Coating composition

Abstract

To provide a coating composition capable of forming a coating film which achieves both high processing adhesiveness and high hardness and preferably to provide a coating composition capable of forming a coating film having also excellent yellowing resistance.SOLUTION: There is provided a coating composition which comprises a coating film forming resin (A), a crosslinking agent (B) and a rust preventing pigment (C), wherein the coating film forming resin (A) includes a urethane resin (A1), the urethane resin (A1) includes a reaction product of a polyol compound (a11) and a polyisocyanate compound (a12), the polyol compound (a11) has a number average molecular weight of 300 or more and 5000 or less and the polyisocyanate compound (a12) contains a compound represented by the following formula (1), toluene diisocyanate and diphenylmethane diisocyanate.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] A painted metal plate obtained by applying paint to a metal substrate such as a cold-rolled steel sheet or a plated steel sheet is also called a pre-coated metal plate (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 plate is processed into various products after being coated with a paint composition on the surface of the metal plate to form a paint film. In the paint composition used for the pre-coated metal plate, a urethane resin or the like is used as the resin for forming the paint film.

[0003] As a composition containing a urethane resin, Patent Document 1 discloses a urethane polymer containing 0.1 to 20% by weight of a urethane bond represented by -(NH-CO-O)- in a resin obtained by polycondensing a copolymer polyester resin having a hydroxyl group and a polyisocyanate compound, and 95 to 60 parts by weight of the urethane polymer, and 5 to 40 parts by weight of an alkyl etherified melamine resin and / or a blocked polyisocyanate resin, which is a paint composition for a pre-coated steel sheet.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since the pre-coated metal sheet is processed into various products after the coating film is formed, the coating film is required to simultaneously satisfy high flexibility, that is, high process adhesion such that it does not crack or peel when, for example, the pre-coated metal sheet is bent during processing, and high hardness. In recent years, there have been demands for more complex and finer shapes, and accordingly, higher process adhesion and hardness have been required. Although urethane resins can have excellent flexibility, adhesion, chemical resistance, mechanical strength, etc., in the case of compositions containing conventionally known urethane resins, it has sometimes been difficult to achieve both high process adhesion and high hardness.

[0006] The present disclosure has been made in view of such circumstances, and an object thereof is to provide a coating composition capable of forming a coating film having both high process adhesion and high hardness, and preferably, an object thereof is to provide a coating composition capable of forming a coating film that is more excellent in yellowing resistance.

Means for Solving the Problems

[0007] The present disclosure provides the following. [1] A coating composition comprising a film-forming resin (A), a crosslinking agent (B), and a rust-preventive pigment (C), wherein the film-forming resin (A) contains a urethane resin (A1), the urethane resin (A1) contains a reaction product of a polyol compound (a11) and a polyisocyanate compound (a12), the number average molecular weight of the polyol compound (a11) is 300 or more and 5,000 or less, the polyisocyanate compound (a12) contains a compound represented by the following formula (1), toluene diisocyanate, and diphenylmethane diisocyanate.

Chemical formula

[10] A step of coating an object to be coated with the coating composition according to any one of [1] to [9] to obtain a coating film, and A step of curing the coating film at a temperature of 150°C or higher and 270°C or lower to obtain a coating film, which is included in a method for manufacturing a coating film.

[11] A method for manufacturing a multilayer coating film including a primer coating film and a topcoat coating film, comprising: A step of coating an object to be coated with the coating composition according to any one of [1] to [9] to obtain a primer coating film; A step of curing the primer coating film at a temperature of 150°C or higher and 270°C or lower to obtain a primer coating film; and A step of forming a topcoat coating film on the primer coating film using a topcoat coating composition, which is included in a method for manufacturing a multilayer coating film. [Advantages of the Invention]

[0008] The coating composition of the present disclosure can form a coating film that achieves both high processing adhesion and high hardness, and preferably, can further form a coating film that is also excellent in yellowing resistance. [Embodiments for Carrying Out the Invention]

[0009] (A) Coating Film-Forming Resin The coating film-forming resin (A) in the coating composition of the present disclosure is not particularly limited as long as it has a functional group capable of reacting with a crosslinking agent (B) and has a coating film-forming ability. The coating film-forming resin (A) includes a urethane resin (A1).

[0010] (A1) Urethane Resin Urethane resin means a resin containing a urethane bond and includes a reaction product of a polyol compound (a11) and a polyisocyanate compound (a12). In the present disclosure, the reaction product of the polyol compound (a11) and the polyisocyanate compound (a12) also includes a compound obtained by reacting the polyol compound (a11) and the polyisocyanate compound (a12) and then further chain-extending with a chain extender. Further, in the present disclosure, the urethane resin also includes a resin obtained by further modifying a resin classified as a urethane resin.

[0011] The reaction between the polyol compound (a11) and the polyisocyanate compound (a12) can be carried out by a known method using each component as a raw material. By appropriately selecting each component composition and reaction conditions, a urethane resin with adjusted molecular weight, hydroxyl value, urethane bond concentration, etc. can be obtained. Further, a catalyst may be used during the reaction to promote the reaction. Examples of the catalyst include known ones such as tin compounds, titanium compounds, zirconium compounds, bismuth compounds, and aluminum compounds.

[0012] The polyol compound (a11) is not particularly limited as long as it is a compound containing two or more hydroxyl groups per molecule. The number of hydroxyl groups contained in the polyol compound is two or more per molecule of the polyol compound, preferably two or more and eight or less, more preferably two or more and six or less, still more preferably two or more and four or less, and particularly preferably two or more and three or less.

[0013] Examples of the polyol compound (a11) include low molecular weight polyols such as ethylene glycol, propylene glycol, diethylene glycol, 1,4 - butanediol, 1,5 - pentanediol, 1,6 - hexanediol, neopentyl glycol, triethylene glycol, glycerin, trimethylolethane, and trimethylolpropane; high molecular weight polyols such as polycarbonate polyol, polyester polyol, polyether polyol such as bisphenol hydroxypropyl ether, polyester amide polyol, acrylic polyol, and polyurethane polyol. As the polyol compound, only one kind may be used, or two or more kinds may be used in combination.

[0014] The polyol compound (a11) preferably contains a high molecular weight polyol, more preferably contains one or more selected from polyester polyol, polyether polyol, and polycarbonate polyol, and still more preferably contains polyester polyol.

[0015] In the present disclosure, for example, a urethane resin obtained using a polyol compound containing a polyester polyol is also referred to as a polyester-based urethane resin. In the formation of such a polyester-based urethane resin, the hydroxyl group of the polyester polyol and the isocyanate group of the polyisocyanate compound undergo polycondensation to form a urethane bond, and the polyester polyol can be extended in molecular weight. As a result, the obtained polyester-based urethane resin contains an ester bond derived from the polyester polyol and a urethane bond derived from the condensation. The above describes the case of a polyol compound containing a polyester polyol, but the same applies to the case of using a polyol compound other than the polyester polyol.

