Masterbatch
A masterbatch is a concentrated mixture of pigments or additives dispersed in a polymer carrier and supplied in granule form. It is used to color plastics or modify their properties during manufacturing. Masterbatches ensure uniform dispersion of additives, reduce production costs, and
enhance the quality and performance of final products. They are typically divided into three main categories: color masterbatch, additive masterbatch, and filler masterbatch—each serving a specific role in plastic processing industries.
Filler Masterbatch
Filler masterbatches are primarily composed of mineral fillers such as calcium carbonate or talc, dispersed in a polymer carrier like polyethylene or polypropylene. They are used to reduce production costs, improve mechanical strength, dimensional stability, and control shrinkage. Filler masterbatches are widely used in industries such as packaging, household items, injection-molded parts, and plastic bags.
Color Masterbatch
Color masterbatches are formulated using high-quality organic or inorganic pigments to deliver a wide spectrum of vibrant, long-lasting colors to plastic products. These masterbatches provide excellent color consistency, thermal stability, and lightfastness. They are ideal for injection molding, packaging films, construction profiles, automotive parts, and toys.
Additive Masterbatch
- Granulated Color Preparations / MasterbatchA masterbatch is today the most preferred type of preparation, well documented by the large volume of sales.
A masterbatch consists of:
- Polymer as carrier
- Colorants
- Dispersing agent
- If necessary, additives such as stabilizers, nucleating agents, antistatic agents, lubricants, and so forth
The concentration of the components varies corresponding with the desired intensity of color and/or hiding power. Very intensive colors with a good hiding power require a high concentration, which very often lies in the range of 50% colorant, 40–45% polymer, and 5–10% dispersing agent.
When the presence of an additive is required in a color preparation, there is no other way than to reduce the concentration of the colorants. The consequence of this is a higher addition of the preparation during the coloring of the polymer. On the other hand, a wide range of additive preparations are commercially available. In such a case, whether to incorporate the additive in the color preparation or apply two separate preparations is a question of economics.
For pastel shades and/or transparent colors, a few percent of colorant in the preparation are enough, especially when a colorant with a high tinting strength can be used to match the desired color. The result is a very diluted masterbatch. In this case, it is not the concentration of the masterbatch that defines the quantity of addition for the later coloring of a polymer but technical considerations. Very small amounts of a masterbatch are difficult to blend homogeneously in a polymer melt; therefore, the coloring of a polymer melt demands a minimum of addition.
The size of the pellets of a masterbatch is usually 2–3 mm (0.075–0.11 in.) in length and 1.5–2.5 mm (0.05–0.09 in.) in diameter, and the addition of such a masterbatch should be not smaller than approx. 1%. Much finer pellets or granules, of course, would allow an addition below 1%, but such types of masterbatches are not yet common for technical and economical reasons.
Considering these two extremes, it is understandable that there is no general rule for the concentration of colorants in a masterbatch. The manufacture of a masterbatch is a multistep process (Fig. 4.3).
- Masterbatch Manufacturing StepsStep 1 – Weighing and Premixing
All powdery components of the recipe are weighed out accurately and premixed.Step 2a – Homogenization of Powdery Components
The powdery components are homogenized in a mixer. Different types of mixers can be used depending on requirements.Step 2b – Blending with Polymer
The homogeneous blend is added to the weighed polymer and blended carefully. The same type of mixer as in Step 2a can be used.Step 3 – Extrusion
The mix is extruded using a twin-screw extruder, as a high shear is necessary for complete dispersion of the colorants in the polymer melt.There are two types of twin-screw extruders:
- Corotating extruder → Provides higher shear, preferred for very hard organic pigments requiring complete dispersion.
- Counterrotating extruder → Provides lower shear, suitable for pigments sensitive to shear, such as pearlescent pigments.
Step 4 – Granulation
Two principal methods are used:- Cord Cutting Method → Colored melt is drawn into cords at the die face of the extruder head, cooled in a water bath, and cut into cylindrical pellets.
- Die Face Pelletizer Method → The melt is cut immediately as it exits the extruder head by rotating knives, then cooled in a water bath, resulting in lens-shaped pellets.
Granulation Methods and Pellet Types
The most preferred method of granulation is to form a cord of colored melt, cool it in a water bath, and cut it into cylindrical pellets.
The main advantage of this procedure is the flexibility in production, since the manufacture of customer-matched color batches is not continuous but batchwise. This batchwise production results not only from the great variation of desired colors but also from the variety of polymers used as carriers. The size of such a batch may vary between 25 kg (55 lb) and several tons.
