Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02260066 1999-O1-08
Particle Filter in the Form of a Pleated Non-woven Layer
The invention relates to a particle filter in the form of a pleated non-woven
layer. Filters of the generic type are used for instance as ambient air
filters,
and in particular as motor vehicle interior filters. During the manufacture of
filters of the generic type, a material disposed in layers is pleated, i.e. it
is
arranged in concertina-type pleats, the distance of these pleats from each
other being customarily fixed by a marginal strip glued on or by clamping
in a frame. A filter of this design is then itself inserted for replacement in
a
filter frame.
Conventionally, various designs are available for the filtration of motor
vehicle interior air:
On the one hand non-woven staple fibers are known, the pleatability of
which is attained by a meshed support sheet for example of polypropylene.
On the other hand there are so-called meltblowns which are placed on
spunbonded fabrics or paper carriers and are united with same by ultrasonic
spots or hot-melt adhesive spots.
The only type of filter which, in this field, does without any supporting
layer is the so-called grit mat which is however flat and non-pleated or
non-pleatable when inserted into the filter receptacle.
All the filter materials that have to be pleated have in common that they
must exhibit a certain rigidity of their own in order for them to maintain
their pleated design when employed in practice, which is why convention-
CONFIRMATION COPY
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ally these non-wovens are laminated, i.e. they are combined with support
layers.
The meltblowns and non-woven staple fibers mentioned either have too
little substance or they are too soft to ensure by themselves proper and du-
rable pleating.
Using support layers results in that, in as much as the cost ef~'ectiveness
ratio is concerned, the costs of a spunbonded fabric for meltblown support
can amount to as much as 70 % of the total cost of the composite. The costs
of a meshed sheet for the support of non-woven staple fibers amount to as
much as 20 %, the total cost being considerably higher than in the case of
the design mentioned above.
The support components are of use exclusively in the sense of mechanical
stabilization, whereas they are substantially useless from the point of view
of filtering technology. Spunbonded fabrics only can retain particles in the
range of > 5 p.m, which is why they are designated as prefilters. However,
particles of this size deposit before reaching the heating or conditioning
chamber for instance of a motor vehicle. Furthermore, a serious drawback
resides in that any addition of non-woven or meshed sheet is always ac-
companied with an increased pressure drop of the entire laminated com-
posite, which may amount to as much as 30 %.
This is an important aspect since today's motor vehicles have an accurately
calculated energy distribution system. Only restricted quantities of energy
are available to the range of heating/venting/conditioning. The costs of ve-
hicle components are allowed to range only within a close compass. On the
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other hand the demands of motor vehicle buyers for equipment conven-
ience and safety are getting higher and higher. From these aspects, particle
filters of as low a pressure drop as possible are of special importance, low
pressure implying a ventilated motor of small dimensions and, therefore,
correspondingly low energy consumption. Furthermore, low differential
pressure also means little noise of the fan for the throughput of certain
quantities of air in the vehicle and consequently increased convenience of
driving.
The demand for filter systems of low differential pressure competes with
the requested filtration capacity and requested service life, i.e. the time in
terms of mileage, for which a filter may remain in a vehicle before it must
be replaced.
Pollen filters which only filter pollen from the air streaming into a vehicle
are of little help to allergic persons. The allergens which the immune sys-
tem of these persons reacts to are proteins, the diameter of which is only a
fraction of the pollen diameter. They are in the range of 0.1 Vim, i.e. in the
most problematic range for particle filters, the so-called MPPS (most pene-
tracing particle size). Consequently, solutions that are to be of some use to
allergic persons must have a filtration capacity of at least 50 %, this filtra-
tion capacity being measured by means of an aerosol, the particles of which
have approximately the same density, for example NaCI. Incorporating fil-
ters of this type in motor vehicles is intended to attain a service life of
30,000 kilometers.
In theory it would be possible to produce non-woven staple fiber and melt-
blown fabrics in such a way that they have sufficient rigidity of their own,
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thus being pleatable. However, it must be taken into consideration that for
non-woven
staple fiber fabrics stabilization takes place either thermally or by binders,
it being
necessary in the former case to accept a comparatively high differential
pressure and
in the latter case to accept very high emission rates. On the other hand, in
order for
meltblown fabrics to be rendered sufficiently stable to be used for instance
in a motor
vehicle interior filter box, a grammage or weight per unit area of more than
130 g/m2
would have to be attained. The diameter of a meltblown fiber is in the range
of
approximately 2pm. Given the grammage and fiber diameter, a non-acceptable
differential pressure has to be expected.
It is an object of the invention to embody a filter arrangement of the type
mentioned
at the outset so that it will combine cost-efficient producibility and
processibility with
a low differential pressure and a long service life.
According to the invention, this object is attained by a single-layer, self
supporting
micro-spunbonded fabric being used as a non-woven material, the grammage
(weight
per unit area) of which ranges from 70 g/m2 to 200 g/m2, preferably from 110
to 150
g/mz, the thickness from 0.7 to 1.5 mm and the fiber thickness from 2 to 20~.m
with
an average fiber thickness of 3 to S~.m.
By advantage, it is provided that the non-woven material has a higher fiber
density on
the flow-off side than on the flow-in side, and that the non-woven material is
a pure-
grade fabric made from PP (polypropylene) or PES (polyester) or PC
(polycarbonate).
The invention also, but not exclusively, relates to the use of a filter
arrangement of
this type as a filter, in particular for motor vehicle interior air.
