JP2023134864A - Method for producing powder coating - Google Patents

Abstract

To provide a method for producing a powder coating which can suppress solid phase reaction during a storage period after production of a powder coating, and is also excellent in finished appearance and coating film performance of an obtained coating film.SOLUTION: A method for producing a powder coating includes adding a glycidyl group-containing acrylic resin (B) having 0.1-1.0 equivalent of an epoxy group per 1 equivalent of a carboxy group of a carboxy group-containing polyester resin (A), to an intermediate composition (X) which is a melt-kneaded material that is composed of the carboxy group-containing polyester resin (A), the glycidyl group-containing acrylic resin (B), a pigment (C) and an additive (D), and is blended with the glycidyl group-containing acrylic resin (B) having 0.5-0.9 equivalent of an epoxy group per 1 equivalent of a carboxy group of the carboxy group-containing polyester resin (A), and mixing and co-crushing the mixture.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a powder coating that can suppress solid phase reactions during storage after production of the powder coating, and has excellent finished appearance and coating performance.

Powder coatings are generally produced by uniformly mixing a binder resin, a curing agent, and if desired pigments, additives, etc. in a mixer, melting and kneading the resulting mixture in a kneader, and then coarsely pulverizing and finely grinding. It can be obtained through a grinding and classification process.

From the perspective of reducing environmental impact, there is a demand for powder coatings that cure at relatively low temperatures, and one such type is an acid/epoxy curing system.For example, as a combination of binder resin and curing agent, carboxy group-containing polyester Resins and glycidyl group-containing acrylic resins are known.

For example, Patent Document 1 discloses an epoxy resin powder coating and a method for producing the same, in which (a) a raw material mixture containing the first epoxy resin and the second epoxy resin and not containing a curing agent is melted. Disclosed is a method for producing an epoxy resin powder coating, comprising the steps of: (b) melt-mixing the remaining raw material mixture containing a curing agent into the molten mixture. .

However, the manufacturing method of epoxy resin powder coatings such as Patent Document 1 does not sufficiently suppress the solid phase reaction during storage after manufacturing the powder coatings, resulting in problems such as poor gloss and reduced adhesion of the coating film. In some cases, a problem occurred in which the membrane performance was poor.

JP2006-96890

The present invention aims to provide a method for producing a powder coating that can suppress solid phase reactions during storage after production of the powder coating, and has excellent finished appearance and coating performance of the resulting coating. Take it as a challenge.

According to one aspect of the invention,
Item 1. A method for producing a powder coating comprising a carboxyl group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), a pigment (C) and an additive (D), the method comprising:
Consisting of a carboxyl group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), a pigment (C), and an additive (D), the glycidyl group-containing acrylic resin is For intermediate composition (X) which is a melt-kneaded product in which resin (B) is blended in an amount having 0.5 to 0.9 equivalents of epoxy groups, 1 carboxy group of carboxyl group-containing polyester resin (A) A method for producing a powder coating, characterized in that a glycidyl group-containing acrylic resin (B) in an amount having 0.1 to 1.0 equivalents of epoxy groups per equivalent is added, mixed, and co-pulverized;
Item 2. A powder coating produced by the method for producing a powder coating according to item 1 above,
Item 3. A coated article on which a coating film of the powder coating according to item 2 above is formed,
is provided.

According to the method for producing a powder coating of the present invention, it is possible to suppress solid phase reactions during the storage period after the production of the powder coating, and the resulting powder has excellent finished appearance and coating performance. A method for producing a paint can be provided.

The method for producing a powder coating of the present invention includes:
A method for producing a powder coating comprising a carboxyl group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), a pigment (C) and an additive (D), the method comprising:
Consisting of a carboxyl group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), a pigment (C), and an additive (D), the glycidyl group-containing acrylic resin is For intermediate composition (X) which is a melt-kneaded product in which resin (B) is blended in an amount having 0.5 to 0.9 equivalents of epoxy groups, 1 carboxy group of carboxyl group-containing polyester resin (A) This is a method for producing a powder coating, which comprises adding, mixing and co-pulverizing an amount of glycidyl group-containing acrylic resin (B) having 0.1 to 1.0 equivalents of epoxy groups per equivalent.

