Patent Description:
Plastic packaging, in particular food-grade plastic packaging, is a field with a huge impact on the market, due to the extensive need of ways of packing, stocking and, regarding the food, preserving it, and due to the environmental impact of the packaging productions.

Lately, there are various packaging options available on the market.

All the packaging options present a lot of environmental issues. <CIT> relates to co-extruded polyethylene film structure that is suitable for use in the preparation of a stand up pouch.

In fact, the European Community in February <NUM> issued a recommendation directing member states to ensure that by <NUM> all packaging is designed for recycling. During operations, it is necessary to redesign the plastic packaging to ensure that it meets the original needs and is sustainable. In the case of plastic, the product is sustainable only if it is recyclable and if the recycling process has a low environmental impact.

To be sustainable, plastic packaging must be recyclable, therefore the following conditions must be met:.

The packaging currently on the market consists of multi-material films, e.g. an outer layer of OPA (biaxially oriented polyamide), PET (polyethylene terephthalate), BOPP (biaxially-oriented polypropylene) and an inner layer of PE, coupled with several types of additives, such as, depending on the need, antibacterial, antioxidant, toughening, homogenizing, opening, slip agents, and adhesive systems in between.

In most of those known multilayer multi-material assembly, adhesive systems must be comprised and are essential, but this complicates the subsequent recycling process. Therefore, at the end of their shorter life, they are delivered in the undifferentiated fraction.

The presence of specific adhesive systems is mandatory since the materials to be employed in said multilayers are chemically different and need a strong "gluing" additive for the materials assembly.

This type of packaging born in the eighties was designed with the aim of protecting, distributing, and promoting the product, but did not consider the recycling process that would need to follow.

In view of this problem, today it is necessary to reinvent plastic packaging to guarantee the same objectives, such as durability, versatility and customization, lightness and chemical resistance, gas and moisture barrier, taking into account at the same time its sustainability and recyclability.

In this sense, another problem rises, when redesigning plastic packaging, it is essential to keep in mind that it must ensure the same performance during use on the current existing packaging machine of final packaging users. Otherwise, a large investment and long times are required for the redesign, modification and replacement of the packaging machinery.

Among the most commonly used machines for plastic packaging purposes are the so-called "Form, Fill & Seal" machines. They are versatile types of machines, which pack an almost unlimited range of different products into bags delivering high performance and reliability. They have the remarkable advantage that the steps of forming, filling and sealing happen in a single work process.

The advantages of this "Form Fill & Seal" packaging machine are connected to the fact that it allows to reach packaging speeds above <NUM> packs/min, therefore it is defined as high speed form fill seal packaging machine. With regard to the transversal sealing, this packaging machine can have a rotary sealing unit called "Long Dwell", where the sealing bars during the sealing phase accompany the advancement of the film before triggering the cut and then the release of the package. The Long Dwell rotary system with straight section has several strengths, which allow to make absolutely hermetic welds at high speed due to the longer contact time (the sealing bars during the welding phase accompany the advancement of the film, increasing its residence time near the heat source) and it avoids stressing the sealing when the product falls into the package, thus reducing the possible negative effects of the violent collision of the falling product against stationary sealing masses.

Other widely used packaging systems seal a lidding film on a tray. The tray can be thermoformed in line by the packaging machine (also called as thermoforming machines) or preformed (also called tray sealer machines).

In addition to the previous systems, there are the so-called "Pouch Fill & Seal machines" where the preformed pouches are filled and sealed.

Nevertheless, these packaging machines have been conceived to process multilayer multi-material assembly and this is in contradiction with the aim of recycling the entire package, that should be manufactured with the same polymer. The recyclability of the final product has a remarkable importance; therefore, it is still required the development of environmentally friendly materials.

Furthermore, even if the same material is used, thus solving the recycling problem, the packaging machine requires specific changes to guarantee the integrity of the final packaging, thus increasing the costs of the packaging.

A first attempt to solve the problem by using the same chemical nature polymer was to reduce the contact time during the welding step in the packaging machines. This is only possible by increasing the temperatures of the sealing bars in order to make the welding process as fast as possible, but this solution was considered not convenient by the packaging final users.

The object of the invention is hence to have a final packaging that can be recycled, while maintaining the same apparatuses and devices already used in the market for packing the products and with same performances.

The inventors have surprisingly found out a new multilayer mono-material PE assembly that can be used in the goods packing machines, with no relevant adaptation, thus obtaining final packaging having optimal mechanical properties and that can be recycled. The final packaging showed lots of remarkable features, such as durability, versatility and customization, lightness and chemical resistance, gas and moisture barrier, while being at the same time environmentally sustainable and recyclable with low effort.

Therefore, in a first aspect the invention relates to a multilayer mono-material PE assembly, comprising at least two layers:.

wherein the difference of the melting point (ΔTm) of the first layer with respect to the second layer is in the range from <NUM> to <NUM>.

In an advantageous and preferred aspect, in the multilayer mono-material PE assembly the difference of the melting point (ΔTm) of the first layer with respect to the second layer is in the range from <NUM> to <NUM>.

In a more advantageous aspect in the multilayer mono-material PE assembly the second layer comprises more than one sublayer, preferably from <NUM> to <NUM> sublayers, which are equal or different with respect to each other.

In a further advantageous aspect, the multilayer mono-material PE assembly further comprises at least one third layer that is a printed layer and/or a varnish layer and/or a metallized layer, being the at least one third layer placed on the first layer and/or between the first and the second layer.

The multilayer mono-material PE assembly contains the first layer of HDPE having a density value equal to or higher than <NUM>/cm<NUM>.

The inventors of the present invention have surprisingly found that they could replace well known multi-material assembly with a multilayer mono-material PE assembly, comprising a polyethylene (PE) blend, thus granting an assembly made of one polymer and avoiding adhesive systems. The multilayer assembly of the invention is advantageously a mono-material assembly, which allows the recycling of the complete material, while reducing or eliminating the amount of contaminants such as adhesive system.

Moreover, the inventors have surprisingly noticed that the specific composition of the PE blend, with the specific concentrations of the single PE-based components, allowed the second layer, comprising at least one sublayer of said polyethylene (PE) blend, to adhere to the first layer, consisting of HDPE, perfectly, strongly and easily when the at least two layers are made of the same PE-based material are present.

Without being bound to any theory, the inventors deem that the reason behind it lies in the specific PE blend of the final second layer with a specific melting temperature (Tm), and that is assembled with the first layer.

