JPH02218766A - Powder coating composition and coated article using same - Google Patents

Abstract

PURPOSE:To provide the title composition capable of efficiently coating in a single operation, free from lifting of the coating film therefrom, excellent in the performance of said coating film, for application to microwave oven parts, etc., comprising a polyester resin and a crosslinking agent consisting of blocked polyisocyanate and polyepoxy compound. CONSTITUTION:The objective composition excellent in heat resistance, economy and low environmental pollution, comprising (A) a polyester resin solid at room temperature 30-250 in hydroxyl value and 10-100 in acid value, from a polycarboxylic acid and 5-60 pts.wt., based on 100 pts.wt. of said resin, of a polyhydric alcohol (e.g. trishydroxyethyl isocyanurate) and/or oxyacid. (B) a crosslinking agent consisting of a blocked polyisocyanate solid at room temperature and polyepoxy compound (e.g. triglycidyl isocyanurate and/or alicyclic polyepoxy compound), and, if needed, (C) polysiloxane fine powder.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides powder coating compositions that have good painted surface appearance (smoothness) and physical properties of the coated film, and particularly excellent heat resistance, and coatings made from the powder coating compositions. Regarding goods.

(Conventional technology) Conventionally, solvent-diluted paints based on polyester resin, imide-modified resin, imide resin, imide amide resin, etc. have been used for coated wires for magnets, microwave parts, and other materials that require heat resistance. It is being

However, all of these methods require the use of special solvents such as cresol, N-methylpyrrolidone, and dimethylformamide, which are also polluting and toxic. These are contrary to recent trends toward pollution-free, resource-saving, and energy-saving. In addition, with these techniques, in order to obtain the desired finish and coating performance, it is necessary to avoid scratches caused by solvents and condensation products.
Painting and baking a thin film of several microns to 10 microns had to be repeated, increasing the coating cost.

These conventional techniques have many problems from the viewpoint of social performance and production costs.

Recently, powder coating using epoxy resin has been proposed in order to improve these problems (disclosed example: US Pat. No. 1,509,379), but sufficient performance has not yet been achieved in terms of heat resistance. do not have.

In addition, attempts have been made to remove the solvent from conventional highly heat-resistant solvent-based paints and create powder paints, but with conventional resin-based paints, it has not been possible to obtain smooth coatings with fewer wrinkles. .

(Problem to be solved by the invention) The present invention aims to solve the following problems.

■ Eliminate the pollution, toxicity, and resource-related issues caused by the solvents in conventional solvent-based paints.

■ Used in general polyester resin powder coatings,
Eliminating the low heat resistance of paints by combining high acid value polyester resin and triglycidyl isocyanurate.

■ Used in general polyester resin powder coatings,
Baking of paints made from a combination of hydroxyl type polyester resin and melamine or block polyisocyanate, or condensation paints made from a combination of tin or titanium catalyst and polyester resin, can sometimes cause the paint film to smudge due to the condensation products that occur. Elimination of.

■ Eliminate poor coating film smoothness and coating performance due to lack of melt fluidity of powder coatings using imide-modified polyester resins, imide resins, imidoamide resins, etc., which are said to have excellent heat resistance of the resins themselves. .

With these conventional techniques (1) to (2), it has not been possible to obtain a coating system that is economical, low-pollution, and has excellent heat resistance, finish quality, and coating performance.

(Means for Solving the Problems) The present inventors have conducted extensive research in order to develop a powder coating that solves the above problems and has excellent heat resistance, electrical insulation, film strength, and film appearance. As a result, in order to increase the heat resistance of the coating film, it is necessary to consider increasing the heat resistance of the main resin itself, and at the same time,
It is very important to sufficiently increase the crosslinking reactivity of the paint, and in order to obtain good paint film appearance, film strength, and heat resistance, it is necessary to select a certain limited combination of curing agents and to It was determined that the amount of curing agent is important. That is, by combining a polyester resin having a certain limited amount of hydroxyl groups and a limited amount of carboxyl groups with a block polyisocyanate and a polyepoxy compound as a crosslinking agent,
We found a means to solve the problem and completed the present invention.

