EP3768769A1

EP3768769A1 - Film for stretch-wrap packaging

Info

Publication number: EP3768769A1
Application number: EP19709064.0A
Authority: EP
Inventors: Bart VAN DEN ESSCHERT; Lucio Baccaro; Attilio SCALA
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2018-03-20
Filing date: 2019-03-12
Publication date: 2021-01-27
Also published as: WO2019179827A1

Abstract

The present invention relates to a film comprising linear low-density polyethylene (LLDPE), wherein the film demonstrates a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress-strain curve dσ/dε is > 5.0 kPa/%, stress and strain being determined in accordance with ISO 527-3 (1995). Such film demonstrates an improvement in the slow penetration puncture resistance, and allows for use of the film in stretch-wrap applications with improved stability, thereby providing a significant benefit for the transportation industry, for example in being able to more stable and safe stack items onto pallets.

Description

Film for stretch -wrap packaging.

[0001] The present invention relates to a film comprising linear low-density polyethylene (LLDPE), in particular to a film for stretch-wrap packaging. The invention also relates to stretch wrapping of objects using such film, and to articles stretch -wrapped with such film, in particular pallets for storing units such as bags containing bulk goods.

[0002] In transportation of goods, particularly in transportation of bulk solids packed in packaging units such as bags or boxes, the transport commonly takes place in the form of pallets onto which a number of such bags or boxes, or even other types of packaging units, are stacked. Transportation via pallets allows for a large plurality of units to be transported jointly, and allows for such plurality of units to be displaceable by a single action, such as by picking it up via a fork lift. This makes transportation far more economical and fast.

[0003] In order to safeguard the stability of such stacks, or even to allow multiple of such packed pallets to be positioned on top of each other, it is required to ensure that the packaging units do not move relative to each other during storage and transportation. A common means of ensuring such movement is restricted or even avoided is by stretch wrapping of the units onto the pallet.

[0004] Stretch wrapping is a technique by which, upon positioning the packaging units onto the pallet, a film is wrapped around the units in such way that all units are enclosed by the film. In order to be suitable for such wrapping, films must comply with certain requirements in terms of their properties. The films must, amongst others, have certain capability of adhering to itself, and certain strength to allow resistance to load forces exerted onto the stacks during storage and transportation.

[0005] It is a well-established practise to use films comprising linear low-density polyethylenes for such stretch-wrap applications. Such films may be single-layer films, or alternatively multi layer films. [0006] Current pallet load regulations, such as EU transportation regulations, however require more stringent properties of the films used for such stretch-wrapping applications, resulting in reduction of risks of load displacement and thereby damage to packed goods, transportation means or even injuries of employees involved in handling and transport of the stretch -wrapped pallets. The stretch-wrapping films according to the current state of art fail to comply with these more stringent regulations.

[0007] In order to meet the above referred regulations, one solution is to increase the thickness of the films. Common stretch-wrap films have a thickness of for example 10 to 50 pm. However, there are a number of disadvantages to increasing thickness to meet tightening regulations. For example, such thicker films are more costly. Further, such films are less transparent, which negatively affects both the aesthetics of the wrapped pallet, as well as the ability to identify the contents, i.e. the packaging units, of the pallet. Thus, a certain transparency is desired.

[0008] Another solution may be to wrap the pallet with a higher density of stretch film, i.e. wrap more layers of the films onto the pallet. Again, this results in a higher film consumption, and thus increased cost, as well as a reduction of the transparency. Thus, also such solution is not particularly desirable.

[0009] For amongst others these reasons, many of the present LLDPE stretch-wrap films fail to qualify, resulting in a need to develop LLDPE films that allow for stable packaging under the EU regulations, such as those of the EUMOS 40509 standard incorporated in EU Directive 2014/47, and further provide desirable properties such as tensile properties and optical properties. A parameter by which the required strength for stable packaging of the films can be observed is the slow penetration puncture resistance as determined in accordance with ASTM D5748-95 (2012).

