JP2020002327A - Water-based coating composition - Google Patents

Abstract

To provide a water-based coating composition capable of both of air dry coating and galling coating, excellent in film forming property, blocking resistance and rust resistance, and capable of forming a coated film containing no environmental load material (lead, chromium or the like).SOLUTION: There is provided a water-based coating composition containing an urethane resin particle (A) having weight average molecular weight of 100,000 to 5,000,000, and glass transition temperature of 30 to 100°C, and an acrylic resin particle (B) having glass transition temperature of -20 to 30°C, with as a solid component amount, the urethane resin particle (A) of 40 to 80 mass% and the acrylic resin particle (B) of 20 to 60 mass% based on solid component total amount of the urethane resin particle (A) and the acrylic resin particle (B).SELECTED DRAWING: None

Description

  The present invention relates to an aqueous coating composition that can be applied to both dry coating and baking coating, and is particularly excellent in the productivity of rust-resistant steel on a production line.

  Conventionally, steel materials such as lightweight steel used for building materials have been coated with rust-preventive paints to impart rust-preventive properties, and solvent-based paints have been used. The paint has been painted.

  In the production line for steel materials such as lightweight shaped steel, the molding oil is applied, the molded steel material is degreased, the steel material is heated to a desired temperature by preheating (about 80 to 110 ° C), and the rust preventive paint is applied airless. Is generally performed.

  Since the above process is performed in a short time (about 5 minutes from steel molding to binding of coated steel), the rust preventive paint must be quick-drying and high-hardness, and the painted steel must be bound within a few minutes. Since they are stacked and conveyed by a crane, they are required to be paints that are also excellent in blocking resistance (the coating films do not adhere to each other (do not stick)).

  In addition, the Ministry of Land, Infrastructure, Transport and Tourism's “Public Building Construction Standard Specifications” stipulates the use of paint that satisfies JIS K5674 (lead / chrome-free rust preventive paint) as a rust preventive paint for steel products and steel structures. Public buildings are also required to be paints that have obtained the JIS certification.

  Patent Literature 1 discloses 10 to 80 parts by weight of a water-based acrylic-modified alkyd resin (A) as a coating composition having excellent oil surface adhesion, high-temperature finish, roll-touch coating releasability, blocking properties, and rust prevention. An aqueous coating composition containing 20 to 90 parts by weight of an aqueous acrylic-modified epoxy resin (B) as a binder is disclosed.

  However, the aqueous coating composition described in Patent Document 1 is excellent in rust prevention and film forming properties (quick drying), but has insufficient blocking resistance.

  Patent Document 2 discloses that 100 to 100 parts by weight of an aqueous resin composition comprising 20 to 100 parts by weight of a styrene-butadiene copolymer having a glass transition point of 30 to 80 ° C and 0 to 80 parts by weight of an ethylene-acrylic acid copolymer A water-soluble solvent in an amount of from 1 to 30 parts by weight, and an aqueous chromium compound in an amount of from 0.01 to 2.0 parts by weight as a chromate ion, and a pH of 7 or more. An anti-rust composition is disclosed.

  However, the water-based rust preventive composition described in Patent Document 2 is excellent in rust prevention, but contains a harmful chromium compound, and therefore is not preferable from the viewpoint of environmental protection.

JP-A-7-300754 JP-A-11-172189

  An object of the present invention is to form a coating film which can be applied to both ordinary dry coating and baking coating, has excellent film forming properties, blocking resistance and rust prevention properties, and does not contain environmentally harmful substances (such as lead and chromium). The purpose of the present invention is to provide a water-based coating composition which can be used.

  The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, urethane resin particles having a specific weight average molecular weight range and a glass transition temperature range, and acrylic resin particles having a specific glass transition temperature range, It has been found that the above problems can be solved by an aqueous coating composition characterized by being contained as a component, and the present invention has been completed.

That is, the present invention
1. A urethane resin particle (A) having a weight average molecular weight of 100,000 to 5,000,000 and a glass transition temperature of 30 to 100 ° C and an acrylic resin particle (B) having a glass transition temperature of -20 to 30 ° C; The urethane resin particles (A) are 40 to 80% by mass, and the acrylic resin particles (B) are 20 to 60% by mass, as the solid content, based on the total solid content of the resin particles (A) and the acrylic resin particles (B). An aqueous coating composition,
2. Further, the aqueous coating composition according to the above item 1, further comprising a rust inhibitor (C),
3. Item 3. The aqueous coating composition according to Item 1 or 2, further containing a pigment (D).
4. The rust preventive (C) and the pigment (D) have a total solid content of 10 to 400% by mass based on the total solid content of the urethane resin particles (A) and the acrylic resin particles (B). Aqueous coating composition according to any one of the above,
5. After applying the aqueous coating composition according to any one of the above items 1 to 4 after preheating the object to be coated, a coating method having a step of drying with residual heat,
Is provided.

  The aqueous coating composition of the present invention has a film-forming property (quick drying) by using, as a resin component, a urethane resin particle having a high glass transition temperature with a high molecular weight and an acrylic resin particle having a low glass transition temperature in combination. It is possible to obtain a coating film having both anti-blocking properties and excellent rust prevention.

  In addition, the water-based paint composition of the present invention can be applied to both dry coating and baking coating. By applying the water-based paint composition of the present invention, if the coating is only for outdoor use at a construction site (normal dry coating). In addition, since coating (usually baking coating) can be efficiently performed even on a production line for coated steel materials, it is possible to obtain an effect of obtaining coated articles such as coated steel materials having excellent rust resistance.

  The aqueous coating composition of the present invention is a urethane resin particle (A) having a weight average molecular weight of 100,000 to 5,000,000 and a glass transition temperature of 30 to 100 ° C, and an acrylic resin having a glass transition temperature of -20 to 30 ° C. An aqueous coating composition containing particles (B), wherein the urethane resin particles (A) and the acrylic resin particles (B) are added to the total solid content of the urethane resin particles (A) and the acrylic resin particles (B). An aqueous coating composition characterized by containing a specific range of solid content.

  Hereinafter, the aqueous coating composition of the present invention (hereinafter, sometimes referred to as “the present coating composition”) will be described in detail.

Urethane resin particles (A)
The urethane resin particles (A) can be generally obtained from a component containing a polyisocyanate component and a polyol component.

  Examples of the polyisocyanate component include alicyclic diisocyanate, aromatic diisocyanate, aliphatic diisocyanate, and polyisocyanate having three or more isocyanate groups in one molecule.

  Examples of the alicyclic diisocyanate include isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, trans-1,4-cyclohexyl diisocyanate, and norbornene diisocyanate.

