High performance extrusion coating of thin … performance...3 Günter Schubert –Hydro Aluminium Rolled Products GmbH, F&E Bonn –High performance extrusion coating and barrier

High performance extrusion coating

of thin aluminium foil and

consequential barrier challenges

Dr. Günter Schubert

Hydro Aluminium Rolled Products GmbH, RDB Bonn, 14.02.2019

2 Günter Schubert – Hydro Aluminium Rolled Products GmbH, F&E Bonn – High performance extrusion coating and barrier of foil – Ametek Seminar 14.02.2018 Montabaur, Germany

Process chain of foil manufacturingHot rolling

Cold rollingSoft foil Hard foil

RoughingCasting slabs Milling Preheating Finishing

Separating / SlittingAnnealing Cold rolling Cold rollingDoubling

Continuous strip casting


Outline

Pinholes in thin aluminium foil

Barrier of laminates with pinholes in aluminium foil

Extrusion coating & laminating

Aluminium foil defects in packages

Possible coating & laminating deficiencies at high speed coating

Coating & laminating of cardboard carrying prepunched holes

Creasing lines of laminates

Consequences for the barrier of coinciding foil break-throughs

and coating & laminating defects

Summary


MattseiteGlanzseite

Directed light reflection Diffuse light reflection

Glossy and matte side of aluminium foil

Glossy side (SEM) Matte side (SEM)


Aluminium foil topography – Glossy side*

* Confocal interferometry

* Confocal interferometry, area 900 x 900 µm


Aluminium foil topography - Matt side

* Confocal interferometry

* Confocal interferometry, area 900 x 900 µm

Aluminium foil topography – Matte side*


Definition of pinhole, hole and break-through

(according to EN 546-4)

Pinholes < 200 µm, statistically distributed

(pores)

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!


Doubled rolled aluminium foil and break-through

(schematic*)

Corrugation of the matt side


Surface crack

Glossy side

Thin position

Glossy side

Surface cracks

Corrugation of the matte side*

Doubled

* Corrugation is displayed greatly magnified

Break-through after separation of

the doubled rolled foil layered



Doubled rolled aluminium foil

(microscope, longitudinal section*)

* At a thickness of 9 µm aluminium foil typically consists of a single grain layer




Break-through after separation of the doubled rolled foil layers

Doubled rolled aluminium foil and break-through

(microscope, longitudinal section*)


Pinhole detection – Using the pinhole camera…

Aluminium foil Pinhole

Detector plain (e.g. the eye)

Cone of

scattered

light

Illumination from the background

12 Günter Schubert – Hydro Aluminium Rolled Products GmbH, F&E Bonn – High performance extrusion coating and barrier of foil – Ametek Seminar 14.02.2018 Montabaur, GermanySource: Passy‘s blog

Genuine starry sky


Porosity in aluminium foil – Starry sky-method *

Source: Passsy‘s blog* Starry sky method: illuminate a photographic paper through a

foil carrying pinholes using a copying machine


Contour and area of a pinhole in aluminium foil *

Rolling direction

* Transmitted light

* Typical pinhole in foil


Typical pinhole size distribution of thin

aluminium foil ( 7µm)

0

10

20

30

40

50

60

70

< 10 µm 10-20 µm 20-50 µm < 50 µm

Rela

tive f

req

uen

cy [

%]

Relevant according EN

Pinhole size category

Not relevant according EN!

Most of the pinholes of thin foil are smaller

than 20 µm and therefore are not counted

according to EN 546-4


Outline










Summary


Q = 4 10-12 · D2

· N · Q100

· —— {1 + 1,149 ·(—)0,8456 }

Example for LDPE

Q100 = Permeation rate for 100µm film, e.g. for LDPE 1610

N = Number of pinholes [1/m²]

D = Average diameter of the pinholes [µm]

Q = Flux (permeation rate) [ml/d · bar · m²]

s = Film thickness [µm]

