JP7792222B2 - paint composition - Google Patents

Description

The present invention relates to a coating composition, a coating film, a substrate with a coating film, and a method for producing the same.

In order to impart properties such as weather resistance, chemical resistance, and abrasion resistance to substrates such as metal substrates, a coating (baking paint) is applied to the metal substrate and baked at high temperatures to harden the resin, forming a coating film.

Known baking paints include melamine-based, fluorine-based, and acrylic-based baking paints, and each type is used depending on the application of the substrate. However, melamine-based baking paints are widely used because they can form coatings with high hardness.
As such melamine-based baking paints, for example, the paints described in Patent Documents 1 and 2 are known.

Japanese Patent Application Laid-Open No. 2003-334490 Japanese Patent Application Laid-Open No. 2000-129201

However, conventional melamine-based baking paints do not have sufficient adhesion to substrates, particularly non-ferrous metal substrates.
Furthermore, depending on the application of the substrate, the coating film formed from the baking paint is required to be solvent resistant. However, coating films formed from conventional melamine-based baking paints tend to blister when they come into contact with strong solvents such as toluene, so there was room for improvement in terms of solvent resistance.

When forming a coating film on a substrate using a baking paint, the substrate temperature of the substrate coated with the baking paint must be raised to a predetermined temperature and maintained at that temperature for a predetermined period of time (the substrate maintenance conditions (substrate temperature x time) at this time are hereinafter also referred to as "substrate keeping conditions").
When conventional baking paints were used, it was not possible to form a coating film with the desired physical properties unless the substrate was kept at a temperature of 120 to 150°C for 10 to 20 minutes. Meanwhile, there has been a growing need for energy conservation in recent years, and in order to meet this need, there has been a demand for paints that can form coating films with the desired physical properties even under low-temperature, short-time substrate-keeping conditions.

The present invention was made in light of the above, and aims to provide a coating composition that can easily form a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance.

After extensive research into ways to solve the above problems, the inventors discovered that a specific coating composition could solve the above problems, leading to the completion of the present invention. An example of the configuration of the present invention is as follows:

<1> A coating composition containing an alkyd resin (A), a melamine resin (B), and an epoxy resin (C),
In the coating composition, the ratio of the number of moles of melamine skeletons (b) to the number of moles of phthalic acid skeletons (a) [(b)/(a)] is 0.87 to 1.52, and
In the coating composition, the ratio of the number of moles (c) of glycidyl skeletons to the number of moles (a) of phthalic acid skeletons [(c)/(a)] is 0.17 to 0.80.
Paint composition.

<2> Contains an alkyd resin (A), a melamine resin (B), and an epoxy resin (C),
a mass ratio [(MB)/(MA)] of the solid content (MB) of the melamine resin (B) to the solid content (MA) of the alkyd resin (A) is 0.85 to 1.45; and
a mass ratio [(MC)/(MA)] of the solid content (MC) of the epoxy resin (C) to the solid content (MA) of the alkyd resin (A) is 0.30 to 1.35;
Paint composition.

<3> The coating composition according to <1> or <2>, wherein the epoxy resin (C) is a resin having two or more epoxy groups per molecule.

<4> The coating composition according to any one of <1> to <3>, further containing a scaly pigment.

<5> The coating composition according to any one of <1> to <4>, which is a baking coating composition.
<6> The coating composition according to any one of <1> to <5>, which is for use on non-ferrous metals.

<7> A coating film formed from the coating composition described in any one of <1> to <6>.

<8> A substrate with a coating film, comprising the coating film according to <7> and a substrate.
<9> The coated substrate according to <8>, wherein the substrate is made of a non-ferrous metal.

<10> A method for producing a substrate with a coating film, comprising the following steps [1] and [2]:
[1] A step of applying the coating composition according to any one of <1> to <6> to a substrate. [2] A step of baking the applied coating composition to form a coating film.

The present invention makes it possible to easily form a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance, even under low-temperature, short-term substrate-holding conditions (e.g., substrate-holding conditions of 120°C for 3 minutes).

≪Paint composition≫
A coating composition according to one embodiment of the present invention (hereinafter also referred to as "the composition") contains an alkyd resin (A), a melamine resin (B), and an epoxy resin (C), and is a coating composition that satisfies the following requirement (I) (hereinafter also referred to as "the composition 1"), or a coating composition that satisfies the following requirement (II) (hereinafter also referred to as "the composition 2"):
Requirement (I): In the present composition 1, the ratio of the number of moles (b) of melamine skeletons to the number of moles (a) of phthalic acid skeletons [(b)/(a)] is 0.87 to 1.52, and
In the present composition 1, the ratio of the number of moles (c) of the glycidyl skeleton to the number of moles (a) of the phthalic acid skeleton [(c)/(a)] is 0.17 to 0.80.
Requirement (II): The mass ratio [(MB)/(MA)] of the solid content (MB) of the melamine resin (B) to the solid content (MA) of the alkyd resin (A) is 0.85 to 1.45, and
The mass ratio [(MC)/(MA)] of the solid content (MC) of the epoxy resin (C) to the solid content (MA) of the alkyd resin (A) is 0.30 to 1.35.

