JPH11100547A - Quick curing epoxy type powdered coating material and catalyst therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for a quick curing epoxy type powdered coating material which accelerates curing reaction of a binder resin and a curing agent at a high temp. without a tendency of early gelation in production. SOLUTION: Applied as a catalyst is an in an imidazole complex wherein a multiple no. of imidazole or its 2- mono or 2,4-dialkyl substd. ligands are coordinated to a central metal selected from the group consisting of Fe, Co, Ni, Cu, Zn and Al. This catalyst is added to a thermosetting resin compsn. for a powdered coating material comprising an epoxy group contg. binder resin and a curing agent. A quick curing type powdered coating material is obtd. which indicates a gelation time of <=40 sec at 200 deg.C while maintaining a longer gelation time of >=3 min at 140 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION The present invention relates to a catalyst used in a fast-curing epoxy powder coating, that is, to promote a reaction between a binder resin of an epoxy powder coating and a curing agent to form a coating film on a substrate. It relates to a catalyst which can be cured in a short time. The present invention also relates to a fast-curing epoxy-based powder coating containing such a catalyst.

[0002] Powder coatings do not contain organic solvents which are a source of air pollution, and are being used in many fields in place of conventional solvent coatings. One of its uses is in-line painting of deformed steel bars for concrete reinforcement, water steel pipes, steel pipes for oil transportation pipelines, and the like.

In this application, a long steel product preheated to a high temperature is coated with a powder coating while being transported while being supported by a conveyor, and the thermosetting of the coating film is performed by the specific heat capacity of the object to be coated. Is allowed. In this case, in order to achieve a reasonable line speed or throughput, a short period of time, for example, 15 seconds, before the powder coating layer applied to the substrate is passed along the transport direction on the next adjacent transport roller. Curing must be completed within at least the extent that the coating film is not damaged by contact with the transport roller.

[0004] One of the methods for enabling such a short and rapid curing is to add an imidazole compound as a catalyst to powder coating particles. Generally, a powder coating is produced by premixing a binder resin, a curing agent thereof, and an additive such as a pigment, melt-kneading, cooling and pulverizing. Melt kneading is usually performed using a device such as a kneader or an extruder at a casing temperature of 80 to 120 ° C. Therefore, if the catalyst significantly accelerates the reaction between the binder resin and the curing agent at the melt-kneading temperature of the raw materials, the kneading operation becomes difficult due to the early gelation, and the kneading work adheres to the inside of the apparatus and it is difficult to remove it. It takes extra effort. In addition, powder coatings that have undergone early gelation have reduced corrosion resistance.

[0005] The imidazole compound itself is a known epoxy resin curing catalyst, but when it is used as a catalyst for a fast-curing powder coating, it tends to gel at an early stage.

Recently, an epoxy resin curing catalyst, which is a metal complex having an adduct of phenylglycidyl ether and an imidazole compound as a ligand, has been disclosed. Polymer
Bulletin 33, 347-353 (1994)
reference. This metal complex reversibly dissociates the imidazole / phenylglycidyl ether adduct at 120 ° C. and exhibits catalytic activity. Therefore, if this metal complex is used in a fast-curing powder coating, premature gelation could be at least partially prevented.

[0007] However, the temperature of the casing of the melt-kneading apparatus is generally 80 to 120 ° C, but the temperature of the melt inside can rise to a temperature higher than the casing temperature due to frictional heat. It is understood that the gel time at 140 ° C. must be 3 minutes or more and the gel time at 200 ° C. must be 40 seconds or less in order to obtain a powder coating which has substantially no tendency to gel at an early stage and can be cured in a short time. Was. The proposed metal complex catalyst proved to be difficult to achieve this goal.

Accordingly, there is a need for a catalyst for a fast-curing epoxy-based powder coating which can overcome or alleviate the above-mentioned disadvantages.

DISCLOSURE OF THE INVENTION The above needs are met by the present invention, in which Fe, Co, Ni, C
An imidazole in which a plurality of imidazole ligands selected from the group consisting of imidazole, 2-alkylimidazole and 2,4-dialkylimidazole are coordinated to a central metal atom selected from the group consisting of u, Zn and Al It can be filled with a fast-curing epoxy powder coating catalyst composed of a metal complex.

