PROCESS FOR PREPARING A CAP OR CLOSURE

Abstract

A process for producing a cap or closure comprising obtaining a polypropylene composition by sequential polymerization comprising the steps: A) polymerizing in a first reactor, preferably a slurry reactor, in the presence of a Ziegler-Natta catalyst monomers comprising propylene and optionally one or more comonomers selected from ethylene and C4-C10 alpha-olefins, to obtain a first propylene polymer fraction having a comonomer content in the range of 0.0 to 1.8 wt %, and a MFR2 in the range of from 12.0 to 40.0 g/10 min, as measured according to ISO 1133 at 230° C. under a load of 2.16 kg; B) polymerizing in a second reactor, preferably a first gas-phase reactor, monomers comprising propylene and one or more comonomers selected from ethylene and C4-C10 alpha-olefins, in the presence of the first propylene polymer fraction, to obtain a second propylene polymer fraction, wherein the polypropylene composition comprising said first and second propylene polymer fractions has an MFR2 in the range of from 12.0 to 60.0 g/10 min, as measured according to ISO 1133 at 230° C. under a load of 2.16 kg, has a comonomer content in the range of from 2.2 to 5.0 wt % and wherein the ratio of the comonomer content of component A) to the comonomer content of the polypropylene composition is 0.35 or less, C) melting, extruding and moulding the polypropylene composition in the presence of at least one nucleating agent to prepare a cap or closure; and D) exposing the cap or closure obtained in step (C) to a cooling rate of 50 K/s or more.

Claims

1. A process for producing a cap or closure comprising obtaining a polypropylene composition by sequential polymerization comprising the steps: A) polymerizing in a first reactor, preferably a slurry reactor, in the presence of a Ziegler-Natta catalyst, monomers comprising propylene and optionally one or more comonomers selected from ethylene and C4-C10 alpha-olefins, to obtain a first propylene polymer fraction having a comonomer content in the range of 0.0 to 1.8 wt %, and a MFR2 in the range of from 12.0 to 40.0 g/10 min, as measured according to ISO 1133 at 230° C. under a load of 2.16 kg; B) polymerizing in a second reactor, preferably a first gas-phase reactor, monomers comprising propylene and one or more comonomers selected from ethylene and C4-C10 alpha-olefins, in the presence of the first propylene polymer fraction, to obtain a second propylene polymer fraction, wherein the polypropylene composition comprising said first and second propylene polymer fractions has an MFR2 in the range of from 12.0 to 60.0 g/10 min, as measured according to ISO 1133 at 230° C. under a load of 2.16 kg, has a comonomer content in the range of from 2.2 to 5.0 wt % and wherein the ratio of the comonomer content of component A) to the comonomer content of the polypropylene composition is 0.35 or less, C) melting, extruding and moulding the polypropylene composition in the presence of at least one nucleating agent to prepare a cap or closure; and D) exposing the cap or closure obtained in step (C) to a cooling rate of 50 K/s or more.

2. A process for producing a cap or closure comprising obtaining a polypropylene composition by sequential polymerization comprising: A) polymerizing in a first reactor, preferably a slurry reactor, in the presence of a Ziegler-Natta catalyst, monomers comprising propylene and optionally one or more comonomers selected from ethylene and C4-C10 alpha olefins, to obtain a first propylene polymer fraction having a comonomer content in the range of 0.0 to 1.8 wt %, and a MFR2 in the range of from 12.0 to 40.0 g/10 min, as measured according to ISO 1133 at 230° C. under a load of 2.16 kg; (B) polymerizing in a second reactor, preferably a first gas-phase reactor, monomers comprising propylene and one or more comonomers selected from ethylene and optionally C4-C10 alpha olefins, in the presence of the first propylene polymer fraction, to obtain a second propylene polymer fraction, (C) polymerizing in a third reactor, preferably a second gas-phase reactor, monomers comprising propylene and one or more comonomers selected from ethylene and optionally C4-C10 alpha olefins, in the presence of the second propylene polymer fraction to obtain a third propylene polymer fraction; wherein the polypropylene composition comprising said first, second and third propylene polymer fractions has an MFR2 in the range of from 12.0 to 60.0 g/10 min, as measured according to ISO 1133 at 230° C. under a load of 2.16 kg, has a comonomer content in the range of from 2.2 to 5.0 wt % and wherein the ratio of the comonomer content of component A) to the comonomer content of the polypropylene composition is 0.35 or less, D) melting, extruding and moulding the polypropylene composition in the presence of at least one nucleating agent to prepare a cap or closure; and E) exposing the cap or closure obtained in step (D) to a cooling rate of 50 K/s or more.

