JP2023133171A - Cross-linked ethylene polymer particle, molded body and manufacturing method of molded body - Google Patents

Abstract

To provide a cross-linked ethylene polymer particle capable of forming a molded body excellent in abrasion resistance, a molded body using the cross-linked ethylene polymer particle, and a manufacturing method of the molded body.SOLUTION: A cross-linked ethylene polymer particle is obtained by cross-linking an ethylene polymer particle satisfying requirements (i) and (ii), and has a gel fraction within a range of 50 to 95%: (i) a specific surface area obtained by a BET method from an absorption-desorption isotherm measured with a nitrogen gas adsorption method is larger than 2.00 m2/g and equal to or smaller than 30.0 m2/g; and (ii) an intrinsic viscosity [η] is 5 to 50 dl/g measured at 135°C in a decalin solvent.SELECTED DRAWING: None

Description

The present invention relates to crosslinked ethylene polymer particles, a molded article containing the crosslinked ethylene polymer particles, and a method for producing the same.

Ethylene polymers with extremely high molecular weights, so-called ultra-high molecular weight ethylene polymers, have superior impact resistance, abrasion resistance, chemical resistance, and strength compared to general-purpose ethylene polymers, and are used as engineering plastics. It has excellent characteristics.

On the other hand, due to the high molecular weight of ultra-high molecular weight ethylene polymers, it is difficult to perform melt molding, which is a common resin molding method. The ram extrusion method for ultra-high molecular weight ethylene-based polymers is a commonly used method for producing molded bodies (Patent Document 1), and uses a specific mold at an extrusion temperature below the melting point of the ethylene-based polymer. It is disclosed that a molded article having a high elastic modulus can be obtained by the above-mentioned ram extrusion method using an ultra-high molecular weight ethylene polymer (Patent Document 2).

Japanese Unexamined Patent Publication No. 6-155553 Japanese Patent Application Publication No. 2015-214061

However, in the ram extrusion method as described in Patent Document 1, the extrusion temperature is set above the melting point of the resin in order to enable extrusion and obtain a uniform molded product. Therefore, since the resin passes through a molten state during molding, the mechanical properties of the resulting molded product generally deteriorate. In addition, although the molded article described in Patent Document 2 has a high elastic modulus, there is no mention of wear resistance, and it exhibits wear resistance, which is one of the superior properties of ultra-high molecular weight ethylene polymers. There remained room for improvement in terms of production of molded bodies.

In view of the above-mentioned background art, the problem to be solved by the present invention is to provide crosslinked ethylene polymer particles capable of producing a molded article with excellent wear resistance, a molded article using the crosslinked ethylene polymer particles, and a molded article using the crosslinked ethylene polymer particles. An object of the present invention is to provide a method for manufacturing a molded article.

The present inventors conducted studies to solve the above problems. As a result, it was discovered that the above-mentioned problems could be solved by the following configuration example, and the present invention was completed. That is, the present invention relates to, for example, the following [1] to [6].

[1]
Crosslinked ethylene polymer particles obtained by crosslinking ethylene polymer particles that meet the following requirements (i) and (ii) and have a gel fraction in the range of 50 to 95%:
(i) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is greater than 2.00 m ² /g and 30.0 m ² /g or less;
(ii) The intrinsic viscosity [η] measured at 135° C. in a decalin solvent is 5 to 50 dl/g.

[2]
The crosslinked ethylene polymer particles according to [1], wherein the ethylene polymer particles satisfy the following requirement (iii):
(iii) The bulk density is 0.01 to 0.20 g/mL.

[3]
The crosslinked ethylene polymer particles according to [1] or [2], which satisfy the following requirement (I):
(I) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is 1.00 to 30.0 m ² /g.

[4]
Crosslinked ethylene polymer particles that satisfy the following requirement (I) and have a gel fraction in the range of 50 to 95%:
(I) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is 1.00 to 30.0 m ² /g.

[5]
A molded article containing the crosslinked ethylene polymer particles according to any one of [1] to [4].

[6]
A step of irradiating ethylene polymer particles that meet the following requirements (i) and (ii) to obtain crosslinked ethylene polymer particles;
A method for producing a molded body, comprising a step of extrusion molding at a temperature lower than the melting point of the crosslinked ethylene polymer particles:
(i) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is greater than 2.00 m ² /g and 30.0 m ² /g or less;
(ii) The intrinsic viscosity [η] measured at 135° C. in a decalin solvent is 5 to 50 dl/g.

According to the present invention, a molded article with excellent wear resistance is obtained by molding by a ram extrusion method using crosslinked ethylene polymer particles (hereinafter also referred to as "crosslinked particles") having a specific gel fraction. can be provided. Further, by using specific ethylene polymer particles as the crosslinked particles, the strength and moldability of the obtained molded product tend to be excellent.

Hereinafter, the crosslinked ethylene polymer particles according to the present invention will be explained in more detail.
[Crosslinked ethylene polymer particles (crosslinked particles)]
The crosslinked ethylene polymer particles according to one aspect of the present invention are characterized by having a gel fraction in the range of 50 to 95%, and are crosslinked ethylene polymer particles that satisfy the following requirements (i) and (ii). It will be done.
(i) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is larger than 2.00 m ² /g and 30.0 m ² /g or less.
(ii) The intrinsic viscosity [η] measured at 135° C. in a decalin solvent is 5 to 50 dl/g.

The gel fraction of the crosslinked particles is 50 to 95%, preferably 60 to 90%, more preferably 70 to 90%, even more preferably 80 to 90%. When the gel fraction is within the above range, the fluidity of the resin is maintained during molding, and molding becomes easy. If the gel fraction is below the above range, the resin will flow out during molding, making it difficult to mold, and the abrasion resistance of the resulting molded product will decrease, and if the gel fraction exceeds the above range, the fluidity of the molecules will deteriorate. becomes significantly worse, resulting in poor moldability. In addition, even when the temperature of the crosslinked particles exceeds the glass transition temperature or melting point, the molecular chains are unable to flow freely, so high-temperature properties can be improved and the shape can be maintained even when subjected to stress. Therefore, it may be possible to maintain mechanical properties.

