JP7698398B2 - water-based paint composition - Google Patents

Description

The present invention relates to an aqueous coating composition.

Traditionally, outdoor substrates such as buildings have been coated with paint for decorative or protective purposes. In general, when exposed outdoors for long periods of time, the surface of the coating film becomes easily soiled by the effects of sand and dust, iron powder, rain (acid rain), sunlight, etc., and the appearance of the coating film deteriorates.

One of the market trends in the field of architectural coatings in relation to these issues is the need for coatings that have the properties to prevent contamination caused by raindrops, so-called low-contamination coatings.

On the other hand, in recent years, there has been a shift to water-based paints in the paint industry. In general, water-based paints tend to be inferior to solvent-based paints in terms of finish and water resistance due to hydrophilic groups and emulsifiers. However, in response to recent market needs, there is a demand for the development of water-based paints that provide good finish and water resistance, as well as the ability to form coatings that exhibit high functionality such as stain resistance.

Known methods for imparting stain resistance to coatings include making the coating water repellent and making it hydrophilic. Coating designers can choose one of these methods depending on the substrate and the type and properties of the stains that may adhere to it.

For example, Patent Document 1 discloses an aqueous coating composition that contains a water-soluble acrylic resin containing a tertiary amino group and a carbonyl group, a carbonyl group-containing acrylic emulsion, and a hydrazide compound.

This aqueous paint composition can form a coating film with excellent stain resistance, and because the tertiary amino group- and carbonyl group-containing water-soluble acrylic resin reacts with the carbonyl group-containing acrylic emulsion, which is the binder component, via the hydrazide compound, which is the curing agent, the stain resistance can be maintained for a long period of time. However, it cannot be denied that the water resistance and weather resistance of the coating film formed when dried at room temperature is insufficient.

In addition, the coating applied to the outdoor substrate must have a suitable degree of flexibility (hereinafter in this specification, this may be referred to as "elasticity") so that it can conform to cracks on the substrate surface.

For example, Patent Document 2 discloses a coating finishing method characterized by coating a surface to be coated with a base conditioner (I) containing an aqueous copolymer dispersion (A) in which the copolymer has a glass transition temperature of -20°C or lower, and then coating the surface with a topcoat paint (II) containing an aqueous copolymer dispersion (B) in which the copolymer has a glass transition temperature of -60 to 0°C and an aqueous copolymer dispersion (C) in which the copolymer has a glass transition temperature of 15 to 50°C in a solids mass ratio of (B)/(C) of 20/80 to 80/20.

However, such a painting finishing method is limited to the use of a base preparation material containing an aqueous dispersion of a copolymer with a low glass transition temperature, and while it is fine when the base surface has been prepared to be smooth, it is not sufficient when the base surface has been prepared to be uneven, such as rippled. Thus, it does not meet the current demand for a topcoat paint that can be applied to various types and shapes of base preparation materials and base surfaces, in other words, has excellent elastic suitability.
JP 2000-119589 A JP 2008-12373 A

The object of the present invention is to provide a water-based paint that combines low contamination and elasticity.

In order to achieve the above object, the present invention includes the subject matter described in the following paragraphs.
Item 1.
The core is a polymer having a glass transition temperature of 5 to 60°C,
The shell is a polymer having a glass transition temperature of 50 to 100°C,
A core/shell emulsion (A) having a ΔTg (glass transition temperature of the shell - glass transition temperature of the core) of 30 to 60°C, and
An aqueous coating composition comprising at least one crosslinking agent (B) selected from the group consisting of hydrazide compounds, glycidyl group-containing compounds, carbodiimide compounds, oxazoline compounds and isocyanate compounds.
Item 2.
The core/shell emulsion (A) comprises
2. An aqueous coating composition according to item 1, wherein the mass ratio of the core polymer to the shell polymer is in the range of 50/50 to 90/10 (the former/the latter).
Item 3.
The solid content of the core/shell emulsion (A) is
3. The aqueous coating composition according to item 1 or 2, wherein the amount of the water-based coating composition is 30 to 99.5 parts by mass based on 100 parts by mass of the solid content of the aqueous coating composition.
Item 4.
4. The aqueous coating composition according to any one of items 1 to 3, further comprising 20 to 200 parts by mass of a titanium oxide pigment (C) based on 100 parts by mass of the solid content of the aqueous coating composition.
Item 5.
5. The aqueous coating composition according to any one of items 1 to 4, further comprising 3 to 15 parts by mass of an organic solvent (D) having a boiling point of 200° C. or higher, based on 100 parts by mass of the solid content of the aqueous coating composition.
Item 6.
6. The aqueous coating composition according to any one of items 1 to 5 above, which is capable of forming a cured coating film having a thickness of 70 μm on a 3.0 mm thick glass plate, and allowing it to age for one week in an atmosphere of 23°C and 50% humidity, has a Martens hardness of 2.0 to 40.0 N/ ^mm2 as measured on the surface of the coating film using an ultra-microhardness tester at a temperature of 23°C and a load of 5 mN/25 s.
Section 7.
7. A method for forming a coating film, comprising the step of coating an article with the aqueous coating composition according to any one of items 1 to 6.
Section 8.
7. A coated article having a cured coating film formed from the aqueous coating composition according to any one of items 1 to 6.

