Technical Field

[01] The present invention relates to the field of high-end medical grade mouth masks. In particular, the present invention relates to a valve system and a mouth mask including the valve system for reducing breathing contamination.

Background

[02] Respirators, also called face masks, or mouth and nose masks, are useful for protecting the human respiratory system by filtering air of contaminants or unwanted particles. Such masks are particularly important in global pandemic times e.g. in the corona virus pandemic, to limit the spread of contagious diseases e.g. viral respiratory infections such as COVID-19, and to protect medical practitioners. The demand for such masks in such times surges. Therefore, there is a clear need for cheap and easily mass-producible masks.

[03] Such respirators have different grades or ratings that represent the degree of protection against different contaminants or unwanted particles. For example, FFP-3 grade masks are useful for the protection of people and medical practitioners against viruses.

[04] EP3375308 European patent application shows a foldable face-piece FFP-3 respirator. The respirator comprises a mask body having a foldable central portion along which the mask can be folded into a collapsed form.

[05] WO2015026593 PCT patent application shows another example of an FFP-3 respirator. Such a respirator has a filter media forming at least part of the respirator body, and a gasket made of a flexible elastomeric conforming to the facial features of the wearer. Summary

[06] It is an object of the present invention to provide reliable medical grade mouth masks which can be manufactured relatively easily, a valve system for such mouth masks as well as relatively easy manufacturing methods for such masks and valve systems. The above objective is accomplished by a method and device in accordance with the present invention.

[07] An aspect of the present invention relates to a valve system for a mouth mask, as claimed in claim 1. The valve system comprises a first rigid member and a second rigid member having at least partially mated surfaces to closely fit to one another, a flexible member and a tightening means, wherein the first rigid member and the second rigid member, the flexible member and the tightening means are configured so that the flexible member, when the tightening means is in position, is centrally tightened between the first rigid member and the second rigid member while edges of the flexible member are loose, so that the flexible member allows air flow through the valve system in a first direction from the first rigid member to the second rigid member caused by breathing out by or exhalation of a user when the valve system is in position and prevents or blocks air flow through the valve system in a second direction from the second rigid member to the first rigid member towards the user when breathing in.

[08] Where in embodiments of the present invention reference is made to rigid members, reference is made to members that are sufficiently rigid to accurately position the flexible member and to accurately maintain the overall position of the flexible member. Furthermore, reference is made to members that are sufficiently rigid to keep a good, fixed connection with the filter material of the mouth mask for which it is used. Nevertheless, it is to be noted that when reference is made to rigid members, this does not require that completely no deformation would be allowable for such members. The allowed deformation should be such that it does not hamper the proper functioning of the valve system and thus that it does not hamper an accurate fixing of the flexible member and/or an accurate fixing of the valve system on the mouth mask. [09] Advantageously, the first rigid member and the second rigid member can be rotationally symmetric. Rotational symmetry can be defined as a property of a shape looking the same after a partial rotation. As such, not only manufacturing of said first and second rigid members can be simplified, but also handling of said rigid members is facilitated and the mounting of the valve system can be simplified since each of these methods of manufacturing or mounting the first and second rigid members can at least partly be independent of an orientation of said rigid members.

[10] An outer shape of the plurality of rigid members may have rotational symmetry. The outer shape of one or more of the rigid members may be cylindrical. It is an advantage of embodiments of the present invention that the design has rotational symmetry thus rendering the system omni-directional. As an advantage, it can be installed at any angular orientation, which results in a reduced mounting complexity. It is further an advantage of embodiments of the present invention that the valve system can be used in any rotational orientation, whereas a plurality of prior art valves can only be used nominally in a pre-determ ined orientation.

[11] The first rigid member and the second rigid member may for example be 3D printed members or thermoplastic members or injection moulded members. In this way, said rigid members may be manufactured relatively easily in a cost-effective way.

[12] A first side of the first member configured to face the flexible member can include a circumferential rim configured to provide a sealing engagement to the flexible member to prevent airflow through the valve system in the second direction from the second rigid member to the first rigid member. In the context of the present application, the wording ‘circumferential’ is not limited to a circumference of strictly curved shapes but can include a circumference or perimeter of other preferably regular polygons. The shape of the rim can preferably correspond to a shape of the flexible member, and may be substantially circular, but may also include other shapes. The rim providing the sealing engagement of the flexible member, in particular of the edges of the flexible member, to said rim can prevent air, especially contaminated air, from flowing through the valve system in the second direction from the second rigid member towards the first rigid member, for example when a user breathes in. At the same time, the central tightening of the flexible member and the circumferential rim can allow air flow in the first direction from the first rigid member to the second rigid member between said rim and the flexible member. In the latter case, pressure of the air flow can detach the edges of the flexible member from the circumferential rim.