Note that the gel fraction can be calculated by dividing the mass of the sample subjected to the extraction operation for a certain period of time by the amount of sample prepared. In the present invention, extraction is performed in o-dichlorobenzene at 145° C. for 2 hours using a Soxhlet extractor, and the gel fraction is calculated from the mass of the sample before and after extraction.

The gel fraction can be adjusted by irradiating the ethylene polymer particles with radiation, and the crosslinked particles can be obtained by irradiating the ethylene polymer particles with radiation so that the gel fraction falls within the above range. can.

It is thought that by irradiating the ethylene polymer particles (hereinafter also referred to as "unirradiated particles") with radiation, molecular chains are cut and crosslinked, and as a result, the molecular chains are joined at crosslinking points. It is thought that the molecular chains are crosslinked in this way and the degree of crosslinking increases, thereby increasing the gel fraction. The degree of crosslinking can generally be adjusted by adjusting the radiation dose.

The melting point (Tm) of the present crosslinked particles is preferably 120 to 160°C, more preferably 125 to 145°C, and even more preferably 130 to 140°C. When the melting point (Tm) is within the above range, the fluidity of the resin is maintained during molding, and molding becomes easy. If the melting point (Tm) is below the above range, the resin will flow out during molding, making molding difficult, and the abrasion resistance of the resulting molded product will decrease. When the melting point (Tm) exceeds the above range, the fluidity of the molecules becomes significantly poor, resulting in poor moldability. In addition, in this specification, melting point (Tm) is measured by DSC measurement, and specifically, it can be measured based on the method described in the Example mentioned later.

Further, the crosslinked particles according to one embodiment of the present invention preferably satisfy the following requirement (I).
(I) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is 1.00 to 30.0 m ² /g.

The specific surface area of the crosslinked particles determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is preferably 1.00 to 30.0 m ² /g, more preferably 1.5 to 28 m 2 /g. .0 m ² /g, more preferably 2.00 to 26.0 m ² /g, particularly preferably 2.00 to 25.0 m ² /g, particularly preferably 2.50 to 10.0 m ² /g.

When the specific surface area is within the above range, a molded article having excellent fluidity, handling properties, and molding processability can be easily obtained. When the specific surface area is less than the above range, adhesion between particles may be poor during molding, resulting in insufficient strength. Furthermore, if the specific surface area exceeds the above range, the handling properties (for example, powder flowability) of the particles may deteriorate, and the moldability may be poor.
In this specification, the specific surface area means the total specific surface area obtained by summing all the specific surface areas determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method. Determined by the measurement method described in the example.

[Ethylene polymer particles (unirradiated particles)]
The crosslinked particles according to the present invention are formed by crosslinking ethylene polymer particles that satisfy the above requirements (i) and (ii). The requirements (i) and (ii) will be explained below.

<Requirement (i)>
The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method of the unirradiated particles is larger than 2.00 m ² /g and 30.0 m ² /g or less, preferably 2.0 m 2 /g or less. .50 to 28.0 m ² /g, more preferably 3.00 to 26.0 m ² /g, even more preferably 5.00 to 16.0 m ² /g. When the specific surface area of the unirradiated particles is within the above range, a molded article having excellent fluidity, handling properties, and molding processability can be easily obtained. When the specific surface area is less than the above range, adhesion between particles may be poor during molding, resulting in insufficient strength. Furthermore, if the specific surface area exceeds the above range, the handling properties (for example, powder flowability) of the particles may deteriorate, and the moldability may be poor.

<Requirement (ii)>
The intrinsic viscosity [η] of the unirradiated particles measured in a decalin solvent at 135° C. is 5 to 50 dl/g, preferably 10 to 50 dl/g, and more preferably 15 to 45 dl/g. When the intrinsic viscosity [η] of the ethylene polymer particles is within the above range, the molded article of the present invention tends to exhibit high strength and excellent moldability. When the intrinsic viscosity [η] exceeds the above range, sufficient extrusion may not be possible and moldability may deteriorate. On the other hand, if the intrinsic viscosity [η] is below the above range, sufficient strength may not be developed due to structural defects originating from the terminals of the polymer chains with low molecular weight that constitute the particles.
In general, an ethylene polymer having an intrinsic viscosity [η] within the above range tends to have an extremely high molecular weight, so it can be said that the ethylene polymer particles in the present invention are made of an ultra-high molecular weight ethylene polymer.

Further, it is more preferable that the unirradiated particles satisfy the following requirement (iii) at the same time as the requirements (i) and (ii).
(iii) Bulk density (B.D.) is 0.01 to 0.20 g/mL.

<Requirement (iii)>
The unirradiated particles have a bulk density (B.D.) of preferably 0.01 to 0.20 g/mL, more preferably 0.02 to 0.20 g/mL, even more preferably 0.03 to 0. It is 15g/mL. When the bulk density (B.D.) is within the above range, fluidity during molding becomes good and moldability tends to be excellent. If it is below the above range, the specific surface area tends to become small, which may be one of the causes of molding defects.
The bulk density is specifically determined by the measuring method described in the Examples below.

Furthermore, it is more preferable that the unirradiated particles satisfy any one or more of the following requirements (iv) to (viii) at the same time as the requirements (i) to (iii). Each requirement will be explained in turn below.

(iv) The magnesium content of the ethylene polymer particles is 10 to 2,000 ppm.
(v) The content of coarse particles in the ethylene polymer particles is 20% by mass or less.
(vi) The acetone extract of the ethylene polymer particles contains a compound (F) having a molecular skeleton of the following general formula [I] in a range of 6 to 1,000 ppm.

(vii) The ethylene polymer constituting the ethylene polymer particles is an ethylene homopolymer or a copolymer of ethylene and a linear or branched α-olefin having 3 to 20 carbon atoms. be.
(viii) The melting point of the ethylene polymer particles is 120 to 160°C.

