An electrostatic spraying apparatus for spraying liquid has a spraying edge 8 provided with teeth 12. No parts of the apparatus provide a low potential influence near the spraying edge, keeping leakage losses to a minimum. At the voltage provided by a high voltage supply, the field strength at the tips of the teeth 12, is sufficient to form one ligament of liquid per tooth. The ligaments break up into droplets which have a size largely independent of fluctuations in field strength caused by varying the distance from the target to be sprayed.
An electrostatic device for spraying liquids comprises a nozzle in the form of a wick which is contacted with a reservoir containing the liquid to be sprayed, high electrical potential being applied to the liquid in the vicinity of the spraying tip of the nozzle whereby the liquid is drawn out preponderantly under the influence of electrical forces into ligaments which break up to form a spray of electrically charged liquid droplets. The wick is fabricated from sheet of a resiliently deformable polymeric foam material of open celled structure and an edge of the sheet material is profiled to form a plurality of sites at which liquid ligaments can be produced. Typically a toothed profile is employed in which a plurality of teeth form the sites at which ligament formation occurs.
A process is disclosed for strengthening and sizing paper which comprises the step of applying a composition comprising (a) an isocyanate and (b) an isocyanate-reactive component comprising at least one polyol having an ethylene oxide content of at least 1%, wherein said composition does not contain water to the paper by means of an electrostatic spraying device having a linear orifice.
An electrostatic atomizer comprises a power source for powering a charge injection device, a controller for controlling the net charge injected by the charge injection device, and a sensor for sensing breakdown precursors in the vicinity of the orifice and producing a feedback signal upon the occurrence of the breakdown precursors. The sensor is in communication with the controller and the controller is responsive to the feedback signal so that upon occurrence of the feedback signal, the controller decreases the net charge injected. A method of minimizing corona-induced breakdown in an electrostatic atomizer comprises the steps of providing a fluent material with a net charge to atomize the fluent material, and responding to the occurrence of breakdown precursors by decreasing the net charge of the liquid to avoid corona-induced breakdown.
A process is disclosed for strengthening and sizing paper which comprises the step of applying a composition comprising (a) an isocyanate and (b) an isocyanate-reactive component comprising at least one polyol having an ethylene oxide content of at least 1%, wherein said composition does not contain water to the paper by means of an electrostatic spraying device having a linear orifice.
An electrostatic atomizer has a power source powering a charge injection device. The power source is arranged to vary the net charge injected by the charge injection device cyclically in accordance with a pattern of variation so that the net charge repeatedly increases to a higher value at or above a long-term breakdown value. The net charge injected is reduced by the power source to a lower value below the long-term breakdown value so that corona-induced breakdown is reduced. A method for electrostatically atomizing a fluent material is provided. The method includes the step of cyclically varying the net charge injected to reduce the occurrence of corona-induced breakdown.
