ITMI20111498A1 - SELF-ADHESIVE SELF-ADHESIVE FILM THAT CAN BE FOLDED IN RELATION TO THE CLOSING FILM, CARRIED OUT TO MANUFACTURE A CONTAINER FOR FOOD AND ITS RELATED CONTAINER PROCESS - Google Patents

Description

Description of the invention entitled:

â € œSELF-ADHESIVE COEXTRUDED FILM AND SEALABLE IN RELATION TO THE CLOSING FILM, SUITABLE TO REALIZE A FOOD CONTAINER AND RELATIVE PROCESS FOR MAKING THE CONTAINERâ €

DESCRIPTION

The present invention relates to a process for making reclosable containers (trays), mainly for packaging food products.

More particularly, the present invention refers to a process for making said resealable containers in which a self-adhesive coextruded film formed by three or more layers is thermolaminated (without the use of glues) directly in line on a sheet of semi-rigid plastic material or rigid, said film being resealable towards the closing film (top) welded along the edge of the container.

Packaging is one of the most critical moments in their process for food companies. The package must essentially protect and preserve the product contained in it for as long as possible, have an attractive appearance to provide a clear message on the characteristics of the product, and at the same time allow an easy and intuitive opening.

A prerogative of the package that appears more and more appreciated is its resealability, that is to say the possibility for the consumer to close the container as hermetically as possible allowing, at the same time, a partial and repeated use of the contents while preserving the characteristics of the produced itself even after it has only been partially consumed.

The possibilities currently offered for the reclosability of food product containers are represented by solutions whose reclosability is entrusted to the lid, the cover film (top) or the tray.

In particular, the solutions offered can be summarized as follows: non-hermetic rigid lid with mechanical reclosability (male-female combination of thermoformed items with closure by means of undercuts): this type of closure requires semi-rigid, very thick lids which must be made by thermoforming, thus requiring an expensive mold for each of the dimensions / formats necessary for each type of tray. In this case, however, it is necessary to use a thermoplastic film to close the tray (under the lid) to ensure airtightness. It is therefore a very expensive solution;

resealable hermetic flexible packaging lid (for example some packs of cheese trays) where reclosability is entrusted to the lid which usually consists of a multilayer film of the type:

PET film splamable glue + PET film + resealable film glue In this case the reclosability is entrusted to the resealable film formed by a coextruded â € œpolyolefin-resin type hot-melt-polyolefìnaâ € or from a film obtained for coating or â € œextrusion coatingâ € of sticky resin between two polyolefins having characteristics of density and molecular weight such as to make them non-adhesive,

Sometimes other films (eg PP or PA) can be used instead of PET, as well as different thicknesses, but in most cases these are multi-layer covering films that require coupling with two-component polyurethane adhesives (glues spreadable) and which normally lead to covering films of higher cost and thickness than those of equivalent non-reclosable covers;

rigid or semi-rigid resealable trays internally coated with a resealable film by coupling with bi-component polyurethane glues. In this case the structure is made up of a rigid PET sheet (or PVC or PP or PS or other) of relatively high thickness (type from 300 Î1⁄4m upwards) which constitutes the preponderant part of the tray. A resealable film of variable thickness but generally around 40-80Î1⁄4m is glued off-line over said sheet, using two-component adhesives. Said resealable film contains inside a sticky layer that can be coextruded with other polymers or spread or cast in â € œextrusion coatingâ € as if it were a closed glue sandwiched between two external non-adhesive layers. In fact, said resealable film is generally formed by a coextruded â € œpolyolefin-resin type hot-melt-polyolefìnaâ € or by a film obtained by spreading or extrusion coating of sticky resin between two polyolefins having characteristics of density and molecular weights such to make them non-adhesive.

This solution suffers from the drawback of first of all requiring an off-line step with respect to the foil production process, then requiring a specific coupling plant separate from the foil extrusion line. This off-line gluing operation clearly requires, in addition to the investment of the necessary plant, also the use of electricity, both for lamination and for drying or crosslinking of the glues.

