Ultrasonic Size Reduction of Ink (e.g. for Inkjet)
Ultrasonic cavitation is an effective means for the dispersing and microgrinding (wet milling) of ink pigments. Ultrasonic dispersers are successfully used in research as well as in industrial manufacturing of UV-, water- or solvent-based inkjet inks.
Nano-Dispersed Inkjet Inks
Ultrasound is very effective in the size reduction of particles in the range from 500µm down to approx. 10nm.
When ultrasonication is used to disperse nanoparticles in inkjet ink, the ink color gamut, durability, and print quality can be substantially improved. Therefore, probe-type ultrasonicators are widely used in the manufacturing of nanoparticle-containing inkjet inks, specialty inks (e.g., conductive inks, 3D-printable inks, tattoo inks) and paints.
The graphs below shows an example for non-sonicated vs ultrasonically-dispersed black pigments in inkjet ink. Ultrasonic treatment was performed with the ultrasonic probe UIP1000hdT. The result of the ultrasonic treatment is a visibly smaller particle size and a very narrow particle size distribution.
How Does Ultrasonic Dispersion Improve Inkjet Ink Quality?
High-intensity ultrasonicators are highly efficient for the dispersion, size reduction and uniform distribution of nanoparticles.
This means that ispersing nanoparticles with ultrasonics in inkjet ink can improve its performance and durability. Nanoparticles are very small particles with sizes in the range of 1 to 100 nanometers, and they have unique properties that can enhance inkjet ink in several ways.
- Firstly, nanoparticles can improve the color gamut of inkjet ink, which refers to the range of colours that can be produced. When nanoparticles are uniformly dispersed with an probe-type ultrasonicator, the ink exhibits consequently more vivid and saturated colours. This is because nanoparticles can scatter and reflect light in ways that traditional dyes and pigments cannot, leading to improved color reproduction.
- Secondly, homogeneously dispersed nanoparticles can increase the resistance of inkjet ink to fading, water, and smudging. This is because nanoparticles can bond more strongly with the paper or other substrate, creating a more durable and longer-lasting image. Additionally, nanoparticles can prevent the ink from bleeding into the paper, which can cause smudging and reduce the sharpness of the printed image.
- Lastly, ultrasonically dispersed nanoparticles can also improve the print quality and resolution of inkjet ink. Ultrasonic dispersers are exceptionally efficient when it comes to milling and blending nanoparticles in liquids. By using smaller particles, the ink can create finer and more precise lines, resulting in sharper and clearer images. This is particularly important in applications such as high-quality photo printing and fine art printing.
Control Over Process Parameters and Dispersion Results
The particle size and the particle size distribution of ink pigments affect many product characteristics, such as tinting strength or printing quality. When it comes to inkjet printing a small amount of larger particles can lead to dispersion instability, sedimentation or inkjet nozzle failure. For this reason it is important for the inkjet ink quality to have a good control over the size reduction process used in production.
Inline Processing of Nano-Dispersions for Inkjet Inks
Hielscher ultrasonic reactors are commonly used in-line. The inkjet ink is pumped into the reactor vessel. There it is exposed to ultrasonic cavitation at a controlled intensity. The exposure time is a result of the reactor volume and the material feed rate. Inline sonication eliminates by-passing because all particles pass the reactor chamber following a defined path. As all particles are exposed to identical sonication parameters for the same time during each cycle, ultrasonication typically narrows and shifts the distribution curve rather than widening it. Ultrasonic dispersion produces relatively symmetrical particle size distributions. Generally, right tailing – a negative skew of the curve caused by a shift to the coarse materials (“tail” on the right) – can not be observed at sonicated samples.
Dispersion under Controlled Temperatures: Process Cooling
For temperature-sensitive vehicles, Hielscher offers jacketed flow cell reactors for all laboratory and industrial devices. By cooling the internal reactor walls, process heat can be dissipated effectively.
The images below show carbon black pigment dispersed with the ultrasonic probe UIP1000hdT in UV ink.
Dispersing and Deagglomeration of Inkjet Inks at Any Scale
Hielscher makes ultrasonic dispersing equipment for the processing of inks at any volume. Ultrasonic lab homogenizers are used for volumes from 1.5mL to approx. 2L and are ideal for the R+D stage of ink formulations as well as for quality testings. Furthermore, feasibility test in the laboratory allow to select the required equipment size for commercial production accurately.
