IE911653A1

IE911653A1 - Geotextile filter material

Info

Publication number: IE911653A1
Application number: IE165391A
Authority: IE
Original assignee: Hoechst Ag
Priority date: 1990-05-15
Filing date: 1991-05-14
Publication date: 1991-11-20
Also published as: JPH04228717A; PT97653A; DE4015505A1; EP0459203A1

Abstract

A geotextile filter material consisting of or containing a non-woven made from synthetic fibres is described, at least some of the synthetic fibres being hollow fibres.

Description

Description Geotextile filter material The present invention relates to a geotextile filter material consisting of or containing a synthetic fiber nonwoven in which at least some of the synthetic fibers are hollow fibers.

Geotextile filters are sheetlike structures which are formed from textile fiber materials and are used as sheetlike filters for civil engineering purposes. Such a filter is used for example to protect the ground from erosion and displacement as a consequence of groundwater or seepage flows or safeguard it against the eroding effects of flow and swell of water courses.

The effectiveness of a geotextile filter as filter must be adapted to the soil on which it rests. Its effective mesh size must on the one hand prevent ground suffusion, i.e. the loss of finely granular soil constituents; on the other hand, however, it should not act as a barrier to liquid but should in special cases even act as a drainage layer.

A geotextile filter must consequently meet strict requirements, for example in respect of its filter performance and dimensional stability under load, its breaking strength, its breaking extension, its response to dynamic stress and its friction coefficients with respect to the soil. Furthermore, these filter and mechanical properties must be stable for a long period, and lastly, for cost reasons, the filter should be manufacturable from a minimum of fiber material.

Detailed rules for the dimensioning of geotextile filters may be found for example in Merkblatt fur die Anwendung von Geotextilien im Erdbau [Directions for the use of geotextiles in civil engineering] section 5.2 ff. from - 2 the German Research Society for Road Transport and Traffic [Forschungsgesellschaft fur Straflen- und Verkehrswesen] and in Merkblatt Anwendung von geotextilen Filtern an Wasserstraflen [Directions concerning the use of geotextile filters at waterways] from the German Institute for Water Engineering [Bundesanstalt fur Wasserbau].

Synthetic fibers are particularly suitable for manufacturing geotextile filter materials because they are resistant to rotting and hence have a high long-term stability. Particularly suitable filter-forming sheet materials are spunbondeds, i.e. consolidated filament web nonwovens, since on the one hand they are particularly inexpensive to produce and on the other because of the random arrangement of the filaments they also have almost unsurpassable advantages in respect of the isotropy of their mechanical properties. However, it is also possible to produce webs which have mechanical properties of a specific anisotropic character by providing them with fiber portions which extend in certain preferred directions , for example card webs.

It has been found that it is frequently very difficult to put the combination of the above-described properties required for geotextile filters into effect in webs with an acceptable layer thickness. Frequently, the particular required combination of permeability and mechanical strength can be obtained only with relatively thick and hence also heavy and relatively costly nonwovens.

It has now been found, surprisingly, that it is possible to satisfy high filter material requirements with nonwovens having a significantly lower basis weight and hence requiring significantly less material when the fiber material of the nonwoven contains hollow fibers. Accordingly, the present invention provides a geotextile filter material which consists of or contains a synthetic fiber nonwoven in which at least some of the synthetic fibers are hollow fibers. - 3 The proportion of hollow fibers in the nonwoven which confers the desired combination of properties on the latter can in certain circumstances be surprisingly small.

Frequently, a marked economic and technical advantage is obtained for the geotextile filter material of the invention even with a nonwoven in which only 10% of the synthetic fibers are hollow fibers.

In general, it is advantageous to use a geotextile filter 10 material in whose nonwoven from 50 to 100% of the synthetic fibers are hollow fibers, although to meet the very highest technical requirement profiles it may of course be necessary to use nonwovens which are 100% hollow fiber.

