RU2792268C2 - Cardboard container laminated with rigid thermoplastic film - Google Patents

Abstract

FIELD: packaging.

SUBSTANCE: invention relates to a laminated cardboard container preferably used in food packaging and concerns a food container. Container 1 contains: cardboard container 10 having hole 11, bottom 12, sidewalls 13, which surround bottom 12 and end with flange 14 from above, which limits container hole 11; thermoplastic film, which is connected to container 10 near bottom 12, near sidewalls 13, and flange 14 by means of heat transfer, wherein the specified thermoplastic film contains at least one polyethylene terephthalate (PET) layer and has a thickness of ≥150 mcm, wherein a density of cardboard container 10 and thickness of thermoplastic film are in the ratio from 2:1 to 1:3 (g/m²:mcm).

EFFECT: invention provides following advantages: trays have an improved support structure with a flat stable flange, which provides a proper distance between stacked trays, thereby facilitating the use of automatic separation systems on a production line; use of rigid material for lamination of cardboard containers provides easier exfoliation of upper closing film without deformation or exfoliation of inner film from cardboard.

8 cl, 3 dwg, 1 tbl

Description

The field of technology to which the invention belongs

The present invention relates to a laminated cardboard container, preferably used in food packaging.

State of the art

In some prior art food preservation carton containers, the inside wall of the package is laminated with a plastic film to seal the carton, which would otherwise be permeable to water and exposed to edible oil.

The plastic lining of the inner wall makes the container suitable for modified atmosphere packaging because the lamination seals the cardboard against atmospheric exposure, which can potentially degrade food quality and cause rancidity.

EP 2441697 describes a process for the manufacture of a laminated carton container suitable for modified atmosphere packaging. The tray blank is bent inside the lower mold and the plastic film is heated by contact with the heated upper mold. The top mold is substantially flat and has holes to draw air into its inner surface to adhere the plastic film to the heated top mold.

A heat-softened plastic film is laminated onto the inner wall of a carton by pressing an upper mold against a lower shell with a folded tray resting thereon.

The upper mold moves towards the plastic film, and therefore towards the cardboard tray, by vacuum, i.e. by drawing in air from below between the upper shell and the lower shell.

To this end, the carton tray has holes formed in the bottom corners of the container, allowing air to escape during vacuum lamination.

Alternatively, a plastic coating can be obtained by simultaneously applying positive pressure over the plastic film by blowing pressurized air and low pressure between the film and the container by drawing air between the two molds.

The method described in existing document EP 2441697 requires pressing a heated plastic film against a carton tray using an upper mold, whether the movement of the upper mold is driven by low pressure alone or by a combination of vacuum and high pressure.

After the laminated containers of the above type have been filled with the food to be packaged, they are sealed with a peelable closure film which is sealed or attached to a plastic coated tray flange.

Plastic films for use in laminating existing carton containers are flexible, similar to the case of a container made according to the process disclosed in the aforementioned EP 2441697.

These flexible films do not contribute to the ultimate rigidity of the container that is essentially provided by the paperboard container, but provide barrier properties to the paper tray, which itself does not have adequate gas and liquid resistance properties.

In addition, the plastic films currently used for laminating carton containers are multi-component films containing at least one layer of binder(s) that can cause the plastic film to adhere to the carton tray using heat sealing systems.

The use of binders that prevent the film from being recycled also affects the recyclability of the inner container because the binders prevent the plastic part from separating properly from the paper part.

Therefore, cardboard containers laminated with flexible plastic films have the following disadvantages:

- they are not suitable for use on production lines with automatic separating systems: the container is too flexible to have a flat, stable flange that would provide a constant distance between the stacked trays, making it difficult to separate them;

- when the tray is opened, the inner film laminated on the cardboard tray is difficult to separate from the outer cardboard, making it difficult to delaminate the cardboard container and the plastic film of the container, thereby preventing proper separation of the constituent materials for recycling.

Disclosure of invention

The applicant has now developed a cardboard container laminated with a rigid plastic film that overcomes the shortcomings of the prior art.

In particular, with the container according to the invention:

- the trays have an improved support structure with a flat, stable flange that ensures proper spacing between stacked trays, thus facilitating the use of automatic separation systems on the production line;

- the use of a rigid material for laminating cardboard containers allows for easier peeling of the top closure film without deforming or peeling the inner film from the cardboard.

