POLYPROPYLENE COMPOSITION WITH EXCELLENT STIFFNESS AND IMPACT STRENGTH

Abstract

The present invention is directed to a polypropylene composition (C) comprising an α-nucleated heterophasic composition (HECO) comprising a (semi)crystalline polypropylene (PP1), an elastomeric ethylene/propylene copolymer (EPR) and a first α-nucleating agent (NU1), an impact modifier comprising a polyethylene (PE) being a copolymer of ethylene and a C.sub.4-C.sub.12 α-olefin and a second α-nucleating agent (NU2). The present invention is further directed to a method for preparing said polypropylene composition (C) and an article comprising said polypropylene composition (C). The present invention is also directed to the use of a composition comprising a polyethylene (PE) being a copolymer of ethylene and a C.sub.4-C.sub.12 α-olefin and an α-nucleating agent (NU2) as an impact modifier.

Claims

1. A polypropylene composition (C), comprising: (a) at least 80.0 wt.-% of an α-nucleated heterophasic composition (HECO), comprising (a1) a (semi)crystalline polypropylene (PP1), (a2) an elastomeric ethylene/propylene copolymer (EPR) dispersed in said (semi)crystalline polypropylene (PP1), (a3) a first α-nucleating agent (NU1), (b) at least 5.0 wt.-% of a polyethylene (PE) being a copolymer of ethylene and a C.sub.4-C.sub.12 α-olefin, and (c) at least 1.4 wt.-% of a second α-nucleating agent (NU2) which is different from the first α-nucleating agent (NU1), based on the overall weight of the polypropylene composition (C).

2. The polypropylene composition (C) according to claim 1, wherein the heterophasic composition (HECO) has: i) a melt flow rate MFR2 (230° C., 2.16 kg) determined according to ISO 1133 in the range of 5.0 to 40.0 g/10 min, and/or ii) a comonomer content in the range of 2.0 to 15.0 mol.

3. The polypropylene composition (C) according to claim 1, wherein the (semi)crystalline polypropylene (PP1) comprises at least two (semi)crystalline polypropylene fractions which differ in the melt flow rate MFR2 (230° C., 2,16 kg) determined according to ISO 1133.

4. The polypropylene composition (C) according to claim 1, wherein the (semi)crystalline polypropylene (PP1) comprises: (a) a first (semi)crystalline polypropylene fraction (PP1a) having a melt flow rate MFR2 (230° C./2.16 kg) in the range of 30.0 to 120.0 g/10 min, and (b) a second (semi)crystalline polypropylene fraction (PP1b) having a melt flow rate MFR2 (230° C./2.16 kg) in the range of 5.0 to 25.0 g/10 min.

5. The polypropylene composition (C) according to claims claim 1, wherein the heterophasic composition (HECO) has a xylene soluble fraction (XCS) in the range of 5.0 to 30.0 wt.-%.

6. The polypropylene composition (C) according to claim 1, wherein the xylene soluble fraction (XCS) of the heterophasic composition (HECO) has: i) an ethylene content in the range of 25.0 to 60.0 mol-%, and/or ii) an intrinsic viscosity (IV) determined according to DIN ISO 1628/1, October 1999 (in Decalin at 135° C.) in the range of 3.0 to 4.5 dl/g.

7. The polypropylene composition (C) according to claim 1, wherein: i) the first α-nucleating agent (NU1) is a polymeric nucleating agent, and ii) the second α-nucleating agent (NU2) is a non-polymeric nucleating agent.

8. The polypropylene composition (C) according to claim 7, wherein the first α-nucleating agent (NU1) is a polymeric vinylcycloalkane.

9. The polypropylene composition (C) according to claim 7, wherein the second α-nucleating agent (NU2) is selected from the group consisting of talc, salts of diesters of phosphoric acid or mixtures thereof.

10. The polypropylene composition (C) according to claim 1, comprising: (a) 80.0 to 95.0 wt.[[-]]% of the heterophasic composition (HECO), (b) 5.0 to 15.0 wt.[[-]]% of the polyethylene (PE) being a copolymer of ethylene and a C.sub.4-C.sub.12 α-olefin, and (c) 1.4 to 5.0 wt.[[-]]% of the second α-nucleating agent (NU2).

11. The polypropylene composition (C) according to claim 1, wherein the polyethylene (PE) is a copolymer of ethylene and 1-butene.

