Heterophasic polypropylene with propylene hexene random copolymer as matrix

Abstract

The present invention is directed to a heterophasic polypropylene composition with improved sterilization resistance and optical properties for blow molding applications, in particular for use in the blow-fill-seal process for preparing bottles. The present invention is further directed to a process for producing such a polypropylene composition using a single-site catalyst and to a container produced from such a polypropylene composition by blow molding, like a bottle, in particular a blow-fill-seal bottle, with improved haze before and after sterilization. The polypropylene composition comprises a blend of a propylene copolymer comprising 2.5 to 12.0 wt % of 1-hexene as a comonomer, and having a melt flow rate MFR.sub.2 of 0.5 to 20.0 g/10 min, and an ethylene homo- or copolymer having a melt flow rate MFR.sub.2 of 0.05 to 30.0 g/10 min and a density of 850 to 940 kg/m.sup.3, wherein the xylene cold solubles (XCS) content of the polypropylene composition is from 5.0 to 30.0 wt %.

Claims

1. A polypropylene composition comprising a blend of: (a) a propylene copolymer comprising 2.5 to 12.0 wt %, based on the weight of the propylene copolymer, of 1-hexene as a comonomer, and having a melt flow rate MFR.sub.2 of 0.5 to 20.0 g/10 min, and (b) an ethylene homo- or copolymer having a melt flow rate MFR.sub.2 of 0.05 to 30.0 g/10 min and a density of 850 to 940 kg/m.sup.3, wherein the ethylene copolymer comprised by the ethylene homo- or copolymer (b) is an ethylene propylene copolymer comprising 6.0 to 25.0 wt % of ethylene, wherein the xylene cold solubles (XCS) content of the polypropylene composition is from 5.0 to 30.0 wt %, and wherein the content of hexane extractables according to FDA of the polypropylene composition is below 1.5 wt %.

2. The polypropylene composition according to claim 1, wherein the blend comprises 70.0 to 95.0 wt %, based on the weight of the blend, of the propylene copolymer (a), and 5.0 to 30.0 wt %, based on the weight of the blend, of the ethylene homo- or copolymer (b).

3. The polypropylene composition according to claim 1, wherein the melting temperature T.sub.m of the polypropylene composition is higher than 120° C.

4. The polypropylene composition according to claim 1, wherein the melt flow rate MFR.sub.2 of the polypropylene composition is from 1.0 to 12.0 g/10 min.

5. The polypropylene composition according to claim 1, wherein the propylene copolymer (a) comprises in addition 0.1 to 3.0 wt %, based on the weight of the propylene copolymer, of ethylene as a comonomer.

6. The polypropylene composition according to claim 1, wherein the content of 1-hexene of the polypropylene composition is 2.0 to 7.0 wt %.

7. The polypropylene composition according to claim 1, further comprising from 0.001 to 0.50 wt % of an α-nucleating agent.

8. The polypropylene composition according to claim 1, wherein the propylene copolymer (a) comprises two propylene copolymer fractions produced in two different polymerization steps, wherein the first fraction has a lower melt flow rate MFR.sub.2 than the second fraction, and wherein the polymerization step for obtaining the second fraction is carried out in the presence of the first fraction.

9. A process for preparing a polypropylene composition according to claim 1, comprising the following steps: (i) polymerising propylene and 1-hexene, and optionally ethylene, in the presence of a single-site catalyst to obtain a fraction (a) having a content of 1-hexene of 2.5 to 12.0 wt %, and optionally a content of ethylene of 0.1 to 3.0 wt %, and having a melt flow rate MFR.sub.2 of 0.5 to 20.0 g/10 min, and (ii) polymerising ethylene, or ethylene and propylene, to obtain a fraction (b) having a melt flow rate MFR.sub.2 of 0.05 to 30.0 g/10 min and a density of 850 to 940 kg/m.sup.3.

10. The process according to claim 9, wherein the polymerization step (ii) is carried out in the presence of fraction (a).

11. The process according to claim 9, wherein the polymerization step (i) is carried out in the absence of fraction (b) and the polymerization step (ii) is carried out in the absence of fraction (a), and fraction (a) and fraction (b) are mixed by compounding to obtain the blend.

