Polyethylene film for heat sealing

Abstract

The present invention relates to a film comprising a sealing layer, the sealing layer comprising polyethylene A, the polyethylene A comprising a structural portion derived from ethylene and a structural portion derived from an alpha olefin containing 4 to 10 carbon atoms, the polyethylene A having a carbon weight of ≥870 and ≤920 kg / m2 measured according to ASTM D792 (2013) 3 , preferably ≥900 and ≤920kg / m 3 The invention relates to a polyethylene A having a density of 1000 nm, wherein the polyethylene A has: a material fraction eluting in analytical temperature rising elution fractionation (a-TREF) at a temperature of ≤30.0°C of ≥5.0 wt% and ≤15.0 wt%, preferably ≥7.5 wt% and ≤12.5 wt%, relative to the total weight of the polyethylene; two distinct peaks in the a-TREF curve at an elution temperature range of 50.0 to 90.0°C, wherein the difference in elution temperature between the two peaks is ≤17.5°C, preferably ≤15.0°C. Such a film allows the film to be sealed at a desired low temperature while still providing the desired seal strength. In addition, such a film exhibits a desired high thermal stability.

Description

[0001] The present invention relates to a polyethylene film for heat sealing, and a multilayer structure comprising such a film. The present invention also relates to an article comprising such a film, and a method for producing a sealed article comprising such a film.

[0002] Films comprising or consisting of polyethylene materials are used extensively in a variety of applications. A specific example of the application of such polyethylene films is food packaging. The use of polyethylene allows for very hygienic packaging of food, helps preserve the packaged product for a long period of time, and can be done in a very economically attractive manner. Furthermore, polyethylene films can be produced with a very attractive appearance.

[0003] Polyethylene materials suitable for producing films include low density polyethylene, also known as LDPE, high density polyethylene, also known as HDPE, and linear low density polyethylene, also known as LLDPE. Particularly suitable for a variety of film applications is linear low density polyethylene.

[0004] The linear low-density polyethylene may be, for example, a polyethylene comprising a moiety derived from ethylene and a moiety derived from an α-olefin comprising 4 to 10 carbon atoms, having a mass fraction of ≥870 and ≤920 kg / m 2 as measured according to ASTM D792 (2013). 3 Preferably, the polyethylene has a density of ≥880 and ≤915 kg / m 3 , more preferably ≥890 and ≤910 kg / m 3 density.

[0005] The LLDPE may, for example, have a melt mass flow rate (MFR2) of ≥0.01 and ≤10.00 g / 10 min, preferably ≥0.10 and ≤5.00 g / 10 min, more preferably ≥0.50 and ≤2.50 g / 10 min, as measured at 190° C. and under a load of 2.16 kg according to ASTM D1238 (2013). Such LLDPE allows the production of films having suitable melt stability and processability.

[0006] In the field of polyethylene film applications in packaging, a particular aspect relates to the sealing of such packaging.

[0007] In commercial use, polyethylene films are used, for example, for packaging products such as foods. The package is filled with the desired product and sealed by contacting two layers of film, such as a tubular film obtained by blown film extrusion, and applying heat to at least a portion of the area where the films are in contact. The applied heat causes local softening of the polyethylene material of the two layers in contact. This results in adhesion between the two layers and, after cooling, a hermetic seal, thereby forming a package that contains the desired contents and is isolated from the surrounding atmosphere.

[0008] This type of packaging is well known in everyday use and allows, for example, a significant increase in the preservation of the contained product.

[0009] In this type of packaging solution, the seal created using heat sealing techniques such as those described above needs to have a certain strength. This is necessary to produce a package that can withstand the forces (forces that the package should be considered resistant to) during production, transportation, and consumer use. Therefore, the strength of the seal should be above a certain threshold.

[0010] Furthermore, considering the efficiency and energy consumption of the packaging process, it is important to be able to produce such seals with desired strength at a desired low sealing temperature. The lower the temperature required to form the seal, the less energy is required. Another benefit of the lower temperature required to form the seal is that the contents of the package are less likely to be exposed to high temperatures, which, for example, in the case of food packaging, can be beneficial for maintaining the quality of the packaged contents.

[0011] Another important property of this type of polyethylene-based packaging solution is its so-called hot-tack strength. In the context of this invention, hot-tack strength is understood to be the strength of a seal created by heat sealing in a polyethylene film immediately after sealing and before the seal cools. Hot-tack strength influences the efficiency of the packaging process using polyethylene film materials, for example, the speed at which a packaging line can operate. The higher the hot-tack strength, the shorter the cooling time required after the seal is formed before further processing of the package. In other words, the sooner the seal reaches a strength level sufficient to withstand applied forces without breaking, the shorter the cycle time in, for example, a continuous packaging machine.