<Carboxy group-containing polyester resin (A)>
The carboxyl group-containing polyester resin (A) is a polyester resin having a carboxyl group, and for example, an acid component mainly composed of polyhydric carboxylic acid and an alcohol component mainly composed of polyhydric alcohol are used as raw materials. It can be obtained by condensation polymerization according to a method.

Examples of the acid component include terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, phthalic acid, hexahydrophthalic acid, tetrahydrophthalic acid, 2,6-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, etc. aromatic dicarboxylic acids and their anhydrides, trivalent or higher aromatic polycarboxylic acids such as trimellitic acid and their anhydrides, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, 1, Examples include saturated aliphatic dicarboxylic acids such as 4-cyclohexanedicarboxylic acid and their anhydrides, lactones such as γ-butyrolactone and ε-caprolactone, and aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid. .

Among the above, terephthalic acid, isophthalic acid, etc. can be preferably used. The above acid components can be used alone or in combination of two or more.

Examples of the alcohol component 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, 1,6-hexanediol, 2,3-pentanediol, 1,4-hexanediol, 1,5-hexanediol, 2,5-hexane Diol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,2-dodecanediol, 1,2-octadecanediol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanediol Linear or branched aliphatic glycols such as methanol, bisphenol A alkylene oxide adduct, bisphenol S alkylene oxide adduct, trivalent or higher polyhydric glycols such as trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, etc. Examples include alcohols.

Among the above, ethylene glycol, neopentyl glycol, etc. can be preferably used. The above alcohol components can be used alone or in combination of two or more.

The acid value of the carboxy group-containing polyester resin (A) is preferably within the range of 10 to 50 mgKOH/g, particularly 15 to 45 mgKOH/g.

The hydroxyl value of the carboxyl group-containing polyester resin (A) is preferably in the range of 0 to 15 mgKOH/g, particularly 0 to 10 mgKOH/g.

The weight average molecular weight of the carboxy group-containing polyester resin (A) is preferably within the range of 5,000 to 15,000, particularly 7,500 to 12,500.

In this specification, the weight average molecular weight and number average molecular weight are the retention time (retention capacity) measured using gel permeation chromatography (GPC), and the retention time (retention capacity) of standard polystyrene with a known molecular weight measured under the same conditions. This value is calculated by converting the molecular weight of polystyrene into the molecular weight of polystyrene. The columns are "TSKgel G-4000H×L", "TSKgel G-3000H×L", "TSKgel G-2500H×L", "TSKgel G-2000H×L" (all manufactured by Tosoh Corporation, product name) ) under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 ml/min, detector: RI.

The glass transition temperature of the carboxy group-containing polyester resin (A) is preferably within the range of 40 to 80°C, particularly 50 to 70°C. The glass transition temperature can be measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121.

Further, the softening temperature of the carboxy group-containing polyester resin (A) is preferably within the range of 90 to 130°C, particularly 100 to 120°C.

<Glycidyl group-containing acrylic resin (B)>
The glycidyl group-containing acrylic resin (B) can be obtained by copolymerizing a polymerizable monomer having at least one glycidyl group with another copolymerizable vinyl monomer.

Examples of the polymerizable monomer having a glycidyl group include glycidyl (meth)acrylate and β-methylglycidyl (meth)acrylate. These can be used alone or in combination of two or more.

Other vinyl monomers copolymerizable with the polymerizable monomer having a glycidyl group have at least one unsaturated bond such as a vinyl group in the molecule, and include derivatives of acrylic acid and methacrylic acid. including.

