Plasma Activation

How can a plasma activation be measured?

  1. Contact angle/wetting angle

  2. The contact angle is the angle formed by an observation of the projection of the resting drop onto the solid by the tangent to the drop shape at the surface of the solid body, at the triple point. According to the physical definition, a surface having a contact angle of less than 90° is hydrophilic (wettable), whereas if it is greater than 90° it is hydrophobic (non-wettable). Plasma treatment can change the contact angle (increase, decrease). An appropriate plasma process or application of a suitable coating in a plasma process can cause hydrophilic surfaces to become hydrophobic (by hydrophilic layers and vice versa).

    Left: Wetting angle measurement device
    Right: Contact angle measurement

  3. Test inks

  4. Measuring means for estimating the surface energy: If the test ink beads after application on the surface, the surface energy of the solid is less than that of the ink; however, if wetting is obtained, then the surface energy of the solid is equal to, or greater than that of the liquid. The total surface tension of a solid can be determined through the use of series of test inks with graduated surface energy. The polar and non-polar component of the surface energy can not be determined with this method however.

  5. Cross Hatch Test

  6. To test the adhesion of paints, a Cross Hatch Test (standards: EN ISO 2409 and ASTM D3369-02) is performed. After painting, the paint layer of the plastic part is cut in a lattice form. Then a standard adhesive tape is stuck to the cut grid, pressed and abruptly withdrawn again. If paint sticks on the tape, the adhesion of the coating is defective. The Cross Hatch thus shows the adhesion of paint coatings on plastic parts.

How can a plasma treatment be detected?

The indicator tags as well as the plasma indicator metal compound provide users of plasma systems with the ability to see at a glance whether a plasma treatment has taken place. The tests can be carried out in virtually no time. They can be used in any plasma system for any treatment whether cleaning, activating, etching or coating. The indicators identify plasma treatment previously carried out on your products and semi-finished products, even after weeks or months.

  1. Indicator tags

  2. Plasma indicator label

    The adhesive label is made of specially coated films, which can be used as a reference and are placed directly in the chamber, or glued to the components. As soon as the dark indicator point has disappeared, the plasma treatment has been successfully completed. The indicator labels can also be used for a system test. Here, a label is laid in the empty vacuum chamber and the plasma ignited.

  3. Plasma indicator metal compound

  4. On the right is the indicator before plasma treatment.
    On the left is the indicator after plasma treatment.

    The plasma indicator is a liquid metal compound, which decomposes in the plasma so that the plasma-treated surface of the object has a shiny metallic surface. A drop applied to the component itself, or a reference sample is transformed in the plasma treatment into a shiny metallic coating that forms on most surfaces and forms a clear contrast to the originally colourless drops. The golden shiny metal film resulting from the plasma is distinguished from all the other colours of the object by its optical reflectivity.