Overcoming Surface Pattern Defects in Flame-Retardant ABS: Root Cause Analysis and Comprehensive Solutions

Overcoming Surface Pattern Defects in Flame-Retardant ABS: Root Cause Analysis and Comprehensive Solutions

In the injection-molding process, “material marking” (also called silver streak, splash, or flow line) is a common quality defect in flame-retardant ABS. It appears as silvery-white streaks, water-like ripples, or cloudy patches on the part surface. These marks not only spoil visual flatness but can also weaken mechanical properties and flame-retardant performance because the affected areas are locally porous. Flame-retardant ABS contains additives such as brominated or phosphorus compounds that are comparatively unstable at high temperature. If molding conditions are not properly controlled, the additives decompose and release gases. When these gases are entrapped in the melt and cannot escape during filling, they leave the surface blemishes known as material marking. Solving the problem therefore demands a multi-dimensional optimization of material, process, mold, and machine.

Material pre-treatment starts with thorough drying. Flame-retardant ABS is inherently hygroscopic, excessive moisture flashes into steam during plasticization and, together with gases from additive decomposition, forms bubbles that later show as marks. A dehumidifying dryer should be used at 80–90 °C for 2–4 h to bring moisture below 0.02 %. Lots that are more moist or have been stored in humid conditions can be dried for 4–6 h. Adding 0.3 %–0.5 % of a silicone-type antifoaming agent or flow promoter lowers melt surface tension, reduces gas retention, and further suppresses marking.

Precise process settings are essential to keep the flame retardant from decomposing. Melt temperature must be held between 190 °C and 230 °C: too low gives poor plasticization and invites gas entrapment, too high accelerates additive breakdown and massive gas release. Injection speed should be moderate—typically 30 %–60 % of maximum screw rpm. Excessive speed subjects the melt to intense shear, locally overheats the resin, and draws in air, too slow allows premature cooling and poor venting. Mold temperature is recommended at 60–80 °C, the higher value slows cooling, gives gases more time to leave through the vent system, and narrows the temperature gap between melt and cavity wall, preventing fog-like chill marks.

Mold design governs how efficiently gas can evacuate. Dead pockets in the cavity or runner are prone to marking, so vent slots 0.02–0.05 mm deep (adjusted for material fluidity) should be added at the parting line, near the gate, and at complex geometry. Clearances between ejector pins and templates can be opened to 0.03–0.05 mm to assist venting. Gate and runner layouts must avoid sharp bends or abrupt restrictions that create high shear. Enlarge gate dimensions by 10 %–20 % (e.g., a round gate from 1.5 mm to 1.8 mm) and use radiused transitions instead of square corners to lower flow resistance and shear heating, reducing the chance of additive decomposition.

Routine machine maintenance is equally indispensable. Left-over resin in the screw and barrel carbonises at high temperature, once mixed with fresh melt it can trigger secondary decomposition and produce impurity-type marks. Every 8–12 h of production or whenever material is changed, purge the screw and barrel with PE or a commercial purging compound, paying special attention to flights, the check ring, and the nozzle—areas where residue easily hides—so that no contaminants remain inside the machine.

By combining the above measures—material drying, process optimization, mold improvement, and equipment upkeep—the generation and entrapment of gases during flame-retardant ABS molding can be greatly reduced, eradicating material marking at its source and securing both appearance and performance.

After these comprehensive countermeasures are in place, the incidence of marking in flame-retardant ABS molding drops markedly. Looking further ahead, however, adopting flame retardants that intrude less on polymer properties is the ultimate way to eliminate marking and upgrade overall performance. Guangzhou Yinsu Flame Retardant Materials, a specialist developer in this field, is introducing a new generation of additives through continuous innovation. Red-phosphorus based ABS-P-20M, with its excellent thermal stability and flame retardancy, dramatically cuts gas evolution caused by additive breakdown and therefore lowers the probability of marking. Halogen-free grade YS-F22B meets high fire-safety requirements in an eco-friendly way, while its influence on mechanical and processing behavior is minimal—ideal for ABS parts where both environmental responsibility and premium quality are demanded. These advanced products not only enhance the processability and service performance of flame-retardant ABS but also provide reliable assurance for the manufacture of top-grade injection-molded articles.