[0012] For these reasons, there is a continuing need in the packaging industry to have available polyethylene films that exhibit a reduction in the temperature at which a seal of a certain defined strength can be produced, wherein the hot tack strength of the seal is particularly high.

[0013] Such a film is now provided according to the invention by a film comprising a sealing layer comprising a polyethylene A comprising a moiety derived from ethylene and a moiety derived from an α-olefin containing 4 to 10 carbon atoms, the polyethylene A having a carbonyl group ≥870 and ≤920 kg / m 3 , preferably ≥900 and ≤920kg / m 3 The density of polyethylene A is:

[0014] a fraction of material ≥5.0 wt.-% and ≤15.0 wt.-%, preferably ≥7.5 wt.-% and ≤12.5 wt.-%, relative to the total weight of the polyethylene, which elutes in analytical temperature rising elution fractionation (a-TREF) at a temperature ≤30.0° C.;

[0015] Two distinct peaks in the a-TREF curve within the elution temperature range of 50.0 to 90.0°C, wherein the elution temperature difference between the two peaks is ≤ 17.5°C, preferably ≤ 15.0°C.

[0016] This film allows the film to be sealed at a desired low temperature while still providing the desired seal strength. In addition, this film exhibits a desired high thermal stability.

[0017] The polyethylene A used in the sealing layer of the film according to the present invention has a viscosity of ≥870 and ≤920 kg / m 3 , preferably ≥880 and ≤915kg / m 3 , more preferably ≥890 and ≤910 kg / m 3 , even more preferably ≥895 and ≤905 kg / m 3 , or ≥900 and ≤920kg / m 3 , preferably ≥900 and ≤915kg / m 3 , more preferably ≥900 and ≤910 kg / m 3 , or even more preferably ≥900 and ≤905 kg / m 3 The use of polyethylene having such a density in the sealing layer of the film according to the invention contributes to improved sealing.

[0018] Polyethylene A preferably exhibits an elution temperature difference, also referred to herein as peak difference, of ≥5.0 and ≤15.0°C between two distinct peaks in the a-TREF curve in the temperature range of 50.0 to 90.0°C. Preferably, the peak difference is ≥10.0 and ≤15.0°C.

[0019] According to the present invention, analytical temperature-rising elution fractionation (also known as a-TREF) can be performed using a Polymer Char Crystaf-TREF 300 equipped with a stainless steel column 15 cm in length and 7.8 mm in internal diameter, using a solution containing 4 mg / mL of sample prepared in 1,2-dichlorobenzene and stabilized at a temperature of 150°C for 1 hour with 1 g / L Topanol CA (1,1,3-tris(3-tert-butyl-4-hydroxy-6-methylphenyl)butane) and 1 g / L Irgafos 168 (tris(2,4-di-tert-butylphenyl)phosphite). The solution can be stabilized for an additional 45 minutes at 95°C with continuous stirring at 200 rpm before analysis. For analysis, the solution is crystallized from 95°C to 30°C using a cooling rate of 0.1°C / min. Elution can be performed from 30°C to 140°C using a heating rate of 1°C / min. The apparatus can be cleaned at 150°C. The injection volume may be 300 μL, and the pump flow rate during elution may be 0.5 mL / min. The volume between the column and the detector may be 313 μL. In the context of the present invention, the fraction eluting at a temperature of ≤30.0°C can be calculated by subtracting the sum of the fractions eluting at >30.0°C from 100%, so that the fractions eluting at ≤30.0°C and the fractions eluting at >30.0°C add up to 100.0% by weight.

[0020] Specifically, a-TREF can be performed using Polymer Char Crystaf-TREF 300, using a solution containing 4 mg / ml polymer in 1,2-dichlorobenzene, wherein the solution is stabilized with 1 g / l 1,1,3-tris(3-tert-butyl-4-hydroxy-6-methylphenyl)butane and 1 g / l tris(2,4-di-tert-butylphenyl)phosphite at a temperature of 150°C for 1 hour and further stabilized at 95°C with continuous stirring at 200 rpm for 45 minutes, wherein the solution is crystallized using a cooling rate of 0.1°C / min from 95°C to 30°C and elution is performed at a heating rate of 1°C / min from 30°C to 140°C before analysis, and wherein the equipment has been cleaned at 150°C.

[0021] Preferably, in the polyethylene A contained in the sealing layer of the film of the present invention, the ratio q2 / q1 of the elution amount of polyethylene A at the maximum value P2 of the peak appearing at the highest temperature in the elution curve in the elution temperature range of 50.0 to 90.0°C in a-TREF to the elution amount (q1) at the maximum value P1 of the peak appearing at the lowest temperature in the range of 50.0 to 90.0°C is ≤1.40, preferably ≥0.75 and ≤1.25, even more preferably ≥1.05 and ≤1.20, and the elution amount is an amount by weight.

