JP2001294805A - Powder coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder coating composition excellent in low-temperature curability and excellent in the appearance of a coating film therefrom even if the viscosity when it is melted is high. SOLUTION: This powder coating composition essentially contains a β- hydroxyalkylamide curing agent of the formula (wherein R1 is H, methyl or ethyl; R2 is H, a 1-5C alkyl or group HOCH(R1)CH2; and A is a bivalent hydrocarbon group) and a carboxyl-containing polyester resin having a resin solid acid value of 10-100 and a softening point of 80-150 deg.C; wherein the volume- average size of the particles is 5-30 μm and the equivalent ratio of the hydroxyl group in the curing agent to the carboxyl group in the above polyester resin is 0.4-1.3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating composition having excellent low-temperature curability and capable of forming a coating film having a high appearance.

[0002]

2. Description of the Related Art As a powder coating, there is widely known a powder coating in which an epoxy resin, an acrylic resin, a polyester resin or the like is used as a main binder and, if necessary, a curing agent such as a polyvalent carboxylic acid, a melamine resin and a blocked isocyanate. These are used in many fields such as home appliances, automobiles, and building materials. Among them, the powder coating composition mainly composed of a thermosetting resin composition, a certain temperature or more,
Usually, baking conditions at a high temperature of 180 ° C. or higher are required.

However, such high-temperature baking requires a large amount of energy and generates a large amount of volatile components, so that it is not environmentally preferable.

Therefore, Japanese Patent Application Laid-Open No. 4-275375 proposes a low-temperature curable powder coating material using a block of polyisocyanate such as tetramethylxylylene diisocyanate as a curing agent. However, a coating film using such a coating material has insufficient mechanical properties.

On the other hand, JP-A-11-228866 discloses a powder coating composition comprising an epoxy-containing vinyl polymer, a carboxyl-containing polyester resin, a β-hydroxyalkylamide curing agent and an epoxy resin as essential coating components. Things have been suggested. The baking temperature of this powder coating composition is 170 ° C., which is only slightly lower than in the past. In addition, this powder coating contains a large amount of an acrylic resin component, which is one of the vinyl copolymers, and has a high viscosity when melted. It was not something.

Generally, in order to improve the appearance of a coating film,
There is known a method for reducing the viscosity of a powder coating at the time of melting as much as possible. For this purpose, the molecular weight and pigment concentration of a resin have been reduced, and a soft component has been added. However,
Since the viscosity at the time of melting depends on the temperature, further lowering the viscosity has been required in low-temperature baking. On the other hand, a decrease in the molecular weight of the resin or the addition of a soft component reduces the mechanical properties of the coating film, and a decrease in the pigment concentration decreases the hiding power, and it is difficult to reduce the melt viscosity as desired. Was.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a powder coating composition which is excellent in low-temperature curability and has an excellent appearance of a formed coating film even if the viscosity at the time of melting is high. is there.

[0008]

The powder coating composition of the present invention has a β-hydroxyalkylamide curing agent represented by the following formula, a resin solid content acid value of 10 to 100, and a softening point of 80.
A powder coating composition containing particles containing carboxyl group-containing polyester resin as a main component and having a volume average particle diameter of 5 to 30 μm,
The ratio of the number of equivalents of the hydroxyl group of the curing agent to the number of equivalents of the carboxyl group of the polyester resin is 0.4 to 1.3.

[0009]

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Wherein R ¹ is a hydrogen atom, a methyl group or an ethyl group, R ² is a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or HOCH (R ¹ ) CH ₂ —, and A is divalent Wherein the minimum melt viscosity of the powder coating composition is 60 to 2
It is preferably 000 poise.

The carboxyl group-containing polyester resin is obtained by polycondensation using isophthalic acid and terephthalic acid as main raw materials, and has a weight average molecular weight of 1,000.
It is preferable that it is ~ 150,000.

Further, the carboxyl group-containing polyester resin is obtained by polycondensation using isophthalic acid as a main raw material as an acid component, and has a weight average molecular weight of 1,000 to 1,000.
It may be 150,000.

On the other hand, the SP value is 9.5 or less, the glass transition temperature (Tg) is 20 ° C. or less, and the number average molecular weight is 300 to 50.
000 may be contained as a surface conditioner, and the content thereof is 0.01 to 5 parts by weight with respect to a total of 100 parts by weight of the curing agent and the carboxyl group-containing polyester resin. Is preferred.

On the other hand, as a fluidity-imparting agent, inorganic fine particles, non-crosslinked organic fine particles having a particle diameter of 0.001 to 0.5 μm, or crosslinked organic fine particles having a particle diameter of 0.01 to 2 μm are further contained. It may be.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The powder coating composition of the present invention comprises β-
It contains particles mainly composed of a hydroxyalkylamide curing agent and a carboxyl group-containing polyester resin having a specific acid value and a softening point.

The β-hydroxyalkylamide curing agent, which is one of the main components of the particles contained in the powder coating composition of the present invention, is represented by the following formula.

