JP2010270167A - Method for manufacturing cross-linked polyethylene tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a cross-linked polyethylene tube that manufactures a cross-linked polyethylene tube with stable dimensions even when the caliber thereof is small, such as 10 mm or less, with good productivity using a one-step molding method. <P>SOLUTION: The method for manufacturing a cross-linked polyethylene tube is provided in which a silane-modified polyethylene resin composition including a polyethylene resin raw material, a silanol condensation catalyst, a silane compound, and a free radical generator is melted, kneaded, and reacted while heated in an extruder, and then extruded in a tubular form and cooled to produce a molded tube comprising the silane-modified polyethylene resin composition. The cross-linked polyethylene tube is obtained by performing a crosslinking process of the molded tube. As the polyethylene resin raw material, a mixture of a high-density polyethylene and a low-density polyethylene is used, of which the density is 0.930-0.940 g/cm<SP>3</SP>, the MFR is 2.0-4.0 g/10 minutes, and the molecular weight distribution (Mw/Mn) is 4.0-5.0, and in which 10-20 wt.% of the low-density polyethylene of the total polyethylene resin raw material is included. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

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

Cross-linked polyethylene pipes are compatible with both "flexibility at normal temperature" and "strength at high temperatures (heat resistance, high creep performance)", as well as corrosion resistance and cold resistance, such as hot and cold water supply pipes and hot water pipes for floor heating. Is used.
As a manufacturing method of this crosslinked polyethylene pipe, there are a two-stage molding method and a one-stage molding method (monosil method) described below (see Patent Documents 1 and 2).

  That is, the two-stage molding method includes a grafting step in which a raw material polyethylene resin (resin before crosslinking), a silane compound, and a radical generator are heated, melted, kneaded, and reacted to obtain a silane-modified polyethylene composition, and The obtained silane-modified polyethylene composition and a polyethylene resin composition containing a silanol condensation catalyst are melted and kneaded while being heated in an extruder, extruded into a tubular shape, and composed of the silane-modified polyethylene composition. After obtaining a molded tube in two stages of the molding process to form a molded tube, the obtained molded tube is subjected to a crosslinking treatment by a silanol condensation reaction in a water atmosphere.

On the other hand, in the one-stage molding method, a raw material polyethylene resin, a silanol condensation catalyst, a silane compound, and a radical generator are melted, kneaded and reacted while being heated in an extruder, and extruded into a tube to be grafted. The forming tube is obtained in one stage, that is, after obtaining the formed tube in one stage, the obtained formed tube is subjected to a crosslinking treatment by a silanol condensation reaction in a water atmosphere.
By the way, the two-stage molding method has two problems, that is, the grafting process and the molding process are performed separately, which increases man-hours, and has a problem that the productivity is worse and the equipment cost is higher than the one-stage molding method. .

On the other hand, the above-mentioned one-stage molding method is superior to the two-stage molding method in terms of productivity and equipment cost. There is a drawback that it is difficult to stably manufacture the polyethylene pipe.
That is, in the one-stage molding method, since a raw material polyethylene resin having a low melt viscosity is used, in the case of a small-diameter pipe whose wall thickness is thinner than that of a large-diameter pipe, The body cannot be retained, so-called “drawdown” occurs, and a cross-linked polyethylene tube having a stable dimension cannot be obtained.

Japanese Patent No. 3902865 Japanese Patent No. 4066114

  In view of the above circumstances, the present invention provides a cross-linked polyethylene pipe that can produce a cross-linked polyethylene pipe having a stable diameter even with a small diameter of 10 mm or less with high productivity using a one-stage molding method. It aims to provide a method.

In order to achieve the above object, a method for producing a crosslinked polyethylene pipe according to the present invention includes a silane-modified polyethylene resin composition containing a raw material polyethylene resin, a silanol condensation catalyst, a silane compound, and a radical generator. After being melted, kneaded and reacted while being heated in, it is extruded into a tube and cooled to form a molded tube made of the silane-modified polyethylene resin composition, and this molded tube is subjected to a silanol condensation reaction in a water atmosphere. In the method for producing a crosslinked polyethylene pipe subjected to crosslinking treatment, the raw polyethylene resin is composed of a mixture of high-density polyethylene and low-density polyethylene containing 10 to 20% by weight of low-density polyethylene in the whole raw polyethylene resin, polyethylene resin, density 0.930~0.940g / cm ^3, MFR 2.0~4.0g / 10 min, a molecular weight distribution (Mw / Mn) is characterized by a 4.0 to 5.0.

  Although the manufacturing method of the crosslinked polyethylene pipe | tube of this invention is not specifically limited, It is suitable for manufacture of the crosslinked polyethylene pipe | tube whose diameter is 10 mm or less.