The present invention relates to a food container 1 containing

- a cardboard container 10 having an opening 11, a bottom 12, side walls 13 which surround the bottom 12 and terminate at the top with a flange 14 which defines the opening 11,

- thermoplastic film 20, which is connected to the container 10 at the bottom 12, at the side walls 13 and the flange 14 by means of heat transfer,

said thermoplastic film 20 contains at least one layer of polyethylene terephthalate (PET) and has a thickness of ≥150 µm,

wherein the density of the container board 10 and the thickness of the thermoplastic film 20 are in a ratio of 2:1 to 1:3 (g/m ² : μm).

Brief description of the drawings

Fig. 1 is a perspective view of container 1;

fig. 2 is a plan view of blank 100;

fig. 3 is a top view of container 1.

Implementation of the invention

In FIG. 1 is a schematic perspective view of a food container 1 of the present invention. In FIG. 3 shows a top view of container 1.

The container 1 contains a cardboard container 10 and a rigid thermoplastic film 20.

The container 10 in particular has a bottom 12, side walls 13 which surround the bottom 12 and end at the top with a flange 14 which defines the opening 11 of the container 10.

The bottom 12 and side walls 13 have inner surfaces which define the inner surface of the container 10.

The container 10 is preferably obtained from the blank 100 shown schematically in FIG. 2.

More preferably, the container 10 is obtained from a separate blank 100.

The blank 100 preferably has fold cutouts 101 at its edges which assist in bending the carton 10 to form the food container 1.

The container 10 is preferably obtained by bending the blank 100 with the adjacent edges of the side walls 13 to form a continuous corner surface.

The blank from which the container 10 is made can be compressed on both sides, so that one compressed side forms the inner surface of the container 10.

The board used for the purposes of the present invention may be of any type of composition that is known in the art and used in food packaging and meets the requirements of the food industry, as well as the requirements in force for modified atmosphere packages.

Preferably, the paperboard used in the present invention is a waterproof paperboard.

More preferably, the board used to form the container 10 has a density of 50-450 g/m ² .

More preferably, the board used to form the container 10 has a thickness of 200-700 microns.

The thermoplastic film 20 contains at least one polyethylene terephthalate (PET) layer and has a thickness of ≥150 µm.

The advantage of using a PET-containing thermoplastic film is that rigid films can be obtained even at small thicknesses, thereby reducing the plastic portion of the container. Rigidity, i.e. the deformation resistance provided by the plastic film also gives shape to the carton container, making it easier to handle the containers during manufacture and distribution.

It should be noted that in the preferred embodiment, the thermoplastic film 20 has a thickness of 150-450 microns.

The thermoplastic film 20 is bonded to the container 10 at the bottom 12, the side walls 13 and the flange 14 of such a container.

The thermoplastic film 20 is bonded to the container 10 by heat transfer.

More preferably, the thermoplastic film 20 is bonded by thermal lamination, which is considered to be a combination of two or more flat paper, plastic or aluminum materials through adhesion to form multilayer structures that combine the properties of each constituent material.

Thermal lamination or hot lamination is performed using thermoplastic materials that are heated and melted to cause two superimposed layers to adhere.

The thermoplastic film 20 is preferably an adhesive, and the term "adhesive" is intended to mean a film that has sealing properties at film heating temperatures without the need for adhesives to hold or molds to adhere to the appropriate surface.

In other words, the thermoplastic film 20 preferably does not contain binders for retention. More preferably, the container 1 of the present invention does not contain any binders (adhesives).

Even more preferably, the thermoplastic film 20 can advantageously be separated from the carton 10 for recycling purposes.

In a preferred embodiment, the thermoplastic film 20 is a multilayer plastic film.

This multilayer plastic film contains at least one top layer and one bottom layer.

This bottom layer faces the inner surface of the container 10 during lamination.

In a preferred embodiment, thermoplastic film 20 comprises at least one layer of amorphous polyethylene terephthalate (A-PET) and one layer of polyethylene terephthalate glycol (PETG). Such a PETG layer is preferably a layer adjacent to the carton, i. e. to the bottom layer.

The use of PETG, which is a polymer obtained by copolymerizing PET with ethylene glycol, has the advantage of allowing the plastic to adhere to the board without the use of adhesives.

Preferably, the thermoplastic film 20 is a single material multilayer film containing layers made from PET and/or PET derivatives.

It should be noted that in another embodiment, the thermoplastic film 20 includes a gas barrier layer containing ethylene vinyl alcohol (EVOH) or polystyrene (PS).

Preferably, the thermoplastic film contains a heat resistant polypropylene (PP) layer.

The container board 10 and the rigid type thermoplastic film 20 are combined to form a container 1 in which the density of the container board 10 and the thickness of the thermoplastic film 20 are in a ratio of 2:1 to 1:3 (g/m ² :μm).

