CA1294733C - Injection-molding polyolefin composition - Google Patents
Injection-molding polyolefin compositionInfo
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- CA1294733C CA1294733C CA000559052A CA559052A CA1294733C CA 1294733 C CA1294733 C CA 1294733C CA 000559052 A CA000559052 A CA 000559052A CA 559052 A CA559052 A CA 559052A CA 1294733 C CA1294733 C CA 1294733C
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- weight
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- intrinsic viscosity
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Abstract
Abstract of the Disclosure An injection-molding polyethylene composition consisting essentially of ultrahigh-molecular-weight polyethylene having a molecular weight of at least about 1,650,000 and low-molecular-wight to high-molecular-weight polyethylene having a molecular weight of, for example, about 1500 to about 360,000. This composition is produced by a multistep polymerization process comprising a step of producing the ultrahigh-molecular-weight polyethylene and a step of producing the low-molecular-weight or high-molecular-weight polyethylene.
Description
SPECIFICATION
INJECTION-MOLDING POLYOLEFIN COMPOSITION
Field of Technology This invention relates to an injection-molding polyolefin composition, and more specifically, to an injection-m~lding polyolefin composition suitable for obtaining injection-molded articles having excellent abrasion resistance and impact strength and being free from delamination.
Background Technology Ultrahigh-molecular-weight polyolefins, for example ultrahigh-molecular-weight polyethylene, have higher impact strength, abrasion resistance, chemical resistance, tensile strength, etc D than general-purpose polyolefins such as general-purpose polyethylene, and have found increasing applications as engineering plastics.
The ultrahigh-molecular-weight polyethylene, however, has the defect that it is very difficult to mold by extrusion or injection-molding because it has a much higher melt viscosity and thus lower flowability than general-purpose polyethylene.
At present, therefore, most articles from ultra-high-molecular-weight polyethylene are produced by com-pression molding, and only some articles such as rods are produced by extrusion-molding at very low speeds.
When such ultrahigh-molecular-weight poly-ethylene having low melt-flowability is molded by an ordinary injection-molding method, shear broken streams of the polymer always form during the filling of the polymer in a mold cavity, and the resulting molded article under-goes delamination like mica and cannot exhibit the excel-lent properties of the ultrahigh-molecular-weight poly-ethylene. Rather, its quality is inferior to that of a molded article of general-purpose polyethylene.
Japanese Patent Publications Nos~ 300~7/1982 and 58010J1985 propose an injection-molding method free from 3~ 733 causing delamination, in which the capacity of a mold cavity is slightly increased before or after a resin is filled in the cavity, and then the resin is compressed to a predetermined volume. This method enabled production of injection-molded articles free from delamination and having the impact strength and abrasion resistance which are the inherent characteristics of the ultrahigh-molecular-weight polyethylene. To perform injection molding by this method, however, it is necessary to use an injection-molding machine equipped with a variable mold cavity system, and the general injection-molding machine for polyethylene cannot be used as it is.
On the other hand, for improving the melt-flow-ability of ultrahigh-molecular-weight polyolefins, mixing of an ultrahigh-molecular-weight polyolefin with a low to a high molecular weight polyolefin was proposed.
Japanese Patent Publication No. 27,06~/1971 discloses an abrasion-resistant polyethylene resin com-position comprising polyethylene having an average mol~
ecular weight of at least 500,000 and 20 to 50 % by weight of polyethylene having a density of at least 0.940 and an average molecular weight of 30,000 to 120,000.
Japanese Patent Publication No. 30,293/1972 discloses a process for producing a material for use in that surface of agricultural machines, earth-moving machines, etc. which comes into contact with the soil, which comprises mixing screw-extrudable polyethylene having a molecular weight of not more than 200,000 and produced by the medium-pressure or the low-pressure method with 10 to 30 % by weight of ultrahigh-molecular-weight polyethylene having a molecular weight of about 1 million and being incapable of screw-extrusion, melting the mixture uniformly, and continuously molding the uniform molten mixture by an extruder.
Japanese Patent Publication No. 41,309/1983 discloses a polyethylene composition comprising a mixture . . .
.~
~Z~733 of 85 to 50 parts by weight of polyethylene having a viscosity average molecular weight of 500~000 to 150,000 and 15 to 50 parts by weight of granular uitrahigh-molecular-weight polyethylene having a viscosity average molecular weight of at least 1 million and a particle size smaller than 10 mesh.
Japanese Laid-Open Patent Publication No.
177,036/1982 discloses an ultrahigh-molecular-weight polyethylene composition having improved moldability comprising 100 part~ by weight of ultrahigh-molecular-weight polyethylene having a molecular weight of at least 1 million and 10 to 60 parts by weight of low-molecular-weight polyethylene having a molecular weight of 5,000 to 20,000. The specification of this patent document states that the moldability of this ultrahigh-molecular-weight polyethylene composition is such that in the production of a slab having a thickness of 50 mm by a compr~ssion mold-ing method, the molding cycle required was decreased to -- 200 C x 2 hours while with the ult~rahigh-molecular-weight polyethylene along a molding cycle of 200 C x 3 hours was required; and that in a ram extrusion method, the speed of pipe extrusion was increased from 5 cm/min. to 10 cm/min~
Japanese Laid-Open Patent Publication No.
126,446/1984 discloses an ultrahigh-molecular-weight polyethylene resin composition comprising 9S to 50 parts by weight of an ultrahigh-molecular-weight polyethylene resin and 5 to 50 parts by weight of a general-purpose polyolefin resin. The specification of this document discloses a composition in which a silane-modified poly-ethylene resin having a melt index of 2.5 or 5~0 g/10 min.as an actual specific example of the general-purpose polyolefin resinO
Japanese Patent Publication No. 41,309/1983 discloses a polyethylene composition comprising a mixture of 85 to 50 parts by weight of polyethylene having a viscosity average molecular-weight of 500,000 to 150,000 ~Z~733 and 15 to 50 parts by weight of granular ultrahigh-molecular-weight polyethylene having a visçosity average molecular weight of at least 1 million and a particle size smaller than 10 mesh. As stated in column 3, lines 17 28 of this document, the moldabil:ity of the ultrahigh-molecular-weight polyethylene in this composition has not improved, but the purpose of providing this composition is to produce a molded article having excellent impact strength by reducing anisotropy utilizing the granular state of the ultrahigh-molecular-weight polyethylene.
The above polyethylesle resin compositions are prepared by mixing ultrahigh-molecular-weight polyethylene with polyethylene or other polyolefins having lower mol-ecular weights.
Japanese Laid-Open Patent Publication No.
94,593/1979 (corresponding to V. S~ Patent No. 4,414,369) discloses a process ~or producing a polyolefin having a broad molecular weight distribution by polymerizing an olefin in the presence of a solvent and hydrogen using a Ziegler-type catalyst of enhanced activity supported on a solid carrier to produce a polyolefin continuously, which comprises continuously feeding a main olefin monomer and at least one olefin comonomer under pressure using a plurality of reactors in which a gaseous phase containing an inert gas is present in the upper part of a first-stage reactor, and copolymerizing these monomers, continuously transferring the polymerization reaction mixture in which high-molecular-weight polymer particles are dispersed in a solvent to a second-stage reactor composed of a vertical stirred vessel maintained at a lower pressure than the first-stage reactor by differential pressures without substantially separating part of the components in the mixture and without using any forced transferring means, continuously performing polymerization in the second~stage stirred vessel in the presence of the main olefin monomer and hydrogen while a gaseous phase exists in the upper ~2~733 part of the stirred vessel, thereby to form a polymer having a lower molecular weight than in the first stage polymerization, continuously withdrawing the polymeriza-tion reaction mixture containing the resulting polymer particles dispersed in a solvent from the second-stage stirred vessel, and recovering the polymer.
Japanese Patent Publ;cation No. 10,724/1984 ~corresponding to U. S. Patent No. 4,336,352) discloses a process in which polyethylenes of different molecular weights are produced by multi-stage continuous poly-merization in at least three polymerization vessels con-nected in series. The purpose of this process is to produce polyethylene having excellent properties and moldability with high productivity. With regard to moldability, this process is for producing polyethylene by extrusion molding, above all blow molding, with improved die swelling. It does not relate to an improvement in an injection-molded article. Even when a composition con-taining not more than 10 % by weight of ultrahigh-molecular-weight polyethylene and having an MI of 0.3 or an intrinsic viscosity ~1 of 2.3 to 3~0 dl~g (corres-ponding to an MI of about 0.2 to 0.8) is used in injection molding, the content of ultrahigh-molecular-weight poly-ethylene is as low as not more than 10 ~ by weight.
Japanese Patent Publication No. 11,349/1971 discloses a process which comprises producing 5 to 30 % by weight of an ethylene/alpha-olefin copolymer having a reduced specific viscosity of 30 to 5 in a first step, and producing polyethylene or an ethylene~alpha-olefin co-polymer having a reduced specific viscosity of 4.6 to 1.5 in a second stage to obtain a homogeneous mixture of it with the polymer obtained in the first stage. The purpose of this process is to improve moldability in the extrusion molding of bottles, cables, pipes, etc. and does not pertain to an improvement in an injection-molded article.
Japanese Laid-Open Patent Publication No.
~29~L733 141,409/1982 discloses a process for producing poly-ethylene which comprises polymerizing ethylene, or co-polymerizing ethylene with an alpha-olefin, using a catalyst comprising a reaction product between a magnesium compound and a titanium halide and an organoaluminum compound; wherein the following three polymerization steps, (a) a step of forming an ethylene polymer or copolymer having an alpha-olefin content of not more than 10 % by weight and an in-trinsic viscosity [~] of 0O3 to 1.5, (b) a step of forming an ethylene polymer or copolymer having an alpha-olefin content of not more than 30 % by weight and an in-trinsic viscosity ~] of 1.5 to 7, and (c) a step of forming an ethylene polymer orcopolymer having an alpha-olefin content of not more than 30 % by weight and an in-- trinsic viscosity ~] of 7 to 40-,-are carried out in any desired sequence, and the poly-merization reactions are carried out while adjusting the ratio of the amounts of the polymers formed in step (a):step (b~:step (c) to 1:0.1-1.5:0.01-1.2.
Japanese Laid-Open Patent Publication ~o.
8713/1983 discloses a process for producing an ethylenic copolymer which comprises copolymerizing ethylene and an alpha-olefin using a catalyst system obtained from ~A~ a solid catalyst component containing at least magnesium, halogen and titanium atoms and (B) an organoaluminum compound in at least two steps, wherein (1) in at least one step, 80 to 20 parts by weight of a copolymer having a high-load melt index o~ 0.03 to 10 g/10 min. and a density of 0.890 g/cm3 to less than 0.905 g/cm3 is produced~
~2) in a second step, 20 to 80 parts by weight , .
