JP7538465B2 - Method for producing ethylene-based polymerization catalyst component, method for producing ethylene-based polymerization catalyst, and method for producing ethylene-based polymer - Google Patents

Description

The present invention relates to a method for producing an ethylene-based polymerization catalyst component, a method for producing an ethylene-based polymerization catalyst, and a method for producing an ethylene-based polymer. More specifically, the present invention relates to an ethylene-based polymerization catalyst component capable of producing an ultra-high molecular weight ethylene polymer, a method for producing an ethylene-based polymerization catalyst, and a method for producing an ethylene-based polymer.

Ethylene-based polymers are key materials that represent plastic materials in industrial fields. Ethylene-based polymers are widely used in a wide variety of technical fields, and therefore require a wide range of properties, such as molecular weight distribution and flowability, as well as mechanical and thermal properties, depending on the application and molding method.
In order to produce such ethylene polymers, various polymerization catalysts have been developed and improved. Among them, Phillips catalysts are used in addition to Ziegler catalysts and metallocene catalysts. Phillips catalysts are chromium catalysts in which a chromium compound is supported on an inorganic oxide carrier such as silica, silica-alumina, or silica-titania, and activated in a non-reducing atmosphere to convert at least some of the supported chromium atoms into hexavalent chromium atoms. Phillips catalysts produce ethylene polymers with a wide molecular weight distribution, and generally have good moldability, making them suitable for blow molding and the like.

In large blow-molded products, creep resistance and impact resistance are important properties. When ethylene polymers with a wide molecular weight distribution obtained using conventional Phillips catalysts are blow-molded into large products, the resulting molded products do not necessarily have a sufficient balance between creep resistance and impact resistance. Creep resistance and impact resistance are contradictory physical properties, and generally, when creep resistance improves, impact resistance decreases, and conversely, when impact resistance improves, creep resistance decreases.

Therefore, if an ethylene polymer having both excellent physical properties such as creep resistance and moldability can be obtained using the Phillips catalyst, it will be a material having a better balance of physical properties and moldability than the conventional level. However, since it is difficult at the present stage to precisely control the catalyst using the Phillips catalyst to introduce an appropriate amount of long chain branches of an appropriate length in an appropriate molecular weight region, no specific guidelines have yet been obtained for a method of improving both physical properties and moldability.
In an attempt to obtain an ethylene polymer having a good balance of physical properties and moldability using a Phillips catalyst, the use of a carrier having a specific structure has been investigated. For example, Patent Document 1 and Patent Document 2 disclose the use of highly porous silica having a specific surface area, average pore volume, and average pore diameter. Patent Document 3 discloses a technique for broadening the molecular weight distribution of a polymer by combining a Phillips catalyst obtained from silica having a specific structure with an organoaluminum compound. Furthermore, Patent Document 4 discloses the use of silica having a unique pore structure and crystallinity.
However, it is difficult to control the molecular weight distribution and composition distribution of the polymer using these catalysts, and it has not been possible to design a catalyst that will produce the desired material properties.

Therefore, attempts have been made to polymerize high molecular weight components and low molecular weight components using separate catalysts. For example, if a high molecular weight component with a high molecular weight and a wide molecular weight distribution is produced, and a low molecular weight component with a low molecular weight and a narrow molecular weight distribution is produced at the same time, the high molecular weight component can be increased and the low molecular weight component can be decreased, and both creep resistance and impact resistance can be improved. From this perspective, Patent Document 5 discloses that high molecular weight polyethylene can be obtained by a Phillips catalyst using a clay mineral as a carrier. Patent Documents 6 and 7 disclose that the molecular weight distribution of the obtained polymer can be controlled by combining a clay mineral with ordinary silica.
Furthermore, Patent Documents 7 and 8 disclose techniques for mixing different inorganic oxides and spray-drying and granulating them by spray-drying granulation.
As described above, various catalysts have been developed and various ethylene polymers have been synthesized, but the ethylene polymers produced using existing catalysts may not provide the desired effects. Therefore, a catalyst technology with good particle properties that can stably produce an ethylene polymer having an ultra-high molecular weight component as one of the variations of ethylene polymers is desired.

Special Publication No. 2002-533536 Patent No. 5821746 Special Publication No. 2006-512454 Special Publication No. 2007-517962 JP 2006-257255 A JP 2008-150566 A International Publication No. 2002/088196 Special Publication No. 2000-513402

The present invention has been made in view of the above-mentioned circumstances, and aims to provide an ethylene-based polymerization catalyst component with good particle properties that can stably produce an ethylene-based polymer having an ultra-high molecular weight component. The present invention also aims to provide a method for producing an ethylene-based polymerization catalyst with good particle properties that can stably produce an ethylene-based polymer having an ultra-high molecular weight component, and a method for producing an ethylene-based polymer that can stably produce an ethylene-based polymer having an ultra-high molecular weight component. As a result of intensive research to solve the above-mentioned problems, the present inventors have found that a catalyst technology with good particle properties that can stably produce an ethylene-based polymer having an ultra-high molecular weight component can be provided by using granulated particles with a specific average particle size obtained by spray-drying and granulating an inorganic oxide with a specific infrared absorption spectrum and average particle size, and based on this finding, the present invention has been completed. The present invention can be realized in the following forms.

[1] A method for producing an ethylene-based polymerization catalyst component, comprising preparing a slurry of the following components A and B in a mixing ratio by weight of component A:component B=1:99 to 100:0, and then spray-drying and granulating the prepared slurry to obtain granulated particles having an average particle size of 1 μm to 500 μm.
Component A: An inorganic oxide having the following properties 1, 2, and 3.
(Characteristic 1) Contains 90% or more by weight of _SiO2 .
(Characteristic 2) The average particle size is 0.01 μm to 3.0 μm.
(Characteristic 3) In an infrared absorption spectrum measured after calcination at 600° C. for 24 hours as a pretreatment for analysis, the ratio Py/Px of the peak intensity Py that is maximum in the range Y of 3700 cm ⁻¹ to 3799 cm ⁻¹ to the peak intensity Px that is maximum in the range X of 3600 cm ⁻¹ to 3699 cm ⁻¹ is less than 10.
Component B: An inorganic oxide having an average particle size of 0.01 μm to 50 μm.

[2] The method for producing an ethylene-based polymerization catalyst component according to [1], wherein the component A further has the following property 4:
(Characteristic 4) In powder X-ray diffraction, it has a peak with a half-width of 0.2° or more and 5° or less at 2θ=23° to 29°.

[3] The method for producing an ethylene-based polymerization catalyst component according to [1] or [2], characterized in that the component B is an inorganic oxide containing 90% by weight or more of _SiO2 .

[4] The method for producing an ethylene-based polymerization catalyst component according to any one of [1] to [3], characterized in that the slurry is adjusted to a combined weight of component A and component B of 5% by weight to 50% by weight ((component A + component B) / water slurry x 100).

