JPH02253076A - Cross-linked polyethylene pipe for hot water supply and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve long life such as pressure-resisting creep property by grafting a polyethylene having specified density and melt index with a silane compound followed by forming into a pipe in the uncross-linked state, and cross-linking the resulting polyethylene by the reaction with a silanol condensation catalyst and/or a water releasing material. CONSTITUTION:A polyethylene having a density of 0.933-0.939g/cm<3> and a melt index of 0.1-0.4g/10min is grafted with a silane compound and formed into a pipe in the uncross-linked state while the intermixture of water, silanol condensation catalyst and water releasing material is avoided as far as possible to prevent cross-linkage. After the molding, the resulting polyethylene is reacted with a silanol condensation catalyst and/or a water releasing material (those in which water is adsorbed to porous material powders such as alumina), and cross-linked. Hence, a hot water supply polyethylene pipe having well-balanced flexibility, short period strength and long period performance can be manufactured with good molding property.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a crosslinked polyethylene pipe for hot water supply for conveying hot water in water heaters, space heaters, etc., and a method for manufacturing the same.

[Conventional technology]

Conventionally, cross-linked polyethylene pipes made of cross-linked polyethylene have been used as piping for hot water supply instead of metal pipes such as stainless steel pipes and steel pipes. Cross-linked polyethylene pipes conventionally used for hot water supply have a density of 0.900 to 0.950 g.
/an? , melt index (hereinafter referred to as MI) 0
．． 5 to 5 g/10 minutes is used.

Such cross-linked polyethylene pipes have excellent flexibility, so bends can be formed without using special tools, and they are easy to work with, have excellent corrosion resistance, and are inexpensive.

However, such conventional cross-linked polyethylene pipes have problems such as pressure creep and poor long-term life.

[Problem to be solved by the invention]

An object of the present invention is to solve the above-mentioned problems by providing a crosslinked polyethylene pipe for hot water supply that has excellent long-term performance, has a good balance between 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. It is to propose.

[Means to solve the problem]

The present invention is the following cross-linked polyethylene pipe for hot water supply and its manufacturing method.

(]) A crosslinked polyethylene pipe for hot water supply, characterized in that it is made of crosslinked polyethylene obtained by crosslinking polyethylene with a density of 0.933 to 0.939 g/c+d and a melt index of 0.1 to 0.4 g/10 minutes.

(2) Polyethylene with a density of 0.933 to 0.939 g/cm3 and a melt index of 0.1 to 0.4 g/10 minutes is grafted with a silane compound and molded into a tubular shape in an uncrosslinked state while preventing crosslinking, A method for producing a crosslinked polyethylene pipe for hot water supply, which comprises reacting and crosslinking a silanol condensation catalyst and/or a water-releasing substance after molding.

In the present invention, the density and
74 polyethylene test method.

The polyethylene used in the present invention before crosslinking has medium density and high molecular weight. High molecular weight polyethylene has low weight, low melt flowability, and poor workability, so it has traditionally been used in an uncrosslinked state for piping systems that do not require strength, such as gas pipes, but crosslinking is difficult. High molecular weight cross-linked polyethylene pipes are not manufactured.

Generally, crosslinked polyethylene pipes are manufactured by extruding a mixture of polyethylene grafted with a silane compound, a silanol condensation catalyst, and/or a water-releasing substance, but crosslinking progresses during the extrusion process. As the molecular weight increases, the fluidity of camphor fat decreases, resulting in low N■
It is difficult to form cross-linked pipes using high molecular weight polyethylene.

In the present invention, a crosslinked pipe can be manufactured using high molecular weight polyethylene by molding the silane compound graft polychelene in an uncrosslinked state while preventing the progress of crosslinking, and then crosslinking it. By manufacturing a crosslinked polyethylene pipe in this manner, it is possible to manufacture a crosslinked polyethylene pipe even if low Ml high molecular weight polyethylene is used. The crosslinked polyethylene pipe thus obtained has excellent long-term performance such as internal pressure creep, and can be used as hot water supply piping for a long period of time.

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

The polyethylene used in the present invention is an ethylene homopolymer, or ethylene and 3 to 20 carbon atoms, preferably 3 to 3 carbon atoms.
~10 α-olefins and/or other thousands of
A copolymer with 0 mol% or less, preferably 10 mol% or less, or a modified product thereof, with a density of 0.933 to
0.939g/! - MI Q, 1 to 0.4 g/10 minutes is used. Examples of the α-olefin include propylene, 1-butene, 1-hexene, 1-octene-1,4-methylpentene, and the like.

Such crosslinking of 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, etc., but crosslinking with a silane compound is particularly preferred.

