JP7597386B2 - Method for producing powder coating composition, method for forming coating film, and method for matching color - Google Patents

Description

This disclosure relates to a method for producing a powder coating composition, a method for forming a coating film, and a method for mixing colors.

In recent years, awareness of reducing environmental impact has increased, and there has been a demand for replacement with environmentally friendly products. Among these, powder coating compositions are widely used for coating home appliances, automobile parts, steel furniture, etc., because they are environmentally friendly, such as being free of organic solvents and being easy to recover.
Such powder coating compositions are usually prepared by combining a plurality of pigmented powder coating compositions to produce a wide range of hues, and are then applied to an object to be coated using an electrostatic coating gun or the like.

For example, Patent Document 1 describes a color matching method in which two or more types of powder paints of different colors are combined to match a target color, and describes sequentially selecting and combining primary color powder paints suitable for matching the target color from a group of achromatic primary color powder paints and a group of chromatic primary color powder paints.
Patent Document 2 describes a powder coating used in a coating method in which two or more powder coatings having different hues are mixed and applied, and describes that the two or more powder coatings have a mass median particle size of 1 to 50 μm and a mass distribution variation coefficient of 50% or less, and are then toned.
Patent Document 3 describes a powder coating used in a coating method in which two or more powder coatings of different hues are mixed and applied, and describes how the difference in the charge quantity of the two or more powder coatings is set to 5.0 μC/g or less before the colors are mixed.
Patent Document 4 describes a method for matching the color of powder paints, which includes a step of dry-blending two or more different primary color powder paints with an average particle size of 20 μm or less to match the colors, and a step of heating this blend with stirring to a temperature at which the particle surfaces melt but the interiors of the particles do not melt, thereby granulating the blend to a particle size within a range suitable for painting.
Patent Document 5 describes a composite powder coating material obtained by granulating and drying a plurality of primary color powder coating materials differing in hue and/or type of coating film-forming resin using a liquid binder, and describes that the liquid binder is a liquid binder having a softening temperature of 20 to 200°C, in which a binder compound having a self-crosslinking functional group and/or a functional group that reacts complementarily with a functional group possessed by the primary color powder coating material is dissolved or dispersed in a solvent that does not dissolve the raw powder coating material.

JP 2002-155223 A Japanese Patent Application Publication No. 10-219142 Japanese Patent Application Publication No. 10-072557 JP 2000-281978 A International Publication No. 2006/057241

According to conventional color matching methods, powder coating compositions of different hues are mixed to prepare a color-matched powder coating composition (also called a "color-matched powder coating composition"). The color-matched powder coating composition obtained is applied to a substrate using an electrostatic coating gun or the like, and then baked to form a coating film.

However, when a coating film is formed from such a toned powder coating composition, there are problems in that the coating film obtained is not smooth enough to be recognized by the naked eye, and the hue of the coating film obtained is non-uniform. Furthermore, it is necessary to prepare a powder coating composition containing fine powder of the required hue for each required hue, and the assortment of such compositions is enormous. Therefore, it has not been easy to tone powder coating compositions of two or more different hues and obtain a coating film of a smooth and uniform hue from the toned powder coating composition.

The present disclosure has been made in consideration of the above circumstances, and aims to provide a method for producing a powder coating composition that can produce a coating film that exhibits a smooth and uniform hue. Furthermore, the present disclosure also aims to provide a method for forming a coating film using such a powder coating composition, and a method for adjusting the color of the powder coating composition.

The present disclosure includes the following aspects.
[1] preparing two or more primary color powder coating compositions;
A step of mixing a part of the two or more primary color powder coating compositions with a cationic compound (D) selected from a cationic polymer, stearyltrimethylammonium chloride, and cetylpyridinium chloride to obtain a preliminary mixture;
and mixing said premix with the remainder of said two or more primary color powder coating compositions to obtain a powder coating composition.
[2] The method according to [1], wherein the two or more primary color powder coating compositions each have a different hue and/or color tone.
[3] The method according to [1] or [2], wherein the primary color powder coating composition has an average particle size (D50) of 25 μm or less.
[4] The method according to any one of [1] to [3], wherein the cationic compound (D) has an amino group and/or a quaternary ammonium salt group, and the softening point of the cationic compound (D) is 50° C. or higher and 180° C. or lower.
[5] The method according to any one of [1] to [4], wherein the mixing of a part of the two or more primary color powder coating compositions with the cationic compound (D) is carried out in a dry manner.
[6] The method according to any one of [1] to [5], wherein mixing a part of the two or more primary color powder coating compositions with a cationic compound (D) to obtain a pre-mixture is carried out by mixing the cationic compound (D) with water and/or a hydrophilic solvent to obtain a solution of the cationic compound, mixing a part of the primary color powder coating compositions with the solution of the cationic compound to obtain a mixed liquid containing a pre-mixture, and removing water and/or the hydrophilic solvent from the mixed liquid to obtain the pre-mixture.
[7] The method according to any one of [1] to [6], wherein the primary color powder coating composition is prepared by mixing a coating film-forming resin (A) and a colorant (B).
[8] The method according to [7], wherein the coating film-forming resin (A) contains a polymer having at least one functional group selected from an acid group, a hydroxyl group, and an epoxy group.
[9] The method according to [7] or [8], wherein the primary color powder coating composition further contains a curing agent (C).
[10] A method for forming a coating film, comprising applying a powder coating composition obtained by the production method according to any one of [1] to [9] to an object to be coated.
[11] A method for matching a powder coating composition, comprising:
Producing two or more primary color powder coating compositions, each having a different hue and/or shade;
A step of mixing at least a portion of the two or more primary color powder coating compositions with a cationic compound (E) selected from a cationic polymer, stearyltrimethylammonium chloride, and cetylpyridinium chloride to obtain a preliminary mixture;
mixing said premix with the remainder of said two or more primary color powder coating compositions to form a powder coating composition.

According to the present disclosure, it is possible to provide a method for producing a powder coating composition that can produce a coating film that exhibits a smooth and uniform hue. Furthermore, the present disclosure can also provide a method for forming a coating film using such a powder coating composition, and a method for adjusting the color of the powder coating composition.

The method for producing the powder coating composition of the present disclosure includes:
Providing two or more primary color powder coating compositions;
mixing at least one of the two or more primary color powder coating compositions with a cationic compound selected from a cationic polymer, stearyltrimethylammonium chloride, and cetylpyridinium chloride to obtain a preliminary mixture;
mixing said premix with the remainder of said two or more primary color powder coating compositions to obtain a powder coating composition.
Hereinafter, the "cationic compound selected from a cationic polymer, stearyltrimethylammonium chloride, and cetylpyridinium chloride" will be simply referred to as the cationic compound.
In addition, hereinafter, the primary color powder coating composition used to obtain a preliminary mixture by mixing with a cationic compound is also referred to as the "first primary color powder coating composition," and the remainder of the primary color powder coating composition used to obtain a powder coating composition by mixing with the preliminary mixture is also referred to as the "second primary color powder coating composition."
In addition, the process of mixing the first primary color powder coating composition with a cationic compound is also referred to as the "first granulation process", and the process of mixing the pre-mixture with the second primary color powder coating composition is also referred to as the "second granulation process".

According to the manufacturing method of the powder coating composition of the present disclosure, a coating film showing a smooth and uniform hue can be realized. Furthermore, even on a coating object having depth, a coating film having a uniform hue and a uniform gloss can be obtained, and the obtained coating film can have high smoothness. Although the present disclosure should not be interpreted as being limited to a specific theory, the reason why the manufacturing method of the present disclosure exhibits such an effect is considered to be as follows. That is, in the manufacturing method of the present disclosure, one of the primary color powder coating compositions and a cationic compound are mixed in advance to form a preliminary mixture, and another primary color powder coating composition is further mixed into the preliminary mixture. The surface of the primary color powder coating composition mixed with the cationic compound is positively charged, while the surface of the remaining primary color powder coating composition added additionally is negatively charged. Therefore, it is considered that the positively charged particles and the negatively charged particles are electrostatically agglomerated and granulated.

As a result, different particles selectively aggregate with each other, and particles of the same color do not easily aggregate with each other, which contributes to minimizing mottling under various coating conditions, and in addition to the effect of reducing or preventing problems such as surface unevenness and color separation, it is possible to have high color reproducibility, such as cosmetic properties and the reproduction of the required uniform hue, uniform saturation, and uniform brightness. In addition, since the aggregation of the first primary color powder coating composition and the second powder coating composition is electrostatically bonded via the cationic compound, the toning powder coating composition can be easily disintegrated when forming a coating film, and as a result of good coating film formability, a smooth coating film can be formed, and further, it is thought that such a coating film has the desired gloss and has little mottling.

