Heterophasic propylene copolymer with low shrinkage

Abstract

A heterophasic propylene copolymer (HECO) comprising a polypropylene matrix having a melt flow rate MFR.sub.2 (230 C.) in the range of 40 to 120 g/10 min and a comonomer content in the range of 30 to 75 mol-% for the preparation of molded articles with low CLTE.

Claims

1. An automotive article comprising at least 60 wt. % of a heterophasic propylene copolymer (HECO) having comonomers being ethylene and/or a C.sub.4 to C.sub.8 -olefin, and comprising: (a) a (semi)crystalline polypropylene (PP) having a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 in the range of 40 to 120 g/10 min; and (b) an elastomeric propylene copolymer (ESC) dispersed in said (semi)crystalline polypropylene (PP); wherein said heterophasic propylene copolymer (HECO) has: (i) a xylene cold soluble (XCS) fraction in the range of 22 to 64 wt. %; (ii) a comonomer content in the range of 30.0 to 75.0 mol %; (iii) a melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 in the range of 15 to 70 g/10 min; and (iv) a xylene cold insoluble (XCI) fraction; wherein further the intrinsic viscosity (IV) of the xylene cold soluble (XCS) fraction of said heterophasic propylene copolymer (HECO) is in the range of 1.30 to 2.20 dl/g; and wherein the intrinsic viscosity (IV) of the xylene cold insoluble (XCI) fraction of the heterophasic propylene copolymer (HECO) is in the range of 1.05 to 1.45 dl/g.

2. The automotive article according to claim 1, wherein the xylene cold soluble (XCS) fraction of the heterophasic propylene copolymer (HECO) has a comonomer content in the range of 40.0 to 75.0 mol %.

3. The automotive article according to claim 1, wherein the comonomers of the heterophasic propylene copolymer (HECO) are ethylene and/or the comonomers of the xylene cold soluble (XCS) fraction of the heterophasic propylene copolymer (HECO) are ethylene.

4. The automotive article according to claim 1, wherein: (a) the xylene cold soluble (XCS) fraction of the heterophasic propylene copolymer (HECO) has an intrinsic viscosity (IV) in the range of 1.30 to 2.00 dl/g, and/or (b) the heterophasic propylene copolymer (HECO) complies with the in-equation (2): $\begin{array}{cc}0.90\frac{\mathrm{IV}\left(\mathrm{XCS}\right)}{\mathrm{IV}\left(\mathrm{XCI}\right)}2.00& \left(2\right)\end{array}$ wherein; IV (XCS) is the intrinsic viscosity (IV) [dl/g] of the xylene cold soluble (XCS) fraction of the heterophasic propylene copolymer (HECO), and IV (XCI) is the intrinsic viscosity (IV) [dl/g] of the xylene cold insoluble (XCI) fraction of the heterophasic propylene copolymer (HECO).

5. The automotive article according to claim 1 wherein the heterophasic propylene copolymer (HECO) complies with the in equation (1): $\begin{array}{cc}\frac{C2\left(\mathrm{XCS}\right)}{C2\left(T\right)}2.5& \left(1\right)\end{array}$ wherein; C2 (XCS) is the comonomer content of the xylene cold soluble (XCS) fraction; and C2 (T) is the comonomer content of heterophasic propylene copolymer (HECO).

6. The automotive article according to claim 1, wherein the heterophasic propylene copolymer (HECO) complies with the in-equation (3): $\begin{array}{cc}\frac{\mathrm{MFR}\left(M\right)}{\mathrm{MFR}\left(T\right)}5.0& \left(3\right)\end{array}$ wherein; MFR (M) is the melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 (g/10 min) of the (semi)crystalline polypropylene (PP); and MFR (T) is the melt flow rate MFR.sub.2 (230 C.) measured according to ISO 1133 (g/10 min) of the heterophasic propylene copolymer (HECO).

7. The automotive article according to claim 1, wherein the (semi)crystalline polypropylene (PP) is a (semi)crystalline propylene homopolymer (H-PP) having a xylene cold soluble (XCS) fraction of less than 4.5 wt. %.

8. The automotive article according to claim 1, wherein the elastomeric propylene copolymer (ESC) is an ethylene propylene rubber (EPR).

