Pressure relief valve for a packaging container

Abstract

The invention relates to a pressure relief valve (10) for a packaging container (1) with a base plate (11) fixed to the wall (2) of packaging container (1), which has a central valve hole (15) covering through holes (3) in the wall (2) of the packaging container (1), and with a lidding film (13) fixed to the base plate (11), wherein between base plate (11) and lidding film (13) a valve diaphragm (12) leaving a channel free is provided, which covers the valve hole (15) and lies tightly on the base plate (11) in the closing position of the pressure relief valve (10), characterized in that the lidding film (1)3 has a thickness of at least 10 μm, preferably (20) to (70) μm, the valve PE diaphragm (12) has a thickness of at least 10μm, preferably 20 to 10 μm, and the base plate (11) has a thickness of at least 100 μm, preferably 150 to 250 μm wherein as material for the lidding film (13),the valve diaphragm (12) a film made of non-stretched, monoaxial, especially in the machine direction, stretched or biaxially stretched HDPE.

Description

[0001] tesa Societas Europaea Norderstedt

[0002] Description

[0003] Pressure relief valve for a packaging container

[0004] The invention relates to a monomaterial fully recyclable valve for controlled degassing of flexible packaging.

[0005] In response to increasingly stringent recycling regulations in flexible packaging, this invention introduces a monomaterial PE degassing valve used in stand up pouches, “monomaterial” means that all film layers in the valve are made from polyethylene.

[0006] Food increasingly being offered in monomaterial stand-up pouches. A stand-up pouch is a flexible package that can stand upright when filled. It is usually made of plastic or a combination of materials that provide durability and protection for the contents. These pouches are often used for food, beverages, cosmetics, and other products. They often have a resealable closure, such as a zipper or screw cap, and offer a space-saving and practical packaging solution.

[0007] The currently existing degassing valves for the stand up pouches in the market consist of multimaterial structure including a combination of PET and PP, with PET already known for its superior stiffness and a very good barrier properties against oxygen and humidity.

[0008] Although PE is a much softer material as compared to PET, the enclosed invention reveals a novel combination of polyethylene (PE) films and converting techniques enabling fully recyclable, all-PE monomaterial relief valves for flexible packaging containers. These valves are designed to maintain excellent barrier properties against oxygen and humidity while enabling compatibility with existing PE recycling stream. The innovation lies in the strategic material selection and manufacturing approach that ensures both functional performance and sustainability. Valves for controlled degassing of packaging are typically used in packaging of goods that emit gases during storage. A particularly important such commodity is coffee. It has the property that it emits carbon dioxide when roasted. This gas release is all the more accelerated the larger the effective coffee surface is, i.e. the finer it is ground. This leads to increased pressure building up in the package, which inflates the package and ultimately leads to bursting.

[0009] At the same time, oxygen absorption through the packaging or valve, which would lead to oxidation and thus weakening and adulteration of the aromas, must be prevented as far as possible.

[0010] In order to alleviate these two competing requirements as far as possible, FR 1 360 753 A proposes to use a diaphragm valve whose extremely high tightness is ensured by treating at least one of the two surfaces with a viscous fluid, preferably a silicone oil.

[0011] Further training of this basic invention is known in numerous forms, see, for example, in EP 0 012 874 A, EP 0 023 703 A, EP 0 450 171 A, EP 0 499 783 A, EP 0 602 418, EP 0 738 227 A and EP 0 760 790 A.

[0012] The pressure relief valve known from EP 0 023 703 A, which is arranged via a through- hole in the wall of the packaging container, has a flexible valve diaphragm that covers a circular valve hole in a base plate tightly glued to the wall of the packaging container and lifts off from the base plate at a certain internal pack pressure, forming an outlet channel through which carbon dioxide gas can flow out of the package into the open air. Even a low internal pack pressure inflates a bag pack made of flexible packaging material unsightly. In the case of the above-mentioned pressure relief valve, which has proven itself in the market, the opening pressure is about 5 mbar.

[0013] In order to reduce the opening pressure, EP 0 738 227 A proposes to replace the circular valve hole with an elongated hole. This allows the opening pressure to be reduced to approx. 3 mbar.

[0014] A relevant pressure relief valve is known from the EP 0 760 790 A, the valve hole of which is formed by at least two intersecting, circular openings.

[0015] In the valves described here, the decisive feature is that the valve is opened with only a low overpressure in the pack of 1 to 7 mbar. The valve should then close securely again immediately after the overpressure drops below the opening pressure specific to the valve, in order to keep the diffusion of oxygen negligible.

[0016] Since this overprint is very small, it has practically no influence on the overall appearance of the packaging. Increased pressure, which inflates the pack and leads to bursting, cannot build up.

