FOAMABLE POLYPROPYLENE COMPOSITION

Abstract

The present invention relates to a polypropylene composition, an injection molded article comprising the polypropylene composition, a foamed article comprising the polypropylene composition as well as the use of said polypropylene composition for reducing the stiffness reduction factor of a foamed injection molded article by at least 200 as determined by the difference of the flexural modulus measured according to ISO 178 of the non-foamed and foamed injection molded article.

Claims

1. A polypropylene composition comprising a) from 65 to 85 wt. %, based on the total weight of the composition, of a polypropylene homopolymer (HPP), b) from 10 to 35 wt. %, based on the total weight of the composition, of a polypropylene copolymer (CPP), c) from 0 to 30 wt. %, based on the total weight of the composition, of a filler (F), and d) from 2.5 to 5 wt. %, based on the total weight of the composition, of at least one additive selected from the group consisting of colorants, pigments, stabilisers, acid scavengers, nucleating agents, foaming agents, antioxidants and mixtures thereof, wherein the sum of the amount of the polypropylene homopolymer (HPP), the polypropylene copolymer (CPP), the filler (F) and the at least one additive in the polypropylene composition is 100.0 wt. %.

2. The polypropylene composition according to claim 1, wherein the composition comprises: a) from 65 to 75 wt. %, based on the total weight of the composition, of the polypropylene homopolymer (HPP), b) from 25 to 35 wt. %, based on the total weight of the composition, of a polypropylene copolymer (CPP), and c) from 2.5 to 5 wt. %, based on the total weight of the composition, of at least one additive selected from the group consisting of colorants, pigments, stabilisers, acid scavengers, nucleating agents, foaming agents, antioxidants and mixtures thereof.

3. The polypropylene composition according to claim 1, wherein the polyproyplene composition has: a) a melt flow rate MFR.sub.2 (230° C.) measured according to ISO 1133 in the range of 15.0 to 80.0 g/10 min; and/or b) a content of volatile organic compounds no greater than 150 μg/g composition in pellet form; and/or c) a glass transition temperature Tg (measured with DMTA according to ISO 6721-7) of −10° C. or above.

4. The polypropylene composition according to claim 1, wherein the composition comprises from 0.1 to 0.5 wt. %, based on the total weight of the composition, of one or more nucleating agents, hydroxybis(2,4,8,10-tetra-tert.butyl-6-hydroxy-12H-dibenzo(d,g)(1,3,2)dioxaphosphocin 6-oxidato)aluminium and mixtures thereof.

5. The polypropylene composition according to claim 1, wherein the polypropylene homopolymer (HPP) has been polymerized in the presence of a Ziegler-Natta catalyst or a single-site catalyst.

6. The polypropylene composition according to claim 1, wherein the polypropylene copolymer (CPP) has been polymerized in the presence of a Ziegler-Natta catalyst or a single-site catalyst.

7. The polypropylene composition according to claim 1, wherein the polypropylene homopolymer (HPP) has: i) a melting temperature Tm measured by differential scanning calorimetry (DSC) in the range from 150 to 160° C., ii) a content of 2.1 erythro regiodefects as determined from .sup.13C-NMR spectroscopy in the range from 0.50 to 1.00 mol. %, iii) an isotactic triad fraction (mm) determined from .sup.13C-NMR spectroscopy of at least 97.5%, and iv) a xylene cold soluble fraction (XCS) determined at 23° C. according ISO 16152 of equal or below 1.5 wt.-%.

8. The polypropylene composition according to claim 1, wherein the polypropylene homopolymer (HPP) has: i) a melting temperature Tm measured by differential scanning calorimetry (DSC) in the range from 162 to 170° C., and/or ii) a content of 2.1 erythro regiodefects as determined from .sup.13C-NMR spectroscopy of ≤0.10 mol. %, and/or iii) an isotactic triad fraction (mm) determined from .sup.13C-NMR spectroscopy in the range from 95.0 to 98.0%, and/or iv) a molecular weight distribution Mw/Mn measured according to ISO 16014 in the range of ≥4.0, and/or v) a xylene cold soluble fraction (XCS) determined at 23° C. according to ISO 16152 in the range from 1.5 to 3.5 wt.-%.

