Abstract:
In a dispensing system for dispensing a product form a canister, which comprises a solid/gas arrangement in which the gas is absorbed onto the solid under pressure and desorbed therefrom when the pressure is released and in which the solid comprises activated carbon and the gas comprises one or more of nitrogen, oxygen, (or mixtures thereof including air) carbon dioxide, nitrous oxide and argon, the container has valve means to allow the gas adsorbed onto the carbon to be desorbed and effect product dispense.

Description:
[0001]     This is a Continuation-In-Part Application of International Application PCT/GB2005/000145 filed Jan. 17, 2005 and claiming the priority of GB applications 0401512.9, 0407991.9, 0419135.9, 0419137.9 and 0426490.9 filed Jan. 23, 2004, Apr. 8, 2004, Aug. 27, 2004, Aug. 27, 2004 and respectively, Dec. 2, 2004.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to systems for dispensing substances from containers and, more particularly, to such systems employing a very simple but effective two phase solid/gas adsorption/desorption mode of operation.  
         [0003]     A large number of products are on the general market packaged in canisters—some of which cause the product to be dispensed therefrom in the form of small or atomized particles and are therefore commonly referred to as ‘aerosols’—which can be dispensed from the canister by means of a pressurized gas (or vapor) which is generated in situ in the canister and acts as a dispensing or propellant gas. Such products include ones for personal care including hair sprays, shaving creams, deodorants and the like and ones for household use including cleaning substances, room fragrances, insect repellents and the like, and many more.  
         [0004]     In some cases, such products are admixed with the pressurized gas in the canister and the operation of a (typically) push-down operating valve causes both the product and the gas to be dispensed from the pack by means of the gas pressure via a ‘dip tube’ extending into the product and linked to a nozzle which is commonly associated with the release valve, all of which are commonly contained in a dispense assembly or dispense block.  
         [0005]     In other cases, the product and pressurized gas are separated from each other within the canister. Typically, some form of divider or membrane is present in the canister, for example, one in the form of a bag containing the product which is sealingly attached to the canister internal wall in the vicinity of the release valve; the gas is present between the divider and the internal walls of the pack, i.e. surrounding the bag and the gas pressure in turn exerts pressure on the product in the bag.  
         [0006]     Alternatively, the divider may be a piston which slides within the canister with the product on one side and a gas on the other side and which acts to drive the product from the canister by the action of gas pressure.  
         [0007]     Whichever type of pressure pack is adopted will depend on the nature of the product and the use to which it is to be put and on the nature and properties of the propellant gas, in particular whether the propellant gas might react with the product or whether, for example, it might be flammable or odorize the product.  
         [0008]     The use of chlorofluorocarbons (CFCs) previously became very popular as propellant gases for such product dispense canisters in that they can be readily condensed and vaporized in a reversible manner responsive to the surrounding pressure. This was followed by the use of hydrofluorocarbons (HFCs) and also hydrochloroflurocarbons (HCFCs) which were regarded as being somewhat more environmentally friendly.  
         [0009]     However, more recently, such propellant gases have in general been phased out owing to their acknowledged environmentally harmful properties, in particular ozone depletion of the upper atmosphere.  
         [0010]     Alternative propellant gases which have been commonly used are certain hydrocarbon gases including liquid petroleum gases (LPGs) such as propane and butane. Such gases, however, are by their nature extremely flammable, are environmentally harmful in some respects and in addition can introduce an odour into the product being dispensed.  
         [0011]     It is known that numerous attempts have been made to replace LPG propellant gases with gases such as air, nitrogen, carbon dioxide and the like. These attempts have largely been effected simply by utilizing a pressurized gas within the canister; in practice, the canister valve is depressed to propel the product from the canister in the general manner described above.  
         [0012]     However such attempts have been largely unsuccessful due to the large pressure changes in the canister during use, commonly leading to reduced dispense characteristics at low pressures and a loss of pressure before full product dispense which results in a slow dispense of the last product from the canister.  
         [0013]     In addition, it is known that there has been considerable effort to develop further alternative propellant systems for such product dispense. For example, there is disclosed in European Patent Application No. 385 773 the use of two-phase gas/solid or gas/liquid or three phase gas/liquid/solid propellant systems in which the solid is a polymer having molecular microvoids occupied by the gas or gas/liquid under pressure and the gas is released therefrom when the pressure of the system is reduced.  