The present composition may satisfy either requirement (I) or (II), but preferably satisfies both requirements (I) and (II).

The (b)/(a) ratio is 0.87 to 1.52, preferably 0.90 to 1.50, more preferably 0.95 to 1.40, and even more preferably 1.00 to 1.30, because this allows a coating film with superior adhesion to the substrate and solvent resistance to be formed under lower baking conditions.

The (c)/(a) ratio is 0.17 to 0.80, preferably 0.20 to 0.80, more preferably 0.25 to 0.70, and even more preferably 0.25 to 0.60, because this allows a coating film with superior adhesion to the substrate and solvent resistance to be formed under lower baking conditions.

The above (a) to (c) can be calculated from ¹³ C-NMR spectrum, specifically by the method described in the examples below.
In the following examples, the peaks near 131 ppm, 166 ppm, 45 ppm, and 50 ppm were used to calculate (a) to (c). However, if, for example, overlap with peaks derived from other structures is observed, the peaks used to calculate (a) to (c) may be changed.

The phthalic acid skeleton specifically has the following structure:

The melamine skeleton specifically has the following structure.

The glycidyl skeleton specifically has the following structure: In the following structure, the single line bonded to the epoxy ring means a CH ₂ -epoxy ring.

The (MB)/(MA) ratio is 0.85 to 1.45, preferably 0.90 to 1.40, and more preferably 0.95 to 1.30, because this allows a coating film with superior adhesion to the substrate and solvent resistance to be formed under lower baking conditions.

The (MC)/(MA) ratio is 0.30 to 1.35, preferably 0.35 to 1.20, and more preferably 0.40 to 0.90, because this allows a coating film with superior adhesion to the substrate and solvent resistance to be formed under lower baking conditions.

Note that (MB)/(MA) and (MC)/(MA) refer to the use of each resin in such a way that, when preparing the composition, the mass ratio of alkyd resin (A) to melamine resin (B) and the mass ratio of alkyd resin (A) to epoxy resin (C) fall within the above-mentioned ranges.

This composition contains a first agent, a second agent (and an nth agent), and is typically stored, preserved, transported, etc. in separate containers, and is mixed immediately before use. Although it may be a two- or more-component composition, a one-component composition is preferred.

The present composition is preferably a baking paint composition, more preferably a paint composition for non-ferrous metals, and even more preferably a baking paint composition for non-ferrous metals, in order to more effectively exhibit the effects of the present invention.
The use of the present composition is not particularly limited, and examples thereof include substrates requiring the formation of a coating film on the surface (e.g., metals, particularly non-ferrous metals), and specific preferred examples include automobile components, construction components, and industrial machinery components (e.g., automobile transmission parts, marine engine oil coolers, office automation equipment components such as printers, air pressure control system components such as compressors, and hydraulic valves for agricultural vehicles), with die-cast components such as aluminum die-cast and zinc die-cast being particularly preferred.

<Alkyd Resin (A)>
The alkyd resin (A) is not particularly limited as long as it has the phthalic acid skeleton and does not have the melamine skeleton or glycidyl skeleton, and any known resin can be used.
The alkyd resin (A) may be used alone or in combination of two or more.

The alkyd resin (A) may be an unmodified alkyd resin, or a modified alkyd resin (e.g., rosin-modified alkyd resin, phenol-modified alkyd resin, epoxy-modified alkyd resin (epoxy-modified alkyd resin does not have a glycidyl skeleton), (meth)acrylic-modified alkyd resin, silicon (silicone)-modified alkyd resin, or urethane-modified alkyd resin).

The alkyd resin (A) can be obtained by conventional methods, but is preferably a resin obtained by polycondensation of a (semi)drying oil or a (semi)drying oil fatty acid, an acid component, and a polyhydric alcohol component.

Examples of the (semi)drying oils include fish oil, dehydrated castor oil, safflower oil, linseed oil, soybean oil, sesame oil, poppy seed oil, perilla oil, hemp seed oil, grape kernel oil, corn oil, tall oil, sunflower oil, cottonseed oil, walnut oil, and rubber seed oil. Examples of (semi)drying oil fatty acids include fish oil fatty acids, dehydrated castor oil fatty acids, safflower oil fatty acids, linseed oil fatty acids, soybean oil fatty acids, sesame oil fatty acids, poppy seed oil fatty acids, perilla oil fatty acids, hemp seed oil fatty acids, grape kernel oil fatty acids, corn oil fatty acids, tall oil fatty acids, sunflower oil fatty acids, cottonseed oil fatty acids, walnut oil fatty acids, and rubber seed oil fatty acids. These may be used alone or in combination of two or more.

The amount of the (semi)drying oil or (semi)drying oil fatty acid used is preferably 20 to 70% by mass, and more preferably 30 to 60% by mass, based on 100% by mass of the monomer components used to synthesize the alkyd resin, in order to easily obtain a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates.

As the acid component, it is preferable to use at least one selected from phthalic acid (ortho-isomer) and phthalic anhydride. Furthermore, as the acid component, in addition to phthalic acid or phthalic anhydride, at least one selected from, for example, isophthalic acid, terephthalic acid, maleic anhydride, trimellitic anhydride, adipic acid, benzoic acid, rosin, and succinic acid may also be used.