That is, according to the present invention, the resin is obtained from a polycarboxylic acid, a polyhydric alcohol, preferably trishydroxyethyl isocyanurate, and an oxyacid used in place of a part thereof if necessary, and the hydroxyl value of the resin is 30 to 25.
0 and an acid value of 10 to 100, a polyester resin (A) that is solid at room temperature, and a block polyisocyanate and a polyepoxy compound that are solid at room temperature, preferably triglycidyl isocyanurate and/or alicyclic compound. It consists of a crosslinking agent (B) made of a polyepoxy compound,
A powder coating composition characterized in that it preferably further contains a fine polysiloxane powder, and a coated article coated with the powder coating composition are provided. The polyester resin in the present invention needs to have both a certain amount of hydroxyl groups and carboxyl groups, and raw materials for the polyester resin include dicarboxylic acids, diols, trivalent or higher polycarboxylic acids, and polyols. , an oxyacid is used if necessary.

Among these raw materials, dicarboxylic acids include dicarboxylic acids, their anhydrides, and esterified products, such as aromatic dicarboxylic acids and their anhydrides such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid. ,
Alicyclic dicarboxylic acids and their anhydrides such as 1,4-cyclohexanedicarboxylic acid, hexahydrophthalic acid, and tetrahydrophthalic acid; aliphatic dicarboxylic acids and their anhydrides such as adipic acid, sebacic acid, dodecanoic acid, succinic acid, and maleic acid; Examples include anhydrides, and lower alkyl esters such as methyl esters and ethyl esters of these dicarboxylic acids.

In addition, as the diol, ethylene glycol, L2-
Propanediol, 1.3-propanediol, 1.4
-butanediol, 1.5-bentanediol, 1.6
-Hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, neopentyl glycol, hydroxypivalic acid - neobentyl glycol ester, 1.4
-Cyclohexane dimetatool, tricyclodecane dimetatool, bisphenol A, hydrogenated bisphenol A, etc. can be mentioned.

In addition, trivalent or higher carboxylic acids include carboxylic acids and their anhydrides, such as trime'J-/toic acid,
There are trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, trimesic acid, etc.

Further, examples of the trivalent or higher polyol include trishydroxyethyl isocyanurate, glycerin, pentaerythritol, trimethylolpropane, trimethylolethane, mannitol, and the like.

In addition to such raw materials, in some cases, an excellent resin can be obtained by substituting 50 mol% or less of oxyacid (including lower alkyl ester) in place of dicarboxylic acid or diol. Examples of the oxyacid include paraoxybenzoic acid, 1,2-hydroxystearic acid, and lower alkyl esters thereof such as methyl ester and ethyl ester.

Polyester resins using these raw materials can be manufactured by conventionally known manufacturing methods.

This resin has a hydroxyl value of 30 to 250 and an acid value of IO to 100.
It is necessary to have both. Among these, the hydroxyl value can be achieved by adjusting the polyhydric alcohol component/polycarboxylic acid component ratio and the amount of the trivalent or higher polyol component. At this time, if trishydroxyisocyanurate is used as a trivalent or higher polyol component in an amount of 5 to 60% by weight in the resin, a powder coating resin particularly excellent in heat resistance can be obtained. In addition, the acid value is determined by stopping the polyester condensation reaction at a high acid value,
Either a method of providing with unreacted carboxylic acid, or a method of providing by half-esterifying polycarboxylic acid anhydride at 150 to 190°C to the hydroxyl groups of the resulting resin after the polyester condensation reaction has proceeded to the acid value of the resin of 15 or less. You can choose. More preferably, the latter half-esterification addition method is preferred in terms of coating film finishing performance. In the case of the half-esterification addition method, the polycarboxylic anhydride to be added can be freely selected from among the carboxylic anhydrides used as raw materials for the polyester resin. Among them, trimellitic anhydride and phthalic anhydride are preferred.

