Polypropylene composition with excellent surface appearance

Abstract

The present invention is directed to a heterophasic polypropylene composition (HC) comprising a modified polypropylene composition (mPP), a process for preparing said heterophasic polypropylene composition (HC) and an article comprising said heterophasic polypropylene composition (HC). The present invention is further directed to the use of a composition comprising a peroxide (PO) and a crosslinking agent (CA) to reduce tigerskin of a polypropylene composition (PP).

Claims

1. A heterophasic polypropylene composition (HC) comprising a modified polypropylene composition (mPP), wherein said modified polypropylene composition (mPP) is obtained by treatment of a polypropylene composition (PP) with a peroxide (PO) and a crosslinking agent (CA), said polypropylene composition (PP) comprising: i) a propylene polymer (PP1), and ii) a plastomer (PL) being a copolymer of ethylene and at least one C4 to C20 α-olefin, wherein; said heterophasic polypropylene composition (HC) has a ratio XCS/XHU in the range of 0.6 to 2.6, wherein XCS is the xylene cold soluble content [in wt. %] of the heterophasic polypropylene composition (HC) and XHU is the xylene hot insoluble content [in wt. %] of the heterophasic polypropylene composition (HC), and wherein the weight ratio of the propylene polymer (PP1) and the plastomer (PL) [w(PP1)/w(PL)] in the modified polypropylene composition (mPP) is from above 1.0 to 3.0, wherein w(PP1) is the overall amount of the propylene polymer (PP1) (in wt. %) within the modified polypropylene composition (mPP) and w(PL) is the overall amount of the plastomer (PL) (in wt. %) within the modified polypropylene composition (mPP).

2. The heterophasic polypropylene composition (HC) according to claim 1, having a xylene hot insoluble content (XHU) in the range of 11.0 to 25.0 wt. %.

3. The heterophasic polypropylene composition (HC) according to claim 1, having a xylene cold soluble content (XCS) determined according ISO 16152 equal or below 29.0 wt. %.

4. The heterophasic polypropylene composition (HC) according to claim 1, having a melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 of at least 10.0 g/10 min.

5. The heterophasic polypropylene composition (HC) according to claim 1, wherein the weight ratio of the propylene polymer (PP1) and the plastomer (PL) [w(PP1)/w(PL)] in the modified polypropylene composition (mPP) is from 1.1 to 1.8.

6. The heterophasic polypropylene composition (HC) according to claim 1, wherein the polypropylene composition (PP) comprises: i) at least 10.0 wt. % of the propylene polymer (PP1), and ii) at least 5.0 wt. % of the plastomer (PL), based on the overall amount of the polypropylene composition (PP).

7. The heterophasic polypropylene composition (HC) according to claim 1, wherein the propylene polymer (PP1) i) is a propylene homopolymer (H-PP1), and/or ii) has a melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 equal or below 35.0 g/10 min.

8. The heterophasic polypropylene composition (HC) according to claim 1, wherein the propylene polymer (PP1) has: i) a first polypropylene fraction (PP1a) having a melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 in the range of 5.0 to 20.0 g/10 min and ii) a second polypropylene fraction (PP1b) having a melt flow rate MFR.sub.2 (230° C., 2.16 kg) determined according to ISO 1133 in the range of 30.0 to 65.0 g/10 min.

9. The heterophasic polypropylene composition (HC) according to claim 1, wherein the plastomer (PL) is a copolymer of ethylene and 1-butene or 1-octene.

10. The heterophasic polypropylene composition (HC) according to claim 1, wherein the plastomer (PL) has: (a) a melt flow rate MFR (190° C., 2.16 kg) measured according to ISO 1133 below 30 g/10 min, (b) a comonomer content, based on the total weight of the plastomer (PL), in the range of 8.0 to 35.0 mol %, and (c) a density below 0.880 g/cm.sup.3.

11. The heterophasic polypropylene composition (HC) according to claim 1, wherein the peroxide (PO) is an alkyl or aryl peroxide.

