This method involves molding a sheet by melting and extruding thermoplastic polymer by T-Die, elongating it by 4-5 folds in the longitudinal direction (machine direction) using the heating roll, and elongating it again by 8-10 folds in the transverse direction on the tenter using hot air until a product is yielded.

■ OPP Film Molded Products

■ Process

Mold Closing Process

The OPP film molding device consists of the extrusion, cooling, elongation, and winding units.

Extrusion unit

The temperature of the extruder is about 240 - 280℃, and varies slightly according to individual company characteristics

Screw Characteristics

1) Discharge resin at a constant speed without variations in extrusion.

2) Fine and uniform mixing and dispersion

3) Broad range of extrusion capabilities, maintaining uniformity

Required characteristics of DIE

1) High degree of precision in thickness

2) No resin residue

3) No leakage of molten resin

Cooling Unit

There is a variation in sheet cooling depending on machines. There are two cooling methods: a water cooling method through the water bath, and an air-cooling method using the chill roll. The Bruckner line is cooled by the water cooling method, and the Mitsubishi line adopts the air cooling method. High cooling temperature causes defects resulting from a high degree of sheet crystallinity. Conversely, when the cooling temperature is too low, curls are created in the sheet, causing processing difficulties.

Elongation Unit

Heat the cooled and hardened sheet by roll up until it melts, elongate it in the machine direction, raise its temperature to melting point with hot air, and elongate it in the transverse direction on the tenter. The purpose of elongation is to improve the mechanical, thermal, and optical, characteristics and barrier properties especially strength and transparency.

MD Elongation

Machine direction elongation is performed at around 110-140℃ with the magnification of elongation by approx. 4-6 fold.

TD Elongation

Transverse direction elongation is performed at 158-172 ℃, and most ruptures occur in this stage. Note, however, that the rupture factors originate from defects in the front-end process.

As a result of elongation, the degree of crystallinity is increased as PP is crystallized in the direction of elongation, improving rigidity and reducing crystal size to produce excellent optical properties.

Winding Unit

In the process of winding elongated film, 1 roll is 8-10m wide, weighing 1-3MT and winding 4000-8000m.

Composition of OPP Film

OPP Film is made up of 3 layers and a special polymer is used as a skin layer at times to render functionality.