MXPA00004030A - Compressed gas propelled aerosol devices - Google Patents

Abstract

A method of reducing the droplet size of a composition 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 x 10-4 C/kg.

Description

AEROSOL DEVICES WITH COMPRESSED GAS PROPULSION The present invention relates to a method for reducing droplet size in aerosol spray devices which use compressed gas as a propellant, and to an apparatus therefor. An aerosol spray device incorporating a liquefied propulsion agent, 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 in aerosolized form using a liquid propulsive agent (typically at 40 psi) have a diameter in the range between 10 to 60 microns, with a maximum distribution between 30 and 40 microns. 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 resulting aerosol is in the range generally between 30 and 110 microns, with a maximum distribution in the range between 70 and 90 microns. In aerosol spray devices containing a liquid propellant such as butane for example, activation of the aerosol device causes the butane to evaporate instantaneously. As a result, there are two mechanisms to disperse the liquid while being ejected 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 device through the head and into the atmosphere. A second mechanism is the evaporation of the liquid propulsive agent, which by itself causes the dispersion of the liquid or aid in it. The net effect is that the spray emerging from said aerosol device contains liquid droplets of a relatively small size, as indicated above. In contrast, aerosol spray devices which use compressed air as the propellant depend entirely on the mechanical forces acting on the liquid when sprayed from the aerosol device in order to disperse it into droplets. Accordingly, the drops are relatively large in size compared to the size of the drops of an aerosol spray device with a liquid propelling agent. The relatively large droplet sizes produced by aerosol spray device using a compressed gas propulsion agent mean that these aerosol spray devices are not suitable for some applications and aerosol spray device incorporating liquid blowing agent should be used . This is because the large droplet sizes produced by said aerosol spray devices are too wet and provide a relatively poor dispersion of the product being sprayed. We have developed a method to reduce the droplet size of the sprayed drops of aerosol spray device using compressed gas propulsion agent. According to the present invention there is provided a method for reducing the drop size of a product sprayed from an aerosol spray device comprising a compressed gas propulsion agent, said method comprising imparting a unipolar charge to the liquid droplets per double layer charge during spraying of aerosol spray device liquid, the unipolar charge being at a level such that said liquid droplets have a charge to mass ratio of at least ± 1 x 10-4 C / kg . It is preferred that the unipolar charge which is imparted to the liquid droplets be generated only by the interaction between the liquid within the aerosol spray device and the aerosol spray device itself when the liquid is sprayed therefrom. In particular, it is preferred that the manner in which the unipolar charge is imparted to the liquid droplets does not yet partially depend on the connection of the spray device e, n aerosol to any charge inducing device, such as a relatively high voltage source. . With such arrangement, the aerosol spray device is totally autonomous making it suitable for use in industrial, institutional or domestic situations. Preferably, therefore, the charge to mass ratio of at least ± 1 x 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 characteristics of the material of the activator, the size and shape of the activator orifice, the diameter of the supply tube, the characteristics of the valve and the formulation of the composition contained within the aerosol spray device in order to obtain said ratio between load and mass per load double layer imparting the unipolar charge to the drops during the spraying of the liquid drops from the orifice of the aerosol spray device. The liquid drops sprayed by the method of the present invention generally have a diameter in the range between 3 and 110 microns, with a proportion of drops having the diameter in the range between 10 and 50 microns, with a maximum diameter range between 20 and 50 microns. and 40 microns. Preferably, the aerosol spray device is a household aerosol device in the form of a hand held aerosol can. The present invention includes within its scope the apparatuses for spraying a liquid composition capable of forming charged droplets, the apparatus comprising: (1) A receptacle for housing the liquid composition; (2) A composition. liquid contained within the receptacle and including a compressed gas propulsion agent; (3) A spray head for ejecting the composition in the form of spray drops; and (4) a conduit system for feeding the composition from the receptacle to the spray head, wherein the composition is formulated and the apparatus constructed in order to obtain