Examples of vinyl monomers include ethylenically unsaturated alkyl carboxylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Ester monomer; cycloalkyl group-containing polymerizable monomers such as cyclopentyl (meth)acrylate and cyclohexyl (meth)acrylate; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, Hydroxyl group-containing ethylenically unsaturated carboxylic acid alkyl ester monomers such as 4-hydroxybutyl (meth)acrylate, reaction products of 2-hydroxyethyl (meth)acrylate and ε-caprolactone; acrylamide, methacrylamide, N - Other amide group-containing ethylenically unsaturated carboxylic acid monomers such as methylol acrylamide, methoxybutylacrylamide, and diacetone acrylamide; vinyl cyanide monomers such as (meth)acrylonitrile and α-chloroacrylonitrile; vinyl acetate, Examples include saturated aliphatic carboxylic acid vinyl ester monomers such as vinyl propionate; styrenic monomers such as styrene, α-methylstyrene, and vinyltoluene. These can be used alone or in combination of two or more. In addition, in this specification, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acrylic acid" means acrylic acid or methacrylic acid. Moreover, "(meth)acryloyl" means acryloyl or methacryloyl, and "(meth)acrylamide" means acrylamide or methacrylamide.

The epoxy equivalent of the glycidyl group-containing acrylic resin (B) is preferably 200 g/eq or more and 500 g/eq or less. Note that the epoxy equivalent can be measured by a method based on JIS K 7236.

The glycidyl group-containing acrylic resin (B) has a glass transition temperature of 50°C to 80°C, particularly 55°C to 75°C, more particularly The temperature is preferably within the range of 60°C to 70°C.

In addition, in this specification, the glass transition temperature Tg of an acrylic resin is a value calculated by the following formula.
1/Tg(K)=W1/T1+W2/T2+...Wn/Tn (1)
Tg (℃) = Tg (K) - 273 (2)
In the formula, W1, W2, . . . Wn are the mass fractions of each monomer, and T1, T2, . . . Tn are the glass transition temperature Tg (K) of the homopolymer of each monomer.

Note that the glass transition temperature of the homopolymer of each monomer is as described in POLYMER HANDBOOK Fourth Edition, J. Brandrup, E. h. Immergut, E. A. The glass transition temperature of monomers not described in the literature is based on the values compiled by Ed. Grulke (1999). Use the value measured by differential scanning thermal analysis.

The weight average molecular weight of the glycidyl group-containing acrylic resin (B) is within the range of 2,000 to 10,000, particularly 4,000 to 8,000, from the viewpoint of compatibility with the carboxy group-containing polyester resin (A) and surface smoothness during coating film formation. It is preferable that

When the glycidyl group-containing acrylic resin (B) has a hydroxyl value, the hydroxyl value is preferably in the range of 0 to 30 mgKOH/g, particularly 0 to 20 mgKOH/g, from the viewpoint of curability and water resistance.

The method for synthesizing the glycidyl group-containing acrylic resin (B) is particularly one in which the monomer having at least one glycidyl group is copolymerized with another vinyl monomer that can be copolymerized therewith. There are no restrictions. For example, it can be carried out by various known methods. For example, a method for obtaining the desired polymer by subjecting the various monomers mentioned above to a radical polymerization reaction in a solution and then removing the solvent, It is preferable because the molecular weight can be easily controlled.

In the final powder coating, the ratio of the carboxy group-containing polyester resin (A) to the glycidyl group-containing acrylic resin (B) is as follows: A quantitative ratio in which the epoxy equivalent of the glycidyl group-containing acrylic resin (B) is within the range of 0.70 to 1.70 equivalents, particularly 0.85 to 1.50 equivalents, and even more particularly 1.00 to 1.40 equivalents. It is preferable to do so.

<Pigment (C)>
Examples of the pigment (C) include rust preventive pigments such as zinc phosphate and aluminum phosphate, extender pigments such as barium sulfate, calcium carbonate, clay, talc, silica, and mica; titanium dioxide, red iron oxide, yellow iron oxide, and carbon. Examples include coloring pigments such as black, phthalocyanine blue, phthalocyanine green, and quinacridone red pigments.

The above pigment (C) can be used alone or in combination of two or more.

<Additive (D)>
In the present invention, the additive (D) refers to all components contained in the powder coating other than the carboxy group-containing polyester resin (A), the glycidyl group-containing acrylic resin (B), and the pigment (C). .

Examples of additives (D) include surface conditioners, plasticizers, ultraviolet absorbers, antioxidants, anti-wrinkle agents, pigment dispersants, etc., and those commonly used in powder coatings are used. can do.

Further, as the additive (D), resins and curing agents other than the carboxy group-containing polyester resin (A) and the glycidyl group-containing acrylic resin (B) can also be used as necessary.
The above additive (D) can be used alone or in combination of two or more.

Furthermore, a curing catalyst can also be used as the additive (D) if necessary.

Examples of the curing catalyst include imidazole compounds, imidazoline compounds and metal salt complexes thereof, tertiary phosphine compounds, quaternary phosphonium salt compounds, and quaternary ammonium salt compounds.

The amount of the curing catalyst is preferably within the range of 0 to 5% by mass based on the total solid content of the carboxy group-containing polyester resin (A) and the glycidyl group-containing acrylic resin (B).

<Production method of powder coating>
In the method for producing a powder coating of the present invention, the pulverized intermediate composition (X), which is the melt-kneaded product, is mixed with 0.1 to 0.1 to 1 equivalent of the carboxyl group of the carboxy group-containing polyester resin (A). This is a method for producing a powder coating material, which comprises adding a glycidyl group-containing acrylic resin (B) in an amount having 1.0 equivalent of epoxy groups, mixing, and co-pulverizing.

<Intermediate composition (X)>
The intermediate composition (X) consists of a carboxyl group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), a pigment (C), and an additive (D),
The glycidyl group-containing acrylic resin (B) is blended in an amount selected to have 0.5 to 0.9 equivalents of epoxy groups per equivalent of carboxyl group in the carboxyl group-containing polyester resin (A). This is a compositional feature.

From the viewpoint of the finished appearance of the resulting coating film and coating film performance such as weather resistance, in the intermediate composition (X), the glycidyl group-containing acrylic resin (B) contains 1 equivalent of the carboxyl group of the carboxyl group-containing polyester resin (A). It is preferable that the amount of epoxy groups is selected to have 0.5 to 0.9 equivalents, particularly 0.7 to 0.9 equivalents of epoxy groups per epoxy group.

The content of the pigment (C) varies depending on the type of pigment used, but is 40 to 120% by mass, based on the total solid content of the carboxy group-containing polyester resin (A) and the glycidyl group-containing acrylic resin (B). In particular, a content of 60 to 100% by mass is preferred from the viewpoint of the finished appearance of the resulting coating film.

The content of the additive (D) varies depending on the type of additive used, but it is 0.1 to 0.1 to the total solid content of the carboxy group-containing polyester resin (A) and the glycidyl group-containing acrylic resin (B). It is preferably 15% by weight, especially 0.50 to 10% by weight.

In the intermediate composition (X), if the amount of the glycidyl group-containing acrylic resin (B) is less than 0.5 equivalent with respect to 1 equivalent of the carboxyl group of the carboxyl group-containing polyester resin (A), the intermediate composition In product (X), the melt-kneadability may decrease due to a decrease in the amount of resin, and the glycidyl group-containing acrylic resin (B) is , if the amount corresponds to more than 0.9 equivalent, it will be insufficient to suppress the solid phase reaction during the storage period after producing the powder coating, and the surface smoothness of the resulting powder coating film will deteriorate. or the gloss may decrease.

The amount of the glycidyl group-containing acrylic resin (B) in the finally obtained powder coating excluding the content in the intermediate composition (X) is added in a subsequent step.

In the intermediate composition (X), if necessary, at least one of the pigment (C) or the additive (D) is blended into the carboxyl group-containing polyester resin (A) in an amount smaller than the final blending amount. You can also do it.

The melt-kneading of the intermediate composition (X) is not particularly limited as long as at least a part of the raw materials can be melted and the whole can be kneaded, and any method used in the production of ordinary powder coatings can be used. This can be done by

The temperature during melt-kneading can generally be in the range of about 80 to 130°C (particularly 80 to 120°C).

Specifically, for example, the above carboxy group-containing polyester resin (A), glycidyl group-containing acrylic resin (B), pigment (C), and additive (D) are mixed using a mixer such as a Henschel mixer or a super mixer. A melt-kneaded product can be obtained by uniformly mixing and then melt-kneading the obtained mixture using a kneader such as a co-kneader, an extruder, or a hot roll.

