Electrostatic Spray Device

Abstract

An electrostatic spray atomisation device is disclosed. The device comprises a spray electrode disposed in a first recess in a dielectric surface, the spray electrode being connected, in use, in an electric circuit with a reference electrode enabling a potential difference to be applied between the spray and reference electrodes to atomise a liquid. Various techniques for dealing with problems of liquid deposition around the electrodes are described. The techniques may be used alone or in combination.

Description

This application claims priority to U.S. Pat. App. No. 60/756,402 filed on Jan. 5, 2005 which is hereby incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to any electrostatic spray system, such as described in European Patent 1399265, which is incorporated herein by reference and U.S. patent application Ser. No. 10/481,583, (US 2004-0251326 A1), filed on Jun. 29, 2004, which is incorporated herein by reference.

European Patent 1399265 discloses one embodiment for liquid to be fed (by any suitable means) to a spray electrode, where an electric field is created between the spray electrode and a discharging electrode by the generation of a potential difference between the two electrodes. European Patent 1399265 also discloses a dielectric surface, which reshapes the electric field in the vicinity of the electrodes and dielectric to maintain an efficient production of droplets from the spray electrode that do not impinge on the dielectric material.

An excellent delivery method with high efficiency and low levels of self deposition of sprayed matter is disclosed. Nevertheless, there are instances when the impact of some of the spray on the dielectric material is inevitable, for example in extremely high air currents, such as found in ventilation ducting or in high winds. In such cases the small amount of spray that lands on the dielectric surface will often evaporate and any residual will have a negligible effect on the performance of the spray system over the normal lifetime of the dispenser.

However, when attempting to dispense heavier liquids, or liquids containing heavier ingredients (where the term heavy is used to describe the compound's inability or low tendency to evaporate), we have found that this residual deposition evaporates too slowly, and over time can begin to interfere with the proper functioning of the dielectric material and thereby the whole dispenser system.

The dispenser's applications may be limited by, for example, limiting the environments in which the dispenser is used, or limiting the specified lifetime of the dispenser in such environments, or limiting or restricting the use of such heavy materials in the liquid being dispensed. However, such limitations are commercially undesirable whereas some definite advantage can be gained from being able to operate in such difficult conditions or from being able to spray matter with a high vapour pressure.

The invention disclosed here controls or eliminates the residual deposition so that the interference with the proper operation of the system is controlled or eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows two views of one possible dispenser spray surface configuration which embodies this invention.

FIG. 2 shows another dispenser spray surface configuration which embodies this invention.

FIG. 3 shows two surface profiles, where 3a represents an ideal surface finish as described in this invention, and 3b a non-ideal surface finish.

FIG. 4 shows the difference in the amount of spreading of an oil drop between a smooth and rough surface as described in this invention.

FIG. 5 illustrates schematically the action of the barrier migration channel in the spreading and migration of a droplet on a vertical surface as one aspect of this invention.

FIG. 6 shows three views of a dispenser as an example of one possible embodiment of this invention.

FIG. 7 shows two possible textured finishes which delay the migration of the residual liquid to the spray electrode.

FIG. 8 shows three different tool treatments, illustrating an advantageous tool design for achieving a preferred surface texture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Means for wicking and directing the flow of liquid matter are known in the art in relation to electrostatic spray systems, but are limited to the supply of liquid matter to be sprayed from a spray electrode or to providing an additional surface from which to evaporate matter which has been sprayed. Wick fed spray electrodes are taught in, for example, U.S. Pat. No. 6,297,499, US Patent application 2004023411, U.S. Pat. No. 7,081,622, European Patent 1095704, U.S. Pat. No. 5,503,335 and Japanese Patent 5192224.

The device taught in U.S. Pat. No. 6,893,618 employs at least one porous fibre trap in a non homogenous electric field in order to capture and then dissipate by evaporation liquid which has been caused to flow through the device.

The wicking system of U.S. Pat. No. 6,871,794 provides a wick on wick device increasing the surface area available for evaporation of wicked liquid.

The liquid dispersion device which is the subject of U.S. Pat. No. 6,729,552 comprises wicking material which aids evaporation of condensed spray by providing a large surface area for evaporation. The wicking material, which is a fabric such as cotton or a thin woven sheet may be assisted in its evaporative function by the heating effect of an optional proximal lamp. This device merely limits the degree to which the device becomes sodden by spraying in harsh conditions and does not provide a means by which the adverse effects of deposition on spraying may be corrected.

In accordance with a first aspect of the invention, there is provided an electrostatic spray atomisation device comprising a spray electrode disposed in a first recess in a dielectric surface, the spray electrode being connected, in use, in an electric circuit with a reference electrode enabling a potential difference to be applied between the spray and reference electrodes to atomise a liquid, characterised in that the first recess is adapted to draw any of the liquid deposited on the surface in the region of the first recess towards the spray electrode such that the deposited liquid establishes an electrical contact with the spray electrode and resists deposition of further liquid by virtue of electrostatic repulsion.

By encouraging liquid deposited on the surface to make electrical contact with the spray electrode, the electric field becomes distorted such that further deposition of liquid in the same area is prevented. The invention therefore provides a self regulating means for further deterring droplets emitted from the spray electrode away from the area of deposition.

Any patch of residual liquid coming into contact with the spray electrode effectively biases the electric field such that liquid emanating from the spray electrode is repelled away from the area of previous residue due to the mutual electrical repulsion between the highly charged spray and the dynamically charged residue. The enormous benefits of this become apparent when considering the management of such a dispenser set up in a strong updraft. The updraft will initially cause a small amount of liquid to be deposited on the spray surface above the spray nozzle. However, once this liquid spreads out and then makes a connection to the spray electrode the field distorts, tending to fire the spray downwards against the updraft. Should the updraft stop, then the residue will continue to spread and evaporate and migrate to the spray electrode, (where it could co mingle with the existing formulation), and as such its distorting effects on the electric field will gradually decrease and return the dispenser to its normal condition.

