Patent Description:
Various processes for producing polymer compositions are known in the art. These comprise multi-stage processes that allow to fine tune the properties of the materials and for example to improve mechanical properties and/or processability or the balance thereof. <CIT> discloses a polymer blend of ethylene alpha olefin copolymers that is obtained by a three step process.

In addition, the use of metallocene catalysts to improve optical properties, like for example transparency and/or mechanical properties are also known in the art. However, in particular good optical appearance remains a significant challenge. This challenge becomes even more apparent and pressing with materials already having particularly good optical properties, especially a high transparency because in such cases, even slight defects such as for example gels can have a significant negative impact on optical appearance.

It is thus the object of the present invention to improve the optical appearance of articles produced with a polymer composition, especially a polymer composition having a high transparency and/or obtained with a metallocene catalyst.

Therefore, the present invention provides a process for producing a polymer composition wherein:.

The process according to the present invention thereby allows to combine good optical properties, especially a high transparency, and/or good mechanical properties and/or a good processability with a good optical appearance, especially a low level of defects, particularly low levels of gels, particularly low levels of gels with a size > <NUM> microns and/or with a size of <NUM>-<NUM> micron and/or with a size of <NUM>-<NUM> micron and/or with a size of <NUM>-<NUM> micron. Gels or defects may thereby especially for example be due to cross-linked and/or high molecular weight polymer components. High-transparency in the sense of the invention may be obtained for example for metallocene LLDPEs and/or may mean for example a light transmission in the visible spectrum of > <NUM> %, preferably > <NUM> %.

Different MFR<NUM> values in the sense of the present invention may thereby be for example values that differ by <NUM>, <NUM>, <NUM> or even <NUM>. That the ethylene polymer components (A), (B) and (C) have different MFR<NUM> values may thereby mean that the multimodal ethylene polymer (a) may be for example bimodal or trimodal from a molecular weight point of view.

The molecular weight distribution (MWD) is thereby equivalent to Mw/Mn as measured by GPC in a suitable way.

The weight percent (wt%) of ethylene polymer components (A), (B) and (C) are given based on the weight of the polymer, namely the multimodal ethylene polymer (a), of the composition and thereby add up to > <NUM> wt%, preferably > <NUM> wt% or <NUM> wt% of the polymer, namely the multimodal ethylene polymer (a), in the polymer composition according to the invention. For avoidance of doubt, this means that values in weight percent (wt%) for ethylene polymer components (A), (B) and (C) may have to be selected, preferably in their respective ranges, so that they add up to > <NUM> wt%, preferably > <NUM> wt% or <NUM> wt% of the polymer, namely the multimodal ethylene polymer (a), in the polymer composition according to the invention.

In a process for producing a polymer composition according to the invention, the second ethylene polymer component (B) may preferably be obtained in the presence of the first ethylene polymer component (A) and/or the third ethylene polymer component (C) may be obtained in the presence of the first ethylene polymer component (A) and/or the second ethylene polymer component (B). Nonetheless (and in contrast to the second ethylene polymer component (B)), third ethylene polymer component (C) as used herein may preferably refer (only) to the component produced in the third polymerization zone, as such.

In a process for producing a polymer composition according to the invention, the first and/or second ethylene polymer components (A) and/or (B) may be copolymers of ethylene and of comonomer selected from of <NUM>-butene, 1hexene and/or <NUM>-octene, preferably <NUM>-butene, and/or in that the third ethylene polymer component (C) is a copolymer of ethylene and of a comonomer selected from <NUM>-butene, 1hexene and/or <NUM>-octene, preferably <NUM>-hexene. This may contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties.

In a process for producing a polymer composition according to the invention, the first and/or second polymerization zone may comprise at least one slurry loop reactor and the third polymerization zone comprises at least one gas phase reactor, preferably connected in series. This may contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties.

In a process for producing a polymer composition according to the invention, the first ethylene polymer component (A) may be produced in a slurry loop reactor and the second ethylene polymer component (B) may be produced in a slurry loop reactors, preferably where both slurry loop reactors are connected in series. This may contribute to improve the homogeneity of the composition.

