Laminate

Stratified

The present invention relates to a method for producing a laminate that is used in container closure systems.

In the packaging of a wide variety of materials ranging from pharmaceutical products to instant coffee it is common to provide a seal in the form of a seal connected to the mouth of the container and a threaded cap that covers and protects the seal, which provides a cap that is sealed. You can close after separating the seal to access the container. Frequently the closure is designed so that the bottom side of the seal has a heat sensitive adhesive coating or a meltable plastic layer coated by a metal sheet. The seal is placed against the mouth of the container and interposed against it by the threaded cap applied. After induction heating, the metal sheet is heated which activates the heat sensitive adhesive layer or melts the plastic layer so that, upon cooling, the seal is attached to the mouth of the container.

A problem encountered with such seals is the difficulty of separating the seal from the container. In this regard, this has been resolved by including a tongue that extends laterally from the mouth of the container and can be picked up by the consumer to facilitate separation of the seal. An example of such a system is the structure called "upper tongue", described in detail in US Patent No. 4,961,986. This system includes a multilayer substrate that is partially de-stratified by providing a tongue that is usually within the circumference of the mouth of the container. In United States Patent Number

4,961,986 this is achieved by forming the substrate of several layers that adhere to each other only in a part of its extension. US Patent No. 4,961,986 further describes that the threaded cap may include some type of cover in addition to the sealing material. In said two component system, in which the sealing and the cover are provided separately, the two components have to be coupled in two different operations.

As this is expensive and increases the complexity of the coupling process, the problem has focused on the development of a single component sealing and covering system that avoids the need for two different coupling operations. For example, patent application EP-A-1472153 describes a single component sealing and covering system, to attach it to a threaded cap, which includes a tab. In the detailed product, the sealing portion of the system adheres to the cover portion by means of a removable layer so that the seal and the cover are separated with a separation force in the range of 20 to 90 g and at a speed of 1,500 mm / min in a 25 mm wide sample.

Another tongue system is the successful "Lift" n "Peel" ® commercial system. This may comprise a primary seal and a secondary cover or only a primary seal and is usually only a primary seal. The tongue is formed by interposing a layer of poly (ethylene terephthalate) in the primary seal that extends only over a portion of the surface of the shell. The poly (ethylene terephthalate) layer is interposed between a foam layer and an upper layer of EVA / PET [EVA = ethylene-vinyl acetate copolymer; PET = poly (ethylene terephthalate)]. When heating, the EVA adheres to the interposed layer and a portion of foam still exposed and, due to the interposed plastic layer, a tongue is formed which is completely within the contour of the cover.

Patent method WO 97/02997 describes a method for including a tongue in a primary sealing laminate. In this case, three feeds are passed to a cold roller in contact with a pressure roller. The first feed that will form the upper layer of the primary sealing laminate is an ethylene-vinyl alcohol barrier layer interposed between two layers of polypropylene. The second feed is an insulating member that can be PET and the third feed is extruded tongue material, for example, polypropylene, which forms a layer across the entire width of the laminate that forms the top layer. The three feeds are brought into contact at the point where they contact the cold roller and the pressure roller. The cold roller cools the extruded tongue material maximizing its amorphous properties and causing the stratification of the three layers.

A problem that can be identified with such systems is that by attaching the system that includes the tab to a container to be sealed, a non-uniform level of bonding to the package is obtained, tending to form stronger bonds below the portion with Cover tab compared to the portion without tongue. There is an additional risk that, by heating the metal sheet of an induction system, the upper sealing layer can be burned when the heat transferred to this layer is too large.

Another problem encountered with such seals is that when used in packages to be stored at low temperatures, for example, in dairy industry applications, after storing at such temperatures, the bond between the substrate seal and the tongue has a tendency to fail. This means that, when the seal is separated from the container, as the joint fails, the tab separates from the substrate seal leaving it attached to the container instead of separating it.

