JP7724070B2 - Piping material for ultrapure water and polyethylene resin composition for ultrapure water piping material - Google Patents

Description

The present invention relates to piping materials for ultrapure water and polyethylene-based resin compositions for use in ultrapure water piping materials. More specifically, the present invention relates to polyethylene-based resin pipes, fittings, valves, etc. used as piping materials for ultrapure water, and polyethylene-based resin compositions for use in ultrapure water piping materials.

In the manufacture of precision devices such as semiconductor devices and liquid crystal display devices, ultrapure water refined to an extremely high level has traditionally been used in wet processes such as cleaning. If metal ions or other impurities are present in the water at a concentration above a certain level, they can be adsorbed onto wafer surfaces and have a negative impact on the quality of the precision devices, so the amount of impurities in the ultrapure water is strictly controlled.

Impurities can also get mixed into ultrapure water in the piping that makes up the ultrapure water transport line. Metals such as stainless steel, which have excellent gas barrier properties, have been used as piping materials, but considering the impact of metal leaching from the piping, it is considered preferable to use resin.

Fluororesin resins are used as resin materials for ultrapure water piping because they are chemically inert, have gas barrier properties, and are highly soluble in ultrapure water. For example, fluororesin double-layered tubes, made of two layers of fluororesin, are used in piping for semiconductor manufacturing equipment and liquid crystal manufacturing equipment. Examples of double-layered fluororesin tubes include those in which the inner layer is made of a fluororesin with excellent corrosion resistance and chemical resistance (e.g., tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), or tetrafluoroethylene-ethylene copolymer (ETFE)) and the outer layer is made of a fluororesin that can suppress gas permeation (e.g., polyvinylidene fluoride (PVDF)).

Patent Document 1 also discloses a multi-layer pipe for piping ultrapure water, characterized by comprising a first resin layer made of fluororesin that comes into contact with the ultrapure water, and a second resin layer made of gas-impermeable resin that is provided on the outer surface of the first resin layer. It also discloses that a third resin layer is provided on the outer surface of the second resin layer to protect the second resin layer, and that polyethylene is used for the third resin layer.

Among the resins used for ultrapure water piping, polyvinylidene fluoride (PVDF) is used in all practical applications in the semiconductor industry, including piping within ultrapure water production equipment and piping for transporting ultrapure water from the equipment to use points, and has become the technical standard for ultrapure water piping.

Recently, as the integration density of semiconductor chips has increased, circuit patterns have become increasingly finer, making them more susceptible to even low-level impurities. As a result, the quality requirements for ultrapure water are becoming increasingly strict. For example, standards for the quality of ultrapure water used in semiconductor manufacturing have been published as SEMI F75, which is updated every two years.

JP 2010-234576 A

Fluororesin piping, such as PVDF, has some disadvantages in terms of ease of installation and cost compared to other common piping. However, as the water quality requirements for ultrapure water become increasingly strict, fluororesin piping is effectively the only option for piping that meets the required water quality.

The present inventors have deliberately focused on alternative materials for piping materials for ultrapure water. For example, polyethylene-based resins, which are excellent in workability and cost, are commonly used as piping materials. However, polyethylene-based resins, which are commonly used as piping materials, are synthesized by polymerization using a chlorine-based catalyst such as a Ziegler catalyst, and require the addition of a neutralizing agent such as calcium stearate to neutralize the catalyst residue after polymerization. Furthermore, among neutralizing agents, fatty acid metal soaps such as calcium stearate not only neutralize chlorine but also exhibit a lubricating effect on molds. Therefore, they are commonly added to piping materials as a surface smoothness improver, regardless of the type of polyethylene polymerization catalyst. For this reason, typical polyethylene-based resin pipes leach a large amount of calcium from the neutralizing agent into the water they transport, making them far below the water quality required for ultrapure water.
On the other hand, polyethylene resins, which are commonly used as general piping materials, have a large shrinkage after solidification, and because the shrinkage rate differs depending on the resin flow direction during molding, the shrinkage anisotropy, which is the ratio of the flow direction to the direction perpendicular to the flow, is large, making it difficult to obtain the perfect circular shape required for piping materials. Normally, to achieve a perfect circular shape in piping materials using polyethylene resins, it is known to knead in a pigment that exhibits a crystal nucleating agent effect in order to control the shrinkage of the polyethylene resin. However, when considering piping materials for ultrapure water, kneading in a pigment into polyethylene resins raises concerns that trace metals derived from the pigment and wax components used as a pigment dispersant will leach out, which could worsen the quality of the ultrapure water.

The object of the present invention is to provide a piping material for ultrapure water and a polyethylene resin composition for ultrapure water piping material that reduces calcium elution, has a small anisotropic shrinkage coefficient, and possesses sufficiently excellent mechanical properties and dimensional stability after molding for use in pressure pipe systems.

After extensive research, the inventors discovered that, with regard to polyethylene resin piping materials, the amount of calcium elution can be significantly reduced by controlling the calcium concentration of the polyethylene resin in contact with ultrapure water on the inner wall side of the piping material to fall within a specific range, and further restricting the structure of a phenolic antioxidant, if added, to a specific type. They also discovered that controlling the MFR, molecular weight, and molecular weight distribution of the polyethylene resin to fall within specific ranges can reduce the shrinkage anisotropy and achieve long-term strength.

That is, the present disclosure provides the following aspects:

The polyethylene resin composition for ultrapure water piping material according to the first aspect is a polyethylene resin composition used for ultrapure water piping material, contains a polyethylene resin, and satisfies the following properties (1) to (5).

Property (1): The melt flow rate (MFR _21.6 ) at a temperature of 190° C. and a load of 21.6 kg is 6 g/10 min or more and 25 g/10 min or less.

Property (2): Density is 0.946 g/cm ³ or more and 0.960 g/cm ³ or less.

Property (3): In the molecular weight distribution measured by GPC, the Mz/Mw, an index showing the breadth of the molecular weight distribution, is 2.5 or more and 5.5 or less.

Property (4): The calcium concentration contained in the polyethylene resin composition is 100 ppm or less.

Property (5): The high molecular weight component contains 20% by weight or more and 50% by weight or less of an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to ¹² carbon atoms, the copolymer having _{an MFR} 21.6 of 0.2 g/ ¹⁰ min or more and 1.0 g/10 min or less and a density of 0.910 g/cm 3 or more and 0.935 g/cm 3 or less.

The polyethylene resin composition for ultrapure water piping material according to the second aspect is the polyethylene resin composition according to the first aspect, in which components with a molecular weight of 3,000,000 or more account for 2% or less of the total molecular weight distribution measured by GPC.

The polyethylene resin composition for ultrapure water piping material according to the third aspect is the polyethylene resin composition for ultrapure water piping material according to the second aspect, and has a rupture time of 100 hours or more in an FNCT test (measured at 80°C and 5 MPa).

The polyethylene resin composition for ultrapure water piping material according to the fourth aspect is the polyethylene resin composition for ultrapure water piping material according to the third aspect, and contains an antioxidant.

The polyethylene resin composition for ultrapure water piping material according to the fifth aspect is the polyethylene resin composition for ultrapure water piping material according to the fourth aspect, wherein the antioxidant includes a phenolic antioxidant that does not contain oxygen derived from groups other than phenol groups.

The polyethylene resin composition for ultrapure water piping material according to the sixth aspect is the polyethylene resin composition for ultrapure water piping material according to the fourth aspect, wherein the antioxidant includes a phenolic antioxidant having oxygen derived from a group other than a phenol group, and the calcium concentration is 50 ppm or less.

The polyethylene resin composition for ultrapure water piping material according to the seventh aspect is a polyethylene resin composition for ultrapure water piping material according to any one of the first to sixth aspects, and is substantially free of stabilizers.

The ultrapure water piping material according to the eighth aspect is a piping material characterized by being molded from the polyethylene resin composition for ultrapure water piping material according to any one of the first to seventh aspects.

The ultrapure water piping material according to the ninth aspect is the ultrapure water piping material according to the eighth aspect, in which the thickness of the layer primarily composed of polyethylene resin is 0.3 mm or more.

The ultrapure water piping material according to the tenth aspect is the ultrapure water piping material according to the ninth aspect, in which the thickness of the layer primarily composed of polyethylene resin is 2.0 mm or less.

The present invention makes it possible to provide a piping material for ultrapure water that reduces calcium elution and has excellent mechanical properties and dimensional stability after molding, as well as a polyethylene resin composition for use as a piping material for ultrapure water.

1 is a schematic cross-sectional view showing a pipe as an example of a piping material for ultrapure water according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing another example of a pipe for ultrapure water piping material according to an embodiment of the present invention. 1 is a diagram showing a joint of an example of a piping material for ultrapure water in an embodiment of the present invention. 1 is a diagram showing a joint of an example of a piping material for ultrapure water in an embodiment of the present invention. 1 is a diagram showing a joint of an example of a piping material for ultrapure water in an embodiment of the present invention. 1 is a diagram showing a joint of an example of a piping material for ultrapure water in an embodiment of the present invention. 1 is a diagram showing a joint of an example of a piping material for ultrapure water in an embodiment of the present invention. 1 is a diagram showing a valve of an example of a piping material for ultrapure water in an embodiment of the present invention. This is the structural formula of Irganox 1010. This is the structural formula of Irganox 1330.

The following describes ultrapure water piping materials in embodiments of the present invention. Note that "ultrapure water piping materials" is a general term for components that make up ultrapure water piping, including pipes, fittings, and valves.

[Pipe configuration]
The tube of this embodiment will be described below.

The pipe of this embodiment has a polyethylene resin layer that forms the inner surface of the pipe and is primarily composed of polyethylene resin. If necessary, a coating resin layer may be provided on the outside of the polyethylene resin layer.

Figure 1 is a schematic cross-sectional view showing an example of a tube according to this embodiment. Figure 2 is a schematic cross-sectional view showing another example of a tube according to this embodiment.

The pipe 10 shown in Figure 1 (an example of a piping material for ultrapure water) has a polyethylene-based resin layer 21 (an example of a layer). The pipe 11 shown in Figure 2 (an example of a piping material for ultrapure water) has a polyethylene-based resin layer 21 that forms the innermost layer and a coating resin layer 22 arranged on the outside of it.

The pipe 10 shown in Figure 1 is formed from a polyethylene-based resin layer 21. The polyethylene-based resin layer 21 forms the inner surface 10a of the pipe 10 (an example of the inner surface of a piping material). The outer surface 10b of the pipe 10 shown in Figure 1 is also formed from a polyethylene-based resin layer 21. The polyethylene-based resin layer 21 is formed into a cylindrical shape to constitute the pipe 10.

In addition, in the pipe 11 shown in Figure 2, the polyethylene-based resin layer 21 forms the inner surface 11a of the pipe 11 (an example of the inner surface of a piping material). In the pipe 11 shown in Figure 2, the outer surface 11b is formed by the coating resin layer 22. The polyethylene-based resin layer 21 is formed in a cylindrical shape so as to constitute the innermost layer of the pipe 11. The coating resin layer 22 is formed in a cylindrical shape so as to cover the polyethylene-based resin layer 21.

Furthermore, in the pipe 11 shown in Figure 2, only one coating resin layer 22 is provided on the outside of the polyethylene resin layer 21, but the number of coating resin layers 22 is not particularly limited and may be one layer or two or more layers.

