KR20180073388A - Coating Composition Having Superior Corrosion-Resistance and Lubricity and Coated Steel Sheet Using the Same - Google Patents

Abstract

The present invention relates to a coating composition having superior corrosion resistance and lubricity, and a coated steel sheet using the same. More specifically, the coating composition, based on the solid content, comprises: 20 to 60 wt% of a urethane-acryl composite resin and a nanosilicate-phenoxy composite resin based on the total weight of the coating composition; 35 to 78.5 wt% of an inorganic corrosion resistant agent based on the total weight of the coating composition including 7 to 35 wt% of a silane A, i.e., an epoxy-based or amino-based silane, 24 to 60 wt% of a silane B, i.e., a vinyl-based silane or an acrylic silane, 3 to 11 wt% of a vanadium phosphate, 0.1 to 2 wt% of a magnesium oxide, 2 to 10 wt% of zinc phosphate, 0.5 to 5 wt% of titanium carbonate, 0.5 to 5 wt% of zirconium oxide and 0.4 to 3 wt% of silica based on the total weight of the coating composition; and a lubricant including 1 to 3 wt% of a wax A and 0.5 to 2 wt% of a wax B based on the total weight of the coating composition, wherein the wax A has an average particle diameter that is 0.5 to 9.5 μm larger than that of the wax B.

Description

(Coating Composition Having Superior Corrosion-Resistance and Lubricity and Coated Steel Sheet Using the Same)

The present invention relates to a coating composition excellent in corrosion resistance and lubricity and a coated steel sheet using the same.

In order to impart corrosion resistance and paint adhesion to galvanized steel sheets, zinc-base alloy coated steel sheets, aluminum-plated steel sheets, aluminum-based alloy coated steel sheets, cold-rolled steel sheets and hot-rolled steel sheets used for automobile materials, And a chromate film containing chromium as a main component is coated on the substrate.

The main chromate treatment includes an electrolytic chromate and a coating type chromate. Of these electrolytic chromate treatments, hexavalent chromium is the main component. In addition, a treatment liquid containing various anions such as sulfuric acid, phosphoric acid, boric acid, Is conducted to the cathode. On the other hand, in the coating type chromate treatment, inorganic colloid and inorganic ion are added to a solution in which a part of hexavalent chromium is reduced in advance in advance to prepare a treatment solution, and then a metal plate is immersed in the treatment solution, Method.

When these methods are used, various measures are required in the working environment and drainage treatment due to the toxicity of hexavalent chromium contained in the chromate treatment liquid. In the case of recycling and disposal of automobiles, household appliances, and building materials using the surface- Causing human and environmental pollution problems.

Accordingly, steel makers are focusing on the development of surface-treated steel plates that do not contain hexavalent chromium and have corrosion resistance and other effects. In addition, the price of zinc, which is the main material of the plated steel sheet plating layer, is rapidly increasing. Therefore, researches for replacing zinc with other elements, reducing the content of zinc, or reducing the amount of plating deposit are continuing.

As a typical technique, Zinc Aluminum-Magnesium (ZAM) is a method for using a small amount of zinc as a substitute material and using aluminum or magnesium, which is a common metal, as a main component of the plating layer. In the case of such an alloy-coated steel sheet, although corrosion resistance above a certain level can be secured, there is a problem that heat resistance, surface appearance, high temperature and high humidity resistance and weldability are heated.

As another method, a technique for reducing the amount of plating on the plated steel sheet has been proposed. However, the plating adhesion amount is a factor that greatly affects the corrosion prevention of the metal and the long-term rust-preventive property. As the adhesion amount of the plating increases, the time required for the occurrence of redness increases, that is, the corrosion resistance increases. Therefore, the zinc plating deposit amount can not be reduced due to the problem of corrosion resistance which occurs quickly.

On the other hand, recent consumer electronics companies are demanding very high lubrication characteristics in door slides which are contained in electronic products such as refrigerators, electric / gas ovens, vending machines and the like. As a result, not only corrosion resistance but also lubrication are required to be developed as one of the items to be further improved in the chromium-free steel sheet for the purpose of temporary anticorrosion.

Accordingly, when a coating solution having improved corrosion resistance and lubricity is developed, both the friction coefficient and the processing blackness are improved, it is expected that the coating solution can be widely applied in related fields.

The present invention relates to an inorganic or organic composite coating composition for forming an inorganic or organic composite coating layer on the surface of a galvanized steel sheet by using the inorganic or organic composite coating composition to greatly improve the corrosion resistance of the steel plate and the processed portion after machining, Thereby improving the lubrication characteristics.

According to one aspect of the present invention, there is provided a coating composition comprising 20 to 60% by weight of a urethane-acrylic composite resin and a nano-silicate-phenoxy composite resin based on the total weight of the coating composition; 7 to 35% by weight, based on the total weight of the inorganic anticorrosive agent, silane A which is an epoxy or amino silane, 24 to 60% by weight of vinyl silane or silane B which is an acrylic silane, 3 to 11% by weight of vanadium phosphate, 2 to 10% by weight of zinc phosphate, 0.5 to 5% by weight of titanium carbonate, 0.5 to 5% by weight of zirconium oxide and 0.4 to 3% by weight of silica, based on the total weight of the coating composition, 35 To 78.5% by weight; And a lubricant comprising 1 to 3% by weight of wax A and 0.5 to 2% by weight of wax B based on the total weight of the coating composition, wherein the wax A has an average particle size of 0.5 to 9.5 [mu] m larger than the average particle size of wax B, A coating composition is provided.