[0016] The polyester polyol may be linear or branched, and typically may be a compound having an ester bond in the main chain and two or more hydroxyl groups at the ends of the main chain. The polyester polyol may be a compound obtained by polycondensation of a polyol component and an acid component such as a polycarboxylic acid and / or an acid anhydride; a compound obtained by ring-opening polymerization of a cyclic ester compound; a copolymer thereof, and the like.

[0017] Examples of the polyol component used in the production of the polyester polyol include diols such as ethylene glycol, propylene glycol, trimethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, and 1,6-hexanediol; triols such as trimethylolethane and trimethylolpropane; and tetraols such as pentaerythritol.

[0018] Examples of the polycarboxylic acid component used in the production of the polyester polyol include aliphatic polycarboxylic acids such as oxalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, hexahydrophthalic acid, and furandicarboxylic acid; and aromatic polycarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, 4,4'-diphenyldicarboxylic acid, and trimellitic acid.

[0019] Examples of the acid anhydride used in the production of the polyester polyol include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hymic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, succinic anhydride, dodecenyl succinic anhydride, and the like.

[0020] The equivalent ratio of the carbonyl group of the polycarboxylic acid and / or acid anhydride to the hydroxyl group of the polyol component (carbonyl group / hydroxyl group) is preferably 1.0 / 1.001 to 1.0 / 2.5, more preferably 1.0 / 1.01 to 1.0 / 2.0. In the present disclosure, the carbonyl group of the acid anhydride includes a carbonyl group generated by hydrolysis of the acid anhydride group.

[0021] Examples of the cyclic ester compound include β-propiolactone, dimethylpropionolactone, butyrolactone, γ-valerolactone, ε-caprolactone, γ-caprolactone, γ-caprylolactone, crotonlactone, δ-valerolactone, δ-caprolactone, and the like. Among them, ε-caprolactone is most preferred. The cyclic ester compound may form a polyester polyol by ring-opening polymerization, or may form a graft chain by ring-opening addition to a polyester polyol or a polyol.

[0022] In the production of the polyester polyol, other reaction components may be used in addition to the polyol component and the acid component. Examples of the other reaction components include monocarboxylic acids, hydroxycarboxylic acids, lactones, drying oils, semi-drying oils, and their fatty acids. More specifically, for example, a monoepoxide compound such as Cardura E (manufactured by Shell Chemical Company) can be mentioned.

[0023] The polyether polyol can be a compound obtained by adding an alkylene oxide to a compound having an active hydrogen-containing functional group. Examples of the compound having an active hydrogen-containing functional group include propylene glycol, trimethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, glycerin, diglycerin, trimethylolethane, trimethylolpropane, water, hexanetriol, and the like. Examples of the alkylene oxide include propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, tetrahydrofuran, and the like.

[0024] The polycarbonate polyol can typically be a reaction product of a polyol component and a carbonate compound; or a reaction product of a polyol component and phosgene.

[0025] Examples of the polyol component used in the production of the polycarbonate polyol include diols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, polyethylene glycol, and polypropylene glycol; trimethylolmethane, trimethylolpropane, ditrimethylolpropane, pentaerythritol, dipentaerythritol, and the like.

[0026] Examples of the carbonate compound used in the production of the polycarbonate polyol include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like.

[0027] In the polyol compound (a11), the total content of the polyester polyol, polyether polyol, and polycarbonate polyol 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, and still more preferably 95% by mass or more and 100% by mass or less in 100% by mass of the polyol compound.

[0028] In one aspect, the acid value of the polyol compound (a11) is 0 mgKOH / g, and in another aspect, preferably it is 0.1 mgKOH / g or more and 30 mgKOH / g or less, more preferably 0.1 mgKOH / g or more and 20 mgKOH / g or less, still more preferably 0.3 mgKOH / g or more and 15 mgKOH / g or less. When the acid value of the polyol compound (a11) is within the above range, productivity and hydrolysis resistance can be improved, the storage stability of the coating composition is good, and a coating film with good water resistance can be formed. Here, in the present disclosure, productivity also means manufacturability, and it means that the solid content concentration and viscosity of the coating composition can be adjusted within an appropriate range so that sufficient coating film appearance and coating film performance required for pre-coated metal sheets can be obtained. That is, when the viscosity of the coating composition is high, the coating workability and the smoothness of the obtained coating film may decrease. On the other hand, if it is diluted with a solvent or the like to lower the viscosity of the coating composition, the solid content concentration becomes low, and thick film coating cannot be performed, so the coating work efficiency is low, and sufficient coating film performance required for pre-coated metal sheets cannot be obtained. In the present disclosure, when the acid value of the polyol compound (a11) is within the above range, the solid content concentration and viscosity of the coating composition can be adjusted within an appropriate range, and it becomes possible to enhance productivity. Note that the acid value in the present disclosure indicates a value in terms of solid content and is a value measured by a method in accordance with JIS K 0070.

[0029] The number average molecular weight of the polyol compound (a11) is 300 or more and 5,000 or less, for example, it may be 300 or more and 3,500 or less, or 300 or more and 2,000 or less. When the number average molecular weight is less than 300, there are concerns such as an increase in resin viscosity and a decrease in alkali resistance. When the number average molecular weight is 5,000 or more, the processing adhesion of the obtained coating film may decrease. In the present disclosure, the number average molecular weight and the weight average molecular weight are values in terms of polystyrene measured by gel permeation chromatography.

[0030] The polyisocyanate compound (a12) is not particularly limited as long as it is a compound containing two or more isocyanate groups per molecule. The polyisocyanate compound (a12) is represented by the following formula (1):

[0031] [Chemical formula] [In formula (1), n represents an integer of 1 or more.] It includes a compound represented by the formula, toluene diisocyanate, and diphenylmethane diisocyanate. By including these compounds in the polyisocyanate compound, the processing adhesion and film hardness of the resulting coating film are good, and furthermore, the yellowing resistance of the resulting coating film can be improved.

[0032] n is 1 or more, preferably 1 or more and 20 or less, more preferably 1 or more and 10 or less.

[0033] The compound represented by formula (1) may contain only one kind or two or more kinds among the compounds in which n is 1 or more in formula (1). Preferably, it may contain two or more compounds in which n is 1 or more. In the compound represented by formula (1), the content of the compound in which n is 1 is preferably 20% by mass or more and 80% by mass or less, more preferably 30% by mass or more and 70% by mass or less, and still more preferably 40% by mass or more and 50% by mass or less.

