Coating composition and coating film forming method

Abstract

The purpose of the present disclosure is to provide a coating composition that exhibits excellent discharge stability. A coating composition according to the present disclosure has the following features.　The coating composition contains a hydroxy group-containing resin (A) and a curing agent (B), and is to be applied to an object to be coated by an inkjet method. When a dynamic viscoelasticity measurement is performed thereon at a temperature of 23°C and a frequency of 0.5 Hz in a stress measurement range of 0.1-20 Pa, the stress σ2 as measured when the storage elastic modulus has decreased by 10% for the first time with respect to the storage elastic modulus G'1 when the stress is 0.1 Pa is in a range of 1.0-15 Pa.

Description

Coating Composition and Coating Film Forming Method

[0001] The present disclosure relates to a coating composition and a coating film forming method.

[0002] The inkjet recording method is a method of recording characters and images by flying droplets of a small amount of ink (coloring liquid or paint) from a fine nozzle and attaching them to a recording medium such as paper. Because of its low noise, simple process, and easy colorization, it has been widely popularized as a household printer.

[0003] In recent years, the inkjet recording method has been expanding also as commercial printing because of advantages such as variable printing and compatibility with a wide range of media. In commercial printing, printing is performed on a variety of papers, which can be roughly classified into plain paper and coated paper.

[0004] Also, direct printing on films and metals other than paper has been increasing, and the required functions are different from those of paper. In particular, it is very difficult to satisfy all the required characteristics for metals, such as adhesion, ink bleeding (image drying property), scratch resistance, light resistance, bleeding, beading, and ejection stability.

[0005] In order to solve such problems, methods such as pre-coating a material for fixing the coating composition when an image by a coating composition such as ink is formed on the surface of the recording medium, or heating the surface have been proposed. However, these proposals have not been widely popularized in terms of working hours and costs because they require cost, working hours, working equipment, etc.

[0006] Also, in non-absorbent media such as metals, because they exhibit a different surface property from paper, the coating composition does not spread and coalesces in droplets, or conversely, spreads too much and drips. Therefore, it is necessary to level the coating composition uniformly after landing, but if this is done, mist will occur during ejection.

[0007] For example, Patent Document 1 discloses a coating composition for precision coating comprising a film-forming resin dispersed in an aqueous medium, a crosslinking agent capable of crosslinking with the film-forming resin, a rheology modifier, a coloring agent, and a swelling solvent for swelling the film-forming resin, wherein the solid content of the coating composition is less than 25% by weight based on the total weight of the coating composition.

[0008] International Publication No. 2020 / 232011

[0009] The technology described in Patent Document 1 has room for improvement in the ejection stability of the coating composition in an inkjet method. The object of this disclosure is to provide a coating composition with excellent ejection stability.

[0010] As a result of diligent research to solve the above problems, the Disclosers have found that the above problems can be solved by using a coating composition that includes a hydroxyl group-containing resin (A) and a curing agent (B), which is applied to a workpiece by an inkjet method, and is characterized in that, in dynamic viscoelasticity measurements under the conditions of a temperature of 23°C, a frequency of 0.5 Hz, and a stress measurement range of 0.1 to 20 Pa, the stress σ2 at which the storage modulus first decreases by 10% is in the range of 1.0 to 15 Pa, with the storage modulus G'1 at a stress of 0.1 Pa as the reference.

[0011] In other words, this disclosure relates to <1> to <11>. <1> A paint composition for application to a workpiece by inkjet method, comprising a hydroxyl group-containing resin (A) and a curing agent (B), characterized in that, in a dynamic viscoelasticity measurement under the conditions of a temperature of 23°C, a frequency of 0.5 Hz, and a stress measurement range of 0.1 to 20 Pa, the stress σ2 at which the storage modulus first decreases by 10% is in the range of 1.0 to 15 Pa, with the storage modulus G'1 at a stress of 0.1 Pa as the reference. <2> The paint composition according to <1>, wherein the storage modulus G'1 is in the range of 1.0 to 30 Pa.

[0012] <3> Temperature 23°C and shear rate 10,000 s -1A paint composition according to <1> or <2>, wherein the viscosity under the conditions is in the range of 10 to 35 mPa·s. <4> A paint composition according to any one of <1> to <3>, further comprising a viscosity modifier (C). <5> A paint composition according to <4>, wherein the content of the viscosity modifier (C) is in the range of 0.4 to 5 parts by mass based on 100 parts by mass of the total resin solids in the paint composition. <6> A method for forming a paint film on a workpiece by ejecting a paint composition containing a hydroxyl group-containing resin (A) and a curing agent (B) onto the workpiece using an inkjet method, wherein the paint composition is characterized in that, in a dynamic viscoelasticity measurement under the conditions of a temperature of 23°C, a frequency of 0.5 Hz, and a stress measurement range of 0.1 to 20 Pa, the stress σ2 at which the storage modulus first decreases by 10% is in the range of 1.0 to 15 Pa, with the storage modulus G'1 at a stress of 0.1 Pa as the reference.

[0013] <7> The coating method according to <6>, wherein the coating composition, in dynamic viscoelasticity measurement under the conditions of a temperature of 23°C and a frequency of 0.5 Hz, has a storage modulus G'1 when the stress is 0.1 Pa in the range of 1.0 to 30 Pa. <8> The coating composition, at a temperature of 23°C and a shear rate of 10,000 s -1 A method for forming a coating film according to <6> or <7>, wherein the viscosity under the conditions is in the range of 10 to 35 mPa·s. <9> A method for forming a coating film according to any one of <6> to <8>, wherein the coating composition further comprises a viscosity modifier (C). <10> A method for forming a coating film according to <9>, wherein the content of the viscosity modifier (C) is in the range of 0.4 to 5 parts by mass based on 100 parts by mass of the total resin solids in the coating composition. <11> A method for forming a coating film according to any one of <6> to <10>, wherein the dry film thickness of the coating film is in the range of 1.0 to 50 μm.

[0014] According to this disclosure, it is possible to provide a paint composition with excellent discharge stability.

[0015] The following details the present disclosure, but these are merely examples of preferred embodiments, and the present disclosure is not limited to these. The paint composition according to the present disclosure is a paint composition that is applied to a workpiece by an inkjet method, comprising a hydroxyl group-containing resin (A) and a curing agent (B), and in dynamic viscoelasticity measurements under the conditions of a temperature of 23°C, a frequency of 0.5 Hz, and a stress measurement range of 0.1 to 20 Pa, the stress σ2 at which the storage modulus first decreases by 10% is in the range of 1.0 to 15 Pa, with the storage modulus G'1 at a stress of 0.1 Pa as the reference.

[0016] [Paint Composition] In this specification, the dynamic viscoelasticity of a paint composition can be measured, for example, using a rheometer with a temperature control mechanism, by the following measurement procedures (1) to (2): (1) Set the paint composition in a cone and plate with a diameter of 50 mm and an inclination of 0.5° connected to the measuring device. (2) Measure the stress dependence of the dynamic viscoelasticity while increasing the stress on a logarithmic gradient under conditions of a temperature of 23°C and a frequency of 0.50 Hz.

[0017] Specifically, the paint composition is left to stand overnight to reach a temperature of 23°C, placed on a rheometer measuring platform, and dynamic viscoelasticity measurements are performed every 10 seconds while the stress is changed logarithmically from 0.1 Pa to 20 Pa under the following measurement conditions, to obtain the storage modulus (G'). A cone and plate viscometer "MCR302e" (product name, manufactured by Anton Paar, 50 mm diameter, 0.5° inclined cone and plate) is used for the measurements.

[0018] From the curve chart obtained from this measurement, with the vertical axis representing the storage modulus G' and the horizontal axis representing the stress σ, the storage modulus G'1 when the stress is 0.1 Pa is determined. The storage modulus G'2 value, obtained by decreasing the G'1 value by 10%, is then determined from the chart, and the stress σ2 value corresponding to the G'2 value is determined. In this specification, if multiple stress σ2 values ​​are obtained, the value at the first decrease is adopted as the stress σ2.

[0019] [Measurement Conditions] • Equipment: Rheometer (Anton Paar, MCR302e) • Measurement: Stress-dependent • Measurement Range: 0.1 Pa to 20 Pa • Stress Change: Logarithmic gradient • Measurement Time: 354 s • Measurement Temperature: 23°C • Frequency: 0.50 Hz • Measurement Gap: 0.05 mm

[0020] If the stress σ2 of the coating composition according to this disclosure is less than 1.0 Pa, the discharge stability of the resulting coating composition and the suppression of mist (scattering of coating when it adheres to the object to be coated) are insufficient. On the other hand, if the stress σ2 exceeds 15 Pa, the discharge stability of the resulting coating composition and the uniformity of the formed coating film are insufficient, which is undesirable.

[0021] The reason why the paint composition relating to this disclosure has excellent discharge stability is not clear, but the following reasons are presumed. When a paint composition is discharged using an inkjet method, a stress is applied to the paint composition to eject it. At this time, using the storage modulus G'1 when the stress is 0.1 Pa as a reference, if the stress σ2 at which the storage modulus first decreases by 10% is 1.0 Pa or more, it is presumed that the resistance to discharge is not too low, enabling stable and uniform discharge. On the other hand, if the stress σ2 is 15 Pa or less, it is presumed that the resistance to discharge is appropriate, reducing the likelihood of discharge clogging, irregular discharge, etc., caused by excessively high resistance.

[0022] The paint composition according to this disclosure has a stress σ2 that is preferably 2.0 Pa or higher, more preferably 3.0 Pa or higher, even more preferably 4.0 Pa or higher, and preferably 12 Pa or lower, more preferably 10 Pa or lower, and even more preferably 9.0 Pa or lower, from the viewpoint of the discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film.

[0023] Furthermore, in the coating composition according to this disclosure, from the viewpoint of discharge stability of the obtained coating composition, suppression of mist, and uniformity of the formed coating film, the storage modulus G'1 in the dynamic viscoelasticity measurement is preferably 1.0 Pa or more, more preferably 1.5 Pa or more, even more preferably 2.0 Pa or more, and preferably 30 Pa or less, more preferably 25 Pa or less, and even more preferably 20 Pa or less.

[0024] Furthermore, the paint composition according to this disclosure is designed to achieve the following points of view: discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film, at a temperature of 23°C and a shear rate of 10,000 s. -1 The viscosity is preferably 10 mPa·s or more, more preferably 12 mPa·s or more, even more preferably 13 mPa·s or more, and preferably 35 mPa·s or less, more preferably 30 mPa·s or less, and even more preferably 25 mPa·s or less.