Therefore, it is clear that a simple and economical method is needed to include a tongue material in a primary sealing laminate, which solves the problems of needing to produce an effective tongue and achieve a uniform level of bonding to the package to be seal.

Patent application WO 2006/108853 describes a method for producing a primary laminate that includes a tongue material and comprising the steps of:

feeding a stratification plant a sealing laminate that includes a heat sealable layer, a sheet of metal sheet and a top layer of polyester,

continuously feed to the stratification plant a tongue material that is narrower than the sealing laminate so that the lower layer of the tongue material and the upper face of the sealing laminate are in non-adhesive contact forming a primary substrate whose upper face is partially composed of the upper face of the tongue material and partially of the upper face of the sealing laminate,

continuously feed the stratification plant a plastic film material having an upper surface and a lower surface so that the lower surface of the plastic film material is in contact with the upper face of the primary substrate, and

continuously extrude a polymeric adhesive between the upper face of the primary substrate and the lower surface of the plastic film material and cool so that the upper layer of the sealing laminate and the plastic film adhere to each other. A secondary sealing material can be attached to the primary laminate, which ultimately forms a joint within a threaded cap to seal a partially empty container. This secondary sealing material may comprise a layer of foam.

In this regard, the present invention provides a method for producing a primary laminate that includes a tongue material and comprising the steps of:

<dl><dt>(to) </dt><dd>feeding a sealing laminate to a stratification plant that includes a layer of melt application adhesive, a sheet of metal sheet and a top layer of foam, </dd></dl>

<dl><dt>(b) </dt><dd>continuously feed to the stratification plant a tongue material that is narrower than the sealing laminate, so that the bottom layer of the tongue material and the top foam layer of the sealing laminate are in non-adhesive contact forming a non-adhesive contact. primary substrate, whose upper face is partially composed of the upper face of the tongue and partly of the upper foam layer of the sealing laminate before reaching the stratification plant, </dd></dl>

<dl><dt>(c) </dt><dd>continuously feed the stratification plant a plastic film material having an upper surface and a lower surface so that the lower surface of the plastic film is in contact with the upper face of the primary substrate, and </dd></dl>

<dl><dt>(d) </dt><dd>continuously extrude between the top layer of the primary substrate and the bottom surface of the plastic film material a polymeric adhesive that is an ethylene copolymer and an alkyl (meth) acrylate having a melt flow index of 1 to 10 dg / min (190 ° C, 2.16 kg) so that the two adhere to each other. </dd></dl>

The bonding force between the top foam layer and the plastic film material is preferably greater than 15 N / 12.5 mm at 330 mm / min when the plastic film and the tongue material are pulled at 90 ° with respect to to the longitudinal axis of the tongue material from the sealing laminate with a separation angle of 180 °. Here, upper surface and lower surface of a component refer to the orientation of the component in the seal formed from the laminate when the seal is used in a container in an upright position.

The apparatus necessary for the method of the present invention must have different unwinding units for the feeds of the laminate and arranged to allow simultaneous unwinding. The laminate feeds are fed to the stratification plant comprising a pressure zone between two rollers. At this point, the feeds adhere to each other producing the primary laminate that includes a tongue material. The adhesive is applied vertically downward in the form of a curtain over the pressure zone where the feed rollers contact. The speed of the feed rollers that form the pressure zone must be greater than the rate of application of the adhesive to prevent the formation of molten adhesive in the pressure zone that could cause a non-uniform coating. The adhesive is applied directly from the nozzle head of an extruder.

The top layer of the sealing laminate is a foam layer. It has been found that the inclusion of a layer of foam is important to ensure a uniform seal in the package to be finally sealed. More specifically, this foam layer has a mattress effect so that there is a pressure equalizing effect that is exerted around the circumference of a closure assembly of the package cut from the

layered on the cap attached to a container when heated by induction to adhere the cover to the mouth of the container. Thus, the difference in thickness of the tongueless portion and the tongue portion does not cause a difference in the strength of the joint formed under these portions. That is to say that a substantially uniform bond strength is obtained between the laminate and the mouth of the container around the entire circumference. The foam layer also serves the purpose of providing integrity and rigidity to the structure.

