Polyethylene composition having high mechanical properties.

COMPOSITION OF POLYETHYLENE THAT HAS HIGH MECHANICAL PROPERTIES

DESCRIPTION OF THE INVENTION

The present invention provides a polyethylene composition suitable for preparing various types of formed articles. In particular, due to its high balance of tensile strength resistance to environmental degradation (FNCT) and impact resistance (Charpy), the present composition is particularly suitable for preparing extruded articles such as pipes, including With a large diameter.

The present invention also relates to a multi-stage polymerization process for preparing the polyethylene composition.

Therefore, the composition of the present invention provides an incomparable balance of mechanical properties and processability with respect to the polyethylene compositions known for the same use, as described in particular in US6201078 and US2004 / 0005424.

In fact, the polymers described in the documents achieve relatively low tensile strength values ​​at a relatively high density, as shown in the examples.

The problem of achieving high impact resistance

Ref. 256129 is not mentioned in US6201078.

Therefore, the present invention provides a

<td>composition of</td><td colspan="2">polyethylene</td><td colspan="2">which has the</td><td colspan="2">following</td>

<td>features:</td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>1) density</td><td>from</td><td> 0,945</td><td colspan="3">at 0.955 g / cm³determined</td><td>from</td>

<td>compliance with the</td><td>ISO</td><td>1183 a</td><td>23 ° C;</td><td></td><td></td><td></td>

<td>2) relationship</td><td>from</td><td colspan="2">MIF / MIP over</td><td>of 3 0</td><td>to 45,</td><td>in</td>

<td>particular of 31</td><td>to 45,</td><td>where</td><td>MIF is the</td><td>index</td><td>flow</td><td>from</td>

<td>melting at 190 ° C cor</td><td>i a</td><td>load</td><td>of 21.60 kg</td><td>and MIP</td><td colspan="2">is the index</td>

melt flow at 190 ° C with a load of 5 kg, both determined in accordance with ISO 1133;

3) SIC index from 1.0 to 2.5;

4) long chain branching index equal to or greater than 0.85, in particular equal to or greater than 0.9;

where the SIC index is the shear induced crystallization index, determined in accordance with the following relationship:

SIC index = (tcomienzo, SIC @ 1000 xt start, rest) / (HLMI) where t_Comienzo, sic @ 100 0 is measured in seconds and is the time required for the beginning of crystallization at a shear rate of 1000 s^_1, the start t, rest is measured in seconds and is the crystallization start time at a temperature of 125 ° C without shear, determined in isothermal mode by differential scanning calorimetry (DSC); HLMI is the melt flow rate determined at 190 ° C with a load of 21.6 kg, in accordance with ISO 1133.

The term "polyethylene composition" is intended to cover, as alternatives, the simple ethylene polymer and the ethylene polymer composition, in particular a composition of two or more components of ethylene polymer, preferably with different molecular weights, the composition is also called bimodal polymer or multimodal in the relevant technique.

Typically the polyethylene composition of the present invention comprises or consists of one or more ethylene copolymers.

All features defined herein, which comprise features 1) to 4) defined above, refer to the ethylene polymer or polymeric ethylene composition. The addition of other components, such as additives normally used in the art, can modify one or more of the characteristics.

In particular, in the presence of carbon black the density can increase from 0.953 to 0.963 g / cm³.

The SIC index may also be affected.

The MIF / MIP ratio provides a rheological measure of molecular weight distribution.

Another measure of molecular weight distribution is provided by the ratio Mw / Mn, where Mw is the average molar mass weight and Mn is the average number of molar mass, both measured by GPC (gel permeation chromatography) as explained In the examples.

Preferred values ​​of Mw / Mn for the polyethylene composition of the present invention range from 25 to 45.

In addition, the polyethylene composition of the present invention preferably has at least one of the following additional characteristics.

Mw equal to or greater than 250000 g / mol, more preferably equal to or greater than 280000 g / mol, in particular equal to or greater than 300000 g / mol;

- MIP: 0.05-1 g / 10 min., In particular 0.1-0.5 g / 10 min;

- MIF: 1-15 g / 10 min;

- Content of comonomers from 1% to 3% by weight, in particular from 1 to 2.5% by weight, with respect to the total weight of the composition.

The comonomer or comonomers present in ethylene copolymers are generally selected from olefins having the formula CH2 = CHR where R is an alkyl, linear or branched radical having 1 to 10 carbon atoms.

Specific examples are propylene, butene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1 and decene-1. A particularly preferred comonomer is hexene-1.

In particular, in a preferred embodiment, the present composition comprises:

A) from 40 to 60% by weight of a homopolymer or copolymer of ethylene (homopolymer is preferred) with a density equal to or greater than 0.960 g / cm³ and an MIE melt flow rate at (190 ° C / 2.16 kg, in accordance with ISO 1133) of 50 to 200 g / 10 min., preferably 50 to 95 g / 10 min;

B) from 40 to 60% by weight of an ethylene copolymer having an MIE value less than the MIE value of A), preferably less than 0.5 g / 10 min.

The amounts in percentages above are given with respect to the total weight of A) + B).

The total amount of comonomer in B) is preferably from 1 to 4% by weight, based on the total weight of B).

As stated above, the present polyethylene composition can be used advantageously in the preparation of extruded articles, in particular pipes, thanks to its valuable mechanical properties.

In fact, it is preferably characterized by the following properties.

- FNCT equal to or greater than 100 hours, in particular equal to or greater than 150 hours at 5 MPa, 90 ° C;

Charpy aFM (0 ° C) equal to or greater than 5 kJ / m², in particular equal to or greater than 9.5 kJ / m²;

Details of the test methods are provided in the examples.

In addition, the polyethylene composition of the present invention can be melt processed at surprisingly high shear rate values, even without experiencing pressure fluctuations and flow instabilities.

While in principle there is no known necessary limitation on the type of polymerization processes and catalysts to be used, it was found that the polyethylene composition of the present invention can be prepared by a gas phase polymerization process in the presence of a catalyst Ziegler-Natta.

