Gold foiling, also known as hot foiling or hot foil printing remains one of the most popular means to transfer words and images onto various media without the need for ink. Gold foiling is not a new process; in fact, it goes back to the Dark Ages, where monks would use the foiling process to decorate the hand-produced books they created.
Today, the same attractive effect can be had, but with a much wider range of materials. Today’s foiling process goes beyond that of the printing of inkjet labels to use not only gold, silver or copper foil, but also metallic and matte colours, and even holographic foil.
Hot foiling uses a machine that heats the material to 200 degrees Celsius. Once heating is complete, the machine applies pressure to adhere the foil to the material being printed on. A negative plate is positioned and then heated, which releases the foil. Although a high temperature is needed in order for this release to occur, the required temperature will vary widely and depend on that material that the foil will be transferred onto.
Hot foil machines can be either standalone and offline, or be in-line with an attachment to a printing press or similar peripherals. Most hot foil machines are sheet-fed, but there are some which are web-fed. Regardless, both require a sophisticated handling system in order to position the substrate and foil correctly between the cylinders or plates that will transfer it to the media being printed.
The Adhesive and Other Materials
As with any printing, the adhesive used is critical in foil printing. Commonly, the adhesive used in foil printing consists of acrylic co-polymer using water as a diluent. A low-quality adhesive will result in an inability of the foil to stretch, leaving cracks. Poor adhesive will also cause the print to lose its softness and smoothness after only a few washes.
Other components of the hot foil include a polyester carrier, a release layer and a number of metal, lacquer and image layers. There is also an outer adhesive layer, called the adhesive sizing layer.
There are a few processes by which foil can be printed onto various materials.
The round-round method works in a similar fashion to a printing press. Dies are mounted on a cylinder that rotates in sync with a counter-cylinder, with the substrate on one and the foil on the other. As they roll, the two are brought together.
The round-flat method uses a rotating cylinder to apply the foil. In this scenario, the die chase moves in a horizontal manner, synchronising with the cylinder. This allows for the delivery of a narrow linear zone of pressure where all of the necessary elements meet.
The flat-flat method works much in the same way that flat-bed die cutters do. Foiling dies are either affixed to a honeycomb chase to allow for flexible positioning, or are in a fixed position between the chase and the lower counter plate, which can be mounted with die counterparts or be completely flat. The press joins upper and lower elements and delivers uniform pressure.
Hot foiling remains the only real way to print glossy silver or gold that will allow it to keep its gloss without drying out. Today’s process offers many colour choices as well as Pantone colour matching. When considering the hot foil process, it’s important to keep in mind that only one colour can be printed at a time and that full-colour capability is not available. As well, there will be variations present in each print, as foil is very easily wrinkled and otherwise changed.