JP2009120846A - Crosslinked polyethylene pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crosslinked polyethylene pipe which is excellent in pressure resistance and has good piping laying properties and productivity. <P>SOLUTION: The crosslinked polyethylene pipe uses, as a base resin, a polyethylene which is produced by polymerization in the presence of a single site catalyst and has a specific density and a specific melt flow rate and of which, in specific measurements, (1) the ratio (Mw/Mn) of weight-average molecular weight (Mw) to number-average molecular weight (Mn) of the total amount of elution is 2.5-9.0, (2) in the integral representation of molecular weight distribution of the total amount of elution, i.e., the relation between log M and w, w is 50% or more when log M=5, and (3) the maximal point temperature TWmax exhibiting the maximal amount of elution is in a predetermined temperature range, and in the integral representation of molecular weight distribution of the total amount of elution eluted in a predetermined temperature range, w is 50% or less when logM=4. The pipe is produced by subjecting a resin composition containing the base resin to silane crosslinking. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cross-linked polyethylene pipe that can be suitably used as a pipe for water supply or hot water supply having excellent moldability and mechanical properties.

  In recent years, plastic piping materials with excellent corrosion resistance and workability have been used as pipes for water supply and hot water supply. Especially, it is necessary to use cross-linked polyethylene pipes that have excellent pressure resistance and creep resistance at high temperatures. It has become mainstream. Among these, silane-crosslinked polyethylene pipes using high-density polyethylene as a base resin have excellent pressure resistance, and are therefore being applied to pipes for water supply with higher water pressure.

  However, when polyethylene having a high density is used as the raw material polyethylene in order to improve pressure resistance, there is a problem that the obtained crosslinked polyethylene pipe is difficult to bend and it is difficult to construct the pipe.

  On the other hand, from the viewpoint of improving the production efficiency of the silane-crosslinked polyethylene pipe, polyethylene having a high melt flow rate (MFR) may be selected as the base resin in order to increase the speed of the production line with as little load on the extruder as possible. preferable. However, the greater the MFR of polyethylene as the base resin, the worse the cross-linking efficiency and the pressure resistance are impaired. Therefore, polyethylene having a very large MFR cannot be used as the base resin, which improves the production efficiency. It was a hindrance.

  The present invention has been made to solve such problems, and an object of the present invention is to provide a cross-linked polyethylene pipe having excellent pressure resistance and excellent piping workability and productivity.

According to the present invention, the following means are provided.
Polymerized using a single site catalyst,
In measurement using a cross fractionation device having a density of 0.938 to 0.950 g / cm ³ , a melt flow rate of 1.0 to 7.0 g / 10 minutes, and a combination of temperature rise elution fractionation and gel permeation chromatograph ,
(1) The ratio of the weight average molecular weight Mw to the number average molecular weight Mn of the total elution amount, Mw / Mn is 2.5 to 9.0,
(2) In the integral display of the molecular weight distribution of the total elution amount, that is, in the curve showing the relationship between logM and w (where M is the molecular weight, w is weight%), w when logM = 5 is 50% or more ,
(3) The maximum point temperature TWmax indicating the maximum elution amount is in the range of 81 ° C to 105 ° C,
In the integral display of the molecular weight distribution of the total elution amount eluted between 30 ° C. lower than the temperature TWmax indicating the maximum elution amount (TWmax-30) ° C. and 15 ° C. lower than the TWmax (TWmax-15) ° C. A crosslinked polyethylene pipe obtained by using polyethylene having a w of 50% or less when log M = 4 as a base resin, and silane-crosslinking a resin composition containing the polyethylene.

  ADVANTAGE OF THE INVENTION According to this invention, the bridge | crosslinking polyethylene pipe which shows high pressure resistance can be provided, without reducing piping workability and productivity. Further, by using a specific molding material for producing a crosslinked polyethylene pipe, it is possible to achieve both productivity and product characteristics.