[0022] In polyethylene A, it is preferred that the difference Δρ (Δρ = ρ2 - ρ1) between the density ρ2 of the polymer material eluted at P2 and the density ρ1 of the polymer material eluted at P1 is ≤ 15 kg / m 3 , preferably ≥10 and ≤15kg / m 3 .

[0023] The polyethylene A used in the sealant layer of the film according to the present invention has a melt mass flow rate (MFR2) of preferably ≥0.01 and ≤10.00 g / 10 min, more preferably ≥0.10 and ≤5.00 g / 10 min, even more preferably ≥0.50 and ≤2.50 g / 10 min, still even more preferably ≥0.50 and ≤1.50 g / 10 min, measured at 190° C. and under a load of 2.16 kg according to ASTM D1238 (2013). Such a polyethylene allows the production of films having suitable melt stability and processability.

[0024] Preferably, the polyethylene A comprises ≥70.0 wt.-%, preferably ≥75.0 wt.-%, more preferably ≥80.0 wt.-% of moieties derived from ethylene, relative to the total weight of the polyethylene. Preferably, the polyethylene A comprises ≥70.0 and ≤98.0 wt.-%, more preferably ≥75.0 and ≤95.0 wt.-%, even more preferably ≥80.0 and ≤90.0 wt.-% of moieties derived from ethylene, relative to the total weight of the polyethylene.

[0025] More preferably, the polyethylene A comprises ≤30.0 wt.-%, preferably ≤25.0 wt.-%, more preferably ≤20.0 wt.-%, relative to the total weight of the polyethylene, of moieties derived from α-olefins containing 4 to 10 carbon atoms. The polyethylene A may, for example, comprise ≥5.0 wt.-%, preferably ≥10.0 wt.-%, more preferably ≥15.0 wt.-%, relative to the total weight of the polyethylene, of moieties derived from α-olefins containing 4 to 10 carbon atoms. For example, the polyethylene A may comprise ≥5.0 and ≤30.0 wt.-%, preferably ≥15.0 and ≤30.0 wt.-%, more preferably ≥15.0 and ≤20.0 wt.-%, relative to the total weight of the polyethylene, of moieties derived from α-olefins containing 4 to 10 carbon atoms.

[0026] The alpha-olefin may comprise 4 to 10 carbon atoms, for example, be selected from 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene, such as being selected from 1-butene, 1-hexene and 1-octene. For example, the alpha-olefin comprising 4 to 10 carbon atoms may be selected from 1-hexene and 1-octene. The moiety derived from the alpha-olefin comprising 4 to 10 carbon atoms may be, for example, a moiety derived from 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene or a combination thereof, preferably a moiety derived from 1-hexene or 1-octene.

[0027] The polyethylene A employed in the sealing layer of the film according to the invention may, for example, comprise ≤30.0% by weight, preferably ≤25.0% by weight, more preferably ≤20.0% by weight, relative to the total weight of the polyethylene, of moieties derived from α-olefins containing 4 to 10 carbon atoms, wherein the α-olefins containing 4 to 10 carbon atoms are selected from 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene, such as selected from 1-butene, 1-hexene and 1-octene. The polyethylene A may, for example, comprise ≥5.0% by weight, preferably ≥10.0% by weight, more preferably ≥15.0% by weight, relative to the total weight of the polyethylene, of moieties derived from α-olefins containing 4 to 10 carbon atoms, wherein the α-olefins containing 4 to 10 carbon atoms are selected from 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene, such as selected from 1-butene, 1-hexene and 1-octene. For example, polyethylene A may comprise, relative to the total weight of the polyethylene, ≥5.0 and ≤30.0 wt. %, preferably ≥10.0 and ≤25.0 wt. %, more preferably ≥15.0 and ≤20.0 wt. % of moieties derived from α-olefins containing 4 to 10 carbon atoms, wherein the α-olefins containing 4 to 10 carbon atoms are selected from 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene, such as selected from 1-butene, 1-hexene and 1-octene. For example, polyethylene A may comprise, relative to the total weight of the polyethylene, ≥5.0 and ≤30.0 wt. %, preferably ≥10.0 and ≤25.0 wt. %, more preferably ≥15.0 and ≤20.0 wt. % of moieties derived from α-olefins containing 4 to 10 carbon atoms, wherein the α-olefins containing 4 to 10 carbon atoms are 1-octene.

[0028] Available through 13 The content of moieties derived from α-olefins and the type of α-olefins were determined by C NMR on a Bruker Avance 500 spectrometer equipped with a cryogenically cooled probe operated at 125°C, with the samples dissolved in C2D2Cl4 containing DBPC as a stabilizer at 130°C.