The dielectric spray surface may be provided with a network of small scale surface troughs (such as described below) which provide a path towards the spray electrode. This spray feedback path is designed to deliberately distort the local electric field under extreme dispersal conditions, and it does so dynamically. When any residual liquid first lands on the dielectric spray surface, it will first spread out usually migrating radially outwards from the point of impact. In the first instance, this helps it to evaporate by spreading the liquid across a large surface area (as in the second aspect of the invention described below), which may be sufficient control if the residual deposition was transitory, such as when there is a sudden gust of air current next to an operating device. If the deleterious cause is chronic, such as when operating inside an air conditioning duct, a greater amount of residual liquid matter might collect and would begin to spread out. Once it has spread out sufficiently, one edge of the residual liquid matter will find a path back to the spray electrode. Whilst most formulations, particularly the component remaining as residual matter on the spray surface, are largely non conducting, they are more conductive than the dielectric itself, or at least the combination of residue and dielectric provide an easier path for the conduction of charge than through or across the dielectric alone. As a result the electric field is biassed towards (strengthened at) the discharge electrode, thereby reducing the amount of liquid being sprayed and increasing the number of ions available to discharge them, and to carry the droplets away from the device.

The reference electrode is normally disposed in a second recess in the dielectric surface.

In a preferred embodiment, the second recess is provided with at least one channel formed in the side of the recess. Typically, the at least one channel is continuous and is formed around the side of the recess.

Alternatively or in addition, the dielectric surface may be provided with at least one channel formed in the surface. The channel may be continuous and it may be disposed around the second recess.

The at least one channel may be in fluid communication with a reservoir for storing excess liquid. The reservoir may be a closed reservoir, or it may simply be a drip tray or any other surface, such as the floor.

The at least one channel may provide a dispersion path for the liquid over a surface, such as the dielectric surface, from which the liquid can evaporate.

The at least one channel may have a v-shaped cross-section, a rounded cross-section, or a semi-circular cross-section.

The provision of the channel helps prevent migration of liquid to the discharging means (i.e. the reference electrode) because any liquid naturally wetting a path from the dielectric surface to the reference electrode will touch the channel, which would carry the liquid away by capillary action, preferably into a separate reservoir. If liquid came into contact with the reference electrode, this would at best counteract the benefits of drawing the liquid back to the spray electrode, and at worst create a short circuit of sorts, which would unnecessarily drain the voltage supply. It is also possible to provide a polished finish of the recess surfaces adjacent to the discharging electrode.

Typically, the first recess is adapted to draw any of the liquid deposited on the surface in the region of the first recess towards the spray electrode by capillary attraction. The capillary attraction may be provided by a channel formed in the side of the first recess, the channel running from the base of the first recess to the periphery of the first recess. Preferably, however, the capillary attraction is provided by an array of channels, each of which is formed in the side of the first recess, the channel running from the base of the first recess to the periphery of the first recess. The array of channels are normally uniformly spaced around the first recess.

The at least one channel or each of the array of channels may be v-shaped in cross-section, rounded in cross-section or semi-circular in cross-section.

In one embodiment, the at least one channel or each of the array of channels is wider at the periphery of the first recess than at the base.

Alternatively, the capillary attraction may be provided by a capillary running from the base of the first recess to the periphery of the first recess.

The first recess may be adapted to draw any of the liquid deposited on the surface in the region of the first recess towards the spray electrode by gravity. This may be in addition to or instead of the capillary attraction referred to above. One way of achieving this is to provide a first recess having a flared profile such that the base of the recess has a narrower diameter than the periphery where it meets the surface. Clearly, the shape of the cross-section of the first recess is not critical. It could be circular, square, triangular, rectangular, elliptical or any other cross-section. Any of these cross-sections could have the flared profile mentioned above, wherein the cross-section in whatever shape is narrower at the base of the recess than at the periphery where it meets the surface.

The dielectric surface may be adapted to draw any of the liquid deposited on the surface in the region of the first recess towards the spray electrode by chemical affinity between the liquid and the dielectric surface.

The chemical affinity may be provided by a oleophilic or oleophobic coating.

Alternatively, the chemical affinity may be provided by a lyophilic or lyophobic coating.

In accordance with a second aspect of the invention, there is provided an electrostatic spray atomisation device comprising a spray electrode disposed in a first recess in a dielectric surface, the spray electrode being connected, in use, in an electric circuit with a reference electrode enabling a potential difference to be applied between the spray and reference electrodes to atomise a liquid, characterised in that the dielectric surface is adapted such that any of the liquid deposited on the surface in use is caused to disperse across the surface, thereby increasing the surface area and evaporation rate of the liquid.

The invention therefore provides a way for driving residual liquid migration by surface tension or other means which, regardless of the surface tension between the residual liquid and the dielectric material of the spray surface, promotes the spreading of the residual liquid in order to maximise the opportunity for it to evaporate, or in the case of more heavy compounds provides an efficient path for their clearance away from the critical area in the vicinity of the electrodes themselves.

A combination of the first and second aspects of the invention provides for an electrostatic spraying device that can clear itself of any residual build up, and in extreme situations where either the environmental conditions or the liquid matter itself would normally limit useful application there is provided a self regulating electric field distortion system to steer the spray away from the troublesome area. This invention thereby expands the environments in which this dispenser may be used, and also extends the range of compounds that may be dispensed through it, providing a significant commercial advantage.

