JP2002138105A - Method of producing ethylenic polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of efficiently producing an ethylenic polymer having excellent balance of impact resistance and environmental stress crack resistance(ESCR) suitable for blow molding of a large container. SOLUTION: This method of producing an ethylenic polymer comprises solution polymerization of ethylene or ethylene and other α-olefin in an inert solvent in the presence of a polymerization catalyst comprising a chromium compound carried on a silica-titania carrier and having pore volume less than 1.5 (cc/g) at a catalyst efficiency higher than 1500 (g-PE/g-catalyst).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing an ethylene-based polymer which has an excellent balance between impact strength and environmental stress cracking (ESCR) and is suitable for large-size blow molding.

[0002]

2. Description of the Related Art Ethylene polymers are widely used as materials for various molded articles, and required characteristics differ depending on molding methods and applications. For example, a polymer having a relatively low molecular weight and a narrow molecular weight distribution is suitable for a product molded by an injection molding method, but in a film molding or blow molding, a molecular weight is relatively high,
Polymers with a broad molecular weight distribution are suitable.

It is known that such an ethylene polymer having a wide molecular weight distribution can be obtained by polymerization using a so-called Phillips catalyst in which chromium trioxide is supported on an inorganic oxide such as silica.

However, in recent years, there has been a demand for higher quality ethylene polymers suitable for large blow molding of gasoline tanks, plastic drums, and the like, and the use of ethylene polymers obtained with a conventional Phillips catalyst has been demanded. When the blow molded body is manufactured by
In particular, the balance between impact strength and environmental stress cracking (ESCR) was not always satisfactory.

[0005]

SUMMARY OF THE INVENTION The present invention provides a method for efficiently and efficiently producing an ethylene-based polymer having a good balance between impact strength and environmental stress cracking (ESCR) and suitable for large blow molding. Things.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above problems, and as a result, using a silica-titania having a specific structure as a carrier in a polymerization catalyst comprising a chromium compound and an inorganic oxide, Furthermore, they have found that the above problems can be overcome by controlling the catalyst efficiency, and have accomplished the present invention.

That is, according to the present invention, a chromium compound is supported on a silica-titania carrier and has a pore volume of 1.5.
(Cc / g) of ethylene or ethylene and another α-olefin in an inert solvent in the presence of less than
An object of the present invention is to provide a method for producing an ethylene-based polymer, wherein solution polymerization is performed with a catalyst efficiency of 500 (g-PE / g-catalyst) or more.

[0008] Further, the present invention provides a method for producing a chromium compound comprising silica
The specific surface area of the polymerization catalyst supported on the titania support is 50 to
The method for producing an ethylene polymer having an average particle diameter of 1000 m ² / g and an average particle diameter of 10 to 200 μm, and the melt index (21.6 kgf) of the ethylene polymer is 1 to 1
0 (dg / min), density: 0.935 to 0.970
(G / cc) is provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The catalyst for polymerization of an ethylene polymer used in the present invention contains a chromium compound supported on a silica-titania carrier as a main component.

The catalyst in which a chromium compound is supported on a silica-titania carrier has a pore volume of less than 1.5 cc / g, preferably less than 1.3 cc / g, and more preferably 0.8 to 1.3 cc / g.
1.3 cc / g is used. 1.5 pore volume
If it is more than cc / g, the polymerization temperature must be lowered to produce a target having a desired melt index, the activity is remarkably reduced, and the productivity is undesirably lowered.
The specific surface area is preferably 50 to 1000 m ² / g, and the average particle size is preferably 10 to 200 μ.

The silica-titania carrier can be obtained by, for example, a method of coprecipitating a silicate and a water-soluble titanium salt when forming silica gel, a method of impregnating silica with TiX ₄ , Ti (OR) ₄ or the like, and a heat treatment. A commercially available product can be obtained and used. Further, a catalyst in which a chromium compound is supported on silica in advance is used, and Ti (O
R) A method of reacting ₄ or the like may be employed.

The titanium content in the silica-titania carrier is:
Generally, titanium atoms having a weight of 0.5 to 8.0% by weight, preferably 1.0 to 5.0% by weight are used. When the titanium content is less than 0.5% by weight, ES
The CR-impact strength balance, especially the ESCR, may be poor.
-Impact strength balance may be reduced.

As the chromium compound supported on the silica-titania carrier, a compound generally used for a Phillips catalyst can be used. Specific examples include chromium halides, oxyhalides, nitrates, acetates, sulfates, chromium-1,3-diketo compounds, chromate esters, and the like. Chromyl, potassium dichromate, ammonium chromate, chromium nitrate, chromium acetate, chromium sulfate, chromium acetylacetonate, bis (tert-butyl) chromate and the like can be used.

