U.S. patent application number 12/096887 was filed with the patent office on 2009-08-27 for vacuum cleaner filter bag.
This patent application is currently assigned to Eurofilters Holding N.V.. Invention is credited to Ralf Sauer, Jan Schultink.
Application Number | 20090211211 12/096887 |
Document ID | / |
Family ID | 37836920 |
Filed Date | 2009-08-27 |
United States Patent
Application |
20090211211 |
Kind Code |
A1 |
Schultink; Jan ; et
al. |
August 27, 2009 |
Vacuum Cleaner Filter Bag
Abstract
The invention relates to a vacuum cleaner filter bag made of a
filter material, comprising at least three layers with at least two
layers of a non-woven or non-woven fabric layer, and at least one
layer of a fibre web layer of fibres and/or filaments, wherein the
at least two non-woven layers and the at least one fibre web layer
are connected to each other by a thermal bonding connection.
Inventors: |
Schultink; Jan; (Overpelt,
BE) ; Sauer; Ralf; (Overpelt, BE) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
Eurofilters Holding N.V.
|
Family ID: |
37836920 |
Appl. No.: |
12/096887 |
Filed: |
December 12, 2006 |
PCT Filed: |
December 12, 2006 |
PCT NO: |
PCT/EP2006/011945 |
371 Date: |
October 10, 2008 |
Current U.S.
Class: |
55/382 |
Current CPC
Class: |
B32B 29/02 20130101;
B32B 2317/12 20130101; B32B 5/26 20130101; B32B 2509/00 20130101;
D04H 13/00 20130101; B01D 39/163 20130101; B32B 2432/00 20130101;
B32B 2439/00 20130101; A47L 9/14 20130101; D04H 1/4291 20130101;
B32B 3/26 20130101; Y10S 55/02 20130101; Y10S 15/08 20130101; B32B
5/022 20130101; B32B 2310/028 20130101; D04H 1/559 20130101; D04H
1/555 20130101 |
Class at
Publication: |
55/382 |
International
Class: |
B01D 46/02 20060101
B01D046/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2005 |
DE |
10 2005 059 214.7 |
Sep 1, 2006 |
EP |
06018324.1 |
Claims
1. Vacuum cleaner filter bag of a filter material comprising at
least three layers with at least two layers of a non-woven or
non-woven fabric layer, and at least one layer of a fibre web layer
of fibres or filaments, wherein the at least two non-woven layers
and the at least one fibre web layer are connected to each other by
a thermal bonding connection.
2. Filter bag according to claim 1, wherein a pressing area
proportion of a thermal bonding pattern is maximally 5% of a
surface of an area of the filter bag through which a flow can pass,
and on average maximally 19 thermal bonding connections per 10
cm.sup.2 are present.
3. Filter bag according to claim 1, wherein an average total
porosity is at least 65%.
4. Filter bag according to claim 1, wherein an average median pore
diameter is at least 120 .mu.m.
5. Filter bag according to claim 1, wherein on average maximally 10
thermal bonding connections per 10 cm.sup.2 are present.
6. Filter bag according to claim 1, wherein the thermal bonding
connection has a star-shaped, punctiform, bar-shaped or linear
design.
7. Filter bag according to claim 1, wherein a pressing area
proportion of the thermal bonding pattern is maximally 2%.
8. Filter bag according to claim 1, wherein the fibres comprise a
form of staple fibres, and wherein the staple fibres comprise split
fibres or crimp fibres.
9. Filter bag according to claim 8, wherein the fibres have a
length of between 1 and 100 mm.
10. Filter bag according to claim 8, wherein the crimp fibres have
different spatial structures, comprising a zig-zag, wave or spiral
type.
11. Filter bag according to claim 8, wherein the crimp fibres
comprise a form of mechanically crimped fibres or autocrimp fibres
or bicomponent fibres.
12. Filter bag according to claim 8, wherein the fibres are
electrostatically charged.
13. Filter bag according to claim 8, wherein the staple fibres
comprise a form of natural or synthetic fibres.
14. Filter bag according to claim 1, wherein a mass per unit area
of the fibre web layer is between 10 and 200 g/m.sup.2.
15. Filter bag according to claim 1, wherein the fibre web layer
has a mass per unit area of at least 5 g/m.sup.2.
16. Filter bag according to claim 15, wherein the non-woven layer
is a scrim.
17. Filter bag according to claim 1, comprising two non-woven
layers between which the fibre web layer is arranged.
