Water-based paint composition and coated body

Abstract

To provide a coating composition which enables formation of a coated body that is excellent in coated film dryness and blocking resistance when an aqueous coating material is coated at a factory, and is excellent in water resistance.SOLUTION: An aqueous coating composition contains a water-dispersible resin (A) and a film-forming auxiliary (B), wherein the water-dispersible resin (A) contains a water-dispersible resin (A-1) which includes a monomer having an SP value of 11.0-13.0 and a monomer having an SP value of 8.5 or more and less than 9.5 as constitutional units and has a weight average molecular weight of 50,000 or more, the film-forming auxiliary (B) contains a film-forming auxiliary having a boiling point of 150-280°C, and a softening point of a coated film formed of the aqueous coating composition is 0-100°C.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aqueous paint composition and a coated body using the paint composition. In particular, when the aqueous paint is applied in a factory, it relates to a paint composition capable of forming a coated body that is excellent in film drying properties, blocking resistance, and water resistance.

Background Art

[0002] As paint compositions applied to metal substrates, various paint compositions have been proposed. From the perspective of reducing environmental impact, aqueous paint compositions are desired and various proposals have been made.

[0003] Japanese Patent Application Laid-Open No. 7-300574 (Patent Document 1) describes an invention related to an aqueous coating composition containing an aqueous acrylic-modified alkyd resin and an aqueous acrylic-modified epoxy resin as binders. Such an invention relates to an aqueous coating composition that is suitable for rust prevention of lightweight steel and is aqueous and has ultra-fast drying properties. The invention described in Patent Document 1 has roll-touch film peelability after a few seconds of coating, oil surface adhesion, high-temperature finishability without sagging over a wide temperature distribution range of 70 to 120 °C, good blocking resistance even in stacking after a few minutes of coating, and can provide a coating film with excellent rust prevention properties. However, since it contains a certain amount of alkyd resin, it has a problem in the drying property of the coating film when coated in a factory at a temperature lower than 70 °C.

[0004] Japanese Patent Application Laid-Open No. 2005-349684 (Patent Document 2) describes an invention that provides a resin-coated surface-treated steel sheet having an excellent blocking-resistant and colorless transparent resin film by using a core-shell type emulsion resin in which the Tg of the outermost shell part is higher than the Tg of the central part of the particles.

[0005] Japanese Patent Publication No. 2020-2327 (Patent Document 3) describes an invention relating to an aqueous coating composition that can be applied by both air-drying and baking coatings and can form a coating film with excellent film-forming properties, blocking resistance, and rust prevention properties. This invention relates to an aqueous coating composition containing urethane resin particles with a glass transition temperature of 30 to 100°C and acrylic resin particles with a glass transition temperature of -20 to 30°C in a certain proportion. The invention described in Patent Document 3 can solve the problem of blocking resistance in factory painting by blending two types of resin components with different glass transition temperatures, but it does not take into consideration film-forming properties or drying properties in the initial stages of coating film formation, and there was room for improvement in the water resistance of the resulting coating film.

[0006] Japanese Patent Publication No. 2009-270034 (Patent Document 4) describes an invention relating to an aqueous resin composition for enamel paints, characterized by containing an aqueous resin dispersion and a crosslinking agent as essential components, and states that a coating film with excellent weather resistance and blocking resistance can be formed by using this aqueous resin composition. Specifically, the aqueous resin dispersion contains an alkoxysilane group-containing polymerizable monomer (A) and a cycloalkyl group-containing polymerizable monomer (B) as high Tg resin components, and states that it is important to use 0.1 to 10% by mass of the total polymerizable monomer used to obtain the aqueous resin dispersion as alkoxysilane group-containing polymerizable monomer, and 5 to 45% of the total polymerizable monomer used to obtain the aqueous resin dispersion as cycloalkyl group-containing polymerizable monomer. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 7-300574 [Patent Document 2] Japanese Patent Publication No. 2005-349684 [Patent Document 3] Japanese Patent Publication No. 2020-2327 [Patent Document 4] Japanese Patent Publication No. 2009-270034 [Overview of the project] [Problems that the invention aims to solve]

[0008] Although the inventions described in Patent Documents 1 to 4 aim to solve the problem of blockage resistance, they do not take into consideration film formation properties or drying properties in the initial stages of coating film formation, and there is room for improvement in the water resistance of the resulting coating film. In particular, when a core-shell type water-dispersible resin with a high Tg of the shell layer or a water-dispersible resin containing alkoxysilane group polymerizable monomers as constituent units is used in an aqueous coating to improve blockage resistance, the resin particles do not fuse completely during drying for coating film formation, making it easy to form interparticle pockets that create small defects. Water penetrates into the coating film through these interparticle pockets, resulting in a deterioration of water resistance.

[0009] Therefore, the object of the present invention is to provide a paint composition that can form a coated body with excellent coating film drying properties, excellent blocking resistance, and excellent water resistance when water-based paint is applied in a factory. [Means for solving the problem]

[0010] To achieve the above objective, the inventors first investigated water-dispersible resins and film-forming aids. To improve blocking resistance, a method of increasing the hardness of the coating film by using a resin with a high glass transition temperature (Tg) is effective. However, film formation (coating formation) of aqueous resin dispersions (dispersions in which water-dispersible resin is dispersed in an aqueous medium) is carried out by the fusion and bonding of resin particles, so film formation tends to be insufficient (this can also worsen water resistance due to the formation of interparticle pockets). For this reason, it is common to use film-forming aids when forming aqueous dispersions containing water-dispersible resins with a high glass transition temperature (Tg), but there was a problem that blocking resistance worsened if the formed coating film was not dried sufficiently. In addition, if water or film-forming aids remain in the coating film, water resistance tends to worsen. Furthermore, if the fusion of resin particles is insufficient, there was also a problem that coating defects were more likely to occur.

[0011] Under these circumstances, the inventors discovered that by combining a water-dispersible resin with a weight-average molecular weight of 50,000 or more, containing monomers with an SP value of 11.0 to 13.0 as constituent units, with a film-forming aid having a boiling point in the range of 150 to 280°C, the fusion of resin particles is promoted, improving film-forming properties and enhancing water resistance. Furthermore, by using monomers with an SP value of 8.5 or more and less than 9.5 as constituent units of such a water-dispersible resin, the drying properties of the coating film can be improved. In addition, the inventors confirmed that if the softening point of the coating film (the temperature at which the storage modulus (E') inflection point is 0°C or higher) is measured by viscoelasticity testing of the formed coating film, a coating film with excellent blocking resistance can be obtained. This led to the completion of the present invention.

[0012] Therefore, the aqueous coating composition of the present invention is an aqueous coating composition comprising a water-dispersible resin (A) and a film-forming aid (B), The water-dispersible resin (A) includes a water-dispersible resin (A-1) having a weight-average molecular weight of 50,000 or more, which comprises monomers with an SP value of 11.0 to 13.0 and monomers with an SP value of 8.5 or more and less than 9.5 as constituent units. The aforementioned film-forming aid (B) includes a film-forming aid with a boiling point in the range of 150 to 280°C. The aqueous coating composition is characterized in that the coating film formed from the aqueous coating composition has a softening point of 0°C to 100°C, where the softening point is the temperature (°C) of the inflection point of the storage modulus (E'(Pa)) obtained by dynamic viscoelasticity measurement (DMA) under the following measurement conditions. <Measurement conditions> Temperature range: -50℃ to 200℃ Heating rate: 5°C / min Measurement length: 20.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0013] Another preferred example of the aqueous coating composition of the present invention further comprises a water-dispersible and / or water-soluble resin other than the water-dispersible resin (A-1).

[0014] Further, the coated body of the present invention is a coated body having a coating film formed from the aqueous paint composition of the present invention described above on a substrate.

Effects of the Invention

[0015] According to the aqueous paint composition of the present invention, it is possible to provide a paint composition capable of forming a coated body that is excellent in coating film drying property, blocking resistance, and water resistance when the aqueous paint is applied in a factory. Further, according to the coated body of the present invention, it is possible to provide a coated body using such an aqueous paint composition.

Modes for Carrying Out the Invention

[0016] The present invention will be described in detail below. The present invention relates to an aqueous paint composition and a coated body.

[0017] One aspect of the present invention is an aqueous paint composition containing a water-dispersible resin and a film-forming aid. In this specification, this aqueous paint composition is also referred to as "the aqueous paint composition of the present invention" or "the paint composition of the present invention". An "aqueous paint composition" is a paint composition containing water as a main solvent. Further, the "water-dispersible resin" is referred to as component (A), and also as "water-dispersible resin (A)". The "film-forming aid" is referred to as component (B), and also as "film-forming aid (B)".

[0018] The water used in the paint composition of the present invention is not particularly limited, but pure water such as tap water, ion-exchanged water, distilled water, etc. is preferably mentioned. Further, when the paint composition is stored for a long time, water sterilized by ultraviolet irradiation or the like may be used in order to prevent the generation of mold and bacteria. In the paint composition of the present invention, the amount of water is preferably 20 to 60% by mass, and more preferably 30 to 50% by mass.

[0019] The coating composition of the present invention contains a film-forming aid (B) from the viewpoint of ensuring the film-forming property of the coating film and thereby obtaining water resistance. The film-forming aid (B) is generally an organic solvent blended for the purpose of imparting film-forming property and does not correspond to the coating film-forming components. The film-forming aid (B) preferably softens the water-dispersible resin (A-1) described later, makes it easier to lower the minimum film-forming temperature (MFT), and volatilizes rapidly from the coating film during drying. From this, the film-forming aid (B) preferably contains a film-forming aid within the range of 150 to 280 °C in boiling point, preferably within the range of 160 to 260 °C. In this specification, the boiling point refers to the boiling point at 1 atmospheric pressure.