In fact, the specific combination of high-density polyethylene (HDPE) having a density value equal or higher than <NUM>/cm<NUM> of the first layer and a second layer comprising a polyethylene (PE) blend with simply lower melting temperature is not enough to ensure a very good adhesion of the layers, without any damage to any of the layers during any of the production steps, especially during welding and sealing.

The inventors noticed that, by tuning the specific composition, namely the PE-based compounds, namely compounds i) and ii) and their mixtures, chosen for the blend, their combination and their amounts, could lead to improved properties and specifically could lead to a layer which maintained or even improved all the mechanical properties of the layers of the prior art, as will be shown in the following. Hence, the PE blend of the invention specifically ensures a remarkable adhesion with the first layer, while being at the same time resistant and flexible and ensuring, when employed in the final multilayer mono-material PE assembly of the invention, good mechanical properties and good recyclability, without any damage to the first layer.

Furthermore, the inventors have surprisingly found out a new multilayer mono-material PE assembly that can be used in the goods packing machines, with no relevant adaptation, thus obtaining final packaging having optimal mechanical properties and that can be recycled. The final packaging showed lots of remarkable features, such as durability, versatility and customization, lightness and chemical resistance, gas and moisture barrier, while being at the same time environmentally sustainable and recyclable with low effort.

The PE-blend of the multilayer mono-material PE assembly of the invention is employed in an optimized extrusion process of production, thus obtaining the multilayer mono-material PE assembly.

In a further aspect the invention concerns a process for preparing the multilayer mono-material PE assembly.

Therefore, the invention relates to a process for preparing the multilayer mono-material PE assembly according to the invention, comprising the steps of:.

As it will be evident from the experimental part the inventors, while optimizing the extrusion process of the invention, tried different conditions for the extrusion group in order to find the optimal final product.

It was surprising that all the parameters usually applied with the prior art multilayer multi-material assembly should have been modified to become milder, thus rendering the process more convenient with less harsh conditions.

The improved process was able to avoid the numerous issues encountered, such as dimensional instability of the multilayer mono-material PE assembly with subsequent film width shrinkage, specifically around <NUM> % shrinkage in transversal direction, and a large reduction in longitudinal direction. While changing the parameters, the inventors were able to obtain a remarkable improvement of the dimensional stability of the multilayer mono-material PE assembly, thus completely avoiding the assembly width shrinkage as it will be evident from the evaluation of the mechanical properties of the multilayer mono-material PE assembly of the invention.

Through the final optimized extrusion process of the invention, it is now possible to obtain a stable, flexible, strong and recyclable multilayer mono-material PE assembly, having comparable if not even better technical and mechanical features, with respect to the prior art multilayer multi-material PE assembly.

Therefore, the inventors of the present invention have surprisingly found that, by employing the polyethylene (PE) blend of the invention as second layer on a first layer of the same chemical nature, they could replace standard multilayer multi-material assembly, providing with a multilayer mono-material PE assembly, reaching the same objectives, such as durability, versatility and customization, lightness and chemical resistance, gas and moisture barrier, taking into account at the same time their sustainability and environmental impact.

Surprisingly, all these features have been reached by using a specific polyethylene (PE) blend for preparing the multilayer mono-material PE assembly of the invention, without the need of non PE-based components normally employed for those packaging, such as adhesive systems, OPA, PET, PP, thus being recyclable.

Therefore, the multilayer mono-material PE assembly according to the invention is without an adhesive system.

Without being bound to any theory and as it will be apparent from the detailed description and from the examples, the features of the multilayer mono-material PE assembly of the invention depend on the specific polyethylene (PE) blend used and said features allow to guarantee the same tightness of the packaging, storage and handling of the final product, with respect to the known multilayers multi-materials film.

Therefore, the multilayer mono-material PE assembly of the invention is obtainable by the process as above outlined.

The final structure and specifically the materials of the multilayer mono-material PE assembly allow to use it in the field of the packaging. Preferably it is used for packing goods, preferably food.

Furthermore, advantageously the multilayer of the invention allowed to pack by using standard packaging machines.

Surprisingly, the multilayer PE assembly of the invention allowed to directly use these packaging machines without any kind of change.

When the inventors realized that they could use as same chemical nature polymer, they encountered a problem during the packaging step, specifically, if any type of multilayer mono-material PE assembly had been used, the first layer and the second layer would have been very similar. This meant that for a multilayer mono-material PE assembly, while sealing the layers, the layers contact area underwent excessive softening, which compromised its integrity and did not allow a proper release for the sealing jaws. This phenomenon would have seriously affected the quality and dimensional stability of the sealed area.

The inventors surprisingly realized that, when the polyethylene (PE) blend is used as second layer in the multilayer assembly on a first layer of HDPE of the same chemical nature, they could overcome this problem, thus ensuring that the material being sealed responds very quickly, avoiding the softening of the external HDPE support. The second layer comprising the PE blend thus adheres perfectly and strongly to the first layer of HDPE, without affecting it nor damaging it in any step of the production, especially during welding and sealing, of the final multilayer mono-material PE assembly.

Lastly, the multilayer mono-material PE assembly is meant to be used in the packaging field, therefore the invention further relates to a use of said multilayer mono-material PE assembly in the packaging field.

The difference of melting points between the first and the second layer allowed to use the packaging machines at temperature capable to weld the packaging without affecting the HDPE film of the multilayer PE assembly.

Advantageously, these packaging machines with the multilayer PE assembly of the invention can work in milder conditions than with the prior art multilayer assembly.

Therefore, the invention also concerns the use of the multilayer mono-material PE in a packaging machine for packing goods, preferably food.

The present invention therefore relates to a multilayer mono-material PE assembly, comprising at least two layers:.

In the present invention, with the following terms:.

Preferably the HDPE is a mono oriented HDPE, mainly oriented in the longitudinal direction with MDO (Machine Direction Orientation) technology, having a density of <NUM>/cm<NUM>.

The specific orientation of the HDPE, specifically MDO, represent a remarkable parameter for the purposes of the present invention.

Firstly, as deemed by the inventors and as will be evident from the following experimental part, the preferred use of a specifically oriented MDO-HDPE allows the final multilayer mono-material of the invention to have a load at break value comparable to the one of the known multi-material multilayers of the prior art and higher than the one reached with an undirected HDPE (taking into account the same HDPE thickness).

Secondly, the use of the specifically oriented MDO-HDPE is also dictated by the need to have a precise control of the ΔTm of the first layer with respect to the second layer.

In fact, the MDO treatment on the HDPE film increases the Tm, thus also increasing the ΔTm between the two layers.

