JPH10193468A - Production of crosslinked polyethylene pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a crosslinked polyethylene pipe having both of 'flexibility at the time of normal temp.' and more excellent 'strength at the time of high temp.' without exerting unnecessary load on an extruder. SOLUTION: A crosslinked polyethylene pipe having strength higher than that of a conventional one can be obtained by using a polyethylenic resin obtained by using a metallocene catalyst as a raw material. By setting the density and melt index of the raw material resin to 0.5-5.5g/10min, a crosslinked polyethylene pipe having both of 'flexibility at the time of normal temp.' and more excellent 'strength at the time of high temp.' can be easily produced without exerting unnecessary load on an extruder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, crosslinked polyethylene pipes have been used as hot water pipes for hot water supply systems and heating systems instead of steel pipes. The crosslinked polyethylene pipe is required to have "flexibility at normal temperature" to reduce the burden on the installer and "high temperature strength (yield strength, creep characteristics, etc.)" required for hot water supply.

However, flexibility at room temperature generally causes a decrease in strength at high temperatures. Therefore, in the conventional technology for manufacturing a crosslinked polyethylene tube, it is impossible to achieve both flexibility at room temperature and strength at high temperatures. There was a problem that it was not easy.

[0004] In order to solve such a problem, Japanese Patent Laid-Open No. 253076/1990 has been proposed. In this proposed method, polyethylene (density: 0.933
0.939 g / cm ³ , melt index; 0.1
To 0.4 g / 10 min), then molding while preventing the progress of crosslinking and then crosslinking with a silanol condensation catalyst or the like to maintain the flexibility and maintain the strength at high temperatures (experimental As data, the breaking water pressure when applying pressure to the inside of the pipe with 80 ° C hot water, the time required for breaking when applying a constant pressure to the inside of the pipe with 80 ° C hot water, and the like are improved.

[0005]

However, in the invention of the above publication, the back pressure rises more than necessary during extrusion molding because the melt index of the raw material polyethylene is low (0.1 to 0.4 g / 10 min). However, there is a problem that an excessive load is applied to a drive motor of the extruder or the like to make molding difficult, and that an outer surface of the formed tube is distorted. Furthermore, the non-uniform distribution of crystals during cross-linking creates fragile parts in the solid structure, which makes it impossible to dramatically improve strength while maintaining flexibility.

The present invention has been made in view of such circumstances, and a cross-linked polyethylene tube having both "flexibility at normal temperature" and more excellent "strength at high temperature" is used in an extruder or the like. It is an object of the present invention to provide a method for producing a crosslinked polyethylene pipe which can be produced without imposing a burden on the pipe.

[0007]

In order to achieve the above object, a method for producing a crosslinked polyethylene pipe according to the present invention provides a method for producing a crosslinked polyethylene tube having a density of 0.1 using a metallocene compound as a polymerization catalyst.
A step of grafting a silane compound to a 934-0.940 g / cm ³ polyethylene-based resin in the presence of a radical generator to modify the silane, a step of forming a tube, and a step of exposing to a water atmosphere to obtain a gel fraction of 65. % Or more.

The properties and the like of the above metallocene compound will be described below. Generally, a metallocene compound is
It is a compound having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds, and one of tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum,
Or a compound in which two or more cyclopentadienyl rings or analogs thereof are present as ligands (ligands).

Examples of the ligand include a cyclopentadienyl ring, an indenyl ring, a cyclopentadienyl ring and an indenyl ring substituted with a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon monosubstituted metalloid group, and a cyclopentadienyl ring. Enyl oligomer rings and the like.

In addition to these π-electron unsaturated compounds,
For example, monovalent anions or divalent anion chelates such as chlorine and bromine, hydrocarbon groups, alkoxides, amides,
Phosphides, arylalkoxides, arylamides,
Aryl phosphide, aryl oxide and the like may be coordinated to the transition metal.

Examples of the hydrocarbon group substituted with the cyclopentadienyl ring and the 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, dimethylsilyltetramethyl Cyclopentadienyl-tert-butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamidohafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamidozirconium dichloride, methylphenylsilyl Tetramethylcyclopentadienyl-tert-butylamido hafnium dichloride, indenyl titanium tris (dimethylamide), indenylthi Niumutorisu (diethylamide), indenyl titanium tris (di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n- propyl amide) and the like.

