POLYOLEFIN RESIN BLENDS FOR HIGH STRESS CRACKING RESISTANCE AND GOOD PROCESSABILITY

Abstract

Polyethylene composition comprising a melt blend, the melt blend comprising: a) a first multimodal polyethylene, the first multimodal polyethylene having a medium weight average molecular weight of a high weight average molecular weight, a density of more than 0.950 to 0.965 g/cm.sup.3 according to ISO 1183 and a MFR.sub.2 of 0.3 to 2.0 g/10 min according to ISO 1133; and b) a second multimodal polyethylene, the second multimodal polyethylene having a high weight average molecular weight, a density of 0.940 to 0.950 g/cm.sup.3 according to ISO 1183 and a MFR.sub.2 of 0.03 to 0.15 g/10 min according to ISO 1133; wherein the polymer composition has a Full Notch Creep Test (FNCT) according to ISO 16770 of at least 58 hours and a Charpy impact strength at a temperature of 23° C. of at least 4 kJ/m.sup.2 according to ISO 179.

Claims

1. A polyethylene composition comprising a melt blend, the melt blend comprising: a) a first multimodal polyethylene, the first multimodal polyethylene having a medium weight average molecular weight from 90,000 to 200,000 g/mol or a high weight average molecular weight from 200,000 to 1,000,000 g/mol, a density of more than 0.950 to 0.965 g/cm.sup.3 according to ISO 1183 and a MFR.sub.2 of 0.3 to 2.0 g/10 min according to ISO 1133; and b) a second multimodal polyethylene, the second multimodal polyethylene having a high weight average molecular weight from 200,000 to 1,000,000 g/mol, a density of 0.940 to 0.950 g/cm.sup.3 according to ISO 1183 and a MFR.sub.2 of 0.03 to 0.15 g/10 min according to ISO 1133; wherein the polymer composition has a Full Notch Creep Test (FNCT) according to ISO 16770 of at least 58 hours and a Charpy impact strength at a temperature of 23° C. of at least 4 kJ/m.sup.2 according to ISO 179.

2. The polyethylene composition according to claim 1, wherein the polymer composition has a FNCT from 58 to 100 hours.

3. The polyethylene composition according to claim 1, wherein the polyethylene composition has a Charpy impact strength at a temperature of 23° C. from 4 to 10 kJ/m.sup.2.

4. The polyethylene composition according to claim 1, wherein the first multimodal polyethylene is a bimodal polyethylene or a trimodal polyethylene and the second multimodal polyethylene is a bimodal polyethylene or a trimodal polyethylene.

5. The polyethylene composition according to claim 4, wherein the bimodal polyethylene comprises 40 to 60% by weight of an ethylene homopolymer and 40 to 60% by weight of an ethylene copolymer, based on the total weight of the bimodal polyethylene respectively, wherein the ethylene copolymer comprises a co-monomer in an amount of at least 0.30 mol % with respect to the total amount of monomer in the ethylene copolymer.

6. The polyethylene composition according to claim 5, wherein the co-monomer is selected from the group consisting of 1-butene, 1-hexene, 1-octene, and mixtures thereof.

7. The polyethylene composition according to claim 4, wherein the bimodal polyethylene has a MFR.sub.2 of 0.02 to 1.0 g/10 min according to ISO 1133 and/or a density of 0.945 to 0.960 g/cm.sup.3, according to ISO 1138.

8. The polyethylene composition according to claim 4, wherein the bimodal polyethylene has a weight average molecular weight of 100,000 to 400,000 g/mol, measured by gel permeation chromatography.

9. The polyethylene composition according to claim 4, wherein the trimodal polyethylene comprises: (A) 30 to 65% by weight, based on the total weight of the trimodal polyethylene, of a low molecular weight polyethylene, wherein the low molecular weight polyethylene has a MFR.sub.2 of 500 to 1,000 g/10 min according to ISO 1133 and a weight average molecular weight (Mw) of 20,000 to 90,000 g/mol, measured by gel permeation chromatography; (B) 5 to 40% by weight, based on the total weight of the trimodal polyethylene, of an ultrahigh molecular weight polyethylene having a weight average molecular weight from 1,000,000 to 5,000,000 g/mol; and (C) 20 to 60% by weight, based on the total weight of the trimodal polyethylene, of a high molecular weight polyethylene having a weight average molecular weight from 200,000 to 1,000,000 g/mol.

10. The polyethylene composition according to claim 4, wherein the trimodal polyethylene has a weight average molecular weight from 80,000 to 500,000 g/mol, measured by gel permeation chromatography.

11. The polyethylene composition according to claim 1, wherein the melt blend comprises 70 to 97% by weight of the first multimodal polyethylene; and 3 to 30% by weight of the second multimodal polyethylene, based on the total weight of the melt blend respectively.