<Requirement (iv)>
According to the method for producing ethylene polymer particles described below, by using a magnesium halide (preferably MgCl ₂ ) during the production of ethylene polymer particles, ethylene polymer particles having a specific surface area within the above range can be easily produced. It tends to be possible to manufacture A part of the magnesium halide used during production usually remains in the ethylene polymer particles, and the magnesium content of the ethylene polymer particles (unirradiated particles) corresponds to the concentration of magnesium halide during production. do.
The magnesium content in the unirradiated particles is preferably 10 to 2,000 ppm, more preferably 20 to 1,500 ppm, and even more preferably 30 to 1,000 ppm. By being within the above range, the ethylene polymer particles in the present invention have better particle fluidity and moldability.

<Requirement (v)>
If the ethylene polymer particles contain many coarse particles of 1 mm or more, sufficient fluidity may not be obtained during transportation after polymerization, and valves, pumps, strainers, etc. may become clogged. From the viewpoint of preventing the above-mentioned defects, the content of coarse particles (amount of coarse particles) in the unirradiated particles is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. , even more preferably 7% by weight or less, particularly preferably 3% by weight or less, especially preferably 1.5% by weight or less. When there are few coarse particles, the particles can be transported easily during the processing process, so that the particles can be shaped uniformly, and a stretched molded article with excellent stretch formability and strength can be obtained.
Incidentally, the above-mentioned coarse particles mean particles with a size of 1 mm or more, and particles that do not pass through a 1 mm x 1 mm mesh sieve when the sieve is sieved for 10 minutes, with an amplitude of 0.5 mm, and at an interval of 15 seconds. It refers to The content of the coarse particles is specifically determined by the measuring method described in the Examples below.

<Requirement (vi)>
The acetone extract of the ethylene polymer particles (unirradiated particles) preferably contains a compound (F) having a molecular skeleton of the following general formula [I]. The acetone extract is a component that is eluted from ethylene polymer particles into acetone after the ethylene polymer particles are brought into contact with acetone. In general, the components eluted into acetone are catalysts, additives, etc. used in the polymerization step among the constituent components of ethylene polymer particles, and also components such as additives that may be used after polymerization. Contained in the acetone extract. Hereinafter, the molecular skeleton represented by the following general formula [I] may be referred to as an "oxyalkylene skeleton".

In the general formula [I], R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms. Examples of the alkyl group having 1 to 12 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, t-butyl group, n-pentyl group, n- Examples include linear or branched alkyl groups such as hexyl, n-heptyl, n-octyl, and n-nonyl groups. It is preferable to use a compound (F) in which R is a hydrogen atom or a methyl group because it has excellent polymerization activity and an effect of suppressing generation of coarse particles, and a hydrogen atom is more preferable.

The compound (F) is an antistatic agent (a compound derived from) that is added during the polymerization step or can be added after the polymerization. Therefore, the content of the compound (F) in the ethylene polymer particles can be adjusted by adjusting the concentration of the compound (F) during the polymerization operation, and can also be adjusted by adding the compound (F) after the polymerization. It's okay. The presence of the compound (F) improves the fluidity of the particles, so that the particles can be shaped uniformly. Furthermore, by adding compound (F) during polymerization instead of adding it after polymerization, compound (F) penetrates into the interior of the polymer particles, making it possible to obtain a molded product with better moldability and strength. .

The compound (F) is preferably a compound having a skeleton in which a hydrogen atom is bonded to an oxygen atom in an oxyalkylene skeleton represented by the general formula [I], particularly preferably a compound represented by the following general formula [F1] Having one or two or more skeletons selected from the group consisting of the structure represented by the following formula [F2] and the structure represented by the following formula [F3] in the molecule. It is a compound.

In the above formula, R has the same meaning as R explained in the above formula [I]. In the above formula, R" represents the same atom or group as R, n and m are integers of 0 or 1, p is an integer of 1 or 2, and the sum of m and p is 2. From the viewpoint of polymerization activity and coarse particle generation suppressing effect, it is preferable to use a compound (F) in which m is 0 and p is 2.

Examples of the compound having the skeleton represented by the general formula [F1] include polyoxyalkylene compounds, such as polyoxyalkylene glycol and ethylenediamine-based polyoxyalkylene polyol.
As for the compound having the skeleton represented by the general formula [F2], aliphatic diethanolamide described in Japanese Patent No. 5796797 can be preferably exemplified.
As for the compound having the skeleton represented by the general formula [F3], tertiary amine compounds described in Japanese Patent No. 5796797 can be preferably exemplified.

The weight average molecular weight (Mw) of the compound (F) is determined by gel permeation chromatography (GPC), and is preferably 500 to 30,000, more preferably 1,000 to 25,500, and It is preferably 1,500 to 20,000, particularly preferably 1,500 to 10,000. When Mw is within the above range, the amount of coarse particles generated can be reduced, so fluidity within the pipe during transfer is improved, and a uniform molded product can be obtained during molding. On the other hand, if Mw is small, there is a risk that the material will bleed out during molding, resulting in poor quality, while if Mw is large, it may be incorporated into the molded product as a foreign substance.

Specific examples of compound (F) include the "ADEKA Pluronic (registered trademark)" series manufactured by ADEKA Corporation. Among these, "ADEKA PLURONIC (registered trademark) L-71 (Mw: 3,760)" and "ADEKA PLURONIC (registered trademark) L-72 (Mw: 4,700)", "ADEKA PLURONIC (registered trademark) L-31 (Mw: 1,700)", "ADEKA PLURONIC (registered trademark) P-85 (Mw: 7,430)", "ADEKA PLURONIC (registered trademark) ) F-68 (Mw: 15,100)”, “ADEKA PLURONIC (registered trademark) F-88 (Mw: 19,300)”, “ADEKA PLURONIC (registered trademark) 17-R2 (Mw: 3,310)” Polyoxyalkylene glycols such as “ADEKA PLURONIC (registered trademark) TR-701 (Mw: 5,060)”, “ADEKA PLURONIC (registered trademark) TR-702 (Mw: 5,390)”, “ADEKA PLURONIC (registered trademark) ethylenediamine-based polyoxyalkylene polyols such as "TR-913R (Mw: 4,560)". Specific examples of compounds (F) other than the above include "Emulgen 108 (Mw: 769)" and "Emulgen 109P (Mw: 970)" manufactured by Kao Corporation; "Amizet (registered trademark)" manufactured by Kawaken Fine Chemicals Co., Ltd. 5C (Mw: 647)" and "Acetylenol (registered trademark) E13T (Mw: 444)."
The compound (F) may be used alone or in combination of two or more.

