CA1218181A - Polyethylene composition - Google Patents

Abstract

Abstract of the Disclosure A polyethylene composition comprising three specific types of polyethylenes; polyethylene (A), polyethylene (B) and polyethylene (C) respectively.
The polyethylene composition has a melt index not less than 0.001 g/10 min. and not more than 10 g/cm and exhibits excellent processability under variant molding techniques. Molded objects exhibit excellent physical properties such as impact strength environmental stress cracking resistance and uniform thickness distribution.
Polyethylene (A) has a molecular weight of from 5,000 to 90,000 and polyethylene (C) has a molecular weight of from 100,000 to 1,500,000 and the ratio of the molec-ular weight of polyethylene (C)/ the molecular weight of polyethylene (A) is from 4 to 200. Polyethylene (B) has a molecular weight of from 50,000 to 500,000, being pre-pared by a polymerization with use of a chromium compound-supported type catalyst capable of producing a specifically conditioned homopolyethylene with respect to the proper-ties of the polymers in terms of flow ratio and die swell.

Description

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BACKGROUND OF THE INVENTION

Field of the Invention . _ _ This invention relates to a polyethylene come position having excellent physical and chemical properties, and excellent moldability. More particularly, it relates to a polyethylene composition which exhibits excellent process ability as well as excellent properties such as high impact resistance, high environmental s-tress cracking resistance (hereinafter referred to as ESQUIRE) and the like in the application of various molding techniques such as blow molding, extrusion molding, injection-blow molding and the like.

Description of the Prior Art In molding by blow molding, extrusion molding, injection-blow molding or the like, polyethylene having relatively high molecular weight as well as relatively broad molecular weight distribution is suitable. Several processes have been proposed in the art for preparation of polyethylene with broader molecular weight distributions.

One of the known processes comprises mixing a high molecular weight polyethylene and a low molecular weight polyethylene. Examples are described in Japanese Patent Publication No. 3215/1~70, Japanese Patent Pub-ligation No. 22007/1970, Japanese Laid-open Patent Pub-ligation No. 100444/1979, Japanese Laid-open Patent Publication No. 100445/1979, Japanese Laid-open Patent Publication No. 161657/1979, Japanese aid open Patent Publication No. 60542/1980, Japanese Laid-open Patent Publication No. 60543~1980, Japanese Laid-open Patent Publication No. 57841/1981, and Japanese Laid-open Patent Publication No. 133136/1982. another known process is a multistage polymerization process in which two or more I

stages of polymerization are involved. Examples of this latter mode of preparation are described in Great Britain Patent Publication Nos. 1,174,542 and 1,233,599, USE
Patent Nos. 4,113,440 and 4,098,974 and Japanese Laid-open Patent Publication No. 47079/1976. The polyethylene prepared by these known processes have wide molecular weight distributions and produce moldings having a good ESQUIRE.

The present inventors have found that although the prior polyethylene have broad molecular distributions and improved ESQUIRE, they exhibit a number of drawbacks with regard to practical characteristics required for both mold-in and molded shaped products. The drawbacks encountered in the prior polyethylene are low impact strength, poor viscoelastic characteristics on melting during molding, and susceptibility to generation of thickness irregularity.
In addition to these drawbacks, prior polyethylene en-counter failures in producing moldings with complicated shapes.

SUMMARY OF THE PRESENT INVENTION
. . _ . .

It is an object of the present invention to minimize the aforesaid drawbacks of the prior polyethylene compositions, and provide an improved polyethylene compost-lion excellent in overall characteristics including both physical properties and process ability. Specifically, the present invention provides a polyethylene composition comprising three types of polyethylene (A), (B) and (C) selected from the group of homopolymers of ethylene and copolymers of ethylene and an ~-olefin, wherein (i) polyp ethylene (A) has a molecular weight of from 5,000 to 90,Q00 (hereinafter referred to MA) and polyethylene (C) has a molecular weight of from 100,000 to 1,500,00~ thereinafter referred to MOHAWK), and the ratio of KIWI it between 4 and 200, (ii) polyethylene (B) has a molecular weight of from 50,000 to 500~000 (hereinafter referred to produced by a polymerization using a chromium compound supported type catalyst which is capable of producing a homopolymer of ethylene in a single stage polymerization, having a flow ratio of from 40 to 150 and a die swell of from I to lOOg/20cm measured at the condition in which the said homopolymer exhibits a melt index of lg/10 min., (iii) the ratio of polyethylene (A) to polyethylene (C) by weight is from 70 to 30 to 30 to 70, and the amount of polyethylene (B) in the composition ranges from 10%
by weight to 75% by weight.

According to the present invention, there is provided a polyethylene composition which is featured by excellence both in physical properties such as impact resistance, ESQUIRE, stiffness and resistivity to heat and in process ability. With these excellent properties in combination, the polyethylene of the present invention is suited to wide varieties of commercial molding applique-lions such as blow, extrusion, injection-blow and the like.

In the polyethylene composition of the present invention, polyethylene (A and polyethylene (C) together can be regarded as one unit component.

The unit component can be a blend of polyethylene (A) with polyethylene (C) in which the respective polyp ethylenes are separately prepared, or a polyethylene come position obtained by a two stage polymerization process.

The unit component has a melt index of from log 10 min. to O.OOlg/10 min., a flow ratio of from 20 to 500, a density of from O.91g/cm3 to 0.98g/cm3 and die swell of from 20 to 50g/20 cm.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing and other features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description taken in connection with the accompanying drawing.

The figure is a flow sheet showing diagrammatical-lye a two stage polymerization process for preparation of polyethylene.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in detail. The polyethylene (A), (B) and (C), the combo-newts of the polyethylene composition of the present in-mention, are selected from the group consisting of home-polymers of ethylene and copolymers of ethylene and an ~-olefin. Copolymeriæable Nylons are those having 3 to 14 carbon atoms such as propylene, butane, pontoon, Helene, 4-methylpentene-l, octane decent and the like.
The molecular weight of the polyethylene (A) (MA) is 5,000 to 90,000. MA less than 5,000 lowers uniform dispersibility of all -the components in the composition and the physical properties of the composition, whereas MA exceeding 90,000 makes it difficult to broaden the molecular weight distribution of the composition within an appropriate range of the molecular weight and lowers the process ability of the composition. Preferred MA is Lowe to 70,000. More preferably, the polyethylene (A) has a relatively narrow molecular weight distribution and a relatively small die swell value. Such a polyp ethylene is preferably produced by a magnesium-containing Ziegler type catalyst which is capable of producing a homopolymer of ethylene in a single stage polymerization having a slow ratio ox 20 to less than 50 and a die swell of 20g/20cm to less than 50g~20cm measured a the condo-.

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lion in which the said homopolymer exhibits a melt index oflg/lO min. The polyethylene (C) has a molecular weight from 100,000 to l,500,000 (MOHAWK). MOHAWK less than 100,000 lowers both the molecular weight of the whole composition and ESQUIRE. MOHAWK more than 1,500,000 may lower uniformity of dispersibility of the component polyethylene in the composition, making the composition unbalanced in both process ability and physical properties or generating of fish-eyes in molding. Preferred MOHAWK is between 200,000 and l,000,000. More preferably, the polyethylene (C) has a relatively narrow molecular weight distribution as well as a relatively smaller die swell value. Such polyethylene has a molecular weight of from 200,000 to l,000,000, and is preferably prepared by a magnesium-containing Ziegler type catalyst capable of producing a homopolymer of ethylene in a single stage polymer-ization having a flow ratio of 20 to less than 50 and a die swell of 20g/20cm to less than 50g/20cm measured at the condition in which the said homopolymer exhibits a melt index of lg/lO min.