The obtained melt-kneaded product is usually cooled and solidified using a cooling roll, a cooling conveyor, etc., and then pulverized to a desired particle size through a pulverization process, whereby the intermediate composition (X), which is a melt-kneaded product, is It can be in the form of a pulverized product.

The intermediate composition (X) can be pulverized by a method commonly used in the production of powder coatings, and specifically, for example, an impact type pulverizer such as a hammer mill, or an air current pulverizer such as a jet mill. This can be done by pulverizing with a pulverizer or the like.

In addition to the above-mentioned method, it is also possible to adopt, for example, a method in which the above-mentioned components are mixed in a solvent, and the resulting mixture is dried and pulverized, or powdered by a spray drying method. The obtained powder can be subjected to the above-mentioned pulverization, if necessary.

The volume average particle diameter of the pulverized intermediate composition (X) is preferably in the range of 30 to 50 μm, particularly 30 to 45 μm, and even more particularly 30 to 40 μm. If the volume average particle diameter is less than 30 μm, it may result in poor pulverization during the pulverization process, and if it exceeds 50 μm, the mixing of each component will be insufficient, resulting in poor appearance and poor coating of the resulting powder coating. Performance may deteriorate.

In this specification, unless otherwise specified, the average particle diameter means the volume average particle diameter (D50). The volume average particle diameter (D50) can be measured, for example, using a particle size measuring device such as a laser diffraction/scattering type particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., Microtrac). Specifically, it refers to a value measured using "Microtrack MT3000II" (manufactured by Nikkiso Co., Ltd.) as a measuring device.

The amount of glycidyl group-containing acrylic resin having 0.1 to 1.0 equivalent of epoxy group per 1 equivalent of carboxyl group of carboxyl group-containing polyester resin (A) to the pulverized product of the intermediate composition (X) above ( B) is added, mixed, and co-pulverized to finally produce a powder coating.

In the addition of the glycidyl group-containing acrylic resin (B), the glycidyl group-containing acrylic resin (B) may be in either a pulverized or unpulverized state.

Similar to the pulverization of the intermediate composition (X), the glycidyl group-containing acrylic resin (B) is pulverized using a method commonly used in the production of powder coatings, specifically, for example, using a hammer mill or the like. This can be carried out by pulverizing with an air flow pulverizer such as an impact pulverizer or a jet mill.

The smaller the amount of glycidyl group-containing acrylic resin (B) when producing the intermediate composition (X) is, the smaller the amount of epoxy equivalent to 1 equivalent of carboxyl group in the carboxy group-containing polyester resin (A), the more the final composition. In order to improve surface gloss and It is preferable from the viewpoint of coating film performance such as impact resistance.

In the above, when the amount of the glycidyl group-containing acrylic resin (B) is set to an amount corresponding to a larger amount of epoxy equivalent with respect to 1 equivalent of the carboxyl group of the carboxyl group-containing polyester resin (A), the carboxy group-containing It is preferable to adjust the epoxy equivalent to 1.05 to 1.80 equivalents, particularly 1.1 to 1.7 equivalents, per 1 equivalent of carboxyl group of the polyester resin (A).

When the glycidyl group-containing acrylic resin (B) is added as a pulverized product, the pulverized glycidyl group-containing acrylic resin (B) has a volume average particle diameter in the range of 10 to 50 μm, particularly 10 to 45 μm, and more particularly 10 to 40 μm. It is preferable that it be within.

If the volume average particle diameter is less than 10 μm, productivity and coating workability may be poor, and if it exceeds 50 μm, mixing with the ground product of intermediate composition (X) will be insufficient, resulting in poor quality of the powder obtained. The finished appearance and performance of the body paint film may deteriorate.

When the intermediate composition (X) also contains at least one of the pigment (C) and the additive (D) in an amount smaller than the final blending amount with respect to the carboxy group-containing polyester resin (A), The following intermediate composition (Y) is added.

