Filter element

A filter element for use in a filter holder having a sealing surface and method of making a filter. The filter being made of a folded material of manufacture having a circumferential sealing rim and having a spacer to keep open the folded areas. The spaced being formed by at least one cover layer folded with the filter. The sealing rim being formed to be received in the sealing surface and with the folds formed by at least one cover layer and the filter material both along and transverse to the folds around the circumference of the at least one cover layer and filter material being pressed into said sealing rim at a temperature above the softening temperature of at least a thermoplastic resin provided in at least one of the layers of the cover and filter material.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The innovation relates to a filter element and more particularly to a 
filter element of the type using parallely folded filter material. 
2. Background Information 
Filter elements of such a type using parallely folded filter material are 
used as replaceable units for insertion in capsules or cartridges of 
respirator face pieces. These filter elements consist of a glass fiber 
fleece as the filter material which is arranged in parallel folds in the 
fashion of an accordion. In order to keep the folds open, i.e. to prevent 
the individual layers of the folds from lying one on top of the other 
during breathing, either thin beads of adhesive or wax which extend in a 
direction transverse to the folds are applied, with the adhesive materials 
penetrating into interspaces between the folds and keeping the folds open 
after having hardened, or the predetermined distance between the folds is 
fixed by a seam with a thick yarn or like measures. 
The outer circumference of the filter element is then provided with a 
form-defining rim which is e.g. made by inserting the filter material, 
which is arranged and fixed in folds, into a cartridge and by inserting a 
wax layer between filter and cartridge in a centrifugal process. Apart 
from the fact that the known filter element is difficult to make and 
rather expensive, the folds of the filter element have sharp filter 
material bends at which the risk arises that the filter material is 
weakened or even destroyed by mechanical impact, whereby the filter 
element becomes useless. 
Another filter element for respirator face pieces comprises a plurality of 
circular flat layers of filter material which are interconnected along 
their outer circumferences by the application of heat and pressure. A 
predetermined number of filter material layers respectively form the upper 
side and lower side of an envelope which surrounds an inner space provided 
with a spacer. The spacer may be in the form of a padding and has a 
relatively small flow resistance. The interior communicates with a 
breather tube of air-impermeable material which is detachably coupled with 
an adapter arranged on a molded mask body of a respirator face piece. 
Hence, air is sucked through the breather tube from the interior which is 
kept open by the spacer, and into which air is again sucked through the 
filter layers of the filter element. Hence, the known filter element 
cannot be inserted into a capsule in a direct manner. Moreover, the filter 
surface is relatively small. 
U.S. Pat. No. 4,678,578 discloses a filter element which can replaceably be 
inserted into a filter housing. This filter element, however, is not used 
for respiratory face pieces with an intermittent suction, but in 
industrial filters for filtering continuous flows in the pharmaceutical, 
cosmetic, photographic, biochemical or other industries. This filter 
element includes a folded filter element whose folds are kept open by 
cover layers. Filter material, cover layer and optionally the envelopes 
have, however, to be embedded in a compact extruded or punched frame of a 
plastic material, which increases the costs of the filter element. 
SUMMARY OF THE INVENTION 
The object of the present innovation is thus to provide a filter element 
which is inexpensive and functions in a reliable manner. 
On account of the innovative design of the present invention, folding of 
the filter material will no longer create sharp bends at which damage 
might occur. Moreover, the filter material proper is protected against 
such damage by the superimposed cover layers and the envelope. Another 
advantage is the very inexpensive production because the troublesome 
application of adhesive or the like is no longer necessary. Nevertheless, 
the folds of the filter material are kept open in an extremely efficient 
manner. The innovative filter element can be inserted immediately and 
directly and optionally without an intermediate layer of a sealing ring 
into the respirator face piece with its sealing rim which is sufficiently 
rigid due to the special manufacture and also sufficiently flexible for 
sealing purposes. 
A filter element for a respirator face piece having a sealing recess, 
comprising, a planar, parallely folded, filter material, a spacer for 
keeping open the folds and, a form-defining outer rim, and wherein the 
spacer is formed by two cover layers, which cover the entire surface of 
the filter material on both sides thereof and are folded together with the 
filter material so that each cover layer contacts itself in neighboring 
folds, and that the form-defining rim is formed as a sealing rim for being 
inserted into the sealing recess and with the filter element formed by 
thermal pressing the cover layers and the filter material at a temperature 
above the softening temperature of at least a thermoplastic resin provided 
in the layers. In a particular embodiment, the cover layers are formed of 
an open net material. 
