Note: Descriptions are shown in the official language in which they were submitted.
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ATOMI S ING NOZ ZLE
The invention relates to atomising nozzles
commonly used for, but not limited to, hand held sprayers
such as so-called aerosols and pump type atomisers,
intended for the application of liquid household, cosmetic
and pharmaceutical products.
Aerosol type sprayers are used throughout the
world for dispensing a wide range of products, for example
hair lacquer, furniture polish, cleaners, paint, insect
killers and medicaments. Until recently,
chlorofluorocarbons (CFCis) were the most common of the
propellant gases used in aerosols because they are inert,
miscible with a wide range of products, are easily
liquefied under low pressures, give a substantially
constant product flow-rate, and can produce sprays of
droplets having mean diameters in the range of 3 to over
100 micrometers. However, in the 1970's it was confirmed
that CFC's were probably responsible for depleting the
Earth's protective ozone layer, and in 1987, most countries
signed the Montreal Protocol to phase out the use of CFC's.
Alternative propellants were then introduced - for example
liquefied hydrocarbon gases such as butane, and carbon
dioxide, which is dissolved in the product, - but these are
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flammable or otherwise harmful to the environment, or react
with the product, and these propellant gases are gradually
being phased out. There has been much development of
aerosols powered by compressed gas (eg nitrogen, air), and
manually operated pump atomisers, and for the majority of
applications the performance of such sprayers is adequate.
The main drawback of these non-CFC sprayers is
that the smallest sized droplet that can be produced is
about 40 micrometers diameter, and despite considerable
development of so-called mechanical breakup nozzles, the
use of high pressure (c 15 bars) pumps, and low
viscosity/surface tension product formulations, 40
micrometers appears to be the lower limit achievable with
prior art methods and devices.
There are aerosol generators used for research
and hospital applications, such as ultrasonic nebulisers
and spinning disc generators, but neither is suitable for
portable, convenient atomisers.
It is also possible to force liquid at high
pressure through a very small hole (5-10 micrometers
diameter) to produce droplets of about 5 micrometers
diameter, but these methods are unsuitable or uneconomic
for large scale manufacture, mainly because of the
difficulty in making very small holes in a suitable
material, and, to prevent blockage of the hole, the need
for exceptional cleanliness in the manufacture of the
parts, together with ultrafiltration of the fluid to be
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sprayed.
For veterinary and some human vaccination
applications, high pressure (125 - 500 bars) spring or gas
operated pumps (so-called needle-less injectors) are in
common use to inject a jet of drug through the skin
("intra-dermal injection") without the use of needles, and
attachments are available to convert the jet to a spray for
administering drugs to the nasal passages of large animals
such as swine. However, the smallest droplet size
obtainable is in the order of 40 micrometers, and the range
of applications for these injectors is limited.
Compressed air atomisers such as air brushes and
commercial paint sprayers consume large quantities of air,
and to obtain droplets of 5 micrometers with water for
example, a gas to liquid ratio of over 30,000:1 is
required, which is impractical for convenient, portable
sprayers.
Nevertheless, there are some applications that
rely on a smaller droplet size for maximum efficacy: space
sprays such as flying insect killers should contain
droplets ideally in the range of 20-30 micrometers diameter
to ensure a long flotation time in the air, and for metered
dose inhalers (MDI's) used for treating certain respiratory
disorders it is essential that the aerodynamic particle
size should be less than 15 micrometers, preferably less
than 5 micrometers, so that the droplets are able to
penetrate and deposit in the tracheobronchial and alveolar
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regions of the lung. For a spray composed of droplets with
a range of sizes, more than 5~ by weight of the droplets
should have an aerodynamic size less than 6.4 micrometers,
preferably more than 20 by weight of the particles have an
aerodynamic size less than 6.4 micrometers.
Inhalers may also be designed to deliver drugs to
the alveolar sacs of the lung to provide a route for
adsorption into the blood stream of drugs that are poorly
adsorbed from the alimentary tract. To reach the alveoli
it is essential that the aerodynamic size of the particles
is less than 10 micrometers, preferably 0.5-5 micrometers.