[0020] Among the film-forming aids (B), examples of the film-forming aids within the range of 150 to 280 °C in boiling point include propylene glycol, propylene glycol monomethyl ether (PGMME), propylene glycol monoethyl ether, propylene glycol monopropyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monon-butyl ether, ethylene glycol monoiso-butyl ether, ethylene glycol monotert-butyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monon-butyl ether, diethylene glycol monoiso-butyl ether, diethylene glycol monotert-butyl ether, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol monobutyl ether, etc. Examples of the film-forming aids with a boiling point of less than 150 °C or exceeding 280 °C include propylene glycol monomethyl ether, ethylene glycol diethyl ether, ethylene glycol monoethyl ether, ethylene glycol isopropyl ether, polyethylene glycol monomethyl ether, benzyl diglycol, triethylene glycol, etc.

[0021] In the paint composition of the present invention, excellent film-forming properties can be obtained by combining the water-dispersible resin (A-1) described later with a film-forming aid having a boiling point in the range of 150 to 280°C. This improves water resistance and also allows for a reduction in the amount of film-forming aid (B) used, thereby further improving the drying properties of the paint film.

[0022] In the coating composition of the present invention, the amount of film-forming aid (B) is preferably 0.1 to 20.0% by mass, and more preferably 0.5 to 10.0% by mass. Furthermore, the proportion of film-forming aids with a boiling point in the range of 150 to 280°C in the total amount of film-forming aid (B) is preferably 50% by mass or more, and more preferably 90% by mass or more. The organic solvent may be used alone or in combination of two or more. In particular, using a combination of a film-forming aid with a boiling point of 150 to less than 200°C and a film-forming aid with a boiling point of 200°C to 280°C results in better coating film drying properties.

[0023] The coating composition of the present invention may contain an additional organic solvent in addition to the film-forming aid (B). The organic solvent other than the film-forming aid (B) is not particularly limited, and any organic solvent commonly used in the coating industry can be used. For example, various organic solvents such as alcohol-based solvents, ketone-based solvents, ester-based solvents, ether-based solvents, hydrocarbon-based solvents, amine-based solvents, and amide-based solvents can be used, but it is preferable to include a water-soluble organic solvent.

[0024] Examples of alcoholic solvents include methanol, ethanol, and butanol; examples of ketone solvents include acetone, methyl ethyl ketone, and methyl isobutyl ketone; examples of ester solvents include ethyl acetate and butyl acetate; and examples of ether solvents include ethylene glycol monoethyl ether and methyl carbitol. Solvents that have both hydroxyl groups and ether bonds, such as ethylene glycol monoethyl ether and methyl carbitol, are classified as ether solvents as described above. Examples of hydrocarbon solvents include aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons, and more specifically, toluene, xylene, solvent naphtha, mineral spirits, hexane, cyclohexane, octane, and terpene oils. Examples of amine-based or amide-based solvents include N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, N-methylethanolamine, and N-methyldiethanolamine.

[0025] If the coating composition of the present invention further contains organic solvents other than the film-forming aid (B), the total amount of organic solvents in the coating composition is preferably 0.1 to 30% by mass, and more preferably 0.5 to 20% by mass. Here, the total amount of organic solvents is the sum of the film-forming aid (B) and the other organic solvents.

[0026] The paint composition of the present invention comprises a water-dispersible resin (A). In this specification, "water-dispersible resin" refers to a resin that can be distributed in water to form a heterogeneous system (e.g., an emulsion or suspension). The water-dispersible resin (A) is dispersed in the paint composition of the present invention.

[0027] Water-dispersible resins can be prepared, for example, by emulsifying the water-dispersible resin in water or by emulsion polymerization of monomer components, using a surfactant as needed while applying forced shear force by using a high-speed stirrer or the like. Alternatively, an aqueous resin dispersion can be prepared by adding a surfactant as needed to a water-dispersible resin polymerized in an organic solvent medium and performing a phase conversion into water, and the organic solvent contained in the aqueous resin dispersion may be removed by distillation or the like as needed. Furthermore, an aqueous resin dispersion can also be prepared by polymerizing in water using water as the medium.

[0028] Water-dispersible resins can be classified into emulsion resins and dispersion resins. Emulsion resins refer to water-dispersible resins obtained by emulsion polymerization. Dispersion resins refer to self-water-dispersible resins, but emulsion resins are excluded in this specification. Also, resins that dissolve in water are water-soluble resins.

[0029] In the paint composition of the present invention, the water-dispersible resin (A) includes a water-dispersible resin (A-1) with a weight-average molecular weight of 50,000 or more, which contains monomers with an SP value of 11.0 to 13.0 and monomers with an SP value of 8.5 or more and less than 9.5 as constituent units. Since the water-dispersible resin (A-1) contains monomers with an SP value of 11.0 to 13.0 as constituent units, film-forming aids (B), particularly those with a boiling point in the range of 150 to 280°C, can easily penetrate the dispersed resin particles, promoting the fusion of resin particles during film formation. This improves film-forming properties and enhances water resistance. Furthermore, since the water-dispersible resin (A-1) also contains monomers with an SP value of 8.5 or more and less than 9.5 as constituent units, it can promote the evaporation of solvents, particularly water, contained in the paint composition, thereby improving the drying properties of the paint film. In addition, the effect of improved water resistance due to monomers with an SP value of 8.5 or more and less than 9.5 can also be obtained.

[0030] The SP value (solubility parameter) is a guideline for determining compatibility. While various calculation and measurement methods exist, in this specification, the SP value refers to the solubility parameter calculated by the Hoy method based on the structure. Here, the SP value of a monomer refers to the SP value of the monomer homopolymer, calculated using the vapor pressure method proposed by Hoy, in accordance with the method described in the literature [KL Hoy, J. Paint Technology, 42,

[0541] , 76 (1970)]. Specifically, the SP value is expressed as δ = (dΣG) / M, where d is the polymer density, M is the molecular weight of the basic structural unit of the polymer, and ΣG is the sum of the molecular attractive constants G corresponding to the atoms (groups) present in the basic structural unit. Furthermore, the SP value of an organic solvent is calculated using the vapor pressure method proposed by Hoy, in accordance with the method described in the literature [KL Hoy, J. Paint Technology, 42,

[0541] , 76 (1970)].

[0031] Examples of monomers with SP values ​​between 11.0 and 13.0 include hydroxyethyl methacrylate (11.9), hydroxyethyl acrylate (12.8), 4-hydroxybutyl acrylate (11.8), hydroxypropyl methacrylate (11.2 / 11.4), and acrylonitrile (12.4). Here, the numbers in parentheses are the SP values ​​of the above monomers (i.e., the SP values ​​of the monomer homopolymers).

[0032] The amount of monomers with an SP value of 11.0 to 13.0 contained as constituent units in the water-dispersible resin (A-1) is preferably 0.1 to 50% by mass, more preferably 1 to 35% by mass, and even more preferably 5 to 25% by mass, relative to the total amount of the water-dispersible resin (A-1). Monomers with an SP value of 11.0 to 13.0 may be used individually or in combination of two or more types.

[0033] Examples of monomers with an SP value of 8.5 or higher and less than 9.5 include ethyl methacrylate (9.4), t-butyl methacrylate (8.8), n-butyl methacrylate (9.3), ethylhexyl methacrylate (9.0), stearyl methacrylate (8.9), isobutyl acrylate (9.4), isobutyl methacrylate (9.3), 2-ethylhexyl acrylate (9.2), cyclohexyl methacrylate (9.48), styrene (9.4), α-methylstyrene (9.0), lauryl methacrylate (9.0), and methacrylic acid (8.2). Here, the numbers in parentheses are the SP values ​​of the above monomers (i.e., the SP values ​​of the monomer homopolymers).

[0034] The amount of monomers with an SP value of 8.5 or more and less than 9.5 included as constituent units in the water-dispersible resin (A-1) is preferably 0.1 to 75% by mass, and more preferably 10.0 to 60.0% by mass, relative to the total amount of the water-dispersible resin (A-1). Monomers with an SP value of 8.5 or more and less than 9.5 may be used individually or in combination of two or more types.

[0035] The water-dispersible resin (A-1) may contain monomers that do not fall under the category of monomers with an SP value of 11.0 to 13.0 or monomers with an SP value of 8.5 or more and less than 9.5 as constituent units. In this specification, such monomers will be described as third monomers.

[0036] The water-dispersible resin (A-1) may contain a hydroxyl group-containing monomer as a third monomer. The hydroxyl group-containing monomer as the third monomer can contribute to improved film-forming properties and thus to improved water resistance, although not to the same extent as monomers with an SP value of 11.0 to 13.0. Examples of hydroxyl group-containing monomers as the third monomer include N-hydroxymethyl(meth)acrylamide, allyl alcohol, and (meth)acrylates having polyoxyethylene chains with hydroxyl groups at the molecular ends.

[0037] The amount of hydroxyl group-containing monomer as a third monomer included as a constituent unit in the water-dispersible resin (A-1) is, for example, 0.1 to 10% by mass, and preferably 0.2 to 5% by mass, relative to the total amount of the water-dispersible resin (A-1). The hydroxyl group-containing monomer as the third monomer may be used alone or in combination of two or more types.

[0038] The water-dispersible resin (A-1) may contain a monomer having a cyclic structure as a third monomer. The monomer having a cyclic structure as the third monomer can contribute to improved water resistance. The cyclic structure is preferably a benzene ring. Examples of the monomer having a cyclic structure as the third monomer include benzyl (meth)acrylate and vinylpyrrolidone.

