General Description
BDS is an amorphous clear material that is more flexible than most other clear materials. K-resin is an example of BDS and is used in food packaging, labelling and twist films, shrink film and flooring systems.
Pre-Production
BDS will absorb 0.08% water in 24 hours at room temperature. This means that drying is not normally necessary. If it is necessary (shown by streaks in the moulding), dry in a hot air oven for as short a time as possible and at the lowest temperature e.g.,1 hour at 60ºC or 30 minutes at 60ºC in a desiccant dryer.
Temperature ºC
Zone No.
Location
From
To
–
Hopper Throat
50
60
1
Barrel Rear (hopper end)
190
210
2
Barrel Middle
190
230
3
Barrel Middle
200
230
4
Barrel Front
210
240
5
Barrel Nozzle
215
240
6
Mould
10
60
Processing Notes
High injection speeds give mouldings with the best high gloss, weld strength, and clarity but too high a speed can cause a drop off in toughness.
Medium screw speeds are preferred – adjust speed (rpm) to suit the moulding cycle, but do not use a screw speed that will give a screw surface speed of greater than 0.7 to 0.75 m/sec.
Back pressure should be kept as low as possible. At a temperature of 200ºC the maximum residence time in the barrel should not exceed 2 minutes. When the temperature is 230ºC then the maximum residence time in the barrel should not exceed 1 minute.
Tool Requirements
Shrinkage values can range from 0.3% to 1.0%. The combination of a sensible injection speed and suitably sized vent offers the best solution for good weld strengths. If ejector pins are used, then the maximum diameter possible should be used to ensure that the moulding does not distort upon ejection.
Typical runner sizes range from 4mm to 7mm in diameter.
Post- Production
It is strongly recommended to purge out with GPPS as degradation can take place if high temperatures have been used. Normal procedure is simply to purge the cylinder empty and, switch off the heaters.