Many of the drugs used in the treatment of
respiratory disorders are insoluble in vehicles such as
water and are dispensed as suspensions. The drugs are
produced in a respirable size of 1-5 micrometers.
Particles of this size tend to block the very small holes
(5-10 micrometers) used by known devices to generate
droplets of about 5 micrometers diameter.
The present invention aims to provide a design of
atomising nozzle which is capable, inter alia, of being
used to give a nozzle which will produce a spray of
droplets of a size suitable for inhalation, without the use
of liquefied gas propellants. However, the present
invention is believed to be capable of being used to give
a nozzle which will produce a spray of droplets having a
mean diameter anywhere in the range of from 0.5 to over 100
micrometers.
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According to the present invention there is
provided an atomising nozzle for producing a spray of
droplets from a liquid passing through the nozzle under
pressure, which nozzle comprises means defining an orifice;
a closure member for the orifice, the orifice-defining
means and closure member being relatively movable with
respect to one another between a first position in which
the closure member cooperates with the orifice to close it
and a second position in which the closure member is spaced
from the orifice-defining means to define a gap
therebetween; and a stop for limiting relative movement
between the orifice-defining means and the closure member
to ensure that the width of the gap cannot exceed that
which will produce a fine spray.
Although the invention is intended mainly for
metered dose inhalers and manually operated pumps, it may
also be applied in other applications requiring small
droplets, for example in certain industrial processes.
In one embodiment of the present invention the
nozzle has a circular orifice which is sealingly closed by
a ball urged by a spring. Under the action of liquid under
pressure, the ball is displaced from the orifice by an
amount determined by the stop, which may be fixed or
adjustable, and the fluid flows through the gap thus formed
and emerges as a thin circular sheet. As the sheet of
liquid expands it becomes thinner, and the outer edge
breaks into droplets, the diameters of which are determined
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by the size of the gap, the pressure of liquid, and the
physical properties of the liquid. When the pressure in
the liquid is reduced below a predetermined level, the ball
is urged by the spring sealingly onto the orifice, thus
preventing ingress of dirt, evaporation of the product, and
atmospheric contamination.
In another embodiment of the invention, the
liquid to be sprayed is caused to flow past a spherical
surface and through a gap formed between that surface and
a circumambient hole in a plate. The plate is preferably
made of a spring material and located so that it is in
sealing contact with the spherical surface as a normally
closed valve. Under the action of liquid under pressure,
the plate is forced away from the spherical surface by an
amount determined by the stop, which may be fixed or
adjustable, and the fluid flows through the gap thus formed
to emerge as a thin circular sheet. As the sheet of liquid
expands, it becomes thinner, and the outer edge breaks into
droplets, the diameter of which are determined by the size
of the gap, the pressure of liquid and the physical
properties of the liquid. When the pressure in the liquid
is reduced below a predetermined level, the spring plate
returns to its original position to seal against the
spherical surface, thus preventing ingress of dirt,
evaporation of the remaining product, and atmospheric
contamination.
Whilst reference has been made above to the use
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of a ball or spherical surface in co-operation with a
circular orifice in a plate or nozzle, other shapes could
be used, for example, a conical surface co-operating with
a circular hole. The precise profile of the surface and
hole will be determined in part by the spray pattern
required, and the present invention provides for all
combinations of surfaces and holes, but it is preferred
that at least one of the components has a varying cross
section so that the gap between them is opened or closed as
a result of relative movement. Since the stop ensures that
the gap is of substantially constant size when the
components are fully apart, an even spray results from the
passage of fluid throughout the length of the gap. The
width of the gap is preferably of the order of 5
micrometers. The ratio of the length of the gap L to the
width of the gap D is preferably not more than 1 and more
preferably not more than 0.5. By the "length" of the gap
we mean the distance which the liquid has to travel in
order to pass through the gap.
The surface finish of the co-operating components
in the region of the gap should be sufficiently fine so as
not to adversely affect the droplet size and pattern of the
spray: for example, a groove in one component would cause
a stream of liquid to issue therefrom, which would probably
not have the required characteristics, and could lower the
pressure in the liquid sufficiently to adversely affect the
quality of spray emerging from the remainder of the gap.
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The finish should be sufficiently fine to ensure efficient
sealing between the components when in the closed position.
