Coating composition

Abstract

To provide a coating composition which has good coating stability (proper range of viscosity), and has good workability and durability of an obtained coating film.SOLUTION: A coating composition contains a coating film formation resin (A) and a crosslinking agent (B), wherein the coating film formation resin (A) contains a polyester resin (A1), the polyester resin (A1) contains a reactant of a polycarboxylic acid and polyol, and the polycarboxylic acid contains, in 100 mol% of the total amount of the polycarboxylic acid, 20 mol% or more of a polycarboxylic acid having a furan skeleton, and 10 mol% or more of a polycarboxylic acid anhydride, and the polyol contains divalent polyol and trivalent polyol.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a paint composition.

Background Art

[0002] A painted metal sheet obtained by painting a metal substrate such as a cold-rolled steel sheet or a plated steel sheet is also called a pre-coated metal sheet (also referred to as "PCM"), and is used as various members such as building members such as shutters, rain doors, doors, roofs, and siding, exterior materials for electrical equipment such as outdoor coolers, and interior materials. Usually, a pre-coated metal sheet is processed into various products after being painted on the surface of the metal sheet with a paint composition to form a paint film.

[0003] Although various types of resins for forming a paint film are used for such applications, among them, polyester resins are widely used because they are relatively inexpensive and have excellent physical properties such as adhesion, flexibility, and hardness.

[0004] Most of the plastics (synthetic resins, polymers) currently in circulation are manufactured from petroleum-derived raw materials, and finally, a large amount of greenhouse gas (GHG) is emitted into the atmosphere when they are discarded and incinerated. Since these are one of the main causes of global warming, various methods for reducing GHG emissions have been studied in recent years as countermeasures. In the paint field, since the main component, the resin for forming a paint film, is made of plastic (synthetic resin, polymer), various methods for manufacturing it using renewable raw materials have been studied. As the renewable raw materials, raw materials derived from biomass (especially plants) have attracted attention.

[0005] Examples of biomass-derived raw materials for polyester resins include succinic acid, glutaric acid, sebacic acid, azelaic acid, ferulic acid, caffeic acid, dimer acid, dimer acid diol, and 2,5-furandicarboxylic acid as polycarboxylic acids. Among these, 2,5-furandicarboxylic acid has attracted attention as an alternative raw material to isophthalic acid and terephthalic acid.

[0006] Patent Document 1 describes a polyester resin that uses a polyvalent carboxylic acid component and a polyhydric alcohol component as copolymerization components. Among the polyvalent carboxylic acid components that make up the polyester resin, it contains 10 mol% or more of a polyvalent carboxylic acid component having a furan skeleton. Among the polyhydric alcohol components that make up the polyester resin, it contains 10 to 50 mol% of an alicyclic diol having 6 or more carbon atoms, and has a glass transition temperature of less than 70°C.

[0007] Patent Document 2 describes a polyester resin that uses a polyvalent carboxylic acid component and a polyhydric alcohol component as copolymerization components. Among the polyvalent carboxylic acid components that make up the polyester resin, it contains 10 mol% or more of a polyvalent carboxylic acid component having a furan skeleton. The polyhydric alcohol component that makes up the polyester resin has two or more types, and has a glass transition temperature of 70°C or more.

[0008] Patent Document 3 describes a polyester resin that uses a polyvalent carboxylic acid component and a polyhydric alcohol component as copolymerization components. Among the polyvalent carboxylic acid components that make up the polyester resin, it contains 10 mol% or more of a polyvalent carboxylic acid component having a furan skeleton. The polyhydric alcohol component that makes up the polyester resin has two or more types, and has an acid value of 70 eq / t or more and 400 eq / t or less.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] In the field of paints, it is required that the paint film obtained from the paint composition exhibits desired performance at an appropriate film thickness and also has a good appearance. For this purpose, it is necessary to have appropriate viscosity behavior at an appropriate solid content concentration, that is, good paint workability.

[0011] However, when using a furan carboxylic acid as a raw material, problems such as an increase in viscosity or crystallization may occur in the production of polyester resins or in the production of paint compositions. Since various physical properties are required for the paint film of PCM as described above, a paint composition that can obtain a paint film satisfying all of them has not been obtained yet.

[0012] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a paint composition having good paint stability (viscosity within an appropriate range) and good processability and durability of the obtained paint film.

Means for Solving the Problems

[0013] The present disclosure includes the following aspects. [1] A paint composition comprising a film-forming resin (A) and a crosslinking agent (B), wherein the film-forming resin (A) includes a polyester resin (A1), the polyester resin (A1) includes a reaction product of a polycarboxylic acid and a polyol, the polycarboxylic acid includes 20 mol% or more of a polycarboxylic acid having a furan skeleton and 10 mol% or more of a polycarboxylic anhydride in 100 mol% of the total amount of the polycarboxylic acid, and the polyol includes a divalent polyol and a trivalent polyol. [2] The paint composition according to [1], wherein the content of the polycarboxylic acid having a furan skeleton is 90 mol% or less in 100 mol% of the total amount of the polycarboxylic acid. [3] The paint composition according to [1] or [2], wherein the content of the trivalent polyol is 5 mol% or more and 30 mol% or less in 100 mol% of the total amount of the polyol. [4] The acid value of the polyester resin (A1) is 1 mgKOH / g or more and 30 mgKOH / g or less, and the coating composition according to any one of [1] to [3]. [5] The hydroxyl value of the polyester resin (A1) is 10 mgKOH / g or more and 150 mgKOH / g or less, and the coating composition according to any one of [1] to [4]. [6] The weight average molecular weight of the polyester resin (A1) is 35,000 or less, and the coating composition according to any one of [1] to [5]. [7] The glass transition temperature of the polyester resin (A1) is -20°C or more and 100°C or less, and the coating composition according to any one of [1] to [6]. [8] The crosslinking agent (B) contains one or more selected from the group consisting of amino resins and blocked polyisocyanate compounds, and the coating composition according to any one of [1] to [7]. [9] The content of the crosslinking agent (B) is 1 part by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the film-forming resin (A), and the coating composition according to any one of [1] to [8].

[10] [1] to [9], and a coating step of applying the coating composition according to any one of them to an object to be coated to obtain a coating film, and A curing step of curing the coating film at a temperature of 150°C or more and 270°C or less to obtain a coating film, and a method for producing a coating film.