In the method of crosslinking with a silane compound, first, a silane compound and a radical generator are blended into the polyethylene, and the silane compound is grafted by heating the polyethylene to a temperature higher than the melting point of the polyethylene. The silane compound blended into polyethylene may be any silane compound having a group having an olefinically unsaturated bond and a hydrolyzable organic group, and is represented by the general formula %. In the formula, R1 and R2 have an olefinically unsaturated bond, are composed of carbon, hydrogen and optionally oxygen, are the same or different groups, and are reactive with free radical sites generated in polyethylene.

Examples of such groups include vinyl, allyl, butenyl, cyclohexenyl, and cyclopentagenyl, with terminal olefinically unsaturated groups being particularly preferred. Other preferred examples include CH having an ester bond of a terminal unsaturated acid.
,=C(C1,)COO(CH2)3-1CH2=C(
CH3)Coo (C,R2)2-0- (CH2)a
-1CH2=C(CH3)C00CH20CH,CH2
(OH)C)I□O(CH,)1 etc. can be given as =6-. Among these, vinyl groups are most suitable. X is an organic group having no olefinic unsaturated bond, such as monovalent hydrocarbon groups such as methyl, ethyl, propyl, tetradecyl, octadecyl, phenyl, benzyl, tolyl, etc. , or a halogen-substituted hydrocarbon group. Groups Y1, Y2, and (3) are each the same or different hydrolyzable groups, such as alkoxy groups such as methoxy, ethoxy, butoxy, and methoxyethoxy, alkoxyalkoxy groups, and acyloxy groups such as formyloxy, acetoxy, and probionoxy. , oxime e.g. -0N=C(CH3)2, -0N=
CHCH2C2H, and -0N=C(C6H5) 2
, or substituted amino groups and arylamino groups such as -
NHCH3, NlIC2H5 and -NH(C, ■,
), and any other hydrolyzable organic group.

The silane compound preferably used in the present invention is a compound represented by the general formula %, particularly the groups Y1, Y2, Y3
Silane compounds with the same values are suitable. Among these, vinyl 1-tris alkoxysilanes such as vinyl trimethoxysilane, vinyl 1-heliethoxysilane, and vinyl tris(methoxyethoxy)silane are most suitable. However, vinylmethyljethoxysilane and vinylphenyldimethoxysilane can be used as well. The blending amount of the silane compound is 0.1 to 1 part by weight of polyethylene.
20 parts by weight, particularly 0.5 to 5 parts by weight, is preferred.

The radical generator used is a compound that can create radical sites in polyolefin under silane grafting reaction conditions and has a half-life of 6 minutes or less at the reaction temperature, preferably 2 minutes or less. can do. These compounds include organic peroxides, effective peresters such as benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, dit
ert-butyl peroxide, 2,5-dimethyl-2
,5 di(peroxybenzoate)hexyne-3,1,
4-bis(tert-butylperoxyisopropyl)
Penzene, lauroyl peroxide, tert-butyl peracetate, 2,5-dimethyl-2,5-di(te)
rt-butylperoxy)hexane-3,2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butylperbenzoate, tert-
Butyl perphenylacetate-1-1 tert-butyl perisobutyrate, tert-butylperu 5ee-octoate, tert-butyl perpivalate, cumyl perpivalate and tart-butyl perdiethyl acetate, as well as other azo compounds such as azobis −
There are isobutyl nitrile and dimethyl azoisobutyrate. Among these are dicumyl peroxide, dite
rt-butyl peroxide, 2,5-dimethyl-2,5-
Di(tert-butylperoxy)hexyne-3, 2,
Dialkyl peroxides such as 5-dimethyl-2,5-di(tert-butylperoxy)hexane and 1,4-bis(tert-butylperoxyisopropyl)benzene are preferred.

An antioxidant can also be added to polyethylene in advance during the graft reaction. For example, polyethylene 10
A known antioxidant can be added in an amount of 0.005 to 10 parts by weight per 0 parts by weight.

These antioxidants may be added and uniformly mixed together with a silane compound, a radical generator, and other additives as necessary.

Antioxidants suitably used in the present invention include known radical inhibitors, and phenolic compounds or amine compounds are particularly preferred, such as (a) monophenolic compounds, (b) bis, tris, or polyphenols. (c) thiobisphenol compound,
and (d) a polyhydric phenol compound, (e) a naphthylamine compound, (f) a diphenylamine compound, or (g) an amine compound consisting of a p-phenylenediamine compound. Compounds having a 2,6-dimethylpiperidine skeleton are also effective.

