HK1141500B - Tab seal for sealing a vessel closed by plug or cap and method for making same - Google Patents

Description

Sealing disc with pull tab for closing a container with a plug or lid closure and method for producing the same

The present invention relates to a novel sealing disk with a pull tab (tab) for closing a container with a plug or lid closure, and a method for its preparation.

The tightness of the container with the stopper or cap closure before its initial opening is obtained by means of a sealing disc which can bond or seal (in particular by means of heat) the mouth of the container.

More particularly, the present invention relates to heat-sealable sealing discs.

Such sealing discs are constituted by a membrane seal which is placed on the entire periphery of the upper edge of the neck or mouth of the container, thereby isolating the container from the outside, and by a support which, on the other hand, is generally thick and which is inserted into the bottom of the stopper without having to be fixed. The support and the film seal may be joined by a temporary adhesive prior to initial opening of the container.

The function of the membrane seal is firstly to make the container safe before initial opening. Moreover, it provides a major external seal. In addition to this, certain properties must be developed that are compatible with the contents to be isolated, for example the film seal must be food grade as long as the contents are themselves food.

As regards the support, it serves to take up the clearance between the bottom of the lid and/or stopper and the upper part of the neck of the container, and in addition it provides secondary tightness when the membrane seal has been partially or completely removed. It is therefore able to withstand a certain compression by means of memory effects, in particular in order to absorb these tolerances.

In practice, the sealing disk is embedded in the bottom of the cap or plug. Once the container is full, the plug or cap with sealing disk is screwed or clipped onto the container. The membrane seal portion of the sealing disk is then brought into contact with the mouth of the container. The film seal then seals the mouth of the container by induction heat sealing. The heat sealing may be effected by the combined action of conductive material embedded in the thickness of the sealing disk which heats up under the action of an electric induction heater causing the sealing membrane to soften over the mouth of the container. The conductive material may be embedded in the support or embedded in the membrane seal. It is typically embedded in the thickness of the membrane seal. Upon initial opening of the container, the support embedded in the bottom of the plug separates from the membrane seal while the membrane seal remains sealed against the mouth of the container. The tightness at the closure position of the container is only provided by the support portion of the sealing disc applied to the mouth of the container by pressure, after the removal of the membrane seal by the consumer.

In order to make it efficient and easy for the consumer to pull open the film seal, it has been proposed to incorporate an easily graspable pull tab on the film seal, for example as described in document FR- A-2716407.

However, the presence of this protruding tab makes it difficult to position the sealing disk at the bottom of the plug or lid due to the extra side thickness. It is also difficult to position the pull tab safely with respect to the threads or clips provided in the plug or lid to avoid the risk of damaging the pull tab when closing or opening the plug or lid.

Document DE 3920324 describes an induction heat sealable sealing disc consisting of a support and a membrane seal provided with a pull tab, which support and membrane seal do not engage each other at any time. In the three embodiments shown, only one (fig. 1) includes a pull tab folded over its entire surface. The pull tab is composed of a combination of a film and a sealing layer, with an aluminum sheet disposed in a support.

The problem to be solved by the present invention is to develop a sealing disc with a pull tab of the type described in document DE 3920324, which has a layer of temporary adhesive between the support and the membrane seal, but without causing the risk of the pull tab adhering to the temporary adhesive during the assembly operation or during the heat-sealing operation.

To solve the problem of the risk of adhesion during induction heating, the applicant has developed a sealing disk having a pull tab in which a folded-back portion in contact with a support is free of a heat-sealing layer, and also developed a method of manufacturing the sealing disk.

In other words, the invention relates to a heat-sealable sealing disk for closing a container with a stopper or lid closure, comprising a support to be placed on the bottom of the stopper or lid, and a film seal applied to the mouth of the container comprising at least one reinforcing film and a heat-sealing film, said film seal having an extension constituting a pull tab, the entire surface of which is folded back onto the surface of the film seal in contact with the corresponding face of the support.

The sealing disk is characterized in that the portion of the pull tab that contacts the support does not have a heat-sealing film after the pull tab has been folded, and in that the support and the membrane seal are joined by a temporary adhesive.

