JPH02145609A - Production of ethylene-based polymer - Google Patents

Abstract

PURPOSE:To inexpensively obtain the title polymer having excellent bulk density and particle size distribution by polymerization in a catalytic system comprising a Mg dialkoxide, Zr compound, Ti compound and an organic halogenated Al compound in a specific ratio. CONSTITUTION:Ethylene alone is polymerized or ethylene is copolymerized with another alpha-olefin in the presence of a catalyst obtained by combining (A) a solid catalytic component prepared by reacting (i) a Mg dialkoxide shown by formula I (R1 is 1-3C alkyl), having <=50mu average particle diameter with (ii) a Zr compound shown by formula II (R<2> is hydrocarbon; X<2> is halogen; n is 0-4), (iii) a Ti compound shown by formula III (R<3> is hydrocarbon, X<3> is halogen; m is 0-4) and an organic halogenated Al compound shown by formula IV (R<4> is hydrocarbon; X<4> is halogen : k is 1-2) in a ratio satisfying formula V ([Mg], [Zr] and [Ti] are gram equivalent of Ng, Zr and Ti, respectively) and formula VI ([X] is gram equivalent of halogen) under a condition not to dissolve the component (i) with (B) an organoaluminum compound.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an improvement in a method for producing ethylene polymers. More specifically, the present invention has superior polymerization activity, is easier to prepare, and is less costly than solid catalyst components used in the production of conventional ethylene-based polymers, and the ethylene-based polymers produced By using a solid catalyst component with excellent properties, it is possible to adjust the molecular weight distribution of the ff1 polymer over a wide range, and to provide an ethylene polymer with good powder properties such as bulk density and powder particle size distribution. This invention relates to a method for efficiently producing an ethylene homopolymer or copolymer suitable for use in blow molded products, films, and the like.

[Prior Art] Conventionally, as a method for producing an ethylene polymer for blow molded products or films, a solid catalyst component obtained by reacting, for example, an organomagnesium compound, a titanium compound, a zirconium compound, and an aluminum halide compound, Methods are known for polymerizing ethylene or mixtures of ethylene and other α-olefins using catalyst systems consisting of combinations with organometallic compounds. For example, (i) magnesium compounds, (11) titanium compounds, (iii) polymerizing an α-olefin using a catalyst system consisting of a combination of a solid catalyst component obtained by reacting a zirconium compound and (iv) an organic aluminum halide compound in a specific ratio and an organic aluminum compound; Method for producing polyolefin with wide molecular weight distribution
Japanese Patent Publication No. 52-39714 and Japanese Patent Publication No. 62-48682 disclose methods for producing polymers with a wide molecular weight distribution using catalyst systems of the same type.

However, in these methods, although polymers having a relatively wide molecular weight can be obtained, the polymerization activity of the catalyst used is not necessarily satisfactory.

Furthermore, using a catalyst system consisting of a combination of a solid catalyst component and an organometallic compound prepared using the same components in different proportions as those described in Japanese Patent Publication No. 55-8083,
A method for producing polyolefin has also been proposed (Japanese Unexamined Patent Publication No. 59-4607).However, in this method, the resulting polyolefin has a narrow molecular weight distribution and is not suitable for blow molded products or films. There is a drawback that there is no

Furthermore, in the conventional technology, when preparing a solid catalyst component, the magnesium compound is dissolved in a solvent, or the magnesium compound is substantially dissolved by reaction with other components, so that the magnesium compound becomes solid. In many cases, a process of precipitating the catalyst component is required, and in this case, the equipment becomes complicated and the installation cost inevitably increases, and it is technically difficult to uniformly precipitate the solid catalyst component. Such problems arise.

[Problems to be Solved by the Invention] The present invention overcomes the drawbacks of the solid catalyst component used in the production of conventional ethylene polymers, and uses a material that increases polymerization activity as the solid catalyst component. In addition to being easy to prepare and low cost, the molecular weight distribution of the resulting polymer can be adjusted over a wide range, and it also provides an ethylene polymer with good powder properties such as bulk density and powder particle size distribution. By polymerizing ethylene alone or a mixture of ethylene and other α-olefins using materials with excellent properties such as vines, we efficiently produce ethylene photopolymers and polymers suitable for use in blow molded products and films. This was done for the purpose of providing a method.