The three-dimensional figure which expressed the molecular weight distribution of Example 2 three-dimensionally with temperature and molecular weight. The three-dimensional figure which expressed the molecular weight distribution of Example 7 in three dimensions with temperature and molecular weight. The three-dimensional figure which expressed the molecular weight distribution of the comparative example 6 in three dimensions with temperature and molecular weight. The differential display of the molecular weight distribution of the total elution amount of the polyethylene of Example 2, and an integral display figure. The differential display of the molecular weight distribution of the total elution amount of the polyethylene of Example 7, and an integral display figure. The differential display of the molecular weight distribution of the total elution amount of the polyethylene of the comparative example 6, and an integral display figure. The elution temperature curve figure of Example 2. FIG. The molecular weight distribution of the eluate eluted between 30 ° C. lower than the temperature TWmax (TWmax-30) ° C. and 15 ° C. lower than the TWmax (TWmax-15) ° C. showing the maximum elution amount of the polyethylene of Example 2. Differential display and integral display diagram. The molecular weight distribution of the eluate eluted between 30 ° C. lower than the temperature TWmax (TWmax-30) ° C. and 15 ° C. lower than the TWmax (TWmax-15) ° C. showing the maximum elution amount of the polyethylene of Example 7. Differential display and integral display diagram. The molecular weight distribution of the eluted fraction eluted between a temperature (TWmax-30) ° C. 30 ° C. lower than the temperature TWmax and a temperature 15 ° C. (TWmax-15) ° C. lower than TWmax indicating the maximum elution amount of the polyethylene of Comparative Example 6. Differential display and integral display diagram.

  As the base resin in the production of the crosslinked polyethylene pipe of the present invention, polyethylene polymerized using a single site catalyst is used. The single site catalyst has a uniform active site and is represented by the following metallocene catalyst. This metallocene catalyst is an unsaturated cyclic compound such as cyclopentadienyl having a transition metal (Ti, Zr, Hf, Ru, V, Cr, etc.) as a ligand as shown in chemical formulas (a) to (e). Is a compound having a structure.

  Methylalumoxane (MAO), which is a compound of trimethylaluminum and water, may be used as a cocatalyst.

  Polyethylene polymerized using a single-site catalyst has a more uniform crystal structure than that polymerized using a conventional multi-site catalyst, and there are many tie molecules that connect crystals. Excellent strength. Therefore, if polyethylene polymerized using a single-site catalyst is used, better pressure resistance can be obtained even if a polymer having a density similar to that of polyethylene polymerized using a multi-site catalyst used in the past is selected. A cross-linked polyethylene tube having the following can be obtained. That is, it is possible to obtain a pressure-resistant cross-linked polyethylene pipe that is superior to the conventional one without reducing the piping workability. Polyethylene polymerized using a conventionally used multi-site catalyst contains a large amount of low molecular weight components containing many short-chain branches, which are called low polymers. This is especially the case for polyethylene with a low average molecular weight, ie, a high MFR. The presence of this raw polymer causes a reduction in crosslinking efficiency, and it is necessary to add more silane compounds and radical generators in order to obtain a predetermined degree of crosslinking. On the other hand, polyethylene polymerized using a single-site catalyst has fewer raw polymers that cause a reduction in cross-linking efficiency than polyethylene polymerized using a multi-site catalyst, and less silane compounds and radical generators are added. A predetermined degree of crosslinking can be obtained. This also makes it possible to select a base resin having a lower average molecular weight, that is, a higher MFR, when polyethylene polymerized using a single site catalyst is used.

If the density of polyethylene is too high, the pressure proof performance is improved, but the pipe workability is lowered. If the density is lowered, the pipe workability is improved, but the pressure proof performance is lowered. Moreover, although productivity will improve when MFR becomes high, reaching | attaining gel fraction will become low, and when MFR becomes low, reaching | attaining target gel fraction will become easy, but productivity will fall. Based on such a tendency, in the present invention, a polyethylene base resin having a density of 0.938 to 0.950 g / cm ³ and an MFR of 1.0 to 7.0 g / 10 min is used. The reason is that if it is within this range, all target values required for pressure resistance, piping workability, and productivity can be satisfied, and more preferably, the density is 0.941 to 0.947 g / cm ³ , MFR3. 0.0 to 6.0 g / 10 min is preferable.

