JP6725895B2 - (Meth)acrylic modified polyester resin, curable resin composition, paint and coated steel sheet - Google Patents

Description

The present invention relates to a (meth)acryl-modified polyester resin, a curable resin composition containing the same, a paint comprising the curable resin composition, and a coated steel sheet having a coating film of the paint.

BACKGROUND ART As a coating method for various metal parts or metal molded products for home appliances, automobile parts, building materials, can-making applications, and the like, a precoating method in which a steel sheet is painted in advance and a postcoating method in which a steel sheet is molded and then painted are known. The steel plate used in the pre-coating method is generally called pre-coated metal (hereinafter abbreviated as "PCM"), and a pre-painted steel plate is cut into various shapes according to the intended use and formed into various shapes. In addition to the hardness and gloss of the coating surface, paints are required to have extremely high processability and weather resistance.

Further, in recent years, in consideration of the influence on the environment, a high solid type PCM paint having a reduced amount of a volatile organic compound (VOC) and a small solvent content has been studied, and a high solid paint is required. Has been.

Conventional PCM paints include various types of paints such as two-component curing type, ultraviolet curing type, and volatile drying type, and there are various types of resin such as polyester resin, fluororesin, and acrylic resin. Of these, a two-component curable coating material containing a polyester resin as a main component is widely used because it has excellent processability.

Examples of the two-component curing type coating material containing the polyester resin as a main component include, for example, terephthalic acid, isophthalic acid, 2-methyl-1,3-propanediol and 1,6-hexanediol as a reaction raw material, and a number average molecular weight ( A paint mainly composed of a polyester resin having a Mn of 11,000 is known (see, for example, Patent Document 1). However, although it has excellent processability, it is a standard required in recent years in terms of making the paint high solid. It didn't extend to.

Therefore, there has been a demand for a material which can realize high solidification of the coating material and which can form a coating film having excellent processability and weather resistance.

JP, 9-12969, A

The problem to be solved by the present invention is to make a coating highly solid and to form a coating film having excellent processability and weather resistance (meth)acryl-modified polyester resin, and curability containing the same. To provide a resin composition, a paint, and a coated steel sheet.

As a result of intensive studies to solve the above problems, the present inventors have used a (meth)acrylic modified polyester resin having a saturated polyester resin and a (meth)acrylic monomer mixture as essential reaction materials. The inventors have found that the above problems can be solved and completed the present invention.

That is, the invention is a (meth)acryl-modified polyester in which a saturated polyester resin (A) and a (meth)acrylic monomer mixture (B) containing a hydroxyl group-containing (meth)acrylic monomer are essential reaction raw materials. A resin, wherein the saturated polyester resin (A) is a polycondensation product of an aliphatic diol (a1) and a dicarboxylic acid (a2) containing an aliphatic dicarboxylic acid, and the content of the aliphatic dicarboxylic acid is Is 5% by mass or more in the dicarboxylic acid (a2), a (meth)acrylic modified polyester resin, a curable resin composition containing the same, a paint and a coated steel sheet.

INDUSTRIAL APPLICABILITY The (meth)acrylic-modified polyester resin of the present invention enables high solidification of a coating, that is, high non-volatile differentiation, and can form a coating film having excellent processability and weather resistance. It can be suitably used as an automotive paint such as a top coating and an automotive repair paint. The "high solid" in the present invention means that the non-volatile content of the coating material is 65% by mass or more.

The (meth)acrylic-modified polyester resin of the present invention is characterized by using the saturated polyester resin (A) and the (meth)acrylic monomer mixture (B) as essential reaction raw materials.

The saturated polyester resin (A) refers to a polyester resin having substantially no aliphatic carbon-carbon double bond.

As the saturated polyester resin (A), one obtained by polycondensing an aliphatic diol (a1) and a dicarboxylic acid (a2) is used.

As the aliphatic diol (a1), at least a (meth)acryl-modified polyester resin capable of forming a coating material having high solidity and capable of forming a coating film having excellent processability and weather resistance is obtained. Those containing an asymmetric diol having one side chain and/or a straight chain diol having no side chain are preferred. The "asymmetric diol" in the present invention refers to a diol having an asymmetric structure.

Examples of the asymmetric diol having at least one side chain include 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,4-butanediol, 2-ethyl-1,4-butane. Examples thereof include diol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 3-methyl-1,5-heptanediol and the like. These asymmetric diols having at least one side chain can be used alone or in combination of two or more. Among these, 2-methyl-1,3-propanediol is preferable.

Examples of the straight chain diol having no side chain include ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7. -Heptanediol, 1,8-octanediol, 1,9-nanodiol, 1,10-dodecanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14- Tetradecanediol, 1,15-pentadecanediol, 1,16-hexadecanediol, 1,17-heptadecanediol, 1,18-octadecanediol, 1,19-nonadecanediol, 1,20-eicosanediol and the like can be mentioned. To be These linear diols having no side chain can be used alone or in combination of two or more kinds. Further, among these, a (meth)acryl-modified polyester resin capable of forming a high solid coating material and capable of forming a coating film having excellent processability and weather resistance is obtained, and therefore 1,6-hexane Diols are preferred.

In addition to the asymmetric diol having at least one side chain and the straight chain diol having no side chain, other diols can be used as the aliphatic diol (a1), if necessary.

Examples of the other aliphatic diols include neopentyl glycol, hydrogenated bisphenol A, hydrogenated bisphenol F, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,2-butanediol, 1,3- Butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,2-hexanediol, 1,4-hexanediol, 2,3-hexanediol, 2,2-diethyl-1,3-propanediol , 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol and the like. These other aliphatic diols can be used alone or in combination of two or more kinds.

The dicarboxylic acid (a2) contains an aliphatic dicarboxylic acid as an essential component because a (meth)acryl-modified polyester resin capable of forming a coating film having excellent processability and weather resistance can be obtained.

Examples of the aliphatic dicarboxylic acid include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, dimer acid, fumaric acid and the like. Examples thereof include methyl ester of dicarboxylic acid and acid chloride. These aliphatic dicarboxylic acids can be used alone or in combination of two or more kinds. Of these, adipic acid is preferable.

The content of the aliphatic dicarboxylic acid is 5% by mass or more in the dicarboxylic acid (a2) because it has excellent compatibility with the (meth)acrylic monomer mixture (B). The range of up to 20% by mass is more preferable.