9. The polypropylene composition according to claim 1, wherein the polypropylene copolymer (CPP) is a random copolymer of propylene with ethylene and/or C4 to C8 alpha-olefins.

10. The polypropylene composition according to claim 1, wherein the polypropylene copolymer (CPP) has: i) a comonomer content in the range from 2.0 to 6.0 wt. %; and/or ii) a melt flow rate MFR.sub.2 (230° C.) measured according to ISO 1133 in the range of 0.1 to 10.0 g/10 min.

11. A injection molded article comprising the polypropylene composition according to claim 1.

12. The injection molded article according to claim 11, wherein the article has: i) a flexural modulus measured according to ISO 178 of at least 1000 MPa; and/or ii) a puncture energy measured according to ISO 6603-2 of at least 3.5 J.

13. A foamed article, comprising the polypropylene composition according to claim 1.

14. A method comprising reducing the stiffness reduction factor of a foamed injection molded article by at least 200 with a polypropylene composition according to claim 1 as determined by the difference of the flexural modulus measured according to ISO 178 of the non-foamed and foamed injection molded article.

Description

EXAMPLES

1. Definitions/Measuring Methods

[0310] 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.

[0311] MFR.sub.2 (230° C.) was measured according to ISO 1133 (230° C., 2.16 kg load).

[0312] The xylene cold solubles (XCS, wt.-%) were determined at 25° C. according to ISO 16152; first edition; 2005-07-01.

[0313] Intrinsic viscosity is measured according to DIN ISO 1628/1, October 1999 (in Decalin at 135° C.).

[0314] Quantification of Microstructure by NMR Spectroscopy

[0315] 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 285 (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.

[0316] 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).

[0317] 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, 331157) 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.

[0318] 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.

[0319] 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))

[0320] 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.

[0321] The mole percent comonomer incorporation was calculated from the mole fraction:

E[mol %]=100*fE

[0322] The weight percent comonomer incorporation was calculated from the mole fraction:

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

[0323] 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.

[0324] 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.

[0325] Glass transition temperature Tg and storage modulus G′ were determined by dynamic mechanical analysis (DMTA) according to ISO 6721-7. The measurements were done in torsion mode on compression moulded samples (40×10×1 mm3) between −100° C. and +150° C. with a heating rate of 2° C./min and a frequency of 1 Hz. While the Tg was determined from the curve of the loss angle (tan(δ)), the storage modulus (G′) curve was used to determine the temperature for a G′ of 40 MPa representing a measure for the heat deflection resistance.

[0326] Puncture energy and Energy to max Force were determined on plaques with dimensions 148×148×2 mm during instrumented falling weight impact testing according to ISO 6603-2. The test was performed at room temperature with a lubricated tup with a diameter of 20 mm and impact velocity of 10 mm/s.

[0327] Number average molecular weight (M.sub.n) and weight average molecular weight (M.sub.w) were determined by Gel Permeation Chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-99. A PolymerChar GPC instrument, equipped with infrared (IR) detector was used with 3× Olexis and 1× Olexis Guard columns from Polymer Laboratories and 1,2,4-trichlorobenzene (TCB, stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 160° C. and at a constant flow rate of 1 mL/min. 200 μL of sample solution were injected per analysis. The column set was calibrated using universal calibration (according to ISO 16014-2:2003) with at least 15 narrow MWD polystyrene (PS) standards in the range of 0.5 kg/mol to 11500 kg/mol. Mark Houwink constants for PS, PE and PP used are as described per ASTM D 6474-99. All samples were prepared by dissolving 5.0-9.0 mg of polymer in 8 mL (at 160° C.) of stabilized TCB (same as mobile phase) for 2.5 hours for PP or 3 hours for PE at max. 160° C. under continuous gentle shaking in the autosampler of the GPC instrument.

[0328] Particle size d.sub.50 and top cut d.sub.95 were calculated from the particle size distribution [mass percent] as determined by gravitational liquid sedimentation according to ISO 13317-3 (Sedigraph).

