JP6778480B2 - Polyethylene polymer and its production method, composition, and crosslinked pipe - Google Patents

Description

The present invention relates to a polyethylene-based polymer, a method for producing the same, a composition, and a crosslinked pipe.

Conventionally, vinyl chloride pipes have been mainly used as water supply pipes for houses, and copper pipes have been mainly used as hot water supply pipes. However, vinyl chloride pipes and copper pipes have a problem of short durability, and in particular, copper pipes have a problem of causing colored water such as blue water and red water and water leakage due to rust. Further, the copper pipe has a drawback that the workability is poor. For this reason, cross-linked polyethylene pipes are being used in recent years. Cross-linked polyethylene pipes are superior to vinyl chloride pipes and copper pipes in that they have high creep characteristics at high temperatures, have a long durability, and have good workability. Therefore, the cross-linked polyethylene pipe is promising as a pipe for water supply, hot water supply, and heating.

As one of the typical methods for producing a cross-linked polyethylene pipe, a resin composition obtained by blending polyethylene with an organic peroxide such as dicumyl peroxide is heated at a temperature equal to or higher than the decomposition temperature of the organic peroxide. However, a method of extruding into a pipe shape is disclosed (see, for example, Patent Document 1). In this production process, the organic peroxide is thermally decomposed into organic radicals, and the action of the organic radicals causes the polyethylene to become radicals, and the cross-linked polyethylene proceeds via the radicals. Further, as another typical method for producing a cross-linked polyethylene pipe, polyethylene is mixed with a silane compound such as vinyltriethoxysilane, an organic peroxide and a silanol condensation catalyst, and the obtained composition is heated. At the same time, a method is disclosed in which a pipe is extruded and then exposed to an environment containing water to promote cross-linking (see, for example, Patent Document 2).

In addition to the cross-linked polyethylene pipe described above, for example, polyethylene polymerized by a Ziegler polymerization catalyst or a Phillips-based polymerization catalyst is disclosed (see, for example, Patent Document 3). Further, an attempt to produce polyethylene having a molecular weight distribution of 2 to 3 by using a catalyst prepared from a metallocene compound and aluminoxane or the like is disclosed (see, for example, Patent Document 4). Further, a crosslinked pipe using polyethylene in which comonomer is uniformly distributed obtained by a metallocene catalyst is disclosed (see, for example, Patent Document 5).
In addition, a method of mixing activated carbon or the like in a pipe and adsorbing an unreacted silane compound or the like eluted from the pipe is also disclosed (see, for example, Patent Document 6).

Tokukousho 45-35558 Gazette Japanese Unexamined Patent Publication No. 57-170913 Japanese Unexamined Patent Publication No. 10-17625 Japanese Unexamined Patent Publication No. 9-208637 Japanese Unexamined Patent Publication No. 10-193468 Japanese Unexamined Patent Publication No. 60-2351

However, cross-linked polyethylene pipes as disclosed in Patent Document 1 and Patent Document 2 generate an odor due to elution of low molecular weight components of polyethylene, uncross-linked silane compounds, etc. from the pipe during water flow. Sometimes. Further, the low molecular weight component of polyethylene tends to be easily crosslinked because the comonomer tends to be inserted, and the high molecular weight component of polyethylene is less likely to be crosslinked than the low molecular weight component. As a result, even if a cross-linked polyethylene pipe is manufactured by adding a large amount of cross-linking agent, sufficient creep characteristics may not be exhibited. Therefore, there is a demand for polyethylene capable of exhibiting sufficient creep characteristics by realizing a production method in which the number of low molecular weight components is reduced and the number of comonomer inserted into the high molecular weight component is increased. ..

Further, in polyethylene as disclosed in Patent Document 3, since the molecular weight distribution of polyethylene is wide and the comonomer component introduced into the high molecular weight component is small, sufficient creep characteristics cannot be exhibited, and particularly hot. Internal pressure creep characteristics are poor. Here, it is considered necessary to add a large amount of unsaturated silane compound, organic peroxide and silanol condensation catalyst in order to sufficiently proceed with the cross-linking of the high molecular weight component. However, when such an addition is performed, it becomes difficult to perform long-term operation of the extruded pipe due to the generation of a large amount of tars during the extruded pipe. In addition, problems such as offensive odors derived from unsaturated silane compounds may occur when water is passed through the pipe.

Further, in the polyethylene using the method for producing polyethylene as disclosed in Patent Document 4, the fluidity becomes insufficient due to the narrow molecular weight distribution of polyethylene. For this reason, especially in the extrusion molding of pipes, heat generation in the extruder becomes large, and early cross-linking may partially occur. In addition, the low molecular weight component of polyethylene may be decomposed by decomposition, and the influence of the low molecular weight component of polyethylene cannot be suppressed. Further, the surface condition of the pipe after molding deteriorates, resulting in poor appearance and a decrease in mechanical strength.

Further, the crosslinked pipe using polyethylene as disclosed in Patent Document 5 uses polyethylene in which a comonomer is easily inserted on the high molecular weight side, but there is no description regarding the influence of the low molecular weight component of polyethylene. The problem caused by the low molecular weight component cannot be solved.

In addition, in the pipe disclosed in Patent Document 6, it is difficult to completely adsorb the low molecular weight component of polyethylene and the unreacted silane compound with activated carbon or the like, and the durability of the pipe is significantly reduced. It ends up.

Therefore, the present invention solves at least a part of the above-mentioned problems of the prior art, has excellent thermal stability, and has extremely few low molecular weight components of polyethylene (hereinafter, also simply referred to as "low molecular weight components"). An object of the present invention is to provide a polyethylene-based polymer having excellent molding processability (for example, no increase in load of an extruder, heat generation, and grain tar during pipe molding).

As a result of diligent research to solve the above-mentioned problems of the prior art, the present inventors have a density in a predetermined range, a melt flow rate and a low molecular weight hydrocarbon component content, and a cross fractionation chromatograph ( We have found that a polyethylene-based polymer in which the maximum temperatures of two elution peaks measured by CFC) are in a predetermined range has excellent thermal stability, extremely few low molecular weight components, and excellent molding processability. It came to.

That is, the present invention is as follows.
[1]
The density is 935 kg / m ³ or more and 955 kg / m ³ or less.
The melt flow rate is 1.0 g / 10 min or more and 10 g / 10 min or less.
The total content of hydrocarbon components with 12 to 34 carbon atoms extracted with hexane is 300 mass ppm or less.
In the dissolution temperature curve of the total amount of polyethylene eluted in the measurement using cross fractionation chromatography, the elution peak having a maximum point temperature of 80 ° C. or higher and lower than 90 ° C. and the elution peak having a maximum point temperature of 90 ° C. or higher and lower than 100 ° C. A polyethylene-based polymer in which at least one of each is present.
[2]
The polyethylene-based polymer according to [1], wherein the chlorine content is 5.0 mass ppm or less with respect to the polyethylene-based polymer.
[3]
The polyethylene-based polymer according to [1] or [2], wherein the total content of Al, Mg, Ti, Zr, and Hf is 20 mass ppm or less with respect to the polyethylene-based polymer.
[4]
The polyethylene-based polymer according to any one of [1] to [3], wherein the amount of double bonds contained in 1000 carbons in polyethylene is 0.05 or less.
[5]
In the dissolution temperature curve of the total polyethylene elution amount in the measurement using the cross fractionation chromatography, the integrated elution amount of less than 80 ° C. is 10% by mass or less with respect to the total elution amount [1] to [4]. ] The polyethylene-based polymer according to any one of.
[6]
The polyethylene-based polymer according to any one of [1] to [5], which is used for a crosslinked pipe.
[7]
The polyethylene-based polymer according to any one of [1] to [6], and an organic peroxide of 0.005 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the polyethylene-based polymer. A composition comprising 0.1 parts by mass or more and 10 parts by mass or less of an organic unsaturated silane compound.
[8]
The composition according to [7], which is used for a crosslinked pipe.
[9]
A crosslinked pipe made of a crosslinked product of the composition according to [7] or [8].
[10]
The crosslinked pipe according to [9], wherein the gel fraction is 65% or more.
[11]
The crosslinked pipe according to [9] or [10], which is used for a pipe for water supply, hot water supply, or heating.
[12]
Polymerized in the presence of at least a carrier material, an organoaluminum compound, a borate compound having active hydrogen, a cyclopentadiene compound, and a supported metallocene catalyst obtained from a transition metal compound of Group IV of the periodic table, and a liquid co-catalyst. A method for producing a polyethylene-based polymer, which comprises a polymerization step for obtaining the polyethylene-based polymer according to any one of [1] to [6].
[13]
The method for producing a polyethylene-based polymer according to [12], wherein the polymerization step is a step of polymerizing by a slurry polymerization method and a two-stage polymerization method using a polymerization medium having 6 or more and 10 or less carbon atoms.

According to the polyethylene-based polymer according to the present invention, it is excellent in thermal stability, extremely few low molecular weight components, and excellent molding processability.

It is an elution temperature-elution amount curve obtained by the cross fractionation chromatography (CFC) measurement in Example 1.

Hereinafter, a mode for carrying out the present invention (hereinafter, also referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the present embodiment, and can be variously modified and implemented within the scope of the gist thereof.

