Is white ink capability really such a big deal?
What do you think?
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By Jeff Edwards, international product marketing manager at Océ Display Graphics Systems
20 July 2012
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 colour set
Why is white ink so important? Are there meaningful applications? Are current implementations up to the task? Embedding white ink capability in a piezoelectric ink-jet printer is tough, but implementing it in a high-quality, credible way is even tougher. Formulating a successful white ink solution presents several unique engineering challenges. The most appropriate pigment material for white is titanium dioxide, which is very heavy compared to the pigments used in the coloured inks and it doesn't like to stay suspended in a fluid. As a result, most white ink-equipped printers go to great lengths to circulate, agitate or otherwise excite the ink during idle times.
Titanium dioxide must also be used in a mass/volume proportion of pigment/ink at least three to four times the normal rate to achieve sufficient optical density. Partly as a result of this high pigment loading, it acts as a thickening agent in the ink. Both these characteristics make it particularly difficult to jet white ink through the tiny nozzles in piezoelectric ink-jet print-heads if it is not very carefully formulated, and consistently manufactured, stored and distributed. These characteristics also usually result in a shorter shelf life than for coloured inks.
A white ink solution must offer sufficient opacity to completely cover the media (no colour show-through) 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 colour in a back-lit 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.
There are other questions to consider, however: can white be printed as a layer underneath and/or on top of the coloured inks? Or printed as a layer between two layers of coloured inks, for day/night back-lit applications? Can white/coloured layered prints be made on both rigid and flexible media? Does white print with the same resolution and/or droplet size as the other colours 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 colour area, or are layered print modes the only ones available? Putting a 'check in the box' next to White Ink Capable is not enough when it comes to this important feature.
Once you've purchased a printer with a credible white ink solution that really works, what do you do with it? The answer of course is, anything you want. When considering transparent media applications there are two possibilities. Rigid media such as polycarbonate, acrylic or PET-G can be used for second surface back-lit applications where the image is viewed from the unprinted side of the media. This is most commonly used for back-lit point-of-purchase and retail advertising displays. The quality of some printers is such that they almost rival the quality of laser-based photographic printing solutions.
A more interesting twist is available on some printers that actually enables the white layer to be printed between two coloured 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 back-lit at night but not during daylight hours, requiring less than half the electricity of standard back-lit prints.
The ability to print in two or three independent layers on flexible (roll-based) media is also important. Flexible transparent or translucent media deliver 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-colour method of printing enables them to be viewed from both sides – doubling the number of potential views in the retail environment.
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 colour. Doors, wood, glass, tiles, carpet, stone, cardboard, metals, foils for packaging, fabrics – the list is endless. And if the system doesn't move the media/object during printing, such as a stationary flat-bed, the choice of includes almost anything you can imagine.
Adding high-value, high-margin propositions that enable printer providers to differentiate their business is a great defence against the commoditisation of wide-format printing. White ink printing – it's real and it's profitable, and that makes it a really big deal.
The full version of this article appears in Issue 1, 2012 of Specialist Printing Worldwide.
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