PROCESS FOR PRODUCING MULTIMODAL POLYETHYLENE BLENDS INCLUDING ULTRA-HIGH MOLECULAR WEIGHT COMPONENTS

Abstract

The present application relates to a process for producing a multimodal polyethylene composition comprising the steps of blending a polyethylene fraction (A-1) having a weight average molecular weight Mw of equal to or more than 700 kg/mol to equal to or less than 10,000 kg/mol and a density of equal to or more than 920 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 and 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 960 kg/m.sup.3 with a weight ratio of (A-1) to (A-2) of 45:55 to 80:20 to form a first polyethylene resin (A) having a Mw of equal to or more than 200 kg/mol to equal to or less than 1500 kg/mol, a melt flow rate MFR.sub.5 (190° C., 5 kg) of 0.001 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 960 kg/m.sup.3, blending the first polyethylene resin (A) with a second polyethylene resin (B) having a Mw of equal to or more than 50 kg/mol to less than 700 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 to form the 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/m3 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 blending step.

Claims

1-15. (canceled)

16. A process for producing a multimodal polyethylene composition comprising the following steps: i) blending a polyethylene fraction (A-1) having a viscosity average molecular weight My of equal to or more than 700 kg/mol to equal to or less than 10,000 kg/mol and a density of equal to or more than 920 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 and a polyethylene fraction (A-2) having a lower Mw as polyethylene fraction (A-1) of 50 to 500 kg/mol and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 with a weight ratio of (A-1) to (A-2) of 45:55 to 80:20 to form a first polyethylene resin (A) having a Mw of equal to or more than 200 kg/mol to equal to or less than 1500 kg/mol, a melt flow rate MFR.sub.5 (190° C., 5 kg) of 0.001 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 960 kg/m.sup.3, ii) blending the first polyethylene resin (A) with a second polyethylene resin (B) having a Mw of equal to or more than 50 kg/mol to less than 700 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 to form the multimodal polyethylene composition, wherein the weight ratio of the first polyethylene resin (A) to the second polyethylene resin (B) in the polyethylene composition is 2:98 to 50:50, and wherein the multimodal polyethylene composition has 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.

17. The process according to claim 16, wherein the first polyethylene resin (A) is formed by melt blending of polyethylene fractions (A-1) and (A-2).

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

19. The process according to claim 16, wherein the second polyethylene resin (B) is blended in powder form with the first polyethylene resin (A) optionally together with additional additives to form the polyethylene composition.

20. The process according to claim 16, wherein the second polyethylene resin (B) is pelletized optionally together with additional additives prior to blending with the first polyethylene resin (A) to form the polyethylene composition.

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

22. The process according to claim 21, wherein the first polyethylene resin (A) and the second polyethylene resin (B) were dry-blended prior to the melt blending step.

23. The process according to claim 16, wherein the second polyethylene resin (B) is a multimodal polyethylene resin.

24. A polyethylene resin (A) comprising a polyethylene fraction (A-1) having a weight average molecular weight Mw of equal to or more than 700 kg/mol to equal to or less than 10,000 kg/mol and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 and a polyethylene fraction (A-2) having a lower Mw as polyethylene fraction (A-1) of 50 to 500 kg/mol and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 with a weight ratio of (A-1) to (A-2) of 45:55 to 80:20, wherein the polyethylene resin (A) has a Mw of equal to or more than 200 kg/mol to equal to or less than 1500 kg/mol, a melt flow rate MFR.sub.5 (190° C., 5 kg) of 0.001 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 960 kg/m.sup.3.