The HDPE has preferably a thickness in the range from <NUM> to <NUM>, more preferably about <NUM>. For example, according to the invention a suitable HDPE is available on the market, from the Supplier "Termoplast" with code "Crystal PE EX" product.

The preferred HDPE had at least a corona treated surface with surface tension ≥ <NUM> dynes/cm prepared for the anchoring of printing inks and a plain surface with surface tension ≤ <NUM> dynes/cm.

The preferred HDPE has the following mechanical characteristics, calculated according to ASTM D882:.

The multilayer mono-material PE assembly of the invention comprises the second layer made of the polyethylene (PE) blend of the invention.

In the first embodiment, the second layer comprises at least one sublayer comprising a polyethylene (PE) blend, said PE blend comprising with respect to the total amount of each sublayer:.

An example of said first embodiment is represented in <FIG>.

In a second embodiment the second layer comprises at least one sublayer comprising a polyethylene (PE) blend, said PE blend comprising with respect to the total amount of each sublayer:.

An example of said second embodiment is represented in <FIG>.

Said component ii) is a polyethylene copolymer selected from the group consisting of polyolefin plastomer (POP), ethylene-vinyl acetate (EVA), ethylene acrylic acid (EAA), ethylene n-butyl acrylate (EBA), ethylene ethyl acrylate (EEA), ethylene <NUM>-ethyl hexyl acrylate (EEHA) and ethylene-methacrylic acid (EMAA) and has the ethylene monomer higher than or equal to <NUM>% wt.

In fact, the inventors deem that a higher concentration of the ethylene monomer is able to assure the PE-based composition of the component ii) and thus the full recyclability of the multilayer mono-material of the invention.

Preferably, the at least <NUM>% of polyethylene component is ethylene-vinyl acetate (EVA) or polyolefin plastomer (POP), more preferably POP.

In a third embodiment the second layer comprises at least one sublayer comprising a polyethylene (PE) blend, said PE blend comprising with respect to the total amount of each sublayer:.

An example of said third embodiment is represented in <FIG>.

Both, component ii) and iii) are in a concentration of at least <NUM>% wt.

The concentration has a remarkable effect on both the chemical and the mechanical properties of the final PE blend, as will be also clear from the experimental part.

In fact, the inventors deem that by decreasing the concentration, at values lower than <NUM>% wt, of the component ii) and iii), the seal initiation temperature (SIT) would be affected. Specifically, said temperature (SIT) would be reduced. Thus, the melting temperature (Tm) of the blend will be reduced, hence decreasing the difference of melting points (ΔTm) of the first layer with respect to the second layer. As will be evident from the following, the difference of melting points (ΔTm) of the first layer, consisting of HDPE, with respect to the second layer, comprising the PE blend, has to be comprised in a specific range, in order to activate the second layer comprising the PE blend, especially during the sealing and welding step, and to enable the second layer to adhere to the first layer, consisting of HDPE, without melting it or damaging it, while keeping stable and high the mechanical properties. Moreover, the component ii) is in a concentration of at least <NUM>% wt, in order to ensure good sealing properties and good stress resistance, as will be evident from the experimental part.

In a preferred embodiment of the invention the second layer comprises more than one sublayer, more preferably from <NUM> to <NUM>, that can be equal or different with respect to each other.

Advantageously, the second layer can further comprise an additive selected from a coloring agent, a colored masterbatch, a TiO<NUM> masterbatch, a slip agent, an anti-blocking agent, an antifogging agent, UV-barrier additive and mixture thereof, preferably in the total amount from <NUM> to <NUM>% wt with respect to the total weight of the sublayer.

The multilayer mono-material PE assembly according to the invention in the sublayer of the second layer contains the polyethylene resin having a density value in the range from <NUM> to <NUM>/cm<NUM>. Preferably said polyethylene resin is LDPE having a density of <NUM>/cm<NUM>, more preferably in an amount from <NUM>% to <NUM>%, even more preferably from <NUM>% to <NUM>% wt, still more preferably of about <NUM>%.

Preferably, the polyethylene resin is generally known on the market as LDPE. An example is LPDE sold by Ineos with product code 23L430.

The multilayer mono-material polyethylene assembly according to the invention, in the sublayer of the second layer contains the polyethylene component. Preferably said polyethylene component is i), i.e. it is a very low-density polyethylene (VLDPE) and/or an ultra low-density polyethylene (ULDPE) and having a density value ≤ <NUM>/cm<NUM>, more preferably is very low-density polyethylene (VLDPE), still more preferably in an amount equal to or higher than 60wt%.

In a further preferred and advantageous embodiment, the second layer comprises a polyethylene (PE) blend, wherein said PE blend comprises, preferably consists of, a very low-density polyethylene (VLDPE) having a density value ≤ <NUM>/cm and suitable food-grade additives.

In other words, the multilayer mono-material PE assembly, according to this embodiment comprises:.

Among the suitable food-grade additives the following can be cited: food-grade coloring agents, food-grade colored masterbatches, food-grade TiO<NUM> masterbatches, food-grade slip agents, food-grade anti-blocking agents, food-grade antifogging agents and/or food-grade UV-barrier additives.

Preferably, said food-grade additives are selected from a food-grade colored masterbatch, a food-grade slip agent and their mixture, more preferably a masterbatch white, in a concentration of <NUM>%, and/or a masterbatch slip, in a concentration of <NUM>%, with respect to the total weight % of the PE blend.

In a more preferred embodiment, the multilayer mono-material PE assembly according to the invention consists of:.

In the multilayer mono-material PE assembly the difference of the melting point (ΔTm) of the first layer with respect to the second layer is in the range from <NUM> to <NUM>, preferably <NUM> to <NUM>.

Without being bond to any theory the inventors deem that this specific polyethylene (PE) blend, when used as second layer in a multilayer assembly on a first layer of HDPE, could overcome the temperature difference problems, ensuring that the material being sealed responds very quickly avoiding the softening of the first layer of the same chemical nature.

In fact, the inventors have noticed that the specific composition of the PE blend, with the specific concentrations of each single PE-based component, allowed the second layer, comprising at least one sublayer of said polyethylene (PE) blend, to be easily activated, especially during the sealing and welding step, and to completely and strongly adheres to the first layer, consisting of HDPE, without melting it or damaging it, while keeping stable and high the mechanical properties, even in this case, when the two layers are made of the same PE-based component.

