Abstract:
The inventive subject matter relates to a device and method of its use in producing small droplets of insecticide. The device produces small droplets through ultrasonic frequency sonication. The device is also capable of inducing and electrical charge on the small droplets for better application to flying insects.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional application, No. 61/708,184, filed Oct. 1, 2012. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The inventive subject matter relates to an insecticide sprayer capable of producing droplets less than 5 μm in size. The sprayer utilizes ultrasonic frequency to produce small droplet size. 
         [0004]    2. Background Art 
         [0005]    Insecticides are typically applied to flying insects by spraying the insecticide with random coating or application based on chance collision with the spray. Current methods of insecticide spraying entail application of a spray with random application of insecticide on the insect as the insect encounters the spray. 
         [0006]    Because most spray contains droplets sizes that are relatively large, often as much as 100 μm, the sprayed material settles relatively quickly. This necessitates forming a spray starting fairly high, often using more chemical than is necessary. Production of smaller droplets is typically is accomplished by vaporizing the material by heating it. This approach, however, is problematic in insecticide application due to the often combustible or flammable nature of the chemicals in insecticide formulations. 
       SUMMARY OF THE INVENTION 
       [0007]    The current invention relates to an insecticide sprayer and method of application of insecticides, capable of producing small size droplets. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1 . Diagram of the device illustrating major components of sprayer. In the figure, dotted lines indicate flow of material, in the form of droplets, air flow or fluid from the reservoir. 
           [0009]      FIG. 2 . Diagram of the sprayer device capable sorting droplets by charge. As illustrated in the figure, sorted material is directed out through the sprayer tube. Unsorted material can be directed into a recollection reservoir. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0010]    Current insecticide spraying equipment are not generally capable of producing fine droplets in the range of 5 μm or less. Small droplets, defined as droplets 5 μm or less, are highly desirable in that small droplets would form a fog-like layer which would accumulate near the ground, where many insects reside. Currently there is only one type of sprayer that is capable of producing droplets less than five microns. This is called a thermo fogger, which uses the latent heat of combustion generated in a chamber that vaporizes the liquid. Unfortunately most of the formulations used in insecticidal spray formulation contain combustible materials. Therefore, use of this approach to produce small droplets may pose a serious safety hazard. This is especially true in areas where combustible materials are present, especially in enclosed or partially enclosed areas. However, use of a thermo fogger to atomize water only results in the formation of droplets in the 27-60 micron range. 
         [0011]    It is an advantage to have small droplets for insecticidal spraying. As such there is a need for an apparatus for making less than 5 μm droplets without using heat and capable of forming less than 5 μm droplets cold spray. The problem is even worse for hand held/backpack portable sprayers where the smallest size attainable with water is 15 μm and the average is in the 50 to 100+μm. Interestingly, most hand-held sprayers using water produce 15 μm droplets or greater. 
         [0012]    Table 1 shows how the droplet size relates, geometrically, to volume of liquid. The small droplets can have the effect of more effectively carrying and adhering to the target of interest. As shown in Table 1, 422 droplets with a diameter of 2 μm contains the same volume as one 15 μm droplet. Similarly, 3375 drops with a 1 μm diameter would contain the same volume as 1 droplet with a diameter of 15 μm. This attribute ensure more efficient use of material and cost savings. 
         [0013]    Additionally, an important attribute of small droplets, especially droplets of less than 5 μm in diameter, is their ability to result in a stable, non-settling fog. A stable non-settling fog with the insecticide formulation would permit many more droplets to be available to contact target insects. Also, the non-settling nature of the fog would allow much greater time for the insects to fly in the presence of the insecticide. Collectively, the characteristics of small, 5 μm droplets increases the efficiency of exposure and delivery of insecticide to the target insects. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 number of 2 
                 # of 1 
               
               
                 Droplet 
                   
                 calculated 
                 number of 4 
                 μm diameter 
                 μm diameter 
               
               
                 Diam- 
                 droplet 
                 volume = 
                 μm droplets 
                 droplets 
                 droplets 
               
               
                 eter 
                 radius 
                 4/3 π r 3   
                 of equal 
                 of equal 
                 of equal 
               
               
                 (in μm) 
                 (in μm) 
                 (in μm 3 ) 
                 volume 
                 volume 
                 volume 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 0.5 
                 0.52 
                   
                   
                 1 
               
               
                 2 
                 1 
                 4.19 
                   
                 1 
                 8 
               
               
                 3 
                 1.5 
                 14.14 
                   
                 3 
                 27 
               
               
                 4 
                 2 
                 33.51 
                 1 
                 8 
                 64 
               
               
                 5 
                 2.5 
                 65.45 
                 2 
                 16 
                 125 
               
