Process for Producing Multimodal Polyethylene in-situ Blends Including Ultra-High Molecular Weight Fractions

Abstract

The present application relates to a process for producing a multimodal polyethylene composition comprising the steps of polymerizing a polyethylene fraction (A-1) having a weight average molecular weight Mw of equal to or more than 500 kg/mol to equal to or less than 10,000 kg/mol and a density of equal to or more than 915 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 in one reaction step and polymerizing a polyethylene fraction (A-2) having a lower weight average molecular weight Mw as polyethylene fraction (A-1) and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 975 kg/m.sup.3 in a second reaction step of a sequential multistage process wherein one of said polyethylene fractions is polymerized in the presence of the other of said polyethylene fractions to form a first polyethylene resin (A) having a weight average molecular weight Mw of equal to or more than 150 kg/mol to equal to or less than 1,500 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 975 kg/m.sup.3, wherein the weight average molecular weight Mw of the first polyethylene resin (A) is lower than the weight average molecular weight Mw of the polyethylene fraction (A-1), blending the first polyethylene resin (A) with a second polyethylene resin (B) having a weight average molecular weight Mw of equal to or more than 50 kg/mol to less than 500 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 970 kg/m.sup.3 to form said multimodal polyethylene composition, wherein the multimodal polyethylene composition a melt flow rate MFR.sub.5 (190° C., 5 kg) of 0.01 to 10 g/10 min and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 970 kg/m.sup.3 a polyethylene composition obtainable by said process and the polyethylene resin of said first polymerization step.

Claims

1-15. (canceled)

16. A process for producing a multimodal polyethylene composition comprising the following steps: a) polymerizing a polyethylene fraction (A-1) having a weight average molecular weight Mw of equal to or more than 500 kg/mol to equal to or less than 10,000 kg/mol and a density of equal to or more than 915 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 in one reaction step and polymerizing a polyethylene fraction (A-2) having a lower Mw as polyethylene fraction (A-1) and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 975 kg/m.sup.3 in a second reaction step of a sequential multistage process wherein one of said polyethylene fractions is polymerized in the presence of the other of said polyethylene fractions to form a first polyethylene resin (A) having a weight average molecular weight Mw of equal to or more than 150 kg/mol to equal to or less than 1,500 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 975 kg/m.sup.3, wherein the weight average molecular weight Mw of the first polyethylene resin (A) is lower than the weight average molecular weight Mw of the polyethylene fraction (A-1); ii) blending the first polyethylene resin (A) with a second polyethylene resin (B) having a weight average molecular weight Mw of equal to or more than 50 kg/mol to less than 500 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 970 kg/m.sup.3 to form said multimodal polyethylene composition, wherein the multimodal polyethylene composition a melt flow rate MFR.sub.5 (190° C., 5 kg) of 0.01 to 10 g/10 min and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 970 kg/m.sup.3 and the weight ratio of said first polyethylene resin (A) to said second polyethylene resin (B) in the polyethylene composition is 2:98 to 40:60.

17. The process according to claim 16, wherein said first polyethylene resin (A) is pelletized prior to blending with said second polyethylene resin (B) to form the polyethylene composition.

18. The process according to claim 16, wherein said first polyethylene resin (A) is blended in powder form with said second polyethylene resin (B) to form the polyethylene composition.

19. The process according to claim 16, wherein said polyethylene fraction (A-2) is polymerized in the presence of said polyethylene fraction (A-1).

20. The process according to claim 16, wherein the polyethylene composition is formed by melt blending of said first polyethylene resin (A) and said second polyethylene resin (B).

21. The process according to claim 16, wherein the amount of said polyethylene fraction (A-1) is 0.5 to 36 wt % of the total amount of the polyethylene composition.

22. A polyethylene resin (A) comprising a polyethylene fraction (A-1) having a weight average molecular weight Mw of equal to or more than 500 kg/mol to equal to or less than 10,000 kg/mol and a density of equal to or more than 915 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 and a polyethylene fraction (A-2) having a lower weight average molecular weight Mw as polyethylene fraction (A-1) of 5 to 400 kg/mol and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 975 kg/m.sup.3, wherein the polyethylene resin (A) has a weight average molecular weight Mw of equal to or more than 150 kg/mol to equal to or less than 1,500 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 975 kg/m.sup.3, wherein the weight average molecular weight Mw of the polyethylene resin (A) is lower than the weight average molecular weight Mw of the polyethylene fraction (A-1) and wherein polyethylene resin (A) is produced by polymerizing polyethylene fractions (A-1) and (A-2) at different stages of a multistage process wherein one of said polyethylene fractions is polymerized in the presence of the other of said polyethylene fractions.