The Ziegler-Natta catalyst comprises the reaction product of an organometallic compound of group 1, 2 or 13 of the periodic table of elements with a transition metal compound of groups 4 to 10 of the periodic table of elements (new annotation). In particular, the transition metal compound can be selected from the compounds of Ti, V, Zr, Cr and Hf and is preferably supported on MgCl₂.

Particularly preferred catalysts comprise the reaction product of the organometallic compound of group 1, 2 or 13 of the periodic table of elements, with a solid catalyst component comprising a Ti compound and an electron donor compound (ED) supported on

MgCl₂.

Preferred organometallic compounds are organ-Al compounds.

Accordingly, in a preferred embodiment, the polyethylene composition of the present invention can be obtained by using a Ziegler-Natta polymerization catalyst, more preferably, a MgCl-supported ZieglerNatta catalyst₂, even more preferably a Ziegler-Natta catalyst comprising the reaction product of:

a) a solid catalyst component comprising a Ti compound and an electron donor compound ED supported on MgCl₂;

b) an organ-Al compound; and optionally

c) an ED external electron donor compound_ext.

Preferably in component a) the ED / Ti molar ratio ranges from 1.5 to 3.5 and the Mg / Ti molar ratio is greater than 5.5, in particular from 6 to 80.

Suitable titanium compounds include tetrahalides or compounds of formula TiX_n (OR¹) 4-n, where 0 &lt;n &lt;3, X is halogen, preferably chlorine and R¹ It is a Ci-Cio hydrocarbon group. Titanium tetrachloride is the preferred compound.

The ED compound is generally selected from alcohol, ketones, amines, amides, nitriles, alkoxysilanes, aliphatic ethers and esters of aliphatic carboxylic acids.

Preferably the compound ED is selected from amides, esters and alkoxysilanes.

Excellent results have been obtained with the use of esters which are therefore particularly preferred as the ED compound. Specific examples of esters are alkyl esters of C1-C20 aliphatic carboxylic acids and in particular C1-C8 alkyl esters of aliphatic monocarboxylic acids such as ethyl acetate, methylformate, ethylformiate, methyl acetate, propylacetate, i-propylacetate, n-butylacetate, i- butylacetate In addition, aliphatic ethers and particularly C2-C20 aliphatic ethers, such as tetrahydrofuran (THF) or dioxane, are also preferred.

In the solid catalyst component MgCl₂ it is the basic support, even if a smaller amount of additional carriers can be used. MgCl₂ it can be used as such or obtained from Mg compounds used as precursors that can be transformed into MgCl₂ by reaction with halogenated compounds. The use of MgCl is particularly preferred.₂ in the active form that is widely known in the patent literature as support for Ziegler-Natta catalysts. USP patents 4,298,718 and USP 4,495,338 were the first to describe the use of these compounds in Ziegler-Natta catalysts. From these patents it is known that magnesium dihalides in the active form used as support and co-support in catalyst components for the polymerization of olefins are characterized by X-ray spectrum in which the most intense diffraction line that appears in the ASTM card reference the spectrum of the non-active halide decreases its intensity and widens. In the X-ray spectrum of the actively preferred magnesium dihalides, the most intense line reduces its intensity and is replaced by a halo whose maximum intensity moves towards the lower angles with respect to the most intense line.

Particularly suitable for the preparation of the polyethylene composition of the present invention are catalysts where the solid catalyst component a) is first obtained by contacting the titanium compound with the MgCl₂, or a precursor Mg compound, optionally in the presence of an inert medium, whereby an intermediate product a ') containing a titanium compound supported on MgCl is prepared₂, whose intermediate product a ') then comes into contact with the ED compound that is added to the reaction mixture alone or in a mixture with the other compounds where it represents the main component, optionally in the presence of an inert medium.

With the term main component it is intended that the compound ED be the main component in terms of molar amount, with respect to the other possible compounds except the inert solvents or diluents used to handle the contact mixture. The treated ED product can then be washed with the appropriate solvents to recover the final product. If necessary, treatment with the desired ED compound may be repeated one or more times.

As mentioned above, the MgC12 precursor can be used as the essential starting Mg compound. This can be selected, for example, from the Mg compound of the formula MgR'2 where the R 'groups can be independently optionally substituted C1-C20 hydrocarbon groups, OR groups, OCOR groups, chlorine, where R is an optionally substituted C1-C20 hydrocarbon group , with the obvious condition that the R 'groups are not simultaneously chlorine. Lewis adducts between MgCl are also suitable as precursors₂ and suitable Lewis bases. A particular and preferred class is constituted by the MgC12 adducts (R¹'0H)_m where the R groups are C1-C20 hydrocarbon groups, preferably C1-C10 alkyl groups and m is from 0.1 to 6, preferably from 0.5 to 3 and more preferably from 0.5 to 2. Adducts of this type can be obtained generally by mixing alcohol and MgC12 in the presence of an inert hydrocarbon immiscible with the adduct, under stirring conditions at the melting temperature of the adduct (100130 ° C). Then, the emulsion is rapidly inactivated, which causes solidification of the adduct in the form of spherical particles. Representative methods for the preparation of these spherical adducts are reported, for example, in USP 4,469,648, USP 4,399,054 and W098 / 44009. Another useful method for spherulization is spray cooling described, for example, in USP 5,100,849 and 4,829,034.

The adducts of MgCla · (EtOH) are particularly interesting _m in which m is 0.15 to 1.7 obtained by subjecting the adducts with a higher alcohol content to a thermal de-alcoholization process carried out in nitrogen flow at temperatures between 50 and 150 ° C until The alcohol content is reduced to the previous value. Such a process is described in EP 395083.

