Ethylene copolymer composition

Abstract

The pipe articles with excellent stress crack resistance can be achieved by providing ethylene copolymer composition comprises ethylene and a C6-C10 -olefin comonomer; the ethylene copolymer having a total density of 0.945-0.980 g/cm.sup.3 and a MFR.sub.5 of 0.10-0.50 g/10 min; and the ethylene copolymer having a comonomer content of 1-5% wt. The ethylene copolymer has M.sub.x/M.sub.y in the range of not less than 14.0; gpcBR in the range of from 0.20 to 0.80; and strain hardening modulus <Gp> in the range of not less than 53.4.

Claims

1. Ethylene copolymer composition comprising an ethylene copolymer comprising an ethylene monomer and a C6-C10 -olefin comonomer; the ethylene copolymer having a total density of 0.945-0.980 g/cm.sup.3 and a melt flow rate under 5 kg load (MFR.sub.5) of 0.10-0.50 g/10 min; the ethylene copolymer having a C6-C10 -olefin comonomer content of 1-5% wt; wherein a M.sub.x/M.sub.y is not less than 14.0 (wherein M.sub.x/M.sub.y is the molecular weight distribution obtained from gel permeation chromatography) and a strain hardening modulus <Gp> of the ethylene copolymer is not less than 53.4 wherein a gpcBR index of the ethylene copolymer is from 0.20 to 0.80 with $\mathrm{gpcBR}==\left[\left(\frac{{\mathrm{KM}}_{V,\mathrm{CC}}^{}}{\left[\right]}\right).Math.{\left(\frac{M_W}{M_{W,\mathrm{CC}}}\right)}^{}-1\right]=\left[\left(\frac{{\left[\right]}_{\mathrm{CC}}}{\left[\right]}\right).Math.{\left(\frac{M_W}{M_{W,\mathrm{CC}}}\right)}^{}-1\right]$ Where M.sub.W,CC, M.sub.V,CC and [].sub.CC are the weight average molecular weight, viscosity average molecular weight, and intrinsic viscosity from conventional gel permeation chromatography (GPC) calculation, respectively, based on the polymer being linear with no Long Chain Branch (LCB), the [] term is the actual intrinsic viscosity, which is the measured value from the online viscometer, calculated by the viscometer peak area method for high precision; Mw is the weight average of absolute molecular weight from LS detector, also calculated by the LS peak area method for high precision; and the values of Mark-Houwink parameters, and K, are 0.725 and 0.0004416, respectively, for polyethylene in 1,2,4-trichlorobenzene (TCB) at 160 C.

2. Ethylene copolymer composition according to claim 1, wherein the M.sub.x/M.sub.y is from 14.0 to 21.

3. Ethylene copolymer composition according to claim 1, wherein the strain hardening modulus <Gp> of the ethylene copolymer is from 53.4 to 72.5.

4. Ethylene copolymer composition according to claim 1, wherein the gpcBR index of the ethylene copolymer is from 0.20 to 0.80.

5. Ethylene copolymer composition according to claim 1, wherein the ethylene copolymer is a bimodal ethylene copolymer comprising a low average molecular weight ethylene homopolymer fraction and a high average molecular weight ethylene copolymer fraction.

6. Ethylene copolymer composition according to claim 1, wherein the -olefin comonomer is selected from the group consisting of 1-hexene, 1-octene, 1-decene, and mixtures thereof.

7. Ethylene copolymer composition according to claim 6, wherein the weight ratio between the low average molecular weight fraction and the high average molecular weight fraction is in the range from 35:65 to 65:35.

8. Ethylene copolymer composition according to claim 5, wherein the bimodal ethylene copolymer comprises 52 to 60% wt of the low average molecular weight ethylene homopolymer fraction and 40 to 48% wt of the high average molecular weight ethylene copolymer fraction.

9. An article comprising a polymer composition according to claim 1.

10. An article according to claim 9 wherein the article is a pressured or non-pressured pipe.

11. The ethylene copolymer composition of claim 2, wherein the M.sub.x/M.sub.y is from 16.0 to 21.

12. The ethylene copolymer composition of claim 3, wherein the strain hardening modulus <Gp> is from 58.9 to 72.5.

13. The ethylene copolymer composition according to claim 4, wherein the gpcBR index of the ethylene copolymer is from 0.20 to 0.60.

14. The ethylene copolymer composition according to claim 13, wherein the gpcBR index of the ethylene copolymer is from 0.20 to 0.50.

15. The ethylene copolymer composition of claim 8, wherein the low average molecular weight ethylene homopolymer fraction has an MFR.sub.2 from 300 to 600 g/10 min and a density >0.970 g/cm.sup.3, and the high average molecular weight ethylene copolymer fraction has an MFR.sub.5 from 0.20 to 0.25 g/10 min and density from 0.952 to 0.955 g/cm.sup.3.

Description

EXAMPLES

(1) In order to produce an inventive bimodal PE resin, the polymerization process and procedure is typically the same as that of CX slurry process. Also, Ziegler-Natta catalyst is used. The comonomer type was applied by 1-hexene. However, the operating conditions have to optimize with polymer design.