12. The polyethylene composition according to claim 1, wherein the polyethylene composition has a MFR.sub.2 of 0.05 to 2.0 g/10 min, according to ISO 1133.

13. The polyethylene composition according to claim 1, wherein the polyethylene composition has a density from 0.945 to 0.960 g/cm.sup.3, according to ISO 1183.

14. The polyethylene composition according to claim 1, wherein the polyethylene composition has a weight average molecular weight of 80,000 to 500,000 g/mol, measured by gel permeation chromatography; and/or a polydispersity index from 10 to 25.

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

16. The polyethylene composition of claim 2, wherein the FNCT is from 58 to 100 hours.

17. The polyethylene composition of claim 4, wherein one of the first multimodal polyethylene and the second multimodal polyethylene is a bimodal polyethylene and the other one of the first multimodal polyethylene and the second multimodal polyethylene is a trimodal polyethylene.

18. The polyethylene composition of claim 17, wherein the first multimodal polyethylene is a bimodal polyethylene and the second multimodal polyethylene is trimodal polyethylene.

19. The polyethylene composition of claim 6, wherein the co-monomer is 1-butene.

20. The article of claim 15, wherein the article is a molding, a pipe, a film, a cap, a closure, a wire, a cable, or a sheet.

Description

EXAMPLES

[0055] The exemplary polyethylene compositions described in the following were prepared in accordance with the above general description regarding “the preparation of multimodal polyethylene”. The compositions for each example were prepared using melt blending techniques by twin screw extruder at temperature 220° C. using different components and formulations as shown in Tables 1 and 2. The properties of polymer blend compositions for each example are shown in Table 3.

Comparative Example

[0056] Comparative Example 1 is a trimodal polyethylene composition produced from Ziegler-Natta catalyst from reactor based which having the polymer composition as shown in Component #4 in Table 1. The % weight fraction ratio of the first ethylene homopolymer, the second ethylene copolymer and the third ethylene copolymer is 50:10:40. The Comparative Example 1 use 1-butene as comonomer in the composition.

Example 1 (Inventive)

[0057] The example 1 was prepared by melt blending from 80% weight fraction of the first bimodal polyethylene (Component #1) and 20% weight fraction of the second bimodal polyethylene (Component #2), respectively. The Component #1 is the Ziegler-Natta catalyst based bimodal polyethylene and has the weight fraction ratio of the first ethylene homopolymer and the second ethylene copolymer equal to 50:50. The Component #2 is also the Ziegler-Natta catalyst based bimodal polyethylene and has the weight fraction ratio of the first ethylene homopolymer and the second ethylene copolymer equal to 52:48. Both the Component #1 and Component #2 use 1-butene as comonomer in the compositions and the detail properties of the Component #1 and #2 are shown in Table 1.

Examples 2-3 (Inventive)

[0058] The example 2-3 were prepared by melt blending from 85, 90% weight fraction of the first bimodal polyethylene (Component #1) and 15, 10% weight fraction of the second trimodal polyethylene (Component #3), respectively. The Component #3 is the Ziegler-Natta catalyst based trimodal polyethylene which produced from slurry polymerization and has the weight fraction ratio of the first ethylene homopolymer, the second ethylene copolymer and the third ethylene copolymer equal to 43:19:38 and use 1-butene as comonomer. The detail properties of the Component #3 is shown in Table 1.

Example 4 (Inventive)

[0059] The example 4 was prepared by melt blending from 80% weight fraction of the first trimodal polyethylene (Component #4) and 20% weight fraction of the second bimodal (Component #2), respectively.

[0060] The results given in Table 3 indicated that the inventive samples (Example 1-4) have significantly higher stress cracking resistance as shown in Full Notch Creep Test (FNCT) results more than 2 times and also impact strength as shown in Chary impact strength at 23° C. higher than trimodal polyethylene resin or Comparative example 1 without loss of stiffness and processability. The higher stress cracking resistance and impact strength of polymer blends come from the higher comonomer content and also higher the high molecular weight parts which shown in broader PDI than Comparative Example 1.

[0061] In addition, these inventive examples also show balance processability by SHI [1/100], even it show lower MFR range than Comparatives example 1. Higher Non-Newtonian index or SHI [1/100] means better processability by extrusion, injection, and blow molding.

[0062] From these polymer properties can have benefit for molded articles.

