JP2013151608A - Powder coating composition and coated article of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder coating composition that forms a coating film excellent in processability, hiding power, and reflectance and smoothness of the coating film.SOLUTION: A powder coating composition includes: (A) a spherical titanium oxide having a refractive index of at least 2.7, which is surface-treated by one or both of a hydrous oxide and an oxide of at least one element chosen from the group comprising aluminum, silicon, and zirconium; (B) a carboxy group-containing resin; (C) β-hydroxyalkylamide compound; and (D) a core/shell-type organic particle in which the glass transition temperature Tg of a material composing a core layer is less than 20°C and a flexural modulus at 23°C thereof is less than 5 MPa, the Tg of a shell layer is at least 30°C, and the shell layer is composed of a polymer material showing 2,000-45,000 MPa of a flexural modulus at 23°C and has an epoxy group or a carboxyl group, wherein the powder coating composition includes 30-55 pts.wt. of the spherical titanium oxide based on 100 pts.wt. of the powder coating composition.

Description

  The present invention relates to a powder coating composition which forms a coating film excellent in high processability, concealability, smoothness and coating film reflectance, and a coated product thereof.

  Thermosetting powder coatings are widely used for outdoor or indoor applications in the field of industrial products such as home appliances, automobiles, vehicles, office supplies, steel furniture and building materials. Mainly epoxy resins and acrylic resins Further, polyester resin-based and epoxy resin / polyester resin-based powder coatings are known. Among these, polyester resin powder coating materials are widely used as coating materials that form a well-balanced coating film excellent in weather resistance and mechanical strength. In addition, it is common to use isocyanate group-containing compounds as curing agents used in polyester resin-based powder coatings, but reaction by-products are generated during curing. A certain hydroxyalkylamide compound has attracted attention from the viewpoint of the environment. For example, Patent Documents 1 and 2 disclose powder coatings containing a hydroxyalkylamide compound.

  Furthermore, in powder coatings for PCM (pre-coated metal) steel sheets, it is required to form a coating film having high processability and high concealing property, and the coating film thickness is 30 μm or more, particularly a white coating. In the case of color, it is necessary to make the film thicker than 50 μm. However, when the film is thick, cracking and peeling are likely to occur during processing. Patent Document 3 discloses a powder coating material in which smoothness and workability are improved by blending core-shell type carboxyl group-containing rubber composite resin particles. However, in the case of a white paint color, the powder coating composition that forms a coating film that satisfies all of high processability, concealability, coating film reflectance and smoothness by the conventional techniques including Patent Document 3. The thing was not obtained.

JP-A-5-156178 JP-A-10-017606 JP 2001-262075 A

  An object of the present invention is to solve the above problems, and provide a powder coating composition that forms a coating film excellent in high processability, concealability, coating film reflectance and smoothness, and a coated product thereof. That is.

In accordance with the present invention,
(A) Spherical titanium oxide having a refractive index of 2.7 or more, which is surface-treated with one or both of a hydrous oxide and an oxide of at least one element selected from the group consisting of aluminum, silicon and zirconium,
(B) a carboxyl group-containing resin,
(C) β-hydroxyalkylamide compound and (D) The glass transition temperature (Tg) of the material constituting the core layer is less than 20 ° C., the flexural modulus at 23 ° C. is less than 5 MPa, Powder having core-shell type organic particles having a Tg of 30 ° C. or higher, a polymer material having a flexural modulus of 2000 to 45000 MPa at 23 ° C., and having an epoxy group or a carboxyl group in the shell layer In the coating composition,
A powder coating composition comprising 30 to 55 parts by weight of the titanium oxide with respect to 100 parts by weight of the powder coating composition is provided.

  According to the present invention, there is provided a coated product obtained by applying the above-described powder coating composition to a metal substrate.

  By applying the powder coating composition of the present invention to a metal substrate, a coating film excellent in high processability, concealability, coating film reflectance and smoothness could be formed.

  Below, the powder coating composition of this invention is demonstrated concretely.

