Object comprising a sealing layer

Abstract

The present invention relates to an object comprising a sealing layer, wherein the sealing layer comprises a polyethylene comprising moieties derived from ethylene and moieties derived from an α-olefin comprising 4 to 10 carbon atoms, the polyethylene having a density of ≥ 870 and ≤ 920 kg / m3, preferably of ≥ 890 and ≤ 910 kg / m3, as determined in accordance with ASTM D792 (2013), wherein the polyethylene has a zero-shear viscosity of ≤ 12.0 kPaꞏs, as determined in accordance with ISO 6721-10 (2015). Such object exhibits a desirably low seal initiation temperature, and a desirably high hot tack strength.

Description

24POLYOQ68-WO-ORD 1Object comprising a sealing layer.

[0001] The present invention relates to an object comprising a sealing layer, in particular to a film or laminate comprising a sealing layer, such as for packaging applications, wherein the sealing layer comprises a polyethylene.

[0002] Objects, such as films or laminates, that comprise a sealing layer comprising polyethylene materials are abundantly used in a wide variety of applications. A particular example where such objects find their application is in packaging, such as food packaging. The use of polyethylenes allows for packaging of products in a hygienic manner, contributes to preservation of the packaged products for a prolonged period, and allows the packaging process to be performed in an economically attractive way. Further, polyethylene packaging materials can be produced with a highly attractive appearance.

[0003] In the field of objects that can be used for packaging, a particular aspect relates to the sealing of such objects. In commercial use, such as in packaging of foodstuff products, the packaging object often is closed by contacting two layers of material with one another, and applying heat to at least that area of those layers where a closed seal is to be formed. The applied heat then leads to local softening of the materials, such as the polyethylenes that may be present in such layers. This leads to a certain adhesion between the two softened layers, which, upon cooling, results in a closed seal, thus forming a packaging object that contains the desired contents separated from the surrounding atmosphere.

[0004] Such packages are well known in everyday applications, and allow for example for a significant increase in the retention time of the contained products.

[0005] In such packaging solutions, the seals that are produced using such heat-sealing technology as described above need to have a certain strength. This is required in order to be able to produce a package that, during production, transport, storage, and consumer use, is able to withstand certain forces that is may be subjected to, and which it should be considered able to withstand. Therefore, the strength of the seal should be above a certain threshold.

[0006] What is further important, in view of the process efficiency of the packaging process as well as the energy consumption during the packaging process, is that such seal having a24POLYOQ68-WO-ORD 2 desirably high strength can be produced at a sealing temperature that is desirably low. The lower the temperature at which the seal can be formed, the less energy is to be employed. A further benefit of a lower temperature that is required for seal formation is that the contents of the package are less subject to elevated temperatures, which, for example in the case of packaging of foodstuffs, may be beneficial for the retention of the quality of the packaged contents.

[0007] A further important property in such packaging solutions based on polyethylene materials is the so-called hot tack strength. In the context of the present invention, the hot tack strength is to be understood as the strength of a seal made in a film by heat-sealing immediately after sealing, before the seal has cooled down; thus the strength at elevated temperature. The hot tack strength affect the efficiency of the packaging process, for example the speed at which the packaging line can be operated. The higher the hot tack strength, the less cooling time is required upon seal formation prior to further processing of the package, i.e. the earlier the strength of a seal is of such magnitude as to be able to withstand exerted forces without damaging the seal, the shorter the cycle time in for example continuous packaging machines.

[0008] It is also desirable that the hot-tack strength is relatively high over a broad temperature range. This allows for being able to produce the seal in a broad operating window; the sealing layer in such situation is more forgiving to change of sealing and operating temperature, thus contributes to flexibility in the packaging process.

