Patent GB-628983-A (GB)
Title: Method and apparatus for making sheet or web material
IPC: B05D1/04
Filed: 1946-09-16
Abstract: <PICT:0628983/IV (a)/1> Films are produced on a moving support member which is moved past a deposit station at which is created an electric field of force through which field the support member moves, <PICT:0628983/IV (a)/2> the material comprising the film being introduced into the said field of force in flowable consistency and transferred along the lines of force and deposited in a layer of predetermined thickness on the support member, and the film is then dried or set to allow of its separation from the support member as a continuous web or discontinuous sheets.  Suitable film-forming materials are liquid or viscous cellulose nitrate, cellulose acetate, synthetic resins and like materials.  The apparatus (Fig. 1) comprises a number of separate deposit stations (Fig. 3), an endless belt 47, a drying and setting chamber 11a, and a wind-up roller 59. Each deposit station comprises a reservoir 13 for the film-forming material communicating with a smaller reservoir or supply tank 18 provided with a row of extrusion nozzles 19 on its underside. Pressure may be applied through a conduit 20 to regulate the flow of material from the nozzles 19, this pressure being registered on a gauge 21. Supported beneath the nozzles is an inclined plate 22 provided with a heater 23 which may be needed to ensure the flowable condition of the film-forming material.  An insulator tube 24 is mounted for limited endwise movement, said tube carrying within itself an electrical conduit 28 which is connected to a source of electrical energy.  An angle strip 26 connects the conduit 28 to a discharge element 29 extending vertically below the tube with its lower end formed into fine-pointed teeth 30.  The element 29 is spaced slightly from the plate 22 so that material can flow from the plate on to the element, where it is held on the teeth by capillarity.  An attraction element 31 in the form of a blade with a knife-like upper edge is sited beneath the belt, the blade being in vertical alignment with the discharge element.  This blade is connected to the exterior of a rigidly-supported insulator tube 33 carrying an electrical conduit 34 which is connected to the opposite side of the source of electrical energy to which conduit 28 is connected.  Electromagnets 35 are mounted on each side of the attraction element and are provided wtth field bars 36 shaped to provide sharp edges adjacent the knife-blade 31.  These, when energized, provide magnetic fields of force which shield and concentrate the electric field between the discharge and attraction elements 29 and 31.  The attraction element and magnets are mounted within a rotating cylinder 27 which serves to support the endless belt 47 upon which the material is deposited. This belt is driven by a driving roller 38 and idler rollers 39, 40, and 41.  The roller 38 is operatively connected by drive trains, each including a clutch and a cam drum to the insulator tube 24 on each deposit station to control the limited endwise oscillating movement.  Air pipes 54 provided with radially-projecting outlet nozzles 55 are located beneath the lower reach of the endless belt, and through these pipes and nozzles hot or cold air or other gas may be blasted on to the material to dry or set it.  A separating device 57 is fixed near the roller 38, the separated material being passed through a drying chamber 11a and wound on a drum or reel 59.  If sheet material is being made, the sheets are carried on a suitable horizontal conveyer through a drier and stacked.  A roller 69 of suitable material such as cloth or wire mesh fabric, may be mounted before the first deposit station to be used in the production of coated fabric or reinforced sheeting or webs.  In order to facilitate the transfer of material on to the belt a terminal 85 is located adjacent the discharge element 29, and a terminal 89 is located closely adjacent the upper surface of the belt, thus enabling pre-charges to be impressed on the material and the belt and so assisting the deposition.  These terminals 85 and 89 are electrically connected to a reversible switch 88, and the discharge and attraction elements 29 and 31 are similarly connected to a second reversible switch 75, so that any predetermined charge can be impressed on the various members. The electromagnets 35 are connected to a switch 99.  Periodic breakage of the electrical circuits results in the production of separate sheets.  If different materials are used in the reservoirs of the deposit stations, laminated sheets can be built up.  If desired, metallic powders may be incorporated in the material so that they are acted upon by the magnetic field of force to assist in deposition, or also the material may be electrically chargeable and adapted to be ionized by the electrostatic field, its transfer being similarly facilitated.