JP2005054125A - Resin composition for silane-crosslinked polyethylene pipe and molded product thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED To actively perform a method for producing a crosslinked polyethylene pipe using a silane compound because the crosslinking operation is easy.
However, in the above production, a polyethylene pipe resin composition to be used for molding is first produced using an extruder. At this time, since it is operated at a high temperature of about 200 ° C., it is likely to cause eyes and eyes. This is an obstacle to work in this law.
Therefore, in the present invention, when a silane crosslinking resin composition obtained by graft copolymerization of polyethylene with a silane compound is produced, a fluorine-based lubricant is added in an amount of 0.005 to 1.0 with respect to 100 parts by weight of the polyethylene. A resin composition for silane-crosslinked polyethylene pipes, characterized by blending parts by weight, was developed.
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Description

  The present invention relates to a resin composition for a silane-crosslinked polyethylene pipe for producing a water-crosslinked polyethylene pipe having properties suitable for transporting fluids such as a gas pipe and a drinking water pipe, and a molded polyethylene pipe using the same. More specifically, the present invention provides a product in which the appearance of the resulting product is improved by significantly reducing the occurrence of eyes and eyes when the resin composition or polyethylene pipe of the present invention is produced.

Polyethylene is well known to improve physical properties such as heat resistance, creep resistance, environmental stress crack resistance and chemical resistance by crosslinking.
However, in the production of the crosslinked polyethylene pipe, the motor load of the molding machine is increased, which causes high cost.
Therefore, water-crosslinked polyethylene pipes are being manufactured. In this production method, in order to reduce the cost, a silane compound is graft-polymerized in advance in the presence of a radical initiator to crosslink between the molecules, and then the resulting graft copolymer is subjected to silanol condensation. Two methods are employed: a Sioplasm method in which a catalyst is added and uniformly kneaded and then molded into a predetermined shape, and a Monosilosil method in which the above raw materials are charged and kneaded into one extruder and extruded.

  The silane-grafted water cross-linking method in which moisture is allowed to act after being extruded by these methods is prosperous because it can be cross-linked at a lower cost than the conventional chemical cross-linking method using an organic peroxide. Development is under consideration.

Japanese Patent Publication No.48-1711 Japanese Patent Publication No.58-25583

The silane graft water cross-linking method is generally used in a molding machine such as an extruder after a small amount of an organic peroxide is graft copolymerized with polyethylene and a silane compound such as vinylalkoxysilane onto polyethylene. The extruded product is subjected to a crosslinking reaction by being exposed to high temperature and high humidity or warm water.
However, since the graft reaction between the silane compound and polyethylene is usually performed at a high temperature of 200 ° C. or higher, the low molecular weight polyethylene component in which the resin composition stagnates and adheres to the die portion of the extruder (or molding) is high temperature. For this reason, the phenomenon of oxidation and deterioration, so-called “eyes” is formed, and the precipitated low molecular weight product damages the appearance of the molded product, making it difficult to produce a beautiful molded product.

  For this reason, conventionally, in the production of water-crosslinked polyethylene pipes, attempts have been made to incorporate general-purpose lubricants such as calcium stearate, calcium stearate, erucic acid amide, etc. However, no satisfactory results have been obtained.

As described above, with the conventional improvement measures, it has been difficult to prevent the eyes from occurring over a long period of time.
In order to eliminate the above-mentioned problems of the prior art, the present invention provides a resin composition for a silane-crosslinked polyethylene pipe that can be continuously operated for a long time while greatly reducing the occurrence of eyes when producing a polyethylene pipe. The issue is to provide

  Therefore, in order to solve these problems, the present inventors in claim 1, when producing a silane crosslinking resin composition obtained by graft-copolymerizing a silane compound to polyethylene, And a silane-crosslinked polyethylene pipe resin composition characterized by comprising 0.005 to 1.0 part of a fluorine-based lubricant.

  As the fluorine-based lubricant used in the present invention, a fluorine resin having a carbon-fluorine bond in the molecule, for example, polytetrafluoroethylene, polytrifluoride ethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer , Tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl Examples thereof include ether ether copolymers.

Among these, a copolymer of vinylidene fluoride and hexafluoropropylene, and a vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer are effective in generating the eye when producing the resin composition of the present invention. It is preferable to prevent and greatly contribute to the improvement of workability.
In addition, you may mix | blend another adjuvant, for example, antioxidant, a coloring agent, etc. with the fluorine-type lubricant used by this invention as needed.

  As the silane compound used in the present invention, an organic silane compound having a vinyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, or vinylmethyldimethoxysilane is used.