  Examples of the aromatic diisocyanate include tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, and 3,3'-dimethyldiphenyl-4,4 '. -Diisocyanate, dianisidine diisocyanate, tetramethylxylylene diisocyanate and the like.

  Examples of the aliphatic diisocyanate include 1,6-hexamethylene diisocyanate, 2,2,4 and / or (2,4,4) -trimethylhexamethylene diisocyanate, and lysine diisocyanate.

  Examples of the polyisocyanate having three or more isocyanate groups in one molecule include, for example, isocyanurate trimer, buret trimer, trimethylolpropane adduct of diisocyanate described above; triphenylmethane triisocyanate, 1- Examples thereof include trifunctional or higher polyisocyanates such as methylbenzol-2,4,6-triisocyanate and dimethyltriphenylmethanetetraisocyanate. These isocyanate compounds are modified such as carbodiimide-modified, isocyanurate-modified and biuret-modified. It may be used in the form of an object.

  The above polyisocyanates may be used in the form of blocked isocyanates blocked by a blocking agent.

  Examples of the polyol component include a polycarbonate polyol, a polyol having an ester bond, a polycaprolactone polyol, a polyether polyol, a low molecular polyol, a polybutadiene polyol, and a silicone polyol.

  Polycarbonate polyol is a compound obtained by a polycondensation reaction between a known polyol and a carbonylating agent by a conventional method. Examples of the polyol include diols and polyhydric alcohols such as trihydric or higher alcohols.

Examples of the diol include 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, and 1,9-diol. Linear diols such as nonanediol and 1,10-decanediol; 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol,
Neopentyl glycol, 2-ethyl-1,6-hexanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,8 Branched diols such as -octanediol, 2,2,4-trimethyl-1,3-pentanediol and 2-ethyl-1,3-hexanediol; 1,3-cyclohexanediol, 1,4-cyclohexanediol, Alicyclic diols such as 4-cyclohexanedimethanol; aromatic diols such as p-xylene diol and p-tetrachloroxylene diol; ether diols such as diethylene glycol and dipropylene glycol. These diols can be used alone or in combination of two or more.

  Examples of the trihydric or higher alcohol include glycerin, trimethylolethane, trimethylolpropane, a dimer of trimethylolpropane, and pentaerythritol. These trihydric or higher alcohols can be used alone or in combination of two or more.

  Known carbonylating agents can be used. Specifically, for example, alkylene carbonate, dialkyl carbonate, diallyl carbonate, phosgene and the like can be mentioned, and one of these can be used or two or more can be used in combination. Of these, preferred are ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, diphenyl carbonate and the like.

  Examples of the polyol having an ester bond include a polyester polyol and a polyester polycarbonate polyol.

  Examples of the polyester polyol include a direct esterification reaction between a polyhydric alcohol and a polyhydric carboxylic acid or an ester thereof, an anhydride thereof, or an ester-forming derivative such as a halide in an amount smaller than the stoichiometric amount of the polyhydric alcohol; And / or those obtained by transesterification.

  Examples of the polyhydric alcohol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, and 2-butyl-2-ethyl-1,3-propanediol. , 1,4-butanediol, neopentyl glycol, 3-methyl-2,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2- Methyl-2,4-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 3,5-heptanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, diethylene glycol, Aliphatic diols such as ethylene glycol, alicyclic diols such as cyclohexane dimethanol and cyclohexane diol, trimethylolethane, trimethylolpropane, hexitols, pentitols, glycerin, trivalent such as pentaerythritol and tetramethylolpropane The above alcohols can be mentioned.

  Examples of the polyvalent carboxylic acid or its ester-forming derivative include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecandioic acid, and 2-methylsuccinic acid 2-methyladipic acid, 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecanedioic acid, hydrogenated dimer acid, Aliphatic dicarboxylic acids such as dimer acid, aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,2- Cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1 Polycarboxylic acids such as alicyclic dicarboxylic acids such as 4-dicarboxylmethylenecyclohexane, nadic acid, and methylnadic acid; trimellitic acids such as trimellitic acid, trimesic acid and trimer of castor oil fatty acid; and polycarboxylic acids thereof. Acid anhydrides, chlorides of the polycarboxylic acid, halides such as bromide, methyl esters, ethyl esters, propyl esters, isopropyl esters, butyl esters, isobutyl esters, lower esters such as amyl esters of the polycarboxylic acids and , Γ-caprolactone, δ-caprolactone, ε-caprolactone, dimethyl-ε-caprolactone, δ-valerolactone, γ-valerolactone, γ-butyrolactone and the like.

  Examples of the above polycaprolactone polyol include ring-opening polymers of caprolactone such as polycaprolactone diol.

  Examples of the low-molecular polyol include polyhydric alcohols exemplified for the polyester polyol.

  Examples of the polyether polyol include ethylene oxide and / or propylene oxide adducts of the above-mentioned low molecular polyol, and polytetramethylene glycol.

  Examples of the silicone polyol include silicone oils having a siloxane bond in the molecule and having a hydroxyl group at the end.

  Further, a diol containing a carboxyl group can be used as the polyol component. Carboxyl group-containing diols are used to introduce hydrophilic groups into polyurethane molecules. The hydrophilic group is a carboxyl group. Specific examples include dimethylolpropionic acid, dimethylolbutanoic acid, dimethylolbutyric acid, dimethylolvaleric acid, and the like.

  In addition to the polyisocyanate component and the polyol component, an amine component can be used if necessary. Examples of the amine component include a monoamine compound and a diamine compound.

  The monoamine compound is not particularly limited, and well-known general monoamine compounds can be used alone or in combination of two or more. Examples of the monoamine compound include alkylamines such as ethylamine, propylamine, 2-propylamine, butylamine, 2-butylamine, tert-butylamine and isobutylamine; aromatic amines such as aniline, methylaniline, phenylnaphthylamine and naphthylamine; cyclohexylamine And alicyclic amines such as methylcyclohexylamine; ether amines such as 2-methoxyethylamine, 3methoxypropylamine and 2- (2-methoxyethoxy) ethylamine; ethanolamine, propanolamine, butylethanolamine and 1-amino-2. -Methyl-2-propanol, 2-amino-2-methylpropanol, diethanolamine, diisopropanolamine, dimethylaminopropylethanolamine, dipropanolamine Emissions, N- methylethanolamine, mention may be made of alkanolamines such as N- ethyl-ethanolamine. Among them, alkanolamines are preferable since they can give good water dispersion stability to polyurethane molecules, and 2-aminoethanol and diethanolamine are particularly preferable from the viewpoint of supply stability.

