GB2036764A - Process for preparing a copolymer - Google Patents

Abstract

Preparing an ethylene copolymer having a melt index of 0.1 to 10 and a density of 0.900 to 0.945 by copolymerizing (1) ethylene, (2) propylene and/or butene-1 and (3) an alpha -olefin having 6 to 12 carbon atoms while maintaining the total amount of said components (2) and (3) in the range of from 1 to 40 mol % of said component (1) and the molar ratio of said component (2) to said component (3) in the range of from 0.01 :0.99 to 0.90:0.10, in a substantially solvent-free vapor phase and in the presence of a catalyst comprising a solid substance and an organoaluminium compound, said solid substance containing magnesium and titanium and/or vanadium.

Description

SPECIFICATION Process for preparing a copolymer This invention relates to a new process for preparing a medium or low density ethylene copolymer according to the vapor phase polymerization method using a Ziegler-type catalyst of high activity.

More particularly, this invention is concerned with a process for preparing an ethylene copolymer having a melt index of 0.1 to 10 and a density of 0.900 to 0.945 by copolymerising (1) ethylene, (2) propylene and/or butene-1 and (3) an a-olefin having 6 to 12 carbon atoms, in a substantially solvent-free vapor phase and in the presence of a catalyst comprising a solid substance and an organoaluminium compound, said solid substance containing magnesium and titanium and/or vanadium.

Heretofore, polyethylenes obtained by polymerization using a catalyst consisting of a transition metal compound and an organometallic compound have generally been prepared by the slurry polymerization method, but usually produced are only those having a density not lower than 0.945 g/cm3 which value is considered to be the limit of preventing the resulting polymer from being deposited on the inner wall or stirrer inside the reactor in polymerization, or fouling.

Medium or low density polyethylenes having a density not higher than 0.945 g/cm3 are usually prepared by the so-called high pressure process using a radical catalyst. But the high-temperature solution polymerization method using a Ziegler-type catalyst also began to be tried quite recently.

Low density polyethylenes according to the high pressure process, as compared with high density polyethylenes, are advantageous in that they are superior in transparency and flexibility, but are disadvantageous in that films formed therefrom are low in stiffness.

Medium density polyethylenes according to the high-temperature solution polymerization method using a Ziegler-type catalyst are disadvantageous in that they are inferior in transparency and films formed therefrom are sticky to the touch.

In reference to the manufacturing method, the high pressure process is disadvantageous in that it requires a very high pressure and also a very high temperature near the temperature at which an organic compound undergoes thermal decomposition, and thus is very dangerous and inevitably requires an increased amount of money to be invested in its manufacturing equipment and also increased operation costs for electric power, etc. The high-temperature solution polymerization method is also disadvantageous in that, since the resulting polyethylene must be handled as a solution, the operation is compelled to be done at a relatively low concentration, resulting in inferior productivity, and in that for the same reason it is impossible to produce polyethylenes of high molecular weight.It is further disadvantageous in that the resulting polymer contains a large amount of wax because the polymerization is carried out at a high temperature, thus requiring an equipment for its separation, and in that the solution polymerization at a high temperature is accompanied by vigorous side reactions such as hydrogenation and dimerization of ethylene, and consequently the unit or consumption of ethylene and that of hydrogen are so much increased.

In the production of polyethylene, moreover, copolymerizing ethylene with another monomer has heretofore been known as the method of lowering the density of polyethylene. However, in preparing a medium or low density polyethylene by the copolymerization of ethylene and other comonomer according to such known method, an extremely excess amount of comonomer is usually required and this is very disadvantageous in point of process. And if the copolymerization is carried out according to the slurry polymerization method, the by-production of a low molecular weight polymer or a solvent-soluble polymer is increased, so that the polymerization product takes in solvent and becomes milky or mushy, which makes reactor operation or slurry transport difficult. In such a condition, moreover, it is no longer easy to separate the polymer from the solvent.Furthermore, there occurs polymer adhesion inside the polymerization vessel due to the fouling of copolymerizate, with the resulting deterioration in heat transfer characteristic making it impossible to control the polymerization temperature.

