Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF DESIGNING IMPROVED
SPRAY DISPENSER ASSEMBLIES
[0001] This application is a continuation-in-part of copending U.S. Patent
Application
No. 10/653,211, filed on September 3, 2003. That application is a continuation-
in-part of
copending U.S. Patent Application No.lO/350,011, which was filed on January
24, 2003.
FIELD OF THE INVENTION
[0002) Our invention relates generally to the field of spray dispenser
assemblies and
methods of designing the same. In particular, our invention relates to the
field of designing
aerosol dispenser assemblies using a liquefied gas propellant to expel a
liquid product from a
container. However, while the specific examples discussed herein focus on
aerosol spray
assemblies, our design method may also be employed to design other spray
dispensers, such
as those operated by pump action.
BACKGROUND OF THE INVENTION
[0003) Aerosol dispensers have been commonly used to dispense personal,
household,
industrial, and medical products, and provide a low cost, easy to use method
of dispensing
such products. Typically, aerosol dispensers include a container, which
contains a liquid
product to be dispensed, such as soap, insecticide, paint, deodorant,
disinfectant, air
freshener, or the like. A propellant is used to discharge the liquid product
from the container.
The propellant is pressurized and provides a force to expel the Liquid product
from the
container when a user actuates the aerosol dispenser by, for example, pressing
an actuator
button.
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[0004] The two main types of propellants used in aerosol dispensers today are
liquefied
gas propellants, such as hydrocarbon and hydrofluorocarbon (HFC) propellants,
and
compressed gas propellants, such as compressed carbon dioxide or nitrogen gas.
To a lesser
extent, chlorofluorocarbon propellants (CFCs) are also used. The use of CFCs
is, however,
being phased out due to the potentially harmful effects of CFCs on the
environment.
[0005] In an aerosol dispenser using the liquefied gas-type propellant, the
container is
loaded with the liquid product and propellant to a pressure approximately
equal to, or slightly
greater than, the vapor pressure of the propellant. Thus filled, the container
still has a certain
amount of space that is not occupied by liquid. This space is referred to as
the "head space"
of the dispenser assembly. Since the container is pressurized to approximately
the vapor
pressure of the propellant, some of the propellant is dissolved or emulsified
in the liquid
product. The remainder of the propellant is in the vapor phase and fills the
head space. As
the product is dispensed, the pressure in the container remains approximately
constant as
liquid propellant evaporates to replenish discharged vapor. In contrast,
compressed gas
propellants are present entirely in the vapor phase. That is, no portion of a
compressed gas
propellant is in the liquid phase. As a result, the pressure within a
compressed gas aerosol
dispenser assembly decreases as the vapor is dispensed.
(0006] A conventional aerosol dispenser is illustrated in FIG. 3, and
generally comprises
a container (not shown) for holding a liquid product and a propellant, and a
valve assembly
for selectively dispensing a liquid product from the container. As illustrated
in FIG. 3, the
valve assembly comprises a mounting cup 106, a mounting gasket 108, a valve
body 110, a
valve stem 1 12, a stem gasket 114, an actuator cap 116, and a return spring
118. The valve
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stem 112, stem gasket 114, and return spring 118 are disposed within the valve
body 110 and
are movable relative to the valve body 110 to selectively control dispensing
of the liquid
product. The valve body 110 is affixed to the underside of the mounting cup
106, such that
the valve stem 112 extends through, and projects outwardly from, the mounting
cup 106. The
actuator cap 1 I 6 is fitted onto the outwardly proj ecting portion of the
valve stem 112 and is
provided with an exit orifice 132. The exit orifice 132 directs the spray of
the liquid product
into the desired spray pattern. A dip tube 120 is attached Lo the lower
portion of the valve
body 110 to supply the liquid product to the valve assembly to be dispensed.
In use, the
whole valve assembly is sealed to the container about its periphery by
mounting gasket 108.
[0007] In operation, when the actuator cap 116 is depressed, the valve stem
112 is
unseated from the mounting cup 106, which unseals the stem orifice 126 from
the stem
gasket 114 and allows the propellant to flow from the container, through the
valve stem I 12.
Flow occurs because propellant forces the liquid product up the dip tube 120
and into the
valve body 110 via a body orifice 122. In the valve body 110, the liquid
product is mixed
with additional propellant supplied to the valve body 110 through a vapor tap
124_ The vapor
tap 124 introduces additional propellant gas into the valve body 110, in order
to help prevent
flashing of the liquefied propellant, and to increase the amount of pressure
drop across the
exit orifice, which has the added benefit of further breaking-up the dispensed
particles. From
the valve body 110, the product is propelled through a stem orifice 126, out
the valve stem
112, and through an exit orifice 132 formed in the actuator cap 116.
[0008] S_C. Johnson & Son, Inc. {S.C. Johnson) employs an aerosol valve
similar to that
shown in FIG. 3 in connection with their line of Glade~ aerosol air
fresheners. The
propellant used to propel the air freshener liquid product from the container
is a B-Series
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liquefied gas propellant having a propellant pressure of 40 psig (B-40), at 70
degrees F (2.72
atm at 294 K). "Propellant pressure" refers to the approximate vapor pressure
of the
propellant, as opposed to "can pressure," which refers to the initial gauge
pressure contained
within a full aerosol container. The B-40 propellant is a composition of
propane, normal
butane, and isobutane. By normal butane it is meant the composition denoted by
the
chemical formula C4H10, having a linear backbone of carbon. This is in
contrast to
isobutane, which also has the chemical formula C4H10, but has a non-linear,
branched
structure of carbon. In order to effectively dispense this air freshener
composition, the
aerosol dispenser used by S.C. Johnson in connection with their line of Glade~
aerosol air
fresheners has a stem orifice diameter of 0.025" (0.635 mm), a vapor tap
diameter of 0.020"
(0.508 mm), a body orifice diameter of 0.062" ( 1.575 mm), and a dip tube
inner diameter of
0.060" (1.524 mm). This current Glade~ aerosol air freshener requires that the
B-40
propellant be present in the amount of approximately 29.5% by weight of the
contents of the
dispenser assembly in order to satisfactorily dispense the air freshener
liquid product.
[0009] Hydrocarbon propellants, such as B-40, contain Volatile Organic
Compounds
(VOCs). The content of VOCs in aerosol air fresheners is regulated by various
federal and
state regulatory agencies, such as the Environmental Protection Agency (EPA)
and California
Air Resource Board (CARB). S_C. Johnson continuously strives to provide
environmentally
friendly products and regularly produces products that exceed government
regulatory
standards. It is in this context that S.C. Johnson set out to produce an
aerosol dispenser
assembly having a reduced VOC content.
[0010] One way to reduce the VOC content in such aerosols is to reduce the
amount of
the propellant used to dispense the liquid product. However, we have
discovered that a
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reduction in the propellant content adversely affects the product performance.
Specifically,
reducing the propellant content in the aerosol air freshener resulted in
excessive product
remaining in the container after the propellant is depeleted (product
retention), an increase in
the size of particles of the dispensed product (increased particle size), and
a reduction in
spray rate, particularly as the container nears depletion. It is desirable to
minimize the
particle size of a dispensed product in order to maximize the dispersion of
the particles in the
air and to prevent the particles from "raining" or "falling out" of the air.
