JP7381466B2 - Water-based coating compositions and coated articles - Google Patents

Description

The present invention relates to an aqueous coating composition that has good film-forming properties at low temperatures and excellent corrosion resistance. The present invention also relates to a coated article having a cured coating film of the aqueous coating composition.

In recent years, from the viewpoint of global environmental protection and health and safety, there has been a shift from solvent-based paints to water-based paints, and water-based anticorrosive paints are also being developed in the field of anticorrosive paints for metal substrates and the like.

Emulsion paints are the mainstream among water-based paints, and emulsion paints contain much less solvent than solvent-based paints, but in order to improve film-forming properties, even though they are water-based, a considerable amount of solvent is used as a film-forming agent. The reality is that paints contain many solvents.

As a method for improving film-forming properties other than adding a film-forming agent, there is a method of softening the emulsion resin, but the hardness of the resulting coating film decreases and coating film performance such as corrosion resistance also decreases.

Patent Document 1 describes an aqueous emulsion (A) of a copolymer having a minimum film-forming temperature of 0°C or lower and a resin glass transition temperature of -20°C to 20°C, and a copolymer emulsion (A) with a glass transition temperature of 20°C or higher. A composition comprising a resin (B) solubilized in water with an alkali of Disclosed is a resin composition for a water-based paint characterized by having a molecular weight in the range of 40%. According to the resin composition for water-based paints, although it does not contain any volatile organic compounds (VOCs) or contains very small amounts of volatile organic compounds, it is comparable to conventional emulsion-based water-based paints containing film-forming agents. It is described that it has low-temperature film forming properties.

Japanese Patent Application Publication No. 11-343464

However, although the resin composition for water-based paints described in Patent Document 1 has improved low-temperature film-forming properties, its anticorrosion properties are insufficient, and improvements are desired.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an aqueous coating composition that has good film-forming properties at low temperatures and also has excellent anticorrosion properties.

As a result of intensive studies to achieve the above object, the present inventors have developed a water-based paint composition containing a specific amount of acrylic resin particles having a weight average molecular weight and acid value within a specific range relative to the base resin particles. It has been found that the above object can be achieved.

That is, the present invention includes the following aspects.

(1) A composition containing resin particles (A) and acrylic resin particles (B),
The resin particles (A) are different from the acrylic resin particles (B),
The acrylic resin particles (B) have a weight average molecular weight of 7,500 to 75,000 and an acid value of 10 to 90 mgKOH/g,
The total solid content of the resin particles (A) is 35 to 90% by weight with respect to the total solid content of the resin particles (A) and the acrylic resin particles (B), and the solid content of the acrylic resin particles (B) An aqueous coating composition having a total amount of 10 to 65% by weight.

(2) The aqueous coating composition according to (1) above, wherein the acrylic resin particles (B) have a glass transition temperature of 0° C. or higher.

(3) The aqueous coating composition according to (1) or (2) above, wherein the difference in SP value between the outermost layer of the resin particles (A) and the acrylic resin particles (B) is within 0.3.

(4) A coated article comprising a base material and a cured coating film of the aqueous coating composition according to any one of (1) to (3) above on the base material.

(5) The coated article according to (4) above, wherein the base material is a metal base material.

The aqueous coating composition of the present invention has the above-mentioned structure, and thus can form a coating film that has good film-forming properties at low temperatures and is also excellent in anticorrosion properties.

Hereinafter, the water-based coating composition of the present invention will be explained in more detail. In addition, in this specification, 'mass %' and 'weight %', and 'mass parts' and 'weight parts' are synonymous, respectively.

The aqueous coating composition according to the present invention is a composition containing resin particles (A) and acrylic resin particles (B), wherein the resin particles (A) are different from the acrylic resin particles (B), and the resin particles (A) are different from the acrylic resin particles (B). The acrylic resin particles (B) have a weight average molecular weight of 7,500 to 75,000 and an acid value of 10 to 90 mgKOH/g, and the above-mentioned The resin particles (A) have a total solid content of 35 to 90% by mass, and the acrylic resin particles (B) have a total solid content of 10 to 65% by mass.

<Resin particles (A)>
The resin particles (A) are a base resin in a water-based coating composition (hereinafter sometimes simply referred to as "composition"). Examples of the resin particles (A) include acrylic resin, acrylic/styrene resin, urethane resin, phenol resin, vinyl chloride resin, vinyl acetate resin, vinyl acetate/acrylic resin, ethylene/vinyl acetate resin, epoxy resin, and epoxy ester resin. , polyester resins, alkyd resins, acrylonitrile/butadiene resins, styrene/butadiene resins, polybutadiene, polyisoprene, silicone resins, fluororesins, etc., and modified products of these resins, such as carbonate-modified urethane resins, acrylic resin-modified resins, etc. Examples include resin particles made of at least one resin selected from epoxy resins, alkyd-modified epoxy resins, polybutadiene-modified epoxy resins, (poly)amine-modified epoxy resins, urethane-modified epoxy resins, and the like. These resin particles may be so-called rubber.