[0009] Presently, certain further drivers emerge that are to be considered in view of optimisation of material formulations that are to be used in sealable objects such as packaging films and laminates. These drivers include a desire for use of material in a single object wherein the materials that are used in that object form part of the same family of materials, for example wherein a very large fraction or preferably all of the polymer materials are from the same polymer family, such as from the family of polyethylenes. In such case, the object is more suitable for recycling purposes, such as for example via mechanical or chemical recycling. The higher the degree of similarity between different polymer materials that are used in an object, the easier to re-use the material in high-value recycling solutions. Another emerging driver is the desire to reduce the quantity of materials that are used in an object such as a packaging application. Reduction of material used in such application not only reduces the carbon footprint throughout the production process, but also reduces the quantity of waste that after the useful service life of the object is to be processed.24POLY0068-WO-ORD 3

[0010] These industry drivers also affect the formulation of materials that are to be used in the sealing layers of such objects. Particularly, a need continues to exist for objects wherein the sealing layers allow for low temperature sealing at high seal strengths and hot tack strengths.

[0011] This is now achieved according to the present invention by an object comprising a sealing layer, wherein the sealing layer comprises a polyethylene comprising moieties derived from ethylene and moieties derived from an a-olefin comprising 4 to 10 carbon atoms, the polyethylene having a density of > 870 and < 920 kg / m3, preferably of > 890 and < 910 kg / m3, as determined in accordance with ASTM D792 (2013), wherein the polyethylene has a zero-shear viscosity of < 12.0 kPa s, as determined in accordance with ISO 6721-10 (2015).

[0012] Such object exhibits a desirably low seal initiation temperature, and a desirably high hot tack strength. In the context of the present invention, the seal initiation temperature is the lowest temperature at which a seal having a strength of 5.0 N / 15mm can be produced, as determined in accordance with ASTM F88 (2015). The hot tack window is to be understood to hot tack strength as determined in accordance with ASTM F1921-B (2021).

[0013] In a particular embodiment, the polyethylene has a long-chain branching (LCB) content of < 4.0 branches per 100,000 carbon atoms, preferably < 3.0, wherein LCB is determined in accordance with the method of the description.

[0014] In a further embodiment, the polyethylene has a fraction of material that is eluted in crystal elution fractionation (CEF) at a temperature < 30.0°C of > 5.0 wt% and < 15.0 wt%, preferably > 7.5 wt% and < 12.5 wt%, more preferably > 7.5 wt% and < 10.0 wt%, wherein CEF is determined in accordance with the method of the description.

[0015] In a further embodiment, the polyethylene has a short chain branching ratio (SCBR) of < 1.00, preferably of > 0.80 and < 1.00, wherein SCBR is defined as:wherein SCB500 is the quantity of short chain branches (SCB) of the polyethylene atMw=500,000 g / mol and SCB is the quantity of short chain branches of the polyethylene at Mw=10,000 g / mol, wherein the SCB quantity is determined via GPC-IR and expressed as the number of branches per 1000 carbon atoms ( / 1000C).24POLYOQ68-WO-ORD 4

[0016] The invention also relates to an embodiment wherein the polyethylene has a melt massflow rate determined at 190°C under a load of 2.16 kg in accordance with ASTM D1238-13 of > 0.2 and < 10.0 g / 10 min, preferably > 0.5 and < 5.0, more preferably > 0.5 and < 2.0.

[0017] It is further preferred that the sealing layer comprises > 50.0 wt% of the polyethylene, with regard to the total weight of the sealing layer, preferably wherein the sealing layer comprises > 60.0 wt% and < 90.0 wt% of the polyethylene.

[0018] The a-olefin may for be selected from 1-butene, 1-hexene and 1-octene, preferably 1- octene, preferably wherein the polyethylene comprises > 15.0 and < 30.0 wt% of moieties derived from 1-octene, with regard to the total weight of the polyethylene.

[0019] The polyethylene may for example comprise > 70.0 wt% of moieties derived from ethylene, with regard to the total weight of the polyethylene.

[0020] The polyethylene may for example be produced via a solution polymerisation process. The polyethylene may be produced using a metallocene-type catalyst.

[0021] The object may for example be a film or a laminate. Such the film or laminate may for example have a thickness of > 1 and < 200 pm, preferably > 10 and < 150 pm, more preferably > 20 and < 125 pm.

[0022] The film or laminate may for example have a multi-layer structure.

[0023] The film or laminate may for example comprise the sealing layer as one outer layer or as both outer layers.

