Production of particulate solid-bearing low density air-permeabl

Details Production of particulate solid-bearing low density air-permeabl Production of particulate solid-bearing low density air-permeabl

1992-06-04

1994-01-25

Owens, Terry J.

Coating processes

Solid particles or fibers applied

427202, 427294, 427296, 118308, 118312, 428283, 4283179, B05D 112

Patent

active

052814378

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a method of producing particulate-solid-bearing air-permeable sheet material capable of achieving high concentrations of particulate solid and/or high air-permeability from a low density (0.25 gm/cm.sup.3 or less) preformed non-woven fabric or open cell foam.


BACKGROUND OF THE INVENTION

The incorporation of particulate solids in air-permeable sheet materials has been practised for a very long time. Particulate solids may be therapeutic materials and may have an antiseptic or similar effect. Alternatively they may be adsorbents of gases (such as for example active carbon particles, which have been incorporated both in fibrous sheets and in cellular foam sheets).
Several methods have been adopted for incorporating particulate solids in permeable sheet material. One of the simplest is to form a laminate of the particulate solid with two sheets of woven cloth by applying to one of them a free flowing powder before the lamination of the two sheets is effected. This method is however rather primitive and the powdered material is not firmly bound but can shake out of the laminate.
Another method has been to impregnate a fibrous web, e.g. thin webs of a non-woven material with a suspension of the particulate material in a solvent carrier which also incorporates a binder (usually an aqueous latex). This method however necessitates the use of very finely ground powders since to maintain the powder in uniform suspension in the carrier liquid (even with the aid of dispersing agents) is difficult if the particle size is too great. This method also suffers from the disadvantage that the particulate solid loses some of its activity by prolonged contact with organic liquids in the suspension and may also become coated with the binder itself thus preventing those particles which are so coated from being active.
Furthermore when the aqueous suspension is dried (usually by the application of heat) the normal migration of the binder from the centre towards the faces of the web tends to take fine particles with it so that it is difficult with the microparticles used in this process to avoid such migration of the particulate solid. This leads to concentration of the particulate solid adjacent to the faces of the resulting web where the binder is also concentrated by the migration effect.
A considerable amount of activity can therefore be lost and although a considerable weight of powder can be incorporated there is a limit to the activity which can be achieved. Furthermore this process is very expensive to operate and is therefore rarely cost effective in a competitive market.
It has also been proposed in the past to tackify the surface of the fibres in a non-woven fabric by for example applying a solvent which plasticises the fibre surface or by heating to soften the surface of thermoplastic fibres in the non-woven material. After tackifying it has been proposed to apply a particulate solid such as an electrically conductive material to the tackified surfaces as from a suspension in a suitable liquid and then to solidify the surfaces as by removal of solvent or cooling so that the particles of solid remain partially embedded in the surfaces of the fibre. In this way a substantial amount of solid particulate material can be incorporated in the non-woven material. Such tackifying methods are however also disadvantageous in that deactivation of active particles can result and in that costs are high.
GB-A-2013102 describes a method of forming a filter material for use in safety clothing whereby adsorber grains initially on the surface of a base material are forced into the base material. An air current can be used to force the grains into the base material after the latter has been wetted. Alternatively the grains can be placed onto the surface of the dry material and forced into position by violent vibration. Filter material made by this method is stated to prevent the passage of liquid droplets as well as of vapours.
EP-A-0272798 describes a method of reducing the penet

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patent: 4800190 (1989-01-01), Smolik
patent: 4961974 (1990-10-01), Jones
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