Film comprising a polyolefin elastomer

Abstract

The present invention relates to a film comprising a polymer composition comprising an ethylene-based copolymer, wherein the ethylene-based copolymer has a chemical composition distribution peak having a full width at half maximum (FWHM) of ≤ 0.300 ml, preferably ≥ 0.150 and ≤ 0.300 ml; wherein the chemical composition distribution is determined by high-temperature liquid chromatography. Such film exhibits a desirably high low-temperature sealing strength of a package.

Description

Film comprising a polyolefin elastomer

[0001] The present invention relates to a film comprising a polyolefin elastomer.

[0002] Polyolefin elastomers are widely used in a large variety of film applications, in which in such applications, benefit is made of a number of desirable properties of such materials. A particularly desirable property is that such polyolefin elastomers can provide certain thermal adhesion properties to a film structure. This is particularly appropriate for preparing many types of packaging, where the contents of a package are to be sealed by adhesion of films to one another.

[0003] It is particularly advantageous that polyolefin elastomers may contribute to the ability to produce packaging films that only include polymer materials of one single genus of polymer materials. For example, the use of polyolefin elastomers may allow for the production of films that comprise only polyethylene-type materials as polymer materials. A particular advantage of such films is that the processing thereof as a waste, that is after having provided its intended service life, allows for application of a wider range of recycling methods, since it no separation of polymer materials of different genera needs to be performed. Polymeric packaging films commonly comprise multiple layers of polymer materials, which may each consist of a unique material formulation, and which individually may comprise polymers of different genera, depending on the needs of the application for which the film is intended. Clearly, there can be advantages in use of material of solely one genus in a film.

[0004] In a particular embodiment of the invention, the film may consist solely of polyethylenetype materials as polymers used therein. For example, the film may consist of polyethylene-type materials and additives, more particularly of polyethylene-type materials and non-polymeric additives. In the context of the present invention, polyethylene-type materials may be understood to be polymers produced using ethylene as its majority monomer, preferably using ethylene as its majority monomer and less than 5.0 wt%, preferably less than 2.0 wt%, or no, of heteroatom-containing compounds as comonomers.

[0005] Furthermore, in the packaging industry, polymer films are abundantly applied for packaging and thereby conservation of all sorts of goods and foodstuffs, including perishable products. For packing such products, an aspect is that during the packaging process itself, theproducts are subjected to deteriorating influences as little as possible. Amongst others such deteriorating influences may include thermal exposure. Still, the sealing of packages produced using polymer films is commonly performed by application of thermal energy to soften a section of the package, and by compressing softened sections together form a seal. In such thermal sealing process, it is desired that the temperature that is to be applied to the film material to induce the softening to an appropriate level for generating a sufficiently strong seal is as low as possible. The lower the sealing temperature, the less exposure the packaged goods will have to thermal deterioration.

[0006] The present invention provides for a film comprising a polymer composition comprising an ethylene-based copolymer, wherein the ethylene-based copolymer has a chemical composition distribution peak having a full width at half maximum (FWHM) of < 0.300 ml, preferably > 0.150 and < 0.300 ml; wherein the chemical composition distribution is determined by high-temperature liquid chromatography.

[0007] Such film allows for preparing a package than is sealable at low temperatures, whilst still creating a seal of sufficiently high strength.

[0008] High-temperature liquid chromatography (HT-LC) measurements for determining the chemical composition distribution may for example be conducted using a PolymerChar (Valencia, Spain) solvent gradient chromatograph equipped with a binary pump (model 1260, Agilent, Waldbronn, Germany). Sample concentrations of ~ 1.0 mg / mL (solvent 1-decanol) may be used. For dissolution, the samples may first be heated in an offline autosampler at 160 °C with shaking until dissolution. Prior to injection, the sample may be allowed a further one hour of dissolution under shaking.

[0009] The following experimental parameters may be chosen: Elution temperature: 160 °C, SGIC flow rate: 0.50 mL / min, injection loop: 100 pL, SGIC stationary phase: Hypercarb® (particle size: 5 pm, column dimensions: 100mm x 4.6 mm (L x I.D.) (Thermofisher Scientific, Dreieich, Germany)). As eluent, a 1-decanol — > TCB gradient may be used with the following program: 0 - 4 min pure 1-decanol, 4 - 34 min linear gradient from 1-decanol to TCB, 34 - 40 min pure TCB. The column may be then purged for 20 min with 1-decanol at a flow velocity of 0.5 mL / min in order to establish the original adsorption equilibrium in the column again.

