EP1395492B1

EP1395492B1 - Hermetically closed container and process for its manufacture

Info

Publication number: EP1395492B1
Application number: EP01950306A
Authority: EP
Inventors: Robert Alois De Coninck; Johannes Lambertus Mensink; Emil Paul Bader, Jr.; Guido Willem Meylemans; Gerard Laurent Philippe Buisson
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 2001-06-14
Filing date: 2001-06-14
Publication date: 2006-08-23
Anticipated expiration: 2021-06-14
Also published as: JP4619652B2; CN1516666A; CN100475658C; EP1395492A1; JP2004535993A; US20040142133A1; DE60122593T2; DE60122593D1; WO2002102670A1

Description

Background of the Invention

The present invention relates to an improved high barrier package for food and non-food products, more particularly to a hermetically closed container for packaging humidity- and oxygen-sensitive solid food products, which is capable to sustain a wide variety of atmospheric conditions and provides benefits in environmental aspects and in its overall manufacturing costs, and a process for its manufacture.
More specifically, the present invention relates to an improved hermetically closed container for packaging humidity- and oxygen-sensitive solid food products, such as crisp food products, such as potato chips, processed potato snacks, nuts, etc., comprising a tube-shaped body made of a composite material comprising an outer coating, at least one outer cardboard layer, an oxygen barrier layer covering the cardboard layer on the inside, and an inner, heat-sealable coating of a thermoplastic material; a closure in the form of a sealed tear-off membrane comprising an oxygen barrier layer and an inner coating of a thermoplastic heat-sealable material; and a deep-drawn bottom made of a composite material comprising an outer varnish layer, at least one cardboard layer, an oxygen barrier layer covering the cardboard layer on the inside, and an inner coating of a heat-sealable thermoplastic material, the bottom with its rim being drawn upwards and outwards over the end face of the body and heat-sealed to the inside and the outside of said body.
Hermetically closed containers of this type are already known.
For example US Patents 3,973,719 and 3,988,185 disclose a container assembly comprising a composite tubular body having an outwardly rolled top rim which body has an asymmetrically tabbed membrane-type closure sealingly secured to the rolled rim and a bottom made of metal sealed by crimping to the bottom end of the tubular body, and a method for its manufacture. Such container assemblies, however, are unsatisfying in view of their metal bottoms, which raise problems as far as manufacture, weight, costs and recycling are concerned.
Existing composite containers of this type available on the market are typically closed on one side with a metal end using the well-known (double-seam) seaming techniques. Metal ends, however, provide a relatively big part of the overall weight of the container, and therefore require a high energy and cause substantial emissions during manufacture. Furthermore, for waste recycling reasons, in a range of countries, the metal end needs to be separated from the rest of the package, causing an inconvenience for the consumer or the institutes responsible for waste recycling.
It is well-known that such metal ends or bottoms limit the use of these kind of packages in micro-wave ovens. In order to be able to heat the enclosed product in the container itself, and therefore increasing the convenience for the consumer and increasing the product range for these kind of packages, the metal end needs to be replaced by a micro-wave resistant material.
In trying to overcome such problems EP-A-O 352 127 discloses an oxygen barrier laminate structure suitable for producing an oxygen impermeable leak free container comprising a mechanically stable structural substrate, an outer layer of a heat-sealable polymer material, a first layer of a caulking polymer resin, an oxygen barrier material which can be selected from a wide range of material including aluminum foil, an extrusion coated inner heat-sealable product contactable polymer material and a sandwich layer of a second caulking polymer, an abuse-resistant polymer resin layer, a third caulking polymer resin, all coextruded in this sequence on the inner surface of the oxygen barrier material layer. However, the outer layer of the heat-sealable polymer material used therein is disadvantageous, in that it tends to discolor and dislocate during heat-sealing, i.e. sticks to the heat-sealing tool used with the high temperature necessary to provide for the desired high machine cycle times.
GB-A-2 176 457 describes a composite end closure member for a composite container according to the preamble of Claim 1, whose body comprises at least one outer cardboard layer, a barrier foil, e.g. of aluminum, covering the same on the inside, and an inner sealable plastic covering, whose closure comprises an optionally tear-off layer with an inner sealable plastic covering and whose deep-drawn bottom to be fitted, following the introduction of the charge, comprises at least one cardboard layer, a metal barrier foil and a sealable plastic covering placed on the inside, the bottom with its rim being drawn upwards and outwards over the end face of the body and is sealed on the inside and outside to said body, wherein the metallic barrier foil of the bottom is arranged on the inside of the cardboard layer and is itself provided on the side with a plastic covering and wherein the bottom is sealed to the body by inductive high frequency.