The inner surfaces 10a, 11a face the flow paths 10c, 11c inside the tubes 10, 11, and can be said to be surfaces that may come into contact with ultrapure water.

[Fitting Configuration]
The joint of this embodiment will be described below.

Examples of fittings that can be used in the present invention include, but are not limited to, sockets, elbows, tees, flanges, etc.

Figures 3A to 3E show examples of joints in this embodiment.

The joint 31 shown in Figure 3A is a socket into which tubes are inserted from both ends to connect the two tubes in a straight line. Joint 31 is, for example, an electrofusion joint.

The fitting 32 shown in Figure 3B is an elbow, used to connect pipes at right angles, for example.

The fitting 33 shown in Figure 3C is a tee. Fitting 33 connects three pipes at 90-degree intervals.

The fitting 34 shown in Figure 3D is a flange. The fitting 34 has a flange portion 34d and is connected to a valve or the like.

The fitting 35 shown in Figure 3E is a reducer. Fitting 35 connects two pipes of different diameters in a straight line.

The configurations of the fittings 31-35 shown in Figures 3A-3E can be applied to the pipe configurations described above, and the cross-sectional shapes are similar to those of the pipe configurations described above (see Figures 1 and 2). That is, each of the fittings 31-35 has a polyethylene-based resin layer 21 that forms the inner surfaces 31a-35a facing the flow path. A coating resin layer 22 may be provided on the outside of the polyethylene-based resin layer 21.

[Valve configuration]
The valve of this embodiment will be described below.

Valves in this embodiment include, but are not limited to, diaphragm valves, ball valves, butterfly valves, globe valves, gate valves, check valves, etc.

Figure 4 shows a butterfly valve as an example of a valve. The butterfly valve 40 shown in Figure 4 comprises a valve body 41, a seat ring 42, a valve stem (not shown), a valve disc 43, and a handle 44. The valve body 41 is disposed between pipe members through which a fluid flows. A through-hole is formed in the valve body 41. The seat ring 42 is attached to the inner circumferential surface of the through-hole in the valve body 41. The valve disc 43 is fixed to the valve stem and rotates with the rotation of the valve stem, compressing the seat ring 42 and thereby blocking the flow path 41a formed inside the seat ring 42. The valve stem is rotated by rotating the handle 44.

The above-described pipe configuration can be applied to the configuration of the seat ring 42, and the cross-sectional shape is the same as the above-described pipe configuration (see Figures 1 and 2). That is, the seat ring 42 has a polyethylene-based resin layer 21 that forms the inner surface 42a facing the flow path 41a. A coating resin layer 22 may be provided on the outside of the polyethylene-based resin layer 21.

[Polyethylene resin layer]
As long as the polyethylene resin composition used in the polyethylene resin layer 21 satisfies the range specified in the present invention, it may be a composition obtained by polymerizing a plurality of ethylene polymers separately and then mixing them in a single polymerization vessel or in a plurality of reactors connected in series or in parallel.

Polyethylene resins may be copolymerized with α-olefins as needed. Examples of α-olefins that can be copolymerized with polyethylene resins include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-butene-1-hexene, 1-butene-4-methyl-1-pentene, and 1-butene-1-octene.

Polyethylene resins are polymerized using a catalyst containing one or more transition metal derivatives.

The Ziegler catalyst used in this embodiment is well known, and examples of the catalyst systems used include those described in Japanese Patent Laid-Open Publication Nos. 53-78287, 54-21483, 55-71707, and 58-225105.

Specific examples include catalyst systems consisting of a solid catalyst component and an organoaluminum compound, which are obtained by contacting a tetravalent titanium compound with the co-ground product obtained by co-grounding aluminum trihalide, an organosilicon compound having an Si-O bond, and a magnesium alcoholate.

The solid catalyst component preferably contains 1 to 15% by weight of titanium atoms. Preferred organosilicon compounds include those containing phenyl or aralkyl groups, such as diphenyldimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, triphenylethoxysilane, and triphenylmethoxysilane.

When producing the co-ground product, the ratio of aluminum trihalide and organosilicon compound used per mole of magnesium alcoholate is generally 0.02 to 1.0 mole, with 0.05 to 0.20 moles being particularly preferred. Furthermore, a molar ratio of aluminum atoms in the aluminum trihalide to silicon atoms in the organosilicon compound of 0.5 to 2.0 is preferred.

The co-ground product can be produced by a conventional method using a mill commonly used in producing this type of solid catalyst component, such as a rotary ball mill, a vibrating ball mill, or a colloid mill. The average particle size of the obtained co-ground product is usually 50 to 200 μm, and the specific surface area is 20 to 200 m ² /g.

A solid catalyst component is obtained by contacting the co-ground product obtained as described above with a tetravalent titanium compound in the liquid phase. The organoaluminum compound used in combination with the solid catalyst component is preferably a trialkylaluminum compound, such as triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, or tri-i-butylaluminum.

The metallocene catalyst used in the present embodiment is a catalyst containing the following catalyst component (A) and catalyst component (B), and is optionally combined with catalyst component (C).
Catalyst component (A): metallocene compound; Catalyst component (B): compound that reacts with catalyst component (A) to form a cationic metallocene compound; Catalyst component (C): fine particle carrier

(1) Catalyst Component (A)
The catalyst component (A) is a metallocene compound of a transition metal of Group 4 of the periodic table. Specifically, compounds represented by the following general formulas (I) to (VI) are used.
(C ₅ H _5-a R ¹ _a ) (C ₅ H _5-b R ² _b )MXY (I)
Q(C ₅ H _4-c R ¹ _c )(C ₅ H _4-d R ² _d )MXY (II)
Q'(C ₅ H _4-e R ³ _e )ZMXY (III)
(C ₅ H _5-f R ³ _f )ZMXY (IV)
(C ₅ H _5-f R ³ _f ) MXYW (V)
Q” (C ₅ H _5-g R ⁴ _g ) (C ₅ H _5-h R ⁵ _h ) MXY (VI)

wherein Q represents a bonding group that bridges two conjugated five-membered ring ligands; Q' represents a bonding group that bridges a conjugated five-membered ring ligand with the Z group; Q" represents a bonding group that bridges ^R4 and ^R5 ; M represents Ti, Zr, or Hf; X, Y, and W each independently represent a hydrogen atom, a halogen atom, a hydrocarbon group of 1 to 20 carbon atoms, an oxygen-containing hydrocarbon group of 1 to 20 carbon atoms, a nitrogen-containing hydrocarbon group of 1 to 20 carbon atoms, a phosphorus-containing hydrocarbon group of 1 to 20 carbon atoms, or a silicon-containing hydrocarbon group of 1 to 20 carbon atoms; and Z represents an oxygen atom, a ligand containing a sulfur atom, a silicon-containing hydrocarbon group of 1 to 40 carbon atoms, a nitrogen-containing hydrocarbon group of 1 to 40 carbon atoms, or a phosphorus-containing hydrocarbon group of 1 to 40 carbon atoms.

R ¹ to R ⁵ each independently represent a hydrocarbon group having 1 to 20 carbon atoms, a halogen group, a halogen-containing hydrocarbon group having 1 to 20 carbon atoms, an alkoxy group, an aryloxy group, an oxygen-containing hydrocarbon group, a sulfur-containing hydrocarbon group, a silicon-containing hydrocarbon group, a phosphorus-containing hydrocarbon group, a nitrogen-containing hydrocarbon group, or a boron-containing hydrocarbon group. Adjacent two R ^{1 s} , two R ² s, two R ³ s, two R ⁴ s, or two R ^{5 s} may be bonded to form a ring having 4 to 10 carbon atoms. Furthermore, a, b, c, d, e, f, g, and h are integers that satisfy the following: 0≦a≦5, 0≦b≦5, 0≦c≦4, 0≦d≦4, 0≦e≦4, 0≦f≦5, 0≦g≦5, and 0≦h≦5.

Specific examples of the bonding group Q bridging two conjugated five-membered cyclic ligands, the bonding group Q′ bridging a conjugated five-membered cyclic ligand and a Z group, and Q″ bridging ^R4 and ^R5 are as follows:

That is, alkylene groups such as methylene and ethylene groups; alkylidene groups such as ethylidene, propylidene, isopropylidene, phenylmethylidene, and diphenylmethylidene; silicon-containing crosslinking groups such as dimethylsilylene, diethylsilylene, dipropylsilylene, diphenylsilylene, methylethylsilylene, methylphenylsilylene, methyl-t-butylsilylene, disilylene, and tetramethyldisilylene; germanium-containing crosslinking groups; alkylphosphines; and amines. Of these, alkylene groups, alkylidene groups, silicon-containing crosslinking groups, and germanium-containing crosslinking groups are particularly preferred.

Specific examples of Zr complexes represented by the above general formulas (I), (II), (III), (IV), (V) and (VI) are shown below, but compounds in which Zr is replaced by Hf or Ti can also be used.
The catalyst component (A) represented by the general formulas (I), (II), (III), (IV), (V) and (VI) may be a compound represented by the same general formula or a mixture of two or more compounds represented by different general formulas.

Compounds of general formula (I):
Biscyclopentadienylzirconium dichloride, bis(2-methylindenyl)zirconium dichloride, bis(2-methyl-4,5-benzoindenyl)zirconium dichloride, bisfluorenylzirconium dichloride, bis(4H-azulenyl)zirconium dichloride, bis(2-methyl-4H-azulenyl)cyclopentadienylzirconium dichloride, bis(2-methyl-4-phenyl-4H-azulenyl)zirconium dichloride, bis(2-methyl-4-(4-chlorophenyl)-4H-azulenyl)zirconium dichloride.
Bis(2-furylcyclopentadienyl)zirconium dichloride, bis(2-furylindenyl)zirconium dichloride, bis(2-furyl-4,5-benzoindenyl)zirconium dichloride.

Compounds of general formula (II):
dimethylsilylenebis(1,1'-cyclopentadienyl)zirconium dichloride, dimethylsilylenebis[1,1'-(2-methylindenyl)]zirconium dichloride, dimethylsilylenebis[1,1'-(2-methylindenyl)]zirconium dichloride, ethylenebis[1,1'-(2-methyl-4,5benzoindenyl)]zirconium dichloride, dimethylsilylenebis[1,1'-(2-methyl-4-hydroazulenyl)]zirconium dichloride, Dimethylsilylenebis[1,1'-(2-methyl-4-phenyl-4-hydroazulenyl)]zirconium dichloride, dimethylsilylenebis{1,1'-[2-methyl-4-(4-chlorophenyl)-4-hydroazulenyl]}zirconium dichloride, dimethylsilylenebis[1,1'-(2-ethyl-4-phenyl-4-hydroazulenyl)]zirconium dichloride, ethylenebis[1,1'-(2-methyl-4-hydroazulenyl)]zirconium dichloride.
Dimethylsilylenebis[1,1'-(2-furylcyclopentadienyl)]zirconium dichloride, dimethylsilylenebis{1,1'-[2-(2-furyl)-4,5-dimethyl-cyclopentadienyl]}zirconium dichloride, dimethylsilylenebis{1,1'-{2-[2-(5-trimethylsilyl)furyl]-4,5-dimethyl-cyclopentadienyl}zirconium dichloride, dimethylsilylenebis{1,1'-[2-(2-furyl)indenyl]}zirconium dichloride, dimethylsilylenebis{1,1'-[2-(2-furyl)-4-phenyl-indenyl]}zirconium dichloride, isopropyl isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride, isopropylidene(cyclopentadienyl)[9-(2,7-t-butyl)fluorenyl]zirconium dichloride, diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride, diphenylmethylene(cyclopentadienyl)[9-(2,7-t-butyl)fluorenyl]zirconium dichloride, dimethylsilylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride, diphenylsilylene(cyclopentadienyl)[9-(2,7-t-butyl)fluorenyl]zirconium dichloride.

