Patent Description:
The present adhesive valve therefore has the purpose of releasing any gas which forms inside the packaging even at very low pressures of the order of <NUM> mbar. Therefore, the present label is not specifically intended for the packaging of food products to be heated in microwaves. The present description also relates to a sheet and a container for food products comprising said adhesive valve as well as a method for manufacturing this adhesive valve or sheet.

The <CIT> describes an adhesive valve which comprises a flexible label having at least one lower surface provided with adhesive, wherein a flexible membrane is applied to the lower surface of the flexible label, is completely covered by the flexible label and has a substantially non-adhesive lower surface. In order to act as a gas venting valve, one or more incisions are formed in the flexible label and positioned straddling the plan-view projection of the perimeter of the flexible membrane. In this known adhesive valve the venting gas throughput is very much influenced by the type of adhesive used to fix the valve to the container, so that if the adhesive is too strong it is difficult for the label to lift up at the incisions, namely opening occurs at relatively high pressures, while if it is too weak there is the risk that the valve does not perform correctly its sealed closure function.

In order to solve this technical problem, the publication <CIT> describes a similar adhesive valve, in which the flexible membrane is always completely covered by the flexible label, but is provided with incisions which intersect with incisions formed in the flexible label.

These known adhesive valves have, however, a mode of operation which can be improved in applications which require a pressure threshold for discharging of the gases inside the packaging which is below the <NUM> mbar of conventional valves and, especially, of the order of <NUM> mbar and, and/or high gas discharging speeds, substantially higher than <NUM> mbar/s, namely of the order of mbar/s and possibly equal to about <NUM> mbar/s.

The publication <CIT> in the name of the same Applicant discloses a valve which, compared to the valves described above, has on the lower face of the label a non-adhesive zone which, in plan view, has a predefined distance from the incisions provided on the said label for discharging the gas. Even though favourably regarded, this solution is such that it is possible to have a discharge pressure not less than about <NUM> mbar.

In order to reduce the opening pressure of these conventional valves, it is possible to move the non-adhesive zone to the and/or use a greater quantity of deactivating agent in order to form the non-adhesive zone on the adhesive face of the label.

However, this requires the adoption of stricter production tolerances which tend to complicate and slow down the production process, with negative consequences for production cost-efficiency.

<CIT> describes an adhesive valve in which the opening pressures of the valve are very low.

In this known adhesive valve there is no adherent portion of the flexible label along the path provided for the gases between the openings in the sheet of the container and the openings in the flexible label, namely there is very broad non-adherent portion which, in plan view, is not spaced from the openings in the flexible label, such that the valve has a relatively limited gas-tightness and therefore requires a given quantity of liquid, in particular oil, arranged between the flexible label and the flexible membrane in order to maintain the gas tightness. This liquid makes the adhesive valve more costly and more difficult to manufacture, preventing also the possibility of having relatively broad openings in the flexible label, otherwise the liquid would escape from the adhesive valve, thus limiting the possibilities of use of the adhesive valve.

Moreover, such a conventional valve has a substantial drawback associated with its suitability for industrial production: in fact the flexible label and the flexible membrane have the same area, with the result that the flexible label cannot adhere to the sheet of the container such that the sheet or strip-like support of the adhesive valves cannot be punched in order to obtain the respective flexible membranes.

Further adhesive valves are known from <CIT> and <CIT>.

The problem underlying the present invention is therefore that of discharging gas at low pressures, namely about <NUM> mbar, or even lower, without giving rise to the aforementioned drawbacks. The task of the present invention is therefore that of providing an adhesive valve which solves this problem.

In connection with this task, an object of the present invention is to provide an adhesive valve which allows faster venting of gases than conventional adhesive valves.

Another task of the present invention is to propose a method for manufacturing an adhesive valve which is simple and low-cost to implement, while allowing the creation of adhesive valves which allow gases to be discharged at low pressures and more rapidly compared to conventional valves.

This task, as well as these and other objects which will become clearer below are achieved by an adhesive valve, a sheet, a container and a method according to the respective attached independent claims.