Known esterification or transesterification catalysts can be used in the condensation reaction of polyester polyols. Examples of such catalysts include metal oxides, halides, acetates, etc. of tin, zinc, lead, manganese, magnesium, etc., and para-toluenesulfonic acid, titanate esters, etc. The amount of these added is preferably 0.01 to 0.5% by weight of the entire system. The polyester resin produced in this manner needs to have both a hydroxyl value of 30 to 250 and an acid value of 10 to 100, as described above. Hydroxyl value less than 30, and/or
If the acid value is less than 10, the crosslinking reactivity is low, so the strength and heat resistance of the resulting coating film will be low, which is undesirable. On the other hand, if the hydroxyl value is more than 250, the resin may gel during resin synthesis. Even if resin can be synthesized, the hygroscopicity of the powder coating becomes too high and the powder coating loses powder fluidity, making it unsuitable for painting. In addition, if the acid value is greater than 100, gelation of the resin may occur during resin synthesis, or gelation may not occur (also, when applied to powder coating).
The melt fluidity of the powder coating decreases, making it impossible to obtain a satisfactory coating.

Next, the crosslinking agent used in combination with the polyester resin will be explained. In the present invention, as the crosslinking agent,
A major feature is that a block polyisocyanate and a polyepoxy compound, which are different from each other, are used together. This eliminates the problem of flaking of the paint film caused by volatilization of the blocking agent when using blocked polyisocyanate alone.
Furthermore, the inventors have discovered that using a polyester compound alone can solve the problems that sufficient crosslinking properties cannot be obtained and the resulting coating film is unsuitable for heat-resistant applications, leading to the present invention.

The block polyisocyanate used at this time is solid at room temperature. For example, it is easily produced by reacting a polyisocyanate obtained by reacting an aromatic, aliphatic, or araliphatic diisocyanate with a low-molecular active hydrogen compound and masking it with a blocking agent. Specific examples of such diisocyanates include tolylene diisocyanate (TDI), 4,4'-diphenylmethane isocyanate (MDI), xylylene diisocyanate (XDI), and hexamethylene diisocyanate (H
MD, 4,4'-methylenebis(cyclohexyl isocyanate) (H1!MDI), methylcyclohexane diisocyanate (HTDI), bis(isocyanatemethyl)cyclohexane (H6XDI), isophorone diisocyanate (IPDI), l-lymethylhexamethylene diisocyanate ( TMDI), dimer acid diisocyanate (DD), lysine diisocyanate (
LDr), etc.

Further, specific examples of low-molecular active hydrogen compounds include water, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, ethanolamine, jetanolamine, hexamethylenediamine, and the like. Furthermore, isocyanurate, uretidione, low molecular weight polyester containing a hydroxyl group, polycaprolactone, etc. are also mentioned as specific examples of such low molecular hydrogen compounds.

Specific examples of blocking agents include alcohols such as methanol, ethanol, benzyl alcohol, phenols such as phenonyl and cresol, caprolactam,
Examples include lactams such as butyrolactam, oximes such as cyclohexanone, oxime, and methyl ethyl ketoxime.

Furthermore, it is also possible to add the above-mentioned active hydrogen compound or an isocyanate compound half-blocked with a blocking agent to a part of the main resin used for making the paint and use it as an internal curing agent.

These blocked isocyanates have a softening temperature of 10°C.
It is preferable that it is -120 degreeC. If the softening temperature is less than 10°C, the powder coating composition will solidify in an environment of room temperature to 40°C, or grain-like lumps will form, making it unusable as a powder coating. In addition, its softening temperature is 120℃
If it exceeds this amount, it will be difficult to homogeneously disperse the blocked isocyanate in the paint when producing a powder paint, and the resulting paint film will have poor performance such as smoothness, film strength, and moisture resistance.

