JPH1017791A - Powder coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a powder coating composition excellent in the surface smoothness of a coating film therefrom, and suitably usable even in the fields requiring high-grade coating film appearance such as in the automotive field, comprising specific indeterminate form particles and spherical particles in specified proportions. SOLUTION: This powder coating composition comprises (A) indeterminate form particles each 8-20μm in average size made of a thermosetting resin (normally comprising thermosetting resin component(s), curing agent component, extender pigment and various additives, and, optionally, color pigment) [e.g. >=35 deg.C in glass transition temperature (Tg)] and (B) spherical particles (e.g. the difference between its Tg and the Tg of the component A is <10 deg.C, esp. its Tg is not higher than the Tg of the component A) in the weight ratio A/B of (95:5) to (5:95).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder paint capable of forming a coating film having excellent surface smoothness.

[0002]

2. Description of the Related Art Powder coatings generally have poor surface smoothness and poor appearance quality compared with solvent-based coatings. There were many restrictions on its use.

[0003]

The reasons for the poor smoothness of the coating film of the powder coating are generally that the particle size of the powder coating is large compared to the film thickness and that the flow of the particles during heating and drying is completely prevented. It is considered that if the crosslinking reaction occurs before this, the air contained in the coating film does not escape completely or is not repaired even if it escapes. For this reason, methods such as reducing the particle size or lowering the glass transition temperature of the paint have been considered,
There are problems such as a decrease in blocking properties. Accordingly, an object of the present invention is to provide a powder coating material that can form a coating film having excellent surface smoothness.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above object, and as a result, have found that the average particle size is 8 to 2 μm.
0 μm and made of irregular particles and spherical particles of a thermosetting resin, wherein the irregular particles and the spherical particles are 9
The inventors have found that the above objects can be achieved by using the composition in a weight ratio of 5: 5 to 5:95, and have reached the present invention.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The irregular particles and spherical particles used in the present invention are made of a thermosetting resin that melts when heated and causes a crosslinking reaction. As the thermosetting resin, those conventionally used as materials used for powder coatings can be used without any particular limitation. Usually, the thermosetting resin is composed of one or more thermosetting resin components, a curing agent component, a coloring pigment, an extender pigment, and various additives,
In the case of a clear paint requiring transparency, a coloring pigment may not be blended. Examples of the thermosetting resin component include an epoxy resin, a polyester resin, an epoxy polyester resin, an acrylic resin, an acrylic-polyester resin, and a fluorine resin. These thermosetting resins usually contain various functional groups for forming a crosslinked structure by reacting with a curing agent. For example, one or two or more functional groups such as a hydroxyl group, a carboxyl group, and a glycidyl group are contained at a required concentration in a resin terminal or a side chain.

On the other hand, a curing agent is a component that reacts with these functional groups under appropriate conditions, and includes, for example, an amide compound, an acid anhydride, a dibasic acid, a glycidyl compound, an aminoplast resin, and a blocked isocyanate. Representative examples thereof include dicyandiamide, acid hydrazide, triglycidyl isocyanurate, and isophorone diisocyanate block. For example, dibasic acids include adipic acid, pimelic acid, suberic acid, sebacic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,20-eicosandicarboxylic acid, hexahydrophthalic acid , Maleic acid, phthalic acid, cyclohexene 1,2-dicarboxylic acid and the like. The above-mentioned thermosetting resin component, curing agent component, and, if necessary, the color pigment, extender pigment, and additives by a conventional method, through various steps such as premixing, heat kneading, cooling, coarse pulverization, fine pulverization, and classification. A powder coating is produced. The irregular particles and the spherical particles can use thermosetting resins having different compositions. The irregular particles used in the present invention are powder particles obtained by the above-mentioned usual production method, and are non-spherical particles.

