POLYETHYLENE COMPOSITION FOR PIPE APPLICATIONS WITH IMPROVED SAGGING PROPERTIES

Abstract

The present invention relates to a polyethylene composition comprising, a base resin (A) comprising a copolymer of ethylene and at least one comonomer selected from alpha-olefins having from three to twelve carbon atoms, wherein the ethylene copolymer comprises a low molecular weight component (A-1) and a high molecular weight component (A-2) with the low molecular weight component (A-1) having a lower weight average molecular weight than the high molecular weight component (A-2), (B) carbon black in an amount of 1.0 to 10 wt % based on the total amount of the polyethylene composition, and (C) optional further additives other than carbon black.

Claims

1-15. (canceled)

16. A polyethylene composition comprising, a base resin (A) comprising a copolymer of ethylene and at least one comonomer selected from alpha-olefins having from three to twelve carbon atoms, wherein the ethylene copolymer comprises a low molecular weight component (A-1) and a high molecular weight component (A-2) with the low molecular weight component (A-1) having a lower weight average molecular weight than the high molecular weight component (A-2), (B) carbon black in an amount of 1.0 to 10 wt % based on the total amount of the polyethylene composition, and (C) optional further additives other than carbon black; wherein the base resin (A) has a density of equal to or more than 943 kg/m.sup.3 to equal to or less than 957 kg/m.sup.3, determined according to ISO 1183, and the composition has a melt flow rate MFRs (190 C., 5 kg) of equal to or more than 0.12 g/10 min to equal to or less than 0.20 g/10 min, determined according to ISO 1133, a shear thinning index SHI.sub.2.7/210 of equal to or more than 80 to equal to or less than 130 and a viscosity at a constant shear stress of 747 Pa, eta.sub.747, of equal to or more than 700 kPas to equal to or less than 1200 kPas.

17. The polyethylene composition according to claim 16, wherein the low molecular weight component (A-1) is an ethylene homopolymer.

18. The polyethylene composition according to claim 16, wherein the low molecular weight component (A-1) has a melt flow rate MFR.sub.2 (190 C., 2.16 kg) of 200 g/10 min to 400 g/10 min, determined according to ISO 1133.

19. The polyethylene composition according to claim 16, wherein the high molecular weight component (A-2) is a copolymer of ethylene and a comonomer selected from alpha-olefins having from three to twelve carbon atoms.

20. The polyethylene composition according to claim 16, wherein the weight ratio of the low molecular weight component (A-1) to the high molecular component (A-2) is from 45:55 to 55:45.

21. The polyethylene composition according to claim 16, wherein the composition has a melt flow rate MFR.sub.21 (190 C., 21.6 kg) of 5.6 g/10 min to 7.0 g/10 min, determined according to ISO 1133.

22. The polyethylene composition according to claim 16, wherein the composition has a density of equal to or more than 953 kg/m.sup.3 to equal to or less than 967 kg/m.sup.3, determined according to ISO 1183.

23. The polyethylene composition according to claim 16, wherein the composition has a shear thinning index SHI.sub.5/200 of equal to or more than 50 to equal to or less than 100.

24. The polyethylene composition according to claim 16, wherein the composition has at least one, preferably both of the following properties a) a weight average molecular weight, Mw, of 250 to 360 kg/mol, more preferably 260 to 340 kg/mol, and/or b) Mz value of 1600 to 2500 kg/mol, preferably 1700 to 2200 kg/mol, even more preferably 1750 to 2150 kg/mol.

Description

EXAMPLES

1. Definitions

[0146] a) Melt Flow Rate

[0147] The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR.sub.5 of polyethylene is measured at a temperature of 190 C. and a load of 5 kg, the MFR.sub.2 of polyethylene at a temperature of 190 C. and a load of 2.16 kg and the MFR.sub.21 of polyethylene is measured at a temperature of 190 C. and a load of 21.6 kg. The quantity FRR (flow rate ratio) denotes the ratio of flow rates at different loads. Thus, .sub.FRR2115 denotes the value of MFR.sub.21/MFR.sub.5. [0148] b) Density

[0149] Density of the polymer was measured according to ISO 1183-1:2004 Method A on compression moulded specimen prepared according to EN ISO 1872-2 (February 2007) and is given in kg/m.sup.3. [0150] c) Comonomer Content

[0151] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers.

