Interfacial Adhesion Failure

102 Pages·2016·1.96 MB·English

Interfacial Adhesion
Failure
Impact on print-coating surface
defects

HAJER KAMAL ALM

DOCTORAL THESIS IN FIBRE AND POLYMER SCIENCE
KTH Royal Institute of Technology
School of Chemical Science and Engineering
Stockholm, Sweden 2016

Academic Dissertation which, with due permission of the KTH Royal
Institute of Technology, is submitted for public defence for the Degree
of Doctor of Philosophy on Friday the 18th November 2016, at 9:00
a.m. in F3, Lindstedtsvägen 26, Stockholm. Opponent: Docent Janet
Preston, Senior Scientist at Imerys Minerals Ltd, United Kingdom
Interfacial Adhesion Failure
Impact on print-coating surface defects
Hajer Kamal Alm
Supervisors:
Prof. Lars Wågberg, Fibre and Polymer Science, KTH, Sweden
Dr. Göran Ström, Innventia AB, Sweden

Opponent:
Doc. Janet Preston, Senior Scientist at Imerys Minerals Ltd, United Kingdom

Examination committee:
Prof. Lars Järnström, Chemical Engineering, Karlstad University, Sweden
Dr. John Kettle, VTT Technical Research Centre of Finland, Finland
Doc. Anna Sundberg, Laboratory of Wood and Paper Chemistry, Åbo Akademi University,
Finland

Cover image:
A microscope picture, taken by Hajer Kamal Alm, of a pull-off area on an ink tack tested
strip demonstrating areas not covered by ink, i.e. where ink-paper coating adhesion had
failed.
Copyright © Hajer Kamal Alm, 2016
No parts of this dissertation may be reproduced without the written permission from the
author.

TRITA-CHE REPORT 2016:35
ISSN 1654-1081
ISBN 978-91-7729-136-7

Printed in 2016 by Universitetsservice US-AB, Stockholm, Sweden
This work is dedicated to my children
Neah & Nelson

“We must accept finite disappointment,
but we must never lose infinite hope”
- Martin Luther King Jr.
Abstract

The primary aim of this work was to develop a solid knowledge on
formulation effects controlling adhesion of offset ink to coated papers and
to identify important factors of the coating and the printing process
affecting it. Focus lay on comprehending the impact of pigment
dispersant, commonly added additionally in excess to already pre-
dispersed pigment slurry, on ink-paper coating adhesion and ultimately
on the print quality of offset prints.

The work covers laboratory investigations, a pilot coating trial designed to
produce coated material with a span in surface chemistry and structure,
and an industrial offset printing trial.
The lab scale studies quantified ink-paper coating adhesion failure
during ink setting with a developed laboratory procedure based on the
Ink-Surface Interaction Tester (ISIT) and image analysis. Additional
polyacrylate dispersant resulted in slower ink setting and reduced ink-
paper coating adhesion, with a dependence on its state of salt
neutralisation and cation exchange, especially in the presence of moisture
and liquid water.
The industrial printing trial on pilot coated papers was designed to
evaluate how these laboratory findings affected actual full scale offset
print quality. These trials confirmed the dispersant-sensitive effect on
ink-paper coating adhesion, especially at high water feeds. Evaluation of
prints from the printing trial resulted in two fundamentally different
types of ink adhesion failure being identified. The first type being
traditional ink refusal, and the second type considered to be a novel
mechanism referred to as ink-lift-off adhesion failure. Ink-lift-off
adhesion failure occurs when ink is initially deposited on the paper but
then lifted off from the paper in a subsequent print unit. In this work, ink
adhesion failure by this ink-lift-off mechanism was observed to occur
more frequently than failure due to ink refusal.

Print quality evaluation of the industrial prints suggested that water
induced mottle was caused by a combination of ink-surface adhesion
failure, creating white spots on the print, together with the commonly
considered variation in ink layer thickness due to emulsified ink.
iv
Keywords
Ink-paper coating adhesion, offset printing, calcium carbonate pigments,
polyacrylate, dispersant, print mottle, surface chemistry, hygroscopy of
surfaces, coating structure, print quality, water interference mottle

v
Sammanfattning

Målet med detta avhandlingsarbete var att öka förståelsen för hur
bestrykningssmetens formulering påverkar färgadhesionen mellan
offsetfärg och bestruket papper samt att identifiera viktiga faktorer i
bestryknings- och tryckprocessen som påverkar färgadhesionen.
Fokus har legat på att förstå effekterna av dispergeringsmedel, som
oftast tillsätts i överskott vid formulering av bestrykningssmeten för att
säkerställa körbarheten under bestrykningsprocessen, på färgadhesionen
och därmed också på tryckkvaliteten på offsettryck.

