It is a molding method that involves extruding polymer resin in the form of thin yarns (similar to noodle strands coming out of a noodle-making machine) through the extruder, cooling it, and elongating it again to enhance the strength of the produced yarns.

■ Monofilament Molded Products

■ Process

Monofilament Molding Device

The monofilament molding device consists of 5 units: extrusion, cooling, elongation, annealing, and winding.

Extrusion Unit

The extrusion nozzle of the Die for monofilament is very small compared to other types of extrusion molding. The non-elongated filament extruded from the nozzle needs to be prevented from melt fracture by mixing the molten resin sufficiently within the extruder and the resin needs to be extruded at a low level of viscosity by raising the temperature of the extrusion molding.

* Melt Fracture: Phenomenon where the surface is not smooth and is rather unevenly destroyed when processing polymer

Types of Dies

Dies are in two types, T-Die and Circular Die.

Cooling Unit

The polymer spun from the die is put into the cooling tank to undergo the cooling process. The refrigerant used for cooling has a small amount of ethylene glycol mixed with water to maintain the temperature within the cooling tank. Excessive quenching creates a cavity in the inner side of the yarn, causing it to break apart at the time of elongation.

Elongation Unit

Since the non-elongated filament lacks practicality due to its low strength, it should be elongated through a dry or wet process to increase its strength. Normally, it is elongated approximately 10-fold in boiling water (the temperature must be maintained above 98°C). Elongation is performed by varying the speed of the transmitting roll and the pulling roll located at the back and front of the elongation tank.

ANNEALING Unit

Annealing is the post-treatment process that is performed to maintain the molded shape by heating the molded polymer. The process is required as the rapidly quenched molded polymer rapidly shrinks in the process of polymer particle crystallization, or the shrinkage shows uneven patterns in the molding.

Winding Unit

The strands of monofilament must be wound individually with fixed tension at all times. Also, the winding motor’s torque should be small enough to prevent breakage of the yarns.