Precautions for Producing Nylon Membrane during Seasonal Climate Change

Seasonal climate change refers to the change of the two major indicators of environmental humidity and temperature; specifically, in spring and summer, especially during the rainy season, the relative humidity in the air is relatively high and can even reach saturation. If you do not pay attention to these differences, it is likely to occur during printing and lamination: the adhesive is often incompletely cured, incompletely dried, and high residual viscosity. In severe cases, it may even cause delamination on the peeling of the composite membrane. In particular, nylon membrane filter is more hygroscopic, and this phenomenon is more likely to occur.

Nylon membrane quality affecting factors

Although nylon membrane filter is a polar material, it also undergoes the process of molecular crystallization in the production process, but not all molecules in polyamide can be crystallized, and there are some non-crystalline amide polar groups. These amide groups can interact with each other. The coordination of water molecules makes the surface of the nylon membrane easy to absorb water molecules with strong polarity, which makes it absorb moisture and become softer, the tensile force is weakened, and the tension is unstable during production, and sometimes a thin layer is formed on the surface of the membrane.

Water membrane prevents the adhesion of ink and adhesive to the membrane, thereby affecting product quality, such as wrinkling, warping, curling of the bag mouth, inaccurate overprinting, misalignment of bag making, compound blistering, spots, crystal dots, and white spots, increased peculiar smell, adhesion of membrane surface, difficulty in coding, etc. In severe cases, the peel strength of the composite will decrease or the bag breakage during high-temperature cooking will increase, and the composite membrane will feel hard and brittle. These are the quality failures caused by the shortcomings of the nylon membrane after it absorbs moisture.

Once the nylon membrane absorbs moisture, its physical properties will change, and the membrane will become soft and wrinkle. For high-speed running solvent-free composites, moisture absorption and wrinkle is a problem difficult to solve. Secondly, the following may all affect the quality of the solvent-free composite product, such as the thickness balance of the nylon membrane, the membrane surface finish, the longitudinal and lateral difference of the heat shrinkage rate, the surface wetting tension, the number of additives and the rise in heat.

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Therefore, in weather changes or wet and rainy seasons, special attention should be paid to the production and use of nylon membranes, so as to avoid unnecessary errors in printing and laminating processes due to excessive humidity in the air and moisture absorption of nylon membranes.

1. Strictly control the temperature and humidity changes in the production environment
Due to the moisture absorption of nylon membrane and a series of adverse consequences caused by moisture absorption, it is very important for the use and storage environment of nylon membrane. Generally, it should be stored at about 23°C, ±3°C, and the dry humidity difference is ideal within the range of 60%RH±5%RH. Nylon membranes should not be placed directly on the floor or in the open air to avoid moisture absorption. The production environment is suggested not over 75% RH. If it reaches 80% RH, production should be stopped (especially compound production).

2. Use as little or no alcohol solvents as possible in printing
Printing nylon membrane has its own polyurethane resin ink. When using polyurethane resin ink, pay attention to adding less or no alcohol diluent solvent. Because the polyurethane resin itself is terminated by -OH, which can react with the isocyanate group -NCO in the curing agent of the polyurethane adhesive, so that the amount of curing agent participating in the reaction of the main agent of the adhesive is reduced, and the bonding strength is affected. If you must add an alcohol diluent solvent, it should be controlled within 5% as much as possible (pay attention to check the purity of the solvent used). And in the printing process, the residual amount of solvent is reduced to a small limit (generally total>3mg/m2).

3. Choose high-quality inks to prevent color migration and color penetration
The use of BOPA membrane in humid seasons or high temperature and high humidity weather should prevent color migration and color penetration in plastic gravure printing. Color migration and color penetration are mainly due to the fact that the small molecules of the pigment in the ink layer perform violent Brownian motion under a certain humidity and temperature, so as to break away from the crystal lattice formed by weak intermolecular forces and follow other organic molecules to move together to spread the color.

In high humidity and high temperature environment, lake pigments such as green lotus, peach, etc. are prone to color migration, especially the printed products, which must be paid attention to when they are stacked. The higher the temperature, the greater the humidity, and the more water molecules, the more serious the decomposition of color material crystals will be affected by water, and the easier it is to produce color penetration. For monoazo pigments, due to their small molecular weight, migration is relatively easy; for bisazo pigments and condensed azo pigments such as benzidine yellow, pigment red 44, etc., due to the greatly increased molecular weight, migration is not easy to occur. Heterocyclic pigments, such as permanent violet, are not prone to migration due to their high molecular weight and stable chemical properties.

4. The quality of the solvent is also very important
The water content, alcohol content, and impurities of the solvent used must be controlled. The quality of various solvents is very important. For example, the water content and alcohol content of ethyl acetate can completely affect the quality of dry composite products. The quality of the solvent determines the residue of the solvent.

Therefore, strict control of the quality of the purchased solvent is a prerequisite guarantee to ensure the quality of printing and composite residues. Secondly, when using water-based inks, special attention should be paid to the ink adhesion rate and the influence of residual solvents. Since water-based inks are alkaline inks, their PH value is generally between 8.0 and 9.0. The solvent used is soft water. Do not use hard water such as tap water or purified water as a diluent to avoid adverse quality reactions.