               
                 10 
                 5 
                 523.60 
                 16 
                 125 
                 1000 
               
               
                 15 
                 7.5 
                 1767.15 
                 53 
                 422 
                 3375 
               
               
                 20 
                 10 
                 4188.79 
                 125 
                 1000 
                 8000 
               
               
                 25 
                 12.5 
                 8181.23 
                 244 
                 1953 
                 15625 
               
               
                 30 
                 15 
                 14137.17 
                 422 
                 3375 
                 27000 
               
               
                 35 
                 17.5 
                 22449.30 
                 670 
                 5359 
                 42875 
               
               
                 40 
                 20 
                 33510.32 
                 1000 
                 8000 
                 64000 
               
               
                 45 
                 22.5 
                 47712.94 
                 1424 
                 11391 
                 91125 
               
               
                 50 
                 25 
                 65449.85 
                 1953 
                 15625 
                 125000 
               
               
                 55 
                 27.5 
                 87113.75 
                 2600 
                 20797 
                 166375 
               
               
                 60 
                 30 
                 113097.34 
                 3375 
                 27000 
                 216000 
               
               
                 65 
                 32.5 
                 143793.31 
                 4291 
                 34328 
                 274625 
               
               
                 70 
                 35 
                 179594.38 
                 5359 
                 42875 
                 343000 
               
               
                 75 
                 37.5 
                 220893.23 
                 6592 
                 52734 
                 421875 
               
               
                 80 
                 40 
                 268082.57 
                 8000 
                 64000 
                 512000 
               
               
                 85 
                 42.5 
                 321555.10 
                 9596 
                 76766 
                 614125 
               
               
                 90 
                 45 
                 381703.51 
                 11391 
                 91125 
                 729000 
               
               
                 95 
                 47.5 
                 448920.50 
                 13396 
                 107172 
                 857375 
               
               
                 100 
                 50 
                 523598.78 
                 15625 
                 125000 
                 1000000 
               
               
                   
               
             
          
         
       
     
         [0014]    In addition to use of small, 5 μm droplets, application of charge to the droplets would be advantageous for further efficiency of application. Where application is intended for flying insects, the charge of the droplets should typically be negatively charged, since insects are believed to induce a positive charge on their bodies during flight. The negatively charged droplets would be attracted to the insect thus making the amount of charged droplets coming into contact with the insect is much greater. 
       EXAMPLE 1 
     Small Droplet Atomizer 
       [0015]    In a preferred embodiment, the inventive device is capable of producing and expelling droplet sizes of liquids, defined as 5 μm or smaller. The device comprises a reservoir ( 1 ), connected, via a connection tube ( 3 ) capable of permitting fluid to pass to a transducer drum ( 5 ). The transducer drum contains one or more transducers ( 9 ) that are electrically connected to a suitable power source ( 17 ). The power source ( 17 ) is capable of generating electrical oscillations in the ultrasonic frequency range. Ultrasonic frequency range is defined as a frequency of oscillation above 19 kHz. 
         [0016]    As an example, in one embodiment, the ultrasonic frequency is approximately 0.8 MHz to approximately 1.7 MHz. Power switching with the power switching transistor can be arranged as Colpitts oscillator. In a preferred embodiment, the frequency is 1.65 MHz. 
         [0017]    Any type of transducer can be utilized, including magnetostrictive or piezo-electric transducers. In a preferred embodiment, piezo-electric transducers are utilized. In one embodiment, the frequency is adjustable to produce the desired droplet size. 
         [0018]    The inventive device can be configured in a number of ways.  FIG. 1  illustrates an example of one embodied configuration of the device. As shown in  FIG. 1 , insecticide is supplied to a transducer drum ( 5 ) from a reservoir ( 1 ), via a connection ( 3 ) between the reservoir ( 1 ) and transducer drum ( 5 ), at one of two ends of the transducer drum ( 5 ) is a fan ( 7 ), which is capable of blowing droplets to the opposite end of the transducer drum ( 5 ) and out of the drum via a sprayer tube ( 11 ). In another embodiment, the reservoir ( 1 ) also comprises a fluid level indicator ( 15 ). 
         [0019]    In a preferred embodiment, fluid in the reservoir ( 1 ) flows through the connection tube ( 3 ) to the transducer drum ( 5 ). In the transducer drum ( 5 ), fluid is subjected to sonication via one or more ultrasonic transducers ( 9 ), which vibrate at ultrasonic frequency. Any type of transducer can be utilized, including magnetostrictive or piezo-electric transducers.  FIG. 1  illustrates the device with a single transducer. Small droplets, of 5 μm or less, are then formed, which are expelled ( 13 ) through the sprayer tube ( 11 ). 
         [0020]    Table 2 illustrates the results of a study using ultrasonic transducer to produce droplets of different fluid materials. In this study, various chemical formulations are emitted from a commercially available ultrasonic humidifier (Hunter® model 31004). The humidifier&#39;s transducer oscillates at an ultrasonic frequency of 1.65 MHz. The transducer is used here as a prototype that would be incorporated into the inventive device of  FIG. 1  or  FIG. 2 . Table 2 shows the range of droplets emitted. DV 0.1  represents 10% of the droplets emitted; DV 0.5  represents the median diameter of the droplets; while DV 0.9  represents the 90% of the droplets size. 
         [0000]    
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Composition of 
                 # of droplets 
                   
