CN112368345A

CN112368345A - Aqueous coating composition

Info

Publication number: CN112368345A
Application number: CN201980045136.5A
Authority: CN
Inventors: 富森岳; 江森丽了
Original assignee: Kansai Paint Co Ltd
Current assignee: Kansai Paint Co Ltd
Priority date: 2018-07-27
Filing date: 2019-07-11
Publication date: 2021-02-12
Also published as: JP7280263B2; WO2020022077A1; JPWO2020022077A1

Abstract

The purpose of the present invention is to provide an aqueous coating composition which has good film-forming properties at low temperatures and is also excellent in corrosion resistance, hardness and water resistance. The present invention relates to an aqueous coating composition containing a core-shell acrylic resin particle (A) comprising at least 1 gradient polymer layer, wherein the shell portion of the core-shell acrylic resin particle (A) has an acid value within the range of 20 to 100 mgKOH/g.

Description

Aqueous coating composition

Technical Field

The present invention relates to an aqueous coating composition having good film-forming properties at low temperatures and excellent corrosion resistance, hardness and water resistance. Further, it relates to a coated article having a cured coating film of the aqueous coating composition.

Background

In recent years, from the viewpoint of global environmental protection and safety and hygiene, the conversion from solvent-based paints to water-based paints has been advanced, and aqueous anticorrosive paints have also been developed in the field of anticorrosive paints for metal substrates and the like.

An emulsion coating is a mainstream in a water-based coating, and the content of a solvent is significantly smaller than that of a solvent-based coating, but in order to improve the film-forming property, it is practical to include a considerable amount of a solvent as a film-forming aid in the coating in spite of its water-based nature.

As a method for improving film forming properties without using a film forming aid (solvent), there is a method of softening an emulsion resin, but the hardness of the obtained coating film is lowered and the film properties such as corrosion resistance are also lowered.

Patent document 1 discloses a method for producing an aqueous emulsion, which comprises subjecting a1 st ethylenically unsaturated compound component (a) having a glass transition temperature of a polymer of-30 ℃ or lower and a2 nd ethylenically unsaturated compound component (B) having a glass transition temperature of a polymer of 30 ℃ or higher to dynamic charge polymerization in an aqueous medium under specific polymerization conditions. It is described that the aqueous emulsion obtained by the production method has good low-temperature film-forming properties without using a solvent such as a film-forming aid, and the obtained resin film has low surface tackiness and excellent durability.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2000-319301

Disclosure of Invention

Problems to be solved by the invention

However, although the aqueous emulsion obtained by this production method is confirmed to have improved low-temperature film-forming properties and viscosity, the hardness of the resulting coating film is insufficient, and improvement is desired.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an aqueous coating composition which is excellent in film-forming properties at low temperatures and is also excellent in corrosion resistance, hardness and water resistance.

Means for solving the problems

As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by an aqueous coating composition containing core-shell acrylic resin particles having at least 1 gradient polymer layer and a shell portion having an acid value in a specific range.

That is, the present invention includes the following aspects.

(1) An aqueous coating composition comprising core-shell acrylic resin particles (A) comprising at least 1 gradient polymer layer,

the acid value of the shell of the core-shell acrylic resin particle (A) is in the range of 20 to 100 mgKOH/g.

(2) The aqueous coating composition according to the above (1), wherein the core-shell acrylic resin particles (A) have a glass transition temperature of-10 ℃ or higher.

(3) The aqueous coating composition according to the item (1) or (2), wherein 80% by weight or more of the total copolymerized components of the core-shell acrylic resin particles (A) is a polymerizable unsaturated monomer having a solubility parameter value of 9.5 or less.

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

The coated article according to the item (4), wherein the substrate is a metal substrate.

ADVANTAGEOUS EFFECTS OF INVENTION

The water-based coating composition of the present invention has the above-described features, and thus can form a coating film having good film-forming properties at low temperatures and excellent corrosion resistance, hardness, and water resistance.

Detailed Description

The aqueous coating composition of the present invention will be described in further detail below. In the present specification, "mass%" and "weight%", and "part by mass" and "part by weight" have the same meanings, respectively.

The aqueous coating composition is characterized by comprising core-shell acrylic resin particles (A) containing at least 1 layer of a gradient polymer, wherein the shell of the core-shell acrylic resin particles (A) has an acid value within the range of 20-100 mgKOH/g.

In the present embodiment, the "shell portion" of the core-shell type acrylic resin particle (a) refers to a polymer layer present in the outermost layer of the resin particle, the "core portion" refers to a polymer layer in the inner layer of the resin particle excluding the shell portion, and the "core-shell type structure" refers to a structure having the core portion and the shell portion.

