Abstract:
An aerosol tip mechanism for an aerosol-type dispenser for dispensing liquid content has a flexible outer shell, a rigid cap portion composed of lower and upper portions, and a rigid nozzle portion having a rigid shaft received within the outlet portion of the flexible outer shell. The rigid shaft interfaces the outlet portion of the outer shell, forming a first normally-closed one-way valve. The lower and upper portions of the rigid cap portion form boots adapted to receive an outlet portion of the flexible outer shell, the boots thereby constraining a lateral motion of the outlet portion of the outer shell, and symmetrically centering the outlet portion around the rigid shaft of the nozzle. The rigid nozzle portion includes a plurality of liquid channels for delivering liquid from a reservoir to a swirling chamber defined within the rigid cap portion, which liquid channels are configured to minimize energy losses of the liquid and promote a more homogeneous fluid particle size in the dispensed aerosol. The aerosol tip mechanism provides for long-term sterility of the stored fluid, which in turn allows for preservation of the sterility of non-chemically preserved formulations, which may be in the form of suspension or liquid gels.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of prior application Ser. No. 09/962,949 filed Sep. 24, 2001, now U.S. Pat. No. 6,685,109. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to generally to a system and method for generating a spray or aerosol-type discharge, and relates more particularly to a system and method for generating a spray or aerosol discharge by means of a mechanical aerosol-tip mechanism which optimally controls the size of fluid particles in the discharge. 
     BACKGROUND INFORMATION 
     One of the problems encountered in the design of mechanical-spray or aerosol-type dispensers without a propellant gas is how to optimally control, and preferably reduce, the size of fluid particles to achieve an aerosol-type spray mist, and to narrow the range of the particle sizes, which translates into an optimal homogeneity of particle sizes. It is known in the art that mechanical energy losses incurred in the dispenser fluid conduit or channel, which energy losses are referred to as “head losses,” are a major contributing factor in the formation of larger fluid-particle sizes in the released aerosol spray. Such head losses may be caused by, for example, interaction of the moving fluid and stationary walls of the dispenser, changes in geometry of the conduit, and other significant changes in the fluid flow pattern. 
     Applying fundamental equations from classical fluid dynamics, it can be shown that the head losses are related to specific geometric parameters of the fluid conduit such as the length and inner diameter of the fluid conduit and the sharpness of turning angles in the fluid path. The Bernoulli equation expresses the head loss (H L ) in terms of the energy conservation principle:                  (                    p   1     γ     +       V   1   2       2                 g       +     z   1       )     -     H   L       =     (                    p   2     γ     +       V   2   2       2                 g       +     z   2       )             (   1   )                                
     where p is pressure, V is velocity, y is fluid density, g is gravitational constant, and z is elevation head. The Darcy-Weisbach equation derives a formula for major head losses in terms of the physical parameters of the fluid channel assuming laminar flow.                  H   L          (   Major   )       =       f        (     L   d     )            (       V   2       2                 g       )               (   2   )                                
     where f is a friction factor, V is the fluid velocity, L is the conduit length and d is the conduit diameter. Furthermore, minor head losses can also be expressed in terms of physical parameters:                  H   L          (   Minor   )       =     K        (       V   2       2                 g       )               (   3   )                                
     where K is a minor loss coefficient related to specific geometry variations. 
     In addition to the physical parameters of the fluid and the conduit channel, another factor that affects the fluid-particle sizes in the released aerosol spray, for example in a one-way spray tip of the type described in U.S. Pat. No. 5,855,322, is the symmetry of the interface between the flexible nozzle portion, which distends in response to applied pressure, and the rigid shaft portion upon which the flexible portion normally rests. Asymmetries in the interface between the flexible portion and the rigid shaft, e.g., when the flexible portion is not properly centered on the rigid shaft, produce variable valve spacing, and result both in uneven fluid-particle size distributions, and in an overall increase of relatively large-sized fluid particles. FIG. 8 illustrates an example of asymmetry which may occur in aerosol tip mechanisms. FIG. 8 shows flexible left and right valve portions  401 ,  402  which are not symmetrically centered with respect to the rigid shaft  405 . As can be discerned, the left flexible valve portion  401  overextends beyond the center axis of the rigid shaft  405 , while the right flexible valve portion  402  under-extends. Other examples of asymmetrical interaction between the rigid shaft and the surrounding valve portions should be readily apparent. 