Furthermore, the use of glues (with and without solvents) involves the risk of the formation of aromatic cores (risk inherent in all couplings with two-component polyurethane adhesives) and in some cases has limits in the overall transparency of the coupled.

The purpose of the present invention is to overcome, at least in part, the disadvantages of the known art by providing a method for obtaining resealable trays - which does not require the use of glues, in particular polyurethane, and offline phases;

- easy to make and with lower energy consumption in its construction, with consequent savings on production costs.

A further object is to provide such a method capable of resulting in a reclosability applicable to any type of tray without requiring molds and the use of a further lid.

Still another object is to provide such a process which requires the use of resealable films with a lower thickness to reduce the weight of the packages and of high transparency to enhance the appearance of the product.

Yet another object is to provide a resealable film which can be advantageously used in the above method, which does not require the use of glues in its manufacture and in its coupling with the tray.

These purposes are achieved by the reclosable film and by the method according to the invention having the characteristics listed in the attached independent claims 1 and 6.

Advantageous embodiments of the invention appear from the dependent claims.

An object of the present invention relates to a process for preparing reclosable containers starting from a sheet of plastic material, rigid or semi-rigid, provided with a closure film (top) and internally covered with a resealable multilayer film in which said resealable film is made to adhere to said sheet by in-line hot lamination during the extrusion of the rigid support itself so as to form a laminate from which the resealable container is then obtained.

The resealable film is a multilayer obtained by coextrusion and is formed at least by a lower self-adhesive layer and / or with a chemical affinity with said sheet, a sticky intermediate layer which subsequently acts as a resealable layer, and an outermost layer to covering of said sticky layer, where however the lower layer can also essentially consist of the sticky resin of the intermediate layer or also contain said resin. In this case the film is made up of only two layers.

By chemical affinity we intend to identify the tendency of some compounds to bind to each other, in particular the tendency of plastic materials to create bonds at the interface such as to have their adhesion without the use of glues but for the sole effect of temperatures and / or pressure.

By thermolamination here we mean the process of hot rolling of plastic materials in the form of a sheet.

The thermo-lamination phase takes place in line with the sheet production process and can take place during the sheet extrusion phase or during the calendering phase of the sheet.

In this way, the use of glues and the off-line gluing phase of the resealable film on the tray of known processes are avoided, with evident savings in time, costs and energy. Furthermore, this method is more advantageous and simpler than the coupling with glue with the reclosable films known in the art.

Generally the leaf is made up of polymeric materials used in the food sector such as polymeric material chosen from PET, PVC, PP, PS, PE, SAN (styrene acrylonitrile copolymer), of various densities and degrees of crisis alignment, such as PET amorphous (APET), direct PET (DPET), copolymer PET and glycol (PETG), polybutylene terephthalate (PBT), shockproof polystyrene (HIPS), crystalline polystyrene (GPPS), but also PC, PMMA, etc.

The resealable film used in the above process is a multilayer film (transparent, white or other colors) which includes

a sticky intermediate layer formed by an adhesive and solid resin, such as a â € œhot melt pressure sensitiveâ € resin, a lower layer formed by a self-adhesive polymeric resin and / or with a chemical affinity with said sheet,

an outermost layer consisting of a thermoplastic polymer resin, generally a polyolefm, a polyester, or a styrene-based resin,

where the lower layer can also contain the â € œhot melt pressure sensitiveâ € resin of the intermediate layer or essentially consist of the â € œhot melt pressure sensitiveâ € resin. In this case the film is made up of only two layers.

Said resealable film is obtained by coextrusion of these layers without the aid of spreadable glues.