According to another aspect of the present invention, A zinc-based plated layer formed on one side or both sides of the base steel sheet; And a coating layer formed on the plating layer, wherein the coating layer is a cured product of the coating composition of the present invention.

When a coating layer is formed on the surface of a galvanized steel sheet using the organic-inorganic hybrid coating composition of the present invention, the corrosion resistance of the flat sheet portion of the steel sheet and the processed portion after machining can be greatly improved. In addition, The friction coefficient is lowered, the scratch resistance of the coating film is improved, and the process blackening property is improved, so that the lubricating property of the entire coating layer is improved.

Fig. 1 is a schematic diagram of measures for securing coating layer lubrication characteristics such as surface slip, scratch, and process blackness according to the distribution of wax A and wax B, which are the lubricants contained in the coating composition.
Fig. 2 shows photographs of corrosion resistance evaluation of the coated steel sheets of Example 2 and Comparative Example 45 after Erickson 6 mm processing.
Fig. 3 is a photograph showing evaluation of the process blackness of the coated steel sheets of Example 2 and Comparative Example 49. Fig.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

The inventors of the present invention have conducted extensive studies for securing the corrosion resistance of a coated steel sheet and have found that the use of a binder resin capable of maximizing the barrier effect of an organic system and the effect of an inorganic rust inhibitor and maximizing the acceptance of an inorganic corrosion- The optimal combination was derived. As a result, the deposition amount of the zinc plating layer is reduced and the organic-inorganic composite coating layer is formed on one side or both sides of the steel sheet, so that the corrosion resistance of the flat plate portion and the bending portion can be secured.

Further, the coating composition of the present invention can be used in combination with wax B as shown in Fig. 1 by mixing different types of waxes having different average particle diameters and specific gravities, thereby obtaining wax A having a specific gravity larger than wax B but lower specific gravity than wax B The wax A is concentrated in the surface layer to improve the slip and lubrication (friction) property of the coating film, and the wax B is uniformly distributed in the coating composition to improve the lubrication property, the scratch resistance and the processing blackness And the like.

The coating composition of the present invention comprises, on a solid basis, 20 to 60% by weight of a urethane-acrylic composite resin and a nano-silicate-phenoxy composite resin based on the total weight of the coating composition; 7 to 35% by weight, based on the total weight of the inorganic anticorrosive agent, silane A which is an epoxy or amino silane, 24 to 60% by weight of vinyl silane or silane B which is an acrylic silane, 3 to 11% by weight of vanadium phosphate, 2 to 10% by weight of zinc phosphate, 0.5 to 5% by weight of titanium carbonate, 0.5 to 5% by weight of zirconium oxide and 0.4 to 3% by weight of silica, based on the total weight of the coating composition, 35 To 78.5% by weight; And a lubricant containing 1 to 3 wt% of wax A and 0.5 to 2 wt% of wax B based on the total weight of the coating composition, wherein the wax A has an average particle diameter larger by 0.5 to 9.5 m than an average particle diameter of the wax B .

The inorganic anticorrosive agent may be contained in an amount of 35 to 78.5% by weight, preferably 35 to 78% by weight, based on the total composition. If the content of the inorganic anticorrosive agent is less than 35% by weight, it is difficult to secure the effect of corrosion resistance. When the content of the inorganic anticorrosive agent is more than 78.5% by weight,

The urethane-acrylic composite resin and the nano-silicate-phenoxy composite resin as the organic resin serve as a binder resin and can contain a large amount of an inorganic anticorrosive agent for ensuring corrosion resistance. The content of the urethane-acrylic composite resin and the nano-silicate-phenoxy complex resin is preferably 20 to 60% by weight based on the solid composition, and if it is less than 20% by weight, the corrosion resistance, solvent resistance and process blackness If the amount is more than 60% by weight, the effect of improving the physical properties due to the addition is insignificant, which is uneconomical.

In order to synthesize the urethane-acrylic composite resin, an urethane dispersion containing an acrylic monomer in the core can be synthesized by first introducing acrylic monomer into the urethane resin. Then, an urethane-acrylic resin can be synthesized by adding an initiator of an acrylic monomer and further performing polymerization reaction at a temperature of 75 to 90 캜 for 6 hours.

Since the urethane-acrylic resin serves as a dispersant in which the urethane resin disperses the acrylic resin without the emulsifier, a resin having relatively excellent corrosion resistance can be obtained. The content of the urethane-acrylic resin is preferably 12 to 30% by weight, and if it is less than 12% by weight, it is difficult to ensure corrosion resistance and solvent resistance. If it is more than 36% by weight, the effect of improving the physical properties is insufficient.

The acrylic monomer may be 2-hydroxyethyl methacrylate, acrylamide or a compound thereof. Also, the acrylic monomer is not a urethane-acrylic resin which is mixed simply by reacting with residual isocyanate contained in the urethane resin, but a urethane-acrylic resin is crosslinked with a urethane or urea bond to form a urethane- Can be obtained.