[0010] The inventors have now succeeded in providing such improvements. This has been achieved according to the invention by a film comprising linear low-density polyethylene

(LLDPE), wherein the film demonstrates a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress-strain curve do/de is > 5.0 kPa/%, stress and strain being determined in accordance with ISO 527-3 (1995). [001 1] Such film demonstrates an improvement in the slow penetration puncture resistance, and allows for use of the film in stretch-wrap applications with improved stability, thereby providing a significant benefit for the transportation industry, for example in being able to more stable and safe stack items onto pallets.

[0012] In particular, the invention relates to a film that demonstrates a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress-strain curve do/de is > 5.0 kPa/%, stress and strain being determined in accordance with ISO 527-3 (1995), tested in the machine direction.

[0013] In certain embodiments, the invention relates to a film that demonstrates a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress- strain curve do/de is > 5.0 kPa/%, preferably > 7.5 kPa/%, more preferably > 10.0 kPa/%, even more preferably > 15.0 kPa/%, even further preferably > 20.0 kPa/%, stress and strain being determined in accordance with ISO 527-3 (1995). For example, the film may demonstrate a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress-strain curve do/de is > 5.0 kPa/% and < 500 kPa/%, preferably > 5.0 kPa/% and < 200kPa/%, more preferably > 7.5 kPa/% and < 200 kPa/%, even more preferably > 10.0 kPa/% and < 200 kPa/%, even further preferably > 15.0 kPa/% and < 20.0 kPa/%, stress and strain being determined in accordance with ISO 527-3 (1995).

[0014] It is preferred that the LLDPE has a density of > 900 and < 940 kg/m³ as determined in accordance with ASTM D1505 (2010). For example, the LLDPE may have a density of > 910 and < 930 kg/m³, preferably > 915 and < 925 kg/m³, even more preferably > 915 and < 920 kg/m³.

[0015] The film may for example have a thickness of < 50 pm, preferably < 30 pm. For example, the film may have a thickness of > 5.0 and < 50 pm, preferably > 5.0 and < 30 pm, more preferably > 10.0 and < 30.0 pm.

[0016] The LLDPE may for example have a melt mass flow rate determined in accordance with ASTM D1238 (2013) of > 0.1 and < 10.0 g/10 min, preferably > 0.3 and < 8.0 g/10 min, more preferably > 0.5 and < 5.0 g/10 min, even more preferably > 1.0 and < 5.0, even further preferably > 2.0 and < 5.0 g/10 min.

[0017] In a preferred embodiment to the invention, the LLDPE is an LLDPE produced in a catalytic process. For example, the LLDPE may be produced in a catalytic process in which the polymerisation reaction is performed in a gas phase, in solution, or in a slurry. For example, the LLDPE may be produced in a catalytic process in which the polymerisation is performed in solution. The LLDPE may be produced using a single-site catalyst. For example, the LLDPE may be produced using a single-site catalyst in a solution process.

[0018] The determination of the derivative function of the stress-strain curve is a general mathematical method, and is well known to the person of skill. The derivative function presents the slope of a curve at a given point along the curve. The stress-strain curve may be obtained by determining the stress at intervals of strain of 10%, preferable of 5%, over the strain range of 100% to 300%, and fitting the measurements to obtain the equation for the stress-strain curve.