[0039] The amount of the cyclic monomer, which is a third monomer included as a constituent unit in the water-dispersible resin (A-1), is, for example, 0.1 to 20.0% by mass, and preferably 1.0 to 10.0% by mass, relative to the total amount of the water-dispersible resin (A-1). The cyclic monomer, which is the third monomer, may be used alone or in combination of two or more types.

[0040] Examples of a third monomer that may be included as a constituent unit of the water-dispersible resin (A-1) include, in addition to the hydroxyl group-containing monomers and monomers having a cyclic structure mentioned above, methyl methacrylate (MMA), butyl acrylate (AB), ethyl acrylate (EA), acrylic acid (AA), glycidyl methacrylate (GMA), and the like.

[0041] The weight-average molecular weight of the water-dispersible resin (A-1) is 50,000 or more, preferably between 60,000 and 500,000. By setting the weight-average molecular weight of the water-dispersible resin (A-1) to 50,000 or more, the penetration of the film-forming aid (B), especially film-forming aids with a boiling point in the range of 150 to 280°C, into the resin is increased, thereby improving film formation. Furthermore, if the weight-average molecular weight of the water-dispersible resin (A-1) is 50,000 or more, coating film performance such as water resistance can also be improved.

[0042] In this specification, the molecular weight of the resin is the weight-average molecular weight measured by gel permeation chromatography [e.g., HLC-8220GPC and HLC-8320EcoSEC instruments manufactured by Tosoh Corporation], and polystyrene is used as the standard substance. The sample to be measured is prepared by dissolving 20-40 mg of resin in 10 ml of tetrahydrofuran or dimethylformamide reagent, and then filtering it through a filter (e.g., PTFE membrane filter T100A025A). At this point, if the sample solution is opaque or if the filter becomes clogged, accurate molecular weight measurement is not possible, and the measurement is deemed impossible. Resins whose molecular weight cannot be measured in this way, so-called unmeasurable resins, are considered to be high molecular weight resins, and their weight-average molecular weight is considered to be 50,000 or more.

[0043] The water-dispersible resin (A-1) is preferably a water-dispersible resin containing an acrylic component as a constituent unit. In this specification, "acrylic component" refers to acrylic acid, methacrylic acid and its derivatives (for example, compounds having a (meth)acryloyl group such as esters and amides of acrylic acid and methacrylic acid, nitrile acrylate, nitrile methacrylic acid, etc.). The acrylic component may be used alone or in combination of two or more types.

[0044] Resins containing acrylic components as constituent units include not only acrylic resins, but also various modified resins such as acrylic styrene resins, acrylic silicone resins, fluorine-modified acrylic resins, fatty acid-modified acrylic resins, urethane-modified acrylic resins, and epoxy-modified acrylic resins.

[0045] In the coating composition of the present invention, the amount of water-dispersible resin (A-1) in the film-forming component is preferably 30 to 90% by mass. The water-dispersible resin (A-1) may be used alone or in combination of two or more types.

[0046] In this specification, the term "film-forming component" refers to the component excluding volatile components such as water and organic solvents, and is the component that ultimately forms a paint film. In this specification, the component remaining after drying the paint composition at 130°C for 60 minutes is treated as the film-forming component. In the paint composition of the present invention, the amount of the film-forming component is, for example, 50 to 70% by mass, and preferably 55 to 65% by mass.

[0047] The coating composition of the present invention may further contain water-dispersible and / or water-soluble resins other than water-dispersible resin (A-1). Here, water-dispersible resins other than water-dispersible resin (A-1) are resins included in water-dispersible resin (A), while water-soluble resins are resins distinct from water-dispersible resin (A). In this specification, water-dispersible and / or water-soluble resins other than water-dispersible resin (A-1) are also referred to as "resin (A-2)". Resin (A-2) may be used alone or in combination of two or more types.

[0048] Examples of resin (A-2) include resin (A-2-1) and resin (A-2-2), among others. Resin (A-2-1) Resin (A-2-1) is a water-dispersible and / or water-soluble resin with a weight-average molecular weight of less than 50,000. In the aqueous coating composition of the present invention, resin (A-2-1) can contribute to improved water resistance. Resin (A-2-2) Resin (A-2-2) is a water-dispersible and / or water-soluble resin with a weight-average molecular weight of 50,000 or more, and does not contain monomers with an SP value of 11.0 to 13.0 or monomers with an SP value of 8.5 or more and less than 9.5 as constituent units. In the aqueous coating composition of the present invention, if resin (A-2-2) is hard, it can contribute to blocking resistance, and if it is soft, it can contribute to film formation. It is preferable that the weight-average molecular weight of resin (A-2-2) is 100,000 or more.

[0049] For aqueous paint compositions such as the aqueous paint composition of the present invention, which are formulated with a water-dispersible resin (A-1) having a weight-average molecular weight of 50,000 or more, and optionally with a resin (A-2-2) and / or a pigment having a weight-average molecular weight of 50,000 or more, it is preferable to use resin (A-2-1) from the viewpoint of further improving the density and water resistance of the formed paint film. For this reason, the paint composition of the present invention preferably contains a water-dispersible and / or water-soluble resin with a weight-average molecular weight of less than 50,000 as resin (A-2-1), and more preferably contains a water-dispersible resin with a weight-average molecular weight of less than 50,000.

[0050] The resin (A-2-1) preferably has a weight-average molecular weight of 1,000 or more and less than 50,000, and more preferably 10,000 or more and less than 50,000. A resin (A-2-1) having such a weight-average molecular weight contributes to the water resistance and substrate adhesion of the coating film.

[0051] The resin (A-2-1) is preferably a resin that contains acrylic components as constituent units. The acrylic components may be used alone or in combination of two or more types.

[0052] In the coating composition of the present invention, the amount of resin (A-2-1) in the film-forming component is preferably 0.5 to 40% by mass, more preferably 1 to 20% by mass, and more preferably 1 to 15% by mass. Resin (A-2-1) may be used alone or in combination of two or more types.

[0053] The resin used in the coating composition of the present invention may have a uniform structure, or it may be resin particles having a heterogeneous structure, and may be in the form of a core-shell emulsion, a sea-island emulsion, or a multilayer emulsion having at least two glass transition temperatures. If a portion of the resin particles have a glass transition temperature in the high-temperature range, preferably 55°C to 155°C, the blocking resistance can be improved. The description of the resin here applies to either a water-dispersible resin (A-1) or a resin (A-2).

[0054] Resin particles can be obtained, for example, by a multi-stage emulsion polymerization method.

[0055] One multi-stage emulsion polymerization method that can be used to manufacture resin particles involves forming an aqueous emulsion containing an ethylenically unsaturated monomer, and then repeatedly performing two or more, usually two to five, conventional emulsion polymerization methods to form an emulsion copolymer of the ethylenically unsaturated monomer that has a heterogeneous structure, i.e., particles consisting of an outermost phase with different properties and one or more internal phases.

[0056] A typical example of a multi-stage emulsion polymerization method is a method in which an emulsifier and polymerization initiator, along with a chain transfer agent and emulsion stabilizer as needed, are present in an aqueous emulsion containing an ethylenically unsaturated monomer, and emulsion polymerization is carried out under heating at a temperature of usually 60 to 90°C, with this process being repeated multiple times.

[0057] Furthermore, examples of ethylenically unsaturated monomers that can be used to form resin particles include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, α-chloroethyl (meth)acrylate, and cyclohexyl (meth)acrylate. (Meth)acrylate monomers such as syl(meth)acrylate, phenyl(meth)acrylate, methoxyethyl(meth)acrylate, ethoxyethyl(meth)acrylate, methoxypropyl(meth)acrylate, and ethoxypropyl(meth)acrylate; styrene and / or styrene derivatives such as methylstyrene, chlorostyrene, and methoxystyrene; carboxyl group-containing monomers such as (meth)acrylic acid, crotonic acid, itaconic acid, itaconic acid half-ester, maleic acid, and maleic acid half-ester; 2 Hydroxyl group-containing monomers such as hydroxyethyl (meth)acrylate, 2(3)-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl acrylate; amide group-containing monomers such as (meth)acrylamide and maleinamide; amino group-containing monomers such as 2-aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, 3-aminopropyl (meth)acrylate, 2-butylaminoethyl (meth)acrylate, and vinylpyridine; glycidyl (meth)acrylate and allyl glycidyl Luethers, epoxy group-containing monomers and oligomers obtained by the reaction of epoxy compounds having two or more glycidyl groups with ethylenically unsaturated monomers having active hydrogen atoms; other N-methylolacrylamides having N-methylol groups; UV-stable monomers such as 4-(meth)-acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(meth)-acryloylamino-2,2,6,6-tetramethylpiperidine, and 4-(meth)-acryloyloxy-1,2,2,6,6-pentamethylpiperidine;UV-absorbing monomers such as 2-[2'-hydroxy-5'-(methacryloyloxymethyl)phenyl]-2H-benzotriazole and 2-[2'-hydroxy-5'-(methacryloyloxyethyl)phenyl]-2H-benzotriazole; vinyl acetate, vinyl chloride, and also ethylene, butadiene, acrylonitrile, and dialkyl fumarates are typical examples.

[0058] The polymer forming at least one phase of the resin particles may have an internal crosslinking structure. The polymer having the internal crosslinking structure can be produced by emulsion polymerization using monomers having two or more polymerizable unsaturated double bonds in the molecule, such as divinylbenzene, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and allyl(meth)acrylate, as part of the ethylenically unsaturated monomer; by emulsion polymerization using a monomer mixture that selectively contains ethylenically unsaturated monomers having a combination of monomers with functional groups that react with each other at the temperature of the emulsion polymerization reaction, for example, a combination of a carboxyl group and a glycidyl group, or a hydroxyl group and an isocyanate group; or by emulsion polymerization using a monomer mixture that contains silyl group-containing ethylenically unsaturated monomers such as (meth)acryloxypropyltrimethoxysilane, (meth)acryloxypropyltriethoxysilane, and (meth)acryloxypropylmethyldimethoxysilane, which undergo hydrolysis condensation reactions.