Owing to its particular non-adherent portion, the adhesive valve allows regulation of the gas flow though the incisions or incision in the sheet which forms the walls of a container onto which the adhesive valve is applied. In particular, the non-adherent portion allows raising of the flexible label of the valve in the presence of gas under pressure, so as to create a gas flow passage between the incisions of sheet and those of the flexible label, even when this sheet is pulled or folded.

Owing to the particular arrangements, dimensions, and forms of the flexible label, the flexible membrane, the non-adherent portion and/or the incision in the flexible label, the effects of any deformation of the adhesive valve on its functionality are further limited.

The valve and the sheet according to the present description may furthermore be manufactured using a relatively simple, low-cost and rapid method, preferably involving mass-production, in particular if continuous and uniform layers are used to form the flexible label, the flexible membrane and/or the adhesive layer between them.

Further advantages and characteristic features of the adhesive valve, the sheet, the container and the method according to the present description will become clear to persons skilled in the art from the following detailed and non-limiting description of embodiments thereof with reference to the attached drawings in which:.

With particular reference to the said figures, an adhesive valve according to the present invention comprises:.

The lower surface 2a of the flexible membrane <NUM> is substantially non-adhesive, and, in plan view, a portion of the flexible membrane <NUM> is arranged under the incision 1b of the flexible label <NUM>.

The flexible label <NUM>, in plan view, has at least one flap which extends beyond the flexible membrane <NUM> in order to adhere to a sheet <NUM> so as to retain on the latter said flexible membrane <NUM>.

In other words, looking at the adhesive valve <NUM> in plan view, the flexible label <NUM> has at least one flap which extends beyond the perimeter of the flexible membrane <NUM>.

The flexible label may have a central part which, in plan view, is superimposed on the flexible membrane <NUM>, for example two opposite ends which extend from the central part beyond a perimeter of the flexible membrane so as to be able to secure it to a sheet <NUM> on which the adhesive valve <NUM> is applied with the flexible membrane arranged between the sheet <NUM> and the flexible layer <NUM>.

With reference to the embodiments shown in the attached <FIG>, by way of a non-limiting example, the flexible label <NUM> and the flexible membrane <NUM> may be configured and joined so that, viewing in plan view adhesive valve <NUM>, the flexible membrane <NUM> is situated within the perimeter of the flexible label <NUM>.

In this way, when it is applied to a sheet <NUM>, as can be seen for example in <FIG>, the adhesive valve <NUM> has a perimetral portion of the flexible label <NUM> which adheres directly to the sheet <NUM> and which surrounds the flexible membrane <NUM>.

According to the present invention, the adhesive valve <NUM> has a particular feature in that the lower surface 1a of the flexible label <NUM> comprises at least one non-adherent portion which in plan view, is adjacent to the flexible membrane <NUM> or at least partially superimposed on the latter.

Furthermore, according to the present invention, the incision 1b, in plan view, crosses the non-adherent portion <NUM> and is not spaced from the latter.

With particular reference to the embodiment of the present invention shown by way of a non-limiting example in <FIG>, the adhesive valve <NUM> comprises, in a manner known per se, at least one flexible label <NUM> having two surfaces and at least one lower surface 1a provided with adhesive. At least one flexible membrane <NUM> having two surfaces may be applied under the lower surface 1a of the flexible label <NUM> and has a substantially non-adhesive lower surface 2a, namely a surface which is not provided with adhesive or in any case is substantially less adherent than the lower surface 1a of the flexible label <NUM> provided with adhesive.

Alternatively or in addition, the upper surface of the flexible membrane <NUM>, in contact with the lower surface 1a of the flexible label <NUM>, is substantially non-adhesive so as to allow gas to penetrate between them overcoming the tendency of natural adhesion of the two surfaces, namely the Van der Vaals force in combination with the accumulation of electrostatic charges due to the chemical nature of the adhesive, which tends to keep them in mutually adhering contact.

