Heat shrink film printing ink selection

Heat shrink film printing ink type

Heat shrinkable inks need to have strong adhesion, flexibility, and considerable heat resistance, and the pigments in the ink cannot be discolored or discolored at high temperatures. This ink requires better performance in all aspects than other inks.

Nobel Ink's marketing development manager believes that there are currently four types of inks that can be used as heat-shrinking materials: solvent-based inks, water-based inks, cationic UV inks, and free-radical UV inks. Solvent-based inks currently have the largest market share, followed by water-based inks.

What needs to be added is that the reason why cationic UV inks cannot be widely used in the field of heat shrink film printing is mainly because the price is too high. Moreover, cationic UV inks are more “difficult” than free radical UV inks. Free radical UV inks are not only relatively inexpensive, but also simple to use, eliminating cumbersome preparations like cationic UV inks.

The largest volume in the heat shrink label market is solvent inks. Large companies are still the main customers of the shrink film market, and large companies often require large-volume, long-lived printing. Solvent based gravure inks are now the most suitable for long live printing, making solvent inks the best choice for the shrink film market. However, with the development of the shrink film market, small brands and small customers gradually show great interest in heat-shrinking materials, which will inevitably drive the growth of inks suitable for short live printing. By then, suppliers and intermediaries will invest in the necessary equipment to make a fuss about water-based inks and free-radical UV inks.

How to choose

Like other packaging printing, in the heat shrink film printing market, it is important to select the most suitable ink for the printed matter. First, determine the print performance in some aspects. Is the use of flexographic or gravure printing? Does the shape of the container require high shrinkage of the material? What happens to the container during the production, transportation and sale of the product? How much friction factor is required? Answer these questions to the customer. At the same time, ink manufacturers can better assist printers in finding ink that best suits their product requirements.

The three factors that ink suppliers and agents must consider first are shrinkage, adhesion, and the ability to release residual solvents—the ability to dry quickly at lower temperatures.

Shrinkage - The most important factor to consider when selecting inks for shrink labels is how well the ink shrinks. Different applications have very different requirements for shrinkage. High shrinkage occasions require 60% to 70% shrinkage, while low ones only require 10% to 20% shrinkage.

Eco-friendly water-based inks have a shrinkage of more than 40%, are very flexible, and cost less than UV inks. Moreover, the surface of the ink is less affected by the movement of atoms in the molecule. Radical UV inks can be cured in real time. This ink is inhibited by oxygen rather than by moisture. In general, the shrinkage is less than 20%. In some substrates, adhesion is limited and there may be atomic movements in chemical molecules on the ink surface. Water-based inks and free-radical UV inks are more suitable for materials with medium and low shrinkage.

Solvent-based inks are similar to aqueous inks in that they are very elastic and have a shrinkage of more than 40%. The drying time required for a solvent-based ink is less affected by the moisture, but it is somewhat affected by the movement of atoms in the chemical molecule. Cationic UV inks produce good adhesion on a wide variety of substrates and have a shrinkage of more than 40%. In addition, the ink can be cured almost in real time, and there are fewer atoms in chemical molecules, but the price is also more expensive than free radical UV inks. The maximum shrinkage of cationic UV inks and solvent inks can reach 70% to 75%, which is more suitable for applications with high shrinkage.

Adhesion - Contact between ink layers is often encountered during printing and rewinding. If a poor adhesion ink is used, then the product's contact with the ink layer at the time of stacking will cause problems. The most common problem is adhesion, where the ink layer sticks from one side of the material to the back of the other. In general, if the ink does not adhere well, you can use a method to increase the oven temperature. However, heat-shrinking materials are sensitive to temperature and cannot increase the temperature to increase ink adhesion. At present, the best adhesion inks are solvent-based inks and cationic UV inks. Water-based inks and free-radical UV inks have always been unsatisfactory in adhesion due to the limitations of their own raw materials. Therefore, many manufacturers have been working hard to improve their adhesion. direction.

Residual solvents - Now there are quite strict national standards for solvent residues, especially for some large companies. If the drying temperature is adjusted to be higher during the drying of the ink, the solvent will evaporate faster, but if the temperature is too high, the material will shrink in advance. Therefore, excessive heat cannot be applied to the shrink film during printing. This requires finding a balance between printing conditions and drying conditions.

Before the printer selects the appropriate ink for a particular heat shrink film, the heat shrink film and the ink must also be rigorously tested for compatibility. General test items include adhesion, water resistance, adhesion, coefficient of friction, residual solvents, and the like.

No matter what kind of ink is best sold, no matter how often ink companies test the compatibility of ink and heat shrinkable material, one thing is convinced: The market share of heat shrinkable ink in the entire industry has been increasing, despite the current The proportion is still relatively small, but its growth rate will be very considerable in the coming years.

Author: Haofa Yi Shanghai University of sources of information: "Printing Technology" 2005, 10 (packaging and decoration printing)