CA1044615A - Low pressure drop filter medium - Google Patents
Low pressure drop filter mediumInfo
- Publication number
- CA1044615A CA1044615A CA217,494A CA217494A CA1044615A CA 1044615 A CA1044615 A CA 1044615A CA 217494 A CA217494 A CA 217494A CA 1044615 A CA1044615 A CA 1044615A
- Authority
- CA
- Canada
- Prior art keywords
- filter medium
- microfibers
- layer
- pressure drop
- air
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D39/00—Filtering material for liquid or gaseous fluids
- B01D39/14—Other self-supporting filtering material ; Other filtering material
- B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
- B01D39/1607—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous
- B01D39/1623—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous of synthetic origin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
- B32B5/22—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed
- B32B5/24—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer
- B32B5/26—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer another layer next to it also being fibrous or filamentary
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
- B32B5/02—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer
- B32B5/022—Non-woven fabric
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2305/00—Condition, form or state of the layers or laminate
- B32B2305/02—Cellular or porous
- B32B2305/026—Porous
Abstract
Abstract A new filter medium, which can remove a high per-centage of fine particles from a gas stream while causing a relatively low pressure drop in the gas stream, comprises a base porous web, one or more lightweight non-self-supporting layers of microfibers collected and carried on the base porous web, and a top porous web. A new aerosol filter apparatus incorporates the new filter medium to provide economical con-sistent filtering of air in a home-office, or industrial en-vironment. In this new filter apparatus, a web of the filter medium extends from a supply roll across a stream of the air being cleaned to a take-up roll; and the filter medium is advanced from the supply roll to the take-up roll to gradu-ally provide a fresh length of filter medium in the air stream.
Description
lU~lS
LOW-PRESSURE-DROP FILTER MEDIUM
A primary deficiency of the conventional mechanical ;
air filters that are used to remove dust and other foreign particles from a home, office, or industrial atmosphere is that they operate at maximum effectiveness for only a short period of tlme. Conventional furnace filters, which take the form of rather thick panels formed of tightly convoluted webs of fine glass ~ibers are an example. Within a few weeks after installation, they have usually collected a sufficient quantity of particles so as to greatly reduce the amount of air that may -be moved through them by an air-blower means. And the less air that moves through the filter, the less the number of particles removed from the air.
The present invention provides improved flltering of room air, and makes possible many other advances in aerosol fllterlng, with a unlque new fllter medlum. Briefly, this new ;
fllter medium comprlses a base porous preformed web; at least one thin lightweight layer of microfibers carrled on the base web;
and a top porous web disposed over the layer of microfibers.
The mlcroflbers used are quite flne, generally being less than ~ ;
about 0.5 micrometer in diameter and preferably being less than about 0.3 micrometer in diameter; and they are included in ..
rather low amount. In fact, the layer of microfibers is so unusually thln and lightweight that the layer is generally not self-supporting. That ii, while the layer of microfibers might be temporarily handleable by itself, it could generally not be practlcably manufactured and wound by ltself in a storage roll, unwound from the storage roll, and laminated to a base porous web. Generally the layer of mlcrofibers ls formed ln sltu on -: . . .
: 1 .~ :.
~.', ~.
: ~V4~15 the base porous web by collecting mlcrofibers from a mass of mlcrofibers directed to the web.
The most suitable microfibers for use in a filter medlum of the invention are solution-blown polymeric micro-fibers. Both melt-blown and solution-blown microfibers (formed by extruding a liquifled (melted or dissolved) normally solid polymeric material through an orifice into a high-velocity gaseous stream that draws out and attenuates the extruded material into very fine fibers, which then solidify during travel in the gaseous stream to a collector) have long been recognized to have good potential in fllter media. See Wente, Van A., "Superfine Thermoplastic Fibers", Industrial Engineer-~; in~ Chemistry, Volume 48, page 1342 et seq (1956) and such patents as Francis, U.S. Pats. 2,464,301 and 2,483,406; Ladisch, `~
U.S. Pat. 2,612,679; Watson, U.S. Pat. 2,988,469; Till et al, U.S. Pat. 3,073,735; and Mabru, U.S. Pat. 3,231,639. Many of these patents are directed to filtration, and some of them,such as Tlll et al, discuss multilayer filter media in which a layer of blown microfibers is used in comblnation with layers of more coarse fibers.
But insofar as known, no one has previously taught -a filter medium comprising a layer of microfibers and support-ing webs such as are included in filter media of the present invention; and no one has previously attained the properties exhibited by filter media of the invention. One unique pro-perty generally exhibited by the new filter medium is an unusually low resistance to the flow of a gas stream. For a given particle penetration through the medium ("partlcle pene-tration" is the number of particles in a gas stream passed by ,, . . . . ~ . ~ , :
0 . ~ .. ,., . ' , ' . ~ .'. . ' :
- , , the filter medium, measured as a percent of the number of : -particles entering the filter medium; "initial particle pene~
tration" is the particle penetration during initial use of :
the filter medium), the filter medium generally causes an un-usually low pressure drop in a gas stream being treated, and the result is that higher volumes of the gas can be moved through the filter medium with lower-powered blower means.
As a brief summary, a filter medium of the invention can be summarized as comprising a multilayer filter medium exhibiting a low pressure drop at a desired particle pen~tra-tion comprising a preformed handleabLe self-supporting porous fibrous base layer, at least one thin lightweight non-self- 1 :
supporting filtration layer of randomly arranged microfibers ..
having an average diameter less than about 0.5 micrometer collected on said base layer by interposing the base layer `~
in a stream of the microfibers, said layer of microfibers weighing less than about 0.01 pound per s~uare yard; and a porous top layer laminated over the layer of microfibers so ~
as to unify the filter medium into a single handleable self- .
supporting sheet material; said base and top layers contrib-uting less than 20 percent of the~pressure drop through the filter medium at a face veIocity of 100 feet per minute; and said layer of microfibers having a relationship of initial particle penetration to pressure drop ~hen tested at a face veIocity of 100 feet per minute within the range defined by curve& C and D shown in Figure 3. ~-The new properties provided by filter media of the invention are:of significant advantage, and one illustration .
is the previously mentioned improvement in filtering of room ..
air. More specifically, the new filter medium makes possible ~ -3-.~,~ ..
.:
iO4~
a new room air cleaner that achieves a steady level of good efficiency over a long operating life. Briefly, such a room air cleaner comprises a) a blower means for drawing air in through an inlet, moving the air along an air path, and then exhausting the air through an outlet, b) a filter medium of -~
the invention stored in a replaceable supply roll and extend-ing across the air path~to a take-up roll, and c) a drive means for aduancing the filter medium at a predetermined rate from the supply roll to the take-up roll. Since the pressure drop through the new filter medium is small, a low-powered, quiet blower means can be used in the device. Further, since the pressure drop remains low for a rather long period of time, the filter medium may be advanced through the room air cleaner at a rather slow rate. For example, a twelve-inch- ~
wide (30-centimeter-wide) web in a 130-cubic-feet-per-minute ~-(400-liter-per-minute) home unit may be advanced at a rate of two inches (5 centimeters) per day or less r meaning that the roll of filter medium is replaced at long intervals of 90 or 180 days.