These block polyisocyanates have an isocyanate group ratio of 0.05 to 0.05 to hydroxyl groups of the main resin polyester.
It is preferable to mix the isocyanate groups in an amount of 1.5 equivalents. If the isocyanate group is less than 0.05 equivalents, the degree of curing of the paint will be insufficient and the film performance such as adhesion, film hardness, and chemical resistance will deteriorate. Inferior. On the other hand, if it exceeds 1.5 equivalents, the coating film becomes brittle,
Furthermore, due to the influence of the excess isocyanate compound, heat resistance, chemical resistance, moisture resistance, etc. are inferior, and since the block polyisocyanate itself is expensive, it is also disadvantageous in terms of cost.

A reaction promoting catalyst can be used in the powder coating composition, if necessary. As this reaction promoting catalyst, a known block isocyanate dissociation catalyst is used. For example, amines such as N, N, N', N'-tetramethylethylenediamine, trimethylenediamine, dibutyltin oxide, dibutyltin laurate, dibutyltin maleate, tetrabutyl-1,3-diacetodistanoxane, Examples include tin compounds represented by stannath dilaurate, stannath diacetate, triphenyltin chloride, and organic acid metal salts represented by zinc octenoate. These are used singly or as a mixture of two or more types.
0.01 to 10 parts by weight. (Hereinafter, parts will be expressed as parts by weight).

Also, what is the polyepoxy compound used as a crosslinking agent?
Compounds having two or more epoxy groups per molecule, such as bisphenol A epoxy resins, novolac epoxy resins,
Alicyclic epoxy resins and other commonly commercially available polyepoxy compounds can be used; specifically, Epicor)
1001, Epicor) 1004, Epicort 1007,
Epicoat 1009 (bisphenol A epoxy resin manufactured by Shell; trade name), 08M438 (Nolac epoxy resin manufactured by Dow Chemical; trade name),
Araldai) CYI75 (Ciba's alicyclic epoxy resin; trade name), triglycidyl isocyanurate, and its derivatives, modified epoxy compounds, specific examples include EH
Examples include P3150 (Daicel Corporation; trade name). Each of these can be used alone or as a mixture of two or more.

Among these polyepoxy compounds, when triglycidyl isocyanurate (abbreviated as TGIC) or alicyclic solid epoxy resin is used, a powder coating composition with particularly excellent heat resistance can be obtained.

These polyepoxy compounds are preferably blended so that the amount of epoxy groups is 0.2 to 2.5 equivalents to the carboxyl groups of the polyester resin. If the amount of epoxy group is less than 0.2 equivalent, the crosslinking density of the resulting cured coating film will be insufficient, and sufficient coating performance will not be obtained.

On the other hand, if the amount exceeds 2.5 equivalents, the reaction will proceed during storage of the paint, making it impossible to use it as a paint after long-term storage, or the excess curing agent will act as a plasticizer, reducing performance such as moisture resistance and heat resistance. do.

A reaction accelerator can be used in the powder coating composition, if necessary. As this reaction promoter, a known catalyst that promotes the ring-opening addition reaction between an epoxy group and a carboxyl group can be used. For example, quaternary ammonium salts such as tetraethylammonium bromide, para-toluenesulfonic acid,
Acids such as phosphoric acid and their salts, and the tin compounds listed above as catalysts for promoting the dissociation reaction of block polyisocyanates can be used.The amount used is 0 to 100 parts of the solid content of the main resin and curing agent. About .01 to 10 parts is preferable.

In addition to the polyester resin as the main resin and the blocked polyisocyanate and polyepoxy compound, preferably triglycidyl isocyanurate, as the crosslinking agent, the powder coating composition of the present invention may further contain fine polysiloxane powder.

