DE4443158A1 - Cleanable gas filter - Google Patents

Abstract

The self-supporting stabilised filter layer (2), or a layer (2) bonded to a carrier material (3), is an active filtering layer (2) of a non-woven fibre, produced in a melt blown process.

Description

The invention relates to cleanable filter media for the Gas filtration.

In the field of gas filtration, predominantly fibrous ones are used today Media used depending on the fiber diameter and Achieve different degrees of packing density. Particularly good degrees of separation, especially in the area of "Most penetrating particle size "(MPPS) measuring range between 0.1 and 1 µm, are made with the finest fibers achieved, which are produced by the meltblown process. The good separation is due to the small fiber diameter Can be 2 µm or less, and especially at the Fact that these materials with an electret charge, so a permanent electrostatic charge on the fiber surface can be equipped, creating smaller particles can be retained as the mechanical pores allow. These filters are designed as storage filters, i. that is, with only relatively low dust concentrations in the Gas (mostly air) dusted and offer one depending on the product different dust storage capacity in the filter matrix. The pressure loss rises continuously until the Final pressure loss is reached and the filter element is replaced must become. There is no regeneration. examples are Engine air filters and cabin filters of motor vehicles, Filters for vacuum cleaners, air conditioners etc.

In the industrial sector there are dust concentrations trations much higher, so that there cleanable Systems have prevailed: As soon as through the dusting maximum pressure difference is reached, by knocking, Shaking, purge air, compressed air pulse etc. from the clean gas side cleaned up here. The cleaning can also be time or  flow / volume controlled and not differential pressure controlled. So that an optimal cleaning is possible, if possible, no deep filtration, but the Filter media must be such that it is used for Surface filtration or as quickly as possible Filter cake build-up comes on the filter surface.

The filter media are depending on the form of assembly Filter element (cartridge, cassette, bag, hose) very much different: papers made from cellulose, synthetic and glass fibers or mixtures thereof, spunbonded nonwovens, needle felts etc. Depending on The required filtration performance is especially spunbonded and needle felts with various types of microporous Coated materials. The spectrum ranges from Acrylic foams up to the PTFE membrane. It shows that the different types of foams and microfiber coatings that reach a minimum of 0.5 dtex for polyester, are still not fine enough in practice and therefore Fine dust penetrates into the depth and the filter medium with the Time clogged. Despite the cleaning, the Initial differential pressure very wide, so that when operating the Filter system the working area between the initial differential pressure (after each cleaning) and the maximum Differential pressure is getting smaller. Membrane coated Materials do offer a high degree of surface filtration and associated with good cleanability, but are mechanical very sensitive and also very expensive and therefore uneconomical. The high filtration performance in the sense of The degree of separation is often not used. The pore size one Membrane is about ten times smaller than that of finest foam coatings. But through the finer pores the resistance of the filter medium increases significantly, what low throughputs or higher energy costs.

The object of the invention is to provide a filter medium for different forms of assembly are available put that in the separation quality between the finest (Foam) coatings on the one hand and the membranes on the other hand, there is a high proportion of surface filtration  and offers good cleanability, as well as less Filter resistor has as membrane filter media. Quality Cleanability means that the initial differential pressure after every cleaning over the multitude of cleaning processes as little as possible.

The object is achieved according to the present invention by the characterizing part of claim 1 specified Features resolved. Advantageous training and further education are in given the subordinate claims.

Accordingly, the idea of the invention consists of according to the Meltblown process manufactured fine fiber nonwovens, the one Allow surface filtration, if necessary in combination or in Filter media that can be cleaned in conjunction with a carrier material produce. The meltblown process is already in itself known form used, for. B. as in Wente, Van A., "Superfine Thermoplastic Fibers", Industrial Engineering Chemestry, Vol. 48, pp. 1342-1346.

