JPH09188833A - Powder coating composition and coating film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acid-epoxy curing powder coating and a coating film forming method using the same which can form a coating film possessing excellent yellowing resistance and appearance. SOLUTION: This powder coating compsn. comprises: an epoxy-contg. acrylic resin prepd. by polymerizing a monomer mixture of 35 to 65wt.% epoxy-contg. ethylenically unsatd. monomer with the balance consisting of other ethylenically unsatd. monomer(s); a polycarboxylic acid; and an antioxidant having an m.p. of 50 to 140 deg.C.

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 preferably used in the field of automobile top coatings and coil coating coatings.

[0002]

2. Description of the Related Art In recent years, paints that release a small amount of solvent into the atmosphere to reduce adverse effects on the environment have been desired, and powder paints have been receiving attention. Further, although deterioration of the coating film due to acid rain has become a problem in recent years, the coating film of acid-epoxy curing system is relatively excellent in acid resistance.

For example, Japanese Patent Laid-Open No. 5-278582 discloses that
A powder coating composition which can be baked at a low temperature and gives a coating film excellent in appearance, weather resistance and blocking resistance is disclosed.

[0004] However, the acid-epoxy curing type coating system remarkably yellows when cured by heating, and it is difficult to design a light color coating such as a white system or a white mica system.

[0005]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide an acid-epoxy curing powder which forms a film excellent in yellowing resistance and appearance. It is an object of the present invention to provide a body paint and a coating film forming method using the same.

[0006]

The present invention comprises (A) (a) 35 to 65% by weight of an epoxy group-containing ethylenically unsaturated monomer, and (b) a balance of other ethylenically unsaturated monomers. Acrylic resin obtained by polymerizing a mixture of monomers, (B) polyvalent carboxylic acid, and (C) melting point 50 to 140
The present invention provides a powder coating composition containing an antioxidant at 0 ° C, which achieves the above object.

Epoxy Group-Containing Acrylic Resin (A) The epoxy group-containing acrylic resin (A) used in the powder coating composition of the present invention is an epoxy group-containing ethylenically unsaturated monomer (a) and a copolymerizable therewith. It is obtained by polymerizing a monomer mixture containing another ethylenically unsaturated monomer (b).

The epoxy group-containing ethylenically unsaturated monomer (a) used in the present invention means a relatively low molecular weight having an epoxy group and a copolymerizable double bond, generally having 10 or less carbon atoms, preferably 8 or less carbon atoms. The compound of For example,
Glycidyl acrylate, glycidyl methacrylate,
Examples include α-methylglycidyl acrylate and α-methylglycidyl methacrylate. These monomers may be used in combination of two or more kinds.

The other ethylenically unsaturated monomer (b) is a compound having a relatively low molecular weight which can coexist with an epoxy group having a copolymerizable double bond. Specifically, (meth) methyl acrylate, (meth) ethyl acrylate, (meth) butyl acrylate, (meth) acrylate isobutyl,
(Meth) t-butyl acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate and (meth) acrylate
Alkyl ester of (meth) acrylic acid such as cyclohexyl acrylate, hydroxyalkyl ester of (meth) acrylic acid such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate, styrene, vinyltoluene, α- Examples include methylstyrene, acrylonitrile, methacrylonitrile, acrylamide, dimethylacrylamide, and dialkyl esters of unsaturated dibasic acids. These monomers may be used in combination of two or more kinds.

The content of the epoxy group-containing ethylenically unsaturated monomer (a) in the above monomer mixture is 35 to 65% by weight, preferably 40 to 62% by weight, more preferably 45 to 65% by weight based on the total amount of the monomer mixture. 60% by weight
It is. When the content is less than 35% by weight, the curability of the obtained coating composition is lowered. When the content exceeds 65% by weight, the transparency of the obtained coating film may be deteriorated and appearance defects may occur.
Further, when the monomer mixture contains 0.1 to 10% by weight of isobutyl methacrylate as the other ethylenically unsaturated monomer (b), the blocking resistance of the obtained powder coating composition is improved.

The above monomer mixture is polymerized by a method well known to those skilled in the art to obtain an epoxy group-containing acrylic resin (A).

The resulting epoxy group-containing acrylic resin (A)
Preferably has an SP value of 11.0 to 11.6, particularly 11.0 to 11.4. By using such an epoxy group-containing acrylic resin (A), it is possible to obtain a powder coating composition having excellent low-temperature curability and a coating film having excellent transparency. Solubility parameter (hereinafter referred to as "SP") values are shown in Suh and Clarke, J. Polym., Sci., A.
-1, 5, pp. 1671 to 1681, 1967, it can be measured according to the method by the drip point titration. For example, the measurement temperature is 20 ° C., and a tetrahydrofuran solvent (THF) is used.

The epoxy group-containing acrylic resin (A) preferably has a glass transition temperature of 20 ° C to 60 ° C, particularly 35 to 58 ° C. When the glass transition temperature is lower than 20 ° C., the powder coating composition obtained has poor blocking resistance. If the glass transition temperature exceeds 60 ° C., the resulting coating film may have poor appearance.

Polyvalent carboxylic acid (B) The polycarboxylic acid (B) used in the present invention is a compound having two or more carboxyl groups. This is a component which cures the coating film by crosslinking the epoxy group-containing acrylic resin (A) by ring-opening addition reaction with the epoxy group contained in the epoxy group-containing acrylic resin (A).

As such a polycarboxylic acid (B),
Aliphatic dibasic acids such as adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, hexadecanedicarboxylic acid, aicosandicarboxylic acid and tetraaicosandicarboxylic acid, and aromatic polycarboxylic acids such as isophthalic acid and trimellitic acid. Acids and alicyclic dibasic acids such as hexahydrophthalic acid and tetrahydrophthalic acid and the like. Among these, decanedicarboxylic acid is particularly preferable.

Antioxidant (C) The antioxidant (C) used in the present invention is not particularly limited as long as it is one commonly used by those skilled in the art, but it is 50 to 140.
Those having a melting point of [deg.] C., particularly 75 to 125 [deg.] C. are preferable. When the melting point of the antioxidant (C) is lower than 50 ° C, the blocking resistance of the resulting coating film is lowered. If it exceeds 140 ° C., the antioxidant becomes difficult to dissolve at ordinary baking temperature, and its aggregate remains on the surface of the coating film, resulting in poor appearance of the coating film.

Preferred antioxidants are phenolic antioxidants, phosphite antioxidants and thioether antioxidants. Particularly preferred antioxidants are phosphite antioxidants.

As the antioxidant, either compound may be used alone, but since the antioxidant mechanism of each antioxidant is different, it is effective to use two or more kinds in combination for the yellowing resistance. is there. Particularly, it is preferable to use a combination of a phenol-based antioxidant and a phosphite-based antioxidant or a thioether-based antioxidant. Most preferably, it is a combination of a phenolic antioxidant and a phosphite antioxidant.

As the phenolic antioxidant, for example,
Sumitizer BHT, Sumilizer S, Sumilizer BP-76, Sumilizer M
DP-S, Sumilizer BP-101, Sumilizer G
A-80, Sumilizer BBM-S, Sumilizer WX
-R, Sumilizer NW, Sumilizer GM, Sumilizer GS, Smithar BHT (2,6-di-t-butyl-4-methylphenol); and Asahi Denka Co., Ltd. Adeka Stab AO-20, Adeka Stab AO-30, Adeka Stab AO- 40, ADEKA STAB AO-50 (n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate), ADEKA STAB AO-6
0 (tetrakis {methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate} methane), ADEKA STAB AO-75, ADEKA STAB AO-8
0 (3,9-bis [2- {3- (3-t-butyl-4-
[Hydroxy-5-methylphenyl) propionyloxy {-1,1-dimethylethyl] -2,4,8,10-
Tetraoxaspiro {5.5} undecane), Adeka Stab AO-330, Adeka Stab AO-616, Adeka Stab AO-635, Adeka Stab AO-658, Adeka Stab AO-15, Adeka Stab AO-18, Adeka Stub 328, Adeka Stub AO-37; Sankyo Sanol LS2626 (1- [2- {3- (3,5-di-
t-Butyl-4-hydroxyphenyl) propionyloxy} ethyl] -4- {3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy}-
2,2,6,6-tetramethylpiperidine) and the like.

The preferred phenolic antioxidant has a melting point of 7
2,6-di-t-butyl-4-methylphenol at 1 ° C., n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, melting point 50 ° C., melting point 115 ° C. Tetrakis {methylene-3- (3
5-di-t-butyl-4-hydroxyphenyl) propionate} methane, melting point 125 ° C. 3,9-bis [2-
{3- (3-t-Butyl-4-hydroxy-5-methylphenyl) propionyloxy} -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro {5.
5} Undecane and 1- [2- {3- with a melting point of 135 ° C.
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionyloxy} ethyl] -4- {3- (3,5-
Di-t-butyl-4-hydroxyphenyl) propionyloxy} -2,2,6,6-tetramethylpiperidine.