As described below, the oxyalkylene skeleton can be identified by known analytical techniques such as nuclear magnetic resonance (NMR) spectroscopy.
The content of compound (F) in the ethylene polymer particles is preferably 6 to 1,000 ppm based on the ethylene polymer particles. When the content of the compound (F) is within the above range, the ethylene polymer particles can be molded at a high stretching ratio and the generation of coarse particles can be suppressed, improving the fluidity in the pipe during transfer. do. Further, from the viewpoint of suppressing the generation of coarse particles, the content is more preferably 8 to 600 ppm, and even more preferably 10 to 400 ppm.
The content of compound (F) in the ethylene polymer particles can be calculated from liquid chromatography mass (LC-MS) analysis or the like.

<Requirement (vii)>
The ethylene polymer constituting the ethylene polymer particles is preferably an ethylene homopolymer or a copolymer of ethylene and a linear or branched α-olefin having 3 to 20 carbon atoms. More preferably, it is an ethylene homopolymer.

The α-olefin having 3 to 20 carbon atoms is preferably an α-olefin having 3 to 10 carbon atoms, more preferably an α-olefin having 3 to 8 carbon atoms. Specifically, linear olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, and 1-decene; 4-methyl-1-pentene, 3-methyl-1-pentene, 3 Branched olefins such as -methyl-1-butene can be mentioned, with propylene, 1-butene, 1-hexene, and 4-methyl-1-pentene being preferred.
The α-olefin may be used alone or in combination of two or more.
The content of α-olefin, that is, the molar ratio of repeating units derived from α-olefin copolymerized with ethylene to all repeating units, is 5 mol% or less, preferably 2 mol% or less, more preferably 0.5 mol% or less. .

When the ethylene polymer constituting the ethylene polymer particles is an ethylene homopolymer, there are few structural defects due to branching, so a molded article with excellent stretch formability and high strength can be obtained. Thus, from the viewpoint of increasing the degree of crystallinity and improving the stretch formability in solid phase stretch molding, an ethylene homopolymer is preferable. On the other hand, in the case of a copolymer of ethylene and α-olefin, if the α-olefin content is higher than the above range, branches derived from α-olefin may cause structural defects and sufficient strength may not be obtained. be. Note that the ethylene content in the ethylene polymer can be measured by a known measurement method such as nuclear magnetic resonance (NMR) spectroscopy or infrared absorption spectroscopy.

Each of the ethylene polymers constituting the ethylene polymer may contain at least one kind of biomass-derived monomer (ethylene, α-olefin having 3 to 20 carbon atoms). The monomers of the same type constituting the polymer may be only biomass-derived monomers, only fossil fuel-derived monomers, or may contain both biomass-derived monomers and fossil fuel-derived monomers. Biomass-derived monomers are monomers made from all renewable natural raw materials and their residues, such as those of plant or animal origin, including fungi, yeast, algae, and bacteria, and with 1x ^14C isotope as carbon. The biomass carbon concentration (unit: pMC) measured in accordance with ASTM ^D6866 is about 100 pMC. Biomass-derived monomers (ethylene, other monomers such as α-olefins) can be obtained, for example, by conventionally known methods.

It is preferable that these ethylene polymers contain structural units derived from biomass-derived monomers from the viewpoint of reducing environmental load (mainly reducing greenhouse gases). If the polymer production conditions such as polymerization catalyst, polymerization process, and polymerization temperature are the same, even if the raw material monomer is a (co)polymer containing a biomass-derived monomer, the ^14C isotope can be 1×10 ^-12 The molecular structure other than the proportion of about 10 ^-14 is equivalent to a (co)polymer made of fossil fuel-derived monomers. Therefore, the performance is said to remain unchanged.

<Requirement (viii)>
The melting point (Tm) of the unirradiated particles is preferably 120 to 160°C, more preferably 130 to 150°C, and even more preferably 135 to 145°C. When the melting point (Tm) is within the above range, the fluidity of the resin is maintained during molding, and molding becomes easy. If the melting point (Tm) is below the above range, the resin will flow out during molding, making it difficult to mold, and the abrasion resistance of the resulting molded product will decrease, and if the melting point (Tm) exceeds the above range, the molecular Fluidity becomes extremely poor and moldability is poor.

<Method for producing ethylene polymer particles>
The method for producing the ethylene polymer particles is not particularly limited, but a method including the following steps [α] and [β] is preferred.

Step [α]: Step (1) of bringing the metal halide and alcohol into contact in a hydrocarbon solvent, and contacting the component obtained in step (1) with an organoaluminum compound and/or an organoaluminum oxy compound. Step (2) of obtaining a suspension <i>,
A step <ii> of bringing the suspension obtained in the step <i> into contact with a transition metal compound (B) represented by the following general formula [II]; and a step of adding the compound (F). iii＞
and carrying out the step <iii> between the step <i> and the step <ii> and/or after the step <ii> to produce a catalyst-containing liquid for olefin polymerization.

