MULTIMODAL POLYETHYLENE SCREW CAP

Abstract

The present invention relates to a multimodal polyethylene composition comprising: (A)35 to 65 parts by weight, preferably 45 to 65 parts by weight, most preferred 50 to 60 parts by weight, of the low molecular weight polyethylene having a weight average molecular weight (Mw) of 20,000 to 90,000 g/mol; (B) 5 to 40 parts by weight, preferably 5 to 30 parts by weight, most preferred 5 to 20 parts by weight, of the first high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000g/mol or the first ultra high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 1,000,000 to 5,000,000g/mol; and (C) 20 to 60 parts by weight, preferably 25 to 60 parts by weight, most preferred 35 to 55 parts by weight, of the second high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 150,000 to 1,000,000g/mol or the second ultra high molecular weight polyethylene having a weight average molecular weight (Mw) of more than 1,000,000 to 5,000,000g/mol, wherein the molecular weight distribution of the multimodal polyethylene composition is from 10 to 25, preferably 10 to 20, determined by Gel Permeation Chromatography; the isothermal crystallization half-time of the multimodal polyethylene composition at a temperature of 123 C. is 7 min or less, preferably 6 min or less, preferably 2- 6 min, according to Differential Scanning Calorimetry; and a spiral flow length at a temperature of 220 C. is at least 200 mm, preferably 250-400 mm and a screw cap comprising the same.

Claims

1. A multimodal polyethylene composition comprising; (A) 35 to 65 parts by weight, preferably 45 to 65 parts by weight, most preferred 50 to 60 parts by weight, of the low molecular weight polyethylene having a weight average molecular weight (Mw) of 20,000 to 90,000 g/mol; (B) 5 to 40 parts by weight, preferably 5 to 30 parts by weight, most preferred 5 to 20 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) 20 to 60 parts by weight, preferably 25 to 60 parts by weight, most preferred 35 to 55 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 molecular weight distribution of the multimodal polyethylene composition is from 10 to 25, preferably 10 to 20, determined by Gel Permeation Chromatography; the isothermal crystallization half-time of the multimodal polyethylene composition at a temperature of 123 C. is 7 min or less, preferably 6 min or less, preferably 2-6 min, according to Differential Scanning calorimetry; and a spiral flow length at a temperature of 220 C. is at least 200 mm, preferably 250-400 mm.

2. The multimodal polyethylene composition according to claim 1, wherein the molecular weight distribution is from 15 to 25, preferably 15 to 20.

3. The multimodal polyethylene composition according to claim 1, wherein the spiral flow length at a temperature of 220 C. is from 250 to 370 mm.

4. The multimodal polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has an average molecular weight from 80,000 to 250,000 g/mol, preferably 80,000 to 200,000 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 30,000 g/mol, preferably 5,000 to 20,000 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 700,000 to 2,500,000 g/mol, preferably 700,000 to 2,000,000 g/mol, and most preferred 700,000 to 1,500,000 g/mol measured by Gel Permeation Chromatography.

7. The polyethylene composition according to claim 1, wherein the multimodal polyethylene composition has a density 0.950 to 0.965 g/cm3, preferably 0.953 to 0.960 g/cm3, according to ASTM D 1505 and/or MI2 from 0.1 to 20 g/10 min, preferably from 0.3 to 17 g/10 min, according to ASTM D 1238.

8. Screw cap comprising the multimodal polyethylene composition according to claim 1.

9. Screw cap according to claim 8 obtainable by injection molding or compression molding.

Description

EXPERIMENTAL AND EXAMPLES

Composition-Related Examples

[0084] The medium or high density polyethylene preparation was carried out in three reactors in series. Ethylene, hydrogen, hexane, catalyst and TEA (triethyl aluminum) co-catalyst were fed into a first reactor in the amounts shown in Table 1. A commercial available Ziegler-Natta catalyst was used. The catalyst preparation is for example described in Hungary patent application 0800771r.

[0085] The polymerization in first reactor was carried out to make a low molecular weight polyethylene or medium molecular weight polyethylene. All of polymerized slurry polymer from first reactor was then transferred to a hydrogen removal unit to remove unreacted gas and some of hexane from polymer. The operating pressure in the hydrogen removal unit was be varied in a range of 100 to 115 kPa (abs) where residual hydrogen was removed more than 98% by weight but not more than 99.8% by weight from hexane before transferring to a second polymerization reactor. Some fresh hexane, ethylene and/or comonomer were fed into second reactor to produce first high molecular weight polyethylene (HMW1). All of polymerized polymer from second reactor was fed into the third reactor which produce second high molecular weight polyethylene (HMW2). Ethylene, comonomer, hexane and/or hydrogen were fed into the third reactor.

Screw Cap-Related Examples

[0086] The examples of polymer compositions for screw cap-related this invention regarding the multimodal polyethylenes were polymerized as shown in Table 1, 2, 3 and 4.