23. A polyethylene composition obtainable by a process comprising the following steps: i) polymerizing a polyethylene fraction (A-1) having a weight average molecular weight Mw of equal to or more than 500 kg/mol to equal to or less than 10,000 kg/mol and a density of equal to or more than 915 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 in one reaction step and polymerizing a polyethylene fraction (A-2) having a lower weight average molecular weight Mw as polyethylene fraction (A-1) of 5 to 400 kg/mol and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 975 kg/m.sup.3 in a second reaction step of a sequential multistage process wherein one of said polyethylene fractions is polymerized in the presence of the other of said polyethylene fractions to form a first polyethylene resin (A) having a weight average molecular weight Mw of equal to or more than 150 kg/mol to equal to or less than 1,500 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 975 kg/m.sup.3, wherein the weight average molecular weight Mw of the first polyethylene resin (A) is lower than the weight average molecular weight Mw of the polyethylene fraction (A-1), ii) blending the first polyethylene resin (A) with a second polyethylene resin (B) having a weight average molecular weight Mw of equal to or more than 50 kg/mol to less than 500 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 970 kg/m.sup.3 to form said multimodal polyethylene composition, wherein the multimodal polyethylene composition a melt flow rate MFR.sub.5 (190° C., 5 kg) of 0.01 to 10 g/10 min and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 970 kg/m.sup.3 and the weight ratio of said first polyethylene resin (A) to said second polyethylene resin (B) in the polyethylene composition is 2:98 to 40:60.

24. The polyethylene composition according to claim 23 having a rating in the ISO 18553:2002 white spot rating test of less than 4.

25. The polyethylene composition according to claim 23 wherein said polyethylene fraction (A-1) is an ethylene homopolymer.

26. The polyethylene composition according to claim 23 wherein said second polyethylene resin (B) is a copolymer of ethylene and at least one alpha-olefin comonomer having from 3 to 12 carbon atoms.

27. The polyethylene composition according to claim 23 having a melt flow rate MFR.sub.21 (190° C., 21.6 kg) of 5 to 20 g/10 min.

28. The polyethylene composition according to claim 23 a viscosity at a shear stress of 747 Pa, eta.sub.747 Pa, of 500 kPas or more.

29. The polyethylene composition according to claim 23 having a z average molecular weight Mz of equal to or more than 1,000 kg/mol to equal to or less than 5,000 kg/mol.

Description

2. Figures

[0222] FIG. 1 Microtome cut for evaluating the White Spot Rating of Example 1

[0223] FIG. 2 Microtome cut for evaluating the White Spot Rating of Example 2

[0224] FIG. 3 Microtome cut for evaluating the White Spot Rating of Example 3

[0225] FIG. 4 Microtome cut for evaluating the White Spot Rating of Comparative Example 4

[0226] FIG. 5 Microtome cut for evaluating the White Spot Rating of Comparative Example 5

[0227] FIG. 6 Microtome cut for evaluating the White Spot Rating of Comparative Example 6

3. Examples

a) Preparation of the Catalyst

Complex Preparation:

[0228] 87 kg of toluene were added into the reactor. Then 45.5 kg Bomag A (butyloctyl magnesium) in heptane were also added in the reactor. 161 kg 99.8% 2-ethyl-1-hexanol were then introduced into the reactor at a flow rate of 24 to 40 kg/h. The molar ratio between BOMAG-A and 2-ethyl-1-hexanol was 1:1.83.

Solid Catalyst Component Preparation:

[0229] 330 kg silica (calcined silica, Sylopol® 2100) and pentane (0.12 kg/kg carrier) were charged into a catalyst preparation reactor. Then EADC (Ethylaluminium dichloride) (2.66 mol/kg silica) was added into the reactor at a temperature of below 40° C. during two hours and mixing was continued for one hour. The temperature during mixing was 40 to 50° C. Then the Mg complex prepared as described above was added (2.56 mol Mg/kg silica) at 50° C. during two hours and mixing was continued at 40 to 50° C. for one hour. 0.84 kg pentane/kg silica was added into the reactor and the slurry was stirred for 4 hours at the temperature of 40 to 50° C. Finally, TiCl.sub.4 (1.47 mol/kg silica) was added during at least 1 hour at 55° C. to the reactor. The slurry was stirred at 50 to 60° C. for five hours. The catalyst was then dried by purging with nitrogen.