[0017] On the other hand, it must be taken into account that the aging of the aromas in the coffee, which is known to be more problematic with ground coffee than with unground coffee, is delayed if a higher carbon dioxide pressure is maintained in the package than previously known.

[0018] DE 10 2006 016 594 A1 is a pressure relief valve for a packaging container with a base plate that has a central valve hole covering through holes in the wall of the packaging container and with a lid film attached to the base plate, whereby a valve diaphragm is provided between the base plate and the lid film that leaves a channel free, which covers the valve hole and lies tightly on the base plate in the closing position of the pressure relief valve.

[0019] The pressure relief valve has the following combination of features:

[0020] • The valve diaphragm has a thickness of at least 10 pm, preferably 20 to 70 pm, and preferably 20 to 30 pm.

[0021] • The base plate has a thickness of at least 100 pm, preferably 150 to 250 pm, and preferably 180 to 200 pm.

[0022] • The lidding film has a thickness of at least 100 pm, preferably 150 to 250 pm, and preferably 180 to 200 pm.

[0023] A major problem with the existing pressure relief valve is the multi-material structure, which means that a combination of different polymer films is used as materials for the individual layers, which massively limits recyclability.

[0024] This problem is solved by a pressure relief valve, as laid down in the main claim. The subject matter of the subclaims is advantageous further training of the subject-matter of the invention as well as a packing equipped with the pressure relief valve.

[0025] Accordingly, the invention relates to a pressure relief valve for a packaging container having a base plate fixed to the wall (the term wall also includes any existing bottoms or lids) of the packaging container, which has a central valve hole covering through holes in the wall of the packaging container, and a lidding film attached to the base plate, wherein a valve diaphragm is provided between the base plate and the lidding film leaving a channel free, which covers the valve hole and lies tightly on the base plate in the closing position of the pressure relief valve.

[0026] The pressure relief valve has the following combination of features:

[0027] • The lidding film has a thickness of at least 10 pm, preferably 20 to 70 pm, and preferably 25 to 40 pm.

[0028] • The valve diaphragm has a thickness of at least 10 pm, preferably 20 to 70 pm, and preferably 25 to 40 pm.

[0029] • The base plate has a thickness of at least 100 pm, preferably 150 to 250 pm, and preferably 180 to 200 pm.

[0030] In a preferred embodiment

[0031] • the lidding PE film has an e-modulus in MD (machine direction) and CD (cross direction) of 1600 to 2300 MPa, preferably of 1700 to 2200 MPa, and / or

[0032] • the valve PE diaphragm has an e-modulus in MD (machine direction) and CD (cross direction) of 1600 to 2300 MPa, preferably of 1700 to 2200 MPa, and / or

[0033] • the PE base plate has an e-modulus in MD (machine direction) and CD (cross direction) of 800 to 1200 MPa, preferably of 900 to 1100 MPa.

[0034] It is essential to the invention that the material used for the lidding film, for the valve diaphragm and for the base plate is a film made of unstretched, monoaxially, especially in the direction of the machine, stretched or biaxially stretched HDPE.

[0035] In accordance with a preferred embodiment, the material used for the lidding film and for the valve diaphragm is a film of monoaxial HDPE, especially in the direction of the machine, stretched or biaxially stretched, and for the base plate a film of unstretched HDPE, in particular produced using the casting film process.

[0036] Preferably, (apart from the usual aggregates such as anti-ageing agents) the lidding film, the valve diaphragm and the base plate consist of a film made of unstretched, mono- or biaxially stretched HDPE. High-density polyethylene (HDPE; High-density polyethylene) is a thermoplastic. HDPE consists of long chains of ethylene monomers (C2H4) with minimal branching. This linear structure allows the molecules to pack tightly together, resulting in a dense and highly crystalline material (high density between 0.94 g / cm3and 0.97 g / cm3).

[0037] HDPE has excellent tensile strength. It is resistant to many chemicals, acids and solvents and has excellent water resistance and high impact resistance.

[0038] The choice of stretched HDPE films for the lidding film and for the valve diaphragm and cast HDPE films for the base plate and reinforcement strip helps to achieve the highest possible rigidity in the construction required for the functionality of the valve as well as for the stamping process.

[0039] The advantage of choosing HDPE over other grades of PE is that the melting point of HDPE is higher, which helps to prevent the film from shrinking or curling during pressure-sensitive coating, an essential step in the production of aroma valves.

[0040] In addition, the lower Tg of HDPE compared to PET and BOPP helps to maintain valve functionality even at very low temperatures such as -50 °C and below. Depending on the variety, the Tg of HDPE is in the range of -100 °C to -120 °C.