The present invention also provides a fast-curing epoxy-based powder coating containing the above-mentioned imidazole metal complex catalyst. The powder coating of the present invention comprises a binder resin having a plurality of epoxy groups in a molecule, a curing agent thereof, and thermosetting resin powder particles containing the imidazole metal complex catalyst.

Detailed Discussion The ligand imidazole compound is selected from imidazole itself, mono- or dialkylimidazoles having alkyl substituents at the 2- or 2- and 4-positions.
In the case of having an alkyl substituent, the alkyl group at the 2-position is preferably selected from alkyl groups having up to 17 carbon atoms, and the alkyl group at the 4-position is preferably selected from alkyl groups having up to 5 carbon atoms. 2-Methylimidazole is sold by Shikoku Chemicals under the trade name 2MZ, 2-undecylimidazole under the trade name C11Z and 4-ethyl-2-methylimidazole under the trade name 2E4MZ. It is convenient and easy to use these commercially available products as raw materials for the imidazole metal complex.

The complex has a central metal (Fe, Co, Ni, C).
u, Zn or Al), for example chloride or nitrate, by reaction with an imidazole compound in a solvent. For example, both components can be dissolved in hot ethanol, reacted under reflux, and then cooled to obtain crystals. In some cases, water or a mixed solvent of water and ethanol could be used.

Binder Resin and Hardener The binder resin and hardener of the epoxy powder coating may be conventional ones. A typical binder resin is a polyglycidyl ether type epoxy resin having an epoxy equivalent of 800-2200. These epoxy resins are produced by reacting polychlorinated polyphenols such as bisphenol A, bisphenol F, and phenol novolak resin with epichlorohydrin in the presence of an alkali. From the viewpoint of corrosion resistance, it is preferable to use a bisphenol epoxy resin and a novolak epoxy resin in combination.

The second type of binder resin is obtained by reacting a polyfunctional epoxy compound, for example, bisphenol diglycidyl ether, with a carboxyl group terminal polyester, and making use of a ring-opening addition reaction of the epoxy group with the carboxyl group to give an epoxy functional group to the polyester chain end. It is a polyester-epoxy resin with attached groups.

A third type of binder resin is glycidyl (meth) acrylate obtained by copolymerizing glycidyl (meth) acrylate, another acrylic monomer such as alkyl (meth) acrylate, and optionally a non-acrylic monomer such as styrene. It is a group-containing acrylic copolymer resin.

Both types of binder resins are well known to those skilled in the art as binder resins for epoxy powder coatings and need not be described in further detail.

Curing agents used in combination with the binder resins described above are also well known to those skilled in the art. Examples of these curing agents include compounds having a plurality of phenolic hydroxyl groups such as bisphenol A, polyfunctional amines such as ethylenediamine and dicyandiamide, polyvalent carboxylic acids such as 1,10-decanediacid, and combinations thereof. is there. For example, when high adhesion is desired, a combination system of a polyhydric phenol and a polyfunctional amine is preferable.

Fast-Curing Powder Coating The fast-curing powder coating of the present invention can be produced according to a method well known to those skilled in the art except that a complex disclosed herein is added as a catalyst. As mentioned earlier,
In order to obtain a powder coating having a gel time of 3 minutes or more at 140 ° C and within 40 seconds at 200 ° C, the molar ratio of the epoxy resin in the binder resin to the imidazole ligand in the complex catalyst is required. Is 1: 0.05-0.5
It is necessary to add the catalyst so that In general, the amount of catalyst added is directly proportional to the fast-curing property and inversely proportional to the flexibility of the coating film.If the amount is too small, the fast-curing property that achieves a reasonable line speed cannot be obtained. Flexibility becomes unsatisfactory. The gel time is from 5 minutes to 10 minutes at 140 ° C., and preferably from 10 to 20 seconds at 200 ° C. To obtain the 140 ° C. and 200 ° C. gel times in this range, the amount of the catalyst described above is required. Becomes Further, the minimum melt viscosity of the powder coating can be secured to 1 to 3000 poise by the addition amount in this range.

Generally, a powder coating is produced by mixing a binder resin, a curing agent, and if necessary, a pigment and other additives, melt-kneading the mixture, cooling, and then pulverizing and classifying. The catalyst is added before the melt-kneading step like other raw materials.

