Frequently asked questions and answers
What are typical starting temperatures for laminating with KDX thermal laminating films?
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What is "Silvering" and what can I do if it occurs?
The typical thermal adhesive will give good adhesion to lith-offset print at temperatures of 205 to 230*F (96 to 110*C). There are many factors in the laminating machine that have to be considered. Higher laminating speeds call for higher temperatures as there are thermal conductivity factors that have to consider. We are talking about the temperature necessary in the adhesive layer to it to adhere to the print and not the temperature of the roll in contact with the base film. At slow speeds a good wrap of the heated laminating roll (270* of wrap), the temperature setting on the laminating roll will be as above, but laminating thicker films and higher speeds will increase these temperature settings to obtain these temperatures in the thermal adhesive layer. OPP films, the most thermally sensitive films used in laminating have laminations as they can distort if too hot. PET and Nylon base films are more thermally stable and will allow higher temperatures of the laminating nip roll for higher operating speeds.
Can we use spray powder when printing before laminating?
No! The powder prevents the thermal adhesive from making a firm contact with the paper substrate and the litho-offset process inks.
It is a good practice to let these warm sheets sit overnight to help set the interlaminar bond as they cool. It also helps hasten the curing of the litho-offset inks by oxidation. The problems can be a cohesive failure ink in that bond causing the laminate to pop off the print in the creased or embossed area.
Can we use an aqueous coating on the ink?
After laminating, can I immediately perform another operation such as embossing or creasing and folding?
Silvering is small air bubbles between the thermal adhesive and the printed substrate. These occur when the paper has greater roughness, insufficient pressure in the lamination nip or the laminating temperature is too low. Generally, the paper is already printed, so that cannot change, but jobs for laminating should be a smoother paper as the ultimate surface appearance is the thermal laminating film.
What to do:
Increase the pressure and bring the lamination nip temperature up until it goes away. If you are the limits of what the laminating machine can do, use a thicker laminating film because generally the thicker films have a greater thickness of thermal adhesive on them.
It is a good practice to avoid the use of aqueous coatings on jobs designated for laminating.
Aqueous coatings are good in the printing process to help prevent offset of print between sheets of a print job. There are some problems to be concerned about when laminating. While print offset, the transfer of ink the backside of the paper, has been prevented, the print under to coating is still uncured. The thermal adhesive will stick to the coating, but the coating is not really stuck to the ink until after the ink has fully oxidized. Now that there is a coating on the ink, the time for the ink to cure by oxidation is now longer.
Some aqueous coatings are formulated with slip additives to help in handling the sheets. Since these coatings are meant to be the final surface, the slip additives will prevent the full adhesion of the thermal adhesive. There are coatings formulated as primers for laminating, but the basic print vehicle needs to be cured for good adhesion which means a longer time until laminating.