[0041] The individual films themselves (lidding film, base plate and / or valve diaphragm can consist of several individual layers, for example layers co-extruded into a film or a film coating. to obtain the desired barrier performance against oxygen and humidity.

[0042] The additional layers can be made or contain aluminum Oxide (AIOx), silicon oxide (SiOx), EVOH (Ethylene Vinyl Alcohol), PVDC (Polyvinylidene Chloride), Acrylic, and Polyamide (PA) etc. The preferable coating weight of such layers is preferably 0.1 to 1 g / m2and most preferably 1 to 5 g / m2.

[0043] In a preferred embodiment lidding film and / or valve diaphragm have such a layer and further preferably coating side is in contact with the adhesive layer.

[0044] Other additives commonly used in films, such as fillers, pigments, anti-aging agents, nucleating agents, impact modifiers or lubricants, can be used to produce the film. Preferably, the proportion of additives is less than one weight part per 100 parts by weight of polymer, and a total of less than 5 parts by weight per 100 parts by weight across all additives. For the purposes of this application, the terms "oriented” and "stretched" are used in synonym). HDPE film is a thermoplastic film produced by cast film production technology. The film produced in this way is also called cast film. In contrast to the stretched HDPE film, which is reinforced by stretching, the polymer chains of the unstretched HDPE film are not oriented and remain in their original molecular structure.

[0045] A cast film made of HDPE is a type of plastic film that is produced by the so-called casting film production process (also known as the "cast" process). In the cast process, the molten HDPE is poured onto a cooled roller and cooled rapidly, creating a smooth and uniform film. It is characterized by high density, strength and resistance to chemicals and moisture.

[0046] The concept of a monoaxial or biaxially oriented carrier layer is familiar to the expert. Following the method used to set the corresponding orientation, the skilled person also speaks of monoaxial or biaxially stretched materials in this respect. In mono- or biaxial stretching, a plastic film, such as a cast or blown film, is tempered inline in film production or offline in a separate process by means of rolling or in a heat channel to a temperature above the glass transition temperature Tg, in particular more than 20 °C above Tg, but below the melting temperature Tm of the film material. The stretching takes place, for example, between two or more rollers running at increasing speed. The temperature control should be very constant and homogeneous during stretching. For example, the stretch factor for monoaxial stretching in the direction of the machine is in the range of 1 :4 to 1 :8. For example, the stretching factor for biaxial stretching is between 1 :4 and 1 :9 in the longitudinal direction, preferably between 1 :4.8 and 1 :6, and in the transverse direction between 1 :4 and 1 :9, preferably between 1 :4.8 and 1 :8.5.

[0047] Biaxially oriented films can alternatively be stretched sequentially, whereby the primary film, after being formed by extrusion with a wide-slot nozzle, is first stretched in the direction of the machine by passing it over a series of rollers, with the transport speed of the film being greater than the speed at which it exits the extrusion die. The film is then stretched in a transverse direction in a drafting unit. Stretching the foil in two directions can also be done in one step (see below). For example, US 4,675,582 A and US 5,072,493).

[0048] Furthermore, preferably the film can be produced using the triple bubble method, which is a film extrusion method. The triple bubble method is an extension of the double bubble process, which is itself a further development of single bubble extrusion. In this process, the film goes through three different bubble formations in three stages: a) Primary Bladder: The molten plastic is extruded through a circular nozzle to form an initial tube. b) Secondary bladder: After cooling, this tube is reheated and inflated into a second, larger bladder. c) Tertiary bubble: The foil is then heated again and formed into a third and final bubble on the

[0049] Each expansion stage allows further orientation and modification of the foil properties. The process provides enhanced control over the properties of the film, including strength, barrier properties, and shrinkage.

[0050] The mechanical properties can be specifically influenced by orientation.

[0051] The principle of stretching lies in the alignment of the polymer molecular chains and the crystal structures formed from them, as well as in the alignment of the amorphous regions in certain preferred directions and the associated increase in strength. In principle, however, the strength is reduced in the direction in which there is no orientation.

[0052] In another advantageous embodiment, the lidding film is attached to the base plate by means of an adhesive layer. Furthermore, preferably the adhesive layer extends over the entire surface of the lidding film, so that the valve diaphragm underneath is firmly bonded to the lidding film by the adhesive layer. This results in an inseparable laminate, the stiffness of which is responsible, among other things, for the fact that the pressure relief valve according to the invention only opens at significantly higher pressures than those previously customary.

[0053] However, the adhesive layer can also be partially applied to the lidding film. For example, the valve diaphragm may be fastened with two parallel strips of adhesive extending longitudinally in the direction of the relief valve, each applied to the edge of the valve diaphragm.

