JPH1180607A - Preparation of thermosetting powder coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for preparing a thermosetting powder coating which can improve the finishing property, the coating workability, and the transfer efficiency by comprising the steps of: dissolving or dispersing a coating component contg. a resin and a crosslinking agent in a solvent having a melting point of a specified temp. or above; lyophilizing the soln. or dispersion; grinding the lyophilized product to obtain a powder; pressing the powder under specified conditions; and grinding. SOLUTION: A coating component comprising as indispensable ingredients a resin, with a glass transition temp. of 40 to 100 deg.C and an no. average mol.wt. of 1000 to 10000, contg. not less than 50 wt.% vinyl copolymer prepd. by copolymerizing 0 to 35 wt.% styrene with 20 to 65 wt.% (meth)acrylate monomer having a 4C or higher branched or cyclic substituent on its side chain and a crosslinking resin is dissolved in a solvent, with an m.p. of -40 deg.C or above, comprising 50 to 100 wt.% t-butanol, 0 to 50 wt.% dioxane, and 0 to 20 wt.% solvent other than described above to obtain a soln. which is then filtered. The filtrate is then lyophilized at 10 to -40 deg.C, pref. -30 to 0 deg.C, followed by powdering to obtain particles. The particles are pressed at a pressure of not less than 200 kg/cm<2> , pref. not less than 250 kg/cm<2> , followed by grinding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel method for producing a thermosetting powder coating.

[0002]

2. Description of the Related Art A conventional powder coating material has been produced by pulverizing and mixing a resin, a cross-linking agent and an additive, then mixing them with a melt kneader, and pulverizing the resulting mixture.

However, in this method, the resin and the cross-linking agent are melted by heat and kneaded, so that the reaction between the resin and the cross-linking agent partially progresses to increase the molecular weight. For this reason, the melt viscosity of the coating material is increased, and the finish is reduced. In some cases, a gel is generated by heat, and this is a fatal defect in the appearance of the coating film, especially in a thin clear coating film. Also, dusts and the like mixed in during production cannot be removed by the conventional production method because it is difficult to filter with the coating composition, and this is a major problem when used as an automotive topcoat clearer that requires a high-quality coating film. . In addition, since the reaction partially proceeds due to heat during production and dust cannot be removed, it is impossible to collect and reuse the paint in applications that require a high-quality coating film appearance.

[0004] We have proposed a freeze-drying method as a new production method, but have the problem that the coating workability and coating efficiency are slightly lower than the high finish based on the excellent heat flow property of the coating. There is a point.

[0005]

SUMMARY OF THE INVENTION The present invention solves the problems of poor coating workability and poor coating efficiency, and makes use of the high heat flow property of the powder coating obtained by the freeze-drying method to achieve a finish. The purpose of this method is to establish a method for producing a powder coating material having excellent properties, coating workability, and coating efficiency.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve such a problem, and as a result, by compressing and pulverizing the powder obtained by the freeze-drying method, all the conventional problems have been solved. It has been found that the problem can be solved, and the present invention has been completed.

More specifically, the present invention relates to particles obtained by dissolving or dispersing a coating component containing (a) a resin and (b) a crosslinking agent as essential components in a solvent having a melting point of -40 ° C. or higher and freeze-drying the powder. Is further compressed at a pressure of 200 kg / cm 2 or more, and then pulverized, and a method for producing a thermosetting powder coating.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As the resin (a) used in the present invention, acryl, polyester, epoxy resin and the like having a functional group such as an epoxy group, a hydroxyl group and a carboxyl group are used.

As the crosslinking agent (b), aliphatic polycarboxylic acids and their (poly) anhydrides, aromatic polycarboxylic acids and their (poly) anhydrides, aliphatic, alicyclic or aromatic polyisocyanates Block isocyanate compounds such as those obtained by blocking with a blocking agent such as phenols, caprolactones and alcohols, and polyepoxy compounds.

The additive (C) can be added as required, and includes, for example, an anti-armpit agent, a surface conditioner, an antioxidant, an ultraviolet absorber, an ultraviolet stabilizer, an antiblocking agent, a flow regulator, and a charge control agent. , A coloring pigment, a filler, a curing accelerator and the like.

The above-mentioned substances are dissolved in a solvent which solidifies at -40 ° C. or higher, and after filtration with a suitable filtration device, usually at 10 ° C.
Freeze at -40 ° C, reduce the pressure, and collect the solvent with a cooling trap. The particles obtained here are compressed at a pressure of at least 200 kg / cm2, preferably at least 250 kg / cm2. The compressed solid is pulverized to obtain a paint, but even if compressed at a pressure of less than 200 kg / cm2, the bulk specific gravity cannot be sufficiently increased,
The coating workability is inferior, and the coating efficiency tends to decrease.
The compression of the powder particles may be performed using a machine such as a tablet compactor or a roller compactor which is a compression compactor.

