Process for producing a heterophasic propylene copolymer having a high xylene cold soluble fraction (XCS)

Abstract

The present invention relates to a process for producing a heterophasic propylene copolymer (RAHECO) having a xylene cold soluble fraction (XCS) determined according to ISO 16152 (25 C.) of more than 30 wt.-%, a heterophasic propylene copolymer (RAHECO) produced by the process as well as an article, preferably a film, a flexible tube or cable insulation, comprising the heterophasic propylene copolymer (RAHECO).

Claims

1. A process for producing a heterophasic propylene copolymer (RAHECO) having a xylene cold soluble fraction (XCS) determined according to ISO 16152 (25 C.) of more than 30 wt %, the process comprising the steps of: a) providing a solid Ziegler-Natta catalyst component that is free of phthalic compounds, b) subjecting the solid Ziegler-Natta catalyst component of step a) to a batch mode catalyst prepolymerization step, wherein the solid Ziegler-Natta catalyst component is prepolymerized in the presence of one or more olefin monomer(s) selected from olefin monomers of 2 to 4 carbon atoms in the presence of an external electron donor (ED) to obtain a prepolymerized solid Ziegler-Natta catalyst, c) polymerizing in one or more polymerization reactor(s) propylene and optionally ethylene and/or a C.sub.4 to C.sub.8 -olefin in the presence of the prepolymerized solid Ziegler-Natta catalyst of step b), forming a first propylene homo- or copolymer, d) polymerizing in one or more further polymerization reactor(s) in the presence of the first propylene homo- or copolymer propylene and ethylene and optionally a C.sub.4 to C.sub.8 -olefin, to obtain the heterophasic propylene copolymer.

2. The process according to claim 1, wherein the solid Ziegler-Natta catalyst component of step a) comprises: (a1) a compound of a transition metal (TM), which transition metal is selected from one of groups 4 to 6 of the periodic table (IUPAC), (a2) a compound of a metal (M) which metal is selected from one of groups 1 to 3 of the periodic table (IUPAC), and (a3) an internal donor (ID) that is a non-phthalic compound.

3. The process according to claim 1, wherein the internal donor (ID) of the solid Ziegler-Natta catalyst component is selected from optionally substituted malonates, maleates, succinates, glutarates, cyclohexene-1,2-dicarboxylates, citraconates, benzoates or derivatives or mixtures thereof.

4. The process according to claim 1, wherein the solid Ziegler-Natta catalyst component is free of an external support material.

5. The process according to claim 1, wherein the batch mode catalyst prepolymerization is carried out in the presence of a co-catalyst (Co) that is a compound of Group 13 metal.

6. The process according to claim 5, wherein a mol ratio of: a) the co-catalyst (Co) to the external electron donor (ED) [Co/ED] is in a range of 0.30 to 1.5, and/or b) the co-catalyst (Co) to a compound of a transition metal (TM) [Co/TM] is in a range of 0.5 to 10.0 in the batch mode catalyst prepolymerization.

7. The process according to claim 1, wherein a weight ratio of the one or more olefin monomer(s) selected from olefin monomers of 2 to 4 carbon atoms to the solid Ziegler-Natta catalyst component (olefin monomer/solid Ziegler-Natta catalyst component) from step b) is in a range of 0.5 to 50.

8. The process according to claim 1, wherein step b) is conducted off-line in batch-mode in an inert medium.

9. The process according to claim 1, wherein the external electron donor (ED) used in the batch mode catalyst prepolymerization is selected from silanes, ethers, esters, amines, ketones, heterocyclic compounds or blends thereof.

10. The process according to claim 1, wherein the process comprises a process prepolymerization step c0) preceding polymerizing steps c) and d), into which step the prepolymerized solid Ziegler-Natta catalyst obtained in step b) is fed.

11. The process according to claim 10, wherein no additional external electron donor (ED) is added into the process prepolymerization step c0) or polymerization steps c) and d).