[0054] However, the adhesive can also be inactivated by printing, irradiation, powdering or other processes familiar to the specialist. The adhesive layer must ensure that the valve diaphragm and the lidding film are firmly bonded to each other. If this is fulfilled, any form of partial application of the adhesive is possible.

[0055] In another advantageous embodiment, an additional adhesive layer is applied to the base plate, in particular over the entire surface, with which the base plate is attached to the substrate.

[0056] The base plate is bonded to the packaging container in a preferred embodiment. Preferably, the side of the base plate facing the packaging container is coated with an adhesive, especially over the entire surface.

[0057] Instead of an adhesive coating, the base plate can also be applied to the packaging by means of a double-sided adhesive tape section.

[0058] To better anchor the pressure-sensitive adhesives on the films, the films can be pre-treated with the well-known measures such as corona, plasma or flames. The use of a primer is also possible. Ideally, however, pre-treatment can be dispensed with.

[0059] This surface treatment, preferably a corona treatment of all the above-mentioned PE films, can increase the surface energy of the films and consequently create a strong adhesive bond. The preferred corona treatment leads to a surface energy of the PE films from originally 30 to 32 mN / m to 40 to 60 mN / m.

[0060] In a preferred embodiment the lidding film and / or the valve diaphragm are corona treated before the final valve lamination and die-cutting.

[0061] The adhesive used is preferably a pressure-sensitive adhesive.

[0062] In accordance with professional understanding, a pressure-sensitive adhesive is an adhesive compound that has pressure-sensitive properties, i.e. the property of forming a permanent bond with an adhesive base even under relatively weak pressure. Corresponding pressure-sensitive adhesive tapes can usually be removed from the adhesive base after use essentially without leaving any residue and are usually permanently self-adhesive even at room temperature, which means that they have a certain viscosity and tack (also referred to as "tack" by experts), so that they wet the surface of a substrate even at low pressure. Without wanting to be bound by this theory, it is often assumed that a pressure-sensitive adhesive can be considered as an extremely high- viscosity liquid with an elastic component, which consequently has characteristic viscoelastic properties that lead to the permanent intrinsic adherence and pressuresensitive adhesive properties described above. It is assumed that with appropriate pressure-sensitive adhesives, mechanical deformation leads to both viscous flow processes and the build-up of elastic restoring forces. The proportional viscous flux serves to achieve adhesion, while the proportional elastic restoring forces are necessary in particular to achieve cohesion. The relationships between rheology and pressure-sensitive adhesion are known in the prior art and are described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology", Third Edition, (1999), pages 153 to 203. To characterize the degree of elastic and viscous content, the storage modulus (G1) and the loss modulus (G") are usually used, which can be determined by dynamic mechanical analysis (DMA), for example using a rheometer, as disclosed for example in the WO 2015 / 189323. In the context of the present invention, an adhesive is preferably understood to be pressure-sensitive and thus a pressure-sensitive adhesive if at a temperature of 23 °C in the deformation frequency range of 100 to 101 rad / sec G' and G" are at least partly in the range of 103 to 107 Pa.

[0063] Preferably, an acrylate-based adhesive compound is used as a pressure-sensitive adhesive.

[0064] The following glue has proven to be particularly suitable.

[0065] Polymer 1

[0066] A conventional 200 L reactor for radical polymerization is filled with 2400 g acrylic acid, 64 kg 2-ethylhexyl acrylate, 6.4 kg N-isopropylacrylamide and 53.3 kg acetone / isopropanol (95:5). After 45 minutes of passing through with nitrogen gas while stirring, the reactor is heated up to 58 °C and 40 g of 2,2'-azoisobutyric acid nitrile (AIBN) is added. The external heating bath is then heated to 75 °C and the reaction is carried out constantly at this outside temperature. After 1 h reaction time, 40 g AIBN is added again. After 5 h and 10 h, dilute with 15 kg acetone / isopropanol (95:5) each. After 6 and 8 hours, 100 g of dicyclohexyl peroxydicarbonate (Perkadox 16®, Akzo Nobel) dissolved in 800 g of acetone are added. The reaction is stopped after 24 hours of reaction time and cooled to room temperature. Acrylate Pressure-Sensitive Adhesive 1

[0067] Polymer 1 is diluted with boiling point gasoline 60 / 95 to a solids content of 30%. Then add 25% by weight (based on polymer 1), rosin resin (glyceryl ester), Foral™ 85 (Eastman Chemical) and 0.3% by weight (based on polymer 1) of aluminum (III) acetylacetonate (as a 3% solution in isopropanol) and completely dissolve.

[0068] Then the solution is coated on the substrate with, for example, spread bar with comma or knives and dried for 10 minutes at 120 °C.