This high frequency heating is stated to be required to provide for the same machine cycle times during manufacture as provided with known containers having a tin plate bottom. It is specifically referred to therein as well that when using a bottom comprising at least one cardboard layer, a metal barrier foil and a sealing plastic covering placed on the inside, the heat-sealing by means of heat exclusively supplied from the outside and thus not by means of inductive high frequency provides only for unsatisfyingly long cycle times.
However, the use of inductive high frequency heating for heat-sealing such composite bottom closures is unsatisfying not only with respect to the machine and operating costs but also requires a certain thickness of the barrier foil which restricts the necessary variation thereof.
Furthermore, when attaching such composite end closure members to the tube part of the body by drawing the rim of the bottom upwards and outwards over the end face of the body, pin holes, cuts or cracking of the barrier layer may occur, which cause that the container loses its hermetic closure and thus its barrier characteristics. This is specifically of a problem when packaging solid crisp food products, which not only deteriorate under the influence of humidity but also are being degraded in the presence of oxygen, so that in case of such pin holes, cuts or cracking of the barrier layers, serious product deterioration can happen during storage. Such effects may be increased when the package is being transported under varying pressure conditions, which may cause an increased contact of the interior of the container with the surrounding atmosphere due to a wide variety of atmospheric conditions, such as high and low temperature, high and low humidity, and high and low altitudes. Such conditions may cause a significant pressure difference between the inside and the outside of the container. Due to this pressure, the container material and hence the barrier layers, are subject to strains which may be so strong that pin holes or crack formation may occur or, when already present after manufacture, such perforations may be increased causing the package to lose its barrier characteristics.
Furthermore, due to the hermetic character, the package may have a high internal pressure at high altitudes, which may cause the package to bulge out. Depending on the shape of the package, this outward bulging may cause the package to show an unstable behavior on the shelf (i.e. wobbling and rocking), hence negatively influencing the purchase behavior.
In addition thereto, the existing composite materials used for the manufacture of such composite containers and bottoms must have properties which allow high machine cycle times including supplying and forwarding the composite raw material in sheet form to the and through the machinery used for cutting, deep-drawing and transporting of the composite bottoms and the likes, which requires a material withstanding such conditions and not causing machine interruptions, which may be caused by the sticking or slipping of the composite laminate because of the outer coating of thermoplastic material.
In addition thereto, after the cutting of the bottom the remaining material of the composite material, the so-called web, needs to be transferred in and/or out of the cutting equipment, where during this transfer the composite material used for forming the tube-shaped body tends to easily break, cause jams and hence influences the reliability of the system.
Similarly, during forming and also during conveying of the composite bottom, friction plays an important role. Too much friction during the forming operation (i.e. deep-drawing) may cause the barrier layer(s) to crack or to result in pin holes. Also depending on the conveying system used, such as air conveying, it is found that too much friction may cause jams. In the heat-sealing operation the material is folded, heated and pressed in its final shape in order to form and close the package. Too much friction between the outer surface and the heated parts causes the material to fold and seal improperly, hence disturbing the quality and reliability of the operation and seal. On the other hand, insufficient friction will cause problems because the composite material will slip from the parts of the machinery used for its processing, which again causes interruptions of the manufacturing process, which is very unwelcome specifically when operating at short machine cycle times.
Furthermore, during the heat-sealing operation using heat exclusively supplied from the outside, the material may discolor and even cause burning marks on the outer resin coating, necessary to protect the outside of the container from humidity, dirt etc. and which may carry printed information for the consumer. However, during the distribution and storage and usage of such containers it is important that they can withstand a certain amount of moisture and are resistant against dirt- or dust-pick up, which is necessary to improve consumer acceptance and convenience.

Objects of the Invention

The object of the present invention therefore is the provision of a hermetically closed container as defined above, which is improved with respect to the properties of the deep-drawn bottom; which allows for the heat-sealing of said bottom to the tube-shaped body of the container by means of a heated pressing tool without causing pin holes, cuts or cracking of the barrier layer(s) in the bottom material; which provides for the necessary stability during and after manufacture, preventing bulging and leaking of the container during transportation and storage under widely differing climate conditions as far as temperature, humidity and pressure is concerned; and, which allows for high machine cycle types by having the sufficient strength, an optimized surface friction and heat stability.
A further object of the present invention is to provide for a process for the manufacture of such hermetically closed containers.

