Face mask

A face mask is disclosed that can be reusable or disposable, and which filters particulate matter and/or noxious or poisonous gasses from breathed air. The mask has a shell that is formed of polymeric closed cell foam that is impermeable to air while having good shape retention that enables the edge of the mask shell to conform and seal to the face of a wearer around their nose and mouth. The foam mask shell has one or more holes through the central portion thereof and a filter is mounted to cover said hole(s) to thereby filter all inhaled air passing through said holes. A one-way valve is mounted through the wall of the mask shell to exhaust exhaled air.

FIELD OF THE INVENTION 
The present invention relates to face masks that cover the nose and mouth 
while filtering breathed air and, in particular, face masks having a 
molded or thermoformed, non-porous or porous shells, and filter cartridges 
or one or more liners or layers of fibrous or other filter material that 
may be inpregnated with a substance to remove noxious or other material 
including gasses from the breathed air. 
BACKGROUND OF THE INVENTION 
Examination of the prior art yields a variety of face masks or respirators 
for treatment of breathed air. Generally, the masks of the prior art may 
be categorized into one of two classes, namely; disposable or single-use 
respirators and replaceable cartridge respirators. 
In general, disposable masks of the prior art are made of a permeable 
fibrous media formed into a cup shape to fit the contour of the face of 
the wearer. In some masks the fibrous media is formed to fit the face of 
the wearer and, simultaneously, achieves a seal against the flow of toxic 
dusts and mists into the breathed air chamber. In other masks a nose clip 
is attached to the face mask and is utilized to achieve a seal around the 
nose area. 
In the majority of disposable fibrous media masks of the prior art, 
breathed air treatment and filtration is achieved by air flow through most 
of the area of the face mask. Although this is relatively costly, since a 
large amount of filtration media is used to fabricate the entire mask 
shell in addition to the excessive between-shell cut-out waste, it is 
advantageous since it results in a relatively lower pressure drop across 
the filtration media for the same breathed air volume flow rate. Those 
masks still have a limited capacity and lack the ability to carry a 
sufficient charge of air treatment substances for the absorption of toxic 
gasses, fumes, vapors, etcetera in order to provide the wearer with 
protection in harmful environments. Thus, such disposable face masks 
cannot meet standards or requirements for governmental approval in such 
applications. For example, it is difficult to impregnate the disposable 
face mask fibrous media with a sufficient charge of activated charcoal 
granules (approximately 100 grams) to pass government requirements for 
paint spray, organic vapor, acid gas or pesticide applications. This is 
due to the limited capacity of the fibrous media for encapsulating or for 
being loaded or impregnated with toxic gas treatment media. In certain 
instances, even when a relatively thicker fibrous shell is used, the 
amount of charcoal encapsulated in the mask shell is insufficient for 
meeting the National Institute for Occupational Safety and Health (NIOSH) 
requirements for certification or approval for paint spray applications. 
In such cases the resulting mask, lacking NIOSH approval, is usually 
referred to as a nuisance mask. 
In many cases, however, where the filtration media is impregnated with air 
treatment substances or is loaded with additional fibrous media, the face 
mask is relatively thicker and a good face-mask fit and seal are much 
harder to achieve. In these cases a nose clip and/or wide, low 
extensibility heavy duty straps are used in order to apply a high force to 
pull the mask against the face of the wearer. As a result, the air seal is 
obtained by deforming the wearer's face to conform to the perimeter of the 
mask, rather than deforming the mask to conform to the face of the wearer. 
Needless to say, such a mask is not comfortable to wear. 
Therefore, a limiting factor in making single use respirators that meet 
NIOSH requirements is that it is very difficult to produce a fibrous media 
mask carrying a weight of approximately 100 grams of activated charcoal 
granules while maintaining the total mass of the mask within bearable 
limits. 
Examination of prior art masks shows that the formation of the majority of 
disposable masks involves heating, stretching and/or compressive 
compaction of the filtration media. Such processing factors may adversely 
influence the effectiveness of the filtration media with regard to its 
filtration efficiency and pressure drop. The examination also shows that, 
in the majority of disposable masks, the area of contact with the face of 
the wearer is of a fibrous nature and thus cannot provide an airtight seal 
similar to an elastomeric material seal as required by regulatory agencies 
for certain applications against toxic gasses and vapors. 
In the manufacture of respirators designed for single use or for a finite 
period use, a significant portion of the overall product cost is the cost 
of the filtration media. As the cost of media (including cut out waste) 
increases, the competetiveness of the overall product in the marketplace 
suffers significantly. This is typically true in all face masks targeted 
to the particulate filtration applications, including toxic dusts and 
mists. In the majority of such masks the area of filtration media in the 
final product is equal to the area of the mask shell. 
