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Introduction to Inkjet Printing Technology

Ingredient Selection for Inkjet Ink Formulation

Conventional Emerging Trends in Inkjet Printing

Standard Test Methods for Pigmented Systems

Standard Test Methods for Pigmented Systems

The desire to develop a universal ink which can enable inkjet printing on chemically diverse textile materials can be achieved by the use of pigments inks because of the mechanism of adhesion to varied substrates.

Standard Test Methods for Pigmented Inkjet Inks


For most inkjet inks containing pigments, it is important that the specific physicochemical properties remain constant over time. Hence, the tests listed below are used to determine the jetting behavior, the tendency of aggregation, thermal, and storage stability. The tests are in no way exhaustive but only suggestive. More tests could be conducted based on:

  • The type of pigment (encapsulated or not, organic or inorganic)
  • The effect required, and
  • The specific properties of the print-head technology available

However, the following tests are essential for the proper functioning of pigmented inkjet inks.

Particle Size
Particle Size
Zeta Potential
Ink Viscosity
Surface Tension
TEST METHODS FOR PIGMENTED INKJET INKS
Aggregation of Pigment Particles
Moisture Content


Particle Size & Distribution

Particle size and particle size distribution of the pigment particles within the inkjet ought to be measured to prevent possible aggregation. These can be determined by the Dynamic Light Scattering method.


Zeta Potential

The zeta potential of the pigment determines the surface charge relative to conductivity and dielectric properties and this can be measured by Zeta Potential Analyzer.


Viscosity

The viscosity of the ink, which determines to a large extent the flow/jetting properties can be tested by a rheometer or viscometer.


Surface Tension

The surface tension determines the rate of wetting and spreading of the ink on a substrate. This property can be determined by an automatic surface tensiometer.


Morphology

The morphology of the pigment particles in a pigmented inkjet ink system can be observed by a transmission electron microscope. The morphology of the pigment particles in the system affects the gloss or otherwise of the ink when printed.


Tendency of Aggregation

The tendency of aggregation by pigment particles in a pigmented inkjet ink during storage can be evaluated by a freeze-thaw stability test in which the ink is frozen at -10°C for 24 h, and the thawed at 60°C for another 24 h.

Similarly, the thermal stability of the pigment ink can be tested by heating at 60°C for 24 h after which the particle size and its distribution within the system is are tested and compared to the initial results.


Propensity of Phase Separation

The propensity of phase separation is determined by centrifuging the pigmented ink for 30 min at 3000 rpm followed by calculating the changes in particle size using the equation below:

Sc = ([d2-d1])/d* 100

where:
           → Sc is the centrifugal stability
           → d1 and d2 are the particle size of the pigment size before and after the treatment respectively


Moisture Content

The moisture content can also be determined by a simple experiment of drying at 60°C until a constant weight is attained after which moisture content can be determined mathematically.


NOTE: The science and the art of pigment dispersion are too broad for this write-up.


Suitable Raw Materials for Digital Inks

View all the commercially available raw materials used for digital inkjet printing inks, analyze technical data of each product, get technical assistance or request samples.



References

  1. Magdassi S. (2010), The Chemistry of Ink Jet Inks - World Scientific Publishing Co. Pte. Ltd.
  2. Tawiah B, Howard E.K, Asinyo B. (2016), The chemistry of inkjet inks for digital textile printing - Review, BEST 4(2016:61-78.
  3. Schulz G. (2002), Textile chemistry of digital printing. Melli Texilberichte/Int. Text Rep (Eng Ed).
  4. Ujiie H. (2006), Digital Printing of Textiles. Woodhead Publishing.
  5. Li, M, Zhang L, Wang, D., Datong W., Agbo, C., Fu, S. (2017), Influence of nano-coated pigment ink formulation on ink-jet printability and printing accuracy. Coloration Technology,133(6), 476-484.
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