Fluid sprinkling – spraying – and diffusing – Processes – Including electrostatic charging
Reexamination Certificate
2000-03-07
2001-03-13
Kashnikow, Andres (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Including electrostatic charging
C239S690000, C239S708000, C239S337000, C043S132100
Reexamination Certificate
active
06199766
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for killing flying insects by spraying insecticide into the air in which the insects are flying, and in particular to methods of improving the targeting of the insects with the insecticide.
The efficiency of insecticide sprays in killing flying insects depends, in part, upon how much of the insecticide contacts the insects which are to be killed. Current methods of applying the insecticide rely on the mechanical interaction between the sprayed droplets of insecticide and each flying insect. Aerosol insecticide sprays may be dispersed into areas through which insects may fly and thus encounter the droplets of insecticide, or aerosol insecticide sprays may be aimed at specific target insects. Due to the high density of insecticide droplets in the plume produced during spraying, there is a high probability that contact will occur between the insects and the droplets. However, when insects are in flight the air disturbances around their bodies caused by the beating of wings may actually push droplets away. The probability of a flying insect coming into contact with one or more aerosol insecticide droplets is thus largely determined by mechanical forces, whilst the probability of knock-down or kill is subsequently determined by the concentration and toxicity of the active ingredient in the insecticide being used.
Spraying apparatus for producing a spray of liquid droplets is well known. For example, such apparatus is known in the domestic environment for producing sprays of droplets of insecticides or polish or air freshening compositions. Generally, such apparatus includes a reservoir for accommodating the liquid composition to be sprayed, a spraying head including a bore through which the composition is expelled in the form of a spray of droplets, and a conduit system whereby the composition can pass from the reservoir to the spraying head. The apparatus may preferably be in the form of an aerosol in which case it includes gas under pressure, possibly in a liquid state, which expels the liquid composition (to be sprayed) from the reservoir to the spraying head and then out of the spraying head in the form of a spray of droplets.
Generally, the droplets leaving the spraying head have a small electrostatic charge created by electron transfer between the liquid and the walls of the apparatus. We have realised that it is necessary to increase the level of charge on the droplets significantly to enable electrostatic attraction to insects and to other objects to occur, thereby enabling enhanced targeting by the spray and also allowing greater dispersion of the droplets in the air.
Further, we have found that components of the apparatus in contact with the liquid have the ability to influence the charge given to the liquid as it is being sprayed. More particularly it has been found that the charge on the droplets increases with an increase in the contact area between the liquid and the bore-defining portions of the spraying head.
SUMMARY AND DISCLOSURE OF THE INVENTION
Accordingly, in one aspect the present invention provides a method of killing flying insects which method comprises spraying into the air in which the insects are flying liquid droplets of an insecticidal composition, a unipolar charge being imparted to the said liquid droplets by double layer charging and charge separation during spraying, the unipolar charge being at a level such that the said droplets have a charge to mass ratio of at least +/−1×10
−4
C/kg
The effect of the charging of the droplets will be to generate an electrical field resulting in the diffusion of the droplets more widely within the space into which they are sprayed.
Flying insects are usually electrically isolated from their surroundings and may be at a potential equal to their surroundings. However, some insects are electrically charged so that they may be at a potential different from their surroundings. In either situation, an isolated insect within a cloud of electrically charged liquid droplets is likely to cause a distortion in the configuration of the electrical field generated by the droplets so that the attraction of the droplets onto each insect will be improved. This amounts to the targeting of each insect.
This improvement in the interaction between the charged droplets and the insects will be due to the combined effect of the additional diffusion forces generated within the charged cloud of droplets by the electrical field leading to modification of the trajectory of each droplet so that each droplet is directed to an insect. The insecticide is attracted to the whole surface of each insect. This improves the targeting of the insecticidal droplets onto the insects.
Insects which can suitably be killed according to the present invention include house flies, mosquitoes, and wasps.
The liquid droplets have a charge to mass ratio of at least +/−1×10
−4
C/kg. The higher the charge to mass ratio of the liquid droplets the more pronounced the interaction with the insects.
The liquid insecticidal composition which is sprayed into the air is preferably a water and hydrocarbon mixture, an emulsion, or a liquid which is converted into an emulsion by shaking the spraying device before use, or during the spraying process. The insecticidal composition is preferably sprayed from an aerosol spray device which is mechanically operated under pressure. More preferably the spray device is a domestic aerosol spray can which is of a size suitable to be used easily with one hand.
Whilst all liquid aerosols are known to carry a net negative or positive charge as a result of double layer charging, or the fragmentation of liquid droplets, the charge imparted to droplets of liquids sprayed from standard aerosol spray devices is such as to give a charge to mass ratio of only of the order of +/−1×10
−8
to 1×10
−5
C/kg.
The invention further relies in one embodiment thereof on combining various characteristics of the spray device in order to maximise the charging of the liquid droplets as they are sprayed from the aerosol spray device. The optimum combination varies for each formulation which is to be sprayed from the device.
Accordingly, in a further aspect the present invention provides a spray device which is capable of imparting by double layer charging and charge separation to liquid droplets of a composition sprayed therefrom a unipolar charge resulting in a charge to mass ratio of at least +/−1×10
−4
C/kg, which spray device comprises:
(i) a reservoir for accommodating the liquid composition,
(ii) a spraying head through which the liquid is expelled in the form of a spray of droplets, and
(iii) a conduit system for feeding the composition from the reservoir to the spraying head wherein
a) the spraying head has a bore through which the liquid is expelled from the apparatus, the bore having an L/a ratio of at least 10, more preferably at least 12, where L is the length of the periphery defining the bore outlet in mm and a is the cross sectional area of the bore outlet in mm
2
; and
b) the apparatus is constructed such that the droplets are expelled from the spraying head at a flow rate of at least 0.5 grams per second and have a charge/mass ratio of at least +/−1×10
−4
C/kg.
The spraying head is preferably in the form of an insert in an actuator through which the liquid is expelled in the form of a spray of droplets.
For the avoidance of doubt, the bore outlet is the end of the bore through which the liquid is expelled in the form of a spray from the apparatus, and may also be termed an orifice.
The electrostatic charge on the droplets may be either a positive charge or a negative charge.
Whilst it is known that reducing the cross sectional area of a circular orifice through which a liquid is sprayed will increase the charge on the liquid sprayed through the orifice, in order to achieve the charge required by the present invention it would be nece
Fox Rodney Thomas
Harrison Neale Mark
Hughes John Farrell
Whitmore Lindsey Faye
Fish & Richardson P.C.
Kashnikow Andres
Nguyen Dinh Q.
University of Southampton
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