HK1135149B - Coated steel sheet - Google Patents

Description

Coated steel sheet

Technical Field

The present invention relates to a coated steel sheet.

Background

Conventionally, steel materials such as galvanized steel sheets and aluminum-plated steel sheets have been subjected to rust prevention treatment with chromate such as 6-valent chromate, and if necessary, they have been coated with an organic resin to impart fingerprint resistance, scratch resistance, and the like, and then coated with various finish paints.

In recent years, with the increasing environmental problems, there has been a trend that chromate treatment applied to conventional steel materials is restricted or prohibited by law. Since the chromate treated layer itself has high corrosion resistance and coating adhesion, these properties are remarkably lowered when the chromate treatment is not performed. Therefore, it is required to form a rust-preventive layer having good corrosion resistance and coating adhesion without carrying out chromate treatment.

Jp-a 11-71536 discloses a coated steel sheet treated with a rust-preventive treatment agent for metal surfaces, wherein the rust-preventive treatment agent is obtained by adding silica and an epoxy compound to a reaction product of an ionomer resin neutralized with a 2-valent metal and an epoxy compound. The coated steel sheet has improved adhesion to a curable resin such as a paint. However, the adhesion to the metal material is poor, and particularly under wet conditions, water penetrates through the film to the metal material interface, causing the film to peel off.

Jp 2000 a-273659 a describes a coated steel sheet having a metal surface treated with a rust-preventive treatment agent obtained by mixing silica, an epoxy compound, a silane coupling agent, and thiosulfate ions with a reaction product of an ionic polymer resin neutralized with a 1-valent metal and a 2-valent metal, a polyolefin resin neutralized with an amine, and an epoxy compound. Since the silane coupling agent is added later to the treated steel sheet, the alkali resistance and the coating adhesion are improved as compared with those of the coated steel sheet disclosed in jp-a-11-71536. However, the adhesion to metal materials is insufficient.

Jp 2003-155451 a discloses a coated steel sheet treated with an aqueous coating agent containing a water-dispersible resin, silica particles and an organic titanate compound. However, the physical properties such as the adhesion to the substrate of the coating and the pressure-resistant oil property are sometimes insufficient, and a coated steel sheet having further improved performance is demanded.

Jp 2005-281863 a describes a coated steel sheet having a coating film formed thereon, the coating film containing a crosslinked resin matrix and an inorganic rust preventive.

Disclosure of Invention

In view of the above-described situation, an object of the present invention is to provide a coated steel sheet having improved properties such as adhesion to a base material and pressure-resistant oiliness.

The present invention relates to a coated steel sheet coated with a composite coating film, wherein the composite coating film is a composite coating film of (A) ethylene-unsaturated carboxylic acid copolymer resin particles having a silanol group and/or an alkoxysilyl group and having an average particle diameter of 20nm to 100nm, (B) silica particles having an average particle diameter of 5nm to 50nm, and (C) an organotitanium compound, and the amount of the coating film in the coated steel sheet is 0.5g/m²～3g/m²。

In the composite coating film, the silica particles (B) are preferably 5 to 100 mass% of the resin particles (a), and the content of titanium atoms is preferably 0.05 to 3 mass% of the total amount of the coating film.

Among the composite coatings, preferred is a coating in which the above-mentioned (a) to (C) and a compound (D) are composited, and the compound (D) is at least one compound selected from the group consisting of a phosphoric acid compound, a thiocarbonyl compound, niobium oxide and a guanidine compound.

The present invention is explained in detail below.

The coated steel sheet of the present invention has a coating film which is a composite of (A) ethylene-unsaturated carboxylic acid copolymer resin particles having a silanol group and/or an alkoxysilyl group and having an average particle diameter of 20 to 100nm, (B) silica particles having an average particle diameter of 5 to 50nm, and (C) an organic titanium compound. The coating film formed by combining the components (A) to (C) is excellent in properties such as corrosion resistance, solvent resistance, alkali resistance, and coating adhesion. In particular, by using resin particles (A) having an average particle diameter of 20nm to 100nm, the uniformity and denseness of the coating film are improved, and the adhesion to the substrate and the pressure-resistant oil properties are remarkably improved.

Examples of the resin particles (a) include resin particles obtained as follows: resin particles are obtained by neutralizing a copolymer resin of ethylene and an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, or maleic anhydride with an alkali metal hydroxide (sodium hydroxide, potassium hydroxide, or the like), ammonia water, or an organic amine, dispersing the neutralized resin in water, and allowing the obtained aqueous dispersion resin solution to act on a silane compound. Among them, resin particles obtained by reacting a water-dispersed resin solution of an alkali-neutralized ethylene-methacrylic acid copolymer resin with a silane compound or the like are preferable in that they can be made fine and can form a high-performance film.