In recent years there have been made various studies for the improvement of catalyst activity. For example, it is known that a catalyst system obtained by attaching a transition metal to a magnesiumcontaining solid carrier such as MgO, Mg(OH)2, MgC12, MgCO3, or Mg(OH)CI, and thereafter combining it with an organometallic compound, can serve as an olefin polymerizing catalyst of extremely high activity. It is also known (see, for example, Japanese Patent Publication No. 12105/64, Belgian Patent No.742,112, Japanese Patent Publications Nos. 13050/68 and 9548/70) that the reaction product of an organomagnesium compound such as RMgX, R2Mg or RMg(OR) and a transition metal compound can serve as a high polymerization catalyst for olefins.

However, even if such Ziegler-type catalysts of high activity are used in the slurry polymerization or solution polymerization of olefins to lower the polymer density, the foregoing drawbacks heretofore have not been eliminated at all.

On the other hand, a vapor phase polymerization of a-olefins such as ethylene and propylene, namely an olefin polymerization is a substantial absence of liquid phase has also been tried in recent years. In this method, a catalyst is fed into a bed consisting of pre-introduced polymer particles and contacts a gaseous, starting olefin to produce an olefin polymer. In this case, using a high activity catalyst can avoid the recovery step for polymerization solvent and also the catalyst separation and inactivation step, so that the process as a whole can be simplified to a large extent. Thus, such a vapor phase polymerization method is an attractive method; however, it still involves many problems to be solved for the preparation of ethylene polymers.For example, the catalyst used should have a sufficiently high activity to the extent that the residual catalyst removing step is ndt needed; there should be no adhesion of the resulting polymer particles to the reactor wall or stirrer; there should occur no abnormal phenomenon which would cause blocking of the polymer discharge port from the reactor or transport line, such as coarsening or agglomeration of polymer particles; ultra-fine particles which scatter easily should be produced in as small a proportion as possible in polymerization; and particle properties, e.g. bulk density, should be satisfactory.

Having made comprehensive studies about these problems, we have found a method capable of solving all of them and capable of performing a vapor phase polymerization of ethylene advantageously on an industrial scale, and we have applied for a patent on that finding. Having also made comprehensive studies about the method of preparing a medium or low density ethylene copolymer by copolymerizing ethylene with other a-olefin according to the vapor phase polymerization method, we have found a method capable of solving all of the aforesaid problems and capable of producing more easily a medium or low density ethylene copolymer having a high melt index, and have applied for a patent also on this finding. (See our copending Patent Applications Nos. 7935232, Serial No. 2033910,7935829, Serial No. 2033911,7936295, Serial No. 2034336 and 7936296, Serial No. 2034337.

This invention relates to the improvement of the aforesaid inventions. That is, what is important in copolymerizing ethylene with an a-olefin according to the vapor phase polymerization method is that, in addition to the foregoing problems, the molecular weight, molecular weight distribution and density should be easy to adjust and the physical properties such as for example transparency and strength of the resulting polymer should be satisfactory. On these problems this invention is a further improvement from the inventions already filed by us, and a new process is here provided.

We have made comprehensive studies on the above problems; as a result, we have solved various problems such as the improvement of particle properties, e.g. bulk density of the resulting polymer particles, the same improvement against coarsening or adhesion of polymer particles, improvement of physical properties, e.g. transparency and strength, improvement of polymerization activity, the requirement that there should be obtained a polymer of high melt index easily, and the requirement, which is most important industrially, that a copolymer having excellent physical properties should be obtained inexpensively. Thus the present invention has been accomplished.

More particularly, we have completed a vapor phase polymerization process for (1) ethylene with a mixture of (2) propylene and/or butene-1 and (3) an a-olefin having 6 to 12 carbon atoms, which process allows a vapor phase polymerization reaction to be carried out in a very stable manner and which process as a whole is very simplified because the residual catalyst removing step can be omitted.

Working the process of this invention allows easy adjustment of molecular weight and allows a copolymer having desired physical properties to be prepared inexpensively, though a detailed description on this respect will be given later in this text. Furthermore it has become clear that the copolymer of (1) ethylene, (2) propylene and/or butene-1 and (3) an a-olefin having 6 to 12 carbon atoms, prepared by working the process of this invention, is superior in strength and in transparency and has a high resistance to environmental stress cracking.