Industrial ultrasonic dispersers are used in the production for batches from 0.5 to approx 2000L or flow rates from 0.1L to 20m³ per hour. Different from other dispersing and milling technologies, ultrasonication can be scaled up easily since all important process parameters can be scaled linearly.
The table below shows general ultrasonicator recommendations depending on the batch volume or flow rate to be processed.
|Batch Volume||Flow Rate||Recommended Devices|
|10 to 2000mL||20 to 400mL/min||UP200Ht, UP400St|
|0.1 to 20L||0.2 to 4L/min||UIP2000hdT|
|10 to 100L||2 to 10L/min||UIP4000hdT|
|15 to 150L||3 to 15L/min||UIP6000hdT|
|n.a.||10 to 100L/min||UIP16000|
|n.a.||larger||cluster of UIP16000|
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How Does Ultrasonic Dispersers Work? – The Working Principle of Acoustic Cavitation
Ultrasonic cavitation is a process that uses high-frequency sound waves to generate small gas bubbles in a liquid. When the bubbles are subjected to high pressure, they can collapse, or implode, releasing a burst of energy. This energy can be used to disperse particles in the liquid, breaking them down into smaller sizes.
In ultrasonic cavitation, the sound waves are generated by an ultrasonic transducer, which is typically mounted on a probe or horn. The transducer converts electrical energy into mechanical energy in the form of sound waves, which are then transmitted into the liquid through the probe or horn. When the sound waves reach the liquid, they create high-pressure waves that can cause the gas bubbles to implode.
There are several potential applications for ultrasonic cavitation in dispersion processes, including the production of emulsions, the dispersion of pigments and fillers, and the deagglomeration of particles. Ultrasonic cavitation can be an effective way to disperse particles because it can generate high shear forces and energy input as well as other important process parameter such as temperature and pressure can be precisely controlled, making it possible to tailor the process to the specific needs of the application. This precise process control is one of the prominent advantages of sonication as high-quality products can be reliable and reproducibly produced and any undesired degradation of particles or liquid is avoided.
Robust and Easy to Clean
An ultrasonic reactor consists of the reactor vessel and the ultrasonic sonotrode. This is the only part, that is subject to wear and it can be easily replaced within minutes. Oscillation-decoupling flanges allow to mount the sonotrode into open or closed pressurizable containers or flow cells in any orientation. No bearings are needed. Flow cell reactors are generally made of stainless steel and have simple geometries and can easily be disassembled and wiped out. There are no small orifices or hidden corners.
Ultrasonic Cleaner in Place
The ultrasonic intensity used for dispersing applications is much higher than for typical ultrasonic cleaning. Therefore the ultrasonic power can be used to assist cleaning during flushing and rinsing, as the ultrasonic cavitation removes particles and liquid residues from the sonotrode and from the flow cell walls.
Literature / References
- Adam K. Budniak, Niall A. Killilea, Szymon J. Zelewski, Mykhailo Sytnyk, Yaron Kauffmann, Yaron Amouyal, Robert Kudrawiec, Wolfgang Heiss, Efrat Lifshitz (2020): Exfoliated CrPS4 with Promising Photoconductivity. Small Vol.16, Issue1. January 9, 2020.
- Anastasia V. Tyurnina, Iakovos Tzanakis, Justin Morton, Jiawei Mi, Kyriakos Porfyrakis, Barbara M. Maciejewska, Nicole Grobert, Dmitry G. Eskin 2020): Ultrasonic exfoliation of graphene in water: A key parameter study. Carbon, Vol. 168, 2020.
- del Bosque, A.; Sánchez-Romate, X.F.; Sánchez, M.; Ureña, A. (2022): Easy-Scalable Flexible Sensors Made of Carbon Nanotube-Doped Polydimethylsiloxane: Analysis of Manufacturing Conditions and Proof of Concept. Sensors 2022, 22, 5147.
- Brad W. Zeiger; Kenneth S. Suslick (2011): Sonofragmentation of Molecular Crystals. J. Am. Chem. Soc. 2011, 133, 37, 14530–14533.
- Poinern G.E., Brundavanam R., Thi-Le X., Djordjevic S., Prokic M., Fawcett D. (2011): Thermal and ultrasonic influence in the formation of nanometer scale hydroxyapatite bio-ceramic. Int J Nanomedicine. 2011; 6: 2083–2095.