[0069] Another adhesive which is suitable as an adhesive layer in the pressure relief valve according to the invention is the following.

[0070] Acrylate Adhesive 2

[0071] The Polytec WP 5044 pressure-sensitive adhesive compound from Avery Dennison is a pressure-sensitive adhesive mass with low surface energy. This is a water-based acrylic adhesive (emulsion adhesive) with high tack, strong initial adhesion and good adhesion at low surface energy (LSE) and has proven to be very suitable for low surface energy substrates such as stretched and unstretched HDPE films.

[0072] The amount of pressure-sensitive adhesive applied to the base plate or to the lidding film is preferably between 20 and 50 g / m2, and preferably between 30 and 35 g / m2.

[0073] Two reinforcement strips may be provided on the pressure relief valve, namely on the edge zones, with which the lidding film is preferably glued to the base plate. The reinforcement strips can also be applied to the lidding film by means of an adhesive, whereby their outer edge should be flush with that of the lidding film.

[0074] The reinforcement strips are preferably made of unstretched, monoaxial, especially in the direction of the machine, stretched or biaxially stretched HDPE, and preferably of unstretched HDPE, produced by the casting film process.

[0075] The amount of pressure-sensitive adhesive applied to the reinforcing strips is preferably between 20 and 50 g / m2, and preferably between 30 and 35 g / m2.

[0076] In another advantageous embodiment, the lidding film and base plate have the same external dimensions, so they are congruent. The lidding film continues to completely cover the base plate, preferably in the case of the finished pressure relief valve, without it protruding. In another advantageous embodiment, the valve hole is designed in the form of a circle or slotted hole, preferably in the form of an ellipse.

[0077] This slotted hole can also be formed, for example, by the fact that the valve hole is formed from at least two intersecting, circular openings (similar to an "8"), the centers of which are further arranged preferably on a common central axis).

[0078] The invention is not limited to the embodiments described. The slotted hole can also have an essentially rectangular shape, the corners of which should be rounded (like a groove) for manufacturing reasons, or a shape that can itself be composed of several geometric shapes arranged in a row (for example, diamonds or circles).

[0079] The slotted hole can be formed by more than two intersecting, circular holes arranged along a common central axis. For example, arrangements in the shape of a cloverleaf are also conceivable.

[0080] Furthermore, preferably the main axis of the slotted hole extends perpendicular to the longitudinal axis of the channel. This is accompanied by the fact that the secondary axis of the slotted hole is aligned parallel to the longitudinal axis of the channel in this case.

[0081] Secondly, it has been shown to be advantageous if the minimum distance of the valve hole, preferably the slotted hole, to one of the edges of the valve diaphragm where the channel ends is between 0.8:7 and 2:7, preferably 1 :7 to 1.5:7, in relation to the width of the valve diaphragm.

[0082] In another advantageous embodiment of the invention, the area of the valve hole is between 5 and 18 mm2, preferably between 8 and 16 mm2, and further preferably between 12 and 13 mm2.

[0083] In other advantageous embodiments of the invention, the following size ratios can be realized in the pressure relief valve:

[0084] • The valve hole has a width / length ratio in the range of 1 : 1 , preferably 1 : 1.3 to 1 :2.

[0085] • The width of the slotted hole is equal to or less than one-fifth of the longitudinal extension of the pressure relief valve in the same direction.

[0086] The following are examples of dimensions for a pressure relief valve, as it is used on packaging in which freshly ground coffee is contained, without being intended to have a restrictive effect in any way: The external dimensions of the valve (and thus those of the base plate and the lidding film) are 20 mm x 20 mm, with the pressure relief valve in the shape of a square with rounded corners. The centrally located valve hole has a diameter of between 3 and 4 mm if it is designed in a circle. As an elongated hole, it has an area that corresponds to that of a circle with a diameter of 3 to 4 mm.

[0087] The valve diaphragm has a width of 5 to 10 mm, preferably 7 mm, and extends in length over the entire pressure relief valve. The valve diaphragm is arranged centrally under the lidding film, so that the longitudinal axis of the pressure relief valve results in a symmetrical structure of the valve. The minimum distance of the valve hole, preferably slotted hole, to one of the edges of the valve diaphragm is between 1 and 3 mm.

[0088] Due to the internal pressure of the packaging, which is higher than usual (the valve opens later), the packaging continues to inflate, which leads to an increase in roundness in the case of bags. This is accompanied by the fact that the pressure relief valves are loaded to a greater extent than before on peeling off the packaging. The adhesive compound described above has proven to be particularly effective with the increased requirements.

[0089] In the sense of the invention, a packaging container is understood to mean all types of flexible or inflexible packaging such as stand-up pouches, flat-bottom pouches or pocket zippers, in which, for example, foodstuffs such as coffee are packaged.

