Drying solvent digital prints
By Denise Nathan
Machine technology has improved leading to faster print output capabilities. There is significant pressure from some customers to have their prints “yesterday” to meet campaign deadlines .While you may strive to provide your customers with a fast efficient service it should never be at the expense of cutting down on post production procedures that can ultimately affect the performance of the graphic. The most critical is drying time.
Digital printing is solvent ink printing. The inks must have time to dry either by heat or evaporation. Graphics may be dry to the touch but if you can still smell the solvents on the print then the solvents are still evaporating, much like when you paint a room.
|The Dry A Print unit|
Solvents that do not evaporate will remain in the film altering the adhesive characteristic and film performance. The solvents can start to break up the PVC, causing shrinkage, waviness of the top sheet, yellowing and brittleness. The solvents can then further penetrate into the adhesive layer. If the graphic has been applied to a substrate, for example glass, the solvents remain trapped between the glass and the film. The trapped solvents bounce back and forth, attacking the adhesive bond and breaking down the adhesive. Typical effects of this are shrinking, peeling and adhesive transfer, where the graphic peels off leaving the adhesive on the substrate. If you remove the graphic you will notice the adhesive has a stringy, rubbery appearance like chewing gum. Remaining solvents can also lead to handling problems and make the application process much more difficult as they cause the vinyl to become softer and stretchier.
|Another typical drying method|
The adhesive properties can also change. Adhesives can become more aggressive making handling and repositioning of a graphic more difficult. Films with special adhesive properties for fast and easy application may lose these characteristics negating any application advantage.
Drying before laminating is also essential or the solvents will remain trapped and continue to attack the media or cause delamination of the laminate.
Drying times will vary significantly depending on a number of factors.
• Type of ink used -True solvent inks take longer to dry than milder eco solvent inks. Typically the recommendation for true solvent is 24 to 48 hours and for eco solvents 6 to 24 hours.
• Brand of ink used - The brand of ink will also have an impact with new rapid dry formulations being released onto the market.
• The amount of ink laid onto the media
• The temperature and humidity levels where the print is left to dry.
• The type of self adhesive PVC media used - Surface porosity will impact on drying times. Softer, more conformable films typically take longer to dry. Different brands dry differently depending on their features and characteristics.
The best methods for drying prints are to hang the graphics or to use professional drying systems post production.
It is critical that you follow the vinyl manufacturer’s recommendations. Not following these guidelines introduces an unnecessary risk. By taking the extra time to dry prints before application you can be assured of trouble free handling and performance and eliminate the possibility of graphic failure.
Denise Nathan is Marketing Manager - MACtac in Oceania