WO2018153795A1

WO2018153795A1 - Container covered with a film

Info

Publication number: WO2018153795A1
Application number: PCT/EP2018/053949
Authority: WO
Inventors: Charles Jacques Madeleine VAN REIJ
Original assignee: Packconnect B.V.
Priority date: 2017-02-24
Filing date: 2018-02-16
Publication date: 2018-08-30
Also published as: EP3585609A1

Abstract

Containers comprising multilayer heat sealable films which show good sealing ability through contaminations and good antifog properties for are disclosed. The multilayer heat sealable films enable a very efficient packaging process and results in containers which are environmentally friendly. The containers may consist out of a tray which consists out of crystalline polyethylene terephthalate (CPET) and/or amorphous polyethylene terephthalate (APET) and the container further consists out of a biaxially oriented multilayer heat sealable film. The containers are used for the packaging of fresh or processed meat, fish or poultry and well as for the packaging of cheese or fruits and vegetables.

Description

CONTAINER COVERED WITH A FILM

FIELD OF THE INVENTION

The invention relates to a container covered with a film.

TECHNICAL BACKGROUND OF THE INVENTION

Containers for the packaging of fresh produce are commonly used. Various containers are used for the packaging of fresh meat and fish. These containers can also be used for ready-made meals and salads as well as for fresh fruits or vegetables.

Various containers are used for the packaging of fresh meat and fish. One such container comprises a tray comprising a polyethylene terephthalate layer and a polyethylene layer, covered by a lidding film. The lidding film comprises a preferably biaxially oriented polyethylene terephthalate layer and a multilayer comprising a polyethylene sealing layer. The multilayer film preferably further comprises a layer of ethylene vinyl alcohol (EVOH) as an oxygen barrier layer. The EVOH layer is bound between the polyethylene sealing layer and another polyethylene support layer via a tie layer during an multilayer extrusion process. The biaxially oriented polyethylene terephthalate layer and the multilayer seal layer are glued together in a lamination step. In another step the lidding film is preferably coated with an antifog coating to ensure a good presentation of the packed produce. These so called APET/PE (amorphous polyethylene terephthalate/polyethylene) containers show good sealing through contamination, they have a high oxygen barrier, they have acceptable antifog properties and the packaging process is very efficient. The problem with APET/PE containers is the limited recycling ability of these containers.

Another container for the packaging of fresh meat and fish comprises a tray consisting out of polypropylene covered with a lidding film. The lidding film for this container preferably consist out of biaxially oriented polypropylene film and a multilayer sealing film. The multilayer film preferably further comprises a layer of ethylene vinyl alcohol (EVOH) as an oxygen barrier layer. The EVOH layer is bound between polypropylene copolymer sealing layer and another polyethylene support layer via a tie layer during an multilayer extrusion process. The biaxially oriented polypropylene layer and the multilayer seal layer are glued together in a lamination step. In another step the lidding film is preferably coated with an antifog coating to ensure a good presentation of the packed produce. These polypropylene containers show good sealing through contamination, they have acceptable antifog properties and the packaging process is very efficient. The problem with polypropylene containers is the low oxygen barrier of the tray. This limits the shelf life of the product which is packed in these containers. Yet another container for the packaging of fresh meat and fish comprises a tray comprising a polystyrene, more preferably an expanded polystyrene layer and a polyethylene layer. The polyethylene layer in the tray preferably further comprises a layer of ethylene vinyl alcohol (EVOH) as the oxygen barrier layer. The EVOH layer is bound between a polyethylene sealing layer and another polyethylene support layer via a tie layer during an multilayer extrusion process. The polystyrene layer and the seal layer are glued together in a lamination step. The lidding film for this container preferably consist out of biaxially oriented polypropylene film and a multilayer sealing film. The multilayer film preferably further consists out of layer of ethylene vinyl alcohol (EVOH) as the oxygen barrier layer. The EVOH layer is bound between a polyethylene sealing layer and another polyethylene support layer via a tie layer during an multilayer extrusion process. The biaxially oriented polypropylene layer and the multilayer seal layer are glued together in a lamination step. In another step the lidding film is preferably coated with an antifog coating to ensure a good presentation of the packed produce. These polystyrene containers show good sealing through contamination, they have a high oxygen barrier, they have acceptable antifog properties and the packaging process is very efficient. The problem with polystyrene containers is the limited recycling ability of these containers.

