JP2008081670A - Powder coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powder coating composition which provides a coating film excellent particularly in machinability in the field of aluminum wheel coating while maintaining usual coating film physical properties, can provide an excellent coating film even when it is applied to a substrate after non-chromate treatment, and can be suitably used, for example, as a primer powder coating material for aluminum wheels. <P>SOLUTION: The powder coating composition comprises powder coating particles made of a polyester resin (i) which comprises 70 mol% or more of terephthalic acid and isophthalic acid based on the total acid component composing the polyester resin and has a resin solid acid number of 10-100 mg KOH/g-solid, and an epoxy resin (ii) having an epoxy equivalent of 100-4,000 mg KOH/g-solid. The powder coating particles further comprises a flexible resin (iii), and the above (iii) is 1-12 mass% based on 100 mass% of the sum of the solids of the above (i) and the above (ii) and has a number average molecular weight of 30,000-100,000. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a powder coating composition.

As a powder coating material, an epoxy resin, a polyester resin or the like as a main binder is used in many fields such as home appliances, automotive parts, and building materials.

However, in powder coatings, it may be necessary to obtain sufficient physical properties such as adhesion, corrosion resistance, water resistance, and smoothness when, for example, coating is performed on a non-chromated metal substrate. is there. In such a powder coating, physical properties of a coating film are improved not only by a main binder but also by an additive (Patent Document 1).

An example of the application of the powder coating is a primer coating for aluminum wheel coating. In such applications, it is required to improve physical properties such as cutting workability, adhesion, and smoothness when applied to a non-chromate treated substrate. That is, since chromate treatment is being restricted in recent years, it is also required to form a coating film having good physical properties on a non-chromate treated aluminum substrate.

Patent Document 2 or Patent Document 3 includes a primer layer made of an epoxy polyester hybrid powder paint formed on an aluminum member, a base coat layer made of an acrylic high solid metallic paint formed on the primer layer, and the above A weather-resistant coating film having a top coat layer made of an acrylic powder clear paint or a clear coat layer made of an acrylic high solid paint formed on a base coat layer is disclosed.

In Patent Document 4, a primer layer made of an epoxy clear paint formed on the surface of an aluminum member, a base coat layer made of an acrylic color clear paint formed on the primer layer, and a base coat layer formed on the base coat layer. An aluminum member formed by forming a weather-resistant coating film having a topcoat layer made of an acrylic clear paint is disclosed.

However, these are examining the weather resistance and corrosion resistance of the coating film formed on the chromate-treated aluminum member, and the cutting workability of the coating film formed on the non-chromate treated substrate has been studied. Not.
JP 2000-345075 A JP-A-5-202319 JP-A-5-209141 Japanese Patent Laid-Open No. 7-80405

In view of the above, in the field of aluminum wheel coating, the present invention provides a coating film particularly excellent in cutting workability while maintaining normal coating film properties, and is also applied to a substrate after non-chromate treatment. An object of the present invention is to provide a powder coating composition that can provide an excellent coating film and that can be suitably used, for example, as a primer powder coating for aluminum wheels.

In the present invention, a polyester resin (i) in which 70 mol% or more of the total acid components constituting the polyester resin are composed of terephthalic acid and isophthalic acid, and the solid content acid value is 10 to 100 mgKOH / g solid content, and the epoxy equivalent is It is a powder coating composition comprising powder coating particles comprising 100 to 4000 mg KOH / g solid epoxy resin (ii), and the mixing ratio of the polyester resin (i) and the epoxy resin (ii) is a solid mass ratio. The powder coating particle further contains a flexible resin (iii), and the flexible resin (iii) includes the polyester resin (i) and the above It is 1-12 mass% with respect to 100 mass% of total solid content of an epoxy resin (ii), It is a number average molecular weight 30,000-100,000, It is a powder coating composition characterized by the above-mentioned.

The flexible resin (iii) is preferably polycaprolactone.
The particle size of the powder coating particles is preferably 25 to 35 μm.
The powder coating composition is preferably a primer powder coating for aluminum wheel coating.

