JP7547769B2 - Ultra-high molecular weight polyethylene - Google Patents

Description

The present invention relates to a new ultra-high molecular weight polyethylene that has a good balance between processability and the mechanical properties of the molded product, and is excellent in elongation, toughness, impact resistance, etc. while maintaining the high mechanical strength that is characteristic of ultra-high molecular weight polyethylene with a narrow molecular weight distribution.

Ultra-high molecular weight polyethylene has traditionally been known to have superior impact resistance, self-lubrication, abrasion resistance, sliding properties, weather resistance, chemical resistance, dimensional stability, etc. compared to general-purpose polyethylene, and to have physical properties comparable to those of engineering plastics.

However, because of its high molecular weight, ultra-high molecular weight polyethylene has low fluidity when melted, and it is difficult to mold it by kneading and extrusion like ordinary polyethylene, which has a molecular weight in the range of several tens of thousands to about 500,000. Therefore, ultra-high molecular weight polyethylene is molded by a method such as direct sintering of the polymer powder obtained by polymerization, compression molding, extrusion molding using a ram extruder in which extrusion molding is performed while intermittently compressing, and a method in which the polyethylene is extruded in a state dispersed in a solvent or the like and then the solvent is removed. However, these molding methods have a high technical difficulty and it is difficult to obtain a molded product. Furthermore, weak points are generated due to the existence of localized high viscosity areas caused by entanglement of polymer chains and the formation of sparse areas during compression due to insufficient fluidity of polymer particles, so that the mechanical strength that the obtained molded product should have cannot be expressed and the mechanical strength is relatively low.

As a means of increasing the mechanical strength of molded bodies, ultra-high molecular weight polyethylene with a narrow molecular weight distribution using catalysts such as metallocene catalysts has been proposed (see, for example, Patent Documents 1 and 2).

Patent No. 4868853 JP 2006-36988 A

However, in the ultra-high molecular weight polyethylene proposed in Patent Documents 1 and 2, although improved performance as a molded product is observed, the higher the molecular weight of the ultra-high molecular weight polyethylene, the higher the melt viscosity becomes, and therefore the higher the molecular weight, the more likely it is that poor fusion occurs at the grain boundaries between particles, and the effect expected from the molecular weight cannot be fully realized, resulting in a poor balance of product properties.

To address this issue, molding is done at temperatures well above the melting point, but this results in issues such as discoloration due to oxidation degradation of the resin.

The present invention has been made in consideration of the above problems, and aims to provide a new ultra-high molecular weight polyethylene that is capable of supplying molded products with an excellent balance of physical properties, including excellent strength, heat resistance, and chemical resistance, as well as excellent processability, elongation, toughness, impact resistance, etc.

As a result of extensive research into solving the above problems, the inventors discovered that ultra-high molecular weight polyethylene that satisfies certain characteristics provides an excellent balance between processability and the mechanical properties of the molded product, and thus completed the present invention.

That is, the present invention relates to an ultra-high molecular weight polyethylene which is characterized by satisfying at least the following characteristics (1) to (4):
(1) The intrinsic viscosity ([η]) measured at 135° C. is 12 dL/g or more and 80 dL/g or less.
(2) In gel permeation chromatography (GPC), the half-value width calculated from a GPC pattern with the common logarithm (log(M)) of the molecular weight (M) on the horizontal axis is 1.3 or less.
(3) In differential scanning calorimetry (DSC), when the temperature is raised from 0° C. to 230° C. at a heating rate of 2° C./min, the measured melting pattern shows a single peak.
(4) In the melting pattern of (3), the temperature on the lower side corresponding to a heat flux that is 10% of the heat flux of the melting peak is 9° C. or more lower than the melting point.

The present invention is described in detail below.

The ultra-high molecular weight polyethylene of the present invention satisfies at least the following characteristics: (1) an intrinsic viscosity ([η]) measured at 135°C of 12 dL/g or more and 80 dL/g or less; (2) in gel permeation chromatography (hereinafter referred to as GPC), a half-width calculated from a GPC pattern with the common logarithm (log(M)) of molecular weight (M) on the horizontal axis is 1.3 or less; (3) in differential scanning calorimetry (hereinafter referred to as DSC), when heated from 0°C to 230°C at a heating rate of 2°C/min, the measured melting pattern shows a single peak; and (4) in the melting pattern of (3), the temperature on the low-temperature side corresponding to a heat flux that is 10% of the heat flux of the melting peak is 9°C or more lower than the melting point.

The ultra-high molecular weight polyethylene of the present invention belongs to the category called polyethylene, and examples thereof include ethylene homopolymers; ethylene-α-olefin copolymers such as ethylene-propylene copolymers, ethylene-1-butene copolymers, ethylene-1-hexene copolymers, and ethylene-1-octene copolymers; and the like.