Desalcoholization can also be carried out by

<td>put on</td><td>adduct</td><td>in</td><td>Contact</td><td>with compounds</td><td>able</td><td>from</td>

<td>react</td><td>with the</td><td colspan="3">alcohol groups</td><td></td><td></td>

<td colspan="2">Usually</td><td colspan="2">these adducts</td><td>desalcoholizados</td><td>too</td><td>I know</td>

<td colspan="2">characterized by</td><td>a</td><td>porosity</td><td>(measured by the</td><td>method</td><td>from</td>

<td>mercury)</td><td>because</td><td>the</td><td>pores with</td><td>radios up to</td><td>0.1 gm</td><td>what</td>

<td>vary from</td><td>0.15 a</td><td> 2,5</td><td colspan="2">cm³/ g preferably of</td><td>0.25 a</td><td> 1,5</td>

<td>cm³/ g.</td><td></td><td></td><td></td><td></td><td></td><td></td>

It is preferred that the desalcoholization reaction be carried out simultaneously with the reaction step that involves the use of a titanium compound. Therefore, these adducts react with the TiX compound_n(0R¹) 4-n (or possibly mixtures thereof) mentioned above which is preferably titanium tetrachloride. The reaction with the Ti compound can be carried out by suspending the adduct in TiCl₄ (usually cold). The mixture is heated at temperatures ranging from 80 to 130 ° C and is maintained at this temperature for 0.5 to 2 hours. Treatment with the titanium compound can be carried out one or more times. Preferably repeated twice. It can also be carried out in the presence of an electron donor compound such as those mentioned above. At the end of this stage the solid is recovered by separating the suspension through conventional methods (such as sedimentation and removal of the liquid, filtration, centrifugation) and can be subjected to solvent washes. While washings are typically carried out with inert hydrocarbon liquids, it is also possible to use more polar solvents (for example, having a higher dielectric constant) such as halogenated hydrocarbons.

As mentioned above, the intermediate product is then contacted with the ED compound under conditions capable of fixing in the solid an effective amount of donor. Due to the high versatility of this method, the amount of donor used can vary widely. By way of example, it can be used in a molar ratio with respect to the Ti content in the intermediate product ranging from 0.5 to 20 and preferably from 1 to 10. While not strictly necessary, contact is typically carried out in a liquid medium such as a liquid hydrocarbon. The temperature at which the contact takes place may vary depending on the nature of the reagents. It is generally in the range of -10 ° to 150 ° C and preferably 0^or at 120 ° C. It is clear that temperatures that cause the decomposition or degradation of any specific reagents should be avoided even if they fall within the generally adequate range. Also, the treatment time may vary depending on other conditions such as the nature of the reagents, the temperature, the concentration, etc. As a general indication, this contact stage can last from 10 minutes to 10 hours, more frequently from 0.5 to 5 hours. If desired, to increase the final donor content, this step may be repeated one or more times. At the end of this stage the solid is recovered by separating the suspension through conventional methods (such as sedimentation and removal of the liquid, filtration, centrifugation) and can be subjected to solvent washes. While washing is typically carried out with inert hydrocarbon liquids, it is also possible to use more polar solvents (for example, having a higher dielectric constant) such as halogenated or oxygenated hydrocarbons.

As mentioned above, the solid catalyst component is converted into catalysts for the polymerization of definas by reaction, in accordance with known methods, with an organometallic component of group 1, 2 or 13 of the periodic table of elements, in particular with an alkyl-Al compound.

The alkyl-Al compound is preferably selected from the trialkyl aluminum compounds such as, for example, triethylaluminum, triisobutylaluminum, tri-n-butyl aluminum, tri-n-hexyl aluminum , tri-n-octylamino . It is also possible to use alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides such as AlEtzCl and AlaEtaCls optionally in admixture with the trialkylaluminum compounds.

The external electron donor compound ED_formert optionally used to prepare the Ziegler-Natta catalysts may be the same or different from the ED used in the solid catalyst component a). Preferably it is selected from the group consisting of ethers, esters, amines, ketones, nitriles, silanes and mixtures thereof. In particular, C2-C20 aliphatic ethers and in particular cyclic ethers, which preferably have 3 to 5 carbon atoms such as tetrahydrofuran and dioxane, can be advantageously selected.

Specific examples of Ziegler catalysts

Natta described above and the methods for its preparation are provided in W02004106388. However, the prior polymerization described therein of the solid catalyst component containing the Ti compound and the electron donor compound ED (solid catalyst component a)) is not comprised in the preferred embodiments in accordance with the present invention.

In particular, the polyethylene composition of the present invention can be obtained by a process in which all polymerization steps are carried out in the presence of the catalyst.

In fact, it was found that by using the polymerization catalyst described above, the polyethylene composition of the present invention can be prepared in a process comprising the following steps, in any order:

a) polymerizing ethylene, optionally together with one or more comonomers, in a gas phase reactor in the presence of hydrogen;

b) copolymerizing ethylene with one or more comonomers in another gas phase reactor in the presence of a smaller amount of hydrogen than in step a);

where in at least one of the gas phase reactors the expanding polymer particles flow upward through the first polymerization zone (riser tube) under fluidization or rapid transport conditions, leave the riser tube and enter the second polymerization zone (downpipe) through which they flow down through the action of gravity, leave the downcomer and re-enter the riser, whereby a circulation of polymer is established between the two polymerization zones.

In the first polymerization zone (riser tube), the fast fluidization conditions are established by supplying a gaseous mixture comprising one or more defined (ethylene and comonomers) at a speed greater than the transport speed of the polymer particles . The speed of the gas mixture is preferably between 0.5 and 15 m / s, more preferably between 0.8 and 5 m / s. The terms transport speed and rapid fluidization conditions are well known in the art; for a definition of these, see, for example, D. Geldart, Gas Fluidisation Technology, page 155 et seq., J. Wiley &amp; Sons Ltd., 1986.

In the second polymerization zone (downpipe), the polymer particles flow through the action of gravity in a densified form, such that the density values ​​of the solid (polymer mass per reactor volume) are reached, which they approach the apparent density of the polymer.

In another way, the polymer flows vertically down through the downcomer in a plug flow (compact flow mode), such that only small amounts of gas are entrained between the polymer particles.

The process allows to obtain from step a) an ethylene polymer with a molecular weight less than the ethylene copolymer obtained from step b).