The present invention is also an aluminum wheel coating method comprising a step of applying the powder coating composition to an aluminum wheel and a step of baking, wherein the baking step is performed at 150 to 170 ° C. This is a method of painting aluminum wheels.
The aluminum wheel coating method preferably further includes a step of applying an intermediate coating and a step of applying a top coating on the coating film formed by the above-described aluminum wheel coating method.
The present invention is also a non-chromate surface-treated aluminum wheel coated product characterized by being coated by the above-described aluminum wheel coating method.
The present invention is described in detail below.

The powder coating composition of the present invention is a powder coating composition in which a polyester resin and an epoxy resin are mixed in a specific ratio, and further includes a specific amount of a flexible resin having a specific molecular weight. It consists of particles. That is, by blending a flexible resin, it is possible to form a coating film excellent in cutting workability while maintaining the performance of a normal coating film such as adhesion, water resistance, corrosion resistance, and chipping resistance. The powder coating composition which can be obtained is obtained.

The flexible resin (iii) is a resin that can impart flexibility to the formed coating film, and examples thereof include aliphatic polyethers, aliphatic polyesters, polyurethanes, and polyamide resins. it can. In particular, polycaprolactone is preferable. The polycaprolactone has a number average molecular weight of 30,000 to 100,000. When the number average molecular weight is less than 30,000, there may be a problem that the corrosion resistance, cutting workability, and chipping resistance are not effective. When the number average molecular weight exceeds 100,000, there may be a problem that the appearance (smoothness) is deteriorated. is there.
The polycaprolactone may be modified with polybasic acid, polyhydric alcohol, hydroxycarboxylic acid, lactone or the like to the extent that the physical properties of the paint are not adversely affected.

Commercially available polycaprolactone can also be used. Examples of commercially available polycaprolactone include Plaxel H5, Plaxel H7 (manufactured by Daicel Chemical Industries), and the like.

In the powder coating composition of the present invention, the flexible resin (iii) has a lower limit of 1% by mass and an upper limit of 12% by mass with respect to 100% by mass of the total solid content of the polyester resin (i) and the epoxy resin (ii). %. When the blending amount is less than 1% by mass, the physical properties of the coating film cannot be sufficiently improved. If it exceeds 12% by mass, not only the physical properties of the coating film (curability) will be lowered, but also the problem of the coating stability (blocking resistance) will be lowered. The lower limit is preferably 2% by mass, and the upper limit is preferably 10% by mass.

The polyester resin (i) used in the powder coating composition of the present invention is as follows.
The polyester resin (i) has a resin solid content acid value of a lower limit of 10 mgKOH / g solid content and an upper limit of 100 mgKOH / g solid content (hereinafter the same). When the acid value is less than 10 mg KOH / g solid content, the curability may be lowered and the mechanical properties may be reduced. On the other hand, when the acid value is greater than 100 mg KOH / g solid content, May decrease. The lower limit is preferably 15 mg KOH / g solid content, and more preferably 20 mg KOH / g solid content. The upper limit is preferably 80 mg KOH / g solids, and more preferably 60 mg KOH / g solids.

The polyester resin (i) preferably has a softening point of a lower limit of 80 ° C. and an upper limit of 150 ° C. When the said softening point is lower than 80 degreeC, there exists a possibility that blocking resistance may fall, and when higher than 150 degreeC, there exists a possibility that the smoothness of the coating film obtained may fall. The lower limit is more preferably 90 ° C, and the upper limit is more preferably 130 ° C.

The polyester resin (i) preferably has a weight average molecular weight of a lower limit of 3000 and an upper limit of 70000. If the weight average molecular weight is less than 3000, the performance and physical properties of the resulting coating film may be reduced. On the other hand, if it is greater than 70000, the smoothness and appearance of the resulting coating film may be reduced. is there. The lower limit is more preferably 4000, and the upper limit is more preferably 50000.

In addition, the acid value of the resin solid content in the present invention can be determined by a method based on JIS K 0070, and the softening point can be determined by a method based on JIS K 2207. In addition, the weight average molecular weight and the number average molecular weight in the present invention are values converted to polystyrene by gel permeation chromatography (GPC).