[0025] In this specification, the temperature is 23°C and the shear rate is 10,000 s. -1 The viscosity is measured as follows: The paint composition is left to stand overnight to reach a temperature of 23°C. The paint composition is placed on a measuring stand, the plate is lowered to the specified gap, trimmed, and the shear viscosity (mPa·s) at a shear rate of 10,000 (1 / s) is measured using a rheometer under the following conditions. A cone plate with a diameter of 50 mm and an angle of 0.5° is used as the plate for the rheometer.

[0026] [Measurement Conditions] • Equipment: Rheometer (Anton Paar, MCR302e) • Measurement: Shear rate dependent • Measurement range: Shear rate 0.01 to 10,000 (1 / s) • Measurement temperature: 23°C • Measurement gap: 0.05 mm

[0027] [Hydroxygroup-containing resin (A)] As the hydroxygroup-containing resin (A) used in the coating composition according to this disclosure, various film-forming resins known for use in coatings can be used. Examples of the hydroxygroup-containing resin (A) include hydroxygroup-containing acrylic resin (A1), hydroxygroup-containing polyester resin (A2), hydroxygroup-containing polyurethane resin, hydroxygroup-containing acrylic-modified polyester resin, hydroxygroup-containing acrylic-modified polyurethane resin, hydroxygroup-containing polyether resin, hydroxygroup-containing polycarbonate resin, and hydroxygroup-containing alkyd resin. These can be used individually or in combination of two or more.

[0028] The hydroxyl group-containing resin (A) described above preferably contains at least one hydroxyl group-containing resin selected from hydroxyl group-containing acrylic resin (A1) and hydroxyl group-containing polyester resin (A2), from the viewpoint of uniformity of the coating film formed by inkjet painting. The hydroxyl group-containing resin (A) described above can be used alone or in combination of two or more types, depending on the desired coating film performance. The content of the hydroxyl group-containing resin (A) in the paint composition according to this disclosure is preferably 40% by mass or more, more preferably 50% by mass or more, and preferably 90% by mass or less, and more preferably 85% by mass or less, based on the total resin solid content in the paint composition.

[0029] In this specification, "solid content" refers to non-volatile components such as resins, curing agents, and pigments that remain after drying at 110°C for one hour. The solid content can be determined, for example, by weighing a sample into a heat-resistant container such as an aluminum foil cup, spreading the sample on the bottom surface of the container, drying it at 110°C for one hour, and then weighing the mass of the components remaining after drying.

[0030] Furthermore, in this specification, "solid content concentration" means the mass percentage of the solid content in the composition. For example, the solid content concentration of a composition can be calculated by measuring the composition into a heat-resistant container such as an aluminum foil cup, spreading the composition on the bottom surface of the container, drying it at 110°C for 1 hour, weighing the mass of the components remaining in the composition after drying, and determining the ratio of the mass of the components remaining after drying to the total mass of the composition before drying.

[0031] In this specification, "total resin solids" refers to a hydroxyl group-containing resin (A) and a curing agent (B) as essential components, and includes resins other than the hydroxyl group-containing resin (A) as described later, as needed. Various additives are not included in the resin.

[0032] [Hydroxygroup-containing acrylic resin (A1)] The above-mentioned hydroxygroup-containing acrylic resin (A1) can usually be produced by copolymerizing a hydroxygroup-containing polymerizable unsaturated monomer (a) and another polymerizable unsaturated monomer (b) copolymerizable with the hydroxygroup-containing polymerizable unsaturated monomer (a) by a known method, such as solution polymerization in an organic solvent or emulsion polymerization in an aqueous medium.

[0033] The above-mentioned hydroxyl group-containing polymerizable unsaturated monomer (a) is a compound having at least one hydroxyl group and at least one polymerizable unsaturated group in one molecule, and examples include monoesterified compounds of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone modified forms of these monoesterified compounds; N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having polyoxyethylene chains with hydroxyl groups at the molecular termini.

[0034] However, in this disclosure, monomers corresponding to the polymerizable unsaturated monomer having an ultraviolet-absorbing functional group (xvii) described later should be defined as "other polymerizable unsaturated monomers (b)" copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer (a), and are excluded from the hydroxyl group-containing polymerizable unsaturated monomer (a). The hydroxyl group-containing polymerizable unsaturated monomer (a) can be used alone or in combination of two or more types.

[0035] In this specification, a polymerizable unsaturated group means an unsaturated group that can undergo radical polymerization. Examples of such polymerizable unsaturated groups include vinyl groups, (meth)acryloyl groups, (meth)acrylamide groups, vinyl ether groups, allyl groups, propenyl groups, isopropenyl groups, and maleimide groups.

[0036] In this specification, "(meth)acrylate" means acrylate and / or methacrylate, and "(meth)acrylic acid" means acrylic acid and / or methacrylic acid. Also, "(meth)acryloyl" means acryloyl and / or methacryloyl. Furthermore, "(meth)acrylamide" means acrylamide and / or methacrylamide.

[0037] The above-mentioned other polymerizable unsaturated monomer (b) can be appropriately selected and used depending on the desired properties of the hydroxyl group-containing acrylic resin (A1). Specific examples of the above-mentioned other polymerizable unsaturated monomer (b) are those listed in (i) to (xix) below. These can be used individually or in combination of two or more. (i) Alkyl or cycloalkyl (meth)acrylates: For example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, tricyclodecanyl (meth)acrylate, etc.

[0038] (ii) Polymerizable unsaturated monomers having an isobornyl group: e.g., isobornyl (meth)acrylate (iii) Polymerizable unsaturated monomers having an adamantyl group: e.g., adamantyl (meth)acrylate (iv) Polymerizable unsaturated monomers having a tricyclodecenyl group: e.g., tricyclodecenyl (meth)acrylate (v) Polymerizable unsaturated monomers containing aromatic rings: e.g., benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene (vi) Polymerizable unsaturated monomers having an alkoxysilyl group: e.g., vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane

[0039] (vii) Polymerizable unsaturated monomers having a fluorinated alkyl group: for example, perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; fluoroolefins, etc. (viiii) Polymerizable unsaturated monomers having a photopolymerizable functional group such as a maleimide group (ix) Vinyl compounds: for example, N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, etc. (x) Polymerizable unsaturated monomers containing a carboxyl group: for example, (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl acrylate, etc. (xi) Nitrogen-containing polymerizable unsaturated monomers: for example, (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, methylenebis(meth)acrylamide, ethylenebis(meth)acrylamide, 2-(methacryloyloxy)ethyltrimethylammonium chloride, adducts of glycidyl (meth)acrylate and amines, etc.

[0040] (xii) A polymerizable unsaturated monomer having two or more polymerizable unsaturated groups in one molecule: for example, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, etc. (xiii) An epoxy group-containing polymerizable unsaturated monomer: for example, glycidyl (meth)acrylate, β-methyl glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, allyl glycidyl ether, etc. (xiv) A (meth)acrylate having a polyoxyethylene chain with an alkoxy group at the molecular end

[0041] (xv) A polymerizable unsaturated monomer having a sulfonic acid group: for example, 2-acrylamido-2-methylpropane sulfonic acid, 2-sulfoethyl (meth)acrylate, allyl sulfonic acid, 4-styrene sulfonic acid, etc.; sodium salts, ammonium salts, etc. of these sulfonic acids (xvi) A polymerizable unsaturated monomer having a phosphoric acid group: acid phosphoxyethyl (meth)acrylate, acid phosphoxypropyl (meth)acrylate, acid phosphoxypoly(oxyethylene) glycol (meth)acrylate, acid phosphoxypoly(oxypropylene) glycol (meth)acrylate, etc. (xvii) A polymerizable unsaturated monomer having an ultraviolet-absorbing functional group: for example, 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2-hydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2-(2'-hydroxy-5'-methacryloyloxyethylphenyl)-2H-benzotriazole, etc.

[0042] (xviiii) Photostable polymerizable unsaturated monomers: for example, 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloylamino-2,2 6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, etc. Polymerizable unsaturated monomers having a (xix) carbonyl group: for example, acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formyl styrene, vinyl alkyl ketones having 4 to 7 carbon atoms (for example, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), etc.

[0043] The above-mentioned hydroxyl group-containing acrylic resin (A1) may also include a so-called urethane-modified acrylic resin, which is obtained by elongating some of the hydroxyl groups in the resin through a urethane reaction with a polyisocyanate compound to increase its molecular weight.

[0044] The content of the hydroxyl group-containing polymerizable unsaturated monomer (a) is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total amount of the hydroxyl group-containing polymerizable unsaturated monomer (a) and the other polymerizable unsaturated monomer (b).

[0045] From the perspective of the weather resistance of the formed coating film, etc., the hydroxyl value of the above-mentioned hydroxyl group-containing acrylic resin (A1) is preferably 1 mgKOH / g or more, more preferably 2 mgKOH / g or more, still more preferably 5 mgKOH / g or more, and preferably 200 mgKOH / g or less, more preferably 150 mgKOH / g or less, still more preferably 100 mgKOH / g or less.

[0046] Also, from the perspective of the discharge stability of the obtained coating composition, etc., the acid value of the above-mentioned hydroxyl group-containing acrylic resin (A1) is preferably 1 mgKOH / g or more, more preferably 2 mgKOH / g or more, still more preferably 5 mgKOH / g or more, and preferably 200 mgKOH / g or less, more preferably 150 mgKOH / g or less, still more preferably 80 mgKOH / g or less.

[0047] Also, from the perspective of suppressing mist of the obtained coating composition and the uniformity of the formed coating film, etc., the weight average molecular weight of the above-mentioned hydroxyl group-containing acrylic resin (A1) is preferably 2,000 or more, more preferably 4,000 or more, still more preferably 8,000 or more, and preferably 5,000,000 or less, more preferably 1,000,000 or less, still more preferably 500,000 or less.

[0048] In this specification, the number average molecular weight and the weight average molecular weight are values obtained by converting the retention time (retention volume) measured using gel permeation chromatography (GPC) into the molecular weight of polystyrene based on the retention time (retention volume) of a standard polystyrene with a known molecular weight measured under the same conditions. Specifically, as a gel permeation chromatograph device, "HLC-8120GPC" (trade name, manufactured by Tosoh Corporation) is used, and as columns, a total of 4 columns of "TSKgel G4000HXL", "TSKgel G3000HXL", "TSKgel G2500HXL" and "TSKgel G2000HXL" (trade name, all manufactured by Tosoh Corporation) are used. As a detector, a differential refractometer is used, and the measurement can be carried out under the conditions of mobile phase: tetrahydrofuran, measurement temperature: 40 °C, and flow rate: 1 mL / min.