  The diamine compound is not particularly limited, and well-known general diamine compounds can be used alone or in combination of two or more. Examples of the diamine compound include low molecular weight diamines obtained by substituting an alcoholic hydroxyl group of the low molecular weight diol exemplified above such as ethylene diamine and propylene diamine with an amino group; polyether diamines such as polyoxypropylene diamine and polyoxyethylene diamine Classes: mensendiamine, isophoronediamine, norbornenediamine, bis (4-amino-3-methyldicyclohexyl) methane, diaminodicyclohexylmethane, bis (aminomethyl) cyclohexane, 3,9-bis (3-aminopropyl) 2,4 Alicyclic diamines such as 8,8,10-tetraoxaspiro (5,5) undecane; m-xylenediamine, α- (m / paminophenyl) ethylamine, m-phenylenediamine, diaminodiphenylmethane, diaminodiphene Aromatic diamines such as sulfonic acid, diaminodiethyldimethyldiphenylmethane, diaminodiethyldiphenylmethane, dimethylthiotoluenediamine, diethyltoluenediamine, α, α′-bis (4-aminophenyl) -p-diisopropylbenzene; hydrazine; the above polyester polyol The dicarboxylic acid dihydrazide compound which is a compound of dicarboxylic acid and hydrazine exemplified as the polyvalent carboxylic acid used in the above can be mentioned. Among these diamine compounds, low molecular diamines are preferred from the viewpoint of handling workability, and among them, ethylenediamine is particularly preferred.

  As the urethane resin particles (A), those having a branched or crosslinked structure in polyurethane molecules can be suitably used. The branched or crosslinked structure can be introduced using an internal branching agent or an internal crosslinking agent. As these internal branching agents and internal crosslinking agents, polyols having a valency of 3 or more can be suitably used, and for example, trimethylolpropane can be mentioned.

  The method for producing the urethane resin particles (A) is not particularly limited, and a well-known general method can be applied. As a production method, a method in which a prepolymer or a polymer is synthesized in a solvent which is inert to the reaction and has a high affinity for water, and is then fed into water and dispersed. For example, a method (a) of synthesizing a prepolymer from a polyisocyanate component and a polyol component in the above-mentioned solvent and reacting it with an amine component used as necessary in water, a polyisocyanate component, a polyol component and a A method (b) of synthesizing a polymer from an amine component used in accordance with the method and feeding and dispersing the polymer into water can be mentioned. The neutralizer component used as needed may be added to the water to be fed in advance, or may be added after the feed.

  Examples of the solvent which is inert to the reaction and has a high affinity for water used in the above preferred production method include acetone, methyl ethyl ketone, dioxane, tetrahydrofuran, N-methyl-2-pyrrolidone and the like. . These solvents can be used usually in an amount of 3 to 100% by mass based on the total amount of the raw materials used for producing the prepolymer or the polymer.

  In the above production method, the compounding ratio is not particularly limited. The mixing ratio can be replaced by the molar ratio of the isocyanate group in the polyisocyanate component and the isocyanate-reactive group in the polyol component and the amine component at the stage of the reaction. If the unreacted isocyanate group is insufficient in the urethane resin particles (polyurethane molecules) dispersed in the urethane resin, the adhesiveness and the strength of the coating may decrease when used as a coating. If present, unreacted isocyanate groups may affect the dispersion stability and physical properties of the paint, so that the isocyanate-reactive group is preferably 0.5 to 2.0 with respect to 1 isocyanate group. Further, the molar ratio of the isocyanate-reactive groups in the polyol component is preferably from 0.3 to 1.0, more preferably from 0.5 to 0.9, based on 1 of the isocyanate groups in the polyisocyanate component. The molar ratio of the isocyanate-reactive groups in the amine component used as needed is preferably from 0.1 to 1.0, more preferably from 0.2 to 0.1, based on 1 of the isocyanate groups in the polyisocyanate component. 5 is more preferred.

Further, it is preferable that the degree of neutralization by the neutralizing agent used as required is set in a range that gives sufficient dispersion stability to the obtained urethane resin particles (A). The equivalent is preferably 0.5 to 2.0 times, more preferably 0.7 to 1.5 times the equivalent of 1 mole of the carboxyl group in the urethane resin particles (A).
In order to improve the dispersibility of the urethane resin particles (A), an emulsifier such as a surfactant may be used.

  Examples of the emulsifier include well-known general anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, polymer surfactants, and reactive surfactants used in urethane resin emulsions. Can be used. Of these, anionic emulsifiers and nonionic emulsifiers can be suitably used.

  Examples of the above anionic surfactant include alkyl sulfates such as sodium dodecyl sulfate and ammonium dodecyl sulfate such as potassium dodecyl sulfate; sodium dodecyl polyglycol ether sulfate; sodium sulfolicinolate; alkali metal salts of sulfonated paraffin; Alkyl sulfonates such as ammonium salts of fluorinated paraffins; fatty acid salts such as sodium laurate, triethanolamine oleate and toluethanolamine aviate; alkyl aryl sulfonates such as sodium benzene sulfonate and alkali metal sulfate of alkali phenol hydroxyethylene; high alkyl naphthalene Sulfonate; Naphthalenesulfonic acid formalin condensate; Dialkyl sulfoco Click salt; polyoxyethylene alkyl sulfate salt; and polyoxyethylene alkyl aryl sulfate salts.

  Examples of the nonionic surfactant include ethylene oxide and / or propylene oxide adducts of alcohols having 1 to 18 carbon atoms, ethylene oxide and / or propylene oxide adducts of alkyl phenol, and ethylene oxide of alkylene glycol and / or alkylenediamine. And / or propylene oxide adducts.

  Examples of the alcohol having 1 to 18 carbon atoms that constitute the nonionic surfactant include methanol, ethanol, propanol, 2-propanol, butanol, 2-butanol, tert-butanol, amyl alcohol, isoamyl alcohol, and tertiary amyl alcohol. Hexanol, octanol, decane alcohol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, and the like. Examples of the alkyl phenol include phenol, methyl phenol, 2,4-di-tert-butyl phenol, and 2,5-di-tert. Butylphenol, 3,5-ditert-butylphenol, 4- (1,3-tetramethylbutyl) phenol, 4-isooctylphenol, 4-nonylphenol, 4-tert-octylphenol, 4-dodecy Phenol, 2- (3,5-dimethylheptyl) phenol, 4- (3,5-dimethylheptyl) phenol, naphthol, bisphenol A, bisphenol F and the like are mentioned. As the alkylene glycol, ethylene glycol, 1,2- Propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5 -Pentanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, etc., and examples of the alkylenediamine include alcohols of these alkylene glycols. Examples include those in which a hydroxyl group is substituted by an amino group. The ethylene oxide and propylene oxide adducts may be random adducts or block adducts.