The content of the acrylic monomer is preferably 2 to 5% by weight, and if the content is less than 2% by weight, the amount of the monomer reacting with the residual isocyanate is small and the degree of crosslinking of the urethane- The effect of the urethane reaction of the acrylic monomer and the isocyanate becomes insignificant, which is uneconomical.

In order to secure the rigidity of the resin by controlling the composition ratio of the isocyanate constituting the hard segment, the equivalent ratio of the NCO group and the OH group (equivalent ratio of NCO / OH) in the polymerization of the urethane- 3. When the value of the equivalence ratio of NCO / OH is less than 1, the process blackening property is weakened. When the value of the equivalence ratio is more than 3, the solution stability and corrosion resistance are poor. Further, in order to secure such an effect, the value of the NCO / OH equivalence ratio is more preferably controlled to 1.3 to 1.9, and most preferably to 1.6.

The nano-silicate-phenoxy composite resin is a resin prepared by adding a nano-silicate anticorrosion agent in the process of synthesizing a phenoxy resin, and can improve the corrosion resistance, the processing blackness, and the chemical resistance of the coated steel sheet.

The content of the nano-silicate-phenoxy resin is preferably 8 to 30% by weight. When the content is less than 8% by weight, it is difficult to secure corrosion resistance and in-process blackening. If the content is more than 30% by weight, Is not economical.

Unlike general phenoxy resins, the monomers used for the synthesis of the phenoxy resins may be alkyl-substituted phenols for improving the crosslinking of the resin and improving the physical properties. Examples of the alkyl-substituted phenol monomers include 4-ethylphenol, 2,6-dimethylphenol, 2-ethylphenol and 2-isopropylphenol (2 -isopropylphenol). < / RTI >

The crosslinking agent is preferably hexamethylenetetramine, and the silicate is preferably added together with the crosslinking agent in an amount of 10 to 50% by weight based on the crosslinking agent. At this time, the particle size of the nanosilicate is preferably 20 nm or less, more preferably 10 to 20 nm. When the particle size is limited, it is possible to increase the density of the resin coating to improve the adhesion of the coating film during bending or the like.

On the other hand, the nanosilicate may be one selected from calcium silicate, lithium silicate, and ammonium hexafluoro silicate.

The nano-silicate-phenoxy composite resin preferably contains 1 to 5% by weight of the nano-silicate based on the total weight of the nano-silicate-phenoxy composite resin. If the content of the nano-silicate is less than 1% by weight, the effect of the corrosion-resistant agent is difficult to exhibit. If the content of the nano-silicate is more than 5% by weight, the improvement of the effect is small.

The lower the weight-average molecular weight (Mw) of the urethane-acrylic composite resin or the nano-silicate-phenoxy composite resin is, the lower the viscosity of the liquid. When additives such as external additives and solvents are added, the solution stability is poor. Properties may be deteriorated. On the other hand, as the weight average molecular weight increases, physical properties such as adhesion and corrosion resistance are excellent, and even when bending or stretching, the coating film is less likely to fall off and exhibits excellent physical properties. Therefore, weight average molecular weight control of the resin is important.

Accordingly, the weight average molecular weight (Mw) of the urethane-acrylic resin or the nano-silicate-phenoxy resin is preferably 40,000 to 90,000. If the weight average molecular weight is less than 40,000, the inorganic corrosion resistance may be precipitated. If the weight average molecular weight exceeds 90000, the corrosion resistance may be deteriorated.

The silane compounds are generally vinyl, epoxy, chloro, amino, acrylic, and the like. The silane A in the present invention is preferably at least one selected from epoxy-based and amino-based silane. The epoxy silane may be gamma glycidoxypropyl triethoxysilane and gamma glycidoxypropyl trimethoxysilane. The epoxy silane may be a gamma glycidoxypropyl triethoxysilane or gamma glycidoxypropyl trimethoxysilane. Meanwhile, the amino-based silane may be gamma aminopropyl triethoxysilane, gamma aminopropyl trimethoxysilane, or the like.

When the content is less than 7% by weight, the solvent resistance and the water repellency of the coating layer are poor and it is difficult to effectively block corrosive factors by ensuring a sufficient hydrophobic period. When the content of silane A is less than 33% by weight, , The solution stability may be deteriorated and the effect of improving the corrosion resistance due to the increase of the content is insignificant, which is uneconomical.

The silane B may be at least one selected from vinyl silane and acrylic silane, and the corrosion resistance of the steel sheet after processing can be maximized by including it in the coating solution composition. The content of the silane B is preferably 24 to 57% by weight. When the content is less than 24% by weight, the effect of corrosion resistance is poor. When the content is more than 57% by weight, the solution stability is lowered. to be. On the other hand, the silane B may be at least one selected from vinyl silane and acrylic silane.

The vanadium phosphate has an effect of improving corrosion resistance, and the content of vanadium phosphate is preferably 3 to 11 wt%. When the content is less than 3% by weight, the corrosion resistance is poor. When the content is more than 11% by weight, the appearance of the steel sheet may be blackened in a high temperature and high humidity atmosphere.