The flexible membrane <NUM> is preferably obtained by means of punching of a support <NUM> made of the same material, in sheet or strip form, which has a greater area than the flexible label <NUM> and on which one or more flexible layers <NUM> of the same type, arranged in at least one row, may be applied. The label or the flexible labels <NUM> may also be obtained by means of punching of a sheet or strip with larger dimensions, having a surface provided with adhesive, wherein the surplus part, namely the part not comprising the label or the labels <NUM>, is removed after application of the labels on the support <NUM>.

The flexible label <NUM> and the flexible membrane <NUM> may be obtained from a film of plastic material suitable for coming into contact with food products, belonging in particular to the group composed of polypropylene (for example with a thickness of between <NUM> and <NUM> microns), polyester (for example with a thickness of between <NUM> and <NUM> microns) or plastic materials with equivalent characteristics. In particular, the film of the layer of the flexible membrane <NUM> may comprise paper, polyethylene terephthalate and/or enriched polypropylene or a PE-RVOH laminate. The film of the flexible label <NUM> may be formed by a laminate with several layers, in particular comprising the same plastic materials, polyethylene, paper, aluminium and/or a polyamide film, for example with a thickness of between for example <NUM> and <NUM> microns, or a PE-EVOH-PE laminate. Moreover, the film of the flexible label <NUM> may be made of recyclable materials such as polylactic acid and/or may be a multilayer laminate, comprising an inner layer, which comprises the lower surface 1a, made for example of a material from among those indicated above, as well as an outer layer, which comprises the upper surface, preferably made of a barrier material which increases the impermeability of the label <NUM>.

Preferably, the material which forms the flexible label <NUM> is less rigid than the material which forms the flexible membrane <NUM>. For example, the flexible label may comprise a combination of polypropylene, which may have a thickness of about <NUM> microns, and PE-EVOH, which may have a thickness of about <NUM> microns, where the flexible membrane <NUM> may comprise a layer of polyethylene terephthalate, having a thickness which may be between about <NUM> microns and <NUM> microns and preferably equal to <NUM> microns.

One or both the surface of the flexible membrane <NUM> may be treated with a material which is preferably suitable for alimentary use and able to make the membrane non-adherent or only slightly adherent, in particular silicone or another coating of a per se conventional, but in any case dry type.

The layer of adhesive which may be applied to the lower surface 1a of the flexible label <NUM> may be an adhesive of the PSA (Pressure Sensitive Adhesive) type, in particular may be an acrylic adhesive which is water-based or of the UV crosslinking type or an acrylic adhesive with organic solvent, or may be a silicone-based adhesive suitable for high temperatures (up to <NUM>) depending on the particular implementational requirements of the invention.

Further characteristics of the materials and method for manufacturing the flexible label <NUM> and the flexible membrane <NUM> may be those described in <CIT> and in the publication <CIT>.

The flexible label <NUM> is shaped with at least one incision 1b so as to connect the two surfaces of the flexible label <NUM>. In particular, the incision 1b may be straight or curved, as in the embodiment shown in <FIG>, or may be closed, so as to define at least one opening, for example a substantially circular hole which may have a diameter not greater than <NUM>, in the flexible layer <NUM>, such that at least one portion of the upper surface of the flexible membrane <NUM> is not covered by the flexible label <NUM>, in plan view.

The incision 1b may form a recess on the edge of the flexible membrane <NUM> so that a portion of the perimeter of the flexible label <NUM>, when viewing the adhesive valve <NUM> in plan view, passes above the flexible membrane <NUM> and this portion therefore divides the flexible membrane <NUM> into a portion not covered by the flexible label <NUM> and into at least one remaining portion covered by the flexible label <NUM>. The area of the portion of the flexible membrane <NUM> covered by the flexible label <NUM> may be greater than the area of the portion of the flexible membrane <NUM> not covered by the flexible label <NUM>. The flexible label <NUM> may have a substantially polygonal and/or curvilinear form, for example a square form, as for example shown in the attached figures, or for example a circular or triangular form, with the corners which are rounded and may be provided with anti-tamper slits, not shown. The flexible label <NUM>, in plan view, may extend over an area which is x mm wide and y mm long, with x and y between <NUM> and <NUM>, in particular between <NUM> and <NUM> and preferably with x = y = <NUM>.

