JP2001152083A - Thermosetting epoxy powder coating for metal tube and coated metal tube using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a powder coating for a metal tube, capable of forming a coating film without having bubbles and having a good storing property. SOLUTION: This powder coating for the metal tube is characterized by blending 0.1-20 pts.wt. range curing agent of hexamethylene diisocyanate- modified 2-methyl-imidazole adduct compound expressed by the formula with 100 pts.wt. epoxy resin having 90-140 deg.C melting point, 1,000-4,000 average molecular weight and 800-4,000 epoxy equivalent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel thermosetting epoxy powder coating for metal pipes and a coated metal pipe.

[0002]

2. Description of the Related Art Conventionally, a coated metal pipe in which powder coating is applied to the inner and outer surfaces of a cast iron pipe has been used as a water pipe. As a powder coating used as the inner and outer surfaces of a water pipe, an epoxy-based thermosetting powder coating obtained by mixing an imidazole-based curing agent and an adipic dihydrazide curing agent with an epoxy resin from the viewpoint of water quality and corrosion resistance is generally used. It is used.

As a method of applying powder coating on the inner and outer surfaces of a metal tube, a metal tube is preheated, and a thermosetting powder coating is applied on the inner and outer surfaces of the tube, and then the preheating of the metal tube or no preheating is performed. After coating a thermosetting powder coating on the inner and outer surfaces of the metal tube, the powder coating is cured by post-heating the metal tube.

[0004] When a conventional epoxy-based thermosetting powder coating is applied to a metal tube, bubbles remain in the coating film or bubbles remain at the interface between the metal tube material and the coating film. Appearance,
Problems such as deterioration of anticorrosion property and workability remain. As a countermeasure, a powder coating compounded with a curing agent of at least one kind of an imidazoline-based curing agent selected from 2-phenyl-2-imidazoline, 2-phenyl-3-imidazoline and 2-phenyl-4-imidazoline is known ( JP-A-9-316368). However, during the storage of the powder coating, the powder coating undergoes a solid-phase reaction on the surface of the powder particles, and as a result, the powder particles are hardly melted and flow by heating, so that the smoothness of the coating film, the physical properties of the coating film, and the water resistance. There is a problem that the properties are inferior.

[0005] The present invention provides a thermosetting powder coating material which is excellent in processability without deteriorating the performance of conventional water quality and the like, can form a cured coating film without foaming, and has excellent storage stability. It is in.

[0006]

Means for Solving the Problems The present inventors have intensively studied to solve the above-mentioned problems. The cause of the deterioration of the corrosion resistance and workability of the coating film is that when the powder coating film is baked, bubbles in the coating film are drawn into the coating film due to the expansion of the air in the holes existing in metal pipes such as cast iron, It is considered that bubbles are generated at the interface between the metal tube material and the powder coating, and in a metal material having such a hole, a hexamethylene diisocyanate modified adduct compound of 2-methyl-imidazole is considered. It has been found that an epoxy powder coating using a curing agent of the formula (1) forms a coating film without foaming, and that a powder coating excellent in storage stability without solid phase reactivity during storage can be provided, thereby completing the present invention. Reached.

That is, the present invention relates to:
° C, average molecular weight 1000-4000, epoxy equivalent 80
The following formula is added to 100 parts by weight of the epoxy resin of 0 to 4000.

[0008]