The core-shell structure is generally a layer structure in which the core portion is completely covered with the shell portion, but depending on the mass ratio of the core portion to the shell portion, the amount of the monomer in the shell portion may be insufficient for forming the layer structure. In such a case, the shell portion may be configured to cover a part of the core portion, without having to have a complete layer structure as described above.

The concept of the multilayer structure in the core-shell structure is similarly applied to the case where the core portion of the core-shell acrylic resin particle (a) has a multilayer structure.

In the present embodiment, the gradient polymer layer refers to a polymer layer having a layer structure in which the composition changes continuously (having a composition gradient).

More specifically, it refers to a polymer layer having a composition gradient in which, for example, the composition of a monomer (or a monomer mixture) changes continuously from a monomer a (or a monomer mixture a) to a monomer B (or a monomer mixture B).

The gradient polymer layer described above can generally be obtained by a well-known polymerization method known as kinetic-feed polymerization. Specifically, for example, in the case of polymerizing 2 kinds of monomers a (monomer mixture a) and B (monomer mixture B), the gradient polymer layer can be obtained by introducing the monomer a (monomer mixture a) into a reaction vessel and performing polymerization while dropping the monomer B (monomer mixture B) into the vessel containing the monomer a (monomer mixture a).

In the above dynamic feed polymerization, a gradient polymer layer having a desired composition gradient can be obtained by setting synthesis conditions (timing of starting mixing of the monomer a (monomer mixture a) and the monomer B (monomer mixture B), a speed of dropping the monomer B (monomer mixture B) into a vessel containing the monomer a (monomer mixture a), a speed of introducing the monomer a (monomer mixture a) into a reaction vessel, and the like).

The core-shell acrylic resin particle (a) has at least 1 layer of the gradient polymer layer, and the gradient polymer layer may be any layer of the core-shell acrylic resin particle (a).

The core-shell acrylic resin particle (a) is generally an acrylic resin particle composed of a core portion of a copolymer (I) containing a polymerizable unsaturated monomer as a copolymerization component and a shell portion of a copolymer (II) containing a polymerizable unsaturated monomer as a copolymerization component. The polymerizable unsaturated monomer means a monomer having a polymerizable unsaturated group.

In the present specification, the polymerizable unsaturated group means an unsaturated group capable of radical polymerization. Examples of the polymerizable unsaturated group include a vinyl group, a vinylidene group, an acryloyl group, and a methacryloyl group.

In the present specification, "(meth) acrylate" means "acrylate or methacrylate". "(meth) acrylic acid" means "acrylic acid or methacrylic acid". Further, "(meth) acryloyl" means "acryloyl or methacryloyl". Further, "(meth) acrylamide" means "acrylamide or methacrylamide".

Examples of the polymerizable unsaturated monomer include a polymerizable unsaturated monomer having 1 polymerizable unsaturated group in 1 molecule and a polymerizable unsaturated monomer having 2 or more polymerizable unsaturated groups in 1 molecule.

Examples of the polymerizable unsaturated monomer having 1 polymerizable unsaturated group in 1 molecule include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, n-hexyl (meth) acrylate, n-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, tridecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, イソステアリルアクリレート "(trade name, available from Osaka-Chemicals Co., Ltd.) (isostearyl acrylate), cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, and mixtures thereof, Alkyl or cycloalkyl (meth) acrylates such as t-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, tricyclodecyl (meth) acrylate and the like; isobornyl group-containing polymerizable unsaturated monomers such as isobornyl (meth) acrylate; polymerizable unsaturated monomers having an adamantyl group such as adamantyl (meth) acrylate; a polymerizable unsaturated monomer having a tricyclodecenyl group such as tricyclodecenyl (meth) acrylate; aromatic ring-containing polymerizable unsaturated monomers such as benzyl (meth) acrylate, styrene, α -methylstyrene and vinyltoluene; polymerizable unsaturated monomers having an alkoxysilyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, γ - (meth) acryloyloxypropyltrimethoxysilane, and γ - (meth) acryloyloxypropyltriethoxysilane; perfluoroalkyl (meth) acrylates such as perfluorobutyl ethyl (meth) acrylate and perfluorooctyl ethyl (meth) acrylate; a polymerizable unsaturated monomer having a fluoroalkyl group such as a fluoroolefin; polymerizable unsaturated monomers having a photopolymerizable functional group such as a maleimide group; vinyl compounds such as N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, and vinyl acetate; a mono-esterified product of (meth) acrylic acid such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate with a 2-membered alcohol having 2 to 8 carbon atoms, an epsilon-caprolactone-modified product of the mono-esterified product, N-hydroxymethyl (meth) acrylamide, allyl alcohol, a (meth) acrylate having a polyoxyethylene chain in which a hydroxyl group is at a molecular end, and the like; carboxyl group-containing polymerizable unsaturated monomers such as (meth) acrylic acid, maleic acid, crotonic acid, and β -carboxyethyl acrylate; nitrogen-containing polymerizable unsaturated monomers such as (meth) acrylonitrile, (meth) acrylamide, N-dimethylaminoethyl (meth) acrylate, N-diethylaminoethyl (meth) acrylate, N-dimethylaminopropyl (meth) acrylamide, and adducts of glycidyl (meth) acrylate and amines; epoxy group-containing polymerizable unsaturated monomers such as glycidyl (meth) acrylate, β -methylglycidyl (meth) acrylate, 3, 4-epoxycyclohexylmethyl (meth) acrylate, 3, 4-epoxycyclohexylethyl (meth) acrylate, 3, 4-epoxycyclohexylpropyl (meth) acrylate, and allyl glycidyl ether; (meth) acrylates having a polyoxyethylene chain with an alkoxy group at the molecular end, and the like.

