SUPERIOR STRESS WHITENING PERFORMANCE FOR BATTERY CASES

Abstract

Injection molded article with reduced stress whitening, said article comprises a composition of a heterophasic propylene copolymer, inorganic filler and optionally low amounts of a high density polyethylene, wherein said heterophasic propylene co polymer has a propylene copolymer as a matrix.

Claims

1-13. (canceled)

14. An injection molded article (IMA) comprising at least 90 wt.-%, based on the total weight of the injection molded article (IMA), of a polypropylene composition (PC), wherein said polypropylene composition (PC) comprises (a) at least 88.25 wt.-%, based on the total weight of the polypropylene composition (PC), of a heterophasic propylene copolymer (RAHECO); (b) 0.005 to 0.350 wt.-%, based on the total weight of the polypropylene composition (PC), of an organic metal deactivator (MD); (c) 0.005 to 0.400 wt.-%, based on the total weight of the polypropylene composition (PC), of a sulphur containing antioxidant (SAO); (d) 0 to 3.0 wt.-%, based on the total weight of the polypropylene composition (PC), of an inorganic filler (F); and (e) 0 to 8.0 wt.-%, based on the total weight of the polypropylene composition (PC), of a high density polyethylene (HDPE); wherein further the heterophasic propylene copolymer (RAHECO) has a comonomer content in the range of 5.0 to 15.0 mol.-%, (ii) has a xylene cold soluble (XCS) fraction in the range of 9.0 to 18 wt.-%, (iii) comprises a propylene copolymer (M) having a comonomer content in the range of 0.4 to 2.0 mol.-%, and (iv) comprises an elastomeric propylene copolymer (R).

15. The injection molded article (IMA) according to claim 14, wherein the injection molded article (IMA) and/or the polypropylene composition (PC) (a) do(es) not contain a high density polyethylene (HDPE); or (b) comprise(s) a high density polyethylene (HDPE), wherein the polypropylene composition (PC) comprises more than 0 to 8 wt.-%, based on the total weight of the polypropylene composition (PC), of the high density polyethylene (HDPE).

16. The injection molded article (IMA) according to claim 14, wherein the injection molded article (IMA) and/or the polypropylene composition (PC) (a) do(es) not contain an inorganic filler (F); or (b) contain(s) an inorganic filler (F), wherein the polypropylene composition (PC) comprises more than 0 to 2 wt.-%, based on the total weight of the polypropylene composition (PC), of the inorganic filler (F).

17. The injection molded article (IMA) according to claim 14, wherein the comonomer of the propylene copolymer (M) is selected from ethylene, C.sub.4 to C.sub.12 α-olefin, and mixtures thereof.

18. The injection molded article (IMA) according to claim 14, wherein (a) the elastomeric propylene copolymer (R) has a comonomer content in the range of 45 to 65 mol.-%; and/or (b) the comonomer of the elastomeric propylene copolymer (R) is selected from ethylene, C.sub.4 to C.sub.12 α-olefin, and mixtures thereof.

19. The injection molded article (IMA) according to claim 14, wherein the heterophasic propylene copolymer (RAHECO) has (a) an amorphous fraction in the range of 8.0 to 15 wt.-%; and/or (b) melt flow rate MFR.sub.2 (230° C.) in the range of 3.0 to 12 g/10 min.

20. The injection molded article (IMA) according to claim 14, wherein the amorphous fraction (AM) of the heterophasic propylene copolymer (RAHECO) has (a) a comonomer content in the range of 35 to 55 mol.-%; and/or (b) an intrinsic viscosity (IV) in the range of 2.0 to 2.8 dl/g.

21. The injection molded article (IMA) according to claim 14, wherein the high density polyethylene (HDPE) has density in the range of 0.940 to 0.970 g/cm.sup.3.

22. The injection molded article (IMA) according to claim 14, wherein the inorganic filler (F) is talc.

23. The injection molded article (IMA) according to claim 14, wherein the organic metal deactivator (MD) is a phenol derivative.