[Polyethylene polymer]
The polyethylene-based polymer of the present embodiment has a density of 935 kg / m ³ or more and 955 kg / m ³ or less, a melt flow rate of 1.0 g / 10 min or more and 10 g / 10 min or less, and 12 carbon atoms extracted with hexane. The total content of hydrocarbon components of 34 or more and 34 or less is 300 mass ppm or less, and the maximum point temperature is 80 ° C or more and less than 90 ° C in the dissolution temperature curve of the total amount of polyethylene eluted in the measurement using cross fractionation chromatography. There is at least one elution peak and an elution peak having a maximum point temperature of 90 ° C. or higher and lower than 100 ° C. Hereinafter, each of the above requirements will be described.

The density of polyethylene-based polymer is not more than 935 kg / m ³ or more 955 kg / m ^3, preferably not more than 937kg / m ³ or more 953kg / m ^3, more preferably 940 kg / m ³ or more 950 kg / m ³ or less is there. When the density of the polyethylene-based polymer is 935 kg / m ³ or more, a crosslinked pipe having high hardness and excellent pressure resistance and long-term acid resistance can be obtained. In addition, the creep characteristics are improved, the odor during water flow is reduced, and the appearance of the pipe is also improved. Further, when the density of the polyethylene-based polymer is 955 kg / m ³ or less, a crosslinked pipe having excellent flexibility and easy construction can be obtained. In addition, the creep characteristics are improved, the odor during water flow is reduced, and the appearance of the pipe is also improved.

The density of the polyethylene-based polymer is not particularly limited, but can be adjusted mainly by the comonomer species and the comonomer content in polyethylene. The density is measured according to JIS K7112, and specifically, it is measured by the method described in Examples described later.

The melt flow rate of the polyethylene-based polymer is 1.0 g / 10 minutes or more and 10 g / 10 minutes or less, preferably 1.2 g / 10 minutes or more and 8.0 g / 10 minutes or less, and more preferably 1.5 g. / 10 minutes or more 6.0 g / 10 minutes. When the melt flow rate is 1.0 g / 10 minutes or more, the molding processability is excellent. In addition, the creep characteristics are improved, the odor during water flow is reduced, and the appearance of the pipe is also improved. Further, when it is 10 g / 10 minutes or less, the pressure resistance is excellent. In addition, the creep characteristics are improved, the odor during water flow is reduced, and the appearance of the pipe is also improved.

The melt flow rate of the polyethylene-based polymer is not particularly limited, but can be adjusted by the molecular weight, the molecular weight distribution, and the density. Specifically, the melt flow rate can be adjusted by adjusting the amount of chain transfer agent such as hydrogen at the time of polymerization and adjusting the amount of comonomer introduced, which will be described later. The melt flow rate is measured at 190 ° C. and 2.16 kg according to JIS K7210, and specifically, it is measured by the method described in Examples described later.

The total content of the hydrocarbon component having 12 or more and 34 or less carbon atoms extracted with hexane in the polyethylene polymer is 300 mass ppm or less, preferably 250 mass ppm or less, and more preferably 200 mass ppm or less. Hereinafter, it is more preferably 150 mass ppm or less. When the total content of the hydrocarbon component having 12 or more and 34 or less carbon atoms is 300 mass ppm or less, the cross-linking agent (organic peroxide, organic unsaturated silane compound, etc., which will be described later) reacts with the hydrocarbon component. On the other hand, the ratio decreases, and on the other hand, the ratio of reacting with the high molecular weight component of polyethylene increases. Therefore, the pressure resistance and durability (particularly creep characteristics) of the crosslinked pipe are increased, and the odor is also reduced. In addition, the amount of low molecular weight components eluted in water during water flow can also be reduced. Further, the amount of the cross-linking agent used can be reduced, which is preferable from an economical point of view.

The total content of hydrocarbon components having 12 or more and 34 or less carbon atoms is not particularly limited, but can be controlled by suppressing the amount of low molecular weight components produced during the production of polyethylene. Specifically, it is a continuous polymerization system in which ethylene gas, a solvent, a catalyst, etc. are continuously supplied into the polymerization system and continuously discharged together with the produced polyethylene, and the polymerization system is made after the catalyst is brought into contact with hydrogen in advance. The low molecular weight component generated by abrupt polymerization can be suppressed by adding the catalyst to the inside and setting the outlet of the catalyst introduction line at a position as far as possible from the outlet of the ethylene introduction line. Further, lowering the polymerization temperature and adjusting the amount of conomomer introduced are also effective for adjusting the total content of hydrocarbon components having 12 or more and 34 or less carbon atoms. Further, by lowering the temperature at the time of melt-kneading and suppressing the formation of decomposition components, it is possible to suppress the formation of the amount of hydrocarbon components having 12 or more and 34 or less carbon atoms. Furthermore, in the slurry polymerization method, a polymerization medium having 6 to 12 carbon atoms is used, the polyethylene and the solvent are separated by the centrifugation method, and the amount of the solvent contained in the polyethylene before drying is 70% by mass with respect to the mass of the polyethylene. Low molecular weight components having 12 or more and 34 or less carbon atoms can be removed from polyethylene as much as possible by the following methods, drying under vacuum using a devolatilization extruder, granulation, and the like. The total content of hydrocarbon components having 12 or more and 34 or less carbon atoms can be measured by the method described in Examples described later.

In the dissolution temperature curve of the total amount of polyethylene eluted in the measurement using the cross fractionation chromatography (hereinafter, also simply referred to as “CFC”) of the polyethylene-based polymer of the present embodiment, the elution peak having the maximum point temperature is at least 2. There are one. Polyethylene-based polymers with excellent pressure resistance, dimensional accuracy, and processability have both an amorphous component that facilitates processing and a crystalline component that enhances pressure resistance, durability, and rigidity. Is preferable. The low temperature side elution peak derived from such an amorphous component (maximum point temperature is 80 ° C. or higher and lower than 90 ° C.) and the high temperature side elution peak derived from the crystalline component (maximum point temperature is 90 ° C. or higher and lower than 100 ° C.). There are at least two. Further, there may be an elution peak other than these, an elution peak having a maximum temperature of 80 ° C. or higher and lower than 90 ° C., and / or an elution peak having a maximum point temperature of 90 ° C. or higher and lower than 100 ° C. The polyethylene-based polymer of the present embodiment is not limited to those containing the amorphous component and the crystalline component, and the elution peak on the low temperature side (maximum point temperature is 80 ° C. or higher and lower than 90 ° C.). ) And the high temperature side elution peak (maximum point temperature is 90 ° C. or higher and lower than 100 ° C.), at least two peaks may be present.

The method for having at least two elution peaks and having the maximum temperature of the elution peak in the range of 80 ° C. or higher and lower than 90 ° C. and 90 ° C. or higher and lower than 100 ° C. is not particularly limited, but is not particularly limited. A method of adjusting the amount of hydrocarbon components of 12 to 34, a method of adjusting the density, melt flow rate, etc. within the range of the present embodiment, mixing polyethylenes having different properties, and stacking polyethylenes having different properties in two stages. There is a method of synthesizing legally.

In the dissolution temperature curve of the total elution amount of polyethylene in the measurement using cross fractionation chromatography, the integrated elution amount of less than 80 ° C. is preferably 10% by mass or less, more preferably 7 with respect to the total elution amount. It is 0.0% by mass or less, more preferably 5.0% by mass or less. When the integrated elution amount below 80 ° C. is 10% by mass or less, it means that there are few low molecular weight components having a large amount of comonomer introduced, which lowers pressure resistance and durability. By suppressing the amount of this low molecular weight component, the crosslinked pipe tends to have excellent pressure resistance and durability.

The means for adjusting the integrated elution amount below 80 ° C. to 10% by mass or less is not particularly limited, but the above-mentioned method for adjusting the amount of hydrocarbon components having 12 or more and 34 or less carbon atoms and the production of low molecular weight components are used. Examples thereof include a method of using a small amount of catalyst, specifically a metallocene-based catalyst, and a method of using the metallocene catalyst of the present embodiment in order to reduce the amount of a low molecular weight component comonomer introduced. It is also effective to adjust the amount of comonomer introduced in order to control the integrated elution amount.

Here, the "cross fractionation chromatography" is an apparatus that combines a temperature-increasing elution fractionation section (hereinafter, also referred to as "TREF section") for performing crystalline fractionation and a GPC section for performing molecular weight fractionation, and is a TREF. It is an apparatus capable of analyzing the interrelationship between the composition distribution and the molecular weight distribution by directly connecting the unit and the GPC unit. The measurement in the TREF unit may be referred to as the measurement in the CFC.

The measurement by the TREF unit is performed as follows based on the principle described in "Journal of Applied Polymer Science, Vol 26, 4217-4231 (1981)". The polyethylene to be measured is completely dissolved in orthodichlorobenzene. Then, it is cooled at a constant temperature to form a thin polymer layer on the surface of the inert carrier. At this time, the highly crystalline component is crystallized first, and then the low crystallinity component is crystallized as the temperature decreases. Next, when the temperature is raised stepwise, the components with low crystallinity are eluted in order, and the concentration of the eluted components at a predetermined temperature can be detected. Here, the "elution peak" indicates a peak in which 5.0% by mass or more is eluted when the temperature rises.

