Introduction
Choosing masterbatch for recycled PS or HIPS is not simply a matter of selecting a colour chip. The colour concentrate must work with the base polymer, processing temperature, mixing equipment, part geometry, surface requirement and normal colour variation of the recycled resin. A colour that looks correct in a laboratory plaque can still create streaks, deposits, weak weld lines or inconsistent production when transferred to a profile or moulded component.
The best starting rule is: use a carrier system compatible with the recycled PS/HIPS base, define colour on a moulded or extruded reference, and validate dosage through a controlled production trial. Do not copy a dosage from another polymer or assume that a higher addition rate always improves coverage.
Cherein offers masterbatch options coordinated with recycled PS and HIPS processing systems. Customer requirements normally include the base resin, target colour, process, surface, expected outdoor or indoor use and order volume. A useful sample plan then evaluates both appearance and processing performance.
This guide explains how buyers and processors should prepare colour information, compare masterbatch options, run a factory test and establish a repeatable incoming and production control plan.
Quick Answer: What Masterbatch Works With Recycled PS and HIPS?
A suitable masterbatch uses a carrier and additive package that disperse in the intended PS or HIPS process without causing unacceptable flow, surface, odour or mechanical changes. The supplier should match the colour against the actual recycled base resin because its undertone and lot variation affect the final shade. Final dosage must be confirmed on the customer’s equipment and product.
Why Recycled Base Resin Changes the Colour-Matching Task
Virgin resin colour is often relatively stable. Recycled PS and HIPS can carry a natural, grey, cream or mixed undertone depending on feedstock and processing. Even within an approved grade, small changes in base colour can shift a pastel, white or bright finished shade.
Base colour contributes to the final colour
Masterbatch does not sit on top of the resin like paint. Pigment and carrier become part of the melt, so the base resin affects hue, brightness and coverage. A blue masterbatch used in a warm cream base may look different from the same dosage in a cool white base. A transparent or low-opacity colour can reveal more lot variation than a high-coverage black.
When requesting a match, send the masterbatch supplier a representative sample of the real recycled resin. If the base grade has an agreed colour range, include samples near both ends of that range. Matching against an unrelated virgin resin creates a laboratory result that may not transfer to production.
Process history changes visual appearance
Residence time, melt temperature, shear, drying or storage condition and regrind proportion can influence colour and gloss. A formulation that survives a short plaque test may shift during a long profile run. The production trial therefore needs enough duration to reveal heat history, plate-out and colour drift.
Surface geometry changes perception
Glossy flat plaques make colour easy to measure, but the final product may be textured, ribbed, foamed, printed, laminated or coated. Evaluate both a standard plaque and the actual product surface. For picture-frame mouldings or decorative profiles, check how the shade looks after hot stamping, wrapping, coating, cutting and installation preparation.
The Five Selection Factors
1. Carrier compatibility
The carrier helps deliver and distribute pigment through the polymer melt. If it is poorly matched to the base resin or process, the result may include weak dispersion, streaks, surface defects, deposits or reduced properties. Ask the supplier to identify the intended polymer family and processing route without relying on a vague “universal” label.
For recycled PS and HIPS, confirm compatibility with the exact grade and whether the application is injection moulding, solid profile extrusion, foamed profile extrusion or compounding. HIPS contains a rubber-modified phase, while general-purpose or recycled PS routes may respond differently. A masterbatch should be evaluated in the material it will actually colour.
2. Pigment and additive suitability
The pigment system must tolerate the processing temperature and intended service environment. Indoor decorative trim, appliance housings and outdoor building profiles can require different light, heat and weathering performance. Regulatory requirements also depend on application and destination market.
Do not assume that a colour is food-contact, toy, electrical or outdoor approved because it is available in pellet form. Ask for application-relevant documentation and have the finished article reviewed against the buyer’s compliance obligations.
3. Coverage and colour strength
Colour strength determines how efficiently a masterbatch reaches the target shade, but stronger is not always better. High pigment loading can reduce the required addition rate, while dispersion and metering become more sensitive. Lower-strength material may be easier to dose on basic equipment but increases the amount of carrier entering the formulation.
Compare candidates at several controlled dosages using the same base resin and process. Record actual weights rather than relying on scoop volume. The correct result is the lowest practical dosage that consistently meets the approved colour and performance requirements, not the lowest number printed on a quotation.