Step [β]: In the presence of the ethylene polymerization catalyst-containing liquid, ethylene is homopolymerized, or ethylene and a linear or branched α-olefin having 3 to 20 carbon atoms are copolymerized. A process for producing ethylene polymer particles by

In formula [II], M represents titanium, zirconium, or hafnium,
m represents an integer from 1 to 4,
R ¹ to R ⁵ may be the same or different and include a hydrogen atom, a halogen atom, a hydrocarbon group, a heterocyclic compound residue, an oxygen-containing group, a nitrogen-containing group, a boron-containing group, a sulfur-containing group, and a phosphorus atom. Indicates a containing group, a silicon-containing group, a germanium-containing group, or a tin-containing group, and two or more of these may be linked to each other to form a ring,
R ⁶ is a hydrogen atom, a hydrocarbon group having 1 to 4 carbon atoms consisting only of primary or secondary carbons, an aliphatic hydrocarbon group having 4 or more carbon atoms, an alkyl group substituted with an aryl group, monocyclic or bicyclic selected from alicyclic hydrocarbon groups, aromatic hydrocarbon groups and halogen atoms,
n is a number that satisfies the valence of M,
X is a hydrogen atom, a halogen atom, a hydrocarbon group, an oxygen-containing group, a sulfur-containing group, a nitrogen-containing group, a boron-containing group, an aluminum-containing group, a phosphorus-containing group, a halogen-containing group, a heterocyclic compound residue, a silicon-containing group group, germanium-containing group, or tin-containing group, and when n is 2 or more, the plurality of groups represented by X may be the same or different from each other, and the plurality of groups represented by X may be bonded to each other. may be used to form a ring.

(Metal halide)
As the metal halide used in the step [α], magnesium halide is preferably used in order to obtain ethylene polymer particles having the specific surface area. Preferred magnesium halides are MgI ₂ and MgCl ₂ , more preferably MgCl ₂ . Obtaining a suspension from MgCl ₂ in step <i> tends to produce ethylene polymer particles with a very high specific surface area.

Furthermore, the concentration of the metal halide (particularly magnesium halide) used in the ethylene polymerization catalyst-containing liquid influences the specific surface area of the ethylene polymer particles, and the higher the concentration, the higher the specific surface area tends to be. be. The concentration of the metal halide (especially magnesium halide) in the ethylene polymerization catalyst-containing liquid is preferably 0.10 to 5.0 mmol/L, and 0.20 to 3.0 mmol/L. More preferably, it is 0.30 to 2.0 mmol/L.

As mentioned above, a portion of the magnesium halide used during production is usually included in the ethylene-based polymer particles, and the magnesium content corresponds to the concentration of magnesium halide during production. The ethylene polymer particles in the present invention preferably contain 10 to 2,000 ppm of magnesium, more preferably 20 to 1,000 ppm, and even more preferably 30 to 500 ppm, in order to achieve the above effects.

(alcohol)
Examples of the alcohol used in the step [α] include alcohols having 1 to 25 carbon atoms. Specifically, methanol, ethanol, propanol, butanol, pentanol, hexanol, 2-ethylhexanol, octanol, dodecanol, octadecyl alcohol, oleyl alcohol, 2-butyloctanol, 2-hexyldecanol, 2-hexyldodecanol, 2- Alcohols with 1 to 25 carbon atoms such as octyl decanol, 2-octyldodecanol, isohexadecanol, isoeicosanol, benzyl alcohol, phenylethyl alcohol, cumyl alcohol, isopropyl alcohol, isobutyl alcohol, isopropylbenzyl alcohol halogen-containing alcohols having 1 to 25 carbon atoms such as trichloromethanol, trichloroethanol, and trichlorohexanol; having alkyl groups such as phenol, cresol, xylenol, ethylphenol, propylphenol, nonylphenol, cumylphenol, and naphthol; Examples include phenols having 6 to 25 carbon atoms, which may be optional.
The alcohol may be used alone or in combination of two or more.

Note that when an alcohol with a relatively large number of carbon atoms, such as an alcohol with 13 to 25 carbon atoms, is present in the ethylene polymerization catalyst-containing liquid, it can be expected that the ethylene polymerization reaction will proceed mildly. As a result, uneven distribution of heat generation during polymerization can be expected to be suppressed. It is thought that suppressing the uneven distribution of heat generation during polymerization leads to suppressing the formation of an entangled structure in the generated polymer chains, and as a result, leads to improved performance of the obtained molded product.

The amount of alcohol to be used is not particularly limited as long as it dissolves the metal halide, but from the viewpoint of easily forming an alcohol complex of the metal halide, it is preferably 0% per mole of the metal halide. .1 to 50 mol, more preferably 0.5 to 30 mol, even more preferably 1 to 20 mol, particularly preferably 2 to 15 mol.

(hydrocarbon solvent)
The hydrocarbon solvent is not particularly limited, but specifically includes aliphatic hydrocarbons such as hexane, heptane, octane, decane, dodecane, and kerosene; alicyclic hydrocarbons such as cyclopentane, cyclohexane, and methylcyclopentane; Examples include aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as ethylene chloride, chlorobenzene and dichloromethane. Among these, decane, dodecane, toluene, xylene, and chlorobenzene are preferred from the viewpoint of solubility and reaction temperature.
The hydrocarbon solvent may be used alone or in combination of two or more.

The amount of the hydrocarbon solvent to be used is not particularly limited as long as it dissolves the metal halide, but it is preferably used per mole of the metal halide from the viewpoint of easily forming an alcohol complex of the metal halide. is 0.1 to 100 mol, more preferably 0.2 to 50 mol, even more preferably 0.3 to 40 mol, particularly preferably 0.5 to 30 mol.

(Organic aluminum compound)
As the organic aluminum compound, a compound represented by the following formula (Al-1) can be used.
R ^a _n AlX _3-n ...(Al-1)
(In formula (Al-1), R ^a is a hydrocarbon group having 1 to 12 carbon atoms, X is a halogen atom or a hydrogen atom, and n is 1 to 3.)

The hydrocarbon group having 1 to 12 carbon atoms is, for example, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Specific examples include methyl group (Me), ethyl group (Et), n-propyl group, isopropyl group, isobutyl group (iso-Bu), pentyl group, hexyl group, 2-ethylhexyl group, octyl group, Examples include isoprenyl group, cyclopentyl group, cyclohexyl group, phenyl group, and tolyl group.