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The filter medium is inexpensive, and the result is that economlcal hlgh-efficiency filtering is made possible indefinitely.
Insofar as known, such a capability in room air cleaning has never before been practicably achieved with mechanical fllters.
In the drawings, Figure 1 is a schematic view of a room air cleaner of the lnventlon;
Figure 2 is an enlarged section through a filter medium of the invention;
Figure 3 shows plots of initlal partlcle penetra-tion versus pressure drop for filter media of the invention, partlcle penetratlon being in percent on the ordinate and ; pressure drop being in lnches of water on the absclssa; and Flgure 4 ls a schematlc diagram of apparatus useful , to prepare a fllter medlum of the present invention.
The illustrative room air cleaner 10 shown in Figure 1 comprises a housing 11 in whlch are mounted a take-up roll 12 and a supply roll 13 of a filter medlum 14. A length of the filter medium extends from the supply roll 13 to the take-up roll 12, and passes through an air stream developed " ~, by a blower means 15. The blower means 15 draws air into the housing 11 through an lnlet 16, forces the air throu~h the length of filter medium between the supply and take-up rolls, and then through an outlet 17 in the housing. A drive motor ' 18 advances the filter medium from the supply roll to the take-j up roll at a predetermined rate. The drlve motor may operate contlnuously or may operate at periodic intervals.
The fllter medium 14, as illustrated ln Flgure 2, comprlses a base porous web 21, an lntermedlate layer 22 of ' ' '.
-4- ~ ~
;" :
;` 1~4~S
microflbers, and a top porous web 23.
The base and top webs exhibit good poroslty, so ,~ that together they contribute only a minor portlon (normally -less than 20 percent) of the pressure drop through a filter medlum of the invention. The base and top porous webs may ,~, ~ take a variety of forms, but typically they are nonwoven .,. :,-, :~ .: .
s~ fibrous webs. In manufacturing such webs, staple fibers are ` -~ typlcally deposlted as a loose web on a cardlng or garneting -,~ machlne, and then are compacted lnto a finished thin web.
, i:~
The web~ may be held in compacted form by a fusing of the ~ -flbers at their polnts of contact or by the use of a blnder resln lightly impregnated lnto the web so as to preserve poro-slty of the web. The fibers in the webs generally comprise 1bers of a synthetlc polymer such as polyethylene terephthalate, but may also lnclude natural flbers. The flbers are typlcally on the order of 1.5 to~3 denier.
The base porous web ls a self-supportlng web that or~most uses has a welght on the order of lO pounds per 320 square yards (1.7 mllllgrams per square centimeter). But ln some~r1lter media of the lnvention ln whlch the base web acts ~ i as~a pref11ter,~the~web may be thicker, havlng a welght on the order~of 50 poundY per 320 square yards (8.5 mllligrams per square~oent1meter). The top porous web is usually s1milar to the baYe porous web, though lt may be of lesser welght and greater poroslty. In some fllter medla of the invention, the top porous web faces an alr stream belng flltered, and in that case it may also be designed to act as a prefllter.
The thickness of a layer of mlcrofibers and the number of such layers used ln a filter medlum of the inventlon ~5~
, .- ~
depends upon the particular use to be made of the ~ilter medium. The filter medium can be designed differently de-pending on the different conditions of use (such as face veloclty of a gas stream being filtered, power of blower means, partlcle penetratlon during a single pass of gas stream being cleaned, and pressure drop) that are desired.
Filter media of the invention can be used as so-called absolute ("HEPA") filters and also as filters that pass a greater percentage of particles but operate at a lower face velocity.
For use in a room cleaner of the invention, the layer of layers of microfibers is generally rather thin, weighing less than 0.01 pound per square yard (0.5 milligram -per square centimeter) and preferably less than 0.005 pound per square yard (0.25 milligram per square centimeter). For other uses the layer or layers may be thicker, though even for an absolute filter the weight will generally be less than o.o6 pound per square yard (3 milligrams per square centimeter) and more often less than 0.03 pound per square yard (1.5 milligram per square centimeter).
As to pressure drop, in room air cleaners of the -~
invention, whlch are typically designed to operate at a face . .
velocity of 100 feet (30 meters) per minute, a filter medium exhibiting a pressure drop of 0.3 - 0.5 inch ~0.75 centimeter ;
to 1.25 centimeter)of water will normally be used. For abso- -lute (HEPA) filters operating at a face velocity of 50 feet (15 meters) per minute, the filter medium will typically ex-hibit a pressure drop on the order of 3 to 4 inches (7.5 to 10 centimeters) of water. And for respiratory fllters, the fllter medlum will generally exhibit a pressure drop of 0.3 ' .. ,~ :......... ' ' . ~,"'.' .'' '.. , .... ' ... -, , '. ; , ~Q4~5 to 0.5 inch (0~75 to 1.25 centimeter) of water at a race velocity of about 15 feet (4.5 meters) per minute.
As previously noted, the preferred microfiber layer comprises solution-blown microfibers. A suitable apparatus , for preparing such a micro~iber layer is shown in Figure 4.
This apparatus includes a stand pipe 25 in which a solution of polymers is stored; a pump 26, such as a Zenith pump; an extrudlng apparatus 27 to which the solution is pumped; and a filter 28 through which the solution passes to remove foreign particles or gels that might otherwise plug the extru-: l dlng orifice. The extruding apparatus 27 comprises an air plenum 29 into which air is fed through an inlet 30. A narrow-,~ ..
I diameter needle 31 inside the plenum is connected to the supply :'1 `- .
conduit of solution. The needle 31 extends through a small opening 32 in a face plate 33 of the plenum 29, with the end of -the needle located a short dlstance beyond the face plate (such as 1.5 millimeters). Air supplied through the inlet 30 , ,-passes out through the opening 32, attenuates the extruded polymer, and carries the resulting microfibers to a base porous web 35. The air stream intersects the web 35 over a second air plenum 39, from which air is exhausted. A screen 40 covers ; ~ :
the opening of the plenum to hold the web flat in the air stream.
~, The web 35 is moved ~rom a supply roll 36, around an idler q roller 37, to a takeup roll 380 Top porous web material is ~ unwound from a supply roll 41 and around an idler roller 42 :
where it ls laminated over the layer of microfibers.
~: :
A wide variety o~ polymers may be used to prepare -the solution-blown microfibers, including polymers based on vinyl chloride, styrene, vinyl butyral, and vinylidene chloride.
_7_ . : ~
15)4~15 :
; These polymers may be dissolved in a variety o~ solvents including toluol, ethanol, tetrahydrofuran, methyl ethyl ketone or mixtures of such solvents to produce a desired viscosity.
