JPH06340026A - Polyethylene-coated steel pipe - Google Patents

Abstract

PURPOSE:To obtain a polyethylene coated pipe which is excellent in wheathering and handling resistance by a method wherein an outer surface of a steel pipe is coated with a polyethylene resin layer consisting of a specific white polyethylene composition via an adhesive layer. CONSTITUTION:An outer surface of a steel pipe is coated, via an adhesive layer, with a polyethylene resin layer of at least 0.5mm film thickness consisting of a white polyethylene composition wherein at least 0.5 pts.wt. of color pigment in which white pigment is at least 75%wt.% is added to 100 pts.wt. of polyethylene. As an adhesive, maleic anhydride modified polyethylene resin should be especially preferable. As the white pigment, titanium, lead, zinc and antimony white pigments are exemplified. Thereby, rise in temperature of polyethylene resin is prevented, and an effect for shielding ultraviolet rays becomes sufficient.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene-coated steel pipe having excellent weather resistance and handling resistance.

[0002]

2. Description of the Related Art The outer surface of a line pipe for transporting oil, natural gas, water, etc. is exposed to river water, drainage, rainwater, the atmosphere, sunlight, etc. in a natural environment, and also exposed to sediment, mud, etc. Since they come into direct strong contact, they are prone to corrosion. For this reason, in recent years, as a countermeasure against this, heavy-corrosion-coated steel materials having excellent corrosion resistance by coating a resin with a thick film (1 to 3 mm) are being used. As the coating resin, polyethylene is often used in consideration of economy and various characteristics. However, polyethylene resin is easily deteriorated by the influence of ultraviolet rays contained in sunlight. Since there is a case of being left in a yard or the like for 3 to 5 years at the time of construction of a line pipe or the like, it is general to add carbon black to polyethylene of the coating layer to improve weather resistance.

[0003]

However, in a place where the temperature in the daytime is 50 ° C. or higher and the sunlight intensity is high, such as in a desert area, polyethylene with carbon black is excellent in weatherability but has a color tone. Is limited to black, the polyethylene coating may reach 80 ° C or higher due to sunlight, and the polyethylene softens. The softened polyethylene is dented by the weight of the pipe itself when stored in the yard, or the surface is easily damaged by handling during transportation or during construction. Since the damaged part needs to be repaired, a great deal of labor and time are required during construction, and the efficiency is significantly reduced economically and time. Therefore, a coating having excellent handling resistance has been desired in a hot place such as a desert area, but no coating satisfying such requirements has been available so far. An object of the present invention is to provide a polyethylene-coated steel pipe having excellent weather resistance (3 to 5 years) and handling resistance.

[0004]

Means for Solving the Problems As a result of studying the temperature rise and weather resistance of the polyethylene coating due to sunlight, the present inventors have found that among the color pigment-containing polyethylene, white polyethylene has excellent sunlight reflectivity. It has been found that the temperature rise of the resin is small and the resin does not easily soften, and that the weather resistance of the pigment in the desert region is 3 to 5 years due to the ultraviolet shielding property of the pigment.

According to the present invention, in a polyethylene-coated steel pipe in which a polyethylene resin layer having a film thickness of 0.5 mm or more is coated on the outer surface of the steel pipe through an adhesive layer, the polyethylene resin layer is used for 100 parts by weight of polyethylene. 75 white pigments
A polyethylene-coated steel pipe excellent in weather resistance and handling resistance, which is characterized by comprising a white polyethylene composition containing 0.5% by weight or more of a coloring pigment of 0.5% by weight or more.

Further, according to the present invention, in a polyethylene-coated steel pipe in which a polyethylene resin layer having a thickness of 0.5 mm or more is coated on the outer surface of the steel pipe through an adhesive layer, the polyethylene resin layer is added to 100 parts by weight of polyethylene. 75 white pigments
A polyethylene coating excellent in weatherability and handling resistance, characterized by comprising a white polyethylene composition containing 0.1 to 0.5 parts by weight of a coloring pigment in an amount of at least 10% by weight and 0.05 parts by weight or more of an antioxidant. Also related to steel pipes.