[0029] Preferably, the polyethylene A has a fraction of ≤ 5.0 wt. %, more preferably ≤ 2.0 wt. % of material eluting in a-TREF in the elution temperature range ≥ 90° C. Even more preferably, the polyethylene A is substantially free of material eluting in a-TREF in the temperature range ≥ 90° C.

[0030] The polyethylene A may, for example, have a weight average molecular weight (M) of ≥75,000 and ≤150,000 g / mol, preferably ≥100,000 and ≤125,000 g / mol. w The polyethylene A may, for example, have a number average molecular weight (M) of ≥20,000 and ≤50,000 g / mol, preferably ≥25,000 and ≤40,000 g / mol. n The polyethylene A may, for example, have a z-average molecular weight (M) of ≥200,000 and ≤400,000 g / mol, preferably ≥250,000 and ≤350,000 g / mol. z ). The polyethylene A may, for example, have a molecular weight distribution M of ≥2.0 and ≤4.0, preferably ≥2.5 and ≤3.5. w / M n In the context of the present invention, M w 、M n and M z It can be measured according to ASTM D6474 (2012).

[0031] Preferably, the sealing layer comprises ≥10.0 wt.-% and ≤90.0 wt.-%, more preferably ≥15.0 wt.-% and ≤85.0 wt.-%, even more preferably ≥25.0 wt.-% and ≤75.0 wt.-%, still even more preferably ≥30.0 ​​wt.-% and ≤70.0 wt.-%, yet even further preferably ≥50.0 wt.-% and ≤70.0 wt.-% of polyethylene A, relative to the total weight of the sealing layer.

[0032] The sealing layer may further comprise a certain amount of polyethylene B, for example, ≥10.0 wt% and ≤70.0 wt%, preferably ≥20.0 and ≤50.0 wt% of polyethylene B relative to the total weight of the sealing layer, preferably wherein polyethylene B is a copolymer comprising a structural portion of ethylene and a structural portion derived from 1-butene, 1-hexene or 1-octene. Preferably, polyethylene B is a copolymer comprising a structural portion derived from ethylene and a structural portion derived from 1-butene.

[0033] For example, polyethylene B may have a value of ≥905 and ≤935 kg / m 3 , preferably ≥910 and ≤930kg / m 3 , more preferably ≥915 and ≤925kg / m 3 density.

[0034] Polyethylene B may, for example, have a melt mass flow rate (MRF2) of ≥0.1 and ≤5.0, preferably ≥0.2 and ≤4.0, more preferably ≥0.5 and ≤3.0, even more preferably ≥0.5 and ≤2.0 g / 10 min.

[0035] Preferably, polyethylene B and polyethylene A are different.

[0036] In certain embodiments of the present invention, it also relates to a film comprising a sealing layer comprising or consisting essentially of:

[0037] (i) Polyethylene A, comprising a structural portion derived from ethylene and a structural portion derived from 1-octene, the polyethylene A having a mass fraction of ≥870 and ≤920 kg / m 2 as measured according to ASTM D792 (2013) 3 , preferably ≥900 and ≤920kg / m 3 A density of wherein the polyethylene A has:

[0038] a fraction of material ≥ 5.0 wt. % and ≤ 15.0 wt. %, preferably ≥ 7.5 wt. % and ≤ 12.5 wt. %, relative to the total weight of the polyethylene, eluting in analytical temperature rising elution fractionation (a-TREF) at a temperature ≤ 30.0° C.; and

[0039] Two distinct peaks in the a-TREF curve in the elution temperature range of 50.0 to 90.0°C, wherein the elution temperature difference between the two peaks is ≤17.5°C, preferably ≤15.0°C;

[0040] and

[0041] (ii) polyethylene B, comprising a copolymer of ethylene moieties and moieties derived from 1-butene or 1-hexene, having a molecular weight of ≥910 and ≤930 kg / m 3 density.

[0042] In a specific embodiment, the present invention also relates to a film comprising a sealing layer comprising or consisting essentially of:

[0043] (i) ≥10.0 and ≤90.0 wt. %, preferably ≥30.0 ​​and ≤70.0 wt. %, relative to the total weight of the sealing layer, of polyethylene A, the polyethylene A comprising a structural portion derived from ethylene and a structural portion derived from 1-octene, the polyethylene A having a mass fraction of ≥870 and ≤920 kg / m2 as measured according to ASTM D792 (2013); 3 , preferably ≥900 and ≤920kg / m 3 A density of wherein the polyethylene A has:

[0044] a fraction of material ≥ 5.0 wt. % and ≤ 15.0 wt. %, preferably ≥ 7.5 wt. % and ≤ 12.5 wt. %, relative to the total weight of the polyethylene, eluting in analytical temperature rising elution fractionation (a-TREF) at a temperature ≤ 30.0° C.; and

[0045] Two distinct peaks in the a-TREF curve within the elution temperature range of 50.0 to 90.0°C, wherein the elution temperature difference between the two peaks is ≤ 17.5°C, preferably ≤ 15.0°C;

[0046] and

[0047] (ii) ≥10.0 and ≤70.0 wt. %, preferably ≥20.0 and ≤50.0 wt. %, relative to the total weight of the sealing layer, of polyethylene B, which is a copolymer comprising a structural portion of ethylene and a structural portion derived from 1-butene or 1-hexene, having a molecular weight of ≥910 and ≤930 kg / m 3 density.

