JP2005321074A - Cross-linked polyethylene pipe manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a cross-linked polyethylene pipe which is extrusion molded while giving graft reaction to a silane compound for compatibly elongating fracture life and securing creeping performance. <P>SOLUTION: In a process for manufacturing the cross-linked polyethylene pipe, a mixture of a polyethylene resin and antioxidant agent (preferably, the antioxidant agent has a content of 0.3-1.5 wt% to the polyethylene resin) is supplied to an extruder, the plasticized resin is extrusion molded into a tubular shape while giving the graft reaction to the silane compound under the existence of radial generating agent and promoting it to be silanol under the existence of silanol catalyst, and then water cross-linking is applied to a molding. The used antioxidant agent is phenol antioxidant agent and phosphor antioxidant agent combined. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a crosslinked polyethylene pipe.

  In recent years, cross-linked polyethylene pipes that are used favorably as hot and cold water supply pipes and floor heating pipes are used in environments where they are exposed to high-temperature water for a long period of time. It is demanded. For this reason, the method of mix | blending an antioxidant is proposed as a means to prevent degradation of a polyethylene-type material conventionally (for example, refer patent document 1).

  In general, a crosslinked polyethylene pipe usually requires a degree of crosslinking of 65% or more in order to ensure the creep performance necessary for long-term use at high temperatures.

However, since an antioxidant usually becomes a reaction inhibiting factor in the graft reaction, the degree of crosslinking tends to be insufficient when the amount added is increased, and the effect of preventing deterioration of the material tends to be insufficient when the amount added is decreased. There was a problem. For this reason, there has been a demand for a method for producing a crosslinked polyethylene pipe that prevents the deterioration of the material and prolongs the fracture life of the pipe while ensuring the creep performance necessary for long-term use.
Japanese Patent No. 3497284

  In view of the above-described conventional problems, the object of the present invention is to provide a crosslinked polyethylene pipe that is extruded while allowing a silane compound to undergo a graft reaction. It is in providing the manufacturing method of a polyethylene pipe.

  The method for producing a crosslinked polyethylene pipe according to claim 1, wherein a mixture comprising a polyethylene resin and an antioxidant is supplied to an extruder, and the plasticized resin is grafted with a silane compound in the presence of a radical generator. In the production process of cross-linked polyethylene pipes, which are silanolized in the presence of a silanol catalyst, extruded into a tubular shape, and then cross-linked by water, the phenolic antioxidant and phosphorus antioxidant are used together as antioxidants It is characterized by being.

  The method for producing a crosslinked polyethylene pipe according to claim 2 is the method for producing a crosslinked polyethylene pipe according to claim 1, wherein the content of the antioxidant is 0.3 to 1.5% by weight based on the polyethylene resin. It is characterized by being.

  The method for producing a crosslinked polyethylene pipe according to claim 3 is the method for producing a crosslinked polyethylene pipe according to claim 1 or 2, wherein the ratio of phenolic antioxidant to phosphorus antioxidant is 1: 3-3. : 1 in combination.

  The method for producing a crosslinked polyethylene pipe according to claim 4 is the method for producing a crosslinked polyethylene pipe according to any one of claims 1 to 3, wherein the melting point of the phenolic antioxidant is 100 ° C or higher. Features.

Hereinafter, the present invention will be described in detail.
Although it does not specifically limit as a polyethylene-type resin in this invention, It is preferable that it is the polyethylene-type resin polymerized using the metallocene compound as a polymerization catalyst.

  In general, a metallocene compound is a compound having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. One or more tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum are used. A compound in which two or more cyclopentadiene rings or analogs thereof exist as ligands.

  Examples of the ligand include, for example, a cyclopentadienyl ring, an indenyl ring, a hydrocarbon group, a substituted hydrocarbon group, or a cyclopentadienyl ring substituted with a monosubstituted hydrocarbon metalloid group, an indenyl ring, and a cyclopentadienyl oligomer ring. Etc.

  In addition to these π-electron unsaturated compounds, for example, monovalent or divalent anion chelates such as chlorine and bromine, hydrocarbon groups, alkoxides, amides, phosphides, arylalkoxides, arylamides, arylphosphides Fido, aryloxide, etc. may be coordinated to the transition metal.

