Multimodal polyethylene composition and a film comprising the same

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, the low molecular weight polyethylene having a weight average molecular weight (Mw) of 20,000 to 90,000 g/mol and having a MFRa from 500 to 1.000 g/10 min according to ASTM D 1238; (B) 8 to 20 parts by weight, preferably 10 to 18 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 parts by weight, most preferred 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 are in the range from 0.920 to 0.950 g/cm3, and wherein the molecular weight distribution of the multimodal polyethylene composition is from 20 to 28, preferably from 24 to 28, measured by gel permeation chromatography, and a film comprising the multimodal polyethylene composition and the use thereof.

Claims

1. A multimodal polyethylene composition comprising; (A) 40 to 65 parts by weight, of a low molecular weight polyethylene, the low molecular weight polyethylene having a weight average molecular weight (Mw) of 20,000 to 90,000 g/mol and having a MI.sub.2 from 500 to 1,000 g/10 min according to ASTM D 1238; (B) 8 to 20 parts by weight of a first high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000 g/mol or a 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 of a second high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000 g/mol or a 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 range from 0.920 to 0.950 g/cm.sup.3, and wherein the polydispersity index (PDI) of the multimodal polyethylene composition is from 20 to 28, measured by gel permeation chromatography.

2. The multimodal polyethylene composition according to claim 1, wherein the MI.sub.2 is from 600 to 800 g/10 min.

3. The multimodal polyethylene composition according to claim 1, wherein the polydispersity index (PDI) is from 23 to 28.

4. 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.

5. 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.

6. 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.

7. The multimodal polyethylene composition according to claim 1 wherein the multimodal polyethylene composition has a density from 0.950 to 0.962 g/cm.sup.3, according to ASTM D 1505 and/or MI.sub.2 from 0.03 to 0.15 g/10 min.

8. Film comprising the multimodal polyethylene composition according to claim 1, wherein the film has a thickness from 4 to 40 m.

9. The multimodal polyethylene composition of claim 1, comprising 43 to 52 parts by weight of the low molecular weight polyethylene.

10. The multimodal polyethylene composition of claim 9, comprising 44 to 50 parts by weight of the low molecular weight polyethylene.

11. The multimodal polyethylene composition of claim 1, comprising 10 to 18 parts by weight of the first high molecular weight polyethylene.

12. The multimodal polyethylene composition of claim 11, comprising 10 to 15 parts by weight of the first high molecular weight polyethylene.

13. The multimodal polyethylene composition of claim 1, comprising 37 to 47 parts by weight of the second high molecular weight polyethylene.

14. The multimodal polyethylene composition of claim 13, comprising 39 to 45 parts by weight of the second high molecular weight polyethylene.

15. The multimodal polyethylene composition of claim 4, wherein the weight average molecular weight is from 200,000 to 350,000 g/mol, measured by Gel Permeation Chromatography.

16. The multimodal polyethylene composition of claim 5, wherein the number average molecular weight is from 7,000 to 12,000 g/mol, measured by Gel Permeation Chromatography.

17. The multimodal polyethylene composition of claim 6, wherein the Z average molecular weight is from 1,000,000 to 2,500,000 g/mol, measured by Gel Permeation Chromatography.

18. The multimodal polyethylene composition of claim 7, wherein the density is 0.953 to 0.959 g/cm.sup.3 according to ASTM D 1505 and/or MI.sub.2 is from 0.03 to 0.12 g/10 min, according to ASTM D 1238.

19. The film of claim 8, wherein the thickness is from 4 to 30 m.

20. The film of claim 19, wherein the thickness is from 4 to 20 m.

Description

DEFINITION AND MEASUREMENT METHODS

(1) MI.sub.2: Melt flow index of polyethylene was measured according to ASTM D 1238 and indicated in g/10 min that determines the flowability of polymer under testing condition at 190 C. with load 2.16 kg.

(2) Density: Density of polyethylene was measured by observing the level to which a pellet sinks in a liquid column gradient tube, in comparison with standards of known density. This method is determination of the solid plastic after annealing at 120 C. follow ASTM D 1505.

(3) Molecular weight and Polydispersity index (PDI): The weight average molecular weight (Mw), the number average molecular weight (Mn) and the Z average molecular weight (Mz) in g/mol were analysed by gel permeation chromatography (GPC). Polydispersity index was calculated by Mw/Mn.

(4) Around 8 mg of sample was dissolved in 8 ml of 1,2,4-trichlorobenzene at 160 C. for 90 min. Then the sample solution, 200 l, was injected into the high temperature GPC with IRS, an infared detector (Polymer Char, Spain) with flow rate of 0.5 ml/min at 145 C. in column zone and 160 C. in detector zone. The data was processed by GPC One software, Polymer Char, Spain.