[0007]

The structure of the present invention will be described in detail below. The steel pipe to be covered in the present invention is not particularly limited, and may be a steel pipe made of any material such as carbon steel and alloy steel,
Especially, it is effective in the case of a line pipe which is handled in a high temperature environment such as a desert.

The outer surface of the steel pipe to be coated is preferably cleaned in advance by appropriately combining physical means such as shot blasting and chemical means such as pickling and alkaline degreasing.

The steel pipe may be subjected to plating or chemical conversion treatment (chromate treatment, zinc phosphate treatment) as a base treatment for improving the adhesion and the corrosion resistance. Further, in order to improve the adhesiveness of the polyethylene resin layer, the surface of the steel material may be previously treated with a suitable primer. As the primer, for example, an epoxy primer or the like can be used. The primer is applied thinly and then dried or is irradiated with ultraviolet rays to be cured. These base treatments may be performed in the same manner as in the conventional case, if necessary.

Since the polyethylene resin has relatively low adhesiveness, an adhesive layer is interposed at the interface between the steel material and the resin layer, and the resin layer is coated on the steel material via the adhesive agent. As an adhesive,
Known adhesives used for polyethylene coating can be used, but maleic anhydride-modified polyethylene resin is preferable because it exhibits particularly high adhesiveness. In addition, an ethylene copolymer (eg, ethylene / vinyl acetate copolymer) adhesive or a polyethylene hot melt adhesive can also be used. The thickness of the adhesive layer is not particularly limited and varies depending on the type of adhesive, but is generally about 0.1 to 0.5 mm.

The thickness of the polyethylene resin layer covering the steel pipe is 0.5 mm or more. Especially for coated steel pipes such as line pipes where importance is attached to corrosion resistance, impact resistance and weather resistance, 1.5-
3 mm is preferred. With a polyethylene coating thinner than 0.5 mm, sufficient impact resistance cannot be obtained. There is no particular upper limit to the film thickness, but if it is thicker than 5 mm, a large amount of resin will be used, which is economically undesirable.

The polyethylene composition constituting the polyethylene resin layer is a white polyethylene composition obtained by adding a coloring pigment mainly composed of a white pigment to a polyethylene resin. The term "white type" as used herein means, among the color pigments to be added,
It means that the white pigment is 75% by weight or more. Also,
The color pigment is a pigment for coloring such as white, red and blue, and does not include extender pigments such as barium sulfate, silica, mica and talc.

It is preferable that the polyethylene resin used has a density of 0.93 or more in the state of not containing a pigment. Since polyethylene with a density lower than 0.93 has a low impact strength, the film thickness must be increased to obtain sufficient impact strength, and a large amount of resin is required.

Examples of the white pigment which is the main component of the color pigment added to the polyethylene resin include titanium white pigment, lead white pigment, zinc white pigment and antimony white pigment. These white pigments may be added alone to obtain a white color, but a white color pigment is mainly used, and a known color pigment other than the white color pigment may be added in an amount of 25% by weight or less based on the total weight of the color pigment to form a light color polyethylene coating. Good. If it is more than this, the color tone becomes too dark, the temperature rise of the polyethylene resin is promoted by the sunlight, and the polyethylene resin is softened, and scratches easily occur due to damage during handling, which is not preferable.

When a pigment for making the color tone white is added in an amount of 0.5 parts by weight or more based on 100 parts by weight of polyethylene,
The effect of preventing the temperature rise of the polyethylene resin and the effect of shielding ultraviolet rays become sufficient, and it is not always necessary to add an antioxidant. There is no particular upper limit to the amount of pigment added, but since excessive addition of pigment reduces the economic efficiency of the product, the amount of pigment added should be 5
It is preferably less than or equal to parts by weight.

