JP3196397B2 - Organic composite coated steel sheet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic composite coated steel sheet in which a chromate treatment layer and a resin film are formed on a zinc-plated steel sheet. Such an organic composite coated steel sheet is used for home electric appliances or building materials.

[0002]

2. Description of the Related Art Zinc or zinc-based alloy coated steel sheets
Zinc-based plated steel sheets) are widely used in various industrial fields because of their excellent corrosion resistance. In particular, in the application of home appliances, the use of unpainted components, which have been used in the past, has been increasing without coating. Therefore, not only corrosion resistance without painting, but also good appearance without painting Is required.

[0003] With regard to the corrosion resistance, the requirements have been met to some extent by performing a corrosion-resistant chromate treatment in which a white rust generation time is about 100 hours in a salt spray test instead of a general chromate treatment as a primary rust preventive. ing. However,
When these chromate-treated steel sheets are stored in an unpainted state, particularly when stored in a high-temperature and humid environment, a so-called black discoloration phenomenon in which the surface becomes blackish over time partially or entirely over time. This may cause a problem that the commercial value is significantly impaired in appearance.

[0004] Black discoloration is considered to be an early corrosion phenomenon. During storage, moisture and oxygen pass through the chromatized film,
It is considered that the formation of oxides, hydroxides, hydrated oxides, and the like in the plating surface layer, which causes the visible light to be easily absorbed and scattered, is the cause of the black appearance. This reaction may be caused by a trace amount of lead or aluminum remaining in the galvanized layer promoting the anodic formation of zinc,
Foreign matter or impurities (for example, SO
₄ ^2- or Cl ^- And the like, and the non-uniform adhesion of plating bath components, impurity ions or oil components in the chromate bath.

In consideration of such a phenomenon, in order to improve the blackening resistance of the zinc-based plated steel sheet, the concentration of impurities in the plated layer is controlled, and the cleaning of the surface after plating is performed. Sufficient effects have not been obtained. Against this background, the following techniques have been proposed to meet the demand for preventing blackening from the viewpoint of plating or chromate treatment. (1) JP-A-60-63385 (hereinafter referred to as prior art 1)

This publication discloses that impurities P in a zinc plating bath are
By controlling the concentration of b ²⁺ to 0.2 ppm or less, the crystal is oriented so as to preferentially precipitate the chemically stable (002) plane of zinc, and the reaction with the chromate treatment layer is suppressed. A technique for preventing blackening has been disclosed. (2) JP-A-60-77988 (hereinafter referred to as prior art 2)

[0007] This publication discloses that Ni ²⁺ /
By setting the Pb ²⁺ ratio to 5 to 500, the Ni ²⁺ / Zn ²⁺ ratio to 1/25 or less, and the Ni ²⁺ concentration to 10 g / l or less, zinc which is stable even in the presence of Pb ²⁺ A technique for preferentially depositing a (002) plane is disclosed. (3) JP-A-63-250496 (hereinafter referred to as Prior Art 3)

[0008] This publication discloses that [Ni] in a galvanizing bath.
Discloses a galvanized steel sheet which has been subjected to electrolytic chromate treatment and contains 30 to 60% by weight of [Ni] / ([Ni] + [Cr] + [O]). (4) JP-A-2-8374 (hereinafter referred to as Prior Art 4)

This publication ^discloses that Pb ²⁺ in a plating bath is 0.1 ^% .
5 ppm or less, Ni ²⁺ is 100 to 300 ppm, Ni ²⁺
A technique is disclosed in which the / Pb ²⁺ ratio exceeds 500, and a coating type chromate treatment containing silica sol or the like is performed on a plating layer formed under such conditions.

[0010]

However, the above-mentioned prior art has the following problems.

That is, the prior arts 1 and 2 have the effect of stabilizing the plating layer and suppressing the non-uniform formation of the treatment layer formed by the reaction type chromate treatment, but the steel sheets manufactured by these techniques have an effect. However, under a severe corrosive environment of high temperature and humidity, blackening cannot always be suppressed.