The intermediate composition (Y) consists of an additional amount of the glycidyl group-containing acrylic resin (B) and an insufficient amount of at least one of the pigment (C) and the additive (D).

The blending amount of each component in the composition of the intermediate composition (Y) corresponds to the blending of the intermediate composition (X), and is an amount that at least compensates for the deficiency in the final blending amount of each component.

The melt-kneading of the intermediate composition (Y) is not particularly limited as long as it is a method that can melt at least a part of the raw materials and knead the entire raw material, similarly to the melt-kneading of the intermediate composition (X). This can be carried out by a method commonly used in the production of powder coatings.

The intermediate composition (Y) can be pulverized in the same manner as the intermediate composition (X).
Any of the production of the pulverized intermediate composition (X), the production of the pulverized glycidyl group-containing acrylic resin (B), and the production of the pulverized intermediate composition (Y) may be performed first, Moreover, they may be performed in parallel.

In the method for producing a powder coating of the present invention, an amount of 0.1 to 1.0 equivalent, which is an additional amount to at least 1 equivalent of carboxyl group of the carboxy group-containing polyester resin (A), is added to the intermediate composition (X). This is a manufacturing method by adding an amount of glycidyl group-containing acrylic resin (B) having epoxy groups, mixing, and co-pulverizing.

In the above-mentioned process, any mixing method can be used without particular limitation as long as it does not generate heat due to normal rotation or high shear action and can uniformly mix the powders.

Specifically, for example, a method of mixing using a general mixer such as a V blender or a conical screw mixer can be mentioned.

In the above process, co-pulverization can be carried out using, for example, an impact type crusher such as a hammer mill, an air flow crusher such as a jet mill, or the like.

The volume average particle diameter of the powder coating material finally produced by the powder coating production method of the present invention is preferably in the range of 30 to 50 μm, particularly 30 to 45 μm, and even more particularly 30 to 40 μm.

If the average volume particle diameter is less than 30 μm, the coating efficiency may deteriorate, and if it exceeds 50 μm, the finished appearance and film performance of the resulting powder coating may deteriorate.

Moreover, after the above-mentioned co-pulverization, classification can be performed as necessary. Classification allows removal of giant particles and microparticles and adjustment of particle size distribution. Classification can be performed using, for example, an air classifier, a vibrating sieve, an ultrasonic sieve, or the like.

In the method for producing a powder coating of the present invention, the amount of the glycidyl group-containing acrylic resin (B) to be melt-kneaded is finally blended with the carboxy group-containing polyester resin (A) in the intermediate composition (X). Since the amount is smaller than the above amount, it is possible to suppress solid phase reactions during the storage period after producing the powder coating.

As a result, it is possible to produce an acid/epoxy curing powder coating that has an excellent finished appearance and excellent coating performance such as adhesion.

The application of the powder coating produced by the powder coating production method of the present invention is not particularly limited, and examples thereof include metal materials such as steel, zinc, aluminum, copper, and tin, and surface treatment of these metals. These metal materials may be coated with a primer or an intermediate coat as necessary.

The powder coating produced by the powder coating production method of the present invention can be coated by applying the powder coating to the surface of the object to be coated to form a desired film, for example, by a conventional method such as an electrostatic spray method or a fluidized dipping method. This is done by coating to a thickness (usually about 30 to 200 μm, preferably about 40 to 100 μm), and then baking and drying (usually at a temperature of about 160 to 210°C for about 30 to 60 minutes). be able to.

Further, it is also possible to coat a preheated object by the above-mentioned conventional method.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited only to these examples. Note that both "parts" and "%" are based on mass.