[0017]

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Here, in the formula, R ¹ is a hydrogen atom, a methyl group or an ethyl group, R ² is a hydrogen atom, and has 1 to 1 carbon atoms.
5 is an alkyl group or HOCH (R ¹ ) CH ₂ —,
Represents a monovalent hydrocarbon group.

Further, in the formula, R ¹ is a hydrogen atom or a methyl group, and R ² is HOCH (R ¹ ) CH ₂
-, A is preferably an alkylene group having 2 to 10 carbon atoms, more preferably 4 to 8 carbon atoms.

The curing agent can be obtained, for example, by reacting a carboxylic acid and / or a carboxylic acid ester with a β-hydroxyalkylamine in the presence of an alkoxide catalyst such as sodium or potassium.

The carboxylic acid or carboxylic acid ester used here includes, for example, succinic acid, adipic acid, glutaric acid, dimethyl succinate, diethyl succinate, dimethyl adipate and the like.

Examples of β-hydroxyalkylamine include N-methylethanolamine, diethanolamine, N-methylpropanolamine and the like.

The carboxyl group-containing polyester resin, which is another main component of the particles contained in the powder coating composition of the present invention, has an acid value of resin solid content of 10 to 100 (mg KO).
H / g solid content; the same applies hereinafter), preferably 15 to
80, and more preferably 20 to 60. When the acid value is less than 10, the curability may be reduced and the mechanical properties may be reduced. On the other hand, when the acid value is more than 100, the water resistance of the obtained coating film may be reduced. The softening point of the carboxyl group-containing polyester resin is from 80 to 150 ° C, preferably from 90 to 130 ° C. If the softening point is lower than 80 ° C., the blocking resistance may decrease. If it is higher than 150 ° C., the smoothness of the obtained coating film may decrease. On the other hand, the weight average molecular weight of the carboxyl group-containing polyester resin is preferably from 1,000 to 150,000, more preferably from 3,000 to 70,000, and even more preferably from 4,000 to 50,000. When the weight average molecular weight is smaller than 1000, the performance and physical properties of the obtained coating film may be reduced, and
When it is larger than 0000, there is a possibility that the smoothness and appearance of the obtained coating film may be reduced.

The acid value of the resin solid content in the present invention is JIS K 0070, and the softening point is JIS K 2
207, respectively. Further, the weight average molecular weight and the number average molecular weight in the present invention can be determined by a method well known by those skilled in the art such as gel permeation chromatography (GPC).

The carboxyl group-containing polyester resin may be a composite of two or more kinds. In that case, the above physical property values and special values mean the values of the composite as a whole.

Such a carboxyl group-containing polyester resin can be obtained by polycondensation of an acid component mainly composed of a polyvalent carboxylic acid and an alcohol component mainly composed of a polyhydric alcohol by a usual method. it can.
By selecting the respective components and the conditions of the condensation polymerization, a carboxyl group-containing polyester resin having the above-mentioned physical properties and special values can be obtained.

The acid component is not particularly restricted but includes, for example, terephthalic acid, isophthalic acid, phthalic acid, trimellitic acid and their anhydrides, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid and the like. Aromatic dicarboxylic acids and anhydrides thereof, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, saturated aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, and anhydrides thereof, and the like. Can be. In addition, γ-butyrolactone, ε-
Examples include lactones such as caprolactone, and corresponding hydroxycarboxylic acids and aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid. The acid component may be of two or more types. Above all, isophthalic acid and terephthalic acid are preferable in terms of durability, physical properties, and price. The proportion of terephthalic acid and isophthalic acid in the total acid component is at least 70 mol%, preferably 7 mol%.
5 mol% or more, particularly preferably 80 mol% or more is suitable. Here, the case where the total proportion of terephthalic acid and isophthalic acid is used as 70% by mole or more as the acid component, particularly means that these are used as main raw materials. As for the upper limit of the content of terephthalic acid and isophthalic acid, the entire amount of the acid component used for preparing the polyester resin may be terephthalic acid and / or isophthalic acid. When it is desired to particularly improve the weather resistance, the proportion of isophthalic acid in the total acid component is preferably at least 70 mol%, more preferably at least 80 mol%, particularly preferably at least 90 mol%. Here, the case where the proportion of isophthalic acid in the total acid component is 70 mol% or more means that isophthalic acid is used as a main raw material.

The alcohol component is not particularly restricted but includes, for example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,5-hexanediol, diethylene glycol, triethylene glycol, Ethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol,
Bisphenol A alkylene oxide adduct, bisphenol S alkylene oxide adduct, 1,2-propanediol, neopentyl glycol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 2,3- Pentanediol, 1,4-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol,
Examples thereof include diols such as 1,2-dodecanediol and 1,2-octadecanediol, and trihydric or higher polyhydric alcohols such as trimethylolpropane, glycerin and pentaerythritol. The alcohol component is 2
There may be more than one species.

