After the Spring Festival, the climate in southern China will gradually warm up and will enter the "Meiyu" season. Meanwhile, the "Meiyu" season will gradually expand to the north. And this year's rainy season seems to have come particularly early, and more rain than in previous years. In this high temperature and rainy season, special attention should be paid to the production and use of nylon film, so as to avoid unnecessary errors in printing and laminating process caused by excessive humidity in the air and moisture absorption of nylon film, which may lead to quality problems of printed products.
Although nylon membrane is a polar material, it has undergone molecular crystallization in the production process, but not all the molecules in polyamide can crystallize. There are also some amorphous amide polar groups. These amide groups can coordinate with water molecules, which makes the surface of nylon film easily inhale water molecules with strong polarity, The moisture absorption of nylon film becomes soft, the tensile force is weakened, and the tension is unstable during production. Sometimes a thin water film is formed on the surface of the film to block the adhesion of ink and adhesive to the film, which affects the product quality. For example, make the printed matter wrinkle, overprint, bag making dislocation, warping, curling, composite film blistering, easy to spot, crystal point and white point. Odor increased, membrane adhesion, difficult to code, etc. In serious cases, the peeling strength of the composite film decreases, or the ink or adhesive transfer or degradation occurs, and the delamination, coding speed decreases or the code cannot be printed. During high temperature cooking, the bag breaking phenomenon increases, and the handle of the composite film becomes hard and brittle. These are the defects caused by the moisture absorption of nylon membrane. Therefore, in the "plum rain" season, the use of nylon film production should pay special attention to the change of weather and temperature and humidity control in the production workshop, in order to prevent the occurrence of various adverse quality factors due to high humidity. The following points for attention are put forward for reference in the daily production process:
1. Strictly control the temperature and humidity of production environment.
Because of the moisture absorption of nylon film and a series of bad quality consequences caused by moisture absorption, it is very important for the use environment and storage environment of nylon film. Generally, it should be stored at about 23 ℃ and ± 3 ℃, and the difference between dry and wet in the range of 50% ± 5%. The nylon film can not be directly placed on the floor or open air to avoid moisture absorption. The difference between dry and wet environment is generally less than 80%. If it reaches 80%, production should be stopped to avoid adverse factors. Exhaust fan and dehumidifier can be added in the production site to strengthen the indoor air circulation. Some enterprises arrange the production of nylon materials at noon. In a word, when the humidity exceeds 70%, it must be used cautiously. When the temperature is low or the humidity is too high, the preheating equipment of printing and laminating machine must be turned on, and the nylon film should be preheated first, and the moisture attached to the nylon film surface should be dried. Although Xiamen Changsu Industrial Co., Ltd. has constant temperature and humidity control in the production process, there may be many unforeseen factors in transportation and use. Special attention should be paid to the temperature and humidity changes of the production environment to facilitate the smooth production.
2. Use less or no alcohol solvent as far as possible.

Printing nylon film has its special polyurethane resin ink. When using polyurethane resin ink, pay attention to less or no alcohol dilution solvent. Because the polyurethane resin itself is terminated by - Oh, - Oh can react with isocyanate NCO in the curing agent of polyurethane adhesive, so that the amount of curing agent participating in the main agent reaction of the adhesive is reduced and the bonding strength is affected. If alcohol diluting solvent must be added, it should be controlled within 8% as far as possible, and the residual solvent should be reduced to the minimum in the printing process (the general total amount is > 3mg / m2). When printing white ink based prints, it is better to add a small amount of curing agent in the white ink to improve the composite fastness. (according to the ink manufacturer according to the requirements of the amount of use). Composite production should be carried out as soon as possible after printing. The remaining materials can be packed with the packaging film containing aluminum foil to prevent moisture intrusion in the air. The remaining film should be placed in a dry and ventilated place. When reusing, it is better to place it in the curing room 2-3 hours in advance to dry the water vapor on the surface of nylon film, so as to prevent the material from being affected by moisture and affect the product quality. If the production of boiling bags, ink must be added to the curing agent to ensure the ink adhesion rate.

3. Pay attention to the quality of the ink to prevent color migration and color penetration.
The use of BOPA film in Meiyu season or high temperature and humidity weather should prevent color migration and color penetration in plastic gravure printing. Color migration and color penetration are mainly due to the intense Brownian motion of small molecules of pigment in the ink layer at a certain humidity and temperature, thus breaking away from the lattice formed by weak intermolecular force and following other organic molecules to do migration movement and disperse color. In the environment of high humidity and high temperature, lake pigments such as blue lotus and peach red are easy to cause color migration, especially for printed finished products, we must pay attention to stacking. The higher the temperature, the higher the humidity, the more water molecules, the more serious the effect of water on the decomposition of color material crystal, and the easier color penetration. For mono tinned azo pigments, because of their small molecular weight, they are easy to migrate; for bisazo pigments and condensed azo pigments such as benzidine yellow and pigment red 44, the molecular weight is greatly increased, so it is not easy to migrate. Heterocyclic pigments, such as YONGGU violet, are difficult to shift due to their high molecular weight and stable chemical properties.
The mechanism of color permeation is complex, which is not only related to the characteristics of pigment itself, such as molecular weight and the influence of water, but also related to the characteristics of film. The reason of color shift and color penetration is the result of the combination of pigment, temperature, humidity and film characteristics. For nylon membrane, non-linear polyethylene film, due to its amorphous state, low crystallinity and large molecular gap, color penetration is easy to occur in high temperature and high humidity environment.