[0019] The LLDPE may comprise moieties derived from ethylene and moieties derived from one or more comonomer. The comonomer may for example be selected from C4-C10 1 -olefins. For example, comonomer may be selected from 1 -butene, 1 -hexene and 1 -octene. For example, comonomer may be 1 -octene. The LLDPE may for example comprise > 90.0 wt%, preferably > 95.0 wt%, even more preferably > 98.0 wt%, of moieties derived from ethylene, with regard to the total weight of the LLDPE. The LLDPE may for example comprise > 90.0 wt%, of moieties derived from ethylene and < 10.0 wt% of moieties derived from one or more comonomer, preferably > 95.0 wt%, of moieties derived from ethylene and < 5.0 wt% of moieties derived from one or more comonomer, more preferably > 98.0 wt%, of moieties derived from ethylene and < 2.0 wt% of moieties derived from one or more comonomer, with regard to the total weight of the LLDPE. For example, the LLDPE may comprise > 90.0 wt%, of moieties derived from ethylene and < 10.0 wt% of moieties derived from one or more comonomer, preferably > 95.0 wt%, of moieties derived from ethylene and < 5.0 wt% of moieties derived from one or more comonomer, more preferably > 98.0 wt%, of moieties derived from ethylene and < 2.0 wt% of moieties derived from one or more comonomer, with regard to the total weight of the LLDPE, wherein the comonomer may be selected from 1 -butene, 1 -hexene and 1 -octene. For example, the LLDPE may comprise > 90.0 wt%, of moieties derived from ethylene and < 10.0 wt% of moieties derived from one or more comonomer, preferably > 95.0 wt%, of moieties derived from ethylene and < 5.0 wt% of moieties derived from one or more comonomer, more preferably > 98.0 wt%, of moieties derived from ethylene and < 2.0 wt% of moieties derived from one or more comonomer, with regard to the total weight of the LLDPE, wherein the comonomer is 1 -octene.

[0020] The film of the present invention may used in a multi-layer film arrangement. For example, such multi-layer film arrangement may comprise at least one layer of the film according to the present invention. For example, such multi-layer film arrangement may comprise one layer of the film according to the present invention. In an alternative embodiment, multiple layers of such multi-layer film arrangement are films according to the present invention. In yet a further alternative embodiment, each of the layers of such multi-layer film arrangement is a film according to the present invention.

[0021] Such multi-layer film arrangement may for example be a 3-layer film arrangement, a 5- layer film arrangement, a 7-layer film arrangement, a 9-layer film arrangement, or an 1 1 -layer film arrangement. For example, such multi-layer arrangement may be a 5-layer film

arrangement or a 7-layer film arrangement. For example, such multi-layer film arrangement may be a 7-layer film arrangement.

[0022] Such multi-layer film arrangement may for example be a 3-layer film arrangement, a 5- layer film arrangement, a 7-layer film arrangement, a 9-layer film arrangement, or an 1 1 -layer film arrangement comprising at least one layer of the film according to the present invention. Such multi-layer film arrangement may for example be a 3-layer film arrangement, a 5-layer film arrangement, a 7-layer film arrangement, a 9-layer film arrangement, or an 1 1 -layer film arrangement comprising one layer of the film according to the present invention. Such multi layer arrangement may for example be a 5-layer film arrangement or a 7-layer film arrangement comprising at least one layer of the film according to the present invention. Such multi-layer arrangement may for example be a 5-layer film arrangement or a 7-layer film arrangement comprising one layer of the film according to the present invention. In an alternative

embodiment, multiple layers of such multi-layer film arrangement are films according to the present invention, wherein the multi-layer arrangement may for example be a 5-layer film arrangement or a 7-layer film arrangement. In yet a further alternative embodiment, each of the layers of such multi-layer film arrangement is a film according to the present invention, wherein the multi-layer arrangement may for example be a 5-layer film arrangement or a 7-layer film arrangement.

[0023] In particular, the multi-layer arrangement may be a 7-layer film arrangement, wherein at least one of the layers is a film according to the invention. More particularly, such multi-layer arrangement may be a 7-layer film arrangement, wherein one of the layers is a film according to the invention. Alternatively, such multi-layer arrangement may be a 7-layer film arrangement, wherein multiple layers of such multi-layer film arrangement are films according to the present invention. Alternatively, such multi-layer film arrangement may be a 7-layer film arrangement, wherein each of the layers of such multi-layer film arrangement are films according to the present invention.

[0024] In such multi-layer arrangement, the layers of the arrangement preferably adhere to each other.