[0024] The film or laminate may for example comprise > 75.0 wt% of ethylene-based polymers, preferably > 80.0 wt%, more preferably > 90.0 wt%, with regard to the total weight of the film or laminate, even more preferably the film or laminate comprises no polymer materials other than ethylene-based polymer materials.

[0025] The film or laminate may for example comprise 3-5 layers.24PGLY0068-WG-ORD 5

[0026] The sealing layer may for example comprise > 98.0 wt% of ethylene-based polymer materials, preferably the sealing layer comprises no polymer materials other than ethylenebased polymer materials, with regard to the total weight of the sealing layer. In the context of the present invention, ethylene-based polymer materials are to be understood to be polymer materials wherein at least 50.0 wt% of the polymeric units is derived from ethylene, preferably at least 70.0 wt%, with regard to the total weight of the ethylene-based polymer. It is preferred that ethylene-based polymer materials do not contain hetero-atoms in the polymeric chain. It is further preferred that such ethylene-based polymers only comprise polymeric units derived from compounds that are free from hetero-atoms.

[0027] The film may for example be produced via cast extrusion processes, via blown films processes, or via cast extrusion followed by solid-state orientation processes, such as tenterframe orientation processes.

[0028] In the context of the present invention, the SCB quantity is determined via infrareddetection gel permeation chromatography (GPC-IR). GPC-IR analysis may for example be performed using a chromatographer, such as a Polymer Char GPC-IR system, equipped with three columns of internal diameter 7.5 mm and 300 mm length, packed with of particles of 13 pm average particle size, such as Polymer Laboratories 13pm PLgel Olexis, operating at 160°C, equipped with an MCT IR detector, wherein 1 ,2,4-trichlorobenzene stabilised with 1 g / l butylhydroxytoluene may be used as eluent at a flow rate of 1 ml / min, with a sample concentration of 0.7 mg / ml and an injection volume of 200 pl, with molar mass being determined based on the universal GPC principle using a calibration made with PE narrow and broad standards in the range of 0.5-2800 kg / mol, Mw / Mn - 4 to 15 in combination with known Mark Houwink constants of PE-calibrant alfa = 0.725 and log K = -3.721. Short chain branching content was determined via IR determination of the intensity ratio of CH3 (ICHS) to CH2 (ICH2) coupled with a calibration curve. The calibration curve is a plot of SCB content (XSCB) as a function of the intensity ratio of ICH3 / ICH2. TO obtain a calibration curve, a group of polyethylene resins (no less than 5) (SCB Standards) were used. All these SCB Standards have known SCB levels and flat SCBD profiles. Using SCB calibration curves thus established, profiles of short chain branching distribution across the molecular weight distribution can be obtained for resins fractionated by the IR5-GPC system under exactly the same chromatographic conditions as for these SCB standards. A relationship between the intensity ratio and the elution volume is converted into SCB distribution as a function of MWD using a predetermined SCB calibration24POLY0068-WO-ORD 6 curve (i.e., intensity ratio of ICH3 / ICH2 VS. SCB content) and MW calibration curve (i.e., molecular weight vs. elution time) to convert the intensity ratio of ICH3 / ICH2 and the elution time into SCB content and the molecular weight, respectively.

[0029] In the context of the present invention, the LCB quantity is determined via the branch-on- branch model according to the formula:14000 LCB = -MN,SWherein LCB is the long-chain branching content in branches per 1000 C atoms of the polymer, MN,S is the number-averaged segmental molecular weight, and bmthe average number of branches per molecule.The MN,S may be determined according to the formula:Mwmay be determined using the method of ASTM D6474 (2012). The bmis a fitting parameter, and the value can be obtained by optimization of calculated results fitting to the experimental linear viscoelasticity data according to methods “Macromolecules 2002,34,2514” and “J. Rheol. 50, 207,2006.

