A seal for a container

[0001] The present invention relates to the sealing of a container for foodstuffs, usually drinkable liquids, which can be subjected to the currently used recycling processes for the recovery of polyethylene terephthalate from bottles, so that it is removed along with materials other than PET.

[0002] Seals suitable for welding around the outlet of a foodstuff container may include a metal foil layer, mainly used for induction heat sealable seals. The metal foil layer has underneath heat-sealing layers to adhere to the bottle outlet, and on the upper side has layers that provide mechanical strength and an upper surface that can be provided with a print or other type of data carrier. Seals provided with a flap entirely inside the seal perimeter are described, for example, in WO 03/066465, US 4961986 and US 6866926. The flap can be formed by protective laminating in a segment of the seal, for example by placing the flap material between an upper layer made entirely of plastic and the bottom layer. The adhesive layer is located between the flap material and the plastic layer and extends between the plastic layer and the part of the bottom layer protruding beyond the flap material.

[0003] Induction heating of the heat seal layer is often carried out after the cap, for example the cap, has been applied to the neck of the container, the seal being previously placed in the cap. It is known that in order to ensure uniform pressure between the cap and the container outlet, so that the seal begins to adhere after the heat seal layer has melted, a flexible layer is used in the seal. This can be achieved by placing a separate secondary insert that is attached to the cap above the seal, e.g. lining material or foam. Alternatively, a layer can be used in the seal itself, placed for example between the metal foil and the top surface. Such an elastic layer can for example be shaped from a foamed polyolefin material.

[0004] At present, the number of attempts to recycle materials used for packaging consumer goods, for example bottles used to store drinking liquids, is increasing. Polyethylene terephthalate is a convenient material commonly used in such bottles and processes for separating PET during recycling from other materials used to make containers, for example materials used in caps, labels and liners (or seals) of caps have been developed. PET has a density greater than 1 g / ml and is conveniently separated from other materials that have a density less than 1 due to a process that uses water baths in which PET sinks and most other materials float on the surface. Like separation labels and other particulate materials, PET needs to be cleaned of residues, for example, adhesives, and washed before it becomes suitable for re-shaping as containers or other end products using techniques that melt the material. Many baths used in the recycling process show a highly corrosive tendency and are used at elevated temperatures, for example above 80 ° C. The materials remain in the bath for several minutes and are mixed in it. It was found that under such conditions, aluminum exposed to liquids may degrade rapidly, which reduces bath life. In addition, due to the fact that one of the purposes of bathing is to remove adhesive residues, these baths often break down adhesive layers used in the production of laminates from which seals are made. If aluminum decomposes, then materials from adjacent layers tend to release. Aluminum has a density greater than 1 g / ml. Depending on how it is placed in the seal, the debris containing the aluminum layer may sink with PET or float on the surface with other materials. We have taken into account that some steps should be taken to avoid sinking of aluminum-containing debris together with PET. The presence of residual aluminum in PET for reuse is very undesirable.

[0005] The new food container seal according to the invention is made of a laminate comprising the following overlapping layers:

a) an upper plastic layer;

b) adhesive layer for foam / and plastic;

c) a foam layer;

d) adhesive layer for foam / foil;

e) metal foil; and

f) heat seal layer;

in which the adhesive layer for plastic / foam adheres the foam to the plastic layer on at least part of their facing surfaces, wherein the adhesive layer for foam / film adheres the foam to the film substantially over the entire area of ​​their facing surfaces with bonding strength of at least 8

N / 12.5 mm, measured in a 180 ° peel test (330 mm per minute, ambient temperature), the measured seal density, determined in accordance with the density measurement method described here, is in the range of 0.6 to 0, 95 g / ml.

[0006] The upper plastic layer is preferably made of a polyester film, for example PET film. Preferably, the top plastic layer is transparent, so that information can be printed on its bottom or on the deeper layer visible through it. Suitably, the top PET layer has a thickness in the range of 10 to 50 μm.

[0007] Preferably, metal foil useful for induction thermal welding is used.

The latest devices for induction thermal welding are suitable for using aluminum foils. Thus, the metal foil is preferably an aluminum foil, for example with a thickness in the range of 10 to 30 μm.

