Ceramic tape is a thin, flexible ceramic sheet used in various high-tech applications, such as electronics, aerospace, and medical devices. As a material, ceramics exhibit high degrees of mechanical strength and thermal resistance and can have dielectric properties. When formed into ceramic tapes, they become an essential component for creating advanced technological products that require compact, low-profile parts.
Ceramic tape is made through a technique known as tape casting, where a ceramic slurry, or slip, is spread using a doctor blade onto a flat surface and then dried to form a consistent, uniform film. This film can be customized in terms of thickness, density, strength, and roughness to meet specific application requirements. These properties are tunable by controlling properties of the slurry, such as viscosity and surface tension, by the selection of ingredients used.
What Materials Are Used in Tape Casting?
Along with ceramic powder (the active component used to create slurries for tape casting), additives and ingredients such as binders, surfactants, solvents, dispersants, and plasticizers are used to control the physical properties that influence the final qualities of ceramic tape. While making up a very small proportion of the overall slurry composition by weight, binders play a significant role in producing high-quality ceramic tape. They are used to hold ceramic powder particles together and provide the green strength necessary to keep the ceramic tape intact while it undergoes drying prior to sintering. The best-performing binders used in tape casting must also burn out cleanly during sintering and contribute minimal amounts of contaminants in ceramic tapes, especially those used in electronic applications.
METHOCEL™ Ceramic Tape Casting Binders
IFF METHOCEL™ is a line of plant-based cellulose ether binders preferred in ceramic tape casting applications. They offer several beneficial characteristics that impart unique and ideal performance advantages, as listed below.
High Binding Efficiency
METHOCEL™ polymers are highly retentive toward water and provide film-forming and surface-active properties that enhance binding activity in aqueous ceramic slurries. Here, the water retention of METHOCEL™ helps make more stable mixes that are smooth and have increased plasticity. The surface-active properties of the METHOCEL™ polymer reduce the surface tension of the slurry, enabling better wetting of particles. This, coupled with METHOCEL™’s film-forming properties, creates a polymer coating around particles, increasing adhesion, cohesion, and green strength within the slip. A comparison of the surface tension reduction of METHOCEL™ versus common surfactants is made below, suggesting that surfactant ingredient requirements may even be reduced in slurry formulations.
Clean Burnout and Low Ash Content
As tape-casted ceramics tend to be used in applications with stringent quality parameters, it is important that the binders do not impart contaminants to the ceramic. METHOCEL™ polymers thermally degrade with first-order kinetics, providing uniform and predictable burnout in accordance with the graph below. METHOCEL™ polymers are also not thermoplastic, so they will not change in terms of physical characteristics prior to the burnout temperature.
When METHOCEL™ is burned out, it leaves very low ash content. This is beneficial since ash content can inhibit crystal growth and lower the melting point of ceramics. In addition, select grades of METHOCEL™ have been developed with low NaCl content. This helps prevent defects in electrical conductivity, allowing high-quality products such as capacitors, resistors, and circuit board substrates to be made.
Thermal Gelation
Unlike other binders used in tape-casted ceramics, METHOCEL™ forms a three-dimensional gel structure at elevated temperatures, which can be leveraged to provide extra stability, increase cohesion, and maintain the integrity of ceramic green tapes during drying and prior to sintering. This property is referred to as thermal gelation. It helps prevent migration of the METHOCEL™ binder during drying and ensures better cross-sectional strength and consistency during high-volume production runs. Below, a graph depicts the effect of thermal gelation in a ceramic mix, where an increase in apparent viscosity and green strength emerges as the thermal gelation temperature for METHOCEL™ A4M is achieved.
Thermal gelation also plays a significant role in improving a wide range of other ceramic manufacturing processes, such as extrusion and injection molding. For more information, check out this article.
METHOCEL™ binders are uniquely equipped to meet the stringent requirements of ceramic tape casting due to their high binding efficiency, low impurity levels, and thermal gelation properties. Their high binding efficiency ensures that ceramic powders are firmly held together, creating strong and cohesive tapes. The clean burnout and low ash content of METHOCEL™ prevent contamination and defects, crucial for applications requiring high-purity materials, such as electronics. Lastly, thermal gelation adds another layer of stability to ceramic tapes during critical phases of the manufacturing process, enhancing the overall integrity and performance of end products. Click below to request a sample today.