Summary of the Invention

It has been found that the above objects can be solved by using a very specific composite material for the bottom of the container, having a defined laminate structure, comprising an outer varnish layer on the outer cardboard surface, providing a specific coefficient of friction, and providing the oxygen barrier with an abuse-resistant reinforcing carrier layer which combination prevents the formation of pin holes, cuts or cracking of the barrier layers during manufacture, even when applying substantial pressure under high heat when bending the rim of the bottom upwards and outwards over the end face of the body, and during storage and transportation. Furthermore, the application of a reinforcing carrier layer for the oxygen barrier layer allows for providing very thin barrier layers, such as an evaporated metal layer of preferably aluminum.
Subject-matter of the present invention therefore is the hermetically closed container according to claims 1 to 9 and the process for its manufacture according to claims 10 to 20.
In the following the invention shall be explained in more detail, making reference to the drawings enclosed.

Brief Description of the Drawings

In said drawings

Figure 1 shows a schematic representation of a prior art container assembly;
Figure 2 a schematic partial cut view of a detail showing the joint where the body is joined with the bottom; and
Figure 3 a schematic representation of the laminate structure of the composite material used for said bottom.

Description of the Preferred Embodiments

As shown in Figure 1, prior composite containers comprise a composite tubular body (1) having an outwardly rolled top rim, a membrane-type closure (2) sealingly secured to the rolled ring so that the peripheral section of the closure conforms radially and circumferentially to an upwardly facing annular area of the rolled ring for the protection of said membrane and additional cap (14), and - not shown - a bottom closure. The bottom closure (3) of such containers normally comprises a metal plate bottom attached by crimping to the tubular body. The tear-off membrane (2) may comprise a pull-tab to remove said membrane from the upper part of the body (1), which opening may thereafter be closed by the cap (14).
As in the prior art containers, the tube-shaped body (1) of the container of the present invention, which may not only be cylindrical as shown in Figure 1 but may also be non-circular in cross section, such as triangular, quadrangular, pentagonal, hexagonal, etc., is made by spirally or longitudinally winding a composite material. As can be seen from Figure 2, the composite material used for the manufacture of the preferably cylindrical tube-shaped body comprises an outer coating (12), at least one outer cardboard layer (11), an oxygen barrier layer (10), covering the cardboard layer on the inside and an inner, heat-sealable coating (9) of a thermoplastic material. The outside can be printed to provide information as to the content of the container.
The closure (2) normally comprises a thin membrane having one or more layers of paper, an oxygen barrier layer, preferably made of aluminum foil, or a polyethylene terephthalate film on which an aluminum layer has been evaporated, and an inner coating of a thermoplastic heat-sealable material. If necessary, adhesive layers may be provided between the paper, the barrier layer and the inner heat-sealable coating.
Subject-matter of the present invention therefore is a hermetically closed container for packaging humidity-sensitive solid food products, comprising a tube-shaped body (1) made of a composite material comprising an outer coating (12), at least one outer cardboard layer (11), an oxygen barrier layer (10) covering the cardboard layer on the inside, and an inner, heat-sealable coating (9) of a thermoplastic material; a closure (2) in the form of a sealed tear-off membrane comprising an oxygen barrier layer and an inner coating of a thermoplastic heat-sealable material; and a deep-drawn bottom (3) made of a composite material comprising an outer varnish layer, at least one cardboard layer, an oxygen barrier layer covering the cardboard layer on the inside, and an inner coating of a heat-sealable thermoplastic material, the bottom with its rim being drawn upwards and outwards over the end face of the body (1) and heat-sealed to the inside and the outside of said body (1), which is characterized in that the composite material of said bottom (3) has a laminate structure comprising from the outside to the inside: a heat-resistant outer varnish layer (4) providing the coated cardboard surface with a coefficient of friction determined with an Instron apparatus according to the ASTM method D 1894-00 of between about 0.10 and 0.45, preferably between about 0.20 and 0.30, at least one cardboard layer (5), an oxygen barrier layer (6), an abuse resistant reinforcing carrier layer (7) for the barrier layer between the cardboard layer (5) and the oxygen barrier layer (6), and an inner heat-sealable coating (8) of a thermoplastic material.