The multilayer mono-material PE assembly according to the invention further comprises at least one third layer that is a printed layer and/or a varnish layer and/or a metallized layer, being one independently to the other, the at least one third layer placed on the first layer and/or between the first and the second layer. The multilayer mono-material polyethylene assembly can comprise a further material selected from the group consisting of EVOH (Ethylene vinyl alcohol), PVOH (polyvinyl alcohol), PVDC (polyvinylidene chloride), a SiO<NUM> based ceramic material, a Al<NUM>O<NUM> based ceramic material, a SiO<NUM>/Al<NUM>O<NUM> based ceramic material, a metallization material and a gas barrier material. Said further material is preferably in the form a coating, for example a EVOH coating, PVOH (polyvinyl alcohol) coating, a PVDC (polyvinylidene chloride) coating, a SiO<NUM> based ceramic coating, a Al<NUM>O<NUM> based ceramic coating, a SiO<NUM>/Al<NUM>O<NUM> based ceramic coating, a metallization coating or a gas barrier coating. More preferably the further material is EVOH (Ethylene vinyl alcohol).

This further material is present in the final multilayer mono-material PE assembly of the invention in an amount not more than <NUM>% wt, more preferably <NUM>% wt, with respect to the total amount of the final PE assembly. Still more preferably, this further material is present in the final multilayer mono-material PE assembly of the invention in an amount not more than <NUM>% wt with respect to the total amount of the final PE assembly.

The inventors deem that a low concentration of said further material, specifically equal or lower than <NUM>% wt, is to be preferred to assure the perfect balance between adhesivity and peal ability of the multilayer mono-material of the invention, while keeping the food grade property of the latter.

Said further material is present independently in the first layer, on the first layer or in the second layer as a further sublayer or it is present in the further third layer. Preferably, the third layer is a varnish layer having a heat resistance equal to or higher than <NUM>.

This third layer facilitates the release from the sealing jaws during the process of the invention. More preferably, this third varnish layer has a thickness equal or lower than <NUM>, more preferably in the range from <NUM> to <NUM>.

In another embodiment this varnish layer is a tactile-effect varnish layer and has preferably a thickness equal or lower than <NUM>, more preferably in the range from <NUM> to <NUM>.

Said very thin third layer does not adversely affect the single-material recycling or the final properties of the recycled product, such as imperfections, surface defects, dots and/or infusions, nor on obtaining a single homogeneous phase. Moreover, such a low thickness of the coating layer guarantees a faster detachment of the multilayer mono-material PE assembly in contact with the sealing bars, thus improving runnability during the packaging phase as it will be more evident in the experimental part.

The multilayer mono-material PE assembly according to the invention has preferably a thickness in the range of at most <NUM>.

In a first embodiment, the multilayer mono-material PE assembly according to the invention has preferably a thickness in the range from <NUM> to <NUM>.

In another embodiment when the varnish layer is a tactile-effect varnish layer, then the multilayer mono-material PE assembly according to the invention has preferably a thickness in the range from <NUM> to <NUM>.

Advantageously, the multilayer mono-material PE assembly according to the invention is without an adhesive system.

As mentioned, the inventors deem that this specific polyethylene (PE) blend, when used as second layer in a multilayer assembly on a first layer of HDPE, could overcome the temperature difference problems, ensuring that the material being sealed responds very quickly avoiding the softening of the first layer of the same chemical nature. Hence, the second layer, comprising the PE blend can be easily activated, especially during the sealing and welding step, completely and strongly adheres to the first layer, consisting of HDPE, without melting it or damaging it, while keeping stable and high the mechanical properties, even in this case, when the two layers are made of the same PE-based component.

A preferred example of the multilayer of the invention having the first, the second and the at least one third layer is represented in <FIG>.

Therefore, the invention relates to a process for preparing the multilayer mono-material PE assembly comprising the steps of:.

Preferably, the process is a continuous process.

The process of the invention in step d) comprises at least one extruder.

In step d) optional additives can be present.

Said additives can be selected from a colouring agent, a coloured masterbatch, a TiO<NUM> masterbatch, a slip agent, an anti-blocking agent, an antifogging agent, UV-barrier additive and mixture thereof, preferably in the total amount from <NUM> to <NUM>% wt with respect to the total weight of the sublayer.

Among them, TiO<NUM> master batch and a slip agent or a mixture thereof are preferred. In the preferred not limiting example of the process of the invention in step d) there are two (screw) extruders, Extruder A and Extruder B.

As above indicated, the "extrusion group" of the step b) is the heart of the "extrusion coating plant" and it consists in at least one extruder. In the preferred embodiment, in the extrusion group two screw extruders (Extruder A and Extruder B) are present. They convey the extrudate, through a feed block to the extrusion flat die, from which an extrudate blade comes out and can be poured on a support as represented in <FIG>. The extrusion group contains also the "Chill roll - Nip roll unit", i.e. a calendering system, wherein the first layer to be coated is fed continuously from an unwind reel over the rubber pressure roll into the nip where the laminate is formed by pressing the two layers together.

In the setting parameters of the extrusion group applied in step f), the temperature profile of the at least one extruder is from <NUM> to <NUM>, preferably <NUM> to <NUM>. More preferably the temperature profile for the at least one extruder has temperature steps of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

Advantageously, the extrusion group position is at a value of Air-Gap of <NUM> the feed block temperature is at a value of <NUM>, and the extrusion flat die temperature is at a value of <NUM>-<NUM>, the Chill-Roll calender temperature is at a value in the range from <NUM> to <NUM>, preferably it is at a value of <NUM>, the Chill-Roll calender pressure is at a value of <NUM> bar (<NUM> atm) and the die offset is at a value of -<NUM>.

Advantageously, the process of the invention can provide for a step a') before step a). In a step a'), the first layer can be coated with at least one third layer that can be one or more of a printed layer, a varnish layer and a metallized layer. Therefore, the at least one third layer can be present on the first layer before the process of the invention.

Preferably step e) of extruding the second layer comprising at least one sub-layer of at least one PE blend takes place directly on the first layer or directly on the at least one third layer.

Advantageously, the at least one third layer is made of a further material selected from the group consisting of EVOH (Ethylene vinyl alcohol), PVOH (polyvinyl alcohol), PVDC (polyvinylidene chloride), a SiO<NUM> based ceramic material, a Al<NUM>O<NUM> based ceramic material, a SiO<NUM>/Al<NUM>O<NUM> based ceramic material, a metallization material and a gas barrier material. More preferably the further material is EVOH (Ethylene vinyl alcohol).

