GB2537756A

GB2537756A - Improved metering valve for dispensing an aerosol comprising a valve stem

Info

Publication number: GB2537756A
Application number: GB1607057.5A
Authority: GB
Inventors: Stephan Nolwenn
Original assignee: Nemera la Verpilliere SAS
Current assignee: Nemera la Verpilliere SAS
Priority date: 2015-04-24
Filing date: 2016-04-22
Publication date: 2016-10-26
Anticipated expiration: 2036-04-22
Also published as: GB2537756B; FR3035382B1; FR3035382A1

Abstract

A metering valve for dispensing an aerosol can have a valve stem 3 moulded from a material essentially consisting of a mixture of polybutylene terephthalate (PBT) and polydimethylsiloxane (silicone). The silicone may be more than 1.5% by weight, relative to the total weight of the stem 3. A process for manufacturing a valve stem 3 for a metering valve may comprise mixing PBT with from 1.5% to 10% by weight, of silicone, relative to the total weight of the mixture; and injecting/moulding the mixture to obtain a valve stem 3 moulded from a material essentially consisting of a mixture of PBT and silicone. The valve stem 3 may have one end positioned on the side of a reservoir 9 and one opposite dispensing end. The valve stem 3 may be slidably mounted by a valve gasket 7 and a chamber gasket 8. Fillers, especially glass fibres, may represent more than 10% of the PBT composition. The valve stem 3 may reduce friction when the valve stem 3 slides between the valve and chamber gaskets, reducing lubricant requirements, while being suitable for sterilisation by irradiation.

Description

Improved metering valve for dispensing an aerosol comprising a valve stem The present invention relates to a metering valve for 5 dispensing an aerosol comprising a valve stem.

Valves are well known in the prior art. Their main application is found in aerosol containers for dispensing products in powder form by means of a propellant (pressurized gas). When they are metering valves, the valves generally comprise a valve body that contains a metering chamber delimited axially by two annular gaskets, a top gasket known as a valve gasket and a bottom gasket known as a chamber gasket, and a valve stem that can be moved in particular between a rest position and an actuating position. According to one example described in the publication EP 0 858 420, the valve stem is forced by an elastic member towards its rest position, in which a stem shoulder formed on said valve stem bears against the lower surface of said valve gasket. In order to actuate the metering valve, the valve stem is pressed, which slides in the valve body within annular gaskets to its actuating position, in which a dose of the product is expelled. The elastic member then returns the valve stem to its rest position.

One problem that is faced with the valve stems of valves, in particular of metering valves, relates especially to the sealing at the valve gasket, and the friction that occurs when sliding the valve stem through the gaskets.

One solution to these drawbacks was made in European patent EP 0 858 420 by providing a valve stem moulded from a material comprising a mixture of acetal resin, polytetrafluoroethylene (PTFE) and silicone, especially in the form of silicone oil. -2 -

However, such a solution is not economical since it requires the use of PTFE in a proportion of at least 10. Furthermore, such valve stems of the prior art are not the most suitable for a medical device comprising a 5 sterile medicament to be dispensed. This is because the acetal resins used, such as polyoxymethylene (POM), do not withstand irradiation sterilization processes very well, and are likely to degrade with use releasing formaldehyde, a product that is toxic for the user, 10 into the product to be dispensed.

Patent application JP 2006 131287 proposes to solve a problem linked to the adhesion of the products to be dispensed to valve stems manufactured from polyoxy-methylene (POM) or from polybutylene terephthalate (PBT). In order to achieve this, the valve stem is moulded from POM or PBT comprising from 0.1% to 1% of silicone in order to prevent the product to be dispensed from adhering to the valve stem. This document specifies that if the silicone concentration is too low the silicone will end up being eliminated too readily from the moulded part, and on the contrary if the silicone concentration is too high, the dispersion of the silicone will not be good, and will interfere with the moulding.

Therefore, there is a need to provide novel, more suitable valves.

The objective of the invention is in particular to propose a metering valve provided with a valve stem that makes it possible to overcome the problems of sealing and of friction.

