Patent Description:
Reusable cartridge pistons are well known in the art and are configured to be moveable along a discharge axis of a reusable cartridge from a storage position into a discharge position, thereby discharging a material stored in a film bag cartridge housed in a sleeve of the reusable cartridge. The sleeve not only supports the film bag but also guides the piston during its movement from the storage position into the discharge position.

For the later purpose, at least an outer side wall of the generally cylindrical shaped piston contacts an inner wall of the sleeve, thereby stabilizing the piston during its movement along the discharge 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 may be replaced by a full new film bag. The reusable cartridge is then ready to be used again. As the reusable cartridge may be used time and again and as only the film bag needs to be replaced, waste can be minimized, as the empty film bag cartridge has a significantly reduced rigidity in comparison to rigid plastic cartridges.

The film bag is typically connected to a head part comprising an outlet from the film bag, this head part is typically also replaced when a film bag cartridge is replaced.

On replacing the head part and the film bag cartridge it can happen that the head part is placed onto the sleeve at the wrong end of the sleeve in such a way that the piston installed in the sleeve cannot engage the film bag in the intended manner.

Prior art pistons are known from <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

For this reason it is an object of the invention to provide a cartridge and a dispensing assembly in which the faulty placement of the film bag cartridge at the sleeve can be avoided in order to form a cartridge that is simplified in its handling. It is a further object of the invention to provide at least some components of the dispensing assembly can then be manufactured in a simpler and more reliable manner in comparison to prior art components of the dispensing assembly.

This object is satisfied by a piston for a cartridge having the features of claim <NUM>.

Such a piston for a support sleeve of a dispensing assembly, in particular comprising one or more film bag cartridges, has an at least substantially cylindrical outer shape and comprises a piston body as well as first and second film bag retainers arranged at opposite sides of the piston body, with the reliability and accuracy as previously only possible at one side of the sleeve.

By forming the piston such that it has two sides which can engage a film bag cartridge means that a faulty placement of the film bag cartridge at the sleeve can be avoided, since both the sleeve and the piston are formed symmetrical in the sense that the head part of a cartridge can be placed at either end of the sleeve and the dispensing assembly can still be used.

In this way a re-usable piston is formed in which both sides of the cylinder can be used to cooperate with a film bag cartridge in a reliable manner.

The piston may be configured for use with a film bag cartridge and each of the first and second film bag retainers may be configured to interact, in particular directly, with said film bag cartridge. In this way the piston is configured to collect loose material of the wall of the film bag cartridge when this is being emptied, as the piston is moved towards the head part on emptying the film bag cartridge. On collecting the loose material of the walls, this material is retained at the film bag retainers and is gradually folded together in a manner similar to that of a concertina.

The piston body has a disc shaped part and first and second projections projecting from the piston body at opposite sides of the body in the direction of the film bag retainers. This is a simple and sturdy design option for the piston body that provides the piston with the desired stability and that is simple to manufacture.

The first and second projections are ring-shaped projections. Such projections are simple to manufacture and enable a simple cost effective assembly of the piston body.

The disc shaped part may comprise ribs at its outer circumferential surface. Such ribs can be used to guide the piston body in a piston sleeve when it is received therein.

Each of the film bag retainers comprises a central projection projecting towards the piston body. Such a central projection can be formed in a cost effective manner in a manufacturing process, e.g. an injection molding process, and may aid in the assembly of the piston.

The central projection cooperates with a respective one of the first and second projections, preferably wherein the central projection may cooperate with a central aperture of the ring shaped projection. Such a design is simple to realize cost effective to manufacture and ensures a reliable and reproducible assembly of the piston.

Each film bag retainer may be received via one of a press-fit, a friction fit or a snap fit connection at the piston body. These are particularly beneficial ways of assembling the piston if this is a multi-component piston. In this connection it should be noted that the piston may also be made integrally as a single part, e.g. in an injection molding process or a 3D printing process.

The first and second film bag retainers may be formed from materials more flexible than a material of the piston body; and/or wherein the first and second film bag retainers may comprise components more flexible than parts of the piston body.

Each film bag retainer may have a central part surrounded by a ring recess and a collar facing the central part. The collar, the ring recess and the central part can be configured to ensure that a material of the film bag cartridge is reliably collected by the film bag containers on dispensing material from the film bag cartridge and on emptying this.

