1. Barrier prediction for aluminium foil in laminates
16TH TAPPI EUROPEAN PLACE CONFERENCE
17th TAPPI European PLACE Conference
20-22 May 2019
Crown Plaza Hotel Porto
Portugal
Barrier prediction for aluminium foil in laminates
Presented by:
Guenter Schubert
Hydro Aluminium
Rolled Products GmbH
R&D Bonn
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2. Structure Manufacturing aluminium foil
Definition of pinhole, hole and break-through
Origin of pinholes in thin aluminium foil
Detecting and measuring pinholes and porosity
Permeation model and calculation scheme
Conclusions

3. Structure Manufacturing aluminium foil
Definition of pinhole, hole and break-through
Origin of pinholes in thin aluminium foil
Detecting and measuring pinholes and porosity
Permeation model and calculation scheme
Conclusions

4. Structure Manufacturing aluminium foil
Definition of pinhole, hole and break-through
Origin of pinholes in thin aluminium foil
Detecting and measuring pinholes and porosity
Permeation model and calculation scheme
Conclusions

5. Structure Manufacturing aluminium foil
Definition of pinhole, hole and break-through
Origin of pinholes in thin aluminium foil
Detecting and measuring pinholes and porosity
Permeation model and calculation scheme
Conclusions

6. Definition of pinhole, hole and break-through (according to DIN/EN 546-4)
Pinholes (pores)  < 200 µm, statistically distributed
Holes  > 200 µm, statistically distributed (no metallurgical inclusions)
Holes from rolling  > 200 µm periodically recurring, e.g. in the distance of a roll circumference
Any kind of holes is not acceptable!

7. Process chain of foil manufacturing
Hot rolling
Cold rolling
Soft foil
Hard foil
Roughing
Casting slabs
Milling
Preheating
Finishing
Separating / Slitting
Annealing
Doubling
Continuous strip casting
600 mm thick ingots are cast, the cast skin with its heterogeneities is removed and the ingots are heated to 500 to 600 °C for hot rolling. Hot rolling is carried out in reversing mode down to 20 to 40mm (roughing) and then in line in a tandem mill down to 2mm to be wound.
An alternative route, using continuous strip casting, also ends up with a metal strip of some single millimetres thickness.
Cold rolling is carried out in 6 to 8 steps reducing thickness by about 50% in each step. Generally an intermediate annealing after the first 2 cold roll passes will take place. Before the last cold roll step, two foils are coiled up together (called “doubled”).
After separating the foil, the foil is cut into customer’s desired dimensions and finally annealed at about 300 °C, carried out in the range of several days, depending on coil width, foil thickness and temperature applied.

8. Pinhole detection – Using the pinhole camera…
Detector plain (e.g. the eye)
Cone of scattered light
Stay with your text inside this frame
Aluminium foil
Pinhole
Detecting pinholes is easy, because foil is absolutely impervious to light and pinholes let the light go through.
Illumination from the background

9. Transport model for laminates carrying pinholes in the aluminium foil
Passage surface area
Polymer
Polymer
Polymer
Polymer Al Al Al Al D
Pinhole
Pore
Pore
Pore
This picture shows how oxygen passes through a laminate. Behind the pinhole the path in the polymer is not directed, but the oxygen molecule can move in any direction with the result of a much larger passage surface area at the interface between the coating and the atmosphere than the projection of the cross-sectional area of the pinhole itself.

10. Conclusions
Aluminium foil as a 100% crystalline metal inhibits any transport of matter
Conditional of manufacturing, there is no thin foil absolutely free of pinholes
As soon as pinholes are coated with polymers, their contribution to a permation rate can not be measured at all
Relative to their size, the effect of small pinholes is stronger
A worst case permeation calculation system gives an indication of permeation rate (input: specific permeation rate and thickness of the polymers on one or both sides of the foil; number and average size of pinholes)
The functional barrier of aluminium foil persists even in the presence of pinholes

11. “Thank You” for your patience
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“Thank You” for your patience
Presented by:
Guenter Schubert Foil Converting -
Hydro Aluminium Rolled Products GmbH, R&D Bonn