The ultra-high molecular weight polyethylene of the present invention has (1) an intrinsic viscosity ([η]) of 12 dL/g or more and 80 dL/g or less, and preferably 14 dL/g or more and 50 dL/g or less, since it has excellent moldability and mechanical properties when molded into a molded article. Here, if the intrinsic viscosity ([η]) is less than 12 dL/g, the mechanical properties will be poor when molded into a molded article. On the other hand, if the intrinsic viscosity ([η]) is more than 80 dL/g, the flowability when melted is low, and the moldability will be very poor.

The intrinsic viscosity ([η]) in the present invention can be measured, for example, by using an Ubbelohde viscometer and measuring a solution with a polymer concentration of 0.0005 to 0.01 wt % in decalin as a solvent at 135°C.

The ultra-high molecular weight polyethylene of the present invention is characterized by being an ultra-high molecular weight polyethylene with a narrow molecular weight distribution, and may contain some low molecular weight components as long as it is mainly composed of ultra-high molecular weight components. (2) In GPC, the half-width calculated from the GPC pattern with the common logarithm (log(M)) of the molecular weight (M) on the horizontal axis is 1.3 or less, which satisfies the characteristics of polyethylene with a narrow molecular weight distribution. Here, if the half-width exceeds 1.3, only molded products with inferior strength such as tensile breaking stress can be obtained. The half-width is the difference between the logM of two points at which half the maximum elution amount is detected in a GPC pattern with the weight fraction of the elution amount of each molecular weight component in the ultra-high molecular weight polyethylene on the vertical axis and the common logarithm of the molecular weight (M) on the horizontal axis.

The ultra-high molecular weight polyethylene of the present invention (3) exhibits a unimodal melting pattern when measured in a DSC when heated from 0°C to 230°C at a heating rate of 2°C/min. A unimodal melting pattern is a melting pattern that does not have either a second or more melting points (melting peaks) or a shoulder. If the polyethylene exhibits a melting pattern other than a unimodal one, only molded articles that are inferior in strength, such as tensile breaking stress, can be obtained.

In the ultra-high molecular weight polyethylene of the present invention, (4) in the melting pattern of (3) above, the low-temperature side temperature corresponding to a heat flux of 10% of the heat flux of the melting peak is at least 9°C lower than the melting point, and preferably at least 10°C lower. The heat flux at each temperature in the melting pattern can be determined as the difference from the baseline (stable temperature range) on the low-temperature side of the melting pattern. Here, if the temperature difference between the low-temperature side temperature corresponding to a heat flux of 10% of the heat flux of the melting peak and the melting point is less than 9°C, the fusion properties during molding are poor, and the desired molded body properties cannot be obtained.

The ultra-high molecular weight polyethylene of the present invention may be in any form so long as it satisfies at least all of the above characteristics (1) to (4), and is preferably composed of at least two components having different molecular weights, such as a high molecular weight component and a low molecular weight component, and is particularly preferably an ultra-high molecular weight polyethylene comprising, as the main components, a high molecular weight component having an intrinsic viscosity ([η]) of 12 dL/g to 100 dL/g and a low molecular weight component having an intrinsic viscosity ([η]) of 1.2 dL/g to 9 dL/g. In this case, the ratio of the intrinsic viscosities ([η]) of the high molecular weight component to the low molecular weight component, [η] high _{molecular weight component} /[η] _{low molecular weight component} , is preferably 1.5 to 20. In the case of ultra-high molecular weight polyethylene composed of a high molecular weight component and a low molecular weight component, the ratio of the low molecular weight component is preferably 1 part by weight or more and 20 parts by weight or less, and particularly preferably 1 part by weight or more and 14 parts by weight or less, per 100 parts by weight of the high molecular weight component, because this improves fusion properties during molding and improves the mechanical properties (strength, elongation, toughness, impact resistance) of the obtained molded body.

The ultra-high molecular weight polyethylene of the present invention is also less likely to cause corrosion of the molding machine during molding, and the use of neutralizing agents such as metal soaps is unnecessary or can be reduced, reducing mold contamination and poor fusion between particles due to bleeding of these neutralizing agents. Therefore, it is preferable that the chlorine content is low, and in particular (5) the chlorine content is preferably 1 ppm or less, and more preferably 0.5 ppm or less.

The ultra-high molecular weight polyethylene of the present invention has excellent fusion properties between raw materials when raw materials such as particles are molded into a molded article, and is excellent in impact resistance, elongation, etc., and among these, (6) it is preferable that the Izod impact strength measured on a test piece sample having a double notch (razor notch) by a method in accordance with ASTM D256 is 60 kJ/ ^m2 or more, and particularly preferably 80 kJ/ ^m2 or more.

