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Inkjet Dyes

Understanding the Chemistry of Inkjet Dyes

As inkjet dyes are indispensable today, no doubt a better understanding of the chemistry of inkjet dyes will certainly lead to a smoother quality finish and add more longevity for the printed item. Researches were done at Helsinki University of Technology to understand the light fastness of inkjet prints for the first time. They applied the Kerr gated resonance Raman spectroscopy for this. In this process, the excitation wavelength was used to selectively raise the Raman signals from the dye molecules of the printing colours. It was found that the Kerr gate rejected fluorescence of the dyes, inorganic pigments and the strong fluorescent optical brighteners. The interactions between the dyes and the coating polymers were studied from shifts in the Raman signals of the dyes. The light induced changes that took place in the chemical structure of the dyes were detected as changes as a result of the intensity of the Raman bands that corresponded to specific chromophores in the dye.
Globally the importance of electronic print processes is constantly gaining prominence. The growth of multi color inkjet technology is especially growing in the home and office segments. A substantial and thriving consumer market for inkjet can be noticed in packaging, publication, and specialty areas.

The quality of an inkjet printing is very much influenced by the physico-chemical properties of printing ink. Here lies the importance of inkjet dyes. Dyes for Inkjet ink are a bit different from the usual dyes that are available for fibers. This is because of the fact that they need to have high purity, and do contain small salt and inorganic matters. Dye inks are prepared by dissolving of the liquid colored dyes into a fluid carrier. This makes the dyes easy to apply. When it is applied to a paper, the dyes are absorbed very uniformly so they reflect light very evenly. As the printing is a high precision job the inkjet dyes need to have superior quality in terms of colors, physical properties, and stability. Generally direct, reactive, and acid dyes are used as dyes for Inkjet Ink.

Inkjet dyes can also come in the form of powders besides the usual liquids.

Powder Dye Inkjet Dye

Given here is a few of the inkjet dyes that are available in the powder form along with its characteristics.

CI Name CI Number Concentration Quality Characteristics
Reactive Red 180 181055 100.00% Salt-free/RO Magenta (standard)
Acid Red 52 45100 400.00% Low salt Standard for toning as well as shading
Acid Blue 9 42090 165.00% Low salt Cyan (standard)
Direct Blue199 74190 175.00% Salt-free/ RO Greenish blue
Acid Yellow 23 19140 200.00% Salt-free/RO Red shaded Yellow (standard)
Direct Black 168 30410 165.00% Salt-free/RO Standard
Direct Black 19 35255 200.00% Salt-free/RO Standard

Functioning of the Inkjet dyes

Inkjet print images,( with dye inks) uses a particular method of fixing the dye firmly for making the prints durable when they are stored.

Dyes that are generally used for inkjet printers is charged to anionic, while cationic substances are used as a fixati for the dye.
Inkjet papers that has cationic polymers, have a superlative effect in fixing the various dyes. As the following diagram illustrates.

Cation Polymers

Selecting the right powder form Inkjet Dyes

  • The powder form inkjet dyes should have a very low salt content.
  • There must be the use of latest technologies like Reverse Osmosis in the desalting process.
  • Must possess a very fine particle size.
  • The dyes must get easily soluble in water and other types of co-solvents.
  • Gives the right storage options.
  • Must be Environment friendly.
  • Last but not the least that gets easily converted into liquid "onsite"
Advantages of Inkjet Dyes

Some of the major advantages of dyes used for inkjet printers are listed below:
  • Offers a wide gamut of colours.
  • Bright intense colours.
  • Wide selection.
  • Stable and soluble.
Drawbacks of Inkjet Dyes

A few of the drawbacks as experienced by the users of the inkjet dyes in the printers is given below.
  • There is a tendency for less stabilization.
  • The print is not as much thick as of a pigment based ink.
  • More damage prone to attacks of sunlight ozone and ultraviolet rays.
Comparison between Inkjet Dyes and Inkjet Pigments

There has been often a dilemma regarding the colouring material of the ink whether to go for dye based inks or opt for pigment based ones. Lets look at the pros and cons of both:

From the point of view of the manufacturers:-
Dye based Ink Pigment Ink
  • As a result of sustained efforts over the years this technology is now very well mastered in the industry. In fact Dye based inks started long before the time that inkjet printers even appeared on the market.
  • The technology of pigment is comparatively difficult to master as the problem of small size of the particles to create in large quantities must be taken into account. As nano-sized particles have to be manufactured that will be coated in a thin resin.
This resin is used for protection of the pigment against external chemical and mechanical attacks. This has a problem too as it also helps in transportation of the particle inside the ink, through the nozzles and finally onto the paper. Thus it is quite clear that these contradictory constraints make this technology a difficult proposition to perfectly master.

From the point of view of users:-
Dye Based Ink Pigment Ink
  • The ink (dye based) is usually cheap though the manufacturing cost is only one factor in ascertaining the selling price of inkjet ink.

  • Dye is usually fragile, when exposed to light and Ultra-violet light, the colored molecules gets broken and loose its color. This results in the prints to loose their original colors and fades overtime.

  • Ozone and several other common pollutants are also able to chemically break down the color molecules.

  • Drying time has a direct bearing with the drying time of the solvent on the paper (often this leads to untimely closing of nozzles, if the ink is set to dry very fast on paper). Consequently, if the ink and its solvent is not quickly absorbed by the paper, there is a risk of ink flow or paper deformation.
  • The Pigment based inks solution gives longevity to. It is thus no surprise that many printers are opting for such pigments.

  • Degradation of pigments by pollutants or ozone is not that much, the presence of the resin coating limiting it further.

  • Color density is generally better, or easier to achieve than with dye-based inks.

  • However talking of limitations pigments shows tendency to promote a defect called bronzing. When brightly lit or if lit with low incidence, the print can show unpleasant metal-like reflections.

  • Manufacturing costs are higher, therefore cost of the ink is higher to the user.


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