  When these emulsifiers are used, any amount can be used without particular limitation, but if the mass ratio to the urethane resin particles 1 is less than 0.05, sufficient dispersibility cannot be obtained. If it exceeds 0.3, the water resistance, strength, elongation and other physical properties of the coating film and the like obtained from the aqueous first colored paint may be reduced. 05-0.2 is more preferred.

  The weight average molecular weight of the urethane resin particles (A) is from 100,000 to 5,000,000, preferably from 200,000 to 5,000,000, and particularly preferably from 300,000 to 3,000,000 from the viewpoint of blocking resistance.

  In the present specification, the 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 standard polystyrene having a known molecular weight measured under the same conditions.

  The glass transition temperature (Tg) of the urethane resin particles (A) is from 30 to 100 ° C, preferably from 40 to 90 ° C, particularly preferably from 40 to 80 ° C, from the viewpoint of blocking resistance and rust prevention. is there.

  In this specification, the glass transition temperature (Tg) of the urethane resin particles (A) is based on differential thermal analysis (DSC). Specifically, using a differential scanning calorimeter “DSC-220U” (manufactured by Seiko Instruments Inc.), the sample was taken in a measuring cup, and the solvent was completely removed by vacuum suction. The calorific value change is measured at a temperature rate in the range of −20 ° C. to + 200 ° C., and the change point of the first baseline on the low temperature side can be measured as the glass transition temperature.

  The average particle diameter of the urethane resin particles (A) is preferably in the range of 10 to 1000 nm, more preferably 10 to 500 nm, and still more preferably 10 to 300 nm, from the viewpoint of film forming properties.

The average particle diameter can be measured using a general measuring means such as laser light scattering.
In the present specification, the average particle size of the resin particles is a value measured at 20 ° C. after dilution with deionized water by a conventional method using a submicron particle size distribution analyzer. As the submicron particle size distribution measuring device, for example, “COULTER N4 type” (trade name, manufactured by Beckman Coulter, Inc.) can be used.

  As the urethane resin particles (A), a commercially available product that satisfies the requirements of the above-mentioned weight average molecular weight and glass transition temperature can also be used. Commercially available products include, for example, Superflex 150 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Adecabon Tyder HUX-232, and Adekabon Tyder HUX-320 (all of which are trade names, manufactured by ADEKA).

Acrylic resin particles (B)
The acrylic resin particles (B) may be either those synthesized by emulsion polymerization or those synthesized by solution polymerization, and both can be used in combination, but are synthesized by emulsion polymerization from the viewpoint of blocking resistance. Can be suitably used.

  Emulsion polymerization can be performed by a conventionally known method such as a seed polymerization method and a mini-emulsion polymerization method.For example, by emulsion polymerization of a polymerizable unsaturated monomer using a polymerization initiator in the presence of an emulsifier. ,It can be carried out.

  More specifically, it is carried out by dissolving the emulsifier in water or an aqueous medium containing an organic solvent such as alcohol as necessary, and dropping the polymerizable unsaturated monomer and the polymerization initiator under heating and stirring. it can. A polymerizable unsaturated monomer previously emulsified using an emulsifier and water can be similarly dropped.

  As the emulsifier, anionic emulsifiers and nonionic emulsifiers are suitable.Examples of the anionic emulsifiers include sodium salts and ammonium salts of alkylsulfonic acid, alkylbenzenesulfonic acid, alkylphosphoric acid and the like, Examples of nonionic emulsifiers include, for example, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonyl phenyl ether, and polyoxyethylene nonyl phenyl ether. Ethylene octyl phenyl ether, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbita Monostearate, sorbitan monostearate, sorbitan trioleate, may be mentioned polyoxyethylene sorbitan monolaurate. A polyoxyalkylene group-containing anionic emulsifier having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group in one molecule; A reactive anionic emulsifier having a group can also be used.

  Specific examples of the reactive anionic emulsifier include Eleminol JS-1, Eleminol JS-2 (manufactured by Sanyo Chemical Industries), S-120, S-180A, S-180, Latemul PD-104, Latemul PD-420, Latemul. PD-430S, Latemul PD-450 (manufactured by Kao Corporation), Aqualon HS-10, Aqualon KH-10 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Adecaria Soap SE-10N, Adecaria Soap SE-20N, Adecaria Soap SR Adecaria Soap ER-10, Adecaria Soap ER-20, Adecaria Soap ER-30, Adecaria Soap ER-40 (manufactured by ADEKA), ANTOX MS-60 (manufactured by Nippon Emulsifier) and the like. Can be.

  One or more dispersion stabilizers such as the emulsifier can be used in the emulsion polymerization reaction.

  The amount of the emulsifier used is preferably 0.1 to 15% by mass, particularly 0.5 to 10% by mass, and more preferably 1 to 5% by mass, based on the total amount of all the monomers used.

  Examples of the polymerization initiator include benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butylperoxylaurate, and tert-butylperoxy. Organic peroxides such as isopropyl carbonate, tert-butylperoxyacetate and diisopropylbenzene hydroperoxide; azobisisobutyronitrile, azobis (2,4-dimethylvaleronitrile), azobis (2-methylpropionnitrile), azobis (2-methylbutyronitrile), 4,4′-azobis (4-cyanobutanoic acid), dimethylazobis (2-methylpropionate), azobis [2-methyl-N- (2-hydro Azo compounds such as [silethyl) -propionamide] and azobis {2-methyl-N- [2- (1-hydroxybutyl)]-propionamide}; persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; Can be mentioned. These polymerization initiators can be used alone or in combination of two or more. Further, if necessary, a reducing agent such as sugar, sodium formaldehyde sulfoxylate, iron complex or the like may be used in combination with the polymerization initiator to form a redox initiator.

  Generally, the amount of the polymerization initiator to be used is preferably about 0.1 to 5% by mass, particularly preferably about 0.2 to 3% by mass, based on the total amount of all the monomers used. The method of adding the polymerization initiator is not particularly limited, and can be appropriately selected according to the type and amount of the polymerization initiator. For example, it may be previously contained in a monomer mixture or an aqueous medium, or may be added at once during polymerization, or may be dropped.

