Note: Descriptions are shown in the official language in which they were submitted.
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PACKAGED PRODUCT AND DEVICE WITH DISPENSING MEANS
10
OF THE INVENTION
This invention rE;lates to a device designed primarily for dispensing or
applying a liquid from a reservoir, for example, a~bottle or a sponge; and to
the
2o packaged product comprising the device containing a liquid.
Many packaged products are sold in containers which have an element
disposed at the outlet of the container which is designed to control the flow
of the
liquid out of the contaiiner. Products sold in dispensing containers include
paint,
glue, shoe polish, health and beauty care lotions, various food and beverage
products and various detergent products. The combination of the container and
the element may be designed to facilitate dispensing, for example the teat on
a
drinks bottle, in particular for babies; or to control the flow of liquid from
the
container, for example a "non-drip valve" on a sauce bottle. One common
dispensing element is made from silicone based compounds and has an opening
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which is activated by internal pressure such as by squeezably deforming the
bottle, or by a baby sucking on the dispensing element. Some dispensing
elements are designed to act like a valve which only opens when a
predetermined internal pressure is exceeded.
s
Another known packaged product for dispensing a liquid comprises a liquid-
containing reservoir and a non-flexible, non-defc~mable plastic resin
dispensing
element. US-A-4 050 826, issued on Sept. 27~' 1977, relates particularly to
antiperspirantldeodorant dispensers comprising a porous, sintered, synthetic
~o plastic dome as the dispensing element. The liquid is intended to drain out
of the
pores, and return to the container, after the applicator has been used.
It is an object of the present invention to provide a device, especially a
packaged product, for dispensing a liquid that can be easily designed to be
non-
drip and non-spill, without the need for an expensive valve component. In one
embodiment of the present invention the device gives an even and controlled
dispensing. In another embodiment of the present invention the device gives a
very high rate dispensing without any dripping of liquid when the dispensing
is
stopped.
SUMMARY OF THE INVENTION
The present invention relates to a packaged product for dispensing a liquid,
comprising a liquid-containing reservoir and a porous membrane, the reservoir
comprising an outlet, characterised in that the membrane is hem~eticafly
sealed
to or around the reservoir so that fluid passing through the outlet must pass
across the membrane, and that the combination of the liquid and the membrane
results in a bubble point greater than 1 kPa, when measured at ambient
3o temperature and pressure using the packaged liquid.
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Another embodiment of the present invention relates to a device for
dispensing a liquid, comprising a liquid reservoir and a porous membrane, the
reservoir comprising an outlet, and the membrane being hermetically sealed to
or
around the reservoir so that fluid passing through the outlet must pass across
the
membrane, wherein the membrane has an average pore size of from 1 to 100
micrometers and a 'thickness of less than 1 mm.
DETAILED DESCRIPTION C?F THE 1NVENTIC~N
The device and packaged product of the present invention work on the
principle of a "closed distribution system". By "closed distribution system"
it is
meant herein that av membrane is saturated with a liquid and that air is
prevented
~5 frorn entering the aystem even under vacuum, provided the vacuum pressure
does not exceed the bubble point pressure of the membrane. Liquid can then be
drawn across the membrane out of the closed distribution system, for example
by
internal pressure or external suction. internal pressure may be generated for
example by squeezably deforming the reservoir. External suction may be
20 generated, for exarnpie in the case of a drinking bottle, by sucking at the
outlet.
External suction m:ay also be generated by the adhesion force of the surface
to
which the liquid is applied, for example in the case of the skin that is
absorbing a
IOtion.
25 However liquid will not be dispensed (i.e. will not spill or drip) from the
reservoir even if the outlet is oriented below the surface of the liquid
provided the
pressure due to th~~ head of liquid does not exceed the bubble point pressure
of
the saturated membrane. In such circumstances air from the external
atmosphere is unable to enter the closed distribution system, and consequently
30 liquid does not leave the closed distribution system.
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The term "fluid" as defined herein comprises liquid or gas.
The term "hermetically sealed" as used herein means that a gas (especially
air) can neither pass from the outside environment to the inside of the
reservoir;
nor from the inside of the reservoir to the outside environment, when the
membrane is saturated with liquid as long as the pressure differential across
the
membrane does not exceed the bubble point pressure. in particular the
membrane to reservoir seal, or the membrane to membrane seal prevents the
~ o leakage of gas across the sealed region.