When the third layer is a printed layer, the third layer can be deposited on the first layer through a rotogravure technology. In another embodiment, the step a') of providing the printing layer can be carried out through flexographic technology, offset UV or EB, digital printing or other types of printing suitable for polyolefin supports.

Before step a), in a step a"), or before d) in a step d)' the first layer can be coated with a primer additive, able to increase the grip of the at least one polyethylene (PE) blend of the second layer on the first layer of the multilayer mono-material PE assembly of the invention.

As it will be evident from Example <NUM> of the experimental part the inventors, while optimizing the extrusion process of the invention, tried different conditions for the extrusion group, in order to find the optimal final product.

It was surprising that all the parameters usually applied with the prior art multilayer assembly should have been modified to become softer, thus rendering the process more convenient with less harsh conditions.

For example, the linear speed was reduced from <NUM>/min to <NUM>/min. The inventors also developed new Chill-roll calender temperatures and pressures, respectively decreasing the first from <NUM> to <NUM> and the second from <NUM> bar (<NUM> atm) to <NUM> bar (<NUM> atm). Even the feed block temperature had to be adjusted, decreasing it from <NUM> to <NUM>-<NUM> and the two temperature profiles of the two Extruders A and B in the preferred embodiment had to be tuned in order to find the specific temperature steps above described.

The quenching step f) is a cooling step from <NUM> to <NUM>, preferably from <NUM> to <NUM>, still more preferably from <NUM> to <NUM>.

All those conditions have been tested and changed in order to succeed in obtaining an improved process, avoiding the numerous issues encountered, such as dimensional instability of the multilayer mono-material PE assembly with subsequent film width shrinkage, specifically around <NUM> % shrinkage in transversal direction, and a large reduction in longitudinal direction. While changing the parameters, the inventors were able to obtain a remarkable improvement of the dimensional stability of the multilayer mono-material PE assembly, thus completely avoiding the film width shrinkage as it will be evident from the evaluation of the mechanical properties of the multilayer mono-material PE assembly of the invention.

Through the final optimized extrusion process of the invention, it is now possible to obtain a stable, flexible, strong and recyclable multilayer mono-material PE assembly, having comparable if not even better technical and mechanical features, with respect to the prior art multilayer multi-material assembly.

Therefore, the inventors of the present invention have surprisingly found that, by employing the PE blend as second layer on a first layer of the same chemical nature, they could replace standard multilayer multi-material assembly, providing with a multilayer mono-material PE assembly, reaching the same objectives, such as durability, versatility and customization, lightness and chemical resistance, gas and moisture barrier, taking into account at the same time their sustainability and environmental impact.

Surprisingly, all these features have been reached by using a multilayer mono-material PE assembly of the invention, without the need of non PE-based additives normally employed for those packaging, such as OPA, PET, PP, EVOH, thus being recyclable.

The final structure and specifically the materials of the multilayer mono-material PE assembly allow to use it in the packaging field.

Furthermore, advantageously, the multilayer mono-material PE assembly of the invention allowed to pack goods by using standard packaging machines. Therefore, the multilayer mono-material PE assembly is used in a packaging machine for packing goods, preferably being said goods food.

This packaging machine starts from a plastic film wound on a reel, wraps the same around a forming tube, overlaps the edges and sealing the ends, seals the packages with the product (food) to be packaged inside. The essential parts of a packaging machine are a power supply group, a reel holder group, a longitudinal welding group, a transversal welding group. The main elements of a packaging machine are undoubtedly the longitudinal and/or transversal sealing groups, in general the most commonly used welding methods in the packaging sector are a hot bar welding, a heat impulse welding, a hot wire welding, an ultrasonic welding and a cold welding. Among the types of welding, the most widespread is hot bar welding, which is based on the properties of thermoplastic materials of being sensitive to heat.

As explained in detail in Example <NUM>, surprisingly the multilayer mono-material PE assembly of the invention allowed to directly use traditional packaging machines without any kind of change, for example "Form Fill & Seal" machines.

Without being bound to any theory, the inventors deem that the specific second layer, comprising the PE blend, of the multilayer mono-material PE assembly has a sufficient melting temperature difference with respect to the first layer, consisting of HDPE, so as to act on the speed in the sealing phase of the multilayer mono-material PE assembly, thus ensuring that the final multilayer mono-material PE assembly of the invention, while being sealed, responds very quickly, thus avoiding the softening of the first layer.

Hence, the second layer, comprising the PE blend can be easily activated, especially during the sealing and welding step, completely and strongly adheres to the first layer, consisting of HDPE, without melting it or damaging it, while keeping stable and high the mechanical properties, even in this case, when the two layers are made of the same PE-based component.

Therefore, the invention provides for a multilayer mono-material PE assembly, wherein the difference of melting points (ΔTm) of the first layer with respect to the second layer in the range from <NUM> to <NUM>, preferably <NUM> to <NUM>.

Specifically, the first layer showed a melting point of <NUM>-<NUM>, preferably <NUM>-<NUM> and the second layer a melting point lower than <NUM>. The difference of melting points between the first and the second layer allowed to use all the traditional packaging machines, preferably "Form Fill & Seal" machines, at temperatures capable to weld the packaging without affecting the HDPE film of the multilayer mono-material PE assembly.

Advantageously, the packaging machines with the multilayer mono-material PE assembly of the invention can work in milder conditions than with the prior art multilayer multi-material assembly.

Therefore, the invention also concerns the use of the multilayer mono-material PE for packing goods, being preferably said goods food. In an advantageous embodiment, the used packaging machine is a "Form, Fill & Seal" packaging machine.

The invention will be further detailed with the following experimental part, reporting examples and tests on the specific PE blend and multilayer mono-material PE assembly of the invention.

The following raw materials have been provided:.

Two different polyethylene (PE) blends, namely PE blend A and PE blend B, were provided in the amounts reported in the Table <NUM>.

A film of high density polyethylene having a density value equal to or higher than <NUM>/cm<NUM>, specifically a mono oriented HDPE layer, mainly oriented in the axial direction with MDO technology, having a density of <NUM>/cm<NUM> and having a thickness of <NUM> was provided. The specific HDPE was available on the market, from the Supplier "Termoplast" with code "Crystal PE EX" product.

The HDPE had a corona treated surface with surface tension ≥ <NUM> dynes/cm prepared for the anchoring of printing inks and a plain surface with surface tension ≤ <NUM> dynes/cm. Said film had the following mechanical characteristics, calculated according to ASTM D882:.

The multilayer mono-material PE assembly was prepared by using an extrusion coating plant as generically represented in <FIG>.