The Mg oxide can be used by dissolving it in an aqueous solution of vanadium phosphate, and thus the effect of improving the corrosion resistance can be exhibited. The content of the Mg oxide is preferably 0.1 to 1.4% by weight. If the content is less than 0.1% by weight, it is difficult to secure the corrosion resistance effect. If the content is more than 1.4% by weight, the stability of the solution may be deteriorated.

The zinc phosphate is included as an auxiliary additive for improving the corrosion resistance, and the content of zinc phosphate is preferably 2 to 10% by weight. When the content is less than 2% by weight, it is difficult to secure the corrosion resistance effect. When the content is more than 10% by weight, the solution stability is lowered and the effect of improving the physical properties with respect to the amount of injection is not significant.

The titanium carbonate is included for the stability of the coating composition and the reactivity of the base steel sheet and the coating composition, and can serve as a coupling agent between the resin and the inorganic material. The content of the titanium carbonate is preferably 0.5 to 3.4% by weight. If the content is less than 0.5% by weight, it is difficult to secure corrosion resistance. If the content is more than 3.4% by weight, the effect of improving the corrosion resistance is small.

The content of zirconium oxide to improve the corrosion resistance is preferably 0.5 to 4% by weight. When the content of zirconium oxide is less than 0.5 wt%, it is difficult to ensure corrosion resistance. When the content of zirconium oxide is more than 4 wt%, the effect of improving the corrosion resistance is small.

The silica is included to improve the corrosion resistance, and mainly colloidal silica can be used. The content of the silica is preferably in the range of 0.4 to 3% by weight, and if it is less than 0.4% by weight, it is difficult to secure the corrosion resistance. If the amount is more than 3% by weight, the stability of the solution may be deteriorated.

The coating composition includes a lubricant that maximizes lubricity and surface hardness of the coated steel sheet to minimize physical damage such as scratches, peeling of the coating film and blackening phenomenon that may occur during processing, thereby improving workability.

In order to ensure processability, properties required for the lubricant are not only required to have physical properties such as surface lubricity, scratch resistance and abrasion resistance, but also compatibility with solutions containing other additives is an important consideration.

For this reason, it is difficult to satisfy all of the above requirements with a specific wax. Therefore, in the present invention, two kinds of waxes including wax A and wax B are simultaneously used.

Wax A is a type which liquefies at a set curing temperature and has a low specific gravity so that surface slipping property is improved and surface lubricity is improved and surface layer lubricity is improved. Examples of the wax A include an amide wax, a polyethylene wax, a polypropylene wax, a carnauba wax, Wax, polyether-modified polysiloxane, and polyether-modified polysiloxane-based wax may be used.

Wax B has a higher specific gravity than wax A, so that it spreads evenly from the surface to the bottom of the solution, and when used together with wax A, maximizes processing lubricity, provides additional surface lubrication, scratch resistance, and process blackness , And the wax B may be at least one wax selected from a polytephenic wax, a polyethylene-Teflon modified wax, and a polypropylene-Teflon modified wax.

It is preferable that the wax A has an average particle diameter of 2 to 10 mu m so that the wax A can be easily liquefied at a set curing temperature. The wax B spreads uniformly throughout the gap between the wax A and the coating composition, Preferably, the wax A has an average particle size of from 3 to 10 mu m, and the wax B has an average particle diameter of from 0.5 to less than 3 mu m.

If the particle size of the wax A is smaller than 2 m, the lubrication effect due to the wax particles is deteriorated. When the particle size exceeds 10 m, the liquefaction of the wax during curing of the coating layer becomes difficult. On the other hand, when the particle diameter of the wax B is less than 0.5 μm, there is no commercially available product. If it exceeds 3 μm, the effect of the wax A is canceled and the effect of improving the lubricity such as process blackening property is not greatly improved.

On the other hand, the wax A of the present invention preferably has an average particle diameter larger than the average particle diameter of the wax B by 0.5 to 9.5 μm, more preferably 0.5 to 4.5 μm, and when the particle diameter difference is less than 0.5 μm, The wax A does not spread to the gap between the waxes A and B and the wax A is less effective in maximizing the lubricity. When the wax A is larger than 9.5 탆, the wax A has a larger particle size than the wax B, There is a limit in improving the surface lubrication and scratch resistance simultaneously.

Furthermore, it is preferable that the average specific gravity of the wax A is 0.85 to 097, the average specific gravity of the wax B is 0.99 to 1.24, and the average specific gravity of the wax B is 0.02 to 0.39 larger than the average specific gravity of the wax A.

When the average specific gravity of the wax A is less than 0.85, the product is not commercialized with respect to the particle diameter of 2 to 10 mu m. When the wax A is more than 0.97, the specific gravity becomes too heavy to lower the density in the surface layer of the coating layer. On the other hand, when the average specific gravity of the wax B is less than 0.99, the wax A is mixed with the wax A in the surface layer and the surface lubricity can be maintained. However, there is a problem that the scratch resistance decreases as the density in the interior decreases. There is a problem in that the wax is concentrated in the lower part, and the waxes tend to be clustered with each other, making it difficult to liquefy or spreading the wax, and the working lubricity due to the wax B is lowered.