When the resin particles (A) are resin particles made of a plurality of resins, the resin particles may be prepared after blending the plurality of resins, or may be a blend of the plurality of resin particles. These resin particles are usually blended into the composition in the form of an emulsion.

In addition, in this embodiment, the resin corresponding to the acrylic resin particles (B) described later is excluded from the resin particles (A).

Among these resin particles (A), acrylic resin particles other than the acrylic resin particles (B) described below can be suitably used from the viewpoint of corrosion resistance and weather resistance of the coating film formed. Furthermore, from the viewpoint of corrosion resistance of the formed coating film and adhesion to metal substrates, epoxy resin particles can be suitably used. From the viewpoint of the toughness of the coating film, urethane resin particles can be preferably used.

The minimum film forming temperature of the resin particles (A) is preferably 10°C or higher, more preferably 15°C or higher, even more preferably 20°C or higher. By setting the minimum film-forming temperature to 10° C. or higher, it is possible to suppress a decrease in the hardness of the resulting coating film.

In this specification, the minimum film forming temperature is a value obtained by measurement according to JIS K 6828-2 (2003). Specifically, the minimum film-forming temperature is defined as the value measured according to JIS K 6828-2 (2003) in a state where 20% by mass of ethylene glycol monobutyl ether is contained based on the total solid content of the resin particles (A).

The average particle diameter of the resin particles (A) is preferably 50 nm or more, more preferably 60 nm or more, and even more preferably 70 nm or more. Moreover, the average particle diameter is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less.

By setting the average particle diameter to 50 nm or more, it is possible to prevent the viscosity from becoming too high and maintain good handling. Furthermore, by setting the average particle diameter to 500 nm or less, the dispersion stability becomes good.

The average particle diameter can be measured using a common measurement method such as laser light scattering.

The average particle diameter of the resin particles (A) in this specification is a value measured at 20°C after diluting with deionized water using a laser light scattering type submicron particle size distribution measuring device. . As a submicron particle size distribution measuring device, for example, "COULTER N4 type" (trade name, manufactured by Beckman Coulter) can be used.

The acrylic resin particles as the resin particles (A) preferably have anionic, nonionic, or cationic hydrophilic groups. The presence of the hydrophilic group allows the acrylic resin particles to be well dispersed in an aqueous medium.

Examples of the anionic hydrophilic group include acidic groups. Examples of the acidic group include a carboxyl group, a sulfonic acid group, a phosphoric acid group, and a phenolic hydroxyl group. These acidic groups may be neutralized with a base such as an amine.

Examples of the nonionic hydrophilic group include a polyethylene glycol group, a polyglycerin group, and a hydrophilic sugar chain group.

Examples of the cationic hydrophilic group include basic groups such as an amino group, an ammonium group, a pyridinium group, a sulfonium group, and a phosphonium group.

The above-mentioned acrylic resin particles can be produced by a known method such as a method in which a polymerizable unsaturated monomer is polymerized by a solution polymerization method in an organic solvent and then dispersed in water to form resin particles, or an emulsion polymerization method in water. It can be obtained by polymerization according to the method described in the following.

It is also possible to employ a so-called core/shell polymerization method in which a mixture of polymerizable unsaturated monomers is fed in multiple stages, or a power feed method in which the composition of the polymerizable unsaturated monomers fed during polymerization is successively changed. Furthermore, two or more types of acrylic resin particles produced by the above method can also be used in combination.

Among these methods, those obtained by emulsion polymerization can be preferably used.

Examples of the polymerizable unsaturated monomer include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate. , tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate , stearyl (meth)acrylate, "isostearyl acrylate" (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate ) Alkyl or cycloalkyl (meth)acrylate such as acrylate; Polymerizable unsaturated monomers having an isobornyl group such as isobornyl (meth)acrylate; Polymerizable unsaturated monomers having an adamantyl group such as adamantyl (meth)acrylate; Styrene, α - Vinyl aromatic compounds such as methylstyrene and vinyltoluene; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyl Polymerizable unsaturated monomers having alkoxysilyl groups such as oxypropyltriethoxysilane; perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; fluorine such as fluoroolefins Polymerizable unsaturated monomers having a photopolymerizable functional group such as a maleimide group; Vinyl compounds such as N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, and vinyl acetate; (Meth)acrylic acid such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and 2 with a carbon number of 2 to 8 Monoesterified product with alcohol, ε-caprolactone modified product of monoesterified product of the (meth)acrylic acid and dihydric alcohol having 2 to 8 carbon atoms, N-hydroxymethyl (meth)acrylamide, allyl alcohol, molecular terminal Hydroxyl group-containing polymerizable unsaturated monomers such as (meth)acrylate having a polyoxyethylene chain where (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, addition of glycidyl (meth)acrylate with an amine compound Nitrogen-containing polymerizable unsaturated monomers such as products; polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule such as allyl (meth)acrylate and 1,6-hexanediol di(meth)acrylate; Glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate , epoxy group-containing polymerizable unsaturated monomers such as allyl glycidyl ether; (meth)acrylates having a polyoxyethylene chain with an alkoxy group at the molecular end; 2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, styrene sulfone Polymerizable unsaturated monomers having a sulfonic acid group such as acid sodium salt, sulfoethyl methacrylate and its sodium salt, ammonium salt; 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxypropyl acid phosphate , 2-methacryloyloxypropyl acid phosphate, and other polymerizable unsaturated monomers having a phosphoric acid group; 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2-hydroxy-4-(3-acryloyl oxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-acryloyloxy-2-hydroxypropoxy) ) Polymerizable unsaturated monomers having ultraviolet absorbing functional groups such as benzophenone and 2-(2'-hydroxy-5'-methacryloyloxyethylphenyl)-2H-benzotriazole; 4-(meth)acryloyloxy-1,2 , 2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloylamino-2,2,6,6 -Tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloylamino -2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1 - UV-stable polymerizable unsaturated monomers such as crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine; acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formylstyrene, Examples include polymerizable unsaturated monomer compounds having a carbonyl group such as vinyl alkyl ketones having 4 to 7 carbon atoms (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), each of which may be used alone. It can be used alone or in combination of two or more.