These monomers may be used alone in 1 kind or in combination in 2 or more kinds depending on the performance required for the core-shell type acrylic resin particle (a).

Examples of the polymerizable unsaturated monomer having 2 or more polymerizable unsaturated groups in 1 molecule include allyl (meth) acrylate, ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, 1, 3-butanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1, 4-butanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerol di (meth) acrylate, 1,1, 1-trihydroxymethyl ethane tri (meth) acrylate, and the like, 1,1, 1-trihydroxymethylpropane tri (meth) acrylate, methylenebis (meth) acrylamide, ethylenebis (meth) acrylamide, triallyl isocyanurate, diallyl terephthalate, divinylbenzene, and the like. These monomers may be used alone in 1 kind, or in combination of 2 or more kinds.

The polymerizable unsaturated monomer having 2 or more polymerizable unsaturated groups in the molecule of 1 above has a function of imparting a crosslinked structure to the copolymer. When a polymerizable unsaturated monomer having 2 or more polymerizable unsaturated groups in 1 molecule is used, the use ratio thereof can be appropriately determined depending on the degree of crosslinking of the copolymer, but usually, the total amount of the polymerizable unsaturated monomer having 2 or more polymerizable unsaturated groups in 1 molecule and the polymerizable unsaturated monomer having 1 polymerizable unsaturated group in 1 molecule is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, further preferably 1% by mass or more, and further preferably 30% by mass or less, more preferably 10% by mass or less, further preferably 7% by mass or less.

The core-shell type acrylic resin particle (a) can be obtained by obtaining an emulsion of the core copolymer (I) by emulsion polymerization of a polymerizable unsaturated monomer mixture, adding the polymerizable unsaturated monomer mixture to the emulsion, and further emulsion polymerization of the mixture to prepare the shell copolymer (II).

The emulsion polymerization for preparing the emulsion of the core copolymer (I) can be carried out by a conventionally known method. For example, the polymerization can be carried out by emulsion-polymerizing a polymerizable unsaturated monomer mixture using a polymerization initiator in the presence of an emulsifier.

As the emulsifier, anionic emulsifiers and nonionic emulsifiers can be suitably used.

Examples of the anionic emulsifier include sodium salts and ammonium salts of alkylsulfonic acid, alkylbenzenesulfonic acid, alkylphosphoric acid, and the like. Examples of the nonionic emulsifier include polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan trioleate, and polyoxyethylene sorbitan monolaurate.

Furthermore, a polyoxyalkylene group-containing anionic emulsifier having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group in 1 molecule; 1 a reactive anionic emulsifier having an anionic group and a radical polymerizable unsaturated group in the molecule.

Examples of the reactive anionic emulsifier include sodium salts of sulfonic acid compounds having a radical polymerizable unsaturated group such as an allyl group, a methallyl group, (meth) acryloyl group, propenyl group, butenyl group, and ammonium salts of the sulfonic acid compounds.

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

Examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, t-butyl peroxide, t-butyl peroxylaurate, t-butyl peroxyisopropylcarbonate, t-butyl peroxyacetate, and diisopropylbenzene hydroperoxide; azo compounds such as azobisisobutyronitrile, azobis (2, 4-dimethylvaleronitrile), azobis (2-methylpropionitrile), azobis (2-methylbutyronitrile), 4' -azobis (4-cyanobutyric acid), dimethyl azobis (2-methylpropionate), azobis [ 2-methyl-N- (2-hydroxyethyl) -propionamide ], azobis { 2-methyl-N- [2- (1-hydroxybutyl) ] -propionamide }; persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate. These polymerization initiators may be used alone or in combination of 2 or more. Further, the polymerization initiator may be used in combination with a reducing agent such as a sugar, sodium formaldehyde sulfoxylate, or an iron complex, if necessary, to prepare a redox initiator.

