1. High Dispersion
Black masterbatch is produced using carbon black. Raw carbon black is a very difficult and messy mixture to handle. It is dusty, lightweight, and fluffy. Unless extensive handling measures are implemented, it can stain machinery and workers, creating a dirty work environment.
For this reason, molders generally pre-disperse the carbon black in a resin carrier—the black masterbatch. This resin carrier is clean, free-flowing, and easy to work with. Furthermore, carbon black, besides being messy, is also difficult to disperse.
If raw carbon black is melted directly during injection molding, the coloring effect will be very poor. Undispersed carbon black streaks and spots will be noticeable next to less pigmented areas. Standard injection molding machines cannot effectively disperse raw carbon black. This difficulty in dispersing carbon black also plagues masterbatch manufacturers. High-load black masterbatches produced using single or twin screw extruders have very poor dispersion properties. When these black masterbatches are compounded or molded by end users, their performance is only slightly better than carbon black, but the results are equally unsatisfactory.
To achieve consistent, high dispersion, carbon black, such as FCM or Banbury blends, must be mixed using high-performance shear mixers. These mixers, with sufficient strength, allow the carbon black and base resin to be thoroughly mixed. The type of carbon black used also affects dispersion. The smaller the carbon black particles, the more difficult it is to disperse.
Thin wax applications are most demanding on dispersion. Masterbatches with poor dispersion can be easily seen from the edges of the finished product. Besides being aesthetically unpleasing, poorly dispersed carbon black in film significantly reduces the weathering resistance of the black film.
Small particles with good dispersion are a key characteristic of the fiber industry, where these fibers are used for rope, yarn, carpet, and other applications. Large machines produce 30,000 strands of fine fiber simultaneously at speeds exceeding 5,000 meters per minute. If the masterbatch’s dispersion is too poor, the fibers will break, causing production downtime. 2. Strong Covering Power
The second factor determining the quality of black masterbatch is covering power. This is particularly important for masterbatches intended for use with scrap or recycled polymers, where the black color is intended to cover other colors in the scrap. Large carbon black particles have poor coloring power and are less able to cover all underlying colors, resulting in an off-color finish. The ability to properly select carbon black with high coloring power to cover existing colors during the melt process is considered covering power.
3. Good Flowability
The third factor determining the quality of black masterbatch is rheology and flowability. If a masterbatch exhibits good dispersion but fails to flow into the molded material, the resulting product will be unsatisfactory.
Typically, the base resin used in masterbatch production has high rheology. To save costs, some masterbatch manufacturers use recycled, scrap, or recycled materials as the resin carrier. The flowability of the masterbatch produced in this manner is significantly reduced. Poor rheology can cause molders to experience difficulties with cycle time and cosmetic appearance. It’s worth noting that if dispersion and rheological properties are poor, some end users may compensate by increasing the dilution ratio, but this only increases the cost of the masterbatch. Masterbatches with minimal dilution ratios produce a uniform, well-dispersed black color. Fourth, High Compatibility
Compatibility is the fourth factor that determines the quality of black masterbatch. Masterbatches produced from off-cuts or recycled materials may contain contaminants or other infusible polymers. This can cause unpredictable and difficult-to-control problems, wasting the end user’s time and materials. In these cases, a primer resin can be used to produce high-quality masterbatches, ensuring good compatibility during the melt process.
High-quality masterbatches can be produced using LLDPE, LDPE, HDPE, PP, PS, SAN, PA, and other materials. Specialized polymer masterbatches are available if engineering grade and stringent physical properties are specified. Several major international masterbatch manufacturers are researching and developing so-called “globally compatible” masterbatches. These masterbatches can be widely compatible with other raw materials, have good rheological properties, and can be flexibly applied.