The present invention is in the field of pressure relief valves for food packages.

Certain food products, for example fresh roasted coffee beans or coffee powder, have a tendency of degassing for some time. Therefore, according food packages, for example coffee bags (coffee pouches) have a pressure relief valve. Pressure relief valves allow the gases - for example carbon dioxide - generated in the interior of the package to evade while preventing the surrounding air to enter into the package so that no oxygen will get into the package and freshness is preserved.

Pressure relief valves usually have a cup-shaped main body, wherein of edge the circumferential wall of the main body is welded or glued to an inside of the package material. Both, the bottom of the main body and the package each have an opening.

On the bottom of the main body lies a disc as valve membrane, with an oil, for example a silicone oil, between the bottom and the disk. If there is an overpressure within the package, the gas communicating through the opening of the bottom lifts the disc, so that the gas can evade into the interior of the main body and from there through the package opening out of the package. When there is no overpressure within the package, the disc lying against the bottom of the main body ensures a leak-tight sealing. Pressure relief valves of this kind are beneficial in that they make possible that fresh food is directly packaged to be delivered to the end customer, without any intermediate re-packaging being necessary. This, in addition to ensuring freshness for the customer, has also advantages in terms of ecology. However, the pressure relief valves add to the environmental footprint of the package.

It would be desirable to have further approaches of improving the eco-balance of the packaging of fresh roasted coffee and other roast products that produce gas after the roasting process.

According to an aspect of the present invention, a pressure-relief valve is provided, the valve comprising a main body equipped to be fastened to a flexible package material, the main body having at least one through hole forming a passage through the main body, a valve membrane lying, on a package side, against the main body in a region around the hole, and a sealing liquid between the main body and the valve membrane. The valve comprises a water-soluble polymer, meaning that at least one component of the valve (for example the main body or an additional component such as a fixing part or a permeable membrane as described hereinafter) is made of a polymer composition that comprises a water-soluble polymer.

A polymer in the context of the present text is deemed to be water-soluble if it dissolves in water at a temperature at that water is liquid at atmospheric pressure. In embodiments, the water-soluble polymer material is water-soluble at room temperature, but in other embodiments may also be soluble at elevated temperature of for example 60°C only (thus only hot-water-soluble). The main body is itself dimensionally stable. It may be equipped to be fastened to the flexible package material by being cup-shaped and having a bottom and a circumferential wall surrounding the bottom, the annular end face of the circumferential wall being attachable to the packaging material. The bottom then comprises the at least one through hole forming the passage through the bottom for the gas produced withing the package. The valve membrane is arranged on the package side of the bottom (in the cup constituted by the main body) and covers the at least one through hole. The side of the bottom opposite to the package side is called “product side” in this text.

In embodiments, if the package is to contain a finely grained product such as coffee powder (ground coffee), the valve further comprises a permeable membrane, which is attached to the product side of the bottom covering the at least one through hole so as to prevent the product from clogging the through opening while being permeable for gases. The permeable membrane may be a fabric membrane. In this text, “fabric” is used to cover all kinds of flexible materials from fibers or yams or threads that are interlocked, including nonwovens, woven or knitted textiles or other textile structures.

In embodiments, the valve further comprises a fixing part. The fixing part is shaped to be placed on the package side of the valve membrane. It prevents the valve membrane from falling out of the main body even in situations in which the valve is subject to substantial mechanical shock. The valve may especially be subject to such shock, during transportation and assembly processes, if it is provided as a bulk material. In a situation of mechanical shock, the fixing part keeps the valve membrane in place even if adhesion by the sealing liquid might not be sufficient to do so. The fixing part may be held relative to the main body by the circumferential wall of the main body forming an undercut, so that the fixing part is clickable into the main body. The water-solubility of the polymer has advantages in recycling processes, be it a composting process or even a paper recycling process.

While water-soluble polymers may be bio-degradable, this is not necessarily the case for all water-soluble polymers. The water-soluble polymer of the valve may be biodegradable in addition to being water-soluble.

In the present text, “bio-degradable” may mean biologically degradable according to the European standard EN 13432 (as of the end of 2021). In addition or as an alternative, it may mean biologically degradable according to the European standard EN 14995 (as of the end of 2021). Thus “bio-degradable” especially refers to “biologically degradable according to EN 13432 and/or according to EN 14995.