[0230] Molar composition of the ready catalyst component is:

Al/Mg/Ti=1.5/1.4/0.8 (mol/kg silica).

b) Polymerization of In-Situ UHMW Polyethylene Master Batch MB1 for Inventive Example 1 (Ex1)

[0231] Into a reactor having a volume of 5.3 L were introduced 850 g propane at the room temperature and 37.6 mg polymerisation catalyst having a solid titanium component prepared according to the procedure presented in point a) above and triethylaluminium as an activator so that the molar ratio Al/Ti=15. The reactor was temperature was set to 40° C. and 20 g of ethylene was fed into the reactor. After 4 minutes' prepolymerization, ethylene was continuously introduced into the reactor to maintain an ethylene pressure of 4 bar. The polymerisation was continued until 106 g monomer consumed. Thereafter reactor temperature was increased to 82° C. Then 56.3 L hydrogen was added, the temperature was increased to 85° C. and ethylene feed was started to maintain total pressure in the reactor of 54.8 bar. The polymerisation was continued until 229.5 g monomer consumed.

[0232] The split of polymer produced during the first step to the polymer produced during the second step was thus 13/87.

[0233] When the first polymerisation step was conducted individually the viscosity average molecular weight was 4280 kg/mol. The resulting polymer blend had MFR.sub.5 of 39 g/10 min.

[0234] The polymerization conditions and properties of the UHMW polyethylene master batch MB1 for inventive example 1 (Ex1) are listed in Table 1.

c) Polymerization of In-Situ UHMW Polyethylene Master Batches MB2-3 for Inventive Examples 2 and 3 (E×2 and E×3)

[0235] The polymerization procedure of Example 1 was repeated with the main difference of using a solid polymerization catalyst component sold by BASF under a trade name of Lynx 200 was introduced into the reactor together with triethylaluminium cocatalyst so that the ratio of aluminium to titanium was 15 mol/mol.

[0236] The polymerization conditions and properties of the UHMW polyethylene master batches MB2-3 for inventive examples 2 (Ex2) and 3 (Ex3) are listed in Table 1.

d) Polymerization of In-Situ UHMW Polyethylene Resins Res4-5 for Comparative Examples 4 and 5 (CE4 and CE5)

[0237] The procedure of Example 2 was repeated except that the second polymerization stage was not conducted. The weight average molecular weight Mw of the polymer was 2,220 kg/mol as UHMW resin res4 for CE4 and of 1,590 kg/mol as UHMW resin res5 for CE5.

[0238] The polymerization conditions and properties of the UHMW polyethylene resins res4-5 for comparative examples 4 (CE4) and 5 (CE5) are listed in Table 1.

TABLE-US-00001 TABLE 1 UHMW polyethylene master batches for Ex1-Ex3 (MB1-MB3) and UHMW polyethylene resins for CE4 and CE5 (res4 and res5): polymerization conditions and properties MB1 MB2 MB3 res4 res5 Cocatalyst TEA TEA TEA TEA TEA Step 1 Temperature [° C.] 40 40 50 40 60 Pressure [bar] 4 6 3 6 6 Al/Ti [mol/mol] 15 15 15 15 15 Split [wt.-%] 13 17 16 100 100 Step 2 Not in use Not in use Temperature [° C.] 85 95 95 H.sub.2 amount (l) 56.3 42.5 42.5 Split [wt.-%] 87 83 84 0 0 MFR.sub.5 [g/10 min] 38.66 2.34 2.17 n.m n.m Mw [kg/mol] 269 310 231 2,238 1,572 Mn [kg/mol] 5.0 6.0 5.3 20 4.1 Mw/Mn 54 52 44 112 383 Mz [kg/mol] 3010 3489 2140 3991 3653 n.m. = not measured

[0239] e) Preparation of the Multimodal Polyethylene Compositions of Inventive Examples 1 to 3 (Ex1-3) and Comparative Examples 4 to 7 (CE4-7)

[0240] The powders of the polyethylene resins of Table 1 were melt blended with commercially available bimodal PE100 resin HE3490-LSH (Borealis AG, Wien), being a bimodal high density polyethylene compound for pressure pipes including carbon black having a density of 959 kg/m.sup.3, and a MFR.sub.5 of 0.25 g/10 min.

