Disc-Jet – Atmospheric Pressure Plasma Source for Surface Treatment

Eco-friendly pre-treatment with plasma

Commercially available atmospheric pressure plasma sources are already being used in a wide range of industries and sectors of industry to clean or activate surfaces. The use of plasma processes, for example, enables varnishes or adhesives to stick to surfaces even without a chemical pre-treatment. This saves money and is eco-friendly. From planar pre-treatments such as corona activation for web goods and selective surface functionalization through to the partial treatment of three-dimensional components, there are many effective solutions available for surface activation, ultra-fine cleaning or coating, depending on the area of application.

Surface treatment of a gear rack.
© Fraunhofer IST
Surface treatment of a gear rack.
Discharge characteristics and operating principle of the sliding discharge plasma jet. Surface treatment of a T-groove.
© Fraunhofer IST
Discharge characteristics and operating principle of the sliding discharge plasma jet. Surface treatment of a T-groove.

The challenge: complex geometries

The plasma treatment of plane and at the same time partially complex geometries such as low-lying grooves, cavities or undercuts represents a particular challenge. Expensive array arrangements of plasma jets or complicated combination solutions are often unavoidable.

An effective and low-cost alternative has been developed at the Fraunhofer IST: the core of the new plasma source concept is a jet-induced, dielectrically impeded sliding discharge which even allows the effective activation or functionalization of geometrically challenging contours.


The operating principle of the new jet

Inside the innovative sliding discharge plasma jet, a cold plasma is first ignited by means of alternating voltage. This is guided via the process gas flow around the internal electrode out of the middle of the nozzle and onto the external earth electrode on the underside of the source. As a result of direct discharge between the internal and external electrode, discharge filaments are formed between them which adapt perfectly to the contours of the substrate surface. The homogeneous sliding discharge produced allows an even and complete treatment of the surface, including any possible recesses or cavities. Depending on the type of source and distance of the source from the substrate (1 - 40 mm), effective bandwidths of between 10 and 120 mm are possible.

Plane slide discharge with exclusion of ambient air in a defined process environment.
© Fraunhofer IST
Plane slide discharge with exclusion of ambient air in a defined process environment.
Surface treatment of a radii groove.
© Fraunhofer IST
Surface treatment of a radii groove.

Process gases

Diverse homogeneous functionalization of the substrate surface is also possible regardless of the substrate thickness and conductivity by choosing the process gas.  The following process gases are possible:

  • Argon
  • Helium
  • Nitrogen
  • Compressed air
  • Inert gas mixtures



Sliding discharge jets are suitable for treating various different materials:

  • Plastics, e.g. ABS, PA, PC, PE, PP, PUR, TPE, silicones
  • Natural materials, e.g. wood, paper, flax, cotton
  • Metals
  • Ceramics
  • Textiles
  • Glassware

The advantages

  • The diversity of possible materials and functionalization options means that the spectrum of applications is very broad.
  • The virtually complete exclusion of ambient air from the discharge area on flat substrates allows oxygen-free surface treatment.
  • The low process temperatures between 30 °C and 60 °C also make the process suitable for temperature-sensitive, organic materials such as paper or wood.
  • The compact structure of the jet allows an easy and straightforward integration into existing process chains, e.g. for the activation and functionalization of surfaces as pre-treatment before painting or bonding processes, or for the ultra-fine cleaning of various materials.


Our offer

  • Specific source and process concepts
  • Application-related scaling of the source concept
  • Prototype production
  • Feasibility studies
  • Personal advice
  • Education and practical training


Fields of application

  • Aerospace
  • Automotive construction
  • Medical technology
  • Architecture and construction
  • Lightweight engineering
  • Printing industry