Examples of the organoaluminum compound represented by the formula (Al-1) include trialkyl aluminum such as trimethylaluminum, triethylaluminum, triisopropylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, tri2-ethylhexylaluminum, etc. Aluminum; alkenylaluminums such as triisoprenylaluminum; dialkylaluminum halides such as dimethylaluminum chloride, diethylaluminum chloride, diisopropylaluminum chloride, diisobutylaluminum chloride, dimethylaluminum bromide; methylaluminum sesquichloride, ethylaluminum sesquichloride, isopropylaluminium sesquichloride , butylaluminum sesquichloride, ethylaluminum sesquibromide; alkylaluminum dihalides such as methylaluminum dichloride, ethylaluminum dichloride, isopropylaluminum dichloride, ethylaluminum dibromide; alkyl aluminum hydride, diisobutylaluminum hydride, etc. Examples include aluminum hydride.

Further, as the organoaluminum compound, a compound represented by the following formula (Al-2) can also be used.

R ^a _n AlY _3-n ...(Al-2)
[In formula (Al-2), R ^a is the same group as in the above formula (Al-1),
Y is a group represented by -OR ^b , -OSiR ^c ₃ , -OAlR ^d ₂ , -NR ^e ₂ , -SiR ^f ₃ or -N(R ^g )AlR ^h ₂ ,
n is an integer from 1 to 2. ]

Examples of R ^b , R ^c , R ^d and R ^h include methyl group, ethyl group, isopropyl group, isobutyl group, cyclohexyl group, and phenyl group.
Examples of the R ^e include a hydrogen atom, a methyl group, an ethyl group, an isopropyl group, a phenyl group, and a trimethylsilyl group.
Examples of R ^f and R ^g include a methyl group and an ethyl group.

Specifically, the following compounds are used as the organoaluminum compound represented by the formula (Al-2).

(1) Compound represented by R ^a _n Al(OR ^b ) _3-n Examples of the compound include dimethylaluminum methoxide, diethylaluminum ethoxide, diisobutylaluminum methoxide, diethylaluminium-2-ethylhexoxide Examples include alkyl aluminum alkoxides such as.

(2) Compound represented by R ^a _n Al(OSiR ^c ₃ ) _3-n Examples of the compound include Et ₂ Al(OSiMe ₃ ), (iso-Bu) ₂ Al(OSiMe ₃ ), (iso- Bu) ₂ Al(OSiEt ₃ ).

(3) Compound represented by R ^a _n Al(OAlR ^d ₂ ) _3-n Examples of the compound include Et ₂ AlOAlEt ₂ and (iso-Bu) ₂ AlOAl(iso-Bu) ₂ .

(4) Compound represented by R ^a _n Al(NR ^e ₂ ) _3-n Examples of the compound include Me ₂ AlNEt ₂ , Et ₂ AlNHMe, Me ₂ AlNHEt, Et ₂ AlN(SiMe ₃ ) ₂ , ( iso-Bu) ₂ AlN(SiMe ₃ ) ₂ .

(5) Compound represented by R ^a _n Al(SiR ^f ₃ ) _3-n Examples of the compound include (iso-Bu) ₂ AlSiMe ₃ .

(6) Compound represented by R ^a _n Al[N(R ^g )AlR ^h ₂ ] _3-n Examples of the compound include Et ₂ AlN(Me)AlEt ₂ , (iso-Bu) ₂ AlN(Et )Al(iso-Bu) ₂ .

Further, as the organoaluminum compound, a compound represented by the following formula (Al-3), which is a complex alkylated product of a Group I metal and aluminum, can also be used.

M ¹ AlR ^j ₄ ...(Al-3)
[In formula (Al-3), M ¹ is a Group I metal atom such as Li, Na or K, and R ^j is a hydrocarbon group having 1 to 15 carbon atoms. ]

Specific examples of the organic aluminum compound represented by the formula (Al-3) include LiAl(C ₂ H ₅ ) ₄ and LiAl(C ₇ H ₁₅ ) ₄ .

Among the organoaluminum compounds described above, compounds represented by the formula (Al-1) are preferred, and include trimethylaluminum, triethylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, diethylaluminium chloride, ethylaluminum sesquichloride, Particularly preferred are ethylaluminum dichloride and diisobutylaluminum hydride.

(organoaluminumoxy compound)
The organoaluminumoxy compound is not particularly limited, and may include conventionally known aluminoxanes (benzene-insoluble organoaluminumoxy compounds exemplified in JP-A-2-78687 and JP-A-2021-147437). (including organoaluminumoxy compounds containing boron) can be used.
Examples of the organic aluminum oxy compound include methylaluminoxane, ethyl aluminoxane, and isobutylaluminoxane, and specific examples include the organic aluminum oxy compounds described in JP-A No. 2021-147437.
The organoaluminumoxy compounds may be used alone or in combination of two or more.

The amount of organoaluminum compound and organoaluminumoxy compound used is preferably 0.1 to 50 mol, more preferably 0.2 to 30 mol, even more preferably 0.5 to 20 mol, especially per mol of metal halide. Preferably it is 1.0 to 10 mol.

[Molded object]
The molded article according to the present invention includes the above-mentioned crosslinked particles. By using the crosslinked particles, the abrasion resistance of the obtained molded article is improved.
The molded product according to the present invention can be produced by various known molding methods described below, and therefore can be widely applied to molded products using general ultra-high molecular weight ethylene polymers. The molded article according to the invention has particularly excellent wear resistance, and is therefore particularly suitable for applications that require excellent wear resistance, such as artificial joints and electric wires.

[Method for manufacturing molded body]
The method for producing a molded article according to the present invention includes a step (step (A)) of obtaining crosslinked ethylene polymer particles by irradiating the ethylene polymer particles with radiation to crosslink them; The method includes a step of molding particles (step (B)).

[Step (A)]
The means for irradiating the ethylene polymer particles with radiation in a sealed state include a vacuum method in which the inside of the container containing the ethylene polymer particles is evacuated to lower the proportion of air; A gas purge method, etc., in which the tank is filled with gas or nitrogen and the air is exhausted, can be adopted. As long as it is sealed, an atmosphere containing some oxygen may be used without using a vacuum method or a gas purge method.

Examples of the radiation include α rays, β rays, γ rays, electron beams, and heavy ion beams, and any of them can be used, but electron beams or γ rays are preferable, and are more preferred from the viewpoint of handling. is an electron beam.

