Thursday, 30 June 2011

Why my ink stinks?

I was printing using an old inkjet printer. I tried to get some quality images printed but the ink ran into each other and the quality stunk.  So I started looking into and understanding why?  I took the ink out of the compartment and held it up in my hand to look at this liquid.  It is a far distant ancestor to the first inks from the Chinese made from around 256 BC in the end of the Warring States Period and produced from soot and animal glue.  My ink in my printer is also far distant from the Indian made 4th century BC called masi, and made of burnt bones, tar, pitch, and other substances.  I doubt the ink producers at Hewlett Packard, Lexmark, Sun Chemicals or Xerox still use bones and animal glue in their ink composition.

So why does my ink stink out of my old in jet printer?  Some of the ink properties that are crucial for performance include low viscosity, optimum surface tension, nanometer particle size for a start.  So I will focus here (as the blog is entitled 72dynes) on the surface tension.  Ink requires that you have the right surface tension and luckily you can measure this surface tension quickly and easily using a tensiometer.  The surface tension affects the substrate wetting, print quality and and adhesion.  It needs to be optimized to improve the jet stability and performance.  An ink formulator (and yes they are still formulating better inks) after 2000 years needs to balance the demands of good jettability, substrate adhesion, print image quality and drop spread.

When parameters like the surface tension are not optimized my ink starts to stink.  When the ink surface tension is much lower than the substrate good substrate wetting and a good drop spread and therefore surface energy of the ink on the paper (or whatever you are printing onto) can be achieved.  If the ink surface tension is too low it can increase it can increase the drop spread reducing the resolution like in my case.  In these case we are talking about static surface tension.

For a dynamic process such as inkjet printing the ink surface tension at extremely short time intervals also should be measured.  The time it takes to go from the ink cartridge to the paper for example.  The dynamic surface tension is thus a critical parameter to understand the time dependent characterization within milliseconds.  So depending on the inks dynamic surface tension dictates how fast you can print the report out of your ink jet printer.

So to ink still stinks and I have gone through a stack of papers trying to print this document!!!   I am not mad since I learned something valuable about surface tension.  Static surface tension is an equilibrium surface tension measurement and represents the minimum value seen by the dynamic testing.  The dynamic testing can show that the surface tension my ink decreases with time due to surface active materials in the sample migrating to a freshly developed surface and reaching equilibrium.  In any case, the dynamic surface tension will not decrease below the static (equilibrium) surface tension over time.