  The density is a value measured at a test temperature of 23 ° C. by D method (density gradient tube method) of JIS K7112 (plastic density and specific gravity measurement method), and MFR is JIS K 7210 (thermoplastic flow test method, test). It is a value measured by a method according to a temperature of 190 ° C. and a test load of 21.18 N).

  As the base resin, the above-mentioned density and MFR polyethylene polymerized using a single site catalyst is used. As described in “JIS K 6922-1: 1997 annex (normative) polyethylene molding material”, here, polyethylene refers to a homopolymer of ethylene, ethylene and an α-olefin having 3 or less carbon atoms of 3 mol or less, such as butene. 1, copolymer of hexene-1, 4-methylpentene-1, octene-1, etc., copolymerization of ethylene and 1 mol% or less non-olefin monomer having only carbon, oxygen and hydrogen in functional groups Includes coalescence. In addition, one or more types of high-density polyethylene polymerized with a multisite catalyst, linear low-density polyethylene, and low-density polyethylene may be blended within a range of 10% by weight or less of the base resin.

  In the present invention, the measurement using a cross fractionation device combining temperature rise elution fractionation and gel permeation chromatograph is performed as follows using a commercially available device. That is, J.H. Appl. Polym. Sci. 26, 4217 (1981), the target polyethylene is first completely dissolved at 140 ° C, cooled from 140 ° C to 0 ° C at -1 ° C / min, and then at 0 ° C for 30 minutes. Measure after holding. The temperature is raised stepwise, the components eluted at each temperature are collected, the gel permeation chromatograph is measured individually for each elution component, and the molecular weight distribution profile for each elution temperature. Get. By adding all the obtained molecular weight distribution profiles for each elution temperature, the molecular weight distribution profile of the entire polyethylene can be obtained. From the data, Nw (number average molecular weight) and Mw (weight average molecular weight) of the entire polyethylene are obtained. When representing the molecular weight distribution for each elution temperature or for the entire polyethylene, an integral representation generally representing the relationship between log M (M is molecular weight) and w (the ratio of the weight of the component of molecular weight M to the total weight w), and It is expressed in the form of differential display obtained by differentiating the curve. Similarly, the elution temperature is limited to a certain range, and the elution amount within the temperature range can be displayed in the same manner.

Example 2 which is one embodiment of the present invention will be described. FIG. 1 is a three-dimensional representation of the molecular weight distribution for the eluted components at each elution temperature in Example 2. FIG. 4 is a plot of the relationship between each elution temperature and the elution amount at that temperature. FIG. 4 shows an integral display and a differential display of the molecular weight distribution of the whole polyethylene obtained by adding all the molecular weight distribution profiles for each elution temperature. In the integral distribution curve in FIG. 4, w when logM = 3.5 is 5% or less, w is 20% or less when logM = 4, and w is 50% when logM = 5. That's it. The temperature TWmax indicating the maximum elution amount is a temperature indicating the maximum elution amount in FIG. 7 in which the total elution amount is plotted for each temperature. In the present invention, this temperature is required to be in the temperature range of 81 to 105 ° C. From the TWmax thus determined, the total amount eluted between a temperature (TWmax-30) ° C. 30 ° C. lower than the temperature TWmax indicating the maximum elution amount and a temperature (TWmax-15) ° C. 15 ° C. lower than the TWmax. The molecular weight distribution of the eluted part can be obtained. The molecular weight distribution is shown in FIG. In the present embodiment, there are two maximum points in the differential display of the molecular weight distribution. When the smallest maximum molecular weight is M1T and the largest maximum molecular weight is M2T,
3 <logM1T <4
4 <logM2T <5.2.
Further, in the present embodiment, in the integral display of the molecular weight distribution of the total amount eluted between (TWmax-30) ° C. and (TWmax-15) ° C. in FIG. 8, w when logM = 4. Is 50% or less.