Finally containers for the packaging of fresh meat and fish can comprise a tray out of polyester. Materials suitable for the container are both rigid and foamed and usually comprise crystalline polyethylene (CPET) or amorphous polyethelene terephthalate (APET). The lidding film which is generally employed comprises biaxially oriented polyethylene terephthalate layer and a sealing layer. To improve the sealing ability of the lidding film to the container the lidding film comprises a heat sealable layer of lower melting or amorphous polyester, for example polyethylene terephthalate glycol (PETG). Usually, the biaxially oriented polyester films suitable for these applications are heat set, i.e. non heat shrinkable or low shrinkable materials. In another step the lidding film is preferably coated with an antifog coating to ensure a good presentation of the packed produce. These polyester containers show good oxygen barrier, they have acceptable antifog properties, show good sealing through contamination and are very good for recycling purposes. The problem with current polyester containers is the limited efficiency in the meat packaging process. Another limitation of the polyester container is the reduced seal strength in freezing conditions. Seal tend to break in freezing conditions upon impact.

All of the described containers are used for the packaging of fresh produce and the packaging can be done on automated packaging machines, e.g. SealPak 750. A roll of the lidding film is fixed on the packaging machine and the trays containing the produce are fed into the machine.

Depending on the size of the packaging machine 2 to 8 trays are processed every turn. The edge of the fresh meat container can be contaminated during the filling of the container with meat or fish. These contaminants can comprise, water, fat, protein, blood, marinade, etc.. It is of utmost importance that the container can be sealed hermetically as leaks will cause loss of produce. The lidding film is heat sealed to the tray and the lidding film gets cut off just outside of the seal area. The remainder of the lidding film, also called the skeleton, is rolled up at the other end of the machine. Sealing time and temperature is very important for the efficiency of the packaging process. Containers which comprise a seal layer of olefinic nature, being either a polyethylene or a polypropylene copolymer can be sealed at temperatures up to 160°C with a dwell time below 1 second. Polyester containers need a sealing temperature up to 210°C and a dwell time of 1,5-3 seconds. Due to the high heat impact of the sealing process on the polyester container the tray must be of higher thickness to ensure enough mechanical strength. The higher material consumption of the polyester container makes it less economical to use these trays.

Upon refrigeration of the fresh produce in these containers a 'fog' may form on the inner food contact side of the film, especially if the produce contains a high moisture content. The term 'fog' describes the collection of small moisture droplets that condense on the inner side of the lidding film. Unfortunately these water droplets may cloud the inner surface of the lidding film and thus obstruct or disrupt the view through the lidding film resulting in a negative consumer perception because of the inability to see clearly the packed food through the plastic lidding film. Polyester containers are dominant in the packaging of fresh fruits and vegetables due to the efficiency in recycling and the availability of effective lidding films. Polyester containers for the packaging of fresh fruits and vegetables are of lesser quality polyester and they also are much thinner than the polyester trays used in the meat industry. Therefore, it is of utmost importance that the lidding film seals at a very low temperature, below 150°C, otherwise the polyester trays will deform which is unwanted. Lidding films suitable for packaging of non-contaminated polyester containers for fruits & vegetables are available from Dupont (Mylar OLAF), Mitsubishi (Hostaphan RHS), Transperent Paper Ltd. (Sarafil HSA101) and others. These lidding films however are not suitable for contaminated seals in the meat industry due to the extreme thin seal layer applied on these films.

There have been several approaches to reduce the negative effect of fogging. One approach involves dispersing one or more antifog agents in the lidding film during the processing of the film. Once in the film, the agents tend to migrate to the surface of the film and raise the surface tension of the film. As a result, the water on the inner side of the film tends to form a more continuous film-like and transparent sheet of water rather than a fog. Another approach to minimize the negative effect of fogging on the inner side of the lidding film involves applying an antifog coating directly to the inner food-side of the lidding film. Although this approach adds the cost of an extra processing step, it provides the benefit of directly applying the antifog agent to the film surface where it is most effective at reducing the negative effects of fogging. Antifog additives either applied via the approach of dispersing or coating to the lidding film also have an effect on the meat or fish packaging operation. Antifog additives tend to hamper the seal through contamination ability of the lidding film which has an effect on the sealing temperatures and dwell times. The antifog additives do not provide a permanent antifog action as the performance of the antifog additives disappear over time and due to transfer of the antifog additives on the film roll from the food-contact surface to the outer surface of the film issues can appear during the printing process of the film.

Upon freezing of the containers, the seal integrity must be guaranteed. To ensure seal integrity of the containers in frozen conditions the seal interface of the container must remain intact in frozen condition.