In the prior art, numerous products and patents are directed towards 
obtaining an effective air-tight seal between the perimeter of the mask 
shell and the face of a wearer. In certain instances a polymeric bead, 
rim, flap, or their combinations are added at the perimeter of the fibrous 
shell face mask. Except for use of a thin rim of impermeable closed cell 
elastomeric material or foam around the perimeter of the face mask in the 
zone in contact with the face of the wearer, examination of prior art 
masks and patents has shown no suggestion or use of impermeable polymeric 
foam materials in the basic shell comprising the body of face masks. 
On the other hand, replaceable cartridge masks of the prior art are 
generally comprised of an elastomeric face piece designed to fit the face 
of the wearer and achieve an air-tight seal with the face of the wearer. 
The elastomeric face piece is usually fitted with at least one opening to 
receive a detachably attached cartridge for treatment of the breathed air. 
The elastomeric face piece is also usually fitted with a one-way 
exhalation valve. 
In order to achieve and maintain an air-tight seal around the perimeter of 
a cartridge, the mask shell is stiffened either through ribbing or through 
the use of increased material thickness, particularly around the cartridge 
receiving opening. Hence, the face mask is generally made of a heavy 
construction and thus feels heavy on the face of the wearer. As an 
example, a replaceable cartridge mask of the prior art was weighed and 
yielded the following data. The total weight of the basic face mask shell 
with mounting straps and two replaceable activated charcoal granule 
filters 15 327 grams. The weight of the two filter cartridges is 183 
grams. The ratio of the weight of the mask functional components (filters) 
to the total mask weight, R=182/327=0.56. 
From a mask wearer's comfort standpoint, while a mask is performing its 
intended function, it may be concluded that it is desirable to maintain 
the ratio R as high as possible, particularly for masks requiring 
relatively heavy functional components (filters). In such cases, as R 
approaches its limit value of 1, the wearer's discomfort is minimized. 
Generally speaking, however, NIOSH approved masks which utilize detachably 
attached, replaceable cartridges are costly since a sizable initial 
capital investment has to be made for the durable face mask shell. Other 
indirect costs include the cost of periodic shell cleaning, sanitization, 
testing for cuts, cracks, leakage, etcetera and storage. In certain work 
places individuals using such durable face masks prefer or require that no 
other co-worker may use the same face mask shell at any other time. This 
is usually done for the prevention of transmittal of communicable diseases 
through breathing contaminated air or through skin or saliva contact with 
a contaminated mask shell. In this case certain face mask shells are 
numbered and designated for use only by certain individuals. 
Additionally, in certain applications, for example in asbestos fiber 
contaminated environments, the subsequent shaking off of the mask shell 
after use contaminates the clean environment. In such cases it is 
desirable to dispose of the entire mask shell and air filtering cartridges 
after each use. Such disposal is costly since a major expense is incurred 
in the cost of the mask shell. On the other hand, recently adopted 
government regulations disallowed approval of conventional disposable face 
masks for use in asbestos fiber contaminated environments. 
Also, most durable masks, particularly approved ones, require a high force 
to pull them against the face of a wearer in order to achieve an effective 
seal with the face of the wearer. When such masks are made of a heavy duty 
construction the need also arises for head-top band in order to prevent 
the mask from falling off the face of the wearer and to maintain a 
complete seal with the face of the wearer. Such head-top band is usually 
branched off the above-the-ear band and is placed on top of the head of 
the wearer of the mask. Such a head-top band is particularly undesirable 
when the wearer's head top is bald at the location of the head-top band. 
As may be concluded from the above, there is a need in the art for an 
inexpensive, flexible shell that is light weight, single-user (single or 
repeated use) face mask which fits around and achieves a complete air 
tight seal with the face of the wearer. Such a mask should have a fit and 
seal that are comparable to the fit and seal obtained with presently 
available elastomeric face pieces, while feeling light and thus relatively 
more comfortable, and being able to carry a charge of air treatment or 
filtration media and/or devices sufficient to perform the desired 
protection against specific environmental hazards. 
The needs of the prior art are met by the face mask taught and claimed 
herein. The novel mask bridges the gap between unapproved disposable masks 
and expensive, approved replaceable cartridge respirators. This mask 
features a reduced cost of filtration media through the use of a 
relatively smaller portion of such media, because the media does not have 
to undergo adverse processing conditions such as heating, stretching 
and/or compressive compaction. 
SUMMARY OF THE INVENTION 
The above needs of the prior art are met by the present novel face mask 
which can be non-disposable or disposable, which filters particulate 
matter, noxious and poisonous gasses from inhaled air, which is of 
relatively light weight, which is soft and flexible and forms a good seal 
to a wearers face around the nose and mouth without the need for tight 
elastic straps, which does not deform the face of the wearer to accomplish 
a good seal, which is comfortable to wear for extended periods of time, 
and which is relatively inexpensive. Such a face mask is a viable 
alternative to prior art rubber shell masks so that each worker may have 
their own reusable mask or may dispose of a mask after a single use. 
