Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Nonwoven fabric – Autogenously bonded nonwoven fabric
Patent
1997-04-04
1999-05-04
McCamish, Marion E.
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Nonwoven fabric
Autogenously bonded nonwoven fabric
442414, 442415, B32B 700, B32B 2734
Patent
active
058997865
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with non-woven fibre fabric and a method of making the same, and is especially concerned with non-woven fibre fabrics suitable for use in self-supporting filter units for filtering a fluid, for example air.
Our co-pending European Patent Applications Nos. EP 0,515,045-A1 and EP 0,549,105-A1, respectively U.S. Pat. No. 5,246,474 and U.S. Pat. No. 5,296,065; are both concerned with such filter units. Each filter unit having at least one passage, and preferably a plurality of passages, defined by fluid perm able wall portions of non-woven fibre fabric, through which the fluid to be filtered can pass and be drawn off along the passage or passages but which prevent the passage of particulate material and/or other debris carried by the fluid. The two European patent applications referred to above describe self-supporting units which are particularly suitable for filtering air in dust filters but may be used for filtering other fluid materials. Our co-pending UK Patent Application No. 9416052.0, filed on Aug. 9, 1994 is also concerned with self-supporting filter units.
In our co-pending patent applications, there are described examples of filter units capable of operating at a relatively high continuous temperature of, for example up to 260.degree. C. and maximum temperatures of up to 300.degree. C. for a temporary period. Such high temperature filter units have utilised a non-woven fibre fabric consisting of staple polyimide fibres to provide wall portions of filter units, through which the air to be filtered passes. In the manufacture of these filter units, the polyimide fibre fabric is heated to a temperature in the region of the glass transition temperature of the fibre which causes the fibres to shrink and become relatively rigid, after the fabric has been allowed to cool. This rigidity ensures that the wall portions of the filter units are relatively rigid and thus, self-supporting when the filter units are held by mounting portion at one end of the unit with the filtration passages extending horizontally, or substantially so.
In the manufacture of the fabric of polyimide fibres, known techniques for producing non-woven fibre fabric from staple fires are used including needling techniques to consolidate the fibres and to entangle the fibres to some extend to provide some strength to the fabric.
Whilst the filtration fabrics made of polyimide staple fibres have been found to perform very satisfactorily at high temperatures, very careful control of the temperature to which the fabric is heated during manufacture of the filter units is required.
In EP 0337597 (Albany Research (UK) Ltd.) there is described polyimide material which is consolidated by shrinkage to provide a structural material. This structural material makes use of the non-uniformity between shrinkage fibre and stable fibres in the material before consolidation on in order to provide reinforcing pillars within the material. Such non-uniformity is unacceptable in a filter material where pore size must be predictable in order to grade the filter.
This is because it has been found that if the fabric is heated to too high a temperature, the shrinkage of the fibres can be so great that the fabric tends to tear; furthermore, excessive shrinkage tends to emphasise any non-uniformity in the fibre mat which may arise, for example at he point where needles have penetrated the fabric during manufacture; and non-uniformities which are emphasised tend to detract from the otherwise relatively smooth surface and provide a surface which is somewhat lumpy in appearance. This is especially undesirable for self-cleaning air filters where it is desirable that the surface of the filtration fabric should be as smooth as possible to ensure ready release of dust when cleaning the filter. On the other hand, restricting the temperature to which fabric is heated during manufacture of the filter units tends to result in units which are less rigid than would be the case were a higher manufacturing temperature to be used and having somewhat lower s
McCamish Marion E.
Ruddock Ula C.
Texon UK Limited
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