Label Printing Snippet Part 5: Hot and cold foil applications
Foil is an embellishment process used in the printing industry to make labels and products more distinct and attractive to the customer. The process can also be used to apply security features.
Application of foil can be done offline on a specialized finishing machine, but it’s more common to have it done inline during the printing process.
Three methods are used for hot foiling:
- Rotary foil unit
Rotary foil units are common for the application of foil and can be either oil or electrically heated.
Consisting of a round brass cylinder engraved with the image, the unit needs to be handled and stored with care, as repairing a damaged cylinder is expensive.
The rotary foil process provides good results on most substrates, but porous substrates can be challenging, as the contact time between the foil and the substrate is considerably less than for semi-rotary or flatbed foiling processes.
Temperature is a factor that is sometimes overlooked; if the cylinder is too hot it can lift the foil. This is commonly wrongly perceived as a lack of sufficient pressure and the printer applies more pressure rather than raising the temperature.
Foil temperature can also vary depending on the brand - the manufacturer should specify the ideal temperature. A temperature between 180 and 220 degrees Celsius is common.
This process of foiling allows more precise adjustments in pressure due to the design and function of the unit.
The semi-rotary unit doesn’t need to change the cylinder size to change the format/print length. Plates are commonly made from magnesium and offer quick changeover times, making them in many ways more efficient than rotary foil units.
This is the oldest method of foiling and the simplest in function and changeover.
These units can be a combined with embossing or die-cutting, or the unit can be used separately, though not on all machines. There’s a heated, removable bed that holds the foil plate and both base and top plate come together to provide the pressure required to transfer the foil.
This yields the best outcome of all three processes due to the contact time and evenly distributed pressure on substrate and foil.
Flatbed foiling offers cheaper tooling, but the press speed can be restricted by the way in which the unit works. Speed is also dependent on the unit you have.
This label was printed using the ABG Bigfoot flatbed unit on an MPS press.
Hot or cold foiling is a great tool for security printing with either micro embossing or printing.
There’s also a great range of specialized foils, from holograms to custom designs, that can be printed in register to help stop or impede counterfeiting of products.
The cold foil application process is relatively new compared with hot foil but offers the same look using a different process.
This is done by using a flexographic printing unit which applies an adhesive using a heavier anilox; the foil meets the substrate at the nip point before passing under the UV lamp. Different thicknesses of adhesive are required depending on the image and image size, e.g.: for broad areas, a lower line count is needed.
For smoother substrates, less adhesive may be required than if the substrate is porous. Pre-coating can help the foiling process. A high lamp power may be needed for coloured foil and the distance between the application of adhesive and contact with the foil should be as short as possible.
Foil is made up of three layers: the carrier (polyester film), the foil colour (a metallic-based pigment), and the release coat (the adhesive activated by heat for the hot foil to be transferred to the substrate).
Cold foil has the same carrier and colour pigment layer, but the release coat is a thermoplastic primer layer or a wax-free or silicone-free layer which will adhere and transfer to the substrate.
This is a quick snippet on foil and the different types of applications that can be used for hot or cold foiling.
There’s a lot to know and learn about this subject. Here I’ve gone through some of the very basics of foiling for those with little or no knowledge of the foiling process.
Kane Marsh is Regional Printing Instructor Asia Pacific with MPS Systems Asia, providing training on MPS' narrow web flexo presses and specialized label applications. Kane has direct print experience on multiple presses in a range of printing technologies including flexo, gravure, offset, screen and a variety of applications.