KR100586454B1 - Anti-corrosion coating composition and zinc-coated steel coated with the composition - Google Patents

Abstract

The present invention relates to an environmentally friendly alkaline water-soluble rust-preventive coating composition which does not contain chromium which can impart excellent corrosion resistance, electrical conductivity and chemical resistance to a galvanized steel sheet and a coated steel sheet prepared therefrom. The anti-corrosive coating composition is 0.5 to 7% by weight of the silane coupling agent, 0.5 to 7% by weight of the silicate compound selected from the group consisting of metal silicates, metal polysilicates and mixtures thereof, 0.1 to 5% by weight of the titanate compound, zirconate 0.05 to 3 wt% of the compound and 1 to 15 wt% of the ethylene acrylate polymer resin and the balance of the solvent. The galvanized steel sheet coated with the coating composition exhibits excellent processed part corrosion resistance and paintability, electrical conductivity, blackening resistance, and chemical resistance.

Galvanized Steel Sheet, Antirust Coating, Ethylene Acrylic Polymer

Description

Anti-corrosion coating composition containing no chromium and galvanized steel sheet coated thereon {ANTI-CORROSION COATING COMPOSITION AND ZINC-COATED STEEL COATED WITH THE COMPOSITION}

In order to prevent surface corrosion of galvanized steel sheet, Chromate coating process has been performed for more than 100 years. Conventional chromate rust coating treatment can be classified into two categories. One is a method for supplementing the anticorrosive function of the resin layer by the resin base treatment and improving the coating adhesion to the steel sheet, an example of which is described in Korean Patent Application No. 1999-51479. Another example is a reactive chromate, an electrolytic reaction type and a spray reaction type. The reactive chromate coating has a coating amount of 5-80mg / [Cr], which is treated in various ways according to the anti-rust properties of the steel sheet.

Chromate containing Cr (VI) has been used for a long time due to its low cost and excellent corrosion resistance, but today, it is known as a primary carcinogen causing laryngeal cancer and regulates its use as an environmentally harmful substance internationally. Countries around the world, including the EU, regulate the use of Cr (VI) with lead (Pb), cadmium (Cd), and mercury (Hg), which previously regulated manufacturing and process emissions. In recent years, there is a regulation on final products. The End of Life Cycle (ELV) Act on Automobiles will be in full force in January 2007. The Restriction of Hazardous Substance (RoHS) regulations for electrical and electronic devices will be implemented in July 2006. From now on, regulations will be implemented to completely prohibit the disposal of products containing environmentally friendly substances. Therefore, the world is currently striving to develop corrosion inhibitors or rust inhibitors that do not use chromium (Cr) for construction, home appliances, and automobiles.

The development of rust free agents that do not contain chromium has been done for a long time from various angles. Representative methods include the use of polymer resins, the molybdenum anion (Molybdate, MoO ₄ ^2- ) passivation film, the method using silica, the method using a heavy acid salt (MH ₂ PO ₄ ) film, tannic acid Research on the coating of organic materials, such as these, has been performed. Recently, many corrosion inhibitors have been developed to enhance corrosion resistance by using zirconium and titanium compounds or silane coupling agents.

However, they are more limited than the chromate coatings, have poor barrier properties, low self-healing properties, and insufficient corrosion resistance. In particular, organic rust inhibitors based on resins are limited in their use for home appliances and automotive parts due to their low weldability and electrical conductivity, since the coating layer is an insulator. Therefore, the development of an inorganic rust preventive agent is required as a means to solve this problem. However, since the inorganic anti-corrosive coating is low in corrosion resistance and poor in chemical resistance, it is necessary to develop an organic-inorganic anti-corrosive coating composition in which an appropriate amount of a polymer resin that binds well with an inorganic anti-corrosive component is solved.

An object of the present invention is to provide an anticorrosive coating composition that does not contain environmentally friendly chromium having excellent paintability, electrical conductivity and chemical resistance while giving excellent corrosion resistance to galvanized steel sheets used in home appliances and automotive parts.

