Piston and method for producing a piston

Abstract

A piston for use with a collapsible film bag cartridge, the piston comprising: a front part (14), a rear part (16) and an intermediate part (18) arranged between the front part (14) and the rear part (16), an extension axis (E) of the piston extending between a front end (10) and a rear end (12) of the piston through the front part (14), the intermediate part (18) and the rear part (16); the front part (14) comprising a head portion (20) radially recessed with regard to the intermediate part (18) and a film bag collector (24) radially extending from an outer side surface (26) of the head portion (20), the film bag collector (24) and the outer side surface (26) of the head portion (20) at least in sections define an annular groove (28) therebetween; wherein the rear part (16) comprises a cavity (30) open to the rear end (12) of the piston, the cavity (30) surrounded by an elastically deflectable wall (34).

Description

[0001] The invention is directed at a piston for use with a collapsible film bag cartridge, the piston comprising a front part, a rear part and an intermediate part arranged between the front part and the rear part, an extension axis of the piston extending between a front end and a rear end of the piston through the front part, the intermediate part and the rear part; the front part comprising a head portion radially recessed with regard to the intermediate part and a film bag collector radially extending from an outer side surface of the head portion, the film bag collector and the outer side surface of the head portion at least in sections define an annular groove therebetween.

[0002] Such kind of piston is well known in the art and may be used for example as a reusable piston configured to be moveable along a discharging axis of a reusable cartridge between a storage position and a discharge position. By moving the piston from the storage position into the discharge position a material stored in a collapsible film bag housed in a sleeve of the reusable cartridge is discharged and the empty collapsed film bag is mainly collected in the annular groove between the outer side surface of the head portion and the film bag collector extending therefrom.

[0003] The sleeve not only supports the film bag normally having a low rigidity but also guides the piston during its movement from the storage position into the discharge position. For the later purpose, at least a radial outer end part of film bag collector may contact an inner surface of the sleeve, thereby stabilizing the piston during its movement along the discharging axis of the reusable cartridge. After the material has been discharged from the film bag, the film bag may be removed from the reusable cartridge and replaced by a full new film bag. The reusable cartridge is then ready to be used again. As the reusable cartridge may be used again and only the film bag needs to be replaced, waste is avoided or at least minimized.

[0004] Typically, the piston is advanced by means of a plunger inserted from a rear side of the cartridge.

[0005] However, in some applications, for example in large scale applications and / or in applications with materials having a high viscosity, it is desirable to drive the piston by means of a fluid, such as a gas or a liquid.

[0006] It is therefore an object of the invention to provide a piston that may be driven by means of a fluid.

[0007] This object is satisfied by a piston comprising the features of claim 1.

[0008] The invention is based on the idea that a piston may be fluidically driven using a fluid such as a gas, like air, or a liquid, like water, in particular a pressurized fluid, if the rear part of the piston comprises a cavity open to the rear end of the piston, the cavity surrounded by an elastically deflectable wall. The cavity is capable of receiving the fluid, such that impinging the piston from its rear end with the fluid, the piston is forced to move forwards. In other words, the cavity receives the pressurized fluid, which pushes the piston forwards. In this regard, impinging the piston with the fluid, deflects the elastically deflectable wall radially outwardly, such that the deflectable wall contacts an inner surface of a reusable cartridge's sleeve, thereby forming a seal between the piston and the sleeve, with the seal preventing that fluid passes by the piston. This increases the efficiency to which the piston is urged forwards by means of the pressurized fluid.

[0009] The piston may therefore be used in large scale applications and / or in applications comprising high viscosity materials. Preferably, the piston may be used to provide higher discharge forces, in particular in comparison to a plunger driven piston.

[0010] It is noted that a forward direction is a direction pointing from the rear end of the piston towards its front end, whereas a rearward direction is a direction pointing in the opposite direction of the forward direction.

[0011] Further aspects and advantages become apparent from the claims, the description and the accompanying drawings.

