This example of white ink in an opaque application shows where white forms part of the image content, and creates a base for the CMYK color set.
Backlit images can be created on transparent media using white ink as a light-diffusing layer.
White ink enables printing or dark or colored substrates.
Using the Day/Night technique—where a white layer is ‘sandwiched’ between two color layers—can also be used to create static cling graphics on clear, flexible material.
This illustration shows how the ink layers are implemented in a Day/Night application.
With all of the features on a wide-format printer, is white ink really important? Formulating a successful white ink solution presents several unique engineering challenges. To begin with, the most appropriate pigment material for white is titanium dioxide, which is very heavy and doesn’t like to stay suspended in a fluid. As a result, most white ink equipped printers go to great lengths to circulate or otherwise “excite” the ink during idle times to keep it well mixed. Titanium dioxide must be used in a mass/volume proportion of pigment/ink at least three to four times the normal rate in order to achieve sufficient optical density. Partly as a result of this high pigment loading, it actually acts as a thickening agent in the ink. These characteristics make it particularly difficult to jet white ink through the tiny nozzles in piezoelectric inkjet print heads and usually result in a shorter shelf life than for colored inks.
A white ink solution must offer sufficient opacity to completely cover the media with a bright, white base when printing on non-white media or objects. It must also have sufficient translucence and smoothness of tone to act as an even light diffuser when printed on top of the color in a backlit application on transparent media. Some wide-format solutions offer mediocre white options that simply are not bright enough, white enough, opaque enough, or smooth enough to use with much commercial credibility.
Understanding the exactly image quality limitations of the white ink implementation is critical but there are other questions to consider:
Can white be printed as a layer underneath and/or on top of the colored inks? Can white be printed as a layer between two layers of colored inks, for day/night backlit applications? Can white/colored layered prints be made on both rigid and flexible media? Does white print with the same resolution and/or droplet size as the other colors for fine detail printing, or is it suitable only as a fill (flood) coating? Can it be printed at full speed when printing a non-interfering spot color area, or are layered print modes the only ones available?
The most important point to take from this is that understanding the image quality and technical capabilities of a printer is critical to successfully implementing this service.
White ink capability dramatically expands the possibilities, especially for flatbed-style printers.
When considering transparent media applications there are two possibilities. Rigid media such as polycarbonate, acrylic, or PET-G can be used for second surface backlit applications where the image is viewed from the unprinted side of the media. This is most commonly used for backlit point-of-purchase and retail advertising displays. A more interesting twist on this technique, available on some printers, enables the white layer to be printed between two colored layers on the same (second) surface of the media. This facilitates the use of the print in a day/night mode where it is actively backlit at night, but not during daylight hours.
Of course, the ability to print in two or three independent layers on flexible (roll based) media is also important. Flexible transparent or translucent media deliver all the same application options as rigid but for lower cost, short-term display purposes. Flexible media also expands use to such applications as static-cling window decoration where the white-between-color method of printing enabling prints to be viewed from both sides.
When considering non-white media things get even more interesting. Imagine being able to print on any reasonably flat object or media, regardless of base color. And if the system doesn’t move the media/object during printing, the choice of substrate expands to include almost anything you can imagine.
White ink capability offers the ability sell high-value backlit graphics on rigid or flexible media. White ink also gives print providers with flatbed printers the ability to create specialty applications on almost any media or object. Adding high-value, high-margin propositions that enable PSPs to differentiate their business is a great defense against the commoditization of wide-format printing.