In the present invention, the raw polyethylene resin has a low-density polyethylene blending ratio of 10 to 20% by weight, a density of 0.930 to 0.940 g / cm ³ , an MFR of 2.0 to 4.0 g / 10 minutes, and a molecular weight distribution. (Mw / Mn) is limited to 4.0 to 5.0.
The reason is as follows.

  That is, if the blending ratio of the low density polyethylene is less than 10% by weight, there is a problem in moldability, and if it exceeds 20% by weight, high creep performance cannot be secured.

When the density of the raw material polyethylene resin is less than 0.930 g / cm ³ , the resulting crosslinked polyethylene tube becomes too soft, and the strength such as pressure resistance is hindered. When the density exceeds 0.940 g / cm ³ , the resulting crosslinked The polyethylene tube becomes too hard and difficult to bend, and is damaged by bending.

  If the MFR of the raw material polyethylene resin is less than 2.0 g / 10 min, the viscosity of the resin becomes high, so that molding becomes difficult, and if it exceeds 4.0 g / 10 min, the viscosity becomes too low and the drawdown phenomenon is caused. As a result, stable dimensions cannot be obtained.

When the molecular weight distribution of the raw material polyethylene resin is less than 4.0, the viscosity of the plasticized resin becomes high, so that molding becomes difficult. When the molecular weight distribution exceeds 5.0, the creep characteristics of the resulting crosslinked polyethylene pipe are deteriorated.
In the present invention, the molecular weight distribution (Mw / Mn) is a value obtained by dividing Mw (weight average molecular weight) measured by a chromatography method by Mn (number average molecular weight) measured by a chromatography method.

The low density polyethylene used in the present invention is not particularly limited, but those having a density of 0.920 to 0.930 g / cm ³ are preferable.
Moreover, although MFR is not specifically limited, 0.5-10 g / 10min is preferable.

The high-density polyethylene used in the present invention is not particularly limited, but those having a density of 0.935 to 0.945 g / cm ³ are preferable.
Although MFR is not specifically limited, 2.0-4.0 g / 10min is preferable.
Although the manufacturing method of the said high density polyethylene is not specifically limited, The method using a metallocene catalyst is preferable.

  The silanol condensation catalyst used in the present invention may be any compound generally used as a catalyst for promoting dehydration condensation between silanols, such as dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, acetic acid. Examples include stannous, cobalt naphthenate, lead naphthenate, ethylamine, dibutylamine, hexylamine, pyridine and the like, inorganic salts such as sulfuric acid and hydrochloric acid, toluenesulfonic acid, acetic acid, stearic acid, maleic acid, etc. 1 type or 2 types or more are preferably used, and dibutyltin dilaurate is more preferably used.

The silane compound used in the present invention is not particularly limited as long as it is a silane compound having an olefinic unsaturated bond and a hydrolyzable organic group, but as a preferred silane compound for use in the present invention, for example, vinyl There are trisalkoxylanes, among which 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 the radical generator used in the present invention include organic peroxides and organic peroxides. Among them, benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl- 2,5-di (peroxybenzoate) hexyne-3, 1,4-bis (t-butylperoxyisopropyl) benzene, lauroyl peroxide, t-butylperacetate, 2,5-dimethyl-2,5-di (t- Butylperoxy) hexyne-3, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, t-butylperbenzoate, t-butylperphenylacetate, t-butylperisobutyrate, t-butylper -Sec-octoate, t-butyl per Bareto, cumyl perpivalate, peroxides such as t- butyl peroxide diethyl acetate, azobis - isobutyronitrile, azo compounds such as dimethyl azoisobutyrate and the like.

As described above, the method for producing a crosslinked polyethylene pipe according to the present invention has a density of 0.930 to 0.940 g / cm ³ , an MFR of 2.0 to 4.0 g / 10 min, and a molecular weight distribution (Mw / Mn). Since a mixture of high-density polyethylene and low-density polyethylene containing 10 to 20% by weight of low-density polyethylene of 4.0 to 5.0 is used as raw polyethylene resin, one-stage molding Even when the method is used and when a small diameter pipe having a diameter of 10 mm or less is manufactured, it can be manufactured with a stable size and high productivity without causing a drawdown phenomenon.

It is a figure showing the correlation between MFR and molecular weight distribution of the cross-linked polyethylene pipes manufactured in Examples and Comparative Examples.

  Hereinafter, specific embodiments of the present invention will be described in detail.

