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The use of cationic UV ink instead of gravure solvent ink in the printing of composite flexible packaging products not only effectively solves the problem of VOC source control, but also meets the safety requirements of food packaging. Some flexible packaging products can even simplify the production process, transforming from inner printed composite printing products to single material surface printed products.
Many products in the petrochemical and building materials industries are packaged in PE bags with a thickness of 100-150 µ m. The printing of packaging bags mostly uses solvent based or water-based inks, which have VOC issues, or printing patterns are prone to sticking, have poor alcohol resistance, and wear resistance.
Printing with free radical UV ink may also have issues with poor adhesion and wear resistance. If the products in the inner packaging are used in the food industry, there may also be safety hazards. Residual monomers, amines, and film-forming aids in water-based inks, as well as residual initiators and unreacted monomers in free radical inks, may migrate and contaminate the finished product.
The natural advantages of cationic UV ink can effectively solve the above problems and meet the safety requirements of food grade products.
At present, solvent based gravure printing is commonly used in the printing of bottle labels in the industry, and a few companies also use solvent based flexographic printing. Regardless of the printing method, VOC is a headache. Due to the fast evaporation rate of solvents, if solvent based flexographic printing is used, the anilox roller and printing plate are particularly prone to blockage, and plate wiping is a very troublesome task. The workload of workers is huge, and it is also easy to damage the printing plate.
When cationic UV ink is used for printing such products, it can effectively solve the above-mentioned VOC and dry plate problems. Meanwhile, cationic UV ink, due to its high polarity and surface tension, will not affect the adhesion of the bottle label.
At present, many companies use free radical UV ink flexographic printing technology for label printing inside the film. Of course, there are also water-based and solvent based ink printing processes. When printing PP materials, due to adhesion issues, the PP material needs to be coated with a layer of primer, which is much more complex and has defects in the appearance of the product. When not polished, the scratch resistance of the primer will not be satisfactory.
Cationic UV ink has excellent adhesion to PP, which can be used as a primer for online UV printing or directly printed without the need for a primer. In addition, cationic UV ink has excellent heat resistance, with a temperature resistance of over 280 ℃ in a short period of time. It will not be washed away by molten rubber during injection molding, making it very suitable for printing inner film labels.
Sanitary products such as diapers and sanitary napkins have close contact with the human body, which requires the ink on sanitary products to be safe, non-toxic, and sweat resistant. Currently, there are two commonly used printing inks: water-based and solvent based. Solvent based inks can bring VOC, and water-based inks are also sensitive to human sweat and often fade. If free radical UV ink is used for printing, safety cannot be guaranteed.
Cationic UV ink is sweat resistant, free of VOC, and has good printing adaptability. The most important thing is the ultra-high conversion rate of cationic epoxy, which ensures the safety of cured ink. Therefore, cationic UV ink is an excellent choice for printing sanitary products.
At present, the packaging of napkins is mostly printed inside, using solvent based ink with the text facing inside the napkins. Why is this design necessary? The main reason is that solvent based inks have poor resistance, and the ink will wear out during transportation, resulting in a deterioration of the appearance of the product. If composite films are used, the cost will also increase. Ink facing inward may also pose safety issues. Residual solvents and harmful substances in ink can be absorbed by tissues, causing odors in mild cases and harmful to the human body in severe cases. This packaging mode, such as changing to water-based ink and free radical UV ink, will make the situation worse because water-based ink has poorer durability, stronger odor, and the taste and harmful substances of free radical UV ink are also not allowed.
In addition to regular dry tissues, wet tissues and makeup remover cotton wet tissues contain about 75% alcohol. If the inner printing method is still used, the ink will be dissolved by alcohol, so currently only composite film can be used for packaging.
The alcohol resistance test of cationic UV ink (99.9% alcohol content) can exceed 100 times. If it is 75% alcohol, it can be soaked for a long time; Another advantage is the excellent wear resistance of cationic UV ink, which can be printed on such packaging materials through surface printing. The gloss, cost, performance, safety, environmental protection, and other properties have made a qualitative leap.
The traditional production process for protective films is "gravure printing+composite+coating", which is complex and costly. Cationic UV ink has excellent adhesion and solvent resistance. After switching to cationic UV ink, the composite process can be omitted and simplified to a simple process of "flexographic printing+coating". This process can not only save 30% of costs, but also save composite equipment and production space.
1) Traceable QR code field
For safety reasons, more and more products require QR code traceability, such as cigarettes, alcohol, drugs, food, beverages, etc. The printing ink for QR codes can be commonly used small character ink or free radical UV ink. The former requires a large amount of solvent, while the latter has significant performance defects. Tetra material with good adhesion such as paper and PVC are still good, and cannot meet the adhesion requirements when printing on PP, PE, PA and other materials.
At present, in addition to the outer layer of flexible packaging products, PP or PE materials are often used, and a large part of bottle caps are also made of PP or PE materials. When printing on these materials, conventional ink cannot balance the properties of adhesion, alcohol resistance, oil resistance, low odor, low migration, and scratch resistance. Only cationic UV ink can fully meet these properties.
2) Personalized printing and short form printing in the field of flexible packaging
The packaging bags for pre made dishes, hot pot seasoning, and other products are mostly made of PP or PE outer materials. The process often involves making blank bags first, and then printing or pasting labels. The labeling process is extremely labor-intensive and material intensive. However, solvent based inks, water-based inks, and free radical UV ink cannot meet the requirements of use due to issues such as adhesion, cooking resistance, oil resistance, alcohol resistance, and migration. In this case, cationic UV ink can meet the above performance and technical indicators.