[0008] The heat-sealable layer may comprise material suitable for melting and sticking to the container outlet, as well as suitable for use in contact with food materials. This layer may also contain other materials, for example to provide strength to the adhering film material. Suitably the heat seal layer comprises a layer of polyester material in combination with a hot melt adhesive material, for example provided as a coextruded material. The connection of the heat-sealable layer to the film should be achieved by known methods, for example using a solvent glue, an aqueous glue, an extrusion glue or a solvent-free glue. The amount of adhesive applied between the film and the heat seal layer is, for example, from 1 to 10 g / m2²preferably from 2 to 6 g / m2².

[0009] The foam layer typically includes polyolefin foam. It is prepared from a material with an initial density below 0.75 g / ml, preferably below 0.7 g / ml, for example 0.65 g / ml or below. To ensure optimal flexibility, the density should be greater than about 0.4 g / ml, preferably at least 0.5 g / ml. Suitably, polyethylene or ethylene copolymer or polypropylene foam is used. The foam thickness is usually adjusted to provide the desired density characteristics for the entire seal. The thickness should therefore be sufficiently large that the total density is less than the maximum density of 0.95 g / ml. Preferably, the measured density is less than 0.90 g / ml, for example as low as 0.85 g / ml, or even less, up to 0.6 g / ml, but is often greater than 0.8 g / ml. Suitably, the foam thickness is preferably at least 100 μm, more preferably at least 125 μm, even more preferably at least 150 μm, for example over 180 μm. Generally, a thickness above 300 μm is undesirable, and it is often less than 250 μm. The foam thickness and density given herein refer to the thickness of the layer prior to lamination with the other sealing components. The density can increase and the thickness decrease to some extent during the lamination steps, although these steps are generally designed to minimize such changes, e.g. by avoiding pressure at the temperature at which the foam material softens. It should be assumed that the foam thickness inside the seal is not less than the thickness of the starting material.

[0010] During the recycling process, the foil must still be glued to the foam to avoid the components containing the metal foil layer together with PET in the flotation bath. Therefore, it is the adhesion between the metal foil and the foam that must be particularly strong and resistant to hot corrosive liquid in the cleaning baths under the conditions of time and mixing. Therefore, the peel force is greater than the favorable minimum.

[0011] The foam can be directly attached to the film by an adhesive coating. Alternatively, there may be additional layers forming part of the adhesive layer between the foil and the foam. Preferably, the adhesive layer between the foam and the metal foil comprises a hot melt material applied by extrusion or, alternatively, a solvent or aqueous adhesive material applied as a liquid between the foil and the foam or a two-component adhesive (polyurethane type) applied as a liquid between the foil and the foam. If a hot melt material is used, its melting point should be selected so that it can be activated during manufacture without activating the heat seal layer already placed on the opposite side of the film. Alternatively, the heat seal layer is applied at a later stage of manufacture to the opposite side of the film.

[0012] The 180 ° peel test used to determine the bond strength between the foam and the foil is carried out as described below, the test being carried out after cutting the sample from the web from which the seal is cut. (Usually, the seal itself is not large enough to serve as a sample of adequate size or sufficient material for peeling to determine the dynamic peel strength value.) Samples are cut from a 12.5 mm wide web taken along the laminate web. The sample should be at least 80 mm long. The peel force is determined between the part in which the upper plastic layer is glued to the foam on the reverse side of the film, at the point where the application of the peel force begins. In order to allow the film and underlying layers to be attached in one of the jaws of the tensile measuring device and the laminate layers containing foam in the other from the jaws, some of the adhesive is initially removed, for example using a suitable solvent that strongly affects the adhesive but does not affect the adhesive other adhesives, and which does not damage the cohesion of other components (foil, PET, foam). As stated, the film and underlying layers are attached in one of the jaws of the tensile measuring device, and the foam and upper layers are attached in the other of the jaws. The jaws are then drawn at an angle of 180 ° at a speed of 330 mm / minute. A 50 N load cell is used in the test. The device is positioned in such a way that it can be extended by at least 25 mm. The results obtained indicate the dynamic peel force for a 12.5 mm wide sample.

[0013] The value of the 180 ° peel strength in this test should preferably be at least 8 N / 12.5 mm wide, preferably at least 9 N, more preferably at least 10 N, for example 11 N or above, often even 15 N .

