High-Performance Plastics Exhibition - Invitation to Exhibit at Plastic Japan

In dispersion engineering, stable quality cannot be achieved solely based on the performance of the equipment. What is important is the overall design of the process, taking into account material properties and process conditions. This is referred to as dispersion process design. Dispersion quality is determined not only by the strength of shear but also by multiple factors such as flow state, residence time, and method of input. If these conditions are not properly designed, localized agglomeration or variation can occur, making it difficult to maintain stable quality. For example, poor wetting during powder input or the occurrence of stagnant areas due to flow bias can lead to clumping or dispersion issues. Additionally, even if the shear energy is sufficient, if it does not act uniformly on all particles, differences in dispersion state will arise. Therefore, in dispersion processes, it is crucial to design "flow," "shear," and "processing time" as an integrated system. This allows for all particles to receive the same dispersion history, achieving uniform and highly reproducible dispersion quality. In particular, inline continuous processing has the advantage of maintaining consistent conditions within the flow, making it easier to ensure reproducibility in process design. Dispersion process design is a key concept for stabilizing quality and successfully scaling up.

In dispersion processes, the variation in quality is one of the significant challenges. Even when processing under the same equipment and conditions, it is not uncommon for the dispersion state to differ from batch to batch. The main factor behind this is the variability in the dispersion history experienced by the particles. In batch processing, the shear and residence time experienced by each particle differ depending on their position and flow state within the tank. As a result, there is a mixture of sufficiently dispersed particles and undispersed particles, leading to variations in quality. This tendency becomes particularly pronounced under high viscosity or high solid content conditions. On the other hand, in continuous processing, particles pass through a consistent processing area, receiving nearly the same dispersion conditions. Because shear energy and residence time can be controlled consistently, the variability in dispersion history is minimized, resulting in a uniform and highly reproducible dispersion state. Moreover, continuous processing is advantageous during scale-up. By adjusting the flow rate, it becomes easier to replicate similar dispersion quality from the lab to mass production. This helps reduce the risk of quality fluctuations during the transition from development to mass production. What is crucial in dispersion processes is to provide the same processing history to all particles. Continuous processing easily meets this condition and is an effective method for stabilizing quality and ensuring reproducibility.

In dispersion engineering, there are many cases where, although the appearance seems mixed, the particles are not actually uniformly dispersed. One of the causes of this is that the aggregation between particles has not been sufficiently resolved. When there is insufficient dispersion energy, the particles do not break down to primary particles, and aggregates remain. Additionally, if the shear conditions or flow state are uneven, the dispersion state can vary locally, resulting in variations in particle size distribution. This is particularly true in high-viscosity systems or high solid content slurries, where low flowability makes it difficult for energy to be transmitted uniformly, leading to dispersion inconsistencies. Furthermore, in batch processing, variations in mixing uniformity and residence time tend to make it difficult to maintain a uniform dispersion state throughout the process. To achieve uniform dispersion, it is important to design dispersion energy according to particle characteristics and to maintain uniform flow conditions in the process design. By maintaining consistent shear conditions, as in inline continuous processing, it is possible to achieve a uniform dispersion state and reproducible quality. The order of input, the wettability of the powder, and the initial mixing state of the dispersion also have a significant impact on uniformity. In particular, if local clumps or uneven distribution occur during powder input, it becomes difficult to resolve them in subsequent dispersion processes, leading to dispersion inconsistencies.

In dispersion processes, the occurrence of agglomerates (clumps) during powder addition, which cannot be resolved in subsequent dispersion stages, is a common issue in many settings. The cause of this is that the powder does not wet uniformly in the liquid, leading to the formation of localized high-concentration areas. These agglomerates are also referred to as "fisheyes," and due to their internal unwetted structure, they are difficult to break apart. Once an agglomerate forms during powder addition, liquid has difficulty penetrating its interior, resulting in only the outer layer being wetted, which makes it hard for the internal particles to be disintegrated. Additionally, depending on the addition position and speed, the powder may float on the liquid surface or remain stagnant without following the flow within the equipment, promoting the formation of agglomerates. Particularly under conditions of high viscosity or high solid content, the low fluidity makes it challenging to achieve uniformity in the initial dispersion stage, leading to a higher likelihood of agglomerates remaining. Such agglomerates may not be completely resolved even with strong shear in subsequent processes, causing variations in the quality of the final product and introducing foreign substances. To prevent the formation of agglomerates, it is crucial to improve wettability during powder addition, ensure appropriate addition positions and flow design, and optimize the initial dispersion. By performing shear and mixing simultaneously right after addition, as in inline powder addition and simultaneous dispersion, it is possible to suppress the formation of agglomerates and achieve stable dispersion quality.