In addition, the dicarboxylic acid (a2) may contain an alicyclic dicarboxylic acid, an aromatic dicarboxylic acid, or an acid anhydride thereof, if necessary. Examples of the alicyclic dicarboxylic acid include 1,3-cyclopentanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid. Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid, p-hydroxybenzoic acid. , P-(2-hydroxyethoxy)benzoic acid, trimellitic acid, pyromellitic acid, phthalic anhydride and the like.

In the polycondensation reaction of the aliphatic diol (a1) and the dicarboxylic acid (a2), an esterification catalyst can be used if necessary.

Examples of the esterification catalyst include metal salts such as titanium, tin, zinc, aluminum, zirconium, magnesium, hafnium and germanium; titanium tetraisopropoxide, titanium tetrabutoxide, titanium oxyacetylacetonate, dibutyltin oxide and dibutyl. Tin diacetate, dibutyltin dilaurate, tin octoate, 2-ethylhexanetin, zinc acetylacetonate, zirconium tetrachloride, tetrazirconium tetrachloride tetrahydrofuran complex, hafnium tetrachloride, hafnium tetrachloride tetrahydrofuran complex, germanium oxide, tetraethoxygermanium, etc. The metal compounds of

The reaction between the aliphatic diol (a1) and the dicarboxylic acid (a2) can be carried out, for example, in the absence of a solvent or in the presence of an organic solvent.

Further, even when the reaction between the aliphatic diol (a1) and the dicarboxylic acid (a2) is carried out in the absence of a solvent, it can be used after being dissolved in an organic solvent.

Examples of the organic solvent include ketone solvents such as methyl ethyl ketone, acetone and isobutyl ketone; cyclic ether solvents such as tetrahydrofuran and dioxolane; ester solvents such as methyl acetate, ethyl acetate and butyl acetate; aromatics such as toluene, xylene and solvent naphtha. Aliphatic solvents such as cyclohexane and methylcyclohexane; alcohol solvents such as carbitol, cellosolve, methanol, isopropanol, butanol, propylene glycol monomethyl ether; alkylene glycol monoalkyl ether, dialkylene glycol monoalkyl ether, dialkylene glycol Examples include glycol ether solvents such as monoalkyl ether acetate. These organic solvents may be used alone or in combination of two or more.

Regarding the weight average molecular weight of the saturated polyester resin (A), it is possible to obtain a (meth)acryl-modified polyester resin capable of forming a coating material with high solidity and capable of forming a coating film having excellent processability and weather resistance. Therefore, the range of 1,000 to 5,000 is preferable, and the range of 2,000 to 3,000 is more preferable.

The weight average molecular weight of the saturated polyester resin (A) is a value measured by a gel permeation chromatography (GPC) method.

The (meth)acrylic monomer mixture (B) essentially contains a hydroxyl group-containing (meth)acrylic monomer.

Examples of the hydroxyl group-containing (meth)acrylic monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and mono(meth)glycerin. ) Examples include (meth)acrylic monomers having a hydroxyl group in the molecule such as acrylic acid ester. These hydroxyl group-containing (meth)acrylic monomers can be used alone or in combination of two or more kinds.

Further, the content of the hydroxyl group-containing (meth)acrylic monomer is preferably 10% by mass or more in the (meth)acrylic monomer mixture. In particular, when the (meth)acrylic-modified polyester resin of the present invention is used for industrial paints such as automobiles and heavy equipment, the range of 20 to 40 mass% is more preferable, and when it is used for PCM paints, 10 to 25 mass%. The range of% is more preferable.

The (meth)acrylic monomer mixture may contain other (meth)acrylic monomers other than the hydroxyl group-containing (meth)acrylic monomer.

Examples of the other (meth)acrylic monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, and (meth). T-butyl acrylate, 2-ethylhexyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, dodecyl (meth)acrylate, (Meth)acrylic acid alkyl ester such as stearyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate; Acrylic acid, β-carboxyethyl (meth)acrylate, 2-(meth)acryloylpropionic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, itaconic acid half ester, maleic acid half ester, maleic anhydride, itaconic anhydride Carboxyl group-containing (meth)acrylic monomers such as acid, β-(meth)acryloyloxyethyl hydrogen succinate, β-(meth)hydroxyethyl hydrogen phthalate and salts thereof; aminomethacrylate (meth)acrylate, (meth)acrylate ) N-monoalkylaminoalkyl acrylate, N,N-dialkylaminoalkyl (meth)acrylate, (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propylacrylamide, diacetone (Meth)acrylamide, N-methylol(meth)acrylamide, N-isopropyl(meth)acrylamide, N-butyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, etc. Amide group-containing (meth)acrylic monomers; vinyl ester compounds such as acrolein, vinyl acetate, vinyl propionate and vinyl versatate; vinyl ether compounds such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, amyl vinyl ether, hexyl vinyl ether A vinyl nitrile compound such as (meth)acrylonitrile; a vinyl monomer having an aromatic ring such as styrene, α-methylstyrene, vinyltoluene, vinylanisole, α-halostyrene, vinylnaphthalene; a functional group such as isoprene, butadiene or ethylene N-vinylpyrrole-free vinyl monomer Heterocyclic vinyl monomers such as redone; (meth)acryloyloxyethyl phosphate, di(meth)acryloyloxyethyl phosphate, tri(meth)acryloyloxyethyl phosphate, caprolactone-modified (meth)acryloyloxyethyl phosphate And a phosphoric acid group-containing (meth)acrylic monomer. These other (meth)acrylic monomers can be used alone or in combination of two or more kinds.

The mass ratio [(A)/(B)] of the saturated polyester resin (A) and the (meth)acrylic monomer mixture (B) enables high solidification of the paint and has excellent processability. Since a (meth)acrylic modified polyester resin capable of forming a coating film having weather resistance is obtained, the range of 15/85 to 50/50 is preferable, and the range of 25/75 to 35/65 is more preferable.