The molecular weight of the polyethylene (B) is 50,000 to 500,000 By The polyethylene (B) is produced by polymerization using a chromium compound supported type catalyst which is capable of producing a homopolymer of ethylene in a single stave polymerization having a flow ratio of from 40 to 150 and a die swell of from 40g/20cm to lOOg/20cm measured at the condition in which the said homopolymer exhibits a melt index of lg/lO min.

A more preferable MOB it from 70,000 to 400,000 prepared by polymerization using a chromium compound sup-ported type catalyst capable of producing a homopolymer of ethylene in a single stage polymerization having a flow ratio of from 50 to 120 and having a die swell of from 50g/20cm to 80g/20cm measured at the condition in which .
I, the said homopolymer exhibits a melt index of lg/10 min.

By a homopolymer of ethylene produced in a single stage polymerization there is meant a homopolyethylene prepared by a known single stage polymerization using a transition metal type catalyst at a fixed condition with respect to polymerization vessel, temperature, pressure, catalyst, molecular weight regulator and other polymer-ization conditions known in the art. Accordingly, the homopolyethylene produced in a single stage polymerization does not include any mixture of homopolyethylene prepared by different conditions, nor includes any homopolyethylene prepared by a two or more stage polymerization.

The density of the polyethylene (A) is from 0.91g/cm3 to 0.98g/cm3. The density of the polyethylene -(B) is from 0.91 to 0.98g/cm3, preferably from 0.~g/cm3 to 0.97g/cm3. The density of the polyethylene (C) is from 0.9lg/cm3 to 0.97g/cm3, preferably in a range from 0.91g/cm3 to 0.95g/cm3 and smaller than the densities of the polyethylene (A) and (B), whereby the polyethylene composition is simultaneously improved in moldability and properties such as impact resistance, ESQUIRE and the like.

In the present invention, MWc/MWA ranges from 4 to 200. A ratio of Mohawk less than 4 effects a narrow molecular weight distribution in the final composition leading to both poor process ability and lowered E5CRo On the other hand a ratio exceeding 200 does not produce any meritorious improvement in moldability and physical properties, and results in disadvantage with reward to commercial production of the composition. A preferred range of ~WC/M~A is from 6 to 150 and the most preferable range is prom 7 to 100. As herein before stated, the molecular weight of the polyethylene (B) By ranges from 50,000 to 500,000 preferably from 70,000 to 400,000.
In the most preferred mode of the composition of the I

present invention, MOB is 1.2 or more, MWB/MWC is 0.9 less and ~7B is lower than the combined molecular weight of the bicomponent composition consisting of polyp ethylene (A) and polyethylene (C) Luke The ratio of the polyethylene (A) to the polyp ethylene (C) by weight ranges from 70:30 to 30:70, more preferably from 60:~0 to 40:60. It the amount of the polyethylene (A) to the amount of the polyethylene (C) exceeds 70 or is less than 30, process ability as well as ESQUIRE will be lowered so that the utility properties of the composition will be unbalanced.

The amount of polyethylene (B) in the compost-lion of the present invention is in a range of from 10 to 75~ by weight, preferably from 15% to 60~ by weight.

An amount of the polyethylene (B) less than 10 tends to produce faults such as lessened process ability, and low impact strength. On the other hand, more than 70% of the polyethylene (B) in the composition lessens the ESC~.

The process for preparation of the polyethylene (A) and the polyethylene (C) will now be described. The polyethylene (A) and (C) are prepared by suspension polyp merization, solution polymerization, gas phase polymerize-lion, and the live using a transition metal type catalyst.
Of the catalyst applicable, a magnesium-containing Ziegler type catalyst is preferred. A magnesium-containing Ziegler type catalyst produce a linear polyethylene containing minimal amounts of unsaturated bonds suck as double bond and long side chains and having a dense and stable crystalline structure. The magnesium-containing Ziegler type catalyst can be made from any type of magnet slum compounds such as inorganic magnesium compounds and organomagnesium compounds.

, I
g Examples of magnesium compounds are magnesium chloride, hydroxy-magnesium chloride, magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium alkyds, organic acid salts of magnesium or complexes thereof with electron donor compounds such as alcohols, esters of carboxylic acids and the like or mixtures thereof, organomagnesium compounds having carbon-magnesium bond, for instance, dialkyl magnesium, alkyd magnesium chloride, alkylmagnesium alkoxides, alkyd magnesium siloxides or complexes thereof with electron donor come pounds such as ethers and the like, a reaction product of the aforesaid organomagnesium compounds and a halogen-axed compound, fox instance, hydrochloric acid, organic chlorides, chlorosilanes, silicon tetrachloride and tin tetrachloride.

The magnesium-containing Ziegler type catalyst comprises an organometallic compound and a reaction product of the above mentioned magnesium source and a titanium and/or vanadium compound. For preparation of polyethylene having a desirable flow ratio as well as a desirable die swell as already described, a specifically preferred catalyst system comprises a solid catalyst come potent (a) and organometallic compound (b).

The solid catalyst component (a) is prepared by reacting compound (I) with compound (II) or by react-in compounds (I), (II) and (III). The compound (I) is an organomagnesium compound represented by the general formula M~Mg~RlpR2q~rys~ wherein is zero or a number more than zero; p, q, r, s, m, and I, have the relation of p + q + r + s = my + I M represents an atom of metal element belonging to group I through group III in the Periodic Table, Al and R2 are hydrocarbon radicals having the same or different numbers of carbon atoms, and Y
represents the same or a different radical selected from the group consisting of halogen, or, o~iR4R5R6, NR7R8 :.

and SR9 wherein R3, R4, R5, R6, R7 and R8 stand for a hydrogen atom or hydrocarbon radical and R9 is a hydra carbon radical. The compound (II) is a titanium compound containing at least one halogen atom, or a vanadium come pound containing at least one halogen atom. The compound (III) is a halide of aluminum, boron, silicon, germanium, tin, terilium and/or antimony.

The organometallic compound (b) is a compound of an element selected from group I to III in the Periodic Table, a preferred compound of which is an organoaluminum compound or a complex containing or~anomagnesium compound.

The reaction of a solid catalyst component (a) with an organometallic compound (b) can be carried out by adding the components to a polymerization system so that they react while the polymerization proceeds. The reaction can also be carried out prior to polymerization. A prefer-red amount of the component (b) by weight to 1 g of solid catalyst component (a) ranges from 1 Molly to 3,000 Molly.
A titanium compound supported on an inorganic magnesium compound may be used instead of a solid catalyst component (a). Among the catalyst systems herein before mentioned, a high activity catalyst system which does not have to be removed from as-polymerized polymer is particularly pro-fireball, and is referred to in Japanese Patent Publication Nos. 36788/1977, 36790/1977, 36791/1977, 36792/1977, 50070/1977, 36794/1977, 36795/1977, 36796/1977, 36915/
1977, 36917/1977, 6019~1978, and Japanese Laid-open Publication Nosy 21876/1976~ 31835/1975, 72044/1975, 78619/1975, and 40695/1978.

Polyethylene PA) and (C), both ox which are separately prepared, can be blended in formulating the polyethylene composition. For a commercial preparation of the polyethylene composition I the present invention, it is preferred that a polyethylene consisting of the By two components is prepared by a two stage polymerization.
Although any known two stage polymerization can be em-plowed, the following process is an especially preferred two stage polymerization for preparation of the polyp ethylenes and (C). In the preferred process, polyp merization is carried out in the presence of saturated hydrocarbon having 4 to 10 carbon atoms.