Therefore, the invention relates to a metering valve for dispensing an aerosol comprising: a metering chamber, and a valve stem provided with one end intended to be -3 -positioned on the side of a reservoir and with one opposite dispensing end, slidably mounted in the metering chamber under the effect of a spring, between a top rest position and a bottom final position, the valve stem sliding through a first gasket referred to as a valve gasket or top gasket and a second gasket referred to as a chamber gasket or bottom gasket, the valve stem being moulded from a material comprising, or that essentially consists of, a mixture of polybutylene terephthalate (PBT) and polydimethylsiloxane, referred to as silicone, said silicone representing more than 1.5% by weight relative to the total weight of the valve stem.

Thus, the inventors have made the surprising observation that the moulding of the valve stem from a material comprising a mixture of PBT and a particular proportion of silicone improves the slip of the valve stem through the gaskets of the valve, thus limiting the frictions when the valve stem slides between the valve and chamber gaskets. The result of this is that a metering valve is provided that overcomes the problems of sealing and of friction, while being more economical to manufacture. In addition, the metering valve comprises a valve stem that is suitable for sterilization by irradiation.

Another advantage of the valve stem that has good slip properties is that it is not necessary to add an external lubricant to the sliding parts (the valve stem and/or the gaskets of the valve) at the sealing zones, which limits on the one hand the contact of the lubricant with the product to be dispensed, and limits or even eliminates the amount of lubricant in the dose administered to the user.

The metering valve is therefore free cf added lubricant, with the exception of a residual amount of -4 -lubricant or slip aid elements required for the manufacture and the handling of certain components of the metering valve and especially of the valve and chamber gaskets when they are made of an elastomer material.

It is understood that "a mixture of polybutylene terephthalate (PBT) and silicone" includes a mixture, on the one hand, of PBT or of a PBT derivative, and, on the other hand, of silicone or of a silicone derivative.

It is furthermore understood that the PBT belongs to the family of thermoplastic polyesters and is a 15 semicrystalline polymer used mainly in injection moulding for technical applications. The PBT is produced by polycondensation of terephthalic acid or of dimethyl terephthalate with 1,4-butanediol, according to processes well known to a person skilled in the art. 20 In the metering valve, the PBT used for moulding the valve stem is used alone, which is the most advantageous, but may also be combined with fillers, especially glass fibres that may represent more than 102 of the composition of the PBT. One example of glass-fibre-filled PBT is sold by DuPont under the name Crastin® SF.

In the metering valve, the silicone used is preferably 30 polydimethylsiloxane (PDMS) used in oil form. It may therefore be referred to as silicone oil.

Unlike a coating, for example by vaporization, of silicone oil, the valve stem proposed is moulded from a material that comprises PBT and silicone in its mass. Thus, the silicone is found partly distributed at the surface of the polymer and may exert its friction-limiting role, but the majority remains trapped in the -5 -mass of the PBT and is therefore less easily eliminated, especially by stripping when subjected to friction or by dissolving in the propellant gases, during uses of the metering valve.

In one advantageous embodiment, the silicone has a kinematic viscosity of more than 1000 cSt or mm2.s-1 at 25°C. The viscosity data is indicated for normal temperature and pressure conditions, i.e. an ambient temperature of 25°C on average (within a range extending from 19°C to 27°C) and at an atmospheric pressure at sea level of 1 atmosphere.

Silicones having a viscosity of more than 1000 cSt have 15 a molar mass of more than 40 000 g.molil.

These viscosities are measured with viscometers known to a person skilled in the art, and especially an Engler viscometer based on the measurement of the flow time of certain liquids through a calibrated orifice of determined dimensions. This viscometer is a purely empirical apparatus that gives, for the viscosity, a conventional value, expressed in degrees Engler. Owing to correlation tables, it is possible to determine the kinematic viscosity in cSt.

The inventors have observed that the moulding of the valve stem of the metering valve with PBT and a silicone oil having a kinematic viscosity as defined above exhibited numerous additional advantages, besides its lubricating properties. Specifically, due to the high molecular weight, the siloxane polymers are entangled in the PBT and are not very likely to be eliminated during the operation of the metering valve.

The result of this is that the valve stem has good slip properties through the gaskets of the valve over time, and that, unlike silicone oils having a viscosity of less than 1000 cSt, they are not likely to be -6 - "stripped" from the valve stem in the presence of propellant gas and dispensed with the medicament.