[11] A method for producing a multilayer coating film including a primer coating film and a topcoat film, A step of forming a topcoat film by applying a topcoat paint composition containing a thermoplastic resin on the primer coating film which is a coating film produced by the production method according to claim 10, and a method for producing a multilayer coating film. [Advantages of the Invention]

[0014] According to the present disclosure, a coating composition can be provided which has good paint stability (viscosity within an appropriate range) and good processability, durability, etc. of the resulting coating film.

Mode for Carrying Out the Invention

[0015] The coating composition of the present disclosure contains a film-forming resin (A) and a crosslinking agent (B). The film-forming resin (A) contains a polyester resin (A1). The polyester resin (A1) contains a reaction product of a polycarboxylic acid and a polyol. The polycarboxylic acid contains 20 mol% or more of a polycarboxylic acid having a furan skeleton and 10 mol% or more of a polycarboxylic anhydride in 100 mol% of the total amount of the polycarboxylic acid. The polyol contains a divalent polyol and a trivalent polyol.

[0016] The coating composition of the present disclosure has good paint stability (viscosity within an appropriate range), and the processability and durability of the coating film obtained using the coating composition of the present disclosure are good. Although the present disclosure should not be construed as being limited to a specific theory, the reason why the coating composition of the present disclosure can exhibit such effects is considered as follows.

[0017] According to the study by the present inventors, since the polycarboxylic acid having a furan skeleton has high crystallinity, when used in combination with a linear polyvalent carboxylic acid, the molecular weight of the resulting polyester resin may increase and the viscosity may increase. However, by using a polycarboxylic acid having high reactivity such as a polycarboxylic anhydride and using a divalent polyol and a trivalent polyol in combination as the polyol, it is considered that it is likely to be affected by steric hindrance during the polycondensation reaction. As a result, it is considered that crystallization and molecular weight increase can be suppressed, and a coating composition having an appropriate viscosity and good paint stability can be obtained while maintaining the coating film properties.

[0018] (A) Film-forming resin: The film-forming resin (A) contains a polyester resin (A1).

[0019] The polyester resin (A1) contains a reaction product of a polycarboxylic acid and a polyol.

[0020] The polycarboxylic acid can typically be a compound having two or more carboxy groups in one molecule. The polycarboxylic acid contains 20 mol% or more of a polycarboxylic acid having a furan skeleton and 10 mol% or more of a polycarboxylic anhydride in 100 mol% of the total amount of the polycarboxylic acid.

[0021] <Polycarboxylic acid having a furan skeleton> In the present disclosure, the polycarboxylic acid having a furan skeleton includes derivatives of the polycarboxylic acid having a furan skeleton.

[0022] In the present disclosure, the furan skeleton is the following formula:

Chemical formula

[0023] The furan skeleton can form a polymer main chain by covalent bonding at its 2- and 3-positions, 2- and 4-positions, 2- and 5-positions, or 3- and 4-positions, and a structure covalently bonded at the 2- and 5-positions is preferable.

[0024] As the polycarboxylic acid and / or its derivative containing the furan skeleton of the present disclosure, it is only necessary that the furan skeleton is contained in the structure of the compound. Such compounds include furandicarboxylic acids and their derivatives, preferably furandicarboxylic acids, and particularly preferably 2,5-furandicarboxylic acid. As the derivative, the C 1-4 alkyl esters are mentioned, preferably methyl ester, ethyl ester, n-propyl ester, isopropyl ester, and more preferably methyl ester. These polycarboxylic acids containing the furan skeleton may be used alone or in combination of two or more.

[0025] In the polycarboxylic acid forming the polyester resin (A1), the content of the polycarboxylic acid having a furan skeleton is 20 mol% or more, preferably 20 mol% or more and 90 mol% or less, more preferably 30 mol% or more and 80 mol% or less, and still more preferably 50 mol% or more and 80 mol% or less. By being within the above range, the environmental load can be reduced, and the adhesion, rigidity, and solvent resistance of the obtained polyester resin to the base material can be good.

[0026] The polycarboxylic acid anhydride means a compound in which at least two of the two or more carboxylic acids contained in the polycarboxylic acid compound are dehydrated and condensed with each other to form an acid anhydride structure -CO-O-CO-. Examples of the polycarboxylic acid anhydride include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hymic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, succinic anhydride, dodecenyl succinic anhydride, endo anhydride, etc. As the polycarboxylic acid anhydride, only one kind may be used, or two or more kinds may be used in combination.

[0027] Among the polycarboxylic acids forming the polyester resin (A1), the content of the polycarboxylic acid anhydride is 10 mol% or more, preferably 10 mol% or more and 80 mol% or less, more preferably 10 mol% or more and 50 mol% or less. By being within the above range, the storage stability of the obtained polyester resin after dissolution in a solvent and after being made into a paint can be good.

[0028] Among the polycarboxylic acids forming the polyester resin (A1), the content of the polycarboxylic acid anhydride can be preferably 10 mol or more and 100 mol or less, more preferably 50 mol or more and 100 mol or less, relative to 100 mol of the polycarboxylic acid having the furan skeleton.

[0029] Among the polycarboxylic acids forming the polyester resin (A1), the total content of the polycarboxylic acid having a furan skeleton and the polycarboxylic acid anhydride can be preferably 5 mol% or more and 100 mol% or less, more preferably 10 mol% or more and 90 mol% or less, still more preferably 30 mol% or more and 80 mol% or less.

[0030] The polycarboxylic acid forming the polyester resin (A1) may contain other polycarboxylic acids in addition to the polycarboxylic acid having a furan skeleton and the polycarboxylic acid anhydride. Examples of the other polycarboxylic acids include phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methyltetraphthalic acid, trimellitic acid, pyromellitic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, lactic acid, dodecenyl succinic acid, cyclohexane-1,4-dicarboxylic acid, etc. These may be used alone or in combination of two or more.

[0031] The polyol means a compound having two or more hydroxy groups in one molecule. The polyol includes a divalent polyol and a trivalent polyol. By including a divalent polyol and a trivalent polyol, the flexibility, rigidity and solvent resistance of the obtained coating film can be good.

[0032] Examples of the divalent polyol include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, hydrogenated bisphenol A, hydroxyalkylated bisphenol A, 1,4-cyclohexanedimethanol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate (BASHPN), N,N-bis-(2-hydroxyethyl)dimethylhydantoin, polycaprolactone polyol, isosorbide, and the like. These may be used alone or in combination of two or more.

