Page 150 - Engineering Plastics Handbook

Acrylonitrile-Butadiene-Styrene (ABS) Resin 123

through a series of coagulation, dehydration, and drying procedures to
obtain the product in powder form. The resulting powder is compounded
together with styrene-acrylonitrile-methyl methacrylate terpolymer as
prepared by bulk polymerization to produce the desired final product.
Although the final product can be generally prepared by mixing pow-
ders having high rubber content, as prepared from the emulsion poly-
merization, with styrene-acrylonitrile-methyl methacrylate terpolymer,
the transparent ABS powder having low rubber content may be prepared
and then used by singly passing through the extrusion and injection pro-
cedures. In addition to the monomers used for polymerization generally
including styrene, acrylonitrile, and methyl methacrylate, such mono-
mers as α-methyl styrene and butyl acrylate can be used for providing
the functionality.
Other products having properties similar to those of the transparent
ABS, transparent HIPS, transparent MBS, etc., can be included. Since
such similar products have the properties and qualities similar to those
of the transparent ABS, the names used may be the same, but the man-
ufacturing methods and compositions differ somewhat.
Although the transparent HIPS and the transparent MBS have no dif-
ferences in their compositions, the difference in their names is caused by
a difference in the manufacturing process. The transparent MBS is pre-
pared by copolymerizing styrene and methyl methacrylate with emulsi-
fied poly(styrene-butadiene) rubber to prepare the grafting copolymer,
which is then compounded with methyl methacrylate-styrene copolymer
as prepared by bulk polymerization. Contrary to this, the transparent
HIPS resin is prepared by introducing monomers (styrene, methyl
methacrylate) and the solvent into solid poly(styrene-butadiene) rubber in
bulk polymerization. The grafting reaction of rubber is continuously raised,
and after polymerization, solvent and residual monomer are removed from
the reaction mixture to obtain the desired resin. In this case, when the poly-
merization is practiced only by the bulk polymerization, the viscosity
inside the reactor is increased such that the rubber content cannot be
increased, and therefore, the product having high impact strength cannot
be produced. To overcome such a disadvantage, the method may also be
practiced in the manner of the bulk suspension reaction wherein bulk
polymerization is practiced at the early stage of the reaction and then in
the remaining stage the reaction is converted to the suspension reaction
during the grafting process after phase transition.
As can be seen from Table 6.12, the transparent ABS uses polybuta-
diene rubber, whereas transparent HIPS or transparent MBS uses
poly(styrene-butadiene) copolymer. Although such a difference in the
rubber used does not have a great influence on properties, it creates a
difference in the refractive index, which in turn creates a difference in the
composition of the shell. The refractive index of poly(styrene-butadiene)