For many years, it was widely accepted that Ceramic Pigments could not be ground into the submicron range (d99 < 1 µm) without a relevant loss of color strength and other physical properties. The widespread use of wet grinding technologies, such as ball mills (Alsing), or more recently, “attrition like” bead mills, led to extremely long processing times to achieve finer product results. As a result of this long grinding process, pigments were undoubtedly damaged to a certain degree, leading to the aforementioned paradigm of “ungrindability” of ceramic pigments below 1 micron.
The introduction of Ceramic Inkjet using drop-on-demand printing technologies pushed the leading technological companies in the field of milling to develop a process based on an optimal combination of dry and wet grinding techniques, to obtain suspensions of ceramic pigments in the sub-micron range (d50 0.15 µ - 0.3 µ / d99 0.6 µ - 0.8 µ). Over 45 million kgs of Ceramic Inkjet Ink supplied, and more than 3 thousand ceramic digital printers worldwide, confirm that this goal was successfully achieved.
The paradigm was broken, presenting new challenges and opportunities in grinding ceramic raw materials, glazes and other related products.
NETZSCH Solutions for Ceramic Applications
NETZSCH has always developed solutions to support inkjet technology. Since the first test batch on a LabStar laboratory mill in December 2005, NETZSCH has been at the forefront of this technology and the first subject matter expert when it comes to processing inkjet materials. Hundreds of NETZSCH machines are in use worldwide, producing ceramic inkjet pigments and in a wide array of other ceramic applications..
Through vast experience and continuing market leadership, NETZSCH is able to develop and select the best solution for every step of the process (e.g. pigment processing, mixing, wet grinding, etc.) in the production of digital glaze, ceramic inkjet, ceramic pigments, In-Glass ceramics inks, technical ceramics, minerals and raw materials and ceramic masses.
Wet Grinding – Zeta® System
From the grinding systems available in the NETZSCH product portfolio (horizontal disk mills, basket mills, vertical mills, etc.), manufacturers of ceramic inkjet pigments have chosen the Zeta® System because it offers clear advantages:
- Very narrow particle size distribution that is easier to control (filtering capability, color intensity, etc.)
- Highest level of productivity
- Total reproducibility of the results
- Fewer grinding beads required
The NETZSCH Zeta® System is based on solid, effective design:
- Smaller grinding chamber (about half the size of a disc mill, with comparable energy input)
- Designed for circulation grinding
- Uses agitator pegs for the greatest efficiency
Recently, NETZSCH introduced the largest recirculation bead mill ever built, capable of processing up to 10,000 liter batches. With the introduction of the LMZ 400, a wide production range is covered. From the 0.62 liter chamber volume of the LabStar to the 400 liter chamber volume of the LMZ 400, scale-up is accurate and reproducible.
The correct formulation and fineness of ceramic pigments is essential to achieving a pigment with a narrow, controlled particle size distribution. NETZSCH offers two solutions for this:
- The CGS Fluidized Bed Jet Mill with ConVor classifier wheel for narrow particle size distribution to d97 < 4 µm - 5 µm, and
- The s-JET® Steam Jet mill capable of much finer particle size distributions
The s-Jet®® technology is an advanced development of the NETZSCH Trockenmahltechnik GmbH well-known Air Jet mill, which uses high pressure superheated steam, instead of air, as grinding media. The use of steam offers a much higher impact velocity as well as entirely new possibilities in the classification process, leading to finenesses never before seen in the Ceramic Pigment industry (a very narrow particle distribution curve down to d50 ≈ 0.45 µm / d97< 1 - 2 µm).
The use of such fine pigments with narrowly-defined particle size distributions in Ceramic Inkjet Inks significantly reduces wet grinding time. Apart from the obvious benefits of reducing the bottleneck of the process, and reduction in energy costs, there are other and even more important advantages realized from the shorter wet process of the ink. It is a well-known fact that wet milling using micro-beads below 0.5 mm creates an increasing amount of ultra-fine particles of pigment in the final ink. This ultra-fine fraction has a very negative effect in color and rheological properties, and reactivity of the ink and has been a constant problem for developers of Ceramic Inkjet Inks. The narrower pigment particle size distribution curve from the s-Jet®®, as well as the shorter wet grinding times, results in a much narrower particle size curve of the ink with less ultra-fine particles and therefore improved color strength (especially in yellow and red brown inks), which will set new standards in the digital decoration of ceramic tiles.
These two improvements - cost reduction and increase of ink quality - will be of extraordinary importance to NETZSCH customers who adopt the s-Jet®® dry grinding technology, in their effort to be competitive in the fast-growing Ceramic Inkjet Inks market.
In addition, this new dry grinding technology offers innovative manufacturing possibilities in the field of tile manufacturing and decoration, such as digital glazing, “simultaneous” drying and grinding of ceramic slurries in the submicron range, etc.