NL2008251C2

NL2008251C2 - Method for producing heat sealable lid materials for food containers.

Info

Publication number: NL2008251C2
Application number: NL2008251A
Authority: NL
Inventors: Jost Orichel
Original assignee: Ar Metallizing N V
Priority date: 2012-02-07
Filing date: 2012-02-07
Publication date: 2013-08-08

Description

METHOD FOR PRODUCING HEAT SEALABLE LID MATERIALS FOR FOOD CONTAINERS

5 FIELD OF THE INVENTION

The present invention relates to heat sealable lid materials for food containers substrates, more specifically to non-woven sheet like materials, such as paper, having a low UV, moisture vapour and oxygen transmission rate. The present invention further relates to a process for the manufacture of such lid materials, and to containers 10 comprising the novel lid materials.

BACKGROUND OF THE INVENTION

Heat-sealable and peelable lid materials are ubiquitously used. They are usually prepared from an aluminium foil, or more lately, from laminates comprising aluminium foil and polyolefin materials, such as polyethylene (PE), poplypropylene (PP), or 15 condensation polymers such as polyethylene terephthalate (PET) or polyamide (PA) foils. These films are often also coated with barrier coatings such as polyvinylidene chloride to improve oxygen barrier properties, and may be provided with a heat sealing material such as wax or hot melt adhesive.

Aluminium foil-based lids require the use of a prodigious amount of aluminium, 20 while presently applied alternatives based on environmentally more friendly materials such as polyesters, papers and cardboards often fail to provide the necessary moisture and oxygen barrier properties alongside resistance to UV light. This is particularly necessary for packaging of perishable goods containing e.g. unsaturated fatty acids such as dairy products, butter and/or chocolates.

25 US-A-5,626,929 discloses a polymer- or aluminium foil- based heated-sealable container lids. WO-A-95/34489 discloses heated-sealable and removable lids made from polymer-coated papers or cardboards.

However, the use of aluminium foil and polymeric laminates or metallized polymers has come under pressure due to the high energy requirement, as well as the 30 difficulty to recycle laminates, leading to a large amount of difficult to recycle waste, which also is not or only slowly biodegradable, and hence gives environmental concerns.

Materials that are readily biodegradable, in particular cellulosic materials, usually do not have required low moisture vapour and oxygen transmission rates to permit the application as flexible food packaging. Yet further, such materials tend to fail to provide 2 safety for use for food packaging and containing the foodstuff in the packaging under the severe process conditions of, for example, retort processing or the end use environments.

Applicants have now surprisingly prepared a non-woven cellulose-based 5 material that offers high barrier properties versus oxygen, water vapour, as well as UV and IR radiation while at the same time offering very high, if not complete recyclability and high biodegradability. Yet further, the material is also easily over-printable. SUMMARY OF THE INVENTION

According to the present invention, there is provided a heat-sealable multilayered cover 10 material for food packaging, comprising a) a non-woven base material layer, b) a metal layer of a thickness in the range of from 10 to 250 nm, c) a gas and/or steam barrier coating layer, and d) a heat sealant layer located on the inner surface of the cover material.

15 The material according to the invention further may preferably comprise a further gas and/or steam barrier layer a’) between the non-woven base material layer, and the metal layer.

The material according to the invention further preferably has a Moisture vapour transmission rate (MVTR, determined according to ISO 2758, at 23°C, 50% RH) of less 20 than 8 g/m2d. It further preferably has an Oxygen transmission rate (OTR, determined according to DIN 53380-S, at 23°C, 50% RH) of less than 60 cm3/m2/d.

It further preferably has a tensile strength (ISO 1924-2) of at least 8,8 kN/m in machine direction, and of at least 3,75 kN/m in cross machine direction. The material according to the invention further preferably has a tear strength (ISO 1974) of at least 25 950 mN in machine direction, and of at least 980 mN in cross machine direction.

The material according to the invention further preferably has a burst strength (ISO 2758) of at least 350 kPa.

It preferably is heat sealable at a temperature in the range of from 200°C to 350°C, more preferably 250°C to 320°C, and even more preferably in the range of from 30 270°C to 300°C. The cycle time for this process preferably is less than 1 second, more preferably less than 0,6 seconds, and most preferably less than 0,5 seconds.

The material according to the subject invention preferably has a WVTR as determined according to ISO 2758 of below 8 g/m2d.

It further preferably has an OTR according to DIN 53380-S of below 60 cm3/m2/d.