On the other hand, the conventional manufacturing method of the powder coating composition with the adjusted color is mainly a dry blend method in which a plurality of powder coating compositions are mixed at room temperature or under heating, or a bonding method in which a plurality of powder coating compositions are mixed with a binder. However, when the powder coating composition after the color adjustment by the dry blend method is applied using an electrostatic coating gun or the like to form a coating film, the desired hue and gloss may not be obtained due to differences in the properties (shape, particle size, specific gravity, etc.) of each powder coating composition and differences in coating conditions such as the shape of the coated object. In addition, when a coating film is formed from the powder coating composition after the color adjustment by the bonding method, a smooth coating surface may not be formed, possibly because the particles of the powder coating composition are bonded to each other.
The following describes in detail the embodiments of the present invention, but the scope of the present invention is not limited to these embodiments.

(Step of Preparing Primary Color Powder Coating Composition)
In the method for producing a powder coating composition of the present disclosure, first, two or more primary color powder coating compositions are prepared. The primary color powder coating compositions may be any powder coating composition having uniform hue, saturation, and gloss, and are not limited to those containing only one type of film-forming resin (A) and/or one type of colorant (B).

It is preferable that the two or more primary color powder coating compositions each have a different hue and/or color tone. This makes it possible to produce a toned powder coating composition having a different hue or color tone from the primary color powder coating composition. The number of types of primary color powder coating compositions may be two or more, and may be, for example, preferably two or more and ten or less, more preferably two or more and eight or less.

The primary color powder coating composition preferably contains at least a film-forming resin (A), and more preferably contains a film-forming resin (A) and a colorant (B).

(Coating film forming resin (A))
The coating film-forming resin (A) preferably contains a polymer having at least one curable functional group selected from an acid group, a hydroxyl group, and an epoxy group. This makes it easier to form a coating film and improves the color uniformity of the primary color. It is believed that the powder coating composition can be relatively negatively charged and easily interacts with the cationic compound described below. As a result, in the premix, the surface of the first powder coating composition is relatively The first powder coating composition can be positively charged and can easily interact with the second powder coating composition on a particle-by-particle basis, so that the resulting color-matching powder coating composition can form a coating film that exhibits a smoother and more uniform hue. The acid group includes a carboxy group, a sulfonic acid group, and a phosphoric acid group, and the carboxy group is preferred.

The film-forming resin (A) is a film-forming component, and may be, for example, a non-reactive resin such as polyolefin resin (polyethylene, polypropylene, etc.), polyamide resin (nylon resin, etc.), or vinyl chloride resin; or a reactive resin such as epoxy resin, amine resin, acid anhydride resin, polyester resin, melamine resin, acrylic resin, polyester resin/epoxy resin, or polybasic acid resin. The film-forming resin (A) preferably contains one or more types selected from acrylic resin, epoxy resin, and polyester resin. For example, from the viewpoint of weather resistance, acrylic resin, or polyester resin may be used, and from the viewpoint of physical performance of the coating film, polyester resin may be used. More specifically, for example, it may be one or more types selected from the group consisting of polyester resin having a curable functional group, epoxy resin having a curable functional group, and acrylic resin having a curable functional group.

The acrylic resin may be a polymer of a monomer mixture containing a (meth)acrylic monomer. The monomer mixture preferably contains a monomer having a functional group capable of reacting with the curing agent (C) described below, and preferably contains a monomer having a functional group capable of reacting with the curing agent (C) and another vinyl monomer copolymerizable with the monomer.

The monomer containing a functional group capable of reacting with the curing agent (C) may be a monomer containing one or more groups selected from an epoxy group, an acid group, and a hydroxyl group, and preferably a monomer containing one or more groups selected from an epoxy group, a carboxy group, and a hydroxyl group.

The monomer having an epoxy group includes glycidyl (meth)acrylate.
The monomer having a carboxy group includes (meth)acrylic acid.
Examples of the monomer having a hydroxyl group include hydroxyl group-containing (meth)acrylic esters such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 2-hydroxy-2-methylpropyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate; addition reaction products of the hydroxyl group-containing (meth)acrylic esters with ε-caprolactone, etc. The monomer having a functional group can be used alone or in combination of two or more.
In the present disclosure, (meth)acrylic acid means acrylic acid and/or methacrylic acid.

Other vinyl monomers copolymerizable with the monomer having the functional group include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, n-, iso-, and tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; and aromatic vinyl monomers such as styrene, α-methylstyrene, and vinyltoluene. These vinyl monomers can be used alone or in combination of two or more.

The content of the acrylic resin contained in the film-forming resin (A) may be preferably 30 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the film-forming resin (A).

As the epoxy resin, an epoxy resin having an average of one or more epoxy groups per molecule is preferred, and specific examples include bisphenol type epoxy resins (A type, B type, F type, etc.); novolac type phenolic resins such as phenol novolac type epoxy resins and cresol novolac type epoxy resins; reaction products of phenol novolac or o-cresol novolac with bisphenol type epoxy resins (A type, B type, F type, etc.) and epichlorohydrin; reaction products of phenol novolac or o-cresol novolac with bisphenol type epoxy resins (A type, B type, F type, etc.). These epoxy resins can be used alone or in combination of two or more types.

The content of the epoxy resin contained in the film-forming resin (A) may be preferably 30 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the film-forming resin (A).

The polyester resin can be a condensation polymer of an acid component mainly composed of a polycarboxylic acid and an alcohol component mainly composed of a polyhydric alcohol.

Examples of the acid component include terephthalic acid, isophthalic acid, phthalic acid, trimellitic acid, pyromellitic acid, and their anhydrides; aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid, and their anhydrides; saturated aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid, and their anhydrides; lactones such as γ-butyrolactone and ε-caprolactone; aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid; and corresponding hydroxycarboxylic acids. Of these, terephthalic acid and isophthalic acid are preferred. From the viewpoint of weather resistance, the content of isophthalic acid in the acid component is preferably 60% by mass or more, and more preferably 80% by mass or more. The acid components can be used alone or in combination of two or more.

Alcohol components include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, 1,12-dodecanediol, 1,8-octadecanediol, Examples of the alcohol components include ethanol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, alkylene oxide adducts of bisphenol A, alkylene oxide adducts of bisphenol S, linear or branched glycols such as neopentyl glycol, trimethylolpropane, glycerin, pentaerythritol, and other polyhydric alcohols having three or more valences, and among these, ethylene glycol, neopentyl glycol, and 1,6-hexanediol are preferred. The alcohol components can be used alone or in combination of two or more.

In one embodiment, the film-forming resin (A) may contain one polyester resin, and in another embodiment, it may contain two or more polyester resins. When the film-forming resin (A) contains two or more polyester resins, the mass ratio of the content of the first polyester resin to the content of the second polyester resin may be 3/7 to 7/3.

The content of polyester resin contained in the film-forming resin (A) may be preferably 30 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the film-forming resin (A).

In the primary color powder coating composition, the film-forming resin (A) may be used alone or in combination of two or more. In one embodiment, the film-forming resin (A) may contain a polyester resin and an epoxy resin. In such an embodiment, the mass ratio of the polyester resin to the epoxy resin may be 3/7 to 7/3.

The acid value of the film-forming resin (A) may be preferably 10 mgKOH/g or more and 500 mgKOH/g or less, more preferably 20 mgKOH/g or more and 400 mgKOH/g or less, and even more preferably 25 mgKOH/g or more and 300 mgKOH/g or less. In one embodiment, the acid value of the film-forming resin (A) may be preferably 300 mgKOH/g or more.
The hydroxyl value of the film-forming resin (A) may be preferably 5 mgKOH/g or more and 200 mgKOH/g or less, more preferably 10 mgKOH/g or more and 150 mgKOH/g or less, and even more preferably 15 mgKOH/g or more and 100 mgKOH/g or less. In one embodiment, the hydroxyl value of the film-forming resin (A) may be preferably 40 mgKOH/g or more, more preferably 60 mgKOH/g or more.
The epoxy equivalent of the film-forming resin (A) may be preferably 250 g/mol or more and 600 g/mol or less, more preferably 350 g/mol or more and 500 g/mol or less.
In the present disclosure, the acid value and hydroxyl value of a resin refer to the acid value of the solid content and the hydroxyl value of the solid content, respectively, and can be measured in accordance with JIS K 0070.
In the present disclosure, the epoxy equivalent can be measured by the hydrochloric acid-pyridine method.
When the coating film-forming resin (A) contains two or more resins, the acid value, hydroxyl value and epoxy equivalent may be the average value of the acid value, hydroxyl value and epoxy equivalent of each resin.

By having the acid value, hydroxyl value or epoxy equivalent of the film-forming resin (A) within the above range, it is believed that the surface of the primary color powder coating composition can be appropriately negatively charged, making it easier to mix the first powder coating composition and the second powder coating composition more uniformly and to adjust the color and granulate the composition.
The acid value, hydroxyl value or epoxy equivalent of the film-forming resin (A) contained in the first primary color powder coating composition and the acid value, hydroxyl value or epoxy equivalent of the film-forming resin (A) contained in the second primary color powder coating composition may be the same or different.

The weight average molecular weight of the coating film-forming resin (A) may be preferably 5,000 to 500,000, more preferably 5,000 to 100,000, and even more preferably 10,000 to 50,000. In one embodiment, the weight average molecular weight of the resin having an epoxy group may be preferably 5,000 to 100,000, and more preferably 10,000 to 50,000.
In the present disclosure, the weight average molecular weight is a polystyrene equivalent value determined by gel permeation chromatography.