  Examples of the hydrocarbon group substituted with the cyclopentadienyl ring and indenyl ring include, for example, methyl, ethyl, propyl, butyl, isobutyl, amyl, isoamyl, hexyl, 2-ethylhexyl, heptyl, octyl, nonyl, decyl, cetyl , Phenyl and the like.

  Examples of such metallocene compounds include cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethylsilyltetramethylcyclopentadiene. Enyl-tert-butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamidohafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamidozirconium dichloride, methylphenylsilyltetramethylcyclo Pentadienyl-tert-butylamido hafnium dichloride, indenyl titanium tris (dimethylamide), indenyl titanium tri (Diethylamide), indenyl titanium tris (di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n- propyl amide) and the like.

  These metallocene compounds act as catalysts in the polymerization of olefins such as ethylene by changing the type of metal and the structure of the ligand and combining with a specific cocatalyst (co-catalyst). Specifically, the polymerization is performed in a system in which methylaluminoxane (MAO), a boron compound, or the like is added to a metallocene compound as a cocatalyst. The usage ratio of the cocatalyst with respect to the metallocene compound is 10 to 1,000,000 mole times, preferably 50 to 5,000 mole times.

The polymerization conditions are not particularly limited, and for example, a solution polymerization method using an inert medium, a bulk polymerization method substantially free of an inert medium, a gas phase polymerization method, and the like can be used. Usually, the polymerization temperature is generally −100 to 300 ° C., and the polymerization pressure is usually atmospheric pressure to 100 kg / cm ² .

  Moreover, as said polyethylene-type resin, the homopolymer of ethylene, the copolymer of ethylene and an alpha olefin, etc. are mentioned. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and the like.

  The silane compound used in the present invention is a silane compound having an olefinic unsaturated bond and a hydrolyzable organic group. Examples of a silane compound having such characteristics and preferable for use in the present invention include vinyl trisalkoxylane, and among these, vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltris (methoxyethoxy) silane are preferable. Further, vinylmethyldiethoxysilane, vinylphenyldimethoxysilane, or the like may be used.

The olefinic unsaturated bond site of the silane compound reacts with a free radical site generated in the polyethylene resin. Examples of radical generators that generate the radicals and that are preferable for the present invention include organic peroxides and organic peroxides. Among them, benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di (peroxybenzoate) hexyne-3, 1,4-bis (tert-butylperoxyisopropyl) benzene, lauroyl peroxide, tert-butyl peracetate, 2,5-dimethyl-2, 5-di (tert-butylperoxy) hexyne-3,2,5-dimethyl-2,5-di (tert-butylperoxy) hexane, tert-butylperbenzoate, tert-butylperphenylacetate, tert-butylperi Preferred are butyrate, tert-butyl per-sec-octoate, tert-butyl perpivalate, cumyl perpivalate, tert-butyl perdiethyl acetate, and other azo compounds such as azobis-isobutylnitrile, dimethyl Examples thereof include azoisobutyrate.

  As the radical generator, it is preferable to use one having a one-minute half-life temperature of 165 ° C. or higher and 190 ° C. or lower. When the 1-minute half-life temperature is less than 165 ° C., the amount of radical generation increases significantly at the initial stage of the reaction, which makes the control of the reaction difficult and makes it difficult to set stable molding conditions. From the cross-linking reaction, a transparent spherical gelled product generally called a scorch is generated in the product, which easily causes problems such as deterioration of the appearance of the product and a decrease in strength. On the other hand, when the temperature exceeds 190 ° C., the graft amount of the silane compound is reduced when the plasticized resin is silane-modified, so that the gel fraction does not become 65% or more and the creep characteristics of the molded product are inferior.

  The silanol condensation catalyst used in the present invention may be any compound generally used as a catalyst for promoting dehydration condensation between silanols. For example, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, acetic acid Compounds such as monotin, cobalt naphthenate, lead naphthenate, ethylamine, dibutylamine, hexylamine, pyridine, inorganic salts such as sulfuric acid, hydrochloric acid, toluenesulfonic acid, acetic acid, stearic acid, maleic acid, etc. One or more are preferably used, and dibutyltin dilaurate is more preferably used.

  In the present invention, a phenol-based antioxidant and a phosphorus-based antioxidant are used in combination as the antioxidant. By using a phenolic antioxidant and a phosphorus antioxidant in combination, it is possible to achieve both a long fracture life and a sufficient creep performance.

