JP2002045780A - Powder coating method by preheating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder paint coating method generating no stringing phenomenon even if a powder paint is thickly applied to a preheated article to be coated. SOLUTION: The article to be coated is preheated to 120-250 deg.C and the powder paint is applied to the preheated article so that the thickness of a coating film becomes 150-1,000 μm. At this time, coating is performed by a friction charge type coating machine.

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 by preheating, and more particularly to a powder coating method in which a powder coating during coating does not cause a stringing phenomenon.

[0002]

2. Description of the Related Art Powder coatings are advantageous in environmental measures because they do not contaminate organic solvents, and have the major feature that a thick film can be formed by a single coating. Therefore, vending machines installed outdoors and air conditioners outdoors It has been used for coating of coating materials, such as machines, building exteriors and building structures such as steel pipes, shaped steel, reinforcing bars, steel wires, etc., which emphasize corrosion resistance and weather resistance, and have demonstrated their performance.

[0003] For example, 150 μm
To obtain a thicker film or more, a general method is to preheat the object to be coated in advance, and to secure the film thickness while melting the powder coating with the heat.

In this case, when the powder coating is applied by a conventionally used corona discharge type electrostatic coating machine, the powder coating melts between the object to be coated and the tip of the coating gun to form a thread ( Hereinafter, this phenomenon will be referred to as “stringing phenomenon”. Then, the powder coating melted in the form of a thread adheres to the tip of the coating gun and disturbs the coating pattern to cause poor coating such as poor smoothness. In addition, if mixed with the recovered paint, the filter for removing foreign matter is clogged, and the reflux to the paint supply tank may not be performed smoothly.

[0005] In order to improve the stringing phenomenon, for example, in Japanese Patent No. 2657384, a specific amount of anhydrous fine silica powder is added to an epoxy powder coating material.
However, in thick coating using a powder composition other than such a specific composition, that is, using a general powder coating, the preheating temperature and the coating voltage are reduced, but the stringing phenomenon is still completely eliminated. unknown.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of coating a powder coating material which does not cause a stringing phenomenon even when a preheated coating material is applied thickly.

[0007]

According to a powder coating method of the present invention, a coating object is preliminarily heated and a powder coating is coated on the coating object. Is what you do. The temperature of the object to be coated at the time of coating by preheating is preferably from 120 to 250 ° C. If the coating film thickness on the object to be coated is in the range of from 150 to 1000 μm, the coating can be sufficiently performed without causing a stringing phenomenon. is there.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail. According to the analysis of the present inventors, the cause of the stringing phenomenon is that an electrostatic electric field generated when a corona discharge type electrostatic coating machine is used for painting is particularly strong at a corner portion or a projection portion of an object to be coated. Become. For this reason, the powder coating concentrates and adheres to these portions, and the raised coating is melted by the heat of the preheating, and scattered into a thin thread by the air at the time of coating. If the air flow is circulating, the blown-out thread-like substance may return to the object to be coated again, accumulate between the coating gun and the object to be coated, and become cotton-like.

However, if a triboelectric coating machine is used, the stringing phenomenon does not occur. The reason is that in the case of the triboelectric charging method, since the above-mentioned electrostatic electric field is not generated, the powder coating is uniformly coated on the object to be coated. In other words, since the paint does not gather at the corners and the protrusions and does not rise, even if the powder coating melts, the stringing phenomenon does not occur due to the air.

[0010] The triboelectric coating machine used in the method of the present invention is also called a triboelectric coating machine or a tribomatic coating machine. When powder paint is conveyed inside the coating gun by air, the charging inside the gun is stopped. Is charged by friction while passing through a tube or the like, and the charged powder coating material is applied to an object to be coated. The coating conditions of the triboelectric coating machine are not particularly limited, and a normally used booth air volume, a distance between objects to be coated, and a coating gun current can be adopted.