The foam may comprise several layers, for example, of coextruded materials having surface layers selected to be compatible with adjacent surfaces. The foam is preferably formed from polymers and copolymers of lower alkenes, preferably ethylene and / or propylene. Foams formed of mixed polymers can be used. Each of the several layers can be formed from the same polymers, mixed in different proportions. The foam layer may be a honeycomb material formed by stretching particulate material containing polymers. In these alveolar films, the polymer may comprise polypropylene. Preferably the film is formed by the inclusion of blowing agents, such as dissolved gases, volatile compounds or compounds that react chemically.

Preferably the foam layer is a pure foam and is composed of medium or high density polyethylene (MOPE or HOPE). To prevent the extruded polymeric adhesive from potentially oozing throughout the structure, it is preferred that the foam has a closed cell structure. In a preferred embodiment, the foam layer is formed from a high density foam. In a particularly preferred embodiment, the foam has a density in the range of 0.5 to 0.8 g / ml, preferably in the range of 0.55 to 0.75 g / ml and most preferably in the range of 0 , 6 to 0.7 g / ml.

In a preferred embodiment of the present invention, the foam layer has a thickness in the range of 75 to 300 Im. To be convenient for the sealing described herein, the foam layer needs to have a reasonable degree of flexibility.

The key issue with respect to foam is the type of polyethylene. If the LOPE ratio is too high, then the melting point determined by differential scanning calorimetry (OCS) will be too low. This will cause the foam to melt in the induction sealing operation causing an exposed aluminum ring around the circumference of the seal. The melting point of the foam is preferably 129 ° C, preferably at least 120 ° C and more preferably at least 125 ° C, for example 128 ° C.

The sheet metal layer and the adhesive layer in the molten state of the sealing laminate are the conventional ones for induction sealing systems. The melt application adhesive is convenient for forming an adhesive seal in a food or beverage container (ie, edible products) that has, for example, a peel strength of 3 to 6 N when 45 ° is removed from the container the cover at room temperature.

It is preferable that one of the components of the primary laminate is printed. This can be achieved in one of two ways: the tongue that forms a part of the primary laminate or the plastic film may include a printed layer.

As indicated above, an essential feature of the primary laminate produced by the method of the present invention is the inclusion of a tongue material so that the seal will have a free tongue. In the primary sealing laminate produced, in which the relative dimensions of the tongue are not limited, it may be preferable, for example, that the tongue is completely within the circumference of the mouth of the container and typically occupies approximately 50% of the sealing surface, when the primary laminate has a diameter less than 36 mm. The width of the tongue can be 10 to 100 mm, for example, 15 to 45 mm. The tongue is provided by adhering the tongue material to the upper polyester layer of the heat sealable laminate. The tongue material that is fed to the stratification plant as detailed in step (b) is narrower than the heat sealable laminate.

Preferably the tongue material is formed of a polyester, more preferably of poly (ethylene terephthalate). In one embodiment of the present invention, the bottom surface of the tongue material that finally contacts the top foam layer of the heat sealable laminate may be coated with a removable material, for example, silicone. This minimizes the possibility that during extrusion, when the finished primary sealing laminate adheres to a container by induction heat sealing operation, the tongue material adheres to the top layer of foam. Typically such removable coatings are not necessary; however, the tongue material may also include a colored or printed layer formed of polyester and bonded to the upper surface of the other polyester layer by an adhesive bonding layer.

In step (b), in one embodiment of the present invention, instead of feeding a single tongue material, the feed may include a plurality of tongue materials disposed along the machine at regularly spaced intervals. In this way, a wide sheet of primary laminate can be formed which can be cut as desired (in line or in subsequent operations) thus improving the efficiency of the system.

