GB1090971A - Method and apparatus for producing microencapsulated particles - Google Patents

Abstract

Particles of a solid material coated with a thermoplastic polymeric material are produced by forming droplets of a feedstock comprising a suspension or solution of the particles in a volatile organic solvent having the polymeric material dissolved therein, and contacting the droplets with steam so that the organic solvent vaporizes and polymer is deposited on the particles. Alternatively, the feedstock may be atomized with steam. The feedstock may itself be dispersed in water or in an immiscible organic solvent. The particles have a diameter of 0.01-100m . The polymer may be cellulose nitrate (Example 1), ethyl cellulose, polyvinyl acetate (Example 4), polypropylene, polyethylene or polystyrene. The organic solvent may have a b.pt. below 100 DEG C., or it may be a mixture in which at least one has a b.pt. above 100 DEG C. (examples are listed). The droplets may be formed by impacting the feedstock under pressure on to a perpendicular target plate, or by centrifugal atomization, (see Fig. 1, not shown), wherein feedstock is fed from pipe 19 on to disc 18 rotated by air drill 4, and steam is fed from pipe 14 into annular vessel 10 and thence through a plurality of holes 13, thus producing horizontal and vertical sprays of feedstock and steam respectively. Various vessels are illustrated for collecting product and solvent (Figs. 2-6, not shown), in which the falling product particles may be sprayed with water and collected in a funnel below the atomizer, or in the base of the vessel in water or on a solid surface, and the organic liquid may be collected in the same vessel with the product or in a separate or adjacent condenser. The particles may be TiO2, sulphur, mercaptobenzthiazole, Zn diethyl dithiocarbomate paraformaldehyde, or Zn isopropyl xanthate.ALSO:Coated particles of TiO2 or sulphur are produced by forming droplets of a feedstock comprising a suspension or solution of the particles in a volatile organic solvent having a thermoplastic polymeric material dissolved therein, and contacting the droplets with steam so that the organic solvent vaporizes and polymer is deposited on the particles. Alternatively, the feedstock may be atomized with steam. The feedstock may itself be dispersed in water or in an immiscible organic solvent. The particles have a diameter of 0.01-100 m . The polymer may be cellulose nitrate, ethyl cellulose, polycarbonate, polyvinyl acetate, polypropylene, polyethylene or polystyrene. The organic solvent may have a b. pt. below 100 DEG C., or it may be a mixture in which at least one has a b. pt. above 100 DEG C. (examples are listed). The droplets may be formed by impacting the feedstock under pressure on to a prependicular target plate, or by centrifugal atomization (see Fig. 1, not shown) wherein feestock is fed from pipe 19 on to disc 18 rotated by air drill 4, and steam is fed from pipe 14 into annular vessel 10 and thence through a plurality of holes 13, thus producing horizontal and vertical sprays of feedstock and steam resp. Various vessels are illustrated for collecting product and solvent (Figs. 2-6, not shown) in which the falling product particles may be sprayed with water and collected in a funnel below the atomizer, or in the base of the vessel in water or on a solid surface, and the organic liquid may be collected in the same vessel with the product or in a separate or adjacent condenser.