Aerosol dispenser and method

An aerosol dispenser is provided which comprises a body (1), a closure (2) sealed to the body (1), and propellant (7) for dispensing material from the interior of the dispenser. The closure (2) is welded to the body (1) by a metal-to-metal weld. Preferably the welding is carried out ultrasonically. A method for assembling the aerosol dispenser is also provided.

This invention relates to an aerosol dispenser, i.e. a dispenser from which 
a material can be dispensed in aerosol form. It is particularly, though 
not exclusively, concerned with metered dose medicament aerosols, for 
example metered dose inhalers. 
The upper portion of one known dispenser is shown in vertical section in 
FIG. 1 of the accompanying drawings. This comprises a metal can body 1 and 
a metal closure 2 having a flange 3 the lower end of which is crimped 
around an upper wall portion 4 of the can body 1. The closure 2 has a 
downwardly opening annular channel 5 within which is received a sealing 
gasket 6. The upper edge of the wall portion 4 of the can body 1 is in 
sealing engagement with the gasket 6. 
The dispenser is provided with a valve arrangement 7, the purpose of which 
is to enable metered doses of a material held under pressure within the 
can body 1 to be dispensed. Most of the details of this are not relevant 
to the present invention, and, furthermore, they are conventional. For the 
purposes of the present discussion it is sufficient to note that the valve 
arrangement 7 includes a metering chamber 8, within which a dose is held 
prior to being dispensed, and a hollow stem 9 which is longitudinally 
movable with respect to the chamber 8. The stem has a transfer port 10 and 
an outlet 11. When the stem is depressed from the position shown, the dose 
passes from the chamber 8 through the port 10 into the stem, and from 
there it passes out through the outlet 11. The stem 9 is in slidably 
sealing engagement with an aperture formed in the centre of a sealing ring 
12. 
Although the materials used for gaskets in aerosol dispensers are carefully 
chosen when medical applications are involved, to be as inert as possible, 
it is nevertheless recognised that it is desirable to reduce the amount of 
gasket material which can come into contact with the material to be 
dispensed. The largest gasket area in FIG. 1 is that presented by the 
gasket 6, and it would therefore be particularly desirable to eliminate 
gasket 6. Such elimination also potentially offers the prospect of a 
cheaper dispenser than FIG. 1, by virtue of the fact that it uses one less 
component. 
It is also desirable to ensure that the aerosol dispenser is as nearly 
leak-proof as possible, and the gasket 6, though found in practice to give 
a good performance in this respect, does offer a potential leakage path 
extending circumferentially around the container. For that reason also, it 
would be desirable to eliminate the gasket and provide a seal between the 
body 1 and closure 2 which offered no such potential leakage path. 
According to the present invention there is provided an aerosol dispenser 
which comprises a body, a closure sealed to the body, and means for 
dispensing material from the interior of the dispenser, wherein the 
closure is welded to the body by a metal-to-metal weld. Preferably the 
welding is carried out ultrasonically. 
The invention also provides a method of assembling an aerosol dispenser 
comprising a metal body, a metal closure, and means for dispensing 
material from the interior of the dispenser, wherein the closure is welded 
to the body by a metal-to-metal seal.

In FIG. 2, the same numerals are used as in FIG. 1 for the corresponding 
parts. It will be seen that the metal body 1 terminates at its upper end 
in an outwardly directed, planar, annular flange 14, and that the 
circumferentially outer portion of the metal closure 2 is likewise in the 
form of a planar, annular flange 15. The flanges 14 and 15 are welded 
together along their mating surfaces 16 by a metal-to-metal weld. It is 
convenient to weld the flanges ultrasonically using conventional apparatus 
as for example is described in U.S. Pat. No. 4,749,437. Ultrasonic welding 
enables only very localised heating to be produced in the region of the 
weld itself. This may enable the can to be filled before the closure is 
secured thereto (the alternative being to fill the can through the valve 
arrangement) since it reduces the risk of the medicament being undesirably 
heated. 
