JPS5836680A - Production of resin coated metallic pipe - Google Patents

Abstract

PURPOSE:To improve impact resistance and the adhesive strength of concrete coating by spraying hot meltable granular materials on the film of a metallic pipe coated with epoxy resin powder thereby forming projections. CONSTITUTION:After a steel pipe 1 which is a metallic pipe is subjected to a pretreatment for the purpose of improving the adhesive strength of epoxy powder coating by blasting 2, the pipe is preheated 3 by oven or induction heating. Thereafter the pipe is subjected to epoxy powder painting 4 by an electrostatic powder painting or fluidized bed coating method. After the painting, the epoxy resin begins to set when the pipe 1 is preheated, but more preferably, granular mateials 5 are sprayed 6 since the initiation of gelation until the completion of setting. Thereafter, the sticking to the epoxy powder film 8 is perfected and the coated steel pipe is cooled by water cooling 7. The use of the materials 5 which are hot meltable, exhibit elasticity or elastoplasticity and have excellent adhesive strength to the underlying epoxy powder coating is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a resin-coated metal tube, and more particularly to a method for manufacturing a metal tube in which irregularities are formed by scattering elastic granules on the coating of an epoxy resin-coated metal tube.

Epoxy powder coatings can be used as external anti-corrosion coatings for steel pipes.Epoxy powder coatings can be obtained through a relatively simple process, and the film thickness is sufficient, making it cheaper than conventional thick film types (3 to 5
Since it is cheaper than polyethylene anticorrosive coating (1nTIL), it has recently been widely used as an external anticorrosive coating for line pipes.

A necessary characteristic that this type of coated steel pipe should have is impact resistance, which can withstand collisions of the steel pipe during handling and transportation, and impact from backfilling earth and sand when buried underground. However, since the epoxy powder coating is a thermosetting resin coating, it is hard and has a thin coating thickness of usually 500 μm or less, so it has low impact resistance. It is particularly vulnerable to impact from sharp objects such as stones. In addition, externally coated steel pipes are often used as submarine piping materials, and the anticorrosive coating is further coated with concrete in order to add weight to the piping and protect the anticorrosive coating. However, since the surface of the epoxy powder coating is extremely smooth, it has poor adhesion to concrete and has the disadvantage that the concrete coating tends to shift.

The present invention solves the above-mentioned conventional problems, and its main purpose is to provide a method for manufacturing resin-coated metal pipes that can simultaneously improve impact resistance and adhesion to concrete coatings applied during submarine piping. be.

That is, in the present invention, heat-sealable and substantially elastic granules are sprinkled on the coating of an epoxy resin powder-coated metal tube, fused onto the coating, and the surface is coated with the granules. It is characterized by the formation of protrusions.

By the way, attempts have been made to sprinkle particulate matter such as sand on polyethylene-coated steel pipes in order to improve their adhesion to concrete. However, even if sand is sprinkled on the epoxy resin powder-coated metal tube, which is the object of the present invention, not only the adhesion is not always good, but also the impact resistance cannot be improved at all. Therefore, the present inventors discovered that by dispersing heat-sealable and substantially elastic granules, the granules can be easily and reliably fused to the epoxy powder coating, and at the same time, external shocks can When the epoxy powder anti-corrosion coating is applied, the protrusions caused by one granule deform and absorb the impact energy, protecting the epoxy powder anti-corrosion coating.Furthermore, we discovered that the granule protrusions improve the adhesion to concrete, and we have developed this book. This led to the invention.

Next, to explain the present invention in detail with reference to FIG. Preheating 3 is performed to about 200 to 250 C by induction heating or the like. Next.

Gepoxy powder coating 4 is performed by electrostatic powder coating or fluidized dipping method. In this coating, it is desirable to adjust the coating thickness to about 250 to 500#. After painting,
The epoxy resin starts to harden by preheating the steel pipe 1, but preferably, during the period from when gelation starts to complete hardening, that is, during the so-called B stage, granule dispersion 6 of granules 5, which will be described in detail later, is carried out. . After that, water cooling 7 completes the adhesion to the jepoxy powder coating 8 and cools the coated steel pipe. Considering the purpose of the present invention, the granular material used in the present invention should have the following characteristics. desirable.

(→ Must be able to be heat fused.

(bj) Shows elasticity or elastoplasticity without being brittle even when subjected to rapid and large impacts.

