JPS6216988B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to an anti-corrosion coated steel pipe in which the outer periphery of the steel pipe is coated with a thermoplastic resin. This type of anti-corrosion coated steel pipe is mainly used for underground burial, and generally asphalt, rubber, oil, etc. are used as the adhesive base between the steel pipe base and the thermoplastic resin coating, which has good corrosion resistance and other physical properties. One using adhesive type adhesive whose main component is E,
There are those using adhesive resins such as V, A, E, E, and A. The above-mentioned adhesive type base is relatively inexpensive, has good resistance to environmental stress cracking, such as repairability of scratches in the film, and can be applied using a very simple hot-melt type base coating method. However, due to the weak film binding force (adhesion force), it expands and contracts significantly due to temperature changes during manufacturing or use, making it impossible to use mechanical joints, and also for welded joints. A major drawback was that it could not be used in high-temperature areas. On the other hand, those using the above adhesive resin as the base have a strong film binding force and little expansion and contraction of the tube end film, but the material cost is very high, and it is difficult to apply the hot melt type base coating method, so die extrusion is used. Because they are often used, the size that can be manufactured is limited by equipment, and they also have disadvantages such as poor environmental stress cracking resistance, and once a crack appears in the film, it quickly expands due to residual stress. The present invention provides a corrosion-resistant coated steel pipe which has excellent properties such as adhesion and environmental stress cracking resistance, and which can be applied with a hot-melt type base coating method. As an adhesive, 10 to 60 parts by weight of a liquid polymer combined from C4 and C5 fractions of petroleum components, 5 to 50 parts by weight of an ethylene copolymer resin, and 5 to 50 parts by weight of an oil-soluble phenol resin.
The basic feature is the use of a resin-based adhesive containing parts by weight, and the use of one or both of adhesive polypropylene and filler added as necessary. . The liquid polymers combined from C4 and C5 fractions of petroleum components in the above adhesive include polycyclopentadiene, 1,3 polypentadiene, 1,4
Maleated compounds such as cis-polybutadiene and 1,2-polybutadiene can be used. In addition, ethylene copolymer resin includes ethylene vinyl acetate copolymer resin,
It is possible to use one or two of the ethylene-ethyl acrylate copolymer resins. As for the oil-soluble phenolic resin, it is preferable to use, for example, one or a mixture of two or more of 100% phenolic resin, drying oil-modified phenolic resin, and natural resin-modified phenolic resin. Note that extender pigments such as calcium carbonate and talc can be used as fillers. When a resin adhesive containing these resins in the above proportions is used as an adhesive between the thermoplastic resin coating of a plastic-coated steel pipe and the steel pipe base, it has an extremely strong coating binding force and effectively controls the expansion and contraction of the tube end coating. At the same time, it improves the environmental stress cracking resistance of the coating, exhibiting excellent effects such as preventing the development of cracks in the coating, and therefore, plastic-coated steel pipes using this material are extremely durable. , it has excellent performance. In addition, this resin adhesive
It has a great manufacturing advantage in that an easy-to-implement hot-melt type coating method can be applied regardless of the size of the steel pipe. Next, the reasons for limiting the components contained in the resin adhesive in the present invention will be described. Liquid polymers combined from C4 and C5 fractions of petroleum components contain less than 10 parts by weight, which increases the viscosity of the adhesive and deteriorates workability, as well as reduces adhesion and prevents the tube end coating from expanding and contracting. I don't get it. 60 again
If the weight part is exceeded, the adhesion will deteriorate again, so
Although the content was set to 60 parts by weight, it is more preferably 20 to 40 parts by weight. Further, the ethylene copolymer resin is effective in improving adhesion when contained in an amount of 5 parts by weight or more, but if it exceeds 50 parts by weight, the viscosity increases, the adhesion again decreases, and the water resistance deteriorates. Therefore, the content rate should be increased to 5 to 50.
The amount is preferably 20 to 40 parts by weight. As for the oil-soluble phenolic resin, if it is less than 5 parts by weight, good water resistance cannot be ensured, and if it exceeds 50 parts by weight, the adhesion to the thermoplastic resin will decrease. Therefore, the amount was set at 5 to 50 parts by weight. Note that the attacking polypropylene added as necessary is effective in improving water resistance and adhesion to the thermoplastic resin, and its effects are best exhibited when the molecular weight is 10,000 to 100,000. Fillers are also effective in reducing expansion and contraction of the tube end coating. Next, the effects of the present invention will be explained using examples. Adhesives (A) to (E) prepared by stirring and mixing each of the ingredients shown in Table 1 in a hot mixer at a heating melting temperature of 160 to 170°C for 1 hour were prepared at 70 to 90°C.
The present invention is applied by coating the surface of a preheated steel pipe to a thickness of 0.1 to 0.5 mm by squeezing and applying hot molten adhesive, and then coating polyethylene with a density of 0.940 to a thickness of 0.6 mm using a die extrusion method. Plastic-coated steel pipes (1) to (5) were obtained. In addition, the adhesive type adhesive (F) and the adhesive type adhesive (g) with the ingredients shown in Table 2 (a) and (b) were used by the ironing method, respectively.
The surface of the steel pipe was coated by die extrusion, and the same polyethylene as described above was coated thereon by die extrusion to obtain conventional plastic-coated steel pipes (6) and (7). These plastic coated steel pipes (1) to (5) and (6), (7)
The following tests were conducted on adhesion, environmental stress cracking resistance, etc. <Test on adhesion> A test piece with a 10 mm x 10 mm bonded area between the coating and the steel pipe base was subjected to a tensile tester at room temperature (25°C).
The tensile strength of the bonded portion when sheared is measured. One cycle consists of immersing a 5.5 m coated steel pipe in hot water for 1 hour and then leaving it at room temperature for 1 hour.
3 cycles at 80°C and 3 cycles at 80°C. At this time, the length of contraction of the tube end coating is measured at the end of a predetermined cycle at each temperature, and the cumulative length of the three values is shown. <Test on environmental stress cracking resistance, etc.> A test piece with a knife notch in the film is immersed in a 1% nonionic surfactant aqueous solution, and the time until cracking occurs is measured. The test results are shown in Table 3.