Compounds of general formula (III):
(tert-butylamido)(tetramethyl-η ⁵ -cyclopentadienyl)-1,2-ethanediylzirconium dichloride, (methylamido)-(tetramethyl-η ⁵ -cyclopentadienyl)-1,2-ethanediyl-zirconium dichloride, (ethylamido)(tetramethyl-η ⁵ -cyclopentadienyl)-methylenediirconium dichloride, (tert-butylamido)dimethyl-(tetramethyl-η ⁵ -cyclopentadienyl)silane zirconium dichloride, (tert-butylamido)dimethyl(tetramethyl- ^{η 5} -cyclopentadienyl)silane zirconium dibenzyl, (benzylamido)dimethyl(tetramethyl- ^{η 5} -cyclopentadienyl)silane zirconium dichloride, (phenylphosphide)dimethyl(tetramethyl-η ⁵ -cyclopentadienyl)silane zirconium dibenzyl.

Compounds of general formula (IV):
(Cyclopentadienyl)(phenoxy)zirconium dichloride, (2,3-dimethylcyclopentadienyl)(phenoxy)zirconium dichloride, (pentamethylcyclopentadienyl)(phenoxy)zirconium dichloride, (cyclopentadienyl)(2,6-di-t-butylphenoxy)zirconium dichloride, (pentamethylcyclopentadienyl)(2,6-di-i-propylphenoxy)zirconium dichloride.

Compounds of general formula (V):
(Cyclopentadienyl)zirconium trichloride, (2,3-dimethylcyclopentadienyl)zirconium trichloride, (pentamethylcyclopentadienyl)zirconium trichloride, (cyclopentadienyl)zirconium triisopropoxide, (pentamethylcyclopentadienyl)zirconium triisopropoxide.

Compounds of general formula (VI):
Ethylene bis(7,7'-indenyl)zirconium dichloride, dimethylsilylene bis{7,7'-(1-methyl-3-phenylindenyl)}zirconium dichloride, dimethylsilylene bis{7,7'-[1-methyl-4-(1-naphthyl)indenyl]}zirconium dichloride, dimethylsilylene bis[7,7'-(1-ethyl-3-phenylindenyl)]zirconium dichloride, dimethylsilylene bis{7,7'-[1-isopropyl-3-(4-chlorophenyl)indenyl]}zirconium dichloride.

In addition, compounds in which the silylene group of these specific examples is replaced with a germylene group are also exemplified as suitable compounds.
Among the catalyst components (A) described above, preferred metallocene complexes for producing a polyethylene resin component are those represented by general formula (I) or general formula (II), and more preferably, the metallocene complex represented by general formula (II) is preferred from the viewpoints of being capable of producing high molecular weight polymers and exhibiting excellent copolymerizability in copolymerization of ethylene with other α-olefins. The ability to produce high molecular weight products has the advantage that polymers of various molecular weights can be designed by various polymer molecular weight adjustment techniques as described below.
Among the metallocene complexes represented by general formula (II), the following two compound groups are preferred in order to satisfy the properties of the polyethylene resin of the present embodiment.

In a preferred embodiment, the first group of compounds is a bridged metallocene complex containing at least one heterocyclic aromatic group as R ¹ to R ² within the compound. Preferred heterocyclic aromatic groups include a group consisting of a furyl group, a benzofuryl group, a thienyl group, and a benzothienyl group. These substituents may further have a substituent such as a silicon-containing group. Among the substituents selected from the group consisting of a furyl group, a benzofuryl group, a thienyl group, and a benzothienyl group, a furyl group and a benzofuryl group are more preferred. Furthermore, it is preferred that these substituents are introduced at the 2-position of a substituted cyclopentadienyl group or a substituted indenyl group, and particularly preferred are compounds having at least one substituted cyclopentadienyl group that does not have any other fused ring structures.

The second group of compounds is bridged metallocene complexes that combine a substituted cyclopentadienyl group with a substituted fluorenyl group.

(2) Catalyst component (B)
The method for producing an ethylene-α-olefin copolymer in the present embodiment is characterized in that, in addition to the catalyst component (A), the olefin polymerization catalyst contains, as essential components, a compound (catalyst component (B), hereinafter sometimes simply referred to as "B") that reacts with the metallocene compound of the catalyst component (A) (hereinafter sometimes referred to as "component (A)" or simply "A") to form a cationic metallocene compound, and, if necessary, a fine particle carrier (catalyst component (C), hereinafter sometimes simply referred to as "C").

One example of the catalyst component (B) that reacts with the catalyst component (A) to form a cationic metallocene compound is an organoaluminum oxy compound.
The organoaluminum oxy-compound has an Al—O—Al bond in the molecule, and the number of bonds is usually in the range of 1 to 100, preferably 1 to 50. Such an organoaluminum oxy-compound is usually a product obtained by reacting an organoaluminum compound with water.
The reaction of organoaluminum with water is usually carried out in an inert hydrocarbon (solvent), which may be an aliphatic hydrocarbon, alicyclic hydrocarbon, or aromatic hydrocarbon such as pentane, hexane, heptane, cyclohexane, methylcyclohexane, benzene, toluene, or xylene, but is preferably an aliphatic hydrocarbon or aromatic hydrocarbon.

The organoaluminum compound used in the preparation of the organoaluminum oxy-compound may be any of the compounds represented by the following general formula (4), but trialkylaluminum is preferably used.
R ⁵ _t AlX ³ _3-t (4)
(In the formula, ^R5 represents a hydrocarbon group having 1 to 18 carbon atoms, preferably 1 to 12 carbon atoms, such as an alkyl group, alkenyl group, aryl group or aralkyl group; ^X3 represents a hydrogen atom or a halogen atom; and t represents an integer satisfying the condition 1≦t≦3.)

The alkyl group of the trialkylaluminum may be any of methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, octyl, decyl, and dodecyl groups, with methyl being particularly preferred.
The organoaluminum compounds may be used in combination of two or more.

The reaction ratio of water to the organoaluminum compound (water/Al molar ratio) is preferably 0.25/1 to 1.2/1, particularly preferably 0.5/1 to 1/1, and the reaction temperature is usually in the range of -70 to 100°C, preferably -20 to 20°C. The reaction time is usually selected in the range of 5 minutes to 24 hours, preferably 10 minutes to 5 hours. The water required for the reaction is not limited to simple water, but may also include water of crystallization contained in copper sulfate hydrate, aluminum sulfate hydrate, etc., or components that can generate water in the reaction system.
Among the above-mentioned organoaluminum oxy compounds, those obtained by reacting alkylaluminum with water are usually called aluminoxanes, and methylaluminoxane (including those essentially consisting of methylaluminoxane (MAO)) is particularly suitable as an organoaluminum oxy compound.
Of course, two or more of the above-mentioned organoaluminum oxy compounds may be used in combination as the organoaluminum oxy compound, or the organoaluminum oxy compound may be used in the form of a solution or dispersion in the above-mentioned inert hydrocarbon solvent.

Other specific examples of the catalyst component (B) include borane compounds and borate compounds.
More specific examples of the borane compound include triphenylborane, tri(o-tolyl)borane, tri(p-tolyl)borane, tri(m-tolyl)borane, tri(o-fluorophenyl)borane, tris(p-fluorophenyl)borane, tris(m-fluorophenyl)borane, tris(2,5-difluorophenyl)borane, tris(3,5-difluorophenyl)borane, tris(4-trifluoromethylphenyl)borane, tris(3,5-ditrifluoromethylphenyl)borane, tris(2,6-ditrifluoromethylphenyl)borane, tris(pentafluorophenyl)borane, tris(perfluoronaphthyl)borane, tris(perfluorobiphenyl), tris(perfluoroanthryl)borane, and tris(perfluorobinaphthyl)borane.

Of these, tris(3,5-ditrifluoromethylphenyl)borane, tris(2,6-ditrifluoromethylphenyl)borane, tris(pentafluorophenyl)borane, tris(perfluoronaphthyl)borane, tris(perfluorobiphenyl)borane, tris(perfluoroanthryl)borane, and tris(perfluorobinaphthyl)borane are more preferred, and even more preferred examples of the compounds are tris(2,6-ditrifluoromethylphenyl)borane, tris(pentafluorophenyl)borane, tris(perfluoronaphthyl)borane, and tris(perfluorobiphenyl)borane.

A first example of the borate compound is a compound represented by the following general formula (5):
[L ¹ −H] ⁺ [BR ⁶ R ⁷ X ⁴ X ⁵ ] ⁻ (5)

In formula (5), L ¹ is a neutral Lewis base, H is a hydrogen atom, and [L ¹ -H] is a Bronsted acid such as ammonium, anilinium, or phosphonium.
Examples of ammonium include trialkyl-substituted ammonium such as trimethylammonium, triethylammonium, tripropylammonium, tributylammonium and tri(n-butyl)ammonium, and dialkylammonium such as di(n-propyl)ammonium and dicyclohexylammonium.

Examples of anilinium include N,N-dialkylanilinium such as N,N-dimethylanilinium, N,N-diethylanilinium, and N,N-2,4,6-pentamethylanilinium.
Further, examples of the phosphonium include triarylphosphoniums and trialkylphosphoniums such as triphenylphosphonium, tributylphosphonium, tri(methylphenyl)phosphonium, and tri(dimethylphenyl)phosphonium.

In addition, in formula (5), R ⁶ and R ⁷ are the same or different aromatic or substituted aromatic hydrocarbon groups containing 6 to 20, preferably 6 to 16, carbon atoms, and may be linked to each other via a bridging group. Preferred substituents for the substituted aromatic hydrocarbon group are alkyl groups typified by methyl, ethyl, propyl, isopropyl, and the like, and halogens such as fluorine, chlorine, bromine, and iodine.
Furthermore, ^X4 and ^X5 are each independently a hydride group, a halide group, a hydrocarbon group containing 1 to 20 carbon atoms, or a substituted hydrocarbon group containing 1 to 20 carbon atoms in which one or more hydrogen atoms have been substituted with halogen atoms.

Specific examples of the compound represented by the above general formula (5) include tributylammonium tetra(pentafluorophenyl)borate, tributylammonium tetra(2,6-ditrifluoromethylphenyl)borate, tributylammonium tetra(3,5-ditrifluoromethylphenyl)borate, tributylammonium tetra(2,6-difluorophenyl)borate, tributylammonium tetra(perfluoronaphthyl)borate, dimethylanilinium tetra(pentafluorophenyl)borate, dimethylanilinium tetra(2,6-ditrifluoromethylphenyl)borate, dimethylanilinium tetra(3,5-ditrifluoromethylphenyl)borate, dimethylanilinium tetra(2,6-difluorophenyl)borate, dimethylanilinium tetra(perfluoronaphthyl)borate, triphenylphosphonium tetra(pentafluorophenyl)borate, and triphenylphosphonium tetra(2,6-ditrifluoromethylphenyl). Examples of such compounds include triphenylphosphonium tetra(3,5-ditrifluoromethylphenyl)borate, triphenylphosphonium tetra(2,6-difluorophenyl)borate, triphenylphosphonium tetra(perfluoronaphthyl)borate, trimethylammonium tetra(2,6-ditrifluoromethylphenyl)borate, triethylammonium tetra(pentafluorophenyl)borate, triethylammonium tetra(2,6-ditrifluoromethylphenyl)borate, triethylammonium tetra(perfluoronaphthyl)borate, tripropylammonium tetra(pentafluorophenyl)borate, tripropylammonium tetra(2,6-ditrifluoromethylphenyl)borate, tripropylammonium tetra(perfluoronaphthyl)borate, di(1-propyl)ammonium tetra(pentafluorophenyl)borate, and dicyclohexylammonium tetraphenylborate.