That is, the present invention
(A) Spherical titanium oxide having a refractive index of 2.7 or more, which is surface-treated with one or both of a hydrous oxide and an oxide of at least one element selected from the group consisting of aluminum, silicon and zirconium,
(B) a carboxyl group-containing resin,
(C) β-hydroxyalkylamide compound and (D) The glass transition temperature (Tg) of the material constituting the core layer is less than 20 ° C., the flexural modulus at 23 ° C. is less than 5 MPa, Powder having core-shell type organic particles having a Tg of 30 ° C. or higher, a polymer material having a flexural modulus of 2000 to 45000 MPa at 23 ° C., and having an epoxy group or a carboxyl group in the shell layer The coating composition is a powder coating composition comprising 30 to 55 parts by weight of spherical titanium oxide with respect to 100 parts by weight of the powder coating composition.

(A) Refractive index 2.7 surface-treated with one or both of a hydrous oxide and an oxide of at least one element selected from the group of aluminum, silicon and zirconium used in the powder coating composition according to the present invention The spherical titanium oxide described above has little degradation of the coating resin due to the photocatalytic effect, has good dispersibility in the resin, and has high visible light reflectance. Therefore, even when spherical titanium oxide is contained in an amount of 30 parts by weight or more based on 100 parts by weight of the powder coating composition, the coating film is excellent in smoothness and exhibits high concealment. The surface treatment amount is in the range of 0.1 to 100% by weight expressed by the total amount converted to oxides of each element (Al ₂ O ₃ , SiO ₂ and ZrO ₂ ) with respect to the spherical titanium oxide. Preferably it is the range of 5-20 weight%. When the amount is less than 0.1% by weight, the smoothness of the coating film is difficult to obtain, and when it exceeds 100% by weight, the refractive index of the spherical titanium oxide becomes low and the desired reflectance cannot be obtained.

  The particle size of the spherical titanium oxide is preferably 0.1 μm to 0.5 μm, more preferably 0.2 μm to 0.3 μm. When the particle diameter is less than 0.1 μm, the concealability of the coating film tends to decrease. On the other hand, when the particle diameter exceeds 0.5 μm, the coating film reflectance may decrease.

  The blending ratio of the spherical titanium oxide is 30 to 55 parts by weight, preferably 35 to 50 parts by weight, and particularly preferably 40 to 45 parts by weight with respect to 100 parts by weight of the powder coating composition. When the blending ratio of the spherical titanium oxide is less than 30 parts by weight, the reflectance of the coating film is lowered, and when it exceeds 55 parts by weight, the appearance and workability of the coating film are lowered.

  As the (B) carboxyl group-containing resin used in the powder coating composition according to the present invention, those conventionally used, for example, in epoxy curable powder coatings can be used. Examples of the carboxyl group-containing resin include carboxyl group-containing polyester resins, carboxyl group-containing acrylic resins, carboxyl group-containing fluorine resins, and carboxyl group-containing silicon resins. These carboxyl group-containing resins preferably have a weight average molecular weight of 500 to 100,000, and more preferably 1000 to 80,000. Further, the glass transition temperature Tg of the resin is preferably 20 to 100 ° C, particularly preferably 25 to 80 ° C. The carboxyl group content is preferably 20 to 300 KOHmg / g, particularly 25 to 200 KOHmg / g in terms of resin acid value.

  Examples of carboxyl group-containing polyester resins include aromatics such as (anhydrous) phthalic acid, isophthalic acid, terephthalic acid, dimethyl isophthalate, dimethyl terephthalate, hexahydro (anhydrous) phthalic acid, and tetrahydro (anhydrous) phthalic acid. Alicyclic dicarboxylic acids and (poly) ethylene glycol, (poly) propylene glycol, butylene glycol, butylene glycol, neopentyl glycol, 1,6-hexanediol, and dihydric alcohols such as dimethylpropionic acid, as required A monocarboxylic acid such as benzoic acid, a trivalent or higher carboxylic acid such as (anhydrous) trimellitic acid, a trivalent or higher valent alcohol such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol Reacted to remain Resulting Te resins. Among the polyester resins, it is preferable to apply the polyester resin mainly containing isophthalic acid as an acid component.