24. The injection molded article (IMA) according to claim 14, wherein the sulphur containing antioxidant (SAO) is di-stearyl-thio-di-propionate (H.sub.37C.sub.18OC(O)CH.sub.2CH.sub.2SCH.sub.2CH.sub.2C(O)OC.sub.18H.sub.37).

25. The injection molded article (IMA) according to claim 14, wherein said injection molded article (IMA) and/or the polypropylene composition (PC) has/have a melt flow rate MFR2 (230° C.) in the range of 4.0 to 10 g/10 min.

26. The injection molded article (IMA) according to claim 14, wherein said injection molded article (IMA) is a battery case.

Description

EXAMPLES

1. Definitions/Measuring Methods

[0283] 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.

[0284] Quantification of Microstructure by NMR Spectroscopy

[0285] Quantitative nuclear-magnetic resonance (NMR) spectroscopy is used to quantify the isotacticity and regio-regularity of the polypropylene homopolymers.

[0286] 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.

[0287] For polypropylene homopolymers approximately 200 mg of material was dissolved in 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2). 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 needed for tacticity distribution quantification (Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443; Busico, V.; Cipullo, R., Monaco, G., Vacatello, M., Segre, A. L., Macromolecules 30 (1997) 6251). Standard single-pulse excitation was employed utilising the NOE and 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, 11289). A total of 8192 (8 k) transients were acquired per spectra.

[0288] Quantitative .sup.13C{.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs.

[0289] For polypropylene homopolymers all chemical shifts are internally referenced to the methyl isotactic pentad (mmmm) at 21.85 ppm.

[0290] 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.

[0291] 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., Macromolecules 30 (1997) 6251).

[0292] 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.

[0293] 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)

[0294] 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. 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).

[0295] 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

[0296] 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

[0297] 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

[0298] 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)

[0299] Characteristic signals corresponding to the incorporation of ethylene were observed (as described in Cheng, H. N., Macromolecules 1984, 17, 1950) and the comonomer fraction calculated as the fraction of ethylene in the polymer with respect to all monomer in the polymer.

[0300] The comonomer fraction was quantified using the method of W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157, through integration of multiple signals across the whole spectral region in the .sup.13C{.sup.1H} spectra. This method was chosen for its robust nature and ability to account for the presence of regio-defects when needed. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents.

[0301] The mole percent comonomer incorporation was calculated from the mole fraction.

[0302] The weight percent comonomer incorporation was calculated from the mole fraction. Melting temperature (T.sub.m): 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 C2 in a heat/cool/heat cycle with a scan rate of 10° C./min in the temperature range of −30 to +225° C. Melting temperature is determined from the second heating step.

[0303] Density is measured according to ISO 1183-1—method A (2004). Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

[0304] MFR.sub.2 (230° C.) is measured according to ISO 1133 (230° C., 2.16 kg load).

[0305] MFR.sub.2 (190° C.) is measured according to ISO 1133 (190° C., 2.16 kg load).

[0306] 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

[0307] The amorphous content (AM) is measured by separating the above xylene cold soluble fraction (XCS) and precipitating the amorphous part with acetone. The precipitate was filtered and dried in a vacuum oven at 90° C.

[00001]$\mathrm{AM}.Math..Math.\%=\frac{100*m.Math..Math.1*v.Math..Math.0}{m.Math..Math.0*v.Math..Math.1}$

wherein [0308] “AM %” is the amorphous fraction, [0309] “m0” is initial polymer amount (g) [0310] “m1” is weight of precipitate (g) [0311] “v0” is initial volume (ml) [0312] “v1” is volume of analyzed sample (ml)

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

[0314] 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.

[0315] Tensile strength; Tensile strain at break (or Elongation at break) are measured according to ISO 527-2 (cross head speed=50 mm/min; 23° C.) using injection molded specimens as described in EN ISO 1873-2 (dog bone shape, 4 mm thickness).

[0316] Izod 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)

[0317] Median particle size d.sub.50 (Laser diffraction) is calculated from the particle size distribution [mass percent] as determined by laser diffraction (Mastersizer) according to ISO 13320-1.

[0318] Specific surface area is determined as the BET surface according to DIN 66131/2.

[0319] Stress whitening was measured according to standard GM9302P using DuPont impact test machine on 3.2 mm (150×90×3.2 mm) thick injection molded plaques.

