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Dry lamination of flexible packaging plastic bags’drop ink’Analysis and Countermeasures

Dry lamination of plastic films is a common lamination method, which integrates the characteristics of various films to meet the needs of different commodities. Dry compounding is a technical process, and it is necessary to have a full understanding of the process in order to have the ability to solve problems. Common failures in the dry lamination process include reduced peel strength and odor failure. Among them, ink loss can also occur. Dropping ink is also known as supporting ink or washing ink. It usually means that when the printing substrate is dry compounded, the printing ink is pulled down by the glue and adheres to the screen roller or smooth roller. When the roller keeps rotating, it is pulled down. The downed ink is transferred to the film during the lamination process, which eventually leads to the incomplete picture and text that has been pulled down, resulting in scrap; or the transferred ink residual layer adheres to the next section, making the picture and text blurry, and still makes it difficult to use. This product is obsolete. People in the industry often complain that ink failure is difficult to solve. This article summarizes the actual situation. Hope to make reference for operators or related technical personnel engaged in the same industry, and exchange and discuss.one,’drop ink’Phenomenon analysis of the effects of poor substrate surface preparation. 1, Gravure printing is to immerse the printing plate in the ink tray, the ink infiltrates the web page, the scraper scrapes off the excess ink, and the ink in the web page is transferred to the printing substrate under a certain pressure of the rubber roller to complete the printing. This process includes two aspects, one is the good infiltration of the mesh and the ink; the other is the infiltration of the ink in the holes and the printing substrate. 2, Gravure printing substrates are often used non-polar film materials such as polyethylene and polypropylene. The surface is dense and smooth. It is an inert surface. The surface free energy is relatively low.2.9—3.0×10-6/cm2, theoretically, the surface free energy is lower than3.3×10-6/CM2The film cannot be used. If the EDM-treated material is measured, the existence of hydroxyl groups and junctions can be found. In addition, the impact of electron beams will also cause micropores on the surface of the film and become rough, which is convenient for the penetration of ink. After the treatment of the film, the printing fastness is greatly increased. The effect of electric spark treatment is related to the amount of new ecological oxygen generated by the voltage of the electric spark. Appropriate conditions can make the surface tension of non-polar polyethylene and polypropylene from the original29-30dyn/cmimprove to40-45dyn/cm. In fact, no matter what kind of plastic is surface-treated, as long as it reaches38dyn/cm, its adhesion fastness will be greatly increased.Dyne pen or self-prepared test solution can be used to detect the surface energy of the printed film. The detection method is to stick a little with a cotton ball and coat the plastic surface. If it does not shrink and spreads flat, it meets the processing requirements. On the contrary, if it is water droplets If the distribution is not enough, the surface energy is lower than the detection requirements, and the ink adhesion is low. Usually the surface energy is clearly defined:bopp38dyn/cm.PET 44yn/cm,NY 52dyn/cm. If it is not handled properly and printed again, it is easy to be pulled off during the compounding process.two,’drop ink’The phenomenon is related to insufficient drying during printingWhen printing, a drying box is used to dry the ink. When drying, the heating wire is usually used to heat and add cold phoenix. The purpose of drying is to make the solvent volatilize cleanly, and at the same time, it is beneficial to the adhesion of the ink layer. If the drying is not sufficient, the solvent is not fully evaporated, the surface layer is dry and the inner layer is not dry, which will not only result in printing’cross color’and the ink will be lost during compounding, especially when compounding is completed immediately after printing. The solution is to adjust the evaporation rate of the solvent and increase the drying temperature to completely dry the ink layer. For the printed substrate, the placement time can be appropriately extended to reduce the film drop during compounding. The ultimate purpose of the glue during compounding is to have a good infiltration coating with the ink layer substrate. If the surface layer is dry but the inner layer is not dry, the surface is diluted by the glue solution, the inner layer is wet and cannot withstand re-wetting, and the ink is diluted. Film peeling occurs due to transfer under pressure, so drying during printing is critical.three,’drop ink’The relationship between phenomenon and glueThe ratio of glue liquid should not only strictly follow the instructions, but also need to be adjusted according to the actual pictures and uses. If the diluent is excessive, the concentration of the glue will be low, and the ink drop phenomenon will also occur. The most direct solution is to increase the concentration of the glue and adjust the diluent to an appropriate range. We noticed that when using one-component hot melt adhesive, the phenomenon of ink drop is more than that of two-component two-component reaction type. If the glue is used incorrectly, the phenomenon of ink washing will also occur. For example, when the ink is a polyamide surface printing ink resin system, it is best to use a suitable one-component hot melt adhesive for coating, and the phenomenon of ink washing is less. If the printing ink is based on the chlorinated polypropylene resin system, it is necessary to use a two-component two-component reactive polyurethane coating cloth. On the contrary, the phenomenon of ink washing is very likely to occur when coating with hot melt adhesive, because they are not allowed to the result of. If a smooth roller is used for sizing coating, the phenomenon of ink washing can be appropriately reduced. If the blade type dry lamination is used, reducing the pressure of the rubber pressure roller and the screen roller can also reduce the phenomenon of ink support.Fourth, other methods to reduce ink drop 1, The smooth roller coating and gluing system is gently rotated by the mesh roller gear. If the smooth roller gear is seriously worn and the bearing runs without oil, it will inevitably cause stop and go, so the possibility of ink loss is very large. In order to reduce this factor, it is necessary to replace the gear or add oil to the roller. Only synchronous operation can effectively reduce the phenomenon of supporting ink. 2, Increase the amount of glue or increase the working concentration 3, Increase the machine speed, reduce the contact time between the ink layer and the glue, and increase the drying temperature accordingly 4, Reduce the pressure of the rubber pressure roller 5, If there is a chemical reaction between the ink and the glue, you should consult the production and supply department, replace the ink or solve it by other methods.To sum up, there are various forms of ink loss, which need to be dealt with in specific situations in actual work, and cannot be generalized.

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