Abstract:
An electrostatic spray nozzle assembly mounted to a panel made of insulating material. The electrostatic spray nozzle assembly includes a nozzle cap having a nozzle outlet, and a liquid tip assembly having a liquid inlet adapted to be connected to a source of coating composition, and a liquid outlet adapted to dispense the coating composition through the nozzle outlet of the nozzle cap. The electrostatic spray nozzle assembly further includes a nozzle body, a first side of the nozzle body adapted to be coupled to the nozzle cap, and a substantially electrically non-conductive panel being positioned between the nozzle body and the nozzle cap. The substantially electrically non-conductive panel is adapted to accumulate an electrostatic charge having a same polarity as that of the coating composition dispensed during a spray operation. Further deposition of spray droplets onto the panel is prevented by electrostatic repulsion forces due to the accumulation of sufficient charge onto the surface of the electrically non-conductive panel from an initial deposit of a small volume of spray.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from and incorporates by reference the entire disclosure of U.S. Provisional Application No. 60/627,480 filed Nov. 12, 2004 and bearing Docket No. 32272-00152USPL and U.S. Provisional Patent Application No. 60/627,191 filed Nov. 12, 2004 and bearing Docket No. 32272-00153USPL. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Technical Field  
         [0003]     This invention relates to electrostatic spraying nozzles. Specifically it relates to electrostatic spray nozzle systems utilizing induction charging or contact charging methods to apply static charge to atomized liquids operating in environments with untrained operators.  
         [0004]     2. Background  
         [0005]     Electrostatic charging of spray is well known in many agricultural and industrial processes. Electrostatic spray nozzles have been successfully developed to increase the deposition efficiency of powder and liquid formulations of agricultural pesticides, paints, and other coatings. Recently electrostatic spray devices have been developed for use by the consumer for applying cosmetics and for sunless tanning. A recent publication by the University of Georgia describes a method for applying decontamination sprays to humans utilizing electrostatic spray nozzles (See, Law and Cooper, 2002 Institute of Physics Conference, Edinburgh, Scotland UK).  
         [0006]     Although electrostatic spray nozzles have been used for many years in a variety of applications, they are generally used in industrial environments with operators trained in the possible hazards associated with the high voltage devices. Electrostatic nozzles have not generally been used in consumer applications where the user is untrained and is unaware of any hazard. Many electrostatic nozzles are operated at voltage levels which can cause an electrical shock hazard. The hazard can come from contact with the high voltage electrode or from wetted nozzle surfaces which create conductive pathways to the high voltage electrode. The safety hazards may be due to contact with the electrical current itself, but more likely the hazard is the reaction to the shock, which may result in bodily harm from falling or contact with an object during involuntary movement away from the source of the shock.  
         [0007]     Wetted or otherwise contaminated nozzle surfaces can cause diminished spray charging due to electrical leakage currents from the electrode to ground. These electrical currents, if excessive, may reduce power supply voltage causing reduced spray charge. In induction charging types of nozzles, such as that U.S. Pat. No. 4,004,733 to Law modified with a dielectric twin-fluid tip and the invention of U.S. Pat. No. 5,765,761 to Law and Cooper, leakage currents may contact the liquid stream and cause reduced charging by decreasing the electrical field between electrode and liquid. This problem is addressed in U.S. Pat. No. 5,704,554 to Cooper and Law. In this nozzle an annular cavity surrounds the nozzle body and a cover to provide for reduced leakage currents. In addition, the liquid stream is insulated by providing a liquid tip which is an integral, non-removable part of the nozzle body.  
         [0008]     These aforementioned nozzles utilize an electrode embedded between layers of insulating material along the atomization channel. This design is safe from operator shock since the embedded electrode design prevents human contact with the electrode. However, gross contamination of the surfaces of these aforementioned nozzles can cause leakage currents from the embedded electrode to elevate the voltage of the upstream-grounded liquid stream. This reduces the internal electric field which is critical for proper induction charging. U.S. Pat. No. 5,704,554 to Cooper and Law addresses solutions to internal and external electrical leakage to the liquid channel from the electrode, but does not address electrical contact from other sources such as from the high voltage connector at the rear of the nozzle. The wire connectors, once contaminated with conductive spray residues, create current pathways to the liquid connections at the rear of the nozzle. In some applications these nozzles have been mounted to panels, tubes or oscillating drums. The lack of a seal between the nozzle surface and the mounting surface causes spray residue to eventually cover both high voltage and low voltage sections of the nozzle.  
