Analysis of Common Faults and Countermeasures of Liquid Packaging Film Printing

Liquid packaging, especially liquid packaging for high-temperature cooking and sterilization processes, has developed rapidly in recent years. The printing inks that are matched with them are also required to be more environmentally-friendly, such as black and white milk PE film for milk packaging, and most of them use solvent-based printing inks to meet environmental standards.

How to judge the quality of liquid packaging film

Liquid packaging film refers to the packaging film of soy sauce and vinegar, which is resistant to acids, alkalis, and nappers. In the middle punch, LLDPE, LDPE, EVA, and masterbatch are commonly used for mixed production. To judge whether a liquid packaging film is good, there are several requirements:

1. The static dynamic friction coefficient of the liquid packaging film is low, generally controlled between 0.2 and 0.4, so that it can be rapidly filled in a short time on the high-speed filling and packaging machine. If the friction coefficient is high and the filling speed is low, the filling will be insufficient in a certain period of time.

2. The liquid packaging film can only be surface-printed, has high fastness, can resist pasteurization and hot filling, and does not cause ink peeling at the temperature of frozen storage of -20°C.

3. Must have sufficient strength to ensure that it will not be pulled under the tension of the high-speed automatic filling machine. In general, the film is a single layer, the thickness of more than 10S, often using high melting index 4-6g/10min and low MI <1g10min of two grades of LDPE mixed, together with the color end of the material blown , Or HDPE and masterbatch mixed after blow molding, high temperature resistant film must be subjected to 121 °C sterilization, with or without shrinkage, good heat sealing properties. Therefore, the correct choice of ink and color masterbatch is required. If the resin in the formulation is too sticky, the melt resin will stick to the sealing edge during frit sealing; if too much smoothing agent is used in the formulation, the fusing strength is not high and the color is easy to turn on.

Ink fastness is not good, easy to decolorize

The factors causing the low ink adhesion of the liquid packaging film include:
1. The corona treatment of the substrate did not reach 40 dyne/cm or more, and the surface was dense, smooth, and the ink affinity was poor.

2. The addition of the oily material in the masterbatch is not enough. Although the gloss is improved and the friction coefficient is reduced, the printing fastness is reduced and the heat-sealing fastness is reduced. Therefore, the choice of masterbatch is very important. Improve the adhesion of the ink to the printed substrate and enhance the compatibility of the binder in the ink with the printed substrate film. Select a solvent that has good swelling or solubility in the printed substrate film, increase the binder content in the ink, and add the amount of tackifier resin in the ink to improve the adhesion of the ink.
3. Add solvent misalignment, not in line with actual standards.
4. The ink is too old and has impurities and must be filtered.
5. The addition solvent contains moisture.

There is a sound when the liquid packaging film is printed, and it adheres after winding.

After the plastic film is reeled by gravure, the printed ink or ink between the printed surfaces is adhered together after being divided and cut to form a package bag, and the printed surfaces cannot be separated. (The ink is caused to fall off when the force is applied, and the product is scrapped.) . The analysis should begin with the possible causes of adhesion, ie, ink stickiness, high humidity, and too much pressure.
1. Intrinsic factors that cause adhesion: The ink itself is poorly heat-resistant and has some tackiness.

When a large amount of solvent remains in the printed ink, it is as if the paint is not dry—though it appears to be dry to the naked eye, it is actually not dry and sticky. After the printed matter is rolled up, the residual solvent is difficult to evaporate, and the resin in the ink cannot be dried and solidified, resulting in severe blocking of the finished product. With sticky products, if measured by gas chromatography, the residual solvent content often reaches tens of thousands of PPM, and the residual solvent will cause the product to contain odors. This not only affects the strength of the composite, it affects the flavor and hygiene standards of the food. Start with the dryer's performance, drying conditions, and load. Second, use fast-drying fluxes as much as possible. Finally, the printed materials should be stored in a damp-proof manner. This is to prevent the moisture in the raw materials from swelling the resin in the ink and creating stickiness.

2. Improper ink ratio causes stickiness. For special performance (heat-resistant, oil-resistant) inks, hardeners are added to the inks. Hardeners are low molecular weight materials that are inherently tacky. The resin is poor in heat resistance. In the preparation of gravure inks using synthetic resins, resins having a high global softening point should be used. Generally, the softening point of the resin selected between 105°C and 0°C is too low to be heat-resistant.

3. Rewind too tightly. In the printing process, the film should not be too tensioned or rolled too long or too tight. Because the printing press keeps running, the winding volume keeps increasing, especially if some local network points are too deep, the area is too large, and the ribs are easy to stick.

4. Insufficient adhesion between ink and substrate. Solving this problem can be tried in two ways. On the one hand, the correct choice of ink is used to control the quality of the ink to adapt it to the substrate. On the other hand, the substrate surface should be treated to increase its affinity for the ink. It is best to perform single-sided treatment to prevent double-sided tension from occurring. This is because the double-sided electrical treatment has a good affinity for the adhesive ink surface and causes anti-adhesion.

To sum up, in addition to the correct selection of film when printing milk ink, we must fully consider the nature of the ink, such as wear resistance, moisture resistance, temperature resistance and so on.

Source: Ink News