[0059] Examples of emulsifiers that can be used to form resin particles include fatty acid salts such as sodium laurate, higher alcohol sulfate salts such as sodium lauryl sulfate, alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, polyoxyethylene alkyl ether sulfates, polyoxynonylphenyl ethersulfonate ammonium, polyoxyethylene-polyoxypropylene glycol ether sulfates, and anionic surfactants such as so-called reactive emulsifiers having a polymerizable carbon-carbon unsaturated double bond in the molecule with a sulfonic acid group or sulfate ester group; nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene nonylphenyl ethers, sorbitan fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene-polyoxypropylene block copolymers, or reactive nonionic surfactants having a polymerizable carbon-carbon unsaturated double bond in the molecule with the backbone of these compounds; cationic surfactants such as alkylamine salts and quaternary ammonium salts; and (modified) polyvinyl alcohol.

[0060] Examples of emulsifiers include anionic emulsifiers, nonionic emulsifiers, cationic emulsifiers, amphoteric emulsifiers, and polymer emulsifiers. These emulsifiers may be used individually or in combination of two or more types.

[0061] Examples of anionic emulsifiers include alkyl sulfate salts such as ammonium dodecyl sulfate and sodium dodecyl sulfate; alkyl sulfonate salts such as ammonium dodecyl sulfonate, sodium dodecyl sulfonate, and sodium alkyldiphenyl ether disulfonate; alkylaryl sulfonate salts such as ammonium dodecylbenzene sulfonate and sodium dodecylnaphthalene sulfonate; polyoxyethylene alkyl sulfonate salts; polyoxyethylene alkyl sulfate salts; polyoxyethylene alkylaryl sulfate salts; dialkyl sulfosuccinates; aryl sulfonic acid-formaldehyde condensates; and Examples include fatty acid salts such as monium laurylate and sodium stearate; sulfate esters or salts thereof having an allyl group, such as bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfonate salt, propenyl-alkyl sulfosuccinate salt, (meth)acrylate polyoxyethylene sulfonate salt, (meth)acrylate polyoxyethylene phosphate salt, and sulfonate salt of allyloxymethylalkyloxypolyoxyethylene; sulfate ester salts of allyloxymethyl alkoxyethyl polyoxyethylene, polyoxyalkylene alkenyl ether sulfate ammonium salt, etc., but the present invention is not limited to these examples.

[0062] Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, condensates of polyethylene glycol and polypropylene glycol, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid monoglycerides, condensation products of ethylene oxide and aliphatic amines, allyloxymethyl alkoxyethyl hydroxypolyoxyethylene, and polyoxyalkylene alkenyl ethers, but the present invention is not limited to these examples.

[0063] Examples of cationic emulsifiers include alkylammonium salts such as dodecylammonium chloride, but the present invention is not limited to these examples.

[0064] Examples of amphoteric emulsifiers include betaine ester type emulsifiers, but the present invention is not limited to these examples.

[0065] Examples of polymer emulsifiers include poly(meth)acrylates such as sodium polyacrylate; polyvinyl alcohol; polyvinylpyrrolidone; polyhydroxyalkyl(meth)acrylates such as polyhydroxyethyl acrylate; and copolymers in which one or more monomers constituting these polymers are copolymerized components. However, the present invention is not limited to these examples.

[0066] Furthermore, as an emulsifier, from the viewpoint of obtaining an aqueous resin composition and aqueous paint that is comprehensively excellent in terms of resistance to hot water whitening, freeze-thaw resistance, and blocking resistance, an emulsifier having a polymerizable group, i.e., a so-called reactive emulsifier, is preferred, and from the viewpoint of environmental protection, a non-nonylphenyl type emulsifier is preferred.

[0067] Examples of reactive emulsifiers include propenyl-alkyl sulfosuccinate salts, (meth)acrylate polyoxyethylene sulfonate salts, (meth)acrylate polyoxyethylene phosphate salts [e.g., Sanyo Chemical Industries, Ltd., product name: Eleminol RS30, etc.], polyoxyethylene alkylpropenylphenyl ether sulfonate salts [e.g., Daiichi Kogyo Seiyaku Co., Ltd., product name: Aqualon HS-10, etc.], allyloxymethylalkyloxypolyoxyethylene sulfonate salts [e.g., Daiichi Kogyo Seiyaku Co., Ltd., product name: Aqualon KH-10, etc.], allyloxymethylnonylphenoxyethyl hydroxypolyoxyethylene sulfonate salts [e.g., ADEKA Corporation, product name: Adekarya Soap SE-10, etc.], allyloxymethyl alkoxyethyl hydroxypoly Examples of polyoxyethylene sulfate salts (e.g., ADEKA Corporation, product names: Adekarya Soap SR-10, SR-30, etc.), bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfonate salts (e.g., Nippon Emulsifier Co., Ltd., product name: Antox MS-60, etc.), allyloxymethyl alkoxyethyl hydroxypolyoxyethylene (e.g., ADEKA Corporation, product name: Adekarya Soap ER-20, etc.), polyoxyethylene alkylpropenylphenyl ethers (e.g., Daiichi Kogyo Seiyaku Co., Ltd., product name: Aqualon RN-20, etc.), allyloxymethyl nonylphenoxyethyl hydroxypolyoxyethylene (e.g., ADEKA Corporation, product name: Adekarya Soap NE-10, etc.) are examples, but the present invention is not limited to these examples.

[0068] In the formation of resin particles, polymerization initiators that have been commonly used in radical polymerization can be used, and among them, water-soluble ones are preferred. Examples include persulfates such as potassium persulfate and ammonium persulfate; azo compounds such as 2,2'-azobis(2-aminodipropane) hydrochloride, 4,4'-azobis-cyanovaleric acid, and 2,2'-azobis(2-methylbutanamide oxime) dihydrochloride tetrahydrate; and peroxides such as hydrogen peroxide and t-butyl hydroperoxide. Furthermore, redox systems combining reducing agents such as L-ascorbic acid and sodium thiosulfate with ferrous sulfate can also be used.

[0069] Examples of chain transfer agents that can be used to form resin particles include alkyl mercaptans, aromatic mercaptans, and halogenated hydrocarbons. Among these, lauryl mercaptan, n-butyl mercaptan, t-butyl mercaptan, octyl mercaptan, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate, 2-methyl-t-butylthiophenol, carbon tetrabromide, and α-methylstyrene dimer are particularly suitable. By using these appropriately, the gloss, film-forming properties, and non-stick properties of the coating film can be controlled.

[0070] Examples of emulsifying stabilizers that can be used to form resin particles include polyvinyl alcohol, hydroxyethylcellulose, and polyvinylpyrrolidone.

[0071] Furthermore, examples of emulsion polymerization methods include the monomer batch loading method, in which monomers are loaded all at once; the monomer dropwise loading method, in which monomers are added continuously; the pre-emulsification method, in which monomers, water, and an emulsifier are pre-mixed and emulsified, and then added dropwise; and methods that combine these methods.

[0072] In the present invention, when producing resin particles by the above method, it is preferable to appropriately select a combination of ethylenically unsaturated monomers such that the theoretical Tg of the water-dispersible resin (A-1), which can be calculated from the FOX formula, is 40°C or higher, more preferably 50°C or higher, more preferably 55°C to 95°C, and more preferably 60°C to 90°C. Since the water-dispersible resin (A-1) has excellent softening properties with film-forming aids and coating film drying properties, setting the Tg of the water-dispersible resin (A-1) to 40°C or higher provides excellent blocking resistance and coating film drying properties, and the softened water-dispersible resin (A-1) during drying forms a dense film, resulting in a coating film with excellent water resistance. [FOX calculation formula] 1 / Tg=W1 / Tg1+W2 / Tg2+···+Wi / Tgi+···+Wn / Tgn In FOX's formula, Tg in the denominator on the left side represents the glass transition temperature (in K) of the polymer component consisting of N types of monomers, Tg(1, 2, i, N) represents the glass transition temperature (in K) of each monomer, W(1, 2, i, N) is the mass fraction of each monomer, and the relationship W1 + W2 + ... + Wi + ... + Wn = 1 holds. Here, the glass transition temperature of a monomer means the glass transition temperature of its homopolymer.

[0073] In the coating composition of the present invention, the total amount of resin in the film-forming component is, for example, 30.0 to 70.0% by mass. Here, the total amount of resin is the sum of the water-dispersible resin (A) [water-dispersible resin (A-1) and water-dispersible resins other than water-dispersible resin (A-1) which may be included] and water-soluble resins which may be included.

[0074] The paint composition of the present invention can use resins commonly used in the paint industry. Specifically, these include acrylic resins, silicone resins, acrylic silicone resins, styrene-acrylic copolymer resins, polyester resins, fluororesins, rosin resins, petroleum resins, coumarone resins, phenolic resins, urethane resins, melamine resins, urea resins, epoxy resins, cellulose resins, xylene resins, alkyd resins, aliphatic hydrocarbon resins, butyral resins, maleic acid resins, fumaric acid resins, vinyl resins, amine resins, ketimine resins, and the like.

[0075] The softening point of the coating film formed from the coating composition of the present invention is 0°C to 100°C, preferably 10°C to 90°C, and particularly preferably 15°C to 80°C. By setting the softening point of the coating film formed from the coating composition of the present invention to 0°C or higher, blocking resistance can be improved, and the coating film will not be damaged even when heavy coated substrates such as steel plates or ceramic building material boards are stacked.

