JP2005139532A - Chromate-free treated plated steel having excellent corrosion resistance and contamination resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide chromate-free treated plated steel having excellent corrosion resistance and contamination resistance. <P>SOLUTION: In the chromate-free treated plated steel, a chromate-free pretreatment film comprising a titanium compound of 10 to 200 mg/m<SP>2</SP>expressed in terms of titanium, or a zirconium compound of 10 to 200 mg/m<SP>2</SP>expressed in terms of zirconium, or a titanium compound and a zirconium compound of 10 to 200 mg/m<SP>2</SP>in total expressed in terms of titanium and zirconium, respectively is formed at least on one side of steel, and, a photocatalytic coating film containing a photocatalytic substance of 10 to 60 mass% is thereafter formed thereon at a thickness of 0.01 to 20 μm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a chromate-free treated plated steel material having excellent corrosion resistance and contamination resistance used for automobiles, building materials, home appliances, and the like.

  Among the plated steel materials, the Al-based alloy plated steel materials disclosed in Patent Document 1 have been widely used in fields such as automobiles, building materials, and home appliances because of their excellent corrosion resistance. Normally, when a plated steel material is used in these fields, a chemical conversion treatment called chromate treatment has been performed for the purpose of improving corrosion resistance. However, in recent years, interest in global environmental problems has increased, and so-called chromate-free plated steel materials that do not use chromate treatment if possible have been desired.

  Research and development relating to chromate-free has been widely performed. For example, Patent Document 2 discloses a technique for treating a compound obtained by polymerizing a compound having a chelate forming ability such as a thiol group or a thioketone group. Certainly, the corrosion resistance is improved by this technique, but since the organic system is mainly used, the corrosion resistance has not reached the level corresponding to the chromate treatment when it is greatly damaged. In the case of organic processing, when used outdoors for a long period of time, dirt in the air becomes rain streaks and adheres to the surface, which causes a problem of deteriorating designability, so-called raindrop contamination.

  A photocatalyst has attracted attention as a technique for improving the contamination resistance and is being used in outdoor building materials. However, since the photocatalyst has a strong oxidizing power, an organic coating film containing a conventional rust preventive pigment cannot be applied to undercoating. On the other hand, the photocatalyst itself also has a photocathode anticorrosive action, but it cannot provide sufficient corrosion resistance, and there is a problem in terms of corrosion resistance.

  As described above, there is currently no chromate-free treated plated steel material having sufficient corrosion resistance and contamination resistance in the plated steel material.

JP-A-46-7161 Japanese Patent Laid-Open No. 11-5061

  This invention solves the said subject, and is providing the chromate free processing plated steel material excellent in corrosion resistance and stain resistance.

In order to solve the above problems, the present inventors have examined in detail the relationship between the corrosion resistance of the plated steel material and the chromate-free treatment. As a result, after forming a chromate-free film having 10 to 200 mg / m ² of one or both of a titanium compound and a zirconium compound on at least one surface of the plated steel material, a photocatalyst film is formed on the chromate-free film by 0.01 to It has been found that by treating with a thickness of 20 μm, a chromate-free plated steel material having excellent corrosion resistance and contamination resistance can be obtained, and the present invention has been achieved.

The gist of the present invention is as follows.
(1) at least on at least one surface of the plated steel material, a chromate-free coating that contains one or both 10 to 200 mg / m ² of titanium compound or zirconium compound (adhesion amount in terms of either or both of titanium or zirconium), Furthermore, it has a photocatalyst coating film having a thickness of 0.01 to 20 μm containing 10 to 60% by mass of a photocatalytic substance, and is a chromate-free treated plated steel material excellent in corrosion resistance and contamination resistance.
(2) The chromate according to (1), wherein the chromate-free film contains 10 to 150 parts by mass of a phosphoric acid compound with respect to 100 parts by mass of the total amount of titanium compound converted to titanium and zirconium compound converted to zirconium. Free-treated plated steel.
(3) In the chromate-free film, magnesium, zinc, aluminum, lanthanum, cerium, hafnium, tantalum, niobium, tungsten, with respect to 100 parts by mass of the titanium equivalent amount of the titanium compound and the zirconium equivalent amount of the zirconium compound, The chromate-free treated plated steel material according to (1) or (2), comprising 5 to 200 parts by mass of at least one compound selected from silicon, manganese, cobalt, and nickel.
(4) The chromate-free treated plated steel material according to (1), wherein the photocatalytic substance is anatase TiO ₂ .