At least the collar and the ring recess may comprise three or more slots that extend from a radial outer side of the collar towards the central part of the film bag retainer. The provision of slots means that the collar can be formed more flexible than other parts of the piston enabling the collar to move relative to other parts of the piston. This movement can be beneficial on collecting and retaining material from walls forming the film bag cartridge.

A base of the recess may be spaced apart from the piston body by a gap, optionally wherein the gap may have a height selected in the range of <NUM> to <NUM>. The provision of a gap between the collar and the piston body ensures a relative movement can take place between the collar and the piston body. This relative movement may be required in order to collect a material of the film bag cartridge.

A surface of the collar facing the central part may comprises one or more recesses and/or one or more projections. The formation of recesses and/or projections at a surface of the collar facing the central part forms a reinforcing member at the collar and hence ensures that these do not prematurely snap off during their interaction with the film bag cartridge in the sleeve.

The central part of the film bag retainer may comprise a front face remote from the piston body, with the front face forming a flat plane or an at least substantially flat plane. A front face with a flat plane ensures that as much material as possible can be urged out of the corresponding film bag cartridge which cooperates with the piston, thereby waste can be reduced.

The front face may project by <NUM>% to <NUM>% of a height of the film bag retainer beyond a height of the collar, with the height of the film bag retainer being measured between the front face and a base of the film bag retainer remote from the front face, said base facing the piston body. Forming the film bag retainers in this way yields positive results on the collection of the material forming the walls of the film bag cartridge. The first and second film bag retainers may each have a shape that resembles that of a bowler hat.

According to a further aspect the present invention relates to a dispensing assembly comprising one or more film bag cartridges, one or more sleeves accommodating a respective one of said one or more film bag cartridges and one or more pistons according to at least claim <NUM>.

in a respective one of said one or more sleeves, optionally with each of said one or more film bag cartridges being filled with a material, especially a mastic material.

The advantages discussed in the foregoing in connection with the piston likewise hold true for the dispensing assembly discussed herein.

The cartridge, in particular the multi-component cartridge, of the dispensing assembly can thus be filled with materials selected from the group of members consisting of topical medications, medical fluids, wound care fluids, cosmetic and/or skin care preparations, dental fluids, veterinary fluids, adhesive fluids, disinfectant fluids, protective fluids, paints and combinations of the foregoing.

Such materials and hence the dispensing assembly can therefore be expediently used in the treatment of target areas such as the nose (e.g. anti-histaminic creams etc.), ears, teeth, i.e. dental applications, (e.g. molds for implants or buccal applications (e.g. aphtas, gum treatment, mouth sores etc.), eyes (e.g. the precise deposition of drugs on eyelids (e.g. chalazion, infection, anti-inflammatory, antibiotics etc.), lips (e.g. herpes), mouth, skin (e.g. anti-fungal, dark spot, acne, warts, psoriasis, skin cancer treatment, tattoo removal drugs, wound healing, scar treatment, stain removal, anti-itch applications etc.), other dermatological applications (e.g. skin nails (for example anti-fungal applications, or strengthening formulas etc.) or cytological applications.

Alternatively the materials and hence the dispensing assembly can also be used in an industrial sector both for the production of products as well as for the repair and maintenance of existing products, e.g. in the building industry, the automotive industry, the aerospace industry, in the energy sector, e.g. for windturbines, etc. The dispensing assembly can, for example, be used for the dispensing of construction material, sealants, bonding material, adhesives, paints, coatings and/or protective coatings.

According to a further aspect the present invention relates to a dispenser comprising one or more push rods and one or more pistons according to at least claim <NUM>, each of said one or more push rods being configured to move a respective one of the pistons to and fro along a dispensing axis of the respective push rod, wherein said one or more push rods can be coupled to said respective one or more pistons or is fixedly connected to said respective one or more pistons.

In this way a particularly simple to handle dispenser is made available.

Further embodiments of the invention are described in the following description of the Figures. The invention will be explained in the following in detail by means of embodiments and with reference to the drawing in which is shown:.

In the following the same reference numerals will be used for parts having the same or equivalent function. Any statements made having regard to the direction of a component are made relative to the position shown in the drawing and can naturally vary in the actual position of the application.