The primary embodiment of the novel mask has an outer shell that is 
thermoformed of cross-linked, closed-cell foam sheet. The foam shell is 
impermeable to air while being soft and flexible, and having good shape 
retention and elasticity. The center area of the shell is perforated with 
multiple holes to permit inhaled air to pass through the otherwise air 
impermeable shell and through the filter liner(s) positioned inside or 
outside the mask over the holes. This mask shell is stiff enough to 
support a variety of filters ranging from a simple fibrous filter liner 
for filtering dust or mist, to an activated charcoal impregnated fibrous 
sheet liner for filtering noxious and poisonous gasses and other dangerous 
materials. The filters may be removable retained to the inside or to the 
outside of the shell over the holes by a force fit retainer or by clips 
that are both easily removed to replace the filter. The removable filters 
may also be attached by self adhesive strips around the periphery of the 
filter. The filter may also be thermobonded or otherwise permanently 
bonded to the inside or outside of the mask over the holes to make a 
disposable version of the mask. When a filter is attached to both the 
inside and to the outside of the shell over the holes, the outer filter 
serves as a pre-filter, and the inner filter serves as a post-filter. 
A one-way exhaust valve may be mounted through the wall of the foam mask 
shell to vent exhaled air. The exhaust valve is located in a position 
where it does not interfere with the filter liner(s). 
In an alternative embodiment of the invention the basic shell may be formed 
of two parts. The periphery of the shell which contacts the face of the 
wearer and makes an air tight seal thereto, and to which straps would 
attach, would be formed of the air impermeable foam material. Attached to 
the shell periphery by thermobonding, adhesives or other methods is a 
piece of air permeable foam that eliminates the need for the holes in the 
primary embodiment of the invention. The filter are still attached to the 
inside and/or the outside of the mask over the air permeable foam 
material. The filters are attached permanently for a disposable mask, and 
are removable as previously mentioned for a reusable mask. 
In still another embodiment of the invention the closed cell foam material 
from which the mask shell is thermoformed is made up of a layered 
material. The outermost layer that is on the side mask shell that contacts 
the face may be of a material that permits more comfortable wearing of the 
amsk, or that is best to reduce chafing or hypoallergenic effects. The 
other layers may be chosen for shape retention, asthetics, or for many 
other reasons. 
In another embodiment of the invention one or more filter cartridges are 
not attached to the inside and/or the outside of the foam shell but, 
rather, are attached through the wall of the shell. The cartridges may be 
detachably fastened to collars that mount through and are fastened to the 
foam shell. 
In yet another alternative embodiment of the invention the mask shell may 
not be formed of closed cell foam, but may comprise a shell that is 
fabricated by thermoforming a sheet of commercially available, synthetic 
fiber, nonwoven, filter material. The shell so formed may be cup-shaped. 
During forming a piece of a fibrous sheet material impregnated with 
activated charcoal or other filtration substance is thermobonded or 
otherwise fastened to the inside of the mask but not overlapping the edge 
of the mask. In this manner the filter material forming the basic mask 
shell also does pre-filtering, and the filter liner affixed to the inside 
of the shell is the post-filter.

DETAILED DESCRIPTION 
In accordance with the present invention it is advantageous to use an 
impermeable polymeric foam as the basic face mask shell. Use of such foam, 
having a significantly lower density results in a generally lower weight 
mask, as well as a highly desirable higher filter media weight to total 
mask weight ratio R. Such a high ratio is not only desirable from a 
comfort standpoint, but also from a cost and overall weight savings, 
particularly for military gas masks. 
For the purpose of describing the present invention an impermeable 
polymeric foam shall be defined as a medium which is impermeable to the 
flow of gasses and liquids and having a mass density lower than the 
product of the standard mass density of water (62.4 lbm/ft.sup.3) and the 
specific gravity of the solid consistency of the polymer or combination of 
polymers from which the mask shell medium is made. For example, an 
impermeable polyethylene foam shall have a density lower than 62.4 
lbm/ft.sup.3 .times.0.91=56.784 lbm/ft.sup.3 and, likewise, a nylon 66 
foam shall have a density lower than 62.4 lbm/ft.sup.3 .times.1.14=71.136 
lbm/ft.sup.3, and so on. accordance with the above definition, an 
initially permeable fibrous sheet or open cell foam sheet coated or sealed 
on one or both sides in order to be impermeable to the flow of fluids may 
be defined as an impermeable foam. Other materials that may alternatively 
be used to make the subject mask shell are combinations or laminates of 
polymeric sheets or films, fibrous webs, fabrics, open cell foams and/or 
closed cell foams. 