12. The process according to claim 1, wherein the single-site catalyst is a metallocene catalyst with the metal being Zr or Hf, and the ligand being based on two 4-phenylindene moieties being linked by the moiety —SiR.sub.2—, wherein each R is independently a C.sub.1-C.sub.20-hydrocarbyl group or tri(C.sub.1-C.sub.20-alkyl)silyl.

13. A container comprising a polypropylene composition according to claim 1, wherein the container is produced from the polypropylene composition by blow molding.

Description

EXAMPLES

1. Definitions/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) Melt Flow Rate

(3) The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR.sub.2 of polypropylene (polypropylene composition of the present invention and propylene copolymer (a)) is determined at a temperature of 230° C. and a load of 2.16 kg. The MFR.sub.2 of polyethylene (ethylene homo- or copolymer (b)) is determined at a temperature of 190° C. and a load of 2.16 kg.

(4) Comonomer Content (Ethylene)

(5) 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-d2 (TCE-d2) along with chromium-(III)-acetylacetonate (Cr(acac).sub.3) resulting in a 65 mM solution of relaxation agent in solvent as described in G. Singh, A. Kothari, V. Gupta, Polymer Testing 2009, 28(5), 475.

(6) To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatory 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 as described in Z. Zhou, R. Kuemmerle, X. Qiu, D. Redwine, R. Cong, A. Taha, D. Baugh, B. Winniford, J. Mag. Reson. 187 (2007) 225 and V. Busico, P. Carbonniere, R. Cipullo, C. Pellecchia, J. Severn, G. Talarico, Macromol. Rapid Commun. 2007, 28, 1128. A total of 6144 (6 k) transients were acquired per spectra. Quantitative .sup.13C {.sup.1H}NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals. 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.

(7) 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.

(8) Characteristic signals corresponding to the incorporation of ethylene were observed (as described in Cheng, H. N., Macromolecules 1984, 17, 1950) and the comonomer fraction calculated as the fraction of ethylene in the polymer with respect to all monomer in the polymer.

(9) The comonomer fraction was quantified using the method of W-J. Wang and S. Zhu, Macromolecules 2000, 33 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.

(10) Comonomer Content (1-Hexene)

(11) Quantitative .sup.13C {.sup.1H} NMR spectra recorded in the molten-state using a Bruker Avance III 500 NMR spectrometer operating at 500.13 and 125.76 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 7 mm magic-angle spinning (MAS) probehead at 180° C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was packed into a 7 mm outer diameter zirconia MAS rotor and spun at 4 kHz. This setup was chosen primarily for the high sensitivity needed for rapid identification and accurate quantification. (Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382., Parkinson, M., Klimke, K., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208:2128., Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373). Standard single-pulse excitation was employed utilising the NOE at short recycle delays of 3s (Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382., Pollard, M., Klimke, K., Graf, R., Spiess, H. W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813.). and the RS-HEPT decoupling scheme (Filip, X., Tripon, C., Filip, C., J. Mag. Resn. 2005, 176, 239., Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown, S. P., Mag. Res. in Chem. 2007 45, 51, S198). A total of 16384 (16k) transients were acquired per spectra.

(12) Quantitative .sup.13C {.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals. All chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

(13) Characteristic signals corresponding to the incorporation of 1-hexene were observed and the comonomer content quantified in the following way.

(14) The amount of 1-hexene incorporated in PHP isolated sequences was quantified using the integral of the αB4 sites at 44.2 ppm accounting for the number of reporting sites per comonomer:
H=IαB4/2

(15) The amount of 1-hexene incorporated in PHHP double consecutive sequences was quantified using the integral of the ααB4 site at 41.7 ppm accounting for the number of reporting sites per comonomer:
HH=2*IααB4

(16) When double consecutive incorporation was observed the amount of 1-hexene incorporated in PHP isolated sequences needed to be compensated due to the overlap of the signals αB4 and αB4B4 at 44.4 ppm:
H=(IαB4−2*IααB4)/2

(17) The total 1-hexene content was calculated based on the sum of isolated and consecutively incorporated 1-hexene:
Htotal=H+HH

(18) When no sites indicative of consecutive incorporation observed the total 1-hexeen comonomer content was calculated solely on this quantity:
Htotal=H

(19) Characteristic signals indicative of regio 2,1-erythro defects were observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253).

(20) The presence of 2,1-erythro regio defects was indicated by the presence of the Pαβ (21e8) and Pαγ (21e6) methyl sites at 17.7 and 17.2 ppm and confirmed by other characteristic signals.

