U.S. patent number RE35,062 [Application Number 08/079,234] was granted by the patent office on 1995-10-17 for filter element.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Gerald M. Brostrom, Daniel A. Japuntich, Sabrina M. Yard.
United States Patent |
RE35,062 |
Brostrom , et al. |
October 17, 1995 |
**Please see images for:
( Certificate of Correction ) ** |
Filter element
Abstract
A filter element adapted for attachment to a respirator face
piece which includes front and rear walls of filter material, a
breather tube, and a porous inner layer which maintains the front
and rear walls in a spaced-apart relationship over substantially
their entire area and which functions to evenly distribute air flow
across the available filter element surface area.
Inventors: |
Brostrom; Gerald M. (St. Paul,
MN), Japuntich; Daniel A. (St. Paul, MN), Yard; Sabrina
M. (St. Paul, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
22719795 |
Appl.
No.: |
08/079,234 |
Filed: |
June 17, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
195029 |
May 17, 1988 |
04886058 |
Dec 12, 1989 |
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Current U.S.
Class: |
128/206.12;
128/206.17; 55/DIG.35; 128/206.15 |
Current CPC
Class: |
A62B
18/08 (20130101); A62B 23/02 (20130101); Y10S
55/35 (20130101) |
Current International
Class: |
A62B
23/02 (20060101); A62B 23/00 (20060101); A62B
007/00 () |
Field of
Search: |
;128/205.27-205.29,206.12,207.15 ;55/DIG.35 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0197941 |
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Oct 1986 |
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EP |
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470850 |
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Sep 1937 |
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GB |
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573951 |
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Dec 1945 |
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GB |
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1041394 |
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Sep 1966 |
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GB |
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Other References
DIN 3181 Part 2, "Atemfilter fur Atemschultzgerate", (Mar. 1980).
.
BS 2090 "Respirators for Protection Against Harmful Dusts and
Gases", (1969). .
BS 4555 "High Efficiency Dust Respirators", (1970). .
20 CFR 11 Subpart K, Sect. 11.130-11.140-12, (1987). .
30 CFR 11 Subpart K, sect. 11.140-4, (1987). .
30 CRF 11 Subpart K, 11.140-9, (1987). .
30 CFR 11 Subpart K, 11.140-11, (1987). .
30 CFR 11 Subpart K, 11.140-6, (1987). .
Military Specification, "Filter Element Set, Chemical-Biological
Mask, M13A2", MIL-F-51425A(EA), 10 Sep. 1986..
|
Primary Examiner: Asher; Kimberly L.
Attorney, Agent or Firm: Griswold; Gary L. Kirn; Walter N.
Truesdale; Carole
Claims
What is claimed is:
1. A filter element comprising
(A) substantially coextensive front and rear walls joined to each
other along their peripheral edges and defining an interior space
between them; the front and rear walls each comprising at least one
layer of a filter material, and the rear wall, including said layer
of filter material, having an opening that provides access to the
interior space defined by the front and rear walls,
(B) a porous layer contained between the front and rear walls
.Iadd.within the interior space .Iaddend.substantially coextensive
with the walls, which maintains the walls .[.is.]. .Iadd.in
.Iaddend.a spaced-apart relationship over substantially their
entire area, and which contributes no more than 50% of the total
pressure drop across the filter element, .Iadd.said porous layer
comprising material selected from the group consisting of woven
webs, nonwoven webs, loose fibers, fiber batts, loose particulate
material, particulate material bonded together in a porous matrix,
or combinations thereof, .Iaddend.and
(C) a breather tube having one end that communicates through said
opening with the .Iadd.porous layer within the .Iaddend.interior
space between the front and rear walls, and adapted at its other
end for securing the filter element to a respirator face piece,
the air being drawn through the front and rear walls into the
porous layer within the space between the front and rear walls, and
from the interior space through the breather tube into a respirator
face piece.Iadd.. .Iaddend.
2. The filter element of claim 1 wherein said front and rear walls
and said porous layer are joined together along their peripheral
edges.
3. The filter element of claim 1 wherein said filter element is
round.
4. The filter element of claim 1 further comprising flexible cover
layers disposed over the exterior surface of the filter
element.
5. The filter element of claim 4 wherein said cover layers comprise
polyolefin.
6. The filter element of claim 1 wherein said at least one layer of
filter material comprises material selected from the group
consisting of nonwoven microfiber webs, fibrillated film webs,
air-laid webs, carded webs, or combinations thereof.
7. The filter element of claim 6 wherein said at least one layer of
filter material comprises material selected from the group
consisting of polyolefin, polycarbonate, polyester, polyurethane,
polyamide, glass, cellulose, carbon, alumina, or combinations
thereof.
8. The filter element of claim 1 wherein said at least one layer of
filter material comprises a plurality of layers of electrically
charged, nonwoven, blown microfiber web.
9. The filter element of claim 8 wherein said electrically charged,
nonwoven, blown microfiber web comprises polyolefin.
10. The filter element of claim 8 wherein said electrically
charged, nonwoven, blown microfiber web comprises
polypropylene.
11. The filter element of claim 1 wherein said at least one layer
of filter element comprises sorbent particle-loaded fibrous
web.
12. The filter element of claim 11 wherein said sorbent
particle-loaded fibrous web is selected from the group consisting
of alumina-particle-loaded or carbon-loaded web. .[.13. The filter
element of claim 1 wherein said porous layer comprises material
selected from the group consisting of woven webs, nonwoven webs,
loose fibers, fiber batts, loose particulate material, particulate
material bonded together in a
porous matrix, or combination thereof..]. 14. The filter element of
claim .[.13.]. .Iadd.1 .Iaddend.wherein said porous layer comprises
material selected from the group consisting of polyolefin,
polycarbonate, polyurethane, polyester, polyamide, glass,
cellulose, carbon, alumina or
combinations thereof. 15. The filter element of claim .[.13.].
