Using Pigments: A challenge to Inkjet formulators Pigments are solid particles in essence, that are not miscible in the continuous phase. They have a tendency to settle and aggregate. Now these sort of destabilisations can have a great deal of impact on the final quality of the end product (things like concentration, gradients, blocking of the jet that leads to inconsistency in the colour, etc can be a source of problem. Therefore, for keeping the pigments in suspension in the cartridge can be a day-to-day challenge for the formulator. So the formulator is in search of constant new ways to prevent agglomerating and avoiding any sort of sedimentation. An Inkjet formulator must keep the following points in mind while using pigments: Effect of Temperature Mixing of pigments Aggregation of Pigment particles

Water-based inkjet inks are primarily used in inkjets of the type standard and thermal. In this type of inks there is presence of volatile organic compounds (VOC) and they do have low level of toxicity, the dry rate is relativey slow on the non-absorbent substrates. They often require a special coated media for optimizing dot gain and drying. They also need lamination to secure water resistance. Originally they were developed for the desktop systems only but moved on to facilitate the growth of inkjet in wide-format graphics.

Of late there is a trend for the inkjet inks to become pigment based. If we analyses the reasons for the spurt in popularity in the application of pigment in inkjet inks the answers would not be very difficult to understand. Pigments give environmental friendly products along with durability and better compatibility with packaging. However one thing needs to be specified here is that the colloidal properties generally associated with pigments are more complex than dyes.

Inorganic pigments
(For use in Achromatic Inks)
To make the white inks, the most important inorganic pigment is Titanium dioxide. Another popular inorganic pigment, calcium carbonate is used as an extender to make white inks. But, if we want to make black ink, then the most randomly used inorganic pigment is carbon black.

We can therefore say that the inorganic pigments that are used for making printing inks are Carbon Black (very important), Titanium Oxide, Molybdenum Red Pigments and iron Blue all with medium usages while Chromate Pigments (sparingly used).

Organic Pigments
(For use in Colored Inks)
Now a days, the inorganic colored pigments are very rarely used because, these pigments contain very high degree of metallic toxics like chromium, cadmium and lead. In their place to create green and blue shades, phtalocyanine pigments are used. For red and yellow shades inks, Azo pigments are very preferred medium.

Whether the molecules of the pigments will absorb light in the visible range or not, depends upon the presence of the conjugated system of double bonds in these molecules.

Advantages- Advantages of pigment based inks are:
Pigments are tiny combinations of a variety of molecules. They are much bigger in size than their dye counterparts. This size advantage translates into:

• Stability
• Lightfastness
• Less susceptibility to environmental factors and oxidising gases.

Downside-
Particles that are found in a dried pigment ink has a surface that is very rough. As a result the light that is reflected of the prints has a predominant tendency toward scattering, giving rise to colour that is less saturated and dull.

• Excellent light and weather fastness.
• 100% of water-fastness on any type of media.
• Excellent color hue and quality for that perfect imaging effect.
• Quick drying.
• Particle size below the level of 0.08 micron.
• No problem of clogging.