The softening point of the film-forming resin (A) may be, for example, 80°C or higher and 130°C or lower, and is preferably 90°C or higher and 120°C or lower. Being within the above range has the advantage that the pigment dispersibility during the production of the powder coating composition is good, and the storage stability of the resulting powder coating composition is good. In this disclosure, the softening point means the Vicat softening temperature measured in accordance with JIS K 7206, with a test load of 10 N and a heating rate of 50°C/hour.

The content of the film-forming resin (A) contained in the primary color powder coating composition is preferably 40 parts by mass or more and 70 parts by mass or less, more preferably 45 parts by mass or more and 70 parts by mass or less, per 100 parts by mass of the primary color powder coating composition. When the content of the film-forming resin (A) in the primary color powder coating composition is within the above range, various physical properties such as adhesion to the substrate and water resistance are good, and a coating film of the desired hue and brightness can be obtained.
In two or more primary color powder coating compositions, the compositions of the film-forming resins (A) contained therein (types, amounts, and ratios when two or more types of film-forming resins (A) are contained) may be the same or different.

(Color Pigment (B))
As the colorant (B), inorganic or organic pigments that are usually used in powder coatings can be used. The colorant (B) can be appropriately selected depending on the hue, brightness, etc. of the coating film. For example, the hue of the coating film can be controlled by using a chromatic pigment, and the brightness and saturation of the coating film can be controlled by using an achromatic pigment. Furthermore, the gloss of the coating film can be controlled by the particle size and content of the colorant (B).

Examples of chromatic inorganic pigments include red iron oxide, chrome titanium yellow, and yellow iron oxide, while examples of achromatic inorganic pigments include titanium oxide and carbon black. Examples of chromatic organic pigments include azo, perylene, condensed azo, nitro, nitroso, phthalocyanine, anthraquinone, quinacridone, and dioxane pigments. Specifically, examples of azo pigments include lake red, fast yellow, disazo yellow, and permanent red, examples of nitro pigments include naphthol yellow, etc., examples of nitroso pigments include pigment green B and naphthol green, examples of phthalocyanine pigments include phthalocyanine blue and phthalocyanine green, examples of anthraquinone pigments include indanthrene blue and dianthraquinonyl red, etc., examples of quinacridone pigments include quinacridone red and quinacridone violet, and examples of dioxane pigments include carbazole dioxazine violet.

In the primary color powder coating composition, the content of the colorant (B) may be preferably 0.05 parts by mass or more and 75 parts by mass or less, more preferably 0.1 parts by mass or more and 70 parts by mass or less, relative to 100 parts by mass of the coating film-forming resin (A). In one embodiment, it may be, for example, 1 part by mass or more and 70 parts by mass or less, and further 3 parts by mass or more and 70 parts by mass or less.
In the primary color powder coating composition, the content of the colorant (B) may vary depending on the type of the colorant (B). For example, the content of the inorganic colorant (B) may be 0.05 parts by mass or more and 75 parts by mass or less, 10 parts by mass or more and 70 parts by mass or less, or even 15 parts by mass or more and 70 parts by mass or less, relative to 100 parts by mass of the coating film-forming resin (A), and the content of the organic colorant (B) may be 0.05 parts by mass or more and 20 parts by mass or less, or even 0.05 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the coating film-forming resin (A).
In the powder coating composition containing two or more primary colors, the composition of the colorant (B) contained therein (type, amount, and ratio when two or more types of colorant (B) are contained) may be the same or different.

(Curing Agent (C))
The primary color powder coating composition of the present invention may contain a curing agent (C) as necessary. In this embodiment, the primary color powder coating composition is produced by mixing the film-forming resin (A), the colorant (B) and the curing agent (C). The order of mixing is not particularly limited, and the film-forming resin (A), the colorant (B) and the curing agent (C) may be mixed simultaneously, or the film-forming resin (A) and the colorant (B) may be mixed in advance, and then the mixture may be further mixed with the curing agent (C).

The curing agent (C) is not particularly limited and may be a known curing agent (C) used in powder coatings. Examples of the curing agent (C) include polycarboxylic acid compounds, acid anhydrides, amino group-containing compounds, epoxy group-containing compounds, β-hydroxyalkylamide compounds (HAA), blocked isocyanate compounds, and amino resins.
In one embodiment, when the coating film-forming resin (A) contains a polymer having an epoxy group, the curing agent (C) is preferably one or more selected from polyvalent carboxylic acid compounds, acid anhydrides, and amino group-containing compounds.
In another embodiment, when the coating film-forming resin (A) contains a polymer having an acid group, the curing agent (C) is preferably one or more selected from epoxy group-containing compounds and β-hydroxyalkylamide compounds.
In yet another embodiment, when the coating film-forming resin (A) contains a polymer having a hydroxyl group, the curing agent (C) is preferably a blocked isocyanate compound or an amino resin.

When considering matte properties, it is preferable that the primary color powder coating composition (B) contains, for example, at least one selected from the group consisting of β-hydroxyalkylamide compounds, blocked isocyanates, and melamine compounds.

Examples of the polycarboxylic acid compound include aliphatic polycarboxylic acids such as adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, hexadecanedicarboxylic acid, eicosanedicarboxylic acid, and tetraeicosanedicarboxylic acid; aromatic polycarboxylic acids such as isophthalic acid and trimellitic acid; and alicyclic polycarboxylic acids such as hexahydrophthalic acid and tetrahydrophthalic acid. Among these, decanedicarboxylic acid is preferred. These can be used alone or in combination of two or more.

Examples of the acid anhydride include the following aliphatic, alicyclic, and aromatic acid anhydrides.
Examples of the aliphatic acid anhydride include succinic anhydride, maleic anhydride, citraconic anhydride, polyadipic anhydride, polyazelaic anhydride, polysebacic anhydride; dodecenyl succinic anhydride, which is liquid at room temperature, poly(ethyloctadecanedioic) anhydride, and poly(phenylhexadecanedioic) anhydride.
Examples of the alicyclic acid anhydride include hexahydrophthalic anhydride, tetrahydrophthalic anhydride, methylcyclohexene dicarboxylic anhydride, HET acid anhydride, himic anhydride, methylcyclohexene tricarboxylic anhydride; and methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl himic anhydride, which are liquid at room temperature.
Examples of aromatic acid anhydrides include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, tetrabromophthalic anhydride, tetrachlorophthalic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bis(anhydrotrimellitate), and glycerol tris(anhydrotrimellitate).

Examples of the amino group-containing compound include dicyandiamide, polyamine compounds, imidazole, etc. Examples of the polyamine compound include polyhydrazide compounds such as adipic acid dihydrazide and sebacic acid dihydrazide. Examples of the imidazole include imidazole compounds containing an alkyl group or a substituted alkyl group as a substituent, such as 2-methylimidazole, 2-ethylimidazole, 2-heptadecylimidazole, 1-benzyl-2-methylimidazole, and 1-(2-cyanoethyl)-2-undecylimidazole; imidazole compounds containing an aminotriazine ring, such as 1-[2-(4,6-diamino-1,3,5-triazin-2-yl)ethyl]-2-methylimidazole and 1-[2-(4,6-diamino-1,3,5-triazin-2-yl)ethyl]-2-ethyl-4-methylimidazole; and salts of imidazole and carboxylic acid, such as a salt of 1-cyanoethyl-2-ethyl-4-methylimidazole and trimellitic acid or a salt of 1-cyanoethyl-2-methylimidazole and trimellitic acid.
The curing rate of the polyvalent carboxylic acid compound, the acid anhydride, and the amino group-containing compound can be adjusted by using them in combination with a known curing accelerator. The curing accelerator is not particularly limited, but examples thereof include tertiary amines such as triethylamine and benzyldimethylamine, imidazoles such as 2-methylimidazole and 2-ethyl-4-methylimidazole, and imidazoline compounds which are precursors thereof, quaternary ammonium salts such as tetramethylammonium bromide and benzyltrimethylammonium bromide, phosphines such as triphenylphosphine and n-butyltriphenyl, and phosphonium salts.

The epoxy group-containing compound is a compound having one or more epoxy groups in one molecule, and examples thereof include triglycidyl isocyanurate, the epoxy resins, and epoxy group-containing acrylic resins.

The β-hydroxyalkylamide compound (HAA) may be a compound represented by the following formula (I):

(wherein R ¹ represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and R ² represents an alkylene group having 1 to 12 carbon atoms).
An example of such a compound that is commercially available is Primid XL-552.

The blocked isocyanate compound refers to blocked isocyanates in which the isocyanate groups are blocked with a blocking agent to prevent them from exhibiting activity at or below a certain temperature, and uretdiones in which isocyanate groups are reacted with each other to form uretdione rings to prevent them from exhibiting activity.
The blocked isocyanate compound is a polyisocyanate compound in which the isocyanate group is blocked with a blocking agent.