The polymers based on vinyl chloride are preferred, for one reason because of processing advantages. Also, filters of ` polyvinyl chloride fibers have been found to develop an elac-trostatic charge during use of the filter, and that charge is believed to improve the ability of the intermediate microfiber layer to attract and hold particulate matter. Such an electrostatic charge also develops on microfibers formed from Qther polymers.
, One feature that is noted under microscopic examin-ation of the layer of solution-blown microfibers in some j~ preferred filter media of the invention is the presence of i rounded particles of the polymer from which the microfibers are formed. It is believed that the rounded particles contri-~; bute to a spacing of the microfibers thatmay be partly respon-' sible for the low pressure drop through the microfiber layer.
~' Generally, these rounded particles, which apparently develop ~
during the microfiber-blowing procedure, are on the order -, . ... .
of 1 to 3 micrometers in diameter.
Figure 3 shows different plots of initial particle penetration versus pressure drop for filter media of the ;~
invention, the ordinate showing partiçle penetration in percent, and the abscissa showing pressure drop in inches of ~: ~
water. Curves A and B define a range of relationships between ~ `
particle penetration and pressure drop that useful filter media of the invention generally exhibit at a face velocity of 20 feet (6 meters) per minute; and curves C and D define a range ~ -.~ '` , -8- ~
.' `' .
''"' ~,. ' , ;, : ; , . ,, ~ .,, , ,., ~ . ; ,,:
.~ .
~ : ; 1~4~1S
of relationships that useful filter media of the invention ; generally exhibit at a face veloclty of 100 feet (30 meters) ` per minute.
As the curves indicate, filter media of the invention . that have higher pressure drops (because of a greater thickness, for example) will have a lower particle penetration. Different .. filter media of the invention may differ in their particular relationshlp of initial particle penetration to pressure drop (depending, for example, on fiber size, fiber density, and ;
other characteristics of the microfiber layer), but generally : they will malntain a basic relationship within the range es-tablished by the two sets of curves ln Flgure 3. Changlng the thickness of a layer of mlcrofibers, or the number of ~
the layers, will also change the values of pressure drop and ~ :
particle penetration exhibited by the filter media, but gener-~, ally, not outside the basic relationship established by the . .
two sets of curves in Figure 3.
T.he curves shown in Flgure 3 provide a useful standard for controlling the process of manufacturing filter medla of t.he i.nvention. The nature of a layer of solutlon-~: blown microfibers may be varied by varying the solids content .~.
of the solution extruded through the microfiber-forming apparatus or the extruding conditions, for example. As a ,. general rule~ the lower the solids content, the lower the 'i: diamete.r of flbers that are formed. If the solids content .. :.
is too low, no fiber structure is formed, while if the solids ~ content is too high t.he microfibers are too coarse for desired - .
filtering properties. The rate of flow of the solution may also be varied, generally under 10 or 15 cubic centlmeters~
. ..
_9 _ ., .
~ .
, . . .. -: . :. . .
.,j . . :, . ~ . i . . .. . .
.: ~
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minute, to control the dimensions of the fibers and the number of fibers, and similarly the velocity of air around the needle may be varied.
One way of determining the proper solids content for any polymer and solvent and the proper extruding conditions is to extrude a set of polymer solutions having different solids contents to form different microfiber layers on a base porous web, and plot the relationship of initial particle penetration versus static pressure for the different layers provided. (Because of the rather high porosity of the base web, the effect of the base porous web on the pressure drop may be disregarded.) The polymer solutions producing layers .. ..
! having a relationship between the curves shown in Flgure 3 are generally suitable solutions.
' .
~ When more than one layer of microfibers is included ~
: ~ -in a filter medium of the invention, those layers will usually ; ;
~; be substantially identical to one another; but they also may :~ differ, as to the material from which the fibers are made, -the dlameter of the fibers, the numerical dènsity of fibers, ;
etc. Plural microfiber layers may lie directly against one .~ .
another (as when microfiber layers are collected on two dif-ferent base porous webs which are then laminated together with the microfiber layers face-to-face) or they may be separated by -. ~ .
other layers, of base porous web, for example.
Filter media of the invention have other uses besides in a room air cleaner. For example, filter media of the inven-tion may be used in respirators worn by a person, with the filter medium of the invention being disposed across the path of air lntake into the respirator. Lightweight face maslcs ., .
-10- `' ' ~.
` 10~61S
of the general cup-shaped configuration shown in U.S. Pats.
3,333,585 or 3,521,630, may be used, for example.
The invention will be further illustrated by the following examples:
Examples 1-7 A variety of polymer solutlons as shown in the followlng table were prepared and extruded onto a base porous web using apparatus as illustrated in Figure 4, in which the extrusion needle was a No. 21 gauge, 1/2-inch-long (1.25-centimeter-long) needle. The base porous web was a carded, random-flber web of 1.75-denier polyester fibers bonded together with alcohol-soluble nylon and having a weight of about 10 pounds per 320 square yards (1.7 milllgrams per square centi-meter). A layer of microflbers weighing on the average about 0.004 pound per square yard (0.2 milligrams per square centi-meter) was collected on the base web. A top porous web like the base web except that it welghed 5 pounds per 320 square yards (0.9 milllgram per square centimeter) was laminated over the layer of mlcrofibers. The materials were then tested for init~al partlcle penetration and static pressures at a face velocity of : . .
100 feet (30 meters) per minute, and the results are reported in Table I. A range of static pressures and initial partlcle penetratlons are reported for each different polymer, because dlfferent samples were prepared uslng dlfferent air pressures ln the plenum.
A standard test apparatus was used in which a Royco Model 256 aerosol generator formed an air stream that contained potasslum chloride particles about 0.1 and 1.0 micrometer in dlameter. The partlcle-containing air stream was conducted - ;; . ~ .
``~ lU4~6~5 through a drler and two rlowmeters into an air plenum having a rixture lnto which a test sample can be inserted in the path o~ the air stream. The air input to the aerosol genera-tor was 20 psi (1.4 kilogram per square centlmeter) gauge, the atomlzer pressure in the aerosol generator was 8 psi (0.56 kllogram per square centimeter) gauge, and the ~low through the drler was 15-30 llters per mlnute. Partlcles were formed by the aerosol generator rrom a solutlon of potasslum chlorlde ln s distllled water havlng a sollds content of 0.5 weight-percent.
Test probes extendlng into the alr plenum on each slde Or the test rlxture measure the number Or partlcles ln the air stream ;~;
on each slde of the test sample. The te~t probes were part Or a rorward-llght-scatterlng llnear photometer ldentlfied a8 T-P-~A--2C manufactured by Alr Technlques Inc. Prlor to lnsertlng the test sample ln the alr plenum, the apparatus ls~;ad~;usted so that the partlcle detectlon apparatus reads . .
lOO;~percent. Arter lnsertlon Or the test sample, the down~
stream probe measures (by a partlcle count) the percentage of partlcles~penetratlng through the test sample. The statlc pressure~at the test sample ls measured wlth a water manometer.
