JP2002285089A - Production method of resin for thermosetting powder coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a resin for a thermosetting powder coating having less foreign body such as dust. SOLUTION: The production method is such that the resin for the thermosetting powder coating is melted by heating and the melt is filtered through a pressure filter. For example, an acrylic resin containing an epoxy group having the melt viscosity of 1 Pa.s-10,000 Pa.s is produced. Concretely, at first a vinyl resin for the thermosetting powder coating is prepared by a solution- polymerization method, then the vinyl resin actually having no solvent is produced, which is melted by heating to get its viscosity of 1 Pa.s-10,000 Pa.s, then filtered through the pressure filter, finally solidified by cooling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, the use of powder coating materials containing almost no volatile substances, mainly solvents, has been rapidly increasing from the viewpoints of pollution prevention and protection of the global environment. Further, from the viewpoint of resource saving, a high finish by thinning the powder coating is demanded.

However, resins used in conventional thermosetting powder coatings must be solid at room temperature and therefore have a high glass transition point, and have high viscosity even when melted by heat. Since it is not possible to filter dust and the like, there has been a problem that, when the film is formed into a thin film, a coating film is generated.

[0004]

Means for Solving the Problems The present inventors have intensively studied to solve such problems. As a result, it has been found that the conventional problems can be solved by filtering the resin for thermosetting powder coating melted by heat with a pressure filter, and the present invention has been completed.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The resin for thermosetting powder coating used in the present invention has been conventionally used as the resin for thermosetting powder coating. They are distributed. As a curable resin, having a functional group such as an epoxy group, a hydroxyl group, a carboxyl group,
An acrylic resin, a polyester resin, an epoxy resin, a silicon resin, a fluorine resin, a modified resin or a mixed resin of two or more of these resins, which are solid at room temperature, are used.

The curable resin has a glass transition temperature of 40 to 10.
0 ° C., preferably in the range of 50 ° C. to 80 ° C., and having a number average molecular weight of 1000 to 30,000, preferably 2000 to 100
00 is preferred. 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. 100 ℃
If it is higher, not only the viscosity at the time of heat flow rises and the finish property decreases, but also the solubility decreases. If the number average molecular weight is less than 1,000, the blocking resistance of the powder coating is poor. If the number average molecular weight exceeds 30,000, the finished appearance of the coating film is inferior, so that it is not preferable. The glass transition temperature can be determined by, for example, DSC (Differential Scanning Calorimeter).

Further, the viscosity of the molten thermosetting resin at the time of pressure filtration is 1 Pa · s to 10000 Pa · s.
Preferably, it is 100 Pa · s to 1000 Pa · s.
If the melt viscosity at the time of filtration is lower than 1 Pa · s, it is difficult to control the pressure by pressurized filtration, and the resistance exceeds 10,000 Pa · s, which makes filtration difficult.

[0008] The pressure for the filtration is 0.01 MPa to
10 MPa, preferably 0.5 MPa to 5 MPa
It is. If the filtration pressure is less than 0.01 MPa, it is difficult to control the pressure, and if it exceeds 10 MPa, the resistance is large and filtration is difficult.

The opening of the sieve for filtration is 1 μm.
m to 100 μm, preferably 3 μm to 50 μm. If the opening is less than 1 μm, the pressure is large and filtration is difficult. If the opening exceeds 100 μm, the gel in the resin cannot be filtered sufficiently. Also, if necessary, for example, an anti-armpit agent, a surface conditioner, an antioxidant, a UV absorber, a UV stabilizer, a blocking inhibitor, a flow regulator,
Additives such as a charge control agent, a filler, and a curing accelerator can be blended.

As the filter capable of precision-filtering the thermosetting powder coating resin melted by heat under pressure, conventional filters can be used without any particular limitation. Examples of such a filter include a Fuji Metal Fiber Filter (manufactured by Fuji Fuji Filter Industrial Co., Ltd.).

