Polyethylene composition suitable for injection moulding applications

Abstract

The present invention relates to a polyethylene composition comprising—a base resin comprising (A) a first ethylene homo- or copolymer component having a melt flow rate MFR2 (2.16 kg, 190° C.) of equal to or more than 150 g/10 min to equal to or less than 300 g/10 min, determined according to ISO 1133, and (B) a second ethylene homo- or copolymer component, —optional carbon black, —optional further polymer component(s) different to the first ethylene homo- or copolymer components (A) and (B), and —optional additive(s); wherein the first ethylene homo- or copolymer component (A) has a lower weight average molecular weight as the second ethylene homo- or copolymer component (B), and the weight ratio of the first ethylene homo- or copolymer component (A) to the second ethylene homo- or copolymer component (B) is from 40:60 to 47:53; the polyethylene composition has a melt flow rate MFR5 (5 kg, 190° C.) of equal to or more than 0.35 g/10 min to equal to or less than 0.60 g/10 min, determined according to ISO 1133. The invention further relates to a process for the production of such a polyethylene composition, an article, such as a pipe or pipe fitting comprising such a polyethylene composition and the use of such a polyethylene composition for the production of such an article.

Claims

1. Polyethylene composition comprising a base resin comprising (A) a first ethylene homo- or copolymer component having a melt flow rate MFR.sub.2 (2.16 kg, 190° C.) of equal to or more than 150 g/10 min to equal to or less than 300 g/10 min, determined according to ISO 1133, and (B) a second ethylene homo- or copolymer component, optional carbon black, optional further polymer component(s) different to the first ethylene homo- or copolymer components (A) and (B), and optional additive(s); wherein the first ethylene homo- or copolymer component (A) has a lower weight average molecular weight as the second ethylene homo- or copolymer component (B), and the weight ratio of the first ethylene homo- or copolymer component (A) to the second ethylene homo- or copolymer component (B) is from 40:60 to 47:53; the polyethylene composition has a melt flow rate MFR.sub.5 (5 kg, 190° C.) of equal to or more than 0.35 g/10 min to equal to or less than 0.60 g/10 min, determined according to ISO 1133; and wherein the composition has a flow rate ratio, being the ratio of MFR.sub.21 to MFR.sub.5, of from 20 to 30.

2. The polyethylene composition according to claim 1, wherein the base resin has a density of equal to or more than 943 kg/m.sup.3 to equal to or less than 952 kg/m.sup.3, determined according to ISO 1183.

3. The polyethylene composition according to claim 1, wherein the first ethylene homo- or copolymer component (A) is an ethylene homopolymer.

4. The polyethylene composition according to claim 1, wherein the second ethylene homo- or copolymer component (B) is a copolymer of ethylene with one or more alpha-olefin comonomers having from 3 to 12 carbon atoms.

5. The polyethylene composition according to claim 1, wherein the composition has a melt flow rate MFR.sub.21 (21.6 kg; 190° C.) of equal to or more than 8.0 g/10 min to equal to or less than 15.5 g/10 min, determined according to ISO 1133.

6. The polyethylene composition according to claim 1, wherein the composition comprises carbon black in an amount of 1.0 to 8.0 wt %.

7. The polyethylene composition according to claim 1, wherein the composition has a density of equal to or more than 955 to equal to or less than 965 kg/m.sup.3, determined according to ISO 1183.

8. The polyethylene composition according to claim 1, wherein the composition comprises: a base resin consisting of (A) a first ethylene homo- or copolymer component having a melt flow rate MFR.sub.2 (2.16 kg, 190° C.) of equal to or more than 150 g/10 min to equal to or less than 300 g/10 min, determined according to ISO 1133, (B) a second ethylene homo- or copolymer component, and an ethylene prepolymer component; carbon black; and optional additives; wherein the first ethylene homo- or copolymer component (A) has a lower weight average molecular weight as the second ethylene homo- or copolymer component (B), and the weight ratio of the first ethylene homo- or copolymer component (A) including the ethylene prepolymer component to the second ethylene homo- or copolymer component (B) is from 40:60 to 47:53; the polyethylene composition has a melt flow rate MFR.sub.5 (5 kg, 190° C.) of equal to or more than 0.35 g/10 min to equal to or less than 0.60 g/10 min, determined according to ISO 1133.