The dielectric spray surface may be provided with a rough surface finish, such as may be obtained by using raw sintered tooling to injection mould the dielectric, or by chemical or laser etching, sand blasting, sand finishing, rough shot peening of a standard injection moulding tool, or by chemical or laser etching, sand blasting, sand finishing, or rough shot peening of the dielectric surface after manufacture, or where the surface is a ceramic by using a coarse sinter. A characteristic of this type of surface is that it has many small sharp peaks, ridges, troughs and valleys whereby the base of the troughs and valleys are sharp and have a low radius of curvature less than 0.5 mm, more preferably below 0.1 mm or more preferably still below 10 μm, and ideally below 1 μm. These troughs and valleys are ideally acute angled. However, obtuse angle valleys are also useful provided that the radius of curvature of the base of the trough is sufficiently small. The distance between consecutive troughs is usually random, but normally distributed about a mean value, which may be called the pattern scale length. In general this scale length is of the order of 1 mm or below, but may be a few hundred microns or below.

The dielectric spray surface may be provided with a textured finish, such as may be obtained by impression from a textured injection moulding tool, or laser cutting, hand sculpting or computer numerical control (CNC) post processing, or branding with a hot textured tool, whereby the textured finish contains a systematic interconnecting network of ridges and troughs and the base of the troughs and valleys are as sharp as possible having a low radius of curvature less than 0.5 mm, more preferably below 0.1 mm or more preferably still below 10 μm, and ideally below 1 μm. These troughs are ideally acute angled. However, obtuse angle troughs are equally useful provided the radius of curvature of the trough is sufficiently small. The distance between consecutive troughs is not of particular importance, although ideally it is less than a distance representing a potential difference of under 100V in the electric field, more preferably 10V, or more preferably still 1V. In practice, this scale-length of the texture pattern therefore depends on the proximity to the electrodes, and is typically approximately 1 mm. However, between the electrodes it may be advantageous to have a scale length of under 100 μm or even 10 μm, yet away from the electrodes it could be as much as 2, 5 or 10 mm depending on the application and relative position of the electrodes and dielectric spray surface.

A combination of textured and surface finishes may be used, to provide both small scale and large scale trough networks. Either alone or in combination these patterned networks provide a means to spread liquid out on the dielectric surface regardless of the relative surface tension between the spray surface and any residue that might happen to land on it. Ideally the radius of curvature of the troughs is sufficiently small that liquid matter can spread out relatively easily regardless of orientation. In other words the sharpness of the troughs has sufficient ‘wicking’ power that the liquid matter can migrate upwards against gravity if the spray surface is vertical. Furthermore, the scale length of the pattern should also be sufficiently small that liquid matter spreads out as evenly as possible so that any effect on the electric field is not localised to a particular trough.

In a preferred embodiment, the reference electrode is disposed in a second recess in the dielectric surface.

The second recess may be provided with at least one channel formed in the side of the recess. The at least one channel may be continuous and formed around the side of the recess.

The dielectric surface may be provided with at least one channel formed in the surface. The channel may be continuous and it may be disposed around the second recess.

The at least one channel may be in fluid communication with a reservoir for storing excess liquid. The reservoir may be a closed reservoir, or it may simply be a drip tray or any other surface, such as the floor.

The at least one channel may provide a dispersion path for the liquid over a surface, such as the dielectric surface, from which it can evaporate.

The at least one channel may have a v-shaped cross-section, a rounded cross-section or a semi-circular cross-section.

The provision of the channel helps prevent migration of liquid to the discharging means (i.e. the reference electrode) because any liquid naturally wetting a path from the dielectric surface to the reference electrode will touch the channel, which would carry the liquid away by capillary action, preferably into a separate reservoir.

Typically, the dielectric surface is adapted such that any of the liquid deposited on the surface in use is caused to disperse across the surface by an array of troughs formed in the surface. The dielectric surface may be formed as a pattern of ridges such that each of the troughs lie between adjacent ridges.

The array of troughs may be formed in a repeating pattern to provide an interconnecting network of troughs. Each of the troughs may have a v-shaped cross-section.

The troughs in the array of troughs may be disposed in a random pattern, thereby providing a random pattern of troughs to present a surface texture.

Then again, the troughs in the array of troughs may be disposed in a non-random pattern, thereby providing a non-random pattern of troughs to present a surface texture. Such a surface may be provided by a brushing process which develops the troughs where the bristles of the brush run.

Typically, at least some of the troughs are of microscopic dimension. In this case, the radii of curvature of the bases of the troughs are below 10 μm, and preferably below 1 μM.

Alternatively, the dielectric surface may be adapted such that any of the liquid deposited on the surface in use is caused to disperse across the surface by at least one channel running from the periphery of the first recess towards the periphery of the surface. The at least one channel may run to the periphery of the surface. The channel may follow a spiral path.

In another alternative, the dielectric surface may be adapted such that any of the liquid deposited on the surface in use is caused to disperse across the surface by a series of concentric circular channels, each channel connected to adjacent channels by one or more linking channels.

In this alternative, the first recess is typically circular, and the linking channels may run radially relative to the centre of the first recess.

These two alternatives provide the dielectric spray surface with liquid migration paths designed to delay the migration of liquid towards the spray electrode by making the migration channels more circuitous. This reduces the directionality of the distortion of the electric field when the liquid comes into contact with the spray electrode, so the response to residual droplets is less directional. This can have advantages where the dispenser is subjected to occasional blasts of air which, while temporarily causing a residue, have no real effect on chronic performance, so the requirement for directional field distortion is not necessary.

The dielectric surface may be adapted such that any of the liquid deposited on the surface in use is caused to disperse across the surface by an oleophilic coating over at least part of the surface.

In this case, the surface may have an oleophobic coating around the second recess, thereby preventing liquid from migrating to the second recess.

A suitable oleophilic treatment is Oxygen plasma, provided by Porton Plasma Innovations (P2i) Ltd, Unit 14, Central 127 Milton Park, Abingdon, Oxfordshire, OX14 4SA, UK. A suitable oleophobic coating is also provided by Porton Plasma Innovations (P2i) Limited.

The dielectric surface may be adapted such that any of the liquid deposited on the surface in use is caused to disperse across the surface by a lyophilic and/or lyophobic coating over at least part of the surface.