As far as in the present text water-soluble polymers are mentioned, such water soluble polymer may optionally be degradable in sewage treatment plants (aerobic biodegradability) in accordance with DIN EN ISO 9888 (as of the end of 2021); determined in accordance with the so-called Zahn-Wellens test.

In embodiments, all components of the valve, i.e., the main body, the valve membrane, and, if present, the permeable membrane and/or the fixing part, respectively, are of bio-degradable materials.

In embodiments, while the valve contains a water-soluble polymer, for example as a material of the main body and/or, if applicable, the fixing part and/or the permeable membrane, the valve membrane is not water-soluble. In embodiments, at least one of the components is made of a polymer composition belonging to a first category of polymer compositions. Polymer compositions of the first category are water-soluble.

In a group of embodiments, polymer compositions of the first category comprise a salt in addition to comprising a water-soluble polymer.

The salt may be present in an amount of at least 1% or at least 2% or at least 3% or at least 10% or at least 15% or even at least 20% or at least 25% with a maximum amount being 55% or 40% or 35%. In the present text, all percentages refer to % by weight unless specified otherwise.

The salt may be a hygroscopic salt.

The salt may comprise a salt of an alkaline metal, an earth alkaline metal, or aluminium salt and/or a mixture thereof. Particular examples include NaCl, Na-citrate, and the respective potassium analogues, magnesium chloride and/or mixtures thereof.

The salt on the one hand may act as lubricant for the polymer in the polymer composition of the first category. The addition of salts to the polymer can enhance the melt flow index (MFI), hence improving hot-melt processability of the polymer composition.

The main body and/or, if applicable, the fixing part may hence be manufactured by injection moulding or other moulding technique if they are made of a polymer composition of the first category that comprises a salt. The same may apply if they are made of a different polymer composition, especially a polymer composition of the first category, but without a salt.

In addition, the salt has been found to also improve solubility, disintegration, and biodegradation speed, for example for composting. The addition of the salt can render a polymer home-compostable, if without the salt it would be capable of being composted industrially only but not per se home-compostable. The salt content, therefore, may be used to tune the properties of the polymer composition depending on the intended use and intended recycling process.

In particular, independent of whether the polymer composition of the first category comprises a salt or not, the water-soluble polymer of a polymer composition of the first category may comprise at least one of poly(vinyl alcohol) (PVOH), celluloseether polymer, Butenediol-Vinyl-Alcohol-Copolymer (BVOH), Polyvinyl butyral (PVB) and Ethylene- Vinyl-Alcohol-Copolymers (EVOH).

Polymer compositions of the first category in particular may comprise a water-soluble polymer that is a vinyl alcohol polymer or -copolymer or a mixture or blend of two or more vinyl-alcohol copolymers. I.e., the water-soluble polymer of may be a polymer that has a plurality of vinyl alcohol [CH2CH(OH)] groups in the polymer chain. These polymers include the mentioned PVOH, BVOH, and EVOH as well as others.

If the water-soluble polymer comprises or a mixture or blend of two or more vinyl- alcohol copolymers, the copolymers can differ in molar mass, molecular architecture, e. g. branching, comonomer type and amount, or other variation parameters. The polymer of polymer compositions of the first category may thus be a vinyl alcohol comprising, especially a vinyl alcohol rich, copolymer or a vinyl alcohol homopolymer. The polymer can in embodiments comprise >75%, in particular >90%, monomer units carrying an OH unit. The water-soluble polymer can comprise further polar comonomers. Examples include maleic acid and maleic acid anhydride, fumaric acid and itaconic acid.

The water-soluble polymer, in particular the polyvinyl alcohol (PVOH), can have a degree of hydrolysis of 70% to 99,9%. The degree of saponification can relate to the performance to the oxygen barrier. Especially, the degree of hydrolysis may be at least 90% or at least 94% or even at least 96%. A higher saponification can relate to a higher oxygen barrier performance.

The polymer composition of the first category can comprise at least one of:

Poly(vinyl alcohol) obtained e.g. by the saponification of Poly(vinyl ester) homopolymers or copolymers, - Ethylene- Vinylalcohol-Copolymers (EVOH),

- Butenediol-Vinylalcohol-Copolymer (BVOH).

