DE20013839U1 - Textile composite - Google Patents

Description

Applicant: BWF Textil GmbH & Co. KG
89362 Offingen

Textile composite material

The invention relates to a textile composite material, in particular a filter material, which consists partly of electrically conductive material and contains at least one support layer formed by threads arranged transversely to one another in the form of a fiber arrangement and at least one matted fiber layer formed by a needled-on fiber fleece.

Electrical charges caused by friction etc. can lead to sparks, which in dusty atmospheres can lead to dust explosions, fires etc. Filter materials therefore need to be electrically conductive so that electrical charges that arise on the filter surface can be conducted to a grounded component. To this end, electrically conductive material in the form of steel fibres, copper fibres or the like has previously been mixed into the fibre fleece used to form the fibre layer. The mixing effort required in this context is comparatively high. In addition, there is a risk that the machines used will become contaminated by the metal fibres mixed into the fibre fleece. A further disadvantage is that only machines without a so-called metal detector can be used, which is undesirable for reasons of production flexibility. A very particular disadvantage is that a comparatively large amount of electrically conductive material is required, the price of which is significantly higher than the price of the fibre fleece without conductive material, which has an adverse effect on production costs. Despite a comparatively high proportion of conductive material,

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However, there is only a very limited discharge effect. In this context, it can be assumed that many conductive fibers have no connection to the other conductive fibers, so that discharge cannot be achieved over long distances. Experience has shown that there is often a local distribution of charges, which still represents a residual risk of sparking.

In order to achieve conductivity over longer distances, threads with conductive material were built into the support layer. However, conductive fibers within the fiber layer were not omitted. The result of this is a particularly high consumption of conductive material, which leads to comparatively high material costs.

Based on this, it is therefore the object of the present invention to improve a textile composite material of the type mentioned above in such a way that not only a high conductivity is ensured, but also a cost-effective production.

The solution of the above-mentioned object, which is aimed at improving the composite material, is achieved according to the invention in that, in the generic arrangement, the conductive material is assigned only to selected threads of the support layer which form a surface grid and whose conductive fibers appear at least partially on the surface of the fiber layer formed by the fiber fleece which itself is free of conductive material.

The fibers of the supporting layer threads containing conductive material appearing on the surface of the fiber layer act advantageously as charge collectors that capture and dissipate electrical charges that form on the surface. These fibers, which act like a "lightning conductor," can be used to dissipate charges over a large area, so that the conductive material can advantageously be limited to the supporting layer threads that form a surface grid. The fibers mentioned have

on the thread side, a reliable connection to the conductive material present along the length of the thread, so that reliable conduction over long distances to a grounded component is guaranteed. Since the conductive material can be limited to selected threads of the support layer, their content of conductive material can be comparatively high despite a comparatively low overall consumption of conductive material, which ensures that on the one hand a comparatively large number of conductive fibers can appear on the surface of the fiber layer and on the other hand a reliable conductor strand is achieved that runs along the entire length of the thread, so that a high level of conductivity that was previously not thought possible can be achieved with comparatively little conductive material. The measures according to the invention therefore lead to advantageous optimization. As a result of the comparatively low consumption of conductive material, overall material costs are also advantageously low. Since the fiber fleece itself is free of conductive material, there is no need for any mixing. Contamination of the machines is also avoided. A further advantage is that machines with metal detectors can also be used, which results in high flexibility in production. In addition, the purity of the fiber fleece used means that comparatively large fiber fleece batches can be produced, which also has a positive effect on production costs. The fibers made of conductive material, which act as charge collectors, can be brought to the surface of the needle felt layer simply by needling it. Additional measures are advantageously not required for this, which results in particularly simple and cost-effective production and therefore particularly low production costs overall. The measures according to the invention therefore completely avoid the disadvantages of the known arrangements described at the beginning and solve the above-mentioned problem in a very simple and cost-effective manner.

Advantageous embodiments and appropriate further developments of the overarching measures are specified in the subclaims.

