1. Influence and control of raw materials and formulas
Raw materials and formulas are the basis for controlling Masterbatch particle size distribution. First, the particle size and properties of the pigment have a significant impact on the final Masterbatch particle size distribution. It is crucial to select pigments with a narrow and stable particle size distribution. When purchasing pigments, strict particle size requirements must be imposed on pigment suppliers and random inspections must be conducted. For example, for some masterbatch with high quality requirements, the deviation of the original particle size of the pigment should be controlled within a very small range. At the same time, the additives in the formula will also affect the particle size distribution. The type and amount of dispersant need to be carefully selected. A suitable dispersant can prevent pigment agglomeration and help to form a uniform particle size. If the amount of dispersant is insufficient, the pigments will easily agglomerate, resulting in larger particle size and uneven distribution; if the amount is too much, it may affect other properties of Masterbatch. Therefore, it is necessary to determine the optimal amount of dispersant through experiments to ensure that the pigment can be evenly dispersed during processing, thereby laying a good foundation for controlling particle size distribution.
2. Key operations in the mixing and dispersing process
In Masterbatch production, the mixing and dispersion process is a key link in controlling particle size distribution. For twin-screw extruders, the screw speed is an important parameter. Appropriately increasing the screw speed can increase the shear force of the material, effectively breaking the pigment agglomerates, thereby reducing the particle size and making the distribution more uniform. However, too high a rotational speed may cause local overheating, change the material properties, and affect the particle size distribution. Usually, the screw speed is controlled within a reasonable range based on equipment performance and material characteristics, such as 150 - 250 rpm. In addition, the temperature setting of the extruder cannot be ignored. Different resin and pigment systems require appropriate temperatures to ensure good mixing and dispersion effects. The appropriate temperature can fully melt the resin and disperse the pigment evenly in the resin. If the temperature is too low, the resin will not melt completely and the pigment will not be evenly dispersed; if the temperature is too high, the resin may decompose. For example, for Masterbatch production with polypropylene-based resin, the temperature is typically set between 180 - 230°C.
3. Parameter adjustment of crushing process
The crushing process directly determines the final particle size and distribution of Masterbatch. When it comes to the selection of crushing equipment, jet pulverizer is one of the ideal devices for controlling particle size distribution. When using an airflow mill, parameters such as airflow pressure, flow rate, and material feed rate need to be accurately adjusted. Appropriately increasing the air flow pressure can make the collision between Masterbatch particles more intense, resulting in a finer particle size. However, if the air flow pressure is too high, it may cause excessive crushing of some particles and broaden the particle size distribution. The feed speed should also match the air flow pressure and flow rate. Too fast a feed speed may lead to insufficient crushing, while too slow a feed speed will reduce production efficiency. For example, in actual production, according to the Masterbatch formula and target particle size range, the appropriate combination of air flow pressure, flow rate and feed rate must be determined through multiple experiments to obtain the ideal particle size distribution.
4. Screening and quality control measures
Screening is the final process to control the particle size distribution of Masterbatch. Through screening equipment such as vibrating screens, select the appropriate mesh size according to the target particle size range. For example, for a Masterbatch with a target particle size of 0.3 - 0.8 mm, the corresponding screen must be selected to remove particles that are too large or too small. During the screening process, the integrity of the screen must be checked regularly to prevent damaged screens from causing unqualified particles to be mixed into the product. At the same time, a strict quality control system should be established, and equipment such as laser particle size analyzers should be used to detect the particle size distribution of Masterbatch. During the production process, sampling is carried out at a certain frequency to detect abnormalities in particle size distribution in a timely manner. If it is found that the particle size distribution does not meet the requirements, the production process must be traced back in time to identify the problem and make adjustments to ensure that the particle size distribution of the product is always under control.