         [0009]     A series of patents to Hartman, U.S. Pat. Nos. 6,003,794, 6,138,922 and 6,227,466, show a set of nozzles encased in a nonconductive tube. This device does not provide a barrier between the high voltage and low voltage sections of a nozzle system as evidenced by the design which has an electrode conductor in contact with the tube wall and penetrating through an opening in the tube. The design includes a non-insulated conductive air conduit and non-insulated conductive nozzle bodies within the tube shell that serve as conductors connected to the electrode voltage. Conductors to the electrode which extend through the tube and contact the exterior portion of the tube are covered on one face with a nozzle cap that does not provide an electrically tight sealing surface between inner and outer portions of the tube. The exposed conductors within the shell are in the vicinity of the liquid channels which are meant to be maintained at earth potential. The non-insulated high voltage air tube and nozzle bodies are likely to allow leakage currents to travel through threaded seams in the liquid channels. This effect will draw excessive electrode current, elevate the liquid electrical potential by contact and reduce charging. In addition, the non-insulated high voltage conduits may pose a significant hazard to those adjusting or maintaining the assembly while it is operating.  
         [0010]     In commercial applications of the nozzle of U.S. Pat. No. 5,704,554 to Cooper and Law, where the nozzles are mounted to an oscillating drum for applications of sunless tanning liquids, the lack of a sealing surface on the nozzle eventually causes liquid to reach the inside of the drum. The presence of this conductive liquid inside the drum provides electrical leakage paths to the liquid channel of the nozzle. Electrical potentials on the liquid have been observed on commercial versions of this system to reach a level of over 80% of the induction electrode voltage. Conductive liquid tube fittings used on the rear of the nozzle accelerate this problem. Because the liquid is near the electrode potential rather than held at ground potential, the induction-charging electric field within the nozzle is greatly reduced, and spray charging is much less than necessary for electrostatic spray deposition. Once the nozzle surfaces have become contaminated they are very difficult to clean to the level necessary to prevent electrical leakage.  
         [0011]     Induction charging nozzles, such as those previously mentioned, also have the inherent drawback of spray being attracted back to the nozzle itself and to surrounding mounting fixtures. The electrode is of opposite polarity to the charged spray cloud. Once the dielectric nozzle surfaces become slightly wetted or otherwise conductive, the surfaces assume the electrode polarity and attract spray from the oppositely charged spray cloud. Excessive liquid returning to the nozzle not only contaminates the nozzle surface further, it causes spray cloud discharge as the liquid pulls into a peaked shape in the direction of the spray cloud space charge field. The point on the liquid droplet peak will produce air ions that can discharge an estimated ⅓ of the spray charge.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     An embodiment of the present invention comprises of an electrostatic charging nozzle having a sealing surface suited to mounting to an insulating panel. The sealing surface is to prevent liquid leakage and to electrically separate high voltage and low voltage components. The panel is charged to the same polarity as the spray cloud to reduce the amount of spray returning to the nozzle and surrounding surfaces, and block nozzle surfaces from becoming coated with conductive residues. The nozzle body is made from a non-conductive material so that it may be safely handled while operating. In addition, the present invention has a removable liquid tip to allow service to this key component of the nozzle while it is mounted to a panel. The nozzle system may be configured as a contact charging system by connecting the liquid directly to a high voltage source. Alternatively, the system may be configured as an induction charging device by energizing a conductive portion of the annular air cap, in a manner similar to that described by U.S. Pat. No. 4,004,733 to Law.  
         [0013]     A sealing surface between nozzle and panel is provided to maintain a tight barrier preventing liquid contamination and electrical flow between sides of the panel barrier. The sealing surface may be on the nozzle body. This configuration allows disassembly of the nozzle from the spraying side of the panel. Alternatively the sealing surface may be on the nozzle cap. This configuration allows disassembly of the spray nozzle from the rear of the panel.  