[0076] In this specification, the softening point of a coating film is the temperature (°C) at the inflection point of the storage modulus (E'(Pa)) determined from the storage modulus (E') versus temperature graph obtained by dynamic viscoelasticity measurement (DMA).

[0077] The details of the method for measuring the storage modulus of a coating film, which is necessary to determine the softening point in this invention, are as follows: A coating composition is applied to a polypropylene (PP) board that has been preheated to 80°C using an applicator so that the dry film thickness is 40 to 100 μm, and an isolated film is obtained by forced drying at 80°C for 30 minutes. The storage modulus (E') of the isolated film is measured using a dynamic viscoelasticity tester (e.g., RSAG2 (manufactured by TA Instruments)) under the following measurement conditions. <Measurement conditions> Temperature range: -50℃ to 200℃ Heating rate: 5°C / min Measurement length: 20.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05% Although the storage modulus of a coating film is the object of measurement in this invention, the JIS K 7244-4:1999 standard "Plastics - Test methods for dynamic mechanical properties - Part 4: Tensile vibration - Non-resonant method," which tests polymers, can be used as a reference when measuring the storage modulus of a coating film.

[0078] From the measurement results of the storage modulus of the coating film, a graph of storage modulus (E') versus temperature (hereinafter also called the storage modulus change curve) is created with the vertical axis representing storage modulus (E') (in Pa) and the horizontal axis representing temperature (in °C). The temperature (°C) at the inflection point of the storage modulus (E') is determined, and this temperature (°C) at the inflection point of the storage modulus (E') is defined as the softening point. The temperature at the inflection point of the storage modulus (E') is the temperature at the intersection of the straight line in the glassy region and the straight line in the transition region of the storage modulus change curve. The "glassy region" is the region where the polymer (mainly resin) constituting the coating film is in a glassy state, and refers to the flat region on the low-temperature side of the storage modulus change curve. The "transition region" is the region where the polymer (mainly resin) constituting the coating film transitions from a glassy state to a rubbery state, and the storage modulus decreases sharply in the transition region. The "straight line in the glassy region" is the straight line before the storage modulus first decreases sharply, and the "straight line in the transition region" is the straight line after the storage modulus first decreases sharply. The "straight line in the glassy region" is extended towards the high-temperature side, and the "straight line in the transition region" is extended towards the low-temperature side, and the intersection point of the two extended lines is found. The temperature indicated by this intersection point is the temperature at the inflection point (softening point) of the storage modulus (E'). The temperature indicated by the intersection point (temperature at the intersection) can be found by drawing a vertical line from the intersection point to the horizontal axis.

[0079] To achieve a coating softening point of 10°C or higher, possible methods include raising the glass transition point of the coating-forming resin such as the water-dispersible resin (A), forming crosslinks within the coating, adjusting the particle size of the water-dispersible resin, or improving the drying properties of the film-forming aid. Furthermore, since the paint composition of the present invention is required to have excellent coating drying properties and water resistance as well as blocking resistance, it is preferable that the coating softening point is 100°C or lower.

[0080] The paint composition of the present invention may contain a crosslinking component as a constituent unit of the resin, or it may contain a crosslinking component as a crosslinking agent or the like. In this specification, a crosslinking component is a component that forms crosslinks in the resin constituting the paint film. By forming crosslinks in the paint film, the blocking resistance in the initial stages of paint film formation is improved, and the water resistance of the paint film after drying can be improved. Generally, the types of crosslinking in resins are broadly classified into interparticle crosslinking and intraparticle crosslinking. Either interparticle crosslinking or intraparticle crosslinking is acceptable, but interparticle crosslinking is preferred. Furthermore, the paint composition containing the crosslinked resin can be used in any form: one-component, two-component, or multi-component.

[0081] To form intraparticle crosslinks, methods include using monomers having two or more polymerizable unsaturated double bonds in their molecules, such as divinylbenzene, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and allyl(meth)acrylate, as crosslinking components; using monomers with functional groups that react with each other at the temperature of the emulsion polymerization reaction, such as monomers with combinations of functional groups like carboxyl and glycidyl groups, or hydroxyl and isocyanate groups, as crosslinking components; and using hydrolyzable silyl group-containing monomers that undergo hydrolysis condensation reactions, such as (meth)acryloxypropyltrimethoxysilane and (meth)acryloxypropylmethyldimethoxysilane, as crosslinking components. Thus, when forming intraparticle crosslinks, the crosslinking components are often the constituent units of the resin.

[0082] Methods for forming interparticle crosslinks include using a combination of monomers having functional groups such as carboxyl groups, glycidyl groups, carbonyl groups, and hydroxyl groups, and a crosslinking agent, as the crosslinking component. When forming interparticle crosslinks, the crosslinking component is often a combination of the constituent units of the resin and the crosslinking agent.

[0083] Examples of carboxyl group-containing monomers that can be used for interparticle crosslinking include (meth)acrylic acid, crotonic acid, itaconic acid, itaconic acid half-ester, maleic acid, maleic acid half-ester, etc. Examples of glycidyl group-containing monomers include glycidyl (meth)acrylate, etc. Examples of carbonyl group-containing monomers include acrolein, diacetone (meth)acrylamide, formyl styrene, (meth)acryloxyalkylpropanal, diacetone (meth)acrylate, acetonyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate-acetylacetate, butanediol-1,4-acrylate-acetylacrylate, vinyl ethyl ketone, vinyl isobutyl ketone, etc. Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2(3)-hydroxypropyl (meth)acrylate, 4-hydroxybutyl acrylate, etc. By using these monomers, functional groups such as carboxyl groups, glycidyl groups, carbonyl groups, and hydroxyl groups can be introduced into the resin.

[0084] Furthermore, crosslinking agents that can be used for interparticle crosslinking by reaction with carboxyl groups in resins include epoxy group-containing silanes, oxazoline group-containing polymers, carbodiimides, ethylene glycol glycidyl ethers, and metal chelates such as titanium chelates. Crosslinking agents that can be used for reaction with glycidyl groups in resins include amino group-containing silanes. Crosslinking agents that can be used for interparticle crosslinking by reaction with carbonyl groups in resins include carbohydrazides, dihydrazides of oxalate, and dihydrazides of malonate. Examples of crosslinking agents include dihydrazide, succinate dihydrazide, glutarate dihydrazide, adipic acid dihydrazide, sebacate dihydrazide, dodecane diacitate dihydrazide, isophthalate dihydrazide, citrate trihydrazide, 1,2,4-benzene trihydrazide, and thiocarbo dihydrazide. Examples of crosslinking agents that can be used for interparticle crosslinking by reaction with hydroxyl groups in the resin include metal alkoxides such as titanium alkoxide and zirconium alkoxide, and metal chelates such as titanium chelate.

[0085] When the coating film formed from the coating composition of the present invention has a crosslinked structure, the crosslinking density of the coating film is 1.0 × 10 -6 ~1.0×10 -2 It is preferable that the value be within the range of (mol / cc). The crosslinking density of the coating film is an indicator of the degree of crosslinking structure formed in the coating film; a higher value indicates a higher proportion of crosslinking structure formed in the coating film. By keeping the crosslinking density of the coating film within the specified range, the blocking resistance in the initial stages of coating film formation is improved, as is the water resistance of the coating film after drying.

[0086] In this specification, the crosslinking density of a coating film is given by the formula n = E' / 3RT, where n is the crosslinking density of the coating film (mol / cc), E' is the storage modulus of the coating film in the flat region at a frequency of 1 Hz (Pa), T is the absolute temperature of the storage modulus of the coating film in the flat region (K), and R is the gas constant (8.31 × 10⁻¹⁰). 6 It is calculated from Pa·cc / mol·K.

[0087] The details of the method for measuring the storage modulus of the flat region of a coating film are as follows: The coating composition is applied to a polypropylene (PP) plate preheated to 80°C using an applicator so that the dry film thickness is 40-100 μm, and an isolated film is obtained by forced drying at 80°C for 30 minutes. The storage modulus of the isolated film is measured using a dynamic viscoelasticity tester (e.g., RSAG2 (manufactured by TA Instruments)) under the following measurement conditions, and the storage modulus of the flat region of the coating film is read. Note that the storage modulus of the flat region of the coating film (E') can also be referred to as the storage modulus of the glassy region of the coating film (E'). <Measurement conditions> Temperature range: -50℃ to 200℃ Heating rate: 5°C / min Measurement length: 20.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0088] The aqueous coating composition of the present invention may contain a pigment. The pigment is not particularly limited, and pigments commonly used in the coating industry, such as rust-inhibiting pigments, extender pigments, and coloring pigments, can be used. The pigment may be used alone or in combination of two or more types.

[0089] When the paint composition of the present invention is used for line corrosion protection coating, it is preferable that it contains a rust-preventive pigment. Examples of rust-preventive pigments include zinc powder, zinc oxide, barium metaborate, calcium silicate, aluminum phosphate, condensed aluminum phosphate, aluminum tripolyphosphate, zinc phosphate, zinc phosphite, potassium phosphite, calcium phosphite, aluminum phosphite, calcium zinc phosphate, aluminum zinc phosphate, zinc phosphate, aluminum phosphate, zinc phosphate molybdate, aluminum phosphate molybdate, magnesium phosphate, vanadic acid / phosphate mixed pigment, etc., with zinc phosphate being particularly preferred. In the paint composition of the present invention, the amount of rust-preventive pigment is, for example, 1 to 8% by mass.

[0090] Examples of extender pigments include silica, talc, mica, calcium carbonate, and barium sulfate. In the paint composition of the present invention, the amount of extender pigment is, for example, 1 to 40% by mass.