18. Filter bag according to claim 17, wherein at least one
non-woven layer comprises a fine filter spunbond fabric layer.
19. Filter bag according to claim 1, further comprising a fine
filter spunbond fabric layer.
20. Filter bag according to claim 19, wherein at least one
non-woven layer comprises a second fine filter spunbond fabric
layer and wherein the fine filter spunbond fabric layers comprise
different filter properties.
21. Filter bag according to claim 1, comprising a further layer
comprising paper, non-woven material or nanofibres.
Description
[0001] The present invention relates to a vacuum cleaner filter bag
with a filter medium comprising at least three layers, wherein at
least two layers consist of a non-woven or non-woven fabric layer,
respectively.
[0002] In recent years, numerous developments have become known
which deal with improving the one- or multi-layered vacuum cleaner
filter bags of paper or paper and tissue, respectively, which have
been known for a long time in prior art. EP 0 388 479 A1 of Gessner
& Co. GmbH describes vacuum cleaner filter bags with an outer
filter paper layer and a melt-spun microfibre non-woven (meltblown
non-woven).
[0003] Multi-layered filter bags of non-wovens (SMS) are disclosed,
for example, in U.S. Pat. No. 4,589,894 and in U.S. Pat. No.
5,647,881 of Minnesota Mining and Manufacturing Company (3M). These
inventions mainly deal with the improvement of dust recovery.
[0004] In EP 0 960 645 A1 and EP 1 258 277 A1 of Airflo Europe
N.V., combinations of non-woven layers are described which have a
particularly long service life and dust recovery capacity.
[0005] EP 1 362 627 A1 of Branofilter GmbH describes filter bags
with a multi-layered design where the fibre diameter distributions
in the coarse dust filter layer and in the fine dust filter layer
are different.
[0006] In EP 1 254 693 A2 of Carl Freudenberg K G, a vacuum cleaner
bag is described where a preliminary filter layer of a dry-laid,
electrostatically charged non-woven is provided in front of a
filter layer.
[0007] Furthermore, in EP 1 197 252 A1 of 3M Innovative Properties
Company, a filter medium of a film fibre non-woven is described
which consists of dry-laid, electrostatically charged fibrillated
fibres which are connected with each other by ultrasonic bonding to
achieve a sufficient strength of the non-woven. Here, it is
essential that there are at least two ultrasonic bond points per
cm.sup.2. Thereby, the individual fibres are connected with each
other by ultrasonic bonding connections. It is said to be an
advantage of such a filter medium that the manufacturing speed is
higher compared to that of needling the fibrous web with a scrim
and, as in this method the use of a scrim is not necessary,
additional air resistance caused by the scrim can be prevented.
Moreover, the film fibre non-woven can be connected to further
non-woven layers. EP 1 197 252 A1 further discloses to employ this
filter medium for air filters. However, the dust storage capacity
of this material is not sufficient for the application as filter
medium in a vacuum cleaner bag.
[0008] Based on the above mentioned prior art, the object of the
present invention is to provide a filter bag, the filter material
of which has a particularly low bulk density, as compared to those
described in prior art, to achieve a superior dust storage
capacity. The filter bag is furthermore said to have a design where
the structure and the associated advantageous properties of the
non-bonded fibre layer are maintained as far as possible.
[0009] This object is achieved by a vacuum cleaner filter bag made
of a filter material which comprises at least three layers with at
least two layers which consist of a non-woven layer, and at least
one layer which consists of a non-woven layer of fibres and/or
filaments, wherein the at least two non-woven layers and the at
least one fibre web layer are connected to each other by a thermal
bonding connection.
[0010] In this context, the terms fibre web and non-woven in the
field of the manufacture of non-wovens are defined and to be
understood in the sense of the present invention as follows. For
the manufacture of a non-woven, fibres and/or filaments are first
laid on a support. Methods of laying are known from prior art.
These laid, loose and yet unbound fibres and/or filaments are
referred to as fibre web (web). By a so-called non-woven bonding
step, finally a non-woven is formed of such a fibre web, the
non-woven having sufficient strength to be e.g. wound on reels.
This latter non-woven bonding step is thus not performed in the
manufacture of the fibre web layer of the invention, instead, the
fibre web is bonded to a non-woven layer or between two non-wovens.
(Details of the use of the above-mentioned definitions and the
above-described methods can be taken from the standard work
"Vliesstoffe", W. Albrecht, H. Fuchs, W. Kittelmann, Wiley-VCH,
2000.)
