Stretched film, laminate having such film, use of such film, and packaging having such film or made of such film

Abstract

The invention relates to a stretch film (10), in particular for producing packaging parts, the stretch film (10) being uniaxially stretched in the machine direction with a stretch ratio of 1.2 to 1.75, preferably 1.3 to 1.5, to a laminate having such a film (10), to the use of such a film (10) and to packaging parts produced using such a film (10).

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a stretch film according to the preamble of claim 1, a laminate having such a film according to the preamble of claim 6, the use of such a film according to the preamble of claim 8, and a package having such a film according to the preamble of claim 11.

[0002] Stretch films for the production of packages have been known for a long time. According to the prior art, stretch films are used, for example, to provide laminates having a directional tearing property, which is helpful when opening a package (usually a tubular bag package). By stretching the film, the molecular chains in the film are stretched in the stretching direction, such that the molecular chains are more or less parallel to each other, and when the package is torn open, the tear essentially extends along the molecular chains through the film rather than through the package film. For this purpose, according to the prior art, very high stretch ratios in the range of at least 1:3 to 1:15 have been used to achieve as uniaxial an orientation as possible of the molecular chains defining the tear line. Such packaging films are described, for example, in German published document DE 10 2011 001 323 A1. As mentioned above, another advantage of such stretch films is that in such films, there are essentially more or less parallel molecular chains, which form crystalline regions in the stretch film, which in turn have barrier properties, particularly with respect to water vapor permeability.

[0003] However, the main disadvantage of such films is that due to the arrangement of their molecular chains, they are practically impossible to seal, even though the base material of the film is actually an easily sealable material such as polyethylene or polypropylene.

[0004] This presents another significant disadvantage, namely that such stretch films known in the prior art can only form part of a package laminate, for example, defining a specific tearing direction of the film and / or providing a specific water vapor barrier property. It is always important to ensure that the stretch film does not impair the performance and functionality of the other films in the laminate, but is dominant enough in terms of its own tearing direction and barrier properties such that these properties are also retained in the entire laminate. In particular, for stretch films in laminates known in the prior art or used according to the prior art, in order to obtain a sealable laminate, it is always necessary to integrate at least one sealing layer into the laminate. However, since the stretch film, i.e., the film oriented in the machine direction itself cannot be sealed, the combination of this additionally required sealing layer with the stretch film can only be achieved by means of an adhesive, which is problematic both in terms of the resulting cost increase and the resulting reduction in chemical resistance. SUMMARY OF THE INVENTION

[0005] The object of the present invention is to provide a stretch film which has good tear and barrier properties while avoiding the above-mentioned drawbacks, as well as laminates having such a film, uses of such a film, and packages made of or having such a film, wherein the stretch film can be produced simply and inexpensively.

[0006] This object is achieved by a stretch film according to claim 1, a laminate having such a film according to claim 6, a use of such a film according to claim 8, and a package made of or having such a film according to claim 11.

[0007] In particular, this object is achieved by a stretch film, in particular a stretch film for producing packages, wherein the stretch film is uniaxially stretched in the machine direction with a draw ratio of 1.2 to 1.75, preferably with a draw ratio of 1.3 to 1.5.

[0008] Surprisingly, it has been found that a basic feature of the present invention is that the stretch film according to the present invention is uniaxially stretched in the longitudinal direction and has only a moderately low draw ratio of 1.2 to 1.75, preferably 1.3 to 1.5.

[0009] It has been found according to the present invention that although such a stretch film already has very good oriented tear properties and very good barrier properties, it still has sufficient non-highly oriented molecular chains so that it still exhibits very good sealing properties, which is different from the stretch films known in the prior art.

[0010] Therefore, within the scope of the present invention, on the one hand, the prejudice that stretch films known in the prior art are not sealable can be refuted, and on the other hand, in order to obtain good tear properties and good barrier properties, as described above, it is necessary to stretch to a draw ratio of up to 1:15 as large as possible.

[0011] According to a preferred embodiment of the present invention, the stretch film comprises a polyester layer or preferably a polyolefin layer, in particular a polyethylene layer, preferably high-density polyethylene such as HDPE, or is made of one of the above materials, optionally in a pure type.

[0012] It is particularly advantageous to use polyethylene to produce the stretch film according to the present invention because polyethylene is a very inexpensive plastic and is a very good material that can be sealed at relatively low temperatures in the range of 80 °C to 130 °C. In addition, polyethylene is easy to process and not complex. High-density polyethylene (such as HDPE) has proven to be particularly suitable for producing the stretch film according to the present invention, having good tear, barrier, and sealing properties.

[0013] As described above, the film stretched according to the present invention can be a film made of a pure type of material (consisting only of polyester, such as polyethylene terephthalate), or, particularly preferably according to the present invention, made only of polyethylene (such as HDPE), particularly preferably HDPE according to the present invention, especially from the perspective of recycling, or it can comprise additional, particularly functional layers.