In the measurement using a cross fractionation device in which polyethylene is combined with temperature rising elution fractionation and gel permeation chromatograph, (1) the ratio of the weight average molecular weight Mw to the number average molecular weight Mn of the total elution amount, and Mw / Mn is 2.5. (2) In the integral display of the molecular weight distribution of the total elution amount, that is, in the curve indicating the relationship between log M and w (where M is the molecular weight and w is weight%), the following characteristics a to d :
a. w when logM = 3.5 is 5% or less, w is 20% or less when logM = 4, and w is 50% or more when logM = 5;
b. The temperature TWmax indicating the maximum elution amount is in the range of 81 ° C to 105 ° C;
c. In the differential display of the molecular weight distribution of the total elution amount eluted between a temperature (TWmax-30) ° C. 30 ° C. lower than the temperature TWmax indicating the maximum elution amount and a temperature (TWmax-15) ° C. 15 ° C. lower than the TWmax Has at least two local maxima;
d. When the minimum maximum molecular weight at the maximum point is M1T, and the maximum maximum molecular weight is M2T,
3 <logM1T <4
4 <logM2T <5.2
The crosslinked polyethylene pipe is excellent in pressure resistance and productivity, and can be suitably used.

e. In the integral display of the molecular weight distribution of the elution of polyethylene that is eluted between (TWmax-30) ° C. and (TWmax-15) ° C., w satisfying that log M = 4 is 50% or less The cross-linked polyethylene pipe characterized by this is excellent in pressure resistance and productivity, and can be used particularly preferably.

The crosslinked polyethylene pipe of the present invention can be prepared by modifying the polyethylene resin composition serving as the above base resin with silane, forming it into a tubular shape, and crosslinking with a silane crosslinking method.
Specifically, as one method, an extruder capable of reaction is used, and a silane compound, a radical generator, a silanol condensation catalyst, and additives such as an antioxidant as necessary are blended into the base resin. The silane-modified resin composition is obtained through steps such as melting, kneading and reaction while heating in an extruder. This is extruded into a tubular shape, formed into a tubular shape, and cooled to form a molded tube made of a silane-modified polyethylene composition. By applying appropriate heat to the molded tube in the presence of water, cross-linking that promotes the silanol condensation reaction is performed. By performing the treatment, a crosslinked polyethylene pipe can be obtained. Such a method is called a one-stage production method of a silane-crosslinked polyethylene pipe.
Alternatively, in the first step, an extruder capable of reaction is used in the first step, and a silane compound and a radical generator are added to the base resin, and additives such as an antioxidant are added as necessary. Here, silanol condensation catalyst is not blended, it is heated in a reactor such as an extruder, melted, kneaded, and reacted through a process such as extrusion into a strand, which is cooled and cut to form a pellet-like silane modified Let it be a polyethylene composition. In the second step, this silane-modified polyethylene composition, for example, a master batch containing a silanol condensation catalyst based on polyethylene prepared in advance in a separate step and an additive such as an antioxidant as necessary, It mix | blends and it is set as a silane modified polyethylene resin composition through the process of melting and kneading | mixing, heating in an extruder. This is extruded into a tubular shape, molded into a tubular shape, and cooled to form a molded tube made of a silane-modified polyethylene resin composition, and the silanol condensation reaction is promoted by applying appropriate heat to the molded tube in the presence of water. A crosslinked polyethylene pipe can be obtained by performing a crosslinking treatment. Such a method is called a two-stage production method of a silane-crosslinked polyethylene pipe.

  The MFR of the silane-modified polyethylene composition greatly affects the productivity in molding the molded tube, that is, in the second step of the one-stage production method or the two-stage production method. The silane-modified polyethylene composition has a lower MFR due to an increase in molecular weight than polyethylene, which is a base resin before silane modification. When extruding a pipe or the like, it is desirable that the MFR of the silane-modified polyethylene composition is in the range of 0.01 to 5.0 g / 10 minutes, and the MFR value can be adjusted by the blending amount of the radical generator. However, the MFR of polyethylene polymerized using a single-site catalyst as a base resin also has a suitable range, and it is preferable to use a 1.0 to 7.0 g / 10 min. Regardless of which method is employed, examples of the crosslinking treatment include a method of immersing in a hot water tank at 85 to 95 ° C. for about 1 to 24 hours and a method of contacting with water vapor for 1 to 24 hours.

