JPH06316033A - Composite tube - Google Patents

Abstract

PURPOSE:To provide a composite tube free from detachment of adhesion of both a resin coating layer and a metal tube and free from shrinkage of the resin coating layer by forming the coating layer of synthetic resin added with a fibrous inorganic filler having a recessed groove in the longitudinal direction at least On the internal surface of the metal tube. CONSTITUTION:A W tube 4 is constituted by forming the coating layer 6 of synthetic resin added with a fibrous inorganic filler having a recessed groove 3 in the longitudinal direction at least on the internal surface of a metal tube 5. In the case, e.g. glass fiber 1 having a cocoon-shaped cross section is used for the fibrous inorganic filler having the recessed groove 3 in the longitudinal direction. Further in the dimension of the recessed groove 3, a side (typical dimension of (a), (b) or the like) of the cross section is set e.g. to 1-20mum. Furthermore, length (c) of fiber is set e.g. to 100mum or above and the longest dimension is set to about 1000mum from a point of dispersibility and moldability. Thereby, even if fluid of high temperature flows for a long time, the composite tube 1, is obtained which is free from detachment of adhesion of both the resin coating layer 6 and the metal tube 5 and free from shrinkage of the resin coating layer 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite pipe, and more particularly to a composite pipe suitable for water supply, drainage and the like and having excellent corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, as a composite pipe used for corrosion resistance, a synthetic resin pipe is adhered to the inner surface of a metal pipe with an adhesive, or a synthetic resin having adhesiveness is heated without using an adhesive. It is known that a synthetic resin coating layer (hereinafter referred to as "resin coating layer") is provided by fusing.
And it is widely used.

However, since the linear expansion coefficient of synthetic resin is remarkably larger than that of metal, when a high-temperature fluid continuously or intermittently flows in such a composite pipe, the resin coating layer is formed. Since it tries to expand and contract in the length direction and the diametrical direction with a larger expansion and contraction amount than metal, and also tries to contract in the length direction due to the release of residual molding strain when molding the resin coating layer, Large repetitive shear forces are generated between the layers.

Due to the repeated shearing force, the decrease in the adhesive force due to the diffusion and permeation of heat and water, the adhesive interface between the two ends up peeling, and the resin coating layer shrinks, causing the pipe of the metal tube to shrink. Withdrawing from the end, the fluid directly touches the metal tube,
It penetrates between the metal tube and the resin coating layer. As a result, rust or corrosion may occur in the metal pipe, causing holes to open, which may cause fluid leakage or other accidents.

Therefore, as a countermeasure against this, there has been proposed a technique of adding a granular inorganic filler to a synthetic resin pipe (resin coating layer) in order to make the linear expansion coefficient of the resin coating layer close to that of a metal pipe. (See JP-A-55-161639).

[0006]

However, JP-A-55-55
In the composite pipe described in Japanese Patent No. 161639, since the granular inorganic filler is used, the effect of suppressing the expansion and contraction of the synthetic resin pipe is not sufficient, the material of the synthetic resin pipe becomes brittle, and the smoothness of the surface is obtained. However, there is a problem that the water absorbability from the surface is high and water easily permeates through the synthetic resin pipe. For these reasons, the technique described in the above publication has not solved the problem of separation between the metal pipe and the synthetic resin pipe. There wasn't.

The present invention has been made in view of the problems of the prior art as described above, and even if a high temperature fluid flows for a long time, the adhesion between the resin coating layer and the metal tube is peeled off, or the resin coating layer is formed. Does not shrink, and is therefore less prone to accidents such as rusting or corrosion of metal pipes, corrosion resistance, heat resistance, and a composite pipe with excellent adhesion and adhesion durability between the metal pipe and the resin coating layer. The purpose is to provide.

[0008]

In order to achieve the above-mentioned object, the composite pipe of the present invention has at least an inner surface of a metal pipe,
The gist is that a synthetic resin coating layer to which a fibrous inorganic filler having a groove in the longitudinal direction is added is formed.