It has been found that when covering the cardboard surface of the deep-drawn bottom (3) with an outer varnish layer (4) providing the coated cardboard surface with a coefficient of friction as defined above and attaching an abuse-resistant reinforcing carrier layer (7) for the barrier layer between said cardboard layer (5) and said oxygen barrier layer (6), all the above outlined problems can be solved in a very easy and elegant way. Namely, the formation of pin holes, cuts or cracking of the barrier layer can be prevented even in case the barrier layer comprises not a rather strong aluminum foil but only a reinforcing carrier layer (7), on which has been provided a continous impermeable aluminum layer by evaporation.
Surprisingly, this laminate structure allows for the manufacture of the containers under consideration, wherein the bottom with its rim is being drawn upwards and outwards over the end face of the body and heat-sealed to the inside and outside of said body using a heated tool providing the necessary heat and pressure to not only shape the deep-drawn prefabricated body around the lower rim of the tube-shaped body (1), but also provide for the necessary heat-sealing, and using machine cycle times corresponding to those used during the manufacture of containers having a metal bottom presently on the market.
In addition thereto, the specified coefficient of friction provided by the outer varnish layer not only prevents protection against humidity-, dirt- or dust-pick up and allows for a desired coloration and/or the application of a text or pictures, but ensures the smooth handling of said material during the manufacture of the sheet material during the stamping, cutting and deep-drawing and the removal of the materials remaining after stamping, i.e. the so-called web and their transportation in the conveying systems used. In addition thereto, when using such a varnish layer, the discoloration and dislocation of the outer coating (12) of the body (1) can be prevented even when using a pressing tool for attaching the bottom to the rim of the tube-shaped body is being operated at high temperatures of above 300°C and with very short machine cycle times, which do not allow for the cooling of the container and bottom being processed.
The hermetic closure or hermiticity of the container of the present invention is defined as the property of sustaining an O₂-level inside the container, corresponding to an average whole container oxygen transmission rate in air at ambient conditions of 23°C, 50% relative humidity and no absolute pressure differential between the outside and the inside of said container of less than 0.0002 ml 02 per day and per cm² container surface.
According to a preferred embodiment of the present invention, the outer varnish layer (4) as shown schematically in Figure 2 is resistant to discoloration and dislocation under the heat-sealing conditions applied. This means that there is neither browning nor attaching or sticking of the varnish to the tool used for the heat-sealing step. Said heat-sealing conditions comprise a dwell time of 1.0 to 4.0 s, preferably 1.6 to 3.0 s, at a temperature of 120°C to 280°C, preferably 170°C to 260°C and a pressure of the heat-sealing tool of 1 to 22 MPa.
Preferably, the outer varnish layer (4) is provided by applying a heat-seal resistant primer, preferably an acrylic resin based primer. Said primer may be applied by spraying, printing, dip-coating, curtain-coating, etc. More preferably the acrylic resin based primer comprises a styrenated acrylic resin. A preferred varnish of this type comprises a water-reducible composition comprising styrenated acrylic resins dispersed in a liquid medium comprising demineralized water, n-propyl alcohol and, if necessary, an anti-foaming and emulsifying agent.
Said heat-seal resistant primer of the outer varnish layer (4) can be colored and/or with a pigment and as well can be provided on its surface with information provided either by printing, by laser engraving or the like.
Preferably, the outer varnish layer (4) which can be applied in one or more layers is present in a total dry weight of 0.6 to 1.8 g/m², preferably 0.8 to 1.2 g/m², on the cardboard layer (5).
According to a further preferred embodiment of the present invention, the oxygen barrier layers (6, 10) and that provided in the closure (2) are made of aluminum, more preferably of an aluminum foil or in the form of an aluminized coating on a carrier layer, such as the carrier layer (7) or a carrier layer used in the composite material forming the tube-shaped body (1). Such aluminum foils preferably have a thickness of 6 to 12 µm, preferably 7 to 9 µm.
In case improved stability of the laminate structure is required, it is preferred to provide between the aluminum foil of the oxygen barrier layer (6, 10) and the surrounding layers, preferably the carrier layer (7) and the cardboard layer (12), an adhesive layer preferably comprising a polyethylene resin, preferably a low density polyethylene resin, a modified polyethylene resin containing vinyl acetate, acrylate and/or methacrylate monomers and/or an ethylene based copolymer having grafted functional groups.
