Note: Descriptions are shown in the official language in which they were submitted.
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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.
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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.
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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
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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
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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,
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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.
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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
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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
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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
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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.