As used herein, "(meth)acrylate" means acrylate or methacrylate. "(Meth)acrylic acid" means acrylic acid or methacrylic acid. Moreover, "(meth)acryloyl" means acryloyl or methacryloyl. Moreover, "(meth)acrylamide" means acrylamide or methacrylamide.

As the acrylic resin, commercially available products can be used. Commercial products of the acrylic resin include, for example, the Polysol (registered trademark) series (manufactured by Showa Denko), the Acryset (registered trademark) series, the U-double (registered trademark) series (all manufactured by Nippon Shokubai Co., Ltd.), and the Boncourt series. , Watersol series (manufactured by DIC), Joncryl (registered trademark) series (manufactured by BASF), Polytron series, Polydulex series (manufactured by Asahi Kasei Chemicals), Aquabrid UM-7760, 4635, Aquabrid UM-7760, 4790 (all manufactured by Daicel Chemical Industries, Ltd.).

When the resin particles (A) are acrylic resin particles, the weight average molecular weight is preferably 100,000 or more, more preferably 150,000 or more, and even more preferably 200,000 or more from the viewpoint of corrosion resistance and hardness. Moreover, the weight average molecular weight is preferably 500,000 or less, more preferably 400,000 or less, and even more preferably 350,000 or less.

When the weight average molecular weight is 100,000 or more, corrosion resistance and hardness are good, and when it is 500,000 or less, good film forming properties are obtained and corrosion resistance is also good.

In this specification, the weight average molecular weight is a value obtained by converting the retention time measured using a gel permeation chromatograph into the molecular weight of polystyrene using the retention time of a standard polystyrene with a known molecular weight measured under the same conditions. .

Specifically, for example, "HLC-8120GPC" (trade name, manufactured by Tosoh Corporation) is used as a gel permeation chromatography device, and one column of "TSKgel G4000HXL" and two columns of "TSKgel G3000HXL" are used. , and one "TSKgel G2000HXL" (trade name, both manufactured by Tosoh Corporation), a differential refractometer was used as a detector, mobile phase: tetrahydrofuran, measurement temperature: 40 ° C. The weight average molecular weight can be determined by measuring at a flow rate of 1 mL/min.

Examples of the epoxy resin include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol AD type epoxy resin; epoxy ester resins obtained by modifying the above bisphenol type epoxy resins with dibasic acids, etc.; Cyclic epoxy resins; polyglycol type epoxy resins; epoxy group-containing acrylic resins, etc. can be used. Among these, bisphenol type epoxy resins, particularly bisphenol A type epoxy resins, can be preferably used from the viewpoint of corrosion resistance of the formed coating film, adhesion to metal substrates, etc.

The epoxy resin particles as the resin particles (A) preferably have an anionic, nonionic, or cationic hydrophilic group. Due to the presence of the hydrophilic group, the epoxy resin particles can be well dispersed in an aqueous medium.

Examples of the anionic hydrophilic group include acidic groups. Examples of the acidic group include a carboxyl group, a sulfonic acid group, a phosphoric acid group, and a phenolic hydroxyl group. These acidic groups may be neutralized with a base such as an amine.

Examples of the nonionic hydrophilic group include a polyethylene glycol group, a polyglycerin group, and a hydrophilic sugar chain group.

Examples of the cationic hydrophilic group include basic groups such as an amino group, an ammonium group, a pyridinium group, a sulfonium group, and a phosphonium group.
Epoxy resin particles can also be obtained by adding an emulsifier to a hydrophobic epoxy resin and dispersing and emulsifying the mixture in water.

Commercially available products can be used as the epoxy resin. Examples of commercially available epoxy resins include Watersol series (trade name, manufactured by DIC Corporation), Modepics series (trade name, manufactured by Arakawa Chemical Co., Ltd.), Adekal Resin (trade name, manufactured by ADEKA Corporation), etc. can.