In accordance with a third aspect of the invention, there is provided an electrostatic spray atomisation device comprising a spray electrode disposed in a first recess in a dielectric surface, the spray electrode being connected, in use, in an electric circuit with a reference electrode enabling a potential difference to be applied between the spray and reference electrodes to atomise a liquid, characterised in that the dielectric surface is in fluid communication with a reservoir to which any of the liquid deposited on the surface may be drawn.

By providing a path or paths from the dielectric surface into a separate, redundancy reservoir the invention is able to cope with the deposition of a large quantity of liquid. This reservoir therefore prevents the dielectric surface becoming entirely saturated with running liquid which could seriously limit the performance of the spray device by removing the liquid to a distal location.

The reservoir is typically either well away from or behind the spray surface, and in any case does not affect the electric field around the electrodes and spray surface should liquid matter gather there. This redundancy reservoir is normally only required in extreme situations where the residual liquid matter will not evaporate from the spray surface of its own accord. Under such circumstances the liquid matter, rather than remaining on the dielectric surface where it could begin to have a detrimental effect on the electric field, will migrate to the redundancy reservoir, where it is held harmlessly out of the way.

In a preferred embodiment, the reference electrode is disposed in a second recess in the dielectric surface. Typically, the second recess is provided with at least one channel formed in the side of the recess. The channel may be continuous and formed around the side of the recess.

The dielectric surface may be provided with a channel formed in the surface. The channel may be continuous and may be formed around the second recess.

Preferably, the at least one channel is in fluid communication with the reservoir for storing excess liquid. The reservoir may be a closed reservoir, or it may simply be a drip tray or any other surface, such as the floor.

The at least one channel may provide a dispersion path for the liquid over a surface, such as the dielectric surface, from which it can evaporate.

The at least one continuous channel may have a v-shaped cross-section, a rounded cross-section or a semi-circular cross-section.

The provision of the channel helps prevent migration of liquid to the discharging means (i.e. the reference electrode) because any liquid naturally wetting a path from the dielectric surface to the reference electrode will touch the channel, which would carry the liquid away by capillary action, preferable into the reservoir.

The dielectric surface is normally in fluid communication with the reservoir by way of one or more conduits leading from the surface to the reservoir.

Liquid deposited on the surface may be drawn to the reservoir by virtue of gravity.

Alternatively or in addition, liquid deposited on the surface may be drawn to the reservoir by virtue of capillary attraction.

The dielectric surface may be adapted to draw any of the liquid deposited on the surface in the region of the first recess towards the spray electrode by chemical affinity between the liquid and the dielectric surface.

The chemical affinity may be provided by a oleophilic or oleophobic coating.

The chemical affinity may be provided by a lyophilic or lyophobic coating.

The device typically further comprises a porous member within the reservoir to absorb liquid. The porous member is typically a sponge.

The first, second and third aspects of the invention may be used alone or in any combination. It is envisaged that there may be provided:

i) a combination of an electrostatic spray atomisation device according to the first aspect with an electrostatic spray atomisation device according to the second aspect;

ii) a combination of an electrostatic spray atomisation device according to the first aspect with an electrostatic spray atomisation device according to the second aspect;

iii) a combination of an electrostatic spray atomisation device according to the second aspect with an electrostatic spray atomisation device according to third aspect; and

iv) a combination of an electrostatic spray atomisation device according to first aspect with an electrostatic spray atomisation device according to the second aspect and with an electrostatic spray atomisation device according to the third aspect.

In each aspect, the invention therefore provides a specially configured dispenser system which addresses the management of build up of residual heavy compounds on the dispenser dielectric spray surface.

There now follows a description of the invention by way of example with reference to the accompanying drawings, in which:

FIG. 1 shows two views of one possible dispenser spray surface configuration which embodies this invention;

FIG. 2 shows another dispenser spray surface configuration which embodies this invention;

FIGS. 3a and 3b show surface profiles according to the invention;

FIGS. 4a to 4f show the spreading of oil droplets on different surfaces as described herein;

FIGS. 5a to 5f illustrate schematically the action of the barrier migration channel;

FIG. 6a to 6c show exemplary views of a dispenser comprising one possible embodiment of this invention;

FIGS. 7a and 7b show possible textured finishes according to the invention which delay the migration of the residual liquid to the spray electrode; and

FIGS. 8a to 8c show different tool treatments, illustrating an advantageous tool design for achieving a preferred surface texture.

FIG. 1 shows two illustrations of a dispenser with one possible dielectric spray surface configuration embodying the present invention. A dielectric spray surface 1 is shown having all the necessary features, including a spray electrode recess 2 and a discharging electrode recess 3 meeting with a dielectric spray surface 4, which has both a macroscopic textured finish and sand blasted roughness. Also illustrated are radial liquid migration channels 5 which provide a passage for liquid residue from the spray surface 4 to the base of the spray electrode (not shown). There are also shown perpendicular barrier channels 6 which further prevent liquid from migrating from the spray surface 4 to the discharging electrode (not shown).

This invention may be used with an electrostatic dispenser such as the one described in European Patent 1399265, which provides a liquid reservoir feeding liquid to the spray electrode and a voltage generation means to create an electric potential between the spray electrode and the discharging electrode. Under normal use, a liquid exposed at the tip of the spray electrode is subjected to a strong electric field which acts against the surface tension of the liquid, causing it to break up into charged droplets. Similarly, the electric field also creates at the discharge electrode ions of opposite polarity to the sprayed liquid Through a combination of these two oppositely charged entities in the space in front of the spray surface 4 the viscous drag of the droplets in the air becomes the dominant force upon them, and they are propelled away from the device under the gentle breeze generated by the initially rapid movement of the original charged entities.

Whilst the action of the dielectric spray surface 4 combined with these charged entities is usually sufficient to keep the spray surface free from impact of the droplets, this is not the always the case under certain extreme conditions. Such extreme conditions include: prolonged or rapid forced air flow towards or across the dispenser; the spraying of certain heavy, non volatile compounds; extended use of a dispenser for periods of the order of a year or fractions thereof depending on the duty cycle of the dispenser; or a combination thereof. Under such conditions it is possible for some of the droplets, or the non volatile fraction thereof to deposit on the spray surface 4. These residual droplets form an undesirable residue on the spray surface.