  The chromate-free-treated plated steel material of the present invention has corrosion resistance comparable to that of chromate even if it does not contain chromate, and also has stain resistance that can prevent raindrop contamination that is a problem in organic chromate-free treatment. . Therefore, it is possible to provide a chromate-free plated steel material suitable for outdoor use, which is a great contribution to the fields of automobiles, building materials, home appliances, and the like.

  The present invention is described in detail below.

  The present invention consists of a synergistic effect of improving corrosion resistance by a chromate-free coating containing one or both of a titanium compound and a zirconium compound as a basic component, and improving corrosion resistance and contamination resistance by a photocatalytic coating.

  Examples of the titanium compound applicable to the present invention include titanium hydrofluoric acid, titanium ammonium fluoride, titanium oxalate potassium, titanium sulfate, titanium chloride, titanium isopropoxide, isopropyl titanate, titanium ethoxide, and titanium-2. -Ethyl-1-hexanolate, tetraisopropyl titanate, tetra-n-butyl titanate, potassium potassium fluoride, sodium titanium fluoride and the like. These can also be used as a mixture.

  Examples of the zirconium compound applicable to the present invention include ammonium zirconium carbonate, zircon hydrofluoric acid, ammonium zircon fluoride, potassium zircon fluoride, sodium zircon fluoride, zirconium acetylacetonate, zirconium butoxide-1-butanol solution, Zirconium-n-propoxide, zirconyl nitrate, zirconium chloride, zirconium carboxylate and the like can be mentioned.

  Titanium compounds and zirconium compounds are excellent in film forming properties, barrier properties, and water resistance, and improve the corrosion resistance of chemical conversion films (pretreatment films).

The amount of the pretreatment film in the present invention is such that the titanium compound is 10 to 200 mg / m ^{2 in} terms of titanium, or the zirconium compound is 10 to 200 mg / m ^{2 in} terms of zirconium, or each of the titanium compound and the zirconium compound is titanium and The total amount is 10 to ²⁰⁰ mg / m ² in terms of zirconium. When the adhesion amount is less than 10 mg / m ^{2 in} terms of the converted value, sufficient corrosion resistance cannot be obtained, and when it exceeds 200 mg / m ² , the corrosion resistance improving effect is saturated, which is not economically preferable.

  Next, by adding a phosphoric acid compound to the chromate-free film of the present invention, an effect of further improving corrosion resistance can be obtained. The phosphate compound is considered to be imparted with further corrosion resistance by binding to metal ions eluted in a corrosive environment and further adsorbing to the metal surface. Examples of the phosphoric acid compound include orthophosphoric acid or orthophosphate, polyphosphoric acid, metaphosphoric acid, pyrophosphoric acid, condensed phosphoric acid such as ultraphosphoric acid, or salts thereof. These phosphoric acid compounds may be used alone or in combination of two or more. The content of the phosphoric acid compound is 10 to 150 parts by mass with respect to 100 parts by mass (converted value) of one or both of titanium and zirconium in the chromate-free coating. If the content of the phosphoric acid compound is less than 10 parts by mass, sufficient corrosion resistance cannot be obtained, and if it exceeds 150 parts by mass, the effect of improving corrosion resistance is saturated, which is economically undesirable.

