JPH0723757B2 - Composite pipe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a composite pipe used as a hot water supply pipe or the like.

(Prior Art) Conventionally, for example, as disclosed in Japanese Patent Publication No. 59-32712, a silicone-grafted polyolefin resin is extrusion-coated on a metal tube coated with vinylperoxysilane,
Next, hydrolyzed polyolefin-coated metal pipes and steel pipes whose inner surface is lined with water-crosslinked polyethylene as shown in Japanese Utility Model Publication No. 59-42550 are known.

(Problems to be Solved by the Invention) However, in the above-mentioned prior art, the former absorbs the deviation due to the difference in linear expansion coefficient between the metal and the polyolefin resin, because vinylperoxysilane lacks flexibility. However, even if the initial adhesiveness is excellent, the adhesive strength decreases when it is subjected to repeated cold and heat cycles.The latter, when used for hot water supply piping, is contained in the surface layer of the lining layer due to chlorine contained in tap water. There is a problem that water bubbles are generated and the lining layer is destroyed, that is, the chlorine resistance is not sufficiently satisfied.

(Means for Solving the Problems) The composite pipe of the present invention was made to solve the above-mentioned drawbacks of the conventional products, and its gist is to provide a high-density polyethylene resin as an inner layer and a silane-grafted modified low-density polyethylene resin. In an intermediate layer and a metal as an outer layer.

That is, a high-density polyethylene resin having excellent chlorine water resistance is arranged in the inner layer in contact with hot water to enhance the adhesiveness between the inner layer and the metal pipe which is the outer layer, so that the intermediate layer has excellent flexibility and high adhesive strength. A silane-grafted modified low density polyethylene resin was arranged to satisfy both chlorine water resistance and adhesion durability.

The high-density polyethylene resin used in the present invention is
The weight average molecular weight is 100,000 or more, preferably 200,000 or more.

The silane-grafted modified low density polyethylene resin used in the present invention has an elastic modulus of 2.5 × 10 ⁹ dyn / cm ² or less, preferably 2.0 × 10 ⁹ dyn / cm ² or less. Further, the modification is carried out by adding 0.1 to 10 parts by weight of an organosilicon compound and 0.001 to 3 parts by weight of a radical generator to 100 parts by weight of a low density polyethylene resin, preferably a linear low density polyethylene resin, and grafting in an extruder. Of.

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

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 outer layer are extruded and coated at the molding position to continuously mold the layers.

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

(Function) Since the composite pipe of the present invention has the high-density polyethylene resin as the inner layer and the silane-grafted modified low-density polyethylene resin as the intermediate layer, it can have both chlorine water resistance and adhesion durability.

(Example) Hereinafter, the Example of this invention is described.

As an example of the present invention, an aluminum long strip having a thickness of 1.5 mm is bent into a cylindrical shape, and the joint is welded to form an inner diameter.
An 80 mm aluminum tube was continuously made and used as the outer layer. On this inner surface, the density is 0.935, the weight average molecular weight is 68,000,
An intermediate layer made of silane-grafted modified linear low-density polyethylene having a modulus of elasticity (E 'value at 90 ° C) of 1.77 × 10 ⁹ dyn / cm ² and a thickness of 0.1 mm was extrusion-coated, and the inner surface had a density of 0. .
952, weight average molecular weight 200,000, elastic modulus 3.20 × 10 ⁹ dyn / cm
^{2. An} inner layer made of high-density polyethylene with a thickness of 2 mm was extrusion coated simultaneously with the intermediate layer to produce a composite pipe. A 50 cm long cut sample was prepared from this composite tube, immersed in chlorine water of 50 ° C and 500 ppm, and a chlorine water resistance test was performed to observe the state of water bubbles on the inner layer surface. Did not occur. In addition, hot water of 90 ℃ and normal temperature water of 30 ℃ 30
After repeating the alternating immersion for 1000 minutes 1000 times, an adhesive durability test was conducted to measure whether or not the adhesive strength was reduced, but the adhesive strength was not reduced.

For comparison, the silane-modified high-density polyethylene (G-
HDPE), high-density polyethylene (HDPE), silane-grafted modified linear low-density polyethylene (G-LLDPE), respectively, the results of examining the adhesion durability and chlorine water resistance in the same manner as in the above example, It is displayed together in the table below.

(Effects of the Invention) According to the present invention, a high density polyethylene resin is used as an inner layer, a silane graft modified low density polyethylene resin is used as an intermediate layer, and a metal is used as an outer layer. Therefore, both chlorine water resistance and adhesion durability are excellent. The composite pipe can be provided at low cost.

Claims (1)

[Claims] 1. A composite pipe comprising a high density polyethylene resin as an inner layer, a silane graft modified low density polyethylene resin as an intermediate layer, and a metal as an outer layer.