.Iadd.1 .Iaddend.wherein said particulate material bonded together
in a porous
matrix comprises sorbent particles. 16. The filter element of claim
15 wherein said porous matrix comprises sorbent carbon particles
bonded
together with polyurethane resin. 17. The filter element of claim
.[.13.]. .Iadd..Iaddend.wherein said porous layer comprises
.Iadd.a
.Iaddend.nonwoven web. 18. The filter element of claim 17 wherein
said non-woven web is selected as from a group consisting of glass
filter paper, air-laid web, carded web, fibrillated film web,
sorbent
particle-loaded fibrous web, or combinations thereof. 19. The
filter element of claim 17 wherein said non-woven web comprises a
blend of staple
and binder fibers bonded together at points of fiber intersection.
20. The filter element of claim 17 wherein the fiber diameter of
said nonwoven web is no less than about 10 microns and the solidity
of said nonwoven web is
no greater than about 11%. 21. The filter element of clahn 18
wherein said
air-laid web comprises polyester. 22. The filter element of claim
18
wherein said carded web comprises polyester. 23. The filter element
of claim 18 wherein said sorbent-particle-loaded fibrous web is
selected from the group consisting of alumina-particle-loaded or
carbon particle-loaded
web. 24. The filter element of claim 1 wherein said porous layer is
0.2 cm
to 4.0 cm thick. 25. The filter element of claim 24 wherein said
porous
layer is 0.3 cm to 1.3 cm thick. 26. The filter element of claim 1
wherein
said of the breather tube is cylindrical in shape. 27. The filter
element of claim 26 wherein the inner diameter of the breather tube
is 1.0 to 4.0
cm. 28. The filter element of claim 27 wherein diameter of the
breather
tube is 1.5 to 3.5 cm. 29. The filter element of claim 1 wherein
said .[.nonwoven web comprises the front and rear walls and the
porous layer.]. .Iadd.front and rear walls and said porous layer
comprise nonwoven
webs..Iaddend. 30. A filter element comprising
(A) substantially coextensive front and rear walls joined to each
other along their peripheral edges and defining an interior space
between them; the front and rear walls each comprising at least one
layer of filter material, and the rear wall, including said layer
of filter material having an opening that provides access to the
interior or space defined by the front and rear walls,
(B) a porous layer contained between the front and rear walls
.Iadd.within the interior space .Iaddend.which is substantially
coextensive with the walls, which maintains the walls in a
spaced-apart relationship substantially their entire area, and
which contributes no more than 50% of the total pressure drop
across the filter element, .Iadd.said porous layer comprising
material selected from the group consisting of woven webs, nonwoven
webs, loose fibers, fiber batts, loose particulate material,
material bonded together in a porous matrix, or combinations
thereof, .Iaddend.and
(C) a breather tube having one end that communicates through said
opening with the .Iadd.porous layer within the .Iaddend.interior
space between the front and rear walls, and adapted at its other
end for securing the filter element to a respirator face
piece.Iadd., .Iaddend.
.Iadd.the air being drawn through the front and rear walls into the
porous layer within the interior space between the front and rear
walls, and from the interior space through the breather tube into a
respirator face piece, .Iaddend.
wherein said filter element will permit no more than 1.5 mg
penetration of silica dust having a geometric means particle
diameter of 0.4-0.6 micrometer through said filter element over a
90 minute period at an air flowrate of 16 liters per minute, a
pressure drop across said filter element before the 90 minute
period of no more than 30 mm H.sub.2 O, and a pressure drop across
the filter element after the 90 minute period of not
more than 50 mm H.sub.2 O. 31. A filter element comprising
(A) substantially coextensive front and rear walls joined to each
other along their peripheral edges and defining an interior space
between them; the front and rear walls each comprising at least one
layer of a filter material, and the rear wall, including said layer
of filter material, having an opening that provides accesss to the
interior space defined by the front and rear walls,
(B) a porous layer contained between the front and rear walls
within the iterior space which is substantially coextensive with
the walls, which maintains the walls in a spaced-apart relationship
over substantially their entire area, and which contributes no more
than 50% of the total pressure drop across the filter element,
.Iadd.said porous layer comprising material selected from the group
consisting of woven webs, nonwoven webs, loose fibers, fiber batts,
loose particulate material, particulate material bonded together in
a porous matrix, or combinations thereof, .Iaddend.and
(C) a breather tube having one end that communicates through said
opening with the .Iadd.porous layer within the .Iaddend.interior
space between the front and rear walls, and adapted at its other
end for securing the filter element to a respirator face piece
.Iadd.
the air being drawn through the front and rear walls into the
porous layer within the interior space between the front and rear
walls, and from the interior space through the breather tube into a
respirator face piece, .Iaddend.
wherein said filter element will permit
(i) no more than about 3.0 percent penetration of 0.3 micrometer
diameter particles of dioctyl phthalate contained in a stream at a
concentration 100 micrograms/l, at a flow rate of 42.5 liters per
minute, and
(ii) no more than 1.5 mg penetration of silica dust having a
geometric means particle diameter of 0.4-0.6 micrometer through
said filter element over a 90 minute period at an air flowrate of
16 liters per minute, a pressure drop across said filter element
before the 90 minute period of no more than 30 mm H.sub.2 O, and a
pressure drop across the filter element
after the 90 minute period of not more than 50 mm of H.sub.2 O. 32.
The filter element of claim 32 wherein said penetration of 0.3
micrometer
diameter particles of dioctyl phthalate is about 0.03 percent. 33.
