Coloring Glass-Fiber-Reinforced Engineering Plastics – Common Problems and Proven Solutions
Coloring glass-fiber-reinforced engineering plastics is one of the most challenging aspects of plastics processing. High processing temperatures, abrasive glass fibers, and complex additive systems place special demands on pigments, masterbatches, and process control. From a technical perspective, it is repeatedly evident that color is not merely an aesthetic detail, but a material-relevant influencing factor.
Pigments: Color Strength vs. Mechanical Performance
A classic example is the use of titanium dioxide (TiO₂) for white coloring. While TiO₂ offers excellent hiding power, its high hardness has a negative effect on glass-fiber-reinforced polymers. During plasticization, this can lead to increased glass fiber breakage—resulting in measurable losses in tensile strength and component service life.
From an expert perspective, the following applies: For glass-fiber-reinforced plastics, softer pigment grades or alternative white systems should be specifically used. In many applications, it is also necessary to assess whether coloring without TiO₂ is technically practical.
Even seemingly “neutral” formulations can exhibit interactions. For example, pigment systems containing zinc sulfide react with copper-containing heat stabilizers in polyamides—resulting in color instability or brownish discoloration. Therefore, a comprehensive chemical assessment of the polymer, pigment, and additive is always crucial.
Thermal Stability: A Critical Quality Factor
Engineering plastics such as PA 66, PC, or PC blends are often processed at temperatures above 280 °C. Pigments and masterbatches with insufficient thermal stability degrade under these conditions—as evidenced by color drift, uneven color tones, or a gray haze.
Particularly critical factors include:
• Material changes (e.g., PA 6 → PA 66)
• Applications with hot runner systems
• Long residence times in the molten state
Best Practice: The thermal stability of the masterbatch should always be significantly higher than the actual processing temperature. Technical data sheets provide important guidance but do not replace application-specific testing.
The Right Masterbatch Base: Compatibility Matters
From a materials science perspective, using a masterbatch base made of the same polymer is the safest approach: PA 6 with PA 6, PBT with PBT, PC with PC. Deviations are possible but require in-depth expertise. In glass-fiber-reinforced systems, incompatibilities lead particularly quickly to streaking, delamination, or mechanical weaknesses.
Conclusion: Coloring is material engineering
The coloring of glass-fiber-reinforced engineering plastics is not a standard process, but rather precise material engineering. Anyone who wants to successfully combine color, mechanical properties, and process reliability needs in-depth material knowledge and practical experience.
As experts in color and additives, we support our customers from pigment selection through masterbatch development to series production—with the goal of achieving stable colors, consistent component properties, and reliable processes.