The polyester resin (i) can be obtained by polycondensation by an ordinary method using an acid component containing a polyvalent carboxylic acid as a main component and an alcohol component containing a polyhydric alcohol as a main component. By selecting the respective components and the conditions for condensation polymerization, a polyester resin (i) having the above physical property values and special values can be obtained.

As said acid component, the ratio of the total of the terephthalic acid and isophthalic acid which occupies in all the acid components is 70 mol% or more, Preferably it is 75 mol% or more, More preferably, it is 80 mol% or more. When the total ratio is within the above range, it is preferable in terms of durability, physical properties, and price. Here, when the total proportion of terephthalic acid and isophthalic acid is used as the acid component by 70 mol% or more, it means that these are used as the main raw materials.
About the upper limit of the said terephthalic acid and isophthalic acid content, it is good also considering the whole quantity of the acid component used for preparation of a polyester resin as a terephthalic acid and / or isophthalic acid. When the weather resistance is particularly desired to be improved, the proportion of isophthalic acid in the total acid component is 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more. Here, the use of 70 mol% or more of isophthalic acid in the total acid component means that isophthalic acid is used as a main raw material.

Other acid components that can be used in the polyester resin are not particularly limited, and examples thereof include fragrances such as phthalic acid, trimellitic acid and anhydrides thereof, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. And saturated aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and anhydrides thereof. . In addition, lactones such as γ-butyrolactone and ε-caprolactone, and corresponding hydroxycarboxylic acids, aromatic oxymonocarboxylic acids such as p-oxyethoxybenzoic acid, and the like can be mentioned.

The alcohol component is not particularly limited. For example, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,5-hexanediol, diethylene glycol, triethylene 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, 1,2-dodecanediol, 1 Diols of 2 octadecanediol etc., trimethylol propane, glycerine, may be mentioned polyhydric alcohols such trivalent or more such as pentaerythritol and the like. Two or more alcohol components may be used.

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

The epoxy resin (ii) used in the powder coating composition of the present invention is as follows.
Examples of the epoxy resin (ii) include those having an average of 1.1 or more epoxy groups in one molecule, such as a reaction product of a novolak type phenol resin and epichlorohydrin, a bisphenol type epoxy. Resin (A type, B type, F type, etc.), hydrogenated bisphenol type epoxy resin, reaction product of novolac type phenol resin and bisphenol type epoxy resin (A type, B type, F type, etc.) and epichlorohydrin, novolac type Reaction product of phenol resin and bisphenol type epoxy resin (A type, B type, F type, etc.), reaction product of cresol compound such as cresol novolak and epichlorohydrin, ethylene glycol, propylene glycol, 1,4-butanediol , Polyethylene glycol, polypropylene glycol Carboxylic acids such as glycidyl ethers, succinic acid, adipic acid, sebacic acid, phthalic acid, terephthalic acid, hexahydrophthalic acid and trimellitic acid obtained by the reaction of alcohol compounds such as sulfur, neopentyl glycol and glycerol with epichlorohydrin Glycidyl esters obtained by reaction of a compound with epichlorohydrin, reaction products of hydroxycarboxylic acid such as p-oxybenzoic acid and β-oxynaphthoic acid with epichlorohydrin, 3,4-epoxy-6-methylcyclohexylmethyl-3 , 4-epoxy-6-methylcyclohexanecarboxylate, alicyclic epoxy compounds such as 3,4-epoxycyclohexylmethyl (3,4-epoxycyclohexane) carboxylate, triglycidyl isocyanurate (TG) IC) and derivatives thereof.

The epoxy equivalent of the epoxy resin (ii) has a lower limit of 100 mgKOH / g solids and an upper limit of 4000 mgKOH / g solids. If the epoxy equivalent is less than 100 mg KOH / g solids, the storage stability of the paint may be reduced, and if it is greater than 4000 mg KOH / g solids, the water resistance of the coating may be reduced. In addition, the epoxy equivalent in this invention can be determined by JISK7236. The lower limit is preferably 100 mg KOH / g solids, and the upper limit is preferably 2000 mg KOH / g solids.

