Abstract:
The invention is a pressurized gas providing and gas pressure regulating device. The invention is a container with an over pressurized second chamber of pressurized gas that can be released to the exterior of the container when a valve that is integrally connected to a piston that along with a first cylinder forms a first chamber that is filled with a comparably less over pressurized gas that pushes the valve open when the gas pressure outside of the container is too low, thereby permitting the over pressurized second chamber to fluidly connect via the valve and thereby increase the pressure outside the container, such as to a volume of gas located below a piston within a fluid dispenser, the first and second chambers are shaped as cylinders and the first cylinder fits within the second chamber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Patent Application No. PCT/IB2004/002522 filed on Aug. 5, 2004 and European Patent Application No. 04405059.9 filed Jan. 30, 2004. 
     FIELD OF THE INVENTION 
     The present invention concerns pressure control device for maintaining a constant predetermined excess pressure in a fluid dispensing container and a method for manufacturing such a pressure control device. 
     BACKGROUND OF THE INVENTION 
     PCT patent application WO-A-99/62791 discloses a fluid dispensing container with a pressure control device. The device described therein is provided for maintaining a constant predetermined pressure in a container which is arranged for dispensing a fluid. The pressure control device has a first chamber and a second chamber, as well as a closing member movable relative to the second chamber for releasing and closing a fluid connection between the first chamber and the container depending on the position of the closing member relative to the second chamber. The first chamber is filled with a gas which, in use, has a higher pressure than the pressure in the container. The second chamber is closed having a gas at a predetermined or reference pressure and is located outside the first chamber. In a first embodiment according to FIG. 2 of WO-A-99/62791, the first chamber is provided as a cup-shaped holder which is placed upside down in the container and has its longitudinal edge joined together with the bottom and the upright sidewall of the vessel or container. In  FIG. 3  a second embodiment is shown in which the diameter of cup-like first chamber is much smaller than the inner diameter of the container. The chamber is centrally disposed within the container and joined at its longitudinal edge with the bottom of the container. In  FIG. 4  a third embodiment is shown in which the same first chamber as in  FIG. 3  is disposed eccentrically with respect to the container. In  FIG. 5  a disc is provided slightly below the middle of the height of the vessel and is gas-tightly connected with the inner wall of the vessel through a sealing ring. This disc divides the vessel into two (fixed arranged) parts. A similar construction is shown in  FIGS. 6   a  and  6   b . Further, in  FIG. 7  the first chamber of pressure control device is designed as a plunger which is sealed to the inner wall of the container with a sealing ring and which can be moved in axial direction within the container. Thus, the plunger divides the container in two parts, wherein the upper part is filled with the fluid to be dispensed. The fluid connection from the first chamber terminates in the lower part. When the pressure in the container drops since fluid has been dispensed by the push button on top of the container, the plunger is moved upwards because of the pressure difference between the lower and the upper part until pressure equilibrium between the lower and the upper part is obtained again. Therefore, the pressure in the lower part has decreased so that the pressure in the second chamber will be higher and the closing member will open the fluid connection between the first chamber and the lower part, so that the pressure in the lower part will rise. The plunger will then be moved upwards again until a pressure equilibrium is achieved corresponding to the predetermined or reference pressure in the second chamber. Finally, in the embodiment according to  FIG. 8  the first chamber is of cylindrical design and has an outer diameter corresponding to the inner diameter of the container and thus fitted tightly within the container. 
     Only the pressure device of FIG. 7 of WO-A-99/62791 is movable in an axial direction. In all other examples the pressure device is fixedly arranged within the container. The complete pressure control device of  FIG. 7  is designed as a plunger which functions as a movable piston expelling the dispensing fluid. However, the design of the pressure control device is disadvantageous because of its large dimensions so that less of the container can be used for dispensing fluid. 
     A further important problem of the above described pressure control devices as a separate module is that the first and second chambers have to be pressurized before mounting in a container. This in practice may be very difficult and costly to achieve e.g. in aluminium aerosol cans where the construction is in one-piece and the production lines run at very high outputs. A further major disadvantage is that it has been shown that the pressure in a separate pressure control device which will be mounted afterwards in a container drops to a large extent during a period of some months which is necessary for storage and distribution in the commercial supply chain. In addition, pressurizing of the pressure control device has to be performed with the fluid connection closed in order to obtain a pressure of the prescribed quantity. Thus the known pressure control devices are not suitable for application in a large industrial scale. 