An embodiment of the invention shall now be explained in more detail with 
reference to the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a filter element 1 which is circular when viewed from above 
and which has a lenticular cross-section and is designed for replaceable 
insertion into a cartridge or filter capsule of a respirator face piece, 
in particular a half mask. The filter element 1 has a planar filter 
material 2 which is drawn in an unbroken black line. The filter material 2 
is covered at both sides by respective cover layers 3a and 3b, 
substantially over its whole surface. The filter material 2 and the cover 
layers 3a and 3b are then arranged in parallel folds 4 in the manner 
illustrated in FIG. 1 in the fashion of an accordion in such a way that 
the cover layers 3a and 3b are adjacent each other in neighboring folds 4. 
The cover layers 3a and 3b act as spacers which keeps the neighboring and 
parallel portions 4a and 4b of the filter material 2 apart, i.e., at a 
distance which permits the unhindered entry of air onto the whole surface 
of the filter material 2. Moreover, the internal cover layer 3a and 3b 
respectively within every fold prevents the filter material 2 from 
terminating in the apex of fold 4 in a sharp bend. The folds 4 are thus 
smoothly rounded and loose, so that mechanical damage to the filter 
material 2 is largely prevented. 
The unit of filter material 2 and cover layers 3a and 3b is surrounded by 
an envelope 5 which respectively consists of an upper circular material 
piece and a lower circular material piece. 
The components of the filter element 1 are held together by a form-defining 
rim 6 in which the two material pieces of the envelope 5, the two cover 
layers 3a and 3b and the filter material 2 are firmly interconnected over 
the whole circumference of the filter element 1. 
Rim 6 extends over the whole circumference and is designed as a sealing rim 
of sufficient width, strength and stiffness, so that, as can be seen in 
FIG. 2, it can be snapped or inserted into a receiving recess 7 of a 
cartridge or capsule 8 of rigid plastic or the like and effectively 
inhibits the passage of air across the receiving recess 7. Any additional 
measures for sealingly receiving a replaceable filter element will 
normally not become necessary owing to this design. It is, however, 
possible to additionally use sealing ring of foamed plastic or to 
additionally secure rim by bonding, in particular by heat sealing or 
ultrasonic welding, in capsule 8. The open side 8a of capsule 8 
communicates either directly or via one of the known inhalation valves 
with the interior of the respirator face piece. 
A melt-blown polypropylene fleece (MBPP) which is inserted in one or 
several layers is especially suited as a filter material. A wide-meshed 
thin net which is much more permeable and relatively thick in comparison 
with the filter material 2 is used for the cover layers 3a, 3b. The net 
which is used for the cover layers 3a, 3b consists expediently of 
polypropylene. A crimped fiber fleece of polypropylene fiber mixture may 
be used for envelope 5, which fiber fleece contains fibers of different 
fiber cross-sections and of different melting points, such as PP fibers 
having two different melting points or PP mixed with a melt fiber based on 
acryl or PVC. However, a plastic grid or the like may be used for the 
envelope 5. 
If the rim 6 is to be used as a sealing rim, it must be of a uniform 
thickness. This is accomplished by molding rim 6 in a thermopressing 
operation in which it is ensured by a correspondingly high pressure and 
corresponding temperatures that rim 6 has a uniform thickness all around 
the filter element (in a direction transverse to or along the folds) 
despite different material amounts. At the same time, the distance between 
the filter folds is not changed owing to the relative stability of the 
cover layer nets, which guarantees excellent performance of the filter 
element. 
To improve the stability of the sealing rim 6, the sealing rim 6 is 
provided with the embossment 9 shown in FIG. 1. Embossment 9 has the shape 
of a step which separates a first portion 6a of sealing rim 6 that is 
positioned in the center plane of filter element 1 from an off-center 
portion 6b, with the angle of slope of step 9 and the size of the 
off-center portion 6b being matched to the degree of the necessary 
stiffness of the sealing rim. The sealing rim 6 must be stiffer for a thin 
filter material and/or small folds than for a thicker filter material or 
higher folds in the case of which it might be enough to provide the step 
in a substantially vertical direction, and to dispense with the second 
portion 6b. 
To manufacture the filter element, webs of the net for the cover layers and 
the necessary layers of filter material are first superimposed in the 
desired sequence. The filter material is subsequently arranged in folds of 
the desired height together with the web layers resting thereon at both 
sides. The size of the webs should expediently be chosen such that the 
width in the finish-folded state in a direction transverse to the folds 
corresponds approximately to the diameter of the finished filter element 
including sealing rim; the length, however, is several times said 
diameter, so that a plurality of filter elements can be obtained from each 
web. 