  By adjusting the amount of silane compound, radical generator and the like so that the gel fraction of the resulting crosslinked polyethylene pipe is 65% or more, preferably 75% or more, a pipe excellent in heat resistance and pressure resistance characteristics It becomes. Here, the gel fraction is a value measured according to JIS K 6787-1997 Water-Linked Polyethylene Pipe Annex 7 (normative) Gel-Frequency Test for Water-Linked Polyethylene Pipe.

The silane compound used in the silane crosslinking method reacts with the polyethylene in the presence of a radical generator described later, and has a general formula RR′SiY ₂ (wherein R is an unsaturated hydrocarbon group such as a vinyl group or an allyl group). Or a hydrocarbonoxy group, Y is a hydrolyzable organic group such as an alkoxyl group represented by a methoxy group, an ethoxy group, or a butoxy group, and R ′ is a substituent similar to R or Y). . More specifically, vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, vinyltris (β-methoxyethoxy) silane and the like can be mentioned. The blending amount of the silane compound is preferably about 0.2 to 5 parts by weight with respect to 100 parts by weight of the base resin.

  The radical generator is not particularly limited as long as it is used for silane crosslinking. For example, dicumyl peroxide, di- (t-butylperoxy) -m-di-isopropylbenzene, 2,5-dimethyl-2. , 5-Di-t-butylperoxyhexane, 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexyne-3, α, α'-bis (t-butylperoxydiisopropyl) Benzene, t-butylperoxycumene, 4,4′-di (t-butylperoxy) valeric acid n-butyl ester, 1,1-di (t-butylperoxy) -3,3,5-trimethylcyclohexane And azo compounds such as azobis-isobutyronitrile and dimethylazoisodibutyrate. The blending ratio of the radical generator depends on the type of radical generator and the amount of additive having a radical scavenging function, but is 0.1 to 10 parts by weight, preferably 0 based on 100 parts by weight of the silane compound. .5 to 5 parts by weight.

  The silanol condensation catalyst is not particularly limited as long as it is used for silane crosslinking. For example, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctate, dioctyltin dilaurate, tin (II) octate, tin naphthenate, Examples include zinc caprylate, tetrabutyl titanate, tetranonyl titanate, and bis (acetylacetonitrile) diisopropyl titanate. The mixing ratio of the silanol condensation catalyst is 0.0005 to 1 part by weight, preferably 0.01 to 0.5 part by weight with respect to 100 parts by weight of the base resin.

  In addition to the above components, additives such as antioxidants, flame retardants, crosslinking aids, weathering agents, colorants, fillers and other stabilizers may be blended in the resin composition of the present invention in appropriate amounts. Antioxidants include 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene and pentaerythrityl-tetrakis [3 (3,5- Di-t-butyl-4-hydroxyphenyl) propionate] and the like. The blending amount of the antioxidant is preferably 0.05 to 0.6 parts by weight, more preferably 0.1 to 0.5 parts by weight with respect to 100 parts by weight of the base resin.