The elution amount and the elution integral amount at each temperature of polyethylene can be obtained by measuring the elution temperature-elution amount curve as follows from the TREF unit. As for the temperature profile of the column, the column containing the filler is first heated to 140 ° C., and a sample solution (for example, concentration: 16 mg / 8 mL) in which polyethylene is dissolved in ortodichlorobenzene is introduced and held for 120 minutes.

Next, the temperature is lowered to 40 ° C. at a temperature lowering rate of 0.5 ° C./min and then held for 20 minutes to deposit the sample on the surface of the filler. After that, the temperature of the column is sequentially raised at a heating rate of 20 ° C./min. The temperature is raised at 10 ° C intervals from 40 ° C to 80 ° C, at 5 ° C intervals from 80 ° C to 85 ° C, at 3 ° C intervals from 85 ° C to 90 ° C, and from 90 ° C to 100 ° C. The temperature is raised at 1 ° C. intervals, and from 100 ° C. to 120 ° C. at 10 ° C. intervals. After holding at each temperature for 20 minutes, the temperature is raised to detect the concentration of the sample (polyethylene) eluted at each temperature. Then, the elution temperature-elution amount curve (see, for example, the measurement result in the example shown in FIG. 1) was measured from the values of the elution amount (mass%) of the sample and the in-column temperature (° C.) at that time. The elution amount at each temperature and the elution integrated amount can be obtained. More specifically, it can be measured by the method described in Examples.

The chlorine content of the polyethylene-based polymer is preferably 5.0 mass ppm or less with respect to the polyethylene-based polymer. It is more preferably 3.0 mass ppm or less, further preferably 1.0 mass ppm or less, and less is preferable. When the chlorine content of the polyethylene-based polymer is 5.0 mass ppm or less, corrosion of molding machines and the like can be suppressed, the amount of metal components contained in the polymer can be reduced, and chlorine and hydrochloric acid are affected. Even when it is used as a covering material for a metal pipe or the like that is easily received, it tends to be able to suppress rust or the like of the protected material. Furthermore, since the reaction between chlorine and hydrochloric acid and organic peroxides and organic unsaturated silane compounds (crosslinking agents) tends to be suppressed, the amount of crosslinking agent used can be reduced and the crosslinking reaction is stable. Due to this, there is a tendency to obtain a crosslinked pipe having excellent dimensional accuracy.

The chlorine content of the polyethylene-based polymer is not particularly limited, but can be controlled by appropriately adjusting the polymerization conditions and the like using a catalyst described later. In addition, the chlorine content of the polyethylene-based polymer can be measured by the method described in Examples.

The total content of Al, Mg, Ti, Zr, and Hf of the polyethylene-based polymer is preferably 20% by mass or less, more preferably 15% by mass or less, based on the polyethylene-based polymer. More preferably, it is 10 mass ppm or less, and less is preferable. When the total content of Al, Mg, Ti, Zr, and Hf of the polyethylene polymer is 20% by mass or less, the generation of gel due to thermal deterioration of polyethylene is suppressed, and the low molecular weight component generated by thermal deterioration is also contained. There is a tendency for less coloring and less coloring of the crosslinked pipe. Further, side reactions with organic peroxides and organic unsaturated silane compounds (crosslinking agents) are also suppressed, and the crosslinking reaction is stabilized, so that a crosslinked pipe having excellent dimensional accuracy tends to be obtained.

The method for controlling the total content of Al, Mg, Ti, Zr, and Hf is not particularly limited, but a method using a co-catalyst having high activity and low Al content, which will be described later, and a catalyst having a low chlorine content are used. A method of suppressing corrosion of a molding machine or the like by using, a method of separating ethylene and a solvent by a centrifugation method, and a method of reducing the amount of solvent contained in polyethylene before drying to 70% by mass or less based on the weight of polyethylene, and a catalyst. The deactivation of the above can be carried out after separating the solvent as much as possible by the centrifugation method. The total content of Al, Mg, Ti, Zr, and Hf is measured by the method described in Examples described later.

The amount of double bonds contained in 1000 carbons in the polyethylene polymer is preferably 0.05 or less. When the amount of double bonds is 0.05 or less, the generation of gel due to thermal deterioration of the polyethylene polymer is suppressed, the amount of low molecular weight components generated by thermal deterioration is also reduced, and as a result, the generation of odor is suppressed. The surface condition of the extruded pipe also tends to be in good condition.

The amount of the double bond is not particularly limited, but it varies depending on the catalyst used and the method for synthesizing polyethylene. Therefore, it can be controlled by appropriately using the catalyst and the method for synthesizing described later. The amount of double bonds in 1000 carbons of polyethylene is measured by the method described in Examples below.

The polyethylene-based polymer is not particularly limited, but is preferably a copolymer of ethylene and another comonomer from the viewpoint of crosslinkability. As the ethylene, propylene and 1-butene are more preferable from the viewpoint of increasing the amount of tertiary carbon that the organic unsaturated silane compound serving as a cross-linking agent easily reacts with. The other comonomer is not particularly limited, and examples thereof include α-olefins and vinyl compounds. The α-olefin is not particularly limited, and examples thereof include α-olefins having 3 to 20 carbon atoms. Specific examples of α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, and 4 Included are −methyl-1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, and 1-tetradecene. The vinyl compound is not particularly limited, and examples thereof include vinylcyclohexane, styrene, and derivatives thereof. If necessary, non-conjugated polyenes such as 1,5-hexadiene and 1,7-octadiene can also be used as other comonomer. The copolymer may be a ternary random polymer. The other comonomer may be used alone or in combination of two or more.

In the polyethylene-based polymer, it is preferable to insert a comonomer within a range in which the heat resistance is not deteriorated. Specifically, the molar ratio of ethylene in the polyethylene-based polymer is preferably 50% or more and less than 100%, more preferably 80% or more and less than 98%, and further preferably 90% or more and 95% or more. Less than%. The amount of polyethylene comonomer can be confirmed by an infrared analysis method, an NMR method, or the like.

The polyethylene-based polymer of the present embodiment is preferably for a crosslinked pipe described later.

[Method for producing polyethylene polymer]
The method for producing a polyethylene-based polymer of the present embodiment includes at least a carrier substance, an organoaluminum compound, a borate compound having active hydrogen (hereinafter, also simply referred to as “borate compound”), a cyclopentadiene compound, and Periodic Table IV. It has a polymerization step of obtaining a polyethylene-based polymer of the present embodiment by polymerizing in the presence of a supported metallocene catalyst prepared from a group transition metal compound and a liquid co-catalyst.

The catalyst used in the method for producing a polyethylene-based polymer is not particularly limited as long as the above-mentioned supported metallocene catalyst is used, and other metallocene catalysts, Ziegler-Natta catalysts, Phillips catalysts and the like can also be used together. By using the supported metallocene catalyst, the low molecular weight component of the polyethylene-based polymer can be reduced. As the metallocene catalyst, those described in JP-A-2006-273977 can be preferably used.

The supported metallocene catalyst can be prepared from at least a carrier substance, an organoaluminum compound, a borate compound having active hydrogen, a borate compound having active hydrogen, a cyclopentadiene compound, and a transition metal compound of Group IV of the Periodic Table. it can.

The average particle size of the carrier substance is preferably 1.0 μm or more and 30 μm or less, more preferably 2.0 μm or more and 20 μm or less, and further preferably 3.0 μm or more and 10 μm or less. When the average particle size is 1.0 μm or more, the obtained polymer particles tend to be suppressed from scattering and adhering. Further, when the average particle size is 30 μm or less, it tends to be possible to suppress the precipitation in the polymerization system caused by the polymer particles becoming too large and the blockage of the line in the post-treatment step of the polymer particles. is there. Further, when the polyethylene is extruded, it tends to be possible to suppress the pressure increase due to the carrier substance remaining in the polyethylene clogging the filter of the extruder. The particle size distribution of the carrier substance is preferably as narrow as possible, and the particle size distribution can be adjusted by removing fine powder particles and coarse powder particles by sieving, centrifugation, or a cyclone.

The compressive strength of the carrier substance is preferably 1.0 MPa or more and less than 10 MPa, more preferably 2.0 MPa or more and less than 8.0 MPa, and further preferably 3.0 MPa or more and less than 6.0 MPa. When the compressive strength is 1.0 MPa or more, it tends to be crushed and reduced in size during catalyst synthesis or feeding, and problems such as scattering and adhesion of the obtained polymer particles can be suppressed. When the compressive strength is less than 10 MPa, the probability that the carrier substance remains in polyethylene without being crushed during polymerization increases, and the problem of impairing the smoothness of the inner surface of the pipe tends to be suppressed.

Further, the obtained supported metallocene catalyst may be washed with a decantation, filtration or the like using an inert solvent for the purpose of removing organoaluminum compounds, borate compounds, etc. that are not supported on the carrier. it can. When producing the polyethylene-based polymer used in the present embodiment, it is preferable to carry out decantation and / or filtration three times or more in order to reduce the low molecular weight component produced by the side reaction.