There are no particular restrictions on the amount of the acid component used, but it is preferably 10 to 50% by mass, and more preferably 20 to 45% by mass, based on 100% by mass of the monomer components used to synthesize the alkyd resin.

Examples of the polyhydric alcohol component include dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 3-methylpentanediol, 1,4-hexanediol, and 1,6-hexanediol, as well as glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol. These may be used alone or in combination.

The amount of the polyhydric alcohol component used is not particularly limited, but is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass, based on 100% by mass of the monomer components used in synthesizing the alkyd resin.

The molar amount of the phthalic acid skeleton in alkyd resin (A), as measured by NMR, is preferably 0.5 to 15 mmol, and more preferably 1 to 10 mmol, per 1 g of solids content of alkyd resin (A), from the viewpoint of easily obtaining a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance.

The weight-average molecular weight (Mw) of the alkyd resin (A) measured by GPC in terms of standard polystyrene is preferably 8,000 to 120,000, more preferably 10,000 to 100,000, from the viewpoints of easily obtaining a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance.

The Mw can be measured by GPC using the following conditions: apparatus (HLC-8220GPC, manufactured by Tosoh Corporation), column (Super H2000 + Super H4000 (manufactured by Tosoh Corporation, inner diameter 6 mm/length 15 cm each)), column temperature (40°C), eluent (tetrahydrofuran), flow rate (0.50 mL/min.), detector (RI), and standard material (polystyrene).

The acid value of the alkyd resin (A) varies depending on the number of carboxy groups contained in the resin, and is therefore an index showing the number of carboxy groups present in the alkyd resin (A).
The acid value of the alkyd resin (A) is preferably 0.5 to 10 mgKOH/g, more preferably 1 to 9 mgKOH/g, from the viewpoint of easily obtaining a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance.

Specifically, the acid value can be measured by the following method.
Accurately weigh 1 to 5 g of resin into a conical beaker, add 30 to 50 ml of a toluene/ethanol = 7/3 (volume ratio) mixed solution to dissolve the resin, add 2 drops of phenolphthalein-ethanol solution as an indicator, and titrate with N/10 potassium hydroxide-ethanol solution. The endpoint of the titration is when the redness of the solution does not disappear for 30 seconds, and calculate using the following formula.
Acid value = (B × f × 5.61) / S
[B: amount of potassium hydroxide-ethanol solution used (ml), f: factor of potassium hydroxide-ethanol solution, S: mass of resin (g)]

The content of the solids of the alkyd resin (A) in the present composition is an amount that satisfies the above-mentioned requirement (I) when the present composition is the present composition 1, and an amount that satisfies the above-mentioned requirement (II) when the present composition is the present composition 2.
The solid content of the alkyd resin (A) is preferably 5 to 45% by mass, more preferably 10 to 35% by mass, based on 100% by mass of the nonvolatile content of the composition, from the viewpoint of easily obtaining a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance.

The nonvolatile content of the composition can be calculated as follows.
1±0.1 g of this composition is weighed out onto a flat-bottom dish, spread evenly using a wire of known mass, and dried at 108°C for 3 hours under normal pressure. The mass of the wire is subtracted from the resulting heating residue to obtain the mass percentage.
In this specification, the components other than the solvent in each raw material (e.g., alkyd resin (A)) are referred to as "solids."

<Melamine resin (B)>
The melamine resin (B) is not particularly limited as long as it is a resin having the melamine skeleton, and any conventionally known resin can be used, but it is preferably a resin that does not have the phthalic acid skeleton or glycidyl skeleton.
The melamine resin (B) may be used alone or in combination of two or more.

Examples of melamine resin (B) include methylated melamine resin, normal butylated melamine resin, isobutylated melamine resin, and octylated melamine resin. These resins include fully alkyl group types, hydroxy group types such as methylol groups, and imino group-containing types. Among these, methylated melamine resin, normal butylated melamine resin, and isobutylated melamine resin are preferred, with normal butylated melamine resin and isobutylated melamine resin being more preferred, due to their excellent adhesion to substrates.

The molar amount of the melamine skeleton in melamine resin (B), as measured by NMR, is preferably 0.5 to 15 mmol, and more preferably 1 to 10 mmol, per 1 g of solids of melamine resin (B), from the viewpoint of easily obtaining a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance.

The number average molecular weight (Mn) of the melamine resin (B) measured by GPC in terms of standard polystyrene is preferably 100 to 10,000, from the viewpoint that a coating film having desired physical properties can be easily formed under low-temperature baking conditions.
The Mn can be measured under the same conditions as those for the Mw.

Commercially available melamine resins (B) may be used, including, for example, the U-Ban series manufactured by Mitsui Chemicals, Inc., the Cymel series manufactured by Allnex Corporation, the Amidia series manufactured by DIC Corporation (e.g., Amidia L-125-60 [isobutylated melamine resin]), and the Melan series manufactured by Showa Denko Materials K.K. (e.g., Melan 2000 [normally butylated melamine resin]).