When the specific gravity difference is less than 0.02, there is a small difference in the specific gravity between the waxes A and B, and therefore, the density of the wax B in the coating layer is lowered in the coating layer, , And when it is more than 0.39, the specific gravity of the wax B is larger than that of the wax A, the distribution of the waxes A and B is uneven in the coating layer due to the fact that they are not uniformly distributed throughout the coating layer, There is a problem that the overall lubricity such as blackening is reduced.

Based on the total weight of the coating composition, the lubricant containing the wax A and the wax B may be in an amount of 1.5 to 5 wt%, more specifically, 1 to 3 wt% of the wax A and 0.5 to 2 wt% of the wax B .

When the amount of the wax A is less than 1 wt%, the weight of the wax A is not sufficient enough to exhibit the lubricant properties, and when the wax A is more than 3 wt% Resulting in nonuniformity thereof, and corrosion resistance after processing is deteriorated. On the other hand, when the wax B is less than 0.5% by weight, there is a problem that the lubricant characteristics such as the wax A are not sufficient enough to exhibit the lubricant properties sufficiently, and the lubricity such as the friction coefficient falls. When the wax B is more than 2% by weight, There is a problem that the lubricating property is maintained while the corrosion resistance after processing is reduced.

On the whole, if the content of the waxes A and B is less than 1.5% by weight based on the total weight of the coating composition, the coefficient of friction of the coating layer becomes high and the surface slip property may be insufficient, On the other hand, when the amount of the wax is more than 5 wt%, the overall lubrication property can be improved, but the stability of the solution itself may be lowered and the corrosion resistance may be deteriorated due to excessive wax particles on the surface of the coating film.

On the other hand, the inorganic corrosion inhibitor may further include thio-urea, and in the case of thio-urea, an organic compound used for preparing resins, medicines and the like, and may be used as a curing accelerator in the present invention. The content of the thio-urea may be 0.5 to 7% by weight based on the inorganic corrosion inhibitor. If the content of the thio-urea is less than 0.5% by weight, the effect of promoting hardening is hardly exhibited. If the content is more than 7% by weight, There is an effect of shortening the time, but the solution stability is reduced.

Since the coating layer is formed on one side or both sides of a steel sheet to be described later by using the coating solution having the above composition, the flat portion of the steel sheet and the corrosion resistance after processing can be maximized.

Since the coating layer is formed on one or both surfaces of the steel sheet using the coating composition having the above composition, the friction coefficient of the surface of the steel sheet is lowered as well as the corrosion resistance effect of the steel sheet to improve the lubricity such as scratch resistance and process blackness Can be further improved.

More specifically, according to another aspect of the present invention, A zinc-based plated layer formed on one side or both sides of the base steel sheet; And a coating layer formed on the plating layer, wherein the coating layer may be a cured product of the coating composition of the present invention described above.

The coated steel sheet may include a coating layer formed on the zinc plated layer, and may be coated on one side or both sides of the zinc plated steel sheet using the coating solution described above. At this time, it is preferable to control the deposition amount of the coating layer to 0.5 to 2 g / m < 2 >. If the adhesion amount is less than 0.5 g / m 2, it is difficult to ensure corrosion resistance. If it exceeds 2 g / m 2, the conductivity of the coating layer is deteriorated.

Hereinafter, the present invention will be described more specifically by way of specific examples. The following examples are provided to aid understanding of the present invention, and the scope of the present invention is not limited thereto.

Example

Comparative Example  1-37

A coating composition corresponding to the composition shown in the following Table 1 was coated on the surface of a hot-dip galvanized steel sheet having a zinc adhesion amount of 40 g / m 2 by a roll coating method to control the adhesion amount to 0.8 g / m 2, 140 to form a coating layer.

The solution stability of each of the coating compositions prepared in the composition shown in the following Table 1 was evaluated and the plate corrosion resistance and the weathering resistance of the coated steel sheet coated with the coating composition were evaluated. A more specific evaluation method is as follows.

Experimental Example  1: Evaluation of solution stability (A)

The solution stability was judged to be defective (X) when the viscosity of the coating composition was increased by 20% or more from the initial stage, or when the solution was precipitated, decomposed and gelated as a result of visual observation.

Experimental Example  2: Evaluation of plate corrosion resistance (B)

The plate corrosion resistance was evaluated by measuring the time required for 5% of white rust to occur in the condition of salt concentration 5%, temperature 35 ℃, and spray pressure 1 kg / cm ² . The evaluation criteria of the plate corrosion resistance were evaluated as follows based on 120 hours.

<Evaluation Criteria>

○: 120 hours or more

X: less than 120 hours

Experimental Example  3: Black degeneration  Evaluation (C)

The chromaticity evaluation was carried out by measuring the color difference (delta E) before and after holding the coated steel sheet for 120 hours in a thermo-hygrostat at a temperature of 50 ° C and a relative humidity of 95%, and based on the required chromium-free coated steel sheet of 2.0 And evaluated as follows.