Preferably, the polymerization of ethylene to produce a relatively low molecular weight ethylene polymer (step a) is performed upstream of the copolymerization of ethylene with a comonomer to produce a relatively high molecular weight ethylene copolymer (step b). For this purpose, in step a) a gas mixture comprising ethylene, hydrogen and an inert gas is introduced into a first gas phase reactor, preferably a fluid bed gas phase reactor. The polymerization is carried out in the presence of the Ziegler-Natta catalyst described above. Preferably, no comonomer is introduced into the first gas phase reactor and a highly crystalline ethylene homopolymer is obtained in step a). However, a minimum amount of comonomer can be introduced with the proviso that the degree of copolymerization in step a) is limited such that the density of the ethylene polymer obtained in step a) is not less than 0.960 g / cm³.

Hydrogen is introduced in an amount that depends on the specific catalyst used and, in any case, suitable for obtaining in step a) an ethylene polymer with an MIE melt flow rate of 50 to 200 g / 10 min. To obtain the above MIE range, in step a) the hydrogen / ethylene molar ratio is indicatively 1 to 3, the amount of ethylene monomer is 5 to 30% by volume, preferably a 5 to 20% by volume, based on the total volume of gas present in the polymerization reactor. The remaining portion of the feed mixture is represented by inert gases and one or more comonomers, if any. The inert gases that are necessary to dissipate the heat generated by the polymerization reaction are conveniently selected from nitrogen or saturated hydrocarbons, where propane is most preferred.

The operating temperature in the reactor of step a) is selected between 50 and 120 ° C, preferably between 65 and 100 ° C, while the operating pressure is between 0.5 and 10 MPa, preferably between 2.0 and 3.5 MPa

In a preferred embodiment, the ethylene polymer obtained in step a) represents from 40 to 60% by weight of the total ethylene polymer produced in the overall process, that is, in the first and second reactors connected in series .

The ethylene polymer from stage a) and the trapped gas are then subjected to a solid / gas separation stage to prevent the gas mixture from the first polymerization reactor from entering the stage b) reactor (second gas phase polymerization reactor). The gas mixture can be recycled back into the first polymerization reactor, while the separated ethylene polymer is introduced into the reactor of step b). A suitable point for introducing the polymer into the second reactor is in the connecting part between the drop tube and the rise tube, where the solid concentration is particularly low, such that the flow conditions are not adversely affected. .

The operating temperature in step b) is in the range of 65 to 95 ° C and the pressure is in the range of 1.5 to 4.0 MPa. The second gas phase reactor is intended to produce a relatively high molecular weight ethylene copolymer by copolymerizing ethylene with one or more comonomers. In addition, to extend the molecular weight distribution of the final ethylene polymer, the reactor in step b) can be conveniently operated by establishing different conditions of monomers and hydrogen concentration within the riser tube and the downstream tube .

For this purpose, in step b) it is possible to prevent the gaseous mixture containing the polymer particles and coming from the riser from entering all or part of the drop tube, in order to obtain two different gas composition zones. This can be achieved by introducing a gaseous and / or liquid mixture into the downcomer through a line placed at a suitable point of the downcomer, preferably at the top of it. The gaseous and / or liquid mixture must have a suitable composition, different from that of the gaseous mixture present in the riser. The flow of the gaseous and / or liquid mixture can be regulated in such a way that an upward flow of gas is generated that runs in the opposite direction to the flow of the polymer particles, particularly in its upper part, which acts as a barrier to the mixing. gas trapped between the polymer particles that come from the riser. In particular, it is advantageous to introduce a mixture with a low hydrogen content to produce the higher molecular weight polymer fraction in the downcomer. One or more comonomers can be introduced into the drop tube of step b), optionally together with ethylene, propane or other inert gases.

The hydrogen / ethylene molar ratio in the drop tube of step b) is between 0.005 and 0.2, the ethylene concentration is between 1 and 20%, preferably between 3 and 10% by volume , the comonomer concentration is between 0.2 and 1.5% by volume, based on the total volume of gas present in the downcomer. The rest is propane or similar inert gases. Since there is a very low hydrogen molar concentration in the drop tube, it is possible to join a relatively high amount of comonomer with the high molecular weight polyethylene fraction when carrying out the process of the present invention.

The polymer particles that come from the downcomer are reintroduced into the uptake tube of step b).

Since the polymer particles continue to react and no more comonomer is introduced into the riser tube, the concentration of the comonomer decreases at a range of 0.1 to 1% by volume, based on the total volume of gas present in the tube going up. In practice, the comonomer content is controlled to obtain the desired density of final polyethylene. In the riser tube of step b) the hydrogen / ethylene molar ratio is in the range of 0.02 to 0.2, the concentration of ethylene is between 5 and 15% by volume based on the Total volume of gas present in the riser. The rest is propane or other inert gases.

More details about the polymerization process described above are provided in WO9412568.

The following examples are provided to illustrate, without limitation, the present invention.

Unless stated otherwise, the following test methods are used to determine the properties reported in the detailed description and in the examples.

Density

Determined in accordance with ISO 1183 at 23 ° C.

Determination of molecular weight distribution

The determination of the molar mass distributions and the Mn, Mw and Mw / Mn averages derived from these was carried out by high temperature gel permeation chromatography using the method described in ISO 16014-1, 2, -4 , from 2003. The specifications in accordance with the aforementioned ISO standards are: Solvent 1,2,4trichlorobenzene (TCB), device temperature and 135 ° C solutions and as a concentration detector an IR-4 infrared detector from PolymerChar (Valencia, Paterna 46980, Spain), suitable for use with TCB. A WATERS Alliance 2000 equipped with the following SHODEX UT-G pre-column and SHODEX UT 806 M (3x) and SHODEX UT 807 (Showa Denko Europe GmbH, Konrad-Zuse-Platz 4, 81829 Muenchen,

Germany) connected in series. The solvent was distilled under vacuum under nitrogen and stabilized with 0.025% by weight of 2,6-di-tert-butyl-4-methylphenol. The flow rate used was 1 ml / min. , the injection was 500μ1 and the polymer concentration was in the range of

