JPH04292630A - Production of silane-cross-linked polyethylene tube - Google Patents

Abstract

PURPOSE:To provide a process for producing a flexible silane-cross-linked polyethylene tube. CONSTITUTION:A silane-cross-linked polyethylene tube having excellent flexibility can be produced by heating and forming a polyethylene for silane-cross- linking and treating with a water-containing fluid at a temperature above the softening point of the polymer, thereby cross-linking the polymer with water.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing cross-linked polyethylene pipes used for floor heating pipes, hot water supply pipes, etc., and in particular to the production of silane cross-linked polyethylene pipes that are flexible and have excellent pipe workability. It is about the method.

0002

BACKGROUND OF THE INVENTION Cross-linked polyethylene pipes have excellent pressure resistance, abrasion resistance, and flexibility, and are often used for floor heating pipes, hot water supply pipes, etc., which require complicated piping. As described in JIS K6769, methods for producing crosslinked polyethylene pipes include a peroxide crosslinking method in which crosslinking is completed during extrusion, and a silane crosslinking method in which crosslinking is performed after extrusion. Silane crosslinked polyethylene is crosslinked by silanol condensation using the reactivity of hydrolyzable silane introduced into polyethylene chains. This can be used in the form of a compound made by blending an organic silane compound, an organic peroxide crosslinking agent, and a silanol condensation catalyst into polyethylene. After extruding this into a tubular shape, it is immersed in hot water at 80 to 95°C to cross-link it. Alternatively, after extrusion molding a compound in which a graftomer obtained by polymerizing an organic silane compound and polyethylene is mixed with polyethylene containing a silanol condensation catalyst, it is then crosslinked in the same manner as the former.

0003

[Problems to be Solved by the Invention] With the recent rapid spread of polyethylene pipes, there has been a demand for piping materials with better workability. and JIS K6769
Two types of pipes) and methods of making the pipes themselves flexible are being considered. However, it is difficult to obtain flexible cross-linked polyethylene pipes using conventional cross-linked polyethylene pipe manufacturing methods. had to use it. As shown in Table 1, which shows the relationship between the density of raw material polyethylene and breaking stress, when the density of conventional products decreases slightly, the breaking stress decreases by 25 to 45%.

0004

[Table 1]

[0005] Generally, when imparting flexibility to a polyethylene molded product, there is a method of adding a lubricant to polyethylene composite to impart flexibility, but this method may cause problems in hygiene and durability. There are many. Therefore, the purpose of the present invention is to develop a method for manufacturing flexible silane-crosslinked polyethylene pipes without adding lubricants or changing the polyethylene raw materials by devising the water crosslinking process after extrusion molding. It is about providing.

[0006]

[Means for Solving the Problems] As a result of intensive studies, the present inventor has discovered that the reason why flexible crosslinked polyethylene pipes cannot be obtained by conventional manufacturing methods is that the pipes are cooled after extrusion molding. They discovered that the crosslinking was caused by the polyethylene being in a crystalline state, and they continued to investigate and found that it was possible to crosslink polyethylene while reducing its crystallinity. It was discovered that this method is effective, leading to the present invention. That is,
The present invention is a method for producing a silane-crosslinked polyethylene pipe with excellent flexibility, which is characterized by heating and molding silane-crosslinked polyethylene, and then treating it with a fluid containing water at a temperature higher than its softening temperature to water-crosslink it. The polyethylene for silane crosslinking used in the present invention may be any one, and commercially available products can also be used. In other words, the highly flexible silane-crosslinked polyethylene pipe of the present invention can be manufactured using not only low-density and medium-density types of polyethylene, but also high-density polyethylene with a high degree of crystallinity produced by a low-pressure method. In this case, the durability of the tube can be greatly improved. This polyethylene-modifying silane compound has the general formula RR'SiY2 (in the formula, R is bonded to a silicon atom through a silicon-carbon bond, and carbon, hydrogen and A monovalent olefinic unsaturated group optionally constituted by oxygen, each Y is a hydrolyzable organic group, and R' is a monovalent hydrocarbon group containing no fatty unsaturation or It is represented by the group Y). Further, a silanol catalyst is also disclosed in the above publication.

[0007]

[Operation] Polyethylene has crystals in its raw material compound as shown in FIG. 1, but during extrusion molding by heating, all the crystals melt and disappear. Crystals are precipitated during cooling after extrusion molding, but in the conventional method, the material is cooled to room temperature, and after the precipitation is completed, it is water-crosslinked with hot water at 80 to 95°C. Therefore, the polyethylene pipe after crosslinking has a high density and poor flexibility. On the other hand, in the present invention, after extrusion molding, crosslinking is performed using a fluid containing water at a temperature higher than the softening temperature, so crystals are hardly present during the crosslinking process, and are precipitated by cooling after the crosslinking process, but due to the crosslinking reaction. The resulting crosslinked structure suppresses crystallization. Therefore, the degree of crystallinity of the polyethylene pipe after crosslinking is lower than that of a silane crosslinked polyethylene pipe produced by a conventional method, and the density can also be kept low, resulting in a product with high flexibility.

[0008]

[Example] The present invention will be explained in detail below using an example. Example 1 The polyethylene compound for silane crosslinking shown in Table 2 was
After forming into a sheet with a hot press heated to 60 ° C., the cooling conditions were changed to crosslink with steam in an oven heated to 125 to 130 ° C. After cooling, the density, degree of crosslinking,
Hardness tests were conducted and the results are shown in Table 2. Also,
As a comparative example, a sample crosslinked under the conventional conditions (immersion in 80° C. hot water for 24 hours) was produced and subjected to similar tests, and the results are shown in Table 3. The measurement of density and degree of crosslinking is based on JIS K6769, and the measurement of hardness is based on JIS K6769.
It was conducted based on K7215.

Example 2 A tube extruded in a conventional manner was tested in the same manner as in Example 1, and the results are shown in Table 4. Further, the breaking stress was measured in accordance with ASTM D 1599 (Standard test method for short-time breaking strength for plastic pipes, tubes, and fittings) using a testing apparatus as shown in FIG. Using a manual water pressure pump, water was injected into the test tube installed in the water tank via a pressure gauge, and the pressure was increased continuously up to 15 kgf/cm2, and after that, the pressure was held for 1 minute every time the pressure was increased by 5 kgf/cm2. . The fracture stress was calculated from the fracture water pressure value obtained in this way using the following formula. σ=P(D-t)/(2t) σ=rupture stress (circumferential stress at time of fracture, kgf/cm2)P
= Breaking water pressure (kgf/cm2) D = Pipe outer diameter (cm2) t = Pipe wall thickness (cm)

0010

[Table 2]

[0011]

[Table 3]

0012

[Table 4]

[0013]

Effects of the Invention As explained above, according to the method of the present invention, it is possible to manufacture cross-linked polyethylene pipes with excellent flexibility, and the durability of cross-linked polyethylene pipes is significantly improved by using high-density polyethylene. can be improved.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically illustrating changes in crystal state due to differences in crosslinking methods according to the present invention and conventional methods.

FIG. 2 is a diagram illustrating a test device used for evaluating fracture stress in the present invention.

Claims (1)

[Claims] 1. A method for producing a silane-crosslinked polyethylene pipe with excellent flexibility, which comprises heating and molding silane-crosslinking polyethylene and then treating it with a fluid containing water at a temperature higher than its softening temperature to effect water crosslinking.