<Evaluation Criteria>

?: Not more than 2.0

X: exceeded 2.0

division Coating solution (% by weight) Quality characteristics V-PO ₄ MgO Silane A Resin ^* Zinc phosphate TiCO ₃ ZrO Silica Silane B A B C Comparative Example 1 2.5 0.7 12 30 3 0.7 1.5 0.8 41 X Comparative Example 2 3.0 Comparative Example 3 5 Comparative Example 4 11 Comparative Example 5 12 X Comparative Example 6 5 0.05 X Comparative Example 7 0.1 Comparative Example 8 1.4 Comparative Example 9 2.0 X Comparative Example 10 0.7 5 X Comparative Example 11 7 Comparative Example 12 33 Comparative Example 13 35 X Comparative Example 14 12 15 X Comparative Example 15 20 Comparative Example 16 60 Comparative Example 17 70 X Comparative Example 18 30 1.5 X Comparative Example 19 2 Comparative Example 20 10 Comparative Example 21 12 X Comparative Example 22 3 0.3 X Comparative Example 23 0.5 Comparative Example 24 3.4 Comparative Example 25 4.0 X Comparative Example 26 0.7 0.3 X Comparative Example 27 0.5 Comparative Example 28 4.0 Comparative Example 29 4.5 X Comparative Example 30 1.5 0.2 X Comparative Example 31 0.4 Comparative Example 32 3.0 Comparative Example 33 3.5 X Comparative Example 34 0.8 20 X Comparative Example 35 24 Comparative Example 36 57 Comparative Example 37 60 X

* Resin: urethane-acrylic resin and nano-silicate-phenoxy resin

In Comparative Example 1, since the content of vanadium phosphide is lower than the range controlled by the present invention, the zinc phosphate layer which inhibits permeation of corrosion factor is insufficient and the corrosion resistance is lowered.

In Comparative Example 5, since the content of vanadium phosphide was higher than the range controlled by the present invention, excessive etching occurred and the black weathering was deteriorated.

In Comparative Example 6, since the content of Mg oxide was lower than the range controlled by the present invention, the corrosion inhibition was insufficient due to insufficient corrosion inhibiting effect through formation of hydrate of Mg.

In Comparative Example 9, since the content of Mg oxide was higher than the range controlled by the present invention, it was present in excess in the solution and reacted with other corrosion-resistant additives, and the solution stability was lowered.

In Comparative Example 10, since the content of silane A was lower than the range controlled by the present invention, the crosslinking effect between the resin of the silane and the inorganic material was insufficient and the corrosion resistance was degraded.

In Comparative Example 13, since the content of silane A was higher than the range controlled by the present invention, solution stability was lowered due to exceeding the silane content which was stably dispersed in the solution.

In Comparative Example 14, since the content of the urethane-acrylic resin and the nano-silicate-phenoxy resin was lower than the range controlled by the present invention, the function of the binder resin was insufficient and penetration of moisture was easy at high temperature and high humidity, .

In Comparative Example 17, the content of the urethane-acrylic resin and the nano-silicate-phenoxy resin was higher than the range controlled by the present invention, so that the content of the inorganic anticorrosive agent was decreased and the corrosion resistance was lowered.

In Comparative Example 18, since the content of zinc phosphate was lower than the range controlled by the present invention, the corrosion resistance of the steel sheet deteriorated due to a lack of a corrosion-assisting role.

In Comparative Example 21, because the content of zinc phosphate was higher than the range controlled by the present invention, the solution stability was degraded due to insufficient mixing and dispersion with other corrosion inhibitors in the solution.

In Comparative Example 22, since the content of titanium carbonate was lower than the range controlled by the present invention, the cross-linking function with the resin was insufficient and the corrosion resistance was degraded.

In Comparative Example 25, since the content of titanium carbonate was higher than the range controlled by the present invention, proper mixing and dispersion with other corrosion inhibitors were not achieved in the solution, and the solution stability was degraded.

In Comparative Example 26, since the content of zirconium oxide was lower than the range controlled by the present invention, the corrosion resistance of the steel sheet was deteriorated due to the lack of a supporting role for corrosion resistance.

In Comparative Example 29, since the content of zirconium oxide was higher than the range controlled by the present invention, proper mixing and dispersion with other corrosion inhibitors were not achieved and the solution stability was degraded.

In Comparative Example 30, since the content of silica was lower than the range controlled by the present invention, the bonding strength with the resin layer was decreased and the corrosion resistance was lowered.

In Comparative Example 33, since the content of silica was higher than the range controlled by the present invention, proper mixing and dispersion with other corrosion inhibitors were not achieved and the solution stability was degraded.

In Comparative Example 34, since the content of silane B was lower than the range controlled by the present invention, the bond with the organic and inorganic additive and the role of increasing the corrosion resistance were weakened and the corrosion resistance of the steel sheet was deteriorated.

In Comparative Example 37, since the content of silane B was higher than the range controlled by the present invention, the solution stability was lowered and the corrosion resistance was decreased.

On the other hand, the other comparative examples show that the solution stability, the corrosion resistance, the solvent resistance and the black marking were evaluated to be somewhat excellent.

Comparative Example  38-48 and Example  1-6

The coating composition of Comparative Example 35 was further comprised of wax A and wax B in the amounts listed in Table 2, wherein the particle size of each wax was limited to about 1 mu m. Thereafter, the coating composition was applied to a hot-dip galvanized steel sheet having a coating amount of 40 g / m 2 by a bar coating method, and then the hot-dip galvanized steel sheet was heated to a temperature of 140 ° C using an induction heater to form a coating layer Respectively.

