Polyethylene composition with reduced gel formation and films comprising such composition

Abstract

The present invention relates to a polymer composition comprising polyethylene and a compound of formula (I) wherein each of R1 and R2 is a moiety comprising 1-40 carbon atoms, wherein R1 and R2 may be the same of may be different. Such polymer composition allows for the suppression of the formation of gels in films produced thereof, in particular after multiple extrusion passes, such as may for example occur when polymer compositions are recycled.

Description

Polyethylene composition with reduced gel formation and films comprising such composition

[0001] The present invention relates to a polymer composition comprising polyethylene wherein gel formation is suppressed. The invention also relates to films produced using such polymer composition.

[0002] Polymer materials are ubiquitously used in a wide variety of applications, including in durable and single-use goods, and in rigid and flexible applications. A particular type of polymer materials that have found widespread use is polyethylene. For example, polyethylene materials are very commonly used in the form of films. Such films can be thin, flexible, transparent, and impermeable. Accordingly, polyethylene films are known to be very suitable products for applications such as packaging, like packaging of perishable goods. In such form, polyethylene films are widespread and part of our everyday life.

[0003] Presently, a desire has emerged to enable the valuable use of materials even after they have ended their intended service life; that is, to seek for valuable use of waste materials. For polymer materials, such as polyethylene materials, a common procedure of re-use is by so- called mechanical recycling. Via mechanical recycling, waste polyethylene materials are remolten and shaped into an all new and useable form, which may for example be a new film material.

[0004] An objective that manufacturers need to ascertain in mechanical recycling is that the properties of the material are not so detrimentally affected by the recycling process that the properties that are required in the new application of the material are not met. For polyethylene films, typical properties that are to be considered in that regard are, as mentioned above, transparency, flexibility, and permeability. The conditions to which the materials are subjected in the course of a mechanical recycling process, which may involve heating to a shaping temperature and shear induced in melt extrusion, are known to induce a certain amount of degradation to the materials.

[0005] Therefore, efforts are to be undertaken to ensure that the polymer materials, in the present case polyethylene materials, have a required high stability not only at their original manufacturing, but preferably even after having been subjected to one or more recycling steps. A particular parameter that is considered to be an indicator for retention of the desirable qualityis the quantity of so-called gels in the films produced of the polyethylene materials. In the context of polyethylene films, gels are considered to be areas of a film containing for example crosslinked or carbonised polymer domains, and thus form defects of optical and / or qualitative nature. In particular in polymer films, which are typically very thin, the presence of gels can be detrimental to both quality and aesthetics of the film. Thus, manufacturers desire to avoid formation thereof.

[0006] In the present invention, the inventors have achieved so by a polymer composition comprising(a) polyethylene; and(b) a compound of formula (I):wherein each of R1 and R2 is a moiety comprising 1-40 carbon atoms, wherein R1 and R2 may be the same of may be different; wherein the polymer composition optionally further comprises:(c) > 250 and < 1000 ppm by weight of 2,6-di-tert-butyl-4- (octadecanoxycarbonylethyl)phenol; and(d) > 250 and < 1000 ppm by weight of zinc oxide; with regard to the total weight of the polymer composition.

[0007] Such polymer composition allows for the suppression of the formation of gels in films produced thereof, in particular after multiple extrusion passes, such as may for example occur when polymer compositions are recycled.

[0008] It is preferred that the composition comprises > 300 and < 700 ppm by weight of 2,6-di- tert-butyl-4-(octadecanoxycarbonylethyl)phenol, more preferably > 400 and < 600 ppm.

[0009] It is preferred that the composition comprises > 300 and < 700 ppm by weight of zinc oxide, more preferably > 400 and < 600 ppm.

[0010] The polymer composition may for example comprise > 250 and < 1500 ppm by weight of the compound (b), with regard to the total weight of the polymer composition, preferably > 250 and < 1100 ppm, even more preferably > 250 and < 750 ppm.

[0011] Polymer composition according to any one of claim 1-2, wherein the polymer composition comprises > 95.0 of polyethylene, preferably > 98.0 wt%, more preferably > 99.0 wt%, even more preferably > 99.5 wt%, with regard to the total weight of the polymer composition. For example, the polymer composition may comprise no polymer materials other than polyethylene.

[0012] In an embodiment, the polymer composition may for example consist of polyethylene, the compound (b), > 250 and < 1000 ppm by weight of 2,6-di-tert-butyl-4- (octadecanoxycarbonylethyl)phenol and > 250 and < 1000 ppm by weight of zinc oxide, with regard to the total weight of the polymer composition.

