GB877083A - Improvements in or relating to coating glass beads for reflex reflectors - Google Patents

Abstract

Small transparent glass beads are coated by forming them into a slurry with an aqueous solution of a silicate, atomizing the slurry to form particles consisting of a glass bead coated with the solution, and at least partially drying the particles while they are free falling. Atomization may be effected by forcing the slurry through a nozzle under pressure, using auxiliary air jets to break it up into droplets. The particles are then collected, preferably treated with an aqueous solution of an acid substance to remove most of the alkali portion from the silicate, when an alkali silicate has been used, and heated at an elevated temperature above the boiling point of water to dry and rigidify the coating. The coating has a refractive index of from 1.45 to 1.5 and may be used as a space coating for glass beads of higher refractive index, e.g. above 1.7, to form spherical lenses of still higher effective refractive index for use in reflex reflective coatings. In an example, glass beads of refractive index 2.49, analyzing 67.5% lead oxide and 32.5% titanium dioxide, are coated to give composite elements of effective refractive index about 2.9. The coating may be coloured by adding a suitable transparent colouring material to the silicate solution. The coating process may be repeated to give the desired thickness. The bead cores may have a partial, e.g. hemispherical coating of a reflective material, e.g. aluminium; or the core may be coated with a silica-containing layer, as described, then hemispherically coated with a reflective material, and additionally coated with silica. The coated beads may be used in liquid paint or lacquer finishes, or they may be bonded in a layer having dispersed therethrough a reflective pigment such at titanium dioxide; the outer surface may be coated with a thin transparent protective layer to give a lenticular surface. Or, hemispherically silvered beads may be used partially embedded in a clear or coloured layer. A smooth surfaced structure may comprise a binder layer in which a reflective pigment is dispersed and in which the backs of a layer of coated beads are bonded. A colour layer may surround the beads without overlying them, and this layer and the fronts of the beads may be covered by a smoothsurfaced transparent protective layer; this and the binder layer may be of N-butyl methacrylate polymer resin or mixtures thereof with other resins. By using different colours in the binder layer, the colour layer and the coating of the beads, colour effects which vary with the lighting may be obtained. Fabrics and other surfaces may be coated with a binder, and the reflective beads pressed into this.