                 DV 0.5   
                   
               
               
                   
                 droplet 
                 measured 
                 DV 0.1   2   
                 (volume 1 ) 
                 DV 0.9   3   
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Water 
                 2274 
                 2.94 
                 4.76 
                 8.53 
               
               
                 2 
                 Water 
                 1904 
                 3.16 
                 5.15 
                 8.78 
               
               
                 3 
                 75% diesel oil; 
                 3547 
                 2.28 
                 3.92 
                 7.92 
               
               
                   
                 23.75% ethyl 
               
               
                   
                 acetate; 5% 
               
               
                   
                 permethrin 
               
               
                 4 
                 50% BVA 13 
                 891 
                 2.66 
                 5.32 
                 7.65 
               
               
                   
                 oil; 50% ethyl 
               
               
                   
                 acetate 
               
               
                 5 
                 47.5% BVA 13 
                 1672 
                 2.2 
                 4.72 
                 9.56 
               
               
                   
                 oil; 47.5% 
               
               
                   
                 ethyl acetate; 
               
               
                   
                 5% permethrin 
               
               
                 6 
                 10% Aqua 
                 1947 
                 1.33 
                 5.74 
                 17.26 
               
               
                   
                 Reslin ® 
               
               
                   
                 Concentrate; 
               
               
                   
                 90% water 
               
               
                 7 
                 10% Aqua 
                 1466 
                 1.5 
                 6.78 
                 14.57 
               
               
                   
                 Kontrol ® 
               
               
                   
                 Concentrate; 
               
               
                   
                 90% water 
               
               
                 8 
                 10% Aqualuer 
                 593 
                 1.18 
                 5.07 
                 8.54 
               
               
                   
                 20-20 ® 
               
               
                   
                 Concentrate; 
               
               
                   
                 90% water 
               
               
                   
               
               
                   1 Median of diameter 
               
               
                   2 Diameter of 10% of droplets 
               
               
                   3 Diameter of 90% of droplets 
               
             
          
         
       
     
         [0021]    As illustrated in Table 2, the humidifier emits droplets within a range of 1.5 μm to 17.26 μm, depending on the source material. For example, the ultrasonic humidifier was able to produce droplets of 47.5% BVA 13 oil (BVA, Inc, Wixom, Mich.) with 47.5% ethyl acetate and 5% permethrin (3-Phenoxybenzyl (1RS)-cis,trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate) with an average diameter (i.e., DV0.5) of 4.72 μm, with 10% of the droplets as small as 2.2 μm. Similarly, 10% Aqua-Kontrol® Concentrate (Masterline®, Univar, Austin, Tex.) and 90% water yielded 10% of the droplets with a diameter of 1.5 μm with an average diameter of 6.78 μm. 
         [0022]    In another study, droplets were created by a prototype mister, fabricated by Humidifirst™, Inc. (Boynton Beach, Fla.). The prototype mister comprised a solenoid valve control of water (i.e., fluid) flow into the humidifier; a float switch to control water level; and a float switch to provide for low water shutdown; a blower fan; and 4 piezoelecrtric crystals (i.e., transducers). Droplet size was monitored by a Phase Doppler Particle Analyzer (PDPA) (TSI, Inc, Shoreview, Minn.). The results of the study are illustrated in Table 3. As illustrate in Table 3, the median volume in this study was 7.13 μm to 7.35 μm, with approximately 10% of the droplets 3.75 μm to 3.82 μm. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 Droplet diameter (μm) 1   
               
             
          
           
               
                   
                   
                   
                 DV.5 
                   
                   
               
               
                   
                   
                   
                 (volume 
                   
                 Mean 
               
               
                   
                   
                   
                 median 
                   
                 Velocity, 
               
               
                 Spray Liquid 
                 Rep 
                 DV.1 
                 diameter) 
                 DV.9 
                 meters/sec 
               
               
                   
               
               
                 Water 
                 1 
                 3.82 
                 7.35 
                 14.60 
                 1.27 
               
               
                 Water 
                 2 
                 3.77 
                 7.13 
                 14.51 
                 1.45 
               
               
                 Water 
                 3 
                 3.75 
                 7.19 
                 16.19 
                 1.44 
               
               
                   
               
               
                   1 DV.1 = 10% of spray volume is contained in droplets of this volume or smaller; DV.5 = 50% of spray volume is contained in droplets of this volume or smaller; DV.9 = 90% of spray volume is contained in droplets of this volume or smaller. 
               