  Further, as a graft initiator for grafting the silane compound onto polyethylene, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, 2,5-dimethyl-2 , 5-di (t-butylperoxy) hexane, m- (t-butylperoxyisopropyl-isopropyl) benzene, dicumyl, and other general-purpose radical generators.

Examples of the polyethylene used in the present invention include low density polyethylene, medium density polyethylene, linear low density polyethylene, and high density polyethylene. Incidentally, these polyethylenes may be used with additives such as antioxidants, colorants and inorganic fillers added.
In particular, high-density polyethylene has excellent creep resistance, and linear low-density polyethylene also has good creep resistance, and these resins are optimal for silane crosslinking resin compositions.

In the present invention, when a silane crosslinking resin composition obtained by graft copolymerizing a silane compound with polyethylene is produced, 0.005 to 1.0 part of a fluorine-based lubricant is blended with 100 parts of polyethylene. .
The amount of fluorine-based lubricant blended in a ratio of 0.005 part to 1.0 part with respect to 100 parts of polyethylene causes generation of eyes even when long run molding or high speed molding is performed by an extruder for molding a tube. Therefore, a molded product having a high surface smoothness can be obtained. In addition, if it is 0.005 part or less, it is difficult to prevent generation | occurrence | production in an eye, and if it exceeds 1.0 part, a molding defect may be caused, which is not preferable.

A second aspect of the present invention is a resin composition for a silane-crosslinked polyethylene pipe, wherein the fluorinated lubricant according to the first aspect is a vinylidene fluoride-hexafluoropropylene copolymer.
The vinylidene fluoride-hexafluoropropylene copolymer can be effectively prevented from being generated in the eyes even when long run molding or high speed molding is performed by an extruder for molding a tube, and is optimal for molding a tube.
A third aspect is a resin composition for a silane-crosslinked polyethylene pipe, wherein the fluorine-based lubricant according to the first aspect is a binary copolymer of vinylidene fluoride and hexafluoropropylene.
Binary copolymer of vinylidene fluoride and hexafluoropropylene can be effectively prevented from occurring in the eyes even when long run molding or high speed molding is performed by an extruder for molding pipes, making it ideal for pipe molding It is.

A fourth aspect of the present invention is a resin composition for a silane-crosslinked polyethylene pipe, wherein the polyethylene according to the first aspect is a high density polyethylene.
A fifth aspect of the present invention is the resin composition for a silane-crosslinked polyethylene pipe, wherein the polyethylene according to the first aspect is a linear low density polyethylene.

A sixth aspect of the present invention is a silane-crosslinked polyethylene pipe, which is formed by pipe forming using the resin composition for a silane-crosslinked polyethylene pipe according to claim 1 and then undergoes a crosslinking reaction by allowing moisture to act on the polyethylene pipe. .
The crosslinking reaction according to claim 6 may be performed using a conventionally known crosslinking means.
For example, when a silane compound is grafted to polyethylene, which is a base resin, a fluorine-based lubricant is blended to form a polyethylene pipe, and then subjected to warm water treatment, whereby an uncrosslinked polyethylene pipe is submerged in a water atmosphere. It can be easily cross-linked by exposure to water, exposure to water, steam or the like.

The silane cross-linked polyethylene pipe of the present invention exhibits excellent durability, especially long-term creep characteristics, excellent heat resistance, and its surface is rich in smoothness, making it ideal as a pipe for gas and drinking water It is.
A seventh aspect of the present invention is a silane-crosslinked polyethylene pipe, wherein the silane-crosslinked polyethylene pipe according to the fifth aspect is a water pipe.
The main pipe is rich in rigidity, and its surface is excellent in smoothness, and has an optimum property as a water pipe buried in the ground.

  The resin composition for a silane-crosslinked polyethylene pipe of the present invention and the molded product thereof may be blended with appropriate amounts of a heat stabilizer, a weather stabilizer, and an antioxidant so long as the properties of the composition are not impaired.

Examples and comparative examples are described below.
Example 1
100 parts linear low density polyethylene with a density of 0.93, MI value of 7 g / 10 min, 2 parts of vinylmethoxysilane, 0.06 part of 1,3-di (t-butylperoxydiisopropyl) benzene, and vinylidene fluoride-hexa A grafted resin composition for a silane-crosslinked polyethylene pipe of the present invention, which is mixed with 0.03 part of a fluoropropylene copolymer, kneaded at an extrusion temperature of 180 to 220 ° C. using a single screw extruder, cut into strands and granulated. Got.