[0152] Quantitative .sup.13C{.sup.1H} NMR spectra recorded in the molten-state using a Bruker Advance III 500 NMR spectrometer operating at 500.13 and 125.76 MHz for .sup.1H and .sup.13C, respectively. All spectra were recorded using a .sup.13C optimized 7 mm magic-angle spinning (MAS) probehead at 150 C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was packed into a 7 mm outer diameter zirconia MAS rotor and spun at 4 kHz. This setup was chosen primarily for the high sensitivity needed for rapid identification and accurate quantification {[1], [2], [6]}. Standard single-pulse excitation was employed utilizing the transient NOE at short recycle delays of 3 s {[1], [3]} and the RSHEPT decoupling scheme {[4], [5]}. A total of 1024 (1k) transients were acquired per spectrum. This setup was chosen due to its high sensitivity towards low comonomer contents.

[0153] Quantitative .sup.13C{.sup.1H) NMR spectra were processed, integrated and quantitative properties determined using custom spectral analysis automation programs. All chemical shifts are internally referenced to the bulk methylene signal (+) at 30.00 ppm {[9]}.

[0154] Characteristic signals corresponding to the incorporation of 1-hexene were observed {[9]} and all contents calculated with respect to all other monomers present in the polymer.

H=I*.sub.B4

[0155] With no other signals indicative of other comonomer sequences, i.e. consecutive comonomer incorporation, observed the total 1-hexene comonomer content was calculated based solely on the amount of isolated 1-hexene sequences:

H.sub.total=H

[0156] Characteristic signals resulting from saturated end-groups were observed. The content of such saturated end-groups was quantified using the average of the integral of the signals at 22.84 and 32.23 ppm assigned to the 2s and 3s sites respectively:

S=(1/2)*(1.sub.2S+I.sub.3S)

[0157] The relative content of ethylene was quantified using the integral of the bulk methylene (+) signals at 30.00 ppm:

E=(1/2)*I.sub.+

[0158] The total ethylene comonomer content was calculated based on the bulk methylene signals and accounting for ethylene units present in other observed comonomer sequences or end-groups:

E.sub.total=E+(5/2)*B+(312)*S

[0159] The total mole fraction of 1-hexene in the polymer was then calculated as:

fH=(H.sub.total/(E.sub.total+H.sub.total)

[0160] The total comonomer incorporation of 1-hexene in mole percent was calculated from the mole fraction in the usual manner:

H[mol %]=100*fH

[0161] The total comonomer incorporation of 1-hexene in weight percent was calculated from the mole fraction in the standard manner:

H[wt %]=100*(fH*84.16)/((fH*84.16)+((1fH)*28.05))

[0162] [1] Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382.

[0163] [2] Parkinson, M., Klimke, K., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208:2128.

[0164] [3] Pollard, M., Klimke, K., Graf, R., Spiess, H. W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813.

[0165] [4] Filip, X., Tripon, C., Filip, C., J. Mag. Reson. 2005, 176, 239.

[0166] [5] Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown, S. P., Mag. Res. in Chem. 2007, 45, S1, S198.

[0167] [6] Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373.

[0168] [7] Zhou, Z., Muemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 2007, 187, 225.

[0169] [8] Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128.

[0170] [9] J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201.

[0171] d) Dynamic Shear Measurements (Frequency Sweep Measurements)

[0172] The characterization of polymer melts by dynamic shear measurements complies with ISO standards 6721-1 and 6721-10. The measurements were performed on an Anton Paar MCR501 stress controlled rotational rheometer, equipped with a 25 mm parallel plate geometry. Measurements were undertaken on compression moulded plates using nitrogen atmosphere and setting a strain within the linear viscoelastic regime. The oscillatory shear tests were done at 190 C. applying a frequency range between 0.0154 and 500 rad/s and setting a gap of 1.2 mm.

[0173] In a dynamic shear experiment the probe is subjected to a homogeneous deformation at a sinusoidal varying shear strain or shear stress (strain and stress controlled mode, respectively). On a controlled strain experiment, the probe is subjected to a sinusoidal strain that can be expressed by

(t)=.sub.0 sin(t) (1)

[0174] If the applied strain is within the linear viscoelastic regime, the resulting sinusoidal stress response can be given by

(t)=.sub.0 sin(t+) (2)

[0175] where .sub.0, and .sub.0 are the stress and strain amplitudes, respectively; is the angular frequency; is the phase shift (loss angle between applied strain and stress response); t is the time.

