Shrink film label printing processing (on)

The market competition has intensified, and many flexo label printing companies have already turned to shrink film labels. The shrink film label market is experiencing rapid growth and its market share continues to expand. It is expected that the annual growth rate can be maintained at between 7% and 10%, far exceeding the annual growth rate of 4% to 5% in the general label market, with huge development potential. .

Shrink film labels can be divided into two categories: Shrink sleeves and Wrap-around labels.

Commonly used shrink film

The thickness of the shrink film is generally about 50 μm. In the past few years, 40 μm and 45 μm thick films have also been widely used. The exact thickness of the shrink film should be determined by its labeling performance on the labeling equipment.

Shrink films are very sensitive to heat, so high temperatures must be avoided during storage, printing, and shipping.

The following commonly used shrink film:

(1) PVC. In the field of shrink film in the United States, PVC shrink film occupies 2/3 of the market share. The shrinkage rate of PVC shrink film is higher, between 40% and 60%, and the cost is lower, and the tensile strength is better. It is suitable for multi-package combination packaging.

The main problem with PVC shrink film is poor environmental protection, plastic container recyclers are reluctant to recycle PVC shrink film. Moreover, the relative density of PVC and PET materials is relatively close to about 1.33. In terms of the current level of technology, it is difficult to distinguish between the two in the recycling process.

(2) PETG. In all types of shrink films, PETG films have the highest shrinkage, which can reach 78%. PETG shrink film occupies a market share of 15% to 20%. Its relative density is 1.28, but its high price hinders its development.

(3) OPS. Compared with PVC shrink film, OPS shrink film has excellent environmental protection; compared with PETG shrink film, OPS shrink film is cheaper and more economical. The current market share of OPS shrink film is 5%, and it still maintains a rapid growth momentum.

The OPS has a relative density of 1.025 and a shrinkage of up to 65%. Moreover, in the contraction process, contraction does not occur substantially in the opposite direction to the contraction.

(4) OPP. Although the shrinkage of the OPP film is low, its application in the area of ​​shrinking around the label can not be ignored, it occupies 18% to 20% of the market share. OPP shrink film is more suitable for approximately cylindrical containers that do not require high shrinkage. The relative density of OPP is 0.90, so it can provide higher output at a very competitive price. OPP shrink film is only suitable for shrink wrapping labels.

In order to improve the scratch resistance of the ink layer and better protect the printed graphics, after printing on the surface of the white OPP film, a layer of other substrate needs to be compounded.

Printing ink

There are four major types of inks used for shrink film printing: solvent inks, water-based inks, cationic UV inks, and free radical UV inks. Judging from the current application situation, solvent-based inks dominate the field of shrink film label printing, followed by water-based inks and radical-type UV inks, and cationic UV inks are expensive due to their high cost and are cumbersome to print. There is less application in the shrink film field.

When selecting suitable shrink film printing inks, the following performance indicators are mainly considered.

(1) COF (Friction Coefficient). For shrink sleeve printing inks, COF is a very important indicator, which determines the slip efficiency of the sleeve on the surface of the container.

(2) Shrinkage. The shrinkage of the ink is also critical for the printing of the shrink film, which must match the shrinkage characteristics of the shrink film. In general, when the shrink film with a higher shrinkage ratio is printed, the shrinkage ratio of the used ink is required to be between 60% and 70%; when the shrinkage film with a lower shrinkage ratio is printed, the shrinkage ratio of the ink is generally between 10% and 20%. between.

Water-based inks, solvent-based inks and cationic UV inks all have a shrinkage of more than 40%, giving them greater flexibility. Among them, cationic UV inks have higher shrinkage and flexibility. Free radical UV inks and EB inks typically have a shrinkage of less than 20% and are less flexible.

(3) Adhesion. Solvent-based inks and cationic UV inks have a wide range of adaptability to thin film materials and good adhesion. Water-based inks and radical-type UV inks have poor adhesion due to the limitations of the chemicals used, and need to be further improved.

(4) Residues and migration of chemicals. It is required that the ink be dried quickly under low heat so as not to migrate residual chemicals onto the printed surface.

Water-based inks are environmentally friendly inks, with less migration of chemicals and are much cheaper than UV inks. The migration of chemical components in solvent-based inks is relatively more. Radical UV inks cure quickly and cure instantly, but the chemicals in the ink may migrate to the surface of the substrate. Cationic UV inks cure instantaneously with less chemical migration, but they are more expensive than free radical UV inks.

At present, the printing method of shrink film labels is still mainly gravure printing, and the share of flexographic printing methods is relatively small. Shrink film labels also have certain requirements for printing equipment, mainly in tension control and heat control.

Since the film material is easily deformed by stretching, it is necessary to precisely control the printing tension when printing such materials. Some older models of presses or printing machines designed specifically for adhesive film labels with substrates are simply not suitable for the printing of shrink film labels.

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.

For shrink sleeve printing, a sealing device is also needed to change the film into a tube and seal the overlapping parts together (to form a seam). Then the film is pressed flat and finally rolled up. . Sealing quality control and testing are very important so as not to affect the subsequent process of labeling. Sealing parts are generally not printed graphics, and to ensure clean, no dirt, otherwise it will affect the fastness to adhesion.

At present, the price of sealing devices is generally between 40,000 and 200,000 US dollars or even higher. Some high-price sealing devices are also equipped with detection devices. If you purchase the testing device separately, the price is between 30,000 and 50,000 U.S. dollars.