With foil blocking, care must be taken in the selection of the foil used. It is recommended that samples of whatever product you are using (along with details of the specific job) are given to your foil supplier to ensure that the foil selected is suitable. Bear in mind that special care must be taken with any subsequent processes that the paper undergoes. This applies to subsequent laser printing, for example, as the foils may re-melt and strip off inside the laser printer.
The type of foil selected will depend a lot on the job in question – fine lines and intricate images would require foil with a clean definition sharp release layer (tight or hard foils). Large solid areas will require foils with a free releasing layer (free or soft foils). Also, the right adhesive system should be selected for printing on an uncoated, laid, patterned paper.
There are special foils available with thermal resistant lacquers and adhesives which are more suitable for subsequent laser printing.
It is always recommended, where the job allows, that the area to be foil blocked is left unprinted. Foiling over litho printed areas can present problems, especially if the ink is not completely dry or cured. Heavy application of UV ink can have the surface of the ink cured, but uncured below the surface – distillates from this uncured ink can interfere with the foil. Foiling on top of ink that contains high wax content is not recommended. If the job has to have foiling on top of ink, then ensure that the inks are foil blockable and consider over-printing the ink with a foil blocking receptive machine varnish which can help the foil adhesive bind onto the ink/paper. Care should be taken when foiling over screen printed images where the foil bleeds off the ink and onto the paper – this can cause the very thin foil to split at the edges of the screen printed image.
Pigment foils can be more demanding as there are generally fewer combination’s of release layers/adhesives to choose from.
It is always recommended that, for a foil blocking job, a sample of the paper, along with details of the job (design, as well as pre and post foiling processes), the foil blocking press and the anticipated running speed be given to your foil supplier to ensure that you have a trouble free run.