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The threads of the support layer, which consist at least partially of conductive material, can thus conveniently delimit a surface pattern of no more than 4 cm ^2. With an area of 4 cm ² , as tests have shown, reliable, surface-wide discharge is ensured without the risk of arcing. Nevertheless, the required use of electrically conductive material is minimized.

Another useful measure can be that the conductive material is formed by metal fibers, whereby the proportion of conductive material in the associated threads of the support layer is advantageously more than 10% by weight, preferably around 20% by weight. As tests have further shown, this results on the one hand in a sufficient number of fibers appearing on the surface of the fiber layer and acting as charge collectors and on the other hand in a conductor strand that reliably runs along the length of the thread and thus the desired optimization of the required use of conductive material, whereby metal fibers can be easily bent on the surface and thus result in particularly effective charge collectors.

Further advantageous embodiments and appropriate further developments of the overarching measures are specified in the remaining subclaims

and can be seen in more detail in the example description below using the drawing.

In the drawing described below:

Figure 1 shows a section through a textile composite material according to the invention in a schematic representation,

Figure 2 is a schematic plan view of the support layer of the arrangement according to Figure 1 and

Figure 3 is a schematic plan view of the arrangement according to Figure 1.

The textile composite material on which Figure 1 is based, which can be used, for example, to form a filter hose that can be placed on a filter basket, etc., and can therefore serve as a filter material, consists of a central support layer 1, onto which a fiber layer 2 that has been matted by a needling process is applied on both sides. The support layer 1, which can be designed as a woven fabric or scrim, etc., consists of threads 3, 3a that are arranged transversely to one another and are designed as warp and weft threads in the embodiment shown, which in turn are designed as a fiber arrangement with a large number of individual fibers 4, as can be seen in Figure 1 from the cut warp threads. The threads 3, 3a can be designed as so-called multifilament threads or twisted threads or the like. The fiber layer 2 is based on a fiber fleece that, as already mentioned above, is matted by a needling process and connected to the support layer 1.

Some of the threads of the support layer 1, in the example shown the threads of the support layer 1 designated 3a, contain electrically conductive material, e.g. in the form of metal fibers, preferably steel fibers and/or copper fibers, etc. For cost reasons, steel fibers are preferably used, which are cheaper than, for example, copper fibers. Fibers made of conductive or conductive polymers are also used.

would be conceivable. This material is particularly cost-effective and particularly easy to process. C-fibers are also conductive and can therefore be used. Mixtures of the above-mentioned conductive materials are also conceivable.

The fiber thickness of the conductive fibers used corresponds approximately to the fiber thickness of the other fibers 4 underlying the threads 3, which can be natural fibers and/or synthetic fibers, as well as the fibers of the fiber fleece underlying the fiber layer 2. In both cases, staple fibers can be used.

The proportion of electrically conductive metal fibers in the total material underlying the associated threads 3a of the support bearings can be in the range of over 10% by weight, preferably in the range of 15-50% by weight, when using metal fibers. A particularly preferred version with steel fibers has a proportion of about 20% by weight, preferably exactly 20%. With polymer fibers, which have a lower specific weight than metal fibers, the weight proportion can be lower and amount to about 3-30% by weight, preferably 10-20% by weight. In general, the smaller the specific weight and the better the specific conductivity of the conductive fibers, the lower the proportion in weight% can be, since this ensures sufficient overall conductivity in any case. Of course, it is also important to ensure that there is a sufficient number of conductive fibers touching each other in order to ensure the desired conductivity over a longer distance. Excellent results were achieved using steel fibers at a volume fraction of about 4%, which corresponds to a weight fraction of 20%.

The above-mentioned threads 3a containing electrically conductive material are shown thicker in Figure 2 than the other threads 3. These threads 3a delimit, as Figure 2 clearly shows, a surface grid, here with a square grid area with the edge length a. This surface grid is selected so that a grid area of at most 4 cm ² , preferably exactly 4

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cm ² . In the example shown with a square grid area, the edge length a is therefore preferably 2 cm.