Another object of the present invention is to provide a galvanized steel sheet coated with the antirust coating composition.

In the present invention, 2 to 5% by weight of a silicate compound selected from the group consisting of 2 to 5% by weight of a silane coupling agent (Silane Coupling Agent), a metal silicate, a metal polysilicate and a mixture thereof, a titanate compound It provides 0.5 to 3% by weight, 0.1 to 1% by weight of the zirconate compound, 3 to 9% by weight of the ethylene acrylate polymer resin and the balance of the solvent.

The present invention provides a steel sheet excellent in corrosion resistance of the flat plate and the processed portion prepared by coating the anti-corrosive coating composition on a galvanized steel sheet, and excellent in electrical conductivity, blackening resistance, and chemical resistance by an organic-inorganic composite anti-corrosion coating.

Hereinafter, the present invention will be described in more detail.

In the case of the organic coating steel sheet using the conventional polymer resin has a disadvantage of small electrical conductivity, in the case of the inorganic coating steel sheet has a disadvantage that is weak in blackening resistance and chemical resistance. In the present invention, a method for solving the problem is to prepare an anti-corrosion coating composition by mixing an inorganic compound having excellent electrical conductivity while reducing the content of the polymer resin.

The anti-corrosive coating composition of the present invention is an organic-inorganic hybrid anti-corrosive coating composition prepared by mixing a water-soluble inorganic coating agent containing a silane coupling agent, a silicate compound, a titanate compound, and a zirconate compound with an organic coating agent of ethylene acrylate polymer resin. to be. The anti-corrosive coating composition of the present invention is environmentally friendly because it does not contain chromium, and has excellent corrosion resistance to plates and processed parts by the self-restoring anti-rust effect of the inorganic coating agent and the protective film anti-rust function of the polymer resin, and the organic-inorganic composite anti-corrosion coating. Steel sheet excellent in conductivity, blackening resistance and chemical resistance can be provided.

The anti-corrosive coating composition according to the present invention is an alkali-based water-soluble solution, which is excellent in coating property on a galvanized steel sheet, is stable at room temperature, has excellent workability, is easy to manufacture, and is cheaper than other conventional chromium-containing rust inhibitors. There is an advantage.

Preferred examples of the silane coupling agent in the anti-corrosive coating composition of the present invention include gamma-glycidoxypropyltrialkoxysilane, gamma-aminopropyltrialkoxysilane, and the like, where alkoxy is preferably alkoxy having 1 to 7 carbon atoms. . More preferred examples thereof include gamma-glycidoxypropyltrimethoxysilane, (CH ₃ O) ₃ Si-C ₃ H ₆ OCH ₂ CH- (η-1,2-O) CH ₂ ), Gamma-glycidoxypropyltriethoxysilane, (C ₂ H ₅ O) ₃ Si-C ₃ H ₆ OCH ₂ CH- (η-1,2-O) CH ₂ ), gamma- Γ-aminopropyltrimethoxysilane, (CH ₃ O) ₃ Si-C ₃ H ₆ NH ₂ , gamma-aminopropyltriethoxysilane, (C ₂ H ₅ O) ₃ Si- C ₃ H ₆ NH ₂ ), and the like. The silane coupling agent is used in an amount of 0.5 to 7% by weight, preferably 2 to 5% by weight. If the amount of the silane coupling agent is less than 0.5% by weight, there is a problem in that a high-quality coated steel sheet cannot be obtained. If the amount of the silane coupling agent is greater than 7% by weight, the coating solution manufacturing cost is high and the economical efficiency is low. The silane coupling agent hydrolyzes the alkoxy ligand in an aqueous solution to -Si (OH) ₃ to bind various inorganic materials as well as a strong bond with the oxide layer on the surface of the steel sheet. In addition, functional groups such as terminal epoxy groups or amino groups serve to form bonds with other organic substances. Therefore, the silane coupling agent forms a bond with various organic materials and inorganic materials and serves to increase corrosion resistance.