:' of a copolymer having a melt index of L0 to 5000 g/10 min.
and a density of 0.905 to 0.940 g/cm3 is produced, whereby a copolymer having a melt index of 0.02 to 30 g/10 min. and a density of 0.890 to 0.935 g/cm3 is produced.
This patent document discloses that the high-load melt index was measured al: a temperature of 190 C
under a load of 21.6 kg in accordance with JIS K-6760.
Japanese Laid-Open Patent Publication No.
871~/1983 discloses a process for producing an ethylenic copolymer using the same catalyst as described in the above~cited Japanese Laid-Open Patent Publication NoO
8713/1983 by multisteppolymerization, wherein (1) in at least one step, 80 to 20 parts by weight of a copolymer of ethylene with propylene and/or butene-l having a high-load melt index of 0.03 to 10 g/10 min. and a density of 0.890 to 0~935 g/cm3 is produced, and (2) in at least one other step, 20 to-80 parts -by weight o~ a copolymer of ethylene and an alpha-olefin having at most 12 carbon atoms as a comonomer having a melt index of 10 to 5000 g/10 min. and a density of 0.89Q to 0.940 is produced, said alpha-olefin con-taining at least 30 mole % of alpha-olefins having 5 to 12 carbon atoms, whereby a copolymer having a melt index of 0.02 to 30 g~l0 min. and a density of 0.890 to 0.936 g/cm3 is produced.
Japanese Laid-Open Patent Publication No.
120,605/1984 discloses a process for producing an ultra-high-molecular-weight polyethylene resin with improved moldability and processability, which comprises poly-merizing monomers using a Ziegler-type catalyst comprising a solid catalyst component containing a transition metal ingredient and an organometallic catalyst component in at least two steps having different monomer compositions and ~Z~733 hydroyen concentrations; wherein in at least one step, propylene or monomers mainly comprising propylene, or butene-l or monomers mainly comprising butene-l are poly-merized in the presence of hydrogen to produce 2 to 60 ~
by weight, based on the entire polymer to be produced, of a polypropylene or polybutene-l component, and in at least one remaining step, ethylene or monomers mainly comprising ethylene are polymeri~ed in th~e substantial absence of hydrogen to produce 98 to 40 ~ by weight, based on the entire polymer produced, of an ultrahigh-molecular-weight polyethylene component.
British Patent No. 1,174,542 discloses a process for the preparation of a homo- or co-polymer of ethylene by a gaseous phase polymerization, or by a suspension poly-merization in which the dispersion medium is in contactwith a gaseous phase, of ethylene or a mixture comprising ethylene and up to 10 % by weight of an alpha-olefin that contains from 3 to 15 carbon atoms, which process com-prises preparing from 5 to 30 % by weight of the total polymer in the presence of from 0 to 10 % of hydrogen, calculated on the total volume of the gaseous phase, and preparing from 70 to 95 % by weight of the total polymer in the presence of from 20 to 80 ~ of hydrogen, cal-culated on the total volume of the gaseous phase, both stages of the polymerization being carried out at a tem-perature within the range of from 50 to 120 C and a pressure of up to 10 atmospheres gauge, in the presence of a catalyst which is present in the first stage in an amount sufficient for both stages, siad catalyst com-prising a) in the case of a suspension polymerization,from 0.05 to 0.3 millimol per litre of di-spersion medium, or in the case of a poly-merization in the gaseous phase, from O.OS to 0.3 millimol per 0.5 litre of reactor volume, of a trivalent titanium compound that contains chlorine, and ~Z'3~733 . g b) from 0.1 to 3.0 millimols of aluminum per litre of dispersion medium or reactor volume, in the form of an aluminum trialkyl having the general formula AlR, in which each R
represents a hydrocarbon radical that con-tains;from 4 to 40 carbon atoms, or in the form of the reaction product of an aluminum trialkyl or an aluminium alkyl hydride with a diolefin that contains fro~ 4 to 20 carbon atoms.
Japanese Laid-Open Patent Publication No.
275,313/1986 laid-open after the priority date of the present application discloses an ultrahigh-molecular-weight polyethylene composition having improved injection-moldability which has an intrinsic viscosity, determined in decalin at 135 C, of 10 to 30 dl/g and obtained by polymerization reaction in at least two steps mentioned below.
(First step) A step of forming 50 to 99.5 parts by weight o~
polyethylene having an intrinsic viscosity, determined in decalin at 135 C, of 12 to 32 dl/g by polymerizing ethylene in the absence of hydrogen or in a lowered hydrogen concentration with a catalyst comprising a solid catalyst component containing at least Mg, Ti and/or V
and an organometallic compound.
5Second step) A step of forming 50 to 0.5 parts by weight of polyethylene by polymerizing ethylene in a hydrogen concentration increased over that in the first step.
Likewise~ European Laid-Open Patent Publication No. 0186995 laid-open after the priority date of the present application discloses a process for producing ultrahigh-mo:Lecular-weight polyethylene having an ~LZ9~3~3 intrinsic viscosity, determined in decalin at 135 C, of 10 to 30 dl/g by polymerization in at least two steps, which comprises (a) a first step of forming 70 to 99.5 parts by weight of polyethylene having an intrinsic viscosity~ determineld in decalin at 135 C, of 12 to 32 dl/g by polymerizing ethylene monomer in the absence of hydrogen or in the presence of hydrogen in a low concentration using a combina-tion catalyst comprising a solid component containing at least ;magnesium, titanium and/or vanadium and an organometallic compounc~, and ~b) a second step of forming 30 to 0.5 parts by weight of polyethylene having an intrinsic viscosity, determined in decalin at 135 C, of 0.1 to S dl/g by polymerizing a freshly fed ethylene monomer in the presence of hydrogen in a high concentration.
--- It is an object of this invention to provide an injection-molding polyolefin composition comprising an ultrahigh-molecular-w~ight polyolefin component and having very good injection-moldability.
Another object of this invention is to provide an injec~ion-molding polyolefin composition which is suitable for obtaining an injection-molded article free from delamination without impairing the inherent excellent mechanical properties, such as high abrasion resistance, of the ultrahigh-molecular-weight polyolefin.
Other objects of the invention along with its advantage will become apparent from the following descrip-tion.
In the present invention, the ultrahigh-mol-ecular-weight polyolefin has an intrinsic viscosity [~]u' measured in decalin at 135 C, of 10 to 40 dl/g, prefer-ably 15 to 35 dl/g.
The other low-molecular-weight or high-molecular-129~733 weight polyolefin, as referred to in this invention, has an intrinsic viscosity 17]h, measured in decalin solvent at 135 C, of less than 10 dl/g, preferably 0.1 to 5 dl/g, more preferably 0.5 to 3 dl/g.
The polyolefin in this invention is a homo-polymer or copolymer of an alpha-olefin such as ethylene, propylene, l-butene, l-pentene, l-hexene, 1-octene, 1-decene, l-dodecene, 4-methyl-1-pentene and 3-methyl-1-pentene. The homopolymer of ethylene or a copolymer comprising ethylene as a main component and another alpha-olefin of the type exemplified above is desirable.
The quantitative proportions of the ultrahigh-molecular-weight polyolefin and the low-molecular-weight or high-molecular-weight polyolefin are such that the ultrahigh-molecular-weight polyolefin accounts Eor 15 to 40 % by weight of the total weight of the two polymer or the low-molecular-weight or high-molecular-weight poly-olefin accounts for 85 to 60 ~ by weight of the total weight of the two polyolefins. The preferred quantitative proportions are such that the proportion of the ultra-high-molecular-weight polyolefin is 20 to 35 % by weight based on the total weight of the two polyolefins.
The injection-molding polyolefin composition of this invention comprises the ultrahigh-molecular-weight polyolefin and the low-molecular-weight or high-mol-ecular-weight polyolefin in the above quantitative pro-portions~ The injection-molding polyolefin composition of this invention has an intrinsic viscosity [~]c' measured in decalin solvent at 135 C, of 4.0 to 10 dl/g and a melting torque T ~kg-cm) of not more than 4.5 kg-cm. The melting torque T is measured by using a JSR curelastometer (made by Imanaka Machine Industry K. K.) under conditions involving a temperature of 240 C, a pressure of 5 kg/cm2, an amplitude of 135 and a frequency number of 6 CPM.
The injection-molding polyolefin composition of this invention preferably has an l~Jc of 4 to 9 dl/g.
1~473~
The injection-molding polyolefin composition of this invention may be prepared by blending the ultrahigh-molecular-weight polyolefin and the low-molecular-weight or high-molecular-weight polyolefin in the proportions mentioned above. It has been found, however, that it can be advantageously prepared by a multistep polymerization method to be described below which comprises polymerizing olefins in the presence of a catalyst formed from a specific highly active solid titanium catalyst component and an organoaluminum compound catalyst component. The multistep polymerization method is carried out by poly-merizing olefins in a multiplicity of stages in the pre-sence of a Ziegler-type catalyst formed from (A~ a highly active titanium catalyst component containing magnesium, titanium and halogen as essential ingredients and (B) an organoaluminum compound catalyst component. Specifically, in at least one polymerization step, an ultrahigh-mol-ecular-weight polyolefin having an intrinsic vi~cosity t~]u f 10 to 40 dlJg is formed, and in-another poly-merization, an olefin is polymerized in the presence ofhydrogen to give a low-molecular-weight or high-molecular-weight polyolefin having an intrinsic viscosity t~]h of 0.1 to 5 dl/g is formed.
The Ziegler-type catalyst used is basically a catalyst having specific properties formed from a solid titanium catalyst component and an organoaluminum compound catalyst component. Preferably, the solid titanium cata-lyst component is, for example, a highly active fine powdery catalyst component which has a narrow particle size distribution and an average particle diameter of about 0.01 to 5 micrometers and in which several fine spherical particles adhere firmly to one another. The highly active fine powdery titanium catalyst component can be prepared, for example, by the method of preparing the solid titanium catalyst component disclosed in Japanese Laid-Open Patent Publication No. 811/1981 in which at a 12~1~733 time of precipita~ing a solid product by contacting a magnesium compound in solution with a titanium compound in solution, the precipitating conditions are strictly ad-justed. For example, in the method disclosed in the above-cited Japanese Laid-Open Patent Publication which involves mixing a hydrocarbon solution of magnesium chloride and a higher alcohol with titanium tetrachloride at low temperatures, and heating the mixture to about 50 to 100 C to precipitate the solid product, the pre-cipitation is carried out in the presence of a slightamount, for example about 0.01 to 002 mole, per mole of ma~nesium chloride, of a monocarboxylic acid ester with strong stirring. If required, the product is washed with titanium tetrachloride. Thus, a solid catalyst component having satisfactory activity and particle form can be obtained. This catalyst component contains about 1 to about 6 % by weight of titanium, and has a halogen/-titanium atomic ratio of abo~t 5 to about 90 and a magnesium/titanium tatomic ratio3 of about 4 to about 50.