Examples of the phosphite type antioxidant include Sumilizer TNP, Sumilizer TPP-R and Sumilizer P-16 manufactured by Sumitomo Chemical Co., Ltd., Adekastab PEP-2, Adekastab PEP-4C and Adekastab PEP manufactured by Asahi Denka Co., Ltd. -8, ADEKA STAB PEP-8F, ADEKA STAB PEP-8W, ADEKA STAB PEP-11
C, ADEKA STAB PEP-24G, ADEKA STAB PEP
-36, ADEKA STAB HP-10, ADEKA STAB 211
2, adekus tab 260, adekus tab P, adekus tab QL, adekus tab 522A, adekus tab 329
K, Adeka Stub 1178, Adeka Stub 1500, Adeka Stub C, Adeka Stub 135A, Adeka Stub 5
17, ADEKA STAB 3010, ADEKA STAB TPP, and the like.

Preferred phosphite antioxidants have the formula:

[0023]

Embedded image

[Wherein R ₁ is a hydrogen atom, a t-butyl group or a phenyl group, and R ₂ is a hydrogen atom, a methyl group or a t-group.
It is a butyl group or a phenyl group, and R ₃ is a hydrogen atom or a methyl group. ] It is a compound which has a structure shown. Specifically, tris (4-t-butylphenyl) phosphite having a melting point of 75 ° C., tris (2-t-butyl-4-methylphenyl) phosphite having a melting point of 110 ° C., melting point 111
And tris (2-t-butyl-5-methylphenyl) phosphite having a melting point of 96 ° C., tris (4-phenylphenyl) phosphite having a melting point of 92 ° C., and the like.

Examples of the thioether antioxidant include Sumilizer TPL-R, Sumilizer TPM, Sumilizer TPS, Sumilizer TP-, manufactured by Sumitomo Chemical Co., Ltd.
D, Sumilizer TL, Sumilizer MB, and ADEKA STAB AO-23, ADEKA STAB AO-41 manufactured by Asahi Denka Co., Ltd.
2S, ADEKA STAB AO-503A and the like.

Further, dilauryl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thio. Dipropionate, bis (2
-Methyl-4- {3-n-alkylthiopropionyloxy} -5-t-butylphenyl) sulfide, pentaerythritol-tetrakis- (β-lauryl-thiopropionate), 2-mercaptobenzimidazole and the like.

Preferred thioether antioxidants are dilauryl-3,3'-thiodipropionate, ditridecyl-3,3'-thiodipropionate, distearyl-3,3.
3'-thiodipropionate, bis (2-methyl-4-)
{3-n-Alkylthiopropionyloxy} -5-t-
Butylphenyl) sulfide.

The above epoxy group-containing acrylic resin (A),
The powder coating composition of the present invention can be obtained by blending the polycarboxylic acid (B) and the antioxidant (C).

The epoxy group-containing acrylic resin (A) and the polyvalent carboxylic acid (B) are the epoxy group contained in the epoxy group-containing acrylic resin (A) and the carboxyl group contained in the polyvalent carboxylic acid (B). Has a molar ratio of 10/10 to 10/5,
In particular, it is preferable that the content be 10/8 to 10/6. If this molar ratio is less than 10/10, the gloss of the coating film obtained will decrease, and if it exceeds 10/5, the thermosetting property of the powder coating composition obtained will decrease.

The antioxidant (C) is 0.1 to 10 parts by weight, preferably 0.5 to 100 parts by weight based on 100 parts by weight of the epoxy group-containing acrylic resin (A) and the polycarboxylic acid (B). 8 parts by weight, more preferably 1 to 7 parts by weight. If the content is less than 0.1 part by weight, the antioxidant effect is insufficient, and if it exceeds 10 parts by weight, the water resistance and blocking resistance of the resulting coating film are deteriorated.

Surface Conditioner (D) The powder coating composition of the present invention may contain a surface conditioner, if necessary. The surface conditioner refers to an additive that promotes fusion between the coating particles of the powder coating material during heating and enhances the transparency of the resulting coating film.

As the surface conditioner, a polymer having a good compatibility with the coating particles of the powder coating is used. The polymer to be used is not particularly limited, but it is 10.4-11.0, especially 1.
SP value of 0.6 to 10.9, and 2500 to 9000,
Particularly, those having a number average molecular weight of 3,000 to 7,000 are preferable. This is because the SP value in this range improves the compatibility between the surface modifier and the epoxy group-containing acrylic resin, and improves the transparency of the resulting coating film. If the molecular weight of the polymer used as the surface conditioner is less than 2500, the blocking resistance of the obtained powder coating composition is lowered and the surface adjusting effect becomes insufficient. If the molecular weight exceeds 9,000, the smoothness of the coating film obtained will be impaired.