According to the present invention, the above composition is prepared by adding t-butanol 5
It is dissolved in a solvent of 0% by weight or more, 50% by weight or less of dioxane, and 20% by weight or less as another solvent. 10 ° C-
Freeze at 40 ° C., and freeze-dry under vacuum to obtain a powder coating. t-Butanol is used in an amount of 50% by weight or more, preferably 70% by weight or more, and more preferably 80% by weight or more. When the content of t-butanol is less than 50% by weight, the solubility of the cross-linking agent is poor, the freezing point of the coating solution is lowered, energy is required for freezing, the vapor pressure of the solvent is lowered, and high pressure reduction is performed during vacuum freeze-drying. It is not preferable because it requires a certain degree and takes a longer time. Dioxane is used in an amount of 50 parts by weight or less, preferably 30% by weight or less, and more preferably 20% by weight or less. Dioxane is 50
When the amount exceeds 10% by weight, not only is it not preferable from the viewpoint of hygiene at the time of production, but also the vapor pressure of the solvent is lowered, and a high degree of reduced pressure is required at the time of vacuum freeze-drying. Other solvents include, for example, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, methanol, ethanol, i
Solvents that do not freeze, such as so-propanol and iso-butanol, and solvents that freeze at relatively high temperatures, such as cyclohexane and cyclohexanol, are used. When the amount of the other solvent is 20% by weight or less, preferably 15% by weight or less, and the amount of the other solvent exceeds 20% by weight, freeze-drying becomes difficult, or the solubility of the resin or the crosslinking agent decreases, Not preferred. The freezing temperature is 10 ° C ~
When the freezing temperature exceeds -10 ° C in the range of -40 ° C to 0 ° C, preferably, the coating solution easily solidifies and handling becomes difficult. If the temperature falls below -40 ° C,
A large amount of energy is required for freezing, and it takes a long time for vacuum freeze-drying, which is not preferable. The resin (a) used in the present invention has a glass transition temperature of 40 to 100 ° C, preferably 50 to 80 ° C, and a number average molecular weight of 1,000 to 10,000, preferably 2,000 to 6,000. If the glass transition temperature is lower than 40 ° C., the resulting powder coating is not preferred because the particles fuse together and the blocking resistance deteriorates. On the other hand, when the temperature is higher than 100 ° C., not only the viscosity at the time of heat flow increases but the finish property decreases, but also the solubility decreases.
On the other hand, when the number average molecular weight is less than 1000, the blocking resistance of the powder coating is inferior, and the coating performance evaluation such as acid resistance and scratch resistance is lowered. When the number average molecular weight exceeds 10,000, the finished appearance of the coating film is inferior, so that it is not preferable.

The glass transition temperature can be determined, for example, by DSC (Differential Scanning Calorimeter).

The resin (a) used in the present invention contains styrene.
0 to 35% by weight, preferably 0 to 30% by weight, 4 carbon atoms in the side chain
The content of the (meth) acrylate monomer having a branched or cyclic substituent is 20 to 65% by weight, preferably 30 to 65% by weight. When styrene is more than 35% by weight, a solvent,
Particularly, the solubility in t-butanol decreases, which is not preferable.

When the amount of the (meth) acrylate monomer having a branched or cyclic substituent having 4 or more carbon atoms is less than 20% by weight, the solubility in a solvent, particularly t-butanol, is undesirably reduced. As a (meth) acrylate monomer having a branched or cyclic substituent having 4 or more carbon atoms, iso-butyl (meth) acrylate, tert-
(Meth) acrylic esters having four or more branched carbon atoms as substituents, such as butyl (meth) acrylate; alicyclic rings, such as cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, and tricyclohexyl (meth) acrylate Having a group as a substituent (meth)
Acrylic esters and the like can be mentioned.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments. Unless otherwise specified, “parts” or “%” represents a weight basis.

Preparation Example of Resin Solution A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, and a dropping device is charged with tert-butanol 10
0 parts, and heated to 82 ° C. while blowing in nitrogen gas to obtain 50 parts of cyclohexyl methacrylate,
A mixed solution of 15 parts of t-butyl methacrylate, 35 parts of glycidyl methacrylate, and 7 parts of azobisdimethylvaleronitrile was dropped over about 3 hours. After the completion of the dropwise addition, the mixture was left at 82 ° C. for 2 hours to terminate the reaction, thereby producing a resin solution.

Example 1 200 parts of a resin solution, 25 parts of dodecanedioic acid and 190 parts of tert-butanol were added, dissolved and cooled at -10 ° C.
Frozen. Thereafter, the pressure was reduced to 1.0 mmHg or less, and the temperature was gradually returned to room temperature so that melting did not occur. The obtained solid was compression-molded with a tablet press at a pressure of 250 kg / cm 2, and the compact was finely pulverized with a pin disk and filtered through 150 mesh to obtain a powder coating.

