papermaking science and technology book 11 … · papermaking science and technology a book series...
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Papermaking Science and Technologya book seriescovering the latesttechnology andfuture trends
Book 11
Second Edition
Totally updated version
Book editorJouni Paltakari, D.Sc. (Tech.), Professor, Department of Forest Products Technology, Helsinki University of Technology
PublisherPaper Engineers’ Association/Paperi ja Puu Oy
Paperi ja Puu Oy
Pigment Coating and Surface Sizing of Paper
10
Table of Contents1 Introduction to pigment coating and surface sizing of paper and board ..........................11
2 Pigment-coated products ....................................................................................................29
3 Base paper ...........................................................................................................................41
4 Coating materials – general ................................................................................................59
5 Pigments ..............................................................................................................................72
6 Binders ...............................................................................................................................191
7 Co-binders and thickeners ................................................................................................226
8 Additives ............................................................................................................................280
9 Surface sizing chemicals ..................................................................................................309
10 Rheology of pigment slurries and coating formulations ..................................................316
11 Coating layer consolidation and formation of the coating layer structure .....................355
12 Coating layer measurement and analysis techniques .....................................................398
13 Coating colour preparation and handling .........................................................................431
14 Coating and surface sizing technologies ..........................................................................460
15 Drying of paper coatings and drying equipment ..............................................................557
16 Process control and automation in coating machine ......................................................587
17 Development trends and future outlook ...........................................................................597
Conversion factors .............................................................................................................605
Index ...................................................................................................................................607
11
Introduction to pigment coating and surface sizing of paper and board
Objectives of coating and surface sizing1 ............................................................................12
How coating affects paper properties2 ................................................................................13
Coating colour composition3 ................................................................................................14
Coating materials3.1 ...................................................................................................................14
Coating colour preparation — coating formulations3.2 ...............................................................16
Surface sizing – general4 ......................................................................................................18
Coating process — general5 ................................................................................................18
Coating process6 ...................................................................................................................19
Coating quality and process runnability6.1 ..................................................................................23
Economics of coating7 ..........................................................................................................24
Coating material viewpoint7.1 .....................................................................................................24
Technological viewpoint7.2 .........................................................................................................25
Appendix — Principle of a form for coating colour make-down ..............................................27
CHAPTER 1
29
CHAPTER 2 Pigment-coated products
Introduction1 ..........................................................................................................................30
Coated paper and board grades2 ..........................................................................................30
Coated papers2.1 .......................................................................................................................30
Coated boards2.2 .......................................................................................................................31
End-use demands for coatings3 ...........................................................................................32
Printing processes3.1 .................................................................................................................32
General 3.1.1 printing paper requirements ..........................................................................33
Requirements for offset printing paper3.1.2 .......................................................................36
Requirements for rotogravure printing paper3.1.3 ..............................................................36
Requirements for flexo printing paper3.1.4 .........................................................................36
Requirements for inkjet printing paper3.1.5 .......................................................................37
Requirements for electrophotography paper3.1.6 ...............................................................37
Summary of requirements for printing3.1.7 ........................................................................37
Converting processes3.2 .............................................................................................................39
References ............................................................................................................................40
41
CHAPTER 10CHAPTER 3 Base paper
Introduction1 ..........................................................................................................................42
Transport mechanisms2 ........................................................................................................43
Coating colour penetration2.1 .....................................................................................................43
Coating colour liquid phase penetration2.2 .................................................................................44
General requirements for base papers and how these are influenced3 .............................46
Strength and its uniformity3.1 .....................................................................................................46
Sheet structure in z-direction3.2 .................................................................................................48
Surface properties and pore structure3.3 ....................................................................................49
Interactions between base paper and coating colour – influence on coated paper 4
properties .............................................................................................................................50
Coating holdout4.1 ......................................................................................................................50
Coating consolidation / coating layer structure4.2 .......................................................................52
Roughening of the base sheet in contact with water4.3 ..............................................................54
Runnability at the coater5 .....................................................................................................54
References ............................................................................................................................56
59
Coating materials – general
Coating pigments1 – general ................................................................................................60
Functions of pigment in the coating layer1.1 ...............................................................................60
Ideal pigment1.2 .........................................................................................................................60
Classification of pigments1.3 ......................................................................................................61
Key properties of pigments1.4 ....................................................................................................62
Criteria for selecting pigments1.5 ...............................................................................................65