Thus, we set out to
develop an aerosol dispenser assembly that can satisfactorily dispense an
aerosol product that
contains, at most, 25% by weight, of a liquefied gas propellant, while
actually improving
product performance throughout the life of the dispenser assembly.
[0011] Consequently, our design method tackled the idea of identifying
preferred
performance characteristics of a spray dispenser (in this case, product
retention, increased
particle size, and the spray rate, which suffer when the VOC content is
reduced) and
providing a novel system for calculating design variables/factors of a spray
dispenser that
achieve the desired performance characteristics. In other words, in developing
a preferred
aerosol dispenser assembly that achieved the preferred spray attributes with a
reduced VOC
content, we simultaneously developed a novel method of calculating design
variables that can
achieve any one of a number of possible performance characteristics without
the need for
repetitive trial and error.
(0012] Given the effect of VOC's on the environment, expected government
restrictions
on the VOC content through government regulations in the future, and the ever
changing
desires of customers of such products unrelated to VOC content, our system is
not only useful
in developing our own products, but also in providing consultation, for a fee,
to other
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manufacturers and the like that desire enhancements for future spray dispenser
products,
aerosol or otherwise.
[0013] Our examples focus on aerosol dispensers inasmuch as we are interested
in
reducing VOC content while optimizing preferred spray attributes. In non-
aerosol
dispensers, it is still desired to optimize performance characteristics to
please customers
and/or provide a device that is more cost effective or easier to manufacture.
On of ordinary
skill in the art would understand that our methods will also apply to non-
aerosol
j0014] To the extent that the following discussion focuses on aerosol
dispenser, it should
be noted that the "life of the dispenser assembly" is defined in terms of the
amount of
propellant within the container (i.e., the can pressure), such that the life
of the dispenser
assembly is the period between when the pressure in the container is at its
maximum (100%
fill weight) and when the pressure within the container is substantially
depleted, i.e., equal to
atmospheric pressure. It should be noted that some amount of liquid product
may remain at
the end of the life of the dispenser assembly. As used herein, all references
to pressure are
taken at 70 °F (294 K), unless otherwise noted.
j0015] One known method of reducing the particle size of a dispensed liquid
product is
disclosed in U.S. Patent No. 3,583,642 to Crowell et al. (the '642 patent),
which is
incorporated herein by reference. The '642 patent discloses a spray head that
incorporates a
"breakup bar" for inducing turbulence in a product/propellant mixture prior to
the mixture
being discharged from the spray head. Such turbulence contributes to reducing
the size of the
mixture particles discharged from the spray head.
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SUMMARY OF THE INVENTION
[0016] Our invention provides a method of determining design parameters for a
design of
an improved spray dispenser and designing the same. More preferably, our
invention is
directed to designing an improved aerosol dispenser assembly that dispenses
substantially all
of a liquid product (i.e., reduces product retention), in accordance with a
predetermined set of
performance characteristics. For example, in an air freshener, consumers
prefer a specific
particle size range and discharge rate. On the other hand, for furniture
polishes, cone angle is
a more critical performance characteristic. More generally, our invention is
directed to a
method of designing a spray dispenser by calculating which design factors, or
combination
thereof, will enhance and/or enable preferred characteristics of the spray
dispenser.
[0017] In one aspect, our method is directed to a method of providing for a
client a
service of determining design parameters for a design of a spray dispenser
assembly for
dispensing a mist and designing the same. The method includes identifying one
or more
preferred performance characteristics of the spray dispenser to be designed
and identifying
design variables of structures of a spray dispenser assembly that affect the
one or more
performance characteristics. In addition, the method includes obtaining test
data indicative of
performance characteristics of spray dispensers at different combinations of
values of the
identified design variables and defining design parameters for the identified
design variables,
based on the test data. Consequently, the defined design parameters provide
the one or more
preferred performance characteristics when embodied in a spray dispenser. The
defined
parameters can be one or more ranges of design variable values that will
provide a spray
dispenser with the desired characteristics, or specific values.
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[0018] In another aspect, our invention is directed to a method of determining
design
parameters for a design of an improved spray dispenser and designing the same.
The method
includes determining the client's one or more preferred performance
characteristics for the
spray dispenser assembly to be designed. Once the preferred characteristics)
are determined,
the method includes identifying design variables of structures of a spray
dispenser assembly
that affect the one or more performance characteristics. In addition, the
method includes
obtaining test data indicative of performance characteristics of spray
dispensers at different
combinations of values of the design variables. Based on that obtained test
data, a step is
performed of defining design parameters for the identified design variables
which provide the
one or more preferred performance characteristics when embodied in a spray
dispenser.
[0019] In yet another aspect, our invention is directed to another method of
designing a
spray dispenser assembly for dispensing a mist. This method also includes
identifying one or
more preferred performance characteristics of the spray dispenser to be
designed. In
addition, the method includes testing design variables of structures of a
spray dispenser
assembly that affect the one or more performance characteristics to determine
the extent to
which variations in a given design variable affect the one or more
perfornlance
characteristics. Further, primary design variables are selected based on the
above
determination and testing is performed on the effects different combinations
of the primary
design variables have on the one or more performance characteristics, in order
to determine
interdependencies and relationships of those primary design variables in
affecting the one or
more performance characteristics. Based on the test data, there are determined
design
parameters for the primary design variables which provide the one or more
preferred
performance characteristics when embodied in a spray dispenser.
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[0020] In addition to these methods, our invention also includes the
production of a
database that can store much of the data necessary for performing the recited
methods. More
specifically, the performance of the above-discussed methods may involve the
performance
of experiments to obtain test data on which the determinations are made and,
when those
experiments are a sampling of the total experimental data needed, the
calculation of the
remaining test data through statistical modeling. This data may be saved to
create a database
of test data. As the database grows, it may be used to avoid repeating the
same experiments
and statistical analysis in the future. Accordingly, the steps of performing
experimentation to
obtain test data and statistical analysis of the test data may simply involve
obtaining the
information from a database, inasmuch as inclusion of the information in the
database
indicates the necessary testing and calculations have already been performed.
[0021 ] In air fresheners, average particle size, as used herein, means
average mean
particle size D(V,0.5) of the dispensed product, as measured by laser
diffraction analysis by a
Malvern~ Mastersizer 2600 Particle Size Analyzer, the aerosol assemblies being
sprayed
from a horizontal distance of 11-16.0" (27.5-40.6 cm) from the measurement
area, and
having a maximum cutoff size of 300 microns. This term is equivalent to mass
mean particle
size.
[0022] As used herein to describe any quantity, dimension, range, value, or
the like, the
term "about" is intended to encompass the range of error that occurs during
any
measurement, variations resulting from the manufacturing process, variation
due to
deformation during or after assembly, or variation that is the compounded
result of one or
more of the foregoing factors.
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[0023) A better understanding of these and other aspects, features, and
advantages of the
invention may be had by reference 1o the drawings and to the accompanying
description, in
which preferred embodiments of the invention are illustrated and described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. I is a cross-sectional perspective view of a first embodiment of
the valve of
the present invention.
