Coating with plasma

Hydrophobic, hydrophilic, scratch protection, ...

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With plasma, components can be tempered with various coats. This is done by supplying gaseous and liquid starting substances. The raw materials, mostly short-chain monomers, crosslink in the plasma to form long-chain polymers. The selection of raw materials determines the coat characteristics:

Hydrophobic (water repellent) | Hydrophilic (water attracting / wetting) | Scratch protection, corrosion protection | Carbon coats | Barrier / Diffusion barrier | PTFE-like| Anti-friction coats / Nonstick coats | Adhesion promoter / Primer | Water / steam barrier | Metallisation | Nano-silver 

Benefits of plasma coating

✓ Extremely thin coats in the nm range are possible
✓ Constant processes suitable for series production possible due to complete automation
✓ Wide range of variants are possible
✓ No temperature increase
✓ No solvents
✓ Excellent penetration into crevices and holes
✓ Suitable for piece goods and bulk material

Coating with plasma polymerisation

For coating with low-pressure plasma, gaseous or liquid monomers are introduced which polymerise under the influence of the plasma. The coating thicknesses achieved with plasma polymerization are in the range of one micrometre. The adhesion of the coatings on the surface is very good.

For coating with the Plasmajet process (atmospheric plasma), the gaseous monomers are introduced directly into the plasma jet by means of a carrier gas. Thus, the plasma focusses the monomer on the surface and polymerises it. The layer thickness is several hundred nanometres.

This process technology is much more complex than for activating and degreasing.

It is used for example to produce barrier coats in fuel tanks, scratch-resistant coats on headlights and CDs, PTFE-like coatings, hydrophobic coats, etc.

There are three coating processes that have established themselves on an industrial scale: 

Hydrophobic coats ► Monomer: e.g. hexamethyldisiloxane (HMDSO)

PTFE-like coats ► Monomer: fluorinated process gases – also refer to epilamisation

Hydrophilic coats ► Monomer: vinyl acetate, hexamethyldisiloxane mixed with oxygen in a given ratio (significantly more HMDSO than O2)

Frequently asked questions

Which effects are possible by coating metals via plasma polymerisation?

Various effects can be generated by coating metals via plasma polymerisation, such as: an activation which remains effective for up to several weeks, and the application not only of decorative but also of functional layers.

In general, use of a sputter system is particularly suitable for metals.

For a permanently hydrophilic coat with HMDSO, mix the gases as follows: HMDSO: O2 = 1:4

For a hydrophobic coat with HMDSO, mix the gases vice versa, i.e.: HMDSO: O2 = 4:1

Can you coat plastics by means of plasma polymerisation?

Coating plastics by means of plasma polymerisation poses no problems at all in most cases.

A scratch-proof coat can for example be applied to CDs and DVDs without affecting their quality.

PTFE-like coatings can be applied to increase the low-friction characteristics of the treated products. Furthermore, functional groups can be attached to the synthetic surface (e.g. amino groups for bio-analytical applications).

Polymerisation can also be carried out in several stages:

Example: 

  1. Activation ► 5 minutes O2
  2. Coating ► 5 minutes HMDSO
  3. “Etching” ► 12 seconds O2
  4. Coating ► 5 minutes HMDSO
  5. “Etching” ► 12 seconds O2
  6. Coating ► 5 minutes HMDSO,

possibly followed by curing of the coat with a few seconds of oxygen plasma. During this step, however, the coat becomes hydrophilic!

Can glass and ceramics be coated by plasma polymerization?

The only difficulty in coating glass and ceramics is the appropriate surface preparation (see Activation and Etching). Once this precondition has been met, coats for a variety of applications are possible.The respective adhesion of the coat must be checked in each case. If "incompatibility" occurs between the coat and the substrate material, it may be necessary to apply intermediate layers as a bonding agent. The picture shows an example for successful hydrophobic and oleophobic coating.

Can you coat textiles by means of plasma polymerisation?

Textiles are extremely well suited for plasma coating. With the current technology, it is still a challenge to make the coats permanently resistant to surfactants. Hydrophobic coats can be achieved by the use of fluorine-based gases/monomers.

Which coats can be generated with atmospheric plasma, and which monomers are used for this purpose? (atmospheric pressure plasma)

Atmospheric plasma is principally suitable for producing hydrophilic, adhesion-promoting and corrosion-preventing coats.

Siliceous and carbonic substances are used as monomers. These include, for example, various acrylates and common silicon-containing monomers of type HMDSO.

Which monomers may not be used? (atmospheric pressure plasma)

Due to their high toxicity, no halogenated gases and monomers may be used in combination with atmospheric plasma (F2, CL2, Br2, I).

Which carrier gases are used for atmospheric plasma coating? (atmospheric pressure plasma)

Typically, the following gases are used:

  • Helium (He)
  • Argon (Ar)
  • Nitrogen (N2)

Which coating thicknesses can be achieved and how do you measure them? (atmospheric pressure plasma)

The layer thickness is several hundred nanometres. A so-called profilometer (e.g. Dektak) is used to reliably measure these thin coats.

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