[0033] In the polyol forming the polyester resin (A1), the content of the divalent polyol is preferably 60 mol% or more and 95 mol% or less, more preferably 70 mol% or more and 95 mol% or less, still more preferably 75 mol% or more and 95 mol% or less in 100 mol% of the total amount of the polyol.

[0034] Examples of the trivalent polyol include glycerin, sorbitol, mannitol, trimethylolethane, trimethylolpropane, trimethylolbutane, hexanetriol, and the like. These may be used alone or in combination of two or more.

[0035] In the polyol forming the polyester resin (A1), the content of the trivalent polyol is preferably 5 mol% or more and 30 mol% or less, more preferably 10 mol% or more and 30 mol% or less, still more preferably 20 mol% or more and 30 mol% or less in 100 mol% of the total amount of the polyol. By being within the above range, the flexibility, rigidity, and solvent resistance of the obtained coating film can be good.

[0036] In the polyol that forms the polyester resin (A1), the content of the trivalent polyol is preferably 5 mol or more and 45 mol or less, more preferably 15 mol or more and 45 mol or less, and still more preferably 25 mol or more and 45 mol or less, based on 100 mol of the content of the divalent polyol.

[0037] In the polyol that forms the polyester resin (A1), the total content ratio of the divalent polyol and the trivalent polyol is preferably 80 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, and still more preferably 95 mol% or more and 100 mol% or less, in 100 mol% of the total amount of the polyol.

[0038] The polyol that forms the polyester resin (A1) may contain other polyols in addition to the divalent polyol and the trivalent polyol. Examples of such other polyols include polyols having a valency of 4 or more, such as pentaerythritol, dipentaerythritol, and tris-(hydroxyethyl) isocyanate. These may be used alone or in combination of two or more.

[0039] In the preparation of the polyester resin (A1), other reaction components may be used in addition to the polycarboxylic acid and the polyol. Examples of other reaction components include monocarboxylic acids, hydroxycarboxylic acids, lactones, drying oils, semi-drying oils, and their fatty acids. More specifically, for example, monoepoxide compounds such as Cardura E (manufactured by Shell Chemical Co., Ltd.) and lactones can be mentioned. The above lactones can form graft chains by ring-opening addition to polyesters of polycarboxylic acids and polyhydric alcohols, and examples thereof include β-propiolactone, dimethylpropionolactone, butyrolactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-caprylolactone, crotonolactone, δ-valerolactone, δ-caprolactone, and the like.

[0040] The polyester resin (A1) may be modified. Examples of modified polyester resins include modified polyester resins such as urethane-modified polyester resins, epoxy-modified polyester resins, acrylic-modified polyester resins, and silicone-modified polyester resins. For example, a urethane-modified polyester resin has a polyester in its main chain and its terminals are modified with isocyanate to be urethane-modified. For example, a silicone-modified polyester resin can be prepared by reacting a polyester resin with an organosilicone (for example, an organosilicone having a number average molecular weight of about 300 to 1,000 and having -SiOCH3 group and / or SiOH group as functional groups). The amount of the organosilicone used for modification is usually about 5 to 50 parts by mass with respect to 100 parts by mass of the polyester resin. Also, the urethane-modified polyester resin can be prepared by reacting the above polyester resin with a polyisocyanate compound.

[0041] The polyester resin (A1) can be produced by polycondensation in a usual method using a polycarboxylic acid and a polyol as raw materials. In one embodiment, such a production method may be a method in which the polycarboxylic acid and the polyol are charged together and then the temperature is raised while stirring and mixing to cause a dehydration polycondensation reaction. In addition, a catalyst may be used for promoting the reaction during polycondensation. Examples of the catalyst include known ones such as tin compounds, titanium compounds, and zirconium compounds.

[0042] The glass transition temperature of the polyester resin (A1) is preferably -20°C or higher and 100°C or lower, more preferably -20°C or higher and 60°C or lower. In one aspect, the glass transition temperature of the polyester resin (A1) may be -20°C or higher and 50°C or lower, and may be -20°C or higher and 30°C or lower. When the glass transition temperature of the polyester resin (A1) is within such a range, the processability and bendability of the resulting coating film can be improved. In another aspect, the glass transition temperature of the polyester resin (A1) may be 50°C or higher and 100°C or lower, and may be 50°C or higher and 60°C or lower. When the glass transition temperature of the polyester resin (A1) is within such a range, even when applied to a powder coating, the hardness of the coating film can be exhibited and the uniform mixing property with other materials can be maintained.

[0043] In the present disclosure, the glass transition temperature is a value measured by a differential scanning calorimeter, and can be measured, for example, by a differential scanning calorimeter DSC-6100 (manufactured by Seiko Instruments Inc.).

[0044] The hydroxyl value of the polyester resin (A1) is preferably 5 mgKOH / g or higher and 200 mgKOH / g or lower, more preferably 5 mgKOH / g or higher and 150 mgKOH / g or lower, still more preferably 7 mgKOH / g or higher and 120 mgKOH / g or lower. When the hydroxyl value of the polyester resin is within the above range, there are advantages such as improved processability.

[0045] The acid value of the polyester resin (A1) is preferably 1 mgKOH / g or higher and 50 mgKOH / g or lower, more preferably 3 mgKOH / g or higher and 30 mgKOH / g or lower, still more preferably 5 mgKOH / g or higher and 25 mgKOH / g or lower. When the acid value of the polyester resin (A1) is within such a range, for example, a pigment dispersion function and a function as an acid catalyst can be expected, and the processability and solvent resistance of the resulting coating film can be good.

[0046] In the present disclosure, both the acid value and the hydroxyl value indicate values in terms of solid content and are values measured by a method conforming to JIS K 0070.

[0047] The weight average molecular weight of the polyester resin (A1) is preferably 2,500 or more and 50,000 or less, more preferably 5,000 or more and 35,000 or less, still more preferably 10,000 or more and 30,000 or less, and even more preferably 15,000 or more and 25,000 or less. By being within the above range, the stability and coating workability of the resulting coating composition and the processability of the resulting coating film can be good.

[0048] In the present disclosure, the weight average molecular weight is a polystyrene equivalent value measured by gel permeation chromatography.

[0049] In the coating film-forming resin (A), the content of the solid content of the polyester resin (A1) is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, still more preferably 95% by mass or more and 100% by mass or less in 100% by mass of the total solid content of the coating film-forming resin (A).