[5] A method for producing an ethylene-based polymerization catalyst, comprising the steps of: (I) preparing a polymerization catalyst comprising:
Step (I): A chromium compound is supported on the granulated particles obtained by the production method according to any one of [1] to [4] to obtain a chromium compound-supported component.
Step (II): The chromium compound-supporting component obtained in step (I) is activated by calcination at 400° C. to 900° C. in a non-reducing atmosphere to convert at least a part of the chromium atoms into hexavalent chromium atoms.

[6] The method for producing an ethylene polymerization catalyst according to [5], characterized in that in step (I), the chromium compound-supported component containing 0.01% by weight to 2.0% by weight of chromium atoms is obtained.

[7] The method for producing an ethylene-based polymerization catalyst according to [5] or [6], characterized in that in step (II), 50% or more of the chromium atoms contained in the chromium compound-supported component are oxidized to hexavalent chromium.

[8] A method for producing an ethylene-based polymer, comprising polymerizing a monomer containing at least ethylene using an ethylene-based polymerization catalyst obtained by the method for producing an ethylene-based polymer according to any one of [5] to [7].

According to the method for producing an ethylene-based polymerization catalyst component of the present invention, an ethylene-based polymer having an ultra-high molecular weight component can be stably produced, and an ethylene-based polymerization catalyst having good particle properties can be provided.
According to the process for producing an ethylene polymer catalyst of the present invention, an ethylene polymer having an ultra-high molecular weight component can be stably produced, and an ethylene polymerization catalyst having good particle properties can be produced.
According to the process for producing an ethylene polymer of the present invention, an ethylene polymer having an ultra-high molecular weight component can be stably produced.

1 is a graph showing infrared absorption spectra of inorganic oxide particles A1 and inorganic oxide particles B1.

Hereinafter, the present invention will be described specifically and in detail for each item.
In this specification, when a numerical range is described using "to", the range includes the lower limit and the upper limit unless otherwise specified. For example, the description "10 to 20" includes both the lower limit "10" and the upper limit "20". In other words, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. Production method of an ethylene-based polymerization catalyst component The production method of an ethylene-based polymerization catalyst component is characterized in that a slurry is prepared from the following components A and B in a mixing ratio by weight of component A:component B=1:99 to 100:0, and then the prepared slurry is spray-dried and granulated to obtain granulated particles having an average particle size of 1 μm to 500 μm.
Component A: An inorganic oxide having the following properties 1, 2, and 3.
(Characteristic 1) Contains 90% or more by weight of _SiO2 .
(Characteristic 2) The average particle size is 0.01 μm to 3.0 μm.
(Characteristic 3) In an infrared absorption spectrum measured after calcination at 600° C. for 24 hours as a pretreatment for analysis, the ratio Py/Px of the peak intensity Py that is maximum in the range Y of 3700 cm ⁻¹ to 3799 cm ⁻¹ to the peak intensity Px that is maximum in the range X of 3600 cm ⁻¹ to 3699 cm ⁻¹ is less than 10.
Component B: An inorganic oxide having an average particle size of 0.01 μm to 50 μm.

2. Method for Producing Granulated Particles Granulated particles are obtained by preparing a slurry of components A and B in a mixing ratio by weight of component A:component B=1:99 to 100:0, and then spray-drying and granulating the prepared slurry. An example of component A is inorganic oxide particles A1 shown below. An example of component B is inorganic oxide particles B1 shown below.

2.1. Inorganic oxide particles A1 as component A
The following inorganic oxide particles A1 are suitable examples of inorganic oxides having the characteristics 1, 2, and 3. In addition to the characteristics 1, 2, and 3, the inorganic oxide particles A1 may also have a characteristic 4 and other characteristics.

(1) Characteristics of inorganic oxide particles A1
Characteristic 1 is a characteristic that the inorganic oxide particles _A1 contain 90% by weight or more of SiO2. In other words, the inorganic oxide particles A1 are inorganic oxides whose main component is _SiO2 . The content of _SiO2 in the inorganic oxide particles A1 may be 90% by weight or more, preferably 95% by weight or more, and more preferably 98% by weight or more. Of course, the content of _SiO2 may be 100% by weight. Since the inorganic oxide particles A1 are particles whose main component is _SiO2 , it is easy to control the shape of the inorganic oxide and has excellent catalytic performance.
When the content is less than 100% by weight, the remaining components may be any inorganic oxide components, but are preferably oxides containing metals of Groups 2, 3, 4, and 13 of the Periodic Table (Periodic Table according to the 1990 Rules for the Nomenclature of Inorganic Compounds).Specific examples include magnesia (MgO), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), zirconia (ZrO ₂ ), and composite oxides thereof, i.e., alumina-titania (Al ₂ O ₃ -TiO ₂ ), alumina-magnesia (Al ₂ O ₃ -MgO), alumina-zirconia (Al ₂ O ₃ -ZrO ₂ ), titania-magnesia (TiO ₂ -MgO), titania-zirconia (TiO ₂ -ZrO ₂ ), etc. Of these, magnesia, alumina and titania are preferred, with alumina and titania being more preferred.

(2) Characteristics 2 of Inorganic Oxide Particles A1
The characteristic 2 is that the inorganic oxide particles A1 have an average particle size of 0.01 μm to 3.0 μm, more preferably 0.05 μm to 2.5 μm, and further preferably 0.1 μm to 2.2 μm.
The average particle size of the particles of the chromium catalyst and its catalyst components can be determined by measuring the particle sizes of 20 particles of the chromium catalyst and its catalyst components using a scanning electron microscope (SEM) and averaging the measured values. In this study, the average particle size (median size) of particles with an average particle size of 0.1 μm or more was determined using a particle size distribution measuring device using the laser diffraction method, and the average particle size of particles with an average particle size of less than 0.1 μm was determined by SEM observation.
In the measurement method using the laser diffraction method, first, 0.05 g of inorganic oxide particles A1 is weighed out and slowly added to 9.95 g of distilled water while stirring with a stirrer to prepare a uniform 0.5 wt% inorganic oxide particles A1/water slurry. This inorganic oxide particles A1/water slurry is used as a sample and measured using a laser diffraction scattering type particle size measuring device (for example, a laser diffraction/scattering type particle size distribution measuring device LA-920 manufactured by Horiba, Ltd.) under the conditions of water as a dispersion medium, a refractive index of 1.3, and a shape factor of 1.0.

