TECHNICAL FIELD

The invention relates to a thermoformable and recyclable packaging film for use in the packaging of food, in particular meat, meat products, milk and dairy products, seafood, and bakery products, as well as non-food products, such as medical products.

BACKGROUND

Packages are used in the food and non-food sectors, and the packages used especially for food products must be created in a way that will ensure that the products remain intact until the end of their shelf life and have certain visual criteria. Polymers with different properties are used according to the product in the package in order to obtain the properties specified in the packaging films that make up the packages. For example, EVOH as a barrier in a packaging film to be used in food products such as meat and meat products, milk and dairy products, seafood, and bakery products, a polyolefin-based compatibilizer that will allow EVOH to adhere to polyolefin, PA, which can provide heat resistance in the outer parts, PP, polyolefin, ionomer, PA, on the source side, raw materials such as EVA, Polyolefin, Plastomer, and ionomer can be used.

In addition to protecting the product and presenting a good visual to the customer, the packaging is now expected to be recyclable. In addition to being recyclable, the need for a packaging film with technical properties that ensure the proper protection of the product in the created packaging has arisen. As a standard, coextruded films made of PA and PE do not undergo the same recycling cycles due to their Tm and Tg, and these films are not considered recyclable.

As a result, all the above-mentioned problems have made it necessary to make an innovation in the related technical field.

BRIEF DESCRIPTION OF THE INVENTION

The present invention relates to a packaging film for eliminating the above-mentioned disadvantages and bringing new advantages to the related technical field. One object of the invention is to produce a recyclable packaging film with high mechanical strength and heat resistance and suitable for thermoforming.

One object of the invention is to produce a packaging film with a homogeneous structure suitable for deep drawing, at the same time, with reduced haze.

One object of the invention is to provide a packaging film with high puncture resistance.

One object of the invention is to provide a packaging film with increased thickness.

The present invention is a thermoformable and recyclable packaging film for use in the packaging of food products such as meat and meat products, milk and dairy products, seafood, and bakery products, in order to achieve all the above-mentioned objectives and which will emerge from the detailed explanation below. Its novelty is that the invention comprises; at least one outer layer on one side to provide heat resistance, at least one blocking layer on the other side to ensure adhesion, at least one barrier layer provided in the middle; a first layer group containing at least one compatibilizer layer, positioned between the blocking layer and barrier layer and the outer layer and barrier layer, connecting them to each other, and a second layer group comprising film layers with the same properties provided in its symmetry, composed of ethylene vinyl alcohol material so that the sum of the weights of the barrier layers is at most 5% of the weight of the packaging film; other film layers being composed of polyolefin-based mono materials.

In a preferred embodiment of the invention; it comprises at least one functional layer positioned between the blocking layer and the barrier layer as well as the outer layer and the barrier layer to ensure physical durability.

In a preferred embodiment of the invention; it comprises at least one base layer positioned between the blocking layer and the barrier layer, as well as the outer layer and the barrier layer to improve mechanical properties and heat interaction.

In a preferred embodiment of the invention; barrier layers are composed of ethylene vinyl alcohol material, with a maximum of 3% of the weight of the packaging film. In a preferred embodiment of the invention; the PE material used in the blocking layer comprises a plastomer having a density of 0.870 g/cm3 and a melting point of 131 ^e C and a plastomer mixture having a density of 0.902 g/cm3 and a melting point of 99 ^e C.

In a preferred embodiment of the invention; compatibilizer layers comprise linear low-density polyethylene grafted with maleic anhydride.

In a preferred embodiment of the invention; compatibilizer layers comprise a specific blend of linear low-density polyethylene and polyethylene copolymer grafted with maleic anhydride.

In a preferred embodiment of the invention; the base layers comprise linear low-density polyethylene 1 -hexene copolymer.

In a preferred embodiment of the invention; the base layers comprise a specific blend of linear low-density polyethylene and polyethylene copolymer.

In a preferred embodiment of the invention; the functional layer comprises an inner functional layer facing the blocking layer and an outer functional layer facing the outer layer, and the outer functional layer comprises a medium-density polyethylene 1 -hexene copolymer and the inner functional layer comprises a linear low-density polyethylene 1 -hexene copolymer so that the packaging film maintains its physical strength and structural properties when interacting with heat and is easier to shape.

In a preferred embodiment of the invention; the outer functional layer comprises a blend of medium-density polyethylene 1 -hexene copolymer and low-density polyethylene.

In a preferred embodiment of the invention; the inner functional layer comprises a blend of linear low-density polyethylene 1 -hexene copolymer and low-density polyethylene.

In a preferred embodiment of the invention; the outer layer packaging film comprises ethylene 1 -hexene copolymer and low-density polyethylene.