[0030] In the context of the present invention, CEF analysis may be performed by CCD analysis performed on a commercial CEF instrument (PolymerChar, Spain) equipped with two detectors; an I R-5 detector which provides information on the sample concentration and comonomer content as well as a viscometer detector. Polymer solutions are prepared at 4 mg / mL concentration level in 1 ,2,4-Trichlorobenzene (TCB) in the auto sampler. The sample solutions are then injected into the system and separated according to its crystallinity. A first separation takes place during the crystallization cycle with a 4C / min cooling rate and a 0.06ml / min flow rate, followed by heating cycle with a 2C / min heating rate and a 1 ml / min flow rate, and then into the detection system. Final test temp is 160C.

[0031] The invention will now be illustrated by the following non-limiting examples.24POLY0068-WO-ORD 7

[0032] In the experiments conducted in the course of the present invention, the following polyethylene materials were used.

[0033] The materials PE1-PE4 were analysed to demonstrate the following product properties:wherein:• The MFR2 is the melt mass-flow rate, determined at 190°C under a load of 2.16 kg, in accordance with ASTM D1238 (2013); • The density is determined in accordance with ASTM D792 (2013)24POLYOQ68-WO-ORD 8• the SCB was determined via GPC-IR; SCB@10K is the SCB at Mw= 10,000 g / mol; SCB@100K is the SBC at Mw= 100,000 g / mol; SCB@500K is the SBC at Mw= 500,000 g / mol; SCBR = SCB@500K / SCB@10K;• the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) were determined in accordance with ASTM D6474 (2012);• the r|o is the zero-shear viscosity as determined by rheological experiments performed on ARES-G2 rotational rheometer from TA Instruments. The 25mm parallel plates were used for the small amplitude oscillatory and large amplitude experiments. The frequency sweep tests were performed at 190 °C, 100-0.01 rad / s, with a strain of 5% in linear viscoelastic region. Obtained data were extrapolated to zero shear according to the the Carreau-Yasuda model.• the LCB is the long-chain branching as determined via the branch-on-branch model according to the method described herein.

[0034] In fig. 1, the CEF elution profiles of each of the polymers PE1-4 are presented, wherein the eluted fraction at given temperature (dW / dT) is plotted against the elution temperature.

[0035] In fig. 2, a plot of the short chain branch content (SCR), in / 1000C, is plotted as function of the molecular weight Mwfor the polymers PE1-4, showing the distribution of the quantity of short chain branches for each molecular weight fraction.

[0036] In fig. 3, a plot of the rheology experiments of the polymers PE1-4 according to the method above is presented.

[0037] Using the materials PE1-4, films were produced using an STSC blow film machine, at an output of 8 kg / h, at a process temperature of 200°C. The films had a thickness of 50 pm.

[0038] Of each of the films that were produced, the hot tack strength was determined of seals produced at different temperatures, in accordance with ASTM F1921-B (2021), on a seal of 15 mm width. In the table below, the hot tack strengths of each of the films is presented, expressed in N. Fig. 4 provides a graphical representation of these data.24POLYOQ68-WO-ORD 9

[0039] Additionally, using the film production settings as indicated above, 3-layer 50pm thickness films were produced according to the formulations as in the table below.24POLYOQ68-WO-ORD 10

[0040] Hot tack strength was tested for each of the above films, results of which are listed in the table below.

[0041] The hot tack strength measurement results of the films F1-4 are presented in fig. 5, the results of films F5-F8 in fig. 6.

[0042] In addition, the seal strength of the films F1-8 was determined. The seal strength was determined in accordance with ASTM F88, using method A, on specimens of 15 mm width. Fin- seals were prepared according to ASTM F2029 at different temperatures. Two samples of the same film were compressed together, with layer C of the first film sample contacting layer C of the second film sample. Seals were produced by applying a force of 3.0 bar for 0.5 sec. The press used for preparing the seal was heated to various temperatures to identify the strength of the seal when produced at different temperatures.24POLYOQ68-WO-ORD 11

[0043] The seal strength was tested using a tensile testing machine with a testing speed of 200 mm / min, and a grip distance of 10 mm. The maximum load was recorded as the seal strength.

[0044] The results of the seal strength testing are presented in the table below, in N / 15 mm.

[0045] The seal strength measurement results of the films F1-4 are presented in fig. 7, the results of films F5-F8 in fig. 8.

