JPH0726707B2 - Composite pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention mainly relates to a composite pipe preferably used as a hot water supply pipe and the like.

(Prior Art) Conventionally, as a pipe material for water supply or hot water supply, for example, in Japanese Utility Model Publication No. 59-42550, it was obtained by spraying powder of a silane-modified water-crosslinked polyethylene resin onto the inner surface of a heated steel pipe. , A lining steel pipe having excellent heat resistance, chemical resistance, and abrasion resistance is disclosed.

Further, JP-B-59-32712 discloses that a silicone-grafted polyolefin resin is extrusion-coated on a vinyl peroxysilane-coated metal tube and then hydrolyzed to form a polyolefin resin-coated metal having excellent adhesiveness. A tube is disclosed.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional technique, the former is excellent in adhesiveness with a metal pipe because an inner layer made of a silane-modified water-crosslinked polyethylene resin is directly formed on the inner surface of the metal pipe. However, there is a problem that the silane modification lowers the crystallinity and deteriorates the corrosion resistance and the blister resistance.

The latter uses vinyl peroxysilane as a primer, so it has excellent initial adhesive strength, but since the elastic modulus of the resin is too large, stress such as repeated flow of hot and cold water causes stress inside the resin. When this occurs, there is a problem that this stress cannot be alleviated and the adhesiveness deteriorates after long-term use.

(Means for Solving the Problems) The composite pipe of the present invention is made to solve the above-mentioned problems, and in a composite pipe in which a synthetic resin is lined on the inner surface of the metal pipe, On the inner surface, an intermediate layer is formed by adding the same metal powder as the metal tube or an oxide powder of the metal to a silane-grafted modified low-density polyethylene resin, and further, on the inner surface of the intermediate layer, a high-density polyethylene resin is formed. The gist is that an inner layer to which the same metal powder as the metal tube or an oxide powder of the metal is added is formed.

In the present invention, the inner layer which is in contact with cold water or hot water is provided with a high density polyethylene resin layer to which the same metal powder as that of the metal tube or oxide powder of the metal is added.

As the high-density polyethylene resin, considering that the chemical solution mainly permeates into the amorphous region of the resin,
In order to enhance the corrosion resistance of the resin, the crystallinity is 60% or more,
It is preferable that the density is 0.95 g / cm ³ or more and the weight average molecular weight is 200,000 or more.

Further, in order to suppress the growth of blisters (blisters) generated in the above resin and improve the blister resistance,
It is preferable that the elastic modulus is 3 × 10 ⁹ dyn / cm ² or more.

Further, in order to further enhance the corrosion resistance and blister resistance of the high-density polyethylene resin, the same metal powder as that of the metal tube or oxide powder of the metal is added to the resin.

The metal powder or oxide powder of the metal used here is added in an amount of 10 to 30% by weight based on the high density polyethylene resin.

If the addition amount of the above powder is less than 10% by weight, there is no effect of improving the corrosion resistance and blister resistance of the resin, whereas if the addition amount exceeds 30% by weight, the weight of the composite pipe is It is not preferable because it becomes too heavy.

Further, the particle size of the metal powder or the oxide powder of the metal used here is preferably in the range of 100 to 500 μm.

When the particle size of the above powder is less than 100 μm, the effect of improving the corrosion resistance and blister resistance of the high-density polyethylene resin decreases, whereas when the particle size exceeds 500 μm, it is uniformly distributed in the resin. Since it is not dispersed and local uneven distribution easily occurs, the effect of improving the corrosion resistance and the blister resistance tends to be reduced.

In the present invention, an intermediate layer formed by adding the same metal powder as the metal tube or an oxide powder of the metal to the silane graft-modified low density polyethylene resin is provided between the inner layer and the metal tube.

The low-density polyethylene resin has a functional group formed inside the molecule by the silane graft modification, and can improve the adhesiveness to the metal tube.

The elastic modulus of the resin is preferably 2.5 × 10 ⁹ dyn / cm ² or less.

By so doing, it is possible to alleviate the internal stress generated by repeating thermal expansion and contraction of the resin, remove the internal stress generated in the resin, and prevent peeling of the adhesive interface and occurrence of blisters.

To obtain the same effect as in the inner layer, the same metal powder as the metal tube or the oxide powder of the metal is added to the intermediate layer, and the addition amount and the particle size range are the same as those in the inner layer. is there.