The aqueous coating composition of the present invention can form a coating film that is low in contamination and has elastic properties.

The aqueous coating composition of the present invention will be described in more detail below.

The aqueous coating composition of the present invention contains a core/shell emulsion (A) in which the core is a polymer having a glass transition temperature of 5 to 60°C, the shell is a polymer having a glass transition temperature of 50 to 100°C, and ΔTg (glass transition temperature of the shell - glass transition temperature of the core) is 30 to 60°C, and at least one crosslinking agent (B) selected from hydrazide compounds, glycidyl group-containing compounds, carbodiimide compounds, oxazoline compounds, and isocyanate compounds.

Core/shell emulsion (A)
In the core/shell emulsion (A) used in the present invention, from the viewpoints of low contamination and elastic suitability of the resulting coating film, the core is a polymer having a glass transition temperature of 5 to 60°C, preferably 10 to 50°C, and more preferably 10 to 40°C, and the shell is a polymer having a glass transition temperature of 50 to 100°C, preferably 60 to 90°C, and more preferably 65 to 85°C, and ΔTg (glass transition temperature of shell - glass transition temperature of core) is 30 to 60°C, preferably 35 to 60°C, and more preferably 40 to 60°C.

A core/shell emulsion is a multi-layered particle consisting of a central layer and an outer shell layer. It is also possible to form another layer between the two layers.

Core/shell emulsions are synthesized by seed emulsion polymerization or multi-stage emulsion polymerization. For example, in the case of two-layered particles, seed particles are first prepared by emulsion polymerization of a first-stage polymerizable unsaturated monomer (one or a mixture of two or more types) that forms a resin with a glass transition temperature of 5 to 60°C, and then in the presence of the seed, a second-stage polymerizable unsaturated monomer (one or a mixture of two or more types) that forms a resin with a glass transition temperature of 50 to 100°C is supplied and emulsion polymerized to obtain a core/shell emulsion. In the case of particles consisting of three or more layers, a process of supplying a polymerizable unsaturated monomer (one or a mixture of two or more types) that forms another resin layer and emulsion polymerizing it is added between the first and second stages.

In this specification, if the absolute temperature of the glass transition temperature Tg (° C.) of each copolymer is Tg″, the following calculation can be performed.
1/Tg"=W1'/T1+W2'/T2...+Wn'/Tn
(wherein W1', W2' . . . Wn' are the weight fractions of each monomer relative to the total monomers used in preparing the copolymer, and T1, T2, . . . Tn are the glass transition temperatures (absolute temperatures) of the homopolymers of each monomer).

From the viewpoint of low contamination and elasticity of the resulting coating film, the mass ratio of the core polymer to the shell polymer is preferably within the range of 50/50 to 90/10, preferably 50/50 to 80/20, and more preferably 50/50 to 70/30.

From the viewpoint of low contamination and elasticity of the resulting coating film, the particle size of the core/shell emulsion is set to be within the range of 100 to 1000 nm, preferably 100 to 500 nm, and more preferably 100 to 300 nm. Outside this range, the elasticity is poor, which is undesirable.

In this specification, the particle size of the core-shell emulsion is the value measured at 20°C after dilution with deionized water using a submicron particle size distribution measuring device "COULTER N4 type" (manufactured by Beckman Coulter, Inc.).

Specific examples of the polymerizable unsaturated monomer include aromatic monovinyl compounds such as styrene, ethylvinylbenzene, α-methylstyrene, and fluorostyrene; vinyl cyanide compounds such as acrylonitrile and methacrylonitrile; acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, n,i,tert-butyl acrylate, 2-ethylhexyl acrylate, β-acryloyloxyethyl hydrogen phthalate, 2-hydroxyethyl acrylate, diacetone acrylamide, 2-acryloyloxy-2-hydroxyethyl phthalate, 2-hydroxy-3-phenoxypropyl acrylate, glycidyl acrylate, and N,N-dimethylaminoethyl acrylate; methyl methacrylate, ethyl methacrylate, n,i,tert-butyl methacrylate, 2-ethylhexyl methacrylate, methoxydiethylene glycol methacrylate, methoxypolyethylene glycol methacrylate, 2-methacryloyloxy-2-hydroxypropyl phthalate, 2-hydroxyethyl methacrylate, and diacetone methacrylate. methacrylic acid ester monomers such as acrylic acid, cyclohexyl methacrylate, glycidyl methacrylate, and N,N-dimethylaminoethyl acrylate; carboxylic acid-containing unsaturated monomers such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid, and their anhydrides; sulfonic acid group- or sulfate group-containing unsaturated monomers such as sulfoethyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and sodium methacryloyloxysulfonate; amide monomers such as acrylamide, methacrylamide, and N,N-dimethylacrylamide; silicon-modified monomers; polyoxyalkylene macromonomers such as polyethylene glycol (meth)acrylate and polypropylene glycol (meth)acrylate; and polyvinyl compounds such as divinylbenzene and 1,6-hexanediol diacrylate.