The flexible membrane <NUM> has a substantially circular form, or polygonal and/or curvilinear form, so that the flexible membrane <NUM> may, in plan view, cover the incision 1b of the flexible label <NUM>.

The lower surface 1a of the flexible label <NUM> comprises at least one non-adherent portion <NUM> which may be obtained by avoiding the application of the adhesive in this portion or more preferably by applying and allowing to dry a substance designed to prevent or limit adhesion, for example in particular an anti-adhesive varnish or lacquer, for example of the type referred to in the sector as "glue killer". Therefore, this substance, once applied onto the adhesive of the flexible label <NUM>, deactivates its adhesive action. The non-adherent portion <NUM> may also be obtained by applying a shaped film onto the adhesive of the flexible label <NUM>.

The non-adherent portion <NUM> covers at least partially a portion of the flexible membrane <NUM>. The flexible membrane <NUM> may have at least one incision 2c, also indicated by way of example in <FIG> by means of a broken-line rectangle, which connects its two surfaces in order to facilitate, also across it, a gas flow from the opening 5a to the incision 1b.

According to the invention the non-adherent portion <NUM> comprises at least a part thereof which, in plan view, extends towards an edge of the flexible membrane <NUM>, tapering towards the latter and widening away from it so that, during use, it is able to define a diverging channel for gas which is directed towards the incision 1b and which penetrates between the flexible membrane <NUM> and the non-adherent portion <NUM>.

For example, <FIG> shows an embodiment of the present invention which has two non-adherent portions <NUM> which, in plan view, are in diametrically opposite positions with respect to the flexible membrane <NUM>. Each has a narrow section which extends straddling the edge of the flexible membrane <NUM> and widens out as far as the incision 1b, which crosses it.

In this way, gas which passes out across the flexible membrane <NUM> and each non-adherent portion <NUM> is released towards each incision 1b.

By way of a non-limiting example, <FIG> show a cross-sectional view of the adhesive valve of <FIG> along the cross-section VII-VII, applied to a sheet <NUM> with an incision 5a which encloses a gas inside it, where the adhesive valve <NUM> is applied on the outside so as to cover the opening 5a with the flexible membrane <NUM>.

With reference to these figures, the operation of the adhesive valve <NUM> is described below, although the same description of operation applies, mutatis mutandis, in general to an adhesive valve according to the present invention.

<FIG> shows a condition in which the pressure of the gas which acts on the inside of the sheet <NUM> is not greater than the pressure of the environment on the outside of the sheet <NUM>.

In this case, the flexible membrane <NUM> adheres to the sheet <NUM>, closing the incision 5a thereof, owing to the adhesion between the flexible membrane <NUM> and the sheet <NUM> which may be produced by the electrostatic charges and/or the Van der Waals interaction.

The incision 1b is closed as a result of the adhesion of the flexible label <NUM> onto the flexible membrane <NUM> which, in each non-adherent portion <NUM>, is due to the Van de Waals interaction between the surfaces in mutual contact.

If the pressure of this gas reaches and/or exceeds a threshold which depends on the force of adhesion between the flexible membrane <NUM> and the sheet <NUM> and between the flexible label <NUM> and the flexible membrane <NUM> - which in the case of an adhesive valve according to the present invention may also be <NUM> mbar or also <NUM> mbar - this gas penetrates between the sheet <NUM> and the flexible membrane <NUM>; then, after passing over the edge of the latter or passing also through the incision 2c, the gas penetrates between the non-adherent portion <NUM> of the adhesive film <NUM> and the upper surface of the flexible membrane <NUM> until it reaches the incision 1b which opens, venting externally, for example as can be seen in <FIG> where the flow path of the gas is schematically indicated by means of a broken line arrow.

<FIG> shows a variant of the adhesive valve <NUM> of <FIG> which differs from the latter in that the two non-adherent portions <NUM> each have two narrow sections which extend towards the edge of the flexible membrane <NUM>, reaching it or passing over it, and two parts which from a respective narrow section widen as far as the incision 1b where they are joined together.