[0176] Dynamic test results are typically expressed by means of several different rheological functions, namely the shear storage modulus, G, the shear loss modulus, G, the complex shear modulus, G*, the complex shear viscosity, *, the dynamic shear viscosity, , the out-of-phase component of the complex shear viscosity, , and the loss tangent, tan , which can be expressed as follows:

[00001]$\begin{array}{cc}{G}^{}=\frac{{}_0}{{}_0}.Math.\cos .Math..Math..Math.\left[\mathrm{Pa}\right]& \left(3\right)\\ G^{}=\frac{{}_0}{{}_0}.Math.\sin .Math..Math..Math.\left[\mathrm{Pa}\right]& \left(4\right)\\ G^{}=G^{}+i.Math..Math.G^{}.Math.\left[\mathrm{Pa}\right]& \left(5\right)\\ {}^{}={}^{}-i.Math..Math.{}^{}.Math.\left[\mathrm{Pa}.Math.s\right]& \left(6\right)\\ {}^{}=\frac{G^{}}{}.Math.\left[\mathrm{Pa}.Math.s\right]& \left(7\right)\\ {}^{}=\frac{G^{}}{}.Math.\left[\mathrm{Pa}.Math.s\right]& \left(8\right)\end{array}$

[0177] Besides the above mentioned rheological functions one can also determine other rheological parameters such as the so-called elasticity index EI(x). The elasticity index EI(x) is the value of the storage modulus, G, determined for a value of the loss modulus, G, of x kPa and can be described by equation 9.

EI(x)=G for (G=x kPa) [Pa] (9)

[0178] For example, the EI(5 kPa) is defined by the value of the storage modulus G, determined for a value of G equal to 5 kPa.

[0179] The determination of so-called Shear Thinning Indexes is done, as described in equation 10.

[00002]$\begin{array}{cc}S.Math..Math.H.Math..Math.I\left(x/y\right)=\frac{{\mathrm{Eta}}^{*}.Math..Math.\mathrm{for}.Math..Math.\left(G^{*}=x.Math..Math.k.Math..Math.\mathrm{Pa}\right)}{{\mathrm{Eta}}^{*}.Math..Math.\mathrm{for}.Math..Math.\left(G^{*}=y.Math..Math.k.Math..Math.\mathrm{Pa}\right)}.Math.\left[\mathrm{Pa}\right]& \left(10\right)\end{array}$

[0180] For example, the SHI.sub.(2.7/210) is defined by the value of the complex viscosity, in Pa.Math.s, determined for a value of G* equal to 2.7 kPa, divided by the value of the complex viscosity, in Pa.Math.s, determined for a value of G* equal to 210 kPa

[0181] The values of storage modulus (G), loss modulus (G), complex modulus (G*) and complex viscosity (*) were obtained as a function of frequency ().

[0182] Thereby, e.g. *.sub.300rad/s (eta*.sub.300rad/s) is used as abbreviation for the complex viscosity at the frequency of 300 rad/s and *.sub.0.05rad/s (eta*.sub.0.05rad/s) is used as abbreviation for the complex viscosity at the frequency of 0.05 rad/s.

[0183] The values are determined by means of a single point interpolation procedure, as defined by Rheoplus software. In situations for which a given G* value is not experimentally reached, the value is determined by means of an extrapolation, using the same procedure as before. In both cases (interpolation or extrapolation), the option from Rheoplus Interpolate y-values to x-values from parameter and the logarithmic interpolation type were applied.

REFERENCES

[0184] [1] Rheological characterization of polyethylene fractions Heino, E. L., Lehtinen, A., Tanner J., Seppl, J., Neste Oy, Porvoo, Finland, Theor. Appl. Rheol., Proc. Int. Congr. Rheol, 11th (1992), 1, 360-362

[0185] [2] The influence of molecular structure on some rheological properties of polyethylene, Heino, E. L., Borealis Polymers Oy, Porvoo, Finland, Annual Transactions of the Nordic Rheology Society, 1995.).

[0186] [3] Definition of terms relating to the non-ultimate mechanical properties of polymers, Pure & Appl. Chem., Vol. 70, No. 3, pp. 701-754, 1998.