  Further, a chain transfer agent can be used for the purpose of adjusting the molecular weight of the obtained acrylic resin particles (B). Examples of the chain transfer agent include compounds having a mercapto group. Specifically, for example, lauryl mercaptan, t-dodecyl mercaptan, octyl mercaptan, 2-ethylhexyl thioglycolate, 2-methyl-5-tert-butylthio Examples include phenol, mercaptoethanol, thioglycerol, mercaptoacetic acid (thioglycolic acid), mercaptopropionate, and n-octyl-3-mercaptopropionate. If used, the amount of the chain transfer agent is generally in the range from 0.05 to 10% by weight, in particular from 0.1 to 5% by weight, based on the total amount of all monomers used. Is preferred.

The concentration of the total polymerizable unsaturated monomer during the emulsion polymerization reaction is usually in the range of 0.1 to 60% by mass, preferably 0.5 to 50% by mass, and more preferably 1.0 to 50% by mass. Is suitable.
The reaction temperature is mainly determined by the initiator. For example, it is preferably 60 to 90 ° C for an azo compound, and preferably 30 to 70 ° C for a redox initiator. Generally, the reaction time can be from 1 to 8 hours.

  As the polymerizable unsaturated monomer, conventionally known ones can be used. For example, a reactive group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers can be used.

  Examples of the reactive group of the reactive group-containing polymerizable unsaturated monomer include a hydroxyl group, an acid group, a carbonyl group, an N-methylol alkyl ether group, an isocyanate group, an epoxy group, an amino group, an alkoxysilyl group, a carbodiimide group, and a hydrazide. Functional groups having reactivity such as groups can be given.

  In this specification, “(meth) acrylate” means “acrylate or methacrylate”. “(Meth) acrylic acid” means “acrylic acid or methacrylic acid”. Further, “(meth) acryloyl” means “acryloyl or methacryloyl”. “(Meth) acrylamide” means “acrylamide or methacrylamide”.

  Examples of the hydroxyl group-containing polymerizable unsaturated monomer include 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, and ε-caprolactone-modified tetrahydro Furfuryl (meth) acrylate, ε-caprolactone-modified hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2-hydroxy -3-butoxypropyl (meth) acrylate, monohydroxyethyl phthalate (meth) acrylate, and the like.

  Among them, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and ε-caprolactone-modified hydroxyethyl (meth) acrylate can be suitably used.

  Examples of the acid group-containing polymerizable unsaturated monomer include a carboxyl group or an acid anhydride group-containing polymerizable unsaturated monomer.

  Examples of the polymerizable unsaturated monomer containing a carboxyl group or an acid anhydride group include, for example, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, β-carboxyethyl acrylate, and acids thereof. Anhydrides can be mentioned. Among these, acrylic acid and methacrylic acid can be suitably used.

  Examples of the acid group-containing polymerizable unsaturated monomer other than a carboxyl group or an acid anhydride group include 2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, styrenesulfonic acid sodium salt, sulfoethylmethacrylate and its sodium salt or ammonium salt. And the like.

  Examples of the carbonyl group-containing polymerizable unsaturated monomer include, for example, acrolein, diacetone acrylamide, diacetone methacrylamide, formylstyrene and vinyl alkyl having 4 to 7 carbon atoms such as vinyl methyl ketone, vinyl ethyl ketone, and vinyl butyl ketone. Ketones and the like can be mentioned. Of these, particularly preferred are diacetone acrylamide and diacetone methacrylamide.

  Examples of the N-methylol alkyl ether group-containing polymerizable unsaturated monomer include N-methylol acrylamidobutyl ether.

  Isocyanate group-containing polymerizable unsaturated monomer is a compound having at least one unblocked isocyanate group and at least one radically polymerizable double bond in one molecule, for example, methacryloyl isocyanate, 2-isocyanateethyl methacrylate, m- or p-isopropenyl-α, α'-dimethylbenzyl isocyanate or a 1: 1 (molar ratio) adduct of a hydroxyl group-containing polymerizable unsaturated monomer and a diisocyanate compound (for example, 2-hydroxyethyl acrylate and isophorone Equimolar adduct with diisocyanate).

  Examples of the epoxy group-containing polymerizable unsaturated monomer include glycidyl acrylate, glycidyl methacrylate, CYCLOMER A-200 (alicyclic epoxy group-containing monomer), and CYCLOMER M-100 (alicyclic epoxy group-containing monomer). Can be.

  Examples of the amino group-containing polymerizable unsaturated monomer include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminopropyl acrylamide, and dimethylaminopropyl methacrylamide.

  Examples of the alkoxysilyl group-containing polymerizable unsaturated monomer include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltributoxysilane, (meth) acryloyloxymethyltrimethoxysilane, and (meth) acryloyloxyethyl. Trimethoxysilane, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane, (meth) acryloyloxyethyltriethoxysilane, (meth) acryloyloxypropyltributoxysilane, vinyltris- β-methoxyethoxysilane, divinylmethoxysilane, divinyldi-β-methoxyethoxysilane and the like can be mentioned.

  Examples of other polymerizable unsaturated monomers include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, and the like. C1-C24 alkyl or cycloalkyl esters of (meth) acrylic acid; methoxybutyl acrylate, methoxybutyl methacrylate, methoxyethyl acrylate, methoxyethyl methacrylate, ethoxybutyl acrylate, ethoxybutyl methacrylate, phenoxyethyl ( C1-C16 alkoxyalkyl ester of (meth) acrylic acid such as meth) acrylate; aromatic unsaturated such as styrene, vinyltoluene, α-methylstyrene, N-vinylpyrrolidone and vinylpyridine Monomers; olefins such as ethylene, propylene, butylene, and pentene; diene compounds such as butadiene, isoprene, and chloroprene; cyclohexenyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, Isobornyl (meth) acrylate, benzyl (meth) acrylate, N-butoxy (meth) acrylamide, adducts of glycidyl (meth) acrylate with amines, etc., vinyl propionate, vinyl acetate, vinyl pivalate, veova monomer (product of Shell Chemical Company) And the like.

  In addition, crosslinked resin particles can be obtained by using a polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule as a monomer component.

  Examples of the polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule include allyl (meth) acrylate, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, and tetraethylene glycol. Di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,4-butanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerol di (meth) acrylate, 1,1,1-trishydroxymethylethanedi (meth) acryle And 1,1,1-trishydroxymethylethanetri (meth) acrylate, 1,1,1-trishydroxymethylpropanetri (meth) acrylate, triallyl isocyanurate, diallyl terephthalate, divinylbenzene and the like. . These monomers can be used alone or in combination of two or more.

  Among the polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule, among all, allyl (meth) acrylate, ethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) Acrylate, neopentyl glycol di (meth) acrylate, and 1,6-hexanediol di (meth) acrylate can be suitably used.