This invention is concerned with a process for preparing an ethylene copolymer having a melt index of 0.1 to 10 and a density of 0.900 to 0.945 by copolymerizing (1) ethylene, (2) propylene and/or butene-1 and (3) an a-olefin having 6 to 12 carbon atoms while maintaining the total amount of the components (2) and (3) in the range of from 1 to 40 mol% of the component (1) and the molar ratio of the component (2) to the component (3) in the range of from 0.01: 0.99 to 0.90: 0.10, in the presence of a catalyst comprising a solid substance and an organoaluminium compound, said solid substance containing magnesium and titanium and/or vanadium.

It has become clear that according to the process of this invention, that is, by copolymerizing in vapor phase (1) ethylene with a mixture of (2) propylene and/or butene-1 and (3) an a-olefin having 6 to 12 carbon atoms in the quantitative ratio specified herein and in the presence of a catalyst comprising a solid substance and an organoaluminium compound, said solid substance containing magnesium and titanium and/or vanadium, the reaction can be carried out in a very stable manner and in an extremely high polymerization activity, with decreased production of coarse or ultra-fine particles, improved particle properties and bulk density, and with little adhesion to the reactor and agglomeration of polymer particles.Besides, it is quite unexpected and surprising that according to the process of this invention, as will be referred to more in detail later in this text, a copolymer having a high melt index and superior physical properties, e.g. transparency, can be obtained easily and that inexpensively.

As we have already found, the vapor phase polymerization reaction of ethylene and propylene, that of ethylene and butene-1 and that of ethylene and a C5 to C18 a-olefin have the respective superior advantages, and the resulting copolymers exhibit superior strength and other physical properties. For example, however, the copolymerization reaction of ethylene and propylene or butene-1 can easily afford a copolymer having a relatively high melt index, but the transparency of the copolymer leaves a little to be further improved though it is superior. On the other hand, in the copolymerization reaction of ethylene and a C5 to C18 a-olefin, the particle properties were good like those in the aforesaid copolymerization reaction of ethylene and propylene or butene-1, but the melt index was relatively low and this tendency became distinct when it was tried to expand the molecular weight distribution. Furthermore, in the copolymerization reactions described in the specifications of our patent applications previously cited, as compared with other known methods, a-olefins as comonomers are incorporated well into copolymers, greatly contributing to the lowering of density and the improvement of transparency.However, such copolymerization reactions are disadvantageous in that the C5 to C18 a-olefins used therein, e.g. hexene-1, 4-methylpentene-1, and octene-1, are very expensive and trying to obtain desired physical properties requires large amounts of these a-olefins, which leads to very expensive copolymers. To solve these problems, therefore, we have made further studies and as a result accomplished this invention.

This invention relates to a process for preparing a copolymer of (1) ethylene, (2) propylene and/or butene-1 and (3) a C6 to C12 ct-olefin, having a melt index of 0.1 to 10 and a density of 0.900 to 0.945, characterized in that the said components (1), (2) and (3) are contacted together in vapor phase and in the presence of a catalyst comprising a solid substance and an organo-aluminium compound, said solid substance containing magnesium and titanium and/or vanadium, while maintaining the total amount of the components (2) and (3) in the range of from 1 to 40 mol% of the component (1) and the molar ratio of the component (2) to the component (3) in the range of from 0.01: 0.99 to 0.90 : 0.10.Thus, by using in the said copolymerization the components (2) propylene and/or butene-1 and (3) a C6to C12 a-olefin in a predetermined ratio so that the total amount of the two is in a predetermined value with respect to the component (1) ethylene, it is made possible to carry out a very stable vapor phase polymerization easily to provide a copolymer having good particle properties, a high melt index, a very high transparency and superior strength and resistance to impact and to environmental stress cracking. This is a great advantage of this invention.It is also a special advantage of this invention that the process of the invention can easily afford a copolymer superior transparency, strength and resistance to impact and to environmental stress cracking, inexpensively without requiring a large amount of expensive colefins such as hexene-1, 4-methylpentene-1 and octene-1. In this invention, moreover, the copolymerization reaction can be carried out even at a relatively low temperature and a medium or low density ethylene copolymer having a high melt index can thereby be obtained easily, and this is very advantageous to the prevention of polymer adhesion to the reactor and its agglomeration.

This point is also an advantage of the invention. Thanks to these advantages, the copolymer of this invention can be obtained efficiently by a vapor phase polymerization as set forth hereinbefore.