Further characteristics of the invention will become clearer from the detailed description that follows, referring to a purely exemplary and therefore non-limiting embodiment illustrated in the attached drawings, in which:

Figure 1 is a schematic sectional view of a portion of a first resealable film suitable for being thermo-laminated on a sheet for a food tray; Figure 2 is a schematic sectional view of a portion of a second resealable film suitable for being thermo-laminated on a sheet for a food tray; figs. 3-5 are schematic views illustrating the thermolamination step of the reclosable film of figs. 1-2 on a sheet of the plastic material carried out in three different ways;

the fìg. 6 is a schematic sectional view of a tray coated with the film of fìg. 1 before applying the covering film;

the fìg. 7 is an enlarged view of the detail indicated with A in fìg. 6.

With reference to figs. 1-2, the resealable film to be thermolaminated on a sheet of plastic material for tray is indicated with the numerical reference 100. It essentially consists of at least two different layers: the layer 1, or lower layer, intended to adhere to the sheet of plastic material of the tray and therefore also defined as â € œself-adhesive layerâ €, it is made up of a polymeric resin capable of adhering due to the effect of temperatures and / or pressure to the sheet on which it is laminated without the need to use conventional glues currently used in the sector.

The resin that forms layer 1 is an extrudable resin and can be:

a polar resin such as for example ÈVA (ethylene-vinyl acetate copolymer), ethylene-acrylic esters copolymers such as for example EMA (ethylene-methylacrylate copolymer), EEA (ethylene-ethylacrylate copolymer), EBA (ethylene-ethyl-ethyl-acrylate copolymer), EHA (ethylene-acetyl-copolymer 2-acrylate) ); ethylene-acrylic acid copolymers such as EAA (ethylene-acrylic acid copolymer), EMAA (ethylene-methacrylic acid copolymer) and relative partially or totally salified derivatives; ethylene terpolymers-acrylic esters-maleic anhydride; ethylene-vinyl acetate anhydride maleic terpolymers; ethylene-acrylic acid-maleic anhydride terpolymers, ethylene-acrylic acid-tertbutylacrylate terpolymers, ionomers and the like, preferably EVA; or

a non-polar but sticky resin, such as very low density polyolefins and / or in the form of elastomers and plastomers, for example VLD-PE (very low density polyethylene), mVLD-PE (metallocene very low density polyethylene); propylene-ethylene copolymers in the form of elastomers and plastomers or other non-crystalline copolymers of PP and the like; or

a non-polar resin and not necessarily sticky but capable of adhering strongly to the leaf by chemical affinity, such as styrene butadiene copolymers, for example SBS (styrene-butadiene / styrene), SEBS (styreneethylene / butylene-styrene), SBBS (styrene / butadiene / butylene / styrene), SIS (styrene -isoprene); or

polyolefins with tackifying additives such as polyisobutylene or amorphous tackifying resins with low molecular weights such as to be sticky (eg hydrocarbon resins); or

mixtures of all the above polymers.

Alternatively the layer 1 could be constituted by the same material as the layer 2 pure or mixed with the other materials indicated above.

In all the cases listed above, the layer can be made to adhere to the leaf also due to the corona treatment.

The resin that forms layer 2 is an adhesive resin, solid, of the â € œhot melt pressure sensitiveâ € type, which comes in the form of granules (not liquid) and which shows properties of rubberiness and stickiness even at low temperatures. for example at room temperature. This layer 2, also known as the `` sticky layer '', represents the mechanically weaker and less rigid layer compared to the other layers of the film 100, and for this reason there is a fracture of the structure of the film 100, in correspondence with this layer 2, when removing the cover film when opening the package.

Furthermore, this resin of the sticky layer 2 is able to be coextruded with the polymers which form the other layers of the resealable film 100 as it is in the form of solid granules which can be inserted into an extruder and subsequently processed in the extrusion head.

