Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having a component wherein a constituent is liquid...
Patent
1996-05-15
1997-12-09
Dudash, Diana
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having a component wherein a constituent is liquid...
427198, 427244, 427245, 427373, 428 357, 4283066, 428357, 428361, 428378, 4283227, B32B 326, B32B 1900, B05D 500, D02G 300
Patent
active
056958714
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the reduction of openness of material so as to reduce the number and/or size of voids. It particularly relates to the treatment of air permeable materials, especially ones which have comparatively open structures which are thereby made less open. The invention also relates to treated material.
The present inventors have previously devised a method of treating a porous material by selectively passing a suspension of a pore modifying agent into its largest pores. Thus EP-A-0,272,798 discloses a process for enhancing barrier properties by creating zones of high surface area within the large, or transport, pores. This can be arranged to have little or no effect on the permeability of the material. WO-A-93/14265 and WO-A-93/24705 disclose further techniques based on selective deposition of treatment agents within the transport pores. However, materials with very open structures do not have pores as such, and the kinds of treatment employed in the earlier work would generally leave them essentially unchanged. The present invention provides a method that can be applied to such open materials. Of course it could also be applied to less "open", more "porous" materials.
Particular examples of "open" materials to which the invention is applicable are non-consolidated (or substantially non-consolidated) fibrous materials which include or consist essentially or largely of a matrix of fibres in regular, semi-regular or random fashion. Such non-consolidated (or substantially non-consolidated) materials are referred to herein as network materials and examples include woven materials, non-woven materials. "air-blown" materials and spun-bonded materials.
The type of "open" material with which the invention is particularly concerned will generally have a voids content of at least 50%, preferably at least 75%.
The openness of a material can be quantified by the ratio of the (average) interfibre distance to the (average) fibre diameter. The ratio is low for a consolidated material, but substantially in excess of unity for an "open" material to which the present invention is particularly applicable (e.g. at least 2, preferably at least 5, possible 10 or more).
There are many uses for materials which act as a barrier to the passage of airborne particles (e.g. micro-organisms) whilst still retaining air permeability. Examples are filter media, various types of clothing, and paper and paper-type materials for use in the packaging of sterile medical items.
It is desirable to be able to produce barrier products from network materials and other materials of comparatively open structure and it is therefore an object of this invention to provide a method of reducing the openness of such materials.
In one aspect the invention provides a method of reducing the openness of an air permeable material comprising: (a) treating it so as to incorporate expandable particles within the material; and thereafter (b) effecting expansion of the particles.
The material will normally be in the form of a web. It should be dimensionally stable. Thus the constituent elements (usually fibres) will generally be connected together, whether chemically, mechanically or physically. Thus the increase in volume of the expanding particles primarily involves their expansion into existing voids, which are thereby reduced. In contrast, if expandable particles are applied to unconnected fibres and expanded, the main effect is to push the fibres apart. The material expands and becomes, if anything, even more open.
The starting material may be a network material. After treatment, it may be a porous material. It may then undergo further, pore-modifying treatment. This may be as previously described by the present inventors in EP-A-0,272,798, WO-A-93/14265 or WO-A-93/24705, whose disclosures are incorporated herein by reference.
The materials to be treated may be wet-laid or non wet-laid materials. Particular examples of wet-laid materials which may be treated are paper and paper-type network materials. Particular examples of non wet-laid
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Sinclair Colin Samuel
Tallentire Alan
Dudash Diana
The Victoria University of Manchester
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