[Means for Solving the Problem] As a result of intensive research to develop a solid catalyst component having the above-mentioned excellent properties, the present inventors have developed a magnesium dialkoxide, a zirconium compound, and a zirconium compound having a specific particle size. A solid catalyst component obtained by reacting a titanium compound and an organic aluminum halide compound in a specific ratio under conditions in which the magnesium dialkoxide is not substantially dissolved has been found to be suitable for the purpose. Based on this finding, we have completed the present invention.

That is, the present invention is directed to (A) (a>-tubular % formula % (1) (R' in the formula is an alkyl group having 1 to 3 carbon atoms) having an average particle diameter of 50 μm or less. Magnesila 11 dialkoxide, (b) - tubular % formula %) (in the formula, R2 is a hydrocarbon group, X2 is a halogen atom, n is a number from 0 to 4), a zirconium compound represented by <c> -m formula % formula % (
[) (R3 in the formula is a hydrocarbon group, is a hydrocarbon group, X'' is a halogen atom, and k is a number from 1 to 2). [Zr], [Ti] and [X] are
(amounts of magnesium, zirconium, titanium, and halogen atoms, respectively expressed in Durham equivalent), and are obtained by reacting them under conditions in which component (a) is not substantially dissolved. A method for producing an ethylene polymer, comprising polymerizing ethylene or a mixture of ethylene and other α-olefins in the presence of a catalyst system consisting of a combination of components and (B) an organoaluminum compound. This is what we provide.

The present invention will be explained in detail below.

In the method for producing an ethylene polymer of the present invention, a catalyst system comprising a combination of (A) a solid catalyst component and (B) an organoaluminum compound is used as a highly active catalyst.

In the preparation of the solid catalyst component (A), the magnesium dialkoxide used as component (a) is as follows:
-Maximum % Those expressed by the formula % (1) (R1 in the formula has the same two meanings as above) and whose average particle diameter is 50 μm or less are used.

R1 in maximum (1) must be an alkyl group having 1 to 3 carbon atoms, that is, a methyl group, ethyl group, rl-propyl group, or isopropyl group, and in the case of an alkyl group having 4 or more carbon atoms, , the magnesium dialkoxide becomes gel-like or liquid-like, and the object of the present invention cannot be achieved. Specific examples of the magnesium dialkoxide include:
Examples include magnesium jetoxide, magnesium jetoxide, magnesium di-n-propoxide, and magnesium diisopropoxide, and one type of these may be used, or two or more types may be used in combination.

In the present invention, the magnesium dialkoxide (component (a)) must have an average particle size of 50 μm or less, preferably in the range of 7 to 20 μm. If the average particle size exceeds 50 μm, the surface area will be small. By controlling the particle size of the magnesium dialkoxide, it is possible to obtain an ethylene polymer powder having a desired particle size.

In the preparation of the <A) solid catalyst component, the zirconium compound used as component (b) is represented by -maximum % formula %) (R2, X2 and n in the formula have the same meanings as above) compound is used. R2 in the maximum (n) above is a hydrocarbon group, which may be a saturated group or an unsaturated group, or may be a linear group, a branched group, or a cyclic group. Hydrocarbon groups may also contain heteroatoms such as sulfur, nitrogen, oxygen, silicon, and phosphorus, but preferred hydrocarbon groups include alkyl groups, alkenyl groups, and cycloalkyl groups having 1 to 20 carbon atoms. , cycloalkenyl groups, aryl groups and aralkyl groups. Specific examples of R2 include methyl group, ethyl group, n-propyl group, isopropyl group, n-
Butyl group, 5ec-butyl group, isobutyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group,
Examples include octadecyl group, allyl group, butenyl group, cyclopentyl group, cyclohexyl group, cyclohexenyl group, phenyl group, tolyl group, benzyl group, and phenethyl group.

Moreover, x2 in the above-mentioned maximum (It) is a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and among these, a chlorine atom and a bromine atom are preferable, and a chlorine atom is particularly preferable.

Typical examples of the zirconium compound represented by -maximum (I[) include, for example, zirconium tetrachloride when n is 0, and monoethoxytrichlorozirconium and mono n- propoxytrichlorozirconium, mono-lobedoxytrichlorozirconium, di-n propoxydichlorozirconium, etc.
is 2, jetoxydichlorozirconium, di-
n-propoxydichlorozirconium, di-n-butoxydichlorozirconium, etc., when n is 3, triethoxymonochlorozirconium, tri-n-propoxymonochlorozirconium, trilobtoxymonochlorozirconium, etc., and when n is 4, Examples include tetraethoxyzirconium, tetra-n-propoxyzirconium, and tetra-n-butoxyzirconium. These zirconium compounds may be used alone or in combination of two or more.