<FIG> shows a cartridge <NUM> configured as a two-component cartridge. The cartridge <NUM> comprises two generally cylindrical cartridge chambers <NUM>, <NUM>. The cartridge chambers <NUM>, <NUM> are each bound by a cartridge wall <NUM>, <NUM> as well as by a head part <NUM>, <NUM>, with each head part <NUM>, <NUM> being arranged at a respective front end <NUM>, <NUM> of the cartridge wall <NUM>, <NUM>. Each cartridge wall <NUM>, <NUM> extends in a longitudinal direction A of the cartridge <NUM> from a respective rear end <NUM>, <NUM> to the respective front end <NUM>, <NUM>.

Each head part <NUM>, <NUM> is a stable shaped part of generally plate-like shape and comprises respective dispensing outlets <NUM>, <NUM> via which a respective medium (not shown) can be dispensed from the cartridge chambers <NUM>, <NUM>. The two dispensing outlets <NUM>, <NUM> extend from the head parts <NUM>, <NUM> as outlet passages <NUM>, <NUM> through a common outlet part <NUM>. A mixing element <NUM> (see <FIG>) or closure part (each not shown) can be connected to the outlet part <NUM>.

Each head part <NUM>, <NUM> has a collar <NUM>, <NUM>, with each collar <NUM>, <NUM> surrounding the dispensing outlet <NUM>, <NUM> in a radially outer region of the head part <NUM>, <NUM>. A radial direction B is indicated relative to the arrow A used to identify the longitudinal direction A. Each collar <NUM>, <NUM> has a length extending in the longitudinal direction A. The front end <NUM>, <NUM> of each cartridge wall <NUM>, <NUM> is sealingly and non-releasably connected to the collar <NUM>, <NUM> of the head part <NUM>, <NUM>. The front end <NUM>, <NUM> of each cartridge wall <NUM>, <NUM> may be connected to an inner or an outer surface of the respective collar <NUM>, <NUM> in a sealing and non-releasable manner.

The cartridge walls <NUM>, <NUM> are each formed from a film <NUM>', <NUM>'. Each rear end <NUM>, <NUM> of the cartridge walls <NUM>, <NUM>, formed from the film <NUM>', <NUM>', is welded shut in a sealing manner in the present example to form a respective film bag cartridge <NUM>.

It should further be noted in this connection that the film <NUM>', <NUM>' forming the cartridge walls <NUM>, <NUM> can be a multilayer film having at least two layers formed from different materials. Such multi-layer films are used e.g. when particularly aggressive substances are stored in the cartridge <NUM>.

It should also be noted that the film <NUM>', <NUM>', regardless of whether it is a film made from one type of material or a multilayered film made from one or more different types of materials, can have a thickness of at most <NUM>, more specifically of at most <NUM>, preferably of approximately <NUM> to <NUM>.

It should also be noted that the cartridge <NUM> can also be configured as a one-component cartridge, comprising only one generally cylindrical cartridge chamber <NUM> with a single head part <NUM> and a film <NUM>' forming the cartridge wall <NUM>. In the following, corresponding features of the one-component cartridge <NUM> and corresponding features of the two-component cartridge <NUM> mutually hold true.

It is necessary that the connection between the film <NUM>', <NUM>' defining the cartridge wall <NUM>, <NUM> to its respective head part <NUM>, <NUM> is tightly sealed and does not leak such that the medium that is to be dispensed via the dispensing outlet <NUM>, <NUM> does not exit from the cartridge <NUM> at any other position other than via the outlet part <NUM>.

<FIG> shows a sectional view of a second type of cartridge <NUM> installed in a dispensing assembly <NUM>. The film bag cartridge <NUM> is configured to discharge two materials M, M', such as a multi-component adhesive comprising a binder and a hardener, i.e. a mastic material M, M'.

The dispensing assembly <NUM> further comprises two sleeves <NUM>, <NUM>' accommodating a respective one of the cartridge chambers <NUM>, <NUM> having the cartridge walls <NUM>, <NUM> formed by the films <NUM>', <NUM>' and a respective piston <NUM>, <NUM>'.

The sleeve <NUM>, <NUM>' is preferably an extruded aluminum sleeve. Alternatively, the sleeve <NUM>, <NUM>' may be formed from an injection molded plastic material.