Embedded image

A thermosetting epoxy powder for metal pipes, characterized by blending a curing agent of a modified adduct compound of hexamethylene diisocyanate of 2-methyl-imidazole in the range of 0.1 to 20 parts by weight. Paint 2,
A melting point of 90 is applied to the inner and / or outer surface of the preheated metal tube.
To 140 ° C., 100 parts by weight of an epoxy resin having an average molecular weight of 1,000 to 4,000 and an epoxy equivalent of 800 to 4,000, a curing agent of a hexamethylene diisocyanate modified adduct compound of 2-methyl-imidazole represented by the formula described in the above item 1 is added. Coated on the inner surface and / or outer surface of the coated metal tube, characterized by being obtained by applying a thermosetting epoxy powder coating for metal tube mixed in the range of 1 to 20 parts by weight. , Melting point 90-140 ° C, average molecular weight 10
100 to 400 parts by weight of an epoxy resin having an epoxy equivalent of 800 to 4000 and 0.1 to 20 parts by weight of a curing agent of a hexamethylene diisocyanate-modified adduct compound of 2-methyl-imidazole represented by the above formula 1 The present invention relates to a coated metal pipe characterized in that a thermosetting epoxy powder coating for a metal pipe mixed in a range is powder-coated and then heated to coat the coating.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The epoxy resin used in the powder coating of the present invention has a melting point of 90 to 140 ° C., preferably 95 to 13 ° C.
5 ° C, average molecular weight of 1,000 to 4,000, preferably 12
It is a thing of 00-3000, an epoxy equivalent of 800-4000, preferably 850-3000. When the melting point is less than 90 ° C., stringiness is caused by powder coating by preheating, so that the smoothness of the coating film is deteriorated, and the molten powder coating material is easily accumulated at the tip of the powder coating gun. The smoothness of the coating film is worsened by being painted,
When the temperature exceeds 140 ° C., the coating material is cured before it melts and flows, and the smoothness of the coating film deteriorates. If the average molecular weight is less than 1,000, the melt viscosity is too low to suppress foaming, while if it is more than 4000, the coating is cured before it melts and flows, so that the smoothness of the coating film deteriorates. If the epoxy equivalent is less than 800, unreacted epoxy groups increase, which is unfavorable in terms of water quality. On the other hand, if it exceeds 4000, the curability of the coating film deteriorates.

As the epoxy resin, conventionally known epoxy resins such as a bisphenol-epichlorohydrin type epoxy resin, an alicyclic epoxy resin, a novolak type epoxy resin and an acrylic epoxy resin can be used. It is particularly preferable to use a bisphenol-epichlorohydrin type epoxy resin from the viewpoints of workability, corrosion resistance, and water pollution resistance. As specific examples of bisphenol-epichlorohydrin type epoxy resin, as a trade name, for example, Epicoat 1004,
Same as left 1007 (above, manufactured by Yuka Shell Epoxy Co., Ltd.), Araldite 6084, same left 6097, same left 60
99 (above, manufactured by Ciba Geigy Corporation), DER-664,
Bisphenol-epichlorohydrin type epoxy resins such as 667 (manufactured by Dow Chemical Company) on the left.

The curing agent used in the powder coating of the present invention is a hexamethylenediisocyanate-modified adduct compound of 2-methyl-imidazole represented by the above formula.

The mixing ratio of the curing agent is 10
The range is preferably 0.01 to 20 parts by weight, more preferably 0.1 to 15 parts by weight, per 0 parts by weight. If the compounding ratio is less than 3 parts by weight, the water resistance, corrosion resistance, workability, etc. decrease, while if it exceeds about 20 parts by weight, the appearance of the coating film deteriorates, which is not preferable.

The powder coating composition of the present invention may further contain other additives such as a coloring agent, a filler, a fluidity-controlling agent, an anti-cissing agent and an anti-dripping agent, if necessary.

The powder coating composition of the present invention is prepared by dry-mixing an epoxy resin, an imidazoline-based curing agent and, if necessary, other additives with a disperser such as a Henschel mixer.
It can be produced by melt-kneading with a disperser such as a shaft extruder, followed by cooling, coarse pulverization, fine pulverization, and filtration (usually 100 mesh).

The powder coating of the present invention can form a coating film by powder coating a metal tube to be coated and baking (for example, at a temperature of about 120 ° C. or higher). As the pipe to be coated, for example, a water pipe, a water pipe of an apartment house,
Cast iron pipes such as hot water pipes and cold and hot water pipes, metal pipes such as zinc-coated pipes, and pipes obtained by subjecting these to surface treatment can be used. As the metal tube, generally used 15 to
Those having a diameter of 60 mm can be used. The pipe to be coated may be a new pipe or an existing pipe (for rehabilitation pipe). In the case of existing pipes, if there is any rust or old coating adhered to the inner surface of the pipe before painting, this may be removed, and pretreatment such as surface treatment may be performed if necessary. it can. The powder coating can be performed by a powder coating method known per se, for example, a coating method such as electrostatic powder coating, triboelectric powder coating, uncharged powder coating, and fluid immersion. The coating thickness is not particularly limited, but is about 30 μm.
A range of m to 1 mm, preferably about 50 μm to 500 μm is suitable.

The metal pipe of the present invention relates to a coated metal pipe obtained by coating the inner and outer surfaces of a preheated metal pipe with the above-mentioned coating film of the thermosetting epoxy powder coating for a metal pipe. The preheating is performed to adhere an appropriate amount of the powder coating to the inner surface of the tube and to cure the coating. Heating is
Usually, about 150-300 ° C, especially about 180-250 ° C, is preferred. Powder coating methods suitable for this method include, for example, electrostatic powder coating, triboelectric powder coating, and uncharged powder coating. The coating thickness is about 100-500μ
m, preferably about 200 to 400 μm. After the powder coating, a cured coating film can be formed by cooling.