Of these, tributylammonium tetra(pentafluorophenyl)borate, tributylammonium tetra(2,6-ditrifluoromethylphenyl)borate, tributylammonium tetra(3,5-ditrifluoromethylphenyl)borate, tributylammonium tetra(perfluoronaphthyl)borate, dimethylanilinium tetra(pentafluorophenyl)borate, dimethylanilinium tetra(2,6-ditrifluoromethylphenyl)borate, dimethylanilinium tetra(3,5-ditrifluoromethylphenyl)borate, and dimethylanilinium tetra(perfluoronaphthyl)borate are preferred.

A second example of the borate compound is represented by the following general formula (6).
[L ² ] ⁺ [BR ⁶ R ⁷ X ⁴ X ⁵ ] ^- (6)

In formula (6), examples of ^L2 include a carbocation, a methyl cation, an ethyl cation, a propyl cation, an isopropyl cation, a butyl cation, an isobutyl cation, a tert-butyl cation, a pentyl cation, a tropinium cation, a benzyl cation, a trityl cation, a sodium cation, and a proton. ^R6 , ^R7 , ^X4 , and ^X5 are defined as in formula (5).

Specific examples of the compound represented by the general formula (6) include trityl tetraphenylborate, trityl tetra(o-tolyl)borate, trityl tetra(p-tolyl)borate, trityl tetra(m-tolyl)borate, trityl tetra(o-fluorophenyl)borate, trityl tetra(p-fluorophenyl)borate, trityl tetra(m-fluorophenyl)borate, trityl tetra(3,5-difluorophenyl)borate, trityl tetra(pentafluorophenyl)borate, trityl tetra(2,6-ditrifluoromethylphenyl)borate, trityl tetra(3,5-ditrifluoromethylphenyl)borate, trityl tetra(perfluoronaphthyl)borate, and thiazolinone. tropinium tetraphenylborate, tropinium tetra(o-tolyl)borate, tropinium tetra(p-tolyl)borate, tropinium tetra(m-tolyl)borate, tropinium tetra(o-fluorophenyl)borate, tropinium tetra(p-fluorophenyl)borate, tropinium tetra(m-fluorophenyl)borate, tropinium tetra(3,5-difluorophenyl)borate, tropinium tetra(pentafluorophenyl)borate, tropinium tetra(2,6-ditrifluoromethylphenyl)borate, tropinium tetra(3,5-ditrifluoromethylphenyl)borate, tropinium tetra(perfluoronaphthyl)borate, NaBPh ₄ , NaB(o-CH ₃ -Ph) ₄ , NaB(p-CH ₃ -Ph) ₄ , NaB(m-CH ₃ -Ph) ₄ , NaB(o-F-Ph) ₄ , NaB(p-F-Ph) ₄ , NaB(m-F-Ph) ₄ , NaB(3,5-F ₂ -Ph) ₄ , NaB(C ₆ F ₅ ) ₄ , NaB(2,6-(CF ₃ ) ₂ -Ph) ₄ , NaB(3,5-(CF ₃ ) ₂ -Ph) ₄ , NaB(C ₁₀ F ₇ ) ₄ , H ^{+ B} ( _3,5 -F ₂ -Ph) ₄ ·2 diethyl ether, H ⁺ Examples include B(C ₆ F ₅ ) ₄ ^-.2 diethyl ether, H ⁺ B(2,6-(CF ₃ ) ₂ -Ph) _4.2 diethyl ether, H ⁺ B(3,5-(CF ₃ ) ₂ -Ph) _4.2 diethyl ether, and H ⁺ B(C ₁₀ H ₇ ) _4.2 diethyl ether. Note that "Ph" above represents a phenyl group.

Among these, trityl tetra(pentafluorophenyl)borate, trityl tetra(2,6-ditrifluoromethylphenyl)borate, trityl tetra(3,5-ditrifluoromethylphenyl)borate, trityl tetra(perfluoronaphthyl)borate, tropinium tetra(pentafluorophenyl)borate, tropinium tetra(2,6-ditrifluoromethylphenyl)borate, tropinium tetra(3,5-ditrifluoromethylphenyl)borate, tropinium tetra(perfluoronaphthyl)borate, NaB(C ₆ F ₅ ) ₄ , NaB(2,6-(CF ₃ ) ₂ -Ph) ₄ , NaB(3,5-(CF ₃ ) ₂ -Ph) ₄ , NaB(C ₁₀ F ₇ ) ₄ , H ⁺ B(C ₆ F ₅ ) ₄ ^-.2 diethyl ether, H ⁺ B(2,6-(CF Preferred are H ⁺ B(3,5-(CF 3 ) ₂ -Ph) ₄ · ₂ diethyl ether, H + B(3,5-(CF ₃ ) ₂ -Ph) ₄ ·2 diethyl ether, and H ⁺ B(C ₁₀ H ₇ ) ₄ ·2 diethyl ether.

Among these, trityl tetra(pentafluorophenyl)borate, trityl tetra(2,6-ditrifluoromethylphenyl)borate, tropinium tetra(pentafluorophenyl)borate, tropinium tetra(2,6-ditrifluoromethylphenyl)borate, NaB(C ₆ F ₅ ) ₄ , NaB(2,6-(CF ₃ ) ₂ -Ph) ₄ , H ⁺ B(C 6 F 5 ) ₄ ^-.2 diethyl ether, H ⁺ B(2,6-(CF ₃ ) _{2 -Ph} ) _4.2 diethyl ether, H ⁺ B( _3,5- (CF ₃ ) ₂ -Ph) _4.2 diethyl ether, and H ⁺ B(C ₁₀ H ₇ ) _4.2 diethyl ether are more preferred.

(3) Catalyst component (C)
The particulate support of catalyst component (C) may be an inorganic support, a particulate polymer support, or a mixture thereof. The inorganic support may be a metal, a metal oxide, a metal chloride, a metal carbonate, a carbonaceous material, or a mixture thereof.
Suitable metals that can be used for the inorganic support include, for example, iron, aluminum, nickel, and the like.

Examples of metal oxides include single oxides or composite oxides of elements in Groups 1 to 14 of the periodic table, such as SiO ₂ , Al ₂ O ₃ , MgO, CaO, B ₂ O ₃ , TiO ₂ , ZrO ₂ , Fe ₂ O ₃ , Al ₂ O _3.MgO , Al _{2 O 3.CaO} , Al ₂ O _{3.SiO 2} , Al ₂ O 3.MgO.CaO, _{Al 2 O 3.MgO.SiO} 2 , Al _{2 O 3.CuO} , Al ₂ O 3.Fe ₂ O ₃ , Al _{2 O} 3.NiO, and SiO 2.MgO.
Here, the above formula is not a molecular formula but represents only the composition, and the structure and component ratio of the composite oxide used in this embodiment are not particularly limited.
Furthermore, the metal oxide used in this embodiment may absorb a small amount of moisture and may contain a small amount of impurities.

As the metal chloride, for example, chlorides of alkali metals and alkaline earth metals are preferred, and specifically, MgCl ₂ , CaCl ₂ and the like are particularly preferred.
As the metal carbonate, carbonates of alkali metals and alkaline earth metals are preferred, and specific examples include magnesium carbonate, calcium carbonate, and barium carbonate.
Examples of carbonaceous materials include carbon black and activated carbon.
Any of the above inorganic carriers can be suitably used in the present disclosure, but metal oxides, silica, alumina, etc. are particularly preferred.

These inorganic supports are preferably used after being calcined in air or in an inert gas such as nitrogen or argon at 200 to 800°C, preferably 400 to 600°C, to adjust the amount of surface hydroxyl groups to 0.8 to 1.5 mmol/g.
The properties of these inorganic carriers are not particularly limited, but it is generally preferred to use inorganic carriers having an average particle size of 5 to 200 μm, preferably 10 to 150 μm, an average pore size of 20 to 1000 Å, preferably 50 to 500 Å, a specific surface area of 150 to 1000 ^{m 2} /g, preferably 200 to 700 m ² /g, a pore volume of 0.3 to 2.5 cm ³ /g, preferably 0.5 to 2.0 cm ³ /g, and an apparent specific gravity of 0.10 to 0.50 g/cm ³ .

The inorganic supports mentioned above can, of course, be used as they are, but they can also be used after being pre-treated by contacting them with an organoaluminum compound such as trimethylaluminum, triethylaluminum, triisobutylaluminum, trihexylaluminum, tripropylaluminum, tributylaluminum, trioctylaluminum, tridecylaluminum, or diisobutylaluminum hydride, or an organoaluminum oxy compound containing an Al-O-Al bond.

The metallocene catalyst according to this embodiment may be prepared by contacting the components (A), (B), and, if necessary, (C) to obtain a catalyst. The method for contacting the components is not particularly limited, and any of the following methods can be used, for example.

(I) The catalyst component (A) is contacted with the catalyst component (B), and then the catalyst component (C) is contacted therewith.
(II) The catalyst component (A) is contacted with the catalyst component (C), and then the catalyst component (B) is contacted therewith.
(III) The catalyst component (B) is contacted with the catalyst component (C), and then the catalyst component (A) is contacted therewith.

Of these contacting methods, (I) and (III) are preferred, with (I) being most preferred. In any of these contacting methods, a method is employed in which the components are contacted with or without stirring in an inert atmosphere such as nitrogen or argon, generally in the presence of a liquid inert hydrocarbon, such as an aromatic hydrocarbon (usually having 6 to 12 carbon atoms) such as benzene, toluene, xylene, or ethylbenzene, or an aliphatic or alicyclic hydrocarbon (usually having 5 to 12 carbon atoms) such as heptane, hexane, decane, dodecane, or cyclohexane.
This contact is desirably carried out at a temperature of usually -100°C to 200°C, preferably -50°C to 100°C, and more preferably 0°C to 50°C, for 5 minutes to 50 hours, preferably 30 minutes to 24 hours, and more preferably 30 minutes to 12 hours.

Furthermore, as mentioned above, when contacting catalyst component (A), catalyst component (B), and catalyst component (C), it is possible to use either an aromatic hydrocarbon solvent in which certain components are soluble or slightly soluble, or an aliphatic or alicyclic hydrocarbon solvent in which certain components are insoluble or slightly soluble.