[0090] The pressure relief valve for a packaging container according to the invention fulfils the requirements placed on the diaphragm valve. It opens at an overpressure between 30 mbar and 120 mbar and closes reversibly after the overpressure drops below the opening pressure, so that the desired overpressure is maintained at all times.

[0091] A silicone oil is preferably used as the sealing fluid for sealing between the base plate and the valve diaphragm.

[0092] If the three layers comprise or consist of unstretched, monoaxial, especially in the direction of the machine, stretched or biaxially stretched HDPE, the result is an optimally functioning valve, i.e. on the one hand, the valve seals the packaging tightly inwards against gases such as oxygen, and on the other hand, the opening takes place at a specified internal pressure of 30 mbar, for example, so that bursting of the packaging is excluded.

[0093] Due to the choice of only one material for the film layers, there is also very good recyclability, whereby the functionality of the valve is at least as good as with the well- known valves. Furthermore, the individual foil layers, which are preferred according to the invention, are very easy to process.

[0094] This novel combination of all PE layers helps to achieve the mono-material structure, for example in the aroma valves that ensure the recyclability of stand up pouches (SUP) packaging made of polyethylene.

[0095] On the basis of the figures described below, a particularly advantageous execution of the invention is explained in more detail, without wanting to restrict the invention unnecessarily. It shows

[0096] Figure 1 the top view of a pressure relief valve according to the invention,

[0097] Figure 2 a packaging container on which the pressure relief valve according to the invention is applied, and

[0098] Figure 3 the pressure relief valve according to Figure 1 in cross-section along the line A-A.

[0099] Figure 1 shows a pressure relief valve 10 according to the invention in the top view and Figure 2 shows a packaging container 1 on which the pressure relief valve 10 according to Figure 1 according to the invention is applied. Figure 3 shows the pressure relief valve 10 according to Figure 1 in cross-section along the line A-A.

[0100] The pressure relief valve 10 comprises a rigid base plate 11 made of an unstretched HDPE film (preferably a cast film) as well as a lidding film 13 which completely covers the base plate 11 and is arranged in a congruent manner, also consisting of a preferably monoaxial, especially in the direction of the machine, stretched or biaxially stretched HDPE foil, both in the shape of a square with rounded corners. Between base plate 11 and lidding film 13, there is a valve diaphragm 12 made of a flexible, thin, preferably monoaxial, stretched or biaxially stretched HDPE film, especially in the machine direction. Two reinforcement strips 33, 34 made of HDPE film are provided on lidding film 13.

[0101] The pressure relief valve 10 is bonded to the underside of the base plate 11 , which has a central valve hole 15, by means of an adhesive layer 16 on the outside of wall 2 of a packaging container 1 , whereby valve hole 15 covers the through holes 3 in wall 2. For example, the through holes 3 are perforated into wall 2 by thin needles. Valve hole 15 is sealed by valve diaphragm 12 by valve diaphragm 12 spanning valve hole 15. The valve diaphragm 12 with its edge areas on the upper side of the base plate 11 is sealed in a nonpressurized state.

[0102] The underside of the lidding film 13 is provided with an adhesive layer 17 over the entire surface, which on the one hand ensures the fixation of the lidding film 13 on the base plate 11 and on the other hand firmly connects the valve diaphragm 12 to the lidding film 13.

[0103] The reinforcement strips 33, 34 are attached to the edge area of the lidding film 13 by means of adhesive layers 23, 24, their outer edge being flush with that of the lidding film 13.

[0104] On a side wall of a packaging bag 1 , in which, for example, freshly roasted coffee is tightly packed, a pressure relief valve 10 is tightly attached to wall 2 above the through holes. If pressure is built up inside the packaging bag 1 by the release of carbon dioxide gas from the packaged goods, for example coffee, the pressure acts on valve diaphragm 12 through the through holes 3 in the wall 2 and the valve hole 15 in the base plate 11 . As the pressure increases, the valve diaphragm 12 in conjunction with the lidding filml 13 bulges and lifts off the top of the base plate 11 in a bubble-like manner, so that finally a channel is formed between the base plate 11 and the valve diaphragm 12, which extends to the edges of the valve diaphragm 12 and through which gas can flow.

[0105] In order to keep the opening pressure of the pressure relief valve 10 correspondingly high, the valve hole 15 is preferably designed in the form of an ellipse 50, whereby the main axis 51 of the ellipse 50 extends perpendicular to the longitudinal axis of the valve diaphragm 12.

