The cold foiling process, as the name implies, involves foil blocking without the use of heat. former hot stamping foils need heat and pressure to change the foil from the carrier film to the substrate being printed, whereas cold foiling does not.
A hot foil ordinarily consists of a polyester carrier, or, more rarely, polypropylene or cellulose film, a issue layer, a lacquered layer, the colour which determines the shade of gold or coloured metallic effect, a layer of vacuum deposited aluminium and ultimately a sized layer to give adhesion to the printed stock. A cold foil has basically the same structure, though cold foiling commonly requires a thinner aluminium layer, and the adhesive layer is not all the time necessary.
Litho Printing
The hot stamping foil is applied to the stock by means of a heated die, set at a climatic characteristic of in the middle of colse to 100 Celsius to over 200C, depending on the type of stamping press being used and the area being blocked. The heat activates both the adhesive layer and the issue layer, and allows change of the foil from the carrier film agreeing to the develop of the die.
A cold foil, on the other hand, requires no heat and adhesion is achieved by means of a wholly distinct mechanism. In cold foiling the develop is not applied by means of a heated die, but is printed in the form a Uv activated adhesive. Any printing technique can theoretically be used in cold foiling, though offset litho and flexo are the most common. The run is started, the develop applied using Uv adhesive from printing plate or blanket, web and cold foil are brought together straight through a nip then the sandwich passed under Uv lamps which cure the adhesive. The cold foil and print webs are separated and rewound. Since the Uv has to penetrated the aluminium layer, this is thinner in cold foiling than with hot foiling. A cold foil must have an visual density low sufficient for it to sufficiently transparent to Uv light to allow it to cure the adhesive in the short time available.
So, in a nutshell, cold foiling involves printing an adhesive, nipping the cold foil sandwich to it, curing, then separation, leaving the foil adhered to the stock agreeing the printed develop of the adhesive.
Traditional cold foiling is commonly reel-to-reel and used in the self-adhesive labelling industry, but modern developments have allowed a viable sheet-fed process to be used.
Whatever recipe is used, cold foiling has yet to give the high shine of former hot foil stamping. The nip, composed of a metal roller and a rubber impression roller, has to spotlessly clean or pinholes will be seen in the done result. Cold foil is prone to pin-holing and other visual defects. The disunion in cold foiling is crucial, as is flatness of the web. Cold foiling is particularly prone to creasing if the webs are not wholly flat when brought together,
Advantages
The advantages of cold foiling are:
1. In-line foiling. The cold foiling unit can be settled in-inline after the printing processes, and if required, in the middle of printing processes. In cold foiling, the process has been converted from a slow hot stamping process to a fast printing process using a cold foil. The printer therefore bypasses an further relatively slow process straight through using a cold foil rather than a hot foil.
2. Fast set-up. The use of accepted printing methods such as offset allows fast set up of cold foil as against hot foil. There is no packing required in cold foiling to ensure even pressure to the substrate since the cold foil is applied to a wet adhesive.
3. The charge of having metal dies cut is eliminated with cold foil. The cold foiling process becomes more inspiring for short runs, where previously dies costs could prohibit this.
4. Since we are using a printing process, there are fewer registration problems with cold foiling. The hot foil process oftentimes present problems in registration which need time to put right.
Disadvantages
1. Cold foil print quality is not as good as that from hot foil. The glow is ordinarily lacking and pinholes are oftentimes a problem.
2. Cold foiling requires complete cleanliness if face defects are to be kept to a minimum, and the hardness, cleanliness, alignment and pressure of the nip roller is extremely important.
3. The power in case,granted by the Uv lamps must be properly maintained or the cold foil will not bind to the partially cured adhesive. In cold foiling, the transmission of the Uv power straight through the foil is critical. Problems can be experienced with deep cold foil colours which act as Uv absorbers, and foiling to black and deep blue substrates can be difficult in cold foiling since these colours consist of pigments which act as Uv absorbers and thus leaves less power to cure the adhesive. For these reasons many suppliers do not offer cold foil in deep shades.
All in all, though, cold foiling is growing in popularity due to the increased profitability it gives, especially in areas where the very top quality of foiling is not necessary. The newer offset cold foiling techniques are rapidly gaining ground on the quality of former hot foils, which is why most hot stamping foil manufacturers now consist of cold foil in their portfolio.
Copyright 2006 Peter Nisbet
Cold Foiling Litho Printing
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