Surface finishes for plastic drinkware: spray coating, soft-touch, frosted and gradient — and how to test them
A finish is what the customer touches first and what fails first. Most finish complaints are not about the colour. They are about a coating that peels at the rim, goes sticky or turns dull in the dishwasher.
Moulded-in or applied
There are two different ways to give a part its look, and they behave very differently:
- Moulded-in: the colour is in the resin (masterbatch) and the texture is in the mould steel. It cannot peel off, because it is the part itself.
- Applied: a coating is sprayed onto the moulded part and cured. It allows effects the resin cannot give — a rubbery feel, a colour fade, a metallic or matte look on a glossy part — but it is a layer that has to stay attached.
Every applied finish adds a process step, so it adds cost and time to the order. Ask for it to be quoted as a separate line, so you can compare it with a moulded-in alternative.
The common finishes
| Finish | How it is made | Main risk | What to check |
|---|---|---|---|
| Spray coating (solid colour or metallic) | Coating sprayed onto the moulded part | Peeling at edges and the rim; scratches | Adhesion, scratch, rub and dishwasher behaviour |
| Soft-touch (rubberised) coating | Soft coating sprayed onto the part | Wear on handled areas; surface turning sticky over time; marks | Adhesion, wear on the grip area, cleaning |
| Frosted — moulded texture | Texture on the mould surface | Uneven texture; scratches show on dark colours | Texture against a limit sample; draft on textured walls |
| Frosted — sprayed | Matte coating sprayed onto a clear or coloured part | Peeling; shine where the surface is rubbed | Adhesion and rub resistance |
| Gradient | Colour sprayed so that it fades along the part | Variation from piece to piece | Fade position and colour against limit samples |
Where applied finishes fail
- Edges and the rim: coatings are thinnest on sharp edges, and the rim is where the mouth, the lid and the dishwasher all work on it.
- Handled areas: grips and handles wear first, especially on soft-touch.
- The dishwasher: heat and detergent attack coatings that are fine by hand. A dishwasher claim on a coated product needs its own test.
- The drinking area: keep coatings off the rim and the inside unless the coating itself has food-contact test reports for that use.
How to test a coating
Agree the tests and the pass level before sampling, and run them on the approved sample and on production:
- Cross-hatch adhesion test: a grid is cut through the coating to the plastic, tape is applied and pulled off, and the result is rated by how much coating comes away — ISO 2409 and ASTM D3359 describe the method. Agree the rating you accept.
- Rub test: rub the surface with a cloth and alcohol, as in our inspection article; the colour must not transfer.
- Dishwasher test: an agreed number of cycles if the product is sold as dishwasher safe, then repeat the adhesion test.
- Appearance: compare against signed limit samples for gloss, texture and, for gradients, the fade.
Frosted by texture: decide it at the mould
A moulded texture is the most durable way to get a frosted look, but it is part of the mould. The texture has to be specified before the steel is finished, and textured walls need more draft to release from the mould. Changing your mind after T1 means re-texturing the tool. If the frosted look is only for one colourway, a sprayed matte finish may be the more flexible choice.
Writing it into the specification
- Finish type, and whether it is moulded-in or applied.
- Areas to be coated, and areas that must stay coating-free — the rim and the inside.
- Colour plaque and signed limit samples for gloss, texture or gradient.
- Adhesion test method and the rating accepted.
- Rub test and, if claimed, dishwasher cycles.
- Care instructions on the pack that match what was tested — for example hand wash only.
A coated sample always looks good on the day it arrives. The specification is what makes the thousandth piece look the same after a month of use.