Comparative Example 1 (CE1)

[0087] A homopolymer was produced in first reactor to obtain a low molecular weight portion before transferring such polymer to hydrogen removal unit. Reactant mixture was introduced into the hydrogen removal unit to separate the unreacted mixture from the polymer. Residual hydrogen was removed 97.6% by weight when hydrogen removal unit was operated at pressure of 150 kPa (abs). The low molecular weight polymer was then transferred to the second reactor to produce a first high molecular weight polymer. Final, produced polymer from second reactor was transferred to the third reactor to create a second high molecular weight polymer. In third, a copolymerization was carried out by feeding 1-butene as a comonomer. As seen in Table 2 and 3, the final melt flow rate of CE1 were quite similar to a final melt flow rate of E1. A decay of charpy impact and flexural modulus were showed in CE1 compared to E1, even it showed lower density of E1.

Inventive Example 1 (E1)

[0088] Example 1 (E1) was carried out in the same manner as Comparative Example 1 (CE1) except that the hydrogen removal unit was operated at pressure of 115 kPa (abs). The residual of hydrogen from first reactor was removed to an extend of 98.5% by weight. The polymer obtained by this process operation had a melt flow rate of 48 g/10 min (5 kg loading) lower than such value obtained from CE1. As seen in Table 2, it revealed an improvement of stiffness-impact balance when the percentage of removed hydrogen residual increases compared with the properties of Comparative Example 1.

[0089] The properties of the invention from inventive examples E1 were compared to the properties of comparative examples CE1.

Comparative Example 2 (CE2)

[0090] Comparative example 2 (CE2) is a bimodal polyethylene produced from Ziegler-Natta catalyst. The weight ratio between the ethylene homopolymer and the ethylene copolymer is in the range of 45:55 to 55:45. A polymer composition comprises a comonomer in an amount of at least 0.40 mol %.

Comparative Example 3 (CE3)

[0091] Comparative example 3 (CE3) is a commercial multimodal high density polyethylene Hostalen ACP5331 UVB plus.

Inventive Example 2 and 3 (E2 and E3)

[0092] Multimodal polyethylene compositions of inventive 2 and 3 (E2 and E3) were produced according to the inventive process with the polymerization condition as shown in Table 3. The different weight fraction in each reactor was defined and 1-butene was applied as comomoner in the 2.sup.nd and 3.sup.rd reactor components. The properties of the invention from inventive examples 2 and 3 (E2 and E3) were compared to the properties of comparative examples 2 and 3 (CE2 and CE3).

[0093] The characteristics and properties of these multimodal polyethylenes are shown in Table 4. The comparisons between the multimodal polymers, but different polymerization process were illustrated. Surprisingly, the multimodal polyethylene according to this invention which contain higher Mz and higher shear thinning shows a significant improvement in processability and stiffness of inventive examples 2 and 3 (E2 and E3) compare to comparative examples 2 and 3 (CE2, CE3) and Inventive examples 1 (E1) compare to comparative example 1 (CE1), respectively.

[0094] The better processability can be investigated in term of both faster cycle time and higher flowability. Faster cycle time was determined by the lower crystallization haft time (ICHT) and higher crystal growth rate (K). The inventive examples 1, 2, and 3 (E1, E2, and E3) show lower ICHT and higher crystal growth rate (K) than comparative examples 1, 2 and 3 (CE1, CE2 and CE3). It is supposed that the ultra high molecular weight produced in the second component following the inventive process can act as a stem for easier nucleation resulting in faster crystallization rate. The flowability is normally determined by spiral flow length at temperature 220 C. The spiral flow length of inventive example E1 has higher than comparative example 1 (CE1), and inventive example 2 and 3 (E2 and E3) have higher than comparative examples 2 and 3 (CE2 and CE3), even inventive examples have lower MI than comparative examples.

[0095] The improvement of stiffness compared to CE2 and CE3 were also investigated. The multimodal polyethylene composition of these invention example 2 (E2) have better flexural modulus than comparative examples 2 and 3 (CE2 and CE3) and also the invention example 1 (E1) has higher flexural modulus than comparative examples (CE1). Because of the multimodal polyethylene according to this invention contain higher Mz shows a significant improvement in stiffness.

[0096] This indicated that the inventive multimodal polyethylene composition provide better processability and higher stiffness with good balance to stress crack resistance beyond prior arts. The invention enhanced significantly improvement of properties for screw cap and closure.