[0012] In order to allow a deflection of the wall surrounding the cavity at the rear part of the piston and yet provide a sufficient stability of the piston, the elastically deflectable wall may be more elastic than at least the head portion of the front part and / or the intermediate part. In other words, the head portion of the front part and / or the intermediate part may be more rigid than the deflectable wall surrounding the cavity at the rear part. In this context, the film bag collector radially extending from the head portion may be more rigid than the wall surrounding the cavity. However, the film bag collector and the wall surrounding the cavity at the rear part may have at least substantially the same flexibility or the film bag collector may be even more flexible than the wall surrounding the cavity at the rear part.

[0013] It is noted that the film bag collector may continuously extend along the piston's circumference. However, in order to enhance the flexibility of the film bag collector, the film bag collector may be segmented by slits radially extending from an outer circumference of the film bag collector towards the head portion of the front part, in particular towards an outer side surface of the head portion. The remaining parts of the film bag collector may form lips between the slits. Preferably, the lips are separated from the intermediate part by an axial gap, thus allowing the lips to be axially deflectable with regard to the extension axis of the piston.

[0014] The piston may be formed as a single piece. This allows for an efficient production of the piston, in particular if the piston is formed as an injection molded part, thereby requiring only one injection mold. However, the entire piston may also be formed by another method, such as 3D printing.

[0015] The piston may not only be formed as a single piece, but also as separate pieces connected to each other. Preferably, the front part and / or the rear part and / or the intermediate part may be formed as separate pieces. This also allows for an efficient production of the piston, because each part may be formed individually. In particular, if the individual parts are formed by injection molding, the injection mold for forming a part of the piston may be less sophisticated, in particular with regard to an injection mold used to form the piston as a single piece. Furthermore, the separate parts may be adapted to the actual demands they need to fulfill. For example, the front part and / or the intermediate part may be formed from a material more rigid than the rear part, i.e. the rear part may be more flexible than the front part and / or the intermediate part which may be less flexible and therefore more stable.

[0016] In this regard, at least one of the front part, the rear part and the intermediate part may be formed by another method than injection molding, such as 3D printing. In particular, the assembled piston may consist of at least one part formed by one method, like injection molding, and at least one other part formed by a different other method, like 3D printing.

[0017] However, all parts of the piston may be formed by the same method, i.e. either by injection molding only or 3D printing only.

[0018] The separately produced parts of the piston may be connected to each other by force fit, for example by a snap fit connection, and / or by material bond, such as using welding like thermal or ultrasonic welding.

[0019] In order to form the piston or parts thereof by injection molding, the piston or the parts may be formed of a thermoplastic material. In particular, the rear part at least in sections, in particular the wall surrounding the cavity at the rear part, may be formed of an elastomeric material and / or a thermoplastic material. Forming the rear part of an elastomeric material, allows to form said elastically deflectable wall surrounding the cavity at the rear part. It is noted that the rear part at least in sections may be formed of an elastomeric and thermoplastic material.

[0020] Furthermore, the rear part may be formed at least in sections from a rubber material or a silicone material.

[0021] The material forming the rear part may have a hardness selected on the Shore A hardness between 10 to 80 Shore A, to allow for an elastic deflection of the wall surrounding the cavity.

[0022] Not only the rear part may be formed of a thermoplastic material. Also, the front part and / or the intermediate part may be formed of a thermoplastic or thermosetting material. Preferably, the thermoplastic material of the front part and / or the intermediate part may have a higher hardness than the thermoplastic material of the rear part.

[0023] Preferable materials which may be used to form the piston or parts thereof are selected from polyoxymethylene (POM), polyethylene (PE), low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), polyamide (PA), polybutylene terephthalate (PBT) or the like.

[0024] Preferably, a wall thickness of the wall surrounding the cavity at the rear part, in particular circumferentially surrounding the cavity, is at least in sections selected to allow for an elastic deflection of the wall upon applying a predetermined pressure. The pressure may be applied to the wall surrounding the cavity at the rear part by impinging the piston with a fluid having pressure of at least 2 bar (2·10 5< kg / (m·s 2< )), preferably of at least 5 bar (5·10 5< kg / (m·s 2< )) and at maximum 10 bar (10·10 5< kg / (m·s 2< )). A preferred application pressure is 6.9 bar (6.9·10 5< kg / (m·s 2< ) or 100 psi.

