2020 will be a major year for sign printers, given the elections looming overhead. With election season comes campaign signs as far as the eye can see: red and blue rectangles sweeping across the landscape, one lawn at a time.
Corrugated plastic, or fluted polypropylene, is the ideal substrate for campaign signs – it’s durable against solvents, oils, and water, rigid, and inexpensive. For campaign signs, which are designed for short-term outdoor use, it is the industry standard. Popular brands include: Coroplast, Plasticor, Cor-X, and Plasticor. The term “coroplast” is often used to describe corrugated plastic. While this is great for sign companies, it can also be a huge headache when it comes to a single word: Adhesion. This affects both screen and digital printers as poor adhesion causes ink to tear, pull away from, and flake off a finished product – causing wasted materials, time, and money.
There’s one thing about corrugated plastic sure to make printers’ hair stand on end – static. Static buildup causes two significant problems. In digital printing, static can lead to the appearance of pinholes and similar defects. This is caused from dust particles becoming attracted to the charge of the static, resulting in areas on the substrate where the ink cannot penetrate. Once the substrate is cleaned these pinholes become apparent. The second issue that arises from static is hazing or ghosting. This is caused from the static charge attracting ink droplets away from their intended area.
Issues with static can be mitigated by wiping both sides of the corrugated plastic with isopropyl alcohol. If working with very large sheets, many shops will use ionized air guns attached to air compressors. This method helps to remove dust and dirt at the same time as removing static.
Other effective means of discharging static include utilizing an ionizing wand. Ionizing wands are single or double barred hand-held rods, which are attached by a grounding magnet and static elastic cord to bare metal. These wands neutralize the static charge as they are passed over the substrate. Double barred ionizing wands neutralize both sides at once.
Adhesion can also be negatively impacted through blocking. When signs are printed using UV technology, they may feel dry to the touch, but they are not completely cured. It is recommended that they be allowed to cure for another 24-28 hours post production to ensure optimal adhesion is achieved. If the signs are stacked without being properly cured, the signs may end up sticking together, leading to ruined signs. One way to help protect against blocking is to place a fan at the end of the production line, as both heat and weight are factors that result in blocking issues. It is also imperative to avoid stacking or placing signs together until they are finished curing. Also do not attempt trimming, cutting, testing, or rough handling during this time.
Sometimes, less really is more. Corrugated plastic is non-absorbent, and too much ink will result in “orange peel” defects. Ensure that your settings are calibrated to apply the least amount of ink possible. You may also consider adding an adhesion promoter, which is often available from your ink supplier.
Proper adhesion is dependent on optimal UV lamp output. Typical inkjet printers experience a UV lamp life of 500 hours, given that the first 300 hours are operated at a low power. In the case of printing on corrugated plastic, however, the life expectancy of the lamp is drastically reduced as most jobs must be ran at a high power setting. Increasing lamp power can improve the bond between ink and substrate, especially when printing multiple coats. The optimal range for UV lamps for printing on corrugated plastic is between 100-200 millijoules.
Our screen ink lines XR, LZII, and Election Series are all designed to provide excellent adhesion to corrugated plastic.
Our digital ink systems Universal, POP G5, POP Kyocera, Checkmate, and UVD POP also exhibit outstanding adhesion.
Call us today at (816)221-5567 for screen and digital inks that demonstrate superior adhesion to corrugated plastic.