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Polyethylene Composition Suitable for the Preparation of Films and Process for Preparing the Same

a polyethylene composition and film technology, applied in the field of polyethylene compositions, can solve the problems of insufficient mechanical strength and poor transparency of polyethylene films based on chromium catalysts, insufficient increase of transparency in film applications in food industry, and insufficient mechanical strength and transparency values, etc., to achieve improved mechanical resistance and optical properties, improve the effect of optical properties and improved processing

Inactive Publication Date: 2009-04-16
BASELL POLYOLEFINE GMBH
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention provides a polyethylene composition with improved processing, mechanical resistance, and optical properties. The composition has a high dart drop impact and high clarity, while maintaining good processability at low temperatures. The composition includes a first polyethylene component with a plurality of ethylene polymer fractions having distinct molecular weights and comonomer contents, and a second polyethylene component with a low or medium density. The composition has a broad molecular distribution and is tailored in terms of comonomer content to improve its mechanical properties. The invention solves the technical problem of providing a polyethylene composition with improved impact resistance and optical properties while maintaining good processability.

Problems solved by technology

Although substantially suitable for the purpose, the polyethylene films based on chromium catalysts suffer from an insufficient mechanical strength and a very poor transparency.
Such values of mechanical strength and transparency are considered unacceptable, particularly in food packaging applications.
Although the compositions made of MDPE and LDPE show an increased transparency, for example in terms of a certain increase of clarity up from an initial value of about 13% (MDPE alone) to a final value 56% (MDPE added with LDPE) at a thickness of 50 μm, a first disadvantage of these compositions is that such increase of transparency is still insufficient for film applications in food industry.
A second disadvantage is that such a relative increase of transparency is obtained at the expenses of the mechanical strength.
Thus, no significant improvement in transparency has been attained by adding a LDPE to a MDPE prepared by means of a chromium catalyst and the relative improvement of the transparency inevitably results in an unacceptable worsening of the mechanical properties of the film.
However, such compositions have the main disadvantage in that the dart drop impact sensibly decreases as the density increases.
The addition of LDPE to such a bimodal composition, however, does not allow to obtain a film product having adequate optical properties.
However, the mechanical strength of the polyethylene film is yet insufficient.
However, the increase of the impact resistance is still insufficient.
However, the dart drop impact and the tear strength of the films prepared starting from such blend are inadequate.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1 (

Invention)

[0132]a) Preparation of the Individual Components

[0133]0.90 kg of 2,6-diacetylpyridine (99%), 2, 56 kg of phosphorus pentoxide (P2O 5), and a solution of 2.14 kg of 2,4-dichloro-6-methylaniline (100%) were solubilized in 20 l of tetrahydrofuran. The mixture was stirred for 15 min and then heated under reflux for 18 hours at 70° C. After completion of the reaction, the obtained suspension was cooled to 20° C., stirred for 30 min and then filtered and washed with 6 l of tetrahydrofuran. The filtrate, having a volume of 26 l, was concentrated under vacuum (250 mm Hg, 55° C.). The volume was reduced by rotary evaporation up to a final concentrate of 3.5 l. 20 l of methanol were added so as to obtain crystallization. The resulting suspension (23.5 l) was filtered and washed with 6 l of methanol, thus resulting in a volume of 27 l. The humid product (1.38 kg) resulting from the filtration was set under drying condition in free air for one night. This gave a first fraction of 1.3...

examples 2-4 (

Invention)

[0141]In Examples 2-4 a first and a second polyethylene components as those described in Example 1 were used, except for the amount of LDPE, which was set to 20%, 30% and, respectively, 40% by weight.

TABLE 1First PE component of Examples 1-4Density [g / cm3]0.939MFR (190 / 21.6) [g / 10 min]28Eta(vis) / Eta(GPC)2.08Mw [g / mol]140000Mw / Mn14.4Mz462000GPC % at molar mass 1 Mio99.3—HC═CH2 [ 1 / 1000C]1.51total-CH3 [ 1 / 1000C]8.0

[0142]Where[0143]density is the polymer density[0144]MFR (190 / 21.6) is the melt flow rate according to standard ISO 1133, condition G[0145]Eta(vis) is the intrinsic viscosity as determined according to ISO 1628-1 and[0146]Eta(GPC) is the viscosity as determined by GPC according to DIN 55672, with 1,2,4-Trichlorobenzene, at 140° C.[0147]Mw is the weight average molar mass;[0148]Mn is the number average molar mass[0149]Mz is the z-average molar mass[0150]GPC % at molar mass 1 Mio is the % by weight according to gel permeation chromatography below a molar mass of 1 Mi...

examples 9-12 (comparative)

[0157]Lupolen 3721 C, which is a MDPE prepared by the use of a chromium catalyst commercially available from Basell (density equal to 0.937 g / cm3, MFR (190 / 21.6) of 12.5 g / 10 min), was used as a first polyethylene component, whose properties are shown in Table 3, while Lupolen 3220 F was used as a second polyethylene component.

TABLE 3First PE component of Examples 9-12Density [g / cm3]0.937MFR (190 / 21.6) [g / 10 min]12.5Eta(vis) / Eta(GPC)2.80Mw [g / mol]240000Mw / Mn12.1Mz1650000GPC % at molar mass 1 Mio95.8—HC═CH2 [ 1 / 1000C]0.72total-CH3 [ 1 / 1000C]5.4

[0158]Granulation and Film Extrusion

[0159]The polyethylene compositions of Example 1-12 were homogenized and granulated on a ZSK 30 (Werner Pfleiderer) with screw combination 8A. The processing temperature was 220° C., the screw speed 250 / min, the output of 20 kg / h.

[0160]Each polyethylene composition of the Examples above was extruded into films by blown film extrusion on a Weber film extruder equipped with a collapsing device with wooden flatt...

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Abstract

A polyethylene composition, in particular suitable for the preparation of films, and a process for preparing the same are described. The polyethylene composition of the invention comprises from 50 to 89% by weight of a first polyethylene component comprising at least one multimodal polyethylene including a plurality of ethylene polymer fractions having distinct molecular weights and comonomer contents, at least one of said plurality of ethylene polymer fractions being prepared by the use of a single site catalyst, and from 50 to 11% by weight of a second polyethylene component comprising a low or medium density polyethylene.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a novel polyethylene composition, to a process for the preparation thereof, as well as to a film comprising such a polyethylene composition.[0002]In the field of preparation of polyethylene films, particularly in the field of medium density (MDPE) and high density (HDPE) films, there is a long-felt need of providing films having, at the same time, a number of mechanical and physical properties, and in particular adequate mechanical strength, processability and transparency, which are normally conflicting with each other.[0003]In the present description and in the following claims, the expression “medium density film” is used to indicate a film having a density ranging from above 0.930 to 0.940 g / cm3, while the expression “high density film” is used to indicate a film having a density above 0.940 g / cm3.[0004]In polyethylene film applications, a possible way to evaluate the above-mentioned properties may be made through the ...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C08L23/06
CPCC08L23/04C08L23/06C08L23/0815C08L2205/02C08L2205/025C08L2205/035C08L2314/06C08L2308/00C08L2666/06C08L2666/02C08J5/18
Inventor KIPKE, JENNIFERMIHAN, SHAHRAMKARER, RAINERAUFFERMANN, JORGHECKER, MANFREDDE LANGE, PAULUSSCHMITZ, HARALD
Owner BASELL POLYOLEFINE GMBH
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