[0049] When the paint composition according to this disclosure is an aqueous paint, the hydroxyl group-containing acrylic resin (A1) preferably includes a water-dispersible hydroxyl group-containing acrylic resin (A1') (hereinafter sometimes abbreviated as "water-dispersible hydroxyl group-containing acrylic resin (A1')") having a core / shell type multilayer structure, comprising a core of copolymer (I) obtained by copolymerizing a polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and a polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule, and a shell of copolymer (II) obtained by copolymerizing the hydroxyl group-containing polymerizable unsaturated monomer (a) and the other polymerizable unsaturated monomer (b) as constituent components, from the viewpoint of the discharge stability of the obtained paint composition.

[0050] Examples of polymerizable unsaturated monomers (c) having at least two polymerizable unsaturated groups in one molecule that constitute the core include allyl (meth)acrylate, ethylene glycoside (meth)acrylate, triethylene glycoside (meth)acrylate, tetraethylene glycoside (meth)acrylate, 1,3-butylene glycoside (meth)acrylate, trimethylolpropanepropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane trimethylpropane Examples include acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, glycerol di(meth)acrylate, 1,1,1-trishydroxymethylethane di(meth)acrylate, 1,1,1-trishydroxymethylethane tri(meth)acrylate, 1,1,1-trishydroxymethylpropane tri(meth)acrylate, triallyl isocyanurate, diallyl terephthalate, and divinylbenzene, which can be used individually or in combination of two or more.

[0051] The content of the polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule is preferably 0.1% by mass or more, preferably 30% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, based on the total mass of the polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and the polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule.

[0052] Furthermore, the polymerizable unsaturated monomer (d) having one polymerizable unsaturated group per molecule that constitutes the core is a polymerizable unsaturated monomer copolymerizable with the polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups per molecule, and includes compounds containing one polymerizable unsaturated group per molecule, such as a vinyl group, a (meth)acryloyl group, an allyl group, etc.

[0053] Specific examples of polymerizable unsaturated monomers (d) having one polymerizable unsaturated group per molecule include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, and tridecyl (meth)acrylate. Alkyl or cycloalkyl (meth)acrylates such as lauryl (meth)acrylate, stearyl (meth)acrylate, "isostearyl acrylate" (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate; polymerizable unsaturated monomers having an isobornyl group such as isobornyl (meth)acrylate; polymers having an adamantyl group such as adamantyl (meth)acrylate. Sexually unsaturated monomers; vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyltoluene; monoesters of (meth)acrylic acid with a dihydric alcohol having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone modified forms of the monoesters of (meth)acrylic acid with a dihydric alcohol having 2 to 8 carbon atoms; allyl alcohol; and polyoxyethylene with hydroxyl groups at the molecular ends. Examples include hydroxyl group-containing polymerizable unsaturated monomers having chains, such as (meth)acrylate; carboxyl group-containing polymerizable unsaturated monomers such as (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate; and nitrogen-containing polymerizable unsaturated monomers such as adducts of (meth)acrylonitrile, (meth)acrylamide, dimethylaminopropyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate with amines. These can be used individually or in combination of two or more.

[0054] On the other hand, as the hydroxyl group-containing polymerizable unsaturated monomer (a) constituting the shell, as mentioned above, examples include monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone modified monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms; allyl alcohol; and (meth)acrylates having polyoxyethylene chains with hydroxyl groups at the molecular ends. These can be used individually or in combination of two or more.

[0055] The content of the hydroxyl group-containing polymerizable unsaturated monomer (a) is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and preferably 35% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, based on the total mass of the hydroxyl group-containing polymerizable unsaturated monomer (a) and the other polymerizable unsaturated monomer (b).

[0056] Furthermore, the other polymerizable unsaturated monomers (b) constituting the shell are as described above. These can be used individually or in combination of two or more. The other polymerizable unsaturated monomers (b) preferably contain a carboxyl group-containing polymerizable unsaturated monomer (e) as at least a part of their components, in order to ensure the discharge stability of the resulting paint composition.

[0057] Examples of the carboxyl group-containing polymerizable unsaturated monomer (e) include (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate, among which (meth)acrylic acid is preferred.

[0058] The content of the carboxyl group-containing polymerizable unsaturated monomer (e) is preferably 1% by mass or more, preferably 40% by mass or less, more preferably 25% by mass or less, and even more preferably 19% by mass or less, based on the total mass of the hydroxyl group-containing polymerizable unsaturated monomer (a) and the other polymerizable unsaturated monomer (b), from the viewpoint of the stability of the water-dispersible hydroxyl group-containing acrylic resin (A1') in an aqueous medium.

[0059] The hydroxyl value of the above-mentioned water-dispersible hydroxyl group-containing acrylic resin (A1') is preferably 1 mg KOH / g or more, more preferably 2 mg KOH / g or more, even more preferably 5 mg KOH / g or more, and preferably 100 mg KOH / g or less, more preferably 90 mg KOH / g or less, and even more preferably 85 mg KOH / g or less, from the viewpoint of weather resistance of the formed coating film.

[0060] Furthermore, the acid value of the water-dispersible hydroxyl group-containing acrylic resin (A1') is preferably 3 mg KOH / g or more, more preferably 4 mg KOH / g or more, even more preferably 5 mg KOH / g or more, and preferably 90 mg KOH / g or less, more preferably 70 mg KOH / g or less, and even more preferably 50 mg KOH / g or less, from the viewpoint of the discharge stability of the resulting paint composition.

[0061] The above-mentioned water-dispersible hydroxyl group-containing acrylic resin (A1') can be obtained, for example, by emulsion polymerization of a monomer mixture (I) containing 0.1 to 30% by mass of a polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups per molecule and 70 to 99.9% by mass of a polymerizable unsaturated monomer (d) having one polymerizable unsaturated group per molecule, to which a monomer mixture (II) containing 1 to 35% by mass of the above-mentioned hydroxyl group-containing polymerizable unsaturated monomer (a) and 65 to 99% by mass of the above-mentioned other polymerizable unsaturated monomer (b) can be added, and further polymerization can be carried out.

[0062] The emulsion polymerization of the above monomer mixture can be carried out by a known method, for example, by using a polymerization initiator in the presence of an emulsifier. Anionic or nonionic emulsifiers are preferred as the emulsifier. Examples of anionic emulsifiers include sodium or ammonium salts of organic acids such as alkyl sulfonic acid, alkylbenzene sulfonic acid, and alkyl phosphoric acid. Examples of nonionic emulsifiers 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.

[0063] As the emulsifier described above, a polyoxyalkylene group-containing anionic emulsifier having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group in one molecule, or a reactive anionic emulsifier having the anionic group and a radically polymerizable unsaturated group in one molecule may be used, and among these, the use of a reactive anionic emulsifier is preferred.

[0064] Examples of the above-mentioned reactive anionic emulsifiers include sodium and ammonium salts of sulfonic acid compounds having radically polymerizable unsaturated groups such as (meth)allyl, (meth)acryloyl, propenyl, and butenyl groups. Among these, ammonium salts of sulfonic acid compounds having radically polymerizable unsaturated groups are preferred because they provide excellent water resistance to the formed coating film. Examples of such ammonium salts of sulfonic acid compounds include commercially available products such as "Latemul S-180A" (trade name, manufactured by Kao Corporation).

[0065] Among the ammonium salts of sulfonic acid compounds having the above-mentioned radical polymerizable unsaturated group, ammonium salts of sulfonic acid compounds having both a radical polymerizable unsaturated group and a polyoxyalkylene group are even more preferred. Examples of commercially available ammonium salts of sulfonic acid compounds having both a radical polymerizable unsaturated group and a polyoxyalkylene group include "Aqualon KH-10" (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and "SR-1025A" (trade name, manufactured by Asahi Denka Kogyo Co., Ltd.).

[0066] The emulsifier described above is used in an amount of preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the total amount of all monomers used, and preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0067] The polymerization initiators mentioned above may be of either oil-soluble or water-soluble types, and include, for example, organic peroxides such as benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl peroxylaurate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, and diisopropylbenzene hydroperoxide; and azobisisobutyronite. Examples include azo compounds such as lyl, azobis(2,4-dimethylvaleronitrile), azobis(2-methylpropionnitrile), azobis(2-methylbutyronitrile), 4,4'-azobis(4-cyanobutanoic acid), dimethylazobis(2-methylpropionate), azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide}; and persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate. These can be used individually or in combination of two or more. In addition, a reducing agent such as sugar, sodium formaldehyde sulfoxylate, or an iron complex may be used in combination with the polymerization initiator as needed to form a redox polymerization system.

[0068] The polymerization initiator described above is used in an amount of preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, based on the total mass of all monomers used. The method of adding the polymerization initiator is not particularly limited and can be appropriately selected depending on its type, amount, etc. For example, the polymerization initiator may be included in the monomer mixture or aqueous medium in advance, or it may be added all at once during polymerization, or added dropwise.

[0069] The above-mentioned water-dispersible hydroxyl group-containing acrylic resin (A1') can be obtained by adding a monomer mixture (II) containing the above-mentioned hydroxyl group-containing polymerizable unsaturated monomer (a) and the above-mentioned other polymerizable unsaturated monomer (b) to the emulsion obtained as described above, and further polymerization.

[0070] The monomer mixture (II) may optionally contain the polymerization initiator, chain transfer agent, reducing agent, emulsifier, and other components mentioned above. While the monomer mixture (II) can be added dropwise as is, it is preferable to disperse the monomer mixture (II) in an aqueous medium and add it dropwise as a monomer emulsion. In this case, the particle size of the monomer emulsion is not particularly limited.

[0071] Polymerization of the above monomer mixture (II) can be carried out, for example, by adding the monomer mixture (II), which may be emulsified, to the emulsion all at once or dropwise, and heating it to a suitable temperature while stirring.

[0072] The water-dispersible hydroxyl group-containing acrylic resin (A1') obtained as described above may have a core / shell type multilayer structure in which a copolymer (I) formed from the monomer mixture (I) containing a polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and a polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule is the core, and a copolymer (II) formed from the monomer mixture (II) containing the hydroxyl group-containing polymerizable unsaturated monomer (a) and the other polymerizable unsaturated monomer (b) is the shell.

[0073] Furthermore, the water-dispersible hydroxyl group-containing acrylic resin (A1') may be obtained as resin particles consisting of three or more layers by adding a step of supplying polymerizable unsaturated monomers (one or a mixture of two or more) to form other resin layers and performing emulsion polymerization between the step of obtaining copolymer (I) and the step of obtaining copolymer (II).