[0011] According to a preferred embodiment of the invention, there
are as little thermal bonding connections as possible, relating to
the complete area of the filter bag through which a flow can pass.
According to the present invention, this is achieved in that,
related to the complete area of the filter bag through which a flow
can pass, on average maximally 19 thermal bonding connections per
10 cm.sup.2 are present, preferably maximally 10 thermal bonding
connections and particularly preferred maximally 5 thermal bonding
connections. The pressing area proportion of the thermal bonding
pattern is maximally 5%, preferably maximally 2%, and particularly
preferred maximally 1% of the area of the filter bag through which
a flow can pass.
[0012] In an advantageous embodiment, the filter bag has the
additional feature of the average total porosity being at least
65%, preferably at least 80%, particularly preferred at least
95%.
[0013] In a further advantageous embodiment, the average median
pore diameter is at least 120 .mu.m, more preferred at least 150
.mu.m, even more preferred at least 180 .mu.m, and particularly
preferred at least 200 .mu.m. The average median means the
arithmetic average value of several measurements of the median of
the examined samples.
[0014] The measuring method for the determination of the average
total porosity and the average median pore diameter according to
the present invention is described more in detail with reference to
FIGS. 15 to 17.
[0015] Due to the fact that a low number of thermal bonding
connections is present, the thickness and thus the bulk of the
material are clearly increased with the same mass per unit area.
Due to the low bulk density of the compound, the material has a
high dust storage capacity.
[0016] With respect to the geometry, i.e. the distribution of the
thermal bonding connections across the area of the filter bag
through which a flow can pass, there are no restrictions for the
present invention, with the proviso that maximally 19 thermal
bonding connections per 10 cm.sup.2 are present, related to the
area of the filter bag through which a flow can pass. The thermal
bonding connections can, as a matter of principle, be evenly
distributed, i.e. at even distances, across the complete area or
else unevenly distributed. The invention thus also includes
embodiments where only in predetermined areas there is a higher
number of thermal bonding connections and where then larger free
areas are formed which are then separated from a next larger free
area by an increased number of thermal bonding connections. One
essential criterion always is that the given maximal number of
thermal bonding connections is not exceeded.
[0017] The thermal bonding connections themselves can have
different geometries. Thus, punctiform, linear, star-shaped or else
bar-shaped thermal bonding connections can be employed. With
respect to the precise embodiment of the thermal bonding
connections, apart from the number of thermal bonding connections
as limiting criterion, only the pressing area proportion of the
thermal bonding pattern has to be taken into consideration, which,
as already mentioned, is maximally 5%, preferably maximally 2%, and
particularly preferred maximally only 1%.
[0018] As to the fabric, the fibre web layer of the invention,
which is present as a compound with the non-woven layer, comprises
all fibres known per se in prior art, in particular staple fibres
and/or filaments. Staple fibres in the sense of the invention also
include fibrillated film fibres (split fibres) and crimp fibres;
here, the staple fibres in the sense of the invention can also be
preferably electrostatically charged.
[0019] As crimp fibres, in particular those proved to be
advantageous which have a spatial structure, such as a zig-zag,
wave and/or spiral structure. The advantage of such fibres is that
they clearly increase the bulk of the medium.
[0020] In this context, the crimp fibre can be a mechanically
crimped fibre, an autocrimp fibre and/or a bicomponent crimp fibre.
Autocrimp fibres are described e.g. in the EP patent 0 854 943 A1
as well as in PCT/GB00/02998. Bicomponent crimp fibres are
available e.g. from the Chisso Corporation in Japan, and crimped
spiral-type polyester staple fibres from Gepeco in the USA.
[0021] In the invention, staple fibres which are selected from
natural fibres and/or synthetic fibres can be employed. Examples of
synthetic fibres are in particular polyolefins and polyester.
Examples of natural fibres are cellulose, wood fibres, capoc,
flax.
[0022] With respect to the arrangement of the layers and the number
of layers, there are no restrictions for the filter bag in
accordance with the invention, with the proviso that at least two
layers each consist of a non-woven layer and at least one fibre web
layer, wherein these two layers are continuously connected to each
other by a thermal bonding, preferably by an ultrasonic bonding
connection, as described above.
