WO2025125184A1

WO2025125184A1 - Polymer composition, film and package having improved hermiticity

Info

Publication number: WO2025125184A1
Application number: PCT/EP2024/085370
Authority: WO
Inventors: Lanya Cheng; Changda LI; Saad Nasser Al-Hussain; Bhaskar Patham; Maria Soliman; Yuan Li
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2023-12-15
Filing date: 2024-12-09
Publication date: 2025-06-19
Anticipated expiration: 2026-06-15

Abstract

The invention relates to a polymer composition comprising: (a) ≥ 50.0 wt%, preferably ≥ 60.0 wt% and ≤ 90.0 wt%, with regard to the total weight of the polymer composition, of a first ethylene-based copolymer having a density of ≥ 850 and ≤ 910 kg/m³, preferably ≥ 870 and ≤ 910 kg/m³, more preferably ≥ 890 and ≤ 910 kg/m³, as determined in accordance with ASTM D792 (2013), and a melt mass-flow rate determined at 190°C under a load of 2.16 kg (MFR2) in accordance with ASTM D1238-13 of ≥ 0.2 and ≤ 10.0 g/10 min; (b) optionally, a second ethylene-based copolymer having a density of ≥ 912 and ≤ 940 kg/m3, preferably ≥ 5.0 and ≤ 20.0 wt% of the second ethylene-based copolymer, with regard to the total weight of the polymer composition; and (c) optionally, a low-density polyethylene having a density of > 900 and < 930 kg/m³, preferably ≥ 5.0 and ≤ 20.0 wt% of the low-density polyethylene, with regard to the total weight of the polymer composition; wherein the first ethylene-based copolymer is an ethylene/1-octene copolymer comprising ≤ 18.0 wt% of polymeric units derived from 1-octene, with regard to the total weight of the first ethylene-based copolymer, and wherein the first ethylene-based copolymer has a molecular weight distribution M_w/M_n of ≥ 3.0, wherein M_w is the weight average molecular weight and M_n is the number average molecular weight, as determined in accordance with ASTM D6474 (2012). Such polymer composition allows for production of packages comprising thermal seals at low temperatures, whilst producing seals of high hermiticity.

Description

Polymer composition, film and package having improved hermiticity.

[0001] The present invention relates to a polymer composition, in particular a polyethylenecomprising polymer composition that allows for achieving improved hermiticity in packaging solutions. The invention also relates to a film comprising the composition, and to a laminate comprising such film. The invention also relates to a package comprising the film or laminate.

[0002] Polymer compositions, such as polyethylene-comprising polymer compositions, are used very ubiquitously in a vast array of materials solutions, such as packaging solutions. Polymer compositions can be formed into a wide range of shapes to enable the creation of a purpose oriented packaging application.

[0003] A particularly advantageous family of polymers is polyethylenes. Polyethylenes are the world’s most abundantly available polymer material; they are readily thermoplastically processable, have a high degree of inertness, have a good mechanical property profile, and have very low permeability, to name only some highly appreciated properties of polyethylenes that make them the number one polymer in the world.

[0004] Notably, polyethylenes are very suitable to use for packaging of perishable products, or products that are susceptible to contamination. For example, a large volume of polyethylenes finds its application in food packaging solutions. Choosing the right polyethylene formulation may allow for production of a package that keeps the food fresh, provides an appropriately robust package, and allows for a package offering that is appealing to customers, and typically in a rather cost-economic way.