[0074] In this disclosure, the "shell" of the water-dispersible hydroxyl group-containing acrylic resin (A1') refers to the polymer layer present on the outermost layer of the resin particles, the "core" refers to the polymer layer in the inner layer of the resin particles excluding the shell portion, and the "core / shell structure" refers to a structure having the core and the shell. The core / shell structure is generally a layered structure in which the core is completely covered by the shell, but depending on the mass ratio of the core to the shell, the amount of monomer in the shell may be insufficient to form a layered structure. In such cases, it is not necessary to have a complete layered structure as described above, and the structure may be one in which a part of the core is covered by the shell, or a structure in which polymerizable unsaturated monomers, which are components of the shell, are graft polymerized onto a part of the core. Furthermore, the concept of a multilayer structure in the core / shell structure also applies when a multilayer structure is formed in the core of the water-dispersible hydroxyl group-containing acrylic resin (A1').

[0075] In the water-dispersible hydroxyl group-containing acrylic resin (A1') having a core / shell type multilayer structure, the ratio of copolymer (I) to copolymer (II) is preferably in the range of 10 / 90 to 90 / 10, more preferably in the range of 50 / 50 to 85 / 15, and even more preferably in the range of 65 / 35 to 80 / 20, in terms of the solid content mass ratio of copolymer (I) to copolymer (II), from the viewpoint of the discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film.

[0076] The average particle size of the water-dispersible hydroxyl group-containing acrylic resin (A1') obtained as described above is preferably 10 nm or more, more preferably 20 nm or more, and preferably 1,000 nm or less, more preferably 500 nm or less.

[0077] In this specification, the average particle size of the hydroxyl group-containing acrylic resin refers to the median of the volume average (D50). The average particle size can be measured at 20°C after dilution with deionized water by a conventional method using a particle size distribution analyzer based on dynamic light scattering. For example, the "ELSZ-2000" (product name, manufactured by Otsuka Electronics Co., Ltd.) can be used as a particle size distribution analyzer based on dynamic light scattering.

[0078] To improve the mechanical stability of the aqueous dispersion particles of the water-dispersible hydroxyl group-containing acrylic resin (A1') obtained, it is desirable to neutralize the acidic groups such as carboxyl groups present in the water-dispersible hydroxyl group-containing acrylic resin (A1') with a neutralizing agent. The neutralizing agent is not particularly limited as long as it can neutralize the acidic groups, and examples include sodium hydroxide, potassium hydroxide, trimethylamine, 2-(dimethylamino)ethanol, 2-amino-2-methyl-1-propanol, triethylamine, and aqueous ammonia. These neutralizing agents are used in amounts such that the pH of the aqueous dispersion of the dispersible hydroxyl group-containing acrylic resin (A1') after neutralization is preferably about 6.5 or higher, and preferably about 9.0 or lower.

[0079] When the coating composition according to this disclosure contains the above-mentioned hydroxyl group-containing acrylic resin (A1), the content of the hydroxyl group-containing acrylic resin (A1) is preferably 1% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less, based on the total resin solid content in the coating composition, from the viewpoint of the discharge stability of the obtained coating composition, suppression of mist, and uniformity of the formed coating film.

[0080] [Hydroxygroup-containing polyester resin (A2)] The above hydroxygroup-containing polyester resin (A2) can be obtained, for example, by using a polyol having two or more hydroxyl groups as the alcohol component and a polycarboxylic acid having two or more carboxyl groups as the acid component, and condensing the alcohol component and the acid component.

[0081] As the polyol mentioned above, polyhydric alcohols having two or more hydroxyl groups in one molecule can be suitably used. Examples of such polyhydric alcohols include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 3-methyl-1,2-butanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, tricycline Examples include dihydric alcohols such as rodecane dimethanol, neopentyl glycol hydroxypivalate, hydrogenated bisphenol A, hydrogenated bisphenol F, and dimethylolpropionic acid; polylactone diols obtained by adding lactone compounds such as ε-caprolactone to these dihydric alcohols; ester diol compounds such as bis(hydroxyethyl) terephthalate; polyether diol compounds such as alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, and polybutylene glycol; trihydric or higher alcohols such as glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tris(2-hydroxyethyl)isocyanuric acid, sorbitol, and mannitol; polylactone polyol compounds obtained by adding lactone compounds such as ε-caprolactone to these trihydric or higher alcohols; and fatty acid esters of glycerin.

[0082] In addition, alcohol components other than the polyols mentioned above can also be used. Such alcohol components are not particularly limited and include, for example, monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, and 2-phenoxyethanol; and alcohol compounds obtained by reacting monoepoxy compounds such as propylene oxide, butylene oxide, and "Cardura E10" (trade name, manufactured by HEXION, a glycidyl ester of a synthetic highly branched saturated fatty acid) with an acid.

[0083] As the polycarboxylic acid mentioned above, compounds commonly used in the production of polyester resins can be used. Examples of such polycarboxylic acids include aliphatic polybasic acids, alicyclic polybasic acids, and aromatic polybasic acids.

[0084] The above-mentioned aliphatic polybasic acids are generally aliphatic compounds having two or more carboxyl groups in one molecule, acid anhydrides of the aliphatic compounds, and esters of the aliphatic compounds. Examples of aliphatic polybasic acids include aliphatic polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanediic acid, dodecanediic acid, brassic acid, octadecanediic acid, citric acid, and butanetetracarboxylic acid; anhydrides of the aliphatic polycarboxylic acids; and lower alkyl esters of the aliphatic polycarboxylic acids having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. The above-mentioned aliphatic polybasic acids can be used individually or in combination of two or more types.

[0085] The above-mentioned alicyclic polybasic acids are generally compounds having one or more alicyclic structures and two or more carboxyl groups in one molecule, acid anhydrides of the same, and esters of the same. The alicyclic structure can mainly be a 4- to 6-membered ring structure. Examples of alicyclic polybasic acids include alicyclic polycarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 3-methyl-1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid; anhydrides of the alicyclic polycarboxylic acids; and lower alkyl esters of the alicyclic polycarboxylic acids having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. The above-mentioned alicyclic polybasic acids can be used individually or in combination of two or more.

[0086] The above-mentioned aromatic polybasic acids are generally aromatic compounds having two or more carboxyl groups in one molecule, acid anhydrides of the aromatic compounds, and esterified products of the aromatic compounds. Examples of aromatic polybasic acids include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, trimellitic acid, and pyromellitic acid; anhydrides of the aromatic polycarboxylic acids; and lower alkyl esters of the aromatic polycarboxylic acids having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. The above-mentioned aromatic polybasic acids can be used individually or in combination of two or more. It is preferable to use phthalic acid, phthalic anhydride, isophthalic acid, trimellitic acid, and trimellitic anhydride as the above-mentioned aromatic polybasic acids, and among these, it is more preferable to use trimellitic anhydride.

[0087] Furthermore, acid components other than the above-mentioned aliphatic polybasic acids, alicyclic polybasic acids, and aromatic polybasic acids can also be used. Such acid components are not particularly limited and include, for example, fatty acids such as coconut oil fatty acid, cottonseed oil fatty acid, hemp seed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, and safflower oil fatty acid; monocarboxylic acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid, cyclohexanoic acid, and 10-phenyloctadecanoic acid; and hydroxycarboxylic acids such as lactic acid, 3-hydroxybutanoic acid, and 3-hydroxy-4-ethoxybenzoic acid. These acid components can be used individually or in combination of two or more.

[0088] The method for producing the above-mentioned hydroxyl group-containing polyester resin (A2) is not particularly limited and can be carried out according to conventional methods. For example, the hydroxyl group-containing polyester resin (A2) can be produced by heating the above-mentioned alcohol component and the above-mentioned acid component in a nitrogen stream at a temperature of about 150 to 250°C for about 5 to 10 hours to carry out an esterification reaction or transesterification reaction between the alcohol component and the acid component.

[0089] When carrying out the esterification or transesterification reaction of the above alcohol component and the above acid component, these components may be added to the reaction vessel all at once, or one or both may be added in several stages. Alternatively, a hydroxyl group-containing polyester resin may be synthesized first, and then the resulting hydroxyl group-containing polyester resin may be reacted with an acid anhydride to perform half-esterification to obtain a carboxyl group and hydroxyl group-containing polyester resin. Alternatively, a carboxyl group-containing polyester resin may be synthesized first, and then the above alcohol component may be added to produce the above hydroxyl group-containing polyester resin.

[0090] In the above esterification or transesterification reactions, known catalysts such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, and tetraisopropyl titanate can be used as catalysts to accelerate the reaction.

[0091] Furthermore, the hydroxyl group-containing polyester resin (A2) can be modified with fatty acids, monoepoxy compounds, polyisocyanate compounds, etc., during or after the manufacture of the resin. Examples of fatty acids include coconut oil fatty acid, cottonseed oil fatty acid, hemp seed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, safflower oil fatty acid, etc. As the monoepoxy compound, for example, "Cardura E10P" (trade name, manufactured by HEXION, a glycidyl ester of synthetic highly branched saturated fatty acid) can be suitably used. As the polyisocyanate compound, the polyisocyanate compounds exemplified in polyisocyanate compound (B2) described later can be used. These can be used individually or in combination of two or more.

[0092] The hydroxyl value of the above-mentioned hydroxyl group-containing polyester resin (A2) is preferably 1 mg KOH / g or more, more preferably 2 mg KOH / g or more, even more preferably 5 mg KOH / g or more, and preferably 200 mg KOH / g or less, more preferably 180 mg KOH / g or less, and even more preferably 170 mg KOH / g or less, from the viewpoint of weather resistance of the formed coating film.

[0093] Furthermore, the weight-average molecular weight of the hydroxyl group-containing polyester resin (A2) is preferably 500 or more, more preferably 1,000 or more, even more preferably 1,200 or more, and preferably 50,000 or less, more preferably 30,000 or less, and even more preferably 20,000 or less, from the viewpoint of discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film.

[0094] Furthermore, the glass transition temperature (Tg) of the hydroxyl group-containing polyester resin (A2) is preferably -20°C or higher, more preferably -10°C or higher, even more preferably -5°C or higher, and preferably 50°C or lower, more preferably 40°C or lower, and even more preferably 35°C or lower, from the viewpoint of the discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film. In this specification, the glass transition temperature (Tg) of the hydroxyl group-containing polyester resin is measured by differential thermal analysis (DSC) using a differential scanning calorimeter.

[0095] The hydroxyl group-containing polyester resin (A2) described above preferably has carboxyl groups, from the viewpoint of discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film. When the polyester resin (A2) described above has carboxyl groups, the acid value of the hydroxyl group-containing polyester resin (A2) is preferably 5 mg KOH / g or more, more preferably 10 mg KOH / g or more, even more preferably 15 mg KOH / g or more, and preferably 150 mg KOH / g or less, more preferably 140 mg KOH / g or less, and even more preferably 120 mg KOH / g or less, from the viewpoint of discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film.

