Discussion on the Preparation of Ceramic Inkjet Inks

Ceramic inkjet inks are a cornerstone of ceramic inkjet technology. Domestic companies relying on expensive imported inks have long faced a challenge in the form of the exorbitant cost of these inks. It is widely known that the price of these inks is 30 times that of regular glaze materials. The issue lies not in the expensive raw materials but in the lack of indigenous technology for development and production within the country.

Requirements for Ceramic Ink Performance

Specific Performance Requirements 

(1) Stability: Ceramic powder materials should exhibit good chemical stability in solvents, without causing any chemical reactions. They should also have physical stability to prevent particle aggregation and precipitation.(2) Rapid Deposition and Strong Adhesion: Ceramic powder particles should quickly and effectively accumulate during inkjet printing, ensuring strong adhesion to create dense printed layers. This is crucial for achieving high sintering density after firing.(3) Color Rendering: Printed colorants must exhibit excellent color performance after high-temperature firing and should be compatible with the base glaze.

Shortcomings of Current Ceramic Inks 

(1) Noticeable Color Deviation: Ceramic inkjet printing exhibits significant color differences in terms of hue, brightness, and saturation compared to traditional oil painting, affecting image quality with unclear shadow layers and notable differences from the original artwork.(2) Insufficient Stability and Flow in Printing: The coloring agents in ceramic inkjet inks exist in a particulate form dispersed in a medium, making them prone to aggregation and settling. This lack of stability can lead to clogging of the printer nozzles. Clogged nozzles can significantly increase the cost of ceramic inkjet printing, as the nozzles are expensive. The stability and flow of ceramic inks are influenced by various factors, including raw materials and production techniques. The larger size of ceramic particles in ceramic inks is a critical factor affecting their stability and flow. Current ceramic inks primarily use nanoscale ceramic particles. These ceramic particles are hard and challenging to create as fine particles, leading to difficulties in achieving good dispersion in the medium.(3) Poor Adhesion to Substrates: Traditional ceramic inkjet inks lack adhesive properties due to the absence of binders. After inkjet printing on substrates, the solvent in the ink evaporates, leaving colorant particles on the surface of the substrate. These colorant layers are susceptible to friction. Additionally, ceramic colorants and solvents in the ink are hygroscopic, and high environmental humidity can lead to increased water absorption in both the ceramic substrate and the ink, damaging unfired ceramic products.(4) Lack of Gloss in Ceramic Inkjet Inks: The colorant layers lack gloss, which necessitates post-printing surface treatments using gloss coatings to enhance the shine on ceramic colorants, adding to the cost of ceramic inkjet products.(5) High Requirements for Inkjet Printing Equipment: Due to the limited fineness of ceramic particles in ceramic ink preparation, their poor dispersion in the medium can lead to difficulties in achieving the required quality, rendering many inkjet printing devices unsuitable for ceramic inkjet printing.

Current Status of Ceramic Ink Research in ChinaCurrently, the main methods for preparing ceramic ink include dispersion methods, sol-gel methods, and reverse-phase microemulsion methods. 

(1) Dispersion Method: This method involves the preparation of a dispersed system, starting from larger material pieces and using mechanical grinding or ultrasonic dispersion to break them down into a dispersed system. Commonly used mechanical grinding equipment includes ball mills, sand mills, and colloid mills, with zirconia beads as grinding media. However, these methods typically achieve particle sizes of only around 1 micron. For example, ball milling is used to prepare BaTiO ceramic ink.(2) Sol-Gel Method: The sol-gel method involves using compounds with high chemical activity as precursors, mixing them uniformly in a liquid phase, and subjecting them to hydrolysis and condensation reactions to form a stable transparent sol system. The sol then slowly aggregates into a three-dimensional gel structure, filled with non-flowing solvent between the gel network, forming the gel. The gel is dried, sintered, and solidified to prepare materials with molecular and even nanostructures. For instance, equal molar ratios of isopropanol titanium and barium acetate are dissolved in acetic acid and water, stirred to mix them evenly at room temperature. KOH (potassium hydroxide) is used to adjust the pH to 13.5. A small amount of polyvinyl butyral is added as a binder, and a small amount of ammonium nitrate is added to enhance the electrical conductivity of the sol. The sol is then concentrated to obtain ceramic ink with different BaTiO (barium titanate) contents.(3) Reverse-Phase Microemulsion Method: Reverse-phase microemulsion refers to water-in-oil (W/O) type microemulsions, where surfactants and co-surfactants are dissolved in non-polar or weakly polar solvents. When the surfactant concentration exceeds the critical micelle concentration (CMC), the solution significantly increases its solubility in polar liquids, such as water and aqueous solutions. However, using the reverse-phase microemulsion method to prepare ceramic ink is a novel approach, and the key lies in obtaining microemulsion systems with the highest possible water content to make ceramic ink practical. For example, FeCl (iron chloride) reverse-phase microemulsion and NH3eH O (ammonium hydroxide) reverse-phase microemulsion are prepared at an optimal water content. The two reverse-phase microemulsions are mixed while stirring, and the reaction leads to Fe：O (iron oxide) reverse-phase microemulsion. During this process, the addition of NH3"H：O reverse-phase microemulsion is determined by controlling the pH. Various physical and chemical properties of ceramic ink, such as viscosity, surface tension, pH, and conductivity, are measured.

Conclusion and DiscussionCeramic ink is formulated from ceramic materials, non-hazardous mediums, and additives. The methods described above all involve processing using particles of ceramic materials at the micrometer level. The ultimate goal in producing ceramic ink is to transform these particles into ceramic ultrafine powders. Achieving good dispersion of these ceramic ultrafine powders in the medium or additives is crucial for obtaining high-performance ceramic ink. Ultrafine powders typically refer to tiny solid particles ranging from 1 to 100 nanometers, including various materials like metals, non-metals, inorganic materials, and biological substances. The degree of fineness of ceramic particles and their good dispersion in the medium are critical factors affecting the quality of ceramic ink.