Preferably, the abuse-resistant reinforcing carrier layer (7) is made of a tough, high strength polymeric material having a tensile strength measured according to ISO 1924 of 200 to 500 N/15mm, preferably 350 to 450 N/15mm under the relevant heat-seal temperatures of 100 to 220°C. This "relevant" heat-seal temperature is the temperature the polymeric material will be subjected to during heat-sealing.
This carrier layer (7) preferably is made of a polyamide such as one of the many nylon-type materials, or a polyester resin, preferably polyethylene terephthalate or ethylene vinyl alcohol copolymers.
The cardboard layers (5, 11) can comprise one single layer or one or more sublayers joined by means of one or more adhesive layers. Preferably the cardboard layer (5) of the bottom (3) is present in a total area weight of 150 to 450 g/m², more preferably of 180 to 340 g/m², whereas the cardboard layer (11) of the outer tube-shaped body (1) is present in a total area weight of 200 to 600 g/m², more preferably 360 to 480 g/m².
The thermoplastic material used for the heat-sealable coating (8, 9) and of the closure (2) is heat-sealable at heat-seal temperatures of 90°C to 200°C, and preferably comprises an ionomer-type resin, or preferably selected from the group comprising salts, preferably sodium or zinc salts, of ethylene/methacrylic acid copolymers, ethylene/acrylic acid copolymers, ethylene/vinyl acetate copolymers, ethylene/methylacrylate copolymers, ethylene/methylacrylate copolymers, ethylene based graft copolymers and blends thereof.
The outer coating (12) of the body (1) and the closure (2) can comprise a low density polyethylene, linear low density polyethylene, medium density polyethylene or mixtures thereof.
Figure 3 shows a schematic representation of a preferred laminate structure of the composite material used for the manufacture of the deep-drawn bottom (3). This structure comprises a cardboard layer (5), which can comprise one layer or one or more sublayers joined by means of one or more adhesive layers, which cardboard layer (5) preferably comprises a 280 g/m² litho paper coated on the outside with a moisture barrier (4) and an overcoat lacquer, covering any imprint provided on said surface. Below the cardboard layer (5) an adhesive layer (13) is provided made of a low density polyethylene resin solidly attaching the abuse-resistant reinforcing carrier layer (7) made of polyethylene terephthalate. Attached to the other surface of the reinforcing carrier layer (7) is the oxygen barrier layer (6) made of aluminum foil which is provided on its inner surface with an inner heat-sealable coating (8) of an ionomer resin as defined above. If desired, an adhesive layer may be introduced between the oxygen barrier layer (6) and the inner heat-sealable coating (8).
A further embodiment of the present invention comprises the process for the manufacture of a hermetically closed container made from a composite material for packaging humidity-sensitive food products compositions comprising a tube-shaped body (1) made of at least one outer cardboard layer (9), an oxygen barrier layer (7) covering the cardboard layer on the inside, and an inner, heat-sealable coating of a thermoplastic material (6); a closure (2) comprising a sealed tear-off membrane comprising an oxygen barrier layer, and an inner coating of a thermoplastic heat-sealable material; and a deep-drawn bottom (3) comprising an outer varnish layer, at least one cardboard layer, an oxygen barrier layer covering the cardboard layer on the inside, and an inner coating of a heat-sealable thermoplastic material, the bottom with its rim being drawn upwards and outwards over the end face of the body (1) and heat-sealed to the inside and the outside of said body (1) characterized by heat-sealing the composite material of said bottom (3) having a laminate structure comprising from the outside to the inside: a heat-resistant outer varnish layer (4) providing the coated surface with a coefficient of friction determined with an Instron apparatus according to the ASTM method D 1894-00 of between about 0.10 and 0.45, preferably between about 0.20 and 0.30, at least one cardboard layer (5), an oxygen barrier layer (6), an abuse resistant reinforcing carrier layer (7) for the barrier layer between the cardboard layer (5) and the oxygen barrier layer (6), and an inner heat-sealable coating (8) of a thermoplastic material, using conductive heating by means of a pressing tool being heated to a temperature of above 300°C via said inner heat-sealable coating (8) to the inner, heat-sealable coating (9) and the outer coating (12) of said body (1).
Preferably said process comprises heat-sealing using a dwell time of 1.0 to 4.0 s, preferably 1.6 to 3.0 s, a temperature of 120°C to 280°C, preferably 170°C to 260°C, and a pressure of 1 to 22 MPa.
The hermetic closure or hermiticity of the container prepared by the process of the present invention is defined as the property of sustaining an O₂-level inside the container corresponding to an average whole container oxygen transmission rate in air at ambient conditions of 23°C, 50% relative humidity and no absolute pressure differential between the outside and the inside of said container of less than 0.0002 ml 02 per day and per cm² container surface.