[0025] FIG. 2 is a front view of the aerosol dispenser assembly of the first
embodiment,
with the container cut away for clarity.
[0026) F1G. 3 is an exploded view of a conventional aerosol valve assembly and
actuator
cap, illustrating the individual components.
[0027] FIG. 4 is a bar graph showing the relative effects of different
variables of a spray
dispenser design on spray dispenser performance characteristics.
[0028] FIGS. SA-SF show summaries of effects of different dispenser variables
on
various spray dispenser performance characteristics.
[0029] FIG. 6 is an example of a contour graph showing product retention as a
function
of vapor trap and propellant level.
[0030] FIG. 7 is an example of a contour graph showing product retention as a
function
of body orifice size and vapor tap size.
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(0031] Throughout the figures, like or corresponding reference numerals denote
like or
corresponding parts.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(0032] As shown in FIG. 2, an aerosol dispenser assembly according to our
invention
generally comprises a container 2 with a valve assembly 4 disposed in the top
thereof for
selectively dispensing a liquid product from the container 2.
(0033] With reference to FIG. 1, the valve assembly 4 further comprises a
mounting cup
6, a mounting gasket 8, a valve body 10, a valve stem 12, a stem gasket 14, an
actuator cap
16, and a return spring 18. The actuator cap 16 defines an exit path 28 and an
actuator orifice
32. The valve stem 12, stem gasket 14, and return spring 18 are disposed
within the valve
body 10 and are movable relative to the valve body 10. The valve body 10 is
affixed to the
underside of the mounting cup 6, such that the valve stem 12 extends through,
and projects
outwardly from, the mounting cup 6. The actuator cap 16 is fitted onto the
outwardly
projecting portion of the valve stem I2, and a dip tube 20 is attached to the
lower portion of
the valve body 10. The whole valve assembly 4 is sealed to the container 2 by
mounting
gasket 8.
[0034] While the dispenser assembly shown in FIG. 1 employs a vertical action-
type cap
16, it will be understood that any suitable valve type may be used, such as,
for example, a tilt
action-type cap. In addition, instead of the simple push-button actuator cap
16 shown in FIG.
l, it will be understood that any suitable actuator may be used, such as, for
example, an
actuator button with an integral overcap, a trigger actuated assembly, or the
like.
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[0035] In operation, when the actuator cap 16 of the dispenser 1 is depressed,
it forces the
valve stem 12 to move downward, thereby allowing the liquid product to be
dispensed. The
propellant forces the liquid product up the dip tube 20 and into the valve
body 10 via body
orifice 22. In the valve body 10, the liquid product is mixed with additional
propellant
supplied to the valve body 10 through a vapor tap 24. The additional
propellant introduced
through the vapor tap 24 prevents flashing of the liquefied propellant, and
increases the
amount of pressure drop across the exit orifice, which simultaneously increase
the particle
break-up. From the valve body I0, the liquid product is propelled through at
least one stem
orifice 26, out the valve stem 12, and through an exit path 28 formed in the
actuator cap 16.
A single stem orifice may be used; however, we have found that using two (as
shown in FIG.
1 ), or preferably four, stem orifices 26 spaced around the periphery of the
valve body 10
facilitates greater flow and superior mixing of the product as it is
dispensed.
[0036) FIG. 1 depicts a breakup bar 30 in the exit path 28, such that the
product is forced
to diverge around the breakup bar 30, thereby inducing turbulence in the flow
of the product,
further reducing the particle size of the product. The product is then
expelled from the
actuator cap 16 through an actuator orifice 32, which disperses the product
and produces a
desired spray pattern. Instead of a breakup bar as shown in FIG. 1, the
dispenser assembly
might employ a pair of breakup plates positioned in or below the exit path 28,
a swirl
chamber positioned immediately upstream of the exit orifice 32, or other
similar mechanical
breakup features. While mechanical breakup features provide some additional
break-up of
the product prior to being dispensed, we have found that other factors have a
much greater
impact on particle size than these mechanical breakup features. Nonetheless,
these
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mechanical breakup features may be used to even further reduce the size of the
dispensed
particles, but such mechanical breakup features are not necessary or
preferred.
(0037] As noted above, we found that reducing the hydrocarbon propellant
content of an
aerosol air freshener to at most 25% by weight adversely affected the product
performance.
Specifically, reducing the propellant content in the aerosol air freshener
resulted in excessive
product retention, decreased spray rate as the container became depleted, and
an increased
particle size. Consequently, the air freshener exhibited excessive raining or
falling out of the
liquid product. In order to correct these adverse effects, we tested various
different types of
propellants, pressures, and valve orifice dimensions to set a threshold design
on which to
develop our system of designing an improved spray dispenser.
[0038] In particular, we tested two types of propellants, A-Series and B-
Series
propellants. Both types of propellants were found to be suitable for
dispensing a liquid
product from a container. We found, however, that the A-Series propellants
that we tested
unexpectedly produced a mist having a significantly smaller particle size than
did the B-
series propellants, under the same conditions. This difference was especially
pronounced
toward the end of the life of the dispenser assembly, when the pressure
remaining in the
container was lower. We believe that the superior mist producing ability of
the A-Series
propellants is due to the absence of normal butane in the A-Series
propellants. As described
above, the B-Series propellants contain a combination of propane, normal
butane, and
isobutane. In contrast, the A-series propellant does not contain any normal
butane. When the
dispenser assembly is shaken prior to use, the liquid product and the
propellant form an oil-
out emulsion. That is, small droplets of the liquid product are coated with a
layer of
fragrance oil and propellant, the aqueous phase liquid product being suspended
in a layer of
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non-aqueous phase propellant and fragrance oil. When the emulsion is expelled
from the
pressurized dispenser assembly, the liquefied gas instantly evaporates,
causing the droplets to
"burst" and creating a fine mist of liquid product in the air. The absence of
normal butane in
the A-Series propellant is thought to facilitate a greater burst of mist,
thereby reducing the
particle size of the dispensed mist. This reduced particle size allows a
greater amount of the
dispensed product to remain suspended in the air for a longer period of time,
thus, increasing
the air freshening efficacy of the product.
(0039] While the invention is disclosed as being primarily used in connection
with a
hydrocarbon propellant, it should be understood that the invention could be
adapted for use
with other sorts of propellants. For example, HFC, dimethyl ether (DME), and
CFC
propellants might also be used in connection with a variation of the dispenser
assembly of our
invention. Also, it should be noted that propellants are typically only
necessary in aerosol
devices. While a preferred embodiment involves designing aerosol dispensers,
other
embodiments may include other spray dispensers, such as pump spray devices in
which a
pumping mechanism is used in the place of a propellant. Other such spray
dispensers are
readily known in the art.
(0040] We tested various different propellant pressures and found that, in
general, higher-
pressure propellants tended to dispense the product as a mist having smatler
particle size than
did lower-pressure propellants. In addition, the higher-pressure propellants
somewhat
reduced the amount of product retained in the container at the end of the life
of the dispenser
assembly. However, simply increasing the pressure in the prior art aerosol
dispensers,
without more, was found to be insufficient to expel a satisfactory amount of
the liquid
product from the container. Thus, we also examined the aerosol valve itself to
determine
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how best to reduce the amount of product retention, while maintaining a
satisfactorily small
particle size of the dispensed product.