[0005] The family of polyethylenes contains a wide array of members. The main categories are high-density polyethylenes (HDPE), linear low-density polyethylenes (LLDPE), low density polyethylenes (LDPE) and polyethylene elastomers/plastomers (POE/POP). Each of HDPE, LLDPE, and POP/POE are produced by catalysed polymerisation processes, typically using heterogenous catalysts such as Ziegler-type catalysts, Chromium-type catalysts, or homogeneous catalysts such as metallocene-type catalysts. Such catalytic polymerisation may be performed at relatively modest pressures and temperatures. [0006] LDPE is produced via a different polymerisation process, being free-radical polymerisation. In such process, LDPE is produced from ethylene at high pressure, such as above 1500 MPa, at temperatures of for example 250-300°C. The free-radical polymerisation is typically initiated by peroxides or other chemical compounds the form radicals under the conditions of LDPE polymerisation. LDPE production may for example be performed in tubular reactors or in autoclave reactors.

[0007] Polyethylenes of the HD PE type may for example have a density of > 940 kg/m², such as > 940 and < 970 kg/m², preferably of > 945 and < 970 kg/m³, more preferably of > 950 and < 965 kg/m³. HDPE type polyethylenes may be homopolymers or copolymers, such as copolymers of ethylene and one or more comonomers, preferably one comonomer, selected from C4-C8 a-olefins, for example wherein the comonomer(s) is selected from 1-butene, 1- hexene and 1 -octene. For example, the HDPE may comprise < 10.0 wt% of moieties derived from the comonomer, preferably < 5.0 wt%, more preferably > 0.1 and < 4.0 wt%, with regard to the total weight of the HDPE.

[0008] Polyethylenes of the LLDPE type may for example have a density of > 910 and < 940 kg/m³, preferably > 915 and < 935 kg/m³, more preferably of > 915 and < 930 kg/m³. LLDPE type polyethylenes preferably are copolymers, preferably copolymers of ethylene and a further C4-C8 a-olefin, for example wherein the further C4-C8 a-olefin is selected from 1-butene, 1- hexene and 1-octene. For example, the LLDPE may comprise > 5.0 wt% and < 40.0 wt% of moieties derived from the comonomer, preferably > 5.0 wt% and < 30.0 wt%, more preferably > 10.0 and < 30.0 wt%, with regard to the total weight of the LLDPE.

[0009] In packaging solutions, a parameter that in many cases is paramount to the suitability of the solution is the hermiticity of a package. In this context, hermiticity means the extent to which the contents of a package are shielded from the environment outside the package. Particularly, when the package is to contain perishable products, or products that are susceptible to contamination, this is a critical parameter.

[0010] A widely applied type of packaging are sealed bag-type packages. Such packages can be produced by providing a film or sheet material that is to be formed into the package, which may be continuously supplied to a hollow forming tube, such as be supplying a roll of the flexible film or laminate. The film may then be wrapped into a tube, for example by wrapping around a forming tube, pulled towards the end of the forming tube, while a seal is made to connect the two long sides of the film together to form a tubular shaped film object. As this seal is made in the direction parallel with the processing direction of the film through the packaging machine, this seal may be referred to as the machine-direction seal.

[0011] The so-formed continuous tube can be formed into package compartments by

[0012] When using a thermoplastic polymer material for the film, a widely used technique for producing the seals is by thermal sealing. This involves subjecting an area of the film where the seal is to be formed to a heat source to bring the part of the film that is to seal to a temperature at which it is sufficiently softened or molten to adhere to a second surface, and contacting that softened area to a surface area to which it is to be sealed to. Commonly, the area to which the softened area is to be sealed to is of the same material, being another area of the same film, and typically this surface is also subjected to a heat source to bring it to a temperature at which it can adhere to the other surface. By so, a thermal seal is formed by contacting two heated and thereby adhesive surfaces with one another.

[0013] In forming a tubular shape from a continuous film or laminate, as presented above, the sealable surface of the film or laminate typically is positioned to be the inner surface of the tubular shape.

[0014] When the machine-direction seal is accordingly formed by contacting the inner surface of two sides of the film or laminate, a fin seal is formed that can be folded to form a fold-over seam.