The amount of the polymerization initiator used is generally preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and further preferably 5% by mass or less, more preferably 3% by mass or less, based on the total amount of all monomers used. The method of adding the polymerization initiator is not particularly limited, and may be appropriately selected depending on the kind and amount thereof. For example, the monomer mixture or the aqueous medium may be contained in advance, or may be added together during polymerization, or may be added dropwise.

The core-shell acrylic resin particle (a) can be obtained by adding a polymerizable unsaturated monomer mixture to the emulsion of the core copolymer (I) obtained above and further polymerizing the mixture to form a shell copolymer (II).

The monomer mixture for forming the shell-side copolymer (II) may contain, as necessary, the above-mentioned polymerization initiator, chain transfer agent, reducing agent, emulsifier and the like as appropriate. The monomer mixture may be directly added dropwise, but it is preferable to add dropwise a monomer emulsion obtained by dispersing the monomer mixture in an aqueous medium. The particle size of the monomer emulsion in this case is not particularly limited.

The polymerization method of the monomer mixture for forming the shell-side copolymer (II) includes, for example, a method in which the monomer mixture or an emulsion thereof is added to the emulsion of the core-side copolymer (I) and heated to an appropriate temperature while stirring, all or gradually dropped.

The core-shell acrylic resin particle (a) thus obtained has a multilayer structure in which the copolymer (I) is used as a core portion and the copolymer (II) is used as a shell portion.

Further, the core-shell type acrylic resin particle (a) may be prepared by adding a polymerizable unsaturated monomer (a mixture of 1 or 2 or more species) for forming another resin layer between the step of obtaining the core copolymer (I) and the step of obtaining the shell copolymer (II) and performing emulsion polymerization, thereby obtaining an acrylic resin particle having 3 or more layers.

The core-shell acrylic resin particle (a) is a resin particle including at least 1 gradient polymer layer, but the gradient polymer layer may be any of the core-shell acrylic resin particles (a).

The resin layer as the gradient polymer layer can be prepared by the above-mentioned kinetic-feed polymerization or the like.

From the viewpoint of corrosion resistance and hardness of the obtained coating film, the ratio of the gradient polymer layer in the core-shell acrylic resin particle (a) is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, and furthermore preferably 90% by mass or less, more preferably 85% by mass or less, further preferably 80% by mass or less, relative to the total amount of all copolymerized components of the core-shell acrylic resin particle (a).

When the ratio is 90 mass% or less, the layer other than the gradient polymer layer in the core-shell acrylic resin particle (a) is present at a constant level or more, and the hardness can be maintained at a constant level or more by the presence of the hard monomer component. Further, when the ratio is 10% by mass or more, the film formability is excellent and good corrosion resistance can be obtained.

From the viewpoint of dispersion stability of the particles and hydrophilicity of the coating film, the acid value of the shell portion (shell copolymer (II) (outermost layer)) of the core-shell acrylic resin particle (a) is preferably 20mgKOH/g or more, more preferably 25mgKOH/g or more, further preferably 30mgKOH/g or more, further preferably 100mgKOH/g or less, more preferably 80mgKOH/g or less, further preferably 60mgKOH/g or less.

When the acid value of the shell portion is 20mgKOH/g or more, the dispersion stability of the particles becomes good, and when the acid value is 100mgKOH/g or less, the hydrophilicity of the coating film becomes too high, and the corrosion resistance and water resistance become poor.

The monomer for imparting an acid value to the shell-type copolymer (II) is preferably a carboxyl group-containing polymerizable unsaturated monomer, from the viewpoint that the neutralizing agent volatilizes and the hydrophilicity is greatly reduced after film formation, and that water resistance and corrosion resistance are favorable.

Acrylic acid and/or methacrylic acid can be particularly suitably used as the carboxyl group-containing polymerizable unsaturated monomer.

In the present specification, the acid value (mgKOH/g) is represented by the mg number of potassium hydroxide when the amount of acid groups contained in sample 1g (solid content 1g in the case of resin) is converted to potassium hydroxide. The molecular weight of potassium hydroxide was set to 56.1.

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

Acid value (mgKOH/g) is 56.1 XV XC/m

V: titration amount (ml), C: concentration of the titration solution (mol/l), m: weight of solid content (g) of sample

From the viewpoint of coating film hardness, the glass transition temperature (Tg) of the core-shell type acrylic resin particles (A) is preferably-10 ℃ or higher, more preferably-5 ℃ or higher, and still more preferably 0 ℃ or higher.

By setting the glass transition temperature (Tg) to-10 ℃ or higher, the hardness of the resulting coating film can be prevented from lowering, and the blotting resistance can be maintained.

In the present specification, when the resin is a copolymer composed of 2 or more monomers, the glass transition temperature (Tg, ° c) of the copolymer can be calculated by the following formula.