A commercial item can also be used for the said epoxy resin (ii). Examples of commercially available products of the epoxy resin (ii) include Epototo YD-128, Epototo YD-014, Epototo YD019, ST-5080, ST-5100, ST4100D (all manufactured by Tohto Kasei Co., Ltd.), EHPA-3150 ( Daicel Chemical Industries, Ltd.), Araldite CY179 (Nippon Ciba-Geigy Corporation), Denacor EX-711 (Nagase Kasei Kogyo Co., Ltd.), Epototo YDPN-639, Epototo YDCN701, Epototo YDCN701 (all manufactured by Toto Kasei), Epicron N -680, Epicron N-695, Epicron HP-4032, Epicron HP-7200H (all manufactured by Dainippon Ink and Chemicals), Araldite PT 810, Araldite PT 910 (Nihon Ciba Geigy), TEPIC (Nissan) Industry Co., Ltd.), and the like.

In the powder coating composition of the present invention, the mixing ratio of the polyester resin and the epoxy resin is in the range of 2/8 to 8/2 in terms of resin solids mass ratio.
When the mixing ratio is less than 2/8, there is a possibility that sufficient physical properties of the coating film may not be obtained. When the mixing ratio exceeds 8/2, there is a possibility that the physical properties of the coating film may be lowered. The mixing ratio is more preferably 3/7 to 7/3.

The powder coating composition of the present invention may contain various additives such as a surface conditioner, a plasticizer, an ultraviolet absorber, an antioxidant, a wax inhibitor, and a charge control agent as necessary.

In particular, as the surface conditioner, from the viewpoint of applicability, (meth) such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, etc. It is preferable to use an acrylic polymer obtained from an alkyl ester of acrylic acid having a number average molecular weight of 300 to 50000, preferably 1000 to 30000, and a glass transition temperature of less than 20 ° C, preferably 0 ° C or less. . When the molecular weight is out of the above range, the surface adjustability cannot be sufficiently imparted, and the prevention of appearance defects such as dents becomes insufficient. Moreover, there exists a possibility that surface adjustability cannot fully be provided as glass transition temperature is 20 degreeC or more. The content of the surface conditioner is preferably a lower limit of 0.01 and an upper limit of 5% by mass in the powder coating composition. If the amount is less than 0.01% by mass, the surface adjustability cannot be sufficiently imparted, and the probability of poor appearance is increased. If the amount exceeds 5% by mass, the blocking property of the paint may be lowered. The lower limit is more preferably 0.05% by mass, and still more preferably 0.1% by mass. The upper limit is more preferably 3% by mass, still more preferably 2% by mass.

Examples of such commercially available surface conditioners include Acronal 4F (manufactured by BASF), Polyflow S (manufactured by Kyoeisha Chemical Co., Ltd.), Regiflow LV (manufactured by ESTRON CHEMICAL), etc. For example, Modaflow III (manufactured by Monsanto), Regisflow P67 (manufactured by ESTRON CHEMICAL), etc. are preferably used. Moreover, you may use the mixture of the acrylic polymer which is a surface adjusting agent, and an epoxy resin so that the usage-amount of an epoxy resin may become in the said range.

The powder coating composition of the present invention may be a clear coating composition or a colored coating composition, and may contain various pigments used in the coating as necessary. The pigment is not particularly limited, and examples thereof include titanium dioxide, bengara, yellow iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone pigment, azo pigment, and other colored pigments, each color metallic pigment, and each color pearl pigment. Examples thereof include metal powders and those subjected to surface treatment, extender pigments such as talc, silica, calcium carbonate, and precipitated barium sulfate. Moreover, in order to reduce gloss, it may contain an inorganic matting agent such as talc, silica, calcium carbonate, barium sulfate, feldspar, wollastonite, or an organic matting agent composed of organic fine particles. Good. The matting agent preferably has a volume average particle size of 3 to 30 μm.

Production of the powder coating composition of the present invention can be carried out using a production method well known in the field of powder coating. For example, after preparing the above-described raw materials, the raw materials are preliminarily mixed using a super mixer, a Henschel mixer, or the like, and the raw materials are melt-kneaded using a kneader such as a kneader or an extruder. The heating temperature at this time must of course be lower than the bake hardening temperature, but it must be a temperature at which at least a part of the raw material can be melted and kneaded as a whole. Generally, it is melt-kneaded within a range of 80 to 120 ° C. Next, the melt is solidified by cooling with a cooling roll or a cooling conveyor, and is pulverized to a desired particle size through coarse pulverization and fine pulverization processes. The powder coating composition of the present invention thus obtained preferably has a volume average particle size of 25 to 35 μm, and is classified by sieving to adjust the particle size distribution by removing large particles and fine particles. It is preferable to go.

