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Color Masterbatch Mixing: Uniform Color and Streak-Free Premixes
release time:
2026-10-12
Color masterbatch mixing guide: premix composition, dispersive vs distributive blending, the causes of color streaks, and how to choose a mixer with real specs.
Color masterbatch turns a dusty, hard-to-dose pigment into a free-flowing pellet that a converter can feed at 1–5% and expect to reproduce the same shade, batch after batch. But the color a molder finally sees is decided well before the extruder — it is decided the first time the pigment, carrier resin and dispersant are blended together. This guide covers the premix and mixing stage of color masterbatch production: what goes into the blend, why streaks appear, and how to select a mixer for the job. For the wider equipment picture, see our plastic mixing equipment and pigment mixing systems pages.
What a color masterbatch is made of
A masterbatch pellet is a concentrate: a high pigment load held in a carrier resin that matches the polymer the customer will later dilute it into. A typical extrusion-grade color masterbatch breaks down roughly like this.
| Component | Typical share | Purpose |
|---|---|---|
| Pigment or dye | 20–50% | Provides the color |
| Carrier resin | 35–50% | Matches the base polymer and carries the pigment |
| Dispersing agents | 2–10% | Wet out the particles and stop them re-agglomerating |
| Processing aids | 1–3% | Improve flow and release |
| Stabilizers | 0.5–2% | Protect pigment and polymer from heat |
Two rules follow. First, the carrier must be compatible with the final resin — a polyethylene carrier for PE extrusion, PP for polypropylene, and engineering resins for ABS or nylon — and its melt flow index should sit close to that of the base resin so the two flow together at the die. Second, because the pigment fraction is high and the particles are very fine, the premix is where uniformity is either won or lost.
Dispersive vs distributive: the two mixing jobs
Compounding is often described as a single operation, but it is really two, and each needs a different action from the mixer.
| Job | What it does | What it prevents |
|---|---|---|
| Dispersive mixing | Breaks pigment agglomerates down to primary particles under high shear | Specks, unmelted spots, weak color strength |
| Distributive mixing | Spreads those particles evenly through the whole batch | Streaks, blotches and batch-to-batch shade drift |
In the dry premix stage the mixer's main job is distributive: coating every carrier granule with pigment so that when the material later enters the extruder there are no pigment-rich and pigment-poor pockets left to streak a film or a molded part.
Why color streaks start at the premix
Most color complaints trace back to one of three origins: under-dispersion at compounding, a carrier mismatch, or process drift at the machine. The premix and blending stage decides the first two.
A premix blender runs dry, before the polymer melts. Its task is to coat the carrier resin evenly with pigment and dispersing agent so that the fine color lot is already spread through the bulk. When that coating step is incomplete — a short cycle time, an over-filled vessel, or a ribbon that simply turns the batch without shearing it — the pigment stays clustered, and the extruder is then asked to fix a problem it cannot see.
Pigment choice raises the stakes. Organic pigments give bright, saturated color but can degrade above roughly 220 °C and may migrate; inorganic pigments tolerate up to about 280 °C with better UV stability but give duller shades. Carbon black and titanium dioxide are the hardest to wet out and the most abrasive to the mixer. A blend that has not been premixed properly shows up later as streaks or specks no matter how carefully the extruder is run.
Tracing color defects back to the mix
| Defect | Likely cause | Where it originates | What to change |
|---|---|---|---|
| Color streaks | Poor distributive mixing, or a carrier mismatch | Premix / compounding | Improve blend uniformity; match the carrier to the base resin |
| Specks, black dots | Too little dispersive shear, or carry-over from a previous color | Compounding hygiene | Raise dispersion energy; purge and clean between colors |
| Splay, silver streaks | Moisture above about 0.05% | Drying and storage | Dry the premix; keep moisture below 0.05% |
| Shade drift between batches | Dosing variance, or uneven pigment distribution | Premix and feeder | Verify the let-down ratio; blend the color through the whole batch |
| Plate-out on the die | Excess wax-based dispersant | Formulation | Reduce stearate content; clean the die regularly |
Notice how many of these rows point back to the blend rather than the extruder. If a batch is already streaky when it reaches the hopper, no downstream setting will fully rescue the shade.