  Although the above-mentioned effects are not necessarily clear, in the method for producing a crosslinked polyethylene pipe using a specific graft reaction as in the present invention, the phenol-based antioxidant contributes to the extension of the fracture life, and the phosphorus-based antioxidant. It is presumed that the oxidizer contributes to ensuring creep characteristics.

  The content of the phenolic antioxidant and the phosphorus antioxidant used in combination is preferably 0.3 to 1.5% by weight based on the polyethylene resin. When the content is less than 0.3% by weight, the fracture life is particularly likely to be insufficient, and when it exceeds 1.5% by weight, the degree of crosslinking may be insufficient.

  Moreover, when the ratio of a phenolic antioxidant and a phosphorus antioxidant is used together in the range of 1: 3 to 3: 1, it is preferable in terms of excellent balance between fracture life and creep characteristics. When the ratio of the phenolic antioxidant is too small, the fracture life tends to be insufficient. Conversely, when the ratio of the phosphorus antioxidant is too small, securing of the degree of crosslinking may be insufficient.

  Furthermore, the melting point of the phenolic antioxidant is preferably 100 ° C. or higher. If the melting point is less than 100 ° C., the diffusion rate becomes too fast and the fracture life may be shortened.

  The method for producing a crosslinked polyethylene pipe according to the present invention comprises supplying a mixture of a polyethylene resin and an antioxidant to an extruder, grafting the plasticized resin with a silane compound in the presence of a radical generator, and silanol. In the production process of a crosslinked polyethylene pipe that is silanolized in the presence of a catalyst and extruded into a tubular shape, then the molded body is water-crosslinked, a phenolic antioxidant and a phosphorus antioxidant are used in combination as antioxidants. Therefore, it is possible to suppress the reaction inhibition in the graft reaction caused by the antioxidant, and to ensure the creep performance necessary for long-term use while extending the fracture life of the tube.

  When the content of the antioxidant is 0.3 to 1.5% by weight based on the polyethylene resin, the ratio of the phenolic antioxidant to the phosphorus antioxidant is in the range of 1: 3 to 3: 1. Further, when the melting point of the phenolic antioxidant is 100 ° C. or higher, the balance between the fracture life and the creep characteristics is improved, and the above effect is further ensured.

Hereinafter, the present invention will be described more specifically by showing examples and comparative examples.
In addition, this invention is not limited only to the following Example.

(Example 1)
For a polyethylene resin obtained by using a metallocene compound as a polymerization catalyst (trade name “HF1030” manufactured by Dow Chemical Co., Ltd.), phenolic antioxidant 1 (“Irganox 1010” manufactured by Ciba Specialty Chemicals Co., Ltd., melting point 110) )) 0.25% by weight and phosphorus antioxidant ("Irgaphos 168" manufactured by Ciba Specialty Chemicals Co., Ltd., melting point 183 ° C) 0.25% by weight was added to adjust the mixture, and the mixture was supplied from the hopper to the extruder. As a result, the water was removed from the vacuum vent hole provided in the cylinder of the extruder from the plasticized resin.

  Into the plasticized resin in the extruder, 3 parts by weight of vinyl ethoxysilane and dicumyl peroxide (1 minute half-life temperature 173 ° C.) with respect to 100 parts by weight of polyethylene resin from the injection hole provided in the cylinder of the extruder ) 0.12 parts by weight of the mixture was injected, and the silane compound was graft-reacted in the presence of a radical generator in an extruder set at a resin temperature of 185 ° C. to modify the silane. Next, the residual monomer was removed from the second vacuum bend hole provided in the cylinder from the silane-modified resin.

  Thereafter, 0.0135 parts by weight of dibutyltin dilaurate is injected into 100 parts by weight of polyethylene resin from the second injection hole provided in the cylinder into the silane-modified resin in the extruder to promote silanolization. I let you.

  Next, after extruding into a tubular shape from a mold, it was exposed to a water atmosphere and water cross-linked to a gel fraction of 65% or more to obtain a cross-linked polyethylene pipe.