The order of preparing the respective polyethylene component is not critical in a two stage polymerization;
polymerization of the polyethylene (A) can precede that of the polyethylene (C), or vice versa. Referring to the Figure, there is shown a preparation of the bicomponent polyethylene by means of a two stage polymerization in which polymerization of the polyethylene (A) precedes the polymerization of the polyethylene I The polyethylene (A) of the lower molecular weight component is first pro-pared under a polymerization pressure of from 1 to 30 kg/cm2G, preferably from 3 to 25k~/cm2G at a polymerize-lion temperature from 60C to 100C, preferably 70C to 90C. The polyethylene (C), which is the higher molecular weight component, is then produced under a polymerization pressure of from 0.5 to 30kg/cm2G, preferably from 0.5 to 20kg/cm2G at a polymerization temperature between 40C
and 110C, preferably between 60C and kiwi Through a line (2), ethylene, Hun, hydrogen and catalyst are fed into a polymerization vessel (1), where the lower molecular weight polyethylene (A) is produced by polymerlza~ion~ A slurry in the polymer-ization vessel (1) is introduced into a flush drum (3), where unrequited ethylene and hydrogen are removed. The removed ethylene and hydrogen are pressurized in a compress son (4) and returned to the polymerization vessel (1).
On the other hand, the slurry in the flush drum (3) is introduced into the second stave polymerization vessel (6) by means of a pump (5). Ethylene, comonomer, hexane and catalyst components are fed through a line (7) into the polymerization vessel (6), where the high molecular weight polyethylene (C) is produced by polymerization, and tune polymer in the polymerization vessel (6) is withdrawn through a post-treatment step (not shown) as a product.

The flow of the foregoing process is one repro-tentative example employable in the preparation of a polyp ethylene component consisting of polyethylene (A) and polyethylene (C). In another case, the polyethylene (C) of the higher molecular weight component may be produced by polymerization in the polymerization vessel (1) and the polyethylene (A) of the lower molecular weight combo-next may be produced by polymerization in the polymerize-lion vessel (6). In the latter case, the flush drum (3) can be omitted. The contents of the latter stage polyp merization vessel (6) may be recycled to the preceding stage polymerization vessel (1). Accordingly, the polyp ethylene (A) and polyethylene (C) can be continuously prepared by using a two stage polymerization.

The polyethylene (B) is prepared by a polymer-ization using a chromium compound supported type catalyst.
A polyethylene prepared by using a chromium compound supported type catalyst contains a relatively larger amount of unsaturated bond such as double bond, and dip-lens in chain branching structure as well as crystalline structure from a polyethylene prepared by using a magnet sium-containing Ziegler type catalyst. Examples of catalyst capable of producing a homopolyethylene having a flow ratio (hereinafter referred to as MIRE of from 40 to 150 and a die swell of from 40g/20cm to 100~/20cm measured at the condition in which the said homopolymer exhibits a melt index of lg/10 min. are a chromium come pound supported on inorganic oxide (c) and such supported chromium compound (c) combined with an organometallic compound Ed). us inorganic oxide support for supported ,:.

catalyst of chromium compound, silica, alumina, silica-alumina, zircon, Thor and the lice, may be used.
Silica and silica-alumina are preferred inorganic oxide type support. A specifically preferred support is come Marshall available silica having a high surface area and high porosity.

The chromium compounds include chromium oxides, chromium compounds capable of at least partially forming chromium oxides, when calcined, such as halides of chromium, oxihalides of chromium, nitrates of chromium, acetates of chromium, chromium sulfates, chromium oxalates, alcoholates of chromium and the like. Examples of these chromium compounds are chromium trioxides Cromwell chloride, potassium dichromate, ammonium chromates chromium nitrate, chromium acetate, chromium acetylacetonate, tert-butyl chromates and the like. Of these, chromium trioxides chromium acetate and chromium acetylacetonate are especially preferred.

The chromium compound is supported by known methods such as impregnation, solvent evaporation and sublimation.

In general, the supporting method to be employed may depend on the kind of chromium compound used. It can be an either aqueous or non-aqueous technique.

For example, in the case of using chromium oxides, water may be used. In the case ox using acetylacetona~e, non-aqueous solvent such as Tulane may be used. The amount of chromium on the support is in the range of from 0.05 to 5 %, preferably from 0.1 % to 3 I, by weight.

The calcination is generally carried out in a non-reducing atmosphere, for instance, in the presence of oxygen. But it can also be conducted in the presence of an inert gas or under a reduced pressure. Preferably calcination is conducted in air substantially free of lZ~8~

moisture. Calcination is conducted at a -temperature not lower than 300C, preferably at a temperature from 400C
to 900C, for several minutes -to about several 10 hours, preferably for 30 minutes to 10 hours. It is recommended that the calcination should be performed in a fluidized state by flowing sufficient dry air.

Of course, it is possible to control the activity of a catalyst and the molecular weight, etc. of a polyp ethylene by adding a titan ate or a fluorine-containing salts or the like during supporting or calcining.

Further, a catalyst prepared by supporting a compound such as sill chromates or a reaction product of amine and chromium trioxides and a compound described be-low:
O O
If 11 (R3Si)2N - Or - N(siR3)2~ R3C - O - Or - OOZIER, O O
O O O
If 11 11 (WRAP - O - Or - O - PYRE
o On the aforesaid support can be used. These catalysts are described in US 2,825,721; 2,951,816;
3,130,188; 3,324,095; 3,709,853; 3,493,554j 3,474,080, EP-A-0067068 and Japanese Laid-open Pa-tent Publication No. 5308/1983.

In the above formulae, R represents a hydra-carbon group.

The supported catalyst of chromium compound combined with organometallic compound comprises a combine-lion of an organometallic compound (d) and solid component ~23~

(c) obtained by supporting a chromium compound on an inorganic oxide.

As an inorganic oxide support, the inorganic oxides as explained already in -the preparation of a sup-ported catalyst of chromium compound can be used.
The following are organometallic compounds (d) to be used in combination with a supported chromium come pound (c).
(1) Organic magnesium complex soluble in an inert hydra-carbon which is represented by Al~Mg~RlpR2qR
wherein and are a number more than 0, p, q, r, s and t are 0 or a number more than 0 and they have the relation of 0 < (sty 1.5 and p+q+r+s+t=
I -I I R1, R2 and R3 are the same or different hydrocarbon groups having 1 to 20 carbon atoms, X
and Y represent the same or different groups select-Ed from or, oSiR5R6R7, NR8R9 and SR10, R4, R5, R6, R7, R8 and R9 represent hydrogen or a hydrocarbon group respectively, and R10 represents a hydrocarbon group.

(2) Organomagnesium compounds soluble in an inert hydra-carbon that is represented by the general formula MgRulRvl~xxyyr wherein R' and R" represent hydrocarbon groups, and at least one of R' and R" is a secondary or tertiary alkyd group containing 4 to 6 carbon atoms, or R' and R" are alkyd groups differing in number of carbon atoms from each other, or at least one of R' and R" is a hydrocarbon group with six or more carbon atoms; X and Y are electronegative groups with an O, N or S atom; u, v, x and y are 0 or a number more than 0 and they have the relation of u+v-~x-~y - 2 and ox -I yokel.

(3) Organomagnesium compounds soluble in an inert hydra-carbon represented by the general formula M~g~RlpR2q R3rXSYt~ wherein an represent numbers more than O, p, q, r, s and t represent 0 or a number more than , ., ~Z~B~

0 and they have the relationship ox 0 - (sty) 1.5 and p-~q-~r-~s+t = my + I M is an atom selected from zinc, boron, beryllium and lithium, m stands for the valence of M; Al, R2 and R3 are the same or different hydrocarbon groups having l to 20 carbon atoms; X and Y stand or the same or different groups selected from or, oSiR5R6R7, NR3R9 and SRl0; R4, R5, R6, R8 and I are hydrogen or a hydrocarbon group;
and Rl0 stands for a hydrocarbon group.