         [0014]     There is additionally disclosed in a further European Patent Application No. 502 678 the use of a three phase gas/liquid/solid propellant system in which the solid is a material such as a foam or a fibrous mass having open voids occupied by the gas/liquid under pressure and the gas is released therefrom when the pressure of the system is reduced.  
         [0015]     It is known that efforts to develop such prior systems were based primarily on the preferred embodiments described in these European applications, namely the use of a gas/liquid/solid system in which carbon dioxide as the gas was dissolved in acetone as the liquid which itself occupied voids in a solid.  
         [0016]     The use of acetone as the liquid in such a system would generally mean that it was useful only in canisters employing a membrane, for example a bag containing the product, in order to separate the propellant system from the product to be dispensed. However, acetone is an aggressive chemical and it is also known that it was found that the use of acetone in such systems tended to cause problems associated with chemical attack of the membrane material and leakage of the acetone through and around the membrane and resulting failure of the membrane.  
         [0017]     A further prior attempt to produce a product dispense system utilizing gas pressure is disclosed in UK Patent Specification No. 1 542 322 in which a propellant gas, including propane/butane, certain CFCs and carbon dioxide, is adsorbed onto a solid with the dispense gas pressure being produced in situ during use of the system by means of bringing the solid into contact with a propellant displacing agent—preferably water—in order to release the adsorbed gas. As such, the system as a whole is necessarily very complex due in particular to the need to employ the propellant displacing agent during use and provide means to bring it into contact with the solid.  
         [0018]     It is therefore the object of the present invention to provide an improved aerosol propellant system that overcomes the problems associated with currently available systems.  
       SUMMARY OF THE INVENTION  
       [0019]     In a dispensing system for dispensing a product form a canister, which comprises a solid/gas arrangement in which the gas is absorbed onto the solid under pressure and desorbed therefrom when the pressure is released and in which the solid comprises activated carbon and the gas comprises one or more of nitrogen, oxygen, (or mixtures thereof including air) carbon dioxide, nitrous oxide and argon, the container has valve means to allow the gas adsorbed onto the carbon to be desorbed and effect product dispense.  
         [0020]     It has now been found that the use of a new system not involving polymeric materials and not involving troublesome liquids or displacing agents and being more suitable for commercially viable assembly into the aerosol canister can provide an efficient sorption/desorption propellant system for product dispense.  
         [0021]     In accordance with the invention, there is provided a dispensing system for dispensing a product from a canister, which comprises a solid/gas arrangement in which the gas is adsorbed onto the solid under pressure and desorbed therefrom when the pressure is released and in which the solid comprises activated carbon and the gas comprises one or more of nitrogen, oxygen (or mixtures thereof, including air), carbon dioxide, nitrous oxide and argon, the container having valve means to allow the gas adsorbed onto the carbonto be desorbed and effect product dispense.  
         [0022]     The gas is preferably carbon dioxide in view of its generally superior adsorption characteristics in relationto activated carbon as an adsorbent.  
         [0023]     The term ‘adsorbed gas’ used herein refers to the gas used in the invention.  
         [0024]     It has been surprisingly found that such a system, despite its simplicity, can provide the basis for an efficient, safe, reliable and reproducible system for product dispense.  
         [0025]     It has been found in particular that the new dispense system can provide—by means of careful selection of the type of activated carbon employed, the amount of carbon, the initial pressure and therefore the amount of gas adsorbed on the carbon—a low pressure change during intermittent use between an initial product dispense and full product dispense from a canister.  
         [0026]     The pressure change afforded by the invention between a ‘full’ and ‘empty’ canister is such that the canister in which it is positioned can maintain an effective discharge of the product with an effective and acceptable controlled spray pattern in terms in particular of its being uniform and/or homogeneous with a predetermined particle size and distribution.  
         [0027]     Systems of the invention have been shown to be particularly suited to the dispensing of products from small, hand-held ‘aerosol’ canisters, for example ones having a 200 or 300 ml capacity. The term ‘aerosol’ when used herein includes any hand-held dispensing devices for the delivery of product whether or not the product is actually atomized or whether or not it incurs any other form of product break-up.  
         [0028]     In the implementation of the invention, and a first embodiment thereof, the dispensing system is preferably incorporated into a canister in which a product to be dispensed is held under gas pressure. In such an embodiment, carbon dioxide desorbed from the carbon adsorbent pressurizes the canister and maintains the pressure therein generally and during actuation of the canister dispensing valve in particular.  