When the contact reactions of each component are carried out in stages, the solvent used in the previous stage may be used as the solvent for the subsequent contact reaction without removing it. Alternatively, after the previous contact reaction using a soluble solvent, a liquid inert hydrocarbon in which certain components are insoluble or poorly soluble (e.g., an aliphatic, alicyclic, or aromatic hydrocarbon such as pentane, hexane, decane, dodecane, cyclohexane, benzene, toluene, or xylene) may be added to recover the desired product as a solid. Alternatively, after partially or completely removing the soluble solvent by drying or other means to recover the desired product as a solid, the subsequent contact reaction of this desired product may be carried out using one of the inert hydrocarbon solvents listed above. This embodiment does not preclude the contact reactions of each component being carried out multiple times.

In this embodiment, the proportions of catalyst component (A), catalyst component (B), and catalyst component (C) used are not particularly limited, but the following ranges are preferred.

When an organoaluminum oxy compound is used as catalyst component (B), the atomic ratio (Al/M) of aluminum in the organoaluminum oxy compound to the transition metal (M) in catalyst component (A) is generally 1 to 100,000, preferably 5 to 1,000, and more preferably 50 to 200. When a borane compound or a borate compound is used, the atomic ratio (B/M) of boron to the transition metal (M) in the metallocene compound is generally 0.01 to 100, preferably 0.1 to 50, and more preferably 0.2 to 10.
Furthermore, when a mixture of an organoaluminum oxy-compound, a borane compound, and a borate compound is used as the catalyst component (B), it is desirable to select the use ratio of each compound in the mixture relative to the transition metal (M) in the same manner as above.

The amount of catalyst component (C) used is 1 g per 0.0001 to 5 mmol of transition metal in catalyst component (A), preferably per 0.001 to 0.5 mmol, and more preferably per 0.01 to 0.1 mmol.

The olefin polymerization catalyst can be obtained as a solid catalyst by contacting catalyst components (A), (B), and (C) with one another using any of the contact methods (I) to (III) described above, and then removing the solvent. The solvent is desirably removed under atmospheric pressure or reduced pressure, at 0 to 200°C, preferably 20 to 150°C, for 1 minute to 50 hours, preferably 10 minutes to 10 hours.

The metallocene catalyst can also be obtained by the following method.
(IV) The catalyst component (A) is contacted with the catalyst component (C) to remove the solvent, thereby obtaining a solid catalyst component, which is then contacted with an organoaluminum oxy compound, a borane compound, a borate compound, or a mixture thereof under polymerization conditions.
(V) An organoaluminum oxy compound, a borane compound, a borate compound or a mixture thereof is contacted with catalyst component (C) to remove the solvent, thereby forming a solid catalyst component, which is then contacted with catalyst component (A) under polymerization conditions.
In the contacting methods (IV) and (V) above, the component ratios, contact conditions and solvent removal conditions can be the same as those described above.

Furthermore, a layered silicate can also be used as a component that serves as both the catalyst component (B) and the catalyst component (C), which are essential components in the process for producing ethylene-α-olefin copolymerization according to this embodiment.
Layered silicates are silicate compounds that have a crystalline structure in which planes formed by ionic bonds or the like are stacked in parallel with each other with weak bonding forces.
Most layered silicates occur naturally as the main component of clay minerals, but these layered silicates are not limited to those that are naturally occurring, and may also be artificially synthesized products.

Of these, smectites, vermiculites, and micas, such as montmorillonite, sauconite, beidellite, nontronite, saponite, hectorite, stevensite, bentonite, and taeniolite, are preferred.

Generally, natural products are often non-ion-exchangeable (non-swellable), and in such cases, it is preferable to subject them to treatment to impart ion-exchangeable (or swellable) properties to give them desirable ion-exchangeable (or swellable) properties. Among such treatments, the following chemical treatments are particularly preferred.
Here, the chemical treatment can be either a surface treatment for removing impurities adhering to the surface or a treatment that affects the crystal structure and chemical composition of the layered silicate.
Specific examples include (i) acid treatment using hydrochloric acid, sulfuric acid, or the like, (ii) alkali treatment using NaOH, KOH, _NH3 , or the like, (iii) salt treatment using a salt comprising a cation containing at least one atom selected from Groups 2 to 14 of the periodic table and at least one anion selected from the group consisting of a halogen atom or an anion derived from an inorganic acid, and (iv) organic substance treatment using alcohol, hydrocarbon compound, formamide, aniline, or the like. These treatments may be performed alone or in combination of two or more.

The particle properties of the layered silicate can be controlled by grinding, granulation, sizing, fractionation, etc. at any time before, during, or after any of the steps. Any appropriate method can be used. Granulation methods in particular include spray granulation, tumbling granulation, compression granulation, agitation granulation, briquetting, compaction, extrusion granulation, fluidized bed granulation, emulsion granulation, and submerged granulation. Of the above, spray granulation, tumbling granulation, and compression granulation are particularly preferred.

The layered silicates described above can, of course, be used as they are, but they can also be used in combination with organoaluminum compounds such as trimethylaluminum, triethylaluminum, triisobutylaluminum, tripropylaluminum, tributylaluminum, trihexylaluminum, trioctylaluminum, tridecylaluminum, and diisobutylaluminum hydride, or organoaluminum oxy compounds containing an Al-O-Al bond.

In the metallocene catalyst according to the present embodiment, the catalyst component (A) can be supported on the layered silicate by bringing the catalyst component (A) and the layered silicate into contact with each other, or by bringing the catalyst component (A), the organoaluminum compound, and the layered silicate into contact with each other.
The method for contacting the components is not particularly limited, and for example, the following methods can be optionally employed.

(VI) The catalyst component (A) is contacted with an organoaluminum compound and then contacted with a layered silicate support.
(VII) After the catalyst component (A) is contacted with the layered silicate support, it is contacted with an organoaluminum compound.
(VIII) The organoaluminum compound is contacted with the layered silicate support, and then contacted with catalyst component (A).

Of these contact methods, (VI) and (VIII) are preferred. In either contact method, the components are typically contacted in an inert atmosphere such as nitrogen or argon, with or without stirring, in the presence of a liquid inert hydrocarbon, typically an aromatic hydrocarbon (typically having 6 to 12 carbon atoms) such as benzene, toluene, xylene, or ethylbenzene, or an aliphatic or alicyclic hydrocarbon (typically having 5 to 12 carbon atoms) such as heptane, hexane, decane, dodecane, or cyclohexane.

The proportions of the catalyst component (A), the organoaluminum compound, and the layered silicate support are not particularly limited, but the following ranges are preferred.
The amount of catalyst component (A) supported is 0.0001 to 5 mmol, preferably 0.001 to 0.5 mmol, and more preferably 0.01 to 0.1 mmol per gram of the layered silicate support.
When an organoaluminum compound is used, the amount of Al supported is desirably in the range of 0.01 to 100 mol, preferably 0.1 to 50 mol, and more preferably 0.2 to 10 mol.

The conditions for supporting and removing the solvent can be the same as those for the inorganic carrier described above.
When a layered silicate is used as a component that serves as both the catalyst component (B) and the catalyst component (C), the polymerization activity is high and the productivity of the ethylene polymer is improved.
The olefin polymerization catalyst thus obtained may be used after prepolymerization of monomers, if necessary.

Metallocene catalysts can be produced by taking into consideration the "catalyst" and "raw material blending ratios and conditions" described in, for example, Japanese Patent Publication No. 2002-535339 and Japanese Patent Application Laid-Open No. 2004-189869, which are publicly known publications. The polymer index can also be controlled by various polymerization conditions, for example, by the methods described in Japanese Patent Application Laid-Open Nos. 2-269705 and 3-21607.

Neutralizing agents include, for example, fatty acid metal salts such as calcium stearate, zinc stearate, and magnesium stearate, as well as hydrotalcites.

However, if polyethylene resin is polymerized using magnesium stearate or hydrotalcite as a neutralizing agent, when the resulting resin is molded into piping material, a large amount of aluminum and magnesium will leach into water, which is not preferred for this embodiment.

In contrast, when polyethylene resin is polymerized using calcium stearate as a neutralizing agent, the metal leaching of aluminum and magnesium described above does not occur, and favorable low leaching properties are achieved, making calcium stearate the preferred neutralizing agent in this embodiment.

High-density polyethylene (HDPE) is preferred as a polyethylene-based resin composition, as it provides sufficient pressure resistance against water pressure during water transport and allows for thin piping. Among HDPEs, HDPE classified as PE100 or higher in the pressure-resistant class according to ISO 9080, ISO 1167, and ISO 12162 is more preferred, as it ensures the long-term durability of piping materials for ultrapure water. Even among HDPEs classified as PE100 or higher, HDPE with high resistance to slow crack growth (slow crack growth resistance) is preferred to further enhance the safety of the pipe system, as well as high fluidity to improve the smoothness of the inner surface of the piping. Note that slow crack growth refers to a type of damage caused by stress concentration, such as scratches in the piping material or the joints between the pipe and fittings.

Specifically, as indexes for a polyethylene resin composition that satisfies the pressure resistance class of PE100 or higher and has good fluidity, the polyethylene resin composition preferably has a melt flow rate (MFR _21.6 ) of 6 g/10 min or more and 25 g/10 min or less at a temperature of 190°C and a load of 21.6 kg, and a density of 0.946 g/cm ³ or more and 0.960 g/cm ³ or less.

If the MFR _21.6 of the polyethylene resin composition is less than 6 g/10 min, the fluidity of the resin material is low, the mold transferability is poor, and the smoothness of the inner surface of the pipe is insufficient. On the other hand, if the MFR _21.6 exceeds 25 g/10 min, it becomes difficult to design a resin that satisfies PE100. Regarding density, if it is less than 0.946 g/ ^cm3 , the pressure resistance performance decreases, making it difficult to reach PE100. On the other hand, if the density exceeds 0.960 g/ ^cm3 , the slow cracking resistance of the pipe material decreases, thereby reducing the safety of the pipe system over long-term use.

Furthermore, if the Mz/Mw ratio of a polyethylene resin composition is less than 2.5, the shrinkage rate of the material itself will be small, but the difference in relaxation time between the various components in the resin composition will be too small, resulting in poor flow when melted, leaving residual strain in the molded article and a large anisotropic shrinkage rate. On the other hand, if the Mz/Mw ratio is greater than 5.5, the resin composition will be more susceptible to molecular orientation, leaving residual strain in the molded article and a large anisotropic shrinkage rate. In addition, since molecular orientation tends to occur more frequently during molding as the number of components with higher molecular weights increases, the anisotropic shrinkage rate will become even larger if components with a molecular weight exceeding 3,000,000 account for more than 2% of the total.

The calcium concentration of the polyethylene resin layer 21 is 100 ppm or less, preferably 60 ppm or less, and more preferably 50 ppm or less. If the calcium concentration exceeds 100 ppm, excessive calcium will leach into the ultrapure water, making it impossible to meet the required quality of ultrapure water.

To further reduce the amount of calcium eluted into ultrapure water, it is preferable that the calcium concentration of the polyethylene resin layer 21 be as low as possible.

The long-term durability required of polyethylene resins is resistance to slow crack growth, and one method for measuring this is the FNCT. The FNCT is a test method that measures slow crack growth below the material's yield stress. Materials with low long-term durability will fail due to slow crack growth in a much shorter time than creep failure, so it can be used as an indicator of long-term durability. Assuming a typical service life of 40 years for a pipe made from polyethylene resin at 20°C, the performance required of the FNCT is preferably such that it will not fail for more than 100 hours when subjected to a stress of 5.0 MPa in an environment of an aqueous surfactant solution at 80°C.

