Cold foil transfer is a modern method of applying metallic particles to a substrate in order to add metallic effects and value to the final product. Cold foil transfer is a common technology in the offset printing industry.
Using a standard offset plate, an image is printed onto a substrate by the use of a tacky adhesive. Foil spools from an unwind and is nipped to a substrate. The aluminium particles from the cold foil layer are released from the polyester film and transferred to the substrate by the tack of the glue.
An image with a bright surface is created on the sheet. Foil that does not adhere to the adhesive remains on the 12um film, and waste is directed to a rewind spool or to a shredder (Vinfoil Infigo systems).
Because the adhesive is applied like a conventional ink, no expensive stamping die has to be created. Once printed, the surface of cold foil images may be overprinted and varnished.
A tacky glue with the same rheology and consistency like an offset ink is printed on top of the substrate in the first printing unit by the use of a conventional offset plate.
Depending on the colour of the cold foil the glue is shaded yellow (golden foil) or grey (silver foil) and can be measured with a densitometer or spectrometer to ensure optimal layer thickness.
In the pressure nip between blanket and impression cylinder the foil web is pressed upon the substrate and the metallized layer is sticking to the areas where the cold foil glue has been applied before.
The backing film containing the particles which were not transferred to the substrate is released from the sheet and rewound to an empty core or in case of Vinfoil’s Infigo schred and sucked away.
In the areas where the glue has been applied to the substrate the metallized layer will adhere to the sheet due to the tack of the cold foil glue.
A fast, flexible and cost-effective finishing technology:
Cold foil offers considerable design scope:
High-quality coated and smooth paper and cardboard are ideally suited for achieving an outstanding rendering of metallic colour tones and effects. Glossy coated printing papers are meeting these requirements very well.
Matt coated papers deliver a less smooth surface. To achieve a matt or bronzing effect, an alternative solution is to apply a matt coating. Uncoated and structured paper varieties are not generally recommended
Paper includes all coated papers with a grammage from 70 to 170 g/m2. Paper in the range 170 – 300 g/m2 is referred to as card board. Coated paper can have a matt, semi-gloss or glossy finish, and is suitable for all printing processes.
The surface of these materials is treated with a binding agent (“coating”). The coating usually comprises chalk, china clay, casein and a plastic dispersion. This gives the material a non-porous, smooth and stable surface.
The coating is applied up to three times using a doctor blade, air knife or a ductor blade. After the application of this coating, all papers initially have a matt finish. To achieve a glossy paper/card, it is passed through a calender that smooths the surface as a result of the pressure applied by two rollers.
Glossy coated printing materials are particularly suitable for cold foiling because they do not fully absorb the cold adhesive. This allows contours and half-tones to be rendered more accurately.
Mainly GC1 grade cardboard is used for cold foil transfer.
This is a multilayer board with a white, wood-free liner, usually multi-coated and a high content of fresh fibre. GD2 qualities with a higher content of recycled fibre are also in use but they require different blankets for the adhesive to avoid delamination and blistering of the board surface.
The main difference between cold foil on GC1 and GD2 boards is the higher smoothness of the metallic result due to the flatter surface of GC1 qualities.
The paper used to produce label materials is well sized and/or film coated on one side.
It also needs to meet the following requirements: puncture resistance, wet strength, low curling tendency, tear resistance, tensile strength and leach porosity.
Feedback from customers showed that the labelling machines are running faster with wet glue labels finished in cold foil compared to hot foil labels due to the higher flatness.