12. The polypropylene composition (C) according to claim 1, wherein the polyethylene (PE) has: i) a density in the range of 890 to 940 kg/m.sup.3, and/or ii) a melt flow rate MFR5 (190° C., 5.0 kg) determined according to ISO 1133 equal or below 3.0 g/10 min.

13. The polypropylene composition (C) according to claim 1, having: i) a flexural modulus determined according to ISO 178 of at least 1400 MPa, and/or ii) a Charpy notched impact strength determined according to ISO 179/1eA at 23° C. of at least 8.0 kJ/m.sup.2.

14. A method for preparing the polypropylene composition (C) according to claim 1, comprising the steps of: i) preparing the α-nucleated heterophasic propylene copolymer (HECO) in a sequential polymerization process comprising at least three reactors, wherein the (semi)crystalline polypropylene (PP1) is produced in the first and/or second reactor in the presence of the first α-nucleating agent (NU1) and the elastomeric ethylene/propylene copolymer (EPR) is produced in a subsequent reactor, and ii) blending the α-nucleated heterophasic propylene copolymer (HECO) obtained in step i) with the polyethylene (PE) being a copolymer of ethylene and a C.sub.4-C.sub.12 α-olefin and the second α-nucleating agent (NU2).

15. (canceled)

16. An article comprising the polypropylene composition (C) according to claim 1.

17. The article according to claim 16, wherein said article is a car seat, a stroller, a baby walker, a toy, a heavy duty pail or a transport packaging.

18. The polypropylene composition (C) according to claim 1, wherein the (semi)crystalline polypropylene (PP1) is a propylene homopolymer (H-PP) comprising: (a) a first propylene homopolymer fraction (H-PP1a) having a melt flow rate MFR2 (230° C./2.16 kg) in the range of 30.0 to 120.0 g/10 min, and (b) a second propylene homopolymer fraction (H-PP1b) having a melt flow rate MFR2 (230° C./2.16 kg) in the range of 5.0 to 25.0 g/10 min.

Description

EXAMPLES

1. Measuring Methods

[0219] 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. [0220] MFR.sub.2 (230° C.) is measured according to ISO 1133 (230° C., 2.16 kg load). [0221] MFR.sub.5 (190° C.) is measured according to ISO 1133 (190° C., 5.0 kg load). [0222] 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 heterophasic propylene copolymer (HECO):

[00002]$\mathrm{MFR}\left(\mathrm{PP}1b\right)={10}^{\left[\frac{\log \left(\mathrm{MFR}\left(\mathrm{PP}1\right)\right)-w\left(\mathrm{PP}1a\right)x\log \left(\mathrm{MFR}\left(\mathrm{PP}1a\right)\right)}{w\left(\mathrm{PP}1b\right)}\right]}$

wherein [0223] w(PP1a) is the weight fraction [in wt.-%] of the first propylene polymer fraction, i.e. the polymer produced in the first reactor (R1), [0224] 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), [0225] 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), [0226] 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), [0227] 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 Microstructure by NMR Spectroscopy

[0228] 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. 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).

[0229] For polypropylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0230] Characteristic signals corresponding to regio defects (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253; Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157; Cheng, H. N., Macromolecules 17 (1984), 1950) or comonomer were observed.

[0231] The tacticity distribution was quantified through integration of the methyl region between 23.6-19.7 ppm correcting for any sites not related to the stereo sequences of interest (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromoleucles 30 (1997) 6251).

[0232] Specifically the influence of regio defects and comonomer on the quantification of the tacticity distribution was corrected for by subtraction of representative regio defect and comonomer integrals from the specific integral regions of the stereo sequences.

[0233] The isotacticity was determined at the pentad level and reported as the percentage of isotactic pentad (mmmm) sequences with respect to all pentad sequences: [mmmm]% =100*(mmmm/sum of all pentads)

[0234] The presence of 2,1 erythro regio defects was indicated by the presence of the two methyl sites at 17.7 and 17.2 ppm and confirmed by other characteristic sites.

[0235] Characteristic signals corresponding to other types of regio defects were not observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253).