Further, the metal pipe of the present invention is obtained by applying the above-mentioned thermosetting epoxy powder coating for metal pipe to the inner and outer surfaces of the metal pipe, and then coating the coating by heating. The present invention relates to a coated metal tube. The heating is usually performed at a raw material temperature of about 150 to 300C, preferably about 160 to 250C. The heating time is usually about 5 to 60 minutes, particularly about 1 to 60 minutes.
0 to 40 minutes is preferred. Examples of the powder coating method include electrostatic powder coating and triboelectric powder coating. The coating thickness is about 100-500 μm, preferably about 2
It is 00 to 400 μm.

[0019]

Next, the present invention will be described in more detail with reference to examples.

Example 1 Epicoat 1004 (manufactured by Yuka Shell Epoxy Co., Ltd.)
Trade name, bisphenol A / epichlorohydrin, epoxy equivalent 875-1025, molecular weight 1400, melting point 97
~ 103 ° C) 1000g

[0021]

(Equation 3)

4 g, titanium dioxide pigment 300 g, sedimentable barium sulfate 200 g, and carbon black pigment 3
g were mixed and dry-dispersed and mixed with a Henschel mixer, and then melt-mixed and dispersed biaxially. After cooling, coarse pulverization, fine pulverization and filtration (150 mesh) were performed to obtain a powder coating material of Example 1.

Embodiment 2 In the embodiment 1, instead of the epicoat 1004,
1004 and Epicoat 1007 (product name, manufactured by Yuka Shell Epoxy Co., Ltd., trade name, bisphenol A / epichlorohydrin, epoxy equivalent 2000 to 2500, molecular weight 2900, melting point 127 to 133 ° C.). A powder coating of Example 2 was obtained in the same manner as in Example 1 except for using the same.

Example 3 HMDI of 2-methyl-imidazole in Example 1
A powder coating of Example 3 was obtained in the same manner as in Example 1, except that 2 g of the modified adduct compound was used.

Example 4 A powder coating material of Example 4 was obtained in the same manner as in Example 1 except that 50 g of the curing agent was used.

Comparative Example 1 A powder coating material of Comparative Example 1 was obtained in the same manner as in Example 1, except that 50 g of 2-phenyl-2-imidazoline was used as a curing agent.

Comparative Example 2 A powder coating material of Comparative Example 2 was obtained in the same manner as in Example 1, except that 70 g of 2-methyl-imidazole was used as a curing agent.

Comparative Example 3 Comparative Example 3 was carried out in the same manner as in Example 1 except that 50 g of adipic dihydrazide was used as a curing agent.
Powder coating was obtained.

Table 1 shows the results of Examples and Comparative Examples.

[0030]

[Table 1] Table 1

In Table 1, performance tests of paints and coatings were conducted by the following methods. Powder paint storage stability: After the powder paint is stored at 40 ° C. for 30 days, the gel time (second) at 140 ° C. is measured, the gel time value after storage is divided by the initial gel time value, and the rate of change Was examined. ○ is 100 ~
At 70%, the solid phase reaction hardly progressed and the smoothness did not change and was good, and for Δ, 69 to 39%, the solid phase reaction partially progressed and a slight decrease in the smoothness was observed. The solid phase reaction is completely progressing, and the smoothness is significantly reduced (appearance of coating film, grid adhesion, salt spray resistance, moisture resistance, water quality) Adjustment of test coating tube: hot coating (preheating) A cast iron pipe (for water pipe) having a diameter of 150 mm and a length of 1 m was placed in a hot air circulating heating furnace and a surface temperature of 20 mm;
Heated to 0 ° C. Next, the cast iron tube is taken out of the heating furnace, and before the cast iron tube is cooled, the above-mentioned powder coating is applied to the inner and outer surfaces of the cast iron tube by an electrostatic powder coating machine so that the film thickness becomes 300 μm. I got

Cold coating (post-heating): The above powder coating is electrostatically applied to the inner and outer surfaces of a cast iron pipe (for water pipe) having the same size as above using an electrostatic powder coating machine so that the film thickness becomes 300 μm. Powder coating, then put in a hot air circulation heating furnace, surface temperature 200
The coated tube was obtained by heating at 30 ° C. for 30 minutes.