[0034] In the polyisocyanate compound (a12), the content of the compound represented by formula (1) is preferably 0.5% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 30% by mass or less, and still more preferably 2% by mass or more and 25% by mass or less. When the content of the compound represented by formula (1) is within the above range, the processing adhesion and hardness of the resulting coating film are good, and furthermore, the yellowing resistance can be improved.

[0035] The toluene diisocyanate may be any of 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, and a mixture thereof.

[0036] In the polyisocyanate compound (a12), the content of toluene diisocyanate is preferably 50% by mass or more and 90% by mass or less, more preferably 55% by mass or more and 85% by mass or less, and still more preferably 60% by mass or more and 80% by mass or less. When the content of toluene diisocyanate is within the above range, the obtained coating film has good process adhesion and hardness, and the yellowing resistance can be further improved.

[0037] The diphenylmethane diisocyanate may be any of 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, and mixtures thereof, and preferably may be 4,4'-diphenylmethane diisocyanate.

[0038] In the polyisocyanate compound (a12), the content of diphenylmethane diisocyanate is preferably 0.5% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 30% by mass or less, still more preferably 2% by mass or more and 25% by mass or less, and particularly preferably 4.8% by mass or more and 24.4% by mass or less. When the content of diphenylmethane diisocyanate is within the above range, the obtained coating film has good process adhesion and hardness, and the yellowing resistance can be further improved.

[0039] In the polyisocyanate compound (a12), the total content of the compound represented by the formula (1), toluene diisocyanate, and diphenylmethane diisocyanate 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, and still more preferably 95% by mass or more and 100% by mass or less.

[0040] The polyisocyanate compound (a12) may contain a compound represented by the formula (1), and polyisocyanate compounds other than toluene diisocyanate and diphenylmethane diisocyanate. Examples of the other polyisocyanate compounds include aliphatic isocyanates such as hexamethylene diisocyanate (HDI); alicyclic diisocyanates such as isophorone diisocyanate (IPDI). The other polyisocyanate compounds may be only one kind, or two or more kinds.

[0041] The chain extender is not particularly limited as long as it is a compound containing one or more active hydrogens in the molecule, and water or an amine compound can be applied. Examples of the amine compound include aliphatic polyamines such as ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, and tetraethylenepentamine; aromatic polyamines such as tolylenediamine, xylylenediamine, and diaminodiphenylmethane; alicyclic polyamines such as diaminocyclohexylmethane, piperazine, 2,5-dimethylpiperazine, and isophoronediamine; hydrazines such as hydrazine, succinic acid dihydrazide, adipic acid dihydrazide, and phthalic acid dihydrazide; and alkanolamines such as hydroxyethyldiethylenetriamine, 2-[(2-aminoethyl)amino]ethanol, and 3-aminopropanediol.

[0042] The molar ratio (NCO / OH) of the isocyanate groups of the polyisocyanate compound (a12) to the hydroxyl groups in the polyol compound (a11) is preferably 0.1 or more and 5 or less, more preferably 0.3 or more and 2 or less, and still more preferably 0.5 or more and 1.2 or less. When the molar ratio (NCO / OH) of the isocyanate groups of the polyisocyanate compound (a12) to the hydroxyl groups in the polyol compound (a11) is within the above range, the processing adhesion of the obtained coating film can be improved.

[0043] The glass transition temperature (Tg) of the urethane resin (A1) can be 50°C or lower, more preferably 20°C or lower, still more preferably -20°C or lower in one embodiment, and can preferably be -50°C or higher and 50°C or lower, more preferably -45°C or higher and 20°C or lower, still more preferably -40°C or higher and -20°C or lower. When the glass transition temperature of the urethane resin (A1) is within the above range, the process adhesion of the resulting coating film, particularly the bendability, can be improved.

[0044] 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.).

[0045] The hydroxyl value of the urethane resin (A1) is preferably 0 mgKOH / g in one embodiment, and in another embodiment, is preferably 5 mgKOH / g or higher and 200 mgKOH / g or lower, more preferably 10 mgKOH / g or higher and 100 mgKOH / g or lower, still more preferably 10 mgKOH / g or higher and 70 mgKOH / g or lower. When the hydroxyl value of the urethane resin (A1) is within the above range, there are advantages such as good hardness and process adhesion of the resulting coating film. The hydroxyl value in the present disclosure indicates a value in terms of solid content and is a value measured by a method conforming to JIS K 0070.

[0046] The acid value of the urethane resin (A1) is 0.1 mgKOH / g or higher and 30 mgKOH / g or lower, and can be, for example, 0.1 mgKOH / g or higher and 20 mgKOH / g or lower, or 0.3 mgKOH / g or higher and 15 mgKOH / g or lower. When the acid value is within the above range, for example, the hydrolysis resistance can be improved, and a coating film having moisture resistance can be formed. Furthermore, excellent corrosion resistance can be ensured.

[0047] In one aspect, the urethane bond concentration (mol% / 100 g) in the urethane resin (A1) is preferably 5 mol% / 100 g or more and 25 mol% / 100 g or less, more preferably 7 mol% / 100 g or more and 20 mol% / 100 g or less, and still more preferably 11.0 mol% / 100 g or more and 16.3 mol% / 100 g or less. When the urethane bond concentration in the urethane resin (A1) is within such a range, the viscosity of the film-forming resin and the process adhesion of the resulting coating composition can be good.

[0048] In the present disclosure, the urethane bond concentration means the concentration (mol%) of urethane bonds (molecular weight = 59) in 100 g of the urethane resin (A1). Specifically, in preparing the urethane resin (A1) by reacting a polyol compound and a polyisocyanate compound, assuming that all of the isocyanate groups contained in the polyisocyanate compound react to form urethane bonds, it can be calculated by the following formula. Urethane bond concentration (mol%) = 59 (g / mol) × [number of isocyanate groups in urethane resin (A1) (mol)] / 100 g Strictly speaking, regarding the above reaction, it is necessary to consider the decrease in the number of isocyanate groups due to the urea-forming reaction, which is the reaction between water contained in the polyol compound and the polyisocyanate compound. However, in the present disclosure, on the premise that the water content contained therein is zero regardless of the composition of the polyol compound, the calculation is performed without taking into account the decrease.

[0049] In one aspect, the aromatic ring concentration (mol% / 100 g) in the urethane resin (A1) is preferably 2 mol% / 100 g or more and 20 mol% / 100 g or less, more preferably 5 mol% / 100 g or more and 18 mol% / 100 g or less, and still more preferably 10.2 mol% / 100 g or more and 11.5 mol% / 100 g or less. When the aromatic ring concentration in the urethane resin (A1) is within such a range, the viscosity of the film-forming resin and the process adhesion of the resulting coating composition can be good.