[0236] The amount of 2,1 erythro regio defects was quantified using the average integral of the two characteristic methyl sites at 17.7 and 17.2 ppm:

P.sub.21e=(I.sub.e6+I.sub.e8)/2

[0237] The amount of 1,2 primary inserted propene was quantified based on the methyl region with correction undertaken for sites included in this region not related to primary insertion and for primary insertion sites excluded from this region:

P.sub.12=I.sub.CH3+P.sub.12e

[0238] The total amount of propene was quantified as the sum of primary inserted propene and all other present regio defects:

P.sub.total=P.sub.12+P.sub.21e

[0239] The mole percent of 2,1 erythro regio defects was quantified with respect to all propene:

[21e] mol % =100*(P.sub.21e/P.sub.total)

[0240] For copolymers characteristic signals corresponding to the incorporation of ethylene were observed (Cheng, H. N., Macromolecules 17 (1984), 1950).

[0241] With regio defects also observed (Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253; Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157; Cheng, H. N., Macromolecules 17 (1984), 1950) correction for the influence of such defects on the comonomer content was required.

[0242] 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.1I.sup.-1} 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.

[0243] 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(Sββ+Sβγ+Sβδ+0.5(Sαβ+Sαγ))

[0244] 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.

[0245] The mole percent comonomer incorporation was calculated from the mole fraction:

E[wt %]=100*fE

[0246] The weight percent comonomer incorporation was calculated from the mole fraction:

E[wt %]=100*(fE*28.06)/((fE*28.06)+((1−fE)*42.08))

[0247] 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.

[0248] 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.

[0249] Intrinsic viscosity is measured according to DIN ISO 1628/1, October 1999 (in Decalin at 135° C.).

[0250] Density is measured according to ISO 1183-187. Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

[0251] The xylene solubles (XCS, wt.- %): Content of xylene cold solubles (XCS) is determined at 25° C. according ISO 16152; first edition; 2005-07-01. The part which remains insoluble is the xylene cold insoluble (XCI) fraction.

[0252] DSC analysis, melting temperature (T.sub.m) and crystallization temperature (T.sub.c): 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 C.sub.2 in a heat/cool/heat cycle with a scan rate of 10° C./min in the temperature range of −30 to +225° C. The crystallization temperature (T.sub.c) is determined from the cooling step, while melting temperature (T.sub.m) and melting enthalpy (H.sub.m) are determined from the second heating step. The crystallinity is calculated from the melting enthalpy by assuming an Hm-value of 209 J/g for a fully crystalline polypropylene (see Brandrup, J., Immergut, E. H., Eds. Polymer Handbook, 3rd ed. Wiley, New York, 1989; Chapter 3).

[0253] Yellowness Index (YI) is a number calculated from spectrophotometry data that describes the change in color of a test sample from clear or white towards yellow. This test is most commonly used to evaluate color changes in a material caused by real or simulated outdoor exposure. The spectrophotonietry instrument is a Spectrafiash SF600 with ColorTools software which calculate the yellowness index E 313 according to ASTM E313. On the sample holder and pipe sample is tested.

[0254] The yellowness index is rated as follows:

TABLE-US-00001 Rating 1 Rating 2 Rating 3 Rating 4 YI according to <(−0.9) (−0.9)-1.5 1.5-6.5 >6.5 ASTM E313

[0255] Flexural Modulus: The flexural modulus was 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.

[0256] The impact strength is determined as Charpy Notched Impact Strength according to ISO 179-1 eA at +23° C. and at −20° C. on injection moulded specimens of 80×10×4 mm prepared according to EN ISO 1873-2.

2. Examples

A. Preparation of the Heterophasic Polypropylene Composition

Preparation of the Catalyst

[0257] 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.

[0258] The catalyst was further modified (VCH modification of the catalyst).

[0259] 35 ml of mineral oil (Paraffinum Liquidum PL68) was added to a 125 ml stainless steel reactor followed by 0.82 g of triethyl aluminium (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.

Preparation of the Heterophasic Polypropylene Compositions (HECO) and the Polypropylene Compositions (C)

[0260] The heterophasic polypropylene compositions (HECO) were prepared in a sequential process comprising a loop (bulk) reactor and two gas phase reactors. The reaction conditions are summarized in Table 1. Subsequently, the polypropylene compositions (C) were prepared by compounding the respective HECO with LLDPE, talc and additives as indicated in Table 2. The properties of the comparative and inventive compositions are summarized in Table 2.

