Reasons and elimination of anti-sticking phenomenon in plastic film printing

Anti-tie (back-adhesion, back-adhesion) refers to the phenomenon that the printing layer adheres to the back side of the film or the printing layer adheres to each other in the process of compounding or bagging after the plastic film is printed and wound. Due to the transfer or pull of the graphic, it often results in a large number of scrapped prints. The anti-sticking phenomenon tends to occur at high temperatures, especially during periods of high humidity. The reason for this is often the result of a combination of environmental, ink, solvent, film, and printing process factors. To solve the anti-sticking phenomenon, it is necessary to analyze specific conditions and rationalize the factors from a comprehensive perspective. The interaction between them.

Commonly used inks for printing plastic films include polyamide surface printing inks, chlorinated polypropylene composite inks, and polyurethane inks. Among these three types, chlorinated polypropylene composite inks have a lower probability of anti-sticking because chlorinated polypropylene composite inks are generally used to print BOPP films. The film is non-polar and the corona treatment on both sides is different. Large, and no corona surface only 32 dyne, and poor affinity with the ink; In addition, chlorinated polypropylene composite ink has good solubility of common solvents, easy to adjust the solubility and volatilization rate during printing Balance adjustment.

In the case of anti-adhesion using polyamide printing inks, the printing film is often a corona LDPE tube, or it is packaged together and placed together after bag making. In terms of ink properties, the softening point of the polyamide binder is generally about 110°C, and it tends to become sticky under relatively high temperature and high humidity conditions. When printing, because the printer considers the effect of electric heating on the overlay accuracy of the LDPE film, it does not dare to heat, or open the cold wind, resulting in excessive residual or surface drying of the solvent in the printing layer. When rewinding, the elongation of the LDPE film is larger. As well as the regularity of the printed pattern, it appears as the diameter of the roll increases. The brute-force phenomenon triggered the anti-adhesion of the ink layer. To solve this kind of problem, it is best to use high-grade ink with relatively low viscosity and high color concentration so that the printing ink layer is thinner. Use idle printing units to increase film drying time and cooling distance. The printed film is made as early as possible and dispersed in the box for a period of time.

Due to its high gloss and good resistance (such as temperature resistance, oil resistance, and weak acidity and alkali resistance), polyurethane ink has developed rapidly in recent years, and its usage has been rising rapidly. In the summer, when polyurethane ink is used to print NY and PET films, anti-sticking phenomenon is more likely to occur. In the actual printing process, the phenomenon of ink reversed due to film failure is relatively easy to eliminate, and due to the inability to grasp the use of ink caused by improper setting of process parameters lead to anti-sticking phenomenon of printing film, it is our printing technicians need to spend Great mind to solve. Polyurethane inks generally use keto solvents such as methyl ethyl ketone as the true solvent, and are used as binder resins for dissolving inks. For example, the commonly used solvents include butanone and isopropanol. Toluene. Among these three solvents, butanone has the fastest rate of volatilization. During the printing process, the amount of butanone was not replenished in a timely manner, causing the ink in the ink tank to swell due to the poor solubility of the resin, and the typographic degree increased. Affects the adhesion of the ink to the film. Therefore, when using a polyurethane ink, butanone must be maintained in a relatively sufficient amount in the dilution solvent. When the polyurethane ink is printed in the summer, the viscosity of the ink rises quickly. The operator must continuously replenish the diluent solvent and keep the ink in the ink tank always at a relatively low viscosity.

A great deal of practical experience shows that the phenomenon of ink anti-sticking caused by the ink-skin surface-drying of polyurethane inks is mostly. To solve this phenomenon, the ink is required to be printed at a low viscosity. In the low-viscosity state, the amount of printing ink is small and the ink layer is thin. Under the effect of a large amount of dilution solvent, the polyurethane ink connecting material molecules are relatively loose, and the shielding ability against solvent volatilization is weak. When the ink is transferred to the film, the solvent can quickly and completely separate from the ink layer in the drying tunnel, and it is not easy to produce a "dry surface" phenomenon. After adjusting the proportion of the solvent and viscosity of the ink, the following points need attention of our operators. First, the temperature and air volume of the drying tunnel should be proportionally balanced. When the temperature is high, the air volume is relatively large, and the temperature of the light or the light energy of the light is liable to cause “drying”, and the proper high temperature and sufficient air volume are maintained before the ink layer can be completely dried. Second, the printed film is cooled. After the final color of the film is printed, it needs to be properly cooled and rewinded. Excess heat is present in the printed film, which may cause softening of the ink layer and exacerbate anti-sticking. Third, the winding tension and film roll diameter. The molecular structure of the polyurethane ink binder and the PET film is similar, and the ink has a good affinity for the PET film. The PET film is a rigid film and has good gas barrier properties. Even a small amount of solvent residue in the printing ink layer may cause an adhesion effect between the ink layer and the back film. Therefore, in practical applications, the PET film is more likely to exhibit anti-sticking phenomenon than the NY film. The winding tension should be as small as possible while ensuring that the film roll is not loose. At the same time, the small roll diameter also ensures that the film fastening force at the inner diameter part is not large.

- The harm caused by the anti-adhesion phenomenon is enormous, and many color printing manufacturers may have encountered similar problems more or less. Therefore, they have also accumulated considerable experience in processing. In the above section, the factors that produce anti-posts are analyzed based on ink performance characteristics and suggestions are made. Hopefully, they can provide some help for the friends of the color printing factory. At the same time, more earnest hopes can get more suggestions and promote our color printing industry. Improvement of technology level.

(Text/Yong Yongyue)