Detta arbete omfattar laboratorieförsök, en pilotbestrykning och en
fullskaletryckning. Pilotförsöken var designade för att studera effekten av
både ytkemi och struktur på tryckkvaliteten vid en storskalig process.
Färgadhesionen vid färgsättningen utvärderades och kvantifierades
under laboratorieförsöken med instrumentet Ink-Surface Interaction
Tester (ISIT) i kombination med bildanalys. Resultaten från dessa försök
visade att extra tillsatts av dispergeringsmedlet polyakrylat resulterade i
en långsammare färgsättning samt en försämrad färgadhesion, som
påverkades av akrylatets motjon, speciellt vid förekomsten av vatten och
fukt.
Fullskaletryckningen som utfördes på pilotbestruka papper var
designad för att utvärdera hur resultaten från laboratorieförsöken faktiskt
påverkar tryckkvaliteten vid en storskalig tryckprocess. Fullskaleförsöken
bekräftar färgadhesionens sensibilitet för dispergeringsmedel, speciellt
vid höga fuktvattenflöden i tryckprocessen. Utvärdering av
fullskaletryckta prover resulterade i identifieringen av två fundamentalt
olika typer av bristfällig färgadhesion. Den första typen är traditionell
färgvägran och den andra typen anses vara en ny mekanism och kallas
färgbortlyftning. Bristfällig färgadhesion inträffar, enligt
färgbortlyftningsmekanismen, när färg initialt har applicerats på pappret
vid en tryckenhet men blir senare bortlyft från pappersytan i efterföljande
tryckenheter. I detta arbete har bristfällig färgadhesion orsakad av denna
färgbortlyftningsmekanism setts inträffa oftare än bristfällig färgadhesion
på grund av färgvägran.

Utvärdering av tryckkvaliteten på de fullskaletryckta proverna föreslog att
vatteninducerad flammighet orsakades av en kombination av bristfällig
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adhesion mellan färg och bestruket papper, vilket resulterade i
uppkomsten av vita fläckar på den tryckta ytan, och en variation i
färgfilmens tjocklek orsakad av emulgerad färg.

Nyckelord
Färgadhesion, offsettryckning, kalciumkarbonat pigment, polyakrylat,
dispergeringsmedel, flammighet, ytkemi, hygroskopiska ytor,
bestrykningsskiktets struktur, tryckkvalitet, vatteninducerad flammighet

vii
List of appended Papers

Paper A
“Characterization of Ink Adhesion Failure; Effect of Pre-dampening of
Carbonate Containing Coatings”, Hajer Kamal, Göran Ström, Joachim
Schoelkopf and Patrick A. C. Gane, Journal of Adhesion
Science and Technology, 2010, 24:3, 449-469

Paper B
“Effect of excess dispersant on surface properties and liquid interactions
on calcium carbonate containing coatings”, Hajer Kamal Alm, Göran
Ström, Katarina Karlström, Joachim Schoelkopf and Patrick A. C. Gane,
Nordic Pulp & Paper Research Journal, 2010, 25:1, 82-92

Paper C
“Temperature and moisture effects on wetting of calcite surfaces by
offset ink constituents”, Hanna Koivula, Hajer Kamal Alm, and Martti
Toivakka, Colloids and Surfaces A: Physicochemical and Engineering
Aspects, 2011, 390, 105-111

Paper D
“Moisture sorption by thin layers of sodium and calcium neutralized
polyacrylate”, Hajer Kamal Alm, Göran Ström, Joachim Schoelkopf and
Patrick A. C. Gane, Presented at the 8th International paper and Coating
Chemistry Symposium, pp.71-73, Stockholm, June 2012

Paper E
“Ink-lift-off during offset printing: a novel mechanism behind ink-paper
coating adhesion failure”, Hajer Kamal Alm, Göran Ström, Joachim
Schoelkopf and Patrick A. C. Gane, Journal of Adhesion
Science and Technology, 2014, 29:5, 370-391

Paper F
“Ink adhesion failure during full scale offset printing: causes and impact
on print quality”, Hajer Kamal Alm, Göran Ström, Joachim Schoelkopf,
Cathy Ridgway and Patrick A. C. Gane, Journal of Print and Media
Technology Research, 2015, 4:4, 257–278

viii
Contribution to the Papers A-F

Hajer Kamal Alm (HKA) is the principal author of all Papers included in
this dissertation with the exception of Paper C. HKA also performed most
of the experimental work with the following exceptions:

 Turbidity analysis (Paper B)
 Mercury porosimetry analysis (Paper B and Paper F)
 Contact angle measurements and surface energy determination (Paper
C)
 SEM and EDS analysis (Paper E)
 Permeability analysis (Paper F)

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Contents

List of symbols _______________________________________ 1
List of abbreviations ___________________________________ 2
1. Introduction _____________________________________ 3
1.1 Setting the scene ____________________________________ 3
1.2. Objective ________________________________________ 4
2. Background ______________________________________ 4
2.1 Pigment coating ____________________________________ 4
2.2 Dispersing agent ___________________________________ 7
2.2.1 Polyacrylate _____________________________________________ 9
2.2.2 Calcium and polyacrylate interactions ___________________________ 10
2.2.3 Polyacrylate chain configuration _______________________________ 12
2.2.4 Polyacrylate stabilization ____________________________________ 13
2.2.5 Polyacrylate dosage _______________________________________ 13
2.3 Lithographic printing process _________________________ 14
2.3.1 Dampening solution _______________________________________ 16
2.3.2 Offset Ink ______________________________________________ 16
2.3.3 Emulsification of ink with fountain solution _______________________ 17
2.3.4 Ink transfer and ink splitting mechanisms ________________________ 17
2.3.4.1 Ink transfer mechanisms _________________________________ 18
2.3.4.2 Ink splitting mechanisms ________________________________ 21
2.3.5 Ink-paper coating interaction _________________________________ 23
2.3.5.1 Ink setting and drying ___________________________________ 23
2.3.5.2 Ink adhesion versus cohesion______________________________ 25
2.3.6 Offset print quality ________________________________________ 27
2.3.6.1 Print gloss___________________________________________ 28
2.3.6.2 Print density _________________________________________ 30
x