1/Tg(K)＝(W1/T1)+(W2/T2)+··(Wn/Tn)

Tg(℃)＝Tg(K)-273

In each formula, n represents the number (natural number) of the monomers used, W1 to Wn represents the weight% of each of the n monomers used for copolymerization, and T1 to Tn represents the Tg (K) of each of the homopolymers of the n monomers. T1 to Tn can be values described in Polymer Hand Book (Second Edition, J.Brantup. E.H.Immergut) pages III-139 to 179.

The glass transition temperature (. degree. C.) of the homopolymer of the monomer, when Tg is unknown, can also be determined as the static glass transition temperature by actual measurement. In this case, for example, a sample is taken into a measuring cup by using a differential scanning calorimeter "DSC-220U" (manufactured by セイコーインスツルメント Co.), the sample is completely removed by vacuum-pumping, then the change in heat is measured in the range of-20 ℃ to +200 ℃ at a temperature-raising rate of 3 ℃/min, and the change point of the first base line on the low temperature side is set as the static glass transition temperature.

From the viewpoint of the corrosion resistance and water resistance of the resulting coating film, it is preferable that 80% by mass or more of all the copolymerization components of the core-shell acrylic resin particles (a) (all the polymerizable unsaturated monomers constituting the core-shell copolymer (I) and the shell-shell copolymer (II)) be a polymerizable unsaturated monomer having a solubility parameter value (SP value) of 9.5 or less. The polymerizable unsaturated monomer having a solubility parameter value (SP value) of 9.5 or less is more preferably 90% by mass or more, and still more preferably 95% by mass or more of the total copolymerization components.

In the present specification, the solubility parameter value (SP value) is a value calculated by the following Fedors formula described in Polymer Engineering and Science, 14, No.2, p.147 (1974).

(in the formula,. DELTA.e 1 represents cohesive energy per unit functional group, and. DELTA.v 1 represents molecular volume per unit functional group.) the SP value of a copolymer or a blend of a mixture of 2 or more resins is the sum of the SP values of the monomer units or the components of the blend multiplied by the mass fraction.

In addition, the weight average molecular weight of the core-shell acrylic resin particles (a) is preferably 40000 or more from the viewpoint of the corrosion resistance, water resistance and hardness of the resulting coating film.

In the present specification, the weight average molecular weight is a value obtained by converting the retention time measured by gel permeation chromatography into the molecular weight of polystyrene by the retention time of standard polystyrene having a known molecular weight measured under the same conditions.

Specifically, for example, as a gel permeation chromatography apparatus, "HLC-8120 GPC" (product name, manufactured by imperial ソー corporation) was used, as a column, a total of 4 of "TSKgel G4000 HXL" 1, "TSKgel G3000 HXL" 2, and "TSKgel G2000 HXL" 1 (product name, both manufactured by imperial ソー corporation) were used, as a detector, and a differential refractive index meter was used, and in a mobile phase: tetrahydrofuran, measurement temperature: 40 ℃, flow rate: the weight average molecular weight can be determined by measuring under the condition of 1 mL/min.

The average particle diameter of the core-shell acrylic resin particles (a) is preferably 50nm or more, more preferably 60nm or more, further preferably 70nm or more, and further preferably 500nm or less, more preferably 400nm or less, further preferably 300nm or less.

By setting the average particle diameter to 50nm or more, the viscosity is not excessively high, and the handling becomes good. Further, dispersion stability is improved by setting the average particle diameter to 500nm or less.

The average particle diameter can be measured by a general measurement means such as laser light scattering.

In the present specification, the average particle diameter of the resin particles is a value measured at 20 ℃ after diluted with deionized water by a conventional method using a submicron particle size distribution measuring apparatus. As the submicron particle size distribution measuring apparatus, for example, "COULTER N4 type" (trade name, manufactured by ベックマン. コールター) can be used.

In order to improve the mechanical stability of the core-shell acrylic resin particles (a), the acid groups such as the carboxyl groups of the acrylic resin particles may be neutralized with a neutralizing agent. The neutralizing agent is not particularly limited as long as it can neutralize an acid group, and examples thereof include sodium hydroxide, potassium hydroxide, trimethylamine, 2- (dimethylamino) ethanol, 2-amino-2-methyl-1-propanol, triethylamine, and ammonia. These neutralizing agents can be used suitably in such an amount that the pH of the aqueous dispersion of the core-shell acrylic resin particles (a) after neutralization is about 6.5 to 9.0.