According to the invention, the tab is constituted by an extension formed in the whole or part of the thickness of the membrane seal. It never consists of a pull tab added to the membrane seal.

There is no limitation on the number of layers that make up the support and membrane seal, it being understood that adhesives may be added, particularly for bonding the membranes together.

Obviously, the sealing disc of the invention has a shape adapted to the shape of the container and of the stopper and may be circular or parallelepiped-shaped.

As regards the support, it can be made of any type of compressible material with memory recovery, in particular expanded polyethylene or expanded polypropylene, optionally with a polyethylene or polypropylene film on at least one of its two faces to obtain a certain rigidity. It may also be made of cardboard. In a particular embodiment, the support comprises a sheet of conductive material, which sheet of conductive material in the support (referred to as "conductive material" in the remainder of the description and in the claims) heats up when an induced current is transmitted, when it is assumed that the membrane seal does not have the sheet of conductive material. In practice, the thickness of the support considered is between 0.5 and 4mm, advantageously between 1 and 2 mm.

The membrane seal will now be described in more detail.

In most cases, a sheet of electrically conductive material, particularly aluminum, is embedded in the membrane seal rather than the support, thereby enabling induction heat sealing of the sealing disk to the mouth of the container in combination with the heat sealing membrane.

In other words, in practice, the film seal comprises a sheet made of electrically conductive material between the reinforcing film and the heat sealing film.

According to the invention, the sealing discs may each have two different general embodiments, one in which the heat-sealing film does not cover the lower surface of the pull tab, and another in which the entire lower surface of the pull tab is covered with the heat-sealing film.

1. Embodiments in which the heat-seal film does not cover the lower surface of the tab

In a first embodiment, the tab is made only in the extension of the reinforcing film, i.e. only over part of the thickness of the film seal. In this case, the tab consists only of the reinforcing film applied to the upper surface of the aluminum sheet. Thus, the actual film seal has a three-layer structure (heat-seal plastic film/conductive material/reinforcing film), while the tab has a single-layer structure (reinforcing film). This particular embodiment serves to avoid the potential risk of the tab adhering to the support at the fold back location during heat sealing, since no heat sealing film is present. Another advantage is that the electric field applied during induction heating is evenly distributed over the periphery of the aluminium sheet, which is not necessarily the case when the pull tab is located in the extension of the sheet. The latter case carries the risk of leakage because the sealing of the film seal to the mouth of the container is incomplete at each side of the bottom of the tab.

In the above embodiment, the ink printing may be directly performed on the aluminum sheet.

A second alternative consists in providing, instead of one reinforcing membrane, two reinforcing membranes. In this case, the film seal comprises two superimposed reinforcing films, namely a lower reinforcing film and an upper reinforcing film, respectively, and a sheet of conductive material embedded between the lower reinforcing film and the heat-seal film.

In this embodiment, it is advantageous that the pull tab is provided only in the extension of the upper reinforcing film. In this case, the first reinforcing film covers the entire upper surface of the aluminum sheet, while the second film covers the entire surface of the first film and has an extension constituting the pull tab.

In a modified embodiment, the upper reinforcing film itself consists of two superimposed reinforcing films, between which printing can be carried out. In this case, the tab is provided in the extension of the two reinforcing films constituting the upper reinforcing film.

2. Embodiments in which the entire tab is covered with a heat-sealable film

In a particular embodiment, the pull tab is formed over the entire thickness of the film seal. Advantageously, the membrane seal comprises an aluminium sheet, the upper surface of which is covered with a reinforcing membrane and the lower surface of which is covered with a heat sealing membrane. In this case, the tab has two equal area regions, a base region and an end region, respectively, separated by a transverse median fold line, the lower surface of the end region being joined to the lower surface of the base region after folding along the line. Thus, when the tab is folded back onto the membrane seal, the upper surface of the base region is in contact with the upper surface of the reinforcement membrane and the upper surface of the end region is in contact with the lower surface of the support. Obviously, the number of reinforcing films can be increased according to the desired characteristics.

