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Reduction in cycle time.

In many cases, increase of melt temperatures by 10 to 15 deg. c. helps in eliminating bubbles.

Processing clarified PP

For injection moulding, the following factors should be considered:

C

Mould

.

temperature

A.

Mould finish

B.

Melt temperature

D

Injectionpress

.

ure/Speed

A highly polished mould for the best clarity

Optical finish Draw finish(not recommended)

Low

melt

temperature.

Raise

the

melt temperature observed. Usually

if bubbles

are

190 to 210

deg.

c. is a good starting point

Mould

temperature

should

be

adjusted to avoid condensation. Raise mould temperature slightly in conjection with melt temperature to solve bubble problems.

  • Low pressure high speed mould filling is best for low haze. "Packing" can cause haze and some loss of impact properties.

Polypropylene grades:

It is obvious from the points discussed so far that the properties of end products are decided by various parameters, viz.,

  • Temperature, pressure, speed and time set on the machine

  • Moulds

  • Resin properties

9

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