(4) Organomagnesium compounds represented by the general formula M~Mg~RlpR2q(OSi~IR3R4)r~ wherein M represents an atom selected from the group consisting of aluminum, zinc, boron and beryllium; Al, R2 and R3 are hydra-carbon groups having l to 20 carbon atoms; R4 stands for hydrogen or a hydrocarbon group having l to 20 carbon atoms; I, and y are a number exceeding 0;
p and q are 0 or a number more than 0 and per =
my + I and m is the valence of M.

(5) Organoaluminum compounds represented by the general formula AlRln(OSiHR2R3)3-n, wherein Al and R2 are hydrocarbon groups with 1 to 20 carbon atoms; R3 no-presents hydrogen or a hydrocarbon group with l to 20 carbon atoms; and n is a number from l to 3.

(6) Organoaluminum compounds having both alkoxy group and hydroxy group represented by the general formula AlRlpHq(OR2)X(OSiHR3R4)y~ wherein the relations of pal, l_q_0, x-0.25, y-0.15, 1.5>x+y_0.5 and p*q+x+y = 3 are satisfied; Al, R2, R3 and R4 are the same or different hydrocarbon groups having from 1 to 20 carbon atoms.

(7) Organoaluminum compounds represented by the general formula Al Run X3-n~ wherein R is a hydrocarbon group, X represents a halogen, Owl or oSiR2R3R4 where Al, R2, R3 and R4 represent hydrocarbon; n is a number satisfying the relationship l_n~3.

(8) Organozinc compound represented by the general formula ZnRmX2_m, wherein R is hydrocarbon group, X represents lo I

owl where R1 is a hydrocarbon group, and m is a number satisfying the relationship l~m'2.

(9) Organolithium compounds represented by the general formula Lit, wherein R is a hydrocarbon group.

(10) Organoboron compounds represented by the general formula BRA X3_Q, wherein R is a hydrocarbon group, X represents halogen or Owl or oSiR2R3R4 where Al, R3 and R4 are hydrocarbon groups, and R2 stands for a hydrogen atom or a hydrocarbon group; Q is a numeral defined as l-Q-3.

The catalyst compositions mentioned above are described in US 3,081,286; 3,476,724; 3,4~5,367;
4,376,720, EP-A-0067598, Japanese Laid-open Patent Publication Nos. 70108/1982; 70190/1982; 198706/1982;
200~05/1982 and 209902/1982.

The polyethylene (B) prepared by using a chromium compound supported catalyst combined with organometallic compounds explained above is especially desirable, since single stage polymerization of ethylene produces a home-polyethylene having a MIX of 50 to 120 and a die swell ox 50 to 80g/20cm measured at the condition in which the said homopolymer exhibits a melt index of lg/10 min.

The polyethylene (B) can be prepared by suspend soon polymerization, solution polymerization, gas phase polymerization and the like using the chromium compound supported catalyst and such supported catalyst combined with said organometallic compounds.

Suspension polymerization is carried out by feeding monomeric Olin at a pressure of 1 to 50kg/cm2G
to an already introduced polymerization solvent and catalyst in a polymerization vessel. The rate of the polymerization may be increased by keeping the tempera-lure of the polymerization system at from 30C to 110C.

Lo Examples of polymerization solvent are aliphatic hydra-carbons such as propane, butane, isobutane, pontoon, isopentane, hexane and Hutton, aromatic hydrocarbons such as Bunsen and Tulane, and cycloaliphatic hydra-carbons such as cyclohexane and methylcyclohexane. A
good powder state of low density copolymer of ethylene and ~-olefin can be obtained by using a polymerization solvent having carbon not more than 4 carbon atoms.

Solution polymerization, generally carried out by feeding monomeric olefin under a pressure of from 1 to 400Kg/cm2G preferably from 10 to 250Kg/cm2G into an already introduced polymerization solvent mentioned above in the presence of a catalyst. The polymerization reaction proceeds at a temperature of 120C to 350C, preferably at 150C to 320C.

Gas phase polymerization is carried out by making monomeric olefin contact with catalyst a-t a them-portray at 30C to 130C under a pressure from 1 to 50 Kg/cm 2 .

In general, fluidized bed technique, moving bed technique or agitating means for mixing is adopted to obtain a good contact of monomeric olefin and catalyst in a polymerization reaction.

The polyethylene composition of the present invention is prepared by mixing the polyethylene I), (B) and (C). Method of mixing the polymers can be any conventionally used methods in the form of powder, slurry, pellet and so on.
When kneading is necessitated, it may be conducted at a temperature of 150C to 300C by using a single or twin-screw extrude, a kneader, or the like machine.

- 19 _ ~2~8~81 The polyethylene composition thus produced has a MI of from 0.001 to lug min. and has a density of from 0.91 to 0.97g/cm3, preferably from 0.935 to yo-yo/
cm3. Its molecular weight distribution is not less than 60, preferably not less than 75 in terms of MIRE

The polyethylene composition for use in inject tion-blow molding should preferably have a MI of from 0.5g/10 min. to 3g/10 min. For use in blow or extrusion molding, the polyethylene composition should have a MI
preferably of from 0.005 to lg/10 min., and most prefer-ably of from O.Olg/10 min. to 0.5g/10 min.

The polyethylene composition of the present invention may contain the materials usually added to polyolefins such as thermal stabilizers, antioxidant, UV-ray absorbers, pigments, antistatic agents, lubricants, fillers, other polyolefins, thermoplastic resins, rubbers and so on, as the case may require.

It is also possible to perform foam-molding of the present composition with a foaming agent incorporated therein. Radical initiators and cross lining agents can be incorporated in the polyethylene composition so as to effect cross-linking.

In the present specification, the respective characteristics of the polyethylene (A), (B) and (C) is represented by MIX and die swell value of a homopoly-ethylene produced in a single stage polymerization mews-used at the condition in which said homopolyethylene exhibits a melt index of lg/10 min. This is because both MIX value and die swell value are the parameters that represent directly the molecular structure of linear polyethylene prepared by a single stage polymerization.
More directly, these parameters are essentially determined by the kind of catalyst used in polymerization. The .

~Z181~31 characteristics of polyolefin in terms of molecular weight and amount of copolymerized ~-olefin are determined by a molecular weight adjusting agent and the amount of co-polymerized monomer which are used in polymerization.
On the other hand, the characteristics pertaining to molecular structures, involving chain branching structure, the presence of unsaturated bonds, molecular distribution and the like are specifically determined according to the kind of catalyst used in polymerization, and can be no-presented by lair as well as die swell.

The reason why the polyethylene composition according to the present invention is excellent in both process ability and physical properties may be considered as described below. The low molecular weight polyethylene moiety having a narrow molecular weight distribution and a low melt elastic recovery effect (the polyethylene (A)) and the high molecular weight polyethylene moiety having a narrow molecular weight distribution and a low melt elastic recovery effect (the polyethylene (C)) are home-generously mixed together with the-polyethylene (B) which has an intermediate molecular weight, a relatively wide molecular weight distribution and an adequately high melt elastic recovery effect, whereby the molecules in the composition are entangled so as to effect an optimal mode of molecular structure.