[0014] The seal density is determined as follows. The diameter of the seal is measured to calculate the surface area. The thickness is measured using a sensor thickness gauge with spring load FTM-1 Baty with a 10 mm foot. The force generated by the springs on the foot is 1.8 to 2.2 N. The cladding is weighed using a suitable weight, for example allowing the value to be measured to at least two (preferably four) decimal places (grams). The density is calculated based on weight and measured dimensions. The density should also take into account the possible presence of the flap, assuming that the seal will be cut so that the flap covers 50% of the seal's surface area. It may be necessary to carry out the test by cutting a suitable sample from the web, before cutting out the seals, if the seal is too small to fit the entire foot of the thickness gauge.

[0015] The seal is generally cut from the laminate web. The invention also provides such a web including;

a) a top layer of polyester;

b) adhesive layer for plastic / foam;

c) a polyolefin foam layer with a thickness in the range of 150 μm to 350 μm;

d) adhesive layer for foam / foil;

e) an aluminum foil layer at least 12 μm thick; and

f) a heat-sealable layer in which the foam / foil adhesive layer sticks the foam to the foil essentially over the entire surface of their facing surfaces with a joint strength of at least 8 N / 12.5 mm measured in the 180 ° peel test described here, wherein the measured density of this laminate determined by the density measurement method described herein is below 0.95 g / ml, preferably below 0.9 g / ml, for example in the range 0.6 to 0.9 g / ml.

[0016] The laminate web can for example be shaped by gluing two previously produced laminates by applying a plastic / foam adhesive layer and / or a foam / film adhesive layer. Thus, it is conveniently provided to provide a pre-formed laminate comprising a heat seal layer, an aluminum foil layer, and a foam layer with a suitable adhesive for the foil / foam to provide adequate peel strength at an angle of 180 °. Next, an upper polyester layer and optionally a flap are applied to this pre-formed laminate by applying a plastic / foam adhesive layer. Suitable methods for applying the adhesive include the use of a solvent or water-based adhesive using liquid coating techniques, extrusion of an extrudable adhesive, such as a polyolefin-based adhesive, especially an ethylene copolymer, by applying a two-component adhesive by liquid coating techniques or in a heat melting process in which the top layer of material plastic contains a surface layer of hot melt material, e.g. ethylene-vinyl acetate, which joins the foam by applying heat from the plastic side towards the laminate layers and pressure. The use of heated and / or cooled rollers to provide pressure allows gluing without damaging other heat-sensitive layers.

[0017] According to another method, a pre-formed laminate of aluminum foil and a heat seal layer is glued to the pre-formed laminate consisting of an upper layer, a plastic / foam adhesive layer and a foam layer, and with a further pre-formed laminate of film and layer heat-sealable by applying an adhesive layer for foam / foil. Such an adhesive can be applied by coating with a solvent or aqueous adhesive material, by extruding a hot melt adhesive or by applying a two-component adhesive.

[0018] Both the plastic / foam adhesive layer and the foam / foil adhesive layer can be applied either in subsequent stages or simultaneously on either side of the foam layer by bringing the upper polyester layer into contact with one foam surface and a pre-formed laminate with aluminum foil and heat seal layers on the other side of the foam with proper application of adhesive layers on each side of the foam.

[0019] In accordance with the present invention, there is also provided a new method of producing a laminate in which

a) a pre-formed laminate comprising a heat-seal layer, a metal foil, a foam / foil adhesive layer and a foam layer, and a plastic film are delivered to the laminating station such that the plastic film is on the foam side of the pre-fabricated laminate;

b) plastic / foam adhesive is applied between the facing surfaces of the plastic film and foam; and

c) pressure is applied to the laminating station and covers the plastic / foam adhesive, as a result of which the surfaces are glued together;

in the pre-formed laminate the foam layer and the metal foil / heat seal layer are combined with a joint strength measured at 180 ° peel strength test (330 mm / min, room temperature) of at least 8 N / 12.5 mm, with wherein the thickness of the foam layer in the pre-formed laminate is at least 175 μm and the density is not more than 0.7 g / ml.

[0020] Preferably, the method comprises placing a flap between the plastic film and the adhesive. Preferably, the foil is an aluminum foil with a thickness of at least 12 μm and the foam has a thickness of at least 190 μm. In the pre-formed laminate, preferably the foam density is not greater than 0.7 g / ml, preferably less than 0.65 g / ml. [0021] The present invention also includes containers sealed with a seal according to the invention usually containing a food substance. The container is preferably a recyclable polyester bottle, preferably containing a drinking liquid. The container can also be provided with a cap over the seal, which can be placed, for example, before induction sealing of the container seal or a dust cap, which can be placed after sealing the seal.