25. A polyethylene composition obtainable by a process comprising the following steps: i) blending a polyethylene fraction (A-1) having a weight average molecular weight Mw of equal to or more than 700 kg/mol to equal to or less than 10,000 kg/mol and a density of equal to or more than 920 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 and a polyethylene fraction (A-2) having a lower Mw as polyethylene fraction (A-1) of 50 to 500 kg/mol and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 with a weight ratio of (A-1) to (A-2) of 45:55 to 80:20 to form a first polyethylene resin (A) having a Mw of equal to or more than 200 kg/mol to equal to or less than 1500 kg/mol, a melt flow rate MFR.sub.5 (190° C., 5 kg) of 0.001 to 40 g/10 min and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3, ii) blending the first polyethylene resin (A) with a second polyethylene resin (B) having a Mw of equal to or more than 50 kg/mol to less than 700 kg/mol, and a density of equal to or more than 910 kg/m.sup.3 to equal to or less than 960 kg/m.sup.3 to form the multimodal polyethylene composition, wherein the weight ratio of the first polyethylene resin (A) to the second polyethylene resin (B) in the polyethylene composition is 2:98 to 50:50, and wherein the multimodal polyethylene composition has 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.

26. The polyethylene composition according to claim 25 having a rating in the white spot area of not more than 5.0%.

27. The polyethylene composition according to claim 25 having a shear thinning index SHI.sub.0.1/100, being the ratio of the complex viscosities determined for the complex shear moduli of 0.1 kPa and 100 kPa, of 7 to 30.

28. The polyethylene composition according to claim 25, wherein the ratio of the complex viscosity at a shear rate of 0.1 Pa of the multimodal polyethylene composition, eta.sub.0.1 (Composition), to the complex viscosity determined for the complex shear modulus of 0.1 kPa of the polyethylene resin (B), eta.sub.0.1 (B), is in the range of 1.1 to 2.5.

29. The polyethylene composition according to claim 25, wherein the amount of polyethylene fraction (A-1) is 0.5 to 30 wt % of the total polyethylene composition.

Description

2. FIGURES

[0236] FIGS. 1 and 2 show the screw design of the extruders used for the production of the pre-blends and the polymers of the examples according to the invention.

[0237] FIG. 1: Leistritz ZSE 27 MAXX screw design for the production of the pre-blends

[0238] Raw material feed at the arrow on the top of the figure; melt exit at the left

[0239] FIG. 2: Coperion ZSK 40 screw design for the production of the polymers of the examples according to the invention

[0240] Raw material feed at the arrow; melt exit at the right

3. EXAMPLES

[0241] a) Polymerization of Reference Example 1 (RE1)

[0242] A loop reactor having a volume of 50 dm.sup.3 was operated continuously at a temperature of 60° C. and a pressure of 62 bar. Into the reactor were introduced 42 kg/h of propane diluent, 2 kg/h of ethylene and 35 g/h of hydrogen. In addition 6.3 g/h of 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 30 mol/mol. The rate of polymer production was about 1.8 kg/h.

[0243] The slurry from the 50 dm.sup.3 loop reactor was withdrawn and transferred continuously to another loop reactor having a volume of 500 dm.sup.3 and which was operated at a temperature of 95° C. and a pressure of 60 bar. Into the reactor were introduced additional propane diluent, ethylene and hydrogen. The ethylene concentration in the fluid mixture was 3.4 mol-%, based on the total number of moles in the fluid mixture, the molar ratio of hydrogen to ethylene 650 mol/kmol. The rate of polymer production was 32 kg/h and the MFR.sub.2 of the ethylene homopolymer was 500 g/10 min.

[0244] The slurry from the loop reactor was withdrawn by using settling legs into a flash vessel operated at a temperature of 50° C. and a pressure of 3 bar where the hydrogen and major part of the hydrocarbons was removed from the polymer. The ethylene homopolymer was directed into a fluidized bed gas phase reactor operated at 85° C. temperature and 20 bar pressure. Into the reactor were introduced additional ethylene, 1-butene comonomer, hydrogen and nitrogen as inert gas. The ethylene concentration was 11 mol-%, based on the total number of moles in the gas mixture. Hydrogen and 1-butene were added so that the bimodal. polymer had a density of 943 kg/m.sup.3, an MFR.sub.5 of 2 g/10 min and a weight average molecular weight Mw of 129 kg/mol. The split between the polymer produced in the loop reactor and the gas phase reactor was 50/50.