<Epoxy resin (C)>
The epoxy resin (C) is not particularly limited as long as it is a resin having the glycidyl skeleton, and any conventionally known resin can be used, but it is preferably a resin that does not have the phthalic acid skeleton or melamine skeleton.
The epoxy resin (C) may be used alone or in combination of two or more.

The epoxy resin (C) is preferably a resin (including polymers and oligomers) having two or more epoxy groups per molecule, as this allows for the easy production of a coating film with excellent solvent resistance.

Examples of epoxy resins (C) include glycidyl ether-type epoxy resins, glycidyl ester-type epoxy resins, glycidyl amine-type epoxy resins, bisphenol-type epoxy resins, novolac-type epoxy resins, cresol-type epoxy resins, dicyclopentadiene-type epoxy resins, aliphatic-type epoxy resins, alicyclic-type epoxy resins, and modified epoxy resins (e.g., phenol-modified epoxy resins, fatty acid-modified epoxy resins, phosphate compound-modified epoxy resins, and epoxidized oil-based epoxy resins).

Specific examples of epoxy resin (C) include bisphenol A-type epoxy resins (bisphenol A-type diglycidyl ethers); bisphenol AD-type epoxy resins; bisphenol F-type epoxy resins; phenol novolac-type epoxy resins; cresol novolac-type epoxy resins; and trishydroxyphenylmethane-type epoxy resins. These may also be hydrogenated (hereinafter also referred to as "hydrogenated") products, or bromides in which at least one hydrogen atom in the resin has been replaced with a bromine atom.

Among the above, bisphenol-type epoxy resins are preferred as the epoxy resin (C), as they have excellent adhesion to substrates and can easily produce coating films with excellent solvent resistance. Bisphenol A-type and bisphenol F-type epoxy resins are more preferred, with bisphenol A-type epoxy resins being particularly preferred.

Examples of the bisphenol A epoxy resin include condensation polymers of bisphenol A diglycidyl ethers such as bisphenol A diglycidyl ether, bisphenol A (poly)propylene oxide diglycidyl ether, bisphenol A (poly)ethylene oxide diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, hydrogenated bisphenol A (poly)propylene oxide diglycidyl ether, and hydrogenated bisphenol A (poly)ethylene oxide diglycidyl ether.

The epoxy resin (C) may be obtained by synthesis using a conventionally known method, or a commercially available product may be used.
Examples of commercially available products that are liquid at room temperature (15 to 25°C, the same applies below) include "E-028" (manufactured by Ohtake Meishin Chemical Co., Ltd., bisphenol A type epoxy resin, epoxy equivalent weight 180 to 190, viscosity 12,000 to 15,000 mPa·s/25°C) and "jER807" (manufactured by Mitsubishi Chemical Corporation, bisphenol F type epoxy resin, epoxy equivalent weight 160 to 175, viscosity 3,000 to 4,500 mPa·s/25°C). Examples of commercially available products that are semi-solid at room temperature include "jER834" (manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, epoxy equivalent weight 230 to 270). Examples of epoxy resins that are solid at room temperature include "jER1001" (manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, epoxy equivalent weight 450 to 500), "jER1004" (manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, epoxy equivalent weight 875 to 975), and "jER1007" (manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, epoxy equivalent weight 1750 to 2200).

Furthermore, solutions obtained by diluting the aforementioned semi-solid or solid epoxy resin with a solvent, such as "E-834-85X" (manufactured by Ohtake Meishin Chemical Co., Ltd., a xylene solution of bisphenol A type epoxy resin (834 type epoxy resin solution), epoxy equivalent 255), "E-001-75X" (manufactured by Ohtake Meishin Chemical Co., Ltd., a xylene solution of bisphenol A type epoxy resin (1001 type epoxy resin solution), epoxy equivalent 475), and "EPICLON N-740-80X" (manufactured by DIC Corporation, a methyl ethyl ketone solution of phenol novolac type epoxy resin, epoxy equivalent 180), can also be used.
In this specification, the epoxy equivalent value refers to the epoxy equivalent per solid content of the epoxy resin.

As the epoxy resin (C), an epoxy resin that is semi-solid or solid at room temperature is preferred, and an epoxy resin that is solid at room temperature is more preferred, because it easily produces a coating film that has excellent adhesion to the substrate and excellent solvent resistance even when baked under low-temperature, short-time substrate-keeping conditions.

The molar amount of the glycidyl skeleton in epoxy resin (C), as measured by NMR, is preferably 0.5 to 15 mmol, and more preferably 1 to 10 mmol, per 1 g of solids of epoxy resin (C), from the viewpoint of easily obtaining a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance.

The epoxy equivalent of the epoxy resin (C) is preferably 150 or more, more preferably 210 or more, and particularly preferably 400 or more, from the viewpoint of easily obtaining a coating film that has excellent adhesion to the substrate and excellent solvent resistance, and is preferably 2200 or less, more preferably 1000 or less.

The weight-average molecular weight of epoxy resin (C) measured by GPC (gel permeation chromatography) is not uniformly determined and depends on factors such as the coating and curing conditions of the resulting composition (e.g., ambient drying or baking), but is preferably 350 to 20,000, and more preferably 450 to 10,000.

