JPS5923575B2 - Polyethylene composition for water pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyethylene composition for producing polyethylene pipes for water service that will not be attacked by tap water even after many years of use.

Polyethylene has excellent chemical resistance, is physiologically non-toxic, is inexpensive, and is easy to process. Since the 1950s, polyethylene has been used as small-diameter water pipes to replace conventional lead pipes and iron pipes. It is widely used.

According to JISK-6762, polyethylene pipes for water supply are classified into type 1 pipes (soft pipes) and type 2 pipes (rigid pipes) according to their tensile strength. However, in some areas, accidents have occurred in which consumer faucets receiving water from branch pipes of Type 1 pipes are blocked by flaky foreign matter that is presumed to have fallen off from polyethylene pipes. This has caused some problems in the water supply industry. Polyethylene's excellent chemical resistance has been generally recognized since its introduction, and in fact, polyethylene containers and tubing are widely used for storing and transporting acids, alkalis, and various other chemicals.

Therefore, it is natural that polyethylene pipes have been adopted for supplying drinking tap water, which contains only trace amounts of impurities. However, when we dug up the polyethylene pipe that caused the faucet blockage accident from the ground and inspected its inner surface, we discovered that there were many water holes on the inside, and that these water holes were interconnected. It was discovered that the surface layer had peeled off in flakes. Conditions may vary depending on the region, but such accidents frequently occur in restaurants, barber shops, etc. that consume relatively large amounts of tap water, so the cause is likely to be water contained in the tap water. This is thought to be caused by disinfectants, namely dissolved chlorine.

This is because the Water Supply Act stipulates that the amount of dissolved chlorine must be 0.1 pμm or more at the end outlet of a water pipe, but in Obe City, where water quality is relatively poor, the amount of chlorine added is large. This is because polyethylene pipes through which a large amount of tap water flows are estimated to come into contact with more chlorine. In order to prove this reasoning, a polyethylene pipe corresponding to JIS 16762 type 1 was immersed in 0.2% chlorine water (2000 ppm) at 60°C for 10 hours, and a polyethylene pipe corresponding to type 2 was soaked in 0.2% chlorine water (2000 ppm) at 60°C. A polyethylene pipe with 0.
When immersed in 2% chlorine water at 60℃ for 40 hours (JIS-6762 dissolution test has a chlorine concentration of 2 pμm).
water at 20° C. for 24 hours), water spots were observed on both specimens.

The results of this experiment revealed that in order to prevent the above-mentioned accident, the first step is to develop a polyethylene composition that is not affected by dissolved chlorine in tap water. The present invention has been made to solve this problem. There is no prior literature regarding such a polyethylene composition, as no accident has ever been experienced in which water droplets occur on the inner surface of a polyethylene pipe for water supply and the inner surface peels off.

In order to solve these technical problems, the present inventors attempted to modify polyethylene by adding amphoteric substances such as calcium hydroxide and zinc hydroxide, as well as various other compounds. Aluminum hydroxide from 0.05 to 5.
It has been found that polyethylene pipes formed from polyethylene compositions containing 0% by weight are less susceptible to attack by dissolved chlorine in water.

As used herein, the term polyethylene refers to low density polyethylene having a density of 0.914 to 0.970;
Refers to medium-density polyethylene or high-density polyethylene singly or as a mixture.

Furthermore, any grade of aluminum hydroxide that is commercially available as a filler can be used as the aluminum hydroxide used in the present invention. High purity and fine particle size are more effective. In the present invention, the effect of aluminum hydroxide added to polyethylene increases in proportion to the amount added, as shown in the examples, so the amount of aluminum hydroxide added is preferably as large as possible.

However, if the amount added is too large, the mechanical strength of the formed polyethylene pipe will be reduced, so 0.05 to 5.0 weight percent of the total polyethylene composition is suitable. In addition, in the present invention, in addition to aluminum hydroxide, antioxidants, colorants, carbon black and other additives and fillers that are usually added to polyethylene compositions may be added as necessary. The present invention will be explained in detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Melt index 0.3 f/10 min and density 0.9
A certain amount of aluminum hydroxide is blended into low-density polyethylene (NUC-8300, manufactured by Nippon Unica Co., Ltd.) having 20 f/d using a Banbury mixer, and then pelletized by a conventional method. The polyethylene composition of the present invention was obtained by dry blending a carbon black masterbatch such that the black content was 2 percent by weight.

The amount of aluminum hydroxide added is 0.01 to the composition.
0.5, 1.0 and 2.0 weight percent. Using the polyethylene composition prepared in this way as a raw material, a diameter of 301! l, wall thickness 31! A polyethylene pipe was extrusion molded, and the obtained pipe was cut into a length of 7 CIL to prepare a test product.
1.2Tf1 per 1ctA of the inner and outer surface area of the sample
1 in 0.2% chlorine water at 60°C,
The surface condition of the sample was observed at regular intervals.

In addition, in order to keep the amount of dissolved chlorine constant, chlorine water is
They were replaced with new ones every hour. The results are shown in Table 1, and the numbers in Table 1 are plotted on a semi-logarithmic graph, which is shown in FIG. The numbers in brackets in the figure represent the sample number. In this example, the degree of occurrence of water spots is defined as 10 when water spots appear on the entire surface of the sample when visually observed, 0 when no spots occur at all, and 1 in between.
It is a qualitative scale divided into 0 stages.

[Brief explanation of drawings]

The figure is a diagram showing the relationship between the immersion time in chlorinated water and the number of sluices generated by plotting the numbers in Table 1 of the main text on a semi-logarithmic graph.

Claims (1)

[Claims] 1. A polyethylene composition for water pipes, characterized in that it contains 0.05 to 5.0 weight percent of aluminum hydroxide.