Understanding Color Masterbatch Manufacturing Process

Color masterbatch is a high-performance, high-concentration colorant mixture made by dispersing pigments or dyes with carrier resin through a rigorous processing method. Masterbatch can be categorized by its use into injection molding masterbatch, blow molding masterbatch, spinning masterbatch, etc. Depending on the quality requirements of the final product, masterbatch can also be divided into different grades. To meet various production demands and objectives, different production processes have been developed for masterbatch manufacturing, there are two kinds of process: dry process and wet process.

Wet Process

Wet process is the color masterbatch through grinding, phase transformation, washing, drying and granulation. When grinding pigments, it is necessary to carry out a series of technical tests, such as determining the fineness of the grinding slurry, the diffusion property, the solid content, etc. The wet process has four methods: ink, washing, kneading and metal soap.

 

1、Ink method

Ink method is the production method of ink paste. The ingredients are ground by three rollers and coated with a low molecular protective layer on the surface of the pigment. After grinding, the ink paste is mixed with the carrier resin, plasticized by a two-roll plasticizer, and finally granulated by a single or twin screw extruder.

ink method

2、Washing method

Washing method is is to use pigments, water and dispersants through the sand mill, so that they become particles smaller than 1 μm. Then the pigments are transferred to oil phase by phase transfer method, through evaporated, concentrated and dried, and after added into the carrier, the color masterbatch was obtained by extrusion and granulation. Phase conversion requires organic solvent and the corresponding solvent recovery device, which is complicated to operate and increase the difficulty of treatment.

Washing method

3、Kneading method

Kneading method is to mix the pigments and the oily carrier, and wash the pigment from the water phase into the oil phase by kneading. The surface of the pigment is covered by the oily carrier to make the pigment disperse stably and prevent condensation. Then the color masterbatch can be obtained by extrusion and granulation.

Kneading method

4、Metal soap method

Metal soap method means that the particle size of the pigments after grinding reaches about 1μm, and the soap liquid is added at a certain temperature to evenly wet the surface of the pigment particles, forming a saponification liquid protective layer (for example, magnesium stearate), which will not cause flocculation and maintain a certain fineness. Then the carrier was added and mixed at high speed, and the color masterbatch was obtained by extrusion and granulation.

Metal soap method

Technical Parameters and Conditions of Wet Process​

  • Aqueous Grinding: Utilizing mechanical force to achieve ultra-fine dispersion and surface wetting of the pigments. During grinding, several technical tests are required, such as determining the fineness, dispersion performance, and solid content of the grinding slurry.
  • Phase Transfer: Leveraging the oil-affinity of pigments, phase transfer technology is used to transfer pigments into the dispersant phase and stabilize them. Typical methods include kneading phase transfer and three-roll ink methods.
  • Washing: Removing unwanted impurities and solvents through washing.
  • Drying: Removing moisture using drying equipment to ensure product quality.
  • Pelletizing: Using a pelletizer to form the dried pigment into solid particles. The pelletizer screw is modular, optimized based on the material system and process formulation requirements, such as length-to-diameter ratio, barrel structure, screw arrangement, screen changer structure, exhaust quantity, and position, and feeding method.

Characteristics of the Wet Process

  • Color Effect: The wet process has significant advantages in color effect, gloss, toughness, and transparency.
  • Dispersion: It produces masterbatch with smaller particle size and better dispersion.
  • Chemical Stability: The products typically exhibit better thermal and light stability because the liquid medium in the wet process can effectively mitigate thermal and light stress on the pigments, enhancing product stability.
  • High Complexity: The wet process involves a complex workflow, including aqueous grinding, phase transfer, washing, drying, and pelletizing.
  • High Technical Requirement: It demands high technical skills from personnel and has a longer production cycle.

Dry Process

Some enterprises in the production of high-grade color masterbatches, will prepare their own pre-dispersed pigments, and then granulate by dry process. Its production conditions present a variety of options with different product requirements.

The most common production process is: high speed mixer + single screw extruder, high speed mixer + twin screw extruder. In order to improve the dispersion of pigments, some enterprises ground the carrier resin into powder. Internal mixer + single screw extruder and internal mixer + twin screw extruder are also two kinds of technical process used to produce high-quality color masterbatch. At present, the color measurement and color matching technology of color masterbatch are more popular, and more high-performance spectrophotometers are introduced to assist in color matching.

Production equipment

The production equipment of color masterbatch includes grinding equipment, high and low speed kneading machine, mixer, extruder, pelletizer, etc.

Grinding equipment includes sand mill, cone mill, colloid mill, high shear dispersion machine and so on.

The kneading machine can exhaust, extract volatiles and dehydrate by vacuumizing and reducing pressure. Use heat conduction oil, steam for heating and water for cooling under thermal working conditions. The discharging method are cylinder turnover discharging, under valve discharging and screw discharging. Kneading paddle adopts frequency converter for speed regulation.

 

The mixer is divided into two kinds: open rubber mixer and closed rubber mixer. Extrusion equipment has single screw extruder, twin screw extruder (parallel co-rotating, parallel counter-rotating, conical co-rotating, conical counter-rotating), multi-screw extruder and non-screw extruder, etc. At present, co-rotating twin-screw extruder is commonly used in extrusion and granulation.

The color masterbatch can basically adapt to the development requirements of the three major synthetic materials of plastics, rubber and chemical fiber, and gradually expand from the main color masterbatch varieties of general plastics to general engineering plastics (PC, PA, POM, PBT/PET, etc.), special engineering plastics (FEP, PVDF, PI, etc.), thermoplastic elastomer (TPU), rubber and other application fields. Functional masterbatches are becoming more and more popular.

Characteristics of the Dry Process

  • Simplicity: The dry process is relatively simple and easy to operate.
  • Lower Equipment Requirements: It requires less sophisticated equipment, making it suitable for small-scale production.
  • Lower Pigment Dispersion: Although it achieves a certain degree of dispersion through physical methods, the absence of a liquid medium may result in less effective dispersion compared to the wet process, potentially affecting the final product’s color effect.
  • Lower Stability: Without a liquid medium, pigments are more prone to thermal and light stress, leading to lower product stability.
  • Inferior Gloss and Transparency: Products from the dry process generally have lower gloss and transparency compared to those from the wet process.

Comparison of Wet Process and Dry Process

Choosing between the wet process and dry process depends mainly on specific production needs and goals. Each process has unique advantages and limitations, and selecting the appropriate one can maximize product quality and production efficiency.

Final Product Effect:

For high color effect, gloss, and transparency with high dispersion requirements, the wet process is recommended. Despite being complex and costly, it offers superior product performance, dispersion, and stability.

Budget:

For limited budgets or small-scale production, the dry process is a viable option. It is simple to operate, requires less equipment, and is suitable for startups or small production lines.

Energy Cost in Production:

The wet process is more complex and costly. It involves strict equipment and process adjustments, including solvent recovery, increasing production costs and energy consumption. Additionally, labor costs for production operators and quality control personnel are higher. In contrast, the dry process offers significant cost advantages by eliminating the need for solvents and steps such as slurry mixing and drying, thus reducing material, time, facility, and labor costs.

Environmental Impact:

The wet process, due to solvent use, may generate more hazardous waste, posing a greater environmental impact. The dry process does not have this issue.

Environmental Impact:

Products manufactured by the wet process typically have better high current tolerance and mechanical properties. The wet process produces membranes with uniform and smaller pore sizes, capable of withstanding larger current charges and discharges, and offering higher longitudinal and transverse strength. The dry process, due to difficulties in controlling pore size and distribution, results in less stable and lower-performance products.

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