In many cases the small quantity of this droplet residue is negligible since it evaporates from the spray surface naturally. However, the dielectric spray surface 4 is provided with a surface finish as well as a textured finish which can be seen as small inter connecting raised elements on the surface with sharp troughs where the interconnected raised elements meet. Both of these features act to draw the liquid away from where it first lands, causing it to spread out, thus increasing the surface area exposed to air and hence increasing the overall evaporation of the residue.

For many applications the enhanced action of spreading out the residue is sufficient to evaporate it and render its effect on the performance of the spray system negligible. However, for particularly sticky, heavy, non volatile liquids this may not be sufficient, and spray feedback migration channels 5 are provided together with the barrier channels 6 to ensure that liquid is more likely to migrate towards the spray electrode. Once residual liquid reaches the spray electrode (and does not reach the discharge electrode) the residue distorts the electric field, by first increasing the field strength around the discharging electrode, thereby increasing the number of ions and attracting them towards the zone of deposition thus hindering and usually preventing further deposition, In addition, by means of the spray feedback migration channels, the field is distorted so that the droplets tend to be sprayed away from the original zone of deposition, attenuating any further deposition.

Finally, if these measures are still not sufficient to prevent some of the droplets from impacting on the spray surface, the excess liquid is drawn down into a redundancy reservoir 8 well away from the spray surface via an excess residue migration path 7.

FIG. 2 shows another spray surface modified according to the present invention, where the spray surface 21 has been provided with a textured finish, and three spray feedback migration channels 22 are provided to make the necessary connection between any residual liquid and the spray electrode should any droplets land on the spray surface.

In this case the dielectric material is made from polypropylene, and has been injection moulded. Other possible materials for the textured spray surface include acrylic, acrylonitrile butadiene styrene (ABS), ceramics and ceramic blends, glass and glass blends, polyethylene terephthalate (PET), nylon (6, 11 and 66), polyether and styrene butadiene blends, polyacetyl polytetrafluoroethylene (PTFE) blends, polybutylene terephthalate (PBT) blended with glass or mineral or mica or combinations thereof, polycarbonate blended with ABS or blends of ABS and glass, polyetherimide, polyethylene, polyketone, polyphenylene sulphide blended with glass, polyphthalamide, polypropylene, polystyrene, polysulfone blended with glass, polyvinylidene fluoride (PVDF), styrene acrylonitrile, as well as reinforced versions of the same plastics using, for example, glass, minerals, aluminium, zinc, steel, tin, copper, mica and blends thereof with each other or with glasses, organic molecules and minerals, for example, such as for changing the colour of the plastic.

FIGS. 3a and 3b illustrate magnified cross sections of two different types of surface finish profile shown as sections through the dielectric spray surface 4. FIG. 3a is a preferred surface finish since it has created sharp troughs in the spray surface 4, which act as microscopic wicking channels to draw any residue liquid away from the deposition zone and to spread it out. This surface finish works well even if the contact angle between the liquid residue and the dielectric spray surface is high. FIGS. 4a to 4f illustrate how surface roughness helps to spread liquid out on a surface.

FIGS. 4a and 4b show a drop of oil on a polished polypropylene surface immediately after deposition on the surface and after an interval of 30 seconds respectively. It is clear that there has been no appreciable spreading of the oil in this time. By contrast FIGS. 4c to 4f show a rough polypropylene surface as described in this invention with a similar oil drop. FIG. 4c shows the drop immediately after deposition on the surface, and FIGS. 4d to 4f show the same drop at consecutive time intervals of 10 seconds after deposition. In the same 30 second interval the drop on the rough surface has spread out over an area approximately 16 times that at the start, improving evaporation of residue from the spray surface.

The traditional Roughness Average (RA) figures are of little use when specifying the finish of the spray surface, as this only indicates the amplitude of the roughness not the acuteness of the trough in the surface. This invention provides for roughness both on the microscopic scale, with a Roughness Average of say 1 μm, up to macroscopic textured finishes where the RA figure is of the order of 1 μm. These extremes of RA figures and those in between them are all valid within the scope of this invention.

Methods used to create the required roughness on the dielectric spray surface generally fall into two categories. The first method is to create an untreated dielectric spray surface in a conventional way, such as CNC milling, casting or injection moulding, and then to provide a post production process. The second method is to employ either a casting or injection moulding process, where the inverse of the required surface finish is produced on the tool, so that when the part is turned out the required finish is created on it by nature of its contact with the inverted pattern on the tool. The latter is likely to be the easier method, provided the quality of the tool does not deteriorate over the course of a production run.

Various post production processes can be used to create the required surface roughness. They range in complexity from sand papering, sand blasting, shot peening to laser etching.

Whilst these provide the rough surface required on the dielectric spray surface 4, these methods can only be used with limited success or ease to create the radial spray feedback migration paths. Sand blasting and shot peening cannot be made directional, and so radial liquid migration channels can only be made in this way by employing a complex set of masks, which would usually be either too delicate or too coarse to be of much practical benefit. Similarly sand papering cannot be used to create a migration pattern. Laser etching is sufficiently flexible to be able to provide a wide variety of patterns including the desired radial pattern, but this is an expensive process and therefore probably uneconomical for most applications.

One simple method of generating the migration path is to score lines in the dielectric spray surface using a sharp, pointed object, such as a razor, scalpel, pin, hook or needle. Such score lines need only be of the order of 0.1 mm to 1 mm deep, and can be less wide than they are deep, such that the width to depth ratio is anything from 1 to 10 or more. This method is particularly suitable for small production volumes or where the dispenser is being assembled by hand.