The subsequent examples show the excellence of the polyethylene composition ox the present invention.
For instance, use of polyethylene having the same molecular weight as the polyethylene (B) and prepared my using a magnesium-containing Ziegler type catalyst in the polyp ethylene composition cannot produce an excellent kirk-teristics in process ability and physical properties as obtained by the composition of the present invention.
As described in detail above, the specific features of the polyethylene composition obtained according to the L8~8~

present invention may be summarized as follows:
(1) The polyethylene composition is excellent in process ability, since flow characteristics and viscoelastic characteristics are well balanced.
In particular, good moldability of the composition in blow molding, extrusion molding of pipes, sheet and the like product, injection-blow molding or the like, gives little thickness irregularity or unevenness in molded products.
(21 The molded articles of the polyethylene compost-lion have great stiffness, impact resistance, and ESQUIRE. All of these characteristics exhibit good practical balance.
(3) Since the polyethylene composition is excellent in physical properties and process ability, thin molded articles can easily be produced. Therefore, it meets the demand OX the age for saving resources and energy.
(4) lolled articles with good appearance are obtained.
(5) The composition can be used for various shaping methods such as injection molding, ~ilm-making, stretching, rotoforming and foaming.

EXAMPLES

The following examples are given to illustrate the invention in more detail and should not be construed as limiting the scope of the present invention.

Designations, and methods and conditions for measurements described in the examples and comparative examples are summarized below:
(i) MI designates the melt index measured at a them-portray of 190C under a load of 2.16 kg in accordance with ASTM D-1238.
(ii) MIX is defined as the quotient of the value measured under the condition of measurement of MI under a load of 21.6 kg divided by MI.

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MIX is a measure of molecular weight disturb-lion. Value of MIX increases as the molecular weight distribution broadens.
(iii) Molecular weight (MY) was calculated from the intrinsic viscosity (n ) measured in a solution of decline at 135C and the equation n = 6.3 x MOE described in Journal of Polymer Science Vol. 36. P 91 (1957). All the molecular weights referred to in the present specification are based on this method.
(iv) Density was measured in accordance with ASTM
D-1505.
(v) Impact strength means the notched Issued impact strength according to ASTM D-256.
(vi) ESQUIRE designates environmental stress cracking resistance.
A 2,000 ml volume bottle with a handle (95 grams) was molded by use of a 60 my screw molding machine at a cylinder temperature of 190C and a mold temperature of 40C. After 200 ml of an aqueous solution containing 33 % non ionic surfactant is charged in the bottle, the bottle is sealed with a stopper and placed in an oven at 60C.
The time until generation of cracks on the bottle is measured.
vow) Impact resistance of a bottle was measured on a bottle molded according to the molding de-scribed above. The bottle is filled with cold water at 13C and sealed with a slapper. And it is repeatedly dropped from the high of 1.9m onto a concrete surface. The number of the repeated droppings before destruction of the bottle is counted.
(viii) Extrusion process ability is expressed by the amount of a composition extruded through the Type A-50 blow molding machine manufactured my PLACE Co., Ltd. at a cylinder temperature of 190C operated at 46 rum of screw rotation.
(ix) Die swell is defined as the weight of 20 cm prison when extruded by use of a die for blow molding with an outer diameter of 15 mm and an inner diameter of lo on under the operating conditions described in (viii).
If no swelling phenomenon occurs, the weight of the prison will be about 15 grams.
(x) Thickness irregularity of the bottle molded in accordance with the molding deserved in the above (vi) was reported. Particularly, the welded pinch-off portion of the handle which is prone to become thinner, was evaluated visually. Double circles mark ( ) indicates an excellent state, circle mark ( o ) indicates a good state, triangle mark ( ) indicates a slightly bad state, and cross mark ( ) in-dilates an extremely bad state.

Example l-l (l) Preparation of catalyst for polyethylene (A) and (C) Two liters of a hexane solution containing l molehill of trichlorosilane (HSiCl3) were placed in an 8 liter autoclave and kept at 50C. 2 liters of a hexane solution containing l molehill of an organ-aluminum-magnesium complex with a composition core-sponging to Al Mg6.o(c2~5)2.o(n~c4H9)9.5(oc4H9)3-5 was added drops to the hexane solution of in-chloxosilane under stirring over two hours. Then the mixture was reacted for a further two hours.
The solid product so obtained was washed two times with 2 liters of fresh hexane by means of recantation.
To the slurry containing the solid product was added 2 liters of titanium tetrachloride, and the reaction was carried out at 130C for two hours so that a solid catalyst component was formed. The solid catalyst component was then isolated and washed with fresh hexane until no free halogen was detected.
This solid catalyst component (a) contained 2.1 %
of titanium by weight.
(2) Preparation of a bicomponent composition consisting of polyethylene and (C) by two stage polymerize-lion.
A two stage polymerization was conducted act cording to the process as shown in the Figure.
First, polymerization for preparation of a low molecular weight polyethylene moiety (A) was carried out in a polymerization vessel (1) with an inner volume of 300 1. The polymerization temperature was 83C and the polymerization pressure was 11 kg/cm2G .
Into the polymerization vessel (1) were fed the above solid catalyst component (a) at a rate of 1.3 Molly (To atom buzzer., triethylaluminum as an organ-metallic compound (b) at a rate of 20 Molly (metallic atom buzzer. and purified hexane at a rate of I
- liters/hr.
Ethylene was also fed at the rate of 7NM3/hr. and hydrogen as a molecular weight regulator was fed so that the hydrogen concentration in the gas phase might become about 90 mow % to effect the first polymerization.
Secondly, in order to prepare a polyethylene (C) moiety, the polymer slurry obtained by the first polymerization in the polymerization vessel (1) was introduced into the flush drum (3) at a pressure of 1 kg/cm2G and at a temperature of 75C, where the unrequited ethylene and hydrogen were separated.
Then the slurry was pressurized by the slurry pump (5) and introduced into the polymerization Bessel (6) of an inner volume of 250 liters. The second polymerization was carried out in the polymer-lion vessel (~) at a temperature ox 80C and a - I -pressure of 8 kg/cm2G. In the second polymerization triethylaluminum at a rate of 7.5 Molly (metallic atom base ho purified hexane at 40 l/hr. and ethylene at the rate of 7.2 NM3/hr. were fed into the polymer-ization vessel (6) and hydrogen and buttonhole were fed whereinto so that the concentration thereof in the gas phase might become about 2 mow % and about 2.5 mow % respectively to effect the second polymer-ization.
The polyethylene product in polymerization vessel to) as prepared by the above two stage polymerization was obtained in the form of powder with an MI of 0.17g/
10 min. and a density of 0.956g/cm3.
The polyethylene as obtained contained 49 by weigh-t corresponding to polyethylene (A) produced in the first polymerization and 51 % by weight corresponding to polyethylene (C) produced in the second polymer-ization according to the computation based on the actual amount of the polymer produced in the polyp merization.
According to the results of the experiment of a single stage polymerization conducted separately in the same manner and conditions as the above, it was estimated that the low molecular weight moiety of the polyethylene (A) produced in the first stage polymerization vessel (1) has a molecular weight of about 13,000 and a density of about 0.97~g/cm3 and that the high molecular weight moiety of the polyethylene (C) produced in the second polymerize-lion vessel (2) has a molecular weight of about 54 x 104 and a density of 0.939g/cm3.
Accordingly, the ratio MWC/MWA ox the bicomponent polyethylene prepared by the above two stage polyp merization was estimated at 41.5. For reference, the homopolyethylene having a MI of lug min.
prepared by a single stage polymerization using the catalyst employed in the above polymerization has , a MIX of 37 and a die swell of 38g/20cm.
(3) Preparation of a catalyst for producing polyethylene (B) (i) Preparation of solid catalyst component (c) Ten grams of chromium trioxides was dips-solved in 2,000 ml of distilled water. 500 g of silica (product of Fuss Davison Co., Grade 952) was immersed in the solution and the slurry was stirred at room temperature for an hour.
this slurry was heated to evaporate water, then the residue was dried under reduced pros-sure at 120C for ten hours. This solid was calcined in a stream of dry air at 700C over 5 hours to give a solid catalyst component (c).
The solid catalyst component (c) was found to contain 1 by weight of chromium.
It was stored in a nitrogen atmosphere at room temperature.
(ii) Preparation of organoaluminum component (d) 100 Molly of triethylaluminum, 50 Molly (based on silicon atom) of methylhydropoly-selection (viscosity at 30C is 30 centistokes) and 150 ml of Newton were weighed and placed in an pressure resistant glass container under an atmosphere of nitrogen. The mixture was reacted at 100C over I hours under stirring by means of a magnetic stirrer to produce an Newton solution of Al(C2H5)2.5(Osi~H-C~3 ; C2H5)0.5 The lo Molly (based on aluminum) of this n-Hutton solution was weighed and placed in a 200 liter flask under nitrogen, and a mixture of 50 Molly of ethanol and 50 ml of Newton was added drops thereto with ice cooling, under stirring, from a dropping funnel. After the drops addition, the mixture was reacted for an hour to obtain a Newton solution of Al(c2H5)2~o(oc2~ls~o~s(osi-H-cH3-c2Hs)o 5.