After the coated tube obtained by the hot coating and the cold coating is cut in the longitudinal direction, the coating applied to the inner and outer surfaces of the tube is coated with the following coating film appearance, grid adhesion, salt spray resistance. sex,
Tests of moisture resistance and water quality (potassium permanganate consumption, residual chlorine reduction) were performed.

Appearance of coating film Smoothness: Yuzu skin on the coating film surface was visually observed.は is good without yuzu skin, Δ is slightly inferior yuzu skin, and x is inferior.

Pinhole: The pinhole on the surface of the coating film was visually observed.は indicates no pinhole, △ indicates pinhole, and × indicates very many pinholes.

Bubble state inside the coating film: Bubbling inside the coating film was visually observed.は indicates no foaming, 発 泡 indicates foaming, and × indicates very foaming.

Bubbling state at boundary: Bubbling at the boundary between the coating film and the material was visually observed. ○ means no foaming, △
Indicates that foaming is observed, and X indicates that foaming is observed very frequently.

Salt spray test: A 240-hour test was conducted according to JIS K-5400. The degree of rust and blistering of the test piece was evaluated. ○ indicates no rust or swelling, Δ indicates slight rust or swelling, and X indicates remarkably inferior rust or swelling.

Hot water resistance test: The test piece was immersed in warm water at 40 ° C. for one month. The degree of rust and blistering of the test piece was evaluated. ○ indicates no rust or swelling, Δ indicates slight rust or swelling, and X indicates remarkably inferior rust or swelling.

Water quality test KMnO4 consumption: JWWA (Japan Water Works Association, hereinafter
Similar meaning) It measured according to the standard of K-135.
The unit is ppm.

Residual chlorine loss: Measured according to the standard of JWWA K-135. The unit is ppm.

(Erichsen value, impact resistance) Adjustment of test coated plate: width 70 mm x length 150 mm x thickness 0.8 mm
The above powder coating is applied to a cast iron plate having a size of 300 μm by an electrostatic powder coating machine so that the film thickness becomes 300 μm, and then placed in a hot air circulation heating furnace at a surface temperature of 200 ° C. for 20 minutes. To obtain a coated plate. The coated plate obtained above was subjected to the following impact test and Erichsen processing test.

Erichsen value: JIS K-5400
Performed according to 8.2. The unit is cm.

Impact test: JIS K-5400
Performed according to 3. Using a DuPont impact tester,
The test was carried out under the conditions of a shooting center 1/2 inch and a weight of 500 g. The falling distance (cm) without cracking and peeling was shown.

[0045]

The powder coating composition of the present invention uses a 2-methyl-imidazole hexamethylene diisocyanate-modified adduct compound represented by the above formula as a curing agent for an epoxy resin. A coating film free of bubbles and free of bubbles at the interface between the metal tube material and the powder coating film can be formed, and at the same time, has an excellent storage effect.

Claims (3)

[Claims] 1. Melting point: 90-140 ° C., average molecular weight: 1000
To 4000, and 100 parts by weight of an epoxy resin having an epoxy equivalent of 800 to 4000 are represented by the following formula: The curing agent for the modified adduct compound of hexamethylene diisocyanate of 2-methyl-imidazole represented by
A thermosetting epoxy powder coating for metal pipes, which is blended in an amount of from 20 to 20 parts by weight. 2. A preheated metal tube having an inner surface and / or an outer surface having a melting point of 90 to 140 ° C. and an average molecular weight of 1,000 to 400.
0, epoxy resin 10 having an epoxy equivalent of 800 to 4000
0-part by weight of 2-methyl- represented by the formula according to claim 1.
A coated metal material obtained by applying a thermosetting epoxy powder coating material for metal pipes obtained by mixing a curing agent of a hexamethylene diisocyanate modified adduct compound of imidazole in a range of 0.1 to 20 parts by weight. tube. 3. A metal pipe having an inner surface and / or an outer surface having a melting point of 9.
A curing agent for a modified 2-methyl-imidazole hexamethylene diisocyanate adduct compound represented by the formula of claim 1 is added to 100 parts by weight of an epoxy resin having a temperature of 0 to 140 ° C., an average molecular weight of 1,000 to 4,000, and an epoxy equivalent of 800 to 4,000. A coated metal pipe obtained by powder coating a thermosetting epoxy powder coating for metal pipe mixed in a range of 1 to 20 parts by weight, and then heating to coat the coating.