When the amount of the pigment added for making the color tone white is as small as 0.5 parts by weight or less with respect to 100 parts by weight of polyethylene, the pigment cannot sufficiently provide ultraviolet shielding properties, and therefore an antioxidant is used in combination. To do. In order to prevent the temperature rise in the desert area and keep the weather resistance for 3 to 5 years,
0.1 to 0.5 parts by weight of a pigment having a white pigment content of 75% by weight or more based on 100 parts by weight of polyethylene, and an antioxidant.
Add 0.05 parts by weight or more. If the amount of the pigment added is less than 0.1 parts by weight, the weather resistance is significantly reduced, which is not preferable.

As antioxidants to be added to polyethylene resin, phenol type antioxidants, aromatic amine type antioxidants, phosphorus type antioxidants, sulfur type antioxidants, hindered piperidine type light stabilizers, etc. Any antioxidant may be used as long as it is used. One kind or two or more kinds of these antioxidants may be added, but the addition of a large amount is not preferable because it impairs the economical efficiency of the product. The total amount of antioxidants added is preferably 2 parts by weight or less with respect to 100 parts by weight of polyethylene.

In addition, one or more known additives such as extender pigments, rust preventive pigments, dispersants, softeners and flame retardants may be further added. It is also possible to add an ultraviolet absorber to the polyethylene resin, but it is not always necessary to add it because the pigment is added and the ultraviolet shielding property is high.

When a white polyethylene resin containing the pigment used in the present invention is produced, a masterbatch in which the pigment is mixed in the polyethylene resin in an amount of about 3 to 50% by weight is prepared. When a polyethylene resin composition is prepared by blending a polyethylene resin not containing the above at a predetermined ratio, it is easy to obtain a homogeneous composition and it is economically advantageous.

The white polyethylene-coated steel pipe of the present invention is excellent in weather resistance due to the ultraviolet shielding property of the added pigment,
Moreover, since it is possible to prevent the temperature rise due to sunlight in the desert area, it is excellent in handling resistance.

The coating of the steel pipe with the above-mentioned white polyethylene composition may be carried out by a coating method similar to the conventional one, and is not limited to a specific method. For example, there is a method in which a steel material is coated with a pressure-sensitive adhesive or an adhesive layer while being continuously extruded by a molding machine. Also, electrostatic powder coating,
It is also possible to coat polyethylene using a coating means such as fluidized dipping or thermal spraying.

[0022]

EXAMPLES Next, the present invention will be described in detail with reference to Examples. After adjusting the surface of the surface of 150 × 70 × 3.2 mm ^t (SS41) by shot blasting (Sa. 2.5 or more), a coating type chromate solution (Kansai Paint Co., Ltd.) was used so that the chromium adhesion amount would be 200 mg / m ² . Chromatization was performed using Cosmer 100). Epoxy primer (Nippon Paint Co., Ltd .; No.66 primer) was applied to this steel plate to a dry film thickness of 30 μm, and the steel plate was applied using a hot press.
By raising the temperature to 190 ° C, the primer was baked and the steel sheet was preheated.

On the other hand, as the anticorrosion polyethylene layer to be coated, medium- and low-pressure polyethylene (SHOREX S4002EX, Showa Denko, trade name) was used, and various pigments were added in amounts shown in Table 1 to obtain a polyethylene layer. A polyethylene-coated steel sheet was obtained by heat-sealing the steel sheet, the polyethylene layer, and maleic anhydride-modified polyethylene (Admer made by Mitsui Petrochemical Co., Ltd.) with a hot press. The thickness of the polyethylene coating was 0.3 mm for the adhesive layer, and the thickness of the polyethylene layer was as shown in Table 1.

This polyethylene-coated steel sheet was exposed in the Saudi Arabian desert area, the maximum daytime temperature of the polyethylene coating was measured, and the drop impact strength at that temperature was measured. After conducting an exposure test in the desert area of Saudi Arabia for 5 years, the drop impact strength at the maximum daytime temperature was measured. The results are shown in Table 1.

