Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
FP-0275
C2 ABSORPTION MEANS -
Back~round of the Invention
A wide variety of emergency breathing
equipment has previously been developed, such as the
protective hood with CO2 absorbant described in
Werjefelt, U.S. Patent 4,fi27,431, and the multilayered
hood with ela tomeric neck ~eal described in copending,
coassigned U.S. Appli~ation Serial No. 120,533, filed
No~ember 13, 1987. This type of equipment general~y
includes a protective hood, a source of oxygen and a
means to remov~, from th_ hood interior, the carbon
dioxide exhaled by t.he wearer.
~ithium hydroxide (LioH) is one compound
commonly used ~o absorb the carbon dioxide. LioH is
often preferred as an absorbent be~ause it provides
acceptable absorption characteristics with acceptable
weight. Particularly in aircraft applications, weight
is an important consideration.
Lithium hydroxide iis readily available in
powder forml which provides al surface area that
maximizes its effectiveness a~s an absorbant. However,
the powder dust is a respiral:ory irritant, and should
therefore be isolated from the wearer.
Previously, scrubbers were constructed by
impregnati~g felt with LioH powder by putting the two
together in a ball mill. The resul~ing loaded felt was
encased in an envelope of semipermeable membrane that
allowed ~as flow through the envelope while retaining
the LioH. Heat sealing of such envelopes was also used
to maintain the uniform diskribution o~ the LioH powder
within the envelopes.
While such previous techniques and designs
were satiSfaGtOry~ continuing effort has been devoted
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to a C02 absorbant system that would provide improved
balance among maximum abso~ption, isolation from the
wearer, ease of manufactur0 and low cost and weight~
Summary of the Invention.
The present invention provides a C02
absorbant which is easily and economically
manufactured, and provides uniform distribution of
absorbant, excellent absorption capability and
isolation of the absorbant from the user.
Specifically, the present invention
provides a C02 absorption means in which the C02
absorbant is uniformly admixed with about from 0.1 to
70%, by weight of the mixture, of a ~ibrous material,
and the C02 absorption means is disposed in the form of
a sheet having a thickness of about from 1 to 25 mm.
Brief Description of the Drawinqs
Figure 1 is a cross~-sectional view of a
pr~ferred Co2 absorption means of the present
invention.
Figure 2 is a perspective view of a
protective hood, partly cut away to show the C02
absorption means of the present invention disposed
2~ inside the hood~
Detailed Description of the Invention
The present invention resides in the
provision of a C02 absorption means which is compounded
with a fibrous material, to uniformly and intimately
admix the absorption means with the fibrous material.
This compounding stabilizes the C02 absorption means,
reducing dusting and the possibility of irritation of
the user. A wide range of compositions of the CO2
a~sorption means and the fibrous material can be used,
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in that the fibrous material can c~mprise about from
0.1 to 70 % by weight of the mixture. Preferably, the
fibrou6 material comprises about from 0.5 to 50 % by
weight of the mixturP, and especially about from 1 to
10%.
C2 absorbants which can be used in the
present invention include alkali and alkaline earth
metal hydroxides and oxides, such as calcium hydroxide,
calcium oxide, sodium hydroxide and barium hydroxide.
Of these, the lithium and sodium salts are preferred,
and lithium hydroxide is particularly preferred. In
general, for the best balance of handing and absorption
characteristic~, lithium hydroxide having a particle
size of about from 5 to 250 microns is used.
The C02 absorption means is admixed, or
compounded, with any fibrous material that can be laid
down in a mat or sheet by wet or dry techniques.
Fibrous materials which can be used include polymeric
fibers such as polyolefins, polyesters, and polyamides
with fiber lengths in the ras~ge of about from 0.1 to 3
inches. Inorganic fibers can also be used.