[13] The valve system may further comprise a fabric barrier configured to cover a side of the second rigid member facing away from the first rigid member. Such a fabric barrier may prevent various types of contaminants, other than air, such as for example droplets or aerosols, to enter the valve system. This can be especially advantageous in healthcare applications, where a user of the valve system may be confronted with splashes of contaminated water, blood or other substances.

[14] The second rigid member can for example have an upstanding circumferential wall allowing fixation of the fabric barrier to the second rigid member, in particular laterally, to said circumferential wall. Fixation can be done in various ways: the fabric barrier may be fixated with a cable tie or an elastic band wrapped around the fabric barrier and around the upstanding circumferential wall. Alternatively, a ring may be snapped, clicked or fastened in any other way over the fabric barrier on the second rigid member. Welding and cutting with ultrasonic or thermal techniques can preferably be avoided.

[15] The fabric barrier may be a polypropylene fabric cover. It is an advantage of embodiments of the present invention that the valve system allows for EN 14683: 2005 certification. It is an advantage of embodiments that the resulting mask when using the valve system is suitable for use in healthcare applications. It is an advantage of embodiments of the present invention that they may provide the necessary protection for Splash Resistance (ASTM F1862-07). It is an advantage that no separate cage for a fabric cover needs to be provided that needs to comprise specific attachment means for attaching to the valve system, in particular to a rigid member of the valve system. It is an advantage that the fabric barrier can be directly connected to the valve body or even that it may be integrated in the valve system. [16] The plurality of rigid members may be adapted for fixing the valve system to the mouth mask, e.g. the filter material of the mouth mask. Such fixation may be directly fixing or indirectly fixing.

[17] It is an advantage of embodiments of the present invention that the valve system can be compact. The valve system can be made compact in that the valve system protrudes only minimally from a mouth mask at least partly covering the face. Due to the fact that the valve system according to embodiments of the present invention only protrudes in a limited way from the face, the moment the valve system can put on the mouth mask does not result in a significantly increased load. Thanks to a relatively light weight of the valve system, the mask will not be deformed, which can increase comfort of the user. Furthermore, it is an advantage of embodiments of the present invention that the mask by only minimally protruding results in a reduced risk of the mask snagging on something, whereby snagging on something may result in the mask being pulled away from the face and thus providing no protection. At the same time, compactness of the valve system can be optimized by having a substantially circular cross-section of the valve system, since a disk is a shape which can maximize surface area, and thus breathing comfort, and minimize linear dimensions.

[18] The flexible member may be a rubber member. Alternatively, the flexible member also may be made of polyisoprene.

[19] The flexible member may be pre-tensioned, so that the flexible member can remain in this pre-tensioned state as much as possible when the valve system is in a closed state, i.e. when the flexible member is in sealing engagement with the rim of the first rigid member. The sealing engagement of the flexible member with the first rigid member can then be independent of air flowing in the second direction. The pre tensioning may be stronger than the gravitational effect. The pre-tensioning may be such that a rotational symmetric pre-tension is present. The pre-tension may be conical.

[20] The tightening means can include a snap-fitted tightening means. The second rigid member, in particular the upstanding circumferential wall, more in particular an inner side of said upstanding circumferential wall, can include an inwardly protruding edge behind which a snap-fitted tightening means can be snapped. Said inwardly protruding edge may a circumferential edge or may be a plurality of interrupted circumferential edges. The first rigid member may for example include an outwardly protruding edge configured to snap behind the inwardly protruding edge of the second rigid member. Any other type of snap-fitted connection may be used as well.

[21] Additionally, or alternatively, the tightening means may comprise a nut and bolt wherein the bolt is configured to extend through at least the first rigid member and the second rigid member. The bolt can preferably extend centrally through said first rigid member and said second rigid member. The tightening means may alternatively also be glue, one or more screws, one or more rivets, etc. The tightening means may be a press-fitted or snap-fitted tightening means with a pin, a thermal welded pin, an ultrasonic welded pin, etc.

[22] The nut and bolt may be an M3 nut and M3 bolt, although the specific size and type is not limiting for the present invention. The nut may be a square shaped nut.

The tightening means may be adapted for providing a watertight fitting of the plurality of rigid members.

[23] It is an advantage of embodiments of the present invention that the valve system may be provided with a single tightening means that binds the valve system and diaphragm or flexible member directly to the mask’s filter material. The corresponding mouth mask therefore can be EN 149:2001 A1:2009 certified. It is an advantage of embodiments of the resulting mask that the mask is suitable for pharmaceutical manufacturing or construction applications.