In general, the adhesive valve <NUM> may comprise a first non-adherent portion 4a of the at least one non-adherent portion <NUM> and a second non-adherent portion 4b of the at least one non-adherent portion <NUM> where the first non-adherent portion 4a and the second non-adherent portion 4b are adjacent, but separated, namely, in plan view, spaced, preferably by a distance of between <NUM> and <NUM>, or may be connected, as shown in <FIG>.

<FIG> and <FIG> show possible embodiments of the present invention showing two pairs of a first non-adherent portion 4a and a second non-adherent portion 4b.

In this way, the two non-adherent portions 4a and 4b may define two "lungs" which are crossed in succession by a gas which crosses the adhesive valve <NUM> so as to be discharged from a container which encloses it.

By suitably choosing the form and dimensions of the two non-adherent portions 4a and 4b as well as the distance between them, their mutual position and their relative forms, it is possible to adjust the pressure at which the adhesive valve <NUM> allows a gas enclosed by a container comprising it, to be released through it.

The first non-adherent portion 4a, in plan view, may extend above the flexible membrane <NUM> and/or straddle a perimetral edge thereof and is not crossed by the incision 1b of the flexible label <NUM>.

The second non-adherent portion 4b, in plan view, may extend above the flexible membrane <NUM> and as far as the incision 1b of the flexible label <NUM> and may be crossed by the incision 1b.

The second non-adherent portion 4b comprises a plurality of its parts, joined together, which, in plan view, extend towards the first non-adherent portion 4a, tapering towards the latter and widening away from it so as to define a plurality of diverging channels for the gas which is directed towards the incision 1b and penetrates between the flexible membrane <NUM> and the second non-adherent portion 4b.

The adhesive valve <NUM> may comprise at least one third non-adherent portion 4c of the at least one non-adherent portion <NUM> which, in plan view, extends between:.

In this way, the third non-adherent portion 4c defines a preferential flow passage for gas between the flexible membrane <NUM>, or an edge thereof, and the flexible label <NUM> towards the edge 1c and/or the notch 1d of the flexible label <NUM>, so as to discharge this gas parallel to the extension of the flexible label <NUM>.

The flexible membrane <NUM> may have at least one through-cut 2d which connects together the two surfaces so as to allow gas to pass through and/or has at least one channel which divides it at least partially.

The through-cut 2d and/or the channel extend between the zone of the flexible membrane <NUM> intended to cover an incision 5a of a sheet <NUM> to which the adhesive valve <NUM> is applicable, and the edge 1c and/or notch 1d of the flexible label <NUM>.

In this way, the gas may be discharged in a direction transverse to the thickness of the adhesive valve <NUM> such that, when the containers which comprise it are stacked together and, therefore, the respective valves are covered by the wall of another container, they are in any case able to discharge gas across the edge 1c and/or across the notch 1d, thus making it possible to avoid the swelling effect which is not liked at all in the packaging of shelf products, such as the packaging of ground coffee.

<FIG> show further variations of embodiment of the adhesive valve <NUM>, according to the present invention.

In particular, the flexible label <NUM> may be annular, namely have a circular form, with an incision 1b which follows a closed circle, in plan view, forming a circular opening which may be centred with respect to the perimeter of the said flexible label <NUM>.

The non-adherent portion <NUM>, in plan view, may extend in the manner of a circle around the incision 1b, surrounding it and may have parts which extend, tapering, towards the incision 1b itself, reaching it.

The perimeter of the non-adherent portion <NUM> remote from the incision 1b may, in plan view, surround the perimeter of the flexible membrane <NUM> which, in plan view, is aligned with the incision 1b so as to close it, except in order to discharge a gas from the inside of the package which comprises the adhesive valve <NUM>.

Alternatively, the adhesive valve <NUM> may have a plurality of non-adherent portions <NUM>, for example two first non-adherent portions 4a and two second non-adherent portions 4b, the first ones 4a of which extend straddling the edge of the flexible membrane <NUM>, in plan view, and the second ones of which extend so as to be crossed by at least part of at least one incision 1b of the flexible label <NUM>.