Coating binders2 – general ...................................................................................................65
Functions of binders2.1 ..............................................................................................................65
Ideal binder2.2 ............................................................................................................................65
Types of binder2.3 ......................................................................................................................66
Criteria for selecting binders2.4 ..................................................................................................67
Binding power of binders2.5 .......................................................................................................68
Binder demand of pigment2.6 .....................................................................................................68
Co-binders and thickeners2.7 .....................................................................................................69
Coating additives3 .................................................................................................................70
References ............................................................................................................................71
CHAPTER 4
72
CHAPTER 5
CHAPTER 5 Pigments
Kaolin 1 ...................................................................................................................................76
Occurrence and mineralogy1.1 ...................................................................................................76
Manufacturing coating kaolin grades1.2 .....................................................................................78
Properties of 1.3 coating kaolins ..................................................................................................79
Particle shape1.3.1 ............................................................................................................79
Particle size1.3.2 ................................................................................................................80
Typical physical properties of North American, and Brazilian kaolins1.3.3 ...........................81
Calcined1.4 , structured and engineered kaolins ..........................................................................82
Dispersion1.5 of kaolins ..............................................................................................................84
Flow properties and 1.6 runnability of kaolin-containing coating colours ......................................86
Kaolin applications in paper and board coating1.7 ......................................................................89
Brazilian kaolin1.7.1 s .........................................................................................................89
North American kaolin1.7.2 s ..............................................................................................89
Structured and engineered kaolins1.7.3 .............................................................................90
Compositions and makedown of coating colours containing kaolin1.8 .........................................90
Properties of coated paper containing kaolin1.9 ..........................................................................91
Woodfree topcoating1.9.1 ..................................................................................................94
LWC/MWC offset1.9.2 ........................................................................................................95
LWC rotogravure1.9.3 ........................................................................................................95
Ground calcium carbonate2 ..................................................................................................98
Material description2.1 ...............................................................................................................98
Classification2.1.1 ..............................................................................................................99
Methods of manufacture2.1.2 ............................................................................................99
Calcium carbonate — solubility2.1.3 ...............................................................................101
Suspension stability — slurries and their response in coating colours2.1.4 ......................101
Product characteristics, availability and handling2.1.5 ......................................................103
Reasons for use in paper coating2.1.6 .............................................................................104
Analytical procedures2.1.7 ...............................................................................................107
73
Pigments
Economic and market factors2.2 ...............................................................................................108
Future outlook2.3 ......................................................................................................................108
Acknowledgements2.4 ..............................................................................................................109
Talc 3 .....................................................................................................................................110
History of talc in paper3.1 .........................................................................................................110
Occurrence and mineralogy3.2 .................................................................................................110
Magnesium carbonate derivative ore bodies3.2.1 .............................................................111
Serpentine derivative ore bodies3.2.2 ..............................................................................111
Silica aluminous rock derivative ore bodies3.2.3 ..............................................................112
Magnesium sedimentary deposit derivative ore bodies3.2.4 .............................................112
Mineralogy and morphology of refined coating talc3.3 ..............................................................113
Structural definition of talc3.3.1 .......................................................................................113
Coating talc morphology3.3.2 ...........................................................................................115
Surface free energy of talc and talc/chlorite mixtures3.3.3 ...............................................115
Processes for refining paper coating talc3.4 ..............................................................................117
Raw material refining processes3.4.1 ..............................................................................117
Milling3.4.2 ......................................................................................................................118
Production of talc slurries3.4.3 .........................................................................................120
Delivery forms, costs and logistics3.4.4 ...........................................................................120
Talc applications in paper coating3.5 ........................................................................................121
Talc in the production of LWC rotogravure publication papers3.5.1 ...................................121
Talc in the production of offset printing grades3.5.2 .........................................................123
Talc in special coating applications3.5.3 ..........................................................................124
Acknowledgements3.6 ..............................................................................................................124
Calcium Sulphate (Gypsum)4 ..............................................................................................125
Properties of Calcium Sulphate (Gypsum)4.1 .............................................................................125
Physical properties4.1.1 ...................................................................................................126
Solubility4.1.2 ..................................................................................................................126
Manufacturing4.2 .....................................................................................................................127
Crystallisation4.2.1 ..........................................................................................................127
Grinding4.2.2 ...................................................................................................................128
Environmental aspects4.2.3 .............................................................................................128
Composition and make-down of gypsum-containing coating colours4.3 ...................................128
Flow properties and runnability of gypsum-containing coating colours4.3.1 .....................129
Coating applications of various grades of gypsum4.3.2 ....................................................130