[0025] The film according to the invention may for example be produced via cast film extrusion. Where the film is part of an arrangement of multiple layers, it is preferred that each of the layers is produced by melt extrusion of the layers on top of each other.

[0026] The film may have a width of > 10 cm and < 300 cm, preferably > 25 cm and < 150 cm, more preferably > 40 cm and < 100 cm.

[0027] The multi-layer film arrangement may for example comprise at least one further film layer comprising a polyethylene other than the LLDPE.

[0028] A multi-layer film arrangement according to the present invention may for example comprise two outer layers, one on each side of the film. Each outer layer thus is adjacent to only one other layer of the arrangement. The outer layers may be of the same composition, or may each be made of a different composition. The outer layer(s) may each individually be made of the film according to the invention. It is also an embodiment of the invention that both outer layers are made of the film according to the invention. The weight fraction of each of the outer layers may each individually be 5.0-30.0 wt% with regard to the total weight of the multi-layer film arrangement, preferably 5.0-20.0 wt%, more preferably 7.5-15.0 wt%. The weight fraction of one outer layer may differ from the other outer layer or may be the same. [0029] Alternatively, each of the outer layers may individually be made of a polyolefin. For example, each outer layer may be made of a polyethylene or a polypropylene, for example a polyethylene having a density of 850-910 kg/m³, or of 910-925 kg/m³, or of 925-945 kg/m³, preferably an ethylene-C4-C8-a-olefin copolymer, such as an ethylene-1 -butene copolymer, and ethylene-1 -hexene copolymer, or an ethylene- 1 -octene copolymer.

[0030] Alternatively, such polyethylene may be a low-density polyethylene obtained by high- pressure free-radical polymerisation, known in the art as LDPE, for example an LDPE having a density of 900-930 kg/m³. The polyethylene may for example have a melt mass-flow rate at 190°C, 2.16 kg of 0.1 -100 g/10 min, preferably 0.5-10.0 g/10 min, more preferably 1 .0-5.0 g/10 min.

[0031] The polypropylene may for example be a homopolymer or a copolymer, such as a propylene-ethylene random copolymer. The polypropylene may for example have a melt mass- flow rate at 230°C, 2.16 kg of 0.1 -100 g/10 min, preferably 0.5-10.0 g/10 min, more preferably 1 .0-5.0 g/10 min.

[0032] The arrangement may comprise a core layer, being the centremost layer in the multi layer film arrangement. The core layer preferably comprises or consists of the film of the present invention. The core layer may for example constitute a weight fraction of 20.0-80.0 wt% with regard to the total weight of the multi-layer film arrangement, preferably 30.0 - 70.0 wt%, more preferably 40.0-65.0 wt%. It is preferred that the core layer of the multi-layer film arrangement is made of the film of the present invention.

[0033] The film according to the present invention may optionally comprise additives. For example, the film may comprise 0.0-2.0 wt%, preferably 0.0-1 .0 wt%, more preferably 0.3-1.0 wt%, of additives, with regard to the total weight of the film. For example, the film may comprise LLDPE and 0.0-2.0 wt%, preferably 0.0-1.0 wt%, more preferably 0.3-1 .0 wt%, of additives, with regard to the total weight of the film. For example, the film may consist of LLDPE and 0.0-2.0 wt%, preferably 0.0-1 .0 wt%, more preferably 0.3-1 .0 wt% of additives, with regard to the total weight of the film. [0034] Suitable additives that may be used in the film according to the present invention include for example UV stabilisers, antistatic agents, slip/anti-block agents, fillers, antioxidants, pigments, and fluor elastomers used as polymer processing aids. Particularly suitable additives that may be used in the film of the present invention are erucamide, stearamide, silica and talc.

[0035] The invention further also relates to the use of the film or the multi-layer arrangement in stretch-wrap packaging of articles. In a further embodiment, the invention also relates to a pallet comprising a number of objects stacked thereon, wherein the objects are fixed onto the pallet by stretch-wrapping using a film or a multi-layer film arrangement according to the invention. In particular, such stacked objects may be bags or boxes. It is preferred that the pallet is a pallet as defined in ISO 6780 (2003), preferably the pallet is an EUR pallet.

