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CALIBRE* polycarbonate resins meet
a wide range of impact requirements- from 1.5 to 18.0
ft-lb/in (80 to 950 J/m) notched Izod impact strength.
However, understanding the "balance" of end-use
temperature and impact requirements is crucial in selecting
a resin for a specific application.
Impact Strength
The impact strength of CALIBRE resins
is measured by notched Izod, tensile impact and instrumented
dart impact testing. CALIBRE polycarbonate resins offer
excellent impact resistance - 18 ft-lb/in (950 J/m)
- with low MFR resins, and good impact of 14 ft-lb/in
(750 J/m) with high MFR resins (ASTM D 256). However,
low temperatures, sharp notches or thick sections may
cause a decrease in impact strength. Also, high levels
of additives, such as colorants, release agents, glass
reinforcement, UV stabilizer and ignition-resistant
packages also affect impact strength, especially in
higher MFR resins.
Whether you're selecting a polycarbonate
material for an existing application, or designing a
new polycarbonate application, mechanical performance
must be considered along with fabrication requirements.
For applications requiring optimum impact properties,
a low melt flow rate material would generally be the
best choice. For applications where impact isn't as
crucial, but optimum processing is a must, a higher
melt flow rate material would be the best selection.
However, CALIBRE polycarbonate resins have been designed
to offer the best of both worlds - outstanding mechanical
properties at higher melt flow rates.
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6- Izod Impact Strength at Various Temperatures, CALIBRE 300 and 300EP Series Resins
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Figures 6 and 7 show the effect of temperature and melt
flow rate on impact values. As the temperature increases,
the mobility of the polymer molecules increases - resulting
in improved ductility and impact strength of the resin.
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7- Notched Izod versus Temperature, CALIBRE 300 and 300EP Series Resins
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Figure 7 clearly demonstrates the importance of selecting
the proper melt flow rate resin when low temperature
environments are a concern. As melt flow rate increases,
the temperature at which the notched Izod impact strength
drops significantly, reflecting a brittle break, increase.
The lower melt flow rate resins remain ductile with
high impact energies at lower temperatures
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8- Notched Izod versus Mel Flow Rate, CALIBRE 300 and 300EP Series Resins
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Figure 8 illustrates melt flow rate versus notched Izod
for three different notch radii. With a 10-mil notch,
polycarbonate resin retains its high impact strength
of 16 to 19 ft-lb/inch (908 to 1015 J/m) for the MFR
shown. When the stress is concentrated on a 6-mil notch,
the impact strength is retained to about 12MFR, at which
point it decreases significantly.
These notched impact resistance studies indicate that
low MFR resins are relatively insensitive to notch sharpness
at least down to a 5-mil notch. However, above about
10 MFR, notch sensitivity may become a more important
factor requiring design consideration.
Part thickness also affects impact strength, as shown
in Table 1. Lower MFR resins retain their high impact
strength in samples up to 0.188 inch (4.8 mm) thick.
The higher MFR resins lose impact in samples that are
between 0.125 and 0.188 inches (3.2 and 4.8 mm) thick.
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| Table 1: Notched Izod for Various Part Thicknesses, CALIBRE 300 and 300 EP Series Resins
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| Part |
Notched Izod, 10-mil notch |
| Thickness |
4 MFR |
6 MFR |
10 MFR |
15 MFR |
22 MFR |
| in |
mm |
ft-lb/in |
J/m |
ft-lb/in |
J/m |
ft-lb/in |
J/m |
ft-lb/in |
J/m |
ft-lb/in |
J/m |
| 0.125 |
3.2 |
18.1 |
966 |
17.3 |
923 |
16.6 |
886 |
16.0 |
854 |
14.0 |
747 |
| 0.188 |
4.8 |
19.0 |
1014 |
18.2 |
971 |
6.5 |
347 |
4.3 |
229 |
1.9 |
100 |
| 0.250 |
6.4 |
3.5 |
187 |
2.6 |
139 |
2.2 |
117 |
1.9 |
101 |
1.8 |
96 |
Instrumented Dart Impact
Tensile Strength
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