The first non-adherent portions 4a and the second non-adherent portions 4b may be spaced apart and, between them, in plan view, at least one auxiliary incision 10b may be provided.

The first non-adherent portions 4a may form a series of lugs which extend towards the incisions 1b where an auxiliary incision 10b may be provided between two lugs, and an incision 2c of the flexible membrane <NUM> may be provided in the region of at least one of the lugs.

The flexible label <NUM> may also have anti-tamper slits <NUM> which, for example, may be arranged in mutually opposite positions and be shaped so as to extend along a curved path and in particular circular or elliptical path so as to define, with their ends, a preferential initial-breakage portion of the flexible label <NUM>, should it be removed from a sheet <NUM> onto which it may have been applied.

A sheet <NUM> designed to close or form a container for food products, for example a sheet of plastic material which may be used to form a bag or be hot-welded to the edges of a rigid tray, may have at least one incision 5a which connects the two surfaces of the sheet <NUM> covered by the adhesive valve <NUM> in order to seal the inside of the container, while allowing gas to be discharged therefrom. The incision 5a in the sheet <NUM> may be straight, curved or closed, so that the portion of the sheet <NUM> surrounded by the incision 5a may be removed and form an opening, which is for example substantially circular. The incision 5a in the sheet <NUM> may also be curved, so as to form a tongue-shaped portion which may bend towards the adhesive valve or the opposite side. At least one layer of adhesive, in particular of the PSA type, for example with a rectangular shape, may be arranged on a portion of the sheet <NUM> around the incision 5a in order to promote adhesion of the flexible label <NUM> to the sheet <NUM>.

Further embodiments may comprise a plurality of incisions 5a, for example a group of closed incisions designed to form small openings, namely small holes, in a portion of the sheet <NUM>.

As already mentioned, the bottom surface 1a of the flexible label <NUM> may be joined together with the upper surface of the sheet <NUM> owing to the adhesive applied to the lower surface 1a so that the flexible membrane <NUM> is arranged between the flexible layer <NUM> and the sheet <NUM>.

In other words, if in a container, which has the sheet <NUM> as a wall, a pressure substantially greater than the pressure outside the container is generated, for example because of cooked food inside the container, the gases under pressure inside the container, penetrating between the flexible membrane <NUM> from the sheet <NUM> and then between the non-adherent portion <NUM> of the flexible label <NUM> of the flexible membrane <NUM>, create a passage between the flexible label <NUM> and the flexible membrane <NUM> so that these gases pass to the outside of container passing via the incision 5a of the sheet <NUM> until they reach the incision 1b of the flexible label <NUM>. When the pressure inside the container becomes again substantially the same as the external pressure, the flexible label <NUM> may adhere again to the flexible membrane <NUM>, closing the gas flow passage between the sheet <NUM> and the flexible label <NUM>, in particular owing to the elasticity of the materials and electrostatic forces and/or Van der Waals forces which are created between the flexible membrane <NUM> and the flexible label <NUM> and, in some cases, between the flexible membrane <NUM> and the sheet <NUM> if the said adhesive is not arranged between them.

A method for manufacturing an adhesive valve (<NUM>) according to the present invention in general has a particular feature in that it comprises the following operating steps:.

At the start of the method, the first layer <NUM>, the support <NUM> and/or the adhesive layer included between them may be continuous and uniform and may form a single strip.

The method may also comprise a step D of forming at least one incision 2c and/or at least one through-cut 2d through each flexible membrane <NUM> of the support <NUM>.

The step B may also involve forming at least one notch 1d passing through the first layer <NUM>.

The method of manufacturing the adhesive valve <NUM> may therefore involve a strip <NUM> preferably wound onto a reel <NUM> being pulled, for example in the direction of the arrows shown in <FIG>, by one or more first auxiliary rollers <NUM>. The strip <NUM> may comprise a first layer <NUM> of suitable material for forming the aforementioned flexible labels <NUM>, which may be joined by means of at least one adhesive layer to a support <NUM> of suitable material for forming the aforementioned flexible membranes <NUM>.