[0023] The non-woven layer of the above described compound is
preferably a support or base layer and has a mass per unit area of
at least 5 g/m.sup.2. A scrim is advantageously used for the
non-woven layer itself. Here, a scrim means any not airtight
material which can serve as base or reinforcing layer. It can be a
non-woven, a woven material or a netting. Preferably, it consists
of a thermoplastic polymer to facilitate the ability of thermal
bonding with the fibre web layer.
[0024] Examples of scrims are spunbond fabrics. However, they can
also be dry- or wet-laid non-wovens which possess sufficient
mechanical stability. The mass per unit area of such a non-woven
layer is, according to the present invention, preferably between 10
and 200 g/m.sup.2, particularly preferred between 20 to 100
g/m.sup.2. The mass per unit area in g/m.sup.2 was determined in
conformity with DIN EN 29073-1. With respect to the mass per unit
area of the fibre web layer, it should be mentioned that the same
is to be determined indirectly by means of the compound of
non-woven layers and fibre web layer, as the determination of the
mass per unit area of the fibre web layer is not possible only on
the basis of its loose structure. The determination was therefore
effected by a subtraction method, i.e. the mass per unit area of
the complete compound, i.e. the compound of non-woven layers and
fibre web layer, was determined, and then the mass per unit area of
the non-woven layers, which can be determined separately, were
subtracted again.
[0025] The thickness of the above-described compound of non-woven
layer and fibre web layer is between 1 and 7 mm, preferably between
2 and 4 mm. The determination of the thickness was performed
according to EDANA 30.5-99, Item 4.2. The apparatus used was a VDM
01 which is available from Karl Schroder K G in Weinheim. As the
measurements according to methods 4.1, 4.2 or 4.3 lead to very
different results, the measurements of the inventive compounds,
i.e. composites, were principally performed according to method
4.2.
[0026] The filter bag according to the invention can naturally, as
described above, comprise further layers in addition to the
compound of the two non-woven layers and the fibre web layer.
Preferably, the filter bag according to the invention can
furthermore comprise further fine filter layers with different
filter properties as required. Here, fine filter spunbond fabric
layers are used as fine filter layers. Fine filter spunbond fabric
layers in the sense of the invention are corresponding layers which
are suited to separate fine particles. Conventional fine fibre
spunbond fabric layers are made according to the meltblowing
process, the flashspinning process or electrostatic spunbonding. As
regards contents, reference is made to the standard work
"Vliesstoffe" by W. Albrecht, H. Fuchs, W. Kittelmann, Wiley-VCH
2000, Chapter 4. In the sense of the invention, fine filter layers
can also consist of dry-laid non-woven of electrostatically charged
fibres.
[0027] The filter bag according to the invention is preferably
connected by a continuous ultrasonic bonding connection through all
layers, i.e. through the non-woven layers and the fibre web layer
as well as the further layers. The filter bag according to the
invention, however, also comprises embodiments where only thermal
bonding connections of the non-woven layers with the fibre web
layer are present, and the further layers are connected with the
compound of the non-woven layers and the fibre web layer either by
gluing or by another connection method.
[0028] The invention will be illustrated more in detail below with
reference to FIGS. 1 to 14.
[0029] FIGS. 1 to 9 schematically show in sections how the filter
material of the filter bag according to the invention can be
structured.
[0030] FIG. 1 shows a two-layered design of a layer 1 in the form
of a non-woven layer which is a scrim in FIG. 1. This scrim layer 1
is connected to a fibre web layer 2 by ultrasonic bonding
connections. In FIG. 1, the further layer required in accordance
with the invention is not depicted.
[0031] The structure of the design of the embodiment shown in FIG.
2 essentially corresponds to that of FIG. 1, however with an
additional layer of a fine filter medium 3, which in this case
represents the third layer. The preferred inflow side is designated
with arrows. In this case, the fine filter layer 3 consists e.g. of
a meltblown non-woven.
[0032] FIG. 3 in turn shows another example, based on FIG. 2, with
an additional protective layer 4 which is here arranged at the
outflow side. This protective layer 4 can be a scrim, preferably a
spunbond fabric.
[0033] The embodiment shown in FIG. 4 is of a layer of a non-woven
1 connected to a fibre web layer 2 attached thereto by thermal
bonding, as described above, here, however, a layer of a protective
non-woven 4 is additionally arranged in front at the inflow side.
The non-woven 1 here is in particular a meltblown non-woven.
[0034] FIG. 5 differs from FIG. 4 by an additional microfibre
non-woven layer 3 arranged at the outflow side.