  The glass transition temperature of the acrylic resin particles (B) is in the range of −20 ° C. to 30 ° C., and more preferably in the range of −10 ° C. to 25 ° C., from the viewpoint of rust prevention and film forming properties.

In this specification, the glass transition temperature Tg (absolute temperature) of the acrylic resin particles (B) is a value calculated by the following equation (1).
_{1 / Tg = W 1 / T} 1 + W 2 / T 2 + ··· W n / T n (1)
[Wherein W ₁ , W ₂ ,..., W _n are mass fractions of each monomer, and T ₁ , T _2, ... T _n are glass transition temperatures (absolute temperatures) of homopolymers of each monomer. is there. ]
The glass transition temperature of the homopolymer of each monomer is determined according to POLYMER HANDBOOK Fourth Edition, J. Am. Brandrup, E .; h. Immergut, E .; A. The glass transition temperature of a monomer not described in the literature is the value obtained by Gulke (1999), and the homopolymer of the monomer is synthesized so that the weight average molecular weight becomes about 50,000, and the glass transition temperature is obtained. Was measured by differential scanning thermal analysis.

  The acrylic resin particles (B) can have an average particle diameter in a range of preferably 10 to 1000 nm, more preferably 20 to 500 nm, and still more preferably 40 to 300 nm, from the viewpoint of dispersion stability of the particles.

When the urethane resin particles (A) and the acrylic resin particles (B) have an acid group in particular, it is preferable to neutralize the urethane resin particles with a basic compound from the viewpoint of dispersion stability.
As the neutralizing agent, ammonia or a water-soluble amino compound, for example, monoethanolamine, ethylamine, dimethylamine, diethylamine, triethylamine, propylamine, dipropylamine, isopropylamine, diisopropylamine, triethanolamine, butylamine, dibutylamine , 2-ethylhexylamine, ethylenediamine, propylenediamine, methylethanolamine, dimethylethanolamine, diethylethanolamine, 2-amino-2-methylpropanol, diethanolamine, morpholine and the like can be suitably used.

  When the urethane resin particles (A) and the acrylic resin particles (B) have a hydroxyl group, the hydroxyl value is preferably from 1 to 150 mgKOH / g, more preferably from 2 to 100 mgKOH / g, and more preferably from 5 to 90 mgKOH / g. g is more preferable.

  Further, the urethane resin particles (A) and the acrylic resin particles (B) may have a core / shell structure. "Shell part" means the polymer layer present in the outermost layer of the resin particles, "core part" means the polymer layer of the resin particle inner layer excluding the shell part, and "core / shell type structure" This means a structure having a core portion and a shell portion. The core / shell type structure generally has a layer structure in which the core portion is completely covered with the shell portion. However, depending on the mass ratio of the core portion and the shell portion, the amount of monomer in the shell portion may be reduced. May not be sufficient to form In such a case, it is not necessary to have a complete layer structure as described above, and a structure in which a shell part covers a part of the core part, or a component of the shell part in a part of the core part May be a structure in which the polymerizable unsaturated monomer is graft-polymerized. Further, the concept of the multilayer structure in the core / shell type structure is similarly applied to a case where a multilayer structure is formed in the core portion in the urethane resin particles (A) and the acrylic resin particles (B). The core / shell structure can be obtained, for example, by reacting monomer compositions having different compositions in multiple stages.

  The aqueous coating composition of the present invention contains, as resin components, 40 to 80% by mass of urethane resin particles (A) and 20 to 60% by mass of acrylic resin particles (B) in a solid content based on the total solid content of both. .

  Preferably, component (A) is 40 to 70% by mass, component (B) is 30 to 60% by mass, more preferably component (A) is 40 to 60% by mass, and component (B) is 40 to 60% by mass. .

  If the component (A) is less than 40% by mass, the resulting coating film may have poor blocking resistance or rust resistance, and if the component (B) is less than 20% by weight, the film-forming properties may be poor. It may be defective.

In the aqueous coating composition of the present invention, a resin other than the component (A) and the component (B) can be used as necessary.

  Specifically, as a urethane resin other than the component (A), an acrylic resin, an epoxy resin, a polyester resin, etc. other than the component (B), and as a curing agent such as an amino resin, a phenol resin, a polyisocyanate compound, a carbodiimide compound, etc. Examples thereof include resins used.

Rust inhibitor (C)
The aqueous coating composition of the present invention preferably contains a rust inhibitor for improving rust resistance.
As the rust preventive, those usually used in paints can be used, and examples thereof include zirconium compounds, vanadium compounds, silicon oxide, and sulfur-containing organic compounds.

Pigment (D)
The aqueous coating composition of the present invention preferably contains a pigment for improving rust prevention. Examples of the pigment include a rust preventive pigment, a coloring pigment, an extender pigment, and the like.

  Examples of the rust preventive pigment include zinc oxide, phosphite compounds, phosphate compounds, nitrite compounds, molybdate compounds, bismuth compounds, and metal ion exchange silica.

  As coloring pigments, titanium oxide, zinc molybdate, calcium molybdate, carbon black, graphite (graphite), iron black (iron black), navy blue, ultramarine, cobalt blue, copper phthalocyanine blue, indanthrone blue, graphite, Synthetic yellow iron oxide, red iron oxide, transparent red iron oxide, bismuth vanadate, titanium yellow, zinc yellow (zinc yellow), ocher, monoazo yellow, disazo, isoindolinone yellow, metal complex salt azo yellow, quinophthalone yellow, benzimidazolone yellow, monoazo red , Unsubstituted quinacridone red, azo lake (Mn salt), quinacridone magenta, ensenthrone orange, dianthraquinonyl red, perylene maroon, perylene red, diketopyrrolopyrrole chromium vermilion, salt Phthalocyanine green, brominated phthalocyanine green, etc.; pyrazolone orange, benzimidazolone orange, mention may be made of dioxazine violet, perylene violet.

  Examples of the extender include clay, silica, barium sulfate, talc, calcium carbonate, white carbon, diatomaceous earth, magnesium aluminum carbonate flake, mica flake, and the like.

  Of the above extenders, barium sulfate and talc can be suitably used from the viewpoint of rust prevention.

  When the coating composition of the present invention contains a rust preventive (C) or a pigment (D), the rust preventive (C) is used based on the total solid content of the urethane resin particles (A) and the acrylic resin particles (B). The total solid content of the pigment and the pigment (D) is preferably from 10 to 400% by mass, particularly from 20 to 350% by mass, and more preferably from 50 to 300% by mass, from the viewpoints of rust prevention and film forming properties.