[0091] Examples of coloring pigments include titanium dioxide, iron oxide, carbon black, lead yellow, molybdate orange, ultramarine, Prussian blue, phthalocyanine blue, phthalocyanine green, quinacridone red, naphthol red, benzimidazolone yellow, Hansa yellow, benzimidazolone orange, and dioxazine violet. In the paint composition of the present invention, the amount of coloring pigment is, for example, 1 to 30% by mass.

[0092] The paint composition of the present invention preferably has a pigment volume concentration (PVC) in the range of 0.1 to 35%, more preferably in the range of 1 to 30%, and even more preferably in the range of 5 to 25%. By setting the PVC within the above specified range, water resistance and blocking resistance can be improved. If the PVC is too high, water permeability increases, and corrosion resistance decreases.

[0093] In this specification, Pigment Volume Concentration (PVC) is the ratio of the total volume of pigment to the total volume of film-forming components in a paint composition, and can be calculated from the composition and specific gravity of each component constituting the film-forming components.

[0094] The coating composition of the present invention may contain, as appropriate, other components such as surface modifiers, wetting agents, dispersants, emulsifiers, thickeners, anti-settling agents, anti-skinning agents, anti-sagging agents, defoaming agents, anti-color separation agents, viscosity modifiers, rheology control agents, leveling agents, defoaming agents, drying agents, plasticizers, preservatives, antifungal agents, antibacterial agents, insecticides, light stabilizers, ultraviolet absorbers, antistatic agents, and conductivity imparters, depending on the purpose.

[0095] The paint composition of the present invention can be prepared by mixing various components as needed. The paint composition of the present invention may be in either a one-component type in which the various components are pre-mixed and used as is at the time of application, or a multi-component type (e.g., a two-component type) in which two or more components (e.g., a main agent and a hardener) that have been stored separately are mixed at the time of application.

[0096] The minimum film-forming temperature (MFT) of the coating composition of the present invention is preferably 0 to 40°C, and more preferably 5 to 30°C. For example, when using a resin with a high glass transition temperature, the minimum film-forming temperature will be higher, but it is possible to set the minimum film-forming temperature lower by appropriately incorporating a film-forming aid.

[0097] In this specification, the minimum film-forming temperature is the lowest temperature at which a uniform, crack-free coating film is formed when the coating composition is dried, and is measured in accordance with JIS K 6828-2:2003.

[0098] The paint composition of the present invention preferably has a viscosity of 1 to 1000 (Pa·s, 23°C) at a shear rate of 0.1 (1 / s), and a viscosity of 0.05 to 10 (Pa·s, 23°C) at a shear rate of 1000 (1 / s). In this specification, viscosity is measured using a rheometer (e.g., a rheometer ARES manufactured by TA Instruments) after adjusting the liquid temperature to 23°C.

[0099] The paint composition of the present invention may be either an enamel paint containing pigments or a transparent clear paint. However, when used as a topcoat layer to protect a metal substrate, it is preferable to use an enamel paint containing rust-preventive pigments, and is also preferable in terms of improving blocking resistance.

[0100] The coating method for the paint composition of the present invention is not particularly limited, and known coating methods such as brush coating, roller coating, trowel coating, spatula coating, flow coater coating, and spray coating (e.g., air spray coating, airless spray coating, etc.) can be used.

[0101] The drying method for the coating composition of the present invention is not particularly limited and may be either natural drying at ambient temperature or forced drying using a drying machine or the like.

[0102] The paint composition of the present invention can be applied under various painting conditions, such as general factory line painting conditions (forced drying, film thickness 15-30 μm) and conditions that conform to the JIS K5674 standard (room drying, film thickness 30 μm).

[0103] The paint composition of the present invention is preferably applied to a preheated steel plate in a 100 μm thickness, and under conditions where the steel plate maintains a temperature of 35 to 45°C, the surface drying time measured according to JIS K 5600-3-2 (Barotini method) is 10 seconds or more and less than 10 minutes, preferably 10 seconds to 5 minutes. Here, "preheated steel plate" refers to a steel plate whose painted surface temperature is maintained at 35 to 45°C. The numerical value "100 μm" in "100 μm coating" refers to the film thickness immediately after coating and before drying. Under these conditions, a surface drying time of 10 seconds or more and less than 10 minutes allows for the formation of a paint film with excellent drying properties during factory painting, and enables the formation of a painted body with excellent blocking resistance.

[0104] Another aspect of the present invention is a coated body having a substrate and a coating film on the substrate, wherein the coating film is formed from the aqueous coating composition of the present invention. In this specification, this coated body will be referred to as "the coated body of the present invention".

[0105] In the coated body of the present invention, the substrates include, for example, plastic substrates such as epoxy resin, ABS resin, polycarbonate, polyvinyl chloride, polystyrene, acrylic resin, such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyolefin, such as polypropylene (PP); metal substrates such as steel, galvanized steel, tin-plated steel, stainless steel, magnesium alloy, aluminum, aluminum alloy, titanium, titanium alloy; inorganic substrates other than metals such as cement, mortar, concrete, slate, gypsum, calcium silicate, glass, ceramic, calcium carbonate, marble, artificial marble; wood substrates such as wood; paper substrates; and composite substrates that combine two or more of these substrates. Furthermore, examples of composite substrates include wood fiber reinforced cement board, fiber reinforced cement board, fiber reinforced cement-calcium silicate board, and various surface treatments, such as oxidation treatment applied to metal substrates, and plastic substrates whose surfaces are coated with inorganic materials (for example, plastic substrates coated with glass).

[0106] The substrate can take on various shapes, such as two-dimensional substrates like films, sheets, or plates, or three-dimensional substrates with complex shapes. The surface of the substrate may be smooth or it may have irregularities.

[0107] The substrate may have undergone pretreatment such as degreasing, chemical treatment, or polishing on its surface, or it may have been coated with a sealer or primer.

[0108] In the coated body of the present invention, the film thickness of the coating is preferably 10 to 200 μm, more preferably 20 to 170 μm, and even more preferably 50 to 150 μm. Since a thinner film thickness results in lower corrosion resistance, and a thicker film thickness tends to reduce drying properties (and further, initial water resistance due to reduced drying properties) and blocking resistance, a coating with a film thickness within the specified range is preferred. Furthermore, when the film thickness of the coating is thin, such as 10 to 50 μm, corrosion resistance can be improved by using an epoxy resin as the resin (A-2). The resin (A-2) is particularly preferably a vinyl-modified epoxy resin.

[0109] The vinyl-modified epoxy resin is not particularly limited, but examples include a reaction product consisting of various components, such as a bisphenol-type epoxy resin, a glycyl group-containing polymerizable vinyl monomer, amines, and, if necessary, reactive components. That is, it is believed that the epoxy groups in the bisphenol-type epoxy resin undergo ring-opening by the amines, and at the same time, amino groups are introduced into the epoxy resin, further improving the inherent properties of the unmodified epoxy resin, such as adhesion. In addition, since the glycyl group-containing polymerizable vinyl monomer reacts with the epoxy groups in the bisphenol-type epoxy resin via the amines, polymerizable unsaturated groups are introduced into the epoxy resin, thereby conferring copolymerizability.

[0110] Other vinyl-modified epoxy resins include resins obtained by graft polymerization of a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer into a bisphenol-type epoxy resin. In these resins, for example, the polymerizable unsaturated monomer component can be graft polymerized into the epoxy resin in the presence of a radical generating agent such as benzoyl peroxide in an organic solvent. [Examples]

[0111] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the examples below. In the resin synthesis examples, "parts" and "%" are expressed on a mass basis unless otherwise specified.

[0112] <<Synthesis of acrylic emulsion>> <Resin 1> In a flask equipped with a stirrer, reflux condenser, thermometer, dropping device, and nitrogen inlet tube, 20.0 parts of deionized water, 0.50 parts of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 0.2 parts of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20) were charged. The mixture was heated to 80°C while purging the flask with nitrogen, and then 0.2 parts of ammonium persulfate were added. Next, a dropwise pre-emulsion was prepared consisting of a monomer emulsion comprising 47.7 parts of monomer mixture 1, 30.0 parts of deionized water, 1.0 part of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 0.4 parts of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20). This pre-emulsion was uniformly added dropwise to the flask over 180 minutes. After the dropwise addition was complete, the contents of the flask were maintained at 80°C for 120 minutes and aged. After cooling to room temperature, the solids content was adjusted to 50% and the pH to 8.5 to obtain the emulsion of resin 1. The glass transition temperature of resin 1 dispersed in the emulsion was 65.0°C, and the weight-average molecular weight was 250,000. The composition of monomer mixture 1 is shown in Table 1. The amounts of each component in the compositions of monomer mixtures 1 to 17 in Tables 1 to 3 are shown in parts by mass.

[0113] <Resin 2-17> Emulsions were prepared in the same manner as for resin 1, except that monomer mixture 1 was replaced with monomer mixtures 2 to 17 shown in Tables 1 to 3. This yielded emulsions of resins 2 to 17.

[0114] *Glass transition temperature The glass transition temperatures (Tg) of resins 1 to 17 were determined using the following FOX formula. The Tg values ​​for each resin are shown in Tables 1 to 3. [FOX calculation formula] 1 / Tg=W1 / Tg1+W2 / Tg2+···+Wi / Tgi+···+Wn / Tgn In FOX's formula, Tg in the denominator on the left side represents the glass transition temperature (in K) of the polymer component consisting of N types of monomers, Tg(1, 2, i, N) represents the glass transition temperature (in K) of each monomer, W(1, 2, i, N) is the mass fraction of each monomer, and the relationship W1 + W2 + ... + Wi + ... + Wn = 1 holds. Here, the glass transition temperature of a monomer refers to the glass transition temperature of its homopolymer.