In a process for producing a polymer composition according to the invention, the first and second polymerization zones each may comprise one slurry loop reactor connected in series, whereby hydrogen is fed only to the first of these slurry loop reactors and both of these slurry loops reactors are otherwise run under the same/similar conditions or different conditions, preferably under the same/similar conditions, whereby preferably both of these slurry loops reactors are run at a temperature of between <NUM> and <NUM> and/or a pressure of <NUM>-<NUM> kPa and/or preferably both of these slurry loops reactors are run at the same temperature ± <NUM> % or ± <NUM> and/or at the same pressure ± <NUM> % or ± <NUM> kPa. Similar conditions in the sense of the present inventions may thereby be conditions that deviate for example only by ± <NUM> %, ± <NUM> % or ± <NUM> %. The same conditions in the sense of the present invention are identical conditions. Different conditions in the sense of the invention may mean different by > ±<NUM> %, preferably > ±<NUM> %. This may further contribute to improve the homogeneity of the composition.

In a process for producing a polymer composition according to the invention, the polymerization of a third ethylene polymer component (C) in a third polymerization zone may preferably conducted in gas phase in the presence of at least one comonomer that is different from the comonomer present in the first and/or second polymerization zone, preferably so that the molecular weight is maximized and/or in the with no hydrogen fed to the second polymerization zone. This may further contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties.

In a process for producing a polymer composition according to the invention, the ethylene polymer component (A) may have an MFR<NUM> of <NUM> to <NUM>, preferably of <NUM> to <NUM>, more preferably of <NUM> to <NUM>/<NUM>, further preferred <NUM> to <NUM>/<NUM> and/or the MFR<NUM> of the ethylene polymer component (A) may be equal or lower than the MFR<NUM> of the ethylene polymer component (B) and/or the ethylene polymer component (B) may have an MFR<NUM> <NUM> to <NUM>/<NUM>, preferably of <NUM> to <NUM>, preferably of <NUM> to <NUM>, more preferably of <NUM> to <NUM>/<NUM>, further preferred <NUM> to <NUM>/<NUM>, further preferred > <NUM> to < <NUM>/<NUM> and/or wherein the MFR<NUM> of the ethylene polymer component (C) may be from <NUM> to <NUM>, preferably <NUM> to <NUM>, preferably <NUM> to <NUM>/<NUM> all measured according to ISO <NUM> at <NUM> under <NUM> or <NUM> load. This may further contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties. In addition, this may also contribute to improve the homogeneity of the composition.

In a process for producing a polymer composition according to the invention, the alpha-olefin comonomer having from <NUM> to <NUM> carbon atoms of ethylene polymer components (A) and (B) may be <NUM>-butene and the alpha-olefin comonomer having from <NUM> to <NUM> carbon atoms of ethylene polymer component (C) may be <NUM>-hexene and/or the multimodal polymer of ethylene (a) may comprise between <NUM> and <NUM> wt% of the ethylene polymer component (A) and/or between <NUM> and < <NUM>, preferably <NUM> and <NUM>, preferably <NUM> and <NUM> wt% of the ethylene polymer component (B) and/or between > <NUM> and <NUM>, preferably > <NUM> and <NUM>, preferably <NUM> and <NUM> wt% of the ethylene polymer component (C). This may further contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties.

In a process for producing a polymer composition according to the invention, the ethylene polymer component (B) may have a density equal or higher than the density of the ethylene polymer component (A). This may contribute to improve the homogeneity of the composition and/or to further improve the optical appearance.

In a process for producing a polymer composition according to the invention, the density of the ethylene component (C) is equal or lower than the density of the ethylene polymer component (A) and/or of ethylene polymer component (B). This may contribute to improve the homogeneity of the composition and/or to further improve the optical appearance.

In a process for producing a polymer composition according to the invention, the density of the ethylene polymer components (A) and (B) may be of <NUM> to <NUM>, preferably <NUM> to <NUM>, preferably > <NUM> to <<NUM>, preferably of <NUM> to <NUM>/m<NUM> and/or the density of polymer component (C) may be of <NUM> to <NUM>, preferably <NUM> to <NUM>, preferably <NUM> to <NUM>, further preferred <NUM> to <NUM> or <NUM> to <NUM>/m<NUM>. This may further contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties. In addition, this may also contribute to improve the homogeneity of the composition.