Due to the lower density of the foam it is possible to form thick, yet 
light face mask shells. This is particularly desirable since a thicker 
shell offers a greater overall stiffness that enables the mask shell to 
retain its shape while being able to carry a large mass of filtration or 
air treatment media without sacrificing on the ease of surface 
deformability of the shell. This is a feature that is essential for an 
effective face fit and seal. As an example, a 1/8 inch thickness lightly 
cross-linked closed cell, polyethylene foam made by Voltek, with a density 
of 2 lbm/ft.sup.3 was formed into a cup shape shell-like face mask having 
rearward projecting protrusions of the type disclosed in U.S. Patent 
4,641,645 which conform the edge of the mask shell to the face of a wearer 
around the nose. These protrusions are shown in FIGS. 2, 3, 7 and 9. The 
formed foam shell, weighing about three grams, was attached to two 
extensible light duty 1/4 inch width braided elastic straps weighing about 
two grams (commonly used for light weight face masks). This basic shell 
was able to carry a load of 150 grams exterior to its surface and, 
alternatively, interior to its surface without collapsing, falling off the 
wearer's face, or losing the air tight seal between its perimeter and the 
face of the wearer. The resulting mask had an R ratio 150/(150+2+3)=0.97 
and was more comfortable to wear for a longer period of time than the 
generally heavier approved masks. Further, it did not require a head-top 
strap as do the majority of approved masks. Generally, an activated 
charcoal granule charge and other media weighing a total of approximately 
one-hundred grams are sufficient for providing the mask wearer with 
protection against a variety of toxic gasses, vapors, etcetera, in 
accordance with NIOSH requirements. 
It is worth noting from an economics standpoint and from a wearer's comfort 
viewpoint, that it is more desirable to use narrower and lighter, more 
extensible bands to hold a mask to the face. This is all possible with the 
present invention. 
In comparison to a continuous uniform phase polymeric material, a polymeric 
foam shell is easier to cut and perforate. Thus, it is possible to obtain 
a shell with a good face seal while utilizing easier and lower capital 
equipment fabrication techniques such as thermoforming. The cutting and/or 
perforating process may be performed on formed foam mask shells obtained 
by thermoforming, injection molding, rotational molding, blow molding or 
any other fabrication technique. Although it is equally functional to use 
a plurality of perforations or a single large cutout, it is preferable to 
use a plurality of perforations. This is particularly advantageous for 
minimization of unsupported filtration media outwardly bulging or inwardly 
retracting during exhalation and inhalation and for obtaining better shape 
retention and support of load interior and/or exterior of the mask shell, 
a well as additional points within the filtration area for anchoring the 
media without blocking of air passage. Such anchoring points help maintain 
the shape of the filtration media even when the interior of the mask is 
highly humid or when such media is wetted by such high humidity. The 
feature of shape retention and resistance to collapsing in the wet 
condition is highly desirable and in certain cases is required for certain 
applications. 
The use of foam for the inner and/or outer surfaces of the shell also 
provides a flexible surface. Such flexibility of the inner and/or outer 
surface offers the additional advantage of providing a conformable surface 
for obtaining a complete seal between a replaceable cartridge, or media 
liner and the shell of the mask. 
In accordance with the present invention, impermeable laminates comprising 
at least one layer of polymeric foam material may be used for fabrication 
of the mask shell. Use of such laminates makes it possible to obtain 
combinations of colors, softness and/or high tack of the side of the mask 
shell in contact with the face of the wearer, and firmness of the outer 
shell while maintaining the low weight of the entire mask shell and Food 
and Drug Administration (FDA) approved and unapproved materials. Such 
laminates also make it possible to reduce the overall material and/or 
fabrication costs and enhance the elastic recovery from deformation, 
strength and mechanical properties of the mask shell, particularly at the 
fixation or threading points or the strap holes. 
The foam density may be as low as 4 oz/ft.sup.3. Experiments conducted on 
lightly cross-linked polyethylene foam mask shells with a variety of 
densities yielded a preferred (although not necessarily optimum) density 
of 4 lb/ft.sup.3. The use of elastomeric polymeric foam makes it possible 
to simultaneously obtain a desired combination of wearer's comfort, 
product competetivness in the market place, and mask functional features 
not possible with any of the prior art masks. For example: (1) clinging to 
the skin of the wearer's face at the perimeter of contact of the mask with 
the face of the wearer, thus ensuring an air-tight seal as effective as 
that obtained from conventional uniform solid phase elastomeric or rubber 
face pieces; (2) softness of contact force between the wearer's face and 
the mask shell, since the ease of deformity of the foam results in 
spreading of the force of applied pull onto the mask shell over a larger 
surface area of the wearer's face, thereby eliminating the harsh or 
excessive loading points on the wearer's face which usually cause redness 
on the wearer's face after even a short duration of wearing the mask; (3) 
lightness of shell yielding improved wearer's comfort and increase of the 
ratio R of weight of the filter media to the total weight of the mask. 
