JP2682120B2 - Cross-linked polyethylene pipe for hot water supply and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a hot water supply cross-linked polyethylene pipe for sending hot water in a water heater, a heater, etc., and a method for producing the same.

[Conventional technology]

Conventionally, as a pipe for hot water supply, a cross-linked polyethylene pipe obtained by cross-linking polyethylene is used instead of a metal pipe such as a stainless pipe or a copper pipe. The cross-linked polyethylene pipe that has been conventionally used for hot water supply has a density of 0.900 to 0.950 g / cm ³ and a melt index (hereinafter, referred to as MI) of 0.5 to 5 g / 10 min. Since such a crosslinked polyethylene pipe has excellent flexibility, it can form a bent portion without using a special tool, has good workability, excellent corrosion resistance, and is inexpensive.

However, such a conventional cross-linked polyethylene pipe has a problem that it is inferior in long-term life such as pressure-resistant creep.

[Problems to be solved by the invention]

In order to solve the above problems, an object of the present invention is to provide a crosslinked polyethylene pipe for hot water supply, which is excellent in long-term performance, has a good balance of flexibility, short-term strength and long-term performance, and is suitable for use as a hot water supply pipe, and a method for producing the same. Is to propose.

[Means for solving the problem]

The present invention is the following crosslinked polyethylene pipe for hot water supply and a method for producing the same.

(1) Density 0.933 to 0.939 g / cm ³ , melt index 0.1
~ 0.4g / 10min polyethylene, grafted with a silane compound, in a non-crosslinked state, molded into a tubular shape while preventing crosslinking,
A cross-linked polyethylene pipe for hot water supply, which is made of cross-linked polyethylene that is cross-linked by reacting a silanol condensation catalyst and / or a water-releasing substance after molding.

(2) Density 0.933 to 0.939 g / cm ³ , melt index 0.1
~ 0.4g / 10min polyethylene, grafted with a silane compound, in a non-crosslinked state, molded into a tubular shape while preventing crosslinking,
A method for producing a crosslinked polyethylene pipe for hot water supply, which comprises reacting a silanol condensation catalyst and / or a water-releasing substance after molding to crosslink.

In the present invention, the density and MI are based on JIS K 6774 polyethylene test method.

The polyethylene before crosslinking used in the present invention has a medium density and a high molecular weight. High-molecular-weight polyethylene has a low MI, low melt flowability, and poor workability, so it has been conventionally used in pipe systems that do not require strength such as gas pipes in an uncrosslinked state, but crosslinking is difficult, High molecular weight crosslinked polyethylene tubing is not manufactured.

Generally, a cross-linked polyethylene tube is manufactured by mixing a silane compound-grafted polyethylene with a silanol condensation catalyst and / or a water-releasing substance and extruding the mixture. , The higher the molecular weight, the lower the fluidity of the resin, low MI
It is difficult to form a cross-linked pipe using the high molecular weight polyethylene.

In the present invention, the silane compound-grafted polythielen is molded in a non-crosslinked state while preventing the progress of crosslinking, and then crosslinked, whereby a crosslinked pipe can be produced even by using high molecular weight polyethylene. By producing a crosslinked polyethylene pipe in this manner, it is possible to produce a crosslinked polyethylene pipe using a low MI, high molecular weight polyethylene. The crosslinked polyethylene pipe thus obtained has excellent long-term performance such as internal pressure creep, and can be used as a hot water supply pipe for a long time.

Even with such a cross-linked polyethylene pipe, the higher the density, the higher the strength, but the flexibility is lowered and the long-term performance is also lowered. Therefore, in the present invention, a crosslinked polyethylene pipe for hot water supply having a balance of flexibility, short-term strength and long-term performance can be obtained by using the above-mentioned specific density, that is, medium density.

The polyethylene used in the present invention is a homopolymer of ethylene, or ethylene and a carbon number of 3 to 20, preferably 3
Copolymer of 10 to 10 mol% or less of α-olefin and / or other monomer, preferably 10 mol% or less, or a modified product thereof, having a density of 0.933 to 0.939 g / c.
m ^3, using one of MI0.1 / 0.4g / 10 min. As the α-olefin, propylene, butene-1, hexene-1,
Examples thereof include octene-1, 4-methylpentene-1.