     A further problem in manufacturing spray/aerosol/dispensers is minimizing the number of components which constitute the spray/aerosol dispenser. As the number of components increases, the difficulty and cost of mass production consequently increases as well. 
     A further related problem is the costly development time needed for components from different subassemblies to be adjusted with the high precision required for alignment, e.g., in a sub-millimeter range. 
     It is an object of the present invention to provide a simple aerosol-type spray-tip mechanism (“aerosol tip mechanism”), e.g., a spray-tip mechanism including a nozzle for dispensing liquid from a pump-type dispenser in aerosol or spray form, which nozzle maximizes the conservation of energy in the fluid flow by minimizing head losses. 
     It is yet another object of the present invention to provide an aerosol-tip spray-tip mechanism in which the components of the outlet valve are centered with respect to one another, e.g., with respect to the central elongated axis of the spray-tip mechanism, thereby ensuring a symmetrical outlet valve interface. 
     It is another object of the present invention to provide a method of ensuring the components of the outlet valve of an aerosol-type spray-tip mechanism to be centered with respect to one another, e.g., with respect to the central elongated axis of the spray-tip mechanism, thereby ensuring a symmetrical outlet valve interface. 
     SUMMARY OF THE INVENTION 
     In accordance with the above objects, the present invention provides an aerosol tip mechanism for an aerosol-type dispenser for dispensing liquid content by application of pressure, which aerosol-tip mechanism has a symmetrical outlet valve, i.e., the components of the outlet valve are centered with respect to the central elongated axis of the aerosol-tip mechanism. The aerosol tip mechanism according to the present invention may be adapted for use with a variety of types of liquid-dispensing apparatuses, for example, aerosol dispensers which channel liquid from a liquid reservoir through the aerosol tip mechanism by application of pressure via a pump mechanism. 
     In one embodiment of the aerosol tip mechanism according to the present invention, the aerosol tip mechanism has a flexible outer shell, a rigid cap portion composed of lower and upper portions, and a rigid nozzle portion having a rigid shaft received within the outlet portion of the flexible outer shell. The rigid shaft interfaces the outlet portion of the outer shell to form a first normally-closed valve. The lower and upper portions of the cap portion form boots which receives the outlet portion of the flexible outer shell and constrains lateral motion of the outlet portion of the outer shell. The boots of the cap symmetrically center the outlet portion of the flexible outer shell around the rigid shaft of the nozzle. 
     In the above-described embodiment, the aerosol tip mechanism further includes a swirling chamber that is laterally delimited by the rigid shaft of the nozzle in a central location and by the lower portion of the cap portion, and vertically delimited above by the outlet portion of the outer shell and underneath by the base connected to the rigid shaft. The aerosol dispenser is in fluid communication with a liquid reservoir from which liquid is channeled through a plurality of fluid channels within the rigid nozzle portion. Each of the fluid channels leads to one of a plurality of spiral feed channels that are gradually curved to minimize head losses as the liquid flows through the feed channels. Liquid channeled through the spiral feed channels continues in a spiral path into the swirling chamber in which the liquid is swirled before being released as an aerosol via the first normally-closed valve. The bottom of the trough (shown as  410  in FIG.  6  and FIG. 8) of the swirling chamber surrounding the nozzle central shaft, which trough receives the flow from each feed channel, has also been designed to minimize the head losses caused by collision of fluid arriving from fluid channels and fluid already orbiting in the trough. A ramp (shown as  411  in FIG. 6) at the end of each fluid channel raises the bottom of the trough so that when the liquid from a feed channel enters the trough, it is disposed at least partially under the already-orbiting fluid from the adjacent feed channel. This arrangement reduces fluid collisions, and as a consequence, when the liquid reaches the upper outlet of the swirl chamber, it has maximal celerity and pressure. 
     The aerosol tip mechanism of a fluid dispenser according to the present invention allows a smaller number of component parts to be assembled and also allows for improved concentricity of the component parts during production. During operation, the aerosol tip mechanism provides for lower head losses and more homogeneous particle sizes. When used in conjunction with a one-way outlet valve, the aerosol tip mechanism also provides for long-term sterility of the stored fluid, which in turn allows for preservation of the sterility of non-chemically preserved formulations. The fluid dispensed may be in form of suspension and liquid gels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view along the length of an aerosol dispenser including one embodiment of an aerosol tip mechanism, including a nozzle portion, according to the present invention. 
     FIG. 2 is a cross-sectional view illustrating the flow path of liquid through the fluid communication path between the pump and the aerosol tip mechanism shown in FIG.  1 . 