[0041] In order to minimize the amount of product retention of the dispenser
assembly,
we found that it was desirable to increase the amount of liquid product
dispensed per unit of
propellant. That is, by making the dispensed ratio of liquid product to
propellant smaller (i.e.,
creating a leaner mixture), the same amount of propellant will be able to
exhaust a greater
amount of liquid product. Several valve components are known to affect the
dispensed ratio
of liquid product to propellant, including the vapor tap, the stem orifice,
the body orifice, the
exit orifice, and the inner diameter of the dip tube.
[0042] In general, we found that decreasing the size of the vapor tap has the
effect of
creating a leaner mixture. However, reducing the size of the vapor tap also
has the side effect
of increasing the particle size of the dispensed product. Conversely, we found
that decreasing
the size of the stem orifice, body orifice, exit orifice and/or dip tube inner
diameter generally
decreases the spray rate and the particle size.
[0043] Based on the above observations, we discovered that certain
combinations of
propellant type, can pressure, and valve orifice dimensions, produced a
dispenser assembly
that contains at most 25% by weight of a hydrocarbon propellant and has
superior product
performance over the prior art dispenser assemblies.
[0044] We also found that A-Series propellants, which are free from normal
butane,
exhibit reduced particle size of the dispensed product.
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(0045] A dispenser assembly having a can pressure of between 55 psig (3.74
atm) and
120 psig (8.17 atm) was found to help reduce product retention while also
reducing the
particle size of the dispensed product. As noted above, can pressure refers to
the initial gauge
pressure contained within the aerosol container. Still higher pressures could
also be
effectively used to dispense the liquid product from the container. As the
pressure within the
aerosol dispenser assembly is increased, however, the strength of the aerosol
dispenser
container (also referred to as an aerosol can) must also be increased. Federal
regulations
(DOT ratings) govern the strength of pressurized containers and specify that
aerosol cans
must meet a certain can rating for a given internal pressure. Specifically,
aerosol cans having
an internal pressure of 140 psig or less at 130 °F (9.~3 atm at 327 K)
are known as "regular"
or "unrated," since a higher DOT rating is not required. Aerosol cans having
an internal
pressure of 160 psig or less at 130 °F (10.9 atm at 344 K) have a DOT
rating of 2P, and cans
having an internal pressure of 180 prig or less at 130 °F (12.3 atm at
355 K) have a DOT
rating of 2Q. The higher the specified can rating, the stronger the aerosol
can must be.
Generally, a can having a higher rating will be more costly due to increased
material and/or
manufacturing costs. Thus, in order to minimize costs, it is preferable to use
the lowest
pressure possible while still maintaining satisfactory product performance. In
this regard, we
found that can pressures of between 55 prig (3.74 atm) and 80 psig (5.44 atm),
again
measured at 70 degrees F (294 K), were especially preferred because they
require a lower can
rating than would higher can pressures and are still capable of achieving the
advantages of
the present invention (i.e., reduced propellant content, reduced particle
size, and minimal
product retention).
(0046] We also found that the dispenser assembly of FIG. 1 was capable of
satisfactorily
dispensing an aerosol product that contains at most 25% by weight of a
liquefied gas
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propellant, when the diameter of the vapor tap 24 is between about 0.013"
(0.330 mm) and
about 0.019" (0.483 mm), the diameter of the stem orifice 26 is between about
0.020" (0.08
mm) and about 0.030" (0.762 mm) when a single stem orifice is used (between
about 0.014"
(0.356 mm) and about 0.025" (0.635 mm) when a pair of stem orifices are used),
the diameter
of the body orifice is between about 0.050" (1.270 mm) and about 0.062" (1.575
mm), the
diameter of the exit orifice 32 is between about 0.015" (0.381 mm) and about
0.022" (0.559
mm), and the inner diameter of the dip tube is between about 0.040" (1.016 mm)
and about
0.060" ( 1.524 mm).
(0047] Thus, any of the above-described valve components, propellant types,
propellant
pressures, and valve orifice dimensions, may be used in combination to provide
a dispenser
assembly according to our invention.
(0048] In a first preferred embodiment of the invention, the aerosol dispenser
assembly I
uses an A-Series propellant having a propellant pressure of about 60 psig (4.1
atm) (i.e., A-60
propellant) to dispense the liquid product from the container 2. In this
embodiment, the
container is initially pressurized to a can pressure of about 70 psig (4.8
atm) to about 80 psig
(5.4 atm). The diameter of the vapor tap 24 in this embodiment is about 0.016"
(0.406 mm).
Two stem orifices 26 are used, each having a diameter of about 0.024" (0.610
mm). The
diameter of the body orifice is about 0.050" ( 1.270 mm), the diameter of the
exit orifice 32 is
about 0.020" (0.508 mm), and the inner diameter of the dip tube is about
0.060" (1.52 mm).
Furthermore, a breakup bar 30 is positioned in the exit path 28 of the
actuator 16 in order to
further reduce the particle size of the dispensed product.
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(0049] A second preferred embodiment of the dispenser assembly 1 employs a
single
stem orifice 26. In this embodiment, the dispenser assembly 1 also uses the A-
60 propellant
and a can pressure of about 70 psig (4.8 atm) to about 80 psig (5.4 atm) to
dispense the liquid
product from the container 2. The diameter of the vapor tap is about 0.016"
(0.406 mm), the
diameter of the single stem orifice is about 0.025" (0.635 mm), the diameter
of the body
orifice is about 0.062" ( 1.575 mm), and the inner diameter of the dip tube is
about 0.060"
(1.524 mm). This embodiment also employs a breakup bar, positioned in the exit
path of the
actuator to further reduce the particle size of the dispensed product. The
following table T. I
describes the performance of the dispenser assemblies according to the first
and second
preferred embodiments, respectively.
Propellant Type A-60 A-60
Propellant Level 24.5 24.5
(wt. %)
Body Orifice Diameter1.58 1.27
(mm)
Va or Tap Diameter 0.406 0.406
(mm)
Stem Orifice Area 0.317 0.584
(mm )
Exit Orifice Diameter0.508 0.508
(mm)
Di Tube Diameter 1.52 1.52
(mm)
Mechanical Breaku Yes Yes
S ray Rate (g/s) I .23 1.27
100% Full
75% Full 1.18 I .1
~
50% Full I .1 1.12
S
25% Full I .07 1.05
Particle Size (pm) 29 29
100% Full
75% Fult 30 30
50% Full 29 32
25% Full 32 34
Retention (wt. %) 1.26 l .76
~
T. 1 - Performance of Embodiments One and Two
[0050] These preferred embodiments of the dispenser assembly are capable of
dispensing
the liquid product contained within the container as a mist having an average
particle size of
less than 35 micrometers (0.0014"), over at least 75°'° of the
life of the dispenser assembly.