In another advantageous embodiment, the siliccne has a kinematic viscosity at 25°C, at a pressure of 1 atmosphere (at; 1 at = 98 066.5 Pa) at sea level, of from 1000 cSt to 100 000 cSt, especially a kinematic viscosity at 25°C of from more than 10 000 cSt to around 100 000 cSt.

A viscosity of from 1000 cSt to 100 000 cSt, at 25°C at a pressure of 1 at at sea level, is understood here to mean a viscosity of 1000 cSt, 2000 cSt, 3000 cSt, 4000 cSt, 5000 cSt, 6000 cSt, 7000 cSt, 8000 cSt, 9000 cSt, 13 000 cSt, 17 000 cSt, 21 000 cSt, 25 000 cSt, 29 000 cSt, 33 000 cSt, 37 000 cSt, 41 000 cSt, 45 000 cSt, 49 000 cSt, 53 000 cSt, 57 000 cSt, 61 000 cSt, 65 000 cSt, 69 000 cSt, 73 000 cSt, 77 000 cSt, 81 000 cSt, 85 000 cSt, 89 000 cSt, 93 000 cSt, 000 cSt, 14 000 cSt, 18 000 cSt, 22 000 cSt, 26 000 cSt, 30 000 cSt, 34 000 cSt, 38 000 cSt, 42 000 cSt, 46 000 cSt, 50 000 cSt, 54 000 cSt, 58 000 cSt, 62 000 cSt, 66 000 cSt, 70 000 cSt, 74 000 cSt, 78 000 cSt, 82 000 cSt, 86 000 cSt, 90 000 cSt, 94 000 cSt, 11 000 cSt, 12 000 cSt, 000 cSt, 16 000 cSt, 19 000 cSt, 20 000 cSt, 23 000 cSt, 24 000 cSt, 27 000 cSt, 28 000 cSt, 31 000 cSt, 32 000 cSt, 000 cSt, 36 000 cSt, 39 000 cSt, 40 000 cSt, 43 000 cSt, 44 000 cSt, 47 000 cSt, 48 000 cSt, 51 000 cSt, 52 000 cSt, 000 cSt, 56 000 cSt, 59 000 cSt, 60 000 cSt, 63 000 cSt, 64 000 cSt, 67 000 cSt, 68 000 cSt, 71 000 cSt, 72 000 cSt, 000 cSt, 76 000 cSt, 79 000 cSt, 80 000 cSt, 83 000 cSt, 84 000 cSt, 87 000 cSt, 88 000 cSt, 91 000 cSt, 92 000 cSt, 000 cSt, 96 000 cSt, 97 000 cSt, 98 000 cSt, 99 000 cSt or 100 000 cSt. -7 -

Such silicone oils are available commercially, especially from Bluestar Silicones, Dow Corning, Wacker Chemie or else from Bluestar Silicones in particular under the trade mark Rhodorsil® Oils 47.

In yet another advantageous embodiment, the mixture of polybutylene terephthalate and silicone comprises more than 1.5% by weight of silicone, and in particular from 1.5% to 10% by weight of silicone relative to the total weight of material of the valve stem.

The expression "more than 1.5% by weight of silicone, and in particular from 1.5% to 10% by weight of silicone" is understood within the invention to mean % % % % % % %amounts of, , , , , , , 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10% by weight of silicone relative to the total weight of material of the valve stem.

More advantageously, the mixture of PBT and silicone oil comprises from 1.5% to 5% by weight of silicone, and especially from 2% to 5% by weight, and in particular 3% by weight of silicone relative to the total weight of material of the valve stem.

Thus, in view of the proportions of silicone used, the PBT represents from 90% to 98.5% by weight relative to the total weight of material of the valve stem. This means that the PBT represents 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98% or 98.3% by weight relative to the total weight of material of the valve stem.

Of course, the PBT mixed with the silicone may also comprise other compounds such as additives, antioxidants, colourants, flame retardants, stabilizers (for example ultraviolet (UV) stabilizers), or any other additive known to person skilled in the art. The -8 -list is given by way of example and does not limit or restrict the scope of the invention. Advantageously, the additives represent up to 2%, preferably 1% of the total composition of the material from which the valve stem is moulded.