The urethane resin particles as the resin particles (A) are generally made of a polyurethane consisting of a polyol such as a polyester polyol or a polyether polyol and a diisocyanate, if necessary, and a polyurethane having two or more active hydrogens such as a diol or diamine. It is obtained by elongating the chain in the presence of a chain extender, which is a molecular weight compound, and stably dispersing it in water, and a wide variety of known products can be used.

Commercial products of the above urethane resin include, for example, Hydran HW-330, Hydran HW-340, and Hydran HW-350 (all manufactured by Dainippon Ink & Chemicals), Superflex 100, Hydran 110, Hydran 150, and Hydran F-8438D. , ADEKA 420 (all manufactured by Daiichi Kogyo Seiyaku), ADEKA BONTIDER HUX-232, ADEKA 260, 320, and ADEKA 350 (all manufactured by ADEKA).

<Acrylic resin particles (B)>
The acrylic resin particles (B) are acrylic resin particles having a weight average molecular weight of 7,500 to 75,000 and an acid value of 10 to 90 mgKOH/g. The acrylic resin particles (B) are a resin that acts as a film-forming aid in the aqueous coating composition. Specifically, in the drying process after coating, the acrylic resin particles (B) diffuse with phase transition, filling the voids between the resin particles (A) that are the base resin. In this way, by suppressing the formation of voids in the coating film during the drying process, even if the composition does not contain any or only a small amount of a film-forming agent such as a solvent, it can be used at low temperatures. Film-forming properties can be improved.

The acrylic resin particles (B) can be obtained by using the same polymerization method as for the acrylic resin particles described in detail in the resin particles (A) and changing the polymerization conditions as appropriate.

From the viewpoint of molecular weight adjustment, the acrylic resin particles (B) are obtained by polymerizing the above-mentioned polymerizable unsaturated monomer in an organic solvent using a solution polymerization method to obtain a copolymer, and then dispersing it in water to form resin particles. The manufactured product can be suitably used.

The weight average molecular weight of the acrylic resin particles (B) is 7,500 to 75,000, preferably 9,000 or more, more preferably 10,000 or more, and preferably 60,000 or less, more preferably 40,000 or less.

By setting the weight average molecular weight to 7,500 or more, good corrosion resistance and hardness can be achieved. Furthermore, by setting the weight average molecular weight to 75,000 or less, sufficient diffusivity can be obtained and good film-forming properties can be obtained.

The acid value of the acrylic resin particles (B) is 10 to 90 mgKOH/g, preferably 20 mgKOH/g or more, more preferably 30 mgKOH/g or more, and preferably 80 mgKOH/g or less, more preferably 70 mgKOH/g or less. It is.

By setting the acid value to 10 mgKOH/g or more, the dispersion stability becomes good. Moreover, by setting the acid value to 90 mgKOH/g or less, water resistance becomes good and sufficient corrosion resistance is obtained.

In this specification, the acid value (mgKOH/g) is expressed in mg of potassium hydroxide when the amount of acid groups contained in 1 g of sample (1 g of solid content in the case of resin) is converted to potassium hydroxide. It is. The molecular weight of potassium hydroxide is 56.1.

The acid value is measured in accordance with JIS K-5601-2-1 (1999). The sample is dissolved in a mixed solvent of toluene/ethanol = 2/1 (volume ratio), titrated with a potassium hydroxide solution using phenolphthalein as an indicator, and calculated using the following formula.

Acid value (mgKOH/g) = 56.1 x V x C/m
V: Titration amount (ml), C: Concentration of titrant (mol/l), m: Solid weight of sample (g)

The glass transition temperature (Tg) of the acrylic resin particles (B) is preferably 0°C or higher, more preferably 10°C or higher, and even more preferably 20°C or higher.
By setting the glass transition temperature (Tg) to 0° C. or higher, it is possible to prevent a decrease in the hardness of the resulting coating film.

In this specification, when the resin is a copolymer consisting of two or more types of monomers, the glass transition temperature (Tg, °C) of the copolymer can be calculated by the following formula.

1/Tg(K)=(W1/T1)+(W2/T2)+...(Wn/Tn)
Tg (℃) = Tg (K) - 273
In each formula, n represents the number of types of monomers used (natural number), W1 to Wn represent the weight percent of each of the n types of monomers used in the copolymerization, and T1 to Tn represent the number of types of the n types of monomers used in the copolymerization. Represents the Tg (K) of each homopolymer. Note that for T1 to Tn, the values described in Polymer Hand Book (Second Edition, edited by J. Brandup and E.H. Immergut) III-139 to 179 can be used.
Furthermore, when the Tg of the monomer homopolymer is not clear, the glass transition temperature (° C.) can also be determined as a static glass transition temperature by actual measurement. In this case, for example, using a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instruments), take the sample into a measuring cup, vacuum suction to completely remove the solvent, and then increase the temperature at 3°C/min. The change in heat value is measured at a temperature rate in the range of -20°C to +200°C, and the point of change of the first baseline on the low temperature side is defined as the static glass transition temperature.