As a method of supporting the chromium compound on the carrier, the chromium compound is dissolved to form a solution, silica-titania is dispersed in the solution, the chromium compound is impregnated, and the powder is separated and dried. Can be done. Also, a solvent distillation method of volatilizing the solvent after adding and mixing silica-titania to the chromium compound solution,
Alternatively, it can be performed by a known method such as a dry sublimation method. As the loading method, an appropriate method is selected depending on the type of the chromium compound used.

The amount of the chromium compound is as follows:
0.05 to 5.0% by weight, preferably 0.3 to 4.0% by weight, more preferably 0.5 to 3.0% by weight based on the weight of the carrier.
% By weight.

When the content of the chromium compound is less than 0.05% by weight, the activity per catalyst is remarkably reduced. When the content exceeds 5.0% by weight, the activity per chromium atom is reduced and ethylene-based weight is reduced. It is not preferable because the chromium content in the coalescence increases.

The carrier supporting the chromium compound is activated by firing. The firing activation is generally performed in a non-reducing atmosphere substantially free of moisture, for example, in the presence of oxygen, but may be performed in the presence of an inert gas. Preferably, dry air is used. The calcination is performed at 400 ° C. or higher, preferably 500 to 900 ° C., for several minutes to 100 hours, preferably 1 to 50 hours. It is preferable to use sufficiently dried air at the time of calcination and to carry out the calcination under a fluidized state.

A known method for adjusting the activity, molecular weight, copolymerizability and the like by adding a fluorine-containing base or the like to the carrier or the material to be fired can also be used. Further, an organometallic compound can be further supported on the obtained catalyst, or can be brought into contact with the organometallic compound during polymerization. As the organometallic compound part, an organometallic compound of Group 1, 2, or 13 of the periodic table, specifically, an organolithium compound, an organomagnesium compound, or an organoaluminum compound is preferably used.

The polymerization of the ethylene polymer is carried out in an inert solvent, and is usually carried out in a hydrocarbon solvent. As hydrocarbon solvents, propane, butane, isobutane, hexane, cyclohexane, heptane, benzene, toluene,
Inert hydrocarbons, such as xylene, alone or in mixtures are used.

The polymerization temperature is generally from 10 to 300 ° C., preferably from 50 to 150 ° C. Any concentration and pressure of the catalyst and ethylene pressure in the reactor can be adopted as long as they are sufficient for the polymerization to proceed. In addition, hydrogen or the like can coexist in the reactor for controlling the molecular weight.

Generally, the polymerization pressure is 0.5 kg / cm ² G
１００100 kg / cm ² G, preferably 1 kg / cm ² G
It is about 50 kg / cm ² G.

In the present invention, the amount of polymer produced per unit weight of the catalyst, that is, the catalyst efficiency is 1300 (g-PE).
/ G-catalyst) or more, preferably 1500 (g-PE /
g-catalyst) or more, particularly preferably 1700 (g-PE /
g-catalyst).

The polymerization amount of the copolymer per unit amount of the catalyst is 1
When it is lower than 500 (g-PE / g-catalyst), the low molecular weight component of the copolymer increases, so that the impact strength decreases. The polymerization amount of the copolymer per unit weight of the catalyst can be controlled within the above range by adjusting the polymerization time.

If necessary, α-olefins such as propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene can be introduced into the reactor and copolymerized. The content of α-olefin in the obtained copolymer is desirably 10 mol% or less, preferably 5 mol% or less.

By the polymerization using the above-mentioned catalyst, an ethylene polymer having an excellent balance between impact strength and environmental stress cracking (ESCR) can be obtained. Therefore, the suitable melt index (HLMI) of 21.6 Kgf at 190 ° C. for large blow molding represented by gasoline tanks, drums and pallets is 1 to 10 g / min, and polymers outside this range are liable to cause molding failure. Not preferred. Further, the density of the polymer is controlled mainly by introducing an α-olefin during the polymerization.
Product characteristics such as CR greatly change. Suitable densities for large blow molded articles are from 0.935 to 0.970 g / cm ³ , which maintains desirable impact strength and ESCR values.