The (meth)acrylic modified polyester resin of the present invention is obtained by, for example, dropping the (meth)acrylic monomer mixture (B) and a polymerization initiator into an organic solvent solution of the saturated polyester resin (A) to cause a reaction. Can be obtained by

Examples of the polymerization initiator include azo compounds such as 2,2′-azobis(isobutyronitrile), 2,2′-azobis(2-methylbutyronitrile) and azobiscyanovaleric acid; tert-butylperoxy. Pivalate, tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, di-tert-butyl peroxide, cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide, tert-butyl Organic peroxides such as peroxy-2-ethylhexyl monocarbonate; inorganic peroxides such as hydrogen peroxide, ammonium persulfate, potassium persulfate and sodium persulfate. These polymerization initiators can be used alone or in combination of two or more kinds.

The weight average molecular weight of the (meth)acryl-modified polyester resin of the present invention is such that the (meth)acryl-modified polyester resin capable of forming a coating with high solidity and capable of forming a coating film having excellent processability and weather resistance is Since it is obtained, the range of 5,000 to 20,000 is preferable, and the range of 7,500 to 12,500 is more preferable.

The hydroxyl value of the (meth)acrylic acid polyester resin of the present invention is a (meth)acrylic modified polyester resin capable of forming a solid coating material and capable of forming a coating film having excellent processability and weather resistance. Therefore, the range of 60 to 150 is preferable. In particular, when the (meth)acrylic-modified polyester resin of the present invention is used for industrial coatings such as automobiles and heavy equipment, the range of 100 to 150 is more preferable, and when it is used for PCM coatings, the range of 60 to 100 is preferable. More preferable.

The curable resin composition of the present invention essentially contains the (meth)acryl-modified polyester resin and a curing agent.

The curing agent may contain a component capable of causing a curing reaction with the (meth)acryl-modified polyester resin of the present invention, and examples of such a component include amino resin, polyisocyanate resin, and resole resin. , Epoxy resin and the like. These may be used alone or in combination of two or more. The component of the curing agent is appropriately selected depending on the application and use environment of the curable resin composition, the physical properties of the desired cured product, etc., as long as the (meth)acryl-modified polyester resin of the present invention is used as the main agent, Regardless of which curing agent is used, the effect of the present invention, which is excellent in the balance between processability and weather resistance in the cured coating film, is sufficiently exhibited.

As the amino resin, for example, a methylolated amino resin synthesized from at least one selected from the group consisting of melamine, urea and benzoguanamine, and formaldehydes; a part or all of the methylol group of the methylolated amino resin. Examples thereof include those which have been alkyl etherified with a lower monohydric alcohol such as methanol, ethanol, propanol, isopropanol, butanol, and isobutanol.

Examples of commercial products of the amino resin include "Cymel 303" (methylated melamine resin), "Cymel 350" (methylated melamine resin) manufactured by Allnex, and "Uban 520" (n- manufactured by Mitsui Chemicals, Inc.). Butylated modified melamine resin), "Uban 20-SE-60" (n-butyl modified melamine resin), "Uban 2021" (n-butyl modified melamine resin), "Uban 220" (n-butyl modified melamine) Resin), "Uban 22R" (n-butylated modified melamine resin), "Uban 2028" (n-butylated modified melamine resin), "Uban 165" (isobutylated modified melamine resin), "Uban 114" (isobutylated) Modified melamine resin), "Uban 62" (isobutylated modified melamine resin), "Uban 60R" (isobutylated modified melamine resin) and the like. When these amino resins are used, an acid compound such as phosphoric acid ester may be added as a curing accelerator.

Examples of the polyisocyanate resin include, butane diisocyanate, hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and aliphatic diisocyanate compounds such as 2,4,4-trimethylhexamethylene diisocyanate; norbornane diisocyanate, isophorone diisocyanate, Alicyclic diisocyanate compounds such as hydrogenated xylylene diisocyanate and hydrogenated diphenylmethane diisocyanate; aromatic diisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, tetramethyl xylylene diisocyanate, diphenylmethane diisocyanate and 1,5-naphthalene diisocyanate; Examples thereof include polymethylene polyphenyl polyisocyanates having a repeating structure represented by the formula (1); their isocyanurate modified products, biuret modified products, allophanate modified products, blocked polyisocyanate resins and the like.

［式中、Ｒ^１はそれぞれ独立に水素原子、炭素原子数１〜６の炭化水素基の何れかである。Ｒ^２はそれぞれ独立に炭素原子数１〜４のアルキル基、又は構造式（１）で表される構造部位と＊印が付されたメチレン基を介して連結する結合点の何れかである。ｍは０又は１〜３の整数であり、ｌは１以上の整数である。］

[In the formula, each R ¹ is independently a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. Each R ² is independently an alkyl group having 1 to 4 carbon atoms, or a bonding point connecting the structural site represented by the structural formula (1) and a methylene group marked with *. m is an integer of 0 or 1 to 3, and l is an integer of 1 or more. ]

Examples of the epoxy resin include polyglycidyl ethers of polyol compounds, polyglycidyl esters of polycarboxylic acid compounds, bisphenol type epoxy resins, novolac type epoxy resins, and the like.

The curable resin composition of the present invention, if necessary, a curing catalyst, a curing accelerator, a pigment, a pigment dispersant, a matting agent, a leveling agent, a drying inhibitor, an ultraviolet absorber, a defoaming agent, a thickener. Alternatively, an anti-settling agent, an organic solvent or the like may be added. The blending ratio of each of these components and the type of the blending are appropriately adjusted depending on the use and desired performance of the curable resin composition. Further, the curable resin composition of the present invention may be a one-pack type or a two-pack type. When the curable resin composition of the present invention is a two-component type, the various additives described above can be added to either or both of the main agent and the curing agent.

The use of the curable resin composition of the present invention is not particularly limited, but since it can form a cured coating film having excellent processability and weather resistance, it can be used for paints and adhesives, particularly PCM paints and automobiles. It can be suitably used as a paint for coated steel sheets such as a top coat paint and a paint for automobiles such as a paint for repairing automobiles.

The coated steel sheet of the present invention refers to one having a cured coating film of a coating material comprising the curable resin composition on the surface of the steel sheet, and the steel sheet is, for example, a galvanized steel sheet, an aluminum-zinc alloy steel sheet or the like plating A steel plate, a zinc-aluminum-magnesium alloy plated steel plate, an aluminum plate, an aluminum alloy plate, an electromagnetic steel plate, a copper plate, a stainless steel plate, etc. may be mentioned.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

The number average molecular weight (Mn) and weight average molecular weight (Mw) of the saturated polyester resin used in the present invention, and the number average molecular weight (Mn) and weight average molecular weight (Mw) of the (meth)acryl-modified polyester resin of the present invention. ) Indicates a value obtained by measurement under the following conditions by a gel permeation chromatography (GPC) method.