These metallocene compounds function as catalysts in the polymerization of olefins such as ethylene by changing the type of metal and the structure of the ligand and combining them with a specific cocatalyst (co-catalyst). Specifically, the polymerization is carried out by reacting a metallocene compound with methylaluminoxane (MA) as a cocatalyst.
O), a boron compound or the like is added. The use ratio of the cocatalyst to the metallocene compound is 10 to 1,0
It is 0.00000 mole times, preferably 50 to 5000 mole times.

The polymerization conditions are not particularly limited.
For example, a solution polymerization method using an inert medium, a substantially inert
Bulk polymerization, gas-phase polymerization, etc.
Wear. Usually, polymerization temperature is -100 ~ 300 ° C, polymerization pressure
Force is normal pressure ~ 100kg / cm ^TwoIs generally
You.

Examples of the polyethylene resin include a homopolymer of ethylene and a copolymer of ethylene and an α-olefin. As an α-olefin,
For example, propylene, 1-butene, 1-pentene, 1-
Hexene, 4-methyl-1-pentene, 1-heptene,
1-octene and the like.

Actually, examples of the polyethylene resin obtained by using a metallocene compound as a polymerization catalyst include, for example, HF manufactured by Dow Chemical Company and EXA manufactured by Exxon Chemical Company.
CT and the like are commercially available.

The metallocene catalyst (compound) having such a structure is characterized in that the properties of each active site are uniform. That is, since the activity of each active site is equal, the molecular weight, molecular weight distribution, composition, and uniformity of the composition distribution of the polymer to be synthesized are improved. Therefore, by using a metallocene catalyst during the production of a polyethylene resin, it is possible to obtain a polyethylene resin having a narrower molecular weight distribution than when a conventional Ziegler catalyst is used. Also L-LDP
For E (linear low density polyethylene), butene,
Copolymerization with higher olefins such as hexene and octene is generally performed. By using a metallocene catalyst, the higher olefins are evenly added to the polyethylene chain, thereby obtaining a copolymer having a homogeneous structure. Obtainable.

Therefore, the polyethylene resin obtained by the metallocene catalyst is composed of lamellar layers having a uniform thickness, and the amount of molecules (tie molecules) that bind the lamellar layers to each other is smaller than that of the conventional resin. It is higher than the polyethylene resin obtained by the Ziegler catalyst, whereby a resin having better breaking properties can be obtained.

The crosslinking method in the production method of the present invention is silane crosslinking. That is, a mixture of the above-mentioned polyethylene-based resin, a silane compound, a radical generator, and a silanol condensation catalyst is melt-kneaded by a kneading apparatus and molded.

The silane compound used is a silane compound having an olefinic unsaturated bond and a hydrolyzable organic group. A silane compound having such characteristics and preferable for use in the present invention includes, for example, vinyltrisalkoxylan, and among them, vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltris (methoxyethoxy) silane are preferable. Further, vinylmethyldiethoxysilane, vinylphenyldimethoxysilane and 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 the radical generator that generates the radical and that is preferable in the present invention include organic peroxides and organic peresters, among which 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 (t
tert-butylperoxy) hexane, tert-butylperbenzoate, tert-butylperphenylacetate, tert-butylperisobutyrate, te
rt-butyl per-sec-octoate, tert-
Butyl perpivalate, cumyl perpivalate, ter
T-butyl perdiethyl acetate and the like are preferable. In addition, there are azo compounds such as azobis-isobutylnitrile and dimethylazoisobutyrate.

In general, when a polyethylene resin polymerized by a conventional Ziegler catalyst or the like is subjected to a crosslinking treatment, creep characteristics, yield strength, and the like are improved due to the presence of the crosslinking molecule. However, on the other hand, since the crystal structure is disturbed by the cross-linking molecules, a fragile portion is generated in the solid structure, stress concentration occurs, and a remarkable improvement in strength cannot be expected.

On the other hand, in the polyethylene resin obtained by using the metallocene catalyst, as described above, since the respective polymerization components are uniformly distributed in the polymer, disorder of the crystal structure due to cross-linking can be minimized. it can. Therefore, more excellent strength can be obtained.