3. The process according to claim 1 or 2, wherein the polymerization is carried out in the presence of a Ziegler-Natta catalyst which is free of a phthalic compound.

4. The process according to any one of the preceding claims, wherein the comonomers are selected from solely ethylene.

5. The process according to any one of the preceding claims, wherein the comonomer content of the polypropylene composition is in the range of 2.2 to 4.5 wt %.

6. The process according to any one of the preceding claims, wherein the nucleating agent is present in the range of from 0.01 to 1.0 wt %, relative to the total amount of polypropylene composition.

7. The process according to any one of the preceding claims, wherein said polypropylene composition has a crystallisation temperature (Tc) of at least 55° C. when subjected to a cooling rate of 100 K/s.; and a crystallisation temperature (Tc) of at least 40° C. when subjected to a cooling rate of 300 K/s.

8. A process as claimed in any preceding claim wherein the cooling rate is 100 to 600 K/s, preferably 100 to 300 K/s.

9. A process as claimed in any preceding claim wherein the melting step is effected at a temperature of at least 200° C.

10. A process as claimed in any preceding claim wherein the moulding in step C) or D) is effected in a mould and after cooling step D) or E), the cap or closure is ejected from the mould and a new cap or closure is then formed in the mould and subjected to cooling step D) or E).

11. A process as claimed in claim 10 wherein the cycle time for each cap to be moulded, cooled, and ejected from the mould is 6.0 secs or less, e.g. 4.7 to 6.0 secs.

12. A cap or closure comprising polypropylene composition and at least one nucleating agent said polypropylene composition having a first homo or copolymer fraction, a second copolymer fraction and optionally a third copolymer fraction, said polypropylene composition having an ethylene content of 2.2 to 5.0 wt % and wherein said polypropylene composition has a crystallisation temperature (Tc) of at least 90° C. when subjected to a cooling rate of 10 K/s. a crystallisation temperature (Tc) of at least 55° C. when subjected to a cooling rate of 100 K/s.; and a crystallisation temperature (Tc) of at least 40° C. when subjected to a cooling rate of 300 K/s.

13. A cap or closure as claimed in claim 12 wherein the polypropylene composition has an MFR2 in the range of from 12.0 to 60.0 g/10 min, as measured according to ISO 1133 at 230° C. under a load of 2.16 kg, and wherein the ratio of the comonomer content of the first homo or copolymer fraction to the comonomer content of the polypropylene composition is 0.35 or less.

14. A cap or closure as claimed in claim 12 or 13 wherein said polypropylene composition comprises a first homo or copolymer fraction, a second copolymer fraction and a third copolymer fraction.

15. A process for producing a cap or closure comprising obtaining a polypropylene composition comprising a nucleating agent and a polypropylene composition having a first homo or copolymer fraction, a second copolymer fraction and optionally a third copolymer fraction, said polypropylene composition having an ethylene content of 2.2 to 5.0 wt % and, wherein said polypropylene composition has a crystallisation temperature (Tc) of at least 90° C. when subjected to a cooling rate of 10 K/s. a crystallisation temperature (Tc) of at least 55° C. when subjected to a cooling rate of 100 K/s.; and a crystallisation temperature (Tc) of at least 40° C. when subjected to a cooling rate of 300 K/s; melting, extruding and moulding the polypropylene composition in the presence of the at least one nucleating agent to prepare a cap or closure; and exposing the cap or closure obtained to a cooling rate of 100 K/s or more.