In the preparation of the solid catalyst component (A), the titanium compound used as the component (C) can be expressed by the maximum % formula % [[] (in which R3, X3 and m have the same meanings as above). Compounds are used. R3 in the above formula (I[l) is a hydrocarbon group, which may be a saturated group or an unsaturated group, or a linear or branched group,
Alternatively, it may be cyclic, and furthermore, sulfur,
Although it may have a heteroatom such as nitrogen, oxygen, silicon, or phosphorus, preferable hydrocarbon groups include an alkyl group having 1 to 20 carbon atoms, an alkenyl group, a cycloalkyl group, a cycloalknyl group, Mention may be made of aryl groups and aralkyl groups. As a specific example of R3,
The same compounds as those exemplified for R2 in the above-mentioned maximum (II) can be mentioned. Moreover, the above-mentioned −maximum (Iff
X3 in ) is a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and among these, a chlorine atom and a bromine atom are preferred, and a chlorine atom is particularly preferred.

Typical titanium compounds represented by -maximum (I[[) include titanium tetrachloride and titanium tetrabromide when m is 0, and ethoxytrichloro when m is 1 Titanium, n-propoxytrichlorotitanium, n-
Butoxytrichlorotitanium, etc., when m is 2, jetoxydichlorotitanium, di-n-propoxydichlorotitanium, di-n-butoxydichlorotitanium, etc., and when m is 3, triethoxymonochlorotitanium, triethoxydichlorotitanium, etc. Examples include n-propoxymonochlorotitanium, tri-n-butoxymonochlorotitanium, and when m is 4, tetraethoxytitanium, tetra-n-propoxytitanium, tetraisopropoxytitanium, tetra-n-butoxytitanium, and the like.

One type of these titanium compounds may be used, or two or more types may be used in combination.

In the preparation of the solid catalyst component (A), the organohalogenated aluminum compound used as the component (d) is -maximum % formula % (1) (R4, X4 and k in the formula have the same meanings as above) ) is used. R' in the maximum (IV) above is a hydrocarbon group, which may be a saturated group or an unsaturated group, a linear group, a branched group, or a cyclic group. The hydrocarbon group may also have a heteroatom such as sulfur, nitrogen, oxygen, silicon, or phosphorus. Preferred hydrocarbon groups include alkyl groups having 1 to 20 carbon atoms, alkenyl groups, and cycloalkyl groups. Mention may be made of radicals, cycloalkenyl groups, aryl groups and aralkyl groups. Specific examples of R4 include the same ones as exemplified for R2 in formula (II) above. Also, the above-maximum (1'V)
X4 in is a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, and among these, a chlorine atom and a bromine atom are preferred, and a chlorine atom is particularly preferred.

Typical examples of organic aluminum halide compounds represented by (maximum NV), for example, when k is 1, include methylaluminum dichloride, ethylaluminum dichloride, n-propylaluminum dichloride, isopropylaluminum dichloride, n- butylaluminum dichloride, isobutylaluminum dichloride, etc.; when n is 2, dimethylaluminum monochloride, diethylaluminum monochloride, di-n-
Examples include propylaluminum monochloride, diisopropylaluminum monochloride, di-n-butylaluminum monochloride, di-isobutylaluminum monochloride, and the like. One type of these organic aluminum halide compounds may be used, or two or more types may be used in combination.

The solid catalyst component (A) in the present invention includes the above-mentioned (a),
(b), (C) and (d) components, respectively, using the relational formula % formula % () (In the formula, [Mg], [Zr], [Ti] and [X] are
Magnesium, zirconium, titanium, and halogen atoms each expressed by Durham equivalent) are used in proportions that satisfy the following conditions, and prepared by reacting them under conditions in which component (a) is not substantially dissolved. Can be done.

If the above value is less than 0.05, the polymerization activity per unit weight of catalyst tends to decrease, and the amount of halogen remaining in the polymer increases, which may lead to undesirable situations such as coloring and foaming. If it is larger than 0.75, the polymerization activity per weight of transition metal decreases, and the amount of transition metal remaining in the polymer increases, which may cause problems such as coloring. Preferably, the value of is in the range of 0.2 to 0.6,
Moreover, the conditions of the above-mentioned relational expression (V) are also conditions in which the magnesium dialkoxide of component (a) is substantially difficult to dissolve.