[0013] The polyethylene in the polymer composition may for example have a density of > 850 and < 970 kg / m3, preferably of > 890 and < 940 kg / m3, more preferably of > 906 and < 929 kg / m3, even more preferably of > 916 and < 925 kg / m3, as determined in accordance with with ASTM D792.

[0014] The polyethylene in the polymer composition may for example have a melt mass-flow rate of > 0.5 and < 10.0 g / 10 min, preferably of > 1.0 and < 5.0 g / 10 min, as determined in accordance with ASTM D1238, at 190°C at a load of 2.16 kg.

[0015] The polyethylene may for example be a copolymer comprising moieties derived from ethylene and moieties derived from a comonomer selected from 1 -butene, 1 -hexene and 1- octene, preferably wherein the polyethylene comprises > 0.1 and < 30.0 wt%, more preferably > 2.0 and < 15.0 wt%, of moieties derived from a comonomer selected from 1-butene, 1-hexene and 1 -octene.

[0016] In the compound (b), R1 or R2, or both R1 and R2, may for example be an alkyl moiety, a substituted or unsubstituted aryl moiety, or an aralkyl moiety. R1 or R2, or both R1 and R2, may for example be a moiety according to formula (II):wherein X indicates the location of connection of the moiety to the oxygen atom in formula (I), and wherein each of R3, R4, R5, R6 and R7 may individually be selected from hydrogen, methyl, t-butyl, and t-butylbenzyl.

[0017] R4, R6 and R7 may for example each be hydrogen. In a particular embodiment, each R4, R6 and R7 are hydrogen, and R3 and R5 are selected from methyl, t-butyl, and t- butylbenzyl. In is particularly preferable that each R4, R6 and R7 are hydrogen, and R3 and R5 are the same and selected from methyl, t-butyl, and t-butylbenzyl.

[0018] For example, R1 and R2 may each be individually selected from:wherein X indicates the location of connection of the moiety to the oxygen atom in formula (I); preferably, wherein R1 and R2 are the same.

[0019] It is particularly preferred that the compound (b) is bis(2,4-dicumylphenyl) pentaerythritol diphosphite.

[0020] A particular embodiment of the invention relates to a a polymer composition comprising:• > 98.0 wt% of polyethylene, preferably a polyethylene having a density of > 906 and < 929 kg / m3, and a melt mass-flow rate of > 0.5 and < 10.0 g / 10 min, as determined in accordance with ASTM D1238, at 190°C at a load of 2.16 kg, wherein the polyethylene is a copolymer comprising moieties derived from ethylene and > 2.0 and < 15.0 wt%, of moieties derived from a comonomer selected from 1 -butene, 1 -hexene and 1 -octene; and• > 250 and < 1100 ppm by weight of bis(2,4-dicumylphenyl) pentaerythritol diphosphite, with regard to the total weight of the polymer composition.

[0021] A further particular embodiment of the invention relates to a polymer composition comprising:• > 98.0 wt% of polyethylene, preferably a polyethylene having a density of > 906 and < 929 kg / m3, and a melt mass-flow rate of > 0.5 and < 10.0 g / 10 min, as determined in accordance with ASTM D1238, at 190°C at a load of 2.16 kg, wherein the polyethylene is a copolymer comprising moieties derived from ethylene and > 2.0 and < 15.0 wt%, of moieties derived from a comonomer selected from 1 -butene, 1 -hexene and 1 -octene; and• > 250 and < 1100 ppm by weight of bis(2,4-dicumylphenyl) pentaerythritol diphosphite; and• > 250 and < 1000 ppm by weight of 2,6-di-tert-butyl-4- (octadecanoxycarbonylethyl)phenol; and• > 250 and < 1000 ppm by weight of zinc oxide; with regard to the total weight of the polymer composition.

[0022] A yet further particular embodiment of the invention relates to a polymer composition consisting of:• polyethylene, preferably a polyethylene having a density of > 906 and < 929 kg / m3, and a melt mass-flow rate of > 0.5 and < 10.0 g / 10 min, as determined in accordance with ASTM D1238, at 190°C at a load of 2.16 kg, wherein the polyethylene is a copolymer comprising moieties derived from ethylene and > 2.0 and < 15.0 wt%, of moieties derived from a comonomer selected from 1 -butene, 1 -hexene and 1 -octene; and• > 250 and < 1100 ppm by weight of bis(2,4-dicumylphenyl) pentaerythritol diphosphite; and• > 250 and < 1000 ppm by weight of 2,6-di-tert-butyl-4- (octadecanoxycarbonylethyl)phenol; and• > 250 and < 1000 ppm by weight of zinc oxide; with regard to the total weight of the polymer composition.