[0036] In a further particular embodiment, the invention also related to the use of a linear low- density polyethylene having, when tested as a film, a stress-strain relationship of the film such that in the whole region of strain of 100-300% the derivative of the stress-strain curve do/de is > 5.0 kPa/%, stress and strain being determined in accordance with ASTM D882 (2012) for improvement of slow penetration puncture resistance in accordance with ISO 527-3 (1995).

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

Materials

[0038] In the experiments that depict the present invention, films were produced using several different LLDPE materials as presented below in table 1 .

Table 1 : Materials used

[0039] Density was determined in accordance with ASTM D792 (2013). Melt mass flow rate was determined in accordance with ASTM D1238 (2013). Manufacturing of films

[0040] The above materials were used to manufacture films. In the experiments of the present invention, 5-layer films having a thickness of 20 pm were produced via cast extrusion using a 5- layer pilot film extrusion line configured as presented in tables 2 and 3. The line comprised five extruders each having a slit die having a width of 600 mm to form an molten extruded film which was solidified on a chill-roll. Extruder 1 was positioned so that molten film exiting extruder 1 contacted chill-roll 1 via the first surface of the film; the film exiting extruder 2 was positioned to contact with its first surface the second surface of the first film; and similar for the films of extruders 3-5 wherein the second surface of the film of extruder 5 was exposed to air. The extruder film first contacted chill-roll 1 and subsequently chill-roll 2. A 5-layer film was thus formed.

Table 2: Configuration of pilot film extrusion line: extruder settings

Table 3: Configuration of pilot film extrusion line: chill-roll settings

The mass fraction presents the fraction of the film that is formed by the extruder in question with regard to the total mass of the 5-layer film.

The length of the extruder is expressed as multiplier of the diameter (D) of the extruder screw.

For all experiments, each of the five extruders were fed with the same material.

Testing of films

[0041] All films that were tested were produced according to the process set out here above. Film 1 was produced using Supeer 8315 as the LLDPE. Film 2 was produced using Supeer 7318 as the LLDPE. Film 3 was produced using Exceed 3518CB as the LLDPE. Samples of each of these films were subjected to characterisations.

Stress-strain analysis

[0042] Samples of the films were subjected to tensile testing in accordance with ISO 527-3

(1995). Samples were used having dimensions 24 mm width and 50 mm length. Testing speed was 500 mm/min.

[0043] At intervals of increasing strain, the force to be applied to maintain this elongation was recorded as stress. In the table 4 below, the stress at various strains in the regime of 100 to 300% strain is presented for the experiments of the present invention, wherein Example 1 is to be understood to be an example according to the invention, and examples 2 and 3 to be examples for comparative purposes. The samples were tested in the machine direction.

Table 4: Stress-strain relationship

[0044] In this table, the strain (e) presents the elongation in % of the sample, the stress (s) presents the force to be applied to maintain the sample at that elongation in MPa, and do/de presents the derivative of the stress-strain curve at a given strain, in kPa/%, indicating the increase of force to be applied to maintain elongation at an increased elongation. [0045] The data in this table demonstrate that the film according to the invention has a derivative of the stress over strain function in the range of 100 to 300% strain that is particularly high, in fact of above 5 kPa/% over the whole of the range of strain of 100-300%. Further, the force to be applied to the material to maintain elongation continues to increase with each higher elongation.

[0046] Further properties of the films of the inventive and comparative experiments were determined, and are below presented in table 5. Table 5: Film properties

[0047] The puncture resistance was determined as the peak force to break (N), expressed in Newton (N) and the energy to break (J), expressed in joule (J) in accordance with ASTM D5748 (1995). The gloss was determined in accordance with ASTM D2457 (2013) as specular gloss at 45° gloss angle, expressed in gloss units (GU). The haze was determined in accordance with

ASTM D1003 (2013).

