Multimodal polyethylene film

Abstract

The present invention relates to a multimodal polyethylene composition comprising: (A) 40 to 65 parts by weight, preferably 43 to 52 parts by weight, most preferred 44 to 50 parts by′ weight, of the low molecular weight polyethylene having a weight average molecular weight (Mw) of 20,000 to 90,000 g/mol, wherein the low molecular weight polyethylene has a MI2 of 500 to 1,000 g/10 min according to ASTM D 1238; (B) 5 to 17 parts by weight, preferably 10 to 17 parts by weight, most preferred 10 to 15 parts by weight, of the first high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000 g/mol or the first ultra high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 1,000,000 to 5,000,000 g/mol; and (C) 30 to 50 parts by weight, preferably 37 to 47 party by weight, most preferably 39 to 45 parts by weight, of the second high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000 g/mol or the second ultra high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 1,000,000 to 5,000,000 g/mol, wherein the density of the first high molecular weight polyethylene or the first ultra high molecular weight polyethylene and the second high molecular weight polyethylene or the second ultra high molecular weight polyethylene is in the same range and both densities are in the range from 0.910 to 0.940 g/cm3; and the molecular weight distribution of the multimodal polyethylene composition is from 18 to 30, preferably 20 to 28, measured by gel permeation chromatography, film comprising the multimodal polyethylene composition and the use thereof.

Claims

1. A multimodal polyethylene composition comprising: (A) 44 to 50 parts by weight of a low molecular weight polyethylene homopolymer having a weight average molecular weight (Mw) of 49,542 to 53,771 g/mol, wherein the low molecular weight polyethylene has a M2 of 500 to 1,000 g/10 min according to ASTM D 1238; (B) 10 to 15 parts by weight of a first high molecular weight polyethylene having a weight average molecular weight (Mw) of 998,032 to 999,438 g/mol wherein the first high molecular weight polyethylene is a copolymer of ethylene and 1-butene; and (C) 39 to 45 parts by weight of a second high molecular weight polyethylene having a weight average molecular weight (Mw) of 199,713 to 212,888 g/mol, wherein the second high molecular weight polyethylene is a copolymer of ethylene and 1-butene, wherein the density of the first high molecular weight polyethylene and the second high molecular weight polyethylene is in the same range and both densities are in the range from 0.910 to 0.940 g/cm.sup.3; and the polydispersity index (PDI) of the multimodal polyethylene composition is from 22 to 24, measured by gel permeation chromatography.

2. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has a weight average molecular weight from 150,000 to 400,000 g/mol, measured by Gel Permeation Chromatography.

3. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has a number average molecular weight from 5,000 to 15,000 g/mol, measured by Gel Permeation Chromatography.

4. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has a Z average molecular weight from 1,000,000 to 3,000,000 g/mol, measured by Gel Permeation Chromatography.

5. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has a density of at least 0.940 g/cm.sup.3, according to ASTM D 1505 and/or MI.sub.2 from 0.03 to 0.10 g/10 min.

6. The multimodal polyethylene composition according to claim 5, wherein the MI.sub.2 is from 0.03 to 0.08 g/10 min.

7. A film comprising the multimodal polyethylene composition according to claim 1, wherein the film has a thickness from 40 to 120 μm.

8. An industrial bag or a geomembrane comprising the film according to claim 7.

9. The multimodal polyethylene composition of claim 1, wherein the polydispersity index is from 22 to 23.

10. The multimodal polyethylene composition of claim 2, wherein the weight average molecular weight is from 200,000 to 300,000 g/mol, measured by Gel Permeation Chromatography.

11. The multimodal polyethylene composition of claim 3, wherein the number average molecular weight is from 7,000 to 13,000 g/mol, measured by Gel Permeation Chromatography.

12. The multimodal polyethylene composition of claim 4, wherein the Z average molecular weight is from 1,000,000 to 2,500,000 g/mol, measured by Gel Permeation Chromatography.

13. The multimodal polyethylene composition of claim 5, wherein the density is from 0.940 to 0.948 g/cm.sup.3, according to ASTM D 1505.

14. The film of claim 7, having a thickness from 45 to 80 μm.

Description

EXAMPLES

(1) To prepare an inventive film from the above inventive compositions, it was surprisingly found that a sub-range of the multimodal polyethylene composition which might be obtained using the inventive reactor system is particularly preferred. In detail, it was found that compositions suitable to form the inventive film are as follows and have the following properties. The following comparative examples refer to the film related compositions.

Example 1 (E1)

(2) The inventive example E1 was produced according to the inventive process for making multimodal polyethylene composition wherein;

(3) the density of the ultra high molecular weight polyethylene and the high molecular weight polyethylene copolymer is in the same range and both densities are in the range from 0.910 to 0.940 g/cm.sup.3; and, wherein the polydispersity index of the multimodal polyethylene composition is from 18 to 30, preferably 20 to 28, measured by gel permeation chromatography.

Example 2 (E2)

(4) The inventive example E2 is the multimodal polyethylene composition produced by inventive process and having polymer as shown in table 3 in the range of claims with MI2 of 0.07 g/10 min and density of 0.9470 g/cm3. It shows good processing in film production and higher output rate with maintaining properties in particular dart drop impact and tear strength at 45 micron film thickness.

Comparative Example (CE1)

(5) The comparative example CE1 was produced according to the inventive process for making multimodal polyethylene composition where in the density of the ultra high molecular weight polyethylene and the high molecular weight polyethylene copolymer is not the same. Also the density and polydispersity index is out of the specific range for high impact film.