In the present invention, the metal pipe includes steel pipe, plated steel pipe, stainless steel pipe, aluminum pipe, copper pipe, etc.
What is generally called a metal tube is used. The inner surface of the metal tube should be degreased with alkali, treated with hydrochloric acid, sulfuric acid, nitric acid, etc. to remove rust and oxide film, then treated with zinc phosphate, iron phosphate, oxalic acid, etc. In order to improve the quality, it is preferable to apply a coupling treatment, a primer treatment with an organic titanate, and a chromate treatment to a galvanized steel pipe.

In the present invention, examples of the synthetic resin include thermoplastic resins such as silane-grafted polyethylene, carboxylic acid-modified polyethylene, polyvinyl acetate, polyvinyl acetal, polyvinyl alcohol and polyamide, epoxy resin, phenol resin, urea resin and polyisocyanate. And other thermosetting resins.

In the present invention, the fibrous inorganic filler having concave grooves in the longitudinal direction is, for example, a cocoon-shaped cross-section glass fiber 1 as shown in FIG. 1 (A) or (A) as shown in (B). Glass fiber 2 having a similar cross section can be used. In FIG. 1, 3 is a longitudinal groove.
The dimension is one side of the cross section (representative dimension of a, b, etc.)
Is preferably 1 to 20 μm and the fiber length c is 100 μm or more, but from the viewpoint of dispersibility and moldability, a fiber length of up to 1000 μm is more preferable.

The addition amount of the fibrous inorganic filler having concave grooves in the longitudinal direction is 1 to 50% by weight, preferably 5 to 30% by weight. If it is less than 1% by weight, the effect of the present invention is not sufficiently exhibited, and if it exceeds 50% by weight, the material of the resin coating layer becomes brittle and the dispersibility and moldability are deteriorated.

Further, synthetic resin includes ordinary glass short fibers, fibrous inorganic fillers such as asbestos, potassium titanate whiskers and wollastonite, mica, talc, calcium carbonate, titanium oxide, silica, calcium sulfate,
Scale-like or granular inorganic fillers such as magnesium carbonate, magnesium hydroxide, magnesium oxide, kaolin clay, wax stone clay, carbon black, graphite, etc., and antioxidants, color masterbatch, etc. may be added. .

In order to improve the adhesiveness of these fillers by blending well with synthetic resin, aminosilane,
Surface treatment with a silane coupling agent such as epoxysilane or a titanium coupling agent is preferably performed.

As a method for forming a resin coating layer containing a fibrous inorganic filler having a concave groove in the longitudinal direction on the inner surface of the metal tube, a synthetic method including the inner surface of the metal tube and the above-mentioned filler molded by extrusion molding is used. After applying the adhesive to the outer surface of the resin pipe,
A method of inserting a synthetic resin tube into a metal tube and heating and expanding with gas to bond it, similarly inserting the above synthetic resin tube into the metal tube and ironing it with a roll or a die while heating the metal tube to reduce the diameter. Adhesion method, powdered resin mixed and dispersed with the above-mentioned filler is fluidized or electrostatically adhered to the inner surface of a heated metal tube to be fused, and a metal strip is continuously formed into a circular shape. A method of melt-extruding a synthetic resin containing the above-mentioned filler into a tubular metal pipe and then fusing the same into a tubular pipe while welding the pipe is used.

The thickness of the resin coating layer to which the fibrous inorganic filler having concave grooves in the longitudinal direction is added has sufficient rigidity so that blister (local swelling) does not occur due to long-term use of the composite pipe. From the necessity, about 0.5 to 5 mm is preferable.

[0017]

The fibrous inorganic filler having concave grooves in the longitudinal direction, which is added to the resin coating layer forming the inner layer of the composite pipe of the present invention, has a linear expansion coefficient remarkably smaller than that of the synthetic resin.

Further, unlike the inorganic particulate fillers used in the above-mentioned prior art, since it exerts an effect of suppressing expansion and contraction of the resin coating layer as a reinforcing material, a resin coating layer having a small residual strain during molding can be obtained. can get.

Therefore, by adding such a filler to the synthetic resin, the expansion and contraction of the resin coating layer due to temperature change is significantly reduced as compared with the prior art, and the residual strain during molding of the resin coating layer is reduced. Therefore, the expansion and contraction of the resin coating layer is further reduced. As a result, the shearing force due to the difference in expansion and contraction between the metal pipe and the resin coating layer is reduced, and the resin coating layer is less likely to peel off from the metal pipe.