[0025] In order to allow the wall surrounding the cavity at the rear part to touch the inner surface of the sleeve during discharge operation, the wall surrounding the cavity at the rear part comprises a side wall that surrounds the cavity in circumferential direction, with the side wall being elastically radially deflectable with regard to the extension axis. To put it figuratively, the piston is inflated at the cavity formed at the rear part. This allows for the wall surrounding the cavity at the rear part to sealingly engage with the inner surface of the sleeve.

[0026] Further sealing may be achieved if a circumferentially extending sealing lip is formed at the rear part, in particular at a rear end section of the rear part. The sealing lip is preferably formed at an outer circumferential surface of the rear part.

[0027] Preferably, the cavity is dome shaped which allows for an optimum reception of the fluid in the piston during discharge operation.

[0028] In order to prevent the fluid from escaping through the piston, the cavity may be closed towards the front end of the piston.

[0029] The cavity may not only be formed in the rear part of the piston, but may also merge into the intermediate part or through the intermediate part into the head portion of the front part. Such kind of configuration allows to use less amount of material to form the piston.

[0030] In this regard, a support structure may be formed at least in that part of the cavity that merges into the intermediate part or through the intermediate part into the head portion of the front part. The support structure enhances stability of the piston.

[0031] It is noted that a thickness of the wall surrounding the cavity at the rear part may be thinner than a thickness of the wall surrounding the cavity in the intermediate part and / or the in the head portion of the front part. Such a configuration allows for the wall surrounding the cavity at the rear part to be deflectable and at the same time provides sufficient stiffness of the remaining parts of the piston, i.e. the intermediate part and / or the head portion of the front part.

[0032] To avoid unwanted tilting of the piston during its advancement, the piston may comprise guidance means formed at an outer circumference of the piston.

[0033] The guidance means may comprise at least one guidance structure at least partially extending in a circumferential direction of the piston. Preferably at least two guidance structures are axially separated in direction of the extension axis of the piston. The at least two axially separated guidance structures may be formed at the intermediate part of the piston. However, at least one of the guidance structures may be formed at the intermediate part, whereas at least one other guidance structure may be formed at the front part and / or the rear part, such as at an outer circumference of the film bag collector and / or an outer circumference of the wall surrounding the cavity at the rear part.

[0034] The guidance means may also consist of a plurality of ribs axially extending in direction of the extension axis and spaced, preferably evenly spaced, along an outer circumference of the piston, in particular along an outer circumference of the piston's intermediate part.

[0035] Guidance of the piston may also be achieved if an outer circumferential dimension of the film bag collector and / or the intermediate part and / or the side wall surrounding the cavity at the rear part are at least substantially the same.

[0036] An axial length of the rear part in direction of the extension axis and an axial length of both of the front part and the intermediate part may be at least substantially the same or may be different. Preferably, the axial length of the rear part is smaller than an axial length of both of the front part and the intermediate part. Such a configuration provides a good trade-off between the stability of the piston at the front part and the intermediate part and sufficient space in the cavity at the rear part to receive the fluid therein.

[0037] However, the axial length of the rear part and the intermediate part may be the same and the front part may be larger or smaller than that.

[0038] The invention is also directed at a method of producing a piston for a collapsible film bag cartridge as described above, wherein a first component selected from at least one of the front part, the rear part and the intermediate part is made by an injection molding or 3D printing process and a second component selected from at least one of the front part, the rear part and the intermediate part is made by another injection molding or 3D printing process, the first component and the second component being different.

[0039] The present disclosure also refers to a method of using a piston as described in the foregoing in a cartridge, wherein the piston is urged by applying a fluid, in particular a pressurized fluid, onto the piston.

[0040] In the following, exemplary embodiments and functions of the present disclosure are described herein in conjunction with the drawings, showing schematically: Fig. 1a perspective view of a piston according to a first embodiment; Fig. 2a perspective cross-sectional view of the piston of Fig. 1; Fig. 3a perspective view of a piston according to a second embodiment; Fig. 4a perspective cross-sectional view of the piston of Fig. 3; Fig. 5a cross-sectional detail of a third embodiment of the piston; Fig. 6a perspective view of a piston according to a fourth embodiment; and Fig. 7a perspective cross-sectional view of the piston of Fig. 6.