In the present invention, from the viewpoint of low contamination and elasticity of the resulting coating film, it is preferable that the acid value of the shell polymer is within the range of 4 to 80 mgKOH/g, preferably 5 to 60 mgKOH/g. Outside this range, the elasticity is poor, which is undesirable.

In addition, using at least one crosslinkable polymerizable unsaturated monomer selected from the above diacetone acrylamide, diacetone methacrylamide, carboxylic acid group-containing unsaturated monomer, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate as at least a part of the polymerizable unsaturated monomers constituting the core-shell emulsion, particularly the polymerizable unsaturated monomers constituting the shell polymer, is advantageous in terms of the elasticity and low contamination of the resulting coating film.

From the viewpoint of low contamination and elasticity of the resulting coating film, the amount of crosslinkable polymerizable unsaturated monomer used is preferably within the range of 0.1 to 20 parts by mass, and more preferably 0.2 to 10 parts by mass, based on 100 parts by mass of the polymerizable unsaturated monomer that constitutes the core-shell emulsion.

The emulsion polymerization is usually carried out in the presence of water and an emulsifier. The emulsifier can be any known anionic surfactant, nonionic surfactant, cationic surfactant, reactive emulsifier, or mixtures thereof, as long as it does not contain a volatile organic compound.

Examples of anionic surfactants include various fatty acid salts, higher alcohol sulfate salts, alkylbenzene sulfonates, polyoxyethylene alkylphenyl ether sulfate salts, and polycarboxylic acid polymer surfactants. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, sorbitan fatty acid esters, and polyoxyethylene-polyoxypropylene block copolymers. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Reactive emulsifiers are surfactants that have a polymerizable group in the molecule, and specific examples include "ADEKA REASOAP SE-10N" (trade name, manufactured by Asahi Denka Kogyo Co., Ltd.) and "Aqualon HS-10" (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

The amount of these emulsifiers used should be in the range of 0.01 to 10% by weight, preferably 0.1 to 5% by weight, based on the total amount of monomers used.

In the above emulsion polymerization, an emulsifier may be added later, if necessary, in order to increase the stability of the particles. A sorbitan-based nonionic surfactant is suitable as the emulsifier to be added later.

In order to polymerize the polymerizable unsaturated monomer in the above emulsion polymerization, a polymerization initiator is usually added. As the polymerization initiator, any conventionally known initiator can be used without any particular limitation as long as it does not generate volatile organic compounds and does not itself fall under the category of volatile organic compounds. Specific examples include water-soluble inorganic peroxides such as hydrogen peroxide; persulfates such as potassium persulfate and ammonium persulfate; and the like. These can be used alone or in combination of two or more. The amount used is preferably 0.1 to 2% by weight based on the amount of the polymerizable unsaturated monomer used. Redox polymerization may also be performed using a combination of a peroxide-based polymerization initiator and a metal ion or a reducing agent as a polymerization initiator.

In the above emulsion polymerization, if necessary, a series transfer agent such as mercaptans, a buffer such as sodium bicarbonate, etc. may be used. However, it is preferable not to use any agent that generates volatile organic compounds or that is itself a volatile organic compound.

In the aqueous coating composition of the present invention, the solid content of the core/shell emulsion (A) is preferably within the range of 30 to 99.5 parts by mass, preferably 40 to 90 parts by mass, and more preferably 50 to 80 parts by mass, based on 100 parts by mass of the solid content of the aqueous coating composition, from the viewpoint of low contamination and elasticity suitability of the resulting coating film.

Crosslinking agent (B)
The crosslinking agent (B) in the aqueous coating composition of the present invention is at least one selected from hydrazide compounds, glycidyl group-containing compounds, carbodiimide compounds, oxazoline compounds and isocyanate compounds. Among them, from the viewpoint of low contamination and elasticity of the obtained coating film, hydrazide compounds, oxazoline compounds and isocyanate compounds are more preferable as the crosslinking agent (B). In addition, one-component coatings are easier to handle than two-component coatings, and from the viewpoint of making the aqueous coating composition of the present invention one-component, hydrazide compounds, carbodiimide compounds and oxazoline compounds are more preferable as the crosslinking agent (B).

Specific examples of hydrazide compounds include dihydrazides of saturated aliphatic carboxylic acids having 2 to 18 carbon atoms, such as oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, and sebacic acid dihydrazide; dihydrazides of monoolefinic unsaturated dicarboxylic acids, such as maleic acid dihydrazide, fumaric acid dihydrazide, and itaconic acid dihydrazide; dihydrazides of phthalic acid, terephthalic acid, or isophthalic acid; and dihydrazides of pyromellitic acid. Examples of the hydrazide include trihydrazide, trihydrazide or tetrahydrazide; nitrilotriacetic acid trihydrazide, citric acid trihydrazide, 1,2,4-benzenetrihydrazide; ethylenediaminetetraacetic acid tetrahydrazide, 1,4,5,8-naphthoic acid tetrahydrazide; polyhydrazide obtained by reacting a low polymer having a carboxylic acid lower alkyl ester group with hydrazine or hydrazine hydrate (hydrazine hydrade), and the like. These can be used alone or in combination of two or more. Among them, from the viewpoint of low contamination and elasticity of the resulting coating film, adipic acid dihydrazide, succinic acid dihydrazide, and sebacic acid dihydrazide are preferred as hydrazide compounds.