[0115] *Weight average molecular weight The weight-average molecular weight was measured by gel permeation chromatography (GPC), and the converted value was obtained from a pre-prepared calibration curve of standard polystyrene. The weight-average molecular weight of each resin is shown in Tables 1-3.

[0116] [Table 1]

[0117] [Table 2]

[0118] [Table 3]

[0119] The abbreviations used for the monomer compositions in Tables 1-3 are as follows: ST-Y: Styrene MMA: Methyl methacrylate EHA: 2-Ethylhexylacrylate AB: Butyl acrylate HEMA: 2-hydroxyethyl methacrylate HEA: 2-hydroxyethyl acrylate AA: Acrylic acid NDM:N-dodecyl mercaptan KBM503: 3-Methacryloxypropyltrimethoxysilane KBM403: 3-Glycidoxypropyltrimethoxysilane

[0120] The items shown as characteristics in Tables 1-3 are as follows: "Amount of monomers with an SP value of 11.0 to 13.0 (%)" indicates the amount (mass %) of monomers with an SP value of 11.0 to 13.0 contained as constituent units in the obtained resin. "Amount of monomers with an SP value of 8.5 or higher and less than 9.5 (%)" indicates the amount (mass %) of monomers with an SP value of 8.5 or higher and less than 9.5 that are included as constituent units in the obtained resin. "Weight-average molecular weight" refers to the weight-average molecular weight of the resin measured according to the above "*Weight-average molecular weight". Here, "Unmeasurable" means that accurate molecular weight measurement was not possible due to the sample solution being opaque and filtration clogging occurring. However, such "unmeasurable" resins are considered to be high molecular weight resins, and their weight-average molecular weight is recognized as 50,000 or higher. In the "Presence or Absence of Crosslinking" section, "Presence" indicates that the obtained resin has a crosslinked structure, and "Absence" indicates that the obtained resin does not have a crosslinked structure. "Tg(°C)" indicates the glass transition temperature (°C) of the resin, determined according to the "*Glass transition temperature" described above. "MFT(°C)" indicates the minimum film-forming temperature (°C) of an acrylic emulsion, measured in accordance with JIS K 6828-2:2003.

[0121] In this specification, resins 1 to 14 and 17 are resins corresponding to water-dispersible resin (A-1), and resins 15 and 16 are resins corresponding to resin (A-2-2).

[0122] ≪Synthesis of resin (A-2-1)≫ <Acrylic Dispersion A> Ten parts of methyl ethyl ketone were charged into a reactor equipped with a stirrer, thermometer, reflux condenser, dropper, and nitrogen inlet tube, and the reactor was heated to 90°C while purging the inside of the reactor with nitrogen. Subsequently, a mixture A-1, which had been stirred and mixed in a separate container beforehand, consisting of 0.3 parts of 2,4-diphenyl-4-methyl-1-pentene (manufactured by NOF Corporation; NOF MSD), 7.9 parts of styrene, 3.9 parts of methyl methacrylate, 6.8 parts of tert-butyl methacrylate, 6.4 parts of n-butyl acrylate, 1.0 part of 2-hydroxyethyl methacrylate, and 0.3 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator), was added dropwise over 3 hours. After the dropwise addition was complete, while maintaining the same temperature, a mixture of 0.3 parts tert-butyl peroxy-2-ethylhexanoate (polymerization initiator) and 1.0 part methyl ethyl ketone, which had been previously mixed in a separate container, was added dropwise over 1 hour. The resulting mixture was stirred for 6 hours while maintaining the same temperature, after which 0.5 parts 2-methacryloyloxyethyl isocyanate and 1.0 part methyl ethyl ketone were added, and stirring was continued for a further 2 hours. Subsequently, a mixture A-2, which had been previously mixed in a separate container, consisting of 1.3 parts styrene, 3.9 parts methyl methacrylate, 1.3 parts n-butyl acrylate, 2.0 parts methacrylic acid, and 0.2 parts tert-butyl peroxy-2-ethylhexanoate (polymerization initiator), was added dropwise over 1 hour. After the dropwise addition was complete, while maintaining the same temperature, a mixture of 0.2 parts of tert-butylperoxy-2-ethylhexanoate (polymerization initiator) and 1.0 part of methyl ethyl ketone, which had been previously mixed in a separate container, was added dropwise over 1 hour. The resulting mixture was reacted by continuing to stir for 6 hours while maintaining the same temperature, and then cooled. 2.3 parts of triethylamine were added to the resulting mixture and stirred, and then 47.86 parts of deionized water were added. From this, 12 parts of methyl ethyl ketone were removed by distillation under reduced pressure (approximately 50 mmHg) at 50°C using an evaporator, and then 7.5 parts of deionized water, 5.0 parts of ethylene glycol mono-n-butyl ether, 0.02 parts of defoamer, and 0.02 parts of preservative were added to obtain acrylic dispersion A with a heating residue of 35%.The resin contained in acrylic dispersion A had a glass transition temperature (Tg) of 50°C and a weight-average molecular weight of 37,000.

[0123] <Acrylic Dispersion B> Ten parts of methyl ethyl ketone were charged into a reactor equipped with a stirrer, thermometer, reflux condenser, dropper, and nitrogen inlet tube, and the temperature was raised to 90°C while purging the inside of the reactor with nitrogen. Subsequently, a mixture B-1, which had been previously stirred and mixed in a separate container, consisting of 0.3 parts of 2,4-diphenyl-4-methyl-1-pentene (manufactured by NOF Corporation; NOFMER MSD), 7.9 parts of styrene, 7.9 parts of methyl methacrylate, 9.2 parts of n-butyl acrylate, 1 part of 2-hydroxyethyl methacrylate, and 0.3 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator), was added dropwise over 3 hours. After the dropwise addition was complete, while maintaining the same temperature, a mixture of 0.3 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator) and 1 part of methyl ethyl ketone, which had been previously stirred and mixed in a separate container, was added dropwise over 1 hour. The resulting mixture was stirred for 6 hours while maintaining the same temperature, then 0.5 parts of 2-methacryloyloxyethyl isocyanate and 1 part of methyl ethyl ketone were added, and stirring was continued for another 2 hours. Subsequently, mixture B-2, which had been previously mixed in a separate container, consisting of 1.3 parts of styrene, 1.3 parts of methyl methacrylate, 3.9 parts of n-butyl acrylate, 2 parts of methacrylic acid, and 0.2 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator), was added dropwise over 1 hour. After the dropwise addition was complete, while maintaining the same temperature, a mixture of 0.2 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator) and 1 part of methyl ethyl ketone, which had been previously mixed in a separate container, was added dropwise over 1 hour. The resulting mixture was stirred for 6 hours while maintaining the same temperature, and then cooled. To the resulting mixture, 2.3 parts of triethylamine were added and stirred, and then 47.86 parts of deionized water were added. From this, 12 parts of methyl ethyl ketone were removed by distillation under reduced pressure (approximately 50 mmHg) at 50°C using an evaporator. Then, 7.5 parts of deionized water, 5 parts of ethylene glycol mono-n-butyl ether, 0.02 parts of defoamer, and 0.02 parts of preservative were added to obtain acrylic dispersion B with a heating residue of 35%. The resin contained in acrylic dispersion B had a glass transition temperature (Tg) of 21°C and a weight-average molecular weight of 40,000.

[0124] <Urethane Dispersion> In a glass round-bottom flask equipped with a stirrer, thermometer, nitrogen inlet tube, and condenser, 261 parts of ETERNACOLL UH-200 (registered trademark; polycarbonate diol manufactured by Ube Industries; number average molecular weight 2000; hydroxyl value 56.1 mg KOH / g; polycarbonate diol obtained by reacting 1,6-hexanediol with dimethyl carbonate), 17.5 parts of 2,2-dimethylolpropionic acid (DMPA), and 166 parts of N-methylpyrrolidone (NMP) were charged under a nitrogen stream. 115 parts of 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI) and 0.3 parts of dibutyltin dilaurylate (catalyst) were added, and the mixture was heated to 90°C and stirred for 5 hours to obtain a polyurethane prepolymer. The free NCO group content at the end of the urethane formation reaction was 2.50%. 512 parts were withdrawn from the reaction mixture after adding 13.3 parts of triethylamine and mixing, and added to 850 parts of water under vigorous stirring. Then, 33.6 parts of a 35% aqueous solution of 2-methyl-1,5-pentanediamine (MPMD) was added to carry out a chain extension reaction, and 22.3 parts of an aqueous solution of 35% butylamine (BA) was added to carry out a molecular end sealing reaction, yielding a urethane dispersion with a heating residue of 35%. The resin contained in the urethane dispersion had a glass transition temperature (Tg) of 30°C and a weight-average molecular weight of 40,000.

[0125] <Epoxy Dispersion> In a reaction apparatus equipped with a stirrer, condenser, thermometer, and nitrogen gas inlet tube, 125 parts methyl ethyl ketone, 210 parts bisphenol A type epoxy resin (manufactured by Toto Chemical Co., Ltd.: Epotote YD-014, epoxy equivalent 950), and 75 parts polyethylene glycol diglycidyl ether (Nagase Chemical Industries Co., Ltd.: Denacol EX-841) were added and dissolved at 100°C under a nitrogen stream. Then, 22.0 parts octylamine and 14.7 parts dibutylamine were added and the mixture was reacted for 5 hours to obtain a modified epoxy resin. Next, a mixture consisting of 16.0 parts acrylic acid, 10.0 parts styrene, 10.0 parts butyl acrylate, 40.0 parts methyl ethyl ketone, and 12.0 parts tert-butyl peroxy-2-ethylhexanoate was added dropwise to the reaction system over 1 hour and the mixture was kept warm for 4 hours. After cooling to 80°C, an aqueous dispersion was obtained by sequentially adding and mixing 21.0 parts of triethylamine and 500 parts of water. Next, the solvent was removed, and the non-volatile content was adjusted to 37.0% with water to obtain an epoxy dispersion with a pH of 9.7. The resin contained in the epoxy dispersion had a weight-average molecular weight of 20,000, an acid value of 31, and a glass transition temperature of 55°C.