Increasing this ratio also reduces the overall material cost of the mask 
and enhances its competetiveness in the marketplace. It also makes it 
equally attractive, from a product costing standpoint, to use such foam 
mask shells for nuisance masks (unapproved) and NIOSH approved 
applications. The lightness of the shell makes it possible to use 
narrower, lighter, more readily extensible bands for holding the mask 
shell onto the face of the wearer without excessive force and preferably 
without a head-top band; (4) obtaining a stiff, yet light mask shell able 
to carry a mass of filtration and/or air treatment media sufficient to 
meet NIOSH approval for certain applications; and (5) enhancing the shape 
retention and recovery from deformation by using elastomeric material 
foams such as polyurethane or lightly cross-linked polyethylene, and 
satisfying NIOSH requirements for elastomeric face pieces for certain 
applications, and other desirable features as described in this 
application. 
The mask of the present invention features a face piece covering mouth and 
nose of a wearer and generally conforming to the contour of the face of 
the wearer in the zone of contact between the face of the wearer and the 
face piece. In addition, the mask has a rear portion mead of impermeable 
material, preferably closed cell polymeric foam or generally impermeable 
polymeric foam. The rear portion has a circumferential zone which is in 
contact with the face of the wearer. This zone is impermeable to air and 
is made of flexible, soft, high-tack, generally elastomeric material in 
order to provide an air-tight and complete seal between the face of the 
wearer and the entire circumferential zone. For lower fabrication costs 
the circumferential zone may be an integral part of the rear portion. It 
may also be an added segment attached to the side of the rear portion 
facing the wearer's face. 
There is also a front portion made of impermeable material preferably 
closed cell polymeric foam or generally impermeable polymeric foam. For 
lower fabrication costs the front portion and the rear portion may be 
integral parts of one continuous impermeable shell formed of polymeric 
closed cell foam or generally impermeable polymeric foam, light 
impermeable polymeric material or laminates of foams and/or other 
polymeric materials. The front portion may also be attached to the rear 
portion in a manner that provides a complete and continuous air tight seal 
in the zone joining the front portion to the rear portion. 
The front portion has at least one circumferential zone on its interior 
surface facing the face of the wearer and/or on its exterior surface. The 
front portion is made permeable to the passage of air, gasses, 
particulates, vapors, etcetera by having a single large cutout area or 
preferably a plurality of smaller cutout areas, holes or perforations 
surrounded by the circumferential zone(s). 
At least one air permeable treatment medium, such as a replaceable or 
permanently attached cartridge is attached to the interior and/or the 
exterior of the front portion in an air-tight manner along the 
circumferential zone, thereby creating a treated air chamber enclosed 
between the interior surface of the air treatment medium, the interior 
surface of the front portion, the interior surface of the rear portion and 
the face of the wearer. 
For the case where more than one air permeable treatment medium are used, 
the first medium may be attached to the exterior of the front portion and 
would thereby act as a pre-treatment or initial pre-filtration medium. 
Such is the case for applications such as paint spray masks and the like. 
The air permeable treatment medium may be attached to the outer portion 
singularly or in combinations, in one location or in a plurality of 
locations, mechanically, frictionally, by a tight fit, by a snap fit, 
adhesively or cohesively (i.e. by interfacial melting or fusion and 
cosolidification), permanently or detachably. 
The outer portion may be shaped to accommodate a cartridge or a plurality 
of cartridges for treatment of breathed air in one location or in a 
plurality of locations. The cartridges may treat the breathed air in 
series or in parallel. Further, the outer portion may be bellows shaped in 
order to accommodate cartridges of various thicknesses. 
In FIG. 1 is shown a front view of a face mask 10 which has only an 
internal filter. The mask comprises an outer shell 11 which is 
thermoformed from a single-layer sheet of cross-linked, closed-cell foam 
that is impermeable to air. Many foam materials may be used but in the 
embodiment of the invention disclosed herein three-sixteenths inch thick 
foam available from Voltek, a division of United Foam Corporation, is 
utilized. This foam material is soft but is thick enough that the 
thermoformed shell has good elastic properties yet is stiff enough that it 
has good shape retention and can support a filter liner and retainer 
therein behind holes 12 as shown in FIG. 3. The holes 12 through the 
central portion of the mask shell 11 may be punched through the foam sheet 
prior to thermoforming of mask shell 11, or may be punched after shell 11 
is formed. Holes 12 are preferably one-quarter inch diameter and the 
spacing between the holes is preferably one half the diameter of the 
holes, but one skilled in the art may vary the diameter and spacing of the 
holes. 