<Other ingredients>
The present composition may contain, as necessary, components other than the resins (A) to (C), such as a scaly pigment, a pigment other than a scaly pigment, an organic solvent, an anti-settling agent (anti-sagging agent), a leveling agent, a reactive diluent, a curing accelerator, an adhesion imparting agent, a plasticizer, a dehydrating agent (stabilizer), a dispersant, an antifoaming agent, an antifouling agent, etc., within a range that does not impair the object of the present invention.
The other components may each be used alone or in combination of two or more.

The other component may be a component having at least one skeleton selected from the group consisting of a phthalic acid skeleton, a melamine skeleton, and a glycidyl skeleton (e.g., a reactive diluent or silane coupling agent having a glycidyl skeleton, or a plasticizer having a phthalic acid skeleton). When using such other components, it is preferable that the other components are used in Composition 1 so as to satisfy Requirement (I), and that the other components are used in Composition 2 so as to satisfy Requirement (II).

When the present composition contains other components having at least one skeleton selected from the group consisting of a phthalic acid skeleton, a melamine skeleton, and a glycidyl skeleton, the content thereof is preferably 3% by mass or less, and more preferably 1% by mass or less, based on 100% by mass of the nonvolatile content of the present composition.

[Scaly pigment]
The scale-like pigment is not particularly limited, and any conventionally known scale-like pigment can be used. Specific examples include mineral pigments, metal pigments, glass flakes, and plastic flakes. Among these, mineral pigments or metal pigments are preferred, and mica, talc, or aluminum flakes are more preferred.

The average aspect ratio of the scaly pigment (median diameter (D50)/average thickness) is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more, from the viewpoints of the solvent resistance of the resulting coating film and improving adhesion to the substrate by internal stress relaxation, and is preferably 150 or less, more preferably 120 or less, and even more preferably 100 or less.
For the same reasons, the D50 of the scaly pigment is preferably 1 μm or more, more preferably 3 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less.

The D50 can be measured using a laser scattering diffraction particle size distribution measuring device, for example, "SALD 2200" (manufactured by Shimadzu Corporation).
The average thickness can be calculated as the average value by observing the main surface (the surface with the largest area) of the scaly pigment using a scanning electron microscope (SEM), for example, "XL-30" (manufactured by Philips), from a direction horizontal to the surface, and measuring the thicknesses of several tens to several hundreds of pigment particles.

When the composition contains a scaly pigment, the content of the scaly pigment is preferably 5 to 60% by mass, and more preferably 10 to 50% by mass, based on 100% by mass of the nonvolatile content of the composition, in order to easily obtain a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance.

[Pigments other than flake pigments]
The pigments other than the scaly pigments are not particularly limited, and examples thereof include extender pigments, coloring pigments, and anti-rust pigments.

The extender pigment may be any conventionally known extender pigment, such as zinc oxide, silica, clay, (potassium) feldspar, calcium carbonate, kaolin, alumina white, white carbon, aluminum hydroxide, magnesium carbonate, barium sulfate (e.g., barite powder), gypsum, rock wool, or glass fiber.

When the composition contains an extender pigment, the content of the extender pigment is preferably 5 to 70% by mass, and more preferably 10 to 60% by mass, based on 100% by mass of the nonvolatile content of the composition.

The color pigment may be any conventionally known color pigment, including, for example, inorganic pigments such as carbon black, titanium dioxide (titanium white), iron oxide (red iron oxide), yellow iron oxide, and ultramarine, and organic pigments such as cyanine blue and cyanine green.

When the composition contains a coloring pigment, the content of the coloring pigment is preferably 10 to 60% by mass, and more preferably 15 to 50% by mass, based on 100% by mass of the nonvolatile content of the composition.

[Organic solvent]
The organic solvent is not particularly limited, but examples thereof include aromatic hydrocarbon solvents such as toluene and xylene, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, ether solvents such as butyl cellosolve, ester solvents such as butyl acetate, alcohol solvents such as isopropanol, n-butanol, and 1-methoxy-2-propanol, and aliphatic hydrocarbon solvents such as mineral spirits, n-hexane, n-octane, 2,2,2-trimethylpentane, isooctane, n-nonane, cyclohexane, and methylcyclohexane.

The present composition preferably contains an organic solvent so that the above-mentioned effects can be more effectively exhibited, and is preferably a solvent-based coating composition containing an organic solvent.
The content of the organic solvent in the present composition is preferably 10% by mass or more, more preferably 20% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less.

[Anti-settling agent]
As the anti-settling agent, conventionally known agents can be used, such as organoclay waxes such as stearates, lecithin salts, and alkylsulfonates of Al, Ca, and Zn, polyethylene wax, amide wax, hydrogenated castor oil wax, synthetic finely powdered silica, and oxidized polyethylene wax. Among these, amide wax, synthetic finely powdered silica, oxidized polyethylene wax, and organoclay wax are preferred.
As such an anti-settling agent, a commercially available product may be used.

When the composition contains an anti-settling agent, the content of the anti-settling agent is preferably 0.1 to 3% by mass based on 100% by mass of the non-volatile content of the composition.