[0096] When the coating composition according to this disclosure contains the above-mentioned hydroxyl group-containing polyester resin (A2), the content of the hydroxyl group-containing polyester resin (A2) is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less, based on the total resin solid content in the coating composition, from the viewpoint of the discharge stability of the obtained coating composition, suppression of mist, and uniformity of the formed coating film.

[0097] [Curing agent (B)] The curing agent (B) is not particularly limited. Examples of the curing agent (B) include curing agents that are reactive with functional groups such as hydroxyl groups contained in the hydroxyl group-containing resin (A). Examples of known curing agents (B) include amino resins (B1), polyisocyanate compounds (B2), blocked polyisocyanate compounds (B3), polyhydrazide compounds, polysemicarbazide compounds, carbodiimide compounds, oxazoline group-containing compounds, epoxy compounds, polycarboxylic acids, etc. The crosslinking agent (B) may be used alone or in combination of two or more types.

[0098] The curing agent (B) described above preferably contains at least one crosslinking agent selected from amino resin (B1), polyisocyanate compound (B2), and blocked polyisocyanate compound (B3) from the viewpoint of weather resistance of the formed coating film, more preferably contains amino resin (B1) and / or blocked polyisocyanate compound (B3), and even more preferably contains amino resin (B1) and blocked polyisocyanate compound (B3).

[0099] [Amino Resin (B1)] As the above amino resin (B1), a partially methylolated amino resin or a fully methylolated amino resin obtained by the reaction of an amino component and an aldehyde component can be used. Examples of the above amino component include melamine, urea, benzoguanamine, acetoganaamine, steroguanamine, spiloganamine, and dicyandiamide. Examples of the above aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

[0100] A methylolated amino resin can also be used in which the methylol group has been partially or completely etherified with a suitable alcohol. Examples of alcohols that can be used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethyl-1-butanol, and 2-ethyl-1-hexanol.

[0101] Melamine resin is preferred as the above amino resin (B1). In particular, methyl etherified melamine resin, in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with methyl alcohol, butyl etherified melamine resin, in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with butyl alcohol, and methyl-butyl mixed etherified melamine resin, in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with methyl alcohol and butyl alcohol, are preferred, and methyl-butyl mixed etherified melamine resin is more preferred.

[0102] Furthermore, the weight-average molecular weight of the melamine resin is preferably 450 or more, more preferably 500 or more, even more preferably 550 or more, and preferably 6,000 or less, more preferably 4,000 or less, and even more preferably 3,000 or less.

[0103] Commercially available melamine resins can be used as described above. Examples of commercially available product names include "Cymel 202", "Cymel 203", "Cymel 211", "Cymel 238", "Cymel 251", "Cymel 254", "Cymel 303", "Cymel 325", "Cymel 327", "Cymel 350", "Cymel 370", "Cymel 385", "Cymel 1156", "Cymel 1158", and "Cymel 1130" (all manufactured by Ornex Japan Co., Ltd.); "Uban 20SE60" and "Uban 28-60" (both manufactured by Mitsui Chemicals, Inc.); and so on.

[0104] If the above paint composition contains the above melamine resin as the curing agent (B), the above paint composition may optionally contain a curing catalyst such as a sulfonic acid such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, or dinonylnaphthalenesulfonic acid; a neutralized salt of the sulfonic acid with an amine; or a neutralized salt of a phosphate ester compound with an amine. The above amino resin (B1) can be used, for example, as a crosslinking agent for a hydroxyl group-containing resin (A).

[0105] [Polyisocyanate compound (B2)] The above polyisocyanate compound (B2) is a compound having two or more isocyanate groups in one molecule. The above polyisocyanate compound (B2) includes, for example, aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, derivatives of said polyisocyanates, and the like.

[0106] Examples of the above aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, dimer diisocyanate, and 2,6-methyl diisocyanatohexanoate (common name: lysine). Examples include aliphatic diisocyanates such as diisocyanates; and aliphatic triisocyanates such as 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

[0107] Examples of the above-mentioned alicyclic polyisocyanates include alicyclic diisocyanates such as 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or mixtures thereof, norbornane diisocyanate, etc.; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)hepta , 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)-2-isocyana Examples include alicyclic triisocyanates such as tomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

[0108] Examples of the above-mentioned aromatic aliphatic polyisocyanates include aromatic aliphatic diisocyanates such as 1,3- or 1,4-xylylene diisocyanate or mixtures thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof; and aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0109] Examples of the above-mentioned aromatic polyisocyanates include aromatic diisocyanates such as m-phenylenediisocyanate, p-phenylenediisocyanate, 4,4'-diphenyldiisocyanate, 1,5-naphthalenediisocyanate, 2,4'- or 4,4'-diphenylmethanediisocyanate or mixtures thereof, 2,4- or 2,6-toluidinediisocyanate or mixtures thereof, 4,4'-toluidinediisocyanate, and 4,4'-diphenyletherdiisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0110] Examples of derivatives of the above-mentioned polyisocyanates include dimers, trimers, biuretes, allophanates, uretodiones, uretoimines, isocyanurates, oxadiazinetriones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like.

[0111] The polyisocyanates and their derivatives described above may be used individually or in combination of two or more. Among these polyisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and their derivatives are preferably used individually or in combination of two or more.

[0112] Furthermore, as the polyisocyanate compound (B2), a prepolymer obtained by urethane reaction of the polyisocyanate and its derivatives with a polyhydric alcohol, a low molecular weight polyester resin, or water under conditions of excess isocyanate groups can also be used.

[0113] If the above paint composition contains a polyisocyanate compound (B2) as a curing agent (B), the paint composition may optionally contain an organometallic compound, an acid compound, a basic compound, etc., as a curing catalyst. The polyisocyanate compound (B2) can be used, for example, as a crosslinking agent for resins containing hydroxyl groups or amino groups.

[0114] [Blocked Polyisocyanate Compound (B3)] The above-mentioned blocked polyisocyanate compound (B3) is a compound obtained by blocking the isocyanate group of the above-mentioned polyisocyanate compound (B2) with a blocking agent.

[0115] Examples of the above-mentioned blocking agents include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, and lauryl alcohol; ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylolurea, methylolmelamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl acrylate. Alcohol-based compounds such as ethyl methacrylate; oxime-based compounds such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; active methylene-based compounds such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; butyl mercaptan, tert-butyl mercaptan, hexyl mercaptan, tert-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, and methylthiopheno Mercaptan-based compounds such as ethylthiophenol; acid amide-based compounds such as acetanilide, acetanisidide, acetotoluid, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, and benzamide; imide-based compounds such as succinimide, phthalimide, and maleimide; amine-based compounds such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazole-based compounds such as imidazole and 2-ethylimidazole;Examples of azole compounds include urea-based compounds such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamic acid ester compounds such as phenyl N-phenylcarbamate; imine-based compounds such as ethyleneimine and propyleneimine; sulfite-based compounds such as sodium bisulfite and potassium bisulfite; and azole compounds. Examples of the above azole compounds include pyrazoles or pyrazole derivatives such as pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole; imidazoles or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-phenylimidazole; and imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline. Suitable blocking agents include oxime-based blocking agents, active methylene-based blocking agents, pyrazoles, or pyrazole derivatives.

[0116] Furthermore, as the blocking agent, a hydroxycarboxylic acid having one or more hydroxyl groups and one or more carboxyl groups, such as hydroxypivalic acid or dimethylolpropionic acid, can also be used.

[0117] If the coating composition according to this disclosure contains the blocked polyisocyanate, the coating composition may suitably contain a blocked polyisocyanate compound obtained by blocking the isocyanate group with the hydroxycarboxylic acid and then neutralizing the carboxyl group of the hydroxycarboxylic acid to impart water dispersibility.

[0118] The weight-average molecular weight of the above-mentioned blocked polyisocyanate compound is preferably 20,000 or more, and preferably 200,000 or less, from the viewpoint of the discharge stability of the resulting paint composition, suppression of mist, uniformity of the formed coating film, and weather resistance.

[0119] If the above paint composition contains a blocked polyisocyanate compound (B3) as a curing agent (B), the above paint composition may optionally contain an organometallic compound, an acid compound, a base compound, etc., as a curing catalyst.

[0120] In the paint composition according to this disclosure, the content of the curing agent (B) is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less, based on the total resin solid content in the paint composition, from the viewpoint of discharge stability of the obtained paint composition, suppression of mist, uniformity of the formed coating film, and weather resistance.

[0121] [Viscosity modifier (C)] The paint composition according to this disclosure preferably contains a viscosity modifier (C) from the viewpoint of the discharge stability of the obtained paint composition and the uniformity of the formed coating film.

[0122] Specific examples of the viscosity modifier (C) mentioned above include, for example, silica-based fine powders, mineral-based viscosity modifiers, barium sulfate fine powders, polyamide (polyamide)-based viscosity modifiers such as fatty acid amides, polyamides, acrylamides, long-chain polyaminoamides, aminoamides and their salts (e.g., phosphates), aminoplast-based viscosity modifiers such as hydrophobic modified ethoxylate aminoplasts, organic resin fine particle viscosity modifiers, diurea-based viscosity modifiers, urethane association-type viscosity modifiers, polyacrylic acid-based viscosity modifiers (also called alkali swelling-type viscosity modifiers), cellulose-based viscosity modifiers, and the like.

[0123] The viscosity modifier (C) described above preferably includes mineral-based viscosity modifiers, polyacrylic acid-based viscosity modifiers, cellulose-based viscosity modifiers, and urethane-associated viscosity modifiers, from the viewpoint of discharge stability of the resulting paint composition, suppression of mist, and uniformity of the formed paint film. More preferably, it includes at least one selected from cellulose-based viscosity modifiers, polyacrylic acid-based viscosity modifiers, and urethane-associated viscosity modifiers, and even more preferably includes a urethane-associated viscosity modifier. These viscosity modifiers can be used individually or in appropriate combinations of two or more types.

[0124] Examples of the above-mentioned mineral-based viscosity modifiers include inorganic layered compound-based viscosity modifiers such as swelling layered silicates having a 2:1 crystal structure. Specifically, these include natural or synthetic smectite group clay minerals such as montmorillonite, saponite, hectorite, stivunsite, beidelite, nontronite, bentonite, and laponite; swelling mica group clay minerals such as Na-type tetrasilicic fluorimica, Li-type tetrasilicic fluorimica, Na-salt type fluorite teniolite, and Li-type fluorite teniolite; vermiculite; substituted or derivative products thereof; and mixtures thereof.