 As the silicate compound, a metal silicate of Formula 1, a metal polysilicate of Formula 2, or a compound thereof may be used.

[Formula 1]

MSiO ₃ (M = Li, Na, or K.)

[Formula 2]

M ₂ Si ₅ O ₁₁ (M = Li, Na, or K).

The silicate compound is a compound having a high corrosion resistance by itself because it forms a three-dimensional network (Network) when coated on a steel sheet. The silicate compound has excellent corrosion resistance as well as a high bonding strength with the zinc plated layer, and thus is widely used for coating, and serves as a crosslinking bond between the plating layer and the resin layer.

The silicate compound is used in an amount of 0.5 to 7% by weight, preferably used in an amount of 2 to 5% by weight. If the amount of the silicate compound is less than 0.5% by weight, the amount of adhesion is small, so that a good quality steel sheet cannot be provided. If the amount of the silicate compound is more than 7% by weight, the amount of adhesion is too large, so that the bonding strength with the resin layer is weak.

As the titanate compound, a compound represented by the following Chemical Formulas 3 to 5 or a mixture of two or more thereof may be preferably used.

[Formula 3]

[Ti ^IV (L ₁ ) ₂ (L ₂ ) ₂ ]

(L ₁ = triethanolaminate and L ₂ = iso- propoxide).

[Formula 4]

[Ti (L ₃ ) ₂ (L ₂ ) ₂ ] (L ₃ = acetylacetonate.)

[Formula 5]

[Ti (L ₄ ) ₂ (OH) ₂ ] (NH ₄ ) ₂ (L ₄ = lactate.)

The titanate compound is used in an amount of 0.1 to 5% by weight, preferably in an amount of 0.5 to 3% by weight. If the amount of the titanate compound is less than 0.1% by weight, high corrosion resistance may not be obtained. If the titanate compound is more than 5% by weight, the production cost of the coating composition increases, which is not preferable because of the problem of low economic efficiency.

As the zirconate compound, a compound represented by the following Chemical Formulas 6 to 8 or a mixture of two or more thereof may be preferably used.

[Formula 6]

[Zr ^IV (L ₁ )] (L ₁ = triethanolaminate.)

[Formula 7]

[Zr ^IV (L ₃ ) ₂ ] (hereinafter, L ₃ = acetylacetonate)

[Formula 8]

[Zr ^IV (L ₄ ) ₂ ] (hereinafter L ₄ = lactate)

The zirconate compound is used in an amount of 0.05 to 3% by weight, preferably in an amount of 0.1 to 1% by weight. If the amount of the zirconate compound is less than 0.05% by weight, high corrosion resistance cannot be obtained. If the amount of the zirconate compound is more than 3% by weight, the production cost of the coating composition increases, which is not economical, which is not preferable.

The titanate compound and the zirconate compound exhibit excellent corrosion resistance even with the addition of a very small amount. The principle is due to the self-healing effect of the compounds on the barrier effect of the aforementioned compounds. I think. That is, a chelate compound having a stable structure in aqueous solution is formed by L ₁ , L ₃ , and L ₄ ligands having 2 or 4 groups binding ability, and isopropoxide group, which is a terminal ligand, is gradually hydrolyzed in the aqueous solution and coated with [M (L ₁ ) (OH) ₂ ] (M = Ti, Zr) It is shown to form an insoluble film. The coated steel sheet is gradually oxidized in air to break the chelate ring, thereby finally forming an oxide film of TiO ₂ and ZrO ₂ . By this process, the zinc layer of the plated steel sheet is protected, and a steel sheet having excellent corrosion resistance is provided.

The inorganic compound has excellent corrosion resistance and electrical conductivity but is vulnerable to chemical resistance. Therefore, to compensate for this, it is supplemented by introducing ethylene acrylate polymer resin. The ethylene acrylate resin used in the present invention is an alkali-based resin such as the inorganic aqueous solution, mixed well with each other, and has excellent solution stability. Therefore, the chromium-free rust preventive solution of the present invention is stable even when stored for a long time, almost no smell of the solution, the viscosity is adjustable to 5 to 12cps has the advantage of excellent workability.

