How to Choose the Right Color Masterbatch for PET Bottles
A practical guide to selecting color masterbatch for PET bottle applications, including food contact compliance.
Why PET Bottles Need Special Masterbatch
PET (polyethylene terephthalate) is the world's most widely used plastic for beverage bottles, with annual production exceeding 500 billion units. Coloring PET requires special consideration because PET has unique characteristics: high processing temperature (260–290°C), sensitivity to moisture (hydrolytic degradation), strict food-contact regulations, and the need for recycling compatibility. Standard masterbatch designed for PE or PP is not suitable for PET applications.
PET-Specific Masterbatch Requirements
| Requirement | Why It Matters for PET | Standard (Non-PET) Consequence |
|---|---|---|
| PET carrier resin | Carrier must match base polymer to avoid haze and property loss | PE carrier causes haze, delamination |
| High-temperature pigments | PET processes at 260–290°C; pigments must survive | Pigment decomposition, gas evolution |
| Low moisture content | PET is hygroscopic; moisture causes hydrolysis and IV drop | Pre-form haze, bubble defects, brittleness |
| Food-contact compliance | Beverage bottles must meet FDA, EU 10/2011, GB 9685 | Regulatory non-compliance |
| NIR transparency | Clear PET bottles must remain detectable for recycling | Sorting failure in recycling facilities |
Carrier Resin for PET Masterbatch
The carrier resin in PET masterbatch must be compatible with PET. Options include:
| Carrier Type | Compatibility | Transparency | Cost | Best For |
|---|---|---|---|---|
| PET (recycled or virgin) | Excellent | High (clear bottles) | Medium | All PET applications (standard) |
| PCT (polycyclohexylene terephthalate) | Excellent | Very high | High | Premium clear bottles |
| Amorphous PET copolymer | Excellent | High | Medium | Colored PET bottles |
| Universal carrier (PE/PP) | Poor (causes haze) | Low | Low | NOT recommended for PET |
Pigment Selection for PET
Not all pigments survive PET's high processing temperatures. Pigment heat stability must exceed the PET processing temperature by at least 20°C:
| Color | Recommended Pigment | Heat Stability | Light Fastness | Food Contact |
|---|---|---|---|---|
| Blue | Cobalt blue (CoAl2O4) | 500°C+ | Grade 8 | Approved |
| Blue | Phthalocyanine blue | 350°C | Grade 7–8 | Approved |
| Green | Chromium oxide green (Cr2O3) | 500°C+ | Grade 8 | Approved |
| Green | Phthalocyanine green | 350°C | Grade 7–8 | Approved |
| Red | Ceramic red (complex inorganic) | 400°C+ | Grade 8 | Approved |
| Yellow | Nickel titanate yellow | 500°C+ | Grade 8 | Approved |
| White | TiO2 (rutile) | 500°C+ | Grade 8 | Approved |
| Black | Carbon black (N330) | 500°C+ | Grade 8 | Approved (food grade) |
Avoid: Diarylide yellows and oranges (decompose above 240°C), some organic reds (gas evolution), and any pigment not on the FDA or EU positive list for food contact.
Bottle Colors and Their Applications
| Bottle Color | Pigment Loading | Typical Application | Recycling Code |
|---|---|---|---|
| Clear (no color) | 0% | Water, carbonated beverages | PET (transparent) |
| Light green | 0.1%–0.3% | Sparkling water, tea | PET green |
| Dark green | 0.5%–1% | Olive oil, juice | PET green (sortable) |
| Light blue | 0.1%–0.3% | Water, sports drinks | PET blue |
| Dark blue | 0.5%–1% | Milk, juice | PET blue |
| Amber/brown | 0.3%–0.8% | Beer, pharmaceuticals | PET amber |
| Black | 1%–2% | Personal care, UV-sensitive products | PET black (NIR issue) |
| White (opaque) | 1%–3% TiO2 | Dairy, personal care | PET white |
The Black PET Problem: NIR Sorting
Black PET bottles colored with conventional carbon black absorb near-infrared (NIR) light, making them invisible to NIR sorting machines in recycling facilities. These bottles end up in landfill or incineration, defeating recycling goals. Solutions include:
- NIR-detectable black masterbatch: Uses a special pigment that reflects NIR light, allowing sorting machines to identify the bottle as PET
- Alternative black pigments: Iron oxide-based black or special polymer-based black that allows NIR transmission
Processing Requirements for PET Masterbatch
- Pre-drying: PET masterbatch must be dried at 120–140°C for 4–6 hours before use to achieve moisture content below 0.005%
- Processing temperature: 260–290°C depending on application (pre-form injection: 270–285°C)
- Screw design: Use a barrier screw with mixing zone for uniform pigment dispersion
- Residence time: Minimize residence time at high temperature to prevent pigment degradation and IV drop
- Dosing accuracy: Use gravimetric dosing for consistent color across production runs
Food Contact Compliance
All pigments used in beverage bottle masterbatch must comply with:
| Regulation | Scope | Key Requirements |
|---|---|---|
| FDA 21 CFR 178.3297 | US food contact colorants | Pigment-specific extraction limits |
| EU 10/2011 | European food contact plastics | Migration limits, positive list |
| GB 9685-2016 | Chinese food contact materials | Approved substance list, SML limits |
| REACH | EU chemical regulation | SVHC compliance, registration |
Conclusion
Coloring PET bottles requires specialized masterbatch with PET-compatible carrier resin, high-temperature-stable pigments, strict moisture control, and food-contact compliance. Avoid universal PE/PP carrier masterbatch for PET applications, as it causes haze, delamination, and regulatory issues. For black PET bottles, use NIR-detectable formulations to maintain recycling compatibility. Contact our technical team for PET-specific masterbatch recommendations and food-contact documentation.
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