Preferably, the container board 10 and the rigid type thermoplastic film 20 are combined to form a container 1 in which the density of the container board 10 and the thickness of the thermoplastic film 20 are in a ratio of 1:1 (g/m ² : μm).

It should be noted that in the preferred embodiment, the container 1 has a total thickness of 200-900 µm.

The bottom 12, side walls 13 and flange 14 of the container 10 are preferably held in the shape of the container 1 by hot lamination of the thermoplastic film 20 on the inner surface of the container 10.

Container 1 is suitable for cooking.

After the container 1 has been filled, it can be sealed, preferably with a peelable plastic closure film, which provides for modified atmosphere packaging.

The composition of the closing plastic film depends on the composition of the thermoplastic film 20 laminated on the container 10.

The container 1 of the present invention is preferably manufactured using the method disclosed in European patent application No. 3222415, which includes the following steps:

- providing a cardboard container having an opening, a bottom and side walls that surround the bottom and end at the top with a flange that defines the opening of the container,

- providing a lower shell, which is specially shaped to accommodate the container and has holes in the form of air channels,

- ensuring the presence of the upper shell, equipped with heating elements,

- ensuring the presence of a plastic film,

- placing a plastic film between the upper shell and the container placed in the lower shell,

- heating the plastic film with the heating elements of the upper shell,

- creating a vacuum between the lower shell and the upper shell, which causes the plastic film to stick to the bottom, side walls and flange of the container,

moreover, the upper shell has a cavity that faces the specified lower shell; the step of providing the carton contains the steps of providing the blank; bending the blank in the lower shell to form a container inside the lower shell; wherein the step of heating said plastic film is performed by radiation.

Compared to existing containers consisting of laminated plastic and laminated cardboard, the container 1 according to the invention provides the following advantages:

- improved peeling between the tray and the top film: the use of a rigid film for hot lamination of the cardboard facilitates the separation of the plastic section from the paper section also due to the absence of adhesive materials,

unstacking of the stack of containers: the containers according to the invention are sufficiently rigid to withstand, without deforming, the unstacking forces applied by automatic tray separating systems on production lines,

- container recycling: container 10 and thermoplastic film 20 can be easily separated and recycled with paper and plastic, respectively. The use of a single material thermoplastic film allows the plastic part to be recycled, unlike multi-component films such as PET+PE, where the PE component combined with PET “contaminates” the material and does not allow it to be easily recycled.

Therefore, the use of a cardboard container laminated with thermoplastic film can reduce the thickness of the film by up to 50% compared to a tray made entirely of plastic.

Examples

Below, by way of explanation only, without limitation, examples of embodiments of the food container according to the present invention are presented.

Claims (13)

1. Food container (1) containing: - a cardboard container (10) having an opening (11), a bottom (12), side walls (13) that surround the bottom (12) and end at the top with a flange (14) that limits the opening (11) of the container, - a thermoplastic film (20) which is connected to the container (10) at the bottom (12), at the side walls (13) and the flange (14) by means of heat transfer, said thermoplastic film (20) contains at least one layer of polyethylene terephthalate (PET) and has a thickness of ≥150 µm, moreover, the density of the container cardboard (10) and the thickness of the thermoplastic film (20) are in the ratio from 2:1 to 1:3 (g/m ² : μm), characterized in that said thermoplastic film contains at least one amorphous polyethylene terephthalate (A-PET) layer and one polyethylene terephthalate glycol (PETG) layer, said PETG layer being the layer adjacent to the cardboard container (10). 2. A container according to claim 1, characterized in that the density of the cardboard of the container (10) and the thickness of the thermoplastic film (20) are in the ratio 1:1 (g/m ² : μm). 3. Container according to claim. 1 or 2, characterized in that the density of the cardboard container (10) is 50-450 g/m ² . 4. Container according to claim 1 or 2, characterized in that the thickness of the thermoplastic film (20) is 150-450 µm. 5. The container according to any one of paragraphs. 1-4, characterized in that the cardboard container (10) has a thickness in the range from 200 to 700 µm. 6. Container according to claim 1, characterized in that said thermoplastic film also contains a gas barrier layer containing ethylene vinyl alcohol (EVOH) or polystyrene (PS). 7. Container according to claim. 1, characterized in that the specified thermoplastic film also contains a heat-resistant layer of polypropylene (PP). 8. Container according to any one of paragraphs. 1-7, characterized in that the cardboard container (10) consists of a separate blank (100).

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