Polymer compositions of the first category in embodiments have a maximum water content of 10%. Especially in embodiments containing a salt, the water content may for example be not more than 5%, especially not more than 1% or not more than 0.5%. Polymer compositions of the first category may further include a plasticizer (liquid or solid) to lower the melt temperature, which is especially beneficial for molding. The plasticizer can in embodiments be hygroscopic. The plasticizer may be selected from the group consisting of polyols (oligo- and polyhydroxy compounds) and low molecular weight amides, especially of trioles, diols, poly-triols, poly-diols, for example glycerine, ethylene glycol, propylene glycol, triethylene glycol, low molecular weight polyethylene glycols; and low molecular weight amides. In embodiments, the plasticizer may be selected from the group consisting of dipropylene glycol, higher oligomers of ethylene glycol or propylene glycol, butylene glycol, glycerol, pentaerythritol, sorbitol, 1,4-Monoanhydrohexitols, 1,4-3, 6- dianhydrohexitols as well as esters of the same. Preferred plasticizers are glycerine, and polypropylene glycol.

The plasticizer may be present in an amount of between 2% and 25%, especially between 5% and 18%, for example between 10% and 15%.

Polymer compositions of embodiments of the first category in embodiments may especially comprise more salt than plasticizer. More in concrete, the ratio between the salt and the plasticizer may be between 1.5: 1 and 6: 1.

It is not excluded that polymer compositions of the first category, in addition to comprising a water-soluble polymer, possibly a salt, and optionally a plasticizer, comprise further constituents, such as a thermal stabilizer (for example a metallic stearate, such as sodium stearate), for example in a concentration of at most 1%, especially at most 0.5%, and/or a an inorganic filler and/or an organic filler, such as cellulose or a filler as described in WO 2021/224 424 and/or other constituents that influence the properties of the composition, or of ingredients thereof. Examples of suitable polymer compositions of the first category may for example be found in WO 2014/155059.

As an alternative to compositions as described in WO 2014/155059, the polymer composition of the first category may comprise, in addition to the polymer (‘resin’, for example the Poly(vinyl alcohol), Ethylene-Vinylalcohol-Copolymers (EVOH), or Butenediol-Vinylalcohol-Copolymer (BVOH) and the plasticizer (but not necessarily the salt) additives, especially saturated fatty acids, a binder, and/or an antioxidant. These additives have proven to be beneficial for the properties of the polymer composition of the first category especially in terms of suitability for the molding process as well as for biodegradation.

Further constituents of the polymer composition of the first category may comprise water (for example between 1% and 10%, especially between 2% and 6%, and additives comprising between 0% or 1% and 5% or 3% fatty acids, a binder (for example between 0% or 1% and 5% or 3%, and or an antioxidant (in an amount of for example less than 0.5%, especially between 0. 1% and 0.3%).

An other example of a suitable polymer composition of the first category comprises between 70% and 85% of polyvinyl alcohol (for example 98% hydrolyzed), between 10% and 15% of glycerol as plasticizer, between 2% and 6% of water, and additives in the form of between 1% and 3% saturated fatty acids, between 1% and 3% of a binder, and between 0.1% and 0.3% of an antioxidant.

In addition - or as an alternative - to comprising one or more polymer compositions of the first category, the valve may comprise a component of a polymer composition of a second category. Like the polymer compositions of the first category, also polymer compositions of the second category may be bio-degradable according to the definition used in the present text. The polymer compositions of the second category are not, however, water-soluble, and in embodiments they do not comprise a salt.

Examples of polymer compositions of the second category have one or more polymers chosen from the group comprising: a Polyhydroxybutyrate (PHB), poly(hydroxy alkanoates) (PHAs), anderer Polyster polyester, (PHB ist Polyester) aliphatic polyester, - poly-4-hydroxybutyrate (P4HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), and polyhydroxyoctanoate (PHO)

Also embodiments of polymer compositions of the second category may have a plasticizer and/or other constituents, for example an organic filler.

The valve membrane may be of a polymer composition of the second category. Especially, it may be preferred if the valve membrane is not water-soluble.

The polymer compositions of the second category may be vapor resistant. In contrast thereto, in embodiments, the main body is of a polymer composition of the first category. Alternatively, the main body may be of a polymer composition of the second category.

If present, the fixing part may be of a polymer composition of the first category. For example, the fixing part may be of the same polymer composition as the main body. Also for the fixing part, there exists the alternative that this component may be of a polymer composition of the second category.