             
          
         
       
     
       EXAMPLE 2 
     Charged Droplet Atomizer 
       [0023]    Flying insects generate an electrical charge as they move through the air. As such, negatively charged particles would be attracted to those regions of the flying insect that have imparted a positive charge. 
         [0024]    Procedures and devices have been described capable of generation of charged droplets. In general, this is conducted by exposing of droplets to a suitable electrical field (Ahn, et al., Biomicrofluidics 3, 044102 (2009); Pilat and Lukas, Air and Waste Manage. Assoc. 54: 3-7 (2004)). Exposing fluids to an electric field is also utilized in electrostatic spray devices and methods (Stark, et al., U.S. Patent Application 2010/0155496 (Jun. 24, 2010)); Imai, et al., U.S. Patent Application 2012/0153055 (Jun. 21, 2012)). 
         [0025]    In one embodiment of the current device, illustrated in  FIG. 2 , fluid from the reservoir ( 1 ) flows through the connection tube ( 3 ) and is discharged into the transducer drum ( 5 ). In the transducer drum ( 5 ), the fluid is subjected to ultrasonic frequency oscillations via one or more ultrasonic transducers ( 9 ). The transducer (s) is electrically connected to a suitable power source ( 17 ) that is capable of generating electrical oscillations of ultrasonic frequency, defined as above 19 kHz. As an example, in one embodiment, the ultrasonic frequency is approximately 0.8 MHz to approximately 1.7 MHz. Power switching, with the power switching transistor, can be arranged as Colpitts oscillator. In a preferred embodiment, oscillation at 1.65 MHz is utilized. 
         [0026]    The ensuing small (5 μm) droplets can then be imparted with a charge. Any number of methods for imparting charge on the droplets is contemplated. However, as an example, illustrated in  FIG. 2 , after creation of the small 5 μm droplets by the transducer, the droplets are forced by the fan ( 7 ) past an electrical field created by electrodes ( 19 ) imparting an electrical charge to the droplets. The charged droplets are then directed into the sprayer tube ( 11 ) and discharged ( 13 ) from the device. Unsorted material can be directed into a recollection reservoir or other collection means for recycling or disposal. 
         [0027]    In another embodiment, charge droplets can be separated based on charge. Any number of separation methods are contemplated. However, as an example, also illustrated in  FIG. 2 , as the droplets move past oppositely charged electrodes ( 21  and  23 ). The deflected droplets are then collected, based on deflection and discharged ( 13 ) via the sprayer tube ( 11 ). 
       EXAMPLE 3 
     Method of Applying Insecticide by Electrostatic Droplets 
       [0028]    In applying insecticide sprays to flying insects, current methods typically entail spraying in the vicinity of the insects and the insects encountering the spray by random collisions with the droplets. Furthermore, since insecticide droplets are typically relatively large, often over 50 μm in diameter, the droplets tend to settle relatively quickly. The rapid settling of insecticide necessitates application of large amounts of material at a height to enable adequate collisions of the insects with the insecticide droplets. The result is that significant amounts of insecticide, which is wasted and not actually encountered by the insect, in order to afford efficacy of the spraying with adequate coverage of area. 
         [0029]    In one embodiment, small, 5 μm diameter droplets, or less, are created with the device described in Example 1. Application of insecticide is then applied to the desired area creating a slow settling fog, since the small droplets will tend to settle to the ground slowly and linger longer in the air. The longer lingering increases the likelihood of collision with the droplets by flying insects. Use of the method would result in the need for less insecticide, with greater insecticide effectiveness. 
         [0030]    In an additional embodiment, an electrical charge can be imparted on the small, i.e., 5 μm or less diameter, droplets, as in Example 2. The charged droplets would linger longer in the air, as a fog, than larger droplets increasing collision of droplets by flying insects. Additionally, the charged droplets will be attracted to the inherent electrical charge on the insects. Use of charged droplets would result in the need for even less insecticide material than if only small droplets were utilized. 
         [0031]    Having described the invention, one of skill in the art will appreciate in the appended claims that many modifications and variations of the present invention are possible in light of the above teachings. It is therefore, to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.