Layer 3 is made up of a polymer resin of a thermoplastic polymer, intended to come into contact with the product contained in the tray and which therefore constitutes the internal part of the tray. This polymer is extrudable and can typically be one, for example PE in all its variants, LD-PE (low density polyethylene), LLD-PE (linear polyethylene) even at very low densities, mLLD-PE (linear metallocene polyethylene ), even at very low densities, MD-PE (polyethylene and medium density), HD-PE (high density polyethylene), PP in all its variants, or ÈVA, or EMA or EBA, ionomer, or similar; or also a polymer of a different nature such as polystyrene (PS), PET, and the like as long as it is compatible in the welding phase with the cover film (top) of the tray and therefore allows a hermetic closure. All these polymers can also be present in a mixture with each other. Said layer 3 is also referred to as the â € œsealing layerâ €.

One or more of the layers 1,2,3 can be added with the traditional additives used in the extrusion of plastic films to give various properties (for example antistatic, antiblocking, slipping, anti-condensation, anti-UV, and others).

A preferred embodiment of said three-layer film 100 is the following: sealing layer 3 LD-PE

sticky layer 2 hot-melt pressure sensitive resin

1 EVA adhesive layer

Said film 100 is obtained by coextrusion of the polymers which form the layers 1,2,3, according to known technique using screw extruders and blown blow molding or flat head extrusion, without the aid of any type of spreadable glue.

Between the layers 1,2,3 of said film 100 there can also be interposed intermediate layers (layers 4 and / or 5) made up of any other type of polymer typically used in the production of films for food packaging and capable of imparting to the film 100 with specific properties, for example with barrier capacity against gases, such as EVOH (ethylene-vinyl alcohol), pVOH (polyvinyl alcohol), PA (polyamide); or polymers introduced in order to control other properties such as mechanical, optical, thermoformability, for example a layer of ionomer, LLD-PE, HD-PE, etc.

Such layers 4 and / or 5 can in turn consist of â € œnâ € layers resulting in a multilayer film 100 according to the present invention.

As illustrated in figures 3-5, during the hot rolling process 10 layer 1 is put in contact with the sheet of rigid or semi-rigid material, which can be PVC, PET, PBT PE, PP, PS, SAN (styrene copolymer - acrylonitrile) or any other material used to make trays, and made to adhere to it by the effect of the temperature and / or pressure used during thermo-lamination, without resorting to the use of coated glues.

The thermo-lamination can be carried out, for example, using a temperature between 60-200 ° C, and a pressure between 1 and 10 bar.

Before carrying out the thermolamination it is also possible to pre-treat the surface of the leaf or film by corona treatment or any other surface pre-treatment to facilitate adhesion between the surface of the leaf and layer 1.

In particular in figs. 3-4 illustrates the thermolamination of the film 100 of the present invention, for example with the layer 3 in PE, on a sheet 10, for example in PET, immediately after the extrusion (fig. 3) and in any case after the extrusion of the leaf (fig. 4) with the surface of the same still hot.

In fact, the sheet 10 just after exiting the extrusion head 11 is at a temperature such that it is not rigid but slightly softened.

The roller 12 which feeds the resealable film 100, cooperating with the roller 13, causes the film 100 to adhere to the softened surface of the sheet 10 thanks to the pressure exerted by the two rollers 12, 13. From here the new laminated coupling 15 passes to a subsequent roller 14 cooling to about 40 ° C, giving rise to a bond between the surfaces in contact with the film 100 and the sheet 10 without the aid of glue.

At the end of this thermolamination, a coupler 15 is thus obtained formed by a laminated sheet with a resealable film, ready to be thermoformed in the form of a tray.

Alternatively, as illustrated in fig. 5, it is possible to carry out the thermo-lamination in a phase subsequent to the extrusion of the sheet 10, after it has passed through a series of rollers 12, 13, 14, and said sheet 10 has cooled. In this case it is necessary to subsequently carry out an appropriate heating of said sheet 10, for example with a plate 20 which emits IR rays, or other known method, in order to slightly soften its surface and allow the resealable film 100 to adhere to the surface softening of said leaf 10, thanks also to the pressure exerted by the two pressure cylinders 17, 17â € ™ and, if necessary, also with the help of the corona treatment.