When casting or injection moulding is used to create the dielectric spray surface 4, the main requirement is to modify the tool so that the resultant dielectric has the required properties, which are a network of inter connecting troughs with sharp bottoms, which means the tool must have a network of inter connecting ridges with sharp peaks. These sharp peaks can be created by using a sintered metal surface in the appropriate region of the production tool, or by creating a textured finish directly on the tool by sanding, sand blasting, shot peening, scouring, scratching, milling, grinding, or chemical etching for example. All of these techniques can also be employed, either on their own or in combination as well as being combined with other surface treatments such as sputtering, chemical vapour deposition of another material, for example Titanium vapour deposition on Steel.

FIGS. 5a to 5c and FIGS. 5d to 5f demonstrate the fate of a droplet 51 sitting on a vertical plane 52, where the plane 52 of FIGS. 5d to 5f also has a barrier clearance trough 53 running vertically down the plane 52. FIGS. 5b and 5c then show how the droplet 51 in FIG. 5a spreads out gradually over the vertical plane. Note it is assumed here that the volume of the liquid residue contained in the droplet is small, and that correspondingly the gravity forces on the droplet 51 are negligible compared to the surface tension forces between the droplet 51 and the plane 52.

In FIG. 5d an identical droplet 51 is shown, but here the plane 52 contains a vertical clearance trough running from top to bottom 53, in a similar fashion to the perpendicular barrier channel 6 shown in FIG. 1. FIGS. 5e and 5f then show that, although at first the droplet 51 expands and spreads out, as soon as it touches the vertical clearance trough 53 the capillary forces suck the liquid out of the droplet 51 and down the clearance channel 53, thus preventing the droplet from spreading across the clearance trough 53. In this way a barrier is set up to prevent residue from migrating off the dielectric spray surface 4 and back onto the discharging electrode. It is assumed here that the discharging electrode is situated somewhere in direct contact with the plane 52 to the right of each picture.

In practice these barrier clearance troughs 53 can be made by hand after the dielectric spray surface has been manufactured using a sharp scoring implement such as a razor, scalpel, pin, hook or needle. In production the surface surrounding the barrier troughs should be as smooth as possible, so any tool used to create the dielectric spray surface should be polished in this area. The trough itself can be a V shaped notch, or a small step (which creates an approximately 90 degree notch), as indicated by feature 6 in FIG. 1.

FIGS. 6a and 6b show two views of a dispenser with an alternative dielectric spray surface 61 embodying this invention. Here the spray surface 61 has been given a microscopic rough finish that is not visible at this scale. A spray electrode recess 62 and discharge electrode recess 63 house a spray electrode 64 and discharge electrode 65 respectively. In this embodiment, only a single spray feedback migration channel 66 is provided together with a plurality of perpendicular barrier channels 67 to prevent any residue on the spray surface 61 from making contact with the discharge electrode 65.

A redundancy reservoir 68 sits below the main dielectric spray surface 61. Excess residue on the spray surface 61 drains via the redundancy conduit channels 69 to reservoir 68.

FIG. 6c shows the redundancy reservoir 68 on its own, and from this it is easy to see that liquid reaching the front of a redundancy conduit channel 69 will be drawn back into the redundancy reservoir 68 by a combination of gravity and capillary forces. Once there it can be prevented from spilling or leaking by an optional porous plug or sponge (not shown) which fills the redundancy reservoir 68.

It should be noted that this particular design, instead of having a microscopic rough finish on the dielectric spray surface 61, could be coated with a oleophilic coating which provides the same ability for residual droplets to quickly spread out across the front surface. In addition an oleophobic coating, such as supplied by Porton Plasma Innovations (P2i) Ltd, Unit 14, Central 127 Milton Park Abingdon, Oxfordshire OX14 4SA, UK, could be applied around the discharging electrode to prevent or at least hinder the migration of residue from the spray surface 61 to the discharging electrode 65.

Without limiting the scope of texture patterns according to the invention, FIGS. 7a and 7b show examples of non homogenous spray feedback migration texture patterns, where 7a forms a spiral arrangement and 7b a staggered arrangement of migration troughs. In both of these arrangements the textured finish is formed by the creation of narrow V notch troughs, whose paths are given by the lines 71 and 72 in the drawing on the dielectric spray surface. These patterns have the added advantage of delaying the time for the liquid residue to reach the spray electrode, thus providing more time for the residue to simply evaporate from the spray surface. Note that whilst the inter trough distance here is of the order of 1 mm, these patterns can be scaled down so this distance is as low as 0.1 mm or so that one trough sits next to its neighbour.

FIGS. 8a to 8c illustrate a beneficial modification to the dimpled dielectric spray surface 4 of FIG. 1. FIG. 8a shows a cross sectional illustration of a tool 81 and resultant dielectric spray surface 82. The sharp peaks required in the tool (e.g. 83) are sometimes difficult to make leading to extra up front manufacturing cost. In FIG. 8b the sharp peaks have become rounded 84, which leads to a corresponding rounding of the troughs formed in the dielectric spray front 85. Such rounded troughs are less suitable at causing liquid residue migration, and are therefore less desirable.

FIG. 8c shows tool peaks 86 which have been modified to maintain troughs with ultra sharp twin edges 87, where the edges themselves (e.g. 88) have the required minimum radius of curvature. Such tools are also much easier to manufacture, as they can be created from a tool like that exemplified in FIG. 8b and simply milled to create the finish shown in FIG. 8c. If the sharp corners ever become slightly blunted, a simple milling operation is all that is required to restore the original sharpness.