4. Addition control of true solvent and false solvent.
Among the mixed solvents added to printing ink, some solvents can dissolve the binder in the ink, which is called true solvent, while some solvent can not dissolve the binder in the ink by single use, which is called false solvent. Due to the different volatility between solvents, if the true solvent volatilizes first, the proportion of solvent in the ink is damaged, and the precipitation of ink resin will occur. Therefore, we should add the true solvent in time. When the solvent balance is poor, we should add some real solvent with slow evaporation speed. In order to keep the balance of solvent volatility. Various types of ink due to the different ink resin, for the use of the true solvent is also different, we must first find out which type of resin ink to use, in order to use what kind of true solvent.
5. The quality of the solvent is also very important.
The water content and alcohol content of the solvent used must be controlled. The quality of various solvents is very important, such as the water content and alcohol content of ethyl acetate can completely affect the quality of dry composite products. It is stipulated in the national standard gb3728-1991. The content of ethyl acetate in superior product should be 99.0%, the moisture content should be 0.1%, the content of ethyl acetate in the first grade should be 98.5%, and the moisture content should be within 0.20%. In dry lamination, the moisture content should not exceed 0.20%, and it should not contain alcohol, amine and active hydrogen. Otherwise, the curing agent will be consumed and the composite peeling fastness, non drying, composite delamination or wrinkling will occur. This is due to the reaction between the main polyurethane agent with - Oh end and the polyurethane curing agent with - NCO end, resulting in the formation of higher molecular weight polyurethane. Therefore, the coordination between them has a fixed ratio, and alcohols with - oh and substances with - NH2 have a greater interference on the composite processing, which will not only produce a lot of non drying phenomenon, but also have many residual solvents, resulting in bubbles and other quality problems. In order to ensure the reasonable matching of the main agent and curing agent of the composite adhesive in high humidity weather, considering the high humidity in the air, the amount of curing agent can be increased by 5% ~ 8% to ensure the normal crosslinking and curing of the adhesive.
6. Gelation and albinism caused by humidity.
Due to the introduction of water into the adhesive system containing isocyanate group (--NCO), gelation and albinism can be caused. The main reason is that 1 mole of water (H2O) can react with 1 mole of curing agent containing isocyanate group (- NCO) to form amine and carbon dioxide. Although the reaction is not very fast, it is much faster than that with the main agent. (some people have done the test more than 10 times faster). Because the curing agent reacts with water first, the ratio of the main agent and curing agent is changed, so that the adhesive can not be cured normally. However, the CO2 gas generated by water swells in the composite product, resulting in bubbles and pinholes. The amine generated by water reaction continues to react with 1 mole of isocyanate group (- NCO) to form biuret, r-nco + R2 -- NH2 -- rnhconhr ↓. The product is a kind of white crystal, insoluble in ethyl acetate and showing the whitening of glue liquid. The resultant biuret gradually accumulates, which makes the composite flower roller blocked, resulting in insufficient glue supply and waste products. Often in the morning the compound glue is still in normal use, in the afternoon, the glue is turbid, white and precipitated, which is the principle. Therefore, in the preparation of adhesive, it should be used as soon as possible, and the curing dose should not be too long. The curing dose should be kept close to the upper limit as far as possible. One strand should not exceed 15% of the normal dosage (it should be adjusted according to the actual situation). Therefore, in this season printing composite use of nylon film is a difficult problem, especially for the composite process is more important.
7. Do a good job of ripening.
It is very important for the curing work of semi-finished products with good printing and lamination, which is the key to the quality of printing. The purpose of curing is to make the adhesive further cross-linked. If fully crosslinked, the molecules arranged in order can improve the composite fastness. On the other hand, the residual solvent in the semi-finished composite membrane can be discharged to reduce the amount of residual solvent, so as to reduce the poor peel strength, poor opening, smell and so on. (when using high barrier materials, such as pet, BOPA and other materials, it is difficult to discharge the residual solvent during the aging process. It must be excluded in printing and composite drying as far as possible, so as to reduce the adverse consequences caused by residual solvents). Whether external heating or internal heating is adopted, the curing indoor temperature is stable and uniform. Generally, it can be cured according to the required time. If the curing time is too short, the adhesive may not be cured completely, which will affect the peel strength and residual odor. If the curing time is too long, it may lead to poor film opening. From the test results, the two-layer or cooking film needs to be cured at low temperature for a long time, while the aluminum coating composite needs to increase the curing temperature and reduce the curing time to reduce the possibility of dealumination. However, the high-temperature cooking bag generally needs to be cured at 50 ~ 55 ℃ for 72 h to meet the curing requirements. Some people in the industry put forward the process of secondary aging, that is, after the multilayer substrate is compounded, it is first put in the drying room at 50 ℃ for 36h, and then it is taken out for cutting and bag making. After that, the semi-finished products and finished products made of bags were put at 70 ℃ for 12h (PE as the inner membrane) or kept at 90 ℃ for 3h (CPP as the inner membrane) for a short time (special aging process). The curing effect is better than one-time long-time aging. In the products with aluminum foil and vacuum aluminum plating, the composite aluminum foil and semi-finished products of aluminum plating are first aged for 24h, then the composite thermal seal layer is compounded and then cured for 24h, so as to improve the composite stripping firmness. Before mass use of the above methods, please do a good experiment to obtain certain parameters before using.
8. Wipe off the attached droplets.
In the high humidity and high temperature season, the cots on the laminating machine and the ink blocking knife of the printing machine are easy to absorb the small water droplets in the air. Once the water droplets accumulate for a long time, they may run into the ink or adhesive, resulting in a series of quality problems. Therefore, in this season, if you find water droplets on the ink blocking knife, guide roller and net roller, you should immediately use a clean cloth or dry towel to wipe off the water drops in case. In addition, exhaust fan can be placed in the room to strengthen the indoor air circulation, but pay attention not to blow against the composite and printing machine, especially the printing plate roller and the composite glue roller.