* Electrode equation according to: W. Prins , J. J. Hermans, “Theory of

Permeation through Metal Coated Polymer Films“,

J. Phys. Chem., 1959, 63 (5), pp 716–720

100s

sD

Empirical “electrode equation“ to calculate

permeation rates through single-side coated foil

carrying pinholes


Polymer

Pore

Al

Polymer

PorePinhole

Polymer BAl

D

Polymer A

Passage

surface area

Transport through a single pinhole in aluminium foil

coated on both sidesC

on

cen

trati

on

of

the

pe

rmean

d

Q1 Q2

= + Qcombined Q1 Q2

1 1 1


Outline










Summary


Compositon of cardboard packages – Extrusion steps – L-I-D

1. Lamination



1. Lamination

2. Inside coating



1. Lamination

2. Inside coating

3. Decor


Compositon of cardboard packages – Extrusion steps – D-L-I

1. Decor



2. Lamination

1. Decor



2. Lamination

3. Inside coating

1. Decor


Outline










Summary


Cross-section through a pinhole in the aluminium

foil of a beverage cardboard package

2004_01595.jpg

100 µm

Pinhole


M1 M2 M3

Edge of a cardboard package with a foil break-through

Position 6

Position 7


M1 M2 M3

Break-through in foil close to a screw cap

Position 6

Position 7Screw cap flange

CardboardFoil

Inside PE coating


M1 M2 M3

Position 6

Position 7

Break-throughs at seal seams in cardboard packages


Outline










Summary


„The nip, i.e. the area formed by the contact between the pressure and

chill rolls, constitutes the heart of the extrusion coating process.

Indeed, in this region, some of the most critical properties, such as

adhesion, barrier properties, optical properties, are achieved or lost.“

C. Sollogoub, J.F. Agassant et al.: Thermomechanical Analysis and Modeling of the

Extrusion Coating Process; Polymer Engineering and Science 2008, 1634-1648

What happens in the nip?


6

Steel

Chill-roll

Start of the

solidification

Solidificatio

n finished?Chill roll

Pressure

1 bar

Line pressure

1 bar

Nip foot 2 cm

Time in the nip

2 ms

Formation of mist from

the melt curtain

Air entrapment

possible

Conditions of high performance extrusion coating –

Extrusion lamination

Melt solidification time 2 ms

(300 °C, 25 µm; according Trouilhet/Morris,

European PLACE Conf. Kopenhagen 1999)

Melt > 320 °C

Draw down ratio > 40

TIAG* > 30 ms

*TIAG = time in air gap

Condensation of mist

on foil surface prior

to coating possible


How complete is bonding between aluminium foil and

extrusion coating?

Machine direction

Aluminium etchedaway – View on thetie layer back side

Alu

min

ium

fo

il

Co

ex

View on tie layer back side

The extrusion

coating‘s back side

(former interface

coating/Al) shows a

perfect surface

topography (as a

negative) of the

foil surface from

rolling


2008_010635

High performance extrusion coating back side in SEM

after chemical removal of the aluminium foil

Area with bubbles

View on tie layer back side

Machine direction

The extrusion

coating‘s back side

(former interface

coating/Al) shows a

perfect surface

topography (as a

negative) of the

foil surface from

rolling

and

numerous bubbles

(assumably air entrainment)


2008_010636

MD

Area with

bubbles

View on the tie layer back side

Machine direction

High performance extrusion coating back side in SEM

after chemical removal of the aluminium foil – Detail

Cross section


6

Steel

Chill-roll

Start of the

solidification

Solidificatio

n finished?Chill roll

Foil surface

temperature 20 °CNip foot 2 cm

Time in the nip

2 ms

Conditions of high performance extrusion coating –

Extrusion coating

Melt curtain

Lamination layer behind the foil

can partly melt again

What happens in the presence of bubbles?