[0041] The drawings described hereinafter show various embodiments of a piston for use with a collapsible film bag cartridge (not shown). Such kind of collapsible film bag may be used to store an adhesive material used for example in constructional applications.

[0042] As the collapsible film bag has a rather low rigidity, the collapsible film bag may be supported by a sleeve of a rigid reusable cartridge (also not shown in the drawings). The rigid cartridge may comprise a rear opening into which the collapsible film bag and subsequently the piston is inserted. Furthermore, the rear part may comprise a fluid connection to provide pressurized fluid to the piston to advance the piston towards a front end of the rigid cartridge comprising an outlet through which material from the collapsible film bag may be discharged as the piston is advanced towards the front end of the rigid cartridge during discharge operation.

[0043] In the following a piston according to a first embodiment will be described with reference to Figs. 1 and 2. The particular differences of the other embodiments shown in Figs. 3 to 7 will then be described with regard to the first embodiment, so that the following description except for the differences basically also applies to the pistons according to the other embodiments.

[0044] The piston according to the first embodiment is made as a single piece made from a single thermoplastic material, such as for example polyethylene (PE), and extends between a front end 10 and a rear end 12. Using a thermoplastic material for producing the piston allows for the piston to be formed by injection molding or by 3D printing.

[0045] The piston comprises a front part 14, a rear part 16 and an intermediate part 18 arranged between the front part 14 and the rear part 16.

[0046] An extension axis E of the piston extends between the front end 10 and the rear end 12 of the piston through the rear part 16, the intermediate part 18 and the front part 14 and defines an axial direction which may be parallel to a longitudinal extension axis of the sleeve and a discharge direction when the piston is assembled to the rigid cartridge.

[0047] The front end 10 is defined by a head portion 20 of the front part 14 and comprises a central flat front surface 22 aligned at least substantially perpendicular to the extension axis E of the piston. However, depending on the application, the central front surface may also have other shapes, in particular the central front surface may be convex or concave.

[0048] As can be seen from Figs. 1 and 2, the head portion 20 is radially recessed with regard to the intermediate part 18.

[0049] A film bag collector 24 in form of a collar or brim radially extends from an outer side surface 26 of the head portion 20 and defines together with the outer side surface 26 of the head portion 20 an annular groove 28 therebetween (Fig. 2). The annular groove 28 is used to collect the emptied collapsed film bag during discharge operation as the piston is moved towards the outlet of the rigid cartridge.

[0050] In the present embodiment, the film bag collector 24 not only radially extends from the outer side surface 26 of the head portion 20, but also in axial direction towards the front end 10 of the piston from the intermediate part 18 (Fig. 2).

[0051] Furthermore, the film bag collector 24 of the first embodiment continuously extends along the circumference of the piston and is not segmented.

[0052] In order to fluidically drive the piston, the piston comprises a substantially dome shaped cavity 30 which is surrounded by a wall 32 and which is closed towards the piston's front end 10. Nevertheless, the cavity 30 is open to the piston's rear end 12 to be capable of receiving a pressurized fluid from the rear end 12 for a forward movement of the piston.

[0053] In particular, the cavity 30 merges from its open end at the rear part 16 through the intermediate part 18 into the head portion 20 of the front part 14.

[0054] In order to prevent that the pressurized fluid passes by the piston, the cavity 30 is circumferentially surrounded by an elastically deflectable side wall 34 at the rear part 16. In particular, the side wall 34 is elastically radially deflectable with regard to the extension axis E, such that applying the fluid at a predetermined pressure to the piston deflects the side wall 34 radially outwardly, thereby bringing the side wall 34 at least in sections into contact with the inner surface of the sleeve. This increases the efficiency with which the piston may be advanced by means of the pressurized fluid.

[0055] Furthermore, by-passing of the pressurized fluid is further prevented by a circumferentially extending sealing lip 36 formed at the outer side of the side wall 34 at the rear end 12 of the piston.