[0050] The biomass degree of the coating film-forming resin (A) is preferably 10% or more, more preferably 30% or more, still more preferably 50% or more, and the upper limit is 100%, and it may be 80% or less. Here, in the present disclosure, the biomass degree refers to the ratio of the solid content mass of plant-derived raw materials, that is, 2,5-furandicarboxylic acid and various glycols produced from plant-derived raw materials, to the total solid content mass of all the raw materials used to constitute the coating composition, and is calculated in accordance with ISO 16620.

[0051] The coating film-forming resin (A) may contain other resins as necessary in addition to the polyester resin (A1). Examples of other resins include thermosetting resins and thermoplastic resins, such as polyester resins not containing 2,5-furandicarboxylic acid, acrylic resins, urethane resins, epoxy resins, chlorinated olefin resins such as chlorinated polyethylene and chlorinated polypropylene; homopolymers or copolymers containing vinyl chloride, vinyl acetate, vinylidene chloride, or the like as monomer components; cellulose resins; acetal resins; alkyd resins; chlorinated rubber resins; modified polypropylene resins (acid anhydride modified polypropylene resins, etc.); fluororesins (for example, vinylidene fluoride resins, vinyl fluoride resins, copolymers of fluorinated olefins and vinyl ethers, copolymers of fluorinated olefins and vinyl esters), xylene resins, and other resins known in the paint field. The other resins may be used alone or in combination of two or more. In addition, by using a thermoplastic resin in combination, better coating film properties, such as coating film strength and elongation, can be obtained.

[0052] The solid content of the film-forming resin (A) may be preferably from 20% by mass to 95% by mass, more preferably from 25% by mass to 30% by mass, and even more preferably from 32% by mass to 80% by mass, based on 100% by mass of the total solid content of the coating composition of the present disclosure.

[0053] In this disclosure, the solid content of a certain component means the heating residue as defined in JIS K 5601-1-2:2008, and the solid content percentage is calculated by measuring the percentage of the mass of the residue after heating at 105°C for 60 minutes to the original mass.

[0054] The content of the thermoplastic resin may be preferably 1 part by mass or more and 20 parts by mass or less, more preferably 2 parts by mass or more and 15 parts by mass or less, and even more preferably 3 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the total amount of the coating film-forming resin (A).

[0055] (B) Crosslinker: The crosslinking agent (B) reacts with the film-forming resin (A) to form a cured coating film, and typically can be a compound having two or more groups capable of reacting with the film-forming resin (A) in one molecule.

[0056] Examples of the crosslinking agent (B) include polyisocyanate compounds; blocked polyisocyanate compounds obtained by blocking the isocyanate groups of polyisocyanate compounds with active hydrogen-containing compounds; amino resins; phenolic resins, etc. It is preferable to contain one or more selected from blocked polyisocyanate compounds and amino resins. By containing the crosslinking agent (B), excellent rust prevention properties can be exhibited over a long period, and further, a coating film exhibiting excellent moisture resistance can be formed.

[0057] The polyisocyanate compound and the polyisocyanate compound constituting the blocked polyisocyanate compound are not particularly limited, and conventionally known ones can be used. Specific examples include, for example, 1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- or 1,4-diisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane (also known as isophorone diisocyanate; IPDI), dicyclohexylmethane-4,4'-diisocyanate (also known as: hydrogenated MDI), 2- or 4-isocyanatocyclohexyl-2'-isocyanatocyclohexylmethane, 1,3- or 1,4-bis-(isocyanatomethyl)-cyclohexane, bis-(4-isocyanato-3-methylcyclohexyl)methane, 1,3- or 1,4-α,α,α'α'-tetramethylxylylene diisocyanate, 2,4- or 2,6-diisocyanatotoluene, 2,2'-, 2,4'- or 4,4'-diisocyanatodiphenylmethane (MDI), 1,5-naphthalene diisocyanate, p- or m-phenylene diisocyanate, xylylene diisocyanate, diphenyl-4,4'-diisocyanate and the like. Further, as the polyisocyanate compound, a cyclic polymer (isocyanurate type) of each diisocyanate, and further an isocyanate-biuret body (biuret type) or an adduct type may be used.

[0058] The polyisocyanate compound may be used alone as only one kind, or two or more kinds may be used in combination. The isocyanurate type polyisocyanate compound is one of those preferably used in the present invention.

[0059] As the polyisocyanate compound, for example, it is preferable to use an aromatic polyisocyanate compound containing one or more aromatic functional groups in the molecule. By using an aromatic polyisocyanate compound, the moisture resistance of the coating film can be improved and the coating film strength can be improved. Examples of the preferably used aromatic polyisocyanate compounds include 2,4- or 2,6-diisocyanatotoluene (TDI), 2,2'-, 2,4'- or 4,4'-diisocyanatodiphenylmethane (MDI), xylene diisocyanate (XDI), naphthalene diisocyanate (NDI), and the like.

[0060] In the polyisocyanate compound constituting the blocked polyisocyanate compound, the isocyanate group content measured in accordance with JIS K 7301-1995 is usually 3 to 20%, preferably 5 to 15% in the solid content of the polyisocyanate compound. When the isocyanate group content is within the above range, the curability of the coating film becomes further better. In addition, it is possible to suppress the excessive increase in the crosslink density of the obtained coating film, and the corrosion resistance can be improved.

[0061] The active hydrogen-containing compound (blocking agent) used for the blocked polyisocyanate compound is not particularly limited, and examples thereof include compounds having an -OH group (such as alcohols and phenols), =N-OH group (such as oximes), =N-H group (such as amines, amides, imides, lactams, etc.), compounds having a -CH2- group (active methylene group), and azoles. Specific examples include, for example, phenol, cresol, xylenol, ε-caprolactam, σ-valerolactam, γ-butyrolactam, methanol, ethanol, n-, i-, or t-butyl alcohol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, benzyl alcohol, formamide oxime, acetaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monoxime, benzophenone oxime, cyclohexanone oxime, dimethyl malonate, ethyl acetoacetate, acetylacetone, pyrazole, and the like. The active hydrogen-containing compound may be used alone or in combination of two or more.