         [0014]     In accordance with an embodiment of the present invention an electrostatic spray nozzle mounted to a panel made of insulating material. In accordance with this embodiment, high voltage nozzle components are not in contact with the panel, and grounded portions of the nozzle are separated from high voltage portions of the nozzle by the panel. A seal on the nozzle surface prevents fluid leakage and the formation of electrical leakage currents to the opposite side of the panel. The insulating surface of the panel accumulates charge of the same polarity as the spray during the spray operation. Further deposition of spray droplets onto the panel is prevented by electrostatic repulsion forces due to the accumulation of sufficient charge onto the surface of the insulating panel from an initial deposit of a small volume of spray. In accordance with an embodiment of the invention, the fluid tip is removable from either the front or the rear of the nozzle body while the nozzle remains mounted to the panel. The insulating panel further serves as a safety device by preventing ready access to high voltage components of the nozzle system.  
         [0015]     An electrostatic spray nozzle assembly in accordance with an embodiment of the present invention comprises a nozzle cap having a nozzle outlet, and a liquid tip assembly having a liquid inlet adapted to be connected to a source of coating composition, and a liquid outlet adapted to dispense the coating composition through the nozzle outlet of the nozzle cap. The electrostatic spray nozzle assembly further includes a nozzle body, a first side of the nozzle body adapted to be coupled to the nozzle cap, and an electrically insulating panel being positioned between the nozzle body and the nozzle cap. In accordance with an embodiment of the present invention the electrically insulating panel is adapted to accumulate an electrostatic charge having a same polarity as that of the coating composition dispensed during a spray operation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  shows components of a panel-mounted electrostatic nozzle system according to an embodiment of the present invention;  
         [0017]      FIG. 2  shows the nozzle system of an embodiment of the present invention mounted to the insulating panel by attaching the non-conductive nozzle body to the panel;  
         [0018]      FIG. 3  shows an embodiment of the nozzle system of the present invention mounted to the insulating panel by attaching the non-conductive nozzle cap to the panel;  
         [0019]      FIG. 4  shows an embodiment of the nozzle system of the present invention with nozzles mounted to an oscillating drum;  
         [0020]      FIG. 5  shows an embodiment of the nozzle system of the present invention with nozzles mounted to a dielectric panel such as may be used in a spray booth; and  
         [0021]      FIG. 6  illustrates a ball and socket mounting of the nozzle system according to an embodiment of the present invention to allow angular positioning of the spray. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Referring now to  FIG. 1 , components of a panel mounted electrostatic spray charging system in accordance with an embodiment of the present invention is illustrated. These components are illustrated as suited for an air atomizing induction charging system. However, it should be understood that the system could be easily configured for contact charging by applying voltage directly to the liquid rather than an induction electrode. The main components of an induction charging system as shown include a nozzle body  10 , removable liquid tip  20 , an electrode retaining cap  30 , an electrode air cap  40  having an air cap outlet  45 , a sealing surface  50   a,    50   b  on the nozzle body  10  and/or the electrode retaining cap  30 , and an electrically insulating panel  60 . In accordance with various embodiments of the present invention, the electrically insulating panel is substantially electrically non-conductive. In accordance with various embodiments of the invention, the insulating panel may be made of a plastic material. In a preferred embodiment of the invention, the insulating panel is made of an insulating material such that electrical resistance of the insulating panel to earth ground is greater than 2 Megaohms. The nozzle body  10  is preferably made from insulating material. The nozzle body  10  itself does not contain a fluid channel but instead includes a central air channel bore so that it allows the insertion of the removable liquid tip  20  in such a way that air from an air inlet  100  is caused to flow around the removable liquid tip  20  inserted into the central air channel bore. In accordance with various embodiments, the removable liquid tip  20  is positioned into and held concentric with the central air channel bore. Preferably the central air channel bore is such that the remove liquid tip  20  may be inserted or removed from either the front or rear sides of the nozzle body  10 . The air inlet  100  is adapted to receive a supply of air or other gas from a source. In various embodiments, the removable liquid tip  20  includes at least one air channel cut  25  (see  FIGS. 2 and 3 ) along a length of the removable liquid tip  20  for allowing air to flow around a liquid outlet of the removable liquid tip  20 .  