TABLE-US-00001 TABLE 1 Polymerization conditions of multimodal polyethylenes for Screw cap-related invention in lab reactor CE1 E1 W.sub.A, % 50 50 W.sub.B, % 10 10 W.sub.C, % 40 40 First reactor Polymerization type Homo Homo Temperature, C. 80 80 Total pressure, kPa 800 800 Ethylene, g 725.21 725.57 Hydrogen, g 1.13 1.13 Hydrogen removal unit Pressure, kPa (abs) 150 115 Hydrogen remove, % 97.7 98.5 Second reactor Polymerization type Copo Copo Temperature, C. 80 80 Total pressure, kPa 300 300 Ethylene, g 145.35 145.21 Hydrogen, g 0 0 1-butene, g 8 8 Third reactor Polymerization type Copo Copo Temperature, C. 80 80 Total pressure, kPa 600 600 Ethylene, g 580.53 580.46 Hydrogen, g 0.59 1.37 1-butene, g 27 27 [0097] W.sub.A means percent by weight of Polymer in the first reactor [0098] W.sub.B means percent by weight of Polymer in the second reactor [0099] W.sub.C means percent by weight of Polymer in the third reactor

TABLE-US-00002 TABLE 2 CE1 E1 Powder MI.sub.5, g/10 min 54.80 48.07 MI.sub.21, g/10 min 641 653 Density, g/cm.sup.3 0.9606 0.9590 IV, dl/g 1.07 1.06 Pellet MI.sub.5, g/10 min 60.62 55.47 MI.sub.21, g/10 min 713.1 752.2 Density, g/cm.sup.3 0.9608 0.9594 IV, dl/g 1.0 1.1 % Crystallinity, % 69.52 65.64 Charpy, 23 C., kJ/m.sup.2 1.5 1.8 Flexural modulus , MPa 1,147 1,196

TABLE-US-00003 TABLE 3 Polymerization conditions of multimodal polyethylenes for Screw cap-related invention from pilot scale E2 E3 Process Parameters Unit (Inventive) (Inventive) 1.sup.st Reactor Split ratio % 58-62 48-52 Temperature ( C.) 81-85 81-85 Pressure Bar 5.5-6.0 4.5-5.0 Hexane flow rate L/h 90.0 63.0 Ethylene flow rate L/h 2310.5 1918.0 Hydrogen flow rate NL/h 188.1 104.336 Catalyst flow rate g/h 3.2 3.1 2.sup.nd Reactor Split ratio % 9-10 12-18 Temperature ( C.) 68-70 68-70 Pressure Bar 1.5-3.0 1.5-3.0 Hexane flow rate L/h 176.2 148.7 Ethylene flow rate L/h 1051.0 1354 Hydrogen flow rate NL/h 0 0 Comonomer/Ethylene Feed 0.0037 0.00239 H.sub.2 removal 98.89 98.99 Flash pressure 0.054 0.056 Comonomer type 1-Butene 1-Butene 3.sup.rd Reactor Split ratio % 28-33 32-38 Temperature ( C.) 70-75 70-75 Pressure Bar 1.5-3.0 1.5-3.0 Hexane flow rate L/h 191.6 164.0 Ethylene flow rate L/h 1980.2 1969.3 Hydrogen flow rate NL/h 39.8 0 Comonomer/Ethylene Feed 0.002 0.00849 Production rate kg/h 30.0 25.0 Comonomer type 1-Butene 1-Butene

TABLE-US-00004 TABLE 4 Polymer compositions and properties of multimodal polyethylenes (pellet) for Screw cap-related invention E1 CE1 E2 E3 CE2 CE3 Properties Inventive Comparative Inventive Inventive Comparative Comparative MI.sub.2 [g/10 min] 14.6 16.8 0.8 0.5 0.9 2.0 MI.sub.5 [g/10 min] 55.47 60.62 3.16 2.12 3.61 6.54 Density [g/cm.sup.3] 0.9594 0.9608 0.9603 0.9582 0.9584 0.9574 IV [cm.sup.3/g] 1.10 1.01 2.01 2.39 1.98 1.12 Mn [g/mol] 6,065 7,036 9,600 9,393 8,847 13,459 Mw [g/mol] 85,150 81,171 174,712 183,319 157,896 119,848 Mz [g/mol] 713,636 677,966 1,359,161 1,436,240 1,058,549 765,341 PDI 14 12 18 20 18 9 Comonomer content 0.83 0.67 0.43 0.52 0.50 0.36 [% mol] ICHT @ 123 C. [min] 3.1 3.2 4.1 6.1 8.2 8.7 Crystal growth rate 1.68E05 1.19E05 2.7E06 1.21E06 1.4E07 5.8E07 constant (K) Tm [ C.] 130 130 130 129 130 130 Tc [ C.] 118 118 119 118 117 117 % Crystallinity 66 66 73 66 69 67 SHI (1/100) 12.2 7.0 23.4 26.1 11.4 3.9 .sub.0.01 [Pa .Math. s] 2,176 1,283 27,870 38,907 20,343 6,873 Spiral flow length @ 350 340 293 282 266 238 220 C. [mm] Flexural modulus 1,196 1,147 1,251 1,258 1,157 1,141 (ISO 178) [MPa] FNCT (ISO 16770) N/A N/A 17 22 18 8 @ 50 C., 6 MPa, 2% wt Arkopal [hr]