With reference to <FIG>, the HDPE film, was wound on a reel and placed on the unwinder of an extrusion coating plant. Through a series of "film guide" rollers the HDPE film was conveyed to the core of an extrusion coating plant, i.e. the extrusion group. The latter, represented in detail also in <FIG>, comprised an extruder A, an extruder B, a feed block, an extrusion flat die and a Chill roll - Nip roll unit. The PE blend A and the PE blend B of Example <NUM> have been uploaded separately into two screw extruders, namely Extruder A and Extruder B, and conveyed through a feed block to the flat die, from which an extrudate made of two sublayers (sublayer A and sublayer B) came out and was poured directly on the HDPE film, thus obtaining a PE assembly comprising a second layer made of two sublayers, from blend A and blend B, respectively.

The following Table <NUM> represents the setting parameters of the extrusion group:.

The HDPE first layer received the casting of extrusion on its plain surface and, by means of a calendaring system, consisting in applying a mutual pressure between two rolls, named Chill roll- Nip roll and represented both in <FIG>, it was cooled down at room temperature with a pressure of <NUM> bar (<NUM> atm), thus obtaining the multilayer mono-material PE assembly of the invention.

This multilayer mono-material PE assembly had a final grammage of <NUM>/m<NUM> ± <NUM>/m<NUM>.

The same materials and procedure as detailed in Example <NUM> was followed, but a step of printing the HDPE film was done before the preparation of the multilayer mono-material PE assembly.

Specifically, the HDPE film has previously been treated with a printing process "in line", thus printing polyurethane inks, such as VarioLam AE series by Flint Group Italia S. , and a PVB based overprint varnish. The HDPE used was then a printed HDPE film.

The multilayer mono-material PE assembly was hence prepared by using an extrusion coating plant as generically represented in <FIG>.

With reference to <FIG>, the HDPE film, thus externally printed, was processed as in example <NUM>.

The HDPE first layer received the casting of extrusion on its plain surface and, by means of a calendaring system, consisting in applying a mutual pressure between two rolls, named Chill roll- Nip roll and represented both in <FIG>, it was cooled down at room temperature with a pressure of <NUM> bar (<NUM> atm), thus obtaining the multilayer mono-material PE assembly of the invention, as shown in <FIG>.

The first layer of the obtained multilayer mono-material PE assembly had a melting point of <NUM> -<NUM>, preferably of <NUM>-<NUM> and the second layer of <NUM>-<NUM> as measured with conventional techniques, specifically with DSC (Differential Scanning Calorimetry) model <NUM> of Perkin Elmer.

A PE blend with linear low-density polyethylene (LLDPE) in place of very low-density polyethylene (VLDPE) of the blend of the invention was prepared. Specifically, the following raw materials have been provided:.

Two different PE blends, namely PE blend A for Extruder A and PE blend B for Extruder B, have been provided as in Example <NUM> and reported in Table <NUM>.

A multilayer mono-material PE assembly was then prepared according to Example <NUM> in the coating extrusion plant of <FIG> and having the extrusion group of <FIG>.

The multilayer mono-material PE assembly was then obtained as in Example <NUM> and named as comparative multilayer mono-material PE assembly <NUM>.

The same raw materials of Table <NUM> were used for preparing the Blend A and Blend B as in Table <NUM> and another comparative multilayer mono-material PE assembly <NUM> was prepared by following the setting parameters of the extrusion group reported in Table <NUM>.

The multilayer mono-material PE assembly of the example <NUM> was then compared with the comparative mono-material PE assemblies. All the three PE assemblies contained two sublayers in the second layer.

The comparative multilayer mono-material PE assembly <NUM> showed remarkable problems of dimensional stability with evident shortening of the width of the HDPE film, reaching even <NUM>% of the total width.

The comparative multilayer mono-material PE assembly <NUM> showed less problems of dimensional stability with less shortening of the width of the HDPE film, reaching <NUM>% of the total width with respect to the comparative multilayer mono-material PE assembly <NUM>.

The multilayer mono-material PE assembly of the example <NUM> showed no problems of dimensional stability with no remarkable shortening of the width of the HDPE film.

The three multilayer mono-material PE assemblies were also compared for the adhesion properties that render them suitable for packaging application, for example packaging with Form, Fill and Seal Machines.

The adhesion between the first and the second layer of the multilayer mono-material PE assembly tested was defined acceptable if the adhesion force resulted in a value higher than <NUM> N/<NUM> (as measured with a test peeling at <NUM>° by using a dynamometer Instron model <NUM> (ASTM F904:<NUM> (<NUM>)).

The comparative multilayer mono-material PE assembly <NUM> could not be tested for adhesion due to the severe shortening of the HDPE film.

The adhesion of the comparative multilayer mono-material PE assembly <NUM> was <NUM>-<NUM> N/<NUM> (as measured with a test peeling at <NUM>° by using a dynamometer Instron model <NUM> (ASTM F904:<NUM> (<NUM>)) that was considered unacceptable for the final application.

The multilayer mono-material PE assembly prepared as in Example <NUM> and having as a second layer of the invention, showed remarkable adhesion properties of the second layer on the first layer made of HDPE, specifically showing values higher than <NUM> N/<NUM>.

The presence in the second layer of a polyethylene component selected from the group consisting of a very low-density polyethylene and an ultra low-density polyethylene and having a density value ≤ <NUM>/cm<NUM>, preferably very low-density polyethylene (VLDPE) allowed thus, to improve the adhesion properties.

The multilayer mono-material PE assembly of the invention was hence not only recyclable but meets all the technical requirements for the final application in packaging.

The assembly of multi-layer mono-material PE of the invention was placed for thermal analysis by differential scanning calorimetry (DSC).

In <FIG> a thermogram obtained by a differential scanning calorimetry (measured with DSC <NUM> Model of Perkin Elmer) of the final multilayer mono-material PE assembly of the invention, as prepared in Example <NUM> and shown in <FIG>, is reported.

The thermogram was recorded at a rate of <NUM>/min in nitrogen (N<NUM>) atmosphere. Three peaks can be observed, and they represent the melting points of the materials contained in the specific blend analyzed. The peak at <NUM> has been assigned to second layer and <NUM> and <NUM> to the first layer such as HDPE polymer.

These peaks demonstrate that, even though the multilayer contained different PE, having the same chemical nature, the final assembly degraded at a very narrow range of temperatures. This meant that the multilayer PE assembly of the invention can be easily recycled.