The invention further provides an atomising
device which comprises an atomising nozzle according to the
present invention, a supply of liquid, and means for
providing liquid under pressure from said supply to said
nozzle.
In one form, the device is an inhalation device,
and the liquid comprises a medicament suitable for
inhalation. The liquid may contain the medicament in
suspension or solution, and the liquid may be an aqueous or
non~aqueous liquid which is physiologically acceptable.
In the accompanying drawings:
Figure 1 illustrates the principle of the
invention and is a cross sectional view of the basic
elements in their normal, non-pressurised relationship.
Figure 2 is a similar view to Figure 1, and shows
the elements in the operating position.
Figures 3 and 4 show a modified form of the
embodiment of Figures 1 and 2.
Figures 5 and 6 show an alternative embodiment of
the principle of the invention, in closed and open position
respectively.
Figure 7 is an enlarged part section showing the
conjunction of the principal components illustrated in
Figures 5 and 6.
Figure 8 shows a section through a modified
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version of the spring plate used in the embodiment Figures
5 and 6.
Figures 9 and 10 show a modified form of the
embodiment of Figures 5 and 6.
Figures 11 and 12 show a spray device for use as
an inhaler, incorporating a nozzle according to the present
invention.
Figure 13 shows the nozzle used in Figures 11 and
12, on a larger scale.
Figure 14 shows another form of spray device
incorporating the nozzle according to the invention.
Figure 15 shows an embodiment of the nozzle
having a gap of adjustable size.
Referring to Figure 1, ball 1 is resiliently
urged by a compression spring 6 into a position in which it
is sealingly located on the circular orifice 3 of nozzle 2.
Stop means 5 is located on the longitudinal axis of the
ball and orifice, and has a gap 8 between the face 9 of the
stop means 5 and the surface of ball 1. Nozzle 2 is in
hydraulic communication with a dispensing means (not shown)
and contains liquid 7 which is to be sprayed.
Referring now to Figure 2, which illustrates the
same components as in Figure 1, pressure has been applied
to the liquid 7 by the dispensing means, and ball 1 is
lifted from the circular orifice 3 against the force of
spring 6 until it stops against the face 9 of stop means 5.
Thus the ball 1 has moved by an amount controlled by the
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gap 8 to form a gap lo, the size of which is less than gap
8 by an amount determined by the ratio of the diameters of
the ball 1 and circular orifice 3. The liquid 7 issues
through the gap 10 as a circular sheet of thickness
initially determined by the size of gap 10. As the liquid
sheet expands it becomes thinner, until the surface tension
of the liquid is unable to maintain homogeneity of the
sheet, and the periphery of the sheet breaks into small
droplets. The size of the droplets is controlled by the
dimension of the gap 10 and the velocity of the liquid,
which in turn depends on the pressure generated in the
dispenser. A smaller gap 10 will generally produce smaller
droplets, provided that the pressure in the liquid is
sufficiently high to overcome the viscous drag created by
the small gap, and accelerate the liquid to form a thin
sheet. (If the pressure is too low, the liquid will merely
ooze from the gap).
When the pressure in the liquid 7 ceases, the
ball 1 is returned to sealing contact with orifice 3 by
spring 6. It is preferable that the contact line between
the ball 1 and orifice 3 is very thin, which may be
facilitated by chamfering the nozzle as at 4, so as to
leave a knife edge. This may have the additional effect of
allowing a wider spray angle Z than possible with a square-
edged orifice.
Figures 3 and 4 show a modification in which the
stop means 5 is replaced by an alternative stop means 5a
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which has a recess sb within which the spring 6 is housed.
When the nozzle goes from the closed position shown in
Figure 3 to the open position shown in Figure 4, the ball
1 seats itself in the open end of the recess. The guidance
which this provides ensures that the ball is correctly
aligned with respect to the end of the conduit 2, with a
uniform annular gap between the orifice 3 and the ball. The
spray produced is thus substantially uniform both in
distribution around the gap and in droplet size.