Example 8 A composlte fllter medlum was prepared by sandwlchlng together rour~thlcknesse,3 or filter medla llke those Or Examplé 5 except that the layer Or mlcroflbers ln each Or the ;rl ~ -thlcknesseo~welghed O.OlZ pound per square yard (0.65 milllgram per square centlmeter). This composlte rllter medlum was compared~wlth two commercial "HEPA" rllters as to the inltlal partlcle penetratlon and statlc pressure. The Plrst commerclal fllter t"Dexter" Brand, Grade X1401) comprlsed resln-treated rro ~ ~A~ `'i` ' ' :~ . j, ,',''' ':
~ lV44~ilS
,. ~ ~^ ~
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o_ o_ o_ o_ ~.
~ I ~ o~ ~o~ ~o ~ô
' ~ ~ ~ ,o, o ,o~ o : ~ ~ ~ ~ W
" ~ s ~ ~
P f~æ ~ ~ P
~ >
t . - 13 ., ~ ..
. . ,.... . ~ i. ~
.. . .
r- , ~ 46~5 ~ ~
~ ~ ~ ~ o~ ' ~
~ 0 .. ~
o ~o ~o ~ .. ''''. '' ~3 ~ 5 ~ ~ ~
o ~0 ~ ~
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0 ~ ~ O ~ ~ ~ æ ~ 3 e~ 14 .~ :
. .
~0~4tj15 glass fibers about 0.2 - 2 micrometers in diameter, and the second commercial filter ("Microsorban" Brand) comprised polystyrene blown microflbers about 0.25 to 2 micrometers in diameter.
The tests were performed by the procedures des-cribed ln Military Standard 282, Test Method 102.1 using dioctylphthalate particles that averaged 0.3 micrometer and a face velocity of 1o.ll - 10.5 feet (about 3.1 meters) per minute. The test measurements were made promptly so as to avoid any effect of dioctylphthalate on the polyvinyl chloride flbers. The results, as presented in Table II, show much lower particule penetration through filter media of the exam-ple at slmilar pressure drops.
TABLE II
Mass of Static microfibers in Initial particle pressure filter medium penetration (inches of water) (pound per sq. yd.) (percent) (mm of water) (milligrams per sq.
~ cm.) First commer- 0.015 2.0 0.153 cial filter ~ (5) (8) medium Second commer- 0.007 2.1 0-337 clal filter (5.3) (18) medium Filter medium 0.003 2.1 o.o48 of the inven- (5.3) (2.6) tion , . ~ . .
; :
~ ' .. : ~ .
,
LOW-PRESSURE-DROP FILTER MEDIUM
A primary deficiency of the conventional mechanical ;
air filters that are used to remove dust and other foreign particles from a home, office, or industrial atmosphere is that they operate at maximum effectiveness for only a short period of tlme. Conventional furnace filters, which take the form of rather thick panels formed of tightly convoluted webs of fine glass ~ibers are an example. Within a few weeks after installation, they have usually collected a sufficient quantity of particles so as to greatly reduce the amount of air that may -be moved through them by an air-blower means. And the less air that moves through the filter, the less the number of particles removed from the air.
The present invention provides improved flltering of room air, and makes possible many other advances in aerosol fllterlng, with a unlque new fllter medlum. Briefly, this new ;
fllter medium comprlses a base porous preformed web; at least one thin lightweight layer of microfibers carrled on the base web;
and a top porous web disposed over the layer of microfibers.
The mlcroflbers used are quite flne, generally being less than ~ ;
about 0.5 micrometer in diameter and preferably being less than about 0.3 micrometer in diameter; and they are included in ..
rather low amount. In fact, the layer of microfibers is so unusually thln and lightweight that the layer is generally not self-supporting. That ii, while the layer of microfibers might be temporarily handleable by itself, it could generally not be practlcably manufactured and wound by ltself in a storage roll, unwound from the storage roll, and laminated to a base porous web. Generally the layer of mlcrofibers ls formed ln sltu on -: . . .
: 1 .~ :.
~.', ~.
: ~V4~15 the base porous web by collecting mlcrofibers from a mass of mlcrofibers directed to the web.
The most suitable microfibers for use in a filter medlum of the invention are solution-blown polymeric micro-fibers. Both melt-blown and solution-blown microfibers (formed by extruding a liquifled (melted or dissolved) normally solid polymeric material through an orifice into a high-velocity gaseous stream that draws out and attenuates the extruded material into very fine fibers, which then solidify during travel in the gaseous stream to a collector) have long been recognized to have good potential in fllter media. See Wente, Van A., "Superfine Thermoplastic Fibers", Industrial Engineer-~; in~ Chemistry, Volume 48, page 1342 et seq (1956) and such patents as Francis, U.S. Pats. 2,464,301 and 2,483,406; Ladisch, `~
U.S. Pat. 2,612,679; Watson, U.S. Pat. 2,988,469; Till et al, U.S. Pat. 3,073,735; and Mabru, U.S. Pat. 3,231,639. Many of these patents are directed to filtration, and some of them,such as Tlll et al, discuss multilayer filter media in which a layer of blown microfibers is used in comblnation with layers of more coarse fibers.
But insofar as known, no one has previously taught -a filter medium comprising a layer of microfibers and support-ing webs such as are included in filter media of the present invention; and no one has previously attained the properties exhibited by filter media of the invention. One unique pro-perty generally exhibited by the new filter medium is an unusually low resistance to the flow of a gas stream. For a given particle penetration through the medium ("partlcle pene-tration" is the number of particles in a gas stream passed by ,, . . . . ~ . ~ , :
0 . ~ .. ,., . ' , ' . ~ .'. . ' :
- , , the filter medium, measured as a percent of the number of : -particles entering the filter medium; "initial particle pene~
tration" is the particle penetration during initial use of :
the filter medium), the filter medium generally causes an un-usually low pressure drop in a gas stream being treated, and the result is that higher volumes of the gas can be moved through the filter medium with lower-powered blower means.
As a brief summary, a filter medium of the invention can be summarized as comprising a multilayer filter medium exhibiting a low pressure drop at a desired particle pen~tra-tion comprising a preformed handleabLe self-supporting porous fibrous base layer, at least one thin lightweight non-self- 1 :
supporting filtration layer of randomly arranged microfibers ..
having an average diameter less than about 0.5 micrometer collected on said base layer by interposing the base layer `~
in a stream of the microfibers, said layer of microfibers weighing less than about 0.01 pound per s~uare yard; and a porous top layer laminated over the layer of microfibers so ~
as to unify the filter medium into a single handleable self- .
supporting sheet material; said base and top layers contrib-uting less than 20 percent of the~pressure drop through the filter medium at a face veIocity of 100 feet per minute; and said layer of microfibers having a relationship of initial particle penetration to pressure drop ~hen tested at a face veIocity of 100 feet per minute within the range defined by curve& C and D shown in Figure 3. ~-The new properties provided by filter media of the invention are:of significant advantage, and one illustration .
is the previously mentioned improvement in filtering of room ..
air. More specifically, the new filter medium makes possible ~ -3-.~,~ ..