[0046] Further 3-layer films of 70 pm thickness were produced according to the formulations in the table below.24POLYOQ68-WO-ORD 12According to the procedure set of above, the hot tack strength and the seal strength of the films F9-10 were tested. Results are presented in the tables below. Figures 9 and 10 show the hot tack strength and seal strength data for these examples.

Claims

24POLYOQ68-WO-ORD 13Claims1. Object comprising a sealing layer, wherein the sealing layer comprises a polyethylene comprising moieties derived from ethylene and moieties derived from an a-olefin comprising 4 to 10 carbon atoms, the polyethylene having a density of > 870 and < 920 kg / m3, preferably of > 890 and < 910 kg / m3, as determined in accordance with ASTM D792 (2013), wherein the polyethylene has a zero-shear viscosity of < 12.0 kPa s, as determined in accordance with ISO 6721-10 (2015).

2. Object according to claim 1 , wherein the polyethylene has a long-chain branching (LCB) content of < 4.0 branches per 100,000 carbon atoms, wherein LCB is determined in accordance with the method of the description.

3. Object according to any one of claims 1-2, wherein the polyethylene has a fraction of material that is eluted in crystal elution fractionation (CEF) at a temperature < 30.0°C of > 5.0 wt% and < 15.0 wt%, preferably > 7.5 wt% and < 12.5 wt%, more preferably > 7.5 wt% and < 10.0 wt%, wherein CEF is determined in accordance with the method of the description.

4. Object according to any one of claims 1-3, wherein the polyethylene has a short chain branching ratio (SCBR) of < 1.00, preferably of > 0.80 and < 1.00, wherein SCBR is defined as:wherein SCB500 is the quantity of short chain branches (SCB) of the polyethylene at Mw=500,000 g / mol and SCB is the quantity of short chain branches of the polyethylene at Mw=10,000 g / mol, wherein the SCB quantity is determined via GPC-IR and expressed as the number of branches per 1000 carbon atoms ( / 1000C).

5. Object according to any one of claims 1-4, wherein the polyethylene has a melt mass-flow rate determined at 190°C under a load of 2.16 kg in accordance with ASTM D1238-13 of > 0.2 and < 10.0 g / 10 min, preferably > 0.5 and < 5.0, more preferably > 0.5 and < 2.0.24POLYOQ68-WO-ORD 146. Object according to any one of claims 1-5, wherein the sealing layer comprises > 50.0 wt% of the polyethylene, with regard to the total weight of the sealing layer, preferably wherein the sealing layer comprises > 60.0 wt% and < 90.0 wt% of the polyethylene.

7. Object according to any one of claims 1-6, wherein the a-olefin comprising 4 to 10 carbon atoms is selected from 1 -butene, 1 -hexene and 1 -octene, preferably 1 -octene, preferably wherein the polyethylene comprises > 15.0 and < 30.0 wt% of moieties derived from 1- octene, with regard to the total weight of the polyethylene.

8. Object according to any one of claims 1-7, wherein the polyethylene comprises > 70.0 wt% of moieties derived from ethylene, with regard to the total weight of the polyethylene.

9. Object according to any one of claim 1-8, wherein the polyethylene is produced via a solution polymerisation process, and / or wherein the polyethylene is produced using a metallocene-type catalyst.

10. Object according to any one of claims 1-9, wherein the object is a film or a laminate.

11. Object according to claim 10, wherein the film or laminate has a thickness of > 1 and < 200 pm, preferably > 10 and < 150 pm, more preferably > 20 and < 125 pm.

12. Object according to any one of claims 10-11 , wherein the film or laminate has a multi-layer structure.

13. Object according to claim 12, wherein the film or laminate comprises the sealing layer as one outer layer or as both outer layers.

14. Object according to any one of claims 12-13, wherein the film or laminate comprises > 75.0 wt% of ethylene-based polymers, preferably > 80.0 wt%, more preferably > 90.0 wt%, with regard to the total weight of the film or laminate, even more preferably wherein the film or laminate comprises no polymer materials other than ethylene-based polymer materials.

15. Object according to any one of claims 12-14, wherein the film or laminate comprises 3-5 layers.

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