2. Examples

[0320] The present invention is illustrated by the following examples.

[0321] Heterophasic propylene copolymer (RAHECO) used for the inventive examples was prepared with one slurry loop reactor and two gas phase reactors by the known Borstar® technology, as disclosed in EP 0 887 379 A1.

[0322] The catalyst used in the polymerization process of the RAHECO has been produced as follows: 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 e.g. in patent publications EP491566, EP591224 or EP586390. The catalyst was prepolymerized with vinyl cyclohexane in an amount to achieve a concentration of 200 ppm poly(vinyl cyclohexane) (PVCH) in the final polymer (see EP 1183307 A1). As co-catalyst triethyl-aluminium (TEAL) and as donor dicyclo pentyl dimethoxy silane (D-donor) were used. The aluminium to donor ratio is indicated in Table 1.

TABLE-US-00001 TABLE 1 Preparation of heterophasic propylene copolymers (RAHECO1) and data of RAHECO2 RAHECO1 RAHECO2 Loop TEAL/Ti [mol/mol] 200 200 TEAL/D donor [mol/mol] 13.3 13.3 Temperature [° C.] 80 80 Pressure [bar] 55 55 C2 [mol %] 1.0 0 MFR.sub.2 (230° C.) [g/10 min] 8.5 7 XCS [wt.-%] 2.5 2.0 Split [wt.-%] 44 43 GPR 1 Temperature [° C.] 85 85 Pressure [kPa] 21 21 C2 [mol %] 1.0 0 MFR.sub.2 (230° C.) [g/10 min] 8.5 7 XCS [wt.-%] 2.0 1.5 Split [wt.-%] 44 43 GPR 2 (Final) Temperature [° C.] 75 75 Pressure [kPa] 18 18 MFR.sub.2 (230° C.) [g/10 min] 7.0 3.5 XCS [wt.-%] 13.0 15.0 AM [wt.-%] 12.0 14.0 C2 of AM [mol %] 45.8 50 IV of AM [dl/g] 2.4 3.3 C2 total [mol %] 8.7 8.8 Split [wt.-%] 12 14 R polymer produced in the GPR2 (=elastomeric propylene copolymer (R)) RAHECO2 the matrix is a propylene homopolymer Polypropylene compositions (PC) according to the present invention were produced by melt blending.

TABLE-US-00002 TABLE 2 Properties of the inventive examples and comparative example Example IE 1 IE 2 IE3 IE4 IE5 CE1 RAHECO1 [wt %]* 98.56 96.56 94.56 92.56 90.56 0.00 RAHECO2 0.00 0.00 0.00 0.00 0.00 90.56 Talc [wt %]* 1.00 1.00 1.00 1.00 1.00 1.00 HDPE [wt %]* 0.00 2.00 4.00 6.00 8.00 8.00 DSTDP [wt %]* 0.22 0.22 0.22 0.22 0.22 0.22 MD [wt %]* 0.05 0.05 0.05 0.05 0.05 0.05 MFR [g/10 min] 7.0 6.6 6.6 6.6 6.6 3.5 Tensile Modulus [MPa] 1420 1330 1320 1290 1260 1330 Tensile strength [MPa] 27.1 27.4 27.4 27.3 27.7 24.8 NIS + 23° C. [kJ/m.sup.2] 7.8 8.9 9.0 9.7 12.0 15.1 Stress whitening [ΔE] 1.17 1.55 1.33 1.31 1.37 2.00 *rest to 100 wt.-% are antioxidants different to DSTDP, like Irganox 1010 Talc is magnesium silicate hydroxide CAS no. 14807-96-6 HDPE is the commercial product MB7541 of Borealis AG having a density of 954 kg/m.sup.3 and a melt flow rate MFR.sub.2 (190° C.) of 4 g/10 min. DSTDP is (Di-Stearyl-Thio-Di-Propionate) (CAS no. 693-36-7). MD is the metal deactivator “N,N′-bis (3(3′,5′-di-tert. butyl-4′-hydroxyphenyl)propionyl)hydrazine” (CAS 32687-78-8).