Surprisingly, it was also found that just electret-charged meltblown nonwovens, one of which, as in DE-OS 43 11 297 described because of the electrostatic Would expect poor cleanability without Have the discharge cleaned well. The electret charge is e.g. B. introduced in a charging process that is known in U.S. patent 4,904,174 (Moosmayer et al.), Additionally or alternatively, the cargo can also be sent to the meltblown railway subsequently introduced (reloading procedures, such as in U.S. Patent 3,998,916 (van Turnhout)).

The differential pressure in a filter system with Filter elements from the filter medium according to the invention is only increased over many cleaning cycles little at and in addition, the separation performance because of Very high charge especially in the area of fine particles.

Depending on the form of assembly, different carriers are used materials used to make the composite of meltblown and  Carrier material to the appropriate mechanical properties lend: Plissable carrier for cartridges and cassettes, so usually spunbonded nonwovens, cellulose papers with Synthetic fiber additive, wet-laid synthetic fiber nonwovens etc. To a to achieve the appropriate stiffness Carrier materials are bound with binders, mostly through Impregnation. The filter medium must be used for hoses and bags be as flexible as possible, therefore the backing material must also be high flexibility with high tensile and bursting strength exhibit. Needle felt is particularly suitable for this Spunbond also possible.

The upstream side of these networks is always the meltblown side. The carrier material plays a role in the function of filtration subordinate role, but significantly influences the mechanical properties of the filter medium such. B. Tensile strength and elongation at break, burst pressure, stiffness or Flexibility etc. There is also a workability Influence such as B. pleatability, weldability, adhesiveness, Sewability etc.

For better abrasion and abrasion resistance, this can Meltblown can be solidified by binders. This can e.g. B. introduced as a powder that is thermally activated be, or a solution or dispersion / emulsion of the Binder in an organic solvent or water, by spraying, spraying, etc., but preferably by Impregnation is applied.

Papers that are used as cleanable filters are in usually impregnated. To move the filtration to the layers close to the surface for improved cleanability the base paper coated with meltblown and the composite of paper and meltblown are impregnated. Likewise is one Meltblown occupancy of impregnated paper is conceivable, whereby then the composite is impregnated or the binder from the meltblown side. Particularly advantageous Designs of paper with meltblown arise when that  Meltblown has a basis weight of 2-30 g / m², preferably in the range of 5-15 g / m².

For use in "heavy" industrial dedusting Impregnation of meltblowns with a basis weight of 30- 100 g / m² particularly advantageous. The binder will Meltblown fleece is very abrasion-resistant and hard-wearing. By Impregnation of the electret character may go partially lost, but can by the reloading procedure cited above be reintroduced.

Regardless of the electrostatic charge, the Meltblown materials due to the very fine fiber diameter of approx. 2 µm and below that a very high fine dust separation, because an enormously large fiber surface is available. result of it is that the dust separation in the near surface Layers are laid, so less depth filtration in favor higher surface filtration arises. This will make it quick built a dust cake that can be cleaned very well can. Even with abrasive processes, i.e. grinding processes through sharp-edged dust particles, a long service life is achieved, because the thickness of the meltblown layer makes it a good one Filtration result is guaranteed when the thickness is through Abrasion was reduced. Here is a crucial disadvantage of membrane-coated filter media that already have a show strong dust penetration, if only the surface is slightly damaged.

By adding to the impregnation liquor there are also more Properties of the filter medium can be changed: anti-adhesive Equipment, hydrophobic, hydrophoboleophobic equipment, Antistatic effect, flame protection, hydrolysis protection etc.

By calendering the already fine pores of the Meltblown fleece can be narrowed even further. This results an even more pronounced surface filtration with good cleanability even with fine or "difficult" Dust. The basis weight of the meltblown is in the Usually less than 70 g / m², preferably in the range 15-40 g / m²  lie. The surface is smoothed by calendering, which further improves cleaning. With calendering under elevated temperature (60-160 ° C, depending on the polymer just below the respective softening temperature, ideally in the range the so-called continuous use temperature +/- 20 ° C) thermal consolidation of the nonwoven and thus improved Abrasion resistance. Also a combination of impregnation and Calendering is possible to get an impregnation with to achieve optimal fiber binding and with calendering the minimum pore size.