[0050] In the present disclosure, the aromatic ring concentration means the concentration (mol%) of aromatic rings (molecular weight = 78) in 100 g of the urethane resin (A1). Specifically, when preparing the urethane resin (A1) by reacting a polyol compound and a polyisocyanate compound, assuming that all of the polyisocyanate compound reacts, it can be calculated by the following formula. That is, in the case of toluene diisocyanate, since it has 1 aromatic ring in 1 molecule, the urethane resin (A1) contains the same number of aromatic rings as the toluene diisocyanate used in the synthesis. Also, in the case of diphenylmethane diisocyanate, since it has 2 aromatic rings in 1 molecule, the urethane resin (A1) contains twice the number of aromatic rings as the toluene diisocyanate used in the synthesis. Aromatic ring concentration (mol%) = 78 (g / mol) × [number of moles of aromatic rings in urethane resin (A1) / 100 g]

[0051] In one aspect, in the urethane resin (A1), the ratio of the urethane bond concentration (mol% / 100 g) to the aromatic ring concentration (mol% / 100 g) (urethane bond concentration / aromatic ring concentration) is preferably 0.8 or more and 2 or less, more preferably 0.9 or more and 1.8 or less, and still more preferably 0.9 or more and 1.5 or less. When the ratio (urethane bond concentration / aromatic ring concentration) in the urethane resin (A1) is within such a range, the obtained coating film may have good process adhesion and yellowing resistance.

[0052] In one aspect, the number average molecular weight (Mn) of the urethane resin (A1) may be 3,000 or more and 7,000 or less, preferably 3,500 or more and 5,500 or less. In one aspect, the weight average molecular weight (Mw) of the urethane resin (A1) is preferably 10,000 or more and 20,000 or less.

[0053] By having the number average molecular weight, the crosslinking reaction between the urethane resin and the crosslinking agent (B) can proceed sufficiently, the hardness of the obtained coating film can be improved, the crosslinking density of the coating film can be set within an appropriate range, and the process adhesion of the obtained coating film can be improved.

[0054] The content rate of the urethane resin (A1) can preferably be 80 mass% or more and 100 mass% or less, more preferably 90 mass% or more and 100 mass% or less, still more preferably 95 mass% or more and 100 mass% or less in 100 mass% of the coating film-forming resin (A).

[0055] In addition to the urethane resin (A1), the coating film-forming resin (A) may contain other resins. Examples of the other resins include epoxy resins and their modified products (such as acrylic-modified epoxy resins); polyester resins and their modified products (such as epoxy-modified polyester resins, silicone-modified polyester resins, etc.); acrylic resins and their modified products (such as silicone-modified acrylic resins, etc.); phenolic resins and their modified products (such as acrylic-modified phenolic resins, epoxy-modified phenolic resins, etc.); phenoxy resins; alkyd resins and their modified products (such as acrylic-modified alkyd resins, etc.); fluororesins and the like. These resins may be used alone only one kind, or two or more kinds may be used in combination.

[0056] In one aspect, from the viewpoint of the balance of the bendability of the obtained coating film, the moisture resistance, corrosion resistance and weather resistance of the obtained coating film, the coating film-forming resin (A) may contain at least one selected from the group consisting of an epoxy resin, a polyester resin, a urethane resin or their modified products in addition to the urethane resin (A1).

[0057] In the coating composition of the present disclosure, the content rate of the coating film-forming resin (A) can preferably be 5 mass% or more and 60 mass% or less, more preferably 15 mass% or more and 50 mass% or less, still more preferably 30 mass% or more and 45 mass% or less in 100 mass% of the total solid content of the coating composition. In the present disclosure, the solid content of a certain component means the heating residue defined in JIS K 5601-1-2:2008, and the solid content rate is calculated by measuring the percentage of the mass of the residue after heating at 105°C for 60 minutes with respect to the original mass.

[0058] The coating composition of the present disclosure may further contain a thermoplastic resin in addition to the film-forming resin (A).

[0059] Examples of the thermoplastic resin include chlorinated olefin resins such as chlorinated polyethylene and chlorinated polypropylene; homopolymers or copolymers having monomers such as vinyl chloride, vinyl acetate, and vinylidene chloride as monomer components; cellulose resins; acetal resins; alkyd resins; chlorinated rubber resins; modified polypropylene resins (such as acid anhydride-modified polypropylene resins); fluororesins (for example, vinylidene fluoride resins, vinyl fluoride resins, copolymers of fluorinated olefins and vinyl ethers, copolymers of fluorinated olefins and vinyl esters), and the like.

[0060] Only one type of thermoplastic resin may be used alone, or two or more types may be used in combination. By using thermoplastic resins in combination, better coating film physical properties, such as coating film strength and elongation, can be obtained.

[0061] (B) Crosslinking agent The crosslinking agent (B) can react with the film-forming resin (A) to form a cured coating film together with the film-forming resin (A). The crosslinking agent (B) can be a compound having two or more functional groups capable of reacting with the film-forming resin (A) in one molecule. By including the crosslinking agent (B), a coating film with high hardness can be obtained.

[0062] Examples of the crosslinking agent (B) include polyisocyanate compounds; blocked polyisocyanate compounds in which the isocyanate groups of polyisocyanate compounds are blocked with active hydrogen-containing compounds (hereinafter also referred to as "BI"); amino resins; phenolic resins, and the like. From the viewpoints of rust prevention and moisture resistance, the crosslinking agent (B) preferably contains one or more selected from blocked polyisocyanate compounds and amino resins. In addition, the entire amount of the polyisocyanate compound (a12) is used in the preparation of the urethane resin (A1), and it is considered that it does not exist theoretically at the stage of preparing the coating composition. Therefore, the polyisocyanate compound contained in the coating composition may be considered to act as a crosslinking agent (B).

[0063] (Polyisocyanate compound and BI) The polyisocyanate compound and the polyisocyanate compound constituting the blocked polyisocyanate compound are not particularly limited. Examples of the polyisocyanate compound include aliphatic polyisocyanate compounds such as 1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- or 1,4-diisocyanate; alicyclic polyisocyanate compounds such as 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; aromatic polyisocyanate compounds such as 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, polymethylene polyphenyl polyisocyanate (polymeric MDI); and polyisocyanate polymers such as isocyanurate, biuret or adduct forms of the above aliphatic polyisocyanate compound, the above alicyclic polyisocyanate compound, and the above aromatic polyisocyanate compound, etc. As the polyisocyanate compound, only one kind may be used, or two or more kinds may be used in combination.

[0064] The polyisocyanate compound as the crosslinking agent (B) preferably contains an aromatic polyisocyanate compound, and more preferably contains 2,4- or 2,6-diisocyanatotoluene (TDI), 2,2’-, 2,4’- or 4,4’-diisocyanatodiphenylmethane (MDI), xylene diisocyanate (XDI), naphthalene diisocyanate (NDI) or polymethylene polyphenyl polyisocyanate (polymeric MDI). Further, the polyisocyanate compound as the crosslinking agent (B) preferably contains a polyisocyanate multimer, and more preferably contains an isocyanurate form.

[0065] In the polyisocyanate compound used for the blocked polyisocyanate compound, the isocyanate group content measured in accordance with JIS K 7301-1995 is preferably 3% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less 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 better. Further, it is possible to suppress the crosslinking density of the obtained coating film from becoming excessively high, and the corrosion resistance can be improved.

[0066] 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. Examples of the active hydrogen-containing compound (blocking agent) include 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. These may be used alone or in combination of two or more.

[0067] The dissociation temperature of the blocked polyisocyanate compound depends on the types of the polyisocyanate compound and the active hydrogen-containing compound constituting the same, the presence or absence of a catalyst, and the amount thereof, but may preferably be 120 to 180°C. When the dissociation temperature of the blocked polyisocyanate compound is within the above range, the stability of the paint can be improved, and since the crosslinking reactivity with the film-forming resin (A) is excellent, a coating film having good moisture resistance can be obtained.

[0068] As the blocked polyisocyanate compound, commercially available products can also be used, and examples of such commercially available products include Desmodur BL3175 manufactured by Sumika Covestro Urethane Co., Ltd., Coronate 2554 manufactured by Tosoh Corporation, and the like.

[0069] (Amino resin) Examples of the amino resin include melamine resin (hereinafter also referred to as "MF") and urea resin, and melamine resin is preferred. The amino resin has excellent crosslinking reactivity with the film-forming resin (A) even without a catalyst, and the resulting coating film can have good moisture resistance.

[0070] Melamine resin is typically a thermosetting resin synthesized from melamine and aldehyde, and has three reactive functional groups -NX in one molecule of the triazine nucleus. 1 X 2 Examples of the 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 four types including a methylol / imino group type containing -N-(CH2OR)(CH2OH) and -N-(CH2OR)(H) or -N-(CH2OH)(H) as a reactive functional group.

[0071] In the present disclosure, among the above melamine resins, it is preferable to use a melamine resin having an average of one or more methylol groups or imino groups in one molecule, that is, a methylol group type, an imino group type, or a methylol / imino group type melamine resin or a mixture thereof. These may be used alone or in combination of two or more.

[0072] Examples of the melamine resin include Mycote 715, a product name of Ornex Japan Co., Ltd.

[0073] (Phenolic resin) Examples of the phenolic resin include glycidyl ether type resins such as condensation products of bisphenol A and epichlorohydrin, and condensation products of bisphenol F and epichlorohydrin; alicyclic epoxy resins, linear aliphatic epoxy resins, bromine-containing epoxy resins, phenol novolak type epoxy resins, cresol novolak type epoxy resins, etc. These may be used alone or in combination of two or more.

[0074] The content of the solid component of the crosslinking agent (B) is preferably 1 part by mass or more and 150 parts by mass or less, more preferably 2 parts by mass or more and 150 parts by mass or less, and still more preferably 5 parts by mass or more and 95 parts by mass or less with respect to 100 parts by mass of the solid component of the film-forming resin (A). When the content of the crosslinking agent (B) is within the above range, the crosslinking reaction can easily proceed, and the moisture resistance of the obtained coating film can be improved.

[0075] (C) Rust preventive pigment In the present disclosure, the rust preventive pigment (C) represents a pigment that exhibits a rust preventive action and can function as an inhibitor. Examples of the rust preventive pigment (C) include basic rust preventive pigments such as lead-based rust preventive pigments, boric acid-based rust preventive pigments, silicic acid-based rust preventive pigments, and alkaline earth metal composite oxide-based rust preventive pigments; passive film-forming rust preventive pigments such as chromic acid-based rust preventive pigments, molybdic acid and / or tungstic acid-based rust preventive pigments, and phosphoric acid-based rust preventive pigments; reducing rust preventive pigments such as metal-based rust preventive pigments, phosphide-based rust preventive pigments, phosphorous acid-based rust preventive pigments, and hypophosphorous acid-based rust preventive pigments; and pigments utilizing shapes such as micaceous iron oxide and leafing aluminum.

[0076] As the rust preventive pigment (C), passive film-forming rust preventive pigments are preferred, and phosphoric acid-based rust preventive pigments are more preferred. Examples of the phosphoric acid-based rust preventive pigments include metal salts of phosphoric acids. Examples of the phosphoric acids include orthophosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, and metaphosphoric acid. Examples of the metals that can be included in the metal salts include iron, aluminum, magnesium, calcium, molybdenum, and zinc. Specific examples of the phosphoric acid-based rust preventive pigments include zinc phosphate, aluminum phosphate, magnesium phosphate, calcium phosphate, aluminum tripolyphosphate, aluminum phosphomolybdate, and aluminum zinc phosphomolybdate.

[0077] As the rust preventive pigment (C), commercially available products may be used. Examples of such commercially available products include LF Bousei ZP-DL, LF Bousei PM-303W, LF Bousei MZP-500, LF Bousei MGM-200, LF Bousei CP-Z, LF Bousei AP-200 (manufactured by Kikuchi Color Co., Ltd.), and the like.

[0078] As the rust preventive pigment (C), only one kind may be used, or two or more kinds may be used in combination.

[0079] The average particle diameter of the rust preventive pigment (C) is preferably 0.1 μm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less. Note that the average particle diameter of the rust preventive pigment (C) can be measured using, for example, a laser diffraction particle size distribution analyzer SALD-2300 (manufactured by Shimadzu Corporation).

[0080] The content of the rust preventive pigment (C) is preferably 1 part by mass or more and 150 parts by mass or less, more preferably 1 part by mass or more and 100 parts by mass or less, and still more preferably 5 parts by mass or more and 80 parts by mass or less with respect to a total of 100 parts by mass of the solid components of the film-forming resin (A) and the crosslinking agent (B). By being within the above range, there is an advantage that the water resistance and corrosion resistance of the obtained multilayer coating film are improved.

[0081] [Other Components] The coating composition of the present disclosure may contain other components other than those described above, if necessary.

[0082] Examples of other components include extender pigments; colorants such as coloring pigments and dyes; pearlescent 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); anti-sagging agents; thickeners; lubricants such as waxes; pigment dispersants; pigment wetting agents; leveling agents; anti-color separation agents; anti-settling agents; defoamers; preservatives; anti-freezing agents; emulsifiers; anti-mildew agents; antibacterial agents; stabilizers; coupling agents; curing catalysts, and the like. These additives may be used alone, or two or more of them may be used in combination.

