CA2271418A1

CA2271418A1 - Gas generating unit

Info

Publication number: CA2271418A1
Application number: CA002271418A
Authority: CA
Inventors: Eddy Vos; Michael Felix Spruyt
Original assignee: Individual
Current assignee: Procter and Gamble Co
Priority date: 1996-11-25
Filing date: 1997-11-18
Publication date: 1998-06-04
Also published as: AR011513A1; EP0844197A1; JP2001506566A; WO1998023504A1; CN1245470A; BR9713544A

Abstract

The present invention relates to a gas generating unit. A further aspect of the invention relates to an aerosol container having the gas generating unit sealed within the aerosol container, and wherein the gas generating unit generates gas to maintain or increase the internal pressure of the aerosol container. The gas generating unit comprises at least two compartments, the first compartment (1) and the second compartment (2) being connected by a sealable communication means (3); the first compartment (1) contains a liquid, wherein at least some of the liquid passes from the first compartment (1) into the second compartment (2) when the sealable communication means (3) is opened, so that the liquid contacts at least one chemical reagent (20) and causes a chemical reaction to take place which generates a gas, wherein the gas generating unit is substantially rigid, and that the wall of the gas generating unit has least one hole (6) so that the gas generated is released.

Description

GAS GENERATING UNIT
The present invention relates to a gas generating unit.
A further aspect of the invention relates to an aerosol container having the gas generating unit sealed within the aerosol container, and wherein the gas generating unit generates gas to maintain or increase the internal pressure of the aerosol container.
One type of unit for releasing gas has been developed for the canned beer industry. W091/07326, published on 30 May l991, discloses a hollow Compartment containing a pressurised gas. The compartment is fitted inside a can of beer so that when the can is opened the hollow compartment releases its contents as a jet of gas into the beer.

Gas generating units could also be useful in aerosol containers, albeit for different reasons. It is well known in the aerosol industry that there is a need to move out HFC propellants on account of their environmental profile. The replacement choice has mostly been the low molecular weight hydrocarbons such as propane, butane, pentane, hexane, etc., but these are flammable gases which may not always be suitable for use inside confined appliances with potential ignition sources. For these reasons, the industry is seeking a move to more environmentally friendly chemicals.
Replacing the organic propellants, such as those listed above, by non-liquifiable propellant gases presents new problems. Unlike more conventional liquifiable organic propellant gases, gases such as carbon dioxide and nitrous oxide cannot be liquified at the pressures obtainable in an aerosol container (i.e. typically 10 to Z2 bar maximum). As the product composition is progressively emptied out of the aerosol canister the carbon dioxide or nitrous oxide in the headspace cannot be replenished as would be the case with liquifiable propellants, and consequently the pressure in the headspace drops. If the headspace pressure drops too low it will no longer be possible to dispense a product from the aerosol container.