Measuring device: High-speed GPC device ("HLC-8220GPC" manufactured by Tosoh Corporation)
Column: The following columns manufactured by Tosoh Corporation were connected in series and used.
"TSKgel G5000" (7.8 mm ID x 30 cm) x 1 "TSK gel G4000" (7.8 mm ID x 30 cm) x 1 "TSK gel G3000" (7.8 mm ID x 30 cm) x 1 This "TSKgel G2000" (7.8 mm ID x 30 cm) x 1 Detector: RI (differential refractometer)
Column temperature: 40°C
Eluent: Tetrahydrofuran (THF)
Flow rate: 1.0 mL/min Injection volume: 100 μL (tetrahydrofuran solution with a sample concentration of 0.4% by mass)
Standard sample: A calibration curve was prepared using the following standard polystyrene.

(Standard polystyrene)
Tosoh Corporation "TSKgel Standard Polystyrene A-500"
Tosoh Corporation "TSK gel standard polystyrene A-1000"
Tosoh Corporation "TSK gel standard polystyrene A-2500"
Tosoh Corporation "TSK gel standard polystyrene A-5000"
"TSK gel standard polystyrene F-1" manufactured by Tosoh Corporation
"TSK gel standard polystyrene F-2" manufactured by Tosoh Corporation
"TSK gel standard polystyrene F-4" manufactured by Tosoh Corporation
Tosoh Corporation "TSK gel standard polystyrene F-10"
Tosoh Corporation "TSK gel standard polystyrene F-20"
Tosoh Corporation "TSK gel standard polystyrene F-40"
Tosoh Corporation "TSK gel standard polystyrene F-80"
Tosoh Corporation "TSK gel standard polystyrene F-128"
Tosoh Corporation "TSK gel standard polystyrene F-288"
Tosoh Corporation "TSK gel standard polystyrene F-550"

(Production Example 1: Production of saturated polyester resin (1) solution)
In a reaction vessel equipped with a stirrer, a condenser and a thermometer, 5 parts by mass of 2-methyl-1,3-propanediol, 8.95 parts by mass of 1,6-hexanediol, 4 parts by mass of trimethylolpropane and neopentyl glycol 28. 0.29 parts by mass, isophthalic acid 44.76 parts by mass, adipic acid 9 parts by mass, and tetraisopropyl orthotitanate 0.01 part by mass were added. An esterification reaction was carried out at 200 to 250° C. for 12 hours while stirring under a nitrogen stream to obtain a saturated polyester resin (1). The number average molecular weight (Mn) of this saturated polyester resin (1) was 1,094, the weight average molecular weight (Mw) was 2,114, the acid value was 2.8 mgKOH/g, and the hydroxyl value was 137 mgKOH/g.

The saturated polyester resin (1) thus obtained was dissolved in butyl acetate to obtain a saturated polyester resin (1) solution having a nonvolatile content of 81.4% by mass. The Gardner viscosity of this saturated polyester resin (1) solution was Z4-Z5.

(Production Example 2: Production of saturated polyester resin (2) solution)
15.59 parts by mass of 2-methyl-1,3-propanediol, 10.25 parts by mass of 1,6-hexanediol, 1.97 parts by mass of trimethylolpropane in a reaction vessel equipped with a stirrer, a condenser, and a thermometer. 17.64 parts by mass of neopentyl glycol, 44.3 parts by mass of isophthalic acid, 10.25 parts by mass of adipic acid, and 0.01 part by mass of tetraisopropyl orthotitanate were added. An esterification reaction was carried out at 200 to 250° C. for 12 hours while stirring under a nitrogen stream to obtain a saturated polyester resin (2). The number average molecular weight (Mn) of this saturated polyester resin (2) was 988, the weight average molecular weight (Mw) was 2,026, the acid value was 2.1 mgKOH/g, and the hydroxyl value was 141.3 mgKOH/g.

The obtained saturated polyester resin (2) was dissolved in butyl acetate to obtain a saturated polyester resin (2) solution having a nonvolatile content of 83.1% by mass. The Gardner viscosity of this saturated polyester resin (2) solution was Z3-Z4.

(Production Example 3: Production of saturated polyester resin (3) solution)
30 parts by mass of 2-methyl-1,3-propanediol, 10 parts by mass of 1,6-hexanediol, 1 part by mass of trimethylolpropane, and 4 parts by mass of neopentyl glycol in a reaction vessel equipped with a stirrer, a condenser, and a thermometer. 35 parts by mass of isophthalic acid, 20 parts by mass of adipic acid, and 0.01 part by mass of tetraisopropyl orthotitanate were added. An esterification reaction was carried out at 200 to 250° C. for 12 hours while stirring under a nitrogen stream to obtain a saturated polyester resin (3). The number average molecular weight (Mn) of this saturated polyester resin (3) was 667, the weight average molecular weight (Mw) was 1,441, the acid value was 7.2 mgKOH/g, and the hydroxyl value was 169.2 mgKOH/g.

The saturated polyester resin (3) obtained above was dissolved in butyl acetate to obtain a saturated polyester resin (3) solution having a nonvolatile content of 87% by mass. The Gardner viscosity of this saturated polyester resin (3) solution was Z2-Z3.

(Production Example 4: Production of saturated polyester resin (4) solution)
In a reaction vessel equipped with a stirrer, a condenser and a thermometer, 23.32 parts by mass of 2-methyl-1,3-propanediol, 3.89 parts by mass of 1,6-hexanediol, 1.94 parts by mass of trimethylolpropane, 12.05 parts by mass of neopentyl glycol, 45.19 parts by mass of isophthalic acid, 13.61 parts by mass of adipic acid, and 0.01 part by mass of tetraisopropyl orthotitanate were added. An esterification reaction was carried out at 200 to 250° C. for 12 hours while stirring under a nitrogen stream to obtain a saturated polyester resin (4). The number average molecular weight (Mn) of this saturated polyester resin (4) was 2,149, the weight average molecular weight (Mw) was 4,968, the acid value was 4.7 mgKOH/g, and the hydroxyl value was 78.6 mgKOH/g. ..

