5.5.3 Flame treatment of plastics
Flame treatment is used on thermoplastic materials to increase the surface tension and hence improve the bonding properties.
Flame treatment is particularly suitable for thermoplastic polymers such as polyethylene (PE) and polypropylene (PP), but is also used on other plastics. Important is that bonding is carried out immediately after the flame treatment.
- Prior to flame treatment the surface must always be thoroughly cleaned and degreased.
- Use a propane or acetylene flame with an excess of oxygen (blue, raging flame)
- The flame is passed across the plastic surface
- Parameters affecting the result: The excess of oxygen, flame-substrate distance, speed at which the flame passes across the surface
- Visible roughening of shiny surfaces; Formation of polar structures on the surface, so enhancing the surface tension
- After the flame treatment, bonding must be carried out immediately
Points to heed:
- Clean the substrates beforehand
- Ensure there is an excess of oxygen in the flame
- Ensure the correct distance between the flame and substrate surface
- Very rapid degradation of the pretreatment effect, so bond the substrates immediately after treating them
- For thin substrates, too long contact and too small flame-substrate distances: Risk of combustion of the plastic surface