The copolymer prepared according to the process of this invention has an extremely high transparency, good appearance and gloss, and excellent flexibility and elasticity even at a low temperature, not to mention at room temperature. Despite possessing such an excellent flexibility, the copolymer in question exhibits a strength equal to or even higher than that of ordinary polyolefins. The copolymer in question scarcely contains unsaturated bond, residual catalyst or other impurities, so it is very superior in weathering- and chemicals resistance and also in electrical characteristics such as dielectric loss, break-down voltage and resistivity. It further exhibits a very high resistance to impact and to environmental stress cracking.

Consequently the copolymer obtained according to the process of this invention can be formed into various products, e.g. films, sheets, hollow containers and electric wires, by the existing molding methods such as extrusion molding, blow molding, injection molding, press forming and vacuum forming, and thus can be used in various applications. Specially in the field of films the copolymer in question exhibits its features because it is superior in strength, elongation, transparency, anti-blocking property, heat-sealing property and flexibility. Furthermore, it is worthy of special mention that the process of this invention can afford a copolymer which when extracted with hexane only gives an extremely small amount of extract and which satisfies the "U.S.Food Medicines Administration Standard on Extracts to be Contacted with Foods" (n-hexane extract not more than 5.5% by weight at 50"C). And the copolymer thus prepared can be used safely as a food packaging film. It is also a suitable resin for blow molding because of its superior transparency, stiffness and resistance to environmental stress cracking. It is further superior in electrical characteristics and is easy to be extrusion-molded, which allow the copolymer in question to be used suitably for electric wires.

The catalyst system used in the invention comprises the combination of a solid substance and an organoaluminium compound, said solid substance containing magnesium and titanium and/or vanadium.

The said solid substance is obtained by attaching in known manner a titanium compound and/or a vanadium compound to an inorganic solid carrier such as metallic magnesium, magnesium hydroxide, magnesium carbonate, magnesium oxide or magnesium chloride; or double salt, double oxide, carbonate, chloride or hydroxide containing magnesium atom and a metal selected from silicon, aluminium and calcium; or an inorganic solid carrier exemplified which has been treated or reacted with an oxygen-containing compound, a sulfur-containing compound, hydrocarbon, or a halogen-containing substance.

By way of illustrating a titanium compound and/or a vanadium compound used in the invention, mention may be made of halides, alkoxyhalides, oxides and halogenated oxides of titanium and/orvanadium,for example, tetravalent titanium compounds such as titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, monoethoxytrichlorotitanium, diethoxydichlorotitanium, triethoxymonochlorotitanium, tetraethoxytitanium, monoisopropoxytrichlorotitanium, diisopropoxydichlorotitanium, and tetraisopropoxytitanium; titanium trihalides obtained by reducing titanium tetrahalides with hydrogen, aluminium titanium or an organometallic compound; trivalent titanium compounds obtained by reducing tetravalent alkoxytitanium halides with an organometallic compound; tetravalent vanadium compounds e.g. vanadium tetrachloride; pentavalent vanadium compounds such as vanadium oxytrichloride and orthoalkylvanadate; and trivalent vanadium compounds such as vanadium trichloride and vanadium triethoxide. Among these titanium compounds and vanadium compounds, tetravalent titanium compounds are specially preferred.

The catalyst used in the invention comprises the combination of a solid substance and an organoaluminium compound, said solid substance obtained by attaching a titanium compound and/or a vanadium compound to a solid carrier as referred to previously. Preferred examples of such catalyst are those obtained by combining an organoaluminium compound with the following solid substances (in the formulae shown below R represents an organic radical and X represents halogen):: MgO-RX-TiCl4 system (see Japanese Patent Publication No.3514/76), Mg-SiCI4-ROH-TiCl4 system (see Japanese Patent Publication No. 23864/75), MgCl2-Al(OR)2-TiCl4 system (see Japanese Patent Publications Nos. 152/76 and 15111/77), MgCl2-aromatic hydrocarbon-TiCI4 system (see Japanese Patent Publication No. 48915/77), MgC12-SiC14-ROH-TiCI4 system (see Japanese Patent Laying Open Print No. 106581/74), Mg(OOCR)2-Al(OR)3-TiCl4 system (see Japanese Patent Publication No. 11710/77), MgCl2-RX-TiCl4system (see Japanese Patent Laying Open Print No.