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Because the dispensed mist has such a small particle size, the particles are
more easily
dispersed in the air and less fallout is experienced. This reduction in the
amount of fallout
increases the dispenser assembly's air freshening efficacy and helps to
prevent undesirable
residue of the liquid product from settling on flat surfaces, such as,
countertops, tables, or
floors.
X0051 ] Moreover, both preferred embodiments of the dispenser assembly are
capable of
dispensing over 98% by weight of the liquid product from the container. It is
important that
substantially all of the product can be dispensed, to ensure that product
label claims will be
met. Also, by minimizing the amount of product retained in the container at
the end of the
life of the dispenser assembly, less liquid product is wasted. This is
important from a
consumer satisfaction standpoint, since consumers tend to be more satisfied
with a dispenser
assembly when substantially all of the liquid product can be dispensed.
X0052] With the foregoing preferred embodiments as a threshold, we began to
take a
more focused approach to reducing the propellant content of a dispenser
assembly even
further. Our goal at this stage was to produce an aerosol dispenser assembly
that could
effectively dispense its contents using as little propellant as possible, but
not more than about
15% liquefied gas propellant by weight. In doing so, we also developed a
method of
achieving improved dispenser characteristics through a novel system of
analyzing factors
affecting such attributes and calculating preferred combinations of the same
to achieve the
desired attributes. At the outset, we note that as the propellant content was
reduced below
about 15%, the stability of the product propellant emulsion began to break
down. That is, at
lower propellant levels, the oil-out emulsion inverted to a water-out
emulsion, thereby
deteriorating the performance characteristics. In contrast to an oil-out
emulsion, a water-out
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emulsion contains small droplets of a non-aqueous phase suspended in an
aqueous phase.
We found that this inversion can be prevented by adjusting the emulsifier. For
example,
lowering the liquefied gas propellant level from 25% to 10% inverted the
emulsion. Addition
of 0.03% by weight of trimethyl stearyl ammonium chloride prevented the
inversion. Of
course, various other stabilizers in various different amounts may also be
effectively used to
prevent the inversion of the emulsion.
j0053] We first identified several "performance characteristics" upon which to
measure
the performance of a given dispenser assembly configuration. For this
embodiment, the
performance characteristics identified were ( l ) the average diameter D in
micrometers of
particles dispensed during the first forty seconds of spray of the assembly,
(2) the average
spray rate Q in grams/second during the first forty seconds of spray of the
assembly, and (3)
the amount of the product R remaining in the container at the end of the life
of the assembly,
expressed as a percentage of the initial fill weight. As used herein, the term
"fill weight"
refers to the weight of all of the contents of the container, including both
the liquid product
and the propellant.
[0054] Based on consumer testing and air freshening efficacy, the particle
size, D, should
preferably be in the range of about I 5 and about 60 micrometers, more
preferably between
about 25 and about 40 micrometers, and most preferably between about 30 and
about 35
micrometers. The spray rate is preferably between about 0.6 and about I .8
g/s, more
preferably between about 0.7 and about 1.4 g/s, and most preferably between
about 1.0 and
about I .3 g/s. The amount of liquid product remaining in the can at the end
of life of the
dispenser assembly is preferably less than about 3% of the initial fill
weight, more preferably
less than about 2% of the initial fill weight, and most preferably less than
about 1% of the
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initial fill weight. Of course, which performance characteristics to study
will depend on the
particular product to be designed. For instance, the present embodiment is
directed to
improving an aerosol-based air freshener. In other embodiments, furniture
sprays, deodorants
and the like could be studied, in which case the characteristics necessary to
please a customer
may also vary. Other important spray attributes that could be identified and
studied include,
but are not limited to, obscuration (a measure of "optical thickness" relating
to concentration
of the particles), plume distance, fill speed, sputter point, stream point,
can pressure, relative
span factor, particle concentration, cone angle, fallout, sound levels, and
spray down (a
measure of the time the device takes to regain pressure after repeated uses
intended to deplete
the pressure level).
(0055] Also, when a non-aerosol device is used, the characteristics of
importance may
also change. For example, in a spray dispenser that uses pump action to
dispense the mist
(e.g., a trigger-type spray bottle), retention, sputter point, stream point,
and can pressure are
not relevant. Also, some trigger sprays introduce air into the liquid to cause
a foam to be
sprayed, in which case the air entrapment could be a characteristic of
interest.
[0056] The desired performance characteristics can be identified by, at least,
internal
analysis by designers in the field, consumer testing, and/or, when the method
is being
performed as a service, provided by a customer/client.
(0057] Such identifications, however, may only provide consumer-described
spray
attributes that are merely subjective observations. It is necessary to convert
such subjective
descriptions into instrumentally measurable values. This is achieved by
establishing
correlation coefficients between consumer benefit statements and instrumental
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measurements. For example, a consumer could describe that the spray is cloudy
or that the
spray has a tendency to "rain" (i.e., droplets rain down from the plume). To
establish the
identity of the quantifiable performance characteristics and preferred values
for the same, we
would provide a focus group with a plurality of spray dispensers Lhat vary in
only one
characteristic (e.g., particle size), and then gauge the group's preferences.
Thus, objectively
quantifiable values can be established based on the ratings of the different
sprays. This can
be repeated as necessary for different characteristics.
[0058] Once the performance characteristics to be analyzed are identified, it
is necessary
to determine factors that are known, or thought, to affect one or more of
these performance
characteristics. Ultimately, in this embodiment, these factors included
propellant content, dip
tube inner diameter, body orifice diameter, vapor tap diameter, stem orifice
diameter,
mechanical breakup elements, exit orifice diameter, and land length
(essentially the axial
length of the exit orifice). Examples of factors in trigger spray devices
could include the exit
orifice size, land length of the exit orifice (i.e., the length of the exit
orifice through which the
ejected mist travels), barrel volume (i.e., the volume in the barrel through
which a plunger
moves to provide the pressure to eject the mist), chamber volume (i.e., the
volume of the
chamber into which the contents of the barrel are ejected), dip tube inner
diameter, and inner
diameter of the barrel.
[0059] Once these factors are identified, they need to be optimized. In some
instances, as
a practical matter, there are too many factors to analyze the interactions of
the factors. In
these cases, a sifting tool such as a 2k factorial analysis may be employed to
identify the
factors of primary interest. Then we employ a statistical tool to measure
interactions of those
primary factors in order to optimize the same. A description of various tools
for performing
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such optimization analyses can be found in statistic text books such as
"Design and Analysis
of Experiments" by Doulas C. Montgomery, published by John Wiley and Sons, New
York,
1997.
[0060] To determine these factors, initial experiments were conducted, varying
each of
these factors individually, as well as others, to determine the magnitude of
the effect each
factor had on the performance characteristics. The control platforms used for
the initial
testing were the original Glade dispenser assembly and the above-described
first and second
preferred embodiments. One or more of these platforms was then modified to
vary each of
the above factors individually. The magnitude of the effect each above-listed
factor had on
the performance characteristics was determined using a 2k factorial
experimental design. The
results of these calculations are shown graphically in FIG. 4.