(21) The total amount of secondary (2,1-erythro) inserted propene was quantified based on the αα21e9 methylene site at 42.4 ppm:
P21=Iαα21e9

(22) The total amount of primary (1,2) inserted propene was quantified based on the main Sαα methylene sites at 46.7 ppm and compensating for the relative amount of 2,1-erythro, αB4 and ααB4B4 methylene unit of propene not accounted for (note H and HH count number of hexene monomers per sequence not the number of sequences):
P12=I.sub.Sαα+2*P21+H+HH/2

(23) The total amount of propene was quantified as the sum of primary (1,2) and secondary (2,1-erythro) inserted propene:
Ptotal=P12+P21=I.sub.Sαα+3*Iαα21e9+(IαB4−2*IααB4)/2+IααB4

(24) This simplifies to:
Ptotal=I.sub.Sαα+3*Iαα21e9+0.5*IαB4

(25) The total mole fraction of 1-hexene in the polymer was then calculated as:
fH=Htotal/(Htotal+Ptotal)

(26) The full integral equation for the mole fraction of 1-hexene in the polymer was:
fH=(((IαB4−2*IααB4)/2)+(2*IααB4))I.sub.Sαα+3*Iαα21e9+0.5*IαB4)+((IαB4−2*IααB4)/2)+(2*IααB4))

(27) This simplifies to:
fH=(IαB4/2+IααB4)/(I.sub.Sαα+3*Iαα21e9+IαB4+IααB4)

(28) The total comonomer incorporation of 1-hexene in mole percent was calculated from the mole fraction in the usual manner:
H[mol %]=100*fH

(29) The total comonomer incorporation of 1-hexene in weight percent was calculated from the mole fraction in the standard manner:
H[wt %]=100*(fH*84.16)/((fH*84.16)+((1−fH)*42.08))
Density

(30) Density is measured according to ISO 1183-187. Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

(31) Differential Scanning Calorimetry (DSC)

(32) Differential scanning calorimetry (DSC) analysis, melting temperature (T.sub.m) and melt enthalpy (H.sub.m), crystallization temperature (TO, and heat of crystallization (H.sub.e, H.sub.CR) are measured with a TA Instrument Q200 differential scanning calorimetry (DSC) on 5 to 7 mg samples. DSC is run according to ISO 11357/part 3/method C2 in a heat/cool/heat cycle with a scan rate of 10° C./min in the temperature range of −30 to +225° C. Crystallization temperature (T.sub.a) and heat of crystallization (H.sub.c) are determined from the cooling step, while melting temperature (T.sub.m) and melt enthalpy (H.sub.m) are determined from the second heating step.

(33) Xylene Cold Soluble (XCS) Content

(34) Xylene Cold Soluble fraction at room temperature (XCS, wt %) is determined at 25° C. according to ISO 16152; 5th edition; 2005-07-01.

(35) Intrinsic Viscosity

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

(37) Hexane Soluble Fraction (C6 FDA)

(38) The amount of hexane extractable polymer according to FDA method (federal registration, title 21, Chapter 1, part 177, section 1520, s. Annex B) was determined from films produced on a PM30 cast film extrusion line with about 220° C. melt temperature with L/D=20 and a screw diameter of 30 mm (feed zone 4 D long, 5.8 mm deep, compression zone 10 D long, metering zone 6 D long, 2.3 mm deep utilising a screen pack 36-400-900-400 mesh/cm.sup.2). A 200 mm die with a 0.55 to 0.60 mm die gap, screw speed: 50 r/min, and chill roll temperature of water: both rolls 40° C. (heating-cooling unit), Air gap: 0.5 mm, Air knife blower air supply: 1 bar. The film thickness is 100 μm. The amount of hexane soluble polymer is determined according to FDA method (federal registration, title 21, Chapter 1, part 177, section 1520, s. Annex B) from the film samples prepared as described above. The extraction was performed at a temperature of 50° C. and an extraction time of 2 hours.

(39) Steam Sterilisation

(40) Steam sterilisation was performed in a Systec D series machine (Systec Inc., USA). The samples were heated up at a heating rate of 5° C./min starting from 23° C. After having been kept for 30 min at 121° C., they were removed immediately from the steam steriliser and stored at room temperature till processed further.

