JPH05331656A - Coating method for polyolefin coated metallic pipe - Google Patents

Abstract

PURPOSE:To rapidly melt a powder adhesive polyolefin resin in a small space and to improve the adhesive power of a coating by incorporating two IR radiation heating stages of specific wavelengths into an extrusion coating line for the above-mentioned resin. CONSTITUTION:A metallic pipe 1 is subjected to a chemical conversion treatment of a chromic acid system in a stage 6 after a surface treatment and further, after the metallic pipe 1 is heated in a heating furnace 7, an adhesive primer is applied thereon in a stage 8 and powder adhesive polyolefin is applied thereon in a stage 9. The metallic pipe is extrusion coated with the polyolefin resin as the upper layer thereof by a device 12. The metallic pipe is heated by the IR radiation heater 20 having a peak at <=1mum wavelength and the IR radiation heater 11 having a peak at 2.0 to 4.5mu after the coating of the powder adhesive polyolefin, by which the melting of the powder adhesive polyolefin layer is accelerated in this coating method for the polyolefin coated metallic pipe.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for coating a polyolefin-coated metal tube.

[0002]

2. Description of the Related Art Among heavy-duty anticorrosion coatings for metal tubes, there is a polyolefin resin coating. Extrusion coating is one of the methods for coating a polyolefin resin. The coating method is such that a metal tube is subjected to a chromic acid conversion treatment after ground treatment such as grit blasting and shot blasting, and the metal tube is further heated, and then adhesiveness is improved. A primer and a powder adhesive polyolefin are sequentially laminated, and a polyolefin resin is extrusion-coated as an upper layer. Adhesion, which is one of the performances of the polyolefin resin coating, naturally depends on the performance of the adhesive primer, but also largely depends on the molten state of the powder adhesive polyolefin. As a method for improving the melting state of the powder adhesive polyolefin, a sufficient interval between the powder adhesive polyolefin coating and the extrusion coating is applied after the powder adhesive polyolefin coating, the powder adhesive polyolefin coating is heated by a hot air heater, and the powder adhesive is used. It may be considered that the coating is performed with an infrared heater after coating with the hydrophilic polyolefin. However, since the temperature of the metal tube during extrusion coating of the polyolefin resin becomes low and reheating is required, the problem that the powder adhesive polyolefin deteriorates and the space problem occurs in the continuous coating line is uniform and sufficient. It is considered that the most effective method is that it is difficult to obtain a sufficient temperature rise and that a space problem occurs in a continuous coating line. Although a method using an infrared heater or a method using a near infrared heater to heat and then a far infrared heater to melt and cure the powder coating is disclosed, the heating method shown in the method has a certain amount of space. This is possible, but it is not always optimal when it is desired to sufficiently melt the powder-adhesive polyolefin in a smaller space in a short time to improve the adhesion. There.

[0003]

In order to solve the above problems, the present invention provides a polyolefin resin by efficiently melting a powder adhesive polyolefin in a small space in a short time in a continuous extrusion line for polyolefin resin. The purpose is to improve the adhesion of the coating.

[0004]

Means for Solving the Problems The present inventors have studied from the two points of effect of heating an infrared heater and promoting an adhesion reaction by absorbing a powder-adhesive polyolefin. As a result, the powder-adhesive polyolefin is efficiently melted. The present invention has been made to accelerate the above-mentioned process and improve the adhesion of the polyolefin resin coating.

That is, according to the present invention, a metal tube is subjected to a chromic acid type chemical conversion treatment after ground treatment such as grit blast and shot blast, and the metal tube is further heated, and then an adhesive primer and a powder adhesive polyolefin are sequentially laminated. In the method for coating a polyolefin-coated metal tube in which a polyolefin resin is extrusion-coated as an upper layer, an infrared radiation heating device having a peak at a wavelength of 1 μm or less and a peak at 2.0 to 4.5 μm after coating a powder adhesive polyolefin. It is a method for coating a polyolefin-coated metal tube, which comprises sequentially or simultaneously heating the infrared radiation heating device.