The particles contained in the powder coating composition of the present invention contain, as main components, the β-hydroxyalkylamide curing agent and the carboxylic acid-containing polyester resin,
The ratio of the number of hydroxyl groups of the curing agent to the number of carboxyl groups of the polyester resin is 0.4%.
-1.3 is preferred.

If the ratio is less than 0.4, the amount of the curing agent becomes small, the curing becomes insufficient, and the mechanical properties of the coating film decrease,
Water resistance may be reduced. When the ratio exceeds 1.3, the amount of the curing agent increases, which is not only economically disadvantageous but also may lower the water resistance of the coating film.

When the carboxylic acid-containing polyester resin has an acid value of 10 to 45, the equivalent ratio may be 0.6 to 1.3, and more preferably 0.7 to 1.2. preferable. Within this range, the curing reaction proceeds without excess and deficiency, and the mechanical properties and water resistance of the coating film become favorable, which is preferable.

On the other hand, when the acid value of the polyester resin is 45
If the acid value is higher than that used in ordinary powder coatings and the low-temperature curability is particularly improved, the equivalent ratio is preferably 0.4 to 1.2, and more preferably 0 to 100. .5-
1.1 is preferred. Outside this range, the mechanical properties of the coating film may decrease, and the water resistance may decrease.

The volume average particle diameter of the particles containing the above curing agent and the above polyester resin as main components is 5 to 30.
μm is preferred. More preferably, 10 to 25
μm. If it is less than 5 μm, the transferability of the powder coating material is reduced, which causes a problem in coating workability and may cause a reduction in coating efficiency. Conversely, if the average volume particle size exceeds 30 μm, the smoothness of the coating film may be reduced, and the appearance of the coating film may be deteriorated. The volume average particle size is
Particle size analyzer (for example, Nikkiso Co., Ltd., Microtrack H
RAX-100).

Further, in order to form a uniform coating film on an object to be coated having a complicated shape having a non-planar part, a powder having a particle diameter of 1/5 or less of the volume average particle diameter is added by 5% by weight. % Is preferable.

The powder coating composition of the present invention preferably has a minimum melt viscosity of 60 to 2000 poise. 200
If it exceeds 0 poise, the volume average particle diameter is 5 to 30 μm when the powder coating applied to the object is melted and flows.
m, the flow is not easily performed, and as a result, the appearance of the coating film is deteriorated. When the particle size is less than 60 poise, not only the effect of the particle size is reduced, but also There is a risk that the sagging property will deteriorate.

Here, the minimum melt viscosity is a viscosity obtained by the following measurement. The coating material is heated at a rate of 10 ° C. per minute until the target temperature is reached, and then the melt viscosity of the coating film is measured over time under the condition of maintaining the target temperature. The lowest viscosity was determined, and this was defined as the lowest melt viscosity. In general, when an object to be coated with a powder coating is heated, the applied powder coating melts with an increase in temperature, and the viscosity decreases with the melting. Then, as the curing reaction progresses with the passage of time, the viscosity gradually increases. As a result, a phenomenon in which the melt viscosity becomes minimum is observed. In the present invention, attention is paid to this minimum melt viscosity, the viscosity falls within the above range, and the volume average particle diameter of the powder coating composition is 5 to 30 μm, so that the appearance of the coating film can be improved. is there.

For the measurement of the minimum melt viscosity, it is preferable to use the complex viscosity by dynamic viscoelasticity measurement.

The particles contained in the powder coating composition of the present invention contain, in addition to the above-mentioned curing agent and carboxyl group-containing polyester resin as main components, methyl (meth) acrylate and ethyl (meth) acrylate as subcomponents. Butyl (meth) acrylate, 2-ethylhexyl (meth)
An acrylate, an alkyl ester of (meth) acrylic acid such as lauryl (meth) acrylate, obtained by using one or more kinds of alkyl esters as raw materials, has an SP value of 9.5 or less, and a number average molecular weight of 300 to 50,000, preferably , 1000
An acrylic resin having a glass transition temperature of ３０30,000 and a glass transition temperature of less than 20 ° C., preferably 0 ° C. or less may be contained as a surface conditioner.

If the SP value exceeds 9.5, the SP value becomes close to the SP value of the carboxyl group-containing polyester resin. Because of high compatibility with polyester resin, it is difficult to positively transfer to the coating film surface,
As a result, it is considered that it is not possible to contribute to the improvement of the flow property on the coating film surface.

Here, the SP value refers to a solubility parameter and is described in a literature (SUH, CLARKE, JPSA).
-1, 5, 1671-1681 (1967), and the measuring method is a method known to those skilled in the art such as a turbidity method.

When the glass transition temperature (Tg) exceeds 20 ° C., the appearance of the coating film may be deteriorated. And if the number average molecular weight is less than 300, even if it migrates on the coating film surface, the effect of contributing to the flowability decreases, and if it exceeds 50,000, it may be difficult to migrate on the coating film surface. is there.