[0007] The spherical particles used in the present invention can be obtained by subjecting the above irregular shaped particles or conventional powder coating particles to spheroidizing treatment by various methods. For example, a heat fusion method in which irregular particles are injected into a stream of heated air or an inert gas to make the particles spherical, a melt spray method in which a molten powder coating material is sprayed, a solvent sprayed after dissolving in a solvent or Liquid spray method,
There are various methods such as a precipitation method of dissolving in a thermal solvent and then cooling to precipitate, a mechanofusion method of mechanically passing amorphous particles between a stator and a rotor, and a hybridizer method. Further, it can also be produced directly from a polymerization method such as a suspension polymerization method or an emulsion polymerization method. Spherical particles may be produced by any of these methods, but it is necessary to avoid alteration of the powder coating particles in the course of the treatment and residual solvent used in the treatment as much as possible. The degree of spheroidization was determined by observing the treated particles with a microscope, without sharp angles clearly formed on two sides like irregular shaped particles, all corners being rounded, and the ratio of the longest diameter to the shortest diameter. Is 2: 1 or less, preferably
Suitably, the ratio is 1.5: 1, more preferably 1: 1 (true sphere). The average particle size of the amorphous particles and the spherical particles is
It is from 8 to 20 μm, preferably from 8 to 18 μm, particularly preferably from 8 to 16 μm. If the average particle size is less than 8 μm, the fluidity of the powder particles is impaired, and the coated surface becomes rough due to electrostatic repulsion due to overcharging of the fine powder particles during electrostatic coating and secondary aggregation of the particles. On the other hand, if it exceeds 20 μm, the unevenness of the coating film becomes large, and it is difficult to realize the smoothness of the surface even in a thick film state.

The mixing ratio of the irregular particles and the spherical particles is 9
5: 5 to 5:95, preferably 90:10 to 10: 9
0, particularly preferably 70:30 to 30:70. If the amount of the irregular particles is less than 5% by weight based on the amount of the irregular particles and the spherical particles, there is a problem that the packing phenomenon proceeds too much and the fluidity of the powder coating is hindered. On the other hand, when the amount of the irregular particles exceeds 95% by weight based on the above-mentioned standard, the smoothness of the coating film is significantly reduced. Generally, in a powder coating composed of irregular particles pulverized by a mechanical method, since the irregular particles each have a distorted shape having sharp portions, the angle of repose of the powder coating is generally large, Poor. Further, the powder coating material has a small apparent specific gravity and is bulky. When electrostatic coating is performed using such a powder coating, the charge concentrates on the sharp tip, forming a kind of bridge between the particles, and a large amount of air is contained in the object to be coated. It can be applied to When heating and drying is performed in such a state, during the melting process, a part of the air near the particle gap that comes into contact with the outside air is discharged out of the coating film, but the deep air is left in the gap. , Some become popping, or some become pinholes, which contribute to coating film defects. On the other hand, when spherical particles are used together with amorphous particles, the apparent specific gravity of the powder coating increases,
It was confirmed that the bulk of the powder coating also decreased. Furthermore, when electrostatic coating is performed, the spherical particles are uniformly charged, so that they do not form a bridge, and in combination with the irregular particles,
It is considered that the material is formed on the substrate in a state close to close packing. Therefore, the encapsulation of air in the coating film is also substantially reduced, and the sharp-angled portions protruding on the coating film surface are reduced.
It is considered that an extremely uniform and excellent smoothness of the coating film plane can be obtained.

The glass transition temperature of the amorphous particles used in the present invention is suitably 35 ° C. or higher, preferably 40 ° C. or higher, and more preferably 50 ° C. If the glass transition temperature of the amorphous particles is 35 ° C. or higher, the particles are less likely to adhere to the device walls and the particles are not fused together during the production process, and blocking during the production process or during storage is prevented. Therefore, it is preferable. On the other hand, the glass transition temperature of the spherical particles used in the present invention preferably has a difference from the glass transition temperature of the irregular particles within 10 ° C., and is preferably a temperature equal to or lower than the glass transition temperature of the irregular particles.
If the difference is larger than 10 ° C., particles having different melting behaviors will coexist, and sometimes it is easy to lose smoothness such as defects of a coating film such as cissing and pinholes, glossiness and unevenness of skin, which is not preferable. When the glass transition temperature of the spherical particles is lower than that of the irregular-shaped particles, melting and flowing of the coating film during heating and drying are assisted, and the coating film contributes to smoothness. In general, the lower the glass transition point, the better the smoothness of the coating film. However, on the other hand, the blocking resistance decreases, and the handling property deteriorates. For this reason, it is necessary to take special measures such as low-temperature storage and transportation. However, even when the glass transition temperature of the amorphous particles that can be easily handled is low, if the spherical particles that sufficiently contribute to the smoothness coexist, the blocking resistance and the like do not need to be deteriorated. Is relatively small. Therefore, the lower the glass transition temperature of the spherical particles, the lower the blending ratio.

