Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Patent
1990-12-03
1993-03-16
Van Balen, William J.
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
427244, 427359, 427369, 427373, 428268, 428269, 428280, 428290, 4283142, B32B 326, B05D 312
Patent
active
051943220
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a coated textile material or fabric comprising a textile substrate having applied thereto a microporous polymeric coating, particularly although not exclusively, for use as a filter fabric for hot gas filtration. The term `coated` is not restricted to application of layers exclusively on the surface of textile substrates but also covers cases where substantial penetration of the textile substrate occurs.
It is well known to form a coated textile material by applying a layer of a mechanically foamed aqueous emulsion of a synthetic elastomeric polymer to a textile substrate using a knife-spreading technique. Usually acrylic emulsions are used and the dried, spread layer is subjected to roller pressure to give a coating of what is commonly termed `crushed foam`. This process has been much used to give light and flexible polymeric coating for the enhancement of furnishing fabrics. Also the process has been used in the production of industrial filter fabrics to give fine open cell structured membranes with excellent gas permeability. In particular, in the context of dust filtration, it has been found that the performance of a filter fabric can be enhanced by coating the fabric with a microporous synthetic elastomer membrane, and that cell size can be controlled to within fine limits. Filtration performance is markedly improved in many applications with reduced pressure drop across the filter and improved particulate retention and cleaning efficiency.
However, there is a requirement for dry filtration media capable of operating at high temperatures such as 190.degree. to 250.degree. C. using specialised fabrics formed from materials such as aramids and polyphenylene sulphide fibres, and difficulty has been encountered in finding suitable polymeric materials which can be conveniently coated onto these specialised fabrics to form satisfactory microporous membranes with adequate temperature resistance, durability and coating adhesion.
Non-aqueous solvent-based solutions and liquids of high temperature-resistant polymers, such as silicones, have been tried but it has not been found possible to obtain a satisfactory fine regular cellular structure using foaming techniques based on chemical blowing agents, coagulation or reticulation. Silicone elastomeric aqueous emulsions are available but the low molecular weight polymers used to obtain satisfactory emulsification may not always be conducive to good temperature resistance and durability.
An object of the present invention is to provide a coated textile material which is convenient to manufacture and which has good permeability and also good temperature resistance and durability.
According to the invention therefore there is provided a coated textile material comprising a textile substrate having applied thereto a microporous coating of an elastomeric co-polymer of which at least one component is a fluorocarbon, characterised in that the coating is formed as a compressed foam layer at the surface of the textile substrate, and set to form a coherent porous membrane.
Using this polymer it has been found possible to achieve a coated textile material having excellent permeability, temperature resistance, substrate/coating adhesion and durability. Also the product can demonstrate excellent chemical resistance and high resilience, and facilitates cleaning of dust cakes.
Moreover, the coated textile material is convenient to manufacture and in particular can be made by application of the polymer from a foamed aqueous emulsion to the textile substrate using a compressive coating technique to give a crushed foam microporous membrane. Thus, and in accordance with a second aspect of the present invention there is provided a method of forming a coated textile material wherein a foamed aqueous emulsion of an elastomeric copolymer of which at least one component is a fluorocarbon is applied to the surface of a textile substrate characterised by use of a compressive coating technique which constrains the foamed emulsion to form a compressed foam layer at s
REFERENCES:
patent: 3713868 (1973-01-01), Gordon et al.
patent: 3804700 (1974-04-01), Hoey
patent: 4001158 (1977-01-01), Lindemann
patent: 4232087 (1980-11-01), Trask
patent: 4547423 (1985-10-01), Kojima et al.
Scapa Group PLC
Van Balen William J.
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