The invention described herein is suitable for the electrostatic dispersal of a wide range of liquids. Suitably such a liquid may comprise a component which is a fragrance oil. The liquid may comprise an insecticide component or components, for example, pyrethroid compounds including:

pyrethrins (such as pyrethrins 1, 3 and 11), e.g. as 25% or 50% pyrethrum extract (the balance typically containing plant oils, other plant extracts and light paraffin oils);

allethrins and related non natural compounds, including d allethrin, bioallethrin, esbiothrin (EBT), S bioallethrin (S Biol); resmethrin and bioresmithrin; bifenthrin, permethrin, deltamethrin, cypermethrin, alpha cypermethrin, cyphenothrin, lambda cyhalothrin, vaporthrin, transfluthrin, prallethrin and selected isomers such as Etoc, tefluthrin, pynamin, pynamin forte, neopynamin, metofluthrin, sumithrin, and imiprothrin.

Active insecticide ingredients of a liquid which may be dispersed by the invention described herein may also include organic phosphorus compounds including, but not limited to, fenitrithion, malathion, ciafos, diazinon, DDVP (dichlorvos), and carbamate compounds including carbaryl.

Active pest control ingredients include synergists, for example piperonyl butoxide which may suitably be used in combination with insecticides such as pyrethrins and other pyrethroids.

Active insect attractant ingredients which may be used include mosquito and tsetse fly attractants such as octenol.

Active insect repellant ingredients of a liquid which may be used include, for example, citronella, DEET (N,N diethyl meta toluamide) or D limonene.

Active air cleaner or freshener ingredients, active anti microbial ingredients, active anti fungal ingredients and active anti allergenic ingredients (which may include compounds known to neutralize or denature allergens), which may collectively be classed as active air sanitizers and may be dispersed by the invention, may include, for example, n alkyl dimethyl benzyl ammonium chlorides, n alkyl dimethyl ethyl benzyl ammonium chlorides, alkyl dimethyl 1 naphthylmethyl ammonium chloride, benzalkonium chloride, 1,2 benzisothiazolin 3 one, isopropanol, orthobenzylparachlorophenol, orthophenylphenol, paratertamylphenol, potassium peroxomonosulphate, sodium dodecylbenzene sulphonate, and sodium hypochlorite. Furthermore, active air sanitizers which may be used may include, for example, compounds which are known to have antioxidant, stabilising or other desirable properties (in particular those which are approved for human consumption), such as salts of acetic acid, salts of benzoic acid, salts of butyric acid, salts of citric acid, salts of lactic acid, salts of propanoic acid, salts of tartaric acid.

Glycols (including dipropylene glycol, propylene glycol, triethylene glycol) may also be used as active air sanitizer components when they are not included as or within the carrier.

Active medicament ingredients of a liquid to be dispersed by the invention may include, for example, ingredients which are diuretics (including bumatenide, furosemide, hydrochlorothiazide, melalazone, spironolactone, torsemide), hypotensive agents (including amiodarone, flecainide, procainamide, sotalol), vasodilators (including benazopril, captopril, enalapril, fosinopril, hydralazine, isosorbide dinitrate, isosorbide mononitrate, lisinopril, moexipril, perindopril, quinapril, ramipril), or otherwise suitable for treating cardiac conditions (including acebutolol, amlodipine, aspirin, atenolol, bepridil, caffeine, candesartan, irbesartan, losartan, valsartan, warfarin, busoprolol, carvedilol, diltiazem, digitoxin, dobutamine, esmolol, felodipine, labetalol, metoprolol, milrinone, nicardipine, nicotine, nifedipine, nisoldipine, propanolol, timolol, verapamil). Active medicaments ingredients of such a liquid may further include, for example, ingredients which are anti microbial i.e. anti bacterial or anti viral (including, acyclovir, adefovir, amantidine, amoxicillin, amoxicillin clavulanate, ampicillin, azithromycin, cefaclor, cefdinir, cefpodoxime proxetil, cefriaxone, cefotaxime, cefuroxime, cefuroxime acetil, clarithromycin, ciprofloxacin, clavulanate potassium, doxycycline, entecavir, famiciclovir, gatifloxacin, gentamicin sulphate, glycyrrhizin, interferon alfa 2b, lamivudine, loracarbef, minocycline, moxifloxacin hydrochloride, oseltamivir, peniciclovir, penicillins, riampin, ribavirin, rimantidine, telithromycin, trimethoprim/sulfamethoxazole, valacyclovir, valacycolvir hydrochloride, vancomycin, zanamivir, zidovudine) or anti fungal (e.g. clotrimazole or fluconazole).

Active medicament ingredients of such a liquid may additionally include, for example, ingredients which are suitable for treating bronchial, pulmonary or rhinal conditions (including albuterol, alupent, beclomethasone, beclomethasone dipropionate, bitolerol mesylate, bosentan, budesonide, cromolyn, ephedrine, epinephrine, flunisolide, fluticasone propionate, formoterol, guaifenesin, L albuterol, mometasone, mometasone furoate, montelukast, nedocromil, omalzimab, pseudophedrine, salmeterol, tertbutaline sulphate, theophylline, triamcinolone, triamcinoline acetonide, zafirlukast, zielutin).

Active medicament ingredients of a liquid to be dispersed by the invention may further include, for example, ingredients which are anti histamine or otherwise anti inflammatory (including azelastine, cetirizine hydrochloride, chlorpheniramine maleate, desloratadine, dimetane, diphenhydramine hydrochloride, loratadine, phenylephrine).

Active medicament ingredients of such a liquid may also include, for example, ingredients which are anti depressant (including amitriptyline, amoxapine, citalopram, clomipramine, desipramine, doxepin, fluoxetine, furazolidone, imipramine, linezolid, maprotiline, nortiptyline, paroxetine, phenelzine, protriptyline, selegiline, sertraline, tranylcypromine).

Active medicament ingredients of such a liquid to be dispersed may still further include, for example, ingredients which are suitable for treating glaucoma (including apraclonidine hydrochloride, betaxolol hydrochloride, brimonidine tartrate, carteolol hydrochloride, dipivefrin hydrochloride, dorzolamide hydrochloride, levobunolol hydrochloride).

