JP2002233819A - Powder coating method of steel and powder coated steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder coating method of steel, by which weather resistance is given to the outside surface of the steel such as a steel pipe, a cast iron pipe, a reinforcing bar, a PC steel wire or the like, the brightness of the coating film is kept even if being exposed by the sun and the striping of the coating film is not generated, and the powder coated steel. SOLUTION: The coating method of the steel is performed by pre-heating the steel, applying an epoxy powder paint and an acryl powder paint on the outside surface of the steel in this order while the surface of the steel is kept at 160-300 deg.C and curing the coating films of both powder paints. Or the powder coating method of the steel is performed by pre-heating the steel, applying the epoxy powder paint on the outside surface of the steel while the surface of the steel is kept at 160-300 deg.C and after curing the coating film, applying the acryl powder paint and curing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating method and a powder coated steel material having excellent weather resistance and corrosion resistance and high coating film adhesion.

[0002]

2. Description of the Related Art Steel materials such as steel pipes, cast iron pipes, and reinforcing steels are generally formed with a coating film of an epoxy powder coating for the purpose of imparting corrosion resistance. In this method of forming an epoxy coating film, a steel material is preheated, an epoxy powder coating material is applied before the steel material is cooled, and is melted and solidified.

[0003] It has been considered that weather resistance is not required because the above steel materials are usually buried in soil or buried in concrete. However, steel materials stored in a material storage area exposed to sunlight or rain and wind have a problem in that the epoxy coating film deteriorates before construction, and in particular, the parts exposed to sunlight have reduced gloss and reduced commercial value.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a steel pipe, a cast iron pipe, a reinforcing steel bar, a PC steel wire or the like having weather resistance on an outer surface thereof, and to maintain a coating film gloss even when exposed to sunlight. It is another object of the present invention to provide a powder coating method and a powder coated steel material for a steel material that can be performed and that does not cause peeling of the coating film.

[0005]

According to the powder coating method for steel material of the present invention, the steel material is preheated, and the surface temperature of the steel material is 160 ° C.
An epoxy powder coating and an acrylic powder coating are applied on the outer surface of the steel material in this order while the temperature is up to 300 ° C., and the coating films of both coatings are cured. That is, the epoxy paint and the acrylic powder paint are applied at a high temperature. In another powder coating method of the present invention, a steel material is preheated and an epoxy powder coating is applied to an outer surface of the steel material while the surface temperature of the steel material is 160 ° C to 300 ° C. After the film is cured, an acrylic powder coating is applied and cured. That is, the epoxy paint is applied at a high temperature, but there is no limit to the coating temperature of the acrylic powder paint.
The temperature may be 0 ° C. or lower.

Examples of the outer surface of the steel material include an outer surface of a steel pipe, an outer surface of a cast iron tube, an outer surface of a reinforcing steel bar, and an outer surface of a PC steel wire.
It is preferable that the acrylic powder paint is applied so as to have a coating thickness of 20 to 100 μm. Further, it is preferable to use an epoxy powder coating material having a gel time of 90 seconds or less (including 90 seconds) at 200 ° C., and an acrylic material having a gel time of 90 seconds or less (including 90 seconds) at 200 ° C. It is also preferred to use powder coatings.

The powder-coated steel material of the present invention is manufactured by any one of the above-mentioned powder coating methods for steel materials.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the powder coating method for a steel material according to the present invention, the steel material is preheated, and an epoxy powder coating is applied to the outer surface of the steel material while the surface temperature of the steel material is 160 ° C. to 300 ° C. And
Next, an acrylic powder coating is applied again. This acrylic coating may be applied within the above-mentioned preheating temperature range, or may be applied separately after the steel material cools, for example, several days later.

As the powder coating method for steel materials, any general method used for powder coating, such as an electrostatic coating method, an electrostatic fluid immersion method, and a fluid immersion method, can be employed. Now, the coating method of the present invention will be described using an electrostatic coating method as an example. 160 ° C. to 300 ° C. to perform electrostatic powder coating
C., preferably 180 to 230.degree. C. After the steel material is grounded, it is performed by spraying the powder coating material on the steel material using a powder coating gun such as a corona charging type coating gun and a friction charging type coating gun. .

When a corona charging type coating gun is used, the charging voltage applied to the powder coating by corona discharge treatment is preferably -30 to -100 kV, and more preferably -50 to -70 kV from the viewpoint of coating efficiency and appearance. Set to. On the other hand, when a triboelectric coating gun is used, the internally generated current value of the powder coating is 1.0 to 1.0 from the viewpoint of coating efficiency and appearance.
It is preferable to perform a triboelectric charging treatment so as to obtain 8.0 μA.