  As the carboxyl group-containing acrylic resin, for example, a carboxyl group-containing radical polymerizable unsaturated monomer (for example, (meth) acrylic acid, maleic anhydride, etc.), a hard acrylic monomer having a glass transition temperature of 40 ° C. or higher (homopolymer) (For example, methyl methacrylate, ethyl methacrylate, iso-butyl methacrylate, ter-butyl methacrylate, ter-butyl acrylate, etc.), soft acrylic monomer having a glass transition temperature of less than 40 ° C. (homopolymer) (for example, methyl acrylate, ethyl Acrylate, n-butyl methacrylate, iso-butyl acrylate, 2 ethylhexyl (meth) acrylate, stearyl methacrylate, hydroxyethyl (meth) acrylate, and hydroxypropyl (meth) acrylate Rate), radical polymerizable unsaturated monomers other than acrylic monomers (for example, styrene, vinyltoluene, α-methylstyrene, (meth) acrylonitrile, and (meth) acrylamide), or functional group-containing radicals other than the above hydroxyl groups Examples thereof include carboxyl group-containing acrylic base resins obtained by radical copolymerization reaction of polymerizable unsaturated monomers (for example, glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, etc.)).

  Examples of the carboxyl group-containing fluorine-based resin include acid group-containing monomers such as maleic anhydride and fluoroolefins (for example, tetrafluoroethylene, trifluoride ethylene, difluoroethylene, and trifluoroethylene chloride 2). Fluorinated ethylene chloride, etc.), and fluorine-containing acrylic monomers (perfluoroalkyl (meth) acrylate (eg, perfluorobutylethyl (meth) acrylate, perfluoroisononylethyl (meth) acrylate), and perfluorooctylethyl (meta And resins obtained by radical polymerization reaction of acrylates and the like)).

  As the carboxyl group-containing silicon resin, in the above carboxyl group-containing acrylic resin, as other monomer components, vinyltrimethoxysilane, (meth) acryloxypropyltrimethoxysilane, (meth) acryloxypropyltrimethylsilane, etc. The resin used as an essential monomer component is mentioned.

  Among the carboxyl group-containing resins described above, a carboxyl group-containing polyester resin is particularly preferable from the viewpoint of processability, smoothness, cost, and the like.

  The blending ratio of the carboxyl group-containing resin (B) is preferably 7 to 99 parts by weight, particularly preferably 15 to 95 parts by weight with respect to 100 parts by weight of the powder coating composition. If the blending ratio of the carboxyl group-containing resin (B) is less than 7 parts by weight, impact resistance, cupping resistance and the like are liable to be inferior, whereas if it exceeds 99 parts by weight, curability and the like tend to be inferior.

  The hydroxyalkylamide compound (C) used in the present invention is represented by the following general formula.

In the formula, R ₁ represents the same or different aliphatic hydrocarbon group having 1 to 4 carbon atoms, and R ₂ represents an aliphatic hydrocarbon group having 2 to 10 carbon atoms. Examples of the aliphatic hydrocarbon group having 1 to 4 carbon atoms of R ₁ include alkylene groups such as CH ₂ , C ₂ H ₄ , C ₃ H ₆ , and C ₄ H ₈ . The alkylene group may be linear or branched. Examples of the aliphatic hydrocarbon group having 2 to 10 carbon atoms of R ₂ include C ₂ H ₄ , C ₃ H ₆ , C ₄ H ₈ , C ₅ H ₁₀ , C ₆ H ₁₂ , and C ₈ H _16. It is done. The alkylene group may be linear or branched.

  The hydroxyalkylamide compound (C) preferably has a melting point of 40 to 200 ° C, more preferably 100 to 150 ° C. Specific examples of the hydroxyalkylamide compound (C) include N, N, N ′, N′-tetrakis (2-hydroxyethyl) adipamide (melting point: about 120 ° C.), and N, N, N ′, N And '-tetrakis (2-hydroxypropyl) adipamide (melting point: about 120 ° C.).

  The mixing ratio of the hydroxyalkylamide compound (C) is preferably 0.5 to 45 parts by weight, particularly preferably 1 to 25 parts by weight with respect to 100 parts by weight of the powder coating composition. If the mixing ratio of the hydroxyalkylamide compound (C) is less than 0.5 parts by weight, the curability tends to be inferior, whereas if it exceeds 45 parts by weight, the impact resistance, cupping resistance, etc. may be inferior.