(3) Characteristics of inorganic oxide particles A1
Property 3 is that in an infrared absorption spectrum, the ratio Py/Px of a peak intensity Py having a maximum in a range Y of 3700 cm ^-1 to 3799 cm ^-1 to a peak intensity Px having a maximum in a range X of 3600 cm ^-1 to 3699 cm ^-1 is less than 10.
In the infrared absorption spectrum, the peak appearing near 3550 cm ⁻¹ is derived from hydrogen-bonded OH groups. The peak appearing near 3650 cm ⁻¹ is derived from OH groups at sites that cannot interact with others. On the other hand, the peak appearing near 3750 cm ⁻¹ is derived from isolated OH groups on the outer surface. Inorganic oxides that satisfy the requirement of the above-mentioned characteristic 3 have a relatively strong peak intensity near 3650 cm ⁻¹ . This indicates that the inorganic oxide particles A1 have a structure that contains many OH groups that are not involved in dehydration condensation even when heated to high temperatures. Such a structure is considered to be a thermally stable regular structure, and it is presumed that the regularity of the structure affects the arrangement of the OH groups.
In the graph of FIG. 1, the infrared absorption spectrum of one example of inorganic oxide particles A1 (Example described later) is shown by a solid line and a dashed dotted line.

(4) Characteristics of inorganic oxide particles A1
The inorganic oxide particles A1 preferably have a peak showing crystallinity at 2θ=23° to 29° with a half width of 0.2° to 5° in powder X-ray diffraction. When the inorganic oxide particles A1 are crystalline, the ethylene-based polymer tends to have a high molecular weight.

(5) Surface Area of Inorganic Oxide Particles A1 The surface area of inorganic oxide particles A1 is not particularly limited. From the viewpoint of supporting chromium atoms in a dispersed state, the surface area is preferably 10 m ² /g or more and 1000 m ² /g or less, more preferably 20 m ² /g or more and 500 m ² /g or less, and even more preferably 50 m ² /g or more and 400 m ² /g or less.

(6) Pore Volume of Inorganic Oxide Particles A1 The pore volume of the inorganic oxide particles A1 is not particularly limited, but the pore volume is preferably 0.05 to 5 mL/g, and more preferably 0.1 to 3 mL/g.

(7) Shape of Inorganic Oxide Particles A1 The shape of the inorganic oxide particles A1 is not particularly limited. For example, the inorganic oxide particles A1 may have a plate-like particle shape (first embodiment).
Alternatively, the inorganic oxide particles A1 may be in a form containing aggregates of plate-like inorganic oxide particles A1 (second form). In this second form, the inorganic oxide particles A1 may be composed only of aggregates. In addition, in this second form, aggregates of plate-like inorganic oxide particles A1 and non-aggregated particles of plate-like inorganic oxide particles A1 may be mixed.
The plate thickness T (nm) of the plate-like inorganic oxide particles A1 is not particularly limited. From the viewpoint of maintaining the crystalline structure and maintaining dispersibility in the polymer during polymerization, the average plate thickness T (nm) of the inorganic oxide particles A1 is preferably 1 nm or more and 100 nm or less, more preferably 5 nm or more and 50 nm or less, and even more preferably 10 nm or more and 40 nm or less.

2.2. Inorganic oxide particles B1 as component B
The ethylene-based polymerization catalyst component can contain inorganic oxide particles B1 in addition to inorganic oxide particles A1.
The inorganic oxide particles B1 are inorganic oxide particles having an average particle size of 0.01 μm to 50 μm. The inorganic oxide particles B1 are preferably amorphous.
The inorganic oxide particles B1 are preferably composed of at least one type of particles selected from the group consisting of particles whose main component is silica (SiO ₂ ), particles whose main component is silica-titania (SiO ₂ -TiO ₂ ), and particles whose main component is silica-alumina (SiO ₂ -Al ₂ O ₃ ). Here, the main component refers to a substance whose content (by weight) is 90% by weight or more.
The silica (SiO ₂ ) content in the particles whose main component is silica (SiO ₂ ) may be 90% by weight or more, preferably 95% by weight or more, and more preferably 98% by weight or more. Of course, the silica (SiO ₂ ) content may be 100% by weight.
The total content of silica (SiO ₂ ) and titania (TiO ₂ ) in the particles whose main component is silica-titania (SiO ₂ -TiO ₂ ) may be 90% by weight or more, preferably 95% by weight or more, and more preferably 98% by weight or more. Of course, the total content of silica (SiO ₂ ) and titania (TiO ₂ ) may be 100% by weight.
The total content of silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) in the particles _whose main component is silica-alumina (SiO 2 -Al 2 O ₃ ) may be 90% by weight or more, preferably 95% by weight or more, and more preferably 98% by weight or more. Of course, the total content of silica ( _{SiO 2} ) and alumina (Al ₂ O ₃ ) may be 100% by weight.
Among these, from the viewpoints of ease of controlling the particle shape of the inorganic oxide and catalyst performance, it is preferable that the inorganic oxide particles B1 are particles whose main component is silica (SiO ₂ ).
When particles whose main component is silica-titania (SiO ₂ --TiO ₂ ) are used, the particles contain titanium atoms in an amount of 0.2 to 40% by weight, preferably 0.5 to 30% by weight, and more preferably 1 to 20% by weight, as the metal component.
Furthermore, when particles whose main component is silica-zirconia (SiO ₂ --ZrO ₂ ) are used, the particles contain 0.2 to 40% by weight, preferably 0.5 to 30% by weight, and more preferably 1 to 20% by weight, of zirconium atoms as the metal component.
Furthermore, when particles whose main component is silica-alumina (SiO ₂ -Al ₂ O ₃ ) are used, the particles contain 0.2 to 40% by weight, preferably 0.5 to 30% by weight, and more preferably 1 to 20% by weight, of aluminum atoms as the metal component.

The average particle size of the inorganic oxide particles B1 is from 0.01 μm to 50 μm, preferably from 0.05 μm to 30 μm, and more preferably from 0.1 μm to 20 μm.
The average particle size of the inorganic oxide particles B1 can be determined in the same manner as the average particle size of the inorganic oxide particles A1.

The surface area of the inorganic oxide particles B1 is not particularly limited. From the viewpoint of supporting chromium atoms in a dispersed state, the surface area is preferably 100 m ² /g or more and 1000 m ² /g or less, more preferably 150 m ² /g or more and 950 m ² /g or less, and even more preferably 200 m ² /g or more and 900 m ² /g or less.

The pore volume of the inorganic oxide particles B1 is not particularly limited. From the viewpoint that the chromium atoms are supported in a dispersed state and that the particles are easily disintegrated during polymerization to allow the polymer to grow, the pore volume is preferably 0.1 mL/g or more and 5.0 mL/g or less, and more preferably 0.2 mL/g or more and 3.0 mL/g or less.

2.3. Mixing ratio of component A and component B (weight ratio)
The mixing ratio of components A and B, in terms of the weight ratio of each, is component A:component B=1:99 to 100:0. The mixing ratio of components A and B is preferably component A:component B=10:90 to 90:10, more preferably component A:component B=15:85 to 90:10, and even more preferably component A:component B=40:60 to 90:10.
The amount of component A is preferably 10 parts by weight or more, more preferably 15 parts by weight or more, and even more preferably 40 parts by weight or more, when the total weight of components A and B is 100 parts by weight. The upper limit of the amount of component A is 100 parts by weight. If the amount of component A is the lower limit or more, a high molecular weight polymer can be obtained.