In yet another advantageous embodiment, the valve and chamber gaskets are positioned respectively at the outlet and the inlet of the metering chamber.

In the present description, the expressions "top" and "bottom" refer to the position of the valve stem relative to the reservoir onto which the metering valve is added. Thus, a bottom position of the valve stem corresponds to a position in which the valve stem is closer to the reservoir than in the case of a top position of the valve stem.

The metering valve proposed is furthermore generally intended to be mounted on a neck of a reservoir containing a fluid product to be dispensed in the form of an aerosol, very particularly a pharmaceutical product. It is intended to be used in the inverted position, also referred to as the "head down" position.

Even more advantageously, the valve and chamber gaskets are made of an elastomer material.

Advantageously, the elastomers used in the gaskets of the metering valve may be made of ethylene-propylenediene monomer (EPDM), of butadiene-acrylonitrile copolymers (NBR), of fluoroelastomers such as Viton® sold by DuPont, or of halogenated or non-halogenated isobutylene/isoprene copolymer. This list is not limiting, and a person skilled in the art may use various known elastomer materials that have elastic properties and that are compatible with a medical use. -9 -

One of the advantageous elastomer materials used for the gaskets of the metering valve is made of chlorobutyl rubber (CIIR).

In yet another embodiment, at least one of the valve and chamber gaskets is moulded from and/or coated with a material having properties that reduce the frictions during the sliding of the valve stem.

In order to increase the slip of the valve stem through the gaskets of the metering valve, and thus to limit the frictions, it may be advantageous to coat the elastomer material of the gaskets of the metering valve with a material that makes it possible to limit the frictions, such as silicone oils. In such a case, it may be advantageous to use an uncoated chamber gasket and a coated valve gasket, which makes it possible to limit the risks of interactions between the silicone oil and the product to be dispensed. It may also be advantageous, optionally in combination with the aforementioned coating, to provide elastomer gaskets additionally comprising a filler of a material comprising fluorine, especially polytetrafluoroethylene (PTFE).

With such combinations, the frictions between the valve stem and the gaskets of the valve are very greatly reduced, thus increasing the service life of the metering valve.

According to another advantageous embodiment, the metering chamber comprises a top compartment and a bottom compartment which are cylindrical, the diameter of the top compartment being greater than the diameter of the bottom compartment, a chamber shoulder being made at the interface between the two top and bottom compartments, the bottom final position of the valve stem being defined by an abutment of a stem shoulder -10 -made on the valve stem with the chamber shoulder at the interface between the two top and bottom compartments.

The metering valve may additionally comprise one or 5 more of the following features: - the stem shoulder is arranged so that the abutting surface extends in a plane perpendicular to the axis of the valve stem. It preferably comprises a projection made on the valve stem, the projection possibly being annular or semi-annular, for example in the form of an annular knurl. The stem shoulder may furthermore comprise an annular or semi-annular projection; - the stem shoulder is arranged so that the abutting surface extends in a plane that is not perpendicular to the axis of the valve stem. For example, it comprises an annular or semi-annular projection that cooperates via a conical or spherical bearing with the metering chamber, or else a conical or spherical surface that cooperates with an annular or semi-annular projection made in the metering chamber, - the stem shoulder is borne by a projection that also provides an abutment function of the valve stem with a top wall of the metering chamber when the valve stem is in the rest position. Thus, use is made of the same projection for providing both the abutting function which defines the bottom final position and that which defines the rest position. As a result more precise doses are obtained, since the metering valve has only the manufacturing tolerances of this projection, whereas in the case where the abutments are provided by two separate parts at a distance from one another, the metering valve would have the manufacturing tolerances of each of these parts.

The invention also relates to a process for manufacturing a valve stem for a metering valve for dispensing an aerosol, said process comprising: -a step of mixing polybutylene terephthalate with from 1.5% to 10 by weight of silicone relative to the total weight of the mixture, in particular with 3% by weight of silicone relative to the total weight of the mixture, -a step of injecting/moulding the above mixture in order to obtain a valve stem, in particular a valve stem moulded from a material that essentially consists of a mixture of polybutylene terephthalate (PBT) and polydimethylsiloxane, referred to as silicone.

