0 Series Tool Case: Available Colours
Line up five or six colourways of one case under the same light and the difference is not only cosmetic. Colour works as a management device on this class of product: which colour belongs to which product line, which batch of compound, which customer, all readable at a glance and harder to lose than a paper label. The cost lands in moulding: let-down ratio, purge time, batch variation and heat build-up in dark shades. All four are cheaper to settle before the tool is cut, and none of them shows in a photograph.
01Compounded Colour Versus a Painted Film
Masterbatch is colour ground into pellets, blended with natural resin at 1% to 3% and moulded straight through. The colour lives in the material, so a scrape exposes the same shade underneath. Paint is a film laid over a finished part, usually 30 μm to 60 μm thick, holding the colour at the surface only; a knock goes through it, and edges wear first.
The split shows up later. A painted part can be sanded and repainted; a compounded one cannot, because the colour is in the resin and a touch-up will always read as a patch. Compounded parts pay elsewhere: leave more than 1% of the previous colour in the barrel and it streaks through the next dark run. Weld lines also show, once they pass 0.02 mm deep.
02Colour as a SKU Marker on the Line
Run three variants of one case down a single line and the shells look identical while the interiors differ. The predictable mistake is a lid on the wrong base. Tie colour to variant and an assembler does not need to read a label, only to look. On mixed-model production that saves more rework than an extra tool would cost, and it is faster than adding a scan step.
Two rules keep colour coding honest. Shades inside one family need enough separation to be told apart at 3 m under shop lighting. And variation must not be left to the batch: each colour gets an archived chip with its code and a permitted ΔE00 ceiling, and incoming resin is checked against that chip rather than against the last delivery.
03Batch Difference: 1.5 ΔE00 as the Inner Line
Colour difference is expressed as ΔE, smaller meaning closer. The eye starts to notice around ΔE 3, so an instrumented ΔE00 ceiling is usually set at 1.5. Halving the visual threshold is deliberate: a case is two parts meeting, and a lid 1.5 away from its base adds up to 3 across the joint, right at the edge of what a customer sees.
Dispersion and melt temperature drive most of it. Poorly dispersed masterbatch leaves light and dark streaks on parts from the same shot; a 10℃ swing in melt moves the lightness of a dark part by a measurable amount. Hold melt within ±5℃, pull first and last parts from each batch, and read them against the chip in a light booth.
04Dark Surfaces Run 8 to 12℃ Hotter
Dark surfaces absorb more. In summer sun a dark shell sits 8℃ to 12℃ above a light one, which will not melt PP or PE but will put thermal strain and distortion into the case. Thin sections and wide flat panels react first: the lid centre lifts slightly, the joint gap opens, and a step can be felt with a fingertip.
So two places matter when specifying dark: lid centre and latch-seat root. Wall thickness changes sharply at both, cooling is uneven, and they distort in opposite directions, one bulging while the other pulls in. The answer is not to avoid dark but to rib the lid, shorten the panel span, and hold shrinkage allowance at the top of the range.
05Purge Cost and the 200-Piece Step
Changing colour stops the machine: pull the screw, clean the barrel, swap the screen, clear the nozzle. That is 20 to 40 minutes, shorter light-to-dark than dark-to-light, plus a few kilograms of transition material. Colour therefore has a floor. Minimum order is commonly set in 200 to 500 piece steps, and below that the purge costs more per case than the masterbatch does.
Scheduling recovers some of it. Run orders light to dark, finish on the darkest, and purge count drops; within one family, go light first and let transition material be downgraded rather than scrapped. The number that really needs limiting is the colour count. Four to six stable shades per family beat a dozen, in stock, chips and purges alike.
| Masterbatch let-down ratio | 1%–3% |
|---|---|
| Batch variation, instrumented | ΔE00 ≤1.5 |
| Visual detection threshold | ΔE ≈3 |
| Colour-change purge time | 20–40 min |
| Barrel carry-over limit | <1% |
| Dark surface rise, full sun | +8–12℃ |
| Visible weld line depth | 0.02 mm |
| Minimum order per colour | 200–500 pcs |
FAQ
Will a dark case distort in strong sun?
It gets hot, though rarely to softening point. A dark surface runs 8℃ to 12℃ above a light one, and the risk sits at thin flat panels and latch-seat roots, where distortion opens the joint first. Measure the gap after two hours in sun; a change beyond 0.3 mm calls for ribbing the lid.
Will a repeat order match the first one?
Close, not identical. The inner ceiling is ΔE00 1.5, about half the visual threshold, which leaves room for a lid and base to meet without a visible step. Ask the moulder to archive a chip per batch and check incoming resin against the chip, not against a previous part.
Can I order just a few dozen?
Technically yes, commercially no. Purging takes 20 to 40 minutes plus transition material, and that fixed cost spread over a few dozen units exceeds the resin in them. Orders are normally set in 200 to 500 piece steps, or the customer takes a stocked colour instead.
Can a scuffed compounded part be touched up?
No. The colour sits in the resin, so a local repair reads as a patch and gets more obvious with each attempt. Scuffs are dressed and left functional. Where appearance must be repairable, specify painted parts, accepting a film of only 30 μm to 60 μm that wears at the edges first.