The acrylic resin is used in an amount of 0.0 with respect to a total of 100 parts by weight of the curing agent and the polyester resin.
A range of 1 to 5 parts by weight, preferably 0.05 to 3 parts by weight, more preferably 0.1 to 2 parts by weight is suitable. If the amount is less than 0.01 part by weight, the surface cannot be adjusted sufficiently, and the probability of poor appearance increases. If the amount is more than 5 parts by weight, the blocking properties of the paint may be reduced.

The powder coating composition of the present invention may further contain inorganic fine particles or organic fine particles as a fluidity imparting agent. By containing such fine particles, the transportability and the blocking property can be further improved.

The inorganic fine particles include hydrophobic silica,
Examples include hydrophilic silica, aluminum oxide, and titanium oxide. Commercially available inorganic fine particles include, for example, AE
ROSIL 130, AEROSIL 200, AER
OSIL 300, AEROSIL R-972, AE
ROSIL R-812, AEROSIL R-812
S, titanium dioxide T-805, titanium dioxide P-25,
Examples thereof include Aluminum Oxide C (manufactured by Nippon Aerosil Co., Ltd.) and Carplex FPS-1 (manufactured by Shionogi & Co., Ltd.). The amount of the inorganic particles added is 0% based on 100 parts by weight of the particles containing the curing agent and the carboxyl group-containing polyester resin as main components from the viewpoints of the effect to be imparted, the smoothness of the coating film and the coating efficiency. .05
２2 parts by weight, preferably 0.1-1 part by weight. If the amount is less than 0.05 parts by weight, the effect is small, and 2
If the amount exceeds the weight part, there is a possibility that the smoothness of the coating film is reduced or gloss is generated.

On the other hand, the organic fine particles have a particle diameter
0.001 to 0.5 μm, preferably 0.01 to 0.
5 μm non-crosslinked organic resin particles or particle diameter,
Crosslinked organic resin particles of 0.01 to 2 μm, preferably 0.01 to 1 μm are preferred. Examples of the organic resin include a vinyl resin, an acrylic resin, an epoxy resin, and a polyester resin, and the acrylic resin is preferable because it can be easily industrially produced.

The non-crosslinked organic resin particles are obtained by, for example, directly manufacturing by emulsion polymerization or suspension polymerization, or by manufacturing a resin by solution polymerization or bulk polymerization, and then pulverizing and classifying the resin. is there. The glass transition temperature (Tg) of the non-crosslinked organic resin particles is 50 to 150 ° C.
Preferably, the temperature is in the range of 70 to 120 ° C. When non-crosslinked organic resin particles are used, when heat is applied to the powder coating, the organic resin fine particles themselves flow to obtain a coating film having an excellent appearance. If the Tg is lower than 50 ° C., it becomes difficult to sufficiently secure the anti-blocking performance of the powder coating during storage, transportation, and the like.
This is because those exceeding 0 ° C. are not very practical. The average particle size of the non-crosslinked organic resin fine particles is 0.001 to
0.5 μm, preferably in the range of 0.01 to 0.5 μm. Further, the amount of addition is determined based on particles 10 containing the above curing agent and carboxyl group-containing polyester resin as main components.
0.05 to 35 parts by weight, preferably 0.1 to 0 parts by weight.
It is about 1 to 10 parts by weight. This is because there is a proportional relationship between the average particle size of the non-crosslinked organic resin fine particles and the amount of addition, and the lower limit of the particle size is about 0.001 μm from the viewpoint of ease of industrial production of the organic resin fine particles. The addition amount of about 0.05% by weight is necessary for the expression of the effect of the addition of the particles, and the addition amount of the resin fine particles required for imparting the blocking resistance increases as the particle diameter increases. If the diameter exceeds 0.5μ, the fluidity of the powder coating deteriorates, and when the powder coating is applied by the coating gun, the powder coating particles adhere to the tip of the coating gun and easily aggregate, and the aggregated particles are scattered. As a result, it is difficult to achieve the object of the invention of obtaining a high-appearance coating film.
It is based on the finding that it is limited to μ, in which case the amount added must be up to about 35% by weight, based on the powder coating.

Examples of monomers used for producing a non-crosslinked acrylic resin include acrylic acid, crotonic acid,
Itaconic acid, maleic acid, fumaric acid, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, acrylamide, methacrylamide, acrylonitrile, Methacrylonitrile, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth)
Acrylate, 2-ethylhexyl (meth) acrylate, styrene and the like can be mentioned.

The crosslinked organic resin particles are fine particles of an organic resin having a three-dimensional structure and are not substantially dissolved in a solvent.
Further, it does not melt by heating at about the baking temperature.

The crosslinked organic resin particles are obtained by producing a resin by solution polymerization or bulk polymerization, and then pulverizing and classifying the resin. It may be obtained, or obtained by performing a crosslinking reaction after formation of non-crosslinked organic resin particles.