[0026]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples, but the present invention is not limited to these Examples. The measurement methods used in the examples and comparative examples are as follows. (1) Pretreatment of polymer powder for physical property measurement Using Toyo Seiki Labo Plastomill, as an additive,
0.15% by weight of IRGANOX1010 manufactured by Ciba-Geigy, 0.30% by weight of IRGAFOS168, 0.05% by weight of DSTP manufactured by Yoshitomi Pharmaceutical Co., and 0.03% by weight of calcium stearate manufactured by NOF Corporation were added under nitrogen.
And kneaded for 5 minutes. (2) Melt index Table 1, condition 7 of JIS K-7210 (1996 version)
The measured value at a temperature of 190 ° C. and a load of 21.6 kgf was indicated as HLMI. (3) Density Measured according to JIS K-7112 (1996 version). (4) Impact strength The -40 ° C. Izod strength measured according to JIS K-7110 (1996 version) was taken as the value of impact strength. (5) ESCR (Environmental Stress Cracking) The F50 value measured by the BT method according to JIS K-6760 (1996 version) was taken as the ESCR value.

Example 1 (1) Preparation of Catalyst In a 200 ml flask equipped with a stirrer, a silica-titania carrier (Ti in carrier) purchased from Crossfield was used.
After adding 10 g of an aqueous solution (content 2.4 wt%) and 40 ml of an aqueous solution of a trichromium compound (2.5 g / L) to form a slurry,
The mixture was stirred at 25 ° C for 2 hours. This slurry was dried at 90 ° C. under reduced pressure to obtain a powdery white solid.

This white solid was placed in a dry air atmosphere at 650
C. for 30 hours to obtain an orange catalyst. The pore volume of this catalyst was 1.1 cc / g, and the average particle size was 67 μm. The specific surface area is 460 m ² / g, and the Cr in the catalyst is
The content was 1.0% by weight. (2) Polymerization 800 ml of isobutane, 10 ml of 1-hexene and 200 mg of the catalyst obtained in the above (1) were charged into a 2.0 L autoclave sufficiently purged with nitrogen, and the internal temperature was raised to 95%.
The temperature was raised to ° C. Then, ethylene was injected and polymerization was carried out for 1 hour while maintaining the ethylene partial pressure at 6 kg / cm ² . After a lapse of a predetermined time, the polymerization was terminated by discharging the content gas out of the system. As a result, 345 g of an ethylene-based polymer was obtained. The polymerization activity per 1 g of the catalyst was 1,730 g / g-cat. Table 1 shows other physical property measurement results.

Example 2 A 2.0 L autoclave sufficiently purged with nitrogen was charged with 800 ml of isobutane, 10 ml of 1-hexene and 130 mg of the catalyst obtained in Example 1, and the internal temperature was raised to 96 ° C. Then ethylene is injected and ethylene partial pressure is 6kg.
/ Cm ² , while performing polymerization for 1.5 hours. After a lapse of a predetermined time, the polymerization was terminated by discharging the content gas out of the system. As a result, 350 g of an ethylene-based polymer was obtained. The polymerization activity per gram of catalyst is 26
It was 90 g / g-cat. Table 1 shows other physical property measurement results.

Example 3 (1) Preparation of catalyst A catalyst was prepared and calcined in the same manner as in Example 1 except that an aqueous solution of chromium acetate was used in place of the aqueous solution of a trichromium compound of Example 1, and a Cr content of 1.0 was obtained. % Catalyst solids were obtained. The specific surface area of this catalyst was 460 m ² / g, the pore volume was 1.1 g / cc, and the average particle size was 68 μm. (2) Polymerization Polymerization was carried out in the same manner as in Example 1 (2), except that 180 mg of the catalyst of (1) was used. As a result, 330
g of an ethylene polymer was obtained. The polymerization activity per 1 g of the catalyst was 1,830 g / g-cat. Table 1 shows other physical property measurement results.

Example 4 (1) A Cr content of 1.0 was prepared in the same manner as in Example 1 except that a toluene solution of acetylacetonatochromium (III) was used instead of the aqueous solution of the trichromium compound of Example 1.
% Solid catalyst was obtained. The pore volume of this catalyst is 1.0
cc / g and the average particle size was 68 μm. (2) Polymerization Polymerization was performed in the same manner as in Example 1 (2), except that 190 mg of the catalyst of (1) was used. As a result, 342
g of an ethylene polymer was obtained. The polymerization activity per 1 g of the catalyst was 1,800 g / g-cat. Table 1 shows other physical property measurement results.

Example 5 (1) Preparation of catalyst The silica-titania of Example 1 (1) was replaced with silica-titania having a Ti content of 3.6% by weight, except that
The catalyst was prepared and calcined in the same manner as in Example 1 to obtain a catalyst solid having a Cr content of 1.0% by weight. The catalyst has a pore volume of 1.0 cc / g, an average particle size of 72 μm and a specific surface area of 4 μm.
It was 90 m ² / g. (2) Polymerization Polymerization was carried out in the same manner as in Example 1 (2), except that 180 mg of the catalyst of (1) was used. As a result, 350
g of an ethylene polymer was obtained. The polymerization activity per 1 g of the catalyst was 1940 g / g-cat. Table 1 shows other physical property measurement results.