The respective sleeve <NUM>, <NUM>' is configured to be coupled to the head part <NUM>, <NUM> of the film bag cartridge <NUM>, with the head parts <NUM>, <NUM> being integrally formed and comprising the common outlet part <NUM>. The outlet part <NUM> can be coupled to the mixing element <NUM> (see <FIG>) in use. In the storage state the outlet part <NUM> can be sealed off using a plunger (not shown) which is inserted into the respective outlet passages <NUM>, <NUM>.

The outlet part <NUM> shown in <FIG> is intended to be connected to the mixing element <NUM> or the plunger via bayonet like connection means, whereas in <FIG> the outlet part <NUM> is intended to be connected to the mixing element <NUM> respectively the plunger via a cap nut (also not shown).

Each piston <NUM>, <NUM>' has an at least substantially cylindrical outer shape and comprises a piston body <NUM> as well as first and second film bag retainers <NUM>, <NUM> arranged at opposite sides of the piston body <NUM>.

Each of the pistons <NUM>, <NUM>' is configured for use with the respective cartridge wall <NUM>, <NUM> of the film bag cartridge <NUM>, and each of the first and second film bag retainers <NUM>, <NUM> is configured to interact, in particular directly, with said walls <NUM>, <NUM> of the film bag cartridge <NUM>.

On moving the respective piston <NUM>, <NUM>' in the sleeve <NUM>, <NUM>' towards the respective head part <NUM>, <NUM> the material M, M' stored in the cartridge chamber <NUM>, <NUM> is dispensed via the common outlet part <NUM>. As the material leaves the cartridge chambers <NUM>, <NUM>, part of the rear end <NUM>, <NUM> of the film <NUM>', <NUM>' forming the cartridge walls <NUM>, <NUM> becomes loose and has to be collected in order to prevent the film <NUM>', <NUM>' from being caught between the pistons <NUM>, <NUM>' and an inner wall <NUM>, <NUM>'.

If the film <NUM>', <NUM>' is caught between the pistons <NUM>, <NUM>' and an inner wall <NUM>, <NUM>', this could either produce a tear in the film <NUM>', <NUM>' which could either render the cartridge <NUM> inoperable or at least significantly reduce the lifetime of the materials M, M' stored in the cartridge <NUM>. Alternatively the loose material could be trapped between the piston <NUM>, <NUM>' and the sleeve <NUM>, <NUM>' causing the piston <NUM>, <NUM>' to be jammed in the sleeve <NUM>, <NUM>' preventing the piston <NUM>, <NUM>' from being moved further towards the head part <NUM>, <NUM>. Both of these scenarios are to be avoided if possible.

The function of the first and second film bag retainers <NUM>, <NUM> is to collect the loose material of the part of the rear end <NUM>, <NUM> of the film <NUM>', <NUM>' forming the cartridge walls <NUM>, <NUM>, by guiding this from the outside of a collar <NUM> of the first and second film bag retainers <NUM>, <NUM> towards a ring recess <NUM> and then towards a central part <NUM> of the film bag retainer <NUM>, <NUM> facing the collar <NUM>.

<FIG> shows a schematic sectional view of the two sleeves <NUM>, <NUM>' with one piston <NUM>' being installed in one of the two sleeves <NUM>'. The respective sleeve <NUM>, <NUM>' comprises projections <NUM> arranged at either end of the respective sleeve <NUM>, <NUM>' at the inner surface <NUM>, <NUM>' of the sleeve <NUM>, <NUM>'. Preferably two or more such projections <NUM> are formed at either end of the respective sleeve <NUM>, <NUM>', with only being shown in the schematic sectional view of <FIG>.

The projections <NUM> are provided at the sleeves <NUM>, <NUM>' in order to prevent the piston <NUM>, <NUM>' from falling out of the sleeve <NUM>, <NUM>'. The piston <NUM>, <NUM>' may have some form of introduction aid (not shown) present at an outer surface thereof, via which the piston <NUM>, <NUM>' can be inserted into the sleeve <NUM>, <NUM>' in a controlled manner. The introduction aid may be present as a groove (not shown) through which the projection <NUM> can be guided on installing the piston <NUM>, <NUM>' in the sleeve <NUM>, <NUM>' of the dispensing assembly <NUM>.

<FIG> shows a schematic view of the piston <NUM>, <NUM>'. Each film bag retainer <NUM>, <NUM> has the central part <NUM> surrounded by the ring recess <NUM> and the collar <NUM> facing the central part <NUM>.