The linear density of the synthetic fibers of the nonwoven of the filter material of the invention is within the range customary for geotextile filter materials. It is accordingly in general between 0.5 and 50 dtex, preferably within the range from 2 to 20 dtex.

In certain instances it may be advantageous to use mixed linear densities? more particularly, in those nonwovens which are not 100% hollow fiber the hollow fibers and the non-hollow fibers can have different linear densities. The synthetic fibers can be continuous filament fibers or staple fibers, advantageously with staple lengths of 2-20 cm.

However, it is also possible without reservation to use nonwovens which contain both continuous filament and staple fibers.

For instance, in many cases the desired combination of properties may be imparted to a continuous filament nonwoven by blending in a suitable proportion of hollow staple fibers.

Of course, it is also possible for mixtures of hollow and non-hollow fibers to be used for forming a staple fiber web nonwoven.

The synthetic fibers present in the nonwovens can have - 4 one or more voids, and the voids can be short or very short in the direction of the fiber axis or they can extend along the entire fiber length. Accordingly, hollow fibers for the purposes of this invention include not only foam fibers but also hollow fibers with one or more voids which extend along major sections or the entire length of the fiber.

Of crucial significance is the void content of the synthetic fibers. Of particular utility for nonwovens of the filters of the present invention are synthetic fibers whose void content is 3 - 40% by volume, preferably 5 20% by volume.

Suitable synthetic fibers for the filters of the invention are usually made of spinnable polyamide, polyethy15 lene, polypropylene or polyester.

Preference is given to synthetic fibers made of polyester, in particular polyethylene terephthalate.

The nonwovens of the filters of the present invention can in principle have been consolidated in any known way. For instance, it is possible to consolidate the web with a binder with which the web is impregnated and which is subsequently cured, or the binder can be a thermobinder which is incorporated into the web, for example in powder or filament form, and which on heating consolidates the web into a nonwoven.

The web-to-nonwoven consolidation can also be effected by calendering, partly to intermingle the filaments mechanically, partly to effect autogenous bonding at the crossing points .

Of particular advantage are those filters of the present invention which comprise mechanically consolidated nonwovens. Mechanical consolidation for the purposes of the present invention is for example needling, or else for example hydrodynamical consolidation as described for example in EP-A-0 108 621. They are notable for particularly good adaptability to the ground underneath.

A further preferred embodiment of the filter material of the present invention is based on a spunbonded, in - 5 particular a spunbonded nonwoven which has been consolidated by needling.

The basis weight of the nonwovens of the filter material of the present invention is preferably 50-2500 g/m2, in particular 200-1500 g/m2. Particular preference is given also to those embodiments of the filter material of the present invention which combine a plurality of the abovementioned preferred features.

The present invention also provides a process for pro10 ducing the geotextile filter material of the present invention by depositing synthetic continuous filament and/or staple fibers in a conventional manner on a moving surface and subsequent consolidation with or without combination with a further textile material, which comprises using hollow fibers for at least some of the deposited synthetic fibers.

To produce staple fiber nonwovens which according to the present invention contain a proportion of hollow fibers, a mixture of hollow and non-hollow staple fibers in the desired mixing ratio can be conventionally dry- or wetlaid to form a web and then consolidated.

However, it is also possible to produce nonwovens from continuous filament fibers and staple fibers by mixing in the staple fibers in the course of the depositing of the continuous filament fibers. In this case, either the continuous filament fibers or the staple fibers may be hollow in whole or in part.

Similarly, if the nonwovens are produced by the spunbonding process it is possible to mix hollow and non30 hollow fibers in the course of the depositing. For instance, the hollow fibers can be produced separately and withdrawn from fiber reservoirs, e.g. bobbin creels, and fed by means of blowing nozzles into the stream of non-hollow fibers traveling in the direction of the moving surface, or the spinneret manifolds which are used for producing the web-forming filaments may in addition to openings for non-hollow fibers contain openings for hollow fibers, the ratio between the various openings and - 6 the amount of filaments spun therefrom corresponding to the target ratio of hollow and non-hollow fibers in the filter of the present invention.

