Standard letdown ratios: 1:50 (2% loading) for vivid colors, 1:100 (1%) for moderate shades, 1:200 (0.5%) for pastel shades. Masterbatch typically contains 20-50% pigment. Higher pigment concentration in masterbatch = higher letdown ratios = more economical processing.
Masterbatch is the standard way to add color to plastic processing. The pigment is pre-dispersed in a polymer carrier (typically the same or compatible with end-product polymer) at high concentration (20-50%), then "letdown" into base polymer at production. This guide covers the math and practical considerations.
The math: letdown ratio and final pigment concentration
If your masterbatch is M% pigment by weight, and you add it to base polymer at letdown ratio 1:N (1 part masterbatch to N parts base polymer), the final pigment loading is:
final pigment % = M% / (1 + N) × (1 + N) / (1 + N) ≈ M% / (1 + N)
Example: 30% pigment masterbatch at 1:50 letdown gives 30/51 = 0.59% final pigment loading. 25% pigment masterbatch at 1:100 gives 25/101 = 0.25% final pigment loading.
Recommended pigment loading by polymer and color depth
| Polymer / End Product | Pastel | Standard | Vivid |
|---|---|---|---|
| HDPE pipe | 0.3-0.5% | 0.5-1.0% | 1.0-2.0% |
| HDPE bottle | 0.3-0.5% | 0.5-1.0% | 1.0-2.0% |
| PP injection moulding | 0.5-1.0% | 1.0-2.0% | 2.0-4.0% |
| PVC pipe rigid | 1.0-2.0% | 2.0-3.0% | 3.0-5.0% |
| PVC profile / cable | 1.0-2.0% | 2.0-3.0% | 3.0-5.0% |
| Engineering plastics (ABS, PC, PET) | 0.5-1.0% | 1.0-2.0% | 2.0-3.0% |
| Films (LDPE, LLDPE, BOPP) | 0.2-0.5% | 0.5-1.0% | 1.0-1.5% |
These are starting points — exact loading depends on the specific pigment's tinctorial strength, the polymer's natural color, and the customer's color target. Always validate with a small batch trial before bulk production.
Why higher concentration masterbatch is better economically
A masterbatch with 30% pigment let down at 1:100 ratio achieves the same final color depth as a masterbatch with 15% pigment let down at 1:50. The former saves 50% on masterbatch volume — meaning lower freight, less inventory, fewer container changes during production.
Practical limit: pigment loading above 50% in masterbatch becomes increasingly difficult to disperse. Most quality masterbatch suppliers offer 25-40% pigment loadings as the sweet spot between concentration and dispersion quality.
Common mistakes
1. Using a low-temperature pigment in a high-temperature polymer. Standard PY3 azo yellow at 200°C max in a PP injection at 280°C will decompose and produce brown specks. Always match heat stability rating to your processing temperature plus 10-20°C safety margin.
2. Carrier polymer mismatch. Masterbatch carrier should be compatible with your end polymer. PE-carrier masterbatch into PP works fine; PE-carrier into nylon or PC may cause delamination or spots.
3. Insufficient mixing during letdown. Some processes (single-screw extrusion of HDPE pipe) have limited mixing capacity. Use higher pigment concentration in the masterbatch to compensate, or specify a pre-dispersed masterbatch grade designed for low-shear letdown.
4. Switching pigment grades without revalidating heat stability. Even within the same CI code (e.g. PY154 from supplier A vs supplier B), different surface treatments and particle sizes can shift heat stability behavior. Always validate every new pigment grade in your specific process before bulk qualification.
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About the Author
Bhargav Kanani is the Sales Director at Kanani Dyes Chem LLP, an ISO 9001/14001/45001/17025 certified manufacturer of organic pigments based in Gujarat, India. With deep expertise in pigment chemistry, manufacturing, and global B2B trade, he advises formulators across paints, coatings, plastics, inks, and specialty applications worldwide.