The preferable discharge rate of each of the above coating guns is 50 to 400 g / min, and the discharge pressure is 4.9 × 10 ⁴ to
It is 4.9 × 10 ⁵ Pa. Further, the distance from the tip of the coating gun to the steel material is preferably 10 to 50 cm. By coating in these ranges, the particles in the powder coating are electrostatically adhered to the steel material with good coating efficiency and the uncured A powder coating layer can be formed.

Since the epoxy resin coated on the preheated steel material starts to melt and flow, it is preferable to use one having a gelation time of less than 90 seconds at 200 ° C., and more preferably 15 to 50 seconds. If the gelling time at 200 ° C. exceeds 90 seconds, it becomes difficult to harden the steel material only by heat storage. The film thickness (set film thickness) after baking is 50 to secure corrosion resistance.
It is preferably from 200 to 200 μm, more preferably from 100 to 150 μm.

An acrylic powder coating is applied over the epoxy powder coating applied by the above method. If the acrylic powder coating is applied while the steel material is at a high temperature following the application of the epoxy powder coating, there is an advantage that the baking step after the coating can be omitted. However, after applying the epoxy powder paint,
Even if the acrylic powder coating is repeatedly applied for a considerable period of time, for example, several hours to several months, the weather resistance, corrosion resistance and coating film adhesion do not decrease.

When the acrylic powder coating is applied to a preheated steel material, if the gelation time is too long, it may be difficult to obtain a coating film having an average thickness by flowing. In addition, even when a cold epoxy coating film is applied on a formed steel material, it may be difficult to obtain a coating film having an average thickness as well as insufficient fluidity control. Therefore, similarly to the above-mentioned epoxy powder coating, at 200 ° C within 90 seconds, furthermore, 15 to 50
Those having a gel time of 2 seconds are preferred. The coating thickness (set film thickness) after baking is 20 to ensure weather resistance.
It is preferably from 100 to 100 μm, more preferably from 30 to 50 μm.

The powder coating used in the present invention comprises a base resin, a curing agent and a pigment as main components. The base resin for the epoxy powder coating includes a glycidyl ester resin,
Glycidyl ether resin which is a condensate of bisphenol A or bisphenol F and epichlorohydrin, alicyclic epoxy resin, aliphatic epoxy resin, bromine-containing epoxy resin, phenol novolak type epoxy resin, cresol novolak epoxy resin, etc. And a compound containing two or more oxirane groups.

The base resin for the acrylic powder coating includes (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, and n- (meth) acrylate.
-Butyl, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, glycidyl (meth)
Examples thereof include those obtained by copolymerizing (meth) acrylic monomers such as acrylate and 2-methylglycidyl (meth) acrylate with styrene and other radically polymerizable monomers.

The base resin can be appropriately blended with another resin and used as, for example, a polyester / epoxy resin or an acrylic / epoxy resin. Examples of polyester resins used for polyester / epoxy resins include polyhydric alcohols such as ethylene glycol, diethylene glycol, propanediol, pentanediol, hexanediol, neopentyl glycol, trimethylolpropane, and pentaerythritol, and maleic acid and terephthalic acid. And those obtained by ester polymerization of a carboxylic acid such as isophthalic acid, succinic acid, glutamic acid, adipic acid, sebacic acid and β-oxypropionic acid or a carboxylic anhydride.

Examples of the curing agent include blocked polyisocyanate compounds such as alicyclic polyisocyanates blocked with ε-caprolactam, uretdione-type polyisocyanate compounds, aliphatic polycarboxylic acids such as sebacic acid, and aminoplasts. Resins, aliphatic acid anhydrides, amine compounds, polyamide resins, imidazole compounds, imidazoline compounds, phenolic resins, epoxy resins, other, triglycidyl isocyanate, triglycidyl isocyanurate, dicyandiamide, hydroxyalkyl Amides and glycoluril can be mentioned, and these curing agents can be appropriately selected according to the functional group of the base resin used.

The mass ratio of the base resin to the curing agent in the powder coating component is from 60:40 to 96:
A range of 4 is preferred. In addition, the base resin and the curing agent,
It is also preferable to use a mixture of two or more types. Further, from the viewpoint of the concealability of the coating film and the physical properties of the coating film, the total amount of the base resin and the curing agent is preferably from 40 to 95 parts by mass in 100 parts by mass of the powder coating component.

The pigment in the above powder coating is powder coating component 1
It is preferable to occupy 5 to 60 parts by mass in 00 parts by mass. When the amount of the pigment is less than 5 parts by mass, the concealing property of the coating film is inferior.
If the amount is more than 10 parts by mass, the bending property of the coating film and the smoothness of the coating film may decrease. Examples of pigments include aluminum flakes, interference mica, various glittering pigments such as colored mica, titanium dioxide, red iron oxide, yellow iron oxide, carbon black, phthalocyanine blue, phthalocyanine green,
Examples include coloring pigments such as quinacridone pigments and azo pigments, extenders such as talc, silica, calcium carbonate, and precipitated barium sulfate, and other rust-preventive pigments.