It is desirable to provide a container for the packaging of for instance fresh meat and fish comprising a tray and lidding film with provide an excellent seal through contamination in combination with an efficient and economical packaging process. It is also desired that the container provides a high oxygen barrier and a very high transparency of the lidding film even when products with high moisture levels are packed. Another desire for the container is a high seal strength under freezing conditions and it is very important in the current environmental climate that the container can easily be recycled according to the principle of the circular economy. Yet another desire for the container is an easy opening by peeling off of the lidding film. Preferably the container only comprises polymer compositions out of one polymer family which are polyesters.

DE 20 2010 008 675 Ul describes a packaging comprising a multilayer film, containing a first polymer layer and a second polymer layer of a lower melting polymer. The container is closed by sealing the film to the container and reopened by peeling of the film. DE 20 2010 008 675 Ul does not disclose i) a second layer containing a thermoplastic copolyetherester elastomer containing polyethylene oxide segments and ii) the packaging of meat or fish and iii) the formation of undesired water droplets underneath the film.

US 2005/0266056 Al describes a multilayer film, containing an inner water absorptive layer that can deliver antimicrobial materials to the enclosed foodstuff and outer impermeable layer. US5888599 describes a multi-layer lidding film and a package with the lidding film heat-sealed thereto as a cover. The multi-layer film comprises: 1) a support layer, such as polyester, 2) a non-crosslinked amorphous acrylic interface layer, and 3) an outer copolyester heat seal layer. This layer 3 is not a copolyetherester, but a copolyester layer. Copolyesters do not have any significant water absorption and therefore lack anti-fog properties. US2005079372 describes blended monolayer films and multilayer films having odor barrier properties, methods of making such films, and bags made from such films.

US2013224411 describes antifog films useful for packaging food, and more particularly to antifog films that can be used as lidding films in trays made of amorphous polyester. The films may include at least one base layer or film, such as a polyester film, and a heat seal layer.

WO2006075141 describes the use of a heat-sealable, composite film comprising a polymeric substrate layer having a first and second surface and disposed on a surface of the substrate layer a barrier layer, wherein (i) the substrate layer has one or more venting means therein; (ii) the thickness of the barrier layer is from about 0.05 to about 30 μηι; (iii) the barrier layer comprises a polyester thermoplastic elastomer; and (iv) the Tensile Elongation At Break of the barrier layer measured according to ASTM D882 is at least 250%, as packaging for an ovenable meal.

It is the purpose of this invention to provide a lidding film which is suitable for polyester containers in the fresh meat packaging industry as well as the fresh fruits and vegetables packaging industry. Such lidding film is not available nowadays.

SUMMARY OF THE INVENTION

The inventor has realized that the application of a polymeric sealing layer with specific properties to, a preferably biaxially oriented, thermoplastic polymer carrier layer, such as a polyethylene terephthalate based lidding film, can advantageously be used to provide a container for the packaging of fresh meat and fish that fulfills some or all desires expressed.

The invention relates to a container comprising a thermoformed polyester tray to which a heat sealable multilayer film is sealed wherein the multilayer film comprises a first layer consisting of a first polymer composition containing at least 80% by weight of a thermoplastic polymer, and a second layer consisting of a second polymer layer containing 60-100% by weight based on the weight of the seal layer of a thermoplastic copolyesterether elastomer or a copolyetheramide elastomer. The thermoplastic copolyesterether elastomer or copolyetheramide elastomer of the second polymer layer has a water absorption above 3 wt.%, more preferably above 5 wt.% and most preferably above 7 wt.%, based on the mass of the thermoplastic copolyesterether elastomer or copolyetheramide elastomer and a melting point between 140°C and 180°C.

The first layer provides a strong carrier layer, the second layer has a number of effects: the low melting point allows sealing to be effected at relatively low temperatures. When said film is used as lidding layer on top of a container the container is not subjected to temperatures that would cause excessive strains in the material. The thickness of the material of the container can thereby be reduced, which saves costs. A second effect of the seal layer is the ability to prevent the formation of 'fog' on the inner side of the packaging film.

Preferably the second polymer layer has a glass transition temperature below -20°C

For the preferred embodiments it holds that a more rigid or crystalline state of the seal layer will lead to seal fracture on impact during freezing conditions. The glass transition temperature, where a polymer composition begins to exhibit rubbery, flexible tendencies instead of rigid, brittle tendencies is a measure for seal integrity of the seal interface. The glass transition temperature of the heat seal layer is preferably lower than the temperature at which is stored to ensure integrity of the seal interface. This further effect of the seal layer in preferred

embodiments is in particular of relevance when the film is used as a lidding film on a container. In preferred embodiments the thermoplastic polymer is a thermoplastic polyester, The thermoplastic polyester is preferably one of polyethylene terephthalate, polyethylene-2,6- naphthalate, poly-l,4-cyclohexanedimethylene terephthalate, poly-l,4-cyclohexanedimethylene terephthalate, or polylactide, most preferably polyethylene terephthalate.