WO 98l23504 PCT/US97/21139 Practical and regulatory limits on pressures within aerosol cans impose an upper limit on the amount of gas that can be charged into the can. Higher amounts of gas would lead to excessive internal pressures and safety hazards.
A gas generating unit within the aerosol container would address these problems.
One method to address these and other problems is proposed in EP-A-0 044 S87, published on 3 February 1982. This application discloses a flexible bag which is assembled with acid and alkali components. The acid and alkali components are brought together to react and release a gas which inflates the bag. However the flexible bag is difficult and expensive to assemble and to place into aerosol cans on an automatic packing line.
An object of the present invention is to provide a gas generating unit which is easy and cheap to manufacture.
A further object of the invention is to provide a gas generating unit which can be charged into aerosol containers on a packing line, even a high-speed packing line, with minimal modification to the line. A still further object of the invention is to provide a gas a generating unit within an aerosol can which generates a gas pressure which will not exceed the can specifications for allowable internal pressure. In WO 98f23504 PCTIUS97f21139 particular it is preferred that the gas generating unit will not generate a pressure greater than 12 bar at 50°C.
The gas generating unit of the present invention comprises at least two compartments, the first compartment and the second compartment being connected by a sealable communication means; the first compartment containing a liquid, wherein at least some of the liquid passes from the first compartment into the second compartment when the sealable communication means is opened, so that the liquid contacts at least one chemical reagent and causes a chemical reaction to take place which generates a gas Summary of the Invention The objects of the invention are achieved by providing a gas generating unit which is substantially rigid, and wherein the wall of the gas generating unit has at least one hole so that the gas generated is released.
In a first embodiment of the present invention the first compartment contains an acid solution, and the second compartment contains a solid carbonate or bicarbonate.
In a second, alternative embodiment of the present inventi4n the first compartment contains water and the second compartment contains a mixture of at least two chemical reagents in solid form, the two chemical reagents being (a) an acid and (b) carbonate or bicarbonate.
Brief Description of the Drawings The figure shows a cross-section taken through one embodiment of a gas generating unit of the present invention.
Detailed Description of the Invention The gas generated by the gas generating unit depends on the chemical reagents selected for the second, or the first and second, compartments. Preferably the alkali component is carbonate or bicarbonate, so the resulting gas is carbon dioxide. As used herein the word "carbonate" is used to express either carbonate or bicarbonate. The carbonate may be used in any salt form, but sodium, calcium and magnesium salts are preferred.
The acid may be any suitable acid, but it is preferably selected from the group consisting of citric acid, malic acid, malonic acid, fumaric acid, glycolic acid, tartaric acid, aspartic acid, succinic acid, glutaric acid, adipic acid, aconic acid, ascorbic acid, hydrochloric acid, sulphuric acid or mixtures thereof.
Particularly preferred are the organic acids, and most particularly preferred is malefic acid.
In a first embodiment of the present invention the first compartment contains an acid solution, and the second compartment contains a solid carbonate or bicarbonate.
In a second, alternative, embodiment of the present invention the first compartment contains water and the second compartment contains a mixture of at least two chemical reagents in solid form, the two chemical reagents being (a) an acid and (b) carbonate or bicarbonate.
The solid form of the carbonate and, when used in solid form, of the acid) may be, for example as a powder or as a tablet. In the second embodiment of the invention the carbonate and acid may be placed in the second compartment as discrete, preferably premixed, powders.
Alternatively either or both of the carbonate and acid may be in the form of separate tablets, or in the form of a mixed carbonate/acid tablet.

The chemical reaction is started when liquid passes from the first compartment into the second compartment through the communication means. The communication means is closed prior to the first release of gas, and is then opened either once, or multiple times. In order to achieve this the communication means is preferably provided with a valve or a rupturable membrane. In one embodiment of the invention the valve is designed to open only once, after which release of substantially a11 of the available gas takes place. In an alternative, preferred, embodiment of the invention the valve is provided with a means for opening the valve when the external pressure drops below a preset minimum, and for closing the valve when the external pressure exceeds a preset maximum. In this embodiment of the invention the release of gas may be repeated many times until all of the chemical reagents axe consumed.
It is preferred that at least a part of the wall of the first compartment is made from a material which is permeable to gas. Preferably at least a part of the wall of the second compartment is also made from a material which is permeable to gas. Most preferably the walls are permeable at least to carbon dioxide.
Referring to the figure, a gas dispensing unit is shown comprising a first compartment 1 and a second WO 98I23504 PCTlUS97/21139 compartment 2. The compartments are connected by a communication means 3 which is closed by a sealing valve 4. The valve is connected to a valve stem 5. The second compartment 2 is in direct communication with the outside of the gas generating unit by means of holes 6 in the wall of the second compartment. The holes are shown blocked by a closing means 7 which prevents product from the outside of the gas generating unit from entering the second compartment 2 and contaminating the reactants. However the closing means is opened by the pressure of gas generated inside the second compartment 2, allowing the gas to pass out of the second compartment 2.
In the preferred embodiment of the invention the first compartment 1 contains water, whilst the second compartment 2 contains a tablet 20 made from dry powders of sodium carbonate and malefic acid. However as disclosed above, various combinations of solutions, powders and different acids and salts are possible.
The walls of both first and second compartments 1, 2 are permeable allowing the whole unit to equilibrate at a starting pressure of, for example, 10 bar. When the external pressure drops below a preset level, a flexible wall 21 expands outwardly decreasing the pressure in the second compartment. The flexible wall 21 is connected through the valve stem 5 to the valve 4. The outward expansion of the flexible wall 21, and the'fact that the pressure in the first compartment exceeds the pressure in the second compartment, causes the valve 4 to move opening the communication means 3 between the first and second compartments 1, 2. This allows water to pass from the first compartment 1 into the second compartment 2, initiating a chemical reaction between the carbonate and the acid which releases carbon dioxide. The carbon dioxide forces the closing means 7 to open, and passes out of the gas generating unit through the holes 6 in the wall of the second compartment 2.
In a further aspect of the invention, the gas generating unit is placed within sealed container having a dispensing means, especially an aerosol container.
Preferably the aerosol container is provided with an initial charge of a propellant gas to pressurise it internally. Particularly suitable propellants include carbon dioxide, nitrogen, nitrous oxides, oxygen, air and mixtures thereof. Liquifiable gases such as fluorocarbons (e. g. CFC, HCFC and HFC), alkanes (e. g.
propane, butane, pentane, hexane) may also be used, but are preferably used in minor amounts to reduce any environmental and flammability concerns. After successive uses of the aerosol container the internal pressure falls. At a certain minimum pressure the gas generating unit acts as described above to release WO 98/23504 PCT/US9?I21139 additional gas into the aerosol container thereby raising the pressure.
Typically the sealed container will comprise a liquid product which is dispensed by means of a dispensing means such as a valve or valve nozzle assembly.
zn a preferred embodiment of the present invention the liquid product is dispensed in the form of a foam when the dispensing means is activated. The use of the gas generating unit means that the density of the foam can be maintained almost constant throughout the life of the container. It is possible to provide a foam which when dispensed in twenty doses, each dose being equal in weight, has a density of the final dose which is no more than 10% higher than the density of the first dose.
To measure foam density a glass beaker, 62mm internal height, 111mm internal diameter is degreased with a standard soap solution and well rinsed with distilled water. The beaker is filled with foam until overflowing, excess foam being scraped off using a straight edge wiped across the top edge of the beaker. The difference in weight of the full beaker (W2) minus the empty beaker (W1) is the weight of foam. The volume of the beaker (V) is known. Foam density is calculated by (W2-W1)/V.