         [0029]     Preferably, the product and the solid/gas arrangement are present in separate compartments in the canister. This is primarily to keep the product and the solid apart from each other in order to hold the solid in a predetermined part of the canister and/or to ensure in particular that the product, which may for example be in aqueous or other type of solution, does not contaminate the solid and thereby detract from its efficiency of adsorption.  
         [0030]     In some instances, the compartments may be separated by means of a wholly or substantially impermeable membrane. This membrane may take the form of a flexible bag which is sealingly attached either to the interior wall of the canister or to the canister operating valve or dispense block and which in use holds the product to be dispensed. The solid/gas arrangement is generally positioned within the canister outside the bag such that pressure is exerted on the exterior of the bag when pressure therein is released on actuation of the valve and a product is dispensed via the valve through a nozzle. An elastic material may be employed to form the bag. Furthermore, the membrane, whether of elastic or non-elastic material may be used and may be sealingly attached to any relevant part of the canister interior.  
         [0031]     The substantially impermeable membrane may alternatively take the form of a piston slidably mounted in the canister interior with the gas/solid arrangement on one side of the piston and the product to be dispensed on the other side such that actuation of a dispense valve causes pressure from gas desorbed from the solid to move the piston and urge the product to be dispensed from the canister via the valve.  
         [0032]     In other instances, the compartments may be separated by means of a fixed partition. Such a fixed partition may usefully be positioned in any useful part of the canister and preferably include the base thereof, to form the solid/gas arrangement compartment therein. It can, for example, be a concave-shaped disc in a ‘flat’ canister base or one of greater concavity than the (usually) concaveshaped canister base (as viewed from the exterior of the canister). It may advantageously be crimped to the canister between the canister wall(s) and its base to form an annular compartment between the disc and the base.  
         [0033]     The solid compartment may also be in the form of a container or ‘widget’that may be fixed to the canister (or part thereof) or allowed to be free within the canister interior.  
         [0034]     In addition, the carbon container may be associated with the canister dip tube, for example by being mounted around the dip tube for ease of assembly of the canister generally and the positioning of the container therein and, separately to allow for a ready filling of the container with adsorbed gas via the dip tube and via a one-way valve therebetween.  
         [0035]     Generally, the product and the solid/gas arrangement of the dispensing system of the invention are present in individual compartments in the canister, which are separated by a partition which may be fixed or displaceable. This keeps the product and the solid apart from each other in order to hold the solid in a predetermined part of the canister and/or to ensure in particular that the product, which may for example be in aqueous or other type of solution, does not contaminate the solid and thereby detract from its efficiency of adsorption.  
         [0036]     With a fixed partition, for example the substantially rigid wall of the carbon container, it is generally required that the gas from the solid/gas compartment can flow into the product compartment, but not vice versa, and this can readily be effected by having a one-way valve in the partition.  
         [0037]     Equally, there is a general need to provide means to allow the introduction of carbon dioxide into the solid/gas compartment prior to use of and during use of the system; this can also be effected by a one-way valve to prevent back flow of the gas from the solid/gas compartment.  
         [0038]     Each one-way valve should be designed such that it operates only under a certain applied pressure, for example a small fraction of 1 bar; otherwise the valve does not open.  
         [0039]     With certain valve designs, it is possible for a single valve to operate separately as a pressure sensitive valve in either direction depending on the requirements of the system.  
         [0040]     In such embodiments, the container for the carbon should have one-way valve means in order to allow the carbon dioxide to be desorbed from the solid and pass into the product compartment when the pressure in the canister falls, ie on operation of the canister dispensing valve, and thereby maintain canister pressures at predetermined levels for further use of the aerosol.  
         [0041]     In all cases, the one-way valve means may be made from any material and be of any suitable form including ones incorporated integrally into the body of the carbon container. One form which is particularly useful may comprise an upstanding valve body terminating in a parallel, double plate arrangement—preferably formed integrally with the wall of a product bag or fixed partition—such that the plates act as a closed valve in their usual position but which can move under their inherent resilience to an open position by virtue of gas pressure impinging thereon in a predetermined (single) direction, ie from the interior of the carbon container; such a valve is sometimes referred to as a ‘sphincter’ valve.  
         [0042]     The one-way valve advantageously is formed integrally with the partition and is preferably made from a plastic material, for example PET or silicone rubber.  