(C) The characteristics of item (a) shall be ensured at a temperature of 140C to 10SOC.

(ψ Excellent adhesion to the underlying epoxy powder coating.

Examples of materials having such properties include copolymer resins of ethylene or propylene and one or more monomers having functional groups, such as maleic anhydride, vinyl acetate, acrylic acid, and acrylic esters; Examples include rubber, modified natural rubber such as hydrochloric acid rubber, and synthetic rubber such as 8-BR or NBR.

Particle size ij of granules: 0.8 mφ to 5. Omφ is preferred.

If the particle size is small, adhesion to concrete and impact resistance will be poor, and even if the particle size is large, the same problem will occur.

The amount of granular material spread (spreading density) is shown in FIG.

The distance d between adjacent grain bodies and the height H of grain bodies are d/H(
1-5, more preferably d/I (≦1.0. If the distance between the particles is long, the impact resistance will decrease. On the other hand, if the distance between the particles is completely in contact with each other, If the spray amount is too large, the shear resistance to the concrete coating will be low and adhesion will be poor.

The timing of dispersing granules should be as follows: In other words, when epoxy resin paint powder is applied, it melts and flows due to the heat retained in the steel pipe, creating a smooth surface.Then, a polymerization reaction occurs due to the heat, and polymerization and three-dimensionalization progress, resulting in a hard surface. Gelation occurs when the filling reaction rate is between 40 and 80 inches. It is necessary to spray it after this molarization until complete hardening at a reaction rate of 1 O -.

Preferably, the reaction rate is within the range of 40 to 801.

When spraying is carried out before gelation when the reaction rate is below 40.

Since the epoxy resin is still in a molten state, the continuity of the coating is disrupted by the dispersed particles, resulting in a decrease in corrosion protection. Further, when the reaction rate is between 80 and 100'j, the adhesion between the granules and the coating is weak, resulting in the granules being chipped due to impact and chipping during concrete coating.

As mentioned above, (1) the present invention company sprinkles heat-sealable and substantially elastic granules on the coating of an epoxy resin powder-coated metal tube, heat-seals them, and (1) protrudes the granules on the surface. This has the advantage of simultaneously improving impact resistance and adhesion to external coating materials such as concrete, which are unavoidable drawbacks of epoxy powder coatings.

Next, examples will be shown.

Similar to the process shown in FIG.
Preheat to
otchkote, 206 NJ) was applied by electrostatic coating.

After that, gelation was confirmed and various granules were sprinkled.

The epoxy resin was completely cured by the heat of the steel pipe, and at the same time, the adhesion between the granules and the coating was completed, and then water-cooled to obtain a coated steel pipe, and a performance test was conducted.

On the other hand, those that do not spray granules and those that have a high reaction rate: 1. Performance tests were also conducted for those with large d/H and those with low reaction rate.

The results of these tests are shown in the table below. In the same table, the epoxy resin reaction rate is 91% as determined by infrared absorption spectrum measurement.
It was calculated from the change in the absorption intensity ratio between 0m-' and 830cm''. Impact resistance is measured by the maximum electric shock energy that does not cause film destruction, and is based on DIN30670 (center of impact 25mφ).Concrete The adhesion with Tokoti Fugu was determined by K in order to examine the shear resistance between (concrete) and (anticorrosion coating).

A punching shear test (shear rate 50 m/m1n) was performed using a 300A specimen under a condition of 20C, and the maximum stress is shown.

As is clear from the table showing the results, Comparative Examples 1 to 4 do not satisfy the expected performance, whereas Examples 1 to 6 simultaneously satisfy both impact resistance and adhesion to concrete coating. ing.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a process example of the method of the present invention, and FIG. 2 is a sectional view of the adhesion of granules. l...Steel pipe 2...Plast treatment 3...
Preheating 4... Epoxy powder coating 5... Granular material 6... Granular material dispersion 7... Water cooling Patent applicant Sumitomo Metal Industries, Ltd. Figure 1 Figure 2 Ba

Claims (1)

[Claims] (1) Sprinkle heat-sealable and substantially elastic granules on the coating of an epochino resin powder-coated metal tube, fuse them onto the coating, and form protrusions of the granules on the coating surface. 1. A method for producing a resin-coated metal tube, comprising: forming a resin-coated metal tube.