[0015] The thus formed, continuous tubular, packaging material can be converted into individual compartments each comprising the desired contents by forming a first perpendicular thermal seal into the tubular shape, introducing the contents to be packed into the package, and forming a second perpendicular thermal seal into the tubular shape at a defined distance upwards from the first perpendicular seal. By so, the tubular shape is formed into a package compartment containing the desired contents to be packed, and the package compartment is completely sealed by ensuring that the machine-direction seal and the two perpendicular seals appropriately connect to each other.

[0016] Packaging techniques as described above are suitable for continuous production of packages. By so, the contents can be packed in very fast and economic operations. Such fast and continuous operations require that the seals can be continuously produced at very high speed, without compromising the package quality.

[0017] The present inventors have now provided therefor by a polymer composition comprising:

(a) > 50.0 wt%, preferably > 60.0 wt% and < 90.0 wt%, with regard to the total weight of the polymer composition, of a first ethylene-based copolymer having a density of > 850 and < 910 kg/m³, preferably > 870 and < 910 kg/m³, more preferably > 890 and < 910 kg/m³, as determined in accordance with ASTM D792 (2013), and a melt mass-flow rate determined at 190°C under a load of 2.16 kg (MFR2) in accordance with ASTM D1238-13 of > 0.2 and < 10.0 g/10 min;

(b) optionally, a second ethylene-based copolymer having a density of > 912 and < 940 kg/m³, preferably > 5.0 and < 20.0 wt% of the second ethylene-based copolymer, with regard to the total weight of the polymer composition; and

(c) optionally, a low-density polyethylene having a density of > 900 and < 930 kg/m³, preferably > 5.0 and < 20.0 wt% of the low-density polyethylene, with regard to the total weight of the polymer composition; wherein the first ethylene-based copolymer is an ethylene/1 -octene copolymer comprising < 18.0 wt% of polymeric units derived from 1-octene, with regard to the total weight of the first ethylene-based copolymer, and wherein the first ethylene-based copolymer has a molecular weight distribution M_w/M_n of > 3.0, wherein M_w is the weight average molecular weight and M_n is the number average molecular weight, as determined in accordance with ASTM D6474 (2012).

[0018] Such polymer composition allows for production of packages comprising thermal seals at low temperatures, whilst producing seals of high hermiticity.

[0019] The first ethylene-based copolymer may for example have a fraction eluted in a-TREF below 30°C of < 10.0 wt%, preferably > 5.0 and < 10.0 wt%.

[0020] The first ethylene-based copolymer may for example have an MFR2 of > 0.2 and < 5.0 g/10 min, preferably > 0.5 and < 5.0 g/10 min, more preferably > 0.5 and < 2.5 g/10 min.

[0021] The first ethylene-based copolymer may for example comprise > 10.0 and < 18.0 wt% of polymeric units derived from 1 -octene, preferably >15.0 and < 18.0 wt%. [0022] The first ethylene-based copolymer may for example have a molecular weight distribution of > 3.0 and < 4.0, preferably of > 3.0 and < 3.5.

[0023] The first ethylene-based copolymer may for example have a chemical composition distribution broadness (CCDB) of < 25.0, preferably > 15.0 and < 25.0, as determined in accordance with the method of the description.

[0024] The first ethylene-based copolymer may for example have a weight average molecular weight (M_w) of > 100 kg/mol, preferably > 102 and < 150 kg/mol.

[0025] The second ethylene-based copolymer may for example be a copolymer of ethylene and 1-butene or 1 -hexene. For example, the second ethylene-based copolymer may comprise > 2.0 and < 25.0 wt% of moieties derived from 1-butene or 1-hexene, preferably > 5.0 and < 15.0 wt%. The second ethylene-based copolymer may for example have a density of > 912 and < 930 kg/m³, preferably > 912 and < 925 kg/m³, more preferably > 915 and < 920 kg/m³. The second ethylene-based copolymer may for example have 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 < 5.0 g.10 min.

[0026] The low-density polyethylene may for example have a density of > 905 and < 928 kg/m³, preferably of > 910 and < 925 kg/m³, more preferably of > 915 and < 925 kg/m³.