The ethylene acrylate polymer resin may be preferably used having a weight average molecular weight (Mw) of 10000 to 20000. The ethylene acrylate polymer resin is preferably a molar ratio of 6: 1 to 3: 1 of ethylene: acrylate and 4: 1. The ethylene acrylate polymer resin is used in an amount of 1 to 15% by weight, preferably in an amount of 3 to 9% by weight. If the amount of the ethylene acrylate polymer resin is less than 1% by weight, there is a problem that cannot provide excellent quality characteristics, and if it exceeds 15% by weight, there is a problem of low corrosion resistance and conductivity, which is not preferable.

The antirust coating composition of the present invention may further comprise a curing agent. The curing agent is 3 to 7 parts by weight and preferably 5 parts by weight based on 100 parts by weight of the ethylene acrylate polymer resin.

As the solvent in the present invention, water may be preferably used, and a solvent containing 1 to 15 parts by weight of isopropyl alcohol may be preferably used with respect to 100 parts by weight of water.

The solids content of the rustproof coating composition is 7 to 22% by weight, and the viscosity is about 5 to 12 cps, which is excellent in workability.

The anti-corrosive coating composition is preferably prepared by mixing an inorganic coating solution and a polymer solution, respectively. Moreover, of course, it can manufacture by adding each component to a solvent.

The anti-corrosive coating composition is coated on an electro-galvanized steel sheet (EG), an alloyed hot dip galvanized steel sheet (GA), a hot dip galvanized steel sheet (GI), and then a steel sheet reaching temperature. (Peak Metal Temperature) It is possible to manufacture a coated steel sheet by baking and drying the water at 120-180 ℃. At this time, the coating thickness is preferably 0.1-1.0 μm, and the adhesion amount is preferably 200-1500 mg / m ² .

The following presents a preferred embodiment to aid the understanding of the present invention. However, the following examples are provided only to more easily understand the present invention, and the present invention is not limited to the following examples.

Examples 1-48 Antirust Coating Composition

Gamma-glycidoxypropyltrimethoxysilane (SinEtsu Chemical Co.) was added to the pure water, phosphoric acid (H ₃ PO ₄ ) was added thereto to pH = 5, and the mixture was stirred for at least 10 hours. A lithium polysilicate compound (Li ₂ Si ₅ O ₁₁ ), a titanate compound of formula 3, and a zirconate compound of formula 6 were added to the solution, followed by stirring for at least 1 hour to prepare a first composition in solution.

100 parts by weight of ethylene acrylate resin and 5 parts by weight of melamine resin as a curing agent were added to the pure water to prepare a second composition in suspension so that the solid content was 13% by weight.

The second solution was added to the first solution to prepare an organic-inorganic hybrid anti-corrosive coating composition having a solid content of 7 to 23 wt% in Examples 1 to 48. The content of each component of the antirust coating composition of Examples 1 to 48 is listed in Table 1 below.

TABLE 1

Examples 49-96: Preparation of Coated Steel Sheets

The anti-corrosive coating compositions of Examples 1-48 were each coated with bar-coat # -3 or continuous coating tester (EG, Electro-Galvanized Steel Sheet), alloyed hot-dip galvanized steel sheet (GA, Galvanealed Steel Sheet). ) And coated with hot dip galvanized steel sheet (GI, Galvanized Steel Sheet) (coating thickness 0.1-1.0 ㎛, coating composition compound adhesion amount 200-1500 mg / m ² ) Temperature) Baked to 120-180 ℃ dried and water cooled to prepare a coated steel sheet.