[0261] As can be seen from the higher values for flexural modulus, stiffness can be significantly improved/maximized for all inventive examples, while impact strength as measured by the Charpy values, especially at +23° C., as well as processability, as evaluated by melt flow rate (MFR) values, both remain on a good/high level. Indeed, improvements of stiffness can be seen for all inventive examples that have higher flexural modulus values, while Charpy values, especially at +23° C., are comparable or higher to/over CE1 as well as comparable to CE2 and processabilty/MFR is better/higher than for CE2 and comparable to CE1.

TABLE-US-00002 TABLE 1 Preparation of the heterophasic propylene copolymers (HECO) CE1 IE1 IE2 IE3 IE4 CE2 IE5 IE6 Prepoly TEAL/Ti [g/t(C3)] 150 150 150 150 150 150 150 150 Donor [g/t(C3)] 40 40 40 40 40 40 40 40 Temperature [° C.] 30 30 30 30 30 30 30 30 Loop (Bulk) (R1) Temperature [° C.] 80 80 80 80 80 80 80 80 MFR [g/10 min] 40.0 68.9 76.4 95.5 81.0 35.0 73.4 87.0 XCS [wt.-%] 1.5 1.8 1.9 1.7 1.6 1.5 1.6 1.6 C2 (calc) [mol %] 0.3 0.3 0.3 0.3 0.3 0 00 0 Split [%] 55 50 50 50 50 58 50 50 1.sup.st GPR (R2) Temperature [° C.] 85 85 85 85 85 85 85 85 Pressure [kPa] 21 21 21 21 21 21 21 21 MFR [g/10 min] 40.0 29.0 31.2 41.5 37.2 35.0 36.5 40.0 XCS [wt.-%] 1.5 1.2 1.3 1.2 1.3 1.0 1.3 1.3 Split [%] 45 50 50 50 50 42 50 50 2.sup.nd GPR (R3) Temperature [° C.] 70 70 70 70 70 70 70 70 Pressure [kPa] 18 18 18 18 18 18 18 18 MFR final [g/10 min] 20.0 17.1 21.5 24.2 18.5 12.0 17.4 24.0 C2 final [mol %] 10.7 5.7 5.0 5.3 6.7 12.9 7.6 5.3 XCS final [wt %] 18.0 12.2 9.8 10.7 13.6 24.0 14.4 10.5 C2 (XCS) final [mol %] 43.6 45.0 46.6 49.0 46.7 47.9 47.5 45.9 IV (XCS) final [dl/g] 2.60 3.23 3.46 4.48 4.28 2.60 4.47 4.13 Split [%] 19 11 8.5 9.5 12.3 25 13.1 9.2

TABLE-US-00003 TABLE 2 Composition and properties of the comparative and inventive examples CE1 IE1 IE2 IE3 IE4 CE2 IE5 IE6 HECO [wt.-%] 98.85 89.35 89.35 89.35 89.35 98.85 89.35 89.35 LLDPE [wt.-%] — 10.0 10.0 10.0 10.0 — 10.0 10.0 Talc [wt.-%] 0.7 2.0 2.0 2.0 2.0 0.7 2.0 2.0 AD [wt.-%] 0.45 0.45 0.45 0.45 0.45 0.45 0.45 0.45 MFR [g/10 min] 20.0 14.0 17.0 19.0 17.0 12.0 14.0 15.0 Tm [° C.] 165.0 167.5 166.9 166.4 165.1 165.0 166.8 166.8 Tcr [° C.] 129.0 130.7 131.3 130.9 132.0 127.0 131.6 131.3 Flexural Modulus [MPa] 1450 1530 1578 1539 1520 1200 1430 1440 Charpy NIS +23° C. [kJ/m.sup.2] 8.5 11.0 8.2 10.0 11.0 14.0 13.0 13.0 Charpy NIS −20° C. [kJ/m.sup.2] 4.5 4.3 3.0 4.3 4.5 6.5 4.5 4.4 HECO is the respective heterophasic propylene copolymer HECO according to Table 1. LLDPE is the commercial ethylene-butene copolymer FB2230 by Borouge having a butene content of 4.36 mol.-%, a melt flow rate MFR.sub.5 (190° C., 5.0 kg) of 0.95 g/10 min and a density of 922.5 kg/m.sup.3. Talc is the commercial Talc HM2L by Imi Fabi S.p.A. or Talc Euzenac A20C by Imerys. AD is a masterbatch of Calcium Stearate, the commercial antioxidant Irganox 1010 by BASF, the commercial antioxidant Irgafos 168 by BASF, and the commercial antistatic agent GMS95.