Specifically, an acrylic polymer is suitable. For example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth ) A polymer obtained by polymerizing one or more kinds of (meth) acrylic esters such as cyclohexyl acrylate, stearyl (meth) acrylate and lauryl (meth) acrylate may be used.

The surface modifier (D) is used in an amount of 0.1 to 4 parts by weight, particularly 0.3 to 2 parts by weight, based on 100 parts by weight of the total amount of the epoxy group-containing acrylic resin (A) and polyvalent carboxylic acid (B). It is preferable that the powder coating composition of the present invention is contained in an amount of 1 part. When the content of the surface conditioner (D) is less than 0.1 part by weight, the smoothness of the coating film obtained is impaired. Also a surface conditioner
If the content of (D) is too large, the blocking resistance of the resulting coating film will decrease.

The powder coating composition of the present invention may contain an ultraviolet absorber, a hindered amine light stabilizer, an antioxidant and the like in order to improve the weather resistance of the coating film. Further, a silicone compound as a surface modifier and Aerosil as a fluidity modifier for adjusting the appearance and fluidity, and resin fine particles for preventing blocking may be added.

When the resin fine particles are used as an anti-blocking agent, the powder of the resin fine particles is added to and mixed with the powder coating composition after preparation. The resin fine particles have an average particle size of 0.01 to 10 μm, preferably 0.03 to 3 μm, a glass transition temperature of 50 to 150 ° C., preferably 70 to 120 ° C., and an SP value of 9 to 15, preferably 10 to 13.

Particles having an average particle size of 0.01 μm or less are difficult to produce, and if it exceeds 10 μm, the amount of particles for imparting blocking resistance becomes large and the appearance is adversely affected. If the glass transition temperature is lower than 50 ° C, the blocking resistance is poor, and if it exceeds 150 ° C, it is not practical.
If the SP value is out of the above range, the compatibility with the base coating material is lowered and the appearance is adversely affected.

The amount added is not particularly limited, but generally 0.05 to 20 parts by weight per 100 parts by weight of the coating composition,
It is preferably 0.1 to 10 parts by weight. If the amount of resin fine particles added exceeds 20 parts by weight, the appearance of the resulting coating film will be poor, and if it is less than 0.05 parts by weight, the blocking resistance will be poor.

However, the powder coating composition of the present invention preferably does not contain a blocked polyisocyanate as a curing agent. When a blocked polyisocyanate is used, the resulting cured coating film is likely to turn yellow, and the blocking agent that blocks the isocyanate group is volatilized during baking, so pinholes are likely to occur in the cured coating film.

The coating composition of the present invention can be applied by an electrostatic coating method or the like. The substrate may be primed or semi-coated, if desired. Known undercoating and intermediate coatings can be used.

The coating composition of the present invention may be advantageously used on any substrate such as wood, metal, glass, cloth, plastics, foams and the like, especially on plastic and metal surfaces such as steel, aluminum and their alloys. Generally, the film thickness will vary depending on the desired application. In many cases, the dry film thickness is 20 μm to 120 μm, preferably 40 μm to 1
00 μm is useful.

After coating the substrate, the coating film is cured. Curing gives a uniform cured coating film at 100 to 250 ° C, preferably 120 to 200 ° C. The curing time varies depending on the curing temperature and the like, but curing at 120 ° C to 200 ° C for 15 to 45 minutes is suitable.

The method of forming a coating film using the coating composition of the present invention includes, for example, a step of applying a water-based or solvent-based base coating on an undercoated or intermediate coated substrate; curing the base coating. A coating film forming method including a step of applying the clear powder coating composition thereon, and a step of curing the base coating film and the clear coating film by heating.

The base paint is not particularly limited, but (a) 5 to 40% by weight of an amide group-containing ethylenically unsaturated monomer, 3 to 15% by weight of an acid-containing ethylenically unsaturated monomer, and 10 to 40% by weight. Of a hydroxyl group-containing ethylenically unsaturated monomer and the remaining amount of another ethylenically unsaturated monomer, obtained by copolymerization
Film-forming vinyl polymers 95-10 polymers obtained by neutralizing at least a part of the acidic groups of 50,000 copolymers
(Solid content); and (b) reacting a diol having a terminal hydroxyl group with a molecular weight of 100 to 5000, a diisocyanate, and a compound having at least one active hydrogen in the molecule and having a hydrophilic group under an isocyanate-rich condition. Urethane-containing water dispersion 5 obtained by dispersing the hydrophilic group-containing oligomer obtained in this way in an aqueous medium containing a primary polyamine, a secondary polyamine, or both.
To 90% by weight (solid content); and the like.

[0045]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. Unless otherwise specified, the blending amount is expressed in parts by weight.