Three slots <NUM> extend from a radial outer side of the collar <NUM> through the ring recess <NUM> towards the central part <NUM> of the film bag retainer <NUM>, <NUM>. The slots <NUM> extend into a sidewall <NUM> of the central part <NUM> up to a front face <NUM> of the respective film bag retainer <NUM>, <NUM>. The slots <NUM> divide the collar <NUM> into respective collar sections <NUM>'. It should be noted in this connection that the slots <NUM> do not have to present at the sidewall <NUM> or they could also only extend e.g. part of the way of a height of the sidewall, in particular e.g. <NUM> % to <NUM>% of the height of the sidewall <NUM> transverse to the recess <NUM>.

The plurality of slots <NUM> separating the plurality of collar sections <NUM>' may have a non-uniform shape, i.e. the slots <NUM> may not have walls that extend in parallel to one another as shown in <FIG>, but the walls of the slots <NUM> may taper apart either in the direction towards the sidewall from the radial outer side or in a direction facing away from the sidewall <NUM>. It is also conceivable that the slots <NUM> may comprise first and second slot sections (not shown), with a spacing between the first slot sections being smaller than a spacing between the second slot sections.

It should be noted in this connection that it is preferred if the first slot section is smaller than the second slot section, with the first slot section preferably being arranged further towards the outer circumference of the piston <NUM>, <NUM>' than the second slot section.

It should further be noted that the slots <NUM> and/or the ring recess <NUM> is/are not specifically limited to their specific shape and form and they may be formed such that they have a polygonal, rectangular, triangular, U-shaped, V-shaped etc. cross-section in the radial direction of the first and second film bag retainers <NUM>, <NUM> extending transverse to the sidewall <NUM>.

It should further be noted that the number of slots is not specifically limited and may be <NUM> to <NUM>, typically <NUM> to <NUM>.

It should further be noted that a thickness of the respective collar section <NUM>' is important. If the thickness is too thin the collar section <NUM>' may be too fragile or breakable, if it is too thick it will not be easily moveable. Thus the typical thicknesses of the collar sections <NUM>' will be on the order of mm's, for example <NUM> or less or <NUM> to <NUM> in thickness.

It should further be noted that the geometric form of the respective collar section <NUM>' is not specifically limited, and it may be polygonal, rectangular, pentagonal, square, hexagonal, octagonal, or triangular etc..

The number of collar sections <NUM>' is also not specifically limited and typically may vary from <NUM> to <NUM>, in particular <NUM> to <NUM>. The larger the number of collar sections <NUM>' is, the more flexible these are and hence a larger number of collar sections <NUM>' is better for larger diameter pistons <NUM>, <NUM>'. The trade-off is that the dies and injection molding equipment required to produce such a piston <NUM>, <NUM>' are more complicated in comparison to pistons <NUM>, <NUM>' having a smaller number of collar sections <NUM>'.

Each of the respective collar sections <NUM>' is moveable relative to the piston head and the piston body <NUM> and the central part <NUM>, <NUM>. The collar sections <NUM>' are in particular resilient or flexible and moveable relative to the piston body <NUM> and the central part <NUM>, <NUM> without breaking, and are typically embodied to be movable based on a force of inserting these into the sleeve mechanically by hand, although one could potentially use compressed air (e.g. <NUM> bar) for assistance.

On dispensing the material stored in the film bag cartridge <NUM> pressures in the range of <NUM> to <NUM> bar are exerted onto the piston body via a dispenser <NUM> (see <FIG>) and to dispense materials stored in the film bag cartridge <NUM>. These pressures are transferred via the piston <NUM>, <NUM>' and the plurality of collar sections <NUM>' to the film bag cartridge <NUM>. The collar sections <NUM>' like the piston <NUM>, <NUM>' have to thus be configured such that they can cope with this transfer of pressures from the dispenser <NUM> to the film bag cartridge <NUM>.

A base <NUM> of the ring recess <NUM> is spaced apart from the piston body <NUM> by a gap <NUM>. In this connection it should be noted that the gap <NUM> may have a height selected in the range of <NUM> to <NUM>.

The size of this gap <NUM> is namely selected to ensure that none of the collar sections <NUM>' is bent over too much and thus eventually breaks away from the piston <NUM>, <NUM>' during the movement of the piston <NUM>, <NUM>' towards the head part <NUM>, <NUM> on dispensing material from the film bag cartridge <NUM>. In this way the piston body <NUM> acts as a support for the plurality of collar sections <NUM>' when these are deflected towards the piston body <NUM> on dispensing materials from the film bag cartridge <NUM>.

