This invention relates to fluid, and in particular but not solely liquid dispensing apparatus and methods and in particular to the electrostatic spraying of liquids. The apparatus and methods may be used for a variety of applications to spray or dispense a number of fluids, in particular but not solely, in the field of medicine to dispense medicaments for inhalation.

Background of the invention There are a number of known devices which dispense a finely divided spray of liquid droplets by electrostatic means. These may find application in, for example, in the spraying of paints or other coating materials, herbicides and other materials. This invention is, in particular directed towards apparatus and methods related to the dispensing of medicines, it is however not solely directed toward this field.

European Patent number 0752918 discloses a dispensing device for comminuting a liquid and the use of such a device, in particular, in medicine. Unshielded electrohydrodynamic comminution means are provided as is a sharp discharge electrode and optionally means to charge the discharge electrode to a polarity opposite to that of the comminution means. The discharge electrode is located so as to direct gaseous ions into the body of the comminuted liquid and to thereby fully or partially discharge the comminuted liquid. The comminution means electrically charges the liquid to a potential sufficent to provide for. the comminution of the liquid. This potential is usually of the order of up to 20 kilovolts. There are limits on the types of liquids that can be dispensed by such a device. A major limiting factor is the resistivitity of the liquid, it is disclosed that the resistivity of the liquid must be in the range of 100 to 100000000 ohm m. This limitation on the resistivity of liquids to be dispensed means that either the resistivity of the liquid to be dispensed must be modified (for example by means of adding alcohol, perhaps over 30% by volume) thus potentially altering other properties of the liquid such as the medical effectiveness or the liquid can not be dispensed. There are further limits on the

surface tension of the liquid which must be less than 40 mN/m and again this may require the addition of modifying agents (such as surfactants) to the liquid to be dispensed so as to bring the surface tension into the required range. This, of course, may alter other properties of the liquid.

There exists a need for apparatus and methods, which can handle the dispensing of liquids with properties outside these ranges. For example known devices are unable to dispense water or liquids close in properties to water. This limits the usefulness of such known devices and methods.

Other known apparatus and methods require a grounded discharge plate in front of the discharge nozzle. This plate has an electrical potential difference to the electrically conducting nozzle. There must, of course, be means by which the dispensed or sprayed fluid can be discharged so as to emerge to where it is required without being drawn to other discharging means such as earthed surfaces which might be the case if the particles were allowed to emerge charged.

Summary of the Invention An object of the present invention is to overcome various problems associated with the prior art methods and apparatus for dispensing fluid.

A further object is to provide apparatus and methods capable of dispensing fluids which have properties, for example, resistivities and viscostities which are outside the range of those capable of being dispensed by the apparatus and methods of the prior art.

According to a first aspect of the present invention there is provided apparatus for generating droplets of fluid, the apparatus comprising: fluid supply means; an electrically conductive or semi-conductive fluid dispensing nozzle receiving fluid supplied by said fluid supply means and having an exit; electrically conducting means surrounding said discharge nozzle and being distal to the fluid dispensing nozzle exit and having an electrical potential difference thereto; characterised in that the inside diameter of the dispensing nozzle is less than 1 millimetre.

Preferably the inside diameter of the dispensing nozzle is less than 0.5 millimetres.

Preferably the inside diameter of the dispensing nozzle is less than 0.1 millimetres.

Preferably the electrically conducting means comprises an annular electrode surrounding the dispensing nozzle.

Preferably the dispensing nozzle is a fine tube such as a blunt syringe needle.

Preferably the potential difference between the dispensing nozzle and the grounding means is 2 kilovolts.

Preferably the fluid supply means supplies fluid at a rate of about 0.5 µ litres / minute to 2 µ litres / minute and less preferably from about 2 µ litres / minute to 5 µ litres / minute.

According to another aspect of the present invention a method of dispensing fluids is provided comprising the steps of : providing means of supplying the fluid to be dispensed, providing means to dispense said fluid through a fluid dispensing nozzle, providing electrically conducting means surrounding said fluid dispensing nozzle, characterised in that the fluid dispensing nozzle has an inside diameter of less than 1 millimetre.

Preferably the inside diameter of the dispensing nozzle is less than 0.5 millimetres.

Preferably the inside diameter of the dispensing nozzle is less than 0.1 millimetres.

Preferably the potential difference between the dispensing nozzle and the grounding means is 2 kilovolts.

Preferably the fluid supply means supplies fluid at a rate of about 0.5 p litres/minute to 2 11 litres/minute and less preferably from about 2 « u litres/minute to 5 p litres/minute.

Brief description of the drawings One preferred form of the present invention is shown in the accompanying figures in which Figure 1 shows a cross sectional view of a fluid dispensing device according to the preferred form of the present invention; Figure 2 shows a cross sectional view of another fluid dispensing device according to another preferred form of the present invention; and Figure 3 shows and inhalation device according to a preferred form of the present invention.

Description of preferred embodiments.

As shown in the figures a preferred form of the present invention provides apparatus 1 for the dispensing of fluid, in particular but not solely for the dispensing of medicines.

Referring to figure 3 the present invention consists of fluid dispensing apparatus 1 having fluid supply means 10. In forms of the present invention the fluid supply means 10 may comprise means for over pressurising the fluid. In a preferred form of the present invention this consists of a liquid feeder 11. The fluid may be stored in a tank or an other cavity. In forms of the invention the tank may comprise a replaceable canister or may in other ways be refillable. In preferred forms of the invention, in which medicines are dispensed the fluid supply means 10 will need to be of a form that does not affect the medical properties of the fluid. The preferred flow rate of fluid is 0.5 microlitres per minute. The liquid feeder 11 may take the form of a pump such as for example a syringe

pump but other alternatives are possible particularly in the preferred form of the invention when a portable or stand-alone device is required.