In general, the materials comprising the pull tab and the reinforcing film are selected such that the strength of the materials is greater than the pulling force on the film seal.

In practice, the reinforcing film is, for example, a biaxially oriented polyester film having a thickness of 4 to 40 μm.

According to another feature, the heat-sealing film is made of a material chosen from polyethylene, polypropylene or polyester.

Furthermore, the aluminum sheet and the heat-seal film are joined by an adhesive such as a two-component isocyanate-hydroxyl adhesive. In another embodiment, the aluminum sheet is coated with a heat sealing layer.

In all cases, the thickness of the membrane seal is in practice 20 to 600 μm.

For temporary bonding between the support and the membrane seal, this can be obtained with a temporary adhesive, such as microcrystalline wax, applied at a plurality of points, or advantageously with an extruded film consisting of, for example, a polymer (such as polyethylene). The adhesive film may also be a coextruded film, each of its two sides having a different adhesive force, the more tacky surface being applied to, for example, the lower surface of the support, and the less tacky surface being applied to the upper surface of the film seal. In practice, coextruded films are polymer (typically synthetic) based films and are carefully selected by one skilled in the art to achieve the desired properties of differential adhesion. Such polymers are for example polymers or copolymers based on acetate, acrylate, polyethylene.

In general, the adhesive must be selected so that the bond between the support and the film seal is less than the bond of the heat-sealable layer to the mouth of the container.

The invention also relates to a method for producing the heat-sealable sealing disk.

1. Embodiments in which the heat-seal film does not cover the lower surface of the tab

In this case, the method of the invention comprises the following steps:

-pre-cutting said pull tab in a strip of reinforcing film,

mechanically inverting the entire surface of the pull tab onto the upper surface of the strip of reinforcing film,

-then permanently joining the lower surface of the strip of reinforcing film to the strip of heat-seal film, the assembly constituting a strip of film seal,

-simultaneously preparing a support strip,

-then temporarily joining the support strip to the film seal with a temporary adhesive to form a sealed wire rod,

-cutting a sealing disc of the desired shape over the entire thickness of the sealing wire rod in a marked manner with respect to the pull tab.

The reinforcing strip is made in a manner known per se by joining strips or films of material constituting the support, in particular those described above.

When the film seal includes a sheet of conductive material, the lower surface of the reinforcing film strip is joined to the upper surface of the sheet of conductive material in the sheet of conductive material/heat seal film assembly.

In embodiments where the membrane seal comprises a lower and an upper reinforcing film in addition to the sheet of conductive material, the tab is disposed only in the extension of the upper reinforcing film, the lower surface of the upper reinforcing film strip being joined to the assembly of: lower reinforcing film strip/sheet of conductive material/heat sealing film.

In the embodiment in which the upper reinforced film itself consists of two reinforced films, the tabs are precut in two pre-joined strips of upper reinforced film, which are then joined with the following assembly: lower reinforcing film strip/sheet of conductive material/heat sealing film.

In general, the bonding force of the one or more reinforcing films to the remainder of the film seal must be greater than the bonding force of the heat seal layer to the mouth of the container.

2. Embodiments in which the entire tab is covered with a heat-sealable film

When the film seal comprises a sheet made of an electrically conductive material, the film seal strip is prepared as follows: at least one reinforcing film is bonded to the sheet of conductive material and then to the heat sealing film.

The tabs are then pre-cut in the film seal strip and then transverse medium fold lines are cut in the tabs. The end of the tab is then folded along a transverse medial fold line onto the lower surface of the tab base, and the tab, with its surface halved, is then folded onto the upper surface of the film seal.

At the same time, a support strip is prepared, which is then temporarily joined with a film seal to form a sealed wire rod. The desired shape of the sealing disc is then cut through the entire thickness of the sealing disc strip.

The above-described process is a preferred embodiment of the present invention and is not intended to be limiting.

The invention and its advantages will be more apparent from the following examples, taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic plan view of a support constituting a gland plate of the present invention.

Fig. 2 is a plan view of a membrane seal member constituting a seal disk of the present invention.