         [0023]     The insulating panel  60  is further provided with a plurality of mounting holes  65 . In one embodiment of the present invention, the nozzle body  10  is fixedly mounted to the insulating panel  60  using mounting hardware that is coupled to the nozzle body  10  and passes through the mounting holes  65 . In still another embodiment, the retaining cap  30  is mounted to the insulating panel  60  using mounting hardware that is coupled to the retaining cap  30  and passes through the mounting holes  65 . In accordance with an embodiment of the invention, the mounting hardware can include bolts, screws, rods, attachment clips, etc. In still other embodiments of the invention, the nozzle body  10  and/or the retaining cap  30  can be affixed to the insulating panel  60  using an adhesive. The insulating panel  60  further includes a void  75  for allowing a portion of the nozzle body  10  to be mounted therethrough. In some embodiments of the present invention, a portion of the retaining cap  30  in contact with the insulating panel  60  is of a diameter such that the mounting holes  65  are covered by the retaining cap  30  to inhibit charge leakage through the mounting holes  65 .  
         [0024]     Still referring to  FIG. 1 , the electrostatic spray charging system further includes a liquid inlet  70  adapted to be connected to a source of spray liquid and supply the spray liquid to the removable liquid tip  20 . The electrostatic spray charging system still further includes an electrode wire  80  adapted to supply an electrostatic charge to the induction electrode air cap  40 . The electrode retaining cap  30  is provided with an spray outlet  90  allowing for a spray of electrostatically charged liquid to be sprayed from the spray nozzle assembly.  
         [0025]     At the beginning of a spraying operation, deposition of a small amount of spray on the surface of the insulating panel  60  causes the insulating panel  60  to be charged by accumulation to the same polarity as the spray cloud. As a result, during the remaining portion of the spraying operation the spray cloud is repelled from the insulating panel  60 , resulting in a reduction in the amount of spray returning to the spray nozzle and surrounding surfaces, as well as blocking nozzle surfaces from becoming coated with conductive residues.  
         [0026]     The sealing surface  50   a  and/or the sealing surface  50   b  functions to prevent, or at least to inhibit, current flow between the electrode air cap  40  of the electrostatic spray nozzle assembly and a pathway to an electrical potential difference, such as a ground. The sealing surface  50   a  and/or the sealing surface  50   b  serves to prevent or inhibit the formation of charge leakage paths, the presence of which will inhibit optimal charging of the spray by the electrode air cap  40 . The prevention or inhibition of current flow between the electrode air cap  40  and components of the electrostatic spray nozzle assembly that are positioned on the opposite side of the insulating panel  60  from the electrode air cap  40  provided by sealing surface  50   a  and/or sealing surface  50   b  also serves to isolate a person that may come in contact with these components from electrical shock. In various embodiments of the present invention, the spray is charged to a negative charge potential with respect to ground, whereas in other embodiments the spray may be charged to a positive charge value with respect to ground.  
         [0027]     Referring now to  FIG. 2 , a side view of an embodiment of the present invention in which a mounting of the nozzle by attaching the nozzle body  10  to the insulating panel  60  is illustrated. In this embodiment, a sealing surface  50   a  is located between the nozzle body  10  and the insulating panel  60 , and may be fixedly mounted to the insulating panel  60 . An example situation in which it may be desirable to implement the embodiment of  FIG. 2  is in situations where it is desired to service the nozzle components from the spray outlet side of the insulating panel  60 . In this case, removal of the nozzle cap  30  allows access to the removable electrode air cap  40  and the removable liquid tip  20 . In this embodiment it is preferable that the sealing surface  50   a  be a flat surface of the nozzle body  10  that contacts the insulating panel  60 .  
         [0028]      FIG. 3  illustrates a mounting of the nozzle assembly in accordance with an embodiment of the present invention in which the nozzle cap  30  is attached to the insulating panel  60 . This mounting configuration is useful when it is desired to have the serviceable components accessible from the rear of the insulating panel  60 . One instance in which this may be desirable may be for use in a spray booth where a service door is provided on the rear of the spray booth. Another instance in which rear access is desirable is in a multiple-nozzle spray panel in which adjacent nozzles are continuously operating while an individual nozzle is serviced or its components are replaced or repaired. In the mounting scenario of  FIG. 3  it is desirable that the sealing surface  50   b  is on a flat area of the fixed nozzle cap  30  that contacts the insulating panel  60 .  