[0125] Examples of the above-mentioned urethane-associated viscosity modifiers include polyether polyol-based urethane prepolymers and urethane-modified polyether-type viscosity modifiers. Examples of commercially available urethane-associated viscosity modifiers include the Adekanol series such as "Adekanol UH-814N," "UH-752," "UH-756VF," "UH-420," and "UH-462" (all manufactured by ADEKA Corporation, "Adekanol" is a registered trademark), "SN Thickener 621N" and "SN Thickener 623N" (both manufactured by Sunopco Corporation), and "Leolate 244" and "Leolate 278" (both manufactured by Elementis Japan).

[0126] Examples of the polyacrylic acid-based viscosity modifiers mentioned above include sodium polyacrylate and polyacrylic acid-(meth)acrylic acid ester copolymers. Examples of commercially available polyacrylic acid-based viscosity modifiers include "Primal ASE-60", "Primal TT615", "Primal RM5" (all manufactured by Dow Chemical Company, "Primal" is a registered trademark), "SN Thickener 613", "SN Thickener 618", "SN Thickener 630", "SN Thickener 634", and "SN Thickener 636" (all manufactured by Sunnopco).

[0127] The solid content acid value of the above polyacrylic acid-based viscosity modifier is preferably 30 mg KOH / g or more, more preferably 80 mg KOH / g or more, and preferably 300 mg KOH / g or less, more preferably 280 mg KOH / g or less.

[0128] Examples of the above-mentioned cellulose-based viscosity modifiers include carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, and cellulose nanofibers. Among these, cellulose nanofibers are preferred from the viewpoint of the discharge stability of the resulting paint composition.

[0129] The above-mentioned cellulose nanofibers are sometimes also referred to as cellulose nanofibrils, fibrated cellulose, or nanocellulose crystals. From the viewpoint of the discharge stability of the resulting paint composition, the above-mentioned cellulose nanofibers preferably have a number-average fiber diameter of 2 nm or more, preferably 500 nm or less, more preferably 250 nm or less, and even more preferably 150 nm or less. Furthermore, from the viewpoint of the discharge stability of the resulting paint composition, the above-mentioned cellulose nanofibers preferably have a number-average fiber length of 0.1 μm or more, preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.

[0130] The number-average fiber diameter and number-average fiber length mentioned above are measured and calculated from images obtained by, for example, dispersing a sample of cellulose nanofibers diluted with water, casting it onto a hydrophilic-treated carbon film-coated grid, and observing it with a transmission electron microscope (TEM).

[0131] The cellulose nanofibers described above can be obtained by defibrating cellulose raw materials and stabilizing them in water. Here, cellulose raw materials refer to various forms of materials mainly composed of cellulose, and specifically include, for example, pulp (wood pulp, jute, Manila hemp, kenaf and other herbaceous plant-derived pulp); natural cellulose such as cellulose produced by microorganisms; regenerated cellulose spun after dissolving cellulose in some solvent such as copper ammonia solution or morpholine derivatives; and fine cellulose obtained by depolymerizing cellulose by hydrolysis, alkaline hydrolysis, enzymatic decomposition, explosion treatment, vibration ball milling, and other mechanical treatments of the above cellulose raw materials.

[0132] Furthermore, anionically modified cellulose nanofibers can also be used as the cellulose nanofibers mentioned above. Examples of anionically modified cellulose nanofibers include carboxylated cellulose nanofibers, carboxymethylated cellulose nanofibers, sulfonic acid group-containing cellulose nanofibers, and phosphate group-containing cellulose nanofibers. The anionically modified cellulose nanofibers can be obtained, for example, by introducing functional groups such as carboxyl groups and carboxymethyl groups into a cellulose raw material using a known method, washing the resulting modified cellulose to prepare a dispersion of modified cellulose, and then defibrating this dispersion. The carboxylated cellulose is also called oxidized cellulose.

[0133] The above-mentioned oxidized cellulose can be obtained, for example, by oxidizing the above-mentioned cellulose raw material in water using an oxidizing agent in the presence of a compound selected from the group consisting of N-oxyl compounds, bromides, and iodides or mixtures thereof. Examples of commercially available cellulose nanofibers include Reocrista® manufactured by Daiichi Kogyo Seiyaku Co., Ltd. and Auro Visco® manufactured by Oji Holdings Corporation.

[0134] If the paint composition according to this disclosure contains the viscosity modifier (C), the content of the viscosity modifier (C) is preferably 0.4 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 0.6 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.5 parts by mass or less, based on 100 parts by mass of the total resin solids in the paint composition, from the viewpoint of the discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed paint film.

[0135] [Other components] The paint composition according to this disclosure may further contain, as necessary, pigments, water, organic solvents, resins other than hydroxyl group-containing resin (A), curing catalysts, dispersants, anti-settling agents, defoaming agents, ultraviolet absorbers, light stabilizers, surface modifiers, etc.

[0136] Examples of the above-mentioned pigments include coloring pigments, extender pigments, and luminescence pigments. These pigments can be used alone or in combination of two or more. When the paint composition according to this disclosure contains the above-mentioned pigments, the amount of the pigment is preferably 0.1 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 2.0 parts by mass or more, and preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 120 parts by mass or less, based on 100 parts by mass of the total resin solids in the paint composition.

[0137] Examples of the above-mentioned coloring pigments include titanium dioxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, surene pigments, perylene pigments, dioxazine pigments, and diketopyrrolopyrrole pigments, with titanium dioxide and carbon black being preferred.

[0138] If the paint composition according to this disclosure contains the above-mentioned coloring pigment, the content of the coloring pigment is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 2.0 parts by mass or more, and preferably 180 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 120 parts by mass or less, based on 100 parts by mass of the total resin solids in the paint composition.

[0139] Examples of the extender pigments mentioned above include barium sulfate, talc, clay, kaolin, barium carbonate, calcium carbonate, silica, and alumina white. Barium sulfate and talc are preferred as the extender pigments.

[0140] If the paint composition according to this disclosure contains the above-mentioned extender pigment, the content of the extender pigment is preferably 1.0 part by mass or more, more preferably 5.0 parts by mass or more, even more preferably 10 parts by mass or more, and preferably 180 parts by mass or less, more preferably 140 parts by mass or less, and even more preferably 120 parts by mass or less, based on 100 parts by mass of the total resin solids in the paint composition.

[0141] Examples of the above-mentioned luminous pigments include aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, glass flakes, aluminum oxide, mica, aluminum oxide coated with titanium oxide and / or iron oxide, and mica coated with titanium oxide and / or iron oxide, with aluminum pigments being preferred. Examples of aluminum pigments include non-leafing aluminum pigments and leafing aluminum pigments, both of which can be used.

[0142] The above-mentioned lustrous pigment is preferably in the form of flakes. The longitudinal dimension of the lustrous pigment is preferably 1 μm or more, more preferably 5 μm or more, and preferably 100 μm or less, and more preferably 40 μm or less. The thickness of the above-mentioned lustrous pigment is preferably 1 μm or more, more preferably 5 μm or more, and preferably 100 μm or less, and more preferably 40 μm or less.

[0143] If the coating composition according to this disclosure contains the above-mentioned luminous pigment, the content of the luminous pigment is preferably 0.1 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 3.0 parts by mass or more, and preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 25 parts by mass or less, based on 100 parts by mass of the total resin solids in the coating composition.

[0144] The coating composition according to this disclosure can be applied by diluting it to an appropriate viscosity by adding water and / or an organic solvent as necessary when using it. Examples of the organic solvent include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester solvents such as ethyl acetate, butyl acetate, methyl benzoate, ethyl ethoxypropionate, ethyl propionate, and methyl propionate; alcohol solvents such as isopropanol, n-butanol, isobutanol, and 2-ethylhexanol; ether solvents such as tetrahydrofuran, dioxane, and dimethoxyethane; glycol ether solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, and 3-methoxybutyl acetate; aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, and the like.

[0145] The solid content concentration of the coating composition according to this disclosure is preferably 5.0% by mass or more, more preferably more than 7.0% by mass, even more preferably 10% by mass or more, and preferably 60% by mass or less, more preferably less than 40% by mass, and even more preferably 30% by mass or less, from the viewpoint of the discharge stability of the obtained coating composition, suppression of mist, and uniformity of the formed coating film.

[0146] Examples of resins other than the hydroxyl group-containing resin (A) include acrylic resins that do not contain hydroxyl groups, polyester resins that do not contain hydroxyl groups, acrylic-modified polyester resins that do not contain hydroxyl groups, acrylic-modified polyurethane resins that do not contain hydroxyl groups, polyurethane resins that do not contain hydroxyl groups, polyether resins that do not contain hydroxyl groups, polycarbonate resins that do not contain hydroxyl groups, epoxy resins that do not contain hydroxyl groups, alkyd resins that do not contain hydroxyl groups, and polyolefin resins that do not contain hydroxyl groups. In particular, from the viewpoint of discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film, it is preferable that the paint composition according to this disclosure contains a polyurethane resin that does not contain hydroxyl groups as at least one of the resins other than the hydroxyl group-containing resin (A) and curing agent (B).

[0147] Examples of polyurethane resins that do not contain the above-mentioned hydroxyl groups include reaction products of isocyanate-terminated prepolymers obtained from polyols and polyisocyanates with hydroxyl-free chain extenders such as diamines. Examples of the above-mentioned polyols include low molecular weight dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, and hexamethylene glycol, and trihydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol. Examples of the above-mentioned polyols include high molecular weight polyether polyols, polyester polyols, acrylic polyols, and epoxy polyols.

[0148] Examples of the above polyether polyols include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Examples of the above polyester polyols include polycondensates of alcohols such as the above-mentioned dihydric alcohols, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol with dibasic acids such as adipic acid, azelaic acid, and sebatic acid, lactone-based ring-opening polymer polyols such as polycaprolactone, and polycarbonate diols. Examples of the above polyester polyols include carboxyl group-containing polyols such as 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid. The above polyols can be used individually or in combination of two or more types.

[0149] Examples of polyisocyanate compounds to react with the polyols mentioned above include aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; isophorone diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and methylcyclohexane-2,4-(or-2,6-) diisocyanate. Alicyclic diisocyanates such as 1,3-(or 1,4-)di(isocyanatomethyl)cyclohexane, 1,4-cyclohexanediisocyanate, 1,3-cyclopentanediisocyanate, and 1,2-cyclohexanediisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethylxylylene diisocyanate, tolylenediisocyanate, and 4,4'-diphenylmethane Aromatic diisocyanate compounds such as diisocyanates, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, (m- or p-)phenylene diisocyanate, 4,4'-biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, bis(4-isocyanatophenyl)sulfone, isopropylidene bis(4-phenylisocyanate); and these Examples include biuret-type adducts and isocyanurate ring adducts of polyisocyanates; polyisocyanates having three or more isocyanate groups in one molecule, such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, and 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanate compounds.