Example 6 Polymerization was carried out in the same manner as in Example 1 (2) except that 180 mg of the catalyst of Example 3 (1) was used, the amount of 1-hexene was 6 ml, and the polymerization temperature was 97 ° C. . As a result, 355
g of polyethylene were obtained.

Comparative Example 1 In a 2.0 L autoclave sufficiently purged with nitrogen, 800 ml of isobutane, 10 ml of 1-hexene and Example 1 were added.
Was charged, and the internal temperature was raised to 93 ° C. Then ethylene is injected and ethylene partial pressure 6k
The polymerization was carried out for 40 minutes while maintaining the g / cm ² . After a lapse of a predetermined time, the polymerization was terminated by discharging the content gas out of the system. As a result, 320 g of an ethylene-based polymer was obtained. The polymerization activity per gram of catalyst is 12
It was 30 g / g-cat. The measurement results of physical properties are shown in Table 1. The impact strength was lower than those of Examples 1 to 5.

Comparative Example 2 (1) Preparation of Catalyst Powder was prepared in the same manner as in Example 1- (1) using silica having a pore volume of 1.1 cc / g, a specific surface area of 360 m ² / g and an average particle size of 80 μm. A white solid was obtained. Further, this white solid was calcined at 650 ° C. for 30 hours in dry air to obtain a catalyst. The Cr content of this catalyst was 1.0% by weight, the pore volume was 1.1 cc / g, and the average particle size was 80 μm. (2) Polymerization was carried out in the same manner as in Example 1 (2) except that 200 mg of the catalyst of the above (1) was used, the amount of 1-hexene was 8 ml, and the polymerization temperature was 97 ° C. As a result, 31
0 g of an ethylene polymer was obtained. The physical property measurement results are shown in Table 1. The ESCR was extremely lower than in Examples 1 to 5.

Comparative Example 3 (1) Preparation of Catalyst Silica-titania carrier E purchased from Crossfield
Using P-50, a catalyst was prepared in the same manner as in Example 1, and further calcined in dry air at 700 ° C. for 30 hours.
A catalyst was obtained. This catalyst had a Cr content of 1.0% by weight, a pore volume of 2.0 cc / g, an average particle size of 95 μm, and a specific surface area of 440 m ² / g. (2) Polymerization was carried out in the same manner as in Example 1 (2) except that 470 mg of the catalyst of (1) was used, the amount of 1-hexene was 12 ml, the polymerization temperature was 85 ° C., and the polymerization time was 2 hours. Was.

As a result, 320 g of an ethylene polymer was obtained. The activity per 1 g of the catalyst was 680 g / g-cat. The measurement results of physical properties are shown in Table 1. Both the impact strength and the ESCR were lower than those of Examples 1 to 5.

Comparative Example 4 (2) Same as Example 1 (2) except that 210 mg of the catalyst obtained in (1) of Comparative Example 3 was used, the polymerization temperature was 82 ° C., and the polymerization time was 4 hours. To perform polymerization. As a result, 330 g of an ethylene polymer was obtained. The activity per 1 g of the catalyst was 1570 g / g-cat. Met. The measurement results of physical properties are shown in Table 1. The impact strength was lower than in Examples 1 to 5.

[0039]

[Table 1]

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[Procedure amendment]

[Submission date] February 1, 2001 (2001.2.1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0038

[Correction method] Change

[Correction contents]

Comparative Example 4 (2) Same as Example 1 (2) except that 210 mg of the catalyst obtained in (1) of Comparative Example 3 was used, the polymerization temperature was 82 ° C., and the polymerization time was 4 hours. To perform polymerization. As a result, 330 g of an ethylene polymer was obtained. The activity per 1 g of the catalyst was 1570 g / g-cat. Met. Table 1 shows the physical property measurement results.

Claims (3)

[Claims] A chromium compound is supported on a silica-titania carrier, and ethylene or ethylene and another α-olefin are mixed in the presence of a polymerization catalyst having a pore volume of less than 1.5 (cc / g). In an inert solvent, 1300 (g-PE / g
(Catalyst) A method for producing an ethylene-based polymer, wherein solution polymerization is carried out with the above catalyst efficiency. 2. A polymerization catalyst comprising a chromium compound supported on a silica-titania carrier and having a specific surface area of 50 to 1000 m ² /
The method for producing an ethylene-based polymer according to claim 1, wherein g and the average particle diameter are 10 to 200 µm. 3. The ethylene polymer has a melt index (21.6 kgf) of 1 to 10 (dg / min) and a density of 0.935 to 0.970 (g / cc).
Or the method for producing an ethylene-based polymer according to 2.