Shrink film flexo printing applications

Faced with the increasingly fierce label printing market, many manufacturers who use flexographic labels to pay attention to shrink film labels, not only because of its development potential as a new technology, but also against those technical requirements are not high, In the label printing market where the cost is not very high, the entry barrier for shrink film labels is high, which can prevent new companies from entering the competition. Traditional flexographic printing plants have begun to purchase some shrink film technology equipment, such as: adhesive devices and new printing equipment. It is expected that the shrink film label will have an annual growth of 7% to 10%. This value is obviously increased by 4% to 5% in the general label market. This result is due to the theme that has been highlighted in the packaging design day: how to quickly catch the eyes of customers. It is this demand that opens the door for the small and medium label market. Of course, the introduction of personalization, ethnicity, and health foods, together with the new label management regulations of the FDA (US Food and Drug Administration), have provided the label market with opportunities for growth and profitability. According to the statistics of the Maryland State Business Development Association, the use of shrink film labels in the United States was 49 million to 53 million pounds (about 300 million U.S. dollars) in 2003. However, gravure printing accounted for most of the market, leaving only 15% to be completed by flexographic printing.

When to enter the label market

Nowadays, all kinds of patented foods and some regional specialty products need different packaging. This just provides a good opportunity for shrink film labeling, combining the characteristics of flexographic printing to fulfill customer requirements. With the development of flexo printing technology, the accuracy of printing has been continuously improved, and the prepress production cost is lower than that of gravure printing. This has enabled flexo printing to play an important role in the label printing market.

If you decide to enter the shrink film label market, it is necessary to refer to the current situation of flexo printing. At present, narrow-web flexographic printing presses are the most competitive with films printed at less than 40 million square meters, while those with more than 40 million square meters are wide-format machines.

For a 40-inch wide reel, 500,000 square meters is the demarcation point between the wide-format flexo and gravure machines. This number depends on many factors, including the cost of the machine and the cost of installation.

Two very different markets

Shrink film labels are divided into two completely different markets due to different processes: shrink tube packaging and wrap packaging. But both technologies can be done with flexo. The term "〝TD" is generally used to refer to a shrink tube package that relies mainly on the transverse shrinkage of the film. The printed film is made into the shape of a tube and fitted over the container, and the film is then heated, causing the film to shrink laterally and bond tightly to the container.

Wrapped packaging is oriented according to the direction of operation of the machine. When the film is heated, it shrinks according to the direction of operation of the machine. We call it MD. The wrapping packaging technology does not require expensive label printing equipment, while the shrink tube packaging <TD> requires high equipment.

Film and casing equipment

Relative to pressure sensitive films, tension control of unsupported films is generally better. Some old label printing companies or companies that are obliged to make pressure-sensitive films generally do not print shrink labels.

In addition to pressure control, thermal control also plays an important role in label printing. The printer must have sufficient heat dissipation to prevent film shrinkage during printing. For shrink film. The heat source is the biggest enemy: we must always pay attention to the contact of the film with an overheated heat source. A new generation of presses are equipped with a heat roller in the printing process to help eliminate heat.

Bonding site, which is a joint part of the tube, forms the film into a tube in one step after the printing, and applies glue at the places where the two sides overlap (forming a tube); and then puts the flattened sleeve back in place. .

Forming and inspecting seams is a labor-intensive task and it is the most important step in the casing process. It is necessary to remove the ink and dirt on the seams so that the adhesive bonds better. When the film is heat-shrinked in the container, be sure to check for cracks when the connector shrinks.

The price of adhesive equipment is from 40,000 to 200,000 US dollars. The higher price configuration has a monitoring system. If you buy a separate monitoring system, the price will range from $30,000 to $50,000.

Labeling equipment

In the manufacturing process of the sleeve, the next step after label printing is packaging. In general, this process uses special equipment to attach the label to the container, although some manufacturers do it manually.

High-end labeling equipment can be sold for $500,000. Labeling equipment, first open the film, punch holes (if necessary), cut to the appropriate length, and then put it on the container and heat the film by steam, infrared or hot air to make it tightly fit the container.

The wrap product is then affixed to the container with a label applied with a conventional device. Different technologies require different agents and heating pipes. During the shrinking process, since the pressure is applied to the adhesive on the film to the film contact point, it is a hot-melt type adhesive (in some cases, a solvent-based adhesive is required). Although UV-type adhesives have a bright future in the era of low shrinkage, there are not many successful cases.