(2) The polymerization catalysts include coordination catalysts of a transition metal called Ziegler-Natta (ZN). The catalyst preparation was described in European patent number 744415 by Mitsui Chemicals Inc. Bimodal polyethylene resins, hereinafter base resin, produced in accordance with two-stage cascade slurry polymerization process and having composition ratios of a) low molecular weight (LMW) HDPE having MFR.sub.2 in the range of 300 to 600 g/10 min, and density 0.970 g/cm.sup.3 and b) high molecular weight (HMW) HDPE having MFR.sub.5 0.20-0.25 g/10 min and density 0.952-0.955 g/cm.sup.3. The LMW HDPE resin is a homopolymer polymerized in the first reactor in the absence of comonomer. The HMW PE resin produced in the second reactor is copolymer containing 1-hexene content (or 1-butene for comparative case II and III) of 1.5-2.5% wt. The 1-butene comonomer is used for comparative II and III. The bimodal resin comprises 52 to 60% wt. of the first polyethylene homopolymer fraction and 40 to 48% wt. of a second polyethylene copolymer fraction.

(3) The obtaining bimodal PE product from the second reactor was dried and the resulting powder sent to a finishing operation where it was compounded with carbon black 2-2.5 wt % in extruder at 260 C. under nitrogen atmosphere with 2000 ppm Ca/Zn stearate and 3000 ppm hindered phenol/phosphate stabilizers and, then, pelletized. Density and MFR were obtained using the pelletized resins.

(4) Plastic pipe is produced by extruding molten polymer through an annular die. The pipe is formed by passing the molten extrudate through a sizing sleeve and then to a cooling tank where water is sprayed on the outer surface. Solidification proceeds from the outer surface radially inward.

(5) Polymerization conditions and polymer properties are shown in Table 1-2, respectively. Testing results and analysis were applied and recorded on the compound.

(6) TABLE-US-00001 TABLE 1 Polymerization conditions of Example 1, Example 2 and Comparative example. Example 1 Example 2 Comparative III Homopolymer Temperature ( C.) 81-85 81-85 81-85 Pressure Bar 7.5-8.0 7.5-8.0 7.0-7.5 Hexane flow L/h 44.8 44.8 32.5 rate Ethylene flow L/h 1244 1258 1436 rate Hydrogen flow NL/h 443 446 193 rate Catalyst flow g/h 3.03 2.79 1.79 rate Production rate kg/h 22 22 25 Copolymer Temperature ( C.) 68-70 68-70 70-75 Pressure Bar 2.0-3.0 2.0-3.0 2.5-3.0 Hexane flow L/h 88 88 714 rate Ethylene flow L/h 2804 2804 2640 rate Hydrogen flow NL/h 1.77 0 2 rate Co-monomer kg/h 1.15 1.43 0.54 Comonomer/ 0.116 0.144 0.045 Ethylene Feed Production rate kg/h 22 22 25 Pressure bar 2.1 2.1 3.0 Comonomer 1-Hexene 1-Hexene 1-Butene

(7) TABLE-US-00002 TABLE 2 Polymer properties of Example 1, Example 2 and Comparative examples. Comparative Comparative Example 1 Example 2 Comparative I II III Density g/cm.sup.3 0.960 0.961 0.959 0.958 0.959 MFR.sub.5 g/10 min 0.21 0.18 0.25 0.22 0.23 1-Hexene % wt 2.11 1.88 1.75 1.56 Content 1-Butene % wt 2.16 Content <Gp> MPa 64.4 63.0 57.1 53.3 45.9 M.sub.x g/mol 651,624 650,823 693,161 626,074 577,229 M.sub.y g/mol 40,726 37,413 43,640 45,081 42,521 M.sub.x/M.sub.y 16.0 17.4 15.9 13.9 13.6 gpcBR 0.418 0.445 0.186 0.020 0.489 ACT h 1436 1466 1309 439 Charpy kJ/m.sup.2 34.8 34.3 37.2 31.5 23.2 (23 C.) Charpy kJ/m.sup.2 17.2 12.8 9.5 15.6 6.7 (30 C.)

(8) TABLE-US-00003 TABLE 3 Comparison of inventive Examples 1 and 2 and the prior art Prior arts Property (EP1985660A1) Example 1 Example 2 Charpy (23 C.), kJ/m.sup.2 34.8 34.3 Charpy (0 C.), kJ/m.sup.2 21.3 27.9 25.6 Charpy (30 C.) kJ/m.sup.2 17.2 12.8 Density natural pellet, g/cm.sup.3 0.947 0.9519 0.9511 ACT, h 1603 1436 1466

(9) As it is shown in Table 3, inventive Examples 1 and 2 have significantly improved charpy impact in comparison with the prior art. To allow the comparison with the prior art, the Experiments shown above with respect to charpy impact have been reproduced for inventive Examples 1 and 2 at 0 C. As it is evident from Table 3, significantly improved charpy impact results (27.9 and 25.6 instead of 21.3) have been achieved using the inventive compositions.

(10) Furthermore, superior slow crack growth, represented by ACT measurement, was observed. When comparing the ACT values of the prior with present invention, it has to be kept in mind that the inventive Examples have a higher density due to the lower amount of comonomer. Since it is well-known that ACT results linearly depend from the comonomer content, the above values indeed suitable to show superiority of the present invention over the prior art.