(a) Compounds belonging to monophenolic compounds include 2,
6-tert-butyl-P-cresol, 2,6-
di-tert-butylphenol, 2,4-dimethyl-
6-tertbutylphenol, 2-methyl-4,6-
Di-nonylphenol, butyl hydroxyanisole, methyl 10-ionized phenol, 2,4.6-tri-tert-butylphenol, n-octadecyl-3-(4'-hydroxy-3',5' di-tert-butylphenol) propionate There is. (b) Bis, tris, or polyphenolic compounds include 4,4-dihydroxydiphenyl, 2,2'methylenebis(4-methyl-6-ter
t-butylphenol), 2,2'-methylenebis(4
-ethyl-6-tart-butylphenol), 2,2
'-Methylenebis(4-methyl-6-cyclohexylphenol), 4,4'-methylenebis(2,6-sheet
ert-butylphenol), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol),
1.1~bis(4-hydroxyphenyl)cyclohexane, 2.2'-dihydroxy-3,3'-di(α-methylcyclohexyl)-5,5'-dimethyl diphenylmethane, 1,3゜5-trimethyl- 2,4,6-tris(3,5-di-tert-butyl4-hydroxybenzyl)benzene, tris(2-methyl-4-hydroxy-
5-tert-butylphenyl)butane, te-1-lakis[methylene-3-(3', 5'-di-tert-butyl-4'-hydroxyphenyl)propionate comethane. (c) 4 for thiobisphenol compounds
．． 4'-thiobis(6-tert-butyl-3-methylphenol), 4,4'-thiobis(6-tert-butyl-0-fresol), 2,2'-thiobis(6-
tert-butyl-4-methylphenol). (
d) Polyhydric phenols or derivatives thereof include 2,5-di-tert-butylhydroquinone, hydroquinone monomethyl ether, and 2,5-di(tertiary amyl)hydroquinone. (e) Naphthylamine compounds include phenyl-α-naphthylamine, phenyl-β-naphthylamine, and aldol-α-naphthylamine; (f)
Diphenylamine compounds include p-isopropoxydiphenylamine, ρ (p-toluene sulfonylamide)
-Diphenylamine, bis(phenyl/impropylidene)-4,4'-diphenylamine, N,N'-diphenyl/ethylenediamine, N,N'-diphenyl/propylenediamine (ka) J, (g) p-phenylenediamine type The compounds include N,N'-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-
phenylene diamine, N.

N'-c(2-naphthyl)-P-phenylenediamine, Ncyclohexyl-N'-phenyl-p-phenylenecyamine, 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.

Among the above radical inhibitors, compatibility with polyethylene,
It is preferable that the product has a good color and is easy to handle, especially the phenolic radical inhibitors (a), (b) and (c), especially the phenolic radical inhibitors (a) and (b). When (C) a thiobisphenol-based radical inhibitor is used in combination, heat resistance can be imparted to polyethylene.

The amount of antioxidant added depends on the type and amount of radical initiator,
It also depends on the reaction conditions and the type of antioxidant.
It should be selected so as not to completely lose the effect of the radical initiator, and it is usually 0.01 to 3 parts by weight, preferably 0.03 to 1 part by weight, per 100 parts by weight of polyethylene. In addition, when blending with a radical crosslinkable polymer, although it varies depending on the type, it is generally blended in an amount of 0.02 to 1 times the amount of the radical initiator to prevent gelation or decomposition during the graft reaction. , preferred for work.

The silane craft polyethylene obtained as described above is molded into a tubular shape in an uncrosslinked state while preventing crosslinking. In order to prevent crosslinking, molding is performed while avoiding contamination with water, silanol condensation catalysts, water-releasing substances, etc. as much as possible. Molding is generally performed by extrusion, but other molding methods may also be used.

The silane gellast polyethylene tube thus obtained is preferably immersed in a solution containing a silanol condensation catalyst and/or a water-releasing substance to carry out a crosslinking reaction. Crosslinking can also be carried out by laminating the obtained resins.

The silanol condensation catalyst used in the present invention includes dibutyltin dilaurate, stannous acetate, tin octoate (tin caprylate), tin naphthenate, zinc caprylate, iron 2-ethylhexanoate, and naphthenic acid. Carboxylate salts such as cobalt, titanate ester]3=14 and organometallic compounds such as chelates, such as titanate tetrabutyl ester, titanate tetranonyl ester and bis(acetylacetonyl[-lyl) di-
These include organic bases such as isopropyl titanate, ethylamine, hexylamine, dibutylamine and pyridine, and acids such as fatty acids.

Among these, organic tin compounds, particularly tin carboxylate-1, such as dibutyltin dilaurate, dibutyltin diacetate, and dibutyltin dioctate are preferred.

Water-releasing substances include powders of porous substances such as alumina and molecular sieves that adsorb water, 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'-benzophenonetetracarboxylic acid, as well as microencapsulated products thereof.

The solvent for dissolving or dispersing the above-mentioned silanol condensation catalyst and/or water-releasing substance may be any solvent as long as it can dissolve or disperse them, such as n-decane. I do.

In addition, as the resin to be laminated to the pipe by adding a silanol condensation catalyst and/or a water-releasing substance, it is preferable to use silane-grafted polyethylene and polyethylene that has melt-fixing properties. , lamination molding is easy and stable molding is possible.