The PBT offers high solidity and high rigidity for a wide range of applications.

This material is sensitive to hydrolysis at high temperatures. This is why it is particularly advantageous to dry it before moulding. Recommended drying conditions (in air) are the following: 120°C for 6 to 8 hours (or 150°C for 2 to 4 hours). The degree of humidity should advantageously be less than 0.03%. If use is made of a desiccator, it is recommended to carry out the drying at 120°C for 2.5 hours.

Generally, the PBT is melted at a temperature within the range from 220°C to 280°C, 250°C being the optimal melting temperature. The melt viscosity of the PBT is relatively low and, due to the rapid crystallization rates, the cycle times are generally short. It is therefore easy to mix other materials therewith, especially silicone oils as described above.

During the injection moulding step, it is advantageous to use a mould heated to a temperature of 15°C to 80°C depending on the type of PBT used (filled or unfilled). The heat dissipation must be rapid and uniform.

In the process proposed, the molten PBT and the silicone are mixed, in a preferential PBT:silicone ratio of from 98.5:1.5 to 90:10, more advantageously in -12 -a ratio of from 98:2 to 95:5, and especially in a ratio of 97:3. In these ratios, only the proportion of PBT and silicone is considered, the other fillers or additives that can be added are not taken into consideration.

The injection of the mixture should advantageously be carried out as rapidly as possible due to the rapid solidification of the PBT. It is generally recommended to carry out an injection into a heated mould as defined above at a pressure of 150 MPa.

Advantageously, the silicone, or polysiloxane, mixed with the polybutylene terephthalate has a kinematic 15 viscosity at 25°C of at least 1000 cSt.

It is also more advantageous to use polysiloxanes having a kinematic viscosity at 25°C, at a pressure of 1 atmosphere at sea level, of from 1000 cSt to 100 000 cSt, and especially of from 10 000 cSt to 000 cSt.

The invention will be better understood on reading the appended figures, which are provided by way of examples 25 and have no limiting nature, in which: - Figure 1 is a longitudinal cross-sectional view of a metering valve according to one embodiment, in the top rest position, the metering chamber being isolated from the outside of the dispensing device and from the inside of the reservoir; - Figure 2 is a view similar to Figure 1, in which the metering valve is in an intermediate position, in which the metering chamber communicates with the inside of the reservoir and is isolated from the outside of the dispensing device; - Figure 3 is a view similar to Figure 1, in which the metering valve is in the bottom final position, in which the metering chamber communicates with the -13 -outside of the dispensing device and is isolated from the inside of the reservoir.

The metering valve 1 represented in Figures 1 to 3 is 5 a valve of metering valve type for dispensing, in aerosol form, a fluid product, especially a medicinal product, by means of a propellant gas, especially of HFA type. Of course, the present invention may also be applied to valves of another type or used in different 10 fields, such as perfumery or cosmetics, and with other propellant gases, for example CFCs or compressed gas.

The metering valve 1 is capable of or suitable for operating in an inverted position, that is to say in the position as represented in the drawings. In other words, the metering valve 1 is intended to be used in a position where the metering valve 1 is located underneath the reservoir 9 containing the product to be dispensed, taking as reference the direction of gravity. The metering valve 1 is also suitable for being mounted on any receptacle or bottle forming a reservoir 9.

With reference to Figures 1 to 3, the metering valve 1 comprises a valve body 11 to which a ring 10 that delimits a metering chamber 2 is added. The metering valve 1 is intended to be firmly attached to the reservoir 9 by means of a ferrule 12 or by any other equivalent means. The valve body 11 is separated from the reservoir 9 by a ring 13 housed in the neck of the reservoir 9. The metering valve 1 additionally comprises a valve stem 3 that is slidably mounted in the metering chamber 2, between a first top position, referred to as the rest position, represented in Figure 1, a second intermediate position for filling the metering chamber 2, represented in Figure 2, and a third dispensing position, or bottom final position, represented in Figure 3, in which the valve stem 3 is -14 -depressed axially towards the inside, or towards the bottom, of the metering valve 1, by being placed in abutment. The valve stem 3 is forced towards its rest position by a spring 6, or elastic return means, which is compressed when a user actuates the metering valve 1 and pushes the valve stem 3 axially inside the metering valve 1. When the user releases his/her actuating force, the compressed spring 6 returns the valve stem 3 from its dispensing position to its rest position.