The liquid co-catalyst is a liquid co-catalyst and is a substance that increases the activity of the supported metallocene catalyst. The liquid co-catalyst is not particularly limited, but can be prepared from, for example, an organic magnesium compound and methylhydropolysiloxane.

The polymerization method in the polymerization step is not particularly limited, and examples thereof include a slurry polymerization method, a gas phase polymerization method, and a solution polymerization method. By these polymerization methods, ethylene or a monomer containing ethylene is (co). It can be polymerized. Among these, a slurry polymerization method capable of efficiently removing heat of polymerization is preferable. In the slurry polymerization method, an inert hydrocarbon medium can be used as the polymerization medium, and the olefin itself can also be used as the polymerization medium.

The inert hydrocarbon medium is not particularly limited, and is, for example, an aliphatic hydrocarbon such as propane, butane, isobutane, pentane, isopentane, hexane, heptane, octane, decane, dodecane, kerosene; cyclopentane, cyclohexane, methylcyclo. Aliphatic hydrocarbons such as pentane; aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as ethyl chloride, chlorobenzene and dichloromethane and mixtures thereof.

In the polymerization step, it is more preferable to use a polymerization medium having 6 or more and 10 or less carbon atoms among the above-mentioned inert hydrocarbon media. When the number of carbon atoms in the polymerization medium is 6 or more, low molecular weight components that react with the cross-linking agent to reduce pressure resistance and durability are relatively easily dissolved, and are removed in the step of separating the polyethylene-based polymer and the polymerization medium. It tends to be easy to do. When the number of carbon atoms in the polymerization medium is 10 or less, the amount of low molecular weight components (medium) remaining in the polyethylene-based polymer is reduced, and the adhesion of polyethylene powder to the reaction vessel is suppressed, which is industrially stable. There is a tendency to be able to drive smoothly.

The polymerization temperature in the polymerization step is preferably 30 ° C. or higher and 100 ° C. or lower, more preferably 35 ° C. or higher and 95 ° C. or lower, and further preferably 40 ° C. or higher and 90 ° C. or lower. If the polymerization temperature is 30 ° C. or higher, industrially efficient production tends to be possible. On the other hand, when the polymerization temperature is 100 ° C. or lower, continuous stable operation tends to be possible.

The polymerization pressure in the polymerization step is preferably normal pressure or more and 2.0 MPa or less, more preferably 0.05 MPa or more and 1.5 MPa or less, and further preferably 0.1 MPa or more and 1.0 MPa or less.

The polymerization in the polymerization step can be carried out by any of a batch type, a semi-continuous type, and a continuous type, and the polymerization is preferably a continuous type. In the continuous type, ethylene gas, solvent, catalyst, etc. are continuously supplied into the polymerization system and continuously discharged together with the produced polyethylene to suppress a partial high temperature state due to a rapid ethylene reaction. It becomes possible and the inside of the polymerization system becomes more stable. When ethylene reacts in a uniform state in the system, it is possible to suppress the formation of branches, double bonds, etc. in the polymer chain. This makes it easier to obtain polyethylene with high cross-linking efficiency.

The polymerization step is preferably a step of polymerizing by a two-step polymerization method in which the polymerization is divided into two or more steps having different reaction conditions. Further, the polymerization step is more preferably a step of polymerizing by a slurry polymerization method and a two-stage polymerization method using a polymerization medium having 6 or more and 10 or less carbon atoms.

The molecular weight of the polyethylene-based polymer is not particularly limited, but is adjusted by allowing hydrogen to be present in the polymerization system, changing the polymerization temperature, or the like, as described in Japanese Patent Application Publication No. 3127133. be able to. It is also possible to control the molecular weight in an appropriate range by adding hydrogen as a chain transfer agent into the polymerization system. When hydrogen in the polymerization system is added, the molar fraction of hydrogen is preferably 0 mol% or more and 30 mol% or less, more preferably 3 mol% or more and 25 mol% or less, and 5 mol% or more and 20 mol% or less. Is even more preferable.

Further, it is preferable that hydrogen is brought into contact with the catalyst in advance and then added into the polymerization system from the catalyst introduction line. Immediately after introducing the catalyst into the polymerization system, the concentration of the catalyst near the outlet of the introduction line is high, and the possibility of a partial high temperature state due to the rapid reaction of ethylene increases, but hydrogen and the catalyst are introduced into the polymerization system. By contacting the catalyst before introduction, it is possible to suppress the initial activity of the catalyst and suppress the production of low molecular weight components. Therefore, it is preferable to introduce hydrogen into the polymerization system in a state of being in contact with the catalyst.

For the same reason as described above, it is preferable that the outlet of the catalyst introduction line in the polymerization system is located as far as possible from the outlet of the ethylene introduction line. Specifically, a method such as introducing ethylene from the bottom of the polymerization solution and introducing the catalyst from the middle between the liquid level and the bottom of the polymerization solution can be mentioned.

The deactivation of the catalyst used in the polymerization step is not particularly limited, but it is preferable that the catalyst is deactivated after the polyethylene and the solvent are separated. By introducing a drug for inactivating the catalyst after separation from the solvent, there is a tendency that precipitation of low molecular weight components, catalyst components and the like contained in the solvent can be reduced.

The agent that inactivates the catalyst is not particularly limited, and examples thereof include oxygen, water, alcohols, glycols, phenols, carbon monoxide, carbon dioxide, ethers, carbonyl compounds, and alkynes. In addition to the above-mentioned inactivating agent, the method for inactivating the catalyst may be a temperature, humidity, or the like.

The solvent separation method in the method for producing a polyethylene polymer can be carried out by a decantation method, a centrifugation method, a filter filtration method or the like, but a centrifugation method having good separation efficiency between the polyethylene polymer and the solvent is more preferable. The amount of the solvent contained in the polyethylene after the solvent separation is not particularly limited, but is 70% by mass or less, more preferably 60% by mass or less, still more preferably 60% by mass or less, based on the mass (100% by mass) of the polyethylene-based polymer. Is 50% by mass or less. By drying and removing the solvent in a state where the solvent contained in the polyethylene-based polymer is small, the metal component and the low molecular weight component contained in the solvent tend to be less likely to remain in the polyethylene. When these components do not remain, a polyethylene-based polymer having high cross-linking efficiency can be obtained, and a cross-linked pipe having excellent pressure resistance and durability can be easily obtained. Therefore, it is preferable to separate the polyethylene polymer and the solvent by a centrifugation method.

The drying temperature in the method for producing a polyethylene polymer is preferably 50 ° C. or higher and 150 ° C. or lower, more preferably 60 ° C. or higher and 140 ° C. or lower, and further preferably 70 ° C. or higher and 130 ° C. or lower. When the drying temperature is 50 ° C. or higher, efficient drying tends to be possible. On the other hand, when the drying temperature is 150 ° C. or lower, it tends to be possible to dry in a state where the decomposition of polyethylene is suppressed.

In the method for producing a polyethylene-based polymer of the present embodiment, other known components and methods useful for producing a polyethylene-based polymer can be used in addition to the above-mentioned components.

〔Composition〕
The composition of the present embodiment (hereinafter, also referred to as “polyethylene-based polymer composition”) is 0.005 parts by mass with respect to the polyethylene-based polymer of the present embodiment and 100 parts by mass of the polyethylene-based polymer. It contains more than 5.0 parts by mass or less of an organic peroxide and 0.1 parts by mass or more and 10 parts by mass or less of an organic unsaturated silane compound.

[Organic peroxide]
The organic peroxide is decomposed into radicals in the extrusion step described later, and the organic unsaturated silane compound can be grafted on the polyethylene-based polymer.

The content of the organic peroxide is 0.005 parts by mass or more and 5.0 parts by mass or less, preferably 0.007 parts by mass or more and 1.0 parts by mass or less with respect to 100 parts by mass of the polyethylene-based polymer. Yes, more preferably 0.01 parts by mass or more and 0.5 parts by mass or less. When the content is 0.005 parts by mass or more, the graft reaction of the organic unsaturated silane compound proceeds efficiently. Further, when the content is 5.0 parts by mass or less, non-uniform cross-linking due to recombination of radicals generated in polyethylene by organic peroxide is suppressed, and deterioration of pipe extrusion workability is suppressed. can do. In addition, the odor of organic peroxide in the water flow of the crosslinked pipe can be reduced.

The organic peroxide is not particularly limited, but for example, dicumyl peroxide, 2,5-dimethyl-2,5-di- (t-butyl-oxy) -hexin-3, 1,3-bis- ( t-Butyl-oxy-isopropyl) -benzene, t-butylcumyl peroxide, 4,4, -di- (t-butylperoxy) valeric acid-butyl ester, 1,1-di- (t-butylperoxy) ) -3,3,5-trimethylcyclohexanexin-3, benzoyl peroxide, dicyclobenzo peroxide, di-t-butyl peroxide, lauroyl peroxide, di-t-butylperoxyisophthalate, and in the molecule Examples thereof include compounds having a butyl group and a peroxide group. Among these, dicumyl peroxide is economical and preferable.