Properties of gypsum-containing coatings and coated papers4.3.3 ..................................130
Coated broke, gypsum solubility and wet end control4.3.4 ...............................................132
74
CHAPTER 5
Precipitated calcium carbonate5 ........................................................................................134
Manufacturing of PCC and PCC coating grades5.1 ....................................................................134
Physical properties of PCC coating grades5.2 ............................................................................137
Compositions and makedown of coating colours containing PCC5.3 ..........................................139
Flow properties and runnability of PCC-containing coating colours5.4 .......................................139
Coating applications of various grades of PCC5.5 ......................................................................141
Properties of coated papers containing PCC5.6 .........................................................................142
Future outlook5.7 ......................................................................................................................144
Summary5.8 .............................................................................................................................145
Synthetic plastic pigment6 s ................................................................................................146
Principal classes6.1 ..................................................................................................................146
Chemical and physical properties6.2 .........................................................................................146
Method of manufacture6.3 ........................................................................................................148
Shipping, handling, and storage6.4 ...........................................................................................148
Application and properties6.5 ...................................................................................................149
Typical formulations6.5.1 .................................................................................................149
Rheology6.5.2 ..................................................................................................................149
Optical performance6.5.3 .................................................................................................150
Specific uses6.5.4 ............................................................................................................150
Specialty uses6.5.5 ..........................................................................................................151
Advancements in hollow-spheres6.5.6 .............................................................................151
Mechanism of performance6.6 .................................................................................................152
Gloss6.6.1 ........................................................................................................................152
Opacity6.6.2 ....................................................................................................................153
Brightness6.6.3 ................................................................................................................153
Bulk6.6.4 .........................................................................................................................153
Thermal insulation6.6.5 ...................................................................................................154
Analytical procedures6.7 ...........................................................................................................155
Critical properties and specifications6.7.1 ........................................................................155
Measurement methods and techniques6.7.2 ....................................................................155
Economic and market factors6.8 ...............................................................................................155
Future outlook6.9 ......................................................................................................................156
Market trends and forecast6.9.1 ......................................................................................156
Impact of developing technologies6.9.2 ...........................................................................156
Alumina trihydrate7 .............................................................................................................157
Origin7.1 ...................................................................................................................................157
Manufacturing process7.2 ........................................................................................................157
75
Pigments
Crystal structure7.3 ..................................................................................................................158
Chemical properties7.3.1 .................................................................................................158
Physical properties7.3.2 ...................................................................................................158
Rheological behaviour7.4 ..........................................................................................................159
Formulation7.5 .........................................................................................................................159
Coating applications7.6 .............................................................................................................159
ATH as an extender7.7 ..............................................................................................................162
Analytical procedures7.8 ...........................................................................................................162
Handling and packaging7.9 .......................................................................................................163
Future outlook7.10 ......................................................................................................................163
Titanium dioxide8 ................................................................................................................164
Introduction8.1 .........................................................................................................................164
Manufacturing titanium dioxide pigments8.2 .............................................................................164
Titanium raw materials8.2.1 ............................................................................................164
Sulphate process8.2.2 .....................................................................................................165
Chloride process8.2.3 ......................................................................................................166
Surface treatment and finishing8.2.4 ...............................................................................167
Properties of titanium dioxide pigments8.3 ...............................................................................167
Chemical and physical properties8.3.1 .............................................................................168
Optical properties8.3.2 .....................................................................................................169
Other properties of 8.3.3 TiO2 pigments ...........................................................................171
Titanium dioxide pigments in paper applications8.4 ..................................................................171
Dispersing of titanium dioxide pigment8.5 s ...............................................................................172
Properties of titanium dioxide pigment slurries8.6 .....................................................................172
Properties of coating colours containing titanium dioxide pigment8.7 ........................................173
Dry hiding8.7.1 of coating colours ....................................................................................177
Properties of coatings and coated papers containing titanium dioxide pigment8.8 .....................177
Optical properties8.8.1 .....................................................................................................178
Interaction of 8.8.2 TiO2 with fluorescent whitening agents ..............................................179
Product safety8.9 ......................................................................................................................180
Future prospects for titanium dioxide pigment8.10 ......................................................................180
References ..........................................................................................................................181
191
CHAPTER 6 Binders
Starch 1 ................................................................................................................................192