The minimum film forming temperature of the acrylic resin particles (B) is preferably less than 10°C, more preferably 7.5°C or less, and even more preferably 5°C or less. By setting the minimum film-forming temperature to less than 10° C., it is possible to prevent a decrease in film-forming properties and achieve good corrosion resistance.

The SP value (solubility parameter value) of the acrylic resin particles (B) is preferably 9.3 or less, more preferably 9.0 or less. By setting the SP value to 9.3 or less, water resistance and corrosion resistance will be excellent.

Further, the SP value difference between the outermost layer (outermost surface layer portion) of the resin particles (A) and the acrylic resin particles (B) is preferably within 0.3, more preferably within 0.2, and within 0.1. is even more preferable. By setting the SP value difference within 0.3, the compatibility is good, the diffusibility is also good, and excellent corrosion resistance is achieved.

In this specification, the solubility parameter value (SP value) is defined in Polymer Engineering and Science, 14, No. 2, p. 147 (1974), which is calculated using the Fedors formula below.

SP=√{Σ(Δe1)/Σ(Δv1)}
(In the formula, Δe1 indicates the cohesive energy per unit functional group, and Δv1 indicates the molecular volume per unit functional group.) In addition, the SP value of a copolymer or a blend that is a mixture of two or more resins is , the SP value of each component of the monomer unit or blend was multiplied by the mass fraction, and the value was the sum of the products.

Moreover, the average particle diameter of the acrylic resin particles (B) is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less.

By setting the average particle diameter to 500 nm or less, good dispersion stability and good diffusivity are achieved, so that excellent corrosion protection is achieved.

In the aqueous coating composition, the total solid content of the resin particles (A) is 35 to 90% by mass with respect to the total solid content of the resin particles (A) and the acrylic resin particles (B), and the acrylic resin particles (B) The total solid content of is 10 to 65% by mass. The total solid content is preferably 40% by mass or more of resin particles (A) and 60% by mass or less of acrylic resin particles (B), and 45% by mass or more of resin particles (A) and 55% by mass of acrylic resin particles (B). % or less, more preferably resin particles (A) are 80% by mass or less, acrylic resin particles (B) are 20% by mass or more, resin particles (A) are 70% by mass or less, acrylic resin particles (B) is more preferably 30% by mass or more.

The total solid content of resin particles (A) is 90% by mass or less, and the total solid content of acrylic resin particles (B) is 10% by mass or more, based on the total solid content of resin particles (A) and acrylic resin particles (B). By doing so, the resulting coating film has good film forming properties. Furthermore, by setting the total solid content of the resin particles (A) to 35% by mass or more and the total solid content of the acrylic resin particles (B) to 65% by mass or less, the resulting coating film will have good corrosion resistance. .

The water-based coating composition is a mixture of resin particles (A) and acrylic resin particles (B), but there are no restrictions on the method of mixing them. That is, either a method of adding acrylic resin particles (B) to resin particles (A) or a method of adding resin particles (A) to acrylic resin particles (B) can be adopted.

Alternatively, a method is adopted in which acrylic resin particles (B) are used as a protective colloid and copolymerized to synthesize an aqueous emulsion, resulting in a composition in which resin particles (A) and acrylic resin particles (B) coexist. You can also do that.

From the viewpoint of storage stability of the paint, the pH of the aqueous paint composition is preferably 5.0 or higher, more preferably 6.0 or higher, and preferably 10.0 or lower, more preferably 9.0 or lower.

In addition, the aqueous coating composition may contain crosslinking agents, curing catalysts, pigments such as coloring pigments, fillers, aggregates, dispersants, wetting agents, thickeners, rheology control agents, surface conditioners, erasers, etc., as necessary. Foaming agents, preservatives, antifungal agents, pH adjusters, rust preventives, antisettling agents, antifreeze agents, antiskinning agents, ultraviolet absorbers, antioxidants, organic solvents, and the like can also be included.

It is preferable that the aqueous coating composition is coated and cured on various substrates, preferably metal substrates, which have been subjected to surface treatment as necessary, to form a cured coating film. The coating can be directly applied once or twice or more to form a coating film by a conventionally known method such as roller coating, spray coating, brush coating, curtain coating, shower coating, or dip coating.

When the base material is a metal base material, by coating and curing the aqueous coating composition according to the present embodiment on the metal base material to form a cured coating film, film forming properties at low temperatures are good, A coated article with excellent corrosion resistance can also be obtained.

The coating film of the aqueous coating composition is preferably cured at room temperature from the viewpoint of energy saving and the like. Note that, from the viewpoint of improving production efficiency, etc., forced drying or heat curing can also be performed.
In addition, the thickness of the cured coating film obtained by applying the water-based coating composition is preferably 10 μm or more, more preferably 20 μm or more, from the viewpoints of corrosion resistance, water resistance, hardness, etc. of the cured coating film formed. The thickness is more preferably 25 μm or more, more preferably 200 μm or less, more preferably 100 μm or less, and even more preferably 60 μm or less.