[Leveling agent]
It is preferable to incorporate a leveling agent into the present composition, as this will improve cissing of the coating film when the composition is applied, improve wettability to the surface of the object to be coated (e.g., substrate), and make it easier to obtain a coating film with a uniform thickness.
The leveling agent is not particularly limited, but examples thereof include various leveling agents such as fluorine-based, acrylic-based, and silicone-based leveling agents.

When the composition contains a leveling agent, the content of the leveling agent is preferably 0.005 to 1.5% by mass, and more preferably 0.01 to 1% by mass, based on 100% by mass of the nonvolatile content of the composition.

<Method for preparing the present composition>
The present composition can be prepared by mixing (kneading) the raw material components of the composition, such as the resins (A) to (C) and the other components used as needed. When preparing the present composition 1, it is preferable to use the raw materials so as to satisfy the requirement (I) in consideration of the amount of each skeleton in the raw materials used, and when preparing the present composition 2, it is preferable to use the raw materials so as to satisfy the requirement (II).
The mixing (kneading) can be carried out using a conventionally known device such as a mixer, disperser, or stirrer, and examples of such devices include a disperser, a mixing/dispersing mill, a mortar mixer, a roll, a paint shaker, and a homogenizer. The mixing (kneading) may be carried out while heating or cooling depending on the season, environment, etc.

<Coating film, coated substrate>
A coating film according to one embodiment of the present invention (hereinafter also referred to as "the coating film") is formed using the present composition, and a substrate with a coating film according to one embodiment of the present invention (hereinafter also referred to as "the substrate with the coating film") is a laminate having the coating film and a substrate.
The present coating film and the present coating film on the substrate with the present coating film may be formed by drying the present composition at room temperature of about 5 to 35°C or by forced drying at about 30 to 90°C. However, in terms of better exerting the effects of the present invention, it is preferable to form the composition by baking it as described below.

The material of the substrate is not particularly limited, and examples thereof include iron and steel (e.g., iron, steel, ferroalloy, carbon steel, mild steel, alloy steel), non-ferrous metals (e.g., zinc, aluminum, copper, and alloys thereof, brass, zinc plating, zinc thermal spraying, zinc phosphate conversion coating, and stainless steel (SUS304, SUS410, etc.)).
Furthermore, when mild steel (SS400, etc.) is used as the substrate, it is desirable to adjust the surface of the substrate (e.g., adjust the arithmetic mean roughness (Ra) to about 30 to 75 μm) by polishing the surface of the substrate by grit blasting, etc., as necessary.
The substrate may be a substrate that has been subjected to a pretreatment such as a cleaning treatment or a blast treatment to remove rust, dirt, etc. adhering to the substrate.

The substrate is not particularly limited, and can be used without limitation on any substrate on whose surface a coating film is required to be formed. However, non-ferrous metal substrates are preferred in that the effects of using the present composition can be more effectively exhibited.
Specific preferred examples of the substrate include automobile components, construction components, and industrial machinery components (e.g., automobile transmission parts, oil coolers for marine engines, parts for office automation equipment such as printers, air pressure control system components such as compressors, and hydraulic valves for agricultural vehicles), and die-cast components such as aluminum die-cast and zinc die-cast are particularly preferred.

The thickness of this coating film is not particularly limited and may be selected appropriately depending on the application for which the coating film is to be used, but is typically 10 to 100 μm, preferably 15 to 80 μm, and more preferably 20 to 60 μm.

<Manufacturing method of substrate with coating film>
A method for producing a substrate with a coating film according to one embodiment of the present invention (hereinafter also referred to as "the method") includes the following steps [1] and [2].
Step [1]: A step of applying the present composition to a substrate. Step [2]: A step of baking the present composition applied to the substrate to form a coating film.

<Step [1]>
The coating method in the step [1] is not particularly limited, and examples thereof include conventionally known methods such as spray coating such as airless spray coating and air spray coating, brush coating, and roller coating.
In such coating, it is preferable to coat the resulting coating so that the dry film thickness falls within the above range.
When applying the composition, the viscosity of the coating composition may be adjusted to an appropriate level, if desired.

<Step [2]>
The baking conditions (substrate keeping conditions) in the step [2] are not particularly limited, but conditions of 100 to 140°C for 1 to 10 minutes are preferred, and from the viewpoint of further exerting the effects of the present invention, conditions of 110 to 130°C for 2 to 8 minutes are more preferred.
The composition of the present invention can provide a coating film that has excellent adhesion to substrates, particularly non-ferrous metal substrates, and excellent solvent resistance, even when baked under such low-temperature, short-time substrate-holding conditions.

The atmosphere in which step [2] is carried out is not particularly limited; it may be carried out in air or in an inert gas atmosphere such as nitrogen or argon. It may also be carried out under normal pressure or under reduced pressure.

The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples.

