Patent Application
20090084870
The present invention relates to systems which deliver liquids and more particularly for systems which deliver liquids under pressure.
Spray systems, particularly pressurized spray systems, are well-known in the art. Such spray systems often utilize a metal can, plastic container or other package charged with a propellant. The propellant pressurizes the contents of the spray system to a pressure greater than atmospheric. Upon release of the propellant pressurizing the contents of the package, the pressure differential causes discharge of the contents to the atmosphere or ambient surroundings.
Typical propellants include compressed gasses, such as nitrogen, or hydrocarbon such as butane. One characteristic common to both compressed gas and hydrocarbon propellants is that the pressure decays with repeated uses, as illustrated. Such pressure decay may transmogrify the delivery characteristics of the contents of the package. However, the pressure decay of a compressed gas system is typically more noticeable throughout the life of the system. In contrast, hydrocarbon systems tend to regenerate, providing a generally more consistent pressure throughout much of the system life. Thus, only compressed gas systems are considered below.
Typical products contained in such packages include cleaners, furniture polish, perfumes, room deodorizers, spray paint, insecticides, lubricants, hair spray, medicine, etc. Each of these products has a desirable range of delivery characteristics, such as flow rate, cone angle and particle size. The flow rate is the amount of product delivered per unit time. The cone angle is the dispersion of the product over a particular area at a particular distance. The particle size is the distribution of average droplet size upon contacting the target surface or ambient at a predetermined distance from the nozzle orifice.
However, over time, the pressure decay of the propellant causes each of these delivery characteristics to change. The user may be able to compensate for some of these changes. For example, as the delivery rate decreases, the user may be able to simply dispense for a longer period of time. Likewise, as the cone angle decreases the consumer may be able to simply sweep the product over a larger area during dispensing or adjust the distance to the target surface.
However, as particle size increases during the pressure decay, the user is not able to compensate. An increase in particle size may be undesirable. For example, as particle size of a hairspray increases, the polymer may become too sticky. As particle size of a furniture polish increases, the polish may smear upon application. Particle size may also affect perfume release or suspension.
Accordingly, there is a need in the art to decouple couple particle size from the number of uses over the life of a product dispensed from a spray system. Some attempts have already been made in the art. For example EP 0,479,796 B1 issued to Pool et al. suggests that having a flow area ratio between the valve port and actuator outlet of at least 2:1 provides advantageous flow characteristics. However, some ratios less than 2:1 have been found to work well while some ratios greater than 2:1 have been found unsuitable. Accordingly, another approach is necessary.
A package for dispensing contents therefrom over a predetermined pressure range and comprising a reservoir for containing product, a valve stem being movable between a closed first position and an open second position, and having an upstream flow restriction therein, one or more tangentials for receiving product from said valve stem, said tangentials having a combined tangential flow area, wherein the ratio of the combined flow area of the tangentials to the upstream flow restriction ranges from 0.8-7.5 and a nozzle for dispensing contents from said container to the ambient.
In
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The contents to be dispensed are contained in a reservoir 12 and may enter the flow path through a dip tube 14. The dip tube 14 may be of constant or variable cross section. If the dip tube 14 has a variable cross section, the portion of the dip tube 14 having the greatest flow restriction (smallest flow area/hydraulic radius) is considered. If the dip tube 14 has a constant cross-section, the area of the dip tube 14 at the inlet is considered.
The contents to be dispensed exit the dip tube 14 and enter a headspace. The headspace is generally a relatively large portion of the flow path and does not typically provide significant flow restriction. From the headspace the contents to be dispensed enter a valve stem 20. The valve stem 20 is part of a movable assembly, which starts/stops the dispensing process upon moving from a first position to a second position. Typically, the user depresses the valve stem 20 to an open position to begin dispensing. The user then releases the valve stem 20, allowing it to return to a closed position in order to stop dispensing. The valve stem 20 may be spring-loaded, or otherwise biased, to allow it to return from the open position to the closed position. The valve stem may be actuated by a push button or trigger 21.
The dispensing system may have a longitudinal axis. Often, the valve stem 20 is parallel, and in a degenerate case, coincident, the longitudinal axis of the dispensing system. The contents to be dispensed may enter the valve stem 20, transverse, and typically radial to, the longitudinal axis. Entrance to the valve stem 20 may be through one, two, or more valve ports 22. If the valve stem 20 has multiple valve ports 22, the combined flow area of all valve ports 22 is considered. A common commercially available system has two equally sized valve ports 22 spaced 180 degrees apart.
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The swirl chamber 26 provides for intermixing of the product to be dispensed and air. Such intermixing helps to atomize the product prior to discharge. The swirl chamber 26 is the portion of the flow path disposed immediately before the outlet nozzle 30. The swirl chamber 26 does not present a significant restriction to the flow path.
Turbulent conditions within the swirl chamber 26 draw in ambient air, which intermix with the contents to be dispensed. The contents are finally dispensed to the atmosphere from an exit orifice in the spray nozzle 30. The exit orifice presents yet another, and final, flow restriction in the flow path.