A filter element comprising
(A) substantially coextensive front and rear walls joined to each
other along their peripheral edges and defining an interior space
between them; the front and rear walls each comprising at least one
layer of a filter material, and the rear wall, including said layer
of filter material, having an opening that provides access to the
interior space defined by the front and rear walls,
(B) a porous layer contained between the front and rear walls
.Iadd.within the interior space .Iaddend.which is substantially
coextensive with the walls, which maintains the walls in a
spaced-apart relationship over substantially their entire area, and
which contributes no more than 50% of the total pressure drop
across the filter element, .Iadd.said porous layer comprising
material selected from the group consisting of woven webs, nonwoven
webs, loose fibers, fiber batts, loose particulate material,
particulate material bonded together in a porous matrix, or
combinations thereof, .Iaddend.and
(C) a breather tube having one end that communicates through said
opening with the .Iadd.porous layer within the .Iaddend.interior
space between the front and rear walls, and adapted at its other
end for securing the filter element to a respirator face piece,
.Iadd.the air being drawn through the front and rear walls into the
porous layer within the space between the front and rear walls, and
from the interior space through the breather tube into a respirator
face piece, .Iaddend.
wherein said filter element will permit no more than 1.5 mg
penetration of lead fume penetration, through said filter element
over a 312 minute period at an air flowrate of 16 liters per
minute, a pressure drop across said filter element before the 312
minute period of no more than 30 mm of H.sub.2 O, and a pressure
drop across the filter element after the 312
minute period of not more than 50 mm of H.sub.2 O. 34. One or more
filter elements of claim 1 in combination with a respirator
comprising a face
piece. 35. One or more filter elements of claim 30 in combination
with a
respirator comprising a face piece. 36. One or more filter elements
of
claim 31 in combination with a respirator comprising a face piece.
37. One or more filter elements of claim 33 in combination with a
respirator comprising a face piece. .[.38. A method of filtering
air comprising drawing air to be filtered through either the front
or rear wall of a filter element comprising
(A) substantially coextensive front and rear walls joined to each
other along their peripheral edges and defining an interior space
between them; the front and rear walls each comprising at least one
layer of a filter material, and the rear wall, including said layer
of filter material, having an opening that provides access to the
interior space defined by the front and rear walls,
(B) a porous layer contained between the front and rear walls which
is substantially coextensive with the walls, which maintains the
walls in a spaced-apart relationship over substantially their
entire area, and which contributes no more than 50% of the total
pressure drop across the filter element, and
(C) a breather tube having one end that communicates through said
opening with the interior space between the front and rear walls,
and adapted at its other end for securing the filter element to a
respirator face piece,
the air being drawn into the interior space between the front and
rear walls, and from the interior space through the breather tube
into a
respirator face piece..]. 39. The filter element of claim 1 wherein
said front and rear walls are joined to each other along their
peripheral edges
by ultrasonic welding. 40. The filter element of claim 1 wherein
the front and rear walls comprise electrically charged, nonwoven,
blown micro fiber web joined to each other along their peripheral
edges by ultrasonic welding, and the porous layer comprises
nonwoven web comprising a blend of
staple fibers bonded together at points of fiber intersection. 41.
The filter element of claim 40 further comprising flexible cover
layers disposed over the exterior surface of said filter element.
Description
TECHNICAL FIELD
The present invention relates to filtration elements used in
respirators or face masks. In another aspect, the present invention
relates to filtration face masks or respirators with detachable
filtration elements.
BACKGROUND
Filtration face masks or respirators are used in a wide variety of
applications when it is desired to protect a human's respiratory
system from particles suspended in the air or from unpleasant or
noxious gases.
Filter elements of respirators my be integral to the body of the
respirator or they may be replaceable, but in either case, the
filter element must provide the wearer with protection from
airborne particles or unpleasant or noxious gases over the service
life of the respirator or filter element. The respirator must
provide a proper fit to the human face without obscuring the
wearer's vision and it is desirable that a respirator require a
minimum of effort to draw air in through the filter media. This is
referred to as the pressure drop across a mask, or breathing
resistance.
To achieve the levels of filter performance such as those defined
in 30 C.F.R 11 subpart K .sctn..sctn.11.130-11.140-12 (1987), DIN
3181 Part 2, "Atemfilter fur Atemschultzgerate" (March, 1980), BS
2091, "Respirators for Protection Against Harmful Dusts and Gases"
(1969), and BS 4555, "High Efficiency Dust Respirators" (1969) the
number of layers of filter material, filter material type, and
available filtration area are important factors in filter element
design. The present invention provides a means of more fully
utilizing a filter element's available filtration area by properly
managing air flow through the filter material of the filter
element. Proper management of air flow can also prevent premature
loading of the filter material immediately opposite the breather or
inhalation tube, which can cause the filter element to collapse
over the breather tube, thereby restricting inhalation and
shortening the service life of the fiber element.
Various filter element designs have been proposed to provide as
much filter surface area as possible while minimizing the
obstruction to the wearer's vision, and/or the pressure drop across
the mask. U.S. Pat. No. 2,320,770 (Cove) discloses a respirator
with detachable filter elements. The filter elements are preferably
rectangular and are made from a sheet of filter material with all
open sides sewn closed. The filter element has a hole adapted to be
attached to the body of the mask. Cover asserts that after being
sewn, the filter element can be turned inside out so the seams and
folds cause the bag to assume a shape and curvature which tends to
keep the sides of the bags apart without the aid of an additional
spacing element. Incoming air is apparently intended to travel
through either the front or back sides of the bag into the space
between these sides and then through the hole inside the mask. U.S.
