Cable jacket

Abstract

The present invention relates to a cable jacket comprising a random heterophasic propylene copolymer, the random heterophasic polypropylene copolymer comprising a matrix (M) being a random propylene copolymer (R-PP) and dispersed therein an elastomeric propylene copolymer (E), wherein the random propylene copolymer (R-PP) comprises a first propylene copolymer fraction (R-PP1) having a comonomer content in the range of 0.8 to 6.0 mol % and a second propylene copolymer fraction (R-PP2) having a comonomer content in the range of 7.2 to 20.0 mol %, based on the overall amount of fractions (R-PP1) and (R-PP2), and wherein the random heterophasic propylene copolymer has MFR2 (230° C.) measured according to ISO 1133 in the range of 0.5 to 15 g/10 min, and Charpy impact strength measured according to ISO 179-1/1eA at −20° C. in the range of 5 to 20 kJ/m.sup.2. The present invention further relates to a power cable comprising the cable jacket.

Claims

1. A cable jacket comprising a random heterophasic polypropylene copolymer, the random heterophasic polypropylene copolymer comprising a matrix (M) being a random propylene copolymer (R-PP) and dispersed therein an elastomeric propylene copolymer (E), wherein the random propylene copolymer (R-PP) comprises a first propylene copolymer fraction (R-PP1) having a comonomer content in the range of 0.8 to 6.0 mol % and a second propylene copolymer fraction (R-PP2) having a comonomer content in the range of 7.2 to 20.0 mol %, based on the overall amount of fractions (R-PP1) and (R-PP2), and wherein said random heterophasic polypropylene copolymer has MFR.sub.2 (230° C.) measured according to ISO 1133 in the range of 0.5 to 15 g/10 min, and Charpy impact strength measured according to ISO 179-1/1eA at −20° C. in the range of 5 to 20 kJ/m.sup.2.

2. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer has Charpy impact strength measured according to ISO 179-1/1eA at −20° C. in the range of 8 to 15 kJ/m.sup.2.

3. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer has Charpy impact strength measured according to ISO 179-1/1eA at 0° C. in the range of 40 to 90 kJ/m.sup.2.

4. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer has Charpy impact strength measured according to ISO 179-1/1eA at 23° C. in the range of 40 to 90 kJ/m.sup.2.

5. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer has a flexural modulus measured according to ISO178 below 400 MPa.

6. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer has a flexural modulus measured according to ISO178 above 200 MPa.

7. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer has MFR.sub.2 (230° C.) measured according to ISO 1133 in the range of 1 to 10 g/10 min.

8. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer constitutes at least 95 wt % of said cable jacket.

9. The cable jacket according to claim 1, wherein said cable jacket is a power cable jacket.

10. A cable comprising the cable jacket according to claim 1.

11. The cable according to claim 10, wherein said cable is a power cable.

12. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer has Charpy impact strength measured according to ISO 179-1/1eA at 0° C. in the range of 50 to 80 kJ/m.sup.2.

13. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer has Charpy impact strength measured according to ISO 179-1/1eA at 23° C. in the range of 50 to 80 kJ/m.sup.2.

14. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer has MFR.sub.2 (230° C.) measured according to ISO 1133 in the range of 2 to 8 g/10 min.

15. The cable jacket according to claim 1, wherein said random heterophasic polypropylene copolymer constitutes at least 97 wt % of said cable jacket.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Measurements Methods

(2) Melting Point

(3) The melting point was determined with differential scanning calorimetry according to ISO11357-3.

(4) Charpy Impact Strength

(5) Charpy impact strength was measured at −20° C., 0° C. and 23° C. according to ISO 179-1/1eA. The test specimens were made from 4 mm thick plaques prepared by compression moulding at 200° C. with cooling rate 15° C./min. The notches were of type A (V-notch) with radius 0.25±0.05 mm. The pendulum energies used were 0.5, 1, 2, and 4 J. Different pendulums were used because according to ISO 179-1/1eA, the absorbed energy at impact needs to be between 10 and 80% of the impact energy. 10 specimens were tested for each test condition and the reported values are the average from 10 measurements. The type of failure is also reported. According to ISO 179-1/1eA, four different types of failure can occur:

(6) C complete break: a break in which the specimen separates into two or more pieces;

(7) H hinge break: an incomplete break such that both parts of the specimen are held together only by a thin peripheral layer in the form of a hinge having low residual stiffness;

(8) P partial break: an incomplete break that does not meet the definition for hinge break;

(9) N non-break: there is no break, and the specimen is only distorted, possibly combined with stress whitening.