The ethylene-methacrylic acid copolymer resin preferably contains methacrylic acid in an amount of 10 to 30% by mass. The ethylene-methacrylic acid copolymer resin may contain other monomers as needed, and the amount of the other monomers is preferably 10% by mass or less. The ethylene-methacrylic acid copolymer resin can be produced by a known method such as polymerization using a high-pressure low-density polyethylene production apparatus.

The resin particles (A) have silanol groups and/or alkoxysilyl groups. The functional group can react with the silica particles (B) and the organotitanium compound (C), and a composite coating film can be formed, and the adhesion to a substrate, pressure resistance, oiliness resistance, and the like can be improved. The alkoxysilyl group in the alkoxysilyl group is not particularly limited, and examples thereof include a trimethoxysilyl group, a dimethoxysilyl group, a methoxysilyl group, a triethoxysilyl group, a diethoxysilyl group, and an ethoxysilyl group. The functional group can be obtained by reacting a silane compound or the like with the aqueous dispersion of the ethylene-unsaturated carboxylic acid copolymer resin. The silane compound is preferably an epoxy group-containing silane compound.

Specific examples of the epoxy group-containing silane compound include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane. These compounds may be used alone, or 2 or more of them may be used in combination. The amount to be mixed is preferably 0.1 to 30% by mass of the epoxy group-containing silane compound relative to the solid content of the aqueous dispersion resin solution. More preferably, it is in the range of 1 to 10% by mass. If the amount is less than 0.1% by mass, the alkali resistance, solvent resistance, coating adhesion and the like of the coating film formed on the surface of the steel material are lowered, while if the amount is more than 30% by mass, the hydrophilicity of the composite coating film becomes too high, and the corrosion resistance may be lowered, or the solution stability of the aqueous coating agent used for forming the composite coating film may be lowered.

In the reaction with the silane compound, an epoxy compound may be used in combination for the reaction. When an epoxy compound is used in combination, the affinity with an organic resin is enhanced, and therefore, when a top coat is applied to the composite coating film, it is sometimes advantageous in improving the coating film adhesion. Examples of the epoxy compound include sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, propylene glycol diglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanurate, bisphenol a glycidyl ether, hydrogenated bisphenol a diglycidyl ether, and the like. These compounds may be used alone, or 2 or more of them may be used in combination.

The resin particles (A) have an average particle diameter of 20 to 100 nm. Here, the average particle diameter can be measured by a particle diameter measuring apparatus based on a dynamic light scattering method, for example, FPAR-1000 (manufactured by Otsuka Denshi Co., Ltd.). The average particle diameter is a cumulative average particle diameter obtained by diluting an aqueous dispersion of the resin particles (A) with ion-exchanged water to a concentration suitable for measurement by the above-mentioned apparatus and measuring the resultant at a liquid temperature of 25 ℃. If the average particle diameter obtained by the above method is less than 20nm, problems such as deterioration of workability and corrosion resistance occur due to excessively high viscosity, excessively high hydrophilicity, and the like. If the average particle diameter exceeds 100nm, there arises a problem that the coating performance is deteriorated in adhesion to a substrate, pressure resistance oil properties and the like.

The average particle diameter of the resin particles (a) can be adjusted within the above range by adjusting the kind of neutralizing agent, the water dispersion condition, the kind of silane compound, the reaction condition of silane compound, the kind of epoxy compound, the reaction condition of epoxy compound, and the like. As for the kind of the neutralizing agent, the use of an alkali metal is preferable in terms of reducing the average particle diameter, and when an amine or ammonia is used, it is preferable to use it in combination with an alkali metal. The water dispersion condition is preferably a condition in which the dispersion is carried out at a high temperature immediately before boiling and at a high stirring speed for a long time. For example, the particles are stirred at a rotation speed of 500 rpm or more for 4 hours or more to obtain the desired particle diameter. As the silane compound and the epoxy compound, water-insoluble low-molecular-weight compounds are preferable, and the reaction is preferably carried out under heating.

The silica particles (B) preferably have an average particle diameter of about 5nm to 50nn, and can be suitably selected from colloidal silica, fumed silica, and the like. Specific examples thereof include SNOWTEX N, SNOWTEX C (Nissan chemical industry), Adelite AT-20N, AdeliteAT-20A (Asahi Denka Kogyo industry), Cataloid S-20L, Cataloid SA (catalytic chemical industry), and the like. These may be used alone, or 2 or more of them may be used in combination.