12. The process according to claim 1, wherein the polymerizing step c) is conducted in at least one slurry-loop reactor.

13. The process according to claim 1, wherein an amount of first propylene homo- or copolymer produced in step c) is in a range of 20 to 80 wt %, based on a total amount of the heterophasic propylene copolymer produced in the process; and an amount of polymer produced in step d) is in a range of 20 to 80 wt %, based on the total amount of the heterophasic propylene copolymer produced in the process.

14. The process according to claim 1, wherein the first propylene homo- or copolymer produced in step c) is a propylene homopolymer or a propylene ethylene random copolymer; and a polymer produced in step d) forms an elastomeric part of the heterophasic propylene copolymer.

15. The process according to claim 1, wherein the heterophasic propylene copolymer produced has i) a xylene cold soluble fraction (XCS) determined according to ISO 16152 (25 C.) of greater than 35 wt %, and/or ii) a comonomer content of greater than 10 wt %.

16. The process according to claim 1, wherein the polymerizing step c) is conducted in at least two polymerization reactors selected from slurry-loop or gas phase reactors.

17. The process according to claim 1, wherein the polymerization step c) is conducted in a combination of one slurry-loop reactor and one gas-phase reactor.

Description

EXAMPLES

1. Measuring Methods

(1) The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

(2) Calculation of comonomer content of the second propylene copolymer fraction (R-PP2):

(3) $\begin{array}{cc}\frac{C\left(\mathrm{PP}\right)-w\left(\mathrm{PP}1\right)C\left(\mathrm{PP}1\right)}{w\left(\mathrm{PP}2\right)}=C\left(\mathrm{PP}2\right)& \left(I\right)\end{array}$ wherein w(PP1) is the weight fraction [in wt.-%] of the first propylene copolymer fraction (R-PP1), w(PP2) is the weight fraction [in wt.-%] of second propylene copolymer fraction (R-PP2), C(PP1) is the comonomer content [in mol-%] of the first propylene copolymer fraction (R-PP1), C(PP) is the comonomer content [in mol-%] of the random propylene copolymer (R-PP), C(PP2) is the calculated comonomer content [in mol-%] of the second propylene copolymer fraction (R-PP2).

(4) Calculation of the xylene cold soluble (XCS) content of the second propylene copolymer fraction (R-PP2):

(5) $\begin{array}{cc}\frac{\mathrm{XS}\left(\mathrm{PP}\right)-w\left(\mathrm{PP}1\right)\mathrm{XS}\left(\mathrm{PP}1\right)}{w\left(\mathrm{PP}2\right)}=\mathrm{XS}\left(\mathrm{PP}2\right)& \left(\mathrm{II}\right)\end{array}$ wherein w(PP1) is the weight fraction [in wt.-%] of the first propylene copolymer fraction (R-PP1), w(PP2) is the weight fraction [in wt.-%] of second propylene copolymer fraction (R-PP2), XS(PP1) is the xylene cold soluble (XCS) content [in wt.-%] of the first propylene copolymer fraction (R-PP1), XS(PP) is the xylene cold soluble (XCS) content [in wt.-%] of the random propylene copolymer (R-PP), XS(PP2) is the calculated xylene cold soluble (XCS) content [in wt.-%] of the second propylene copolymer fraction (R-PP2), respectively.

(6) Calculation of melt flow rate MFR.sub.2 (230 C./2.16 kg) of the second propylene copolymer fraction (R-PP2):

(7) $\begin{array}{cc}\mathrm{MFR}\left(\mathrm{PP}2\right)={10}^{\left[\frac{\log \left(\mathrm{MFR}\left(\mathrm{PP}\right)\right)-w\left(\mathrm{PP}1\right)\log \left(\mathrm{MFR}\left(\mathrm{PP}1\right)\right)}{w\left(\mathrm{PP}2\right)}\right]}& \left(\mathrm{III}\right)\end{array}$ wherein w(PP1) is the weight fraction [in wt.-%] of the first propylene copolymer fraction (R-PP1), w(PP2) is the weight fraction [in wt.-%] of second propylene copolymer fraction (R-PP2), MFR(PP1) is the melt flow rate MFR.sub.2 (230 C./2.16 kg) [in g/10 min] of the first propylene copolymer fraction (R-PP1), MFR(PP) is the melt flow rate MFR.sub.2 (230 C./2.16 kg) [in g/10 min] of the random propylene copolymer (R-PP), MFR(PP2) is the calculated melt flow rate MFR.sub.2 (230 C./2.16 kg) [in g/10 min] of the second propylene copolymer fraction (R-PP2).

