Place for, company logo from speaker Adhesion to Foil – More than Just a One-Sided Story Günter Schubert Otto Plassmann Session: Barrier Packaging - Paper 7698
Structure • Introduction to aluminium foil surfaces • Storage of semi-finished laminates • Surface change during storage • Case studies in adhesion failure • Examination of foil/film interfaces using IR-ATR • Carbonyl Index –not only an issue of PE oxidation • Conclusions PE Adhesion to Foil – More than Just a One-Sided Story 2
Delaminations Occurring in Extrusion Coatings Delamination Aluminium foil LDPE Printed paper Pouch for a typical German barbecue spice mixture Adhesion to Foil – More than Just a One-Sided Story 3
Structure of a Flat Pouch Internal contact with packaged good Flat pouch PE coex 30 µm Alufoil 9 µm PE ex 20 µm Paper 60 g/m² PE (printed) Pouch for a typical German barbecue spice mixture Adhesion to Foil – More than Just a One-Sided Story 4
Coil Annealing Oxygen can enter the coil Core Rolling oil can exit via the coil ends Furnace Inside the coil Furnace t begin concentration t 1 Roling oil t 2 t 3 t end Adhesion to Foil – More than Just a One-Sided Story Adhesion to Foil – More than Just a One-Sided Story 5
Oxide Growth During Coil Annealing Before annealing After annealing Thin film of rolling oil Rolling oil residues Top layer 1-8 nm 1-6 nm Oxide Top layer Barrier layer 1-2 nm 2-8 nm Barrier layer Aluminium Aluminium Metal/oxide interface where oxide growth takes place If annealing time is too long, the oxide layers of adjacent surfaces can stick together - resulting in poor decoiling and the risk of web breaks Adhesion to Foil – More than Just a One-Sided Story 6
Coiling Pressure Distribution in a Coil (Schematic) Relative pressure Low Core High Adhesion to Foil – More than Just a One-Sided Story 7
Wettability Profile Across a Foil Web Wettability High Moderate High (water) Relative Moderate High Moderate winding pressure Adhesion to Foil – More than Just a One-Sided Story 8
Different Types of Chemical Bonding to Aluminium Foil CH 2 CH 2 C = O O (CH 2 ) 6 Graft silane HO - C O O Hydrogen bond C = O H Si - O - Soap O OH OH O O O Al - O - Al - O Al - O - Al - O - Al - Al - O - Al - O - Al O O Oxide Top layer Barrier layer Al - O - Al - O - Al Metal Adhesion to Foil – More than Just a One-Sided Story 9
Practice of Storage of Single-Side Converted Aluminium Foil Contact between the blank side and the adjacent coated side can lead to a transfer of matter and adversely affect adhesion in the subsequent converting step (e.g. a 50 g/m²-paper with 4 – 8% humidity contains 2 - 4 g/m² water) Side A coated Side B blank Adhesion to Foil – More than Just a One-Sided Story 10
Hydroxylation of an Oxide Layer on Aluminium Foil Exposed to Air H R O O C O H C OH R R H OH R O O C OH C H O OH H H H H O O O O H H H H Oxide layer Aluminium oxide layer Aluminium foil Adhesion to Foil – More than Just a One-Sided Story 11
Hydroxylation and Oxide Growth on an Al/PE Laminate Stored at Elevated Temperature with High Humidity 0,40 *Al-Verbund, 16 825 311 Al-Seite, Polymer abgezogen, good, MW3, GG 0,38 *Al-Verbund, 16 825 312 Al-Seite, Polymer abgezogen, bad, MW3, GG 0,36 0,40 *Al-Verbund, 16 825 311 Al-Seite, Polymer abgezogen, good, MW3, GG --- IR-ATR of aluminium surface of newly produced laminate 0,38 0,34 *Al-Verbund, 16 825 312 Al-Seite, Polymer abgezogen, bad, MW3, GG 0,36 0,32 --- IR-ATR of aluminium surface after storage 0.30 0,34 0,30 0,32 0,28 0,26 Absorbance 0,24 0,22 Ext inkt 0.20 0,20 ion ν (O-H) ∼ 3300 cm -1 ν (A-O) ∼ 950 cm -1 0,18 0,16 0,14 0,12 0.10 0,10 0,08 0,06 0,04 0,02 0.00 0,00 4000 1500 3000 2000 2000 1000 500 4000 3000 2000 1500 1000 Wellenzahlen (cm-1) 500 Wave number [cm -1 ] Adhesion to Foil – More than Just a One-Sided Story 12
Changes Occurring in Oxide Layer on Aluminium Foil Exposed to Air H R H O H O C O OH H R O H O C O O OH C H H R R H R OH H H C C O H H O H H O O O O O Hydroxylated top layer Aluminium oxide layer Oxide layer Aluminium foil Adhesion to Foil – More than Just a One-Sided Story 13
Bonding to an Oxide Layer on Aluminium Foil Exposed to Air CH 2 O Polymer chain of coating CH 2 CH 2 C R CH 2 CH 2 OH H R O H CH 2 CH 2 C H O CH H R R OH O C C C H O H H H H H O O O O O O O O Hydroxylated top layer Aluminium oxide layer Oxide layer Aluminium foil Adhesion to Foil – More than Just a One-Sided Story 14
Coiling and Storage of Aluminium Foil Converted on One Side - Transfer of Matter from the Adjacent Surface Clay-coated paper Extruded PE Aluminium foil Adhesion to Foil – More than Just a One-Sided Story 15
Transfer of Ester Wax Species in a Coil from a Coated Paper to an Aluminium Surface 0,20 0.20 *Al-Verbund, Schlechtmuster "Bad, 2.5 Monate", Rand, MW3, GG *Al-Verbund, Gutmuster "48h", Rand, MW3, GG 0,18 0.18 0,16 0.16 Surface plaque after 0,14 0.14 a storage time of 10 Absorbance ν (Al-O) 950 cm -1 weeks 0,12 0.12 Ext inkt 0,10 0.10 ion Newly produced 0,08 0.08 laminate, aged for 0,06 0.06 3d/40°C in a stack 0,04 0.04 0,02 0.02 0,00 0.00 4000 1500 3000 2000 2000 1000 500 4000 3000 2000 1500 1000 Wellenzahlen (cm-1) 500 Wave number [cm -1 ] Processing aid on foil surface leads to poor ink adhesion Adhesion to Foil – More than Just a One-Sided Story 16
Coiling and Storage of Aluminium Foil Converted on One Side – an Adhesion Issue Extrusion coating Aluminium foil Printing pattern Adhesion to Foil – More than Just a One-Sided Story 17
Printing-Pattern-Related Adhesion of an Extrusion Coating on Aluminium Foil Areas of good adhesion Areas of poor adhesion O Adhesion to Foil – More than Just a One-Sided Story 18
Different Peel Patterns of the PE Coating Area with the best adhesion Stick-slip pattern ⊥ Peel direction MD + peel direction Area with the poorest adhesion No peel pattern O Adhesion to Foil – More than Just a One-Sided Story 19
Examination of Peel Interfaces between Coating and Foil Using IR-ATR Pressure stamp Delaminated interface (on coating or foil) Diamond crystal ZnSe crystal IR spectrometer Adhesion to Foil – More than Just a One-Sided Story Adhesion to Foil – More than Just a One-Sided Story 20
IR-ATR Spectra of Outer Coating Surface and Peel Interfaces 0,034 0.30 0,032 *Polymer, Zone good, glänzende Seite, MW3, ATR *Polymer, Zone good, matte Seite, MW3, ATR 0,030 *Polymer, Zone bad, glänzende Seite, MW3, ATR 0,028 *Polymer, Zone bad, matte Seite, MW3, ATR 0,026 Absorbance 0,024 Ester species present in cases of 0.20 0,022 poor adhesion ( ν (C=O) 1739 cm -1 ) 0,020 Ext 0,018 inkt ion Acid compounds 0,016 ν (C=O) 1719 cm -1 0,014 0,012 0.10 0,010 0,008 0,006 0,004 0,002 0,000 0.00 1800 1750 1700 1650 1800 1750 1700 1650 Wellenzahlen (cm-1) Wave number [cm -1 ] O Adhesion to Foil – More than Just a One-Sided Story 21
Preparation of Interfaces in Aluminium/ Polyethylene Laminates for IR-ATR Aluminium foil dissolved in dilute acid Coating (single or coex) Side A Side B Aluminium foil LDPE-lamination layer Information depth of IR-ATR Cardboard or paper ~ 2 - 4 µm Adhesion to Foil – More than Just a One-Sided Story 22
Polyethylene Surface at the Frontier of Acid Attack on Aluminium Aluminium, not yet dissolved PE-coating surface for examination Frontier of acid attack Adhesion to Foil – More than Just a One-Sided Story 23
Oxidation Index Dependent on the Surface Preparation Method 0,065 *Al-Verbund, LD MFR4, Poly/Al-Seite, HCl, 2cm, GG *Al-Verbund, LD MFR4, Poly/Al-Seite, HCl, 19cm, GG *Al-Verbund, LD MFR4, Poly/Al-Seite, HCl, 37.5cm, GG 0,060 0.60 *Al-Verbund, LD MFR4, Poly/Al-Seite, HCl, 56cm, GG *Al-Verbund, LD MFR4, Poly/Al-Seite, HCl, 73cm, GG 0,055 *Al-Verbund, LD MFR4, Poly/Al-Seite, Polymer abgezogen, 2cm, GG ν (C=O) 1719 cm -1 *Al-Verbund, LD MFR4, Poly/Al-Seite, Polymer abgezogen, 19cm, GG 0,050 *Al-Verbund, LD MFR4, Poly/Al-Seite, Polymer abgezogen, 37.5cm, GG Absorbance (scale) 0.50 *Al-Verbund, LD MFR4, Poly/Al-Seite, Polymer abgezogen, 56cm, GG 0,045 *Al-Verbund, LD MFR4, Poly/Al-Seite, Polymer abgezogen, 73cm, GG 0,040 Al foil dissolved Ext 0.40 in acid 0,035 inkt ion 0,030 0,025 0.30 PE peeled off - 0,020 lower intensity! 0,015 0.20 0,010 0,005 -0,000 0.00 1800 1750 1700 1650 1600 1550 1800 1750 1700 1650 1600 1550 Wellenzahlen (cm-1) Wave number [cm -1 ] Adhesion to Foil – More than Just a One-Sided Story 24
Preparation of Interfaces in Aluminium/ Polyethylene Laminates by Peeling Functional groups close to the surface Better adhesion leads to elongation of the coating and lower concentration of C=O-groups Extrusion coating close to the Aluminium foil surface Functional groups close to the surface Oxide layer + coating Peel direction ∼ 180 ° residues Extrusion coating Aluminium foil Adhesion to Foil – More than Just a One-Sided Story 25
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