The ultra-high molecular weight polyethylene of the present invention preferably has a tensile elongation at break (TB) and intrinsic viscosity ([η]) that satisfy the following relationship (a):
TB≧3200×[η] ^-089 (a)
The ultra-high molecular weight polyethylene of the present invention preferably has a particulate shape since this provides excellent handleability, and when it has a particulate shape, it preferably has a bulk density of 300 kg/ ^m3 or more and 600 kg/ ^m3 or less since this provides excellent fluidity and filling properties, particularly during molding. The bulk density can be measured, for example, by a method in accordance with JIS K6760 (1995).

In addition, since the moldability is particularly excellent, (8) the median diameter is preferably 5 μm or more and 500 μm or less, particularly preferably 5 μm or more and 300 μm or less, and further preferably 50 μm or more and 300 μm or less. The median diameter is the particle size at which the cumulative weight is 50% when the particle size distribution is calculated, and is generally taken as a guide to the average particle size and is also expressed as D50. The particle size distribution can be, for example, a sieving test method using a standard sieve specified in JIS Z8801, a laser diffraction method, or a method of analyzing the particle size distribution of particles observed by an optical or electron microscope through image analysis, etc.

Since the ultra-high molecular weight polyethylene of the present invention has excellent moldability and the physical properties of the resulting molded article are good, the geometric standard deviation of the particle size distribution is preferably 0.25 or less, particularly preferably 0.15 or less. The geometric standard deviation is determined by measuring the particle size distribution by the method for measuring the median size, plotting the particle size and the weight fraction on a logarithmic probability paper, and using the particle size (median size, D50) corresponding to a weight fraction of 50% accumulated from the smaller mesh side and the particle size (D84) corresponding to a weight fraction of 84% accumulated from the smaller mesh side, according to the following relational formula (b).
Standard deviation = log (D84/D50) (b)
The method for producing the ultra-high molecular weight polyethylene of the present invention is not particularly limited, and among them, a method that enables efficient production of the ultra-high molecular weight polyethylene of the present invention will be exemplified below.

Examples of efficient methods for producing the ultra-high molecular weight polyethylene of the present invention include a method of polymerization in multiple stages under multiple polymerization conditions, which results in components with different molecular weights, a method of polymerization in which two types of transition metal compounds, etc., are supported on a catalyst carrier and polymerized to produce polymers with different molecular weights under the same conditions, and a combination of these two methods.

As a catalyst for producing these two-component polyethylenes, it is preferable to use a catalyst system using a transition metal compound, which can produce polyethylene with a narrow molecular weight distribution.Specific examples include metallocene complexes, which are complexes that form a sandwich structure with two ligands and a central metal selected from ligands having a cyclopentadienyl skeleton such as a (substituted) cyclopentadienyl ring, a (substituted) indenyl ring, a (substituted) fluorenyl ring, or a (substituted) azulenyl ring; half-metallocene complexes, which are complexes having one (substituted) cyclopentadienyl ring, a (substituted) indenyl ring, or a (substituted) fluorenyl ring; post-metallocene complexes such as silylamide complexes, phenoxyimide complexes that do not have a cyclopentadienyl skeleton and have ligands such as an alkoxy group, an amide group, or an imino group, and pyridylimino complexes; and the like.

Then, examples of methods include a method in which these transition metal compounds are polymerized by gas phase polymerization or suspension polymerization under conditions in which polyethylene does not dissolve in the polymerization solvent, using particles of a carrier such as an ionized ionic compound, a clay compound, or an aluminoxane-supported co-catalyst, or, if these co-catalysts are particulate, a supported catalyst in which the transition metal compound is supported on the particles.

One example of a catalyst system using a transition metal compound for producing ultra-high molecular weight polyethylene with a suitable molecular weight distribution is a metallocene catalyst obtained from at least a transition metal compound (A), an organo-modified clay (B) modified with an aliphatic salt, and an organoaluminum compound (C).

Examples of the transition metal compound (A) (hereinafter referred to as component (A)) include transition metal compound complexes having a (substituted) cyclopentadienyl group and a (substituted) fluorenyl group, transition metal compound complexes having a (substituted) cyclopentadienyl group and a (substituted) indenyl group, transition metal compound complexes having a (substituted) indenyl group and a (substituted) fluorenyl group, etc., and examples of the transition metal in these cases include zirconium, hafnium, etc.

Examples of the organically modified clay (B) (hereinafter referred to as component (B)) modified with an aliphatic salt include clays modified with aliphatic salts such as aliphatic ammonium salts and aliphatic phosphonium salts.

The clay compound constituting component (B) may be any that belongs to the category of clay compounds, and may be a natural or synthetic product. Examples of such compounds include kaolinite, talc, smectite, vermiculite, mica, brittle mica, and argillite. Among these, smectite, particularly hectorite or montmorillonite, is preferred. Component (B) can be obtained by introducing the aliphatic salt between the layers of the clay compound to form an ion complex.