12. The heterophasic polypropylene composition (HC) according to claim 1, wherein the crosslinking agent is a compound of formula (I): ##STR00005## wherein M.sup.2+is a divalent metal ion and R.sup.1 is hydrogen or methyl.

13. A moulded article, comprising the heterophasic polypropylene composition (HC) according to claim 1.

14. A process for the preparation of the heterophasic composition (HC) according to claim 12, wherein the polypropylene composition (PP) comprising the propylene polymer (PP1), the plastomer (PL) and optionally the propylene homopolymer (H-PP) is extruded in an extruder in the presence of the peroxide (PO) and the crosslinker (CA).

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) Quantification of Polymer Microstructure by NMR Spectroscopy

(3) Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content 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 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.

(4) 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).

(5) 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.

(6) 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.

(7) 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(5ββ+5βγ+5βδ+0.5(Sαβ+Sαγ))
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))
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.

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

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

(10) 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.

(11) Calculation of melt flow rate MFR.sub.2 (230° C.) of the second polypropylene fraction (PP1b), i.e. the polymer fraction produced in the second reactor (R2), of the propylene polymer (PP1):

(12) $\mathrm{MFR}\left(\mathrm{PP}1b\right)={10}^{\left[\frac{\log \left(\mathrm{MFR}\left(\mathrm{PP}1\right)\right)-w\left(\mathrm{PP}1a\right)\times \log \left(\mathrm{MFR}\left(\mathrm{PP}1a\right)\right)}{w\left(\mathrm{PP}1b\right)}\right]}$
wherein w(PP1a) is the weight fraction [in wt.-%] of the first propylene polymer fraction, i.e. the polymer produced in the first reactor (R1), w(PP1b) is the weight fraction [in wt.-%] of the first second propylene polymer fraction, i.e. the polymer produced in the second reactor (R2), MFR(PP1a) is the melt flow rate MFR.sub.2 (230° C.) [in g/10 min] of the first propylene polymer fraction, i.e. the polymer produced in the first reactor (R1), MFR(PP1) is the melt flow rate MFR.sub.2 (230° C.) [in g/10 min] of the first and second propylene polymer fractions, i.e. the polymer produced in the first and second reactor (R1+R2), MFR(PP1b) is the calculated melt flow rate MFR.sub.2 (230° C.) [in g/10 min] of the second propylene polymer fraction, i.e. the polymer produced in the second reactor (R2).
Quantification of Comonomer Content in Plastomer by NMR Spectroscopy

(13) Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers. Quantitative .sup.13C {.sup.1H}NMR spectra recorded in the molten-state using a Bruker Advance 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 150° 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 transient NOE at short recycle delays of 3s [Pollard, M., Klimke, K., Graf, R., Spiess, H. W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813; Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382] 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, S1, S198]. A total of 1024 (1 k) transients were acquired per spectrum. This setup was chosen due its high sensitivity towards low comonomer contents. Quantitative .sup.13C {.sup.1H}NMR spectra were processed, integrated and quantitative properties determined using custom spectral analysis automation programs. All chemical shifts are internally referenced to the bulk methylene signal (δ+) at 30.00 ppm [J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201].

(14) Characteristic signals corresponding to the incorporation of comonomers were observed [J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201] and all contents calculated with respect to all other monomers present in the polymer.

(15) [For further information see Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225 and Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128]

(16) Comonomer content in plastomer (PL) was measured in a known manner based on Fourier transform infrared spectroscopy (FTIR) calibrated with .sup.13C-NMR, using Nicolet Magna 550 IR spectrometer together with Nicolet Omnic FTIR software. Films having a thickness of about 250 μm were compression molded from the samples. Similar films were made from calibration samples having a known content of the comonomer. The comonomer content was determined from the spectrum from the wave number range of from 1430 to 1100 cm.sup.−1. The absorbance is measured as the height of the peak by selecting the so-called short or long base line or both. The short base line is drawn in about 1410-1320 cm.sup.1 through the minimum points and the long base line about between 1410 and 1220 cm.sup.1. Calibrations need to be done specifically for each base line type. Also, the comonomer content of the unknown sample needs to be within the range of the comonomer contents of the calibration samples.

