Today's KNOWLEDGE Share : Issues with Color Masterbatches in Injection Molding

Today's KNOWLEDGE Share

Understanding Common Issues with Color Masterbatches in Injection Molding:

The use of color masterbatches is prevalent in injection molding. However, over the years, I have frequently encountered several issues that typically result in surface defects on the molded parts.

These issues can be categorized into three main scenarios:

1. Incompatible Carrier Materials

Sometimes, masterbatches (e.g., with 50% pigment and 50% carrier) use a high-flow carrier like LLDPE, even when the host polymer to be colored is not LLDPE-based.

Issue: The incompatible high-flow carrier is pushed to the surface by hydrodynamic forces. For instance, small amounts of LLDPE in a nylon part can readily create blisters or delamination.

2. Neglecting to Dry the Masterbatch

In nylon or polyester parts, even when the masterbatch uses the correct carrier (same as the host matrix to be colored), users often neglect to dry the masterbatch, drying only the bulk resin to be molded.

Issue: Users may assume that the small amount of masterbatch added doesn’t need drying. However, a very wet, small amount of carrier can cause surface blooming, silver streaks, and potentially significant hydrolytic degradation issues in sensitive materials like PET or PBT.

3. Improper Dispersion of Masterbatch

Even when the masterbatch uses the correct carrier and is properly dried before feeding into the hopper, part issues can still arise.

Issue: The problem often stems from less than perfect dispersion of the masterbatch in the injection molding machine screw. These screws are not always ideally designed and may lack the ability to fully disperse the pigment, leading to color issues due to inhomogeneous color concentrate.

Understanding and addressing these common issues can significantly improve the quality of injection molded parts. Ensuring compatibility of carriers, proper drying of materials, and optimal dispersion techniques are crucial steps in achieving defect-free products.

source:Vito leo

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