The irradiation dose of the radiation varies depending on the olefin species constituting the unirradiated particles used, but is preferably 10 to 700 kGy, more preferably 20 to 500 kGy, and still more preferably 40 to 300 kGy. When the irradiation dose is 700 kGy or less, decomposition that occurs simultaneously with molecular chain crosslinking due to radiation irradiation is less likely to occur, and it is possible to prevent the gel fraction from remaining high, which is preferable. It is preferable that the irradiation dose is 10 kGy or more because crosslinking will proceed sufficiently without the crosslinking rate of molecular chains becoming too slow. The irradiation dose of the radiation is expressed as a dose proportional to the energy absorbed by a unit mass, and gray (Gy) represents the amount of energy absorbed by a substance when the radiation hits that substance. It is a unit.

[Process (B)]
In step (B), the crosslinked ethylene polymer particles are molded by various known molding methods, specifically, extrusion molding, press molding, injection molding, calendar molding, blow molding, etc. can do. When performing the above-mentioned molding process, a known molding machine compatible with various molding methods, such as an extrusion molding machine, a press molding machine, an injection molding machine, a calendar roll, and a transfer molding machine, is used. Furthermore, the molded body obtained by the above molding method can be subjected to secondary processing by thermoforming or the like, or can be laminated with other materials.

Among the above-mentioned molding methods, when an ultra-high molecular weight ethylene polymer is used as a raw material, extrusion molding or press molding is preferred, and extrusion molding is more preferred. Examples of the extrusion method include general extrusion methods used for extrusion molding of thermoplastic resins, such as screw extrusion method and ram extrusion method. It is particularly preferable that the molded article of the present invention be molded by a ram extrusion method.

When employing the ram extrusion molding method for the method of producing the molded article of the present invention, crosslinked particles are filled into a ram cylinder and compressed with a plunger. A squeezing die is connected to the tip of the extruder used, and the compressed crosslinked particles are extruded through the squeezing die to obtain a molded body. The drawing die used for extrusion molding has bending elasticity that A1>A2, where A1 is the cross-sectional area of the inlet of the drawing die, and A2 is the cross-sectional area of the tip (exit) of the drawing die. It is preferable from the viewpoint that it tends to have excellent strength properties such as strength. That is, it is preferable that the cross-sectional area of the molded body to be manufactured is smaller than the cross-sectional area of the inlet of the drawing die. In the present invention, a mold for filling or compressing crosslinked particles may be installed in front of the drawing die mold.

When employing the ram extrusion method, the extrusion temperature of the compressed crosslinked particles is usually set in the range of 100 to 135°C, and extrusion molding is preferably carried out at a temperature lower than the melting point of the crosslinked particles used. In addition, by using the drawing die mold, the pressure during extrusion is higher than that in the normal ram extrusion molding method, which increases the mobility of crosslinked particles and improves the fluidity of particles, resulting in excellent moldability. It is in.

Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to these Examples.

[Measurement of physical properties of ethylene polymer particles (unirradiated particles)]
In the following examples, the specific surface area, intrinsic viscosity [η], bulk density, and melting point of the ethylene polymer particles (unirradiated particles) were measured according to the following methods.

(Specific surface area)
Adsorption and desorption isotherms of ethylene polymer particles were measured by a nitrogen gas adsorption method using a high-precision gas adsorption device (LA-950, manufactured by Microtrac Bell Co., Ltd.).
The specific surface area of the ethylene polymer particles was determined from the adsorption/desorption isotherm using the BET method as an analysis method.
Note that before measuring the adsorption/desorption isotherm, deaeration treatment was performed using a pretreatment device (BELPREP VAC-II, manufactured by Microtrac Bell Co., Ltd.).

(Intrinsic viscosity [η])
The intrinsic viscosity [η] of the ethylene polymer particles is determined by dissolving the particles in decalin and measuring the particles in decalin at a temperature of 135°C using a fully automatic viscosity measuring device (manufactured by Rigosha Co., Ltd., VMR-053UPC). did.

(bulk density)
The bulk density of the ethylene polymer particles was measured using a standard bulk specific gravity meter (JIS K-6720 for vinyl chloride, manufactured by Tsutsui Rikagaku Kiki Co., Ltd.). An attached 100 mL SUS container whose mass had been measured in advance was set, and ethylene polymer particles were filled through the funnel of a standard bulk specific gravity meter (manufactured by Tsutsui Rikagaku Kiki Co., Ltd., JIS K-6720 for vinyl chloride). Excess ethylene polymer particles on the SUS container were removed with a spatula to accurately adjust the volume to 100 mL, and the mass was measured again to calculate the bulk density.

(melting point)
Using a differential scanning calorimeter (Discovery DSC2500 manufactured by TA Instruments), a sample (approximately 5 mg) was heated under a nitrogen atmosphere (1) at a rate of 10°C/min from 30°C to 200°C and held for 10 minutes; 2) After cooling to 30°C at 10°C/min and holding at 30°C for 1 minute, (3) heating up to 200°C at 10°C/min. The temperature at the apex of the crystal melting peak in the heating process of (1) above was defined as the melting point.

[Measurement of physical properties of crosslinked ethylene polymer particles (crosslinked particles)]
In the following examples, the gel fraction of crosslinked particles was measured according to the method described below. The specific surface area and melting point of the crosslinked particles were measured in the same manner as for the non-irradiated particles.

(gel fraction)
The gel fraction of the crosslinked particles was determined by placing approximately 25 mg of the sample into a metal mesh using a Soxhlet extractor, and extracting the sample in o-dichlorobenzene at 145°C for 2 hours. It was calculated using the following formula from the mass of .
Gel fraction (%) = (sample remaining in wire mesh [g]/amount of preparation [g]) x 100

[Measurement of physical properties of molded object]
In the following examples, the amount of wear of the molded bodies was measured according to the following method.

(Amount of wear)
A glass abrasion element (U-shaped, width 20 mm, height 30 mm, thickness 4.5 mm), a load of 3 kg was applied to this glass abrasion element, and the molded body was reciprocated 5 times in the length direction at a stroke of 100 mm and a test speed of 30 reciprocations/min. A sliding test was conducted ,000 times, the mass of the molded body before and after the test was measured, and the amount of wear (mg) was calculated.

