OEM Color Matching: Aging Drift and Delta-E Tolerances

A brand approved a warm sand finish for a new diffuser line. The first two molding orders matched the master swatch. By the third order, the same part number looked visibly greyer on the shelf. No one had changed the pigmentation; the resin lot and the process had drifted. This note explains how to lock colour so it survives shipping and aging.

Why do molded parts not match the approved master after a few months?

Colour drifts through three paths: different resin lots with slightly different base tint, process changes such as barrel temperature and residence time, and post-mold effects such as heat aging and UV exposure. Any one can move the part away from the master that was approved on a warm afternoon in a design studio.

Storage conditions matter too. Parts kept near a hot window or in a warm container can shift before they are ever assembled, so the shelf colour is not the molding colour. The master itself must be protected and re-checked on a schedule.

What is delta-E and which tolerance applies?

Delta-E is a numeric distance between two colours in a standard colour space, so a smaller number means a closer match. It is calculated from instrumented measurements following a defined method, such as that described in ASTM D2244 practice. A single number is only meaningful with the illuminant, the instrument, and the measurement geometry stated.

Tolerance depends on the surface. Small cosmetic parts often hold tighter limits than large housings, and textured surfaces read differently from gloss. Industry practice sets the tolerance by how close two parts sit in use, not by one number for the whole product.

Which resins shift colour most under UV and heat?

Light or pastel colours and unfilled or lightly filled resins tend to shift most, because a small change in the base reads as a large visual move. Warm whites and beiges are especially sensitive. Stabilizer packages and pigment carriers strongly affect how fast the drift appears.

Dark and saturated colours hide more, but they fade differently over time. Where two materials must match in one product, for example a plastic housing and a membrane, each pair should be verified together rather than independently.

How do we set a colour standard that survives production?

Freeze a physical master and a numeric target, define the illuminant and instrument, and require each lot to be measured against both. Add an aging check, such as oven or light exposure under a stated method, so slow drift is caught before the shelf. Keep the master in controlled storage and retire it on a set interval.

Record the resin lot with the colour reading so drift can be traced. If a lot fails, the record shows whether the resin or the process moved. Without that link, colour disputes turn into guesswork.

What do we write into the RFQ to lock colour?

State the resin grade, the pigment system, the numeric target, the delta-E limit, the measurement conditions, and the required aging check. Require a retention sample per lot. Then name the response if a lot falls outside the limit, so both sides know the consequence before the press runs.

Prepared by 燕七.