[0048] In certain embodiments thereof, the present invention also relates to embodiments wherein the film may further comprise polyethylene C in the sealing layer. Preferably, polyethylene C is different from either polyethylene A or polyethylene B.

[0049] The polyethylene C may preferably be a low density polyethylene (LDPE). For example, the polyethylene C may be a polyethylene having a density of ≥910 and ≤930 kg / m 3 , preferably ≥915 and ≤925kg / m 3 For example, the polyethylene C may be an LDPE having an MFR2 of ≥0.5 and ≤10.0 g / 10 min, preferably ≥0.5 and ≤5.0 g / 10 min, more preferably ≥1.0 and ≤3.0 g / 10 min.

[0050] The sealing layer may, for example, comprise ≧5.0 and ≦50.0 wt.-%, preferably ≧10.0 and ≦30.0 wt.-%, of polyethylene C relative to the total weight of the sealing layer.

[0051] Preferably, the polyethylene C is a LDPE homopolymer.

[0052] A particularly preferred embodiment of the present invention relates to a film comprising a sealing layer comprising or consisting essentially of:

[0053] (i) Polyethylene A comprising a structural portion derived from ethylene and a structural portion derived from 1-octene, the polyethylene A having a mass fraction of ≥870 and ≤920 kg / m 2 as measured according to ASTM D792 (2013) 3 , preferably ≥900 and ≤920kg / m 3 The density of polyethylene A is:

[0054] a fraction of material ≥ 5.0 wt. % and ≤ 15.0 wt. %, preferably ≥ 7.5 wt. % and ≤ 12.5 wt. %, relative to the total weight of the polyethylene, eluting in analytical temperature rising elution fractionation (a-TREF) at a temperature ≤ 30.0° C.; and

[0055] two distinct peaks in the a-TREF curve within the elution temperature range of 50.0 to 90.0°C, wherein the elution temperature difference between the two peaks is ≤ 17.5°C, preferably ≤ 15.0°C;

[0056] (ii) polyethylene B, which is a copolymer comprising a structural portion of ethylene and a structural portion derived from 1-butene or 1-hexene, having a molecular weight of ≥910 and ≤930 kg / m 3 density; and

[0057] (iii) Polyethylene C, which is a low-density polyethylene homopolymer having a mass fraction of ≥910 and ≤930 kg / m 3 density.

[0058] In particular, the present invention relates to a film comprising a sealing layer comprising or consisting essentially of:

[0059] (i) ≥10.0 and ≤90.0 wt %, preferably ≥30.0 ​​and ≤70.0 wt %, relative to the total weight of the sealing layer, of polyethylene A, wherein the polyethylene A comprises a structural portion derived from ethylene and a structural portion derived from 1-octene, and the polyethylene A has a mass fraction of ≥870 and ≤920 kg / m 2 as measured according to ASTM D792 (2013); 3 , preferably ≥900 and ≤920kg / m 3 A density of wherein the polyethylene A has:

[0060] a fraction of material ≥ 5.0 wt. % and ≤ 15.0 wt. %, preferably ≥ 7.5 wt. % and ≤ 12.5 wt. %, relative to the total weight of the polyethylene, eluting in analytical temperature rising elution fractionation (a-TREF) at a temperature ≤ 30.0° C.; and

[0061] Two distinct peaks in the a-TREF curve within the elution temperature range of 50.0 to 90.0°C, wherein the elution temperature difference between the two peaks is ≤ 17.5°C, preferably ≤ 15.0°C;

[0062] (ii) ≥10.0 and ≤70.0 wt. %, preferably ≥20.0 and ≤50.0 wt. %, relative to the total weight of the sealing layer, of polyethylene B, which is a copolymer comprising a structural portion of ethylene and a structural portion derived from 1-butene or 1-hexene, having a molecular weight of ≥910 and ≤930 kg / m 3 density; and

[0063] (iii) ≥10.0 and ≤30.0 wt% of polyethylene C relative to the total weight of the sealing layer, which is a low-density polyethylene homopolymer with a density of ≥910 and ≤930 kg / m 3 density.