Examples of polyisocyanate compounds include aliphatic diisocyanate compounds such as hexamethylene diisocyanate, trimethylene diisocyanate, 1,4-tetramethylene diisocyanate, pentamethylene diisocyanate, lysine diisocyanate, and 1,3-butylene diisocyanate; alicyclic diisocyanate compounds such as isophorone diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methylcyclohexane-2,4-(or -2,6-) diisocyanate, 1,3-(or 1,4-)di(isocyanatomethyl)cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, and 1,2-cyclohexane diisocyanate; xylylene diisocyanate, metaxylylene diisocyanate, tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4' -Aromatic diisocyanate compounds such as diphenylmethane diisocyanate and (m- or p-)phenylene diisocyanate; polyisocyanate compounds having three or more isocyanate groups such as triphenylmethane-4,4',4"-triisocyanate; adducts obtained by reacting a polyisocyanate compound in an amount such that the isocyanate groups are in excess with respect to the hydroxyl groups of a polyol such as ethylene glycol, propylene glycol, 1,4-butylene glycol, polyalkylene glycol, trimethylolpropane, or hexanetriol; biuret-type adducts and isocyanuric ring-type adducts such as hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and 4,4'-methylenebis(cyclohexylisocyanate), etc.

Examples of blocking agents used to block polyisocyanate compounds include phenol-based, lactam-based, oxime-based, pyrazole-based, and triazole-based blocking agents. Specific examples of these blocking agents include phenol-based blocking agents such as phenol, cresol, xylenol, nitrophenol, chlorophenol, ethylphenol, hydroxydiphenyl, t -butylphenol, methyl hydroxybenzoate, etc.; lactam blocking agents include ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propiolactam, etc.; oxime blocking agents include acetamide oxime, formamide oxime, acetone oxime, methyl ethyl ketone oxime, butanone oxime, methyl isobutyl ketone oxime, methyl amyl ketone oxime, diacetyl monooxime, benzophenone oxime, cyclohexanone oxime, methyl hexanone oxime, etc.; pyrazole blocking agents include 1,2-pyrazole, 3,5-dimethylpyrazole, etc.; triazole blocking agents include 1H-1,2,4-triazole, 1H-1,2,3-triazole, 1H-1,2,4-triazole-3-thiol, 1H-1,2,3-triazolo[4,5-b]pyridine, etc.

Examples of the amino resin include melamine resin, urea resin, and benzoguanamine resin. The amino resin is obtained by condensing an amino compound with an aldehyde compound and then etherifying the resulting mixture with a lower monohydric alcohol. Examples of the amino resin include melamine, urea, and benzoguanamine. Examples of the aldehyde compound include formaldehyde and acetaldehyde. Examples of the lower monohydric alcohol include methanol, ethanol, propanol, and butanol.

The curing agent (C) may contain other curing agents (C). Examples of such curing agents (C) include polyisocyanate compounds such as tris(2,3-epoxypropyl)isocyanate, tolylene diisocyanate, and xylylene diisocyanate, or blocked isocyanate groups at the molecular terminals of prepolymers thereof with conventional blocking agents such as lactam compounds and oxime compounds; epoxy curing agents such as bisphenol A diglycidyl ether; alkoxysilane curing agents such as methoxysiloxane oligomers and ethoxysilane oligomers; polyaziridine curing agents such as adipic acid dihydrazide and succinic acid dihydrazide; and oxazoline curing agents such as 1,4-bis(2-oxazolinyl-2)-benzene and 1,2,4-tris(2-oxazolinyl-2)-benzene.

In one embodiment, the primary color powder coating composition may contain a polyester or acrylic resin having a hydroxyl group as the film-forming resin (A) and a blocked isocyanate blocked with at least one blocking agent selected from the group consisting of oxime-based, pyrazole-based, and triazole-based blocking agents as the curing agent (C).

In this embodiment, the average hydroxyl value of the hydroxyl-containing polyester or acrylic resin is preferably 40 mgKOH/g or more, and more preferably 60 mgKOH/g or more, from the viewpoint of the matting effect.
The blocked isocyanate is preferably a blocked isocyanate blocked with at least one blocking agent selected from the group consisting of methyl isobutyl ketone oxime, methyl ethyl ketone oxime, 1,2-pyrazole, 3,5-dimethylpyrazole, 1H-1,2,4-triazole, 1H-1,2,3-triazole, 1H-1,2,4-triazole-3-thiol, and 1H-1,2,3-triazolo[4,5-b]pyridine. In order to obtain a sufficient matte effect, the blocked isocyanate preferably has a dissociation temperature of the blocking agent or uretdione ring of 160° C. or less, more preferably 140° C. or less.

The amount of the curing agent (C) in the primary color powder coating composition varies depending on the types of the coating film-forming resin (A) and the curing agent (C), and can be appropriately set. For example, the amount of the curing agent (C) is preferably 1 part by mass or more and 200 parts by mass or less, more preferably 5 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the coating film-forming resin (A).
In one embodiment, when a film-forming resin (A) having a hydroxyl group is used as the film-forming resin (A) of the primary color powder coating composition, it is preferable to use the blocked isocyanate as the curing agent (B), and the content of the blocked isocyanate may be preferably 10 parts by mass or more and 80 parts by mass or less, more preferably 15 parts by mass or more and 60 parts by mass or less, per 100 parts by mass of the film-forming resin (A) having a hydroxyl group.

In addition, the curing agent (C) in the present disclosure is preferably used in an amount such that the equivalent ratio (hereinafter also referred to as the "equivalent ratio of reactive groups") between the total of the acid groups, hydroxyl groups, and epoxy groups contained in the coating film-forming resin (A) and the total of the groups capable of reacting with the acid groups, hydroxyl groups, and epoxy groups (e.g., acid groups, hydroxyl groups, amino groups, and isocyanate groups) contained in the curing agent (C) is, for example, preferably 0.1 or more and 3 or less, more preferably 0.8 or more and 1.2 or less.

In one embodiment, the primary color powder coating composition may contain a resin having a hydroxyl group and a resin having an epoxy group as the coating film-forming resin (A), and may contain a carboxyl group-containing compound and a blocked isocyanate as the curing agent (C). By using such a primary color powder coating composition, a higher matte effect can be obtained and popping and show-through can be prevented.
Here, "popping" refers to a coating abnormality formed by foaming on the surface or inside of the coating film when applying the powder coating composition, and "see-through" refers to a situation in which the surface of the coated object is not sufficiently concealed by the coating film, allowing the surface of the coated object to be seen through the coating film.

In the same embodiment, the resin having an epoxy group may be an acrylic resin having an epoxy group and/or an epoxy resin, and from the viewpoint of the matte effect, it is preferable that the resin has an epoxy group.

In the same embodiment, the blocked isocyanate may be any of the blocked isocyanates described above, and preferably includes a blocked isocyanate blocked with ε-caprolactam. The content of the blocked isocyanate blocked with ε-caprolactam may be preferably 20% by mass or more, more preferably 50% by mass or more, based on 100% by mass of the total amount of the blocked isocyanates. When the content is within the above range, foaming can be suppressed.
The content of the blocked isocyanate is preferably 15 parts by mass or more and 60 parts by mass or less, more preferably 20 parts by mass or more and 60 parts by mass or less, relative to 100 parts by mass of the total amount of the resin having a hydroxyl group, the resin having an epoxy group, and the carboxy group-containing compound. When the content of the blocked isocyanate is within the above range, a good matting effect is obtained, and foaming on the surface or inside of the coating film can be suppressed.

Furthermore, in the same embodiment, the molar ratio of epoxy groups to carboxy groups (epoxy groups/carboxy groups) contained in the primary color powder coating composition may be preferably 0.5 to 2.0, more preferably 0.8 to 1.2. When the ratio is within the above range, the resulting coating film may have good matte properties and water resistance.
In two or more primary color powder coating compositions, the composition of the curing agent (C) that may be contained (type, amount, and ratio when two or more types of curing agent (C) are contained) may be the same or different.

In the same embodiment, the combination of the film-forming resin (A) and the curing agent (C) is preferably such that the film-forming resin (A) contains a polyester resin having a hydroxyl group and/or an acrylic resin having a hydroxyl group, and the curing agent (C) contains a blocked isocyanate blocked with at least one blocking agent selected from the group consisting of oxime-based, pyrazole-based and triazole-based blocking agents; or the film-forming resin (A) contains a resin having a hydroxyl group and a resin having an epoxy group, and the curing agent (C) contains a carboxyl group-containing compound and a blocked isocyanate. In the above two combinations, the molar ratio of the hydroxyl group and the blocked isocyanate contained in the film-forming resin (A) (hydroxyl group/blocked isocyanate) is preferably 0.5 to 2.0, more preferably 0.8 to 1.2. When the ratio is within the above range, the matte effect and physical properties of the resulting coating film are good.

(Curing catalyst)
The primary color powder coating composition may further contain a curing catalyst. By containing the curing catalyst, it is easy to adjust the gel time (the time until the coating film is cured). Examples of the curing catalyst include tin-based catalysts, imidazole compounds, imidazoline compounds, metal complexes of imidazole compounds and/or imidazoline compounds, tertiary phosphine compounds, quaternary phosphonium salts, and quaternary ammonium salts.