Hereinafter, the present invention will be explained in more detail with reference to Production Examples, Examples, and Comparative Examples. However, the present invention is not limited to these. In each example, "parts" and "%" are based on mass unless otherwise specified. Further, the film thickness of the coating film is based on the cured coating film. Note that a blank column in the table indicates that the component is not included.

<Production of resin particles (A)>
Manufacturing example 1
In a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, deionized water and Newcol (registered trademark) 707SF (trade name, manufactured by Nippon Nyukazai Co., Ltd., an anionic surfactant, Solid content: 30% by mass) was added, and after sufficient nitrogen substitution, the temperature was raised. The internal temperature was maintained at 82 ° C. while stirring at about 100 rpm, and the (A1) component shown in Table 1 was emulsified using a homomixer (hereinafter referred to as (A1) component emulsion. (A2) component, (B1) ) component and (B2) component are written in the same way.), and initiator 1 aqueous solution (in Table 1, VA-057 is the product name, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., 2-2'-azobis[N- (2-carboxyethyl)-2-methylpropionediamine]tetrahydrate) was added dropwise over 3 hours to polymerize. After the dropwise addition was completed, the reaction was carried out at 82° C. for 0.5 hours, and an aqueous solution of initiator 2 was added dropwise over a period of 0.5 hours. After completion of the dropwise addition, the mixture was reacted at 82°C for 1.5 hours, and then cooled to 25°C. Finally, the neutralizing agent shown in Table 1 was added, and resin particles (A-1) with a solid content concentration of 40.0% by mass (outermost layer SP value 9.01, weight average molecular weight approximately 160,000, minimum film forming temperature An emulsion with a temperature of 15°C was obtained.

The emulsion had a viscosity (measured with a B-type viscometer, 60 rpm, 20° C.) of 420 mPa·s, a pH of 9.2 (measured with a pH meter), and an average particle diameter of 130 nm.

Manufacturing example 2
Into a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, deionized water and Newcol 707SF were charged in amounts shown in Table 1, and after sufficient nitrogen substitution, the temperature was raised. The internal temperature was maintained at 82° C. while stirring at about 100 rpm, and dropwise addition of an emulsified component (A1) shown in Table 1 using a homomixer and an aqueous solution of initiator 1 was started to polymerize. The dropping rate was approximately 146.0 parts/hour for the component (A1) emulsion and approximately 6.6 parts/hour for the aqueous initiator 1 solution. At the same time as the addition of the component emulsion (A1) was completed, the component emulsion (B2) shown in Table 1 was started to be added dropwise at a rate of about 146.0 parts/hour. After the addition was completed, the reaction was carried out at 82° C. for 0.5 hour, and an aqueous solution of initiator 2 was added dropwise at a rate of about 3.3 parts/hour. After completion of the dropwise addition, the mixture was reacted at 82°C for 1.5 hours, and then cooled to 25°C. Finally, the neutralizing agent shown in Table 1 was added, and resin particles (A-2) with a solid content concentration of 40.0% by mass (outermost layer SP value 9.03, weight average molecular weight approximately 200,000, minimum film forming temperature 20°C) was obtained.

The emulsion had a viscosity (measured with a B-type viscometer, 60 rpm, 20° C.) of 400 mPa·s, a pH of 9.2 (measured with a pH meter), and an average particle diameter of 120 nm.

Manufacturing example 3
Into a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, deionized water and Newcol 707SF were charged in amounts shown in Table 1, and after sufficient nitrogen substitution, the temperature was raised. The internal temperature was maintained at 82° C. while stirring at about 100 rpm, and dropwise addition of an emulsified component (A1) shown in Table 1 using a homomixer and an aqueous solution of initiator 1 was started to polymerize. The dropping rate was approximately 146.0 parts/hour for the component (A1) emulsion and approximately 6.6 parts/hour for the aqueous initiator 1 solution. At the same time as the dropping of the component emulsion (A1) was completed, dropping of the component emulsion (A2) shown in Table 1 was started. At the same time, the (B1) component emulsion shown in Table 1 was added dropwise to the (A2) component emulsion. The dropping rate of the component emulsion (B1) was set at a rate at which the dropping of the component emulsion (A2) was completed at the same time as the dropping of the component emulsion (A2), that is, in this production example, about 73.0 parts/hour. Thereafter, component (B2) emulsion was added dropwise at a rate of about 146.0 parts/hour. After the addition was completed, the reaction was carried out at 82° C. for 0.5 hour, and an aqueous solution of initiator 2 was added dropwise at a rate of about 3.3 parts/hour. After completion of the dropwise addition, the mixture was reacted at 82°C for 1.5 hours, and then cooled to 25°C. Finally, the neutralizing agent shown in Table 1 was added, and resin particles (A-3) with a solid content concentration of 40.0% by mass (outermost layer SP value 9.03, weight average molecular weight approximately 220,000, minimum film forming temperature An emulsion with a temperature of 18°C was obtained.