  In the aqueous coating composition of the present invention, if necessary, a catalyst, a pigment dispersant, a solvent, a film-forming aid, an anti-settling agent, a rheology control agent, an antifoaming agent, a coating surface adjusting agent, an ultraviolet absorber, Additives such as an ultraviolet stabilizer and a pH adjuster can be contained.

  The water-based coating composition of the present invention is capable of forming a coating film excellent in quick-drying property, blocking resistance, coating workability, and also excellent in rust prevention properties, for example, steel materials used for building material applications and the like. In particular, it can be used particularly preferably as a rust-preventive paint for lightweight shaped steel.

  More specifically, the steel material to be coated with the water-based coating composition of the present invention is, for example, a C-shaped steel such as a lip grooved steel, a light grooved steel, a deformed light grooved steel, and an equilateral light mountain shape. Examples include steel, L-angles such as unequal-sided light-angle shaped steels, lightweight shaped steels such as square steel pipes and deck plates, and the like, and steels obtained by subjecting these steels to chemical conversion treatment such as phosphate treatment.

  The water-based coating composition of the present invention may be formed on the steel material by a known method such as a roll coating method, a spray coating method, a brush coating method, an electrostatic coating method, an immersion method, an electrodeposition coating method, a curtain coating method, and a roller coating method. The aqueous coating composition of the present invention is applied by a method and dried to form a coating film.

  The film thickness of the coating film of the aqueous coating composition of the present invention is not particularly limited, but it can be usually applied in a range of 10 to 100 μm, preferably 10 to 80 μm.

  The aqueous coating composition of the present invention can be any of normal dry coating and baking coating, and the heating and drying conditions of baking coating may be set as appropriate.For example, in a steel material production line, usually, a material is prepared by preheating. After coating at a temperature of 70 to 200 ° C., preferably 80 to 120 ° C., the coating can be performed by drying for 3 to 5 minutes with residual heat (material temperature immediately after coating (about 60 to 100 ° C.)).

  Hereinafter, the present invention will be described more specifically with reference to Production Examples, Examples, and Comparative Examples. However, the present invention is not limited by these. In each example, “parts” and “%” are based on mass unless otherwise specified. The thickness of the coating is based on the cured coating.

Production example 1 of urethane resin particles (A-1)
In a reaction vessel equipped with a thermometer, a thermostat, a stirrer, and a reflux condenser, 68.9 parts of "Kuraray polyol P1010" (trade name, manufactured by Kuraray, methylpentanediol adipate, molecular weight: about 1000), and dimethylolpropionic acid 2 .9 parts, trimethylolpropane 1.5 parts, "Neostan U-600" (trade name, Nitto Kasei, bismuth-based catalyst) 0.1 part, and methyl ethyl ketone solvent 100 parts were charged, and the temperature was raised to 80 ° C with stirring. After that, 30.8 parts of dicyclohexylmethane 4,4'-diisocyanate was added dropwise over 30 minutes. Thereafter, a urethanization reaction was carried out at 80 ° C., and the mixture was cooled to room temperature to obtain a prepolymer solution of a polyurethane resin having a terminal isocyanate group.

  Thereafter, stirring was continued, and the resin viscosity was reduced with 100 parts of methyl ethyl ketone solvent. Then, 1.2 parts of dimethylethanolamine was added to neutralize the mixture, and 148.8 parts of deionized water was added as needed to disperse in water. Phase emulsification).

  After completion of the aqueous dispersion (emulsification), 0.6 parts of ethylenediamine was added, and the mixture was heated to 40 ° C and stirred for 2 hours. Thus, a chain extension reaction between the terminal isocyanate group of the urethane resin and the diamine was performed.

  Thereafter, stirring was continued, and the solvent was removed under reduced pressure while the temperature was raised to 60 ° C. When all the mixed methyl ethyl ketone solvent was distilled off, the pressure was returned to normal pressure, and after cooling, the excessively distilled deionized water was corrected to obtain a urethane resin particle (A-1) having a mass solid content concentration of 40%. An aqueous dispersion was obtained.

  The glass transition temperature of the obtained urethane resin particles (A-1) is 70 ° C. (measured using a differential scanning calorimeter “DSC-220U” (manufactured by Seiko Instruments Inc.)), and the average particle diameter is 330 nm (sub Using a micron particle size distribution analyzer “COULTER N4 type” (manufactured by Beckman Coulter, Inc.), dilute with deionized water and measure at 20 ° C.), acid value 12 mgKOH / g, hydroxyl value 0 mgKOH / g, weight average The molecular weight was 700,000.

Production example 2 of acrylic resin particles (B-1)
In a reaction vessel, 40 parts of deionized water, 3.3 parts of “Newcol 707SF” (manufactured by Nippon Emulsifier Co., anionic emulsifier having a polyoxyethylene chain, solid content of 30%) and a monomer mixture (47.8 parts of styrene, 2-ethylhexyl) (47.8 parts of acrylate, 0.9 part of 2-hydroxyethyl acrylate and 3.5 parts of methacrylic acid), and the mixture is stirred and mixed in a nitrogen stream, and 4 parts of a 3% aqueous solution of ammonium persulfate is added at 60 ° C. Was. Then, the temperature was raised to 80 ° C., and a pre-emulsion comprising the remaining 99 parts of the monomer mixture, 3.3 parts of “Newcol 707SF”, 8 parts of 3% ammonium persulfate and 35 parts of deionized water was pumped over 4 hours by a metering pump. The mixture was added to the reaction vessel, and aged for 1 hour after the addition was completed. Thereafter, 10 parts of deionized water was added, the pH was adjusted to 8.5 with aqueous ammonia, and an acrylic resin particle (B-1) dispersion having a solid content of 50% was obtained.

  The obtained acrylic resin particles (B-1) have a glass transition temperature of −6.0 ° C. and an average particle size of 165 nm (using a submicron particle size distribution analyzer “COULTER N4 type” (manufactured by Beckman Coulter, Inc.)). , Diluted with deionized water and measured at 20 ° C.), the hydroxyl value was 4.4 mg KOH / g, and the acid value was 22.8 mg KOH / g.

Production examples 3 to 6 of acrylic resin particles (B-2) to (B-5)
In the same manner as in Production Example 2, acrylic resin particles (B-2) to (B-5) were produced. Table 1 shows the glass transition temperature, average particle size, hydroxyl value and acid value of the obtained acrylic resin particles. The acrylic resin particles (B-2) are core-shell type acrylic resin particles, and the acrylic resin particles (B-4) and (B-5) are for comparative examples.

