Heat Shrink Tubing: Flexo Printing (Part 2)
Shrinking ink chemicals
The friction coefficient of the ink plays an important role on the label. The efficiency of the sleeve sliding on the container depends on the coefficient of friction. Few ink chemicals are suitable for flexographic printing.
Eco-friendly water-based inks can shrink more than 40 percent, 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 chemical molecules.
Solvent inks are similar to water-based inks. They are very elastic and can shrink more than 40 percent. The drying time required for a solvent-based ink is less affected by moisture, but it is somewhat affected by the movement of atoms in the chemical molecule. For most films, solvent inks have the highest adhesion.
The UV radical ink cures instantly. This ink is inhibited by oxygen rather than by moisture. In general, the shrinkage is less than 20%. In some substrates, its adhesion is limited. The surface of the ink may exhibit atomic movements in chemical moieties. Two types of free radical inks are now available in the market:
UV uses a photosensitizer to absorb ultraviolet light and begin the hardening process. The electron beam produces polymerization, eliminating the use of sensitizers.
UV cationic inks produce adhesion in a wide variety of substrates and have a shrinkage of more than 40 percent. This ink tends to be more elastic. In addition, this ink can harden almost instantaneously, and there are fewer atoms in the chemical molecule, but the price is also more expensive than UV radical ink.
Graphic Design Advice
The flat design of the shrink label needs to take into account the shape of the container, and the key image should not be placed in a high shrinkage place as much as possible. Another factor to consider is where the barcode is placed. Bar codes are generally printed vertically to prevent image distortion and affect sketching.
A series of computer programs can interpret distorted images, but remember that in some cases (especially low-shrinkage printing), distorting images is useless.
About shrink film
The typical shrink film thickness is within fifty micrometers (one thousandth of an inch). Thinner, only 40-45 micron shrink films have been introduced in the past few years. The label processing performance of the equipment used by the label manufacturer determines the acceptable shrink film thickness. In general, label manufacturers can expect a higher shrink film shrinkage.
Although the design of the shrink film is to shrink in a specific direction, there is also a slight contraction in the opposite direction. Since the shrink film is sensitive to heat, care must be taken to ensure that the shrink film is stored, printed, and transported. Most film manufacturers suggest that the film should be stored in a controlled environment, approximately 75-85 degrees Fahrenheit, until it needs to be labeled on the container.
Mathematical programs are used to determine the minimum shrinkage rate required for a particular container, and the resulting value is used to determine the shrinkage demand for the film. The shrinkage of the film must not be lower than this value. If the diameter of a container suddenly changes, it will greatly increase the demand for high-strength substrates.
To calculate the width of the printed label, the width of the widest position of the container can be added twice to the width of the overlapping interface; the sleeve must be added four millimeters to allow the sleeve to slide on the container.
PVC (Polyvinyl Chloride) - Two-thirds (approximately 34 million pounds) of the shrink film used today is a PVC shrink film. PVC has gained a lot of attention in the industry. The shrinkage rate of PVC shrink film is maintained at 40% to over 60%, shrinkage is high and the cost is low, it is the choice of many American companies. The strength of PVC makes it suitable for multiple packaging and anti-theft device edge banding.
However, PVC continues to create environmental problems. Plastic container recyclers like to exclude PVC during the recycling process, especially to separate them from PETG (polyester) containers. However, because the proportion of PVC and PETG is close to 1.33, with today's technology, it is impossible to separate the two in the recycling process.
The shrinkage of PETG (polyester film) is as high as 78%, which was previously considered to be a substitute for PVC. The market share of polyester film is about 15 to 20 percent. The PETG market is growing, but the PVC market is not. The proportion of PETG is 1.28, making it comparable to PVC. However, due to the high raw material costs of PETG, it hindered its market growth, especially the existing newer, more competitive materials entering the market.
OPS (polystyrene membrane) - relatively new in the US home market, but has become a popular choice for many users throughout the world. OPS is more environmentally friendly than PVC and economical than PETG. OPS currently has a 5% share in the US home market. Its apparent growth rate is just around the corner.
Since OPS shrinks by as much as 65%, it can rival other high-shrinkage products. The proportion of OPS is 1.025, and the profit advantage is 20% higher than that of PVC and PETG. Another advantage of using OPS is that it contracts little in the opposite direction, and does not even shrink.
Although OPP (polyvinyl chloride) is not high in shrinkage, it has been given a cup in the ring can shrink film market, with a market share of 18% to 20%. OPP is suitable for containers that require low shrinkage and are near cylindrical. The proportion of OPP is 0.90, the price is competitive, and the output is large, hindering other substrates from entering this targeted market.
Printed on a white OPP surface, a laminating film is used to resist rubbing. The OPP differs from the other substrates mentioned above in that it is designed specifically for the ring tank type.
Future film
Nowadays, several companies are studying the potential of non-petrochemical environmental protection films. This film was even tried as a basic material for the container. This material is PLA (resin) and can be completely used as a compost and biodegradable. Due to the increase in the price of petrochemical products relied on by the industry, PLA has naturally become another choice for printing materials. Although this kind of printing material is a bit ultra-modern, it should be introduced into the market earlier than expected.
Entering the shrink film market must be timely and take pains. In the long run, investment in this market should be profitable. However, important technical issues cannot be solved independently, so your production team must include printer manufacturers, ink and film suppliers.
Source: Graphic Arts 250
About the author: Roger Brown is the marketing manager of Columbus Plastic Supplies Inc., the capital of the state of Ohio.