In general, polypropylene is currently the only material that can be used for wrapping printing. It only applies to a material with a maximum shrinkage of 20%, while solvent-based adhesives make polypropylene wrinkle. Because of the higher starting temperature of heat shrinkage of polypropylene. The compressed air flow shrink oven is generally selected to serve as a contraction.

Shrink ink chemical composition

The coefficient of friction of the ink plays an important role in the application of the sleeve label, which determines the efficiency of the label sliding across the container. There are few inks that are generally suitable for flexographic printing.

Environmentally friendly water-based inks are not only very elastic, but also have a shrinkage rate of more than 40%. It costs less than UV inks and is less affected by the movement of atoms in chemical molecules.

Similar to water-based inks, solvent-based inks are also very elastic, with shrinkage exceeding 40%. The drying of a solvent-based ink is also less affected by moisture, but it is affected by the movement of atoms in chemical molecules.

UV radical ink can be instantly cured. This ink is affected by oxygen rather than moisture. Generally, the shrinkage of UV radical ink is less than 20%. On some printing materials, its adhesion is limited. Both free radical inks are now difficult to market.

1. UV inks use sensitizers to absorb UV light and begin hard curing.
2. The electron beam produces polymerization and eliminates the need for photosensitizer.

For most printing materials, UV cationic inks are suitable, and its shrinkage capability can exceed 40%. This ink is also very elastic. In addition, this ink can be cured almost instantly, but the price is much more expensive than UV radical ink.

Advice on prepress design

For prepress designers who shrink labels, be sure to consider the shape of the container, and try not to place the key image in a highly constricted place. The other is to consider where to place the barcode. Bar codes are generally printed vertically to prevent image distortion and affect scanning.

Many computer programs can interpret distorted images, but in some cases (particularly low shrinkage applications), distorted images are considered waste.

Knowledge about shrink film

The thickness of a typical shrink film is within 50 μm. It has been relatively thin in the past few years, and its thickness is about 40 μm to 45 μm. The thickness of the film used is determined by the type of label printer. It is generally recommended that label printers purchase some of the more expensive shrink films, which have a higher shrinkage. Although the shrink film is designed to shrink in a certain direction, there is also a slight contraction in the opposite direction. Since the shrink film is sensitive to heat, extreme care must be taken in the storage, printing, and transportation of the shrink film. Most film manufacturers recommend that the film should be stored in an easily controllable environment. The temperature should be 210C to 320C before the label is attached to the container.

By calculating the minimum contraction rate required for the container, the value obtained is used as a reference for the shrinkage requirements of the film. The shrinkage of the film must not be lower than this value. If the diameter of a container suddenly changes, then it is important to choose a film with a stronger contraction force.

In order to calculate the printing width of the label, the width of the container can be doubled to overlap the width twice. The sleeve should be added 4mm, so that the sleeve can slide on the container.

PVC <polyvinyl chloride>, 2/3 of the shrink film used is PVC shrink film. The reason why PVC is valued in the industry is that its shrinkage capacity is maintained at 40% ~ 60%, while its cost is low and its strength is very high. It is suitable for multiple packaging and anti-theft device edge banding.

However, the environmental pollution caused by PVC cannot be ignored. Plastic container recyclers generally do not accept PVC in the recycling process, and in particular separate them from PETG (ethylene glycol polyester) containers. Because the proportions of PVC and PETG are close to 1.33, today's technology is very difficult to separate the two in the recycling process. PETG (ethylene glycol polyester), which has a high shrinkage of 78%, was previously considered to be PVC substitute and has a market share of 15% to 20%. Now that the PETG market is growing, PVC is regressing. However, due to the high cost of PETG raw materials, it hindered further development, especially when newer, more competitive materials entered the market.

OPS (Directed Polystyrene) has become a printing material that many countries in the world like to choose. OPS is more environmentally friendly than PVC and economical than PETG. The OPS shrinks up to 65%. Comparable with other high shrinkage films. The proportion of OPS is 1.025, and the profit advantage is 20% higher than PVC and PETG. Another advantage of using OPS is that it shrinks little in the opposite direction and does not even shrink.

Although OPP (Oriented Stretched Polypropylene) does not have good shrinkage, it has a place in the film wrapping market and its market share reaches 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, successfully blocking the entry of other printing materials.

Printing on a white OPP surface requires adding something else to stop the friction. OPP is different from the printing materials mentioned earlier. It is designed specifically for wrapping.

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