Or, 01% &lt;conc. &lt;0.05% w / w The molecular weight calibration was established through the use of monodispersed polystyrene (PS) standards from Polymer Laboratories (currently Agilent Technologies, Herrenberger Str. 130, 71034 Boeblingen, Germany)) in the range of 580g / mol to 11600000g / mol and additionally with hexadecane. The calibration curve below was adapted to polyethylene (PE) by means of the universal calibration method (Benoit H., Rempp

P. and Grubisic Z., &amp; in J. Polymer Sci., Phys. Ed., 5, 753 (1967)). The Mark-Houwing parameters used here were for PS: k_$= 0.000121 dl / g, a_Ps = 0.706 and for PE k_PE= 0.000406 dl / g, oc_Pe = 0.725, valid in TCB at 135 ° C. Data recording, calibration and calculation were carried out with the use of NTGPC_Control_V6.02.03 and NTGPC_V6.4.24 (HS GmbH, HauptstraBe 36, D-55437 Ober-Hilbersheim, Germany) respectively.

Shear-induced crystallization test

This method is used to determine the start time of the shear-induced crystallization (SIC) of the polymer, t_Comienzo, sic. The samples are pressed by fusion at 210 ° C, 4 min., Under 2 00 bar in a laboratory press on Imm plates of thickness. The disk samples are cut with a diameter of 25mm. The samples are inserted into the oscillating plate shear rheometer. A Physica MCR 301 rotating rheometer from AntonPaar was used.

Then, the sample was melted within the test geometry at 190 ° C for 4 minutes, cooled with ~ 10K / min. at the test temperature, T = 125 ° C and it was warmed for 5 minutes. Consequently, a continuous shear was applied at a constant shear rate and the shear viscosity was controlled as a function of time. The experiment was repeated applying each time a different shear rate that varied from 0.05 to 0.5 s^_1. The start time for SIC, t_Comienzo, sic, was taken at the point where viscosity had increased by 50% of its steady state value q @ 125 ° C. The steady state value is the average continuous shear fusion viscosity measured at the specific temperature.

The logt graph_Comienzo, sic against log shear rate provides a linear function (of type y = Ax + B) that is extrapolated at a shear rate of 1000 s^_1 (relevant to the process) to determine the value of t_Comienzosic @ 1000.

The SIC index below is calculated in accordance with the following relationship:

SIC index = (t_Comienzo, SIC @ 1000 X t start, rest) / (HLMI)

The tcomienzo, rest (in seconds) is the beginning of crystallization at a temperature of 125 ° C under resting conditions, that is, without shear, measured in isothermal mode in a differential scanning calorimetry apparatus, DSC, as explained then.

HLMI is the melt flow rate (g / lOmin.) Measured at T = 190 ° C with 21.6 kg load, in accordance with ISO 1133.

The same protocol is described in the following documents.

- I. Vittorias, Correlation among structure, processing and product properties, Würzburger Tage 2010, Wolfgang Kunze TA Instrumente, Germany.

- Wo DL, Tanner RI (2010), The impact of blue organic and inorganic pigments on the crystallization and rheological properties of isotactic polypropylene, Rheol. Minutes 49, 75.

Derakhshandeh M., Hatzikiriakos SG, Flow-induced crystallization of high-density polyethylene: the effects of shear and uniaxial extension, Rheol. Minutes, 51, 315-327, 2012.

Isothermal DSC

The start, resting t the start time when no deformation is applied at 125 ° C, is determined by the method of iso-DSC (Isothermal differential scanning calorimetry). It is measured at 125 ° C on a TA Instruments Q2000 DSC device. The determination of tcomienzo, rest is done by using the commercially available software TA Universal Analysis

2000 Sample preparation and installation follow DIN EN ISO 11357-1: 2009 and ISO 11357-3: 1999.

melt flow rate

Determined in accordance with ISO 1133 at 190 ° C with the specified load.

long chain branching index (LCB)

The LCB index corresponds to the branching factor g ', measured for a molecular weight of 10⁶ g / mol The branching factor g ', which allows to determine long chain branching at a high Mw, was measured by gel permeation chromatography (GPC) coupled with laser light scattering (MALLS) as described below. The parameter g 'is the ratio of the average square radius of rotation of the linear polymer having the same molecular weight. Linear molecules show a g 'of 1, while values ​​less than 1 indicate the presence of LCB. The values ​​of g 'as a function of molar weight, M, were calculated from the equation:

g¹ (M) = &lt;Rg²&gt; sample, M / &lt;Rg²&gt; ref. linear, M where &lt;Rg²&gt;, M is the root of the mean square radius of rotation for the molar weight fraction M.

The turning radius for each eluted fraction of GPC (as described above but with a flow rate of 0.6 ml / min. And a column packed with 30pm particles) was measured by light scattering analysis at different angles . Therefore, from this configuration of MALLS it is possible to determine the molar weight M and &lt;Rg²Sample, and define a g 'to a measured M = 10⁶ g / mol &lt;Rg²&gt; ref. linear, m is calculated by the relationship established between the turning radius and the molecular weight for a linear polymer in solution (Zimm and Stockmayer WH 1949)) and is confirmed by measuring a linear PE reference with the same apparatus and methodology described.

The same protocol is described in the following documents.

Zimm BH, Stockmayer WH (1949) The dimensions of chain molecules containing branches and rings. J Chem Phys 17

Rubinstein M., Colby RH. (2003), Polymer Physics, Oxford University Press.

Comonomer Content

The comonomer content is determined by IR in accordance with ASTM D 6248 98, using a Bruker Tensor 27 FT-IR spectrometer, calibrated with a chemometric model to determine the ethyl or butyl side chains in PE for butene or hexane as comonomer, respectively.