[0187] e) Eta 747 Pa (Sagging):

[0188] One method which correlates well with the sagging properties, and is used in connection with the present invention relates to the rheology of the polymer and is based on determination of the viscosity of the polymer at a very low, constant shear stress. A shear stress of 747 Pa has been selected for this method. The viscosity of the polymer at this shear stress is determined at a temperature of 190 C. and has been found to be inversely proportional to the gravity flow of the polymer, i.e. the greater the viscosity the lower the gravity flow.

[0189] The determination of the viscosity at 747 Pa shear stress is made by using a rotational rheometer, which can be a constant stress rheometer as for example an Anton Paar MCR Series Rheometer. Rheometers and their function have been described in Encyclopedia of Polymer Science and Engineering, 2nd Ed., Vol. 14, pp. 492-509. The measurements are performed under a constant shear stress between two 25 mm diameter plates (constant rotation direction). The gap between the plates is 1.2 mm. An 1.2 mm thick polymer sample is inserted between the plates.

[0190] The sample is temperature conditioned during 2 min before the measurement is started. The measurement is performed at 190 C. After temperature conditioning the measurement starts by applying the predetermined stress. The stress is maintained during 1800 s to let the system approach steady state conditions. After this time the measurement starts and the viscosity is calculated.

[0191] The measurement principle is to apply a certain torque to the plate axis via a precision motor. This torque is then translated into a shear stress in the sample. This shear stress is kept constant. The rotational speed produced by the shear stress is recorded and used for the calculation of the viscosity of the sample.

[0192] f) Molecular Weight

[0193] Molecular weight averages (Mz, Mw and Mn), Molecular weight distribution (MWD) and its broadness, described by polydispersity index, PDI=Mw/Mn (wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) were determined by Gel Permeation Chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-99 using the following formulas:

[00003]$\begin{array}{cc}{M}_n=\frac{{.Math.}_{i=1}^N.Math.A_i}{.Math.\left(A_i/M_i\right)}& \left(1\right)\\ M_w=\frac{{.Math.}_{i=1}^N.Math.\left(A_i{M}_i\right)}{.Math.A_i}& \left(2\right)\\ M_z=\frac{{.Math.}_{i=1}^N.Math.\left(A_i{M}_i^2\right)}{.Math.\left(A_i/M_i\right)}& \left(3\right)\end{array}$

[0194] For a constant elution volume interval V.sub.i, where A.sub.i and M.sub.i are the chromatographic peak slice area and polyolefin molecular weight (MW).

[0195] A PolymerChar GPC instrument, equipped with infrared (IR) detector was used with 3Olexis and 1Olexis 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. 200L 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 11 500 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 160 C. under continuous gentle shaking in the autosampler of the GPC instrument.

[0196] g) Tensile Modulus (23 C.)

[0197] As a measure for stiffness, the tensile modulus (E-modulus) of the compositions was measured at 23 C. on compression molded specimens according to ISO 527-2:1993. The specimens (1B type) were cut from plaques of 4 mm thickness prepared by compression molding according to ISO 293:2004 using the conditions defined in chapter 3.3 of ISO 1872-2:2007. The modulus was measured at a speed of 1 mm/min.

[0198] h) Tensile Properties (23 C.)

[0199] The tensile strength, including tensile stress at yield, strain at yield and elongation at break (i.e. tensile strain at break) is measured according to ISO 527-1 (cross head speed 50 mm/min) at a temperature of 23 C.

[0200] i) Pressure Test on Un-Notched Pipes (PT); Resistance to Internal Pressure

[0201] The resistance to internal pressure has been determined in a pressure test on pressure test on un-notched 32 mm SDR 11 pipes having a length of 450 mm is carried out in water-inside and water-outside environment according to ISO 1167-1:2006. End caps of type A were used. The time to failure is determined in hours. The following conditions were applied: hoop stress of 5.5 MPa at a temperature of 80 C.

2. Materials

[0202] a) Inventive Example Ex1

[0203] Into a first loop reactor having a volume of 50 dm.sup.3 and operating at a temperature of 60 C. and a pressure of 65 bar propane (C3, 50 kg/h), ethylene (C2, 2 kg/h), and hydrogen (H2, 10 g/h) were introduced for conducting a pre-polymerization step. In addition a commercially available, solid polymerisation catalyst component Lynx 200 sold by BASF Catalyst LLC was introduced into the reactor together with triethylaluminium cocatalyst so that the ratio of aluminium to titanium was 15 mol/mol. The polymerization rate was 1.9 kg/h.