9. A polyethylene composition obtainable by a multistage process, the process comprising a) polymerizing ethylene in the presence of a Ziegler-Natta catalyst for obtaining an intermediate material, the intermediate material having a melt flow rate MFR.sub.2 (2.16 kg, 190° C.) of equal to or more than 150 g/10 min to equal to or less than 300 g/10 min, determined according to ISO 1133, b) transferring the intermediate material to a gas phase reactor (i) feeding ethylene and at least one alpha-olefin comonomer having from 3 to 12 carbon atoms to the gas phase reactor (ii) further polymerizing the intermediate material to obtain a base resin which comprises the intermediate material in an amount of 40 to 47 wt % of the base resin, c) extruding the base resin, optionally in the presence of carbon black and/or further additive(s), into a polyethylene composition having a melt flow rate MFR.sub.5 (5 kg, 190° C.) of equal to or more than 0.35 g/10 min to equal to or less than 0.60 g/10 min, determined according to ISO 1133; wherein the composition has a flow rate ratio, being the ratio of MFR.sub.21 to MFR.sub.5, of from 20 to 30.

10. An article comprising the polyethylene composition according to claim 1.

11. The article according to claim 10 being a pipe or pipe fitting.

12. The article according to claim 11, wherein the pipe has a pressure resistance of at least 50 h, determined according to ISO 1167-1:2006 at a hoop stress of 5.5 MPa and 80° C.

13. The article according to claim 11, wherein the pipe has a pressure resistance of at least 350 h, determined according to ISO 1167-1:2006 at a hoop stress of 5.3 MPa and 80° C.

14. The article according to claim 10, wherein the pipe has a slow crack propagation resistance of at least 700 h, determined in the Notched Pipe Test according to ISO 13479-2009 at a hoop stress of 4.6 MPa and 80° C.

15. An article comprising the polyethylene composition according to claim 9.

16. The polyethylene composition according to claim 1, having a Charpy notched impact strength, determined according to ISO 179eA at a temperature of −20° C., of more than 8.0 kJ/m.sup.3.

17. A polyethylene composition consisting of a base resin consisting of (A) a first ethylene homopolymer component having a melt flow rate MFR.sub.2(2.16 kg, 190° C.) of equal to or more than 170 g/10 min to equal to or less than 230 g/10 min, determined according to ISO 1133, (B) a second ethylene copolymer component, being a copolymer of ethylene and 1-hexene, and an ethylene homopolymer prepolymer component; carbon black; and optional additives; wherein the first ethylene homopolymer component (A) has a lower weight average molecular weight than the second ethylene copolymer component (B), and the weight ratio of the first ethylene homopolymer component (A) including the ethylene prepolymer component to the second ethylene copolymer component (B) is from 42:68 to 46:54; the polyethylene composition has a melt flow rate MFR.sub.5 (5 kg, 190° C.) of equal to or more than 0.42 g/10 min to equal to or less than 0.57 g/10 min, determined according to ISO 1133, wherein the composition has a flow rate ratio, being the ratio of MFR.sub.21 to MFR.sub.5, of from 23 to 28.

18. The polyethylene composition according to claim 17, wherein the base resin has a density of equal to or more than 946 kg/m.sup.3 to equal to or less than 950 kg/m.sup.3.

19. The polyethylene composition according to claim 17, wherein the base resin has a hexene content of 0.45 mol % to 1.5 mol %.

20. The polyethylene composition according to claim 17, wherein the composition has a MFR.sub.21 (21.6 kg, 190° C.) of equal to or more than 11.0 g/10 min to equal to or less than 13.0 g/10 min, determined according to ISO 1133.

21. The polyethylene composition according to claim 1 having a Charpy notched impact strength, determined according to ISO 179eA at a temperature of −20° C. of at least 9.3 kJ/m.sup.3.

Description

EXAMPLES

(1) 1. Definitions

(2) a) Melt Flow Rate

(3) 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, FRR.sub.21/5 denotes the value of MFR.sub.21/MFR.sub.5.

(4) b) Density

(5) 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.

(6) c) Comonomer Content

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

(8) 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 (1 k) transients were acquired per spectrum. This setup was chosen due to its high sensitivity towards low comonomer contents.

(9) 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 (δ+) at 30.00 ppm {[9]}.

(10) 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

(11) 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

(12) 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 2 s and 3 s sites respectively:
S=(1/2)*(I.sub.2S+I.sub.3S)

(13) The relative content of ethylene was quantified using the integral of the bulk methylene (δ+) signals at 30.00 ppm:
E=(1/2)*I.sub.δ+

(14) 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+(3/2)*S

(15) The total mole fraction of 1-hexene in the polymer was then calculated as:
fH=(H.sub.total/(E.sub.total+H.sub.total)

(16) The total comonomer incorporation of 1-hexene in mole percent was calculated from the mole fraction in the usual manner:
H[mol %]=100*fH