a mass to load ratio of at least ± 1 x 10 ~ 4 C / kg by means of loading by double layer imparting a unipolar charge to the drops during the spray of the drops from the aerosol spray device. The ratio between mass and charge indicated above implies a considerable increase in the charge imparted to the droplets, as compared to the known position with aerosol spray devices. For example, the charge imparted to liquid drops sprayed from standard aerosol spray devices, which use liquid propellants, provides a mass to charge ratio of only on the order of ± 1 x 10 ~ 8 C / kg. It is expected that aerosol spray devices with liquid blowing agent give higher mass to charge ratios than would be obtained with a conventional aerosol spray device with compressed gas propulsion agent. Typically, aerosol products driven by compressed gas will have a mass to load ratio of ± 5 x 10 ~ 8 C / kg to 1 x 10 ~ 6 C / kgf. The unipolar load which is imparted to the drops during spraying has two effects. Since all the drops have the same charge polarity, they are repelled one from the other. Therefore, there is no or little coalescence of the drops and, in contrast, they tend to separate more compared to no-load drops. Additionally, if the forces of repulsion of the charge within the drops is greater than the surface tension force of the drops, the drops are broken into a plurality of smaller drops (exceeding the Rayleigh limit). This process continues until the two opposing forces are balanced or the drop has evaporated. By means of the present invention, aerosol spray devices can be produced by using compressed gas propulsion agent which provide considerably lower droplet diameters and therefore allow aerosol spray devices to be used in previously applied applications. not available for said devices with compressed gas propulsion agent. For example, compressed gas propulsion agents can be used for anti-perspirant, hair fixatives, insecticides, agricultural products, environment refreshers, waxes and polishes, oven cleaners, starches and fabric finishes, foot care products , institutional and for industrial and professional products. In general, the liquid composition which is sprayed into the air using an aerosol spray device is a mixture of water and hydrocarbons, or emulsion, or a liquid which is converted into an emulsion by stirring the aerosol spray device before it is used. , or during the spraying process. While it is known that all aerosols have a negative or positive charge as a result of double-layer loading, or because of the fragmentation of the drops of sprayed liquid, the charge imparted to the drops of liquid sprayed from standard devices is only in the order of ± 1 x 10 ~ 8 and 1 x 10"5 C / kg The invention depends on the combination of various characteristics of an aerosol spray device to increase the charge of the liquid when sprayed from the aerosol spray device. A typical aerosol spray device comprises: 1. An aerosol can containing the composition to be sprayed from the device and a compressed gas propulsion agent 2. A tube extending into the can, the upper end of the tube is connected to a valve 3. An actuator located on the valve, which is capable of being depressed in order to operate the valve, and 4. An insert provided on the actuator comprising an orifice from which the composition is sprayed. A preferred aerosol spray device for use in the present invention is described in GB patent 9722611.2 filed on October 28, 1997. It is possible to impart larger loads to the liquid drops by selecting the aspects of the aerosol device including the material, form and dimensions of the actuator, the actuator insert, the valve and the tube and the characteristics of the liquid which is to be sprayed, so that the required level of charge is generated as the liquid is dispersed in the form of droplets. Several characteristics of the on-spray system increase the double layer loading and load exchange between the liquid formulation and the surfaces of the aerosol system. These increases are obtained by factors which increase the turbulence of the flow through the system and increase the frequency and speed of contact between the liquid and the interior surface of the container, valve and actuator system. By way of example, the characteristics of the actuator can be improved to increase the load levels of the liquid sprayed from the container. A smaller orifice in the actuator insert, a size of 0.45 mm or less, increases the charge levels of the liquid sprayed through the actuator. The selection of the material for the actuator can also increase the charge levels of the sprayed liquid from the device with materials such as nylon, polyester, acetal, PVC and polypropylene tending to increase the load levels. The geometry of the hole in the insert can be improved to increase the load levels in the liquid when being sprayed through the actuator. The inserts that promote the mechanical dispersion of the liquid provide better load. The actuator insert of the spray device may be formed of a conducting, insulating, semiconductor or static dissipating material.

