Coating processes – Foraminous product produced – Filter – sponge – or foam
Patent
1994-09-08
1998-05-05
Dudash, Diana
Coating processes
Foraminous product produced
Filter, sponge, or foam
427158, 427199, 427203, 427348, 427365, B05D 112, B05D 312, B05D 500
Patent
active
057471100
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to porous webs having desired characteristics; to methods of producing such webs; and to uses thereof.
EP-A-0272798 (DRG) describes barrier products which prevent the passage of airborne micro-organisms therethrough whilst still retaining air permeability. These barrier products are produced by treating an air permeable product (eg paper) having a range of pore sizes with a particulate pore modifying agent (preferably of at least one substantially uniform size range) under conditions such that the pore modifying agent is selectively incorporated in the pores at the upper end of the size range. As a result, the pore modifying agent provides (in the pores at the upper end of the size range) zones of high surface area which restrict the passage of micro-organisms through the material.
The treatment of the porous material may be effected by applying a pressure differential across the faces of the material, and treating the higher pressure side with a suspension or dispersion (most preferably an aerosol) of the pore modifying agent. The inertial conditions of this treatment process are an important factor in ensuring that the pore modifying agent is selectively incorporated in the pores at the upper end of the size range. The results are explained with reference to the structure of an idealised pore which extends from one side of the material to the other and which has a large chamber between the ends of the pore and also having one or more "constrictions", the smallest of which is the minimum cross-section of the pore which determines the pore size.
With the low inertia conditions the pore modifying agent follows the flow stream into a chamber of the pore and is captured within this chamber by Brownian motion. Under the medium inertia conditions, the momentum of the pore modifying agent is too great for Brownian motion capture with the result that the particles leave the flow stream and impact on the walls of the pore in the region of, and within, the constriction. Using high inertia conditions the pore modifying agent is unable to follow the flow stream and simply impacts onto the surface of the material to form a dusting.
For the purposes of providing an enhancement of barrier performance, the low inertia treatment condition is the highly preferred method. An improvement of barrier performance can also be obtained with the medium inertia treatment. However, the high inertia conditions do not improve barrier performance.
The sole aim of the disclosure in EP-A-0272798 is to provide an increase in barrier performance. We have however now established that porous materials (with a range of pore sizes) may be provided with other characteristics by incorporating selected particulate materials in the pores at the upper end of the size range.
According to a first aspect of the present invention there is provided a product which comprises a porous material having pores with a range of sizes and wherein over at least a part of the area of the material the pores at the upper end of the size range have incorporated selectively therein at least one particulate material chosen from
(i) an agent which modifies at least one of the following properties of the material by effecting a change in pore size distribution:
(ii) a light scattering agent
(iii) an ion exchange resin
(iv) a catalyst
(v) a pigment, dye, or other marking agent
(vi) an agent that modifies the response to calendering
(vii) an odour removing agent
(viii) an adhesive agent
(ix) an absorbent agent
A second aspect of the present invention provides a method of producing a product in accordance with the first aspect of the invention, the method comprising treating a porous material having pores with a range of sizes so as to incorporate selectively in those pores at the upper end of the size range over at least a part of the area of the material a particulate material as set out under at least one of (i)-(ix) above. The preferred treatment method is to establish a pressure differential across the material (eg. by applying a reduced p
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Sinclair Colin Samuel
Tallentire Alan
Bowater Packaging Limited
Dudash Diana
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