Specific examples of glycidyl group-containing compounds include glycidyl ether compounds such as diglycidyl ether, 2-glycidylphenyl glycidyl ether, and 2,6-diglycidylphenyl glycidyl ether; epoxy resins having glycidyl ether groups or glycidyl ester groups, such as bisphenol A type epoxy resins, bisphenol F type epoxy resins, cresol novolac type epoxy resins, and phenol novolac type epoxy resins; and (co)polymers of glycidyl group-containing polymerizable unsaturated monomers, such as glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and allyl glycidyl ether, and other polymerizable unsaturated monomers, as necessary. These can be used alone or in combination of two or more.

A carbodiimide compound is, for example, a compound obtained by reacting isocyanate groups of a polyisocyanate compound with each other to remove carbon dioxide. The carbodiimide compound is desirably water-soluble or water-dispersible, and is not particularly limited, but is desirably a compound having a carbodiimide equivalent in the range of 100 to 800, preferably 200 to 600. Examples of corresponding commercially available products include "Carbodilite V-02", "Carbodilite V-02-L2", "Carbodilite V-04", "Carbodilite E-01", and "Carbodilite E-02" (all trade names manufactured by Nisshinbo). These can be used alone or in combination of two or more kinds.

Specific examples of oxazoline compounds include low molecular weight poly(1,3-oxazoline) compounds such as 2,2'-p-phenylene-bis-(1,3-oxazoline), 2,2'-tetramethylene-bis-(1,3-oxazoline), and 2,2'-octamethylene-bis-(2-oxazoline); and vinyl polymers containing 1,3-oxazoline groups obtained by copolymerizing homopolymers of 1,3-oxazoline group-containing vinyl monomers such as 2-isopropenyl-1,3-oxazoline with various vinyl monomers copolymerizable therewith. It is desirable for the compound to be water-soluble or water-dispersible, and although there are no particular limitations, it is desirable for the compound to have an oxazoline group equivalent in the range of 100 to 800, preferably 200 to 600. Commercially available examples of such polyoxazoline compounds include "Epocross K-1000", "Epocross K-1020E", "Epocross K-1030E", "Epocross K-2010E", "Epocross K-2020E", "Epocross K-2030E", "Epocross WS-500", and "Epocross WS-700" manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd. These can be used alone or in combination of two or more types.

Specific examples of isocyanate compounds include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of these polyisocyanates. These can be used alone or in combination of two or more.

In the aqueous coating composition of the present invention, the solid content of the crosslinking agent (B) is preferably within the range of 0.1 to 1.0 parts by mass, preferably 0.2 to 0.9 parts by mass, and more preferably 0.3 to 0.8 parts by mass, based on 100 parts by mass of the solid content of the aqueous coating composition, from the viewpoint of low contamination and elasticity of the resulting coating film.

Titanium oxide pigment (C)
From the viewpoint of base hiding power, the aqueous coating composition of the present invention may further contain a titanium oxide pigment (C) in addition to the above components (A) and (B).

Titanium oxide pigment (C) is a white pigment and can impart a white color to the coating film formed. Titanium oxide pigment (C) may have either the rutile or anatase crystal type, but the rutile type is preferred because it provides excellent weather resistance to the coating film formed and excellent hiding power for the base color. Titanium oxide pigment (C) may also be titanium oxide whose surface has been coated with inorganic oxides such as aluminum oxide, zirconium oxide, and silicon dioxide; or organic compounds such as amines and alcohols.

When the aqueous coating composition of the present invention contains titanium oxide pigment (C), the content of titanium oxide pigment (C) is preferably within the range of 20 to 200 parts by mass, preferably 40 to 160 parts by mass, and more preferably 50 to 120 parts by mass, per 100 parts by mass of the solid content of the resin contained in the aqueous coating composition, from the viewpoint of low contamination and excellent elasticity properties of the resulting coating film. In this specification, unless otherwise specified, the above core/shell emulsion (A) and crosslinking agent (B) are considered to be included in the above resin.

Organic solvents having a boiling point of 200° C. or higher (D)
From the viewpoint of elastic suitability, the aqueous coating composition of the present invention may further contain, in addition to the components (A) and (B), an organic solvent (D) having a boiling point of 200°C or higher, preferably 210 to 300°C, and more preferably within the range of 220 to 290°C.