Preferably, the piston <NUM>, <NUM>' is an injection molded part injection molded from one or more materials, in particular one of POM, PTFE, PA or a polymer or a thermoset material having a hardness measured with the Shore D Durometer selected in the range of 55D to 100D.

As is well known in the art, a hot injection molded material may shrink during its cooling. However, in order to overcome this drawback, and in particular to retain the size of the plurality of collar sections <NUM>', each collar section <NUM>' may comprise one or more recesses (not shown) on an inner surface thereof facing the sidewall <NUM>. The recesses may also be formed on an outer portion of the collar section <NUM>' facing away from the sidewall <NUM>. It is to be understood, that the outer portion of the collar section may also be formed without a recess.

Furthermore, in order to guide the piston <NUM>, <NUM>' during its movement along a dispensing axis D (see <FIG>) of the cartridge <NUM>, the piston body <NUM> may comprise a plurality of guide structures. The guide structures are presently formed as axially aligned ribs <NUM> protruding from the piston body <NUM>. The ribs <NUM> could be configured to engage corresponding channels (not shown) present in the sleeve <NUM>, <NUM>'.

Alternatively, the guide structures of the piston <NUM>, <NUM>' may also be formed as channels, if the inner surface <NUM>, <NUM>' of the sleeve <NUM>, <NUM>' comprises corresponding protrusions (also not shown).

In this connection it should be noted that the sleeve <NUM>, <NUM>' may be formed without such guide structures and simply have the inner wall <NUM>, <NUM>' formed without recesses or protrusions as currently shown in <FIG>.

In this connection it should be noted that also the piston <NUM>, <NUM>' may be formed without such guide structures.

<FIG> shows an exploded view of a further piston <NUM>, with the first and second retainers <NUM>, <NUM> being separate from the piston body <NUM>. The piston <NUM> comprises twenty collar sections <NUM>' in comparison to the piston <NUM> of <FIG>.

The piston body <NUM> has a disc shaped part <NUM> and first and second projections <NUM>, <NUM> projecting from the piston body <NUM> at opposite sides of the body <NUM> in the direction of the film bag retainers <NUM>, <NUM>.

The disc shaped part <NUM> of the piston body <NUM> comprises a base plate <NUM> and a plurality of webs <NUM> arranged at either side of the base plate <NUM>. The plurality of webs <NUM> extend radially inwardly from an outer circumferential wall <NUM> of the disc shaped part <NUM> of the piston body <NUM>.

The webs <NUM> may extend over <NUM> to <NUM> % of a length of the disc shaped part <NUM> between the first and second projections <NUM>, <NUM> and the outer circumferential wall <NUM>. In the present example the webs extend over <NUM>% of the length of the disc shaped part <NUM>.

If provided the plurality of webs <NUM> can namely strengthen both the piston body <NUM> and the outer circumferential wall <NUM> of the piston body <NUM> such that the piston body <NUM> is formed less flexible than the collar <NUM> of the respective first and second retainer <NUM>, <NUM>.

Also visible are a plurality of apertures <NUM> arranged at the disc shaped part <NUM> of the piston body <NUM>. The plurality of apertures <NUM> provide the possibility of enabling an exchange of air at the piston <NUM> on using the piston <NUM> in the dispensing assembly <NUM>.

<FIG> shows a schematic sectional view of the piston of <FIG> along the sectional line A:A. As is visible the first and second projections <NUM>, <NUM> are ring-shaped projections. Moreover, the first and second film bag retainers <NUM>, <NUM> comprises a central projection <NUM> projecting towards the piston body <NUM>. The central projection <NUM> cooperates with a respective one of the first and second projections <NUM>, <NUM> by engaging one of the two central apertures <NUM> of the respective ring shaped projection <NUM>, <NUM>.

In the present example the film bag retainers <NUM>, <NUM> is received via a snap-fit connection present between central projection <NUM> and the central aperture <NUM>. The snap-fit connection being formed by an annular groove <NUM> present at the central aperture <NUM> cooperating with a circumferential lip <NUM> present at the central projection <NUM>. In this connection it should be noted that the groove could also be present at the central projection <NUM> and the circumferential lip could be present at the central aperture <NUM>.