[0014] According to a particularly preferred embodiment, the stretched film is further preferably a multi-layer blown film. Such a blown film can be produced particularly simply and inexpensively, and, in particular, can also have a very high surface output with a very large variety of film layers in a very variable manner, which very advantageously affects the manufacturing cost of the film according to the present invention.

[0015] However, according to another embodiment of the present invention, in addition to possibly containing polyethylene terephthalate and preferably containing polyethylene according to the present invention, the stretched film further comprises a barrier layer material, such as polyamide and / or ethylene-vinyl alcohol copolymer (EVOH). In this way, in addition to high water vapor impermeability, a very high barrier effect against gases such as carbon dioxide and oxygen can be achieved in a very simple and advantageous manner, such that the film stretched according to the present invention can be very generally used in many fields where water vapor and gas impermeability are important, for example, for products that themselves contain gases, particularly carbon dioxide or are sensitive to oxidation. In addition, the stretched film according to the present invention can be applied in tropical regions with very high air humidity.

[0016] According to another preferred embodiment of the present invention, the stretched film can be formed as a composite of the following layers: polyethylene, particularly HDPE / primer / barrier layer material, i.e., EVOH or polyamide / primer / polyethylene, particularly HDPE. As found according to the present invention, such a stretched film can be excellently used as a high-barrier film that is impermeable to water vapor and gases, particularly oxygen and carbon dioxide.

[0017] In addition, the stretched polyethylene film according to the present invention has excellent stiffness, which is particularly evident in the form of high flexural stiffness with a modulus of elasticity in the range of 700 N / mm 2 to 1000 N / mm 2 preferably in the range of 745 N / mm 2 to 980 N / mm 2 and particularly preferably in the range of 760 N / mm 2 to 960 N / mm 2 Therefore, the stretched film according to the present invention is very suitable for the production of packaging that can stand upright.

[0018] Furthermore, the object of the present invention is also achieved by including a stretched film according to the above description or a laminate consisting of such a stretched film, provided that the stretched film itself is multi-layered.

[0019] Such a laminate exhibits very good properties in terms of its barrier properties and tightness, whereby the laminate can achieve a water vapor permeability in an environment with a relative humidity of 85%, for example, in the range of less than 0.5 g / m 2 / day down to a value of less than 0.1 g / m 2 / day. Similarly, the laminate according to the present invention can reduce the oxygen permeability to less than 0.5 cm 3 / m 2 / day or even less than 0.2 cm 3 / m 2 / day at a temperature of 23 °C and a relative humidity of 85%. The oxygen permeability measurement is carried out according to DIN standard 53380-3. The measurement of water vapor permeability is carried out according to DIN standard 53122-2.

[0020] A basic feature of the present invention is that the stretched film provides a sealing layer for the laminate. For this purpose, the stretched film according to the present invention has an external sealing medium, such as polyethylene, which has been stretched together with the film. In order to produce a laminate according to the present invention, any other layer of the laminate is joined to the stretched film in such a way that the sealing layer of the stretched film is arranged in the outermost part of the laminate, i.e., forms the outermost layer of the laminate.

[0021] Furthermore, the object of the present invention is also achieved by using a stretched film according to the above description, since the stretched film is used for producing laminates, in particular packaging laminates and / or for producing packages.

[0022] Due to the linearly optimized tear properties of the film stretched according to the present invention and the laminate produced with such a stretched film, such a package can be opened particularly easily without the risk of diagonal tearing or unintentional damage to the package, which could result in loss of the package contents.

[0023] As described above, in the case where the stretched film is used for producing a laminate, the stretched film or the outermost layer of the stretched film constitutes the sealing layer of the laminate.

[0024] Therefore, according to the present invention, the stretched film or the outermost layer of the stretched film is also used for sealing the package to be produced.

[0025] Furthermore, the object of the present invention is also achieved by a packaging element, in particular a tubular bag packaging element with or without a bottom, wherein the packaging element is made of a stretch film as described above. In a similar manner, the packaging element can also be produced using or from a laminate as described above. As mentioned above, such a packaging element has excellent opening properties as well as very good water vapor barrier properties, and also has very good oxygen and carbon dioxide sealing properties when ethylene-vinyl alcohol copolymer (EVOH) and / or polyamide are used in the film and / or laminate stretched according to the present invention.

[0026] As described above, the packaging element is sealed by the stretch film or the outermost layer of the stretch film, in particular a stretched polyethylene film or film layer. The production of the packaging element can be carried out in such a way that two or more blanks of the stretch film according to the present invention or laminates according to the present invention are used, and each blank is connected to the packaging element through their sealing layers; optionally, a single blank of the stretch film according to the present invention or a laminate according to the present invention can be folded so that the respective sealing layers facing each other are joined to form the packaging element.