[24] The valve system can further comprise a third rigid member configured to be fixated to a second side of the first member facing away from the flexible member wherein a mouth mask, in particular a filter fabric of the mouth mask, is at least partly clampable between said third rigid member and said first rigid member. The third rigid member may include similar features as the first rigid member and the second rigid member: the third rigid member can preferably be rotationally symmetrical. The third rigid member may be an injection-moulded member or for example a 3D printed member. The third rigid member may be configured to be snap-fitted to the first rigid member. The third rigid member may include a flange, preferably an outwardly extending flange. The second side of the first rigid member may also include a corresponding flange, preferably an outwardly extending flange. A mouth mask, in particular a filter fabric, may then at least partly be clampable between the outwardly extending flanges. Such a third rigid member can provide a fixation or mounting of the valve system to a mouth mask, which can be manufactured relatively easily together with the valve system and which can simplify the manufacturing of a mouth mask including such a valve system.

[25] Alternatively, the third rigid member may be configured to be tightened to the first rigid member by a nut and bolt, the bolt being configured to not only extend through the first and second rigid member but also through the third rigid member. The flexible member and the tightening means may be configured for simultaneously, using the same tightening means, tightening the flexible member between the first rigid member and the second rigid member and fixing the valve system to the mouth mask. Such fixing may be fixing the valve system to a material of the mouth mask. In some embodiments, such fixing may be fixing the valve system to filter material of the mouth mask. It may be advantageous that the valve system is adapted for providing an accurate positioning and operation of the flexible member and an accurate fixing of the valve system to the filter material of the mouth mask, by using a single tightening means.

[26] In a further aspect, the present invention also relates to a mouth mask for covering mouth and nose, the mouth mask comprising a filter fabric, configured to removably cover a mouth and a nose, the filter fabric comprising an opening, and the mouth mask further comprising a valve system as previously described, the valve system being mountable on the opening in the filter fabric. It is to be noted that in some embodiments, mounting of the valve system may be directly to the filter fabric, whereas in other embodiments the valve system may be indirectly mounted on the opening of the filter fabric, e.g. via a plastic ring.

[27] The third rigid member of the valve system may be adapted for being mounted at an inner side of the filter fabric, i.e. the side facing a mouth and nose of a user, and the first rigid member of the valve system may be adapted for being mounted at an outer side of the filter fabric, i.e. the side facing away from a mouth and nose of a user, so as to mount the valve system onto the filter fabric.

[28] The mouth mask may be a medical healthcare grade mask.

[29] According to a further aspect, the present invention also relates to a method of manufacturing a valve system for a mouth mask, the method comprising manufacturing a first rigid member and a second rigid member having at least partially mated surfaces to closely fit to one another, obtaining a flexible member and a tightening means, combining the first rigid member and the second rigid member, the flexible member and the tightening means so that so that the flexible member, when the tightening means is in position, is centrally tightened between the first rigid member and the second rigid member while edges of the flexible member are loose, so that the flexible member allows air flow through the valve system in a first direction from the first rigid member to the second rigid member caused by breathing out when the mouth mask is in position and prevents airflow through the valve system in a second direction from the second rigid member to the first rigid member towards the user when breathing in. This method of manufacturing a valve system can provide one or more of the above-mentioned advantages.

[30] Manufacturing the rigid members may comprise 3D printing or injection moulding said rigid members, which can provide a relatively easy and cost-effective manufacturing of the valve system. Additionally, 3D printing can offer an accessible way to test and tune dimensions and functionality of the valve system under various conditions.

[31] According to a further aspect of the invention, a method of manufacturing a mouth mask including a valve system as previously described is also provided, wherein a step of combining the first rigid member, the second rigid member, the flexible member and the tightening means such that the flexible member, when the tightening means is in position, is centrally tightened between the first rigid member and the second rigid member while perimetral edges of the flexible member are loose, is performed before a step of mounting the valve system on the opening of the filter fabric. In this way, the valve system can be tested for compliance to standard grading levels before being mounted into a mouth mask, which can again simplify the manufacturing process of the mouth mask.

[32] The above and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. Corresponding elements are designated with corresponding reference signs.