The maximum daytime temperature in the Saudi Arabian desert area was 58 ° C. for the white one and 82 ° C. for the carbon black added. If the drop impact strength is less than 1.0 kg ・ m, it may be scratched during construction or the coating may be crushed by the weight of the pipe itself when stored in the yard. Those with a weight of more than kg · m were evaluated as ◯, and those with a weight of less than 1.0 kg · m were evaluated as x. The weather resistance after 5 years of exposure was also evaluated in the same manner.

In Examples 1 to 14 according to the present invention, the drop impact strength is 1.0 kg · m or more even after the exposure, and the weather resistance is maintained. When the pigment addition concentration is less than 0.5 as shown in Examples 11 to 13, by adding an antioxidant, the weather resistance is maintained for 5 years and the impact strength is 1.
Holds 0 kg ・ m or more.

On the other hand, the polyethylene with carbon black added as in Comparative Examples 1 and 2 has no change in physical properties after exposure for 5 years, but since the maximum daytime temperature reaches 82 ° C., the impact strength itself is 1.0 kg.・ It is smaller than m.

As shown in Comparative Example 3, when the amount of the pigment added was less than 0.5 parts by weight without adding the antioxidant, the impact strength remarkably decreased after 5 years of exposure and became lower than 1.0 kg · m. Even if the amount of the added pigment is less than 0.5 part by weight, it is possible to maintain the impact strength at 1.0 kg · m after 5 years of exposure by setting the film thickness to 3 mm as shown in Comparative Example 4. However, the impact strength retention is low due to deterioration due to sunlight, and the amount of resin used increases as the film thickness increases, resulting in a significant decrease in economic efficiency.

As shown in Comparative Examples 5 to 7, when the amount of the pigment other than the white pigment exceeds 1/4 of the total amount of the color pigments, the absorption of sunlight increases and the resin temperature rises, resulting in a low impact strength. Become. That is, in order to obtain the same impact strength as that of white polyethylene, it is necessary to make the film thickness larger than that of white polyethylene, which is economically disadvantageous.

As shown in Comparative Example 8, the pigment addition amount was 0.5
When the amount is less than 5 parts by weight and the addition amount of the antioxidant is less than 0.05 part by weight, the impact strength after 5 years of exposure is significantly reduced due to deterioration due to sunlight. Further, as shown in Comparative Example 9, even if the amount of the antioxidant is 0.05 parts by weight or more, if the amount of the pigment added is less than 0.1 parts by weight, the weather resistance is significantly lowered.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

Industrial Applicability As described above, the white polyethylene-coated steel pipe of the present invention is a coated steel pipe having excellent handling resistance and weather resistance. In the conventional coated steel pipe, only the weather resistance was improved, and the handling resistance was not considered at all. INDUSTRIAL APPLICABILITY According to the present invention, a great amount of labor and time for repairing damage due to handling during storage, transportation, and construction of a steel pipe, which is a problem in a desert area, can be reduced, and it is a practically useful invention.

Claims (2)

[Claims] 1. A polyethylene-coated steel pipe in which a polyethylene resin layer having a film thickness of 0.5 mm or more is coated on the outer surface of the steel pipe via an adhesive layer, wherein the polyethylene resin layer contains 100 parts by weight of polyethylene and 75 parts by weight of a white pigment. A polyethylene-coated steel pipe having excellent weather resistance and handling resistance, which is characterized by comprising a white polyethylene composition containing 0.5% by weight or more of a coloring pigment in an amount of at least 0.5% by weight. 2. In a polyethylene-coated steel pipe in which a polyethylene resin layer having a thickness of 0.5 mm or more is coated on the outer surface of the steel pipe via an adhesive layer, the polyethylene resin layer contains 75 parts by weight of polyethylene and 75% of white pigment. A polyethylene coating excellent in weatherability and handling resistance, characterized by comprising a white polyethylene composition containing 0.1 to 0.5 parts by weight of a coloring pigment in an amount of at least 10% by weight and 0.05 parts by weight or more of an antioxidant. Steel pipe.