Polyethylene compositions with reduced gel formation and films comprising such compositions

Abstract

The present invention relates to a polymer composition comprising polyethylene and a compound of formula (I) wherein R1 and R2 are each a moiety comprising 1 to 40 carbon atoms wherein R1 and R2 may be the same or different. Such polymer compositions are capable of inhibiting the formation of gels in films produced therefrom, particularly after multiple extrusion processes, such as when the polymer compositions are recovered. (I)

Description

Technical Field

[0001] This invention relates to a polyethylene polymer composition in which gel formation is suppressed. The invention also relates to films produced using this polymer composition. Background Technology

[0002] Polymer materials are widely used in a variety of applications, including durable and disposable goods, as well as in both rigid and flexible applications. One particular type of polymer material that has been found to be widely used is polyethylene. For example, polyethylene materials are very commonly used in the form of films. Such films can be thin, flexible, transparent, and impermeable. Therefore, polyethylene films are known to be very suitable products for applications such as packaging (e.g., packaging of perishable goods). In this form, polyethylene films are ubiquitous and part of our daily lives.

[0003] Currently, there is a need to realize valuable uses for materials even after they have reached the end of their expected lifespan; that is, to seek valuable uses for waste materials. For polymer materials such as polyethylene, a common reuse procedure is through so-called mechanical recycling. Through mechanical recycling, waste polyethylene material is remelted and molded into entirely new usable forms, which can be, for example, new membrane materials.

[0004] The objective that manufacturers need to determine in mechanical recycling is that the material's properties will not be adversely affected by the recycling process to the point that the properties required for the material's new application are not achieved. For polyethylene films, as mentioned above, typical properties to consider in this regard are transparency, flexibility, and permeability. The conditions the material is subjected to during mechanical recycling processes (which may involve heating to molding temperatures and shear induced in melt extrusion) are known to induce a certain degree of degradation in the material.

[0005] Therefore, efforts should be made to ensure that the polymer material (in this case, polyethylene) possesses the required high stability not only during its original manufacture but also preferably even after undergoing one or more recycling steps. A specific parameter considered an indicator of desirable quality retention is the amount of so-called gel in the membrane produced from the polyethylene material. In the context of polyethylene membranes, gel is considered to be membrane regions containing, for example, cross-linked or carbonized polymer domains, thus forming defects in optical and / or quality properties. Particularly in polymer membranes (which are typically very thin), the presence of gel is detrimental to the quality and aesthetics of the membrane. Therefore, manufacturers wish to avoid its formation. Summary of the Invention

[0006] In this invention, the inventors achieved this by comprising a polymer composition containing the following:

[0007] (a) polyethylene; and

[0008] (b) Compounds of formula (I):

[0009] (I)

[0010] R1 and R2 are each structural parts containing 1-40 carbon atoms, and R1 and R2 can be the same or different.

[0011] The polymer composition optionally further comprises:

[0012] (c) ≥250 and ≤1000 ppm by weight of 2,6-di-tert-butyl-4-(octadecyloxycarbonylethyl)phenol; and

[0013] (d) Zinc oxide ≥250 and ≤1000 ppm by weight;

[0014] Relative to the total weight of the polymer composition.

[0015] This polymer composition can suppress the formation of gel in the film produced from it, especially after multiple extrusion passes, such as when the polymer composition is recycled.

[0016] Preferably, the composition comprises ≥300 and ≤700 ppm by weight, more preferably ≥400 and ≤600 ppm of 2,6-di-tert-butyl-4-(octadecyloxycarbonylethyl)phenol.

[0017] Preferably, the composition contains ≥300 and ≤700 ppm by weight, more preferably ≥400 and ≤600 ppm of zinc oxide.

[0018] The polymer composition may, for example, contain ≥250 and ≤1500 ppm by weight, preferably ≥250 and ≤1100 ppm, more preferably ≥250 and ≤750 ppm, of compound (b) relative to the total weight of the polymer composition.

[0019] The polymer composition according to any one of claims 1-2, wherein the polymer composition comprises ≥95.0 wt%, preferably ≥98.0 wt%, more preferably ≥99.0 wt%, and even more preferably ≥99.5 wt% of polyethylene, relative to the total weight of the polymer composition. For example, the polymer composition may not contain polymer materials other than polyethylene.

[0020] In one embodiment, the polymer composition may, for example, consist of polyethylene, compound (b), ≥250 and ≤1000 ppm by weight of 2,6-di-tert-butyl-4-(octadecyloxycarbonylethyl)phenol, and ≥250 and ≤1000 ppm by weight of zinc oxide, relative to the total weight of the polymer composition.

