JP2000109751A - Epoxy resin composition for powder coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition bakable at low temperatures, excellent in processability, and affording coating film with corrosion resistance and impact resistance and excellent smoothness. SOLUTION: This epoxy resin composition for powder coating material comprises [A] an epoxy resin component and [B] a curing agent component, wherein a bisphenol-type solid epoxy resin 500-2,500 g/eq in epoxy equivalent accounts for >=70 wt.% of the component [A], and the component [B] is a terminated bisphenol F-type phenolic curing agent 300-800 g/eq in phenolic hydroxyl equivalent and 70-120 deg.C in softening point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epoxy resin composition for powder coatings having excellent low-temperature curability and useful for anticorrosion coatings.

[0002]

2. Description of the Related Art Epoxy resins have excellent mechanical properties, chemical resistance, corrosion resistance, and electrical properties, and are widely used as powder coatings. Based on its anti-corrosion properties, it is widely used as an anti-corrosion paint for steel pipes, reinforcing bars and the like. However, in order to protect the reinforced concrete from bending contained in reinforced concrete, such as bending workability and impact resistance in a cold environment of 0 ° C. or lower, such as in the case of coating of reinforced concrete contained in reinforced concrete, salt contained in concrete material. Was not sufficiently satisfactory with a conventional powder coating using a bisphenol A type epoxy resin. Japanese Patent Publication No. 62-57667 discloses a powder coating suitable for use in such a severe environment, including a bisphenol A type epoxy resin, a novolak type epoxy resin, and a rubbery substance having a reactive functional group containing butadiene as a main component. A powder coating comprising a linear phenol resin having phenolic hydroxyl groups at both ends is disclosed. Japanese Patent Publication No. 57814/1994 discloses a powder coating in which a bisphenol A type epoxy resin and an alkylphenol novolak epoxy resin are used in combination, and these are reacted with a linear phenol resin having bisphenol A at both ends in the presence of a catalyst. Is disclosed. However, although the above powder coatings are excellent in impact resistance and workability, the corrosion resistance of the coating film was not satisfactory. In addition, when baked at a low temperature, there are problems such as poor smoothness, impact resistance and workability of the coating film.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and problems of epoxy powder coatings, and powders having excellent smoothness, impact resistance, workability, corrosion resistance, etc. of coating films even at low temperature baking. A coating composition is provided. That is, the gist of the present invention is:
In an epoxy resin composition for powder coatings comprising an epoxy resin component [A] and a curing agent component [B], 70% by weight or more of the epoxy resin component [A] is a bisphenol type solid having an epoxy equivalent of 500 to 2500 g / eq. Less than 30% by weight of an epoxy resin is a cresol novolac type epoxy resin, and the curing agent component [B] is bisphenol A
Bisphenol F1.2 containing 25 to 45 mol% of a para-paramethylene conjugate in 1.0 mol of a liquid epoxy resin and / or bisphenol F liquid epoxy resin and having a binuclear purity of 90% by weight or more A phenolic hydroxyl group equivalent having a phenolic hydroxyl equivalent of 300 to 800 g / eq and a softening point of 70 to 120 ° C. and having a terminal bisphenol F type. It is assumed that.

In the present invention, 70% by weight or more of the epoxy resin [A] has an epoxy equivalent of 500 to 2500.
g / eq bisphenol type solid epoxy resin, 30
Less than weight% is made of cresol novolak type epoxy resin. The bisphenol type epoxy resin,
Bisphenol A type epoxy resin and / or bisphenol F type epoxy resin, specifically, YD-902 manufactured by Toto Kasei Co., Ltd. as bisphenol A type epoxy resin
YD-903, YD-904, YD-012, YD-0
13, YD-014, YDF-803 and YDF-200 manufactured by Toto Kasei as bisphenol F type epoxy resin
4. YD-6108 manufactured by Toto Kasei Co., Ltd. may be used as a copolymerizable epoxy resin of bisphenol A and bisphenol F, and one or more of these may be used in combination. The cresol novolak epoxy resin is obtained by reacting cresol novolak resin obtained by reacting orthocresol and formaldehyde under an acidic catalyst under an excess of epichlorohydrin and an alkali metal catalyst. Is YDCN-701, YD manufactured by Toto Kasei
CN-702, YDCN-703, YDCN-704 and the like. It is desirable that the epoxy resin [A] component contains less than 30% by weight of a cresol novolak type epoxy resin. If the content is 30% by weight or more, it becomes hard and brittle. If the amount is less than 2% by weight, the curability becomes slow, so that it is preferably 2 to 25% by weight, more preferably 5 to 25% by weight.
To 15% by weight.