As detailed in step (c), the third feed that is fed to the stratification plant is a plastic film material. Preferably the plastic film is selected from the group consisting of polyester, preferably poly (ethylene terephthalate), polyamide, polypropylene or a composite. Most preferably, the plastic film is made of poly (ethylene terephthalate). The width of this material is the same or a little smaller than the width of the heat sealable laminate. The adhesive curtain will extend out of the edge of the plastic film material and the portion of the edge that forms a wider bead is collected on the foam face of the sealing laminate to be cut and separated, minimizing waste of expensive PET.

Preferably this plastic film layer is transparent so that the printing of the lower layers is visible to the end users. Preferably the thickness of the plastic film is at least 20 Im. More preferably the thickness of the plastic film is in the range of 20 to 40 Im. In a preferred embodiment of the present invention in which the material of the plastic film is PET, this film preferably has a surface with better adhesive properties, for example, formed by coextrusion. Preferably the plastic film is subjected to a corona discharge treatment on the surface that ends up being the outermost surface of the product, this treatment being carried out upstream of the stratification plant. This is done to ensure that the bond formed to the polymeric adhesive in step (d) is strong enough. Examples of suitable PET materials include Lumirror 10.47, which is a film that is coextruded on one face and commercially available from Toray.

Before reaching the stratification plant, the bottom face of the tongue material and the top foam layer of the heat sealable laminate contact. There is no adhesion between the two feeds. The two feeds are fed to the stratification plant in contact with each other. To achieve this, the two feeds must approach the stratification plant from the same face with respect to the extruder. The combination of the heat sealable laminate and the tongue material in contact with each other is called the primary substrate when they pass together to the stratification plant. Since the tongue material is necessarily narrower than the heat sealable laminate, the upper face of the primary substrate presented to the laminate plant is partially formed from the upper face of the tongue material and partially from the upper foam layer of the heat sealable laminate.

In the stratification plant, the primary substrate contacts the plastic film material that is fed simultaneously to the stratification plant but from the opposite side of the adhesive curtain. At the point where the upper face of the primary substrate contacts the lower surface of the plastic film material, the polymeric adhesive is continuously extruded between the two surfaces. The result is that the plastic film material adheres to the entire surface of the upper face of the primary substrate. This means that in a part of the width the plastic material will adhere to the upper foam layer of the heat sealable laminate and in the remaining part of the width the plastic film material will adhere to the upper layer of the tongue material. This means that, in a preferred embodiment in which the primary laminate is cut, the result is that a portion of the tongue is formed that is completely within the circumference of the seal.

The joint formed between the top foam layer of the heat sealable laminate and the plastic film material must have a strength greater than 15 N / 12.5 mm at 330 mm / min when the tongue formed of the tongue material and the film material of plastic are pulled from the heat sealable laminate at 90 ° with respect to the longitudinal axis of the tongue [which is the longitudinal direction (machine direction) of the manufacturing apparatus] with an angle of separation of the 180 ° stratified. This is to ensure that when the tongue is used to separate the seal from the container, the plastic film of the tongue remains adhered to the primary laminate after the application of a detachment force to the tongue.

The take-off test is conveniently performed using a Hounsfield tensile tester. Each test is performed on three samples. The samples are cut from a 12.5 mm wide strip taken along the laminate. The samples must be at least the length of the distance between two strips of tongue material. One end of the sample should be cut from the tongue near a longitudinal edge, allowing the tongue that comprises tongue material and plastic film material to separate from the heat sealable laminate. The tongue material is mounted on a tension gauge jaw, the heat sealable laminate being fixed on the other jaw. The jaws are separated at an angle of 180 °. A 50 N load cell is used for the test. The device is adjusted to allow an elongation of at least 25 mm with a speed of 330 mm per minute.

The recorded results include the "initial peel force", which is the force necessary to overcome the initial resistance of the tongue to be de-stratified. Subsequently, the "force of movement" is measured, which is the force necessary to continue separating the strip from the heat sealable laminate. In general the force of movement is substantially constant. In the present product, the initial detachment force is the most important since assuming that it is greater than the force necessary to detach the seal from the top of the container to which it is attached, the plastic tongue / film will remain attached to the sealed when the detachment begins, the force necessary to continue this detachment being less when the seal is detached from the container.