[0027] Other embodiments of the present invention result from the dependent claims. Description of the Drawings

[0028] The present invention will now be described with reference to exemplary embodiments, which will be explained in more detail with reference to the accompanying drawings. Here,

[0029] Figure 1 A schematic diagram showing an embodiment of the stretch film according to the present invention is shown. Detailed Description

[0030] In the following description, the same reference numerals are used for components having the same and similar functions.

[0031] Figure 1 A schematic diagram showing an embodiment of the stretch film 10 according to the present invention is shown. The stretch film 10 has an inner barrier layer material 30, which can be ethylene-vinyl alcohol copolymer (EVOH) or polyamide if necessary, to reduce the permeability of gases such as carbon dioxide or oxygen to the lowest possible level. The barrier layer 30 has a thickness in the range of 1 μm to 5 μm, but can also be in the range of 1.5 μm to 4 μm or in the range of 2 μm to 3 μm according to requirements.

[0032] The primer layer 40 adjoins the barrier layer 30 on both sides, wherein the applied weight of the solvent-based primer or preferably the water-based primer ranges from 0.2 g / m 2 to 2 g / m 2 and preferably ranges from 0.3 g / m 2 to 1 g / m 2within the range of, and particularly preferably between 0.4 g / m 2 to 0.6 g / m 2 within the range of, according to the present invention, this corresponds to a layer thickness within the range of 0.2 μm to 2 μm, preferably between 0.3 μm to 1 μm, and particularly preferably between 0.4 μm to 0.6 μm.

[0033] As the outermost layer of the stretched film 10 according to the present invention, the polyolefin layer 20 (i.e., a polyethylene layer with high density, especially an HDPE layer) is respectively arranged in Figure 1 which are respectively arranged behind the primer layer 40 on both sides. The thickness of the polyolefin layer 20 or the HDPE layer can be the same or different, and is within the range of 2 μm to 40 μm, preferably between 3 μm to 30 μm, and particularly preferably between 4 μm to 20 μm.

[0034] The stretched film according to the present invention is also very suitable for producing very strong tubular bags, especially tubular bags with a standing bottom, for packaging volumes up to 10 kg or more, which are particularly suitable for items that must be kept dry. Such packages have excellent water vapor and gas (especially oxygen and carbon dioxide) barrier properties and high sealing strength, as proven by drop tests of filled packages from a height of up to two meters.

[0035] An example of a specific layer structure of a laminate using the stretched film according to the present invention can be, for example, the following layer sequence:

[0036] Example 1:

[0037] A transparent film that can be printed on the reverse side (i.e., an oriented polyethylene terephthalate with a layer thickness of 12 μm / reverse printing layer (e.g., as a gravure or flexographic printing layer) / an adhesive layer with an application weight of 3 g / m 2 and an LLDPE film stretched in the machine direction at a draw ratio of 1:1.5 with a layer thickness of 100 μm according to the present invention.

[0038] Example 2:

[0039] A transparent film that can be printed on the reverse side (i.e., biaxially oriented polypropylene with a layer thickness of 12 μm) / reverse printing layer (e.g., as a gravure or flexographic printing layer) / an adhesive layer with an application weight of 3 g / m 2 and an LLDPE film stretched in the machine direction at a draw ratio of 1:1.5 with a layer thickness of 100 μm according to the present invention.

[0040] Example 3:

[0041] Transparent film 20 (i.e., polyethylene stretched or oriented at a ratio of 1:1.5 in the machine direction and having a layer thickness of 20 μm) / Reverse printing layer (e.g., as a gravure or flexographic printing layer) / Adhesive layer with an application weight of 3 g / m 2 LLDPE film stretched or oriented at a ratio of 1:1.5 in the machine direction and having a layer thickness of 100 μm according to the present invention.

[0042] Example 4 combines low-temperature sealability and optimized water vapor and gas (and especially oxygen and carbon dioxide) impermeability:

[0043] Transparent film (i.e., oriented polyethylene terephthalate with a layer thickness of 12 μm) / Reverse printing layer (e.g., as a gravure or flexographic printing layer) / Inner laminate layer (i.e., polyethylene with an application weight of 20 g / m 2 LLDP stretched or oriented at a ratio of 1:1.6 in the machine direction and having a layer thickness of 30 μm according to the present invention) / Outer laminate layer (i.e., polyethylene with an application weight of 20 g / m 2 LLDPE film with a layer thickness of 40 μm as a low-temperature sealing layer).

