| 摘要 |
<p>A porous material (e.g. a paper 6) has pores with a range of sizes. A pore modifying agent (comprising particles 8 of a narrow size range) is selectively incorporated within the larger pores (7) to provide zones (9) of high surface area. These greatly reduce the penetrability of the material (e.g. by micro-organisms) while having relatively little effect on its air-permeability. The modifying agent (8) may be incorporated by creating a pressure difference across the material (2), and treating it with a dispersion (e.g. an aerosol) of the modifying agent (8), under conditions of low inertia, and incorporating only a small amount of the agent (8) (e.g. under 1% w/w).</p> |