Furthermore, if the value of is larger than 3, there will be too much (b) component and (c
) If the amount of components is too small, the polymerization activity per weight of transition metal may decrease. Also, if the amount of halogen used is too large, unnecessary halogen may cause corrosion of the equipment and increase catalyst cost. There is a risk of causing

Further, it is desirable that the component (b) and the component (C) be used in a ratio that satisfies the relational expression 0%. This [Zrl/[T
If the value of i ] is less than 0.2, the molecular weight distribution of the resulting polymer may become too narrow, while if it is greater than 20, the polymerization activity tends to decrease. Furthermore, (a>component and (
Regarding the usage ratio with component d), (a) component/(d)
A range in which the component molar ratio is greater than 0.1 and less than 100,
It is desirable to use both components so that the number is preferably in the range of 1 to 40.

In the preparation of the solid catalyst component (A), the above (a), (
There is no particular restriction on the order in which components b), (c) and (d) are brought into contact; ,
A method in which components (a), (c), (b) and (d) are contacted in sequence is preferably used. This contact is usually carried out in an inert solvent. Examples of the inert solvent include pentane, hexane, cyclohexane,
One or more hydrocarbon solvents selected from heptane and the like are preferably used.

In addition, if you heat the (a) and (b) components, or the (a) and (c) components before adding the (d) component, the catalyst components may adhere to the preparation tank. It is preferable to add component (d), which is undesirable due to the possibility of the reaction occurring, gradually while maintaining the temperature of the system in the range of 10 to 50°C so that the reaction proceeds uniformly. It is desirable to complete the addition within about 3 hours since the activity of the catalyst tends to decrease if it exceeds about 3 hours. If the temperature of the system when adding component (d) deviates from the above range, the resulting polymer will be in the form of fine powder, which is not preferable.

In this way, the solid catalyst component (A) in the present invention is obtained in a slurry state in the reaction product liquid. This slurry-like reaction product liquid may be used as it is as a catalyst component for ethylene polymerization, or after the solid catalyst component is separated and recovered from the reaction product liquid, it may be washed as necessary and used as a catalyst component for ethylene polymerization. As a separation method in this case, a known method such as a centrifugation method or a filtration method can be used, and washing can be performed using an inert hydrocarbon solvent such as pentane, hexane, cyclohexane, heptane, etc. This can be done using

The ethylene polymerization catalyst of the present invention contains the solid catalyst component (A) obtained as described above and the organoaluminum compound (B) component.
The solid catalyst component of component A) may be used as a reaction product liquid slurry as described above, or it may be separated and recovered from the slurry and used by dispersing it in an inert hydrocarbon solvent at an appropriate concentration in an inert gas. You can.

There are no particular restrictions on the organoaluminum compound used as the component (B), but usually the one expressed by the formula % is used.R% and R6 in formula 6 are alkyl groups, alkenyl groups, cycloalkyl groups. , a cycloalkenyl group, an aryl group, an aralkyl group, and the like, and X5 is a halogen atom such as a chlorine atom or a bromine atom.

Examples of such organic aluminum compounds include trimethylaluminum, triethylaluminum, triisopropylaluminum, triisobutylaluminum, diethylaluminum monochloride, diisopropylaluminum monochloride, diisobutylaluminum monochloride, diethylaluminum monomethoxide, dimethylaluminum monoethoxide , diethylaluminium monobutoxide, diethylaluminum monophenoxide, ethylaluminum dichloride, isopropylaluminum dichloride, methylaluminum sesquichloride, ethylaluminum sesquichloride, and the like.

These compounds may be used alone or in combination of two or more.

The ratio of the solid catalyst component (A) to the organic aluminum compound (B) is such that the ratio of aluminum atoms to the total of titanium atoms and zirconium atoms in the solid catalyst component is usually 1 to 1000, preferably 1 to 1000 in atomic ratio. 10-200
is selected to be within the range of The catalyst containing the solid catalyst component and the organoaluminum compound may be prepared separately from the configuration of the polymerization reaction system described later, or may be prepared substantially simultaneously with the configuration of the polymerization reaction system.