  In the chromate-free film of the present invention, magnesium, zinc, aluminum, lanthanum, cerium, hafnium, tantalum, niobium, tungsten, silicon, manganese, cobalt, nickel oxide, hydroxide, complex fluoride, nitrate, One or more metal compounds selected from sulfates, phosphates, etc., 5 to 200 masses per 100 mass parts of the total amount of titanium equivalents of titanium compounds and zirconium equivalents of zirconium compounds constituting the chromate-free coating By including the portion, the corrosion resistance can be further improved. If it is less than 5 parts by mass, the added effect is not observed, and if it exceeds 200 parts by mass, the effect of improving corrosion resistance is saturated, which is uneconomical.

  The chromate-free film of the present invention may contain a gloss adjusting agent such as silica, and may contain a surface smoothing agent, an ultraviolet absorber, a hindered amine light stabilizer, a viscosity adjusting agent, and the like as necessary.

  The chromate-free film of the present invention can be applied by any method. Examples thereof include a bar coater, spray coating, brush coating, roll coater, overflow curtain coater, slit curtain coater, roller curtain coater, T-die, and multilayer curtain coater.

The photocatalyst coating layer processed on the chromate-free coating of the present invention has two functions of corrosion resistance and contamination resistance. A photocatalytic substance undergoes a photocathode anticorrosion reaction when excited with light having a wavelength that has energy greater than the band gap. For example, in TiO ₂ , the photocathode protection reaction is sufficiently caused by the ultraviolet rays of about 350 nm contained in sunlight, and if the underlying steel is exposed due to large scratches on the plated steel material, the corrosion of the iron surface can be suppressed. it can.

  In the corrosion resistance of the present invention, under the conditions where light such as sunlight or fluorescent lamp hits, the anti-corrosion effect by the photocatalyst coating and the anti-corrosion effect by the chromate-free coating are exhibited, It has the feature that the anticorrosion effect by only a pre-treatment film works.

  Since the photocatalytic coating film has a strong oxidizing power, if there is an organic coating layer therebelow, there is a problem that the organic coating layer is decomposed. On the other hand, in the present invention, sufficient durability is provided by applying a chromate-free film made of an inorganic material under the photocatalyst coating layer.

  Further, since the surface of the photocatalyst coating film can be made hydrophilic, when used outdoors, it can exhibit a so-called soil release effect in which dirt is washed away in rain.

As the photocatalytic substance used in the photocatalytic coating film of the present invention, TiO ₂ , ZnO, WO ₃ , FeTiO ₃ , SrTiO _3, etc. can be used. The film thickness of the photocatalyst coating film is 0.01 to 20 μm. If it is less than 0.01 μm, the effect of the photocatalyst is insufficient and the corrosion resistance is insufficient. On the other hand, if it exceeds 20 μm, the photocatalyst coating film cracks and peels during severe processing, resulting in poor corrosion resistance. A more preferable film thickness is 1 to 10 μm. As the photocatalytic substance, anatase-type TiO ₂ that is chemically stable and inexpensive is suitable.

  The coating material for forming the photocatalyst coating layer is not particularly limited, and examples thereof include organosilica sols in which a photocatalytic substance is dispersed, sols such as alumina sols, and alkoxide coatings. The photocatalyst coating layer can be applied by any method. Examples thereof include a bar coater, spray coating, brush coating, roll coater, overflow curtain coater, slit curtain coater, roller curtain coater, T-die, and multilayer curtain coater.

  The chromate-free coating and the photocatalytic coating of the present invention can be simultaneously applied using a multilayer curtain coater, and dried and cured simultaneously.

  The plated steel material applicable to the present invention is not particularly limited, but is galvanized steel material, zinc-iron alloy plated steel material, zinc-nickel alloy plated steel material, zinc-chromium alloy plated steel material, zinc-aluminum alloy plated steel material, aluminum Examples include plated steel materials, zinc-aluminum-magnesium alloy plated steel materials, zinc-aluminum-magnesium-silicon alloy plated steel materials, aluminum-silicon alloy plated steel materials, galvanized stainless steel materials, and aluminum plated stainless steel materials.