Let-down ratio: the number the premix has to hit
The let-down ratio (LDR) is the share of masterbatch added to natural resin at the machine — usually 1–5%, and up to 10% for very deep colors. The working formula is:
Addition rate = target pigment percentage in the finished part ÷ pigment percentage in the masterbatch × 100.
A 40% pigment masterbatch used to hit a 2% target works out at 5% addition. The higher the loading, the lower the LDR — and the more precise the dosing and the more uniform the premix must be, because a small variation in a heavily loaded masterbatch lands directly in the finished shade.
Choosing a mixer for the color masterbatch premix
Batch size, throughput and pigment sensitivity shape the choice. The three platforms below cover most color masterbatch premix duties.
| Mixer | Best for | Why it works |
|---|---|---|
| DJH double-shaft paddle mixer | Fast batch premixing of color and additive masterbatches | Two counter-rotating paddle shafts fluidize the bed and reach a uniform blend in a short cycle |
| DLH ribbon mixer | Economical, repeatable batches from pilot to tonnage | Inner and outer ribbons create convection that suits free-flowing powders and frequent color changes |
| DSHL conical screw mixer | Shear-sensitive, pearlescent or metallic pigments, low-residue changeovers | Gentle, low-shear circulation with minimal heel, so it will not smear effect pigments |
For lines that run color continuously instead of in batches, the DJHX continuous twin-shaft paddle mixer blends in a fluidized zone and discharges without opening the vessel. To see how these machines sit alongside the rest of a plastics line, read our overview of plastic compounding and masterbatch mixing.
Technical parameters
Representative DJH double-shaft paddle mixer models. Working volume is quoted for powder with a bulk density of 1; final selection must be calculated from your own material and process data.
| Model | Working volume (L) | Motor power (kW) | Speed (r/min) | Overall size (mm) | Weight (kg) |
|---|---|---|---|---|---|
| DJH-500 | 200–300 | 7.5 | 37 | 1450×1500×950 | 800 |
| DJH-1000 | 400–600 | 11 | 33 | 1800×1800×1350 | 1150 |
| DJH-2000 | 800–1200 | 18.5 | 31 | 2200×2400×1600 | 2800 |
| DJH-5000 | 2000–2500 | 37 | 23 | 2950×3050×2040 | 6000 |
| DJH-10000 | 4000–5500 | 55 | 21 | 3550×3350×2400 | 9500 |
Representative DLH ribbon mixer models.
| Model | Working volume (L) | Total power (kW) | Speed (r/min) | Overall size (mm) | Weight (kg) |
|---|---|---|---|---|---|
| DLH-500 | 180–300 | 7.5 | 49 | 2800×920×1320 | 680 |
| DLH-1000 | 350–600 | 11 | 42 | 3180×1020×1550 | 1200 |
| DLH-2000 | 700–1000 | 18.5 | 42 | 3750×1290×1820 | 2200 |
| DLH-5000 | 2000–3000 | 30 | 31 | 4700×1610×2260 | 4300 |
| DLH-10000 | 3200–5000 | 55 | 27 | 5720×2520×2840 | 7900 |
FAQ
- What is the difference between color masterbatch and pigment powder? Masterbatch is a pre-dispersed concentrate in pellet form; pigment powder is a raw, dusty material that needs lengthy mixing and dust control. Masterbatch doses cleanly and reaches uniform color faster.
- Why does my color shift from batch to batch? Usually uneven pigment dispersion in the premix, dosing drift, or lot-to-lot pigment variation. Check blend uniformity and the let-down ratio first, then verify every incoming batch.
- How much masterbatch should I add? Most color masterbatches are let down at 1–5%, but the correct figure comes from the pigment loading. Confirm it with a color trial against an approved sample before a full run.
- Can one mixer handle both premixing and dispersion? A high-intensity mixer such as the DJH covers dry premixing and solid-liquid additions; the final dispersive work still happens in the extruder. The premix decides whether the extruder starts from an even blend or a blotchy one.
- What mixer is best for effect pigments? Shear-sensitive pigments such as pearlescent and metallic types prefer a gentle, low-shear mixer like the DSHL conical screw mixer, which avoids damaging the platelet structure.
Choosing the right premix mixer is the cheapest place to fix color — it prevents streaks before they are made rather than screening them out afterwards. Send us your material, batch size and target color and our engineers will recommend a configuration. For the full range, start with our plastic mixing equipment page.
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