Plasma Surface Activation

Plasma surface activation is effective at altering the surface of a polymer by attaching polar or functional groups to it. Many polymers, in particular polyolefins such as polyethylene and polypropylene, are chemically inert and cannot bond easily to other materials, displaying poor adhesion with inks, paint and glues. The reason for this is the absence of polar and reactive functional groups in their structure.

Plasma surface activation renders many polymers receptive to bonding agents and coatings. Oxygen is usually used as the process gas, however, many plasma activations can also be carried out with just ambient air. Parts remain active for a few minutes up to several months, depending on the particular material that has been plasma treated. Polypropylene for example can still be reprocessed several weeks after treatment.

How Plasma Surface treatment Works

UV radiation and active oxygen species from the plasma break up separating agents, silicones and oils from the surface. These are pumped away by the vacuum system. Active oxygen species (radicals) from the plasma bind to active surface sites all over the material, creating a surface that is highly ‘active’ to bonding agents.

 Before plasma treatment                During plasma treatment                 After plasma treatment

A scientific illustration of a part prior to plasma surface activationA scientific illustration of a part during plasma surface activation to improve adhesionA scientific illustration of an oxygen activated, easy to treat surface after plasma surface activation

Plasma surface activation treatment is suitable for e.g.:

  • general plastics and rubber
  • medical plastics
  • consumer electronics plastics
  • automotive components
  • aerospace components

 


 Tests of Plasma Surface Activation

The effects upon a plasma treated activated surface are readily seen during subsequent product processing steps but there are a number of formal test methods that demonstrate the results too:

Contact angle measurements

Untreated surface                      Plasma treated surface

A metal part with a water droplet on the surface displaying inherent hydrophobic properties prior to plasma surface activation A metal part with a water droplet on the surface displaying newly produced hydrophilic properties after plasma surface activation

Water beads on an untreated surface but spreads out (has lower contact angle) on a plasma treated and activated surface

 


Dyne test inks

A set of surface test inks

Dyne test inks indicate a specific level of surface energy.

 

 


Grid cut test

Untreated surface                      Plasma treated surface

A plastic part displaying poor paint adhesion prior to plasma treatment - grid cut test A plastic part displaying improved paint adhesion after plasma treatment - grid cut test

Grid test cut methods (DIN EN ISO 2409) clearly demonstrate the enhanced bonding (right image) to plasma activated surfaces after treatment.

 


 

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