[0064] In the context of the present invention, an embodiment in which the sealing layer of the film consists essentially of polyethylene A, polyethylene B and / or polyethylene C is to be understood as one in which layer A of the film consists of polyethylene and additives known in the field of polyethylene films, such as up to 1.0% by weight of additives relative to the total weight of the film. Suitable additives may, for example, include UV stabilizers, antioxidants and processing aids.

[0065] The sealing layer may, for example, have a thickness of 1-100 μm, preferably 5-50 μm, more preferably 5-25 μm, more preferably 5-15 μm.

[0066] In one embodiment, the membrane consists of a sealing layer.

[0067] Polyethylene can be produced, for example, via a solution polymerization process, preferably by polymerization of ethylene with 1-hexene and / or 1-octene.Polyethylene can be produced, for example, using a metallocene-type catalyst, preferably by polymerization of ethylene with 1-hexene and / or 1-octene.

[0068] In certain embodiments, the present invention also relates to certain multilayer film structures comprising a film according to the present invention. For example, the present invention also relates to a multilayer film structure comprising a film according to the present invention, wherein the film is arranged in the multilayer film structure such that at least one of the outer surfaces of the multilayer film structure is composed of a sealing layer. Alternatively, the present invention also relates to a multilayer film structure comprising a film according to the present invention, wherein the film is arranged in the multilayer film structure such that both outer surfaces of the multilayer film structure are composed of a sealing layer.

[0069] In another embodiment, the present invention relates to a multilayer film structure comprising two outer layers and at least one inner layer positioned between the two outer layers, wherein one of the outer layers consists of a sealant layer, or wherein both outer layers each consist of a sealant layer.

[0070] The multilayer film structure may, for example, comprise 3 to 15 layers, preferably 3 to 11 layers, more preferably 3 to 7 layers. The multilayer film structure may, for example, comprise 3 layers, or 5 layers, or 7 layers.

[0071] The multilayer film structure may have a thickness of, for example, 2-150 μm, preferably 20-100 μm, more preferably 25-75 μm.

[0072] In a specific embodiment, the present invention also relates to a method of preparing an article comprising a sealing film, the method comprising the following steps in the following order.

[0073] Providing a film or multilayer film structure according to the present invention;

[0074] providing an object comprising a surface for sealing with a film or multi-layer film structure;

[0075] Arranging the film or multi-layer film structure and the object so that layer A of the film or multi-layer film structure and the surface for sealing of the object can contact each other;

[0076] At a temperature of ≥60 and ≤80°C, applying ≥0.3N / mm 2 The membrane is brought into contact with the surface for sealing under a pressure of 1 to 5 seconds;

[0077] To obtain heat-sealed products.

[0078] The present invention also relates to an article comprising a film sealed to a surface, wherein the article comprises a film or multilayer film structure according to the present invention, or wherein the article is produced according to the method according to the present invention. For example, such an article may be a package for containing food, or a package containing food.

[0079] The invention will now be illustrated by the following non-limiting examples.

[0080] In the experiments conducted during the present invention, the following polyethylene materials were used.

[0081]

[0082] Materials PE1 and PE2 were analyzed to show the following product properties:

[0083] PE1 PE2 MFR2(g / 10min) 1.0 1.0 <![CDATA[Density (kg / m 3 )]]> 900 900 a-TREF fraction ≤30°C (wt%) 10.8 15.4 P1(℃) 62.5 59.1 P2(℃) 75.1 79.3 Peak difference(℃) 12.6 20.2 <![CDATA[q1]]> 0.0618 0.0459 <![CDATA[q2]]> 0.0686 0.0739 <![CDATA[q2 / q1]]> 1.11 1.61 <![CDATA[ρ1(kg / m 3 )]]> 896 892 <![CDATA[ρ2(kg / m 3 )]]> 908 911 <![CDATA[Δρ(kg / m 3 )]]> 12 19

[0084] in:

[0085] MFR2 is the melt mass flow rate measured according to ASTM D1238 (2013) at 190°C under a load of 2.16 kg.

[0086] Density was measured according to ASTM D792 (2013).

[0087] The a-TREF fraction ≤ 30°C is the fraction eluted in the a-TREF analysis performed as described above at below 30°C.

[0088] P1 is the temperature at which the first peak appears in the a-TREF analysis in the elution interval of 50.0 to 90.0°C, that is, the peak eluting at the lowest temperature.

[0089] P2 is the temperature at which the second peak, ie, the peak eluting at the highest temperature, appears in the elution interval of 50.0 to 90.0°C in the a-TREF analysis.

[0090] The peak difference refers to the elution temperature difference between the two peaks P2 and P1 (P2-P1).

[0091] q1 refers to the elution amount relative to the total elution amount eluted at temperature P1, expressed as a weight fraction.

[0092] q2 refers to the elution amount relative to the total elution amount eluted at temperature P2, expressed as a weight fraction.