Pressure

1 bar

Line pressure

(profile)

1 bar


Aluminium foil

Other side coating

Coextrusion layers

Mask Mask Mask

Ion beam cross sectioning - Preparation of a laminate

to show the contour of interfacial bubbles

Documentation of

the cross section

by electron

microscopy


Example of bubbles in laminates in cross section

Paperboard

Lamination layer

Aluminium foil

PE (coex)

Bubble, due to a thin

place in the paperboard


Example of bubbles in laminates in cross section

Paperboard

Lamination layer

Aluminium foil

PE (coex)

Bubble on the lamination layer side

Secondary bubbles on the

coex coating side


Example of bubbles in laminates in cross section - Detail

Al

PE

PE

PE

Bubble on lamination layer side

Secondary bubbles on the coex coating

side as a consequence of the

compressibility of the bubble in the

lamination layer

Lamination layer

Aluminium foil

PE (coex)

Edge of the bubble

indicates, that the

lamination layer has

been partly remelted

and compressed

during extrusion

coating on the bottom

side of the foil


Outline










Summary


Melt

Die

Alufoil

Extrusion laminating foil and cardboard (schematic)

Chill-roll

Presseur Support roll

Cardboard


Extrusion laminating foil and cardboard with

pre-punched holes (schematic)

Die

Chill-roll

Presseur Support roll

Position 12:00h

Position 6:00h

Position 12:00h

Position 6:00h

Alufoil

Edges of holes: inconsistencies of nip pressure

Melt


Extrusion coating on the aluminium foil inside the

laminate on cardboard with pre-punched holes

(schematic)

Chill roll

Presseur Support roller

Die

Melt curtain

Cardboard/PE/Alu/PE-coex

Melts


12:00h 3:00h

6:00h 9:00h

Edges of pre-punched holes in cardboard in detail


Zone of almost no

laminating pressure

Alufoil

Lamination-PE

Cardboard

Chill roll supports

aluminium foil

mechanically

Pressure roll

Attention: contact

melt-pressure roll

(release properties

recommended)

Pre-punched hole at the nip – LID I. Lamination

Zone of almost no

laminating pressure

Zone of high pressure

at the cardboard edge


6:00h

12:00h


Alufoil Cardboard

Lamination-PE

Pressure roll

Zone of no

lamination pressure

Inside coating





Chill roll supports

aluminium foil via

coating melt

6:00h

12:00h

Pre-punched hole at the nip – LID II. Inside coating

Zone of no

lamination pressure


Karton

Presseurwalze

Stanzlochkante

2016-1134 Presseurkontakt am Stanzlochauslauf -Schematisch

6:00hAlufoil

Lamination-PE

Inside coating

Pressure roll

Attention: Alufoil,

embedded between

PE layers is pressed

through the

prepunched hole and

therefrom stressed

Chill roll:

restricted

support for the

aluminium foil

12:00h





Zone of no

lamination pressure

Zone of no

lamination pressure

Cardboard

Prepunched hole at the nip – LID III. Decor coating


Cross sections of edges of prelaminated holes

(good performance)

M6 Nutzen 1 12:00h M6 Nutzen 3 12:00h

Edge well bonded Rather well bonded position


Cross sections of edges of prelaminated holes

(critical in performance)

M6 Nutzen 1 12:00h M6 Nutzen 3 12:00h

Incomplete bonding between

lamination layer and Al

Incomplete bonding between

lamination layer and Al


View from inside View from outside

View on an prelaminated hole position from inside

and outside a laminate


Lamination layer

Aluminium foil

Lamination layer

Cardboard

Coextrusion layers

Chemical removal of

aluminium foil

View on the lamination

layer formerly in contact

with the aluminium foil

SEM-view on the lamination layer formerly in contact

with the aluminium foil at a prelaminated hole

Diameter of PPLH 7 mm


View on the lamination layer formerly in contact with

the aluminium foil at a prelaminated hole - Details

The bubble, i.e. non-bonding area is completely surrounding the

prelaminated hole („communicating pipe“)

