which does not contain hydrotalcite, the filamentous corrosion on coated plate D prepared with the coating composition according to the present invention reached 4.1 mm. It was hot.

Example 3 A coating composition was prepared by adding the same hydrotalcite as used in Examples 1 and 2 to an anionic electrodeposition coating, and this composition was applied to a steel plate treated with zinc phosphate. Filamentous corrosion was observed on the painted plate.

That is, two types of paint compositions were added to a commercially available anionic electrodeposition paint (manufactured by Shinto Paint Co., Ltd., trade name: Super Anion), in which 3% and 6% by weight of the hydrotalcite were added to the film-forming components. Prepared.

Next, a steel plate treated with zinc phosphate in the same manner as in Example 1 was electrodeposited to a dry film thickness of 20 μm, and baked at 170° C. for 30 minutes. The obtained coated plate was subjected to the filamentous corrosion test described above.

In addition, for comparison, we prepared a paint that did not contain hydrotalcite, painted it in the same way, and baked it.
A filiform corrosion test was conducted on this material.

As shown in Figure 3, when the filamentous corrosion of coated plate E that does not contain hydrotalcite reaches 9.1 mm, the coated plate F that contains 3% by weight of hydrotalcite
The thread-like corrosion was 5.3 mm, or the thread-like corrosion of the coated plate G containing 6% by weight was 2.2 mm.

As is clear from the examples above, adding the hydrotalcite used in the present invention to a coating film-forming component containing a resin has a remarkable effect of preventing filiform corrosion of painted plates.

Furthermore, it can be seen that the coating composition used in the present invention exhibits excellent effects in the salt spray test.

[Brief explanation of drawings]

The figures show examples of the present invention; FIG. 1 is a diagram showing the results of a filiform corrosion test in Example 1, FIG. 2 is Example 2, and FIG. 3 is Example 3.

Claims (1)

[Claims] 1. A coating film-forming component containing a resin, and the coating film-forming component
A filamentous corrosion-resistant coating composition characterized by containing 0.5 to 20 parts by weight of hydrotalcite per 100 parts by weight. 2. The coating composition according to claim 1, wherein the resin is an aminoalkyd resin, an acrylic resin, a boiled oil, a phenolic resin, an oil-modified butadiene resin, or an epoxy resin. 3 Hydrotalcite is a double salt of Mg and Al, and its chemical formula is Mg ₄ Al ₂ (OH) ₁₂ CO ₃・3H ₂ O,
Mg ₆ Al ₂ (OH) ₁₆ CO ₃・5H ₂ O or Mg ₆ Al ₇
The coating composition according to claim 1, which is (OH) ₁₆ CO ₃ .4H ₂ O.