The curing agent [B] in the present invention can be obtained by subjecting a bisphenol-type epoxy resin to bisphenol F polyaddition reaction. In this reaction, bisphenol F is reacted in a range of 1.2 to 3.0 mol with respect to 1.0 mol of the bisphenol type epoxy resin. When the molar ratio is less than 1.2 mol, the molecular weight becomes high, so that the fluidity at the time of baking decreases, and the corrosion resistance of the coating film decreases. When the molar ratio is more than 3.0 mol, the impact resistance and processability decrease. is there. More preferably, it is in the range of 1.5 to 2.5 mol. As the bisphenol-type epoxy resin that can be used in the reaction, a liquid resin resin is preferable. Specific examples include bisphenol A type type epototo YD-8125 (epoxy equivalent; 172 g / eq) and YD-128 (epoxy equivalent; 187 g / eq) manufactured by Toto Kasei, and bisphenol F type type YDF-8170 (epoxy equivalent). 160 g / eq),
YDF-170 (epoxy equivalent 170 g / eq) and the like. Further, bisphenol F that can be used in the reaction includes a para-para-methylene conjugate of 25 to 4
It is preferable that the content is within a range of 5 mol% and the binuclear purity is 90% by weight or more. If the content of the para-para-methylene complex exceeds 45 mol%, the effect of improving the bending workability and impact resistance of the powder coating cannot be obtained, and if it is less than 25 mol%, the corrosion resistance is poor. It is. More preferably, the content of the para-para-methylene conjugate is in the range of 30 to 40 mol%. The content of other ortho-para-methylene bonds and ortho-ortho-methylene bonds may be 60 to 70 mol% in total, and the content of each bond is not particularly limited. Further, bisphenol F is preferably composed of only binuclear phenol, but may contain trinuclear or higher polynuclear phenol in a small amount of less than 10% by weight. If the polynuclear phenol is contained in an amount of 10% by weight or more, the objects of the present invention such as processability and impact resistance cannot be achieved.

As a method of reacting a bisphenol type epoxy resin with bisphenol F, in the presence of a catalyst,
It can be produced by reacting at 100 ° C. to 250 ° C. for 1 hour to 10 hours. Examples of usable catalysts include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; tertiary amines such as triethylamine and benzyldimethylamine; 2-methylimidazole;
-Imidazoles such as methylimidazole, quaternary ammonium salts such as tetramethylammonium bromide and benzyltrimethylammonium bromide, phosphines such as triphenylphosphine and tributylphosphine, n-butyltriphenylphosphonium bromide,
And phosphonium salts such as ethyltriphenylphosphonium iodide. The amount of the catalyst used is 10 to 10,000 pp based on bisphenol F used in the reaction.
m is preferably within the range.

The curing agent component [B] in the present invention can be obtained by the above reaction, and has a phenolic hydroxyl equivalent of 300 to 800 g / eq and a softening point of 70 to 12
It is a phenolic curing agent of terminal bisphenol F type at 0 ° C. When the phenolic hydroxyl equivalent is less than 300 g / eq and the softening point is less than 70 ° C., even if it is solid at ordinary temperature, it is easy to block, and the bending workability and impact resistance become insufficient, while the phenolic hydroxyl equivalent is 800 g / eq. Those having an eq and a softening point of more than 120 ° C. are not preferable because the softening point becomes high and kneading in the coating process becomes insufficient.