     It is therefore an object of the present invention to provide a container with a pressure control device which is simpler in construction and for the manufacturing process, such that the volume of the container can be used to a greater extent. It is another object of the invention to provide a pressure control device for a container which can easily be pressurized after being assembled to the container. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention, the above and other objects are accomplished by a pressure control device for use in a pressure control system having a fluid dispensing container for maintaining a constant predetermined excess pressure. The pressure control comprises a cylinder having an open end and a closed end, and a piston movable within the cylinder and defining a first chamber to be filled with a gas for exerting the predetermined excess pressure, a second chamber, a passageway from the second chamber to the outside of the device leading to the fluid dispensing container, and a valve for releasing and closing the passageway. The second chamber is formed by a high-pressure container with a closed end and an open end provided with a rim part. The high-pressure container is filled with a gas at a pressure higher than the predetermined excess pressure. The piston includes means for actuating the valve dependent from the pressure difference between the first chamber and the fluid dispensing container so that if the fluid pressure in the fluid dispensing container drops below the predetermined excess pressure, gas flows from the second chamber to the fluid dispensing container until the container pressure approximately equals the predetermined excess pressure. A closure is mounted to the rim part of the high-pressure container in order to close the second chamber, wherein the first chamber is part of the closure such that the high-pressure container encompasses the cylinder of the first chamber. 
     The above and other objects are also accomplished by a method of manufacturing a pressure control device in accordance with the present invention comprising forming a first cylinder, and forming the piston, the valve elements, the high-pressure container with the closed end and the rim part at the open end, and the closure out of a synthetic material of high stability. A central opening is formed in the bottom of the high-pressure container and the piston is assembled with a sealing ring in the first cylinder. A gas is filled in the first chamber at a predetermined pressure. The first cylinder is mounted with respect to the valve such that the actuating means of the piston is positioned correctly with respect to the valve. The closure is mounted to the high-pressure container. 
     A main advantage of the present invention is that the pressure control device can be pressurized after implementation and filling of the liquid dispensing bottle. Since the second chamber is encompassing the first chamber, a very compact pressure control device will be obtained so that the total usable space in the bottle is much larger as in known embodiments. As the pressure control device can be fabricated in advance and can be implemented easily in existing plastic bottles, the existing production and filling procedures for e.g. cosmetic products can be maintained with only little additional arrangements in the production line. 
     Further advantages of the invention are disclosed in the dependent claims and in the following description in which an exemplified embodiment of the invention is described with respect to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a pressure control device of the present invention in perspective view and in cross-section, wherein the valve is closed. 
         FIG. 2  illustrates the pressure control device of  FIG. 1 , wherein the valve is open. 
         FIG. 3  illustrates the pressure control device of  FIG. 1  only in cross-section. 
         FIG. 4  illustrates an exploded view of the pressure control device of  FIG. 1 . 
         FIG. 5  illustrates a fluid dispensing container with a pressure control device and a movable piston in accordance with an embodiment of the present invention, wherein the valve is closed. 
         FIG. 6  illustrates the fluid dispensing container of  FIG. 5 , wherein the valve is open. 
         FIG. 7  illustrates a fluid dispensing container with a pressure control device and a spray valve with dip-tube arrangement in accordance with an embodiment of the present invention. 
         FIG. 8  illustrates a partial cross-sectional view of a ring shaped insert and cylindrical clamping means forming part of the pressure control device of  FIG. 1 . 
         FIG. 9  illustrates a perspective, partial cross-sectional view of the insert and cylindrical clamping means of  FIG. 8 . 
         FIG. 10  illustrates a perspective, partial cross-sectional view of the insert of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Specific numbers dedicated to elements defined with respect to a particular figure will be used consistently in all figures if not mentioned otherwise. 