The method of determining the characteristic value used in this embodiment will be described below. The polystyrene-reduced number average molecular weight measured by molecular weight gel permeation chromatography (GPC) was used as the molecular weight.

SP value Sue and Kurake, J. Polym., Sci., A-1, 5,
It was measured according to the method of turbidity described in pages 1671 to 1681, 1967. The measurement temperature is 20 ° C,
Tetrahydrofuran (THF) was used as a solvent.

Glass transition temperature (Tg) Determined by differential scanning calorimeter (DSC) measurement.

Pulverized paint particle size The average value of 50% cumulative weight average particle size measured using Microtrac "MK-2" (manufactured by Nikkiso Co., Ltd.) was defined as the paint particle size.

The resin fine particle size resulting laser light scattering method of emulsion (Coulter Mod
The weight average particle diameter measured by el N4) was defined as the resin fine particle diameter.

Synthesis Example 1 Synthesis of Epoxy Group-Containing Acrylic Resin (A) A reaction vessel equipped with a thermometer, a stirrer, a cooling tube, a nitrogen introducing tube and a dropping funnel was charged with 63 parts by weight of xylene and heated to 130 ° C.
Heated. Using a dropping funnel in this container, 45 parts by weight of glycidyl methacrylate, 20 parts by weight of styrene, 27 parts by weight of methyl methacrylate, 8 parts by weight of isobutyl methacrylate, and 6 parts by weight of t-butylperoxy-2-ethylhexanoate. Parts, and 6 parts by weight of xylene were added dropwise at a constant rate separately over 3 hours. After the dropping was completed, the mixture was held for 30 minutes, and then 0.1 part by weight of t-butylperoxy-2-ethylhexanoate and 7 parts by weight of xylene were added dropwise at a constant rate over 30 minutes using a dropping funnel. After dropping,
After holding at 130 ° C for 1 hour, xylene was removed by vacuum distillation to obtain acrylic resin A-1 having SP value of 11.3 and Tg of 52 ° C.

Synthesis Examples 2 to 6 Epoxy group-containing acrylic resins A-2 to A-6 were prepared in the same manner as in Synthesis Example 1 except that the compositions shown in Table 1 below were used. SP of the obtained epoxy group-containing acrylic resin
Values and Tg are also shown in Table 1.

[0053]

[Table 1] Epoxy group-containing acrylic resin (A) A-1 A-2 A-3 A-4 A-5 A-6 Epoxy group-containing GMA 45 40 60 40 45 45 Monomer (a) α-MGM-5- − − − Epoxy group-containing ST 20 20 23.5 13.2 21.2 1.5 Copolymer with monomer MMA 27 27 8.5 33 28.4 13 Other compatible iBMA 8 8 8 8-8 monomer (b) nBMA − − − 5.8 5.4 32.5 SP value 11.3 11.5 11.3 11.3 11.3 11.2 Tg (° C) 52 53 43 50 51 30 GMA: Glycidyl Methacrylate α-MGM: α-Methylglycidyl Methacrylate ST: Styrene MMA: Methyl Methacrylate iBMA: Isobutyl Methacrylate nBMA: n-Butyl Methacrylate

Synthesis Example 7 Synthesis of Surface Conditioner (D) 90 parts by weight of xylene was charged into a reaction vessel equipped with a thermometer, a stirrer, a cooling tube, a nitrogen introducing tube and a dropping funnel, and 120 ° C.
Heated. Using a dropping funnel in this container, 50 parts by weight of ethyl acrylate, 50 parts by weight of n-butyl acrylate and 3 parts of t-butylperoxy-2-ethylhexanoate
Part by weight was added dropwise at a constant rate over 3 hours. After the dropping was completed, the mixture was kept for 30 minutes, and then 0.3 parts by weight of t-butylperoxy-2-ethylhexanoate and 10 parts by weight of xylene were added dropwise at a constant rate over 30 minutes using a dropping funnel. 120 more after dropping
After being kept at ℃ for 2 hours, xylene was removed by distillation under reduced pressure to obtain a surface conditioner D- having an SP value of 10.7 and a number average molecular weight of 6000.
1 was obtained.

Synthesis Examples 8 to 10 Surface conditioners D-2 to D-4 were prepared in the same manner as in Synthesis Example 7 except that the compositions shown in Table 2 below were used. Table 2 also shows the SP value and the number average molecular weight of the obtained surface conditioner.