Specific examples of the organotitanium compound (C) include dipropoxybis (triethanolamine) titanium, dipropoxybis (diethanolamine) titanium, dibutoxybis (triethanolamine) titanium, dibutoxybis (diethanolamine) titanium, dipropoxybis (acetylacetonato) titanium, dibutoxybis (acetylacetonato) titanium, dihydroxybis (lactic acid) titanium monoammonium salt, dihydroxybis (lactic acid) titanium diammonium salt, propanedioxytitanium bis (ethylacetoacetate), oxotitanium bis (monoammonium oxalate), isopropyltris (N-amidoethyl-aminoethyl) titanate and the like. These may be used alone, or 2 or more of them may be used in combination.

The composite coating is a coating in which the resin particles (A), the silica particles (B), and the organic titanium compound (C) are bonded to each other. That is, the functional group on the surface of the resin particle, the functional group on the surface of the silica particle, and the functional group of the organic titanium compound (C) form a bond, and are in a state of being complexed.

The above-mentioned bonds are considered to be mainly bonds formed by reaction of Si-OR groups and/OR Si-OH groups of the resin particles (A), Si-OH groups on the surface of the silica particles (B), and Ti-OR' groups and/OR Ti-OH groups of the organic titanium compound (C), Si-O-Si bonds, Si-O-Ti-O-Si bonds, etc. By these bonds, an advantageous effect that the organic resin particles and the inorganic particles form a chemically strong bond can be obtained. Further, since the particle diameters of the resin particles (a) and the silica particles (B) are within a specific range, the bonds between the particles in the composite coating are formed at a high density, and the composite coating is chemically stable and has high microscopic homogeneity. Therefore, it is presumed that a particularly significant effect can be obtained.

The composite coating may further comprise a compound (D) which is at least one compound selected from the group consisting of a phosphoric acid compound, a thiocarbonyl compound, niobium oxide and a guanidine compound. This means that 2 or more of a phosphoric acid compound, a guanidine compound, a thiocarbonyl compound, and niobium oxide may be mixed, or any one of them may be mixed. That is, the composite coating film may be formed by compounding at least one selected from the group consisting of a phosphoric acid compound, a thiocarbonyl compound, niobium oxide, and a guanidine compound in addition to the essential components of the resin particles (a), the silica particles (B), and the organic titanium compound (C).

Examples of the phosphate compound include phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid and tetraphosphoric acid, and phosphate salts such as triammonium phosphate, diammonium phosphate, trisodium phosphate and disodium phosphate. These compounds may be used alone, or 2 or more of them may be used in combination. When the phosphoric acid compound is used, phosphate layers are formed on the surfaces of the metal substrates by the phosphoric acid ions to be in a passive state, thereby improving rust prevention.

The thiocarbonyl compound, niobium oxide and guanidine compound are effective for preventing white rust of zinc steel sheet and the like in particular, as in the case of chromium compounds conventionally used for imparting corrosion resistance.

The thiocarbonyl compound is represented by the following general formula (1).

Wherein X, Y are the same or different and each represents H, OH, SH or NH₂Or represents the presence or absence of OH, SH or NH₂And a C1-15 hydrocarbon group which may be substituted or unsubstituted with-O-, -NH-, -S-, -CO-or-CS-, wherein X and Y may be bonded to form a ring.

The thiocarbonyl compound represented by the above general formula (1) is a compound having a thiocarbonyl group represented by the following formula (I), and among them, a thiocarbonyl group having a nitrogen atom or an oxygen atom represented by the following formula (II) is preferable.

Further, a compound which can form a thiocarbonyl group-containing compound in an aqueous solution or in the presence of an acid or a base may also be used. Examples of the thiocarbonyl compound include thiourea represented by the following formula (III) and derivatives thereof, for example, methylthiourea, dimethylthiourea, trimethylthiourea, ethylthiourea, diethylthiourea, 1, 3-dibutylthiourea, phenylthiourea, diphenylthiourea, 1, 3-bis (dimethylaminopropyl) -2-thiourea, ethylenethiourea, propylenethiourea and the like.

Examples of the carbothioic acid represented by the following formula (IV) and salts thereof include thioacetic acid, thiobenzoic acid, dithioacetic acid, sodium methyldithiocarbamate, sodium dimethyldithiocarbamates, triethylamine dimethyldithiocarbamates, sodium diethyldithiocarbamates, piperidine pentamethylenedithiocarbamates, piperidine dithiocarbamate, potassium o-ethylxanthate, and the like.

These thiocarbonyl compounds may be used alone or in combination of 2 or more. Among the above thiocarbonyl compounds, a water-insoluble thiocarbonyl compound may be once dissolved in an alkaline solution and then added to the mixture, and the mixture may be mixed with a coating agent to be used.

For the above niobium oxide, niobium oxide colloidal particles are preferable. This enables formation of a coating film in which niobium oxide colloidal particles are compounded, thereby further improving corrosion resistance. When the average particle diameter of the niobium oxide colloidal particles is small, the particles are more stable, and a dense niobium oxide-containing coating film can be formed, whereby stable rust prevention can be imparted to the treated object, and therefore, the particles are more preferable.