(17) 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)+((1−fH)*28.05)) [1] Klimke, K., Parkinson, M., Piel, C., Kaminsky, W., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2006; 207:382. [2] Parkinson, M., Klimke, K., Spiess, H. W., Wilhelm, M., Macromol. Chem. Phys. 2007; 208:2128. [3] Pollard, M., Klimke, K., Graf, R., Spiess, H. W., Wilhelm, M., Sperber, O., Piel, C., Kaminsky, W., Macromolecules 2004; 37:813. [4] Filip, X., Tripon, C., Filip, C., J. Mag. Reson. 2005, 176, 239. [5] Griffin, J. M., Tripon, C., Samoson, A., Filip, C., and Brown, S. P., Mag. Res. in Chem. 2007, 45, S1, S198. [6] Castignolles, P., Graf, R., Parkinson, M., Wilhelm, M., Gaborieau, M., Polymer 50 (2009) 2373. [7] Zhou, Z., Muemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 2007, 187, 225. [8] Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128. [9] J. Randall, Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201.

(18) d) Pressure Test on Notched Pipes (NPT); Slow Crack Propagation Resistance.

(19) The slow crack propagation resistance is determined according to ISO 13479-2009 in terms of the number of hours the pipe withstands a certain pressure at a certain temperature before failure. The pressure test is carried out on notched SDR11 pipes having a outer diameter of 110 mm. A pressure of 9.2 bars and a temperature of 80° C. have been used. Notching is made with a climb milling cutter with a 60° included-angle V-cutter conforming to ISO 6108, having a cutting rate of 0.010±0.002 (mm/rev)/tooth. The used cutter has 24 teeth and the speed of the cutter is 680 rpm. The remaining ligament is 0.82-0.78 times the minimum wall thickness. The depth of the notch is calculated using equation below. h is the notch depth in mm. The four notches are equally placed in the pipe circumference. The length of the notch is 110±1 mm.
h=0.5[d.sub.em−√{square root over ((d.sub.em.sup.2−b.sub.S.sup.2))}]+0.866b.sub.S
where b.sub.s is the width of machined surface of the notch in mm; d.sub.em is the measured mean pipe outside diameter in mm.

(20) e) Pressure Test on Un-Notched Pipes (PT); Resistance to Internal Pressure

(21) 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. A hoop stress of 5.5 MPa at a temperature of 80° C. and at a hoop stress at 5.3 MPa tested at a temperature of 80° C. was applied.

(22) f) Rapid Crack Propagation

(23) The rapid crack propagation (RCP) resistance of a pipe is determined according to a method called the S4 test (Small Scale Steady State), which has been developed at Imperial College, London, and which is described in ISO 13477: 1997 (E). According to the RCP-S4 test a pipe is tested, which has an axial length not below 7 pipe diameters. The outer diameter of the pipe is about 110 mm or greater and its wall thickness about 10 mm or greater. When determining the RCP properties of a pipe in connection with the present invention, the outer diameter and the wall thickness have been selected to be 250 mm and 22.7 mm, respectively. While the exterior of the pipe is at ambient pressure (atmospheric pressure), the pipe is pressurised internally, and the temperature of the pipe is kept constant at a temperature of 0° C. The pipe and the equipment surrounding it are thermostatted to a predetermined temperature. A number of discs have been mounted on a shaft inside the pipe to prevent decompression during the tests. A knife projectile is shot, with well-defined forms, towards the pipe close to its one end in the so-called initiating zone in order to start a rapidly running axial crack. The initiating zone is provided with an abutment for avoiding unnecessary deformation of the pipe. The test equipment is adjusted in such a manner that crack initiation takes place in the material involved, and a number of tests are effected at varying temperatures. The axial crack length in the measuring zone, having a total length of 4.7 times the pipe diameter, is measured for each test and is plotted against the set test temperature. If the crack length exceeds 4.7 times the pipe diameter, the crack is assessed to propagate. If the pipe passes the test at a given pressure, the pressure is increased successively until a pressure is reached, at which the pipe no longer passes the test and the crack propagation exceeds 4.7 times the pipe diameter. The critical pressure (p.sub.crit), i.e. the ductile brittle transition pressure as measured according to ISO 13477: 1997 (E) is the highest pressure at which the pipe passes the test. The higher the critical pressure (p.sub.c) the better, since it results in an extension of the applicability of the pipe. In case the rapid crack propagation resistance of the composition is reported, a specimen as defined above has been prepared and the rapid crack propagation resistance determined thereon.

(24) g) Charpy Notched Impact Strength

(25) Charpy impact strength was determined according to ISO179/1eA:2000 on V-notched samples of 80*10*4 mm.sup.3 at −20° C. (Charpy impact strength (−20° C.)). Samples 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.