[0150] Examples of diamines used as hydroxyl group-free chain extenders include ethylenediamine, propylenediamine, and xylylenediamine.

[0151] The polyurethane resin that does not contain hydroxyl groups can, for example, be an aqueous dispersion in water. The average particle size of the aqueous dispersion of the polyurethane resin that does not contain hydroxyl groups is preferably 10 nm or more, more preferably 20 nm or more, and preferably 1,000 nm or less, and more preferably 500 nm or less. The average particle size of the aqueous dispersion of the polyurethane resin that does not contain hydroxyl groups refers to the median of the volume average (D50) and can be measured using the same method as for the "average particle size of hydroxyl group-containing acrylic resin".

[0152] If the coating composition according to this disclosure contains a polyurethane resin that does not contain hydroxyl groups, the content of the polyurethane resin that does not contain hydroxyl groups is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, even more preferably 7.0% by mass or more, and preferably 60% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total resin solid content in the coating composition, from the viewpoint of discharge stability of the obtained coating composition, suppression of mist, uniformity of the formed coating film, and weather resistance.

[0153] The paint composition relating to this disclosure may be either a one-component paint or a multi-component paint, but a one-component paint is preferred from the viewpoint of having no paint mixing process and having excellent productivity, as well as simplifying the maintenance of painting machinery.

[0154] [Method for forming a coating film] The method for forming a coating film according to the present disclosure is a method for forming a coating film on a workpiece by ejecting a coating composition containing a hydroxyl group-containing resin (A) and a curing agent (B) onto the workpiece using an inkjet method, wherein the coating composition, in dynamic viscoelasticity measurements under the conditions of a temperature of 23°C and a frequency of 0.5 Hz, has a stress σ2 in the range of 1.0 to 15 Pa when the storage modulus of elasticity first decreases by 10%, with the storage modulus of elasticity G'1 at a stress of 0.1 Pa as the reference.

[0155] The material of the object to be coated is not particularly limited, and examples include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, and zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, and various fiber-reinforced plastics (FRP); inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth.

[0156] Furthermore, the surface of the object to be coated may be a metal surface such as an automobile body panel, automobile parts, household electrical appliances, or a metal substrate such as steel plates that make up these, which has been subjected to surface treatment such as phosphate treatment, chromate treatment, or composite oxide treatment.

[0157] Even if the above surface treatment has been applied, or even if it has not been applied, a coating film may be formed on the object. For example, the substrate (the object to be coated) may be surface-treated as needed, and then a primer coating film may be formed thereon, or an intermediate coating film may be formed on the primer coating film, or a topcoat film may be formed on the intermediate coating film. The above primer coating film, intermediate coating film, and topcoat film can be formed, for example, if the object to be coated is an automobile body, using known primer, intermediate coating, and topcoat paints that are normally used in the painting of automobile bodies.

[0158] The dry film thickness of the coating film formed by the coating film forming method according to this disclosure varies depending on the application of the object to be coated and is not particularly limited, but from the viewpoint of the discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film, it is preferably 1.0 μm or more, more preferably 2.0 μm or more, even more preferably 8.0 μm or more, and preferably 50 μm or less, more preferably 45 μm or less, and even more preferably 30 μm or less. In this specification, the dry film thickness is determined by measurement with an electromagnetic film thickness meter.

[0159] When applying the above-mentioned paint composition using an inkjet method, the distance between the discharge port and the object to be coated is preferably 0.1 mm or more, more preferably 0.5 mm or more, even more preferably 1.0 mm or more, and preferably 50.0 mm or less, more preferably 30.0 mm or less, and even more preferably 10.0 mm or less, from the viewpoint of suppressing the resulting paint composition mist and ensuring uniformity of the formed coating film.

[0160] The frequency used when applying the above-mentioned paint composition by inkjet method is preferably 10 Hz or higher, more preferably 30 Hz or higher, even more preferably 50 Hz or higher, and preferably 10,000 Hz or lower, more preferably 5,000 Hz or lower, and even more preferably 3,000 Hz or lower, from the viewpoint of the discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film.

[0161] When applying the above-mentioned paint composition using an inkjet method, the supply pressure of the paint composition is preferably 0.001 MPa or higher, more preferably 0.005 MPa or higher, even more preferably 0.01 MPa or higher, and preferably 10 MPa or lower, more preferably 5.0 MPa or lower, and even more preferably 1.0 MPa or lower, from the viewpoint of the discharge stability of the obtained paint composition, suppression of mist, and uniformity of the formed coating film.

[0162] When applying the above-mentioned paint composition using an inkjet method, the scanning speed of the liquid ejection head that ejects the paint composition is preferably 10 mm / s or more, more preferably 15 mm / s or more, even more preferably 20 mm / s or more, preferably 1,500 mm / s or less, more preferably 1,000 mm / s or less, and even more preferably 800 mm / s or less, from the viewpoint of suppressing mist of the obtained paint composition and ensuring uniformity of the formed coating film.

[0163] When applying the above-mentioned paint composition using an inkjet method, the pitch when scanning the liquid ejection head that ejects the paint composition is preferably 0.001 mm or more, more preferably 0.005 mm or more, even more preferably 0.010 mm or more, and preferably 1.0 mm or less, from the viewpoint of suppressing mist of the obtained paint composition and ensuring uniformity of the formed coating film.

[0164] The present disclosure will be further described below with reference to manufacturing examples, examples, and comparative examples. However, the present disclosure is not limited thereto. In each example, "parts" and "%" are based on mass unless otherwise specified. The film thickness of the coating is based on the cured coating.

[0165] [Production of hydroxyl group-containing acrylic resin (A1)] [Production Example 1] 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., emulsifier, 97% active ingredient) were charged into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device. The mixture was stirred and mixed in a nitrogen stream and the temperature was raised to 80°C.

[0166] Next, 1.72 parts of the monomer emulsion (1) and 5.3 parts of a 6% ammonium persulfate aqueous solution were introduced into the reaction vessel, and the contents of the reaction vessel were maintained at 80°C for 15 minutes. Then, the remaining monomer emulsion (1) was added dropwise to the reaction vessel, which was maintained at the same temperature, over a period of 3 hours, and after the dropwise addition was complete, the contents were allowed to mature for 1 hour. Subsequently, the monomer emulsion (2) was added dropwise to the reaction vessel over a period of 1 hour, and the contents were allowed to mature for 1 hour. Then, 42 parts of a 5.0% dimethylethanolamine aqueous solution were gradually added to the reaction vessel while the contents were cooled to 30°C, and the contents were discharged while being filtered through a 100-mesh nylon cloth to obtain an aqueous dispersion of hydroxyl-containing acrylic resin (A1-1) with a solid content of 30%. The obtained hydroxyl-containing acrylic resin (A1-1) had an acid value of 16 mg KOH / g, a hydroxyl value of 66 mg KOH / g, and a glass transition temperature of 21°C. The hydroxyl group-containing acrylic resin (A1-1) corresponds to the water-dispersible hydroxyl group-containing acrylic resin (A1') having the core / shell type multilayer structure described above.

[0167] Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of "Aqualon KH-10", 2 parts of methylenebisacrylamide, 5 parts of styrene, 15 parts of methyl methacrylate, 5 parts of 2-hydroxyethyl methacrylate, and 23 parts of n-butyl acrylate were mixed and stirred to obtain monomer emulsion (1).

[0168] Monomer emulsion (2): 42 parts of deionized water, 0.72 parts of Aqualon KH-10, 0.05 parts of ammonium persulfate, 2.5 parts of methacrylic acid, 10 parts of 2-hydroxyethyl methacrylate, 5 parts of styrene, 12.5 parts of methyl methacrylate, 10 parts of n-butyl acrylate, and 10 parts of n-butyl methacrylate were mixed and stirred to obtain monomer emulsion (2).

[0169] [Production Example 2] 35 parts of propylene glycol monomethyl ether were charged into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropper. After raising the temperature of the contents of the reaction vessel to 85°C, a mixture of 30 parts methyl methacrylate, 20 parts 2-ethylhexyl acrylate, 29 parts n-butyl acrylate, 15 parts 2-hydroxyethyl acrylate, 6 parts acrylic acid, 15 parts propylene glycol monomethyl ether, and 2.3 parts 2,2'-azobis(2,4-dimethylvaleronitrile) was added dropwise to the reaction vessel over 4 hours. After the dropwise addition was complete, the contents were aged for 1 hour. Subsequently, a mixture of 10 parts propylene glycol monomethyl ether and 1 part 2,2'-azobis(2,4-dimethylvaleronitrile) was added dropwise to the reaction vessel over 1 hour. After the dropwise addition was complete, the contents were aged for 1 hour. Furthermore, 7.4 parts of diethanolamine and 13 parts of propylene glycol monomethyl ether were added to the reaction vessel to obtain a hydroxyl group-containing acrylic resin (A1-2) solution with a solid content of 55%. The obtained hydroxyl group-containing acrylic resin (A1-2) had an acid value of 47 mg KOH / g, a hydroxyl group value of 72 mg KOH / g, and a weight-average molecular weight of 58,000.

[0170] [Production of hydroxyl group-containing polyester resin (A2)] [Production Example 3] In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and water separator, 174 parts of trimethylolpropane, 327 parts of neopentyl glycol, 352 parts of adipic acid, 109 parts of isophthalic acid and 101 parts of 1,2-cyclohexanedicarboxylic acid anhydride were charged. The contents of the reaction vessel were heated from 160°C to 230°C over 3 hours, and the contents were kept at 230°C while the generated condensed water was removed by distillation using a water separator, and the reaction was carried out until the acid value was 3 mg KOH / g or less. To this reaction product, 59 parts of trimellitic anhydride were added, and an addition reaction was carried out at 170°C for 30 minutes. After the contents were cooled to below 50°C, 2-(dimethylamino)ethanol was added to the reaction vessel in an equivalent amount to the acid groups to neutralize the acid groups, and then deionized water was gradually added to the reaction vessel to obtain a hydroxyl group-containing polyester resin (A2-1) solution with a solid content of 45% and a pH of 7.2. The obtained hydroxyl group-containing polyester resin (A2-1) had a hydroxyl value of 128 mg KOH / g, an acid value of 35 mg KOH / g, and a number-average molecular weight of 1,440.