The membrane has an average pore size of no more than 100 micrometers,
preferably no more than 50 micrometers, more preferably no more than 10
micrometers, and most preferably of no more than 5 micrometers. it is also
t5 preferred that the membrane has a pore size of at least 1 micrometer,
preferably
at least 3 micrometers. It is further preferred that the pore size
distribution is such
that 95% of the pores have a size of no more than 100 micrometers, preferably
no more than 50 micrometers, more preferably no more than 10 micrometers,
and most preferably of no more than 5 micrometers.
The membrane has an average thickness of less than 1 mm, preferably less
than 100 micrometers, more preferably less than 30 micrometers, and even more
preferably the membrane has an average thickness of no more than 10
micrometers, and most preferably of no more than 5 micrometers.
The term "oleophilic" as used herein refers to materials having a receding
contact angle for the oily liquid to be transported of less than 90 degrees,
preferably less than 70 degrees, more preferably less than 50 degrees, even
more preferably less than 20 degrees, and most preferably less than 10
degrees.
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The term "hydroi~hilic" as used herein refers to materials having a receding
contact angle for distilled water of less than 90 degrees, preferably less
than 70
degrees, more preferably less than 50 degrees, even more preferably less than
20 degrees, and most preferably less than 10 degrees.
Reservoir
The term "reservoir" as used herein refers to a bulk region which holds or
o stores a liquid prior to application or dispensing. In one aspect of the
present
invention the liquid is stored or held in the pores of a bulk material which
is
located in the reservoir. In an alternative aspect of the present invention
the
reservoir contains nc~ material other than the liquid itself. In this aspect
the
reservoir is defined t>y a wall region, such as may be found in a bottle or a
~5 container, for example .
A key requirement for the reservoir is to have a low average flow resistance,
such as expressed by having a permeability k of at feast 10-" m2, preferably
more
than 10$ m2, more preferably rr~ore than 10'' m2, and most preferably more
than
20 1 Or m2. In the first aspect of the present invention, high permeabiiities
for the bulk
materials can be achieved by utilizing material providing relatively high
porosity.
Such a porosity; whi::h is commonly defined as the ratio of the volume of the
materials that makes up the porous materials to the total volume of the porous
materials, and as determined via density measurements commonly known,
2s should be at least 50e%, preferably at least 80%, more preferably at least
90%, or
even exceeding 98%, or 99%.
In the second aapect of the present invention the bulk material essentially
consisting of a single pore, or void space, the porosity approaches or even
3o reaches 100%. In this. case the bulk region is a liquid reservoir such as a
bottle or
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some other type of container which is defined by a wail region, and the volume
of
the liquid reservoir is variable. Preferably the volume is varied either by
flexibly
deforming the wall region, or by the action of a piston.
When present the bulk material can have pores which are larger than about
200 Vim, 500 Vim, 1 mm or even 9 mm in diameter or more. Such pores may be
smaller prior to the fluid transport, such that the bulk material may have a
smaller
volume, and expand just prior or at the liquid contact. Preferably, if such
pores
are compressed or collapsed, they should be able to expand by a volumetric
expansion factor of at least 5, preferably more than 10. Such an expansion can
be achieved by materials having an elastic modulus of more than the external
pressure which, however, must be smaller than the bubble point pressure. High
porosities can be achieved by a number of materials, well known in the art as
such. For example fibrous members can readily achieve such porosity values.
~5 Non-limiting examples for such fibrous materials that can be comprised in
the
bulk region are high-loft non-wovens, e.g., made from polyolefin or polyester
fibers as used in the hygienic article field, or car industry, or for
upholstery or
HVAC industry. Other examples comprise fiber webs made from cellulosic fibers.
2o Such porosities can further be achieved by porous, open celled foam
structures, such as, without intending any limitation, for example
polyurethane
reticulated foams, cellulose sponges, or open cell foams as made by the High
Internal Phase Emulsion Polymerization process (HIPE foams), all well known
from a variety of industrial applications such as filtering technology,
upholstery,
25 hygiene and so on. Such porosities can be achieved by wall regions which
circumscribe voids defining the bulk material, such as exemplified by pipes.
Alternatively, several smaller pipes can be bundled. Such porosities can
further
be achieved by "space holders", such as springs, spacer, particulate material,
corrugated structures and the Pike. The bulk material pore sizes or
permeabilities
30 can be homogeneous throughout the bulk material, or can be inhomogeneous.
