JPH10212434A - Powder coating material of epoxy-hardening type polyester resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder coating material formable of a coating film having excellent low temperature hardenability. SOLUTION: This powder coating material is a thermosetting coating material containing (A) a carboxyl group-containing polyester base material resin and (B) a polyepoxide cross-linking agent. In the coating material, the component B is preferably a novolak-type epoxide and has 1,000-10,000 number-average molecule weight, 500-2,000 epoxy equivalent, >=2.40 average epoxy functional group number and 50-140 deg.C softening temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel epoxy-curable polyester resin powder coating.

[0002]

2. Description of the Related Art Powder coatings have many characteristics, such as being less polluting, easier to manage lines, and easier to collect paints than conventional solvent-based coatings. Therefore, it is used in many fields.

Heretofore, there has been known an epoxy-curable polyester resin powder coating obtained by mixing a carboxyl group-containing polyester resin as a base resin with a polyepoxide as a crosslinking agent. However, the conventionally used polyepoxide has a poor curing property and requires a baking temperature of 160 ° C. or more, requires large drying equipment, and consumes a large amount of energy such as electricity and fuel required for baking. High and economically disadvantageous. In addition, there has been a problem that the baking time is long for an object having a large heat capacity.

[0004]

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, when a specific novolak-type polyepoxide crosslinking agent was used as a crosslinking agent for polyester resin, the temperature of 140 ° C. It has been found that the composition can be sufficiently cured at a certain baking temperature and can provide excellent coating film performance, and the present invention has been completed.

That is, the present invention provides: (A) a carboxyl group-containing polyester base resin,
And (B) a thermosetting powder coating containing a polyepoxide crosslinking agent, wherein the (B) polyepoxide crosslinking agent has a weight average molecular weight of 1,000 to 10,000 and an epoxy equivalent of 500 to
1. an epoxy-curable polyester resin powder coating material having an average number of epoxy groups of 2.40 or more and a softening temperature of 50 to 140 ° C .; (B) An epoxy-curable polyester resin powder coating, wherein the polyepoxide crosslinking agent is a novolak-type polyepoxide.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester resin (A) used in the present invention is a polyester resin containing a carboxyl group in the molecule, and particularly has an acid value of about 15 to 200 KOH.
mg / g, preferably 20-80 KOH mg / g, softening point about 30-150 ° C, preferably about 70-130 ° C, weight average molecular weight about 1000-20,000, preferably about 2
000-5000 is good. The resin may contain a hydroxyl group.

In the polyester resin (A), if the acid value is less than about 15 KOH mg / g, the low-temperature curability decreases, while if it exceeds about 200 KOH mg / g, the water resistance of the coating film is undesirably reduced. When the softening temperature is lower than about 30 ° C., the storage stability (blocking resistance and the like) of the powder coating material is reduced. On the other hand, when the softening temperature is higher than 150 ° C., the flowability of the coating material is reduced, and the coating film smoothness is deteriorated. Not preferred. If the weight-average molecular weight is less than about 1000, the coating properties such as weather resistance will decrease, and if it exceeds about 20,000, the appearance of the coating will deteriorate, which is not preferable.

The polyester resin (A) is prepared by, for example, appropriately selecting the types and mixing ratios of an acid component and an alcohol component so as to satisfy the above-mentioned conditions, for example, a conventionally known esterification reaction, transesterification reaction and the like. It can be produced by a reaction method. Examples of the acid component and the alcohol component constituting the polyester resin (A) include, for example, terephthalic acid, isophthalic acid and anhydrides thereof, and lower alkyl esters thereof, adipic acid, sebacic acid, and succinic acid. , Maleic acid, fumaric acid, tetrahydrophthalic acid, hexahydrophthalic acid and anhydrides thereof, and alcohol components such as ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-
Butanediol, 1,6-hexanediol, neopentylglycol, trimethylolethane, trimethylol
Lupropane, glycerin, pentaerythritol and the like are exemplified.

