JPS59201820A - Preparation of polyethylene coated steel pipe having coloring layer - Google Patents

Abstract

PURPOSE:To obtain a polyethylene coated steel pipe having a coloring layer by a method wherein polyethylene is extruded to coat the outer surface of a steel pipe and, thereafter, a polyethylene powder or tape containing a coloring pigment is brought into contact with the outer surface of the coating layer before the outer surface temp. of said coating layer is lowered to the m.p. thereof or less. CONSTITUTION:Polyethylene 3 is extruded to coat the outer surface of a steel pipe 2 and a polyethylene powder 5 or a polyethylene tape 8 containing a coloring pigment is brought into contact with the outer surface of the polyethylene coating layer 3 before the outer surface temp. of said polyethylene coating layer 3 is lowered to the m.p. thereof or less melt and weld the aforementioned polyethylene powder 5 or the polyethylene tape 8 by the holding heat of the extrusion coated polyethylene coating layer 3. By this method, a polyethylene coating steel pipe having a coloring layer can be prepared in high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a polyethylene coated steel pipe having a polyethylene thin film colored layer.

,I? Polyethylene-coated steel pipes are widely used in Tsukibu lines due to their excellent anti-corrosion properties. In particular, the traditionally used asphalt-based coatings have the disadvantage of being prone to cracking in cold regions and sagging in tropical regions, so polyethylene coatings, which have stable strength from low to high temperatures, are rapidly replacing asphalt coatings. by the way,
The polyethylene used for the coating contains a large amount of carbon black in order to improve its weather resistance and durability and provide corrosion protection for several decades, giving it the same black color as overhead cables. .

There are no problems with this black color when it comes to ordinary underground pipelines, and many pipelines have actually been constructed. However, when applying mortar lining to the inner surface of a black polyethylene-coated steel pipe in a tropical region, the black polyethylene absorbs the radiant heat of sunlight, raising the temperature inside the pipe to over 60°C and causing the mortar to harden rapidly. The problem of peeling occurs. Furthermore, when polyethylene-coated steel pipes are used as heavy-duty anti-corrosion piles for offshore structures, the black color may be removed due to aesthetic concerns.

The purpose is to reduce heat absorption and further improve the surface appearance.

When painting the surface of polyethylene, since polyethylene does not have polar groups, ordinary liquid paints will not adhere to it, and the only way to do so is to completely fuse the same polyethylene type.

In this case, in order to fuse the polyethylene coated surface and the coating material, it is necessary to heat the polyethylene coating to its melting point, which is usually much higher than the melting point of the coating material.
Since it is formed by extruding polyethylene that has been heated and melted to 0°C or higher using an extruder, VCS = polyethylene coating material is brought into contact with the coated polyethylene before it has cooled below its melting point, and the polyethylene coating is melted by the heat retained in the polyethylene coating. Once coated, fusion coating can be applied simultaneously with polyethylene coating.

The polyethylene-based coating material may be any material mixed with polyethylene, including polyethylene, ethylene-vinyl acetate copolymer, maleic anhydride-modified polyethylene, and many others. Next, the shape may be powder, tape, or similar.

When the shape is a powder, the particle size does not need to be particularly specified unless aesthetics are taken into account, but in order to achieve a smooth and uniform surface (C finish), it is desirable to use 50 mesh d's of powder.

Further, the thickness of the colored layer is 50 μm or more in the case of white color to block solar radiant heat, but 100 μm or more is suitable for obtaining a uniform layer.

Note that if a color other than white is required for aesthetic reasons, fusion coating can be easily performed by using polyethylene powder mixed with a pigment of a color other than white.

Polyethylene-based powder can be easily fused and coated on the surface simply by contacting the polyethylene coated with the polyethylene, provided that the melting point of the powder is higher than the melting point of the polyethylene. For example, if you spray with an electrostatic powder coating gun, you can easily fusion coat about 50μ, but if you try to fusion coat more than 100μ, you will need to take measures such as increasing the number of guns, which will increase equipment costs. Connect. By the way, when spraying with an electrostatic powder coating gun, the coating efficiency is about 50
The remaining 50% of the powder comes into contact with the surface of the coated polyethylene and then scatters.

This phenomenon can be observed not only when spraying but also when powder is sprinkled, and it is difficult to coat more than 50μ with one sprinkling.

In order to compensate for this defect, immediately after spraying or sprinkling the powder, as shown in Figure 1, the polyethylene powder 5 is pressed against the polyethylene coating B with a presser roll 4 made of fluororubber or silicone to prevent the powder from scattering. , just prevent it from falling. In this case, the closer the pressing position is to the position where the powder is sprinkled, the thicker the powder is applied, and in order to obtain a thickness of 100μ or more, it is necessary to press the powder with the pressing roll 4 within 50 mm from the position where the powder is sprinkled. In addition, if the pressing pressure is high, the powder can be thickly fused and applied, and 1
1k to get 00μ! A pressing pressure of Icnj or higher is required.