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The bulk materi<31 can have various forms or shapes. The bulk material can
be cylindrical, ellipsoidal, sheet like, stripe like, or can have any
irregular shape.
The bulk material can have constant cross-sectional area, with constant or
varying cross-sectional shape, like rectangular, triangular, circular,
elliptical, or
irregular.
The absolute si~:e of the bulk material should be selected to suitably match
the geometric requirements of fhe intended use. Generally, it will be
desirable to
o have the minimum dimension for the intended use. The benefit of the designs
according to the present invention is to allow much smaller cross-sectional
areas
than conventional materials. The dimensions of the bulk material are
determined
by the permeability oi~ said bulk material, which can be very high, due to
possible
large pores, as the bulk material does not have to be designed under the
~s contradicting requirernents of high flux (i.e. large pores) and high
vertical liquid
transport (i.e. small pores). Such large permeabilities allow much smaller
cross-
sections, and hence very different designs.
The bulk material can be essentially non-deformable, i.e. maintains its
2o shape, form, volume under the normal conditions of the intended use.
However,
in many uses, it will be desirable, that the bulk material is soft and
pliable. The
bulk material can change its shape, such as under deforming forces or
pressures
during use, or under the influence of the fluid itself. The deformability or
absence
thereof can be achieved by selection of one or more materials as the bulk
25 material (such as a fibrous member).
The confining separations of the bulk material may further comprise
materials which signi~fcantly change their properties upon wetting, or which
even
may dissolve upon wetting. Thus, the bulk material may comprise an open cell
3o foam material having a relatively small pore at least partially being made
of
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soluble material. such as pofyvinylalcohol or the like. The small porosity can
draw
in liquid at the initial phase of liquid transport, and then rapidly dissolve
so as to
then leave large voids filled with liquid. Alternatively, such materials may
fail larger
pores, completely or partially. For example, the bulk material can comprise
soluble materials, such as poly{vinyl) alcohol or polyvinyl) acetate.
Membrane
The term 'membrane" as used herein is generally defined as a material or
region that is permeable for liquid, gas or a suspension of particles in a
liquid or
gas. The membrane may for example comprise a microporous region to provide
liquid permeability through the capilliaries. Microporous hydrophobic
membranes
will typically allow gas to permeate, while water-based liquids will not be
~5 transported through the membrane if the driving pressure is below a
threshold
pressure commonly referred to as "breakthrough" or "bridging" pressure. In
contrast, hydrophilic microporous membranes will transport water based
liquids.
Once wetted, however, gases (e.g. air) will essentially not pass through the
membrane if the driving pressure is below a threshold pressure commonly
2o referred to as °bubble point pressure". Hydrophilic monolithic films
will typically
allow water vapour to permeate, while gas will not be transported rapidly
through
the membrane. Similarly membranes can also be used for non-water based
liquids such as oils. For example most hydrophobic materials will be in fact
oleophilic: A hydrophobic but oleophilic microporous membrane will therefore
be
25 permeable for oil but not for water.
Membranes are often produced as thin sheets, and they can be used atone
or in combination with a support layer (e.g. a nonwoven) or in a support
element
(e.g. a spiral holder). Other forms of membranes include but are not limited
to
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polymeric thin layers directly coated onto another material, bags corrugated
sheets.
Further known membrarfes are "activatable" or "switchable" membranes
that can change thein,~ properties after activation or in response to a
stimulus. This
change in properties might be permanent or reversible depending on the
specific
use. For example, a hydrophobic microporous layer may be coated with a thin
dissolvable layer e.g. made from polyvinyl}alcohol. Such a double layer system
will be impermeable to gas. However, once wetted and the poly(vinyl)alcohol
film
has been dissolved, the system will be permeable for gas but still impermeable
for liquid. Conversely, if a hydrophilic membrane is coated by such a soluble
layer, it might became activated upon liquid contact to allow liquid to pass
through, but not air.
~5 Another useful membrane parameter is the permeability to thickness ratio,
which in the context of the present invention is referred to as "membrane
conductivity". This reflects the fact that, for a given driving force, the
amount of
liquid penetrating through a material such as a membrane is on one side
proportional to the ~>ermeability of the material, i.e. the higher the
permeability,
2o the more liquid will penetrate, and on the other side inversely
proportional to the
thickness of the material. E~~ence, a material having a lower permeability
compared to the same material having a decrease in thickness, shows that
thickness can compensate fos~ this permeability deficiency (when regarding
high
rates as being desirable). Typical kld for packaged products or devices
according
25 to the present invention is from about 1 x 70'9 to about 500 x 10-9 m,
preferably
from about 100 x 10-9 to about 500 x 10-9 m. Preferably the k/d is at least 1
x 10''
and more preferably at least 1 x 10-5 m.