In a process for producing a polymer composition according to the invention, the density of the multimodal polymer of ethylene (a) may be of <NUM> to <NUM>, preferably of <NUM> to <NUM>, kg/m<NUM> and/or the MFR<NUM> of the multimodal polymer of ethylene (a) may be between <NUM> and <NUM>, preferably <NUM> and <NUM>, preferably <NUM> and <NUM>/<NUM> and/or wherein the multimodal polymer of ethylene (a) has MFR<NUM>/ MFR<NUM> of <NUM> to <NUM>, preferably <NUM> to <NUM>, preferably <NUM> to < <NUM>, preferably > <NUM> to < <NUM> and/or the multimodal polymer of ethylene (a) has an MFR<NUM> of <NUM> to <NUM>, preferably > <NUM> to < <NUM>/<NUM>. This may further contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties.

In a process for producing a polymer composition according to the invention, the multimodal polymer of ethylene (a) may have a number of gels per square meter with a size of <NUM>-<NUM> micron of <NUM> to below <NUM>, preferably below <NUM>, preferably below <NUM> and/or or wherein the multimodal polymer of ethylene (a) has a number of gels per square meter with a size of <NUM>-<NUM> micron of <NUM> to below <NUM>, preferably below <NUM>, below <NUM>, below <NUM>, below <NUM> and/or or wherein the multimodal polymer of ethylene (a) has a number of gels per square meter with a size > <NUM> micron of <NUM> to below <NUM>, preferably below <NUM>, preferably below <NUM>, preferably below <NUM>, preferably below <NUM> and/or a number of gels per square meter with a size of <NUM>-<NUM> micron of <NUM> to below <NUM>, preferably below <NUM>, preferably <NUM> preferably below <NUM>. This may contribute to further improve the optical appearance.

In a process for producing a polymer composition according to the invention, the multimodal polymer of ethylene (a) may be produced using a single site catalyst preferably a substituted and/or bridged bis-cyclopentadienyl zirconium or hafnium catalyst, preferably the ethylene polymer components (A), (B) and (C) of the polymer of ethylene (a) may be produced using same single site catalyst, preferably a substituted and/or bridged bis-cyclopentadienyl zirconium or hafnium catalyst and/or may have each an MWD of between <NUM> and <NUM>, preferably <NUM> and <NUM>, preferably > <NUM> and < <NUM>. This may further contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties. In addition, this may also contribute to improve the homogeneity of the composition and/or the optical appearance.

The present invention also concerns a pipe, cap, closure, rotomolded article, artificial grass mat, geomembrane, blow molded article and/or mono or multilayer film comprising a polymer composition produced using a process according to the invention. Such articles may show good optical properties, especially a high transparency, and/or good mechanical properties and/or a good processability in combination with a good optical appearance, especially a low level of defects, particularly low levels of gels, particularly low levels of gels with a size > <NUM> microns and/or with a size of <NUM>-<NUM> micron and/or with a size of <NUM>-<NUM> micron and/or with a size of <NUM>-<NUM> micron. This may contribute to improve optical appearance.

To produce polymer compositions, such as in the present invention, two or more reactors or zones connected in series as described in <CIT> can be used.

According to the present invention, the main polymerization stages are preferably carried out as a combination of slurry polymerization/gas-phase polymerization. The slurry polymerization is preferably performed in a so-called slurry loop reactor.

Optionally, the main polymerization stages may be preceded by a pre-polymerization, in which case a prepolymer (P) may be produced in the amount of for example <NUM> to < <NUM>% preferably <NUM> to <NUM> % by weight of the total amount of polymers is produced. The pre-polymer may be an ethylene homo- or copolymer, preferably an ethylene copolymer, further preferred with <NUM>-butene or <NUM>-hexene.