         [0043]     With a displaceable partition, this will generally be impermeable to the gas and may take the form, for example, of a bag for holding the product or a piston slideable within the canister with the desorbed gas from the carbon deforming the bag or moving the piston within the canister under the increased gas pressure applied thereon during actuation of the dispensing valve.  
         [0044]     In different embodiments of the invention, the dispensing system may be implemented with a product not held before its dispense under gas pressure. In such embodiments, the desorbed gas is not used to effect product dispense until it is required in use. These embodiments may be put into effect by restraining the gas pressure in the solid/gas container and effecting its release therefrom via valve means only when required during product dispense.  
         [0045]     In these different embodiments of the invention, the desorbed gas may be used to effect product dispense by: 
    i) causing the desorbed gas pressure to act directly on a product to effect product dispense, for example by urging the product through a dip tube inserted into the product in the canister, or     ii) causing the desorbed gas pressure to act indirectly on the product to effect product dispense, for example by its acting on a piston slideably supported in a canister body or part thereof, or     iii) causing the desorbed gas to effect product dispense by fluid dynamic (fluidic) action through the formation of a vacuum into which a product is drawn, sucked or otherwise urged, for example by causing desorbed gas to flow through a venturi in which the gas flow is increased and the pressure is decreased in the ‘throat’ 0  thereof, ie a partial vacuum is formed, and to which the product container can be linked to effect product dispense.    
 
         [0049]     In these separate embodiments of the invention, it may be advantageous —especially in regard to paragraphs i) and ii) above—to provide valve means to release the pressure applied directly or indirectly to the product to effect its dispense when the canister is being used.  
         [0050]     Use of the separate embodiments with an unpressurized canister is particularly useful in the case of a product in which the propellant gas can dissolve.  
         [0051]     In all embodiments, the carbon is advantageously held in a container which is preferably proximate to the dispensing block, for example by being attached thereto or may be less firmly linked, for example via a tube through which the carbon dioxide can be introduced into the container.  
         [0052]     In such preferred embodiments, the dispensing block itself advantageously incorporates a canister dispensing valve and passageways linking the interior of the canister with the exterior thereof via the valve. As such, the dispensing block, together with the carbon container, can readily and effectively be sealingly inserted into an aperture in the canister during canister assembly.  
         [0053]     In particular, the linkage of the container to the dispensing block generally allows firstly for a ready operation of the pressure pack and secondly allows for a simple mode of manufacture and assembly of the aerosol canister by allowing for the dispensing block—incorporating the canister dispensing valve, necessary passageways linking the interior of the canister with the exterior thereof, and also the carbon container linked thereto—to be inserted into an aperture in the canister, ideally the top of the canister, advantageously in a single assembly step.  
         [0054]     The invention therefore allows canisters of standard designs to be employed without modificationto the body thereof in order to suit implementation of the invention generally and to include canisters made of either steel or aluminum or other material.  
         [0055]     In preferred embodiments, the dispensing block and the carbon container are advantageously joined, for example by being made as an integrally formed unit, for example with the carbon container being situated beneath the dispensing block in a normal upright orientation of the canister. It is also advantageous for a dip tube to depend from the dispensing block, preferably being positioned centrally (axially) in the carbon container and, during use of the propellant system, extending into the body of the canister which includes the product to be dispensed.  
         [0056]     The container for the carbon can be, for example, made of a flexible plastic/polymer material in the form of a bag or alternatively be cylindrical in shape and advantageously made from a more rigid material, again preferably from a plastic/polymer material. The container is preferably cylindrical in shape.  
         [0057]     In general, it is preferred for the carbonto be placed in the container prior to the final assembly of the canister, ie prior to insertion of the dispensing block and into the product itself to which the container is linked into the canister aperture as described above.  
         [0058]     The product to be dispensed by the system of the invention is commonly inserted into the canister via a dip tube depending from the dispensing block and through which, during use of the aerosol, the product is dispensed via the dispensing valve in the reverse direction. The solid/gas container is advantageously linked to the dispensing block, for example by being positioned co-axially about the dip tube and as such can be regarded as an integral part of the dispensing block. In such cases, the block as a whole can therefore readily be placed in a canister aperture simultaneously during assembly of the canister.  
         [0059]     Means must also be provided for the introduction of the gas under pressure into the carbon container in order to cause it to be adsorbed onto the carbon and subsequently desorbed therefrom on operation of the dispensing valve. This can be effected, for example, by providing a suitable route via the dispensing block into the container interior and including (as described above) a one-way valve to prevent back flow of the gas.  