[0241] All the samples were produced with a co-rotating twin screw extruder Coperion ZSK 18. The temperature in the beginning of the melting zone of the extruder was set to 150° C. and in all the remaining zones to 230° C. The throughput was 0.8 kg/h and the screw speed was 120 RPM.

[0242] For inventive examples 1 to 3 (Ex1-3) the UHMW polyethylene master batches MB1-3 of Table 1 were used, for comparative examples 4 and 5 (CE4 and CE5) the UHMW polyethylene resins res4-5 of Table 1 were used together with a low molecular weight (LMW) ethylene homopolymer resin, produced in the presence of Lynx 200 catalyst (BASF) and TEA cocatalyst, having a density of >970 kg/m.sup.3 and a weight average molecular weight Mw of 28 kg/mol, a number average molecular weight Mn of 4 kg/mol and a z average molecular weight Mz of 224 kg/mol.

[0243] For Comparative example 6 (CE6) commercially available UHMW polyethylene master batch M2 (M2 MB) (Jingchem) having a weight average molecular weight of 760 kg/mol was used. Comparative example 7 (CE7) refers to the PE100 resin HE3490-LSH without addition of a UHMW polyethylene resin.

[0244] The composition of the samples is listed in Table 2.

TABLE-US-00002 TABLE 2 Composition of the multimodal polyethylene compositions of Inventive examples 1 to 3 (Ex1-3) and Comparative examples 4 to 7 (CE4-7) Ex1 Ex2 Ex3 CE4 CE5 CE6 CE7 HE3490 [wt %] 84 88 87 88 87 93 100 MB1 [wt %] 16 MB2 [wt %] 12 MB3 [wt %] 13 Res4 [wt %] 2 Res5 [wt %] 2 LMW [wt %] 10 11 M2 MB [wt %] 7

[0245] After compounding the homogeneity of the samples are detected via light microscope and quantified as white spot rating (WSR). The microtome cuts for evaluating the WSR for Examples Ex1-3 and Comparative Examples CE4-6 are shown in FIGS. 1-6.

[0246] Further the viscosity at a shear stress of 747 Pa is determined. The results are listed in Table 3.

TABLE-US-00003 TABLE 3 Properties of the multimodal polyethylene compositions of Inventive examples 1 to 3 (Ex1-3) and Comparative examples 4 to 7 (CE4-7) Ex1 Ex2 Ex3 CE4 CE5 CE6 CE7 WSR 0.83 0.58 1.50 7.00 4.67 5.6 2.42 MFR.sub.5 [g/10 min] 0.29 0.22 0.32 0.28 0.26 0.17 0.28 MFR.sub.21 [g/10 min] 14.2 10.8 9.7 10.1 10.4 6.8 10.6 Mw [kg/mol] 222 237 247 243 232 259 228 Mz [kg/mol] 1510 1615 1705 1605 1555 1551 1350 Eta.sub.747 [kPa .Math. s] 941 1295 1175 902 766 n.d. 428 n.d. = not determined

f) Polymerization of In-Situ UHMW Polyethylene Master Batches MB8 to MB11

[0247] The polymerization procedure of Example 1 was repeated except that the conditions and properties were as given in Table 4

g) Preparation of Comparative UHMW Polyethylene Master Batch MB12

[0248] For the preparation of the comparative UHMW master batch MB12 commercially available UHMW polyethylene master batch M2 (M2 MB) (Jingchem) having a weight average molecular weight of 760 kg/mol was compounded with a low molecular weight (LMW) ethylene homopolymer resin as described above in a weight ratio of 50:50.

[0249] The properties of the comparative UHMW polyethylene master batch MB12 12 is listed in Table 4.