42584/77), Mg-POCI3-TiCl4 system (see Japanese Patent Publication No. 153/76), MgCl2-AlOCl-TiCl4 system (see Japanese Patent Laying Open Print No. 133386/76).

In another example of catalyst system which is used suitably in this invention, the reaction product of an organomagnesium compound such as a so-called Grignard compound and a transition metal compound is used as the solid substance and it is combined with an organoaluminium compound. As the organomagnesium compound there may be used those represented by the general formulae RMgX, R2Mg and RMg(OR) wherein R is an organic radical and Xis halogen, and ether complexes thereof, as well as these organomagnesium compounds after modification with other organometallic compounds such as organosodium, organolithium, organopotassium, organoboron, organocalcium and organozinc.

Examples of such catalyst systems include the combination of an organoaluminium compound and the following solid substances: RMgX-TiC14 system (see Japanese Patent Publication No. 39470/75),

(see Japanese Patent Laying Open Print No.119977174),

(see Japanese Patent Laying Open Print No. 119982/74).

In these catalyst systems, a titanium compound and/or a vanadium compound may be used as the mixture or the addition product with an organocarboxylic acid ester. The foregoing magnesium-containing solid carriers may be contacted, before their use, with an organocarboxylic acid ester. And an organoaluminium compound may be used as the mixture or the addition product with an organocarboxylic acid ester.

Furthermore, in every case in this invention, the catalyst system may be prepared in the presence of an organocarboxylic acid ester.

As the organocarboxylic acid ester referred to above there may be employed various aliphatic, alicyclic and aromatic carboxylic acid esters preferably C7 to C72 aromatic carboxylic acids. Examples are alkylesters such as methyl and ethyl of benzoic acid, anisic acid and toluic acid.

To illustrate organoaluminium compounds which may be used in the invention, mention may be made of those represented by the general formulae RBAI, R2AIX, RAIX2, R2AIOR, RAI(OR)X and R3Al2X3wherein R, which may be same or different, is C1 to C20 alkyl or aryl and Xis halogen, such as triethylaluminium, triisobutylaluminium, trihexylaluminium, trioctylaluminium, diethylaluminium chloride, ethylaluminium sesquichloride, and mixtures thereof.

The amount of an organoaluminium compound to be used in the invention is not specially limited, but usually it is in the range of from 0.1 to 1000 molls per mol of the transition metal compound.

The polymerization reaction is carried out by polymerizing in vapor phase a mixture of (1) ethylene, (2) propylene and/or butene-1 and (3) a C6to C12 a-olefin. Known reactors may be used such as a fluidized bed and an agitation vessel.

Polymerization reaction conditions involve temperatures usually in the range of from 20 to 11 00C, preferably from 50 to 100 C, and pressures in the range of from atmospheric pressure to 70 kg/cm2-G, preferably from 2 to 60 kg'cm2-G. Adjustment of the molecular weight may be performed by changing the polymerization temperature, the molar ratio of catalyst or the amount of comonomer, but the addition of hydrogen into the polymerization system is more effective for this purpose.Of course, using the process of this invention there can be conducted, without any trouble, two or more stage polymerization reactions involving different polymerization conditions such as different hydrogen and comonomer concentrations and different polymerization temperatures.

In this invention, moreover, the foregoing catalyst systems may be contacted with an a-olefin and thereafter used in the vapor phase polymerization reaction, whereby the polymerization activity can be improved to a large extent and the operation performed more stably than in untreated condition. In this case, various a-olefins are employable, but preferably C3 to C12 a-olefins and more preferably C3 to C8 a-olefins, for example, propylene, butene-1, pentene-1, 4-methylpentene-1, heptene-1, hexene-1, octene-1, and mixtures thereof.The temperature and time in the above contact treatment for the catalyst used in the invention with an a-olefin can be selected in a wide range, for example, in the range of from 0 to 200"C, preferably from 0" to 1 10"C, and in the range of from 1 minute to 24 hours.