The material properties of the polyethylene resin composition preferably have a pressure resistance of "PE100" or higher as specified in the ISO 9080, ISO 1167, and ISO 12162 standards. "PE100" refers to polyethylene in which the LPL value, calculated by extrapolating the minimum guaranteed stress after 50 years at 20°C using a multiple correlation average, is 10 MPa or more and 11.19 MPa or less in the classification table specified in ISO 12162, after measuring the stress-rupture time curve for at least 9,000 hours at three different temperatures, with the maximum and minimum temperatures separated by at least 50°C.

The polyethylene resin layer 21 may or may not contain an antioxidant. Examples of antioxidants include phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, aromatic amine-based antioxidants, and lactone-based antioxidants.

Phenol-based antioxidants include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N'-hexane-1,6-diylbis[3-(3,5- di-tert-butyl-4-hydroxyphenyl)propionamide], benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy, C7-C9 side chain alkyl ester, 3,3',3'',5,5',5''-hexa-tert-butyl-a,a',a''-(mesitylene-2,4,6-triyl)tri-p-cresol, 4,6-bis(dodecylthiomethyl)-o-cresol, 4,6-bis(octyl methylthiomethyl)-o-cresol, ethylene bis(oxyethylene) bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1 , 3,5-tris[(4-tert-butyl-3-hydroxy-2,6-xylyl)methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,6-di-tert-butyl-4-[4,6-bis(octylthio)-1,3,5-triazin-2-ylamino]phenol, and diethyl[{3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl}methyl]phosphonate, etc.

When using a phenolic antioxidant, a single type may be used, or two or more types may be used in combination. However, in order to prevent calcium elution, it is preferable that the antioxidant does not contain oxygen derived from groups other than the phenol group. Examples include 3,3',3",5,5',5"-hexa-tert-butyl-a,a',a"-(mesitylene-2,4,6-triyl)tri-p-cresol, 2,6-di-tert-butyl-4-[4,6-bis(octylthio)-1,3,5-triazin-2-ylamino]phenol, 4,4',4"-(1-methylpropanyl-3-ylidene)tris(6-tert-butyl-m-cresol), and 6,6'-di-tert-butyl-4,4'-butylidenebis-m-cresol. Furthermore, when a phenolic antioxidant containing oxygen derived from a group other than the phenol group is used as the antioxidant, the calcium concentration in the polyethylene resin is preferably 50 ppm or less. Examples of functional groups containing oxygen derived from a group other than the phenol group include ester groups, carbonyl groups, carboxy groups, ether groups, nitro groups, nitroso groups, amide groups, azoxy groups, and sulfo groups.

Phosphorus-based antioxidants include tris(2,4-di-tert-butylphenyl)phosphite, tris[2-[[2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosphen-6-yl]oxy]ethyl]amine, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, bis[2,4-bis(1,1-dimethylethyl)-6-methylphenyl]ethyl ester phosphorous acid, and tetrakis(2,4-di-tert-butylphenyl)(1,1-biphenyl)-4,4'-diylbisphosphonite.

Sulfur-based antioxidants include dilauryl thiodipropionate, dimyristyl thiodipropionate, distearyl thiodipropionate, and pentaerythrityl tetrakis(3-laurylthiopropionate).

Examples of aromatic amine antioxidants include monoamine compounds such as diphenylamine compounds, quinoline compounds, and naphthylamine compounds, and diamine compounds such as phenylenediamine compounds and benzimidazole compounds.
Examples of diphenylamine compounds include p-(p-toluenesulfonylamide)-diphenylamine, 4,4'-(α,α-dimethylbenzyl)diphenylamine, and 4,4'-dioctyldiphenylamine derivatives.

Examples of the quinoline compounds include 2,2,4-trimethyl-1,2-dihydroquinoline polymers.
Examples of naphthylamine compounds include phenyl-α-naphthylamine and N,N'-di-2-naphthyl-p-phenylenediamine.

Examples of phenylenediamine compounds include N-N'-diphenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N-phenyl-N'-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine, a mixture of N-N'-diphenyl-p-phenylenediamines, diaryl-p-phenylenediamine derivatives, or mixtures thereof.

Examples of benzimidazole compounds include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, zinc salt of 2-mercaptobenzimidazole, and zinc salt of 2-mercaptomethylbenzimidazole.

Examples of lactone antioxidants include the reaction product of 3-hydroxy-5,7-di-tert-butyl-furan-2-one and o-xylene.

From the viewpoint of suppressing the effects of oxygen and ensuring desirable strength, the content of the antioxidant in the polyethylene resin layer 21 is, for example, 0.01% by weight or more, preferably 0.03% by weight or more, and more preferably 0.05% by weight or more. The upper limit of the antioxidant content is, for example, 5% by weight or less, preferably 1% by weight or less, and more preferably 0.5% by weight or less.

The polyethylene resin layer 21 may or may not contain a light stabilizer, but it is preferable that it contains substantially no light stabilizers in order to prevent the leaching of total organic carbon (TOC). Examples of light stabilizers include hindered amine light stabilizers (HALS). Here, "substantially free" means that light stabilizers are not actively added, but that unavoidable contamination as impurities is tolerated. The lower the concentration of light stabilizers that are inevitably mixed in as impurities, the better, for example, 600 ppm or less.

Hindered amine light stabilizers include N-H hindered amine compounds, N-R hindered amine compounds, and N-OR hindered amine compounds.

Examples of N-H hindered amine compounds include Tinuvin 770DF, Chimassorb 2020FDL, and Chimassorb 944FDL (all trade names, manufactured by BASF), Adekastab LA-68 and Adekastab LA-57 (all trade names, manufactured by Adeka Corporation), Cyasorb UV-3346, and Cyasorb UV-3853 (all trade names, manufactured by Sun Chemical Co.), etc.

Examples of N-R hindered amine compounds include Tinuvin 622SF, Tinuvin 765, Tinuvin PA144, Chimassorb 119, Tinuvin 111 (all trade names, manufactured by BASF), Savostab UV119 (trade name, manufactured by Sabo Corporation), Adekastab LA-63P, and Adekastab LA-52 (all trade names, manufactured by Adeka Corporation).

Examples of N-OR hindered amine compounds include Tinuvin 123, Tinuvin 5100, Tinuvin NOR371FF, and Flame Stab NOR116FF (all trade names, manufactured by BASF Corporation).

The polyethylene resin layer 21 may or may not contain an ultraviolet absorber (UVA). Examples of ultraviolet absorbers include benzophenone-based ultraviolet absorbers, salumarate-based ultraviolet absorbers, benzocoat-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, and quenchers. For polyethylene or polypropylene, benzophenone-based ultraviolet absorbers and benzotriazole-based ultraviolet absorbers are particularly preferred.

Benzophenone-based ultraviolet absorbers include 2-hydroxy-4-methoxy-benzophenone.
Examples of the benzotriazole-based ultraviolet absorber include 2-(2-hydroxy-5-methylphenyl)benzotriazole (Sumisorb 200, manufactured by Sumika Chemtex Co., Ltd.), 2-(2-hydroxy-5-t-butyl-5-methylphenyl)-5-chlorobenzotriazole (Tinuvin 326, manufactured by BASF), 2-(2-hydroxy-3,5-di-t-butylphenyl)-5-chlorobenzotriazole (Tinuvin 327, manufactured by BASF), and 2-(2-hydroxy-3,5-di-t-amylphenyl)benzotriazole (Tinuvin 328, manufactured by BASF).

The density of the polyethylene resin composition of the polyethylene resin layer 21 is preferably 0.946 g/cm or more, more preferably 0.947 g/cm ^{or more} , and even more preferably 0.948 g/cm ^{or more} , from the viewpoint of obtaining good rigidity of the polyethylene resin composition. Furthermore, the density is preferably 0.960 g/cm ^{or less} , more preferably 0.957 g/cm ^or less, and even more preferably 0.953 g/cm ^{or less} , from the viewpoint of obtaining good long-term durability and ^flexibility of the polyethylene resin composition. The density is a value measured in accordance with JIS K6922-2:1997.

The polyethylene resin composition of the polyethylene resin layer 21 has a melt flow rate (MFR _21.6 ) of 6 g/10 min or more and 25 g/10 min or less at a temperature of 190°C and a load of 21.6 kg. From the viewpoint of obtaining good processability of the polyethylene resin composition, the MFR _21.6 is preferably 8 g/10 min or more, more preferably 12 g/10 min or more, and even more preferably 15 g/min or more. Furthermore, from the viewpoint of obtaining good long-term durability of the resin, the MFR _21.6 is preferably 22 g/10 min or less, more preferably 20 g/10 min or less. The MFR _21.6 is a value measured in accordance with JIS K6922-2:1997.

In the molecular weight distribution of the polyethylene resin composition of the polyethylene resin layer 21 measured by GPC, the Mz/Mw, which is an index showing the breadth of the molecular weight distribution, is 2.5 or more and 5.5 or less. From the viewpoint of fluidity, it is preferably 2.7 or more, more preferably 3.0 or more. Furthermore, from the viewpoint of molecular orientation, it is preferably 5.3 or less, more preferably 5.0 or less.

In the molecular weight distribution of the polyethylene resin composition of the polyethylene resin layer 21 measured by GPC, components with a molecular weight of 300,000 or more account for 2% or less of the total. From the viewpoint of molecular orientation, this is preferably 1.5% or less of the total, and more preferably 1.0% or less.

When a coating resin layer 22 is provided on the outside of the innermost polyethylene resin layer 21 that forms the inner surface 11a, 31a-35a, 42a (an example of the inner surface of the piping material) of the ultrapure water piping material, the thickness of the innermost polyethylene resin layer 21 is preferably 0.3 mm or more, and more preferably 0.4 mm or more, taking into consideration the strength of the entire ultrapure water piping material and the calcium concentration contained in the coating resin layer 22. The upper limit of the thickness is preferably 2.0 mm or less, and more preferably 1.5 mm or less.

When no coating resin layer 22 is provided on the outside of the polyethylene resin layer 21 that forms the inner surface 10a, 31a-35a, 42a (an example of the inner surface of the piping material) of the ultrapure water piping material, the thickness of the polyethylene resin layer 21 is not particularly limited, and the lower limit of the thickness is, for example, 0.3 mm or more.

[Coating resin layer]
The type of the coating resin layer 22 is not particularly limited, and may be a polyethylene resin layer made of a polyethylene resin, a gas barrier resin layer made of a gas barrier resin, or a combination thereof.

When a polyethylene-based resin layer is provided as the coating resin layer 22, the polyethylene-based resin can be appropriately selected from the polyethylene-based resin compositions that are the main components of the innermost polyethylene-based resin layer 21 described above.

Of the polyethylene resins mentioned above, HDPE is preferred from the viewpoint of suppressing the elution of low molecular weight components and/or durability when pipes are cleaned with chemicals.

The polyethylene resin that is the main component of the polyethylene resin layer of the coating resin layer 22 may be the same as or different from the polyethylene resin composition that is the main component of the innermost polyethylene resin layer 21. However, when the two layers are laminated in contact with each other, it is more preferable that the two layers be made of the same type of polyethylene resin, from the viewpoint of improving the adhesion between the two layers and achieving the desired strength.

