Inkjet Printing on Glossy Paper
Printing on glossy paper captures everyone’s attention, materials printed on glossy substrates look more vibrant and generally have a wider range of colours. In addition, images reproduce with more contrast and they look sharper. However, there are also special considerations when printing on glossy paper and other substrates. The materials have to be handled carefully because oil from fingerprints affect the inkjet inks. Moreover, finger smudges can harm the end product.
UV-Curable or Water-Based?
The printing company generally chooses the ink based on the inkjet systems installed and water-based and UV curable inks are the most popular. Unlike printing on matte surfaces, glossy substrates require additional effort to achieve the shiny and expensive looking results. Inks have to be tuned to the surface tension of the glossy surface, the ink droplets must have just enough dot gain, meaning that the droplets spread out when applied to the substrate. If there is too much dot gain then the printing will be blurry. Optimal dot gain is necessary to avoid the white lines between the passes of the inkjet printhead.
Pre-treating glossy paper with primers defeats the intended effect of the shiny product, this is due to the tendency of primers to dull the surface. Other methods must be used to cure the ink after printing.
The inks on glossy surfaces do not absorb into the material, rather the droplets adhere to the shiny surface. A quick drying method avoids ink smearing, if the printing system uses UV curable inks or LED curable inks, the heat from the wavelength of mercury vapour lights or LED lights quickly cure the ink. UV curable inks will come at a higher cost.
Curing and Drying Inks
UV curable 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.
Corona Treating the Paper
Another method for improving inkjet printing on glossy paper or plastics uses a corona or air plasma pre-treatment. 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. However, the corona treatment fades after a short period 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 on can expect to see.