Simultaneous stretching
The main points of the simultaneous stretching process are the water treatment tank, the primary film after cooling roller passes through water treatment tank before stretching, the film absorbs moisture and forms hydrophilic bond in 6 molecules, this weakens the hydrogen bond energy, making synchronous stretching possible. The structure of the water tank is upper with a plurality of sleeve rollers, and a torque motor is used to drive the film to prevent the stretching phenomenon in the roller. In addition, the treatment tank is also equipped with heating and water temperature control devices. Although the equipment of the simultaneous stretching method is expensive, the quality of the film is good.
Sequential stretching
The key to the sequential drawing process is that the product must be stretched when PA6 is not crystallized. The measure adopted is that the molten material is cooled immediately after flowing out of the T-die, In addition, the distance between two-step stretching shall be as small as possible, after lengthwise stretching, cooling should also be carried out. The temperature of the two-step drawing is generally controlled at about 90 °C. In order to eliminate the tensile stress, the film after transverse stretching should be heat-set, and the length of heat-set is longer than Bopp and Bopet. There are special requirements for the oven and air nozzles.
Simultaneous vs. Sequential
| Items | Unit | Simultaneous nylon print | Sequential nylon print | Note |
| Tensile Strength(MD/TD) | Mpa | 200/230 | 240/260 | 20% |
| Elongation (MD/TD) | % | 90-110 | 100-130 | 18% |
| Heat Shrinkage (MD/TD) | % | 1.5/0.8 | 2.0/2.0 | 160℃，5min |
| Treatment Level | Dyn/cm | 52-56 | 52-56 | One-side |
| Haze | % | ＜2 | ＜2 | |
| WVTR | g/m²/atm/24h | ≤260 | ≤260 | |
| OTR | cm3/(m2.atm.24h) | ≤50 | ≤50 | |
| Gloss at 45 ° | % | ＞95 | ＞95 | |
| Temperature | ℃ | -60-150 | -60-150 |