~8~8~

(4) Preparation of polyethylene (B) A polyethylene (B) was prepared by a single stage polymerization using a polymerization vessel having an inner volume of 200 liters.
The polymerization was carried out at a temperature ox ~3C under a pressure of 11 kg/cm2G, and the polyp merization was controlled so as to produce the polymer at 10.5 kg/hr.
As a catalyst, the solid component (c) prepared in I at a rate ox 3.lg/hr. and organoaluminum component (b) produced in -(it) at a rate of 3 Mueller. were introduced together with purified grade of hexane furnished at a rate of 40 l/hr.
The concentration ox hydrogen as a molecular weight regulator was adjusted at 30 mow % of the total gas phase so that a polyethylene (B) with a molecular weight of about 110,000, a MIX of I and a density of 0.967g/cm3 was produced.
In addition to the above, it was found that the homopolyethylene having a MI of lg/10 min. prepared in a single stage polymerization using this catalyst has a MIX of 71 and a die swell of 64g/20 cm.
(5) Preparation of the polyethylene composition The powder of the bicomponent polyethylene consisting of the polyethylene and (C) as pro-pared in the above described two stage polymerization and the polyethylene (B) as prepared above were mixed in a ratio of 60:40 by weight, and then, to this mixture, 300 Pam of tetrakis[methylene-3-~3',5'-di-t-butyl-~'-hydroxyphenylpropionate~ methane and 300 Pam of dilauryl-3,3'-thiodlpropionic acid ester as antioxidant were added. Then, the mixture was thoroughly mixed by stirring in a Herschel mixer.
queue mixture was kneaded at 220C in an FCM machine manufactured by Ferret Co. and then the kneaded product was extruded at 200C by a single-screw extrude to produce a polyethylene composition.

~218~8~
- I -As seen from Table l, the polyethylene composition was excellent both in process ability and in physical properties.

Example l-2 and l-3 The polyethylene (A), (BY and (C), all ox which were prepared in Example 1-l, were blended in various ratios to produce several polyethylene compositions as tabulated in Table l. The manners and conditions for the respective polyethylene compositions with respect to mixing, kneading, kinds of additives and amount thereof and extruding were the same as those employed in Example l-l. The properties of these polyethylene compositions were evaluated. The results are shown in Table l.

comparative Example 1-l and 1-2 Lowe polyethylene I (B) and (C), all of which were prepared in Example l-l, were blended in various ratios to produce several comparative polyethylene come positions as tabulated in Table l. For each comparative polyethylene composition except the combination ratio of the respective polyethylene component the manners and conditions of the blending kneading and extruding were the same as those in Example l-l.

The properties ox the comparative polyethylene ohm-positions were evaluated. The results are shown in Table l.

Comparative Example l-3 The bicomponent polyethylene consisting ox polyp ethylenes and (C) as produced in Example l-l was poulticed in the same manner as in Example l-l with respect to he additives and condition ox kneading, extrusion and so on, and the properties of the poulticed bicomponent polyethylene were evaluated. The results are shown in Table 1.

Comparative example 1-4 The polyethylene (By as prepared in Example 1~1 was poulticed in the same manner as in Example 1-1 with respect to the additives and the conditions of kneading, extrusion and so on, and the poulticed polyethylene (B) was evaluated. The results are shown in Table 1.

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~8~81 Example 2-1 (1) Preparation of catalyst for producing both polyp ethylene (A) and (C).
138 g of do n~butylmagnesium, 19 ox in-ethyl aluminum and 2 liters of Newton were fed into a stirring tank of 4 liters. The mixture was reacted at 80C for 2 hours to synthesize an organ-aluminum-magnesium-complex having the composition AQM~6(C2Hs)3(n-C4H9)12-After the removal of water and oxygen by means of replacement of dried nitrogen, 800 ml of the n-Hutton solution containing 4~0 Molly (54g) of the organoaluminum-magnesium complex and 800 ml of n-Hutton solution containing 400 Molly ox titanium tetrachloride were reacted at -20C under stirring for 4 hours. The formed solid insolubly in a hydra-carbon was isolated and washed with fresh Newton to give 106 g of a solid catalyst component (a).
(2) Preparation of polyethylene (A) and polyethylene (C) As polyethylene components for preparation ox polyethylene compositions, polyethylene (A) and (C) were prepared by the hollowing processes and condo-lions using the above catalyst in the polymerization vessel used for the preparation ox the polyethylene (B) described in Example 1-1~ The polymerization were carried out at 86C under a polymerization pressure of 12 kg/cm2G. Triethylaluminum (b) and the solid catalyst component (a were fed together with hexane which was fed at a rate of 30 Q/hr.into the polymer-ization vessel. Triethylaluminum (b) was kept at 15 Mueller. in the vessel and the feeding rate of the solid catalyst component (a) was kept so that a polyethylene produced at a rate of 8 grow. hydrogen was also fed as a molecular weight regulator.
Buttonhole was used as a comonomer. The gaseous come position in the poly~lerizatiQn was adjusted so as to produce a low molecular weight IOWA of 35,000 (polyethylene (A)) and hazing a density of Q.950 ~8~8~l g/cm3, wherein the concentration of hydrogen was about 4B mow % and the concentration of buttonhole was about 7 mow %. the efficiency of the catalyst was 170,000 g polymer per l g of titanium.
In the preparation of the higher molecular polyp ethylene (polyethylene (C)), the gaseous phase composition in the polymerization vessel was ad-jutted so as to produce a polymer having a molecular weight (MOHAWK) of 280,000 and a density of 0.935 g/cm3, where the concentration of hydrogen was about 10 mow % and that of buttonhole was about 6 mow %. The efficiency of the catalyst was 410,000 g polymer per 1 g of titanium.
In addition, it was found that this catalyst produced a homopolyethylene having a I of 1.0 g/
10 min. a MIX of 39 and a die swell of 41 g/20 cm by a single stage polymerization.
(3) Preparation of a catalyst for production of posy-ethylene (B).
(i) Preparation of solid catalyst component (c) Solid catalyst component (c) was prepared and stored by repeating the preparation of solid component (c) described in Example 1-1 except for the following conditions. In this example, chromium trioxides in Example l-l was replaced by 25 g of MindWrite of chromium acetate (III), and the calcination temperature used in Example 1-1 was replaced by 600C.
(ii) Preparation of organomagnesium component (d-l) 13.80 g of di-n-butylmagnesium, 2.85 g of triethylaluminum and 200 ml of Newton were introduce into a 5Q0 ml flask, and the mixture was reacted at 80C under stirring for two hours to product an organomagnesium complex corresponding to AlMg4(C~Hs)3(n-C4Hg)8-The reacted solution was then cooled down to a temperature of 10C. 50 ml of Newton solution containing 50 Molly of n-octanol was added drops to the cooled reaction solution to obtain a solution of organomagnesium complex containing Alec group.
It was found by gas chromatographic analysis that the complex had a composition correspond-in to AlMg4(c2~s)2~7o(n-c~Hg)6~2~(on-c8Hl7)2~o2 The analysis was conducted by measuring the alcohol converted from all of the allele groups and alkoxy groups by hydrolysis of the o~ydized product that had been obtained by oxidizing a part of the above complex solution with dried air.
(4) Production of polyethylene (B) The polyethylene (B-l) was prepared using the polymerization vessel, the polymerization tempera-lure, the polymerization pressure and the production rate as described in Example 1-1.
Into the polymerization vessel, the solid component (c) prepared in I of this example and organ-aluminum component (d-1) were introduced in company with Hun which was fed at a rate of 40 l/hr.
The feeding rate of the solid component (c) and the organoaluminum component (d-l) were adjusted to 2.92 g/hr. and 3 Mueller. respectively. The concentra-lion of hydrogen was kept at 12 mow % and that of buttonhole 1.5 mow %. The polyethylene (B-l) produced had a molecular weight of 150,000, a MIX of 95 and a density of 0.959 g/cm3.
A homopol~ethylene produced by a single slave polyp merization using the same catalyst condition has a MI of 1.0 g/10 min., has a MIX of 61 and a die swell of 64 g/20 cm.
(5) Preparation of polyethylene composition - The polyethylene (A), and (B-l) and (C), all 12~