Fig. 3 shows a cross-sectional view of a sealing disk of the invention before engagement of the membrane seal portion and the support portion according to the first embodiment.

Figure 4 shows a cross-sectional view of a sealing disk of the invention prior to engagement of a membrane seal portion and a support portion according to a second embodiment.

Fig. 5 shows a film seal in a third embodiment, wherein the pull tab is provided over the entire thickness of the film seal.

Fig. 6 shows a cross-sectional view of the sealing disk in fig. 5 before the membrane seal portion and the support portion according to the second embodiment are engaged.

Example 1

The sealing disk according to the invention is an induction heat sealable sealing disk. In particular, the sealing disk, designated by reference numeral 1 in fig. 1, is composed of a support 2 (fig. 1) and a membrane seal 3 (fig. 2) with a pull tab 4. As shown in FIG. 3, the support comprises a layer 5 made of foamed polypropylene or polyethylene and has a thickness of 1.4 to 1.7 mm. The film seal 3 is an induction heat-sealable film seal, and is composed of an aluminum sheet 6 and a heat-sealable plastic film 7 such as polyethylene, combined by an adhesive (not shown). The membrane seal also has a reinforcing membrane 8 extending as a tab 4. As shown in fig. 3, the pull tab 4 is constituted solely by the reinforcing membrane 8, is within the sealing disc before being pulled apart, and is folded back on itself over its entire length between the upper surface of the membrane seal 3 and the lower surface of the support 2. According to the present invention, the support and the film seal are joined by the temporary adhesive film 9 shown in fig. 3. The temporary film is a polyethylene type extruded film.

In this embodiment, the film seal has a reinforcing film applied to the surface of the aluminum sheet, and the pull tab consists of only the reinforcing film.

In practice, these sealing discs are placed on the bottom of the stopper, which is then screwed or clipped in, making it suitable for use on the container neck. The sealing disk is induction heat sealed.

As for the method, a film seal is first fabricated. To this end, the tab is precut on the reinforcing film and then turned over onto the film. Winding the reinforcing film and then unwinding it on the assembly formed by the aluminium sheet and the heat-seal film; the aluminum sheet was coated with an adhesive. While making the support strip. The support is joined with the film seal thus formed using a temporary adhesive. The sealing disc is cut to the desired shape in thickness and separated from the location of the pull tab.

Example 2

In this embodiment shown in fig. 4, the film seal comprises a printed layer 10, said printed layer 10 being coated with a first reinforcing film 11, the surface of which corresponds to the surface of the film seal. The first reinforcing film 11 is in turn covered with a second reinforcing film 12, said second reinforcing film 12 having an extension constituting the actual tab 4.

The fabrication method is the same as the previous method except that the pre-cut second reinforcement film is joined to the assembly formed by the first reinforcement film/aluminum/heat seal film.

Example 3

In this embodiment, the heat-sealable sealing disk has a pull tab 4 (fig. 5) made over the entire thickness of the sealing disk. More specifically, as shown in fig. 2, the film seal 3 is constituted by a heat-seal film 7, a conductive material sheet 6, and a reinforcing film 8 from the bottom up. The tab 4 is divided into two equal parts, a base 4a and an end 4b, respectively, separated by a transverse median fold line 13.

Fig. 6 shows the sealing disk before the membrane seal portion and the support portion are engaged. As shown in the figure, the upper surface of the portion 4a is folded back onto the upper surface of the reinforcing film 8, while the lower surface of the portion 4b covered with the heat-sealing film 7 is folded back onto the lower surface of the portion 4a also covered with the heat-sealing film. Thereby engaging the portions 4a and 4b with each other. The upper surface of the portion 4b without the heat-seal film comes into contact with the lower surface of the support after being separated from the support.

The above description clearly describes the invention and its advantages, especially the advantage of making a sealing disc with a pull tab that is folded back within the thickness of the sealing disc so that the sealing disc properly locates the stopper bottom without the risk of creating additional thickness or tearing the pull tab when opening or closing the container. Furthermore, and most importantly, despite the presence of the temporary adhesive, there is no heat-sealable film on the portion of the tab that is in contact with the support, so the problem of tab adhesion upon opening can be solved.

