Ingredient Selection for Inkjet Ink Formulation
Introduction to Inkjet Printing Technology
Conventional Emerging Trends in Inkjet Printing
Conventional Emerging Trends in Inkjet Printing
The traditional & emerging applications of inkjet printing include:
Traditional |
Emerging |
- Marking of packages
- Graphics applications for indoors and outdoors sign posters, trade show displays, billboards, & banners
|
- Printing/decoration of textiles
- 3D rapid prototyping
- Printed electronic circuits
- LCD functional layers
- Fuel cells, batteries and solar panels
|
In textile, it is envisioned that digital inkjet will overtake the conventional textile printing systems such as flatbed or rotary screen printing, which is the most commercial form of textile printing. Unlike the traditional methods of textiles printing with rollers or rotary screen screens, inkjet printing does not require screen manufacture, which cuts down costs considerably.
Also, machine set‐up time for print registration is much faster and easier compared to the most advanced conventional systems in the industry. More importantly, there are no costs involved in making up print pastes since the inks are usually supplied in replaceable cartridges.
The initial low printing speed associated with inkjet printing and the associated high cost of ink has become history over the last 5 years due to the significant developments in inkjet printing speed. This, together with the trend towards printing short runs and mass customization has made inkjet printing more viable compared to the traditional textile printing systems.
Currently, with printing speeds of up 3,500 m2/h by MS LaRio; it is not hard to imagine that within the next few years, developments in the technology in inkjet textile printing machines will exceed the speeds of rotary screen-printing machines besides their advantage of low effluent production and less space requirement for operations.
Now that you've learned about the ingredient selection for inkjet inks along with the traditional & current trends, let's walk through the standards test methods for pigmented inks.
Why Pigmented Inks Instead of Dye-based Inks?
Why Pigmented Inks Instead of Dye-based Inks?
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 & 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])/d1 * 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
- Magdassi S. (2010), The Chemistry of Ink Jet Inks - World Scientific Publishing Co. Pte. Ltd.
- Tawiah B, Howard E.K, Asinyo B. (2016), The chemistry of inkjet inks for digital textile printing - Review, BEST 4(2016:61-78.
- Schulz G. (2002), Textile chemistry of digital printing. Melli Texilberichte/Int. Text Rep (Eng Ed).
- Ujiie H. (2006), Digital Printing of Textiles. Woodhead Publishing.
- 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.