In the method of the present invention, the powder coating used is not particularly limited, and may be an epoxy resin, an acrylic resin,
Examples include powder coatings made of polyesters, epoxy polyesters, and copolymers or mixtures of these resins. In the case of an acrylic resin or the like which is hardly triboelectrically charged due to the properties of the resin, a charge control agent can be added. Among these resin systems, epoxy resin systems are most suitable for use in the present method because of their good triboelectric charging.

The object to be coated by the method of the present invention is not particularly limited, but the temperature of the object to be coated during preheating is kept in the range of 120 to 250 ° C. Is in the range of 150 to 1000 μm. Examples of such a material to be coated include untreated steel, iron such as zinc steel, metal such as aluminum, copper and alloys thereof, and, as the shape of the material to be coated, a steel pipe, a cast iron pipe, Shaped steel, rebar, steel wire and the like can be mentioned. The preheating of the object to be coated is usually performed by induction heating or heating by a gas furnace. In this case, it is necessary to perform the preheating within a range where the temperature of the object to be coated can be maintained in consideration of the heat storage amount depending on the shape and thickness of the object and the interval from the preheating to the coating. Generally, the temperature is often set to be higher by about 10 to 30 ° C. than the temperature at the time of coating.

[0013]

Next, the present invention will be described more specifically with reference to examples and comparative examples. Example 1 An SS400 black scale steel plate (length 150 mm, width 70 mm and thickness 3.2 mm) was used as an object to be coated.
The two test pieces preheated to 40 ° C. were subjected to powder coating at 3 to 5 μA using a triboelectric coating machine (“The Friction SFC-QTR”, manufactured by Matsuo Sangyo Co., Ltd.). The booth used for painting is 1.2m high, 1.5m wide and 1.2m deep.

The powder coating is an epoxy resin powder coating ("Powax E200 Gray", manufactured by Nippon Paint Co., Ltd.) 50
g, and the distance from the coating gun to the object to be coated is 20
0 mm. Also, at a distance of 1 m behind the object,
A grid-like wire mesh having a size of 00 × 600 mm in width, a wire diameter of 3 mmφ, and an interval of 50 mm was placed, and the weight of the thread paint adhered to the wire mesh was measured. Table 1 shows the results.

[0015]

[Table 1]

Examples 2 and 3, Comparative Examples 1 and 2, Examples 2 and 3 were carried out in the same manner as in Example 1 except that the type of the triboelectric coating machine was changed. As a comparative example, two types of corona discharge type electrostatic coating machines were prepared, and a voltage of -70 was used.
Coating was performed in the same manner as in Example 1 under the KV conditions. Table 1 shows the results.

As is apparent from the above results, in the coating of this embodiment using the triboelectric coating machine, the preheating 20
No stringing occurred at both 0 ° C and 240 ° C. On the other hand, when the corona discharge type electrostatic coating machine of the comparative example was used, a large amount of stringing material was generated, and it was found that the amount increased further when the preheating temperature of the object to be coated was increased.

[0018]

According to the powder coating method of the present invention, since a triboelectric coating machine is used, even if the object to be coated is preheated, a stringing phenomenon does not occur during coating. Therefore, it is possible to increase the coating film thickness by one coating, and it is possible to increase the coating efficiency. According to the coating method of the present invention, since it is possible to easily secure a thick film, steel pipes, building steel, reinforcing bars, steel wires and the like, such as building structures, coating of the object to be coated with emphasis on corrosion resistance and weather resistance. Optimal.

Claims (3)

[Claims] 1. A method of preheating an object to be coated and coating a powder coating on the object to be coated, wherein the coating is performed by a triboelectric coating machine. Method. 2. A powder coating method according to claim 1, wherein the temperature of the object to be coated at the time of coating by preheating is 120 to 250 ° C. 3. The coating thickness on the object to be coated is 150 to 100.
The powder coating method according to claim 1, wherein the thickness is 0 μm.