Once the coupling 15 has then been thermoformed to produce a tray 200 of the desired shape (fig. 6), it is possible to fill it with the food product, and seal the sealing film 300 (fig. .6) around the edges of said tray 200. Said closing film 300 can be any non-reclosable closing film known in the art, for example a polylaminate formed by one or more layers (eg PET / PE).

When the tray 200 is opened, which has been closed by said closing sheet (top) 300 welded along the edge of said tray 200, the layer 3 will remain integral with said closing sheet 300, while the layer 3 sticky 2 will remain partially or completely attached to the layer 3, integral with the closing sheet 300, or to the layer 1 integral with the tray 200: in all these cases the sticky layer 2 will allow the resealability of the covering film 300 to the tray 200.

The Applicant has found that a multilayer film 100 as defined above is able to be thermolaminable on the sheet and to impart resealability to the tray on which it has been thermolaminated: the solutions available on the market are reclosable lids or resealable trays obtained by coupling. by means of glues.

The advantages of the present process are considerable compared to known solutions. In particular, with respect to resealable lids, the present process:

allows a reduction in the thickness of the covering film (and therefore in the weight of the packaging and consequently in the solid waste to be disposed of)

allows greater versatility in the lid (because the reclosability is entrusted to the tray)

it presents a considerable economic and electrical energy saving. Furthermore, compared to resealable trays (obtained by coupling with glues), the present process has the following advantages:

simpler technology that involves a single step since it is a direct coupling on the production lines and does not require specific off-line coupling systems

the use of glues and solvents is avoided with the consequent environmental damage and problems related to sensory aspects and organoleptic properties of the film itself

the risk of the formation of aromatic amines is completely avoided (risk always connected with the coupling with two-component polyurethane adhesives)

more controllable aesthetic quality of the covering film (there is no formation of bubbles, risk inherent in coupling with two-component adhesives)

cheaper than the equivalent solution obtained by coupling with glues and significantly lower energy consumption.

Naturally, the invention is not limited to the particular embodiments previously described and illustrated in the annexed drawings, but numerous detailed modifications can be made to it, within the reach of the person skilled in the art, without thereby departing from the scope of the art. The invention itself, as defined in the appended claims.

Claims (11)