     In  FIGS. 1 and 2  a pressure control device  1  for maintaining a constant predetermined excess pressure in a container is shown in cross-section and in a perspective view. The device  1  consists of a substantially cylindrical container  2  with a tapered neck portion  3  and a flange  4 , on which a ring-shaped insert or closure  5  having a steplike funnel  6  is mounted. The cylinder  2 —indicated as “the second cylinder” in the claims—forms a second chamber  7  of the pressure control device  1 . The outer rim  8  of the insert  5  has an outer downwardly directed ring part  9 A and an inner downwardly directed ring part  9 B, which ring parts include a groove  10 . The insert  5  is mounted to the flange  4  of the cylinder  2  by ultrasonic welding. For that reason the inner surface of the groove  10  of the insert  5  has a saw-tooth or fluted structure used as energy directors during the welding process for a very strong hermetic joint. The lower end  11  of the funnel  6  is closed with a small central opening  12 . A cup-like piston  13  with an outer sealing or O-ring  14  is inserted in a cup-like cylinder  15 . The space between the piston  13  and the cup-like cylinder  15 —indicated as “the first cylinder” in the claims—defines a first chamber  16 . The piston  13  has downward a protruding stem  17  with a broader cylindrical end portion  18 . The diameter of the central opening  12  is slightly larger than the diameter of the cylindrical end portion  18 , so that this portion  18  can slide through the opening  12 . The funnel  6  has a downwardly projecting cylindrical clamping portion  19  with a ring-shaped barb  20  which clamps a ring-cylinder  21 . The upper end  22  of the ring-cylinder  21  pinches a sealing or O-ring  23 . In  FIG. 1  the upper rim  24  of the cylindrical end portion  18  is lying against O-ring  23 , which is the closed position of a valve  25 , that is formed by piston  13  with stem  17  and cylindrical end portion  18  and pinched sealing or O-ring  23 . 
     The cup-like cylinder  15  is enclosed by a cylindrical clamping means  26  which comprises a cylindrical cup  27  which exactly surrounds the cup-like cylinder  15  and has an upper crown  28  with openings  29  between dents  30 . The cup  27  has in its upper closing three vents  31 , from which only one can be seen in  FIGS. 1 and 2 . Further, a number of L-shaped small projections or ribs  38  (shown more clearly in  FIG. 10 ) are provided on the inside of the funnel  6  which are equally distanced from each other. The projections or ribs  38  are provided at the lateral and the bottom side of the funnel  6 . Therefore, there is space between the cylindrical cup  27  and the funnel  6 , which defines a passageway from opening  12  up to the upper side of the insert  5 . The passageway provides a path for fluid communication from the second chamber  7 , through the valve  25  and past the first chamber  16 , as illustrated in  FIG. 2  by arrows A. 
     In  FIGS. 8-10 , the insert  5  and the cylindrical clamping means  26  are shown in cross-section and in perspective view. As shown, the cylindrical cup  27  sits on the L-shaped projections or ribs  38 , leaving a space between the projections or ribs  38  through which fluid from the second chamber  7  can pass. As can also be seen more clearly, the inner surface of the insert  5  includes recesses  39  through which fluid from the second chamber  7  may pass, as illustrated by arrow A in  FIG. 9 . Fluid can also flow through the openings  29  in the crown  28  of the cylindrical clamping means  26 , as illustrated by arrow B in  FIG. 9 . 
     The cylinder  2  is widened gradually towards its end and has a broader end portion  32  with an inwardly projecting rim  33  on which the end portion of a container rests (see  FIGS. 5 and 6 ). The bottom part  34  of the cylinder has a ring-shaped depression  35 , which is reinforced at the inner side of the cylinder  2 , with a central opening  36 , in which a so-called Nicholson plug  37  made of rubber is pressed. The bottom part  34  may have been reinforced by radial supporting ribs, in order to resist the deformation caused by the high pressure during elevated temperature storage conditions. Instead of a Nicholson plug other types of sealing elements can be used, e.g. an alternative type of a rubber bung, or mushroom shaped grommets or so called rubber rope seals, heat staking or use of a ball-bearing such as in cigarette lighters. 
       FIG. 2  shows the valve  25  of the pressure control device  1  in the open position.  FIG. 3  is a cross-section of the pressure control device  1  as depicted in  FIG. 2 . 