For a porous membrane to be functional once wetted (permeable for liquid,
3o not-permeable for air), at least a continuous layer of pores of the
membrane
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always need to be filled with liquid and not with gas or air. Therefore
evaporation
of the liquid from the membrane pores must be minimized, either by a decrease
of the vapour pressure in the liquid or by an increase in the vapour pressure
of
the air.
5
The evaporation prior to use of the liquid from the packaged product can
also be minimised by a vapour tight cap or by completely wrapping the packaged
product, for example in the case of a sponge, into a film. A suitable film may
be
made from various materials, for example polyethylene.
0
The present invention is useful as a liquid applicator or dispenser.
Examples of liquids which may be applied or dispensed using the packaged
product or device of the present include: paint, glue, shoe polish, health and
beauty care lotions, detergent compositions and various food and beverage
~5 products. In particular, for beverage products, the present invention may
be
designed for use as a drinking bottle. Other specific examples include paint
applicators wherein a packaged paint product is dispensed, optionally via an
applicator such as a brush or roller; skin creams or lotions, including
cosmetics
(such as lipsticks and nail varnishes) and pharmaceutical compositions, to be
2o applied to the body; detergent solutions for cleaning hard surfaces such as
work
surfaces, windows and floors. In the fatter case, the device of the present
invention can be integrated into a floor mop.
25 Test method: Bubble Point Pressure (membrane)
The following procedure applies when it is desired to asses the bubble point
pressure of a membrane.
3o First, the membrane material is connected with a plastic funnel (available
from Fischer Scientific in Nidderau, Germany, catalog number fi25 617 20) and
a
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length of tube. The fmnnel and tlhe tube are connected in an air tight way.
Sealing
can be made with F'arafilm M (available from I=lecher Scientific in Nidderau,
Germany, catalog number 617 800 02). A circular piece of membrane material,
slightly larger than thE: open area of the funnel, is sealed in an air tight
way with
the funnel. Sealing is made with suitable adhesive, e.g. Pattex from Henkel
KGA,
Germany). The lower end of the tube is left open i.e. not covered by a
membrane
material. The tube sh;ouid be of sufficient length, i.e. up to 10m length may
be
required.
In case the tesl: material is very thin, or fragile, it can be appropriate to
support it by a very open support structure (as e.g. a layer of open pare non-
woven material) before connecting it with the funnel and the tube. In case the
test specimen is not of sufficient size, the funnei may be replaced by a
smaller
one (e.g. Catalog # X326 616 02 from Fisher Scientific in Nidderau). If the
test
specimen is too large size, a representative piece can be cut out so as to fit
the
funnel.
The testing liquid can be the transported liquid (i.e. oil or grease), but for
ease of comparison, the testinc,~ liquid should a sblution 0.03% TRITON X-100,
2o such as available from MERCK KGaA, Darmstadt, Germany, under the catalog
number 1.086039 in distilled or deionized water, thus resulting in a surface
tension of 33 mNlm.
Whilst keeping 'the lower (open) end of the funnel within the liquid in the
reservoir, the part of the funnel with the membrane is taken out of the
liquid. if
appropriate, but not necessarily, the funnel with the membrane material should
remain horizontally aligned.
Whilst slowly continuing to raise the membrane above the reservoir, the
3o height is monitored, and it is carefully observed through the funnel or
through the
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membrane itself (optionally aided by appropriate lighting) if air bubbles
start to
enter through the material into the inner of the funnel. At this point, the
height
above the reservoir is registered to be the bubble point height.
From this height H the Bubble point pressure BPP is calculated as:
BPP = p ~ g ~ H with the liquid density p, gravity constant g ( g ~ 9.81
mls2).
in particular for bubble point pressures exceeding about 50 kPa, an
alternative determination can be used, such as commonly used for assessing
bubble point pressures for membranes used in filtration systems. Therein, the
membrane is separating two liquid filled chambers, when one is set under an
increased gas pressure (such as an air pressure), and the point is registered
when the first air bubbles "break through".