(Example 2)
0.45% by weight of phenolic antioxidant 1 (“Irganox 1010” manufactured by Ciba Specialty Chemicals, melting point 110 ° C.) and polyethylene antioxidant (“Irgaphos 168 manufactured by Ciba Specialty Chemicals) relative to polyethylene resin ”, Melting point 183 ° C.) A crosslinked polyethylene tube was obtained in the same manner as in Example 1 except that 0.45% by weight was added.

(Example 3)
0.45% by weight of phenolic antioxidant 2 (“Irganox 1330” manufactured by Ciba Specialty Chemicals, melting point 240 ° C.) and polyethylene antioxidant (“Irgaphos 168 manufactured by Ciba Specialty Chemicals) relative to polyethylene resin ”, Melting point 183 ° C.) A crosslinked polyethylene tube was obtained in the same manner as in Example 1 except that 0.45% by weight was added.

Example 4
Phenolic antioxidant 1 (“Irganox 1010” manufactured by Ciba Specialty Chemicals Co., Ltd., melting point 110 ° C.) 0.6% by weight with respect to the polyethylene resin, and phosphorus antioxidant (“Irgaphos 168 manufactured by Ciba Specialty Chemicals Co., Ltd.). “Melting point: 183 ° C.) A crosslinked polyethylene tube was obtained in the same manner as in Example 1 except that 0.6% by weight was added.

(Comparative Example 1)
Cross-linked polyethylene pipe in the same manner as in Example 1 except that only 0.5% by weight of phenolic antioxidant 1 (“Irganox 1010” manufactured by Ciba Specialty Chemicals, melting point 110 ° C.) was added to the polyethylene resin. Got.

(Comparative Example 2)
Cross-linked polyethylene pipe in the same manner as in Example 1 except that only 0.5% by weight of phenolic antioxidant 2 (“Irganox 1330” manufactured by Ciba Specialty Chemicals, melting point 240 ° C.) was added to the polyethylene resin. Got.

(Comparative Example 3)
A crosslinked polyethylene tube was obtained in the same manner as in Example 1 except that only 0.9% by weight of a phosphorus-based antioxidant (“Irgaphos 168” manufactured by Ciba Specialty Chemicals, melting point 183 ° C.) was added to the polyethylene resin. It was.

The following evaluation was performed using the obtained polyethylene pipe. The evaluation results are shown in Table 1.
(Destruction life)
Antioxidant ability calculated | required with the following method as an evaluation of a destruction lifetime was measured. The greater the antioxidant capacity (the longer the time), the better the fracture life.
Antioxidant capacity measurement method: Measured in DSC (Differential Scanning Calorimeter) until the heat of decomposition starts at 228 ° C in an oxygen atmosphere.
(Creep characteristics)
As an evaluation of creep characteristics, the degree of crosslinking obtained by the following method was measured. The larger the degree of crosslinking, the better the creep characteristics.
Crosslinking degree measurement method: A sample cut out from a crosslinked polyethylene tube was extracted with a Soxhlet extractor using xylene as a solvent at a boiling point temperature for 10 hours, and the weight of the extraction residue was weighed and determined according to the following formula.
Degree of crosslinking (%) = [residual extraction weight (g) / sample weight before extraction (g)] × 100

  As is clear from Table 1, in the examples of the present invention, it was found that the balance between the antioxidant capacity and the degree of crosslinking was excellent, and both the fracture life and the creep characteristics could be exhibited in a well-balanced manner.

Claims (4)

  A mixture comprising a polyethylene resin and an antioxidant is supplied to an extruder, and the plasticized resin is grafted with a silane compound in the presence of a radical generator, and the silanolization is promoted in the presence of a silanol catalyst to form a tubular shape. Production of a crosslinked polyethylene pipe characterized in that a phenolic antioxidant and a phosphorus antioxidant are used in combination as antioxidants in the production process of a crosslinked polyethylene pipe for water-crosslinking the molded body after extrusion molding Method.   The method for producing a crosslinked polyethylene pipe according to claim 1, wherein the content of the antioxidant is 0.3 to 1.5% by weight based on the polyethylene resin.   The method for producing a crosslinked polyethylene pipe according to claim 1 or 2, wherein the ratio of the phenolic antioxidant and the phosphorus antioxidant is used in the range of 1: 3 to 3: 1. The method for producing a crosslinked polyethylene pipe according to any one of claims 1 to 3, wherein the phenolic antioxidant has a melting point of 100 ° C or higher.