Dust filter bag

A dust filter bag made of a fiber layer laminated together with a paper layer, where the fiber layer is composed of polymer fibers and is arranged on the downstream-gas side of the paper layer.

FIELD OF THE INVENTION 
This invention relates to a dust filter bag made of a fiber layer laminated 
together with a paper layer. 
BACKGROUND OF THE INVENTION 
In general, very diverse demands are made of such filter bags. For example, 
one goal in the design of such bags is to obtain a high level of filter 
effect, i.e., a high degree of dust collection. To that end, the filter 
pores must be sufficiently small. At the same time, however, the filter 
pores of the dust filter bag must not become clogged, either, so that a 
high suction or blowing output (e.g., of a vacuum cleaner) is maintained, 
and the need to replace the dust filter bag before a certain amount of 
filling has occurred, simply due to clogging, is avoided. 
Furthermore, the dust filter bags must demonstrate sufficient mechanical 
strength, so that they do not tear or burst when they are set into place 
or when they are full. A corresponding level of strength is also necessary 
for the production of the bags, which entails a plurality of several 
folding steps. 
Dust filter bags which are made of a porous non-woven material and a filter 
paper are known from European Patent No. 0 635 297 A1, and are processed 
to make double-ply dust filter bags. A melt-blown microfiber non-woven 
material can be used as the non-woven material, which covers the inside of 
the dust filter bag and reinforces the dust filter bag. Unfortunately, the 
degree of reinforcement provided by this bag is less than satisfactory. 
Other dust filter bags are known from European Patent No.0 338 479 B1. The 
dust filter bag described there is composed of an outer layer of filter 
paper and a non-woven material. The non-woven material is structured as a 
microfiber non-woven material and faces the upstream side of the filter 
bag. In this connection, the microfibers of the non-woven material in the 
thermoplastic state can be directly deposited onto and connected with the 
filter paper. The microfiber non-woven material can be connected with a 
support element which is also made of non-woven material. 
A disadvantage of the known dust filter bags is that in response to sucking 
in water or other liquid that may be drawn in with the air that is to be 
cleaned, the outer layer of filter paper becomes soft and loses its 
strength, creating the risk during vacuuming or removal of the dust filter 
bag of a tear in the bag or a soiling of the surroundings. The filter 
action with regard to microparticles is not very satisfactory. 
SUMMARY OF THE INVENTION 
The present invention overcomes the deficiencies of the known designs. A 
fiber layer made of synthetic polymer fibers is arranged on the downstream 
side of the paper layer. Consequently, damage to the paper layer does not 
compromise the strength of the filter bag as it does in other known 
arrangements. Even if the paper layer tears open inside the dust filter 
bag, the outflow of dust particles from the interior of the dust filter 
bag is prevented by the outer fiber layer. The fibers can be 
electrostatically charged in order to achieve an improvement in the 
filter, with regard to microdust. 
In addition to the fiber layer of polymer fibers arranged on the downstream 
side, a supplemental, additional fiber layer of synthetic, polymer fibers 
can be provided on the dust air (upstream) side, if necessary, resulting 
in a further improvement in certain properties. However, this makes the 
dust filter bag more expensive. Therefore, in the preferred embodiment, a 
layer of synthetic, polymer fibers is provided only on the downstream 
side. 
The fiber layer can be composed of an inherently stable non-woven material, 
in order to ensure that even if the paper layer is completely destroyed, 
the dust filter bag will remain sufficiently stable and effective as a 
filter. Hygienic disposal of the dust filter bag, even though it may be at 
least partially filled with dust, is therefore possible even in such 
cases. The non-woven material can be reinforced to be resistant to 
moisture in that the fibers and/or filaments of which it is composed are 
glued and/or interlaced together, and can contain melted polymer areas, if 
necessary, and be additionally reinforced in itself and connected to the 
paper layer by these areas. In this connection, it has proven to be 
advantageous that the polymer areas be selectively fused together so as to 
form window-like structures. In this way, reinforcement zones are obtained 
which impart improved strength to the non-woven material, particularly if 
the polymer areas are structured or formed in bar form. 
To form dust chambers, the polymer areas can be distributed in the manner 
of a honeycomb or waffle pattern. While the paper itself acts in a rigid 
and non-resilient manner because of its paper bond, the fibers of the 
fiber layer are not so constrained. Indeed, during its intended use as a 
filter bag, the air pressures encountered elastically deforms the fiber 
layer on the downstream side in the intermediate zones of the honeycomb or 
waffle pattern, resulting in the formation of dust chambers, in which 
microdust can accumulate. Such a structure has proven to be especially 
effective at extracting allergens. 
The polymer areas can penetrate at least partially into the paper layer, 
resulting in additional, impact-resistant reinforcement of the fiber 
structure. The brittle structure of the paper bond is thereby enhanced. 
The moisture resistance and/or continued tear resistance of the paper 
layer is markedly improved by the penetration by the polymer areas. 
On the other hand, use of the paper layer, which is advantageous for 
producing folds, can be maintained in spite of the possibility of water 
absorption. This is because the paper layer makes it possible for the dust 
filter bag to be folded at all, as compared with a fiber layer composed 
purely of polymer fibers. Foldability can be improved by a denser pattern 
of the melted polymer areas in the area of the edges. 
The bars which are formed in the polymer contact areas do not have to be 
structured so that they are connected to one another, but rather can also 
be offset relative to one another and do not touch. 
According to another embodiment of the invention, the dust filter bag is 
designed so that the fiber layer includes at least two component layers. 
This is particularly advantageous if the component layers are intended to 
fulfill different functions. 
In particular, the component layer facing further downstream from the paper 
layer of the dust filter bag can be made of a spun-bonded material. This 
spun-bonded material generally demonstrates a high level of resistance to 
wear. This is important if the dust filter bag comes into contact with 
rough surfaces during production, installation, or operation. 
Furthermore, at least one component layer made of microfibers and 
sandwiched between the outer spun-bonded layer and the paper layer can be 
present. In this layer, which can be composed of a melt-blown non-woven 
material, improved filter properties are achieved, particularly with 
regard to microdust, thereby expanding the range of use of the dust filter 
bag. 
A particularly good cleaning effect along with sufficient mechanical 
strength of the dust filter bag is obtained if the fiber layer composed of 
microfibers has a surface weight of 5 g/m.sup.2 to 40 g/m.sup.2 (ISO 536), 
with a total weight of the fiber layer of 5 to 50 g/m.sup.2. 
It is advantageous that the paper layer have a surface weight of 20 
g/m.sup.2 to 100 g/m.sup.2 (ISO 536). 
The air permeability of the product, ready for use, is 100 to 300 l/m.sup.2 
s with a differential pressure of 200 Pa (DIN 53887).