Further, various additives can be added to the powder coating as required. Examples of such additives include silicones such as dimethylsilicone and methylsilicone and surface modifiers such as acrylic oligomers, foam inhibitors such as benzoin and benzoin derivatives, anti-bake agents, curing catalysts, curing accelerators, plasticizers and the like. Agents, antistatic agents, charge control agents such as particulate aluminum oxide, ultraviolet absorbers, light stabilizers, antioxidants, pigment dispersants, flame retardants,
Fluidity-imparting agents can be mentioned.

In order to produce a powder coating, the above-mentioned powder coating components are dry-blended, and then kneaded while heating and melting the coating raw material mixture using an extruder. I do. After further pulverizing the coarsely pulverized particles thus obtained, fine particles and coarse particles are removed by using a classifier, whereby a powder coating having a predetermined particle size distribution can be produced.

The powder coating produced by the above production method preferably has a volume average particle size of 10 to 50 μm, more preferably 20 to 40 μm.
The volume average particle diameter can be determined by a particle diameter measuring device using a laser light scattering method generally used in the field of powder coatings. When the volume average particle size is less than 10 μm, the coating production process may be complicated, and the efficiency of applying the powder coating to an object to be coated may decrease. On the other hand, the volume average particle diameter is 50 μm
If it exceeds, uneven coating is noticeable when the film thickness is thin,
The concealability of the coating film and the smoothness of the coating film may be reduced.

[0025]

Next, the present invention will be described more specifically with reference to examples and comparative examples. In addition, the compounding amount represents a mass part unless there is particular notice. In addition, the names of raw materials, paints, and devices represent trade names unless otherwise specified.

Example 1 [Preparation of Epoxy Powder Coating] 68 parts of bisphenol A type epoxy resin ("Epototo YD014", manufactured by Toto Kasei Co., Ltd.), 10 parts of phenolic curing agent ("Epicure-17")
1 ", Yuka Shell Epoxy Co., Ltd.), carbon black 1
("MA100", manufactured by Mitsubishi Chemical Corporation) and 21 parts of calcium carbonate ("Supermixer", manufactured by Nippon Spindle Co., Ltd.) for about 3 minutes to obtain a mixture. Next, the mixture was melt-kneaded at about 100 ° C., cooled to room temperature, coarsely pulverized by a pulverizer (“Atomizer”, manufactured by Fuji Paudal Co.), and further finely pulverized by a jet mill (“IDS- Type 2 ", manufactured by Nippon Pneumatic Industries)
And finely pulverized.

The powder thus obtained is subjected to an airflow classifier (“D
(S-2 type, manufactured by Nippon Pneumatic Industries Ltd.) to remove fine particles and coarse particles. The obtained epoxy powder coating material had a volume average particle diameter of 35 μm and a gelation time of 25 seconds / 200 ° C. The volume average particle size is
Particle size analyzer (“Microtrack HRAX-100”,
The gelation time was measured using a gelling tester (manufactured by Nissin Kagaku Co., Ltd.) and the hot plate of the tester was set at 200 ° C., and about 0.2 g of the paint was applied to the hotplate. The paint was lifted gently while stirring it with a Teflon (registered trademark) pencil-shaped rod while stirring, and the end point was defined as the point at which the stringing state due to melting between the hot plate and the Teflon rod disappeared during this operation. The time from the start point to the end point was defined as the gelation time from the time when the paint was placed.

[Preparation of Acrylic Powder Coating] 68 parts of glycidyl methacrylate-modified acrylic resin (“FINEDIC A207S”, manufactured by Dainippon Ink and Chemicals, Inc.)
12 parts of 10-decanedicarboxylic acid, 3 parts of bisphenol A type epoxy resin ("Epototo YD014", manufactured by Toto Kasei Co., Ltd.), 1 part of defoamer (benzoin), 1 part of flow modifier ("Leveler P", Nippon Paint Co., Ltd.) ), 1 part of carbon black ("MA100", manufactured by Mitsubishi Chemical Corporation), and 14 parts of calcium carbonate, and an acrylic powder coating was prepared in the same manner as the above epoxy powder coating. The obtained powder coating has a volume average particle size of 35 μm and a gel time of 45 μm.
Sec / 200 ° C.