In another preferred embodiment the polyester tray contains a seal layer consisting out of or comprising a copolyetherester elastomer or copolyetheramide elastomer. The seal layer is located towards the lidding/sealing film.

In yet another aspect, embodiments of the invention provides a method of packaging a food product, such as fresh produce that includes heat sealing of the lidding film of the invention to a tray containing a food item.

In still another aspect, embodiments of the invention provide a method for the packaging of fresh produce that includes closing a bag made from the lidding film according to the invention, wherein the bag contains a food item.

DETAILED DESCRIPTION OF THE INVENTION

The lidding film used in the container according to the invention comprises a first or carrier layer which consists out of a first polymer composition which consists of at least 80% by weight of a thermoplastic polymer such as a thermoplastic polyester.

Suitable polyesters for this purpose are polyesters of ethylene glycol and terephthalic acid (=polyethylene terephthalate, PET), of ethylene glycol and naphthalene-2,6-dicarboxylic acid (=polyethylene-2,6-naphthalate, PEN), of 1,4-bishydroxymethylcyclohexane and terephthalic acid (=poly-l,4-cyclohexanedimethylene terephthalate, PCDT), and also of ethylene glycol, naphthalene-2,6,dicarboxylic acid and biphenyl-4,4-dicarboxylic acid (=polyethylene 2,6- naphthalate bibenzoate, PEMBB). Another suitable thermoplastic polymer is polylactide or polylactic acid. Preference is given to polyesters which contain ethylene units and consist, based on the dicarbolyate units, of at least 90 mol %, more preferable at least 95 mol %, of terephthalate or 2,6-naphthalate units. The remaining monomer units stem from other dicarboxylic acids or diols. Advantageously, copolymers of mixtures or blends of the homo-and or copolymers mentioned can also be used for the first polymer layer. In the specification of the amounts of the dicarboxylic acids, the total amount of all the dicarboxylic acids adds up to 100 mol %. Similarly, the total amount of all the diols also adds up to 100 mol%. Other dicarboxylic acids and diols than the aforementioned can be used for the polymer composition of the first polymer layer. These dicarboxylic acids and diols are known to people skilled in the art. It is particularly advantageous when a polyester based on terephthalate and small amounts (< 5 mol %) of isophthalic acid or based on small amounts (< 5 mol %) of naphthalene-2,6-dicarboxylic acid is used in the in composition of the polymer formulation of the first polymer layer. In this case, the produce ability of the film and the optical properties of the film are particularly good. The first polymer layer then comprises substantially a polyester copolymer which is composed predominantly out of terephthalic acid and isophthalic acid units and/or terephthalic acid and naphthalene-2,6-dicarboxylic acid units and of ethylene glycol units. The particularly preferred copolyesters which provide the desired properties of the film are those which are composed of terephthalate and isophthalate units and of ethylene glycol units.

The polymers of the first polymer layer may additionally comprise customary additives such as stabilizers (UV, hydrolysis), flame-retardant substances or fillers. They are appropriately added to the polymer or the polymer mixture before melting.

In prior art it is also known to apply gas barrier coatings of SiOx or AlOx onto a substrate by means of plasma enhanced chemical vapor deposition (PECVD). The advantages with a SiOx gas barrier layer compared to other gas barrier materials are firstly that it has a positive environmental profile, secondly, that it is not affected when in contact with surrounding moisture or liquid, it is transparent and since it is applied in very thin layers, also flexible and resistant to cracking when bent or folded. The first polymer layer can comprise a thin layer of SiOx or AlOx gas barrier coating applied by means of plasma enhanced chemical vapor deposition.

Between the first and second polymer layer preferably one or more tie layers are present. The lidding film according to the invention comprises a second polymer layer which consists out of a second polymer composition which comprises at least 50 wt.% of a thermoplastic

polyetherester elastomer, more preferably at least 75 wt.%, even more preferably even more than 95 wt. %. The second polymer composition may comprise an additional polymer. As additional polymer the additional polymer composition may comprise any type of polymer which is not compatible with the thermoplastic polyetherester elastomer of the second polymer layer. According to the present invention, the proportion of the thermoplastic polyetherester elastomer incompatible polymer is from 3 to 40 % by weight, based on the mass of the second polymer layer. In a preferred embodiment, the proportion of the polymer is from 5 to 30 % by weight and in the particularly preferred embodiment it is from 7 to 25% by weight, likewise based on the mass of the second polymer layer.