         [0060]     Overall, therefore, and in all embodiments of the invention, the product dispensing system provides a simple and effective way of utilizing gas desorbed from the adsorbent per se in order to provide a sufficient gas volume to produce an initial gas pressure and thereafter to maintain gas volumes, and necessary gas pressures, to enable a complete product dispense to be effected.  
         [0061]     In all embodiments of the invention, a pressure regulator may be used to regulate the gas pressure released from the adsorbent of the dispense system of the invention to a predetermined pressure level or within a predetermined range of pressure. For example, a 10 bar(a) pressure provided by desorbed gas may be regulated to produce propellant gas at 3 bar(a).  
         [0062]     With regard to the gas, it should be introduced into the dispensing system under pressure and which will be adsorbed onto the carbon such that its molecules are much more closely packed together than in the usual gaseous form at the same temperature and pressure.  
         [0063]     This means that, when the gas is introduced under pressure into a “gas space” surrounding the carbon, considerably more gas will be adsorbed onto the carbon. Consequently, as the system is activated, typically by actuating the pressure release valve, there will in practice be only a relative and surprisingly small pressure reduction within the system which, in use of the system, therefore allows for the effective dispensing of all of the product.  
         [0064]     In preferred embodiments utilizing carbon dioxide gas, it is injected initially under pressure in liquid form, for example down a dip tube depending from or integrally formed with the valve block.  
         [0065]     Adding the carbon dioxide in this way will generally produce a mixture of carbon dioxide snow and cold carbon dioxide gas.  
         [0066]     Using carbon dioxide in the form of a liquid or snow can in practice at least partially thermally balance the heat of adsorption of the carbon dioxide onto the carbon and maintain temperatures close to ambient.  
         [0067]     A double valve arrangement may be employed for measuring exact quantities of liquid carbon dioxide present between two valves positioned in a delivery tube of constant cross-section so as to define the required volume of gas needed for each canister as they pass along a conveyor assembly line. This is preferably effected by closing the upstream valve once the required volume of carbon dioxide is present between the valves and allowing the volume to ‘vaporize’, and to urge the stream of snow/gas into the canister.  
         [0068]     The gas may also be charged into the container in the form of solid carbon dioxide which is easy to handle and affords the benefits described above for liquid carbon dioxide.  
         [0069]     In general, it is beneficial to charge the gas into the container by means other than a ‘bung hole’ in the base of the canister as the presence of a bung hole may lead to gas leakage during storage/use of the canister.  
         [0070]     Activated carbons are well known per se and have the advantage that they are relatively inexpensive; they are non-polymeric substances. In general, activated carbons are manufactured from a variety of carbonaceous materials including (1) animal material (blood, flesh, bones, etc), (2) plant materials such as wood, coconut shell, corn cobs, kelp, coffee beans, rice hulls and the like and (3) peat, coal, tars, petroleum residues and carbon black.  
         [0071]     Activation of the raw carbonaceous materials can be effected in a variety of known ways including calcining at high temperature (eg 500° C. -700° C.) in the absence of air/oxygen followed by activation with steam, carbon dioxide, potassium chloride or flue gas at, say, 850° C. to 900° C., followed by cooling and packaging.  
         [0072]     Selected activated carbons are suitable for use in the systems of the invention, for example ones having a density of from 0.2 g/cm 3  to 0.55 g/cm 3 , preferably 0.35 g/cm 3  to 0.55 g/cm 3 .  
         [0073]     The quantity of carbon required in implementing the invention will vary depending on parameters including the gas employed, the initial and final pressures during the dispense of product, the nature of the product and its physical characteristics and the desired properties of the dispensed product. As such, the carbon may advantageously occupy from 5 to 95% of the canister interior volume.  
         [0074]     In the case of a standard size (300 ml) canister, it is preferred for many product types to have a carbon content of from 5 to 30% of carbon (by volume) which generally equates, for selected carbons, to the presence of 10 to 60 ml of carbon, more preferably 30 to 50 ml of carbon, for example 40 ml of carbon.  
         [0075]     With other product types, especially those of relatively high concentration of active ingredient(s), the carbon content may usefully be from 30 to 95%, preferably from 60 to 90%.  