[0023] The invention also, in certain of its embodiments, relates to films comprising at least one layer comprising or consisting of the polymer composition according to the invention. It is particularly preferred that such film has a thickness of > 25 pm and < 300 pm. such film may for example be produced via cast film extrusion, or by blown film extrusion. Preferably, the film is a multilayer film, particularly preferably a multilayer film having a thickness of > 25 pm and < 300 pm. Such multilayer film may for example comprise three, five, or seven film layers, which each may be of the same composition, or may differ in their composition.

[0024] In particular, the invention relates to a film comprising at least one layer consisting of a polymer composition comprising:• > 98.0 wt% of polyethylene, preferably a polyethylene having a density of > 906 and < 929 kg / m3, and a melt mass-flow rate of > 0.5 and < 10.0 g / 10 min, as determined in accordance with ASTM D1238, at 190°C at a load of 2.16 kg, wherein the polyethylene is a copolymer comprising moieties derived from ethylene and > 2.0 and < 15.0 wt%, of moieties derived from a comonomer selected from 1 -butene, 1 -hexene and 1 -octene; and• > 250 and < 1100 ppm by weight of bis(2,4-dicumylphenyl) pentaerythritol diphosphite, with regard to the total weight of the polymer composition.

[0025] In a further embodiment, the invention also relates to the use of the polymer composition according to the invention for reduction of gel formation in films.

[0026] In particular, the invention relates to the use of a polymer composition comprising:• > 98.0 wt% of polyethylene, preferably a polyethylene having a density of > 906 and < 929 kg / m3, and a melt mass-flow rate of > 0.5 and < 10.0 g / 10 min, as determined in accordance with ASTM D1238, at 190°C at a load of 2.16 kg, wherein the polyethylene is a copolymer comprising moieties derived from ethylene and > 2.0 and < 15.0 wt%, of moieties derived from a comonomer selected from 1 -butene, 1 -hexene and 1 -octene; and• > 250 and < 1100 ppm by weight of bis(2,4-dicumylphenyl) pentaerythritol diphosphite, with regard to the total weight of the polymer composition, for reduction of gel formation in films.

[0027] Even more particularly, the invention relates to the use of a polymer composition comprising:• > 98.0 wt% of polyethylene, preferably a polyethylene having a density of > 906 and < 929 kg / m3, and a melt mass-flow rate of > 0.5 and < 10.0 g / 10 min, as determined in accordance with ASTM D1238, at 190°C at a load of 2.16 kg, wherein the polyethylene is a copolymer comprising moieties derived from ethylene and > 2.0 and < 15.0 wt%, of moieties derived from a comonomer selected from 1 -butene, 1 -hexene and 1 -octene; and• > 250 and < 1100 ppm by weight of bis(2,4-dicumylphenyl) pentaerythritol diphosphite; and• > 250 and < 1000 ppm by weight of 2,6-di-tert-butyl-4- (octadecanoxycarbonylethyl)phenol; and• > 250 and < 1000 ppm by weight of zinc oxide; with regard to the total weight of the polymer composition for reduction of gel formation in films.

[0028] The invention will now be illustrated by the following non-limiting examples.

[0029] In a 25 mm twin-screw melt extruder having a length to diameter L / D ratio of 56, a number of compositions of polyethylenes and additives were prepared as reflected in table 1 below. The compositions were prepared at an extruder melt temperature of 180 °C, under a nitrogen blanket.Table 1 : Experimental Compositions

[0030] The LLDPE material used in the experiments above was SABIC 318BJ, an LLDPE polyethylene material having a density of 918 kg / m3and a melt mass-flow rate of 2.8 g / 10 min. 318BJ is a copolymer of ethylene with 1 -butene as comonomer.

[0031] Of each of the compositions as described above, a sample was taken, of which films were produced to determine the gel content in such film.

[0032] A quantity of the material was subjected to multiple further extrusion passes, to measure the effect of multiple extrusions, and thus multiple melt cycles, to the gel content. These further extrusion passes were performed using the melt extruder as described above, at a melt temperature of 200°C, using ambient atmospheric blanket. After each pass, a sample was taken of each composition for gel content determination. Each composition as obtained by the original extrusion cycle for preparation was further subjected to three subsequent extrusion passes.

[0033] For gel content determination, the samples were processed into cast films, followed by the assessment of the gel count. The cast film extrusion was performed using an OCS extruder running at a maximum set temperature of 230 °C (melt temperature 226 - 227 °C), followed by cooling of the film on chilled rollers (25 °C) at a take up speed of 3.2 m / min.