The prior arts 3 and 4 attempt to suppress blackening by improving the chromate treatment or the plating layer and the chromate treatment, and are effective in a relatively mild storage state. Is recognized. However, in a severe environment, the effect of suppressing blackening is insufficient, and it is not possible to simultaneously satisfy blackening resistance, fading resistance due to chromium elution, and corrosion resistance. Further, the steel sheet in these techniques tends to have handling flaws in processes such as slitting and transporting, and it is not possible to avoid deterioration of corrosion resistance in that portion.

On the other hand, as a zinc-based plated steel sheet,
Although a resin layer having a resin layer provided on a heat-treated layer has also been developed, there is nothing aimed at improving the resistance to blackening, and the fact is that the blackening resistance is poor when actually tested.

The present invention has been made in view of such circumstances, and has as its object to provide an organic composite coated steel sheet which is excellent in blackening resistance and hardly generates flaws while maintaining good corrosion resistance. I do.

[0015]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a steel plate provided with a zinc or zinc-based alloy plating layer, and a metal chromium equivalent formed on the plating layer of the steel plate. 1 mg / m ² 200 mg / m ² or more A chromate treatment layer having the following adhesion amount, and a resin film formed on the chromate treatment layer to a thickness of 0.1 to 5 μm, wherein the main component of the resin film is ethylene and α, β
-Provided is an organic composite coated steel sheet characterized by being an ethylene ionomer resin having an ethylenically unsaturated carboxylic acid as a main chain component and neutralizing 60 to 80% of carboxyl groups with metal ions.

Further, 200 mg / m ^{2 in} terms of metallic chromium is applied to a steel sheet provided with a zinc or zinc-based alloy plating layer. A chromate treatment layer having the following adhesion amount is formed, and on top of that, ethylene and an α, β-ethylenically unsaturated carboxylic acid are used as main chain components, and 60 to 80% of the carboxyl groups are formed by metal ions. A water-dispersible resin solution prepared by mixing a resin containing a hydrated ethylene ionomer resin as a main component and water containing no emulsifier is applied and dried to have a thickness in the range of 0.1 to 5 μm. The present invention provides a method for producing an organic composite coated steel sheet, characterized by forming a resin coating of (1).

The inventors of the present application have conducted intensive studies to solve the above-mentioned problems in the zinc-based galvanized steel sheet. As a result, a chromate treatment layer was formed on the galvanized steel sheet, By forming a special resin layer which can be dispersed in water without using an emulsifier, it has been found that a steel sheet which is excellent in blackening resistance and hardly generates flaws or the like can be obtained while maintaining good corrosion resistance. That is, on a chromate treatment layer having a predetermined thickness, the chromate treatment layer has a specific thickness range, the main components are ethylene and an α, β-ethylenically unsaturated carboxylic acid as a main chain component, and By forming a coating film of an ethylene ionomer resin in which 60 to 80% is neutralized with metal ions, it is possible to improve the blackening resistance and the flaw resistance etc. by a barrier effect caused by its molecular structure. I found it. The present invention has been made based on such findings of the present inventors.

In the present invention, the main component of the resin film formed as the upper layer is a main chain of a copolymer of ethylene and an α, β-ethylenically unsaturated carboxylic acid and, if necessary, other copolymers. Having a basic structure of 60
It is an ethylene ionomer resin in which about 80% is neutralized with metal ions. α, β-ethylenically unsaturated carboxylic acid includes acrylic acid, methacrylic acid, fumaric acid, itaconic acid, maleic acid, etc., and when focusing on the quality such as blackening resistance and corrosion resistance in a particularly severe environment, Methacrylic acid is particularly excellent. The molecular weight of the copolymer is usually preferably 10,000 to 200,000, preferably 50,000 to 1,000,000.
50,000 are particularly preferred.