Pat. No. 2,220,374 (Lewis) discloses a respirator which includes a
rigid mask and a face mold attached to the mask. The rigid mask
includes an air inlet opening and filtering means covering the
opening. The filtering means comprises a shell having perforations
on at least three sides, filtering material located inside the
shell and a filter spreading member adapted to hold the filtering
material in a position exposing the filtering material to direct
contact with the air entering the perforations. U.S. Pat. No.
2,295,119 (Malcom et al.) discloses a respirator comprising a face
piece adapted for the wearer's nose and mouth attached to two
removable, egg-shaped filter boxes. The filter boxes have inner and
outer, perforated members or covers which form a filter chamber,
and two filter elements positioned between the inner and outer
members of the filter box whose peripheral portions are compressed
and sealed between the outer and inner members of the filter box.
One of the filter elements is at attached to the filter box and
face piece by a locking member which secures the filter element
around the air entrance opening of the face piece. Preferably, the
filter box also includes a means to engage the outer filter element
and space it from the inner filter element inside the filter box
such as a member in the shape of a reverse curve which is pan of
the locking member which clamps the filter material around the air
entrance opening of the face piece. U.S. Pat. No. 2,206,061
(Splaine) discloses a respirator comprising a face piece adapted to
fit over the nose and mouth of the wearer which is adapted to fit
into the open ends of two filters. The filters extend laterally in
opposite directions from the face piece. The filters are relatively
narrow, tapering from a rounded end at the bottom towards the top
so that the side walls substantially meet at the top edge and
contain light coil spring extending along the bottom portion of
each filter to help keep the filters in an expanded condition. U.S.
Pat. No. 4,501,272 (Shigematsu et al.) discloses an embodiment of a
dust-proof respirator with an intake chamber assembly comprising an
intake cylinder fitted airtight into a mounting mouth of a mask
body with a front wall positioned opposedly to the intake cylinder
and a rear wall composed of a filtration medium fastened to the
intake cylinder and along the peripheral edge of the front wall.
Filtration medium is also fastened to the front of the intake
chamber, resulting in increased filtration area.
The present invention provides, in an easily manufactured form, a
filter element of compact size and a nature capable of low air flow
resistance and high filtration efficiency which satisfies various
performance specifications of U.S. and foreign countries some of
which have been set forth above. None of the prior art teaches a
combination of features like those of the present invention having
the advantages of the present invention.
SUMMARY OF THE INVENTION
The present invention provides a filtration element comprising
(A) substantially coextensive front and rear walls joined to each
other along their peripheral edges, and each comprising at least
one layer of filter material,
(B) a porous layer, hereinafter occasionally referred to as a
baffle component, contained between the front and rear walls which
is substantially coextensive with the walls, which maintains the
walls in a spaced-apart relationship to one another substantially
over their entire area, and which contributes no more than 50% of
the total pressure drop across the filter element, and
(C) a breather tube bonded to the rear wall of the filter element
and having a means of attachment for securing the filter element to
a respirator face piece.
An advantage of the filter elements as described is that they be
adapted to perform at high efficiency levels with respect to the
filtration of dusts, mists, or fumes without producing large
pressure drops.
One embodiment of the filter element of this invention will permit
no more than 1.5 mg penetration of silica dust with a geometric
mean particle diameter of 0.4-0.6 micrometer, over a 90 minute
period, at a flow rate of 16 liters/min., measured in accordance
with procedures set out 30 C.F.R. 11 subpart K .sctn.11.140-4
(1987) and will have a pressure drop across said filter element
before the 90 minute period of no more than 30 mm H.sub.2 O and
after the 90 minute period of no more than 50 mm H.sub.2 O where
said pressure drops are measured in accordance with the procedures
set forth in 30 C.F.R. 11 subpart K .sctn.11.140-9 (1987). A second
embodiment of the filter element of this invention will permit no
more than about 3.0 percent penetration of 0.3 micrometer diameter
particles of dioctyl phthalate (DOP), and preferably no more than
about 0.03 percent, contained in a stream at a concentration of 100
microgram/l, at a flow rate of 42.5 liters/min. measured in
accordance with the procedures set forth in 30 C.F.R. 11 subpart K
.sctn.11.140-11 (1987) and permit no more silica dust penetration
and no greater pressure drops before or after the 90 minute period
than those levels set out above measured in accordance with the
procedures specified above. A third embodiment of the filter
elements of this invention will permit no more than 1.5 mg of lead
fume penetration, measured as the weight of lead, through a filter
element over a 312 minute period at an air flow rate of 16
liters/min and will have a pressure drop before the 312 minute
period of no more than 30 mm H.sub.2 O and after the 312 minute
period of no more than 50 mm H.sub.2 O measured in accordance with
the procedures set forth in 30 C.F.R. 11 subpart K
.sctn..sctn.11.140-6 and 11.140-9 ( 1987).
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a half-mask respirator fitted with filter elements of the
present invention, one of which is shown in an exploded manner to
illustrate a means by which the filter elements can be joined to
the respirator face piece.
FIG. 2 is a cross-section of a representative filter element of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
The filter element 1 of this invention comprises front wall 3, a
rear wall 4, and layer of porous material 5 serving to spsce the
front and rear walls and functioning as a baffle component to more
evenly distribute air flow through the filter element, and a
breather tube 8. The front wal1 3, rear wall 4, and baffle
component 5 are substantially coextensive with each other and said
baffle component 5 is contained between the front and walls 3,4.
The filter element 1 can have various shapes such as round,
rectangular, or oval, but preferably, the filter element is round
as depicted in FIGS. 1 and 2. Filter element size can vary
depending upon the materials of construction selected for the
filter element 1 and upon various design and performance criteria
known to those skilled in the art, e.g., the desired pressure drop
across the filter, and the type and amount of dust, mist, or fumes
to be removed from the wearer's inhaled air. However, the shape and
size of a filter element should not obstruct the wearer's eyesight
when mounted on the respirator face piece 15. The front and rear
walls 3,4 are joined along their peripheral edges by a number of
bonding methods such as thermomechanical methods (e.g., ultrasonic
welding), sewing, and adhesive such that a bond 6 is formed that
prevents the leakage of air into or out of the filter element 1.