The silane-grafted modified low density polyethylene resin used in the present invention comprises 100 parts by weight of the low density polyethylene resin, 0.1 to 10 parts by weight of an organosilicon compound and 0.0
The amount is 01 to 3 parts by weight and is grafted in an extruder.

As the organosilicon compound, a hydrolyzable methoxy group,
A compound containing an organic functional group such as an ethoxy group, such as vinyltrimethoxysilane or vinyltriethoxysilane, is preferably used.

As the radical generator, dicumyl peroxide, t-butyl peroxide, etc. are preferably used.

Examples of the metal pipe used in the present invention include a steel pipe, a cast iron pipe, a copper pipe, an aluminum pipe, and the like, and it is preferable to use an aluminum pipe or a steel pipe from the viewpoint of adhesiveness with a resin.

The composite pipe of the present invention is gradually processed from a long strip-shaped sheet of metal into an arc shape to a circular shape to form a metal pipe, and an extrusion die is inserted inside the metal pipe at a position before becoming a metal pipe, The intermediate layer and the inner layer are extruded and coated at the molding position to continuously mold.

Further, in the composite pipe of the present invention, a resin coating may be applied to the outside of the metal pipe.

(Operation) In the composite pipe of the present invention, the same metal powder or oxide powder of the metal as the metal pipe is added to the inner layer and the intermediate layer formed on the inner surface of the metal pipe. The coefficient can be reduced to approach the coefficient of thermal expansion of the metal tube, and even if both layers expand and contract due to temperature rise and fall, the internal stress that is generated is not so large, so the adhesive strength between layers decreases. It is possible to prevent the occurrence of blisters.

In addition, the water that has penetrated into the inner layer and the intermediate layer collides with the powder to prevent the diffusion movement, so that the corrosion resistance is improved and the formation of blisters can be prevented.

(Examples) Hereinafter, examples of the present invention will be described, but the present invention is not limited to the examples.

Experimental Example-1 A long aluminum strip having a thickness of 1.6 mm was bent into a cylindrical shape, and then the joint portion was welded to continuously form an aluminum tube having an inner diameter of 80 mm.

On the inner surface of this aluminum tube, the density was 0.921 g / cm ³ , the elastic modulus was 1.77 × 10 ⁹ dyn / cm ² , and the weight average molecular weight was 43,000.
An intermediate layer (0.5 mm thickness) containing 20% by weight of 300 μm aluminum powder was extrusion coated, and then the inner surface of this intermediate layer had a density of 0.964 g / cm ³ , an elastic modulus of 3.87 × 10 ⁹ dyn / cm ² , A high-density polyethylene resin having a weight average molecular weight of 410,000 was extrusion-coated with an inner layer (1.5 mm thickness) obtained by adding 20% by weight of aluminum powder having an average particle diameter of 300 μm to prepare a lining pipe, and then the outer surface of the lining pipe. Then, a 20 mm thick medium density polyethylene resin foam was coated to form a composite tube. A cut sample of 50 cm in length was cut from this composite pipe, and hot water of 90 ° C and normal temperature water of 25 ° C were alternately passed through the cut sample for 15 minutes, and a repeated water flow test was conducted 6000 times. No peeling, blistering, blistering, or cracking was observed in the inner layer resin of the composite pipe.

Experimental Example-2 Instead of the aluminum long strip, a 1.6 mm thick steel long strip was used, and instead of aluminum powder,
A composite pipe was produced in the same manner as in Experimental Example-1 except that 20% by weight of iron powder having an average particle size of 300 μm was added, and the same method as in Experimental Example-1 was repeated for 6000 times. However, no peeling, blistering, blistering, or cracking was found in the inner layer resin of the composite pipe.

(Effect of the invention) Since the composite pipe of the present invention is configured as described above, it has excellent adhesiveness, corrosion resistance and blister resistance, and even when used for a long period of time, delamination or delamination in the outer layer, the intermediate layer and the inner layer Since no blister is generated, it can be suitably used as a hot water supply pipe.

Claims (1)

[Claims] 1. A composite pipe in which a synthetic resin is lined on the inner surface of the metal tube, the inner surface of the metal tube is made of a silane-grafted modified low-density polyethylene resin, the same metal powder as the metal tube or an oxide of the metal. A composite pipe in which a powder-added intermediate layer is formed, and further, an inner layer in which the same metal powder as the metal pipe or an oxide powder of the metal is added to the high-density polyethylene resin is formed on the inner surface of the intermediate layer. .