Fine spherical particles having a narrow par-ticle size distribution and an average particle diameter of usually 0.01 to 5 micrometers r preferably 0.05 to 3 micrometers, which are obtained by subjecting a slurry of the solid titanium ca~alyst component prepared as above to high-speed shear treatment are also preferably used. For high-speed shear treatment, a method is employed in which the slurry of the solid titanium catalyst component is treated with a commercial homomixer in an inert gaseous atmosphere for a suitable period of time. To prevent a reduction in catalyst performance at this time, there may also be employed a method in which an organoaluminum compound is added in a proportion equimolar to titanium.
The treated slurry may be filtered through a sieve to remove coarse particles. By these methods, highly active fine powdery titanium catalyst components can be obtained.
~2~9~7~3 -- lDL -- J
The injection-molding polyolefin composition of this invention may be produced by slurry polymerization of olefins in at least two steps at a temperature of usually 0 to 100 C in a hydrocarbon medium such as pentane, hexane, heptane or kerosene using the highly active fine powdeey titanium catalyst component and an organoaluminum compound catalyst component optionally in combination with an electron donor. Examples of the organoaluminum com-pound catalyst component are trialkyl aluminums such as triethyl aluminum or triisobutyl aluminum, dialkyl aluminum chlorides such as diethyl aluminum chloride or diisobutyl aluminum chloride, alkyl aluminum sesqui-chlorides such as ethyl aluminum sesquichloride, or mixtures of theser A multistep polymerization apparatus consisting of at least two polymerization vessel usually connected in series is used in the multistep polymerization process of olefins, and the polymerization is carried out in two steps, three steps, ... or n steps. The multistep poly-merization may also be carried out batchwise in a single polymerization vessel. It is necessary, in at least one polymerization vessel in the multistep polymerization process, to form a specific amount of an ultrahigh-molecular-weight polyolefin. The step in which to form the ultrahigh-molecular-weight polyolefin may be a first polymerization step or an intermediate polymerization step or may comprise two or more stages. From the viewpoint of the polymerization treatment operations and the control of the properties of the resulting polyolefin r it is pre-ferred that the ultrahigh-molecular-weight polyolefin be formed in the first polymerization step. Preferably, in the above polymerization step, 15 to 40 % of olefins to be polymerized in all steps are polymerized to give an ultra-high-molecular-weight polyolefin having an intrinsic viscosity ~]u ~measured in decalin solvent at 135 C) of 10 to 40 dl/g; and further, by polymerizing 18 to 37 % by ~z~a733 weight, especially 21 to 35 % by weight, of oléfins to be polymerized in the entire polymerization steps, an ultra-high-molecular-weight polyolefin having an intrinsic viscosity [~]u f 15 to 35 dl/g, especially 18 to 30 dl/g, is formed.
In the multistep polymerization process, the polymerization in the step of forming the ultrahigh-mol-ecular-weight polyolefin may be carried out in the pre-sence of a catalyst composed o~E the highly active titanium catalyst component ~A) and the organoaluminum compound catalyst component (B). The polymerization may be carried out by a vapor-phase polymerization method or a liquid-phase polymerization method. In any case, in the step of forming the ultrahigh-molecular-weight polyolefin, the polymerization reaction can be carried out in the presence of an inert medium as required. For e~ample, the vapor-phase polymerization method may be carried out in the presence of a diluent composed of an inert medium if required. The liquid-phase polymerization method may be carried out in the presence of a solvent composed of an inert medium as required.
In the polymerization step of forming the ultra-high-molecular-weight polyolefin, it is preferred to use the highly-active titanium catalyst component (A) in an ~mount of about 0.001 to about 20 milligram atoms, es-pecially about 0.005 to about 10 milligram-atoms, as ~itanium atoms per liter of the medium, and the organo-aluminum compound catalyst component ~B~ in an amount ~orresponding to an Al/Ti atomic ratio of from about 0.1 to about 1,000, especially from a~out 1 to about 500. The temperature of the polymerization step of forming the ultrahigh-molecular-weight polyolefin is usually about -20 to about 120 C, preferably about 0 to about 100 C, especially preferably from about 5 to about 95 C. The pressure used in the polymerization reaction is within a range of pressures under which the liquid-phase 4~
polymerization or the vapor-phase polymeri 2 ation is pos-sible at the above temperatures. For example, it is atmospheric pressure to about 100 kg/cm2, preferably from atmospheric pressure to about 50 g/cm2. The polymeriza-tion time in the polymerization step is set such that theamount of the pre-polymerized polyolefin formed is at least about 1000 g, preferably at least about 2000 g, per milligram of Ti in the highly active titanium catalyst component. To form the ultrahigh-molecular-weight poly-olefin in the above polymerization step, the polymeriza-tion reaction is preferably carried out in the absence of hydrogen. After the polymerization reaction, the polymer may be isolated in an atmosphere of an inert medium and stored.
Examples of the inert medium that can be used in the polymerization step of forming the ultrahigh-molecular-weight polyolefin include aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, octane, decane and kerosene, alicyclic hydrocarbons such as cyclopentane and cyclohexane, aromatic hydrocarbons such as ~enzene, toluene and xylene, halogenated hydrocarbons such as dichloroethane, methylene chloride and chlorobenzene r and mixtures of these. Use of the aliphatic hydrocarbons is especially preferred.
In the polymerization step of forming a poly-olefin having an intrinsic viscosity of less than 10 dl~g in the process used in this invention, the remaining olefins are polymerized in the presence of hydrogen. If this polymerization step is the first polymerization step, the aforesaid catalyst composed of the highly active titanium catalyst compnent ~A) and the organoaluminum compound catalyst component ~B) is fed. If this poly-merization step is the second or subequent step, the catalyst contained in the polymerization product solution formed in the preceding step may be used directly. Or as required, the highly active titanium catalyst component ~.;2 9~7~3 (A) and/or the organoaluminum compound catalyst (B) may be additionally supplied. The proportion of the starting olefin polymerized i~ this polymerization step is 5 to 70 ~ by weight, preferably 20 to 60 % by weight, es-pecially preferably 25 to 55 % by weight, based on theentire olefin components polymerized in the entire poly-merization steps.
The proportion of hydrogen fed in this poly-merization step is usually 0.01 to 50 moles, preferably O.OS to 30 moles, per mole of the olefin ~ed in this step.
Preferably, the concentration of the catalyst components in the polymerization product solution in the polymerization vessel in this polymerization step is adjusted to about 0.001 to about 0.1 milligram atom, preferably about 0.05 to about 0.1 milligram-atom, cal- ;
culated as titanium atoms in the above treated catalyst, and the Al/Ti atomic ratio in the polymerization system is adjusted to from about 1 to about 1000, preferably from about 2 to about 500. For this purpose, the organo-aluminum compound catalyst component ~B) may, as required, be additionally used. Hydrogen, electron donors, halo-genated hydeocarbons, etc. may be caused to be present in the polymerization system in order to adjust the molecular weight, molecular weight distribution, etc.
The polymerization temperature is preferably within temperatures at which slurry polymerization or vapor-phase polymerization is possible~ and is at least about 40 C, especially about 50 to about 100 C. The polymerization pressure that can be recommended is atmos-pheric pressure to about 100 kg/cm2, especially pre~erably atmospheric pressure to about 50 kg/cm2. The polymeriza-tion time may desirably be such that the amount of the polymer formed is at least about 1000 g, especially pre-ferably at least about 5000 g, per milligram-atom of titanium in the titanium catalyst component.
This step may be carried out by a vapor-phase .
~ l z~733 polymerization method or by a liquid-phase polymerization method. Of course different polymerization conditions may be employed in different polymerization steps. As the liquid-phase polymerization method, a slurry suspension-polymerization method is preferably employed. In anycase, the polymeri~ation reaction in the above polymeriza-tion step is carried out in the presence of an inert medium solvent. For example, t:he vapor phase polymeriza-tion may be carried out in the presence of a diluent composed of an inert medium ancl the liquid-phase slurry polymerization may be carried out in the presence of an inert solvent. Examples of the inert medium may be the same as the inert media exemplified with regard to the step of forming the ultrahigh-molecular-weight polyolefin.
The polymerization reaction is carried out so that the polyolefin composition obtained in the final polymerization step has an l~]c of usually 4.0 to 10 dl/g, preferably 4 to 9 dl/g, and a melting torque of not more than 4.5 kg-cm.
The multistep polymerization method may be carried out batchwise, semicontinuously or continuously.
Olefins to which the multistep polymerization method can be applied may be alpha-olefins such as ethylene, propylene, l-butene, l-pentene, l-hexene, 1-octene, 1 decene, l-dodecene, 4~methyl-1-pentene and 3-methyl-1-pentene. It may be applied to the production of homopolymers of these alpha-olefins, or the production of copolymers of at least two of theseO Preferably, the method of this invention is applied to the production of an ethylenic polymer such as an ethylene homopolymer or a copolymer of ethylene as a major component and other alpha-olefin.
The injection-molding polyolefin composition of this invention may contain additives normally used for addition to polyolefins, such as thermal stabilizers, weatherability stabilizers, pigments~ dyes, lubricants, ~ ~94733 inorganic fillers or reinforcing agents such as carbon black, talc or glass fibers, fire retardants and neutron shielding agents within the range which does not impair the objects of this invention.
E~fects of the Invention The injection-molding polyolefin composition of this invention can be injection-molded without substan-tially impairing the inherent excellent mechanical pro-perties (such as abrasion resistance), chemical resist-ance, lubricity and non-water-absorption of ultrahigh-molecular-weight and without molding failure and delami-nation in a molded article which are the defects of ultrahigh-molecular-weight polyolefin in the case of using a general-purpose injection-molding machine. Accordingly it can be conveniently used in various applications in-cluding not only bearings, gears and cams but also sliding members in household electrical appliances, and office automation machines in which conventional general-purpose polyolefins cannot ~ind use because of poor abrasion resistance~
The following examples illust-rate the present invention in more detail. The invention, however, should not be restricted to these examples unless it departs from its scope.
The intrinsic viscosity [~h f the low-mol-ecular-weight or high-molecular-weight polyethylene in the polyethylene compositions in the following examples was calculated by the following procedure.
~1) The density du of the ultrahigh-molecular-~eight polyethylene and the density dc of the final poly-e~hylene composition were measured, and the density dh of the low-molecular-weight or high-molecular-weight poly-ethylene is calculated in accordance with the following e~uation.
dc - (du x a) dh =
~25~4~33 wherein dh, dc and du are as defined above, a is the proportion of the ultrahigh-molecular-weight polyethylene in the final polyethylene composi-tion, and b is the proportion of the low-mol-ecular-weight or high-molecular-weight poly-ethylene in the final polyethylene composition.