In the aqueous coating composition, resin particles other than the core-shell type acrylic resin particles (a) may be used as necessary. Specifically, examples thereof include, for example, resin particles comprising at least 1 resin selected from the group consisting of acrylic resins, acrylic/styrene resins, urethane resins, phenol resins, vinyl chloride resins, vinyl acetate/acrylic resins, ethylene/vinyl acetate resins, epoxy ester resins, polyester resins, alkyd resins, acrylonitrile/butadiene resins, styrene/butadiene resins, polybutadiene, polyisoprene, silicone resins, fluorine resins, and the like, and resins obtained by modifying these resins, for example, carbonate-modified urethane resins, acrylic resin-modified epoxy resins, alkyd-modified epoxy resins, polybutadiene-modified epoxy resins, (poly) amine-modified epoxy resins, urethane-modified epoxy resins, and the like. These resin particles may be so-called rubber. However, the core-shell acrylic resin particles (a) are excluded.

When the resin particles are formed of a plurality of resins, the resin particles may be formed by blending a plurality of resins, or may be a blend of a plurality of resin particles. These resin particles can be usually blended in the form of an emulsion in an aqueous coating composition.

From the viewpoint of storage stability of the coating material, the pH of the aqueous coating composition is preferably 5.0 or more, more preferably 6.0 or more, and further preferably 10.0 or less, more preferably 9.0 or less.

The aqueous coating composition may further contain, if necessary, a crosslinking agent, a curing catalyst, a pigment such as a coloring pigment, a filler, an aggregate (aggregate), a dispersant, a wetting agent, a thickener, a rheology control agent, a surface conditioner, an antifoaming agent, an antiseptic, a fungicide, a pH adjuster, a rust inhibitor, a setting inhibitor, an antifreeze, an antiskinning agent, an ultraviolet absorber, an antioxidant, an organic solvent, and the like.

The aqueous coating composition is preferably formed into a cured coating film which is applied to various substrates, preferably metal substrates, which are optionally subjected to a base treatment, and cured. The coating can be formed by directly coating 1 or 2 or more times by a conventionally known method such as roll coating, spray coating, brush coating, curtain coating, spray coating, dip coating, and the like.

When the substrate is a metal substrate, a cured coating film is formed by applying the aqueous coating composition according to the present embodiment to the metal substrate and curing the coating film, whereby a coated article having good film-forming properties at low temperatures and excellent corrosion resistance can be obtained.

From the viewpoint of energy saving and the like, the coating film of the aqueous coating composition is preferably cured at normal temperature. In addition, from the viewpoint of improving the production efficiency, the resin composition may be forcibly dried and cured by heating.

The thickness of the cured coating film obtained by applying and curing the aqueous coating composition is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 25 μm or more, and further preferably 200 μm or less, more preferably 100 μm or less, even more preferably 60 μm or less, from the viewpoint of the corrosion resistance, water resistance, hardness, and the like of the cured coating film formed.

Examples

The present invention will be described in more detail below with reference to production examples, examples and comparative examples. However, the present invention is not limited thereto. In each example, "part" and "%" are based on mass unless otherwise specified. Further, the film thickness of the coating film is based on the cured coating film. The blank column in the table indicates that the component is not contained.

< production of core-Shell acrylic resin particles >

Production example 1

Deionized water (DIW) charged in an amount shown in table 1 (shi Write み) and Newcol (registered trademark) 707SF (trade name, manufactured by japan emulsifier corporation, anionic surfactant, solid content 30 mass%) were charged into a polymerization apparatus equipped with a stirrer, a thermometer, and a reflux condenser, and the temperature was raised after sufficient replacement with nitrogen gas. The internal temperature was maintained at 82 ℃ while stirring at about 100rpm, and a substance obtained by emulsifying the component (a1) shown in table 1 (hereinafter referred to as a component (a1) emulsion, similarly described with respect to the component (a2), the component (B1) and the component (B2)) and an aqueous solution of initiator 1 (in table 1, VA-057 is a trade name, fuji フィルム and shiko, 2-2' -azobis [ N- (2-carboxyethyl) -2-methylpropanediamine ] tetrahydrate salt) were added dropwise and polymerized using a homomixer.

Regarding the dropping speed, the emulsion of the component (A1) was set to about 146.0 parts/hr, and the aqueous solution of the initiator 1 was set to about 6.6 parts/hr. At the same time as the completion of the addition of the (a1) component emulsion, the addition of the (a2) component emulsion shown in table 1 was started. At the same time, the (B1) component emulsion shown in table 1 was added dropwise to the (a2) component emulsion. (B1) The dropping rate of the component emulsion was set to a rate at which the dropping of the component emulsion was completed simultaneously with the completion of the dropping of the component emulsion (a2), that is, about 73.0 parts/hour in this production example. Then, the component emulsion (B2) was added dropwise at about 146.0 parts/hour.

After completion of the dropwise addition, the reaction was carried out at 82 ℃ for 0.5 hour, and an aqueous solution of initiator 2 was added dropwise at about 3.3 parts/hour. After the end of the dropwise addition, the reaction was carried out at 82 ℃ for 1.5 hours and then cooled to 25 ℃. Finally, the neutralizing agent shown in table 1 was added to obtain an emulsion of core-shell acrylic resin particles (a-1) (shell acid value 34mgKOH/g, core layer (homogeneous layer/gradient polymer layer)/shell layer mass ratio 75 (25/50)/25) having a solid content mass concentration of 40.0%.