Examples of the colorant and extender incorporated in the irregular or spherical particles of the present invention include titanium dioxide, ben pattern, yellow iron oxide, carbon black, phthalocyanine blue, and quinacridone red pigment. And organic or organic pigments. As other optional components, various additional components conventionally used in powder coatings can be blended. For example, a surface modifier such as polysiloxane and polyalkyl acrylate, a plasticizer, an ultraviolet absorber, an antioxidant, an antioxidant such as benzoin, a pigment dispersant, an amine compound, an imidazole compound, and a cation initiator are optionally added. Agents.

The method for coating the powder coating of the present invention is not particularly limited, and any known and common method such as, for example, an electrostatic spray coating method or a fluid immersion coating method can be employed without any particular limitation. . The object to which the powder coating of the present invention is applied is not particularly limited as long as it can withstand baking, and examples thereof include various materials such as a steel plate, a zinc phosphate treated steel plate, an aluminum plate, and a coating film. Can be mentioned. The powder coating of the present invention can be coated with the same or different coating, and then further applied and baked at the same time.

[0012]

EXAMPLES The present invention will be described by way of Examples and Comparative Examples.
Although described in more detail, the scope of the present invention is not limited by these Examples and Comparative Examples. Examples 1 to 4 and Comparative Examples 1 and 2 < Preparation of Powder Coating> Epoxy group-containing acrylic resin having the properties shown in Table 1 below was prepared by using 1,10-decanedicarboxylic acid (DDA) as a curing agent. And a carboxyl group in a molar ratio of 1: 1 and melt-kneaded at 100 ° C. with an extruder. The obtained pellets are pulverized by a pin mill and classified to obtain an average particle size of 13 μm.
m, powder coating consisting of irregular shaped particles, A-1, B-1, C
-1 was obtained. <Preparation of Spherical Particles> A part of the powder coating composed of the irregular particles is taken out, and is brought into contact with a gas phase heated to 250 ° C. for a few seconds by a heat fusion method to perform spheroidization treatment to obtain an average particle size. Powder coatings a-1, b-1, and c-1 consisting of spherical particles having a diameter of 13 μm were obtained. The ratio between the longest diameter and the shortest diameter of the spherical particles was about 1: 1 as determined by microscopic observation, and the spherical particles had a true spherical shape. <Coating plate preparation method> After performing a surface treatment of zinc phosphate on a rolled steel plate, performing cationic electrodeposition coating, and further applying a solvent type acrylic metallic base coating material including an aluminum paste to a plate coated with an intermediate coating material, A powder clear paint shown in Table 2 below was electrostatically coated on the preliminarily dried material at 100 ° C. for 10 minutes so as to have a film thickness of 35 to 40 μm.
After drying by heating for 20 minutes, various tests described below were performed to examine the characteristics of the coating film. Table 2 shows the results.

The test method used in Examples and Comparative Examples is as follows.
It is as follows. Apparent specific gravity (loose apparent specific gravity) The apparent specific gravity was measured according to the method for measuring bulk specific gravity according to JIS-K-5101. 10 cm of powder coating passed through a 140 mesh sieve with blocking resistance
A (height) × 3 cm (diameter) test tube was filled up to a height of 5 cm, left in a high-temperature device at 40 ° C. for 72 hours, then observed for the state of blocking, and evaluated in the following four steps. ：: Completely no blocking ：: Slight blocking observed Δ: Slight blocking observed X: Appearance (visual observation) where blocking was observed The state of the coating film was visually observed and evaluated according to the following criteria. A: Very good B: Good B: Slightly poor X: Poor glossiness Gloss 60-degree gloss was measured according to JIS-K-5400 60-degree specular gloss measurement method. The sharpness was measured by a portable image clarity measuring device HA-IMC type. Surface roughness (Ra) A center line average roughness (cutoff value) of 0.8 mm was measured by SURFCOM (Tokyo Seimitsu).