Such polyethylene may be crosslinked with a crosslinking agent such as a silane compound or divinylbenzene, or may be directly crosslinked with an organic peroxide, radiation or the like, but a crosslinking with a silane compound is particularly preferable.

The method of cross-linking with a silane compound is to first mix the polyethylene with a silane compound and a radical generator,
The silane compound is grafted by heating above the melting point of polyethylene. The silane compound blended with polyethylene is
Any silane compound having a group having an olefinically unsaturated bond and a hydrolyzable organic group may be used, and may be represented by the general formula R ¹ R ² SiY ¹ Y ² , R ¹ XSiY ¹ Y ² , or R ¹ SiY ¹ Y ² Y. Indicated by ³ . In the formula, R ¹ and R ^{2 each} have an olefinic unsaturated bond, are composed of carbon, hydrogen and optionally oxygen, and are the same or different groups, respectively, and are reactive with the free radical site generated in polyethylene. Examples of such groups are vinyl, acrylic, butenyl, cyclohexenyl,
There is cyclopentadienyl, and a terminal olein-containing saturated group is particularly preferable. Another preferable example is CH ₂ ═C (CH ₃ ) COO (CH ₂ ) ₃ having an ester bond of a terminal unsaturated acid.
_{-, CH 2 = C (CH} 3) COO (CH 2) 2 -O- (CH 2) 3 -, C
H ₂ C (CH ₃ ) COOCH ₂ OCH ₂ CH ₂ (OH) CH ₂ O (CH ₂ ) ₃ − and the like can be mentioned. Of these, the vinyl group is most suitable. X is an organic group having no olefinic unsaturated bond, and examples thereof include monovalent hydrocarbon groups such as methyl, ethyl, propyl, tetradecyl, octadecyl, phenyl, benzyl, and tolyl. Alternatively, a halogen-substituted hydrocarbon group may be used. The groups Y ¹ , Y ² and Y ³ are the same or different hydrolyzable groups, and examples thereof include alkoxy groups such as methoxy, ethoxy, butoxy and methoxyethoxy, alkoxyalkoxy groups, formyloxy,
Acetoxy, acyloxy groups such as propionoxy, oxime example _{-ON = C (CH 3) 2} , -ON = CHCH 2 C 2 H 5 and _{-ON = C (C 6 H 5} ) 2 or a substituted amino group and arylamino, groups such as -NHCH _3, -NHC ₂ H ₅ and -NH (C ₆ H
₅ ) and any other hydrolyzable organic group.

The silane compound preferably used in the present invention is a compound represented by the general formula R ¹ SiY ¹ Y ² Y ³ , and a silane compound having the same groups Y ¹ , Y ² and Y ³ is particularly suitable. Of these, vinyltrisalkoxysilanes such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltris (methoxyethoxy) silane are most suitable. However, vinylmethyldiethoxysilane, vinylphenyldimethoxysilane and the like can be used as well. The amount of the silane compound to be blended is 0.1 to 20 parts by weight, preferably 0.5 to 5 parts by weight, based on 1 part by weight of polyethylene.

As the radical generator used, a compound capable of forming a radical site in the polyolefin under the silane graft reaction condition and having a half-life of 6 minutes or less at the reaction temperature, particularly preferably a half-life of 2 minutes or less is used. can do. These compounds include organic peroxides, organic bell esters such as 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,
There are tert-butyl perphenyl acetate, tert-butyl perisobutyrate, tert-butyl per-sec-octoate, tert-butyl perpivalate, cumyl perpivalate and tert-butyl perdiethyl acetate, and other azo compounds such as There are azobis-isobutyl nitrile and dimethyl azoisobutyrate. Among these, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexyne-3,2,5-dimethyl-2,5-di (tert
Dialkyl peroxides such as -butylperoxy) hexane and 1,4-bis (tert-butylperoxyisopropyl) benzene are preferred.

At the time of graft reaction, an antioxidant may be added to polyethylene in advance. For example polyethylene 10
A known antioxidant can be added in an amount of 0.005 to 10 parts by weight based on 0 part by weight. These antioxidants may be added together with the silane compound, the radical generator and, if necessary, other additives, and mixed uniformly.