By blending polysiloxane fine powder, the heat resistance of the obtained coating film is improved, and at the same time, the scuffing resistance is improved, and work management during painting can be facilitated. Such fine polysiloxane powder is a solid resin synthesized from an organic siloxane compound, and either one synthesized into a true spherical shape or one prepared by pulverizing a solid resin to adjust the particle size is used. In order to effectively affect the heat resistance and underarm properties of the coating film, it is preferable to use particles with an average particle size of 0.3 to 30 μm. These organopolysiloxane grains can be used as commercially available products.
Examples include the Torefill R series and the Torefill E series (hereinafter referred to as Tore Silicone ■; trade name).

The polysiloxane fine powder is preferably used in an amount of 0 to 60 parts per 10.0 parts of the total of the main resin polyester, the crosslinking agent block polyisocyanate, and the polyepoxy compound, preferably triglycidyl isocyanurate. If more than 60 parts are used, the strength of the resulting coating film will be poor and the smoothness of the coating film will be impaired, making it impossible to use it as a coating film.

Coated articles coated with the powder coating composition of the present invention include, for example, microwave oven parts, water heaters, tubes, electromagnetic coils, coated electric wires, pressure-resistant elements, and in particular heat-resistant coated electric wires and the like. Materials that require good properties and insulation properties are suitable.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Production Examples, Examples, and Comparative Examples.

Production Example 1 [Production of polyester resin (■)] 637 g of neopentyl glycol was placed in a 4-neck, 5-liter separable flask equipped with a rectification column.

151 g of ethylene glycol, 950 g of trishydroxyethyl isocyanurate, 806 g of isophthalic acid, and 806 g of terephthalic acid were added, and 3.3 g of monobutyl hydroxytin oxide was added as an esterification catalyst.
It was heated to 60°C.

After reaching 160°C, the temperature is increased to 240°C over 3.5 hours. After further stirring at 240°C for 1 hour, the mixture was cooled to 170°C. The resin acid value at this time was 6. When the temperature reached 170℃, 281g of trimellitic acid and 65g of toluene were added.
g and was kept at 170° C. for 3 hours while stirring. Thereafter, toluene was distilled off under reduced pressure. The obtained polyester resin (1) contained 29% by weight of THEIC, had an acid value of 44, a hydroxyl value of 109.50%, and a Gardner viscosity of the cyclohexanone solution of X.

(THEIC = I-lishydroxyethyl isocyanurate) Production Example 2 [Production of polyester resin ■] 160 g of neopentyl glycol in the same manner as Production Example 1
, 377 g of ethylene glycol,) 1983 g of 1-1-lishydroxyethyl isocyanurate.

378 g of isophthalic acid, 1513 g of terephthalic acid.

4.0 g of monobutyl hydroxytin oxide was added and heated to 160°C. In addition, it took 3.5 hours to complete 240
℃ and held at 240℃ for 30 minutes, then heated to 170℃.
Cooled to ℃. The resin acid value at this time was 6.5.

294 g of trimellitic anhydride and 85 g of toluene at 170°C
g and was maintained at a temperature of 170 to 180° C. with stirring. The toluene was then removed by vacuum;
A polyester resin ■ was obtained. This resin has THEIC of 4
Contains 6.2% by weight, its acid value is 40, and its hydroxyl value is 17.
8. The Gardner viscosity of a 50% cyclohexanone solution is Z
,Met.

Production Example 3 [Production of Polyester Resin (1)] In the same manner as in Production Examples 1 and 2, 425 g of ethylene glycol, 630 g of neopentyl glycol, 394 g of glycerin, and 853 g of isophthalic acid were prepared.

Acid value 50 from terephthalic acid 1422g, monohydroxytin oxide 3.5g, trimellitic anhydride 204g
, a polyester resin (2) having a hydroxyl value of 156 was synthesized.