The amount of the silanol condensation catalyst and the water-releasing substance to be blended into the resin can be greater than the amount that is conventionally blended into the polyolefin together with a silane compound.

Its blending amount can be varied within a wide range depending on the application and the rate and proportion of the silanol crosslinking reaction.
Further, since the resin is not gelled by such a compound, the moldability is stable and good.

As an example of the blending amount, if a small amount of these compounds is blended into the silane-grafted polyolefin layer as described above, this should be taken into consideration, but usually 0 to 60 parts of the silanol condensation catalyst is added to 100 parts by weight of the resin. Parts by weight, in particular 0.5 to 30 parts by weight, and water-releasing substances 0 to 50 parts by weight, in particular 0.2 to 10 parts by weight are used.

When a silane-grafted polyethylene pipe is immersed in a solution of a silanol condensation catalyst and/or a water-releasing substance, or laminated with a resin containing these, the silanol catalyst and/or water-releasing substance penetrates into the pipe, causing a crosslinking reaction. happen. Although this reaction proceeds at room temperature, it is preferably carried out under heating, for example at 70 to 100°C. When resins are laminated, it is preferable to perform water treatment, particularly hot water treatment.

The cross-linked polyethylene pipe thus produced can be used for hot water supply, such as hot water supply systems and heating systems.

〔Effect of the invention〕

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

Furthermore, according to the method for manufacturing a crosslinked polyethylene pipe for hot water supply of the present invention, the crosslinked polyethylene pipe has excellent moldability and can be easily manufactured even though high molecular weight polyethylene with low melt flowability is used.

〔Example〕

Examples of the present invention will be described below.

Example 1 Medium density polyethylene (density 0.936
g/aJ, MI 0.2 g/10 min), 200 parts by weight of vinyltrimethoxysilane and 3 parts by weight of Perhexa 25B (manufactured by NOF Corporation, trademark) as an organic peroxide were mixed, and the mixture was extruded using an extruder. By heating and kneading at 230°C, a granular compound of vinyltrimethoxysilane grafted polyethylene was obtained. This compound was molded into a pipe using an extrusion molding machine. The obtained pipe was immersed in a 7% n-decane solution of dioctyltin, and a crosslinking reaction was carried out at 95°C for about 20 hours to obtain a crosslinked polyethylene pipe (outer diameter 13 mm, inner diameter 1.0 mm). .

The resulting 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) using the following measurement methods. The results are shown in Table 1.

Gel fraction measurement method ■Drying of sample = 110℃ 1 hour (vacuum) ■Measurement of sample weight: Approx. 0.2g Weight measurement before extraction...A (g) Place in extraction net and measure weight...・B (g)■ Uncrosslinked portion extract liquid: paraxylene, temperature 138.5°C
(boiling point), stirring extraction 3 hours ■Drying = 110℃ 1 hour (
(vacuum) ■Weight measurement after extraction: As is at the edge of the net...C (g)
■ Gel fraction uncrosslinked weight = B-C Water pressure is applied to a pipe with a length of 500 mm at 80°C, and the water pressure (kg/a#) at the time of breakage is measured. The amount of water supplied at this time is set so that the time required to reach the maximum pressure is 40 seconds.

Internal pressure load: 15kg/clj at 80℃ for a pipe with a length of 500mm
Then, a water pressure of 14.3 kg/a# is applied, and the time until destruction is measured.

Bending stress measurement method Support both ends of a pipe with a length of 150 mm, and place 20 mm in the center.
A strain is applied at mm/m1y1, and the yield point stress (kg#J) is measured.

Comparative Examples 1 to 3 Polyethylene used in Example 1 was molded into a pipe without crosslinking (Comparative Example 1),
Table 1 shows the results of a similar test performed on polyethylenes having different densities and MIs that were grafted, pipe-formed, and crosslinked in the same manner as in Example 1 (Comparative Example 2.3).

From the results in Table 1, it can be seen that the samples of the examples are superior in short-term strength and long-term performance, particularly in long-term performance, compared to those of the comparative examples, and have a good balance of flexibility, short-term strength, and long-term performance.

Claims (2)

[Claims] (1) A crosslinked polyethylene pipe for hot water supply, characterized in that it is made of crosslinked polyethylene obtained by crosslinking polyethylene with a density of 0.933 to 0.939 g/cm^3 and a melt index of 0.1 to 0.4 g/10 min. (2) Polyethylene with a density of 0.933 to 0.939 g/cm^3 and a melt index of 0.1 to 0.4 g/10 minutes is grafted with a silane compound and molded into a tubular shape in an uncrosslinked state while preventing crosslinking. A method for producing a cross-linked polyethylene pipe for hot water supply, characterized in that the pipe is cross-linked by reacting a silanol condensation catalyst and/or a water-releasing substance after molding.