[0106] In the case of overpressure in packaging bag 1 , the valve diaphragm 12 lifts off from the base plate 11 from vertices 52, 53 of ellipse 50. It follows that the position of vertices 52, 53 influences the opening pressure of the pressure relief valve 10. Once the overpressure in packaging bag 1 has been released, valve diaphragm 12 reattaches itself to base plate 11.

[0107] For better sealing, a drop of sealant is usually inserted between the base plate 11 and the valve diaphragm 12 in the generic pressure relief valves. This is usually done directly before the pressure relief valve 10 is attached to the wall 2 of the packaging bag 1. The drop is applied centrally through the valve hole 15 to the underside of the valve diaphragm 12, and it takes some time for it to disperse in the channel. Due to the shape of the valve hole according to the invention, the sealant gets particularly quickly between the base plate 11 and the valve diaphragm 12, so that the further processing of the pressure relief valves 10 or the filling and evacuation of the packaging bag 1 can take place directly after the pressure relief valves 10 have been attached to the packaging bag.

[0108] Examples

[0109] Below three examples explain the invention in a relatively simpler way.

[0110] The combination of materials shown in Example 1 results in a fully functional degassing valve while the combinations shown in Example 2 and Example 3 do not.

[0111]

[0112] While if an expert person chooses even the best PE films available in the market which inherently have low stiffness and poor oxygen barrier the valve is not functional at all i.e. the opening and closing pressure of the valve are too low or even the valve is just open due to lower flatness of the structure. At the same time if the layer combination as per Example 2 and Example 3 are used the Oxygen transmission rate is too high which is not acceptable for aroma valve functionality for long term shelf life of the packed food.

[0113] The invention discloses this unique combination of special materials in such an inventive style that even with a soft material like PE a fully functional design of degassing aroma valve can be built.

[0114] Test Methods

[0115] Unless expressly stated otherwise, the measurements are carried out in a test climate of 23 ± 1 °C and 50 ± 5 % relative humidity.

[0116] Elastic Modulus and Thermal Shrinkage Behavior

[0117] The elastic modulus of the films is measured according to DIN EN ISO 527-3 / 2 / 300, while the thermal shrinkage behavior is determined according to ASTM D 2732.

[0118] The mechanical properties are determined in a tensile / elongation test. The tensile elongation behavior is measured on type 2 samples (rectangular test strips with a length of 150 mm and a width of 15 mm if possible) according to DIN EN ISO 527-3 / 2 / 300. A test speed of 300 mm / min, a clamping length of 100 mm, and a preload of 0.3 N / cm are applied. The samples are cut with sharp blades for data collection.

[0119] OTR / WVTR

[0120] The determination of oxygen permeability (OTR) and water vapor permeability (WVTR) is carried out according to DIN 53380 Part 3 or ASTM F-1249.

[0121] The determination of oxygen permeability (OTR) and water vapor permeability (WVTR) is carried out according to DIN 53380 Part 3 or ASTM F-1249. Oxygen permeability is measured at 23°C and a relative humidity of 50%. Water vapor permeability is determined at 37.5°C and a relative humidity of 90%. The results are normalized to a film thickness of 50 pm.

[0122] Peel Strength (Adhesive Strength, KK)

[0123] To measure the adhesive forces, 19 mm wide test strips were applied bubble-free to a finely ground (sandpaper with FEPA grit 240) stainless steel plate and pressed with a rubber-wrapped 2-kg roller at a speed of 10 m / min. The steel plate and the protruding end of the adhesive tape were then clamped into the ends of a tensile testing machine in such a way that a peel angle of 180° was created. The adhesive tape was peeled off the steel plate at a speed of 300 mm / min. The adhesive strength is given in N / cm.

[0124] Opening and Closing pressure

[0125] The opening and closing pressure of the valves is measured as follows:

[0126] Mount the aroma valve on a sealed test fixture simulated for a flexible packaging. Gradually increase internal pressure using air or inert gas. Record the pressure at which the valve first opens (opening pressure). Slowly decrease pressure and record when the valve reseals (closing pressure). Repeat the test for consistency and document results.

[0127] The combination of the films used in Example 1 results in a fully functional degassing valve with a monomaterial structure.

Claims

Claims1 . Pressure relief valve 10 for a packaging container 1 with a base plate 11 fixed to the wall 2 of packaging container 1 , which has a central valve hole 15 covering through holes 3 in the wall 2 of the packaging container 1 , and with a lidding film 13 fixed to the base plate 11 , wherein between base plate 11 and lidding film 13 a valve diaphragm 12 leaving a channel free is provided, which covers the valve hole 15 and lies tightly on the base plate 11 in the closing position of the pressure relief valve 10, characterized in that the lidding film 13 has a thickness of at least 10 pm, preferably 20 to 70 pm, the valve PE diaphragm 12 has a thickness of at least 10 pm, preferably 20 to 70 pm, and the base plate 11 has a thickness of at least 100 pm, preferably 150 to 250 pm wherein as material for the lidding film 13, the valve diaphragm 12 a film made of non-stretched, monoaxial, especially in the machine direction, stretched or biaxially stretched HDPE.