As the organoaluminum compound (C) (hereinafter referred to as component (C)), any compound that falls within the category of organoaluminum compounds can be used, such as alkylaluminums such as trimethylaluminum, triethylaluminum, and triisobutylaluminum.

Regarding the method of preparing the organic transition metal compound catalyst, any method may be used as long as it is possible to prepare a catalyst containing the (A), (B) and (C) components. For example, a method of mixing the (A), (B) and (C) components in a solvent that is inert to them or using the monomer to be polymerized as a solvent can be mentioned. There is also no restriction on the order in which the (A), (B) and (C) components are reacted with each other, and there is also no restriction on the temperature and time at which this treatment is carried out. It is also possible to prepare a catalyst using two or more types of each of the (A), (B) and (C) components.

The polymerization conditions, such as the polymerization temperature, polymerization time, polymerization pressure, and monomer concentration, when producing the ultra-high molecular weight polyethylene of the present invention can be selected arbitrarily, and it is preferable to carry out the polymerization at a temperature of 0 to 100°C, for a polymerization time of 10 seconds to 20 hours, and at a polymerization pressure of normal pressure to 100 MPa. It is also possible to adjust the molecular weight using hydrogen or the like during polymerization. The polymerization can be carried out by any of a batch method, a semi-continuous method, and a continuous method, and it is also possible to carry out the polymerization in two or more stages by changing the polymerization conditions. The polyethylene obtained after the polymerization is also obtained by separating and recovering it from the polymerization solvent by a conventionally known method, and drying it.

The molded article made of the ultra-high molecular weight polyethylene of the present invention can be obtained by a known molding method. Specific examples include extrusion molding such as ram extrusion, compression molding, powder coating, sheet molding, roll molding, and stretch molding in a state dissolved or mixed in various solvents. Thus, the molded article of the present invention has high strength even after molding, and can be used for lining materials, parts such as gears in manufacturing machines for food, semiconductors, optical materials, medical components, etc., prosthetic limbs, artificial joints, sporting goods, microporous membranes, nets, ropes, gloves, etc.

The ultra-high molecular weight polyethylene of the present invention has a narrow molecular weight distribution and is excellent in elongation, toughness, impact resistance, etc. while having high strength. It is an ultra-high molecular weight polyethylene with an excellent balance between processability and the mechanical properties of the molded product. Therefore, the molded product obtained has excellent mechanical strength, heat resistance, and abrasion resistance, and has excellent properties as a base material for various industrial equipment, etc.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Unless otherwise noted, the reagents used were either commercially available or synthesized according to known methods.

A jet mill (Seishin Enterprise Co., Ltd., (product name) CO-JET SYSTEM α MARK III) was used to grind the organically modified clay, and the particle size after grinding was measured using a Microtrack particle size distribution measuring device (Nikkiso Co., Ltd., (product name) MT3300) using ethanol as a dispersant.

The preparation of the catalyst for ultra-high molecular weight polyethylene production, the production of ultra-high molecular weight polyethylene, and the solvent purification were all carried out under an inert gas atmosphere. The hexane solution of triisobutylaluminum (20 wt%) manufactured by Toso Finechem Co., Ltd. was used.

Furthermore, the physical properties of the ultra-high molecular weight polyethylene in the examples were measured using the methods shown below.

～Measurement of intrinsic viscosity～
The measurement was carried out using an Ubbelohde viscometer, using decalin as a solvent, at 135° C., and with an ultra-high molecular weight polyethylene concentration of 0.005 wt %.

～GPC measurement～
A GPC apparatus (SSC-7110, product name, manufactured by Senshu Scientific Co., Ltd.) and columns (one TSKguardcolumnH _HR (S)HT, product name, manufactured by Tosoh Corporation, and two TSKgelGMH _HR -H(S)HT, product name, manufactured by Tosoh Corporation) were used, the column temperature was set to 210° C., and 1-chloronaphthalene was used as the eluent for the measurement. The measurement sample was prepared at a concentration of 0.5 mg/ml, and 0.2 ml was injected for measurement. The molecular weight calibration curve was calibrated using a polystyrene sample with a known molecular weight. The molecular weight was calculated by converting it into the molecular weight of polyethylene using the Q factor.

In the obtained GPC pattern (the vertical axis is the weight fraction of the elution amount of each molecular weight component, and the horizontal axis is the common logarithm of the molecular weight (M)), the half-width was calculated as the difference between the logM values of the two points where half the maximum elution amount was detected.