Antioxidants preferably used in the present invention include known radical inhibitors, especially phenolic compounds,
Alternatively, amine compounds are preferable, for example, (a) monophenol compounds, (b) bis, tris or polyphenol compounds, (c) thiobisphenol compounds, and (d) polyhydric phenol compounds and (e) naphthylamine compounds. Compound, (f) diphenylamine compound, or (g) p-phenylenediamine compound. A compound having a 2,6-dimethylpiperidine skeleton is also effective.

(A) 2,6 for compounds belonging to monophenol compounds
-Di-tert-butyl-p-cresol, 2,6-di-tert
-Butylphenol, 2,4-dimethyl-6-tert-butylphenol, 2-methyl-4,6-di-nonylphenol, butyl hydroxyanisole, styrenated phenol, 2,4,6-tri-tert-butylphenol, n- Octadecyl-3- (4'-hydroxy-3 ', 5'-di-
tert-butylphenol) propionate.
(B) 4,4-dihydroxydiphenyl, 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 2,2 'for bis, tris or polyphenol compounds
-Methylenebis (4-ethyl-6-tert-butylphenol), 2,2'-methylenebis (4-methyl-6-cyclohexylphenol) 4,4'-methylenebis (2,6-di-tert-butylphenol), 4, 4'-butylidene bis (3-methyl-6-tert-butylphenol), 1,1-
Bis (4-hydroxyphenyl) cyclohexane, 2,
2'-dihydroxy-3,3'-di (α-methylcyclohexyl) -5,5'-dimethyldiphenylmethane, 1,3,5-
Trimethyl-2,4,6-tris (3,5-di-tert-butyl-
4-hydroxybenzyl) benzene, tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, tetrakis [methylene-3- (3 ', 5'-di-tert]
-Butyl-4'-hydroxyphenyl) propionate] methane. (C) Thiobisphenol-based compounds include 4,4'-thiobis (6-tert-butyl-3-methylphenol) and 4,4'-thiobis (6-tert-butyl-
o-cresol) and 2,2'-thiobis (6-tert-butyl-4-methylphenol). (D) 2,5-Di-tert-butylhydroquinone, hydroquinone monomethyl ether, 2,5-
Di- (tertiary amyl) hydroquinone and the like. (E) The naphthylamine compounds include phenyl-α-naphthylamine, phenyl-β-naphthylamine and aldol-α-.
There are naphthylamines, and (f) diphenylamine compounds include p-isopropoxydiphenylamine and p- (p
-Toluenesulfonylamide) -diphenylamine,
Bis (phenyl isopropylidene) -4,4'-diphenylamine, N, N'-diphenylethylenediamine,
There is N, N'-diphenyl propylenediamine,
(G) P-phenylenediamine compounds include N, N'-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine and N, N'-
Di- (2-naphthyl) -p-phenylenediamine, N-
Cyclohexyl-N'-phenyl-p-phenylenediamine, N, N'-bis (1-methylheptyl) -p-phenylenediamine, N, N'-bis (1,4-dimethylpentyl) -p-phenylenediamine, N, N'-bis (1-ethyl-3-methylpentyl) -p-phenylenediamine and the like.

Of the above radical inhibitors, those which have good compatibility with polyethylene, good hue of products, and are easy to handle are preferred. Among them, the phenol radical inhibitors of (a), (b) and (c), particularly When (a) and (b) the phenol radical inhibitor and (c) thiobisphenol radical inhibitor are used in combination, heat resistance can be imparted to polyethylene.

The blending amount of the antioxidant varies depending on the type of the radical initiator, the blending amount, the reaction conditions or the type of the antioxidant, and should be selected so that the action of the radical initiator is not completely lost. Usually, 0.01 to 3 parts by weight, particularly 0.03 to 1 part by weight is suitable for 100 parts by weight. When blending with a radical-crosslinkable polymer, it varies depending on each type, but generally, blending in an amount of 0.02 to 1 times the blending amount of the radical initiator prevents gelation or decomposition during the graft reaction, Above all preferred.

The silane-grafted polyethylene obtained as described above is in an uncrosslinked state and is formed into a tubular shape while preventing crosslinking. In order to prevent cross-linking, molding is carried out while avoiding contamination of water, silanol condensation catalyst, water-releasing substance, etc. as much as possible. Molding is generally performed by extrusion molding, but other molding methods may be used.