The fiber fleece on which the fiber layer 2 is based, which does not contain any electrically conductive material, is, as already mentioned above, connected and matted to the support layer 1 by a needling process. The needles used to carry out the needling process are arranged and/or designed in such a way that when needling, they redirect fibers from the threads 3a of the support layer 1 containing electrically conductive material and bring them at least partially to the surface of the fiber layer 2, as is indicated in Figure 1 by the fiber pieces 4a extending from the threads 3a of the support layer 1. These can end on the surface of the fiber layer 2 or form a loop that appears on the surface. As expected, a proportion of fiber pieces 4a corresponding to the proportion of conductive fibers in the threads 3a of the support layer 1 consists of conductive material. In tests, excellent results were achieved with a puncture density of 800 punctures per cm ² . The penetration depth should be selected so that the needles penetrate through the substrate, ie emerge on the side opposite to the penetration side, before turning back.

These fiber pieces 4a made of conductive material form, as can be seen from Figure 3, traces 5 appearing on the surface of the fiber layer 2 of charge collectors ending on the surface of the fiber layer 2 or reversing there, which function like "lightning conductors" and transport any charges that arise into the associated threads 3a of the support layer 1, which in turn can be connected to a grounded component. The traces 5 run according to the course of the threads 3a of the support layer 1 containing conductive material and accordingly also delimit a surface grid, here with the edge length a.

The fibre pieces 4a, which end at the surface of the fibre support 2 or turn around there and consist of electrically conductive material, run out of the

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associated threads 3a and therefore introduce electrical charges arising on the surface of the fiber layer 2 into the associated threads 3a from which they emerge. The charges introduced into the threads 3a containing conductive material in this way are passed on over greater distances by the conductive material extending in the longitudinal direction of the thread and are discharged into the earth via a grounded component contacted with it, for example a head of the filter basket. The collecting function of the fiber pieces 4a consisting of electrically conductive material can be further improved by carrying out a singeing process after the needling process. This exposes the fiber pieces 4a on the surface, which improves the surface effect. This can be further improved if a calendering process is then carried out in which protruding unevenness is pressed down. In some cases it may be sufficient to carry out just one of the processing steps mentioned above.

Claims (9)

1. Textile composite material, in particular filter material, which consists partially of electrically conductive material and contains at least one support layer ( 1 ) formed by threads ( 3 , 3a ) arranged transversely to one another and designed as a fiber arrangement and at least one matted fiber layer ( 2 ) formed by a needled-on fiber fleece, characterized in that the conductive material is assigned only to selected threads ( 3a ) of the support layer ( 1 ) which form a surface grid and whose conductive fibers appear at least partially on the surface of the fiber layer ( 2 ) formed by the fiber fleece which itself contains no conductive material. 2. Composite material according to claim 1, characterized in that the threads ( 3a ) of the support layer ( 1 ), which consist at least partially of conductive material, delimit a surface grid with a grid area of at most 4 cm ² , preferably of 4 cm ² . 3. Composite material according to one of the preceding claims, characterized in that the conductive material of the threads ( 3a ) of the supporting layer ( 1 ) is at least partially formed by metal fibers, preferably steel fibers. 4. Composite material according to claim 3, characterized in that the proportion of conductive material in the associated threads ( 3a ) of the support layer ( 1 ) when using metal fibers is more than 10% by weight, preferably in the range of 15-50% by weight. 5. Composite material according to claim 3 or 4, characterized in that the proportion of conductive material in the associated threads ( 3a ) of the support layer ( 1 ) is 20 % by weight when steel fibers are used. 6. Composite material according to claim 1 to 3, characterized in that the conductive material of the threads ( 3a ) of the support layer ( 1 ) is at least partially formed by conductive and/or conductively made polymer fibers. 7. Composite material according to claim 6, characterized in that the proportion of the conductive material in the associated threads ( 3a ) of the support layer ( 1 ) when using polymer fibers is 3-30 % by weight, preferably 10-20% by weight. 8. Composite material according to one of the preceding claims, characterized in that the supporting layer ( 1 ) is designed as a supporting fabric. 9. Composite material according to one of the preceding claims, characterized in that at least the threads ( 3a ) of the supporting layer ( 1 ) which partially consist of electrically conductive material are constructed from staple fibers.