         [0076]     In the case of the higher concentration products in particular, but also generally, the product dispensed from the nozzle of a canister incorporating a system of the invention may advantageously be improved by causing a separate bleed of gas to be directed into the dispensing valve or block and therein to mix with the product being expelled therefrom in order to effect a greater dispersion of the dispensed product.  
         [0077]     Such improvements are especially useful with more concentrated and/or more viscous products which might otherwise be difficult to disperse adequately for obtaining an effective spray pattern or whatever.  
         [0078]     In preferred embodiments of the invention, the activated carbon is present in the form of one or more pellets or torroids, ie in a much larger size than the granules in which it is normally supplied, for example of a size of at least 0.5 cm in length or greater. Such pellets or torroids may be fabricated by sintering or other binding processes and preferably will allow for a much larger surface area for the carbon dioxide and therefore a commensurately larger and more effective gas release on a reduced pressure.  
         [0079]     The pellets or torroids can advantageously be manufactured as sticks or tubes and/or with surface ribs or grooves or with apertures therethrough; all such forms can be capable of aiding adsorption/desorption of the gas.  
         [0080]     In general, specific ways of treating and/or handling the carbon are important aspects of the invention and may be essential for the implementation of dispensing systems of the invention.  
         [0081]     In particular, it has been found that there may be a propensity for the required properties of the carbonto degrade after the carbon activation process. Such degradation may include adsorption sites on the carbon being blocked by a gas or gases present in the atmosphere present around the carbon and which cannot subsequently be displaced by the gas that is to be adsorbed as the working gas in the dispensing systems of the invention. Although the blocking process may be reversible in certain cases, displacement by the preferred gas may not be effected completely and therefore would detract from the subsequent adsorption of the gas. In some instances, desorption of the initially held gas may be aided by high temperature and/or vacuum.  
         [0082]     In accordance with preferred aspects of the invention, therefore, the activated carbon is held, advantageously from the time of its production, under a blanketing atmosphere; this atmosphere may comprise the adsorbed gas itself, or a gas or gases (including mixtures with the adsorbed gas) that do not prevent the adsorbed gas subsequently occupying the carbon adsorption sites, in particular by virtue of being held at the adsorption sites on the carbon less strongly than the adsorbed gas.  
         [0083]     Certain gases, including water vapor, are more strongly held at the carbon adsorption sites than the adsorbed gas and carbon dioxide in particular and therefore should be rigorously excluded from the atmosphere around the carbon; subsequent attempts to dislodge the strongly held gases will not be successful.  
         [0084]     Although some gases are less strongly held at the adsorption sites than carbon dioxide and other adsorbed gases, they may still interfere with the subsequent adsorption efficiency characteristics of the adsorbed gas and should be avoided as blanketing gases.  
         [0085]     In the case of carbon dioxide as the adsorbed gas, the blanketing atmosphere preferably includes or comprises carbon dioxide itself. This can be especially advantageous in the implementation of the invention in dispensing systems when the carbon dioxide is preferably adsorbed onto the carbon at elevated temperatures. Other suitable gases include helium and hydrogen which are generally capable of being displaced from the adsorption sites by carbon dioxide. The potential use of other blanketing gases can be established by a skilled adsorption scientist on a theoretical or practical basis.  
         [0086]     Adsorption is an exothermic process in which considerable amounts of heat may be generated. The adoption of these preferred embodiments with a blanketing atmosphere that includes carbon dioxide itself is beneficial in that it allows an initial level of adsorption of carbon dioxide to occur—together with a dissipation of the generated heat—prior to the use of the carbon in dispensing systems of the invention. This can lead to significant advantages from the resultant lower amounts of heat generated when the remaining carbon dioxide is adsorbed under pressure in subsequent high speed production of canisters incorporating the dispensing systems of the invention.  
         [0087]     With all adsorbed gases, the blanketing of the carbon is preferably effected from the time of cooling and is preferably maintained continuously up to the time of (final) assembly of the canisters in which the dispensing systems are employed. To achieve this, the use of containers for holding the blanketed carbon is required in order to isolate the carbon from undesirable gases.  
         [0088]     In any event, the carbon granules or pellets or torroids may advantageously be pre-saturated with carbon dioxide (or other adsorbed gas) prior to use in order to improve the adsorption parameters. The granules/pellets/torroids may be advantageously cooled in such pre-saturation processes by use of cooled carbon dioxide, for example solid carbon dioxide or snow being in contact with the granules or pellets.  