16. A cap or closure obtained by a process according to claims 1 to 11, such as a screw cap.

17. Use of a polypropylene composition and at least one nucleating agent said polypropylene composition having a first homo or copolymer fraction, a second copolymer fraction and optionally a third copolymer fraction, said polypropylene composition having an ethylene content of 2.2 to 5.0 wt % and, wherein said polypropylene composition has a crystallisation temperature (Tc) of at least 90° C. when subjected to a cooling rate of 10 K/s. a crystallisation temperature (Tc) of at least 55° C. when subjected to a cooling rate of 100 K/s.; and a crystallisation temperature (Tc) of at least 40° C. when subjected to a cooling rate of 300 K/s; to reduce the cycle time in cap or closure production.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0204] FIG. 1 shows the relationship between crystallsiaiton temperature and cooling rate for the inventive and comparative examples.

[0205] FIG. 2(a) is a Schematic diagram of the CRYSTEX QC instrument and FIG. 2(b) shows elution of the EP copolymer sample and obtained soluble and crystalline fractions in the TREF column (column filled with inert material e.g. glass beads) (see Del Hierro, P.; Ortin, A.; Monrabal, B.; ‘Soluble Fraction Analysis in polypropylene, The Column Advanstar Publications, February 2014. Pages 18-23).

EXAMPLES

I. Measuring Methods

[0206] a) Melt Flow Rate

[0207] 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 is determined ata temperature of 230° C. and under a load of 2.16 kg.

[0208] b) DSC Analysis

[0209] The crystallisation temperature is measured with a TA Instrument Q2000 differential scanning calorimetry device (DSC) according to ISO 11357/3 on 5 to 10 mg samples, under 50 mL/min of nitrogen atmosphere. Crystallisation temperatures were obtained in a heat/cool/heat cycle with a scan rate of 10° C./min between 30° C. and 225° C. Crystallisation temperatures were taken as the peaks of the endotherms and exotherms in the cooling step and the second heating step respectively.

Fast Scanning Calorimetry (FSC)

[0210] A power-compensation-type differential scanning calorimeter Flash DSC1 from MettlerToledo was used to analyze isothermally and non-isothermally the crystallization behavior in the range of cooling rates from 10° to 10.sup.3 K s−1. The instrument was attached to a Huber intracooler TC45, to allow cooling down to about −100° C. The preparation of samples includes cutting of thin sections with thickness of 10 to 15 pm from the surface of pellets. The specimens were heated to 200° C., kept at this temperature for 0.1 s and cooled at different cooling rates to −33° C. which is below the glass transition temperature of the mobile amorphous fraction of iPP. The furnace of the instrument was purged with dry nitrogen gas at a flow rate of 30 mL /min. The sensors were subjected to the so called conditioning procedure which includes several heating and cooling runs. Afterwards, a temperature correction of the sensor was performed. Before loading the sample a thin layer of silicon oil was spread on the heating area of the sample sensor to improve the thermal contact between the sensor and the sample. The sensors are developed by Xensor Integration (Netherlands). Each sensor is supported by a ceramic base plate for easy handling. The total area of the chip is 5.0×3.3 mm.sup.2; it contains two separate silicon nitride/oxide membranes with an area of 1.7×1.7 mm.sup.2 and a thickness of 2.1 mm each, being surrounded by a silicon frame of 300 μm thickness, serving as a heat sink. In the present work additional calibrations were not performed. Further details to the technique as such are given here: [0211] E. lervolino, A. van Herwaarden, F. van Herwaarden, E. van de Kerkhof, P. van Grinsven, A. Leenaers, V. Mathot, P. Sarro. Temperature calibration and electrical characterization of the differential scanning calorimeter chip UFS1 for the Mettler-Toledo Flash DSC 1. Thermochim. Acta 522, 53-59 (2011). V. Mathot, M. Pyda, T. Pijpers, G. Poel, E. van de Kerkhof, S. van Herwaarden, F. van Herwaarden, A. Leenaers. The Flash DSC 1, a power compensation twin-type, chip-based fast scanning calorimeter (FSC): First findings of polymers. Thermochim. Acta 552, 36-45 (2011). [0212] M. van Drongelen, T. Meijer-Vissers, D. Cavallo, G. Portale, G. Vanden Poel, R. Androsch R. Microfocus wide-angle X-ray scattering of polymers crystallized in a fast scanning chip calorimeter. Thermochim Acta 563, 33-37 (2013).