     FIG. 3 shows an exemplary frontal elevation of the nozzle portion of the aerosol tip according to an embodiment of the present invention. 
     FIG. 4 shows an enlarged cross-sectional view along the length of the cap element of the aerosol tip of the embodiment shown in FIG.  3 . 
     FIG. 5 shows a top plan view of an embodiment of the nozzle portion of the aerosol tip of the embodiment shown in FIG.  3 . 
     FIG. 6 shows a perspective view of the ramp section and center shaft of the nozzle portion of the embodiment shown in FIG.  3 . 
     FIG. 7 shows a cross section of the outlet section of the aerosol-tip mechanism according to the present invention. 
     FIG. 8 shows a cross section of an aerosol-tip mechanism, illustrating an example of asymmetry which may occur in aerosol-tip mechanisms. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An aerosol-type dispenser system  1  including a first exemplary embodiment of an aerosol tip mechanism  2  according to the present invention is shown in FIG.  1 . As shown in FIG. 1, a first exemplary embodiment of the aerosol tip  2  according to the present invention is coupled to a body portion  103  which has a substantially tubular shape and to a piston  110  having a substantially tubular portion  112  extending inside and along the body portion  103 . The body portion  103  includes a lower base portion  1031  that extends radially beyond a lower end of the body portion  103  in a flange-like structure which is against the piston shoulder  1101  when the pump is in its resting position. A flexible outer shell  40  covers both the aerosol tip mechanism  2  and the body portion  103 . The tubular portion of the piston contains a hollow axial inner channel  1041  which communicates fluid toward the body portion  103  via a radial channel  114  on each side of the inner channel  1041  when the pump is in a loaded or “cocked” position. 
     As shown in FIG. 1, the inner channel of the piston  1041  is in fluid communication with a liquid reservoir  115 . The overall pump mechanism  120 , which includes the piston  110 , the body portion  103 , and the flexible outer shell  40 , channels the liquid from the liquid reservoir  115  along a fluid communication path encompassing the radial opening  114  in the piston  110  and a compression chamber  125 . In this regard, it should be noted that the aerosol tip according to the present invention is intended to be used in conjunction with a wide variety of liquid dispensing systems, one example of which (shown in FIG. 1) combines a spring mechanism (defined by portion  40 A of the flexible outer shell  40 ) and a collapsible bladder  124 . The collapsible bladder is surrounded by a rigid spray container  1102 . It should be understood that the pump mechanism  120  is merely an exemplary representation of a wide variety of dispensing systems. In the configuration shown, the piston  110  and the rigid spray container  1102  comprise one piece. 
     When the piston  110  is slid downward relative to the body portion  103 , liquid from the liquid reservoir  115  is initially channeled through the radial opening  114  in the piston  110  and subsequently channeled into the compression chamber  125  when the pump is cocked. When the piston  110  is released, the spring mechanism forces the piston  110  upward, in turn forcing the trapped liquid through outflow channel holes  208   a ,  208   b ,  208   c  of the nozzle and upward to the aerosol tip  2  of the dispenser system. FIG. 2 is a cross-sectional view showing one of the channel holes, hole  208   a.    
     FIG. 7 shows a first exemplary embodiment of the aerosol tip mechanism  2  according to the present invention. The tip mechanism  2  includes a rigid annular cap portion  20 , which has an inner cap portion  21  situated beneath a cap flange  22 , and a rigid nozzle portion  24  having a shaft  28  received within the center of the inner portion  21  of the annular cap  20 . A swirling chamber  32  lies in the space defined by the inner portion  21  of the cap  20  and the rigid center shaft  28 . A flexible outer shell  40 , which surrounds and substantially constrains the nozzle portion  24  and the cap flange  22 , interfaces with the inner cap portion  21  and the center shaft  28  to form a normally-closed one-way outlet valve  35  which encloses the swirling chamber  32 . When the pressure in the swirling chamber  32  is high enough to expand the thick base  35   a  of the one-way outlet valve  35 , the thin and distal portion  35   b  of the valve subsequently opens (at which time the thick base  35   a  has already collapsed back to its normally-closed position), thereby providing for one-way discharge of fluid from the outlet valve. 