The polyethylene resin layer in the coating resin layer 22 preferably contains an antioxidant. Examples of antioxidants include phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, aromatic amine-based antioxidants, and lactone-based antioxidants. To suppress the effects of oxygen and ensure desirable strength, the content of the antioxidant in the polyethylene resin layer in the coating resin layer 22 is, for example, 0.01% by weight or more, preferably 0.1% by weight or more. The upper limit of the antioxidant content is, for example, 5% by weight or less, preferably 1% by weight or less, and more preferably 0.5% by weight or less.

When a gas barrier layer is provided as the coating resin layer 22, the gas barrier layer need only be laminated on the outside of the innermost polyethylene resin layer 21. The gas barrier layer may constitute the outermost layer of the ultrapure water piping material (e.g., pipe 11), or another layer may be provided further outside the gas barrier layer.

The provision of a gas barrier layer is preferable because it can effectively prevent gas dissolution into ultrapure water. The gas barrier layer also prevents oxygen from penetrating from the outer surface 11b of the piping material for ultrapure water (e.g., pipe 11) into the innermost polyethylene-based resin layer 21 or an outer polyethylene-based resin layer provided as needed, thereby improving the long-term strength of the piping material for ultrapure water (e.g., pipe 11).
This prevents oxygen from penetrating from the outer surface 11b of the piping material for ultrapure water (e.g., pipe 11) into the innermost polyethylene-based resin layer 21 or an outer polyethylene-based resin layer provided as needed, thereby improving the strength of the piping material for ultrapure water (e.g., pipe 11). The provision of a gas barrier layer is also preferable in that it can effectively prevent gas dissolution into ultrapure water.

Examples of materials for the gas barrier layer include polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride resin (PVDC), and polyacrylonitrile (PAN), with polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH) being preferred.

The thickness of the gas barrier layer is not particularly limited as long as it is thick enough to ensure the gas barrier properties of the polyethylene resin, but examples include 30 to 300 μm, preferably 50 to 250 μm, and more preferably 70 to 250 μm.

[Ultra-pure water piping applications]
The piping material for ultrapure water according to the embodiment of the present invention is used for transporting ultrapure water. Specifically, the piping material for ultrapure water according to the embodiment of the present invention can be used as piping within an ultrapure water production apparatus, piping for transporting ultrapure water from an ultrapure water production apparatus to a use point, piping for returning ultrapure water from a use point, etc.

The ultrapure water piping material of the embodiment of the present invention is preferably used as water piping for nuclear power generation, where the required quality of ultrapure water is particularly strict, or as ultrapure water transport piping used in pharmaceutical manufacturing processes, or in wet processing processes such as cleaning in the manufacturing process of semiconductor devices or liquid crystals, more preferably semiconductor devices. The semiconductor devices in question are preferably those with a higher degree of integration, and more specifically, are more preferably used in the manufacturing process of semiconductor devices with a minimum line width of 65 nm or less. Examples of standards related to the quality of ultrapure water used in semiconductor manufacturing include SEMI F75.

Furthermore, because the ultrapure water piping material according to the embodiment of the present invention has a polyethylene resin layer, it is easy to work with. For example, fusion work such as butt fusion welding and EF (electrofusion) welding can be easily performed at relatively low temperatures.

[Manufacturing piping materials for ultrapure water]
The piping material for ultrapure water according to the embodiment of the present invention can be manufactured by preparing a polyethylene resin, which is the main component of the polyethylene resin layer 21 that forms the inner surfaces 10a, 11a, 31a to 35a, and 42a of the piping material, and, if necessary, a coating resin that forms the outer coating resin layer 22, and co-extrusion molding the layers so that each layer has a predetermined thickness. Because the piping material for ultrapure water according to the embodiment of the present invention is made of a polyethylene resin, it can be manufactured inexpensively.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
[Examples 1 to 5] [Comparative Examples 1 to 3]
The following materials were prepared and evaluated as follows:
(antioxidant)
Irganox 1010 (manufactured by BASF Japan)
Irganox 1330 (manufactured by BASF Japan)
Figure 5 shows the structural formula of Irganox 1010. Figure 6 shows the structural formula of Irganox 1330.

Example 1
(1) Continuous polymerization of polyethylene resin using Ziegler catalyst (preparation of solid catalyst component)
A 1 L pot (milling vessel) containing approximately 700 10 mm diameter magnetic balls was charged with 20 g of commercially available magnesium ethylate (average particle size 860 μm), 1.66 g of granular aluminum trichloride, and 2.72 g of diphenyldiethoxysilane in a nitrogen atmosphere. These were co-milled using a vibrating ball mill at an amplitude of 6 mm and a frequency of 30 Hz for 3 hours. After co-milling, the contents were separated from the magnetic balls in a nitrogen atmosphere.

5 g of the co-ground product obtained in this manner and 20 ml of n-heptane were added to a 200 ml three-necked flask. 10.4 ml of titanium tetrachloride was added dropwise at room temperature while stirring, and the mixture was heated to 90°C and stirred for 90 minutes. The reaction system was then cooled, the supernatant liquid was removed, and n-hexane was added. This procedure was repeated three times. The resulting pale yellow solid was dried at 50°C under reduced pressure for 6 hours to obtain a solid catalyst component.

(Production of polyethylene resin composition)
Dehydrated and purified isobutane was continuously fed into a 100 L first polymerization liquid-packed loop reactor at a rate of 63 L/hr, triisobutylaluminum at a rate of 20 g/hr, the solid catalyst at a rate of 3.6 g/hr, and ethylene at a rate of 7 kg/hr. Hydrogen (to control MFR) and 1-hexene as a comonomer (to control density) were also added to achieve the target MFR of _21.6 and comonomer content. Copolymerization of ethylene and 1-hexene was carried out under conditions of 85°C, polymerization pressure of 4.3 MPa, and average residence time of 0.9 hr. A portion of the polymerization reaction product was sampled and its physical properties were measured, revealing an MFR of _21.6 , a density of 0.924 g/cm3, and a polymerization pressure of 4.3 ^MPa .

Next, the entire isobutane slurry containing the polymerization product of the first step was introduced as it was into a second step reactor having an internal volume of 200 L, and the second step polymerization was carried out under the conditions of isobutane at 40 L/hr, ethylene at 7 kg/hr, 85°C, polymerization pressure of 4.2 MPa, and average residence time of 0.9 hr, without adding any catalyst. In this second step, hydrogen and 1-hexene were supplied so as to produce substantially the same polymer as in the first step. A portion of the polymerization reaction product after the second step was sampled and its physical properties were measured, resulting in an MFR of _21.6 , a density of 0.3 g/10 min, and a density of 0.922 g/cm ³ .

Next, the entire isobutane slurry containing the second step polymerization product was introduced directly into a 400 L third step reactor, and without adding any catalyst or 1-hexene, isobutane was continuously fed at 87 L/hr and ethylene at 18 kg/hr. Hydrogen was further fed so as to achieve a target MFR of _21.6 , and the third step polymerization was carried out under conditions of 90°C, a polymerization pressure of 4.1 MPa, and an average residence time of 1.5 hr. The polyethylene polymer discharged from the third step reactor was dried, and the resulting polymer powder was melt-kneaded with predetermined additives to produce a polyethylene resin composition. Measurements showed an MFR of _21.6 , 19 g/10 min, and a density of 0.950 g/cm ^3. The proportions of the polymers (high molecular weight components) produced in both the first and second steps were 20 wt %.

On the other hand, the MFR of the polyethylene polymer of the low molecular weight component produced in the third step was determined by separately polymerizing it under the polymerization conditions of the third step, and was found to be 150 g/10 min. Furthermore, the density of the polyethylene polymer of the low molecular weight component produced in the third step was determined to be 0.970 g/ ^cm3 , using the fact that the density after the third step and the density after the second step are additivity-based in terms of weight percent. The results are shown in Table 1.

For Examples 2 and 3 and Comparative Examples 1 to 3, the same production method as in Example 1 was used, but the amount of hydrogen supplied, the amount of 1-hexene supplied, and the polymerization ratio of each component were adjusted to achieve the desired MFR and density.

Examples 4 and 5
(2) Homopolymerization of polyethylene resin using Ziegler catalyst <Production of Ziegler catalyst>
20 g of commercially available magnesium ethoxide, 1.64 g (12.3 mmol) of granular aluminum trichloride, and 2.40 g (8.81 mmol) of diphenyldiethoxysilane were co-ground to obtain 10.0 g of the co-ground product, to which 40 ml of heptane and 10.0 g (52.7 mmol) of titanium tetrachloride were added dropwise at room temperature, the mixture was heated to 90° C., and stirring was continued for 90 minutes. Washing with hexane at room temperature yielded 15.6 g of a solid catalyst.

<Production of polyethylene resin (medium molecular weight component, low molecular weight component)>
A 2.0 L autoclave, thoroughly purged with nitrogen, was charged with 1.0 mmol of triisobutylaluminum (0.50 mol/L hexane solution) and 1.0 L of isobutane, and the internal temperature was raised to 90°C. Hydrogen was then further charged, and 20 mg of solid catalyst was introduced under pressure with ethylene. Polymerization was continued for 1 hour while maintaining the ethylene partial pressure. Thus, an ethylene polymer having an MFR of 100 g/10 min and a density of 0.969 g/ ^cm3 was obtained. Furthermore, by carrying out the same procedure except for the amount of hydrogen, an ethylene polymer having an MFR of 0.2 g/10 min and a density of 0.940 g/ ^cm3 and an ethylene polymer having an MFR of 150 g/10 min and a density of 0.969 g/ ^cm3 were obtained, respectively.
(3) Homopolymerization of polyethylene resins using metallocene catalysts

<Production of Metallocene Catalyst A>
A cylindrical flask equipped with an induction stirrer and thoroughly purged with nitrogen was charged with 3 g of silica having an average particle size of 11 μm (average particle size 11 μm, surface area 313 m ² /g, pore volume 1.6 cm ³ /g), and 75 ml of toluene was added. The flask was heated to 75°C in an oil bath. An 8.0 ml aliquot of a toluene solution of methylaluminoxane (manufactured by Albemarle Corporation, 3.0 mol-Al/L) was dispensed into a separate flask. A toluene solution (15 ml) of dimethylsilylenebis[1,1'-{2-(2-(5-methyl)furyl)-4-(p-isopropylphenyl)-indenyl}]zirconium dichloride (63.4 mg, 75 μmol) was added to the toluene solution of methylalumoxane at room temperature, and the mixture was heated to 75°C and stirred for 1 hour. This toluene solution was then added with stirring to a toluene slurry of silica heated to 75°C, and the mixture was maintained for 1 hour. Thereafter, 175 ml of n-hexane was added while stirring at 23°C, and after 10 minutes, stirring was stopped and the mixture was left to stand. After the catalyst was allowed to settle sufficiently, the supernatant was removed and 200 ml of n-hexane was added. After stirring once, the mixture was again left to stand and the supernatant was removed. This operation was repeated three times to remove components liberated in the n-hexane. Furthermore, the solvent was distilled off under reduced pressure while heated to 40°C. After the degree of vacuum reached 0.8 mmHg or less, drying under reduced pressure was continued for a further 15 minutes to obtain silica-supported metallocene catalyst A.

<Production of antifouling component B>
3 g of n-octylated polyethyleneimine (in which 0.5 n-octyl groups were introduced per monomer unit of polyethyleneimine) derived from polyethyleneimine (molecular weight 10,000) and 1 g of phytic acid, a phosphate ester compound, were mixed and stirred at room temperature in 100 mL of xylene to form a salt. Then, 6 g of dioctyl sulfosuccinate magnesium salt was mixed to obtain antifouling component B.