3

Preferably, the tensile strength in machine direction (MD) according to ISO 1924-2 is at least 8,8 kN/m. Preferably, the tensile strength in cross machine direction (CD) according to ISO 1924-2 is at least 3,75 kN/m. Preferably, the tear strength in machine direction (MD) according to ISO 1974is at least 950 mN. Preferably, the tear strength in 5 cross machine direction (CD) according to ISO 1974 980 mN. Preferably, the burst strength according to ISO 2758 is at least 350 kPa all at 23°C, 50% RH. With respect to the subject invention, the water vapour transmission rate (MVTR) is determined at 38°C and 50% relative humidity (RH). The oxygen transmission rate (OTR) is expressed in cm3/m2/day, and is determined at 23°C and at 50% relative humidity (RH).

10 Without wishing to be bound to any particular theory, it is believed that the barrier coating layers and the metal layer act synergistically, whereby the metal layer effectively blocks or reduces open pores left in the first coating layer such that hitherto unreported gas and water vapour barrier properties are obtained, but at the same time providing the material with UV light resistance.

15 More beneficially, this is achieved without the need to resort to a polymeric polyolefin- or PET based synthetic polymer film or to aluminium foil. Moreover, the paper coating is fully recyclable, since the thin layers of metal and first coating layer will not disturb the degradability or recyclability of the paper. Yet further, since the metal layer is very thin, the first coating layer also effectively acts as a base coating which fills 20 minor surface imperfections and provides a smooth surface to receive the metal deposit and thereby further increases the barrier properties.

The non-woven sheetlike substrate a) preferably is a single side coated sheetlike non-woven cellulosic material, or a double side coated sheet-like non-woven cellulosic material, more preferably C1/S and C2/S paper or cardboard. The non-woven 25 material preferably comprises a cellulosic material, preferably paper of cardboard, and/or polymeric material selected from polyolefins, polystyrene and/or polycondensation polymers. Typical coated paper materials include so-called C/1S and C/2S papers, which is used to indicate on which side of a particular paper a coating is applied. C/1S indicates "coated on one side." C/2S indicates "coated on two sides”. This 30 is expressed material according to the invention may further comprise one or more coating layers a”) and a’”) directly adjacent to the non-woven base material.

The paper material preferably is approved for use with the food materials to be packaged, such as by FDA approval. The front side, i.e. the side facing the outside of 4 the container, and not the product may advantageously be printed in conventional offset, flexo or gravure print.

The paper material preferably is approved for use with the food materials to be packaged, such as by FDA approval. The front side, i.e. the side facing the outside of 5 the container, and not the product may advantageously be printed in conventional offset, flexo or gravure print.

The metal layer b) preferably is selected from the group of aluminium, silver, tin, zinc, gold, platinum, titanium, gold, lead, nickel and tantalum, and/or alloys or combinations thereof, with aluminium or its alloys being most preferred.

10 The barrier coating a’) and c) may be any kind of coating that alios to reduce gas and moisture to pass through the composite material. The barrier coat typically has a dry film thickness of between 10 pm and 0.5 pm, preferably less than 5 pm, more preferably less than 4 pm, and most preferably less than 3 pm. The top coat preferably has a dry thickness of at least 0.5 pm, more preferably at least 0.6 pm, and 15 most preferably at least 0.7 pm. The barrier coat typically is preferably applied at a solids content of between 6 and 0.5 g/m2, preferably between 3 and 0.6 g/m2, more preferably between 2 and 0.85 g/m2.

The barrier coating may comprise a copolymer of vinylidene chloride, a film forming protein, comprising also specific clays suitable for barrier coating.

20 The protein preferably is selected from the group consisting of whey protein isolate, whey protein concentrate, hydrolyzed whey protein, soy protein isolate or concentrate, beta-lactoglobulin, alpha-lactalbumin, milk casein, egg white protein, wheat gluten, cottonseed protein, peanut protein, rice protein, or pea protein, or any combination thereof. These proteins may be in a denatured or native, undenatured form, 25 or mixtures of thereof, and provide the substrate with a high moisture barrier, in particular if combined with a polymer crosslinker or binder. The latter may advantageously comprise a polyol compound, including but not limited to saccharides such as sucrose, maltose, trehalose, cellobiose, and/or lactose; modified or unmodified starch, or a polymer polyol such as polyvinylalcohol or ethylenevinyl alcohol. The 30 polvinylalcohol may preferably be derived from a hydrolysed polyvinylacetate polymer. The benefit of this coating composition is that it is fully biodegradable, and allows full recyclability of the thus prepared flexible packaging material in the case of cellulosic, i.e. paper or cardboard substrates, and were found by the applicant to result in very high 5 gas barrier, i.e. high oxygen and water vapour barrier properties when combined with the metal layer.

The copolymer of vinylidene chloride is usually referred to as polyvinylidene chloride or PVDC. The PVDC barrier coating composition provides a water vapour 5 barrier layer, which combined with the metal layer of step b), giving low gas permeability, thereby yielding a structure having excellent water and gas barrier properties, and were found by the applicant to result in very high gas barrier, i.e. high oxygen and water vapour barrier properties when combined with the metal layer.