Next, to explain one preferred example of the polymerization method of ethylene alone or a mixture of ethylene and other α-olefins in the method of the present invention, first, carbonization of an inert solvent such as pentane, hexane, cyclohexane, heptane, etc. Adding predetermined amounts of a solid catalyst component (A) and an organic aluminum compound (B) to a hydrogen solvent,
Next, ethylene or a mixture of ethylene and other α-olefins is introduced into this system and polymerization is carried out. There are no particular restrictions on the polymerization method or system, such as solution polymerization, suspension polymerization, or gas phase polymerization. Any method including legal methods can be used, and both continuous polymerization and discontinuous polymerization are possible.

Regarding the mixing ratio of each component to compose the reaction system,
Taking the case of solution polymerization and suspension ffi as an example, the above (A
) The solid catalyst component of the component usually has a total of titanium atoms and zirconium atoms of 0.0005 to 1 ozg atoms/l.
, preferably in the range of 0.001 to Lag atoms/l, while the organic aluminum compound of component (B) has Aj! /Ti+Zr atomic ratio is usually in the range of 1 to 1000, preferably 10 to 200.

In addition, the pressure of the reaction system is usually normal pressure to 100 kg/c.
m2, preferably in the range of 3 to 50 kg/cm2, and the reaction temperature is usually 20 to 200°C, preferably 5
It is selected within the range of 0 to 150°C. The reaction time is usually 5
The time period ranges from about 30 minutes to 10 hours, preferably from 30 minutes to 5 hours.

Molecular weight adjustment during polymerization is possible by adjusting polymerization conditions such as polymerization temperature, catalyst concentration, catalyst composition, catalyst/monomer ratio, etc., but it is more effective to carry out in the presence of hydrogen.

In the method of the present invention, when a mixture of ethylene and Ike's α-olefin is used as a raw material monomer, other α-olefins may be used.
-Olefins such as propylene, butene-1
, pentene-1, octene-1,4-methylpentene-
1, vinylcyclohexane, etc. One type of these α-olefins may be used, or two or more types may be used in combination.

Furthermore, in the present invention, in addition to the above-mentioned catalyst components, in the catalyst group or the polymerization reaction system, as desired,
Furthermore, ethylene may be polymerized by adding an organometallic compound such as organic zinc or various additives that are usually added during ethylene polymerization using a Ziegler catalyst.

The ethylene polymer thus produced can be recovered by a conventional method.

According to the method of the present invention, the activity of the catalyst used is extremely high;
Since the monomer/catalyst ratio can be made sufficiently large, it is not necessarily necessary to provide a special decatalyst step.

Note that FIG. 1 shows a flowchart of an example of an embodiment of the present invention.

[Example] Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

The physical properties of the obtained polymer were determined as follows.

(i) M r z, +g Based on JIS, it was determined as a melt index under the condition of 190″C1 load of 2.16 kg.

(2) F, R.

MI2=MI2.6 for g (190℃, load 2
1.6Ag) and calculate the melt flow ratio (F, R,
) was used to evaluate the molecular weight distribution.

(Examples 1 to 3) (1) Preparation of solid catalyst components Zr (〇-n-Bu) in the amounts shown in Table 1, and Ti
(0-n-Bu)<e? 50 zl of dissolved hexane,
While stirring, 20"
After dropping for 15 minutes at a temperature of C, E
50% by weight hexane dilution of tAI2c12 92'Il
was added dropwise over a period of 120 minutes at a temperature of 35°C while stirring, and the mixture was allowed to react for another 120 minutes while flowing down three chambers. Next, wash with dry hexane until no chlorine is detected in the liquid, and then wash the entire volume with hexane for 500yi! Closed.

(2) Production of ethylene polymer In an autoclave with a capacity of 11 equipped with a stirrer, n-
Add 400x (l) of hexane, raise the temperature to 80°C, fully replace the internal atmosphere with hydrogen gas, and add 2.9k of hydrogen.
g/cx”・G, and then ethylene was added to 5,4
1, which introduced up to kg/cz'・G, then added 0 to this.
．． The solid catalyst component obtained in (1) above containing 0.10 mmol of Ti and 0.50 mmol of triisobutylaluminum
IIIol was added and polymerization was carried out for 1 hour while supplying ethylene so as to maintain the total pressure at 5.4 kg/cm2·G. The results are shown in Table 2.