Example 1
Carboxy group-containing polyester resin (A1) (neopentyl glycol/terephthalic acid/isophthalic acid = 38.8/5.7/55.5 mass ratio, hydroxyl value 8 mgKOH/g, acid value 35 mgKOH/g, weight average molecular weight 10, 500, glass transition temperature 60°C) 45.6 parts, glycidyl group-containing acrylic resin (B1) (glycidyl methacrylate/methyl methacrylate/styrene/n-butyl methacrylate = 20/60/10/10 mass ratio, epoxy equivalent 350 g/eq , weight average molecular weight 6500, glass transition temperature 65°C) 3.65 parts, JR605 (manufactured by Teika Co., Ltd., titanium oxide) 47 parts, and C17Z (manufactured by Shikoku Kasei Co., Ltd., imidazole-based epoxy resin curing accelerator) 0 An intermediate composition (X1) (volume average particle size: 35 μm) was obtained by preparing and mixing 1 part of the mixture, melting and kneading with an extruder, cooling, and pulverizing with an atomizer.

After that, 3.65 parts of the above-mentioned glycidyl group-containing acrylic resin (B1) was added, and then finely pulverized using an atomizer and filtered through 150 mesh to obtain powder coating No. 1 (volume average particle diameter 33 μm) was obtained.

Example 2
Powder coating no. I got 2.

Example 3
Performed in Example 1 except that the glycidyl group-containing acrylic resin (B1) in the intermediate composition (X1) was 4.38 parts, and the amount of the post-added glycidyl group-containing acrylic resin (B1) was 5.84 parts. Powder coating No. 1 was prepared in the same manner as in Example 1. I got 3.

Example 4
Powder coating No. 1 was prepared in the same manner as in Example 1 except that the glycidyl group-containing acrylic resin (B1) in the intermediate composition (X1) was changed to 5.11 parts. I got 4.

Example 5
Performed in Example 1 except that the glycidyl group-containing acrylic resin (B1) in the intermediate composition (X1) was 5.84 parts, and the amount of the post-added glycidyl group-containing acrylic resin (B1) was 5.11 parts. Powder coating No. 1 was prepared in the same manner as in Example 1. Got 5.

Example 6
Performed in Example 1 except that the glycidyl group-containing acrylic resin (B1) in the intermediate composition (X1) was 6.57 parts, and the amount of the post-added glycidyl group-containing acrylic resin (B1) was 0.73 parts. Powder coating No. 1 was prepared in the same manner as in Example 1. I got 6.

Example 7
Powder coating No. 1 was prepared in the same manner as in Example 1 except that the glycidyl group-containing acrylic resin (B1) in the intermediate composition (X1) was changed to 6.57 parts. I got a 7.

Comparative example 1
Performed in Example 1 except that the amount of glycidyl group-containing acrylic resin (B1) in the intermediate composition (X1) was 2.19 parts, and the amount of post-added glycidyl group-containing acrylic resin (B1) was 7.30 parts. Powder coating No. 1 was prepared in the same manner as in Example 1. I got 8.

Comparative example 2
Performed in Example 1 except that the glycidyl group-containing acrylic resin (B1) in the intermediate composition (X1) was 2.92 parts, and the amount of the post-added glycidyl group-containing acrylic resin (B1) was 0.73 parts. Powder coating No. 1 was prepared in the same manner as in Example 1. I got a 9.

Comparative example 3
Powder coating no. Got 10.

Comparative example 4
Performed in Example 1 except that the glycidyl group-containing acrylic resin (B1) in the intermediate composition (X1) was 6.57 parts, and the amount of the post-added glycidyl group-containing acrylic resin (B1) was 8.03 parts. Powder coating No. 1 was prepared in the same manner as in Example 1. I got 11.

Comparative example 5
Performed in Example 1 except that the amount of the glycidyl group-containing acrylic resin (B1) in the intermediate composition (X1) was 7.30 parts, and the amount of the post-added glycidyl group-containing acrylic resin (B1) was 7.30 parts. Powder coating No. 1 was prepared in the same manner as in Example 1. I got 12.

In addition, powder coating No. The volume average particle diameters of Nos. 1 to 12 were all 33 μm, and each powder coating No. In Nos. 1 to 12, the volume average particle diameters of the corresponding intermediate compositions were all 35 μm.

Each powder coating No. obtained in Examples 1 to 7 and Comparative Examples 1 to 5 The following performance tests and evaluations were conducted for Nos. 1 to 12.