The spray system according to the present invention may have a product volume of at least 30, 60 or 90 ml, but less than 1000, 800 or 600 ml. The propellent may provide a gage pressure of at least 1, 2, or 3 kg/square centimeters, and less than 12, 10 or 8 kg/square centimeters. Of course one of ordinary skill will recognize that the system of the present invention may have an initial pressure greater than that claimed herein below, and pass through the pressure range claimed herein below with efficacious results throughout the claimed pressure range.
For typical consumer product contents sprayed in ordinary household use, the contents may be sprayed in a generally circular pattern having a diameter of at least 6, 8 or 10 cm and less than 35, 30 or 25 cm. For typical consumer product contents sprayed in ordinary household use, the contents may be sprayed in a generally circular pattern having a cone angle of at least 20, 25 or 30 degrees and less than 150, 120, 90, 70 or 50 degrees.
The typical consumer product may be discharged at a spray rate of at least 1, 2 or 3 grams per second, and less than 25, 20 or 15 grams per second. The spray system of the present invention may be used with a product comprising an oil-in-water emulsion, having a density of approximately one and a total solids of about seven percent, and approximately seven percent emulsified polydimethelsiloxane oils. The product may have a flat viscosity of about 20 Pa·s until a shear of about 0.3 inverse seconds and a shear thinning behavior for all increasing shear rates above 0.3 inverse seconds, passing through 10 pa-s at a shear rate of 1 inverse second, and 0.5 Pa·s at a shear rate of 30 inverse seconds. DC 200, available from Dow Coming, of Midland Mich., has been found suitable for the spray systems of the present invention.
The product contents may have a particle size distribution, which yields a Sautem mean diameter of at least 40, 45, 50, 55 or 60 microns and less than 100, 90, 80 or 70 microns. Particle size may be measured using a spray particle analyzer available from Malvern Instruments, Ltd. of Worcestershire, United Kingdom.
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The upstream flow restriction is defined as the smallest flow area the contents must pass through prior to the tangentials 24 and nozzle 30 to be discharged from the package 10 to the ambient. If a portion of the flow path has parallel channels, the cumulative area of all parallel channels is considered in determining the area, and hence upstream flow restriction, of the flow path. For a typical system according to the present invention, the upstream flow restriction may occur at the valve ports 22, although the invention is not so limited. For the embodiments described herein, the area providing the upstream flow restriction is circular in shape and is provided by two equally sized flow areas taken in parallel, although the invention is not so limited.
One of ordinary skill will recognize that flow resistance may be provided independent of area. For example, flow resistance may be provided using bends, surface finish, hydraulic radius, and other physical parameters which affect boundary layer, etc
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As the area of the exit orifice of the spray nozzle 30 increases, the tangential flow area may likewise increase. This proportional relationship provides a flow area ratio between the maximum flow restriction area and the tangential flow area of at least 0.5, 1.0 or 1.5 and less than 8, 7 or 6. Surprisingly, it has been found the ratio of flow areas between the tangentials 24 and the spray nozzle 30 has more effect on particle size than other flow path characteristics described in the literature.
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For the flow restriction of 0.006 square millimeters, good results, i.e. differences in particle size of less than 5 microns appear to occur throughout the range of flow area ratios ranging from 0.8-2.5 for pressures ranging from 8.8 to 5.6 kg/square centimeter. Greater differences in particle size occur throughout the same range of flow area ratios for pressures less than 5.6 kg/square centimeter.
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For the flow restriction of 0.010 square millimeters, the best results appear to occur at flow area ratios less than 2.0. Such results are qualitatively better at relatively greater pressures.
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For the flow area restriction of 0.016 square millimeters, the best results appear to be obtained at flow area ratios less than 2.5 and from about 3.5 to 4.3. Such results are qualitatively better at relatively lower pressures.
A difference in particle size of approximately 10 microns or less, and particularly approximately 5 microns or less is considered over an operative pressure range is considered to be relatively constant. The foregoing data, which illustrate a relatively constant particle size are shown in Table 1 below. Table 1 shows the upstream flow restriction in square millimeters for various flow area ratios of the area of the upstream flow restriction to the area of the tangentials 24 over a pressure range from 8.8-2.3 kg/square centimeters and useable to obtain a particle size difference of approximately 5 microns or less over such pressure range. Table 2 illustrates the same data for a particle size difference ranging from approximately 5-10 microns.
Thus, it appears that for many applications requiring only a 10 micron tolerance, a upstream flow restriction of 0.016, coupled with a flow area ratio of 2.3-7.5 at pressures from 5.6-2.3 kg/square centimeter and ranging from 3.0-7.5 for pressures of 8.8-5.6 kg/sq centimeter is suitable. If a smaller upstream flow restriction of 0.010 square millimeters is selected, this geometry would be usable with a flow area ratio of 1.5-4.4. If the application required a 5 micron tolerance, any of the entries in Table 1 would be suitable.