TABLE-US-00004 TABLE 4 UHMW polyethylene master batches MB8-MB11 and comparative UHMW polyethylene master batch MB12: polymerization conditions and properties MB8 MB9 MB10 MB11 Cocatalyst TEA TEA TEA TEA MB12 Step 1 Temperature 70 70 50 50 [° C.] Pressure [bar] 4 6 3 6 Split [wt.-%] 48 74 51 77 Step 2 Temperature 85 85 85 85 [° C.] Split [wt.-%] 52 26 49 23 MFR.sub.5 0.06 0.06 0.01 0.01 0.01 [g/10 min] MFR.sub.21 2.1 0.14 1.5 0.10 0.76 [g/10 min] MFR.sub.21/MFR.sub.5 35 2.3 153 10 76 Mw [kg/mol] 422 654 708 809 558 Mn [kg/mol] 5.8 10 5.6 8.7 8.0 Mw/Mn 72.5 66.3 127.2 93.4 65.7 Mz [kg/mol] 2520 2425 2725 3185 n.d. Density 973.6 965.1 971.1 964.1 967.1 [kg/m.sup.3] Eta.sub.0.05 [kPa .Math. s] 1437 2528 2393 5538 1638 Eta.sub.747 [kPa .Math. s] 12776 19171 46558 912740 n.d WSR 2.17 2.83 4.0 4.33 9.3 n.d. = not determined

h) Preparation of the Multimodal Polyethylene Compositions of Inventive Examples 8 to 10 (Ex 8-10), Inventive Examples 11 to 16 (Ex 11-16) and Comparative Example 17 (CE17)

[0250] The UHMW master batches MB8 to MB10 of Table 4 were melt blended with commercially available bimodal PE100 resin HE3490-LSH (Borealis AG, Wien), being a bimodal high density polyethylene compound for pressure pipes including carbon black having a density of 959 kg/m.sup.3, and a MFR.sub.5 of 0.25 g/10 min.

[0251] For inventive examples 8 to 10 (Ex 8-10) the resins of compounded pellets of UHMW polyethylene master batches MB8 to MB10 were blended with HE3490-LSH, whereas for inventive examples 11 to 16 (Ex 11-16) the dried powders of UHMW polyethylene master batches MB8 to MB11 were blended with HE3490-LSH.

[0252] The same compounding conditions were used as described above for Examples 1 to 3.

[0253] The composition of the samples is listed in Table 5.

[0254] Comparative example 17 (CE17) refers to the PE100 resin HE3490-LSH without addition of a UHMW polyethylene resin.

TABLE-US-00005 TABLE 5 Composition of the multimodal polyethylene compositions of Inventive examples 8-11 (Ex8-10), Inventive examples 11-16 (Ex 11-16) and Comparative example 17 (CE17) CE17 Ex8 Ex11 Ex12 Ex9 Ex13 Ex10 Ex14 Ex15 Ex16 HE3490 [wt %] 100 94 94 91.5 96 96 91.2 91.2 94 96 Pellets 6 MB8 [wt %] Pellets 4 MB9 [wt %] Pellets 8.8 MB10 [wt %] Powder 6 9.5 MB8 [wt %] Powder 4 MB9 [wt %] Powder 8.8 6 MB10 [wt %] Powder 4 MB11 [wt %]

[0255] After compounding the homogeneity of the samples are detected via light microscope and quantified as white spot rating (WSR). Further the viscosity at a shear stress of 747 Pa is determined. The results are listed in Table 6.

TABLE-US-00006 TABLE 6 Properties of the multimodal polyethylene compositions of Inventive examples 8 to 10 (Ex8-10), Inventive examples 11 to 16 (Ex 11-16) and Comparative example 17 (CE17) CE17 Ex8 Ex11 Ex12 Ex9 Ex13 Ex10 Ex14 Ex15 Ex16 WSR 2.42 1.92 2.25 2.83 1.67 3.42 2.25 3.33 3.17 4.0 MFR.sub.5 [g/10 min] 0.28 0.23 0.28 0.20 0.21 0.25 0.17 0.19 0.20 0.18 MFR.sub.21 [g/10 min] 10.6 8.6 10.0 8.2 8.1 7.9 8.0 7.6 8.0 7.1 Mw [kg/mol] 228 251 260 265 249 248 292 305 272 278 Mz [10.sup.6 g/mol] 1.35 1.44 1.74 1.80 1.50 1.54 2.18 2.24 1.74 1.78 Eta.sub.747 [kPa .Math. s] 428 607 624 724 604 613 1267 1195 988 966 Density [kg/m.sup.3] 961.2 962.4 961.5 962.4 962.3 961.4 963.4 962.1 961.7 961.6