The present invention will be further described based on examples.
Example 1
(When manufacturing cross-linked PE pipes by a two-stage manufacturing method)
[Silane-modified polyethylene composition]
Vinyl trimethoxysilane 2.2 parts by weight, dicumyl peroxide 0.11 parts by weight with respect to 100 parts by weight of polyethylene polymerized using a single site catalyst at a density of 0.938 g / cm ³ and MFR 2.1 g / 10 min (5.0 parts by weight with respect to 100 parts by weight of vinyltrimethoxysilane) and a mixture obtained by mixing with a tumbler was set to a reaction zone temperature of 210 ° C. and a strand die temperature (T1) of 223 ° C., a screw diameter of 50 mm, Extruded into a strand shape with a single screw extruder of L / D = 30, cooled, and cut to obtain a pellet-like compound of a silane-modified polyethylene composition.
[Catalyst masterbatch]
1 part by weight of dibutyltin dilaurate with respect to 100 parts by weight of polyethylene similar to the above (final amount of 0.05 part by weight with respect to 100 parts by weight of the base resin), 1,3,5-trimethyl-2, Blended 5 parts by weight of 4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene and set the strand die temperature (T2) to 200 ° C., screw diameter 50 mm, L / D = Extruded into a strand shape with 30 single-screw extruders, cooled, and cut to produce a pellet-shaped antioxidant and a silanol condensation catalyst master batch.
[Production of cross-linked polyethylene pipe]
The obtained silane-modified polyethylene composition and the catalyst master batch were mixed in a tumbler at a ratio of 95 parts by weight: 5 parts by weight, and the pipe die temperature (T3) was set to 223 ° C., screw diameter 50 mm, L / D = 30 Was extruded into a tubular shape with a single-screw extruder and vacuum-formed and cooled to obtain a molded tube having an inner diameter of 10 mm and a wall thickness of 1.5 mm. The obtained molded tube was immersed in warm water at 95 ° C. for 24 hours to produce a crosslinked polyethylene tube of Example 1.

(Examples 2-5, 7) (Comparative Examples 1-6)
Using the polyethylene shown in Table 1 as the base resin, the silane-modified polyethylene composition obtained in the same procedure as in Example 1 and the catalyst master batch were mixed in the same ratio as in Example 1 to produce a crosslinked polyethylene tube. .

(When producing a cross-linked polyethylene pipe by a one-stage production method)
(Example 6)
[Catalyst masterbatch]
1 part by weight of dibutyltin dilaurate, 1,3,5-trimethyl-2,4 per 100 parts by weight of polyethylene polymerized using a single site catalyst and having a density of 0.941 g / cm ³ and MFR 3.5 g / 10 min , 6-Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, 5 parts by weight, melted with heating in a single screw extruder with a screw diameter of 50 mm and L / D = 30 After the kneading, extrusion was performed from a strand die set at a temperature (T2) of 200 ° C. into a strand shape, and cooling and cutting were performed to prepare a pellet-shaped antioxidant and a catalyst master batch.
[Production of cross-linked polyethylene pipe]
To 100 parts by weight of polyethylene similar to the above, 2.6 parts by weight of vinyltrimethoxysilane and 0.13 parts by weight of dicumyl peroxide (5 parts by weight with respect to 100 parts by weight of vinyltrimethoxysilane) The mixture mixed by the tumbler was set at a reaction zone temperature of 210 ° C. with a single screw extruder having a screw diameter of 50 mm and L / D = 30, and heated, melted, kneaded, and reacted, and the temperature (T3) 222 It was extruded into a tubular shape from a pipe die set at 0 ° C., and after vacuum forming and cooling, a formed tube having an inner diameter of 10 mm and a wall thickness of 1.5 mm was obtained. The obtained molded tube was immersed in warm water at 95 ° C. for 24 hours to produce a crosslinked polyethylene tube of Example 6.

Table 1 shows the density of the base resin polyethylene, the MFR, and the MFR after silane modification. The density is a value measured at a test temperature of 23 ° C. by D method (density gradient tube method) of JIS K7112 (plastic density and specific gravity), and MFR is JIS K 7210 (thermoplastic flow test method, test). It is a value measured by a method according to a temperature of 190 ° C. and a test load of 21.18 N). In addition, the measuring method of the gel fraction of Table 1 is a value measured according to the gel fraction test method of the crosslinked polyethylene pipe for water supply Annex 7 (normative) water supply polyethylene pipe for JIS K 6787-1997. Moreover, the cross fractionation apparatus which combined the temperature rise elution fractionation and the gel permeation chromatograph used Mitsubishi Chemical cross fractionation chromatograph CFCT105A, and measured the molecular weight distribution of the elution component in each temperature. The measurement conditions are as follows.
(Measurement condition)
Column configuration: Shodex AD-806M / S (Showa Denko KK)
GPC measurement temperature: 140 ° C
Solvent: Ortho-dichlorobenzene Flow rate: 1.0 ml / min Sample concentration: 0.4 g / 100 ml (containing 0.1% of antioxidant BHT)
Injection volume: 0.5 ml Detector: Infrared detection (3.42 μ)
Elution temperature: 29 fractions 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 49, 52, 55, 58, 61, 64, 67, 70, 73, 76, 79, 82, 85 , 88, 91, 95, 100, 120, 140 ° C
Coating: Precolumn coating conditions are as follows: 140 ° C to 0 ° C, cooled over 140 minutes (-1 ° C / min)
Conversion of molecular weight Using a general calibration curve, it was converted to molecular weight as polyethylene.