Furthermore, a fluidity imparting agent or a charge adjusting agent may be externally added to the surface of the powder coating obtained by the above production method. The fluidity-imparting agent not only provides fluidity to the powder coating itself, but can also improve blocking resistance. As the fluidity-imparting agent, hydrophobic silica, hydrophilic silica, aluminum oxide, titanium oxide or the like can be applied. Examples of such commercially available fluidity-imparting agents include AEROSIL 130, AEROSIL 200, AEROSIL 300, AEROSIL R-972, AEROSIL R-812, AEROSIL R-812S, titanium dioxide T-805, and titanium dioxide P-25. Aluminum Oxide C (manufactured by Nippon Aerosil Co., Ltd.), Carplex FPS-1 (manufactured by Shionogi Pharmaceutical Co., Ltd.) and the like can be exemplified. The addition amount of the fluidity-imparting agent is preferably 0.05 to 2% by mass, more preferably 0, with respect to 100% by mass of the powder coating, from the viewpoint of the effect to be imparted and the smoothness of the coating film. 0.1 to 1% by mass. If it is less than 0.05% by mass, the effect is small, and if it exceeds 2% by mass, the smoothness of the coating film may be lowered or gloss may be lost.

The powder coating composition of the present invention can be coated and then heated to obtain a coating film. The powder coating composition of the present invention may be used for forming a single layer coating film or for forming a multilayer coating film. The above powder coating composition is applied directly to the surface of the substrate as an undercoat paint, that is, a primer, and forms an undercoat film at a low baking temperature, for example, 140 to 160 ° C., on which an intermediate paint or an overcoat paint is applied. You may do. When used for the formation of such a multilayer coating film, the powder coating composition of the present invention has excellent adhesion, corrosion resistance, water resistance, cutting workability, and non-chromate treated substrate. Effects such as physical properties are exhibited, and a multilayer coating film having excellent physical properties can be formed.

In this case, the intermediate coating material and the top coating material may be any type of coating material such as a solvent-based coating material, a water-based coating material, and a powder coating material, and include a clear coating material, a colored base coating material, and a volatile pigment. Etc.

Further, the powder coating composition may be used as an intermediate coating or top coating. A multilayer film may be formed at a time at a low baking temperature. As the undercoat paint for forming the undercoat, known materials such as an electrodeposition paint and a primer can be used.

The method for applying is not particularly limited, and methods well known by those skilled in the art such as spray coating method, electrostatic powder coating method, fluidized dipping method, etc. can be used. An electrostatic powder coating method is preferably used. Although the coating film thickness at the time of apply | coating the powder coating composition of this invention is not specifically limited, It can set to 40-200 micrometers.

The heating conditions vary depending on the amount of functional groups involved in curing and the amount of curing accelerator. For example, the heating temperature for baking is 120 to 200 ° C., preferably 140 to 180 ° C., but 150 to 170 ° C. It can also cope with low temperature curing. The heating time can be appropriately set according to the heating temperature.

On the other hand, the volume average particle size of the powder coating composition is preferably 25 to 35 μm. If it is less than 25 μm, the coating workability may be reduced. When it exceeds 35 μm, a coating film having a high appearance cannot be obtained. The volume average particle diameter can be measured by a particle diameter measuring apparatus using electromagnetic wave scattering such as Microtrac-II manufactured by Reed & Northrop.

The powder coating composition of the present invention can be used in a wide variety of applications, but exhibits excellent properties particularly when used as a primer coating for aluminum wheel coating. The powder coating composition of the present invention can form a coating film having physical properties excellent in adhesion, corrosion resistance, water resistance, and cutting workability as described above, particularly when applied to a substrate after non-chromate treatment. In addition, since it exhibits excellent coating film properties, it is excellent as a primer coating for aluminum wheels that require these properties.