/0061] The 2k factorial design was also performed with respect to other
performance
characteristics, as shown in FIGS. SA-SF. As would be appreciated by one
ordinary skill in
the art, numerous other performance characteristics could be studied using the
listed factors,
as well as other such factors. Because retention, discharge rate and particle
size were of
primary importance in this embodiment, we focused on the same for this
embodiment.
[0062] From this list we selected the five factors ("critical factors") having
the greatest
effect (negative or positive) on the important performance characteristics to
perform further
experimentation. The critical factors selected were dip tube inner diameter,
vapor tap
diameter, body orifice diameter, stem orifice diameter, and exit orifice
diameter.
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(0063] Thus, the 2k factorial design was primarily used to identify primary
factors to be
studied. More specifically, lacking in the 2k factorial design is an
assessment of variable
interactions. It is possible that the effects of important factors are
interdependent; that is,
their responses are not linear with respect to one another. To address the
interaction, a matrix
study is preferred. Traditionally, matrix experiments measure variable
interactions. Valve
requirements do not lend themselves to matrix experiments. The number of
variables to
measure is simply too large. If run at three different levels, ten variables
would require 1000
experiments. And this would only yield quadratic interaction terms. As will be
discussed
below, cubic terms come into the picture. Cubic terms require no fewer than 5
levels of each
variable, or 100,000 experiments.
[0064] Fortunately, modern statistics provides a tool for reducing the number
of
experiments to a manageable number. A software package from Stat-Ease, Inc.
(Design
Expert) is a particularly useful statistical tool for this problem.
(0065] Thus, instead of using the Box-Behnken design or the D-Optimal design
from the
outset, it was therefore desirable to begin with the factorial screening
design discussed above.
Once the 2k factorial design was completed, the variables with the largest
primary effects
were selected for optimization. Thus, screening designs can be used to reduce
experiment
requirements down to a manageable number. Conclusions from such a screening
design
should be taken as interesting and suggestive, but not definitive. The purpose
of the
screening design is to identify the most important factors. More detailed
study is required to
optimize those factors.
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X0066] In this embodiment, the important variables identified were propellant
level, exit
orifice, vapor tap, body orifice, and dip tube inner diameter. Particle size
was increased by
reducing the propellant level (the project goat) and reducing the vapor tap
size (conserves
propellant), and was decreased by making the exit orifice smaller. This
suggests that
performance changes in particle size, due to reduced propellant levels and
smaller vapor taps,
can be offset by decreasing the size of the exit orifice. In order to reduce
the exit orifice size,
the stem cross section should be enlarged to maintain discharge rate.
[0067] While we knew that the critical factors had a pronounced effect on the
performance characteristics, we were unsure if they varied independently of
one another. To
determine interdependencies, it was necessary to generate a table showing
performance
characteristics for every combination of every value of the critical factors
within a desired
range.
(0068] If each of the critical factors was to be varied through ten different
sizes, for
instance, it would have required one hundred thousand different trials to
complete the table
referred to above. Rather than run all of those different experiments, we used
a Response
Surface Method to select a limited sample of experiments. Based on our limited
sample of
experiments, we were able to generate a complete table of performance
characteristics for
every possible variation of the critical factors, using the Response Surface
Method to
interpolate the missing data points. Fifty-seven experiments were conducted --
a Box-
Behnken Design consisting of twenty-nine experiments, the results of which are
set forth in
table T.2 below, and a D-Optimal Design consisting of twenty eight
experiments, the results
of which are set forth in table T.3 below. Descriptions of these two methods
can be found in
"Design and Analysis of Experiments."
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(0069) A single design capable of predicting cubic interaction teens was not
possible in
this situation because, as discussed, the required combinations of variables
were not readily
available from valve suppliers. Also, as discussed above, where there are
fewer factors to
analyze, the critical factors can be determined without a 2k factorial design.
Other
combinations of design screenings may also be employed depending on the
circumstances
and limitations of the individual analyses.
[0070] The data was entered lo the design expert software and modeled with
cubic terms.
The D-optical design uses seven levels of each variable and is specifically
designed to obtain
excellent modeling with cubic terms. The quality of modeling is, of course,
limited by the
quality of the data used to generate the model.
/0071] Figure 6 shows the retention level on the z-axis, as a function vapor
tap on the x-
axis and propellant level on the y-axis, in the form of a contour graph.
Figure 6 is just one
example of such modeling that can be achieved using the D-optimal design data.
The
important idea to be exemplified by this graph is that the vapor tap has a far
greater effect on
the retention than the propellant level. The propellant level has only a
slight effect on the
retention, rising gradually as propellant level drops.
X0072] Body orifice and dip tube ID were not available in the multitude of
levels required
for a D-optimal study, so a second, Box-Behnken-type experiment set was
developed around
these data using only three levels of each variable. The Box-Behnken
experiment varied four
variables from high to low. The 3-D graphic procedure allowed us to apply any
two variables
against each other while holding the other two variables fixed. With four
variables, there are
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six unique combinations of variables that can be applied against each other.
Assuming that
the other variables are held constant at high, medium, or tow settings, then
there are five plots
for each variable combination. In total, to completely show the response
surface of a single
response, thirty plots would be required. With three essential responses
(particle size, spray
rate and retention) a total of ninety graphs would be required to show this
complete picture.
A discussion of all such graphs is not necessary for purposes of describing
the present
embodiment. However, for explanatory purposes, Figure 7 shows one such graph.
The plot
of retention as a function of body orifice and vapor tap shows that the vapor
tap exhibits
quick control over the retention, while the body orifice has a slight effect.
[0073] Accordingly, because of all of the factors analyzed in our study, a
large amount of
data was obtained. In order to simplify the "optimization" process, we tried
to combine the
responses into a single factor. This single factor is a combination of the
three factors,
weighted empirically until a single number was generated that seemed to
correlate well with
the overall performance, as discussed in more detail below. Of course, the
step proved
helpful in the described embodiment, but may not be necessary in all cases.
Instead, the
results of the design screenings could be evaluated alone to determine the
design parameters
of primary factors for achieving desired performance characteristics when
those factors are
embodied in a spray dispenser assembly.
