Principle of surface modification by corona/gas plasma
When a dielectric material (insulator) is inserted between metal electrodes and high-frequency, high-voltage electricity is applied, filamentary plasma called streamer corona is randomly formed between the electrodes both temporally and spatially.
The discharge does not develop into an arc discharge because it goes through a dielectric. The streamer also repeats being generated and disappearing in nanoseconds. Development into high-temperature plasma is resultantly inhibited.
This type of plasma is called non-equilibrium plasma or low-temperature plasma.
Ionization due to collision
Electrons discharged from the electrode due to corona discharge are accelerated in the electrical field and collide with electrons and molecules in the atmosphere, resulting in their excitation, dissociation or ionization.
Electrons are also discharged from ionized atoms and molecules, and as high-energy electrons keep doubling, streamer corona is repeatedly generated.
The pictures on the left show some parts of the ionization process caused by collision. Notably, the bottom picture shows a process called penning ionization, which makes a great contribution during corona discharge in gas.
Generation of functional group
Reactions in the gas phase
A variety of gas-phase reactions take place in a high-energy space during discharge. For example, in the atmosphere, ionization and dissociation of oxygen molecules in the air cause generation of oxygen radicals and ozone.
Polymer surface modification
Polymer surface modification (introduction of functional group)
High-energy electrons reach the surface layer of the polymer film that passes through the opposite side. This triggers an action that cuts out the main chain or side chain of polymer binding.
The cut-off polymer surface layer becomes chemically radical, and when oxygen radicals or the ozone layer in the gas phase are combined with the main chain or side chain, a polar functional group such as the hydroxyl group or carbonyl group is introduced and the surface is made hydrophilic.
This significantly improves the printing property, adherence property, lamination, etc. with hydrophobic polymer.
The influence of the surface modification will not extend more than 0.1 um from the surface, which means that the properties of the base material itself will not be affected.
Atmospheric-pressure plasma treatment in gas enables provision of selectivity to the type of functional group and increasing radicals on the surface. Therefore, this treatment is drawing attention in the field of new functional materials.
Learning about corona treatment
- What is corona treatment?
- Applications of corona treatment
- Principle of surface modification by corona/gas plasma
- Configuration of a corona treater
- Basic structure of a treating station
- Wettability (wetting tension) and watt density
- How to measure the effect of treatment
- Ozone exhaust
- Our corona treatment experiment systems
- Order placement process