[Coating Method] A 16 mm thick 100 mm × 100 mm mild steel plate (SS400) was subjected to sandblasting as a test piece, and the surface was treated so that the surface roughness became 10 to 30 μm in Ra. Next, the test piece was heated to 200 ° C., and placed on a grounded conductive horizontal belt conveyor so that its plane was perpendicular to the coating direction,
The coating gun was set so that the distance from the tip of the gun head of the corona charged coating gun (“PG-1”, manufactured by GEMA) to the test piece was 15 cm, and the coating gun applied voltage was −60.
The epoxy powder paint prepared above was applied at a kV of 80 to 100 μm in film thickness.

Then, in the same coating method, the acrylic powder paint prepared as described above was superimposed on the epoxy powder paint to a thickness of 30 μm.
Painted at ４０40 μm. At this time, the interval from the end of epoxy powder coating to the start of acrylic powder coating is 5 seconds,
The test piece temperature at the end of the acrylic powder coating was 180 ° C. Thereafter, the coating film was cured by standing to cool. The test piece was evaluated as follows, and the results are shown in Table 1. <Accelerated weather resistance test> Dew cycle sunshine weather ometer ("WEL-Sunshine-DC",
(Suga Test Machine Co., Ltd.), and observe the coating film after the lapse of 1000 hours. The gloss retention% before and after the test and the color difference ΔE
Was evaluated. <Salt spray test> Cross-cut the coating surface of the test piece.
A salt spray test was performed according to IS Z-2371. <Adhesion test> The adhesion of the coating film was tested by a grid tape method based on JIS K-5400. First, the test piece is immersed in boiling water for 8 hours, and then 25 squares of 1 mm × 1 mm are cut on the coating surface with a cutter knife. Next, a transparent adhesive tape is stuck on the grid and peeled off vertically. At this time, the number of grids where the coating film remains is counted.

Examples 2 to 6 and Comparative Examples 1 to 3 The conditions of Example 1 (coating thickness of epoxy powder coating and acrylic powder coating, gel time, preheating temperature of test specimen,
Coating interval of both powder coatings and presence or absence of post-heating)
, And various test pieces were prepared and evaluated. Table 1 shows these conditions and evaluation contents.

[0032]

[Table 1]

As is clear from the results shown in Table 1, the coated mild steel sheets formed in the examples had a gloss retention of 9%.
The color difference ΔE was 3% or more, and the color difference ΔE was 0.5 or less, and the weather resistance was excellent. In addition, the peeling by the salt spray test was as small as 0 to 1 mm, and the corrosion resistance was sufficient. Further, in the cross-cut adhesion test, there was no peeling of the coating film (25/25) and the adhesion was excellent.

[0034]

According to the powder coating method for steel material of the present invention, an epoxy powder coating is applied, and then an acrylic powder coating is applied thereon, so that the corrosion resistance of the epoxy coating and the weather resistance of the acrylic coating are both obtained. A coated film can be formed. Further, by preheating the steel material to 160 ° C. to 300 ° C. and applying the epoxy powder coating, the adhesiveness with the acrylic coating film to be superimposed thereon is dramatically improved. Therefore, the powder-coated steel material of the present invention coated by the above method has excellent weather resistance, so that the coating does not fade and lose its luster even when stored in a material storage place or the like exposed to the outside air, and has anticorrosion properties. Because of its excellent coating film adhesion, it can be used as a coated steel in various fields such as painted steel pipe, painted cast iron pipe, painted rebar, painted PC steel wire, and the like.

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Claims (7)

[Claims] 1. A steel material is preheated, and the surface temperature of the steel material is 16
A powder coating method for a steel material, wherein an epoxy powder coating and an acrylic powder coating are applied to the outer surface of the steel material in this order while the temperature is 0 ° C to 300 ° C, and the coating films of the two coating materials are cured. 2. The steel material is preheated, and the surface temperature of the steel material is 160 ° C.
An epoxy powder coating is applied to the outer surface of the steel material while the temperature is up to 300 ° C., and an acrylic powder coating is applied after the coating film of the epoxy powder coating is cured, and then cured. Painting method. 3. The steel material outer surface is a steel tube outer surface, a cast iron tube outer surface,
The powder coating method for a steel material according to claim 1 or 2, wherein the steel material is an outer surface of a reinforcing bar. 4. An epoxy powder coating composition having a coating thickness of 50 to 2
The powder coating method for steel material according to any one of claims 1 to 3, wherein the coating is performed so as to have a thickness of 20 to 100 m, and the acrylic powder coating is applied so as to have a coating thickness of 20 to 100 m. 5. The powder coating method for steel according to claim 1, wherein an epoxy powder coating having a gel time of 90 seconds or less at 200 ° C. is used. 6. The powder coating method for a steel material according to claim 1, wherein an acrylic powder coating having a gel time of 90 seconds or less at 200 ° C. is used. 7. A powder-coated steel material produced by the method for powder-coating steel material according to any one of claims 1 to 6.