Coloring is the first impression of a plastic product and the easiest place for disputes to arise. This page explains color matching and sampling, ΔE control, white and black masterbatch selection, effect masterbatch processing, and how to troubleshoot fading and migration — all answers come from production-line practice.
Matching workflow: customer provides a color number or sample → spectrophotometer reads Lab values → select a heat- and weather-matched pigment combination → small extruder trial → standard plaque issued → on-machine verification and fine-tuning. Professional matching must consider pigment heat stability (processing temperature), migration resistance (end use) and lightfastness (indoor/outdoor) — it is not simply mixing colors.
Yes. Provide a Pantone number (e.g. PANTONE 485C) or a RAL number and the colorist works from the corresponding card's Lab values. Note that color cards are printed or coated colors; on plastic the same number is affected by resin base color, gloss and transparency — final matching is against the plastic standard plaque.
Industry practice: ΔE≤1.0 is excellent for appearance parts, ΔE≤1.5 is acceptable for general appearance parts, ΔE≤2.0 for structural parts. What matters more is batch-to-batch stability: seal a first-article standard and compare every batch against it. We normally deliver appearance-part masterbatch at ΔE≤1.0-1.5.
Four causes: pigment batch variation (same chemistry, different makers), carrier base-color drift, processing temperature and shear differences changing how the pigment develops, and dosing or mixing fluctuation. Countermeasures: lock pigment suppliers and formula, keep a retained standard for comparison, and fix the process parameter window.
Four indicators: TiO2 content (50% or more recommended for appearance parts), TiO2 type (rutile beats anatase in weatherability and hiding), whiteness and yellowness index, and dispersion grade (thin-wall parts need high dispersion). Outdoor parts must use rutile with a UV package; indoor low-cost parts can use medium-grade white.
Typical injection molding 1%-3%; high hiding demands (dark regrind base, high whiteness requirements) 3%-6%; film blowing 2%-5%. It depends on masterbatch concentration and part wall thickness: thin walls are hard to cover, so take the higher value. Determine the economical ratio by trial — do not apply one rule everywhere.
Typical black masterbatch runs 20%-45% carbon black. High-gloss, high-jetness parts (appliance panels) use high-color carbon black at 40%-50% concentration with 1%-2% letdown; ordinary structural parts use 25%-30% concentration at 2%-3% letdown. Carbon black punishes both poor dispersion (black specks) and insufficient concentration (grayish parts).
Check three things first: is the letdown sufficient, does the masterbatch's carbon black concentration meet spec, is dispersion complete. Escalation order: raise letdown by 0.5 points on trial → switch to higher concentration → check mixing uniformity and back pressure. Long-term fix: move to a higher-concentration, high-color black masterbatch.
Gray is one of the hardest colors: the white/black ratio is extremely sensitive to slight base-color shifts, and yellowish TiO2 makes it look dirty. The professional approach is matching software against Lab target values with fixed pigment grades, then locking the formula after the customer approves the first plaque. In production, never casually swap white or black masterbatch brands.
Fluorescent pigments have limited heat stability (mostly 220-260°C) and will decompose and discolor on high-temperature engineering plastics; migration resistance and lightfastness are also weaker than regular pigments, so outdoor parts fade. Key points: low temperature, large gates, fast injection, avoid residence; for outdoor use switch to high-lightfastness fluorescent systems or reduce fluorescent intensity.
Pearlescent pigments are mica platelets; excessive shear breaks the layers and kills the pearl effect. Points: enlarge gates and runners, lower screw speed and back pressure, avoid fine screen packs that block the platelets; in blown film the platelets orient and create a pearlescent flow pattern — a feature or a defect, depending on intent.
Metallic effects rely on aligned aluminum flakes. To improve brightness: use a high-gloss base resin, raise mold temperature, increase injection speed so flakes orient with the flow, avoid over-shearing the flakes, and polish the mold. Trial effect parts on your own mold first to confirm the look.
Night-glow masterbatch contains luminescent powder (strontium aluminate types); it needs a relatively high letdown (5%-15%) for visible afterglow, and the pellets are hard — watch screw wear. Make parts thicker (afterglow correlates with thickness), use a transparent or light base color, and avoid stacking with strongly hiding pigments.
Thermochromic masterbatch uses microencapsulated liquid crystals or leuco dyes that change structure and reveal or lose color across a set temperature range, commonly triggered at 15°C, 31°C, 44°C and similar points. The microcapsules fear strong shear; processing temperature is usually capped at 230°C, suiting low-temperature PP/PE products such as cups and bath toys.
Marble and wood grain use 'two masterbatches blended together' or dedicated pattern masterbatch: two masterbatches with distinct flow behavior and color are mixed at a ratio without full homogenization so the pattern streaks naturally. The key is controlling mixing time and screw shear — too uniform becomes a solid color, too little gives harsh blotches; set parameters by trial.
