Preparation of ABS latex

Generally, ABS resins are produced in the form of a bimodal type comprised of two kinds of particle sizes for better surface and impact resistance properties. In this case, either (1) the graft polymerization is also accomplished in the concurrent presence of two kinds of polybutadiene latex having different particle sizes, or (2) respective polybutadiene latexes, after the graft polymerization is accomphshed, may be mixed in a certain ratio to prepare the product. The particle size is generally in the range of 0.1 to 0.4 xm. 

Polybutadiene latex comprising large and small particles is introduced in a graft polymerization reactor. Stjrrene and acrylonitrile monomers are added in a certain quantity to the reactor, and the molecular weight regulator, initiator, activator, and emulsifier as required for 

The coagulated ABS slurry is centrifuged to remove water and then washed to remove the impurities. The removed water is piurified through the fdtering apparatus and then recycled. The water content after drying is kept below 2%. The fluidized-bed type of dryer is generally used. 

According to the mass process, polybutadiene rubber is dissolved in the mixed solution of styrene and acrylonitrile monomers, and then the reaction proceeds to prepare the ABS resin. For polybutadiene rubber, the method for grinding and then adding the rubber is utihzed. Contrary to the emulsion process, the particles of polybutadiene rubber are not present before the reaction, and therefore, the shape and distribution of particles appear to be different from those of the emulsion process. The molecular weight of polybutadiene rubber to be used is about 200,000, with the cis-1,4 ratio being about 40%. The amoimt of polybutadiene rubber used should be kept to 20% due to the problem related to a viscosity of polymerization solution. 

The radical prepolymerization occiurs in the oil-in-oil emulsion state. As the reaction proceeds, the copolymer of styrene and acrylonitrile is produced, and when the ratio between the produced copolymer and polybutadiene rubber reaches 1 1, the phase inversion occurs. Thereafter, styrene/acrylonitrile copolymer is present in the continuous phase, and polybutadiene rubber is present in the dispersed phase. In general, the phase inversion is terminated when the polymerization conversion rate reaches about 15%. The particle size is varied depending on the change in stirring rate, the viscosity ratio between the rubber phase and the monomer phase, and the interfacial tension. 

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