The niobium oxide colloidal particles are particles in which an oxide of niobium is dispersed in water in a fine particle state, and for example, are particles in which niobium oxide is not strictly formed but an amorphous state is formed in an intermediate state between niobium hydroxide and niobium oxide.

As the niobium oxide particles to be added to the aqueous coating agent used for forming the composite coating, a niobium oxide sol produced by a known method can be used. The niobium oxide sol is not particularly limited, and examples thereof include niobium oxide sols produced by a known method described in, for example, Japanese patent application laid-open Nos. 6-321543, 8-143314 and 8-325018. Further, a commercially available niobium oxide sol available from woodchemical corporation may be used.

The niobium oxide colloidal particles preferably have an average particle diameter of 100nm or less. The average particle diameter is more preferably 2nm to 50nm, and still more preferably 2nm to 20 nm. The niobium oxide colloidal particles are more preferably small in average particle diameter because they are more stable and can form a dense niobium oxide-containing film, thereby imparting stable rust resistance to the treated object. The average particle diameter of the niobium oxide colloidal particles can be measured by using a particle diameter measuring apparatus based on a dynamic light scattering method, for example, model FPAR-1000 (manufactured by Otsuka Denshi Co., Ltd.).

The guanidine compound is represented by the following formula (2).

Wherein X 'and Y', which may be the same or different, represent H, NH₂Phenyl or methylphenyl (tolyl), X 'and Y' may have H, NH₂Phenyl or methylphenyl (tolyl) group as a substituent and may contain-C (═ NH) -, -CO-or-CS-.

Examples of the guanidine compound include guanidine, aminoguanidine, guanylthiourea, 1, 3-di-o-tolylguanidine, 1-o-tolylbiguanide, and 1, 3-diphenylguanidine. The guanidine compounds can be used alone, or in combination of 2 or more.

In the composite coating, the silica particles (B) are preferably 5 to 100% by mass relative to the resin particles (a). When the content of the silica particles (B) is less than 5% by mass, the hardness and corrosion resistance of the coating film formed on the steel material surface may be lowered. When the silica particles (B) are contained in an amount of more than 100% by mass, the film formability and water resistance may be lowered. More preferably 10 to 50% by mass.

In the composite coating, the content of titanium atoms is preferably 0.05 to 3% by mass based on 100% by mass of the total coating. When the content of titanium atoms is less than 0.05% by mass, the composition of the components in the formed film may be insufficient, and the performance of the film may be deteriorated. When the content of titanium atoms exceeds 3 mass%, the hydrophilicity of the coating film becomes too high, and the performance of the coating film may be deteriorated, or the bath stability of the aqueous coating agent to be used may be deteriorated. The content of titanium atoms is more preferably 0.2 to 2 mass%.

When the composite coating contains a phosphoric acid compound, the content of the phosphate radical is preferably 0.01 to 5% by mass in 100% by mass of the coating. If the content of the phosphate group is less than 0.01% by mass, the corrosion resistance is insufficient, and if it exceeds 5% by mass, the aqueous dispersion resin used may gel and thus the coating may not be performed. The content of phosphate groups is more preferably 0.05 to 3 mass%.

When the composite coating contains a thiocarbonyl compound, the content of the thiocarbonyl compound is preferably 0.01 to 5% by mass in 100% by mass of the coating. When the content of the thiocarbonyl compound is less than 0.01% by mass, the corrosion resistance is insufficient, and when it exceeds 5% by mass, the corrosion resistance is saturated, which is not economical, and the aqueous dispersion resin to be used is gelled and may not be applied. The content of the thiocarbonyl compound is more preferably 0.05 to 5% by mass.

When the composite coating contains niobium oxide, the content of niobium oxide is Nb₂O₅In terms of conversion, the content is preferably 0.01 to 5% by mass in 100% by mass of the coating film. When the content of niobium oxide is less than 0.01% by mass, sufficient rust prevention property cannot be obtained, which is not preferable. Even if the content of niobium oxide exceeds 5 mass%, no improvement in effect is observed, and it is uneconomical. The content of niobium oxide is more preferably 0.05 to 3% by mass.

When the composite coating contains a guanidine compound, the content of the guanidine compound is preferably 0.01 to 5% by mass based on 100% by mass of the coating. When the content of the guanidine compound is less than 0.01% by mass, the corrosion resistance is insufficient, and when it exceeds 5% by mass, the corrosion resistance is saturated, which is not economical, and the aqueous dispersion resin used is gelled and may not be applied. The content of the guanidine compound is more preferably 0.05 to 3% by mass.