The crosslinked organic resin fine particles preferably have an average particle size of 0.01 to 2 μm, and if the average particle size exceeds 2 μm, the fine particles tend to become lumpy at the time of coating. The amount is preferably 0.05 to 10 parts by weight, and more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the particles containing the curing agent and the carboxyl group-containing polyester resin as main components. is there. If the amount is less than 0.1 part by weight, there is no effect of improving the blocking resistance, and if it exceeds 10 parts by weight, the appearance may be deteriorated.

The crosslinked organic resin fine particles are preferably obtained from a vinyl resin, an acrylic resin, an epoxy resin, a polyester resin or the like, like the non-crosslinked organic resin particles. Among them, the acrylic resin is industrially produced. It is preferable because it is easy to perform.

The crosslinked organic resin particles obtained from this acrylic resin can be obtained, for example, from a mixture of 1% by weight or more of a crosslinkable acrylic monomer and another monomer.
The crosslinkable acrylic monomer is a monomer having at least two radically polymerizable unsaturated groups in a molecule, or at least two kinds of monomers each having a functional group capable of reacting with each other and a radically polymerizable unsaturated group. Means If the amount of the crosslinkable acrylic monomer is less than 1% by weight, a sufficient crosslinked structure cannot be obtained, and there is a possibility that a part of the crosslinkable acrylic monomer dissolves and swells in the powder coating at the time of baking to reduce the smoothness of the coating. is there.

Examples of the monomer having at least two radically polymerizable unsaturated groups in the molecule include a polymerizable unsaturated monocarboxylic acid ester of a polyhydric alcohol, a polymerizable unsaturated alcohol ester of a polybasic acid and 2 Aromatic compounds substituted with two or more vinyl groups are exemplified. Examples thereof are ethylene glycol di (meth) acrylate, triethylene glycol di (meth)
Acrylate, tetraethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, 1,4-butanediol (meth) acrylate, neopentyl glycol di (meth) Acrylate,
1,6-hexaneol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerol di (meth) acrylate, 1,1,1-trishydroxymethylethanedi (meth) acrylate , Triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl terephthalate, diallyl phthalate, allyl (meth) acrylate and divinylbenzene.

Examples of combinations of monomers having two radically polymerizable unsaturated groups each carrying a mutually reactive functional group include glycidyl acrylate,
There are epoxy group-containing ethylenically unsaturated monomers such as glycidyl methacrylate and carboxyl group-containing ethylenically unsaturated monomers such as acrylic acid, methacrylic acid and crotonic acid. Other combinations of functional groups that can react with each other include an amino group and a carboxylic acid group, and an epoxy group and a carboxylic acid or an anhydride thereof. Includes

As the above-mentioned other monomers, there may be mentioned the monomers used for producing the above-mentioned non-crosslinked acrylic resin.

In the powder coating composition of the present invention, the particles containing the above-mentioned curing agent and the above-mentioned polyester resin as main components may contain a pigment and an additive, if necessary.

When the above pigment is contained, the type thereof is not particularly limited, and specific examples thereof include titanium dioxide, red iron oxide, yellow iron oxide, carbon black, phthalocyanine blue,
Color pigments such as phthalocyanine green, quinacridone pigments and azo pigments, metallic pigments of each color, pearl pigments of each color, metal powders and surface-treated ones, talc, silica, calcium carbonate, precipitated barium sulfate, etc. Pigments and the like can be mentioned. Further, in order to reduce the gloss, it is preferable to include an inorganic matting agent such as talc, silica, calcium carbonate, barium sulfate, feldspar, wollastonite, or an organic matting agent composed of organic fine particles. The volume average particle size of the matting agent is 3 to
It is preferably 30 μm.

As the above additives, for example, a charge control agent,
Examples include a plasticizer, an ultraviolet absorber, an antioxidant, and an anti-armpit agent. As these, those commonly used in powder coatings can be used.

Next, a method for producing the powder coating composition of the present invention will be described. That is, the present invention is based on particles having a specific particle diameter, which are obtained by using the β-hydroxyalkylamide curing agent and the carboxyl group-containing polyester resin composition having a specific range of acid value and softening point as main components, as a main component. The powder coating composition is obtained. Furthermore, it can be obtained by adding fine particles having a smaller particle diameter than the particle diameter of the particles as a fluidity-imparting agent.

First, the above-mentioned β-hydroxyalkylamide curing agent and the above-mentioned carboxyl group-containing polyester resin composition, which are the main constituents of the above-mentioned particles, and if necessary, the above-mentioned surface conditioner, pigment, and other additives are provided. A fixed amount is charged and uniformly mixed by a mixer. As the mixer, a general mixer such as a Henschel mixer, a ball mill, or a Banbury mixer is used.

Next, the obtained mixture is melt-kneaded. Here, it is heated and melted by a kneader such as an extruder or a hot roll. Next, the pellets obtained in the melt-kneading step are pulverized using a pulverizer such as an atomizer or a jet mill. Also, after melt kneading and mixing the above components,
The resulting mixture can be directly used to obtain powdery particles by a spray drying method. The thus obtained powder coating composition of the present invention preferably has a volume average particle diameter of 5 to 30 μm, and after performing classification for adjusting the particle size distribution by removing giant particles and fine particles. Is preferred.

