Abstract:
A novel pressure control device is provided comprising a first cylinder ( 3 ) at a predetermined excess pressure, a piston ( 4 ) with a sealing ring ( 5 ) being movable within said first cylinder, and a second cylinder ( 7 ). The first cylinder ( 3 ) is encompassed by the second cylinder ( 7 ) as to form a ring-shaped passage which is leading to the outside. A valve in said passageway is released and closed by a stem ( 14 ) of the piston ( 4 ). The open end of the first cylinder ( 3 ) is provided with at least one axially directed incision ( 37 ), such that the piston ( 4 ) with the sealing ring ( 5 ) introduced in the first cylinder ( 3 ) and covering the end of the incision ( 37 ) is in a non-pressurized position. The stem ( 14 ) has a stop element ( 15 ) which closes the valve in the upper position of the piston, wherein the piston stroke essentially defines the excess pressure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in International Patent Application No. PCT/IB2005/052571 filed on Aug. 1, 2005. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention concerns a pressure control device for a fluid dispensing container for maintaining a constant predetermined excess pressure and a method for manufacturing such a pressure control device. 
       BACKGROUND OF THE INVENTION 
       [0003]    Containers with pressure control devices are known in patent literature since almost thirty years but until today no commercial products are available on the market. 
         [0004]    In EP-A-0 349 053 a pressure capsule for a spray can is described, which consists of two chambers. The first chamber is filled with a fluid under relatively high pressure and the second chamber is filled with a fluid with a pressure equal to the overpressure which normally exists in the spray can and needed for expelling a liquid. In the wall of the second chamber a membrane controls a valve. A plug in the wall keeps the fluid under pressure so that the valve keeps closed. 
         [0005]    In WO-A-93/22222 (Cruysberghs) published in 1993 a pressure control device for maintaining a constant pressure in a container is disclosed in principle. Many different embodiments of the device are described, but in practice none was realized in commercial scale. 
         [0006]    Another example of such a pressure control device is known from PCT patent application WO-A-99/62791. 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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    It is therefore an object of the present invention to provide a pressure control device for a fluid dispensing container which is simpler in construction. Another object of the invention is to provide a manufacturing process of the pressure control device which may be assembled easily in a fluid dispensing container. 
       SUMMARY OF THE INVENTION 
       [0010]    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. This means that the pressure control device may be pressurized at the same time as the bottle of fluid container is filled. Thus there is no need to pressurize the device in advance as was necessary with previous pressure control devices as e.g. described above. 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. 
         [0011]    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. It shows 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  illustrates a pressure control device of the present invention in a perspective, exploded and bottom view, wherein some parts are shown at a larger scale, 
           [0013]      FIG. 2  illustrates the pressure control device of  FIG. 1  in top view, 
           [0014]      FIG. 3  illustrates an exploded view from the bottom and from the top for explanation of the assembling of the pressure control device, 
           [0015]      FIG. 4  illustrates a cross-section through a part of the assembled pressure control device in perspective view, and 
           [0016]      FIG. 5  illustrates three cross-sectional views of the assembled pressure control device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Specific numbers dedicated to elements defined with respect to a particular figure will be used consistently in all figures if not mentioned otherwise. 
         [0018]    In  FIGS. 1 and 2   a  pressure control device  1  for maintaining a constant predetermined excess pressure in a container is shown in perspective and in exploded view. The device  1  comprises a first chamber  2  provided by a first cylinder or cup-like insert  3  with a movable piston  4  with a large O-ring  5  and a second chamber  6  provided by a bottle-type second cylinder  7  with an open end  8  and a closed end  9 . The open end  8  of the cylinder  7  has a tapered neck part  10  and a flange  11 , on which a ring-shaped insert or closure  12  with a stepped funnel  13  is mounted, in which the cup-like insert  3  is fixed. The piston  4  has a stem  14  with an end part  15  of larger diameter ( FIG. 2 ). A stop element  16  with an sealing O-ring  17  are mounted at the other end of the closure  12 , which provides together with a valve seat in the closure a closing or regulating valve. At the bottom  9  of the cylinder  7  is mounted a sealing or Nicholson plug  18  in an opening  19  for pressurizing the cylinder  7 . 
