|
|
|
|
|
NYLON 6 (KOPA6) |
|
|
 |
|
 |
Processing of KOPA6 |
|
1. Pre-Drying
NYLON6 has a high water-absorption rate. When resin absorbs water
it causes hydrolysis during the injection molding process,
resulting
in degradation of properties and unsatisfactory molded parts.
Therefore, pre-drying is essential prior to injection molding.
Drying equipment may include a hot-air dryer or a dehumidified
dryer,
the latter being more efficient.Normally, a dehumidified dryer
operated
4 to 6 hours at a temperature of 75-85 (167~185 )will reduce water content
to
0.1% or lower.
2. Injection Molding |
|
|
2-1 Selection of Injection Molding Machine
For molding KOPA6, a screw-type injection molding machine works
best, with a minimum 20 L/D screw and a compression ratio of
3-4, and a chrome-plated nitrogenous steel base.
As nylon 6 has such low viscosity when melted, compared with
otherresins, this may cause reverse flow of molten polymer.
Therefore, the injection moldingmachine must be equipped with a
screw head having a reverse-flowblocking valve. It is also
advisable to use an intermittent nozzle to prevent nozzle drool.
2-2 Temperatures of Cylinder and Nozzle
Resins are melted by the heater located inside the cylinderand
by the share stress generated between the screw and cylinder
barrel. Generally, the bottom side of a hopper is sufficiently
cool for smooth transportation of pellets. The melting zone is
set at a temperature suitablefor melting down resins, and the
nozzle area is set a temperature 10(50) lowerthan the melting zone,
thus preventing nozzle drool.
If the temperature of the melting zone is too high, thermal
degradation andsubstance volatility can occur, causing bubbles
or silver streaks in the the produced part.
Conversely, if the temperature of the melting zone is too low,
the flowability of the resin is reduced. This necessitates
excessive injection pressure, thus degrading the properties of
the produced part.
2-3 Mould Temperature
Mold temperature affects product appearance and the accuracy of
product dimensions, and has a direct effect on productivity due
to shortened cycles. If the mold temperature is too low,
productivity increasesdue to faster cooling, but cosmetic and
mechanical properties are degradeddue to reduced material flow.
It is essential to set the proper mold temperature necessary to
maintain properties as required by the particular product
specification, because KOPA6 is a crystalline polymer, and
crystallization varies based on cooling speed.(Normally, the
mold temperature of KOPA6 should be set at 60~80(140~176).)
If the mold temperature is uneven over melting zones, product
warpage can occur.
2-4 Injection pressure
Molten polymer flows through the mold cavity under the force of
injection pressure, and a considerable amount of pressure is
lost as material flows through the narrow sprue, runner, gate,
etc. Normally, the pressure applied to the cavity may require
about 300~500kg/㎠ per projected area of the produced part.
If injection pressure is too great, residual stress is increased
due to over-charge that can cause horizontal strength
degradation. If the pressure is too low, it can cause short
shots, shrinkage, and bubbling.Also, in order to compensate for
the 15~25% volume decrease incurred during material cool-off, a
holding pressure of 30~80% of the initial injectionpressure is
required.
|
|
 |
|
|
|
2-5 Molding Conditions for KOPA6 |
|
Item |
Unit |
KN111
KN131
KN171 |
KN136 |
KN1322
VO |
KN173HI |
KN133G
30 |
Cylinder
Tempera
true |
Rear
Middle
Front
Nozzle |
|
220(428 )
240(464)
240(464)
230(446) |
220(428)
240(464)
240(464)
240(464) |
220(428)
240(464)
240(464)
235(455) |
235(455)
245(473)
245(473)
250(482) |
240(464)
255(491)
260(500)
255(491) |
|
Mould
Temperature |
|
80(176) |
80(176) |
80(176) |
70(158) |
80(176) |
Injection
Pressure |
1stPressure
2ndPressure |
Kg/㎠
Kg/㎠ |
850
450 |
900
450 |
1000
500 |
950
450 |
1300
600 |
|
Back
Pressure |
Sec |
5 |
5 |
8 |
5 |
7 |
|
Injection Time |
Sec |
4 |
4 |
4 |
4 |
4 |
|
Cooling Time |
Sec |
20 |
10 |
17 |
25 |
17 |
|
Injection Speed |
1st step
2nd step
3rd step |
Low
Middle
Low |
Low
Middle
Low |
Low
Middle
Middle |
Middle
High
Low |
Middle
High
Middle |
3. Extrusion Molding
Nylon 6 has very low melt viscosity and is highly sensitive to
temperature changes. Generally, a temperature of 15~60(59~140) above the melt
point should be maintained. Consideration should also be given to the
fact that nylon 6 is highly water-absorbent and its residual monomer is
easily melted down.
Being affected by moisture, extrusion molded parts may contain bubbles
and result in degradation of mechanical properties, and the lowered melt
viscosity caused by the residual monomer, which adhere to the die mouth
or its surroundings and the part itself after being extruded from die in
a sublimate. This may produce defective molded products.
Therefore, moisture content must be controlled at 0.1% or lower, the
residual time inside the extruder must be minimized, and a die without
dead space should be used |
|
| <Example> Extrusion
molding for Monofilament |
| Item |
KN177N,KN577N |
| Diameter of Monofilament |
0.4 ~ 0.6 mm |
| Spinneret Size |
2.0 ~ 3.6 mm in dia. X 15
~ 20 holes |
|
Cylinder
Temperature |
|
#1(Feeding) |
200 ~ 230
(392~446) |
|
#2(Melting) |
250 ~ 270
(482~518) |
|
#3(Metering) |
230 ~ 260
(446~500) |
| Die Temperature |
230 ~ 250
(446~482) |
| Quenching Water
Temperature |
7 ~ 8
(44.6~46.4) |
|
Stretching
Speed |
|
1st
godet roll |
15 ~2 m/min |
|
2nd
godet roll |
60 ~80 m/min |
|
3rd
godet roll |
80 ~100 m/min |
|
4th
godet roll |
75 ~90 m/min |
| Stretch Ratio |
1: 4.0~5.0 |
| Hot Water Batch
Temperature |
90 ~ 95
(194~203) |
|
For
Stretching |
| Hot Air Temperature
|
200 ~ 250
(392~482) |
|
For
Stretching |
|
|
|
|
|
|
|