         [0029]      FIG. 4  illustrates an embodiment of the present invention in which a nozzle assembly is mounted on an oscillating spray nozzle drum  110 . The nozzle drum  110  is mounted on a pivot axis  120  which allows the nozzle drum to oscillate during a spraying operation, which allows the nozzle drum  110  to be pivoted to create a sweeping spray effect. In accordance with the embodiment of the invention of  FIG. 4 , the outer surfaces of the nozzle drum  110  are constructed of electrically insulating material through which are mounted one or more nozzle assemblies each comprised of a nozzle cap  30  (or electrode retaining cap), an electrode air cap  40 , a removable liquid tip  20 , and a nozzle body  10 . An example application of the embodiment of  FIG. 4  is for use in spray booths that provide for the application of sunless tanning media onto humans. In an embodiment of the present invention, a sealing surface  50   a  may be provided between the nozzle body  10  and the mounting surface of the nozzle drum  110  and/or a sealing surface  50   b  may be provided between the nozzle cap  30  and the mounting surface of the nozzle drum  110 . In still another embodiment, the nozzle system can be mounted either with the nozzle cap  30  or the nozzle body  10  providing the sealing surface.  
         [0030]      FIG. 5  illustrates a multiple nozzle spray panel in accordance with an embodiment of the present invention such as may be used in a spray booth. The spray system of  FIG. 5  includes one or more nozzle assemblies each comprised of a nozzle cap  30 , an electrode air cap  40 , and a nozzle body  10 , mounted to through the surface of an insulating plastic panel  130 . A sealing surface may further be provided between the nozzle body  10  and the plastic panel  130  and/or between the nozzle cap  30  and the plastic panel  130 . In still other embodiment of the present invention, the nozzle system can be mounted by the nozzle cap  30  or the nozzle body  10  depending on which side of the plastic panel  130  it is desired to have service access.  
         [0031]      FIG. 6  illustrates a nozzle assembly mounted within a socket in an insulating (or non-conductive) panel. As illustrated in  FIG. 2 , the nozzle assembly includes a nozzle cap  140  and a sealing surface  160  mounted on a first side of an insulating panel  60 , and a nozzle body  170  mounted on a second side of the insulating panel  60 . The nozzle cap  140  includes a jet outlet  150  which allows a spray of spray liquid to exit the nozzle assembly during a spraying operation.  
         [0032]     The sealing surface  160  functions to prevent, or at least to inhibit, current flow between an electrode (not shown) of nozzle assembly and a pathway to an electrical potential difference, such as a ground. The sealing surface  160  serves to prevent or inhibit the formation of charge leakage paths, the presence of which will inhibit optimal charging of the spray by the electrode. The prevention or inhibition of current flow between the electrode and components of the electrostatic spray nozzle assembly that are positioned on the opposite side of the insulating panel  60  from the electrode provided by sealing surface  160  also serves to isolate a person that may come in contact with these components from electrical shock. In various embodiments of the present invention, the spray is charged to a negative charge potential with respect to ground, whereas in other embodiments the spray may be charged to a positive charge value with respect to ground.  
         [0033]     This mounting arrangement allows the nozzle to pivot against the sealing surface  160  of the spherically-shaped nozzle to allow adjustment of the direction angle of the spray jet such that the nozzle can be set at a particular orientation. Position A of  FIG. 6  illustrates the nozzle assembly in which the jet outlet  150  has been rotated in an up position. Position B of  FIG. 6  illustrates the nozzle assembly in which the jet outlet  150  has been rotated in a midway position. Position C of  FIG. 6  illustrates the nozzle assembly in which the jet outlet  150  has been rotated in a down position. In various embodiments of the invention, the nozzle is pivotally mounted such that the side to side orientation of the nozzle can be changed. Although the embodiment of  FIG. 6  illustrates a nozzle body pivotally mounted within a socket of an insulating panel, it should be understood that other methods of pivotally mounting the nozzle body can be used such as using a pivot pin.  
         [0034]     Although various embodiments of the nozzle assemblies of the present invention have been illustrated as being mounted to a flat insulating panel, it should be understood that other panel shapes can be used. For example, the nozzle assemblies of the present invention may be mounted within a curved insulating panel or a faceted insulation panel.  
         [0035]     Although the various embodiments of the present invention have been described for use in the application of tanning solutions to a human subject, it should be understood that the present invention can also be applied to other cosmetic spray applications, as well as for the application of medicinal and decontaminant sprays, for example, antibiotics, antitoxins, disinfectants, sanitizers, etc. Further, although a preferred embodiment of the method and apparatus of the present invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it is understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the claims.