The particles thus obtained can be used as a powder coating as it is, but may be a powder coating further containing the fine particles.

The fine particles may be added before the pulverization of the pellets, or may be added to the particles after the pulverization or classification, and may be stirred and mixed by a mixer such as a super mixer. By such an addition method, it is considered that the fine particles are usually attached to the surface of the particle or slightly embedded in the surface of the particle in the powder coating.

After the powder coating composition of the present invention is applied to an object to be coated, a coating film can be obtained by heating. The object to be coated is not particularly limited, and specific examples thereof include an iron plate, a steel plate, an aluminum plate, and the like, and a surface-treated one thereof. In this case, the powder coating composition may be directly applied to the object to be coated as an undercoat, that is, a primer to form an undercoat, on which an intermediate coating and a topcoat may be applied. In addition, the object to be coated has already been subjected to an undercoat or the like, and the powder coating composition is coated on the undercoat film,
It may be applied as an intermediate coating or a top coating. As the undercoat paint for forming the undercoat, known paints such as an electrodeposition paint and a primer can be used.

The method of coating is not particularly limited, and a method well known by those skilled in the art such as a spray coating method, an electrostatic powder coating method, a fluid immersion method and the like can be used. From the viewpoint, the electrostatic powder coating method is preferably used.

The coating film thickness when applying the powder coating composition of the present invention is not particularly limited, but can be set to 20 to 100 μm.

The heating conditions vary depending on the functional groups involved in curing and the amounts of curing accelerators. For example, the heating temperature is 100 to 230 ° C., preferably 140 to 200 ° C. It can be set appropriately according to the temperature.

[0068]

The present invention will be further described with reference to the following examples, but the present invention is not limited to these examples. In the examples, “%” and “parts” are based on weight unless otherwise specified.

Production Example 1 (Production Example of Paint Pellets) Krill Coat CC7630 (manufactured by Daicel UCB, a carboxyl group-containing polyester resin, weight average molecular weight of 9000, polycondensate of isophthalic acid, terephthalic acid, neopentyl glycol and ethylene glycol) , 95 parts by weight of an acid value, a softening point of 110 ° C.) and 5 parts by weight of Primid XL552 (a compound of a structural formula represented by the following formula with a β-hydroxyalkylamide curing agent manufactured by EMS-PRIMD, hydroxyl equivalent: 84): Acronal 4F
(Manufactured by BASF, acrylic polymer Tg is -55 ° C, S
P value is 9.3, number average molecular weight is 16500, surface conditioner)
0.5 parts by weight, 1 part by weight of benzoin, and Taipa C
R-90 (Ishihara Sangyo Co., Ltd., rutile type titanium dioxide pigment)
Using 50 parts by weight and 35 parts by weight of sedimentable barium sulfate 100 (manufactured by Sakai Chemical Industry Co., Ltd.) as raw materials using a mixer supermixer (manufactured by Nippon Spindle Co., Ltd.) for about 3 minutes, and further using a melt kneader Conneader (Bus) About 11
The mixture was melt-kneaded at 0 ° C. Thereafter, the obtained melt-kneaded product was cooled to room temperature to obtain a paint pellet.

Here, Primid XL552 is a substance represented by the following structural formula.

[0071]

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Production Example 2 (Production Example of Non-Crosslinked Organic Resin Particles) In a reaction vessel equipped with a stirrer, a cooler and a temperature controller, 380 parts of deionized water and MON2 nonionic surfactant were added.
2 parts (manufactured by Sanyo Chemical Co., Ltd.) were charged and dissolved while maintaining the stirring temperature at 80 ° C., and a solution prepared by dissolving 1 part of ammonium persulfate in 10 parts of deionized water as an initiator was added thereto. Then 85 parts of methyl methacrylate, 5 parts of styrene
And a mixed solution consisting of 10 parts of n-butyl methacrylate was added dropwise over 60 minutes. After dropping, stirring was continued at 80 ° C. for 60 minutes. Thus, the nonvolatile content is 20%, and the particle size is 0.
An emulsion of 03-0.05μ was obtained. The emulsion was spray-dried to obtain non-crosslinked resin fine particles having a Tg of 100 ° C.