The terms hard segments and soft segments in relation to thermoplastic polyetherester elastomers can be explained as follows. The soft segments are the polyether segments, having a weakening point below room temperature. The hard segments are the polyester segments, having a weakening temperature above room temperature.

The hard polyester segment of the thermoplastic polyetherester elastomer is preferably consisting out of dicarboxylic acids and diols. Most preferable dicarboxylic acids for the hard polyester segment are terephthalic acid and isophthalic acid. Most preferable diols for the hard polyester segment are ethylene glycol and 1,4-butanediol. Preference is given to polyester hard segments which contain 1,4-butylene units and consist, based on the dicarboxylate units, of at least 70 mol %, more preferable at least 80 mol %, of terephthalate, the remainder dicarboxylate units being isophthalate units. In the specification of the amounts of the dicarboxylic acids, the total amount of all the dicarboxylic acids adds up to 100 mol %. Similarly, the total amount of all the diols also adds up to 100 mol%.

The thermoplastic polyetherester elastomer may contain between 10 and 90 wt. % of the polyethylene oxide soft segments, preferably between 15 and 70 wt. %, more preferably between 20 - 60 wt.%, most preferably between 25 and 50 wt. %. This ensures good anti-fog properties of the packaging. The polyethylene oxide segments may be incorporated in the thermoplastic polyetherester elastomer as poly(ethylene oxide)diol soft segments and/or poly(ethylene oxide/polypropylene oxide/polyethylene oxide)diol soft segments. Next to above described soft segments, the thermoplastic copolyetherester elastomer may comprise further soft segments. These further soft segments may comprise amongst others poly(tetramethylene oxide) diol.

Preferably the polyetherester is derived from terephthalic acid or isophthalic acid and butanediol for the polyester part of the copolyetherester and also preferably polyethylene oxide for the polyether part of the copolyetherester and most preferably both of these features are combined. The polymer of the second polymer layer may additionally comprise customary additives such as stabilizers (UV, hydrolysis), flame-retardant substances, processing aids, anti-block additives or fillers. They are appropriately added to the polymer or the polymer mixture before melting. Examples and preparation of copolyether esters are for example described in Handbook of Thermoplastics, ed. O.Olabishi, Chapter 17, Marcel Dekker Inc., New York 1997, ISBN 0-8247- 9797-3, in Thermoplastic Elastomers, 2nd Ed, Chapter 8, Carl Hanser Verlag (1996), ISBN 1- 56990-205-4, in Encyclopedia of Polymer Science and Engineering, Vol. 12, Wiley & Sons, New York (1988), ISBN 0-471-80944, p.75-117, and the references cited therein.

Suitable copolyether esters can include products commercially available from companies under tradenames, for example, Hytrel™ available from E. I. du Pont de Nemours and Company (DuPont), Riteflex™ available from Ticona, and Arnitel™ available from DSM.

The absorptive layer in the film may also comprise copolyetheramides. Such copolyetheramides can comprise or consist of crystalline polyamide and non-crystalline polyether blocks.

Polyamides may be nylon 6 or nylon 12. A commercially available series of polyetheramides are available under the tradename Pebax™ from Arkema.

The thickness of the first polymer layer may be between 5 micrometers and 100 micrometers. Preferably the thickness of the first layer is between 10 micrometers and 50 micrometers more preferably between 10 micrometers and 30 micrometers.

The thickness of the second layer may be between 1 micrometer and 100 micrometers.

Preferably the thickness of the second layer is between 5 micrometers and 50 micrometers, more preferably between 10 micrometers and 30 micrometers.

The multi-layer packaging film according to the invention can be produced according to a coextrusion cast film process or a coextrusion blown film process. After coextrusion, the cast film is preferably biaxially oriented. The coextrusion blown film process can be a single bubble blown film process or a double or triple bubble blown film process. Preferably the blown film process is a double or triple blown film process, such that a biaxially oriented blown film has been produced. It is also possible to apply the second layer by lamination or extrusion coating onto the first layer, which preferably has been biaxially oriented before. The multi-layer packaging film according to the invention may be printed.

The film optionally contains perforations, preferably in the form of micro-perforations. The size of the perforation is preferably between 50 micrometers and 300 micrometers and even more preferably between 70 and 130 micrometers. Preferably laser technology is used for the formation of the perforations. Preferably the number of perforations are up to 1000 per m² and more preferably up to 500 per m². The invention is illustrated by figures herein, in which:

Figure 1 is a sectional view of film (1) according to the present invention comprising a carrier (2) layer, a tie layer or bonding layer (3) and a heat seal layer (4).