(41) Flexural Modulus

(42) The flexural modulus was determined in 3-point-bending at 23° C. according to ISO 178 on 80×10×4 mm.sup.3 test bars injection moulded in line with EN ISO 1873-2.

(43) Notched Impact Strength (NIS)

(44) The Charpy notched impact strength (NIS) was measured according to ISO 179 1eA at +23° C., using injection moulded bar test specimens of 80×10×4 mm.sup.3 prepared in accordance with EN ISO 1873-2.

(45) Haze

(46) Haze was determined according to ASTM D1003-00 on 60×60×1 mm.sup.3 plaques injection moulded in line with EN ISO 1873-2. Hence, haze is determined on 1 mm thick plaques.

(47) Clarity and Haze Measurement on 0.3 mm Thick EBM Bottles

(48) Clarity and haze of bottles were determined according to ASTM D1003. The measurement is done on the outer wall of the bottles. The top and bottom of the bottles are cut off. The resulting round wall is then split in two, horizontally. Then from this wall six equal samples of approximately 60×60 mm are cut from close to the middle. The specimens are placed into the instrument with their convex side facing the haze port. Haze and clarity are measured for each of the six samples. The reported value is the average of these six parallels.

2. Examples

(49) Preparation of the Catalyst System for the Inventive Examples

(50) The catalyst used in the inventive examples is prepared as described in detail in WO 2015/011135 A1 (metallocene complex MC1 with methylaluminoxane (MAO) and borate resulting in Catalyst 3 described in WO 2015/011135 A1) with the proviso that the surfactant is 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-1-propanol. The metallocene complex (MC1 in WO 2015/011135 A1) is prepared as described in WO 2013/007650 A1 (metallocene E2 in WO 2013/007650 A1).

(51) Polymerization and Pelletization

(52) Polymerization was performed in a Borstar pilot plant comprising a prepolymerisation reactor, a loop reactor and one or two gas phase reactors. The polymerisation conditions are indicated in Table 1.

(53) Polymer P1 is produced in the above-mentioned pilot plant comprising a prepolymerisation reactor, a loop reactor and two gas phase reactors. P1 is the basis of Inventive Example 1, 1E1.

(54) Polymer P2 is produced in the above-mentioned pilot plant comprising a prepolymerisation reactor, a loop reactor and a phase reactor. P2 is the basis of Inventive Examples 2 and 3, 1E2 and IE3.

(55) Both polymers P1 and P2 were compounded in a co-rotating twin-screw extruder Coperion ZSK 57 at 220° C. with 0.2 wt % of Irganox B225 (1:1-blend of Irganox 1010 (Pentaerythrityl-5 tetrakis(3-(3′,5′-di-tert.butyl-4-hydroxytoluyl)-propionate and tris (2,4-di-t-butylphenyl) phosphate) phosphite) of BASF AG, Germany) and 0.1 wt % calcium stearate followed by solidification of the resulting melt strands in a water bath and pelletization.

(56) Compounding

(57) All further melt mixing was performed in a Thermo Fisher (PRISM) TSE 24 twin-screw extruder at 220° C. followed by solidification of the resulting melt strands in a water bath and pelletization.

(58) The polypropylene composition of IE2 is obtained by mixing P2 with 10 wt % of Vistamaxx™ 6202, a propylene ethylene random copolymer commercially available from ExxonMobil having an ethylene content of 15 wt %, a density of 862 kg/m.sup.3, and a melt index at 190° C. with a load of 2.16 kg (ASTM D1238) of 9.1 g/10 min.

(59) The polypropylene composition of IE3 is obtained by mixing P2 with 10 wt % of LE6609-PH, a low-density polyethylene commercially available from Borealis AG, Austria, having a density (ISO 1183) of 930 kg/m.sup.3, and a melt flow rate at 190° C. with a load of 2.16 kg (ISO 1133) of 0.3 g/10 min.

(60) CE1 is a comparative heterophasic propylene copolymer based on a Ziegler-Natta type catalyst (ZNC) as described in WO 2017/005667 A1, IE1.

(61) CE2 is the commercial grade LE6609-PH available from Borealis AG, Austria and is a low density polyethylene (LDPE) having a density of 930 kg/m.sup.3 and an MFR (190° C./2.16 kg) of 0.3 g/10 min.