Alternatively, as shown in Fig. 2, two presser rolls 4 and 7 with a small pressing force are arranged in succession, and the pressure is continuously applied from the two presser rolls 4°7vc. This has the same effect as increasing the pressure. In addition, the position of the presser roll can be any position on the steel pipe.
You can choose freely.

Note that the presser roll is not limited to fluororubber or silicone rubber, and may be any material as long as it does not adhere to polyethylene and has side heat properties higher than the melting point of the powder material (100° C. to 120° C.).

Next, if the shape of the coloring material is a tape, as shown in Figure 6, at a position shifted by one pitch in diameter of the extruded polyethylene coating,
A colored layer can be easily provided by pressing the polyethylene tape 8 against the polyethylene coating 6 using the pressure roll 4. In this case, of course, since the extrusion-coated polyethylene has a melting point higher than that of the polyethylene tape 8, the two are completely fused together, and since the heat retained by the coating is large, the overlapping portions of the tapes are also sufficiently fused.

The thickness of the polyethylene tape 8 can be freely selected, but if it is too thin, it may wrinkle or break when wrapped, so it is better to have a thickness of 100 μm or more for better workability.

As with the powder method, the pressure roll 4 does not adhere to polyethylene such as fluororubber or silicone, and has a melting point (
Any material may be used as long as it has a heat resistance of 100°C to 120°C or higher. In the case of the tape method, the purpose of using a pressure roll is to prevent wrinkles and air bubbles from being drawn in, so there is no need to use a large pressure, and a pressure of about 0.7 vcni at most is sufficient. Note that if you use the tape in conjunction with a pressure roll and have pinholes in the tape to release air bubbles, the aesthetic appearance will be further improved.

In addition, in FIGS. 1 to 6, 1 is a T-die of the extruder, 2 is a steel pipe that is transferred while being rotated, and 6 is a scraping impeller.

Next, examples of this invention will be shown.

Example 1 In FIG.

Covering line: Polyethylene extrusion wrapping line using T-die method Steel pipe diameter: 1500mm (outer diameter) Covering polyethylene: Black 6-thickness powder polyethylene: White 7M/I: 35,50 Metsunyu pass Melting point 100°C Pressing roll: Silicone rubber roll Pressure roll pressure crab IKg/crl Covered polyethylene temperature: 100°C Result (1) Result (2) As a result, the coating polyethylene needs to be heated to 100°C or higher, and the pressure roll pressure must also be IKg/ca or higher. Appropriate.

Example 2 In fig.

Coated polyethylene/Temperature: 100℃ Pressure roll pressure crab O-5 to 9/aA Result As shown in Figure 2, the pressure roll was placed under the steel pipe.
I got the same result yesterday. Furthermore, if two pressure rolls are installed in succession, the coating thickness can be increased even if the roll pressure is low.

Example In FIG.

Covering polyethylene temperature: 100°C tape
: Low density polyethylene, M, I.

6.5. Melting point: 100° C., thickness: 100 μm, green pressing roll pressure: 0.5 Kr/cJ Results: A uniform green surface layer was obtained.

As described above, the method of the present invention involves coating the outer surface of a steel pipe with polyethylene by extrusion, and then, before the outer surface temperature of the polyethylene coating layer has cooled below its melting point, polyethylene powder containing a coloring pigment is added. Alternatively, a colored layer is provided on the surface of the polyethylene coating layer by bringing a polyethylene tape into contact with the outer surface of the polyethylene coating layer, and causing the polyethylene powder or polyethylene tape to be bonded by heat retained in the extrusion-coated polyethylene coating layer. Highly efficient and high quality coloring*
The production of polyethylene-covered steel pipes with +J capability is possible.

46 simple illustrations'f! , Explanation Figure 1 is a first embodiment of the present invention, and shows a state in which colored powder is fused and applied to a polyethylene coating layer 11111
Figure 2 is a side view of the second embodiment of the invention, in which two pressure rolls are used, and Figure 6 is the sixth embodiment of the invention.
It is a side view which shows the state which is an Example and shows the state in which the colored polyethylene tape is coated one by one.

1 is T-tie, 2 is steel pipe, and 6 is coated polyethylene.

4 is a press roll, 5 is polyethylene powder, 6 is a scraping impeller, 7 is a press roll, and 8 is a polyethylene tape.

Claims (1)

[Claims] After extrusion coating the outer surface of the steel pipe with polyethylene, before the outer surface temperature of the polyethylene coating layer has cooled below its melting point, a polyethylene powder or a polyethylene tape containing a color pigment is brought into contact with the outer surface of the polyethylene coating layer, A method for manufacturing a polyethylene-coated steel pipe having a colored layer, characterized in that a colored layer is provided on the surface of the polyethylene coating layer by melting and fusing the polyethylene powder or polyethylene tape using the heat retained in the extrusion-coated polyethylene coating layer.