[0083] As the other components, one or more selected from extender pigments, coloring pigments, and brightening pigments (hereinafter collectively referred to simply as "other pigment components") may be included, or one or more selected from extender pigments and coloring pigments may be included.

[0084] Examples of the extender pigment include titanium oxide, calcium carbonate, barium sulfate, clay, talc, mica, glass fiber, etc. Among these, it is preferable to include titanium oxide, calcium carbonate, precipitated barium sulfate, talc, and clay. These may be used alone, or two or more of them may be used in combination.

[0085] Examples of the coloring pigment include colored inorganic pigments such as carbon black, graphite, iron oxide, and cold dust; colored organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone, perylene, anthrapyrimidine, carbazole violet, anthrapyridine, azo orange, flavanthrone yellow, isoindoline yellow, azo yellow, indanthrone blue, dibromoanthrasone red, perylene red, azo red, and anthraquinone red. These may be used alone, or two or more of them may be used in combination.

[0086] Examples of the brightening pigment include aluminum foil, bronze foil, tin foil, gold foil, silver foil, titanium metal foil, stainless steel foil, alloy foils such as nickel-copper, and foil pigments such as foil-shaped phthalocyanine blue. These may be used alone, or two or more of them may be used in combination.

[0087] When the other components include the other pigment components, the content of the other pigment components may preferably be 1 part by mass or more and 50 parts by mass or less, more preferably 10 parts by mass or more and 45 parts by mass or less, based on 100 parts by mass in total of the solid components of the film-forming resin (A) and the crosslinking agent (B).

[0088] When the other components include the other pigment components, the content of the rust preventive pigment (C) is preferably 0 parts by mass or more and 100 parts by mass or less, more preferably 20 parts by mass or more and 100 parts by mass or less, still more preferably 40 parts by mass or more and 100 parts by mass or less, and even more preferably 40 parts by mass or more and 80 parts by mass or less, out of a total of 100 parts by mass of the rust preventive pigment (C) and the other pigment components.

[0089] Examples of the solvent 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 spirit, Solvesso 100, Solvesso 150 (all are aromatic hydrocarbon-based solvents, manufactured by Shell Chemical Company), etc. These may be used alone or in combination of two or more.

[0090] The solid content of the coating composition of the present disclosure can be preferably 10% by mass or more and 80% by mass or less, more preferably 15% by mass or more and 75% by mass or less, and still more preferably 15% by mass or more and 73% by mass or less.

[0091] (Properties and state of the paint) The paint composition of the present disclosure may be an aqueous paint or an organic solvent-based paint.

[0092] The paint 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. Furthermore, it may be used as an intermediate coat paint formed in the intermediate layer between the undercoat paint and the topcoat paint.

[0093] In another aspect, the paint composition of the present disclosure may be used as a paint composition for forming a single-layer paint film rather than for forming a multi-layer paint film.

[0094] The paint composition of the present disclosure can exhibit excellent corrosion resistance and moisture resistance regardless of where it is used in the multi-layer paint film. The undercoat paint, topcoat paint, and intermediate coat paint other than the paint composition of the present disclosure may be conventionally known ones. For example, as the undercoat paint, conventionally known non-chromium rust preventive paints and the like can be mentioned, and as the topcoat paint and intermediate coat paint, polyester resin-based paints, fluororesin-based paints, and the like can be mentioned.

[0095] The paint composition of the present disclosure is preferably used as an undercoat paint. When the paint composition of the present disclosure is used as an undercoat paint, it exhibits particularly good adhesion at the contact surface with the paint film formed by the topcoat paint or intermediate coat paint that is in direct contact with the undercoat paint.

[0096] [Method for Preparing Paint Composition] The method for preparing the paint composition according to the present disclosure is not particularly limited. The paint composition according to the present disclosure can be prepared, for example, by mixing a film-forming resin (A), a crosslinking agent (B), a rust preventive pigment (C), and optionally used thermoplastic resin, extender pigment, coupling agent, curing catalyst, 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 paint composition of the present disclosure may be a two-component paint comprising a main component containing a film-forming resin (A) and a rust preventive pigment (C), and a crosslinking agent component containing a crosslinking agent (B).

[0097] [Object to be coated] The object to be coated on which the coating film is formed by the 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.

[0098] Examples of the steel sheet include, for example, galvanized steel sheet, cold-rolled steel sheet, stainless steel sheet, aluminum plate, and the like.

[0099] Examples of the galvanized steel sheet include zinc-containing plated steel sheets that utilize the sacrificial anticorrosion of zinc, specifically, hot-dip galvanized steel sheets, electro-galvanized steel sheets, alloyed hot-dip galvanized steel sheets, aluminum-zinc plated steel sheets, nickel-zinc plated steel sheets, magnesium-aluminum-zinc plated steel sheets, magnesium-aluminum-silica-zinc plated steel sheets, and the like.

[0100] The steel sheet is preferably one that has been surface-treated with a chemical conversion treatment agent before coating. 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 that does not contain heavy metals is preferred.

[0101] [Method for manufacturing anti-rust coating film] In one embodiment, the present disclosure provides a method for manufacturing a coating film, including a step of coating the object to be coated with the coating composition of the present disclosure to obtain a coating film, and a step of curing the coating film at a temperature of 150 °C or higher and 270 °C or lower to obtain a coating film.

[0102] In one aspect, when the coating composition of the present disclosure is used for a primer coating film, the present disclosure provides A method for manufacturing a multi-layer coating film including a primer coating film and a topcoat coating film, A step of coating the object to be coated with the coating composition to obtain a primer coating film, A step of curing the primer coating film at a temperature of 150 °C or higher and 270 °C or lower to obtain a primer coating film, and A method for manufacturing a multilayer coating film is also provided, which includes a step of forming a topcoat film on the primer film using a topcoat paint composition.

[0103] 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, an airless spray, an electrostatic spray, and a curtain flow coater can be adopted.

[0104] The coating film of the present disclosure 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 highest temperature reached by the object to be coated such as a steel plate) is, for example, 150°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, further, excellent rust prevention can be exhibited over a long period, and further, a coating film having excellent moisture resistance can be formed.

[0105] The baking time (curing time) is, for example, 10 to 200 seconds. For example, when forming a multilayer coating film composed of two layers, a primer coating film and a topcoat film, after applying the primer coating composition, baking may be performed, and then, the topcoat coating composition may be applied and baking of the topcoat film may be performed, or after applying the primer coating composition, the topcoat coating composition may be applied wet-on-wet without performing baking, and baking may be performed simultaneously.

[0106] The film thickness (dry film thickness) of the coating film of the present disclosure is usually 1 to 30 μm, and for example, in the case of a topcoat film, it is preferably 10 to 30 μm.