Mask shell 11 also has two elastic straps 13 and 14 attached thereto on rim 
15. Straps 13 and 14 go behind the head of a wearer of mask 10 when the 
mask is worn and hold mask 10 comfortably to the wearer's face without 
deforming the face while maintaining an air-tight seal between the rim 15 
of mask shell 11 and the face of a wearer. The straps 13 and 14 are 
stapled to rim 15 in the preferred embodiment of the invention, but may 
also be sewn, thermobonded or adhesively attached thereto in a manner well 
known in the art. Although straps 13 and 14 are shown as single pieces of 
elastic material, in an alternative embodiment of the invention straps 13 
and 14 may be made adjustable in a manner well known in the art. 
In FIG. 1 is also shown a one-way exhaust valve 16 of a type known and used 
extensively in the face mask art. Valve 16 is mounted in a hole or a 
suitably shaped cavity (FIGS. 2 and 3) through the lower portion of mask 
shell 11 so as not to interfere with a filter liner (not shown) inside of 
mask 10 behind all of holes 12. Valve 16 permits a wearer of the mask to 
inhale through the filter liner but on exhalation valve 16 opens to vent 
exhaled air. 
Although not specifically shown in FIG. 1, but shown in FIG. 3, there is a 
filter 17 mounted in the interior of mask shell 11 behind all of holes 12 
to filter inhaled air passing through holes 12. As described in detail 
further in this specification internal filter 17 may also be retained 
inside of mask shell 11 by a snap-in retainer (not shown) which is shown 
in FIGS. 3 and 4 to produce a reusable mask 10. With a reusable face mask 
the filters may be periodically changed to continue the use in the same 
environment, or changed to a new type of filter for use in a new 
environment. However, the snap-in retainer may be dispensed with and 
filter 17 may be permanently fastened inside of mask shell 11 by 
thermobonding or adhesives in a manner well known in the art to produce a 
disposable face mask that is used only once and then discarded. 
When wearing face mask 10 shown in FIG. 1, mask shell 11 is flexible enough 
and is shaped so that it easily conforms to the contours of a wearer's 
face around the nose and mouth and deformation of the wearer's face is not 
required to achieve a good seal. In addition, rim 15 is soft enough that 
it fits very comfortably to the face of the wearer, generally with less 
force than prior art disposable masks that are stiff because of how they 
are fabricated. Accordingly, face mask 10 may be comfortably worn for long 
periods of time. 
In FIG. 2 is shown a side cross-sectional view of a face mask 10 with an 
external filter 18 mounted thereon. This mask also comprises an outer 
shell 11 which is thermoformed from a single-layer sheet of cross-linked, 
closed-cell foam that is impermeable to air, and exhaust valve 16. Mask 10 
also has holes 12 through the front of foam mask shell 11. In a disposable 
version of mask 10 external filter 18 is fastened over holes 12 by 
thermobonding or by adhesives to create a disposable mask. However, 
external filter 18 may also be removably attached to the outside of mask 
shell 11 by a retainer arrangement such as shown and described hereinafter 
with reference to FIG. 5 to create a reusable face mask. With a reusable 
face mask the filters may be periodically changed to continue the use in 
the same environment, or changed to a new type of filter for use in a new 
environment. 
In FIG. 3 is shown a side cross sectional view of face mask 10. One-way 
exhaust valve 16 is seen mounted through the wall of the lower portion of 
mask shell 11 where it does not interfere with filter 17. Filter 17 may be 
permanently fastened inside of mask shell 11 over holes 12 by 
thermobonding or by adhesives for a disposable mask, or filter 17 may be 
detachably fastened inside of mask shell 11 over holes 12 by a snap-in 
retainer 19 as shown to create a reusable mask. Further details of 
retainer 19 are shown in FIG. 4, and further details of how retainer 19 
holds replaceable filter 17 inside of mask shell 11 by being held in a 
molded recess around the inner wall of the shell 11 are shown in FIG. 4a. 
The construction of an exemplary multilayer filter 17 is shown in FIG. 6. 
Basically, internal filter 17 is prefabricated with one or more than one 
layer and then is stamped out in flat rectangular or other shape pieces. 
In a multilayer version of filter 17 there is a first layer (not shown) of 
a fibrous material impregnated with activated charcoal. There is also a 
second layer (not shown) that is attached to the activated charcoal layer. 
The second layer is preferably a net layer for appearance purposes. Filter 
17 fits in the middle of the inside of mask shell 11 covering all of holes 
12. Due to the flexibility of filter 17 it readily conforms to the inside 
of the central portion of mask shell 11. 
In FIG. 4 is shown an isometric sectional view of snap-in retainer 19. 