Brief Description of the Drawings

[33] FIG. 1 shows a perspective and exploded view of a cross section of a first embodiment of a valve system according to a first aspect of the present invention;

[34] FIG. 2 shows a perspective and exploded view of the valve system of Figure

1 ;

[35] FIG. 3 shows a perspective view of the valve system of Figure 2 when assembled;

[36] FIG. 4 shows a front view of the valve system of Figure 3;

[37] FIG. 5 shows a back view of the valve system of Figure 3;

[38] FIG. 6 shows a perspective, exploded and schematic view of an embodiment of a mouth and nose mask with the valve system according to an aspect of the present invention;

[39] FIG. 7 shows a cross-sectional top view of the valve system of Figure 3 in an open mode;

[40] FIG. 8 shows a cross-sectional top view of the valve system of Figure 3 in a closed mode;

[41] FIG. 9 shows the valve system of Figure 3 further including a fabric barrier;

[42] FIG. 10 shows the valve system of Figure 9 with an assembled fabric barrier;

[43] FIG. 11 and FIG. 12 illustrate a method of assembling a mouth mask according to a further aspect of the present invention;

[44] FIG. 13 shows a perspective and exploded view on a cross-section of a second embodiment of a valve system according to a first aspect of the invention;

[45] FIG. 14 shows a perspective front view on a second embodiment of a mouth mask according to a further aspect of the invention; [46] FIG. 15 shows a perspective and exploded view of the mouth mask shown in FIG. 14;

[47] FIG. 16 shows a perspective and exploded back view of the valve system included in the mouth mask of FIG. 14;

[48] FIG. 17 shows a cross-sectional view of the mouth mask of FIG. 14 with the valve system in an open mode;

[49] FIG. 18 shows a cross-sectional view of the mouth mask of FIG. 14 with the valve system in a closed mode.

Detailed Description of Embodiment(s)

[50] In a first aspect, embodiments of the present invention relate to a valve system for a mouth mask. Such a valve system may be especially suitable for creating a medical healthcare grade mouth mask, although embodiments are not limited thereto. The valve system comprises a plurality of members, at least two of the members having at least partially mated surfaces so as to closely fit to one another. In some embodiments at least three members may be used. In some embodiments the plurality of members may be a plurality of 3D printed members, although embodiments are not limited thereto and for example moulded, like injection moulded, members, also could be used. Such members may be made of thermoplastics, although other materials also may be used. More generally, 3D print materials with the required rigidity may be used. The valve system further comprises a flexible member and a tightening means. The flexible member may be for example a rubber member, but alternatively also may be made of any other suitable material, for example a material having a shore-A hardness between 30 and 95, for example around more or less 65. In some embodiments the flexible member may be made of silicone rubber or may be made of polyisoprene. The tightening means may be any type of tightening means such as a nut and bolt or another fixing means such as a glue, ... According to at least some embodiments, the flexible means is pre-tensioned. Such pre-tensioning may be a rotational symmetric pre-tensioning.

[51] FIG. 1 shows a perspective and exploded view of a cross section of a first embodiment of a valve system according to a first aspect of the present invention. The valve system 100 comprises at least three 3D printed thermoplastic members 101 , configured to fit to one another. As indicated above, it is not strictly required that the members are 3D printed, nor that there are at least three members. The at least three 3D printed members 101 , which may for example be thermoplastic members or photopolymer resins or members made of any other suitable material, may for example comprise a first member 104, a second member 103, and a third member 102. The at least three 3D printed thermoplastic members 101 may for example comprise polylactic acid (PLA) or polyethylene terephthalate (PET) thermoplastic. In some embodiments, the at least three 3D printed thermoplastic members 101 may for example be cylindrical.

[52] The valve system 100 further comprises a tightening means, in the present example being an M3 square nut 105 and an M3 bolt 106. The at least three 3D printed thermoplastic members 101 are configured to be tensioned by the tightening means, e.g. the M3 square nut 105 and the M3 bolt 106. The at least three 3D printed thermoplastic members 101 may alternatively be tensioned by a plurality of M3 square nuts 105 and a plurality of M3 bolts 105. The at least three 3D printed thermoplastic members 101 may alternatively be tensioned by different means of tensioning.

[53] The valve system 100 further comprises a flexible member 107, in the present embodiment being a rubber member 107. Two adjacent members of the at least three 3D printed thermoplastic members 101 encompass and tighten the rubber member 107. The rubber member 107 is tightened at a centre point thereof by the two adjacent members of the at least three 3D printed thermoplastic members 101 , and wherein edges of the rubber member 107 are kept loose. The rubber member 107 acts as a valve system by allowing air flow in a first direction, and disallowing air flow in a second direction different than the first direction.