[0048] The tensile properties were determined in accordance with ASTM D882 (2012).

Determined were the tensile modulus (TM) in both the machine direction (MD) and the transverse direction (TD), expressed in MPa; the tensile strength (TS) in both MD and TD, expressed in MPa; and the elongation at break (EB) in both MD and TD, expressed in %. [0049] The above results demonstrate the film according to the invention, having stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress- strain curve do/de is > 5.0 kPa/%, to have a higher puncture resistance that comparative films, exemplified by the inventive film having higher peak force to break as well as higher energy to break, both parameters indicating higher puncture resistance, which in turn indicates better stability of pallets of packed goods wrapped with film of the present invention. Such higher puncture resistance is particularly related to resistance to puncturing on sharp edges on the corners of the pallets and the packed items on the pallets. Consequently, a film having higher puncture resistance as does the film of the present invention may be used in stretch-wrapping of pallets with improved process continuity, i.e. reduced disturbance of the packaging process caused by breaking of the film during the packaging process. The film of the present invention further is shown to have desirable tensile properties, as well as good optical properties.

Claims

1 . Film comprising linear low-density polyethylene (LLDPE), wherein the film demonstrates a stress-strain relationship such that in the whole region of strain of 100-300% the derivative of the stress-strain curve do/de is > 5.0 kPa/%, stress and strain being determined in accordance with ISO 527-3 (1995).

2. Film according to claim 1 wherein the LLDPE has a density of > 900 and < 940 kg/m³ as determined in accordance with ASTM D1505 (2010).

3. Film according to any one of claims 1 -2 wherein the LLDPE has a melt mass flow rate determined in accordance with ASTM D1238 (2013) of > 0.1 and < 10.0 g/10 min.

4. Film according to any one of claims 1 -3, wherein the film has a thickness of < 50 pm, preferably < 30 pm and/or a width of > 10 cm and < 300 cm, preferably > 25 cm and < 150 cm.

5. Film according to any one of claims 1 -4, wherein the LLDPE comprises moieties derived from ethylene and moieties derived from 1 -octene.

6. Film according to any one of claims 1 -5 wherein the LLDPE is produced using a single site catalyst.

7. Multi-layer film arrangement comprising at least one layer being a film according to any one of claims 1 -6.

8. Multi-layer film arrangement according to claim 7 wherein at least one of the layers of the multi-layer film arrangement comprises the LLDPE and 0.0-2.0 wt% of additives, with regard to the total weight of the LLDPE and the additives.

9. Multi-layer film arrangement according to claims 7-8 wherein at least one of the layers of the multi-layer film arrangement consist of the LLDPE and 0.0-2.0 wt% of additives, with regard to the total weight of the LLDPE and the additives.

10. Film according to any one of claims 1 -6 or multi-layer film arrangement according to any one of claims 7-9 wherein the LLDPE is produced via a solution polymerisation process.

1 1. Use of the film according to any of the claims 1 -6 or the multi-layer film arrangement

according to claims 7-9 in stretch-wrap packaging of articles.

12. Pallet comprising a number of objects stacked thereon, wherein the objects are fixed onto the pallet by stretch-wrapping using a film according to any one of claims 1 -6 or a multi layer film arrangement according to any one of claims 7-9.

13. Pallet according to claim 10, wherein the stacked objects are bags or boxes.

14. Pallet according to any one of claims 10-1 1 , wherein the pallet is a pallet as defined in ISO 6780 (2003), preferably the pallet is an EUR pallet.

15. Use of a linear low-density polyethylene having, when tested as a film, a stress-strain relationship of the film such that in the whole region of strain of 100-300% the derivative of the stress-strain curve do/de is > 5.0 kPa/%, stress and strain being determined in accordance with ASTM D882 (2012) for improvement of slow penetration puncture resistance in accordance with ISO 527-3 (1995).