Production Example 4 [Production of polyester resin ■] Ethylene glycol 4 was prepared in the same manner as Production Examples 1 and 2.
15 g, neopentyl glycol 781 g, THE
IC194g, isophthalic acid 1111g, terephthalic acid 1111g, monohydroxytin oxide 3
．． A polyester resin with an acid value of 20 was synthesized from 5 g, and 371 g of trimellitic anhydride was added as a half ester, and THE! A polyester resin (2) containing 5.5% by weight of IC and having an acid value of 80 and a hydroxyl value of 29 was synthesized.

Production Example 5 [Production of polyester resin ■] Ethylene glycol 3 was prepared in the same manner as Production Examples 1 and 2.
15 g, 381 g of neopentyl glycol, 1514 g of trishydroxyethyl isocyanurate, 1444 g of terephthalic acid, 842 g of isophthalic acid, and 3.3 g of monobutyl hydroxytin were reacted at 160°C to 240°C. After cooling to 160°C, 105 g of trimellitic anhydride was added, and the reaction was continued at 160°C for 1.5 hours, and then cooled to obtain polyester resin (2). The resulting resin had an acid value of 15 and a hydroxyl value of 92. 50
% Gardner viscosity of the cyclohexanone solution was Z, TII[! The IC content was 36.9% by weight.

Example 1 To 100 parts of the polyester resin obtained in Production Example 1, 025 parts of blocked polyisocyanate, 7 parts of epoxy compound, 05 parts of organic polysiloxane gel particles, 20 parts of red iron pigment, and a coating surface conditioner (A ), 2 parts of coating surface conditioner (B), and 0.05 part of tin-based catalyst are sufficiently mixed and stirred using a normal tri-blend device. The resulting mixture is passed through a conventional melt mixing extruder (for example, Busu PR-46).
The mixture was mixed at 80° C. to 125° C. and cooled. After coarsely or finely pulverizing the mixed lumps or pellets,
The powder coating composition of Example 1 was obtained by removing coarse particles from the 200 mesh (74 μm) sieve using a device. This powder coating exhibited no shape changes such as profking after a 10-day storage test at 40°C, and no change in melt flowability (baking is the finish of the paint film) was observed after storage at 40°C for 30 days. There wasn't.

This powder coating was applied to a 1 fl thick degreased steel plate using an electrostatic powder coating device, and baked in a furnace at an ambient temperature of 300°C for 4 hours.
The cured coating of Example 1 was obtained by baking for a minute. This coated object had a smooth finish with a diameter of 10 to 70 μm, no wrinkles or pinholes, sufficient coating strength, moisture resistance, and heat-resistant softening temperature of 300°C.

Examples 2 to 5 and Comparative Examples 1 to 5 Powder coating compositions were obtained using the mixed compositions given in the ratios in Table 1 in the same manner as in Example 1, and powder coating compositions were obtained in the same manner as in Example 1. Electrocoating was applied, and coated objects of each Example and Comparative Example were obtained under the baking conditions shown in Table 2. The properties of each paint and coating film were as shown in Table-2.

: Polypolypolypolyester resin ■ = Ester resin according to Production Example 1 ■ = Ester resin according to Production Example 2 ■ = Ester resin according to Production Example 3 ■ = Ester resin according to Production Example 4 ■ = A according to Production Example 5 : NC010HB : C-C /C0OH polyepoxy compound ■=P↑810 (manufactured by Ciba Geigy, TGIC) Polyepoxy compound ■= E)lP3150 (alicyclic solid polyepoxy compound manufactured by Daicel Industries, Ltd.) Polysiloxane ■=Tolvers 120 (Toshiba Silicone, Inc.) manufactured by Polysiloxane Gel Fine Particles 2μ
) Polysiloxane ■ = Torvaas 240 (manufactured by Toshiba Silicone Co., Ltd., polysiloxane gel fine particles 4μ
) Block polyisocyanate ■ = 81530 (Hul
(Manufactured by LS; Softening point: -85°C) Block polyisocyanate ■-PW4403N (Manufactured by Takeda Pharmaceutical Co., Ltd.; Softening point = 70°C) Paint surface conditioner A = Modaflow (Manufactured by Monsanto, anti-cissing agent) Paint surface adjustment Agent B = benzoin tin curing accelerator = Formate TK-1 (manufactured by Takeda Pharmaceutical Co., Ltd.; organic tin compound) Titanium white = CR85 (manufactured by Ishihara Sangyo Co., Ltd., white pigment) Red red iron - Red red iron KNO-W (manufactured by Toda Shiroki Co., Ltd.) ) Examples 6-7 Powder coating composition of Example 1 (Example 6) and Example 2
Using each of the powder coating compositions (Example 7), electrostatic dynamic dip coating was carried out on a rectangular annealed copper wire with a thickness of 2111 mm and a width of 8 mm.
Insulated wires having film thicknesses of p and m were obtained.