The amount of the curing agent [B] can be determined stoichiometrically as appropriate according to the epoxy equivalent of the epoxy resin [A] and the phenolic hydroxyl equivalent of the curing agent [B]. However, the phenolic hydroxyl group of the curing agent [B] is preferably 0.6 to 1.3 equivalents, preferably 0.1 equivalent, per equivalent of epoxy group of the epoxy resin [A].
It is in the range of 7 to 1.0 equivalent.

[0009] In addition to the epoxy resin [A] and the curing agent [B], the powder composition of the present invention may contain titanium oxide, talc, calcium carbonate, barium carbonate, silica, mica, alumina, carbon, etc., depending on the purpose of use. An extender such as black, a coloring agent, a curing accelerator such as 2-methylimidazole, 2-phenylimidazole and imidazolines, a flow regulator, and other additives can be blended.

As a method for producing the powder coating composition of the present invention, an epoxy resin [A], a curing agent [B] and, if necessary, other materials are preliminarily mixed, followed by melt-kneading with an extruder or the like.
After cooling, it can be coarsely pulverized and further obtained by adjusting the particle size distribution with a classifier. The powder coating composition of the present invention can be applied to a metal such as steel or aluminum, glass, plastic or the like by a usual method such as an electrostatic coating method.
Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In the examples and comparative examples, the number of parts by weight of each component indicates parts by weight unless otherwise specified.

[0011]

EXAMPLES Reference Example 1 Epototo YD was placed in a reaction vessel equipped with a stirrer, thermometer, condenser and nitrogen supply device.
-128 (bisphenol A type epoxy resin manufactured by Toto Kasei; epoxy equivalent = 187 g / eq) 52 parts, BPF
(Bisphenol F manufactured by Honshu Chemical Co., Ltd., binuclear purity; 9
2%, para-para-methylene conjugate; 34 mol%) 48
Were added, and 0.05 part of n-butyltriphenylphosphonium bromide was added and reacted at 160 ° C. for 5 hours to obtain a phenolic hydroxyl equivalent of 463 g / eq and a softening point of 8
7 ° C bisphenol F phenolic curing agent (B
-1) was obtained. The phenolic hydroxyl group equivalent is determined by reacting phenolic hydroxyl groups with tetrabutylammonium hydroxide in a mixed solution of 96% by weight of tetrahydrofuran and 4% by weight of methanol to form a color, and measuring the absorbance at 305 nm using a spectrophotometer. It was obtained by conversion using a calibration curve previously prepared by the same operation using bisphenol F as a standard. The softening point is JIS K-
7234.

REFERENCE EXAMPLE 2 Epototo YDF-170 (bisphenol F manufactured by Toto Kasei Co., Ltd.)
Type epoxy resin; epoxy equivalent of 169 g / eq)
Parts, 50 parts of BPF, 0.05 parts of n-butyltriphenylphosphonium bromide were added and reacted at 160 ° C. for 5 hours to give a phenolic hydroxyl equivalent of 463 g.
/ Eq, a phenolic curing agent (B-2) of terminal bisphenol F having a softening point of 84 ° C was obtained.

Example 1 Epotote YD-903 (epoxy equivalent 800 g / e)
q, bisphenol A epoxy resin with a softening point of 95 ° C)
398 parts, 44 parts of Epototo YDCN-703 (cresol novolak type epoxy resin having an epoxy equivalent of 205 g / eq, softening point of 80 ° C.), 249 parts of phenolic curing agent (B-1) obtained in Reference Example 1, 2 -After premixing 4 parts of methylimidazole, 300 parts of titanium oxide, and 5 parts of Modaflow (a flow control agent manufactured by Monsanto) with a Henschel mixer, Extruder PCM-3 manufactured by Ikegai Iron Works Co., Ltd.
Using 0, the resin temperature was set to 110 ° C., and the mixture was melt-kneaded, pulverized, and a product having passed 100 mesh was used as the powder coating material of Example 1.