Production Example 3 (Production example of crosslinked organic resin particles) In a reaction vessel equipped with a stirrer, a nitrogen inlet tube, a temperature controller, a condenser, and a decanter, 134 parts of bishydroxyethyltaurine, 130 parts of neopentyl glycol, azelaine 236 parts of an acid, 186 parts of phthalic anhydride and 27 parts of xylene were charged and heated. Water generated by the reaction was removed by azeotropic distillation with xylene. The temperature was raised to 190 ° C over about 2 hours from the start of reflux, stirring and dehydration were continued until the acid value corresponding to carboxylic acid reached 145, and then cooled to 140 ° C. Then, the temperature of 140 ° C. was maintained, and glycidyl versatate (trade name “Kajura E1”) was used.
314 parts) in 30 minutes.
Stirring was continued for another hour to complete the reaction. The resulting polyester resin having a zwitterionic group had an acid value of 59 and a hydroxyl value of 90. Next, 282 parts of deionized water, 10 parts of the polyester resin having amphoteric group and 0.75 parts of dimethylethanolamine were charged into a reaction vessel equipped with a cooler and a temperature controller, and the temperature was adjusted to 8 under stirring.
The solution was dissolved while being kept at 0 ° C., and a solution prepared by dissolving 4.5 parts of azobiscyanovaleric acid in 45 parts of deionized water and 4.3 parts of dimethylethanolamine was added. Next, 70.7 parts of methyl methacrylate, 9 parts of n-butyl acrylate 9
A mixed solution consisting of 4.2 parts, 70.7 parts of styrene, 30 parts of 2-hydroxyethyl acrylate and 4.5 parts of ethylene glycol dimethacrylate was dropped over 60 minutes. After the addition, 1.5 parts of azobiscyanovaleric acid was further added to 15 parts of deionized water and 1.4 parts of dimethylethanolamine.
Was added to the mixture and stirring was continued at 80 ° C. for 60 minutes. As a result, the nonvolatile content was 45%, the pH was 7.2, and the viscosity was 92 c.
An emulsion having a ps (25 ° C.) and a particle diameter of 0.156 μ was obtained. This emulsion was spray-dried to obtain crosslinked resin particles.

Production Example 4 (Powder Coating B1) The paint pellets obtained in Production Example 1 were pulverized using a pulverizer atomizer (manufactured by Fuji Paudal Co.), and the obtained powder was subjected to an airflow classifier DS-2. Type (made by Nippon Pneumatic Industries Co., Ltd.)
And then removing the fine particles and the coarse particles to obtain a volume average particle diameter of 25 μm and a volume average particle diameter of 1 μm.
A powder coating composition B1 having a content of powder having a particle diameter of / 5 or less of 2% by weight was obtained.

Production Example 5 (powder paint B2) 100 parts of the paint pellets obtained in Production Example 1 and 0.3 part of Aerosil R-972 (manufactured by Nippon Aerosil Co., Ltd., particle diameter: about 16 nm) as inorganic fine particles were crushed by a pulverizer. The obtained powder was pulverized using an atomizer, and the obtained powder was classified using an airflow classifier DS-2 to remove fine particles and coarse particles, thereby obtaining a volume average particle diameter of 24 μm and a 1 / l of the volume average particle diameter. 5
A powder coating composition B2 having a content of powder having the following particle diameter of 2.1% by weight was obtained.

Production Example 6 (Powder Coating B3) The paint pellets obtained in Production Example 1 were pulverized using a pulverizer atomizer, and the obtained powder was classified using an airflow classifier DS-2. Particles 10 from which fine particles and coarse particles have been removed
To 0 part, 1 part of the non-crosslinked resin particles of Production Example 2 was added and dry-mixed with a Henschel mixer (manufactured by Mitsui Miike Seisakusho) for 30 seconds to obtain a volume average particle diameter of 25 μm and 1/5 of the volume average particle diameter. A powder coating composition B3 having a content of powder having the following particle diameter of 2% by weight was obtained.

Production Example 7 (Powder Coating B4) The paint pellets obtained in Production Example 1 were pulverized using a pulverizer atomizer, and 1 part of the crosslinked resin particles of Production Example 3 was added to 100 parts of the obtained powder. Then, the mixture was dry-mixed with a Henschel mixer for 30 seconds and classified using an airflow classifier DS-2 to remove fine particles and coarse particles, thereby obtaining a volume average particle diameter of 24 μm and a volume average particle diameter of 1/5. A powder coating composition B4 having a content of powder having the following particle diameter of 1.9% by weight was obtained.

Production Example 8 (Powder Coating B5) The powder coating composition obtained by pulverizing the paint pellets obtained in Production Example 1 using a pulverizer atomizer and removing coarse particles using a 150 mesh sieve. B5 was obtained. The volume average particle diameter was 40 μm, and the content of powder having a particle diameter of 1/5 or less of the volume average particle diameter was 5.4% by weight.

Production Example 9 (powder paint B6 ) 85 parts by weight of Finedick M8020 (hydroxyl polyester resin, hydroxyl value 30, weight average molecular weight 18,000, manufactured by Dainippon Ink and Chemicals, Inc.) and Vestagon B-15
30 (manufactured by Degussa-Hüls, a blocked isocyanate curing agent), 15 parts by weight of Acronal 4F, 0.5 part by weight of benzoin, 1 part by weight of typaque CR-90
And 50 parts by weight of barium sulfate and 35 parts by weight of sedimentable barium sulfate were mixed for about 3 minutes using a supermixer (manufactured by Nippon Spindle Co., Ltd.), and further using a melt kneader (kneader). At about 110 ° C. Thereafter, the obtained melt-kneaded product was cooled to room temperature to obtain a paint pellet.