[0021] The polyethylene in the polymer composition may, for example, have a strength of ≥850 and ≤970 kg / m³. 3 Preferred weight is ≥890 and ≤940 kg / m³. 3 More preferably ≥906 and ≤929kg / m 3 Even more preferred is ≥916 and ≤925kg / m 3 The density, as determined according to ASTM D792.

[0022] 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 ≥1.0 and ≤5.0 g / 10 min, as determined according to ASTM D1238 at 190°C under a load of 2.16 kg.

[0023] Polyethylene may be, for example, a copolymer comprising a structural portion derived from ethylene and a structural portion 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 a structural portion derived from a comonomer selected from 1-butene, 1-hexene and 1-octene.

[0024] In compound (b), R1 or R2, or both R1 and R2, may be, for example, an alkyl moiety, a substituted or unsubstituted aryl moiety, or an aralkyl moiety. R1 or R2, or both R1 and R2, may be, for example, a moiety according to formula (II):

[0025] (II)

[0026] Where X represents the position where the structural part is connected to the oxygen atom in formula (I), and R3, R4, R5, R6 and R7 can each be independently selected from hydrogen, methyl, tert-butyl and tert-butylbenzyl.

[0027] R4, R6, and R7 may each be hydrogen, for example. In one specific embodiment, R4, R6, and R7 are each hydrogen, and R3 and R5 are selected from methyl, tert-butyl, and tert-butylbenzyl. Particularly preferred is that R4, R6, and R7 are each hydrogen, and R3 and R5 are the same and selected from methyl, tert-butyl, and tert-butylbenzyl.

[0028] For example, R1 and R2 can be selected independently from:

[0029]

[0030] Where X represents the position where the structural part is connected to the oxygen atom in formula (I); preferably, R1 and R2 are the same.

[0031] Particularly preferred is compound (b) which is bis(2,4-dicumylphenyl)pentaerythritol diphosphite.

[0032] One specific embodiment of the present invention relates to a polymer composition comprising:

[0033] Polyethylene with ≥98.0 wt%, preferably having ≥906 and ≤929 kg / m³. 3 The polyethylene having a density and a melt mass flow rate of ≥0.5 and ≤10.0 g / 10 min, as determined according to ASTM D1238 at 190 °C under a load of 2.16 kg, wherein the polyethylene is a copolymer comprising a structural moiety derived from ethylene and a structural moiety of ≥2.0 and ≤15.0 wt% derived from comonomers selected from 1-butene, 1-hexene, and 1-octene; and

[0034] ≥250 and ≤1100 ppm by weight of bis(2,4-dicumylphenyl)pentaerythritol diphosphite, relative to the total weight of the polymer composition.

[0035] Another specific embodiment of the present invention relates to a polymer composition comprising:

[0036] Polyethylene with ≥98.0 wt%, preferably having ≥906 and ≤929 kg / m³. 3 The polyethylene having a density and a melt mass flow rate of ≥0.5 and ≤10.0 g / 10 min, as determined according to ASTM D1238 at 190 °C under a load of 2.16 kg, wherein the polyethylene is a copolymer comprising a structural moiety derived from ethylene and a structural moiety of ≥2.0 and ≤15.0 wt% derived from comonomers selected from 1-butene, 1-hexene, and 1-octene; and

[0037] ≥250 and ≤1100 ppm by weight of bis(2,4-dicumylphenyl)pentaerythritol diphosphite; and

[0038] ≥250 and ≤1000 ppm by weight of 2,6-di-tert-butyl-4-(octadecyloxycarbonylethyl)phenol; and

[0039] ≥250 and ≤1000 ppm by weight of zinc oxide;

[0040] Relative to the total weight of the polymer composition.

[0041] Another specific embodiment of the present invention relates to a polymer composition comprising:

[0042] Polyethylene, preferably having a strength of ≥906 and ≤929 kg / m³. 3 The polyethylene having a density and a melt mass flow rate of ≥0.5 and ≤10.0 g / 10 min, as determined according to ASTM D1238 at 190 °C under a load of 2.16 kg, wherein the polyethylene is a copolymer comprising a structural moiety derived from ethylene and a structural moiety of ≥2.0 and ≤15.0 wt% derived from comonomers selected from 1-butene, 1-hexene, and 1-octene; and

[0043] ≥250 and ≤1100 ppm by weight of bis(2,4-dicumylphenyl)pentaerythritol diphosphite; and

[0044] ≥250 and ≤1000 ppm by weight of 2,6-di-tert-butyl-4-(octadecyloxycarbonylethyl)phenol; and

[0045] ≥250 and ≤1000 ppm by weight of zinc oxide;

[0046] Relative to the total weight of the polymer composition.