[0022] The invention is further illustrated by the attached drawings, in which Figure 1 is a cross-sectional view of a single fragment according to one embodiment of the invention;

[0023] Figure 2 is a cross-sectional view of a seal provided with a flap according to another embodiment of the invention, Figure 3 is a schematic diagram of a part of the production line of the form shown in Figure 2; and Figure 4 is a perspective view of part of the line shown in the figures.

[0024] As shown in Figure 1, the seal 1 comprises a top plastic layer 2, a foam layer 3, a metal foil 4, a heat seal layer 5 comprising a combination of a layer 6 of adhesive, an additional layer of plastic film 7 and a heat seal layer 8. In addition, the film contains a layer 9 of adhesive for foam / film and a layer 10 of adhesive for plastic / foam.

[0025] In a preferred embodiment of the invention, the thickness of the foam layer 3 is about 190 Pm and it is made of polyethylene foam with an initial density of about 0.63 g / ml. The plastic film layer 2 is preferably transparent PET, for example with a thickness in the range 15 to 30 μm, preferably about 23 μm. The metal foil is 15 μm thick aluminum foil. The heat-sealable pre-laminate 5 is made of a PET layer about 12 μm thick, with a coextruded adhesive layer 6, for sticking to the film 4. The adhesive is usually about 12 μm thick, for example up to 15 μm thick. The hot melt layer 8 generally has a thickness of about 12 μm.

[0026] The adhesive layer 10 is preferably made of an extrudable thermoplastic material, for example an ethylene copolymer, for example with vinyl acetate, (meth) acrylic acid or acrylate esters.

[0027] The seal shown in Figure 1 is preferably cut out to include a small flap extending beyond the periphery of the outlet of the container closed by the seal according to the invention. The flap may be folded when placing the seal in the outlet of the filled container, or may protrude beyond the circumference of the container outlet during welding. Welding occurs due to induction heating of the metal foil 4, which causes the fusible layer 8 to melt to connect the seal to the container outlet.

[0028] The second embodiment of the invention shown in Figure 2 is a flap seal 11. They are made of a plastic layer 12, a foam layer 13, a film layer 14 and a heat seal layer 15. The adhesive layer 19 sticks the foam 13 to the film 14 while the layer the adhesive 20 adheres the plastic film layer 12 to the foam layer 13. According to this embodiment, the flap layer 21 is also provided. It is placed between the adhesive layer 20 and the foam layer 13, which adheres to the plastic film layer 12, leaving the connection 22 between the plastic film 21 and the foam 13 without adhesion. This allows the consumer to lift the flap to remove the seal from the container.

[0029] The embodiment shown in Figure 2 is preferably made by providing a plastic film for producing layer 12 and flap 21, to a lamination station with pre-formed laminate of foam 13 and film 14, together with the appropriate adhesive 19 and heat-sealable part 15, with glue applied on the lamination stand. The adhesive can be applied by pouring the extruded material, for example as shown in Figures 3 and 4. Alternatively, instead of pouring the extruded material, the liquid can be applied by means of a roller, knife or other liquid coating device to the interface. Alternatively, the heat seal layer on the underside of the plastic film can be fused by applying pressure.

[0030] Figure 3 is a schematic of the method for producing the flap seal shown in Figure 2.

[0031] The pre-formed laminate 27, comprising as an upper surface a layer 13 of foam, also comprising foil 14 and a corresponding layer 19 of adhesive and heat seal layer 15, is directed from the roller 23 towards the lamination station 26. From the roll 24, the flap material is introduced, typically containing a plurality of bands of the flap material actually positioned across the direction of the device, from the roll 24. The flap material and the pre-formed laminate 27 are fed together to lamination station 26. Laminating station 26 is also fed with a plastic film layer 12 from coil 28. Plastic film 12 is fed to the lamination station in such a way that it lies on the surface of the foam / flap and is glued to it with glue 20, in this case fed by pouring from extruder 29. Pressure is applied between the pressure roll 30 and roll 31, which can be heated or cooled if desired. The produced laminate is then wound on a roll 32. Optionally, the web is cut before winding and, for example, coils are obtained comprising a single web of flap material from which seals can be cut. Alternatively, the web comprising multiple webs of flap material may be wound as a single coil and cut immediately prior to use.