.:
iO4~
a new room air cleaner that achieves a steady level of good efficiency over a long operating life. Briefly, such a room air cleaner comprises a) a blower means for drawing air in through an inlet, moving the air along an air path, and then exhausting the air through an outlet, b) a filter medium of -~
the invention stored in a replaceable supply roll and extend-ing across the air path~to a take-up roll, and c) a drive means for aduancing the filter medium at a predetermined rate from the supply roll to the take-up roll. Since the pressure drop through the new filter medium is small, a low-powered, quiet blower means can be used in the device. Further, since the pressure drop remains low for a rather long period of time, the filter medium may be advanced through the room air cleaner at a rather slow rate. For example, a twelve-inch- ~
wide (30-centimeter-wide) web in a 130-cubic-feet-per-minute ~-(400-liter-per-minute) home unit may be advanced at a rate of two inches (5 centimeters) per day or less r meaning that the roll of filter medium is replaced at long intervals of 90 or 180 days.
~3a-, .. ~, . , lS
The filter medium is inexpensive, and the result is that economlcal hlgh-efficiency filtering is made possible indefinitely.
Insofar as known, such a capability in room air cleaning has never before been practicably achieved with mechanical fllters.
In the drawings, Figure 1 is a schematic view of a room air cleaner of the lnventlon;
Figure 2 is an enlarged section through a filter medium of the invention;
Figure 3 shows plots of initlal partlcle penetra-tion versus pressure drop for filter media of the invention, partlcle penetratlon being in percent on the ordinate and ; pressure drop being in lnches of water on the absclssa; and Flgure 4 ls a schematlc diagram of apparatus useful , to prepare a fllter medlum of the present invention.
The illustrative room air cleaner 10 shown in Figure 1 comprises a housing 11 in whlch are mounted a take-up roll 12 and a supply roll 13 of a filter medlum 14. A length of the filter medium extends from the supply roll 13 to the take-up roll 12, and passes through an air stream developed " ~, by a blower means 15. The blower means 15 draws air into the housing 11 through an lnlet 16, forces the air throu~h the length of filter medium between the supply and take-up rolls, and then through an outlet 17 in the housing. A drive motor ' 18 advances the filter medium from the supply roll to the take-j up roll at a predetermined rate. The drlve motor may operate contlnuously or may operate at periodic intervals.
The fllter medium 14, as illustrated ln Flgure 2, comprlses a base porous web 21, an lntermedlate layer 22 of ' ' '.
-4- ~ ~
;" :
;` 1~4~S
microflbers, and a top porous web 23.
The base and top webs exhibit good poroslty, so ,~ that together they contribute only a minor portlon (normally -less than 20 percent) of the pressure drop through a filter medlum of the invention. The base and top porous webs may ,~, ~ take a variety of forms, but typically they are nonwoven .,. :,-, :~ .: .
s~ fibrous webs. In manufacturing such webs, staple fibers are ` -~ typlcally deposlted as a loose web on a cardlng or garneting -,~ machlne, and then are compacted lnto a finished thin web.
, i:~
The web~ may be held in compacted form by a fusing of the ~ -flbers at their polnts of contact or by the use of a blnder resln lightly impregnated lnto the web so as to preserve poro-slty of the web. The fibers in the webs generally comprise 1bers of a synthetlc polymer such as polyethylene terephthalate, but may also lnclude natural flbers. The flbers are typlcally on the order of 1.5 to~3 denier.
The base porous web ls a self-supportlng web that or~most uses has a welght on the order of lO pounds per 320 square yards (1.7 mllllgrams per square centimeter). But ln some~r1lter media of the lnvention ln whlch the base web acts ~ i as~a pref11ter,~the~web may be thicker, havlng a welght on the order~of 50 poundY per 320 square yards (8.5 mllligrams per square~oent1meter). The top porous web is usually s1milar to the baYe porous web, though lt may be of lesser welght and greater poroslty. In some fllter medla of the invention, the top porous web faces an alr stream belng flltered, and in that case it may also be designed to act as a prefllter.
The thickness of a layer of mlcrofibers and the number of such layers used ln a filter medlum of the inventlon ~5~
, .- ~
depends upon the particular use to be made of the ~ilter medium. The filter medium can be designed differently de-pending on the different conditions of use (such as face veloclty of a gas stream being filtered, power of blower means, partlcle penetratlon during a single pass of gas stream being cleaned, and pressure drop) that are desired.
Filter media of the invention can be used as so-called absolute ("HEPA") filters and also as filters that pass a greater percentage of particles but operate at a lower face velocity.
For use in a room cleaner of the invention, the layer of layers of microfibers is generally rather thin, weighing less than 0.01 pound per square yard (0.5 milligram -per square centimeter) and preferably less than 0.005 pound per square yard (0.25 milligram per square centimeter). For other uses the layer or layers may be thicker, though even for an absolute filter the weight will generally be less than o.o6 pound per square yard (3 milligrams per square centimeter) and more often less than 0.03 pound per square yard (1.5 milligram per square centimeter).
As to pressure drop, in room air cleaners of the -~
invention, whlch are typically designed to operate at a face . .
velocity of 100 feet (30 meters) per minute, a filter medium exhibiting a pressure drop of 0.3 - 0.5 inch ~0.75 centimeter ;
to 1.25 centimeter)of water will normally be used. For abso- -lute (HEPA) filters operating at a face velocity of 50 feet (15 meters) per minute, the filter medium will typically ex-hibit a pressure drop on the order of 3 to 4 inches (7.5 to 10 centimeters) of water. And for respiratory fllters, the fllter medlum will generally exhibit a pressure drop of 0.3 ' .. ,~ :......... ' ' . ~,"'.' .'' '.. , .... ' ... -, , '. ; , ~Q4~5 to 0.5 inch (0~75 to 1.25 centimeter) of water at a race velocity of about 15 feet (4.5 meters) per minute.
As previously noted, the preferred microfiber layer comprises solution-blown microfibers. A suitable apparatus , for preparing such a micro~iber layer is shown in Figure 4.
This apparatus includes a stand pipe 25 in which a solution of polymers is stored; a pump 26, such as a Zenith pump; an extrudlng apparatus 27 to which the solution is pumped; and a filter 28 through which the solution passes to remove foreign particles or gels that might otherwise plug the extru-: l dlng orifice. The extruding apparatus 27 comprises an air plenum 29 into which air is fed through an inlet 30. A narrow-,~ ..
I diameter needle 31 inside the plenum is connected to the supply :'1 `- .
conduit of solution. The needle 31 extends through a small opening 32 in a face plate 33 of the plenum 29, with the end of -the needle located a short dlstance beyond the face plate (such as 1.5 millimeters). Air supplied through the inlet 30 , ,-passes out through the opening 32, attenuates the extruded polymer, and carries the resulting microfibers to a base porous web 35. The air stream intersects the web 35 over a second air plenum 39, from which air is exhausted. A screen 40 covers ; ~ :
the opening of the plenum to hold the web flat in the air stream.