The folded webs are subsequently supported in a direction transverse to the 
folds, so that the folds do not burst open, and are guided through a 
thermopressing tool, with a smooth layer of the material of the envelope 
being placed at both sides of the folded layers prior to the 
thermopressing operation, if desired. The plastic material is softened in 
the thermopressing tool in the area of sealing rim 6 at least to such an 
extent that upon the application of pressure and under compensation of 
different material amounts it can be pressed into a compact sealing rim 
which is stiffened by a step and of uniform thickness and width over its 
whole circumference. The filter element is subsequently either punched out 
or cut out, the future position of the step being defined by the position 
of the cut. 
The novel filter element of the present invention in which the folds of the 
filter material are kept open by cover layers offers a greatly reduced 
breathing resistance in comparison with a filter material that has only 
been folded, and is thus much more comfortable for the wearer. The 
differences in breathing resistance are shown in Table 1. 
TABLE 1 
______________________________________ 
Distance given between the Folds 
Number Filter 
Test Contact 
Breathing 
Filter of Surface 
Surface 
Flow Vol. 
Resist. 
Material 
Layers Shape cm.sup.2 
cm.sup.2 
l/min PA 
______________________________________ 
MBPP 1 Folds 900 100 95 610 
MBPP + 1 Folds 900 100 95 77 
Cover 
______________________________________ 
"Number of layers" means the number of layers of the filter material in 
this table and in the following tables, "filter surface" means the active 
surface of the filter material and "test surface" is the cross-sectional 
surface of the filter element 1 in a top view on FIG. 1. 
The degree of passage for harmful substances can be reduced by increasing 
the number of layers of the filter material. However, as shown in Table 2, 
the resistance increases in such a case. 
TABLE 2 
______________________________________ 
Efficiency of a Filter Element, 
Folded with Cover Layers 
Contact Degree 
Number Filter Test Flow Breathing 
of 
Filter of Surface Surface 
Vol Resist. 
Pass. 
Material 
Layers cm.sup.2 
cm.sup.2 
l/min PA NaCL % 
______________________________________ 
MBPP + 1 900 100 95 77 0.63 
Cover 
MBPP + 2 900 100 95 148 0.06 
Cover 
MBPP + 3 900 100 95 258 0.002 
Cover 
______________________________________ 
It has been found that it is of great importance to the design of the 
filter element to determine the combinational ratio between the height and 
the number of folds for achieving maximum efficiency. When the filter 
surface is increased by increasing the height or the number of folds, the 
performance of the filter element deteriorates from a specific 
combinational magnitude onwards. This will become clearly apparent in the 
following Tables 3 and 4 through the increase in resistance at the same 
deposition performance. 
TABLE 3 
______________________________________ 
Test Contact Breathing 
Degree 
Number of 
Height of 
Surface Flow Vol. 
Resistance 
of Passage 
Folds Folds cm.sup.2 
l/min PA NACL % 
______________________________________ 
5 3.5 cm 50 47.5 235 0.01 
10 3.5 cm 50 47.5 346 0.002 
15 3.5 cm 50 47.5 768 0.002 
______________________________________ 
TABLE 4 
______________________________________ 
Test Contact Breathing 
Degree 
Number of 
Height of 
Surface Flow Vol. 
Resistance 
of Passage 
Folds Folds cm.sup.2 
l/min PA NACL % 
______________________________________ 
5 2.5 cm 50 47.5 195 0.03 
10 2.5 cm 50 47.5 260 0.002 
15 2.5 cm 50 47.5 380 0.002 
______________________________________ 
In a modification of the embodiment depicted and illustrated above, the 
filter element may also be shaped in different ways. The reinforcement on 
the sealing rim need not necessarily be a step, but may also be in the 
form of a bead, a circumferential rib or the like. With a corresponding 
material available in the area of the sealing rim, the latter may also be 
designed as a simple circumferential flange. Instead of the webs for the 
cover layers, a crimped fiber fleece with a low breathing resistance may 
be used. Instead of polypropylene, other thermoplastic materials may be 
used. The filter material may also be chosen in response to the respective 
requirements. 
Although the invention has been described with reference to a particular 
embodiment, it is to be appreciated that various adaptations and 
modifications may be made and the invention is only to be limited by the 
appended claims.