Retainer 19 is molded of a flexible thermoplastic material that can bend 
as it is inserted into the interior of mask shell 11 and is held in a 
groove therein as shown in detail in FIG. 4a. The plastic from which 
retainer 19 is molded is also tough, and coupled with the thickness of the 
retainer it does not break easily. The outer edges 20 snap into the 
aforementioned groove around the interior of mask shell 11 to retain 
filter 17 inside mask shell 11. On assembly into face mask 10 retainer 19 
also deforms to match the contour of the inside of mask shell 11. There 
are also ribs 21 that help hold internal filter 17 against the inner 
surface of mask shell 11 over holes 12. Ribs 21 have much space between 
them so they do not materially impede the flow of inhaled air passing 
through filter 17 to the inside of mask 10. It should be appreciated that 
there may be many designs of retainer 19 that will work with the mask. 
When it is desired to replace filter 17, retainer 19 is grasped near one 
edge and pulled, removing the retainer from the inside of mask shell 11. 
The spent filter 17 is then removed and replaced with a new filter 17, and 
retainer 19 is then reinstalled. 
In FIG. 4-a is a cross sectional view of mask shell 11 that shows groove 22 
that is formed around the inside of shell 11 during thermoforming. 
Retainer 19 is shown in its snapped-in position with its outer edges 20 in 
a force fit engagement in groove 22. It can be seen that on insertion 
retainer 19 deforms to hold filter 17 inside of mask shell 11 up against 
holes 12. This force fit engagement maintains a good seal so that no 
inhaled air passes around filter 17. 
While the description of FIGS. 1 through 3 has been for masks in which the 
filter 17 may be removed and be replaced, the retaining means 19 may be 
eliminated and filter 17 may be thermobonded or adhesively bonded to the 
inside and/or the outside of mask shell 11. This makes a disposable face 
mask 10 that is replaced after a single use. 
The interior view of mask 10 shown in FIG. 3 is for a version of the mask 
wherein there is only the interior filter 17. With this version snap-in 
retainer 19 is used. When a version of mask 10 has both an interior filter 
17 (FIG. 1) and an exterior filter 18 (FIG. 2), different filter retainer 
means may be utilized. This different retainer means is retainer means 23 
shown in FIG. 5. Retainer means 23 jointly holds both interior filter 17 
and external filter 18 at the same time. Retainer 23 comprises pieces 24 
through 27 that are molded out of a thermoplastic, or are made out of 
metal. Piece 24 is a rectangular, or other suitable shape, frame having a 
number of central area holes or rib pieces alike snap-in retainer 19 and 
that serve the same purpose, and having a number of protrusions 25 around 
its edge as shown. Piece 26 is another rectangular, or other suitable 
shape, frame having the same dimensions as frame 24 and may also have 
holes or rib elements but having number of holes 27 therethrough instead 
of protrusions 25. The holes 27 are located around the edge of frame piece 
26 in exact registration with protrusions 25 around the edge of frame 
piece 24. In manufacture mask shell 11 has a number of holes 28 made 
therethrough that are equal in number to the number of protrusions 25 and 
are of the same diameter as holes 27. These extra holes 28 through mask 
shell 11 surround holes 12 through which inhaled air passes. The outer 
dimensions of the edges of filter 17 and 18 are such that they just fit 
within protrusions 25. Alternatively, filters 17 and 18 may have the same 
outer edge dimensions as frame pieces 24 and 26. When this is the case 
there are a number of holes (not shown) through filters 17 and 18 around 
their edges. The diameter of these holes is the same as holes 27 and they 
are in the same positions. 
On assembly of filter retainer 23 to mask shell 11 with filters that have 
no holes through them, external filter 18 is laid on the ribs of frame 
piece 24 between protrusions 25. The protrusions 25 are then inserted from 
the front of mask 10 through the corresponding holes around the holes 12 
to the inside of mask shell 11. Frame piece 26 is then placed in the 
inside of mask shell 11 so that the portions of protrusions 25 extending 
to the inside of mask shell 11 pass through its holes 27. Retainer clips 
29 are then placed on each protrusion 25 and pressed on to pinch mask 
shell 11 and filters 17 and 18 between frame pieces 24 and 26 as shown in 
FIG. 5. The ribs of frame pieces 24 and 26 hold filters 17 and 18 up 
against holes 12 through which inhaled air passes. 
When filters 17 and 18 have holes around their periphery external filter 18 
is first assembled to frame piece 24 so that protrusions 25 pass through 
the holes. After frame piece 24 is assembled to mask shell 11 as described 
in the last paragraph, the inner filter 17 is assembled so the protrusions 
25 pass through the holes around its periphery. The frame piece 26 and 
clips 29 are assembled as described in the last paragraph. It would be 
obvious that one skilled in the art can devise many different ways of 
jointly retaining inner and outer filters 17 and 18 to mask shell 11 so 
that inhaled air cannot pass around the edges of the liners. 