[0027] The invention also relates to a film comprising or consisting of a layer comprising or consisting of the polymer composition. In an embodiment, such layer consists of the polymer and optionally a slip agent, preferably an erucamide, and/or an antiblock agent, preferably a natural silicate.

[0028] The film may for example be a cast film or a blown film. In a certain embodiment, the film is a multilayer film, and the layer is a sealing layer positioned as one outer layer of the film. For example, the film may be a 3-layer film, a 5-layer film or a 7-layer film. The film may for example have a first outer layer, a second outer layer, and one or more inner layers, wherein the second outer layer is the sealing layer. The first outer layer and each of the one or more inner layers may be of the same composition.

[0029] The invention also relates to a laminate comprising at least a first film adhered to a second film, wherein the first film is the film according to the invention, and wherein the first film is adhered to the second film via its first outer layer. [0030] Such laminate may for example comprise, in this order, the first film, the second film and a third film, wherein:

• the second film is a metallic film, preferably an aluminium film; and

• the third film is a polymer film, preferably a bidirectionally oriented polyethylene (BOPE), bidirectionally oriented polypropylene (BOPP) or bidirectionally oriented polyethylene terephthalate (BOPET) film; preferably wherein the first film is laminated to the second film and the second film laminated to the third film by an adhesive layer.

[0031] The invention also relates to package comprising or consisting of the laminate according to the invention, preferably wherein the package is a form-fill-seal package, wherein the sealing layer forms the inner layer of the package, and wherein the one or more seals to close the form-fill-seal package are thermal seals.

[0032] The invention also relates to the use of a sealing layer comprising a first ethylene-based copolymer having a density of > 850 and < 910 kg/m³, preferably > 870 and < 910 kg/m³, more preferably > 890 and < 910 kg/m³, as determined in accordance with ASTM D792 (2013), and 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; wherein the first ethylene-based copolymer is an ethylene/1 -octene copolymer comprising < 18.0 wt% of polymeric units derived from 1 -octene, with regard to the total weight of the first ethylene-based copolymer, and wherein the first ethylene-based copolymer has a molecular weight distribution M_w/M_n of > 3.0, wherein M_w is the weight average molecular weight and M_n is the number average molecular weight, as determined in accordance with ASTM D6474 (2012), to improve the hermeticity as tested in accordance with ASTM D3078-94 of a form-fill-seal package.

[0033] The comonomer content and the comonomer type may be determined by ¹³C NMR, such as 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.

[0034] In the context of the present invention, the CCDB is determined according to formula I: 100

formula I wherein

• T_n-2 is the moment calculated according to the formula II:

formula II and

• T_Z+2 is the moment calculated according to the formula III:

formula III wherein

• w(i) is the sampled weight fraction in wt% with regard to the total sample weight in a-TREF analysis of a sample (i) taken at temperature T(i), where T(i) > 30°C, the area under the a-TREF curve being normalised to surface area = 1 for T(i) > 30°C; and

• T(i) is the temperature at which sample (i) is taken in a-TREF analysis, in °C.

[0035] According to the invention, analytical temperature rising elution fractionation, also referred to as a-TREF, may be carried out using a Polymer Char Crystaf-TREF 300 equipped with stainless steel columns having a length of 15 cm and an internal diameter of 7.8 mm, with a solution containing 4 mg/ml of sample prepared in 1 ,2-dichlorobenzene stabilised with 1 g/l Topanol CA (1 ,1 ,3-tri(3-tert-butyl-4-hydroxy-6-methylphenyl)butane) and 1 g/l Irgafos 168 (tri(2,4-di-tert-butylphenyl) phosphite) at a temperature of 150°C for 1 hour. The solution may be further stabilised for 45 minutes at 95°C under continuous stirring at 200 rpm before analyses. For analyses, the solution was crystallised from 95°C to 30°C using a cooling rate of 0.1°C/min. Elution may be performed with a heating rate of 1°C/min from 30°C to 140°C. The set-up may be cleaned at 150°C. The sample injection volume may be 300 pl, and the pump flow rate during elution 0.5 ml/min. The volume between the column and the detector may be 313 pl. The fraction that is eluted at a temperature of <30.0°C may in the context of the present invention be calculated by subtracting the sum of the fraction eluted >30.0°C from 100%, thus the total of the fraction eluted < 30.0°C, and the fraction eluted >30.0°C to add up to 100.0 wt%.