  The core-shell type resin particles (D) used in the powder coating composition according to the present invention have a glass transition temperature (Tg) of the material constituting the core layer of less than 20 ° C., and flexural elasticity at 23 ° C. The rate is less than 5 MPa, the Tg of the shell layer is 30 ° C. or more, the bending elastic modulus at 23 ° C. is composed of a polymer material having 2000 to 45000 MPa, and the shell layer has an epoxy group or a carboxyl group. . Preferably, the glass transition temperature (Tg) of the material constituting the core layer is less than 15 ° C., the flexural modulus at 23 ° C. is less than 4.5 MPa, and the Tg of the shell layer is 35 ° C. or more. The flexural modulus at ℃ is 5000 to 40000 MPa.

  If the Tg of the material composing the core layer is 20 ° C. or higher, the stress applied to the core portion cannot be absorbed, so that the impact strength cannot be improved and the stress cannot be relaxed. Further, if the flexural modulus at 23 ° C. is 5 MPa or more, the stress applied to the core part cannot be absorbed, so that the impact strength cannot be improved and the stress cannot be relaxed. When the glass transition temperature Tg of the shell layer is less than 30 ° C., the particles are fused with each other during storage of the powder coating material to form a small lump, and this small lump is clogged in the transport pipe of the electrostatic coating machine. This may cause paint troubles and paint film scum. If the bending elastic modulus at 23 ° C. is less than 2000 MPa, rubber elasticity is exhibited during mechanical pulverization of the powder coating material, and pulverization becomes difficult. If the bending elastic modulus at 23 ° C. is greater than 45000 MPa, the shell layer Becomes hard, the cupping resistance is lowered, and sufficient workability cannot be imparted to the coating film.

  The core-shell type organic particle diameter is preferably 0.05 μm to 150 μm, more preferably 0.1 μm to 80 μm. When the particle diameter is less than 0.05 μm, the coating workability associated with the decrease in fluidity of the powder coating is lowered, while when it exceeds 150 μm, the smoothness of the coating film is deteriorated.

  The rubbery polymer that forms the core layer is a polymer of an unsaturated monomer that forms a rubbery polymer. Specific examples of the unsaturated monomer include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and lauryl (meth). Alkyl (meth) acrylates such as acrylate: Vinyl esters such as vinyl acetate: Vinyl halides such as vinyl chloride, vinyl fluoride, vinylidene chloride, and vinylidene fluoride or vinylidene halides: (meth) acrylonitrile, (meth) acrylamide, etc. Nitrogen-containing unsaturated monomers: Aromatic compounds such as styrene, α-methylstyrene, and vinyl toluene: Hydroxyl-containing unsaturated monomers such as hydroxyethyl (meth) acrylate and methylol (meth) acrylamide: (meth) Unsaturated acid such as acrylic acid Butadiene, and diene monomers such as isoprene and the like. These monomers can be used alone or in combination of two or more. Typical examples of the polymer include, for example, poly (meth) acrylate rubber, polybutadiene rubber, polyisoprene rubber, polyvinyl chloride, styrene-butadiene rubber, styrene-butadiene-styrene rubber, styrene-isoprene-styrene rubber, styrene. -Butylene rubber, styrene-ethylene rubber, ethylene-propylene rubber, etc. are mentioned. Among these, poly (meth) acrylate rubber, polybutadiene rubber, polyisoprene rubber, and styrene-butadiene rubber are particularly preferable. The Tg of the core layer-forming polymer prepared from the raw material is preferably less than 20 ° C.

  The shell layer is a polymer having an epoxy group or a carboxyl group, and preferably forms a vinyl polymer. The vinyl polymer is an unsaturated monomer containing a carboxyl group or an epoxy group (for example, 2- (meth) acryloyloxyethyl succinic acid, 2- (meth) acryloyloxyethylphthalic acid, 2- (meth) acryloyl). It is prepared by polymerizing oxyethylmaleic acid, 2- (meth) acryloyloxyethylhexahydrophthalic acid, bisphenol A type epoxy (meth) acrylate, urethane (meth) acrylate, and the like. These monomers may be used alone or in admixture of two or more. The glass transition temperature of the shell layer is preferably 30 ° C or higher, more preferably a vinyl polymer adjusted to a range of 50 to 100 ° C.