(62) Preparation of the Bottles

(63) Bottles of 1 litre capacity were produced on a “Fischer Müller” Blow Moulding Machine.

(64) The main processing parameters for the production were: Temperature profile: 180 to 200° C. applied in extruder, adapter and head Melt temperature measured: 190° C. Speed of extruder (revolution per minute; rpm): 13 to 16 rpm Die gap for producing 0.6 mm thick bottles was adjusted to get a bottle with a weight of 40 g with the commercial Borealis grade RB307MO (random propylene copolymer with a density of 902 kg/m.sup.3 and an MFR.sub.2 of 1.5 g/10 min) Cycle time: 12 to 16 seconds

(65) For producing 0.3 mm thick bottles, the die gap was adjusted to get a bottle with a weight of 25 g with the commercial Borealis grade RB307MO.

(66) The bottles had an outer diameter of 90 mm, wall thickness of 0.3 mm or 0.6 mm respectively, an overall-height of 204 mm and a height of the cylindrical mantle of 185 mm.

(67) The properties of the inventive and comparative examples (compositions and bottles) are listed in Table 2.

(68) TABLE-US-00001 TABLE 1 Polymerisation details of polymers P1 and P2 P1 P2 Prepolymerization Temperature ° C. 20 20 Pressure kPa 5256 5023 Residence time h 0.4 0.5 Loop reactor Temperature ° C. 70 70 Pressure kPa 5280 5244 H2/C3 ratio mol/kmol 0.1 0.1 C6/C3 ratio mol/kmol 8.9 8.2 Residence time h 0.4 0.4 C6 wt % 1.8 1.4 MFR g/10 min 2.1 1.4 Split wt % 38 45 Gas phase reactor 1 Temperature ° C. 80 80 Pressure kPa 2500 2500 H2/C3 ratio mol/kmol 1.4 1.5 C6/C3 ratio mol/kmol 9.4 9.0 Residence time h 0.4 0.4 MFR(GPR1) wt % 0.8 1.4 C6(GPR1) wt % 11.9 7.9 MFR g/10 min 1.3 1.4 C6 wt % 6.9 5.0 Split wt % 38 55 Gas phase reactor 2 Temperature ° C. 80 — Pressure kPa 2500 — H2/C2 ratio mol/kmol 2.9 — C2/C3 ratio mol/kmol 300 — Residence time h 0.4 — Split % 24 — C6 total wt % 5.2 5.0 C2 total wt % 3.5 0 XCS wt % 23.2 11.1 MFR g/10 min 1.3 1.4

(69) TABLE-US-00002 TABLE 2 Properties of inventive and comparative examples IE1 IE2 IE3 CE1 CE2 MFR g/ 1.3 1.8 1.8 1.4 0.6 10 min T.sub.m ° C. 140 139 136 148 118 T.sub.c ° C. 89 91 92 115 104 C6(FDA) % 0.91 n.d. n.d. 3.28 0.76 XCS wt % 23.2 19.6 10.1 21.0 0.5 IV(XCS) dl/g 2.3 n.d. n.d. 2.3 n.d. C6 total wt % 5.2 4.5 4.5 0 0 C2 total wt % 3.5 1.5 10 8 100 C6(XCS) wt % 3.7 n.d. n.d. 0 0 C2(XCS) wt % 4.7 n.d. n.d. 15.7 100 Flexural modulus MPa 588 535 563 467 331 Charpy NIS 23° C. kJ/m.sup.2 7.4 6.5 6.2 76.8 72.5 Charpy NIS −20° C. kJ/m.sup.2 1.06 n.d. n.d. 1.07 n.d. Haze 1 mm % 30.0 29.0 26.5 28.5 48.0 Bottle (0.3 mm) Haze b.s. % 13 13 11 32 24 Clarity b.s. % 67 60 63 62 89 Haze a.s. % 16 14 10 26 33 Clarity a.s. % 68 61 60 66 86 a.s.: after sterilization b.s.: before sterilization

(70) As can be seen from the examples, the propylene copolymer (a) comprising 1-hexene as comonomer is an excellent matrix for making transparent heterophasic polypropylene compositions which have improved sterilization resistance (sufficiently high melting temperature) and optical properties (low haze of bottles before and after sterilization). The polypropylene compositions according to the present invention are accordingly perfectly applicable for blow molding applications, in particular for use in the blow-fill-seal process for preparing bottles.