[0107] According to the coating composition of the present disclosure, in the obtained coating film, high processing adhesion and high hardness can be achieved simultaneously, and further, good yellowing resistance can be obtained. Therefore, the coating composition of the present disclosure can be preferably used as various members such as pre-coated metal plates, for example, building members such as shutters, window sashes, doors, roofs, and sidings, exterior materials for electrical equipment such as outdoor units of coolers, and interior materials.

Examples

[0108] The present disclosure will be described in more detail by the following examples, but the present disclosure is not limited thereto.

[0109] (Production Example A1-1) Preparation of polyol compound (a11-1) Into a reaction vessel equipped with a thermometer, a condenser and a stirrer, 609.7 parts by mass of adipic acid, 501.6 parts by mass of 1,6-hexanediol, 238.9 parts by mass of neopentyl glycol and 0.07 parts by mass of Neostan U-100 as a reaction catalyst were mixed, and the temperature was gradually raised to 220 ° C in a nitrogen stream. While distilling off the generated water, an esterification reaction was carried out for about 3 to 5 hours until the acid value became 1 mgKOH / g or less (dehydration amount: 150.2 parts by mass) to obtain a polyol compound (a11-1).

[0110] Preparation of polyisocyanate compound (a12-1) In another container, 900.0 parts by mass of Coronate T-80 and 100.0 parts by mass of Millionate MR-200 were mixed to prepare a polyisocyanate compound (a12-1).

[0111] Preparation of coating film-forming resin (A1-1) Into a reaction vessel equipped with a thermometer, a condenser and a stirrer, 765.0 parts by mass of the polyol compound (a11-1), 255.0 parts by mass of the polyisocyanate compound (a12-1) and 255.0 parts by mass of cyclohexanone were mixed and held at 80 ° C for 1 hour for reaction. After confirming the disappearance of the NCO group by IR, 725.0 parts by mass of cyclohexanone was added to obtain a polyester-based urethane resin (A1-1) (solid content concentration: 51.0 mass%).

[0112] (Production Examples A1-2) to (A1-12), (a1-13) to (a1-18)) As raw materials for the polyol compound, the polycarboxylic acid component and the polyol component shown in Table 1 were used, and as the polyisocyanate compound, the polyisocyanate compounds shown in Tables 2 and 3 were used. Except for these, coating film-forming resins (A1-2) to (A1-12), (a1-13) to (a1-18) were produced in the same manner as in Production Example (A1-1).

[0113]

Table 1

[0114]

Table 2

[0115]

Table 3

[0116] Each component used in the preparation of the urethane resin (A1) is as follows. Polyisocyanate compound (a12): · Millionate MT (manufactured by Tosoh Corporation, monomeric MDI (4,4-MDI (diphenylmethane diisocyanate)), isocyanate group content: 34% by mass · Millionate MR-200 (manufactured by Tosoh Corporation, crude MDI (diphenylmethane diisocyanate: 48% by mass, compound represented by formula (1): 52% by mass)), isocyanate group content: 31% by mass · Coronate T-80 (manufactured by Tosoh Corporation, toluene diisocyanate (TDI)), isocyanate group content: 48% by mass · HDI (manufactured by Tosoh Corporation, hexamethylene diisocyanate), isocyanate group content: 50% by mass Others: · Solvent 1: cyclohexanone (manufactured by Shoei Chemical Industry Co., Ltd.) · Reaction catalyst: Neostan U-100 (manufactured by Nitto Kasei Co., Ltd., dibutyltin dilaurate), non-volatile content: 100% by mass

[0117] Preparation of coating composition 1 100.5 parts by mass of a coating film-forming resin (A1), 2.2 parts by mass of cyclohexanone, 5.1 parts by mass of Solvesso 100, 30.3 parts by mass of titanium oxide, and 32.2 parts by mass of magnesium hydroxide (C1) were mixed and dispersed using a sand mill (dispersion medium: glass beads) until the maximum particle diameter of the pigment coarse particles became 15 μm or less to prepare a dispersion composition 1. To the obtained dispersion composition 1, 29.6 parts by mass of a crosslinking agent (B1) and 0.2 parts by mass of SCAT-24 (manufactured by Nitto Kasei Co., Ltd.) as a curing catalyst were added and uniformly mixed with a disper to prepare a paint composition 1.

[0118] Each component used in the preparation of the paint composition is as follows. Crosslinking agent (B): · Crosslinking agent (B1) (polyisocyanate compound); Desmodur BL3575 (manufactured by Sumika Covestro Urethane Co., Ltd., blocked polyisocyanate), blocked body of hexamethylene diisocyanate (HDI) (isocyanurate type, blocking agent: dimethylpyrazole), isocyanate group content: 10.5 mass%, solid content concentration: 75 mass% · Crosslinking agent (B2) (amino resin); Mycote 715 (manufactured by Ornex Japan Co., Ltd., imino group type melamine resin), solid content concentration: 80 mass% Rust preventive pigment (C): · Rust preventive pigment (C1) Magnesium oxide RF-10CS (manufactured by Ube Materials Co., Ltd., magnesium oxide) · Pigment: Typepake CR-95 (manufactured by Ishihara Sangyo Co., Ltd., titanium oxide) · Curing catalyst: SCAT-24 (manufactured by Sakai Chemical Industry Co., Ltd., dibutyltin dilaurate), non-volatile content: 100 mass% · Solvent 1: Cyclohexanone (manufactured by Shoei Chemical Industry Co., Ltd.) · Solvent 2: Solvesso 100 (manufactured by Shell Chemical Co., Ltd., aromatic organic solvent)

[0119] (Preparation of treated steel sheet) After subjecting an aluminum-zinc plated steel sheet (210×297×0.4 mm) to alkaline degreasing, a non-chromium chemical conversion treatment was performed by applying Surf Coat EC2310 (phosphate-based surface treatment agent; manufactured by Nippon Paint Surf Chemicals Co., Ltd.) as a surface treatment agent to both the front and back surfaces of the steel sheet, followed by drying to obtain a treated steel sheet.

[0120] 1) Heat resistance to yellowing The coating composition obtained in the above Production Example was applied to the surface of the treated steel sheet using a bar coater so that the dry film thickness became 5 μm, and baking was performed at a maximum reaching temperature of 215°C for 40 seconds to form an undercoat film (before the test).

[0121] Furthermore, the undercoat film was baked at a maximum reaching temperature of 245°C for 40 seconds (after the test). For the obtained undercoat films before and after the test, color measurement (b value) was performed using a color difference meter CR-400 (manufactured by Konica Minolta). The color difference (Δb) was calculated according to the following formula, and the yellowing resistance was evaluated according to the following criteria. Color difference (Δb) = b value after the test - b value before the test ○: Δb is less than 0.1 and almost no yellowing of the coating film is observed. △: Δb is 0.1 or more and less than 0.3, and some yellowing is observed. ×: Δb is 0.3 or more and distinct yellowing is observed.