(5) Film bubble stability: It was determined during the blown film process, the axial oscillation of the film bubble was observed during increasing the nip roll take up speed and continue more than 30 minute. Good bubble stability is defined when film is not oscillating and bubble is not break.

(6) Output: The film was blown following the blown film conditions. Then the film was collected for a minute and weight. The output of film from unit of g/min is then calculated and reported in the unit of kg/hr.

(7) Dart drop impact: This test method follow method A of ASTM D1709 that covers the determination of the energy that cause plastic film to fail under specified conditions of free-falling dart impact. This energy is expressed in terms of the weight of the falling from a specified height, 0.660.01 m, which result in 50% failure of specimens tested.

(8) Puncture resistance: This testing is in-housed method that a specimen is clamped without tension between circular plates of a ring clamp attachment in UTM. A force is exerted against the center of the unsupported portion of the test specimen by a solid steel rod attached to the load indicator until rupture of specimen occurs. The maximum force recorded is the value of puncture resistance

(9) Tensile strength of film: The test methods cover the determination of tensile properties of film (less than 1.0 mm. in thickness) followed ASTM D882. The testing employs a constant rate of grip separation, 500 mm/min.

(10) Tear strength: This test method covers the determination of the average force to propagate tearing through a specified length of plastic film using an Elmendorf-type tearing tester followed ASTM D 1922

(11) Melt strength and Draw down ratio (DD): They are determined using GOEFFERT Rheotens. The melt extrudate is performed by single screw extruder with 2 mm die diameter at melt temperature 190 C., the extrudate pass through Rheotens haul-off with controlled the ramp speed. The haul-off force is record. The force(N) is collect as a function of draw ratio(DD). Melt strength and draw down ratio is define as the force at break and draw down ratio at break respectively.

Examples

(12) To prepare an inventive film from the above compositions, it was found that a sub-range of multimodal polyethylene compositions which might be obtained using the inventive reactor system are particularly preferred. In detail, the 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.

(13) The inventive example E1 was produced follow the disclosed process to make the multimodal polyethylene composition as shown in table 1. The specific multimodal polyethylene compositions enhance superior properties of film in particular the ability to make thin film. The thin film is represented the low thickness of the film such as 5 micron. It could be also refer to the ability to down-gauge the film thickness with equivalent properties to conventional film thickness.

(14) The inventive example E2 is the multimodal polyethylene composition produced by the disclosed process and having polymer as shown in table 3 in the range of claims with MI.sub.2 of 0.114 g/10 min and density of 0.9570 g/cm3. It shows good processing in film production and higher output rate with maintaining properties in particular dart drop impact and puncture resistance at 12 micron film thickness.

(15) TABLE-US-00001 TABLE 1 Process condition of inventive example 1, E1, inventive example 2, E2 and comparative example 3, CE3 Condition Unit CE3 E1 E2 1st Reactor Split ratio % 49-50 45-47 45-47 Temperature ( C.) 81-85 81-85 81-85 Pressure kPa 700-750 650-700 580-620 Hydrogen flow rate NL/h 246 226 248 2nd Reactor Split ratio % 6-8 10-12 10-12 Temperature ( C.) 70-75 70-75 70-75 Pressure kPa 150-300 150-300 150-300 Hydrogen flow rate NL/h 0 0 0 Co-monomer kg/h 0.031 0.010 0.0135 Comonomer/Ethylene Feed 0.018 0.0033 0.0046 H2 removal 99.0 98.9 99.4 Comonomer type 1-Butene 1-Butene 1-Butene 3rd Reactor Split ratio % 42-43 42-43 42-43 Temperature ( C.) 70-75 70-75 70-75 Pressure kPa 150-300 150-300 150-300 Hydrogen flow rate NL/h 12.85 13.02 17.28 Co-monomer kg/h 0.052 0.0152 0.0099 Comonomer/Ethylene Feed 0.0048 0.0013 0.0009 Comonomer type 1-Butene 1-Butene 1-Butene

(16) The comparative example 1 (CE1) is the commercial resin EL-Lene H5604F with MI.sub.2 of 0.03 g/10 min and density of 0.9567 g/cm.sup.3. It is the bimodal polyethylene produced in slurry cascade process.

(17) The comparative example 2 (CE2) is the blend of CE1 with commercial resin LLDPE, Dow Butene 1211, with MI.sub.2 of 1.0 g/l0 min and density of 0.9180 g/cm.sup.3. It is the practical way in film production to get better film strength in particular dart drop impact and tear strength.