[Organic unsaturated silane compound]
The content of the organic unsaturated silane compound is 0.1 parts by mass or more and 10 parts by mass or less, preferably 0.3 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the polyethylene-based polymer. , More preferably 0.5 parts by mass or more and 4.0 parts by mass or less. When the content is 0.1 part by mass or more, silane cross-linking in the case of a cross-linked pipe can be sufficiently promoted. Further, when the content is 10 parts by mass or less, it is possible to suppress a decrease in the extrusion moldability of the pipe due to the occurrence of rheumatism, an increase in the load when the pipe is extruded, and the like.

The organic unsaturated silane compound is not limited as long as it can be silane crosslinked, and is, for example, vinyl trimeticisilane, vinyltriethoxysilane, vinyltributoxysilane, allyltrimethoxysilane, vinylmethyldimethoxysilane, and vinyltris. Examples thereof include (β-methoxyethoxy) silane. Such an organic unsaturated silane compound can react with radicals in a polyethylene-based polymer generated by the action of an organic peroxide and can be grafted on the polyethylene-based polymer.

[Silanol condensation catalyst]
The polyethylene-based polymer composition may further contain a silanol condensation catalyst. The silanol condensation catalyst can crosslink the silane compound grafted onto the polyethylene-based polymer in the presence of water and / or water vapor.

The silanol condensation catalyst is not particularly limited, and for example, dibutyltin dilaurylate, stannous acetate, stannous caprylate, tin naphthenate, zinc caprylate, iron 2-ethylhexanoate, cobalt naphthenate, and titanic acid. Examples thereof include tetrabutyl ester, ethylamine, dibutylamine, dibutyltin dilaurylate, dibutyltin diacetate, and dibutyloctate.

The content of the silanol condensation catalyst is preferably 0.001 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the polyethylene-based polymer composition. When the content is 0.001 part by mass or more, the silane cross-linking tends to proceed efficiently in a short time. On the other hand, when the content is 10 parts by mass or less, the elution of the silanol condensation catalyst when water is passed through the crosslinked pipe tends to be suppressed.

At the time of producing the polyethylene-based polymer composition, the form of the polyethylene-based polymer is not particularly limited, and is, for example, any form of pellets and powder. Further, the organic peroxide, the organic unsaturated silane compound, and the silanol condensation catalyst may be contained alone or as a masterbatch with the polyethylene-based polymer.

The composition of the present embodiment may further contain additives such as a neutralizing agent, an antioxidant, and a light-resistant stabilizer.

The neutralizing agent is used as a chlorine catcher, a molding processing aid, or the like contained in the composition. The neutralizing agent is not particularly limited, and examples thereof include stearates of alkaline earth metals such as calcium, magnesium, and barium. The content of the neutralizing agent is not particularly limited, but is preferably 5000 mass ppm or less, more preferably 4000 mass ppm or less, and further preferably 3000 mass ppm or less with respect to the composition. Further, the polyethylene-based polymer obtained by the slurry polymerization method using the metallocene catalyst described above can exclude the halogen component from the catalyst constituent components, and in this case, the neutralizing agent may not be contained. preferable.

The antioxidant is not particularly limited, but is, for example, dibutylhydroxytoluene, pentaerythyl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3). , 5-Di-t-Butyl-4-hydroxyphenyl) Propionates and other phenolic antioxidants can be mentioned. The content of the antioxidant is not particularly limited, but is preferably 5000 mass ppm or less, more preferably 4000 mass ppm or less, and further preferably 3000 mass ppm or less with respect to the composition.

The light-resistant stabilizer is not particularly limited, and is, for example, 2- (5-methyl-2-hydroxyphenyl) benzotriazole and 2- (3-t-butyl-5-methyl-2-hydroxyphenyl) -5-chloro. Bentotriazole-based light-resistant stabilizers such as benzotriazole; bis (2,2,6,6-tetramethyl-4-piperidin) sebacate, poly [{6- (1,1,3,3-tetramethylbutyl) amino- 1,3,5-triazin-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-) Examples thereof include hindered amine-based light-resistant stabilizers such as piperidine) imino}]. The content of the light-resistant stabilizer is not particularly limited, but is preferably 5000 mass ppm or less, more preferably 4000 mass ppm or less, and further preferably 3000 mass ppm or less with respect to the composition.

The content of the above additive contained in the composition can be determined by extracting the additive in the composition with tetrahydrofuran (THF) for 6 hours by Soxhlet extraction, and separating and quantifying the extract by liquid chromatography. it can.

In addition to the above, the polyethylene-based polymer composition of the present embodiment includes known phenol-based stabilizers, organic phosphite-based stabilizers, organic thioether-based stabilizers, stabilizers such as metal salts of higher fatty acids; pigments, weather resistance. Agents, dyes, nucleating agents, lubricants such as calcium stearate; inorganic fillers such as carbon black, talc and glass fiber, or compounding agents added to polyolefins such as reinforcing materials, flame retardants and neutron blocking agents of the present invention. It can be added within a range that does not impair the purpose. Further, an adsorbent such as activated carbon may be added in order to suppress the elution of unreacted organic unsaturated silane compound, silanol condensation catalyst, and organic peroxide from the crosslinked pipe.

The composition of this embodiment is preferably for a crosslinked pipe described later.

[Bridge pipe]
The crosslinked pipe of the present embodiment comprises a crosslinked product of the composition of the present embodiment. Specifically, a crosslinked pipe can be obtained by molding the composition into a pipe shape and advancing the crosslinking reaction.

The method for producing the crosslinked pipe is not particularly limited as long as it is produced from the crosslinked product of the composition. For example, (1) a polyethylene polymer, an organic peroxide, an organic unsaturated silane compound, and a silanol condensation catalyst are extruded. After melting and mixing with, the pipe is formed, and the obtained pipe is crosslinked with a silyl group in the presence of warm water or water vapor.
(2) A polyethylene-based polymer, an organic peroxide, and an organic unsaturated silane compound are once melt-mixed with an extruder, a silanol condensation catalyst is added to the obtained composition to form a pipe, and the pipe is heated with warm water. Or a method of cross-linking a silyl group in the presence of water vapor,
(3) A method in which a pipe is formed using a composition containing polyethylene, an organic peroxide, and an organic unsaturated silane compound, and the pipe is exposed in the presence of warm water or water vapor containing a silanol condensation catalyst to crosslink the silyl group. Can be mentioned.

The gel fraction of the crosslinked pipe is preferably 65% or more. The gel fraction is not particularly limited, but can be a high value when the organic silane compound in the crosslinked product is uniformly grafted and the silane group is uniformly crosslinked by the silanol condensation catalyst. Empirically, crosslinked pipes with a high gel fraction are excellent in mechanical strength such as short-term and long-term hot internal pressure creep. In a conventional crosslinked pipe using a polyethylene-based polymer, it is necessary to use a large amount of an organic unsaturated silane compound in order to obtain a high gel fraction. Moreover, in the conventional crosslinked pipe using a polyethylene-based polymer, even if a high gel fraction is achieved, the hot internal pressure creep property is not sufficient. On the other hand, in the crosslinked pipe using the polyethylene-based polymer of the present embodiment, a high gel fraction can be obtained even with a small amount of the organic silane compound added, and sufficient pressure resistance and durability tend to be achieved.

Here, the gel fraction is a value measured according to the gel fraction test method of JIS K 6787-1997 cross-linked polyethylene pipe for water supply, Annex 7 (regulation). Next, a method for measuring the gel fraction of the crosslinked pipe will be described. Cut 10 g of the crosslinked pipe, extract with a Soxhlet extractor using a xylene solvent for 10 hours, measure the remaining amount of extraction, and calculate by the following formula.
Gel fraction (%) = (remaining extraction amount (g) / 10 (g)) x 100
More specifically, it is obtained by the method described in Examples described later.

[Use]
The polyethylene-based polymer of the present embodiment has a small number of terminal vinyl groups (the amount of double bonds in 1000 carbons), is excellent in thermal stability, has extremely few low molecular weight components, and is excellent in molding processability. Therefore, the load increase of the extruder, heat generation, and eye tar during pipe forming are reduced. Further, since the crosslinked pipe obtained from this polyethylene-based polymer has excellent durability and less odor in water flow, it is particularly preferably used for pipes for water supply, hot water supply, and heating.

Hereinafter, the present embodiment will be described in more detail based on the examples, but the present embodiment is not limited to the following examples. First, the measurement methods and evaluation criteria for each physical property and evaluation will be described below.

(Physical Properties 1) Density The densities of the polyethylene-based polymers obtained in Examples and Comparative Examples were measured by JIS K7112: 1999 and the density gradient tube method (23 ° C.).

(Physical properties 2) Melt flow rate (MFR)
The melt flow rate of each polyethylene-based polymer obtained in Examples and Comparative Examples was measured by JIS K7210 Code D: 1999 (temperature = 190 ° C., load = 2.16 kg).