Next, the paint pet obtained here was pulverized using a pulverizer atomizer, and coarse particles were removed using a 150-mesh sieve to obtain a powder coating composition B6.
I got The volume average particle diameter was 37 μm, and the content of powder having a particle diameter of 1/5 or less of the volume average particle diameter was 4.5% by weight.

Example 1 The powder coating composition B1 obtained in Production Example 4 was 0.8 mm
Electrostatic spray coating with a corona charging type coating gun to a thickness of about 60 μm on a zinc phosphate-treated steel sheet.
The coating was baked at 25 ° C. for 25 minutes, and the coating film performance was evaluated by the following method. Table 1 shows the results.

<Blocking Property> The obtained powder coating composition was stored at a constant temperature of 40 ° C. for 2 weeks, and then evaluated by a residual ratio on a 25-mesh sieve.

<Minimum Melt Viscosity> 0.4 g of the obtained powder coating composition was molded under pressure to prepare pellets having a diameter of 2 cm. The complex viscosity of the obtained pellet was determined by a cone plate type dynamic viscoelasticity measuring apparatus MR300 (manufactured by Rheology) under the following conditions. Temperature rise start temperature: 20 ° C Temperature rise rate: 10 ° C / min. Achieving and holding temperature: 150 ° C Cone diameter: 1.73 cm Cone angle: 1.92 degrees Frequency: 2 Hz

<Erichsen value> JIS K5400
It was determined from the extrusion distance until cracks and peeling of the coating film occurred when the test piece was deformed using an Erichsen testing machine based on 8.2.2.

<Evaluation of Appearance> Surface roughness (Ra) was determined using Handysurf E-30A (manufactured by Tokyo Seiki Co., Ltd.) at a cutoff value of 2.5 mm. The higher the value, the poorer the appearance.

Examples 2 to 4 The powder coating compositions B2 to B4 obtained in Production Examples 5 to 6 were
It was used in each of Examples 2 to 4 and evaluated in the same manner as in Example 1. Table 1 shows the results.

Comparative Examples 1 and 2 The powder coating compositions B5 and B6 obtained in Production Examples 8 and 9 were used in Comparative Examples 1 and 2, respectively.
The evaluation was performed in the same manner as described above. Table 1 shows the results.

[0088]

[Table 1]

As can be seen from the results of the examples, a sufficiently cured product can be obtained and the appearance of the coating film can be improved even if the baking temperature is significantly lowered to 30 ° C. from the conventional 180 ° C. did it.

[0090]

According to the powder coating composition of the present invention, the baking temperature can be greatly reduced as compared with the prior art. In addition, the appearance of the obtained coating film can be further improved while maintaining or improving the physical property values.

Claims (8)

[Claims] 1. Particles mainly composed of a β-hydroxyalkylamide curing agent represented by the following formula and a carboxyl group-containing polyester resin having a resin solid content acid value of 10 to 100 and a softening point of 80 to 150 ° C. A powder coating composition containing, wherein the volume average particle diameter of the particles is 5 to 30 μm
Wherein the ratio between the number of equivalents of hydroxyl groups of the curing agent and the number of equivalents of carboxyl groups of the polyester resin is 0.4 to 0.4.
1.3. A powder coating composition which is 1.3. Embedded image (Wherein R ¹ is a hydrogen atom, a methyl group or an ethyl group,
R ² represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms or HOCH (R ¹ ) CH ₂ —, and A represents a divalent hydrocarbon group. ) 2. The powder coating composition according to claim 1, having a minimum melt viscosity of 60 to 2000 poise. 3. The polyester resin is obtained by polycondensation using isophthalic acid and terephthalic acid as main components as acid components, and has a weight average molecular weight of 1,000 to 15,000.
The powder coating composition according to claim 1, which is 0. 4. The powder coating composition according to claim 1, wherein the polyester resin is obtained by polycondensation using isophthalic acid as a main ingredient as an acid component, and has a weight average molecular weight of 1,000 to 150,000. 5. A glass transition temperature (T) having an SP value of 9.5 or less.
g) is 20 ° C. or less, and the number average molecular weight is 300 to 50,000.
Acrylic resin as a surface conditioner, the curing agent and the carboxyl group-containing polyester resin in total of 10
The powder coating composition according to any one of claims 1 to 4, wherein the composition is contained in an amount of 0.01 to 5 parts by weight based on 0 parts by weight. 6. The powder coating composition according to claim 1, further comprising inorganic fine particles as a fluidity imparting agent. 7. The fluidity-imparting agent having an average particle size of 0.0
The powder coating composition according to any one of claims 1 to 5, further comprising non-crosslinked organic resin particles having a particle size of from 01 to 0.5 µm. 8. The fluidity-imparting agent having an average particle size of 0.0
The powder coating composition according to any one of claims 1 to 5, further comprising crosslinked organic resin particles having a size of 1 to 2 µm.