An alternative embodiment is shown in Figures 5
and 6. In this case, Figure 5 shows a spherical surface 20
which is located at the outer edge of the discharge conduit
21 containing the liquid to be sprayed 22. A spring plate
24 having a circular orifice 25 is held against the
spherical surface 20 so that the circular orifice 25 makes
sealing contact with the spherical surface 25, and the
outer edge of the spring plate 24 is in sealing contact
with the abutment face 26 of conduit 21, thus preventing
the passage of liquid 22. A plate 27 having a circular
hole 29 is assembled on to the outer face of spring plate
24 so that the hole 29 is co-axial with orifice 25. A step
or recess 30 in plate 27 provides a gap 28 between the
spring plate 24 and plate 27, the assembly of the two
plates being held in sealing contact with the abutment 26
by retaining member 33, which may be a crimped-on ring as
shown.
Referring to Figure 6, the liquid 22 is
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pressurised by the dispensing means (not shown), and forces
plate 24 away from the spherical surface 20, against the
inherent bias provided by the fact that the plate 24 is a
spring plate, to create the gap 32 between the circular
orifice 25 and spherical surface 20. The size of the gap
32 is determined by the size of the gap 28 and by the
diameter of the hole 29 in the plate 27, which, between
them, determine the extent to which the spring plate 24 can
flex. The liquid issues from the gap 32 as a thin circular
sheet, the outer edge of which breaks into droplets as
previously described. The edge of the circular orifice 2S
in spring plate 24 may have a chamfer 40 as shown in Figure
7, which may permit a wider spray angle than possible with
a square-edged orifice. The spring plate 24 may have
corrugations co-axial with the orifice 25 as shown in
Figure 8, which will facilitate the flexing of the spring
plate. When the pressure is removed from the liquid 22,
the spring plate 24 returns to sealing contact with the
spherical surface 20.
In Figures 5 and 6 the spherical surface 20 is
shown diagrammatically as being at the end of a rod, and
means (not shown) would be required to support the rod with
respect to the fluid discharge conduit 21. Figures 9 and 10
show a modified embodiment in which there is a spherical
surface 20a formed on a disc 50 which is secured to, or
integral with, the inner wall of the conduit 21. The disc
50 is provided with at least one port 51 through which
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liquid can pass from the interior of the conduit 21 to the
region immediately below the plate 24.
Figures 11 to 13 show a spray device
incorporating an atomising nozzle according to the present
invention. It is intended for use as an inhalation device.
It comprises a reservoir 60 of liquid 61. The liquid 61
may, for example, consist of an aqueous suspension of a
medicament suitable for treatment of a condition such as
asthma. The lower end of the reservoir is defined by a
piston 62 which is longitudinally slidable within the
reservoir. Beneath the piston is a stopper 63 which has at
least one orifice 64 therein to permit air to enter the
space beneath the piston.
The upper end of the reservoir has a neck portion
65 to which a closure member 66 is secured. A portion 67 of
the closure member extends within the neck, and an O-ring
seal 68 provides a seal between the neck portion 65 and the
portion 67. The closure member 66 has a passage 69
therethrough and a tube 70 is secured in the upper portion
of this passage. The lower portion of the passage defines
an orifice 71, above which is a tapered portion defining a
seat for a check valve ball 72. The ball is urged against
the seat by a compression spring 73.
An outlet member 74 is mounted on the closure
member 66 so as to be movable with respect thereto. The
outlet member 74 comprises a generally cylindrical part 7S
the lower end of which engages over the closure member 66.
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14
The part 75 is prevented from separating from the closure
member 66 by interengaging flanges 76 and 77 thereon. The
outlet member 74 further comprises an outlet spout 78
through which a user can inhale through his or her mouth.
In the case of an inhaler for nasal use, the spout 78 would
be replaced by an appropriate nasal outlet.
In the region of the junction between the
cylindrical part 75 and the outlet 78, the outlet member 74
has an inwardly extending wall 79 which serves to retain an
atomising arrangement 80. This includes a block 81 which
has a hollow lower portion 82 which surrounds the upper
end of the tube 70 and which is free to enter a cavity 83
in the upper end of the closure member 66. The hollo~
portion 82 has an outwardly extending flange 84 at its
upper end, and a compression spring 85 is mounted between
the flange and the closure member 66.