The ions used for neutralizing carboxylic acids include metal ions of alkali metals and alkaline earth metals, metal compound ions such as transition metal hydroxides, and organic amines and transition metals. Of these, a sodium ion is particularly preferred from the viewpoints of blackening resistance, corrosion resistance and chemical stability of the coating.

As for the degree of neutralization, from the viewpoint of obtaining good blackening resistance and corrosion resistance even at a low drying temperature of 80 ° C.,
A range of 60 to 80% is preferred. If it is less than 60%, the blackening resistance is insufficient, and if it exceeds 80%, the viscosity increases and the stability of the chemical solution decreases, and the hygroscopicity increases, so that the blackening resistance and corrosion resistance decrease.

Α, β- in the ethylene ionomer molecule
When the amount of the ethylenically unsaturated carboxylic acid exceeds 20 mol%, the water solubility increases, and the blackening and corrosion resistance of the coating decrease. Adhesive strength is reduced, and a desired film cannot be obtained. Therefore, the amount is preferably in the range of 3 to 20 mol%, more preferably in the range of 10 to 15 mol%.

In the present invention, since the resin constituting the resin layer has an ionic cross-linking structure, it is possible to form a water-dispersed coating liquid without using an emulsifier which may cause deterioration of film properties. And a thin film can be easily coated on the surface of the steel sheet. Since the dried film is strongly adhered to the substrate and is chemically stable, the steel sheet on which such a film is formed exhibits excellent blackening resistance and corrosion resistance. In addition, since the steel sheet has a strong resin film formed thereon, scratches are unlikely to occur.

In the present invention, the thickness of the resin film is 0.1
-5 μm, preferably 0.3-3 μm. If it is less than 0.1 μm, a barrier effect for suppressing blackening resistance of the resin film cannot be expected at all, and it is not preferable because scratches due to handling or the like cannot be prevented. On the other hand, if the thickness exceeds 5 μm, it is not preferable because the film is easily peeled off when subjected to severe processing. In the resin coating of the present invention, metal oxides, pigments and dyes, and other additives for imparting various functions may be added as necessary.

The formation of the composite resin film can be performed, for example, by the following method. That is, first, the coating liquid of the composition containing the above-described composite resin as a main component is applied by a known coating method such as a roll coater, a curtain roll coater, or a spray, or A zinc-coated steel sheet which has been subjected to a chromate treatment is immersed in the film, and the coating amount is controlled by rolling or air blowing to form a film, and then the film is dried. Drying may be carried out at room temperature, but is usually carried out by heating the steel sheet to a temperature of about 60 ° C. or higher, preferably 80 to 200 ° C., using a hot air oven or an induction heating device.

Examples of the zinc-based plated steel sheet include an electro-pure galvanized steel sheet in which black discoloration is particularly concerned, another zinc-based plated steel sheet having a plating layer formed by an electroplating method or a hot-dip plating method, or a zinc-based alloy. A plated steel sheet is exemplified.

The chromate treatment layer has an effect of imparting excellent corrosion resistance to the steel sheet and facilitating the formation of a resin film. The chromate treatment for forming this layer may be a known chromate treatment such as a reaction type, a coating type, and an electrolytic type.
00mg / m ² It is necessary to form a chromate layer. 1mg / m ² If less than 200, the corrosion resistance is insufficient, and 200 mg / m ² If it exceeds, not only the corrosion resistance improving effect commensurate with the amount cannot be obtained, but also cohesive failure of the chromate-treated layer is likely to occur when bending or the like accompanied by deformation of the steel sheet is performed. The more preferable amount of the chromate-treated layer is 10 to 100 mg / m ² per one side of the steel sheet in terms of chromium metal. Within the range.

To give a specific example, first, the composition of the reaction type chromate treatment solution is 1 to 1 in terms of metal chromium.
00 g / l of a water-soluble chromium compound and 0.2 to 20 g /
l of sulfuric acid as a main component, and the content of trivalent chromium in all chromium is 50% by weight or less, preferably 20 to 35% by weight or less. Metal ions such as Zn ²⁺ , Co ²⁺ , Fe ³⁺ and other mineral acids such as phosphoric acid and hydrofluoric acid.