Examples of the tin catalyst include dibutyltin dilaurate, dibutyltin distearate, tin bis(2-ethylhexanoate), n-butyltris(2-ethylhexanoate), di-n-butylbis(2-ethylhexanoate), di-n-butylbis(2,4-pentanedionate), dioctyldilauryltin, tetra-n-butyltin, tetra-n-octyltin, dibutyltin diacetate, tetrabutyldiacetoxydistannoxane, tin acetylacetone, dibutyltin oxide, and dimethyltin oxide.

The imidazole compound is not particularly limited, but examples thereof include alkyl imidazoles such as 2-ethyl-4-methylimidazole, 1-methylimidazole, 1,2-dimethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, and 2-isopropylimidazole; carbamyl alkyl-substituted imidazoles such as 1-(2-carbamylethyl)imidazole; and 1-cyanoethyl-2-methylimidazole. Examples of the imidazoles include cyanoalkyl-substituted imidazoles such as 2-phenylimidazole, 2-phenyl-4-methylimidazole, aromatic-substituted imidazoles such as 1-benzyl-2-methylimidazole, alkenyl-substituted imidazoles such as 1-vinyl-2-methylimidazole, allyl-substituted imidazoles such as 1-allyl-2-ethyl-4-methylimidazole, and polyimidazoles, but preferred are alkylimidazoles and aromatic-substituted imidazoles.

The imidazoline compound is not particularly limited, but examples thereof include 2-phenylimidazole, 2-methylimidazoline, 2-undecylimidazoline, and 2-heptadecylimidazoline.

The metal complex of the imidazole compound and/or the imidazoline compound can be, for example, a complex of the imidazole compound or the imidazoline compound with a metal salt. Such metal salts are not particularly limited, but examples thereof include those composed of metals such as copper, nickel, cobalt, calcium, zinc, zirconium, silver, chromium, manganese, tin, iron, titanium, antimony, and aluminum, and salts such as chloride, bromide, fluoride, sulfate, nitrate, acetate, malate, stearate, benzoate, and methacrylate.

The tertiary phosphine compound is not particularly limited, but examples thereof include triphenylphosphine, tritolylphosphine, etc.

The quaternary phosphonium salt is not particularly limited, but examples thereof include benzyltriphenylphosphonium chloride, butyltriphenylphosphonium bromide, ethyltriphenylphosphonium iodide, and ethyltriphenylphosphonium bromide.

The quaternary ammonium salt is not particularly limited, but examples thereof include tetraethylammonium chloride, tetraethylammonium bromide, and benzyltrimethylammonium bromide.

The curing catalyst may be, for example, 0.0001 parts by mass or more and 10 parts by mass or less per 100 parts by mass of each primary color powder coating composition. By keeping the curing catalyst content within the above range, the gel time of the resulting powder coating composition can be adjusted to a desired range.

(Other additives)
The primary color powder coating composition may further contain other additives. As other additives, additives commonly used in the field of powder coatings can be used, such as heat stabilizers, light stabilizers, slip agents, lubricants, plasticizers, antistatic agents, crystal nucleating agents, flow agents such as acrylate polymers, crosslinking accelerators such as various catalysts and organic tin compounds, pinhole inhibitors such as benzoin, extender pigments, modifiers, surface conditioners, ultraviolet absorbers, antioxidants, and popping inhibitors. When these additives are contained, the amount of each can be 0.1 parts by mass or more and 5 parts by mass relative to 100 parts by mass of the coating film-forming resin (A).

By including the above-mentioned extender pigment, it is possible to easily adjust the specific gravity of the primary color powder coating composition, and also to improve the mechanical properties of the resulting coating film. Examples of extender pigments include talc, silica, calcium carbonate, barium sulfate, etc.

The modifier may be a resin different from the film-forming resin (A), and examples of such resins include polyester resin, polyethylene resin, modified polyethylene resin, epoxy resin, ethylene vinyl acetate resin, ethylene ethyl acrylate resin, ethylene acrylic acid resin, and nylon. Among these, thermoplastic resins such as polyethylene resin, modified polyethylene resin, and ethylene acrylic acid resin, which have a relatively low softening point, are preferred. The content of the modifier may be preferably 0.1 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the film-forming resin (A).

The surface modifier can adhere to the surface of the powder coating and control the fluidity and chargeability of the powder coating. Examples of the surface modifier include inorganic fine particles such as silica and aluminum oxide (alumina); and organic particles such as acrylic resin. The particle diameter of such a surface modifier can be, for example, 1 μm or more and 50 μm or less. The content of the surface modifier can be, for example, 0.01 parts by mass or more and 5 parts by mass or less in 100 parts by mass of each primary color powder coating composition. In the manufacturing method disclosed herein, the surface modifier is not essential, and even if a surface modifier is not added, a powder coating composition capable of realizing a coating film showing a smooth and uniform hue can be manufactured.

The average particle diameter (D50) of the primary color powder coating composition may be preferably 1 μm or more and 25 μm or less, more preferably 5 μm or more and 23 μm or less, and even more preferably 5 μm or more and 20 μm or less. When the average particle diameter (D50) of the primary color powder coating composition is within the above range, it becomes easier to obtain a coating film that shows a smoother and more uniform hue.

In this disclosure, unless otherwise specified, the average particle size refers to the volume average particle size (D50). The volume average particle size (D50) can be measured using a particle size measuring device such as a laser diffraction/scattering type particle size distribution measuring device (Microtrack, manufactured by Nikkiso Co., Ltd.).

(Preparation of Primary Color Powder Coating Composition)
The primary color powder coating composition may be prepared by purchasing a commercial product, or may be prepared by manufacturing. The primary color powder coating composition may be manufactured by a known method. For example, the primary color powder coating composition may be manufactured by a manufacturing method including mixing the coating film-forming resin (A) with the colorant (B), curing agent (C), curing catalyst, and other additives used as necessary (mixing step), melt-kneading the obtained mixture (melting kneading step), and cooling the obtained melt-kneaded product (cooling step) and pulverizing (pulverizing step), and the manufacturing method may further include classifying the obtained pulverized product.

The order of mixing the film-forming resin (A), the colorant (B), the curing agent (C), the curing catalyst, and other additives, which are used as necessary, is not particularly limited. In one embodiment, the film-forming resin (A) and the colorant are mixed with the curing catalyst and other additives, and then the mixture is further mixed with the curing agent (C), but is not limited thereto.
The mixing can be carried out using a super mixer, a ribbon blender, a drum blender, a Henschel mixer, etc. The mixing is preferably carried out at room temperature, for example, at 10 to 40°C, preferably 15 to 35°C.

The melt kneading can be carried out using a kneader such as a kneader or an extruder. The heating temperature during melt kneading is lower than the bake hardening temperature, and is preferably a temperature at which at least a part of the raw materials can be melted and the entire raw materials can be kneaded, generally about 80 to 140° C. In one embodiment, the kneading is carried out at a temperature of 80 to 120° C.
In the present invention, when melt kneading is performed, the kneading temperature is higher than the granulation temperature in the granulation step described below, for example, higher than the softening point of the film-forming resin (A) having the highest softening point among the film-forming resins (A) contained in the primary color powder coating composition.

The molten mixture can be cooled, for example, with a cooling roll, a cooling conveyor, or the like. The resulting solidified material can be pulverized in one step or in two or more steps. For example, coarse pulverization can be followed by fine pulverization. The pulverization can be carried out using a pulverizing device such as a hammer mill or a jet impact mill.

By the classification, large particles and small particles can be removed, and the particle size distribution can be narrowed. For example, an air classifier, a vibrating sieve, an ultrasonic sieve, etc. can be used for classification. By the classification, the average particle size of the obtained particles can be adjusted to 15 to 30 μm.

(First granulation process)
Next, a part of the two or more primary color powder coating compositions is mixed with a cationic compound (D) to obtain a preliminary mixture, whereby the surface of a part of the primary color powder coating compositions (first primary color powder coating composition) can be positively charged.

The part of the two or more primary color powder coating compositions means a part of two or more portions of the two or more primary color powder coating compositions to be mixed, and may be a part or all of one type of primary color powder coating composition, or may include two or more primary color powder coating compositions. In a preferred embodiment, the part of the two or more primary color powder coating compositions may be a part or all of one type of primary color powder coating composition.

(Cationic Compound (D))
In the present disclosure, the cationic compound (D) refers to a cationic polymer containing an amine base or a quaternary ammonium base, stearyltrimethylammonium chloride, or cetylpyridinium chloride .

Examples of compounds that can be used as the cationic polymer include polyamidepolyamine-epichlorohydrin condensates, condensates of amines and epichlorohydrin, polyallylamine hydrochloride, polyethyleneimine, polyamidine, naturally occurring cationic polymers (cationized products of chitin, chitosan, starch, or cellulose), polymers and copolymers of acrylates, methacrylates, acrylamides, and the like having a quaternary ammonium base, polymers and copolymers of diallyldimethylammonium chloride, and poly(vinylbenzyltrimethylammonium chloride).