Exceptions are standard batches in white, black, and a few other standard colors, where the second method of granulation is usually applied.
Cylindrical Pellets
- Diameter: 1.5–2 mm (0.05–0.075 in.)
- Length: 2–3 mm (0.075–0.11 in.)
The effective size of these pellets depends on:
- The boring diameter in the extruder head.
- The degree of expansion of the colored polymer melt after leaving the extruder.
In the compression section in front of the extruder head, the polymer melt is compressed. Upon exiting, the melt expands to its original volume. If the borings are too small, the cord cannot be drawn satisfactorily. If too large, cutting problems arise.
Since polymers are poor heat conductors, the inside of the cord may remain hot and insufficiently solid after water cooling, making clean cutting difficult.
Lens-Shaped Pellets
Lens-shaped pellets are common for natural-colored polymers and typical for white and black batches.
- In such preparations, colorant concentration is 60–75%, while the polymer share drops to 15–25%.
- Such highly concentrated batches cannot be granulated by the usual cord-cutting method.
- They require a die face pelletizer, where:
- The melt is pressed through extruder head borings into fast-running water.
- Rotating knives cut the melt directly into small pieces.
- Water speed must be high enough to separate each still-soft pellet.
In the water:
- Cylindrical pellets tend to round into a spherical form (the most stable physical shape).
- Simultaneously, the pellet surface cools quickly.
- These counteracting effects result in lens-shaped pellets.
Micropellets
The process has been modified to produce very fine, nearly spherical micropellets.
- Disadvantage: High production cost.
- Advantage: Extremely high number of particles per weight unit compared to normal cylindrical pellets.
Key benefits of micropellets:
- Can be metered well below 1% directly on the plasticizing screw.
- Achieve homogeneous dispersion in the polymer melt, minimizing color streaks.
- Especially useful for pastel shades and transparent colors, since:
- Very low concentrations of colorants are required to avoid streaking.
- Preparations can be more highly concentrated compared to normal masterbatch.
Cost Comparison:
- Masterbatch: Cheaper to produce but requires higher addition levels.
- Micropellets: More expensive to produce but require significantly lower quantities for effective polymer coloring.
Alternative Pellet Manufacturing Methods
Technically, there are further methods to manufacture pellets or granules.
One example is a modification of the spray drying process:
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The conventional spray drying process is used to produce very fine granules starting from an aqueous slurry.
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Fine droplets, produced by a spraying nozzle or a fast-rotating disk, are dried in a stream of hot air, resulting in very fine spherical, often hollow granules.
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Instead of an aqueous solution, a melt consisting of colorants and binder can be sprayed into a stream of cold air.
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This process results in very fine spherical but solid granules.
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Since the spraying nozzle requires a light-flowing melt, normal polymers cannot be used as binders.
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Possible binders are oligomers (waxes) or resins.
Color preparations based on this process are commercially available and are sometimes used for polymer coloring.
Masterbatch: Advantages and Limitations
A masterbatch is the most expensive color preparation of all types because of:
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The high number of steps involved in production.
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The high energy requirement of extrusion.
Another disadvantage is the possible incompatibility of polymers when blended. Therefore, it is recommended to use the same type of polymer as the carrier for the color preparation and for the polymer that will be colored.
Universal and Partial Universal Batches
Sometimes so-called “universal batches” are offered on the market.
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The term “universal” implies compatibility with all polymers.
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In practice, this is not realistic due to the chemical diversity of polymers.
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Not all colorants are applicable in every polymer because of factors such as:
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Heat stability
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Light fastness
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Weather resistance
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Migration of dyes in partially crystallized polymers
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For example:
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In polyethylene (PE), many colorants are applicable.
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In polyamide (PA), the range of usable colorants is much more limited.
Therefore, true universal batches are impossible. However, in practice, “partial universal batches” are sometimes used — for instance, coloring PA with special PE-based color preparations, provided there are no special requirements regarding product quality.
Advantages of Masterbatch
Despite its disadvantages, the advantages of masterbatch predominate, particularly regarding ease of handling (see Table 4.1).
Key advantages include:
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Very good metering accuracy
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Dust-free handling
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Minimal effort for changing colors during production
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Complete dispersion of pigments in the polymer during extrusion
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Optimal utilization of the tinting strength of the colorants
This explains why the masterbatch remains the most preferred type of color preparation.
You can contact us to place an order.
Exporter of masterbatch, compound, carbon black, and additives used in the rubber and plastic industry.
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