~, The web 35 is moved ~rom a supply roll 36, around an idler q roller 37, to a takeup roll 380 Top porous web material is ~ unwound from a supply roll 41 and around an idler roller 42 :
where it ls laminated over the layer of microfibers.
~: :
A wide variety o~ polymers may be used to prepare -the solution-blown microfibers, including polymers based on vinyl chloride, styrene, vinyl butyral, and vinylidene chloride.
_7_ . : ~
15)4~15 :
; These polymers may be dissolved in a variety o~ solvents including toluol, ethanol, tetrahydrofuran, methyl ethyl ketone or mixtures of such solvents to produce a desired viscosity.
The polymers based on vinyl chloride are preferred, for one reason because of processing advantages. Also, filters of ` polyvinyl chloride fibers have been found to develop an elac-trostatic charge during use of the filter, and that charge is believed to improve the ability of the intermediate microfiber layer to attract and hold particulate matter. Such an electrostatic charge also develops on microfibers formed from Qther polymers.
, One feature that is noted under microscopic examin-ation of the layer of solution-blown microfibers in some j~ preferred filter media of the invention is the presence of i rounded particles of the polymer from which the microfibers are formed. It is believed that the rounded particles contri-~; bute to a spacing of the microfibers thatmay be partly respon-' sible for the low pressure drop through the microfiber layer.
~' Generally, these rounded particles, which apparently develop ~
during the microfiber-blowing procedure, are on the order -, . ... .
of 1 to 3 micrometers in diameter.
Figure 3 shows different plots of initial particle penetration versus pressure drop for filter media of the ;~
invention, the ordinate showing partiçle penetration in percent, and the abscissa showing pressure drop in inches of ~: ~
water. Curves A and B define a range of relationships between ~ `
particle penetration and pressure drop that useful filter media of the invention generally exhibit at a face velocity of 20 feet (6 meters) per minute; and curves C and D define a range ~ -.~ '` , -8- ~
.' `' .
''"' ~,. ' , ;, : ; , . ,, ~ .,, , ,., ~ . ; ,,:
.~ .
~ : ; 1~4~1S
of relationships that useful filter media of the invention ; generally exhibit at a face veloclty of 100 feet (30 meters) ` per minute.
As the curves indicate, filter media of the invention . that have higher pressure drops (because of a greater thickness, for example) will have a lower particle penetration. Different .. filter media of the invention may differ in their particular relationshlp of initial particle penetration to pressure drop (depending, for example, on fiber size, fiber density, and ;
other characteristics of the microfiber layer), but generally : they will malntain a basic relationship within the range es-tablished by the two sets of curves ln Flgure 3. Changlng the thickness of a layer of mlcrofibers, or the number of ~
the layers, will also change the values of pressure drop and ~ :
particle penetration exhibited by the filter media, but gener-~, ally, not outside the basic relationship established by the . .
two sets of curves in Figure 3.
T.he curves shown in Flgure 3 provide a useful standard for controlling the process of manufacturing filter medla of t.he i.nvention. The nature of a layer of solutlon-~: blown microfibers may be varied by varying the solids content .~.
of the solution extruded through the microfiber-forming apparatus or the extruding conditions, for example. As a ,. general rule~ the lower the solids content, the lower the 'i: diamete.r of flbers that are formed. If the solids content .. :.
is too low, no fiber structure is formed, while if the solids ~ content is too high t.he microfibers are too coarse for desired - .
filtering properties. The rate of flow of the solution may also be varied, generally under 10 or 15 cubic centlmeters~
. ..
_9 _ ., .
~ .
, . . .. -: . :. . .
.,j . . :, . ~ . i . . .. . .
.: ~
, lrJ~iilS
minute, to control the dimensions of the fibers and the number of fibers, and similarly the velocity of air around the needle may be varied.
One way of determining the proper solids content for any polymer and solvent and the proper extruding conditions is to extrude a set of polymer solutions having different solids contents to form different microfiber layers on a base porous web, and plot the relationship of initial particle penetration versus static pressure for the different layers provided. (Because of the rather high porosity of the base web, the effect of the base porous web on the pressure drop may be disregarded.) The polymer solutions producing layers .. ..
! having a relationship between the curves shown in Flgure 3 are generally suitable solutions.
' .
~ When more than one layer of microfibers is included ~
: ~ -in a filter medium of the invention, those layers will usually ; ;
~; be substantially identical to one another; but they also may :~ differ, as to the material from which the fibers are made, -the dlameter of the fibers, the numerical dènsity of fibers, ;
etc. Plural microfiber layers may lie directly against one .~ .
another (as when microfiber layers are collected on two dif-ferent base porous webs which are then laminated together with the microfiber layers face-to-face) or they may be separated by -. ~ .
other layers, of base porous web, for example.
Filter media of the invention have other uses besides in a room air cleaner. For example, filter media of the inven-tion may be used in respirators worn by a person, with the filter medium of the invention being disposed across the path of air lntake into the respirator. Lightweight face maslcs ., .
-10- `' ' ~.
` 10~61S
of the general cup-shaped configuration shown in U.S. Pats.
3,333,585 or 3,521,630, may be used, for example.
The invention will be further illustrated by the following examples:
Examples 1-7 A variety of polymer solutlons as shown in the followlng table were prepared and extruded onto a base porous web using apparatus as illustrated in Figure 4, in which the extrusion needle was a No. 21 gauge, 1/2-inch-long (1.25-centimeter-long) needle. The base porous web was a carded, random-flber web of 1.75-denier polyester fibers bonded together with alcohol-soluble nylon and having a weight of about 10 pounds per 320 square yards (1.7 milllgrams per square centi-meter). A layer of microflbers weighing on the average about 0.004 pound per square yard (0.2 milligrams per square centi-meter) was collected on the base web. A top porous web like the base web except that it welghed 5 pounds per 320 square yards (0.9 milllgram per square centimeter) was laminated over the layer of mlcrofibers. The materials were then tested for init~al partlcle penetration and static pressures at a face velocity of : . .
100 feet (30 meters) per minute, and the results are reported in Table I. A range of static pressures and initial partlcle penetratlons are reported for each different polymer, because dlfferent samples were prepared uslng dlfferent air pressures ln the plenum.
A standard test apparatus was used in which a Royco Model 256 aerosol generator formed an air stream that contained potasslum chloride particles about 0.1 and 1.0 micrometer in dlameter. The partlcle-containing air stream was conducted - ;; . ~ .
``~ lU4~6~5 through a drler and two rlowmeters into an air plenum having a rixture lnto which a test sample can be inserted in the path o~ the air stream. The air input to the aerosol genera-tor was 20 psi (1.4 kilogram per square centlmeter) gauge, the atomlzer pressure in the aerosol generator was 8 psi (0.56 kllogram per square centimeter) gauge, and the ~low through the drler was 15-30 llters per mlnute. Partlcles were formed by the aerosol generator rrom a solutlon of potasslum chlorlde ln s distllled water havlng a sollds content of 0.5 weight-percent.