Origin and manufacture of starch1.1 .........................................................................................192
Handling of starch1.2 ................................................................................................................195
Modification of starch1.3 ..........................................................................................................197
1.3.1 Degradation ............................................................................................................198
1.3.2 Substitution .............................................................................................................198
General characteristics of 1.4 starch as a binder in surface sizing and coating ...........................198
Surface sizing1.4.1 ..........................................................................................................198
Coating1.4.2 ....................................................................................................................200
Effects of starch on the properties of paper and board in sizing and coating1.5 .........................204
Surface sizing1.5.1 ..........................................................................................................204
Coating1.5.2 ....................................................................................................................204
Latex 2 ..................................................................................................................................207
Introduction2.1 .........................................................................................................................207
What is a “latex”?2.2 ................................................................................................................207
Physicochemical characterisation of polymer dispersions used as paper coating binders2.3 .....208
Emulsion polymerisation2.4 ......................................................................................................210
Storage and 2.5 handling of latexes ...........................................................................................212
Types of paper coating latexes and their characteristics2.6 .......................................................213
PVAc latex2.6.1 es ............................................................................................................214
Acrylic based latex2.6.2 es ...............................................................................................214
Styrene-butadiene latex2.6.3 es ........................................................................................214
Other latexes2.6.4 ............................................................................................................215
Properties of styrene-acrylic and styrene butadiene-latexes2.6.5 .....................................215
Impact of latex on the paper coating process and paper quality2.7 ...........................................218
Influence of latex on the coating colour2.7.1 ....................................................................218
Coated Paper 2.7.2 ..........................................................................................................219
Printing2.7.3 ....................................................................................................................221
Trends and outlook2.8 ...............................................................................................................224
References ..........................................................................................................................225
226
CHAPTER 7Co-binders and thickeners
Carboxy methyl cellulose1 ..................................................................................................228
Introduction1.1 .........................................................................................................................228
Manufacturing and chemistry of CMC1.2 ..................................................................................228
CMC grades for sizing and pigment coating of paper1.3 ............................................................229
Addition of CMC1.4 to the coating colour mixture ......................................................................230
Effect of CMC on coating colour water retention properties1.5 ..................................................230
Effect of CMC on coating colour flow properties1.6 ...................................................................233
Effect of CMC on coating properties1.7 .....................................................................................234
Soy protein2 .........................................................................................................................237
Introduction2.1 .........................................................................................................................237
Origin, manufacturing, and chemistry2.2 ...................................................................................237
Soy protein product range2.3 ....................................................................................................240
Key mechanism in coatings2.4 .................................................................................................241
Coating 2.5 rheology ..................................................................................................................241
Runnability and water-holding capacity2.6 ................................................................................243
Anti-blocking and calender hazing2.7 .......................................................................................243
Soy protein coating: formulation strategy2.8 .............................................................................244
Preparation of soy protein2.9 for coating formulations ..............................................................244
Conclusion2.10 ...........................................................................................................................245
Polyvinyl alcohol3 ................................................................................................................246
Manufacture3.1 ........................................................................................................................246
Composition, structure, and properties3.2 .................................................................................246
Dissolution procedure, speed of dissolution and aging of PVOH solutions3.3 .............................247
Polyvinyl alcohol grades for coating3.4 .....................................................................................248
Effect on coating colour/flow properties3.5 ...............................................................................248
Polyvinyl alcohol as coating binder3.6 .......................................................................................250
227
Co-binders and thickeners
Polyvinyl alcohol for 3.7 surface sizing .......................................................................................251
Effect on optical brightening agents/carrier properties3.8 .........................................................252
Mechanism of PVOH as a 3.8.1 carrier ..............................................................................252
Comparison of different co-binders3.8.2 ..........................................................................252
Which PVOH grade to select for optimum 3.8.3 whiteness .................................................253
Amount of PVOH to be used3.8.4 ......................................................................................253
Which OBA works best with PVOH3.8.5 ............................................................................253
Performance/economy balance when using OBA/PVOH combinations3.8.6 .......................254
Synthetic co-binders and thickeners by4 ...........................................................................256
Introduction4.1 .........................................................................................................................256
Synthetic thickener4.2 s ............................................................................................................256
Chemical structure4.2.1 ...................................................................................................256
Main functions of thickeners4.2.2 ....................................................................................258
Thickening mechanism4.2.3 s in the aqueous phase .........................................................258
Thickening mechanism4.2.4 s in the coating colour ..........................................................259
Influence of synthetic thickeners on 4.2.5 water retention .................................................260
Rheology4.2.6 of synthetic thickeners ..............................................................................262
Associative thickener4.3 s .........................................................................................................263
Chemical structure and classification4.3.1 .......................................................................263