The weight average molecular weight of the cationic polymer may be preferably from 100 to 10,000, more preferably from 200 to 6,000, and even more preferably from 300 to 3,000. When the number average molecular weight of the cationic polymer is within the above range, the cationic polymer can be mixed more uniformly with the first primary color powder coating composition, the hue of the resulting coating film can be made more uniform, and the occurrence of mottled patterns can be further suppressed.

The amine value of the cationic polymer is more than 0 mgKOH/g, preferably 1 mgKOH/g to 900 mgKOH/g, more preferably 20 mgKOH/g to 700 mgKOH/g. When the amine value of the cationic polymer is in the above range, the cationic polymer can be mixed more uniformly with the first primary color powder coating composition, the hue of the resulting coating film can be made more uniform, and the occurrence of mottled patterns can be further suppressed.
In the present disclosure, the amine value can be measured in accordance with JIS K 7237.

The cationic polymer is preferably in a solid state at room temperature (25°C). When the cationic polymer is in a solid state at room temperature, blocking can be suppressed when storing the obtained color-matching powder coating composition. The softening point of the cationic polymer can be preferably 30°C or more and 180°C or less, more preferably 50°C or more and 170°C or less, and even more preferably 80°C or more and 160°C or less. When the softening point of the cationic polymer is in the above range, the cationic polymer and the first primary color powder coating composition can be mixed more uniformly, the hue of the obtained coating film can be made more uniform, and the occurrence of mottled patterns can be further suppressed. In addition, there is also an advantage that the smoothness of the obtained coating film can be further improved. In addition, when the first primary color powder coating composition and the cationic compound (D) are mixed, there is usually no change in the hue or saturation of the first primary color powder coating composition.

The content of the cationic compound (D) may be preferably 0.01 to 2 parts by mass, more preferably 0.02 to 1 part by mass, and even more preferably 0.03 to 0.5 parts by mass, relative to a total of 100 parts by mass of the primary color powder coating compositions (first primary color powder coating composition and second primary color powder coating composition) used in the preparation of the toned powder coating composition. By using the amount of the cationic compound (D) within the above range, the charge on the particle surface of the first primary color powder coating composition can be made appropriately positive, the hue of the resulting coating film can be made more uniform, and the occurrence of mottled patterns can be further suppressed.

The mixing of the first primary color powder coating composition and the cationic compound (D) is not particularly limited and can be carried out by a dry or wet method.

In one embodiment, when the mixing is performed dry, the solid cationic compound (D) may be added while mixing the first primary color powder coating composition.

In another embodiment, when the mixing is performed in a wet manner, the cationic compound (D) is dissolved in a solvent in advance to prepare a cationic compound solution. The cationic compound solution may then be added while mixing the first primary color powder coating composition. In such an embodiment, it is preferable to remove the solvent after mixing the first primary color powder coating composition and the cationic compound solution. Therefore, in order to remove the solvent, the mixing may be continued until the solvent evaporates and the entire mixture is powdered. In addition, the mixture of the first primary color powder coating composition and the cationic compound solution may be subjected to a decompression treatment (preferably vacuum suction) to remove the solvent. The solvent used to prepare the cationic compound solution is not particularly limited, and examples thereof include alcohol solvents such as methanol, ethanol, isopropyl alcohol, and butanol; water; and a mixture of water and an alcohol solvent.

The mixing can be carried out using a mixer such as a super mixer, ribbon blender, drum blender, or Henschel mixer. When using a rotary mixer, the rotation speed may be 3 to 2,000 rpm.

The mixing step is preferably carried out at a temperature in the range of -5 to 50°C. Within this range, the primary color powder coating composition can be mixed uniformly, and the occurrence of mottled patterns in the resulting coating film can be further suppressed. The mixing time in the mixing step can be, for example, preferably 10 minutes or more and 2 hours or less, more preferably 30 minutes or more and 1 hour or less.

(Second granulation process)
In the second granulation step, the pre-mixture is mixed with the remainder of the two or more primary color powder coating compositions to obtain a powder coating composition.
It is believed that the cationic compound is adhered to the particle surfaces of the first primary color powder coating composition contained in the pre-mixture, and by mixing this pre-mixture with the remainder of the two or more primary color powder coating compositions (second primary color powder coating composition), the first primary color powder coating composition and the second primary color powder coating composition are bonded on a particle-by-particle basis and toned, and a granulated, toned powder coating composition can be obtained.

Here, the particles of the color-matched powder coating composition obtained in the second granulation step can be pulverized into primary particles by vigorously stirring.
More specifically, for example, when the toning powder coating composition is stirred for about 1 minute at a peripheral speed of the stirring blade of 10 m/s or more, most of the particles of the toning powder coating composition can return to the state of primary particles having an average particle diameter equivalent to the average particle diameter of the original color powder coating composition measured before granulation. Thus, in the present disclosure, granulation means preparation of particles that can be broken down into primary particles by applying a certain impact. As a result, in the obtained coating film, in addition to the effect of being able to smooth the surface, contributing to the minimization of mottling, and reducing or preventing problems such as surface unevenness and color separation, it can have high color reproducibility, such as cosmetic properties, and being able to reproduce the required uniform hue, uniform saturation, and uniform brightness.

The mass ratio of the first primary color powder coating composition to the second primary color powder coating composition may be, for example, preferably 1/10 to 50/10, more preferably 2/10 to 20/10, and even more preferably 5/10 to 15/10. By having the mass ratio within the above range, the first primary color powder coating composition and the second primary color powder coating composition can be mixed more uniformly, and the occurrence of mottled patterns in the resulting coating film can be further suppressed.

The means for mixing the preliminary mixture with the second primary color powder coating composition is not particularly limited. For example, a dry mixer such as a Henschel mixer, ribbon blender, drum blender, or super mixer may be used. When a rotary mixer is used, the rotation speed may be 3 to 2,000 rpm. The ratio of the rotation speed during mixing in the first granulation step to the rotation speed during mixing in the second granulation step (rotation speed in the first granulation step/rotation speed in the second granulation step) may be preferably 0.1 to 10, more preferably 0.2 to 5. The larger the ratio, the better the uniformity of the hue tends to be, and the smaller the ratio, the better the smoothness of the resulting coating film tends to be.

The mixing temperature when mixing the preliminary mixture and the second primary color powder coating composition is preferably room temperature. The mixing temperature may be preferably 10°C or higher and 40°C or lower, more preferably 15°C or higher and 35°C or lower. The mixing time is not particularly limited, and is, for example, 1 minute to 30 minutes. The mixing conditions can be appropriately set depending on the type of primary color powder coating composition used, and the color-matched powder coating composition is prepared by mixing two or more primary color powder coating compositions so that they are uniformly dispersed.

The color-matched powder coating composition obtained by the manufacturing method disclosed herein does not need to be further classified, but may be further classified if necessary.

Although the first granulation step and the second granulation step have been described above, these steps may be repeated multiple times. That is, the toned powder coating composition may be used as the first or second primary color powder coating composition. In one embodiment, the first toned powder coating composition may be mixed with a cationic compound to obtain a premixture, and the premixture may be mixed with the primary color powder coating composition to obtain the second toned powder coating composition. Alternatively, the primary color powder coating composition may be mixed with a cationic compound to obtain a premixture, and the premixture may be mixed with the first toned powder coating composition to obtain the second toned powder coating composition. Furthermore, the first toned powder coating composition may be mixed with a cationic compound to obtain a premixture, and the premixture may be mixed with the second toned powder coating composition to obtain the third toned powder coating composition.

The pigment mass concentration in the toning powder coating composition may be preferably 10% by mass or more and 50% by mass or less, more preferably 20% by mass or more and 40% by mass or less.

The average particle size (D50) of the toning powder coating composition may be preferably 10 μm or more and 50 μm or less, more preferably 12 μm or more and 40 μm or less, and even more preferably 15 μm or more and 30 μm or less.
In addition, the ratio of the average particle diameter (D50) of the toning powder coating composition to the average particle diameter (D50) of the entire primary color powder coating composition (average particle diameter of the toning powder coating composition/average particle diameter of the primary color powder coating composition) may be preferably 1 or more and 2 or less, more preferably 1 or more and 1.5 or less, and even more preferably 1 or more and 1.2 or less.

According to the manufacturing method of the present disclosure, the obtained color-matching powder coating composition has a first primary color powder coating composition and a second primary color powder coating composition that are aggregated via a cationic compound. Therefore, when measuring the average particle size, the color-matching powder coating composition is crushed, and it is considered that the particle size range is the same as that of the primary color powder coating composition. As a result, the productivity of coating film formation can be improved. Furthermore, since the coating property can be made uniform, the occurrence of color separation, color unevenness, gloss unevenness, etc. can be greatly suppressed or prevented.

<Coating film formation method>
The present disclosure further includes a method for forming a coating film, which comprises applying the color-matched powder coating composition obtained by the above-mentioned production method to an object to be coated.