Figure 2 is a sectional view of film (1) according to the present invention comprising a carrier (2) layer, a tie layer or bonding layer (3) and a heat seal layer (4) in which there is dispersed a non-compatible polymer (5).

Figure 3 is a sectional view of the film (1) after having been sealed to a tray (6) to form a container according to the invention having a food product (7) therein. The heat seal layer (4) is in contact with the tray with the carrier layer (2) uppermost.

Figure 4 is a sectional view of film (1) according to the present invention comprising a carrier layer consisting out of PET (2) which stops water vapor units which have been absorbed by the heat seal layer (4) as water units (9) out of the atmosphere inside the packaging which contains water vapor units (8).

Figure 5 is a sectional view of the film (1) after having been sealed to a tray (6) equipped with an additional layer (10) of thermoplastic copolyetherester or copolyetheramide elastomer to form a container according to the invention having a food product (7) therein. The heat seal layer (4) is in contact with the additional layer (10) of the tray with the carrier layer (2) uppermost. Examples

The following samples are merely used illustrative and are not to be construed as to limit the scope of the invention. Water absorption is determined according to ISO 62; method 1. The melting point and the glass transition temperature of the resins is determined according to ISO 11357.

Materials used:

BOPET carrier film: Sarafil TF, a 100% PET based material, 12 micrometers available from Transparent Paper Ltd.

COPE 1: Thermoplastic copolyesters ether heat sealable resin: Hytrel HTR8171 available from E. I. du Pont de Nemours and Company (DuPont). The heat seal resin has a water absorption of 54 wt%, a melting point of 150°C and a glass transition temperature of -42°C. COPE 2: Thermoplastic copolyesters ether heat sealable resin: Hytrel G3548 available from E. I. du Pont de Nemours and Company (DuPont). The heat seal resin has a water absorption of 7 wt%, a melting point of 157°C and a glass transition temperature of -58°C.

COPE 3: Thermoplastic copolyesters ether heat sealable resin: Hytrel HTR8206 available from E. I. du Pont de Nemours and Company (DuPont). The heat seal resin has a water absorption of 30 wt%, a melting point of 200°C and a glass transition temperature of - 38°C. COPE 4: Thermoplastic copolyesters ether heat sealable resin: Arnitel VT3108 available from DSM Engineering Plastics. The heat seal resin has a water absorption of 33 wt%, a melting point of 185°C and a glass transition temperature of - 45°C.

COPE 5: Thermoplastic copolyesters ether heat sealable resin: Hytrel 4056 available from E. I. du Pont de Nemours and Company (DuPont). The heat seal resin has a water absorption of 0,7 wt%, a melting point of 152°C and a glass transition temperature of -50°C. Topseal film: Ecolite® , a pure PET based lidding film for PET based trays and containers available from Flextrus AB, Sweden.

Preparation of the multilayer heat sealable films comprising the carrier layer and the heat sealable layer.

The carrier films were used as received and the films were subsequently coated with a primer layer, the water was evaporated to leave the primer material behind and the pretreated carrier films were coated using conventional coating means with the heat seal layers described. Table 1 lists the films made out of the different combinations of carrier films and heat seal films.

The films according to example 1 & 2 and comparative examples 1-3 were cut into rolls of 230 mm width and sealed onto standard polyester trays type P24/50 available from Impacked International on a Sealpack 750 topseal apparatus. To test the seal through contamination ability of the heat seal layer the edges of the trays were manually contaminated by rubbing chicken fillets over the seal edge of the trays. Seal conditions for the first seal trial are 210°C, 2 seconds at 4 bars sealing pressure. Seal conditions for the second seal trial are 170°, 2 seconds at 4 bars sealing pressure. Each tray was filled with 2 chicken fillets.

The clean seal tests have been done with films according to example 1 & 2 and comparative examples 1-3 on salad bowls type V129 available from Impacked International on a Sealpack 750 topseal apparatus. Seal conditions for the first seal trial are 150°C, 1 second at 2 bars sealing pressure. Seal conditions for the second seal trial are 130°, 1 second at 2 bars sealing pressure. Seal strength measurements were done using a 'SafeSeal' vacuum tester available from

Impacked International. The tester consists out of an enclosed container which can be partially filled with water and a vacuum can be applied on the container. The seal test is done by submerging the sealed tray in water and applying a vacuum on the container. The partial pressure at which the first air bubbles are escaping from the sealed tray is a measure for the seal strength of the heat seal layer on the PET tray. A partial pressure above -0,20 bar is regarded insufficient, a partial pressure between -0,20 & -0,30 bar is regarded to be poor, a partial pressure between -0,30 & -0,40 is regarded as good and finally a partial pressure below -0,40 bar is regarded as excellent. The results of the sealing tests are listed in Table 2.