The amount of an -olefin to be contacted with the catalyst can also be selected in a wide range, but usually 1 g. to 50,000 g., preferably 5 g. to 30,000 g., of a-olefin is used per gram of the foregoing solid substance, and it is desirable that 1 g. to 500 g. of the a-olefin per gram of the foregoing solid substance be reacted. The pressure in the above contact treatment may be chosen optionally, but usually and desirable it is in the range of from -1 to 100 kg/cm2G.

In the treatment with an ct-.olefin, an organoaluminium compound may be combined wholly with the foregoing solid substance and thereafter the resulting mixture may be contacted with an a-olefin, or it may be combined partially with the foregoing solid substance, then the resulting mixture contacted with an a-olefin and the remaining portion of the organoaluminium compound separately added in the vapor phase polymerization reaction of ethylene. The aforesaid contact treatment for the catalyst used in the invention with an a-olefin may be performed, without any trouble, in the presence of hydrogen gas or other inert gas such as nitrogen, argon or helium.

The component (3) used in the invention, namely a-olefins having 6 to 12 carbon atoms, may be straight chained or branched. Examfples are hexene-1,4-methylpentene-1, heptene-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, and mixtures thereof, among which hexene-1 and 4-methylpentene-1 are preferred.

The mixing ratio of (2) propylene and/or butene-1 and (3) a C6to C12 a-olefin, which are used in the process of the invention, should be such that the molar ratio of (2) to (3) is in the range of from 0.01: 0.99 to 0.90 0.10; and the amount of the components (2) and (3) used should be such that the total amount of the two is in the range of from 1 to 40 mol% of the amount of ethylene used.

If the mixing ratio of (2) and (3) and the total amount of (2) and (3) with respect to ethylene are outside the above ranges, it is impossible to obtain the object product of this invention, namely an ethylene-a-olefin copolymer having a melt index of 0.1 to 10 and a density of 0.900 to 0.945.

The amount of these comonomers used can be adjusted easily by control of the gaseous composition in the polymerization vessel.

In the copolymerization according to the process of this invention, moreover, there may be added various dienes such as butadiene, 1,4-hexadiene, 1,5-hexadiene, vinyl norbornene, ethylidene norbornene, and dicyclopentadiene.

Working examples of this invention are given below, but these are for illustration only to work the invention and are not intended to place limitation thereon.

Example 1 1 kg. of anhydrous magnesium chloride, 50 g. of benzyl chloride and 170 g. of titanium tetrachloride were subjected to ball milling for 16 hours at room temperature under a nitrogen atmosphere to give a solid substance which contained 35 mg. of titanium per gram thereof.

There were used a stainless steel autoclave as a vapor phase polymerization apparatus, a blower, a flow rate adjuster and a dry cyclone to form a loop, and the temperature of the autoclave was adjusted by flowing warm waterthrough the jacket.

Into the autoclave held at 70"C were fed the solid substance prepared above and triethylaluminium at the rates of 250 mglhr and 50 mmol/hr, respectively, and an adjustment was made so that in the vapor phase in the autoclave there were 3.5 mol% propylene, 3.5 mol% 4-methylpentene-1, 75 mol% ethylene and 18 mol% hydrogen. Under this condition a polymerization was made while recycling the intrasystem gases by the blower. The resulting ethylene copolymer had a bulk density of 0.399 g/cc, a melt index (MI) of 2.4 g/10 min and a density of 0.924 g/cc, and the greater part thereof was powdered with particle sizes within the range of from 250 to 500 it. The polymerization activity per gram of titanium was 1 95,000g. copolymer, and thus it was high.

After continuous operation for 10 hours, the interior of the autoclave was checked to find that it was clean with no polymer adhesion.

The copolymer was formed into an inflation film, which was superior in both strength and transparency.

The film when extracted with hexane for 4 hours at 50oC gave only a very small amount,1.1%, of extract, from which it is seen that this film is very advantageous to its practical use.

In the case of using a single comonomer, as will be shown in the following Comparative Examples 1 and 2, in the former example the density is not lowered sufficiently and in the latter the melt index becomes far smaller at the same hydrogen concentration. In contrast therewith, in the present example of this invention it is apparent that a low density copolymer having a sufficiently high melt index can be obtained easily and inexpensively though the expensive comonomer, 4-methylpentene-1, is used only in a very small amount.

Comparative Example 1 Polymerization was carried out in the same manner as in Example 1 except that the gaseous composition in the vapor phase was made 75 mol% ethylene, 7 mol% propylene and 18 mol% hydrogen without using 4-methylpentene-1.