[0010] Detection may be done using the evaporative light scattering detector (Agilent, United Kingdom) with the following conditions: Nebulizer (90 °C), Evaporator (95 °C), Gas flow 0.3 L / min.Data collection may be performed using the PSS software and further evaluation carried out using OriginPro software (version 2019b) (OriginLab Corporation, Northhampton, MA, USA) as well as Excel 365 (Microsoft Corporation (Redmond, WA, USA)).

[0011] For example, the ethylene-based copolymer may comprise units derived from ethylene and comonomer units derived from 1 -butene, 1 -hexene or 1 -octene.

[0012] It is preferred that the ethylene-based copolymer comprises > 5.0 and < 40.0 wt% of comonomer units, preferably > 10.0 and < 35.0 wt%, more preferably > 15.0 and < 30.0 wt%, even more preferably > 20.0 and < 30.0 wt%, with regard to the total weight of the ethylenebased copolymer.

[0013] It is also preferred that the ethylene-based copolymer has a monomodal chemical composition distribution, wherein the chemical composition distribution is determined by high- temperature liquid chromatography.

[0014] The ethylene-based copolymer may for example have a melt mass-flow rate of > 2.0 and < 25.0 g / 10 min, preferably of > 4.0 and < 20.0 g / 10 min, more preferably of > 4.0 and < 15.0 g / 10 min, as determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg (MFR2). For example, the ethylene-based copolymer may have and MFR2 of 4.0-8.0 g / 10 min. Alternatively, the ethylene-based copolymer may have and MFR2 of 8.0-15.0 g / 10 min.

[0015] The ethylene-based copolymer may for example have a density of > 850 and < 900 kg / m3, preferably of > 860 and < 890 kg / m3, more preferably of > 865 and < 885 kg / m3, even more preferably of > 865 and < 880 kg / m3, as determined in accordance with ASTM D792 (2008).

[0016] The ethylene-based copolymer may for example have an Mw / Mnof > 2.0 and < 4.0, wherein Mwis the weight average molecular weight, and Mnis the number-average molecular weight, as determined in accordance with ASTM D6474 (2012).

[0017] The polymer composition may for example comprise > 5.0 and < 50.0 wt% of the ethylene-based copolymer, with regard to the total weight of the polymer composition, preferably > 10.0 and < 40.0 wt%, more preferably > 10.0 and < 30.0 wt%.

[0018] The polymer composition may for example comprise a polyethylene having a density of > 901 kg / m3, preferably of > 905 and < 935 kg / m3, preferably wherein the polyethylene is different from the ethylene-based copolymer.

[0019] The polyethylene may for example have a melt mass-flow rate of > 0.1 and < 10.0 g / 10 min, at 2.16 kg 1 190°C, preferably of > 0.5 and < 5.0 g / 10 min.

[0020] The polymer composition may for example comprise > 45.0 wt% of the polyethylene, preferably > 55.0 wt%, more preferably > 65.0 wt%, with regard to the total weight of the polymer composition.

[0021] The polyethylene may for example be a copolymer of ethylene and a comonomer selected from 1 -butene, 1 -hexene and 1 -octene.

[0022] The film may for example be a monolayer film or a multilayer film, comprising the polymer composition in at least one of its layers. In an embodiment, the film may be a multilayer film comprising the polymer composition in one or both of its outer layers.

[0023] The film may for example have a thickness of > 25 pm and < 500 pm, preferably of > 25 pm and < 200 pm.

[0024] The film may for example be a blown film, a cast film, a solid-state monoaxially-oriented film, or a solid-state biaxially oriented film.

[0025] The film may for example be a multilayer film comprising an inner layer comprising a high-density polyethylene (HDPE), a low-density polyethylene (LDPE) or a linear low-density polyethylene (LLDPE) and one or both outer layers comprising the polymer composition.

[0026] The film may for example be used of a film for improvement of the low-temperature sealing strength of a package.

[0027] The invention will now be illustrated by the following non-limiting examples.Materials

[0028] In the examples according to the present invention, the materials as listed in the below table 1 were used to prepare polymer compositions.Table 1 : Materials