Moreover, the coating method of the aluminum wheel which has the process of apply | coating the above-mentioned powder coating composition to an aluminum wheel, and the process of baking, and the said baking process is performed at 150-170 degreeC is also one of this invention. It is. Examples of the coating method include those described above.
The coating method of the aluminum wheel may further include a step of applying an intermediate coating and a step of applying a top coating on the coating film formed by the above-described coating method. As the intermediate coating material and the top coating material, those described above can be used.

In addition, a non-chromate surface-treated aluminum wheel coated product coated by the above-described coating method using the powder coating composition is also one aspect of the present invention.
Examples of the non-chromate surface-treated aluminum wheel include those obtained by surface-treating an aluminum wheel by a known method using a known surface treating agent not containing chromium.

The powder coating composition of the present invention has the above-described configuration, and when applied to an aluminum wheel, it has sufficient chipping resistance and forms a coating film with excellent cutting workability after painting and baking. To do.

According to the present invention, a powder coating composition capable of forming a coating film having excellent cutting processability, practically sufficient strength, good coating appearance, and chipping resistance while maintaining normal coating film properties. Things can be provided.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited only to these examples. In the examples, “parts” means “parts by mass” unless otherwise specified.

<Surface treatment>
The aluminum wheel was degreased and washed with water, and subjected to pickling treatment, water washing, chemical conversion treatment, water washing and post-treatment under the conditions shown below, followed by drying. Washing with water was performed with a tap water shower, and each process was performed by a dip method. Drying was performed with an electric dryer at 120 ° C. for 25 minutes.

(A) Degreasing solution: 2% (w / v) Surf Cleaner 53 (manufactured by Nippon Paint)
Treatment temperature: 50 ° C. Treatment time: 3 minutes (B) pickling treatment solution: 3% (w / v) Surf Cleaner 355A (manufactured by Nippon Paint _{Co.; FeSO 4 · 7H 2 O 0.81g} / L, 98% sulfuric acid 12.1 g / L, pH 0.9)
Treatment temperature: 40 ° C. Treatment time: 3 minutes (C) Chemical conversion treatment solution: 2.5% (w / v) Alsurf 501N-1 (manufactured by Nippon Paint Co., Ltd .; zirconium phosphate-based treatment agent; (NH ₄ ) ₂ ZrF ₆ 0.12 g / L, 75% H ₃ PO ₄ 0.10 g / L, 55% HF 0.02 g / L, 42% HBF ₄ 0.16 g / L, pH 3.5)
Treatment temperature: 40 ° C. Treatment time: 45 seconds (D) Post-treatment treatment liquid: Powernix 110F-2 (manufactured by Nippon Paint Co., Ltd .; component is modified epoxy emulsion; non-volatile content 36% by mass), resin solid content is 2% by mass Diluted with water so that it becomes a processing temperature: 25 ° C. processing time: 1 minute

<Manufacture of powder paint>
Powder coating 1
Fined M8962 (Dainippon Ink & Chemicals, polyester resin, terephthalic acid component 100 mol%, acid value 33, softening point 112 ° C.) 50 parts by mass, Epototo YD-014 (manufactured by Tohto Kasei Co., epoxy resin, epoxy Equivalent 950) 50 parts by mass, acronal 4F (manufactured by BASF, acrylic polymer, surface conditioner having a number average molecular weight of 16500), 0.5 parts by mass, benzoin 1 part by mass, TYPE CCR-90 (manufactured by Ishihara Sangyo Co., Ltd.) , Rutile type titanium dioxide pigment) 65 parts by mass and Plaxel H5 (manufactured by Daicel Chemical Industries, polycaptolactone, number average molecular weight 50,000) 10 parts by mass using a mixer super mixer (manufactured by Nippon Spindle Co., Ltd.) Mix, further melt melt knead at about 110 ° C using a melt kneader Conyder (Bus), solidify by cooling to room temperature It was. The cooled and solidified product was roughly pulverized to obtain powder coating pellets. Then, it grind | pulverizes using a grinder atomizer (product made from Fuji Paudal), a pulverized material passes a screen mesh of 0.7 mm space | interval, passes a 325 mesh Tyler standard sieve (pore diameter of 44 micrometers), and is larger than 44 micrometers. Particles are removed, and the resulting powder is classified using an airflow classifier DS-2 type (manufactured by Nippon Pneumatic Industry Co., Ltd.) to remove fine particles and coarse particles, thereby obtaining a powder coating composition. It was. The volume average particle diameter was 27 μm.
The volume average particle size is obtained by dispersing about 0.1 g of a sample in 5 g of a 0.5% Triton X (Union Carbide, surfactant) aqueous solution, using Honey as a solvent, Microtrac. It was measured after dropping into 9320X-200 and dispersing with ultrasonic waves (40 W for 10 seconds).