9. The automotive article according to claim 1, wherein the heterophasic propylene copolymer (HECO) has: (a) impact strength at +23 C. of at least 10 kJ/m.sup.2; and/or (b) a coefficient of linear thermal expansion (CLTE) performed in a temperature range from 30 to +80 C. of not more than 92 m/mK.

10. The automotive article according to claim 1, wherein the heterophasic propylene copolymer (HECO) has: (a) a shrinkage in flow (60602 mm) of below 0.50%, and/or (b) a shrinkage across flow (60602 mm) of below 0.70%.

11. The automotive article according to claim 1, wherein the automotive article is an exterior automotive article.

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 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-d2) along with chromium-(III)-acetylacetonate (Cr(acac)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.

(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(S+S+S+0.5(S+S))

(8) 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.

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

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

(11) 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.

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

(13) Xylene cold soluble fraction (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.

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

(15) The flexural modulus was determined in 3-point-bending according to ISO 178 on 80104 mm.sup.3 test bars injection molded at 23 C. in line with EN ISO 1873-2.2.

(16) Charpy notched impact strength is determined according to ISO 180/1A at 23 C. and at 20 C. by using injection moulded test specimens as described in EN ISO 1873-2 (80104 mm).

(17) Coefficient of linear thermal expansion: The coefficient of linear thermal expansion (CLTE) was determined in accordance with ISO 11359-2:1999 on 10 mm long pieces cut from the core of the same injection molded specimens as used for the flexural modulus determination The measurement was performed in a temperature range from 30 to +80 C. at a heating rate of 1 C./min and in a temperature range from 23 to +80 C. at a heating rate of 1 C./min, respectively.

(18) Shrinkage measurement on quadratic plaques: Shrinkage was determined on injection moulded quadratic plaques (60602 mm). The film gated specimens were moulded on an Engel V60 injection moulding machine, equipped with a small ( 22 mm; L/D=20) screw according to EN ISO 1873-2. Process parameters were 200 C. melt temperature, 100 mm/s flow front velocity, holding pressure time 10 seconds, hydraulic holding pressure level 10 bar. After a time span of at least 96 h after demoulding the dimensions (length and width) of the plaques were measured and compared to the dimensions of the cavity at room temperature.

(19) Polymerization of Comparative HECO CE1

(20) Catalyst Preparation:

(21) The catalyst used in the polymerization processes was the commercial ZN104 of Basell with triethyl-aluminium (TEAl) as co-catalyst and dicyclo pentyl dimethoxy silane (donor D) as donor.

(22) The Al/donor ratio was 5 mol/mol, and the Al/Ti ratio was 200 mol/mol. A Borstar PP pilot plant comprised of a stirred-tank prepolymerization reactor (R1), a liquid-bulk loop reactor (R2) and three gas phase reactors (R3 to R5) was used for the main polymerization. The resulting polymer powders were compounded in a co-rotating twin-screw extruder Coperion ZSK 57 at 220 C. with 0.2 wt.-% of Irganox B225 (1:1-blend of Irganox 1010 (Pentaerythrityl-tetrakis(3-(3,5-di-tert.butyl-4-hydroxytoluyl)-propionate and tris (2,4-di-t-butylphenyl) phosphate) phosphite) of BASF AG, Germany) and 0.05 wt.-% calcium stearate.

(23) TABLE-US-00001 TABLE 1a Polymerization of comperative HECO CE1 (Part 1) CE1 Prepoly (R1) Residence time [h] 0.1 Temperature [ C.] 30.3 Loop (R2) Residence time [h] 0.6 Temperature [ C.] 70 H.sub.2/C.sub.3 ratio [mol/kmol] 13.9 MFR [g/10 min] 35 XCS [wt %] 2.0 C2 content [mol %] 0 split [wt %] 32.5 1.sup.st GPR (R3) Residence time [h] 0.6 Temperature [ C.] 78.4 Pressure [kPa] 2214 H.sub.2/C.sub.3 ratio [mol/kmol] 78 MFR [g/10 min] 35 XCS [wt %] 2.0 C2 content [mol %] 0 split [wt %] 34.5