4. Dispersion
Good dispersion means pigment is distributed sufficiently and consistently for the intended product. Poor dispersion can appear as streaks, agglomerates, specks, pressure changes, screen blockage or weak colour areas. ISO 23900 describes methods for assessing dispersion and dispersibility of pigments in plastics; the appropriate method depends on the polymer, form and purpose of the comparison.
For routine factory evaluation, inspect plaques or profiles under controlled light, cut sections where useful and monitor screen pressure or deposits during the run. If the application has strict requirements, agree a defined laboratory method with the supplier. Results should be compared under the same preparation and detection conditions.
5. Effect on processing and properties
Masterbatch changes the formulation. Its carrier, pigment and additives can affect flow, shrinkage, gloss, impact response, stiffness, odour and thermal behaviour. A colour approval without a process and product check is incomplete.
Measure the properties that matter for the part. For injection moulding, record pressure, cycle, part weight, dimensions and assembly. For extrusion, monitor output, die pressure, motor load, surface, dimensions and cutting. If impact is critical, test coloured finished parts rather than assuming the natural resin result still applies.
How to Write a Useful Colour-Matching Brief
Send the supplier enough information to reproduce the requirement:
- Actual recycled PS or HIPS base resin and lot identification;
- Application and processing method;
- Approved physical colour sample or quantified colour target;
- Surface texture, gloss and opacity expectation;
- Existing masterbatch, dosage and known production issues;
- Processing-temperature window and expected residence time;
- Indoor or outdoor service and expected lifetime;
- Applicable restricted-substance, customer or market requirements;
- Monthly production volume, trial quantity and packaging preference.
Photographs can help explain the product but should not be the only colour reference. Send a physical sample where colour accuracy matters. If a customer requires a colour difference tolerance, agree the instrument, illuminant, observer condition, measurement area and sample preparation.
Building a Dosage Trial
Use a dosage ladder
Begin with the supplier’s recommended starting point, then test at least one controlled step below and above where practical. The exact values depend on colour strength, base undertone, equipment and product. Avoid publishing or adopting one universal percentage for every masterbatch.
Prepare enough mixture for the process to stabilize. Use a gravimetric feeder where available. If manual pre-mixing is used for a sample, document the method because hand mixing can make a small trial look better or worse than normal production.
Keep the base resin constant
Use one representative base-resin lot during initial comparison. Changing both resin and masterbatch at the same time makes the cause of colour variation unclear. After selecting a candidate, repeat the trial with additional approved base-resin lots to test robustness.
Separate start-up pieces
Colour from the previous run may remain in the screw, barrel, die or hot runner. Purge with a documented method and separate transition material. Evaluate parts only after the colour and process have stabilized.
Record more than colour
For every dosage, record:
- Actual base and masterbatch weight;
- Machine, screw and feeding method;
- Temperature and speed settings;
- Output, pressure or cycle response;
- Colour reading or visual approval result;
- Gloss, streaks, specks and surface defects;
- Deposits, filter pressure or cleaning observations;
- Part weight, critical dimensions and relevant mechanical checks.
The trial sheet becomes the foundation for a production specification and future complaint investigation.
Factory Testing for Injection Moulding
Injection-moulded colour plaques are useful for first comparison, but a real component adds wall-thickness changes, weld lines, gates and texture. Run the candidate in the actual mould where possible.
Inspect colour near the gate and at the end of fill. Look for flow lines, streaks, gloss changes and pigment concentration around weld lines. Compare multiple cavities if the tool has more than one. If colour differs by cavity, investigate mould balance and processing before blaming the masterbatch.
Check impact-sensitive features after colouring. Some pigments and carriers can affect performance or make existing moulding stress more visible. Assemble the part, test clips and bosses, and compare to the uncoloured control under the same conditions.
Factory Testing for Profile Extrusion
Profile extrusion needs a longer observation window. Record colour at start-up, after stabilization and later in the run. Watch for die lines, streaks, plate-out, pressure increase and screen changes.
For picture-frame or decorative profiles, inspect the product after downstream operations. Hot stamping, film lamination, printing, cutting, mitre joining and installation preparation can reveal poor adhesion, colour show-through or edge chipping. The masterbatch is one part of a complete profile formula, so approve the finished decorated profile rather than only the base extrusion.