If necessary, additives to be added to the raw materials to be melt-kneaded include titanium dioxide, iron oxide, carbon black, phthalocyanine blue, phthalocyanine green,
Color pigments such as quinacridone pigments and azo pigments; extender pigments such as talc, calcium carbonate, and precipitated barium sulfate; acrylic resins or polysiloxanes as surface conditioners; plasticity; ultraviolet absorbers; antioxidants; , An anti-blocking agent, benzoin and the like.

After preparing the raw materials as described above, the raw materials are preliminarily mixed using a super mixer, a Hensiel mixer or the like, and the raw materials are melted and mixed using a kneader such as a kneader or an extruder. The heating temperature at this time must be lower than the bake hardening temperature, but it must be a temperature at which at least a part of the raw material can be melted and kneaded as a whole. Generally, the mixture is melted and kneaded in the range of 80 to 120 ° C. Next, the melt is solidified by cooling with a cooling roll, a cooling conveyor, or the like, and is pulverized to a desired particle size through coarse pulverization and fine pulverization steps. In this case, the volume average particle diameter of the particles is generally 5 to 50 μm. It is preferable to carry out classification after sieving in order to remove the giant particles and fine particles and adjust the particle size distribution before shipping.

The powder coating material of the present invention can be used to preheat a long steel substrate such as a steel pipe or a concrete reinforcing bar to a high temperature of 200 ° C. or more, apply it in-line while transporting, and use the specific heat capacity of the substrate in a short time. Suitable for heat curing coating method. In this case, the coating method is preferably an electrostatic spray coating method, more specifically, a corona charging type spray coating method or a triboelectric charging type spray coating method. In the case of the corona charging method, either the external charging method or the internal charging method may be employed.

In the following Synthesis Examples, Examples and Comparative Examples, “parts” and “%” are based on weight.

Synthesis Example 1 of imidazole metal complex 0.134 g of copper (II) chloride in 10 ml of hot ethanol
(1 mmol) and 0.16 g of 2-methylimidazole
(2 mmol), refluxed for 3 hours, cooled, and n-
Hexane is added, and the precipitated yellow-green crystals are filtered, dried, and dichlorobis (2-methylimidazole) copper (II)
0.24 g was obtained. Elemental analysis C ₈ H ₁₂ N ₄ CuCl ₂ Calculated: C32.17; H4.05; N18.76 Found: C34.5; H4.4; N20.1

Synthesis Example 2 0.36 g of 2-methylimidazole in Synthesis Example 1
(4.4 mmol), and dichlorotechrakis (2-methylimidazole) copper (I
I) 0.46 g was obtained. Elemental analysis: C ₁₆ H ₂₄ N ₈ CuCl ₂ Calculated: C 41.52; H 5.23; N24.21 Experimental: C41.3; H5.1; N24.2

Synthesis Example 3 In Synthesis Example 1, 2 was used in place of 2-methylimidazole.
0.98 g of undecyl imidazole (4.4 mmol
l) and 0.36 g of dichlorotetrakis (2-undecylimidazole) copper (II) as hexacoordinate green crystals
I got Elemental analysis: C ₅₆ H ₁₀₄ N ₈ CuCl ₂ Calculated: C 65.69; H 10.24; N 10.94 Experimental: C 67.1; H 10.9; N 11.4

Synthesis Example 4 Zinc (II) nitrate hexahydrate 0.2 in 10 ml of hot ethanol
97 g (1 mmol) and 2-methylimidazole 0.1 g.
36 g (4.4 mmol) was added, and the mixture was refluxed for 3 hours and then cooled. Crystals precipitated by adding n-hexane were filtered, dried, and dinitrate tetrakis (2-methylmidazole) zinc (II) as white crystals. 0.40 g was obtained. Elemental analysis: C ₁₆ H ₂₄ N ₁₀ O ₆ Zn Calculated: C 37.11; H 4.67; N 27.05 Experimental: C 38.1; H 4.7; N 27.5

EXAMPLES AND COMPARATIVE EXAMPLES Preparation of Powder Coating According to the formulations shown in Table 1 (Example) and Table 2 (Comparative Example), the raw materials were premixed with a Henschel mixer (Mitsui Miike Seisakusho) and then mixed with a kneader ( Melted and kneaded at a casing temperature of about 100 ° C., cooled to room temperature and pulverized with an atomizer (manufactured by Fuji Paudal).
The powder was classified using a mesh sieve to obtain a powder coating having a volume average particle size of 40 μm.