(8) Calculation of comonomer content of the elastomeric propylene copolymer (E), respectively:

(9) $\begin{array}{cc}\frac{C\left(\mathrm{RAHECO}\right)-w\left(\mathrm{PP}\right)C\left(\mathrm{PP}\right)}{w\left(E\right)}=C\left(E\right)& \left(\mathrm{IV}\right)\end{array}$ wherein w(PP) is the weight fraction [in wt.-%] of the random propylene copolymer (R-PP), i.e. polymer produced in the first and second reactor (R1+R2), w(E) is the weight fraction [in wt.-%] of the elastomeric propylene copolymer (E), i.e. polymer produced in the third reactor (R3) C(PP) is the comonomer content [in mol-%] of the random propylene copolymer (R-PP), i.e. comonomer content [in mol-%] of the polymer produced in the first and second reactor (R1+R2), C(RAHECO) is the comonomer content [in mol-%] of the propylene copolymer, i.e. is the comonomer content [in mol-%] of the polymer obtained after polymerization in the third reactor (R3), C(E) is the calculated comonomer content [in mol-%] of elastomeric propylene copolymer (E), i.e. of the polymer produced in the third reactor (R3).

(10) MFR.sub.2 (230 C./2.16 kg) is measured according to ISO 1133 at 230 C. and 2.16 kg load.

(11) Quantification of Microstructure by NMR Spectroscopy

(12) Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content and comonomer sequence distribution of the polymers. Quantitative .sup.13C{.sup.1H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 10 mm extended temperature probehead at 125 C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2) along with chromium-(III)-acetylacetonate (Cr(acac).sub.3) resulting in a 65 mM solution of relaxation agent in solvent (Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatary oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128). A total of 6144 (6k) transients were acquired per spectra.

(13) Quantitative .sup.13C{.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present. Characteristic signals corresponding to the incorporation of ethylene were observed Cheng, H. N., Macromolecules 17 (1984), 1950).

(14) With characteristic signals corresponding to 2,1 erythro regio defects observed (as described in L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 2000, 100 (4), 1253, in Cheng, H. N., Macromolecules 1984, 17, 1950, and in W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157) the correction for the influence of the regio defects on determined properties was required. Characteristic signals corresponding to other types of regio defects were not observed.

(15) The comonomer fraction was quantified using the method of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157) through integration of multiple signals across the whole spectral region in the .sup.13C{.sup.1H} spectra. This method was chosen for its robust nature and ability to account for the presence of regio-defects when needed. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents.

(16) For systems where only isolated ethylene in PPEPP sequences was observed the method of Wang et. al. was modified to reduce the influence of non-zero integrals of sites that are known to not be present. This approach reduced the overestimation of ethylene content for such systems and was achieved by reduction of the number of sites used to determine the absolute ethylene content to:
E=0.5(S+S+S+0.5(S+S))

(17) Through the use of this set of sites the corresponding integral equation becomes:
E=0.5(I.sub.H+I.sub.G+0.5(I.sub.C+I.sub.D))

(18) using the same notation used in the article of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157). Equations used for absolute propylene content were not modified.

(19) The mole percent comonomer incorporation was calculated from the mole fraction:
E [mol %]=100*fE

(20) The weight percent comonomer incorporation was calculated from the mole fraction:
E [wt %]=100*(fE*28.06)/((fE*28.06)+((1fE)*42.08))

(21) The comonomer sequence distribution at the triad level was determined using the analysis method of Kakugo et al. (Kakugo, M., Naito, Y., Mizunuma, K., Miyatake, T. Macromolecules 15 (1982) 1150). This method was chosen for its robust nature and integration regions slightly adjusted to increase applicability to a wider range of comonomer contents.