The emulsion had a viscosity (measured with a B-type viscometer, 60 rpm, 20° C.) of 710 mPa·s, a pH of 9.2 (measured with a pH meter), and an average particle diameter of 100 nm.

The minimum film forming temperature of resin particles (A-1) to resin particles (A-3) is the value measured by adding 20% by mass of ethylene glycol monobutyl ether to the total solid content of each resin particle. .

Production example 4
20 parts of ethylene glycol monobutyl ether and 14 parts of propylene glycol monomethyl ether were charged into a reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen inlet tube, and a dropping device, and after raising the temperature to 115°C, 10 parts of styrene, 20 parts of methyl methacrylate, 30 parts of n-butyl acrylate, 30 parts of i-butyl methacrylate, 1 part of acrylic acid, 9 parts of methacrylic acid, 15 parts of propylene glycol monomethyl ether, and Perbutyl O (registered trademark, manufactured by NOF Corporation, polymerization initiator) , solid content 100%) was added dropwise over 4 hours, and the mixture was aged for 1 hour after the addition was completed. Thereafter, a mixture of 5 parts of propylene glycol monomethyl ether and 8 parts of perbutyl O was added dropwise over 1 hour, and the mixture was aged for 1 hour after the addition was completed. Then, by cooling to room temperature, a solution of acrylic copolymer 1 with a solid content of 65% by mass was obtained. The obtained acrylic copolymer 1 had an SP value of 9.12, an acid value of 66 mgKOH/g, and a weight average molecular weight of about 2,200.

In a four-necked flask equipped with a reflux tube, a thermometer, and a stirrer, 65 parts of the solution of the above acrylic copolymer 1 (solid content 42 parts), Epicoat (registered trademark) 1009 (trade name, manufactured by Japan Epoxy Resin Co., Ltd., epoxy After adding 58 parts of resin (solid content 100%, epoxy equivalent: approx. 3500, weight average molecular weight approx. 3900), 11.6 parts of diethylene glycol monobutyl ether, and 28.4 parts of propylene glycol monomethyl ether, and heating to 100°C to dissolve. , the reaction was carried out for about 2 hours. After that, an equivalent amount of aqueous ammonia (25%) was neutralized, and then deionized water was added with stirring. ℃) A dispersion was obtained.

The obtained resin particles (A-4) had an average particle diameter of 200 nm and an acid value of 44 mgKOH/g.

<Manufacture of acrylic resin particles (B)>
Manufacturing example 5
20 parts of ethylene glycol monobutyl ether and 14 parts of propylene glycol monomethyl ether were charged into a reaction vessel equipped with a thermometer, a thermostat, a stirring device, a reflux condenser, a nitrogen introduction tube, and a dropping device, and after raising the temperature to 115°C, 20 parts of styrene, A mixture of 20 parts of n-butyl acrylate, 19 parts of methyl methacrylate, 35 parts of i-butyl methacrylate, 5 parts of acrylic acid, 1 part of methacrylic acid, 15 parts of propylene glycol monomethyl ether, and 7.0 parts of perbutyl O as an initiator was heated for 4 hours. The solution was then added dropwise, and the mixture was aged for 1 hour after the completion of the addition. Thereafter, a mixture of 5 parts of propylene glycol monomethyl ether and 1.0 part of perbutyl O was added dropwise over 1 hour, and the mixture was aged for 1 hour after the addition was completed. Aqueous ammonia (solid content: 25%) was added to the obtained acrylic resin to neutralize it by equivalent amount, and then deionized water was added while stirring to disperse the resin. Thereafter, the solvent propylene glycol monomethyl ether was removed under reduced pressure, and deionized water was added again to obtain an acrylic resin particle (B-1) dispersion with a solid content of 30% by mass. The obtained acrylic resin particles (B-1) have a weight average molecular weight of 9000, an acid value of 45.4 mgKOH/g, a glass transition temperature of 41.7°C, an SP value of 8.98, an average particle diameter of 180 nm, and a minimum The film forming temperature was 0°C.

Production examples 6 to 15
In Production Example 5, each acrylic resin particle (B-2) to (B-11) was obtained in the same manner as Production Example 5, except that the composition was as shown in Table 2. Perbutyl O was used as the initiator in all cases as in Production Example 5 (the distribution ratio was the same as in Production Example 5). Table 2 also shows the weight average molecular weight, acid value, glass transition temperature, SP value, average particle diameter, and minimum film forming temperature (° C.) of each of the obtained acrylic resin particles. Note that acrylic resin particles (B-8) to (B-11) are used as comparative examples.

<Manufacture of water-based paint composition>
Example 1
DISPERBYK (registered trademark) -190 (trade name, manufactured by BYK, pigment dispersant, solid content 40%) 3 parts (solid content 1.2 parts), BYK (registered trademark) -024 (trade name, manufactured by BYK, Antifoaming agent, solid content 100%) 0.4 parts, JR-603 (trade name, manufactured by Teika Corporation, titanium oxide, solid content 100%) 35 parts, Super SS (trade name, manufactured by Maruo Calcium Co., Ltd., calcium carbonate, Pigment paste (P1) (solid content 64.2%) was mixed with 15 parts (solid content 100%), 25 parts deionized water, and 2 parts dipropylene glycol monomethyl ether, and after adding glass beads, dispersed in a paint shaker for 60 minutes. ) was obtained.