Claims

What is claimed is:

1. A gas generating unit comprising at least two compartments, the first compartment (1) and the second compartment (2) being connected by a sealable communication means (3);
the first compartment (1) containing a liquid, wherein at least some of the liquid passes from the first compartment (1) into the second compartment (2) when the sealable communication means (3) is opened, so that the liquid contacts at least one chemical reagent (20) and causes a chemical reaction to take place which generates a gas, characterised in that the gas generating unit is substantially rigid, and that the wall of the gas generating unit has at least one hole (6) so that the gas generated is released.

2. A gas generating unit according to claim 1 wherein the first compartment (1) contains an acid solution, and the second compartment (2) contains carbonate or bicarbonate.

3. A gas generating unit according to claim 1 wherein the first compartment (1) contains water and the second compartment (2) contains a mixture of at least two chemical reagents in solid form, the two chemical reagents being (a) an acid and (b) carbonate or bicarbonate.

4. A gas generating unit according to any of claims 1 to 3 wherein the sealable communication means (3) comprises a valve mechanism (4) and means for opening the valve (5) when the external pressure drops below a preset minimum, and for closing the valve mechanism (4) when the external pressure exceeds a preset maximum.

5. A gas generating unit according to claim 1 wherein the second compartment (2) has a wall, the wall having a hole (6), the hole (6) being closed by a closing means (7) which allows gas to pass out of the second compartment (2), but does not allow product outside of the unit to enter the second compartment (2).

6. A gas generating unit according to claim 1 wherein the first and second compartments (1, 2) have a wall, at least a part of the wall being impermeable to liquid, but permeable to gas.

7. A gas generating unit according to claim 6 wherein the permeable part of the wall is permeable to carbon dioxide.

8. A sealed container having a dispensing means, especially an aerosol container, the container having a gas generating unit according to any of the previous claims within the container.

9. A sealed container according to claim 8 further comprising a liquid product, wherein the liquid product is dispensed in the form of a foam when the dispensing means is activated.

10. A sealed container according to claim 9 wherein the foam, when dispensed in twenty doses, each dose being equal in weight, has a density of the final dose which is no more than 10% higher than the density of the first dose.