[0126] <<Preparation of water-based paints>> Water-based paints were prepared by stirring the emulsions of resins 1 to 17 with a disperser, according to the formulations shown in Tables 4 to 11. The amounts of each component in the formulations shown in Tables 4 to 11 are expressed in parts by mass. Tables 4 to 11 also show the softening point of the coating film formed from the water-based paint, the minimum film-forming temperature (MFT) of the water-based paint, and the pigment volume concentration (PVC). Next, the drying properties, blocking resistance, initial water resistance, and corrosion resistance of the water-based paint were evaluated. The results are shown in Tables 4-11. The evaluation method will be described later.

[0127] The components shown in the formulations in Tables 4-11 are as follows: <Water-dispersible resin (A-1) or resin (A-2-2)> The emulsions of resins 1 to 17 are emulsions of resins 1 to 17 prepared according to the above-described "Synthesis of Acrylic Emulsions". <Resin (A-2-1)> Acrylic dispersion A, acrylic dispersion B, urethane dispersion, and epoxy dispersion are dispersions of resins prepared according to the above-described "Synthesis of Resin (A-2-1)". • Water-soluble acrylic resin a: "JYONCRRYL JDX-6180", manufactured by BASF Japan, heating residue 27%, Tg 134℃ • Water-soluble acrylic resin b: "JYONCRRYL 6610", manufactured by BASF Japan, heat residue 34%, Tg 85℃ • Water-soluble acrylic resin c: "JYONCRRYL 63J", manufactured by BASF Japan, heating residue 30%, Tg 73℃ * The weight-average molecular weight of water-soluble acrylic resins a to c was all within the range of 1,000 to less than 50,000. <Film-forming aid> • Diethylene glycol diethyl ether (boiling point 189°C) • Ethylene glycol mono-n-butyl ether (boiling point 170°C) • Diethylene glycol mono-n-butyl ether (boiling point 230°C) • Polyethylene glycol monomethyl ether (boiling point 295°C) <Pigments> • Extender pigment (precipitating barium sulfate): "Precipitating Barium 100", manufactured by Sakai Chemical Industry Co., Ltd. • Rust-preventive pigment (zinc phosphate): "K-WHITE #140W", manufactured by Teika Co., Ltd. • Coloring pigment (titanium dioxide): "R-32", manufactured by Sakai Chemical Industry Co., Ltd. <Other> • Dispersant: "DISPERBYK-194N", manufactured by Big Chemie Japan Co., Ltd.

[0128] In Tables 4-11, "Heating Residue (%)" is synonymous with the amount (mass%) of film-forming components in the water-based paint. "PVC (%)" represents the pigment volume concentration, which is the percentage (%) of the total volume of pigment within the total volume of film-forming components in a water-based paint. "MFT(°C)" indicates the minimum film-forming temperature (°C) of water-based paints, measured in accordance with JIS K 6828-2:2003. The "softening point (°C)" indicates the softening point (°C) of the coating film measured according to the <softening point of coating films formed from water-based paints> described below.

[0129] <Softening point of a coating film formed from water-based paint> An aqueous coating was applied to a polypropylene (PP) plate, which had been preheated to 80°C, using an applicator to achieve a dry film thickness of 50 μm. The coating was then forcibly dried at 80°C for 30 minutes to obtain an isolated film. The storage modulus (E') of isolated films at various temperatures was measured using a dynamic viscoelasticity testing machine (RSAG2 (TA Instruments Inc.)) under the following measurement conditions. Based on the measurement results of the storage modulus of the coating film, a curve of change in the storage modulus was created with the vertical axis representing the storage modulus (E') (in Pa) and the horizontal axis representing temperature (in °C). The temperature (°C) at the inflection point of the storage modulus (E') was determined and defined as the softening point. <Measurement conditions> Temperature range: -50℃ to 200℃ Heating rate: 5°C / min Measurement length: 20.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0130] ≪Evaluation Method≫ <Drying> After applying a water-based paint to a steel plate with a surface temperature maintained at 40°C ± 5°C to achieve an immediate film thickness of 100 μm, the surface drying properties of the resulting paint film were evaluated according to the test method (Barotini method) of JIS K 5600-3-2 while the painted surface of the steel plate was maintained at 40°C ± 5°C. The time it took for the Barotini paint to be removed by lightly brushing it off without damaging the surface of the paint film was defined as the surface drying time, and the drying properties were evaluated according to the following criteria. ◎: Surface drying time is less than 3 minutes. ○: Surface drying time is 3 minutes or more but less than 5 minutes. △: Surface drying time is 5 minutes or more but less than 10 minutes. ×: Surface drying time is 10 minutes or more

[0131] <Blocking resistance> Two 100×100×0.3mm tinplate plates, with their surface temperature maintained at 80℃±5℃, were coated with water-based paint to achieve an immediate film thickness of 100μm. The plates were then force-dried at 100℃ for 30 minutes to prepare test specimens. The two test specimens were stacked with their painted surfaces facing inward, and evenly distributed under a load of 20kg (0.2kg / cm²). 2 A weight was placed on the material, and it was pressurized for 30 minutes while being maintained at 40°C ± 5°C. After removing the weight, the blocking resistance was evaluated based on the degree of adhesion and peeling according to the following criteria. ◎: No adhesion was observed, and no marks were left on the surface of the coating. ○: Slight pressure adhesion is observed, but no marks are left on the surface of the coating. △: Pressure adhesion is observed, leaving marks on the surface of the coating. ×: Adhesion is observed, and peeling is observed on the surface of the coating.

[0132] <Initial water resistance> Using an SS400 blast plate maintained at a surface temperature of 80°C ± 5°C, a water-based paint was applied to achieve a dry film thickness of 100 μm. After forced drying at 100°C for 30 minutes, the lower half of the resulting test plate was immersed in 23°C tap water for 24 hours. The appearance of the removed test plate was immediately observed, and the initial water resistance was evaluated according to the following criteria. ◎: There was no blistering in the immersed area of ​​the coating, and there was no visible difference in hue compared to the unimmersed area. ○: There was no blistering in the paint film of the immersed area, but the difference in hue between it and the unimmersed area was clear. △: Some blistering was observed in the coating of the immersed area. ×: Blistering was observed across the entire coating in the immersed area.

[0133] <Corrosion Resistance> Since the film-forming properties and water resistance of the coating also affect its corrosion resistance, we evaluated its corrosion resistance as follows. Using an SS400 blast plate maintained at a surface temperature of 80°C ± 5°C, a water-based paint was applied to achieve a dry film thickness of 100 μm. The plate was then force-dried at 100°C for 30 minutes, and cross-cuts were made in the resulting coating to prepare test plates. The prepared test plates were then sprayed with salt water for one week according to the method of JIS Z2371:2015. The test plates were evaluated based on the following evaluation criteria. The portion of the coating without cross-cuts was designated as the general portion, and the portion with cross-cuts was designated as the cut portion. ◎: There is no rust or blistering in the general area, and blistering is only present in areas less than 1 mm from the cut in the cut section. ○: There is no rust or blistering in the general area, and blistering is only present in areas less than 3mm from the cut in the cut section. △: No rust or blistering in the general area, and blistering only in areas less than 5mm from the cut incision. ×: Blisters have formed in areas more than 5mm from the cut incision, and rust and blistering are present in the general area.

[0134] [Table 4]

[0135] [Table 5]

[0136] [Table 6]

[0137] [Table 7]

[0138] [Table 8]

[0139] [Table 9]

[0140] Table 10

[0141] Table 11

Claims

1. An aqueous coating composition comprising a water-dispersible resin (A) and a film-forming aid (B), The water-dispersible resin (A) includes a water-dispersible resin (A-1) having a weight-average molecular weight of 50,000 or more, which comprises monomers with an SP value of 11.0 to 13.0 and monomers with an SP value of 8.5 or more and less than 9.5 as constituent units. The amount of monomers with an SP value of 11.0 to 13.0 contained as constituent units in the water-dispersible resin (A-1) is 5 to 50% by mass. The aforementioned film-forming aid (B) includes a film-forming aid with a boiling point of 150 to less than 200°C and a film-forming aid with a boiling point of 200°C to 280°C. The aqueous coating composition comprises resin (A-2-1) and / or resin (A-2-2), wherein resin (A-2-1) is a water-dispersible and / or water-soluble resin having a weight-average molecular weight of less than 50,000, and resin (A-2-2) is a water-dispersible and / or water-soluble resin having a weight-average molecular weight of 50,000 or more, and does not contain monomers with an SP value of 11.0 to 13.0 or monomers with an SP value of 8.5 or more and less than 9.5 as constituent units. The aqueous paint composition is characterized in that the softening point of the coating film formed from the aqueous paint composition is 0°C to 100°C, where the softening point is the temperature (°C) of the inflection point of the storage modulus (E'(Pa)) obtained by dynamic viscoelasticity measurement (DMA) under the following measurement conditions. <Measurement conditions> Temperature range: -50°C to 200°C Heating rate: 5°C / min Measurement length: 20.0 mm Measurement width: 8.0 mm Frequency: 1 Hz Distortion: 0.05%

2. A coated body having a coating film formed on a substrate from the aqueous coating composition described in claim 1.

Images