Powder paint 2
Instead of Plaxel H5 of the powder coating 1, powder coating is performed in the same manner as the powder coating 1 except that 10 parts by mass of Plaxel H7 (manufactured by Daicel Chemical Industries, polycaptolactone, number average molecular weight 70,000) is added. A composition was prepared to obtain a powder coating material 2 having a volume average particle size of 27 μm.

Powder coating 3
A powder coating composition was prepared in the same manner as the powder coating 2 except that 2 parts by mass of Plaxel H7 was added to the powder coating 2, and a powder coating 3 having a volume average particle size of 27 μm was obtained.

Powder coating 4
A powder coating composition was prepared in the same manner as in the powder coating 1 except that the plaque paint H5 was not added in the powder coating 1, and a powder coating 4 having a volume average particle size of 27 μm was obtained.

Powder coating 5
A powder coating composition was prepared in the same manner as in the powder coating 2 except that 15 parts by mass of Plaxel H7 was added to the powder coating 2 to obtain a powder coating 5 having a volume average particle size of 27 μm.

Each of the powder coatings 1, 2, 3, 4, 5 is subjected to the above surface treatment at an applied voltage of 80 kV using a corona discharge electrostatic powder coating machine (trade name “MXR-100VT-mini” manufactured by Asahi Sunac Corporation). Painted on finished aluminum wheels. Then, a coated plate was prepared by baking at 160 ° C. for 20 minutes (coating material holding time).
Superlac AS70 11SV-14 (acrylic solvent type paint, manufactured by Nippon Paint Co., Ltd.) was applied to the obtained coating film so as to have a dry film thickness of 20 μm, set for 10 minutes, and then heated at 140 ° C. for 20 minutes. After sufficiently cooling to room temperature, Superlack 5000 AW-10 (acrylic solvent-type paint, manufactured by Nippon Paint Co., Ltd.) as a low solid solvent clear paint was applied in one stage to a dry film thickness of 40 μm and set for 7 minutes. Then, it heated at 140 degreeC for 20 minute (s), produced the multilayer coating film, and evaluated the coating-film performance with the following method. The results are shown in Table 1 as Examples 1, 2, and 3 and Comparative Examples 1 and 2, respectively. In addition, about the powder coating material 5, stability was bad and could not be used for coating.

<Performance evaluation method>
All the performance evaluations were performed using a surface-treated aluminum wheel coated with the above-mentioned powder coating and cut into an appropriate size. Moreover, about the workability and appearance evaluation, it tested using the said painted aluminum wheel itself. The obtained results are shown in Table 1.

Adhesion test Adhesion test Each test piece is coated with 10 vertical and horizontal cuts at 1 mm intervals using a cutter, and cellophane tape is affixed to it and peeled off. The counted eyes were counted (cross-cut eye test).

Water resistance test Hot water immersion test Each test piece was immersed in warm water of 60C for 72 hours, then left for 24 hours, and then the same cross-cut test as the adhesion test was performed.