<Production of polyethylene resin composition (high molecular weight component)>
A loop-type slurry reactor having an internal volume of 290 L was supplied with 115 L/h of dehydrated and purified isobutane, 0.13 mol/h of triisobutylaluminum, and 6 ml/h of antifouling component B, and the temperature inside the reactor was set to 80°C. Ethylene, 1-hexene, and hydrogen were supplied while intermittently discharging from the reactor so as to maintain the pressure at 4.2 MPaG, and the molar ratio of 1-hexene to ethylene in the liquid during polymerization was adjusted to 0.019, and the molar ratio of hydrogen to ethylene was adjusted to 3.5 × ¹⁰

Next, a hexane slurry of catalyst A diluted to 0.3 g/L with hexane was fed to the reactor at 3 L/h to initiate polymerization, and ethylene was fed so that the ethylene concentration in the reactor reached 10 vol%. The produced polyethylene was intermittently discharged together with isobutane, flashed, and then sent to a product silo. As a result, polyethylene was produced at a rate of 11 kg/h, with an HLMFR of 0.2 g/10 min and a density of 0.922 g/ ^cm3 .
The polyethylene resin compositions and ethylene polymers produced above were melt-kneaded in the blending ratios shown in Table 1 using a twin-screw extruder at a barrel temperature of 210° C. to obtain Examples 4 and 5.

(1) Calculation of Mz/Mw by GPC (gel permeation chromatography) Measurement was carried out under the following conditions.
Apparatus: WATERS 150C
Column: Three AD80M/S columns manufactured by Showa Denko Co., Ltd. Measurement temperature: 140°C
Concentration: 1mg/1ml
Solvent: o-dichlorobenzene

The molecular weight calculation and column calibration were carried out according to the following methods.
The GPC chromatography data was input into a computer at a frequency of one point per second, and data processing was carried out according to the description in Chapter 4 of "Size Exclusion Chromatography" by Sadao Mori, published by Kyoritsu Shuppansha. The Mw value and Mz value were calculated, and then the Mz value was divided by the Mw value to calculate Mz/Mw.
The column was calibrated by measuring a series of monodisperse polystyrenes manufactured by Showa Denko K.K. (S-7300, S-3900, S-1950, S-1460, S-1010, S-565, S-152, S-66.0, S-28.5, S-5.05), n-eicosane, and n-tetracontane at 0.2 mg/ml each, and a calibration curve was prepared by fitting the relationship between the elution peak time and the logarithm of the molecular weight with a fourth-order polynomial.
The molecular weight of polystyrene (MPS) was converted to the molecular weight of polyethylene (MPE) using the following formula: MPE = 0.468 × MPS

(2) FNCT (Full Notch Tensile Creep Test)
Measurements were performed at 80°C and 5 MPa in accordance with the full-circumference notched tensile creep test of JIS K6774 (1995) Appendix 1. Test specimens were cut out from compression-molded sheets with a thickness of 6 mm prepared under the conditions of JIS K6922-2 (1997) Table 2, and notched all around (test specimen thickness 6 mm, notch depth 1 mm, all around). The test solution in which the samples were immersed was a 1% aqueous solution of sodium lauryl sulfate. The standard value that the FNCT must meet was a time to failure of 100 hours or more at 80°C and 5 MPa.

(3) Shrinkage anisotropy evaluation: Using a 100-ton injection molding machine manufactured by FANUC Corporation, a 130 x 130 x 2 mm flat plate was molded with a film gate (gate thickness 0.2 mm) on one side under the following molding conditions: molding temperature 190°C, mold temperature 40°C, injection speed 50 mm/s, maximum injection time 2 seconds, dwell pressure 66 MPa, and cooling time 20 seconds. After molding, the flat plate was left at 23°C for 48 hours. The machine direction width (MD) of the flat plate was measured 30 mm below the gate finish, and the width (TD) of the flat plate was measured 30 mm below the edge of the edge perpendicular to the machine direction. The MD/TD ratio was calculated as the shrinkage anisotropy. The standard value that must be met for shrinkage anisotropy was a shrinkage anisotropy of 2.5 or less.

The results of the polyethylene resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 3 and the results of the mechanical properties are shown in Table 1.
In addition, Examples 1 to 5 and Comparative Examples 1 to 3 were the same except for the resin component, and calcium stearate was added so that the calcium concentration in the resin was approximately 40 ppm, and 1000 ppm of Irganox 1010 was also added as a phenolic antioxidant.

(Table 1)

As shown in the table above, comparing Examples 1 to 5 with Comparative Examples 1 to 3, it was confirmed that the polyethylene resin composition according to the present embodiment has a good balance between dimensional stability and durability, as shown in Examples 1 to 5. Comparative Examples 1 and 2, in which the proportion of components with molecular weights exceeding 3,000,000 is more than 2% and the Mz/Mw, which indicates the spread of the molecular weight distribution, is more than 5.5, have good durability, but the shrinkage anisotropy exceeds 2.5, resulting in large shrinkage anisotropy, which is thought to result in low circularity of the molded article and make poor connection of joints more likely to occur.
On the other hand, Comparative Example 3, which satisfies the specific requirements of this embodiment except for the density of the high molecular weight component being 0.935 g/ ^cm3 or less, has excellent dimensional stability, but the amount of copolymerized α-olefin is insufficient, resulting in a low probability of tie molecule presence and an FNCT of less than 100 hours, which is thought to raise concerns about damage to the pipe material over long-term use. Thus, the polyethylene resin compositions that do not satisfy the specific requirements of this embodiment have a poorer balance between dimensional stability and durability than the polyethylenes of Examples 1 to 5. (Comparative Examples 1 to 3)

(4) Preparation of Polyethylene Resin Composition Sheet In this example, various evaluations were carried out in a sheet form rather than a tubular form.
According to the formulation shown in Table 2 below, polyethylene resin pellets were heat-pressed at 200°C for 3 minutes to form a 180 mm x 180 mm x 1 mm sheet to obtain a test sample.

(5) Calcium Concentration Evaluation The sheet was cut to prepare test pieces weighing 0.1 g, which were then fed into a microwave decomposition system (MARS6 manufactured by CEM) together with 6 mL of nitric acid, and the test pieces were decomposed by microwaves. After decomposition, 1 mL of hydrogen peroxide was added, and then ultrapure water was added to bring the volume to 25 mL. The calcium concentration of the solution was measured using an ICP device (SPS5100 manufactured by SII Technology), and the calcium concentration of the polyethylene resin composition sheet was calculated.

(6) Evaluation of calcium elution amount Three samples were prepared by cutting the above sheet into 30 mm x 50 mm pieces, and after washing the samples with ultrapure water according to the method based on the SEMI F40 standard, they were sealed in a PFA container together with 100 mL of ultrapure water. The PFA container was then left to stand at 85°C ± 5°C for ⁷ days to allow elution, after which the amount of calcium elution was measured using an ICP-MS device (Agilent Technologies, model number Agilent 7500cs). The standard value that must be met for the amount of calcium elution was set to 15 μg/m2 or less.

Calcium elution characteristics were evaluated in Examples 1, 6-8, and Comparative Example 4 using the same polyethylene resin composition as in Example 1, but varying the calcium concentration and type of phenolic antioxidant. The results are shown in Table 2.

(Table 2)

As shown in Table 2 above, when the calcium concentration of the polyethylene resin composition sheet was 100 ppm or less (Examples 1, 6 to 8), the amount of calcium elution was less than 15 μg/ ^m2 , and calcium elution could be effectively suppressed.

On the other hand, when the calcium concentration of the polyethylene resin composition sheet was more than 100 ppm (Comparative Example 4), the amount of calcium elution exceeded 15 μg/m ² .

Furthermore, as shown by a comparison between Example 1 and Example 3, and a comparison between Example 2 and Example 4, even when the calcium concentration in the polyethylene resin is approximately the same, the amount of calcium elution is suppressed more when Irganox 1330 is added as a phenolic antioxidant than when Irganox 1010 is added. The following factors are presumed to be the causes of this.

In other words, because Irganox 1010 contains oxygen in its molecules derived from sources other than phenol groups, the molecule is highly polar and is prone to leaching out of polyethylene resins. Furthermore, due to its high polarity, Irganox 1010 is prone to intermolecular forces acting between it and calcium components, and there is a possibility that when Irganox 1010 leaches out, it may also induce the leaching of calcium components. For this reason, it is believed that adding Irganox 1010 makes it easier for calcium components to leach out.

On the other hand, Irganox 1330 is a molecule with low polarity, containing no oxygen other than that derived from phenol groups, and is therefore presumed not to be involved in the leaching of calcium components.

Based on the above results, when adding a phenolic antioxidant, it is preferable that the antioxidant does not contain oxygen derived from anything other than phenol groups, in order to reduce the amount of calcium elution.

Furthermore, when using a phenolic antioxidant containing oxygen derived from a group other than the phenol group as the antioxidant, it is preferable that the calcium concentration in the polyethylene resin be 50 ppm or less.

10, 11 Pipes 10a, 11a Inner surface 10b, 11b Outer surface 21 Polyethylene resin layer (an example of a layer)
22 Coating resin layer

Claims (6)

A polyethylene-based resin composition for use in a piping material for ultrapure water, the polyethylene-based resin composition comprising a polyethylene-based resin and an antioxidant, wherein the antioxidant is 3,3',3'',5,5',5''-hexa-tert-butyl-a,a',a''-(mesitylene-2,4,6-triyl)tri-p-cresol, and the polyethylene-based resin composition for use in a piping material for ultrapure water satisfies the following properties (1) to (6):
Property (1): The melt flow rate (MFR _21.6 ) at a temperature of 190° C. and a load of 21.6 kg is 6 g/10 min or more and 25 g/10 min or less.
Property (2): Density is 0.946 g/cm ³ or more and 0.960 g/cm ³ or less.
Property (3): In the molecular weight distribution measured by GPC, Mz/Mw, which is an index showing the breadth of the molecular weight distribution, is 2.5 or more and 5.5 or less.
Property (4): The calcium concentration contained in the polyethylene resin composition is 100 ppm or less.
Property (5): The high molecular weight component contains 20% by weight or more and 50% by weight or less of an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to ¹² carbon atoms, the copolymer having _{an MFR} 21.6 of 0.2 g/ ¹⁰ min or more and 1.0 g/10 min or less and a density of 0.910 g/cm 3 or more and 0.935 g/cm 3 or less.
Property (6): In the molecular weight distribution measured by GPC, components having a molecular weight of 3,000,000 or more account for 2% or less of the total. The time to fracture in FNCT (measured at 80°C and 5 MPa) is 100 hours or more.
The polyethylene resin composition for use as a piping material for ultrapure water according to claim 1. Substantially free of light stabilizers
The polyethylene resin composition for use as a piping material for ultrapure water according to claim 1 or 2 . A piping material for ultrapure water, characterized by being molded from the polyethylene resin composition according to any one of claims 1 to 3 . The thickness of the layer containing a polyethylene resin as a main component is 0.3 mm or more.
The piping material for ultrapure water according to claim 4 . The thickness of the layer containing a polyethylene resin as a main component is 2.0 mm or less.
The piping material for ultrapure water according to claim 4 .