(10) MFR

(11) The melt flow rate MFR was measured in accordance with ISO 1133. The polyethylene examples have been analysed at 190° C. with a load of 2.16 kg and the polypropylene samples at 230° C. and 2.16 kg load.

(12) Shore D

(13) Shore D hardness was tested on a durometer hardness tester Bareiss HPE II. Samples for testing were prepared from 2 mm thick plaques produced by compression moulding at 180° C. for the comparative examples CE1 and CE2 and at 230° C. for the inventive example IE1. Cooling rate was 15° C./min. After compression moulding, the plaques were conditioned for at least one hour at room temperature before the metal frames were removed.

(14) The Shore D hardness after 3 seconds was determined according to ISO 7619-1, and the Shore D hardness after 1 second were determined according to ISO 868, with the deviation that the median value is reported. The reported values are median values from five measurements.

(15) Flexural Modulus

(16) Flexural modulus was determined according to ISO 178, which describes the procedure for a 3 point bending test. For the inventive example IE1, injection moulded specimens were used, produced according to ISO 1873-2. The test specimens for the comparative examples CE1 and CE2 were prepared by die cutting from 4 mm thick compression moulded plaques prepared according to ISO 1872-2.

(17) XCS

(18) Xylene cold soluble fraction was measured according to according ISO 16152 (25° C.), first edition; 2005 Jul. 1.

(19) Poly(Propylene-Co-Ethylene)-Ethylene Content—.sup.13C NMR Spectroscopy

(20) Quantitative .sup.13C{.sup.1H} NMR spectra were recorded in the solution-state using a Bruker Avance 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-d2 (TCE-d2) 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 (6k) transients were acquired per spectra.

(21) Quantitative .sup.13C{.sup.1H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals. 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) and the comonomer fraction calculated as the fraction of ethylene in the polymer with respect to all monomer in the polymer: fE=(E/(P+E). 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. For systems with very low ethylene content where only isolated ethylene in PPEPP sequences were observed the method of Wang et. al. was modified reducing the influence of integration of sites that are no longer 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)). 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. The mole percent comonomer incorporation was calculated from the mole fraction: E [mol %]=100*fE. The weight percent comonomer incorporation was calculated from the mole fraction: E [wt %]=100*(fE*28.06)/((fE*28.06)+((1−fE)*42.08)).

Examples

(22) Materials

(23) PP is soft random heterophasic propylene copolymer having MFR.sub.2 (230° C./2.16 kg) of 3.8 g/10 min, measured according to ISO 1133, Flexural Modulus of 327 MPa, measured on injection moulded specimens, conditioned at 23° C. and 50% relative humidity according to ISO 178, and melting temperature (DSC) of 149° C., measured according to ISO 11357-3.

(24) PP was produced as follows:

(25) Preparation of the Catalyst

(26) The catalyst used in the polymerization processes for PP was prepared as follows:

(27) Used Chemicals:

(28) 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; and Heptane, provided by Chevron.

(29) Preparation of a Mg Alkoxy Compound

(30) 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).

(31) Preparation of Solid Catalyst Component

(32) 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 as described above 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. The thus obtained catalyst was used along with triethyl-aluminium (TEAL) as co-catalyst and dicyclopentyl dimethoxy silane (D-Donor) as donor.

