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This low cost resin in a homopolymer, copolymer
and random copolymer form is plastic injection
molded by Rebling Plastics for many unique applications.
Typical reasons for choosing polypropylene are:
cost; chemical resistance; electrical insulating
properties; translucence and “live hinge”
applications. Rebling Plastics molds polypropylene
for several end use applications including: protective
caps for electrical contacts; battery housings;
and small containers that rely on the “live
hinge” capabilities of polypropylene.
Properties of Polypropylene
plastic
The chemical resistance of polypropylene is outstanding.
It is unaffected by dilute and concentrated mineral
acids and bases, inorganic salts, solvents and
higher molecular weight aliphatics. Chlorinated
hydrocarbons will cause it to swell and soften.
Polypropylene is, however, attacked by halogens
and other strong oxidizing agents.
Polypropylene is available in many grades including:
glass and /or mineral filled resins; homopolymer
and random copolymer vesions; flame retardant
grades and specialty grades. The material in its
natural state is translucent and can be molded
in an unlimited number of colors. Polypropylene
is also available in many melt flow rates ranging
from less than 1 to over 60 g/10min. As the melt
flow increases, the ability to mold thin wall
parts increases while the mechanical properties
of polypropylene exhibit some reduction.
The copolymer versions of polypropylene offer
enhanced mechanical properties at low temperatures,
particularly impact strength. Live hinge applications
such as a box and lid connected through a thin
web of plastic that is flexed each time the lid
is opened or closed are typically designed with
polypropylene. Due to its high fatigue resistance,
polypropylene is the ideal candidate for these
applications as it can withstand the repetitive
stresses of flexing the hinge when the lid is
installed on the attached box. When molding a
part with a “live hinge” feature, the
optimum hinge life will be developed if the part
is flexed to orient the molecular structure of
polypropylene while the part is still warm from
the molding cycle. Rebling Plastics utilizes post
molding fixtures to orient the molecular structure
of polypropylene. Gate location is also critical
for a live hinge design. In general, the gate
location should allow the melt front of the material
to be parallel to the hinge.
The Homopolymer grades of polypropylene when
compared to the Random Copolymer grades offer
higher stiffness and strength as noted by the
flexural modulus and tensile strength of the materials.
The impact strength of the homopolymer grades
however is not as high as those of the random
copolymer.
The heat resistance of polypropylene makes it
suitable for applications where autoclaving is
required such as medical or laboratory instruments.
It typically has a melting point of over 300°F.
The chemical resistance and translucence of this
material also are key factors in selecting polypropylene
for food and beverage containers. Many of these
containers are recycled and the resin identification
code for this material looks like this:
Secondary Operations for Polypropylene
plastic parts
Polypropylene is available in many extruded shapes
such as bars, rods & tubing. Parts can be
easily fabricated from these extrusions using
standard metal working tools. Rebling Plastics
is able to provide a full range of secondary operations,
such as turning, drilling, tapping and grinding,
as well as ultrasonic
insertion, ultrasonic
welding, pad printing and assembly.
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