ParticleSpraySpray
Size Rate
Exit VaporDip Body Particle@ 200g Rate@ 200g
Fill
OrificeTap Tube OrificeSize Weight FullFill Retention
ID Full Weight
Trial(mm) (mm) (mm) (mm) (pm) (pm) ( (g/s) (Wt. CV
's %)
1 0.6350.3303.099 0.63540.0 47.9 1.4081.360 1.62 27
2 0.3300.1271.524 0.63540.0 38.4 0.7160.588 2.70 31
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3 0.6 0.1271.5240.63544.7 47.7 1.4511.349 0.00 35
35
4 _ 0.3301.5240.63534.7 36.7 0.8770.676 10.23 36
0.457
0.4570.5081.0160.63521.7 89.4 0.5550.947 22.59 38
6 0.4570.3301.5240.63534.6 37.4 0.8470.599 17.34 54
7 0.4570.3301.5240.63533.8 38.6 0.8600.599 19.34 57
8 0.4570.3301.0160.33026.9 62.9 0.6180.487 23.59 53
9 0.4570.1271.5240.33033.8 41.2 0.7160.639 1.78 13
0.4570.5083.0990.63529.1 40.7 0.6660.390 33.55 84
11 0.3300.3303.0990.63535.2 33.6 0.5670.422 17.22 58
12 0.4570.1273.0990.63547.8 48.1 1.2821.187 0.00 41
13 0.3300.3301.0160.63527.5 55.1 0.4310.418 33.40 82
14 0.4570.3301.5240.63534.9 38.2 0.8260.641 6.60 27
0.4570.1271.0160.63541.3 41.3 1.0180.868 0.15 24
16 0.3300.3301.5241.27034.7 27.3 0.5650.317 30.08 90
17 0.3300.3301.5240.33023.1 46.2 0.3530.413 33.59 72
18 0.3300.5081.5240.63522.7 44.3 0.3570.492 35.37 76
19 0.4570.1271.5241.27050.0 48.2 1.3571.200 0.00 48
0.4570.3303.0990.33026.8 64.9 0.6180.538 23.71 54
21 0.4570.3301.5240.63535.1 38.5 0.9040.?51 13.05 44
22 0.6350.5081.5240.63530.8 51.5 0.9750.748 31.04 79
23 0.4570.3303.0991.27046.1 43.8 1.1860.982 0.00 36
24 0.6350.3301.5241.27042.0 49.1 1.3541.043 0.83 30
0.4570.5081.5240.33027.3 61.0 0.6200.479 26.33 61
26 0.4570.3301.0161.27029.1 50.5 0.7230.390 32.74 82
27 0.6350.3301.5240.33034.4 45.5 0.7310.398 39.11 111
28 0.6350.3301.0160.63536.6 52.2 1.0430.719 19.65 63
29 0.4570.5081.5241.27027.2 56.8 0.6710.790 28.73 67
T. 2 - Experimental Data for Box-Behnken Design
PropellantVapor Exit ParticleSpray
ContentTap OrificeSize Rate Retention
rial (Wt. (mrn) (mm) Full Full (Wt.
%) (pm) (g/s) %)
1 14.5 0.508 0.330 20.0 0.323 22.15
2 13 0.635 0.508 22.3 0.489 21.15
3 19 0.635 0.635 27.4 0.972 18.63
4 13 0.406 0.330 26.7 0.404 30.46
5 19 0.127 0.330 39.8 0.760 0.00
6 17 0.635 0.457 18.6 0.528 21.18
7 13 0.330 0.635 43.9 1.182 10.82
8 17 0.457 0.406 26.9 0.593 20.18
9 19 0.330 0.330 29.4 0.503 13.15
10 19 0.635 0.457 20.1 0.511 16.72
11 13 0.127 0.330 42.0 0.764 0.00
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12 15 0.127 0.635 45.8 1.542 0.00
13 19 0.127 0.457 42.6 1.079 0.09
14 19 0.457 0.508 28.0 0.788 16.62
I S 17 0.127 0.457 44.7 1.149 0.00
16 14.5 0.254 0.330 40.7 0.727 9.04
17 19 0.127 0.635 42.0 1.514 0.00
18 17.5 0.508 0.584 28.4 0.942 11.54
19 I3 0.635 0.635 34.0 0.958 27.13
20 13 0.406 0.330 26.1 0.407 28.98
21 13 0.635 0.635 31.4 0.733 31.06
22 16 0.406 0.635 33.6 1.152 10.11
23 16 0.406 0.508 30.5 0.843 18.36
24 17 0.635 0.508 23.2 0.629 16.90
25 15 0.635 0.635 26.7 0.810 27.08
26 17 O.I27 0.406 43.1 1.012 0.00
27 13 0.127 0.330 42.4 0.775 2.36
28 19 0.635 0.508 19_6 0.560 21.04
T. 3 - Experimental Data for D-Optimal Design
[0074] Each of the characteristics, D, Q, and R, were weighted according to a
number of
different considerations, including its relative effect on the acceptability
of the dispenser
assembly to the consumer. The weighting process was iterated sequentially,
through trial and
error, until minimum values were achieved for samples known to have the best
performance.
The acceptability of the dispenser assembly to a consumer is given as the
"quality" of the
dispenser assembly and is represented by the Clark/Valpey (CV) factor --
smaller values of
CV being more acceptable to consumers than larger ones. We found that,
generally, a
dispenser assembly having a quality value much greater than about 25 is
unacceptable to
most consumers. Accordingly, a dispenser assembly according to our invention
should have
a CV value of at most about 25, where CV = 2.5(D-32) + I O~Q-1.1 ~ + 2.6R.
(0075] At a propellant level of I4.5°,% by weight and using an actuator
cap 16 with a swirl
chamber, we found that the body orifice diameter should preferably be between
about 0.010"
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(0.254 mm) and about 0.025" (0.635 mm), and more preferably between about
0.010" (0.254
mm) and about 0.015" (0.381 mm). The vapor tap diameter should preferably be
between
about 0.003" (0.076 mm) and about 0.010" (0.254 mm), and more preferably
between about
0.005" (0.127 mm) and about 0.008" (0.203 mm). The at least one stem orifice
should
preferably have a total area of at least about 0.000628 in2 (0.405 mm2), and
more preferably
at least about 0.000905 in2 (0.584 mmZ). The exit orifice diameter should
preferably be
between about 0.013" (0.330 mm) and about 0.025" (0.635 mm), and more
preferably
between about 0.015" (0.381 mm) and about 0.022" (0.559 mm). And the dip tube
inner
diameter should preferably be between about 0.040" (1.016 mm) and about 0.122"
(3.099
mm), and more preferably between about 0.050" (1.270 mm) and about 0.090"
(2.286 mm).
Not every combination of the above valve orifice dimensions will result in an
aerosol
dispenser assembly having a quality value of at most 25. However, most aerosol
valves of
this type having a quality value of at most 25 will have orifice dimensions
that fall within the
above ranges. Because the performance characteristics are not directly
proportional to any
one of the critical factors, and because the critical factors are not
independent of one another,
it is difficult to determine what combination of valve dimensions will result
in the optimum
quality of the dispensed spray. The tables T.4-T.8 below show how quality
changes as the
critical factors are varied through a representative range of values around
the preferred valve
configuration.
Vapor Body Stem Exit
Tap OrificeOrificeDip tubeOrificeD Q R CV
(mm) (mm) (mm2) (mm) (mm) (p.m)(g/s)(wt.
%)
0.127 0.330 1.824 1.524 0.457 36 0.720.58 15
-
,
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_0.1_27 _0.457 1.824 1.524 0_.45_7_ 461.08 0.46 36
0.12 0.635 ~ 1.824 ~ 1.52.457 ~ 48 1.17 0.54 42
T.4 - Variation of Body Orifice Diameter
Vapor Body Stem Exit
Tap OrificeOrificeDip OrificeD Q R CV
mm) (mm) (mm2 tube (mm) (pm) (g/s)(wt.