Active medicament ingredients of such a liquid may also include, for example antineoplastic agents (including anastrozole, bicalutamide, carbiplatin, cisplatin, docetaxel, etoposide, exemestane, flutamide, gefitinib, gemcitabine, irinotecan, megestrol, letrozole, nilutamide, paclitaxel, tamoxifen citrate, vinorelbine).

Active medicament ingredients of a liquid which may be dispersed by the invention may yet further include, for example, ingredients which are anti spasmodic and/or anti Parkinsonian agents (including amomorphine, belladonna, benztropine mesylate, biperiden hydrochloride, bromocriptine, carbidopa, entacapone, glycopyrrolate, levodopa, orphenadrine citrate, pergolide, pramipexole, procyclidine hydrochloride, ropinirole, selegiline, talcapone, trihexyphenidyl hydrochloride).

In addition, active medicament ingredients of such a liquid may include, for example ingredients which have anaesthetic properties (including, benzocaine, bupivacaine, chloroprocaine, lidocaine, mepivacaine, nesacaine, prilocalne, procaine, tetracaine).

Active medicament ingredients of a composition may also include, for example keratolytic agents (including anthralin, calcipotriene, salicylic acid, tazarotene) and PDEV (Phosphodiesterase V) inhibitors such as sildenafil, vardenafil, tadalafil and nicotinic receptor agonists e.g. nicotine.

Active medicament ingredients of such a liquid may further include, for example, ingredients which are analgesic (including, acetaminophen, capsaicin, celecoxib, choline magnesium trisalicylate, codeine, etodolac, hydrocone, ibuprofen, indomethacin, ketoprofen, ketorolac tromethamine, meloxicam, methyl salicylate, morphine, nabumetone, naproxen, naproxen sodium, oxaprozin, oxycodone, paracetamol, D phenylalanine, piroxicam, propoxyphene, salsalate, sulindac, tramadol, valdecoxib).

The invention described herein is suitable for the electrostatic dispersal of liquids into harsh environments where there is a strong cross wind, such as within the ventilation ducting or air conditioning or heating unit of a building (temporary or otherwise), car, aeroplane, helicopter, train, lorry, van, or other mode of transport or when the air around the dispenser is blustery, such as when a dispenser is situated outdoors.

The invention described herein is suitable for the electrostatic dispersal of liquids into excessively humid environments where there is a possibility of water vapour condensing onto the dielectric spray surface. Whilst initially, such condensation or humidity, might adversely effect the electric field, the configuration described in this invention offers the best possible management of surface condensed water, and also the fastest route for system recovery, since the water will begin to collect and migrate according to the various surface treatments, so the system will dynamically and automatically compensate for the changes on the dielectric spray surface. Note that the system is equally suitable for the dispersal into other saturated vapour environments, where for example the dispenser is being used to atomise a liquid compound into a sealed environment, and where the vapour concentration of the compound would be expected to approach its saturation level.

Other applications and modifications thereof will be apparent to persons skilled in the art.

The described embodiments of the invention are intended to be exemplary and numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims. Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only, and is not to be taken by way of limitation. It is appreciated that various features of the invention which are, for clarity, described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable combination.

The spirit and scope of the present invention are to be limited only by the terms of the appended claims.

Claims

1. An electrostatic spray atomisation device comprising: a spray electrode disposed in a first recess in a surface, the spray electrode being operatively connected through an electric circuit to a reference electrode, where the region of the surface adjacent to the first recess has a shape to draw liquid deposited on the region towards the spray electrode.

2. The apparatus of claim 1 where the surface is a dialectric.

3. The apparatus of claim 1 where the surface is characterized by being one or a combination of: oleophillic, oleophobic, lyophilic or lyophobic.

4. The apparatus of claim 1 where the shape is comprised of one or more channels in the surface.

5. The apparatus of claim 1 where the shape is comprised of a rough texture whose Roughness Average is between approximately 1 micron to approximately 1 millimeter.

6. The apparatus of claim 4 where at least one of said channels is in liquid communication with a reservoir.

7. The apparatus of claim 2, wherein the reference electrode is disposed in a second recess in the surface, said second recess having a side wall.

8. The apparatus of claim 7, wherein the second recess is comprised of at least one channel formed in the side wall of the recess.

9. The apparatus of claim 4, wherein the at least one of said channels provides a dispersion path for the liquid over the surface.

10. The apparatus of claim 4, wherein the at least one channel has either or both a substantially v-shaped cross-section or a cross section with a radius of curvature less than approximately 0.5 millimeters.

11. The apparatus of claim 4, wherein the at least one channel has either or both a substantially rounded or a semi-circular shaped cross-section.

12. The apparatus of claim 6, wherein liquid deposited on the surface is drawn to the reservoir at least partially by virtue of gravity.

13. The apparatus of claim 6, wherein liquid deposited on the surface is drawn to the reservoir at least partially by virtue of capillary attraction.

14. The apparatus of claim 14, wherein the surface is adapted to draw any of the liquid deposited on the surface in the region of the first recess towards the spray electrode by chemical affinity between the liquid and the surface.

15. The apparatus of claim 14, wherein the chemical affinity is provided by either a oleophilic or oleophobic coating.

16. The apparatus of claim 1, wherein the chemical affinity is provided by either a lyophilic or lyophobic coating.

17. The apparatus of claim 6, further comprising a porous member within the reservoir to absorb liquid.

18. The apparatus of claim 17, wherein the porous member is a sponge.

19. An electrostatic spray atomisation device comprising: a spray electrode that emits a liquid disposed in a first recess in a dielectric surface, the spray electrode being operatively connected through an electric circuit to a reference electrode, whereby an electric field is generated between the spray electrode and the reference electrode when the electric circuit is provided power, and further comprising a means to distort the electric field when the liquid is deposited on the surface adjacent to the first recess.

20. In an electrostatic spray atomization device comprised of a spray electrode that sprays a liquid and an adjacent surface, a method of controlling dispersal of the liquid on the adjacent surface comprised of: causing the liquid deposited on the adjacent surface to make electrical contact with the spray electrode.