[0245] The resulting polymer powder was dried from hydrocarbons and mixed with 3000 ppm of Irganox B225, 1000 ppm of calcium stearate and 2.4% of carbon black, based on the final composition. A part of the mixture was then extruded into pellets by using a CIM90P twin screw extruder (manufactured by Japan Steel Works).

[0246] b) Production of the Pre-blends

[0247] PB1:

[0248] An ultra high molecular weight polyethylene (UHMWPE-GC002, supplied by Jingchem Corporation, Beijing, China, and having a viscosity average molecular weight of 1,650,000 g/mol, a density of 0.934 g/cm.sup.3, a bulk density of 0.42 g/cm.sup.3, and a content of volatile matter of 0.12% by weight was mixed with Irganox B225 and calcium stearate so that the powder mixture contained 0.3 parts per hundred of B225 and 0.15 parts per hundred of calcium stearate. This powder mixture was separately dosed into the hopper of an extruder together with also separately dosed bimodal polymer pellets produced according to the Reference Example 1 above so that final blend of PB1 contained 50% by weight of the UHMWPE—additive mixture and 50% by weight of the pellets of Reference Example 1. Both components were extruded by using a Leistritz ZSE 27 MAXX twin screw extruder (screw diameter 28.3 mm, OD/ID 1.66) with a screw design according to FIG. 1 (L/D 18). The adjusted barrel temperature during the extrusion was 170° C. and the screw speed was 500 min.sup.−1. At the exit of the extruder the melt was passed through a die plate and cut to pellets. The throughput was 10 kg/h.

[0249] The white spot area was determined from the polymer of PB1 and it was found to be 2.36%.

[0250] PB2:

[0251] For the production of PB2 procedure for the production of PB1 was repeated except that the adjusted barrel temperature was maintained at 200° C.

[0252] The white spot area of the polymer of PB2 was 1.3%.

[0253] PB3:

[0254] For the production of PB3 procedure for the production of PB2 was repeated except that the amount of the UHMWPE—additive mixture was 70% by weight and the amount of the pellets of Reference Example 1 was 30% by weight.

[0255] The white spot area of the polymer of PB3 was 1.8%.

[0256] c) Production of the Examples According to the Invention

Inventive Example 1 (Ex1)

[0257] A dry blend of the pellets produced according to Reference Example 1 (80% by weight) and the pellets of pre-blend PB1 (20% by weight) was made. The mixture was then extruded in a Coperion ZSK40 twin screw extruder with a screw design according to FIG. 2. An increasing temperature program from 200° C. to 220° C. was adjusted, the screw speed was 150 min.sup.−1 and the throughput was 25 kg/h. At the end of the extruder the melt was passed through a die plate, cooled in a water-bath and cut to pellets. From the pellets the dispersion (as the white spot area) and the dynamic viscosity was measured. Table 1 shows the WSA, η.sub.0.1, η.sub.100, SHI.sub.0.1/100, MFR.sub.5 and density.

Inventive Example 2 (Ex2)

[0258] The procedure of Inventive Example 1 was followed except that the pellets of pre-blend PB2 were used instead of those of pre-blend PB1. Table 1 shows the WSA, η.sub.0.1, η.sub.100, SHI.sub.0.1/100, MFR.sub.5 and density.

Inventive Example 3 (Ex3)

[0259] The procedure of Inventive Example 1 was followed except that pellets of pre-blend PB3 were used so that the amount of Reference Example 1 material was 85.7% by weight and the amount of the material of pre-blend PB3 was 14.3% by weight. Table 1 shows the WSA, η.sub.0.1, η.sub.100, SHI.sub.0.1/100, MFR.sub.5 and density.

Inventive Example 4 (Ex4)

[0260] The procedure of Inventive Example 1 was followed except that 60 percent by weight of the pellets of the Reference Example 1 and 40% by weight of the pellets of pre-blend PB1 were used. Table 2 shows the WSA, η.sub.0.1, η.sub.100, SHI.sub.0.1/100, MFR.sub.5 and density.

