Fluid sprinkling – spraying – and diffusing – Electrostatic type
Patent
1994-07-18
1996-04-02
Merritt, Karen B.
Fluid sprinkling, spraying, and diffusing
Electrostatic type
239145, B05B 5025, B05B 516
Patent
active
055033350
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the electrostatic spraying of liquids.
It is known from Applicant's prior EP-A-120633 to effect electrostatic spraying by the application of high potential to liquid supplied to a nozzle which comprises a porous wick-type element formed of the types of porous felt or fibre bundles or plastic pads widely used in graphic implements such as felt or porous plastic tip markers or felt- or fibre-tip pens. In the case of porous pad or fibre bundle nozzle constructions, reference is made to the use of nozzles having a point, bullet head or hemispherical configuration. In the case of felt-tip markers, reference is made to such markers having a chisel-edge configuration.
It is also known from Applicant's prior EP-A-243031 to provide an electrostatic spraying device in which the droplet size can be controlled without the aid of a field adjusting electrode (FAE) by forming a spraying edge of the device with a toothed profile so as to afford a plurality of sites at which the liquid is drawn out preponderantly by electrostatic forces into ligaments which break up into electrically charged particles. The spraying edge is defined by a component over a surface of which the liquid is fed by gravity towards a toothed edge of the component.
The present invention is concerned with an improved form of electrostatic spraying device in which supply of liquid to the spraying edge is rendered substantially independent of gravity without the need for employing a source of pressure in order to effect liquid feed.
According to one aspect of the present invention there is provided an electrostatic spraying device comprising: a spraying nozzle in the form of a wick type element: a reservoir for containing liquid to be supplied to the nozzle; and means for applying high voltage to the liquid at the nozzle to cause the liquid to be drawn into ligamentary form and thereafter break up into electrostatically charged droplets: said element being composed of a foam material having an open cell structure through which the liquid is drawn by capillary action.
In contrast with the above mentioned prior art, the spraying nozzle in a device according to said one aspect of the present invention comprises a foam material through which the liquid is drawn by capillary action.
Preferably the foam material is resiliently deformable. The use of a spraying nozzle composed of a resiliently deformable material confers reduced susceptibility to spraying being deleteriously affected as a result of impacts to the nozzle in use. For instance, where as in the prior art a nozzle is composed of a relatively rigid structure such as a bundle of fibres, an impact to the nozzle may result in splitting of the bundle or one or more fibres breaking off from the bundle. Depending on the extent of the damage, the nozzle may cease to function altogether or it may produce a spray in directions which are not desired--for example, towards the body of the sprayer with consequent contamination. In contrast, a nozzle composed of a resiliently deformable material, if impacted, will usually absorb the impact by yielding or deflecting and then resile to its former orientation.
Conveniently the foam material is shaped so as to present at least one feature from which the liquid discharges in the form of a plurality of ligaments.
Advantageously the foam material is in the form of a sheet and is shaped in such a way that each such feature presents a crest extending between opposite faces of the sheet.
Where the foam material is formed from sheet material, each such feature may be formed by cutting the foam material through its thickness.
In one embodiment of the invention, the foam material is in the form of a sheen and is formed with a toothed profile presenting at least one crest extending between opposite faces of the sheet. Usually the included angle at the crest will be no greater than 100.degree..
In accordance with a preferred feature of the invention the element terminates in at least one tip having a chisel edge configuration, with an edge which is sub
REFERENCES:
patent: 4846407 (1989-07-01), Coffee et al.
patent: 5196171 (1993-03-01), Peltier
Patent Abstracts of Japan, Jul. 1985--publication No. JP58067375, application No. JP810165816, abstract vol. 007155.
Green Michael L.
Noakes Timothy J.
Imperial Chemical Industries plc
Merritt Karen B.
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