[0093] ρ1 is the density of the polymeric material eluted in the a-TREF analysis at temperature P1.

[0094] ρ2 is the density of the polymeric material eluted in the a-TREF analysis at temperature P2.

[0095] Δρ is the difference in density ρ2-ρ1 between the polymeric materials eluting at peak temperatures P1 and P2.

[0096] Using these materials, two different types of blown films were produced using a Labtech LF400-COEX machine with a 25 mm screw diameter and a length-to-diameter ratio (L / D ratio) of 30. The films were produced at 190°C, a blow-up ratio of 2.5, a die gap of 2 mm, a frost line height of 16 cm, and a throughput of 8 kg / h. The films of Inventive Example 1 and Comparative Example 5 had a thickness of 30 μm. The film of Example 1 consisted of PE1, and the film of Example 5 consisted of PE2.

[0097] In Examples 2-4 of the present invention and Comparative Examples 6-8, the film had a thickness of 50 μm and included a first layer having a thickness of 37.5 μm and containing 75.0 wt.% PE3 and 25.0 wt.% PE4, and a second sealing layer having a thickness of 12.5 μm. The following table shows the composition of each second film layer used in various experiments demonstrating the present invention.

[0098] Example Second (sealing) layer composition 2 20.0 wt% PE4, 60.0 wt% PE3, 20.0 wt% PE1 3 20.0 wt% PE4, 40.0 wt% PE3, 40.0 wt% PE1 4 20.0 wt% PE4, 20.0 wt% PE3, 60.0 wt% PE1 6 (Comparison) 20.0 wt% PE4, 60.0 wt% PE3, 20.0 wt% PE2 7 (Comparison) 20.0 wt% PE4, 40.0 wt% PE3, 40.0 wt% PE2 8 (Comparison) 20.0 wt% PE4, 20.0 wt% PE3, 60.0 wt% PE2

[0099] The films of Examples 1-8 produced according to the above formulations and methods were analyzed and tested as follows: In each film, the seal strength at a given temperature was determined according to ASTM F88 (2015) for a seal produced at a given temperature, expressed in N, with a seal width of 15 mm.

[0100] Example 2 3 4 6 7 8 Seal strength at 80°C 0.2 0.3 1.3 0.0 0.0 0.0 Seal strength at 85°C 0.3 0.6 8.0 0.0 0.0 0.0 Seal strength at 90°C 0.4 2.1 9.0 0.2 0.2 0.6 Seal strength at 95°C 0.6 9.3 9.8 0.2 0.4 7.0 Seal strength at 100°C 2.0 10.0 10.4 1.2 7.2 9.2 Seal strength at 105°C 10.0 10.8 11.8 6.0 9.6 9.6 Seal strength at 110℃ 10.6 11.4 12.2 9.8 10.4 10.4 Seal strength at 120℃ 13.2 13.4 13.0 12.2 12.4 12.6 Seal strength at 130°C 14.3 14.4 14.0 13.6 14.2 13.2

[0101] Figure 1 A plot of seal strength versus sealing temperature for the experimental films is presented.

[0102] From the above results, it can be observed that the films of the invention allow seals with some improved strength to be produced by heat sealing at particularly low sealing temperatures.

[0103] To evaluate the retention of seal strength after exposure to certain heat conditions, the films of Examples 1 and 5 were subjected to a heat aging process in which the films were conditioned at 45°C, 25% RH for 24 hours. Seal strength at various sealing temperatures was then measured according to the method indicated above. The results are presented in the table below.

[0104] experiment 1A 1B 2A 2B Seal strength at 80°C 3.8 3.8 3.9 3.1 Seal strength at 90°C 5.3 5.2 4.8 4.5 Seal strength at 100°C 6.5 6.5 6.1 5.7 Seal strength at 110℃ 6.6 6.8 6.6 6.1

[0105] In this table, Experiment 1A shows the seal strength data of the film of Example 1 that was not subjected to an aging process, and Experiment 1B shows the seal strength data of the film of Example 1 that was subjected to a heat aging process. It can be observed that the strength of the seals of the film of Example 1 does not differ regardless of whether they were produced using aged or unaged samples; in the case of the film of Example 2, a deterioration in the seal strength can be clearly observed.