  The core / shell type resin particles can be produced by a conventionally known method, for example, emulsion weight in which a vinyl unsaturated monomer and a radical polymerizable initiator are added in the presence of a core layer polymer emulsion in advance. It can be obtained by a combination method or a suspension polymerization method.

  The blending ratio of the (D) core / shell type resin particles is preferably 0.5 to 15 parts by weight with respect to 100 parts by weight of the coating composition. If the blending ratio of the resin particles is less than 0.5 parts by weight, the cupping resistance tends to be lowered and the workability may be deteriorated, and if it exceeds 15 parts by weight, the smoothness of the coating film may be lowered. .

  In the powder coating composition according to the present invention, powders such as fillers, coloring pigments, bright pigments, fluidity modifiers, polymer fine particles for design, surface modifiers, curing accelerators, and slipperiness-imparting agents Paint additives and the like can be blended.

  The powder coating composition according to the present invention is coated with electrostatic powder by, for example, electrostatic powder spray or a triboelectric coating machine, and is usually coated in a range of preferably 20 to 300 μm, more preferably 30 to 150 μm. can do. The baking condition of the coating film is usually 2 to 60 minutes at an object temperature of 160 to 230 ° C.

  The powder coating composition according to the present invention can be applied to a conventionally used substrate. As the base material, for example, metal materials such as steel, zinc, aluminum, copper, and tin, those obtained by subjecting these metals to surface treatment, and primers and intermediate coating as necessary on these metal materials. For example, the applied undercoating film. Moreover, as an applicable field | area, it can apply to vehicle relations, household appliance relations, construction relations, road relations, office equipment, etc., for example.

  Further, from the viewpoint of high reflectivity of the coating film, the reflectance of the coating film is preferably 85% or more at λ = 555 nm, more preferably 90% or more, and further preferably 92% or more.

  Hereinafter, the present invention will be described in more detail with reference to examples. In the examples, “parts” and “%” are based on weight.

<Preparation of core / shell type acrylic resin particles A>
Add 1500 g of deionized water and 300 g of 5% polyvinyl alcohol aqueous solution to a 5 L polymerization vessel and stir at 6000 rpm with 6 g of lauroyl peroxide as a polymerization initiator in advance using a homomixer (manufactured by ASONE Co., Ltd.). A monomer mixed solution consisting of 576 g of dissolved n-butyl acrylate, 12 g of 1,4-butylene glycol diacrylate and 12 g of allyl methacrylate was added all at once and dispersed for 1 hour to obtain a monomer dispersion. The polymerization vessel was equipped with a stirrer and a reflux condenser, and the temperature was raised to 70 ° C. while stirring under a nitrogen stream. After reacting for 2 hours as it was, sampling was performed from the generated suspension of polymer particles, and the polymerization conversion rate of the monomer was measured and found to be 94%. Next, the obtained suspension of polymer particles was cooled to 60 ° C., and a monomer emulsion for the second stage reaction described below was continuously added to the suspension over 15 minutes.

  The monomer emulsion for the second stage reaction was 352 g methyl methacrylate, 40 g ethyl acrylate, 10 g methacrylic acid, 8 g ethylene glycol dimethacrylate, 4 g 2,2'-azobisisobutyronitrile, 1% sodium dodecyl sulfonate. Prepared with 100 g of aqueous solution and 100 g of deionized water. At this time, stirring was performed at 4500 rpm. When polymerization was started and exotherm was observed, the temperature was raised to 80 ° C., and an aging reaction was performed for 3 hours. After cooling the obtained suspension to room temperature, it was dehydrated and washed using a centrifuge, and further air-dried at 60 ° C. overnight to obtain core-shell type acrylic resin particles A containing carboxyl groups. Obtained.