  In addition, after plating, before the coating of the present invention is formed, surface adjustment with a sulfuric acid Co solution, a nickel sulfate solution, or the like may be performed to prevent discoloration of the plating.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.
(1) Production of chromate-free treated plated steel material As the plated steel material of the present invention, a molten 55% Al-43.5% Zn-1.5% Si alloy-plated steel sheet (double-sided plating adhesion amount: 150 g / m ² ) was used. The plate thickness is 0.6 mm.

As the chromate-free treatment chemicals, those shown in Table 1 were used. After application, a chromate-free film having the composition shown in Table 2 was obtained by heating and curing at 100 ° C. using a bar coater. After that, a sol in which trimethoxysilicate and colloidal silica are added to butyl cellosolve is coated with a paint in which anatase-type TiO ₂ with an average particle size of 10 nm is dispersed with a bar coater and heat cured at 250 ° C. to form a photocatalytic coating film. Formed. Table 3 shows the amount of chromate-free coating (in terms of titanium and zirconium) and the thickness of the photocatalytic coating.

(2) Corrosion resistance test
Each sample produced in (1) was subjected to 6 mm of Erichsen processing, and according to the salt spray test method described in JIS Z 2371, the sample was sprayed with a 5% NaCl aqueous solution at an ambient temperature of 35 ° C. The white rust area ratio in the Erichsen processed part after 48 hours was measured. Based on the following evaluation criteria, ◎ and ○ were regarded as acceptable.

Evaluation standard for corrosion resistance ◎: No white rust ○: White rust area ratio less than 10% △: White rust area ratio 10% or more and less than 50% ×: White rust area ratio 50% or more
(3) Contamination resistance test
From each sample produced in (1), we prepared raindrop contamination test specimens (roof surface 100 × 100mm, evaluation surface 100 × 145mm, angle 120 ° between them) as shown in FIG. An exposure test was conducted for three months outdoors in Futtsu City, and the degree of rain streaks on the evaluation surface was visually evaluated. The evaluation criteria were as follows, with ◎ and ○ as acceptable.

Evaluation criteria for contamination resistance ◎: No rain streaks are observed ○: Slight rain streaks are observed △: Rain streaks are observed ×: Rain streaks are clearly seen

The above evaluation results are shown in Table 3. From Table 3, the chromate-free treated plated steel material of the present invention is excellent in corrosion resistance and contamination resistance in any case. When the pretreatment film is thinner than the range of the present invention, the corrosion resistance is inferior, and when the photocatalyst coating layer is thin or the content of TiO ₂ is small, the contamination resistance is inferior. Moreover, when the photocatalyst coating layer was thicker than the range of the present invention, white rust was conspicuous in the Erichsen processed part.

The figure which shows the shape of a raindrop exposure test body.

Claims (4)

On at least one surface of the plated steel material, at least, (adhesion amount at the exchange of one or both of titanium or zirconium) one or both of 10 to 200 mg / m ² of titanium compound or zirconium compound and chromate-free coating that contains, further that A chromate-free treated plated steel material excellent in corrosion resistance and contamination resistance, characterized by having a photocatalyst coating film having a thickness of 0.01 to 20 μm containing 10 to 60% by mass of a photocatalytic substance.   2. The chromate-free treatment according to claim 1, wherein the chromate-free film contains 10 to 150 parts by mass of a phosphoric acid compound with respect to 100 parts by mass of the total amount of titanium equivalent of titanium compound and zirconium equivalent of zirconium compound. Plated steel.   In the chromate-free film, magnesium, zinc, aluminum, lanthanum, cerium, hafnium, tantalum, niobium, tungsten, silicon, manganese with respect to 100 parts by mass of titanium equivalent amount of titanium compound and zirconium equivalent amount of zirconium compound 3. The chromate-free treated plated steel material according to claim 1 or 2, which contains 5 to 200 parts by mass of at least one compound selected from cobalt, nickel and nickel. _2. The chromate-free treated plated steel material according to claim 1, wherein the photocatalytic substance is anatase TiO ₂ .

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