The characteristics of the tube can be improved to increase the loading levels of the sprayed liquid from the container. A narrow tube, for example, with an inner diameter of approximately 1.27 mm, increases the liquid loading levels, and the material of the tube can also be changed to increase the load. The characteristics of the valve can be selected which increase the ratio between mass and load of the liquid product when being sprayed from the container. A small tail hole on the cover, approximately 0.65 mm increases the load to mass ratio during spraying. A small number of holes in the tube, for example 2 x 0.5 mm, also increases the load production during spraying. Changes in the product formula also affect the load levels. A formulation containing a mixture of hydrocarbons and water, or an emulsion of a non-miscible hydrocarbon and water, will carry a higher charge to mass ratio when sprayed from the aerosol device than formulations of water alone or hydrocarbon alone. It is preferred that a composition for use in the present invention comprises an oil phase, an aqueous phase, a surfactant and a compressed gas propelling agent.

Preferably the oil phase includes a Cg-C12 hydrocarbon, which is preferably present in the composition in an amount between 2 and 10% w / w. Preferably the surfactant is glyceryl oleate or a polyglycerol oleate, which is preferably present in the composition in an amount between 0.1 and 1.0% w / w. Droplets of liquid sprayed from the aerosol spray device will have diameters in the range between 3 and 110 microns, preferably a proportion of the drops will have a diameter in the range between 10 to 50 microns with a maximum of drops of approximately 40 microns . The liquid which is sprayed from the aerosol spray device may contain a predetermined amount of a particulate material, for example, calcined silica, or a predetermined amount of a volatile solid material, such as menthol or naphthalene. A "can for the aerosol spray device according to the invention is formed of aluminum, or sheet of can with lacquer or without lacquer, or the like.The insert of the activator can be formed, for example, of acetal resin. The lateral opening of the valve plunger for said device may preferably be in the form of two openings of diameters of 0.51 mm The present invention will be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic section through an aerosol spray apparatus according to the invention, Figure 2 is a diagrammatic section through the valve assembly of the apparatus of Figure 1, Figure 3 is a section through cut through the actuator insert of the assembly shown in Figure 2, Figure 4 shows the configuration of the interior of the spray head shown in Figure 3 when viewed in the direction A, Figure 5 m shows the configuration of the turbulence chamber of the spray head shown in the Figure 3 when seen at address B; and Figure 6 illustrates the results showing the efficacy of the present invention. With reference to Figures 1 and 2, an aerosol spray device according to the invention is shown. It comprises a can 1, formed of aluminum or tin foil with lacquer or without lacquer or the like in a conventional manner, defining a container 2 for a liquid 3 that has a conductivity such that the liquid droplets can carry an appropriate electrostatic charge. Also located in the can is a gas under pressure which is capable of forcing the liquid 3 out of the can 1 by means of a conductive system comprising a tube 4 and a valve assembly and actuator 5. The tube 4 includes one end 6 which ends in the peripheral part of the bottom of the can 1 and another end 7 which is connected to the tail part, of the valve assembly 9 fixed to an opening in the upper part of the can and includes a lower portion 10 defining a hole 11 in the tailpiece in which the end 7 of the tube 4 is connected. The tailpiece includes a perforation 12 of a relatively narrow diameter in the lower portion 11 and a relatively larger diameter in its upper portion 13. The valve assembly also includes a tube 14 mounted within the bore 12 of the tailpiece and arranged to be displaced axially within the bore 12 against the action of the spring 15. The valve plunger 14 includes an integral core 16 having one or more side openings (piston bores) 17 (see Figure 2). The valve assembly includes an actuator 18 having a central core 19 which accommodates the plunger of the valve 14 so that the core 16 of the piston tube 14 is in communication with the core 19 of the actuator. A passage 20 in the actuator extending perpendicularly to the web 19 joins the web 19 with a recess including a post 21 on which a spray head in the form of an insert 22 is mounted including a core 23 which is in communication with the passage 20. A ring 24 of elastomeric material is provided between the outer surface of the plunger of the valve 14 and, normally, this sealing ring closes the side opening 17 in the plunger of the valve 14. The construction of the valve assembly is such that when the actuator 18 is manually depressed, it pushes the valve 14 down against the action of the spring 15 as shown in Figure 2 so that the seal ring 24 stops closing the side opening 17. In this position, a track for the receptacle 2 is provided to the core 23 of the spray head so that the liquid can be forced, under gas pressure in the can, towards the spray head by means of the system of duct comprising the tube 4, the tail piece 19 and the passage 20. Preferably the side opening 17 joining the core of the plunger of the valve 16 to the core 12 of the tail piece, is in the form of two holes each having a diameter of not less than 0.51 mm to improve the generation of electrostatic charge. In addition, the diameter of the tube 4 is preferably as small as possible, for example, 1.2 mm, in order to increase the load imparted to the liquid. Also, the generation of charge is improved if the diameter of the hole 11 of the tailpiece is as small as possible, eg, not more than 0.64 mm. With reference to Figure 3, a section through the actuator of the apparatus of Figures 1 and 2 is shown on a larger scale. For simplicity, the core 23 is shown as a single cylindrical opening in this Figure. However, the core 23 preferably has the configuration, for example, as shown in Figure 4. The openings of the core 23 are indicated by the reference number 31 and the portions defining the opening of the core are indicated by the number reference 30. The total peripheral length of the portions defining the opening at the outlet of the core is Andicated by L (in mm) and a_ is the total area of the opening at the outlet of the core (in mm2) and the values for L and a_ are indicated in Figure 4. L / a is greater than 8 and it has been found that this condition is particularly conducive to load development because it means an increase in the contact area between the actuator insert and the liquid that passes through it.