The polyepoxide crosslinking agent (B) used in the present invention has a number average molecular weight of 1,000 to 10,000, preferably 1,000 to 5,000, and an epoxy equivalent (g, eq) of 5
0.00 to 2000, preferably 500 to 1500, and an average number of epoxy functional groups (number average molecular weight / epoxy equivalent) of 2.4.
0 or more, and a softening temperature of 50 to 140 ° C, preferably 5
It is a polyepoxide at 0 to 120 ° C. If the number average molecular weight is less than 1,000, the processability of the coating film deteriorates, while
If it exceeds 0000, the smoothness of the coating film deteriorates. If the epoxy equivalent is less than 500, the storage stability (blocking resistance and the like) of the powder coating material is poor, and if it exceeds 2000, the low-temperature curability deteriorates, which is not preferable. When the average number of epoxy functional groups is less than 2.40, coating performance such as water resistance, corrosion resistance and workability is inferior at low temperature baking at about 140 ° C.
Further, as the upper limit of the number of functional groups, from the viewpoint of coating film appearance,
Particularly, the number is preferably 3.0 or less. When the softening temperature is lower than 50 ° C., the storage stability of the powder coating (blocking resistance, etc.)
On the other hand, when the temperature exceeds 140 ° C., the fluidity of the paint decreases, and the smoothness of the coating film deteriorates.

As the polyepoxide crosslinking agent (B), a conventionally known one can be used without any particular limitation as long as it falls within the above range. As the polyepoxide crosslinking agent (B), for example, novolak type polyphenol resin (resin containing 2.4 or more phenolic hydroxyl groups)
And epichlorohydrin, or the novolak type polyphenol resin, bisphenol (A type, B type, F type, etc.) and epichlorohydrin, or the novolak type polyphenol resin and bisphenol (A, B, or F)
Type) epoxy resin (for example, Epicoat 828, Epicoat 834 “trade name, manufactured by Yuka Shell Epoxy Co., Ltd.”) or the novolak type polyphenol resin, the bisphenol type epoxy resin, and the bisphenol Can be used so that the number average molecular weight, the epoxy equivalent, the number of epoxy functional groups, and the softening temperature fall within the above ranges. In addition to the above, a hydroxyl group-containing polyepoxide (for example, Epicoat 10
04 (trade name, manufactured by Yuka Shell Epoxy Co., Ltd.) with a polyisocyanate (eg, isophorone diisocyanate).
Those modified in g) can also be used.

Specific examples of the polyepoxide crosslinking agent (B) include, for example, ZX-1469 (trade name, manufactured by Toto Kasei Co., Ltd., number average molecular weight: about 1571, epoxy equivalent: 650, epoxy average functional group number: 2.41, softening temperature). 95 ° C), YD
-661 (manufactured by Yuka Shell Epoxy Co., Ltd., trade name, number average molecular weight 1361, epoxy equivalent 487, epoxy average functional group number 2.79), Santoto ST-4000 (manufactured by Toto Kasei Co., Ltd., trade name) , A number average molecular weight of about 1755, an epoxy equivalent of 704, an epoxy average functional group number of 2.49, and a softening temperature of 88 ° C).

The mixing ratio of the carboxyl group-containing polyester base resin (A) and the polyepoxide cross-linking agent (B) is about 50 in terms of the total weight of the base resin (A) and the cross-linking agent (B). ~ 70% by weight, preferably about 5%
The range is 5 to 65% by weight, the crosslinking agent (B) is about 30 to 50% by weight, preferably about 35 to 45% by weight. When the amount of the base resin (A) is less than about 50% by weight and the amount of the cross-linking agent (B) exceeds about 50% by weight, the low-temperature curability and the appearance of the coating film deteriorate, while the amount of the base resin (A) decreases by about 70% by weight. Crosslinking agent (B)
Is less than about 30% by weight, the low-temperature curability is undesirably reduced. In the powder coating of the present invention, it is preferable to use an imidazole compound or a metal salt complex thereof as a curing catalyst for the base resin (A) and the crosslinking agent (B).