The determination of anti-fog properties of films has been done with the so called hot fog test. A jar filled with water and lidded with a glass plate is placed into an oven at 70°C. An airgap of 2 cm is kept between the water level and glass plate. After the water is heated in the oven to 65°C the jar is removed and the glass plate is replaced quickly with the test substrate. The speed at which visual fog formation appears underneath the film is a measure for the anti-fog properties of the film. Anti-fog properties are considered poor if fog appears within 5 seconds, moderate if it appears between 5 to 10 seconds and good is it appears between 10 to 15 seconds. If the film stays clear for maximum 15 seconds anti-fog properties are excellent.

Seal integrity tests at freezing conditions (Freezer test) have been done with the equal sealed trays as have been used for the contaminated seal trial with seal condition 1 (210°C, 2 seconds at 4 bars). The trays have been stored in a freezer at -20°C for one week. Next to the freezer a metal ramp with a length of 80 centimeters was positioned in an angle of 60° to the floor. The seal integrity was tested by sliding the frozen trays from the ramp onto the floor. The seal integrity was inspected visually and rated as 'intact' or 'broken'. Results of the anti-fog trail and the freezer test are listed in Table 3.

Table 2.

Test Seal strength contaminated Seal strength clean

(P24/50 tray) (VI 29 tray)

Seal temperature 210°C 170°C 150°C 130°C

Partial pressure Partial pressure Partial Pressure Partial Pressure [bar] [bar] [bar] [bar] Example 1 - 0,37 - 0,31 -0,43 -0,38

Example 2 -0,36 -0,31 -0,41 -0,38

Comp. Example 1 - 0,42 NO SEAL -0,15 NO SEAL

Comp. Example 2 - 0,40 NO SEAL NO SEAL NO SEAL

Comp. Example 3 - 0,33 - 0,28 -0,41 -0,34

Comp. Example 4 - 0,54 NO SEAL -0,57 -0,51

Table 3.

The results are clear indications for the purpose of this invention. The purpose of this invention is to provide a lidding film which is suitable for polyester containers in the fresh meat packaging industry as well as the fresh fruits and vegetables packaging industry.

The film according to example 1 & 2 is able to i) seal through contamination at 170°C ii) seal on clean PET trays at 130°C iii) show good to excellent anti-fog properties and iv) stays intact at freezing conditions during an impact test.

The films according to any of the comparative examples 1-4 fail on 1 or more aspects of the purpose of the invention. The film according to comparative example 1 & 2 fail on the decreased seal through contamination test as well as the clean seal test. The film according to comparative example 3 fails in the anti-fog test and the film according to comparative example 4 fails in the decreased seal through contamination trial as well as the freezer test.

It will be clear that the invention is not restricted to the given examples. For instance a combination of PLA (PLA=polylactic acid or polylactide) and COPE1 is an also preferred embodiment. PLA is a polyester which is commercial available and helps in sustainability. In the method of the invention a thermoformed polyester tray is filled with a food item.

To the thermoformed tray a heat sealable multi-layered film is sealed the multilayered film comprising a carrier layer and a heat-seal layer, wherein the carrier layer consists of;

a. a polymer composition consisting of at least 80% by weight of thermoplastic polymer based on the total weight of the carrier layer and the heat seal layer consists of;

b. 60-100% by weight based on the weight of the seal layer of a thermoplastic copolyesterether elastomer or a copolyetheramide elastomer

and the thermoplastic copolyesterether elastomer or copolyetheramide elastomer has; i. a water absorption above 3 wt%, based on the mass of the thermoplastic copolyesterether elastomer or copolyetheramide elastomer

ii. a melting point between 140° and 180°C.

iii. a glass transition temperature below -20°C In preferred embodiments of the method according to the invention the carrier layer and/or the heat seal layer comprises any one or more, alone or in any combination of the above described features for preferred embodiments of the container according to the invention. Sealing of the multilayer film to the tray may be accomplished by application of heat or by other methods such as the application of ultrasound.

With respect to the differences with some of the previously mentioned documents the following is remarked:

US5888599 describes a multi-layer lidding film having an outer copolyester heat seal layer. This layer is not a copolyetherester, but a copolyester layer. Copolyesters do not have any significant water absorption and therefore lack anti-fog properties. Furthermore, the co-polyesters described in US5888599 are amorphous solvent-based polymers. Amorphous polymers do not have a melting point.

