Ultrasound for Dispersing and Grinding: Paint & Pigments

Power ultrasound is well known for its intense and precisely controllable milling and dispersing effects. Industrial ultrasonicators provide a highly uniform particle size distribution in the micron- and nano-range. Industrial ultrasonicators process easily large volume streams of high viscosities and fulfil a homogeneous wetting, dispersing, deagglomeration and milling.

Paint Manufacturing with Ultrasound

Improve your Paints, Colors and Coatings with Sonication:

  • Formulation: Whether high viscosities, high particle loads, aqueous- or solvent-based – with Hielscher’s industrial inline ultrasonicators you can process any formulation.
  • Micron- and Nano-Size: The cavitational high shear forces reduce particles to minute particle diameters and provide an uniform dispersion.
  • Optical Properties: To obtain the correct optical properties, pigment particle size have to be controlled. Usually, opacity correlates with particle size: the finer the particle size, the more opacity. For example, TiO2 is specifically processed to a particle size of 0.20 to 0.3 micron, which is approximately the equivalent to one-half the wavelength of light. Ultrasonication reduces the TiO2 pigments to their optimum size, so that ultimate hiding is obtained.
  • High-Performance Particles: Smaller particle sizes result in greater colour saturation, colour consistency and stability. The intense, yet precisely controllable ultrasound forces allow for producing modified and functionalized nano-particles, such as coated particles, SWNTs, MWCNTs and core-shell particles. Such particles show unique characteristics and elevate paint or coating formulations to a new level of quality and functionality (e.g. UV resistance, scratch resistance, strength, adhesiveness, high heat resistance, infrared and solar reflectivity).
  • Modified Particles: Surface modified pigments have very low viscosity at high pigment loadings (2.5cP at 10% solids), superior suspension stability and high purity
Pigment pastes are milled and dispersed using ultrasound cavitation and high-shear forces

Ultrasonic processing is a powerful method for milling and dispersing pigment pastes.

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Pigment pastes are milled and dispersed using ultrasound cavitation and high-shear forces show a significant size reduction and uniform distribution.

Pigment pastes are milled and dispersed using ultrasound cavitation and high-shear forces show a significant size reduction and uniform distribution. The plot above shows the increasing size reduction at increasing ultrasonic energy.

Use ultrasonics for the production of

  • final formulations
  • master batches of pigment paste
  • refining particles after conventional milling

For the production of paint, the components such as pigments, binders/ film formers, diluents/ solvents, resins, fillers and additives have to mixed together into a homogeneous formulation. Pigments are the determining component that gives paint its color. The most important white pigment is TiO2, which needs to be milled to a optimum particle size between 0.2 and 0.3 microns in diameter to show the desired grade of whiteness, brightness, opacity and a very high refractive index. The ultrasonic shear forces provide a very effective and energy-effective deagglomeration and dispersion of TiO2 particles (see chart below).
Ultrasonic milling and dispersing influences the quality of paint improving its color strength, density, fineness of grinding, dispersion and rheology.

Ultrasonic Dispersing & Grinding Conditions

The quality of paints and coatings relies on the homogenous dispersion of the pigments. Hielscher Ultrasonics supplies effective milling and grinding equipment for paint dispersion, especially for for formulations with high pigment loads. The mechanism of ultrasonic dispersers for milling & grinding, deagglomeration and dispersion applications is also based on the shear principle generated by ultrasonic cavitation. The cavitational forces necessary for the dissociation of the particles are produced by high pressure differences, local hot spots and liquid jets, which results in the particle break-up by inter-particle collision.
Industrial ultrasonic dispersers such as the UIP16000 have the capacity to process high volume streams of paints and coatings.

In this video we show you a 2 kilowatt ultrasonic system for inline operation in a purgeable cabinet. Hielscher supplies ultrasonic equipment to almost all industries, such as the chemical industry, pharmaceutical, cosmetics, petrochemical processes as well as for solvent based extraction processes. This purgeable stainless steel cabinet is designed for operation in hazardous areas. For this purpose, the sealed cabinet can be purged by the customer with nitrogen or fresh air to prevent flammable gases or vapors from entering the cabinet.

2x 1000 Watts Ultrasonicators in Purgeable Cabinet for Installation in Hazardous Areas

Power ultrasonics for milling, grinding and dispersing of pigments, paint and colors. (Click to enlarge!)

Ultrasonic Processing: 7x UIP1000hdT

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The video is demonstrating ultrasonic dispersion of red color using the UP400St with a S24d 22mm probe.

Ultrasonic Red Color Dispersion using the UP400St

Dispersion of Nanoparticles

Ultrasonic grinding and dispersing is often the only method to process nano particles efficiently in order to obtain primary particles. A small primary particle size results in a large surface area and correlates with the expression of unique particle characteristics and functionalities. At the same time, a smaller particle size is associated with a high surface energy for more severe aggregation and reactivity, so that the intense ultrasonic dispersing forces are required to disperse the nano particles homogeneously into the formulation.
Furthermore, an ultrasonic surface treatment can modify the nano particles which leads to improved dispersability, dispersion stability, hydrophobicity and other features.
Researchers have recommended the ultrasonic dispersion method for nano particles as preferred solution, “because the material dispersed by the ultrasonic method is much purer than that produced by bead milling”[Kim et al. 2010].

Ultrasonicator UP200St (200W) dispersing carbon black in water using 1%wt Tween80 as surfactant.

Ultrasonic Dispersion of Carbon Black using the ultrasonicator UP200St

The ultrasonic dispersion technique has many advantages in comparison with traditional milling technologies such as three-roll, ball or media mills. (Click to enlarge!)

Ultrasonic dispersing has significant advantages against conventional milling techniques

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The Hielscher SonoStation makes the sonication of mid-size batches using a flow cell reactor easy.
The compact SonoStation combines a 38 liter agitated tank with an adjustable progressive cavity pump that can feed up 3 liters per minute into one or two ultrasonic flow cell reactors.

Ultrasonic Mixing Station - SonoStation with 2 x 2000 Watts Homogenizers

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, Issue 1. January 9, 2020.
  • Kim, Moojoon; Kim, Jungsoon; Jo, Misun; Ha, Kanglyeo (2010): Dispersion effect of nano particle according to ultrasound exposure by using focused ultrasonic field. Proceedings of Symposium on Ultrasonic Electronics 6-8 December, 2010. 31, 2010. 549-550.
  • Pekarovicov, Alexandra; Pekarovic, Jan (2009): Emerging Pigment Dispersion Technologies. Industry insight Pira International 2009.

Facts Worth Knowing

Ultrasonic tissue homogenizers are often referred to as probe sonicator/ sonificator, sonic lyser, ultrasound disruptor, ultrasonic grinder, sono-ruptor, sonifier, sonic dismembrator, cell disrupter, ultrasonic disperser, emulsifier or dissolver. The different terms result from the various applications that can be fulfilled by sonication.

Ultrasonic Dispersion of UV Black Ink: Ultrasound results in a homogeneous fine dispersion (Click to enlarge!)

UV-Black Pigments: Before and After Ultrasonication