[0056] In the present embodiment, elastic deflection of the side wall 34 at the rear part 16 is possible by choosing the thickness of the side wall 34 surrounding the cavity 30 at the rear part 16 to be thinner than a thickness of the remaining wall 32 surrounding the cavity 30 at the intermediate part 18 and the head portion 20 of the front part 14. By doing so, the elastically deflectable side wall 34 is more elastic than the head portion 20 and the intermediate part 18.

[0057] In particular, as can be seen from Fig. 2, the side wall 34 surrounding the cavity 30 at the rear part 16 tapers from the intermediate part 18 towards the rear end 12 of the piston. That is, the thickness of the side wall 34 surrounding the cavity 30 at the rear part 16 is not only thinner than the remaining wall 32 surrounding the cavity 30 at the intermediate part 18 and the head portion 20, but also decreases towards the rear end 12 of the piston. Such a configuration further enhances the flexibility of the side wall 34 at the rear part 16 and brings the side wall 34 even better into contact with the inner surface of the sleeve upon applying a pressure onto the piston.

[0058] Furthermore, to enhance the stability of the piston at its front part 14 and the intermediate part 18, a support structure 38 is formed in the cavity 30 in the head portion 20 and the intermediate part 18.

[0059] In the present embodiment, the support structure 38 is formed by a central tube 40 axially extending with regard to the extension axis E of the piston and multiple support walls 42 radially extending in a star like manner between an outwardly facing surface 44 of the tube 40 and an inner surface 46 of the head portion 20 and the intermediate part 18.

[0060] In order to prevent unwanted tilting of the piston during its advancement, the piston comprises guidance means 48.

[0061] In the present embodiment, the guidance means 48 is formed by a plurality of guidance structures 50 radially protruding from an outer circumference of the intermediate part 18.

[0062] In particular, a pair of guidance structures 50 is axially spaced with regard to the extension axis E. Furthermore, multiple pairs of guidance structures 50 are equally spaced in a circumferential direction of the intermediate part 18.

[0063] It is to be noted that instead of a pair of axially spaced guidance structures 50, the guidance structure 50 may be formed as a rib continuously extending in the axial direction at the outer side surface of the intermediate part 18.

[0064] Alternatively, instead of segmenting the guidance structures 50 in the circumferential direction, as shown for example in Fig. 1, each guidance structure 50 may continuously extend in the circumferential direction, as can be seen for instance in Fig. 6.

[0065] It is further noted, that at least one of the guidance structures 50 may be formed at an outer circumference of the film bag collector 24 and / or the outer circumference of the side wall 34 at the rear part 16.

[0066] Now turning to Figs. 3 and 4, a second embodiment of a piston is described.

[0067] The piston of the second embodiment basically corresponds to the piston of the first embodiment, except that the film bag collector 24 is not continuously extending into the circumferential direction, but is rather segmented into a plurality of lips 52 by means of slits 54 radially extending from an outer circumference of the film bag collector 24 towards the outer side surface 26 of the head portion 20.

[0068] Furthermore, an axial gap is formed between the film bag collector 24 and the intermediate part 18, thereby allowing for the lips 52 to be axially deflectable.

[0069] Fig. 5 shows a detail of a third embodiment of a piston.

[0070] The piston according to the third embodiment basically corresponds to the piston according to the second embodiment, except that the piston is not formed as a single piece, but rather from multiple pieces connected to each other.

[0071] In particular, the rear part 16 is formed separate to the front part 14 and the intermediate part 18. Nevertheless, the rear part 16 is connected to the intermediate part 18.

[0072] In the present embodiment, the rear part 16 is connected to the intermediate part 18 by means of material bond. For this purpose, the rear part 16 comprises an annular protrusion 56 formed opposite to the rear end 12. The annular protrusion 56 of the rear part 16 is received in a corresponding annular groove 58 formed in the intermediate part 18.

[0073] Local heating, in particular occurring during a multiple component injection molding process, partly melts the material at the annular protrusion 56 and / or the annular groove 58 thereby connecting the rear part 16 to the intermediate part 18 after solidification of the molten material.