(2) Low-molecular-weight or high-molecular-weight polyethylenes having various intrinsic viscosities were produced under substantially the same polymerization conditions (including the monomer composition and cata-lyst) as the conditions for producing the low-molecular-weight or high-molecular-weight polyethylene of which density d was calculated as above except that the partial hydrogen pressure was varied~ The relation between the densities and the intrinsic viscosities [~] of the result-ing polyethylenes was determined.
The density d determined in (1) above of the low-molecular-weight or high-molecular-weight polyethylene - in the polyethylene composition of this invention is taken as the density in the above relation, and the intrinsic viscosity [~]h is determined from the above relation.
- ~3~ The density of each of the samples was determined by the following procedure. Two sets of a stacked structure composed of an aluminum plate 13 x 300 x 300), an asbestos plate (5 x 250 x 250), a stainless plate (3 x 220 x 220) and a polyester film stacked in this order were prepared. One set was placed on the heating plate of a compression molding machine so that the polyester film was directed upward. A molding frame (2 x 200 x 200) was placed on it and the other set was superimposed on the frame so that the polyester film faced downward.
The sample was put in the frame and melted at 190 C+2 C without pressure, and then molded under-a pressure of 300 kg/cm2 for 5 minutes. Thereafter, the sample was cooled to 60 C at a cooling rate of 15+2 C/
min., and taken out. The sample was maintained for 1 hour - ~25~L733 in a constant-temperature oil vessel at 120-~0.2 C and cooled to room temperature at a cooling rate of 1.5 C/
min~ over the course of 1 hour. After cooling, the sample was taken out, and left to stand at room temperature for 1 hour. Then, the density of the sample was measured by a density gradient method (ASTM D-1505~.
Example 1 Preparation of a catalyst sample Anhydrous magnesium chloride (47.6 g; 0.5 mol), 0.25 liter of decane and 0.23 liter (1.5 mol) of 2-ethyl-hexyl alcohol were heated at 130 C for 2 hours to form a uniform solution, and then 7.4 ml (50 mmol) of ethyl benzoate was added. The uniform solution was added drop-wise with stirring over 1 hour to 1.5 liters of TiC14 maintained at -5 C. The reactor used was a 3-liter separable glass flask, and the stirring speed was adjusted to 950 rpmO After the addition, the temperature was raised to 90 C, and the reaction was carried out at 90 C
for 2 hours-. After the reactioni-the solid portion was collected by filtration, and washed fully with hexane to give a highly active fine powdery titanium catalyst com-ponent containing 3.8 % by weight of titaniu~ atoms.
Polymerization Continuous polymerization was carried out by using a continuous two-step polymerization apparatus consisting of two 220-liter polymerization vessel con-nected to each other in series. To the first-step poly-merization vessel (to be abbreviated as the polymerization - vessel 1) in the continuous two-step polymerization ap-paratus 130 liters of n-hexane was added, and the tem-perature was raised to 60 C. n-Hexane t35 liters/hr), triethyl aluminum t45 mM/hr), the titanium catalyst com-ponent tl.0 milligram-atom/hr as titanium atoms~ and ethylene gas t4.3 Nm3/hr) were continuously introduced into the polymerization vessel 1. By using a pump, the resulting polymerization reaction mixture slurry in the ;~294733 polymerization vessel 1 was fed to the second-step poly-merization vessel ~to be referred to as the polymerization vessel 2), and the level of the polymerization vessel 1 was maintained at 130 liters. The polymerization pressure in the polymerization vessel 1 at this time was 4.7 kg/
cm2_G .
In addition to the polymerization mixture in slurry sent from the polymerization vessel 1, n-hexane and ethylene gas were continuously introduced into the poly-merization vessel 2 at a rate of 25 liters/hr and 11.2Nm3/hr, respectively. A moder,ate amount of hydrogen gas was added to adjust the composition of the vapor phase of the vessel 2 to an ethylene/hydrogen mole ratio of 1000:30O
The slurry formed by the polymerization reaction was intermittently withdrawn Erom the bottom of the poly-merization vessel 2 by using a timer valve, and the level of the polymerization vessel 2 was maintained at 120 liters. In the polymerization vessel 2, the polymeriza-tion temperature was 85 C and the polymerization pressure was 7.2 kg/cm . The resulting polymer was separated from`
the solvent by a centrifuge, and dried in a stream of N2.
The 17] and contents of the components of the resulting polyolefin composition, the [~1 of the com-position and its melting torque T were measured by the following methods.
t~]: intrinsic viscosity measured in decalin solvent at 135 C
Melting torque (T): The stress torque of the sample in the molten state which ~as measured~by using a JSR curelastometer (made by Imagawa Machine Industry R. K.~ under conditions involving a temperature of 240 C, a pressure of 5 kg/cm , an amplitude of +3 and a frequency of 6 CPM.
Injection mold_ng One hundred parts by weight of the polyolefin composition was mixed with 0.1 part by weight of tetra-kistmethylene(3,5-di-tert-butyl~4-hydroxy3hydrocinnamate]-methane (IRGANOX 1010, a tr ~ for a product of Japan Ciba-Geigy Co.), 0.1 part by weight of tetrakislmethylene-(2,4-di-tert-butylphenyl)-4,4-biphenylenediphosphite~
(Sandostab P-EPQ, a- ~ ~ for a product of Sandoz AG) and 0.12 part by weight of calcium stearate (a product of Nippon Oils and Fats Co., Ltd.) by a Henschel mixer.
Then, the mixture was molded into a rectangular plate ~130 x 120 x 2 mm) and cut to prepare test samples~
Injection-molding conditions Cylinder temperature (C): 200/230/270/270 Injection pressure (kg/cm2): primary/secondary = 1000/~00 Cycle (seconds): primary/secondary/cooling = 5/3/25 Injecting speed (-): 2/10 Screw rotating speed (rpm): 97 Mold temperature (C): water cooled ~32 C) - - The properties of the samples were evaluated by the following methods.
Tensile test The tensile test was conducted in accordance with ASTM D-638 except that a test specimen having the shape of ASTM No. 4 was used and the tensile speed was set at 50 mm/min. The stress at yield (YS: kg/cm2), tensile strength at break (TS: kg/cm2) and elongation at break (EL: %) of the test sample was determined.
Izo impact strength (kg-cm/cm?
Measured in accordance with ASTM D256 on a notched test sample.
Olsen rigidity (kg/cm2?
Measured in accordance with ASTM D747.
Friction-abrasion test The test was conducted by using a Matsubara-type friction-abrasion tester (made by Toyo Baldwin Company) under a compression load of 3.4 kg/cm2 at a friction speed ~2~ 3 of 30 m/min. for 24 hours, and the amount of loss by abrasion and the coefficient of friction were determined.
Appearance The surface condition of a molded rectangular plate was visually observed and rated on the scale of the following four grades.
(A): No flowmark existed.
~B): Slight flowmarks were observed~
~C): Flowmarks were! observed.
~D): Flowmarks exis;ted throughout.
Delamination The end of a molded sample was ~haven by a knife, and delamination was evaluated on the scale of the following four grades.
lD): The surface was easily peeled.
tC): The surface was slightly peeled.
~B): The surface was hardly peeled.
(A): The surface was not peeled at all.
Examples 2-6 In each run, Example 1 was repeated except that the polymerization conditions were changed as indicated in Table 1, and the molecular weights of the ultrahigh-molecular-weight polyethylene and the low-molecular-weight or high-molecular-weight polyethylene and the ratio between the amounts of the ultrahigh-molecular-weight polyethylene and the low-molecular-weight or high-mol-ecular-weight polyethylene were changed. The results are shown in Table 2.
Referential Examples 1-2 Commercial ultrahigh-molecular-weight poly-ethylene tHizex MillionR240M, a ~ e-for a product of ~ Mitsui Petrochemical Industries, Co., Ltd.) was injection-molded by the same method as in Comparative Example 3 using an injection-molding machine having a screw of the three-stage compression type.
Furthermore, commercial injection-molding high-~2~4~3 5 - ~ rqden~A~
density polyethylene (Hize*~ 2208J, a ~de~ for a product of Mitsui Petrochemical Industries, Ltd.) was injection-molded by the same method as in Example 1.
The results are also shown in Table 2.
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; . 3~ 5 ~ 5 ~ ~ ~ ~ ~ 5 5 3i ~ fi
INJECTION-MOLDING POLYOLEFIN COMPOSITION
Field of Technology This invention relates to an injection-molding polyolefin composition, and more specifically, to an injection-m~lding polyolefin composition suitable for obtaining injection-molded articles having excellent abrasion resistance and impact strength and being free from delamination.
Background Technology Ultrahigh-molecular-weight polyolefins, for example ultrahigh-molecular-weight polyethylene, have higher impact strength, abrasion resistance, chemical resistance, tensile strength, etc D than general-purpose polyolefins such as general-purpose polyethylene, and have found increasing applications as engineering plastics.
The ultrahigh-molecular-weight polyethylene, however, has the defect that it is very difficult to mold by extrusion or injection-molding because it has a much higher melt viscosity and thus lower flowability than general-purpose polyethylene.
At present, therefore, most articles from ultra-high-molecular-weight polyethylene are produced by com-pression molding, and only some articles such as rods are produced by extrusion-molding at very low speeds.
When such ultrahigh-molecular-weight poly-ethylene having low melt-flowability is molded by an ordinary injection-molding method, shear broken streams of the polymer always form during the filling of the polymer in a mold cavity, and the resulting molded article under-goes delamination like mica and cannot exhibit the excel-lent properties of the ultrahigh-molecular-weight poly-ethylene. Rather, its quality is inferior to that of a molded article of general-purpose polyethylene.
Japanese Patent Publications Nos~ 300~7/1982 and 58010J1985 propose an injection-molding method free from 3~ 733 causing delamination, in which the capacity of a mold cavity is slightly increased before or after a resin is filled in the cavity, and then the resin is compressed to a predetermined volume. This method enabled production of injection-molded articles free from delamination and having the impact strength and abrasion resistance which are the inherent characteristics of the ultrahigh-molecular-weight polyethylene. To perform injection molding by this method, however, it is necessary to use an injection-molding machine equipped with a variable mold cavity system, and the general injection-molding machine for polyethylene cannot be used as it is.
On the other hand, for improving the melt-flow-ability of ultrahigh-molecular-weight polyolefins, mixing of an ultrahigh-molecular-weight polyolefin with a low to a high molecular weight polyolefin was proposed.