The outer varnish layer (4) provided is according to a preferred embodiment of the process claimed resistant to discoloration and dislocation under the heat-sealing conditions applied.
The heat-sealing conditions under which the varnish layer (4) applied is resistant to discoloration, i.e. browning, and dislocation, i.e. sticking and assembling to the surface of the heat-sealing tool used, under heat-sealing conditions, comprising a dwell time of 1.0 to 4.0 s, preferably 1.6 to 3.0 s, at a temperature of 120°C to 280°C, preferably 170°C to 260°C and a pressure of the heat-sealing tool of 1 to 22 MPa.
Preferably, an outer varnish layer (4) is present which comprises a heat-seal resistant primer, preferably an acrylic resin based primer or preferably a primer comprising a styrenated acrylic resin. A preferred varnish of this type comprises a water-reducible composition comprising styrenated acrylic resins dispersed in a liquid medium comprising demineralized water, n-propyl alcohol and, if necessary, an anti-foaming and emulsifying agent.
The varnish layer can either be colored and/or contain a pigment or may carry a written or picture information provided by printing or by laser engraving etc.
According to a preferred embodiment of the present invention the outer varnish layer (4) provided on the laminate structure used for the bottom (3) is provided to a dry weight of 0.6 to 1.8 g/m², preferably 0.8 to 1.2 g/m², on the cardboard layer (5).
Preferably, the oxygen barrier layers (6, 10) of the composite materials used are made of aluminum, more preferably of an aluminum foil or an aluminized coating on the carrier layer (7). The aluminum foil of the oxygen barrier layer (6, 10) and of the closure (2) has a thickness of 6 to 12 µm, preferably 7 to 9 µm.
According to a further preferred embodiment of the present invention a laminate structure can be used for the manufacture of the deep-drawn bottom (3), which comprises an adhesive layer (13) between the aluminum foil of the oxygen barrier layer (6) and the carrier layer; or between the aluminum foil of the oxygen barrier layer (10) and the outer cardboard layer (11). Said adhesive layers may comprise a polyethylene resin, preferably a low density polyethylene resin, a modified polyethylene resin containing vinyl acetate, acrylate and/or methacrylate monomers and/or an ethylene based copolymer having grafted functional groups.
Preferably, the laminate structure of the bottom (3) comprises an abuse resistant reinforcing carrier layer (7) made of a tough, high strength polymeric material having a tensile strength measured according to ISO 1924 of 200 to 500 N/15mm, preferably 350 to 450 N/15mm under heat-seal temperatures of 100 to 220°C. This "relevant" heat-seal temperature is the temperature the polymeric material will be subjected to during heat-sealing.
More preferably, said carrier layer (7) is made of a polyamide or polyester resin, preferably polyethylene terephthalate or polybutylene terephthalate, or an ethylene vinyl alcohol copolymer.
The cardboard layers (5, 11) can comprise one single layer or one or more sublayers joined by means of one or more adhesive layers. Preferably the cardboard layer (5) of the bottom (3) is present in a total area weight of 150 to 450 g/m², more preferably of 180 to 340 g/m², whereas the cardboard layer (11) of the outer tube-shaped body (1) is present in a total area weight of 200 to 600 g/m², more preferably 360 to 480 g/m².
According to a preferred embodiment of the present invention thermoplastic heat-sealable material is heat-sealable at heat-seal temperatures of 90 to 200°C and comprises an ionomer-type resin. Preferred ionomer-type resins are selected from the group comprising salts, preferably sodium or zinc salts, of ethylene/methacrylic acid copolymers, ethylene/acrylic acid copolymers, ethylene/vinyl acetate copolymers, ethylene/methylacrylate copolymers, ethylene/methylacrylate copolymers, ethylene based graft copolymers and blends thereof.
Preferably, the body (1) used in the process of the present invention comprises an outer coating (12) of a low density polyethylene, linear low density polyethylene, medium density polyethylene or mixtures thereof.
The present invention thus provides for a hermetically closed container for packaging humidity- and oxygen-sensitive solid food products, preferably crisp carbohydrate-based, salted, crisp food products, such as potato chips, processed potato snacks, nuts, etc. and which provides the necessary hermetic closure under widely varying climate conditions of high and low temperature, high and low humidity and high and low pressure, which can be manufactured according to the process claimed in an easy low-cost process involving usual conductive heating technology and usual handling and operating machines, which container provides for high structural stability at low weight and easy recycling with low environment pollution.
In normal practice, the containers of the present invention are prefabricated comprising the closure (2) in form of the membrane covered with the overcap (14) and are filled from the open bottom side, whereafter the deep-drawn bottom (3) is sealed to the body (1) providing the seam on the bottom of the container.