These will be described with reference to Table 1. This table shows crystal melting data (data before and after cross-linking of a polyethylene resin obtained with a metallocene catalyst and a polyethylene resin obtained with a Ziegler catalyst) measured using a differential scanning calorimeter (DSC). Have been.

[0025]

[Table 1]

Here, the DSCpeak half width refers to the temperature width at half the height of the crystal melting peak. In this table, when comparing the half widths, before crosslinking, the resin with the metallocene catalyst is narrower by 0.9 (° C) than the resin with the Ziegler catalyst, and after crosslinking, the resin with the latter is narrower than the former. But 4.8 (° C.) narrower.

This indicates that the resin polymerized with the metallocene catalyst has a more uniform component distribution and the thickness of the lamella layer is more uniform with respect to the resin polymerized with the Ziegler catalyst. This shows that the latter crosslinked product is more uniformly distributed with respect to the former crosslinked product. It also shows that the lamellar layer having a uniform thickness has a more remarkable effect through the cross-linking treatment.

For these reasons, the polyethylene-based resin obtained using the metallocene catalyst exhibits uniform cross-linking upon addition of the silane compound. Therefore, by sufficiently dispersing and distributing the cross-linking agent, a uniform crystal distribution can be obtained. (This crystal distribution can be proved by analytical means such as small-angle X-ray scattering.)

Therefore, it is possible to avoid concentration of stress on the fragile portion when applying stress, and to provide high-temperature strength (yield strength, creep characteristics) superior to that of a conventional crosslinked polyethylene pipe having a non-uniform crystal distribution. be able to.

In the crosslinked polyethylene pipe of the present invention, the density of the raw polyethylene resin is 0.932.
It is preferably from 0.940 g / cm ³ to 0.940 g / cm ³ . In general, the higher the density, the higher the strength but the lower the flexibility. Therefore, the medium density as described above (0.932-0.
By using 940 g / cm ³ ), it is possible to obtain a tube in which flexibility and strength are balanced.

In the crosslinked polyethylene pipe of the present invention, the raw material polyethylene resin preferably has a melt index in the range of 0.5 to 5.5 g / 10 min, and more preferably 0.9 to 5.5. 5g / 10
min.

If this value is less than 0.5, the back pressure at the time of extrusion molding rises, and an excessive load is applied to the drive motor of the extruder, etc., making molding difficult. On the other hand, if it exceeds 5.5, the melt viscosity becomes insufficient and it becomes difficult to form a tube. Therefore, by taking values between them, it becomes possible to obtain a crosslinked polyethylene having both the ease of molding and the shape retention during molding in a well-balanced manner.

In the present invention, the silane-modified polyethylene tube is cross-linked so as to have a gel fraction of 65% or more, and preferably 70% or more. If the gel fraction does not reach 65%, the creep properties will be inferior even if a polyethylene having a suitable density and viscosity average molecular weight is used.

Hereinafter, a method for measuring the gel fraction will be described.
A sample of crosslinked polyethylene is extracted with a Soxhlet extractor using xylene as a solvent at the boiling point for 10 hours, and the weight of the unextracted residue is measured according to the following equation.

[0035]

(Equation 1)

[0036]

EXAMPLES Examples of the method for producing a crosslinked polyethylene pipe of the present invention will be described below together with comparative examples.

Example 1 A polyethylene resin obtained by using a metallocene compound as a polymerization catalyst (manufactured by Dow Chemical Company, trade name "HF1030", density: 0.935)
g / cm ³ , melt index; 2.6 g / 10 mi
n) 100 parts by weight, 3 parts by weight of vinyltrimethoxysilane, 0.12 parts by weight of dicumyl peroxide, and 0.0135 parts by weight of dibutyltin dilaurate were mixed and melt-kneaded in an extruder to perform crosslinking. Extrusion was performed to obtain a crosslinked polyethylene tube.

Comparative Example 1 The procedure was the same as in Example 1 except that the density of the polyethylene resin was 0.940 g / cm ³ .

Comparative Example 2 The procedure was the same as in Example 1 except that the density of the polyethylene resin was 0.931 g / cm ³ .