The composite coating may contain other components than the components (a) to (D). For example, a lubricant and a pigment may be mixed. As the lubricant, conventionally known lubricants such as fluorine-based, hydrocarbon-based, fatty acid amide-based, ester-based, alcohol-based, metallic soap-based, and inorganic lubricants can be used. As the above pigment, for example, titanium dioxide (TiO) can be used₂) Zinc oxide (ZnO), calcium carbonate (CaCO)₃) Barium sulfate (BaSO)₄) Alumina (Al)₂O₃) Kaolin, carbon black, iron oxide (Fe)₂O₃、Fe₃O₄) And various coloring pigments such as inorganic pigments and organic pigments.

The composite coating can be formed by treating the surface of the base material with a coating agent for steel containing necessary components to form the coating. The coating agent for steel is preferably aqueous. A particularly preferred embodiment of the aqueous coating agent for steel materials is, for example, an aqueous coating agent in which resin particles (A) obtained by reacting an aqueous dispersion of a neutralized product of the ethylene-unsaturated carboxylic acid copolymer with a silane compound and an epoxy compound used as needed, silica particles (B), an organotitanium compound (C), and, as needed, at least one compound selected from the group consisting of phosphoric acid compounds, thiocarbonyl compounds, niobium oxide, and guanidine compounds are mixed. The aqueous coating agent for steel material in this case may be one obtained by mixing these components, and the order of addition is not particularly limited, and can be produced, for example, as shown in the following (1).

(1) The aqueous dispersion of the neutralized product of the ethylene-unsaturated carboxylic acid copolymer resin is appropriately heated under stirring, a silane compound and an epoxy compound used as needed are added thereto to react, silica particles (B) and an organic titanium compound (C) are mixed with the obtained resin particles (a) to prepare an aqueous composition, and at least 1 compound (D) selected from the group consisting of phosphoric acid compounds, thiocarbonyl compounds, niobium oxide and guanidine compounds is further mixed as needed.

A solvent and/or a leveling agent may be used in the aqueous coating agent for steel material to form a more uniform and smooth coating film. The solvent is not particularly limited as long as it is a solvent generally used for a coating material, and examples thereof include hydrophilic solvents such as alcohols, ketones, esters, and ethers, and leveling agents such as silicones.

The composite coating film can be formed by applying the aqueous coating agent for a steel material to the surface of a steel material. For example, when zinc-coated steel or uncoated steel is coated, the above-mentioned aqueous coating agent for steel is applied to a coating object which is degreased as necessary. The coating method is not particularly limited, and a commonly used roll coating, air spraying, airless spraying, dipping, or the like can be appropriately used. In order to improve the curability of the coating film, it is preferable to heat the coating object in advance or to heat-dry the coating object after coating. The temperature at which the coated object is heated is 50 ℃ to 250 ℃, preferably 100 ℃ to 220 ℃. When the heating temperature is less than 50 ℃, the evaporation rate of water is slow, and sufficient film-forming properties cannot be obtained, resulting in a decrease in solvent resistance and alkali resistance. On the other hand, when the heating temperature exceeds 250 ℃, the resin is thermally decomposed, the solvent resistance and alkali resistance are reduced, and the appearance is deteriorated due to yellowing. The drying time in the thermal drying after coating is preferably 1 second to 5 minutes.

In the coated steel sheet, the coating amount of the composite coating is 0.5g/m²～3g/m². The coating amount is less than 0.5g/m²In this case, the corrosion resistance is lowered. The coating amount is more than 3g/m²In this case, the problem of the decrease in adhesion to the substrate occurs.

The coated steel sheet of the present invention may be used after a coating film is formed by applying a top coat to the composite coating film. Examples of the top coat include coatings made of acrylic resins, acrylic-modified alkyd resins, epoxy resins, urethane resins, melamine resins, phthalic resins, amino resins, polyester resins, vinyl chloride resins, and the like.

The coating film thickness of the top coat is appropriately determined depending on the use of the rust-proof metal product, the kind of the top coat used, and the like, and is not particularly limited. The film thickness is usually about 5 to 300. mu.m, more preferably about 10 to 200. mu.m. The formation of a coating film of the top coat can be carried out as follows: a finish paint is applied to the coating film formed from the aqueous coating agent for steel material, and the coating film is dried and cured by heating. The drying temperature and time are appropriately adjusted depending on the kind of the top coat to be applied, the film thickness of the coating film, and the like, and usually, the drying temperature is preferably 50 to 250 ℃ and the drying time is preferably 5 minutes to 1 hour. The top coat can be applied by a conventionally known method in accordance with the form of the coating material.

