- October 01, 2003, Dr. Wilhelm Munninger, Frantschach Inncoat
Silicone release coating on liners for self-adhesive laminates is not only the preserve of label stocks. The large-format, self-adhesive graphic arts market uses significant volumes of silicone-coated release liner on laminates that may be computer cut, screen printed, or — increasingly today — digitally printed.
Digital imagers have encountered a particular problem with water-based ink jet print in relation to silicone transfer, which can cause deformation of the printed image. This is a serious matter when the order may be for a “one off” billboard with a short turnaround, and the cost of reprinting a large-format, self-adhesive graphic can be high.
Silicone transfer occurs during in-line silicone coating of a liner. Silicone is coated as a liquid, which is then solidified on the substrate through a chemical reaction and heat.
However, even today, state-of-the-art silicone chemistry cannot achieve a full 100% cure of the siliconized surface layer. Directly following the siliconization process — when the coated release liner is rolled up — microscopic traces of the former silicone liquid can be transferred to the liner's reverse side.
Usually, following siliconization, the release liner will be laminated with an adhesive layer and a facestock — film or paper — to complete the self-adhesive material “sandwich.” Again, the material will be rolled up — and in the process, the facestock will come into contact with the reverse side of the release liner.
At this point, the silicone traces picked up following siliconization may re-transfer to the surface of the facestock. Polyethylene (PE) coated papers and polyvinyl chloride (PVC) films particularly are susceptible to such silicone transfer — and cast and calendered PVCs are the preferred substrates for most self-adhesive outdoor advertising printed by water-based ink jet.
Print Surface Contamination
If the two-step silicone transfer process has occurred, the imaging process will encounter problems. The silicone residue will conflict strongly with the printing inks, causing either complete print voids on part of the substrate's surface or improper ink bonds.
While screen printing and solvent-based ink jet are sufficiently robust to cope with and overcome the effects of silicone transfer, water-based ink jet inks and electrostatic toner are far more likely to be affected by such surface contaminants.
As water-based ink jet has gained in popularity, a newly developed liner deals with this problem. The new liner is coated on the reverse (non-siliconized) side with a patented lacquer that absorbs any silicone traces and locks them into its body, so that transfer is not possible.
Produced in one pass on unique in-line coating machines, the liner enables self-adhesive laminate manufacturers to deliver materials that they — and their digital imaging customers — will find printable and not susceptible to the surface blemishes caused by silicone transfer.
The liner offers other refinements to the self-adhesive laminate: sealed edges for extra protection against escaped silicone traces and exceptional layflat qualities. The liner also features an anti-static finish, which minimizes the effects of static charge during laminate conversion.
All in all, the new liner represents a significant technical advance in “engineering” substrates for self-adhesive, water-based ink jet print — and a savings in time, cost, and frustration for laminator and digital printer alike.