[0204] The slurry was withdrawn intermittently from the prepolymerization reactor and directed to a second loop reactor having a volume of 500 dm.sup.3 and operating at a temperature of 95 C. and a pressure of 65 bar. Additionally, propane, ethylene and hydrogen were fed to the second loop reactor whereby the ethylene concentration and the hydrogen to ethylene ratio for example Ex 1 are listed in Table 1. The production split, the density and melt index of the polymer fractions produced in the second loop reactor are listed in Table 1.

[0205] The slurry was withdrawn intermittently from the second loop reactor by using settling legs and directed to a gas phase reactor. The gas phase reactor was operated at a temperature of 85 C. and a pressure of 20 bar. Additional ethylene, 1-hexene comonomer, and hydrogen were fed whereby the ethylene concentration, the 1-hexene to ethylene ratio and the hydrogen to ethylene ratio as well as the production split and the density of the polymers of example Ex 1 withdrawn from the gas phase reactor are listed in Table 1.

[0206] The resulting polymer was purged with nitrogen (about 50 kg/h) for one hour, stabilised with commercial stabilisers, 1100 ppm of lrganox 1010, 1100 ppm Irgafos 168 and 1500 ppm Ca-stearate and then extruded together with 3.0 wt % carbon black to pellets in a counter-rotating twin screw extruder CIM90P (manufactured by Japan Steel Works) The temperature profile in each zone was 90/120/190/250 C.

[0207] The properties of the compounded composition are shown in Table 1.

[0208] b) Comparative Example CE2

[0209] As comparative example CE2 commercially available black bimodal HDPE grade for PE100 pipes (for thick wall pipes) has been tested. The properties of the PE100 HDPE resin are shown in Table 1.

[0210] c) Pipe Preparation

[0211] The compounded compositions of Inventive Example Ex1 and Comparative Examples CE1 were extruded to SDR 11 pipes for the pressure resistance tests in a Battenfeld 1-60-35-B extruder at a screw speed of about 200 rpm, and the conditions as listed in Table 2. The temperature profile in each barrel zone was 220/210/210/210/210 C.

[0212] The results of the pipe tests are shown in Table 2.

TABLE-US-00001 TABLE 1 Polymerization conditions Ex1 Prepolymerizer: Temperature [ C.] 60 Pressure [bar] 65 Split [wt %] 2.3 Loop: Temperature [ C.] 95 Pressure [bar] 65 H.sub.2/C.sub.2 [mol/kmol] 1050 C.sub.2-concentration [mol %] 2.6 Production Rate [kg/h] 37 Split [wt %] 48.7 MFR.sub.2 [g/10 min] 325 Density [kg/m.sup.3] 970 Gas phase: Temperature [ C.] 85 Pressure [bar] 20 H.sub.2/C.sub.2 [mol/kmol] 12.6 C.sub.6/C.sub.2 [mol/kmol] 68 C.sub.2-concentration [mol %] 15 Production Rate [kg/h] 38 Split [wt %] 49 Density [kg/m.sup.3] 949 Composition Properties: Ex. 1 CE2 Density [kg/m.sup.3] 962 961 MFR.sub.5 [g/10 min] 0.16 0.17 MFR.sub.21 [g/10 min] 6.2 6.6 FRR.sub.21/5 39 39 Mw [kg/mol] 285 267 Mz [kg/mol] 1885 1705 MWD (Mw/Mn) 36 19 Eta (0.05 rad/s) [Pa .Math. s] 234000 282000 Eta (300 rad/s) [Pa .Math. s] 1141 1265 SHI.sub.2.7/210 109 72 SHI.sub.5/200 69 49 Eta.sub.747 [kPa .Math. s] 868 870 C.sub.6 content [mol %] 0.80 Tensile Modulus [MPa] 1042 1300 Tensile Strength [MPa] 28.4 37 Tensile Stress at yield [MPa] 28.4 25 Elongation at break [%] 640 760

TABLE-US-00002 TABLE 2 Pipe Properties Ex1 Pipe Extrusion Melt Pressure, 32 mm [bar] 315 Melt Temperature, 32 mm [ C.] 200 Melt Pressure, 110 mm [bar] 321 Melt Temperature, 110 mm [ C.] 190 Pressure Test 80 C., 5.5 MPa [h] 240 Failure mode D Failure mode: D = ductile failure mode B = brittle failure mode