         [0089]     In preferred embodiments and as stated above, the carbon granules/pellets/torroids are usefully kept in contact with a source of carbon dioxide or other adsorbed gas, especially cold gas, liquid or snow, prior to placement in a canister and this may provide sufficient adsorbed gas for use in the system without the need to add further amounts of gas.  
         [0090]     In the case of certain products, it has been found that it may be useful for optimum dispense characteristics to pre-treat the product with adsorbed gas prior to, or during, its introduction into the canister. This can be especially useful in the case of highly soluble gases such as carbon dioxide, ie ‘pre-carbonation’. Such a process is more useful in the case of product to be admixed with the adsorbed gas in the canister; it may, however, also apply to product present in the canister separated from the adsorbed gas by a moveable partition including a bag whether or not the partition allows for a certain leakage of gas therethrough.  
         [0091]     Working canisters incorporating the product dispense systems of the invention have been made to good effect in terms in particular of initial and final gas pressures during full product dispense as exemplified below with carbon dioxide adsorbed gas in particular:  
                                                       Canister volume   300 ml           Carbon volume    50 ml           ‘Free’ canister volume   250 ml           Liquid product volume   225 ml           Initial gas pressure    6 bara           Final gas pressure    4 bara (following full product dispense)                      
 
         [0092]     Tests on a canister containing a larger carbonto product volume ratio resulted in a proportionately lower change between initial and final pressures.  
         [0093]     All tests were conducted using activated carbon samples treated and handled with a carbon dioxide blanketing atmosphere from the time of cooling during production of the carbon.  
         [0094]     Tests with other adsorbed gases produced similar results depending on the adsorption characteristics of the individual gases.  
         [0095]     The invention will be described below in greater detail with reference, by way of example only, to the accompanying drawings. 
     
    
     Brief Description of the Drawings  
       [0096]      FIG. 1  shows a schematic vertical section through a canister incorporating a dispensing system of the invention;  
         [0097]      FIG. 2  shows a sectional view through the canister of  FIG. 1  along the line II-II; and  
         [0098]      FIG. 3  shows a schematic vertical section through a canister of different design to that of  FIG. 1  incorporating a dispensing system of the invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0099]     With reference to the drawings and to  FIG. 1  in particular, there is shown a canister  1  incorporating a pressure pack dispensing system of the invention. The canister  1  comprises a cylindrical main body portion  2 , a circular base portion  3  of concave shape (external view) and a circular top portion  4  of convex shape (external view), all made of aluminum alloy material.  
         [0100]     The base portion  3  is sealingly crimped around its periphery to the lower edge of the main body portion  2  in a manner known per se for aerosol canister in particular.  
         [0101]     Sandwiched and sealingly held within the crimped structure between the main body portion  2  and the base portion  3  is a circular partition  5  made of plastic and having a greater concavity shape than the base portion  3 .  
         [0102]     The base portion  3  has a small circular “bung”  6  at its centre made of rubber (or other elastomer) and the partition  5  has an upstanding one-way valve  7  allowing for the flow of fluid from a compartment  8  formed between the base portion  3  and the partition  5  and into the upper compartment containing the substance to be dispensed but not vice-versa.  
         [0103]     The one-way valve  7  comprise two upstanding plates  9 ,  10  (see  FIG. 2 ) which are formed integrally with the partition  5  and which, by virtue of the relative positioning of the plates  9 ,  10  and the nature of the plastic material from which they are made, are biased to lie adjacent each other in the vicinity of their ends furthest from the partition  5 .  
         [0104]     As such, the one-way valve  7  will open by parting the plates  9 ,  10  when there is, in use, an excess pressure in the compartment  8  over that in the interior of the remainder of the canister  1 .  
         [0105]     The plates  9 ,  10  will not part and the valve  7  will therefore not operate in the opposite direction as any excess pressure in the canister  1  will not cause such parting by virtue of the shape of the adjacent ends of the plates.  
         [0106]     The top portion  4  is sealingly crimped around its periphery to the upper edge of the main body portion  2  again in a manner known per se for aerosol canisters in particular.  
         [0107]     Positioned centrally of the top portion  4  in an aperture thereof is an operating valve system  11  comprising a valve seat  12  against which a ball valve member  13  is in its “closed” position held but which can be unseated in its “open ” position by depression of an operating button  14  against the action of a spring  15 . Release of the button  14  causes re-seating of the valve member  13  by means of the spring  15 .  