The emulsion had a viscosity (measured with a B-type viscometer, 60rpm, 20 ℃) of 680 mPas, a pH of 9.2 (measured with a pH meter), and an average particle diameter of 105 nm.

Production examples 2 to 10

Each of the core-shell acrylic resin particles (a-2) to (a-10) (all of which were core layers (═ uniform layers/gradient polymer layers)/shell layers having a mass ratio of 75(═ 25/50)/25) was obtained in the same manner as in production example 1, except that the compounding composition was changed to the compounding composition shown in table 1 in production example 1. The core-shell acrylic resin particles (A-9) and (A-10) were those for comparative examples.

Production example 11 (for comparative example)

A polymerization apparatus equipped with a stirrer, a thermometer and a reflux condenser was charged with deionized water and Newcol707SF in amounts shown in Table 1 (Shi Write み), and the contents were sufficiently replaced with nitrogen gas, followed by heating. While the internal temperature was maintained at 82 ℃ with stirring at about 100rpm, an aqueous solution of initiator 1 and a substance obtained by emulsifying component (a1) shown in table 1 using a homomixer was added dropwise to the mixture, and polymerization was carried out. Regarding the dropping speed, the emulsion of the component (A1) was set to about 146.0 parts/hr, and the aqueous solution of the initiator 1 was set to about 6.6 parts/hr. At the same time as the completion of the dropwise addition of the emulsion of component (a1), the emulsion of component (B1) shown in table 1 was started to be added dropwise at about 146.0 parts/hour. After completion of the dropwise addition, the reaction was carried out at 82 ℃ for 0.5 hour, and an aqueous solution of initiator 2 was added dropwise at about 3.3 parts/hour. After the end of the dropwise addition, the reaction was carried out at 82 ℃ for 1.5 hours and then cooled to 25 ℃. Finally, the neutralizing agent shown in table 1 was added to obtain an emulsion of core-shell acrylic resin particles (a-11) (shell acid value 34mgKOH/g, core layer (homogeneous layer/gradient polymer layer)/shell layer mass ratio of 50(═ 50/0)/50 (no gradient polymer layer)) having a solid content mass concentration of 40.0%.

The emulsion had a viscosity (measured with a B-type viscometer, 60rpm, 20 ℃) of 620 mPas, a pH of 9.2 (measured with a pH meter), and an average particle diameter of 110 nm.

Production example 12 (for comparative example)

A polymerization apparatus equipped with a stirrer, a thermometer and a reflux condenser was charged with deionized water and Newcol707SF in amounts shown in Table 1 (Shi Write み), and the contents were sufficiently replaced with nitrogen gas, followed by heating. The internal temperature was maintained at 82 ℃ while stirring at about 100rpm, and an aqueous solution of initiator 1 and the component (A1) shown in Table 1 emulsified with a homomixer were added dropwise over 3 hours to polymerize. After completion of the dropwise addition, the reaction was carried out at 82 ℃ for 0.5 hour, and an aqueous solution of initiator 2 was added dropwise over 0.5 hour. After the end of the dropwise addition, the reaction was carried out at 82 ℃ for 1.5 hours and then cooled to 25 ℃. Finally, the neutralizing agent shown in Table 1 was added to obtain an emulsion of core-shell acrylic resin particles (A-12) (shell acid value: 34mgKOH/g, single-layer homogeneous composition particles) having a solid content mass concentration of 40.0%.

The emulsion had a viscosity (measured with a type B viscometer, 60rpm, 20 ℃) of 520 mPas, a pH of 9.2 (measured with a pH meter), and an average particle diameter of 108 nm.

TABLE 1

< production of Water-based coating composition >

Example 1

3 parts of DISPERBYK (registered trademark) -190 (trade name, BYK Co., Ltd., pigment dispersant, solid content 40%) (solid content 1.2 parts), 0.4 part of BYK (registered trademark) -024 (trade name, BYK Co., Ltd., antifoaming agent, solid content 100%), 35 parts of JR-603 (trade name, テイカ Co., titanium oxide, solid content 100%), 15 parts of スーパー SS (trade name, manufactured by pill tail カルシウム Co., Ltd., calcium carbonate, solid content 100%), 25 parts of deionized water and 2 parts of dipropylene glycol monomethyl ether were mixed and added with glass beads, and then dispersed for 60 minutes by a paint shaker (paint) to obtain a pigment paste (P1) (solid content 64.2%).