Comparison of the mechanical properties of a multilayer mono-material PE assembly of the invention with respect to a prior art multilayer multi-material PE assembly.

A multilayer mono-material PE assembly of the invention, having a first layer of <NUM> thickness and prepared according to Example <NUM> was compared for mechanical properties with a prior art multilayer multi-material assembly as shown in <FIG>. The prior art multilayer contained a first layer of <NUM> OPA + <NUM> PE, an intermediate layer of adhesive system and an inner layer of PE.

Both the multilayer assemblies were tested for mechanical properties, specifically Elastic Modulus Yield Strength, Load at Break and Elongation at Break according to ASTM <NUM>.

The dynamometric measurement was carried out with Dynamometer Instron Modello <NUM>.

In Table <NUM> dynamometric measurement values are reported:.

From Table <NUM> it is evident that, the multilayer mono-material PE assembly of the invention showed comparable or even better mechanical properties, with respect to the known prior art multilayer multi-material layer assembly, being therefore more flexible and resistant.

Comparison of the seal strength of a multilayer mono-material PE assembly of the invention with respect to a prior art multi-material assembly.

A multilayer mono-material PE assembly of the invention, prepared according to Example <NUM> and shown in <FIG>, has been compared with a prior art multilayer multi-material assembly shown in <FIG>. The prior art multilayer contained a first layer of <NUM> OPA + <NUM> PE, an intermediate layer of adhesive system and an inner layer of PE.

The resistance of the weld, specifically the seal strength, was evaluated according to ASTM F88 under the experimental conditions summarized in Table <NUM>:.

The results obtained by the test are summarized in Table <NUM>.

<FIG> represents the results of the test of the multilayer of the invention. From Table <NUM> it is evident that, the multilayer mono-material PE assembly of the invention showed comparable resistance of the weld properties, with respect to the known prior art multi-material assembly, being well known as resistant and protective material.

Slipperiness COF (Coefficient of Friction) measurements were carried out with the aim of guaranteeing good runnability on vertical packaging machines, according to ASTM D1894.

The COF (Coefficient of Friction) was measured as internal/internal friction coefficient with Friction Peel Tester model <NUM> of Rycobel.

Acceptable values were considered comprised in the range from <NUM> and <NUM>. The multilayer mono-material PE assembly of the invention as prepared in Example <NUM> showed dynamic COF values int/int of <NUM> - <NUM>, therefore highly compliant to ensure runnability on VFFS vertical packaging machines.

The multilayer mono-material PE assembly of the invention, prepared according to Example <NUM> and shown in <FIG>, was tested on the "Form Fill & Seal" packaging machines of the Comet series from PFM manufacturer.

Said packaging machine was chosen for the test, since it has a very effective sealing system for multilayer films, but it is also extremely thermally stressful for multilayer mono-material PE assembly of the invention. In fact, the "Long Dwell" rotary system with a straight section of the machine causes a long contact of the multilayer assembly with the sealing bars and therefore with the heat source. This more easily can trigger the softening of the coupled structure of the multilayer assembly.

Specifically, the test consisted in packaging of a single piece of mozzarella with the multilayer mono-material PE assembly of the invention. The packaging was carried out by using the same machine condition as normally used for a single piece of mozzarella packed with a prior art multilayer multi-material assembly having layers of OPA <NUM> + PE <NUM> as represented in <FIG>.

The machine conditions used for the test were as in following Table <NUM>:.

Under these operating conditions it was possible to carry out a complete packaging test and to verify the integrity of the packages obtained.

The multilayer mono-material PE assembly of the invention showed to resist and adapt to "Form Fill & Seal" packaging machines.

The final package met the requirements of the food field for this kind of packaging. This confirmed that the multilayer mono-material PE assembly of the invention was immediately marketable without the need for long and expensive investments to change the machinery available on the marked and already used for food packaging.

A PE blend with LDPE and very low-density polyethylene (VLDPE) in an amount lower than <NUM>%, instead of an amount of the at least <NUM>% of VLDPE of the blend of the invention, was prepared.

Specifically, the following raw materials have been provided:.

A multilayer mono-material PE assembly was then prepared as in Example <NUM> in the coating extrusion plant of <FIG> and having the extrusion group of <FIG>. The following Table <NUM> represents the setting parameters of the extrusion group:.

This multilayer mono-material PE assembly had a final grammage of <NUM>,<NUM>/m<NUM> ± <NUM>/m<NUM>.

The multilayer mono-material PE assembly was then obtained as in Example <NUM> and named as multilayer mono-material PE assembly <NUM>, with the multilayer structure represented in <FIG>, but with a different PE blend A and PE blend B composition, as shown in Table <NUM>, not being part of the invention.

A PE blend with LDPE and a component ii), specifically EAA, in an amount of at least <NUM>% was prepared.

As shown in Table <NUM>, a blend A and a blend B with at least <NUM>% of only component ii) is prepared, specifically <NUM>% of EAA (ethylene acrylic acid copolymer).

The multilayer mono-material PE assembly was then obtained as in Example <NUM> and named as another multilayer mono-material PE assembly <NUM>, with the multilayer structure represented in <FIG> and having the PE blend A and PE blend B shown in Table <NUM>.

A PE blend with at least <NUM>% of a mixture of component i), specifically <NUM>% of very low density PE (VLDPE), and component ii), specifically <NUM>% of PolyOlefin Plastomer (POP) was prepared.

The multilayer mono-material PE assembly was then obtained as in Example <NUM> and named as another multilayer mono-material PE assembly <NUM>, with the multilayer structure represented in <FIG>, and having the PE blend A and PE blend B shown in Table <NUM>.

Evaluation of the seal strength of a multilayer mono-material PE assembly of the invention according to Example <NUM> with respect to a multilayer mono-material PE assembly according to Example <NUM>.

A multilayer mono-material PE assembly of the invention, prepared according to Example <NUM> and shown in <FIG>, has been compared with a multilayer mono-material PE assembly prepared according to Example <NUM> and shown in <FIG>. The resistance of the weld, specifically the seal strength, was evaluated according to ASTM F88 under the experimental conditions summarized in Table <NUM>.

<FIG> represents the results of the test of the multilayer of the invention according to Example <NUM>, in comparison with a multilayer mono-material PE assembly according to Example <NUM>.

From Table <NUM> it is evident that, the multilayer of the invention according to Example <NUM>, thus having at least <NUM>% of component i), more specifically <NUM>% of VLDPE + <NUM>% of LDPE, has remarkably higher value of seal strength, more specifically at least <NUM> times higher than the multilayer according to Example <NUM>, thus having <NUM>% of component i), more specifically VLDPE, in both PE blend A and PE blend B.