[0035] The example of the structure according to the invention
shown in FIG. 6 starts from the design according to FIG. 5, then,
however, it has an additional protective layer 4 at the outflow
side.
[0036] FIG. 7 shows a laminate of two layers of non-woven 1
connected to each other by ultrasonic bonding points between which
the fibre web layer 2 is located.
[0037] FIG. 8 represents an embodiment of the structure according
to the invention based on FIG. 7, here, however, with a layer of a
filter medium 3 arranged at the outflow side.
[0038] FIG. 9 shows a structure based on FIG. 8 with an additional
layer 4 at the outflow side. In FIGS. 1 to 9 described above, the
respective structures are only described schematically according to
the sequence of layers. The above described structures are then
preferably connected by ultrasonic bonding connections.
[0039] In Tables 1 to 11 (FIGS. 10 to 12), the measuring results
which have been achieved by means of the above described
embodiments according to FIGS. 1, 3 and 4 are summarized, in
comparison to an embodiment according to EP 1 197 252 A1. In the
examples according to FIGS. 1, 3 and 4, a compound which comprises
0.2 thermal bonding points per cm.sup.2 was employed. In the
comparison examples, 2.5 thermal bonding points per cm.sup.2 were
selected. As can be taken from Tables 1 to 11, the materials
according to the invention are in particular characterized in that
they are thicker than the comparison materials by 15 to 42%. It
should be in particular pointed out that this leads to the bulk of
the materials according to the invention also being higher by a
corresponding amount, namely by 15 to 42%, than in the comparison
examples. Now, the superior effect of the materials according to
the invention is based on this extremely high bulk, the materials
thereby having an above-average dust storage capacity (also see
FIG. 14).
[0040] FIG. 13a now shows in the form of a 3D graphic how the low
number of thermal bonding points affects the structure of the
material. In FIG. 13a, a material is shown which corresponds to the
design according to FIG. 7, i.e. it is a material consisting of a
fibre web layer which is connected between two layers of spunbond
fabric by ultrasonic bonding connections. In the example according
to FIG. 13a, approx. 0.2 thermal bonding points per cm.sup.2 were
used. FIG. 13a illustrates the pad-like design leading to the high
bulk as described above. In the example according to FIG. 13a, as
fibre web layer 100% of split fibres of polypropylene have been
employed. The spunbond fabric also consists of polypropylene. The
design of the filter medium represented in FIG. 13b analogously
corresponds to that which has been already described in FIG. 13a,
however with the difference that here 2.5 thermal bonding points
per cm.sup.2 are present. This makes clear that by the design
according to the invention in the form of a small number of thermal
bonding connections, a clear advantage with respect to the bulk of
the material is achieved.
[0041] As is now represented in FIG. 14, the embodiment according
to the invention leads to a clear increase of the dust storage
capacity compared to the filter media as they are described in
prior art which comprise 2.5 thermal bonding points per cm.sup.2.
The measuring results represented in FIG. 14 have been performed as
follows:
[0042] Vacuum cleaner used: Miele Performance 2300 [0043] Typ: HS
05 [0044] Model: S749 [0045] No.: 71683038
[0046] Performance setting: Maximum
[0047] Size of filter bags: 295 mm.times.270 mm
[0048] Dust used for test: DMT Type 8
[0049] Test procedure: The dust bag to be tested is incorporated
into the apparatus after the apparatus has warmed up for 10
minutes. The flow rate without dust charge is read after a running
period of the apparatus of 1 min. Subsequently, the first dust
portion of 50 g is sucked in within 30 sec. After 1 min., the
present flow rate (in m.sup.3/h) is read. This step is
correspondingly repeated for the following dust additions, until
400 g of dust have been added.
[0050] Filter medium: Spunbond fabric 17 g/m.sup.2, fibre web 50
g/m.sup.2, [0051] Spunbond fabric 17 g/m.sup.2
[0052] Thermal bonding
[0053] pattern: 1. 2.5 points/cm.sup.2, evenly distributed [0054]
2. 0.2 points/cm.sup.2, evenly distributed
[0055] The measured values given in the examples were determined by
the following determination methods:
[0056] Thickness:
[0057] 30.5-99 Item 4.2 apparatus VDM 01, available from Karl
Schroder K G in Weinheim.
[0058] As the measurements according to methods 4.1, 4.2 or 4.3
lead to very different results, the measurements of the laminates
according to the invention were in principle performed according to
method 4.2 (for bulky nonwovens with a maximum thickness of 20
mm).