[54] FIG. 2 shows a perspective and exploded view 200 of the valve system of Figure 1 including non-tensioned i.e. non-assembled 3D printed thermoplastic members 101. FIG. 3 shows a perspective view 300 of the valve system of Figure 2 when assembled. FIG. 4 shows a front view 400 of the valve system of Figure 3 and FIG. 5 shows a back view 500 of Figure 3. [55] In a second aspect, embodiments of the present invention relate to a mouth mask comprising the valve system for such a mask. The mouth mask typically may be suitable for covering both the mouth and the nose and may be a medical healthcare grade mask. The mouth mask further comprises a filter fabric configured to removably cover a mouth and a nose of a user. The filter fabric may have one or more layers of fabric. The removably attachment of the mouth mask to a head of a user can be achieved using at least one strap. The at least one strap may be attached to at least one end of the mouth mask. For example, the mouth mask may be placed on the mouth and the nose of the user, and the mouth mask may be attached to the head of the user by extending at least one strap around the head of the user. The mouth mask may alternatively be removably attached by having two straps extend around two ears of the user. The strap may comprise elastic material, e.g. stretching fabric.

[56] FIG. 6 shows a perspective, exploded and schematic view of an embodiment of a mouth and nose mask with a valve system according to an aspect of the present invention. The filter fabric 601 further comprises an opening 602. The opening 602 is hollow and can have a circular geometry. The opening 602 may alternatively have a square geometry, or any other geometry. The geometry may be adapted to the geometry of the valve system.

[57] The plurality of members 101 are further configured to be tensioned or tightened in a mating way by the tightening means, e.g. a M3 square nut 105 and a M3 bolt 106 through the opening 602. The members 101 may alternatively be configured to be tensioned by the tightening means through a dedicated opening through the filter fabric 601. The members 101 may alternatively in some exemplary embodiments be configured to be tensioned by a plurality of M3 square nuts 105 and a plurality of M3 bolts 106 through a plurality of dedicated openings or through the opening 602. The members 101 are further configured to be fitted and clamped watertight on one another through the opening 602 and onto the filter fabric 601.

[58] At least one member of the members 101 is mounted on an inner side 603 of the mouth and nose mask 600, e.g. the third member 102. The inner side 603 is identified as a side that is in direct contact with the mouth and the nose of the user. Further, at least one member of the plurality of members 101 is mounted on an outer side 604 of the mouth and nose mask 600, e.g. the second member 103. The outer side 604 is identified as a side that is on an opposite side than the inner side 603, e.g. as a side that is on a different side than the inner side 603, e.g. as a side that is not in direct contact with the mouth and the nose of the user, e.g. as a side that is in contact with potential contaminants in an atmosphere. Further in some exemplary embodiments, at least one member of the plurality of members 101 may be mounted on either the inner side 603 or the outer side 604 of the mouth and nose mask 600, e.g. the first member 104 on the outer side 604 of the mouth and nose mask 600.

[59] In some exemplary embodiments, at least two adjacent members of the plurality of members 101 encompass the filter fabric 601 , e.g. the third member 102 and the first member 104 or e.g. the second member 103 and the first member 104. At least another two adjacent members of the plurality of members 101 encompass the rubber member 107, e.g. the third member 102 and the first member 104 or e.g. the second member 103 and the first member 104. The rubber member 107 may be silicone rubber. In some exemplary embodiments the flexible member may be a silicone rubber having a thickness in a range of more or less 0.1 - 1.0 mm, for example around 0.3 mm and having a shore-A hardness in a range of more or less 30 - 95, for example of around 65.

[60] The operation of the mask, during use, will now be further described, with reference to the exemplary embodiment, the present invention not being limited thereto. The valve system operates in two modes, an open mode and a closed mode. FIG. 7 shows a cross-sectional top view of the valve system of FIG. 3 in an open mode 700. In the open mode, e.g. during exhaling, an outgoing air flow 701 flows from the inner side 603 to the outer side 604 around the flexible member 107, as shown in FIG. 7. The flexible member 107 is made loose such that the outgoing air flow 701 flows easily from the inner side 603 to the outer side 604 around said loose edges, i.e. the flexible member 107 is sufficiently open to allow the outgoing air flow 701.

[61] FIG. 8 shows a cross-sectional top view of the valve system of FIG. 3 in a closed mode 800. Further, in the closed mode, an ingoing airflow 801 is blocked by the flexible member 107, i.e. an ingoing air flow 801 cannot flow from the outer side 604 to the inner side 603 through or around the valve system, as shown in FIG. 8. The flexible member 107 is held by the 3D printed thermoplastic members 101 such that it prevents the ingoing air 801 from flowing from the outer side 604 to the inner side 603. The incoming air thus does not pass through the valve system but can only pass through the filter material of the mouth mask.

[62] FIG. 9 shows the valve system 900 of FIG. 3 further including a fabric barrier, for example a blood barrier fabric as shown in FIG. 9. The blood barrier fabric 901 can cover one of the members 101 mounted on the outer side 604 of the mouth and nose mask, for example the second member 103, as shown in an example 1000 in FIG. 10. The blood barrier fabric 901 may further be tightened on the second member 103 and the first member 104 using a cable tie 1102 or in any other way. The use of a cable tie can also be seen in the embodiments shown in FIG. 11 and FIG. 12.

[63] FIG. 11 and FIG. 12 illustrate a method of assembling a valve system and a mouth mask according to further aspects of the present invention. The method comprises manufacturing, e.g. 3D printing, a plurality of members, at least two members having at least partially mated surfaces so as to closely fit to one another. It also comprises obtaining a flexible member and a tightening means. It further comprises combining the plurality of members, the flexible member and the tightening means so that the flexible member is positioned between the at least two members so that the flexible member, when the tightening means is in position, is tightened between the at least two of the plurality of members whereby the edges of the flexible member are loose so that the flexible member functions as a valve system allowing air flow through the valve system in a first direction caused by breathing out when the mouth mask is in position and preventing air flow through the valve system in a second direction towards the user when breathing in.

[64] In FIG. 11a, an exploded view of a mouth mask 1110 including an embodiment of a valve system as shown in FIG. 1 is shown. The valve system 1100, which is shown in FIG. 11b when assembled, can further comprise a fabric barrier 1101 such as a blood barrier, as shown in FIG. 9 - 10. In the present embodiment, the blood barrier 1101 has a cap-like shape and can be tightened to the second rigid member of the valve system by a cable tie 1102. After assembling or mounting the valve system to the mouth mask, in which the valve system is tightened by a nut and bolt tightening means, the assembled mouth mask 1110 is shown in FIG. 11c. The mouth mask may be tightened to a wearer’s head, either by using a head band (not shown) configured to extend around a wearer’s head or by ear bands configured to extend around the ears of a wearer, or by any other suitable means as known to the person skilled in the art.

[65] In FIG. 12a the valve system of FIG. 11 is shown. The blood barrier 1101 can be simplified, as shown in FIG. 12b and can only include a fabric barrier without being pre-shaped into a cup-like shape. The blood barrier 1201 can still be advantageously fastened to the second rigid member of the valve system with a cable tie or by any other suitable fastening means. An advantage of the blood barrier 1201 and the cable tie is that said blood barrier and cable tie can easily be obtained and exchanged on an existing mouth mask 1210, also when the mask and the valve system have been previously mounted.

[66] FIG.13 shows a perspective and exploded view on a cross-section of a second embodiment of a valve system according to a first aspect of the invention. The valve system 1 for a mouth mask comprises a first rigid member 2 and a second rigid member 3, which have at least partially matable surfaces to closely fit to one another. The valve system 1 further comprises a flexible member 4. Contrary to the embodiments of the valve system shown in preceding figures, the present embodiment does not include a nut and bolt tightening means. The first rigid member 2 and the second rigid member 3 are tightened together by a snap-fitted tightening means. An upstanding side wall 5 of the second rigid member 3 may thereto include an inwardly protruding edge 6 which may be configured to snap-fit behind an outwardly protruding edge of the first rigid member 2, as can be seen on FIG. 15. The flexible member 4 is preferably a rubber member. The first rigid member 2 and the second rigid member 3 are preferably injection moulded members. The first rigid member 2 and the second rigid member 3 can be rotationally symmetric. In the present embodiment, the first and the second rigid members 2, 3 are rotationally symmetric in a third degree, i.e. these members can be rotated into three distinct orientations while remaining to look the same. This feature of rotational symmetry has the advantage that the mounting of the valve system can be simplified since orientation is not an issue to be taken into account. The third degree of rotational symmetry is a compromise between solidity and ease of manufacturing. Other degrees of symmetry are possible as well. The valve system 1 can further comprise a third rigid member 7. Said third rigid member 7 is preferably also an injection moulded member. The third rigid member 7 can also be rotationally symmetric and may even be circularly symmetric. The third rigid member 7 is configured to be fixated to a second side 8 of the first member 2 facing away from the flexible member 4. The third rigid member 7 can be configured such that a mouth mask, in particular a filter fabric of the mouth mask, is at least partly clampable between said third rigid member 7 and said first rigid member 2. Thereto, the third rigid member 7 can include an outwardly extending flange 9 and the first rigid member 2 can also include a corresponding outwardly extending flange 10 between which flanges 9, 10 a fabric 11 of a mouth mask 12 may be clamped, as shown in FIG. 14. To improve clamping of the fabric 11 and to avoid potential rotation of the valve system 1 in a mouth mask, the third rigid member 7, in particular the outwardly extending flange 9, can include a groove 13 which is configured to guide protruding elements, such as small spikes 14 of the first rigid member 2. Said spikes 14 may protrude from the outwardly extending flange 10 towards the second side 8 of the first rigid member 2. Again, the third member 7 is not tightened to the other rigid members by a bolt and nut tightening means, but the third member may be snap-fitted to the first rigid element 2. The third member 7, in particular an upstanding side wall of the third rigid member 7, can for example include an inwardly protruding bevelled edge 15 behind which dedicated hooks or snapping elements included in the first rigid member 2 may be snap-fitted.

[67] FIG. 14 shows a perspective front view on a second embodiment of a mouth mask according to a further aspect of the invention. The mouth mask 12 comprises a filter fabric 11 , which may be a single layer filter fabric, more preferably a double layer fabric, still more preferably a triple layer filter fabric. The mouth mask 12 further comprises a valve system T. In the present embodiment, the valve system T may be similar to the valve system 1 as described in FIG. 13 including a first, second and third rigid element as well as a flexible member 4. The mouth mask 12 may be tightened to a wearer’s head, either by using a head band configured to extend around a wearer’s head or by ear bands configured to extend around the ears of a wearer. Said head band or ear bands may be attached to the lateral ends 11a of the mouth mask 12 in any suitable way known to the person skilled in the art. They may be made of an elastic material or of any other suitable material. The valve system T can slightly protrude from the mouth mask and have a height measured from the mouth mask in a direction substantially perpendicular to the mouth mask in a range between more or less 0.5 cm to 2.5 cm, preferably more or less 1 .5 cm.

[68] FIG. 15 shows a perspective and exploded front view of the mouth mask shown in FIG. 14. As can be seen in FIG. 14 and 15, the valve system is preferably mounted centrally on the mouth mask 12. The fabric 11 can thereto include an opening, of which shape and size can be adapted to the valve system, through which an upstanding circumferential wall 23 of the third rigid member can at least partly extend. As could already be seen in previous figures, the flexible member 4 can preferably include a substantially central hole 20. The first rigid member 2 can include a substantially cylindrical element 21 which is configured to engage the hole 20 of the flexible member 4. The first rigid member 2, in particular a first side of the first rigid member 2 configured to face the flexible member 4, can include a circumferential rim 22 configured to provide a sealing engagement to the flexible member 4. A diameter of the rim 22 is preferably slightly larger than a diameter of the flexible member 4.

[69] In addition to the members 2, 3, 4 and 7 as described in FIG.13, the valve system T may further comprise a fabric barrier 16, e.g. a polypropylene fabric barrier, configured to cover a side of the second rigid member 3 facing away from the first rigid member 2 and/or from the flexible member 4. The fabric barrier 16 may for example be a blood barrier. The fabric barrier 16 may be a two-dimensional filter tissue and may be pre-cut into a shape corresponding to the valve system, for example into a substantially round shape. Alternatively, the fabric barrier 16 may be three-dimensionally pre-shaped as a sort of cap configured to be put on the second rigid member 3. The second rigid member 3 can preferably include an upstanding circumferential wall 5 allowing fixation of the fabric barrier 16 to the second rigid member 3, in particular to said circumferential wall 5. The second rigid member 3, in particular the upstanding wall 5, can further include an outwardly protruding flange 17 which can prevent an attachment of the fabric barrier 16 to slip off the second rigid member 3. The fabric barrier 16 may be attached to the second rigid member 3 by any known attachment means, for example by a cable tie as illustrated in FIG. 11 or 12. Alternatively, the valve system 1’ may include a fourth rigid member 18 which is configured to hold the fabric 16 on the second rigid member 3. The fourth rigid member 18 may also be injection-moulded and can preferably be rotationally symmetric. The fourth rigid member 18 can have a ring-like shape. The fourth rigid member 18 may include an inwardly protruding edge 19 which may be snap-fitted around the outwardly protruding flange 17 of the second rigid member 3. The inwardly protruding edge 19 may be a circumferential edge. Alternatively, the fourth rigid member 18 may include a plurality of inwardly protruding edges 19 each extending around part of the circumference of the fourth rigid member 18. Said plurality of edges 19 may be substantially equally distributed along said circumference and may for example include three edges 19, of which two can be seen in FIG. 16.

[70] FIG. 16 shows a perspective and exploded back view of the valve system included in the mouth mask of FIG. 14. The tightening means between the first rigid member 2 and the second rigid member 3 can for example be a snap-fitting. An upstanding side wall 5 of the second rigid member 3 may thereto include an inwardly protruding edge 6 which may be configured to snap-fit behind an outwardly protruding edge 24 of the first rigid member 2. The inwardly protruding edge 6 may be a continuous circumferential edge or may be an interrupted circumferential edge, as shown in FIG.16. The interruptions 25 of the circumferential edge 6 are preferably shorter than a circumferential width of the outwardly protruding edges 24 of the first rigid member 2. The first rigid member 2 preferably includes three outwardly protruding edges 24. They are configured to snap-fit behind the circumferential edge 6 of the second rigid member 3. Optimal tightening can be obtained when all of the outwardly protruding edges 24 fully engage the inwardly protruding circumferential edge 6 of the second rigid member 3, but even in sub-optimal tightening, i.e. when one or more of the outwardly protruding edges 24 faces one of the interruptions 25, the tightening can still be ensured by the larger protruding edges 24 still partly engaging the circumferential edges 6 on both sides of an interruption 25 being smaller than the protruding edge 24 of the first rigid member 2.

[71] The flexible member 4 is centrally tightened between the first rigid member 2 and the second rigid member 3. Thereto, the first rigid member 2 can include a substantially cylindrical element 21 which is configured to engage the hole 20 of the flexible member 4. When the valve system is tightened, the substantially cylindrical element 21 can extend through the hole 20 in the flexible member 4. The second rigid member 3 can include a central capping element 26 configured to be put over the substantially cylindrical element 21.

[72] As previously described, the first rigid member 2 may include a plurality of small spikes 14, for example substantially conically shaped spikes, protruding from an outwardly extending flange 10. Said spikes 14 may at least partly grip a fabric of a mouth mask and prevent the valve system from rotating on the mouth mask. Tightening of the valve system T to a mouth mask 12 may for example be done by snap-fitting the third rigid member 7 to the first rigid member 1 while clamping a fabric 11 of the mouth mask 12 in between said third rigid member 7 and said first rigid member 2. The first rigid member 2 may thereto include one or more snapping elements 27 or hooks, for example three snapping elements 27 which are configured to snap-fit behind the inwardly protruding bevelled edge 15 of the third rigid element 7.

FIG. 17 shows a cross-sectional view of the mouth mask of FIG. 14 with the valve system T in an open mode while FIG. 18 shows a cross-sectional view of the mouth mask of FIG. 14 with the valve system in a closed open mode. The first rigid member 2 and the second rigid member 3, the flexible member 4 and the tightening means are configured such that the flexible member 4, when the tightening means is in position, is centrally tightened between the first rigid member 2 and the second rigid member 3 while circumferential or peripheral edges of the flexible member 4 are loose, so that the flexible member 4 allows air flow through the valve system T in a first direction 28 from the first rigid member 2 to the second rigid member 3 caused by breathing out by a user when the mouth mask is in position and prevents air flow through the valve system T in a second direction 29 from the second rigid member 3 to the first rigid member 2 towards the user when breathing in. The central capping element 26 of the second rigid member 3 can centrally tighten the flexible member 4 while perimetral edges of the flexible member 4 remain loose. When the valve system T is tightened, for example snap-fitted together, an internal part around the first rigid element 2, from which the substantially cylindrical element 21 can protrude, and the capping element 26 of the second rigid member 3. The first rigid member 2 can include a circumferential rim 22 configured to provide a sealing engagement to the flexible member to prevent air flow through the valve system in the second direction 29 from the second rigid member 3 to the first rigid member 2. The rim 22 can advantageously be slightly higher than the central seating 30 of the flexible member 4 around the substantially cylindrical element 21 where the capping element 26 is configured to centrally tighten the flexible member 4. As a result, the flexible member 4 can be pre-tensioned, for example conically pre-tensioned to ensure that the flexible member 4 can remain in this pre-tensioned state, resulting in a closed mode of the valve system T. The fabric barrier 16 can preferably be open to air circulation at all time and is preferably only configured to prevent droplets to enter the valve system T.

[73] Although the present invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied with various changes and modifications without departing from the scope thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. In other words, it is contemplated to cover any and all modifications, variations or equivalents that fall within the scope of the basic underlying principles and whose essential attributes are claimed in this patent application. It will furthermore be understood by the reader of this patent application that the words "comprising" or "comprise" do not exclude other elements or steps, that the words "a" or "an" do not exclude a plurality, and that a single assembly, such as a computer system, a processor, or another integrated unit may fulfil the functions of several means recited in the claims. Any reference signs in the claims shall not be construed as limiting the respective claims concerned. The terms "first", "second", third", "a", "b", "c", and the like, when used in the description or in the claims are introduced to distinguish between similar elements or steps and are not necessarily describing a sequential or chronological order. Similarly, the terms "top", "bottom", "over", "under", and the like are introduced for descriptive purposes and not necessarily to denote relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and embodiments of the invention are capable of operating according to the present invention in other sequences, or in orientations different from the one(s) described or illustrated above.