  From the differential scanning calorimetry (DSC) measurement of the core-shell type acrylic resin particles A, the glass transition temperature (Tg) of the core layer polymer phase was −20 ° C., and the flexural modulus at 23 ° C. was 3.8 MPa. . The glass transition temperature of the shell layer polymer phase was 83 ° C., and the flexural modulus at 23 ° C. was 9500 MPa. The average secondary particle diameter measured with a high-resolution laser diffraction scattering particle size distribution analyzer LS 13-320 (Beckman Coulter, Inc.) was 0.2 μm.

<Preparation of core / shell type acrylic resin particles B>
It was produced in the same manner as the core-shell type acrylic resin particles A except that the second stage reaction was stirred at a rotational speed of 5000 rpm. The glass transition temperature of the rubber layer polymer phase was −22 ° C., and the flexural modulus at 23 ° C. was 4.2 MPa. The glass transition temperature of the shell layer polymer phase was 80 ° C., and core-shell type acrylic resin particles B containing a carboxyl group having a flexural modulus of 16400 MPa at 23 ° C. were obtained. The average secondary particle diameter was 14 μm.

<Preparation of core / shell type acrylic resin particles C>
It was produced in the same manner as the core-shell type acrylic resin particles A except that the second stage reaction was stirred at a rotational speed of 4000 rpm. The glass transition temperature of the rubber layer polymer phase was −21 ° C., and the flexural modulus at 23 ° C. was 3.7 MPa. The glass transition temperature of the shell layer polymer phase was 82 ° C., and core-shell type acrylic resin particles C containing a carboxyl group having a flexural modulus of 20600 MPa at 23 ° C. were obtained. The average secondary particle size was 45 μm.

<Preparation of core / shell type acrylic resin particles D>
It was produced in the same manner as the core-shell type acrylic resin particles A except that the second-stage reaction was stirred at a rotational speed of 3000 rpm. The glass transition temperature of the rubber layer polymer phase was −19 ° C., and the flexural modulus at 23 ° C. was 3.8 MPa. The glass transition temperature of the shell layer polymer phase was 83 ° C., and core-shell type acrylic resin particles D containing carboxyl groups having a flexural modulus of 26700 MPa at 23 ° C. were obtained. The average secondary particle diameter was 78 μm.

<Preparation of core / shell type acrylic resin particles E>
It was produced in the same manner as the core-shell type acrylic resin particles A, except that the second-stage reaction was stirred at a rotational speed of 2500 rpm. The glass transition temperature of the rubber layer polymer phase was −19 ° C., and the flexural modulus at 23 ° C. was 3.6 MPa. The glass transition temperature of the shell layer polymer phase was 83 ° C., and core-shell type acrylic resin particles E containing a carboxyl group having a flexural modulus of 32400 MPa at 23 ° C. were obtained. The average secondary particle diameter was 115 μm.

<Preparation of core / shell type acrylic resin particles F>
It was produced in the same manner as the core-shell type acrylic resin particles A except that the second stage reaction was stirred at a rotational speed of 2000 rpm. The glass transition temperature of the rubber layer polymer phase was −19 ° C., and the flexural modulus at 23 ° C. was 4.0 MPa. The glass transition temperature of the shell layer polymer phase was 83 ° C., and core-shell type acrylic resin particles F containing a carboxyl group having a flexural modulus of 40900 MPa at 23 ° C. were obtained. The average secondary particle diameter was 132 μm.

<Preparation of core / shell type acrylic resin particles G>
It was produced in the same manner as the core-shell type acrylic resin particles A except that 10 g of methacrylic acid was changed to 10 g of 2,3-epoxypropyl methacrylate and the second stage reaction was stirred at a rotational speed of 4000 rpm. The glass transition temperature of the rubber layer polymer phase was −22 ° C., and the flexural modulus at 23 ° C. was 3.2 MPa. The glass transition temperature of the shell layer polymer phase was 91 ° C., and core-shell type acrylic resin particles G containing an epoxy group having a flexural modulus of 17800 MPa at 23 ° C. were obtained. The average secondary particle size was 43 μm.

