Key Points for Controlling Color Uniformity in TPE Raw Materials During Injection Molding Production

In injection molding production, the color uniformity of TPE raw materials directly impacts product appearance and competitiveness. Due to TPE's multi-component blending characteristics, issues like color spots, color differences, and flow marks are prone to occur. Precise control across six core processes is essential. Let's explore these with the Zhongsu Wang editorial team.

I. Selecting the Right Raw Material and Pigment Combination

Prioritize using TPE raw materials from the same batch and with identical hardness. Avoid mixing TPE with different matrix types to prevent color differences caused by varying dye absorption capacities. For pigments, prefer masterbatch due to its superior dispersion, stable coloring, and suitability for mass production. If using powdered pigment, pair it with TPE-specific dispersants to prevent agglomeration and color spots.

II. Proper Raw Material Pre-Treatment

TPE readily absorbs moisture and oil contaminants. Prior to coloring, materials must undergo drying treatment at temperatures that prevent softening or caking. Ensure materials are thoroughly dry and free of stickiness post-drying. For oil-contaminated surfaces, wipe with anhydrous ethanol or use low-temperature hot air blowing to prevent pigment adhesion issues.

III. Ensure Thorough Compounding

For large-scale production, use a twin-screw extruder to control screw speed and barrel temperature, balancing dispersion with degradation prevention. Single-screw injection molding requires pre-mixing in a high-speed mixer. Adjust masterbatch dosage based on concentration and target color, conducting small-scale trials before bulk production to avoid excessive amounts that degrade TPE performance or cause color migration.

IV. Optimize Injection Parameters

Follow a gradient temperature ramp to prevent premature melting of raw material or pigment separation. Adjust mold temperature based on TPE hardness—slightly lower for soft grades, slightly higher for hard grades—to avoid flow marks or color migration. Maintain a medium, constant injection speed, slightly faster for thin walls and slower for thick walls. Set holding pressure time to eliminate shrinkage marks and prevent color unevenness.

V. Thorough Equipment Cleaning

When switching to light or transparent colors, first clean the barrel with the base-color TPE. For stubborn residues, add a small amount of white oil as an aid. Disassemble and clean the nozzle. Blow out the hopper with compressed air. Only proceed to batch production after trial runs show no abnormalities to prevent cross-contamination.

VI. Troubleshooting Common Issues

Color spots can be resolved by adjusting dispersants, enhancing cleaning, or filtering raw materials. Color inconsistencies require controlling masterbatch dosage, optimizing mixing parameters, and calibrating temperature control;

Darkening near gates can be reduced by lowering injection speed and optimizing gate size;

Fading necessitates switching to heat-resistant pigments and selecting specialized masterbatches.

In summary, achieving uniform TPE coloring demands meticulous control at every stage. Flexibly adjust based on material properties, equipment capabilities, and product requirements to ensure consistent, high-quality results.