[0062] The dissociation temperature of the blocked polyisocyanate compound by heat depends on the types of the polyisocyanate compound and the active hydrogen-containing compound constituting it, the presence or absence of a catalyst, and its amount. In the present disclosure, a blocked polyisocyanate compound having a dissociation temperature (in the non-catalyzed state) of 120 to 180°C by heat is preferably used. By using a blocked polyisocyanate compound having a dissociation temperature within this range, the stability of the paint can be improved, and since it has excellent crosslinking reactivity with the film-forming resin (A), a coating film with good moisture resistance can be obtained. Examples of the blocked polyisocyanate compound having a dissociation temperature of 120 to 180°C include, for example, Desmodur BL3175 manufactured by Sumika Covestro Urethane Co., Ltd., Coronate 2554 manufactured by Tosoh Corporation, and the like.

[0063] In the present disclosure, the blocked polyisocyanate compound may be denoted as (BI).

[0064] Examples of the amino resin include melamine resin and urea resin, and among them, melamine resin is preferably used.

[0065] Generally, melamine resin means a thermosetting resin synthesized from melamine and aldehyde, and has three reactive functional groups -NX1X2 in one molecule of the triazine nucleus. Examples of melamine resin include a fully alkylated type containing -N-(CH2OR)2 [R is an alkyl group, the same hereinafter] as a reactive functional group; a methylol group type containing -N-(CH2OR)(CH2OH) as a reactive functional group; an imino group type containing -N-(CH2OR)(H) as a reactive functional group; and a methylol / imino group type containing -N-(CH2OR)(CH2OH) and -N-(CH2OR)(H), or containing -N-(CH2OH)(H). Four types can be exemplified.

[0066] Among the above melamine resins, it is preferable to use a fully alkylated melamine resin. Examples of such resins include methylated melamine resin, butylated melamine resin, methyl and butyl mixed melamine resin, isobutylated melamine resin, etc. Among these, methylated melamine resin, butylated melamine resin, and methyl and butyl mixed melamine resin are preferable.

[0067] Commercially available products may also be used as the melamine resin. Examples of commercially available products include Cymel 303, Cymel 254, Cymel 1170, Cymel 235, Cymel 238, Cymel 1123, Mycote 715 (all manufactured by Daicel Ornex Co., Ltd.), Sumimal M-40S (manufactured by Sumitomo Chemical Co., Ltd.), Super Bekkamin J-820-60, Super Bekkamin L-121-60 (all manufactured by DIC Corporation), Uban 20SE-60 (manufactured by Mitsui Chemicals, Inc.), etc.

[0068] The above melamine resin may be used alone or in combination of two or more. In one embodiment, the above melamine resin and a polyisocyanate compound may be used in combination. Also, if necessary, a metal catalyst such as a tin compound or a titanium compound may be used.

[0069] The amount of the crosslinking agent (B) is preferably 1 to 150 parts by mass, more preferably 2 to 150 parts by mass in terms of solid content based on 100 parts by mass of the solid content of the film-forming resin (A). By including the crosslinking agent (B) under such conditions, excellent rust prevention performance can be exhibited over a long period, and furthermore, a coating film with excellent moisture resistance can be formed.

[0070] When a melamine resin is used as the crosslinking agent (B), the coating composition of the present disclosure may further contain a curing catalyst. Examples of the curing catalyst include sulfonic acid compounds, such as aliphatic sulfonic acids like methanesulfonic acid; aromatic sulfonic acids like p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, etc. Only one type of curing catalyst may be used, or two or more types may be used in combination.

[0071] When a blocked polyisocyanate compound and / or a polyisocyanate compound is used as the crosslinking agent (B), the coating composition of the present disclosure may further contain a curing catalyst. Examples of the curing catalyst include tin catalysts, amine catalysts, lead catalysts, etc., and among them, organic tin compounds are preferably used. Examples of the organic tin compound include dibutyltin dilaurate (DBTL), dibutyltin oxide, tetra-n-butyl-1,3-diacetoxystannoxane, etc. Only one type of curing catalyst may be used, or two or more types may be used in combination.

[0072] The content of the curing catalyst is, for example, 0.1 to 10 parts by mass, or may be 0.1 to 1.0 parts by mass with respect to 100 parts by mass in total of the solid contents of the film-forming resin (A) and the crosslinking agent (B). By being within the above range, the reactivity of the coating composition during film formation can be improved, and the solvent resistance, corrosion resistance, etc. of the obtained coating film can be good.

[0073] [Other Components] The coating composition of the present disclosure may contain other components other than those described above, if necessary. Other components include, for example, extender pigments; colorants such as coloring pigments and dyes; rust preventive pigments, bright pigments; solvents; ultraviolet absorbers (such as benzophenone-based ultraviolet absorbers); antioxidants (such as phenolic, sulfide-based, and hindered amine-based antioxidants); plasticizers; surface modifiers (such as silicone and organic polymers); sag inhibitors; thickeners; lubricants such as waxes; pigment dispersants; pigment wetting agents; leveling agents; color separation preventives; precipitation preventives; defoamers; preservatives; antifreeze agents; emulsifiers; fungicides; antibacterial agents; stabilizers; coupling agents; curing catalysts, etc. These additives may be used alone, only one kind, or in combination of two or more kinds.

[0074] Examples of solvents include water; glycol-based organic solvents such as ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate; alcohol-based organic solvents such as methanol, ethanol, and isopropyl alcohol; ether-based organic solvents such as dioxane and tetrahydrofuran; ester-based organic solvents such as 3-methoxybutyl acetate, ethyl acetate, isopropyl acetate, and butyl acetate; ketone-based organic solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, and isophorone; and N-methyl-2-pyrrolidone, toluene, pentane, iso-pentane, hexane, iso-hexane, cyclohexane, solvent naphtha, mineral spirits, Solvesso 100, Solvesso 150 (all aromatic hydrocarbon-based solvents, manufactured by Shell Chemical Company), etc. These may be used alone, only one kind, or in combination of two or more kinds.

[0075] The paint composition of the present disclosure may be an aqueous paint or an organic solvent-based paint.

[0076] The coating composition of the present disclosure may be applied as an undercoat paint, also called a primer. It may also be used as a topcoat paint applied over the undercoat paint. In another aspect, the coating composition of the present disclosure may be used as a coating composition for forming a single-layer coating film rather than for forming a multi-layer coating film.

[0077] The coating composition of the present disclosure can exhibit excellent corrosion resistance and moisture resistance regardless of where it is used in the multi-layer coating film. The undercoat paint, topcoat paint, and intermediate coat paint other than the coating composition of the present disclosure may be conventionally known. For example, as the undercoat paint, conventionally known non-chromium rust preventive paints and the like may be mentioned, and as the topcoat paint, alkyd resin-based paints, acrylic resin-based paints, fluororesin-based paints, and the like may be mentioned.