TABLE-US-00001 TABLE 1 Properties of ethylene polymers Component Component Component Component #1 #2 #3 #4 Key properties Unit Bimodal PE Bimodal PE Trimodal PE Trimodal PE Mw of 1.sup.st fraction g/mol 47,935 49,832 51,000 64,490 ethylene homopolymer in 1.sup.st reactor Mw of 2.sup.nd fraction g/mol 163,051 290,000 218,000 193,778 ethylene copolymer in 2.sup.nd reactor Mw of 2.sup.nd fraction g/mol — — 275,357 162,148 ethylene copolymer in 3.sup.rd reactor MFR.sub.2 of Pellet g/mol 0.92 0.03 0.04 0.96 MFR.sub.5 of Pellet g/10 mol 3.49 0.18 0.21 3.91 Density of Pellet g/cm.sup.3 0.9565 0.949 0.9437 0.9567 Comonomer content % mol 0.52 0.73 0.99 0.44 (1-Butene) in Pellet Mw of Pellet g/mol 158,543 306,966 213,392 155,398 Mn of Pellet g/mol 8,983 9,356 11,796 10,638 Mz of Pellet g/mol 1,003,632 2,073,745 1,295,187 1,302,926 PDI of Pellet — 17.65 32.81 18.09 14.61

TABLE-US-00002 TABLE 2 Blend compositions of this invention Example CE.sub.1 EX.sub.1 EX.sub.2 EX.sub.3 EX.sub.4 1.sup.st Multimodal Component #4 Component #1 Component #1 Component #1 Component #4 component (Trimodal PE) (Bimodal PE) (Bimodal PE) (Bimodal PE) (Trimodal PE) 1.sup.st component 100 80 90 85 80 weight fraction (%) 2.sup.nd Multimodal — Component #2 Component #3 Component #3 Component #2 component (Bimodal PB) (Trimodal PE) (Trimodal PE) (Bimodal PE) 2.sup.nd component — 20 10 15 20 weight fraction (%)

TABLE-US-00003 TABLE 3 Physical properties of the blend compositions Key properties CE.sub.1 EX.sub.1 EX.sub.2 EX.sub.3 EX.sub.4 MFR.sub.2 [g/10 min] 0.96 0.43 0.72 0.55 0.37 Density [g/cm.sup.3] 0.9567 0.9551 0.9549 0.9543 0.9546 1-Butene content [% mol] 0.50 0.56 0.64 0.64 0.54 Mw [g/mol] 155,398 180,314 159,185 164,023 179,882 Mn [g/mol] 10,638 10,878 9,046 9,252 10,892 Mz [g/mol] 1,302,926 1,229,914 1,008,241 1,024,795 1,211,848 PDI 14.61 16.58 17.60 17.73 16.52 Crystallinity [%] 64.68 61.46 62.17 61.78 61.53 SHI [1/100] 7.2 9.4 7.4 7.7 9.4 Tensile modulus 966 1043 991 988 971 (ISO 527)-1B [MPa] Charpy impact strength @ 23° C. 3.6 6.5 5.2 5.8 7.2 (ISO 179) [kg/m.sup.2] FNCT (ISO 16770) @ 50° C., 20 68 73 77 60 6 MPa, 2% wt Arkopal [hr]

TABLE-US-00004 TABLE 4 Blend composition of comparative example 2 Example Comparative Example 2 1.sup.st Multimodal component Component #1 (Bimodal PE) 1.sup.st component weight fraction (%) 50 2.sup.nd Multimodal component Component #3 (Trimodal PE) 2.sup.nd component weight fraction (%) 50

TABLE-US-00005 TABLE 5 physical properties of comparative example 2 Comparative Key properties Example 2 MFR.sub.2 [g/10 min] 0.07 Density [g/cm.sup.3] 0.9513 1-Butene content [% mol] 0.7317 Mw [g/mol] 197,045 Mn [g/mol] 10,745 Mz [g/mol] 1,209,872 PDI 18.34 Crystallinity [%] 57.64 SHI [1/100] 10.94 Tensile modulus 730 (ISO 527)-1B [MPa] Charpy impact strength @ 23° C. 11.38 (ISO 179) [kg/m.sup.2] FNCT (ISO 16770) @ 50° C., 130 6 MPa, 2% wt Arkopal [hr]

[0063] Comparative Example 2 comprises 50% by weight of the first multimodal polyethylene and 50% by weight of the second multimodal polyethylene as shown in table 4 and has a Charpy impact strength @23° C, of 11.38 kg/m.sup.2, FNCT of 130 hours and MFR.sub.2 of 0.07 g/10 min (in claim 12, the polyethylene composition has MFR2 in the range of 0.05 to 2.0 g/10 min) as shown in table 5. Adding higher portion of the second multimodal polyethylene, which in general has higher molecular weight than the first multimodal polyethylene, results in increased ESCR and impact strength and decreased MFR.sub.2.

[0064] The blend having hi ESCR and impact strength, and low MFR.sub.2 shows disadvantages with balancing processability. Therefore, the comparative Example 2 having the aforementioned Charpy impact strength and MFR.sub.2 is out of scope of preferred embodiments according to this invention and it is less suitable for injection cap and closure applications.

[0065] 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.