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[Table] As is clear from the tests and test results in the above table, the plastic-coated steel pipe of the present invention has extremely good film binding force. The test results also demonstrated the excellent resistance to environmental stress cracking and water resistance of the coated steel pipe of the present invention. As explained above, the coated steel pipe of the present invention can simultaneously ensure excellent adhesion, environmental stress cracking resistance, and water resistance, so it has excellent performance and durability for gas piping and other underground piping. This is something to look forward to.

Claims (1)

[Scope of Claims] 1. 10 to 60 parts by weight of a liquid polymer combined from C4 and C5 fractions of petroleum components, 5 to 50 parts by weight of ethylene copolymer resin, and 5 to 50 parts by weight of oil-soluble phenol resin to the base material of the steel pipe. 1. A plastic-coated steel pipe characterized by being coated with an adhesive base containing a thermoplastic resin and coated with a thermoplastic resin. 2 The base material of the steel pipe contains 10 to 60 parts by weight of a liquid polymer combined from C4 and C5 fractions of petroleum components, 5 to 50 parts by weight of an ethylene copolymer resin, and 5 to 50 parts by weight of an oil-soluble phenol resin, and further contains an attack material. 1. A plastic-coated steel pipe characterized by being coated with an adhesive base containing polypropylene and/or a filler, and coated with a thermoplastic resin. 3 The liquid polymer contained in the base adhesive applied to the steel pipe base is polycyclopentadiene, 1,3
polypentadiene, 1,4 cis polybutadiene,
The plastic-coated steel pipe according to claim 1 or 2, characterized in that it is a maleide of 1,2 polybutadiene. 4. Claim 1, characterized in that the ethylene copolymer resin contained in the base adhesive applied to the base of the steel pipe is an ethylene-vinyl acetate copolymer resin and/or an ethylene-ethyl acrylate copolymer resin. Or the plastic-coated steel pipe according to item 2. 5 The oil-soluble phenolic resin contained in the base adhesive applied to the steel pipe base is 100% phenolic resin,
The plastic-coated steel pipe according to claim 1 or 2, characterized in that it is one or a mixture of two or more of a drying oil-modified phenolic resin and a natural resin-modified phenolic resin. 6 The molecular weight of the adhesive polypropylene contained in the base adhesive applied to the steel pipe base is 10,000.
The plastic-coated steel pipe according to claim 2, characterized in that the plastic-coated steel pipe has a particle size of 100,000 to 100,000.