[0329] DSC analysis, melting temperature (Tm) and crystallization temperature (Tc): measured with a TA Instrument Q2000 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° C. to +225° C. Crystallization temperature and heat of crystallization (Hc) are determined from the cooling step, while melting temperature and heat of fusion (Hf) are determined from the second heating step.

[0330] Cell structure of the foamed parts was determined by light microscopy from a cross-section of the foamed injection-molded plate.

[0331] Volatile organic content (VOC) is measured according to VDA 278, October 2011.

[0332] Total carbon emission was determined according to VDA 277:1995 from pellets

2. Examples

[0333] Synthesis of Metallocene:

[0334] The metallocene (rac-anti-dimethylsilandiyl(2-methyl-4-phenyl-5-methoxy-6-tert-butylindenyl)(2-methyl-4-(4-tert-butylphenyl)indenyl)zirconium dichloride) has been synthesized as described in WO 2013/007650. The metallocene containing catalyst was prepared using said metallocene and a catalyst system of MAO and trityl tetrakis(pentafluorophenyl)borate according to Catalyst 3 of WO2015/11135 with the proviso that the surfactant is 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-1-propanol.

TABLE-US-00001 TABLE 1 Polymerization process conditions and properties of the polypropylene homopolymer HPP1 B1 Prepoly reactor Temp. (° C.) 20 Press. (kPa) 5238 B2 loop reactor Temp. (° C.) 70 Press. (kPa) 5292 H2/C3 ratio (mol/kmol) 0.42 Polymer Split (wt.-%) 49.0 MFR2 (g/10 min) 91.0 XCS (%) 1.4 B3 GPR Temp. (° C.) 80 Press. (kPa) 2406 H2/C3 ratio (mol/kmol) 3.2 Polymer Split (wt.-%) 51.0 MFR2 (g/10 min) 71.0 XCS (%) 1.3

[0335] The random propylene/1-hexene copolymer was produced in a multistage process with a prepolymerization reactor followed by one slurry loop reactor and one gas phase reactor. As catalyst the metallocene containing catalyst prepared as described above was used. The polymerization process conditions, the properties of the propylene polymer fractions and of the random propylene/1-hexene copolymers (C3C6-1) are shown in table 2.

TABLE-US-00002 TABLE 2 Polymerization process conditions and properties of the polypropylene homopolymer CPP1 B1 Prepoly reactor Temp. (° C.) 20 Press. (kPa) 5023 Residence time (min) 30 B2 loop reactor Temp. (° C.) 70 Press. (kPa) 5244 H2/C3 ratio (mol/kmol) 0.1 C6/C3 ratio (mol/kmol) 8.2 Residence time(h) 0.4 C6 content (loop) (wt. %) 1.4 MFR loop (g/10 min) 1.4 Split (wt.-%) 45 B3 GPR Temp. (° C.) 80 Press. (kPa) 2500 H2/C3 ratio (mol/kmol) 1.5 C6/C3 ratio (mol/kmol) 9.0 MFR2 (g/10 min) Residence time(h) 0.4 C6 content (loop) (wt.-%) 7.9 MFR (GPR) 1.4 Split (wt.-%) 55 Final polymer MFR (g/10 min) 1.4 C6 content (wt.-%) 5.0 XCS (wt.-%) 11 Tm (° C.) 139 Tc (° C.) 91

[0336] The polypropylene compositions were prepared by mixing in a co-rotating twin-screw extruder ZSK18 from Coperion with a typical screw configuration and a melt temperature in the range of 200-220° C. The melt strands were solidified in a water bath followed by strand pelletization.