[0056]

[Table 2] Surface modifier (D) D-1 D-2 D-3 D-4 Ethyl acrylate 50 50 50 70 n-Butyl acrylate 50 50 50 30 t-Butylperoxy- 2-ethylhexanoate 36 2.6 3 SP value 10.7 10.7 10.7 10.9 Number average molecular weight 6000 3000 7000 6000

Synthesis Example 11 Preparation of resin fine particles In a reaction vessel equipped with a stirrer, a cooler, and a temperature controller, 380 parts by weight of deionized water and a nonionic surfactant "MON" were used.
2 "(manufactured by Sanyo Kasei Co., Ltd.), and the stirring temperature is 80
Dissolve while maintaining at ℃, ammonium persulfate 1
A polymerization initiator solution having 10 parts by weight of deionized water dissolved therein was added.

Then, a mixed solution of 61 parts by weight of methyl methacrylate, 36 parts by weight of styrene and 3 parts by weight of butyl methacrylate was added dropwise over 60 minutes. After completion of dropping, stirring was continued at 80 ° C. for 60 minutes. Thus, an emulsion having a nonvolatile content of 20% and a particle size of 0.03 to 0.05 μm was obtained. This emulsion is spray dried to give a dissolution parameter of 10, glass transition temperature of 110 ° C. and average particle size of 0.03.
Resin fine particles of ˜0.05 μm were obtained.

Example 1 Preparation of powder coating composition 100 parts of epoxy group-containing acrylic resin A-1, 27.3 parts of decanedicarboxylic acid, 2,6-di-t-butyl-4
-Methylphenol 1.27 parts, tris (4-t-butylphenyl) phosphite 2.54 parts, surface conditioner D-
After mixing 0.76 parts of benzoin and 0.64 parts of benzoin, the resulting mixture was melt-kneaded using Busconida (manufactured by Buss), extruded and cooled to obtain a solid coating composition. Ultracentrifugal pulverization using an "ultracentrifugal pulverizer" manufactured by Mitamura Riken Kogyo Co., Ltd., classification (150 mesh), and further classification 1
0.2 parts of "Aerosil R-974" manufactured by Nippon Aerosil Co., Ltd. was added to 100 parts and well mixed to obtain an average particle diameter of 25 μm.
A powder coating composition I of was obtained.

The color difference and blocking resistance of the obtained powder coating composition were evaluated according to the following procedures. Table 3 shows the results
And 4.

Gradient coating of only the powder coating was applied onto the color difference white plate and baked at 150 ° C. for 25 minutes. The b value at a film thickness of 60 μm of the obtained coated plate was measured with an SM color computer “SM-4” manufactured by Suga Test Instruments Co., Ltd., and the difference in the b value from the white plate was defined as the color difference (Δb).

The anti-blocking paint was put in a 50 ml sample bottle, left at 30 ° C. for 2 months and then taken out, and the state of aggregation of the paint was evaluated. ⊚: No agglomerates exist ○: A small amount of agglomerates is easily crushed ×: Agglomerates are not crushed

Example 2, Comparative Example 1 and Comparative Example 11 Powder coating compositions II, XII and XVI were prepared in the same manner as in Example 1 except that the compositions shown in Tables 3 and 4 below were used.
I was obtained. The average particle size of the obtained powder coating composition is shown in Table 3.
And 4.

Examples 3 to 10 and Comparative Examples 2 to 4 Using the compositions shown in Tables 3 and 4 below, "Labo Jet LJ-N" manufactured by Nippon Pneumatic Co., Ltd. was used instead of ultracentrifugal pulverization.
Powder coating compositions III to X and XIII to X in the same manner as in Example 1 except that jet pulverization is performed using the "mold".
I got V. The average particle size of the obtained powder coating composition is shown in Table 3.
And 4.

[0065] The powder coating composition IV obtained in Example 11 Example 4, Synthesis Example 11
In the same manner as in Example 4 except that the resin fine particles obtained in 2) were added in an amount of 2 parts with respect to 100 parts of the powder coating composition and dry-blended with a Henshall mixer, the resin fine particles were formed on the surface of the powder coating composition. The powder coating composition XI which adhered was obtained.

Comparative Example 5 The powder coating composition XV obtained in Comparative Example 4 was prepared according to Synthesis Example 11
In the same manner as in Comparative Example 4 except that the resin fine particles obtained in 2) were added in an amount of 2 parts with respect to 100 parts of the powder coating composition and dry-mixed with a Henshall mixer, the resin fine particles were formed on the surface of the coating particles. Adhering powder coating composition XVI was obtained.

