Due to the hygroscopicity of nylon film and a series of adverse consequences caused by moisture absorption, there are certain requirements for the environment of flexible packaging color printing plants. Generally, it should be stored at about 23 ℃, ± 3 ℃, and the difference of dry humidity is within the range of 60% RH ± 5% RH. Nylon membrane cannot be placed directly on the floor or in the open air to avoid moisture absorption. The wet-dry difference in the production environment generally does not exceed 75% RH. If it reaches 80% RH, production should be stopped (especially compound production) to avoid undesirable causes. If the task must be put into operation, the exhaust fan and dehumidifier can be added to the production site to strengthen indoor air circulation and reduce the production environment humidity to below 70% RH for production. In short, it must be used with caution when the humidity exceeds 70% RH. When the temperature is low or the humidity is too high, the preheating equipment of the printing and laminating machine must be turned on. The nylon film is preheated and dried and attached to the surface of the nylon film. Moisture to facilitate the smooth progress of printing and compound production; due to the large temperature change during the winter and spring seasons, pay attention to the effective adjustment of the temperature of the mixed solvent when using mixed solvents to prevent the solvent from volatilizing too fast or the residual solvent too. More quality accidents.
The workshop environment control can keep the humidity at 50% ～ 60% RH, and the summer temperature is best at 20 ～ 22 ℃. This is because the printing workshop will produce a lot of heat energy during the production process. Controlling the temperature and humidity guarantees the printing quality. primary condition.
In dry and solvent-free compounding processes, different types of two-component polyurethane adhesives have different sensitivity to water and alcohol. Exceeding the range may cause non-compliance. If the sensitivity is out of range, (the higher) the flexibility becomes worse, and the compounded product sometimes becomes hard and brittle. Therefore, it will seriously affect the composite effect, because the solvent-free polyurethane adhesive contains NCO groups, which can react with active hydrogen atoms. These reactions will consume isocyanate and reduce the amount of reaction involved in the glue solution, while releasing carbon dioxide. Making the adhesive layer contain bubbles is extremely unfavorable for compounding, and also causes surface dryness or reduced adhesive strength. For nylon film, cellophane and other highly hygroscopic materials, the residual solvent and humidity in the air after printing should be strictly managed and controlled.
In the nylon membrane family, the PA6 membrane has the highest water absorption rate, and the saturated water absorption rate can reach about 9%. After the biaxially stretched nylon film absorbs moisture, in addition to wrinkling, it will also elongate horizontally and shorten vertically, and increase with humidity. The elongation becomes larger, and the elongation can be up to 1.5%. If the humidity is 75% RH, the lateral elongation is about 0.37%, and the longitudinal direction is -0.28%; if the humidity is increased to 85% RH, the lateral elongation is 0.5%, and the longitudinal direction is -0.38%. After the nylon membrane absorbs moisture, its stress-strain curve changes significantly. After the nylon film absorbs moisture, it will not have a great impact on the corona effect, but it will have a greater impact on the adhesion of the ink and adhesive. Generally, when the moisture content of nylon film exceeds 3%, it will not only affect the adhesion of ink and adhesive, but also make the film feel hard, and the surface yellowing will affect the appearance. Therefore, special attention should be paid to flexible packaging color printing factories to prevent the nylon film from being absorbed by moisture.
Author: Chen Mengjie
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