The saturated polyester resin (4) obtained above was dissolved in a mixed solvent of 800 parts by mass of an aromatic solvent (“Solveso 100” manufactured by Exxon Mobil Ltd.) and 200 parts by mass of propylene glycol monomethyl ether acetate to give a nonvolatile content of 78. A 0.3% by mass saturated polyester resin (4) solution was obtained. The Gardner viscosity of this saturated polyester resin (4) solution was ZZ1.

(Production Example 5: Production of saturated polyester resin (5) solution)
In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 30.81 parts by mass of 2-methyl-1,3-propanediol, 6.85 parts by mass of 1,6-hexanediol, 1.17 parts by mass of trimethylolpropane, 4.25 parts by mass of neopentyl glycol, 38.44 parts by mass of isophthalic acid, 18.49 parts by mass of adipic acid, and 0.01 part by mass of tetraisopropyl orthotitanate were added. An esterification reaction was carried out at 200 to 250° C. for 12 hours while stirring under a nitrogen stream to obtain a saturated polyester resin (5). The number average molecular weight (Mn) of this saturated polyester resin (5) was 1,234, the weight average molecular weight (Mw) was 2,998, the acid value was 6 mgKOH/g, and the hydroxyl value was 113.5 mgKOH/g.

The obtained saturated polyester resin (5) was dissolved in butyl acetate to obtain a saturated polyester resin (5) solution having a nonvolatile content of 82.2% by mass. The Gardner viscosity of this saturated polyester resin (5) solution was XY.

(Production Example 6: Production of saturated polyester resin (6) solution)
In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 25.76 parts by mass of 2-methyl-1,3-propanediol, 2.02 parts by mass of trimethylolpropane, 12.63 parts by mass of neopentyl glycol, and 40 parts of isophthalic acid. 0.4 parts by mass, terephthalic acid 16.67 parts by mass, adipic acid 2.53 parts by mass, and tetraisopropyl orthotitanate 0.01 part by mass were added. An esterification reaction was carried out at 200 to 250° C. for 12 hours while stirring under a nitrogen stream to obtain a saturated polyester resin (6). The number average molecular weight (Mn) of this saturated polyester resin (6) was 1,763, the weight average molecular weight (Mw) was 4,028, the acid value was 4.5 mgKOH/g, and the hydroxyl value was 94.4 mgKOH/g. ..

The saturated polyester resin (6) obtained above was dissolved in butyl acetate to obtain a saturated polyester resin (6) solution having a nonvolatile content of 72% by mass. The Gardner viscosity of this saturated polyester resin (6) solution was Z1-Z2.

(Example 1: Preparation of (meth)acrylic modified polyester resin (1) solution)
Into a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 17.41 parts by mass of the saturated polyester resin (1) solution obtained in Production Example 1 and 20.38 parts by mass of butyl acetate were charged, and the temperature was raised to 120 to 130°C. Warmed. Then, over 4 to 6 hours, 4.96 parts by mass of the (meth)acrylic monomer mixture described in Table 1, (2-ethylhexanoyl)(tert-butyl)peroxide, and 0.5 parts by mass of 1-dodecanethiol. Parts were dropped. Thereafter, 0.07 parts by mass of tert-butylbenzoyl peroxide was added, and the mixture was allowed to stand at 120 to 130° C. for 2 hours to obtain a (meth)acryl-modified polyester resin (1) solution having a nonvolatile content of 70.5% by mass. The (meth)acrylic modified polyester resin (1) solution had a number average molecular weight (Mn) of 2,942, a weight average molecular weight (Mw) of 8,468, an acid value of 11 mgKOH/g, and a hydroxyl value (solid content) of 141 mgKOH. /G, the Gardner viscosity was Z1-Z2.

(Example 2: Preparation of (meth)acrylic modified polyester resin (2))
15.76 parts by mass of the saturated polyester resin (2) solution obtained in Production Example 2, 5.22 parts by mass of glycidyl odecanoate, and 26.25 parts by mass of butyl acetate in a reaction vessel equipped with a stirrer, a condenser, and a thermometer. It was charged and the temperature was raised to 120 to 130°C. Next, 4.02 parts by mass of the (meth)acrylic monomer mixture shown in Table 1 and (2-ethylhexanoyl)(tert-butyl)peroxide were added dropwise over 4 to 6 hours. Thereafter, 0.07 parts by mass of tert-butylbenzoyl peroxide was added, and the mixture was allowed to stand at 120 to 130° C. for 2 hours to obtain a (meth)acryl-modified polyester resin (2) solution having a nonvolatile content of 72.3% by mass. The (meth)acrylic modified polyester resin (2) solution has a number average molecular weight (Mn) of 2,593, a weight average molecular weight (Mw) of 6,660, an acid value of 15.2 mgKOH/g, and a hydroxyl value (solid content). Was 143 mgKOH/g and the Gardner viscosity was Z4-Z5.

(Example 3: Preparation of (meth)acrylic modified polyester resin (3))
18.30 parts by mass of the saturated polyester resin (3) solution obtained in Production Example 3 and 21.26 parts by mass of butyl acetate were placed in a reaction vessel equipped with a stirrer, a condenser, and a thermometer, and the temperature was raised to 120 to 130°C. Warmed. Then, over 4 to 6 hours, the (meth)acrylic monomer mixture shown in Table 1, (2-ethylhexanoyl)(tert-butyl)peroxide 4.89 parts by mass, and 1-dodecanethiol 0.5 parts by mass. Parts were dropped. Then, 0.07 parts by mass of tert-butylbenzoyl peroxide was added, and the mixture was allowed to stand at 120 to 130° C. for 2 hours to obtain a (meth)acryl-modified polyester resin (3) having a nonvolatile content of 76.5% by mass. The (meth)acrylic modified polyester resin (3) solution had a number average molecular weight (Mn) of 2,363, a weight average molecular weight (Mw) of 6,873, an acid value of 11.2 mgKOH/g, and a hydroxyl value (solid content). Was 140 mgKOH/g and the Gardner viscosity was ZZ1.