[0014]

Table 1 Powder coating A-1 B-1 C-1 Resin properties Epoxy group equivalent 500 450 400 Glass transition temperature (° C) 55 50 40 Melting temperature (° C) 95-100 90-95 85-90

[0015]

[Table 2] Example 5 and Comparative Example 3 The average particle diameter was 6 μm, 13 μm and 22 μm in the same manner as in Example 1 except that the obtained amorphous particles were classified.
A powder coating composed of three types of irregularly shaped particles was produced.

On the other hand, in the same manner as in Example 1, the average particle diameter was 6 μm, 13 μm and 2 μm, respectively, from the irregular particles.
2 μm spherical particles were produced. The irregularly shaped particles and the spherical particles obtained as described above were blended at the blending ratio shown in Table 3 below to produce a powder coating. Next, the obtained powder coating was applied in the same manner as in Example 1, and various tests were performed. The results are shown in Table 3.

[0017]

Table 3 Example Comparative Example Powder Coating 53 4 Particles Amount (parts by weight) Amorphous Particles (Average Particle Size) 6 μm 50 13 μm 50 22 μm 50 Spherical Particles (Average Particle Size) 13 μm 50 50 50 Powder Characteristics Appearance (visual) of paint ○ × △ Gloss 91 75 85 Vividness ○ × △ Surface roughness Ra 0.07 0.53 0.48 Examples 6 to 7 Irregular particles B- produced in Example 1 1 and C-1 (each having an average particle diameter of 13 μm) and spherical particles c-1 (an average particle diameter of 13 μm) were prepared. These irregular particles and spherical particles were mixed at a weight ratio of 50:50 to prepare a powder coating.

The obtained powder coating was applied in the same manner as in Example 1 and various tests were conducted. The results are shown in Table 4 below.

[0019]

Table 4 Example 6 7 Particle blending amount (parts by weight) Irregular particles B-1 70 C-1 50 Spherical particles c-1 50 30 Characteristic appearance of powder coating (visual appearance) ◎ ○ Gloss 94 90 Sharpness ◎ ○ Surface roughness Ra 0.06 0.18 From the results of the above Examples and Comparative Examples, in Examples 1 to 7, powder coatings having good coating film performance were obtained. In contrast, in Comparative Example 1 using only irregular particles and Comparative Example 2 using only spherical particles, blocking resistance, sharpness, and surface roughness Ra were poor, and the average of irregular particles was low. In Comparative Example 3 in which the particle diameter is less than 8 μm, the appearance (visual), glossiness, sharpness, and surface roughness Ra are poor, and in Comparative Example 4 in which the average particle diameter of the irregular particles exceeds 20 μm. , Appearance (visual) and sharpness were poor.

[0020]

According to the present invention, a powder paint having excellent surface smoothness of a coated film after baking can be obtained.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoshiaki Yamamoto 878 Nishinomon, Mitsubuchi, Komaki City, Aichi Prefecture Inside the Komaki Plant of Dainippon Paint Co., Ltd. Inventor Hiroshi Igarashi 878 Nishinomon, Mitsubuchi, Komaki City, Aichi Prefecture Dainippon Paint Co., Ltd.

Claims (3)

[Claims] 1. An irregular particle and a spherical particle having an average particle diameter of 8 to 20 μm and made of a thermosetting resin, wherein the irregular particle and the spherical particle are in a weight ratio of 95: 5 to 5:95. A powder coating composition for use in a powder coating composition. 2. The amorphous particles have a glass transition temperature of 35.
The powder coating composition according to claim 1, which is not lower than ℃. 3. The powder coating composition according to claim 1, wherein the difference between the glass transition temperature of the irregular particles and the glass transition temperature of the spherical particles is within 10 ° C.