The invention is also a method for producing a thermoformable and recyclable packaging film for use in the packaging of food products such as meat and meat products, milk and dairy products, seafood, and bakery products. Its novelty is in that it comprises the steps of obtaining the first layer group and second layer group by blow extrusion method in a water- cooled extruder and blocking the same by means of pressure-applying rollers. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows a schematic view of the packaging film of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In this detailed description, the packaging film (10) of the invention is described only by means of examples that will not have any limiting effect for a better understanding of the subject matter.

The packaging film (10) of the invention is a flexible multi-layer film suitable for thermoforming for use in the packaging of food and non-food products such as meat and meat products, milk and dairy products, seafood, and bakery products. The said packaging film (10) is especially used as a sub-film for packaging. The packaging film (10) comprises a first layer group (101 ) and a second layer group (102), which turn into a singular structure when combined. The first layer group (101 ) and the second layer group (102) are configured to have the same chemical properties. The packaging film (10) is generally formed by adhering the first layer group (101) and the second layer group (102) symmetrically to each other. The layers where the first layer group (101) and the second layer group (102) adhere to each other are defined as a blocking layer (15).

The first layer group (101) and the second layer group (102) comprise a barrier layer (11 ) in the middle and a compatibilizer layer (12) on both sides of the barrier layer (11 ). The layers on the outermost side of the first layer group (101 ) and the second layer group (102) are defined as the outer layer (16). The layers lined up from the barrier layer (11) to the blocking layer (15) and the outer layer (16) are the compatibilizer layer (12), a base layer (13), and a functional layer (14). The functional layer (14) facing the outer layer (16) is the outer functional layer (142). The functional layer (14) facing the blocking layer (15) is defined as the inner functional layer (141).

In other words, when the first layer group (101 ) and the second layer group (102) are combined, the outer layer (16) is structured on both sides of the packaging film (10). The core part of the packaging film (10) is formed by the blocking layers (15). Between the blocking layers (15) and the outer layers (16), there is an inner functional layer (141), base layer (13), compatibilizer layer (12), a barrier layer (11 ), one more compatibilizer layer (12), base layer (13), and outer functional layer (142) line up symmetrically from the blocking layer (15) to the outer layer (16) The structural properties of the film layers of the packaging film (10) are described below.

Polyolefin (PO) based plastomer is used for the blocking layer (15). In an alternative embodiment of the invention, polyethylene (PE) based plastomer is used for the blocking layer (15). In another alternative embodiment of the invention, a polypropylene (PP) based plastomer is used for the blocking layer (15). In the embodiment, the blocking layer (15) has a density of 0.860 gr/cm3 - 0.940 gr/cm3. The blocking layer (15) used in an embodiment of the invention has a density of 0.860 gr/cm3 - 0.880 gr/cm3. The said blocking layer (15) is obtained by mixing two different densities of plastomer in one embodiment. In case it is obtained with two different plastomers it may contain a mix of a PE-based plastomer with a density of 0.860 gr/cm3 - 0.880 gr/cm3 and a melting point of 130 ^e C (±20 ^e C) and another PE-based plastomer mixture with a density of 0.890 gr/cm - 0.930 gr/cm3 and a melting point of 100 ^e C (±20 ^e C). Due to the material used, a blocking is obtained between the first layer group (101) and the second layer group (102).

Ethylene vinyl alcohol (EVOH) material is used in the barrier layers (11) of the packaging film (10). The ratio of the EVOH material to the total material used for the total packaging film (10) is provided at a maximum of 5% by weight. The barrier layer (11) has a thickness that will provide adequate barrier properties. This thickness is provided so that the weight of the EVOH material does not exceed 5% by the weight of the total packaging film (10). In another embodiment, this thickness is provided so that the weight of the EVOH material does not exceed 3 wt% of the total packaging film (10). The packaging film (10) thus obtained complies with the regulations for recyclable packaging made of mono material.

The compatibilizer layers (12) connect the barrier layers (11) and other polyolefin-based film layers within the packaging film (10). Since EVOH contains a polar group and polyolefins are nonpolar, the compatibilizer layers (12) are included in the packaging film (10), thereby overcoming the difficulty of co-extruding polar groups and nonpolar chains. Compatibilizer layers (12) are provided at minimum thickness. In a preferred embodiment, the compatibilizer layer (12) consists of linear low-density polyethylene grafted with maleic anhydride alone. In an alternative embodiment, the compatibilizer layer (12) is formed from a mixture of linear low-density polyethylene grafted with maleic anhydride and a polyolefin-based polymer in a certain ratio.

The base layers (13) meet the requested mechanical properties and heat interaction of the packaging film (10). Accordingly, the base layers (13) are composed of linear low-density polyethylene 1 -hexene copolymer. Alternatively, PE and PE copolymers can be used. In one embodiment, the base layers (13) are formed from a mixture of linear low-density polyethylene 1 -hexene copolymer and low-density polyethylene at certain proportions. In base layers (13), structures with higher density and homogeneous free ends are preferred compared to other layers. Thus, the heat dissipation between the layers of the packaging film (10) becomes more efficient.