[0059] Mass per unit area [g/cm.sup.2]: DIN EN 29073-1
[0060] Bulk [cm.sup.3/g]:
[0061] Thickness (EDANA 30.5-99 Item 4.2)/mass per unit area (DIN
EN 29073-1)
[0062] Bulk density [g/cm.sup.3]:
[0063] Mass per unit area (DIN EN 29073-1)
[0064] Thickness (EDANA 30.5-99 Item 4.2)
[0065] In FIG. 15, the principle of measurement for the
determination of the average total porosity and the average median
pore diameter are schematically illustrated.
[0066] FIG. 16 shows a device which is employed for the
determination of the average total porosity and the average median
pore diameter.
[0067] Table 9 (FIG. 17) represents the measured values with
respect to the average total porosity and the average median pore
diameter.
[0068] The measured values were determined according to the method
given below.
[0069] To determine the average total porosity and the average
median pore diameter, the methodology of the extrusion of a wetting
liquid was used. The measurements were performed by means of a PMI
liquid extrusion porosimeter. Below, reference will be made to
FIGS. 15 and 16.
[0070] 1. Principle of Measurement
[0071] As the differential free surface energy of the system
wetting liquid 20/sample 12 is lower than the differential free
surface energy of the system air/sample 12, the pores of a sample
spontaneously fill with wetting liquid 20. The wetting liquid 20
can be removed from the pores by increasing the differential
pressure 22 of an inert gas 18 on the sample 12. It was shown that
the differential pressure 22 required to displace the wetting
liquid 20 from a pore is determined by the size of the pore
(Akshaya Jena, Krishna Gupta, "Characterization of Pore Structure
of Filtration Media", Fluid Particle Separation Journal, 2002, 4
(3), p. 227-241). The correlation between the differential pressure
22 of the inert gas 18 and the pore size is represented by equation
1.
p=4.gamma. cos .theta./D (1)
wherein p is the differential pressure 22 of an inert gas on the
sample, .gamma. is the surface tension of the wetting liquid 20,
.theta. is the contact angle of the wetting liquid 20 on the pore
surface, and D is the pore diameter the definition of which is
quoted for an irregular cross-section by the following equation
(2).
D=4(cross-sectional area)/(cross-sectional circumference) (2)
[0072] If the sample 12 is applied to a membrane 25 and the pores
of the sample 12 and the membrane 25 are filled with a wetting
liquid 20, the application of a pressure 23 on the sample 12 leads
to a displacement 23 of the liquid from the pores of the sample 12
and to a flowing out 24 of the liquid 20 through the membrane 25.
If the largest pore of the membrane 25 is smaller than the smallest
pore of interest of the sample 12, the liquid 20 is displaced from
the pores of interest of the sample 12 and will flow out of the
membrane 25, however, the pressure 22 will not be sufficient to
completely remove the liquid 20 from the pores of the membrane 25,
the gas will not be able to flow through the pores of the membrane
25 filled with liquid and out of the same. Thus, by means of the
differential pressure 22 and the flown-out volume of the liquid 20,
the diameter or the volume of the pores, respectively, can be
determined (A. Jena und K. Gupta, "A Novel Technique for Pore
Structure Characterization without the use of Any Toxic Material",
Nondestructive Characterization of Materials XI, Ed.: Robert E.
Green, Jr., B. Boro Djordjevic, Manfred P. Hentschel,
Springer-Verlag, 2002, p. 813-821).
[0073] 2. Experimental Setup
[0074] Basis of the PMI liquid extrusion porosimeter 5 (FIG. 16) is
the methodology of liquid extrusion. The sample chamber 6 of the
porosimeter 5 consists of a cylindric PVC container the diameter of
which is 45 mm and the depth of which is 45 mm. A relatively wide
meshed open netting 7 made of rust-resistant steel wire rests on a
strip at the bottom of the sample chamber 6. Underneath the netting
7, the sample chamber 6 is connected to the bottom side of a
cylindric acrylic vessel of which the diameter is 40 mm and the
depth is 40 mm, by means of a flexible tube 8 having a diameter of
only a few mm. The vessel 9 as well as its cover 10 are placed on a
pair of scales 11 (manufacturer: Mettler, weight resolution 0.0001
g). A cylindric inset 13 (40 mm diameter, 40 mm height) is placed
on the sample 12 within the sample chamber 6. The upper side of the
inset 13 comprises a notch for an O-ring 14. A pneumatically
operated device 15 which comprises a piston 16 guided in a cylinder
is mounted on the sample chamber 6. The piston 16 is hollow to
ensure a flow of the test gas 18 into the sample chamber 6. A flat
disk 17 of rust-resisting steel which is thermally bonded to the
bottom side of the piston 16 presses the inset 13 against the
O-ring 14 on the upper side of the inset 13 and thus prevents the
test gas 18 from escaping. The piston 16 is controlled
pneumatically. The test gas 18 and the gas 19 for operating the
piston 16 are supplied separately.