in the form of powder, were mixed at a ratio of 38:35:27. To this mixture was added 500 Pam of n-octa-decyl-~-(4'-hydro~Yy-3',5'-di-tert-butylpheenyl) preappoint and 200 Pam of tetr=akis (2,4-di-tert-butyl-phenol) 4,4'-biphenylenediphosphonite and 500 Pam of calcium Stewart as anti-thermoxidizing agent.
A polyethylene composition was produced employing the same conditions as described in Example 1-1 with respect to mixing, kneading, extrusion and so on.
The properties of the composition are tabulated in Table 2.

Example 2-2 The solid catalyst component (c) as used in Example 2-1 and the organomagnesium component (d-2) prepared by the following method were combined.
if) Preparation of organomagnesium component (d-2) To a 500 ml flask, 13.80 g of di-n-butylmag~esium, 2.06 g of diethylzinc were charged together with 200 ml of Newton, and the mixture was reacted with stirring at a temperature of 80C for 2 hours to obtain a Newton solution of an organomagnesium complex corresponding to ZnMg6(c2Hs~2~n-c4H9)l2-- - (2) Preparation of polyethylene (B-2) Into the same polymerization vessel as used in Example 1 were charged with the solid component (c) prepared in Example 2-1 at a rate of 2.48 g/hr. and the organomagnesium complex (d-2) at a rate of 2.6 Mueller. as catalyst together with hexane at 40 l/hr.
The polymerization temperature, and pressure and production rate were the same as in Example 1-1.
Polymerization was conducted in the presence of hydrogen at a concentration of about 15 mow % and buttonhole at a concentration of about 1.5 mow %.
The product polyethylene had a molecular weight of 140, oat, air of 88 and a density of 0.959 g~cm3 ;

lo For reference, a homopolyethylene having a MI of lo glue min. prepared by using this catalyst has a MIX of 58 and a die swell of 61 g/20 cm.
(3) Preparation of polyethylene composition The polyethylene I and (C), which were prepared in Example 2-l, and the polyethylene (B-2) were compounded and poulticed in the same manner as described in Example 2-l to produce a composition of which the properties are shown in Table 2.

Comparative Example 2-l Employing the same catalyst as used in prepare-lion of the polyethylene and (C) in Example 2-l, polyethylene (B-3) was produced. Polyethylene compost-lions were prepared in the same manner and conditions as described in Example 2-1 except that polyethylene, (B-3) and (C) were used as polyethylene components. The properties of the polyethylene are shown in Table 2, which was prepared by the following polymerization.

Polyethylene (B-3) had a molecular weight of 160,000, a MIX of 43 and a density of 0.960 g/cm3.

In the preparation of polyethylene polymerize-lion was carried out in the same manner as used in the preparation of polyethylene and (C) except that the concentration of hydrogen and that of buttonhole were about 32 mow % and about 0.3 mow % respectively.

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Example 3 (1) Preparation of polyethylene (A) and (C) In this example, a polyethylene (A) and a polyp ethylene (C) were prepared in the same manner as used in Example 2-1 with respect to the conditions of polymerization, vessel, polymerization temperature, polymerization pressure and production rate. The catalyst was the same as described in the prepare-lion of the polyethylene (A) and the polyethylene (C) in Example 1-1.
In the preparation of polyethylene (A) of this ox-ample, hydrogen concentration in the polymerization system was adjusted so as to produce a polyethylene having a molecular weight of 12,000. In the pro-parathion of polyethylene (C) of this example, hydrogen concentration and octene-l concentration were adjusted so as to produce a polyethylene having a molecular weight of 700,000 and a density of 0.942 g/cm3.
Hydrogen concentrations in the polymerization system were about 88 mow for the preparation of polyp ethylene (A) and about 3 mow % for the preparation of polyethylene (C). In the case of the preparation of polyethylene (C), the concentration of octene-l was kept about 3 mow %.
(2) Preparation of polyethylene (B) Polyethylene (B) having a molecular weight of 250,000 ox this example was prepared by employing the catalyst used in preparation of the polyethylene (B) in Example 1~1 in the same manner as descried in Example 1-1 except that a hydrogen concentration of 1 mow % was used.
(3) Preparation of polyethylene composition The polyethylene I (B), and (C) all of which were prepared in this example, were mixed at the ratio as tabulated in Tale 3 and processed in the same manner as described in example 1-1 to produce a polyethylene composition. The properties ,, .

I

of the polyethylene compositions are shown in Table 3.

Comparative Example 3 Except that polyethylene (A) and (C) both of which were prepared in Example 3, were mixed at a ratio given in Table 3, a polyethylene composition consisting of polyethylene and (C) was produced by blending and kneading in the same manner and conditions as used in Example 1.
The properties of the polyethylene composition are shown in Table 3.

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Example 4-1 (1) Polyethylene (A) and polyethylene (C) The polyethylene produced by the two stage polyp merization in Example 1-1 was used for the component of polyethylene (A) and polyethylene I
(2) Preparation of catalyst for production of polyp ethylene (B).
10 g of chromium trioxides was dissolved in 2,000 ml of distilled water. 500 g of commercial silica (Grade 952 manufactured by Fuji Davison Come puny) was immersed in the chromium trioxides swallowtail-lion and the mixture was stirred at room temperature or an hour. Then, the obtained slurry was heated until the water thereof was removed by evaporation.
After the removal of water was completed, the solid residue was dried at 120C under a reduced pressure for ten hours. The dried solid was then calcined at 800C under a stream of dried air for 5 hours to obtain a solid catalyst component (C). The solid catalyst component (C) was found to contain 1 by weight of chromium and stored in a nitrogen atmosphere at room temperature.
(3) Preparation of polyethylene (B) polyethylene (B) was produced my a single stage polymerization process in a polymerization vessel having a capacity of 200 liters. The polyp merization temperature and the polymerization pros-sure were 86C and if kg/cm2G, respectively.
Polymerization was controlled so as to produce a polymer at a rate of 10.5 kg/hr.
The solid catalyst component (C) prepared in (2) was charged at a fate of 3.1 g~hx. together with purified grade Hun which was fed at a rate of I
l/hr. into the polymerization vessel.
Hydrogen was used as a molecular weight regulator.
In the gaseous phase, the concentration of hydrogen was kept at about 30 mow % and that ox buttonhole was 0.6 mow I.
The polyethylene (B) thus produced had a molecular weight of 100,000 and a density of 0.964g/cm3.
On the other hand, a homopolyethylene having a MI
ox 1.0 g/10 min., which was obtained under use of this catalyst, had a MIX of 70 and a die swell of 49 g/20 cm.
to) Preparation of polyethylene composition The polyethylene (A, (C) and (B), all of which were produced in this example were mixed at ^ a ratio as shown in Table 4. To this mixture, 300 Pam of tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl) proprionate] methane and 300 Pam of di-lauryl 3,3'-thiodipropionic acid ester as anti-oxidants were added, and the mixture was thoroughly mixed by agitation. The thus obtained mixture was kneaded at a temperature of 220C by means of a FCM
machine manufactured by Ferret Co. The kneaded product was poulticed by extruding at a temperature of 250C using a single screw type extrude. The poulticed polyethylene composition was extremely excellent in both process ability and physical proper-ties as seen in Table 4.