From the surface of the resin coating layer, water in the pipe,
Even if water vapor, fluid, etc. are absorbed, as shown in FIG. 2, the flow path in the resin coating layer is lengthened by the fibrous inorganic filler having a concave groove in the longitudinal direction and is accumulated in the concave groove portion. Therefore, diffusion and penetration in the resin coating layer are prevented.
As a result, the adhesive strength between the metal tube and the resin coating layer is reduced, the progress of rust and corrosion of the metal tube is delayed, and the adhesiveness is maintained for a long period of time.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings by embodiments. (Example)

The steel strip is continuously fed from the feeding machine,
While forming a circular cross section with a circular pipe forming machine and welding both ends of the steel strip with a welding machine to produce a steel pipe with an outer diameter of 114.3 mm and a wall thickness of 2.0 mm, Eyebrow cross-section glass fibers having an inner surface subjected to aminosilane surface treatment as shown in FIG. 1 (A) (manufactured by Nitto Boseki Co., Ltd. dimensions a: 13 μm, b: 26 μm, c (average fiber length): 5
(00 μm) 20% by weight of water-crosslinkable silane-modified polyethylene is melted and kneaded in an extruder to be extrusion-coated,
A composite pipe 4 including a steel pipe 5 and a resin coating layer 6 as shown in FIG. 2 was obtained. The resin coating layer 6 had a thickness of 2 mm.

The composite pipe 4 was subjected to a deterioration accelerating test in which the inner surface was immersed in hot water at a temperature difference of 85 ° C. and the outer surface thereof at a temperature difference of 65 ° C. As a result, after 2000 hours, the resin coating layer 6
Was partially peeled from the steel pipe 5.

(Comparative Example 1) A composite pipe comprising a steel pipe and a resin coating layer containing no filler was obtained in the same manner as in Example except that the filler was not added to the water-crosslinkable silane-modified polyethylene. .

The composite pipe was subjected to the same deterioration acceleration test as in the example. As a result, a part of the resin coating layer was peeled off from the steel pipe after 200 hours.

(Comparative Example 2) A filler having a surface treated with aminosilane and having a diameter of 13 μm and an average fiber length of 500.
A composite consisting of a steel pipe and a resin coating layer containing ordinary glass short fibers in the same manner as in Example except that 20% by weight of ordinary (circular cross-section) short glass fibers (manufactured by Nitto Boseki Co., Ltd.) was added. Got a tube.

This composite pipe was subjected to the same deterioration acceleration test as in the example, and as a result, a part of the resin coating layer was peeled off from the steel pipe after 600 hours.

[0028]

As is apparent from the above description, the composite pipe of the present invention has a coating layer of synthetic resin to which at least the inner surface of the metal pipe is added a fibrous inorganic filler having concave grooves in the longitudinal direction. Since it is formed, the linear expansion coefficient is remarkably reduced as compared with the conventional composite pipe, and the residual strain during molding of the resin coating layer is reduced. Further, even if a fluid is absorbed from the surface of the resin coating layer, diffusion / permeation in the resin coating layer is hindered, it is difficult to reach the interface between the metal and the resin coating layer, and the rust and corrosion of the metal pipe progress slowly.

As a result of the above, the composite pipe of the present invention has corrosion resistance,
It has excellent heat resistance and maintains good adhesion between the metal tube and the resin coating layer for a long period of time.

It is to be noted that the concave grooves of the fibrous inorganic filler may form minute voids in the resin coating layer, or the concave grooves may impart flexibility to the fibrous inorganic filler. However, the effect of reducing running water noise when the fluid passes through the composite pipe was also observed.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a fibrous inorganic filler having a concave groove in the longitudinal direction, and FIG. (B) is another example.

FIG. 2 is a partially cutaway front view showing a composite pipe of an embodiment.

[Explanation of symbols]

 1 Mayu-shaped cross-section glass fiber 3 Recessed groove 4 Composite pipe 5 Steel pipe 6 Resin coating layer

Claims (1)

[Claims] 1. A composite pipe characterized in that a coating layer of a synthetic resin to which a fibrous inorganic filler having a groove in the longitudinal direction is added is formed on at least the inner surface of the metal pipe.