  1 to 3 are three-dimensional diagrams in which the molecular weight distributions of Examples 2 and 7 and Comparative Example 6 are displayed in three dimensions by temperature and molecular weight. 4 to 6 show the differential display and integral display of the molecular weight distribution of the total elution amount of the polyethylene base resins of Examples 2 and 7 and Comparative Example 6, respectively. The Y axis is displayed as a percentage of the whole, and when it is multiplied by 100, a weight fraction (%) is obtained. FIG. 7 shows the elution temperature curve of Example 2. FIGS. 8 to 10 show the maximum elution amounts of the polyethylene base resins of Examples 2 and 7 and Comparative Example 6 at a temperature 30 ° C. lower than the temperature TWmax (TWmax-30) ° C. and a temperature 15 ° C. lower than TWmax (TWmax-15) ° C. The differential display and the integral display of the molecular weight distribution eluted between and are shown. In this case as well, the weight fraction (%) can be obtained by multiplying the Y axis by 100 times. While calculating Mw / Mn of Examples 2 and 7 and Comparative Example 6, the value of w when logM = 3.5, the value of w when logM = 4, the value of w when logM = 5, A temperature TWmax indicating the maximum elution amount, a temperature elution between 30 ° C. lower than the temperature TWmax indicating the maximum elution amount (TWmax-30) ° C. and 15 ° C. lower than the TWmax (TWmax-15) ° C. Logarithm values logM1T, logM2T of the smallest maximum molecular weight M1T and the largest maximum molecular weight M2T at the maximum points of differential display of the molecular weight distribution, elution eluted between (TWmax-30) ° C. and (TWmax-15) ° C. In the integral display of the molecular weight distribution of minutes, the value of w when logM = 4 was read. The values are shown in Table 2. The blending amounts of vinyltrimethoxysilane and dicumyl peroxide used when adjusting the silane-modified polyethylene composition and the set temperatures (T1, T3) of the die were as shown in Table 3.

Evaluation was performed on the crosslinked polyethylene pipe by the following three items.
(Pressure resistance)
JIS K 6787-1997 Cross-linked polyethylene pipe for water supply Annex 4 (normative) Test is performed at a test temperature of 95 ° C. and a circumferential stress of 4.6 MPa in a hot internal pressure creep test method for cross-linked polyethylene pipe for water supply, and the pipe breaks. The time until was measured. The target value is 170 h or more, preferably 500 h or more.

(Piping workability)
The maximum pushing force when inserting a cross-linked polyethylene pipe into a high-density polyethylene sheath pipe was measured. The Saya tube used for the test is a general model pipe with an inner diameter of 22 mm, a length of 15 m, four horizontal bends with a bend radius of 450 mm and a bend angle of 90 °, and a rising bend with a bend radius of 150 mm and a bend angle of 90 °. One place is provided. The target value is 300N or less, preferably 260N or less.

(productivity)
JIS K 6787-1997 Cross-linked polyethylene pipe for water supply Appearance and shape, Section 7. The maximum value of the production rate for obtaining a tube that meets the dimensions and tolerances was expressed in m / min. The size of the tube was representatively taken for a nominal diameter of 10. The target value is 9 m / min, preferably 10 m / min or more. These results are shown in Table 1.

