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Both the high impact, medium impact and crystal
versions of polystyrene are injection molded at
Rebling Plastics for a variety of applications.
Typical uses for this versatile material are compact
disc cases, packaging applications and household
appliances. Like other amorphous thermoplastics,
Polystyrene has predictable and uniform material
shrinkage in all directions which minimizes warpage
of plastic injection molded parts. Another benefit
of this uniform shrinkage characteristic is that
it enables the molder and mold maker to more accurately
predict the final dimensions of the molded part.
In the natural state, Polystyrene is a clear
transparent material. The term "crystal styrene"
is generally used to describe this transparent
grade which has light transmission properties
approaching 90 percent. In this state, polystyrene
is somewhat brittle, but with the addition of
rubber compounds, the impact resistance is dramatically
improved while tensile strength and stiffness
are reduced. This blended material is commonly
referred to as High Impact Polystyrene or HIPS.
The HIPS material however is no longer clear and
transparent.
Flame retardant grades and high gloss grades
of polystyrene are also molded at Rebling Plastics.
The choice of available color concentrates for
this material is almost limitless. The resin identification
code for Polystyrene is:
Properties of Polystyrene plastic
Although polystyrene can be supplied with UV
inhibitors and colored to minimize UV absorption,
this plastic injection molding material is not
recommended for continuous outdoor use. Intermittent
and short term outdoor usage is acceptable, but
the material is best suited for indoor applications.
Polystyrene is chemically resistant to water,
alkalis and dilute mineral acids, but is attacked
by organic solvents such as esters, ethers and
ketones.
Crystal polystyrenes typically have heat deflection
temperatures at 264 psi in the range of 155°F
to 200°F while specialty grades of this material
can be up to 210°F. The tensile strength of
the crystal grade material ranges from 5000 to
7000 psi while the impact grades range from 3000
to 4000 psi. The rubber impact modifier is responsible
for this tensile strength reduction. However,
the notched impact strength for the HIPS material
is typically 2.5 ft-lbs./inch; a factor seven
times higher than the crystal version.
The flexural modulus of the crystal grades is
generally 450,000 psi dropping to 250,000 psi
for the high impact grades. The flexural modulus
term is an indication of the stiffness of the
material, with higher numbers indicating higher
stiffness.
Secondary Operations for Polystyrene
plastic parts
Polystyrene is readily decorated
using the pad printing and hot stamping processes
at Rebling Plastics. Vacuum metallizing, wherein
a thin layer of aluminum is applied, can also
be provided. Post molding machining operations
including drilling, tapping, turning and milling
of the high impact grade version is also routinely
handled by Rebling Plastics.
Polystyrenes are ultrasonically
welded at Rebling Plastics. Excellent joint
strength is achieved when both parts to be welded
are made from polystyrene.
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