The silane-grafted polyethylene pipe thus obtained is
The crosslinking reaction is preferably carried out by immersing in a solution containing a silanol condensation catalyst and / or a water-releasing substance, but the resin obtained by blending the silanol condensation catalyst and / or the water-releasing substance is laminated to perform the crosslinking. You can also

The silanol condensation catalyst used in the present invention is dibutyltin dilaurate, stannous acetate, stannous octoate (stannous caprylate), tin naphthenate, zinc caprylate, 2-
Carboxylates such as iron ethylhexanoate, cobalt naphthenate, organometallic compounds such as titanates and chelates such as tetrabutyl titanate, tetranonyl titanate and bis (acetylacetonitrile) di-isopropyl titanate. , Organic bases such as ethylamine, hexylamine, dibutylamine and pyridine, acids such as fatty acids. Among these, organotin compounds, especially tin carboxylates, such as dibutyltin dilaurate, dibutyltin diacetate and dibutyltin dioctate are preferable.

Further, the water-releasing substance, alumina, those obtained by adsorbing water to the powder of porous substances such as molecular sieves, gypsum, inorganic compounds such as aluminum hydroxide, vinyl alcohol, polyvinyl alcohol, maleic acid, pyromellitic acid, There are organic compounds such as trimellitic acid and 3,3 ', 4,4'-benzophenone tetracarboxylic acid, and further microencapsulated products thereof.

The solvent that dissolves or disperses the silanol condensation catalyst and / or the water-releasing substance may be any solvent that can dissolve or disperse them, and examples thereof include n-decane and the like. I do.

Further, as the resin to be blended with the silanol condensation catalyst and / or the water-releasing substance and laminated on the pipe, polyethylene having melt-fixing property with silane-grafted polyethylene is suitable, and if the contacting layers are similar polyethylene, Laminate molding is also easy and stable molding is possible.

The silanol condensation catalyst and the water-releasing substance can be added to the resin in a larger amount than in the case where the silanol condensation catalyst and the water-releasing substance were conventionally added to the polyolefin together with the silane compound.

The compounding amount can be varied in a wide range according to the rate and ratio of the silanol crosslinking reaction depending on the application, and the resin is not gelated by such a compounding, so the moldability is stable. And good.

As an example of the blending amount, when a small amount of these compounds is blended in the silane-grafted polyolefin layer as described above, it is carried out in consideration of them, but usually, relative to 100 parts by weight of the resin, the silanol condensation catalyst 0 to 60 is used. Parts by weight, especially 0.
5-30 parts by weight, water-releasing substance 0-50 parts by weight, especially 0.2-
10 parts by weight is used.

When the silane-grafted polyethylene pipe is dipped in a solution of a silanol condensation catalyst and / or a water-releasing substance or laminated with a resin containing them, the silanol catalyst and / or the water-releasing substance penetrates into the pipe to cause a crosslinking reaction. Occur. This reaction proceeds even at room temperature, but under heating,
For example, it is preferably carried out at 70 to 100 ° C. When the resins are laminated, it is preferable to perform water treatment, especially hot water treatment.

The cross-linked polyethylene pipe manufactured in this way can be used for hot water supply, hot water supply systems, heating systems, and the like.

〔The invention's effect〕

The cross-linked polyethylene pipe for hot water supply of the present invention has a specific density,
Since it is a cross-linked product of MI medium density high molecular weight polyethylene,
It has a good balance of flexibility, short-term strength and long-term performance, and has excellent performance as a hot water supply pipe.

Further, according to the method for producing a cross-linked polyethylene pipe for hot water supply of the present invention, it is possible to easily produce a cross-linked polyethylene pipe with excellent moldability, although a high-molecular-weight polyethylene having a small melt flowability is used.

〔Example〕

 Hereinafter, examples of the present invention will be described.