The peel test is schematically illustrated in Figure 4. This figure shows the tongue formed of the tongue material 8, adhesive film 9 and plastic film 10, the tongue being mounted on the upper jaw 30 of the tension meter. The heat sealable laminate formed by the foam layer 7, metal sheet 5 and application adhesive in molten state 4 is mounted on the lower jaw 31 of the tension meter. The jaws move apart in the direction of the arrow, noting the force necessary to separate the materials at an angle of 180 °. The figure is schematic, with the thickness greatly exaggerated.

Much research has been done on the selection of a polymeric adhesive that can be extruded as described in the present method but without taking into account the problem that the bond formed becomes brittle when stored at low temperatures. Additionally, it is necessary that the adhesive has a sufficiently high surface energy to adhere to plastic materials, such as PET, but does not damage the used metal rollers. In this regard, it has surprisingly been found that these problems can be solved by selecting a polymeric adhesive having a melt flow index in the range of 1 to 10 dg / min, preferably less than 5 dg / min (ASTM O1328; 190 ° C, 2.16 kg). The adhesive must be able to be extruded at sufficiently low temperatures to avoid damaging (melting) the foam layer but must have high enough tear strength at low storage temperatures and at room temperature to avoid de-stratification of the seal during separation of the sealed container using the Adhered tongue. Materials with melting points (ASTM O3418) in the range of 70 to 100 ° C and densities in the range of 0.920 to 0.955 g / cm 3 are suitable, for example about 0.940-0.945 g / cm 3. Copolymers of ethylene with C1-12 alkyl esters (meth) acrylates (for example, acrylate or methacrylate esters), especially C1-4 alkyl esters, preferably acrylic acid, especially butyl acrylate or methyl acrylate can be used. The copolymers are random copolymers, for example, with acrylate molar ratios of 0.5 to 25%, especially in the range of 1 to 20%. Convenient copolymers are available in the Bynel 2200 series, from OuPont. Other copolymers that have a higher melt flow index and that may be suitable for laminates that are not used at temperatures below the freezing point are Lotryl MA series copolymers. Preferably the polymeric adhesive has a melt flow index of about 2 dg / min (190 ° C, 2.16 kg). A particularly preferred polymeric adhesive is an ethylene / methyl acrylate copolymer having a melt flow rate of about 2 dg / min, marketed as Bynel 22E780.

In the process of the present invention, in step (d), the polymeric adhesive is extruded through the nozzle head. The nozzle head is preferably at a temperature in the range of 300 to 330 ° C. The height of the nozzle head from the pressure zone is preferably in the range of 10 to 30 cm, more preferably in the range of 15 to 25 cm, for example, approximately 20 cm. The width of the groove is approximately 0.5-1.0 mm. The speed of the pressure rollers in the stratification plant is preferably in the range of 20 to 100 m / min, more preferably 50 to 80 m / min. In order that the rollers can operate with a feed having a non-uniform surface due to areas where a tongue is present and areas where a tongue is not present, it is preferable that the feed rollers have a Shore hardness At about 70-90, for example, a Teflon coated roller pressing against a cold metal roller.

After extrusion of the polymeric adhesive, pressure is applied to the primary laminate by means of cold pressure rollers downstream of the stratification plant to facilitate adhesion. Preferably the cold pressure rollers have a temperature of about 23 ° C.

In a preferred embodiment of the present invention, the coating weight of the adhesive layer is in the range of 25 to 45 g / m2.

So that any impression on the tongue material can be seen, preferably the polymeric adhesive is transparent.

In a further aspect of the present invention, the primary laminate that includes a tongue material can be subsequently wound onto a final roller, optionally after being cut. Alternatively, cutting can be done at a different stage, for example, at a different location.

