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Polypropylene Felt: a Spunbonded Web, Kinney 1967
A polypropylene felt made without weaving or needling: hot filaments are spun, pulled down by an air jet, given an electric charge so they spread apart, and laid in loops on a moving table until they form an even sheet. Kinney's patent (Du Pont, US 3,338,992, 1967) gives every setting for polypropylene. The corona runs at 20 to 25 kV: keep clear of it while it is live.
The picture: the patent's own Fig. 1 (the process) and Fig. 7 (the web).
Advanced
1 day
Instructions
1
1
Melt and spin
Melt and spin
Melt polypropylene of melt index 10 in a screw extruder, no hotter than 290 °C. Meter it at 12 g a minute through a 1/4 in. sand filter and a 20-hole spinneret (holes 0.015 in. across): pack block 275 °C, spinneret 260 °C.
Materials for this step:
Polypropylene Pellets500 gTools needed:
Plastic Extruder
Spinneret
Pyrometer
Balance Scale
Leather Gloves2
2
Quench
Quench
Cool the bundle of filaments in a 6 in. quench chimney blowing 40 cubic feet a minute of room air in from the side.
Tools needed:
Air Compressor3
3
Draw with the air jet
Draw with the air jet
Lead the bundle 72 in. down into an air draw jet run at 25 psi: it pulls the filaments with about 3 g of tension and stretches them.
Tools needed:
Air Draw JetAir Compressor
Pressure Gauge4
4
Charge the filaments
Charge the filaments
8 in. above the jet, let the filaments brush a 1 1/4 in. bar turning at 10 rpm, with a four-point corona 5/8 in. from it at minus 20 to 25 kV (100 to 150 µA). The charge pushes them apart. Keep clear while it is live.
Tools needed:
Corona Charging Unit5
5
Lay the web
Lay the web
Catch the filaments on a grounded 47 in. square table that moves 26 in. a minute one way and 570 in. a minute the other. Each layer weighs 0.5 oz per square yard; lay several for each sheet.
Tools needed:
Laydown Table6
6
What you get
What you get
An even sheet of fine filaments, about 2.5 denier each, tenacity 2.0 g per denier, stretching 300 % before they break.
Tools needed:
Balance ScaleMaterials
1- Placeholder
Tools Required
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