DETAILED DESCRIPTION 
FIG. 1 shows an embodiment of a three ply dust filter bag according to the 
invention. It is made of a paper layer 2 which faces dust gas side 
(upstream, or intake) side 1. 
Facing downstream side 3 is a fiber layer of polymer material, which is 
formed from a spun-bonded material 4 composed of thermoplastic fibers. 
Between paper layer 2 and spun-bonded material 4, there is an additional 
fiber layer of polymer material which is composed of a melt-blown 
non-woven material 5 made of thermoplastic fibers. 
Paper layer 2 and melt-blown non-woven material 5 essentially lie loosely 
one on the other, so that an interstice 6 is present. Likewise, 
spun-bonded material 4 lies loosely on melt-blown non-woven material 5, 
with an interstice 7 being enclosed in partial areas. 
To increase the strength of spun-bonded material 4, it can be reinforced at 
spaced apart locations by point bonding, causing surface structures 8 to 
be present. 
FIG. 2 shows the downstream surface of the dust filter bag. Melted polymer 
areas 9 can be seen, which are present in the form of bars 10. Bars 10 are 
arranged offset relative to one another, and do not touch each other. 
Fundamentally, they can be assigned to one another in any desired pattern, 
and can form a waffle or honeycomb pattern, for example. It is practical, 
in this context, if the individual chambers are formed by transverse 
connections merging with one another, in order to optimally utilize the 
entire available filter surface and avoid pressure peaks in individual 
chambers. For this purpose, the bar structures, as a whole, can also be 
formed by a sequence of individual bonding zones which are spaced at a 
distance from one another. 
Bars 10 thereby delimit dust pockets 11, 11', which are connected with, and 
merge onto, one another because of the non-interconnected structure of 
polymer areas 9, i.e., bars 10. 
Since dust pockets 11 are not sealed relative to one another, a material 
exchange from one dust pocket 11 into an adjacent dust pocket 11' is also 
possible, for example, after the pores of one chamber have become clogged, 
if those of an adjacent chamber are still available. 
From this point of view, the most varied forms of the arrangement of the 
bars or other polymer areas are conceivable, in order to increase the 
strength and, at the same time, permit a definition of dust pockets 
relative to one another. 
FIG. 3 shows a cross-section of the bag taken in the area of polymer areas 
9. i.e. bars 10. Polymer areas 9 can be produced by ultrasound 
calendering. In this connection, the thermoplastic material of spun-bonded 
material 4 and of melt-blown non-woven material 5 is made to melt at 
previously determined locations., and is bonded with paper layer 2 under 
high pressure. The type of paper is without significance, in and of 
itself, as long as suitable filter properties are present. 
In this context, the melted thermoplastic material of spun-bonded material 
4 and melt-blown non-woven material 5 penetrates at least partially into 
paper layer 2. In polymer areas 9, the original properties of spun-bonded 
material 4 and of melt-blown non-woven material 5 are no longer 
maintained, due to the calendering, and in particular, these areas are no 
longer or only insignificantly filter-active. 
Between polymer areas 9, interstices 6 form dust pockets 11 which hold the 
microdust (to the extent that it is not stored directly in the paper) in 
the melt-blown non-woven material 5. Spun-bonded material 4, having 
greater strength values and therefore a relatively lesser filter effect, 
is used to protect melt-blown non-woven material 5, which is more 
sensitive to abrasion and wear. Essentially, the spun-bonded material 4 
serves to protect the melt-blown non-woven material 5 against wear, and 
imparts significantly improved tear strength to the dust filter bag 12, 
while avoiding any significant impairment of the filter effect, 
particularly if wetting has occurred. By this arrangement, should the 
paper layer 2 of dust filter bag 12 tear the bag as a whole would not 
completely lose its filter effect. It is even possible that paper layer 2, 
after becoming wet, dries again during normal use without any noteworthy 
impairment of the filter effect. 
FIG. 4 shows a three-ply dust filter bag 12 with a plurality of folds 13. 
Paper layer 2, spun-bonded material 4, and melt-blown non-woven material 5 
are not inserted into one another but rather, proceeding from a planar 
material, are formed to produce dust filter bag 12 by being folded on 
itself. 
Paper layer 2, spun-bonded material 4, and melt-blown non-woven material 5 
are connected with one another via polymer areas 9. If liquid penetrates 
into the interior which is defined by paper layer 2 facing the interior 
upstream side, and if paper layer 2 becomes soft as a result, spun-bonded 
material 4 thus reliably holds dust filter bag 12 together. 
In principle, a single non-woven material of polymer fibers can substitute 
for spun-bonded material 4 and melt-blown non-woven material 5, if the 
filter properties and strength properties are sufficient.