(17) MFR.sub.2 (230° C.) is measured according to ISO 1133 (230° C., 2.16 kg load).

(18) MFR.sub.2 (190° C.) is measured according to ISO 1133 (190° C., 2.16 kg load).

(19) The xylene cold solubles (XCS, wt.-%): Content of xylene cold solubles (XCS) is determined at 25° C. according to ISO 16152; first edition; 2005-07-01. The part which remains insoluble is the xylene cold insoluble (XCI) fraction.

(20) The xylene hot insolubles (XHU, wt.-%): The gel content is assumed to be identical to the xylene hot insoluble (XHU) fraction, which is determined by extracting 1 g of finely cut polymer sample with 350 ml xylene in a Soxhlet extractor for 5 hours at the boiling temperature. The remaining solid amount is dried at 90° C. and weighed for determining the insolubles amount.

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

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

(23) Flexural Test: The flexural modulus and flexural strength were determined in 3-point-bending according to ISO 178 on injection molded specimens of 80×10×4 mm prepared in accordance with ISO 294-1:1996.

(24) Charpy notched impact strength is determined according to ISO 180/1A at 23° C. by using injection moulded test specimens as described in EN ISO 1873-2 (80×10×4 mm).

(25) Shrinkage: The shrinkage is determined on centre gated, injection moulded circular disks (diameter 180 mm, thickness 3 mm, having a flow angle of 355° and a cut out of 5°). Two specimens are moulded applying two different holding pressure times (10s and 20s respectively). The melt temperature at the gate is 260° C., and the average flow front velocity in the mould 100 mm/s. Tool temperature: 40° C., back pressure: 600 bar.

(26) After conditioning the specimen at room temperature for 96 hours the dimensional changes radial and tangential to the flow direction are measured for both disks. The average of respective values from both disks are reported as final results.

(27) Flow Marks

(28) The tendency to show flow marks was examined with a method as described below. This method is described in detail in WO 2010/149529, which is incorporated herein in its entirety.

(29) An optical measurement system, as described by Sybille Frank et al. in PPS 25 Intern. Conf. Polym. Proc. Soc 2009 or Proceedings of the SPIE, Volume 6831, pp 68130T-68130T-8 (2008) was used for characterizing the surface quality.

(30) This method consists of two aspects:

(31) 1. Image Recording:

(32) The basic principle of the measurement system is to illuminate the plates with a defined light source (LED) in a closed environment and to record an image with a CCD-camera system. A schematic setup is given in Figure 1.

(33) 2. Image Analysis:

(34) The specimen is floodlit from one side and the upwards reflected portion of the light is deflected via two mirrors to a CCD-sensor. The such created grey value image is analyzed in lines. From the recorded deviations of grey values the mean square error (MSE) is calculated allowing a quantification of surface quality, i.e. the larger the MSE value the more pronounced is the surface defect.

(35) Generally, for one and the same material, the tendency to flow marks increases when the injection speed is increased.

(36) For this evaluation plaques 440×148×2.8 mm with grain VW K50 and a filmgate of 1.4 mm were used and were produced with different filling times of 1.5, 3 and 6 sec respectively.

(37) Further conditions:

(38) Melt temperature: 240° C.

(39) Mould temperature 30° C.

(40) Dynamic pressure: 10 bar hydraulic

(41) The smaller the MSE value is at a certain filling time, the smaller is the tendency for flow marks.

(42) The glass transition temperature Tg and the storage modulus G′(23° C.) are determined by dynamic mechanical analysis according to ISO 6721-7. The measurements are done in torsion mode on compression moulded samples (40×10×1 mm.sup.3) between −100° C. and +150° C. with a heating rate of 2° C./min and a frequency of 1 Hz.