The advantage of calendered fine fiber fleece from meltblown compared to calendered spunbonded fabrics or needle felts regardless of any electret charge in it, that much smaller due to the small fiber diameter Pore diameter achieved with comparable air permeability can be because the number of air vents very is much higher.

With thermal calendering, the electret charge may lost in whole or in part. Through the above Reloading process, however, it can be reintroduced and so maximum with minimal pore size and electret charge Separation quality can be achieved.

Calendering the meltblown without a carrier has the advantage that the carrier is not compacted by calendering. Heavily compressed carrier materials such as B. certain spinning types of fleece or other materials that are among the Calendering conditions do not cause excessive loss Air permeability can also suffer along with the Meltblown can be calendered as a composite.

In addition, the upstream side of the meltblown can with a Protective layer, e.g. B. against a thin network or spunbond mechanical influences influences are protected. These Possibility of surface protection of the flow Meltblown side can be independent of the other pretreatment of the meltblown, B. for electret materials,  uncharged, impregnated and / or calendered meltblown materials etc. The protective layer can also be used before, during or be applied after this pretreatment.

Depending on the application, a wide variety of polymers are available for this Meltblown conceivable, e.g. B. polypropylene, polyethylene, polyester (especially PBT and PET), polycarbonate and high temperature resistant plastics such as polyphenylene sulfide, polyimide, Polyether (ether) ketone etc.

The carrier material can be independent of the composition of matter be chosen by meltblown. Be special chemical or thermal resistance is required, it is an advantage if the respective durability of the carrier material is not is worse than that of meltblown. You choose for that Carrier material the same type of plastic as for the Meltblown, are the resistance of the carrier material and Meltblown almost the same.

Various known processes can be used as composite technology be used, e.g. B. welding under temperature or with Ultrasound, high frequency etc., gluing with spray adhesive, the dry physically and are chemically reactive if necessary. Powder, which are activated thermally and are chemically reactive if necessary, or application of hot melt, which may be chemically reactive.

In the following, the invention will be explained in more detail by means of examples explains:

They show

Fig. 1 Invention filter media of Example 1 in cross-section,

Fig. 2 inventive filter medium of Example 2 in cross section,

Fig. 3 Inventive Filter medium according to Example 3 in cross-section,

Fig. 4 inventive filter medium according to Example 4 in cross section and

Fig. 5 inventive filter medium according to Example 5 in cross section.

In example 1, the cleanable filter medium ( 1 ) consists of a spray adhesive composite made of polypropylene meltblown ( 2 ) and a spunbonded fabric ( 3 ) which is impregnated for greater rigidity and good pleatability. The meltblown with a surface weight of 40 g / m² has a permanent electret charge, so that the permeability for fine dust in the MPPS range is 1/10 to 1/100 or less compared to various types of paper and spunbonded nonwovens. However, the air permeability is very high at 300 l / m²s (at 20 mm WS). The pressure drop also remains clear over a large number of cleaning cycles, ie at least 30% less than that of spunbonded fabrics.

In example 2, the structure is similar: an electret-charged meltblown ( 4 ) made of polypropylene with a mass of 30 g / m² is connected to a stiff, plissable spunbonded fabric ( 5 ) made of polypropylene. To protect the meltblown side, it is covered with a 17 g / m² spunbond ( 6 ) made of polypropylene. The bond is made by ultrasonic welding so that all three layers are connected to each other. The non-woven cover protects the meltblown layer from abrasive dust and fraying.

In example 3, a meltblown ( 7 ) with 10 g / m² of PBT is deposited on paper ( 8 ) without electret charging. The paper and meltblown are impregnated, regardless of whether both are impregnated together or separately. The composite is made with spray adhesive. The meltblown layer increases the degree of separation and, above all, the ability to be cleaned: The meltblown-coated paper stabilizes during cleaning with a differential pressure that is about two thirds higher than that of identical paper without a meltblown layer. Due to the impregnation, the meltblown layer is abrasion-resistant and durable, so that cartridges made from this filter medium have a long service life.