Two alternative procedures will now be mentioned with reference to FIGS. 3 
and 4 for forming the weld between the flanges 14 and 15. In the first as 
depicted in FIG. 3, an ultrasonic welding head travels circumferentially 
along the flanges until a complete revolution has been performed. This can 
be done relatively simply though the welding time is then quite long. The 
welding head can comprise two wheels 17 and 18, one of which engages 
flange 14 and the other of which engages flange 15. Each wheel is 
rotatable about an axis extending radially with respect to the annular 
flange. The wheels are urged towards one another, and at least one of them 
is vibrated at an ultrasonic frequency along its axis of rotation. 
In the second procedure as depicted in FIG. 4, a torsional weld is formed. 
This involves placing a fixed member or anvil 19 on one side of the pair 
of flanges (preferably abutting flange 14), and bringing into contact with 
the other flange (preferably flange 15) a welding horn in the form of a 
ring 20 which is coaxial with the flange and which vibrates at an 
ultrasonic frequency about its axis of rotational symmetry. 
The following tables set out the mean, maximum and minimum results of 
testing for leakage and moisture ingression in the case of metal closures 
sealed to metal cans by ultrasonic welding, and metal closures sealed to 
metal cans by conventional crimping. The results are summarised in the 
graphs of FIGS. 5 and 6, which plot the average results attained in each 
test. The leakage tests were carried out using a number of samples of 
cariclosure, and in each case the cans were filled with a quantity of 
propellant and the amount of propellant which had leaked from the can was 
determined at intervals by weighing the sealed can. The moisture 
ingression tests were also carried out using a number of samples of 
caniclosure, and in each case a quantity of hygroscopic material 
(molecular sieve pellets) was sealed in a can and the amount of moisture 
which had been absorbed by the material was determined at intervals by 
weighing the sealed can. 
The results of the leakage tests show that cans with closures sealed by 
ultrasonic welding exhibit lower leakage at each weighing interval both 
under ambient atmospheric conditions and under conditions of high 
temperature (40.degree. C.) and high relative humidity (85%). 
The results of the moisture ingression tests show that under ambient 
atmospheric conditions the two methods of sealing gave similar effects. 
However, under conditions of high temperature (40.degree. C.) and high 
relative humidity (85%), no moisture ingression could be detected with the 
ultrasonic weld, whereas significant moisture ingression occurred with the 
crimped seal. 
TABLE 1 
______________________________________ 
LEAKAGE TEST RESULTS 
______________________________________ 
Propellant Filled Ultrasonic Weld-Sealed Inhalers 
Ambient Storage - sample size: 11 inhalers 
Weight Loss(g) 
7 days 14 days 2l days 
28 days 
______________________________________ 
Mean -0.001 
0.000 
0.001 
Maximum 0.000 
0.001 
0.002 
Minimum -0.002 
-0.002 -0.001 
0.000 
______________________________________ 
40.degree. C./85% Relative Humidity Storage - sample size: 10 inhalers 
Weight Loss (g) 
7 days l4 days 2l days 
28 days 
______________________________________ 
Mean 0.002 0.013 
Maximum 0.002 
0.009 0.061 
Minimum -0.002 
0.000 
0.002 
______________________________________ 
Propellant Filled Crimp-Sealed Inhalers 
Ambient Storage - sample size: 14 inhalers 
Weight Loss (g) 
7 days l4 days 2l days 
28 days 
______________________________________ 
Mean 0.001 0.003 0.011 
Maximum 0.002 0.006 0.015 
Minimum -0.002 
0.000 
0.002 
0.008 
______________________________________ 
40.degree. C./85% Relative Humidity Storage - sample size: 15 inhalers 
Weight Loss (g) 
7 days l4 days 2l days 
28 days 
______________________________________ 
Mean 0.019 0.031 