2.4. Spray drying granulation of granulated particles In the spray drying granulation of granulated particles, water or an organic solvent such as methanol, ethanol, chloroform, methylene chloride, pentane, hexane, heptane, toluene, xylene, etc. can be used as a dispersion medium for the raw material slurry. Water is preferably used as the dispersion medium.

In the spray drying granulation of granulated particles, the slurry is preferably adjusted to 5% by weight to 50% by weight ((Component A+Component B)/water slurry×100) as the combined weight of Components A and B. The slurry concentration is more preferably 10% by weight to 45% by weight, and even more preferably 15% by weight to 40% by weight. The temperature at the inlet of the hot air in the spray drying granulation differs depending on the dispersion medium, but in the case of water, for example, the temperature is 80° C. to 260° C., and preferably 100° C. to 220° C.
In addition, organic substances, inorganic solvents, inorganic salts, and various binders may be used during granulation, such as sugar, dextrose, corn syrup, gelatin, glue, carboxymethylcelluloses, polyvinyl alcohol, water glass, magnesium chloride, aluminum sulfate, aluminum chloride, magnesium sulfate, alcohols, glycol, starch, casein, latex, polyethylene glycol, polyethylene oxide, tar, pitch, alumina sol, silica gel, gum arabic, and sodium alginate.

2.5. Average particle size of granulated particles The average particle size of granulated particles is 1 μm to 500 μm. The average particle size of granulated particles is preferably 2 μm to 300 μm, more preferably 5 μm to 200 μm. As a method for adjusting the average particle size of granulated particles, a method of controlling the slurry concentration during spray drying granulation or the slurry supply rate can be considered. If the average particle size is equal to or greater than the lower limit, the granulated particles are easily handled when carrying out steps (I) and (II) in the production method for an ethylene-based polymerization catalyst described below, which is preferable. If the average particle size is equal to or less than the upper limit, the granulated particles are less likely to collapse when carrying out steps (I) and (II), which is preferable.

If the average particle size of the granulated particles and their components is not adjusted, the particle size distribution may broaden when water is used as a measurement solvent in measuring the particle size distribution of the granulated particles. This is presumably due to the progression of particle collapse of the granulated particles. When granulated particles having the above average particle size are obtained using inorganic oxide particles A1 and inorganic oxide particles B1 having the above average particle size, the broadening of the particle size distribution of the granulated particles can be suppressed even when water is used as a measurement solvent in measuring the particle size of the granulated particles.

2.6. Estimation of the mechanism of action by which the particle collapse of granulated particles is suppressed It is believed that granulated particles maintain their particle shape mainly due to the interaction of surface OH groups. On the other hand, when the components of the granulated particles show different crystallinity, such as crystalline silica and amorphous silica, the structure and properties of the surface OH groups of the crystalline silica and amorphous silica are different. It is estimated that one of the causes of particle collapse of granulated particles is that the surface OH groups of the components are not able to interact with each other. It is believed that the use of crystalline silica having a planar structure with a specific particle size (small particle size) increases the contact efficiency between crystalline silica particles or between the surfaces of crystalline silica and amorphous silica. As a result, it is estimated that granulated particles with a particle size distribution that is less likely to spread are obtained due to the interaction between the components caused by the increase in contact efficiency, not the interaction of the surface OH groups.
It is considered that the crystalline silica having specific characteristics used in the present invention has a different crystal structure from amorphous silica, and has a specific surface OH group structure.Phillips catalyst is an ethylene-based polymerization catalyst with hexavalent chromium atoms supported on the surface OH group.In such an ethylene-based polymerization catalyst, it is considered that the polymer obtained has a high molecular weight due to the influence of the specific OH group structure of the crystalline silica having specific characteristics used in the present invention.

3. Method for Producing an Ethylene-Based Polymerization Catalyst The method for producing an ethylene-based polymerization catalyst includes the following step (I) and then step (II).
Step (I): A chromium compound is supported on the granulated particles to obtain chromium compound-supported components F1 and F2.
Step (II): The chromium compound-supporting components F1 and F2 obtained in step (I) are activated by calcination at 400° C. to 900° C. in a non-reducing atmosphere, so that at least a part of the chromium atoms is made hexavalent.

3.1. Production of chromium compound-supported components F1 and F2 in step (I) The chromium compound-supported component F1 is obtained by mixing granulated particles containing inorganic oxide particles A1 (component A) and inorganic oxide particles B1 (component B) with a chromium compound D (first embodiment). The chromium compound-supported component F1 has a configuration in which the chromium compound D is supported on a mixed carrier containing inorganic oxide particles A1 (component A) and inorganic oxide particles B1 (component B). The chromium compound-supported component F1 is activated in a non-reducing atmosphere to produce a chromium catalyst G1.
The chromium compound-supported component F2 is obtained by mixing granulated particles containing inorganic oxide particles A1 (component A) without inorganic oxide particles B1 (component B) with a chromium compound D (second embodiment). The chromium compound-supported component F2 has a structure in which the chromium compound D is supported on inorganic oxide particles A1 (component A), which are an inorganic oxide support. The chromium compound-supported component F2 is activated in a non-reducing atmosphere to produce a chromium catalyst G2. The method for producing the chromium catalyst G2 is the same as the method for producing the chromium catalyst G1, except that the granulated particles do not contain inorganic oxide particles B1 (component B), and therefore a description thereof will be omitted.

Here, the chromium catalyst G1 will be described. The chromium catalyst G1 is a catalyst in which a chromium compound E is supported on inorganic oxide particles A1 (component A) and inorganic oxide particles B1 (component B).
Chromium catalyst G1 is a chromium catalyst in which at least some of the chromium atoms are hexavalent, and is generally classified as a catalyst called a Phillips catalyst.
An outline of this catalyst is described in the literature such as Kazuo Matsuura and Naotaka Mikami (eds.), "Polyethylene Technology Reader," p. 81, 2001, Kogyo Chosakai, M. P. McDaniel; Advances in Catalysis Vol. 33 p. 47 (1985), Academic Press Inc., M. P. McDaniel "Handbook of Heterogeneous Catalysis" p. 2400 (1997) VCH, M. B. Welch et al. "Handbook of Polyolefins Synthesis and Properties" p. 21 (1993) Marcel Dekker.