After removing the glass beads, 175 parts (solid content 70 parts) of the emulsion of the resin particles (A-1) obtained in Production Example 1 were added to 80 parts (solid content 51 parts) of the obtained pigment paste (P1), Production Example 100 parts (solid content 30 parts) of the acrylic resin particle (B-1) dispersion obtained in step 5, 0.5 part BYK-348 (trade name, manufactured by BYK, surface conditioner, solid content 100%) and SN By mixing and stirring 2.5 parts (solid content 0.5 part) of Thickener 660T (trade name, manufactured by San Nopco Co., Ltd., thickener, solid content 20%), an aqueous solution with a pH of 8.2 and a paint solid content of 43% by mass was prepared. Paint composition no. I got 1.

Examples 2 to 11, Reference Example 12 and Comparative Examples 1 to 7
In Example 1, each aqueous coating composition No. 2~No. I got 19.

The SP value difference (SP value difference between the outermost layer of the resin particles (A) and the acrylic resin particles (B)) is also shown in Tables 3 and 4.

Preparation of test plates Each water-based coating composition obtained in Examples 1 to 11, Reference Example 12, and Comparative Examples 1 to 7 above was placed on a 70 mm x 150 mm x 0.8 mm cold rolled steel plate that had been polished and degreased. No. 1~No. No. 19 was coated using air spray so that the cured film thickness was 40 μm. Next, each test plate was left to stand at 23° C. and 65% RH for 7 days to form a cured coating film on the steel plate.

Evaluation of test plates The following tests were conducted on each of the obtained test plates. The evaluation results are also shown in Tables 3 and 4.

Corrosion resistance: For each test plate, cross-cut scratches were made in the coating film with a knife so as to reach the base material, and the test was conducted for 120 hours in accordance with JIS K 5600-7-1 (1999) "Resistance to neutral salt spray". A salt spray resistance test was conducted. Evaluation was made according to the following criteria based on the width of rust and blisters from knife scratches. The smaller the maximum width of rust and blisters, the better the corrosion resistance, and if the evaluation is A to C, the corrosion resistance is good.

A: The maximum width of rust and blisters is less than 1mm from the cut part (one side)
B: The maximum width of rust and blisters is 1 mm or more and less than 2 mm from the cut part (one side)
C: The maximum width of rust and blisters is 2 mm or more and less than 3 mm from the cut part (one side)
D: The maximum width of rust and blisters is 3 mm or more and less than 5 mm from the cut part (one side)
E: The maximum width of rust and blisters is 5mm or more from the cut part (one side)

Water resistance: Each test plate was immersed in deionized water at 23°C for 48 hours, and the coated surface was evaluated according to the following criteria. If the evaluation is ◎ or ○, the water resistance is good.
◎: Good and no problem.
○: Some glossiness is seen, but it is at a practical level.
△: Either blisters or dull spots are observed.
×: Either blistering or dullness is significantly observed.

Gloss: For each test plate, the specular gloss (60°) of the painted surface was measured in accordance with JIS K 5600-4-7 (1999) "Specular gloss". If the specular gloss (60°) of the painted surface is 70 or more, the gloss is good.

Pencil hardness: For each test plate, the pencil hardness of the painted surface was measured in accordance with JIS K 5600-5-4 (1999) "Scratch hardness (pencil method)". The pencil hardness is F, HB, B, and 2B in descending order of hardness, and if the hardness is B or higher, the hardness is good.

Although the invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application (Japanese Patent Application No. 2018-141568) filed on July 27, 2018, the contents of which are incorporated herein by reference.

According to the present invention, it is possible to provide an aqueous coating composition that has good film-forming properties at low temperatures and also has excellent coating film performance such as corrosion resistance.

Claims (4)

A composition containing resin particles (A) and acrylic resin particles (B),
The resin particles (A) are different from the acrylic resin particles (B),
The acrylic resin particles (B) have a weight average molecular weight of 7,500 to 75,000 and an acid value of 10 to 90 mgKOH/g,
The total solid content of the resin particles (A) is 35 to 90% by weight with respect to the total solid content of the resin particles (A) and the acrylic resin particles (B), and the solid content of the acrylic resin particles (B) The total amount is 10 to 65% by weight,
An aqueous coating composition in which the SP value difference between the outermost layer of the resin particles (A) and the acrylic resin particles (B) is within 0.3 . The aqueous coating composition according to claim 1, wherein the acrylic resin particles (B) have a glass transition temperature of 0°C or higher. A coated article comprising a base material and a cured coating film of the aqueous coating composition according to claim 1 or 2 on the base material. The coated article according to claim 3 , wherein the base material is a metal base material.