The interior of the hollow portion 82
communicates via a passage 86 with an atomising nozzle 90
according to the invention. This is shown on a larger scale
in Figure 13. As can be seen there, it corresponds
substantially to what is shown in Figures 9 and 10, and
comprises a spring plate 91 which cooperates with a
spherical surface 92 formed on a disc 93. The disc 93 is
provided with at least one port 94 therethrough.
In operation, the user places his or her mouth
over the spout 78 and squeezes the reservoir 60 and outlet
member 74 together against the force of the compression
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spring 85 to bring the device into the position shown in
Figure 12. During this operation, the ball 72 prevents
liquid leaving the reservoir 60 through the orifice 71, and
the tube 70 acts as a piston to expel part of the liquid
above the ball through the nozzle 90 where it forms an
atomised spray. The quantity of liquid expelled in this
way constitutes a metered dose, metering being effected by
the stroke of the piston. The user inhales this spray.
When the user ceases to hold the reservoir 60 and outlet
member 74 together, the spring 85 forces them apart. This
creates a suction effect within the tube 70 which draws the
ball 72 away from its seat and permits liquid to pass from
the reservoir through the orifice 71 to replenish what has
just been dispensed through the nozzle 90. As the volume of
liquid within the reservoir is reduced, the piston 62
slides upwardly under the force of the atmospheric pressure
below it, air reaching the underside of the piston through
the port 64.
Figure 14, shows another embodiment of spray
device. The fiyure shows the device in the discharge
position. In this embodiment, a valve of similar design to
that used as the atomising nozzle is used also as a non-
return inlet valve. Figure 14 shows an actuator 101
sealingly located on a hollow stem 104 which is integral
with a hollow piston 107. Piston 107 is slidingly located
within the cylinder 115, the cylinder being formed as the
inner part of a pump body 108. The body is retained by a
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16
snap fit or other convenient method of retention in a
closure 105, a gasket 106 providing a seal between the stem
104 and the closure 105. Gasket 106 is free to flex with
axial displacement of the piston and stem, whilst
maintaining a seal. A plurality of cantilever springs 109,
formed integrally with piston 107, urges the piston in an
outward direction by reacting against a conical surface 110
formed in the lower part of the pump body 108. The piston
is prevented from coming out of the pump body 108 by an
abutment 116 closing on to the gasket 106 which is
supported by the inside of the closure 105.
The lower end of the pump body 108 contains a
spherical surface 111. A flexible diaphragm 112 with a
circular hole therein is sealingly located in the pump body
108 so that the edge of the hole is in sealing engagement
with the spherical surface 111. The combination of
diaphragm 112 and surface 111 acts as a normally closed
non-return valve 120. The extreme lower part of the pump
body 108 terminates in a diameter adapted to sealingly
retain a dip tube 113. The conduit defined by the dip tube
113 and extreme lower part of the pump body 108 is in
communication with an annulus 119 formed between the
spherical surface 111 and the diaphragm 112 via one or more
ports 117. The actuator 101 has a spherical surface 103,
and a flexible diaphragm 102 with a circular hole therein,
the edge of which hole is in sealing engagement with the
spherical surface 103. The diaphragm 102 is sealingly
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located by a snap it or other convenient method within the
actuator 101, and the combination of diaphragm 102 and
surface 103 acts as a combined non-return valve and
atomising nozzle 121. The hollow stem 104 is in
communication with annulus 114 via a port 118.
In operation, the actuator is depressed and
allowed to return several times to prime the pump, the
valves 120 and 121 cooperating to draw liquid from a
reservoir (not shown) and to discharge the liquid from the
atomising nozzle.
Figure 15 shows an atomising nozzle in which,
unlike those described so far, a means is provided for
enabling the gap through which the liquid passes to be
adjusted. The nozzle comprises a body 201 which has a
threaded exterior to receive a threaded cap 202. The eap
may be adjusted to alter a gap 203 formed between a faee
204 of the cap and a flexible diaphragm 205. In this way
the discharge characteristies may be readily adjusted; for
example a spray may be adjusted from a fine to a eoarse
droplet size.
The description "liquid" used in this
specification includes solutions, suspensions and
emulsions.