't 5
Determination of Pore Size
Optical determination of pore size is especially used for thin layers of
porous system by using standard image analysis procedures known to the.
ski4led_
2o person.
The principle of the method consists of the following steps: 1 ) A thin layer
of
the sample material is prepared by either slicing a thick sample into thinner
sheets or if the sample itself is thin by using it directly. The term "thin"
refers to
25 achieving a sample caliper low enough to allow a clear cross-section image
under the microscope. Typical sample calipers are below 200Nm. 2) A
microscopic image is obtained via a video microscope using the appropriate
magnification. Best results are obtained if about 10 to 100 pores are visible
on
said image. The image is then digitized by a standard image analysis package
3o such as OPTIMAS by BioScan Corp. which runs under Windows 95 on a typical
IBM compatible PC. Frame grabber of sufficient pixel resolution (preferred at
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least 1024 x 1024 pixels) should be used to obtain good results. 3) The image
is
converted to a binaryr image a sing an appropriate fihreshold level such that
the
pores visible on the image arE~ marked as object areas in white and the rest
remains black. Automatic threshold setting procedures such as available under
OPTIMAS can be used. 4) Z'he areas of the individual pores (objects) are
determined. OPTIMAS offers fully automatic determination of the areas. 5) The
equivalent radius for each pore is determined by a circle that would have the
same area as the pore. If A is i:he area of the pore, then the equivalent
radius is
given by r=(Al~)'r. The average pore size can then be determined from the pore
o size distribution using standard statistical rules. For materials that have
a not
very uniform pore size it is recommended to use at least 3 samples for the
determination.
Optionally comnnercially available test equipment such as a Capillary Flow
1 s Porometer with a pressure range of 0-1380 kPa (0-200psi), such as supplied
by
Porous Materials, Inc, Ithaca, Jew York, US model no. CFP-1200AEXi, such as
further described in respective user manual of 2197, can also be used to
determine bubble point pressurae, pore size and pore size distribution.
Determinations of call&~
The caliper of trEe wet sample is measured (if necessary after a stabilization
time of 30 seconds;) under the desired compression pressure for which the
experiment will be run by using a conventional caliper gauge (such as supplied
by AMES, Waitham, MASS, US) having a pressure foot diameter of 1 1I8 "
(about 2.86 cm), exerting a pressure of 0.2 psi (about 1.4 kPa) on the sample,
unless otherwise desired.
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Determination of ~ermeabiliy and conductivi~r
Permeability and conductivity are conveniently measured on commerciafky
available test equipment.
For example, equipment is commercially available as a Permeameter such
as supplied by Porous Materials, Inc, Ithaca, New York, US under the
designation PM! Liquid Permeameter. This equipment includes two Stainless
Steel Frits as porous screens, also specified in said brochure. The equipment
~o consists of the sample cell, inlet reservoir, outlet reservoir, and waste
reservoir
and respective filling and emptying valves and connections, an electronic
scale,
and a computerized monitoring and valve control unit. A detailed explanation
of-a
suitable test method using this equipment is also given in the applicants co
pending application PCT/US98113497, filed on 29~' June 1998 (attorney docket
no. CM1841FQ).
Exams
2o Example 1
A sponge comprises a polyurethane bulk material completely surrounded by
a polyamide membrane. The membrane was sealed to itself at both ends of the
sponge, as well as along the length of the sponge so that all fluid passing
into or
out of the sponge must pass through the membrane. The membrane had an
average pore size of 20 micrometers, an open area of 14%, a caliper of 55
micrometers and was manufactured by Sefar Inc., of Ruschlikon, Switzerland,
number 03-20/14. The bulk material which is 100 mm tong, 90 mm wide and 5
mm deep, it had 10 pores per inch, and was manufactured by Kureta of
3o Stadtallendorf, Germany (K-S ppi 10).
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The sponge was soaked in water so that all of the membrane was wetted.
Little or no water drips out of the .sponge, however water is transferred to
the skin
when the sponge is rubbed on the arm.
5
Example 2
A sponge comprises a polyurethane bulk material completely surrounded by
1o a polyamide membrave. The membrane was sealed to itself at both ends of the
sponge, as well as along the length of the sponge so that ail fluid passing
into or
out of the sponge must pass through the membrane. The membrane had a~
average pore size of 20 micrometers, an open area of 14%, and was
manufactured by Verseidag-Techfab of Geldern IMaldeck, Germany under the
~ trade name ivlonodur PA20. The bulk material which is 100 mm long, 90 rnm
wide and 5 mm deep, it had 10 pores per inch, and was manufactured by
Recticel of Westfalen, Belgium under the name Tn1110.
