Fluid sprinkling – spraying – and diffusing – Processes – Including electrostatic charging
Reexamination Certificate
2000-06-28
2001-08-28
Morris, Lesley D. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Processes
Including electrostatic charging
C239S337000, C239S493000, C239S690000, C239S708000
Reexamination Certificate
active
06279834
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to method of reducing the droplet size in aerosol spray devices which use a compressed gas propellant, and to an apparatus therefor.
An aerosol spray device incorporating a liquefied propellant, such as liquid butane produces an aerosol in which the liquid droplets are of relatively small size. For example, various known products which are produced as an aerosol spray using a liquefied propellant such as liquid butane (typically at 40 psi) having a diameter in the range of from 10 to 60 micrometers, with a peak distribution at around 30 to 40 micrometers. In comparison, if the liquid butane in such products is replaced by compressed gas at a pressure of 130 psi, the diameter range of the liquid droplets in the resultant aerosol spray is generally in the range of from 30 to 110 micrometers, with a peak distribution in the range of from 70 to 90 micrometers.
In aerosol spray devices which contain a liquefied propellant, such as butane the activation of the aerosol device causes the butane to evaporate instantly. As a result there are two mechanisms for the breaking up of the liquid while it is being expelled from the aerosol device. The first mechanism is the application of mechanical forces which act on the liquid as it is forced out of the body of the aerosol spray device through the spray head and into the atmosphere. The second mechanism is the evaporation of the liquid propellant, which itself causes or assists in the break-up of the liquid. The net effect is that the spray emerging from such an aerosol device contains liquid droplets of a relatively small size, as discussed above.
In contrast aerosol spray devices which use compressed air as the propellant rely entirely on the mechanical forces acting upon the liquid as it is sprayed from the aerosol device in order to break it up into droplets. Accordingly, the droplets are of relatively large diameter as compared to the size of the droplets from an aerosol spray device with a liquid propellant.
The relatively large droplet sizes produced by aerosol spray devices using a compressed gas propellant means that these aerosol spray devices are not suitable for some applications and aerosol spray devices incorporated liquefied propellants must be used. This is because the large droplet sizes produced by such aerosol spray devices are too wet and give a relatively poor dispersion of the product being sprayed.
We have now developed a method of reducing the droplet size of droplets sprayed from aerosol spray devices using a compressed gas propellant.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of reducing the droplet size of a product sprayed from an aerosol spray device comprising a compressed gas propellant, which method comprises imparting a unipolar charge to the liquid droplets by double layer charging during the spraying of the liquid droplets from the aerosol spray device, 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.
It is preferred that the unipolar charge which is imparted to the liquid droplets is generated solely by the interaction between the liquid within the aerosol spray device and the spray device itself as the liquid is sprayed therefrom. In particular, it is preferred that the manner in which a unipolar charge is imparted to the liquid droplets does not rely even partly upon the connection of the aerosol spray device to any external charge inducing device, such as a source of relatively high voltage. With such an arrangement, the aerosol spray device is entirely self-contained making it suitable for use both in industrial, institutional and domestic situations. Preferably, therefore the charge to mass ratio of at least +/−1×10
−4
C/kg is imparted to the liquid droplets as a result of the use of an aerosol spray device with at least one of the features of the material of the actuator, the size and shape of the orifice of the actuator, the diameter of the dip tube, the characteristics of the valve and the formulation of the composition contained within the aerosol spray device being chosen in order to achieve the said droplet charge to mass ratio by double layer charging imparting the unipolar charge to the droplets during the actual spraying of the liquid droplets from the orifice of the aerosol spray device.
The liquid droplets sprayed by the method of the present invention generally have a diameter range of from 3 to 110 micrometers, with a proportion of the droplets having a diameter in the range of from 10 to 50 micrometers, with a peak diameter range of from 20 to 40 micrometers.
Preferably, the aerosol spray device is a domestic aerosol spray device in the form of a hand-held aerosol can.
The present invention includes within its scope apparatus for spraying a liquid composition capable of forming charged droplets, the apparatus comprising:
(1) a reservoir for accommodating the liquid composition;
(2) a liquid composition contained within the reservoir and including a compressed gas propellant;
(3) a spray head for expelling the composition in the form of a spray of droplets; and
(4) a conduit system for feeding the composition from the reservoir to the spray head,
wherein the composition is formulated and the apparatus is constructed in order to achieve a charge to mass ratio of at least +/−1×10
−4
C/kg by double layer charging imparting a unipolar charge to the droplets during the spraying of the droplets from the aerosol spray device.
DETAILED DISCLOSURE OF THE INVENTION
The charge to mass ratio stated above implies a considerable increase in charge imparted to the droplets, compared with the position with known aerosol spray devices. For example, the charge imparted to the droplets of liquids sprayed from standard aerosol spray devices, which use liquefied propellants, provides a charge to mass ratio only of the order of +/−1×10
−8
to 1×10
−5
C/kg. Aerosol spray devices with liquefied propellants would be expected to give higher charge to mass ratios than would be obtained with a “conventional”, compressed gas propellant aerosol spray device. Typically, compressed gas driven aerosol products will have a charge to mass ratio of +/−5×10
−8
to 1×10
−6
C/Kg.
The unipolar charge which is imparted to the droplets during spraying has two effects. Since all of the droplets have the same polarity charge, they are repelled from one another. Accordingly, there is little or no coalescence of the droplets and, in contrast, they tend to spread out to a great extent as compared to uncharged droplets. In addition, if the repulsive forces from the charge within the droplets is greater than the surface tension force of the droplets, the droplets are caused to fragment into a plurality of smaller droplets (exceeding the Rayleigh limit). This process continues until either the two opposing forces are equalised or the droplet has evaporated.
By means of the present invention, aerosol spray devices may be produced making use of compressed gas propellant which give considerably reduced droplet diameters and therefore allow the aerosol spray devices to be used in applications previously not available for such compressed gas propelled devices.
For example, compressed gas propellants may be used for antiperspirants, hair sprays, insecticides, horticultural products, air fresheners, waxes and polishes, oven cleaners, starches and fabric finishes, shoe and leather care products, glass cleaners and various other household, institutional, professional and industrial products.
In general the liquid composition which is sprayed into the air using the aerosol spray device is a water and hydrocarbon mixture, or emulsion, or a liquid which is converted into an emulsion by shaking the spraying device before use, or during the spraying process.
Whilst all liquid aerosols are known to carry a net negative or positive charg
Fox Rodney Thomas
Harrison Neale Mark
Hughes John Farrell
Whitmore Lindsey Faye
Fish & Richardson P.C.
Morris Lesley D.
Reckitt & Colman Products Limited
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