Specific examples of the organic solvents having a boiling point of 200°C or higher include, for example, ethylene glycol mono-i-propyl ether, ethylene glycol dibutyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-i-butyl ether, diethylene glycol mono-n-propyl ether, diethylene glycol mono-i-propyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-n-propyl ether, and dipropylene glycol mono-i-propyl ether. glycol ethers such as propyl ether, diethylene glycol dibutyl ether, dipropylene glycol monobutyl ether, and tripropylene glycol monobutyl ether; and ester compounds such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 2,2,4-trimethyl-1,3-pentanediol-1,3-diisobutyrate, 2,2,4-trimethyl-1,3-pentanediol mono 2-ethylhexanoate, and 2,2,4-trimethyl-1,3-pentanediol di 2-ethylhexanoate. These can be used alone or in combination of two or more.

Among these, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and/or 2,2,4-trimethyl-1,3-pentanediol diisobutyrate are preferred from the standpoint of low contamination and elasticity of the resulting coating film.

When the aqueous coating composition of the present invention contains an organic solvent (D) having a boiling point of 200°C or higher, the content of the organic solvent (D) is preferably within the range of 3 to 15 parts by mass, preferably 4 to 14 parts by mass, and more preferably 5 to 13 parts by mass, per 100 parts by mass of the solid content of the aqueous coating composition.

Other Components The aqueous coating composition of the present invention may contain resins other than the above components (A) and (B) as necessary. Examples of such resins include emulsions other than component (A), water-soluble acrylic resins, polyester resins, epoxy resins, urethane resins, etc., which may be used alone or in combination of two or more.

Specific examples of emulsions other than component (A) include acrylic emulsions, urethane emulsions, silicone emulsions, fluorine emulsions, silicon-modified acrylic emulsions, silicone-modified acrylic emulsions, urethane-modified acrylic emulsions, and fluorine-modified acrylic emulsions. These can be used alone or in combination of two or more.

When the aqueous coating composition of the present invention contains a resin other than the above components (A) and (B), the content of the resin other than the above components (A) and (B) is preferably within the range of 1.0 to 15.0 parts by mass, preferably 2.0 to 12.0 parts by mass, and more preferably 3.0 to 9.0 parts by mass, based on 100 parts by mass of the resin solids, from the viewpoint of low contamination and elasticity of the resulting coating film.

The aqueous coating composition of the present invention may further contain, as necessary, pigments other than the titanium oxide pigment (C), organic solvents other than the organic solvent (D) having a boiling point of 200°C or higher, pigment dispersants, surface conditioners, leveling agents, defoamers, surfactants, anti-settling agents, thickeners, anti-mold agents, anti-algae agents, preservatives, plasticizers, fillers, dispersants, ultraviolet absorbers, light stabilizers, etc.

Examples of pigments other than the titanium oxide pigment (C) include color pigments, extender pigments, metal powders, etc. These can be used alone or in combination of two or more kinds.

Examples of the color pigments include inorganic color pigments such as zinc oxide, iron oxide, yellow lead, etc., and organic color pigments such as phthalocyanine blue and benzidine yellow. Examples of the extender pigments include quartz powder, talc, alumina oxide, calcium carbonate, precipitated barium sulfate, mica, etc. Examples of the metal powders include stainless steel powder, zinc powder, aluminum powder, bronze powder, mica powder, etc.

Extender pigments may be used as pigments, as they have particularly good low-staining and weather resistance properties.

When the aqueous coating composition of the present invention contains the above-mentioned extender pigment, the content of the extender pigment in terms of solids is preferably within the range of 1 to 100 parts by mass, preferably 5 to 90 parts by mass, and more preferably 10 to 80 parts by mass, based on 100 parts by mass of resin solids, from the viewpoints of low contamination and weather resistance, etc.

The aqueous coating composition of the present invention may be a one-component composition or a two-component composition, and when it is a two-component composition, it is generally used by mixing the base agent containing component (A) and the curing agent containing component (B) immediately before painting. When the aqueous coating composition of the present invention is a two-component composition, it may contain a curing catalyst to promote the reaction between the core/shell emulsion (A) and the crosslinking agent (B).

Coating method: The substrate to which the aqueous coating composition of the present invention is applied is not particularly limited, and examples thereof include metal surfaces that have been primed as desired (e.g., iron plate surfaces, galvanized surfaces, stainless steel surfaces, aluminum surfaces, etc.), alkaline substrates (e.g., concrete, stone, mortar, slate, slate roofing tiles), ceramic substrates, plastics, wood, etc., as well as the surfaces of old coating films on the surfaces of these substrates.

The substrate may also be coated with a sealer and/or a surface conditioner. In particular, the aqueous coating composition of the present invention has excellent elasticity properties, so the effects of the present invention can be more pronounced when the composition is coated on a surface conditioner.

There are no particular limitations on the applications of the coating, but it is suitable for the exterior walls of buildings and structures.

The aqueous coating composition of the present invention can be applied by known methods such as spray coating, roller coating, brush coating, and flow coating.

The aqueous coating composition of the present invention can have a solids content of 10 to 60%, preferably 15 to 55%, when applied.

The coating amount of the aqueous coating composition of the present invention can be adjusted appropriately depending on the application, and is not particularly limited, but is generally within the range of 30 to 400 g/m ² , or 50 to 250 g/m ² .