With reference to Figure 1, the valve stem 3 is in the top rest position and cooperates axially with the valve gasket 7 borne by the valve body 11 and separating the ring 10 from the ferrule 12. Sealing is then created between the top part 5 of the valve stem 3 and the valve gasket 7. Advantageously, the radial interference of the external diameter of the valve stem 3 and internal diameter of the valve gasket 7 is less than 1 mm, and in particular around 0.6 mm, in the sealing zone, which is capable of generating frictions during the actuation of the valve stem 3.

In order to overcome these drawbacks linked to the need to create sealing at the top part 5 of the valve stem 3 in the zone of cooperation with the valve gasket 7, the valve stem 3 is advantageously moulded from a material comprising PBT and silicone having a kinematic viscosity of more than 1000 cSt.

Advantageously, the valve stem 3 may be provided with a stem shoulder 31 or annular, or partially annular projection. This stem shoulder 31 abuts, in the rest position, against the valve gasket 7 thus increasing the sealing of the top part of the metering chamber 2.

Still in the rest position, the bottom part of the metering chamber 2 is also isolated from the reservoir 9 by the abutment of a cap 41 with the chamber gasket 8 -15 -housed in the valve body 11. By crushing the chamber gasket 8, the metering chamber 2 is therefore hermetically isolated from the reservoir 9, so that, if the metering valve 1 is positioned in the "head up" position (the metering valve 1 being positioned the other way round to that represented in the figures), the product contained in the metering chamber 2 cannot escape towards the reservoir 9.

With reference to Figure 2, the metering valve 1 is represented in an actuating position referred to as the intermediate position. It is understood from this figure that the valve stem 3 may slide through the valve gasket 7 and chamber gasket 8. The frictions of the top part of the valve stem 3 with the valve gasket 7 are reduced, especially due to the presence of silicones having a viscosity of greater than 1000 cSt in the material forming the valve stem 3.

In this intermediate position, the valve stem 3 is moved towards the bottom of the metering valve 1, exerting a pressure on the spring 6, the metering valve 1 in its intermediate position enables the aerosol to enter from the reservoir 9 into the metering chamber 2, via the bottom part of the metering chamber 2. Indeed, the axial movement of the valve stem 3 will lift the cap 41 away from the chamber gasket 8, thus leaving a space between the bottom part of the valve stem 3 and the valve gasket 7. In order to make such a space possible, the bottom part 4 of the valve stem 3 has a diameter both smaller than the diameter of the top part 5 of the valve stem 3, and smaller than the diameter of the orifice of the chamber gasket 8.

With reference to Figure 3, the metering valve 1 is represented in its bottom final position, referred to as the dispensing position. It is understood from this figure that the valve stem 3 has slid through the valve -16 -gasket 7 and chamber gasket 8. In this position, the metering chamber 2 is in communication with the outside by means of a radial channel 30 that opens into an axial dispensing channel 32 made in the top part 5 of the valve stem 3.

In the bottom part of the metering chamber 2, sealing is created at the chamber gasket 8 by axial cooperation with a part of the valve stem 3 intermediate between the top part 5 and the bottom part 4. Thus, the metering chamber 2 is isolated from the reservoir 9 thus preventing the contents of the reservoir 9 from escaping completely to the outside.

Advantageously, as represented in Figures 1 to 3, the metering chamber 2 consists of a top compartment 21 and of a bottom compartment 22 which are cylindrical, the diameter of the top compartment 21 being greater than the diameter of the bottom compartment 22. A chamber shoulder 23 is made at the interface between the two top and bottom compartments 21, 22. In other words, the metering chamber 2 of the metering valve 1 is formed in the following manner: - the top compartment 21 of the metering chamber 2 is 25 essentially cylindrical of circular cross section, having a first determined diameter, and - the bottom compartment 22 of the metering chamber 2 is essentially cylindrical of circular cross section, having a second determined diameter; the second diameter of the bottom part of the metering chamber 2 being smaller than that of the top part of the metering chamber 2, the two cylinders of the top compartment 21 and bottom compartment 22 being coaxial and juxtaposed in the 35 axial direction, one being in the extension of the other, the sum of the volumes of the two cylinders, from which the volume of the valve stem 3 in this zone is -17 -subtracted, defining the volume of the dose dispensed by the metering valve 1, during the actuation thereof.