[0078] The coating composition of the present disclosure is preferably used as an undercoat paint. When the coating composition of the present disclosure is used as an undercoat paint, it exhibits particularly good adhesion at the contact surface with the coating film formed by the topcoat paint that is in direct contact with the undercoat paint.

[0079] The solid content of the coating composition of the present disclosure may be preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 75% by mass or less, still more preferably 50% by mass or more and 75% by mass or less in 100% by mass of the total amount of the coating composition.

[0080] The biomass degree of the coating composition of the present disclosure is preferably 1% or more, more preferably 3% or more, still more preferably 5% or more, and may be 80% or less, or may be 60% or less.

[0081] [Method for preparing the coating composition] The method for preparing the coating composition according to the present disclosure is not particularly limited. The coating composition according to the present disclosure can be prepared, for example, by mixing a film-forming resin (A), a crosslinking agent (B), and optionally used rust preventive pigments, thermoplastic resins, extender pigments, coupling agents, curing catalysts, and other additives using a mixer such as a roller mill, ball mill, bead mill, pebble mill, sand grind mill, pot mill, paint shaker, or disper. In another aspect, the coating composition of the present disclosure may be a two-component paint composed of a main component containing a film-forming resin (A) and optionally used rust preventive pigments, and a crosslinking agent component containing a crosslinking agent (B).

[0082] [Object to be coated] The object to be coated on which the coating film is formed by the rust preventive coating composition of the present disclosure is not particularly limited as long as corrosion resistance is required. For example, a steel sheet serving as a base material such as pre-coated metal (painted steel sheet) can be mentioned.

[0083] Examples of the steel sheet include galvanized steel sheet, cold rolled steel sheet, stainless steel sheet, aluminum sheet, etc.

[0084] Examples of the galvanized steel sheet include zinc-containing plated steel sheets that utilize the sacrificial anticorrosion of zinc, specifically, hot-dip galvanized steel sheet, electro-galvanized steel sheet, alloyed hot-dip galvanized steel sheet, aluminum-zinc plated steel sheet, nickel-zinc plated steel sheet, magnesium-aluminum-zinc plated steel sheet, magnesium-aluminum-silica-zinc plated steel sheet, etc.

[0085] The steel sheet is preferably one that has been surface-treated with a chemical conversion treatment agent before painting. The surface treatment may be performed by a known method, and examples thereof include non-chromate treatments such as chromate treatment and zinc phosphate treatment. Further, the surface treatment can be appropriately selected according to the steel sheet to be used, but a treatment containing no heavy metals is preferred.

[0086] [Method for manufacturing the coating film] In one embodiment, the present disclosure provides a method for manufacturing a rust-preventive coating film, which includes a coating step of applying the coating composition of the present disclosure to an object to be coated, and a step of curing the coating composition at a temperature of 150°C or higher and 270°C or lower.

[0087] As a method for applying the coating composition of the present disclosure to an object to be coated, conventionally known methods such as a roll coater and a curtain flow coater can be employed.

[0088] The coating film of the present invention can be formed by performing a baking treatment of heating the object to be coated after applying the coating composition to an object to be coated such as a steel plate. The baking temperature (the maximum temperature reached by the object to be coated such as a steel plate) is, for example, 180°C or higher and 270°C or lower. By curing the coating composition of the present disclosure at such a temperature, a coating film having sufficient strength can be formed. By being able to form a coating film having sufficient strength, furthermore, excellent rust-preventive properties can be exhibited over a long period, and furthermore, a coating film exhibiting excellent moisture resistance can be formed.

[0089] The baking time (curing time) is, for example, 10 to 200 seconds. For example, when forming a multilayer coating film composed of two layers of a primer coating film and a topcoat coating film, after applying the primer coating composition and performing baking, and then applying the topcoat coating composition and performing baking of the topcoat coating film, it may be possible, or after applying the primer coating composition, applying the topcoat coating composition wet-on-wet without performing baking and performing baking simultaneously.

[0090] The film thickness (dry film thickness) of the coating film of the present invention is usually 1 to 30 μm, and for example, in the case of the topcoat coating film, it is preferably 5 to 25 μm.

Examples

[0091] The present invention will be described more specifically by the following examples, but the present invention is not limited thereto.

[0092] (Production Example A-1) [Preparation of Coating Film Forming Resin (A1) (Polyester Resin (A1-1))] Into a reaction vessel equipped with a thermometer, a condenser, and a stirrer, 293 parts by mass of 2,5-furandicarboxylic acid, 290 parts by mass of tetrahydrophthalic anhydride, 313 parts by mass of neopentyl glycol, and 101 parts by mass of trimethylolpropane were mixed. The temperature was raised to 220 °C over 5 hours in a nitrogen stream, and while distilling off the generated water, an esterification reaction was carried out for about 10 hours until the acid value reached 10 mgKOH / g (water removal amount: 68.4 parts by mass). Then, after lowering the temperature of the reaction vessel to 50 °C, 621 parts by mass of cyclohexanone was mixed to obtain a polyester resin (A1-1) (solid content concentration: 60% by mass).

[0093] (Production Example A-1) to (Production Example A-33), (a1-1) to (a1-4) The polyester resins (A1-2) to (A1-33), (a1-1) to (a1-4) were prepared in the same manner as in (Production Example A-1) except that the types and amounts of the respective components were the types and amounts described in Table 1. The composition and various characteristic values are shown in Table 1.

[0094] (Example 1) 220 parts by mass of the polyester resin (A1-1), as pigments, 62 parts by mass of TITANIX JR-603, 80 parts by mass of aluminum silicate, 12 parts by mass of TAROX synthetic iron oxide LL-XLO, 3 parts by mass of red iron oxide CM-25P, and 1.0 part by mass of SUNBLACK X15, as a pigment dispersion resin, 13 parts by mass of Floren G-700, as solvents, 56 parts by mass of xylene and 16 parts by mass of isobutanol were mixed, and using a sand mill (dispersion medium: glass beads), the mixture was dispersed until the maximum particle size of the pigment coarse particles became 20 μm or less to prepare a dispersion composition. To the obtained dispersion composition, 34 parts by mass of a crosslinking agent (B1), 1 part by mass of Disparon OX-811 as a surface conditioner, and 1 part by mass of dodecylbenzenesulfonic acid as a curing catalyst were added and uniformly mixed with a disperser to prepare Paint Composition 1.