Example 2 and Comparative Examples 1 to 4 The same procedure as in Example 1 was carried out except that the compression pressure after freeze-drying was changed as shown in Table 1. Comparative Example 5 A solvent was removed from the resin solution (A) by distillation under reduced pressure to obtain a solid resin. 100 parts of this solid resin and 25 parts of dodecane diacid
The parts were dry-blended with a Henschel mixer at room temperature and then melt-kneaded with an extruder. Next, after cooling, the mixture was finely pulverized with a pin disk and filtered with 150 mesh to obtain a powder coating.

The results are shown in Table 1.

[0021]

[Table 1]

The tests in Table 1 were performed as follows.

Preparation condition of coating film An epoxy-based cationic electrodeposition paint is electrodeposited on a 0.8 mm thick dull steel plate which has been subjected to a chemical conversion treatment with zinc phosphate to a dry film thickness of 20 μm and baked. A surface coater coated with an automobile was baked on the coating film so as to have a dry film thickness of 20 μm, and then ground with a # 400 sandpaper and drained and dried. Next, Magiccron Basecoat H
M-22 (manufactured by Kansai Paint Co., Ltd., metallic paint,
(Trade name) was applied so as to have a cured film thickness of about 15 μm, and was baked and cured at 140 ° C. for 30 minutes in a drier to obtain a test material. Then, the surface of the material is electrostatically coated with a powder coating so that the film thickness becomes about 50 microns, and dried by a dryer.
The composition was cured by heating at 60 ° C. for 30 minutes. The following test was performed on the obtained coated plate.

Coating appearance: The finished appearance of the coating is glossy,
The smoothness was evaluated according to the following criteria.は: good, △: poor smoothness, x: very poor smoothness.

60 ° gloss: The specular reflectance at 60 ° is J
It was measured according to ISK-5400.

Coating workability: Using an electrostatic coating machine (PG-1, manufactured by Matsuo Sangyo Co., Ltd.), a baking thickness of 50 μm was applied to a 300 mm × 400 mm tin plate under coating conditions of −70 KV and a discharge rate of 150 g / min. The coating workability at the time of electrostatic coating was evaluated according to the following criteria. ：: Discharge unevenness, no paint adhered to the tip of the gun, excellent in paint workability. △: Discharge unevenness, paint adhered to the tip of the gun, poor paint workability. ×: Discharge unevenness, paint to the tip of gun. Adhesion is large and coating workability is extremely poor.

Coating efficiency: vertical size 300 mm ×
An electrostatic coating machine (PG-) is placed on a 300 mm x 1 mm (thick) tin plate from a distance of 20 cm (distance between the workpiece and the tip of the gun).
1, Matsuo Sangyo Co., Ltd.) -70KV, discharge rate 15
From the result of coating at 0 g / min for 10 seconds, the coating efficiency was determined by the following formula.

Coating efficiency = coating amount / ejection amount × 100 (%) Angle of repose: A powder tester (Hosokawa Micron Corporation, trade name) was used. The angle of the ridgeline of the mountain that was deposited when the powder coating material was allowed to flow down on the circular table was measured. The smaller the angle, the better the fluidity.

Bulk density: Measured according to JIS K-5101 20 apparent bulk density.

[0030]

According to the present invention, the powder obtained by freeze-drying
By compressing with a pressure of g / cm2 or more and re-grinding, the bulk specific gravity can be increased.

Further, by utilizing the freeze-drying method, there is no reaction due to heat at the time of production, and the coating film has excellent heat flow property and therefore excellent finish.

Further, the paint can be recovered and reused, and the obtained particles can be compressed and reground to increase the bulk specific gravity of the particles. It is possible to improve the fluidity, coating workability, and coating efficiency of the paint.

The powder coating obtained in this manner is particularly suitable for use as a clear coating on automobiles, which requires high finishing properties.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshio Ogoshi 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Prefecture Kansai Paint Co., Ltd.

Claims (5)

[Claims] (1) Dissolving or dispersing a coating component containing (a) a resin and (b) a crosslinking agent as essential components in a solvent having a melting point of -40 ° C. or higher, and further pulverizing the particles by a freeze-drying method to 200 kg / c.
A method for producing a thermosetting powder coating, comprising compressing at a pressure of m2 or more and then pulverizing. 2. The method according to claim 1, wherein the solvent is 50 to 100% by weight of t-butanol, 0 to 50% by weight of dioxane, and 0 to 20% by weight of another solvent. 3. The method according to claim 1, wherein the solvent is 80% by weight or more of t-butanol. 4. The method for producing a thermosetting powder coating according to claim 1, wherein the resin (a) is a vinyl copolymer having a glass transition temperature of 40 to 100 ° C. and a number average molecular weight of 1,000 to 10,000. 5. A resin (a) having 0 to 35% by weight of styrene and having a branched or cyclic substituent having 4 or more carbon atoms in a side chain (meth)
The method for producing a thermosetting powder coating according to claim 1 or 4, wherein the amount of the acrylate monomer is 50% by weight or more of a vinyl copolymer obtained by copolymerizing 20 to 65% by weight.