(Physical properties 3) Amount of hydrocarbon component having 12 to 34 carbon atoms extracted with hexane 10 g of each polyethylene-based polymer obtained in Examples and Comparative Examples, and 40 mL of PCB test hexane manufactured by Wako Pure Chemical Industries, Ltd. It was placed in a 180 mL volume SUS container and sealed. The entire SUS container was immersed in a hot water bath at 70 ° C., extracted for 2 hours while shaking at a speed of 50 min ^-1 , and then immersed in water at 20 ° C. for rapid cooling. The supernatant was filtered through a glass syringe equipped with a 0.2 μm filter (manufactured by PTFE) to prepare a sample. The standard substances having 12 and 14 carbon atoms are special grade n-dodecane and n-tetradecane manufactured by Wako Pure Chemical Industries, Ltd., and the standard substances having 16 to 34 carbon atoms are ASTM D5442 C16-C44 Qualitative Retition manufactured by Sigma Aldrich. Time Mix was dissolved in PCB test hexane manufactured by Wako Pure Chemical Industries, Ltd. and used as a standard substance.

The above sample is a glass 3 mmφ x 1.5 m column filled with a gas chromatograph GC-2014AF manufactured by Shimadzu Corporation and a Silicone OV-1 (3%) / CW80-100 mesh / AW-DMCS treatment manufactured by Shinwa Kako Co., Ltd. Was measured using. The temperature was measured under the conditions that the injection temperature was 300 ° C., the detection temperature was 290 ° C., the initial temperature was 100 ° C. for 2 minutes, the temperature was raised at 10 ° C./min, and the temperature was maintained at 280 ° C. for 10 minutes. The amount of hydrocarbon component having 12 or more and 34 or less carbon atoms was calculated from the ratio with the peak area of the standard reagent.

(Physical properties 4) CFC elution amount (TREF elution amount)
For each of the polyethylene-based polymers obtained in Examples and Comparative Examples, the elution temperature-elution amount curve by temperature elution fractionation (TREF) was measured as follows, and the elution amount and elution integral amount at each temperature were measured. I asked. First, the temperature of the column containing the filler was raised to 140 ° C., and a sample solution (for example, concentration: 16 mg / 8 mL) in which polyethylene was dissolved in ortodichlorobenzene was introduced and held for 120 minutes.

Next, the temperature was lowered to 40 ° C. at a temperature lowering rate of 0.5 ° C./min and then held for 20 minutes to deposit the sample on the surface of the filler. Then, the temperature of the column was sequentially raised at a heating rate of 20 ° C./min. The temperature is raised at 10 ° C intervals from 40 ° C to 80 ° C, at 5 ° C intervals from 80 ° C to 85 ° C, at 3 ° C intervals from 85 ° C to 90 ° C, and from 90 ° C to 100 ° C. The temperature was raised at 1 ° C. intervals, and from 100 ° C. to 120 ° C. at 10 ° C. intervals. After holding at each temperature for 20 minutes, the temperature was raised to detect the concentration of the sample (polyethylene) eluted at each temperature. Then, the elution temperature-elution amount curve (Fig. 1) was measured from the values of the elution amount (mass%) of the sample and the in-column temperature (° C.) at that time, and the elution amount and the elution integral amount at each temperature were measured. Obtained.
Equipment: Polymer ChaAR Automated 3D analyzer CFC-2
Column: Stainless steel micro ball column (3/8 "od x 150 mm)
Eluent: o-dichlorobenzene (for high performance liquid chromatography)
Sample solution concentration: Sample (polyethylene) 20 mg / o-dichlorobenzene 20 mL
Injection volume: 0.5 mL
Pump flow rate: 1.0 mL / min Detector: Polymer ChAR infrared spectrophotometer IR4
Detected wavenumber: 3.42 μm
Sample dissolution conditions: 140 ° C x 120 min dissolution

(Physical properties 5) Chlorine content Approximately 0.05 g of each polyethylene-based polymer obtained in Examples and Comparative Examples was placed in a quartz boat and burned by AQF-100 in an automatic combustion device manufactured by Mitsubishi Analytech Co., Ltd. It was. The generated combustion gas was absorbed into an absorbent solution to which tartaric acid was added in advance, and quantification was performed by an internal standard method using tartaric acid as an internal standard substance with an ion chromatograph analyzer ICS-1500 manufactured by Dionex.

(Physical properties 6) Total content of Al, Mg, Ti, Zr, and Hf Approximately 0.2 g of each polyethylene-based polymer obtained in Examples and Comparative Examples was weighed in a PTFE decomposition vessel, and high-purity nitric acid (Kanto). Chemical Co., Ltd.) was added, and pressure decomposition was performed by a microwave decomposition apparatus ETHOS-TC manufactured by Milestone General Co., Ltd. Then, pure water purified by an ultrapure water production apparatus manufactured by Nippon Millipore Co., Ltd. with a total volume of 50 mL was used as a test solution. Inductively coupled plasma mass spectrometer (ICP-MS) X series 2 manufactured by Thermo Fisher Scientific Co., Ltd. is used for the above test solution, and Al, Mg, Ti, Zr, and Hf are quantified by the internal standard method. Was done.

(Physical properties 7) Amount of double bond The amount of double bond of each polyethylene-based polymer obtained in Examples and Comparative Examples is the heterogeneous bond of polyethylene described in the "Polymer Handbook" (Japan Analytical Chemical Society). It was measured according to the quantitative method of. Amount of double bonds (number / 1000 C-) is trans 963cm ^-1 (pieces / 1000 C-), terminal vinyl (pieces / 1000 C-) of 910 cm ^-1, measuring the absorbance A of vinylidene 888 cm ^-1 (pieces / 1000 C-) I asked for it. The calculation formula is shown below.
Double bond amount = 0.083A963 / (ρ × t) + 0.114A910 / (ρ × t) + 0.109A888 / (ρ × t)
A is the absorbance, ρ is the density (g / cm ³ ), and t is the thickness (mm).

(Physical properties 8) Gel fraction The gel fraction of each cross-linked pipe obtained in Examples and Comparative Examples was measured by JIS K 6787-1997 Cross-linked polyethylene pipe for water supply Annex 7 (Specification) Gel content of cross-linked polyethylene pipe for water supply. The test was performed according to the rate test method.

(Evaluation 1) Odor Each of the crosslinked pipes obtained in Examples and Comparative Examples was immersed in warm water at 50 ° C. for 24 hours, and the odor was evaluated from the odor of the immersed warm water according to the following criteria.
Good: Ester odor is strongly felt.
Yes: A slight ester odor is felt.
Impossible: No ester odor is felt.

(Evaluation 2) 95 ° C. Hot internal pressure creep rupture time Time until cracking or leakage occurs when a circumferential stress of 5.5 MPa is applied to each of the crosslinked pipes obtained in Examples and Comparative Examples in warm water at 95 ° C. Was measured and evaluated as the 95 ° C. hot internal pressure creep rupture time.

(Evaluation 3) Appearance of pipes The appearance of the pipes was evaluated according to the following criteria by visually confirming each of the crosslinked pipes obtained in Examples and Comparative Examples.
◯: When the wall thickness of the crosslinked pipe is not uneven and the appearance of the pipe surface is good.
X: When the crosslinked pipe is soft and meandering, the wall thickness of the pipe is uneven and the appearance of the pipe surface is visually poor.

(Saturated adsorption amount of Lewis acidic compound on the precursor of carrier [C])
First, spherical silica was prepared as a precursor of the carrier [C]. Next, triethylaluminum (Lewis acidic compound) was prepared as the activator compound (E-1). Spherical silica was heat-treated at 400 ° C. for 5 hours in a nitrogen atmosphere. The average particle size after the heat treatment was 3 μm, the compressive strength was 6 MPa, and the amount of surface hydroxyl groups was 1.85 mmol / g. In a nitrogen atmosphere, 4 g of this heat-treated spherical silica was added to a glass container having a capacity of 0.2 L, and 80 mL of hexane was added and dispersed to obtain a silica slurry. 10 mL of a hexane solution of triethylaluminum (concentration 1 mol / L) was added to the obtained silica slurry at 20 ° C. with stirring, and then the mixture was stirred for 2 hours to react triethylaluminum with the surface hydroxyl group of silica to obtain a hexane slurry. .. As a result of quantifying the amount of aluminum in the supernatant of this hexane slurry, the saturated adsorption amount of triethylaluminum with respect to spherical silica was 2.1 mmol / g.

(Preparation of carrier [C])
Spherical silica (40 g) after heat treatment was dispersed in 800 mL of hexane in a nitrogen-substituted 1.8 L autoclave to obtain a slurry. While keeping the obtained slurry at 20 ° C. under stirring, 80 mL of a hexane solution of triethylaluminum (concentration 1M) was added, and then the mixture was stirred for 2 hours to prepare 880 mL of a hexane slurry of carrier [C] on which triethylaluminium was adsorbed.

(Preparation of Transition Metal Compound [D])
As the transition metal compound (D-1), [(N-t-butylamide) (tetramethyl-η5-cyclopentadienyl) dimethylsilane] titanium-1,3-pentadiene (hereinafter, abbreviated as "titanium complex"). ) Was prepared. Further, as the organic magnesium compound (D-2), composition formula AlMg ₆ (C ₂ H ₅ ) ₃ (C ₄ H ₉ ) ₁₂ (hereinafter, abbreviated as “Mg 1”) was prepared. This Mg1 was synthesized by mixing a predetermined amount of triethylaluminum and dibutylmagnesium in hexane at 25 ° C. 200 mmol of the titanium complex is dissolved in 1000 mL of Isopar® E (manufactured by Exxon Mobile Chemical), 20 mL of a hexane solution of Mg1 (concentration 1 M) is added, and hexane is further added to adjust the titanium complex concentration to 0.1 M, and the transition The metal compound [D] was obtained.