～Melt pattern measurement～
Using a differential scanning calorimeter (DSC) (manufactured by SII NanoTechnology, Inc., product name: DSC6220), the temperature was raised from 0°C to 230°C at a heating rate of 2°C/min, and then the ultra-high molecular weight polyethylene was allowed to stand for 5 minutes to completely melt. The crystalline melting peak at this time was taken as the melting point (Tm). The amount of the ultra-high molecular weight polyethylene sample was 5 mg.

The heat flux was determined by taking 30°C, where the heat flux is stable, as the standard, and determining the difference between the measured heat flux at 30°C and the measured heat flux at a target temperature such as the melting point as the heat flux at that temperature. The heat flux at the melting point (Tm) was then calculated, and two temperatures were determined where the heat flux was 10% of that, and the temperature difference between one of these points, which was lower than the melting point, and the melting point was determined.

～Measurement of chlorine content～
Ultra-high molecular weight polyethylene was completely combusted in a combustion furnace, and the combustion gas was blown into an absorbing liquid to absorb chlorine ions. The chlorine content in the ultra-high molecular weight polyethylene was measured by ion chromatography (manufactured by Tosoh Corporation, product name: IC2010) using this absorbing liquid.

～Measurement of bulk density～
The measurement was performed according to a method in accordance with JIS K6760 (1995).

~Measuring median diameter and standard deviation~
Using nine types of sieves (mesh size: 710 μm, 500 μm, 355 μm, 250 μm, 180 μm, 150 μm, 106 μm, 75 μm, 53 μm) specified in JIS Z8801, the weight of the particles remaining on each sieve obtained when classifying 80 g of ultra-high molecular weight polyethylene was integrated from the side with the smaller mesh size, and the median size was determined by measuring the particle size at 50% weight. The geometric standard deviation was calculated by the following formula.
Standard deviation = log(D84/D50)
Here, D84 is the particle size corresponding to a weight fraction of 84% accumulated from the smaller mesh size side in a plot on log probability paper.

-Measurement of tensile breaking stress and nominal tensile breaking strain-
Polyethylene was filled into a metal frame of 150 mm x 150 mm, sandwiched between polyethylene terephthalate films, preheated at 190 ° C for 5 minutes, and then heated and compressed at 190 ° C and a press pressure of 20 MPa. Then, the mold temperature was 120 ° C and cooled for 10 minutes to obtain a pressed sheet with a thickness of 8 mm. Using a test piece cut out from this sheet, the tensile stress at break and the nominal tensile strain at break were measured using a tensile tester (manufactured by A & D Co., Ltd., (trade name) Tensilon RTG-1210) in accordance with JIS K 6922-2 (2005).

-Measurement of Izod impact strength-
A compression molded body molded in the same manner as for the tensile stress at break and the nominal tensile strain at break was cut to a length of 63.5 mm, a width of 12.7 mm, and a thickness of 6.35 mm, and then a double notch (razor notch, notch distance 3.56 mm) was added as a post-processing to prepare a test piece. The double notch Izod impact strength was measured using the test piece at a hammer capacity of 4 J and a temperature of 23° C. in accordance with ASTM D256.

Example 1
(1) Preparation of organically modified clay 300 ml of industrial alcohol (manufactured by Japan Alcohol Sales Co., Ltd., (trade name) Ekinen F-3) and 300 ml of distilled water were placed in a 1-liter flask, 15.0 g of concentrated hydrochloric acid and 64.2 g (120 mmol) of dioleylmethylamine (manufactured by Lion Corporation, (trade name) Armin M2O) were added, and the mixture was heated to 45 ° C. to disperse 100 g of synthetic hectorite (manufactured by BYK Japan, (trade name) Laponite RDS), and then heated to 60 ° C. and stirred for 1 hour while maintaining the temperature. After filtering the slurry, it was washed twice with 600 ml of water at 60 ° C. and dried in a dryer at 85 ° C. for 12 hours to obtain 160 g of organically modified clay. This organically modified clay was pulverized by a jet mill to a median diameter of 7 μm.

(2) Preparation of a suspension of a catalyst for producing ultra-high molecular weight polyethylene A 300 ml flask equipped with a thermometer and a reflux condenser was purged with nitrogen, and then 25.0 g of the organically modified clay obtained in (1) and 108 ml of hexane were added, followed by the addition of 0.600 g of diphenylmethylene(cyclopentadienyl)(2-(dimethylamino)-9-fluorenyl)zirconium dichloride and 142 ml of 20% triisobutylaluminum, and stirring for 3 hours at 60° C. After cooling to 45° C., the supernatant was removed and washed twice with 200 ml of hexane, followed by the addition of 200 ml of hexane to obtain a suspension of a catalyst for producing polyethylene (solid weight content: 11.5 wt %).