Examples of the steel material of the present invention include zinc-plated steel sheets such as zinc-plated steel sheets, zinc-nickel-plated steel sheets, zinc-iron-plated steel sheets, zinc-chromium-plated steel sheets, zinc-aluminum-plated steel sheets, zinc-titanium-plated steel sheets, zinc-magnesium-plated steel sheets, zinc-manganese-plated steel sheets, zinc-aluminum-magnesium-plated steel sheets, and zinc-aluminum-magnesium-silicon steel sheets, and steel materials containing a small amount of cobalt, molybdenum, tungsten, nickel, titanium, chromium, aluminum, manganese, iron, magnesium, lead, bismuth, antimony, tin, copper, cadmium, arsenic, etc. as a different metal element or impurity in these plating layers, and steel materials in which inorganic substances such as silica, alumina, and titania are dispersed. Further, the aqueous coating agent for steel materials can also be applied to multilayer plating combining the above plating and other types of plating (e.g., iron plating, iron-phosphorus plating, nickel plating, cobalt plating, etc.). Further, the present invention can be applied to aluminum plating or aluminum-based alloy plating. The plating method is not particularly limited, and any known plating method, hot dip plating method, vapor deposition method, diffusion plating method, vacuum plating method, or the like may be used.

The coated steel sheet having a coating film formed by coating the surface of a steel material with the aqueous coating agent for steel material is imparted with corrosion resistance, adhesion to a base material, solvent resistance, alkali resistance and pressure resistance oil properties, and the coating film formed on the steel sheet has good coating adhesion to the top coat film in the case of a steel sheet having a coating film formed by further coating a top coat.

According to the present invention, a coated steel sheet having an organic-inorganic composite coating film excellent in adhesion to a base and pressure-resistant oil properties can be obtained without impairing the corrosion resistance, solvent resistance, alkali resistance, and coating adhesion of the steel sheet.

Detailed Description

The present invention will be described more specifically below with reference to production examples of aqueous dispersion resins, examples, and comparative examples. In the following description, "%" of the concentration means "% by mass" as a whole.

Production example of resin particles (A-1)

An ethylene-methacrylic acid copolymer resin (methacrylic acid content: 18%), sodium hydroxide 5% with respect to the resin, and deionized water were charged into a reaction vessel, and stirred at 95 ℃ for 6 hours, thereby obtaining an aqueous resin dispersion having a solid content of 20%. Further, to this aqueous resin dispersion, pentaerythritol polyglycidyl ether in an amount of 0.4% and γ -glycidoxypropyltrimethoxysilane in an amount of 1.2% were added and reacted at 85 ℃ for 2 hours, whereby an aqueous dispersion of resin particles (A-1) having silanol groups and/or methoxysilyl groups was obtained, the solid content of which was 21%. The resin particles (A-1) had an average particle diameter of 72nm as measured by a particle diameter measuring instrument FPAR-1000 (manufactured by Otsuka electronics Co., Ltd.) according to the dynamic light scattering method.

Production example of resin particles (A-2)

An ethylene-methacrylic acid copolymer resin (methacrylic acid content: 20%), 3.7% sodium hydroxide, 6.3% 25% ammonia water (concentration: 25%) and deionized water were charged into a reaction vessel, and stirred at 95 ℃ for 6 hours to obtain a resin aqueous dispersion having a solid content of 20%. Further, to this aqueous dispersion resin solution, 0.6% of pentaerythritol polyglycidyl ether and 1.2% of γ -glycidoxypropyltriethoxysilane were added and reacted at 85 ℃ for 2 hours to obtain an aqueous dispersion of resin particles (A-2) having silanol groups and/or ethoxysilyl groups in a solid content of 21%. The average particle diameter of the resin particles (A-2) measured in the same manner as above was 84 nm.

Production example of resin particles (A-3)

An ethylene-methacrylic acid copolymer resin (methacrylic acid content: 20%), sodium hydroxide corresponding to 5.6% of the resin and deionized water were charged into a reaction vessel, and stirred at 95 ℃ for 6 hours, thereby obtaining an aqueous dispersion resin solution having a solid content of 20%. Further, 0.8% of glycerol polyglycidyl ether and 0.8% of gamma-glycidoxypropyltrimethoxysilane were added to the aqueous dispersion of the resin, and the mixture was reacted at 85 ℃ for 2 hours to obtain an aqueous dispersion of resin particles (A-3) having silanol groups and/or methoxysilyl groups in a solid content of 21%. The average particle diameter of the resin particles (A-3) measured in the same manner as above was 76 nm.