(26) 2. Examples

(27) a) Polymerization of Inventive Example IE1

(28) A loop reactor having a volume of 50 dm.sup.3 was operated at 60° C. and 65 bar pressure. For producing a prepolymer fraction 50 kg/h of propane diluent, 2 kg/h ethylene and 10 g/h of h of hydrogen were introduced into the reactor. In addition, commercially available Ziegler-Natta catalyst Lynx 200 polymerisation catalyst (BASF SE) was introduced into the reactor together with triethylaluminium cocatalyst so that the ratio of aluminium to titanium was 15 mol/mol. No comonomer was introduced into the reactor. The polymerisation rate was 1.9 kg/h and the conditions in the reactor as shown in Table 1.

(29) The polymer slurry was withdrawn from the loop reactor and transferred into a loop reactor having a volume of 500 dm.sup.3. This second loop reactor was operated at 95° C. and 65 bar pressure. Into the reactor were introduced 90 kg/h of propane diluent, ethylene and hydrogen whereby the molar hydrogen to ethylene ratio for example IE1 is listed in Table 1. The polymerisation rate was about 33 kg/h and the conditions in the reactor as shown in Table 1.

(30) The polymer slurry was withdrawn from the second loop reactor and transferred into a flash vessel operated at 3 bar pressure and 70° C. temperature where the hydrocarbons were substantially removed from the polymer. The polymer was then introduced into a gas phase reactor operated at a temperature of 85° C. and a pressure of 20 bar. In addition ethylene, 1-hexene, nitrogen as inert gas and hydrogen was introduced into the reactor whereby the molar 1-hexene to ethylene ratio and the molar hydrogen to ethylene ratio as well as the production split, the melt flow rates and the density of the polymers of IE1 withdrawn from the gas phase reactor are listed in Table 1. The polymerisation rate was about 40 kg/h. The conditions are shown in Table 1.

(31) The resulting polymer was purged with nitrogen (about 50 kg/h) for one hour, stabilised with 2200 ppm of Irganox B225 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.

(32) b) Comparative Examples CE1 and CE2

(33) Comparative Examples CE1 to CE2 were polymerized using the same catalyst and cocatalyst components with a ratio of aluminium to titanium of 15 mol/mol and the same reactor configuration as Inventive Example IE1. The polymerization conditions and feeds to the different reactors are shown in Table 1. The resultant base resins of Comparative Examples CE1 and CE2 were treated and compounded as Inventive Example IE1.

(34) c) Pipe Preparation

(35) The compounded compositions of Inventive Example IE1 and Comparative Examples CE1 and CE2 were extruded to SDR 11 pipes for the pressure resistance tests and the Notched Pipe test.

(36) For the Rapid Crack Propagation Test (S4) pipes with a diameter of 250 mm and a wall thickness of 22.7 mm were extruded.

(37) The results of the pipe tests are shown in Table 2.

(38) TABLE-US-00001 TABLE 1 Polymerization conditions CE1 CE2 IE1 Prepolymerizer: Temperature [° C.] 60 60 60 Pressure [bar] 65 65 65 Production rate [kg/h] 1.9 1.9 1.9 Split [wt %] 2.3 2.3 2.3 Loop: Temperature [° C.] 95 95 95 Pressure [bar] 65 65 65 H.sub.2/C.sub.2 [mol/kmol] 1100 1100 920 C.sub.2-concentration [mol %] 2.6 2.5 2.7 Production Rate [kg/h] 35 33 33 Split [wt %] includes prepoly 47 45 45 MFR.sub.2 [g/10 min] 325 325 200 Gas phase: Temperature [° C.] 85 85 85 H.sub.2/C.sub.2 ratio [mol/kmol] 57 64 56 C.sub.6/C.sub.2 [mol/kmol] 64 65 64 C.sub.2-concentration [mol %] 15 16 17 Production Rate [kg/h] 40 40 40 Split [wt %] 53 55 55 Density [kg/m.sup.3] 949 949 949 Composition Properties: Density [kg/m.sup.3] 960 960 960 MFR.sub.5 [g/10 min] 0.50 0.55 0.45 MFR.sub.21 [g/10 min] 14 15 12 FRR.sub.21/5 28 27 27 Charpy NIS (−20° C.) 8.0 8.0 9.5

(39) TABLE-US-00002 TABLE 2 Pipe properties CE1 CE2 IE1 Pressure resist. (5.5 MPa) [h] 28 35 160 Pressure resist. (5.3 MPa) [h] 330 233 863 Notched Pipe Test (4.6 MPa) [h] 650 693 1043 p.sub.c (S4-Test) (0° C.) [bar] ≧10 n.d. ≧10