(3) Production of ultra-high molecular weight polyethylene 1.2 liters of hexane, 1.0 ml of 20% triisobutylaluminum, and 398 mg (corresponding to 45.8 mg of solid content) of the suspension of the catalyst for producing polyethylene obtained in (2) were added to a 2-liter autoclave equipped with an ethylene integrating flowmeter, and ethylene was continuously supplied so that the partial pressure was 0.9 MPa to perform slurry polymerization of ethylene. Ethylene polymerization (polymerization of high molecular weight components) was continued until the ethylene supply amount (consumption amount) in the integrating flowmeter reached 190 g, and then the autoclave was rapidly cooled to 50 ° C., and depressurized and purged with nitrogen were repeated to remove residual ethylene. After heating to 60 ° C. again, ethylene and hydrogen were continued to be supplied so that the ethylene partial pressure was 0.9 MPa and the hydrogen concentration in the gas phase of the autoclave was maintained at 2.4% relative to ethylene, and ethylene polymerization (polymerization of low molecular weight components) was continued until the ethylene supply amount in the integrating flowmeter reached 10 g. The pressure was then released, and the slurry was filtered and dried to obtain 198 g of ultra-high molecular weight polyethylene. The physical properties of the obtained ultra-high molecular weight polyethylene are shown in Table 1.

Comparative Example 1
(1) Preparation of organically modified clay and (2) preparation of suspension of catalyst for polyethylene production The same procedures as in Example 1 were carried out.

(3) Production of ultra-high molecular weight polyethylene 1.2 liters of hexane, 1.0 ml of 20% triisobutylaluminum, and 425 mg (corresponding to 48.9 mg of solid content) of the suspension of the catalyst for producing ultra-high molecular weight polyethylene obtained in (2) were added to a 2-liter autoclave, and the temperature was raised to 60° C., and then ethylene and hydrogen were continued to be supplied so that the ethylene partial pressure was 0.9 MPa and the hydrogen concentration in the gas phase of the autoclave was maintained at 600 ppm relative to ethylene, and ethylene polymerization was continued until the ethylene supply amount (consumption amount) in the integrating flow meter reached 200 g. Thereafter, the pressure was released, and the slurry was filtered and dried to obtain 201 g of ultra-high molecular weight polyethylene. The physical properties of the obtained ultra-high molecular weight polyethylene are shown in Table 2. The particles of this Comparative Example 1 had a lower nominal tensile break strain and Izod impact strength than those of Example 1.

Comparative Example 2
(1) Preparation of solid catalyst component 50 g (2.1 mol) of metallic magnesium powder and 210 g (0.62 mol) of titanium tetrabutoxide were placed in a 1-liter glass flask equipped with a thermometer and a reflux condenser, and 320 g (4.3 mol) of n-butanol in which 2.5 g of iodine had been dissolved was added at 90° C. over 2 hours. The mixture was stirred at 140° C. for 2 hours under a nitrogen blanket while removing the generated hydrogen gas to obtain a homogeneous solution. Then, 2100 ml of hexane was added.

90 g of this component (equivalent to 0.095 moles of magnesium) was placed in a 500 ml glass flask and diluted with 59 ml of hexane. 106 ml of a hexane solution containing 0.29 moles of isobutylaluminum dichloride was added dropwise at 45°C over a period of 2 hours, and the mixture was stirred at 70°C for an additional hour to obtain a solid catalyst component. The remaining unreacted materials and by-products were removed using a decantation method using hexane, and the composition was analyzed, revealing that the titanium content was 7.5 wt%.

(2) Production of ultra-high molecular weight polyethylene 1.2 liters of hexane, 1.0 ml of 20% triisobutylaluminum, and 4.9 mg of the solid catalyst component obtained in (1) were added to a 2-liter autoclave, and the temperature was raised to 80° C., after which ethylene and hydrogen were continued to be supplied so that the ethylene partial pressure was maintained at 0.6 MPa and the hydrogen concentration in the gas phase of the autoclave was maintained at 0.2% relative to ethylene. After 90 minutes, the pressure was released, and the slurry was filtered and dried to obtain 182 g of ultra-high molecular weight polyethylene. The physical properties of the obtained ultra-high molecular weight polyethylene are shown in Table 2.

The resulting ultra-high molecular weight polyethylene had a low tensile stress at break. It also contained 3 ppm of chlorine.

Example 2
(1) Preparation of organically modified clay and (2) preparation of suspension of catalyst for polyethylene production The same procedures as in Example 1 were carried out.

