PET Packaging
PET packaging is a food-contact application processed at high temperature, so the colorant has to be both compliant and physically stable in the melt. Dye-based black masterbatches achieve transparency easily but carry a migration risk into the contents, which is why a dye-free nano carbon black route is used where food contact and low migration are the priority. The same colorant also has to survive drying, extrusion and blow moulding without degrading the resin, so the masterbatch is judged on the whole process rather than on colour alone.
Key Requirements in This Application
Food-contact compliance
Colorants for food-contact PET must be permitted under the applicable regulation and must be used within the specified conditions. The masterbatch is formulated to meet the colorant provisions of FDA 21 CFR 178.3297 for polymers, in the context of PET packaging under 21 CFR 177.1640.
Dye-free, low-migration colour
Acid dyes used for smoke-grey PET can leach into the contents and stain preforms, moulds and tooling. A dye-free carbon black route removes the migrating species and reduces the risk of taint and staining over shelf life.
Dispersion in the PET melt
Carbon black agglomerates that survive the extruder appear as specks and gels in the bottle wall, and they can also act as stress points. Nano-scale dispersion is required to keep the preform and bottle optically clean.
Processing stability
PET is dried and processed at high temperature, and the masterbatch must not raise acetaldehyde or degrade intrinsic viscosity beyond what the process can tolerate. Carrier choice and moisture control both matter here.
Controlled transparency or opacity
Some packs need a translucent smoke effect while others need full opacity. The loading and the particle size of the carbon black determine which effect is achieved, so dosage must follow the target appearance rather than a fixed percentage.
Reheat behaviour in blow moulding
Carbon black absorbs infrared energy, so a black preform reheats differently from a clear one. The loading has to be set with the reheat profile in mind; a level that gives the right shade but leaves the preform too cool will cause blow-out or poor wall distribution in the mould.
End-of-life sorting
Carbon black is not detected by the near-infrared sensors used to sort packaging waste, which affects how a black pack is handled at end of life. This is a property of the pigment rather than a defect, but it belongs in the packaging decision and should be stated plainly rather than implied to be neutral.
Colour uniformity around the wall
Blow moulding stretches the preform unevenly, so the wall is thinner at the base and shoulder than at the label panel. A colorant that is not fully dispersed reads differently at different wall thicknesses, which appears as a shade band that follows the bottle geometry. Uniform nano dispersion keeps the shade consistent from base to neck, where a coarser pigment would show a visible gradient around the circumference.
Recommended DENSON Series
Transparent nano carbon black masterbatch using a dye-free formulation, intended for packaging where migration and staining must be avoided while a translucent black appearance is required. The nano dispersion keeps the bottle wall free of visible specks at low loading.
View seriesHigh-concentration dye-free black masterbatch for deep black coloration, formulated so that a lower addition level achieves the target opacity in the bottle wall without pushing the reheat profile outside the blow moulding window.
View seriesTechnical Considerations
- Dry the masterbatch and the PET to the process specification before extrusion, because moisture drives hydrolysis and acetaldehyde formation.
- Set the addition level from the target appearance, then confirm colour and haze on the blown bottle rather than on a pressed plaque.
- Check dispersion on the preform as well as the bottle, since specks that disappear in a thick section can still show in a thin wall.
- Keep barrel temperature and residence time within the validated window, because overheating raises acetaldehyde regardless of the colorant.
- Re-confirm food-contact compliance documentation whenever the pigment source or masterbatch grade changes.
- Review the reheat lamps and preform temperature profile after changing addition level, because a darker preform needs a different energy input to blow correctly.
Testing and Compliance
Food-contact compliance
Compliance is documented against the colorant provisions of FDA 21 CFR 178.3297, with the PET article considered under 21 CFR 177.1640, together with migration testing appropriate to the intended use conditions.
Dispersion and appearance
Dispersion is inspected for specks and gels in the preform and bottle, with colour and haze measured on the finished article; particle size distribution to ISO 13320 characterises the nano carbon black.
Processing behaviour
Intrinsic viscosity and acetaldehyde are monitored through extrusion and blow moulding to confirm that the masterbatch does not degrade the resin beyond the process window.
Container performance
Top load, wall thickness distribution and drop performance are checked on the blown bottle, because a colorant that changes reheat behaviour can produce a bottle that looks correct but fails mechanically.
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