(22) The relative content of isolated to block ethylene incorporation was calculated from the triad sequence distribution using the following relationship (equation (I)):

(23) $\begin{array}{cc}I\left(E\right)=\frac{\mathrm{fPEP}}{\left(\mathrm{fEEE}+\mathrm{fPEE}+\mathrm{fPEP}\right)}100& \left(I\right)\end{array}$ wherein I(E) is the relative content of isolated to block ethylene sequences [in %]; fPEP is the mol fraction of propylene/ethylene/propylene sequences (PEP) in the sample; fPEE is the mol fraction of propylene/ethylene/ethylene sequences (PEE) and of ethylene/ethylene/propylene sequences (EEP) in the sample; fEEE is the mol fraction of ethylene/ethylene/ethylene sequences (EEE) in the sample.

(24) Intrinsic viscosity is measured according to DIN ISO 1628/1, October 1999 (in Decalin at 135 C.).

(25) The xylene cold solubles (XCS, wt.-%): Content of xylene cold solubles (XCS) is determined at 25 C. according ISO 16152; first edition; 2005 Jul. 1. The part which remains insoluble is the xylene cold insoluble (XCI) fraction.

2. Examples

(26) The catalysts used in the polymerization processes for the heterophasic propylene copolymers of the present invention were prepared as follows:

(27) Reference Catalyst

(28) Preparation of the solid catalyst component

(29) Used Chemicals: TiCl.sub.4 (CAS 7550-45-90) was supplied by commercial source. 20% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et)), provided by Crompton 2-ethylhexanol, provided by Merck Chemicals 3-Butoxy-2-propanol, provided by Sigma-Aldrich bis(2-ethylhexyl)citraconate, provided by Contract Chemicals Viscoplex 1-254, provided by Evonik Heptane, provided by Chevron

(30) Preparation of Mg Complex

(31) 3.4 litre of 2-ethylhexanol and 810 ml of propylene glycol butyl monoether in a molar ratio 4/1) were added to a 20% reactor. Then, 7.8 litre of a 20% solution in toluene of BEM (butyl ethyl magnesium) provided by Crompton GmbH was slowly added to the well stirred alcohol mixture. During the addition, the temperature was kept at 10 C. After addition, the temperature of the reaction mixture was raised to 60 C. and mixing was continued at this temperature for 30 minutes. Finally, after cooling to room temperature the obtained Mg-alkoxide was transferred to a storage vessel.

(32) 21.2 g of Mg alkoxide prepared above was mixed with 4.0 ml bis(2-ethylhexyl) citraconate for 5 min. After mixing the obtained Mg complex was used immediately in the preparation of catalyst component.

(33) Preparation of the Solid Catalyst Component

(34) 19.5 ml titanium tetrachloride was placed in a 300 ml reactor equipped with a mechanical stirrer at 25 C. Mixing speed was adjusted to 170 rpm. 26.0 of Mg-complex prepared above was added within 30 minutes keeping the temperature at 25 C. 3.0 ml of Viscoplex 1-254 and 24.0 ml of heptane were added to form an emulsion. Mixing was continued for 30 minutes at 25 C. Then, the reactor temperature was raised to 90 C. within 30 minutes. The reaction mixture was stirred for further 30 minutes at 90 C. Afterwards, stirring was stopped and the reaction mixture was allowed to settle for 15 minutes at 90 C.

(35) The solid material was washed with 100 ml of toluene, with of 30 ml of TiCl4, with 100 ml of toluene and two times with 60 ml of heptane. 1 ml of donor was added to the two first washings. Washings were made at 80 C. under stirring 30 min with 170 rpm. After stirring was stopped, the reaction mixture was allowed to settle for 20-30 minutes and followed by siphoning.

(36) Afterwards, stirring was stopped and the reaction mixture was allowed to settle for 10 minutes decreasing the temperature to 70 C. with subsequent siphoning, and followed by N.sub.2 sparging for 20 minutes to yield an air sensitive powder.

(37) Catalyst has a surface area measured by BET method below 5 m.sup.2/g, i.e. below the detection limit. Ti content was 2.6 wt-%.

