A carrier resin is the polymer a pigment or additive is compounded into so it can be dosed as a pellet — the base polymer of a masterbatch. Here “resin” means a thermoplastic pellet, so this is a different thing from the casting or epoxy resin of the craft trade, and from the base polymer of a purging compound, which a few suppliers also call a carrier.
What the Carrier Resin Does in a Masterbatch
In a masterbatch the carrier is the medium the pigment or additive is dispersed into during compounding, and the vehicle that delivers that dispersion into your melt unchanged.
The carrier also puts the additive into a form a converter can handle. Compounded and pelletised, a pigment that would otherwise arrive as dust meters accurately on automatic dosing equipment or pre-blends with the base resin without segregating, and it stays protected through the concentrate’s own heat history until it is let down.
How Much Carrier Resin Ends Up in the Part
The carrier ends up as roughly half a percent to six percent of the finished part, depending on how heavily the concentrate is loaded and how much of it you add.
Loading sets the first half. A conventional black concentrate carries 25–40 % carbon black and a high-load black up to 55 %, while a high-concentration black or white concentrate is specified at 30–50 % carbon black or 50–70 % titanium dioxide. So the carrier is about half of an ordinary black and can fall to a third of a heavily loaded white.
The addition rate sets the second half, and it follows what the additive has to do in the application rather than a single house figure: 1–3 % concentrate in injection moulding, 4–10 % in film, 6.25 % where a black is doing maximum UV protection. Multiply the two and a commercial black leaves roughly 0.6–1.8 % carrier in a moulded part and 2.4–6 % in blown film.
Which Polymers Are Used as Carrier Resins
The carrier normally comes from the same polymer family as the base resin, so the commodity polymers do most of the work — polyethylene above all, then polypropylene and the styrenics, with engineering-resin carriers sold for the bases that need them.
| Carrier | Base polymers it serves | Note |
|---|---|---|
| LDPE / LLDPE | PE film and moulding, HDPE, most PP | The default polyolefin carrier; melts at 104–110 °C, well below any PP base |
| HDPE | HDPE film, pipe and moulding | Chosen where the concentrate is heavily loaded and the base is a pipe or pressure grade |
| PP homopolymer, random or block | PP fibre, film and injection moulding | Matched to the base’s own grade family |
| SAN, or ABS itself | ABS | SAN is the continuous phase of ABS |
| PS | PS and HIPS | Same-family carrier; no substitute for SAN in an ABS base |
| PA6 or another lower-melting nylon | PA66, filled and unfilled nylons | PA6 melts at 220 °C against PA66’s 260 °C |
| PET | Polyester fibre and film | Specified on intrinsic viscosity rather than melt flow |
| PBT or PC | PC/PBT blends | Either component of the blend can carry the concentrate |
| EVA or wax | Sold as a universal carrier | Low melting; acceptable in polyolefins, not in engineering resins |
What Properties a Carrier Resin Needs
A carrier grade has to flow more freely than the base resin so the concentrate softens first and spreads, survive two heat histories, wet pigment at high loading, and bring as little of its own additive package as possible.
Flow only compares when the two figures were measured the same way. A PE carrier is quoted at 190 °C and 2.16 kg, a PP base at 230 °C and 2.16 kg, and a nylon on melt volume rate at 275 °C and 5 kg — three numbers sharing a unit and nothing else. ISO 1133 and ASTM D1238 cover the same test but differ in technical content, so the standard belongs in the comparison alongside temperature and load.
Producers sell carrier grades on filler acceptance above 80 %. The carrier must bring no stabiliser chemistry of its own, which is why carrier grades are offered with a deliberately low anti-oxidant package or unstabilised in powder form.
Dispersion itself is specifiable: the filter pressure value test of ISO 23900-5 is the acceptance figure to name on an enquiry.
Why the Carrier Resin Must Match the Base Polymer
Because the carrier stays in the part: a polymer that does not mix with the base resin remains a separate phase with high interfacial tension at the boundary, which coarsens the structure and costs mechanical properties.
The rule has named exceptions, and there are few of them. SAN carries an ABS concentrate. A lower-melting nylon works in a higher-melting one, PA6 into PA66. In a blend such as PC/PBT, a concentrate based on either component works. LDPE and LLDPE carriers are accepted in HDPE and usually in polypropylene, with living hinges as the known trap.
Universal Carrier Resins
A universal carrier is a low-melting ethylene polymer, usually EVA or LDPE, or a wax, sold with a datasheet that lists every polymer family and never names the carrier itself.
Within the polyolefins the claim largely holds. A polyolefin base tolerates a few percent of another ethylene polymer.
Outside the polyolefins it fails on temperature alone. EVA’s producer puts the degradation ceiling at 240 °C for an 18 % vinyl acetate grade and 220 °C for a 27 % one, and those grades melt at 83 °C and 72 °C. PA6 does not melt until 220 °C and is moulded at 250–270 °C, so an EVA-carried concentrate spends its whole residence time above the ceiling its own producer set.
What Goes Wrong With the Wrong Carrier
A carrier mismatch usually presents as a processing problem and gets blamed on the machine or on a bad lot of base resin. Colour streaks and patchy dispersion are the mild version.
In one documented case, a grey concentrate on an EVA carrier went into a PC/PBT part with a long, thin core. The part distorted, cycle time went from 32 to 51 seconds, and a concentrate rebuilt on a PBT carrier brought it back to 32.
In another, an LDPE-carried universal was added to a polycarbonate with an MFR of 10 g/10 min and the moulded parts came out at 30–40 g/10 min. The same tool running natural resin gave only a 20–25 % rise.
How to Check Which Carrier Resin Your Masterbatch Uses
Ask, and get the answer on paper. The carrier polymer is a line you can require on the technical datasheet, have restated on the certificate of analysis for the lot you receive, and write into the purchase order.
When a datasheet claims compatibility with every polymer family and names no carrier, that carrier is an ethylene polymer or a wax. Query “suitable for all polymers” before the order rather than after the first moulding trial.
When the concentrate is contract-made to your recipe, the carrier is your specification and not the compounder’s default.
When the paperwork stays silent, a lab settles it quickly: a DSC scan puts a melting point on the carrier, and infrared identifies the polymer where the melting point alone is ambiguous.