         [0019]    In  FIG. 1   a  the stop element  16  is shown in enlargement. It comprises a cylindrical part  20  and a larger ring part  21  with on the underside thereof serrated teeth  22  for ultrasonic welding on the lower rim  23  of the closure  12 . In the inner circular hollow  24  of the stop element  16  three guiding ribs  25  distanced at an angle of 120° to each other are provided for guiding the piston stem  14 . Further the piston stem  14  has two grooves parallel to the stem axis for venting the gas or air with high pressure over the regulating valve provided by the end part  15  of the stem  14  and the small O-ring  17 . These grooves are extending up to the end part  15 . In  FIG. 1   b  the closure  12  is shown in enlargement. As can be seen a large rim part  26  is provided having a ring-shaped groove  27  with a ring of inner teeth  28  and a ring of outer teeth  29  for ultrasonic welding the closure  12  to the flange  11  of the cylinder  7 . In  FIG. 1   c  the cup-like insert  3  is shown in enlargement and showing a circular top plate  31  (see  FIG. 2   c ) provided with six indents  32 , regularly distributed over the rim, forming projections  33  with serrated teeth  34  underneath. Further at the open end  36  of the cylindrical cup  3  axially directed incisions  37  are provided. If assembled the piston  4  with the sealing ring  5  is just covering the ends of the incisions  37  in a pressure equilibrium, i.e. at the initial or non-pressurized position. Additionally, in direct vicinity of the open end of the insert  3  the inner wall  38  there may be provided an inner step  39  at the ends of the incisions  37 , on which step  39  the piston  4  with its sealing O-ring  5  is laying in the initial or not-pressurized position (see below). For lowering the friction between the sealing O-ring  5  and the wall of the cup-like insert  3   a  friction reducing gel, e.g. of silicones or graphite oil, is used to cover the sealing ring  5 . 
         [0020]    In  FIG. 2  and  FIGS. 2   a ,  2   b  and  2   c  which are numbered commensurate to the elements shown in  FIGS. 1   a ,  1   b  and  1   c , the same pressure control device  1  as in  FIG. 1  is depicted upside down. 
         [0021]      FIGS. 3   a  and  3   b  show the assembling positions of the different parts as described above. 
         [0022]    In  FIG. 4  partly a cross-section of the assembled pressure control device  1  is shown, whereas the arrows  35  direct to the welding areas between the closure  12  and the flange  11  of the second cylinder  7 , between the projections  33  and an inner ring-step  40  of the funnel  13 , and between the ring part  21  of the stop element  16  and the lower rim  23  of the closure  12 . 
       Working 
       [0023]    The function of the above described pressure control device  1  is as follows: in the second chamber  6  an inert gas, especially normal air, with an overpressure of approximately 8 bar is filled in. In the assembled position the first chamber  2  is at normal air pressure, wherein the sealing ring  5  of the piston  4  is just covering the ends of incisions  37  or is laying on the inner step  39 , respectively. The force exerted on the stem  14  by the overpressure in the second chamber  6  pushes the piston towards the circular top plate  27  of the insert  3 , until the valve between the stop element  16  and the sealing O-ring  17  will be closed. Since the pressure in the space above the piston  4  raises according to the Law of Boyle-Gay Lussac and the overall temperature will be constant, the pressure in the first chamber  2  will be proportional to the volume at the valve closing position and the volume at the initial position and normal pressure. Over the incisions  32  and the indents  28  of the insert  3  there is a passageway from the second chamber  6  over the valve to the outside, i.e. over the top plate  27  of the insert  3 . The so assembled pressure control device  1  is mounted at the bottom of a fluid container with e.g. a spraying valve which is actuated by a knob. If the pressure in the container is equal to the control pressure in the first chamber  2  the regulating valve of the pressure control device  1  remains closed. However, if some of the fluid is dispensed over the spraying valve, the pressure in the container drops and the regulating valve will be opened, so that gas with overpressure will flow from the second chamber  6  to the container. As the pressure in the container will equalize quite fast to the control pressure the regulating valve will be closed again. 
         [0024]    If a larger amount of fluid will be spent over the spraying valve, the regulating valve will oscillate between the open and closed positions. In practice the piston will be moved only some tenth or hundredth of millimeter by a rolling motion of the sealing O-ring  34  to open and close the valve. 
       Practical Calculations 
       [0025]    Mathematical models of the pressure control device show that the control pressure obeys following equation: 
         [0000]    
       