The method for coating the polyolefin-coated metal tube according to the present invention will be specifically described below.

FIG. 1 is a diagram showing the coating structure of a polyolefin-coated metal tube. In the figure, 1 is a metal tube, 2 is a chemical conversion treatment layer, 3 is an adhesive primer layer, 4 is an adhesive polyolefin layer, and 5 is a polyolefin layer. A chromic acid-based chemical conversion treatment layer 2 is formed on the metal tube 1 after ground treatment such as grit blast and shot blast, and the metal tube 1 is further heated, and then an adhesive primer layer 3 is formed. Powder adhesive polyolefin is applied as the adhesive polyolefin layer 4 in a state where the adhesive primer layer 3 is cured or semi-cured. When the adhesive polyolefin layer 4 is in a molten or semi-molten state, a polyolefin resin is extrusion-coated to form a polyolefin layer 5. In the above coating method, if the melting of the adhesive polyolefin layer 4 is insufficient, at the interface between the adhesive polyolefin layer 4 and the polyolefin 5,
The polyolefin layer 5 is sufficiently melted and adheres due to heat at the time of extrusion coating, but the reactivity and wettability are insufficient at the interface between the adhesive polyolefin layer 4 and the adhesive primer layer 3, and sufficient adhesion is obtained. It cannot be obtained stably.

FIG. 2 schematically shows an example of the method for coating a polyolefin-coated metal pipe of the present invention. In the figure, 1 is a metal tube, 6 is a chemical conversion treatment step, 7 is a heating furnace, 8 is an adhesive primer coating step, 9 is a powder adhesive polyolefin coating step, and 10 is an infrared radiation heating device having a peak at a wavelength of 1 μm or less. , 11 is an infrared radiation heating device having a peak at 2.0 to 4.5 μm, and 12 is a polyolefin extrusion coating device.

In the present invention, after the powder adhesive polyolefin coating is applied, the infrared radiation heating device 10 having a peak at a wavelength of 1 μm or less, and the infrared radiation heating device 11 having a peak at a wavelength of 2.0 to 4.5 μm. Is used together to accelerate the melting of the powder adhesive polyolefin layer.

In the present invention, the infrared radiation heating device 10 having a peak at a wavelength of 1 μm or less mainly exhibits the heating effect of the metal tube 1. Therefore, when the thickness of the metal tube 1 is relatively large, the infrared radiation heating device and the powder adhesive polyolefin which increase the output or the number of the infrared radiation heating device 10 having a peak at a wavelength of 1 μm or less are used. It is desirable to consider the heating effect to a greater extent by shortening the gap with the painted metal tube.

The infrared radiation heating device 11 having a peak at a wavelength of 2.0 to 4.5 μm exhibits the heating effect of the metal tube 1 and the absorption wavelength of a general adhesive polyolefin is 2.
Since it is distributed in the range of 0 to 4.5 μm, it has an effect of promoting melting and reaction by absorbing infrared rays. Therefore, it contributes not only to maintaining the temperature of the metal tube but also to improving the wettability with the adhesive primer and the adhesiveness due to reaction.

Regarding the proper arrangement of the infrared radiation heating device 10 having a peak at a wavelength of 1 μm or less and the infrared radiation heating device 11 having a peak at a wavelength of 2.0 to 4.5 μm, the melting property of the powder adhesive polyolefin Generally, after being sufficiently heated by the infrared radiation heating device 10 having a peak at a wavelength of 1 μm or less, 2.0 to
Infrared radiation heating device having a peak at a wavelength of 4.5 μm 1
It is desirable to arrange so that the temperature is maintained by 1 and the melting of the adhesive polyolefin layer 4 is accelerated by infrared absorption. The output ratios of the infrared radiation heating device 10 having a peak at a wavelength of 1 μm or less and the infrared radiation heating device 11 having a peak at a wavelength of 2.0 to 4.5 μm are determined by the thickness of the metal tube 1 and the powder adhesive polyolefin. Should be determined by the nature and thickness of the.