[0074] The rear part 16 may also be connected to the intermediate part 18 by mechanical means, for example by using a snap-fit connection.

[0075] In this regard, it is noted that the rear part 16 is formed from a material different to a material used for the intermediate part 18 and the front part 14. Such kind of piston comprising different parts may be obtained from a multiple component injection molding process or a multiple 3D printing process.

[0076] In the present embodiment, the rear part 16 is formed from elastomeric as well as thermoplastic material, such as low density polyethylene (LDPE), whereas the intermediate part 18 and the front part 14 are each formed of a thermoplastic material having a higher hardness than the material of the rear part 16, such as for example of polyoxymethylene (POM).

[0077] However, the rear part 16 may be formed from the same material as the intermediate part 18 and the front part 14. In this regard, the side wall 34 surrounding the cavity 30 may be designed sufficiently thin to be radially elastically deflectable upon applying a predetermined pressure onto the piston, for example of at least 5 bar (5·10 5< kg / (m·s 2< )) and preferably of 6.9 bar (6.9·10 5< kg / (m·s 2< ) or 100 psi.

[0078] It is further noted that front part 14 and the intermediate part 18 may be formed by injection molding and / or 3D printing and the rear part 16 may be formed by another injection molding process and / or another 3D printing process.

[0079] Now referring to Figs. 6 and 7, a fourth embodiment of a piston is described. The piston according to the fourth embodiment basically corresponds to the piston according to the second embodiment, but is formed from separate pieces instead of a single piece, as will be described hereinafter.

[0080] Furthermore, the piston according to the fourth embodiment comprises two axially spaced guidance structures 50 continuously extending in the circumferential direction of the intermediate part 18 instead of the segmented guidance structures 50 shown in Fig. 3. However, the piston according to the fourth embodiment may also comprise such kind of guidance structures 50 like those described with regard to the piston of the first or second embodiment.

[0081] Even further, the piston according to the fourth embodiment differs from the piston according to the second embodiment in that the cavity 30 merges only into the intermediate part 18.

[0082] As already mentioned, the piston according to the fourth embodiment comprises of separate pieces connected to each other. In particular, the front part 14 is a piece separate to the intermediate part 18 and the rear part 16.

[0083] In order to connect the pieces, the intermediate part 18 forms a stud 60 axially extending opposite to the cavity 30 and radially recessed with regard to the outer circumference of the intermediate part 18. The stud 60 is received in a corresponding space 62 formed inside the head portion 10 of the front part 14. The stud 60 of the intermediate part 18 and the front part 14 are connected to each other by means of snap fit connection 64. However, the stud 60 may also be connected to the front part 14 by material bond.

[0084] In the present embodiment, the stud 60 is formed as a solid truncated cone. However, the stud 60 may also be formed as a solid cylinder. Furthermore, the cavity 30 may also at least partially extend through the stud 60.

[0085] The stud 60 received in the head portion 20 of the front part 14 increases mechanical stability of the piston and may entirely fill the space 62 inside the head portion 20.

[0086] However, in order to save material, the space 62 formed in the head portion 20 may only be partly filled with the stud 60, as shown in Fig. 7. The remaining part of the space 62 may comprise a support structure 38, as also shown in Fig. 7, which may be similar to the support structure 38 described with regard to the first embodiment. However, a support structure may not be required if the front part 14 comprises sufficient stability.

[0087] In the piston according to the fourth embodiment, the front part 14 is made of a material having a higher hardness than the material used for the intermediate part 18 and the rear part 16. In this case, the front part 14 is made of polyoxymethylene (POM) and the intermediate part 18 and the rear part 16 are made of polyethylene (PE). However, as described above, the front part 14, the intermediate part 18 and the rear part 16 may also be formed of the same material.

[0088] Like the piston of the third embodiment, the front part 14 may be formed by an injection molding or 3D printing process and the intermediate part 18 and the rear part 16 may be formed by another injection molding or 3D printing process.

