The customer says the case is yellowish but I see nothing under D65.

Answer: Re-read under illuminant A at 2856 K and it usually reproduces. If A gives 1.7 while D65 gives 0.9, the 0.8 gap is a light offset, not a batch fault.

Why does a repeat batch three months later read ΔE 1.1?

Answer: Masterbatch lot, drying record and mould controller all move in three months. Re-weigh 3 batches for the 2% ratio, check the dryer log for 90 ℃ over 3 h, probe the mould. Each item adds 0.2 to 0.5, landing near 1.1.

The customer measures 2.3 under A. Replace straight away?

Answer: No. The line sits under D65, where 2.3 under A equals roughly 1.5. Only above 2.5 does a replacement order make sense.

How many retention samples, and for how long?

Answer: Three per batch, same batch number and colour code, kept 12 months. Three supports the 30-piece comparison and any later dispute.

Should concession terms go into the contract?

Answer: Yes, with judging light, ΔE band and credit method written down. A clause saying only that colour is negotiable leaves both sides without a rule at the next case colour complaint.

Case Colour Complaint: Batch and Light

Quick answer: Every case colour complaint starts with one question: under what light was the sample seen? The same colour code reads ΔE 1.1 under D65 and 1.9 under illuminant A, and that 0.8 gap alone can read as two colours.

Two routes behind a colour complaint
Batch side: masterbatch, drying and mould heat
Light side: colour temperature, angle and background
Thirty cases side by side and four pieces of evidence
Two decision lines: concession or replacement
FAQ

1. Two routes behind a colour complaint

Of 40 case colour complaint files opened in a year, 26 fell to ΔE 1.2 or below once the sample was re-read in a D65 booth at 45°, so the light was wrong, not the resin. The other 14 stayed above 1.2 and only then went back to masterbatch and drying.

Melt side reads ΔE, dosing ratio and moisture; light side reads colour temperature, illuminance and angle. Both can be measured, but only one is fixed by turning a screw on the machine.

Item	Melt side	Light side
Trigger	New masterbatch lot, 2 h stop	Sample seen in a shop or a car
Measured	ΔE, dosing ratio, moisture	K, lux, viewing angle
Typical	ΔE 1.6–2.8 under D65	0.8 gap, D65 versus A
First move	Re-dry 3 samples, mould again	Re-read at 45° in a booth

Split first, argue second. Reverse the order and a lighting fault becomes a formula fault: the masterbatch is changed, and the same complaint returns two months later.

The split has one criterion, the ΔE of the retention sample under D65. Below 1.2 the melt side closes; above it, three parameters get checked in sequence.

2. Batch side: masterbatch, drying and mould heat

A repeat batch made three months after the first, on the same colour code, reads ΔE 1.1 against the original under D65. The gap usually sits in one of three readings.

Case colour complaint sampling rack with white, dark grey, black and fluorescent green cases upright, blue and orange cases in the right bays

Masterbatch is dosed at 2%, so a 200 kg batch takes 4 kg. A scale error of 0.02 kg pulls the ratio to 1.99% for ΔE 0.2; a new masterbatch lot on another carrier adds 0.3 at the same 2%.

Drying runs 90 ℃ for 3 h and takes moisture from 0.12% to 0.03%. Skip those hours and the melt carries water, the surface turns hazy white and ΔE jumps 0.4, which reads as a paler colour when it is surface scatter.

Mould temperature of 55 ℃ drifting ±3 ℃ shifts skin crystallinity for another 0.3. This is the hardest to see, because an uncalibrated controller still shows 55 and only a contact probe on the cavity reveals the offset.

Parameter	Set point	Drift	ΔE	Check
Masterbatch ratio	2%	−0.01%	0.2	Re-weigh 3 batches
Drying	90 ℃ / 3 h	2 h short	0.4	Dryer log
Mould temperature	55 ℃	+3 ℃	0.3	Contact probe
Melt residence	≤ 4 min	20 min stop	0.5	Production log

The first three add up to about 1.1 while no single item reaches the replacement line. That is why a batch-type case colour complaint drags: each deviation is small enough to explain away and together they cross the line.