Example 4-2 Polyethylene (A), (C) and (B), all of which were produced in the preceding example, were mixed in the compounding parts as shown in Tale 4. A polyethylene composition was produced in the same manner and conditions as in Example 1-1 with respect to the additives, mixing, kneading, extrusion, and the like. The properties of the polyethylene composition are also shown in Table 4.

Comparative Example 4-4 . Polyethylene (A), to) and By all of which Lowe 31 were produced in Example 4-1, were mixed in the parts given in Table 4, in the same manner as in Example 4-1 with respect to the additives, conditions of mixing, kneading, extrusion, and the like. The properties of the polyethylene compositions were evaluated and the results are shown in Table 4.

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Example 5 (1) The polyethylene consisting of polyethylene (A) and (C) as prepared by the two stage polymerization in example 1-1 was used as polyethylene (A) and (C).
(2) Preparation of polyethylene (B) Except that AQ(C2Hs)2(oC2Hs) was used as an organometallic component (d) of catalyst, a polyp ethylene (B) was produced by polymerizing ethylene at the conditions as used in the preparation of the polyethylene (B) in example 1-1. The polyethylene (B) obtained had a molecular weight of about 110,000, a MIX of 60 and a density of 0.967g/cm3.
For reference, the homopolymer of ethylene which have a MI of l.Og/lOmin., produced by a single stage polymerization, have a MIX of 73, a die swell of 59g/20cm.
(3) Preparation of polyethylene composition A polyethylene composition was made from the materials set forth above in proportions indicated in Table 5.
- The conditions and manners of compounding were the same as in Example 1-1 with respect to the additives, conditions of mixing, kneading, extrusion and the like.
The properties of the polyethylene composition were deter mined and shown in Table 5.

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JO
CJ~ C
by a us Jo O Go a U) ox 'I
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cq MY; I
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I _, ._ _ _ C
a I o u Jo o C C
p. U I
a) to JO -I
o o o E C
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J- ,_ o a 6 C
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so o ox CJ _, .. _ __ Pi o Jo Jo a . I;
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I
Jo o _ _ us a I::
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En act p: us X JO I_ _ aye ¢ I, I S TV

.. I_ .. _ I, .. _ _ . _ . .. . . . _ . _ .. _ . . . _ ...

- I -It is understood that the specification and examples are illustrative but not limitative of the present invention and that other embodiments within the spirit and scope of the invention will suggest themselves to those skilled in the art.

Claims (9)

What we claim is:

1. A polyethylene composition comprising three types of polyethylenes(A), (B) and (C) selected from the group consisting of homopolymers of ethylene and copolymers of ethylene and an .alpha.-olefin, wherein (i) the polyethylene (A) has a molecular weight of from 5,000 to 90,000, the polyethylene (C) having a molecular weight of from 100,000 to 1,500,000 and the ratio of the molecular weight of the polyethylene (C)/ the molecular weight of polyethylene (A) being between 4 and 200, (ii) the polyethylene (B) has a molecular weight of from 50,000 to 500,000 produced by a poly-merization using a chromium compound supported type catalyst capable of producing a homopolymer of ethylene in a single stage polymerization having a flow ratio of from 40 to 150 and a die swell of from 40 to 100 g/20 cm measured at the condition in which the said homopolymer exhibits a melt index of 1 g/10 min., (iii) the ratio of the polyethylene (A) and the poly-ethylene (C) by weight is from 70 to 30 to 30 to 70, and the amount of the polyethylene (B) in the composition ranges from 10 % by weight to 75 % by weight, and (iv) the melt index of the composition is not less than 0.001 g/10 min., and not more than 10 g/10 min.

2. A polyethylene composition according to claim 1, wherein the polyethylene (A) and the polyethylene (C) are prepared by a two stage polymerization.

3. A polyethylene composition according to claim 1, wherein the polyethylene (B) is produced by poly-merization using a chromium compound supported type catalyst combined with an organometallic compound capable of producing a homopolymer of ethylene in a single stage polymerization having a flow ratio of from 50 to 120 and a die swell of from 50 g/20 cm to 80 g/20 cm measured at the condition in which the said polyethylene exhibits a melt index of 1 g/10 min.

4. A polyethylene composition according to claim 1, wherein the molecular weight of the polyethylene (B) is within a range from 70,000 to 400,000 and the ratio of the molecular weight of polyethylene (B)/the molecular weight of the polyethylene (A) is 1.2 or more, the ratio of the molecular weight of the polyethylene (B)/ the molecular weight of polyethylene (C) is 0.9 or less, and the molecular weight of the polyethylene consisting of the poly-ethylene (A) and the polyethylene (C) is higher than that of the polyethylene (B).

5. A polyethylene composition according to claim 1, wherein the polyethylene (A) has a molecular weight of from 10,000 to 70,000 and the polyethylene (C) has a molecular weight of from 200,000 to 1,000,000 produced by polymerization using a magnesium contain-ing Ziegler type catalyst which is capable of produc-ing a homopolymer of ethylene in a single stage polymerization having a flow ratio of 20 to less than 50 and a die swell of 20 g/20 cm to less than 50 g/20 cm measured at the condition in which the said homopolymer exhibits a melt index of 1 g/10 min.

6. A polyethylene composition according to claim 1, wherein the density of the polyethylene composition is in a range of from 0.935 g/cm3 to 0.965 g/cm3.

7. A polyethylene composition according to claim 1, wherein the polyethylene (A) has a molecular weight of from 10,0000 to 70,000 and the polyethylene (C) has a molecular weight of from 200,000 to 1,000,000 which are produced by a polymerization using a magnesium-containing Ziegler type catalyst which is capable of producing a homo-polymer of ethylene in a single stage polymerization having a flow ratio of from 20 to less than 50 and a die swell of from 20 g/20 cm to less than 50 g/20 cm measured at the condition in which the said homopolymer exhibits a melt index of 1 g/10 min.
the polyethylene (B) is produced by a polymerization using a chromium compound supported type catalyst combined with an organometallic compound which is capable of producing in a single stage polymeriza-tion a homopolymer of ethylene having a flow ratio of from 50 to 120 and a die swell of from 20 g/20 cm to 80 g/20 cm measured at the condition in which the said homopolymer exhibits a melt index of 1 g/
10 min.

8. A polyethylene composition according to claim 7, wherein the density of the polyethylene composition is in a range of from 0.935 g/cm3 to 0.965 g/cm3.

9. A polyethylene composition according to claim 1, wherein the polyethylenes (A) and (C) are produced by a polymerization using a magnesium-containing Ziegler type catalyst.