The electrically conducting fluid dispensing nozzle 2 is illustrated in the figures. In preferred forms of the present invention this may take the form of a small diameter blunt syringe needle. The inside diameter of the dispensing nozzle 2 is less than 1 millimetre and in preferred forms of the invention is less than 0.5 millimetres in an especially preferred forms of the invention the inside diameter of the liquid dispensing nozzle 2 is less than 0.1 millimetres. Suitable dispensing nozzles 2 may be machined or as mentioned above a small diameter blunt syringe needle may be used. The syringe needle may be made blunt but filing or cutting e. g. sawing it. In other forms a suitable small diameter tube could be used. The nozzle 2 is required to be electrically conductive and to be made of a material that does not affect the properties of the fluid to be dispensed. Such a suitable needle 2 may comprise a steel e. g. stainless steel or other non-reactive material hollow needle. The needle 2 could be injection moulded plastic with a electrically conducting piece which, in use, is in contact with the fluid to be dispensed.

Surrounding the fluid dispensing nozzle, at least in part, is electrically conducting means 3.

The means 3 is distal to the exit of the fluid dispensing nozzle 2. In preferred forms of the present invention the electrically conducting means 3 is in the form of an annular ring and completely surrounds the nozzle 2. In other less preferred forms of the invention there may be a break in the electrically conducting means 3. This may allow an electrically non- conducting support 6 to be attached to the fluid dispensing nozzle 2. The electrically conducting means 3, in use, has an electrical potential difference to the electrically conductive fluid dispensing nozzle 2. In preferred forms of the present invention the potential difference is + 2 kilovolts. For example the potential difference could be as a result of the electrically conducting means 3 having an electrical potential of + 2 kilovolts and the dispensing nozzle 2 being at + 4 kilovolts. It has been found that if the electrically conducting means 3 is actually grounded, that is, at a potential of 0 volts the droplets are drawn to the electrically conducting means 3 and are thus not dispensed properly. The

potential difference may be greater than or less than 2 kilovolts but it has been found that this level gives the best results.

The potential difference may be produced by a number of means for example a high voltage DC/DC converter 14.

The small distance between the electrically conducting means and the nozzle as well the particular configuration pictured means that this nozzle is optimised to create a strong electric field. The configuration adopted also contributes to a compact geometry suitable for preferred forms of the invention, which are used to provide an inhalator.

The electrically conducting means 3 may have a variety of shapes but is preferably in the form of a ring or a cylinder. In the preferred form of the invention as illustrated the electrically conducting means 3 consists of a cylinder 7 with a frusto conical transition portion 8 and a second narrower cylinder 9. The electrically conducting means 3 is preferably made from a metallic material. It may be machined or less preferably moulded.

An insulating material such as a plastic material or preferably a ceramic preferably occupies the volume 6 between the fluid dispensing nozzle 2 and the electrically conducting means 3. The purpose of this material is to both electrically insulating the electrically conducting means 3 from the fluid dispensing nozzle 2 and to support the dispensing nozzle 2 inside the electrically conducting means 3. The dispensing nozzle 2 should be centred in the electrically conducting means 3. This can allow the device 1 to be more compact in construction, which can be an advantage in producing a unit for use in an inhaler.

As mention above the flowrate of fluid in a preferred form of the present invention is 0.5 microlitres a minute. In some applications this may be sufficient. However in some other applications, for example, the dispensing of medicines to be inhaled this might not be enough. In these cases a further preferred form of the present invention provides a plurality of nozzles 2. For example, there may be ten nozzles 2 in close proximity to each other. It is preferable that the fluid dispensing nozzles 2 in this case are very close to each other in order to ensure that the fluid dispensed is in a single flow of droplets. In forms of this preferred form of the invention the electrically conducting means 3 means may

comprise means which surrounds all of the fluid dispensing nozzles 2. In other, less preferred forms of the invention each fluid dispensing nozzle 2 may have an individual electrically conducting means 3 surrounding it. It has been found that the preferred form of the invention as described above, namely the form utilising ten fluid dispensing nozzles 2 can provide sufficient flow rate for the adequate dosing of medicines for inhalation.

It has been found that preferred forms of the present invention can provide for the dispensing of water whereas other prior art devices require the surface tension or resistively of water to be altered by the addition of agents to insure that the fluids surface tension or resistivity is at the required level.

Preferred forms of the present invention are able to dispense a variety of substances, including medicines such as: one or more of a bronchodilator, steroid, analgesic, antibiotic, anti-inflammatory, anti-allergic, anticholinergic, therapeutic protein and therapeutic peptide.

Preferred forms of the present invention are able to provide particles which are in the respirable range, that is, of a size between 2 and 5 microns. It has been found that particles of this size provide the best medical effect. The fact that preferred forms of the invention can dispense fluids having a great range of surface tensions or resistivitys enables a wider range of substances to be dispensed without the addition of other fluid property changing agents.

In preferred forms of the invention there is provided a portable inhalation device 20. In such a device a source of electrical potential 15 is provided. For example a dc power supply such as a dry cell battery is provided along with means 14 to convert the voltage of the battery to the potential required to provide the potential of 2 kilovolts. There is also provided a container or a canister 10 containing the medicine to be inhaled. Such a container or canister 10 is preferably refillable or replaceable. The fluid discharged must

also be discharged prior to inhalation. There must therefor be discharging or neutralising means present (not illustrated) This can be achieved by the known technique of corona discharging. Additional electronic means 14 may also be provided to, for example, count the doses of medicine dispensed, provide an indication of the time of the last dose inhaled or to collect and preferably indicate the compliance of a user with a predetermined dosing regime.

Finally, it will be understood that the present invention is not restricted to the described embodiments but can be modified in many different ways within the scope of the appended claims.