0.048 
Maximum 0.009 
0.023 
0.036 
0.056 
Minimum 0.003 
0.016 
0.026 
0.042 
______________________________________ 
TABLE 2 
______________________________________ 
MOISTURE INGRESSION TEST RESULTS 
______________________________________ 
Silica Gel Filled Ultrasonic Weld-Sealed Inhalers 
Ambient Storage - sample size: 11 inhalers 
Weight Gain (g) 
7 days l4 days 2l days 
28 days 
______________________________________ 
Mean 0.001 
0.001 
0.000 
Maximum 0.002 
0.002 0.003 
0.002 
Minimum 0.000 
0.000 0.001 
-0.002 
______________________________________ 
40.degree. C./85% Relative Humidity Storage - sample size: 15 inhalers 
Weight Gain (g) 
7 days l4 days 21 days 
28 days 
______________________________________ 
Mean 0.002 0.002 
0.003 
Maximum 0.005 
0.003 
0.004 0.004 
Minimum 0.001 
0.001 
0.002 0.002 
______________________________________ 
Silica Gel Filled Crimp-Sealed Inhalers 
Ambient Storage - sample size: 15 inhalers 
Weight Gain(g) 
7 days l4 days 21 days 
28 days 
______________________________________ 
Mean -0.001 
-0.001 0.000 
-0.002 
Maximum 0.000 
0.001 0.001 
0.000 
Minimum -0.002 
-0.002 -0.002 
-0.003 
______________________________________ 
40.degree. C./85% Relative Humidity Storage - sample size: 15 inhalers 
Weight Gain 
7 days 14 days 21 days 
28 days 
______________________________________ 
Mean 0.005 0.007 
0.008 
Maximum 0.004 
0.006 0.009 
0.009 
Minimum 0.000 
0.003 0.007 
______________________________________ 
When the flanges 14 and 15 have the form shown in FIG. 2, the contents of 
the dispenser, being under pressure, exert a peel force on the weld 
between the flanges. A welded joint is relatively weak under a peel force, 
though nevertheless strong enough to withstand any force to which it is 
reasonably likely to be exposed. If, however, it is desired to avoid 
exposing the welded joint to a peel force, the flanges can alternatively 
have the shape in FIG. 7 wherein the flanges are axially directed and 
cylindrical. To achieve this, either the flanges may be welded in the form 
shown in FIG. 2, and then bent through 90.degree., or they may be bent 
first and welded afterwards. 
In the latter case, the weld may be formned by an ultrasonic welding device 
shown in FIG. 7 in which a first wheel 21 travels around the outside of 
the flange 14, and a second wheel 22, mounted eccentrically with respect 
to the longitudinal axis of the dispenser, contacts the inside of the 
flange 11 at a point which moves around the flange 15 in unison with the 
movement of the first wheel until a complete revolution of the flange has 
been performed. During this process, the wheel 21 vibrates ultrasonically 
along its axis of rotation (i.e. up and down as drawn), the wheels 21 and 
22 simultaneously being urged towards one another with a substantial 
force. Means (not shown) are provided to ensure that the closure does not 
fall into the can body during the sealing process. The second wheel 22 has 
the shape of an inverted cup, in order to avoid being fouled by the valve 
stem 9 and the adjacent portion of the closure 2. 
An alternative to the flange shape of FIG. 7 as a way of avoiding 
subjecting the weld joint to a peel force is shown in FIG. 8, in which the 
flanges are welded in the shape shown in FIG. 2, and then bent downwardly. 
Correctly carried out, ultrasonic welding should give a completely 
leak-proof seal between the flanges. However, it is possible as a 
precaution to further seal the flanges together by having interengaging 
U-shaped portions on the body and closure. This is shown in FIG. 9, and 
FIGS. 10a to 10c show successive steps in sealing the closure to the body 
to form the construction shown in FIG. 9. The ultrasonic weld is formed 
after the closure 2 and can body 1 have been formed as shown in FIG. 10a 
and assembled with one another, but before the rolling and crimping 
operations of FIGS. 10b and 10c have been carried out.