How to Determine the Addition Ratio of PE Black Masterbatch
Short Answer
The addition ratio is the share of masterbatch in the total mix. If the masterbatch is the only source of carbon black, the carbon black content of the final product equals the masterbatch's carbon black content multiplied by the addition ratio. How much carbon black the product needs depends on whether the target is opacity or jetness, on the product thickness, the PE type, the dispersion and any product standard that applies. The calculation gives a starting point; the final ratio should be confirmed by a trial on your own line.
Terms: Addition Ratio, Let-Down Ratio and Final Concentration
| Term | Meaning | Example |
|---|---|---|
| Addition ratio (dosage) | Masterbatch as a percentage of the total mix | 2% = 2 kg masterbatch in 100 kg of total material |
| Let-down ratio (LDR) | Masterbatch to natural resin, often written as 1:X | 1:49 = 1 part masterbatch to 49 parts resin = 2% |
| Final carbon black concentration | Carbon black as a percentage of the final product | 0.8% |
Always state the basis. "2 parts per 100 parts of resin" is not exactly 2% of the total: it is 2 / 102, or about 1.96%. For an LDR of 1:X, the addition ratio is 1 / (1 + X).
The Mass-Balance Calculation
Final carbon black content = carbon black content of the masterbatch × addition ratio.
Hypothetical example, not a ZFH formulation and not a recommended addition ratio: a black masterbatch containing 40% carbon black, added at 2% of the total compound, contributes 0.40 × 0.02 = 0.008 = 0.8% carbon black to the final compound.
This simple calculation assumes that the masterbatch is the only source of carbon black and that the addition ratio is by mass of the total mix. If recycled black resin or another black component is used, its carbon black must be added. The calculation also assumes accurate dosing, which should be checked in production.
The same relationship works in reverse: the addition ratio needed equals the target carbon black content divided by the masterbatch's carbon black content. For example, a target of 1.0% with a 40% masterbatch requires 1.0% ÷ 40% = 0.025 = 2.5% (arithmetic only).
| Masterbatch carbon black | 1% addition | 2% addition | 3% addition |
|---|---|---|---|
| 30% | 0.3% | 0.6% | 0.9% |
| 40% | 0.4% | 0.8% | 1.2% |
| 50% | 0.5% | 1.0% | 1.5% |
The table shows arithmetic only. It is not a dosing recommendation for any product.
What Determines the Carbon Black Content You Need
Opacity or Jetness
If the product must block light, as with thin film or bags, the carbon black content needed depends strongly on thickness. If it must look deep black, as with a visible molded part, the carbon black grade, the dispersion and the surface finish matter as much as the amount, and extra carbon black beyond a certain point adds little. See why higher carbon black content does not always mean higher blackness.
Thickness
A thin film needs a higher final carbon black content than a thick molded part to reach the same opacity. A thick part may be fully opaque at a low content, so increasing the addition ratio then mainly adds cost.
Dispersion and Carrier Compatibility
Poorly dispersed carbon black contributes less color, so a poorly dispersing masterbatch may seem to need a higher addition ratio. A carrier that blends well with the PE grade helps the carbon black to distribute evenly at a lower ratio.
Product Requirements
Outdoor products and products that rely on carbon black for UV protection can have their own requirements. For example, pressure-pipe standards for black polyethylene compounds specify a carbon black content range, and ISO 6964:2019 gives a test method for carbon black content in polyolefin pipes and fittings. Where such a standard applies, it overrides any rule of thumb.
LDPE, LLDPE, HDPE and Recycled PE
| Material and application | What to consider |
|---|---|
| LDPE film and bags | Opacity at low thickness; film defects; carrier melt behavior close to the film resin |
| LLDPE film, including stretch and agricultural film | Higher melt viscosity and mixing demand; outdoor and UV requirements where relevant |
| HDPE molded, blow molded and pipe products | Thicker walls; jetness or opacity target; product standards; mechanical requirements |
| Recycled PE | Variable background color and contamination; may already contain carbon black; melt flow varies between lots |
Recycled PE: Special Considerations
Recycled PE often has a gray or mixed background color that has to be covered, so it may need more carbon black than virgin resin for the same appearance. Some recycled feedstock is already black and contains carbon black, which must be included in the calculation. Because feedstock can vary from lot to lot, the addition ratio should be checked when the recycled material changes. See our recycled black masterbatch guide.
Dosing in Practice
- Gravimetric dosing is generally more accurate than volumetric dosing, which is affected by pellet bulk density.
- Calibrate dosing units and check actual consumption: kilograms of masterbatch used per kilogram of product over a run.
- Large differences in pellet size or shape between masterbatch and resin can cause separation in the hopper; premixing or feeding close to the throat can help.
- At very low addition ratios, small dosing errors become a large share of the total, which can show as color variation.
Confirming the Ratio by Trial
- Define the target and how it will be measured, for example opacity at the product thickness or an L* value against an approved reference, measured the same way each time.
- Calculate a starting addition ratio from the masterbatch's carbon black content and the target content.
- Run a short ladder of addition ratios around that starting point on the production line.
- Check appearance, opacity, defects, processing and any mechanical or product requirements at each level.
- Choose the lowest ratio that meets all requirements with a safety margin, then confirm it on a full production run.
Frequently Asked Questions
Is there a standard addition ratio for PE black masterbatch?
No. The ratio depends on the masterbatch's carbon black content, the product thickness, whether opacity or jetness is the target, the PE type, the dispersion and any product standard. It should be set by calculation and confirmed by trial.
Does a higher-concentration masterbatch let me use a lower addition ratio?
For the same final carbon black content, yes, in proportion to the concentration. The blackness and dispersion can still differ, so the result should be checked in a trial.
Is "2 parts per hundred" the same as 2%?
Not exactly. 2 parts of masterbatch per 100 parts of resin is 2 / 102, about 1.96% of the total. Always state which basis is used.
How do I account for recycled black resin?
Estimate or measure the carbon black that the recycled resin already contains and add it to the contribution from the masterbatch. Because recycled lots vary, confirm the result by trial.
Related Guides
- Why higher carbon black content does not always mean higher blackness
- How to evaluate black masterbatch dispersion
- Recycled black masterbatch guide
Black Masterbatch for PE
ZFH offers standard PE/EVA black masterbatch and rPE recycled black masterbatch in grades with different carbon black contents. Share the PE grade, product type and thickness, the target and your current addition ratio, and contact ZFH to plan a trial.
Technical References
- ASTM D1603-20 — Carbon black content in olefin plastics
- ISO 6964:2019 — Polyolefin pipes and fittings: determination of carbon black content by calcination and pyrolysis — test method
These references describe test methods for carbon black content. They are not results for any ZFH grade, and the calculations in this article are illustrative.