If present, the permeable membrane may be of a polymer composition of the first category. It is possible that the permeable membrane is of the same composition as the main body, although in embodiments the composition will be different, for example in that it contains a higher portion of the plasticizer than the main body.

The main body may comprise a grease groove. Grease grooves are shallow indentations on the surface region of the main body against which the valve membrane lies. Grease grooves act to accommodate excess sealing liquid and act as a reservoir for it. They are beneficial and often necessary to ensure that the space between the valve membrane and the surface against which it lies is always evenly provided with the sealing liquid.

In a group of embodiments, the bottom of the main body has at last one outer grease groove that comprises a radial extension. An outer grease groove in this is a groove in the bottom located at a radially outer position, i.e. at a radial distance from the at least one through hole. Especially, the outer grease groove(s) may be closer to the circumferential wall than to the center of the bottom. The outer grease groove or a system of outer grease grooves will, with the exception of the radial extension, generally run along a circumferential direction, for example with the main portions being parallel to the circumferential wall (parallel meaning that the normal distant is constant).

The radial extension is a portion of the grease groove that extends away from a main portion of the grease groove into a radial direction.

The radial extension has the advantage of reducing the adhesion of the membrane, depending on its size, thereby making a control of the adhesion of the membrane possible.

The background is the following: For a certain size of the pressure relief valve and its valve membrane, the adhesion force between the main body and the valve membrane may be too high for certain applications. For example, in some cases the pressure necessary to lift the valve membrane may become too high and the return of the valve to a closed state may be more unpredictable if a high amount of gas has evaded after the valve membrane has been lifted - for example in the case of comparably large packages. For other packages, however, a comparably high adhesion is necessary to ensure sufficient tightness. This could in principle be dealt with by making the valve in different sizes. However, it makes the manufacturing more complicated if different valve sizes need to be provided for different kinds of packages. Another prior art approach is to use sealing liquids of different compositions depending on the desired adhesion force. However, it is a challenge to fine tune adhesion forces by changing the chemical composition without making compromises in terms of other properties - especially if the materials of the valve membrane and of the main body are chosen in view of other properties and if there is no degree of freedom in adapting those. The approach with a radial extension makes possible that standard size of the main body and the valve membrane and a sealing liquid with a comparably high tendency to adhere are used for all packages. Due to the extension, the effective length of a path along which the valve membrane adheres to the main body surface is reduced. Thereby, the adhesion to be overcome by a pressure rise in the package until the valve is actuated is reduced also, the reduction of the adhesion force to be overcome being the greater the greater the size of the radial extension. Thus, in order to adapt the valve for different applications, demanding different actuation pressures/triggering pressures, only one parameter, namely the size (radial dimension) of the radial extension needs to be changed.

The radial extension may especially be an inward extension.

In a group of embodiments, the main body comprises a plurality of outer grease grooves. For example, the outer grease grooves may comprise a circular array of at least two outer grease grooves together forming an (interrupted) ring.

Especially, the outer grease grooves may comprise a circular array of first outer grease grooves and a circular array of second outer grease grooves, the first outer grease grooves being arranged around the second outer grease grooves. In such a configuration, the second outer grease grooves may be staggered with respect to the first outer grease grooves, so that the second outer grease grooves cover gaps between first outer grease grooves, whereby there is no radial line from a center of the bottom to its periphery (to the circumferential wall) that would not be interrupted by an outer grease groove. In embodiments in which the outer grease grooves are provided in at least one circular array, one inward extension may be present per grease groove. If there are several circular arrays, an inward extension per grease groove of one of the arrays may be sufficient.

In embodiments with two circular arrays of grease grooves, the radial inward extension(s) may be inward extension(s) of the first outer grease grooves. They may extend through gaps between second outer grease grooves optionally to positions radially inwardly of the positions of the second outer grease grooves.

In addition to the above-described function of regulating the adhesion force, the radial extensions thereby balance the distribution of the sealing liquid between the first and second grease grooves.

The main body on the inside of the circumferential wall in the plane defined by the valve membrane may comprise an extension accommodating groove. The extension accommodating groove provides a space into which the valve membrane can expand so that it does not bulge upon an expansion, for example if it takes up moisture.