[0095] (Examples 2 to 28, Comparative Examples 1 to 4) Paint Compositions 2 to 32 were prepared in the same manner as the preparation method of Paint Composition 1, except that the types and amounts of the respective components were the same as those described in Tables 1 and 2. The compounding amounts in the tables indicate the amounts as they are (amounts including both solid components and liquid components).

[0096]

Table 1

[0097]

Table 2

[0098] Each component used in the preparation of the paint composition is as follows. Crosslinking agent (B) · Crosslinking agent (B1) (amino resin); Cymel 303LF (manufactured by Ornex Japan Co., Ltd., fully alkylated melamine resin), solid content concentration: 100% by mass · Crosslinking agent (B2) Desmodur BL3575 (manufactured by Sumika Covestro Urethane Co., Ltd., blocked polyisocyanate), hexamethylene diisocyanate (HDI) isocyanurate type blocked body, solid content concentration: 75% by mass

[0099] Details of other components are as follows. Pigment dispersion resin; · Floren G-700 (manufactured by Kyoeisha Chemical Co., Ltd.), carboxyl group-containing polymer modified product; solid content concentration: 100% by mass Surface conditioner; · Disparon OX-811 (manufactured by Enomoto Kasei Co., Ltd.), acrylic surface conditioner; solid content concentration: 30% by mass Pigment; · Titanix JR-603 (manufactured by Teika Co., Ltd.), titanium dioxide · Aluminum silicate (manufactured by BURGESS PIGMENT) · Sunblack X15 (manufactured by Asahi Carbon Co., Ltd.), carbon black · Red iron oxide CM-25P (manufactured by Toda Pigment Co., Ltd.) ·TAROX Synthetic Iron Oxide LL-XLO (manufactured by Titanium Industry Co., Ltd.), yellow iron oxide Curing catalyst; ·Hardening Catalyst 1: Dodecylbenzenesulfonic acid (manufactured by Kao Corporation), acidic catalyst; solid content concentration: 96% by mass ·Hardening Catalyst 2: Dibutyltin dilaurate (manufactured by Nitto Kasei Co., Ltd.), metal catalyst; solid content concentration: 100% by mass Solvent; ·Xylene (manufactured by Shouei Chemical Co., Ltd.), aromatic solvent ·Isobutanol (manufactured by Shouei Chemical Co., Ltd.), alcohol solvent ·Cyclohexanone (manufactured by Shouei Chemical Co., Ltd.), ketone solvent

[0100] Preparation of test plates After degreasing an aluminum-zinc plated steel sheet (210×300×0.35 mm) with alkali, a non-chromium chemical conversion treatment was performed by applying Surfcoat EC2310 (phosphate-based surface treatment agent: manufactured by Nippon Paint Surf Chemicals Co., Ltd.) to the front and back surfaces of the steel sheet, and then it was dried.

[0101] The paint composition obtained above was applied to the surface of the treated steel sheet with a roll coater so that the dry film thickness was 5 μm, and then baked at a maximum temperature of 230 °C for 50 seconds to form a coating film, thereby obtaining a test panel.

[0102] Evaluation items 1) Stability of the paint composition 60 parts by mass of the obtained polyester resin (A1) and 40 parts by mass of cyclohexanone were placed in a 300 mL four-necked flask, heated to 70 °C, and mixed with a stirrer at a rotation speed of 150 rpm to prepare a resin varnish. After allowing the resin varnish to stand at 23 °C for 1 day, its viscosity was measured using a B-type viscometer DV1M (manufactured by Eiko Seiki Co., Ltd.), and the stability of the resin varnish was evaluated according to the following criteria. ○ was considered as passing. ○: The viscosity of the resin varnish is less than 5,000 mPa·s. △: The viscosity of the varnish is 5,000 mPa·s or more and less than 10,000 mPa·s. ×: The viscosity of the resin varnish is 10,000 mPa·s or more (including those with no fluidity).

[0103] 2) Solvent resistance (xylene rubbing resistance) Each test piece was attached to the evaluation table of the wear resistance tester IMC-155F (manufactured by Imoto Seisakusho Co., Ltd.) with adhesive tape, and a rubbing test was conducted. The measurement conditions were as follows: using gauze containing xylene as the abrasives, a load of 1 kg, a reciprocating speed of 30 times / minute, and a reciprocating distance of 70 mm. The number of rubbing reciprocations until the substrate of the base steel plate was exposed was measured and evaluated according to the following criteria. ○ or above was considered qualified. ◎: Even when the number of reciprocations is 100 times or more, the substrate is not exposed. ○: When the number of reciprocations is 80 times or more and less than 100 times, the substrate is exposed. △: When the number of reciprocations is 30 times or more and less than 80 times, the substrate is exposed. ×: When the number of reciprocations is less than 30 times, the substrate is exposed.

[0104] 3) Alkali resistance Each painted steel plate was cut into 5 cm × 10 cm pieces, and each test piece was immersed in a 5% sodium hydroxide aqueous solution at 23°C for 48 hours, then taken out, washed with water, and dried at room temperature. For this painted steel plate test piece, the bulge evaluation of the flat part was performed according to ASTM D714-56. Here, ASTM D714-56 evaluates the size (average diameter) and density of each bulge by comparing with the standard judgment photos and shows grade symbols. For the size, there are four levels in the order of 8 (diameter about 1 mm), 6 (diameter about 2 mm), 4 (diameter about 3 mm), 2 (diameter about 5 mm), and for the density, there are five levels from the smallest as F, M, MD, D. Note that those with no bulge were regarded as 10, and 8 or above was considered qualified.

[0105] 4) Boiling water resistance The painted steel plate obtained above was cut into 5 cm × 10 cm pieces, and the obtained test pieces were immersed in boiling water at about 100°C for 5 hours, then taken out, and the appearance of the coating film on the surface side was evaluated in the same manner as the alkali resistance test, and 8 or above was considered qualified.