The aqueous coating composition of the present invention can be easily crosslinked even under room temperature drying conditions, but forced drying or heat drying may also be used if necessary.

Cured coating film obtained by curing the aqueous coating composition of the present invention is excellent in both stain resistance and elasticity, and has the following properties: The aqueous coating composition of the present invention is applied to a 3.0 mm thick glass plate to form a cured coating film with a thickness of 70 μm, and after aging for one week in an atmosphere of 23°C and 50% humidity, the Martens hardness of the coating film surface measured with an ultra-microhardness tester at a temperature of 23°C and a load of 5 mN/25 s is 2.0 to 40.0 N/mm ² , preferably 2.5 to 30.0 N/mm ² , and more preferably 3.0 to 20.0 N/mm ² .

The tensile modulus of the cured coating film obtained by curing the aqueous coating composition of the present invention is preferably 50 to 600 N/mm ² , more preferably 70 to 500 N/mm ² , and even more preferably 90 to 400 N/mm ² . The tensile modulus was measured by applying an emulsion sample to a degreased tin plate using a 250 μm applicator, drying at 20° C. for 7 days, and then peeling off the coating film using mercury. The peeled coating film was measured using an EZ Test manufactured by Shimadzu Corporation.

The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples. Note that "parts" and "%" are all based on mass.

Preparation of Core/Shell Emulsion Production Example 1
A 2-liter four-neck flask was fitted with a condenser, a thermometer, and a dropping funnel, and 350 parts of deionized water and 10 parts of Nucol 707SF (Note 1) were charged, and the air inside was replaced with nitrogen, after which the inside temperature was raised to 80° C. with stirring. Next, 3% of a pre-emulsion made by emulsifying the components shown below and 80 parts of a 2.5% aqueous solution of ammonium persulfate were added to the reaction vessel, and the temperature was maintained at 80° C. for 20 minutes.
Deionized water 550 parts Styrene 170 parts Methyl methacrylate 660 parts n-butyl acrylate 270 parts 2-hydroxyethyl acrylate 270 parts 2-hydroxyethyl methacrylate 20 parts Acrylic acid 10 parts New Coal 707SF (Note 1) 50 parts Then, the remaining pre-emulsion was continuously dropped into the reaction vessel over 4 hours. After the dropwise addition, the mixture was stirred at 80°C for 1 hour, and then 50 parts of deionized water was added all at once. Next, in a separate vessel, the components of the composition below and 80 parts of a 2.5% aqueous ammonium persulfate solution were stirred and emulsified, and the resulting emulsion was continuously dropped into the reaction vessel over 1 hour.
Deionized water 500 parts Styrene 150 parts Methyl methacrylate 320 parts n-butyl acrylate 30 parts 2-hydroxyethyl acrylate 30 parts 2-hydroxyethyl methacrylate 20 parts Acrylic acid 10 parts Diacetone acrylamide 40 parts Newcol 707SF (Note 1) 80 parts After the completion of the dropwise addition, the mixture was aged for 2 hours after the completion of the dropwise addition. Then, the mixture was cooled to 30°C, and the solid content was adjusted to 47% and the pH to 8.5 using ammonia water and deionized water to obtain a core/shell emulsion (A-1) consisting of two-layer structure particles with a crosslinked inner layer. The obtained core/shell emulsion (A-1) had an average particle size of 160 nm.
(Note 1) Newcol 707SF: Trade name, manufactured by Nippon Nyukazai Co., Ltd., anionic surfactant having a polyoxyethylene chain, non-volatile content 30%
Production Examples 2 to 9
Core/shell emulsions (A-2) to (A-9) were obtained in the same manner as in Production Example 1, except that the blending compositions in Table 1 were used.