Preferably, the baffle component 5 is also joined to the front and
rear wall 3,4 through the bond 6.
The filter element 1 has a breather tube 8 which can have various
shapes and can be formed from various materials such as synthetic
resin or rubber. Preferably the breather tube is made of a
synthetic resin which is heat sealable, e.g., polypropylene and is
cylindrical in shape. The breather tube 8 can be mounted anywhere
along the interior 10 or exterior 12 surface of the rear wall 4 but
preferably the breather tube 8 is mounted centrally to the interior
surface 10 of the rear wall 4. The breather tube 8 may be mounted
to the chosen wall surface 10 or 12 using any suitable means, e.g.,
adhesive or ultrasonic welding. The rear wall 4 has an opening 7
adapted to fit the breather tube 8. The breather tube 8 is bonded
to the rear wall 4 to prevent air leakage into or out of the filter
element 1. Preferably, the breather tube 8 has a flange 13 on the
end of the breather tube 8 articulating with the interior surface
10 of the rear wall 4. This flange 13 provides a convenient surface
14 for bonding to the interior surface of the rear wall 10. The
other end of the breather tube 8 can be adapted to either join
directly with the respirator face piece 15, or as illustrated m
FIG. 1, to join to an adapter 17 which is joined to the respirator
face piece 15. One advantage of this invention is that the wearer
can conveniently test the fit or airtightness of the seal between
the wearer's face and the face piece 15 by pressing against the
exterior surface 9 of the front wall 3 opposite the breather tube 8
to cause the front wall 3 and baffle component 5 to collapse
against the breather tube opening 2 thereby blocking off air flow
through the filter element 1. The wearer then inhales while the
face piece 15 is held against his face thereby creating a negative
pressure differential in the face piece. The wearer can then
determine whether there are leaks between the face piece 15 and his
face because these areas will fail to seal. Since it is most
convenient for the wearer to press against the front wall with his
hand, and more preferably with one or more of his fingers, the
inner diameter CID) of the breather tube is preferably 1.0 to 4.0
cm, and more preferably 1.5 to 3.5 cm. However, for any particular
filter element construction, e.g., filter element diameter,
materials of construction, filter element thickness, and breather
tube outer diameter (OD) the smaller the breather tube (ID), the
larger the pressure drop across the filter element.
Optionally, the breather tube 8 may include a valve, typically a
diaphragm valve 18 as depicted in FIG. 1. The valve allows the
wearer to draw filtered air out of the filter element 1 into the
respirator face piece 15 but prevents the wearers exhaled air from
entering the filter element 1, thereby directing exhaled air out of
the face piece 15 through an exhalation point such as an exhalation
valve 19. Preferably, the optional valve is part of the respirator
face piece 15 or the adapter 17.
The front and rear walls 2,4 are comprised of material which can
function as filter material, with or without an outer cover or
scrim. The selection of the materials of construction for the front
and rear walls 3,4 will depend upon design factors well known to
those skilled in the art, such as the type of environment in which
a respirator equipped with the filter elements is to be used, and
performance requirements such as the pressure drop across the
respirator, the type and mount of dust, mist, or fume to be removed
from the wearer's inhaled air, and design requirements set out in
30 C.F.R. 11, subpart K .sctn..sctn.11.130-11.140-42 (1987), herein
incorporated by reference. While the front and rear walls 3,4 of
the filter element 1 can each be comprised of only a single layer
of filter material, a plurality of layers is preferred for high
performance filter elements. By using a plurality of layers of
filter material, web irregularities which could lead to premature
penetration of particles though a single layer of filter material
can be minimized. However, very thick walls should be avoided
because they create problems in assembling the filter element 1 and
could cause the filter element 1 to become so thick that it could
obstruct the wearer's vision when in use. Examples of suitable
filter material include nonwoven web, fibrillated film web,
air-laid web, sorbent-particle-loaded fibrous web such as those
described in U.S. Pat. No. 3,971,373 (Braun), glass filter paper,
or combinations thereof. The filter material my comprise, for
example, polyolefins, polycarbonate, polyesters, polyurethanes,
glass, cellulose, carbon, alumina or combinations thereof.
Electrically charged nonwoven microfiber webs (See U.S. Pat. No.
4,215,682 (Kubik et al.) or U.S. Pat. No. Re. 30,782 (Van
Turnhout)) are especially preferred. A filter material comprising a
plurality of layers of charged, blown polyolefin microfiber (BMF)
web is preferred, with an electrically charged polypropylene web
being more preferred. Carbon-particle- or alumina-particle-loaded
fibrous webs, are also preferred filter media for this invention
when protection from gaseous materials is desired.
The front and rear walls 3, 4 preferably include outer cover layers
3a, 4a respectively which my be made from any woven or nonwoven
material such as spunbonded web, thermally bonded webs (e.g.,
air-laid or carded), or resin-bonded webs. Preferably, the cover
layers are made of spun-bonded or carded, thermally bonded webs
with high hydrophobicity such as those made of polyolefins, e.g.,
polypropylene. The cover layers protect and contain the filter
material, and may serve as an upstream prefilter layer.
