Nonwoven filtration and drainage felts - of synthetic fibres and resin binder, have higher water transmission at the core than at the surface, useful e.g. for land drainage

摘要

Nonwoven fabric felts for use as filters and draining materials comprises synthetic staple fibres and/or filaments bonded with a separate binder, such that the water transmission of the felt is greater at the core than at the surface. The felts are less sensitive to the type of material to be drained and the amt. of water to be transmitted than prior art felts of this type with a homogeneous structure. The felt is e.G. of polyester or polyamide fibres with a styrene-butadiene copolymer or polyamide fibres with a binder. The felt density in the core may be less than at the surface, or (pref.) the binder content of the core zone may be less than that in the surface layers. Pref. the binder content in the core zone is 0.2-5 wt. % esp. 0.5-3.5 wt. % and that in the surface areas is 6-35 wt. % esp. 9-25 wt. %. The core zone is e.g. 1-3mm. thick and the neighbouring surface layers are each 1-3mm. thick. The felts are esp. useful for land drainage purposes, for passage of the water present in the soil in an upwards or downwards direction. The material may be mounted e.g. as separate strips 5-50cm. wide introduced into vertical holes 1-50m. deep bored into the ground.