Patent GB-1403296-A (GB)
Title: Method for coating discrete particles
IPC: B01J2/30
Filed: 1973-08-29
Abstract: 1403296 Coating particles POTTERS INDUSTRIES INC 29 Aug 1973 [5 Sept 1972] 40735/73 Headings B2E and B2L Discrete particles are coated by continuously advancing a mass of discrete particles along a feed path, applying a polymerisable coupling agent to the particles at a first location along the feed path to provide an uncured coating on the surface of each particle, the coupling agent being a reactive chemical which can be polymerised in situ by the application of heat, initiating the polymerisation of the coated particles by the application of heat thereto as the particles continue their movement along the feed path, adding an anti-caking agent to the particles at a second location along the feed path, and completing the polymerisation of the particles by continuing the application of heat thereto as the particles move along the feed path downstream of the second location. The particles may be glass beads for use as fillers for plastics. The coupling agent may be an amino silane. The anti-caking agent may be an amine salt of a hydrophilic colloid. As shown in Figure 1 glass spheres stored in feed hopper 10 are withdrawn by feeders 11 and advanced to the lower end of elevator 12, discharged from the upper end of the elevator 12 at a uniform rate of 1000 lbs-5000 lbs per hour into an elongated, horizontally disposed screw conveyor 15. The screw conveyor 15 is provided with an in-feed section 20, and intermediate mixing section 21 and an out-feed section 22. The screw of the conveyor 15 rotates within an elongated trough 30 provided with an electrical resistance heating element 31 also of trough shaped configuration and extending from a point immediately downstream of the in-feed section 20 and along the mixing section 21 and the major portion of the out-feed section 22. Conveyor trough 30 includes a discharge opening 35 communicating with a conduit 36 leading to a scalping sifter 37. The spheres pass through the sifter 37 into a bagging hopper 38 and led to a bagging screw 39. A coupling agent and an anti-caking agent are added to the spheres at successive points by feeders 40 and 41. As shown in Figure 3 the flights of the screw 17 in conveyor sections 20 and 22 include smooth continuous faces and the screw flights in the intermediate section 21 are modified by a series of mixing bars 25 and the rectangular openings 26. Coupling agent within storage tank 44 is introduced into the conveyor 15 through a shut-off valve 47, a flow meter 48, a line 49 and a spray nozzle 50. Feeder 41 for the anti-caking agent comprises a low volume, high accuracy volumetric feeder. The spheres within the in-feed section 20 are disposed at the bottom portion of the trough 30 at a level indicated by dotted line 67. As the spheres reach section 21 their rate of movement increases as a result of the mixing bars 25, the openings 26 and the paddles 27 so that the spheres in section 21 rise to a level 68 to completely submerge the feed screw 17. As the mass of coated spheres enters the out-feed section 22 the agitation of the spheres drops and the rate of movement to the spheres is increased to reduce their level to that shown by line 70.