Formation of pigment dispersion
In the production process of masterbatch, the quality is closely related to the dispersion of pigments. Solving the problem of pigment dispersion has also become one of the key factors for masterbatch factories to expand their application markets and reduce costs.
The problem of pigment dispersion is related to the properties of the pigment itself. Primary particles of organic pigments (0.1-0.5um) are not tiny particles in an inert state. Due to factors such as the surface state of primary particles and inter-particle gravity, hydrogen bonding, polarity and other factors, they are often in an active state. In the process of manufacturing and using pigments, primary particles aggregate to form secondary particles, which appear as independent particles with a larger particle size (5-50um). The primary particles and secondary particles may further form tightly combined agglomerates to form relatively loose agglomerates (50-1000um).
Brief description of pigment dispersion solutions
Contemporary masterbatch factories use the "wetting" theory to disperse pigments, that is, selecting appropriate dispersion media and production processes to achieve good dispersion effects. In the actual production process, due to the different types of pigments and the fact that pigment manufacturers are limited by multiple factors such as technology and cost, the quality differences between batches of the same product are even uneven, which greatly improves the selection of appropriate masterbatch factories. Difficulty of raw materials. The cost that masterbatch producers invest in raw material control is invisible, and is intuitively reflected in varying degrees of production operation and management difficulties. Due to differences in production processes, some companies have insufficient pigment dispersion, which has greatly increased coloring costs.
Reprocessing pigments to improve their dispersion and color stability has a long history. CIBA Company published a patent for the preparation of organic pigment preformulation in 2004, opening up a new picture for subsequent explorers. Producers use specific organic pigment derivatives, mix them with appropriate dispersants, grind them in a water medium, and then squeeze and dry the ground materials to obtain a powdery pigment preform. Sun chemical also used the water squeeze phase transfer method to launch pre-dispersed pigment products using low molecular weight polymers as carriers. The principle is to put the polymer and pigment filter cake into the kneader. After heating, stirring and kneading, the pigment is adsorbed by the polymer. The resulting material is vacuumed at high temperature to remove moisture. After the material is cooled, it is crushed into a granular pigment pre-preparation.
However, this type of treatment method has not been widely used in the market due to high pollution, small output and high cost. Subsequently, pigment preformulations using PP wax and PE wax as carriers appeared in the masterbatch industry. The principle is to use the resin melt to transfer shear stress, so that the dispersant coats the pigment particles to achieve dispersion. The quality of pigments in such products accounts for about 50%, which is similar to the products of the above-mentioned companies.
Comparison of similarities and differences in coloring methods
Common methods for preparing color masterbatch include using pigment toner, using high-concentration single-color masterbatch, and using pre-dispersed pigments. Due to different physical properties, the three show different advantages and disadvantages. The table below compares the differences between the three in many aspects.
In summary, pigment toner has the lowest coloring cost, but the dust pollution is serious and it is difficult to meet the current national requirements for environmental protection and production safety. Masterbatch manufacturers need to pay more environmental protection costs to create a green and compliant production environment. In addition, powdered pigments are difficult to measure, which poses challenges to large-scale, fully automated production. Many pigment products are difficult to disperse due to product characteristics, and many masterbatch manufacturers have limited knowledge of pigment dispersion processes and invest too much time and energy in quality control of incoming materials. Otherwise, low yields may occur during use. The problem, especially for spinning fiber applications, such as nylon spinning, polypropylene and polyester long fibers, etc., is that the dispersion of pigments and toners is often difficult to meet.
Masterbatch has good dispersion and high color stability, but its cost is higher than pigment toner. In fact, the dispersibility of masterbatch still depends to a large extent on the dispersion of the pigment itself. If the dispersion of the pigment is not good, even repeated extrusion and granulation will not help. The limitation of using single-color masterbatch to prepare color masterbatch lies in its carrier limitation and the possibility of affecting the physical properties of the product.
Pre-dispersed pigments have the characteristics of both pigment toners and single-color masterbatch, their dispersibility is greatly improved, and they can also achieve low or even no dust. However, common pre-dispersions on the market contain a high proportion of additives (40-50%), which can still damage the physical properties of downstream products. At present, pre-dispersed pigments with high pigment content have appeared on the market. Among them, the effective mass ratio of pre-dispersed pigments reaches more than 70%, and the proportion of additives is reduced to less than 30%, which can greatly reduce the impact on product performance.
In terms of usage, the common way to prepare masterbatch using pigment toner is to use a high mixer to mix raw materials. The formulation of the formula, the selection of raw materials, and the configuration of high-mixing equipment have a significant impact on the quality of the final product. Different from domestic masterbatch manufacturers who use a heated high-mixing equipment, many foreign masterbatch manufacturers use a combined mixing equipment of heated high-mixing and cooling low-mixing. Spread into fully coated, dust-free small particles. When using single-color masterbatch and pre-dispersed pigments, the above-mentioned premixing process can be abandoned, and masterbatch products can be prepared in the form of ordinary stirring or primary and secondary feeding, or can be equipped with automatic feeding and automatic metering systems. This will greatly reduce production costs and reduce pollution while improving production efficiency.
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