(Example 4: Preparation of (meth)acrylic modified polyester resin (4))
22.05 parts by mass of the saturated polyester resin (4) solution obtained in Production Example 4, 12.88 parts by mass of butyl acetate, 19.24 parts by mass of propylene glycol monomethyl ether acetate in a reaction vessel equipped with a stirrer, a condenser, and a thermometer. Parts were charged and the temperature was raised to 120 to 130°C. Next, over 4 to 6 hours, the (meth)acrylic monomer mixture shown in Table 1, (2-ethylhexanoyl)(tert-butyl)peroxide 3.15 parts by mass, and 1-dodecanethiol 0.45 parts by mass. Parts were dropped. Then, 0.06 parts by mass of tert-butylbenzoyl peroxide was added, and the mixture was allowed to stand at 120 to 130° C. for 2 hours to obtain a (meth)acryl-modified polyester resin (4) solution having a nonvolatile content of 65% by mass. The (meth)acrylic modified polyester resin (4) solution had a number average molecular weight (Mn) of 3,172, a weight average molecular weight (Mw) of 8,126, an acid value of 7.5 mgKOH/g, and a hydroxyl value (solid content). Was 77.4 mgKOH/g, and the Gardner viscosity was L.

(Example 5: Preparation of (meth)acrylic modified polyester resin (5))
In a reaction vessel equipped with a stirrer, a condenser and a thermometer, 25.25 parts by mass of the saturated polyester resin (5) solution obtained in Production Example 5, 17.04 parts by mass of butyl acetate, 3.01 parts by mass of propylene glycol monomethyl ether acetate. Parts were charged and the temperature was raised to 120 to 130°C. Then, over 4 to 6 hours, the (meth)acrylic monomer mixture shown in Table 1, (2-ethylhexanoyl)(tert-butyl)peroxide 3.94 parts by mass, and 1-dodecanethiol 0.54 parts by mass. Parts were dropped. Then, 0.07 parts by mass of tert-butylbenzoyl peroxide was added, and the mixture was allowed to stand at 120 to 130° C. for 2 hours to obtain a (meth)acryl-modified polyester resin (5) solution having a nonvolatile content of 73.7% by mass. The (meth)acrylic modified polyester resin (5) solution had a number average molecular weight (Mn) of 2,144, a weight average molecular weight (Mw) of 7,441, an acid value of 7.4 mgKOH/g, and a hydroxyl value (solid content). Was 80.6 mg KOH/g, and the Gardner viscosity was VW.

Table 1 shows the compositions of the (meth)acrylic modified polyester resins (1) to (5) obtained in Examples 1 to 5.

(Comparative Production Example 1: Preparation of acrylic resin solution (C1-1))
Butyl acetate was put into a reaction vessel equipped with a stirrer, a condenser, and a thermometer, and the temperature was raised to 120 to 130°C. Then, the acrylic monomer mixture used in Example 5 was added dropwise over 4 to 6 hours. Then, tert-butylbenzoyl peroxide was added, and the mixture was allowed to stand at 120 to 130° C. for 2 hours to obtain an acrylic resin solution (C1-1) having a nonvolatile content of 70.8 mass %. The acrylic resin solution (C1-1) had a number average molecular weight (Mn) of 2,742, a weight average molecular weight (Mw) of 7,841, an acid value of 6.6 mgKOH/g, and a hydroxyl value (solid content) of 73. 3 mgKOH/g, the Gardner viscosity was YZ.

(Comparative Example 1: Preparation of mixed solution (C1) of acrylic resin and polyester resin)
The acrylic resin solution (C1-1) obtained in Comparative Production Example 1 and the saturated polyester resin (5) solution obtained in Production Example 5 were mixed at 25° C. so that the polyester amount was the same as in Example 5. Thus, a mixed solution (C1) of an acrylic resin and a polyester resin was obtained.

(Comparative Example 2: Preparation of (meth)acrylic modified polyester resin (C2))
In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 46.7 parts by mass of the saturated polyester resin (6) solution obtained in Production Example 6, 1.41 parts by mass of butyl acetate, 12.7 parts by mass of propylene glycol monomethyl ether acetate. Parts were charged and the temperature was raised to 120 to 130°C. Then, over 4 to 6 hours, the (meth)acrylic monomer mixture shown in Table 2, 2.39 parts by mass of (2-ethylhexanoyl)(tert-butyl)peroxide, and 0.27 parts by mass of 1-dodecanethiol. Parts were dropped. Then, 0.05 part by mass of tert-butylbenzoyl peroxide was added, and the mixture was allowed to stand at 120 to 130° C. for 2 hours, but the solution was separated into two layers, and the intended (meth)acryl-modified polyester resin solution was not obtained. ..

(Example 6: Preparation of white paint (1))
In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 26.4 parts by mass of the (meth)acryl-modified polyester resin (4) solution obtained in Example 4 and titanium oxide (“Ti-Pure R960” manufactured by Dupont Co., Ltd. 34 0.3 parts by mass, 0.3 parts by mass of silica (“Avosil R972” manufactured by Evonik Industries), an aromatic solvent (“Solvesso 100” manufactured by ExxonMobil Ltd.) and propylene glycol monomethyl ether acetate in a mass ratio of 7:3. The mixed solvent (4.1 parts by mass) was mixed and dispersed until the particle size became 10 μm or less.Then, 26.4 parts by mass of the (meth)acryl-modified polyester resin (4) solution and the amino resin ( 6.1 parts by mass of "Cymel 303LF" manufactured by Allnex, 0.6 parts by mass of catalyst ("Nacure 5225" manufactured by King, Inc.), 0.3 parts by mass of matting agent ("Syloid ED3" manufactured by Allnex), and leveling agent. A mixed solvent obtained by mixing 0.5 parts by mass (“Modaflow 2100” manufactured by Allnex), an aromatic solvent (“Solvesso 100” manufactured by ExxonMobil Ltd.) and propylene glycol monomethyl ether acetate in a mass ratio of 7:3. 0 part by mass was added and mixed, and the Ford cup #4 viscosity at 25° C. was adjusted to about 100 seconds to obtain a white paint (1).

(Example 7: Preparation of white paint (2))
The same procedure as in Example 6 was repeated except that the (meth)acrylic-modified polyester resin (4) solution used in Example 6 was replaced with the (meth)acrylic-modified polyester resin (5) solution obtained in Example 5. A white paint (2) was obtained.