The baffle component 5 maintains the front and rear walls 3,4 in a
substantially spaced-apart relationship and also causes inhaled air
to be drawn more evenly across the filter element 1. This results
in more even loading of dust, mist, or fumes contained in inhaled
air across the entire area of the filter element 1, in longer
filter element service life, and for a given filter element
construction, lower pressure drops across the filter element 1. The
baffle component 5 can be made of woven or nonwoven webs, loose
fibers, fiber batts, loose particulate material, e.g., carbon
particles, particulate material bonded, e.g., with polyurethane
together in a porous matrix, or combinations thereof. The baffle
component material contained between the front and rear walls forms
a porous layer that contributes no more than 50%, and preferably no
more than 30%, of the pressure drop across the filter element.
Examples of suitable baffle component materials are glass filter
paper, air-laid webs, carded webs, fibrillated film webs,
sorbent-particle-loaded fibrous webs, bonded sorbent particle
matrices, or combinations thereof. Preferably, the baffle component
5 comprises compressable, resilient, nonwoven web such as those
formed by performing carding or air laying operations, (e.-g.,
Rando Webbers) on blends of staple and binder fibers such that the
fibers are bonded together at points of fiber intersection after
the operation. The baffle component 5 can be made from natural
materials such as glass, cellulose, carbon, and alumina, synthetic
materials such as polyester, polyamide, and polyolefin,
polycarbonate, polyurethane, or combinations thereof. Preferably,
the baffle component 5 comprises polyester or polyolefin. Also
preferred when protection from hazardous gases or vapors is desired
are sorbent-particle-loaded fibrous webs, and particularly carbon-
or alumina-particle loaded webs, or sorbent-particles, e.g., carbon
or alumina which may or may not be bonded together.
The baffle component 5 should have sufficient void volume or
porosity, and be thin enough to prevent the pressure drop across
the filter element from becoming unacceptably high. It should also
be thin enough to make assembly of the filter element 1 easy and to
prevent the filter element 1 from becoming so thick that it
obstructs the wearer's vision when the filter element 1 is mounted
on a respirator face piece. One skilled in the art will understand
that the maximum acceptable pressure drop across the filter element
1 is determined by the comfort requirements of the wearer, and that
as a practical matter, sometimes these pressure drops are
determined by the standards, and measured according to the
procedures set out in 30 C.F.R. 11, subpart K
.sctn..sctn.11.130-11.140-12 (1987). The proper selection of baffle
component thickness and baffle component structural features (i.e.,
percent solidity defined by the equation, %
solidity=100.times.[density of the porous layer/density of the
material used to make the porous layer], fiber diameter or particle
size, and material of construction) can provide a thin baffle
component 5, which if compressible is resilient, and is rigid
enough to support the front and rear wails 3,4 in a spaced-apart
relationship while maintaining an acceptable pressure drop across
the filter element 1 and while functioning to evenly distribute
dust, mist, or fume loading across the filter element 1 surface. A
thin baffle component also permits a thinner filter element which
will be less obstructive to the wearer's vision. Generally, the
baffle component 5 should be 0.2 cm to about 4.0 can thick, and
preferably 0.3 cm to 1.3 cm thick. Preferably, a baffle component 5
comprising a nonwoven material should have at least a 10 micrometer
average fiber diameter and a solidity of 11 percent or less.
Filter elements of the present invention are further described by
way of the non-limiting examples below.
EXAMPLES
The silica dust loading test was performed in accordance with 30
C.F.R. 11subpart K .sctn.11.14-4.
The lead fume test was performed in accordance with 30 C.F.R. 11
subpart K .sctn.11.140-6.
The DOP filter test was performed in accordance with 30 C .F.R.
subpart K .sctn.11.140-11.
Pressure drops across the filter elements were determined in
accordance with procedures described in 30 C.F.R. 11 subpart K
.sctn.11.140-9.
Filter elements were assembled by cutting the appropriate diameter
circular front and rear walls, baffle component, and any cover
layers from various materials which are specified below. A hole
approximately 3.27 cm in diameter was cut through the rear wall of
each filter element and the cover layer, if any, covering the rear
wall. Each filter element had a cylindrical, 3.27 cm OD, 3.14 cm
ID, 0.572 cm cut long, polypropylene breather tube with a 0.526 cm
wide flange around the outer diameter of one end. The unflanged end
of the breather tube was inserted through the hole in the rear wall
and any cover layer and pulled through the hole until one surface
of the flange contacted the interior surface of the rear wall. This
flange surface was then bonded to the rear wall surface. Where the
rear wall material was a polypropylene blown microfiber (BMF) web,
the flange was ultrasonically welded using a Branon ultrasonic
welder to the interior surfare of the rear wall. Where the rear
wall was made of a fiberglass material, the flange was bonded to
the interior surface of the rear wall using a layer of 3M
Jet-melt.RTM. adhesive 3764. The various layers were assembled in a
sandwich like structure where the baffle component was the
innermost layer surrounded by the front and rear walls, and any
cover layers fomed the outermost layers of the sandwich. The
peripheral edges of the polypropylene BMF, front and rear walls and
baffle component were then ultrasonically welded together. The
peripheral edges of the front and rear walls and baffle component
of the filter element made with fiberglass paper were sealed using
the hot melt adhesive described above.
EXAMPLES 1-12
The effect of fiber diameter and percent solidity of a nonwoven
baffle component on pressure drop across the filter element is
illustrated by the following examples. Circular filter elements
10.16 cm in diameter with front and rear walls made of six layers
of electrically charged polypropylene BMF web similar to that
described in U.S. Pat. No. 4,215,682 (Kubik et al.), basis weight
of approximately 55 g/m.sup.2 were constructed. The baffle
components were 0.51 cm thick and were made of web which was
prepared by carding blends of polyester (PET) staple fiber of the
specified diameter, and binder fibers (i.e. a sheath/core fiber
comprising a polyester terephalate core having a melting
temperature of approximately 245.degree. C. and a sheath comprising
a copolymer of ethylene terephthalate and ethylene isophthalate,
available as Melty Fiber Type 4080 from Unitika Ltd, Osaka Japan)
of various diameters, in a 65:35 PET/binder fiber weight ratio and
subsequently placing the carded web in a circulating air oven at
143.degree. C. for about 1 minute to activate the binder fibers and
consolidate the web. The various solidities, of the baffle
component, fiber diameters of the PET and binder fibers, and
average fiber diameters of the fiber blends used in the baffle
component web are summarized in Table 1. The filter elements were
assembled according to the procedure described above. Pressure
drops were measured for each filter element using the procedure
referenced above. The pressure drops are summarized in Table 1.