Production example of resin particles (A-4)

An ethylene-methacrylic acid copolymer resin (methacrylic acid content: 20%), sodium hydroxide in an amount corresponding to 5.6% of the resin and deionized water were charged into a reaction vessel, and stirred at 95 ℃ for 2 hours, thereby obtaining an aqueous dispersion resin solution having a solid content of 20%. Further, 0.8% of glycerol polyglycidyl ether and 0.8% of gamma-glycidoxypropyltrimethoxysilane were added to the aqueous dispersion of the resin, and the mixture was reacted at 85 ℃ for 2 hours to obtain an aqueous dispersion of resin particles (A-4) having silanol groups and/or methoxysilyl groups in a solid content of 21%. The average particle diameter of the resin particles (A-4) measured in the same manner as above was 128 nm.

Production example of resin particles (A-5)

An ethylene-methacrylic acid copolymer resin (methacrylic acid content: 20%), ammonia water (concentration: 25%) in an amount corresponding to 15.8% of the resin, and deionized water were charged into a reaction vessel, and stirred at 95 ℃ for 2 hours, thereby obtaining an aqueous dispersion resin solution having a solid content of 20%. Further, hydrogenated bisphenol A diglycidyl ether in an amount of 1.2% and gamma-glycidoxypropyltrimethoxysilane in an amount of 1.2% were added to the aqueous dispersion of the resin, and the mixture was reacted at 85 ℃ for 2 hours to obtain an aqueous dispersion of resin particles (A-5) having silanol groups and/or methoxysilyl groups in a solid content of 21%. The average particle diameter of the resin particles (A-5) measured in the same manner as above was 145 nm.

Production example of resin particles (A-6)

A2% aqueous solution of sodium lauryl sulfate was added to the reaction vessel, and ammonium persulfate was added to make 0.3% of the above aqueous solution while maintaining the temperature at 80 ℃. Immediately after the addition, an unsaturated monomer mixture composed of styrene, methyl methacrylate, 2-ethylhexyl acrylate, methacrylic acid and γ -methacryloxypropyltrimethoxysilane in a mass ratio of 30:34:30:2:4 was added dropwise, and the entire amount of the mixture was added equally over 2 hours. Stirring was continued for 1 hour at the above temperature, followed by cooling and adjustment of the pH to 8 with aqueous ammonia to obtain an aqueous dispersion of resin particles (A-6) having silanol groups and/or methoxysilyl groups with a solid content of 21%. The average particle diameter of the resin particles (A-6) measured in the same manner as above was 80 nm.

Example 1

Preparation of aqueous coating agent

An aqueous dispersion of silica having an average particle diameter of 15nm, dipropylbis (triethanolamine) titanium, diammonium hydrogen phosphate and thiourea were mixed in this order with the composition shown in table 1 in the aqueous dispersion of the resin particles (a-1) to prepare an aqueous composition having a solid content of 18%.

Production of test plate

An electrogalvanized steel sheet (zinc adhesion: 20 g/m) having a thickness of 0.8mm was coated with a 2% aqueous solution of an alkaline degreasing agent (SURF CLEANER-155, manufactured by Nippon paint Co., Ltd.) at 60 ℃²) Spray treatment was performed for 2 minutes to degrease, and after washing with water, hot air drying was performed. After cooling, the above aqueous coating agent was applied to the degreased treated sheet with a bar coater so that the amount of the dried coating film was 1g/m²And baking the steel plate by using a hot air drying furnace with the atmosphere temperature of 500 ℃ to ensure that the temperature of the steel plate reaches 180 ℃ to prepare the test plate.

Evaluation method

The corrosion resistance, adhesion to a substrate, solvent resistance, alkali resistance, pressure resistance, and adhesion to a coating were evaluated. The evaluation was performed by the following method, and the results are shown in table 1.

< Corrosion resistance >

The end face and the back face of the test panel were sealed with a seal tape, and 5% saline solution was sprayed at 35 ℃ to evaluate the area ratio of white rust generation after 120 hours according to the following evaluation criteria.

Very good: no white rust

O: the area generating white rust is less than 10 percent

And (delta): the area generating white rust is more than 10 percent and less than 30 percent

X: the area of white rust generation is more than 30 percent

< adhesion to substrate >

A test plate within 1 hour after coating was extruded by a cup-shaped extrusion machine for 8mm, and after processing, Cellotape (registered trademark) (manufactured by Michikon corporation) was attached to the extruded portion, and the state of the coating film after forced peeling was evaluated by the following evaluation criteria.

Very good: no peeling occurred

O: slight peeling

And (delta): partial peeling

X: complete stripping

< solvent resistance >

After the test plate was set on a friction tester, the test plate was immersed in absorbent cotton impregnated with ethanol at a pressure of 0.5Kgf/cm²The load of (1) was applied to 10 wipes (reciprocating), and the load was changed to 0.5Kgf/cm using absorbent cotton impregnated with kerosene²The film was wiped 50 times (back and forth), and the state of the film after wiping was evaluated according to the following evaluation criteria.