TABLE-US-00003 TABLE 3 Overview of the composition for inventive and comparative examples CE1, CE2, IE1, IE2 and IE3 IE1 IE2 IE3 CE1 CE2 HPP1 [wt.-%] 66.5 66.5 96.5 HPP2 [wt.-%] 66.5 96.5 CPP1 [wt.-%] 30 CPP2 [wt.-%] 30 30 Additives [wt.-%] 3.5 3.5 3.5 3.5 3.5 HPP1 is an isotactic unimodal polypropylene homopolymer of Borealis AG having a melt flow rate MFR.sub.2 (230° C.) of about 71 g/10 min, and is prepared in the presence of a single-site catalyst as outlined in table 1. HPP2 is the commercial unimodal polypropylene homopolymer HJ120UB of Borealis AG having a melt flow rate MFR.sub.2 (230° C.) of about 75 g/10 min, a Tm of 164° C., a density of 0.905 g/cm.sup.3, and is prepared in the presence of a Ziegler-Natta catalyst. CPP1 is a propylene-hexene random copolymer of Borealis AG having MFR.sub.2 (230° C.) 1.4 g/10 min, C6 content of 5 wt.-% and is prepared in the presence of a single-site catalyst as outlined in table 2. CPP2 is the commercial propylene-ethylene random copolymer RB206MO of Borealis AG, having a C2 content of 3.1 wt.-%, MFR.sub.2 (230° C.) 1.9 g/10 min, contains about 0.10% of ADK STAB NA-21 nucleating agent based on hydroxybis (2,4,8,10-tetra-tert.butyl-6-hydroxy-12H-dibenzo(d,g)(1.,3,2) dioxaphosphocin 6-oxidato) aluminium and is prepared in the presence of a Ziegler-Natta catalyst. Additives includes 1.5 wt.-% carbon black, 0.2 wt.-% of the nucleating agent Hyperform HPN-20E from Milliken & Company, 0.15 wt.-% of the antioxidant Irganox B215FF of BASF AG, Germany, 0.15 wt.-% calcium stearate, and 1.5 wt.-% of a carrier material.

[0337] The mechanical characteristics of the inventive examples IE1, 1E2 and 1E3 and of comparative examples CE1 and CE2 are indicated in table 4 below.

TABLE-US-00004 TABLE 4 Characteristics of the prepared polypropylene (PP) compositions IE1 IE2 IE3 CE1 CE2 Properties from pellets MFR.sub.2 [g/10 min] 16.5 19.9 20.5 75 70 Total carbon emissions [μgC/g] 9 3 25 40 4 VOC/FOG [μg/g] 21/57 16/64 136/421 170/506 17/79 Tm [° C.] 153 155 163 165 156 Tc [° C.] 120 123 128 129 123 Tg [° C.] 2 0 −2.1 −2 2 G′ [MPa] 817 840 917 1210 1030 Non-foamed injection molded plates, 2 mm Flexural modulus [MPa] 1543 ± 8  1552 ± 19 1717 ± 4  1958 ± 20 1792 ± 16 Puncture energy, 23° C. [J] 10 5 4.5 0.8 3 VOC/FOG μg/g  8/43  4/47  89/303 110/384  4/46 Foamed injection molded plates, core back, 3 mm Flexural modulus [MPa] 1064 ± 20 1185 ± 40 1242 ± 41 1191 ± 33 1107 ± 40 Puncture energy, 23° C. [J] 10 9 5 2 2 Cell size [μm]  68 ± 18  110 ± 19  122 ± 33 105 ±± 22  77 ± 19 VOC/FOG μg/g 32/78 22/75 215/485 276/577 22/97 Stiffness reduction 479 367 475 767 685 factor (flexural modulus non-foamed − flexural modulus foamed)

[0338] From table 4, it can be gathered that the polypropylene composition provides excellent foamability and mechanical properties. By using the composition of the inventive examples it is possible to obtain foamed injection-moulded plates having fine cellular structure and keep at the same time good balance in mechanical properties. Beside the fine cell structure and preserved mechanical properties the inventive non-foamed and foamed compositions show low content of volatile organic compounds. IE1 is a blend of CPP1 with HPP1 from CE2. Blending the CPP1 with the HPP1 triggers formation of fine cell and homogeneous cell structure of the foamed parts which is not the case if only a HPP1 is used. The same effect is observed when CPP2 is added to a propylene homopolymer. It can be seen that the foamed parts show lower flexural modulus than the non-foamed parts. This decrease is measured by stiffness reduction factor which in case of the IE1, IE2 and IE3 has the lowest values. Comparison of the properties of the foamed parts among the examples reveals that the inventive examples have higher puncture energy (IE1, IE2) and higher stiffness (IE3) than the foamed comparative examples (CE1, CE2).