Hot foil stamping
Hot foil stamping is a finishing method used to give texts and patterns an eye-catching appearance. The foil can have a glossy or matt finish with a coloured, metallic or holographic appearance. The size of the area that can be covered varies from very small details, such as letters, to large, solid areas.
The hot foil stamping operation
The foil is carried on a heat-resistant film. During the operation the paperboard and the foil are kept parallel. A heated matrix, which is fitted to the stamping plate or cylinder, relieves the foil from the carrier and makes it adhere to the paperboard.
Since the carrier film reacts with the foil due to the pressure and heat of the stamping process, the composition of the paperboard surface is essential to provide good runnability and satisfactory bonding of the foil. The paperboard surface must be very smooth and free from impurities and spray powder. The size of the area which can be hot foil stamped varies from small, such as lettering, to large areas.
If the foil covers a relief pattern, hot foil stamping is performed at the same time as embossing to minimise the risk of misregister between the relief and the foil.
For the best visual appearance of the foil, it is important to have a clean and very smooth paperboard surface with a minimum of interfering surface irregularities, since these are strongly accentuated when foiled. The tool’s ability to conduct heat and the smoothness of the tool surface are equally important factors. To produce the best gloss during longer runs, the surface of the tool should be polished.
Hot foil stamping and embossing at the same time.
The composition of hot foil stamping films. Click to enlarge images.
Key paperboard characteristics
For the best visual appearance of the foil, a smooth surface with a minimum of interfering surface structure is important, since surface irregularities are strongly accentuated when foiled.
Key paperboard features when performing hot foil stamping:
• surface structure
• surface strength
• flatness and dimensional stability at the specified moisture content.
Hot foil stamping in practice
The following factors are essential for good hot foil stamping:
• foil type
• time of pressure (seconds)
• pressure (bar)
• temperature (°C).
Testing the hot foil stamping result
Visual inspection of the result, including comparison with proofs.
|Poor foil adhesion
||• Insufficient heat
|Air blisters under the foil
||• Excessive heat
• Paperboard surface not smooth enough
|Foil lacquer matt
||• Excessive pressure
|Irregularities in foil lacquer
||• Insufficient heat