The surface portion of the main body against which the valve membrane lies may be flat as opposed to curved (vaulted) surface portions of prior art valves. Such a flat structure may be beneficial especially if the valve membrane and/or the main body is/are made of bio-degradable material, since then the adhesion force does not alter when properties such as the material elasticity slightly change because of the take-up of moisture or because of ageing. The flat structure is especially beneficial together with the extension accommodating groove because the combination allows a precise placement of the valve membrane - by adapting the diameter to the inner diameter of the cup-shaped main body - without entailing the risk of the membrane becoming vaulted or otherwise deformed when expanding.

In a group of embodiments, especially if the valve has a permeable membrane, the main body has at least one indentation on the product-side, thus forming an indented portion. The at least one through hole - or at least one of the through holes - has its product-side mouth in the indented portion. Thereby, the mouth of the through hole(s) on the product side is offset with respect to a product-side outermost plane. This means that if a permeable membrane is present, the mouth of the through hole(s) is offset with respect to a plane of the permeable membrane. This is beneficial especially if the permeable membrane and the main body both comprise a water-soluble polymer, for example by being made of polymer compositions of the first category. Namely, packaged food products also if they are dry often comprise a residual moisture. This is for example the case for roast coffee (ground or in beans). This residual moisture can cause the water-soluble polymer to absorb some water and to thereby become sticky. This tendency is potentially increased in polymer compositions of the first category, due to the salt content. If the permeable membrane sticks to the main body, however, ventilation in ‘horizontal’ directions (directions parallel to the plane defined by the main body’s bottom) between the permeable membrane and the main body is prevented. Therefore, the gases can only diffuse through the small area of the permeable membrane that has the diameter of the through hole. This may be unsatisfactory in that such a small area may easily be subject to clogging etc. The approach with the through hole(s) being arranged in an indented portion solves this problem. The indented portion can effectively constitute a system of ventilation grooves, with spacers between them.

In embodiments, the spacers have rounded edges. Therefore, there is less risk of damaging the permeable membrane when the package is subject to mechanical stress. In addition to concerning a pressure relief valve, the invention also concerns a package, especially a coffee pouch for coffee beans or ground coffee. The package comprises flexible, pliant packaging material as well as a pressure relief valve as described in the present text. The main body of the pressure relief valve is attached to the packaging material. Especially, the annular end face of the pressure relief valve may be attached to the packaging material, with the valve membrane (and if present the fixing part) being arranged in the hollow space between the bottom of the main body and the packaging material. The packaging material is generally gas-tight but has an opening or other permeable structure at a position encompassed by the circumferential wall of the main body.

Hereinafter, embodiments of the present invention are described with reference to drawings. In the drawings, same number designate same or corresponding elements. The drawings show:

Fig. 1 An exploded view of the components of a pressure relief valve;

Fig. 2 a main body in a view;

Fig. 3 a view of the cut assembled valve;

Fig. 4 the main body in a different view;

Fig. 5 yet a further view of the main body;

Fig. 6 a further view of the cut assembled valve; and

Fig. 7 schematically, the valve in a package.

The pressure relief valve shown in Figures 1, 3 and 6 comprises a main body 1 that is also shown in Figures 2, 4 and 5. The main body 1 has an overall shape of a flat cup, with a bottom 11 and a circumferential wall 12. The bottom 11 has a sealing surface and, opposite the sealing surface, a product-side surface.

The circumferential wall 12 surrounds the sealing surface of the bottom 11 and has, at its end opposite the bottom 11, a flange 13, i.e. an outwardly protruding collar, so that the annular end face 16 that carries a package-side energy directing rib 18 is broader. The bottom as at least one through hole 14 - in the depicted embodiment there are three through holes 14 - that is covered by the valve membrane 2 lying against the bottom 11 on the sealing surface thereof. Between the bottom 11 and the valve membrane 2 there is a thin layer of a sealing liquid, especially an oil, for example a silicone oil. Silicone oils are known for this purpose. Hence, the sealing liquid is not described in any more detail in the present text.

The pressure relief valve for use is placed inside of a gastight flexible package in that the annular end face of the circumferential wall 11 is bonded to the package inner surface, for example by welding. The package material has at least one gas passage (for example at least one small through hole or a permeable section) at a place surrounded by the annular end face. If there is an overpressure inside the package, the gas will cause the valve membrane 2 to be lifted from the bottom 12, whereby a gas passage is created. Excess gas can then evade through the through hole(s) 14, between the valve membrane and the bottom and through the gas passage of the package. When there is no overpressure inside the package, the membrane closes the package by lying against the bottom, with the sealing liquid adhering to the bottom and the valve membrane by capillary forces forming a seal.