In addition, the test plates were each powder coating No. 1 to 12, electrostatic powder coating was applied to a cold rolled steel plate using an electrostatic coating machine PG-1 (manufactured by Asahi Sunac Co., Ltd., trade name) so that the dry film thickness was 70 μm, and the coating was applied at 180°C for 30 minutes. It was made by curing for minutes.

Table 1 shows each powder coating No. The compositions and performance test results of Nos. 1 to 12 are also shown.

The compounding equivalents in the table are as follows.

Equivalent (total): Epoxy equivalent of glycidyl group-containing acrylic resin (B1) per equivalent of carboxyl group of carboxyl group-containing polyester resin (A1) in the finally produced powder coating (in intermediate composition (X) ); Epoxy equivalent equivalent of glycidyl group-containing acrylic resin (B1) per equivalent of carboxy group of carboxyl group-containing polyester resin (A1) in intermediate composition (X) (post-added amount); Carboxy group-containing polyester resin (A1) The epoxy equivalent of the glycidyl group-containing acrylic resin (B1) of the post-addition amount per 1 equivalent of the carboxyl group of

Storage stability of paints: Each powder paint is stored in a closed container at 30°C for one month. Thereafter, a test plate was prepared using the powder coating, and the finished appearance was evaluated based on the following criteria.
○: There is almost no change compared to the test plate made with the powder paint before storage.
△: Slightly inferior in smoothness compared to the test plate made with powder paint before storage.
×: The smoothness is significantly deteriorated compared to the test plate prepared with the powder paint before storage. Or it doesn't flow at all.

Cross-cut adhesion: 50 squares of 2 mm were made on a test plate using a cutter knife, cellophane adhesive tape was strongly pressed onto the surface of the squares, and the tape was peeled off from the coating in a short period of time, and evaluated according to the following criteria.
○: Peeling is observed at a peeling area ratio of 1 to 2% △: Peeling is observed at a peeling area ratio of 3 to 5% ×: Peeling is observed at a peeling area ratio of 6% or more Weight drop resistance (shock resistance test) : In accordance with JIS K 5600-5-3 (1999), impact was applied to the painted surface of the test plate at -30°C under the conditions of a weight of 500 g, a point of impact of 1/2 inch in diameter, and a height of 50 cm. added. Next, cellophane adhesive tape was applied to the area where the impact was applied, and the tape was instantly peeled off.The degree of peeling of the coating film was evaluated using the following criteria.
○: No peeling is observed on the painted surface △: Slight peeling is observed on the painted surface ×: Significant peeling is observed on the painted surface Pellet flow property: Approximately 0.8 g of powder paint is applied to a powder coating of approximately 13 mm in diameter and approximately 13 mm in height. It was pressure-molded at 20 kg/ ^mm2 into a 4 mm cylindrical shape and was attached with double-sided tape to an aluminum plate kept at an angle of 45 degrees, and heated at 170°C for 10 minutes to allow it to flow. The sag length was measured.
○: Hanging length is 30 mm or more △: Hanging length is 20 mm or more and less than 30 mm ×: Hanging length is less than 20 mm

It is possible to provide a method for producing a powder coating material that can suppress solid phase reactions during storage after production of the powder coating material, and has excellent finished appearance and coating performance of the resulting coating film.

Claims (3)

A method for producing a powder coating comprising a carboxyl group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), a pigment (C) and an additive (D), the method comprising:
Consisting of a carboxyl group-containing polyester resin (A), a glycidyl group-containing acrylic resin (B), a pigment (C) and an additive (D),
An intermediate composition that is a melt-kneaded product in which the glycidyl group-containing acrylic resin (B) is blended in an amount having 0.5 to 0.9 equivalents of epoxy groups per 1 equivalent of carboxyl groups in the carboxyl group-containing polyester resin (A). To product (X), add and mix an amount of glycidyl group-containing acrylic resin (B) having 0.1 to 1.0 equivalents of epoxy groups per 1 equivalent of carboxyl group of carboxyl group-containing polyester resin (A), A method for producing a powder coating characterized by co-pulverization. A powder coating produced by the method for producing a powder coating according to claim 1. A coated article on which a coating film of the powder coating according to claim 2 is formed.