         
           
             
               P 
               c 
             
             = 
             
               
                 - 
                 
                   ( 
                   
                     
                       
                         P 
                         R 
                       
                       * 
                       
                         V 
                         2 
                       
                       * 
                       
                         A 
                         1 
                       
                     
                     - 
                     
                       
                         P 
                         I 
                       
                       * 
                       
                         V 
                         1 
                       
                       * 
                       
                         A 
                         2 
                       
                     
                   
                   ) 
                 
               
               
                 
                   V 
                   2 
                 
                 * 
                 
                   ( 
                   
                     
                       A 
                       2 
                     
                     - 
                     
                       A 
                       1 
                     
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    wherein
 
P C =control or excess pressure,
 
P R =pressure in the second chamber,
 
P I =pressure in the initial position (normal air pressure)
 
A 1 =area of the piston stem
 
A 2 =area of the piston
 
V 1 =volume in the first chamber above the piston in the initial position,
 
V 2 =volume in the first chamber above the piston in the pressurized position,
 
         [0026]    Thus, this equation allows to calculate the container pressure when the pressure in the second chamber  6  and the dimensions of the piston  4  and the piston stem  14  are determined. The equation further shows that the control pressure P C  in the first chamber  2  slightly increases as the pressure in the second chamber P R  decreases until the P R  equals P C , where the pressure control device  1  remains open. Thus, the equation also allows to determine the minimal pressure P R  for dispensing all the fluid in the container. 
         [0027]    At predetermined geometrical dimensions of the piston  4  and the piston stem  14  the volume V 2  is defining the control or excess pressure P C . Thus, by amending only the thickness of the piston  4  different control pressures P C  can be provided at the same geometry of the cup-like insert  3 . 
       Manufacturing Process 
       [0028]    The cup-like insert  3  and the closure  12  are moulded from polyethylene terephthalate (PET). The piston  4  with piston stem  14  and the stop element  16  are moulded from polyoximethylene (POM). The bottle-like cylinder  7  is injection blow moulded from PET. The main advantages of the injection blow moulding process for producing the cylinder  7  is that different sizes can be produced with the same tool, 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. 
         [0029]    The assembling process is as follows: firstly piston  4  with its sealing O-ring is introduced into the cup-like insert  3 . Then the insert  3  is pressed into the funnel  13  of the closure  12  until the projections  33  with its serrated teeth  34  are lying firmly to the ring step of the funnel  13 . The insert  3  is then ultrasonic welded to the funnel  13 . Thereafter the stop element  16  with the small sealing O-ring  17  are pushed over the piston stem  14  and the stop element  16  is clamped with a snap-fit connection to the funnel  13  and thus pinching the O-ring  17  between the funnel  13  and the upper side of the step element  16 . Then the ring part  20  of the stop element  16  is ultrasonic welded to the lower rim of the funnel. At the end the closure  12  is mounted to the flange  11  of the cylinder  7  and ultrasonic welded thereto. The so assembled pressure control device  1  is ready for use to be mounted in a fluid dispensing container e.g. with a spraying nozzle. Thereinafter the cylinder  7  is pressurized with an inert gas or air with an overpressure of e.g. 8 bar, so that the piston  4  is moved upwards and the regulating valve provided by the piston stem  14  and the small O-ring  17  is closed and the container is pressurized with the predetermined excess pressure. Assembling may be done also in a somewhat different sequence, if required. 
         [0030]    It is clear that the elements may be fixed also by other welding methods like rotation welding, laser welding or any other well-known plastics welding method, or by adhesives or mechanical fastening, e.g. snap-fit or screws. 
         [0031]    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. 
         [0032]    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.