(Comparative Example 3: Preparation of white paint (3))
In the same manner as in Example 6 except that the mixed solution (C1) of the acrylic resin and the polyester resin obtained in Comparative Example 1 was used in place of the (meth)acrylic modified polyester resin (4) solution used in Example 6. A white paint (3) was obtained.

(Comparative Example 4: Preparation of white paint (4))
In the same manner as in Example 6 except that a saturated polyester resin solution (“Beckolite GS-13” manufactured by DIC Corporation) was used instead of the (meth)acrylic modified polyester resin (4) solution used in Example 6. A white paint (4) was obtained.

(Comparative Example 5: Preparation of white paint (5))
Example 6 except that a saturated polyester resin solution (“Beckolite GS-37-1” manufactured by DIC Corporation) was used instead of the (meth)acrylic modified polyester resin (4) solution used in Example 6. White paint (5) was obtained in the same manner.

(Comparative Example 6: Preparation of white paint (6))
White color was obtained in the same manner as in Example 6 except that the acrylic resin solution (C1-1) obtained in Comparative Production Example 1 was used in place of the (meth)acrylic modified polyester resin (4) solution used in Example 6. A paint (6) was obtained.

(Comparative Example 7: Preparation of white paint (7))
In the same manner as in Example 6 except that a saturated polyester resin solution (“Beckolite GS-12” manufactured by DIC Corporation) was used instead of the (meth)acrylic modified polyester resin (4) solution used in Example 6. A white paint (7) was obtained.

A coated steel sheet was prepared using the white paint obtained in the above Examples and Comparative Examples.

(Examples 8 and 9: Preparation of coated steel sheets (A) and (B))
The white paints (1) and (2) obtained in Examples 5 and 6 were coated on a hot-dip galvanized chromate-treated steel sheet having a thickness of 0.5 mm by a bar coater so that the film thickness was 15 to 20 μm, and the thickness was 250. The coated steel sheets (A) and (B) were obtained by heating and drying in an oven at ℃ for 20 seconds (metal peak temperature was 210° C.).

(Comparative Examples 8 to 11: Preparation of coated steel plates (C) to (F))
The white paints (3) to (6) obtained in Comparative Examples 3 to 6 were coated on a hot-dip galvanized chromate-treated steel sheet having a thickness of 0.5 mm with a bar coater so that the film thickness was 15 to 20 μm, and the temperature was 230° C. In an oven for 40 seconds (metal peak temperature is 230° C.) to obtain coated steel plates (C) to (F).

(Examples 10 and 11: <with primer layer> Preparation of coated steel plates (G) and (H))
As a primer layer, a saturated polyester resin (“Beckolite GS-12” manufactured by DIC Co., Ltd.) was coated on a hot-dip galvanized chromate-treated steel sheet having a thickness of 0.5 mm with a bar coater so that the film thickness was 5 μm, and the temperature was 250° C. And dried for 20 seconds in the oven (metal peak temperature is 210° C.) to form a primer layer.The white paints (1) and (2) obtained in Examples 5 and 6 were then applied to the surface of the primer layer. Coating was performed with a bar coater so that the film thickness was 15 μm, and heating and drying was performed in an oven at 250° C. for 40 seconds (metal peak temperature was 210° C.) to prepare coated steel plates (G) and (H).

(Comparative Examples 12 to 14: <With Primer Layer> Preparation of Painted Steel Sheets (I) to (K))
As a primer layer, a saturated polyester resin (“Beckolite GS-12” manufactured by DIC Co., Ltd.) was coated on a hot-dip galvanized chromate-treated steel sheet having a thickness of 0.5 mm with a bar coater so that the film thickness was 5 μm, and the temperature was 250° C. Was heated and dried for 20 seconds in the oven (metal peak temperature was 210° C.) to form a primer layer, and then the white paints (3), (6) and (7) obtained in Comparative Examples 3, 6 and 7 were The surface of the primer layer is coated with a bar coater so that the film thickness is 15 μm, and is heated and dried in an oven at 250° C. for 40 seconds (metal peak temperature is 230° C.) to prepare coated steel plates (I) to (K). did.

The following evaluations were carried out using the coated steel sheets obtained in the above Examples and Comparative Examples.

[Pencil hardness measurement method]
The hardness of the coated surface of each of the coated steel sheets (A) to (K) was measured by a method according to EN 13523-4.

[Gloss measurement method]
The 60° reflectance of the coated surfaces of the coated steel sheets (A) to (K) was measured by a method according to EN 13523-2.

[Evaluation method of workability (crack-free test)]
The flexibility of the coating film was evaluated by a T-bend bending test. Specifically, in accordance with EN 13523-7, the coated steel sheets (A) to (K) obtained above were bent by 180°, and cracks generated at the bent portions were observed with a 10-fold loupe. When the coated steel sheet is bent 180° without pinching anything in the bent portion, 0T is set, and when X sheets of the same thickness as the coated steel sheet are bent in the bent portion, the bent portion is set to (X/2)T. The minimum value that does not cause cracks was evaluated.

[Processability evaluation method (tape test)]
The flexibility of the coating film was evaluated by a T-bend bending test. Specifically, in accordance with EN 13523-7, the coated steel sheets (A) to (K) obtained above were bent 180°, and an adhesive tape manufactured by Nichiban Co., Ltd. was attached to the bent portion and rapidly peeled off. The film was evaluated by the presence or absence of peeling. When the coated steel sheet is bent 180° without pinching the bent portion, it is 0T, and when the bent portion is X sheets of the same thickness as the coated steel sheet, it is (X/2)T. The minimum value that does not occur was evaluated.

[Weather resistance evaluation method]
A weather resistance test was performed using a "QUV accelerated weather resistance tester" manufactured by Q-Lab. Specifically, the coated steel sheets (A) to (K) obtained above were kept at 60° C. for 4 hours while being irradiated with UV (UV-A lamp), and then 2000 hours in a cycle of 4 hours at 50° C. under a wet condition. The weather resistance test was conducted and the gloss retention rate of the coating film surface was evaluated.