The resulting copolymer had a bulk density of 0.393, Ml of 2.6 and a density of 0.934, and the polymerization activity per gram of titanium was 203,200g.copolymer.

A film was formed from the copolymer in the same way as in Example 1, but it was inferior in transparency and strength to the one formed in Example 1. The hexane extract of the so-formed film was 5% and thus was comparatively small in amount, but when compared with that in Example 1, it is a large amount and is not desirable in practicai use.

Comparative Example 2 Polymerization was carried out in the same manner as in Example 1 except that the gaseous composition in the vapor phase was made 68 mol% ethylene, 7 mol% 4-methylpentene-1 and 25 mol% hydrogen without using propylene.

The resulting copolymer had a bulk density of 0.395, Ml of 2.2 and a density of 0.918, and the polymerization activity was 135,600 g.copolymer/g.Ti, from which it is seen that an attempt to give about the same melt index as that in Example 1 requires a larger amount of hydrogen and that the expensive 4-methylpentene-1,which therefore results in lowering of the polymerization activity.

Example 2 Polymerization was carried out in the same manner as in Example 1 except that the gaseous composition in the vapor phase was made 4 mol% butene-1, 4 mol% 4-methylpentene-1, 72 mol% ethylene and 20 mol% hydrogen.

The resulting ethylene copolymer was powdered having a bulk density of 0.382, Mi of 2.2 and a density of 0.925, and the polymerization activity was 189,500 g.copolymer g.Ti. The hexane extract of the copolymer was 0.8% and thus was very small amount.

After continuous polymerization for 10 hours, the interior of the autoclave was checked to find no polymer adhesion therein.

Thus, it is seen that at a lower hydrogen content there can easily be obtained product with a high melt index.

The copolymer was formed into an inflation film, which was superior in both transparency and strength.

Example 3 830 g. of anhydrous magnesium chloride, 50 g. of aluminium oxychloride and 170 g. of titanium tetrachloride were subjected to ball milling for 16 hours at room temperature under a nitrogen atmosphere to give a solid substance which contained 41 mg. of titanium per gram thereof.

The solid substance prepared above and triethylaluminium were fed at the rates of 200 mg/hr and 50 mmol/hr, respectively, and a polymerization was made at 70"C in the same way as in Example 1.

After continuous polymerization for 10 hours, the interior of the autoclave was checked to find no polymer adhesion therein.

The resulting copolymer had a bulk density of 0.387, Ml of 2.1, a density of 0.917 and an average particle size of 250 jsl, and the polymerization activity was 226,500 g.copolymer/g.Ti.

Thus, it is seen that at a low temperature of 70"C there is obtained product with a high melt index in high polymerization activity, and that the particle properties are good.

The copolymer was formed into an inflation film without pelletizing to find that the stability of bubble was good and the correction of thickness deviation was easy, and that the film was superior in both transparency and strength.

Example 4 Using the catalyst system prepared in Example 3 there was conducted polymerization in the same manner as in Example 2.

The polymerization was continued for 10 hours, but there was neither pipe clogging nor defective heat transfer. After termination of the polymerization, the interior of the autoclave was checked to find that it was clean.

The resulting polymer was a clean powder with a bulk density of 0.392, and the melt index and density thereof were 2.0 and 0.915, respectively. The polymerization activity was 210,800 g-copolymer/g-Ti, and/thus there was obtained product with a high melt index in a very high polymerization activity.

The copolymer was press-formed into a sheet 0.2 mm thick, whose strength and elongation were measured and found to be 205 kglcm2 and 650%, respectively.

Example 5 830 g. of anhydrous magnesium chloride, 120 g. of pyrene and 170 g. of titanium tetrachloride were subjected to ball milling in the same manner as in Example 1 to give a solid substance which contained 40 mg. of titanium per gram thereof.

Polymerization was carried out in the same way as in Example 1 except that the solid substance prepared above was used as a catalyst component.

The resulting copolymer had a bulk density of 0.397, Ml of 2.6 and a density of 0.925, and the polymerization activity was 187,000 gcopolymer/gTi.

After continous operation for 10 hours, the interior of the reactor was checked to find no polymer adhesion therein.