After removing the glass beads, 250 parts (solid content 100 parts) of the emulsion of the core-shell acrylic resin particles (A-1) obtained in production example 1, 0.5 parts of BYK-348 (trade name, BYK Seisakusho, surface conditioner, solid content 100%), 2.5 parts (solid content 0.5 parts) of SN シックナー 660T (trade name, サンノプコ Sekusho, thickener, solid content 20%) and 10 parts of dipropylene glycol monomethyl ether were mixed and stirred with 80 parts (solid content 51.4 parts) of the pigment paste (P1) obtained, thereby obtaining an aqueous coating composition No.1 having a pH of 8.2 and a coating solid content of 44.5% by mass.

Examples 2 to 8 and comparative examples 1 to 4

Aqueous coating compositions nos. 2 to 12 were obtained in the same manner as in example 1, except that the compounding composition in example 1 was changed to the compounding composition shown in table 2.

Table 2 also shows the glass transition temperatures (Tg, ° c) of the core-shell acrylic resin particles (a-1) to (a-12) of the respective aqueous coating compositions and the ratio (mass%) of the polymerizable unsaturated monomer having a solubility parameter value of 9.5 or less in all copolymerized components (SP value 9.5 or less monomer ratio (mass%)).

< production of test plate >

The respective aqueous coating compositions Nos. 1 to 12 obtained in examples 1 to 8 and comparative examples 1 to 4 were coated on a cold-rolled steel sheet (base material) of 70mm X150 mm X0.8 mm which had been subjected to polishing and degreasing, respectively, using air blasting so that the thickness of the cured coating film became 40 μm. Next, the steel sheet was left at 23 ℃ and 65% RH for 7 days to obtain each test piece having a cured coating film formed thereon.

< evaluation of test plate >

The following tests were carried out on each of the test panels obtained. The evaluation results are shown in table 2.

Corrosion resistance: a120-hour salt spray resistance test was performed on each test panel by causing a cross-cut to the coating film with a knife so as to reach the base material in accordance with JIS K5600-7-1 (1999) "mist spray resistance (mist spray resistance with neutral salt spray)". The scale and the bulge width due to the cut were evaluated according to the following criteria. The smaller the maximum width of rust and bulge, the more excellent the corrosion resistance, and if evaluated as a to C, the corrosion resistance was good.

A: the maximum amplitude of rust and swelling is less than 1mm (single side) from the cutting part

B: the maximum range of rust and swelling is more than 1mm and less than 2mm (single side)

C: the maximum range of rust and swelling is more than 2mm and less than 3mm (single side)

D: the maximum width of rust and swelling is more than 3mm and less than 5mm (single side)

E: the maximum range of rust and swelling is more than 5mm (single side) from the cutting part

Water resistance: each test piece was immersed in deionized water at 23 ℃ for 48 hours, and the coated surface was evaluated according to the following criteria. The water resistance was good if the evaluation was ∈ or ≈ o.

Very good: good and no problem.

O: while dullness of gloss was slightly observed (ツヤビケ) it was a practical level.

And (delta): either swelling or dullness was observed.

X: either swelling or dullness was significantly observed.

Gloss: the specular gloss (60 ℃) of the coated surface was measured for each test plate in accordance with JIS K5600-4-7 (1999) "specular gloss (swamp degrees with glasses)". When the coated surface has a specular gloss (60 ℃ C.) of 70 or more, the gloss is good.

Pencil hardness: the pencil hardness of the coated surface was measured in accordance with JIS K5600-5-4 (1999) "scratch hardness (pencil method) (scratch resistance っかき hardness (resistance ))". The pencil hardness is F, HB, B, 2B in order from hard, and if the hardness is B or more, the hardness is good.

TABLE 2

Although the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be added without departing from the spirit and scope thereof. The present application is based on the japanese patent application published on 27/7/2018 (japanese patent application 2018-141479), the contents of which are incorporated herein by reference.

Industrial applicability

The present invention provides an aqueous coating composition which has good film-forming properties at low temperatures and is excellent in film-forming properties such as corrosion resistance, hardness and water resistance.

Claims

1. An aqueous coating composition comprising core-shell acrylic resin particles A comprising at least 1 gradient polymer layer,

the acid value of the shell of the core-shell acrylic resin particle A is within the range of 20 to 100 mgKOH/g.

2. The aqueous coating composition according to claim 1, wherein the glass transition temperature of the core-shell acrylic resin particles A is-10 ℃ or higher.

3. The aqueous coating composition according to claim 1 or 2, wherein 80% by weight or more of the total copolymerized components of the core-shell acrylic resin particles A are polymerizable unsaturated monomers having a solubility parameter value of 9.5 or less.

4. A coated article having:

a base material, and

a cured coating film of the aqueous coating composition according to any one of claims 1 to 3 on the substrate.

5. The coated article according to claim 4, wherein the substrate is a metal substrate.