Nylon film moisture absorption principle
Nylon film moisture absorption principle： BOPA film is made of Polyamide 6(Nylon 6) as raw material. Polyamides contain polar amide groups (- CO-NH-), in which one -NH-group energy and one -C. The formation of hydrogen bonds is one of the important factors for the high crystallinity of polyamide. Although nylon membrane is a polar material, it also undergoes the process of molecular crystallization in the production process, but not all the molecules in Polyamide can crystallize, there are also some non-crystalline amide polar groups, these amides can coordinate with water molecules, which makes nylon film easily absorb water molecules with strong polarity, so that nylon film becomes soft, tensile force is weakened, tension is unstable during production and use.
Influence of dimensions after nylon film moisture absorption
Nylon film moisture absorption, in addition to cause wrinkling, also caused the transverse elongation and longitudinal shortening, the elongation can reach 1%~ 1.2%, serious can reach 1.5% above. Such as 1000mm wide nylon film in humidity above 80%RH environment, after 10mins will become 1100-1150mm.
| RH | transverse elongation | Longitudinal elongation |
| 32℃/50%RH | 0.23% | 0 |
| 32℃/60%RH | 0.30% | -0.16% |
| 32℃/70%RH | 0.37% | -0.28% |
| 32℃/80%RH | 0.50% | -0,38% |
| Time(s) | Temperature(℃) | Humidity(%) | Moisture (%) |
| 30 | 30 | 75 | 0.25% |
| 60 | 30 | 75 | 1% |
| 90 | 30 | 75 | 1.5% |
| 120 | 30 | 75 | 2% |
| 180 | 30 | 75 | 2.75% |
| 240 | 30 | 75 | 3% |
How to judge the nylon film absorbs moisture too much
To judge whether the nylon film is hygroscopic, first look at the surface of the film whether there is shrinkage and wrinkling, whether there is wrinkling on the end of the surface roll, or cut a piece of film, use a balance to get a reading, put it into the oven at 70 °C for about 2 hours, then remove it and weigh it again, to calculate the moisture content of the membrane. If more than 3%, the membrane should be used after treatment. If removed from the oven after the film, found hard feel, shrinkage and wrinkling phenomenon that the film moisture absorption is too much. Therefore, nylon membrane into the warehouse must be sampled to check the original membrane moisture content, to better production.
How to prevent nylon film moisture absorption
1) General production environment temperature of 23 °C± 3 °C, humidity in 60% ± 5%. Humidity over 75% RH recommends careful use of composite equipment or stop composite production. It is better to open the preheating system printing.
2) Pay attention to the humidity and dew point of the production workshop: in the season of high humidity and high temperature, the humidity of the workshop and the storeroom increases, the humidity of all raw materials and the surface of the plastic film increases, and the water molecule becomes a poor medium, should immediately use a clean cloth wipe off the water to prevent nylon film absorption of more water.
3) For the film moisture requirements should not be trivialized, we must check the film moisture content before production, if more than 3% should be treated carefully before use.
4) Storage and packaging protection. BOPA water absorption, saturated moisture absorption can reach 9%. Once the film absorbs moisture, it changes and the film becomes soft and wrinkled, which affects the dimensional stability. The unused BOPA film must be wrapped with good barrier aluminium foil to prevent moisture, it is best to use it in 45 ~ 50℃curing room drying for 1~ 2 hours, in wet weather or low-temperature use, the following preheating system shall be installed to remove moisture from the BOPA film. And nylon film once moisture, become soft wrinkle, can not continue to use otherwise easy to produce quality problems.