Japanese Patent Publication No. 27,06~/1971 discloses an abrasion-resistant polyethylene resin com-position comprising polyethylene having an average mol~
ecular weight of at least 500,000 and 20 to 50 % by weight of polyethylene having a density of at least 0.940 and an average molecular weight of 30,000 to 120,000.
Japanese Patent Publication No. 30,293/1972 discloses a process for producing a material for use in that surface of agricultural machines, earth-moving machines, etc. which comes into contact with the soil, which comprises mixing screw-extrudable polyethylene having a molecular weight of not more than 200,000 and produced by the medium-pressure or the low-pressure method with 10 to 30 % by weight of ultrahigh-molecular-weight polyethylene having a molecular weight of about 1 million and being incapable of screw-extrusion, melting the mixture uniformly, and continuously molding the uniform molten mixture by an extruder.
Japanese Patent Publication No. 41,309/1983 discloses a polyethylene composition comprising a mixture . . .
.~
~Z~733 of 85 to 50 parts by weight of polyethylene having a viscosity average molecular weight of 500~000 to 150,000 and 15 to 50 parts by weight of granular uitrahigh-molecular-weight polyethylene having a viscosity average molecular weight of at least 1 million and a particle size smaller than 10 mesh.
Japanese Laid-Open Patent Publication No.
177,036/1982 discloses an ultrahigh-molecular-weight polyethylene composition having improved moldability comprising 100 part~ by weight of ultrahigh-molecular-weight polyethylene having a molecular weight of at least 1 million and 10 to 60 parts by weight of low-molecular-weight polyethylene having a molecular weight of 5,000 to 20,000. The specification of this patent document states that the moldability of this ultrahigh-molecular-weight polyethylene composition is such that in the production of a slab having a thickness of 50 mm by a compr~ssion mold-ing method, the molding cycle required was decreased to -- 200 C x 2 hours while with the ult~rahigh-molecular-weight polyethylene along a molding cycle of 200 C x 3 hours was required; and that in a ram extrusion method, the speed of pipe extrusion was increased from 5 cm/min. to 10 cm/min~
Japanese Laid-Open Patent Publication No.
126,446/1984 discloses an ultrahigh-molecular-weight polyethylene resin composition comprising 9S to 50 parts by weight of an ultrahigh-molecular-weight polyethylene resin and 5 to 50 parts by weight of a general-purpose polyolefin resin. The specification of this document discloses a composition in which a silane-modified poly-ethylene resin having a melt index of 2.5 or 5~0 g/10 min.as an actual specific example of the general-purpose polyolefin resinO
Japanese Patent Publication No. 41,309/1983 discloses a polyethylene composition comprising a mixture of 85 to 50 parts by weight of polyethylene having a viscosity average molecular-weight of 500,000 to 150,000 ~Z~733 and 15 to 50 parts by weight of granular ultrahigh-molecular-weight polyethylene having a visçosity average molecular weight of at least 1 million and a particle size smaller than 10 mesh. As stated in column 3, lines 17 28 of this document, the moldabil:ity of the ultrahigh-molecular-weight polyethylene in this composition has not improved, but the purpose of providing this composition is to produce a molded article having excellent impact strength by reducing anisotropy utilizing the granular state of the ultrahigh-molecular-weight polyethylene.
The above polyethylesle resin compositions are prepared by mixing ultrahigh-molecular-weight polyethylene with polyethylene or other polyolefins having lower mol-ecular weights.
Japanese Laid-Open Patent Publication No.
94,593/1979 (corresponding to V. S~ Patent No. 4,414,369) discloses a process ~or producing a polyolefin having a broad molecular weight distribution by polymerizing an olefin in the presence of a solvent and hydrogen using a Ziegler-type catalyst of enhanced activity supported on a solid carrier to produce a polyolefin continuously, which comprises continuously feeding a main olefin monomer and at least one olefin comonomer under pressure using a plurality of reactors in which a gaseous phase containing an inert gas is present in the upper part of a first-stage reactor, and copolymerizing these monomers, continuously transferring the polymerization reaction mixture in which high-molecular-weight polymer particles are dispersed in a solvent to a second-stage reactor composed of a vertical stirred vessel maintained at a lower pressure than the first-stage reactor by differential pressures without substantially separating part of the components in the mixture and without using any forced transferring means, continuously performing polymerization in the second~stage stirred vessel in the presence of the main olefin monomer and hydrogen while a gaseous phase exists in the upper ~2~733 part of the stirred vessel, thereby to form a polymer having a lower molecular weight than in the first stage polymerization, continuously withdrawing the polymeriza-tion reaction mixture containing the resulting polymer particles dispersed in a solvent from the second-stage stirred vessel, and recovering the polymer.
Japanese Patent Publ;cation No. 10,724/1984 ~corresponding to U. S. Patent No. 4,336,352) discloses a process in which polyethylenes of different molecular weights are produced by multi-stage continuous poly-merization in at least three polymerization vessels con-nected in series. The purpose of this process is to produce polyethylene having excellent properties and moldability with high productivity. With regard to moldability, this process is for producing polyethylene by extrusion molding, above all blow molding, with improved die swelling. It does not relate to an improvement in an injection-molded article. Even when a composition con-taining not more than 10 % by weight of ultrahigh-molecular-weight polyethylene and having an MI of 0.3 or an intrinsic viscosity ~1 of 2.3 to 3~0 dl~g (corres-ponding to an MI of about 0.2 to 0.8) is used in injection molding, the content of ultrahigh-molecular-weight poly-ethylene is as low as not more than 10 ~ by weight.
Japanese Patent Publication No. 11,349/1971 discloses a process which comprises producing 5 to 30 % by weight of an ethylene/alpha-olefin copolymer having a reduced specific viscosity of 30 to 5 in a first step, and producing polyethylene or an ethylene~alpha-olefin co-polymer having a reduced specific viscosity of 4.6 to 1.5 in a second stage to obtain a homogeneous mixture of it with the polymer obtained in the first stage. The purpose of this process is to improve moldability in the extrusion molding of bottles, cables, pipes, etc. and does not pertain to an improvement in an injection-molded article.
Japanese Laid-Open Patent Publication No.
~29~L733 141,409/1982 discloses a process for producing poly-ethylene which comprises polymerizing ethylene, or co-polymerizing ethylene with an alpha-olefin, using a catalyst comprising a reaction product between a magnesium compound and a titanium halide and an organoaluminum compound; wherein the following three polymerization steps, (a) a step of forming an ethylene polymer or copolymer having an alpha-olefin content of not more than 10 % by weight and an in-trinsic viscosity [~] of 0O3 to 1.5, (b) a step of forming an ethylene polymer or copolymer having an alpha-olefin content of not more than 30 % by weight and an in-trinsic viscosity ~] of 1.5 to 7, and (c) a step of forming an ethylene polymer orcopolymer having an alpha-olefin content of not more than 30 % by weight and an in-- trinsic viscosity ~] of 7 to 40-,-are carried out in any desired sequence, and the poly-merization reactions are carried out while adjusting the ratio of the amounts of the polymers formed in step (a):step (b~:step (c) to 1:0.1-1.5:0.01-1.2.
Japanese Laid-Open Patent Publication ~o.
8713/1983 discloses a process for producing an ethylenic copolymer which comprises copolymerizing ethylene and an alpha-olefin using a catalyst system obtained from ~A~ a solid catalyst component containing at least magnesium, halogen and titanium atoms and (B) an organoaluminum compound in at least two steps, wherein (1) in at least one step, 80 to 20 parts by weight of a copolymer having a high-load melt index o~ 0.03 to 10 g/10 min. and a density of 0.890 g/cm3 to less than 0.905 g/cm3 is produced~
~2) in a second step, 20 to 80 parts by weight , .
:' of a copolymer having a melt index of L0 to 5000 g/10 min.
and a density of 0.905 to 0.940 g/cm3 is produced, whereby a copolymer having a melt index of 0.02 to 30 g/10 min. and a density of 0.890 to 0.935 g/cm3 is produced.
This patent document discloses that the high-load melt index was measured al: a temperature of 190 C
under a load of 21.6 kg in accordance with JIS K-6760.
Japanese Laid-Open Patent Publication No.
871~/1983 discloses a process for producing an ethylenic copolymer using the same catalyst as described in the above~cited Japanese Laid-Open Patent Publication NoO
8713/1983 by multisteppolymerization, wherein (1) in at least one step, 80 to 20 parts by weight of a copolymer of ethylene with propylene and/or butene-l having a high-load melt index of 0.03 to 10 g/10 min. and a density of 0.890 to 0~935 g/cm3 is produced, and (2) in at least one other step, 20 to-80 parts -by weight o~ a copolymer of ethylene and an alpha-olefin having at most 12 carbon atoms as a comonomer having a melt index of 10 to 5000 g/10 min. and a density of 0.89Q to 0.940 is produced, said alpha-olefin con-taining at least 30 mole % of alpha-olefins having 5 to 12 carbon atoms, whereby a copolymer having a melt index of 0.02 to 30 g~l0 min. and a density of 0.890 to 0.936 g/cm3 is produced.
Japanese Laid-Open Patent Publication No.
120,605/1984 discloses a process for producing an ultra-high-molecular-weight polyethylene resin with improved moldability and processability, which comprises poly-merizing monomers using a Ziegler-type catalyst comprising a solid catalyst component containing a transition metal ingredient and an organometallic catalyst component in at least two steps having different monomer compositions and ~Z~733 hydroyen concentrations; wherein in at least one step, propylene or monomers mainly comprising propylene, or butene-l or monomers mainly comprising butene-l are poly-merized in the presence of hydrogen to produce 2 to 60 ~
by weight, based on the entire polymer to be produced, of a polypropylene or polybutene-l component, and in at least one remaining step, ethylene or monomers mainly comprising ethylene are polymeri~ed in th~e substantial absence of hydrogen to produce 98 to 40 ~ by weight, based on the entire polymer produced, of an ultrahigh-molecular-weight polyethylene component.
British Patent No. 1,174,542 discloses a process for the preparation of a homo- or co-polymer of ethylene by a gaseous phase polymerization, or by a suspension poly-merization in which the dispersion medium is in contactwith a gaseous phase, of ethylene or a mixture comprising ethylene and up to 10 % by weight of an alpha-olefin that contains from 3 to 15 carbon atoms, which process com-prises preparing from 5 to 30 % by weight of the total polymer in the presence of from 0 to 10 % of hydrogen, calculated on the total volume of the gaseous phase, and preparing from 70 to 95 % by weight of the total polymer in the presence of from 20 to 80 ~ of hydrogen, cal-culated on the total volume of the gaseous phase, both stages of the polymerization being carried out at a tem-perature within the range of from 50 to 120 C and a pressure of up to 10 atmospheres gauge, in the presence of a catalyst which is present in the first stage in an amount sufficient for both stages, siad catalyst com-prising a) in the case of a suspension polymerization,from 0.05 to 0.3 millimol per litre of di-spersion medium, or in the case of a poly-merization in the gaseous phase, from O.OS to 0.3 millimol per 0.5 litre of reactor volume, of a trivalent titanium compound that contains chlorine, and ~Z'3~733 . g b) from 0.1 to 3.0 millimols of aluminum per litre of dispersion medium or reactor volume, in the form of an aluminum trialkyl having the general formula AlR, in which each R
represents a hydrocarbon radical that con-tains;from 4 to 40 carbon atoms, or in the form of the reaction product of an aluminum trialkyl or an aluminium alkyl hydride with a diolefin that contains fro~ 4 to 20 carbon atoms.
