Page 149 - Engineering Plastics Handbook

122 Engineering Plastics

products including flame-retardant grade, antistatic grade, environ-
mental stress chemical resistance (ESCR) grade, and extrusion grade into
the market. Such various grade products have been prepared by methods
for changing the constitutional ratio of the transparent ABS resin, or for
controlling the kinds of rubbers, particle size, gel content, and the com-
position ratio between resin and rubber, for controlling the grafting ratio
or molecular weight of resin, and for changing the additives. Since it is nec-
essary to vary the properties while maintaining the transparency, the vari-
ation range is relatively limited in comparison to other ABSs (Table 6.11).
For example, in the case of the transparent ABS with flame-retardant func-
tionality most commercially available grades are at the level of UL V-2.
The reason is that the flame retardant lowers the transparency of ABS,
and so the kinds and amount are limited. The antistatic-grade product
11
includes product having a surface resistance of about 10 Ω. Contrary to
16
the general transparent ABS having a resistance value of about 10 Ω, anti-
static-grade surface resistance is lowered by using the antistatic agent. It
can be used for semiconductor carriers, etc. The ESCR grade product is
reinforced by controlling the molecular weight and gel content. In general,
while the transparent ABS is characterized by weakness against chemi-
cals in comparison to the general ABS, the ESCR grade is reinforced.
The transparent ABS is prepared by different methods by the makers,
but is generally prepared by emulsion polymerization and bulk poly-
merization. Specifically, for transparent ABS, the grafting copolymer
having a core-shell structure is prepared by emulsion polymerization;
the ternary copolymer comprised of styrene, acrylonitrile, and methyl
methacrylate is prepared by bulk polymerization; and then the two
kinds of copolymers are mixed. The process is substantially identical to
the process for preparing the general ABS, except that the composition
is different. The grafting copolymerization is practiced by introducing
the emulsifier, initiator, activator, and monomer into emulsified polybu-
tadiene rubber; then the resulting copolymer thus prepared is passed

TABLE 6.11 Properties of Various Transparent ABSs

Grades (LG product) General- High
purpose impact ESCR Antistatic
ASTM test Unit (TR-558A) (TR-557) (TR-552) (TR-300)
Izod impact D256 kg⋅cm/cm 11 15 25 10
Tensile strength D638 kg/cm 2 500 430 390 430
Tensile elongation D638 % 50 50 50 55
Flexural strength D790 kg/cm 2 800 670 600 700
Flexural modulus D790 kg/cm 2 23,800 20,500 17,700 22,000
Haze D1003 % 1.5 2.0 2.4 5.0
Total transmittance D1003 % 91 90 90 88
Flame class (UL certification) HB HB HB V–2