Inventive Example 5 (Ex5)

[0261] The procedure of Inventive Example 4 (Ex4) was followed except that the pellets of pre-blend PB2 were used instead of those of pre-blend PB1. Table 2 shows the viscosity and WSA. Table 2 shows the WSA, η.sub.0.1, η.sub.100, SHI.sub.0.1/100, MFR.sub.5 and density.

Inventive Example 5 (Ex5)

[0262] The procedure of Inventive Example 4 (Ex4) was followed except that the pellets of pre-blend PB3 were used instead of those of pre-blend PB1. Table 2 shows the viscosity and WSA. Table 2 shows the WSA, η.sub.0.1, η.sub.100, SHI.sub.0.1/100, MFR.sub.5 and density.

Comparative Example 1 (CE1)

[0263] An ultra-high molecular weight PE (UHMWPE-GC002, supplied by Jingchem Corporation, Beijing, China, and having a viscosity average molecular weight of 1 650 000 g/mol, a density of 0.934 g/cm.sup.3, a bulk density of 0.42 g/cm.sup.3, and a content of volatile matter of 0.12% by weight was mixed with Irganox B225 and calcium stearate so that the powder mixture contained 0.3 parts per hundred of B225 and 0.15 parts per hundred of calcium stearate. This powder mixture was separately dosed into the hopper of a Leistritz ZSE 27 MAXX extruder together with also separately dosed bimodal polymer pellets produced according to the Reference Example 1 above so that final blend contained 10% by weight of the UHMWPE—additive mixture and 90% by weight of the pellets of Reference Example 1. The polymer mixture was extruded by using a Leistritz ZE 27 MAXX twin screw extruder (screw diameter 28.3 mm; L/D 36) with a screw design according to FIG. 3. The adjusted barrel temperature during the extrusion was 200° C. to 220° C. and the screw speed was 500 min.sup.−1. The throughput was 10 kg/h.

[0264] At the end of the extruder the melt was passed through a die plate, cooled in a water-bath and cut to pellets. The pellets were then dried and recovered. From the pellets the dispersion (as the white spot area) and the dynamic viscosity was measured. Table 1 shows the WSA, η.sub.0.1, η.sub.100, SHI.sub.0.1/100, MFR.sub.5 and density.

[0265] d) Results

TABLE-US-00001 TABLE 1 Example Ex1 Ex2 Ex3 RE1 CE1 Amount 10 10 10 0 10 UHMW- PE [wt %] WSA [%] 0.34 0.75 0.68 n.d. 5.28 η.sub.0.1 [Pas] 21550 16330 16050 12450 16620 η.sub.100 [Pas] 1510 1370 1315 1060 1295 SHI.sub.0.1/100 14.3 11.9 12.2 11.7 12.8 η.sub.0.1 (Ex)/η.sub.0.1 1.73 1.31 1.30 — 1.33 (RE1) MFR.sub.5 1.10 1.54 1.38 n.d. 1.32 [g/10 min] Density 945 948 946 n.d. 945 [kg/m.sup.3]

TABLE-US-00002 TABLE 2 Example Ex4 Ex5 Ex6 RE1 CE1 Amount 20 20 20 0 10 UHMW- PE [wt %] WSA [%] 1.13 0.48 1.15 n.d. 5.28 η.sub.0.1 [Pas] 19560 17370 20030 12450 16620 η.sub.100 [Pas] 1450 1500 1580 1060 1295 SHI.sub.0.1/100 13.5 11.6 12.7 11.7 12.8 η.sub.0.1 (Ex)/η.sub.0.1 1.57 1.40 1.61 — 1.33 (RE1) MFR.sub.5 0.96 1.30 1.09 n.d. 1.32 [g/10 min] Density 947 947 947 n.d. 945 [kg/m.sup.3]

[0266] In Table 1 and 2: n.d. not determined