     FIG. 3 shows an enlarged view of an embodiment of the rigid nozzle portion  24  of the aerosol tip  2  according to the present invention. The nozzle  24  includes a circular base section  201  widening in a radial direction along the elongated axis of the dispenser system, and the base section  201  is connected to a circular rim  203 . On top of the circular rim  203 , the nozzle  24  narrows along the elongated axis in a conic section  205 . Vertical outflow channel holes, such as  208   a  which extends through the rim  203  and the conic section  205 , provide fluid communication channels for liquid entering the swirling chamber, as shown in FIG.  2 . The conic section  205  narrows into a cylindrical section  241  which, in between each of the outflow paths of the outflow channel holes, presents an undercut or depression  211  designed to accept and fasten corresponding cap latches  255  of the cap  20 , which is shown in FIG. 4, to form a tight seal between the cap  20  and the nozzle  24  of the aerosol tip  2 . A valve section  207  is formed between the flexible shell  40  and the cylindrical portion  241 . 
     Referring back to FIGS. 2 and 5, liquid forced upward through the channel holes  208   a ,  208   b ,  208   c  in the nozzle  24  are channeled along the vertical section  207  to a nozzle spiral feed channel section  210 . It is noted that although there are three channel holes in the figures, this number is merely-exemplary. Referring to FIG. 5, which shows a top plan view of the nozzle  24 , the channel holes  208   a ,  208   b ,  208   c  feed liquid via valve section  207  to the bottom of corresponding spiral feed channels  218   a ,  218   b , and  218   c , and it should be apparent that the interface between the nozzle  24  and the cap  20  define the spiral feed channels and the connection section between the channel holes and the feed channels. 
     A brief description of the fluid mechanics involved in the spiral feed channels  218   a, b, c  and the swirling chamber  32  is helpful here. The swirling chamber  32  is used to create a spray pattern for the discharged aerosol, and several factors affect the physical characteristics of discharged spray pattern. First, the length of the interface defining the outlet valve  35  is the main parameter controlling the cone angle of the spray pattern, i.e., the shorter the length of the interface at the outlet valve  35 , the wider the spray pattern. Second, the greater the pressure differential between the outside and the inside of the outlet valve  35 , the greater the homogeneity of the particles and the smaller the particle size. Third, the smaller the diameter of the opening defined by the separated outlet valve  35 , the smaller the particle size in the spray. Additionally, the symmetry and tightness of the outlet valve  35  impacts the size of the aerosol droplets because of asymmetries in the interface, e.g., if the portion of the flexible outer shell comprising part of the outlet valve  35  is not centered on the center shaft  28 , then the tightness of the valve will not be uniform and the valve  35  will not be able to achieve the desired aerosol spray. 
     In order to increase the homogeneity of the spray-particle size and generally reduce the particle size, the dispensing system according to the present invention maximizes the relative pressure differential between the outside and the inside of the outlet valve  35  by means of minimizing the resistance sources in the fluid path, also referred to as “head loss” in fluid mechanics. In this regard, the following parameters are minimized: the length of the fluid channels incorporated in the present invention; the rate of reduction of the fluid-channel width as the fluid channel approaches the swirling chamber  32 ; and the rate of change of the fluid-channel angle relative to the swirling chamber, i.e., the transition angle between the channel holes  208   a ,  208   b ,  208   c  and the corresponding spiral feed channels  218   a ,  218   b , and  218   c  are inclined as gradually as possible without unduly extending their overall length in order to reduce the K factor of the minor loss equation (3). 
     As can be seen from FIGS. 5 and 6, each spiral feed channel  218   a ,  218   b  and  218   c  is widest at its respective bottom portion and becomes narrower as it gradually curves upward in a clockwise direction around the center shaft  28  so that the head loss is reduced due to two effects: a) because of the shorter length of the narrow end of the feed channels, and b) the smoother curve between the vertical portion of the shaft  28  and the horizontal end of the feed channels. Liquid that is channeled upwards along the spiral channels  218   a ,  218   b ,  218   c  travels along a gradual, clockwise-curving path (such as path  240  shown in FIG. 6) and suffers only relatively minor head losses because of the absence of sharp edges or turns along the path which contribute to head losses. Each spiral feed channel  218   a, b, c  narrows into a ledge surrounding the center shaft  28 , each of which feed channel ends with an upwardly sloping and curving ramp  220   a ,  220   b ,  220   c . Liquid streams travel along the ramps  220   a, b, c , and spiral upwards around the center shaft  28  in an annular swirling chamber  32  situated between the shaft and the cap portion  20  which has an internal profile complementary to the ramp of the nozzle. Because the ramps  220   a, b  and  c  are angled 120 degrees apart from one another, the spiral trajectories of the liquid channeled from each ramp into the swirling chamber  32  are spaced apart from one another such that the liquid expelled in trajectory  230   a  from the ramp  220   a  to the chamber  32  reaches halfway to the top of the swirling chamber before this liquid merges with the liquid  230   b  entering the swirling chamber  32  from an adjacent spiral feed channel  218   b . The mutual non-interference of liquid flowing in the separate trajectories  230   a ,  230   b ,  230   c  (not shown) from the corresponding spiral feed channels  218   a ,  218   b ,  218   c  also assists in minimizing head losses, as interference between the liquid streams can also cause head losses and/or turbulence. Using the embodiment of the aerosol tip incorporating the spiral feed channels  218   a ,  218   b , and  218   c  and the swirling chamber shown in FIG. 6, the average particle size of the discharged spray pattern is below 40 μm, and is sprayed in a more homogeneous pattern as judged by the narrow deviation of particle sizes according to the Melverne test. 