In the case there is a pre-polymerization the weight percent (wt%) of ethylene polymer components (A), (B) and (C) are given based on the weight of the polymer, namely the multimodal ethylene polymer (a), of the polymer composition and thereby add up to > <NUM> wt%, preferably > <NUM> wt%, of polymer, namely the multimodal ethylene polymer (a), in the polymer composition according to the invention, so that the weight percent (wt%) of ethylene polymer components (A), (B), (C) and prepolymer (P) have to be selected in their respective ranges to add up to <NUM> wt% based on the weight of polymer, namely the multimodal ethylene polymer (a), in the polymer composition. This may further contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties. In addition, this may also contribute to improve the homogeneity of the composition and/or the optical appearance.

The prepolymerization may thereby be carried out in the smallest of the reactors used, whereby preferably prepolymerization is carried out at temperature lower than the temperature in the first and/or second polymerization zone, preferably at a temperature lower than both slurry loop reactors, preferably in the range of <NUM> to < <NUM> and/or prepolymerization is carried out at a pressure of <NUM>-<NUM> kPa and/or in that the concentration of hydrogen (in mol/kmol) in the prepolymerization zone is the same as the concentration of hydrogen (in mol/kmol) in the first polymerization zone ± <NUM> %, preferably ± <NUM> %, preferably ± <NUM> %. This may further contribute to improve and/or optimize material properties, especially optical properties such as transparency, and/or mechanical properties. In addition, this may also contribute to improve the homogeneity of the composition and/or the optical appearance.

If a pre-polymerization takes place, in this case all of the catalyst is preferably charged into the first prepolymerization reactor and the pre-polymerization is performed as slurry polymerization. Such a polymerization leads to less fine particles being produced in the following reactors and to a more homogeneous product being obtained in the end.

The resulting multimodal polymer of ethylene (a) consists of an intimate mixture of the polymers from the three main reactors, the different molecular-weight-distribution curves of these polymers together forming a molecular-weight-distribution curve having a broad maximum or three maxima, i.e. the end product is a trimodal polymer mixture.

The polymer composition according to the invention may also comprise additives like process aids, antioxidants, pigments, UV-stabilizers and the like. Usually, the amount at those additives may be <NUM> to <NUM> wt% or > <NUM> to <NUM> wt%, based on the weight of the total composition. This means that the amount of polymer, namely the multimodal ethylene polymer (a), in the polymer composition may <NUM> wt% to <NUM> wt% or <NUM> wt% to < <NUM> wt%.

Three samples IE1 IE2 and CE of were produced using prepolymerization followed by polymerization in a first slurry reactor (loop reactor <NUM>) by feeding ethylene (C2), one metallocene catalyst as described below, <NUM>-butene (C4) as comonomer, hydrogen and propane as a diluent. Whereby the first slurry loop reactor is connected in series with another slurry reactor (loop reactor <NUM>), so that the first ethylene polymer component (A) produced in the loop reactor <NUM> is fed to the loop reactor <NUM>. Ethylene (C2) is thereby polymerized in the presence of the polymer produced in the loop reactor <NUM>, <NUM>-butene (C4) as comonomer and hydrogen to produce a second ethylene component (B). The loop reactor <NUM> is thereby connected in series to a gas phase reactor (GPR), so that the second ethylene component (B) is fed to the GPR and ethylene is polymerized in the GPR with <NUM>-hexene (C6) as comonomer as well as hydrogen to obtain a third ethylene polymer component (C), so as to produces multimodal polymers of ethylene (a).

The process comprises of a flash between loop2 reactor and GPR reactor, in order to remove the diluent and unreacted monomer(s).

The polymerization conditions are given in Table <NUM> below.

The MWD of each sample was determined to be in the range from <NUM>-<NUM> by GPC. Similarly, the MWD of each ethylene polymer component was determined to be in the range of <NUM> to <NUM> by GPC.

<NUM> grams of a metallocene complex bis(<NUM>-methyl-<NUM>-n-butylcyclopentadienyl) zirconium (IV) dichloride (CAS no. <NUM>-<NUM>-<NUM>) and <NUM> of a <NUM>% solution of commercial methylalumoxane (MAO) in toluene were combined and <NUM> dry purified toluene was added. Thus, obtained complex solution was added onto <NUM> silica carrier Sylopol <NUM> SJ (supplied by Grace) by very slow uniform spraying over <NUM> hours. The temperature was kept below <NUM>. The mixture was allowed to react for <NUM> hours after complex addition at <NUM>.