     In  FIG. 4  an exploded view of the elements of the pressure control device  1  is shown. Especially, the construction of the cup  27  with crown  28  can be seen more properly. One can further see that the stem  17  has two grooves  40  and  41 , which are provided at opposite sides of the stem  17 . In continuation of grooves  40  and  41  there are provided in opposite directions two grooves  42  and  43  at the underside of the piston  13 . Thus, in the open position of valve  25 , where the piston  13  is lying on the bottom side of the funnel  6 , there is a passageway from the open valve  25  along the inner bottom side and the lateral side of funnel  6  around the cylindrical clamping means  26  and over and through the openings  29  of crown  28  up to the top of insert  5 , as illustrated by arrows A and B in  FIGS. 2 ,  8  and  9 . 
     In  FIG. 5  the pressure control device  1  is mounted in a container  50  having a per se known pressure valve  51  and a flexible piston  52  made of a suitable thermoplastic material such as high-density polyethylene which is movable within the container  50 . The flexible piston  52  is formed as a cup-like cylinder or dome following more or less the upper contour of the insert  5 . The piston  52  has further a broad ring-cylinder shaped sealing  53 , which is contacting the inner wall of the container  50  with an upper sealing lip  53  and a lower sealing lip  54 . The upper sealing lip  53  is provided as a scraper with a sharp rim so that the liquid filled in the container  50  will be scraped from inner wall of the container  50 , so that no material or at most only a very thin liquid film remains at the inner wall. A separate rubber o-ring assembled around the piston  52  can also be considered where a gas tight seal is needed. The sealing lip  54  is wedge-shaped and has a somewhat larger contact area than the upper sealing lip  53 . As can be seen the container  50  is formed as a bottle of cylindrical form. The cylinder  2  of the pressure control device  1  is widened to its end so that there is a interference press-fit connection between the inner side of the bottle  50  and the outer side of the cylinder  2 . In addition in the neighborhood of the end portion  55  the bottle  50  is laser welded to the cylinder  2  providing a very strong and hermetic seal. Although a ring cylindrical bottle  50  is shown here, other bases like an ellipse or a quadrant can be used for the cylindrical bottle. The bottle can also be oval shaped. The shape of the cylinder  2  of the pressure control device  1  should then be adapted accordingly. 
     Working 
     The function of the above described pressure control device is as follows: in the second chamber  7  an inert gas, especially normal air, with an overpressure as required but preferably of around 8 bar is filled in. Valve  24  is in its closed position ( FIG. 1 ). In the first chamber  16  a gas, especially normal air, with a constant predetermined excess pressure of 1.5 to 2.0 bar, preferably at 2.0 bar, is filled in. If the pressure in container  50  drops below the predetermined or excess pressure, which occurs if liquid in the container  50  is dispensed by valve  51 , the pressure in the passageway also drops. Thus, there is no more pressure equilibrium between the first chamber  16  and the passageway, and the piston  13  is moved downwardly from the closed position of valve  25  ( FIG. 1 ) to the open position ( FIG. 2 ). Because there is an overpressure in the second chamber  7  of the cylinder  2 , there will be an airflow over the passageway to the container  50 , i.e. underneath the flexible piston  52  which will be moved upwards until there is pressure equilibrium again between the first chamber  16  and the passageway (or container  50 ). In the equilibrium situation the valve  25  is closed again and the pressure underneath and the pressure above the flexible piston  52  will be the same. The piston  13  is moved in a reciprocating or oscillating manner to open and close the valve  25  until the equilibrium situation is reached. Since piston  13  and stem  17  are light-weighted the reciprocating movement between the open and closed position of valve  25  is very fast, such that the equilibrium situation is reached almost immediately. 
     In order to dispense completely all fluid from the container at a constant pressure or continuous flow-rate an excess pressure must be upheld in the container until the end. This can only be afforded if at the end as the last bit of liquid should be dispensed the overpressure in the second chamber  7  is at least equal to the predetermined excess pressure of the first chamber  16 . This means that following equation should be fulfilled:
 
 P   2   ≧P   1 *(1 +V   1   /V   2 )
 
wherein
         P 1 =the predetermined excess pressure   P 2 =the initial pressure in the second chamber   V 1 =the volume of the container   V 2 =the volume of the second chamber       

     This means that the smaller the volume V 2  is with respect to the volume V 1 , the higher is the overpressure P 2 . Thus, since the design of the cylinder  2  is more critical at higher pressures there is a practical limit for the smallest size of cylinder  2  which depends on the material properties, the manufacturing methods, etc. 