(Example 4) In Example 1, Ti(0-n-BLI)4 was replaced by Ti
(Other than changing to 0-i-P rL, it was carried out in the same manner as in Example 1. Table 1 shows the catalyst preparation conditions, and Table 2 shows the polymerization results.

(Examples 5 to 8) Except for changing the temperature and time required for dropping a 50 weight hexane diluted solution of EtlCl as shown in Table 1,
It was carried out in the same manner as in Example 1. The results are shown in Table 2.

(Example 9) The average particle diameter of Mg(○Et)2 in Example 1 was set to 6μ.
The same procedure as in Example 1 was carried out except that m was changed.

The catalyst preparation conditions are shown in Table 1, and the polymerization results are shown in Table 2.

(Comparative Example 1) In Example 1, Zn(0-n-Bu)4 and Ti(0
The same procedure as in Example 1 was carried out except that the amount of -n-Bu) used was changed as shown in Table 1.

The results are shown in Table 2. In the zero comparative example, the polymerization activity was low, and coloration of the polymer was observed.

(Comparative Example 2) Zr(0-n-Bu)<, T i (
Mix ○−n Bu)< and Mg(○Et)2, add hexane, and make the total amount 200++4! After closing and stirring for 20 hours under reflux, add E and tA.
ICI2 diluted with 50% hexane 3101I! was added dropwise over 240 minutes at 35° C. while stirring, and reacted for 120 minutes under reflux.Then, the solution was washed with dry hexane until no chlorine was detected in the solution, and the total volume was made up to 500 zl with hexane. Thereafter, ethylene was polymerized in the same manner as in Example 1. The results are shown in Table 2.

In this comparative example, deposits were formed on the vessel wall during the preparation of the solid catalyst component and remained until the end. In addition, the polymerization activity was low, and coloring of the polymer was observed.

(Comparative Example 3) The same procedure as in Example 1 was carried out except that M g (OE t )2 having an average particle diameter of 56 μm was used. Table 1 shows the catalyst preparation conditions, and Table 2 shows the polymerization results.

In this comparative example, the polymerization activity was low, and the obtained polymer contained a large amount of both fine powder and coarse powder.

(The following is a blank space) [Effects of the Invention] The method of the present invention is based on the combination of a solid catalyst component obtained by reacting magnesium dialkoxide, a zirconium compound, a titanium compound, and an organic aluminum halide compound with an organic aluminum compound as a polymerization catalyst. A method for producing an ethylene heavy body by polymerizing ethylene alone or a mixture of ethylene and other α-olefins using a solid catalyst component prepared in the method of the present invention. It has superior polymerization activity, is easier to prepare, and is lower in cost than ethylene polymers, and the molecular weight distribution of the resulting ethylene polymer can be adjusted over a wide range. It is possible to provide an ethylene polymer with good powder properties.

The ethylene polymer obtained by the method of the present invention is suitable for use in, for example, blow molded products and films.

I can stay.

[Brief explanation of the drawing]

Claims (1)

[Claims] (1) (A) (a) Magnesium with an average particle diameter of 50 μm or less, represented by the general formula Mg(OR^1)_2, (R^1 in the formula is an alkyl group having 1 to 3 carbon atoms) Dialkoxide, (b) general formula Zr(OR^2)_nX^2_4_-_n (R^2 in the formula is a hydrocarbon group, X^2 is a halogen atom,
n is a number from 0 to 4), (c) a zirconium compound represented by the general formula Ti(O
R^3)_mX^3_4_-_m (R^3 in the formula is a hydrocarbon group, X^3 is a halogen atom,
m is a number from 0 to 4) and (d) a titanium compound represented by the general formula AlR^4_kX^4_3_-_k (in the formula, R^4 is a hydrocarbon group, X^4 is a halogen atom,
is a number of 1 to 2) Each of the organic aluminum halide compounds represented by
5 and ([Zr]/[Ti])・([X]/{[Mg]+[T
i]+[Zr]})≦3([Mg], [Zr],
[Ti] and [X] are the amounts of magnesium, zirconium, titanium, and halogen atoms, respectively, expressed in gram equivalent), and under conditions where component (a) is not substantially dissolved. It is characterized by polymerizing ethylene alone or a mixture of ethylene and other α-olefins in the presence of a catalyst system consisting of a combination of a solid catalyst component obtained by reacting them and (B) an organoaluminum compound. A method for producing an ethylene polymer.