Paint and coating test gel time: 1 g of a sample was dropped into a gelling tester (manufactured by Nissin Chemical Co., Ltd.) heated to a predetermined temperature and stirred. Measure the time from the start of stirring until the sample does not pull the thread,
Gel time was used.

Minimum melt viscosity measurement: 0.5 g of the pelletized sample was subjected to MR-30 at a frequency of 0.1 Hz.
The temperature was raised from 105 ° C. to 230 ° C. at a heating rate of 20 ° C./min in a 0 liquid meter (manufactured by Rheology), and a temperature-viscosity curve was created, from which a minimum melt viscosity was determined.

Corrosion resistance: A mild steel plate of 70 mm × 150 mm × 9 mm was blasted to a surface roughness of 45 to 80 μm, preheated to 240 ° C., and immediately coated with a powder coating by a corona charging spraying method. The coating was cured by specific heat capacity. Note that PGC-1 manufactured by Matsuo Co., Ltd. was used as a coating machine, and the coating was performed under the conditions of a gun distance of 150 mm, a voltage of 60 kV, and a discharge rate of 300 g / min. The thickness of the obtained cured coating film was about 200 μm.

The test piece prepared in this manner was subjected to SST
(Salt spray test) The peeling width of the coating film from the cut portion was measured over 1000 hours. ◎ Peel width 2 mm or less 〇 Peel width 2 mm to 4 mm △ Peel width 4 mm to 6 mm × Peel width 6 mm or more

Elongation: A tin plate having a thickness of 0.3 mm is overlaid on a mild steel plate of 70 mm × 150 mm × 9 mm and fixed.
It was preheated to 0 ° C., taken out, and immediately coated with a powder coating in the same manner as above, and cured to form a cured coating film having a thickness of about 200 μm. The obtained cured coating film was peeled from the tin plate using mercury to obtain a sample. This coating film was subjected to a tensile test using a Tensilon tester (manufactured by Toyo Baldwin Co., Ltd.), and the elongation at the breaking point was determined. The measurement conditions are a tensile speed of 10 mm / min and a measurement temperature of −10 ° C. ◎ 7% or more ６ 6-7% △ 5-6% × less than 5%

Film appearance: The condition of the film surface was visually evaluated. ◎ Smooth 〇 Yuzu skin is observed △ Some dents × Notable dents

Manufacturing workability: The inside of the kneader after kneading the raw materials was visually evaluated for dirt.殆 ど Almost no dirt △ Partly dirt × Almost all dirt

The test results are shown in Tables 1 and 2.

[0037]

[Table 1]

[0038]

[Table 2]

Note 1) Bisphenol A epoxy resin manufactured by Yuka Ciel Epoxy Co., Ltd. Note 2) Novolac type epoxy resin manufactured by Yuka Ciel Epoxy Co., Ltd. Note 3) Fine powder silica manufactured by Nippon Aerosil Co., Ltd. Note 4) 2-Methylimidazole Note 5) 2 -Undecyl imidazole

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kei Aoki 19-17 Ikedanakamachi, Neyagawa-shi, Osaka Japan Paint Co., Ltd.

Claims (7)

[Claims] 2. The method according to claim 1, wherein the elements are Fe, Co, Ni, Cu, Zn and Al.
A plurality of imidazole ligands selected from the group consisting of imidazole, 2-alkylimidazole and 2,4-dialkylimidazole to a central metal atom selected from the group consisting of Curable epoxy powder coating catalyst. 2. The catalyst according to claim 1, wherein the ligand is imidazole, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole or 4-ethyl-2-methylimidazole. 3. A binder resin having a plurality of epoxy groups in a molecule, a curing agent which reacts with the binder resin,
A fast-curing powder coating comprising powder particles of the thermosetting resin composition containing the catalyst according to claim 1. 4. A binder resin having an epoxy equivalent of 800-2.
The powder coating according to claim 3, which is 200 polyglycidyl ether type epoxy resin. 5. The molar ratio of the imidazole ligand in the metal complex to the epoxy group in the binder resin is 1:
The powder coating according to claim 3, wherein the ratio is 0.05 to 0.5. 6. The powder coating according to claim 3, wherein the gel time is at least 3 minutes at 140 ° C. and within 40 seconds at 200 ° C. 7. The powder coating according to claim 3, wherein the minimum melt viscosity is from 1 to 3000 poise.