Corrosion resistance test Salt spray test The surface of each test piece is cross-cut with a cutter knife, sprayed with salt water at 35 ° C for 1200 hours using a 5 mass% NaCl aqueous solution, left for 24 hours, and around the cut part The degree of corrosion within 2 mm was measured according to the following criteria.
○: No abnormalities such as blistering, rust, etc. ×: Abnormal

Cutting workability The aluminum wheel coated as described above is cut and subjected to non-chromate chemical conversion treatment again. Then, as a low solid solvent clear paint, Super Lac 5000 AW-10 (acrylic solvent-type paint, (Manufactured by Nippon Paint Co., Ltd.), one-stage coating was performed so that the dry film thickness was 40 μm, setting was performed for 7 minutes, and then heated at 140 ° C. for 20 minutes to prepare a multilayer coating film. The state of the coating film defect in the cut portion was evaluated according to the following criteria.
○: Good △: Somewhat bad ×: Bad

Re-cutting workability The above-cut / solvent-coated aluminum wheel was cut again and subjected to non-chromate conversion treatment again, and then super-lacquer 5000 AW-10 (acrylic solvent-type paint) as a low solid solvent clear paint. (Manufactured by Nippon Paint Co., Ltd.), one-stage coating was performed so that the dry film thickness was 40 μm, setting was performed for 7 minutes, and then heated at 140 ° C. for 20 minutes to prepare a multilayer coating film. The coating state of the recut portion was evaluated according to the following criteria.
○: Good △: Somewhat bad ×: Bad

Chipping resistance After cooling the obtained coated plate to −30 ° C., it was attached to a sample holder of a stepping stone testing machine (manufactured by Suga Test Instruments Co., Ltd.) so that the stone penetration angle would be 90 °, and 100 g No. 7 crushed stone was sprayed at an air pressure of 3 kg / cm ² , and the crushed stone collided with the coated plate. The degree of peeling scratches (number, size, location of destruction) at that time was evaluated in five levels. The evaluation criteria are shown below.
Evaluation standard 1: There is a large scratch on the entire surface, with peeling from the substrate 2: There is a certain amount of peeling scratch on the entire surface, with peeling from the substrate 3: Some with some peeling scratches, no peeling from the substrate 4: One There is a small scratch on the part, no peeling from the substrate 5: almost no destruction

Appearance evaluation The finished appearance and smoothness of the painted aluminum wheel were visually evaluated. The smoothness was evaluated according to the following criteria.
○: Good △: Somewhat bad ×: Bad

From Table 1, it was found that the coating film formed from the powder coating composition of the example was excellent in cutting workability in addition to appearance, adhesion, water resistance, corrosion resistance, and chipping resistance. . In Comparative Example 2, the stability was poor and the coating could not be performed and the predetermined evaluation could not be performed.

Since the powder coating material of the present invention is as described above, it has sufficient chipping resistance when applied to an aluminum surface (for example, an aluminum wheel), and the finished appearance, smoothness, and machinability after baking. It is possible to provide an excellent aluminum surface.

Claims (7)

More than 70 mol% of the total acid component constituting the polyester resin is composed of terephthalic acid and isophthalic acid, and the resin solid content acid value is 10 to 100 mgKOH / g solid content, and the epoxy equivalent is 100 to 4000 mgKOH. / G is a powder coating composition comprising powder coating particles comprising a solid epoxy resin (ii),
The mixing ratio of the polyester resin (i) and the epoxy resin (ii) is in the range of 2/8 to 8/2 in terms of solid content mass ratio,
The powder coating particles further contain a flexible resin (iii),
The flexible resin (iii) is 1 to 12% by mass with respect to a total solid content of 100% by mass of the polyester resin (i) and the epoxy resin (ii), and has a number average molecular weight of 30,000 to 100,000. There is provided a powder coating composition. The powder coating composition according to claim 1, wherein the flexible resin (iii) is polycaprolactone. The powder coating composition according to claim 1 or 2, wherein the particle diameter of the powder coating particles is 25 to 35 µm. The powder coating composition according to claim 1, 2 or 3, which is a primer powder coating for aluminum wheel coating. A method of applying the powder coating composition according to claim 1, 2, 3, or 4 to an aluminum wheel, and a coating method of an aluminum wheel comprising a baking step,
The method for painting an aluminum wheel, wherein the baking step is performed at 150 to 170 ° C. 6. The method for coating an aluminum wheel according to claim 5, further comprising a step of applying an intermediate coating and a step of applying a top coating on the coating film formed by the method for coating an aluminum wheel according to claim 5. A non-chromate surface-treated aluminum wheel coating product, which is coated by the aluminum wheel coating method according to claim 5 or 6.