Tensile strength resistance to environmental degradation for creep test (FNCT)

The tensile strength resistance to environmental degradation of polymer samples is determined in accordance with the international standard ISO 16770 (FNCT) in aqueous surfactant solution. A 10 mm thick sheet molded by compression was prepared from the polymer sample. The bars with a square cross section (10x10x100 mm) are cut by using a razor blade on all four sides perpendicular to the tension direction. A notching device described in M. Fleissner in Kunststoffe 77 (1987), page 45 is used for the notch marked with a depth of 1.6 mm. The applied load is calculated from the tensile force divided by the initial ligament area. The ligament area is the remaining area = total cross-sectional area of ​​the sample minus the area of ​​the notch. For the FNCT sample: 10x10 mm² - 4 times of trapezoidal notch area = 46.24 mm² (the remaining cross section for the crack interruption / propagation process). The test sample is loaded with a standard condition suggested by ISO 16770 with a constant load of 5 MPa at 90 ° C in an aqueous solution of ARKOPAL N100 at 2% by weight and anionic surfactant GENAPOL Pasta at 5%. The time until the test sample is broken is detected.

Charpy aFM

The fracture resistance is determined using an internal method on test bars measuring 10 x 10 x 80 mm that were cut from a compression molded sheet with a thickness of 10 mm. Six of these test bars are drilled in the center by using a razor blade in the aforementioned drilling device for FNCT. The depth of the notch is 1.6 mm. The measurement is carried out substantially in accordance with the Charpy measurement method in accordance with ISO 179-1, with modified test samples and a modified impact geometry (distance between the supports). All test samples are conditioned at the measurement temperature of 0 ° C for a period of 2 to 3 hours. The test sample below is placed without delay on the support of a pendulum impact tester in accordance with ISO 179-1. The distance between the supports is 60 mm. The fall of the hammer 2 J is triggered with a fall angle set at 160 °, a pendulum length of 225mm and an impact speed of 2.93 m / s. The fracture resistance value is expressed in kJ / m² and is given by the ratio of the impact energy consumed and the initial transverse area in the notch, aFM. Here only values ​​for a complete fracture and hinge fracture can be used as the basis for a common meaning (see suggestion for ISO 179-1).

Examples 1 to 4 and comparative example 1

Process settings

In the example, the process of the invention was carried out under continuous conditions in a plant comprising two gas phase reactors connected in series as shown in Figure 1.

Comparative example 1 was carried out in the same plant also under continuous conditions.

Example 1

The solid catalyst component was prepared as described in example 13 of W02004106388. The molar ratio of AcOEt / Ti was 8.

Polymerization

7 g / h of the solid catalyst component prepared as described above was introduced, with the use of 5 kg / h of liquid propane, in a prior contact apparatus, in which a mixture of triisobutylaluminum (ΤΙΒΆ) was also administered and diethyl aluminum chloride (DEAC) as well as tetrahydrofuran (THF). The weight ratio between TIBA and DEAC was 7: 1. The weight ratio between alkyl aluminum and the solid catalyst component was 10: 1. The weight ratio between alkyl aluminum and THF was 70. The previous contact step was carried out with stirring at 50 ° C with a total residence time of 70 minutes.

The catalyst enters the first gas phase polymerization reactor of Figure 1 via line 10. In the first reactor, ethylene was polymerized with the use of H2 as a molecular weight regulator in the presence of propane as an inert diluent. . 35 kg / h of ethylene and 62 g / h of hydrogen were introduced into the first reactor via line 9. No comonomer was introduced into the first reactor.

The polymerization was carried out at a temperature of 7 5 ° C and a pressure of 2.5 MPa. The polymer obtained in the first reactor was discharged discontinuously by means of line 11, separated from the gas in the gas / solid separator 12 and reintroduced into the second gas phase reactor by means of line 14.

The polymer produced in the first reactor had an MIE melt index of approximately 90 g / 10 min. and a density of 0.968 kg / dm³.

The second reactor was operated under polymerization conditions of approximately 80 ° C and a pressure of

2.5 MPa 16 kg / h of ethylene and 1.2 kg / h of 1-hexene were introduced into the downpipe 33 of the second reactor via line 46. 5 kg / h of propane, 17.5 kg / h of ethylene and 1.0 g / h of hydrogen were introduced via line 45 into the recycling system.

To extend the molecular weight distribution of the final ethylene polymer, the second reactor was operated by establishing different conditions of monomers and hydrogen concentration within the riser 32 and the downstream tube 33. This is achieved by introducing by means of of line 52, 150 kg / h of liquid stream (liquid barrier) at the top of the downpipe 33. The liquid stream has a different composition than the gas mixture present in the riser tube. The different concentrations of monomers and hydrogen within the riser tube, the downstream tube of the second reactor and the liquid barrier composition are indicated in Table 1. The liquid stream of line 52 comes from the condensation stage in the condenser 49, under operating conditions of 60 ° C and 2.5 MPa, where a part of the recycle stream is partially cooled and condensed. As shown in the figure, a separation vessel and a pump are placed in order downstream of the condenser 49. The final polymer is

<td>discharge</td><td>so</td><td>gave</td><td colspan="2">continued through</td><td>from</td><td>the line</td><td> 54 .</td>

<td>The</td><td>process</td><td>from</td><td>polymerization</td><td>in</td><td>the</td><td>second</td><td>reactor</td>

<td>produced</td><td colspan="2">fractions</td><td>polyethylene</td><td>from</td><td>a</td><td colspan="2">molecular weight</td>

relatively high Table 1 specifies the properties of the final product. It can be seen that the melt index of the final product decreases compared to the ethylene resin produced in the first reactor, which shows the formation of high molecular weight fractions in the second reactor.

The first reactor produced about 53% by weight (% by weight divided) of the total amount of the final polyethylene resin produced by the first and second reactor. At the same time, the polymer obtained has a relatively wide molecular weight distribution as seen by an MIF / MIP ratio equal to 33.

Example 2

The process of the invention was carried out with the same configuration and the same polymerization catalyst as in Example 1. Also, the process conditions and consequently the properties of the polymer obtained from the first reactor were the same.

The second reactor was operated under polymerization conditions of approximately 80 ° C and a pressure of

2.5 MPa 16 kg / h of ethylene and 1.5 kg / h of 1-hexene were introduced into the drop tube of the second reactor via line 46. 5 kg / h of propane, 20.0 kg / h of ethylene and 0.5 g / h of hydrogen was introduced via line 45 into the recycling system.

