Chrome Oxide Green for Plastics and Construction: Heat-Stable Colour
In plastics and construction, a colourant earns its place only if it survives processing first. Chrome oxide green does more than survive — it sails through temperatures that vaporise organic pigments.
Heat stability that matches processing
The colour-card value of 982 °C (HDPE, DIN EN 12877-2) means the pigment is essentially unaffected by any thermoplastic processing window. Injection moulding, extrusion, rotomoulding — the green that goes in is the green that comes out, batch after batch.
No migration, no warping
Migration resistance is rated 5 (DIN 14469-4) and the warpage rating in plastics is 1 — the best class. Unlike organic pigments that plasticise the melt and distort crystallisation, Cr₂O₃ particles sit inert in the matrix: dimensional stability and food-packaging-safe colour behaviour come free.
Outdoor structures built to fade nothing
For cement, tiles, roof elements and façade panels the decisive property is the same lightfastness 8/8 that protects coatings: thirty years of sun, rain and frost without visible colour shift. Specify GREEN 1000 for vivid emerald tones or GREEN 1002 for deep blue-shade greens.
CONTINUE READING
Processing windows by polymer
| Polymer | Processing temp | PG17 fit | Note |
|---|---|---|---|
| PE / PP | 180–230 °C | Excellent | Standard grade, no degradation |
| PVC | 170–200 °C | Excellent | Alkali-stable, no HCl interaction |
| ABS / PC | 230–280 °C | Excellent | Micronized for tinting strength |
| PA (nylon) | 260–290 °C | Excellent | Stable well above melt temperature |
| Fluoropolymers | 300+ °C | Excellent | The only green that survives |
HDPE pipe colour that survives the barrel and the trench
An HDPE pipe is the longest-lived colour job in the plastics industry. Sewer pipes are extruded at 190–230 °C, butt-welded on site at 200–220 °C, stored in open yards under full sun, and then buried for fifty to a hundred years. The green on that pipe is not decoration — it is identification. Colour coding is how a gas line is not mistaken for a sewer line, how a water main is found again in a trench full of conduits, and how an inspector accepts an installation at a glance. A green pipe that fades to grey before installation is not a cosmetic failure; it is a product that has lost its specification, and it gets rejected on that ground alone. The same pigment must therefore survive three very different environments: the heat of the barrel and the weld zone, the UV of the storage yard, and the wet soil chemistry of the service life. That is a three-part specification, and there is exactly one green that passes all three parts.
Chromium oxide green passes them for one structural reason — the colour is the crystal, not a coating on it. In the barrel, thermal stability to 982 °C means the weld zone's brief 220 °C spike is irrelevant, and weld lines come out the same green as the pipe body instead of showing the bleached rings that organic greens leave. In the yard, Cr₂O₃ is UV-opaque: it absorbs the ultraviolet that would otherwise attack the polyethylene surface beneath it, so the pigmented layer doubles as a weathering skin. In the trench, the pigment is insoluble — groundwater, soil acids, and the sulphide chemistry of buried service can do nothing to a material that does not dissolve in them. Pipe makers who run green sewer pipe on chromium oxide learn the practical version of this within a season: no field complaints about patchy colour, no storage-yard rejects after a hot summer, and no rework of weld zones. At 0.5–1.5 % loading, the pigment costs a fraction of the pipe's resin bill and carries the entire identification function of the product for its full service life.
The 10-year garden furniture warranty, priced in grams
Garden furniture is the most honest warranty market in plastics, because the number is written on the box: ten years against UV degradation, in full sun, outdoors. The arithmetic behind that warranty deserves to be run in public. A polypropylene chair weighs about 2.5 kg; at 1.5–2.5 % pigment loading it carries 40–60 grams of green pigment, which at current prices is roughly US$0.30–0.60 per chair. The entire ten-year fade warranty rests on that. When the pigment fails, the cost of the claim is not the pigment — it is a replacement chair, freight in both directions, disposal of the failed unit, and the customer who buys a different brand next time. A single claim costs more than the pigment of hundreds of chairs. Viewed from the warranty department, the green pigment is the cheapest insurance policy in the product: half a dollar of chromium oxide underwriting a ten-year promise that organic greens routinely break inside three summers.
The test that the furniture industry actually uses is xenon-arc exposure to ISO 4892-2, typically 3,000–5,000 hours, and the acceptance criterion is a ΔE number, not a photograph. Organic greens land at ΔE 8–15 after the equivalent of a few summers outdoors; chromium oxide lands below 3 after the equivalent of more than a decade, because there is no chromophore for the xenon lamp to break. There is a second effect that matters as much as the colour itself: UV stabilizers protect the polymer, not the pigment. A green that absorbs UV itself — as Cr₂O₃ does — protects the polymer skin beneath it, so the chair keeps its gloss and surface integrity longer where it is green. The warranty on a garden chair is a contract written in grams of pigment. The maker who writes that contract on chromium oxide is pricing a promise it can actually keep; the maker who writes it on an organic green is pricing one it cannot, and the market finds out in summer three. Run the same arithmetic for a decking plank carrying a 15-year warranty and the conclusion only gets stronger: across the whole garden-products range, the pigment line item remains the cheapest promise the maker will ever write, and the one with no co-signer.