[0044] Example 5 combines low-temperature sealability and optimized water vapor and gas (and especially oxygen and carbon dioxide) impermeability:

[0045] Transparent film (i.e., polyethylene stretched or oriented at a ratio of 1:5 in the machine direction and having a layer thickness of 20 μm) / Reverse printing layer (e.g., as a gravure or flexographic printing layer) / Inner laminate layer (i.e., polyethylene with an application weight of 20 g / m 2 LLDP stretched or oriented at a ratio of 1:1.6 in the machine direction and having a layer thickness of 30 μm) / Outer laminate layer (i.e., polyethylene with an application weight of 20 g / m 2 LLDPE film with a layer thickness of 40 μm as a low-temperature sealing layer).

[0046] In this text, the term "low-temperature sealing layer" means that the sealing layer according to the present invention is a very thin layer in the range of 2 μm to 40 μm, preferably in the range of 3 μm to 30 μm, and particularly preferably in the range of 4 μm to 20 μm, which is formed by itself as a blown film, that is, as a single-layer blown film or as the outermost layer of a multi-layer blown film. The main advantage of the blown film used as the low-temperature sealing layer or the outermost layer of the blown film is that the material thickness of this sealing layer according to the present invention is very thin, and when the sealing fixture is applied to the outer layer, it heats up to the initial sealing temperature very quickly, that is, almost spontaneously, unlike in the prior art, where the thickness of the sealing layer is in the range greater than 50 μm, but most are even in the range of 100 μm to 140 μm, and a large amount of sealing medium must first be heated in order to also reach the initial sealing temperature on the outermost side of the laminate opposite to the visible side of the laminate.

[0047] In the context of the present invention, the initial sealing temperature is understood as the temperature at which the outer surface of the sealing layer melts, so that it is possible for this outer surface of the sealing layer to fuse with the corresponding object to be sealed.

[0048] According to Examples 4 and 5, the water vapor and gas barrier layer of the laminate is improved in an extremely advantageous manner by using an LLDPE film unidirectionally stretched in the machine direction according to the present invention, and this film has been stretched to a layer thickness of 30 μm at a draw ratio of 1:1.6.

[0049] In particular, the above Examples 3 and 5 represent particularly preferred embodiments according to the present invention because their recyclability is particularly advantageous due to the substantially pure type of structure of the described laminates.

[0050] At this point, it should be noted that all the above parts, especially the details shown in the drawings, are considered essential to the present invention when observed individually and in any combination. Their modifications are known to those skilled in the art.

[0051] List of reference numerals

[0052] 10 Stretched film

[0053] 20 Polyolefin layer / Polyethylene layer / HDPE

[0054] 30 Barrier layer material

[0055] 40 Primer layer

Claims

1. A stretch film (10), especially a stretch film for use in the production of packages, characterized in that, the stretch film (10) is uniaxially stretched in the machine direction at a draw ratio of 1.2 to 1.75, preferably at a draw ratio of 1.3 to 1.

5.

2. The stretch film according to claim 1, characterized in that, the stretch film (10) is or comprises a polyolefin layer (20), especially a polyethylene layer, preferably high-density polyethylene such as HDPE.

3. The stretch film according to any one of the preceding claims, characterized in that, the stretch film (10) is a blown film, preferably a multi-layer blown film.

4. The stretch film according to any one of the preceding claims, characterized in that, the stretch film (10) contains a barrier layer material (30), especially polyamide and / or ethylene-vinyl alcohol copolymer (EVOH).

5. The stretch film according to any one of the preceding claims, characterized in that, the stretch film (10) is formed as a composite of the following layers: polyethylene (20), especially HDPE / primer (40) / barrier layer material (30), i.e. EVOH or polyamide / primer (40) / polyethylene (20), especially HDPE.

6. A laminate, especially a laminate for use in the production of packages, characterized in that, the laminate comprises a stretch film (10) according to any one of the preceding claims.

7. The laminate according to claim 6, characterized in that, a stretch film (10) according to any one of claims 2 to 7 above, especially the stretched polyethylene film, is the sealing layer of the laminate.

8. Use of a stretch film (10) according to any one of claims 1 to 5 above for the production of a laminate, especially a packaging laminate and / or a package.

9. The use according to claim 8, characterized in that, the stretch film (10) or the outermost layer of the stretch film (10) is the sealing layer of the laminate.

10. The use according to any one of claims 8 or 9 above, characterized in that, the stretch film (10) or the outermost layer of the stretch film (10) is used to seal the package.

11. A package, especially a tubular bag package, produced using a stretch film (10) according to any one of claims 1 to 5 above or made of the stretch film and / or using a laminate according to any one of claims 6 or 7 above or made of the laminate.

12. The package according to claim 11, characterized in that, the package is made of a stretch film (10), especially a stretched polyethylene film, according to any one of claims 2 to 5 above, and is encapsulated through the stretch film (10) or the outermost layer of the stretch film (10), especially the stretched polyethylene film or the polyethylene layer, using the same type of stretch film (10) or different sealing media.

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