2. Examples

(43) Preparation of PP1

(44) Preparation of the Catalyst

(45) First, 0.1 mol of MgCl.sub.2×3 EtOH was suspended under inert conditions in 250 ml of decane in a reactor at atmospheric pressure. The solution was cooled to the temperature of −15° C. and 300 ml of cold TiCl.sub.4 was added while maintaining the temperature at said level. Then, the temperature of the slurry was increased slowly to 20° C. At this temperature, 0.02 mol of dioctylphthalate (DOP) was added to the slurry. After the addition of the phthalate, the temperature was raised to 135° C. during 90 minutes and the slurry was allowed to stand for 60 minutes. Then, another 300 ml of TiCl.sub.4 was added and the temperature was kept at 135° C. for 120 minutes. After this, the catalyst was filtered from the liquid and washed six times with 300 ml heptane at 80° C. Then, the solid catalyst component was filtered and dried. Catalyst and its preparation concept is described in general e.g. in patent publications EP 491566, EP 591224 and EP 586390.

(46) The catalyst was further modified (VCH modification of the catalyst). 35 ml of mineral oil (Paraffinum Liquidum PL68) was added to a 125 ml stainless steel reactor followed by 0.82 g of triethyl aluminum (TEAL) and 0.33 g of dicyclopentyl dimethoxy silane (donor D) under inert conditions at room temperature. After 10 minutes 5.0 g of the catalyst prepared above (Ti content 1.4 wt.-%) was added and after additionally 20 minutes 5.0 g of vinylcyclohexane (VCH) was added. The temperature was increased to 60° C. during 30 minutes and was kept there for 20 hours. Finally, the temperature was decreased to 20° C. and the concentration of unreacted VCH in the oil/catalyst mixture was analysed and was found to be 200 ppm weight.

(47) TABLE-US-00001 TABLE 1 Polymerization of PP1 PP1 Prepoly Residence time [h] 0.38 Temperature [° C.] 30 Co/ED ratio [mol/mol] 11 Co/TC ratio [mol/mol] 180 Loop (R1) Residence time [h] 0.35 Temperature [° C.] 80 H.sub.2/C.sub.3 ratio [mol/kmol] 5 Split [%] 60 MFR [g/10 min] 10 XCS [wt %] 1.0 1.sup.st GPR (R2) Residence time [h] 1.5 Temperature [° C.] 80 Pressure [bar] 24 H.sub.2/C.sub.3 ratio [mol/kmol] 140 Split [%] 40 MFR [g/10 min] 20 XCS [wt %] 2.0

(48) The PP1 powder was stabilized in a twin-screw extruder with a standard additive packing including 0.4 wt.-% Talc (Talc HM 2 by IMI), 0.1 wt % Irganox B 215 FF, and 0.07 wt % calcium stearate supplied by Croda.

(49) Preparation of the Modified Polypropylene Composition (mPP)

Example CE1 (Comparative)

(50) 60.0 wt.-% of PP1 and 40.0 wt.-% of the ethylene-butene copolymer Engage HM 7487 by Dow were melt blended on a co-rotating twin screw extruder. The polymer melt mixture was discharged and pelletized.

Example CE2 (Comparative)

(51) To a mixture of 58.0 wt.-% of PP1 and 40.0 wt.-% of the ethylene-butene copolymer Engage HM 7487 by Dow, 2.0 wt.-% of a masterbatch of 5 wt.-% 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane with polypropylene, were dosed in the main hopper of a twin screw extruder ZSK 18 (screw length 40 D) with a temperature profile 20/190/220/225/230/230/210/200° C. and a screw speed of 300 rpm. The polymer melt mixture was discharged and pelletized.