[0013]

EXAMPLES Examples of the present invention will be described in detail below. After cleaning a steel plate (400 mm x 9 mm x 12 m) by grit blasting, a chromic acid type chemical conversion treatment is applied by brushing, and then heated to 200 ° C in a heating furnace,
The adhesive primer was spray coated to a film thickness of 50 μm, and then the powder adhesive polyethylene was electrostatically coated to a film thickness of 100 μm. 30 seconds later, an infrared radiation heating device having a peak at a wavelength of 0.8 μm (cylindrical type, width 200 mm, output 32 kW)
/ M ² ) and infrared radiation heating device having a peak at a wavelength of 2.4 μm (cylindrical type, width 200 mm, output 32 kW /
m ² ) were continuously arranged, and the powder-adhesive polyethylene-coated steel pipe was moved at a distance of 200 mm from the two infrared radiation heating devices at a moving speed of 1.5 m / min.
Thirty seconds after that, polyolefin was extrusion-coated to a film thickness of 2.5 mm. In addition, as a comparative example, a steel pipe without infrared heating was also prepared. Then, the temperature of the steel pipe immediately before coating with the powder adhesive polyethylene and the temperature of the steel pipe immediately before extrusion coating with polyethylene were measured with a radiation thermometer. Further, with respect to the obtained steel pipe, a test piece of 150 mm × 75 mm was cut from 44 places at a pitch of 90 ° in the circumferential direction and a pitch of 1 m in the length direction, and the adhesive force (peel strength) was measured. Table 1 shows the temperature and adhesion of the steel pipes of Examples and Comparative Examples. It can be seen that the Examples have a heating effect of infrared rays and exhibit stable adhesion.

[0014]

[Table 1]

[0015]

EFFECTS OF THE INVENTION According to the present invention, a polyolefin-coated metal tube can be obtained which efficiently promotes melting of the powder-adhesive polyolefin in a small space in a short time and exhibits a stable adhesive force over the entire surface.

[Brief description of drawings]

FIG. 1 is a coating configuration diagram of a polyolefin-coated metal tube which is a target of the present invention.

FIG. 2 is a schematic view of an example of a method for coating a polyolefin-coated metal tube of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Metal tube 2 ... Chemical conversion treatment layer 3 ... Adhesive primer layer 4 ... Adhesive polyolefin layer 5 ... Polyolefin layer 6 ... Chemical conversion treatment step 7 ... Heating furnace 8 ... Adhesive primer coating step 9 ... Powder adhesive polyolefin coating step 10 ... Infrared radiation heating device having a peak at a wavelength of 1 μm or less 11 ... Infrared radiation heating device having a peak at a wavelength of 2.0 to 4.5 μm 12 ... Polyolefin extrusion coating step

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Kusano No. 1 Kimitsu, Kimitsu City Kimitsu Steel Works, Nippon Steel Corporation Inside the Kimitsu Factory, Nippon Steel Corrosion Co., Ltd. (72) Toyoo Ando Kimitsu, Kimitsu City 1 Address Inside the Kimitsu Works, Nippon Steel Co., Ltd.

Claims (1)

[Claims] 1. A metal tube is subjected to a chromic acid-based chemical conversion treatment after a base treatment, the metal tube is further heated, and then an adhesive primer and a powder adhesive polyolefin are sequentially laminated, and a polyolefin resin is extrusion-coated as an upper layer. In the method for coating a polyolefin-coated metal tube according to claim 1, heating with an infrared radiation heating device having a peak at a wavelength of 1 μm or less and an infrared radiation heating device having a peak at 2.0 to 4.5 μm after coating the powder adhesive polyolefin. A method for coating a polyolefin-coated metal tube, which comprises: