What Is a Shrink Label?
Shrink labels are resin labels that shrink when heated.
They are used for beverage and cosmetic container labels because they fit uneven or curved shapes.
Uses of Shrink Labels
Shrink labels are often used for PET bottle labels because they shrink when heated and conform to uneven surfaces. It is difficult to print pictures and text directly on the curved and uneven surfaces of PET bottles, so the most common method is to print on shrink labels and attached to PET bottles.
This is commercially very valuable because it allows for variation in the design of PET bottles by simply switching shrink labels.
Principle of Shrink Labels
Shrink labels are processed shrink films, which are processed into a cylindrical shape by pasting the edges of shrink films that have been processed into sheets together. In other words, it can be manufactured from the same material as shrink film. However, since shrink labels are used to decorate and protect tubular products such as PET bottles, they are made of a material that shrinks only horizontally, with almost no vertical shrinkage.
Typical materials used are PET (polyethylene terephthalate) and PS (polystyrene), which are the same materials used for PET bottles. A mixed of PET and PS (hybrid styrene) is sometimes used. PVC (polyvinyl chloride) is suitable when chemical resistance is required.
When used as a label for PET bottles, the prescribed printing is first applied to the shrink film, which is then processed into a cylindrical shrink label. Next, the shrink label is placed on the PET bottle, and the bottle is placed in a warm air tunnel to heat-shrink the shrink label so that it adheres to the uneven surface of the PET bottle.
The heating process may cause thermal deformation of the PET bottles and other packaged items. When working with shrink labels, it is necessary to check the temperature required for heat shrinking of the shrink film and the heat resistance temperature of the product to be packaged.
Other Information on Shrink Labels
1. Printing on Shrink Labels
When printing on shrink labels, the transparent shrink film that makes up the label will show through even when printed in color. This can result in unintended color tints or characters that are difficult to read.
As a countermeasure, there is a technique to make the contrast and text clearer by applying a white ink undercoat, and printing is performed in the following process:
- Create the image data to be printed by dividing it into layers, and add a white-filled layer to the bottom layer. If you want to make a part of the illustration transparent, leave the part to be transparent without painting it white.
- Place the shrink label on the printer and print only the base layer.
- Re-insert the shrink label into the printer and print all layers except the base layer.
2. Heat Shrink Method for Shrink Labels
Heat-shrinking shrink labels requires heating with warm air or hot water. The most common means of applying heat is a warm-air tunnel, but other methods include hot baths and hair dryers.
Hot Bath
Water is heated in a water tank, and once the water reaches a predetermined temperature, shrink labels are immersed in the water to heat and shrink them. The advantage of this method is that the area immersed in the hot water can be heated evenly, but it cannot be used for items that should not be exposed to water because the shrink labels will get wet.
Dryer
Some products can be heat-shrunk with a hair dryer, usually a high-temperature dryer for shrink labels. The advantage is that it is easy to operate, but the disadvantage is that it is difficult to apply heat evenly.
3. Merits and Demerits of Shrink Labels
This section describes the advantages and disadvantages of shrink labels.
Advantages
Since shrink film is laminated together to form a cylindrical shape, the size can be set in millimeter increments, allowing for careful processing to suit the container. Printing is done after printing on the shrink film, so there is no uneven printing.
Disadvantages
PET and PS films, which are typical shrink label materials, have high shrink temperatures, and some products cannot be processed.