(3) Production of ultra-high molecular weight polyethylene 1.2 liters of hexane, 1.0 ml of 20% triisobutylaluminum, and 405 mg (corresponding to 46.6 mg of solid content) of the suspension of the catalyst for producing polyethylene obtained in (2) were added to a 2-liter autoclave equipped with an ethylene integrating flowmeter, and the temperature was raised to 60°C. After that, ethylene polymerization was continued until the ethylene partial pressure was 0.9 MPa and the ethylene supply (consumption) in the integrating flowmeter reached 180 g. The autoclave was then rapidly cooled to 50°C, and pressure was reduced and nitrogen purging was repeated to remove residual ethylene. After the temperature was raised again to 60°C, ethylene and hydrogen were continued to be supplied so that the ethylene partial pressure was 0.9 MPa and the hydrogen concentration in the gas phase of the autoclave was maintained at 2.3% relative to ethylene, and ethylene polymerization was continued until the ethylene supply in the integrating flowmeter reached 20 g. Thereafter, the pressure was reduced, and the slurry was filtered and dried to obtain 203 g of ultra-high molecular weight polyethylene. The physical properties of the resulting ultra-high molecular weight polyethylene are shown in Table 1.

Comparative Example 3
(1) Preparation of organically modified clay and (2) preparation of suspension of catalyst for polyethylene production The same procedures as in Example 1 were carried out.

(3) Production of ultra-high molecular weight polyethylene 1.2 liters of hexane, 1.0 ml of 20% triisobutylaluminum, and 430 mg (corresponding to 49.5 mg of solid content) of the suspension of the catalyst for producing ultra-high molecular weight polyethylene obtained in (2) were added to a 2-liter autoclave, and the temperature was raised to 60° C., after which ethylene was continuously fed so as to maintain the partial pressure at 0.9 MPa, and ethylene polymerization was continued until the ethylene feed (consumption) amount measured by the integrating flow meter reached 200 g. Thereafter, the pressure was released, and the slurry was filtered and dried to obtain 203 g of polyethylene having an intrinsic viscosity ([η]) of 21 dL/g.

(4) Production of polyethylene 1.2 liters of hexane, 1.0 ml of 20% triisobutylaluminum, and 350 mg (corresponding to 40.3 mg of solid content) of the suspension of the catalyst for producing ultra-high molecular weight polyethylene obtained in (2) were added to a 2-liter autoclave, and the temperature was raised to 60° C., after which ethylene and hydrogen were continued to be supplied so that the ethylene partial pressure was maintained at 0.9 MPa and the hydrogen concentration in the gas phase of the autoclave was maintained at 2.3% relative to ethylene, and ethylene polymerization was continued until the ethylene supply amount (consumption amount) measured by the integrating flow meter reached 200 g. Thereafter, the pressure was released, and the slurry was filtered and dried to obtain 208 g of polyethylene with an intrinsic viscosity ([η]) of 3.0 dL/g.

(5) Blend of ultra-high molecular weight polyethylene 180 g of the ultra-high molecular weight polyethylene produced in (3) and 20 g of the polyethylene produced in (4) were dry blended to obtain a dry blend with an ultra-high molecular weight polyethylene to polyethylene blend ratio (weight conversion) of 90/10. The physical properties of this dry blend are shown in Table 2. This blend had lower nominal tensile break strain and Izod impact strength than Example 2.

Figure 1 shows the melting patterns in differential scanning calorimetry of the particle blend of Comparative Example 3 and the ultra-high molecular weight polyethylene of Example 2. The particle blend of Comparative Example 3 has two melting points, whereas Example 2 has only one melting point, despite containing polyethylene of roughly the same molecular weight and blend ratio.

Example 3
(1) Preparation of organically modified clay The organically modified clay was prepared in the same manner as in Example 1.

(2) Preparation of a suspension of a catalyst for polyethylene production A 300 ml flask equipped with a thermometer and a reflux condenser was purged with nitrogen, and then 25.0 g of the organically modified clay obtained in (1) and 108 ml of hexane were added, followed by the addition of 0.786 g of diphenylmethylene(cyclopentadienyl)(2-(dimethylamino)-9-fluorenyl)hafnium dichloride and 142 ml of 20% triisobutylaluminum, and stirring for 3 hours at 60° C. After cooling to 45° C., the supernatant was removed and washed twice with 200 ml of hexane, followed by the addition of 200 ml of hexane to obtain a suspension of a catalyst for polyethylene production (solid weight content: 12.5 wt %).

(3) Production of ultra-high molecular weight polyethylene To a 2-liter autoclave equipped with an ethylene integrating flow meter, 1.2 liters of hexane, 1.0 ml of 20% triisobutylaluminum, and 315 mg (corresponding to 39.4 mg of solid content) of the suspension of the catalyst for polyethylene production obtained in (2) were added, and the temperature was raised to 70° C., after which 0.1 g of butene was added. Furthermore, ethylene and hydrogen were continued to be supplied so that the ethylene partial pressure and the hydrogen concentration in the gas phase of the autoclave could be maintained at 0.9 MPa and 100 ppm relative to ethylene, and ethylene polymerization was continued until the amount of ethylene supplied (amount consumed) reached 193 g as measured by the integrating flow meter. The autoclave was then rapidly cooled to 50° C., and the residual ethylene was removed by repeatedly depressurizing and purging with nitrogen. After the temperature was raised again to 70°C, 0.05 g of butene was added, and the supply of ethylene and hydrogen was continued so that the ethylene partial pressure was maintained at 0.9 MPa and the hydrogen concentration was maintained at 1.4% relative to ethylene, and ethylene polymerization was continued until the amount of ethylene supplied reached 10 g as measured by the integrating flow meter. The pressure was then released, and the slurry was filtered and dried to obtain 210 g of ultra-high molecular weight polyethylene. The physical properties of the obtained ultra-high molecular weight polyethylene are shown in Table 1.