[0213] c) Comonomer Content

Poly(propylene-co-ethylene)—Ethylene Content by IR Spectroscopy

[0214] Quantitative infrared (IR) spectroscopy was used to quantify the ethylene content of the poly(ethylene-co-propene) copolymers through calibration to a primary method.

[0215] Calibration was facilitated through the use of a set of in-house non-commercial calibration standards of known ethylene contents determined by quantitative .sup.13C solution-state nuclear magnetic resonance (NMR) spectroscopy. The calibration procedure was undertaken in the conventional manner well documented in the literature. The calibration set consisted of 38 calibration standards with ethylene contents ranging 0.2-75.0 wt % produced at either pilot or full scale under a variety of conditions. The calibration set was selected to reflect the typical variety of copolymers encountered by the final quantitative IR spectroscopy method.

[0216] Quantitative IR spectra were recorded in the solid-state using a Bruker Vertex 70 FTIR spectrometer. Spectra were recorded on 25×25 mm square films of 300 um thickness prepared by compression moulding at 180-210° C. and 4-6 mPa. For samples with very high ethylene contents (>50 mol %) 100 um thick films were used. Standard transmission FTIR spectroscopy was employed using a spectral range of 5000-500 cm.sup.−1, an aperture of 6 mm, a spectral resolution of 2 cm.sup.−1, 16 background scans, 16 spectrum scans, an interferogram zero filling factor of 64 and Blackmann-Harris 3-term apodisation.

[0217] Quantitative analysis was undertaken using the total area of the CH.sub.2 rocking deformations at 730 and 720 cm.sup.−1 (A.sub.Q) corresponding to (CH.sub.2)>.sub.2 structural units (integration method G, limits 762 and 694 cm.sup.−1). The quantitative band was normalised to the area of the CH band at 4323 cm.sup.−1 (AR) corresponding to CH structural units (integration method G, limits 4650, 4007 cm.sup.−1). The ethylene content in units of weight percent was then predicted from the normalised absorption (A.sub.Q/A.sub.R) using a quadratic calibration curve. The calibration curve having previously been constructed by ordinary least squares (OLS) regression of the normalised absorptions and primary comonomer contents measured on the calibration set.

Poly(propylene-co-ethylene)—Ethylene Content for Calibration Using .sup.13C NMR Spectroscopy

[0218] Quantitative .sup.13C{.sup.1H} NMR spectra were recorded in the solution-state using a Bruker Avance 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 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 (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 (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. Characteristic signals corresponding to the incorporation of ethylene were observed (Cheng, H. N., Macromolecules 17 (1984), 1950) and the comonomer fraction calculated as the fraction of ethylene in the polymer with respect to all monomer in the polymer: fE=(E/(P+E) The comonomer fraction was quantified using the method of Wang et. al. (VVang, 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. The mole percent comonomer incorporation was calculated from the mole fraction: E [mol %]=100*fE. The weight percent comonomer incorporation was calculated from the mole fraction: E [wt %]=100*(fE*28.06)/((fE*28.06)+((1−fE)*42.08))

[0219] d) Xylene Soluble Content (XCS, Wt %)

[0220] The content of the polymer soluble in xylene is determined according to ISO 16152; 5.sup.th edition; 2005-07-01 at 25° C.

[0221] e) Tensile Modulus

[0222] Tensile Modulus is measured according to ISO 527-1:2012/IS0527-2:2012 at 23° C. and at a cross head speed=50 mm/min; using injection moulded test specimens as described in EN ISO 1873-2 (dog bone shape, 4 mm thickness).

[0223] f) Charpy Notched Impact

[0224] Charpy notched impact strength is determined according to ISO 179/1eA at 23° C. on injection moulded test specimens as described in EN ISO 1873-2 (80×10×4 mm).

[0225] g) Haze

[0226] Haze is determined according to ASTM D1003 on injection moulded plaques having 1 mm thickness and 60×60 mm.sup.2 area produced as described in EN ISO 1873-2.

