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Application of Dyes and Pigments
Colourants for Printing Inks
Dyes for Water Based Inkjet Inks Pigments for Water Based Inkjet Inks

How The inkjet ink creates colour

Inkjet printers, similar to computer monitors, create colors by a process in which droplets of the main primary colors are tightly positioned. This process is known as Dithering. Generally printers procure inks from the subtractive colors. They are namely cyan, magenta and yellow. If black is added to the mix then the standard printing combination of the four colors are obtained. CYMK (cyan, yellow, magenta and black). It is these primary colors (CYMK) that are dithered for the formation of the entire spectrum of colors.

Dithering breaks down the color pixels into array of dots. Now each of the dots can be made up of one of the basic colors, or can be even left blank. In the process of printing, each of the pigments in the ink has a tendency to absorb light differently. This effectively means that only a part of the visible light spectrum gets reflected back to the eye. This is the reason why the CYMK process is also known as subtractive printing.
We all use inkjet inks in our printers of various hues and application. But do we know that the most vital part of the inkjet printer is the ink that we use in the cartridge. In fact the determinants of the quality of printing are the type, quality, and the quantity of ink in the cartridge. Inkjet inks are classified into the following four types of categories:
  • Water based
  • Solvent-based
  • Oil-based
  • Curing
  • Hybrid ink
Buying Tips

Obey the rules- First and foremost is to obey the printer manufacturer's advices.

Watch out for compatibility- The association of ink and paper is a complex one and difficult to optimize. It has been often seen that bargain-priced inks or papers leads to results that is not upto the mark.

Working ink-paper pairs- Normally the following combination has been seen to work better:
  • Dye/ colorant + coated paper
  • Pigment + nanoporous paper
Smart Choice between pigments and dyes- Remember the choice you make is some sort of a delicate balance between quality of the colour and the factor of longevity. If your need is extreme long life, then go for pigments, but don't forget they may have a reduced color quality in comparison to dyes. Dyes are the way to go if your criteria is good life and and colour.

See the colour gamut comparison charts in proper perspective- Do not hesitate to ask for direct comparison prints on exactly the type of media that you would be using. As a thumb rule you should desist from using pigment inks in printers that are designed for dyes. It may work, but there is possibility of landing you in trouble.

Water based inkjet inks

Water based inkjet inks are very common inks that are used for printing. Basically, the water or aqueous ink formulations comprises mainly of a carrier fluid that is able to keep the liquid in a liquid state thus acting as a sort of carrier for the fluid. They do not contain any volatile organic compounds in them and has a very low level of toxicity. They are generally used for application in paper.

However they are not ideal for high resolution printing, as they have a tendency to bleed or feather. Water-based inkjet inks as a product can be broadly classified into two general categories:-

Dyes for Water Based Inkjet Inks Pigments for Water Based Inkjet Inks


The following diagram illustrates both the types
Colourants

As is clear from the diagram a dye is the type of colourant where it gets fully dissolved in the carrier fluid. Whereas pigments are fine powders of solid colourants that gets dispersed in the colour fluid. To understand the role of dyes and pigments in Water based inkjet inks, first there is a need to look at the basic ingredients of a water based inkjet inks.

Ink component Use wt-%
Colourant It gives the ink it's basic function - absorbing of light of the specific wave length band 2-8
Carrier fluid Suspends or helps in dissolving the colourant 35-80
Surfactant Helps to promote wetting by lowering the surface tension 0.1-2.0
Humectant Helps in inhibiting evaporation(mixes with the carrier fluid) 10-30
Penetrant Helps to penetrate ink in the paper surface 1-5
Dye solubilizer Helps to promote dye solubility in the carrier fluid 2-5
Anticockle additive Checks interaction with paper fibers that can very well lead to paper cockle 20-50


Pigment or Dye: The Great Debate

There has been a great debate regarding which medium is better whether dyes or pigments. Though there is no conclusive evidence regarding the superiority, but both Dyes and Pigment-based inks have their plus and minuses. While water based inkjet inks using dyes has been a traditionally favoured process. But with changing times pigment based inks are getting increasingly accepted as a choice. The following sections give some comparisons between the two.

Dye Based Ink Pigment Based Ink
Pluses
  • Soluble and stable
  • Vast colour pallete
  • Enormous range
  • Bright and intense colour
  • Dyes are far efficient in Graphic printing
    • Larger colour pallete
    • Bright and vibrant colours
Minuses
  • Shows tendency for fading
  • Shows limited resistance to water
  • Nozzle crusting
Latest Trend: Manufactures are now opting for combination inks with improved light and water fastness but not at the cost of colour intensity.

Pluses
  • Water fastness shows marked improvement
  • Improved light fastness
  • Distinct improvement in Archivability
  • Clarity of Print
  • Pigments good in Outdoor Application
Minuses
  • Range limited
  • Tendency to clog
  • Expensive
  • Colours not that vibrant and bright


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