Production of polystyrene reflector beads

#Reference is made to the application of Ronald A. Fava et al, Docket 79S8, Ser. No. 146,923 filed May 5, 1980 concerning PRODUCTION OF REFLECTOR BEADS FROM PRECURSOR BEADS FOR EXPANDABLE POLYSTYRENE, all the disclosure of said application being deemed here reiterated and incorporated herein.

#This invention relates to production of small polystyrene beads so that they are crystal clear instead of cloudy.

#Heretofore reflector plastic beads have been made from a variety of plastics by a variety of methods. Such approaches for forming crystal clear spheroids useful as reflector beads generally require specialized factories so that occasional production of clear beads has generally not been deemed an appropriate business practice. The demand for clear beads has been expanding by reason of the usefulness of small clear beads as reflectors in signs, movie screens and the like.

#The invention is further clarified by reference to a plurality of examples.

#A batch of polystyrene beads having an average diameter of 1/32 of an inch was prepared following the general procedure shown for Example IV of Grim 2,673,194. A solution of 0.008 part of sodium oleate was dissolved in 40 parts of distilled water to which was added 0.5 parts of hydroxy apatite having a particle size of reasonably uniform nature and of the order of 0.03 to 0.06 micron. The combination of the organic dispersing agent, that is, sodium oleate, and the inorganic sub-micron particle, that is, the hydroxy apatite, is important in the suspension polymerization for achieving the beads of reasonably uniform size. The aqueous suspension of hydroxy apatite was modified by the addition of 60 parts of styrene containing 0.105 parts of benzylperoxide, corresponding to 0.175% of the benzylperoxide catalyst in the styrene. This mixture was agitated in a flask provided with an axial impeller-type agitator and suspended swirl baffles to form a suspension. The suspension thus formed was heated at 90.degree. C. with continued agitation in a nitrogen atmosphere for 20 hours. The styrene polymerized to provide a suspension of polystyrene beads. The reaction mixture was allowed to cool. The pH of the dispersion medium, which was 5.6 at the finish of the polymerization, was changed to pH 2 by the addition of concentrated hydrochloric acid. The thus cooled and acidified suspension of polystyrene beads in water was centrifuged to separate the polystyrene beads, which were washed with water at ambient temperature and dried. The beads, which had an average diameter of about 1/32 inch, had a molecular weight of about 228,000. Appropriate tests were conducted by molding the beads.

#At the elevated temperature, the polymer tends to trap tiny micelles of water in some of the beads. Such water is volatilized from the bead during the drying step, thus providing tiny air cells near the bead surface. Such air cells are believed to impart cloudiness to the appearance of such beads.