KR100979010B1 - High anticorrosive coating solution for zinc coated steel sheet and the zinc coated steel sheet therefrom - Google Patents

Abstract

The present invention relates to a method for producing antirust coating solution for galvanized steel sheet,

In the anti-corrosive coating solution for galvanized steel sheet, based on the total weight in the anti-rust coating solution,

5-15% by weight of a colloidal aqueous solution containing lithium polysilicate of Li ₂ Si ₅ O ₁₁ ;

1-10% by weight of an organic titanium complex of [Ti ^IV (L ₁ ) (L ₂ ) ₂ ], wherein L ₁ = triethanolamineto, L ₂ isopropoxide; And

An antirust coating solution for galvanized steel sheet and a galvanized steel sheet coated with this solution are provided, wherein 3-10% by weight of? -glycidoxy propyl trimethoxysilane is added.

The anti-corrosive coating solution of the present invention is useful as an anti-corrosive coating solution for environmentally friendly high corrosion-resistant galvanized steel sheet without containing chromium and having excellent corrosion resistance and resin adhesion.

Lithium polysilicate, titanium, rust preventive, galvanized steel, silica

Description

High corrosion resistant anticorrosive coating solution for galvanized steel sheet and galvanized steel sheet coated with this solution {HIGH ANTICORROSIVE COATING SOLUTION FOR ZINC COATED STEEL SHEET AND THE ZINC COATED STEEL SHEET THEREFROM}

The present invention relates to an anti-corrosion coating solution for galvanized steel sheet and a galvanized steel sheet coated with this solution, and more particularly, to an anti-corrosive coating solution for galvanized steel sheet made by adding a specific Ti-based compound without using chromium. The present invention relates to a coated galvanized steel sheet.

In order to prevent surface corrosion of galvanized steel sheet, Chromate coating process has been performed for more than 100 years. Chromate, which contains Cr (VI), has been used for corrosion protection for a long time due to its low cost and excellent corrosion resistance, but it is regulated as an environmentally harmful substance internationally as it is classified as a primary carcinogen causing laryngeal cancer. The automotive industry has regulated the use of Cr (VI) with lead (Pb), nickel (Ni) and copper (Cu) since 2003.In 2008, the European Union (EU) regulated the use of waste electrical (electronic) devices. The company is planning to completely prohibit the disposal of products containing substances such as chromium (Cr), lead (Pb), mercury (Hg) and cadmium (Cd). Therefore, we are currently striving to develop corrosion inhibitors that do not use chromium, that is, rust inhibitors, for construction, home appliances, and automobiles worldwide.

The development of rust free agents that do not contain chromium has been done for a long time from various angles. Representative examples of the molybdenum anion (Molybdate, MoO ₄ ^2- ) passivation film, a method using a MH ₂ PO ₄ film, and tannic acid, such as tannic acid, have been studied. However, these methods are not practically used as a substitute for chromate of galvanized steel sheets because of their low barrier property and self-healing and poor corrosion resistance compared to chromate coatings. Therefore, there is a continuing need for new environmentally friendly rust inhibitors that do not contain chromium.

Accordingly, it is an object of the present invention to provide an environmentally friendly anti-corrosive coating solution for galvanized steel sheet having excellent corrosion resistance without chromium by adding an organic titanium complex compound and a silane crosslinking agent to a lithium polysilicate aqueous solution.

Another object of the present invention is to provide a galvanized steel sheet coated with the rustproof coating solution for the galvanized steel sheet.

According to one aspect of the invention,                     

In the anti-corrosive coating solution for galvanized steel sheet, based on the total weight in the anti-rust coating solution,

5-15% by weight of a colloidal aqueous solution containing lithium polysilicate of Li ₂ Si ₅ O ₁₁ ;

1-10% by weight of an organic titanium complex of [Ti ^IV (L ₁ ) (L ₂ ) ₂ ], wherein L ₁ = triethanolamineto, L ₂ isopropoxide; And

An anti-corrosion coating solution for galvanized steel sheet is provided, wherein 3-10% by weight of γ-glycidoxy propyl trimethoxysilane is added.