To extend the molecular weight distribution of the final ethylene polymer, the second reactor was operated by establishing different conditions of monomers and hydrogen concentration within the riser 32 and the downstream tube 33. Again 150 kg / h barrier Liquid were introduced via line 52. The gas compositions of the riser tube, the downstream tube and the liquid barrier are indicated in Table 1. The liquid stream of line 52 comes from the condensation stage in condenser 49, under operating conditions of 57 ° C and 2.5 MPa, where a part of the recycle stream is cooled and partially condensed.

The first reactor produced about 50.7% by weight (% by weight divided) of the total amount of the final polyethylene resin produced by the first and second reactor. At the same time, the polymer obtained has a relatively wide molecular weight distribution as seen by a ratio of MIF / MIP equal to 34.

Example 3

The process of the invention was carried out with the same configuration and the same polymerization catalyst as in Example 1. Also, the process conditions and consequently the properties of the polymer

<td>obtained</td><td>of the</td><td>first</td><td>reactor were the</td><td>same.</td><td></td>

<td>The</td><td colspan="2">second</td><td>reactor was operated</td><td>in conditions</td><td>from</td>

<td colspan="3">polymerization of.</td><td>about 80</td><td>° C and a pressure</td><td>from</td>

<td>2.5 MPa</td><td> 18</td><td>kg / h</td><td>of ethylene and 1.6</td><td>kg / h of 1-hexene</td><td>I know</td>

<td colspan="2">introduced eron</td><td>in the</td><td>down tube</td><td>second reactor</td><td>by</td>

<td>source of</td><td>the</td><td>line</td><td colspan="2">46. ​​5 kg / h of propane, 16.0 kg / h</td><td>from</td>

ethylene and 1.7 g / h of hydrogen were introduced via line 45 into the recycling system.

To extend the molecular weight distribution of the final ethylene polymer, the second reactor was operated by establishing different conditions of monomers and hydrogen concentration within the riser 32 and the downstream tube 33. 300 kg / h of liquid barrier they were introduced via line 52. The gas compositions of the riser, the downstream tube and the liquid barrier are indicated in Table 1. The liquid stream of line 52 comes from the condensation stage in the condenser 49, under operating conditions of 60 ° C and 2.5 MPa, where a part of the recycle stream is partially cooled and condensed.

The first reactor produced about 53.8% by weight (% by weight divided) of the total amount of the final polyethylene resin produced by the first and second reactor. At the same time, the polymer obtained has a relatively wide molecular weight distribution as seen by a ratio of MIF / MIP equal to 34.

Example 4

The process of the invention was carried out with the same configuration and the same polymerization catalyst as in Example 1. Also, the process conditions and consequently the properties of the polymer obtained from the first reactor were the same.

The second reactor was operated under polymerization conditions of approximately 80 ° C and a pressure of

2.5 MPa 20 kg / h of ethylene and 1.35 kg / h of 1-hexene were introduced into the downstream tube of the second reactor via line 46. 5 kg / h of propane, 31.0 kg / h of ethylene and 0.7 g / h of hydrogen were introduced via line 45 into the recycling system.

To extend the molecular weight distribution of the final ethylene polymer, the second reactor was operated by establishing different conditions of monomers and hydrogen concentration within the riser 32 and the downstream tube 33. 150 kg / h of liquid barrier they were introduced via line 52. The gas compositions of the riser, the downstream tube and the liquid barrier are indicated in Table 1. The liquid stream of line 52 comes from the condensation stage in the condenser 49, under operating conditions of 56 ° C and 2.5 MPa, where a part of the recycle stream is cooled and partially condensed.

The first reactor produced about 5 0.3% by weight (% by weight divided) of the total amount of the final polyethylene resin produced by the first and second reactor. At the same time, the polymer obtained has a relatively wide molecular weight distribution as seen by an MIF / MIP ratio equal to 33.

Comparative Example 1

The polymerization was carried out by using the same configuration as in Example 1, but the polymerization catalyst was the same as that used in Example 6 of W02005019280.

8 g / h of the solid catalyst component prepared as described above was introduced, with the use of 5 kg / h of liquid propane, in a prior contact apparatus, in which triethylaluminum (TEA) was also administered as well as tetrahydrofuran ( THF). The weight ratio between alkyl aluminum and the solid catalyst component was 5: 1. The weight ratio between alkyl aluminum and THF was 44. The previous contact stage was carried out with stirring at 50 ° C with a total residence time of 70 minutes.

The catalyst enters the first gas phase polymerization reactor of Figure 1 via line 10. In the first reactor ethylene was polymerized with the use of H₂ as a molecular weight regulator in the presence of propane as an inert diluent. 40 kg / h of ethylene and 75 g / h of hydrogen were introduced into the first reactor via line 9. No comonomer was introduced into the first reactor.

The polymerization was carried out at a temperature of 80 ° C and a pressure of 2.4 MPa. The polymer obtained in the first reactor was discharged discontinuously by means of line 11, separated from the gas in the gas / solid separator 12 and reintroduced into the second gas phase reactor by means of line 14.

The polymer produced in the first reactor had an MIE melt index of approximately 100 g / 10 min. and a density of 0.968 kg / dm³.

The second reactor was operated under polymerization conditions of approximately 80 ° C and a pressure of 2.1 MPa. 12 kg / h of ethylene and 1.5 kg / h of 1-hexene were introduced into the downpipe 33 of the second reactor via line 46. 5 kg / h of propane, 26.5 kg / h of ethylene and 1.2 g / h of hydrogen were introduced via line 45 into the recycling system.