Clays that are particularly useful for barrier coating s include dispersed clay, 10 especially nanoparticulate clay. These clays may preferably be employed with a hydrophilic polymer, such as polyvinyl alcohol (PVA) or ethylene-vinyl alcohol copolymer (EVOH), preferably in combination with a polymeric acrylic dispersion. The clay used is more preferably nanoparticulate. A nanoparticulate clay is a clay with particles having at least one dimension in the nanometre range, i.e. of less than 100 nm. 15 Typical nanoparticulate clay particles have a maximum dimension of less than 100 nm, for example a maximum dimension of less than 50 nm, such as a maximum dimension of less than 20 nm. More preferably a portion of the clay mineral has been intercalated or exfoliated during the dispersion process. There is no restriction on the type of clay used in this invention provided it is sufficiently dispersible in an aqueous medium and 20 that it is capable of being intercalated or exfoliated during dispersion. In an exfoliated form the aspect ratio of the clay, i.e. the ratio between the length and thickness of a single clay 'sheet' will have an impact on the level of oxygen barrier achieved. The greater the aspect ratio, the more the rate of oxygen diffusion through the dry coating and laminate will be reduced. Clay minerals with aspect ratios between 20 and 10,000 25 are preferably used. Particularly preferred are those minerals having an aspect ratio greater than 100. Examples of suitable clays include kaolinite, montmorillonite, atapulgite, illite, bentonite, halloysite, kaolin, mica, diatomaceous earth and fuller's earth, calcined aluminium silicate, hydrated aluminium silicate, magnesium aluminium silicate, sodium silicate and magnesium silicate. Commercial examples of suitable materials are 30 Cloisite Na+ (available from Southern Clay), Bentone ND (available from Elementis). Of these, the montmorillonite clays, are preferred, nanoparticulate clays being most preferred. The barrier coating composition is preferably applied in the form of a solution or dispersion of the clay and the polymer in a suitable solvent. The solvent is preferably aqueous, and is more preferably water, optionally containing a small quantity of a 6 miscible co-solvent, such as an alcohol, for example ethanol, n-propanol or isopropanol or a ketone such as acetone. If desired, in addition to the hydrophilic polymers, PVA and/or EVOH, other polymers or resins may be included in the coating composition, provided these co-resins are themselves compatible in the final composition. Examples 5 of such polymers and resins include solution acrylics, acrylic emulsions, polyesters, alkyds, sulphopolyesters, polyurethanes, vinyl acetate emulsions, poly( vinyl butyral), poly(vinyl pyrrolidone), polyethylene imine), polyamides, polysaccharides, proteins, epoxy resins and the likes. It is also possible to include sol-gel precursors in these compositions, e.g. a hydrolysate of tetraethyl orthosilicate.

10 These barrier coatings have been found to provide excellent gas barrier properties, but were found by the applicant to result in very high gas barrier, i.e. high oxygen and water vapour barrier properties when combined with the metal layer.

The heat sealant is sealable at a range of from 200°C to 370°C with a cycle time of less than 1 second. Typical heat sealants are well known in the art, and include wax 15 or hot melt adhesives.

The present invention further relates to a product package comprising a lid material as described herein before, and further comprising a container heat-sealed to the lid material. The present invention also further relates to a product package wherein the container comprises polyolefin, polystyrene, polyester, a polylactic acid, starch 20 and/or coated cardboard.

The subject invention further relates to a process for preparing a heat-sealable multilayered cover material for food packaging, comprising the steps of: i) optionally depositing on a non-woven sheetlike substrate a first barrier coating composition, and 25 ii) applying a metal layer by vacuum deposition on the non-wioven substrate or the first coating layer, iii) applying at least one barrier coating on the metal layer, and iv) applying a heat sealant layer on the barrier coating layer.

The vacuum deposited metal adheres to the surface of the non-woven material 30 or trhe optional barrier coating a’. The resulting metal coating thickness typically is in a range of from 40-3000 Angstrom, preferably at least 50, more preferably at least 100 Angstrom, but may generally be in the range of from 10 to 250 nm. Preferably, the metallised substrate may be subjected to calendaring to increase smoothness prior to, after the base coat application, or after the metallization step.

7

Advantageously, the coating layers, i.e. optional barrier coating layer i), metal layer ii) and second barrier coating iii), and finally a heat sealant coating may together synergistically provide an even higher barrier effect. To achieve this matter, the desired water vapour and oxygen permeability barrier may be distributed between the three 5 layers. The barrier coating iii) may be obtained in one or more coating operations, preferably in several successive coatings operations.