Example 1
High-density polyethylene (density 0.941 g / cm ³ , MFR 2.5 g / 10 minutes) and low-density polyethylene (density 0.921 g / cm ³ , MFR 0.5 g / 10 minutes) in a weight ratio of 9 to 1 By blending, a raw material polyethylene resin A having a density of 0.938 g / cm ³ , MFR of 2.2 g / 10 min, and a molecular weight distribution of 4.6 was obtained.
3 parts by weight of vinylethoxysilane as a silane compound, 0.12 parts by weight of dicumyl peroxide (1 minute half-life temperature 173 ° C.) as a radical generator, 100 parts by weight of the obtained raw material polyethylene resin A, silanol The dibutyltin dilaurate as the condensation catalyst was put in an extruder set at a resin temperature of 185 ° C. so that the blending ratio was 0.0135 parts by weight, and the inner diameter was 7.0 mm and the outer diameter was 10. A 0 mm shaped tube was extruded.
Then, the obtained molded tube was put in a treatment tank filled with water vapor and crosslinked to obtain a crosslinked polyethylene tube.

(Example 2)
High-density polyethylene (density 0.941 g / cm ³ , MFR 2.5 g / 10 min) and low-density polyethylene (density 0.921 g / cm ³ , MFR 0.5 g / 10 min) in a weight ratio of 8 to 2. By blending, a raw material polyethylene resin B having a density of 0.938 g / cm ³ , MFR of 3.9 g / 10 minutes, and a molecular weight distribution of 4.2 was obtained.
Using the obtained raw polyethylene resin B, a crosslinked polyethylene pipe was obtained in the same manner as in Example 1.

(Example 3)
High-density polyethylene (density 0.941 g / cm ³ , MFR 2.5 g / 10 minutes) and low-density polyethylene (density 0.921 g / cm ³ , MFR 0.5 g / 10 minutes) in a weight ratio of 9 to 1 By blending, a raw material polyethylene resin C having a density of 0.939 g / cm ³ , MFR 2.2 g / 10 min, and molecular weight distribution 4.9 was obtained.
Using the obtained raw polyethylene resin C, a crosslinked polyethylene pipe was obtained in the same manner as in Example 1.

Example 4
High-density polyethylene (density 0.941 g / cm ³ , MFR 5.0 g / 10 min) and low-density polyethylene (density 0.930 g / cm ³ , MFR 0.3 g / 10 min) to 85:15 by weight ratio By blending, a raw material polyethylene resin D having a density of 0.939 g / cm ³ , MFR 3.8 g / 10 min, and molecular weight distribution 4.8 was obtained.
A crosslinked polyethylene pipe was obtained in the same manner as in Example 1 by using the obtained raw polyethylene resin D.

(Example 5)
High-density polyethylene (density 0.941 g / cm ³ , MFR 2.0 g / 10 minutes) and low-density polyethylene (density 0.921 g / cm ³ , MFR 7.0 g / 10 minutes) in a weight ratio of 9 to 1 By blending, a raw material polyethylene resin E having a density of 0.938 g / cm ³ , an MFR of 2.2 g / 10 min, and a molecular weight distribution of 4.2 was obtained.
Using the obtained raw polyethylene resin E, a crosslinked polyethylene pipe was obtained in the same manner as in Example 1.

(Example 6)
High-density polyethylene (density 0.941 g / cm ³ , MFR 5.0 g / 10 min) and low-density polyethylene (density 0.928 g / cm ³ , MFR 1.0 g / 10 min) in a weight ratio of 8 to 2. By blending, a raw material polyethylene resin F having a density of 0.931 g / cm ³ , MFR of 3.0 g / 10 min, and a molecular weight distribution of 4.3 was obtained.
Using the obtained raw polyethylene resin F, a crosslinked polyethylene pipe was obtained in the same manner as in Example 1.

(Comparative Example 1)
In place of the raw material polyethylene resin A, only high density polyethylene (density 0.947 g / cm ³ , MFR 4.9 g / 10 min, molecular weight distribution 4.8) was used as the raw material polyethylene resin in the same manner as in Example 1 to cross-linked polyethylene. Got the tube.

(Comparative Example 2)
High-density polyethylene (density 0.941 g / cm ³ , MFR 5.0 g / 10 minutes) and low-density polyethylene (density 0.930 g / cm ³ , MFR 0.3 g / 10 minutes) in a weight ratio of 8 to 2. By blending, a raw material polyethylene resin G having a density of 0.938 g / cm ³ , MFR of 4.2 g / 10 minutes, and a molecular weight distribution of 3.9 was obtained.
Using the obtained raw polyethylene resin G, a crosslinked polyethylene pipe was obtained in the same manner as in Example 1.