To extend the molecular weight distribution of the final ethylene polymer, the second reactor was operated by establishing different conditions of monomers and hydrogen concentration within the riser 32 and the downstream tube 33. This is achieved by introducing by means of of line 52, 200 kg / h of liquid stream (liquid barrier) at the top of the downpipe 33. The liquid stream has a different composition than the gas mixture present in the riser tube. The different concentrations of monomers and hydrogen within the riser tube, the downstream tube of the second reactor and the liquid barrier composition are indicated in Table 1. The liquid stream of line 52 comes from the condensation stage in condenser 49, under operating conditions of 53 ° C and 2.1 MPa, where a part of the recycle stream is cooled and partially condensed. As shown in the figure, a separation vessel and a pump are placed in order downstream of the condenser 49. The final polymer is

<td>discharge</td><td>so</td><td>gave</td><td colspan="2">continued through</td><td>from</td><td>line 54</td>

<td>The</td><td>process</td><td>from</td><td>polymerization</td><td>in</td><td>the</td><td>second reactor</td>

<td>produced</td><td colspan="2">fractions</td><td>polyethylene</td><td>from</td><td>a</td><td>molecular weight</td>

relatively high Table 1 specifies the properties of the final product. It can be seen that the melt index of the final product decreases compared to the ethylene resin produced in the first reactor, which shows the formation of high molecular weight fractions in the second reactor.

The first reactor produced about 50% by weight (% by weight divided) of the total amount of the final polyethylene resin produced by the first and second reactor. At the same time, the polymer obtained has a relatively wide molecular weight distribution as seen by an MIF / MIP ratio equal to 38.8.

Table 1

<td></td><td>Example one</td><td>Example two</td><td>Example 3</td><td>Example 4</td><td>Comp. one</td>

<td>Operating conditions of the first reactor</td><td></td><td></td><td></td><td></td><td></td>

<td>Molar ratio of h₂/ c₂h₄</td><td> 2,4</td><td> 1,9</td><td> 1,9</td><td> 2,0</td><td> 1,7</td>

<td>c₂h₄%</td><td> 13,5</td><td> 13,2</td><td> 15,1</td><td> 15,4</td><td> 14</td>

<td>Division (% by weight)</td><td> 53,0</td><td> 50,7</td><td> 53,8</td><td> 50,3</td><td> 50</td>

<td></td><td></td><td></td><td></td><td></td><td></td>

<td>Operating conditions of the second reactor</td><td></td><td></td><td></td><td></td><td></td>

<td>Molar ratio of H₂/ C₂H₄ ascent tube</td><td> 0,028</td><td> 0,017</td><td> 0,056</td><td> 0,020</td><td> 0,038</td>

<td>C₂H₄% ascent tube</td><td> 5,8</td><td> 8,1</td><td> 6,6</td><td> 10,9</td><td> 15</td>

<td>C₆Hi₂ ascent tube</td><td> 0, 09</td><td> 0,85</td><td> 0,76</td><td> 0,58</td><td> 1,2</td>

<td>Molar ratio of H₂/ C₂H₄ down tube</td><td> 0,039</td><td> 0,026</td><td> 0,025</td><td> 0,030</td><td> 0,04</td>

<td>C₂H₄% lowering tube</td><td> 2,3</td><td> 3,2</td><td> 1,6</td><td> 3,8</td><td> 5,4</td>

<td>C₆Hi2 down tube</td><td> 0,90</td><td> 0,94</td><td> 0,99</td><td> 0,63</td><td> 2,2</td>

<td>Molar ratio of H₂/ C₂H₄ barrier</td><td> 0,005</td><td> 0,005</td><td> 0,010</td><td> 0,005</td><td> 0,01</td>

<td>C₂H₄% barrier</td><td> 3,9</td><td> 5,7</td><td> 4,1</td><td> 8,0</td><td> 6,5</td>

<td>C₆H12 barrier</td><td> 0,80</td><td> 1,13</td><td> 1,28</td><td> 0,81</td><td> 2,7</td>

<td></td><td></td><td></td><td></td><td></td><td></td>

<td>Properties of the final polymer</td><td></td><td></td><td></td><td></td><td></td>

<td>MIP [5 kg] (g / 10 min.)</td><td> 0,29</td><td> 0,20</td><td> 0,32</td><td> 0,18</td><td> 0,21</td>

<td>MIF [21.6 kg] (g / 10 min.)</td><td> 9,6</td><td> 6,8</td><td> 11</td><td> 5,9</td><td> 8,15</td>

<td>MIF / MIP</td><td> 33</td><td> 34</td><td> 34</td><td> 33</td><td> 38,8</td>

<td>Density (g / cm³)</td><td> 0,9515</td><td> 0,948 4</td><td> 0,949 5</td><td> 0,9508</td><td> 0,9487</td>

<td>Mw [g / mol]</td><td>3.4E + 5</td><td>3.7E + 5</td><td>3.5E + 5</td><td>3,2E + 5</td><td>3.6E + 5</td>

<td>Mz [g / mol]</td><td>2E + 6</td><td>1.8E + 6</td><td>2.3E + 6</td><td>1.3E + 6</td><td>5, OE + 6</td>

<td>Mw / Mn</td><td> 35</td><td> 31</td><td> 38</td><td> 38</td><td> 52</td>

<td>LCB</td><td> 0,96</td><td> 0,9</td><td> 0, 9</td><td> 0,9</td><td> 0,69</td>

<td>Content of comonomers (C₆Hi₂) GO [%]</td><td> 1,4</td><td> 1,6</td><td> 1,7</td><td> 1,2</td><td> 1,6</td>

<td>SIC index</td><td> 1,2</td><td> 1,8</td><td> 1,4</td><td> 2,1</td><td> 1,9</td>

<td>FNCT 5 MPa / 90 ° C (hours) **</td><td> 214</td><td> 358</td><td> 121</td><td> &gt;1000</td><td> 93</td>

<td>Charpy aFM, T = 0 ° C [kJ / m²]</td><td> 12,9</td><td> 16,7</td><td> 13,0</td><td> 17,2</td><td> 8,9</td>

Notes: C2H4 = ethylene; C4H8 = butene; CsHi₂ = hexene; ** 5% Genapol Pasta aqueous solution and 2% Arkopal N100.

It is noted that in relation to this date, the best method known by the applicant to implement said invention is that which is clear from the present description of the invention.

CLAIMS