Examples of the imidazole compounds include, for example,
2-ethyl-4-methylimidazole, 1-methylimidazole, 1,2-dimethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2-hepta Alkyl imidazoles such as decyl imidazole and 2-isopropyl imidazole; carbamyl alkyl-substituted imidazoles such as 1- (2-carbamylethyl) imidazole; cyanoalkyl-substituted imidazoles such as 1-cyanoethyl-2-methylimidazole , 2-phenylimidazole, aromatic-substituted imidazoles such as 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and alkenyl-substituted imidazoles such as 1-vinyl-2-methylimidazole. Allyls such as 1-allyl-2-ethyl-4-methylimidazole Conversion imidazo - Le acids and Poriimidazo - le, and the like. The imidazole compounds are preferably alkyl imidazoles and aromatic-substituted imidazoles.

The metal salts used in the metal salt composite include, for example, copper, nickel, cobalt, calcium, zinc, zirconium, silver, chromium, manganese, tin,
Compounds of metals such as iron, titanium, antimony and aluminum with salts such as chloride, bromide, fluoride, sulfate, nitrate, acetate, maleate, stearate, benzoate and methacrylate. The body is included.

In the above-mentioned composite, it is particularly preferable to use zinc or copper as the metal, since there is no discoloration of the coating film due to baking.

In the above complex, the metal salts include
Preferred are zinc chloride, zinc acetate, copper chloride and the like.

The curing catalyst is used in an amount of about 0.1 to 10 based on 100 parts by weight of the total of the base resin (A) and the crosslinking agent (B).
It is preferably in the range of 0.5 to 5 parts by weight.

In the powder coating of the present invention, in addition to the above-mentioned components, an organic coloring pigment, an inorganic coloring pigment, a filler, a curing catalyst other than the above, an ultraviolet stabilizer, an ultraviolet absorber, a fluidity regulator, An inhibitor and the like can be blended.

The powder coating composition of the present invention is prepared by, for example, a conventional method, for example, mixing the base resin (A), the crosslinking agent (B) and other components as necessary, dry-blending with a mixer, and then heating and melting. It can be manufactured by kneading, cooling, coarse pulverization, fine pulverization and filtration.

[0020] The powder coating of the present invention is obtained by applying powder coating to an object to be coated,
Baking (eg, at a temperature of about 140 ° C. for about 30 minutes, at about 200 ° C. for about 15 minutes) can form a cured coating. As the material to be coated, a conventionally known material can be used without any particular limitation as long as it is a material capable of electrostatic powder coating. Examples of the object to be coated include metals, metals subjected to surface treatment, glasses, and those obtained by coating these materials with paint.

The electrostatic powder coating is preferably carried out by a method known per se, for example, electrostatic powder coating, triboelectric powder coating or the like. The coating thickness is not particularly limited, but is about 20 μm.
Suitable ranges are from m to 150 μm, especially from about 30 μm to 100 μm.

[0022]

The present invention will be described below in detail with reference to examples.

Example 1 A carboxyl group-containing polyester resin (average molecular weight of about 6
600, softening temperature 112 ° C, acid value 26KOHmg / g,
Terephthalic acid / neopentyl glycol / 1,6-hexanediol = 62.8 / 31.4 / 5.8 weight ratio) 6
350 g, 50 g, ZX-1469 (trade name, number average molecular weight: 1571, epoxy equivalent: 650, epoxy average functional group: 2.41 and softening temperature: 95 ° C., manufactured by Toto Kasei Co., Ltd.)
g, 500 g of titanium dioxide (Tape CR-95, trade name, manufactured by Ishihara Sangyo Co., Ltd.), dry blending (Henschel mixer), melt mixing and dispersion (biaxial extruder kneader), cooling, Coarse pulverization, fine pulverization (atomizer), and filtration (150 mesh sieve) were performed to produce a powder coating material of Example 1.