The resin composition and a catalyst master batch (for example, 100 parts of linear low density polyethylene mixed with 1 part of dioctyltin dilaurate and an antioxidant) are mixed in a ratio of 19: 1 to obtain a uniaxial A polyethylene tube having an outer diameter of 13 mm and an inner diameter of 10 mm was extrusion-molded using an extruder.
The extruded polyethylene pipe was immersed in warm water at a temperature of 95 ° C. for 70 hours to subject the polyethylene to a crosslinking treatment to produce the silane-crosslinked polyethylene pipe of the present invention.
Next, the following measurements were performed in Table 1 and the results were displayed.

Table 1 shows the results obtained by visually measuring the effect of preventing the eyes generated during the production of the resin composition for a silane-crosslinked polyethylene pipe and the smoothness and surface roughness of the surface of the water-crosslinked silane-crosslinked polyethylene pipe. Show.
In addition, similarly to Example 1, it measured similarly about Examples 2-4 and Comparative Examples 1-4, and examined the result.

(1) After 6 hours from the start of molding, the degree of occurrence of eyes and eyes was monitored by the die lip and the condition of eyes and eyes was measured according to the following criteria.
◎ …… No adhesion to eyes or eyes on the die lip.
○ …… Slight adhesion to the eyes is observed.
× …… Brown eyes and outbreaks are observed.

(2) Smoothness of molded product surface For the silane-crosslinked polyethylene pipe obtained by molding, the smoothness of the molded product surface is visually determined according to the following criteria.
◎ …… The surface is rich in smoothness.
○ …… The surface is almost smooth.
× …… The surface is slightly smooth.

Example 2
Example 1 is the same as Example 1 except that the linear low-density polyethylene used in Example 1 is replaced with high-density polyethylene having a density of 0.948 and an MI value of 0.05.
Example 3
Example 1 is the same as Example 1 except that the vinylmethoxysilane used in Example 1 is replaced with a binary copolymer of vinylidene fluoride and hexafluoropropylene.

Example 4
Density 0.948, MI value 0.05 high density polyethylene 100 parts, vinylmethoxysilane 2 parts, 1,3-di (t-butylperoxydiisopropyl) benzene 0.06 parts, vinylidene fluoride-hexafluoropropylene copolymer 0.03 part of the coalescence and dibutyltin dilaurate were supplied to a single screw extruder, and a polyethylene tube having an outer diameter of 30 mm and an inner diameter of 25 mm was extruded at a temperature of 200 ° C.
The obtained polyethylene pipe was subjected to a crosslinking treatment by being immersed in warm water at a temperature of 95 ° C. for 3 days to produce a silane-crosslinked polyethylene pipe of the present invention.

Comparative Example 1
Example 1 is the same as Example 1 except that the amount of fluorinated hexafluoropropylene used in Example 1 is 0.003 part.
Comparative Example 2
Example 1 is the same as Example 1 except that the amount of fluorinated hexafluoropropylene used in Example 1 is 2.0 parts.

Comparative Example 3
Example 3 is the same as Example 3 except that the amount of the binary copolymer of vinylidene fluoride and hexafluoropropylene used in Example 3 is 0.0003 part.
Comparative Example 4
Example 3 is the same as Example 3 except that the amount of the binary copolymer of vinylidene fluoride and hexafluoropropylene used in Example 3 is 2.0 parts.

The silane cross-linked resin composition of the present invention greatly contributes to the improvement of workability by adding a fluororesin when kneading polyethylene and a silane compound, and hardly generating an eye even at a high temperature operation around 200 ° C. ing.
The obtained molded product has a smooth surface and a tube.

Claims (7)

When a silane crosslinking resin composition obtained by graft copolymerizing a silane compound with polyethylene is produced, 0.005 to 1.0 part by weight of a fluorine-based lubricant is blended with 100 parts by weight of the polyethylene. A resin composition for a silane-crosslinked polyethylene pipe. A resin composition for a silane-crosslinked polyethylene pipe, wherein the fluorine-based lubricant according to claim 1 is a vinylidene fluoride-hexafluoropropylene copolymer. A resin composition for a silane-crosslinked polyethylene pipe, wherein the fluorine-based lubricant according to claim 1 is a binary copolymer of vinylidene fluoride and hexafluoropropylene. The resin composition for silane-crosslinked polyethylene pipes, wherein the polyethylene according to claim 1 is high-density polyethylene. 2. The resin composition for a silane-crosslinked polyethylene pipe, wherein the polyethylene according to claim 1 is a linear low density polyethylene. A silane-crosslinked polyethylene pipe, wherein the silane-crosslinked polyethylene pipe is formed by using the resin composition for a silane-crosslinked polyethylene pipe according to claim 1 and then undergoing a crosslinking reaction by allowing moisture to act on the pipe. The silane cross-linked polyethylene pipe according to claim 5, wherein the silane cross-linked polyethylene pipe is a water pipe.