[0075] 3. Wetting Liquid
[0076] In all tests, Galwick, which is a perfluorinated polymer
(oxidized and polymerized 1,1,2,3,3,3-hexafluoropropene), was used
as wetting liquid. The liquid is inert, the surface tension is 16
Dynes/cm. Due to the very low surface tension of the test liquid,
the contact angle is near 0.degree. (Vibhor Gupta and A. K. Jena,
"Substitution of Alcohol in Porometers for Bubble Point
Determination", Advances in Filtration and Separation Technology,
American Filtration and Separation Society, 1999, 13b, p.
833-844).
[0077] 4. Test Gas
[0078] In all tests, dry and purified compressed air was used. To
remove solid particles, the air was filtered, the moisture was
removed by the standard drying methods known to the expert from
prior art.
[0079] 5. Automated Test Performance, Data Acquisition and
Management
[0080] The test performance, data acquisition as well as the data
reduction were performed in a completely automated manner by using
a computer and appropriate software. The test procedure was
performed automatically after the sample chamber 6 had been charged
with a sample 12, so that accurate and reproducible results could
be obtained.
[0081] 6. Test Procedure
[0082] a) Preparation of the Measuring Instrument
[0083] The sample chamber 6, the vessel 9 on the pair of scales 11,
the netting 7 at the bottom of the sample chamber 6 and the inset
13 were cleaned with alcohol to remove impurities. The O-rings 14
were also cleaned and greased. A Millipore membrane 25 with a
maximum pore diameter of 0.45 .mu.m was placed on the netting 7. It
has to be taken care that the membrane 25 is undamaged, i.e. that
it does not comprise any defects, cracks or other damages, as this
could otherwise lead to falsified measuring results. Now, wetting
liquid 20 which flows into the sample chamber 6 via the tube 8 was
put into the vessel 9. In the process, enough wetting liquid 20 was
added to reach a liquid level in the sample chamber 6, such that
the liquid 20 just covers the netting 7. This ensures a complete
wetting of the membrane. After a certain period, a constancy of the
indication of the scales 11 was reached, indicating that a
stationary state was reached.
[0084] b) Preparation of the Samples
[0085] For the measurement, filter bags were used which were made
of a filter bag material consisting of a compound of a fibre web
layer enclosed between two non-woven layers. The non-woven layers
(spunbond layers) are formed of polypropylene fibres. The fibre web
layer consists of polypropylene staple fibres (split fibres having
a length of 60 mm). The filter material is connected by point-like
thermal bonding connections which are introduced by means of
ultrasonic bonding. Three samples were examined which had different
numbers of thermal bonding points, namely 16, 70 and 95, in each
case related to 100 cm.sup.2, which are evenly distributed across
the surface. Then, circular samples 12 having a diameter of 45 mm
were punched out of the filter bags. The samples 12 were weighed
and the thickness was determined according to EDANA 30.5-99 Item
4.2 (cf. p. 8, 1. 3-13). It was difficult to make any statements
about the thickness which is due to the soft nature and the uneven
surface of the sample 12. The bulk density .rho..sub.b was
calculated. This bulk density corresponds to that of the dry
sample. The upper layer of the sample 12 was scratched with a knife
(Stanley knife). Each cut had a length of 10 mm and a width of 1
mm. To find out an adequate number of cuts, samples 12 having
different numbers of cuts were examined. Based on the results
obtained with these samples 12, it was found out that five cuts per
sample 12 are adequate; thus, all examinations were performed with
five cuts per sample 12. The five cuts were arranged analogously to
the arrangement of the points of a five on a dice.
[0086] c) Wetting and Charging of the Sample
[0087] The sample was placed into a vessel containing wetting
liquid 20. In the process, the sample 12 absorbed the wetting
liquid 20 and showed a tendency to swell. It was taken care that
the sample 12 was not completely immersed in the liquid 20 to avoid
inclusions of air in the sample 12. The wetted sample 12 was
subsequently placed on the membrane 25 within the sample chamber 6.