[0047] In some embodiments, the invention also relates to a membrane comprising at least one layer, said layer comprising or consisting of a polymer composition according to the invention. Particularly preferred is that such a membrane has a thickness of ≥25 μm and ≤300 μm. For example, such a membrane can be produced by cast film extrusion or blown film extrusion. Preferably, the membrane is a multilayer membrane, and particularly preferably, it is a multilayer membrane having a thickness of ≥25 μm and ≤300 μm. Such a multilayer membrane may, for example, comprise three, five, or seven membrane layers, each of which may have the same composition or may differ in composition.

[0048] Specifically, the present invention relates to a membrane comprising at least one layer, said layer being composed of a polymer composition comprising:

[0049] Polyethylene with ≥98.0 wt%, preferably having ≥906 and ≤929 kg / m³. 3 The polyethylene having a density and a melt mass flow rate of ≥0.5 and ≤10.0 g / 10 min, as determined according to ASTM D1238 at 190 °C under a load of 2.16 kg, wherein the polyethylene is a copolymer comprising a structural moiety derived from ethylene and a structural moiety of ≥2.0 and ≤15.0 wt% derived from comonomers selected from 1-butene, 1-hexene, and 1-octene; and

[0050] ≥250 and ≤1100 ppm by weight of bis(2,4-dicumylphenyl)pentaerythritol diphosphite, relative to the total weight of the polymer composition.

[0051] In another embodiment, the invention also relates to the use of the polymer composition according to the invention for reducing gel formation in a membrane.

[0052] Specifically, the present invention relates to the use of polymer compositions for reducing gel formation in membranes, said polymer compositions comprising:

[0053] Polyethylene with ≥98.0 wt%, preferably having ≥906 and ≤929 kg / m³. 3 The polyethylene having a density and a melt mass flow rate of ≥0.5 and ≤10.0 g / 10 min, as determined according to ASTM D1238 at 190 °C under a load of 2.16 kg, wherein the polyethylene is a copolymer comprising a structural moiety derived from ethylene and a structural moiety of ≥2.0 and ≤15.0 wt% derived from comonomers selected from 1-butene, 1-hexene, and 1-octene; and

[0054] ≥250 and ≤1100 ppm by weight of bis(2,4-dicumylphenyl)pentaerythritol diphosphite, relative to the total weight of the polymer composition.

[0055] More specifically, the present invention relates to the use of polymer compositions for reducing gel formation in membranes, said polymer compositions comprising:

[0056] Polyethylene with ≥98.0 wt%, preferably having ≥906 and ≤929 kg / m³. 3 The polyethylene having a density and a melt mass flow rate of ≥0.5 and ≤10.0 g / 10 min, as determined according to ASTM D1238 at 190 °C under a load of 2.16 kg, wherein the polyethylene is a copolymer comprising a structural moiety derived from ethylene and a structural moiety of ≥2.0 and ≤15.0 wt% derived from comonomers selected from 1-butene, 1-hexene, and 1-octene; and

[0057] ≥250 and ≤1100 ppm by weight of bis(2,4-dicumylphenyl)pentaerythritol diphosphite; and

[0058] ≥250 and ≤1000 ppm by weight of 2,6-di-tert-butyl-4-(octadecyloxycarbonylethyl)phenol; and

[0059] ≥250 and ≤1000 ppm by weight of zinc oxide;

[0060] Relative to the total weight of the polymer composition.

[0061] The invention will now be illustrated by the following non-limiting embodiments.

[0062] Example

[0063] Various compositions of polyethylene and additives, as shown in Table 1 below, were prepared in a 25 mm twin-screw melt extruder with a length-to-diameter (L / D) ratio of 56. The compositions were prepared under a nitrogen blanket at an extruder melt temperature of 180°C.

[0064] Table 1: Experimental Compositions

[0065]

[0066] The LLDPE material used in the above experiment was SABIC 318BJ, which has a strength of 918 kg / m³. 3 LLDPE polyethylene material with a density of 2.8 g / 10 min and a melt flow rate of 2.8 g / 10 min. 318BJ is a copolymer of ethylene and 1-butene as comonomers.

[0067] For each of the above compositions, a sample is taken out, and a membrane is produced from the sample to determine the gel content in the membrane.