         [0108]     A tube  16  depends downwardly from the valve system  11  and a discharge line for the substance to be dispensed is formed from the lower end of the tube  16 , through the tube  16  itself and via the valve mechanism to a discharge port  17  in the operating button  14 .  
         [0109]     In the manufacture of the canister  1 , activated carbon  18  is included in the compartment  8  between the base portion  3  and the partition  5  and the substance to be dispensed is charged into the canister  1  above the partition  5  via the aperture in the top portion prior to installation of the valve system  11 .  
         [0110]     With the valve system  11  in place, carbon dioxide gas or liquid is loaded into the compartment  8  by means of a needle injection through the rubber bung  6 , causing its adsorption into the activated carbon  18  in the compartment  8 . The carbon dioxide gas pressure in the compartment  8  equalizes the pressure in the canister  1  surrounding the substance to be dispensed via the one-way valve  7 .  
         [0111]     In use of the canister  1 , the carbon dioxide pressure generated by the pressure pack system of the invention will, when the operating button  14  is depressed, urge the substance being dispensed from the canister  1  via the tube  16  and the valve system  11  and the discharge port  17 .  
         [0112]     With reference to  FIG. 3 , there is shown a canister  31  incorporating a pressure pack dispensing system of the invention. The canister  31  comprises a cylindrical main body portion  32 , an integrally formed circular base portion  33  of concave shape (external view) and a circular top portion  34  of convex shape (external view), all made of an aluminum alloy material.  
         [0113]     Positioned centrally of the top portion  34  is an aperture  35  and sealingly held therein is a dispensing block  36  having a main passageway  37  therethrough and an associated valve  38  for allowing, in use, product to be dispensed from the interior of the canister. Biasing means, for example a spring (not shown), urges the valve towards a closed position.  
         [0114]     The passageway  37  is linked at one end to a reciprocatable valve actuating hollow tube  39  and at the other end to a ‘dip’ tube  40  extending into the main body portion  32 .  
         [0115]     An operating cap  41  is positioned over the dispensing block  36  and movement (depression) thereof towards the body portion  32  actuates the hollow tube  39  and causes opening of the valve  38 .  
         [0116]     A further passageway  42  in the dispensing block  36  has an opening adjacent the operating cap  41  and extends into the interior of a canister  44  attached to the dispensing block  36  and forming an integral unit therewith.  
         [0117]     A one-way valve  45  is present in the passageway  42  to allow flow of fluid into the container  44  but not vice versa. A further one-way valve  46  is present in the base of the container  44  to allow flow of carbon dioxide from the container  44  and into the canister  31  when the pressure in the canister falls below that of the container  44 .  
         [0118]     In assembling the canister including the pressure pack of the invention, the dispensing block  36  (to include the dip tube  40  and the linked container  44 ) is sealingly inserted into the aperture  35  in the canister top portion in a single assembly step.  
         [0119]     The canister is filled with liquid product to be dispensed via a needle inserted into the hollow tube  39  and operates to open the valve  38  against the action of the biasing means in order to allow the liquid to flow through the passageway  37  and dip tube  40  and fill the canister up to the product level  47 .  
         [0120]     The container  44  is pre-packed with activated carbon held under an atmosphere of carbon dioxide since its production and additionally pre-flushed with carbon dioxide. After insertion of the dispensing block, etc into the aperture  35  and product into the canister interior, a source of carbon dioxide gas under pressure is attached to the passageway  42  for pressurization of the container  44  via the one-way valve  46  and to cause the adsorption of the carbon dioxide onto the activated carbon in the container. The presence of the further one-way valve  46  allows the carbon dioxide to pressurize the head space above the product in the canister  31  until the respective pressures are substantially equalized.  
         [0121]     The operating cap  41  is then fitted over the dispensing block and the aerosol canister is ready for use. Depression of the operating cap  41  moves the tube  39  and actuates the valve  38  to allow product to pass up the dip tube  40  and be dispensed from the canister via the passageway  37 , the tube  39  and a passageway (not shown) in the operating cap  41  to a nozzle  48  in the cap  41 , all under the carbon dioxide gas pressure present in the head space.  
         [0122]     Resulting loss of carbon dioxide pressure in the head space is replenished by an automatic flow of gas from the container  44  via the one-way valve  46 . Pressure in the container  44  itself is maintained by desorption of further gas from the activated carbon.