Example CE3 (Comparative)

(52) To a mixture of 57.0 wt.-% of PP1 and 40.0 wt.-% of the ethylene-butene copolymer Engage HM 7487 by Dow, 3.0 wt.-% of a masterbatch of 5 wt.-% 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane with polypropylene, were dosed in the main hopper of a twin screw extruder ZSK 18 (screw length 40 D) with a temperature profile 20/190/220/225/230/230/210/200° C. and a screw speed of 300 rpm. The polymer melt mixture was discharged and pelletized.

Example CE4 (Comparative)

(53) To a mixture of 56.0 wt.-% of PP1 and 40.0 wt.-% of the ethylene-butene copolymer Engage HM 7487 by Dow, 4.0 wt.-% of a masterbatch of 5 wt.-% 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane with polypropylene, were dosed in the main hopper of a twin screw extruder ZSK 18 (screw length 40 D) with a temperature profile 20/190/220/225/230/230/210/200° C. and a screw speed of 300 rpm. The polymer melt mixture was discharged and pelletized.

Example 1E4 (Inventive)

(54) To a mixture of 48.0 wt.-% of PP1 and 40.0 wt.-% of the ethylene-butene copolymer Engage HM 7487 by Dow, 2.0 wt.-% of a masterbatch of 5 wt.-% 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane with polypropylene, 2.0 wt.-% of zinc diacrylate (Dymalink 633 by Total Cray Valley) and 8.0 wt.-% of a propylene homopolymer (HC001), were dosed in the main hopper of a twin screw extruder ZSK 18 (screw length 40 D) with a temperature profile 20/190/220/225/230/230/210/200° C. and a screw speed of 300 rpm. The polymer melt mixture was discharged and pelletized.

(55) TABLE-US-00002 TABLE 2 Compositions and properties of the comparative and inventive examples of the modified polypropylene composition (mPP) CE1 CE2 CE3 CE4 IE1 PP1 [wt.-%] 60 58 57 56 48 PP2 [wt.-%] 0 0 0 0 8 PL [wt.-%] 40 40 40 40 40 POX PP [wt.-%] 0 2 3 4 2 CA [wt.-%] 0 0 0 0 2 MFR [g/10 min] 7.0 28.9 34.5 38.5 10.4 Flexural modulus [MPa] 1016 759 730 686 631 Flexural strength [MPa] 21.8 16.9 16.4 15.3 13.9 Charpy notched impact [kJ/m.sup.2] 64.8 8.7 10.2 8.6 62.9 strength (+23° C.) Charpy notched impact kJ/m.sup.2] 12.4 6.6 8.2 7.4 nd strength (−20° C.) Mould average shrinkage [%] 1.25 1.76 1.81 1.83 nd MSE [—] 225 6.0 2.4 6.5 3.2 XCS [wt.-%] 41.1 40.4 40.2 40.1 21.7 XHU [wt.-%] 0.01 0.04 0.04 0.05 18.01 IV(XCS) [dl/g] 2.03 1.74 1.76 1.77 1.45 IV(XCI) [dl/g] 1.70 1.07 0.91 0.93 0.76 IV(XCS)/IV(XCI) [—] 1.19 1.62 1.93 1.90 1.90 DMTA tanδ [° C.] −58.1 −56.0 −56.0 −56.0 −56.1 G′(23° C.) DMTA [MPa] 419 322 314 288 245 PP2 is a polypropylene homopolymer for general purpose injection moulding, free of slip and antiblock agents and without calcium stearate, comprising 500 ppm precipitated calcium carbonate (Socal U1S1, distributed by Solvay Chemicals) as particulate acid scavenger, with MFR (230° C./2.16 kg) of 2.0 g/10 min and a density of 905 kg/m.sup.3. PL is the commercial ethylene-butene copolymer Engage HM 7487 by Dow having a density of 0.860 g/cm.sup.3, a melt flow rate MFR.sub.2 (190° C., 2.16 kg) of 2.0 g/10 min and a 1-butene content of 19.1 mol-%. PDX PP is a masterbatch of 5 wt.-% 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane with polypropylene. CA is the zinc diacrylate Dymalink 633 by Total Cray Valley