[0068] A certain amount of the material was subjected to multiple further extrusion processes to measure the effect of multiple extrusions and therefore multiple melt cycles on the gel content. These further extrusion processes were performed using a melt extruder as described above at a melt temperature of 200°C using an ambient atmospheric blanket. After each process, a sample of each composition was taken for gel content determination. Each composition obtained from the initial extrusion cycle used for preparation was also subjected to three subsequent extrusion processes.

[0069] To determine the gel content, samples were processed into cast films, and then the gel count was evaluated. The cast film was extruded using an OCS extruder operating at a maximum set temperature of 230°C (melt temperature 226-227°C), and then cooled on cooling rollers (25°C) at a winding speed of 3.2 m / min.

[0070] The gel content in a cast film system was determined by online measurement using an FSA-100 membrane surface analyzer (software version 6.3.4.2), available from Optical Control Systems GmbH, positioned between the cooling roller system and the clamping rollers. The membrane surface analyzer includes a CCD line scan camera with 50 μm resolution. Therefore, the smallest identifiable defect has dimensions of 50 μm in length and 50 μm in width. The membrane surface analyzer includes a halogen-based illumination system, generating continuous images of the membrane surface. Defect determination was performed using image recognition software integrated with the FSA-100 membrane surface analyzer, provided by Optical Control Systems GmbH. A total surface area of ​​6.0 m² was tested. 2 The number of membrane samples was counted. The number of gels with a length and / or width >600 μm was counted, and the results are shown in Table 2 below.

[0071] Table 2: Gel Count Results

[0072]

[0073] In the table above, step 1 corresponds to the extrusion step used to produce the formulation; steps 2-4 represent further extrusion steps.

[0074] The above results clearly demonstrate that the use of the formulations of the present invention results in the inhibition of gel formation, especially after multiple extrusion processes.

Claims

1. A polymer composition comprising: (a) polyethylene; and (b) Compounds of formula (I): (I) R1 and R2 are each structural parts containing 1-40 carbon atoms, and R1 and R2 can be the same or different. Optionally, the polymer composition further comprises: (c) ≥250 and ≤1000 ppm by weight of 2,6-di-tert-butyl-4-(octadecyloxycarbonylethyl)phenol; and (d) Zinc oxide ≥250 and ≤1000 ppm by weight; Relative to the total weight of the polymer composition.

2. The polymer composition according to claim 1, wherein the polymer composition comprises ≥250 and ≤1500 ppm by weight of compound (b) relative to the total weight of the polymer composition.

3. The polymer composition according to any one of claims 1-2, wherein the polymer composition comprises ≥95.0 wt%, preferably ≥98.0 wt%, of polyethylene relative to the total weight of the polymer composition.

4. The polymer composition according to any one of claims 1-3, wherein the polymer composition does not contain polymer materials other than polyethylene.

5. The polymer composition according to any one of claims 1-4, wherein the polyethylene has a strength of ≥850 and ≤970 kg / m³. 3 Preferred weight is ≥890 and ≤940 kg / m³. 3 More preferably ≥906 and ≤929kg / m 3 Even more preferred is ≥916 and ≤925kg / m 3 The density was determined according to ASTM D792.

6. The 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 ≥1.0 and ≤5.0 g / 10 min, as determined according to ASTM D1238 at 190°C under a load of 2.16 kg.

7. The polymer composition according to any one of claims 1-6, wherein the polyethylene is a copolymer comprising a structural portion derived from ethylene and a structural portion 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 a structural portion derived from a comonomer selected from 1-butene, 1-hexene and 1-octene.

8. The polymer composition according to any one of claims 1-7, wherein in compound (b), R1 or R2, or both R1 and R2 are alkyl moieties, substituted or unsubstituted aryl moieties, or aralkyl moieties.

9. The polymer composition according to any one of claims 1-8, wherein R1 or R2, or both R1 and R2 are structural portions according to formula (II): (II) Where X represents the position where the structural part is connected to the oxygen atom in formula (I), and R3, R4, R5, R6 and R7 can each be independently selected from hydrogen, methyl, tert-butyl and tert-butylbenzyl.

10. The 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, tert-butyl and tert-butylbenzyl.

11. The polymer composition according to any one of claims 1-9, wherein R1 and R2 are each independently selected from: Where X represents the position where the structural part is connected to the oxygen atom in formula (I); preferably R1 and R2 are the same.

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

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

14. The membrane according to claim 13, wherein the membrane is a multilayer membrane, preferably a multilayer membrane having a thickness of ≥25μm and ≤300μm.

15. Use of the polymer composition according to any one of claims 1-12 for reducing gel formation in a membrane.

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