If the line uses a blowing agent or foaming route, verify that the masterbatch does not create unacceptable cell, density or surface changes. Results from solid PS cannot automatically be transferred to a foamed profile.
Colour Approval and Batch Control
Establish three references
Keep an approved masterbatch sample, an approved base-resin sample and an approved finished plaque or part. This separates questions about concentrate colour, base variation and production output.
Define what the COA should cover
The useful COA fields depend on the product and agreement. They may include identification, appearance, colour result against an agreed method, moisture or other relevant controls. The COA should connect to the lot on the bags and the retained sample.
Inspect incoming material
At receipt, verify product and lot labels, packaging integrity, quantity, pellet appearance and documents. Keep masterbatch sealed, dry and protected from contamination. Follow the current handling guidance rather than a generic drying condition.
Control change
Ask the supplier to communicate changes that could affect colour or processing, including pigment route, carrier, formulation, manufacturing location or key raw-material source. A formally agreed change-control expectation reduces surprise during repeat orders.
Troubleshooting Common Problems
Colour is correct in the plaque but wrong in the product
Check surface texture, wall thickness, base-resin lot, gloss, processing temperature and residence time. Reproduce the actual product condition during colour approval.
Streaks appear during extrusion
Review pre-mixing, feeder stability, carrier compatibility, melt temperature, screw mixing and dispersion. Inspect whether streaks contain pigment agglomerates or degraded material. Increasing dosage may make the defect worse.
Colour drifts during a long run
Check dosing consistency, hopper segregation, base-resin change, heat history and deposits. Compare retained samples from the beginning and end of the run.
Deposits build on the die or mould
Examine the additive and pigment package, temperature, residence time, venting and interaction with the full formulation. Record the time to deposit formation so candidate systems can be compared fairly.
The coloured part becomes brittle
Confirm actual dosage, carrier compatibility, contamination and processing condition. Test the finished part against the uncoloured control. Do not assume the masterbatch is the only cause until the base lot and moulding history are reviewed.
Commercial Questions for a Masterbatch Supplier
- Is the proposed carrier intended for this recycled PS or HIPS grade and process?
- Was the colour matched using our actual base resin?
- What starting dosage and trial ladder do you recommend?
- What colour and dispersion checks are available?
- Which application or market limitations should the buyer review?
- Can you retain a sample and reproduce the approved shade for repeat orders?
- What minimum order, lead time, packaging and lot size apply?
- How will formulation or raw-material changes be communicated?
Price per kilogram should be converted to colour cost per tonne of finished compound and then checked against reject rate, cleaning, downtime and appearance acceptance. A concentrated product can cost more per kilogram and still be more economical if it produces stable colour at a lower controlled dosage.
Conclusion
The right masterbatch for recycled PS and HIPS combines carrier compatibility, sufficient colour strength, reliable dispersion and acceptable effects on processing and finished-part performance. Match with the real recycled base, approve a physical reference, test a dosage ladder and extend the trial long enough to reveal deposits and colour drift.
Colour control is a system: base resin, masterbatch, dosing, machine, tool, surface and inspection condition all matter. A supplier that understands those connections can help reduce trial cycles and repeat-order risk.
Ask for a PS/HIPS Colour Trial
Send Cherein your base-resin sample, target colour or physical part, application, process, surface requirement and estimated demand. We can discuss a compatible masterbatch sample and a practical trial plan for recycled PS or HIPS.
Frequently Asked Questions
Can one universal masterbatch colour both PS and HIPS?
Sometimes a product may be marketed for broad use, but compatibility and performance still need to be verified in the exact PS or HIPS grade and process. Carrier, pigment, dosage and additives can behave differently across formulations.
What masterbatch dosage should I use?
Use the supplier’s grade-specific starting recommendation and validate a controlled dosage ladder. There is no universal percentage because pigment strength, base colour, opacity, equipment and product thickness differ.
Why does recycled resin need a new colour match?
The recycled base has its own undertone and normal lot range. A masterbatch matched in virgin resin may produce a different hue, brightness or coverage in recycled PS or HIPS.
How should colour be approved?
Use a physical plaque or finished product made from the proposed base resin and process. Where a numeric tolerance is required, agree the instrument, viewing condition, sample preparation and acceptance rule.
Can masterbatch reduce impact strength?
Any formulation change can affect finished properties. The effect depends on carrier, pigment, additives, dosage and processing. Test coloured finished parts against the agreed control when impact performance matters.