Japanese Laid-Open Patent Publication No.
275,313/1986 laid-open after the priority date of the present application discloses an ultrahigh-molecular-weight polyethylene composition having improved injection-moldability which has an intrinsic viscosity, determined in decalin at 135 C, of 10 to 30 dl/g and obtained by polymerization reaction in at least two steps mentioned below.
(First step) A step of forming 50 to 99.5 parts by weight o~
polyethylene having an intrinsic viscosity, determined in decalin at 135 C, of 12 to 32 dl/g by polymerizing ethylene in the absence of hydrogen or in a lowered hydrogen concentration with a catalyst comprising a solid catalyst component containing at least Mg, Ti and/or V
and an organometallic compound.
5Second step) A step of forming 50 to 0.5 parts by weight of polyethylene by polymerizing ethylene in a hydrogen concentration increased over that in the first step.
Likewise~ European Laid-Open Patent Publication No. 0186995 laid-open after the priority date of the present application discloses a process for producing ultrahigh-mo:Lecular-weight polyethylene having an ~LZ9~3~3 intrinsic viscosity, determined in decalin at 135 C, of 10 to 30 dl/g by polymerization in at least two steps, which comprises (a) a first step of forming 70 to 99.5 parts by weight of polyethylene having an intrinsic viscosity~ determineld in decalin at 135 C, of 12 to 32 dl/g by polymerizing ethylene monomer in the absence of hydrogen or in the presence of hydrogen in a low concentration using a combina-tion catalyst comprising a solid component containing at least ;magnesium, titanium and/or vanadium and an organometallic compounc~, and ~b) a second step of forming 30 to 0.5 parts by weight of polyethylene having an intrinsic viscosity, determined in decalin at 135 C, of 0.1 to S dl/g by polymerizing a freshly fed ethylene monomer in the presence of hydrogen in a high concentration.
--- It is an object of this invention to provide an injection-molding polyolefin composition comprising an ultrahigh-molecular-w~ight polyolefin component and having very good injection-moldability.
Another object of this invention is to provide an injec~ion-molding polyolefin composition which is suitable for obtaining an injection-molded article free from delamination without impairing the inherent excellent mechanical properties, such as high abrasion resistance, of the ultrahigh-molecular-weight polyolefin.
Other objects of the invention along with its advantage will become apparent from the following descrip-tion.
In the present invention, the ultrahigh-mol-ecular-weight polyolefin has an intrinsic viscosity [~]u' measured in decalin at 135 C, of 10 to 40 dl/g, prefer-ably 15 to 35 dl/g.
The other low-molecular-weight or high-molecular-129~733 weight polyolefin, as referred to in this invention, has an intrinsic viscosity 17]h, measured in decalin solvent at 135 C, of less than 10 dl/g, preferably 0.1 to 5 dl/g, more preferably 0.5 to 3 dl/g.
The polyolefin in this invention is a homo-polymer or copolymer of an alpha-olefin such as ethylene, propylene, l-butene, l-pentene, l-hexene, 1-octene, 1-decene, l-dodecene, 4-methyl-1-pentene and 3-methyl-1-pentene. The homopolymer of ethylene or a copolymer comprising ethylene as a main component and another alpha-olefin of the type exemplified above is desirable.
The quantitative proportions of the ultrahigh-molecular-weight polyolefin and the low-molecular-weight or high-molecular-weight polyolefin are such that the ultrahigh-molecular-weight polyolefin accounts Eor 15 to 40 % by weight of the total weight of the two polymer or the low-molecular-weight or high-molecular-weight poly-olefin accounts for 85 to 60 ~ by weight of the total weight of the two polyolefins. The preferred quantitative proportions are such that the proportion of the ultra-high-molecular-weight polyolefin is 20 to 35 % by weight based on the total weight of the two polyolefins.
The injection-molding polyolefin composition of this invention comprises the ultrahigh-molecular-weight polyolefin and the low-molecular-weight or high-mol-ecular-weight polyolefin in the above quantitative pro-portions~ The injection-molding polyolefin composition of this invention has an intrinsic viscosity [~]c' measured in decalin solvent at 135 C, of 4.0 to 10 dl/g and a melting torque T ~kg-cm) of not more than 4.5 kg-cm. The melting torque T is measured by using a JSR curelastometer (made by Imanaka Machine Industry K. K.) under conditions involving a temperature of 240 C, a pressure of 5 kg/cm2, an amplitude of 135 and a frequency number of 6 CPM.
The injection-molding polyolefin composition of this invention preferably has an l~Jc of 4 to 9 dl/g.
1~473~
The injection-molding polyolefin composition of this invention may be prepared by blending the ultrahigh-molecular-weight polyolefin and the low-molecular-weight or high-molecular-weight polyolefin in the proportions mentioned above. It has been found, however, that it can be advantageously prepared by a multistep polymerization method to be described below which comprises polymerizing olefins in the presence of a catalyst formed from a specific highly active solid titanium catalyst component and an organoaluminum compound catalyst component. The multistep polymerization method is carried out by poly-merizing olefins in a multiplicity of stages in the pre-sence of a Ziegler-type catalyst formed from (A~ a highly active titanium catalyst component containing magnesium, titanium and halogen as essential ingredients and (B) an organoaluminum compound catalyst component. Specifically, in at least one polymerization step, an ultrahigh-mol-ecular-weight polyolefin having an intrinsic vi~cosity t~]u f 10 to 40 dlJg is formed, and in-another poly-merization, an olefin is polymerized in the presence ofhydrogen to give a low-molecular-weight or high-molecular-weight polyolefin having an intrinsic viscosity t~]h of 0.1 to 5 dl/g is formed.
The Ziegler-type catalyst used is basically a catalyst having specific properties formed from a solid titanium catalyst component and an organoaluminum compound catalyst component. Preferably, the solid titanium cata-lyst component is, for example, a highly active fine powdery catalyst component which has a narrow particle size distribution and an average particle diameter of about 0.01 to 5 micrometers and in which several fine spherical particles adhere firmly to one another. The highly active fine powdery titanium catalyst component can be prepared, for example, by the method of preparing the solid titanium catalyst component disclosed in Japanese Laid-Open Patent Publication No. 811/1981 in which at a 12~1~733 time of precipita~ing a solid product by contacting a magnesium compound in solution with a titanium compound in solution, the precipitating conditions are strictly ad-justed. For example, in the method disclosed in the above-cited Japanese Laid-Open Patent Publication which involves mixing a hydrocarbon solution of magnesium chloride and a higher alcohol with titanium tetrachloride at low temperatures, and heating the mixture to about 50 to 100 C to precipitate the solid product, the pre-cipitation is carried out in the presence of a slightamount, for example about 0.01 to 002 mole, per mole of ma~nesium chloride, of a monocarboxylic acid ester with strong stirring. If required, the product is washed with titanium tetrachloride. Thus, a solid catalyst component having satisfactory activity and particle form can be obtained. This catalyst component contains about 1 to about 6 % by weight of titanium, and has a halogen/-titanium atomic ratio of abo~t 5 to about 90 and a magnesium/titanium tatomic ratio3 of about 4 to about 50.
Fine spherical particles having a narrow par-ticle size distribution and an average particle diameter of usually 0.01 to 5 micrometers r preferably 0.05 to 3 micrometers, which are obtained by subjecting a slurry of the solid titanium ca~alyst component prepared as above to high-speed shear treatment are also preferably used. For high-speed shear treatment, a method is employed in which the slurry of the solid titanium catalyst component is treated with a commercial homomixer in an inert gaseous atmosphere for a suitable period of time. To prevent a reduction in catalyst performance at this time, there may also be employed a method in which an organoaluminum compound is added in a proportion equimolar to titanium.
The treated slurry may be filtered through a sieve to remove coarse particles. By these methods, highly active fine powdery titanium catalyst components can be obtained.
~2~9~7~3 -- lDL -- J
The injection-molding polyolefin composition of this invention may be produced by slurry polymerization of olefins in at least two steps at a temperature of usually 0 to 100 C in a hydrocarbon medium such as pentane, hexane, heptane or kerosene using the highly active fine powdeey titanium catalyst component and an organoaluminum compound catalyst component optionally in combination with an electron donor. Examples of the organoaluminum com-pound catalyst component are trialkyl aluminums such as triethyl aluminum or triisobutyl aluminum, dialkyl aluminum chlorides such as diethyl aluminum chloride or diisobutyl aluminum chloride, alkyl aluminum sesqui-chlorides such as ethyl aluminum sesquichloride, or mixtures of theser A multistep polymerization apparatus consisting of at least two polymerization vessel usually connected in series is used in the multistep polymerization process of olefins, and the polymerization is carried out in two steps, three steps, ... or n steps. The multistep poly-merization may also be carried out batchwise in a single polymerization vessel. It is necessary, in at least one polymerization vessel in the multistep polymerization process, to form a specific amount of an ultrahigh-molecular-weight polyolefin. The step in which to form the ultrahigh-molecular-weight polyolefin may be a first polymerization step or an intermediate polymerization step or may comprise two or more stages. From the viewpoint of the polymerization treatment operations and the control of the properties of the resulting polyolefin r it is pre-ferred that the ultrahigh-molecular-weight polyolefin be formed in the first polymerization step. Preferably, in the above polymerization step, 15 to 40 % of olefins to be polymerized in all steps are polymerized to give an ultra-high-molecular-weight polyolefin having an intrinsic viscosity ~]u ~measured in decalin solvent at 135 C) of 10 to 40 dl/g; and further, by polymerizing 18 to 37 % by ~z~a733 weight, especially 21 to 35 % by weight, of oléfins to be polymerized in the entire polymerization steps, an ultra-high-molecular-weight polyolefin having an intrinsic viscosity [~]u f 15 to 35 dl/g, especially 18 to 30 dl/g, is formed.
