Corona and Plasma Technology

Scanmaster Seminar

Anno 2016

Why Surface Treatment ?

Improved Adhesion Improved Wettability Surface Cleaning

Overview Surface TreatmentSurface Treatment Technologies

Cleaning Solvent based cleaning liquidsWaterbased cleaning liquides

Mechanical Surface Treatment Sand blastingBrushingBlasting

Chemical Surface Treatment Chemical PicklingReactive gasses

Thermal Surface Treatment Gas Flame Treatment

Electrical Surface Treatment Corona Discharge-Free air Discharge-DBD (Dielectric Barrier Discharge)-Nozzle Plasma-Arc corona

Low pressure Plasma-with non polymerized gasses-with polymerized gasses

Coating MetalisingNon Metalic coating -Anorganic coating-Organic coating-Painting with colour-Primer

High energy sources/beam Electron beamLaserUV

The SurfaceOuter surface layers play an important role to surface properties

”uncleanness” like dust, dirt oil etc. >1µm

Adsorption layers, such as gasses and moist 1-10nm

Reactive layers, like oxides,

additives, release agents etc. 1-10nm

Adhesion point – surface

Modified polymer structure

Non modified polymer

material.

The Surface

Bild: Dipl.-Ing. (FH) Simone Fischer

Substrate surface

Roughness &Gloss

CorrosionOptical propertiesDiffusion

OxidationCorrosion Passivierung

1st atomic layerAdhesion WettabilityKatalyseBioverträglichkeitMikrorauheit

Reaction on the Surface

Surface treatment

Bild: Dipl.-Ing. (FH) Simone Fischer

- Radicals created by the plasma discharge breaks the polymer bonds on the surface.

- Oxygen containing groups will be introduced into the polymer surface

� Increased wettability on the polymer surface

Surface Energy ExamplesSurface Energy – Polymers Necessary surface energy for

successful bond with :

PTFE < 20 mN/m UV based inks 48-56 mN/m

Silicone < 20 mN/m Water based inks 50-56 mN/m

PP 30 mN/m Coatings 46-52 mN/m

PE 32 mN/m UV based adhesives

44-50 mN/m

PS 34 mN/m Water based adhesives

48-56 mN/m

PC 34 mN/m

ABS 34 mN/m

XLPE 32 mN/m

PUR 34 mN/m

Wettability Surface Pre-Treatment effect on the wettability of Polymer surfaces

Impro

ved a

dhesio

n

Increased surface pre-treatmentBild: Dipl.-Ing. (FH) Simone Fischer

Polymer surface

Surface Energy

Contact Angle:

� The wettability can be measure using contact angle

meters

� Both Polar and Non Polar measurements are

possible

� The contact angle is measure as the tangent line

from the ”coroner of the water droplet”

Surface EnergyNorms for measuring surface energy

� The measured value is referred to as mN/m or

dyne/cm

� If the dispensed liquid pulls together and forms

droplets (within 2-3 seconds) the value is not

achieved

� This type of surface measurement is based on ISO

8296. Method for determining surface energy on PE

film.

Surface Energy

Low Surface Energy Liquid does NOT wet the surface

High Surface EnergyLiquid does wet the surface

Surface EnergyMeasuring the cleaning effect on Stainless steel

Surface Energy - Conclusion

NOTE!

� A high Dyne level (mN/m) does not automatically mean

that good adhesion is guaranteed

� Test inks can be used, with background in adhesion tests,

to verify treatment levels

� Test inks can ”detect” dirty areas on the material.

� Adhesion tests is always recommended

Over Treatment

Treatment time

Over Treatment

Surface Energy

Adhesion

Shelf Life of Surface Treatment

Shelf Life

Pulling force MPa

Shelf Life of Surface Treatment

The shelf life of treated surfaces is very different and varies

from minutes to years. Most materials is in the range ”weeks”

Factors:

� Material

� Surface treatment method

� Plasma vs. Gas flame treatment

� Level of additives

� Age of polymer on time of treatment

� Air humidity

� Temperature

� Etc.

Corona vs. Plasma Treatment

What is the difference between Corona and Plasma Treatment ?

Everything is a Plasma and for instance Corona is just a part of a Plasma !

Plasma Treatment

Corona – Low frequency

DBD – Dielectric Barrier Discharge

Corona – High frequency

Jet System –

Atmospheric Plasma

Gas flame treatment

Vacuum System