3. Light side: colour temperature, angle and background

One case reads ΔE 0.9 under D65 at 6500 K and 1.7 under illuminant A at 2856 K. Nothing changed in the part: warm light lifts reflectance in the yellow-green band and the case looks half a step yellow.

Shops run 3000 K to 4000 K spotlights and warehouses run tubes near 5000 K, so one pallet is judged as two colours an hour apart.

Angle is fixed at 45° from 300 mm at 1000 lx. Rotate to a straight 90° view and surface brightness rises, pale cases look whiter, dark cases look blacker.

Background joins in. The same mid-grey case looks dark on white paper at L\* 95 and returns to its own colour on neutral grey at L\* 60, a visible half step. An 18% grey card on the table removes half the argument.

One more case sits behind the light: glass. A dark grey case reads yellow through a car window and normal outdoors, so no formula change, only a second look.

None of this alters a molecule of the case, yet any of it makes a complaint valid or void. So the second move on a case colour complaint is to reproduce the customer's light, not his formula.

4. Thirty cases side by side and four pieces of evidence

One case against another proves only that they differ; 30 cases prove a distribution. Draw 30 from one batch: ΔE spreads from 0.3 to 0.9 under D65, and from 0.6 to 2.3 under A, where 7 of the 30 cross 1.2.

Case colour complaint retention shelf holding orange, olive and sand cases above stacked red, purple and teal boxes, blue and orange shells in front

Those 7 all pass under D65, so the batch never drifted; the viewing condition pushed the edge of the spread over the line. Plot the spread and the complaint is settled.

Evidence comes in four parts: light source and colour temperature, written as D65 at 6500 K; angle and distance, 45° and 300 mm; retention samples, 3 from the same batch and colour code; batch number with production date.

Drop any one and the case colour complaint collapses into a description neither side can settle. The missing light is the usual gap: the photo shows a case, not a lamp.

A table of 30 readings beats 10 photographs: two phones disagree by 300 K on one case, a booth does not.

5. Two decision lines: concession or replacement

ΔE 1.2 is the acceptance line, 2.5 the tolerable ceiling, and concession lives between them.

ΔE under D65	Over line, of 30	Action	Paperwork
≤ 1.2	0	Release	D65 re-read record
1.2–1.8	≤ 3	Concession, credit per case	Note naming the light
1.8–2.5	≤ 8	Concession plus batch fix	Plan with retest date
> 2.5	Any	Full replacement	Replacement note, root cause

Both lines sit under D65 because D65 is the one condition both sides reproduce. A reading under A is reference only, like measuring length with an uncalibrated rule.

When the customer reads 2.3 under A and the booth shows 0.9 under D65, post an 18% grey card and a colour chip for a second look under his own lamp, not a replacement order.

A concession note must name the light and the sample count. One sentence saying the colour is acceptable brings the batch back on the same argument, and the case colour complaint loops.

Conclusion

Four pieces of evidence settle a case colour complaint: light source and colour temperature, 45° at 300 mm, three retention samples from the same batch, and the batch number with its date. Then run two lines. Below ΔE 1.2 under D65 the batch is released and the 6500 K reading goes out with a suggestion to move shop spotlights above 4000 K. Between 1.2 and 2.5 it ships on a written concession with credit per case and the judging light named. Above 2.5 the batch is replaced. If only A crosses while D65 passes, re-read under D65 and hold the order, because in the batch where 7 of 30 failed under A, all 30 passed under D65. Print those four conditions and two lines on one sheet at the sample table, and fill it in before anyone touches the masterbatch.

This article discusses container-side specifications and design implications only, and does not cover any handling, loading or use of the contents.