Example 4
(1) Preparation of organically modified clay and (2) preparation of suspension of catalyst for polyethylene production The same procedures as in Example 3 were carried out.

(3) Production of ultra-high molecular weight polyethylene 1.2 liters of hexane, 1.0 ml of 20% triisobutylaluminum, and 295 mg (corresponding to 36.7 mg of solid content) of the suspension of the catalyst for polyethylene production obtained in (2) were added to a 2-liter autoclave equipped with an ethylene integrating flowmeter, and the temperature was raised to 70° C., and then ethylene and hydrogen were continued to be supplied so that the ethylene partial pressure was maintained at 0.9 MPa and the hydrogen concentration in the gas phase of the autoclave was maintained at 90 ppm relative to ethylene. Ethylene polymerization was continued until the ethylene supply amount (consumption amount) measured by the integrating flowmeter reached 184 g. The autoclave was then rapidly cooled to 50° C., and pressure reduction and nitrogen purging were repeated to remove residual ethylene. The temperature was raised again to 70° C., and then ethylene and hydrogen were continued to be supplied so that the ethylene partial pressure was maintained at 0.9 MPa and the hydrogen concentration was maintained at 1.1% relative to ethylene. Ethylene polymerization was continued until the ethylene supply amount measured by the integrating flowmeter reached 16 g. The pressure was then released, and the slurry was filtered and dried to obtain 205 g of ultra-high molecular weight polyethylene. The physical properties of the obtained ultra-high molecular weight polyethylene are shown in Table 1.

: Melting pattern in differential scanning calorimetry of the blend of the ultra-high molecular weight polyethylene obtained in Example 2 and the blend obtained in Comparative Example 3.

The ultra-high molecular weight polyethylene of the present invention has a narrow molecular weight distribution and is excellent in elongation, toughness, impact resistance, etc. while having high strength. It is an ultra-high molecular weight polyethylene with an excellent balance between processability and the mechanical properties of the molded product. Therefore, the molded product obtained has excellent mechanical strength, heat resistance, and abrasion resistance and has excellent properties as a base material for various industrial equipment, etc., and therefore has extremely high industrial applicability.

Claims (5)

The ultra-high molecular weight polyethylene is a transition metal-metallocene complex catalyst-based polyethylene that satisfies at least the following characteristics (1) to (4):
(1) The intrinsic viscosity ([η]) measured at 135° C. is 12 dL/g or more and 80 dL/g or less.
(2) In gel permeation chromatography (GPC), the half-value width calculated from a GPC pattern with the common logarithm (log(M)) of the molecular weight (M) on the horizontal axis is 1.3 or less.
(3) In differential scanning calorimetry (DSC), when the temperature is raised from 0° C. to 230° C. at a heating rate of 2° C./min, the measured melting pattern shows a single peak.
(4) In the melting pattern of (3), the temperature on the lower side corresponding to a heat flux that is 10% of the heat flux of the melting peak is 9° C. or more lower than the melting point. 2. The ultra-high molecular weight polyethylene according to claim 1, further satisfying the following characteristic (5):
(5) The chlorine content is 1 ppm or less. 3. The ultra-high molecular weight polyethylene according to claim 1 or 2 , further satisfying the following characteristic (6) :
(6) The Izod impact strength measured on a double-notched (razor notched) test piece sample in accordance with ASTM D256 is 60 kJ/m2 ^or more. The ultra-high molecular weight polyethylene according to any one of claims 1 to 3 , further comprising a particle shape and satisfying the following properties (7) and (8) :
(7) The bulk density is 300 kg/m3 ^or more and 600 kg/m3 ^or less.
(8) The median diameter is 5 μm or more and 500 μm or less. The ultra-high molecular weight polyethylene according to any one of claims 1 to 3, further comprising: (9) a particle shape, and from a particle size distribution determined by a particle size-weight integral using a sieve specified in JIS Z8801, the standard deviation obtained as shown in the following formula (b) is 0.15 or less :
Standard deviation = log (D84/D50) (b)
(Here, D50 is the median diameter, and D84 is the particle diameter at a weight fraction of 84%.)