Claims

A hermetically closed container for packaging humidity sensitive solid food products, comprising a tube-shaped body (1) made of a composite material comprising an outer coating (12), at least one outer cardboard layer (11), an oxygen barrier layer (10) covering the cardboard layer on the inside, and an inner, heat-sealable coating (9) of a thermoplastic material; a closure (2) in the form of a sealed tear-off membrane comprising an oxygen barrier layer and an inner coating of a thermoplastic heat-sealable material; and a deep-drawn bottom (3) made of a composite material comprising an outer varnish layer, at least one cardboard layer, an oxygen barrier layer covering the cardboard layer on the inside, and an inner coating of a heat-sealable thermoplastic material, the bottom with its rim being drawn upwards and outwards over the end face of the body (1) and heat-sealed to the inside and the outside of said body (1), characterized in that the composite material of said bottom (3) has a laminate structure comprising from the outside to the inside: a heat-resistant outer varnish layer (4) providing the coated cardboard surface with a coefficient of friction determined with an Instron apparatus according to the ASTM method D 1894-00 of between about 0.10 and 0.45, preferably between about 0.20 and 0.30, at least one cardboard layer (5), an oxygen barrier layer (6), an abuse resistant reinforcing carrier layer (7) for the barrier layer between the cardboard layer (5) and the oxygen barrier layer (6), and an inner heat-sealable coating (8) of a thermoplastic material.
The hermetically closed container according to claim 1, characterized in that said hermetic closure corresponds to an average whole container oxygen transmission rate in air at a ambient conditions of 23°C, 50% relative humidity and no absolute pressure differential between the outside and the inside of said container of less than 0.0002 ml O₂ per day and per cm² container surface.
The hermetically closed container according to claim 1 or 2, characterized in that said outer varnish layer (4) is resistant to discoloration and dislocation under heat-sealing conditions comprising a dwell time of 1.0 s to 4.0 s, at a temperature of 120°C to 280°C, preferably 170°C to 260°C and a pressure of the heat-sealing tool of 1 MPa to 22 MPa.
The hermetically closed container according to any one of claims 1 to 3, characterized in that said outer varnish layer (4) comprises a heat-seal resistant primer, preferably an acrylic resin based primer
The hermetically closed container according to any one of claims 1 to 4, characterized in that said oxygen barrier layers (6, 10) are made of aluminum.
The hermetically closed container according to claim 5, wherein said oxygen barrier (6) comprises an aluminum foil or an aluminized coating on the carrier layer (7), characterized in that an adhesive layer (13) is provided between the aluminum foil of the oxygen barrier layer (6) and the carrier layer (7).
The hermetically closed container according to any one of the preceding claims, characterized in that an adhesive layer is provided between the aluminum foil of the oxygen barrier layer (10) and the outer cardboard layer (11).
The hermetically closed container according to any one of the preceding claims, characterized in that said abuse resistant reinforcing carrier layer (7) is made of a tough, high strength polymeric material having a tensile strength measured according to Iso 1924 of 200 to 500 N/15mm, preferably 350 to 450 N/15mm under the relevant heat-seal temperatures of 100°C to 220°C.
The hermetically closed container according to any one of the preceding claims, characterized in that said cardboard layers (5, 11) comprise one layer or one or more sub layers joined by means of one or more adhesive layers, wherein the cardboard layer (5) of the bottom (3) is present in a total area weight of 150 g/m² to 450 g/m², preferably of 180 g/m² to 340 g/m² whereas the cardboard layer (11) of the outer tube-shaped body (1) is present in a total area weight of 200 g/m² to 600 g/m², preferably of 360 g/m² to 480 g/m².