Example 6 Polymerization was carried out in the same manner as in Example 1 except that the catalyst prepared in Example 5 was used and the temperature was adjusted to 80C and that the gaseous composition in the vapor phase was made 4 mol% butene-1, 2 mol% Dialen 610 (a mixture of hexene-1, octene-1 and decene-1 in equal amounts, a product of Mitsubishi Kasei Co.), 74 mol% ethylene and 20 mol% hydrogen.

The resulting ethylene copolymer had a bulk density of 0.364, Ml of 6 and a density of 0.905, and the polymerization activity was 135,600 gcopolymer/gTi.

After continuous polymerization for 10 hours, the interior of the reactor was checked to find no polymer adhesion therein.

As is recognized in the present example of this invention, it is apparent that even in the case of using a high grade a-olefin mixture such as Dialen 610 there is easily obtained product with high melt index and low density.

Claims (18)

1. A process for preparing an ethylene copolymer having a melt index of 0.1 to 10 and a density of 0.900 to 0.945, which process comprises copolymerizing (1) ethylene, (2) propylene and/or butene-1 and (3) an a-olefin having 6 to 12 carbon atoms while maintaining the total amount of said components (2) and (3) in the range of from 1 to 40 mol% of said component (1) and the molar ratio of said component (2) to said component (3) in the range of from 0.01: 0.99 to 0.90 : 0.10, in a substantially solvent-free vapor phase and in the presence of a catalyst comprising a solid substance and an organoaluminium compound, said solid substance containing magnesium and titanium and/orvanadium.

2. A process according to claim 1, in which said solid substance containing magnesium and titanium and/orvanadium is obtained by attaching a titanium compound and/or a vanadium compound to a magnesium-containing inorganic solid compound.

3. A process according to claim 2, in which said magnesium-containing inorganic solid compound is selected from metallic magnesium, magnesium hydroxide, magnesium carbonate, magnesium oxide and magnesium chloride.

4. A process according to claim 2, in which said magnesium-containing inorganic solid compound is selected from double salt, double oxide, carbonate, chloride and hydroxide containing magnesium atom and a metal selected from silicon, aluminium and calcium.

5. A process according to claim 2,3 or 4 in which said magnesium-containing inorganic solid compound is further treated or reacted with an oxygen-containing compound, a sulfur-containing compound, a hydrocarbon, or a halogen-containing substance.

6. A process according to any one of claims 2 to 5 in which said titanium compound and/or vanadium compound is (are) a halide, an alkoxyhalide, an oxide or a halogenated oxide of titanium and/or vanadium.

7. A process according to any one of claims 2 to 5 in which said titanium compound and/or vanadium compound is (are) used as the mixture or the addition product with an organocarboxylic acid ester.

8. A process according to any one of claims 2 to 7 in which said magnesium-containing inorganic solid compound is contacted, before its use, with an organocarboxylic acid ester.

9. A process according to any one of claims 2 to 8 in which said organoaluminium compound is used as the mixture or the addition product with an organocarboxylic acid ester.

10. A process according to any one of claims 1 to 9 in which said catalyst is prepared in the presence of an organocarboxylic acid ester.

11. A process according to any one of claims 7,8,9 and 10, in which said organocarboxylic acid ester is selected from alkylesters of benzoic acid, anisic acid and toluic acid.

12. A process according to any one of claims 1 to 11 in which said copolymerization is carried out at a temperature in the range of from 20 to 11 0'C and at a pressure in the range of from atmospheric pressure to 70 kg/cm2G.

13. A process according to any one of claims 1 to 12 in which said copolymerization is carried out in the presence of hydrogen.

14. A process according to any one of claims 1 to 13 in which, before initiating the copolymerization, said catalyst system is contacted with an a-olefin having 3 to 12 carbon atoms for 1 minute to 24 hours at a temperature in the range of from 0" to 200"C and at a pressure in the range of from -1 to 100 kg/cm2.G.

15. A process as claimed in claim 1, substantially as hereinbefore described with particular reference to the Examples.

16. A process as claimed in claim 1, substantially as shown in any one of the Examples.

17. A copolymer of ethylene, propylene and/or butene-1, and an ot-olefin having 6 to 12 carbon atoms, when prepared by the process claimed in any one of the preceding claims.

18. An article fabricated from the polymer claimed in claim 17.