(33) Polymerization of RAHECO

(34) TABLE-US-00001 TABLE 1 C2 ethylene Prepolymerization RAHECO TEAL/Ti [mol/mol] 201 TEAL/donor [mol/mol] 7.90 Temperature [° C.] 30 res.time [h] 0.33 Loop Temperature [° C.] 70 Pressure [kPa] 5500 Split [%] 30.8 H2/C3 ratio [mol/kmol] 1.15 C2/C3 ratio [mol/kmol] 3.77 MFR2 [g/10 min] 6.0 XCS [wt.-%] 5.3 C2 content [mol-%] 3.0 GPR 1 Temperature [° C.] 80 Pressure [kPa] 2700 Split [%] 46.2 H2/C3 ratio [mol/kmol] 2.6 C2/C3 ratio [mol/kmol] 46.7 MFR 2 [g/10 min] 2.2 XCS [wt.-%] 17.9 C2 content [mol-%] 8.7 GPR 2 Temperature [° C.] 71 Pressure [kPa] 2600 Split [%] 23.0 C2/C3 ratio [mol/kmol] 252 H2/C2 ratio [mol/kmol] 84 MFR2 [g/10 min] 1.2 XCS [wt.-%] 39.0 IV (XCS) [dl/g] 2.2 C2 (XCS) [mol-%] 34.5 C2 content [mol-%] 20.9 H2/C3 ratio hydrogen/propylene ratio C2/C3 ratio ethylene/propylene ratio H2/C2 ratio hydrogen/ethylene ratio GPR 1/2 1.sup.st/2.sup.nd gas phase reactor Loop loop reactor

(35) The RAHECO was visbroken in a twin-screw extruder using an appropriate amount of (tert.-butylperoxy)-2,5-dimethylhexane (Trigonox 101, distributed by Akzo Nobel, Netherlands) to achieve a MFR.sub.2 of 3.8 g/10 min. The product PP was stabilized 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 0.1 wt.-% calcium stearate.

(36) PE1 is a bimodal LLDPE having density of 923 kg/m.sup.3 (ISO 1872-2/ISO 1183) and MFR2 (190° C./2.16 kg) of 0.85 g/10 min (ISO 1133).

(37) PE2 is a bimodal HDPE having density of 946 kg/m3 (ISO 1872-2/ISO 1183) and MFR.sub.2 (190° C./2.16 kg) of 0.5 g/10 min (ISO 1133).

(38) All the materials are commercially available from Borealis AG. The grades used in the comparative examples are bimodal polyethylene grades designed for cable jacketing applications.

(39) Table 2 provides an overview of relevant jacketing properties for the comparative examples CE1, CE2 and the inventive example IE1.

(40) From the Table, a large difference in melting point between PP on one hand and PE1 and PE2 on the other hand becomes apparent. The melting point of PP is 21° C. higher than that of PE2 and 25° C. higher than that of PE1. The higher melting point means maintained solid state mechanical properties at temperatures of 130° C. and above where the polyethylene materials are melted.

(41) Further, the examples in Table 2 show that the impact strength of the material of the inventive example IE1 is higher compared to the material of CE2, and at similar level compared to the material of CE1. Standard polypropylene materials have the disadvantage of low impact strength at temperatures below 0° C., and are therefore normally not considered for cable jacketing applications. The impact strength of the material in IE1, however, shows similar temperature dependence as the material used in CE1.

(42) TABLE-US-00002 TABLE 2 CE1 CE2 IE1 Material PE1 PE2 PP Melting point (° C.) 124 128 149 MFR.sub.2 2.16 kg, 190° C. (g/10 min) 0.85 0.5 — MFR.sub.2 2.16 kg, 230° C. (g/10 min) — — 3.8 Flexural modulus (MPa) 400.sup.1 1000.sup.1 327 Shore D 1s; 3s 54; 53 63; 61 49; 44 Charpy impact strength 23° C. (kJ/m.sup.2) 75.9 (P) 8.9 (H) 69.1 (P) Charpy impact strength 0° C. (kJ/m.sup.2) 87.1 (P) 4.7 (C) 68.6 (P) Charpy impact strength −20° C. (kJ/m.sup.2) 10.8 (C) 3.5 (C) 10.2 (C) .sup.lObtained from product data sheets

(43) Although the present invention has been described with reference to various embodiments, those skilled in the art will recognize that changes may be made without departing from the scope of the invention. It is intended that the detailed description be regarded as illustrative, and that the appended claims including all the equivalents are intended to define the scope of the invention.