At this time, polyethylene wax was used for wax A, and polypropylene-teflon modified wax was used for wax B.

The corrosion resistance, the coefficient of friction, and the process blackness were evaluated after the Erickson 6 mm process was performed on the steel sheet prepared as described above. The evaluation results are shown in Table 2 below.

The corrosion resistance evaluation, the friction coefficient evaluation, and the processing blackness evaluation method after the specific Ericsson 6 mm processing are described below.

Experimental Example  4: Evaluation of corrosion resistance after Erickson 6mm processing (D)

The erosion resistance evaluation after Erickson 6 mm was carried out in a salt spray test under the conditions of a salt concentration of 5%, a temperature of 35 ° C. and a spray pressure of 1 kg / cm ² , The time was measured.

At this time, the Erickson process was press-processed into a circular shape with respect to a specimen size of 75 mm x 150 mm, and was formed into a concave shape with a height of 6 mm in cross section.

<Evaluation Criteria>

○: 96 hours or more

X: Less than 96 hours

Experimental Example  5: Evaluation of friction coefficient (E)

The coated steel sheet was cut into a size of 50 (W) x 200 (L) mm and then the friction tip (size: 35 * 45 mm) was moved under a load (N) of 600 kg, a speed of 1000 mm / min, Was calculated as a friction coefficient ( m ) value. At this time, the friction coefficient calculation formula is as follows.

When the value of the friction coefficient obtained as a result of the calculation was 0.12 or less, the evaluation was evaluated as good (O), and when it was 0.12 or more, the evaluation was evaluated as defective (X).

Experimental Example  6: Process blackness  Evaluation (F)

After the coated steel plate was cut to a size of 50 × 50 mm and the friction tip was reciprocated 10 times at a force of 0.25 kgf / mm ^{2 in} the uncoated state, blackening phenomenon such as blackening due to film breakage due to friction or insufficient slip property Were observed.

At this time, it was evaluated as good (O) when the blackening occurred at 5% or less, and poor (X) when it was 5% or more at all.

division Wax A (wt%) Wax B (% by weight) Corrosion resistance after processing (D) Coefficient of friction (E) Process blackness (F) Comparative Example 38 0.3 - ○ X X Comparative Example 39 0.5 - ○ ○ X Comparative Example 40 One - ○ ○ X Comparative Example 41 - 0.3 ○ X X Comparative Example 42 - 0.5 ○ X X Comparative Example 43 - One ○ ○ X Comparative Example 44 0.5 One ○ ○ X Example 1 One One ○ ○ ○ Example 2 2 One ○ ○ ○ Comparative Example 45 4 One X ○ ○ Comparative Example 46 6 One X ○ ○ Example 3 One 0.5 ○ ○ ○ Example 4 One 2 ○ ○ ○ Comparative Example 47 One 3 X ○ ○ Example 5 2 0.5 ○ ○ ○ Example 6 2 2 ○ ○ ○ Comparative Example 48 2 3 X ○ ○

Comparative Examples 38-43 show the results of evaluating only one type of lubricant among the waxes A and B. [ As described above, when only one type of lubricant is used, it is confirmed that the corrosion resistance is good, while the friction coefficient and the processing blackness are poor.

That is, with only one type of lubricant, it is difficult to improve both the scratch resistance and the process blackness of the entire coating layer by improving the surface slip property and reducing the physical damage.

In Comparative Example 44, the corrosion resistance was good after the Ericsson processing, but the weight was not enough to sufficiently exhibit the lubricant properties, resulting in a decrease in the process blackness.

In Comparative Examples 45 to 48, all the wax particles were excessively distributed in the coating layer as the lubricant component entered excessively, and the lubricating properties including the coefficient of friction and the process blackness were good, but the coating layer itself was nonuniform Corrosion resistance was reduced after Ericsson processing.

Example  8-10 and Comparative Example  49-50

The particle sizes of wax A (polyethylene wax) and wax B (polypropylene-teflon modified wax) used in the coating composition of Example 2 were 5 탆 and 1 탆, respectively, and specific gravities were 0.89 and 1.12, respectively. These wax A And the average particle size of the wax B were changed as shown in Table 3.

Thereafter, the coating composition was applied to a hot-dip galvanized steel sheet having a coating amount of 40 g / m 2 by a bar coating method, and then the hot-dip galvanized steel sheet was heated to a temperature of 140 ° C using an induction heater to form a coating layer Respectively.

The corrosion resistance, the coefficient of friction and the blackening resistance of the steel sheet prepared as described above were evaluated in the same manner as in Experimental Examples 4 to 6, and the evaluation results are shown in Table 3 below.

division Wax A Particle Size (탆) Wax B Particle Size (탆) Corrosion resistance after processing Coefficient of friction Process blackness Comparative Example 49 One One ○ X X Example 7 3 One ○ ○ ○ Example 2 5 One ○ ○ ○ Example 8 10 One ○ ○ ○ Example 9 3 0.5 ○ ○ ○ Example 10 3 One ○ ○ ○ Comparative Example 50 3 7 X ○ ○

In Comparative Example 49, the corrosion resistance after the Erickson process was good, but both the wax A and the B had a particle size smaller than the reference size, and the lubricant properties were not sufficiently exhibited, resulting in a decrease in the friction coefficient and the process blackness.