US2005079372 describes a multilayer film consisting of a non-elastic polyester film and an elastic copolyester film. The films are used for making bags. No mention is made of a heat sealing layer or a carrier layer. The only specific example uses Arnitel EM630. Arnitel EM630 has a water absorption level 0,6 wt.%, far below the present invention. No teachings about glass transition temperatures are provided nor are any values provided for glass transition temperatures. US2013224411 uses a separate anti-fog layer coated onto the heat seal layer. Furthermore, the heat seal layer disclosed in US201322441 does not consist out of a copolyetherester or copolyesterether. The heat seal layer of US201322441 has no anti-fog properties and is thus completely different from the heat- and anti-fog seal layer according the invention. WO2006075141 describes a self-venting sealing film for ovenable meals. The self-venting film has a substrate layer with one or more venting means therein. This directly implies that the high oxygen barrier which is needed for sealing film in fresh meat packaging can not be achieved anymore. Furthermore, WO2006075141 makes no reference to melting points, glass transition temperature or antifog properties.

It is remarked that the terms copolyetherester and copolyesterether used above describe the same substances, namely copolymers comprising an ether and an ester. Both terms are used in literature for such substances.

Claims

Claims:

1. A container comprising a thermoformed polyester tray (6) to which a heat sealable multilayer film (1) is sealed wherein the multilayer film comprises a carrier layer (2) and a heat- seal layer (4), the carrier layer consisting of a first polymer composition containing at least 80% by weight of a thermoplastic polymer, and the heat-seal layer consisting of a second polymer layer containing 60-100% by weight based on the weight of the seal layer of a thermoplastic copolyesterether elastomer or a copolyetheramide elastomer wherein the thermoplastic copolyesterether elastomer or copolyetheramide elastomer of the heat-seal layer has a water absorption above 3 wt.% based on the mass of the thermoplastic copolyesterether elastomer or copolyetheramide elastomer and a melting point between 140°C and 180°C and a glass transition temperature below -20°C.

2. The container according to claim 1, wherein the copolyesterether elastomer or copolyetheramide elastomer comprises poly(ethylene oxide) diol soft segments.

3. The container as claimed in claim 1 wherein copolyesterether elastomer or

copolyetheramide elastomer comprises poly(ethylene oxide/polypropylene oxide/polyethylene oxide) diol soft segments.

4. The container as claimed in any one of the claims 1 to 3, wherein the thermoplastic polymer is a thermoplastic polyester.

5. The container according to claim 4, wherein the thermoplastic polyester one of polyethylene terephthalate, polyethylene-2,6-naphthalate, poly-l,4-cyclohexanedimethylene terephthalate, poly-l,4-cyclohexanedimethylene terephthalate, or polylactide is.

6. The container according to claim 5, wherein the thermoplastic polymer is polyethylene terephthalate.

7. The container according to any one of the preceding claims, wherein the container (6) is provided of an additional layer (10) comprised of or comprising thermoplastic copolyetherester or copolyetheramide elastomer.

8. The container according to any one of the preceding claims wherein the heat-seal layer (4) comprises up to 40 wt%, based on the mass of the heat-seal layer, of a polymer which is not compatible with the thermoplastic polyetherester elastomer or the copolyetheramide elastomer.

9. The container according to any one of the preceding claims, wherein the multilayer film (1) is a blown or cast film.

10. The container according to any one of the preceding claims wherein the multilayer film (1) is oriented in two directions.

11. The container according to any one of the preceding claims wherein the carrier layer (2) has a thickness between 10 and 100 micrometers.

12. The container according to any one of the preceding claims wherein the heat-seal layer has a thickness between 5 and 50 micrometers.

13. The container according to any one of the preceding claims wherein a tie or bonding layer (3) extends between the carrier and heat-seal layer.

14. The container according to any one of the preceding claims 1-13 wherein the multilayer film (1) has been sealed to the thermoformed polyester tray by a thermal sealing method.

15. The container according to any one of the preceding wherein the multilayer film (1) is sealed to the thermoformed polyester tray by the application of ultrasound.

16. The container according to any of the preceding claims 1-13 wherein the multilayer film (1) is perforated.

17. The container according to any of the preceding claims wherein in the container a food item is packed.

18. The container according to claim 17, wherein the food item is fresh or processed meat, fish or poultry.

19. The container according to claim 17, wherein the food item is cheese.

20. The container according to claim 17, wherein the food item is fruit a vegetables.

21. Method for producing a container according to any of the claims 1-20 wherein the multilayer film is sealed to the tray using a thermal sealing method or using an ultrasonic sound sealing method.