Production Example 10
A 2-liter four-neck flask was fitted with a condenser, thermometer, and dropping funnel, and 350 parts of deionized water and 10 parts of ADEKA REASOAP SR-1025 (Note 2) were charged, and the air inside was replaced with nitrogen, after which the internal temperature was raised to 80°C with stirring. Next, 3% of a pre-emulsion made by emulsifying the components shown below and 80 parts of a 2.5% aqueous solution of ammonium persulfate were added to the reaction vessel, and the temperature was maintained at 80°C for 20 minutes.
Deionized water 350 parts Methyl methacrylate 450 parts n-Butyl methacrylate 40 parts 2-Hydroxyethyl acrylate 230 parts 2-Hydroxyethyl methacrylate 40 parts Acrylic acid 10 parts Diacetone acrylamide 10 parts Vinyl triethoxysilane 20 parts Adeka Reasoap SR-1025 (Note 2) 80 parts Then, the remaining pre-emulsion was continuously dropped into the reaction vessel over 2 hours. After the dropwise addition, the mixture was stirred at 80°C for 1 hour, and then 60 parts of deionized water was added all at once. Next, in a separate vessel, the components of the composition below and 80 parts of a 2.5% aqueous ammonium persulfate solution were stirred and emulsified, and the resulting emulsion was continuously dropped into the reaction vessel over 1 hour.
Deionized water 300 parts Methyl methacrylate 200 parts n-Butyl methacrylate 40 parts 2-Hydroxyethyl acrylate 50 parts 2-Hydroxyethyl methacrylate 10 parts Acrylic acid 10 parts Diacetone acrylamide 10 parts Vinyl triethoxysilane 20 parts Adeka Reasoap SR-1025 (Note 2) 50 parts After the dropwise addition, the mixture was aged for 2 hours after the dropwise addition. The mixture was then cooled to 30°C, and the solid content was adjusted to 48% and the pH to 8.8 using ammonia water and deionized water to obtain a core/shell emulsion (CS-1) consisting of two-layer structure particles having an alkoxysilyl group. The obtained core/shell emulsion (CS-1) had an average particle size of 150 nm. The glass transition temperature of the core was 0°C, and the glass transition temperature of the shell was 55°C.
(Note 2) ADEKA REASOAP SR-1025: Trade name, manufactured by ADEKA, non-nonylphenol reactive emulsifier, non-volatile content 25%
Preparation of water-based paint composition
Example 1
A stirred mixing vessel was charged with 55 parts (solids) of the core/shell emulsion (A-1), 0.5 parts (solids) of adipic acid hydrazide, 40 parts (solids) of "Ti-Pure R-706" (trade name, manufactured by Chemours, titanium oxide pigment), 3 parts (solids) of the core/shell emulsion (CS-1), 7 parts of 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, 5.5 parts of 2,2,4-trimethylpentanediol-1,3-diisobutyrate, and 0.5 parts of monoethylene glycol, and the resulting mixture was stirred and mixed to obtain an aqueous coating composition (1).

Examples 2 to 14, Comparative Examples 1 to 5
Each coating composition was obtained in the same manner as in Example 1, except that the formulations shown in Table 2 were used.

The numbers in Table 2 indicate the amount of liquid for solvents and the amount of solids for other materials.

The components in Table 2 are as follows:
"Carbodilite E-05" product name, manufactured by Nisshinbo Chemical Inc., polyvalent carbodiimide, NCN equivalent: 310,
"Takenate WD-730" product name, manufactured by Mitsui Chemicals, Inc., water-dispersible polyisocyanate

Adjustment of the workpiece Workpiece 1
On a "slate board" (product name, manufactured by Partec, slate test panel), "Ecocation Sealer" (product name, manufactured by Kansai Paint, architectural acrylic silicone resin-based sealer paint) was applied with a brush so that the coating amount was 100 g/ ^m2 , and the coating was dried at room temperature for 24 hours to form a coating film. Next, "Ares Elastic Holder Waterproof Type" (product name, manufactured by Kansai Paint, synthetic resin emulsion-based multi-layer finishing coating material) was applied with a porous roller so that the coating amount was 1,000 g/ ^m2 , so that the shape was ripple-like, and the coating was dried at room temperature for 24 hours to form the coated object 1.

Object to be coated 2
On a "slate board" (product name, manufactured by Paltec, slate test panel), "Ecocation Sealer" (product name, manufactured by Kansai Paint, architectural acrylic silicone resin-based sealer paint) was applied with a brush so that the coating amount was 100 g/ ^m2 , and the paint was dried at room temperature for 24 hours to form a coating film. Next, "Ares Rubber Tile New Rough" (product name, manufactured by Kansai Paint, synthetic resin emulsion-based multi-layer coating material) was applied with a lysine gun so that the coating amount was 800 g/ ^m2 to create an uneven shape, and the paint was dried at room temperature for 24 hours. After that, the same paint was applied with a tile gun so that the coating amount was 1,000 g/ ^m2 , and the paint was dried at room temperature for 24 hours to form a coated object 2.

Object to be coated 3
"Supersaurus II" (product name, Kansai Paint Co., Ltd., architectural turpentine-soluble modified epoxy resin-based undercoat paint) was applied with a brush onto "A1050P" (product name, manufactured by Partec Co., Ltd., aluminum panel) in an amount of 140 g/ ^m2 , and the paint was dried at room temperature for 24 hours to form a coating film, which was used as the coated object 3.

Evaluation of Coating Film The performance of the coating film of each test plate obtained as described above was evaluated. The results are shown in Table 1.

Tensile modulus of elasticity: Each of the aqueous coating compositions obtained in the above examples was applied onto a polypropylene plate using a 250 μm applicator, and after drying for 7 days under an atmosphere of 23° C. and 50% humidity, the coating film was peeled off. The peeled coating film was measured using an EZ Test manufactured by Shimadzu Corporation.

Martens hardness Each aqueous coating composition obtained in the above examples was applied to a glass plate using a 250 μm applicator, and dried for 7 days under an atmosphere of 23° C. and 50% humidity to obtain a test plate. Measured using PICODENTOR HM500 (product name; manufactured by Fisher Instruments). At that time, the load was 5 mN/25 s, a diamond cone was used as a needle, and the measurement was performed at a face angle of 136°.