Claims (14)

1. A heat-sealable sealing disk for closing a container having a plug or lid closure comprising a support to be placed on the bottom of the plug or lid and a film seal comprising at least one reinforcing film and a heat-sealable film for application to the container mouth, the film seal having an extension constituting a pull tab, the entire surface of the pull tab being folded back onto the face of the film seal in contact with the corresponding face of the support, wherein after the pull tab has been folded, the portion of the pull tab in contact with the support is free of heat-sealable film, and wherein the support and the film seal are joined by a temporary adhesive.

2. A gland plate according to claim 1 wherein said support is made of expanded polyethylene or expanded polypropylene, optionally with a polypropylene film on at least one of its two faces.

3. The sealing disk of claim 1 wherein said membrane seal comprises a sheet of electrically conductive material between said reinforcement membrane and said heat sealing membrane.

4. The sealing disk of claim 3 wherein said pull tab is formed only in the extension of said reinforcement membrane.

5. The sealing disk of claim 1 wherein said membrane seal comprises two superimposed reinforced membranes, a lower reinforced membrane and an upper reinforced membrane, respectively, and a sheet of conductive material embedded between said lower reinforced membrane and said heat sealing membrane.

6. The sealing disk of claim 5 wherein said pull tab is disposed only in the extension of said upper reinforcement membrane.

7. A gland plate according to claim 5 wherein said upper reinforcing membrane itself is constituted by two superimposed reinforcing membranes and wherein said pull tab is provided in the extension of the two reinforcing membranes constituting said upper reinforcing membrane.

8. The sealing disk of claim 1 wherein said membrane seal comprises an aluminum sheet having an upper surface covered with said reinforcing membrane and a lower surface covered with said heat sealing membrane, and wherein said pull tab is disposed throughout the thickness of the extension of said membrane seal and has two equal area regions separated by a transverse midline fold line, a base region and an end region, respectively, the lower surface of said end region being engaged with the lower surface of said base region after folding along said midline.

9. The sealing disk according to claim 1, wherein the reinforcing film is a biaxially oriented polyester film having a thickness of 4 to 40 μm.

10. The sealing disk of claim 1 wherein the temporary bonding agent is in the form of an extruded or coextruded film.

11. A method of preparing a heat-sealable sealing disk for closing a container having a plug or lid closure, the sealing disk comprising a support to be placed on the bottom of the plug or lid, and a membrane seal applied to the mouth of the container comprising at least one reinforcing membrane and a heat-sealable membrane, the membrane seal having an extension constituting a pull tab, the entire surface of the pull tab being folded back onto the face of the membrane seal which contacts the corresponding face of the support, wherein:

-pre-cutting the pull tab in the strip of reinforced film,

mechanically inverting the entire surface of the pull tab onto the upper surface of the strip of reinforcing film,

-then permanently joining the lower surface of the strip of reinforcing film to the strip of heat-seal film, the resulting assembly constituting the strip of film seal,

-simultaneously preparing a support strip,

-then temporarily joining the support strip to the film seal with a temporary adhesive to form the sealing wire rod,

-cutting the sealing disc of the desired shape over the entire thickness of the sealing wire rod in a marked manner with respect to the pull tab.

12. The method of claim 11, wherein when the film seal includes a sheet of conductive material, a lower surface of the reinforcing film strip is bonded to an upper surface of the sheet of conductive material in the sheet of conductive material/heat seal film assembly.

13. The method of claim 12, wherein when the film seal comprises a lower reinforced film and an upper reinforced film, the pull tab is disposed only in the extension of the upper reinforced film, the lower surface of the upper strip of reinforced film being joined to the assembly of: lower reinforcing film strip/sheet of conductive material/heat sealing film.

14. The method according to claim 13, wherein when the upper reinforced film itself consists of two reinforced films, the tabs are precut in two strips of previously joined upper reinforced film, which are then joined to the following assembly: lower reinforcing film strip/sheet of conductive material/heat sealing film.