Example 2 In Example 1, 2-undecylimidazole was used as a curing catalyst in an amount of 1 to 1000 g of the total weight of the resin and the curing agent.
A powder and a paint of Example 2 were produced in the same manner as in Example 1 except that 0 g was blended.

Example 3 In Example 2, the mixing ratio of the resin and the curing agent was 550 g.
A powder coating was produced in the same manner as in Example 2 except that the amount was 450 g.

Comparative Example 1 In Example 1, YD-90 was used instead of ZX-1469.
2 (manufactured by Toto Kasei Co., Ltd., trade name, number average molecular weight 135)
0, epoxy equivalent 630, average number of epoxy functional groups 2.1
It was manufactured in the same manner as in Example 1 except that 0 pieces (softening temperature: 88 ° C.) were used.

Comparative Example 2 In Example 1, Epon 10 was used in place of ZX-1469.
02 (manufactured by Yuka Shell Epoxy Co., Ltd., trade name, number average molecular weight 1176, epoxy equivalent 639, epoxy average functional group number 1.84, softening temperature 78 ° C.) in the same manner as in Example 1 Manufactured.

Table 1 shows the coating film performance test results of the examples and comparative examples.

[0029]

[Table 1]

In Table 1, the test was performed as follows.

Preparation of coated plate: A zinc phosphate treated steel plate was coated with electrostatic powder so as to have a film thickness of about 60 μm, and 140 ° C.
Baked for 30 minutes was used as a test.
In Table 1, the coating film appearance, specular reflectance, and smoothness were tested by the following methods.

Coating appearance: The coating surface was visually observed and evaluated. ◎ indicates that there was no abnormality such as smoothness and shrinkage at all, and は indicates that there was some abnormality such as smoothness and shrinkage but was good. Is markedly inferior with abnormalities such as smoothness and shrinkage.

Specular reflectance: 60 according to JIS K-5400
The degree of specular gloss was measured.

Impact resistance: According to JIS K-5400 Dupont-type impact test, weight 500 g, diameter of wick 1/2
The maximum weight height (cm) that does not cause damage to the coating film in inch conditions is indicated. The maximum is 50 cm.

Bending resistance: Bending resistance tester (10 m in diameter)
The test was performed according to JIS K-5400 using a m, 6 mm core rod).は: No cracks and peeling, Δ: Cracking and peeling were observed and X: Cracking and peeling were observed and markedly inferior.

Adhesion on Gobang eyes: One hundred squares of 1 mm square were formed on the coating film with a cutter knife, and a peeling test was carried out with a cellophane tape adhesive tape. The number of remaining squares was checked.

Boiling aqueous solution: The coated plate was immersed in boiling water for 4 hours and then subjected to the above-mentioned adhesion test.

Corrosion resistance: A cross cut was made with a knife so as to reach the substrate from the top of the coating film, and this was JIS Z-23.
The salt spray test was conducted according to No. 71 for 240 hours. ◎ indicates rust or peel width of less than 1 mm, は indicates rust or peel width of 1 mm or more and less than 2 mm, △ indicates rust or peel width of 2 mm or more and less than 4 mm, and X indicates 5 mm or more.

[0039]

The powder coating composition of the present invention uses the above-mentioned specific polyepoxide crosslinking agent as a curing agent for the carboxyl group-containing polyester resin.
Crosslinks at a temperature of about ℃ (low temperature range in the field of powder coatings), and exhibits a remarkable effect of forming a coating film with excellent performance such as processability and corrosion resistance of the crosslinked coating film. .

Claims (2)

[Claims] 1. A thermosetting powder coating material containing (A) a carboxyl group-containing polyester base resin and (B) a polyepoxide crosslinking agent, wherein (B) the polyepoxide crosslinking agent has a number average molecular weight of 1,000 to 10,000 and an epoxy equivalent of 5
An epoxy-curable polyester resin powder coating characterized by having an average number of epoxy groups of 2.000 or more and a softening temperature of 50 to 140 ° C. 2. An epoxy-curable polyester resin powder coating, wherein the polyepoxide crosslinking agent (B) is a novolak-type polyepoxide.