The chromium compound E is not particularly limited as long as it is a chromium compound in which at least some of the chromium atoms are hexavalent. For example, the chromium compound E is derived from chromium oxide, chromium halide, oxyhalide, chromate, dichromate, nitrate, carboxylate, sulfate, chromium-1,3-diketo compound, chromate ester, etc. (hereinafter, the trivalent chromium compounds such as chromium oxide to chromate ester listed here are also referred to as "chromium compound D"). The chromium compound D is supported on the inorganic oxide particles A1 and the inorganic oxide particles B1, and then activated in a non-reducing atmosphere to become the chromium compound E. The hexavalent chromium compound E may be directly supported on the inorganic oxide particles A1 and the inorganic oxide particles B1.
More specific examples of the chromium compound D include chromium (III) oxide, chromium trichloride, chromyl chloride, potassium chromate, ammonium chromate, potassium dichromate, chromium nitrate, chromium sulfate, chromium acetate, tris(2-ethylhexanoate)chromium, chromium acetylacetonate, bis(tert-butyl)chromate, etc. In particular, chromium compound D is preferably chromium (III) oxide, chromium acetate, or chromium acetylacetonate.
It is known that even when a chromium compound having an organic group, such as chromium acetate or chromium acetylacetonate, is used, the organic group portion is burned by activation in a non-reducing atmosphere, which will be described later, and ultimately reacts with hydroxyl groups on the surface of the inorganic oxide support, as in the case of using chromium (III) oxide, and at least a part of the chromium atoms becomes hexavalent and is fixed in the form of a chromate ester structure (see V. J. Ruddick et al.; J. Phys. Chem. Vol. 100, p. 11062 (1996); S. M. Augustin et al.; J. Catal. Vol. 161, p. 641 (1996)).

The following methods can be used to mix the granulated particles with the chromium compound D. Suitable examples include a method in which the granulated particles are impregnated with a solution of the chromium compound D and then the solvent is removed, and a method in which the chromium compound D is sublimated without using a solvent. Other known methods can also be used. The support method is appropriately selected depending on the type of chromium compound D used.

In step (I), chromium compound-supported components F1 and F2 containing 0.01% to 2.0% by weight of chromium atoms may be obtained. The content of chromium atoms in chromium catalysts G1 and G2 is not particularly limited, but from the viewpoint of preventing the supported chromium atoms from agglomerating with each other and being efficiently activated, it is preferably 0.01% to 2.0% by weight, more preferably 0.1% to 2.0% by weight, and even more preferably 0.2% to 1.5% by weight.

During the supporting of chromium compound D or during activation described below, a known method for adjusting the ethylene polymerization activity or the molecular weight and molecular weight distribution of the obtained ethylene polymer by adding a fluorine compound such as ammonium silicofluoride or ammonium hydrogen difluoride, a titanium alkoxide such as titanium tetraisopropoxide, a zirconium alkoxide such as zirconium tetrabutoxide, an aluminum alkoxide such as aluminum tributoxide, an organoaluminum such as trialkylaluminum, an organomagnesium such as dialkylmagnesium, or a metal alkoxide, or an organometallic compound, may be used in combination.
In these metal alkoxides or organometallic compounds, the organic group portion is burned by activation in a non-reducing atmosphere, and is oxidized to a metal oxide such as titania, zirconia, alumina or magnesia, which is contained in the catalyst. In addition, the fluorine compound is thermally decomposed during activation to fluorinate the inorganic oxide support.
These methods are generally or in detail described in documents such as C. E. Marsden; Plastics, Rubber and Composites Processing and Applications Vol. 21 p. 193 (1994), T. Pullukat et al.; J. Polym. Sci., Polym. Chem. Ed. Vol. 82 p. 118 (1980), M. P. McDaniel et al.; J. Catal. Vol. 82 p. 118 (1983).

3.2. Calcination activation treatment of chromium compound-supported components F1 and F2 in step (II) In step (II), the granulated particles supporting chromium compound D obtained in step (I) are calcined in an activation furnace to perform activation. The activation is performed in a non-reducing atmosphere that is substantially free of moisture. For example, it is performed under oxygen or air, but an inert gas may also be present. Preferably, it is performed under a fluidized state using air that has been sufficiently dried by passing molecular sieves or the like through it.
The activation temperature is 400°C to 900°C, preferably 430°C to 900°C, and more preferably 450°C to 850°C. The activation time is not particularly limited. The activation time is preferably 30 minutes to 48 hours, more preferably 1 hour to 35 hours, and even more preferably 2 hours to 30 hours. By the activation, at least a part of the chromium atoms of the chromium compound D supported on the granulated particles is oxidized to hexavalent atoms, and the chromium compound E is chemically fixed to the granulated particles. If the activation is performed at a temperature lower than 400°C, the polymerization activity decreases, and if the activation is performed at a temperature higher than 900°C, sintering occurs and the activity decreases.

In step (II), it is preferable to oxidize 50% or more of the chromium atoms contained in the chromium compound-supported components F1 and F2 to a hexavalent state. More preferably, 60% or more of the chromium atoms contained in the chromium compound-supported components F1 and F2 are oxidized to a hexavalent state. The upper limit of the chromium atoms oxidized to a hexavalent state is 100%. The ratio of the chromium atoms oxidized to a hexavalent state is adjusted by the activation temperature and time.
The total amount of chromium atoms can be measured by a general metal analysis method, such as plasma emission spectrometry or X-ray fluorescence spectrometry. The valence of chromium can be roughly known by visually observing the color change of the solid product (generally, hexavalent chromium is yellow to orange, trivalent chromium is green, and divalent chromium is blue), but for quantitative analysis, chelate titration and absorptiometry are known as simple methods. Specifically, it is described in "Experimental Chemistry Lecture 15 Analysis" edited by the Chemical Society of Japan, Maruzen (1991), pp. 246-248. For example, in the case of trivalent chromium, an excess of EDTA (ethylenediaminetetraacetic acid) of a known concentration is added to trivalent chromium in an acidic solution, boiled for 5-10 minutes, and titrated with a standard solution of trivalent iron to quantitatively determine the amount. In addition, in the case of hexavalent chromium, it is possible to quantitatively determine the amount by measuring the absorbance at a wavelength of 366 nm, taking advantage of the fact that it exists as CrO ₄ ^2- in an alkaline solution.

The surface area of the chromium catalyst G1 is not particularly limited, but is usually from 10 m ² /g to 1000 m ² /g, preferably from 20 m ² /g to 950 m ² /g, and more preferably from 50 m ² /g to 900 m ² /g.
The pore volume of the chromium catalyst G1 is not particularly limited, but is usually from 0.05 to 5.0 mL/g, preferably from 0.1 to 3.0 mL/g, and more preferably from 0.1 to 2.5 mL/g.
The average particle size of the particles of the chromium catalyst G1 is not particularly limited, but from the viewpoint of handling, the average particle size is preferably 1 μm or more and 500 μm or less, more preferably 2 μm or more and 300 μm or less, and even more preferably 5 μm or more and 200 μm or less.