[Synthesis Example 1]
A reactor equipped with a stirrer, a cooler, a thermometer, a nitrogen gas inlet pipe, and a dehydration device was charged with 20.9 parts by mass of tall oil fatty acid, 24.5 parts by mass of phthalic anhydride, 0.6 parts by mass of benzoic acid, 15.7 parts by mass of glycerin, and 1.8 parts by mass of xylene, and the reaction was carried out at 200°C under a nitrogen atmosphere until the acid value of the reaction product became 13 or less, and then the reaction was cooled.
After cooling, 36.4 parts by mass of xylene was added to the container, thereby obtaining an alkyd resin solution A with a solid content of 60% by mass.
The acid value of the alkyd resin in alkyd resin solution A was 6.7 mg KOH/g, and the Mw of the alkyd resin was 32,000.

[Synthesis Example 2]
A reactor was charged with 350.0 parts by mass of soybean oil, 0.2 parts by mass of lithium naphthenate, and 29.0 parts by mass of glycerin, and the resulting mixture was heated to 150°C under a nitrogen stream, and 60.0 parts by mass of pentaerythritol was added thereto. The mixture was then heated to 260°C and maintained at that temperature for 4 hours, and then cooled to 200°C.
Thereafter, 167.3 parts by mass of phthalic anhydride, 2.4 parts by mass of maleic anhydride, and 29.4 parts by mass of xylene as a reflux solvent were added.
The temperature was then raised to 220°C, kept at 220°C for 5 hours, and then cooled. 362.5 parts by mass of turpene was added to prepare an alkyd resin solution B with a solid content of 60% by mass.
The acid value of the alkyd resin in alkyd resin solution B was 7.0 mgKOH/g, and the Mw of the alkyd resin was 64,000.

[Example 1]
A mill base was obtained by mixing and strongly dispersing 18 parts by mass of alkyd resin solution A, 2.2 parts by mass of xylene, 4.7 parts by mass of n-butyl alcohol, 18.9 parts by mass of titanium dioxide, and 0.47 parts by mass of an anti-settling agent.
To the obtained mill base, 15.7 parts by mass of melamine resin A, 7.2 parts by mass of epoxy resin, 0.04 parts by mass of leveling agent, 11.6 parts by mass of scaly pigment, and 16.4 parts by mass of xylene were added and stirred to prepare a coating composition.

[Examples 2 to 11 and Comparative Examples 1 to 4]
A coating composition was prepared in the same manner as in Example 1, except that the raw materials shown in Table 1 were used in the amounts (parts by mass) shown in Table 1.

The raw materials used in preparing the coating composition are as follows:
"Alkyd resin solution A": the alkyd resin solution prepared in Synthesis Example 1, solid content = 60% by mass
"Alkyd resin solution B": alkyd resin solution prepared in Synthesis Example 2, solid content = 60 mass%
"Melamine resin A": Amidia L-125-60 (manufactured by DIC Corporation), isobutylated melamine resin, solid content = 60% by mass
"Melamine resin B": Melan 2000 (manufactured by Showa Denko Materials Co., Ltd.), normal butylated melamine resin, solid content = 60 mass%
"Epoxy resin": E-001-75X (manufactured by Ohtake Meishin Chemical Co., Ltd.), solid content = 75 mass%, epoxy equivalent = 475
・ "Titanium dioxide": Typaque R-930 (manufactured by Ishihara Sangyo Kaisha, Ltd.)
"Scaly pigment": Micro Ace L-1 (manufactured by Nippon Talc Co., Ltd.), fine powder talc "Leveling agent": BYK-310 (manufactured by BYK Japan Co., Ltd.), silicone-based leveling agent, solid content = 25% by mass
"Anti-settling agent": PEW-20X (manufactured by Ohtake Meishin Chemical Co., Ltd.), oxidized polyethylene wax, solid content = 20% by mass

<Calculation of the number of moles of phthalic acid skeleton, melamine skeleton, and glycidyl skeleton>
The solvent extract (acetone:toluene = 1:1, volume ratio) of the prepared coating composition was placed in a recovery flask and concentrated using an evaporator. The extract was then azeotropically distilled twice with chloroform and dried under reduced pressure at 40°C. Approximately 3 mL of deuterated chloroform and approximately 45 mg of chromium acetylacetate were added to approximately 300 mg of the resulting dried product to prepare an NMR sample solution.

Using the obtained NMR sample solution, ¹³ C-NMR was measured under the following conditions.
・Device: AVANCEIII400 (manufactured by Bruker)
Measurement method: IGD (inverse gated decoupling) method Observed nucleus: 13C
・Observation frequency: 100.6MHz
Lock solvent: deuterated chloroform Number of data points: 65536
Delay time: 5 seconds; Accumulation count: 8192 times; Measurement temperature: room temperature; Sample rotation speed: 20 Hz

(1) Number of moles of phthalic acid skeleton (a)
The peak observed in the vicinity of ¹³¹ ppm in the C-NMR corresponds to a peak corresponding to the sum of four carbon atoms in the phthalic acid skeleton. Therefore, one-fourth of the integral value (area) of the peak in the vicinity of 131 ppm was calculated as the number of moles (a) of the phthalic acid skeleton.