Comparative Example 1

The curing agent in which the chromium reduction ratio (Cr ³⁺ / Cr ⁶⁺ ) described in Korean Patent Application No. 1999-51479 is 0.52 and an epoxy silane coupling agent and phosphoric acid are contained in the main solution to which colloidal silica, hydrofluoric acid, and phosphoric acid are added. Coated chromate rust preventive coating composition prepared by adding was prepared. The anti-corrosive coating composition was coated on an electro-galvanized steel sheet (EG) in the same manner as in the examples, and then baked at an automatic discharge hot air drying furnace at 120-180 ° C. And water cooled to prepare a coated steel sheet.

Comparative Example 2 and Comparative Example 3

The reactive chromate coated steel sheet commercialized by POSCO Co., Ltd. was prepared using chromium (Cr) coating amount of 20 mg (electrolytic type, EL) (Comparative Example 2) and 80 mg (spray type, CH) (Comparative Example 3) steel sheet. And evaluated. Comparative Example 2 and Comparative Example 3 are chromate coated on an electro-galvanized steel sheet (EG).

Performance evaluation

The steel sheets used in the Examples and Comparative Examples are as follows. Electro galvanized (EG) steel sheet 20-40g / m ² per side, alloyed hot dip galvanized (GA) steel plate 20-60g / m ² per side, Fe content in plated layer 9-14%, hot dip galvanized (GI ) A steel sheet of 40-90 g / m ² per side of the steel sheet was used.

Corrosion resistance was generated by spraying the specimen prepared in the above example with a spray pressure of 35 ° C., 5% NaCl, and dispersion pressure of 1 Kg / m ² using a salt spray device (Japanese Industrial Standard Test JIS E2731). It evaluated by the time required until. The corrosion resistance of the processed part was evaluated by the salt spray test of the above conditions by processing the specimen of 25mmΦ, 7mm Ericsson (Ericksen). The average rating was 48Hr when the coating amount was 200 ~ 500mg / m ² , 72Hr when 500 ~ 800mg / m ² , and 92Hr after 800Hg / m ² . The corrosion resistance evaluation of the processed part was evaluated by the occurrence of white rust when half the plate corrosion resistance.

[Evaluation Criteria] ◎; Less than 5% of white rust, ○; 5-20%, Δ; More than 20%.

In the case of solvent coating, Melamine-Alkyd resin was coated on galvanized steel sheet with Bar coater # 3 with a thickness of about 20㎛, then baked at 30 ° C at 160 ° C for steel sheet and cooled by water. Was produced. The prepared specimen was put in distilled water at 50 ° C. and dipped for 240 hours and then dried. 100 sheets of checkerboard-shaped scales were made on the coating surface of the specimen at 1 mm intervals, 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.

[Evaluation Criteria] ◎; No peeling, ○; Peeling rate less than 5%, (triangle | delta); Peeling rate 5% or more.

Electrodeposition coating was subjected to electrodeposition coating in galvanized steel sheet under the condition of H automobile company 20 (m or less) and then evaluated by the checker scale in the same manner as the solvent coating.

The blackening resistance test was evaluated by examining the color difference (△ E) after 110 hours at a temperature of 60 degrees and a humidity of 95%.

Conductivity was evaluated by measuring the resistance value (mΩ) of the coated surface using a LORESTA GP instrument.

Weldability was spot welding using air-compression welding machine (DAIHEN PRA-33A), and the welding appearance of surface appearance after welding using CF type electrode under pressure of 250kgf and welding time of 13 cycles is possible. The current range KA was measured and evaluated.

Anti-fingerprint was evaluated by measuring the color difference (△ E) after immersing the coated steel plate in artificial fingerprint solution for 5 seconds.

Solvent resistance evaluation was evaluated by measuring the color difference (△ E) that discoloration of the coating film after rubbing the MEK (Methyk Ethyl Ketone) solvent 10 times in gauze.

The evaluation results are shown in Table 2.

 TABLE 2

As shown in Table 2, at least 48 hours (5% occurrence time of white rust) was exhibited in the evaluation of plate corrosion resistance for all the galvanized steel sheets used in the present invention. Corrosion resistance tended to increase as the solid content or inorganic component content increased. In addition, since the adhesion between the steel sheet and the resin is excellent, and excellent in electrical conductivity, chemical resistance and weldability, it provides a chromium-free rust-proof coated steel sheet for automobiles and various home appliances.