For transparent coloring choose dye-type or high-clarity organic pigment masterbatch; avoid TiO2 and inorganic pigments (they cloud the part). Heat stability and migration resistance must both fit; for food-contact parts confirm the dye complies with regulations. For haze-critical items (bottle caps, lamp covers), ask the supplier for transmittance data.
For outdoor parts avoid easily faded azo reds and yellows and fluorescent shades; prefer inorganic pigment systems (titanium yellow, iron oxide red, cobalt blue) or high-grade lightfast organic pigments (phthalocyanine blue and green, quinacridone red), plus a UV masterbatch (HALS + UV absorber) for double protection. Dark outdoor parts also need heat-absorption deformation checks.
Pigments for food contact must be listed in FDA 21 CFR or EU 10/2011 / GB 9685 and meet overall migration limits; vivid red, yellow and orange options are fewer than for industrial parts, and heavy metals and aromatic amines are restricted. Confirm 'food-grade use' in writing when purchasing; the supplier proposes a compliant scheme with reports.
Close to it: high-gloss base resin + high-dispersion black or colored masterbatch + high mold temperature and a polished tool. The keys are pigment dispersion grade and carrier cleanliness (few black specks). Compared with paint-free resin it lacks the mica and aluminum-flake effects, but for standard high-gloss parts the cost advantage is clear — trial first, then decide.
Three routes: matte masterbatch (with silica or talc types), in-mold texturing, or switching to a matte-grade resin. Matte masterbatch is flexible but affects melt flow and mechanics — use cautiously on thin-wall parts; for demanding appearance parts, in-mold texturing is the most stable option.
Streaks usually come from large melt-speed differences between masterbatch and base resin, uneven plasticization, or poor pigment dispersion. Fixes: switch to a same-family high-flow carrier masterbatch, raise screen mesh to force dispersion, moderately raise melt temperature and back pressure, and keep letdown within limits. Film should use film-dedicated masterbatch, not injection grades.
At weld lines the pigments converge and the color difference shows. Mitigation: raise melt and mold temperatures so the fronts merge well, improve venting, relocate the gate, and choose a well-dispersed lower-concentration masterbatch (high concentration accentuates local enrichment at the line). Evaluate weld-line positions together with the color scheme at the design stage.
Migration is pigment or additive moving from inside the part to the surface — seen as staining, fogging, or color that rubs off. Causes are usually small pigment molecules, poor resin compatibility, or the presence of plasticizer. Fixes: choose high-molecular-weight pigments, use dedicated carrier masterbatch, add anti-migration agents in soft PVC and similar systems, and verify by trial.
Four big causes: insufficient light and weather fastness (no lightfast system outdoors), insufficient heat stability (color already shifted during processing), oxidation (missing antioxidant package), and migration. First decide whether the part left the factory off-color or drifted in use: discoloration at processing → check heat stability; fading in use → check weatherability and the UV package.
Standard methods: press the part against white PVC or a light-colored plaque under heat and pressure and observe staining, or run migration tests per the GB/T cyclic standards. Outdoor and household parts should also be tested for lightfastness (xenon arc) and heat (elevated-temperature storage). Ask the supplier for the data — do not judge by looks alone.
The two materials must be compatible with matched shrinkage; each masterbatch feeds its own barrel. A typical pairing is rigid ABS + soft TPE overmolding, with TPE-dedicated masterbatch on the soft side. The second shot's processing temperature must not burn the first shot's already-colored part — select both masterbatches for the highest temperature involved.
Transparent masterbatch is designed for low haze (dye systems); at a normal 1%-2% letdown the effect on light transmission is very small. But accidentally using a masterbatch containing TiO2 or high filler will cloud the part instantly. For haze-sensitive parts (lamp covers, bottles) choose dye masterbatch and require haze data from the supplier.
When dark shades (bright red, deep blue, black) under-cover on light bases or regrind: raise the letdown, switch to higher concentration, or prime the base first (gray or white masterbatch to adjust the base color) and then apply the color. Often the most economical fix is moving the base color toward the target instead of endlessly deepening the top color.
Sequence: purge with a high-melt-index general purging compound (or regrind) → for dark-to-light changes add a little white masterbatch to help → light-to-dark can transition directly → black-white swaps waste the most material, so schedule them apart. For high-value transparent parts, dedicate a machine to light colors to cut purge losses.
Regular colors need 1-2 rounds: the first round gives 2-3 close ratios, then fine-tune and seal the standard in the second round. Effect colors (metallic, pearlescent, fluorescent) and strict-match key accounts may need 2-4 rounds. Providing a physical sample is much faster than a color number alone — it significantly lifts the first-round hit rate.
Send the part, the service conditions and your monthly volume — we will propose an equivalent grade, a sample and a quote.