Test probes extendlng into the alr plenum on each slde Or the test rlxture measure the number Or partlcles ln the air stream ;~;
on each slde of the test sample. The te~t probes were part Or a rorward-llght-scatterlng llnear photometer ldentlfied a8 T-P-~A--2C manufactured by Alr Technlques Inc. Prlor to lnsertlng the test sample ln the alr plenum, the apparatus ls~;ad~;usted so that the partlcle detectlon apparatus reads . .
lOO;~percent. Arter lnsertlon Or the test sample, the down~
stream probe measures (by a partlcle count) the percentage of partlcles~penetratlng through the test sample. The statlc pressure~at the test sample ls measured wlth a water manometer.
Example 8 A composlte fllter medlum was prepared by sandwlchlng together rour~thlcknesse,3 or filter medla llke those Or Examplé 5 except that the layer Or mlcroflbers ln each Or the ;rl ~ -thlcknesseo~welghed O.OlZ pound per square yard (0.65 milllgram per square centlmeter). This composlte rllter medlum was compared~wlth two commercial "HEPA" rllters as to the inltlal partlcle penetratlon and statlc pressure. The Plrst commerclal fllter t"Dexter" Brand, Grade X1401) comprlsed resln-treated rro ~ ~A~ `'i` ' ' :~ . j, ,',''' ':
~ lV44~ilS
,. ~ ~^ ~
~,~,b~ oO '`~
o_ o_ o_ o_ ~.
~ I ~ o~ ~o~ ~o ~ô
' ~ ~ ~ ,o, o ,o~ o : ~ ~ ~ ~ W
" ~ s ~ ~
P f~æ ~ ~ P
~ >
t . - 13 ., ~ ..
. . ,.... . ~ i. ~
.. . .
r- , ~ 46~5 ~ ~
~ ~ ~ ~ o~ ' ~
~ 0 .. ~
o ~o ~o ~ .. ''''. '' ~3 ~ 5 ~ ~ ~
o ~0 ~ ~
^ ~ ~
0 ~ ~ O ~ ~ ~ æ ~ 3 e~ 14 .~ :
. .
~0~4tj15 glass fibers about 0.2 - 2 micrometers in diameter, and the second commercial filter ("Microsorban" Brand) comprised polystyrene blown microflbers about 0.25 to 2 micrometers in diameter.
The tests were performed by the procedures des-cribed ln Military Standard 282, Test Method 102.1 using dioctylphthalate particles that averaged 0.3 micrometer and a face velocity of 1o.ll - 10.5 feet (about 3.1 meters) per minute. The test measurements were made promptly so as to avoid any effect of dioctylphthalate on the polyvinyl chloride flbers. The results, as presented in Table II, show much lower particule penetration through filter media of the exam-ple at slmilar pressure drops.
TABLE II
Mass of Static microfibers in Initial particle pressure filter medium penetration (inches of water) (pound per sq. yd.) (percent) (mm of water) (milligrams per sq.
~ cm.) First commer- 0.015 2.0 0.153 cial filter ~ (5) (8) medium Second commer- 0.007 2.1 0-337 clal filter (5.3) (18) medium Filter medium 0.003 2.1 o.o48 of the inven- (5.3) (2.6) tion , . ~ . .
; :
~ ' .. : ~ .
,
Claims (21)
1. A multilayer filter medium exhibiting a low pressure drop at a desired particle penetration comprising a preformed handleable self-supporting porous fibrous base layer; at least one thin lightweight non-self-supporting filtration layer of randomly arranged microfibers having an average diameter less than about 0.5 micrometer collected on said base layer by interposing the base layer in a stream of the microfibers, said layer of microfibers weighing less than about 0.01 pound per square yard; and a porous top layer laminated over the layer of microfibers so as to unify the filter medium into a single handleable self-supporting sheet material; said base and top layers contributing less than 20 percent of the pressure drop through the filter medium at a face velocity of 100 feet per minute; and said layer of microfibers having a relationship of initial particle penetration to pressure drop when tested at a face velocity of 100 feet per minute within the range defined by curves C and D shown in Figure 3.
2. A filter medium of claim 1 in which the layer of microfibers weighs less than about 0.01 pound per square yard.
3. A filter medium of claim 1 which exhibits a pressure drop of less than about 0.5 inch of water at a face velocity of 100 feet per minute.
4. A filter medium of claim 1 that exhibits a pressure drop of about 3 to 4 inches of water at a face velocity of 50 feet per minute.
5. A filter medium of claim 1 that exhibits a pressure drop of about 0.3 to 0.5 inch of water at a face velocity of 15 feet per minute.
6. An aerosol filter apparatus comprising a) blower means for drawing the aerosol through an inlet, moving the aerosol along a path, and then exhausting the aerosol through an outlet, b) a filter medium of claim 1 stored in a replaceable supply roll and extending across said path to a take-up roll, and c) drive means for advancing the filter medium at a predetermined rate from the supply roll to the take-up roll.
7. A respirator adapted to be worn by a person, in which a filter medium of claim 1 is disposed across the path of air intake into the respirator.
8. A filter medium of claim 1 in which the micro-fibers comprise a polymer based on vinyl chloride.
9. A room air cleaner comprising a) blower means for drawing air through an inlet, moving the air along an air path, and then exhausting the air through an outlet, and b) a filter medium of claim 1 disposed across the air path.
10. A room air cleaner of claim 6 in which the filter medium is stored in a supply roll and extends across the air path to a take-up roll, and the room air cleaner includes drive means for advancing the filter medium at a predetermined rate from the supply roll to the take-up roll.
11. A filter medium of claim 1 in which the layer of microfibers comprises solution-blown microfibers.
12. A filter medium of claim 9 in which the layer of microfibers includes rounded nonfibrous particles of the polymer from which the solution-blown microfibers are made.
13. A filter medium of claim 11 in which the micro-fibers have an average diameter less than about 0.3 micro-meter.
14. A multilayer filter medium exhibiting a low pressure drop at a desired particle penetration comprising a preformed handleable self-supporting porous fibrous base layer; at least one thin lightweight filtration layer of solution-blown polymeric randomly arranged microfibers having an average diameter less than about 0.5 micrometer deposited on said base layer, said layer of microfibers weighing less than 0.01 pound per square yard; and a porous top layer laminated over the layer of microfibers so as to unify the filter medium into a single handleable self-supporting sheet material; said base and top layers contributing less than 20 percent of the pressure drop through the filter medium when tested at a face velocity of 100 feet per minute.
15. A filter medium of claim 14 in which the layer of solution-blown microfibers includes rounded nonfibrous particles of the polymer from which the solution-blown micro-fibers are made.
16. A filter medium of claim 14 in which the microfibers have an average diameter of less than 0.3 micro-meter.
17. A filter medium of claim 14 in which said layer of microfibers has a relationship of initial particle penetration to pressure drop when tested at a face velocity of 100 feet per minute within the range defined by the curves C and D shown in Figure 3.