According to another aspect of the present invention, there is provided a galvanized steel sheet coated with the rustproof coating solution for galvanized steel sheet.

Hereinafter, the present invention will be described in detail.

The inventors have unexpectedly found that the anti-corrosive coating solution made by adding a specific lithium polysilicate colloid aqueous solution, an organic titanium complex compound and a silane crosslinking agent can impart excellent corrosion resistance to steel sheets, especially galvanized steel sheets, without containing chromium.                     

According to the present invention, it is possible to produce an anti-corrosive coating solution for galvanized steel sheet which can impart environment-friendly and high corrosion resistance without using chromium which is conventionally used.

Lithium polysilicate used in the present invention is composed of the following formula (1).

Li ₂ Si ₅ O ₁₁

Lithium polysilicate composed of Chemical Formula 1 is to give a good corrosion resistance by forming a coating layer of a three-dimensional network structure when coated on a steel sheet. At this time, the lithium polysilicate colloidal aqueous solution is added to the antirust coating solution based on the total weight, 5-15% by weight. If the addition amount of the lithium polysilicate is less than 5% by weight it is difficult to expect excellent corrosion resistance, and if more than 15% by weight it is not economical because not only corrosion resistance but also the price increases.

The organotitanium complex used in the present invention consists of the following formula (2).

[Ti ^IV (L ₁ ) (L ₂ ) ₂ ], where L ₁ = triethanolamineto, L ₂ = isopropoxide

The organic titanium complex compound has a stable chelate of L ₁ ligand, triethanolamineto, and the L ₂ ligand, i.e., isopropoxide group, which is a terminal ligand, is gradually hydrolyzed in an aqueous solution to stabilize the solution, and gradually Substitution reactions have been shown to form [Ti (L ₁ ) (OH) ₂ ] (L ₁ = triethanolamineto) insoluble coatings. At this time, the organic titanium complex compound is added to the antirust coating solution based on the total weight, 1-10% by weight. If the content is less than 1% by weight, the concentration of the titanium complex compound is too dilute to expect corrosion resistance, and when it is added more than 10% by weight, the corrosion resistance does not increase any more and it is uneconomical.

In addition, the organic titanium complex compound may be used in the form dissolved in a suitable solvent. For example, the organotitanium complex may be added in the form of 80 wt% dissolved in 2-propanol.

The silane crosslinking agent used in the present invention is composed of γ-glycidoxypropyltrimethoxysilane.

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The silane crosslinker acts as a binder to bind various inorganic materials by hydrolysis of the methoxy ligand in the aqueous solution to -Si (OH) ₃ . At this time, the silane crosslinking agent is added to the antirust coating solution based on the total weight, 3-10% by weight. If the silane crosslinking agent is added in less than 3% by weight it is difficult to expect a sufficient role of the binder, when added in more than 10% by weight is not preferable because the corrosion resistance does not increase any more and the properties such as weldability, degreasing resistance is worse. not.

These three compounds form a three-dimensional network to further increase the corrosion resistance of the steel sheet. In addition, since the bonding strength between the steel sheet and the polymer resin layer is excellent, it is possible to provide a steel sheet excellent in chipping resistance (chiping), which is particularly important in automotive steel sheets.

In addition, it is preferable to adjust the pH of the coating solution to 4-6 by adding phosphoric acid (H ₃ PO ₄ ) to promote the hydrolysis of the silane crosslinker. If the pH of the coating solution is 4 or less, the hydrolysis rate is advantageous, but the solution stability when mixed with the silicate is inferior. And when the pH is 6 or more, the hydrolysis rate is too slow to inhibit the corrosion resistance due to incomplete polymer reaction during coating. More preferably, the coating solution is adjusted to pH 5 by adding phosphoric acid.