[0171] [Production of polyurethane resin that does not contain hydroxyl groups] [Production example 4] In a reaction vessel equipped with a thermometer, a stirrer and reflux condenser, 211.9 parts of "PTMG1000" (trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol with a number average molecular weight of 1,000), 11.5 parts of 2,2-dimethylolpropionic acid, 6.9 parts of trimethylolpropane, 112.2 parts of isophorone diisocyanate and 298.5 parts of methyl ethyl ketone were charged. After replacing the reaction system with nitrogen gas, the contents of the reaction vessel were reacted at 80°C under stirring to obtain a methyl ethyl ketone solution of NCO-terminated urethane prepolymer with a free isocyanate group content of 3.2%. The obtained methyl ethyl ketone solution was cooled to 40°C, and 493.2 g of deionized water containing 9.8 parts of N-ethylmorpholine was added to the methyl ethyl ketone solution and emulsified. Then, 159.2 parts of a 5% aqueous ethylenediamine solution were added, and after stirring for 60 minutes, the methyl ethyl ketone was removed by distillation under reduced pressure and heating. The concentration was adjusted with deionized water to obtain a polyurethane resin dispersion with a solid content of 35%, an acid value of 14 mg KOH / g, and an average particle size of 120 nm, which does not contain hydroxyl groups.

[0172] [Production of Pigment Dispersion] [Production Example 5] In a container equipped with a stirring device, 9.1 parts (5 parts solids) of the hydroxyl group-containing acrylic resin (A1-2) solution obtained in Production Example 2, 3 parts of carbon black (manufactured by Mitsubishi Chemical Corporation, Carbon MA-100, solid content concentration 100% by mass), and 50 parts of deionized water were placed. The contents of the container were mixed uniformly to form a mixed solution, and 2-(dimethylamino)ethanol was added to the mixed solution to adjust the pH to 7.5. Next, the pH-adjusted mixed solution was placed in a wide-mouthed glass bottle, glass beads with a diameter of approximately 1.3 mmφ were added as a dispersion medium, and the bottle was sealed. The mixture was dispersed in a paint shaker for 4 hours to obtain pigment dispersion (P-1).

[0173] [Preparation of Paint Composition] [Example 1] 62.1 parts (8 parts solids) of the pigment dispersion (P-1) obtained in Production Example 5, 116.7 parts (35 parts solids) of the aqueous dispersion of hydroxyl group-containing acrylic resin (A1-1) obtained in Production Example 1, 44.4 parts (20 parts solids) of the hydroxyl group-containing polyester resin (A2-1) solution obtained in Production Example 3, 42.9 parts (30 parts solids) of "Cymel 250" (trade name, manufactured by Ornex Japan, melamine resin, solid content concentration 70%), and 28.6 parts (10 parts) of the polyurethane resin dispersion that does not contain hydroxyl groups obtained in Production Example 4 were uniformly mixed, and then 2.34 parts (0.75 parts solids) of "UH-756VF" (trade name, manufactured by ADEKA, urethane association type viscosity modifier, solid content concentration 32%), 2-(dimethylamino)ethanol and deionized water were added to prepare a paint composition No. 8.0 with a solid content concentration of 20%. I got 1.

[0174] [Examples 2-16 and Comparative Examples 1-3] Paint compositions No. 2-19 were obtained in the same manner as in Example 1, except that the compound composition was as shown in Tables 1 and 2 below. The amounts of each material in the tables are expressed as solid content. In Tables 1 and 2, "polyester resin" is abbreviated as "PE" and "acrylic resin" is abbreviated as "Ac".

[0175] [Measurement of stress σ2 and storage modulus G'1 (dynamic viscoelasticity measurement under conditions of temperature 23°C and frequency 0.50 Hz)] Dynamic viscoelasticity measurements were performed on paint compositions No. 1 to 19 obtained in Examples 1 to 16 and Comparative Examples 1 to 3 under conditions of temperature 23°C, frequency 0.50 Hz, and stress measurement range 0.1 to 20 Pa, according to the method described herein. The measurement results are also shown in Tables 1 and 2.

[0176] [Shear rate 10,000 s] -1 [Measurement of viscosity in the following conditions] For paint compositions No. 1 to No. 19 obtained in Examples 1 to 16 and Comparative Examples 1 to 3, the viscosity was measured at a temperature of 23°C and a shear rate of 10,000 s. -1 The viscosity was measured according to the method described herein. The evaluation results are also shown in Tables 1 and 2.

[0177]

[0178]

[0179] The components listed in the table are as follows: (Note 1) "Primal ASE-60": Product name, manufactured by Dow Chemical, polyacrylic acid-based viscosity modifier, solid content concentration 28% (Note 2) "Primal RM-12W": Product name, manufactured by Dow Chemical, urethane association-type viscosity modifier, solid content concentration 19%

[0180] [Preparation of Test Coated Boards] [Examples 17-36 and Comparative Examples 4-6] Degreased and zinc phosphate treated steel plates (JIS G3141, size 400 mm x 300 mm x 0.8 mm) were electrodeposited with cationic electrodeposition paint "Elecron GT-10" (product name: manufactured by Kansai Paint Co., Ltd., using a blocked polyisocyanate compound as a curing agent in an epoxy resin polyamine-based cationic resin) based on the cured coating film to a thickness of 20 μm, and then heated at 170°C for 20 minutes to crosslink and cure, forming an electrodeposited coating film.

[0181] Next, each of the paint compositions No. 1 to 19 was filled into an "X JET" (product name, manufactured by Engineering Lab Co., Ltd., high viscosity micro-volume piezo jet dispenser, nozzle diameter 100 μm). Then, each of the paint compositions No. 1 to 19 was applied to a region 10 mm inward from the edge of the workpiece on which the electrodeposited coating film had been formed (a rectangular region of 390 x 290 mm) at a speed of 50 mm / s, a pitch of 0.5 mm, and a distance of 10 mm between the nozzle and the workpiece, with the frequency and supply pressure adjusted according to the target dry film thickness. The surface was then heated at 140°C for 30 minutes to crosslink and harden, forming a coating film, which was then used as a test coated panel.

[0182] [Evaluation of Discharge Stability] When coating the above test coated board, the behavior of the discharged paint composition was observed from the discharge port to the coated board using a "FASTCAM Mini UX-100" (manufactured by Photron Co., Ltd., high-speed camera) to evaluate the discharge stability. A and B are considered acceptable. The evaluation results are shown in Table 3. A: Discharge was regular, and discharge along the direction of discharge was observed. B: Discharge was sometimes slightly irregular, and some scattering was observed, but it was at an acceptable level. C: Discharge was irregular, and a lot of scattering was observed, which was at a problematic level. D: Discharge was intermittent, or there was no discharge at all. In Comparative Example 5, discharge was not possible, so it was not possible to evaluate the uniformity of the coating film and the scattering (mist) upon impact.

[0183] [Evaluation of Coating Uniformity] The test painted panels obtained above were visually observed to evaluate the uniformity of the painted surface. A and B are considered acceptable. The evaluation results are shown in Table 3. A: A highly uniform coating was formed (no dot marks, distortion, or gaps in the coating surface were observed at the edges). B: Slight dot marks, distortion, or gaps in the coating surface were observed (not visible from a distance of 50 cm). C: Dot marks, distortion, or gaps in the coating surface were observed (visible from a distance of 50 cm, but not from a distance of 100 cm). D: Dot marks, distortion, or gaps in the coating surface were clearly visible (visible from a distance of 100 cm).

[0184] [Evaluation of Splash (Mist) During Coating] When coating the above test coating board, the amount of splash (mist) generated when the droplets of the dispensed paint composition adhere to the object to be coated was observed using a "FASTCAM Mini UX-100" (Photron Co., Ltd., high-speed camera) from an oblique upward direction within a range where the application of the paint composition droplets could be confirmed, and the amount of splash (mist) during coating was evaluated. A and B are considered passing grades. The evaluation results are shown in Table 3. A: No mist generation was observed. B: A small amount of mist was observed (not visible from a distance of 50 cm). C: Mist generation was observed (visible from a distance of 50 cm, but not from a distance of 100 cm). D: Significant mist generation was observed (visible from a distance of 100 cm).

[0185]

Claims

1. A paint composition comprising a hydroxyl group-containing resin (A) and a curing agent (B), which is applied to a workpiece by an inkjet method, characterized in that, in a dynamic viscoelasticity measurement under the conditions of a temperature of 23°C, a frequency of 0.5 Hz, and a stress measurement range of 0.1 to 20 Pa, the stress σ2 at which the storage modulus first decreases by 10% is within the range of 1.0 to 15 Pa, with the storage modulus G'1 at a stress of 0.1 Pa as the reference.

2. The coating composition according to claim 1, wherein the storage modulus G'1 is in the range of 1.0 to 30 Pa.

3. Temperature 23°C and shear rate 10,000 s -1 The paint composition according to claim 1 or 2, wherein the viscosity under the specified conditions is in the range of 10 to 35 mPa·s.

4. The paint composition according to any one of claims 1 to 3, further comprising a viscosity modifier (C).

5. The paint composition according to claim 4, wherein the content of the viscosity modifier (C) is in the range of 0.4 to 5 parts by mass based on 100 parts by mass of the total resin solids in the paint composition.

6. A method for forming a coating film on a workpiece by ejecting a coating composition containing a hydroxyl group-containing resin (A) and a curing agent (B) onto the workpiece using an inkjet method, wherein the coating composition, in dynamic viscoelasticity measurements under conditions of a temperature of 23°C, a frequency of 0.5 Hz, and a stress measurement range of 0.1 to 20 Pa, has a stress σ2 in the range of 1.0 to 15 Pa at which the storage modulus first decreases by 10%, with the storage modulus G'1 at a stress of 0.1 Pa as the reference.

7. The method for forming a coating film according to claim 6, wherein the coating composition has a storage modulus G'1 when the stress is 0.1 Pa, measured in a dynamic viscoelasticity test at a temperature of 23°C and a frequency of 0.5 Hz, and the storage modulus G'1 is in the range of 1.0 to 30 Pa.

8. The paint composition was tested at a temperature of 23°C and a shear rate of 10,000 s. -1 The method for forming a coating film according to claim 6 or 7, wherein the viscosity under the specified conditions is in the range of 10 to 35 mPa·s.

9. The method for forming a coating film according to any one of claims 6 to 8, wherein the coating composition further comprises a viscosity modifier (C).

10. The method for forming a coating film according to claim 9, wherein the content of the viscosity modifier (C) is in the range of 0.4 to 5 parts by mass based on 100 parts by mass of the total resin solids in the coating composition.

11. The method for forming a coating film according to any one of claims 6 to 10, wherein the dry film thickness of the coating film is in the range of 1.0 to 50 μm.

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