How to Prevent Film Haze When Using Filler Masterbatch
Film haze can increase when mineral filler is introduced into PE blown film, particularly when particles scatter light or disperse poorly. This technical guide explains the difference between haze and clarity, common formulation and processing factors, and a practical trial method for balancing transparency, film strength and material cost.
Haze and Clarity Are Not the Same Measurement
Haze describes transmitted light scattered outside a specified angular range, while clarity describes how sharply an object can be seen through film. A film may transmit much of the incoming light but still look cloudy because of scattering. Manufacturers should define whether the customer cares about measured haze, visual clarity, gloss, or all three. ASTM D1003 is commonly used for haze and luminous transmittance testing of transparent plastics; select the applicable method and equipment for the product.
Why Mineral Fillers Can Scatter Light
Particles and the polymer matrix can have different refractive indices, producing scattering at their interfaces. Larger particles, agglomerates and poor dispersion may make the effect more visible. The final outcome depends on particle-size distribution, filler concentration, the carrier resin, film thickness and the morphology formed during cooling. No filler can be assumed optically invisible simply because the pellets appear uniform.
Check the Masterbatch Before Changing the Machine
Compare masterbatch grades using their documented particle and dispersion characteristics where available. Confirm the polymer carrier is appropriate for the base resin and processing temperature. Look for visible contamination, clumps or unusual moisture-related handling issues. Sodium sulfate can be moisture-sensitive in some circumstances; protect material according to the supplier’s storage recommendations and investigate water-related defects rather than assuming every white spot is a filler agglomerate.
Process Variables That Affect Film Appearance
Blow-up ratio, drawdown, frost-line height, cooling-air balance, melt temperature and film thickness can affect polymer crystallization and surface appearance. These variables may influence haze even without a filler change. When troubleshooting, hold processing conditions steady and change one factor at a time. If the baseline film already has high haze, first confirm resin and cooling conditions before attributing the issue to the filler.
A Controlled Haze Trial
Measure baseline haze and thickness on film made without filler. Add the proposed grade at a controlled level, then measure samples after stable production is reached. Record haze, transmittance, gloss if relevant, thickness profile, visible defects, tensile properties and bubble stability. Repeat under the same test method and compare samples at equivalent thickness. A trial that lowers material cost but exceeds the buyer’s haze limit is not a successful formulation.
Transparency Trade-Offs in Different Bag Applications
Transparent packaging film may have strict haze and gloss limits, whereas opaque garbage bags may prioritize strength, sealing and cost. A filler grade suitable for the latter should not automatically be promoted for the former. Define the end-use appearance target before selecting a grade. In multilayer film, skin layers can influence surface appearance, but they do not remove light scattering from a filled core.
When to Request Technical Support
Send your resin blend, nominal film thickness, machine configuration, target haze or transparency requirement and proposed filler loading. Ask for trial samples and measurable acceptance criteria. Kovicrea’s filler product range includes grades positioned for different film requirements, but actual optical results must be verified on the intended formulation and line.
Explore Related Technical Resources
Continue learning in the Kovicrea Technical Insights center, or compare application-oriented grades on our sodium sulfate filler masterbatch product page. For a broader overview, read our Na₂SO₄ filler masterbatch technical guide.