Inkjet Printing An Evolution of Ink

Originally Published Through Yahoo Voices

From the Brush to the Pen to the Printhead

Inkjet printers. Just about everybody has at least one. there’s a pretty good chance that as you’re reading this article, you’ve got an inkjet printer sitting on your desk or close by that is attached to the computer via either a usb or parallel cable.
The main companies at play in the Inkjet world are Canon, Epson, HP, and Lexmark. Some may say, what about Dell? Truth be told, all Dell Printers are Lexmark machines that have been repackaged. Lexmark was not an innovator in inkjet printing though, it’s the Johnny-come-lately of the bunch. Epson, HP and Canon worked to develop and perfect the technology that allows for thousands of tiny nozzles to accurately spray ink onto paper in such a way as to make wonderful prints come out of such a simple machine.

There are two main technologies at work within an inkjet printhead. There is either a Thermal Drop on Demand or DOD printhead, or a Piezoelectric DOD printhead. Thermal printheads use a printhead that contains thousands of microscopic cavity, each one fitted with a heating element. Upon command, the heater fires, causing a bubble to form at the top of the droplet of ink within the cavity and as such, ink is forced out of the bottom of the cavity, where it strikes the paper beneath. This process of heating the drop or bubble of ink was how the term bubblejet printer came to be used by Canon for it’s early inkjet printers. Canon was the originator of the thermal inkjet process, back in 1977.

In Piezoelectric printheads the technology is quite different. While the ink cavity is similar, instead of a heating element, a tiny piece of piezoelectric material sits behind each droplet of ink. When voltage is applied, the piezo material flexes, pushing ink out of the cavity by generating a pressure wave. This has the advantage of no wear and tear via heating/cooling cycles, and less chance of ink drying out as it is not effected by heating or cooling cycles.

Both technologies work with the same basic ink structures, although each company has highly specialized and secret ink formulations. Surface tension within the ink itself keeps the cavities filled; as the bubble contracts it draws more ink from the reservoir to fill the gap left by the deployed droplet.

At this point, piezo inkjet technology is the faster competitor, with a cut sheet printer able to produce approximately 150 letter sized sheets of full color print per minute.

The inks themselves have undergone dramatic evolutions from the original days of a water based dye held in a suspension to be squirted out on demand. Most home inkjet printers still use water based ink, so don’t get your home printed pictures wet – they’ll run all over the place. A select few higher end home inkjets and most commercial printers now use solvent based ink.

*Solvent inks use VOC’s or Volatile Organic Compounds to act as both a carrier and a suspension for the pigments that make up the colour. The most common VOCs used in solvent ink are Cyclohexanone and MEK. both of which are classified as toxic and require full ventilation for any printer that is using them as an ink suspension.

*A subset of solvent inks are eco-solvents – which use a milder form of VOC to reduce fumes and thereby improve air quality. Sometimes these are promoted as Green inks – but in reality, they are as environmentally damaging as their heavy duty siblings – just not as immediately toxic with the gassing and fumes.

UV Inks are another type of development in inkjet printing. The printhead within a UV printer includes UV arc lamps which instantly cure the ink as it hits the paper. There is no outgassing, virtually no ink absorption into the paper or printing substrate, and this type of ink is virtually permanent. Unfortunately, the color range is limited compared to liquid suspension inks as well as a solid ink is not flexible so this format won’t work on t-shirts or banners. UV Inks have a solid market that was normally taken up by screen printing though, stickers are now mostly UV ink produced in the thousands at a fraction of the cost of setting up a screen print and running a press.

Latex ink is a new innovation that HP has developed for it’s wide format thermal inkjet printers. It has latex paint particles suspended in a water/glycol aqueous mix that is sprayed onto the substrate using a style similar to normal thermal printing. As the ink dries it becomes very permanent, like paint, and can withstand outdoors sunlight and weather if printed onto an outdoor capable material like vinyl.

Although the inkjet printhead has remained functionally unchanged since the early 80’s when the technology was perfected, the new input is in the ink. How to produce the best colour spread, longest lasting duration at full brightness; and of course, how to do it at the lowest cost.

For the home user, we still get stuck with limited life inkjets that allow for high quality prints that can last quite a long time, under certain conditions, but compared to traditional photo developing techniques and the ‘wet lab’ process – ink technology still has a ways to go to really compete with silver nitrate and the colour range of chemically processed film.

The days of a signwriter taking brushes and stencils and painting billboards or large signs are long past. Most if not all signage nowadays is produced digitally, either with inkjet, or with cut adhesive vinyl. The brush is no longer in play for a commercial enterprise.

The same goes for copywriters or editors. The days of doing manual markup on a manuscript is long gone, now it’s all done electronically, and output by laser or inkjet much faster than a traditional printing press using ink and movable type.

Inkjet technology and the science behind the ink formulations are constantly being developed and are evolving faster than most of us realize. The technology contained within the home inkjet which is pretty much a throwaway printer represents tens of billions of dollars invested over more than 30 years of development. Pretty remarkable for a bit of plastic sitting on your desk, eh?