Therefore, <FIG> and Table <NUM> clearly show the importance of the mandatory feature of the specific concentration of component i) of the PE blend A and PE blend B in terms of mechanical properties of the final multilayer assembly.

Evaluation of the seal strength of a multilayer mono-material PE assembly of the invention according to Example <NUM> with respect to a multilayer mono-material PE assembly according to Example <NUM> and a multilayer mono-material PE assembly according to Example <NUM>.

A multilayer mono-material PE assembly of the invention, prepared according to Example <NUM> and shown in <FIG>, has been compared with a multilayer multi-material assembly prepared according to Example <NUM> and shown in <FIG> and a multilayer multi-material assembly prepared according to Example <NUM> and shown in <FIG>.

The resistance of the weld, specifically the seal strength, was evaluated according to ASTM F88 under the experimental conditions summarized in Table <NUM>.

<FIG> represents the results of the test of the multilayer of the invention according to Example <NUM>, with respect to a multilayer mono-material PE assembly according to Example <NUM>, thus having a PE blend with LDPE and a component ii), specifically EAA, in an amount of at least <NUM>%, and a multilayer mono-material PE assembly having a PE blend according to Example <NUM>, thus made with at least <NUM>% of a mixture of component i), specifically <NUM>% of very low density PE (VLDPE), and component ii), specifically <NUM>% of PolyOlefin Plastomer (POP).

From Table <NUM> it is evident that, the multilayer mono-material PE assembly of the invention according to Example <NUM>, thus having a mixture of component i), specifically <NUM>% of VLDPE, and component ii), specifically <NUM>% of POP, has better properties with respect to the multilayer mono-material PE assembly of the invention according to Example <NUM>, even though it does not reach the highest values of the multilayer mono-material PE assembly of the invention according to Example <NUM>. More specifically it is evident that the use of at least <NUM>% of a comonomer ii), for example POP, in the PE blend of the invention, increases the seal strength, hence the adherence of the second layer comprising the PE blend of the invention with the first layer, consisting of HDPE, and decreases the sealing start temperature (SIT) of the final assembly, as showed in <FIG> and listed in the following Table <NUM>.

This property remarkably improves the blends of the invention and their use into packaging, which should be resistant, flexible and remain completely adherent at the same time, during the whole process of welding and sealing.

In addition, <FIG> shows that the multilayer mono-material PE assemblies according to both Examples <NUM> and <NUM>, thus having an addition of copolymers, such as EEA and POP, showed very good values of layer adhesion (as measured with a test peeling at <NUM>° by using a dynamometer Instron model <NUM> (ASTM F904:<NUM> (<NUM>)) between the first layer and the second layer, respectively in the range from <NUM> to <NUM> N / <NUM> and higher than <NUM> N/<NUM>.

As already explained, the adhesion between the first and the second layer of the multilayer mono-material PE assembly tested was defined acceptable if the adhesion force resulted in a value higher than <NUM> N/<NUM> (as measured with a test peeling at <NUM>° by using a dynamometer Instron model <NUM> (ASTM F904:<NUM> (<NUM>)).

Both multilayers, according to Example <NUM> and <NUM>, satisfied the optimal values for adhesion, but the mixture of component i) and ii), specifically the multilayer mono-material PE assembly according to Example <NUM> ensures a higher value of seal strength, as can be clearly appreciated in <FIG>.

This demonstrates the improvement in the blend of the invention, when a copolymer, such as POP, is further added into a blend already containing VLDPE.

Evaluation of the thermal degradation properties of multilayer mono-material PE assemblies of the invention according to Examples <NUM>, <NUM> and <NUM>, via Differential.

The assemblies of multi-layer mono-material PE of the invention were placed for thermal analysis by differential scanning calorimetry (DSC) (measured with DSC <NUM> Model of Perkin Elmer). All thermograms were recorded at a rate of <NUM>/min in nitrogen (N<NUM>) atmosphere.

In <FIG> it is shown the thermogram of the final multilayer mono-material PE assembly of the invention, as prepared in Example <NUM> and shown in <FIG>.

Three peaks can be observed, and they represent the melting points of the materials contained in the specific blend analyzed. The peaks under <NUM>, specifically at <NUM> in <FIG>, <NUM> in <FIG> and <NUM> in <FIG>, have been assigned to the second layer made of the specific PE blends, while the peaks over <NUM>, specifically around <NUM> and <NUM>, are assigned to the first layer, such as HDPE polymer.

The three thermograms demonstrate that the addition of a copolymer in the PE blend of the invention, such as EAA for the PE blend analyzed and shown in <FIG> and POP for the PE blend analyzed and shown in <FIG>, does not alter the chemical behavior of the final PE blend and, thus, does not change the ΔTm between the two layers, since it has relatively little influence on the degradation temperature of the PE blend.

Hence, the addition of copolymers improves the seal strength and decrease the SIT (Sealing Initiation Temperature) of the final multilayer mono-material PE assemblies of the invention, and it does not change the mandatory feature of the ΔTm between the two layers, specifically the first layer of HDPE and the second layer of the PE blend.

Claim 1:
A multilayer mono-material PE assembly, comprising at least two layers:
- a first layer consisting of one film of high-density polyethylene (HDPE) having a density value equal to or higher than <NUM>/cm<NUM>, and
- a second layer comprising at least one sublayer comprising a polyethylene (PE) blend, each PE blend comprising with respect to the total amount of each sublayer:
- from <NUM> to <NUM> wt% of polyethylene resin having a density value in the range from <NUM> to <NUM>/cm<NUM>,
- at least <NUM> wt% of a polyethylene component selected from the group consisting of
i) a very low-density polyethylene (VLDPE) and/or an ultra low-density polyethylene (ULDPE) and having a density value ≤ <NUM>/cm<NUM>,
ii) a polyethylene copolymer selected from the group consisting of polyolefin plastomer (POP), ethylene-vinyl acetate (EVA), ethylene acrylic acid (EAA), ethylene n-butyl acrylate (EBA), ethylene ethyl acrylate (EEA), ethylene <NUM>-ethyl hexyl acrylate (EEHA) and ethylene-methacrylic acid (EMAA), wherein the ethylene monomer is higher than or equal to <NUM> wt% and
iii) a mixture of i) and ii), and
wherein the difference of the melting point (ΔTm) of the first layer with respect to the second layer is in the range from <NUM> to <NUM>.