Example 1 Medium density polyethylene (density 0.936 g / c) obtained by copolymerizing 99 mol% of ethylene and 1 mol% of 4-methylpentene-1.
m ³ , MI 0.2 g / 10 min) 100 parts by weight, 200 parts by weight of vinyltrimethoxysilane and 3 parts by weight of Perhexa 25B (trademark of NOF CORPORATION) as an organic peroxide are mixed and heated to 230 ° C. with an extruder. By kneading, a granular compound of vinyltrimethoxysilane-grafted polyethylene was obtained. This compound was molded into a pipe by an extruder. 10% by weight of dioctyltin in the obtained pipe
It was dipped in an n-decane solution and subjected to a crosslinking reaction at 95 ° C for about 20 hours to obtain a crosslinked polyethylene pipe (outer diameter 13 mm, inner diameter 10 mm).

The obtained pipe was tested for gel fraction (degree of crosslinking), pipe breaking water pressure (short-term strength), internal pressure load breaking time (internal pressure creep), and bending stress (flexibility) by the following measuring methods. Table 1 shows the results.

Gel fraction measurement method Sample drying: 110 ° C for 1 hour (vacuum) Weight measurement of sample: approx. 0.2 g Weight measurement before extraction… A (g) Weight measurement in extraction net basket… B (g) Uncrosslinked Part extraction extract: paraxylene, temperature 138.5 ℃
(Boiling point), stirring extraction 3 hours Drying: 110 ° C 1 hour (vacuum) Weight measurement after extraction: net basket as it is ... C (g) gel fraction Pipe breaking water pressure measurement method A pipe with a length of 500 mm is loaded with water pressure at 80 ° C and the water pressure (kg / cm ² ) at the time of breaking is measured. The amount of water supplied at this time is set so that it takes 40 seconds to reach the maximum pressure.

Internal pressure load breakdown time 15kg / cm ² and 14.3kg / cm at 80 ℃ in a pipe with a length of 500mm
Load the water pressure of ² and measure the time (time) until it breaks.

Bending stress measurement method Supports both ends of a 150 mm long pipe with 20 mm / mi in the center.
Strain is given by n and stress at yield point (kg / cm ² ) is measured.

Comparative Examples 1 to 3 Molded into pipes without performing grafting and crosslinking with the polyethylene used in Example 1 (Comparative Example 1),
And polyethylene with different densities and MI,
Table 1 shows the results of the same test performed on the materials that were grafted, formed into a pipe and crosslinked in the same manner as in Example 1 (Comparative Examples 2 and 3).

From the results in Table 1, it can be seen that the examples are superior to the comparative examples in short-term strength and long-term performance, particularly long-term performance, and are balanced in flexibility, short-term strength, and long-term performance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akio Nakashiba 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi, Osaka, Osaka Gas Co., Ltd. (72) Fumio Hase 6 Waki, Waki-cho, Kaku-gun, Yamaguchi Prefecture Chome 1-2 Mitsui Petrochemical Co., Ltd. (72) Inventor Kazunori Mito 6 1-2 Waki, Waki-cho, Kuga-gun, Yamaguchi Prefecture Mitsui Petrochemical Co., Ltd. (72) Inventor Toshio Shiabuchi Osaka Prefecture 2-10-16 Minamikagaya, Suminoe-ku, Osaka City Shinwa Sangyo Co., Ltd. (72) Inventor, Mikio Nakaoka 2-10-16 Minamikagaya, Minamikagaya, Suminoe-ku, Osaka City, Osaka (56) References JP-A-58-37391 (JP, A) JP-A-63-29701 (JP, A) JP-A-57-127187 (JP, A)

Claims (2)

(57) [Claims] 1. A polyethylene having a density of 0.933 to 0.939 g / cm ³ and a melt index of 0.1 to 0.4 g / 10 min, which is not cross-linked by grafting a silane compound and is formed into a tubular shape while preventing cross-linking. A crosslinked polyethylene pipe for hot water supply, characterized by comprising a crosslinked polyethylene crosslinked by reacting a condensation catalyst and / or a water-releasing substance. 2. A polyethylene having a density of 0.933 to 0.939 g / cm ³ and a melt index of 0.1 to 0.4 g / 10 min, which has been grafted with a silane compound and is formed into a tubular shape while preventing cross-linking in a non-crosslinked state, and a silanol after the molding. A method for producing a crosslinked polyethylene pipe for hot water supply, which comprises crosslinking by reacting a condensation catalyst and / or a water-releasing substance.