Adding masterbatch to plastics is a relatively simple but precisely controlled process. The primary goal is to evenly disperse the concentrated masterbatch into the base resin (binder), ultimately producing a plastic product with consistent color and excellent performance. The following are the key addition methods and steps:
1. Mixing:
First, determine the appropriate ratio of masterbatch to base resin (binder) based on the desired color depth of the final product, the pigment concentration of the masterbatch, and the processing technology. This ratio typically ranges from 1% to 5%, but can be lower or higher (e.g., for white or black masterbatches or special effect masterbatches).
Ensure that the carrier resin of the masterbatch selected is highly compatible with the base resin to be colored (e.g., using a PP carrier masterbatch to color PP plastic).
2. Mixing:
This is the most common and critical step. Weighed base resin pellets and the appropriate proportion of masterbatch pellets are placed in a mixing device and dry blended.
Common equipment includes drum mixers, conical blenders, and high-speed blenders. Purpose: To physically and uniformly mix the masterbatch particles with the base resin particles.
Key Points:
Mixing Time: Long enough to ensure uniformity, but avoid excessive mixing time that may cause powdering or static cling.
Equipment Selection: Select appropriate equipment based on batch size and mixing uniformity requirements.
Environment: Maintain a dry environment to protect the raw materials from moisture.
3. Feeding Process Equipment:
The mixed resin/masterbatch mixture is fed into the hopper of the plastics processing equipment via a feeding system.
Dedicated Feeders: For production lines with high automation or high precision requirements, loss-in-weight or volumetric feeders are often used. These devices have two hoppers:
One for the base resin and one for the masterbatch.
The feeder measures and continuously delivers the two materials in a precise, pre-set ratio to a downstream mixing device (such as a static mixer) or directly into the main hopper/barrel of the processing equipment. This method provides more precise and consistent mixing and is suitable for large-scale production.
4. Melting, Shearing, and Dispersion:
The mixed material enters the heated barrel of the processing equipment (such as an injection molding machine, extruder, or blown film machine).
In the barrel, the material is heated to melting temperature.
The rotation of the screw provides strong shear forces. This melting and shearing process is crucial:
It melts the masterbatch particles.
It breaks up highly concentrated pigment clumps.
The shear forces evenly disperse the pigment throughout the base resin melt.
Key Points:
Temperature Control: Ensure that the temperature is sufficient to fully melt the masterbatch carrier and base resin, but not exceed the thermal stability limit of the pigment (especially for certain organic pigments).
Screw Design/Speed: Provide sufficient shear forces to achieve good dispersion. Poor dispersion can result in "color spots" or "streaks" on the finished product.
5. Molding/Processing:
The evenly colored and well-plasticized melt is conveyed to the mold (injection molding), die (extrusion, blown film, cast film), or other forming area, where it is ultimately cooled and formed into the desired plastic product shape.
Key Quality Control Points:
Dispersion: Check the final product for undispersed pigment particles (color spots).
Color Consistency: Use a colorimeter or other tool to measure color differences (ΔE values) between different batches or different locations within the same batch.
Physical Properties: Ensure that the addition of the masterbatch does not negatively impact the key properties of the plastic (such as strength, toughness, and weather resistance).
Batch Stability: Ensure that the color and addition ratio of the masterbatch remain consistent across batches.
In summary, the main steps are: Accurate Proportioning -> Thorough Dry Blending (or Precise Measuring Using a Feeder) -> Feeding into Processing Equipment -> Using Shear Force During the Melt Process to Achieve Uniform Dispersion -> Molding.
Important Notes:
Carrier Matching: The masterbatch carrier resin must be compatible with the base resin; otherwise, poor dispersion, delamination, or reduced product performance may occur.
Addition Amount: Follow the supplier's recommendations to avoid over-addition (which increases cost and may affect performance) or under-addition (which may result in substandard color). Drying: If the resin or masterbatch is hygroscopic, it should be dried before mixing or processing.
Equipment Cleaning: When changing colors, be sure to thoroughly clean the mixing equipment, hopper, barrel, screw, and mold/die to prevent color contamination.
Pigment Properties: Understand the pigment's thermal stability, migration, and weather resistance to select appropriate processing conditions.
By following the correct addition method and controlling key parameters, masterbatch can be efficiently and stably incorporated into plastics, resulting in vibrant, uniformly colored plastic products with reliable performance.
