In recent years, the annual output of beverages in China has shown an annual growth rate of 10% to 20%. According to statistics, in 2005 its total output was close to 30 million tons. In 2006, many beverage companies increased their production by 40% to 50% over the same period of last year. It can be said that the beverage industry is currently one of the fastest growing industries in the food industry. In this huge market cake, juice drinks account for about 10%, and tea drinks account for about 15%. The beverage giants are rushing to the beach beverage market. Unified, Huiyuan, Master Kong, Pepsi, Coca-Cola, Nongfu Spring, Robust, and Yinlu all launched their latest beverages. The beverage industry is so hot that it is used in beverage packaging. Naturally, as a shrink label that highlights the brand's image, natural benefits have been gained, and a variety of shrink label printing inks are used to achieve excellent label printing.
Choose a shrink label printing ink need to understand
There are a lot of shrink label printing inks. How to choose the proper ink type? The ink supplier must first understand the following information.
â— Printing Methods Flexographic printing and gravure printing are mainly used for shrink label printing. The ink printability of different printing methods is different.
â— Container shape The shape of different containers has different requirements for the shrinkage of the material.
â— The printing materials with different printing materials such as PVC, OPS, OPP, PETG and other materials have different requirements for the ink.
â— Storage and Transportation Environment of the Product During the production, transportation and sales of the product, what happens to the container, how much friction coefficient is required, what is the temperature and humidity environment, and whether there are special requirements (shrinking labels for beer and beverage products Need good ice water resistance) etc.
Only after understanding the above factors can we select suitable inks from the aspects of shrinkage, adhesion, and ability to release residual solvents (ability to quickly dry at lower temperatures).
â— Shrinkage This is the primary consideration when selecting heat-shrinkable label printing inks. Because different products have very different requirements for shrinkage. High shrinkage products require a shrinkage of 60% to 70%, and low shrinkage rates of only 10% to 20%. The shrinkage properties and applications of different types of inks are shown in Table 1.
â— Adhesion When printing and rewinding, ink layers will often come in contact with each other if poor adhesion inks are used. Then, problems occur when the product is in contact with the ink layer. The most common problem is adhesion. 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. For the moment, the best adhesion inks are solvent inks and cationic UV inks. Water-based inks and free-radical UV inks have relatively poor adhesion due to their own raw material limitations.
• Residual Solvents National standards now have fairly stringent standards for residual solvent. Some printing plants set the drying temperature higher during the drying process of the ink in order to make the solvent evaporate faster, but this would cause the material to shrink in advance. Therefore, excessive heat cannot be applied to the shrink label during printing. This requires finding a balance between printing conditions and drying conditions.
In addition, printers must also rigorously test the heat shrink film and ink compatibility before choosing the right ink for a particular heat shrink label.
General test items include adhesion, water resistance, adhesion, coefficient of friction, residual solvents, and the like.
The characteristics and application of various shrink label printing inks
At present, there are four types of inks that can be used as heat-shrinkable materials: cationic UV inks, radical UV inks, solvent-based inks, and water-based inks.
The following uses one-to-one analysis of the inks used on shrink labels.
1. Cationic UV ink
Cationic UV inks are used less often in the field of heat shrink film printing, mainly due to the fact that their price is too high and a specific device needs to be used to catalyze the polymerization reaction by using photoinitiators under UV light to generate acidic substances. The cationic agent induces a chain reaction of epoxy groups until the oxygen bond is broken or a glassy polymer is formed and the chain reaction is terminated. The infrared light emitted by the UV lamp is the key to controlling the reaction rate and complete reaction. Cationic polycondensation reaction must fully understand the nature of the film to avoid ink cracking, to ensure complete ink curing.
â— cationic ink advantages
The reaction type is a gradual ring-opening polymerization reaction of a typical epoxy group, which increases the content of the active component of the ink and is almost completely converted into an ink film.
â— cationic ink disadvantages
1 longer reaction time. Since the cationic polycondensation reaction is slower than the radical polycondensation, it takes a long time and the ink film is cross-linked and adhered to the substrate to reduce the pressure on the substrate. The shrinkage of the ink film of the cationic cured product is generally less than 5%.
2 Because the reaction rate is slower than radical polymerization, high temperature curing is often required. High-temperature curing, combined with low ink film shrinkage, can often cause the film edges to be uneven and not smooth. In general, the selection of 80W UV light source can ensure the rapid and complete curing cationic ink. If the temperature is lower than this temperature, the durability and adhesion of the ink film will be significantly reduced, and the odor will be large.
3 The cation polycondensation reaction will be terminated by the influence of atmospheric humidity. Hot and humid weather can cause constant changes in the ink properties. Therefore, the temperature and humidity control system is an essential device for cationic UV printing.
4 ink composition is difficult to choose. First, the price of the basic ingredients of cationic inks is higher than that of free radical inks. Second, since the alkaline substances delay or even inhibit the progress of the reaction, the content of such substances in the ink cannot be too high. Acidic substances can also not be used in excess, otherwise it will increase the viscosity of the ink into a gel. For this reason, ink engineers must strictly control the type of pigment in the ink composition, and perform surface treatment on the pigment to make its pH value neutral. Therefore, many pigments cannot be used because they cannot meet the UV ink fluidity and viscosity requirements.
5 There are high requirements for dispersants. Cationic inks have strict regulations on the type of dispersant, which in turn limits the amount of pigment added in the ink, resulting in poor color performance of the printing ink layer, and graphic colors are not bright.
6 Cationic initiators contain heavy metal elements and release a small amount of benzene, which pollutes the environment and endangers the health of workers.