Definition
A laboratory high-speed disperser is a miniaturized process equipment used to evenly disperse solid particles or powders in a liquid matrix. It mainly generates strong mechanical shear force and turbulence through the high-speed rotating dispersion head, so that the agglomerated particles are broken and stably suspended in the liquid phase system, which belongs to the liquid-solid phase mixing and refining treatment unit. This equipment is commonly used for formulation development and process condition screening in coatings, inks, adhesives, food additives, cosmetics, fine chemicals and other fields.
How it works:
The core working part of the equipment is the dispersion head, which is usually composed of a stator and a rotor. The rotor rotates driven by a high-speed motor that can rotate at speeds of up to thousands of revolutions per minute. When the material passes through the narrow gap between the stator and the rotor, it is subjected to multiple effects: the shear force generated by the rotor blade tears the particles agglomeration; The material is thrown towards the inner wall of the stator under high-speed rotation, causing impact. The flow velocity gradient in the gap causes local turbulence, which further enhances the dispersion effect. At the same time, the centrifugal force promotes the circulation of the material in the container, causing the undispersed particles to pass through the dispersion head repeatedly until the system reaches a homogeneous state. During the whole process, the viscosity of the liquid phase, the particle size of the dispersed solid and the surface wettability directly affect the dispersion efficiency and final fineness.
Measurement method
Common indicators for evaluating the effect of high-speed dispersers include dispersion fineness, dispersion uniformity and dispersion stability. The dispersion fineness is mostly measured using a scraper fineness meter (Heegman fine meter), and the maximum particle size of the particle aggregate is read out by observing the scratch break point formed by the particles on the scraper plane, expressed in microns. The dispersion uniformity can be observed by microscopy to count the number of particles greater than a certain particle size in the field of view at 100x to 400x magnification, or the particle size distribution curve can be measured by a laser particle size analyzer. The dispersion stability is recorded by static sedimentation method or centrifugal sedimentation method to record the height of the upper layer of clear liquid or the proportion of sediment after a certain period of time. For paste or high-viscosity samples, a rheometer can also be used to measure yield stress and thixotropy, indirectly characterizing the uniformity of the material's internal structure.
Influencing factors
The dispersion efficiency and final effect are affected by multiple process parameters. The higher the speed, the greater the shear force, but too high the speed may cause liquid splashing or local heating, resulting in a decrease in viscosity or volatilization of components. The dispersion time should be optimized according to the characteristics of the material, and if the time is insufficient, the dispersion will be incomplete, and the time may lead to secondary agglomeration. The temperature of the material needs to be properly controlled, and the temperature increase can help reduce the viscosity of the liquid phase and promote dispersion, but too high a temperature will destroy the heat-sensitive components. In addition, geometric parameters such as the distance between the dispersion head and the bottom of the container, the ratio of the inner diameter of the container to the diameter of the dispersion head, and the filling amount of the material also affect the circulation efficiency. Solids content is as important as liquid phase surface tension, high solids content or high surface tension will increase dispersion resistance, and need to be matched with a higher power disperser.
Applications:
In coating laboratories, high-speed dispersers are used to pre-disperse pigments and fillers into resin solutions to prepare color pastes or semi-finished products. The ink industry uses this equipment to evenly distribute carbon black or color pigments in the connector and ensure the color consistency of the printed product. In the development of adhesives, thickeners, thixotropic agents or reinforcing fillers are mixed into the matrix to adjust the adhesion properties. In the food sector, high-speed dispersers are used to emulsify or disperse stabilizers, colors, flavoring particles, e.g. pre-dispersion of beverage suspensions. Cosmetics laboratories rely on this equipment to evenly disperse powders such as titanium dioxide and iron oxide in creams or lotions to ensure uniform color and sun protection effect. In addition, the formulation optimization of conductive paste, ceramic paste, and electronic glue in fine chemicals also needs to be optimized with the help of this equipment to achieve the requirements of fineness and dispersion stability.
Key points of selection
When selecting the type, the viscosity range of the treated material should be considered first, and the standard dispersion head can be selected for low-viscosity liquids such as aqueous solution or solvent-based systems, and high-viscosity paste materials should be equipped with a higher power motor and a stronger dispersion tooth structure. The throughput determines the container capacity, typically 50 ml to 5 liters at the laboratory level, and benchtop models with interchangeable containers are advisable for small batch development. The speed adjustment method is preferably stepless speed change, which is convenient for accurately setting the shear strength. The material of the dispersion head needs to adapt to the chemical properties of the material, stainless steel 316L is a universal choice, and strong acid-alkali or chlorine-containing solvents should consider Hastelloy or ceramic coatings. In addition, the equipment should also have a stable clamping system to prevent vessel displacement during high-speed operation, and be equipped with a timing controller and temperature monitoring interface to meet the requirements of process reproducibility. Ease of cleaning is also important, and the easily removable dispersion head shortens the cleaning time when switching recipes.