JPH0765701B2 - Polyethylene resin pipe - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyethylene resin pipe having improved chlorine resistance and suitable for water supply.

(Prior art and its problems) Polyethylene pipe is widely used as a water pipe because of its high strength and flexibility, but when it is used for a long time, water bubbles are generated on the inner surface of the pipe due to chlorine for sterilization in tap water. Has a problem that the inner wall is peeled off in a thin film form.

It is known that carbon black added to polyethylene pipes for imparting weather resistance influences the peeling with chlorine water, and carbon black should not be blended on the inner surface of the pipe that comes in contact with chlorine water. It has been proposed (Japanese Patent Publication No. 59-31929).

According to this, the peeling by chlorine water is considerably improved, but it is not improved over the original performance of the polyethylene resin,
Furthermore, there is a demand for a pipe that can reliably prevent peeling for a long period of time.

(Means for Solving Problems) The present invention is to meet the above-mentioned demands, in which the outermost layer is formed of a carbon black-added polyethylene-based resin to maintain weather resistance, and the polyethylene resin of the innermost layer is It is a pipe with added chlorine to improve chlorine resistance.

The present invention will be described in detail below.

The polyethylene-based resin which is the main component of the pipe of the present invention includes linear low-density polyethylene (LLDPE), low-density polyethylene, medium-density polyethylene, and high-density polyethylene, which may be a homopolymer or a small amount. It may be a copolymer containing a copolymerization component (for example, propylene, 1-butene, 1-pentene, vinyl acetate, acrylic acid), or a mixture of two or more polyethylene resins.

The carbon black added to the outermost layer of the pipe may be one conventionally used such as furnace black or channel black. The amount of addition depends on the thickness of the outermost layer,
In order to impart weather resistance to the pipe, about 1 to 5% by weight is added to the resin.

The zeolite added to the innermost layer of the pipe has a general formula of M ₂ O ・ Al ₂ O ₃・ mSiO ₂・ nH ₂ O (wherein M represents Na or an equivalent amount of metal, and m is 1.
5 to 20 and n represents 0 to 10), and there are various types such as A-type zeolite, P-type zeolite, and X-type zeolite. In the present invention, Na ₂ O.Al A type zeolite represented by ₂ O ₃ .2SiO ₂ .nH ₂ O or CaO.Al ₂ O ₃ .2SiO ₂ .nH ₂ O (n = 3 to 5) is particularly preferable.

The amount of zeolite added is preferably in the range of 0.1 to 2% by weight based on the resin.

By adding zeolite to the resin in the innermost layer, a higher chlorine water resistance than that of the polyethylene resin (without carbon black) is obtained.

The thickness of the outermost layer is 0.5 mm to give the pipe weather resistance.
Or more, preferably 2 mm or more, and the thickness of the innermost layer is
Make it 0.5 mm or more so that chlorine water does not penetrate inside the pipe.

In the pipe of the present invention, the composition of the core is not particularly limited as long as the outermost layer and the innermost layer have the above-mentioned composition, but from the viewpoint of easiness of production, and performance of sufficiently providing weather resistance and chlorine water resistance, carbon It is practical to have a two-layer structure including a black-added outer layer and a zeolite-added inner layer. The outer layer and the inner layer may be made of the same type of resin, or different types may be used.

In order to manufacture the pipe of the present invention, a multilayer extruder may be used and the multilayer pipe may be extruded using a multilayer annular die.

(Example 1) By a two-layer extrusion molding method, polyethylene pipes (nominal diameter 13, outer diameter 21.5 mm, thickness) with the material configurations shown in Table 1 Nos. 2 and 3
3.5 mm) was manufactured.

As a polyethylene resin, LLDPE (MFR 0.5, density 0.9
22), the thickness of the outer layer was 2.5 mm, and the thickness of the inner layer was 1.0 mm.

For comparison, Table 1 No.
The pipe shown in 1 was manufactured with the same dimensions.

Then, each pipe was immersed in chlorine water having a chlorine concentration of 2000 ppm, pH 7, and a temperature of 70 ° C. to carry out a chlorine water resistance accelerating test, and the generation time of water bubbles was examined.

The water bubble generation time (unit: time) was evaluated on a scale of 10 with a score of 0 when there was no change and a score of 10 when peeling occurred, and a score of 2 (4 water bubbles with a diameter of 0.4 mm or more / cm ² It was evaluated in terms of the time until the occurrence of water) and the time until a score of 8 (generation of 20 water bubbles having a diameter of 0.4 mm or more / cm ² ) was reached. The results are shown in Table 1.

From the above results, it is understood that the pipe of the present invention (No. 3) has improved chlorine water resistance as compared with the conventional pipe.

(Example 2) As polyethylene resin, high density polyethylene (MFR
Two types of pipes shown in Table 2 were produced in the same manner as in Example 1 except that 0.2 and density 0.955) were used, and the chlorine water resistance was evaluated in the same manner as in Example 1. The results are also shown in Table 2.

As is clear from Table 2, the pipe of the present invention (No. 5)
Excellent chlorine resistance.

Front page continuation (72) Inventor Yoshimi Takiguchi 2480 Sanchi, Hiratsuka-shi, Kanagawa Mitsubishi Plastics Co., Ltd. Hiratsuka factory (56) References JP 56-80458 (JP, A) Jitsuko 58-51487 ( JP, Y2)

Claims (1)

[Claims] 1. A polyethylene resin pipe having an outermost layer made of a polyethylene resin added with carbon black and an innermost layer made of a polyethylene resin added with zeolite.