In the multistep polymerization process, the polymerization in the step of forming the ultrahigh-mol-ecular-weight polyolefin may be carried out in the pre-sence of a catalyst composed o~E the highly active titanium catalyst component ~A) and the organoaluminum compound catalyst component (B). The polymerization may be carried out by a vapor-phase polymerization method or a liquid-phase polymerization method. In any case, in the step of forming the ultrahigh-molecular-weight polyolefin, the polymerization reaction can be carried out in the presence of an inert medium as required. For e~ample, the vapor-phase polymerization method may be carried out in the presence of a diluent composed of an inert medium if required. The liquid-phase polymerization method may be carried out in the presence of a solvent composed of an inert medium as required.
In the polymerization step of forming the ultra-high-molecular-weight polyolefin, it is preferred to use the highly-active titanium catalyst component (A) in an ~mount of about 0.001 to about 20 milligram atoms, es-pecially about 0.005 to about 10 milligram-atoms, as ~itanium atoms per liter of the medium, and the organo-aluminum compound catalyst component ~B~ in an amount ~orresponding to an Al/Ti atomic ratio of from about 0.1 to about 1,000, especially from a~out 1 to about 500. The temperature of the polymerization step of forming the ultrahigh-molecular-weight polyolefin is usually about -20 to about 120 C, preferably about 0 to about 100 C, especially preferably from about 5 to about 95 C. The pressure used in the polymerization reaction is within a range of pressures under which the liquid-phase 4~
polymerization or the vapor-phase polymeri 2 ation is pos-sible at the above temperatures. For example, it is atmospheric pressure to about 100 kg/cm2, preferably from atmospheric pressure to about 50 g/cm2. The polymeriza-tion time in the polymerization step is set such that theamount of the pre-polymerized polyolefin formed is at least about 1000 g, preferably at least about 2000 g, per milligram of Ti in the highly active titanium catalyst component. To form the ultrahigh-molecular-weight poly-olefin in the above polymerization step, the polymeriza-tion reaction is preferably carried out in the absence of hydrogen. After the polymerization reaction, the polymer may be isolated in an atmosphere of an inert medium and stored.
Examples of the inert medium that can be used in the polymerization step of forming the ultrahigh-molecular-weight polyolefin include aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, octane, decane and kerosene, alicyclic hydrocarbons such as cyclopentane and cyclohexane, aromatic hydrocarbons such as ~enzene, toluene and xylene, halogenated hydrocarbons such as dichloroethane, methylene chloride and chlorobenzene r and mixtures of these. Use of the aliphatic hydrocarbons is especially preferred.
In the polymerization step of forming a poly-olefin having an intrinsic viscosity of less than 10 dl~g in the process used in this invention, the remaining olefins are polymerized in the presence of hydrogen. If this polymerization step is the first polymerization step, the aforesaid catalyst composed of the highly active titanium catalyst compnent ~A) and the organoaluminum compound catalyst component ~B) is fed. If this poly-merization step is the second or subequent step, the catalyst contained in the polymerization product solution formed in the preceding step may be used directly. Or as required, the highly active titanium catalyst component ~.;2 9~7~3 (A) and/or the organoaluminum compound catalyst (B) may be additionally supplied. The proportion of the starting olefin polymerized i~ this polymerization step is 5 to 70 ~ by weight, preferably 20 to 60 % by weight, es-pecially preferably 25 to 55 % by weight, based on theentire olefin components polymerized in the entire poly-merization steps.
The proportion of hydrogen fed in this poly-merization step is usually 0.01 to 50 moles, preferably O.OS to 30 moles, per mole of the olefin ~ed in this step.
Preferably, the concentration of the catalyst components in the polymerization product solution in the polymerization vessel in this polymerization step is adjusted to about 0.001 to about 0.1 milligram atom, preferably about 0.05 to about 0.1 milligram-atom, cal- ;
culated as titanium atoms in the above treated catalyst, and the Al/Ti atomic ratio in the polymerization system is adjusted to from about 1 to about 1000, preferably from about 2 to about 500. For this purpose, the organo-aluminum compound catalyst component ~B) may, as required, be additionally used. Hydrogen, electron donors, halo-genated hydeocarbons, etc. may be caused to be present in the polymerization system in order to adjust the molecular weight, molecular weight distribution, etc.
The polymerization temperature is preferably within temperatures at which slurry polymerization or vapor-phase polymerization is possible~ and is at least about 40 C, especially about 50 to about 100 C. The polymerization pressure that can be recommended is atmos-pheric pressure to about 100 kg/cm2, especially pre~erably atmospheric pressure to about 50 kg/cm2. The polymeriza-tion time may desirably be such that the amount of the polymer formed is at least about 1000 g, especially pre-ferably at least about 5000 g, per milligram-atom of titanium in the titanium catalyst component.
This step may be carried out by a vapor-phase .
~ l z~733 polymerization method or by a liquid-phase polymerization method. Of course different polymerization conditions may be employed in different polymerization steps. As the liquid-phase polymerization method, a slurry suspension-polymerization method is preferably employed. In anycase, the polymeri~ation reaction in the above polymeriza-tion step is carried out in the presence of an inert medium solvent. For example, t:he vapor phase polymeriza-tion may be carried out in the presence of a diluent composed of an inert medium ancl the liquid-phase slurry polymerization may be carried out in the presence of an inert solvent. Examples of the inert medium may be the same as the inert media exemplified with regard to the step of forming the ultrahigh-molecular-weight polyolefin.
The polymerization reaction is carried out so that the polyolefin composition obtained in the final polymerization step has an l~]c of usually 4.0 to 10 dl/g, preferably 4 to 9 dl/g, and a melting torque of not more than 4.5 kg-cm.
The multistep polymerization method may be carried out batchwise, semicontinuously or continuously.
Olefins to which the multistep polymerization method can be applied may be alpha-olefins such as ethylene, propylene, l-butene, l-pentene, l-hexene, 1-octene, 1 decene, l-dodecene, 4~methyl-1-pentene and 3-methyl-1-pentene. It may be applied to the production of homopolymers of these alpha-olefins, or the production of copolymers of at least two of theseO Preferably, the method of this invention is applied to the production of an ethylenic polymer such as an ethylene homopolymer or a copolymer of ethylene as a major component and other alpha-olefin.
The injection-molding polyolefin composition of this invention may contain additives normally used for addition to polyolefins, such as thermal stabilizers, weatherability stabilizers, pigments~ dyes, lubricants, ~ ~94733 inorganic fillers or reinforcing agents such as carbon black, talc or glass fibers, fire retardants and neutron shielding agents within the range which does not impair the objects of this invention.
E~fects of the Invention The injection-molding polyolefin composition of this invention can be injection-molded without substan-tially impairing the inherent excellent mechanical pro-perties (such as abrasion resistance), chemical resist-ance, lubricity and non-water-absorption of ultrahigh-molecular-weight and without molding failure and delami-nation in a molded article which are the defects of ultrahigh-molecular-weight polyolefin in the case of using a general-purpose injection-molding machine. Accordingly it can be conveniently used in various applications in-cluding not only bearings, gears and cams but also sliding members in household electrical appliances, and office automation machines in which conventional general-purpose polyolefins cannot ~ind use because of poor abrasion resistance~
The following examples illust-rate the present invention in more detail. The invention, however, should not be restricted to these examples unless it departs from its scope.
The intrinsic viscosity [~h f the low-mol-ecular-weight or high-molecular-weight polyethylene in the polyethylene compositions in the following examples was calculated by the following procedure.
~1) The density du of the ultrahigh-molecular-~eight polyethylene and the density dc of the final poly-e~hylene composition were measured, and the density dh of the low-molecular-weight or high-molecular-weight poly-ethylene is calculated in accordance with the following e~uation.
dc - (du x a) dh =
~25~4~33 wherein dh, dc and du are as defined above, a is the proportion of the ultrahigh-molecular-weight polyethylene in the final polyethylene composi-tion, and b is the proportion of the low-mol-ecular-weight or high-molecular-weight poly-ethylene in the final polyethylene composition.
(2) Low-molecular-weight or high-molecular-weight polyethylenes having various intrinsic viscosities were produced under substantially the same polymerization conditions (including the monomer composition and cata-lyst) as the conditions for producing the low-molecular-weight or high-molecular-weight polyethylene of which density d was calculated as above except that the partial hydrogen pressure was varied~ The relation between the densities and the intrinsic viscosities [~] of the result-ing polyethylenes was determined.
The density d determined in (1) above of the low-molecular-weight or high-molecular-weight polyethylene - in the polyethylene composition of this invention is taken as the density in the above relation, and the intrinsic viscosity [~]h is determined from the above relation.
- ~3~ The density of each of the samples was determined by the following procedure. Two sets of a stacked structure composed of an aluminum plate 13 x 300 x 300), an asbestos plate (5 x 250 x 250), a stainless plate (3 x 220 x 220) and a polyester film stacked in this order were prepared. One set was placed on the heating plate of a compression molding machine so that the polyester film was directed upward. A molding frame (2 x 200 x 200) was placed on it and the other set was superimposed on the frame so that the polyester film faced downward.
The sample was put in the frame and melted at 190 C+2 C without pressure, and then molded under-a pressure of 300 kg/cm2 for 5 minutes. Thereafter, the sample was cooled to 60 C at a cooling rate of 15+2 C/
min., and taken out. The sample was maintained for 1 hour - ~25~L733 in a constant-temperature oil vessel at 120-~0.2 C and cooled to room temperature at a cooling rate of 1.5 C/
min~ over the course of 1 hour. After cooling, the sample was taken out, and left to stand at room temperature for 1 hour. Then, the density of the sample was measured by a density gradient method (ASTM D-1505~.
Example 1 Preparation of a catalyst sample Anhydrous magnesium chloride (47.6 g; 0.5 mol), 0.25 liter of decane and 0.23 liter (1.5 mol) of 2-ethyl-hexyl alcohol were heated at 130 C for 2 hours to form a uniform solution, and then 7.4 ml (50 mmol) of ethyl benzoate was added. The uniform solution was added drop-wise with stirring over 1 hour to 1.5 liters of TiC14 maintained at -5 C. The reactor used was a 3-liter separable glass flask, and the stirring speed was adjusted to 950 rpmO After the addition, the temperature was raised to 90 C, and the reaction was carried out at 90 C
for 2 hours-. After the reactioni-the solid portion was collected by filtration, and washed fully with hexane to give a highly active fine powdery titanium catalyst com-ponent containing 3.8 % by weight of titaniu~ atoms.