The O-ring 14 was placed on the sample 12 and the inset 13 on the
O-ring 14.
[0088] d) Performance of the Test
[0089] All information concerning the sample 12 including the
identification number were stored in a computer. The units as well
as the various functions to be measured were also entered.
Subsequently, the test was carried out.
[0090] The piston 16 was lowered by computer control to press the
inset 13 onto the O-ring 14. To avoid leakages, a predetermined
pressure was applied on the O-ring 14. The scales 11 were tared.
Subsequently, the test gas 18 was slowly introduced through the
piston 16 to the surface of the sample 12. The gas pressure 22 was
computer controlled, increased in small increments, thus an
adjustment of a balance of the system was achieved before the data
were recorded. The computer stored the data of the pressure and the
change of weight of the liquid by means of the scales 11. The
results were also graphically represented to follow the progress of
the test. To obtain the results at the end of the test, the data
were printed in various ways.
[0091] 7. Results
[0092] The measuring device 5 recorded the weight increase of the
wetting liquid 20 which was displaced from the sample 12 by means
of the scales 11 and converted the weight of the liquid 20 by means
of the density to the corresponding volume. This result represents
the cumulative pore volume. Equally, the pore diameter was
calculated from the gas pressure of the test gas 18 determined by
the measuring device 5, which test gas was used to displace the
wetting liquid 20 from the pores of the sample 12. Thus, the
cumulative pore volume could be recorded as function of the pore
diameter. The porosity P (in %) was calculated from the bulk
density Pb and the total pore volume V according to equation
(3).
P=(V.rho..sub.b).times.100 (3)
[0093] By means of the measuring device 5, the median pore diameter
could also be calculated. The median pore diameter is defined such
that 50% of the complete pore volume come from pores which are
larger than the mean pore, and 50% of the complete pore volume come
from pores which are smaller than the mean pore. The arithmetic
average of several measurements of the used samples is given in
Table 9 (FIG. 17) as average median pore diameter. As can be taken
from Table 9, the filter material of the bag according to the
invention has an extremely high average total porosity of up to
96.8%. With an increasing number of thermal bonding connections,
the total porosity then falls to a value of 67.4%. Correspondingly,
the average median pore diameter falls from 201.8 .mu.m to 129.1
.mu.m. As the results indicate, the filter bags according to the
invention have an extremely high porosity, which finally leads to
an above-average dust storage capacity.
[0094] 8. Discussion of the Measurement Method
[0095] In the measurement methodology used, the pore diameter and
the pore volume of a sample are calculated from the measured gas
pressure required to displace the wetting liquid from the pores, as
well as from the measured volume of the liquid displaced from the
pores. The pores in the non-woven layers (spunbond layers) of the
sample attached at the top and at the bottom are much smaller than
the pores of the fibre web layer in the central layer. From
equation 1 one can see that the gas pressure required to displace a
liquid from the layers placed at the top and at the bottom has to
be much higher than that which is required for the fibre web layer.
In the examination of the filter bags, a displacement of the liquid
20 from the pores of the central fibre web layer will not occur
before the liquid has been displaced from the pores of the spunbond
non-woven layer attached at the top. The high pressure required to
displace the liquid from the small pores of the spunbond non-woven
layer attached at the top will also displace liquid from the larger
pores of the central fibre web layer. Thus, the diameter of the
small pores of the spunbond non-woven layer attached at the top is
measured as the diameter of the pores in the fibre web layer as
central layer. The determined pore volume will be close to the pore
volume of the central layer as the volume of the small pores in the
very thin layers attached at the top and at the bottom is
negligible, compared to the large volume of the large pores in the
thick central layer.
[0096] The test procedure used in this examination also includes
the introduction of several cuts on the upper layer. By the cuts,
large openings were included in the upper layer such that the test
gas could pass the small pores of the upper layer. In the process,
the diameter and the volume of the small pores in the upper layer
were not measured. Thus, the liquid was displaced from the central
layer with small pressures which correlate with the large pores in
the fibre web layer. The spunbond non-woven layer attached as lower
layer did not have any influence on the test as the liquid which
was displaced from the pores of the fibre web layer by means of gas
pressure simply flowed through the lower spunbond non-woven layer,
and the gas pressure was thus not suited to displace liquid from
the lower layer. Thus, the diameter and the volume of the pores in
the fibre web layer were determined with this test.
* * * * *