(Preparation of activator [E])
As the activating compound (E-2), bis (taroalkyl hydride) methylammonium-tris (pentafluorophenyl) (4-hydroxyphenyl) borate (hereinafter abbreviated as "borate") was prepared. Further, as the activating compound (E-3), an organoaluminum compound and ethoxydiethyl aluminum were prepared. 5.7 g of borate was added to 50 mL of toluene and dissolved to obtain a 100 mM toluene solution of borate. 5 mL of a hexane solution of ethoxydiethylaluminum (concentration 1M) was added to this toluene solution of borate at 25 ° C., and hexane was further added to adjust the volate concentration in the toluene solution to 80 mM. Then, the activator [E] was prepared by stirring at 25 ° C. for 1 hour.

(Preparation of metallocene-supported catalyst [A])
To 880 mL of the slurry of carrier [C] obtained by the above operation, 50 mL of the activator [E] obtained by the above operation was added with stirring at 20 ° C., and the reaction was continued for 10 minutes. Next, 40 mL of the transition metal compound component [D] obtained by the above operation was added with stirring, and the reaction was continued for 3 hours to obtain a slurry. Further, a purification operation of removing the supernatant of this slurry, adding hexane and stirring was carried out three times to prepare a metallocene-supported catalyst [A] (simply indicated as [A] in Table 1).

(Preparation of liquid co-catalyst [B])
The above Mg1 was prepared as the organic magnesium compound [G]. As compound [J], methylhydropolysiloxane (viscosity at 25 ° C., 20 cm Stokes, manufactured by Shin-Etsu Chemical Co., Ltd.) was prepared. To a 200 mL flask, 40 mL of hexane and Mg1 were added with stirring so that the total amount of Mg and Al was 37.8 mmol, and 40 mL of hexane containing 2.27 g (37.8 mmol) of methylhydropolysiloxane was added at 25 ° C. Was added with stirring, and then the temperature was raised to 80 ° C. and the mixture was reacted under stirring for 3 hours to prepare a liquid co-catalyst [B].

(Preparation of Ziegler catalyst [H])
2740 mL of trichlorosilane (HSICl ₃ ) as a 2 mol / L n-heptane solution was charged into a fully nitrogen-substituted 15 L reactor, kept at 50 ° C. with stirring, and the composition formula AlMg ₆ (C ₂ H ₅ ) ₃ (N-C ₄ H ₉ ) _10.8 (On-C ₄ H ₉ ) Add 7 L of n-heptane solution (5 mol in magnesium equivalent) of the organic magnesium component indicated by _1.2 over 3 hours, and further add 1 hour at 50 ° C. The reaction was carried out with stirring. After completion of the reaction, the supernatant was removed from the reaction solution containing the solid, and the obtained solid was washed with 7 L of n-hexane four times to obtain a slurry. The solid separated and dried was analyzed by solid 1 per gram, Mg8.62mmol, Cl17.1mmol, contained n- butoxy _{(On-C 4 H 9)} 0.84mmol.

The slurry containing 500 g of the solid obtained as described above was reacted with 1250 mL of an n-hexane solution of 1 mol / L of n-butyl alcohol at 50 ° C. for 1 hour under stirring. After completion of the reaction, the supernatant was removed from the reaction solution containing the solid, and the obtained solid was washed once with 7 L of n-hexane to obtain a slurry. The slurry was kept at 50 ° C., 500 mL of an n-hexane solution of 1 mol / L diethyl aluminum chloride was added under stirring, and the mixture was reacted for 1 hour. After completion of the reaction, the supernatant was removed from the reaction solution containing the solid, and the obtained solid was washed twice with 7 L of n-hexane to obtain a slurry. The slurry was kept at 50 ° C., 78 mL of an n-hexane solution of 1 mol / L diethylaluminum chloride and 78 mL of an n-hexane solution of 1 mol / L titanium tetrachloride were added, and the mixture was reacted for 1 hour. Further, 234 mL of an n-hexane solution of 1 mol / L diethyl aluminum chloride and 234 mL of an n-hexane solution of 1 mol / L titanium tetrachloride were added to the reaction solution, and the mixture was reacted for 2 hours. After completion of the reaction, the supernatant was removed from the reaction solution containing the solid, and the mixture was washed 4 times with 7 L of n-hexane while maintaining the internal temperature at 50 ° C., and the solid catalyst Ziegler catalyst [H] (Table 1). Among them, simply indicated as [H]) was obtained as a hexane slurry solution. This solid catalyst contained 2.8% by weight titanium.

[Example 1] Polyethylene polymerization step As the first-stage polymerization, a Vessel-type 340L polymerization reactor equipped with a stirrer is used under the conditions of a polymerization temperature of 60 ° C., a polymerization pressure of 0.25 MPa, and an average residence time of 3.3 hours. Continuous polymerization was performed. Dehydrated normal hexane 40 L / hour as a solvent, the above-mentioned supported metallocene catalyst [A] as a catalyst at 50.0 mg / hour, and a liquid co-catalyst [B] at 4 mmol / hour in terms of Al atom, with respect to the vapor phase concentration of ethylene. The first-stage polymerization was carried out by supplying 1-butene to 0.36 mol% and hydrogen to 0.21 mol%, respectively. Dehydrated normal hexane is supplied from the bottom of the polymerizer, hydrogen is supplied from the catalyst introduction line together with the catalyst from the middle of the liquid surface and the bottom of the polymerizer in order to contact the catalyst in advance, and ethylene is supplied from the bottom of the polymerizer. did. The polymerization slurry in the polymerization reactor was guided to a flash tank having a pressure of 0.05 MPa and a temperature of 70 ° C. so that the level of the polymerization reactor was kept constant, and unreacted ethylene, 1-butene and hydrogen were separated.

Next, the mixture was continuously transferred to a Vessel-type 300L polymerization reactor equipped with a second-stage stirrer, and the polymerization temperature was 75 ° C., the polymerization pressure was 0.82 MPa, and the average residence time was 0.5 hours. went. The second-stage polymerization was carried out by supplying 190 L / hour of dehydrated normal hexane as a solvent and 0.74 mol% of 1-butene and 0.20 mol% of hydrogen with respect to the vapor phase concentration of ethylene. The polymerization slurry in the polymerization reactor was guided to a flash tank having a pressure of 0.05 MPa and a temperature of 50 ° C. so that the level of the polymerization reactor was kept constant, and unreacted ethylene, 1-butene and hydrogen were separated.

Subsequently, the polymerization slurry in the polymerization reactor was continuously sent to a centrifuge to separate the polymer from other solvents and the like to obtain polyethylene powder. The content of the solvent and the like with respect to the polymer at that time was 45% by mass. The separated polyethylene powder was dried while blowing nitrogen at 85 ° C. In this drying, steam was sprayed on the polymerized powder to deactivate the catalyst and co-catalyst.

The obtained polyethylene powder was TEX-44 manufactured by Japan Steel Works, Ltd. (screw diameter 44 mm, L / D = 35. L: polymerization reactor) without using additives such as neutralizers and antioxidants. The distance from the raw material supply port to the discharge port (m), D: the inner diameter of the polymerization reactor (m). The same shall apply hereinafter), and melt-kneaded at a resin temperature of 195 ° C. Granulated to obtain a polyethylene-based polymer. Table 1 shows various physical properties and evaluation results of the obtained polyethylene polymer. In addition, FIG. 1 shows an elution temperature-elution amount curve obtained by CFC measurement.

With respect to 100 parts by mass of the above polyethylene-based polymer, which is an ethylene-butene-1 copolymer, 2.0 parts by mass of vinyltrimethoxysilane and perhexa 25B as an organic peroxide (manufactured by Nippon Oil & Fats Co., Ltd.) 0. 1 part by mass, 0.05 part by mass of dioctyltin dilaurylate, tetrax as a phenolic antioxidant [methylene-3- (3', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate] 0.2 parts by mass of methane, 0.25 parts by mass of 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, n-octadecyl −3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate 0.25 parts by mass, tetrakis (2,4-di-t-butylphenyl) -4,4'as a phosphorus-based heat stabilizer 0.05 parts by mass of -biphenylene-di-phosphonite and 0.15 parts by mass of calcium stearate were mixed and mixed with Hensiel. Then, a polyethylene resin composition was extruded into a pipe shape by combining a single shaft extruder RH501 (screw diameter 50 mm, L / D = 30) manufactured by Reifenhauser and a pipe-shaped die. After cooling, a pipe having an outer diameter of about 18 mm and a wall thickness of about 2.5 mm was obtained. Then, it was immersed in warm water at 95 ° C. for 24 hours to proceed with the silanol condensation reaction to obtain a crosslinked pipe. Table 1 shows various physical properties and evaluation results of the obtained crosslinked pipe.