Bubble area

Bubble area


Coextrusion layers

View on the backside of

the coextrusion coating

Chemical removal

of aluminium foil

Aluminium foil

Lamination layer

Cardboard

Coextrusion layers

Diameter of PPLH 7 mm

SEM-view on the backside of a coextrusion coating at

a prelaminated hole


SEM-view on the backside of a coextrusion coating

at a prelaminated hole - Details

The bubbles are surrounding the complete prelaminated hole, intermitted by

polymer bridges

Bubble

area

Bubble

area

Bubble

area

Bubble

area


3:00h9:00h

6:00h

Operator side Middle Drive side

* Diameter of PPLH 20 mm

MD

Appearance of the foil in prelaminated holes after

lamination (example, own trials)

Lamination conditions mechanically not symmetrical!


Break-throughs in the circumference of a

prelaminated hole (own trials)

Illuminated from the backside

View on foil View on cardboard

Field of

break-throughs

Field of

break-throughs

MD


OTR of laminate M1 at overcoated hole-position

Contribution of OCH to OTR: 0.18 cm³ O2 / package∙year∙bar

No visible break-through

MD



Contribution of OCH to OTR: 0.28 cm³ O2 / package∙year∙bar

MD



Contribution of OCH to OTR: Absolute failure regarding OTR

This break-through leads to

indisputably high OTR

MD


OTR of laminate M4 at the overcoated hole-position

Contribution of OCH to OTR: 5.0 cm³ O2 / package ∙ year ∙ bar

Barrier performance

significantly affected

MD


Outline










Summary


Creasing lines of cardboard packages

(own lamination trials, here creasing after lamination)


L1 L

Separation between

PE and cardboard

Notch

Break-through

Creasing lines of cardboard packages after folding

Break-through

Break-through


No foil breaks

Separation

between PE

and cardboard

Creasing lines of cardboard packages after folding

L2 L


M1 M2 M3

Examples of creasing lines of a real package in

transmission light microscopy

Position 6

Position 7


SEM-view on the backside of an inner coating along a

creasing line (creasing before lamination)

Width of the

creasing line

Along the creasing line frequent bubbles


SEM-view on a lamination layer’s bonding side to foil

along a creasing line (creasing before lamination)

Width of the

creasing line

Along the creasing line frequent bubbles


Outline










Summary


Barrier considerations for prelaminated holes for the

case of incomplete bonding between aluminium foil

and coatings on either side of the foil and the

presence of break-throughs

Effective cross section Effective cross section

Lateral distribution of oxygen

From both sides well-covered Break-through at position of incomplete PE bonding

It is essential to avoid break-throughs in the region of prelaminated holes

or to obtain complete bonding of extrusion coatings on aluminium!


Outline










Summary


End and summary

• Aluminium foil as 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 well-coated with polymers, their contribution to a

permeation rate can not be measured at all

• Relative to their size, the effect of small pinholes is stronger

• The example of cardboard packages shows deficiencies in extrusion coating

and lamination, incomplete bonding between foil and polymers, in particular

in the region of pre-punched and laminated holes in the cardboard

• Formation of additional break-throughs in foil can occur during converting

and packing

• Incomplete bonding of coatings coinciding with any kind of break-through in

foil can significantly affect barrier performance of the final package


Claudia Seeger, Heidrun Päseler, Karen Westphal, Bettina Schröder,

Petra Zaied, Markus Lang and Hans-Joachim Krupp R&D Bonn, for

their excellent work in metallography and SEM

Holger Aretz, Galyna Laptyeva, R&D, Michael Eberhard, Stefan Holz,

Hydro Aluminium Grevenbroich, for support and serious discussion

Thomas Hentschel, Joachim Höfler and Klaus Vieregge, R&D, and

Michael Wimmer, Hydro Aluminium Grevenbroich, for proof-reading

Hans-Peter Wagner and Andreas Roos, Ametek, for OTR assistance

and measurements

Thank you for listening!

Acknowledgement to the contributors

75

Documents

High performance extrusion coating of thin … performance...3 Günter Schubert –Hydro Aluminium Rolled Products GmbH, F&E Bonn –High performance extrusion coating and barrier