Many different configurations can be adopted in order to produce a high ratio L / a without the cutting area a_ being reduced to a value which would allow low liquid flow rates. For this reason, for example it is possible to use configurations of the core of the insert of the actuator (i) wherein the outlet of the core comprises a plurality of segment-type openings (with or without a central opening); (ii) wherein the opening together forms an outlet in the form of a mesh or grid; (iv) where the exit is generally cross-shaped; (v) where the opening together defines an outlet in the form of concentric rings; and combinations of these configurations. Particularly preferred are actuator insert configurations wherein a tongue-shaped portion protrudes into the liquid flow and can therefore vibrate. This vibrating property can produce a turbulent flow and improve the electrostatic charge separation of the double layer, allowing more charge to move within the bulk of the liquid. With reference to Figure 5, a plan view of a possible configuration of the turbulence chamber 35 of the insert of the actuator 22 is shown. The turbulence chamber includes four side channels 37 that surround the core 23. In use, the fluid driven from the container 2 by the pressurized gas travels along the passage 20 and strikes the normal channels 36 to the longitudinal axis of the channels. The arrangement of the channels is such that the liquid tends to follow a circular motion before entering the central area 37 and from there to the core 23. As a consequence, the liquid is subed to a substantial turbulence which improves the electrostatic charge in the liquid The present invention will now be described, by way of example, with reference to Figure 6 of the accompanying drawings which show the size distribution of the particles using different aerosol compositions. EXAMPLE The aerosol compositions used in this example were based on the Antibacterial Spray for Dettox rooms manufactured by Reckitt and Colman Products Limited. Three aerosol systems were compared, as follows: (A) Dettox with liquid butane gas blowing agent in a standard aerosol can. (B) Dettox with 130 psi air propulsion agent in a standard aerosol can. (C) Dettox with 130 psi compressed air blowing agent in a standard aerosol can. The level of charge of the droplets eed from this spray can was artificially increased to a mass to load ratio of approximately -1 x 10 ~ 6 C / kg by applying a load of -10 kv to the can seam from a source of high voltage power. The particle sizes of the liquid sprays emitted by the aerosol spray devices were measured using a Malvern particle size analyzer located 50 cm from the aerosol can. The resulting particle size distributions measured are shown in Figure 6. It can be seen that the standard aerosol spray device using liquid butane gas blowing agent produces a particle size distribution in the range between 10 and 60 microns. , with a maximum between 30 and 40 microns. The distribution of particle diameters for the standard system using compressed air blowing agent is increased to a particle diameter in a range between 30 and 100 microns with a maximum between 70 and 90 microns. In contrast, the use of a system involving a compressed air propulsion agent and a device that imparts a larger unipolar load to the liquid droplets results in a distribution of particle diameters between 3 and 110 microns, with most particles with a diameter between 10 and 50 microns with a maximum range between 20 and 30 microns. It has been found that, when using compressed air blowing agent that imparts a relatively high load to liquid droplets, an aerosol spray device can be used in all previously known aerosol applications, compressed air devices remain excluded from some applications due to the relatively large size of the droplets resulting in an aerosol spray considered to be excessively moist and with an excessively poor dispersion.