Why organic greens die young in polymers
The failure of organic greens in long-life plastics is chemistry, not bad luck. An organic pigment is a molecule whose colour depends on a conjugated chromophore; ultraviolet light supplies exactly the energy that chromophore absorbs, and the absorbed energy breaks the molecule's bonds. The pigment literally photocleaves — the green bleaches, or shifts to a dirty yellow-brown as degradation products accumulate. In polymers the exposure is multiplied, because the pigment is distributed through the surface layers of the product and every granule is a tiny solar panel aimed at the sun. Heat adds a second front: at the processing temperatures of engineering resins — 260–320 °C for polyamide, 300–380 °C for fluoropolymers — organic chromophores decompose in the barrel itself, off-gassing, discolouring, and depositing on tooling. The plastics industry's workaround is to load more stabilizer and hope; the honest workaround is to use a pigment that has no chromophore to break.
Migration is the third failure and the one buyers forget to test. Organic pigments dissolve slightly in molten polymers and re-crystallise at the surface on cooling, blooming out as a haze or transferring colour to whatever the product touches — the hands that carry the chair, the packaging film, the PVC layer behind the profile. Food-contact regulations make migration a compliance issue, not just a cosmetic one. Chromium oxide green has none of these failure modes: the colour lives in the lattice, the lattice is stable past 1,000 °C in inert conditions, and the pigment is insoluble in the polymer — it stays where the compounder put it, at the loading the compounder specified. Lightfastness 8/8 and weatherfastness 5/5 are the industry shorthand for that. When a buyer asks why the green that "looks the same" in the colour chip costs more, the answer is the chip's blind spot: a chip shows only day one. The first two summers of the two pigments are identical. The warranty is decided in summers three through ten, and only one pigment shows up for that fight with its colour intact.
Pigment specification by polymer family
| Polymer / application | Processing window | Where other greens fail | DELIKECOLORS grade |
|---|---|---|---|
| HDPE sewer & duct pipe | 190–230 °C | Weld-zone bleaching, storage-yard UV fade | GREEN 1000 / 1001 |
| PP garden furniture | 220–260 °C | 10-year outdoor UV warranty exposure | GREEN 1020 / 1025 |
| PVC building profiles | 170–210 °C | Alkali contact, re-grind heat history | GREEN 1002 / 1061 |
| PA / engineering resins | 260–320 °C | Organics decompose in the barrel | GREEN 1062 / 1071 |
| Fluoropolymers / high-temp parts | 300–380 °C | Only inorganic pigments survive | GREEN 1072 / 1073 |
Furniture makers insure a ten-year UV warranty with less than a euro of pigment per unit, and the market still shops that line item as if it were trivial. The numbers: 40–60 grams of chromium oxide green per chair, US$0.30–0.60 of pigment, against a claim that costs the retail price twice over once freight and disposal are counted. Every other supplier in that chair — the resin producer, the stabilizer house, the mould maker — has an OEM partner to share blame with when the product fails. The pigment is the one component where the maker carries the warranty alone, which is why it is also the one component where cheaping out is mathematically indefensible. Buyers keep asking for the cheapest green that "looks the same"; the honest answer is that the first two summers look identical and the warranty is decided in summers three through ten. Our furniture grades ship with lightfastness 8/8 and weatherfastness 5/5 on the certificate of analysis, and we recommend xenon-arc 5,000 hours as the acceptance test — because a colour chip is a photograph of day one, and a warranty is a promise about year ten. The two documents should be written with different inks.
FAQ
What loading gives full opacity in HDPE? Green pipe reaches full identification colour at 0.5–1.5 % pigment by weight; deep furniture tones run 1.5–2.5 %. Micronized grades reach hiding at the bottom of the range, which matters where every gram counts in the part cost.
Does chromium oxide green wear out screws and barrels? Cr₂O₃ is a hard mineral, but at 0.5–2.5 % loading the abrasion contribution is negligible next to glass fibre or mineral fillers. Micronized grades at D50 ≤0.5 μm minimise mechanical wear further and pass fine screen packs.
Can it be used with recycled resin? Yes — better than most pigments. Chromium oxide survives repeated heat histories without colour drift or decomposition by-products, so regrind and PCR streams stay on-colour, and the 982 °C stability means nothing degrades in the barrel.
Is it suitable for food-contact layers? Chromium oxide green does not migrate — it is insoluble in the polymer — which is the key requirement for regulated applications. For food-contact use, specify micronized grades with Cr(VI) ND and request the compliance data with the lot.
Will colour vary between batches? DELIKECOLORS production is released against reference standards with lot-to-lot ΔE ≤1.0 printed on the certificate. For a ten-year warranty product, that consistency is the difference between a matched reorder and a mismatched one — ask for the certificate, not just the sample bag.