The use of finishes Paper and board finishing - Polymer finishing — AQA A-Level Design and Technology: Product Design
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The use of finishes Paper and board finishing - Polymer finishing explained
Pigments colour a polymer throughout its mass rather than sitting on the surface as a paint would.
Read the full explanation
The most common industrial route is masterbatch: a concentrated pigment dispersed in a carrier polymer, supplied as granules and blended with natural polymer granules in a known let-down ratio before the mix enters the moulding machine, so the screw's mixing action distributes colour evenly. Colour can also be added directly as dry powder or liquid colorant at the hopper. For glass-reinforced plastic (GRP), a pigmented gel coat is sprayed into the mould first; it cures as the visible coloured surface layer, protecting the laminate beneath. Smart pigments change appearance in response to a stimulus: thermochromic pigments shift colour with temperature and phosphorescent pigments absorb light and re-emit it in the dark. These are added by the same masterbatch or compounding routes.
Your focus
- Describe how masterbatch pigment is blended into polymer before moulding.
- Explain the role of a pigmented gel coat in GRP components.
- Distinguish thermochromic from phosphorescent pigments by their stimulus and effect.
The use of finishes Paper and board finishing - Polymer finishing exam tips
Marking Points
- Masterbatch is a concentrated pigment in a carrier polymer, blended with natural granules before moulding so colour is dispersed through the melt.
- Pigment added at the hopper (dry powder or liquid colorant) colours the whole moulding, not just its surface.
- In GRP, a pigmented gel coat is applied to the mould face and forms the coloured outer surface layer of the finished component.
- Thermochromic pigments change colour in response to temperature change.
- Phosphorescent pigments absorb light and re-emit it, giving a glow-in-the-dark effect.
- Smart pigments are incorporated by compounding or masterbatch in the same way as conventional pigments.
Examiner Tips
- 💡Name the specific route (masterbatch, hopper addition, gel coat) rather than saying only that colour is added.
- 💡Link each smart pigment to its stimulus: temperature for thermochromic, light for phosphorescent.
- 💡Use a product example, such as a colour-changing kettle or a glow-in-the-dark toy, to show the pigment's function.
Common Mistakes
- Treating pigment as a surface coating applied after moulding: correct this by explaining that pigment is dispersed through the polymer melt so the colour is integral to the moulding.
- Assuming GRP colour comes from pigment mixed through the resin laminate: correct this by identifying the pigmented gel coat as the coloured surface layer applied to the mould first.
- Confusing thermochromic with phosphorescent pigments: correct this by stating that thermochromic responds to temperature while phosphorescent stores and re-emits light.