As a specific example of the coating type chromate treatment liquid, a solution having the same composition as that of the above-mentioned reaction type chromate treatment may be used.
A water-soluble organic polymer resin containing a large amount of carboxyl groups in the molecule and compatible with a liquid having the same composition as the above-mentioned reaction type chromate treatment liquid is added, and the pH is adjusted to 2.0 to 3.5.
Adjusted to. The organic polymer preferably has an average molecular weight of 1,000 to 500,000. The amount of addition is generally 0.02 in terms of resin content.
３０30 g / l. In any case, the adhesion amount of the chromate layer as the first layer is, as described above, 1 to 200 mg / m ^{2 in} terms of chromium metal. It is sufficient if it is within the range.

[0029]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. (Synthesis example of composite resin)

A resin obtained by neutralizing an ethylene-methacrylic acid copolymer having a methacrylic acid content of 20 mol% with sodium hydroxide to a degree of neutralization of 70% was placed in a homomixer maintained at 170 ° C. and having an effective volume of 18 liters. A melt of the above resin is supplied at a flow rate of 4 kg / hr, and water is supplied at a flow rate of 18 liter / hr, and vigorous stirring is performed to produce a water-dispersed resin liquid, while keeping the liquid level constant. This aqueous dispersion type resin liquid was continuously withdrawn. As a result, a water-dispersed resin liquid containing no emulsifier and having a solid content of 20.4% was obtained. In addition, resin solutions having different types of copolymers, neutralized metal ions, and different degrees of neutralization were synthesized under basically the same conditions. In addition, another resin containing an emulsifier was also synthesized as a resin used in Comparative Examples. The resins are clearly shown in Tables 1 and 2 described below. (Examples 1 to 15)

Sheet thickness 0.8 mm, plating amount 20 g / m ² Electrogalvanized steel sheet or 0.8mm thick, plating amount 60
g / m ² A reaction type chromate treatment or a coating type chromate treatment was performed on the galvanized layer of the hot-dip galvanized steel sheet, and dried to form a chromate treated layer having an adhesion amount shown in Table 1.

Next, the water-dispersed resin solution synthesized as described above and shown in Table 1 was applied by a roll coater on the steel sheet on which the chromate treatment layer was formed, and then the temperature of the steel sheet was raised to 80 ° C. by a hot air drying oven. , And the coating liquid was dried by heating until a resin film was formed. By the above procedure,
An organic composite coated steel sheet having a plating layer, a chromate treatment layer, and a resin coating under the conditions shown in Table 1 was obtained. (Comparative Examples 1 to 9)

In these comparative examples, the same electrogalvanized steel sheet as in the example was used, and the amount of deposition was 40 g / m ² on the plating layer by reactive chromate treatment. Was formed. Various resins other than those described above were used, and a resin film was formed under the conditions shown in Table 2 in the same manner as in the examples. The amounts of chromate adhering in Tables 1 and 2 are expressed in terms of metal chromium. The steel sheets of such Examples and Comparative Examples were evaluated for blackening resistance and corrosion resistance by the tests described below. The results are shown in Tables 1 and 2. (1) Blackening resistance test

A high temperature and humidity environment of 50 ° C. and 95% RH
It was left for a few days and the L value before and after the test (JIS Z8730)
6.3.2 (1980), the change in Hunter's color difference formula) was used to evaluate the blackening resistance. The evaluation criteria are as follows. ◎: L value change is less than 1 ○: L value change is 1 to 3 Δ: L value change is 3 to 5 ×: L value change exceeds 5 (2) Corrosion resistance

Evaluation was made based on the presence or absence of white rust after being left in the above environment for 60 days. In the table, “absent” indicates that no white rust was generated, and “presence” indicates that white rust was clearly generated in a dotted manner.