[0227] h) Crystex Analysis

Crystalline and Soluble Fractions Method

[0228] The crystalline (CF) and soluble fractions (SF) of the polypropylene (PP) compositions as well as the comonomer content and intrinsic viscosities of the respective fractions were analysed by the CRYSTEX QC, Polymer Char (Valencia, Spain).

[0229] A schematic representation of the CRYSTEX QC instrument is shown in FIG. 2a. The crystalline and amorphous fractions are separated through temperature cycles of dissolution at 160° C., crystallization at 40° C. and re-dissolution in a 1,2,4-trichlorobenzene (1,2,4-TCB) at 160° C. as shown in FIG. 1b. Quantification of SF and CF and determination of ethylene content (C2) are achieved by means of an infrared detector (IR4) and an online 2-capillary viscometer which is used for the determination of the intrinsic viscosity (IV).

[0230] The IR4 detector is a multiple wavelength detector detecting IR absorbance at two different bands (CH3 and CH2) for the determination of the concentration and the Ethylene content in Ethylene-Propylene copolymers. 1R4 detector is calibrated with series of 8 EP copolymers with known Ethylene content in the range of 2 wt.-% to 69 wt.-% (determined by 13C-NMR) and various concentration between 2 and 13 mg/ml for each used EP copolymer used for calibration.

[0231] The amount of Soluble fraction (SF) and Crystalline Fraction (CF) are correlated through the XS calibration to the “Xylene Cold Soluble” (XCS) quantity and respectively Xylene Cold Insoluble (XCI) fractions, determined according to standard gravimetric method as per ISO16152. XS calibration is achieved by testing various EP copolymers with XS content in the range 2-31 Wt %.

[0232] The intrinsic viscosity (IV) of the parent EP copolymer and its soluble and crystalline fractions are determined with a use of an online 2-capillary viscometer and are correlated to corresponding IV's determined by standard method in decalin according to ISO 1628. Calibration is achieved with various EP PP copolymers with IV=2-4 dL/g.

[0233] A sample of the PP composition to be analysed is weighed out in concentrations of 10 mg/ml to 20 mg/ml. After automated filling of the vial with 1,2,4-TCB containing 250 mg/l 2,6-tert-butyl-4-methylphenol (BHT) as antioxidant, the sample is dissolved at 160° C. until complete dissolution is achieved, usually for 60 min, with constant stirring of 800 rpm.

[0234] As shown in a FIGS. 2a and 2b, a defined volume of the sample solution is injected into the column filled with inert support where the crystallization of the sample and separation of the soluble fraction from the crystalline part is taking place. This process is repeated two times. During the first injection the whole sample is measured at high temperature, determining the IV[dl/g] and the C2[wt %] of the PP composition. During the second injection the soluble fraction (at low temperature) and the crystalline fraction (at high temperature) with the crystallization cycle are measured (Wt % SF, Wt % C2, IV).

EP means ethylene propylene copolymer.
PP means polypropylene.

II. Inventive Example

[0235] a) Catalyst ppreparation

[0236] For the preparation of the catalyst 3.4 litre of 2-ethylhexanol and 810 ml of propylene glycol butyl monoether (in a molar ratio 4/1) were added to a 20.0 l reactor. Then 7.8 litre of a 20.0% solution in toluene of BEM (butyl ethyl magnesium) provided by Crompton GmbH, were slowly added to the well stirred alcohol mixture. During the addition, the temperature was kept at 10.0° C. After addition, the temperature of the reaction mixture was raised to 60.0° 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.

[0237] 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 the catalyst component.

[0238] 19.5 ml of titanium tetrachloride was placed in a 300 ml reactor equipped with a mechanical stirrer at 25.0° C. Mixing speed was adjusted to 170 rpm. 26.0 g of Mg-complex prepared above was added within 30 minutes keeping the temperature at 25.0° C. 3.0 ml of Viscoplex® 1-254 and 1.0 ml of a toluene solution with 2 mg Necadd 447™ was added. Then 24.0 ml of heptane was added to form an emulsion. Mixing was continued for 30 minutes at 25.0° C., after which the reactor temperature was raised to 90.0° C. within 30 minutes. The reaction mixture was stirred for a further 30 minutes at 90.0° C. Afterwards stirring was stopped and the reaction mixture was allowed to settle for 15 minutes at 90.0° C. The solid material was washed 5 times: washings were made at 80.0° C. under stirring for 30 min with 170 rpm. After stirring was stopped the reaction mixture was allowed to settle for 20-30 minutes and followed by siphoning.