[Example 2]
As the first-stage polymerization, under the conditions of a polymerization temperature of 75 ° C. and a polymerization pressure of 0.19 MPa, 1-butene is supplied so as to be 0.13 mol% and hydrogen is 0.15 mol% with respect to the vapor phase concentration of ethylene, and the second stage is polymerized. As the polymerization of the eyes, a polyethylene polymer and a crosslinked pipe were obtained by the same operation as in Example 1 except that 1-butene was 0.64 mol% and hydrogen was 0.17 mol% with respect to the vapor phase concentration of ethylene. It was. Table 1 shows various physical properties and evaluation results.

[Example 3]
As the first-stage polymerization, 1-butene was supplied so as to be 0.43 mol% and hydrogen 0.22 mol% with respect to the vapor phase concentration of ethylene, and as the second-stage polymerization, 1 was supplied with respect to the vapor phase concentration of ethylene. A polyethylene-based polymer and a crosslinked pipe were obtained by the same operation as in Example 1 except that the content was 0.82 mol% of butene and 0.14 mol% of hydrogen. Table 1 shows various physical properties and evaluation results.

[Example 4]
As the first-stage polymerization, under the condition of a polymerization temperature of 75 ° C., 1-butene was supplied so as to be 0.08 mol% and hydrogen was 0.19 mol% with respect to the vapor phase concentration of ethylene, and as the second-stage polymerization, ethylene was supplied. A polyethylene-based polymer and a crosslinked pipe were obtained by the same operation as in Example 1 except that 1-butene was 0.45 mol% and hydrogen was 0.20 mol% with respect to the gas phase concentration of. Table 1 shows various physical properties and evaluation results.

[Comparative Example 1]
As the first-stage polymerization, under the conditions of a polymerization temperature of 80 ° C. and a polymerization pressure of 0.97 MPa, 1-butene was supplied so as to be 0.38 mol% and hydrogen was 0.25 mol% with respect to the vapor phase concentration of ethylene, and the second stage was polymerized. A polyethylene-based polymer and a crosslinked pipe were obtained by the same operation as in Example 1 except that the eyes were not polymerized. Table 1 shows various physical properties and evaluation results. Here, the elution peak in the (physical property 4) CFC elution amount was a single peak represented as the elution peak maximum temperature 1.

[Comparative Example 2]
As the first-stage polymerization, 1-butene was not used, and hydrogen was supplied so as to be 0.23 mol% with respect to the vapor phase concentration of ethylene, and as the second-stage polymerization, the polymerization pressure was 0.57 MPa. A polyethylene-based polymer and a crosslinked pipe were obtained by the same operation as in Example 1 except that 1-butene was 1.90 mol% and hydrogen was 0.24 mol% with respect to the vapor phase concentration of ethylene. Table 1 shows various physical properties and evaluation results.

[Comparative Example 3]
As the first-stage polymerization, under the condition of a polymerization temperature of 75 ° C., 1-butene was supplied so as to be 0.95 mol% and hydrogen 0.20 mol% with respect to the vapor phase concentration of ethylene, and as the second-stage polymerization, the polymerization was carried out. The polyethylene-based polymer and cross-linking were carried out in the same manner as in Example 1 except that 1-butene was 0.50 mol% and hydrogen was 0.23 mol% with respect to the vapor phase concentration of ethylene under the condition of a pressure of 0.80 MPa. Got a pipe. Table 1 shows various physical properties and evaluation results.

[Comparative Example 4]
As the first-stage polymerization, under the conditions of a polymerization temperature of 73 ° C. and a polymerization pressure of 0.30 MPa, a Cheegler catalyst [H] was used as a catalyst at 10 mg / hour, a liquid co-catalyst component was used at 10 mmol / hour in terms of Al atom, and the vapor phase concentration of ethylene was 1-butene was supplied so as to be 0.95 mol% and hydrogen was 0.20 mol%, and as the second-stage polymerization, the vapor phase concentration of ethylene was adjusted under the conditions of a polymerization temperature of 86 ° C. and a polymerization pressure of 0.25 MPa. On the other hand, a polyethylene-based polymer and a crosslinked pipe were obtained by the same operation as in Example 1 except that 1-butene was 12.6 mol% and hydrogen was 11.6 mol%. Table 1 shows various physical properties and evaluation results.

[Comparative Example 5]
As the first-stage polymerization, 1-butene was supplied so as to be 0.43 mol% and hydrogen 0.18 mol% with respect to the vapor phase concentration of ethylene, and as the second-stage polymerization, 1 was supplied with respect to the vapor phase concentration of ethylene. A polyethylene-based polymer and a crosslinked pipe were obtained by the same operation as in Example 1 except that the content was 1.34 mol% of butene and 0.14 mol% of hydrogen. Table 1 shows various physical properties and evaluation results.

[Comparative Example 6]
As the first-stage polymerization, under the condition of a polymerization temperature of 75 ° C., 1-butene was supplied so as to be 0.08 mol% and hydrogen was 0.22 mol% with respect to the gas phase concentration of ethylene, and as the second-stage polymerization, ethylene was supplied. A polyethylene-based polymer and a crosslinked pipe were obtained by the same operation as in Example 1 except that 1-butene was 0.10 mol% and hydrogen was 0.22 mol% with respect to the gas phase concentration of. Table 1 shows various physical properties and evaluation results.

[Comparative Example 7]
As the first stage polymerization, polyethylene is polymerized using a reaction tank adjacent to each of the outlets of the hexane supply line, the hydrogen supply line, the ethylene supply line, and the catalyst supply line at the bottom of the polymerizer, and ethanol is added to the polyethylene slurry. Was added to deactivate the catalyst, and then the obtained polyethylene slurry was filtered to separate the polyethylene powder and the solvent, etc., except that the polyethylene polymer and the crosslinked pipe were operated in the same manner as in Example 1. Got The content of the solvent and the like with respect to the polymer after filtration was 250%. Table 1 shows various physical properties and evaluation results.

The polyethylene-based polymer according to the present invention has a small number of terminal vinyl groups, is excellent in thermal stability, has extremely few low molecular weight components, and is excellent in molding processability. Therefore, the crosslinked pipe obtained from the polyethylene-based polymer has excellent durability, has less odor in water flow, and does not have problems such as an increase in the load of the extruder during pipe molding, heat generation, and eye shaving, and is therefore particularly for water supply. , Suitable for hot water supply and heating pipes.

Claims (14)

The density is 935 kg / m ³ or more and 955 kg / m ³ or less.
The melt flow rate is 1.0 g / 10 min or more and 10 g / 10 min or less.
The total content of hydrocarbon components with 12 to 34 carbon atoms extracted with hexane is 300 mass ppm or less.
In the dissolution temperature curve of the total amount of polyethylene eluted in the measurement using cross fractionation chromatography, the elution peak having a maximum point temperature of 80 ° C. or higher and lower than 90 ° C. and the elution peak having a maximum point temperature of 90 ° C. or higher and lower than 100 ° C. A polyethylene-based polymer in which at least one of each is present. The polyethylene-based polymer according to claim 1, wherein the chlorine content is 5.0 mass ppm or less with respect to the polyethylene-based polymer. The polyethylene-based polymer according to claim 1 or 2, wherein the total content of Al, Mg, Ti, Zr, and Hf is 20 mass ppm or less with respect to the polyethylene-based polymer. The polyethylene-based polymer according to any one of claims 1 to 3, wherein the amount of double bonds contained in 1000 carbons in polyethylene is 0.05 or less. According to claims 1 to 4, the integrated elution amount of less than 80 ° C. is 10% by mass or less with respect to the total elution amount in the dissolution temperature curve of the total elution amount of polyethylene in the measurement using the cross fractionation chromatography. The polyethylene-based polymer according to any one item. The polyethylene-based polymer according to any one of claims 1 to 5, which is used for a crosslinked pipe. The polyethylene-based polymer according to any one of claims 1 to 6, and an organic peroxide of 0.005 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the polyethylene-based polymer. A composition comprising 0.1 parts by mass or more and 10 parts by mass or less of an organic unsaturated silane compound. The composition according to claim 7, which is for a crosslinked pipe. A crosslinked pipe comprising a crosslinked product of the composition according to claim 7 or 8. The crosslinked pipe according to claim 9, wherein the gel fraction is 65% or more. The crosslinked pipe according to claim 9 or 10, which is used for a pipe for water supply, hot water supply, or heating. Polymerized in the presence of a supported metallocene catalyst obtained from at least a carrier substance, an organoaluminum compound, a borate compound having active hydrogen, a cyclopentadiene compound, and a transition metal compound of Group IV of the periodic table, and a liquid co-catalyst. A method for producing a polyethylene-based polymer, which comprises a polymerization step for obtaining the polyethylene-based polymer according to any one of claims 1 to 6. The method for producing a polyethylene-based polymer according to claim 12, wherein the polymerization step is a step of polymerizing by a slurry polymerization method and a two-stage polymerization method using a polymerization medium having 6 or more and 10 or less carbon atoms. The method for producing a polyethylene-based polymer according to claim 12 or 13, wherein the liquid co-catalyst is a liquid co-catalyst prepared from an organic magnesium compound and methylhydropolysiloxane.