     Returning to FIG. 7, the mechanism for ensuring the centering of the flexible outer shell  40  over the center shaft  28 , thereby ensuring a symmetrical and tight outlet valve interface  35  between the flexible outer shell  40  and the center shaft  28 , is illustrated. The outlet portion of the outer shell  40  rests between the upper, or the flange, portion  22  and the lower portion  21  of the cap  20  in the shape of a foot, with the heel  401  and the “toes”  402  of the outlet portion of the shell  40  forming the outlet valve  35  in conjunction with the rigid shaft, and the “heel” of the outlet portion immovably fixed in the boots  303  where the flange  22  connects to the lower portion  21  of the rigid cap  20 . The rigid cap  20  is also immovably fixed in relation to the center shaft  28 , such that there is an annular clearance and constant distance  310  between the lower portion of the cap  21  and the shaft  28 , which clearance  310  provides space for the swirling chamber  32 , and also fixes the distance between the boots  303  and the outlet valve  35 , providing for exact concentricity between the components during assembly. For the purpose of providing a firm guide for centering the cap  21  onto the shaft  28 , both components are made from rigid materials such as poly acetal, polycarbonate or polypropylene, while the elastic outlet valve portion  35 , made from KRATON™, polyethylene, polyurethane or other plastic materials, thermoplastic elastomers or other elastic materials, is free to adjust and fit concentrically within the rigid boots  303 . By constraining the lateral movement of the outer shell  40 , the length of the outlet valve  35  can be precisely dimensioned to tightly enclose the swirling chamber  32  without having to add additional constraints to account for improper alignment during assembly. 
     The one-way valve described herein prevents external contaminants from contacting the fluid within the spray container, and allows the fluid to remain sterile indefinitely. An advantage of the aerosol tip according to the present invention is that the number of parts which constitute the aerosol tip mechanism is reduced in comparison to conventional aerosol-tip and nozzle mechanisms, i.e., these conventional mechanisms typically include gaskets and dead volumes, as well as allowing direct communication between the pump and the external air, making a one-way valve of the type described herein impracticable. As can be seen from FIG. 7, the aerosol tip according to the present invention can be made from three discrete parts: a flexible outer shell  40 , a rigid cap portion  20  and a rigid nozzle portion  24  including a rigid shaft portion. Because only three discrete parts are required, the cost and complexity of manufacturing are reduced. 
     Yet another advantage of the aerosol tip according to the present invention is that the configuration of the outlet valve portion  35  of the aerosol tip is preserved and prevented from either over and under-extending laterally with respect to the shaft of the nozzle portion in response to the forces applied by the pressurized fluid in the fluid channel. 
     Still another advantage of the aerosol tip according to the present invention is that the average fluid-particle size in the dispensed aerosol spray is optimally controlled and generally reduced owing to the configuration of the fluid channels which are designed specifically to limit head losses. Average fluid-particle size is also optimally controlled by maintaining exact concentricity of the components of the symmetrical outlet valve, which greatly reduces the risk of undesirable discharge-particle characteristics and assures-better reproducibility of desired discharge-particle characteristics from pump to pump. 
     While specific embodiments have been described above, it should be readily apparent to those of ordinary skill in the art that the above-described embodiments are exemplary in nature since certain modifications may be made thereto without departing from the teachings of the invention, and the exemplary embodiments should not be construed as limiting the scope of protection for the invention as set forth in the appended claims.