The sponge w~~s soaked in Nivea Body (~PIiIkT"" sold by Beiersdorf of
2o Hamburg, Germany ;~o that all of the membrane was wetted. Little or no
liquid
drips out of the sponge, however liquid is transferred to the skirl when the
sponge is rubbed on the arm.
Example 3
A sponge comprises a polyurethane bulk material completely surrounded by
a polyamide membrane. The membrane was sealed to itself at both ends of the
sponge, as well as allong the length of the sponge so that all fluid passing
into or
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out of the sponge must pass through the membrane. The following membranes
were used:
(i) 03-50137 having an average pore size of 50 micrometers, an open area of
37%, a caliper of 50 micrometers;
(ii) 03-511 having an average pore size of 5 micrometers, an open area of 1 %,
a
caliper of 75 micrometers;
(iii) 03-10/2 having an average pore size of 10 micrometers, an open area of
2%,
a caliper of 45 micrometers;
(iv) 03-20!14 having an average pore size of 20 micrometers, an open area of
14%, a caliper of 55 micrometers;
all of which are manufactured by Sefar Inc., of Ruschlikon, Switzerland.
The bulk material which was 100 mm long, 90 mm wide and 5 mm deep, it
had 10 pores per inch, and was manufactured by Kureta of Stadtallendorf,
~s Germany (K-S ppi 10).
The sponge was soaked in Nivea Body MilkT"" sold by Beiersdorf of
Hamburg, Germany so that alf of the membrane was wetted. little or no liquid
drips out of the sponge, however liquid is transferred to the skin when the
2o sponge is rubbed on the arm.
It was found that the different membranes used in Example 3 provided a
different thickness of liquid. The 03-5/1 membrane resulted in a liquid
thickness
of 40 micrometers; the 03-10/2 membrane resulted in a liquid thickness of 34
25 micrometers; and the 03-20114 membrane resulted in a liquid thickness of
174
micrometers.
Example 4
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An elastomeric structure was made out of than large pore mesh having a
pore size of 5mm forming a void and giving volume for 250 m! fluid. The
structure
is completely surrounded by a polyamide membrane so that fluid passing into or
out of the void must pass through the membrane. The membrane is sealed to
itself at both ends of the mesh, as well as along the length of the mesh. The
membrane had a porE~ size of 20 micrometers, an open area of 14%, a caliper of
5~ micrometers and is manufactured by Sefar Inc. of Ruschlikon, Switzerland
under the product code 03-20/14.
o The membrane is wetted and the structure compressed, it remains in its
compressed state. Once the membrane comes into contact with liquid, the
elastic
forces relax and liquid is absorbed rapidBy into the sponge.
5 Example ~
A membrane w,as hermetically sealed over the opening of a bottle of Mr
Proper, 500 ml, manufactured by Procter & Gamble. The membrane was made
of poiyamide, had a pore size of 5 micrometers, an open area of 1 %, a caliper
of
20 75 micrometers and is manufactured by Sefar Inc. of Ruschlikon, Switzerland
under the product code 03-5/1.
Once the membrane was. wetted the bottle can be held upside down and
little or no cleaning liquid will drip out of the /bottle. However, liquid was
25 dispensed rapidly when the bottle was compressed manually. When the bottle
was released again, the elasticity of the bottle itself re-expanded the bottle
allowing the inner pressure to rise without drying the membrane.
3o Example fi
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Use baby drinking bottle NUK bottle MAPA GmbH Gummi- & Plastikwerke,
Postfach 1280, D-27392 Zeven, Germany with a Learner's spout. The membrane
was hermetically seated to the opening of the bottle. The membrane was made
of polyamide had a pore size of 20 micrometers, an open area of 14%, a caliper
of 55 micrometers. It was manufactured by Sefar Inc. of Ruschlikon,
Switzerland
under the product code 03-20/14.
Once the membrane was wetted the bottle can be held upside dowh and
little or no liquid will drip out of the bottle, however, the baby can drink
easily out
of the bottle. Once the inner pressure gets below the bubble point pressure,
air
wilt transfer through the membrane allowing the inner pressure to rise again.
The
membrane remained wet and the bottle fully functional.