Elasticity: Evaluation was performed under the conditions of the JIS-A6909 hot and cold cycle test for architectural finish coating materials. Each aqueous coating composition was applied to the coating materials 1 and 2, and dried for 7 days under an atmosphere of 23°C and 50% humidity. Each test specimen was immersed in tap water at 23±2°C for 18 hours, immediately cooled in a thermostat at -20±2°C for 3 hours, and then immediately heated in another thermostat at 50±3°C for 3 hours. This 24-hour cycle was repeated 10 times, and then left to stand in a test room for 2 hours, and the presence or absence of cracks, peeling, and swelling of the coating film was evaluated visually and with a magnifying glass.
◎: No cracks, peeling, or swelling was observed with the naked eye or with a magnifying glass.
○: No cracks, peeling, or swelling was observed with the naked eye, but any of cracks, peeling, or swelling was observed with a magnifying glass.
x: Any of cracks, peeling, and swelling is visually observed.

Stain resistance Each aqueous coating composition was applied to a substrate 3 with a film thickness or coating amount of 100 g/ ^m2 so that the coating surface was smooth, and then dried for 24 hours at 23°C and 50% humidity to prepare a test specimen. The test surface was fixed in Ota-ku, Tokyo, facing south and at an angle of 30 degrees to the horizontal, and the staining state after six months of exposure was evaluated visually according to the following criteria. The color difference ΔE before and after exposure was also evaluated using a colorimeter "CR-400" (product name, manufactured by Minolta Co., Ltd.).
◎: ΔL is less than 5 (dirt is barely noticeable),
○: ΔL is 5 to 10 (some dirt is observed, but it is practical).
x: ΔL exceeds 10 (stains are noticeable).

Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-mentioned embodiments, and various modifications based on the technical concept of the present invention are possible.

Claims (8)

The core is a polymer having a glass transition temperature of 5 to 50°C,
The shell is a polymer having a glass transition temperature of 50 to 90°C,
A core/shell emulsion (A) having a ΔTg (glass transition temperature of the shell - glass transition temperature of the core) of 40 to 60°C;
The aqueous coating composition contains at least one crosslinking agent (B) selected from a hydrazide compound, a glycidyl group-containing compound, a carbodiimide compound, an oxazoline compound, and an isocyanate compound, and 3 to 15 parts by mass of an organic solvent (D) having a boiling point of 200°C or higher, based on 100 parts by mass of the solid content in the aqueous coating composition, and the polymerizable unsaturated monomer constituting the core contains 2-hydroxyethyl (meth)acrylate and (meth)acrylic acid,
the polymerizable unsaturated monomer constituting the shell comprises 2-hydroxyethyl (meth)acrylate, (meth)acrylic acid, and diacetone (meth)acrylamide;
An aqueous coating composition characterized in that the organic solvent (D) having a boiling point of 200° C. or higher contains 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate , provided that the aqueous coating composition does not include a carbonyl group-containing copolymer (I) obtained by copolymerizing a monomer mixture containing a carbonyl group-containing polymerizable unsaturated monomer (a), a carboxyl group-containing polymerizable unsaturated monomer (b), and a hydrophilic polymerizable unsaturated monomer (c) other than the monomers (a) and (b) in the presence of a hydrophilic organic solvent, the total copolymerization ratio of the carboxyl group-containing polymerizable unsaturated monomer (b) and the hydrophilic polymerizable unsaturated monomer (c) being 30 mass % or more in the total polymerizable unsaturated monomers used in the production of the copolymer (I), and the copolymerization ratio of the carboxyl group-containing polymerizable unsaturated monomer (b) being within the range of 0.1 to 70 mass %. The core/shell emulsion (A) comprises
2. The aqueous coating composition according to claim 1, wherein the mass ratio of the core polymer to the shell polymer is in the range of 50/50 to 90/10. The aqueous coating composition according to claim 1 or 2, wherein the solid content of the core/shell emulsion (A) is 30 to 99.5 parts by mass based on 100 parts by mass of the solid content of the aqueous coating composition. The aqueous coating composition according to any one of claims 1 to 3 further contains 20 to 200 parts by mass of titanium oxide pigment (C) based on 100 parts by mass of the solid content of the resin contained in the aqueous coating composition. 5. The aqueous coating composition according to claim 1, further comprising a core/shell acrylic emulsion having an alkoxysilyl group other than component (A). The aqueous coating composition according to any one of claims 1 to 5, which is capable of forming a cured coating film having a thickness of 70 μm on a glass plate having a thickness of 3.0 mm, and aging the coating film for one week under an atmosphere of 23°C and humidity of 50%, the Martens hardness of the coating film surface measured at a temperature of 23°C and a load of 5 mN/25 s using an ultra-microhardness tester is 2.0 to 40.0 N/ ^mm2 . A method for forming a coating film, comprising the step of applying the aqueous coating composition according to any one of claims 1 to 6 to a substrate. A coated article having a cured coating film formed from the aqueous coating composition according to any one of claims 1 to 6 .