<Preparation of core / shell type acrylic resin particles H>
It was produced in the same manner as the core-shell type acrylic resin particles A except that 10 g of methacrylic acid was changed to 10 g of 2-hydroxymethacrylate and the second-stage reaction was stirred at a rotational speed of 4000 rpm. The glass transition temperature of the rubber layer polymer phase was −22 ° C., and the flexural modulus at 23 ° C. was 3.6 MPa. The glass transition temperature of the shell layer polymer phase was 88 ° C., and core-shell type acrylic resin particles H containing a hydroxyl group having a flexural modulus of 19200 MPa at 23 ° C. were obtained. The average secondary particle size was 40 μm.

<Preparation of core / shell type acrylic resin particles I>
It was produced in the same manner as the core-shell type acrylic resin particles A, except that 10 g of methacrylic acid was changed to 10 g of butyl methacrylate and the second stage reaction was stirred at a rotational speed of 4000 rpm. The glass transition temperature of the rubber layer polymer phase was −22 ° C., and the flexural modulus at 23 ° C. was 4.1 MPa. The glass transition temperature of the shell layer polymer phase was 83 ° C., and core-shell type acrylic resin particles I having no functional group having a flexural modulus of 10200 MPa at 23 ° C. were obtained. The average secondary particle size was 46 μm.

  Table 1 shows the results of glass transition temperature and flexural modulus of the obtained core-shell type acrylic resin particles A to I.

(Examples 1-22 and Comparative Examples 1-14)
The raw materials shown in Tables 2-3 were blended, put into a high speed mixer, and mixed for 1 minute. Then, kneading is performed using a biaxial kneader (manufactured by Toshiba Corporation) whose temperature is adjusted to 120 ° C., and the discharged kneaded material is cold-rolled with a cooling roll and then pulverized with a pin mill, Classification was performed to obtain each powder coating composition (50% volume average particle size: 30 μm).

Note 1) CRYLCOAT 1510-0 [trade name, manufactured by CYTEC; polyester resin A, acid value 70 mgKOH / g, Tg 58 ° C.]
Note 2) CRYLCOAT 1701-0 [trade name, manufactured by CYTEC; polyester resin B, acid value 36 mgKOH / g, Tg 62 ° C.]
Note 3) CRYLCOAT 2433-2 [trade name manufactured by CYTEC; polyester resin C, acid value 33 mgKOH / g, Tg 60 ° C.]
Note 4) CRYLCOAT 2496-2 [trade name, manufactured by CYTEC; polyester resin D, acid value 25 mgKOH / g, Tg 62 ° C.]
Note 5) CRYLCOAT 2630-2 [trade name manufactured by CYTEC; polyester resin E, acid value 33 mgKOH / g, Tg 62 ° C.]
Note 6) M-8961 (Dainippon Ink Chemical Co., Ltd .; polyester resin F, acid value 33 mgKOH / g, Tg 59 ° C.)
Note 7) M-8962 (Dainippon Ink & Chemicals, Inc .; polyester resin G, acid value 34 mg KOH / g, Tg 57 ° C.)
Note 8) M-8420 [manufactured by Dainippon Ink & Chemicals, Inc .; acrylic resin A, acid value 33 mgKOH / g, Tg 58 ° C.]
Note 9) A-239-X [Dainippon Ink Chemical Co., Ltd .; acrylic resin B, acid value 16 mgKOH / g, Tg 54 ° C.]
Note 10) PRIMID XL-552 [manufactured by EMS Griltech; N, N, N ′, N′-tetrakis (2-hydroxyethyl) adipamide (β-hydroxyalkylamide compound)]
Note 11) PF85 [manufactured by Kyoeisha Chemical Co .; organic copolymer]
Note 12) Benzoin [Wako Pure Chemical Industries;
Note 13) CR-90 [manufactured by Ishihara Sangyo Co., Ltd .; rutile titanium oxide, surface treatment: aluminum oxide or silicon oxide, surface treatment amount: 10%, average particle size: 0.25 μm, refractive index: 2.7 ]
Note 14) TI-PURE R-960 [manufactured by DuPont Co., Ltd .; rutile titanium oxide, surface treatment: aluminum oxide and silicon oxide, surface treatment amount: 11%, average particle size: 0.50 μm, refractive index: 2 .7]
Note 15) GTR-100 [manufactured by Sakai Chemical Industry Co., Ltd .; rutile titanium oxide, surface treatment: aluminum oxide and zirconium oxide, surface treatment amount: 15%, average particle size: 0.26 μm, refractive index: 2. 7]
Note 16) JA-1 [manufactured by Teika Co., Ltd .; anatase type titanium oxide, surface treatment: none, surface treatment amount: 0%, average particle size: 0.18 μm, refractive index: 2.5]
Note 17) Precipitable barium sulfate # 100 [manufactured by Sakai Chemical Co., Ltd .; precipitable barium sulfate]

