Page 136 - Engineering Plastics Handbook

110 Engineering Plastics

this step, stirring is conducted at a low shear rate so that the monomer
can be retained within rubber.
After the reaction is completed, the resulting product is transported to
the devolatilization step. In this step, residues including residual monomers
are removed by using water or methanol. Such materials have the solu-
bility for polymer solutions and play a role in preventing the foaming phe-
nomenon by lowering the partial pressure of monomer. The methods for
removing residual monomers include falling strand devolatilization, extru-
sion devolatilization, film evaporation, etc. The last two methods are supe-
rior in view of their effect, but have the disadvantage of high cost.

Flame-Retardant ABS
Flame-retardant ABS has excellent properties and processability and
therefore has been most widely used as the parts of office automation
(OA) equipment including copiers and printers and various kinds of elec-
tric and electronic equipment as well as computer monitor housings.
Further, since recently safety has been emphasized, the application field
and use of flame-retardant resin have been expanded, and the require-
ments in the market have been diversified according to the environmen-
tal problems. In this section, we review the overall present situation and
future prospects of flame-retardant ABS resins.
The flame-retardant ABS resin is prepared by addition of flame retar-
dant, impact modifier, lubricant, and stabilizer. As the flame retardant,
halogen-based organic compounds containing bromine, chlorine, etc., are
mainly used. Although phosphorus-based flame retardant may be used, its
use is limited to only low levels of flame-retardant products (V-2).
Therefore, in the following we focus on halogen-based flame retardant, as
flame-retardant ABS generally uses halogen-based flame retardant.
As the flame retardant, organic halogen compounds having a bromine
(Br) content of at least 50% are mainly used, and they can be added to the
level of at least 5 to 20 parts by weight per 100 parts of resin (phr) depend-
ing on the flame-retardant rating of the final product and the flame-retard-
ing efficiency of flame retardant, to readily obtain UL-94 V-2 to V-0. Since
the flame retardant in flame-retardant resin determines the flame-retar-
dant property, and furthermore, influences the properties and character-
istics of the resin itself, it is important to select the flame retardant
according to the desired characteristic properties required for the final
product. The kinds and properties of flame retardants used in flame-retar-
dant ABS are shown in Table 6.1.
Tetra-bromo bisphenol-A is the most widely used flame retardant for
flame-retardant ABS, since it is relatively inexpensive and has excellent
flame resistance, in comparison to other flame retardants. Although it
has the advantage of excellent fluidity, it is required to use a suitable