In general, the heat sealable laminate of the present invention is obtained in the form of wide strips. Therefore, to form the tabs, it is necessary to cut the wide strips of the heat sealable laminate to form narrower strips. These narrower strips can be punched or cut to form a seal ready to be applied to a container. It is necessary to cut the wide strips to narrower strips with precision to ensure that the cuts are made in the correct positions to produce the tabs. Then the seal can be punched out from the narrowest strips produced in the cutting stage and can be fixed on the top of a threaded cap. This can be done in a procedure or location other than the method of manufacturing the heat sealable laminate. The packaging to which the sealing is applied can be made of glass or plastic material, such as polyethylene, polyester, polyvinyl chloride, polypropylene or acrylonitrile-butadiene-styrene polymer.

A threaded cap equipped with a seal such as the one described above can be threaded into the open mouth of a container, the seal being thus interposed between the open mouth of the container and the top of the cap. The sealing is then adhered by the application adhesive in the molten state on the lower surface of the laminate to the open mouth of the container by induction heating.

As described above, one of the objectives of the present invention is to provide a primary laminate that includes a tongue that produces a seal that can be effective even after prolonged storage of the laminate at low temperatures. In this regard, the applicant of the present invention has developed a rigorous test to determine whether a given seal is likely to fail at low temperatures. The primary laminate that includes a tongue material produced by the method according to the present invention is cut into three sample discs that are attached to the mouth of a container. Samples are taken from three different positions of the laminate, specifically on the left side, center side and right side. Two different types of containers are tested, the first one being a polyethylene bottle, of the chimney type, of 1 liter used in dairies and the second being a 150 ml polyester bottle called a "round load" bottle. Sample discs are sealed at the mouth of these bottles using the head and the sealing conditions indicated in the following table. Meanwhile, a metal plate is placed at the base of a freezer and its temperature is followed using a calibrated thermometer equipped with a magnetic thermocouple.

Table 1

<dl><dt>Sealed to polyethylene container </dt><dd>Sealed to polyester container </dd></dl>

<dl><dt>Temperature (° C) of the metal plate placed in the freezer </dt><dd>-23 to -27 -18 to -22 </dd></dl>

<dl><dt>Freezer type </dt><dd>Drawer Bank </dd></dl>

<dl><dt>Used bottle </dt><dd>1 liter fireplace "Round load", 150 ml </dd></dl>

<dl><dt>Equipment </dt><dd>Enercon sealing head Relco sealing head </dd></dl>

<dl><dt>Torque (N) </dt><dd> 1,5 1,2 </dd></dl>

<dl><dt>Distance adjustment (mm) </dt><dd>8 4 (4x1 mm EPE spacers) </dd></dl>

<dl><dt>Power setting </dt><dd> 75% "1" </dd></dl>

<dl><dt>Time / speed </dt><dd>Speed ​​= 24 m / min Time = "1" </dd></dl>

After sealing the samples were cooled for at least 2 minutes. The caps were removed and the bottles were placed in the freezer upside down in direct contact with the metal plate at the base of the freezer. Samples were maintained for a minimum of 2 minutes. Seals were separated from the mouths of the bottles while still in the freezer. When the entire seal could be separated from the mouth of the bottle without the plastic film material separating from the adhesive, the test result is positive. A sample fails when the plastic layer separates from the foam, which can be seen when the surface of the top plastic film layer is completely transparent instead of still having foam attached. When a sample fails, it is retested the next day. If the problem persists, the sample is rejected.

An advantage of the seals produced by the method of the present invention is that they can always be used to seal containers of edible products that need to be stored at low or high temperatures, even as low as -30 ° C or as high as 30 ° C. The invention is particularly useful when the storage temperature is in the range of 0 to 6 ° C.

An embodiment of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a cross section of an example of primary laminate including a tongue material formed in accordance with the method of the present invention, with a very exaggerated vertical dimension.

Figure 2 is a schematic diagram of the stratification apparatus used in the method of the present invention.

Figure 3 is a perspective view of a part of the apparatus illustrated in Figure 2.