Production Examples 1 to 5 and Comparative Examples 1 to 7 of aqueous coating compositions
The raw materials were sufficiently mixed with a stirrer according to the formulations shown in Tables 2 and 3 below, and the pigment was dispersed until the tub (particle diameter of the pigment coarse particles) became 30 μm or less. Then, 20 parts of ethylene glycol monobutyl ether was added. In addition, the mixture was stirred well. Thereafter, the solid content was adjusted by adding deionized water, whereby each aqueous coating composition No. having a solid content of 50% was prepared. 1 to No. 12 were produced. The compositions in Tables 2 and 3 are mass ratios of solid contents.

  In addition, Superflex 150, Superflex 830HS, Superflex 460, and Superflex 130 used in Examples and Comparative Examples are all urethane resin particles manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

Production of test plate Production of Test Plate 1 After polishing a polished steel plate of cold rolled steel of 70 × 150 × 0.8 mm with a water-resistant abrasive paper having a particle size of 280, degreased with toluene to obtain a test material. .

  (I) The aqueous coating composition No. 1 obtained in Example 1 was applied to the above-mentioned material using a film applicator so that the cured film thickness became 35 μm. 1 was coated and dried in an environment of 23 ° C. and 50% humidity for 8 hours to obtain a test plate I-1.

  (II) After heating the above two materials so that the surface temperature becomes 100 ° C., the aqueous coating composition No. 1 obtained in Example 1 was spray-coated so that the cured film thickness became 35 μm. 1 was coated to obtain two test plates II-1.

  (III) The aqueous coating composition No. 1 obtained in Example 1 was spray-coated on the above material so that the cured film thickness became 35 μm. 1 was coated and cured in an environment of 23 ° C. and 50% for 7 days to obtain a test plate III-1.

Aqueous coating composition No. Production of Test Plates Nos. 2 to 12 In the same manner as in the production of the test plate of No. 1, the aqueous coating composition No. 1 was prepared. Using Test Nos. 2 to 12, test plates I-2 to I-12, II-2 to II-12, and III-2 to III-12 were obtained, respectively.

Performance Test and Performance Evaluation The performance of each test plate I-1 to I-12, II-1 to II-12, and III-1 to III-12 obtained in the production of the test plate was evaluated according to the following test method. Was. The test results are shown in Tables 2 and 3 below. In each test result, the evaluation levels of ◎, 及 び, and △ are acceptable levels.

Film-forming property: The film-forming property was evaluated by visually observing each of the test plates I-1 to I-12 and observing the presence or absence of cracks in the coating film with a microscope (magnification: 30 times).
：: No cracking of the coating film was observed even when observed with a microscope (30 times magnification).
Δ: Cracks were not visually observed, but cracks were observed in the coating film when observed with a microscope (30 times magnification).
×: Cracking of the coating film is visually observed.

Blocking resistance: The painted surfaces of two plates of each of the test plates II-1 to II-12 are overlapped with each other, and a weight is placed thereon so as to have a weight of 40 kgf / cm ^2, and held for 1 hour under a constant temperature environment. did. Thereafter, the weight was removed, the temperature was cooled to room temperature, and the blocking resistance was evaluated from the pressure-bonded state and the degree of peeling. In the following evaluation criteria, the higher the temperature, the more severe the test conditions.
◎: Test performed at 55 ° C., no pressure bonding of two sheets was observed.
：: No crimping of the two plates was observed at 45 ° C.
△: No crimping of the two plates was observed at 35 ° C.
Δ: The test was conducted at 35 ° C., and pressure bonding was observed on the two plates, but no destruction of the coating film was observed when the two plates were peeled off.
×: The test was conducted at 35 ° C., and pressure bonding was observed on the two plates, and destruction of the coating film was observed when the two plates were peeled off.

Adhesion: 100 pieces of 2 mm x 2 mm gobangs were made on the coated surface of each test plate II-1 to II-12 according to JIS K 5600-5-6 (1990), and an adhesive tape was stuck on the surface. Then, the remaining state of the peeled-off paint film after rapid peeling was examined, and the adhesion was evaluated according to the following criteria.
A: Remaining number / total number = 100/100 No marginal defects were found on the goban.
：: The remaining number / total number = 100/100, and a marginal edge is recognized in the goban.
Δ: Remaining number / total number = 80 to 99/100 ×: Remaining number / total number = 0 to 99/100 Rust prevention: The back and end of each test plate III-1 to III-12 The same aqueous coating composition No. as the surface After coating and drying using 1 to 12 and making a cut in accordance with a) of 7.5 (How to make a cut) in JIS K 5600-7-9, a cut is made and then attached to JIS K 5600-7-9. The cycle corrosion test under the conditions shown in Book 1 (Cycle D) was performed for 36 cycles.

After the completion of 36 cycles, the test plate was thoroughly washed with ion-exchanged water, the surface moisture was wiped off, and the rust prevention was evaluated as follows. In the evaluation, sites within about 10 mm around the test piece were excluded from the evaluation, and stains due to rust juice were also excluded from the evaluation.
A: No swelling, peeling or rust was observed on the general surface of the test plate, and the swelling or maximum rust width around the cut was within 1 mm.
：: No blister, peeling or rust was observed on the general surface of the test plate, and the blister or maximum rust width around the cut was more than 1 mm and less than 2 mm.
Δ: Blistering, peeling or rust is observed on a part of the general surface of the test plate.
×: Either blistering, peeling or rust is observed on the entire surface of the test plate.

  Both dry coating and baking coating are possible, and can be applied not only outdoors at construction sites, but also on production lines for painted steel, etc. Can be manufactured with high productivity.

Claims (5)

  A urethane resin particle (A) having a weight average molecular weight of 100,000 to 5,000,000 and a glass transition temperature of 30 to 100 ° C and an acrylic resin particle (B) having a glass transition temperature of -20 to 30 ° C; The urethane resin particles (A) are 40 to 80% by mass, and the acrylic resin particles (B) are 20 to 60% by mass, as the solid content, based on the total solid content of the resin particles (A) and the acrylic resin particles (B). An aqueous coating composition characterized by the following.   The aqueous coating composition according to claim 1, further comprising a rust inhibitor (C).   The aqueous coating composition according to claim 1, further comprising a pigment (D).   The rust preventive (C) and the total solid content of the pigment (D) are 10 to 400 mass% with respect to the total solid content of the urethane resin particles (A) and the acrylic resin particles (B). An aqueous coating composition according to any one of the preceding claims.   A coating method comprising a step of preheating an object to be coated, coating the aqueous coating composition according to any one of claims 1 to 4, and then drying it with residual heat.