The first layer <NUM>, the support <NUM> and/or the adhesive layer included between them are preferably continuous and uniform and for example formed as strips.

A first of the auxiliary rollers <NUM> may separate the first layer <NUM> from the support <NUM>, these being able to be pulled separately by other auxiliary rollers <NUM>, for example as shown in <FIG>.

The first layer <NUM> of the strip <NUM> may be provided with a series of non-adherent portions <NUM> which may be arranged at regular distances one after the other on the adhesive surface of the first layer <NUM> which, with reference to the example shown in <FIG>, is directed upwards.

The series of non-adherent portions <NUM> may be arranged by an applicator <NUM> which, for example, applies and dries an anti-adhesive substance onto the non-adherent portions <NUM>, for example a lacquer.

The first layer <NUM> may be provided with a series of incisions 1b arranged at the same regular distances between the non-adherent portions <NUM>, by a perforator device <NUM>, for example a laser perforator, if necessary with the aid of a sensor <NUM> designed to detect the position of a non-adherent portion <NUM> on the first layer <NUM>, so that the non-adherent portion <NUM> is crossed by the incision 1b, viewing it in plan view.

The incisions 1b in the first layer <NUM> may also be formed before forming the non-adherent portions <NUM>.

The support <NUM> of the strip <NUM> may be joined to the first layer <NUM> by one or more second auxiliary rollers <NUM>, with the non-adherent portions <NUM> arranged between the first layer <NUM> and the support <NUM>.

The first layer <NUM> of the strip <NUM> may then be punched by a first mechanical punch, in particular a roller punch <NUM>, so as to form in the first layer <NUM> a series of flexible labels <NUM> where the cut made by the punch may surround the non-adherent portions <NUM>, being separated from these or also intersecting them if it is required to provide the possibility if venting gas, including through the side edge of the flexible label <NUM>.

In particular, the material of the first layer <NUM> which is surplus with respect to the series of flexible labels <NUM> (not shown in the figures) may be removed. The support <NUM> of the strip <NUM> may be punched by a second mechanical punch, in particular a roller punch <NUM>, so as to form in the support <NUM> a series of flexible membranes <NUM> which are each covered by a flexible label <NUM> with the non-adherent portion <NUM> arranged between them. In this way, the strip <NUM> acts as a support for a series of adhesive valves <NUM> as described above, which are formed by a flexible label <NUM>, a flexible membrane <NUM> and a non-adherent portion <NUM> arranged between the flexible label <NUM> and the flexible membrane <NUM>.

Thus the strip <NUM>, together with the adhesive valves <NUM>, may be wound onto a reel <NUM>.

With reference to <FIG> it can be seen that, during a first operating step of the method for manufacturing a sheet <NUM> in order to form containers, a support membrane <NUM>, preferably wound onto a reel <NUM>, is pulled, for example by one or more first auxiliary rollers <NUM>, following which a punch <NUM> forms the incisions 5a in the support membrane <NUM>.

If necessary, an applicator <NUM> applies adhesive layers onto the support membrane <NUM> close to the incisions 5a, after which a labelling machine <NUM> applies adhesive valves <NUM>, for example removing them from the strip <NUM>, on top of the incisions 5a of the support membrane <NUM>, with the lower surface <NUM> of the flexible label <NUM> in contact with the sheet <NUM> in the manner described above. The sheet <NUM> with one or more adhesive valves <NUM> according to the present description, where necessary pulled by further auxiliary rollers <NUM>, is wound onto a reel <NUM>.

During a subsequent step, not shown in the Figures, the sheet <NUM> may be removed from the reel <NUM> and cut to obtain a plurality of sections which comprise at least one adhesive valve <NUM> and may be used to form packaging for alimentary use, for example as a cover of a container in which the sheet portion <NUM> is joined to the edge of other sheet sections to form the container, in particular by means of adhesive or heat-welding.