Claims (1)

1. CLAIMS A method for reducing the drop size of a composition sprayed from an aerosol spray device comprising a compressed gas propulsion agent, said method comprises imparting a unipolar charge to the liquid droplets by means of double layer loading during the spraying of the drops of liquid from the aerosol spray device, the unipolar charge being of a level such that said drops have a mass to charge ratio of at least ± 1 x 10 ~ 4 C / kg. A method according to claim 1 wherein the aerosol spray device is a household aerosol device. A method according to claim 1 or according to claim 2 wherein the product contained in the aerosol spray device is an emulsion. A method according to any of the preceding claims wherein the drops of liquid have a diameter in the range between 3 and 110 microns with a proportion of the drops having a diameter in the range between 10 and 50 microns. A method according to claim 4 wherein the drops have a maximum diameter range between 20 and 40 microns. A method according to any of the preceding claims wherein the ratio between the load and the mass of at least ± 1 x 10-4 C / kg is imparted to the drops of liquid as a result of the use of an aerosol spray device with at least one of the characteristics of the actuator material, the size and shape of the actuator orifice, the diameter of the tube, the characteristics of the valve and the formulation of the composition contained within the aerosol spray device being selected in order to to obtain said relation between charge and droplet mass by double layer loading by imparting the unipolar charge to the drops during the spraying of the liquid droplets from the orifice of the aerosol spray device. A method according to any of the preceding claims wherein the aerosol spray device contains a composition comprising an oil phase, an aqueous phase, a surfactant and a compressed gas propulsion agent. A method according to claim 7 wherein the oil phase includes a Cg-Cl 2 hydrocarbon. 9. A method according to claim 8 wherein the Cg-C 2 hydrocarbon is present in the composition in an amount between 2 and 3. and 10% weight / weight. 10. A method according to claims 7 to 9 wherein the surfactant is glyceryl oleate or a polyglycerol oleate. 11. A method according to claims 7 to 10 wherein the -surfactant is present in the composition in an amount between 0.1 and 1.0% w / w. 12. An apparatus for spraying a liquid composition capable of forming charged droplets, the apparatus comprising: (1) a receptacle for accommodating the liquid composition; (2) a liquid composition contained within the receptacle and including a compressed gas propulsion agent; (3) a spray head for ejecting the composition in the form of dew drops; and (4) a system of conduits for feeding the composition from the receptacle to the spray head; wherein the composition is formulated and the apparatus is constructed in order to obtain a load to mass ratio of at least ± 1 x 10-4 C / kg by means of double-layer loading imparting a unipolar charge to the drops during spraying of the drops from the aerosol spray device. A method for reducing the size of the drops in an aerosol spray device with compressed gas, in accordance with claim 1 substantially as described herein with reference to any of the Examples. An apparatus for spraying a liquid composition capable of forming charged droplets according to claim 12, the apparatus being substantially as described herein in Figures 1 to 5 of the accompanying drawings.