TABLE 1 ______________________________________ Ave. Nominal Nominal
fiber Web Ex- staple fiber binder fiber diameter soli- Pressure am-
diameter diameter micro- dity drop ple (micrometers) (micrometers)
meters) (%) mm H.sub.2 O) ______________________________________ 1
39.3 39.3 39.3 0.84 21.1 2 39.3 39.3 39.3 1.38 23.4 3 39.3 39.3
39.3 1.60 19.5 4 23.8 24.9 24.2 0.84 25.5 5 23.8 24.9 24.2 1.44
29.0 6 23.8 24.9 24.2 1.89 28.6 7 17.6 20.3 18.6 1.06 23.9 8 17.6
20.3 18.6 1.63 31.6 9 17.6 20.3 18.6 2.13 36.5 10 13.4 14.3 13.8
0.83 40.8 11 13.4 14.3 13.8 1.25 33.3 12 13.4 14.3 13.8 1.79 43.5
______________________________________
The data shows that both the average fiber diameter and solidity of
the nonwoven material comprising the baffle component affects the
pressure drop across the filter element and that fiber diameters as
low as 13.8 micrometers produced acceptably low filter element
pressure drops.
EXAMPLES 13-16
Circular filter elements similar to those described in Examples
1-12 were assembled except that these filter elements had baffle
components made of woven (scrim) and nonwoven materials of various
thicknesses. The woven web used to made the baffle components was a
polypropylene rectangular mesh scrim 0.05 cm thick commercially
available from Conwed as ON 6200. The nonwoven web used for the
baffle component was made according to a similar procedure used to
made the nonwoven baffle web used in Examples 1-12 except that a
50:50 blend of a 51 micrometer diameter polyester staple fiber and
20.3 micrometer diameter, Eastman T-438, polyester binder fiber was
used, and the web was calendered to a thickness of 0.07 cm after it
came out of the oven. The pressure drops across the filter elements
were measured according to the procedure referenced above. The
baffle component materials and pressure drops are reported in Table
2.
TABLE 2 ______________________________________ Pressure Baffle
Solidity Thickness drop Example type (%) (cm) (mm H.sub.2 O)
______________________________________ 13 Scrim.sup.a 8.1 0.05
>100 (1 layer) 14 Scrim.sup.a 8.1 0.20 29 (4 layers) 15
Nonwoven.sup.b 10.7 0.20 55 (3 layers) 16 Nonwoven.sup.b 10.7 0.41
29 (6 layers) ______________________________________ .sup.a woven
scrim .sup.b polyester nonwoven web
The data shows that woven and nonwoven baffle components with
solidifies as high as 8-10.7 % and thickness as low as 0.2 cm
produced filter elements having acceptable pressure drops. The data
also shows that baffle component solidity and thickness affect the
pressure drop across the filter, so both should be considered when
selecting baffle component material.
EXAMPLES 17-22
7.6, 10.2 and 12.7 cm diameter filter elements were prepared in the
manner described above except that one set of filter elements with
these diameters had front and rear walls made of two single layers
of fiber glass paper (available from Hollingsworth & Vose, #HE
1021 Fiberglass Paper) and another set of filter elements with the
same diameters had walls made of a single layer of the same
electrically charged polypropylene BMF web used in Examples 1-12.
The nonwoven web used for the 0.64 cm thick baffle components used
in each filter element was made according to a similar procedure
used to make the nonwoven baffle web used in Examples 1-12 except
that a 20.3 micrometer diameter, Melty Fiber binder fiber was used.
The filter elements were subjected to the silica dust loading test
referenced above. Dust penetration and initial and final pressure
drops were measured and are reported in Table 3. After testing, the
filters were inspected to determine the evenness of particulate
loading across the surface of the filter element. The inspected
filters were evenly loaded with particulate material over both the
surfaces of the front and rear walls.
TABLE 3 ______________________________________ Initial Final Filter
pressure pressure Filter dia. Pen. drop drop Example media (cm)
(mg) (mm H.sub.2 O) (mm H.sub.2 O)
______________________________________ 17 Fiberglass 7.6 1.45 10.1
33.4 18 Fiberglass 10.2 1.49 6.3 * 19 Fiberglass 12.7 2.94 4.6 6.7
20 BMF 7.6 0.22 5.8 15.8 21 BMF 10.2 0.15 3.7 4.8 22 BMF 12.7 0.18
2.8 3.1 ______________________________________ *Filter broke
The data demonstrates that charged polypropylene BMF filter media
permits less penetration of silica dust during the test period and
produces lower pressure drops across the filter element over the
test period than fiberglass paper. Therefore, filter elements
utilizing the BMF media can be made in smaller sizes and still
offer comparable performance levels to larger filter elements using
the fiberglass media.