In Comparative Example 50, as the size of the solid wax B particles became excessively large, the coating solution did not completely melt even at a curing temperature of 140 ° C during curing, and remained in the coating layer. Thus, the resin component of the coating layer and cross- cross-linking), thereby promoting corrosion and reducing corrosion resistance.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, But will be obvious to those of ordinary skill in the art.

Claims (21)

On solid basis,
20 to 60% by weight of a urethane-acrylic composite resin and a nano-silicate-phenoxy composite resin based on the total weight of the coating composition;
7 to 35% by weight, based on the total weight of the inorganic anticorrosive agent, silane A which is an epoxy or amino silane, 24 to 60% by weight of vinyl silane or silane B which is an acrylic silane, 3 to 11% by weight of vanadium phosphate, 2 to 10% by weight of zinc phosphate, 0.5 to 5% by weight of titanium carbonate, 0.5 to 5% by weight of zirconium oxide and 0.4 to 3% by weight of silica, based on the total weight of the coating composition, 35 To 78.5% by weight; And
A lubricant comprising from 1 to 3% by weight of wax A and from 0.5 to 2% by weight of wax B, based on the total weight of the coating composition,
Wherein the wax A has an average particle size larger than the average particle size of the wax B by 0.5 to 9.5 [mu] m.
The coating composition according to claim 1, wherein the content of the urethane-acrylic composite resin is from 12 to 30% by weight based on the total weight of the coating composition, and the content of the nano-silicate-phenoxy hybrid resin is from 8 to 30% by weight.
The coating composition according to claim 1, wherein the urethane-acrylic composite resin or the nanosilicate-phenoxy composite resin has a weight average molecular weight (Mw) of 40,000 to 90,000.
The coating composition according to claim 1, wherein the urethane-acrylic composite resin is synthesized using an acrylic monomer which is 2-hydroxyethyl methacrylate, acrylamide or a compound thereof.
The coating composition according to claim 4, wherein the content of the acrylic monomer in the urethane-acrylic composite resin is 2 to 5% by weight.
The coating composition according to claim 1, wherein the urethane-acrylic composite resin has an NCO / OH equivalent ratio of 1 to 3.
The method of claim 1 wherein the nanosilicate-phenoxy complex resin uses at least one alkyl-substituted phenol monomer selected from 4-ethylphenol, 2,6-dimethylphenol, 2-ethylphenol, and 2-isopropylphenol &Lt; / RTI &gt;
The coating composition according to claim 1, wherein the nanosilicate-phenoxy composite resin comprises a nanosilicate in an amount of 1 to 5% by weight based on the total weight of the nanosilicate-phenoxy composite resin.
The coating composition of claim 1, wherein the nanosilicate-phenoxy composite resin comprises a nanosilicate having an average particle size of 20 nm or less.
The coating composition of claim 1, wherein the nanosilicate-phenoxy complex resin comprises at least one nanosilicate selected from calcium silicate, lithium silicate, and ammonium hexafluorosilicate.
The coating composition of claim 1, wherein the silane A is at least one selected from an epoxy-based silane and an amino-based silane.
12. The coating composition of claim 11, wherein the epoxy silane is gamma glycidoxypropyl triethoxy silane and gamma glycidoxypropyl trimethoxy silane.
12. The coating composition of claim 11, wherein the amino-based silane is gammaaminopropyltriethoxysilane and gammaaminopropyltrimethoxysilane.
The coating composition according to claim 1, wherein the silane B is at least one selected from vinyl silanes and acrylic silanes.
The wax according to claim 1, wherein the wax A is at least one selected from an amide wax, a polyethylene wax, a polypropylene wax, a carnauba wax, a microcrystalline wax, a polyether modified polysiloxane and a polyether modified polysiloxane wax, Wherein the wax B is at least one wax selected from a polytetron wax, a polyethylene-Teflon modified wax and a polypropylene-Teflon modified wax.
The coating composition according to claim 1, wherein the wax A has an average particle diameter of 2 to 10 mu m and the wax B has an average particle diameter of 0.5 to 3 mu m.
The coating composition of claim 1, wherein the average specific gravity of the wax A is from 0.85 to 0.97 and the average specific gravity of the wax B is from 0.99 to 1.24.
The coating composition of claim 1, wherein the average specific gravity of the wax A is greater than the average specific gravity of the wax B by 0.02 to 0.39.
The coating composition according to claim 1, wherein the inorganic corrosion inhibitor further comprises thio-urea, and the content of thio-urea is 0.5 to 7 wt% based on the total weight of the inorganic corrosion inhibitor.
Base steel sheet;
A zinc-based plated layer formed on one side or both sides of the base steel sheet; And
And a coating layer formed on the plating layer, wherein the coating layer is a cured product of the coating composition of any one of claims 1 to 19.
21. The coated steel sheet according to claim 20, wherein the coating amount of the coating layer is 0.5 to 2 g / m &lt; 2 &gt; based on one side of the steel sheet.

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