[0239] Wash 1: washing was made with a mixture of 100 ml of toluene and 1 ml donor

[0240] Wash 2: washing was made with a mixture of 30 ml of TiCl4 and 1 ml of donor.

[0241] Wash 3: washing was made with 100 ml of toluene.

[0242] Wash 4: washing was made with 60 ml of heptane.

[0243] Wash 5: washing was made with 60 ml of heptane under 10 minutes stirring.

[0244] Afterwards stirring was stopped and the reaction mixture was allowed to settle for 10 minutes while decreasing the temperature to 70° C. with subsequent siphoning, followed by N.sub.2 sparging for 20 minutes to yield an air sensitive powder.

[0245] Inventive example (IE) was produced in a pilot plant with a prepolymerization reactor, one slurry loop reactor and two gas phase reactors. The solid catalyst component described above along with triethyl-aluminium (TEAL) as co-catalyst and dicyclopentyl dimethoxy silane (D-donor) as external donor, were used in the inventive process.

[0246] The polymerization process conditions and properties of the propylene polymer fractions are described in Table 1.

[0247] The polypropylene composition is then extruded with a nucleating agent in a co-rotating twin screw extruder type Coperion ZSK 40 (screw diameter 40 mm, L/D ratio 38). The temperatures in the extruder were in the range of 190-230° C. In the inventive example, 0.05 wt % of Irganox 1010 (Pentaerythrityl-tetrakis(3-(3′,5′-di-tert. butyl-4-hydroxyphenyl)-propionate, CAS No. 6683-19-8, commercially available from BASF AG, Germany), 0.05 wt % of Irgafos 168 (Tris (2,4-di-t-butylphenyl) phosphite, CAS No. 31570-04-4, commercially available from BASF AG, Germany), 0.10 wt % of Calcium stearate (CAS. No. 1592-23-0, commercially available under the trade name Ceasit FI from Baerlocher GmbH, Germany) and 0.06 wt % of Glycerol monostearate (CAS No. 97593-29-8, commercially available with 90% purity under the trade name Grindsted PS 426 from Danisco A/S, Denmark), 0.17 wt % Millad 3988 (CAS No. 135861-56-2, Milliken) were added to the extruder as additives. 0.3 ppm of Poly Vinyl Cyclo Hexane (PVCH) was added via a nucleating masterbatch

Said nucleating masterbatch is a PP-homopolymer, MFR 20, and comprises ca 15 ppm of PVCH as polymeric nucleating agent.

[0248] Following the extrusion step and after solidification of the strands in a water bath, the resulting polypropylene composition was pelletized in a strand pelletizer.

TABLE-US-00001 TABLE 1 Polymerization process conditions and properties of the propylene polymer fractions IE1 Pre-polymerization reactor Temperature [° C.] 30 Catalyst feed [g/h] 4.4 TEAL/propylene [g/t propylene] 170 Residence Time [min] 20 Loop reactor (first propylene polymer fraction) Temperature [° C.] 70 Pressure [kPa] 5400 Split [%] 46.8 H.sub.2/C.sub.3 ratio [mol/kmol] 1.9 C.sub.2/C.sub.3 ratio [mol/kmol] 3.2 MFR.sub.2 [g/10 min] 22 C.sub.2 content after loop [wt %] 0.5 reactor First gas-phase reactor - Temperature [° C.] 80 Pressure [kPa] 1820 Split [%] 43.2 H.sub.2/C.sub.3 ratio [mol/kmol] 27.1 C.sub.2/C.sub.3 ratio [mol/kmol] 7.9 MFR.sub.2 [g/10 min] 17.4 C.sub.2 content after 1.sup.st gas [wt %] 1.4 hase reactor Second gas-phase reactor - Temperature [° C.] 80 Pressure [kPa] 2500 Split [%] 10 H.sub.2/C.sub.3 ratio [mol/kmol] 27.5 C.sub.2/C.sub.3 ratio [mol/kmol] 68.9 MFR.sub.2 [g/10 min] 17.3 C.sub.2 content final [wt %] 2.5 C2 ratio (final/fraction 1) 0.2 *Split relates to the amount of propylene polymer produced in each specific reactor.