In general, the proportion of deposited hollow fiber in a filter of the present invention is at least 10%.

Preferably, the proportion of deposited hollow fiber is 50-100%, and if maximum effects are to be achieved, 100% of the deposited fibers will be hollow fibers.

The web-to-nonwoven consolidation is effected in a conventional manner using a binder, especially a thermobinder, or by calendering or preferably by needling. Binders can be for example polymer solutions or dispersions or latices, which are applied to the web by impregnation or spraying and which, after the liquid phase has evaporated, leave delicate membranes stretched out at the crossing points of the filaments.

However, it is also possible to use thermosetting binders which harden with or without heating and stabilize the fibers at the crossing points. It can be similarly advantageous to use thermobinders, which are incorporated into the web for example in the form of powders or preferably in the form of fibers and which, as the web is heated beyond their melting point, run together at the crossing points of the fibers and form bonding points which, after cooling back down, consolidate the web to give a nonwoven.

Similar consolidation can be obtained by autogenous bonding of the filaments at their crossing points by subjecting the web to calendering in the vicinity of the melting point of the filaments.

Preference is given to a mechanical consolidation. This puts no chemical or thermal stresses on the filament material whatsoever, so that the advantageous physical properties which are imparted to the filaments from their manner of production, for example by high-speed spinning and drawing operations, are passed on in full to the - 7 nonwoven.

The geotextile filters of the present invention may either consist only of one nonwoven of the abovedescribed kind or else may contain in addition to the 5 nonwoven further textile materials, for example woven fabrics or some other additional textile layer (for example a drainage layer). These additional layers turn the nonwoven into a textile composite material which is suitable for additional civil engineering purposes and the filter effect of which is essentially due to the properties of the web material.

Claims

What is claimed is:

1. A geotextile filter material consisting of or containing a synthetic fiber nonwoven, wherein at least some of the synthetic fibers are hollow

2. The geotextile filter material of claim 1, wherein at least 10% of the synthetic fibers are hollow fibers .

3. The geotextile filter material of either claims 1

4. The geotextile filter material of at least one of claims 1 to 3, wherein the voids of the hollow fibers extend along the entire fiber length. 15

5. The geotextile filter material of at least one of claims 1 to 4, wherein the void content of the synthetic fibers is 3-40% by volume, preferably 5-20% by volume. 5 fibers.

6. The geotextile filter material of at least one of 20 claims 1 to 5, wherein the synthetic fibers are made of polyester, preferably polyethylene terephthalate.

7. The geotextile filter material of at least one of claims 1 to 6, wherein the nonwoven has been consolidated with a binder. 25

8. The geotextile filter material of at least one of claims 1 to 6, wherein the nonwoven has been consolidated mechanically.

9. The geotextile filter material of at least one of claims 1 to 8, wherein the nonwoven is a filament 30 nonwoven, i.e. a spunbonded nonwoven. -διό. A process for producing the geotextile filter material of claim 1 by depositing synthetic continuous filament and/or staple fibers in a conventional manner on a moving surface to form a web and subsequent consolidation with or without combination of the nonwoven with a further textile material, which comprises using hollow fibers for at least some of the deposited synthetic fibers.

10. And 2, wherein 50-100%, preferably 100%, of the synthetic fibers are hollow fibers.

11. The process of claim 10, wherein at least 10% of the deposited synthetic fibers are hollow fibers.

12. The process of either of claims 10 and 11, wherein 50 - 100%, preferably 100%, of the deposited fibers are hollow fibers.

13. The process of at least one of claims 10 to 12, wherein the web-to-nonwoven consolidation is effected using a binder or preferably mechanically. - 10

14. A geotextile filter material as claimed in claim 1, substantially as hereinbefore described.

15. A process as claimed in claim 10, substantially as hereinbefore described.

16. A geotextile filter material as claimed in claim 1, whenever produced by a process claimed in a preceding claim.