The substrate is not particularly limited, and specific examples thereof include iron plates, steel plates, aluminum plates, ceramic plates, and their surface-treated counterparts. Further examples thereof include members processed into complex shapes. Specific examples of the substrate include steel furniture, electronic parts, office automation equipment, home appliances, building materials, and automobile parts.
A surface-treated substrate may also be used. The coating film formed on the substrate may be a single layer of the toned powder coating composition obtained by the toning method of the present invention, or the toned powder coating composition may be applied as a topcoat coating on an undercoat coating. As the undercoat coating for forming the undercoat coating, known coating materials such as electrodeposition coatings and primers may be used.

The method for applying the toned powder coating composition is not particularly limited, and may be any method well known to those skilled in the art, such as spray coating, electrostatic powder coating, fluidized bed coating, etc. From the viewpoint of coating efficiency, electrostatic powder coating is preferred.
The coating thickness (dry coating thickness) when applying the color-matching powder coating composition is preferably 20 μm or more and 100 μm or less, more preferably 40 μm or more and 70 μm or less, from the viewpoint of preventing the coating film from becoming mottled and transparent and preventing the generation of bubbles on the surface or inside of the coating film.

The baking temperature and time after application of the toned powder coating composition will vary depending on the type and amount of the curing agent (C) used, but the temperature is preferably 120 to 140°C, more preferably 140 to 220°C, for example 150 to 200°C, and in one embodiment 175 to 195°C, from the viewpoint of preventing the formation of bubbles on the surface or inside the coating film. The baking time can be set appropriately depending on the baking temperature.

<Method of Matching Powder Coating Composition>
The present disclosure provides a method for matching a powder coating composition, comprising:
Producing two or more primary color powder coating compositions, each having a different hue and/or shade;
mixing at least a portion of the two or more primary color powder coating compositions with a cationic polymer, stearyltrimethylammonium chloride, and a cationic compound selected from cetylpyridinium chloride to obtain a preliminary mixture;
and mixing the premix with the remainder of the two or more primary color powder coating compositions to form a powder coating composition.

Each of the above steps can be carried out under the conditions described above using the raw materials and means described above as the manufacturing method for the powder coating composition. According to this color-matching method, two or more primary color powder coating compositions can be mixed uniformly, and a color-matched powder coating composition can be obtained that can realize a coating film that exhibits a smooth and uniform hue.

The coating film formed from the color-matched powder coating composition obtained by the present invention exhibits a smooth and uniform hue. Furthermore, according to the manufacturing method of the present invention, two or more different pigments are evenly dispersed in the resulting coating film, which leads to improved cosmetic properties, improved hiding power, and minimal mottling. Furthermore, since it also has excellent charge control technology, it can suppress or reduce surface unevenness and contribute to eliminating color separation. In addition, since it is possible to control the gloss, the number of primary colors can be minimized.

The present invention will be described in more detail with reference to the following examples, but is not limited thereto. In the examples, "parts" and "%" are by weight unless otherwise specified.

(Production Example 1)
120 parts by mass of (A-1) as the coating resin (A), 20 parts by mass of (C-1) as the curing agent, 80 parts by mass of (B-1) as the colorant (B), 0.6 parts by mass of KF-54 as the surface conditioner, 1.6 parts by mass of benzoin as the popping inhibitor, and 0.6 parts by mass of dibutyltin dilaurate as the curing catalyst were mixed at a temperature of 20° C. for 3 minutes using a Supermixer (manufactured by Kawata Corporation). A mixture was prepared by this process.

The mixture was then kneaded at 100° C. and 100 rpm using a Buss Co-Kneader (Buss Co.), rolled and cooled with a cooling roller attached to the device, and pulverized and classified with a pulverizer Pulperizer ACM10A (Hosokawa Micron Co., Ltd.) to obtain a powder with an average particle size (D50) of 19 μm.
150 parts by mass of the obtained powder and 0.45 parts by mass of AEROSIL R972 (manufactured by Nippon Aerosil Co., Ltd.) as a flowability modifier were uniformly mixed in a Henschel mixer to prepare primary color powder coating composition 1. The average particle size (D50) of the obtained primary color powder coating composition was 19 μm.
The average particle size (D50) was measured using a particle size analyzer Microtrac HRA model 9320-X100 (manufactured by Nikkiso Co., Ltd.).

(Production Examples 2 to 13)
Primary color powder coating compositions 2 to 16 were prepared in the same manner as in Example 1, except that the film-forming resin (A), colorant (B), curing agent (C) and other additives were changed as shown in Table 1. The raw material composition in each production example and the average particle size (D50) of the obtained primary color powder coating composition are shown in Table 1. In Table 1, "equivalent ratio of reactive groups" means the equivalent ratio between the total of acid groups, hydroxyl groups and epoxy groups contained in the film-forming resin (A) and the total of groups (e.g., acid groups, hydroxyl groups, amino groups and isocyanate groups) that can react with acid groups, hydroxyl groups and epoxy groups contained in the curing agent (C).

(Production of Powder Coating Composition)
Example 1
<First granulation step>
(Example)
First, as the cationic compound (D-1), 1.0 part by mass of stearyltrimethylammonium chloride was mixed with 100 parts by mass of water and stirred until the solution became transparent to the naked eye, to prepare an aqueous solution of the cationic compound.
100 parts by mass of the primary color powder coating composition 1 was charged into a mixer/agitator 5XDMV-Qr (manufactured by Shinagawa Kogyosho Co., Ltd.), and while mixing at 20 rpm, 16 parts by mass of the aqueous solution of the cationic compound was sprayed and added over 5 minutes. Thereafter, mixing was continued for 60 minutes under the same conditions to obtain a first granule.
Next, while stirring the first granules under the same conditions, 100 parts by mass of the raw powder coating composition 2 was added and mixed for 5 minutes to obtain a powder coating composition. The series of production steps was carried out at 20° C. (room temperature).

(Formation of coating film)
The substrate was a 0.8 x 70 x 150 mm JIS G 3141 (SPCC-SD) cold-rolled steel plate that had been subjected to zinc phosphate treatment and then solvent degreased. This substrate was coated with a powder paint electrostatic applicator OPTI hand gun (manufactured by Graco) at a discharge rate of 120 g/min, a set voltage of 100 kV, a set current of 70 μA, free ion removal, and a gun distance of 15 cm, to a film thickness of 50 to 60 μm, and baked at 180° C. for 20 minutes, and then subjected to testing.

(Examples 2 to 9, 11 to 16)
A coating film was formed in the same manner as in Example 1, except that the cationic compound, primary color powder coating composition, and granulation conditions were changed as shown in Table 2. The blending amounts shown in Table 2 are the solid content amounts of each.
(Example 10)
In the first granulation step, 100 parts by mass of primary color powder coating composition 1 and 0.2 parts by mass of cationic compound (D-2) were mixed for 3 minutes at 1,200 rpm using a Supermixer (manufactured by Kawata Co., Ltd.) to obtain a first granule. Next, while stirring the first granule under the same conditions, 100 parts by mass of the raw powder coating composition 2 was added and mixed for 5 minutes to obtain a powder coating composition. The series of production steps were carried out at 25°C (room temperature).

(Comparative Example 1)
100 parts by mass of primary color powder coating composition 1 and 100 parts by mass of primary color powder coating composition 2 were charged into a mixer/stirrer 5XDMV-Qr (manufactured by Shinagawa Kogyosho Co., Ltd.) and mixed at 20 rpm for 5 minutes to obtain a powder coating composition. The series of production steps was carried out at 25°C (room temperature).

(Comparative Example 2)
First, 2 parts by mass of the other polymer (d-1) and 98 parts by mass of methanol were mixed and stirred until the mixture became transparent to the naked eye, to prepare a polymer solution.
100 parts by mass of primary color powder coating composition 1 and 100 parts by mass of primary color powder coating composition 2 were charged into a mixer/stirrer 5XDMV-Qr (manufactured by Shinagawa Kogyosho Co., Ltd.), and while stirring at 20 rpm, 100 parts by mass of the polymer solution was sprayed over 10 minutes. Thereafter, mixing was continued for 60 minutes under the same conditions to obtain a powder coating composition.

(Comparative Example 3)
100 parts by mass of primary color powder coating composition 1 and 100 parts by mass of primary color powder coating composition 2 were charged into a mixer/stirrer 5XDMV-Qr (manufactured by Shinagawa Kogyosho Co., Ltd.), and while stirring at 20 rpm, 4 parts by mass of the polymer solution was sprayed over 10 minutes. Thereafter, mixing was continued for 60 minutes under the same conditions to obtain a powder coating composition.

(Comparative Example 4)
100 parts by mass of primary color powder coating composition 1 and 100 parts by mass of primary color powder coating composition 2 were charged into a mixer/stirrer 5XDMV-Qr (manufactured by Shinagawa Kogyosho Co., Ltd.), and 0.5 parts by mass of other polymer (d-3) was sprayed over 10 minutes while stirring at 20 rpm. Thereafter, mixing was continued for 60 minutes under the same conditions to obtain a powder coating composition.

(Comparative Example 5)
100 parts by mass of primary color powder coating composition 1 and 100 parts by mass of primary color powder coating composition 2 were charged into a mixer/stirrer 5XDMV-Qr (manufactured by Shinagawa Kogyosho Co., Ltd.), and while stirring at 20 rpm, 3 parts by mass of other polymer (d-4) was sprayed over 10 minutes. Thereafter, mixing was continued for 60 minutes under the same conditions to obtain a powder coating composition.