(38) Inventive Catalyst

(39) The catalyst of the Reference Catalyst was batch-mode prepolymerised with 1-butene in the presence of dicyclopentyl dimethoxy silane as the external donor (ED) and cocatalyst (TEAL) in a catalyst vessel under nitrogen blanket at a temperature of 20-30 C. with Al/Ti molar ratio of 1 and Al/ED molar ratio of 0.75. The weight ratio of 1-butene/catalyst in the vessel was 2/1 resulting in a batch-mode prepolymerized catalyst with a polymerization degree of 2 g polymer/1 g catalyst (100% conversion).

Comparative Example 1

(40) The catalyst prepared according to the Reference catalyst was used as such (=comparative catalyst) along with triethyl-aluminium (TEAL) as co-catalyst and dicyclopentyl dimethoxy silane as external donor (ED) in the polymerization process. Polymerisation conditions and results are disclosed in Table 1.

Reference ExamplePropylene Homopolymerization

(41) The inventive catalyst was used in a process for producing a propylene homopolymer in a process comprising a process prepolymerization step, polymerization in a loop reactor followed by polymerization in a gas phase reactor. No comonomers were added into the process and no external donor was used. Conditions and results are disclosed in Table 1.

Inventive Example 1

(42) The actual polymerization of propylene with ethylene to produce the heterophasic propylene copolymer was carried out using the Inventive catalyst without an external donor. Conditions and results are disclosed in Table 1.

(43) Based on the XCS of reference example (homoPP), it has been simulated how much the XCS would increase if there is no external donor present in the polymerisation process for producing heterophasic polymerisation using Inventive catalyst.

(44) TABLE-US-00001 TABLE 1 Conditions and results Comparative Inventive Reference Example 1 Example 1 example Example heterophasic PP heterophasic PP homoPP Prepolymerization Catalyst Comparative Inventive catalyst Inventive catalyst catalyst Catalyst feed g/h 2 1.8 2.3 Cocatalyst, TEAL feed 180 180 150 g/t C3 ED feed g/t C3 20 No feed No feed B1 Temperature ( C.) 30 30 30 B1 Residence time (h) 0.33 0.33 0.33 Loop B2 Temperature ( C.) 70 70 80 B2 H2/C3 ratio 0.9 0.9 0.5 (mol/kmol) B2 C2/C3 ratio 4.2 4.0 0 (mol/kmol) B2 Split % 37 35 65 B2 MFR2 (g/10 min) 6.9 7.5 6.9 B2 XCS (%) 6.8 8 5.0 B2 C2 content (%) 2.4 2.15 0 GPR1 B3 Temperature ( C.) 80 80 80 B3 H2/C3 ratio 2.7 2.6 8.0 (mol/kmol) B3 C2/C3 ratio 45.3 46.6 0 (mol/kmol) B3 Split % 33 35 35 B3 MFR2 (g/10 min) 1.8 1.9 9.6 B3 XCS (%) 21.3 27.0 4.2 B3 Ethene content (%) 6.9 7.4 0 GPR2 B4 Temperature ( C.) 70 70 B4 C2/C3 ratio 329.2 303.2 (mol/kmol) B4 H2/C2 ratio 79.3 85.7 (mol/kmol) B4 Split % 30 30 B4 MFR2 (g/10 min) 1.0 1.0 B4 XCS (%) 38.9 52.0 B4 Ethene content (%) 14.9 14.4 B4 Viscosity of AM 3.1 2.9 (dl/g) B4 Ethene of AM (%) 30.6 33 Final PP Mixer MFR2 (g/10 1.0 1.0 9.8 product min) PP Mixer viscosity of 3.0 3.0 AM (dl/g) PP Mixer ethene 14.8 14.6 0 content (%) PP Mixer XCS (%) 38.5 52.0 3.8 PP Mixer BD 376 361 425 PP Mixer PSD avg 0.7 0.8 0.8

(45) As can be seen from the examples, using the batch-prepolymerized catalyst of the invention it is possible to produce heterophasic propylene-ethylene polymers with a similar ethylene content, but still having a higher XCS.

(46) Because no external donor is needed in the actual polymerization stage (comprising also the process prepolymerization step) the polymer has higher purity as the compounds used as external donor, which is desired in some applications such as in food and in the mechanical field.