Claims

1. A film comprising a sealing layer, the sealing layer comprising polyethylene A, the polyethylene A comprising a structural portion derived from ethylene and a structural portion derived from an α-olefin containing 4 to 10 carbon atoms, the polyethylene A having a mass fraction of ≥870 and ≤920 kg / m 2 as determined according to ASTM D792 (2013) 3 density; Wherein the polyethylene A has: a fraction of ≥5.0 wt % and ≤15.0 wt % of material relative to the total weight of the polyethylene A eluting in an analytical temperature-rise elution fractionation at a temperature ≤ 30.0° C.; and Two distinct peaks in the analytical temperature rise elution fractionation curve in the elution temperature range of 50.0 to 90.0°C, wherein the elution temperature difference between the two peaks is ≥5.0°C and ≤17.5°C; wherein the sealing layer comprises polyethylene B, wherein the polyethylene B is a copolymer comprising a moiety of ethylene and a moiety derived from 1-butene, 1-hexene or 1-octene; and The sealing layer comprises polyethylene C, wherein the polyethylene C is a low-density polyethylene homopolymer.

2. The film according to claim 1, wherein the polyethylene A has a hardness of ≥900 and ≤920 kg / m2 as measured according to ASTM D792 (2013). 3 density.

3. The film according to claim 1, wherein the polyethylene A has a material fraction eluting in an analytical temperature-rise elution fractionation at a temperature of ≤ 30.0°C of ≥ 7.5 wt% and ≤ 12.5 wt% relative to the total weight of the polyethylene A. The film according to claim 1 , wherein the polyethylene A has two different peaks in an analytical temperature rising elution fractionation curve in the elution temperature range of 50.0 to 90.0° C., wherein the elution temperature difference between the two peaks is ≤15.0° C.

5. The membrane according to claim 1, wherein the ratio q2 / q1 of the elution amount q2 of polyethylene A at the maximum value P2 of the peak appearing at the highest temperature in the elution curve in the elution temperature range of 50.0 to 90.0°C to the elution amount q1 at the maximum value P1 of the peak appearing at the lowest temperature in the range of 50.0 to 90.0°C in the analytical temperature rise elution fractionation is ≤1.40, and the elution amount is an amount by weight.

6. The membrane according to claim 1, wherein the ratio q2 / q1 of the elution amount q2 of polyethylene A at the maximum value P2 of the peak appearing at the highest temperature in the elution curve in the elution temperature range of 50.0 to 90.0°C to the elution amount q1 at the maximum value P1 of the peak appearing at the lowest temperature in the range of 50.0 to 90.0°C in the analytical temperature rise elution fractionation is ≥0.75 and ≤1.25, and the elution amount is an amount by weight.

7. The membrane according to any one of claims 1 to 6, wherein the polyethylene A has a material fraction of ≤ 5.0% by weight eluting in an analytical temperature rising elution fractionation at an elution temperature range of ≥ 90°C. 8 . The film according to claim 1 , wherein the sealing layer comprises ≧10.0 wt % and ≦90.0 wt % of the polyethylene A, relative to the total weight of the sealing layer.

9. The film according to any one of claims 1 to 6, wherein the sealing layer comprises ≥ 30.0 wt% and ≤ 70.0 wt% of the polyethylene A. 10 . The film according to claim 1 , wherein the sealing layer comprises ≧10.0 wt % and ≦70.0 wt % of polyethylene B, relative to the total weight of the sealing layer.

11. The film according to claim 5 or 6, wherein The composition of the polyethylene A is determined by analyzing the temperature rise elution fractionation. The difference Δρ between the density ρ2 of the polymer material eluted at P2 and the density ρ1 of the polymer material eluted at P1 is Δρ (Δρ=ρ2-ρ1) ≤ 15 kg / m 3 .

12. The film according to any one of claims 1 to 6, wherein the α-olefin containing 4 to 10 carbon atoms is 1-octene.

13. The film according to any one of claims 1 to 6, wherein the polyethylene A comprises ≥ 15.0 and ≤ 30.0 wt% of moieties derived from 1-octene. 14 . The film according to claim 1 , wherein the polyethylene A comprises ≥ 70.0 wt % of moieties derived from ethylene, relative to the total weight of the polyethylene A.

15. The film according to any one of claims 1 to 6, wherein the polyethylene A is produced via a solution polymerization process, and / or wherein the polyethylene A is produced using a metallocene-type catalyst.

16. The film according to any one of claims 1 to 6, wherein the sealing layer has a thickness of 1 to 100 μm.

17. The film according to any one of claims 1 to 6, wherein the film consists of the sealing layer.

18. A multi-layer film structure comprising the film of any one of claims 1-17, wherein the film is arranged in an arrangement of the multi-layer film structure such that one or both of the outer surfaces of the multi-layer film structure is constituted by the sealing layer.

19. The multilayer film structure according to claim 18, comprising two outer layers and at least one inner layer located between the two outer layers, wherein one of the outer layers is constituted by the sealing layer, or wherein both outer layers are constituted by the sealing layer.

20. The multilayer film structure according to any one of claims 18-19, wherein the structure comprises 3-15 layers.

21. The multilayer film structure according to any one of claims 18-19, wherein the structure has a thickness of 2-150 μm.

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