It can therefore be understood how an adhesive valve, a sheet which comprises said valve, a container which comprises said valve and a method for the manufacture thereof are able to perform the task and achieve the predefined objects.

In particular, a container which incorporates an adhesive valve according to the present invention is able to avoid the swelling or "puffing" effect which has a particularly negative effect on the appearance of the product.

In fact the present adhesive valve allows gas to be discharged also at very low pressures, for example even at <NUM> mbar, and at speeds substantially higher than in the conventional solutions, namely even at <NUM> mbar/s.

In particular, the fact that the non-adherent portion has one or more parts which taper towards the edge of the flexible membrane and, vice versa, widen out towards the incision of the flexible label means that it is possible to form substantially funnel-like passages between the non-adherent portion and the flexible membrane, these preventing entry of the outside air, i.e. towards the inside of the sheet which supports the adhesive valve, while making venting towards the outside easier.

In particular, not only is the venting, from the inside to the outside, performed by an adhesive valve according to the invention, substantially faster than that of conventional valves, but it also enables a substantial equilibrium of the pressure inside and outside the container to be achieved.

As regards the manufacture of the adhesive valve according to the present invention, it is greatly simplified.

In fact, in order to obtain in conventional valves a non-adherent zone close to, but spaced from the discharge incision, strict tolerances and slower production speeds were required in order to ensure a high quality of the product.

Differently, with the adhesive valve manufacturing method according to the present invention it is possible obtain the non-adherent portion for example by applying a glue killer in a single step, defining therefore the form and the size of the non-adherent portion as well as the number of non-adherent portions to be obtained.

In other words, the non-adherent portion or non-adherent portions may be obtained by means of a single pressing plate (for example in a so-called "flexo" printing system), thus avoiding the need for pressing to be subject to strict tolerance constraints, as in the case of the conventional solutions. This ensures a greater precision during production as well as a reduction in the production complexity and increase in productivity.

Overall, with an adhesive valve according to the present invention it is possible to obtain the discharging of gases inside the package also at pressure values below the <NUM> mbar of conventional valves and, especially, of the order of <NUM> mbar and preferably even as low as <NUM> mbar, obtaining moreover high gas discharging speeds, namely substantially higher than <NUM> mbar/s, i.e. of the order of mbar/s and even about <NUM> mbar/s.

The invention thus devised may be subject to numerous modifications and variations, all of which fall within the scope of protection of the attached claims.

Moreover, all the details may be replaced by other technically equivalent elements.

Claim 1:
Adhesive valve (<NUM>) comprising:
- at least one flexible label (<NUM>) which has an upper surface and a lower surface (1a), wherein at least the lower surface (1a) is provided with adhesive and at least one incision (1b) connects the two surfaces; wherein at least one portion of the lower surface (1a) is provided with adhesive;
- at least one flexible membrane (<NUM>) which has an upper surface and a lower surface (2a) and which adheres to the at least one portion provided with adhesive of the lower surface (1a) of the flexible label (<NUM>);
wherein the lower surface (2a) of the flexible membrane (<NUM>) is substantially non-adhesive, wherein, in plan view, a portion of the flexible membrane (<NUM>) is arranged under the incision (1b) of the flexible label (<NUM>), wherein the flexible label (<NUM>), in plan view, has at least one flap which extends beyond the flexible membrane (<NUM>) in order to adhere to a sheet (<NUM>) so as to retain on the latter said flexible membrane (<NUM>);
wherein the lower surface (1a) of the flexible label (<NUM>) comprises at least one non-adherent portion (<NUM>) which, in plan view, is adjacent to the flexible membrane (<NUM>) or at least partially superimposed on the latter; wherein the incision (1b), in plan view, crosses said at least one non-adherent portion (<NUM>) and is not spaced from the latter;
characterised in that
the non-adherent portion (<NUM>) comprises at least a part thereof which, in plan view, extends towards an edge of the flexible membrane (<NUM>), tapering towards the latter and widening away from it so as to define a divergent channel for gas which is directed towards the incision (1b) and penetrates between the flexible membrane (<NUM>) and the non-adherent portion (<NUM>).