Details of the invention will become apparent from the ensuing description, in
conjunction with the drawings, in which:
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FIG. 1 is a diagrammatic illustration of the principle of formation of varying
fiber
thicknesses in the case of spun-bonded fibers manufactured according to the
micro
spunbonding method;
FIG. 2 is a diagrammatic illustration of the fiber arrangement in the non-
woven on the
flow-off side;
FIG. 3 is a diagrammatic illustration of the fiber arrangement in the non-
woven on the
flow-in side; and
FIG. 4 is a diagrammatic perspective illustration of a filter arrangement
comprising a
pleated non-woven according to the invention in a frame.
FIG. 1 illustrates the fiber arrangement as created during the spunbonding
process
and as utilized for the filter arrangement according to the invention. It is
to be seen
that on the one hand a "core" of thick fibers of a thickness of 10 to 33 gm is
provided
and that on the other hand individual salient fiber ends only have a thickness
of 1 to 3
Vim.
The manufacture of a micro-spunbonded fabric of the type under regard is
described
in detail in DE 41 23 122 A1. Surprisingly, it has been found that, while the
requested
parameters are observed, a manufacturing technique of this type will create a
non-
woven layer which, even without lining and without a supporting layer, will
have a
sufficient rigidity of its own for it to be pleated. A special advantage
resides in that
the inherent rigidity is virtually isotropic, i.e. the same flexural rigidity
is attained in
every direction of the non-woven. This may be due to the fact that on the one
hand a
non-woven layer of the type under regard has a fiber thickness of 3 to 5 ~.m,
which
conditions the excellent filter properties, but on the other hand also thicker
fibers of
up to 20 pm are available which form a type of a natural support structure
without, as
opposed to the lined support layers of the prior art, negatively affecting the
filter
properties, in particular in the sense of an increase of the differential
pressure.
Especially favorable properties can be attained by subsequent ultrasonic
treatment
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and calendering. The lower fiber density and higher roughness on the flow-in
side
help attain that arriving particles are reliably retained, whereas the higher
fiber
density and lower roughness on the flow-off side ensure that no particles
reach the
range of the filtered air. In the manufacturing process which is typical for
micro-
spunbonded fabrics, this design can be put into practice in that the side of
the non-
woven on which the non-woven is deposited during manufacture is employed as a
flow-off side when the fabric is inserted in the filter.
Details of the invention will become apparent from the ensuing description of
a
preferred embodiment as compared to background art filter material. Such a
prior art
filter material is commercially available for instance under the trademark
HeIsatech
8504.
Backt~a-ound Art Exemplary Embodiment
C~rammage in g/m2: 100 130
Thickness in mm: 0.8 1.0
Fiber thickness in stn: approx. 3 2 - 20 (higher fiber
thicknesses are obtained
by fiber bunching)
Fiber orientation: random lengthwise of the sheet
on the flow-off side,
random on the flow-in
side
Fiber structure: three-layer laminate, progressive:
varying fiber density high fiber density on
of the individual flow-off side, low fiber
layers density on flow-in side
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Fiber material: PP/PES PP
Flexural rigidity:
(Schlenker process,
DIN 53864) in cN/cm= lengthwise 9.6 lengthwise=crosswise 26.7
crosswise 12.2
The fibers are comparatively hot when deposited under pressure so that
they bond together and a rigid pleatable mat originates.
Series Material Micro-Spunbond
Comparison Measurements Background Art acc. to Example
Pressure drop at 3.8 m3/min 60 Pa 40 Pa
(flow-in surface 0.06 m2)
Filtration capacity using NaCI 50 % 50
with 0.3 - 0.5 ~m of particle diameter
Pressure drop at a volume flow 300 Pa 80 Pa
of 3.8 m'/min (flow-in surface 0.06 m2)
after aging on an aging test distance,
actuated by 50,000 m3 of road air
on a much-used road
Fogging value (condensate value) < 5 mg/g < 0.5 mg/g
Combustion rate acc, to MVSS 302 30 mm/min no combustion
(DIN 75200)
Number of layers in 3 1
the filtering medium
Material components PP / PES PP
Operating temperature -40 - 100°C -40 - 100°C
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As opposed to a prior art filter, a filter according to the invention excels
additionally
by an improved service life without the filtration capacity being affected.
A comparison of FIGS. 2 and 3 shows that the fibers are aligned lengthwise on
the
flow-off side, correspondingly having a comparatively high fiber density,
whereas
FIG. 3 shows that the fibers are deposited randomly on the flow-in side,
correspondingly having a Iow density.
FIG. 4 illustrates a filter arrangement with a pleated non-woven material 1,
the
pleating, i.e the folding of the non-woven material, being roughly outlined by
a lateral
dashed line. The pleated non-woven material 1 is fixed in a frame 2, which has
lengthwise sides 3 and narrow sides 4, and consists of the same plastic
material as the
non-woven material 1 so that only pure-grade plastic material has to be
handled
during waste disposal.
The non-woven pleated layer is located in a flat filter box with pleat heights
ranging
from 10 mm to 100 mm. Preferably, the fibers of the non-woven layer are curled
and
random on the flow-in side, and are placed in substantially lengthwise
alignment on
the flow-off side. The structure should be such that an initial pressure loss
is less than
50 Pa at a velocity of flow through the filter arrangement of less than 250
m3/min/m2.