(mm) %)
0.127 0.330 1.824 1.524 0.457 36 0.72 0.58 15
0.203 0.330 1.824 1.524 0.457 32 0.69 11.6 34
0.254 0.330 1.824 1.524 0.457 31 0.68 14.7 40
T.5 - Variation of Vapor Tap Diameter
Vapor Body Stem Exit I
Tap OrificeOrificeDip OrificeD Q R CV
(mm) (mm) (mm2) tube (mm) (pm) (g/s)(wt.
(mm) %)
0.127 0.330 1.824 1.524 0.330 31 0.43 10.8 32
0.127 0.330 1.824 1.524 0.381 33 0.63 5.8 22
0.127 0.330 1.824 1.524 0.457 36 0.72 0.58 15
0.127 0.330 1.824 1.524 0.559 35 0.83 5.9 26
0.127 0.330 1.824 1.524 0.635 38 1.01 17.4 61
T.6 - Variation of Exit Orifice Diameter
Vapor Body Stem Exit
Tap OrificeOrificeDip OrificeD Q R CV
(mm) (mm) (mm2) tube (mm) (p,m)(g/s) (wt.
(mm) %)
0.127 0.330 0.405 1.524 0.457 <36 <0.72 >0.58 <25
0.127 0.330 0.584 1.524 0.457 <36 <0.72 >0.58 <25
0.127 0.330 1.824 1.524 0.457 36 0.72 0.58 15
T.7 - Variation of Stem Orifice Area
Vapor Body Stem Exit
Tap OrificeOrificeDip OrificeD Q R CV
(mm) (mm) (mm2) tube (mm) (pm) (g/s) (wt.
(mm)
0.127 0.330 1.824 1.016 0.457 34 0.71 6.9 27
0.127 0.330 1.824 1.270 0.457 34 0.72 5.8 24
0.127 0.330 1.824 1.524 0.457 36 0.72 0.58 15
0.127 0.330 1.824 2.286 0.457 35 0.76 4.2 22
0.127 0.330 1.824 3.099 0.457 35 0.86 11.6 40
T.8 - Variation of Dip Tube Inner Diameter
(0076] From our complete tabular data, we were able to determine which
combinations of
valve orifice dimensions minimized the value of CV and provided the best
performance at a
propellant content of 14.5%. In particular, we found that a valve according to
a third
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embodiment, having a body orifice diameter of about 0.013" (0.330 mm), a vapor
tap
diameter of about 0.005" (0.127 mm), an exit orifice diameter of about 0.018"
(0.457 mm), a
dip tube inner diameter of about 0.060" ( 1.524 mm), and at least one stem
orifice having a
total area of at least about 0.002827" (1.824 mm) provided the best
performance for an
aerosol air freshener. The third embodiment is substantially the same as the
first embodiment
in many respects, the main differences being the lower possible propellant
content and the
different ranges of orifice sizes. In this embodiment, A-60 propellant was
again used as the
propellant, and a swirl chamber mechanical breakup element was employed. Of
course, no
such mechanical breakup element is required.
[0077] The above tables were generated based on experimental data using
dispenser
assemblies having a propellant content of 14.5%. Gradual increases in
propellant content, of
course, significantly improve the quality of the dispensed sprays. Thus, by
increasing the
propellant content slightly, a broader range of valve orifce dimensions become
acceptable.
That is, a broader range of valve orifice dimensions will achieve an
acceptable quality value.
For example, simply increasing the propellant content of the preferred
embodiment by 2%,
the quality value was cut almost in half, from 15.3 to 8.8. We envision that
many
applications may benefit from using an aerosol dispenser assembly having a
propellant
content of less than 25%, but greater than the 14.5% achieved by our
invention.
[0078) We believe it would be possible to produce an aerosol dispenser
assembly that
requires even less than 14.5% propellant to dispense its contents by employing
some of the
other factors that were thought to affect the performance characteristics. For
example, by
providing an even smaller vapor tap, by incorporating some form of mechanical
breakup
element, by experimenting with different propellant types, by employing
different land
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lengths, and/or by using different materials for construction, we envision
being able to
achieve satisfactory performance with as little as about 10% propellant
content.
[0079] Of course, different products, such as paint, deodorant, hair
fixatives, and the like,
will have different material properties and may, therefore, require different
valve orifice
sizes. In addition, different products may have different spray
characteristics that are
acceptable to consumers. Therefore, a different forn~ula for quality may have
to be
developed for each different product, in order to determine the appropriate
valve orifice sizes
for that product. We believe, however, that some products, such as
insecticides, will have
similar physical properties to the aerosol air fresheners upon which our study
was based.
Accordingly, we would expect such insecticides to have the same or similar
formula for
quality.
[0080] As discussed, in addition to simple methods of designing improved spray
dispensers, our invention is directed to a consulting service for designing,
or identifying
necessary design characteristics, for improved spray dispenser assemblies. The
service may
include identifying for (or obtaining from) a client preferred performance
characteristics for a
spray dispenser, aerosol or otherwise. Once the desired performance
characteristics are
identified, the process involves identifying the factors of the design of the
spray assembly
that affect those characteristics. As discussed above, it is preferable to
determine the primary
factors of concern from the numerous possible factors that may affect the
design
characteristics. This can be determined through institutional knowledge,
previously
performed (and preferably cataloged studies), and/or experimentation. As in
the above-
discussed embodiment, when numerous factors are involved, a 2k factorial
design may be
performed to identify the critical factors of interest.
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[0081) Once the critical or primary factors are determined, it is preferable
to perform a
screening design, such as a Box-Behnken design, D-Optimal design, etc., and/or
combinations thereof. By performing the same, the number of experiments needed
to
produce the necessary data can be reduced to a manageable number, and tedious
trial and
error is avoided. The results of the design screening can be used to identify
the preferred
combinations of factors that achieve the desired performance characteristics
of the spray
assembly. Of course, this can be obtained as a ranges of possible combinations
that achieve
the desired results, or specific values that result the optimization of the
performance
characteristics.
[0082] The consultation client could then be charged for the design
specifications
necessary to achieve the performance characteristics at issue.
(0083) Also, given that many of the experiments performed to provide the
necessary data
for this process may be repetitive for different analyses, the test date can
be compiled in a
computer database for later referral. This would reduce the need for continued
experimentation over time, and with the consultation business, provide
continued additions to
the database at a profit, rather than proving a drag on one's own business
resources. With the
development of a database, some of the steps of the method could be replaced
with a step of
referring to the previously acquired Lest data.
[0084] Also, we also envision providing, for a fee, software that would allow
a client to
perform the method on its own. Specifically, our invention encompasses
software including
code for performing the methods of our invention. Further, with an expanded
database, the
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database could be incorporated into the software to reduce the need for
experimentation on
the client side.
(0085] The embodiments discussed above are representative of preferred
embodiments of
the present invention and are provided for illustrative purposes only. They
are not intended
to limit the scope of the invention. Although specific components,
configurations, materials,
etc., have been shown and described, such are not limiting. For example,
various other
combinations of valve components, propellant types, propellant pressures, and
valve orifice
dimensions, can be used without departing from the spirit and scope of our
invention, as
defined in the claims, In addition, the teachings of the various embodiments
may be
combined with one another, as appropriate, depending on the desired
performance
characteristics of the valve.
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