Polymerization Continuous polymerization was carried out by using a continuous two-step polymerization apparatus consisting of two 220-liter polymerization vessel con-nected to each other in series. To the first-step poly-merization vessel (to be abbreviated as the polymerization - vessel 1) in the continuous two-step polymerization ap-paratus 130 liters of n-hexane was added, and the tem-perature was raised to 60 C. n-Hexane t35 liters/hr), triethyl aluminum t45 mM/hr), the titanium catalyst com-ponent tl.0 milligram-atom/hr as titanium atoms~ and ethylene gas t4.3 Nm3/hr) were continuously introduced into the polymerization vessel 1. By using a pump, the resulting polymerization reaction mixture slurry in the ;~294733 polymerization vessel 1 was fed to the second-step poly-merization vessel ~to be referred to as the polymerization vessel 2), and the level of the polymerization vessel 1 was maintained at 130 liters. The polymerization pressure in the polymerization vessel 1 at this time was 4.7 kg/
cm2_G .
In addition to the polymerization mixture in slurry sent from the polymerization vessel 1, n-hexane and ethylene gas were continuously introduced into the poly-merization vessel 2 at a rate of 25 liters/hr and 11.2Nm3/hr, respectively. A moder,ate amount of hydrogen gas was added to adjust the composition of the vapor phase of the vessel 2 to an ethylene/hydrogen mole ratio of 1000:30O
The slurry formed by the polymerization reaction was intermittently withdrawn Erom the bottom of the poly-merization vessel 2 by using a timer valve, and the level of the polymerization vessel 2 was maintained at 120 liters. In the polymerization vessel 2, the polymeriza-tion temperature was 85 C and the polymerization pressure was 7.2 kg/cm . The resulting polymer was separated from`
the solvent by a centrifuge, and dried in a stream of N2.
The 17] and contents of the components of the resulting polyolefin composition, the [~1 of the com-position and its melting torque T were measured by the following methods.
t~]: intrinsic viscosity measured in decalin solvent at 135 C
Melting torque (T): The stress torque of the sample in the molten state which ~as measured~by using a JSR curelastometer (made by Imagawa Machine Industry R. K.~ under conditions involving a temperature of 240 C, a pressure of 5 kg/cm , an amplitude of +3 and a frequency of 6 CPM.
Injection mold_ng One hundred parts by weight of the polyolefin composition was mixed with 0.1 part by weight of tetra-kistmethylene(3,5-di-tert-butyl~4-hydroxy3hydrocinnamate]-methane (IRGANOX 1010, a tr ~ for a product of Japan Ciba-Geigy Co.), 0.1 part by weight of tetrakislmethylene-(2,4-di-tert-butylphenyl)-4,4-biphenylenediphosphite~
(Sandostab P-EPQ, a- ~ ~ for a product of Sandoz AG) and 0.12 part by weight of calcium stearate (a product of Nippon Oils and Fats Co., Ltd.) by a Henschel mixer.
Then, the mixture was molded into a rectangular plate ~130 x 120 x 2 mm) and cut to prepare test samples~
Injection-molding conditions Cylinder temperature (C): 200/230/270/270 Injection pressure (kg/cm2): primary/secondary = 1000/~00 Cycle (seconds): primary/secondary/cooling = 5/3/25 Injecting speed (-): 2/10 Screw rotating speed (rpm): 97 Mold temperature (C): water cooled ~32 C) - - The properties of the samples were evaluated by the following methods.
Tensile test The tensile test was conducted in accordance with ASTM D-638 except that a test specimen having the shape of ASTM No. 4 was used and the tensile speed was set at 50 mm/min. The stress at yield (YS: kg/cm2), tensile strength at break (TS: kg/cm2) and elongation at break (EL: %) of the test sample was determined.
Izo impact strength (kg-cm/cm?
Measured in accordance with ASTM D256 on a notched test sample.
Olsen rigidity (kg/cm2?
Measured in accordance with ASTM D747.
Friction-abrasion test The test was conducted by using a Matsubara-type friction-abrasion tester (made by Toyo Baldwin Company) under a compression load of 3.4 kg/cm2 at a friction speed ~2~ 3 of 30 m/min. for 24 hours, and the amount of loss by abrasion and the coefficient of friction were determined.
Appearance The surface condition of a molded rectangular plate was visually observed and rated on the scale of the following four grades.
(A): No flowmark existed.
~B): Slight flowmarks were observed~
~C): Flowmarks were! observed.
~D): Flowmarks exis;ted throughout.
Delamination The end of a molded sample was ~haven by a knife, and delamination was evaluated on the scale of the following four grades.
lD): The surface was easily peeled.
tC): The surface was slightly peeled.
~B): The surface was hardly peeled.
(A): The surface was not peeled at all.
Examples 2-6 In each run, Example 1 was repeated except that the polymerization conditions were changed as indicated in Table 1, and the molecular weights of the ultrahigh-molecular-weight polyethylene and the low-molecular-weight or high-molecular-weight polyethylene and the ratio between the amounts of the ultrahigh-molecular-weight polyethylene and the low-molecular-weight or high-mol-ecular-weight polyethylene were changed. The results are shown in Table 2.
Referential Examples 1-2 Commercial ultrahigh-molecular-weight poly-ethylene tHizex MillionR240M, a ~ e-for a product of ~ Mitsui Petrochemical Industries, Co., Ltd.) was injection-molded by the same method as in Comparative Example 3 using an injection-molding machine having a screw of the three-stage compression type.
Furthermore, commercial injection-molding high-~2~4~3 5 - ~ rqden~A~
density polyethylene (Hize*~ 2208J, a ~de~ for a product of Mitsui Petrochemical Industries, Ltd.) was injection-molded by the same method as in Example 1.
The results are also shown in Table 2.
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Claims (13)
1. An injection-molding polyolefin composition characterized in that (1) it comprises an ultrahigh-molecular-weight polyolefin having an intrinsic viscosity, measured in decalin solvent at 135 °C, of 10 to 40 dl/g and a low-molecular-weight or high-molecular-weight polyolefin having an intrinsic viscosity, measured in decalin solvent at 135 °C, of less than 10 dl/g, (2) the proportion of the ultrahigh-molecular-weight polyolefin is in the range of is to 40 % by weight based on the total weight of the ultrahigh-molecular-weight polyolefin and the low-molecular-weight or high-molecular-weight polyolefin, (3) it has an intrinsic viscosity [?]c, mea-sured in decalin solvent at 135 °C, of 4.0 to 10 dl/g, and (4) it has a melting torque T of not more than 4.5 kg-cm.
2. The injection-molding polyolefin composition set forth in claim 1, wherein the ultrahigh-molecular weight polyolefin and the low-molecular-weight or high-molecular-weight polyolefin are produced by a multistep polymeriza-tion process which comprises polymerizing an olefin in at least one polymerization step to form an ultrahigh-molecular-weight polyolefin having an intrinsic viscosity of 10 to 40 dl/g and polymerizing an olefin in another polymerization step in the presence of hydrogen to form a low-molecular-weight or high-molecular-weight polyolefin having an intrinsic viscosity of less than 10 dl/g, both in the presence of a Ziegler-type catalyst formed from (A) a highly active titanium catalyst component containing magnesium, titanium and halogen as essential ingredients and (B) an organoaluminum compound catalyst component.
3. The composition set forth in claim 1 wherein the polyolefin is polyethylene.
4. The composition set forth in claim 1 wherein the ultrahigh-molecular-weight polyolefin has an intrinsic viscosity of 15 to 35 dl/g.
5. The composition set forth in claim 1 wherein the intrinsic viscosity of the low-molecular-weight or high-molecular-weight polyolefin is 0.1 to 5 dl/g.
6. The composition set forth in claim 1 wherein the intrinsic viscosity of the low-molecular-weight or high-molecular-weight polyolefin is 0.5 to 3 dl/g.
7. The composition set forth in claim l wherein the proportion of the ultrahigh-molecular-weight polyolefin is 20 to 35 % by weight based on the total weight of the ultrahigh-molecular-weight polyoelfin and the low-molecular weight or high-molecular weight polyolefin.
8. The composition set forth in claim 1 which has an intrinsic viscosity of 4 to 9 dl/g.
9. An injection-molding polyolefin composition characterized in that (1) it comprises an ultrahigh-molecular-weight polyolefin having an intrinsic viscosity, measured in decalin solvent at 135 °C, of 10 to 40 dl/g and a low-molecular-weight or high-molecular-weight polyolefin having an intrinsic viscosity, measured in decalin solvent at 135 °C, of less than 10 dl/g, (2) the proportion of the ultrahigh-molecular-weight polyolefin is in the range of 15 to 40 % by weight based on the total weight of the ultrahigh-molecular-weight polyolefin and the low-molecular-weight or high-molecular-weight polyolefin, (3) it has an intrinsic viscosity [?]c, mea-sured in decalin solvent at 135 °C, of 4.0 to 10 dl/g, (4) it has a melting torque T of not more than 4.5 kg-cm, and (5) the ultrahigh-molecular-weight polyolefin and the low-molecular-weight or high-molecular-weight polyolefin are produced by a multistep polymerization process which comprises polymerizing an olefin in at least one polymerization step to form an ultrahigh-molecular-weight polyolefin having an intrinsic viscosity of 10 to 40 dl/g and polymerizing an olefin in another polymerization step in the presence of hydrogen to form a low-molecular-weight or high-molecular-weight polyolefin having an intrinsic viscosity of less than 10 dl/g, both in the presence of a Ziegler-type catalyst formed from (A) a highly active titanium catalyst component containing magnesium, titanium and halogen as essential ingredients and (B) an organoaluminum compound catalyst component.
10. The composition as defined in any one of claims 1 to 9, which, when molded into an article by an injection molding process, has an abrasion resistance better than an article produced by the same injection molding process using only the ultrahigh-molecular-weight polyolefin.
11. The composition as defined in claim 10, which, when molded into the article, has less than 2.3 mg of an abrasion loss as measured by abrasing a rectangular plate test sample of the size 130 x 120 x 2 mm under a compression load of 3.4 kg/cm2 at a friction speed of 30 m/min. for 24 hours using a Matsuba-type friction-abrasion tester.
12. The composition set forth in claim 11, which, when molded into the article, has no more than 0.3 mg of an abrasion loss.
13. The composition set forth in claim 11 or 12, which, when molded into the article, has a tensile elongation at break (EL) of 110 to 280% as measured in accordance with ASTM D-633 except that a test specimen having a shape of ASTM No.4 is used and a tensile speed is set at 50 mm/min.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000559052A CA1294733C (en) | 1988-02-17 | 1988-02-17 | Injection-molding polyolefin composition |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000559052A CA1294733C (en) | 1988-02-17 | 1988-02-17 | Injection-molding polyolefin composition |
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| Publication Number | Publication Date |
|---|---|
| CA1294733C true CA1294733C (en) | 1992-01-21 |
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| CA000559052A Expired - Fee Related CA1294733C (en) | 1988-02-17 | 1988-02-17 | Injection-molding polyolefin composition |
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| Country | Link |
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| CA (1) | CA1294733C (en) |
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1988
- 1988-02-17 CA CA000559052A patent/CA1294733C/en not_active Expired - Fee Related
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