CLAIMS 1. Multi-layer resealable film (100) suitable for being laminated onto a sheet of plastic material, rigid or semi-rigid, for containers comprising an outermost layer (3) consisting of a thermoplastic polymeric resin, preferably polyolefin and its copolymers, ionomers, polyester or styrene-based polymers, characterized in that it further comprises a sticky intermediate layer (2) formed by an adhesive and solid resin, preferably a â € œhot melt pressure sensitiveâ € resin, a lower layer (1) intended to contact said sheet formed by a self-adhesive polymeric resin and / or having a chemical affinity with said sheet, said lower layer (1) optionally being able to comprise the adhesive resin of the layer (2) or be formed essentially from said adhesive resin, said layers (1,2,3) being coextruded to form said multilayer film (100). 2. Film according to claim 1 wherein the lower layer (1) of the reclosable film (100) is made up of a polymeric resin chosen from polar resins, such as for example ÈVA (ethylene-vinyl acetate copolymer), ethylene-acrylic esters copolymers such as for example EMA (ethylene methylacrylate copolymer), EEA (ethylene-ethylacrylate copolymer) EBA (ethylene-ethylen-butylacrylate copolymer), EHA (ethylene-ethylen-ethyl acrylate copolymer) acrylate); ethylene-acrylic acid copolymers such as EAA (ethylene-acrylic acid copolymer), EMAA (ethylene-methacrylic acid copolymer) and relative derivatives partially or totally salified; ethylene terpolymers-acrylic esters-maleic anhydride; ethylene-vinyl acetate anhydride maleic terpolymers; terpolymers ethylene acrylic acid maleic anhydride, terpolymers ethylene acrylic acid-tertbutyl acrylate, ionomers and the like, preferably ÈVA; non-polar but sticky resin, such as very low density polyolefin and / or in the form of elastomers and plastomers such as VLD-PE (very low density polyethylene), mVLD-PE (metallocene very low density polyethylene); elastomers and plastomers propylene-ethylene copolymers and the like; non-polar resin and not necessarily sticky but able to adhere strongly to the leaf by chemical affinity, such as styrene butadiene copolymers, for example SBS (styrene-butadiene / styrene), SEBS (styreneethylene / butylene-styrene), SBBS (styrene / butadiene / butylene / styrene), SIS (styreneisoprene); polyolefins with tackifying additives such as polyisobutylene or amorphous tackifying resins with low molecular weights such as to be sticky (eg hydrocarbon resins). a â € œhot-melt pressure sensitiveâ € resin similar to that of layer (2), said resins being able to also be mixed with each other in such ratios as to have a self-adhesive layer (1). 3. Film according to claim 1 or 2 in which the outermost layer (3) is made up of a thermoplastic polymer resin chosen from PE in all its variants, LD-PE (low density polyethylene), LLD-PE (polyethylene linear) even at very low densities, mLLD-PE (linear metallocene polyethylene), even at very low densities, MD-PE (polyethylene and medium density), HD-PE (high density polyethylene), PP in all its variants, ÃVA, ethylene-acrylic esters copolymers, ionomers, or the like; or also a polymer of a different nature such as polystyrene (PS) and styrene resins, PET, and the like. 4. Film according to claim 3 wherein said reclosable film (100) further comprises intermediate layers (4,5), interposed between the inner layer (1) and the outermost layer (3) and formed by other polymers typically used in the ™ food packaging capable of imparting barrier properties and / or mechanical and / or optical properties and / or thermoformability to the film (100), 5. Multi-layer resealable film (100) according to any one of the preceding claims in which one or more of the three layers (1,2,3) are additives with the traditional additives used in the extrusion of plastic films to confer antistatic, antiblocking, sliding, anti-condensation, anti-UV, and similar properties. 6. Process for preparing reclosable containers (200) starting from a sheet (10) of plastic material, rigid or semi-rigid, equipped with a closure film (300) and internally covered with a resealable coextruded multilayer film (100) as defined in any one of the preceding claims 1-5 characterized in that said reclosable film (100) is made to adhere to said sheet (10) by means of in-line hot lamination to form a laminate (15) to obtain said reclosable containers (200). 7. Process according to claim 6 in which said hot rolling is carried out by means of rollers (12,13, 17, 17â € ™) during the step of extrusion of the sheet (10) or in the step of calendering of the sheet (10 ). 8. Process according to claim 7 in which, before the coupling by means of pressure rollers (17, 17â € ™), a heating of the sheet (10) is provided, preferably with hot cylinders, a plate or a heating panel (20) , quartz lamps or anything else that can bring the support sheet or the film to the temperature suitable for lamination, with the possible use of corona treatment. 9. Process according to any one of the preceding claims 6-8 in which the sheet (10) is formed by a polymeric material selected from PET, PVC, PP, PS, PE, SAN (styrene acrylonitrile copolymer), amorphous PET (APET) , Direct PET (DPET), copolymer PET and glycol (PETG), PBT, impact resistant polystyrene (HIPS), crystalline polystyrene (GPPS), PC, PMMA. 10. Process according to any one of the preceding claims 6-9 in which there is also provided a step of forming the laminate (15) in the form of a container (200) and a step of sealing said closing film (300) onto said container (200). Resealable container (200) obtained from the process as defined in any one of the preceding claims 6-10.