Currently, there are four types of inks that can be used as shrink sleeve printing: solvent inks, water-based inks, UV inks (including cationic UV inks, and free-radical UV inks). So how do you choose the right type of ink? The author believes that the printing plant and ink supplier first understand the following information:

â—† Printing method

Different printing methods The printability of the ink is different. Flexographic printing and gravure printing are mainly used for shrink label printing. Solvent printing inks are generally used for gravure printing, and PVC, high shrinkage PVC, PETG, OPS and OPP films can be selected for printing materials. While printing on flexographic printing presses, environmentally friendly water-based inks are mainly used.

â—†The shape of the container

Different container shapes have different requirements for the shrinkage of the material. For example, an approximately cylindrical container with a low shrinkage requirement may consider the use of OPP or PVC materials, while a container with more curved or streamlined designs may consider an OPS film with high shrinkage and strength. OPS film can be closely attached to various shapes of containers, not only can print exquisite designs, but also to meet the use of a variety of different shapes and new packaging containers. OPS is non-toxic, odorless, oil-resistant, and complies with food hygiene standards. It allows designers to use eye-catching colors to achieve 360° label design, give full play to creativity and imagination, and make the label pattern more vivid and prominent. The image on the shelf creates an unexpected container effect. For example, the newly-produced curved glass bottles for domestic Blue Ribbon beer use a high shrinkage OPS substrate and use a solvent-based adhesive for labeling.

â—†Print material

Different printing materials such as PVC, OPS, OPP, PETG and other materials require different inks. PVC, PETG, and OPS account for 90% to 95% of the shrink label market. Because different films have their own surface characteristics, each film requires the use of a specific ink composition in order to obtain suitable properties. However, in order to reduce the number of press cleaning, reduce cross-contamination, and control the amount of ink, general-purpose inks will have a good development. This type of ink is suitable for a variety of shrink label materials. Flexsysure XSUV radically curable inks from XSYS can provide 70% shrinkage for a wide range of film materials, including PVC, OPS, OPP, PET, and PETG, and can be used for both surface and in-print. Fujifilm's Uvisleeve UV flexographic printing inks can be used with a variety of P-end fatigue actuators according to the shrinking process (friction coefficient, which determines the slippage efficiency of the label on the surface of the container), low chemical odor and maximum Shrinkage to facilitate shrinkage of a variety of label materials. The role of low COF is mainly reflected in the seaming process, which allows the sleeve to quickly pass through the labeling device after being sealed. In addition the company can also provide high opacity white ink.

â—†Product storage and transportation environment

In the process of production, transportation and sales of the product, what happens to the container, how much friction coefficient is required, and what is the temperature and humidity environment? Is there a special request? For example, shrink sleeves for beer and beverage products require good ice-water resistance.

After understanding the above factors, we can choose the right ink from the aspects of shrinkage, adhesion and the ability to release residual solvents (the ability to quickly dry at lower temperatures):

Shrinkage rate

This is the primary consideration when selecting heat-shrinkable label inks. Because different products have very different requirements for shrinkage. Products with high shrinkage rate require 60% to 70% shrinkage, while low products require only 10%–20% shrinkage.

Adhesion

When printing and rewinding, the contact between ink layers occurs from time to time. If a poor adhesion ink is used, problems with the contact of the ink layer occur when the product is deposited. 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. 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 the limitations of their own raw materials;

â—‡ Residual solvent (VOC)

The national standard now has quite strict standards for the amount of solvent residues. Some printing plants adjust the drying temperature to a relatively high level during the ink drying process in order to volatilize the solvent faster, which leads to the material pre-shrinkage. Therefore, excessive heat cannot be applied to the shrink label during printing. This requires finding a balance between printing conditions and drying conditions. In the printing of shrink film labels, the heat control of the printing press is also very important. It is required that the printing machine must be able to disperse and eliminate heat and prevent the shrink film from shrinking during the printing process. Some newer presses are equipped with chill rolls to remove heat and lower the temperature of the film.

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

Ink type Shrinkage performance

Free-radical UV inks cure in real time and generally have a shrinkage of less than 20%. In some substrates, adhesion is limited and there may be atomic movements in chemical molecules on the ink surface. Suitable for materials with medium and low shrinkage

Cationic UV inks produce good adhesion on a wide variety of substrates. Cationic UV inks shrink more than 40%. Maximum shrinkage can reach 70% to 75%, more suitable for high shrinkage applications. The ink can be cured in real time and the atoms in the chemical molecules move less, but the cost is also more expensive than free radical UV inks

Solvent-based inks have a shrinkage rate of more than 40% and a maximum shrinkage rate of 70% to 75%. The drying time required for solvent-based inks is less affected by moisture, but is more affected by the movement of atoms in chemical molecules. Suitable for high shrinkage materials

Eco-friendly water-based inks have a shrinkage of more than 40%, are very elastic, and cost less than UV inks. The surface of the ink is less affected by the movement of atoms in the molecule. Suitable for medium and low shrinkage materials