4. Ethylene-Based Polymerization Catalyst The ethylene-based polymerization catalyst can be used by being introduced into a polymerization reactor in advance in the presence or absence of a solvent, or in the presence or absence of an organometallic compound.
The ethylene-based polymerization catalyst may contain components other than the chromium catalysts G1 and G2, so long as they do not impair the effects of the present invention.
The other components are not particularly limited, and the content (wt%) of the other components is preferably 5 wt% or less.
When an ethylene-based polymer is obtained by using an ethylene-based polymerization catalyst using the above-mentioned granulated particles, the polymer BD (bulk density) of the ethylene-based polymer can be improved. This is believed to be because the use of the above-mentioned granulated particles suppresses the generation of fine particle components of the ethylene-based polymerization catalyst component, improving the particle properties of the obtained ethylene polymer. The generation of fine particle components is suppressed because the particle strength of the granulated particles is improved by adjusting the particle diameter of each component. Furthermore, when an ethylene-based polymer is obtained by using an ethylene-based polymerization catalyst using such granulated particles, a higher molecular weight ethylene polymer is obtained as the mixing ratio of component A increases. This is because the polymerization active species obtained from component A produces an ultra-high molecular weight ethylene polymer, and is clearly a high molecular weight ethylene polymer compared to the polymerization active species obtained from component B.

5. Method for Producing Ethylene-Based Polymer In the method for producing an ethylene-based polymer of the present invention, a monomer containing at least ethylene is polymerized using the above-mentioned ethylene-based polymerization catalyst.

5.1 Polymerization Method The process for producing an ethylene polymer of the present invention can be carried out by a liquid phase polymerization method such as slurry polymerization or solution polymerization, or a gas phase polymerization method.
The liquid phase polymerization method is usually carried out in a hydrocarbon solvent, such as propane, n-butane, isobutane, n-pentane, isopentane, hexane, heptane, octane, decane, cyclohexane, benzene, toluene, xylene, or a mixture of such inert hydrocarbons.
In the gas phase polymerization method, a commonly known polymerization method such as a fluidized bed or a stirred bed can be used in the presence of an inert gas. In the gas phase polymerization method, a so-called condensing mode can be used in which a medium for removing polymerization heat is optionally used.
As a polymerization method, not only single-stage polymerization in which an ethylene polymer is produced using one reactor, but also multi-stage polymerization can be carried out by connecting at least two reactors. In the case of multi-stage polymerization, two reactors are connected, and a reaction mixture obtained by polymerization in the first reactor is then continuously fed to the second reactor, in a two-stage polymerization method. The transfer from the first reactor to the second reactor is carried out through a connecting pipe. This transfer is preferably carried out by utilizing the pressure difference caused by the continuous discharge of the polymerization reaction mixture from the second reactor.

5.2. Polymerization Conditions The polymerization temperature in the liquid phase or gas phase polymerization method is generally 0°C to 300°C, practically 20°C to 200°C, preferably 50°C to 180°C, and more preferably 70°C to 150°C.
The catalyst concentration and ethylene concentration in the reactor can be any concentration sufficient to drive the polymerization. For example, the catalyst concentration can range from about 0.0001% by weight to about 5% by weight, based on the weight of the reactor contents, for liquid phase polymerization. Similarly, the ethylene concentration can range from 0.1 MPa to 10 MPa total pressure for gas phase polymerization.
If necessary, hydrogen can be introduced into the polymerization reactor to adjust the molecular weight.

5.3. Copolymerization In the process for producing an ethylene-based polymer of the present invention, in addition to ethylene homopolymerization, α-olefins such as propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. may be introduced into a polymerization reactor alone or in combination to be copolymerized, if necessary.
The α-olefin content in the resulting ethylene copolymer is desirably 15 mol % or less, preferably 10 mol % or less.

5.4. Organometallic Compounds In the polymerization, an organometallic compound may be introduced as a co-catalyst and brought into contact with the ethylene-based polymerization catalyst for the purpose of finely adjusting the molecular weight or molecular weight distribution of the ethylene-based polymer or for the purpose of removing impurities in the polymerization system as a scavenger.
In particular, organometallic compounds have the effect of improving the catalytic activity of ethylene-based polymerization catalysts and the effect of making hydrogen more effective as a molecular weight regulator.
As the organometallic compound, organometallic compounds of Groups 1, 2, and 13 of the periodic table, specifically organolithium compounds, organomagnesium compounds, organoaluminum compounds, and organoboron compounds are preferably used, with organoaluminum compounds and organoboron compounds being more preferred.

The organolithium compound includes alkyllithium, specifically, methyllithium, n-butyllithium, and the like.
The organic magnesium compound includes dialkyl magnesium, specifically, butylethyl magnesium, and dibutyl magnesium.
The organoaluminum compound includes trialkylaluminum and dialkylaluminum alkoxides, specifically, trimethylaluminum, triethylaluminum, triisobutylaluminum, and diethylaluminum ethoxide.
The organoboron compound includes trialkylboranes, specifically triethylborane.
The amount of the organometallic compound to be contacted is such that the molar ratio of metal atoms to chromium atoms is 0.2 to 1,000, preferably 0.5 to 100.

The resulting ethylene-based polymer is then preferably kneaded. Kneading can be carried out using a single-screw or twin-screw extruder or a continuous kneader. The resulting ethylene-based polymer can then be molded, such as by blow molding, by a conventional method.

6. Effects of the Present Embodiment According to the ethylene-based polymerization catalyst component and the method for producing an ethylene-based polymer catalyst of the present embodiment, an ethylene-based polymerization catalyst having good particle properties and capable of stably producing an ethylene-based polymer having an ultra-high molecular weight component can be obtained. According to the method for producing an ethylene-based polymer of the present embodiment, it becomes possible to design an HDPE material (high density polyethylene material) having an excellent balance between durability and fluidity.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples as long as they do not deviate from the gist of the invention.

1. Methods for Measuring Physical Properties The methods for measuring physical properties used in the examples and comparative examples are as follows.
(1) Measurement of peak intensity in infrared absorption spectrum of inorganic oxide particles A1 (infrared spectroscopy)
The inorganic oxide was filled into a sample holder for diffuse reflection IR in a glove box purged with high-purity argon, and the sample surface was smoothed.Then, the sample was sealed with a lid with a window and placed in an IR measurement device for measurement.
The measurement conditions are as follows.
Apparatus: FT/IR-6600 manufactured by JASCO Corporation
Detector: TGS
Photometry method: Diffuse reflection method Wavelength range: 1000 to 4000 cm ^-1
Resolution: 4 ^cm
Number of measurements: 512 Atmosphere: Argon (2) Powder X-ray Diffraction (XRD): Powder X-ray diffraction was measured using the following apparatus and conditions.
Equipment: Rigaku X-ray Diffractometer Smartlab
X-ray source: Cu-Kα rays (using Kβ absorption plate), tube voltage 40kV, tube current 30mA
Optical system: focusing method, divergence slit 2/3 degrees, scattering slit 2/3 degrees, receiving slit 0.300 mm
Scan mode: 2θ/θ scan 2θ scan range: 3.0000-55.0000 degrees Angle step width: 0.0200 degrees Scan speed: 4.0000 degrees/min Detector: scintillation counter (3) Surface area and pore volume After each silica sample was heated and thoroughly dried under reduced pressure, a nitrogen adsorption isotherm was measured at liquid temperature using a Quantachrome Autosorb 3B. The pore volume was calculated from the amount of adsorption at a relative pressure of 0.95 of the obtained adsorption isotherm, and the specific surface area was calculated by performing a BET multipoint analysis. Furthermore, the average pore diameter was calculated according to formula (1) by assuming the pore structure to be cylindrical. In this formula, D _ave indicates the average pore diameter, V _total indicates the pore volume, and S _BET indicates the specific surface area by the BET multipoint method.
D _ave =4V _total /S _BET formula (1)
Furthermore, the mesopore distribution was determined by BJH analysis, and the pore volume in a specified range was calculated.
(4) SEM Observation: SEM observation was carried out using the following equipment and conditions.
Equipment: Hitachi FE-SEM
Pressurizing voltage: 1 kV
Equipment magnification: 20k
WD: 4mm
(5) HLMI: Measured in accordance with ASTM-D-1238-57T at 190° C. and a load of 21.6 kg.
(6) Hexavalent chromium content: An aqueous NaOH solution (0.1 M) was added to the catalyst component to dissolve hexavalent chromium, and a portion of the solution was sampled and the absorbance at a wavelength of 366 nm was measured to determine the content.
(7) Average particle size: Measurement was performed using a laser diffraction/scattering type particle size distribution measuring device LA-920 manufactured by Horiba, Ltd. under the conditions of water as a dispersion solvent, a refractive index of 1.0, and a shape factor of 1.0, and the median diameter was taken as the average particle size.