[0029] The materials PE1-PE3 were analysed to identify material characteristics and properties, the results of which are provided in the table 2 below.Table 2: Properties and characteristics of the materialsWherein: • Density is determined in accordance with ASTM D792 (2008), expressed in g / cm3;• MFR2 is the melt mass-flow rate, as determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg, expressed in g / 10 min;• comonomer content is the wt% of polymeric units derived from the comonomer in the ethylene-based polymers, as determined using13C Nuclear Magnetic Resonance on a Bruker Avance 500 spectrometer equipped with a cryogenically cooled probe head operating at 125°C, whereby the samples were dissolved at 130°C in C2D2CI4 containing DBPC as stabiliser;• Tp,mis the peak melting temperature as determined using differential scanning calorimetry (DSC) in accordance with ASTM D3418 (2008), expressed in °C;• Tcis the crystallisation temperature as determined using differential scanning calorimetry (DSC) in accordance with ASTM D3418 (2008), expressed in °C;• Mnis the number average molecular weight, Mwis the weight average molecular weight, and Mzis the z-average molecular weight, wherein Mn, Mw, and Mzare each expressed in kg / mol, and determined in accordance with ASTM D6474 (2012);• Unsaturations is the sum of vinyl unsaturations, and vinylidene unsaturations, expressed in number of unsaturations per 100000 chain carbon atoms, and are determined by1H NMR on a Bruker Avance 500 spectrometer equipped with a cryogenically cooled probe head operating at 125°C, whereby the samples are dissolved at 130°C in C2D2CI4 containing DBPC as stabiliser.• CCD - FWHM is the full width at half maximum of the peak of the chemical composition distribution (CCD), wherein the CCD is obtained by high-temperature liquid chromatography (HT-LC).

[0030] HT-LC measurements were conducted using a PolymerChar (Valencia, Spain) solvent gradient chromatograph equipped with a binary pump (model 1260, Agilent, Waldbronn, Germany). Sample concentrations of - 1.0 mg / mL (solvent 1-decanol) were used. For dissolution, the samples were first heated in an offline autosampler at 160 °C with shaking until dissolution. Prior to injection, the sample was allowed a further one hour of dissolution under shaking.

[0031] The following experimental parameters were chosen: Elution temperature: 160 °C, SGIC flow rate: 0.50 mL / min, injection loop: 100 pL, SGIC stationary phase: Hypercarb® (particle size: 5 pm, column dimensions: 100 x 4.6 mm (L x I.D.) (Thermofisher Scientific, Dreieich, Germany)). As eluent, a 1-decanol — > TCB gradient was used with the following program: 0 - 4 min pure 1-decanol, 4 - 14 min linear gradient from 1-decanol to TCB, 14 - 18 min pure TCB. The column was then purged for 20 min with 1-decanol at a flow velocity of 0.5 mL / min in order to establish the original adsorption equilibrium in the column again.

[0032] Detection was done using the evaporative light scattering detector (PL-ELS 1000, Polymer Labs, U.K) with the following conditions: Nebulizer (160 °C), Evaporator (250 °C), Gas flow 1.5 L / min. Data collection was performed using the PPS software and further evaluation was carried out using OriginPro software (version 2019b) (OriginLab Corporation, Northhampton, MA, USA) as well as Excel 365 (Microsoft Corporation (Redmond, WA, USA)).

[0033] The chemical composition distribution as obtained for each of the polymers PE-1 and 3 is presented in figure 1.Compositions

[0034] Using the above-listed materials, the compositions according to the below formulations were produced.Table 3: Compositions

[0035] For each of the examples 1-2, 2-layer films were produced via blown film extrusion comprising 60 wt% of a first layer consisting of the PE2, and 40 wt% of a second layer having a composition as in table 3 above. The blown film had a final thickness of 50 pm, and was produced on a blown film extrusion line operated with a blow-up ratio of 2.5. The extruder feeding the material for the first layer was operated at set temperatures of 170-180°C, resulting in a melt temperature of 178°C, and a melt pressure of 12.3 MPa. The extruder feeding the material for the second layer was operated at set temperatures of 170-180°C, resulting in a melt temperature of 179°C, and a melt pressure of 20.6 MPa. The temperature of the mandrel was 180°C. The temperature of the air used to blow the film was 24°C.

[0036] The films produced according to the process as described above were subjected to determination of properties as displayed in the table below.Table 4: Film properties

[0037] Therein MD indicates machine direction, i.e. the direction of the film in which the film is extruded from the blown film die, and TD indicated transverse direction, i.e. the direction perpendicular to the machine direction.

[0038] The tensile properties 1% secant modulus (expressed in MPa), yield stress (in N / mm2), elongation at yield (in %), stress at break (in N / mm2), elongation at break (in %) and tensile strength (in N / mm2) were tested in accordance with ASTM D882 of 2018, at 23°C, using specimens of 50 mm width, at test speed of 500 mm / min; except for 1% secant modulus were the test speed was 5 mm / min.