(2) Number of moles of melamine skeleton (b)
The peak near ¹⁶⁶ ppm observed by C-NMR corresponds to an overlapping peak of a peak corresponding to the sum of three carbon atoms in the melamine skeleton and a peak corresponding to the sum of two carbon atoms in the phthalic acid skeleton. Therefore, the number of moles of melamine skeletons (b) was calculated as one-third of the value obtained by subtracting twice the number of moles of phthalic acid skeletons calculated in (1) above from the integrated value of the peak near 166 ppm.

(3) Number of moles of glycidyl skeleton (c)
The average value of the integrated values of the peaks near 45 ppm and 50 ppm observed by the ¹³ C-NMR was calculated as the number of moles (c) of the glycidyl skeleton.

The mole numbers (a) to (c) calculated above were used to calculate (b)/(a) and (c)/(a). The results are shown in Table 1.

<Solvent resistance>
The prepared coating composition was applied to a zinc phosphate-treated steel sheet (SPCC-SD 3118) so that the dry film thickness was 30 μm, and the applied coating composition was baked under substrate keeping conditions of 110°C x 3 minutes to produce a substrate with a coating film.
The lower half of the prepared coated substrate was immersed in a plastic container containing toluene at 23° C. for 24 hours. After immersion, the coated substrate was removed from the plastic container, and the proportion of the area where swelling occurred in the toluene-immersed portion was visually observed and evaluated according to the following evaluation criteria. The results are shown in Table 1.
Good: When the area of the part immersed in toluene is taken as 100%, the total area of the swollen parts of the coating film was less than 5%. Fair: When the area of the part immersed in toluene is taken as 100%, the total area of the swollen parts of the coating film was 5% or more but less than 20%. Poor: When the area of the part immersed in toluene is taken as 100%, the total area of the swollen parts of the coating film was 20% or more.

Note that toluene is a strong solvent, and the solvent resistance test described above is conducted under conditions stricter than those specified for solvent resistance in, for example, JIS K 5651:2002. In tests conducted under such strict conditions, coatings that receive an O rating are considered to have excellent resistance to other solvents as well.

<Adhesion>
The prepared coating composition was applied to an aluminum die-cast substrate so that the dry film thickness was 30 μm, and the applied coating composition was baked under substrate keeping conditions of 120°C x 3 minutes to produce a substrate with a coating film.
Using the prepared substrates with the coating film, adhesion was evaluated according to the cross-cut method (cross-cut interval: 1 mm) of JIS K 5600-5-6:1999 based on the following evaluation criteria. The results are shown in Table 1.
○: When the total area of the squares formed by cross-cutting is taken as 100%, the total area of the peeled parts is less than 10%. △: When the total area of the squares formed by cross-cutting is taken as 100%, the total area of the peeled parts is 10% or more but less than 40%. ×: When the total area of the squares formed by cross-cutting is taken as 100%, the total area of the peeled parts is 40% or more.

Claims (12)

A coating composition containing an alkyd resin (A), a melamine resin (B), and an epoxy resin (C),
the epoxy equivalent of the epoxy resin (C) is 150 or more and 2200 or less;
In the coating composition, the ratio of the number of moles of melamine skeletons (b) to the number of moles of phthalic acid skeletons (a) [(b)/(a)] is 0.87 to 1.52, and
In the coating composition, the ratio of the number of moles (c) of glycidyl skeletons to the number of moles (a) of phthalic acid skeletons [(c)/(a)] is 0.17 to 0.80.
Paint composition. Contains an alkyd resin (A), a melamine resin (B), and an epoxy resin (C),
the epoxy equivalent of the epoxy resin (C) is 150 or more and 2200 or less;
a mass ratio [(MB)/(MA)] of the solid content (MB) of the melamine resin (B) to the solid content (MA) of the alkyd resin (A) is 0.85 to 1.45; and
a mass ratio [(MC)/(MA)] of the solid content (MC) of the epoxy resin (C) to the solid content (MA) of the alkyd resin (A) is 0.30 to 1.35;
Paint composition. 3. The coating composition according to claim 1, further comprising an organic solvent, the content of which is 10% by mass or more and 70% by mass or less. The coating composition according to any one of claims 1 to 3, wherein the epoxy resin (C) is at least one selected from the group consisting of glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, bisphenol type epoxy resins, novolac type epoxy resins, cresol type epoxy resins, dicyclopentadiene type epoxy resins, aliphatic type epoxy resins and alicyclic type epoxy resins other than modified epoxy resins. The coating composition according to any one of claims 1 to 4 , wherein the epoxy resin (C) is a resin having two or more epoxy groups in one molecule. The coating composition according to any one of claims 1 to 5 , further comprising a scaly pigment. The coating composition according to any one of claims 1 to 6 , which is a baking coating composition. The coating composition according to any one of claims 1 to 7 , which is for use on non-ferrous metals. A coating film formed from the coating composition according to any one of claims 1 to 8 . A coated substrate comprising the coating film according to claim 9 and a substrate. The coated substrate of claim 10 , wherein the substrate is a non-ferrous metal substrate. A method for producing a substrate with a coating film, comprising the following steps [1] and [2]:
[1] A step of applying the coating composition according to any one of claims 1 to 8 to a substrate; [2] A step of baking the applied coating composition to form a coating film.