2. Examples and Comparative Examples (1) Examples 1 to 4
(1.1) Infrared absorption spectrum of inorganic oxide particle A1 In Examples 1 and 2, "Sun Lovely" (manufactured by AGC Si-Tech Co., Ltd.) having an average particle size of 2.1 μm was used as the inorganic oxide particle A1. Hereinafter, this inorganic oxide particle A1 will be referred to as inorganic oxide particle A1-1. The infrared absorption spectrum of inorganic oxide particle A1-1 is shown by a solid line in FIG. 1. In the infrared absorption spectrum of inorganic oxide particle A1-1, the maximum peak in range X was 3646 cm ^-1 , and the peak intensity Px was 1.94. In addition, the maximum peak in range Y was 3746 cm ^-1 , and the peak intensity Py was 1.16. The peak intensity ratio Py/Px was 0.60.
In Examples 3 and 4, "Sun Lovely" (manufactured by AGC Si-Tech Co., Ltd.) having an average particle size of 1.6 μm was used as the inorganic oxide particles A1. Hereinafter, this inorganic oxide particle A1 will be referred to as inorganic oxide particles A1-2. The infrared absorption spectrum of the inorganic oxide particles A1-2 is shown by a dashed dotted line in FIG. 1. In the infrared absorption spectrum of the inorganic oxide particles A1-2, the maximum peak in range X was 3646 cm ^-1 , and the peak intensity Px was 1.78. Furthermore, the maximum peak in range Y was 3746 cm ^-1 , and the peak intensity Py was 1.83. The peak intensity ratio Py/Px was 1.03.
(1.2) Structural Analysis Data of Inorganic Oxide Particles A1 The structural analysis data of inorganic oxide particles A1-1 is as follows. Note that the surface area and pore volume were not measured.
<Structural Analysis Data of Inorganic Oxide Particle A1-1>
XRD: Peak at 2θ=26.2°, half width 1.9°
_SiO2 purity: 99% or more (weight basis)
Average particle size: 2.1 μm
The structural analysis data of the inorganic oxide particles A1-2 is as follows: The surface area and pore volume were not measured.
<Structural Analysis Data of Inorganic Oxide Particle A1-2>
XRD: Peak at 2θ=26.2°, half width 1.6°
_SiO2 purity: 99% or more (weight basis)
Average particle size: 1.6 μm
(1.3) Infrared absorption spectrum of inorganic oxide particles B1 In Examples 1 to 4, amorphous silica aggregates having an average particle size of 12.0 μm were used as inorganic oxide particles B1. The infrared absorption spectrum of inorganic oxide particles B1 is shown by a short dashed line in FIG. 1. In the infrared absorption spectrum of inorganic oxide particles B1, the maximum peak in range X was 3698 cm ^-1 , and the peak intensity Px was 0.44. The maximum peak in range Y was 3746 cm ^-1 , and the peak intensity Py was 6.17. The peak intensity ratio Py/Px was 14.02.
(1.4) Structural Analysis Data of Inorganic Oxide Particles B1 The structural analysis data of inorganic oxide particles B1 is as follows.
<Structural Analysis Data of Inorganic Oxide Particles B1>
XRD: A broad peak characteristic of amorphous material at around 2θ=22° BET method: Surface area: 313 m ² /g
Pore volume: 1.7 mL / g
_SiO2 purity: 99% or more (weight basis)
Average particle size: 12.2μm
(1.5) Preparation of Chromium Catalyst G1 Inorganic oxide particles A1 (component A) and inorganic oxide particles B1 (amorphous silica aggregate, component B) were blended so that the mixing ratio was the ratio in Table 1 in terms of the respective weight ratios. In the column of component ratio in Table 1, the number on the left side is the ratio of component A, and the number on the right side is the ratio of component B. That is, in Example 1, the mixing ratio of inorganic oxide particles A1 (component A) and inorganic oxide particles B1 (component B) was 25:75, and in Example 2, the mixing ratio of inorganic oxide particles A1 (component A) and inorganic oxide particles B1 (component B) was 50:50. A total of 150 g of the blended inorganic oxide particles A1 and inorganic oxide particles B1 was slurried in 600 mL of distilled water. The above inorganic oxide particle/water slurry was spray-dried and granulated using a spray-drying granulation device (Okawahara Kakoki Co., Ltd. "L-8") under the following conditions.
Atomizer type: M type rotary disc Atomizer rotation speed: 10,000 rpm
Slurry supply rate: 1.0 L / h
Inlet temperature: 150°C
After granulation, the granulated particles were collected from the bottom of the main body. The average particle size (median diameter) of the granulated particles is shown in Table 1.

10 g of the resulting granulated particles were immersed in an aqueous solution in which 0.22 g of chromium acetate was dissolved in 50 ml of distilled water, and then the water was removed by distillation to obtain chromium-containing silica with a chromium content of 0.5% by weight. The chromium-containing silica was then activated under dry air atmosphere at 730°C for 12 hours to obtain chromium catalyst G1 (Phillips type catalyst). Upon activation, the chromium-containing silica changed color from light blue to light orange. This indicates that the chromium atoms had been converted to hexavalent atoms. Essentially 99% by weight of the trivalent chromium had been converted to hexavalent chromium.

(1.6) Ethylene polymerization Into a 1.5 L polymerization vessel thoroughly purged with nitrogen, the respective chromium catalysts obtained in (1.5) in the amounts shown in Table 1, 2 g of 1-hexene, and 700 mL of isobutane were introduced, and the internal temperature was raised to 103° C.
Then, ethylene was injected and polymerization was carried out at a polymerization temperature of 103° C. while maintaining the ethylene partial pressure at 1.4 MPa. The polymerization was then terminated by discharging the content gas outside the system.
The polymerization conditions and results are summarized in Table 1.

