Rapid Productivity Fuels Growth
Growth has come rapidly for productivity improving cold foiling. Foiling is known for its ability to add eye-catching visual effects to all aspects of printing creating brand differentiation. Foiling has proven to be effective in attracting and persuading shoppers to choose one product over another.
Cold foiling, first developed in the 1990s for the rotary narrow web printing industry evolved from hot foil stamping. The objective was to deliver a fast, in-line, cost-effective option for hot foil stamping. Now mature, the technology has been adapted by most printing processes including flexo, sheet, and web-fed offset and digital.
Foiling, whether achieved by cold foiling or hot stamping, is a decorative metallic and color-combining technique used to enhance graphics. A broad range of rich, brilliant, metallic/color, consumer-attracting effects can be produced.
Hot Foil Stamping
Hot foil stamping uses an engraved brass die, unique to a job, and a heated press. Under heated pressure, a foil layer is transferred from a thin plastic film carrier using a hot melt adhesive. It is a slow process, mostly used offline over preprinted graphics on non-heat sensitive substrates. Transferred foil is generally limited to text and bold images. An advantage of hot stamping is its鈥� ability to produce a mirror like finish, unlike cold foil which is limited because its metalized layer is thinner. This is necessary because UV energy has to pass through the layers of cold foil in order to cure a UV adhesive image printed on a substrate. Cold foil, after application, is a very thin two microns thick.
Cold Foil Process
Cold foiling is the process of using a UV curable adhesive to transfer easy-release metallic foils to a substrate. Cold foil has a similar structure to hot foil consisting of layers of material differing, with a release coating reacting to shear instead of heat. The adhesive coating is formulated to have an affinity for a UV adhesive printed onto a substrate.
Critically, in cold foiling, the metalized layer must enable UV curing energy to pass through it to effectively activate and cure the UV adhesive.
COLD FOIL CONSTRUCTION
- Polyester film carrier
- Release coating
- Color coating
- Metallizing
- Adhesive affinity coating
The construction of cold foil for both sheet-fed and web-fed printing processes is the same, consisting of five layers. Both require the same three-step process to apply foiling to a substrate.
- Print tacky adhesive onto substrate
- Apply and nip foil and UV cure adhesive
- Remove foil film carrier
Cold Foil Process
In the illustration, an unwind/rewind unit applies and nips the cold foil film to a tacky UV adhesive imaged substrate. The UV adhesive is cured through the metallized foil, followed by the spent carrier film being stripped and rewound. The foiled image area is released from the carrier onto the substrate wherever the UV adhesive has been printed and cured.
Many OEM press manufacturers now make available cold foil units, either as a fully integrated unit or as an optional add-on unit. The cold foiling market demand is now being met by new presses set up to apply cold foiling and old presses being retrofitted. Cold foiling uses inexpensive, quickly made printing plates, while hot stamping requires a costly engraved die.
The chemistry key to the cold foil process differs from that of hot foil stamping, in that it is dependent on a peel-off technique and not heat. Therefore, heat-sensitive substrates, such as flexible packaging films, plastic laminate tubing, shrink sleeves, and other thermally sensitive stocks can be accommodated.
Cold foiling excels in handling large coverage areas, fine lines, gradients, halftones, over-printing, and top coating, with the ability to offer multi-colored creative effects.
Hot stamping in contrast uses heat and pressure to activate release and adhesive coatings to effect transfer/adhesion to a substrate. This limits its use to non-heat sensitive substrates.
Cold foiling needs smooth surface substrates in order to produce the best image results with films, coated papers, and boards all in high-volume use. Generally, all films (PE, PP, PET, PVC), perform ideally since they are non-porous and do not allow absorption of the UV adhesive.
Sheet Fed Cold Foiling
In a sheet-fed offset press, cold foiling systems are installed to use the first and second printing units. The first unit using a standard printing plate applies a UV adhesive in an image area. The second unit nips the cold foil film to the substrate, after which the UV adhesive is cured. The waste carrier web is then rewound above the third print unit. This action peels the foil from the plastic carrier web leaving metallized foil attached to the substrate’s image areas.
Similarly, in flexo, a UV adhesive is applied using a printing unit and polymer printing plate.
Cold Foiling in Digital Printing
Digital printing cold foiling is expanding too, using conventional cold foils, applied to label and packaging substrates using UV adhesives. Several equipment manufacturers are supplying cold foiling units that can be added in the converting section of a digital press. Features include variable text, and security/ holographic images.
After printing cold foil is generally over-coated with UV decorative-protective coatings offering a range of finishes from high gloss to matte.
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