Masterbatch for Film Extrusion: Dispersion, Gels, and Thin-Film Color Consistency

The Challenge of Coloring Thin Films

Film extrusion — both blown and cast — presents the most demanding color requirements in the packaging industry. Film thicknesses of 15–80 μm leave almost no room for dispersion errors: a single undispersed pigment agglomerate or gel particle becomes a visible defect, and color must remain consistent across the entire web width and roll length. Masterbatch for film extrusion is therefore engineered for exceptional dispersion, low gel formation, and consistent processing.

Blown film is produced by extruding molten polymer through an annular die and inflating it with air, while cast film is extruded through a flat die onto a chill roll. Both processes use polyolefins — primarily LLDPE, LDPE, HDPE, and PP — at high line speeds up to 300 m/min.

Key Requirements for Film Masterbatch

Carrier Resin and Melt Flow Index Matching

The carrier resin's melt flow index (MFI) must be compatible with the base film resin. Mismatched MFI causes uneven distribution and visible streaks. General guidance:

• LLDPE film (MFI 0.5–2): Use an LLDPE or LDPE carrier with similar MFI.
• LDPE film (MFI 0.3–4): LDPE carrier with MFI 2–8 for easy dispersion.
• HDPE film (MFI 0.2–1): HDPE or LDPE carrier matched to the HDPE grade.
• PP film (BOPP/CPP): PP homopolymer carrier.

Controlling Gel Formation

Gels are small, hard particles that appear as fish-eyes in film. They originate from three sources:

1. Polymer gels: High-molecular-weight or cross-linked resin fractions that do not melt fully. Minimized by clean resin and proper melt temperature.
2. Pigment agglomerates: Undispersed pigment clusters. Prevented by high-shear dispersion.
3. Degradation gels: Overheated or oxidized polymer. Prevented by controlled temperature and residence time.

For high-clarity film, masterbatch must contribute zero additional gels. MHK Color film grades are formulated with low-gel carriers and screened through fine filter packs during production.

White and Black Masterbatch for Film

• White film masterbatch: 50–75% TiO2 for opacity in milk film, label film, and hygiene packaging. High dispersion prevents streaks.
• Black film masterbatch: 40–50% carbon black for mulch film, garbage bags, and light-barrier packaging. NIR-detectable grades support recyclability.
• Color film masterbatch: High-tint formulations for shopping bags, shrink film, and packaging graphics.

Additive Masterbatch for Film

Film production commonly requires functional additives combined with color:

• Antiblock: Prevents film layers sticking during winding (silica-based).
• Slip: Reduces coefficient of friction for smooth bag opening (erucamide/oleamide).
• Antistatic: Prevents dust attraction on packaging film.
• UV stabilizer: For agricultural and outdoor film (HALS-based).

Conclusion

Film masterbatch must deliver flawless dispersion, minimal gels, and consistent color at high line speeds. MHK Color formulates film-grade masterbatch with MFI-matched carriers, low-gel resins, and rigorous dispersion testing. Tell us your film type, thickness, and line speed for a tailored recommendation.