The main body 1 on the inside of the circumferential wall 12 and in the plane defined by the valve membrane 2 comprises an extension accommodating groove 41. It has been found that such groove 41 is beneficial for the following reason: The valve membrane 2 may be of a bio-degradable polymer composition. It has been found that in contrast to prior art valve membrane materials, these materials may have a tendency to be subject to changes in the dimension depending on the environmental conditions. For example, they may slightly expand if subject to moisture.

In embodiments, the pressure relief valve has a permeable membrane 3 in addition to the main body 1 and the valve membrane 2. In contrast to the valve membrane 2, the permeable membrane 3 is gas permeable. It may for example be a fabric, such as a nonwoven fabric. The permeable membrane is attached to the product-side surface of the bottom and covers at least the through opening(s) 14. The permeable membrane is useful if the package contains a finely grained product, especially ground coffee in that it prevents the product from clogging the opening(s) and from getting into contact with the sealing liquid and the valve membrane 2. It is not necessary for packages containing for example coffee beans or other coarse products.

The permeable membrane 3 may be of a polymer material, for example by being a fabric of thermoplastic fibers. It may in embodiments be welded to the main body. To this end, the main body has a product-side energy directing rib 38 on the side facing the packaged product.

In the side of the sealing surface, the main body has a plurality of grease grooves. More in concrete the main body has an inner grease groove 21 surrounding the opening and moreover has a ring of three first outer grease grooves 22 and a ring of three second outer grease grooves 23, the first outer grease grooves 23 being arranged around the second outer grease grooves 22. The outer grease grooves 22, 23 generally run in a circumferential direction, each having a main portion 27 extending circumferentially, parallel to the circumferential wall. The second outer grease grooves 23 each have an outward extension 24 extending radially outwardly from the main portion 27 into the gaps between the first outer grease grooves 22. The first outer grease grooves 22 each have an inward extension 25 extending radially inwardly from the main portion 27 into the gaps between the second outer grease grooves 23 and even extending to further radially inwardly.

In the present text, “radial” as well as “outward” or “inward” or “circumferential” are meant to refer to an axis 10 of the main body; the presence of a central axis does not necessarily imply an axial symmetry, though such symmetry with is an option.

The outer grease grooves have the function of serving as a reservoir for the sealing liquid. To this end, they are located at a radial position so as to be covered by the valve membrane (see for example Fig. 3 or Fig. 6). For example when the valve is, for example during transportation of the valve prior to the bonding to the package or during transportation of the package with the valve, subject to temporary mechanical loads, it may be that sealing liquid is forced out from between the bottom 11 and the valve membrane 2. The grease groove ensures that thereafter capillary forces can draw sealing liquid from the grease grooves underneath the valve membrane again. Similar considerations apply to the manufacturing process: because of the grease grooves, it is sufficient that a drop of sealing liquid is dispensed onto the bottom or the membrane, and the grease grooves ensure that the sealing liquid is well distributed and the sealing membrane uniformly adheres to the bottom all around the through holes 14.

In addition to having this well-known function, the special structure of the outer grease grooves 22, 23 makes possible a better control of the adhesion forces. Namely, the distance between the inner grease groove 21 and the outer grease grooves 22, 23 defines the minimal length pi of a path along which the adhesion force has to be overcome to trigger the valve by lifting the valve membrane 2 from the bottom 11. If no inner grease groove would be present, the quantity of interest would be the distance between the through hole(s) 14 and the inward extension 25.

As is illustrated in Fig. 5, this path length pi may be controlled by choosing the length of the inward extensions 25.

Both, the outward extensions 24 and the inward extensions 25 have the further function of distributing the sealing liquid between the grease grooves. For example, because of the outward extensions 24 and the inward extensions 25, sealing liquid may communicate between the first and second outer grease grooves and between different first grease grooves and different second grease grooves.

The system comprising a circular array of at least two (three in the depicted embodiment) first outer grease grooves 22 and/or a circular array of at least two (three in the depicted embodiment) second outer grease grooves 23 nevertheless features the advantage, over an arrangement in which the grease groove would be an uninterrupted ring, that the sealing liquid is well distributed along the periphery of the bottom 11 even in situations in which the valve is kept in an unchanged a vertical orientation for a long time.

