Surface treatments and finishes

Some polymers that are formed in a mould are self-finishing, meaning that the inside surface of the mould is so smooth that the form that is taken from it is also smooth. A motorbike helmet is a good example - the outside of the helmet is smooth because of the mould it was made in.

Once a polymer has been cut or shaped from its original stock form, the edge that has been cut can be rough and will need to be finished. Using acrylic as an example:

  1. a profile is likely to be marked on the acrylic
  2. a cut that is close to the line will be made with a saw of choice
  3. a file can be used to remove more acrylic, so the profile is closer to the line
  4. abrasive paper, often called wet and dry paper is then used to remove the file marks from the acrylic, known as ‘rubbing down’
  5. once the file marks are removed, a fine abrasive paper can be used to achieve a matt finish
  6. if a gloss finish is required, then an electric buffer or car body polish can transform the matt finish to a glossy one
A gloved hand using a buffing machine to polish a car for painting.
An electric buffer

It is possible to add a personalised pattern to a polymer using a sublimation printer, which can look like a regular inkjet printer but has sublimation ink in the printer cartridges:

  1. a sublimation printer is used to print onto coated, heat-resistant paper
  2. the paper is then placed on top of the polymer and heated, using a heat press, to around 180 to 200 °C
  3. once hot, the polymer is removed
  4. the paper can be removed from the polymer, transferring the image from the paper to the polymer

Common polymers to which sublimation patterns are added are high impact polystyrene (HIPS) and acrylic.

Vinyl cutters can be used to cut sheets of self-adhesive vinyl, which can be used for signs on cars, vans and shop fronts. The sheet vinyl is available in many colours and is bought on a roll. A vinyl cutter is a computer-controlled machine - the cutting tools moves along vector paths, which have been set out within the design. Long signs can be cut as the vinyl is on a roll that feeds into the machine.

A vinyl cutting machine in the process of cutting.
A vinyl cutter
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