[0067]

[Table 3]

[0068]

[Table 4]

Example 12 Preparation of Coated Plate A 0.8 mm thick phosphoric acid-treated steel plate was coated with a cationic electrodeposition paint (“Power Top U-50” manufactured by Nippon Paint Co., Ltd.) and an intermediate coating (manufactured by Nippon Paint Co., Ltd.). "Olga P-2") was applied to a process test plate coated with a dry film thickness of 25 μm and 40 μm, respectively, and a water-based base paint (manufactured by Nippon Paint Co., Ltd., Example 1 of US Pat. No. 5,183,504) was used as a dry film. Thickness 15 μm
To form a base coating film by air-spraying and predrying at 80 ° C. for 5 minutes.

The above water-based coating composition was prepared by mixing 56.2 parts of an acrylic resin varnish having a number average molecular weight of 12,000, a hydroxyl value of 70, an acid value of 58 and a nonvolatile content of 50% obtained in Preparation Example 1 of the same document, and Mitsui Higashi. Pressure Chemical Co., Ltd. methylated melamine "Cymel 303" 15.0 parts, acid value 16.2 and non-volatile content 33% urethane Elma John 21.5 parts, Toyo Aluminum Co., Ltd. aluminum flake content 65% aluminum pigment paste " Alpaste 7160N "7.5 parts and Sakai Chemical Co., Ltd. isostearic acid phosphate" Phophorex A-180L "1.0 parts.

On the base coating film, the powder coating composition I obtained in Example 1 was wet-on-wet to have a film thickness of 60 μm.
And electrostatically coated so as to be 25 ° C. for 25 minutes to obtain a test coated plate.

The performance of the obtained coating film was evaluated as follows. Table 5 shows the results.

Evaluation of Appearance The smoothness and gloss of the coating film surface were visually observed. ○: good ×: bad

Water resistance The obtained cured coating film was immersed in tap water at 40 ° C. for 10 days, and then the surface of the coating film was visually evaluated according to the following criteria.

◯: No change was observed ×: Change was observed

The surface of the xylene-resistant coating film was rubbed back and forth 10 times with gauze impregnated with xylene, and the state of the coating film was visually observed. ○: No change was observed ×: Trace was observed

Example 13 Phosphoric acid-treated steel sheet having a thickness of 0.8 mm was coated with a cationic electrodeposition coating (Power Top U-50 manufactured by Nippon Paint Co., Ltd.) and an intermediate coating (Olga P-2 manufactured by Nippon Paint Co., Ltd.). Solvent coated high solid base paint (Nippon Paint Co., Ltd.)
(Manufactured by K.K.) was used to perform air spray coating to a dry film thickness of 16 μm, and setting was performed for about 7 minutes to form a base coating film.

The solvent-type high solid base paint was blended with an acrylic resin (nonvolatile content 8% by Nippon Paint Co., Ltd.).
0%, hydroxyl value 100, acid value 30 and number average molecular weight 1
800) 20 parts, Nippon Paint Co., Ltd. polyester (nonvolatile content 80%, hydroxyl value 100, acid value 12 and number average molecular weight 2600) 30 parts, Mitsui Cyanamid Melamine resin Cymel 202 "(nonvolatile content 80%) 40 Part, 10 parts of melamine resin “Cymel 327” (nonvolatile content 90%) manufactured by Mitsui Cyanamide Co., Ltd., 10 parts of “Alpaste A160-600” (nonvolatile content 65%) manufactured by Toyo Aluminum Co., Ltd. and 7 parts of isopropyl alcohol.

On the base coating film, the powder coating composition I obtained in Example 1 was wet-on-wet to have a film thickness of 60 μm.
And electrostatically coated so as to be 25 ° C. for 25 minutes to obtain a test coated plate.

The performance of the obtained coating film was evaluated in the same manner as in Example 12. Table 5 shows the results.

Examples 14-23 and Comparative Examples 5-8 Example 1 except that the powder coating compositions shown in Table 5 were used.
A test coated plate was prepared in the same manner as in 2, and the coating film was evaluated. Table 5 shows the results.

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[Table 5] Example Powder coating composition base Top (powder) Appearance Water resistance Xylene resistance 12 Water-based I ○ ○ ○ 13 Solvent-based I ○ ○ ○ 14 Water-based II ○ ○ ○ 15 Water-based III ○ ○ ○ 16 Water-based IV ○ ○ ○ 17 Aqueous V ○ ○ ○ 18 Aqueous VI ○ ○ ○ 19 Aqueous VII ○ ○ ○ 20 Aqueous VIII ○ ○ ○ 21 Aqueous IX ○ ○ ○ 22 Aqueous X ○ ○ ○ 23 Aqueous XI ○ ○ ○ Comparative Example 6 Aqueous XII ○ ○ ○ Comparative Example 7 Aqueous XIII ◎ ○ ○ Comparative Example 8 Aqueous XIV × ○ ○ Comparative Example 9 Aqueous XV ○ × ○ Comparative Example 10 Aqueous XVI ○ × ○ Comparative Example 12 Aqueous XVII × ○ ○

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EFFECT OF THE INVENTION An acid-epoxy curing type powder coating which forms a coating excellent in yellowing resistance and appearance and a coating forming method using the same are provided.