[0036] Particularly, a-TREF may be carried out using a Polymer Char Crystaf-TREF 300 using a solution containing 4 mg/ml of the polymer in 1 ,2-dichlorobenzene, wherein the solution is stabilised with 1 g/l 1,1,3-tri(3-tert-butyl-4-hydroxy-6-methylphenyl)butane and 1 g/l tri(2,4-di- tert-butylphenyl) phosphite) at a temperature of 150°C for 1 hour, and further stabilised for 45 minutes at 95°C under continuous stirring at 200 rpm, wherein the prior to analyses the solution is crystallised from 95°C to 30°C using a cooling rate of 0.1°C/min, and elution is performed at a heating rate of 1°C/min from 30°C to 140°C, and wherein the equipment has been cleaned at 150°C.

[0037] The invention will now be illustrated by the following non-limiting examples.

[0038] In the examples of the present invention, the following materials were used:

[0039] Properties of the polyethylene-type materials used in the examples are presented in the table below:

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)

• The fraction a-TREF <30°C is the fraction eluted in an a-TREF analysis conducted as described above below 30°C;

• The weight-average molecular weight (M_w) and the number-average molecular weight (M_n) were determined in accordance with ASTM D6474 (2012).

• The comonomer content indicates the weight quantity of units present in the polymer that are derived from the comonomer, also referred to as the quantity of moieties derived from the comonomer, with regard to the total weight of the polymer, expressed in wt%;

• The comonomer type indicates the type of comonomer used in the production of the polymer, where C8 is 1 -octene;

• The peak melting temperature (T_p.m) is determined using differential scanning calorimetry according to ASTM D3418 (2008), expressed in °C;

• The CCDB is the chemical composition distribution broadness calculated according to the method described herein above.

[0040] For demonstrating the present invention, a number of multilayer laminates were produced having the structure A // B // C // D // E // F // G.

Wherein A is a BOPET film; B and D are adhesive layers; C is an aluminium film; and E//F//G is a coextruded 3-layer film produced by blow film extrusion according to the conditions set out below:

[0041] In the coextruded film, the layer E and F both comprised 80 wt% of the LLDPE and 20 wt% of the LDPE. The layer E in the film had a thickness of 15 pm, the layer F has a thickness of 30 pm.

[0042] In the coextruded film, the layer G was the sealing layer. To demonstrate the effect of the invention, experiments were performed using different compositions of the sealing layer G, as per the table below. In each example, the sealing layer had a thickness of 15 pm.

[0043] In the table above, all percentages are weight percentages with regard to the total weight of the sealing layer.

[0044] The laminates were converted into pouches for hermiticity testing. Such pouches were prepared using the laminates of each of the examples 1-7 above. The pouches were prepared using an EPlus model RAD-G4 VFFS machine, an industrial multiple lane stick pouch machine. The line speed was 80 packs/min/lane. The vertical seal was sealed at 180°C to ensure that no leakage could occur along the vertical seal. By horizontal sealing, pouches were made having a size of 45 mm width and 180 mm length. The seal in the horizontal direction was made at a pressure of 0.35 MPa, using a sealing time of 0.35 s. A range of sealing temperatures was applied.