The present invention specifically relates to a method for producing a thermosetting powder coating material which contains substantially no solvent after producing a vinyl resin for a thermosetting powder coating solution by a solution polymerization method. A vinyl resin is produced, and then the obtained vinyl resin for a thermosetting powder coating is heated and melted so as to have a viscosity of 1 Pa.s to 10,000 Pa.s, then filtered by a pressure filter, and then cooled. By solidifying, the solid resin used for the thermosetting powder coating can be produced.

The solid resin thus obtained is roughly pulverized. Next, the thermosetting resin, the curing agent, and the additives are dry-blended, and then melt-kneaded, coarsely ground, finely ground, and classified, whereby the thermosetting powder coating of the present invention is produced.

[0013]

Hereinafter, the present invention will be described in detail with reference to examples. Unless otherwise specified, “parts” or “%” represents a weight basis.

Example 1 A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser and a dropping device was charged with 100 parts of xylene, and heated to 82 ° C. while blowing nitrogen gas to obtain cyclohexyl methacrylate. A mixed solution of 50 parts, 15 parts of methyl 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 complete the reaction, and xylene was removed by heating and reducing the pressure. (Manufactured by Kogyo Co., Ltd.), followed by cooling and coarse pulverization. After dry-blending 250 parts of dodecanedioic acid in 1000 parts of the thermosetting resin at room temperature with a Henschel mixer,
It was melt-kneaded with an extruder. Next, after cooling, it was pulverized and filtered to obtain a thermosetting clear resin powder coating material having an average particle size of about 20 microns.

Example 2 A fuel cell was manufactured in the same manner as in Example 1 except that the pressure filtration filter was changed to 10 μm.

Comparative Example 1 A powder coating was produced in the same manner as in Example 1 except that the filtration under pressure was not carried out.

The results are shown in Table 1.

[0018]

[Table 1] Table 1

The tests in Table 1 were performed as follows. Finish appearance of coating film: Thickness after zinc phosphate chemical conversion treatment.
An epoxy-based cationic electrodeposition paint was electrodeposited on an 8 mm dull steel plate so as to have a dry film thickness of 20 microns, and baked. Next, a powder coating is electrostatically applied to the surface of the material so that the film thickness becomes about 50 μm, and dried at 160 ° C. for 30 minutes.
And heat cured for a minute. The following test was performed on the obtained coated plate and evaluated according to the following criteria.は: good with no lumps on the coating film; も の: slight lumps on the coating film; x: very large lumps on the painted surface. Number of spots on painted surface: thickness 0.3 mm, length x width = 300 x 4
Paint on 10 50mm tinplates in the same manner as above,
After making the coated board, the bumps on the coated surface were counted.

Paint filtration residue (dust inspection): The powder coating was completely dissolved in solvent tetrahydrofuran, filtered through a 325 mesh stainless screen, and the filtration residue remaining on the screen was examined with an optical microscope. Observed. The evaluation was performed according to the following criteria. ○ indicates no filtration residue.
Δ indicates that some filtration residue is observed. X: Those with a large amount of filtration residue.

Claims (4)

[Claims] 1. A method for producing a resin for a thermosetting powder coating, wherein the resin for a thermosetting powder coating melted by heat is filtered by a pressure filter. 2. The thermosetting powder coating resin according to claim 1, wherein the viscosity of the thermosetting powder coating resin melted by heat is 1 Pa.s to 10,000 Pa.s. Production method. 3. The method for producing a thermosetting powder coating resin according to claim 1, wherein the thermosetting powder coating resin is an epoxy group-containing acrylic resin. 4. After producing a vinyl resin for thermosetting powder coating by a solution polymerization method, the solvent is removed to produce a vinyl resin for thermosetting powder coating substantially containing no solvent.
Then, the obtained vinyl resin for thermosetting powder coating is 1P
4. The composition according to any one of claims 1 to 3, wherein the composition is heated and melted to a viscosity of from 1 to 10,000 Pa.s, then filtered by a pressure filter, and then cooled to solidify. Production method of resin for thermosetting powder coating.