Figure 4 is a cross section of a sample of the primary laminate subjected to the 180 ° peel test to check the strength of the extruded adhesive.

Figure 5 is a perspective view showing the seal placed in the mouth of a container.

Example

Commercially obtained from Isco Jacques Schindler is a sealing laminate (1) comprising a heat sealable layer (4) (applied in the molten state), a metal sheet layer (5) and a top layer (7) of polyethylene foam. This sealing laminate is wound on a first feed roller (13) of the stratification apparatus.

The second feed roller (14) is the one that provides the tongue material which, in this case, is a layer (8) of polyethylene terephthalate. The width of the layer (8) of poly (ethylene terephthalate) is in the range of 25-60 mm.

A third feed roller (15) is loaded with the plastic film material, in this case a PET material (10) that can be obtained commercially from Toray, Europe. The thickness of the PET material (10) is in the range of 23-36 Im. The PET material (10) used is a coextruded PET material available from Toray as Lumirror 10.47. The coextruded surface layer ensures optimum adhesion to the adjacent foam layer of the sealing laminate.

The sealing laminate (1), tongue material (8) and PET material (10) are fed simultaneously to the stratification plant (6) in which an extruder (17) is located vertically above the pressure rollers (18 and 19). Before reaching the stratification plant (6), the sealing laminate (1) and the tongue material (8) contact forming a primary substrate (1a).

Then, ethylene-methyl acrylate copolymer is continuously extruded (9) with a melt flow index of 2 dg / min (ASTM O1238; 190 ° C, 2.16 kg) forming a curtain at the exit of the extruder (17) between the upper face of the primary laminate (1a) and the lower face of the PET material (10). The height of the nozzle head above the pressure zone was approximately 20 cm. The conditions of the extrusion, that is, the weight of adhesive to be extruded, its speed and the temperature of the extruder head were such that, in the area of ​​pressure for adhesion, a temperature greater than about 200 ° C is obtained, for example, a temperature of approximately 250 ° C maximum. Roller 18 is a cold stainless steel roller while roller 19 has a Teflon coated surface with a Shore A hardness of 75. The rollers 18 and 19 move at a speed of 70 m / min with respect to the adhesive application speed, the pressure between both rollers being selected to prevent the curtain from wrinkling in the pressure zone. The lower face of the PET material (10) and the resulting primary laminate (1b) that includes a tongue material is passed with the lower face of the PET material in contact with a cold roller (18) at a temperature of approximately 23 ° C to be wound on the end product roller (32). This process is schematically illustrated in Figure 2.

The initial peel strength was measured as explained above and illustrated in Figure 4, of a primary laminate formed using a PET material (10) with a thickness of 36 Im and a PET tongue material with a thickness of 12 Im on the upper surface of the polyethylene foam sealing laminate, in which the coating weight of the extruded copolymer (9) of ethylene-methyl acrylate was 40 g / m2. The value was greater than 15 N / 12.5 mm at 330 mm / min.

The coating weight was determined as follows: a 0.5 to 1 m length of polyester supported on paper was transferred to the stratification plant between the primary substrate 1a and resin 9. Then a curtain of ethylene-methyl acrylate copolymer was continuously extruded between the upper polyester face of the polyester supported on paper and the lower face of the PET material (10) under the conditions of line movement. Then several 10x10 cm samples were cut across the entire width of the continuous band and their weight in grams was noted. With this figure, the weight of the polyester supported on paper and the PET material (10) was subtracted and the result was multiplied by 100 to give the coating weight in g / m2.

The sealing laminate was then cut into narrow strips. Oe these strips, circular discs were punched to form discs of the sealing laminate (16), that is, sealed. The seals were fixed inside screw caps. The threaded cap equipped with the seal was then threaded into the open mouth of a bottle. Then the cap and bottle assembly underwent an induction heating stage in which the metal sheet is heated around its periphery by the generation of parasitic currents which, in turn, melts the heat sealable layer (4) to join the sealed to the open neck of the bottle.