(6) TABLE-US-00001 TABLE 1 Process condition of inventive example (E1 and E2) and comparative example (CE1) Comparative Inventive Inventive Condition Unit Example CE1 Example E1 Example E2 1st Reactor Split ratio % 46-49 45-47 45-48 Temperature (° C.) 78-81 81-85 81-85 Pressure kPa 800-850 600-650 600-650 Hydrogen flow rate NL/h 220 229 235 2nd Reactor Split ratio % 15-20 10-12 11-14 Temperature (° C.) 70-75 70-75 70-75 Pressure kPa 230-280 150-300 150-300 Hydrogen flow rate NL/h 0 0 0 Co-monomer kg/h 0.69 0.71 NA Comonomer/ — 0.216 0.222 NA Ethylene Feed H2 removal 99.6 98.9 99.4 Comonomer type — 1-butene 1-butene 1-Butene 3rd Reactor Split ratio % 32-35 40-41 39-42 Temperature (° C.) 70-75 70-75 70-75 Pressure kPa 300-400 150-300 150-300 Hydrogen flow rate NL/h 9.5 9.3 9.1 Co-monomer kg/h 0.80 0.75 0.8160 Comonomer/ — 0.073 0.068 0.0737 Ethylene Feed Comonomer type — 1-butene 1-butene 1-Butene

Comparative Example 2 (CE2)

(7) The comparative example 2 (CE2) is the polyethylene blend consisting of 60 wt % bimodal HDPE, 20 wt % LLDPE with 1-butene comonomer and 20 wt % LLDPE with 1-Octene comonomer where in; HDPE is the commercial resin EL-Lene™ H5604F with MI.sub.2 of 0.03 g/10 min and density of 0.958 g/cm.sup.3 LLDPE with 1-butene comonomer is the commercial resin Dow™ Butene 1211 with MI.sub.2 of 1.0 g/10 min and density of 0.918 g/cm.sup.3 LLDPE with 1-Octene comonomer is the commercial resin Dowlex™ 2045G with MI.sub.2 of 1.0 g/10 min and density of 0.922 g/cm.sup.3

(8) It is generally known that the blend of HDPE with LLDPE is the practical way in film manufacturing to get better film strength in particular dart drop impact and tear strength.

(9) From the molding composition so prepared, a film was produced in the following way. A film having a thickness of 45 micron was produced on the internal blown film machine comprising a single screw extruder connecting with tubular blow film apparatus. The temperature setting from extruder to the die is from 175 to 205° C. The screw speed and nip roll take up speed are 60 rpm and 20 rpm, respectively. The film were produced at a blow-up ratio of 4:1 and a neck height of 30 cm with bubble diameter of 23 cm and film lay flat of 39 cm.

(10) The films were further evaluated for processability and mechanical properties in both machine direction, MD and transverse direction, TD as shown in table 2.

(11) TABLE-US-00002 TABLE 2 Properties of polyethylene compositions and film thereof. Comparative Comparative Inventive Inventive Properties Example CE1 Example CE2 Example E1 Example E2 Resin Ml.sub.2, g/10 min 0.049 0.221 0.03 0.07 Ml.sub.2 of LMW, 640 N/A 729 573 g/10 min Density, g/cm.sup.3 0.942 0.942 0.948 0.947 Density of 0.942 N/A 0.924 0.921 HMW1, g/cm.sup.3 Density of 0.903 N/A 0.929 0.928 HMW2, g/cm.sup.3 Mn, g/mol 8,104 10,992 10,960 11,466 Mw, g/mol 259,821 237,557 250,707 264,346 Mz, g/mol 2,231,636 1,886,133 1,530,608 1,527,506 PDI 32.1 21.6 22.9 23.0 Melt strength N/A 0.22 0.24 0.23 at break, N Draw down N/A 10.9 11.3 11.5 ratio at break Film Film 45 45 45 45 Thickness, micron Output, kg/hr N/A 15 17 18 Bubble Oscillating Good Good Good Stability Dart drop N/A 203 343 285 impact, g Tensile N/A 501 535 481 Strength at Break (MD), kg/cm.sup.2 Tensile N/A 325 519 419 Strength at Break (TD), kg/cm.sup.2 Elongation at N/A 736 763 672 Break (MD), % Elongation at N/A 738 764 844 Break (TD), % Tear Strength N/A 83 92 84 (MD), g Tear Strength N/A 583 428 541 (TD), g Puncture N/A 11.11 11.82 9.75 Energy, N-cm/u Max Seal N/A 2.019 2.141 NA strength @140 C. (kgf)

(12) TABLE-US-00003 Mw, fraction A Mw, fraction B Mw, fraction C Example (g/mol) (g/mol) (g/mol) E1 49,542 998,032 199,713 E2 53,771 999,438 212,888

(13) The comparative example CE1 produced according the inventive process with the composition out of the specific range of multimodal polyethylene composition for high impact film. The bubble was found to be oscillating during the film forming. The melt fracture and gel were found and effect to the overall film appearance. So the film was not further evaluated for mechanical properties. It was supposed that too much ultrahigh molecular weight was incorporated in the comparative example CE1. The problem was not found in the inventive example E1 and E2 which produced according to the inventive process with the specific range of multimodal polyethylene composition for high impact film. The results obviously showed the significantly improvement of output and mechanical properties including dart drop impact and tensile strength over the comparative example CE2 even the LLDPE is included in the formulation. Other properties are mostly equivalent to the blend of HDPE with LLDPE.

(14) The evidence supports that the multimodal polyethylene composition produced according to the inventive process with specific range of multimodal polyethylene composition provides a good balance of mechanical strength with processing properties for industrial film and geomembrane.

(15) The features disclosed in the foregoing description and in the claims may, both separately and in any combination, be material for realizing the invention in diverse forms thereof.