Fibrous materials which are preferred in the
present invention are fluoroc:arbons, such as
polytetrafluoroethylene. That ~ommercially availa~le
from E. I. du Pont de Nemours and Co. as ~Teflon
TFE3512~, when ~ormed into ~ibrids, has been found to
: be particularly satisfactory. Other fluorocarbons
which can be used include that commercially available
from E. I. du Pont de Nemours and Co. as Teflon K10
3~ fluoropolymer. A preferred polypropylene which can be
used i~ that commercially available from E. I. du Pont
de NemourR and Co. in the form of polypropylene fibrids
as ~Pulp Plus.~
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The fibrous material can either ~e used in a
~ibrilated form or it can be simultaneously fibrilated
and compounded with the C02 absorbant. While the use
of prefibrilated material, such as the polypropylene
5 fibrids noted above, is satisfactory, it is pre~erred
to simultaneously fibrilate the material and compound
it with the C02 absorption means. This simultaneous
- fibrilation and compounding results in a greater degree
of^encapsulation of the absorbant, and a more stable
structure.
After compounding of the CO2 absorption means
with the fibrous material, it is cast into sheet form.
Generally, the compounded material is dispersed in a
fluid to facilitate casting. Fluids which can be used
include any that do not dissolve the fibrous material
or the C02 absorption means under the conditions used,
such as aliphatic and aromatic hydrocarbon solvents.
Naptha, however, is a preferred dispersion aid. The
dispersion can be cast into sheet form using
conventional paper~making techniques.
In the alternative, ~he compounded C02
absorption means can be pelletized and incorporated
into a sheet structure by dry techniques. For example,
the p~llitized C02 absorption means can be spread
between two sheets of permeable membrane and then
needle-punched for structural integrityO
Regardless of whether a wet or dry
preparation method is used, the absorbant and the
fibrous material in the sheets of CO2 absorption means
are uni~ormly admixed. For example, ln a four square
inch ~heet of the absorption means, the relative
concentration of the absorbant and the fibrous
material will generally not vary more than about 20% by
volume.
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It is preferred that a C02 permeable membrane
be bonded to at least one surface of the compounded C02
absorption means, and especially to both surfaces. It
has been found that these layers improve the overall
strength of the absorbant structure. A wide variety of
membranes can be used, so long AS the membrane does
not significantly inhibit air flow through the
absorbant. The fabric preferably has a pore size of at
least about 0.1 micron. A particularly satisfactory
material is tha~ commercially available from
E. I. du Pont de Nemours and Co. as Nomex hydrolaced
~abric.
The membrane or fabric can be applied to the
compounded C02 absorption means before or a~ter
formation of the sheet. For example, the absorbant
sheet can be cast onto a layer of permeable fabric from
a dispersion~
The C02 absorbant sheet is preferably
mechanically treated to impart threa dimensional
inte~rity. Ultrasonic bonding, heat bonding, stitching
or hydrolacing with an appropriate liquid can be so
used to advantage. However, needling with con~entional
apparatus such as a needleloom, used for felting, is
preferred for ~uch treatment.
In the preferred manufacturing technigues
used in the present invention, LioH powder is combined
with a high-fibrillating fluoropolymer in a high shear
mixer which results in a dustless mass o~ material.
This mass is then dispersed in non-~olvent using a high
shear mixer and the slurry is deposited onto a
permeable Rheet usin~ conventional paper ~aking
equipment. ~he resulting sheet is dried and a ~econd
permea~le sheet is put on top. The entire sandwich is
then mechanically treated, for example, using a
needleloom.
In Figure 1, the preferred construction of
the C02 absorption means is shown. There, the
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absorbant 31 is intimately admixed with fibrous
material 32, and disposed in the form of a ~heet.
Permeable fabric layers 33 and 34 are bonded to each
surface of the admixed absorbant and fibrous material.
The absorption mean~ of the present invention
can be used in the protective hoods constructed
according to the general configuration, and with the
materials specified in, th~ aforemantioned Werjefelt,
U.S. Patent 4,627,431, and copending, coassigned U.S.
Application Serial No. 120,533, filed November 13,
1987, both of which are hereby incorporated by
reference.