(18) The comparative example 3 (CE3) is the multimodal polyethylene composition produced by the disclosed process and having the composition and molecular weight distribution out of the specific range of composition for thin film.

(19) From the molding composition so prepared, a film was produced in the following way. The films having different thickness and output were prepared 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 to prepare different film thickness in each experiment is defined in table 2. The film was 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.

(20) TABLE-US-00002 TABLE 2 Experiment and conditions for film preparation Experiment 1 Experiment 2 Experiment 3 Blown film parameter (Ex. 1) (Ex. 2) (Ex. 3) Film thickness 12 5 5 Screw speed (rpm) 85 85 60 Nip roll take up 80 150 95 speed (rpm) BUR 4:1 4:1 4:1 Neck height (cm) 30 30 30

(21) The films were further evaluated for processability and mechanical properties in both machine direction, MD and transverse direction, TD as shown in table 3.

(22) TABLE-US-00003 TABLE 3 Properties of polyethylene compositions and film thereof Properties CE1 CE2 CE3 E1 E2 Resin MI.sub.2, g/10 min 0.03 0.065 0.08 0.08 0.114 MI.sub.2 of LMW NA NA 624 715 722 Density, g/cm.sup.3 0.9567 0.9521 0.9548 0.9566 0.9570 Density of HMW1, NA NA 0.9212 0.9237 0.9213 g/cm.sup.3 Density of HMW2, NA NA 0.9464 0.9465 0.9472 g/cm.sup.3 Mn (g/mol) 7,788 8,298 9,579 9,027 8856 Mw (g/mol) 240,764 276,362 284,257 232,875 228400 Mz (g/mol) 1,817,918 1,956,827 1,666,188 1,403,576 1346144 PDI 30.9 33.3 29.7 25.8 25.7 Melt strength at 0.28 0.25 0.22 0.26 NA break, N Draw down ratio at 10.5 12.2 12.8 12.5 NA break Film Ex. 1 Ex. 2 Ex. 3 Ex 1 Ex 1 Ex. 1 Ex. 2 Ex 1 Output, kg/hr 16.0 NA 12.8 19.1 18.8 19.7 19.9 20.3 Film thickness, 12 5 5 12 12 12 5 12 micron Screw speed, rpm 85 85 60 85 85 85 85 85 Nip roll take up 80 150 95 80 80 80 150 80 speed, rpm Blow up ratio, 4:1 4:1 4:1 4:1 4:1 4:1 4:1 4:1 BUR Bubble Stability Good Bubble Good Good Good Good Good Good Break Dart drop impact, g 105 113 140 130 159 108 124 Tensile Strength at 722 889 428 826 895 1068 537 Break (MD), kg/cm.sup.2 Tensile Stregnth at 501 574 320 484 745 499 537 Break (TD), kg/cm.sup.2 Elongation at 266 52 161 226 417 192 226 Break (MD), % Elongation at 510 388 390 554 605 365 488 Break (TD), % Tear Strength 4.14 8.4 7.8 4.74 6.6 2.3 5.5 (MD), g Tear Strength 50 14 49 47 60 27 26 (TD), g Puncture Energy, 26 39 21 31 31 46 29 N-cm/u

(23) The inventive example 1 and 2, E1 shows superior properties of 12 micron film prepared by the same conditions compared to comparative examples, CE1, CE2 and CE3. E2 shows maintain film property and higher output with good bubble stability. In particular dart drop impact strength, tensile strength of film in both directions and puncture resistance. Also the film is produced with higher output.

(24) Further experiment to make a thin film at 5 micron was performed in Experiment 2. The Inventive example E1 show better draw ability at higher output which can be easily drawn into 5 micron film with good bubble stability and good mechanical strength. The same experiment was applied to the comparative example CE1 however bubble break was suddenly found. It was possible to make the 5 micron film with CE1 only in the case of lowering output by reducing screw speed and nip roll take up speed as done in Experiment 3. This is also related to draw down at break measured by rheoten. The inventive example 1 E1 has higher draw down at break compared to comparative example CE1.

(25) Moreover the properties of the 5 micron film made by inventive example E1 in Experiment 2 are also equivalent to 12 micron film made by CE1 with Experiment 1 in particular dart drop impact strength, tensile strength at break and puncture resistance. This also indicated the ability to downgauge the film thickness without sacrifice of mechanical properties. It was also possible to obtain good mechanical properties without use of LLDPE as compared to comparative example CE2.

(26) These results support that the inventive multimodal polyethylene composition provide better balance of mechanical strength with high output for thin film preparation.

(27) 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.