(24) TABLE-US-00002 TABLE 1b Polymerization of comperative HECO CE1 (Part 2) CE1 2.sup.nd GPR (R4) Residence time [h] 0.6 Temperature [ C.] 71 Pressure [kPa] 2292 C.sub.2/C.sub.3 ratio [mol/kmol] 715 H.sub.2/C.sub.2 ratio [mol/kmol] 219 MFR [g/10 min] 12 XCS [wt %] 19 C2 content [mol %] 12 split [wt %] 21 3.sup.rd GPR (R5) Residence time [h] 0.6 Temperature [ C.] 83 Pressure [kPa] 1383 C.sub.2/C.sub.3 ratio [mol/kmol] 747 H.sub.2/C.sub.2 ratio [mol/kmol] 203 MFR.sub.2 [g/10 min] 13 XCS [wt %] 30 IV of XCI [dl/g] 1.5 IV of XCS [dl/g] 2.2 C2 of XCS [mol %] 47 C2 content [mol %] 20 split [wt %] 12

(25) Polymerization of Inventive HECOs IE1 to 1E4 (Bench Scale)

(26) Examples were accomplished in a 21.3 l autoclave equipped with control valves for dosing the reactor with monomers, hydrogen and for flashing. The dosage of monomers and hydrogen into the reactor was monitored by flow controllers and also by monitoring the mass of their respective reservoirs. The temperature of the reactors was controlled via cooling/heating of water in the double jacket around the reactors including sensors in both the top and bottom of the reactor. Helical stirrers with magnetic coupling were used for effective mixing inside the reactor and the stirring rates could be varied during the course of the reaction.

(27) Catalyst Preparation:

(28) Used Chemicals:

(29) 20% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et), BEM), provided by Chemtura 2-ethylhexanol, provided by Amphochem 3-Butoxy-2-propanol-(DOWANOL PnB), provided by Dow bis(2-ethylhexyl)citraconate, provided by SynphaBase TiCl.sub.4, provided by Millenium Chemicals Toluene, provided by Aspokem Viscoplex 1-254, provided by Evonik Heptane, provided by Chevron

(30) Preparation of a Mg Alkoxy Compound

(31) Mg alkoxide solution was prepared by adding, with stirring (70 rpm), into 11 kg of a 20 wt-% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et)), a mixture of 4.7 kg of 2-ethylhexanol and 1.2 kg of butoxypropanol in a 20 l stainless steel reactor. During the addition the reactor contents were maintained below 45 C. After addition was completed, mixing (70 rpm) of the reaction mixture was continued at 60 C. for 30 minutes. After cooling to room temperature 2.3 kg g of the donor bis(2-ethylhexyl)citraconate was added to the Mg-alkoxide solution keeping temperature below 25 C. Mixing was continued for 15 minutes under stirring (70 rpm).

(32) Preparation of Solid Catalyst Component

(33) 20.3 kg of TiCl.sub.4 and 1.1 kg of toluene were added into a 20 l stainless steel reactor. Under 350 rpm mixing and keeping the temperature at 0 C., 14.5 kg of the Mg alkoxy compound prepared in example 1 was added during 1.5 hours. 1.7 l of Viscoplex 1-254 and 7.5 kg of heptane were added and after 1 hour mixing at 0 C. the temperature of the formed emulsion was raised to 90 C. within 1 hour. After 30 minutes mixing was stopped catalyst droplets were solidified and the formed catalyst particles were allowed to settle. After settling (1 hour), the supernatant liquid was siphoned away. Then the catalyst particles were washed with 45 kg of toluene at 90 C. for 20 minutes followed by two heptane washes (30 kg, 15 min). During the first heptane wash the temperature was decreased to 50 C. and during the second wash to room temperature.

(34) Polymerization

(35) Bulk:

(36) The reactor is initially purged with propylene and then filled with 5930 g of propylene and 3 litres of hydrogen for the pre-polymerisation. The catalyst as defined above (a suspension in a mineral oi) was mixed with a solution of TEAl and D-donor at a preset TEAl/Ti ratio of 250 mol/mol and TEAl/Donor ratio of 10 mol/mol for 5 minutes before being added to the reactor. The catalyst loading vessel is then flushed with 250 g propylene to ensure all of the catalyst mixture is added to the reactor. The reactor then undergoes pre-polymerisation at 30 C. for 6 minutes while stirring at 350 rpm. Subsequently, the reactor is heated up to 80 C. to initiate bulk conditions. While in transition the desired amount of hydrogen is added to the reactor via a flow controller. Hydrogen is always added in bulk and not added continuously during the reaction. Once the desired reactor conditions are reached, the reactor is held at a constant pressure by dosing with propylene. This transition time to reach the bulk conditions was typically 19 minutes. After the specified bulk residence time, the reactor is purged to 0.5 barg with a stirring speed of 100 rpm to continue to a gas phase step.