It is also conceivable that each film bag retainer <NUM>, <NUM> is received via one of a friction fit or a press-fit connection at the piston body <NUM>. It is also conceivable that the piston <NUM> is made in one piece e.g. in an injection molding process or a 3D printing process and hence that no central projection cooperating with a central aperture is provided.

In this connection it should be noted that a material of the film bag retainer <NUM>, <NUM> can be different from a material of the piston body <NUM>, or it can be made from the same material as the piston body <NUM>. In any event the collars <NUM> of the first and second film bag retainers <NUM>, <NUM> have to be designed such that they are more flexible than a material of the piston body <NUM> in order to enable a relative movement between the collar <NUM> and the piston body <NUM>.

The central parts <NUM> of the film bag retainers <NUM>, <NUM> comprises the front face <NUM> remote from the piston body <NUM>, with the front face <NUM> forming a flat plane or an at least substantially flat plane.

The front face <NUM> projects by <NUM>% to <NUM>% of a height of the film bag retainer <NUM>, <NUM> beyond a height of the collar <NUM>, with the height of the film bag retainer <NUM>, <NUM> being measured between the front face <NUM> and a base <NUM>' of the film bag retainer <NUM>, <NUM> remote from the front face <NUM>, said base <NUM>' facing the piston body <NUM>.

The first and second film bag retainers <NUM>, <NUM> also comprise a plurality of support webs <NUM>' arranged at a side of the central part <NUM> that is remote from the front face <NUM>, i.e. at the side of the film bag retainer <NUM>, <NUM> having the central projection <NUM>.

It should be noted in this connection that an outermost diameter of the collar <NUM> is preferably equal to an outermost diameter of the piston body <NUM>. It should be noted that it is also possible that the outermost diameter of the collar <NUM> is selected in the range of <NUM>% to <NUM>% of the outermost diameter of the piston body <NUM>.

The piston <NUM>, <NUM>' may have an outermost diameter selected in the range of <NUM> to <NUM>, in particular <NUM> to <NUM>, especially <NUM> to <NUM>; and/or a height measured between the front faces <NUM> of the first and second film bag retainers <NUM>, <NUM> selected in the range of <NUM> to <NUM> in particular <NUM> to <NUM>.

<FIG> shows a dispenser <NUM> in which the dispensing assembly <NUM> installed in a reception space <NUM> thereof. The mixing element <NUM> is connected to the outlet part <NUM> of the dispensing assembly <NUM>. Only part of the mixing element <NUM> is visible in the drawing of <FIG>.

The dispenser comprises two push rods <NUM>, with the push rods <NUM> being configured to move the respective piston <NUM>, <NUM>' to and fro along the dispensing axis D of the respective push rod <NUM>, wherein said push rods <NUM> can be coupled to said piston <NUM>, <NUM>' or is fixedly connected to said piston <NUM>, <NUM>'.

As the push rods <NUM> move the pistons <NUM>, <NUM>' along the dispensing axis D of the reusable film bag cartridge <NUM>, the front face <NUM> facing away from the piston base <NUM> pushes against the film bag cartridge <NUM>, thereby urging the material stored inside the film bag cartridge <NUM> out of the outlet part <NUM> and through the mixing element <NUM>.

Claim 1:
A piston (<NUM>, <NUM>') for a support sleeve (<NUM>, <NUM>') of a dispensing assembly (<NUM>), in particular comprising one or more film bag cartridges (<NUM>), the piston (<NUM>, <NUM>') having an at least substantially cylindrical outer shape and comprising a piston body (<NUM>) as well as first and second film bag retainers (<NUM>, <NUM>) arranged at opposite sides of the piston body (<NUM>), wherein the piston body (<NUM>) has a disc shaped part (<NUM>) and first and second projections (<NUM>, <NUM>) projecting from the piston body (<NUM>) at opposite sides of the piston body (<NUM>) in the direction of the film bag retainers (<NUM>, <NUM>),
characterised in that
the first and second projections (<NUM>, <NUM>) are ring-shaped projections, wherein each of the film bag retainers (<NUM>, <NUM>) comprises a central projection (<NUM>) projecting towards the piston body (<NUM>), and wherein the central projection (<NUM>) cooperates with a respective one of the first and second projections (<NUM>, <NUM>).