"Production of test plates"
In the powder coating compositions prepared in Examples 1 to 22 and Comparative Examples 1 to 14, a 0.8 mm thick zinc phosphate-treated steel sheet was suspended in the vertical direction, and a corona charging electrostatic powder coating machine ( Asahi Sunac Co., Ltd. (PG-1 type) is applied electrostatically to a film thickness of 60 μm at a voltage of −60 kV, and baked in an electric furnace at 180 ° C. for 20 minutes, until it reaches room temperature. It stood to cool and produced the test board. The following evaluation was performed using the obtained test plate, and the results are shown in Tables 2 to 4.

<Smoothness>
The finished appearance of the coating surface was observed with the naked eye.
◎; Very good with no irregularities,
○: Some irregularities are seen, but good,
△: Unevenness is seen and inferior,
X: Unevenness is extremely inferior.

<Glossy coating film>
Measured according to JIS K-5400 7.6 (1990) (reflectance 60 degrees).

<Copping resistance>
The Erichsen value was measured according to JIS K-5400 8.2 (1990). The extrusion distance (mm) until cracking and peeling occurred in the coating film was measured.

<Impact resistance test>
According to JIS K-5400 8.3.2 (1990) DuPont impact resistance test, the coated plate was coated under the conditions of a falling weight of 1000 g, an impact point diameter of 1/2 inch, and a falling weight height of 50 cm. Impact was applied to the front and back surfaces. Subsequently, the cellophane adhesive tape was affixed to the part which applied the impact, and the degree of peeling of the coating film when the tape was instantaneously peeled was evaluated.
○: no peeling on the coated surface
Δ: Slight peeling is observed on the coated surface,
X: Significant peeling is observed on the coated surface.

<Coating reflectance (λ = 555 nm)>
The reflectivity including specularly reflected light at a wavelength of 555 nm using CM-2500d manufactured by Konica Minolta Co., Ltd. (using an integrating sphere and diffusing illumination at 8 ° direction) was expressed as a percentage when the magnesium oxide white plate was taken as 100.

<Concealment>
In accordance with JIS K 5600-4-1, the black-and-white concealment test plate was coated and baked. The color difference (ΔE) between the white part and the black part was measured using CR-300 manufactured by Konica Minolta.
○: ΔE is 0.5 or less Δ: ΔE is greater than 0.5 and 1.0 or less ×: ΔE is greater than 1.0

Claims (4)

(A) Spherical titanium oxide (B) carboxyl group-containing resin having a refractive index of 2.7 or more, which is surface-treated with one or both of a hydrous oxide and an oxide of at least one element selected from the group consisting of aluminum, silicon and zirconium ,
(C) β-hydroxyalkylamide compound and (D) The glass transition temperature (Tg) of the material constituting the core layer is less than 20 ° C., the flexural modulus at 23 ° C. is less than 5 MPa, Powder having core-shell type organic particles having a Tg of 30 ° C. or higher, a polymer material having a flexural modulus of 2000 to 45000 MPa at 23 ° C., and having an epoxy group or a carboxyl group in the shell layer A powder coating composition comprising 30 to 55 parts by weight of the spherical titanium oxide with respect to 100 parts by weight of the powder coating composition in the coating composition.   The powder coating composition according to claim 1, wherein the carboxyl group-containing resin is a resin having a polyester structure.   A coated product obtained by applying the powder coating composition according to claim 1 or 2 to a substrate.   The coated article according to claim 3, which has a coating film characterized by having a reflectance at λ = 555 nm of 90% or more.