     In a practical example the volume of the container V 1  is 150 ml, wherein the volume of the liquid to be dispensed is to a maximum of 90% of the container volume, i.e. 135 ml. The overpressure P 2  of the second chamber  7  is initially 8.0 bar and the working or predetermined excess pressure P 1  is 2.0 bar. The volume V 2  of the second chamber  7  is 50 ml. 
     The required working pressure P 1  is dependent on the viscosity and or other physical properties of the liquid to be dispensed. A typical working pressure needed for low or medium viscosity gel or cream (e.g. cosmetics) is 1.5 to 2.0 bar, for post-foaming gel in a pressurized formulation is 3.0 bar, for high viscosity filler (e.g. acrylic resin) is 2.0 to 2.5 bar, a wet liquid spray is 3.0 bar, a fine liquid spray is 4.0 to 5.0 bar, and a dry to very dry liquid spray is over 6.0 bar. 
     In the last case the overpressure P 2  is 24.0 bar if the volume V 1  of the container is 150 ml and the volume V 2  of the second chamber  7  is 50 ml. Therefore the construction of the cylinder  2  of the pressure control device  1  has to be very stable in order to withstand such high overpressures. Also the governmental regulations for pressurized containers must be fulfilled, which concerns the stability and choice of the material used for the cylinder  2 , etc. Therefore, the process for producing the above described pressure control device  1  is also very important, which is described hereinafter. 
     In  FIG. 7  a fluid dispensing container  60  is shown in cross-section, in which the pressure control device  1  is mounted in a similar manner as in the container  50  of  FIGS. 5 and 6 . At the upper end  61  of the container  60  a conventional dispensing valve  62  with a push button actuator  63  comprising a spray nozzle  64  is mounted by circumferential ringshaped rim  65  which is crimped to the upper end  61 . The lower end  67  of the valve  62  is provided with a hollow dip-tube  68  of a plastic material such as polypropylene or polyethylene. The length of the dip-tube  68  is long enough that the lower end  69  merely contacts the cylindrical cup  27  of the pressure control device  1  (cf.  FIG. 1 ). The dip-tube may also be positioned in between the outside of the cylinder and the inside of the container wall. The lower tube end  69  may be cut-off obliquely so that blocking thereof by a too close contact with the surface of the cylindrical cup  27  is prevented. The working of the container  60  is similar as for the container  50  of  FIGS. 5 and 6 . 
     It has been proven in a series of practical tests that the pressure in the container  50  or  60  remains constant independent from the filling rate, i.e. during dispensing the fluid product the predetermined excess pressure remains constant until all fluid is dispensed. 
     Clearly the container  50  with the flexible piston  52  is more suited for fluid with a higher viscosity like a cream or gel, whereas the container  60  with the spray nozzle  64  is more suited for low-viscosity fluid like airfreshners, deodorants, spray paints and the like. 
     Manufacturing Process 
     The cylinder  2  of the pressure control device  1  is preferably injection blow moulded from polyethylene terephthalate (PET). The main advantages of the injection blow moulding process for producing the cylinder  2  is that different sizes can be produced with the same tooling, or with minimal changes, and that the orientation of the stretched PET material during the blowing process leads to a higher crystalline structure which gives high strength and good gas barrier properties. It has been proved that the construction of the cylinder  2  with neck portion  3 , flange  4  and widened or broader end portion  32  with a wall thickness of typically 1.5 to 2.0 mm is very strong and most suitable for containing high gas pressures. 
     The neck portion  3  remains the same for all sizes of the cylinder  2  which allows the efficient standardization of components and manufacturing processes and assembly equipment. The central opening or hole  35  is made in the bottom of the cylinder  2 . This can be done by drilling or, which is more advantageous, during the injection blow moulding process in that the outer shape of the moulding tool has a pin at the bottom for shaping the central opening or hole  35 . For the laser welding process mentioned above a tapered area on the outside diameter of the cylinder is provided in order to obtain an optimal interference press-fit with the container or bottle  50 . 