EXAMPLES 23-26
Three circular filter elements having diameters of 7.6, 10.2 and
12.7 cm were constructed according to the procedure described
above, using front and rear walls made of two single layers of
fiberglass paper (available from Hollingsworth & Vose, #HE 1021
Fiberglass Paper), and baffle components 0.64 cm thick, made of
nonwoven baffle component web identical to that used in Examples
17-22. Additionally, three circular, 10.2 cm diameter filter
elements were constructed using front and rear walls made of a
single layer of the same electrically charged polypropylene BMF web
used in Examples 1-12 and 0.64 cm thick baffle components made of
the same nonwoven baffle component web used in Examples 17-22. The
filter elements used in Example 26 also incorporated a cover layer
over the front and rear walls made of material similar to the
baffle component web used in Examples 17-22, except that the web
was calendered to a thickness of 0.033 cm after it came out of the
oven. The filters were assembled and subjected to the lead fume
loading test referenced above. Initial and final pressure drops
across the filter elements and the level of lead fume penetration
through the filters were measured. After testing, the filter
elements were visually inspected to determine if there had been
even loading of the lead fume across the surface of loaded across
both the front and rear wall surfaces.
Filter construction diameter and lead fume penetration test data
are reported in Table 4.
TABLE 4 ______________________________________ Initial Final Filter
Pressure pressure Filter dia. Pen. drop drop Example media (cm)
(mg) (mm H.sub.2 O) (mm H.sub.2 O)
______________________________________ 23 Fiberglass 7.6 0.30 10.8
>115 24 Fiberglass 10.2 0.30 6.2 >115 25 Fiberglass 12.7 0.22
4.9 >115 26* BMF 10.2 0.28 3.2 41.5
______________________________________ *average of three
samples
The data shows that the polypropylene, BMF filter media provides
the wearer with protection against lead fumes with significantly
lower pressure drops than filter elements made with fiberglass
media.
EXAMPLES 27-35
Circular filter elements ranging in diameter from 7.6 to 10.2 cm
were constructed using a single layer of fiberglass paper
(available from Hollingsworth & Vose, Hovoglas.RTM. #HB-5331
Fiberglass Paper) for front and rear walls and a 0.64 cm thick
baffle component made of the same web as the baffle components used
in Examples 23-26. Additionally, a set of circular filter elements
ranging in size from 7.6 to 10.2 cm diameter with front and rear
walls made of a plurality of layers of the same electrically
charged polypropylene BMF used in Examples 1-12 and a 0.64 cm thick
baffle component made of the same web as the baffle components used
in Examples 23-26 were constructed in accordance with the procedure
described above. All of the filter elements were subjected to the
DOP penetration test referenced above. The filter wall material,
number of layers of filter material, filter diameter, DOP
penetration, and pressure drops across the filter measured after
the DOP penetration test are summarized in Table 5.
TABLE 5 ______________________________________ Final Layers Filter
pressure Filter of filter Dia. Pen. drop Example Media media (cm)
(%) (mm H.sub.2 O) ______________________________________ 27
Fiberglass 1 11.4 0.015 27.5 28 BMF 5 7.6 0.013 29.5 29 BMF 5 8.3
0.006 25 30 BMF 6 10.2 0.001 20.5 31 BMF 5 10.2 0.004 16.5 32 BMF 4
10.2 0.011 13.0 33 BMF 4 7.30 0.10 25.0 34 BMF 2 7.6 2.5 12 35 BMF
1 7.6 30.0 5 ______________________________________
EXAMPLE 36
Five, 10.2 cm diameters circular filter elements were made which
were identical to those used in Example 30. The filters were
subjected to the silica dust test referenced above. The average
silica dust penetration through the filter elements was 0.05 mg,
the average pressure drop across the filter element before the test
was 20.5 mm H.sub.2 O, and the average pressure drop across the
filter element area the test was 22.4 mm H.sub.2 O. After the test
the filter elements were visually inspected to determine the
evenness of particle loading on filter evenly loaded with silica
dust over both the front and rear walls of the filter element.
EXAMPLES 37-41
Circular filters elements similar to those described in Examples
1-12 were assembled except that these filter elements had baffle
components made of particles of various diameters and materials.
The particulate material when held between the front and rear walls
formed a porous layer. Several of the examples were carbon
particles classified by sieving. One of the examples was
polybutylene resin pellets of uniform size. The pressure drop
across the filter elements were measured according to the procedure
referenced above, The baffle component materials and pressure drops
are reported in Table 6.
TABLE 6 ______________________________________ Average particle
Pressure Baffle diameter Thickness drop Example material (mm) (cm)
(mm H.sub.2 O) ______________________________________ 37 carbon .93
.99 47.0 38 carbon 1.09 .86 40.1 39 carbon 1.29 .89 33.9 40 carbon
1.7 .91 32.6 41 polybutylene 3.0 1.02 24.7
______________________________________
The data shows that there is a definite relationship between
diameter and pressure drop. Particle sizes above 1.5 mm will give
acceptable pressure drops.
EXAMPLES 42
Filter elements 10.2 cm in diameter were constructed using front
and rear walls of a single layer of the polypropylene BMF web used
in Examples 1-12 and 0.64 cm thick baffle components made of the
same nonwoven baffle component web used in Examples 17-22. Each
filter element had a cylindrical, polypropylene breather tube. The
breather tubes had various inner diameter but their outer diameter
was 3.27 cm. The filter elements were assembled according to the
procedure described above and the pressure drop across each filter
element was measured according to the procedure referenced above.
The breather tube inner diameters and pressure drops are summarized
in Table 7.
TABLE 7 ______________________________________ Pressure Breather
tube drop DOP pen Example ID (cm) (mm H.sub.2 O) (%)
______________________________________ 42 1.27 5.1 9.5 43 1.59 3.7
10.1 44 1.91 3.2 9.7 ______________________________________
The data shows that for a given filter construction the larger the
breather tube inner diameter the lower the pressure drop across the
filter element.
Various modification and alterations of this invention will become
apparent to those skilled in the art without departing from the
scope and spirit of this invention.
* * * * *