JP2874210B2 - Method of manufacturing plastic outer coated steel pipe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plastic outer-coated steel pipe and a method for producing the same.

[Prior Art] As a conventional plastic outer surface coated steel pipe having improved corrosion resistance on the outer surface of the steel pipe, there is one described in JP-B-56-43031. This is accomplished by applying a thermosetting resin to the outer surface of a steel pipe 21 to form a primer layer 22 as shown in FIG.
After heating the surface of 22 to a temperature not higher than the melting point of the modified polyolefin resin, a modified polyolefin resin layer 23 is coated and fused on the outer surface of the primer layer 22, and then a polyolefin resin jacket is overlaid and coated on the outer surface. It is manufactured by.

Conventional plastic outer-coated steel pipe is manufactured by the above-mentioned method, so only the corrosion resistance of the outer surface of the steel pipe is emphasized, and the corrosion resistance of the inner surface is not so important, for example, an application that does not allow water to pass through the pipe, Was used to. However, in the case of an application in which water is passed through a pipe such as a fire extinguisher pipe, corrosion resistance of the inner surface of the pipe is also required. In such an application, the inner surface of the steel pipe needs to be galvanized.

[Problems to be Solved by the Invention] However, the galvanizing of the steel pipe employs a method of immersing the entire steel pipe in a galvanizing tank, which is generally called soaking, so that the inner and outer surfaces of the steel pipe are galvanized. Then, even if the outer surface of the galvanizing tank is coated with polyolefin as described above to produce a plastic outer surface coated steel pipe, the adhesion between the galvanized layer and the polyolefin coating is poor, as shown in Table 1. However, there is a problem that the adhesiveness is reduced in a short time. That is, the first
The table shows the results of the peel strength test that measures the adhesive strength of the coating specified in JIS G 3469 (polyethylene coated steel pipe). The peel strength per 1 cm width of the polyolefin coating is as follows. From 23 kg / cm at the beginning, 22 kg / cm hardly changed after 15 days, whereas those coated with polyolefin on galvanized steel pipes were initially coated at 15 kg / cm, and after 15 days, 0 to 3 kg / c
m, there was a problem of extremely lowering, and the corrosion resistance of the outer surface of the steel pipe could not be increased.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a method of manufacturing a galvanized plastic outer coated steel pipe having high corrosion resistance on the outer surface of the steel pipe.

[Means for Solving the Problems] In the method for producing a plastic outer surface coated steel pipe according to the present invention, after galvanizing the inner and outer surfaces, the tube end is closed and sealed, and pickling is performed to remove galvanized outer surfaces. From, after applying a primer on the outer surface to form a primer layer and heating the surface to a temperature equal to or higher than the melting point of the modified polyolefin resin,
This is a method for producing a plastic outer-coated steel pipe in which a modified polyolefin resin layer is coated and fused on the outer surface of the primer layer, and then the outer surface is overlaid with a polyolefin resin jacket.

[Action] In the method for producing a plastic outer surface coated steel pipe according to the present invention, the inner and outer surfaces are galvanized, the tube ends are sealed and pickled, the outer surface is zinc-plated, and the outer surface is coated with a primer. After coating to form a primer layer and heating the surface to a temperature above the melting point of the modified polyolefin resin,
A modified polyolefin resin layer is coated and fused on the outer surface of the primer layer, and then a polyolefin resin jacket is overlaid and coated on the outer surface. The purpose of galvanizing the steel pipe is to improve the corrosion resistance of the inner surface of the steel pipe coated on the outside of the plastic. Inevitably, galvanized layers are formed on the inner and outer surfaces of the steel pipe. The galvanized layer on the inner surface of the steel pipe is effective for improving the corrosion resistance of the inner surface of the steel pipe. However, the galvanized layer on the outer surface of the steel pipe has poor adhesion to the primer layer coated thereon, causing a reduction in corrosion resistance. For the above reasons, the galvanized layer on the outer surface of the steel pipe was removed by pickling. In this way, a primer layer, a modified polyolefin layer, and a polyolefin layer are formed in this order on the outer surface of the steel pipe. However, since these are the same as those of the conventional plastic outer coating steel pipe, the plastic outer coating is not changed. The inner surface of the steel pipe has good corrosion resistance on the inner and outer surfaces, and also has good adhesiveness of the coating on the outer surface.

[Embodiment] A method for producing a plastic outer surface coated steel pipe according to one embodiment of the present invention will be described with reference to FIG. FIG. 1 is a sectional view of a plastic outer-coated steel pipe manufactured by a method for manufacturing a plastic outer-coated steel pipe according to one embodiment of the present invention. Steel pipe 1
Is dipped in a galvanizing bath to form a galvanized layer on both sides of the steel pipe 1. Then, after both pipe ends are covered, pickling is performed in an acid pickling tank to remove the galvanized layer on the outer surface of the steel pipe 1 so that the galvanized layer 2 remains only on the inner surface of the steel pipe 1.

Next, a primer layer 3 is formed for the purpose of strengthening the adhesion stability between the modified polyolefin resin and the steel pipe 1. The primer layer 3 is formed by applying a thermosetting resin such as an epoxy resin, for example, and is preferably applied with a thermosetting resin of a quick curing type at a relatively low temperature. The coating method is as follows. That is, a steel pipe 1 whose surface has been cleaned cleanly.
Passes through a tank in which thermosetting resin is stored. At the outlet of the tank, the resin adhering to the outer surface of the steel pipe 1 is scraped off with a ring-shaped rubber, a brush, or the like.
A film having a thickness of 60 μm is formed.

A modified polyolefin resin layer 4 is formed on the outer surface of the primer layer 3. The modified polyolefin resin is a polyolefin resin modified with an unsaturated carboxylic acid or an anhydride thereof, and is obtained by blending a polyolefin resin obtained by grouting an unsaturated carboxylic acid or an anhydride thereof with an unmodified polyolefin resin. Etc. are included. As the base polyolefin resin, specifically, low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymer, ethylene -1-butene copolymer, propylene-1-butene copolymer, and mixtures thereof.

Furthermore, a polyolefin resin jacket is overlaid on the outer surface of the modified polyolefin resin layer 4 and extrusion-coated to form a polyolefin resin layer 5.

In the method for manufacturing a plastic outer-coated steel pipe of the embodiment of the present invention, since the plastic outer-coated steel pipe is manufactured as described above, the corrosion resistance of the inner surface of the steel pipe is good,
It is possible to obtain a steel pipe coated with a plastic outer surface having good adhesion of the plastic resin on the outer surface of the steel pipe.

[Effect of the Invention] According to the present invention, it is possible to obtain a plastic outer-coated steel pipe having good corrosion resistance on both the inner and outer surfaces.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a plastic outer-coated steel pipe manufactured by a method of manufacturing a plastic outer-coated steel pipe according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view of a conventional plastic outer-coated steel pipe. 1 ... steel pipe, 2 ... galvanized layer, 3 ... primer layer, 4 ... modified polyolefin resin layer, 5 ... polyolefin resin layer.

Claims (1)

(57) [Claims] (1) After galvanizing the inner and outer surfaces, seal the tube end and seal and pickle, remove the zinc plating on the outer surface, apply a primer to the outer surface to form a primer layer, and form a primer layer. After heating to a temperature equal to or higher than the melting point of the modified polyolefin resin, the modified polyolefin resin layer is coated and fused on the outer surface of the primer layer, and the outer surface of the plastic is further coated with a polyolefin resin jacket. Manufacturing method of coated steel pipe.