How to Mix Varnishes with Nanofillers

Varnish production requires powerful mixing equipment that can handle nano-particles and pigments, which must be uniformly dispersed into the formulation. Ultrasonic homogenizers are highly efficient and reliable dispersing technique which provide a homogeneous distribution of the nanoparticles into polymers.

Varnish Production with High-Performance Ultrasonic Mixers

A varnish is described as a clear transparent hard protective coating or film, which is formulated from resins (e.g., acrylic, polyurethane, alkyd, shellac), drying oil, a metal drier, and volatile solvents (e.g., naphtha, mineral spirit or thinner). When varnish dries, its contained solvent evaporates, and the remaining constituents oxidize or polymerize to form a durable transparent film. Varnishes are mostly used as protective coatings for wooden surfaces, paintings, and various decorative objects, whilst UV curing varnishes are used in automobile coatings, cosmetics, food, science and other branches.

Ultrasonic Dispersion of Nano-Silica in Varnish

A common example for ultrasonic dispersing is the incorporation of colloidal silicas, which are usually added for giving varnishes thixotropic properties.
For instance, nano-silica filled polyetherimide varnish shows an increased lifetime up to thirty times higher than a standard one. Nano-silica improves varnish properties as its electrical conductivity, its DC and AC dielectric strengths and its bonding strength. Ultrasonic dispersers are therefore widely used for the production of electrically conductive coatings.
Other silicate minerals, wollastonite, talc, mica, kaolin, feldspar, and nepheline syenite are cheap fillers and widely used as so-called extender pigments, which are added to modify rheology (viscosity), sedimentation stability and film strength in coatings.

Research Proven Superiority of Ultrasonicators for Nanofiller Dispersion

Monteiro et al. (2014) compared common dispersing technologies – namely rotor-stator mixer, Cowles impeller, and ultrasonic probe-type disperser – regarding their efficiency in dispersing titanium dioxide (TiO2, anatase). Ultrasonication revealed to be the most efficient to disperse the nanoparticles in water using conventional Na-PAA polyelectrolyte, and excelled mixing with a rotor-stator or Cowles impeller significantly.
The Details of the Study: Different dispersion techniques were compared in order to identify the most effective in creating a well deagglomerated nano-TiO2 aqueous suspension. Sodium salt of polyacrylic acid (Na-PAA), conventionally used in industry for TiO2 aqueous dispersions was used as reference dispersant. Fig. 1 shows the volume particle size distributions (PSD) obtained, using Cowles disperser (30 min at 2000 rpm), rotor-stator mixer (30 min at 14000 rpm), and probe-type ultrasonication (Hielscher UIP1000hdT, 2 min at 50% amplitude). “Using Cowles disperser the particles sizes were in three different ranges: 40–100 nm, 350–1000 nm and 1200–4000 nm. The larger agglomerates clearly dominate the distribution, showing that this technique is inefficient. The rotor-stator also provided unsatisfactory results, independently of the nanoparticles being added at once or gradually along the mixing time. The major difference observed in the Cowles’s result is related to the shifting of the middle peak to the higher particle size, partly merging with the right-most peak. On the other hand, use of ultrasounds yielded a much better result, with a narrow peak centred at 0.1 nm and two much smaller ones in the 150–280 nm and 380–800 nm ranges.”

Particle size distributions of nano-TiO2 aqueous dispersions (10mgmL−1, pH = 9) prepared using different dispersion techniques. Ultrasonication gives the smallest TiO2 nanoparticles and the narrowest particle size reduction curves. When dispersant (Na-PAA) was used, the ratio to nano-TiO2 was 1:1.
(study and graphic: © Monteiro et al., 2014)

Spray-dried TiO2 before and after ultrasonic milling

This result agrees with the work by Sato et al. (2008), reporting better results with ultrasonication than with other techniques for dispersing nanosized TiO2 particles in water. The shock waves created by acoustic / ultrasonic cavitation lead to highly intense interparticle collisions and efficient particle milling and deagglomeration to uniform nano-scale fragments.
(cf. Monteiro et al., 2014)

High-Performance Ultrasonic Homogenizers for Varnish Production

When nanoparticles and nanofillers are used in industrial manufacturing processes such as the production of varnishes and coatings, dry powder must be homogeneously mixed into a liquid phase. Nano-particle dispersion requires a reliable and effective mixing technique, which applies enough energy to break agglomerates in order to unleash the qualities of nano-scale particles. Ultrasonicators are well known as powerful and reliable dispersers, therefore used to deagglomerate and distribute various materials such as silica, nanotubes, graphene, minerals and many other materials homogeneously into a liquid phase such as resins, epoxies and pigment master batches. Hielscher Ultrasonics designs, manufactures and distributes high-performance ultrasonic dispersers for any kind of homogenization and deagglomeration applications.
When it comes to the production of nano-dispersions, precise sonication control and a reliable ultrasonic treatment of the nanoparticle suspension are essential in order to obtain high-performance products. Hielscher Ultrasonics’ processors give you full control over all important processing parameters such as energy input, ultrasonic intensity, amplitude, pressure, temperature and retention time. Thereby, you can adjust the parameters to optimized conditions, which leads subsequently to high-quality nano-dispersion such as nanosilica or nano-TiO2 slurries.

For any volume / capacity: Hielscher offers ultrasonicators and a broad portfolio of accessories. This allows for the configuration of the ideal ultrasonic system for your application and production capacity. From small vials containing a few millilitres to high volume streams of thousands of gallons per hour, Hielscher offers the suitable ultrasonic solution for your process.
High viscosities: Ultrasonic inline systems easily process paste-like formulations, e.g. pigment master batches, where a pigment is mixed at high particle loading uniformly in a mixture of plasticizer, monomer and polymer.
Robustness: Our ultrasonic systems are robust and reliable. All Hielscher ultrasonicators are built for 24/7/365 operation and require very little maintenance.
User-friendliness: Elaborated software of our ultrasonic devices allows the pre-selection and saving of sonication settings for a simple and reliable sonication. The intuitive menu is easily accessible via a digital coloured touch-display. The remote browser control allows you to operate and monitor via any internet browser. Automatic data recording saves the process parameters of any sonication run on a built-in SD-card.
Excellent energy efficiency: When compared to alternative dispersion technologies, Hielscher ultrasonicators excel with outstanding energy efficiency and superior results in particle size distribution.
High-Quality & Robustness: Hielscher ultrasonicators are recognized for their quality, reliability and robustness. Hielscher Ultrasonics is an ISO certified company and put special emphasis on high-performance ultrasonicators featuring state-of-the-art technology and user-friendliness. Of course, Hielscher ultrasonicators are CE compliant and meet the requirements of UL, CSA and RoHs.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators: