Determination of Metal Adhesion Strength
of Metallized Films by Peel Tests
E. Kucukpinar1, K. Noller1, M. Jesdinszki1, N. Rodler1, V. Cassio2, D. Blondin2 ,
and H.-C- Langowski1
1
Fraunhofer Institute for Process Engineering and
Packaging (Fraunhofer IVV), Freising, Germany
2
MET-LUX S.A.
Site du PED
L-4801 Rodange
WEB COATING & HANDLING CONFERENCE,
8-11 June, 2014, Portugal
© Fraunhofer
Outline
 Introduction
 Peel test procedures for metal adhesion
 Experimental results and problems
 Alternative peel test aproaches
 Summary and Conclusions
© Fraunhofer
Outline
 Introduction
 Peel test procedures for metal adhesion
 Experimental results and problems
 Alternative peel test aproaches
 Summary and Conclusions
© Fraunhofer
Metallized films in Packaging Industry
Metallizer:
- Pre-treatment
- Vacuum web
coating
Converter:
Lamination
and printing
SUBSTRATE FILM
(e.g. BOPP, PET)
METALLIZED FILM
METALLIZED LAMINATES
Sealable top layer
(e.g. PE)
PET substrate film
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PACKED
END-PRODUCT
Film Producer:
Substrate film
production
Metallized Films in Packaging Industry
 Metallized Films
 Metallized film production worldwide: 2.4 x 1010 m2 / year (source AWA 2011)
 About 85% of metallized films are used in flexible packaging
 Worldwide flexible packaging market: € 50 billion
 Why metallisation?
 Barrier improvement up to factor 100, longer shelf life of packed products
 Barrier to light
-------- 300 nm
 Decorative
 Higher productivity
 Low-cost production
Al layer, ca. 50 nm
SiOx layer, ca. 60 nm
 Important quality parameter
 Adhesion strength between thin metallised layer and the substrate
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Metallised Films in Packaging Industry
PE / Adhesive / PET 12 µm / MET / Adhesive / Printing / PET 12 µm
 Metal adhesion problem:
PET 12 µm
substrate
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 Unexpected de-lamination between
PET 12 µm substrate film and the
metallised layer
 ~ 100 % metal transfer to the
adhesive laminated top layer
Metallised Films in Packaging Industry
 Products sensitive to oxygen and water / water losses
 (BO)PET substrates for high oxygen barrier
 (BO)PP substrates for general purposes
Laminate
bond
strength
Metal
adhesion
© Fraunhofer
Heat sealing layer
adhesive
Adhesive
Barrier layer
Substrate film
Al layer
Outline
 Introduction
 Peel test procedures for metal adhesion
 Experimental results and problems
 Alternative peel test aproaches
 Summary and Conclusions
© Fraunhofer
Peel Test Procedures
Metal adhesion: EAA-Peel test
Laminated-film: EAA
(used in peel tests)
Metal layer
Substrate film (e.g. PET)
Peel direction
Double-sided
adhesive tape
Al-plate (1 mm thick)
Peel-off angle:
180o
.
Peel distance
Fixed in the bottom clamp
© Fraunhofer
Laminate bond strength, sealed-seam
strength: 90o peel test
What do you really measure in a peel test?
A.J. Kinloch et. al., Int. J. of Fracture 66 (1994) 45 - 70
Measurement distance (mm)
Force-Displacement Curve in an
Ideal Peel Test
© Fraunhofer
Measured work consists of:
• Delamination
• Elastic deformation
• Plastic deformation
Just a fraction of the work
goes into delamination
Properties of Extruded EAA-film
Ethylene
(E)
Water &
moisture
resistance
Polarity
Themoplasticity
Softening
Flexibility
Adhesion
Crystallinity
Low heat seal
temperature
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Peel Test Parameters
Acrylic Acid
(AA)
Procedure
EMA
AIMCAL
EAA
(9%
acrylic
acid)
Seal Parameters
EAA
Thickness
DuPont
Primacor
1410
25 µm
Dow
Chemical
DAF899
25 µm
(oC)
t
(s)
P
(bar)
105
20
4
104.4
(220 oF)
15
1
T
Outline
 Introduction
 Peel test procedures for metal adhesion
 Experimental results and problems
 Alternative peel test aproaches
 Summary and Conclusions
© Fraunhofer
Metallized Films – Thermal Evaporation
Vacuum Metallization
Process:
•
•
•
Typical width: 2.4 up to 4.5 m
Max. web speed: 18 m/s
Annual output: Some
hundreds of millions of m²
Three PET (12 µm)
films with different
surface properties
were selected:
7
Winding
chamber
8
6
5
1
3
Evaporation
chamber
• Sample - A
• Sample - B
• Sample - C
1 Unwinder
2 Spread roll
3 Plasma treatment
4 Evaporation source
5 Process roll
6 In-line optical monitor
7 Tension roll
8 Rewinder
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4
2
EAA-Peel Test: Sample-A (Metallized PET)
After EAA - peel test
PET-A 12µm / met // EAA
Peak-3
Peak-1
2.0
Force (N/15 mm)
Peak-2
Peak-4
1.5
Successful
EAA-peel test!
1.0
„0.7“
0.5
Peak-4
Peak-3
Peel
distance:
Peak-2
≈ 41 mm
Peak-1
Average of 10 specimens
Representative test specimen
0.0
0
20
40
60
80
Measurement distance (mm)
Representative
test specimen
Source: M. Jesdinszki, C. Struller, N. Rodler, E. Kucukpinar, H.-C. Langowski, D. Blondin and V. Cassio, J. Adhesion Sci. Technol., 2012
© Fraunhofer
EAA-Peel Test: Sample-B (Metallized PET)
PET-B 12µm / met // EAA
Improved Adhesion (B)
4.0
Force (N/15 mm)
3.5
„3“
3.0
Problematic
EAA-peel
measurement!
2.5
Partial
delamination
of Aluminum!
2.0
1.5
Peel
distance:
≈ 30 mm
Representative test specimen-1
Representative test specimen-2
1.0
0.5
0.0
0
20
40
60
80 100 120 140 160
Specimen-1
Specimen-2
Measurement distance (mm)
Source: M. Jesdinszki, C. Struller, N. Rodler, E. Kucukpinar, H.-C. Langowski, D. Blondin and V. Cassio, J. Adhesion Sci. Technol., 2012
© Fraunhofer
EAA-Peel Test: Sample-C (Metallized PET)
PET-C 12µm / met // EAA
Further Improved
Adhesion (C)
6
Force (N/15 mm)
5
4
Problematic
EAA-peel
measurement!
„4“ ?
„5“ ?
3
No
delamination
of Al, EAA film
stretching
2
EAA-film
1
Peel
distance:
≈ 30 mm
Representative test specimens
0
0
20
40
60
80
100
120
140
160
Measurement distance (mm)
Source: M. Jesdinszki, C. Struller, N. Rodler, E. Kucukpinar, H.-C. Langowski, D.
Blondin and V. Cassio, J. Adhesion Sci. Technol., 2012
© Fraunhofer
Representative test
specimens
Outline
 Introduction
 Peel test procedures for metal adhesion
 Experimental results and problems
 Alternative peel test aproaches
 Summary and Conclusions
© Fraunhofer
Mechanical Properties of Extruded, Heat - Sealable Films
 EAA
 Amorphous Polyamide (aPA)
 Amorphous poly(ethylene terephthalate) (aPET)
90
aPA
90
70 aPET
60
50
40
aPET
80
EAA
30
20
10
Force (N/15 mm)
Tensile Stress (MPa)
80
70
60
50
40
30
aPA
20
10
0
0
100 200 300 400 500 600 700
Tensile Strain (%)
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EAA
0
0
20
40
60
80 100 120 140
Tensile Strain (%)
Alternative Approaches – aPET Peel Test
3.0
PET 12µm / met // aPET
Average
Typical range
A
B
C
Force (N/15 mm)
2.5
Sample-C
Laminate-C (c)
2.0
1.5
Sample-B
Laminate-B (c)
1.0
0.5
Sample-A
Laminate-A (c)
0.0
0
20
40
60
80
Measurement distance (mm)
Full delamination of Al
© Fraunhofer
Correct sequence (A < B < C)
Alternative Approaches: EAA, aPA, aPET Peel Test
Comparisons
PET 12µm / met // EAA
PET 12µm / met // aPA
PET 12µm / met // aPET




Peeled laminates are no chains
that break at the weakest link
If you like reliable results, avoid
the use of yielding polymers in
peel tests!
Relative rankings are only
possible with identical polymer
films
But: If you just like high figures
for your customers, use yielding
polymers, also in laminates
© Fraunhofer
Average Peel Force (N/15 mm)
Peel
tests
EAA
(25 µm)
aPA
(20 µm)
aPET
(100 µm)
(A)
0.67
0.2
0.4
Al layer partially
peeled off
Stretching of
EAA-film
0.3
0.7
Al layer not
peeled off at all
EAA-film
stretches
Measured Force:
≥ 3.4 N/15 mm
0.8
1.8
•
(B)
•
•
(C)
•
•
Alternative Approaches: PE-LD Peel Test
PET 12µm / met / Adhesive / PE-LD
Lamination of low density polyethylene (PE-LD) film (30 µm) by polyurethane based adhesive
Bench - scale lamination: K-bar
© Fraunhofer
Pilot - scale lamination
Alternative Approaches: PE-LD Peel Test
Bench - scale lamination
Pilot - scale lamination
1.2
1.2
Sample-B
Force (N/15 mm)
Force (N/15 mm)
Sample-B
1.0
1.0
0.8
0.6
Sample-A
0.4
Average
0.2
0.8
0.6
Sample-A
0.4
Average
0.2
Typical range
Typical range
0.0
0.0
0
20
40
60
Measurement distance (mm)
© Fraunhofer
80
0
20
40
60
Measurement distance (mm)
80
Alternative Approaches: PE-LD Peel Test
Average Peel Force (N/15 mm)
Peel
tests
EAA
(25 µm)
(Bench)
(Pilot)
(A)
0.7
0.6
0.6
0.8
0.8
•
(B)
•
•
(C)
•
•
© Fraunhofer
Al partially peeled
off
Stretching of
EAA-film
Al not peeled off
at all
EAA-film
stretches
≥ 3.4 N/15 mm
Sample-A
Sample-B
Sample-C
PE-LD (30 µm)
„Bench“„Pilot“ „Bench“„Pilot“ „Bench“„Pilot“
≥ 2.4
≥ 2.8 N/15
Current standards, e.g. EN ISO 11339 or EN 1895 (similar)
Required results:
EN ISO 11339: max., average
and min. force
EN 1895: average forces
© Fraunhofer
Current standards, e.g. DIN 55529
Required results:
• Initial force
• Average separation force
• Maximum force
• Fracture images
(see examples)
Where are e.g.
• delamination distances?
• elastic or plastic deformation?
© Fraunhofer
Summary and Conclusions
 There is a lack of test methodologies for the measurement of metal adhesion
on polymeric substrates
 Current measurement standards are largely incomplete
 The available EAA-peel tests are not always applicable by the metallizing
companies due to the overstretching of the EAA-film during the peel test
 Mechanically stronger heat sealable films may be more promising
 Peel test results of laminates are influenced by several factors, which are
usually not recorded during the measurements such as peel distance, peel-off
angle, and thickness, elastic, viscoeleastic properties of the peeled material,
 Relations to practical load conditions are still not known
 There is still a considerable amount of work to be done about development of
adhesion test methods relevant to packaging and packaging materials!
© Fraunhofer
Thank you for your attention!
Published in the Special Issue of Journal of Adhesion Science and Technology
„Adhesion Aspects in Packaging Industry“:
Evaluation of adhesion strength between thin aluminum layer and poly(ethylene
terephthalate) substrate by peel tests – A practical approach for the packaging
industry
Marius Jesdinszki, Carolin Struller, Norbert Rodler, Esra Kucukpinar and Horst-Christian Langowski
Fraunhofer Institute for Process Engineering and Packaging, Giggenhauser Strasse 35, 85354
Freising, Germany
and David Blondin and Valerio Cassio
MET-LUX Vacuum Metallizing, B.P. 28, Site du P.E.D., L-4801 Rodange
© Fraunhofer