[0045] For each of the examples, packs that were produced according to the conditions as set out above were subjected to hermiticity testing. Hermeticity testing was performed according to ASTM D3078-94 on PARAM, MFY-01. The sample pouches were submerged in water in a sealed tank, at room temperature, and the pressure in the tank was reduced to 40 kPa. The pouch was monitored for 30 second to identify air bubbles escaping from the pouch.

[0047] In the table above, the values are presented for hermiticity of the examples wherein the horizontal seal was produced at 140°C.

[0048] In the table above, it can be observed that the example 7, wherein the 75% of the POE3 was used in the sealing layer, exhibited 100% hermiticity for pouches sealed at 140°C.

[0049] In addition to the hermiticity, the seal strength and the hot tack strength were also tested. 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, wherein the films were protected with a 12 pm BOPET sheet. The press used for preparing the seal was heated to various temperatures to identify the strength of the seal when produced at different temperatures.

[0050] 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.

The values in the table above are the seal strengths of the horizontal seals produced at the sealing temperature as indicated in the table, expressed in N / 15mm.

Claims

1. Polymer composition comprising:

2. Polymer composition according to claim 1 wherein the first ethylene-based copolymer has a fraction eluted in a-TREF below 30°C of < 10.0 wt%, preferably > 5.0 and < 10.0 wt%, as determined according to the method of the description.

3. Polymer composition according to any one of claims 1-2, wherein the first ethylene-based copolymer has a chemical composition distribution broadness (CCDB) of < 25.0, preferably > 15.0 and < 25.0, as determined in accordance with the method of the description.

4. Polymer composition according to any one of claims 1-3, wherein the first ethylene-based copolymer has a weight average molecular weight (M_w) of > 100 kg/mol, preferably > 102 and < 150 kg/mol.

5. Film comprising or consisting of a layer comprising or consisting of the polymer composition according to any one of claims 1-4.

6. Film according to claim 5, wherein the layer consists of the polymer composition of claim 1-4, and optionally a slip agent, preferably an erucamide, and/or an antiblock agent, preferably a natural silicate.

7. Film according to any one of claims 5-6, wherein the film is a cast film or a blown film.

8. Film according to any one of claims 5-7, wherein the film is a multilayer film, and the layer is a sealing layer positioned as one outer layer of the film.

9. Film according to claim 8, wherein the film is a 3-layer film, a 5-layer film or a 7-layer film.

10. Film according to any one of claims 8-9, wherein the film has a first outer layer, a second outer layer, and one or more inner layers, wherein the second outer layer is the sealing layer.

11. Film according to claim 10, wherein the first outer layer and each of the one or more inner layers are of the same composition.

12. Laminate comprising at least a first film adhered to a second film, wherein the first film is the film according to any one of claims 10-11 , wherein the first film is adhered to the second film via its first outer layer.

13. Laminate according to claim 12, wherein the laminate comprises, in this order, the first film, the second film and a third film, wherein:

• the second film is a metallic film, preferably an aluminium film; and

14. Package comprising or consisting of the laminate according to any one of claims 12-13, preferably wherein the package is a form-fill-seal package, wherein the sealing layer forms the inner layer of the package, and wherein the one or more seals to close the form-fill- seal package are thermal seals.

15. Use of a sealing layer comprising a first ethylene-based copolymer having a density of > 850 and < 910 kg/m³, preferably > 870 and < 910 kg/m³, more preferably > 890 and < 910 kg/m³, as determined in accordance with ASTM D792 (2013), and 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; wherein the first ethylene-based copolymer is an ethylene/1 -octene copolymer comprising < 18.0 wt% of polymeric units derived from 1 -octene, with regard to the total weight of the first ethylene-based copolymer, and wherein the first ethylenebased copolymer has a molecular weight distribution M_w/M_n of > 3.0, wherein M_w is the weight average molecular weight and M_n is the number average molecular weight, as determined in accordance with ASTM D6474 (2012); to improve the hermeticity as tested in accordance with ASTM D3078-94 of a form-fill-seal package.