[Manufacture example 1]
≪Manufacture of ethylene polymer particles≫
<Preparation of component (i)>
66.1 g (0.694 mol) of anhydrous magnesium chloride, 246 g (246 g) of dehydrated decane, and 271 g (2.08 mol) of 2-ethylhexyl alcohol were charged into a 1 L glass container equipped with a stirrer and sufficiently purged with nitrogen, and reacted at 145°C for 4 hours. A uniform transparent component (i') of 1.0 mol/L in terms of Mg atoms was obtained.
The component (i') was diluted with dehydrated decane to obtain a homogeneous and transparent component (i) having a concentration of 0.25 mol/L in terms of Mg atoms.

<Ethylene polymerization>
721 kg of dehydrated decane and 2.7 mol of triisobutylaluminum (calculated as Al atoms) were charged into a 1.6 m ³ reactor equipped with a stirrer and sufficiently purged with nitrogen. After raising the temperature to 60° C., 0.86 mol of component (i) was charged in terms of Mg atoms, and the mixture was stirred for 15 minutes. Thereafter, the reactor was cooled to 40° C., and ethylene gas was blown into the reactor until the internal pressure reached 0.1 MPaG. Next, 4.3 mmol of the following transition metal compound (B-1) in terms of Ti atoms was charged, followed by 5.8 g of ADEKA Pluronic (registered trademark) L-71 (manufactured by ADEKA Corporation) and 2.7 NL of hydrogen. After charging, a polymerization reaction was carried out at 50° C. for 117 minutes while supplying ethylene gas so that the total pressure was 0.6 MPaG. After the polymerization was completed, the mixture was filtered and washed with decane, washed with hexane, and dried under reduced pressure at 80° C. for 18 hours to obtain 52.5 kg of ethylene polymer particles. The obtained ethylene polymer particles (unirradiated particles) were evaluated for various physical properties according to the above method. The results are shown in Table 1.

[Example 1]
≪Production of crosslinked ethylene polymer particles≫
<Radiation (electron beam) irradiation>
The ethylene polymer particles obtained in Production Example 1 were sealed together with an oxygen absorber in an aluminum zipper bag. In order to uniformly irradiate the electron beam, the thickness of the bag containing the ethylene polymer particles and the oxygen scavenger was leveled to 2 cm or less. The bag containing the sample was irradiated with an electron beam in an oxygen-free environment at an acceleration voltage of 2 MeV and an irradiation dose of 50 kGy to obtain crosslinked ethylene polymer particles. The irradiation dose was measured by attaching a dosimeter (FTR-125 manufactured by Fuji Film Co., Ltd.) to the aluminum zipper bag. The obtained crosslinked ethylene polymer particles (crosslinked particles) were evaluated for various physical properties according to the method described above. The results are shown in Table 1.

≪Preparation of molded body≫
After setting the obtained crosslinked ethylene polymer particles in a cylinder using Capillarograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd.), the extrusion temperature was set to 130°C, and the extrusion speed was 100 mm/min. An extrusion molded product (length 10 cm, width 6 mm, thickness 2 mm) was produced by passing through a drawing die mold having the same shape. The concave tapered drawing die had an entrance cross-sectional area of 0.79 cm ² , an exit cross-sectional area (rectangular) of 0.12 cm ² , and a length of 3 cm. The cylinder diameter was 1 cm, and the cylinder cross-sectional area was 0.79 ^cm2 , which was the same as the drawing die entrance cross-sectional area. A wear test was carried out on the obtained molded article according to the method described above. The results are shown in Table 1.

[Example 2 and 3]
Crosslinked ethylene polymer particles and molded bodies were obtained in the same manner as in Example 1, except that electron beam irradiation was performed at the irradiation dose shown in Table 1. Various physical properties of the obtained crosslinked particles and molded bodies were evaluated according to the above-mentioned methods. The results are shown in Table 1.

[Comparative example 1]
≪Preparation of molded body≫
In Example 1, the obtained ethylene polymer particles were not irradiated with radiation (electron beam), that is, ethylene polymer particles that had not been irradiated with electron beams were used to prepare the molded body. A molded article was obtained in the same manner as in Example 1 except for the above. The amount of wear of the obtained molded article was evaluated according to the method described above. The results are shown in Table 1.

The molded product using uncrosslinked, unirradiated particles that was not subjected to electron beam irradiation (Comparative Example 1) had a greater amount of wear than the molded product using crosslinked particles (Examples 1 to 3). It became.

Claims (6)

Crosslinked ethylene polymer particles obtained by crosslinking ethylene polymer particles that meet the following requirements (i) and (ii) and have a gel fraction in the range of 50 to 95%:
(i) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is greater than 2.00 m ² /g and 30.0 m ² /g or less;
(ii) The intrinsic viscosity [η] measured at 135° C. in a decalin solvent is 5 to 50 dl/g. The crosslinked ethylene polymer particles according to claim 1, wherein the ethylene polymer particles satisfy the following requirement (iii):
(iii) The bulk density is 0.01 to 0.20 g/mL. The crosslinked ethylene polymer particles according to claim 1, which satisfy the following requirement (I):
(I) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is 1.00 to 30.0 m ² /g. Crosslinked ethylene polymer particles that satisfy the following requirement (I) and have a gel fraction in the range of 50 to 95%:
(I) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is 1.00 to 30.0 m ² /g. A molded article comprising the crosslinked ethylene polymer particles according to any one of claims 1 to 4. A step of irradiating ethylene polymer particles that meet the following requirements (i) and (ii) to obtain crosslinked ethylene polymer particles;
A method for producing a molded body, comprising a step of extrusion molding at a temperature lower than the melting point of the crosslinked ethylene polymer particles:
(i) The specific surface area determined by the BET method from the adsorption/desorption isotherm measured by the nitrogen gas adsorption method is greater than 2.00 m ² /g and 30.0 m ² /g or less;
(ii) The intrinsic viscosity [η] measured at 135° C. in a decalin solvent is 5 to 50 dl/g.