~he hoods in which the present inv~ntion can
be used can have the tubular configuration shown in
U.S. Patent 4,627,431, with a æubstantially circular
top section attached to a tubular side section. Such a
configuration is show in Figure 2, in which generally
tubular portion 1, having upper end 2 and lower end 3,
has a continuous sidewall which forms the basic
component of the hood. The upper end of the tubular
portion is bonded to circular top portion 5O
Substantially annular resilient neck seal 6 is attached
to the inner side portion of l:he lower end of the
tubular portion, the neck seal having an opening 7 for
admitting at least the head of the user to form a
closure around the user. C02 absorption means 8 is
encased in envelopes 9 and attached to the interior
sidewall of the tubular portion ~f the hood~ If
external air sources are intended to be used for the
hood, the construction ~referably Purther comprises
inflow valve 10 and outflow valve 11~
The admixing or compounding of the absorbant
wi~h the fibrous component, in a~cordance with the
present invention, ~ubstantially reduces the problems
associated with dust from the absorbant. The use of
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paper making techniques allows a uniform distribution
of the absorbant within the resultant structure. The
layers o~ fibrous sheet, and especially the preferred
materials, add strength and fire resistance The
preferred mechanical treatment insures long term
mechanical integrity of the ~crubber and prevents
substantial migration or settling of absorbant powder
in the scrubber. Since the absorbant is so effectively
bound by the fibrous material and the mechanical
trsatment, the costly envelopes of expanded
polytetrafluoroethylene are not required. Instead, the
~sandwich can be inserted into a permeable envelope of
sufficient strength for the intended use and a~fixed to
the interior of an emergency support unit.
The present invention is further illustrated
in the following specific example.
Example
60 grams of environmental grade anhydrous
LioH powder ~6-14 Tyler mesh) was ground to a particle
size of about 10 microns in a hammer mill. The LioH
was mixed with polytetrafluoroethylene (TFE) powder
(commercially available from E. I. du Pont de Nemours
and Co. as ~Teflon ~FE3512~) in a ratio of 98% LioH, 2
Teflon by weight, at 212 degrees F for 5 minutes in a
high shear Banbury mixer. The resultant mass o~
material was dispersed in one guart of a hydrocarbon
liquid ~VM&P Naptha) ~sing a Waring blender and blended
to uniformity. The mixture was further diluted with
VM&P Naptha to a final guantity of about 3 gallons with
~tirring adequate to maintain a unifo~m dispersion.
A O.9 ounce/square yard, 12~ x 12n ~heet of
permea~le fabric (commercially available from
E~ I. du Ront de Nemours and Co. as Nomex splunlaced
fabric) was laid onto the screen of a laboratory size
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paper making machine. The LiOH~Teflon/Naptha slurry
was poured in to provide an effective LioH loading of
60 grams/sq. ft. 15~ of mercury vacuum was applied and
then the 2 layer structure was pressed at 60 psi. The
resulting paper was dried at 230F for one hour.
Finally, a second 0.9 oz./sq. yd., 12~ x 12n sheet of
permeable spunlaced spunbonded ~abric was added ancl the
entire structure was needled on a Dilo needlelQom.
Several identical composite sheets were made as
described above, pieced together and cut as required
(using an industrial-type sewing machine) to form five
individual pieces; one about 6~x12~, ~wo about 6~x24
and two about 18~x4n. The composite sheets were
then incorporated into individual 2-layer melt-blown
polypropylene envelopes ~outer layer 35 grams/square
meter, inner layer 20 grams/square meter). The
envelope is formed using traditional sewing
techniques. Buttonholes were included for ease of
attachment in a smoke hood, and additional stitching
lines were added to aid ~olding these scrubbers and
placement within the hood.
Emergency life support hoods incorporating
the scrubbers were tested, ancl passed the tests for
aircraft crewmembers describec1 in the FAA action
notice, A8150.2 of September 1, 1987. The tests model
the wor~load of an aircraft crewmember while putting
out an on-board ~ire.
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