Dust filter bag

Details Dust filter bag Dust filter bag

1999-07-21

2001-02-27

Hruskoci, Peter A. (Department: 1724)

Gas separation

Flexible or collapsible bag type

Seaming, reinforcing or bag structure

C055S486000, C055SDIG002, C015S347000, C015SDIG008

Reexamination Certificate

active

06193773

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a dust filter bag made of a fiber layer laminated together with a paper layer. A wide variety of demands are placed on such filter bags. One goal is to obtain a high filtration effect, i.e. a high level of retention. For this, the filter pores must be sufficiently small. At the same time, however, the filter pores of the dust filter bag must not clog up, so that a high level of suction or blowing performance, for example of a vacuum cleaner, is maintained, and there is no need to replace the dust filter bag for that reason alone before a specific fill level is reached.
In addition, the dust filter bag must exhibit sufficient mechanical strength so as not to tear or burst while being installed or when full. Appropriate strength is also necessary for manufacturing the bag by way of multiple folding operations.
BACKGROUND OF THE INVENTION
Dust filter bags that are made of a porous nonwoven fabric and a filter paper are known from European Patent 0 635 297 A1, and are processed into double-layer dust filter bags. A melt-blown fine fiber batt, which covers the inner side of the dust filter bag and reinforces the dust filter bag, can be used as the nonwoven fabric. However, the reinforcing effect presented by this approach is not satisfactory.
Further dust filter bags are known from European Patent 0 338 479 B1. The dust filter bag described therein comprises a filter-paper outer ply and an internally located nonwoven fabric. The nonwoven fabric is configured as a fine-fiber nonwoven fabric and is also arranged on the inflow side. The fine fibers of the fine-fiber nonwoven fabric can be applied in the thermoplastic state directly onto the filter paper and joined to it. The fine-fiber nonwoven fabric can be joined to a support element which is also made of nonwoven fabric. To produce the semifinished bag, a tube is formed from the laminate and is closed with a longitudinal seam. Pieces of finite length are then cut off from the endless tube on a bottom-seam drum. An air pulse is used to open the tube ends on one side in order to ensure the formation of tabs which are turned over and adhesively bonded to one another. However, because the two internally located nonwoven fiber plies can easily weld to one another during the cutting process, they can no longer reliably be opened with the air pulse.
German Patent 196 06 718 A1 furthermore discloses a multiple-ply filter pouch that has a first inner ply made of a fine-fiber nonwoven fabric, a second outer ply made of a plastic matted-fiber material, and a third ply, arranged before the first ply in the flow direction, made of a paper material. This creates the filtration effectiveness of the ply made of paper material, since with an external arrangement, the actual filtering effect occurs first.
A further disadvantage of the known dust filter pouches is the fact that when water or other fluid is drawn in along with the air being cleaned, the filter paper ply softens and its strength is impaired, creating the risk of tearing and contamination of the environment during vacuum cleaning or when the dust filter bag is removed. The filtering effect in terms of ultrafine particles is less than satisfactory.
SUMMARY OF THE INVENTION
The present invention provides a bag in which the fiber layer contains melted polymer regions and, because of the polymer regions, is additionally consolidated within itself and joined to the paper layer. The polymer regions have a welded surface area of 0.5 to 10% of the surface. Consequently, loss of strength in the paper layer no longer results in damage to the dust filter bag. Even in the event of tearing in the paper layer in the interior of the dust filter bag, emergence of dust particles from the interior of the dust filter bag is prevented by the externally located fiber layer. The presence of a welded area of the polymer regions equaling 0.5 to 10% of the surface area, preferably 1 to 3%, results in sufficient laminate strength with a tolerable increase in the pressure differential.
Despite the possibility for water uptake, the use of the paper layer, which is advantageous for the creation of folds, can be retained. The reason is that only with a paper layer, as opposed to a pure fiber layer made of polymer fibers, does the dust filter bag become foldable. Foldability can be improved by way of a denser pattern of melted polymer regions in the region of the edges.
A minimum extension of the polymer regions of 1 mm in terms of length and/or width, and optionally also diameter, has proven particularly suitable for creating sufficient adhesion of the fiber structure on the paper layer.
The polymer regions can be penetrated at least partially into the paper layer, in which they bring about an additional and semi-hard consolidation of the fiber structure. The fragile structure of the paper bond is thereby changed positively. The moisture resistance and/or tear resistance of the paper layer are definitely improved by the polymer regions.
The thickness of the polymer region can be less than the thickness of the layers resting against one another in isolation, but in particular less than the thickness of the paper layer outside the polymer region. The gas permeability in the polymer region is thereby reduced to a fraction of the value outside the polymer region. In this region, the fiber layer—made of synthetic polymer fibers—is compressed into a compact material.
The fibers can be electrostatically charged in order to achieve an improvement in the filtering effect with respect to ultrafine dusts.
In addition to the fiber layer made of polymer fibers arranged on the downstream (clean-air)side, it is optionally possible to provide on the dusty-air side a further, supplementary fiber layer made of synthetic polymer fibers, and to bring about a further improvement in specific properties. This requires accepting, however, an increase in the cost of the dust filter bag. What is preferred in the context of the present invention is therefore an embodiment in which a layer of synthetic polymer fibers is provided only on the downstream side.
The fiber layer can be made of an at least inherently strong nonwoven fabric, so that even if the paper layer is completely destroyed, the dust filter bag remains sufficiently stable and effective in terms of filtration. Hygienic disposal of the dust filter bag that is at least partly filled with dust is thus possible even in such cases. The nonwoven fabric can be consolidated in moisture-stable fashion by mutual adhesive bonding and/or wrapping of the fibers and/or threads constituting it; optionally it can contain melted polymer regions and can additionally, by way of such regions, be consolidated within itself and joined to the paper layer. In this context, it has proven to be advantageous that the polymer regions be melted in window-like fashion. This results in consolidation zones that impart improved strength to the nonwoven fabric, in particular if the polymer regions are of bar-shaped configuration.
The polymer regions can be divided in the manner of a honeycomb or waffle pattern in order to form dust chambers. While the paper, because of its paper bond, behaves in rigid and inflexible fashion with respect to the air pressure that acts on it while the dust filter bag is being used as intended, what results on the downstream side is an elastic deformation of the fiber layer in the in-between zones of the honeycomb or waffle pattern. This results in the formation of dust chambers in which ultrafine dusts can collect. An embodiment of this kind has therefore proven to be excellent especially in terms of the retention of allergens.
The bars forming the polymer regions need not be configured in linked fashion, but rather can also be offset from one another, i.e. can be arranged without contact.
According to a further aspect of the invention, the dust filter bag is configured so that the fiber layer comprises at least two sublayers. This is particularly advantageous if the sublayers are to perform different functions.
In particular, the sub

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