In FIG. 6 is shown an exemplary filter 17 or 18 that is a multilayer filter 
liner. This exemplary multilayer filter has a first layer 29 of a fibrous 
material used for filtering dust and mist form inhaled air. The second 
layer 30 is a fibrous material that is impregnated with activated charcoal 
or other chemicals for absorbing noxious or poisonous gasses and mists and 
airborne particulate matter. Such a material is available from Extraction 
Systems, Norwood, Massachusetts. A net like material forms the third layer 
31. Layer 31 is that layer of inner filter 17 which faces the inside of 
mask shell 11, or is that layer of filter 18 that is seen on the outside 
of mask 10 and are provided for aesthetic appearance only. Layer 31 may be 
"Delnet", a non-woven, porous net material manufactured by the Hercules 
Corporation. 
In FIG. 7 is shown an alternative embodiment of the invention in which the 
snap-in retainer 19 or combination retainer 23 previously described are 
not utilized. Rather, provision is made to removably attach an external 
filter 18 by means of a self adhesive strip 32 attached to the edge. To 
implement this embodiment a flat, rectangular, oval or other plastic 
mounting piece 33 is attached to the front of mask shell 11 as shown in 
FIG. 7. The purpose of mounting piece 33 is to provide a base to which a 
self adhesive filter 18 may be attached. Mounting piece 33 surrounds holes 
12 through which inhaled air passes and it may be attached by 
thermobonding, adhesive bonding or by some other technique. The wearer of 
mask 10 takes a replacement external filter 18 that has a self adhesive 
strip fastened around the edge thereof and peels off an easy release 
protective cover strip (not shown) that is well known in the pressure 
sensitive self adhesive art. Filter 18 is then placed on mounting piece 33 
so that the self adhesive strip fastens filter 18 thereto. When it is time 
to replace filter 18 the edge thereof is grasped and it is peeled from 
mounting piece 33. A new self adhesive filter 18 is then affixed to 
mounting piece 33. In an alternative embodiment of the invention mounting 
piece 33 is fastened to the inside of foam mask shell 11 and self adhesive 
filter are attached therto inside of the mask rather than on the outside. 
Where needed, a mounting piece 33 may be fastened to both the inside and 
the outside of foam mask shell 11 and self adhesive filters 17 and 18 may 
be attached to both mounting pieces 33. In this manner mask 10 may be used 
to provide filtering against selective combinations of noxious and 
poisonous gasses, dusts and mists. 
In an alternative embodiment filters 17 and/or 18 may be filter cartridges 
of types known in the art. In yet another embodiment filter 17 and/or 18 
may be permanently and directly mounted against foam mask shell 11 
covering all holes 12 by a variety of techniques well known in the art. 
In FIG. 8 is shown an embodiment of the invention that has a foam mask 
shell 11. At least one larger hole 37 is punched through shell 11 and a 
collar 38 is thermobonded, friction snap-fit or adhesive bonded through 
the wall of mask shell 11 in hole 37. Alternatively, large hole 37 may be 
substituted with a permeable formed cavity suitably shaped to accept a 
filter cartridge. For example, by having a plurality of holes for flow of 
air therethrough. Walls of such a formed cavity may have a straight or a 
corrugated (bellows like) shape. Alternatively, there may be two holes or 
cavities 37 and two collars 38, but only one is shown in FIG. 8 for ease 
of representation. Collar 38 may be of cylindrical or other shape and a 
passage or hole 39 through it is used to mount a replaceable cartridge 
filter 40 of the type well known in the art. Cartridge filter 40 has an 
extension 41 having, in essence, an outside dimension approximately equal 
to the inside dimension of the cylindrical passage 39 through collar 38. 
To mount cartridge filter 40 its extension 41 is inserted into passage 39 
where it makes a relatively tight friction fit that retains filter 40 
therein. In addition, no unfiltered air can pass through this joint. To 
replace a cartridge filter 40 it is grasped and twisted back and forth 
while pulling it away from mask shell 11. When it is removed a new filter 
cartridge 40 is installed. There are many different types of filter 
cartridges that may be interchanged to use mask 10 in FIG. 8 in many types 
of environments. Alternatively, filter cartridge 40 may be attached to 
mask shell 11 in a permanent manner by a variety of methods well known in 
the art. This foam shell mask is then a replacement for the more 
conventional type of "gas mask" except that it is less expensive, much 
lighter and is more comfortable to wear. Being less expensive, such masks 
will not be shared with the attendant problems of mask care and 
communicable disease concerns described in the Summary of the Invention. 
While what has been described hereinabove are the preferred embodiments of 
the invention, it will be obvious to those skilled in the art that 
numerous changes may be made without departing from the spirit and scope 
of the invention. For example elastic straps 13 and 14 may be attached to 
mask shell 11 by passing them through holes in rim 15 of the mask.