(2) Comparative Examples 1 and 2
(2.1) Preparation of chromium catalyst according to comparative example A chromium catalyst according to a comparative example was prepared in the same manner as in the example, except that "Sun Lovely" (manufactured by AGC Si-Tech Co., Ltd.) having an average particle size of 4.5 μm was used instead of the inorganic oxide particles A1.
The infrared absorption spectrum of "Sun Lovely" with an average particle size of 4.5 μm is shown by the long dashed line in Figure 1. In the infrared absorption spectrum of this inorganic oxide particle, the maximum peak in range X was 3659 cm ^-1 , and the peak intensity Px was 1.32. The maximum peak in range Y was 3747 cm ^-1 , and the peak intensity Py was 0.86. The peak intensity ratio Py/Px was 0.65.
(2.2) Structural analysis data of inorganic oxide particles used in comparative examples The structural analysis data of the inorganic oxide particles used in the comparative examples is as follows. These inorganic oxide particles are inorganic oxide particles that satisfy the requirements of Property 1 and Property 3 except for Property 2 related to the average particle size in Component A of the present invention.
<Structural Analysis Data of Inorganic Oxide Particles of Comparative Examples>
XRD: Peak at 2θ=25.8°, half width 1.5°
BET method: Surface area 84m ² /g
Pore volume: 0.2 mL / g
_SiO2 purity: 99.5% (weight basis)
Average particle size: 4.5 μm

(2.3) Ethylene Polymerization Ethylene polymerization was carried out in the same manner as in Example (1.6) except that the chromium catalyst was changed as shown in Table 1.
The polymerization conditions and results are summarized in Table 1.

3. Consideration of the Results of Examples and Comparative Examples In the examples and comparative examples, the polymerization activity, HLMFR and density (polymer BD) of the obtained ethylene polymers are shown in Table 1.

Comparing Examples 1 to 4 and Comparative Examples 1 and 2, the median diameter of the granulated particles in the laser particle size measurement was 78.8 μm to 85.9 μm in Examples 1 to 4, whereas in Comparative Examples 1 and 2, the median diameter of the granulated particles measured under the same conditions was 18.2 μm or 19.8 μm, which was very small, even though the granulation was performed under the same conditions. This is considered to be due to the particle collapse of particles that were originally large in the laser particle size measurement. This is also shown in the results when used as a catalyst component. Comparing the powder BD of the polymers in the Examples and Comparative Examples, Examples 1 to 4 show large values of 0.35 to 0.38 g/cc, whereas Comparative Examples 1 and 2 show low values of 0.30 g/cc or less. It is presumed that this is due to the deterioration of the shape of the catalyst or polymer due to particle collapse and the broadening of the particle size distribution of the polymer. As in Examples 1 to 4, it was suggested that the use of crystalline silica having a specific particle size and a specific structure (infrared absorption spectrum) can suppress particle collapse of the catalyst component and polymer, making it possible to obtain a catalyst component and a polymer with good powder properties.
From the above results, it was confirmed that _, in an ethylene-based polymerization catalyst containing plate-like silica aggregates (silica aggregates having a planar structure) having a peak intensity ratio Py/Px of less than 10 and containing 90% by weight or more of SiO2, by using granulated particles having a specific average particle size obtained by spray-drying and granulating an inorganic oxide having a specific average particle size, an ethylene-based polymer having an ultrahigh molecular weight component and good particle properties can be produced.

The present invention is not limited to the embodiments detailed above, and various modifications and variations are possible within the scope of the claims of the present invention.

According to the present invention, an ethylene-based polymer having an ultra-high molecular weight component can be produced. This ethylene-based polymer can be used in a wide range of applications, and is therefore of great industrial value.

Claims (8)

A method for producing an ethylene-based polymerization catalyst component, comprising preparing a slurry of the following components A and B in a mixing ratio by weight of component A:component B=1:99 to 100:0, and then spray-drying and granulating the prepared slurry to obtain granulated particles having an average particle size of 1 μm to 500 μm.
Component A: An inorganic oxide having the following properties 1, 2, and 3.
(Characteristic 1) Contains 90% or more by weight of _SiO2 .
(Characteristic 2) The average particle size is 0.01 μm to 3.0 μm.
(Characteristic 3) In an infrared absorption spectrum measured after calcination at 600° C. for 24 hours as a pretreatment for analysis, the ratio Py/Px of the peak intensity Py that is maximum in the range Y of 3700 cm ⁻¹ to 3799 cm ⁻¹ to the peak intensity Px that is maximum in the range X of 3600 cm ⁻¹ to 3699 cm ⁻¹ is less than 10.
Component B: An inorganic oxide having an average particle size of 0.01 μm to 50 μm , which is composed of at least one type of particle selected from the group consisting of particles whose main component is silica (SiO ₂ ), particles whose main component is silica-titania (SiO ₂ -TiO ₂ ), and particles whose main component is silica-alumina (SiO ₂ -Al ₂ O ₃ ) (here, the main component is a substance whose content (weight %) is 90% or more). The method for producing an ethylene-based polymerization catalyst component according to claim 1, wherein the component A further has the following property 4:
(Characteristic 4) In powder X-ray diffraction, it has a peak with a half-width of 0.2° or more and 5° or less at 2θ=23° to 29°. 3. The method for producing an ethylene-based polymerization catalyst component according to claim 1 or 2, characterized in that the component B is an inorganic oxide containing 90% by weight or more of _SiO2 . The method for producing an ethylene-based polymerization catalyst component according to any one of claims 1 to 3, characterized in that the slurry is prepared so that the combined weight of component A and component B is 5% by weight to 50% by weight ((component A + component B) / water slurry x 100). A process for producing an ethylene-based polymerization catalyst, comprising the steps of:
Step (I): A chromium compound is supported on the granulated particles obtained by the production method according to any one of claims 1 to 4 to obtain a chromium compound-supported component.
Step (II): The chromium compound-supporting component obtained in step (I) is activated by calcination at 400° C. to 900° C. in a non-reducing atmosphere to convert at least a part of the chromium atoms into hexavalent chromium atoms. The method for producing an ethylene-based polymerization catalyst according to claim 5, characterized in that in step (I), the chromium compound-supported component containing 0.01% by weight to 2.0% by weight of chromium atoms is obtained. The method for producing an ethylene-based polymerization catalyst according to claim 5 or 6, characterized in that in step (II), 50% or more of the chromium atoms contained in the chromium compound-supported component are oxidized to hexavalent chromium. A method for producing an ethylene-based polymer, comprising polymerizing a monomer containing at least ethylene using an ethylene-based polymerization catalyst obtained by the production method according to any one of claims 5 to 7.