[0039] The puncture resistance was obtained as the maximum force achieved when subjecting the film to a test in accordance with ASTM D5748 of 1995, tested at a speed of 250 mm / min at 23°C, expressed in N.

[0040] The Elmendorf tear resistance was determined in accordance with ASTM D1922 of 2015 as the propagation tear resistance, expressed in g / pm.

[0041] In addition, the adhesive properties of the second layer were determined by analysis of the seal strength of seals prepared at various temperatures, determined in accordance with ASTM F88 of 2015, using specimens of 15 mm width, expressed in N, as well as the hot tack strength at various temperatures of sealing, determined in accordance with ASTM F1921 of 2012, also expressed in N. The obtained values are presented in the table below, as well as in the figures 2-3.Table 5: Film seal properties

[0042] The above results show that the examples of the invention demonstrate an improved seal strength for seal produced at lower temperatures, as well as an increased hot tack force at lower sealing temperatures. For many applications, notably for packaging of perishable products, there is a desire for being able to seal packages at a low temperature whilst still achieving an appropriately high strength of the seal.

Claims

Claims1. Film comprising a polymer composition comprising an ethylene-based copolymer, wherein the ethylene-based copolymer has a chemical composition distribution peak having a full width at half maximum (FWHM) of < 0.300 ml, preferably > 0.150 and < 0.300 ml; wherein the chemical composition distribution is determined by high-temperature liquid chromatography.

2. Film according to claim 1 , wherein the ethylene-based copolymer comprises units derived from ethylene and comonomer units derived from 1 -butene, 1 -hexene or 1 -octene.

3. Film according to any one of claims 1-2, wherein the ethylene-based copolymer comprises> 5.0 and < 40.0 wt% of comonomer units, preferably > 10.0 and < 35.0 wt%, more preferably > 15.0 and < 30.0 wt%, even more preferably > 20.0 and < 30.0 wt%, with regard to the total weight of the ethylene-based copolymer.

4. Film according to any one of claims 1-3, wherein the ethylene-based copolymer has a monomodal chemical composition distribution, wherein the chemical composition distribution is determined by high-temperature liquid chromatography.

5. Film according to any one of claims 1-4, wherein the ethylene-based copolymer has a melt mass-flow rate of > 2.0 and < 25.0 g / 10 min, preferably of > 4.0 and < 20.0 g / 10 min, more preferably of > 4.0 and < 15.0 g / 10 min, as determined in accordance with ASTM D1238 (2013) at 190°C under a load of 2.16 kg.

6. Film according to any one of claims 1-5, wherein the ethylene-based copolymer has a density of > 850 and < 900 kg / m3, preferably of > 860 and < 890 kg / m3, more preferably of> 865 and < 885 kg / m3, even more preferably of > 865 and < 880 kg / m3, as determined in accordance with ASTM D792 (2008).

7. Film according to any one of claims 1-6, wherein the ethylene-based copolymer has an Mw / Mnof > 2.0 and < 4.0, wherein Mwis the weight average molecular weight, and Mnis the number-average molecular weight, as determined in accordance with ASTM D6474 (2012).

8. Film according to any one of claims 1-7, wherein the polymer composition comprises > 5.0 and < 50.0 wt% of the ethylene-based copolymer, with regard to the total weight of the polymer composition, preferably > 10.0 and < 40.0 wt%, more preferably > 10.0 and < 30.0 wt%.

9. Film according to any one of claims 1-8, wherein the polymer composition comprises a polyethylene having a density of > 901 kg / m3, preferably of > 905 and < 935 kg / m3, preferably wherein the polyethylene is different from the ethylene-based copolymer.

10. Film according to claim 8, wherein the polyethylene has a melt mass-flow rate of > 0.1 and < 10.0 g / 10 min, at 2.16 kg 1 190°C, preferably of > 0.5 and < 5.0 g / 10 min.

11. Film according to any one of claims 9-10, wherein the polymer composition comprises > 45.0 wt% of the polyethylene, preferably > 55.0 wt%, more preferably > 65.0 wt%, with regard to the total weight of the polymer composition.

12. Film according to any one of claims 9-11 , wherein the polyethylene is a copolymer of ethylene and a comonomer selected from 1 -butene, 1 -hexene and 1 -octene.

13. Film according to any one of claims 1-12, wherein the film is a monolayer film or a multilayer film, comprising the polymer composition in at least one of its layers.

14. Film according to any one of claims 1-13, wherein the film is a blown film, a cast film, a solid-state monoaxially-oriented film, or a solid-state biaxially oriented film.

15. Use of a film according to any one of claims 1-14 for improvement of the low-temperature sealing strength of a package.

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