  Examples 1 to 6 show the ranges of the polyethylene density and melt flow rate and the characteristics a. ~ E. It is the example which produced the crosslinked polyethylene pipe | tube using the polyethylene resin composition which satisfy | fills as a base resin. In all evaluation items of pressure resistance performance, piping workability, and productivity, each target value was exceeded. In particular, Examples 2 and 3 use those having a density and MFR in a particularly preferable range as polyethylene as the base resin, and therefore exceed particularly preferable values in all of the evaluation items of pressure resistance performance, piping workability, and productivity. It was. Further, when Example 5 and Example 7 having the same base resin density and MFR were compared, Example 5 was particularly superior in pressure resistance and piping workability to Example 7. In addition, Example 2 and Example 6 are examples in which the same polyethylene is used as a base resin, Example 2 is an example in which a crosslinked polyethylene pipe is produced by using a two-stage production method, and Example 6 is a one-stage production method. Comparing the evaluation results of the two, it was found that there was no significant difference, and that the present invention exhibited the effect regardless of which method was used.

  The crosslinked polyethylene pipe of Comparative Example 1 was inferior in pressure resistance because the density of the polyethylene used was small. The crosslinked polyethylene pipe of Comparative Example 2 had a high density of polyethylene used and was inferior in pipe workability. The cross-linked polyethylene pipes of Comparative Examples 3 to 5 are prepared using polyethylene polymerized with a base resin using a multi-site catalyst. The cross-linked polyethylene pipe of Comparative Example 3 had a density almost the same as that of Example 4, but was inferior in pressure resistance. In Comparative Example 4, the pressure resistance of Comparative Example 3 was improved and polyethylene having a low MFR value was selected as the base resin, which resulted in low productivity. In Comparative Example 5, the MFR was kept high so as to ensure the productivity, and the lowest density polyethylene capable of clearing the pressure resistance of the target value was selected as the base resin, but the piping workability was inferior. These results indicate that a crosslinked polyethylene pipe based on polyethylene polymerized using a multi-site catalyst cannot satisfy the three performances simultaneously. Comparative Example 6 is an example in which polyethylene having a density and MFR which are the same values as in Example 2 but polymerized using a multisite catalyst was used as a base resin, and the pressure resistance was low.

  In addition, the MFR of the silane-modified polyethylene composition decreases as the molecular weight increases as compared with polyethylene, which is the base resin before silane modification. When the reduction rate is compared, the range of the polyethylene density and the melt flow rate and the characteristics a. ~ E. In Examples 1 to 5 using a polyethylene resin composition satisfying the above as the base resin, the ratio of the MFR of the silane-modified polyethylene composition to the MFR of polyethylene as the base resin was 0.57 to 0.81. As can be seen from this, the rate of decrease in MFR due to silane modification is low, and it is possible to reduce the load on the extrusion screw and the resin pressure when extrusion molding the silane-modified polyethylene composition to produce a molded tube. This is an effect of the present invention.

Claims (1)

Polymerized using a single site catalyst,
In measurement using a cross fractionation device having a density of 0.938 to 0.950 g / cm ³ , a melt flow rate of 1.0 to 7.0 g / 10 minutes, and a combination of temperature rise elution fractionation and gel permeation chromatograph ,
(1) The ratio of the weight average molecular weight Mw to the number average molecular weight Mn of the total elution amount, Mw / Mn is 2.5 to 9.0,
(2) In the integral display of the molecular weight distribution of the total elution amount, that is, in the curve showing the relationship between logM and w (where M is the molecular weight, w is weight%), w when logM = 5 is 50% or more ,
(3) The maximum point temperature TWmax indicating the maximum elution amount is in the range of 81 ° C to 105 ° C,
In the integral display of the molecular weight distribution of the total elution amount eluted between 30 ° C. lower than the temperature TWmax indicating the maximum elution amount (TWmax-30) ° C. and 15 ° C. lower than the TWmax (TWmax-15) ° C. A crosslinked polyethylene pipe obtained by using polyethylene having a w of 50% or less when log M = 4 as a base resin, and silane-crosslinking a resin composition containing the polyethylene.

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