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Claims (18)

[Claims] 1. A polymerized monomer mixture containing (A) (a) 35 to 65% by weight of an epoxy group-containing ethylenically unsaturated monomer, and (b) a residual amount of another ethylenically unsaturated monomer. A powder coating composition containing an epoxy group-containing acrylic resin; (B) a polycarboxylic acid; and (C) an antioxidant having a melting point of 50 to 140 ° C. 2. The molar ratio of the epoxy groups contained in the epoxy group-containing acrylic resin (A) and the carboxyl groups contained in the polycarboxylic acid (B) is 10/10 to 10/5, The powder according to claim 1, wherein the content of the oxidizing agent (C) is 0.1 to 10 parts by weight based on 100 parts by weight of the total amount of the epoxy group-containing acrylic resin (A) and the polycarboxylic acid (B). Body coating composition. 3. The powder coating composition according to claim 1, which contains a phosphite-based antioxidant as the antioxidant (C). 4. A phenol-based antioxidant and a phosphite-based antioxidant as the antioxidant (C).
A powder coating composition as described in the above. 5. The phosphite antioxidant is of the formula: [In the formula, R ₁ is a hydrogen atom, a t-butyl group or a phenyl group, R ₂ is a hydrogen atom, a methyl group, a t-butyl group or a phenyl group, and R ₃ is a hydrogen atom or a methyl group. ] The powder coating composition of Claim 3 or 4 which has a structure shown by these. 6. The powder coating composition according to claim 1, further comprising (D) a surface modifier. 7. The content of the surface conditioner (D) is 0.1 to 4 parts by weight based on 100 parts by weight of the total amount of the epoxy group-containing acrylic resin (A) and the polyvalent carboxylic acid (B). The powder coating composition according to claim 6. 8. The powder coating composition according to claim 1, wherein the monomer mixture contains 40 to 62% by weight of the epoxy group-containing ethylenically unsaturated monomer (a). 9. The powder coating composition according to claim 1, wherein the epoxy group-containing acrylic resin (A) has an SP value of 11.0 to 11.6. 10. The epoxy group-containing acrylic resin (A)
The powder coating composition according to claim 1, having a glass transition temperature of 20 ° C or higher. 11. The powder according to claim 1, wherein the monomer mixture contains 0.1 to 10% by weight of isobutyl methacrylate as the other ethylenically unsaturated monomer (b) based on the total amount of ethylenically unsaturated monomer. Body coating composition. 12. The powder coating composition according to claim 1, wherein the polycarboxylic acid is decanedicarboxylic acid. 13. The powder coating composition according to claim 1, wherein the coating particles have an average particle size of 15 microns or less. 14. An average particle size of 0.01 to 10 μm and a glass transition temperature of 50 to 15 attached to the surface of paint particles.
The resin fine particles having a 0 ° C. and SP value of 9 to 15 are contained.
The powder coating composition according to any one of 1 to 13. 15. A clear powder coating composition containing the powder coating composition according to claim 1 as a binder component. 16. A step of applying a water-based or solvent-based base coating material onto a substrate having an undercoat or an intermediate coating; the clear powder according to claim 1, without curing the base coating film. A method for forming a coating film, which comprises a step of applying the body coating composition; and a step of curing the base coating film and the clear coating film by heating. 17. The base coating comprises (a) 5-40% by weight of an amide group-containing ethylenically unsaturated monomer, 3-15% by weight of an acid-containing ethylenically unsaturated monomer, 10-40% by weight of a hydroxyl group. Number average molecular weight 6000 to 50 obtained by copolymerizing ethylenically unsaturated monomer and the remaining amount of other ethylenically unsaturated monomer
Film-forming vinyl polymer 95 to 10 polymer (solid content) obtained by neutralizing at least a part of the acidic group of the 000 copolymer; and (b) a molecular weight of 10 having a terminal hydroxyl group.
A hydrophilic group-containing oligomer obtained by reacting 0 to 5000 diol, diisocyanate and a compound having at least one active hydrogen in the molecule and having a hydrophilic group under an isocyanate-rich condition is used as a primary polyamine. Alternatively, urethane-containing water dispersions 5 to 90 obtained by dispersing in a water medium containing a secondary polyamine or both
The method for forming a coating film according to claim 16, which is an aqueous dispersion composition containing 50% by weight (solid content). 18. A coated article obtained by the method according to claim 16.