The weight average molecular weight Mw and the molecular weight distribution (MWD = Mw/Mn wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) is measured by a method based on ISO <NUM>-<NUM>:<NUM>. A Waters 150CV plus instrument, equipped with refractive index detector and online viscosimeter was used with <NUM> x HT6E styragel columns from Waters (styrenedivinylbenzene) and <NUM>,<NUM>,<NUM>-trichlorobenzene (TCB, stabilized with <NUM>/L <NUM>,<NUM>-Di tert butyl-<NUM>-methyl-phenol) as solvent at <NUM> and at a constant flow rate of <NUM>/min. <NUM>µL of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO <NUM>-<NUM>:<NUM>) with <NUM> narrow MWD polystyrene (PS) standards in the range of <NUM>/mol to <NUM><NUM>/mol. Mark Houwink constants were used for polystyrene and polyethylene (K: <NUM> ×<NUM>-<NUM> dL/g and a: <NUM> for PS, and K: <NUM> ×<NUM>-<NUM> dL/g and a: <NUM> for PE). All samples were prepared by dissolving <NUM> - <NUM> of polymer in <NUM> (at <NUM>) of stabilized TCB (same as mobile phase) and keeping for <NUM> hours at <NUM> and for another <NUM> hours at <NUM> with occasional shaking prior sampling in into the GPC instrument.

Gel content was analyzed by an Optical Control System (OCS Film-Test FSA100) with a CCD (Charged-Coupled Device) camera provided by Optical Control Systems GmbH, which measures gels and defects in the film produced from the compositions. The gels and defects are recognized optoelectronically by their different light transmittance compared to the film matrix.

A translucent <NUM> thick cast film was photographed using high resolution line cameras and appropriate background illumination. The number and the area of gels per total film area are then calculated using an image recognition software.

The film defects/gels are measured and classified according to their size (longest dimension).

Cast film preparation, extrusion parameters:.

The defects were classified according to the size (µm)/m2:.

The results are also shown in Table <NUM> below. One can see that optical appearance is improved as the number of gels decreases for IE1 & IE2 compared to CE.

Claim 1:
A process for producing a polymer composition characterized in that a first ethylene polymer component (A) is obtained in a first polymerization zone by polymerization conducted in slurry in the presence of ethylene, at least one comonomer selected from alpha-olefins having from <NUM> to <NUM> carbon atoms and optionally hydrogen and a second ethylene polymer component (B) is obtained in a second polymerization zone by polymerization conducted in slurry in the presence of ethylene, first ethylene polymer component (A), at least one comonomer selected from alpha-olefins having from <NUM> to <NUM> carbon atoms and optionally hydrogen and a third ethylene polymer component (C ) is obtained in a third polymerization zone by polymerization conducted in gas phase in the presence of ethylene, optionally hydrogen and at least one comonomer selected from alpha-olefins having from <NUM> to <NUM> carbon atoms, to produce a multimodal polymer of ethylene (a) with at least one comonomer selected from alpha-olefins having from <NUM> to <NUM> carbon atoms,
- which has
a) a density between <NUM> and <NUM>/m<NUM>,
b) MFR<NUM> of <NUM> to <NUM>/<NUM> (according to ISO <NUM> at <NUM> under <NUM> load),
c) MWD of <NUM> to <NUM>,
- which comprises at least
- between <NUM> to < <NUM> wt% of an ethylene polymer component (A),
- more ethylene polymer component (B) than ethylene polymer component (A) and
- between > <NUM> and <NUM> wt% of an ethylene polymer component (C) and wherein the densities of ethylene polymer components (A) and (B) are each between <NUM> and <NUM>/m<NUM> and the density of ethylene polymer component (C) has a density between <NUM> and <NUM>/m<NUM>, wherein further the ethylene polymer components (A), (B) and (C) have different MFR<NUM> values.