[0106] 5) Workability (adhesion) Each painted steel sheet obtained in the examples and comparative examples was cut into 5 cm × 3 cm pieces, and pre-bent using a creasing machine (manufactured by Ueshima Seisakusho) so that the painted film surface faced the front side. Two steel sheets of the same thickness (0.35 mm) were sandwiched between the test pieces and bent using a press machine (manufactured by Kyoritsu Kogyo Co., Ltd.). Next, a cellophane tape (registered trademark) (LP-24, manufactured by Nichiban Co., Ltd.) was adhered to the processed part of the painted steel sheet and peeled off all at once. The state of the painted film at the peeled part was visually observed, and the adhesion of the painted film at the processed part was evaluated according to the following criteria. A score of 4 or more was considered a pass. 5: No metal substrate is observed at the tape-peeled part. 4: A metal substrate part is observed in an area of more than 0% and less than 20% of the tape-peeled part. 3: A metal substrate part is observed in an area of 20% or more and less than 50% of the tape-peeled part. 2: A metal substrate part is observed in an area of 50% or more and less than 80% of the tape-peeled part. 1: A metal substrate part is observed in an area of 80% or more of the tape-peeled part.

[0107] 6) Workability (crack resistance) Each painted steel sheet obtained in the examples and comparative examples was cut into 5 cm × 3 cm pieces, and pre-bent using a creasing machine (manufactured by Ueshima Seisakusho) so that the painted film surface faced the front side. Five steel sheets of the same thickness (0.35 mm) were sandwiched between the test pieces and bent using a press machine (manufactured by Kyoritsu Kogyo Co., Ltd.). The state (cracks) of the painted film at the processed part was observed with a 15× magnifying glass, and the workability was evaluated according to the following criteria. A score of 4 or more was considered a pass. The test conditions were a temperature of 23°C and a humidity of 60 RH%. 5: No cracks are observed at the processed part. 4: Cracks are observed in an area of more than 0% and less than 20% of the processed part. 3: Cracks are observed in an area of 20% or more and less than 50% of the processed part. 2: Cracks are observed in an area of 50% or more and less than 80% of the processed part. 1: Cracks are observed in 80% or more of the area of the processed part.

[0108] 7) Corrosion resistance (salt spray test) A cut mark with a length of 70 mm was made on each test piece with a cutter knife so as to reach the base material, and a salt spray test (SST) was carried out for 1,000 hours with a salt spray tester ST-11L (manufactured by Suga Test Instruments Co., Ltd.) in accordance with the neutral salt spray resistance test method described in JIS K 5600-7-1 (JIS Z 2371). The corrosion state of the cross-cut part was visually observed and evaluated according to the following criteria based on the average value of the swelling widths (sum of both sides) on the left and right at the base material exposure part with a cut width of 0.5 mm. Pass was defined as ○ or above. ◎: The swelling width of the cross-cut part is less than 5 mm. 〇: The swelling width of the cross-cut part is 5 mm or more and less than 10 mm. △: The swelling width of the cross-cut part is 10 mm or more and less than 15 mm. ×: The swelling width of the cross-cut part is 15 mm or more.

[0109]

Table 3

[0110]

Table 4

[0111] Examples 1 to 28 are examples of the present invention, and the obtained coating compositions had good stability and were able to obtain coating films excellent in processability and durability.

[0112] Comparative Example 1 is an example in which the content of the polycarboxylic acid having a furan skeleton and the polycarboxylic anhydride is less than 20 mol% and 10 mol%, respectively, in 100 mol% of the total amount of the polycarboxylic acids constituting the coating film-forming resin (A1), and the solvent resistance and processability of the obtained coating film were not sufficiently satisfactory. In Comparative Examples 2 and 4, the content of polycarboxylic anhydride was less than 10 mol% in 100 mol% of the total amount of polycarboxylic acids constituting the coating film-forming resin (A1), and the stability of the resulting coating composition and the durability of the resulting coating film were not sufficiently satisfactory. Comparative Example 3 is an example in which the polyol constituting the coating film-forming resin (A1) does not contain a trivalent polyol, and the durability of the resulting coating film was not sufficiently satisfactory.

Industrial Applicability

[0113] The coating composition of the present disclosure has good coating stability (viscosity within an appropriate range), and good processability and durability of the resulting coating film. Therefore, the coating composition of the present disclosure is preferably used for coating various members such as metal substrates such as cold-rolled steel sheets and plated steel sheets, particularly building members such as steel furniture, shutters, rain doors, doors, roofs and siding, exterior materials for electrical equipment such as outdoor coolers, and interior materials.

Claims

1. A paint composition comprising a film-forming resin (A) and a crosslinking agent (B), wherein the film-forming resin (A) includes a polyester resin (A1), the polyester resin (A1) includes a reaction product of a polycarboxylic acid and a polyol, the polycarboxylic acid includes 20 mol% or more of a polycarboxylic acid having a furan skeleton and 10 mol% or more of a polycarboxylic anhydride in 100 mol% of the total amount of the polycarboxylic acid, and the polyol includes a divalent polyol and a trivalent polyol.

2. The paint composition according to Claim 1, wherein the content of the polycarboxylic acid having a furan skeleton is 90 mol% or less in 100 mol% of the total amount of the polycarboxylic acid.

3. The paint composition according to Claim 1, wherein the content of the trivalent polyol is 5 mol% or more and 30 mol% or less in 100 mol% of the total amount of the polyol.

4. The paint composition according to Claim 1, wherein the acid value of the polyester resin (A1) is 1 mgKOH / g or more and 30 mgKOH / g or less.

5. The paint composition according to Claim 1, wherein the hydroxyl value of the polyester resin (A1) is 10 mgKOH / g or more and 150 mgKOH / g or less.

6. The paint composition according to Claim 1, wherein the weight average molecular weight of the polyester resin (A1) is 35,000 or less.

7. The paint composition according to Claim 1, wherein the glass transition temperature of the polyester resin (A1) is -20°C or more and 100°C or less.

8. The paint composition according to Claim 1, wherein the crosslinking agent (B) includes one or more selected from the group consisting of an amino resin and a blocked polyisocyanate compound.

9. The paint composition according to Claim 1, wherein the content of the crosslinking agent (B) is 1 part by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the film-forming resin (A).

10. A coating process of applying the paint composition according to any one of Claims 1 to 9 to an object to be coated to obtain a coating film, and a curing process of curing the coating film at a temperature of 150°C or more and 270°C or less to obtain a coating film, the method for producing a coating film comprising the above processes.

11. A method for producing a multilayer coating film including a primer coating film and a topcoat film, the method comprising a step of forming a topcoat film by applying a topcoat paint composition containing a thermoplastic resin onto the primer coating film which is a coating film produced by the production method according to Claim 10.

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