The anti-corrosive coating solution of the present invention made as described above is coated on a galvanized steel sheet, and the applicable galvanized steel sheet includes an alloyed hot dip galvanized steel sheet, a hot dip galvanized steel sheet, an electric galvanized steel sheet, and a Zn-Ni low galvanized steel sheet. .

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

Preparation of antirust coating solution

To the pure water, a silane crosslinking agent (γ-glycidoxypropyltrimethoxysilane; SinEtsu Chemical Co.) was added in varying amounts to 3-10% by weight as shown in Table 1, followed by phosphoric acid (H ₃ PO ₄ ). Was added to adjust the pH to 5 and then stirred for at least 10 hours. To this solution, lithium polysilicate colloid aqueous solution (SiO ₂ content 20 wt%, pH = 11; Dupont Chemical Co.) consisting of Formula 1 was added in varying amounts to 5-15 wt% as shown in Table 1. Then, the organic titanium complex of Formula 1 (dissolved at 80% by weight in 2-propanol; Aldrich Chemical Co.) was added in varying amounts to 1-10% by weight as shown in Table 1 By stirring, 27 kinds of antirust coating solutions were prepared.

Inventive Example 1-27: Preparation of alloyed hot dip galvanized (GA) coated steel sheet

The anti-corrosive coating solutions prepared above were coated on an alloyed hot dip galvanized steel sheet (GA) having a plating amount of 20-60 g / m2 per side and a Fe content of 10-12% by using a bar-coat # -3 (coating) Thickness 0.5-1.0㎛) The coated specimen was prepared by drying for 10 seconds at 120-160 ° C. at a steel sheet reaching temperature (PMT) in a hot air drying furnace.

Inventive Example 28-54: Preparation of hot dip galvanized (GI) coated steel sheet

The anti-corrosive coating solutions prepared above were coated on a hot dip galvanized steel sheet (GI) having a plating amount of 40-90 g / m2 per side using a bar-coat # -3 (coating thickness 0.5-1.0 μm) and the steel sheet in a hot air drying furnace. A coated specimen was prepared by drying at 120-160 ° C. for 10 seconds at room temperature and cooling with water.

Inventive Example 55-81: Preparation of an electro galvanized (EG) coated steel sheet

The anti-corrosive coating solutions prepared above were coated on an electrogalvanized steel sheet (EG) having a plating amount of 20-60 g / m2 per side using a bar-coat # -3 (coating thickness 0.5-1.0 μm) and the steel sheet in a hot air drying furnace. A coated specimen was prepared by drying at 120-160 ° C. for 10 seconds at room temperature and cooling with water.

Inventive Example 82-108: Preparation of Zn-Ni electro-galvanized (Zn-Ni) coated steel sheet

Coating the anti-corrosive coating solutions prepared on the Zn-Ni electrogalvanized steel sheet (Zn-Ni) having a plating amount of 10-40 g / ㎡ per side, 10-14% Ni content in the coating layer using a bar-coat # -3 Coating specimens were prepared by drying (coating thickness 0.5-1.0 μm) in a hot air drying furnace at 120-160 ° C. for 10 seconds and then water cooling.

Conventional Example 1-4

As described in Korean Patent Application No. 1999-51479, a chromium reduction ratio (Cr3 + / Cr6 +) is 0.52, and an epoxy silane crosslinking agent and a curing agent containing phosphoric acid are added to a main solution containing colloidal silica, hydrofluoric acid, and phosphoric acid. The coated chromate rust preventive solution thus prepared was coated on each zinc plate in the same manner as described above.

Performance evaluation

Corrosion resistance evaluation-Using the salt spray device (JIS E2731) cooled by cooling the prepared specimens with a spray pressure of 5% NaCl, dispersion pressure 1Kg / ㎡ and measuring the time required to generate 5% white rust Was investigated.