In the bottom final position, the stem shoulder 31 comes into contact with the chamber shoulder 23 thus limiting the axial actuation of the valve stem 3, and in particular enabling the spring 6 not to be compressed to its maximum extent.

The use of the valve stem 3 moulded from the material described above therefore enables a better slip through the valve gasket 7 and chamber gasket 8, while making it possible to ensure the necessary sealings, even within the context of the use of propellant gases that create a pressure at the gaskets. This better sliding also has the effect of increasing the rapidity of movement of the valve stem 3 and reducing the stiffness of the spring 6.

The invention is not limited to the embodiments presented and other embodiments will be clearly apparent to a person skilled in the art. In particular it is possible to propose structural improvements of the valve body, of the metering chamber or else of the valve stem for the purpose of improving the accuracy of the dispensing of the pharmaceutical product intended to be delivered, or to improve the longevity of the metering valve.

Claims

-18 -CLAIMS 1. Metering valve (1) for dispensing an aerosol characterized in that it comprises: -a metering chamber (2), and -a valve stem (3) provided with one end intended to be positioned on the side of a reservoir (9) and with one opposite dispensing end, slidably mounted in the metering chamber (2) under the effect of a spring (6), between a top rest position and a bottom final position, the valve stem (3) sliding through a first gasket referred to as a valve gasket (7) and a second gasket referred to as a chamber gasket (8), the valve stem (3) being moulded from a material that essentially consists of a mixture of polybutylene terephthalate (PBT) and polydimethylsiloxane, referred to as silicone, said silicone representing more than 1.5% by weight relative to the total weight of the stem.
2. Metering valve (1) according to Claim 1, in which the silicone has a kinematic viscosity of more than 1000 cSt at 25°C.
3. Metering valve (1) according to Claim 1 or 2, in which the silicone has a kinematic viscosity at 25°C of from 1000 cSt to 100 000 cSt, especially a kinematic viscosity at 25°C of from more than 10 000 cSt to around 100 000 cSt.
4. Metering valve (1) according to any one of the preceding claims, in which the mixture of polybutylene terephthalate and silicone comprises from 1.5% to 10% by weight of silicone relative to the total weight of material of the valve stem (3), and especially 3% by weight of silicone relative to the total weight of material of the valve stem (3).
5. Metering valve (1) according to any one of the -19 -preceding claims, in which the valve gasket (7) and chamber gasket (8) are pcsitioned respectively at the outlet and at the inlet of the metering chamber (2).
6. Metering valve (1) according to any one of the preceding claims, in which the valve gasket (7) and chamber gasket (8) are made of an elastomer material comprising chlorobutyl rubber.
7. Metering valve (1) according to any one of the preceding claims, in which at least one of the valve gasket (7) and chamber gasket (8) is moulded from and/or coated with a material having properties that reduce the frictions during the sliding of the valve stem (3).
8. Metering valve according to any one of the preceding claims, in which the metering chamber (2) comprises a top compartment (21) and a bottom compartment (22) which are cylindrical, the diameter of the top compartment (21) being greater than the diameter of the bottom compartment (22), and in which a chamber shoulder (23) is made at the interface between the two top and bottom compartments (21, 22), the bottom final position of the valve stem (3) being defined by an abutment of a stem shoulder (31) made on the valve stem (3) with the chamber shoulder (23).
9. Process for manufacturing a valve stem (3) for a 30 metering valve (1) for dispensing an aerosol, said process comprising: -a step of mixing polybutylene terephthalate with from 1.5% to 10% by weight of silicone relative to the total weight of the mixture, -a step of injecting/moulding the above mixture in order to obtain a valve stem (3) moulded from a material that essentially consists of a mixture of polybutylene terephthalate (PBT) and polydimethyl- -20 -siloxane, referred to as silicone.
10. Process according to the preceding claim, in which the silicone mixed with the polybutylene terephthalate 5 has a kinematic viscosity at 25°C of at least 1000 cSt.