In embodiments, the pressure relief valve in addition to the main body 1 and the valve membrane 2, and, as the case may be, to the permeable membrane 2 has a fixing part 4. The fixing part 4 is optional and may serve as a spacer between the flexible package material and the valve membrane 2, making sure that the valve membrane 2 cannot be displaced even in events of severe mechanic concussion. In the depicted embodiment, the fixing part 4 is star shaped with three rays. The it has a distance keeping first rib 51 and a distance keeping second rib 52. The overall star shape and the distance keeping ribs 51, 52 constitute a material saving shape nevertheless having a stable orientation. Also, the star shape ensures some elasticity of the fixing part 4.

As can be seen for example in Fig. 6, the shape of the circumferential wall 12 forms a slight undercut 42 on the inside, with the inner surface of the main body being slightly conical. Due to this undercut shape, the fixing part 4 can be clicked into the main body and due to its elasticity remains there.

On the product facing side, the main body 1 is structured to comprise a system of ventilation grooves 31 and spacers 33. The system is such that the through holes 14 are on a bottom of a ventilation groove, i.e., at a position where the product-side surface is indented. Radial channels 32 that belong to the system of ventilation grooves 31 ensure that the gases diffusing through the permeable membrane into the ventilation channels can get to the through holes 14. Thereby, the gases encounter less resistance and can diffuse through a comparably large surface portion in that the membrane is not pressed, by overpressure within the package, against a flat surface. Rather, the spacers 33 keep it away from the plane in which the through holes 14 have their mouths.

A further effect of the system of ventilation grooves is that the permeable membrane 3 is prevented from sticking to the main body in a region around the through holes 14. Such sticking could occur for example during the process of bonding the permeable membrane 3 to the main body by ultrasonic welding.

As is illustrated for example, in Fig. 5, the spacers 33 have rounded edges 35 so that there is less risk of damaging the permeable membrane when the package is subject to mechanical stress. The overall shape of the main body with the flange 13 and the broadened end face 16 (that is bonded to the package material) yields a further improvement, relating to the process of bonding the valve to the package material and to the stability of the bond. Namely, the shoulder that is defined by the flange being an outwardly protruding collar yields a coupling face 17 on which a tool for bonding the valve to the package material can directly act. Thereby, the energy - usually ultrasonic energy - coupled by the tool into the main body 1 for the bonding process does not need to be coupled through the entire height (axial extension) of the main body but only across the thickness of the flange 13. This makes the bonding process more efficient compared to a situation in which the tool would press against the product-side end face of the main body.

The tool may for example be a tube shaped sonotrode, with a tube diameter approximately corresponding to the diameter of the flange 13.

However, the flange 13 and the broadened end face 16, are just optional. In alternative embodiments, the main body 1 does not have this structure. The main body 1 also in these alternative embodiments is weldable to the package material in that a sonotrode impinges on the product-side end face of the main body. Also in these embodiments, the used sonotrode may optionally be tube shaped, with a tube diameter being greater than an outer diameter of the region that has the system of ventilation grooves and spacers. However, alternatively, the sonotrode then may have a flat outcoupling face.

In the depicted embodiment, the main body 1, the fixing part 4 and the permeable membrane 3 are all made of polymer compositions comprising a water-soluble polymer and for example further comprising a salt:

The main body 1 and the fixing part 4 are injection molded from a polymer composition comprising PVOH obtained e.g. by the saponification of Poly(vinyl ester), a salt (especially sodium chloride), and glycerine. In an alternative embodiment, the main body 1 and the fixing part 4 are injection molded from a polymer composition comprising PVOH obtained e.g. by the saponification of Poly(vinyl ester), for example 98% hydrolysed, between 10% and 15% of glycerol as plasticizer, between 2% and 6% of water, and additives in the form of between 1% and 3% saturated fatty acids, between 1% and 3% of a binder, and between 0.1% and 0.3% of an antioxidant. The polymer compositions of the main body and the fixing part may be identical.

The permeable membrane is a textile of fibers of a polymer composition also comprising PVOH obtained e.g. by the saponification of Poly(vinyl ester), a salt (especially sodium chloride), and glycerine

The valve membrane 2 is made of PHB.

All components are thus bio-degradable.

Figure 7 schematically shows a package with the valve. The main body 1 is welded to the packaging material 60. The packaging material has a through hole 61 for the gases to be released.