The application process of the coating to a substrate is preferably done by means of one or more optionally engraved cylinder(s), ensuring the right amount of drying energy and humidification steps are applied to the substrate. The machine may 10 use corona treatment to regulate the surface energy of the substrate prior to coating. The engraved cylinder(s) are preferably housed in a closed chamber, more preferably in overpressure, and advantageously use doctor blades for the application. The application may be performed in a single, double, or multiple layers, preferably in a single or double layer.

15 The above described film structure may also comprise one or more additional layers wherein these layers may independently comprise a further barrier coating, a turra pori coating, and an adhesive or tie material.

The composite structures according to the present invention are particularly useful in peelable lidstock applications for retortable packaging. The subject invention 20 also relates to the use of a substrate or packaging for the packaging of perishable goods, including but not limited to food, preferably dairy products such as yoghurt, milk, cream, condensed milk and/or baby formula and/or coffee.

Description of the Figures

Figure 1: Figure 1 depicts the layer built-up of a preferred embodiment of the 25 subject invention. The outside of the material is towards optional coating layer a’”, the inside pointing towards the food product is located at the heat sealant d) . The layers are a 2-sided coated paper material a with coating layers a” and a’”; a first barrier layer a’), a vacuum deposited metal layer b, a second barrier coating layer c) and a heat sealant d).

30 Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred 8 to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

Claims

A heat-sealable multi-layer cover material for packaging food, comprising e) a non-woven base material layer, f) a metal layer with a thickness that is in a range of 10-250 nm, g) forming a gas and / or steam barrier coating layer, and h) a heat seal layer located on the inner surface of the cover material. 10

The material of claim 1, further comprising a gas and / or steam barrier layer a ') between the non-woven base material layer and the metal layer.

The material of claim 1 or claim 2, further comprising one or more coating layers a ") 15 and a" ") located immediately adjacent to the non-woven base material.

4. A material according to any one of the preceding claims, wherein the non-woven material comprises a cellulose material, preferably paper or cardboard, and / or a polymeric material selected from polyolefins, polystyrene and / or polycondensation polymers.

The material according to any of the preceding claims, wherein the metal is selected from the group of aluminum, silver, tin, zinc, gold, platinum, titanium, gold, lead, nickel, and tantalum, and / or alloys or combinations thereof. 25

A material according to any one of the preceding claims, with a moisture vapor permeability (moisture vapor transmission rate - MVTR, ISO 2758, at 23 ° C, 50% relative humidity) that is less than 8 g / m2d.

A material according to any one of the preceding claims, with an oxygen permeability (oxygen transmission rate - OTR - DIN 53380-S, at 23 ° C, 50% relative humidity) that is smaller than 60 cm3 / m2 / d.

A material according to any one of the preceding claims, with a tensile strength (ISO 1924-2) of at least 8.8 kN / m in the machine direction, and of at least 3.75 kN / m in a direction that is transverse to the machine direction.

A material according to any one of the preceding claims, with a tensile strength (ISO 1974) of at least 950 mN in the machine direction, and of at least 980 mN in a direction that is transverse to the machine direction.

A material according to any one of the preceding claims, with a bursting compressive strength (ISO 2758) of at least 350 kPa. 15

A material according to any one of the preceding claims, wherein the heat-sealable material is heat-sealable at 220 ° C to 320 ° C, with a cycle time of less than 1 second.

12. Product package comprising a lid material according to any one of the preceding claims, and which furthermore comprises a container that is thermally welded with the lid material.

A product package according to claim 11, wherein the container comprises a polyolefin, polystyrene, polyester, polylactic acid, starch and / or coated cardboard. 25

A method for manufacturing a heat-sealable multi-layer cover material for food packaging according to any of claims 1-10, comprising the steps of: i. optionally depositing a first coating composition that forms a barrier on a non-woven sheet substrate, and ii. applying by vacuum deposition a metal layer on the non-woven substrate or on the first coating layer, iii. applying a barrier coating to the metal layer, and iv. applying a heat sealable layer to the barrier coating layer.

15. A method according to claim 14, wherein the substrate is a sheet-shaped non-woven cellulosic material coated on one side, or a sheet-shaped non-woven cellulosic material coated on both sides.

The method of claim 14 or claim 15, wherein the substrate comprises a fibrous material such as a fabric, paper, or cardboard.

The method of any one of claims 14-16, wherein the metal is selected from a group of aluminum, silver, tin, zinc, gold, platinum, titanium, gold, lead, nickel, and tantalum, and / or alloys or combinations thereof .

18. Method according to any of claims 14-17, further comprising adding an additional step v) with applying an upper coating to an uncoated side of the substrate as obtained in step iv).

19. Use of a substrate or of a package according to any one of claims 1-13, for packaging perishable goods, including, but not limited to, food, preferably dairy products such as yogurt, milk, cream , condensed milk, and / or baby milk and / or coffee.