The anti-corrosive coating composition of the present invention is an organic-inorganic composite anti-corrosive made by adding a titanate compound and a zirconate compound to an aqueous solution of ethylene acrylate, a silane coupling agent, and a silicate compound without using chromium, which is a conventional environmental load material. The coating composition is environmentally friendly and easy to manufacture and work. The coated galvanized steel sheets (EG, GA, GI) are excellent in corrosion resistance, electrical conductivity, paintability and chemical resistance.

Claims (8)

0.5 to 7 wt% of a silane coupling agent (Silane Coupling Agent); 0.5 to 7 wt% of a silicate compound selected from the group consisting of metal silicates, metal polysilicates and mixtures thereof; 0.1-5% by weight of titanate compound; 0.05-3% by weight of zirconate compound; 1 to 15% by weight of ethylene acrylate polymer resin; And Antirust coating composition containing remainder of solvent. The anti-corrosion coating composition of claim 1, wherein the silane coupling agent is any one selected from the group consisting of gamma-glycidoxypropyltrialkoxysilane, gamma-aminopropyltrialkoxysilane, and mixtures thereof. The method of claim 2, wherein the silane coupling agent is gamma-glycidoxypropyltrimethoxysilane (γ-glycidoxypropyltrimethoxysilane, (CH ₃ O) ₃ Si-C ₃ H ₆ OCH ₂ CH- (η-1,2-O ) CH ₂ ), gamma-glycidoxypropyltriethoxysilane, (C ₂ H ₅ O) ₃ Si-C ₃ H ₆ OCH ₂ CH- (η-1,2-O) CH ₂ ) , Gamma-aminopropyltrimethoxysilane, (CH ₃ O) ₃ Si-C ₃ H ₆ NH ₂ ), gamma-aminopropyltriethoxysilane, (C ₂ H ₅ O ) ₃ Si-C ₃ H ₆ NH ₂ ), and mixtures thereof. The anti-corrosion coating composition of claim 1, wherein the silicate compound is selected from the group consisting of a metal silicate of Formula 1, a metal polysilicate of Formula 2, and a compound thereof. [Formula 1] MSiO ₃ (M = Li, Na, or K.) [Formula 2] M ₂ Si ₅ O ₁₁ (M = Li, Na, or K). The anti-corrosive coating composition according to claim 1, wherein the titanate compound is selected from the group consisting of compounds represented by the following Chemical Formulas 3 to 5 and mixtures of two or more thereof. [Formula 3] [Ti ^IV (L ₁ ) ₂ (L ₂ ) ₂ ] (L ₁ = triethanolaminate and L ₂ = iso- propoxide). [Formula 4] [Ti (L ₃ ) ₂ (L ₂ ) ₂ ] (L ₃ = acetylacetonate.) [Formula 5] [Ti (L ₄ ) ₂ (OH) ₂ ] (NH ₄ ) ₂ (L ₄ = lactate.) The anti-corrosive coating composition according to claim 1, wherein the zirconate compound is selected from the group consisting of compounds represented by the following Chemical Formulas 6 to 8 and mixtures of two or more thereof. [Formula 6] [Zr ^IV (L ₁ )] (L ₁ = triethanolaminate.) [Formula 7] [Zr ^IV (L ₃ ) ₂ ] (hereinafter, L ₃ = acetylacetonate) [Formula 8] [Zr ^IV (L ₄ ) ₂ ] (hereinafter L ₄ = lactate) Galvanized steel sheet coated with the antirust coating composition according to any one of claims 1 to 6. The method of claim 7, wherein the galvanized steel sheet is an electro-galvanized steel sheet (EG, Electro-Galvanized Steel Sheet (GA), galvanealed steel sheet (GA), or hot-dip galvanized steel sheet (GI, Galvanized Steel Sheet) Phosphorus Galvanized Steel Sheet.