Very good: no trace of the wiping surface

O: slight trace on the surface to be cleaned

And (delta): white marks on the wiping surface

X: disappearance of coating film on wiping surface

< alkali resistance >

The test plate prepared immediately after the preparation of the aqueous coating agent and the test plate prepared after 10 days from the preparation were immersed in a 2% aqueous solution of an alkaline degreasing agent (SURF CLEANER-53, manufactured by Nippon paint Co., Ltd.) at 55 ℃ for 30 minutes while stirring, and the state of the coating after immersion was evaluated according to the following evaluation criteria.

Very good: no peeling occurred

O: slight peeling

And (delta): partial peeling

X: complete stripping

< pressure resistance type oiliness >

The test piece was immersed in a pressure oil (G6318SK, manufactured by japan hydraulic oil corporation) at room temperature for 24 hours, and the state of the film after immersion was evaluated according to the following evaluation criteria.

Very good: no discoloration

O: slightly change color

And (delta): mottle

X: peeling off

< coating adhesion >

The melamine alkyd paint (ス - パ - ラック 100, manufactured by Nippon paint Co., Ltd.) was applied to the surface of the test plate with a bar coater so that the dry film thickness was 20 μm, and the plate was baked at 120 ℃ for 25 minutes to prepare a coated plate. Then, the coated plate was immersed in boiling water for 30 minutes, left to stand for 24 hours, and then pressed 7mm by a cup-punch tester, and Cellotape (registered trademark) (manufactured by mikimura corporation) was attached to the pressed portion, and the state of the coating after forced peeling was evaluated by the following evaluation criteria.

Very good: no peeling

O: slight peeling

And (delta): partial peeling

X: complete stripping

Examples 2 to 9 and comparative examples 1 to 3

Test plates were produced and evaluated in the same manner as in example 1, except that the composition of the aqueous coating agent was changed as described in table 1. The results are shown in Table 1.

Examples 10 to 18 and comparative examples 4 to 6

The original plate used in the test was changed from the electrogalvanized steel plate to a hot-dip galvanized steel plate having a thickness of 0.8mm (zinc adhesion amount: 60 g/m)²) Except for this, test plates were similarly prepared and evaluated using the same aqueous coating solutions as in examples 1 to 9 and comparative examples 1 to 3 as described in table 2. The results are shown in Table 2.

From the results of the above examples, it is understood that the coated steel sheet of the present invention has excellent properties in various physical properties such as corrosion resistance, adhesion to a substrate, solvent resistance, alkali resistance, pressure resistance, oil resistance, and coating adhesion.

Industrial applicability

The coated steel sheet of the present invention can be suitably used for automobiles, home appliances, building material products, and the like.

Claims (5)

1. A coated steel sheet coated with a composite coating film, wherein the composite coating film is a composite coating film of an ethylene-unsaturated carboxylic acid copolymer resin particle A having a silanol group and/or an alkoxysilyl group and having an average particle diameter of 20 to 100nm, a silica particle B having an average particle diameter of 5 to 50nm, and an organotitanium compound C capable of reacting with the silanol group and/or the alkoxysilyl group of the resin particle A and an Si-OH group on the surface of the silica particle B; in the composite coating film, the silica particles B are5 to 100 mass% of the resin particles A, the content of titanium atoms being 0.05 to 3 mass% of the total amount of the coating film; the coating amount of the composite coating of the coated steel sheet is 0.5g/m²～3g/m²。

2. The coated steel sheet according to claim 1, wherein in the composite coating film, the silica particles B are 10 to 50 mass% of the resin particles A, and the content of titanium atoms is 0.2 to 2 mass% of the total amount of the coating film.

3. The coated steel sheet according to claim 1 or 2, wherein the resin particles a are made of an ethylene-methacrylic acid copolymer resin.

4. The coated steel sheet according to claim 1 or 2, wherein the composite coating is a coating in which the A to C and a compound D are combined, and the compound D is at least one compound selected from the group consisting of a phosphoric acid compound, a thiocarbonyl compound, niobium oxide, and a guanidine compound.

5. The coated steel sheet according to claim 1 or 2, wherein the organic titanium compound C is one or more selected from the group consisting of dipropoxybis (triethanolamine) titanium, dipropoxybis (diethanolamine) titanium, dibutoxybis (triethanolamine) titanium, dibutoxybis (diethanolamine) titanium, dipropoxybis (acetylacetonato) titanium, dibutoxybis (acetylacetonato) titanium, dihydroxybis (lactic acid) titanium monoammonium salt, dihydroxybis (lactic acid) titanium diammonium salt, propanedioxytitanium bis (ethylacetoacetate), oxotitanium bis (monoammonium oxalate) and isopropyltris (N-amidoethyl-aminoethyl) titanate.