(37) GPR1

(38) Once the desired purge pressure (0.5 barg) was achieved, the transition to the EPR gas phase (GPR1) began. The stirring rate of the reactor was increased to 200 rpm and the reactor was dosed with propylene, ethylene and hydrogen as the temperature and pressure were increased to 80 C. and 25 barg, respectively. The transition time between the Bulk and the GPR1 was typically between 8 to 10 minutes. The comonomers were added to maintain a desired gas ratio. Once the reactor reached the desired temperature, the pressure was held constant at the desired level by dosing with ethylene/propylene at the appropriate gas ratio. The amount of polymer being produced could be monitored by measuring the amount of propylene and ethylene added during the course of the reaction. After a desired split level was reached, the reactor followed the termination procedure outlined below.

(39) Reaction Termination:

(40) After the reaction is completed the stirring speed is reduced to 100 rpm and the gas mixture purged from the reactor to 0 barg. Residual gases are removed from the reactor by treating the reactor with several nitrogen/vacuum cycles. This cycle involves putting the reactor under vacuum for several minutes, filling up to ambient pressures with nitrogen and then repeating the process several times. The product is then safely removed from the reactor.

(41) Post Reactor Treatment

(42) All polymer powders were blended with 0.05 wt % calcium stearate and 0.20 wt % Songnox 11B FF using a twin-screw extruder TSE16TC. The calcium stearate and Songnox 11B are standard antioxidant agents used for stabilizing the polymer powder. During the compounding the following temperature profile was set: 190, 210, 230, 210 C.

(43) The analytics of the prepared samples can be gathered from Tables 2 and 3, IE1 to 1E4.

(44) TABLE-US-00003 TABLE 2 Polymerization of inventive HECOs IE1 to IE4 IE1 IE2 IE3 IE4 Bulk Residence time [h] 0.5 0.5 0.5 0.5 split [wt.-%] 50.4 64.4 64.3 55.1 MFR [g/10 min] 45 68 45 92 C2 [mol-%] 0 0 0 0 XCS [wt.-%] 2.0 2.0 2.0 2.0 H.sub.2 in liquid [mol-%] 0.74 1.07 0.74 1.40 GPR Residence time [h] 1.3 0.5 0.6 1.0 Split [wt.-%] 49.6 35.7 35.7 44.9 C2/(C2 + C3) [mol/mol] 0.40 0.55 0.71 0.70 H2/C2 [mol/kmol] 410 215 298 318 Final MFR, total [g/10 min] 31 26 20 32 C2 total [mol-%] 30.7 30.5 35.7 47.6 XCS [wt.-%] 49 35.0 30.8 37.0 C2/XCS [mol-%] 48.1 61.9 66.9 72.5 IV/XCI [dl/g] 1.40 1.27 1.40 1.19 IV/XCS [dl/g] 1.32 1.71 1.38 1.62

(45) TABLE-US-00004 TABLE 3 Properties IE1 IE2 IE3 IE4 CE1 MFR [g/10 min] 31 26 20 32 13 SHif [%] 0.00 0.21 0.06 0.17 0.79 SHaf [%] 0.24 0.58 0.00 0.41 0.92 FM [MPa] 410 813 831 718 790 CHI(23) [kJ/m.sup.2] 49 17 10 21 35 CHI(20) [kJ/m.sup.2] 54 7 4 9 7 CLTE23 [m/mK] 58 98 88 84 110 CLTE30 [m/mK] 62 88 80 80 96 SHif Shrinkage in flow SHaf Shrinkage across flow FM Flexural Modulus CHI(23) Charpy impact strength at 23 C. CHI(20) Charpy impact strength at 20 C. CLTE23 CLTE +23/80 C./MD CLTE30 CLTE 30/80 C./MD