Comparative Example 3 Polyethylene resin obtained by using a Ziegler catalyst as a polymerization catalyst (manufactured by Dow Chemical Company, trade name "Dowlex 2037", density: 0.1%).
935 g / cm ³ , melt index; 2.6 g / 1
0 min) 100 parts by weight, 1 part by weight of vinyltrimethoxysilane, 0.04 part by weight of dicumyl peroxide, and 0.0135 part by weight of dibutyltin dilaurate were melt-kneaded in an extruder to perform crosslinking. Extrusion was performed to obtain a crosslinked polyethylene tube.

Comparative Example 4 The procedure was the same as Comparative Example 3 except that the melt index of the polyethylene resin was 0.4 g / 10 min.

Table 2 shows the densities and melt indexes of the polyethylene resins used in Example 1 and Comparative Examples 1 to 4.

[0043]

[Table 2]

With respect to the crosslinked polyethylene pipes obtained in Example 1 and Comparative Examples 1 to 4, the following items were measured according to the respective methods. Table 3 shows the results. (1) Tensile elastic modulus measurement (flexibility of pipe) This was performed according to JIS-K-7113.

(2) Measurement of internal creep at 95 ° C. hot pressure (strength of tube) A circumferential stress of 4.8 MPa was applied to the tube in hot water of 95 ° C., and cracking or leakage occurred in one hour. The determination was made according to JIS-K-6769.

(3) Measurement of load current value of extruder (moldability of tube) (4) Measurement of resin pressure (moldability of tube) Measured by a resin pressure gauge attached near the resin outlet of the adapter part (measuring part).

[0047]

[Table 3]

From Table 3, it can be seen that Example 1 has a good balance in tensile modulus, internal pressure creep, and extruder load current value. However, Comparative Example 1 has a large tensile modulus and is inferior in flexibility. Further, those of Comparative Examples 2 and 3 are weak in strength and cannot withstand high water pressure at high temperatures,
In the case of Comparative Example 4, the moldability was poor, a load was imposed on the extruder, and surface irregularities also occurred.

That is, the tube of Example 1 has a high balance of strength at high temperature and easiness of molding while maintaining flexibility at normal temperature, as compared with the conventional tube. I have.

The embodiments of the present invention are not limited to those described above. For example, as a silanol condensation catalyst, in addition to dibutyltin dilaurate, stannous acetate, stannous octoate (stannous caprylate) may be used. Tin), tin naphthenate,
Carboxylates such as zinc caprylate, iron 2-ethylhexanoate, and cobalt naphthenate may be used, and other organic metal compounds such as titanates and chelate compounds.
Among them, tetrabutyl titanate, tetranonyl titanate, bis (acetylacetonitrile) di-isopropyl titanate, organic bases such as ethylamine, hexylamine, dibutylamine and pyridine, and acids such as fatty acids can also be used. Good.

Further, as preferable kneading apparatuses in the practice of the present invention, for example, a single-screw extruder, a twin-screw extruder, a Banbury mixer, a kneader, a calender roll and the like can be mentioned.

[0052]

According to the method for producing a crosslinked polyethylene pipe of the present invention, since a polyethylene resin obtained by using a metallocene catalyst is used as a raw material, a polyethylene resin obtained by using a conventional Ziegler catalyst is used as a raw material. Thus, a crosslinked polyethylene pipe having higher strength can be obtained.

Further, since the density and melt index of the raw material resin are within the above-mentioned ranges, a crosslinked polyethylene tube having both “flexibility at normal temperature” and more excellent “strength at high temperature” is extruded. It can be easily manufactured without imposing an unnecessary load on a machine or the like.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 105: 24 B29L 23:00

Claims (2)

[Claims] 1. A step of grafting a silane compound on a polyethylene resin having a density of 0.932 to 0.940 g / cm ³ polymerized using a metallocene compound as a polymerization catalyst in the presence of a radical generator to modify the silane with silane. And a step of forming into a tube, and exposing to a water atmosphere to obtain a gel fraction of 65.
% Of a crosslinked polyethylene pipe. 2. The polyethylene resin before the silane modification has a melt index of 0.5 to 5.5 g / 10.
The method for producing a crosslinked polyethylene pipe according to claim 1, wherein the temperature is min.