Example 2 398 parts of Epototo YD-903, Epotote YDC
44 parts of N-703, 249 parts of phenolic curing agent (B-2) obtained in Reference Example 2, 2-methylimidazole 4
Parts, 300 parts of titanium oxide and 5 parts of Modaflow were premixed with a Henschel mixer. Thereafter, a coating material was prepared in the same manner as in Example 1 to obtain a powder coating material of Example 2.

Comparative Example 1 Bisphenol A type T as a phenolic curing agent
H-4000 (manufactured by Toto Kasei Co., Ltd., phenolic hydroxyl equivalent; 400 g / eq, softening point: 80 ° C.) Except for changing to 215 parts, a paint was prepared in the same manner as in Example 1 to obtain a powder paint of Comparative Example 1. Was.

The powder coatings obtained in Examples and Comparative Examples were coated on a substrate (sandblasted steel plate; 70 × 150 × 0.8 m).
m) was subjected to a test for smoothness, impact resistance and workability with respect to a coating film having a thickness of about 100 μm obtained by electrostatic coating and baking and curing at 130 ° C. and 180 ° C. Table 1 shows the results. The evaluation method was as follows. -Smoothness: The appearance of the coating film was visually judged. ○: good,
Δ: Slightly inferior, ×: Inferior • Impact resistance: The state of the coating film after the test was visually determined with a DuPont impact tester at a 1/2 inch hammer, a load of 1 kg and a height of 50 cm. ；: No abnormality, ×: Abnormality such as crack.・ Eriksen: Using an Erichsen tester, 7 punches
mm: Extrusion, and the presence or absence of cracks or peeling of the coating film were visually determined. ○: No abnormality, ×: Abnormality such as cracking or peeling.・ Corrosion resistance: JIS. K
The test was performed according to 7.4 of 5400 (salt spray test). After 500 hours, forced peeling was performed with a cutter. The numerical values in Table 1 indicate the peel width (m) from the cross cut portion.
m) was measured.

[0017]

[Table 1]

[0018]

As shown in the Examples, the epoxy resin composition for powder coatings of the present invention is a powder coating mainly containing a bisphenol A type terminal phenolic curing agent which is conventionally used as shown in Comparative Examples. It is possible to obtain a cured coating film having excellent coating film physical properties at the time of low-temperature curing as compared with the epoxy resin composition for use.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuyuki Takeda 3-17-14 Higashikasai, Edogawa-ku, Tokyo Tokyo Metropolitan Chemical Research Laboratory F-term (reference) 4J036 AA05 AD08 AF08 DB12 DC41 FA03 FA05 JA03 4J038 DB061 DB071 JA64 KA03 NA03 PA02 PA18 PC02 PC03 PC08

Claims (4)

[Claims] 1. An epoxy resin composition for powder coating comprising an epoxy resin component [A] and a curing agent component [B], wherein 70% by weight or more of the epoxy resin component [A] has an epoxy equivalent of 500 to 2500 g / eq. bisphenol type solid epoxy resin, wherein the curing agent component [B] is a bisphenol F type phenolic curing agent having a phenolic hydroxyl equivalent of 300 to 800 g / eq and a softening point of 70 to 120 ° C. An epoxy resin composition for powder coatings, characterized by comprising: 2. The curing agent component [B] contains 25 to 45 mol% of a para-para-methylene conjugate in 1.0 mol of bisphenol A liquid epoxy resin and / or bisphenol F liquid epoxy resin. 2. The epoxy resin composition for a powder coating according to claim 1, wherein the epoxy resin composition is obtained by reacting 1.2 to 3.0 mol of bisphenol F having a binuclear purity of 90% by weight or more. 3. The epoxy resin composition for a powder coating according to claim 1, wherein the epoxy resin component [A] contains less than 30% by weight of a cresol novolak type epoxy resin. 4. The powder according to claim 1, wherein the phenolic hydroxyl group of the curing agent [B] comprises 0.6 to 1.3 equivalents per equivalent of epoxy group of the epoxy resin [A]. Epoxy resin composition for body paint.