[0122] (Preparation of test plates) The coating composition 1 obtained above was applied to the surface of the treated steel sheet using a bar coater so that the dry film thickness became 5 μm, and baking was performed at a maximum reaching temperature of 215°C for 40 seconds to form an undercoat film.

[0123] Next, Nippesu Super Coat 300HQ (polyester-based topcoat paint; manufactured by Nippon Paint Industrial Coatings Co., Ltd.) as a topcoat paint composition was applied onto the undercoat film using a bar coater so that the dry film thickness became 10 μm, and baking was performed at a maximum reaching temperature of 210°C for 40 seconds to obtain a test plate having a multilayer coating film.

[0124] 2) Coating hardness (scratch resistance test) Each test plate obtained above was cut into 5 cm × 10 cm to obtain test pieces. At room temperature of 23°C, using a coin scratch tester, while keeping the edge of a 10-yen coin at a 45-degree angle on the coated surface of each test piece and applying a load of 1 kg, the 10-yen coin was pulled 50 mm at a speed of 10 mm / second to make 5 scratches on the coated surface. The degree of exposure of the metal substrate with respect to the total area of the scratches was evaluated according to the following criteria. If the area of the scratched part was less than 10%, it was evaluated as good. ○: No metal substrate is observed in the scratched part. △: The metal substrate is observed in 10% or more and less than 50% of the area of the scratched part. ×: The area of the scratched part is 75% or more, or almost no coating film remains and the metal substrate is clearly observed.

[0125] 3) Process adhesion (Workability) Each test plate obtained above was cut into a size of 5 cm × 3 cm to obtain test pieces. At room temperature of 20°C, with the surface of each test piece facing outward, a 2T bending processed part was provided at the center. That is, the test piece was bent with the surface facing outward, and two steel plates with the same thickness as the test piece (0.4 mm) were sandwiched inside, and in that state, the test piece and the steel plates were bent 180 degrees with a vise. The state of the coating film at the bent part was visually observed and evaluated according to the following criteria. ○: No cracks or peeling of the coating film are observed in the processed part △: Slight cracks or peeling of the coating film are observed in the processed part ×: Obvious cracks or peeling of the coating film are observed in the processed part

[0126] (Adhesion) In the above workability test, a cellophane adhesive tape was attached to the bent part of the test piece subjected to 2T bending, and when the tape was instantly peeled off, the degree of peeling of the coating film at the bent processed part was evaluated according to the following criteria ○: No peeling of the coating film is observed in the processed part △: Slight peeling of the coating film is observed in the processed part ×: Obvious peeling of the coating film is observed in the processing part

[0127] 4) Long-term adhesion For each test panel obtained above, it was cut to be 5×12 cm to obtain test pieces. A polyester tape was attached to cover the edge part, and a 4T bending processed part was provided at the center part. That is, each test piece was bent with its surface facing outward, and four steel plates with the same thickness (0.4 mm) as the test piece were sandwiched inside, and the test piece and the steel plates were bent 180 degrees with a vise. For the test pieces after bending, using a super accelerated weather resistance tester SUV-F2 (manufactured by Iwasaki Electric Co., Ltd.) and a humidity resistance tester CT-3 type (manufactured by Suga Test Instruments Co., Ltd.), a UV irradiation test was carried out under the conditions of an irradiation time of 24 hours, a black panel temperature of 63 °C, and an ultraviolet intensity of 100 mW / cm 2 , and a test cycle in which a wetting test was carried out under the conditions of a test time of 24 hours, a tank temperature of 50 °C, and a tank humidity of 98% or more was repeated 10 cycles as one cycle. Then, at a room temperature of 20 °C, a cellophane adhesion tape was adhered to the bending processed part, and the ratio of the coating film remaining on the processed part when it was peeled off rapidly was visually observed and evaluated according to the following criteria. ○: 100% of the coating film remained △: 50% or more and less than 100% of the coating film remained ×: Less than 50% of the coating film remained

[0128]

Table 4

[0129]

Table 5

Industrial Applicability

[0130] According to the coating composition of the present disclosure, in the obtained coating film, high processing adhesion and high hardness can be achieved simultaneously, and further, the yellowing resistance can be good. Therefore, the coating composition of the present disclosure can be preferably used as various members such as pre-coated metal plates, for example, building members such as shutters, window sashes, doors, roofs and sidings, exterior materials for electrical equipment such as outdoor coolers, and interior materials.

Claims

1. A paint composition comprising a film-forming resin (A), a crosslinking agent (B), and a rust-preventive pigment (C), wherein the film-forming resin (A) contains a urethane resin (A1), the urethane resin (A1) contains a reaction product of a polyol compound (a11) and a polyisocyanate compound (a12), the number average molecular weight of the polyol compound (a11) is 300 or more and 5,000 or less, and the polyisocyanate compound (a12) contains a compound represented by the following formula (1), toluene diisocyanate, and diphenylmethane diisocyanate. 【Chemical Formula 1】 [In formula (1), n represents an integer of 1 or more.]

2. The content of toluene diisocyanate is 50% by mass or more and 90% by mass or less in 100% by mass of the total amount of the polyisocyanate compound, and the content of diphenylmethane diisocyanate is 4.8% by mass or more and 24.2% by mass or less in 100% by mass of the total amount of the polyisocyanate compound. The paint composition according to claim 1.

3. The urethane bond concentration in the urethane resin (A1) is 11.0 mol% / 100 g or more and 16.3 mol% / 100 g or less. The paint composition according to claim 1.

4. The aromatic ring concentration in the urethane resin (A1) is 10.2 mol% / 100 g or more and 11.5 mol% / 100 g or less. The paint composition according to claim 1.

5. In the urethane resin (A1), the ratio of the urethane bond concentration to the aromatic ring concentration (urethane bond concentration / aromatic ring concentration) is 0.9 or more and 1.6 or less. The paint composition according to claim 1.

6. The glass transition temperature of the urethane resin (A1) is 50°C or lower. The paint composition according to claim 1.

7. The coating composition according to claim 1, wherein the crosslinking agent (B) contains one or more selected from the group consisting of polyisocyanate compounds, amino resins, and phenolic resins.

8. The coating 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 solid content of the film-forming resin (A).

9. The coating composition according to claim 1, wherein the content of the rust preventive pigment (C) is 1 part by mass or more and 150 parts by mass or less with respect to 100 parts by mass of the total solid content of the film-forming resin (A) and the crosslinking agent (B).

10. A step of applying the coating composition according to any one of claims 1 to 9 to an object to be coated to obtain a coating film, and A method for producing a coating film, comprising a step of curing the coating film at a temperature of 150°C or higher and 270°C or lower to obtain a coating film.

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