[0089] Finally, it is noted that, although not shown, the front part 14, the intermediate part 18 and the rear part 16 may each be different pieces connected to each other. In this regard, each of the front part 14, the intermediate part 18 and the rear part 16 may be made of a different material or at least two of these parts may be made of the same material.List of reference signs

[0090] 10front end 12rear end 14front part 16rear part 18intermediate part 20head portion 22front surface 24film bag collector 26outer side surface 28annular groove 30cavity 32wall 34side wall 36sealing lip 38support structure 40tube 42support walls 44outwardly facing surface 46inner surface 48guidance means 50guidance structure 52lip 54slit 56annular protrusion 58annular groove 60stud 62space 64snap fit connection Eextension axis

Claims

1. A piston for use with a collapsible film bag cartridge, the piston comprising: a front part (14), a rear part (16) and an intermediate part (18) arranged between the front part (14) and the rear part (16), an extension axis (E) of the piston extending between a front end (10) and a rear end (12) of the piston through the front part (14), the intermediate part (18) and the rear part (16); the front part (14) comprising a head portion (20) radially recessed with regard to the intermediate part (18) and a film bag collector (24) radially extending from an outer side surface (26) of the head portion (20), the film bag collector (24) and the outer side surface (26) of the head portion (20) at least in sections define an annular groove (28) therebetween; wherein the rear part (16) comprises a cavity (30) open to the rear end (12) of the piston, the cavity (30) surrounded by an elastically deflectable wall (34).

2. The piston according to claim 1, wherein the elastically deflectable wall (34) is more elastic than at least the head portion (20) of the front part (14) and / or the intermediate part (18).

3. The piston according to claim 1 or 2, wherein the piston is formed as a single piece or as separate pieces connected to each other, in particular the front part (14) and / or the rear part (16) and / or the intermediate part (18) formed as separate pieces.

4. The piston according to claim 3, wherein the rear part (16) and / or the intermediate part (18) and / or the front part (14) are formed from different materials.

5. The piston according to one of the preceding claims, wherein the rear part (16) at least in sections, in particular the wall (34) surrounding the cavity (30) at the rear part (16), is formed of an elastomeric material and / or a thermoplastic material.

6. The piston according to claim 5, wherein the front part (14) and / or the intermediate part (18) are formed of a thermoplastic or thermosetting material, in particular with the thermoplastic material of the front part (14) and / or the intermediate part (18) having a higher hardness than the thermoplastic material of the rear part (16).

7. The piston according to one of the preceding claims, wherein a wall thickness of the wall (34) surrounding the cavity (30) at the rear part (16), in particular circumferentially surrounding the cavity (30), is at least in sections selected to allow for an elastic deflection of the wall (34) upon applying a predetermined pressure.

8. The piston according to one of the preceding claims, wherein the wall (34) surrounding the cavity (30) at the rear part (16) comprises a side wall (34) that surrounds the cavity (30) in circumferential direction, with the side wall (34) being elastically radially deflectable with regard to the extension axis (E).

9. The piston according to one of the preceding claims, wherein a circumferentially extending sealing lip (36) is formed at the rear part (16), in particular at a rear end section of the rear part (16).

10. The piston according to one of the preceding claims, wherein the cavity (30) is dome shaped.

11. The piston according to one of the preceding claims, wherein the cavity (30) is closed towards the front end (10) of the piston.

12. The piston according to one of the preceding claims, wherein the cavity (30) merges into the intermediate part (18) or through the intermediate part (18) into the head portion (20) of the front part (14).

13. The piston according to claim 12, wherein wherein a thickness of the wall (34) surrounding the cavity (30) at the rear part (16) is thinner than a thickness of the wall (32) surrounding the cavity at the intermediate part (18) and / or the head portion (20) of the front part (14).

14. The piston according to one of the preceding claims, wherein guidance means (48) are formed at an outer circumference of the piston, in particular the guidance means (48) comprising at least one guidance structure (50) at least partially extending in a circumferential direction of the piston.

15. A method of producing a piston for a collapsible film bag cartridge according to one of the preceding claims, wherein a first component selected from at least one of the front part (14), the rear part (16) and the intermediate part (18) is made by an injection molding or 3D printing process and a second component selected from at least one of the front part (14), the rear part (16) and the intermediate part (18) is made by another injection molding or 3D printing process, the first component and the second component being different.

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