[0036]

[Table 1]

[0037]

[Table 2]

As apparent from Table 1, Examples 1 to 15
Showed good blackening resistance and corrosion resistance. In particular, it was confirmed that Examples 1 to 10 using an ethylene-methacrylic acid copolymer as the ethylene ionomer resin exhibited particularly good blackening resistance.

On the other hand, as is apparent from Table 2,
Comparative Examples 1 to 9 gave insufficient results. That is, Comparative Examples 1 and 2 have a degree of neutralization, Comparative Example 3 has a thickness of the resin film, and Comparative Examples 4 to 9 all have poor blackening resistance because the type of resin of the resin film is outside the scope of the present invention. In many cases, the corrosion resistance was poor.

FIG. 1 shows the degree of neutralization of the base resin.
FIG. 1 shows the effect of the degree of neutralization on blackening resistance in Examples 1-3 and Comparative Examples 1 and 2, with the horizontal axis representing the degree of neutralization and the vertical axis representing the degree of blackening resistance. FIG. As is clear from this figure, it was confirmed that particularly excellent blackening resistance was exhibited when the degree of neutralization was 60 to 80%.

The effects of the thickness of the resin film on blackening resistance are described in Examples 1, 9, and 10 and Comparative Example 3.
When the film thickness is from 0.3 to 3.0 µm, particularly excellent blackening resistance is exhibited, but when the film thickness is out of the range of the present invention, which is 0.05 µm, it is confirmed that the blackening resistance is inferior.

As to the base resin, when the base resin other than the ethylene ionomer resin is used as described above, the black resin is inferior in blackening resistance as in Comparative Examples 4 to 9, but the ethylene eye monomer resin is used as the base resin. By doing so, good blackening resistance as in Examples 1 to 15 can be obtained. Furthermore, even when the same ethylene-based eye monomer resin was used, methacrylic acid was used in comparison with Examples 11 to 15 in which α, β-ethylenically unsaturated carboxylic acid other than methacrylic acid was used as a copolymer component. 2 shows particularly excellent resistance to blackening.

[0043]

According to the present invention, there is provided an organic composite coated steel sheet excellent in blackening resistance while maintaining good corrosion resistance, and a method for producing the same.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the degree of neutralization on blackening resistance.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-156779 (JP, A) JP-A-3-131371 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 7/14 B05D 7/24 301 B05D 7/24 302 B32B 15/08 C23C 22/00

Claims (4)

(57) [Claims] And 1. A zinc or steel plates zinc-based alloy plating layer is applied, it is formed on the plated layer of the steel sheet, chromate treatment with a deposition amount of 1 mg / m ² or more 200 mg / m ² or less reckoned as metal chromium And a resin film formed on the chromate-treated layer in a thickness of 0.1 to 5 μm, wherein the main components of the resin film are ethylene and α, β-ethylenically unsaturated carboxylic acid. An organic composite coated steel sheet, which is an ethylene ionomer resin in which 60 to 80% of carboxyl groups are neutralized with sodium ions as a main chain component. 2. The organic composite coated steel sheet according to claim 1, wherein the α, β-ethylenically unsaturated carboxylic acid is methacrylic acid. 3. A chromate-treated layer having an adhesion amount of 200 mg / m ² or less in terms of metallic chromium is formed on a steel sheet provided with a zinc or zinc-based alloy plating layer, and ethylene and α, β- A resin containing an ethylenically unsaturated carboxylic acid as a main chain component, an ethylene ionomer resin having 60 to 80% of carboxyl groups neutralized with sodium ions as a main component, and water containing no emulsifier. A method for producing an organic composite coated steel sheet, wherein a water-dispersed resin solution prepared by mixing is applied and dried to form a resin film having a thickness in the range of 0.1 to 5 μm. Wherein said alpha, a method of manufacturing an organic composite coated steel sheet according to claim 3, β- ethylenically unsaturated carboxylic acid characterized in that it is a methacrylic acid.