Few things capture one’s attention quite like printing on glossy paper. Materials printed on glossy substrates look more vibrant and generally offer a wider range of colors for designs. Additionally, images look sharper and reproduce with more contrast.
For all the benefits of printing on glossy paper and other substrates, there are also special considerations. The materials must be handled carefully because oils from fingerprints affect the inkjet inks. Moreover, finger smudges can harm the end product.
As the holiday season nears, expect to see more glossy catalogs and other mailings fighting to capture your eye and attention.
UV-Curable vs. Water-Based Inks
Printing companies generally choose their inks based on the inkjet systems they have installed. Water-based and UV-curable inks are the most popular.
Unlike printing on matte surfaces, glossy substrates require additional effort to achieve their shiny, expensive-looking results. The inks have to be tuned to the surface tension of the glossy surface so that ink droplets have just enough “dot gain,” meaning the droplets spread out when applied to the glossy substrate.
If there is too much dot gain, the printing will be blurry. Optimal dot gain avoids producing white lines between passes of the inkjet printhead.
Meanwhile, pretreating glossy paper with primers defeats the intended effect of the shiny product, as primers tend to dull glossy surfaces.
Other methods must be used to cure the ink after printing because the inks on glossy substrates do not absorb into the material; instead, ink droplets adhere to the shiny surface.
A quick-drying curing method avoids ink smearing on these surfaces. If the printing system uses UV-curable or LED-curable inks, the heat from the wavelength of mercury vapor lights or LED lights quickly cures the ink. However, UV-curable inks will come with a higher cost.
Curing and Drying Inks
UV curable inkjet inks are the fastest growing ink segment in the digital printing market, far surpassing the growth rates of aqueous and solvent-based inks.
Printing systems using the less-expensive water-based inks may use tunnel dryers, infrared light, or heated platens before or after printing or external fans.
Also, both piezo and thermal printheads raise the temperature of the inks. The warmer ink aids the curing.
Kao Collins manufactures both UV-curable and LED-curable inks, as well as water-based inks.
Corona Treating the Paper
Another method for improving inkjet printing on glossy paper or plastics uses a corona or air plasma pretreatment. The low-temperature process uses high voltage applied to an electrode that temporarily changes the surface tension of the substrate, which helps the ink bond to the surface. The corona treatment fades after a short period, however, so corona treating and printing should happen at the same time.
Inkjet printing speeds now rival legacy offset or flexographic printing systems. Inkjet printing also offers the distinct advantage of cheaper set-up costs, which makes shorter print runs for glossy products more cost-effective.
Glossy books, direct mail, and promotional advertising are some of the most common end products one can expect to see from digital inkjet printers. And rest assured, you’ll be seeing plenty of them this holiday season.