A process for the manufacture of a hermetically closed container made from a composite material for packaging humidity sensitive solid food products, comprising a tube-shaped body (1) made of at least one outer cardboard layer (9), an oxygen barrier layer (7) covering the cardboard layer on the inside, and an inner, heat-sealable coating of a thermoplastic material (6); a closure (2) in the form of a sealed tear-off membrane comprising an oxygen barrier layer, and an inner coating of a thermoplastic heat-sealable material; and a deep-drawn bottom (3) comprising an outer varnish layer, at least one cardboard layer, an oxygen barrier layer covering the cardboard layer on the inside, and an inner coating of a heat-sealable thermoplastic material, the bottom with its rim being drawn upwards and outwards over the end face of the body (1) and heat-sealed to the inside and the outside of said body (1), characterized in that said process comprises the step of heat-sealing the composite material of said bottom (3) having a laminate structure comprising from the outside to the inside: a heat-resistant outer varnish layer (4) providing the coated surface with a coefficient of friction determined with an Instron apparatus according to the ASTM method D 1894-00 of between about 0.10 and 0.45, preferably between about 0.20 and 0.30, at least one cardboard layer (5), an oxygen barrier layer (6), an abuse resistant reinforcing carrier layer (7) for the barrier layer between the cardboard layer (5) and the oxygen barrier layer (6), and an inner heat-sealable coating (8) of a thermoplastic material, using conductive heating by means of a pressing tool being heated to a temperature of above 300°C via said inner heat-sealable coating (8) to the inner, heat-sealable coating (9) and the outer coating (12) of said body (1).
The process according to claim 10, characterized in that said heat-sealing is conducted using a dwell time of 1.0 s to 4.0 s, a temperature of 120°C to 280°C, preferably 170°C to 260°C, and a pressure of 1 MPa to 22 MPa.
The process according to claim 10, characterized in that said hermetic closure corresponds to an average whole container oxygen transmission rate in air at a ambient conditions of 23°C, 50% relative humidity and no absolute pressure differential between the outside and the inside of said container of less than 0.0002 ml O₂ per day and per cm² container surface.
The process according to claims 10 to 12, characterized in that said outer varnish layer (4) is resistant to discoloration and dislocation under heat-sealing conditions comprising a dwell time of 1.0 to 4.0 s, at a temperature of 120°C to 280°C, preferably 170°C to 260°C, and a pressure of the heat-sealing tool of 1 MPa to 22 MPa.
The process according to claims 10 to 13, characterized in that said outer varnish layer (4) comprises a heat-seal resistant primer, preferably an acrylic resin based primer.
The process according to any of claims 10 to 14, characterized in that said outer varnish layer (4) is applied to a total dry weight of 0.6 g/m² to 1.8 g/m², preferably 0.8 g/m² to 1.2 g/m², on the cardboard layer (5).
The process according to any of claims 10 to 15, characterized in that said oxygen barrier layers (6, 10) are made of aluminum.
The process according to claim 16, wherein said oxygen barrier (6) comprises an aluminum foil or an aluminized coating on the carrier layer (7), characterized in that an adhesive layer (13) is provided between the oxygen barrier layer (6) and the carrier layer (7).
The process according to any one of the preceding claims, characterized in that an adhesive layer is provided between the oxygen barrier layer (10) and the outer cardboard layer (11).
The process according to any one of the preceding claims, characterized in that said abuse resistant reinforcing carrier layer (7) is made of a tough, high strength polymeric material having a tensile strength measured according to Iso 1924 of 200 to 500 N/15mm, preferably 350 to 450 N/15mm under the relevant heat-seal temperatures of 100°C to 220°C.
The process according to any one of the preceding claims, characterized in that said cardboard layers (5, 11) comprise one layer or one or more sub layers joined by means of one or more adhesive layers, wherein the cardboard layer (5) of the bottom (3) is present in a total area weight of 150 g/m² to 450 g/m², preferably of 180 g/m² to 340 g/m², whereas the cardboard layer (11) of the outer tube-shaped body (1) is present in a total area weight of 200 g/m² to 600 g/m², preferably 360 g/m² to 480 g/m².