Thanks to the structural properties of the functional layers (14), the physical durability of the packaging film (10) and the preservation of its structural properties when interacting with heat are ensured. In addition, forming of the packaging film (10) is facilitated by the structural feature of the functional layer (14). Since the heat source contacts the packaging film (10) from the outer layer (16) during the packaging process, the outer layer (16) of the packaging film (10) interacts the most with the heat. Therefore, the interaction with heat in the outer functional layer (142) is more than in the inner functional layer (141). Therefore, the material content of the inner functional layer and the outer functional layer (142) varies. Since high- density and straight-chain films interact with heat harder, at least one of the medium-density polyethylene 1 -hexene copolymer and low-density polyethylene or their mixtures are used in the outer functional layer (142) by using this advantage of the polymer. In the inner functional layer (141 ), linear low-density polyethylene 1 -hexene copolymer and at least one low-density polyethylene or mixtures thereof are used.

The outer layer (16) comprises ethylene 1 -hexene copolymer and low-density polyethylene and provides high heat resistance.

Except for the barrier layer (11), the other layers of the packaging film (10) are composed of polyethylene-based materials in the preferred embodiment as mentioned above. As polyolefin, any polymerized or copolymerized olefin can be used instead of polyethylene. The said olefins can be butene or octene olefin copolymers, ethylene-propylene copolymers, and butene octene terpolymers. These olefins can be supplied in linear, branched, cyclo, substituted, unsubstituted or modified forms.

The packaging film (10) is considered recyclable since the ratio of EVOH in the total packaging film (10) by weight does not exceed 5% and the other material that makes up the packaging film (10) apart from EVOH is polyolefin of the same type.

The packaging film (10) is produced by the blowing extrusion method in a water-cooled extruder. The production method mentioned is carried out using cold water at about 10 °C. After the first layer group (101) and the second layer group (102) are extruded, they are blocked and become inseparable by pressure-applying rollers without allowing them to cool. The packaging film (10) of the invention is thereby formed and acts as a single film. The number of layers of the packaging film (10) created is increased with this production method. The resulting packaging film (10) has 18 layers. The packaging film (10) can be produced in a thickness between 120 microns and 500 microns. With the increase in thickness, the amount of deep drawing, mechanical strength, and hardness of the film increase. In addition, thicker packaging films (10) are preferred for packages that are more difficult to pack, in other words, with hard and sharp corners. The resulting packaging film (10) also provides high puncture resistance, and a film that is easy to thermoform is obtained because it is obtained symmetrically from the combination of the first layer group (101 ) and the second layer group (102). In this production method, since the packaging film (10) coming out of the extruder head cools rapidly, more amorphous regions are formed on it compared to other methods, and the packaging film (10) has a transparent appearance. In addition, the flexibility of the packaging film (10) increases, and it becomes easier to form.

The polymers described in this specification for the outer layer (16) and the outer functional layer (142), which are the layers used in the layers close to the outer environment of the packaging film (10) of the invention act to increase the resistance against external factors such as heat, physical, and chemical resistance. The polymers mentioned in this specification for the base layer (13) and functional layer (14), which are the layers in the middle of the packaging film (10) act to increase mechanical strength and facilitate formability.

Packaging film (10) with the structural details given above has low haze, high heat resistance, high puncture resistance, and high breaking strength and can work in forming machines in wide temperature ranges. The packaging film (10) can take form in forming machines at forming temperatures between 90-130 °C and forming times between 0.5-3 seconds. The haze value of the packaging film (10) before forming can be between 5-20% depending on the thickness and structure.

The following are the comparative test results for various thicknesses of the packaging film containing polyamide and polyethylene, and the packaging film (10) of the invention. The puncture resistance test was performed as per ASTM F 1306 standard; the haze was measured as per ASTM D1003 standard, and the modulus of elasticity was measured as per ASTM D882 standard. MD denotes the machine direction and CD donates the machine width direction.

Table 1 - Comparative test results of PA-PE structure and packaging film of the invention

According to the test results given in Table 1 , although polyamide (PA) is not used in the packaging film (10), the details of which are explained above, it is seen that the values do not deviate significantly and are preserved. When analyzed in detail, it is observed that haze does not increase; the puncture resistance and elasticity modules do not decrease significantly and still have close values. This shows that while the packaging film (10) of the invention is suitable for recycling, it also meets the requested results and the values do not change at an unacceptable rate.

The protection scope of the invention is given in the attached claims and cannot be strictly limited to what has been described in this detailed description for illustrative purposes. It is clear that those skilled in the art can put forth similar embodiments in the light of what has been described above, without departing from the main theme of the invention.

REFERENCE NUMERALS IN THE FIGURES

10 Packaging film

101 First layer group

102 Second layer group

11 Barrier layer 12 Compatibilizer layer

13 Base layer

14 Functional layer

141 Inner functional layer

142 Outer functional layer 15 Blocking layer

16 Outer layer