18. A respirator adapted to be worn by a person in which a filter medium of claim 14 is disposed across the path of air intake into the respirator.
19. A filter medium of claim 14 in which said layer of microfibers weighs less than about 0.005 pound per square yard.
20. A multilayer filter medium exhibiting a low pressure drop at a desired particle penetration comprising a preformed porous nonwoven fibrous base layer; at least one thin lightweight filtration layer of solution-blown polymeric randomly arranged microfibers having an average diameter less than about 0.5 micrometer deposited on said base layer, said layer of microfibers weighing less than 0.01 pound per square yard and having insufficient integrity to be removed from the base layer and wound and unwound by itself from a storage roll, but contributing at least 80 percent of the pressure drop through the filter medium when measured at a face velocity of 100 feet per minute; and a porous top layer laminated over the layer of microfibers so as to unify the filter medium into a single handleable self-supporting sheet material.
21. A filter medium of claim 20 in which said layer of microfibers has a relationship of initial particle pene-tration to pressure drop when tested at a face velocity of 100 feet per minute within the range defined by curves C and D
shown in Figure 3.
shown in Figure 3.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US43788074A | 1974-01-30 | 1974-01-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1044615A true CA1044615A (en) | 1978-12-19 |
Family
ID=23738304
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA217,494A Expired CA1044615A (en) | 1974-01-30 | 1975-01-07 | Low pressure drop filter medium |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS6036807B2 (en) |
| CA (1) | CA1044615A (en) |
| DE (1) | DE2503615C2 (en) |
| FR (1) | FR2258888B1 (en) |
| GB (1) | GB1481666A (en) |
| IT (1) | IT1029389B (en) |
Families Citing this family (26)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4188197A (en) * | 1975-09-25 | 1980-02-12 | Dennison Manufacturing Company | Particulate filtering |
| IT1077372B (en) * | 1977-03-29 | 1985-05-04 | Montedison Spa | REFINEMENTS IN MIXTURE FILTERS OF SYNTHETIC FIBERS WITH CELLULOSE |
| JPS54112071A (en) * | 1978-02-22 | 1979-09-01 | Mitsui Petrochemical Ind | Method of filtering liquid |
| JPS6022100B2 (en) * | 1978-05-01 | 1985-05-31 | 東亜燃料工業株式会社 | Manufacturing method of nonwoven fabric |
| JPS6056825B2 (en) * | 1978-05-01 | 1985-12-12 | 東亜燃料工業株式会社 | Manufacturing method of nonwoven fabric |
| JPS5624013A (en) * | 1979-05-04 | 1981-03-07 | Nitta Kk | Structure of air filter element |
| US4548628A (en) * | 1982-04-26 | 1985-10-22 | Asahi Kasei Kogyo Kabushiki Kaisha | Filter medium and process for preparing same |
| US4436780A (en) * | 1982-09-02 | 1984-03-13 | Kimberly-Clark Corporation | Nonwoven wiper laminate |
| DE3428359A1 (en) * | 1984-08-01 | 1986-02-06 | Düpro AG, Romanshorn | Air-cleaning device |
| DE3517923A1 (en) * | 1985-05-18 | 1986-11-27 | Hölter, Heinz, Dipl.-Ing., 4390 Gladbeck | Method of producing naturally scented breathing air |
| US4714647A (en) * | 1986-05-02 | 1987-12-22 | Kimberly-Clark Corporation | Melt-blown material with depth fiber size gradient |
| JPH0729010B2 (en) * | 1986-12-16 | 1995-04-05 | 富士通株式会社 | Electrophotographic device |
| DE3731575A1 (en) * | 1987-09-19 | 1989-03-30 | Freudenberg Carl Fa | FILTER PACK |
| DE3812849C3 (en) * | 1988-04-18 | 1996-03-21 | Gessner & Co Gmbh | Dust filter bag, its manufacture and use |
| IT216762Z2 (en) * | 1989-07-19 | 1991-10-03 | Alcantara Spa | COUPLED ITEM, CONTAINING A LAYER OF NON-WOVEN MICROFIBROUS MATERIAL, USEFUL IN THE FURNITURE AND TRANSPORT SECTOR. |
| JPH02289161A (en) * | 1989-08-03 | 1990-11-29 | Toray Ind Inc | Production of laminated nonwoven fabric sheet for microfilter |
| JPH0493020U (en) * | 1989-12-25 | 1992-08-13 | ||
| DE4134222C2 (en) * | 1991-10-16 | 2002-09-19 | Mhb Filtration Gmbh & Co Kg | Filters for passenger compartments |
| DE4212112A1 (en) * | 1992-04-10 | 1993-10-14 | Sandler C H Gmbh | Multi-layer filter material |
| US5350443B2 (en) * | 1993-04-19 | 1999-08-10 | Von Hasso Bluecher | Filter sheet material for passenger cabins in motor vehicles |
| DE19605863A1 (en) * | 1996-02-16 | 1997-08-21 | Reemtsma H F & Ph | Cigarette filter |
| EA013385B1 (en) * | 2004-06-09 | 2010-04-30 | Пэтоджен Римувал Энд Дайэгностик Текнолоджиз Инк. | Devices and methods for removing target agents from a sample |
| US20070074628A1 (en) * | 2005-09-30 | 2007-04-05 | Jones David C | Coalescing filtration medium and process |
| DE102006017553B3 (en) | 2006-04-13 | 2007-12-27 | Eurofilters N.V. | Filter bag for a vacuum cleaner |
| CN103760065B (en) * | 2013-06-28 | 2016-01-06 | 中国石油化工股份有限公司 | A kind of method of testing of polymer solution flow effective apparent viscosity and test macro thereof |
| DE102016125182A1 (en) * | 2016-12-21 | 2018-06-21 | Groz-Beckert Kg | Process for producing fibers and nonwovens by solution blow spinning and nonwoven fabric made therewith |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5316696Y2 (en) * | 1971-12-03 | 1978-05-02 |
-
1975
- 1975-01-07 CA CA217,494A patent/CA1044615A/en not_active Expired
- 1975-01-29 IT IT47904/75A patent/IT1029389B/en active
- 1975-01-29 GB GB3884/75A patent/GB1481666A/en not_active Expired
- 1975-01-29 DE DE2503615A patent/DE2503615C2/en not_active Expired
- 1975-01-29 FR FR7502707A patent/FR2258888B1/fr not_active Expired
- 1975-01-29 JP JP50012271A patent/JPS6036807B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| IT1029389B (en) | 1979-03-10 |
| JPS6036807B2 (en) | 1985-08-22 |
| JPS50108677A (en) | 1975-08-27 |
| DE2503615A1 (en) | 1975-07-31 |
| FR2258888A1 (en) | 1975-08-22 |
| GB1481666A (en) | 1977-08-03 |
| DE2503615C2 (en) | 1986-10-23 |
| FR2258888B1 (en) | 1981-12-11 |
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