[Evaluation method of stain resistance]
About 2 ml of 10% carbon black aqueous dispersion was dropped on the coated steel plates (A) to (K) obtained above, dried at 80° C. for 24 hours, wiped off with a pad soaked with water, and evaluated according to the following criteria. ..

◯: No mark is left on the surface of the coated steel sheet.
Δ: Traces slightly remain on the surface of the coated steel sheet.
X: A mark remains on the surface of the coated steel sheet.

Table 3 shows the evaluation results of the coated steel sheets (A) to (F) prepared in Examples 8 and 9 and Comparative Examples 8 to 11.

Table 4 shows the evaluation results of the coated steel sheets (G) to (K) prepared in Examples 10 and 11 and Comparative Examples 12 to 14.

(Example 12: Preparation of clear paint (1))
In a reaction vessel equipped with a stirrer, a condenser, and a thermometer, 87.8 parts by mass of the (meth)acryl-modified polyester resin (5) solution obtained in Example 5, amino resin ("Cymel 303LF" manufactured by Allnex Co.) 10. 0 parts by mass, a catalyst ("Nacure 5225" manufactured by King) 0.9 parts by mass, a leveling agent ("Modaflow 2100" manufactured by Allnex) 0.5 parts by mass, an aromatic solvent ("Solvesso 100 manufactured by Exxon Mobil Ltd.") )) and propylene glycol monomethyl ether acetate at a weight ratio of 7:3, 0.8 parts by weight of a mixed solvent is added and mixed, and the Ford cup #4 viscosity at 25° C. is adjusted to about 100 seconds. Then, clear paint (1) was obtained.

(Example 13: Preparation of coated steel plate (L))
The clear coating material (1) obtained in Example 12 was applied to a hot-dip galvanized chromate-treated steel sheet having a thickness of 0.5 mm by a bar coater so that the film thickness was 15 to 20 μm, and the oven was heated at 250° C. for 20 seconds. It was heated and dried (metal peak temperature was 210° C.) to obtain a coated steel plate (L).

Examples 8 and 9 shown in Table 3 are examples of white paints using the (meth)acrylic modified polyester resin of the present invention, and both have a high nonvolatile content of 73.3% by mass. It was confirmed that it was possible to create a highly solid paint. Further, it was confirmed that the coating film of the white paint is excellent not only in excellent workability and weather resistance but also in coating hardness and stain resistance.

On the other hand, Comparative Example 8 is an example of a white paint using a mixed solution of an acrylic resin and a polyester resin, which has a high nonvolatile content and is capable of producing a high solid paint, but the coating film of the paint is It was confirmed that the gloss retention was as low as 60% and the weather resistance was insufficient.

Comparative Examples 9 and 10 are examples of white paints using a saturated polyester resin, but the nonvolatile content is low at 64.3% by mass (Comparative Example 9) and 63.2% by mass (Comparative Example 10), and high solids. It was confirmed that it was not possible to create a perfect paint. In addition, it was confirmed that the coating film of the white paint had extremely low gloss retention rates of 30% (Comparative Example 9) and 55% (Comparative Example 10), and the weather resistance was remarkably insufficient.

Comparative Example 11 is an example of a white paint using an acrylic resin solution, which has a high non-volatile content and is capable of producing a high solid paint, but the coating film of the paint has insufficient processability. I was able to confirm that there is.

Examples 10 and 11 and Comparative Examples 12 to 14 shown in Table 4 relate to coated steel sheets in which a primer layer is provided between the steel sheet and the white paint. It was confirmed that the coating film of the white paint on the coated steel sheets obtained in Examples 10 and 11 was excellent not only in excellent workability and weather resistance but also in coating hardness and stain resistance.

Example 13 shown in Table 5 is an example of a clear paint using the (meth)acrylic modified polyester resin of the present invention. It was confirmed that the coating film of the clear paint on the coated steel sheet obtained in Example 13 has not only excellent workability and weather resistance, but also excellent coating film hardness and stain resistance.

Claims (12)

A (meth)acryl-modified polyester resin comprising a saturated polyester resin (A) and a (meth)acrylic monomer mixture (B) containing a hydroxyl group-containing (meth)acrylic monomer as essential reaction materials,
The saturated polyester resin (A) is a polycondensation product of an aliphatic diol (a1) and a dicarboxylic acid (a2) containing an aliphatic dicarboxylic acid,
The aliphatic diol (a1) is 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,4-butanediol, 2-ethyl-1,4-butanediol, 2-methyl-1, Containing one or more selected from 3-propanediol, 3-methyl-1,5-pentanediol, 3-methyl-1,5-heptanediol,
Content of the said aliphatic dicarboxylic acid is 5 mass% or more in the said dicarboxylic acid (a2), The (meth)acrylic modified polyester resin characterized by the above-mentioned. The mass ratio [(A)/(B)] of the saturated polyester resin (A) and the (meth)acrylic monomer mixture (B) is in the range of 15/85 to 50/50. The (meth)acrylic-modified polyester resin described. The (meth)acrylic-modified polyester resin according to claim 1 or 2, wherein the aliphatic diol (a1) further contains a linear diol having no side chain. The content of the aliphatic dicarboxylic acids, the dicarboxylic acid (a2) in the range of 10 to 20% by mass claims 1-3 of according to any one of (meth) acrylic-modified polyester resin. The saturated polyester resin weight average molecular weight of (A) is set forth in any one a is the claims 1-4 range 1,000-5,000 (meth) acrylic-modified polyester resin. The (meth) acrylic monomer mixture (B) is, the hydroxyl group-containing (meth) according to any one of claims 1 to 5 acrylic monomer are those containing more than 10 wt% (meth) acrylic Modified polyester resin. The (meth) acrylic weight average molecular weight of the modified polyester resin is set forth in any one of claims 1 to 6 in the range of 5,000 to 20,000 (meth) acrylic-modified polyester resin. The (meth) hydroxyl value of the acrylic-modified polyester resin, a is claim 1-7 set forth in any one range of 60 to 150 (meth) acrylic-modified polyester resin. Either one of claims (meth) acrylic-modified polyester resin, curable resin composition characterized by containing a curing agent according to claim 1-8. A coating material comprising the curable resin composition according to claim 9 . The coating composition according to claim 10, which has a nonvolatile content of 65% by mass or more. A coated steel sheet having a cured coating film of the coating material according to claim 10 or 11 .