Color Masterbatch for PET Preforms and Bottles: Clarity, Stability, and Recyclability

Coloring PET Preforms Without Sacrificing Clarity

PET (polyethylene terephthalate) is the world's dominant beverage packaging resin, processed into preforms via injection molding and then stretch-blow molded into bottles. Coloring PET is uniquely challenging: the polymer is highly sensitive to hydrolysis and thermal degradation, and the bottle must retain clarity, intrinsic viscosity (IV), and recyclability. Masterbatch for PET preforms must therefore be engineered specifically for PET's processing window.

PET is processed at 260–290°C, where residual moisture causes hydrolytic degradation that reduces IV and produces acetaldehyde (AA) — a compound that affects beverage taste. This places strict limits on pigment thermal stability and masterbatch moisture content.

Key Requirements for PET Masterbatch

Carrier Resin Selection

The carrier resin in PET masterbatch is critical. Unlike PE/PP masterbatch, PET masterbatch must use a PET-compatible carrier to avoid haze and IV loss. Common carriers include:

• PET (bottle-grade or fiber-grade): Best clarity and IV retention, but higher melt viscosity.
• PETG or copolyester: Lower melting point, easier processing, slight clarity trade-off.
• PBT: Lower melt temperature, good pigment wetting, minor haze impact.

Pigment Selection for PET

PET masterbatch uses heat-stable pigments that survive 280°C processing without degrading or generating AA:

• Inorganic pigments: Titanium dioxide (white), iron oxides (amber/brown), ultramarine blue, chromium oxide green — excellent heat stability.
• Organic pigments: Phthalocyanine blue/green (300°C stable), selected azo pigments for reds/yellows — must be verified for PET heat stability.
• Reheat additives (for hot-fill): Black-based or antimony-free reheat masterbatch improves preform heating in stretch-blow molding.

Recyclability and rPET

The beverage industry's push toward circularity has made PET recyclability a critical masterbatch consideration. Color choices directly affect recycling: clear and light-blue PET has the highest recycling value, while heavily pigmented bottles can contaminate the recycling stream. Masterbatch suppliers increasingly offer:

• Recycle-friendly colors: Shades that sort well in NIR and color-sorting systems.
• rPET-compatible masterbatch: Formulations that mask the yellowing of recycled PET.
• Antimony-free options: For brands moving away from antimony-based reheat agents.

Processing Recommendations

1. Pre-dry masterbatch to below 200 ppm moisture before use.
2. Use low AA-generating pigments for water and carbonated beverage applications.
3. Match carrier IV to the base resin to avoid haze and weld-line issues.
4. Monitor color at multiple points — PET color can shift slightly through reheat and blowing.

Conclusion

PET preform masterbatch is a specialized product where carrier compatibility, pigment heat stability, moisture control, and recyclability all matter. MHK Color supplies PET-specific color and reheat masterbatch engineered for clarity, low AA, and IV retention. For beverage, personal care, or pharmaceutical PET applications, contact our team with your target color and processing conditions.