Details of the raw materials used are shown below.
(A-1) FineDic M8020 (manufactured by DIC Corporation, polyester resin having hydroxyl groups), hydroxyl value: 30 mg KOH/g, softening point: 110° C.
(A-2) FineDic M8023 (manufactured by DIC Corporation, polyester resin having hydroxyl groups), hydroxyl value: 40 mgKOH/g, softening point: 106° C.
(A-3) GV-126 (manufactured by Japan U-Pica Corporation, polyester resin having a carboxy group), acid value: 30 mg KOH/g, softening point: 120° C.
(A-4) A278 (DIC Corporation, acrylic resin having epoxy groups), epoxy equivalent: 480 g/eq, softening point: 103° C.
(A-5) NT-114 (manufactured by Nippon Steel Chemical & Material Co., Ltd., epoxy resin), epoxy equivalent: 440 g/eq, softening point: 96° C.
Colorant (B)
(B-1) TIPAKEC CR90 (manufactured by Ishihara Sangyo Kaisha, Ltd., titanium oxide)
(B-2) Mitsubishi Carbon Black MA100 (manufactured by Mitsubishi Chemical Corporation, carbon black)
(B-3) Firstgen Blue NK (manufactured by DIC Corporation, blue organic pigment)
Hardener (C)
(C-1) VESTAGON B1530 (manufactured by Evonik Industries, blocked isocyanate), NCO equivalent: 280 g/eq
(C-2) Primid XL-552 (manufactured by EMS Co., Ltd., β-hydroxyalkylamide (HAA))
(C-3) GV-230 (Japan U-Pica Corporation, polyester resin), acid value: 48 mg KOH/g
(C-4) Dodecanedicarboxylic acid (DDDA) (manufactured by Tokyo Chemical Industry Co., Ltd., polycarboxylic acid compound)
(C-5) Dicyandiamide (Tokyo Chemical Industry Co., Ltd., amino group-containing compound)
Cationic Compound (D)
(D-1): Kotamin 86P Conc. (Kao Corporation, stearyl trimethyl ammonium chloride), softening point: 95 to 104° C., weight average molecular weight: 333, amine value: 168 mg KOH/g
(D-2) Cetylpyridinium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), softening point: 80 to 84°C, weight average molecular weight: 358, amine value: 157 mgKOH/g
(D-3) Polylysine (manufactured by JNC Corporation), softening point: 172°C, weight average molecular weight: 4,700, amine value: 600 mgKOH/g
(D-4) Koyo Chitosan (manufactured by Koyo Chemical Co., Ltd., chitosan), softening point: 200° C. or higher, weight average molecular weight: 100,000, amine value: 298 mg KOH/g
Other polymers:
(d-1) Dry transparent white lac (Nippon Shellac Kogyo Co., Ltd., shellac resin), softening point: 70 to 75°C, amine value: 0 mgKOH/g
(d-2) Polyethylene glycol 4000 (manufactured by Tokyo Chemical Industry Co., Ltd., polyethylene glycol), softening point: 54 to 58° C., weight average molecular weight: 2,700 to 3,400, solid content concentration: 5% by mass (aqueous solution), amine value: 0 mg KOH/g
(d-3) EMUSTAR-0136 (paraffin wax, manufactured by Nippon Seiro Co., Ltd.), softening point: 60° C., average particle size: 0.50 μm or less, solid content concentration: 40% by mass (water dispersion), amine value: 0 mg KOH/g
(d-4) A-6001 (manufactured by Resitex, acrylic resin emulsion), softening point: 70 to 80° C., solid content: 63 to 67% by mass (water dispersion), amine value: 0 mg KOH/g
Other additives:
Surface conditioner: KF-54 (Shin-Etsu Chemical Co., Ltd., silicone-based)
Armpit irritation prevention agent: Benzoin (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
Flowability adjuster: AEROSIL R972 (manufactured by Nippon Aerosil Co., Ltd., silica)
Extender pigment: Precipitated barium sulfate 100 (Sakai Chemical Industry Co., Ltd., barium sulfate)

The coating films obtained in Examples 1 to 16 and Comparative Examples 1 to 5 were evaluated as follows. The evaluation results are shown in Tables 2 and 3.

<Resistance to color separation>
The coating films obtained in the Examples and Comparative Examples were visually observed for mottling and evaluated for color separation resistance. The evaluation criteria were as follows: △ or higher was considered to be acceptable.
⊚: When viewed from a distance of 50 cm, the mottled pattern of color tones cannot be recognized. ◯: When viewed from a distance of 50 cm, the mottled pattern of color tones can be slightly recognized. △: When viewed from a distance of 50 cm, the mottled pattern of color tones can be clearly recognized, but
When viewed from a distance of 80 cm, it is not recognizable or is only slightly recognizable. ×: When viewed from a distance of 80 cm, the mottled pattern of the color tone is clearly recognizable.

<Smoothness>
The arithmetic mean waviness (Wa value) of the coating films obtained in the examples and comparative examples was measured using a surface roughness measuring instrument Surfcom TOUCH50 (manufactured by Tokyo Seimitsu Co., Ltd.) in accordance with JIS B 0601 to evaluate the smoothness of the coating films. The evaluation criteria are as follows. The measurement conditions were cutoff value: 0.8 mm, scanning speed: 2 mm/s. A score of △ or higher was considered to be acceptable.
◯: Wa is less than 0.9.
Δ: Wa is 0.9 or more and less than 1.1.
×: Wa is 1.1 or more.

Examples 1 to 16 are examples of the present disclosure, and the resulting coating films exhibited a smooth and uniform hue.
On the other hand, in Comparative Example 1, which does not include the first granulation step, color separation was not suppressed, the coating film appeared mottled, and a uniform hue could not be obtained.
Comparative Examples 2 to 5 are examples in which no cationic compound was used, and no smooth coating film could be obtained.

The manufacturing method and coating film formation method disclosed herein can provide a coating film that is smooth and exhibits a uniform hue. Therefore, the manufacturing method disclosed herein can be applied to general industrial applications such as home appliances, automobile parts, and steel furniture.

Claims (10)

Providing two or more negatively charged primary color powder coating compositions;
mixing a portion of the two or more primary color powder coating compositions with a cationic compound (D) selected from a cationic polymer, stearyltrimethylammonium chloride, and cetylpyridinium chloride to obtain a positively charged preliminary mixture;
and mixing the premix with the remainder of the two or more primary color powder coating compositions to obtain a powder coating composition;
The two or more primary color powder coating compositions each contain at least the same or different film-forming resin (A),
The method for producing a powder coating composition, wherein the film-forming resin (A) contains a polymer having at least one curable functional group selected from an acid group, a hydroxyl group, and an epoxy group, and the amount of the cationic compound (D) is 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the total of the two or more primary color powder coating compositions. The manufacturing method according to claim 1, wherein the two or more primary color powder coating compositions each have a different hue and/or tone. The manufacturing method according to claim 1, wherein the average particle size (D50) of the primary color powder coating composition is 25 μm or less. The method according to claim 1, wherein the cationic compound (D) has an amino group and/or a quaternary ammonium base, and the softening point of the cationic compound (D) is 50°C or higher and 180°C or lower. The manufacturing method according to claim 1, wherein mixing of a portion of the two or more primary color powder coating compositions with the cationic compound (D) is carried out in a dry manner. The manufacturing method according to claim 1, wherein mixing a portion of the two or more primary color powder coating compositions with a cationic compound (D) to obtain a premixture is carried out by mixing the cationic compound (D) with water and/or a hydrophilic solvent to obtain a solution of the cationic compound, mixing a portion of the primary color powder coating compositions with the liquid of the cationic compound to obtain a mixed liquid containing the premixture, and removing water and/or the hydrophilic solvent from the mixed liquid to obtain the premixture. The method according to claim 1, wherein the primary color powder coating composition is prepared by mixing a film-forming resin (A) and a colorant (B). The method according to claim 1, wherein the primary color powder coating composition further contains a curing agent (C). A coating film forming method comprising applying a powder coating composition obtained by the manufacturing method according to any one of claims 1 to 8 to a substrate. A method for matching a powder coating composition, comprising the steps of:
Producing two or more primary color powder coating compositions each having a different hue and/or tone and being negatively charged ;
mixing at least a portion of the two or more primary color powder coating compositions with a cationic compound (D) selected from a cationic polymer, stearyltrimethylammonium chloride, and cetylpyridinium chloride to obtain a positively charged preliminary mixture;
mixing the premix with the remainder of the two or more primary color powder coating compositions to form a powder coating composition;
The two or more primary color powder coating compositions each contain at least the same or different film-forming resin (A),
The coating film-forming resin (A) contains a polymer having at least one curable functional group selected from an acid group, a hydroxyl group, and an epoxy group,
The color matching method, wherein the amount of the cationic compound (D) is 0.01 parts by mass or more and 2 parts by mass or less per 100 parts by mass in total of the two or more primary color powder coating compositions.