[0249] Its properties are compared to RE420MO (a polypropylene random copolymer of MFR 13 g/10 min and IE2 of WO2009/021686).

[0250] Results are presented in FIG. 1 and table 2. As can be seen in FIG. 1, the inventive example shows mono-crystalline behaviour (no transition to mesophase) with cooling rate up to 600 k/s.

[0251] The comparative example has a much lower cooling rate. Starting from 50 K/s, a new crystallisation peak appears at a much lower Tc which is the crystallisation of the mesophase. Crystallisation stops at the cooling rate of 200 k/s.

[0252] IE1 has much faster crystallisation rate measured as Tc with a broader cooling rate range.

TABLE-US-00002 TABLE 2 Polypropylene composition properties. CE IE1 MFR-final g/10 min 13 17.3 Tensile modulus MPa 1124 1398 Tensile strength MPa 29 33 NIS-B kJ/m2 6.2 5.8 Haze-1 mm % 16 18.1 SF wt % 8.02 8.2 C2 wt % 3.03 2.5 C2(SF) wt % 15.3 12.4 C2(CF) wt % 2.5 1.7 IV dl/g 1.7 1.6 IV(SF) dl/g 0.5 0.6 IV(CF) dl/g 1.8 1.7 Top load force on cap N 1553 1741

[0253] Screw caps type PCO 1810 were made by injection moulding the polypropylene composition on an ENGEL Speed 180/45 injection moulding machine, equipped with a 12 cavity tool for screw caps.

[0254] The tool was supplied by Husky/KTW.

[0255] Injection moulding was done with an injection speed: 170 cm.sup.3/sec, a holding pressure. 860 bar and melt temperature of 230° C. or 240° C. and tool temperature of 12° C.

Cycle and cooling times are given in Table 3 to 5.

TABLE-US-00003 TABLE 3 Crystallisation temperatures at fast cooling rates Cooling rate [K/sec] CE (RE420MO) IE K/s Tc. mono Tc. meso Tc. mono 0.05 124 0.16 120 127 0.5 116 1 102 116 2 97 113 3 94 112 4 91 110 5 90 108 6 89 108 7 88 106 8 86 106 9 85 105 10 84 104 20 81 99 30 75 96 40 72 93 50 70 26 91 60 65 23 89 70 59 21 87 80 58 19 85 90 55 17 84 100 54 15 83 200 52 11 72 300 63 400 58 500 57 600 53

TABLE-US-00004 TABLE 4 Processing behaviour of the Inventive Example at various cycle times and mass temperatures Inventive example Cooling Cycle-time time Mass Temperature Mass Temperature [sec] [sec.] 240° C. 230° C. 5.1 2.5 Good (minimal Angel Good (minimal Angel Hair & high tips) Hair & high tips) 4.9 2.3 Good (High Tips) Good (minimal Angel Hair & high tips) 4.7 2.1 sometimes demoulding sometimes demoulding problems problems 4.5 1.9 Demoulding problems Demoulding problems (ring tears off) 4.3 1.7 Not Possible Demoulding problems (ring tears off)

TABLE-US-00005 TABLE 5 Processing behaviour of the comparative Example at various cycle times and mass temperatures Comparative Example Cooling Cycle-time time Mass Temperature Mass Temperature [sec] [sec.] 240° C. 230° C. 5.1 2.5 Good (minimal Angel Good (minimal Angel Hair & high tips) Hair & high tips) 4.9 2.3 Demoulding Good (minimal Angel problems Hair & high tips) 4.7 2.1 major demoulding Demoulding problems (ring problems tears off) 4.5 1.9 Not Possible major demoulding problems (ring tears off) 4.3 1.7 Not Possible Not Possible