Comparative Example 6 Using the powder coating composition of Comparative Example 1 and under the same conditions as in Example 6, an insulated wire having the same film thickness of 70 μm was obtained.

Table 3 shows the characteristics of the insulated wires obtained in Example 6, Example 7, and Comparative Example 6. The test method is LIS-(1
:3003.

(Effects of the Invention) For example, the present invention has the following advantages: Firstly, when painting Class F, Class 8 insulated wires, and other materials that require heat resistance, conventional solvent-based paints are difficult to coat to a specified film thickness. However, by using the powder coating composition of the present invention, it has become possible to perform coating with high production efficiency and at low cost in one coating. Second, conventional solvent-based coating line equipment required explosion-proof equipment, but with the use of the powder coating composition of the present invention, these are no longer necessary.
Equipment costs can be reduced. Thirdly, by replacing conventional solvent-based paints with powder paints using the powder paint composition of the present invention, the emission of highly polluting solvents into the atmosphere is eliminated, making a large social contribution.

According to the present invention, fourthly, the low heat resistance of the paint due to the combination of a high acid value type polyester resin and triglycidyl isocyanurate, which is used in general polyester resin powder paints, is solved.

According to the present invention, fifthly, a paint made of a combination of a hydroxyl type polyester resin and melamine or a block polyisocyanate, which is used in a general polyester resin powder paint, or a paint made of a combination of a tin or titanium catalyst and a polyester resin. The combination of the above and the like eliminates the smearing of the paint film caused by the condensation products that sometimes occurs when using paints based on demonomer condensation.

According to the present invention, sixthly, the coating film is caused by insufficient melt flowability of powder coatings using imide-modified polyester resins, imide resins, imidoamide resins, etc., which are said to have excellent heat resistance. Eliminates poor smoothness and coating performance.

Therefore, according to the present invention, it is possible to obtain a coating system that is economical, has low pollution properties, and has excellent heat resistance, finish quality, and coating performance, which could not be obtained with the prior art.

According to the present invention, coated articles such as microwave oven parts, pressure-resistant elements, and electromagnetic coils are further provided, which are coated with the powder coating composition of the present invention.

Procedural amendment March 29, 1989

Claims (1)

[Scope of Claims] 1. Obtained from polycarboxylic acid, polyhydric alcohol, and oxyacid used in place of some of them if necessary, and the resin has a hydroxyl value of 30 to 250 and an acid value of 10 to 250.
100, a polyester resin (A) that is solid at room temperature, and a crosslinking agent (B) that is composed of a block polyisocyanate and a polyepoxy compound that are solid at room temperature. 2. The powder coating composition according to claim 1, which contains 5 to 60 parts by weight of trishydroxyethyl isocyanurate as a polyhydric alcohol component per 100 parts by weight of the solid content of the polyester resin (A). 3. The powder coating composition according to claim 1 or 2, wherein the polyepoxy compound is triglycidyl isocyanurate and/or an alicyclic polyepoxy compound. 4. The powder coating composition according to claim 1, 2 or 3, further comprising a polysiloxane fine powder. 5. A coated article coated with the powder coating composition according to any one of claims 1 to 4.