Patent GB-1381067-A (GB)
Title: Varying density cartridge filters
IPC: D04H3/03
Filed: 1973-03-19
Abstract: 1381067 Annular filter cartridge CELANESE CORP 19 March 1973 [24 March 1972] 13050/73 Heading B1D [Also in Division D1] An annular cartridge filter comprises non- woven autogeneously bonded continuous synthetic organic filaments, the density of the filter varying in the radial direction by at least 10%. The filter is formed by extruding molten dissolved or plasticised polymer through spinneret 16. Preferably the polymer is heated to 150 to 350‹C above its softening point. The polymer is alternated by converging gas streams supplied by slits 18, to 0.1 to 50 denier. Preferably the gas streams converge at a point outside the cross-section of the polymer stream. The annular cartridge is built up as the drawn tacky continuous filament collects in random array upon mandrel 24 which is rotated and reciprocated in the direction of its axis. Roll 28 applies pressure to consolidate the annular body. The density of successive layers may be varied by varying at least one of the pressure applied by roller 28, the speed of rotation of the mandrel 24, the distance between mandrel and spinneret 16, the temperature of extrusion or the speed of extrusion.  The density of successive layers of the annular cartridge may also be varied by using a sequence of extruders. In the embodiment of Figs. 3, 4 (not shown) a linear array of extruders 48 apply successive filamentary layers to a rotating mandrel to form an infinite hollow cylinder that is slowly moved forward axially and is finally cut into sections. In the embodiment of Fig. 6 (not shown) three extruders are spaced at 90‹ intervals around a turntable carrying four rotating axially reciprocating mandrels. The turntable is rotated through 90‹ at intervals to form three layers upon each mandrel. The synthetic polymer may be stereospecific crystalline ethylene or polypropylene, nylon 6, nylon 66, polyethylene terephthalate cellulose acetate, cellulose secondary triacetate polyurethane, polystyrene and polymers and copolymers of vinyl chloride, vinyl acetate, vinylidene chloride, vinyl acetate and acrylonitrile. The density at each point in the cartridge is less than 50% of the density of the polymer and is preferably 0:1 to 0.5 g/c.c. The density variation across the thickness is preferably at least 10% advantageously at least 20%. Normally the density is higher on the inside although the converse is possible. The density may decrease smoothly from the inside or in up to 4 sharp steps. The density may increase slightly (less than 5%) on moving outwards due to the distance from the extruder decreasing as the cartridge builds up, decrease sharply by more than 10%, increase slightly and finally drop sharply by more than 10%. Solids such as activated carbon, silica gel, non exchange resins, deodorizers, decolourisers or diatomaceous earth may be incorporated into the filter. Preferably the inner and outer 1/8" to 3/16" are free of the solids. The solids may be applied to the idler roll 28 as an aqueous slurry or dropped from hopper 32. In a less preferred embodiment the solid particles are extruded with the synthetic polymer. The cartridges can be deformed under high mechanical stress but have sufficient strength to resist deformation under normally experienced fluid pressures.