(Comparative Example 3)
High-density polyethylene (density 0.941 g / cm ³ , MFR 5.0 g / 10 min) and low-density polyethylene (density 0.928 g / cm ³ , MFR 1.0 g / 10 min) in a weight ratio of 9 to 1 By blending, a raw material polyethylene resin H having a density of 0.937 g / cm ³ , MFR of 4.2 g / 10 minutes, and a molecular weight distribution of 5.2 was obtained.
A crosslinked polyethylene pipe was obtained in the same manner as in Example 1 using the obtained raw polyethylene resin H.

(Comparative Example 4)
High-density polyethylene (density 0.941 g / cm ³ , MFR 2.5 g / 10 min) and low-density polyethylene (density 0.928 g / cm ³ , MFR 1.0 g / 10 min) in a weight ratio of 9 to 1 By blending, a raw material polyethylene resin I having a density of 0.938 g / cm ³ , an MFR of 1.8 g / 10 min, and a molecular weight distribution of 5.5 was obtained.
Using the obtained raw polyethylene resin I, a crosslinked polyethylene pipe was obtained in the same manner as in Example 1.

(Comparative Example 5)
High-density polyethylene (density 0.941 g / cm ³ , MFR 2.5 g / 10 min) and low-density polyethylene (density 0.930 g / cm ³ , MFR 0.3 g / 10 min) in a weight ratio of 8 to 2. By blending, a raw material polyethylene resin J having a density of 0.938 g / cm ³ , an MFR of 1.8 g / 10 min, and a molecular weight distribution of 3.8 was obtained.
Using the obtained raw polyethylene resin J, a crosslinked polyethylene tube was obtained in the same manner as in Example 1.

  Formability during molding of molded pipes of Examples 1 to 6 and Comparative Examples 1 to 5, resin pressure (pipe moldability), motor load of extruder (pipe moldability), and obtained cross-linked polyethylene pipe Appearance, gel fraction (pipe strength), tensile yield strength (pipe strength), flexural modulus (pipe flexibility) were examined, and the results are shown in Table 1.

Regarding the formability, those that can be molded without causing drawdown were evaluated as “◯”, those that did not cause drawdown were evaluated as “Δ”, those that were difficult to mold were evaluated as “×”, and those that could not be molded and evaluated as “X”.
The resin pressure was measured with a resin pressure gauge attached near the resin outlet of the adapter part.
As the motor load, the load current value of the extruder was measured.
As for the tube appearance, it was visually evaluated that the glossy and non-concave portion was evaluated as “◯”, the glossy portion was uneven but “Δ”, the non-glossy portion and the uneven portion was evaluated as “X”.
The gel fraction was determined based on the method of JIS K 6769.
The tensile yield strength was determined based on the method of JIS K 6769.
The flexural modulus was determined based on the method of JIS K 7113.

  From Table 1 above, according to the production method of the present invention, a cross-linked polyethylene pipe having a good balance between formability and appearance (gloss) and having both flexibility at normal temperature and strength at high temperature is a small diameter pipe. It can be seen that it can be obtained stably.

  FIG. 1 shows the MFR and molecular weight distribution of the raw polyethylene resins used in Examples 1 to 6 and Comparative Examples 1 to 5 by comparing the MFR on the horizontal axis and the molecular weight distribution on the vertical axis.

  Using the raw polyethylene resins A to F obtained in Examples 1 to 6, a crosslinked polyethylene pipe having an inner diameter of 10 mm and an outer diameter of 13 mm and a crosslinked polyethylene pipe having an inner diameter of 5 mm and an outer diameter of 6.3 mm were obtained in the same manner as in Example 1. When each was molded, the evaluations of the formability and the tube appearance were the same as those in Examples 1 to 6.

Claims (2)

A silane-modified polyethylene resin composition containing a raw material polyethylene resin, a silanol condensation catalyst, a silane compound, and a radical generator is melted, kneaded and reacted while being heated in an extruder, and then extruded into a tube and cooled. Thus, in the method for producing a crosslinked polyethylene pipe in which the molded pipe is made of the silane-modified polyethylene resin composition, and the molded pipe is subjected to a silanol condensation reaction in a water atmosphere, the raw polyethylene resin has a low density. It consists of a mixture of high-density polyethylene and low-density polyethylene containing 10 to 20% by weight of polyethylene, and the density of the raw polyethylene resin is 0.930 to 0.940 g / cm ³ , and the MFR is 2.0 to 4.0 g / 10 min, molecular weight distribution (Mw / Mn) of 4.0 to 5.0 Manufacturing method of ethylene pipe.   The method for producing a crosslinked polyethylene pipe according to claim 1, wherein a crosslinked polyethylene pipe having a diameter of 10 mm or less is obtained.

Images