     The other parts of insert  5 , i.e. the funnel  6 , the cup-like piston  13 , the ring-cylinder  21  and the cylindrical clamping means  26 , are made by injection moulding of any suitable synthetic material like PET or the like. The cup-like cylinder  15  made of aluminum is positioned at the correct position over the piston  13  with surrounding O-ring  14  under air pressure, and three of four inward indentations are made at the open end of the cylinder  15  to prevent escape of the piston  13 . In this manner the first chamber  16  is maintained at the predetermined excess pressure. Thereinafter the cylindrical clamping means  26  is put over the cylinder  15 , whereas the air between the cylinder  15  and the cylindrical cup  27  will escape through vents  31 , and is snapped in position in the funnel  6 . As can be seen in  FIGS. 1 and 2 , for this reason there is provided a small ring groove  60 , in which outer ring parts  61  of the crown dents  30  can be snap fitted. Alternatively, the cup-like cylinder  15  can also be made of PET or any other hard synthetic material. Instead of indentations the outer edge of the cylinder  15  can be assembled into position by ultrasonic welding or some other suitable method. 
     The container or bottle  50  is injection stretch blow-moulded (ISBM) from a proper pre-form made of any suitable synthetic material like PET or the like. The PET pre-form has already the shape of a bottle in a smaller format. Pre-forms may first be made separately on very high output production scale and are therefore very economical. The ISBM process has the same advantages of the abovementioned injection blow-moulding process used for producing the cylinder  2 , but with the additional important benefit in that the PET material is stretched bi-axially, that is both radially and lengthwise, which gives rise to even better stretch and gas barrier properties even with a thin wall thickness of typically 0.3 to 0.6 mm depending on the container design. After stretch blow-moulding the end part of the container bottle  50  may be cut-off to provide an open end for receiving the piston  52  and cylinder. 
     The flexible piston  52  is assembled into the bottle  50  and the bottle  50  with its open end portion  50  is put over the cylinder  2  of the pressure control device  1 . In order to obtain a hermetic seal between the bottle  50  and the cylinder  2 , the bottle  50  is laser-welded to the cylinder  2 . For this reason the bottle  50  is made of a transparent plastic material like PET and the cylinder  2  is at least impregnated at a small distance from the bottle end portion  53  at a ring-cylindrical circumference with a infrared or laser energy absorbing material known as “carbon black”. The bottle  50  with the cylinder  2  is turned over its longitudinal axis during a laser beam is directed perpendicularly towards the outer surface of the bottle  50 . The used semiconductor laser equipment is the NOVALAS-C system of Leister Process Technologies, Sarnen, Switzerland with a wavelength of 820 nm. The power of the used laser beam was 25 Watt (continuous), the rotational speed was 3.5 revolutions/sec and the laser beam was applied during approximately 10 revolutions. 
     Although laser welding has been proven as giving the best results for joining the pressure control device to the bottle  50  other suitable joining methods, like ultrasonic welding or gluing with an appropriate plastic adhesive can also be used. 
     The main advantages of the described manufacturing method is that the pressure control device can be produced and its first chamber can be pressurized and delivered to the manufacturer of the container, and the manufacturer can produce the container or bottle by injection stretch blow-moulding, which is a standard known process, cut-off the bottom of the container or bottle, join the pressure control device with the bottle e.g. by laser welding, insert the pressure valve  51 , fill in the liquid over the pressure valve  51 , and finally pressurize the second cylinder through the rubber plug  37  in a conventional manner. The additional production steps can easily be introduced in the known production and filling processes for aerosol containers as used in cosmetics or the like, wherein e.g. the liquid product is filled in through the open neck of the container or through the dispensing valve  51 . 
     A further advantage of the invention is that, since only normal air or any other suitable inert gas is used for the pressure filling, the process facilities, equipment and manufacturing environment and operating procedures do not need to take account of the special safety requirements normally needed for dangerous flammable propellants. 
     While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present invention.