2. The pressure relief valve according to claim 1 , characterized in that the lidding film 13 is attached to the base plate by means of an adhesive layer 17.

3. The Pressure relief valve according to claim 1 or 2, characterized in that the lidding film 13 and the base plate 11 have the same external dimensions.

4. The pressure relief valve according to at least one of claims 1 to 3, characterized in that the valve hole 15 is designed in the form of a circle or an elongated hole 50, preferably in the form of an ellipse 50, and / or the main axis 51 of the slotted hole 50 extends perpendicular to the longitudinal axis of channel 19.

5. The pressure relief valve according to at least one of the previous claims, characterized in that the minimum distance of the valve hole 15, preferably slotted hole 50, to one of theedges of the valve diaphragm 12 is between 0.8:7 and 2:7 in relation to the width of the valve diaphragm 12.

6. The pressure relief valve according to at least one of the previous claims, characterized in that the area of valve hole 15 is between 5 and 18 mm2, preferably between 8 and 16 mm2, and preferably between 12 and 13 mm2, the valve hole 15 has a width / length ratio in the range of 1 :1 , preferably from 1.3 to 1 :2, and / or the width of the slotted hole 50 is equal to or less than one-fifth of the longitudinal extension of the pressure relief valve 10 in the same direction.

7. The pressure relief valve according to at least one of the previous claims, characterized in that the valve hole 15 is formed from at least two intersecting, circular openings.

8. The pressure relief valve according to at least one of the previous claims, characterized in that as material for the lidding film 13 and for the valve diaphragm 12 a film made of monoaxial, especially in the machine direction, stretched or biaxially stretched HDPE and for the base plate 11 and the reinforcement strips 33, 34 a film made of unstretched HDPE is used.

9. The pressure relief valve according to at least one of the previous claims, characterized in that• the lidding PE film has an e-modulus in MD (machine direction) and CD (cross direction) of 1600 to 2300 MPa, preferably of 1700 to 2200 MPa, and / or• the valve PE diaphragm has an e-modulus in MD (machine direction) and CD (cross direction) of 1600 to 2300 MPa, preferably of 1700 to 2200 MPa, and / or• the PE base plate has an e-modulus in MD (machine direction) and CD (cross direction) of 800 to 1200 MPa, preferably of 900 to 1100 MPa• the PE reinforcement stripes have an e-modulus in MD (machine direction) and CD (cross direction) of 800 to 1200 MPa, preferably of 900 to 1100 MPa.

10. The pressure relief valve according to at least one of the previous claims, characterized in that the lidding film 13, the base plate 11 , the valve diaphragm 12 and / or the reinforcement stripes 33, 34 are corona treated.11 . The pressure relief valve according to at least one of the previous claims, characterized in that the lidding film 13, the base plate 11 and / or the valve diaphragm 12 have on at least one side an additional like aluminum oxide (AIOx), silicon oxide (SiOx), EVOH (Ethylene Vinyl Alcohol), PVDC (Polyvinylidene Chloride), Acrylic, and Polyamide (PA), preferably with a coating weight of 0.1 to 1 g / m2and most more preferably 1 to 5 g / m2.

12. The pressure relief valve according to at least one of the previous claims, characterized in that the stretching factor for monoaxial stretching in the machine direction is in the range of 1 :4 to 1 :8 and / or the stretching factor for biaxial stretching in the longitudinal range between 1 :4 and 1 :9 and in the transverse direction between 1 :4 and 1 :9.

13. Packaging container with a pressure relief valve 10 located on it, wherein a base plate 11 is attached to a wall 2 of packaging container 1 , which has a central valve hole 15 covering through holes 3 in wall 2 of the packaging container 1 , and with a lidding film 13 attached to base plate 11 , wherein a valve diaphragm 12 leaving a channel free is provided between base plate 11 and lidding film 13, which covers the valve hole 15 and lies tightly in the closing position of the pressure relief valve 10 on the base plate 11 , wherein the lidding film 13 has a thickness of at least 10 pm, preferably 20 to 70 pm, the valve diaphragm 12 has a thickness of at least 10 pm, preferably 20 to 70 pm, and the base plate 11 has a thickness of at least 100 pm, preferably 150 to 250 pm, wherein as a material for the lidding film 13 and for the valve diaphragm 12 a film made of monoaxial or biaxially stretched HDPE, especially in the direction of the machine, and for the base plate 11 a film made of unstretched HDPE.

Images