Evaluation of Resin Adhesiveness (Film Adhesiveness)-Melamine epoxy-based resin was coated on a galvanized steel sheet with a thickness of about 1 μm, and then baked at 12 ° C. at 160 ° C. for 12 seconds, followed by water cooling to prepare a specimen. It was put in distilled water at 50 ℃, soaked for 240 hours and dried. 100 sheets of checkerboard-shaped scales were made at 2 mm intervals on the coating surface of the specimen, and the adhesion of the coating film was evaluated by the number of coating films peeled off the tape when the coating film was peeled off with scotch tape.

Surface Appearance and Solution Stability-The surface appearance and solution stability were examined for color, wettability, solution aging, and presence or absence of sediment.

Each evaluation result is shown to the following Table 1a-1d.                     

TABLE 1a

TABLE 1b

TABLE 1c

TABLE 1d

1) GA; An alloyed hot-dip galvanized steel sheet, the plating amount was 40g / m2 per side, the Fe content in the plating layer was 10-12%, GI; Hot dip galvanized steel plate plating amount is 60g / ㎡ per side, EG; Electro-galvanized steel plate, the coating amount was 30g / m2 per side, Zn-Ni; Zn-Ni alloyed electroplating steel plate, the plating amount is 30g / m2 per single side and the Ni content in the plating layer is 12%.                     

2-4) The organotitanium complex and lithium polysilicate (Li ₂ Si ₅ O ₁₁ ) used a reagent sold by Dupont, and a silane crosslinker was purchased from SinEtsu.

5) Surface appearance was judged by sensory test by color, wettability, etc.

6) The resin adhesiveness was evaluated by the number of coating films peeled off the tape as described above (excellent: 3 or less, usually 4-10).

7) The solution stability was judged by the sensory test on the aging of the solution and the presence or absence of sediment (very good: more than 5 weeks, excellent: only 1-2 weeks).

8) corrosion resistance; Time required to generate 5% white rust (very good: 200 hours or more, excellent: 100-200 hours, normal: 72-100 hours)

As shown in Table 1a-1d, the corrosion resistance of the galvanized steel sheet coated with the coating solution to which the compound according to the present invention is added was excellent at least 48 hours (5% occurrence time of white blue), and also excellent. It is considered to be useful for various coating bases due to its excellent adhesion with resin. In addition, the anti-corrosive coating solution prepared according to the present invention is stable even for a long time storage, and exhibited excellent workability due to the low viscosity of the solution.

Since the coating solution of the present invention has not only the same or more corrosion resistance than the conventional example using chromate, but also has excellent surface appearance and solution stability, it is a chromium-free coating type anticorrosive for reinforcing corrosion resistance of alloyed hot-dip galvanized steel sheet. It will be very useful when applied.

According to the present invention, there is provided an rust-free coating solution for galvanized steel sheet that does not contain chromium.

In addition, the anti-corrosive coating solution for galvanized steel sheet of the present invention is excellent in corrosion resistance, surface appearance and solution stability, stable at room temperature, excellent in workability, easy to manufacture and does not contain other chromium-containing anti-rust coating solutions. There is an inexpensive advantage.

Claims (3)

In the anti-corrosive coating solution for galvanized steel sheet, based on the total weight in the anti-rust coating solution, 5-15% by weight of a colloidal aqueous solution containing lithium polysilicate of Li ₂ Si ₅ O ₁₁ ; 1-10% by weight of an organic titanium complex of [Ti ^IV (L ₁ ) (L ₂ ) ₂ ], wherein L ₁ = triethanolamineto, L ₂ isopropoxide; And 3-10% by weight of γ- glycidoxyoxytrimethoxysilane is added, And anti-corrosive coating solution for galvanized steel sheet, characterized in that the pH is adjusted to 4-6 by the addition of phosphoric acid. delete Galvanized steel sheet coated with the anti-corrosive coating solution for galvanized steel sheet of claim 1.