In Example 4, a meltblown ( 9 ) made of PBT (polybutylene terephthalate) with 25 g / m² was calendered under the influence of temperature of 140 ° C. and then connected to the carrier material ( 10 ). The carrier consists of a wet-laid polyester fleece that has also been impregnated. By reducing the pore diameter, the differential pressure stabilizes at an even lower level than in Example 3, although the air permeability is lower when new.

The cleanable filter medium in example 5 is intended for use as a filter hose or bag under more extreme conditions such as high raw gas dust content or high abrasiveness of the dust. That is why the filtration layer consists of 80 g / m² PBT meltblown ( 11 ), which is impregnated for maximum abrasion resistance. The backing material must be as flexible as possible with high tensile strength, low elongation and high burst pressure. For this purpose, a needle felt ( 12 ) made of polyester is used, which has a support fabric ( 13 ). In contrast to the high basis weights of around 550 g / m² that are otherwise common in dedusting, a quality of only 400 g / m² is used here, since the filtration performance is determined almost exclusively by the meltblown. Due to the fact that the pores are smaller by a factor of 3 than with foam coatings, the surface filtration is more pronounced, which is evident in long-term use after a large number of cleaning cycles in the significantly lower pressure loss.

Claims (12)

1. Self-supporting or by a composite with a carrier material ( 3 , 5 , 8 , 10 , 12 ) stabilized cleanable filter medium for the filtration of gases, characterized in that the active filtration layer ( 2 , 4 , 7 , 9 , 11 ) from one There is a nonwoven fabric that is manufactured using the meltblown process. 2. Filter medium according to claim 1, characterized in that the meltblown layer ( 2 , 4 ) has an electret character. 3. Filter medium according to claim 1 or 2, characterized in that the meltblown layer ( 7 , 11 ) alone or together in combination with the carrier material ( 8 , 12 ) is solidified by binders. 4. Filter medium according to claim 3, characterized in that the application of the binder in the meltblown layer ( 7 , 11 ) is carried out by impregnation. 5. Filter medium according to one of claims 1-4, characterized in that the meltblown layer ( 9 ) alone or in combination with the carrier material ( 10 ) is compressed by calendering. 6. Filter medium according to claim 5, characterized in that the calendering of the meltblown layer ( 9 ) is carried out with a roller temperature of over 60 ° C, preferably over 80 ° C. 7. Filter medium according to one of claims 1-6, characterized in that the calendering of the meltblown layer ( 9 ) is calendered in the region of the continuous use temperature of the respective polymer with a deviation of 20 ° C up and down. 8. Filter medium according to one of claims 1-7, characterized in that the meltblown layer ( 2 , 4 , 7 , 9 , 11 ) before, during or after the production of the composite, the calendering or the impregnation by an overlying protective layer, in particular a Spunbond ( 6 ) or a net or grid is protected, which preferably has a weight per unit area between 10 and 50 g / m². 9. Filter medium according to one of claims 1-8, characterized in that the polymer of the meltblown ( 2 , 4 , 7 , 9 , 11 ) is polypropylene. 10. Filter medium according to one of claims 1-8, characterized in that the polymer of the meltblown ( 2 , 4 , 7 , 9 , 11 ) is polycarbonate or polyester, preferably polybutylene terephthalate. 11. Filter medium according to one of claims 1-10, characterized in that the carrier material ( 3 , 5 , 8 , 10 ) is stiff and pleatable, preferably a paper ( 8 ), spunbonded nonwoven ( 3 , 5 ) or wet-laid synthetic fiber fleece ( 10 ) , which is optionally impregnated. 12. Filter medium according to one of claims 1-10, characterized in that the carrier material is flexible, in particular a needle felt ( 12 ), which preferably has a support fabric ( 13 ).