[0034] The gel content was determined via on-line measurement of the film in the cast film system using an FSA-100 film surface analyser obtainable from Optical Control Systems GmbH software version 6.3.4.2, wherein surface analyser is the positioned between the chill roll system and the nip rolls. The film surface analyser comprised a CCD line scan camera with a resolution of 50 pm. The smallest defects that could be identified accordingly had a dimension of 50 pm length and 50 pm width. The film surface analyser comprised halogen based illumination system. A continuous image of the film surface was thus produced. The determination of defects was performed using image recognition software provided by Optical Control Systems GmbH integrated with the FSA-100 film surface analyser. A film sample with a total surface size of 6.0 m2was tested. The number of gels having length and / or a width of > 600 pm were counted, results of which are shown in table 2 below.Table 2: Gel count results

[0035] In the table above, pass 1 corresponds to the extrusion pass for production of the formulation; passes 2-4 indicate the further extrusion passes.

[0036] The above results clearly show that use of the formulations of the present invention lead to suppression of the formation of gels, in particular after multiple extrusion passes.

Claims

Claims1. Polymer composition comprising(a) polyethylene; and(b) a compound of formula (I):wherein each of R1 and R2 is a moiety comprising 1-40 carbon atoms, wherein R1 and R2 may be the same of may be different; wherein the polymer composition optionally further comprises:(c) > 250 and < 1000 ppm by weight of 2,6-di-tert-butyl-4- (octadecanoxycarbonylethyl)phenol; and(d) > 250 and < 1000 ppm by weight of zinc oxide; with regard to the total weight of the polymer composition.

2. Polymer composition according to claim 1 , wherein the polymer composition comprises > 250 and < 1500 ppm by weight of the compound (b), with regard to the total weight of the polymer composition.

3. Polymer composition according to any one of claims 1-2, wherein the polymer composition comprises > 95.0 of polyethylene, preferably > 98.0 wt%, with regard to the total weight of the polymer composition.

4. Polymer composition according to any one of claims 1-3, wherein the polymer composition comprises no polymer materials other than polyethylene.

5. Polymer composition according to any one of claims 1-4, wherein the polyethylene has a density of > 850 and < 970 kg / m3, preferably of > 890 and < 940 kg / m3, more preferably of > 906 and < 929 kg / m3, even more preferably of > 916 and < 925 kg / m3, as determined in accordance with with ASTM D792.

6. Polymer composition according to any one of claims 1-5, wherein the polyethylene has a melt mass-flow rate of > 0.5 and < 10.0 g / 10 min, preferably of > 1.0 and < 5.0 g / 10 min, as determined in accordance with ASTM D1238, at 190°C at a load of 2.16 kg.

7. Polymer composition according to any one of claims 1-6, wherein the polyethylene is a copolymer comprising moieties derived from ethylene and moieties derived from a comonomer selected from 1-butene, 1-hexene and 1-octene, preferably wherein the polyethylene comprises > 0.1 and < 30.0 wt%, more preferably > 2.0 and < 15.0 wt%, of moieties derived from a comonomer selected from 1-butene, 1-hexene and 1-octene.

8. Polymer composition according to any one of claims 1-7, wherein in the compound (b), R1 or R2, or both R1 and R2, is an alkyl moiety, a substituted or unsubstituted aryl moiety, or an aralkyl moiety.

9. Polymer composition according to any one of claims 1-8, wherein R1 or R2, or both R1 and R2, is a moiety according to formula (II):wherein X indicates the location of connection of the moiety to the oxygen atom in formula (I), and wherein each of R3, R4, R5, R6 and R7 may individually be selected from hydrogen, methyl, t-butyl, and t-butylbenzyl.

10. Polymer composition according to claim 9, wherein R4, R6 and R7 are hydrogen, preferably wherein R3 and R5 are the same and selected from methyl, t-butyl, and t- butylbenzyl.

11. Polymer composition according to any one of claims 1-9, wherein R1 and R2 are each individually selected from:wherein X indicates the location of connection of the moiety to the oxygen atom in formula (I); preferably, wherein R1 and R2 are the same.

12. Polymer composition according to any one of claims 1-11, wherein the compound (b) is bis(2,4-dicumylphenyl) pentaerythritol diphosphite.

13. Film comprising at least one layer comprising or consisting of the polymer composition according to any one of claims 1-12.

14. Film according to claim 13, wherein the film is a multilayer film, preferably a multilayer film having a thickness of > 25 pm and < 300 pm.

15. Use of the polymer composition according to any of claims 1-12 for reduction of gel formation in films.

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