Associative thickeners in comparison with conventional synthetic thickeners4.3.2 ...........266
Synthetic co-binder4.4 s ............................................................................................................267
Chemical structure4.4.1 ...................................................................................................267
Main functions of co-binders4.4.2 ....................................................................................268
Influence of co-binders and thickeners on 4.5 coating properties ...............................................268
Binding power4.5.1 and water resistance ........................................................................269
Brightness4.5.2 and opacity .............................................................................................269
Smoothness4.5.3 and gloss .............................................................................................269
Porosity4.5.4 , print gloss and glueability ...........................................................................270
Printability4.5.5 ................................................................................................................270
Application4.6 ...........................................................................................................................271
Preparing coating colours4.6.1 .........................................................................................271
Applications in coatings applied to different grades of paper4.6.2 ....................................272
Summary4.7 .............................................................................................................................273
References ..........................................................................................................................275
For further reading about soy protein ...................................................................................278
280
CHAPTER 8 Additives
Introduction1 ........................................................................................................................282
Coating dispersants2 ...........................................................................................................282
Dispersion2.1 ............................................................................................................................282
General aspects concerning dispersions2.1.1 ...................................................................282
Wetting2.1.2 ....................................................................................................................283
Disruption of particle clusters2.1.3 ...................................................................................283
Stabilisation2.1.4 .............................................................................................................284
General aspects concerning dispersants2.2 ..............................................................................285
Amount of dispersant required for stabilisation2.3 .....................................................................286
Dispersant types2.4 ..................................................................................................................287
Polyacrylate salts2.4.1 .....................................................................................................287
Other dispersants2.4.2 .....................................................................................................287
Foam control agents3 in surface sizing and paper coating ...............................................287
Physicochemical basis of 3.1 foam formation and stabilisation ..................................................288
Physicochemical basis of 3.2 foam control .................................................................................289
Foam3.3 and foam control in surface sizing and paper coating .................................................290
Process design and 3.3.1 mechanical foam control ...........................................................290
Chemical foam control3.3.2 .............................................................................................291
Methods of 3.3.3 foam measurement ................................................................................291
Dosage of foam control agents3.3.4 .................................................................................291
Adverse effects of foam control agents3.3.5 .....................................................................292
Conclusion3.4 ...........................................................................................................................292
Water retention4 , rheology modifiers and pH control ........................................................292
Optical brightening agents5 ................................................................................................295
Chemical structure and fluorescence5.1 ...................................................................................295
Types of optical brightener5.2 ...................................................................................................296
Role of carrier5.3 ......................................................................................................................297
281
Additives
Lubricants6 ..........................................................................................................................298
Calcium stearate6.1 ..................................................................................................................298
Wax emulsions6.2 .....................................................................................................................299
Other lubricants6.3 ...................................................................................................................299
Insolubilisers7 ......................................................................................................................299
Types of insolubiliser7.1 ............................................................................................................299
Glyoxal and its resin derivatives7.1.1 ...............................................................................300
Melamine- and urea-formaldehyde resins7.1.2 ................................................................300
Zirconium-based crosslinkers7.1.3 ..................................................................................300
Use of 7.2 crosslinkers ...............................................................................................................301
Preservatives8 .....................................................................................................................302
Types of 8.1 preservative ...........................................................................................................303
Conclusions8.2 .........................................................................................................................304
References ..........................................................................................................................306
309
CHAPTER 9 Surface sizing chemicals
Background and target of surface sizing1 .........................................................................310
Surface sizing materials2 ....................................................................................................310
Starch2.1 ..................................................................................................................................311
Carboxy methyl cellulose2.2 .....................................................................................................312
Polyvinyl alcohol2.3 ..................................................................................................................312
Surface 2.4 sizing additives .......................................................................................................312
Effect of size properties in sizing process3 ........................................................................313
Surface size formulations4 .................................................................................................313
Pigmented surface sizing5 ..................................................................................................314
References ..........................................................................................................................315
316
CHAPTER 10 Rheology of pigment slurries and coating formulations
Introduction1 ........................................................................................................................318
Definitions of key rheological terms2 .................................................................................319
Types of flow behaviour3 ....................................................................................................320
Shear-rate-dependent rheology3.1 ...........................................................................................320
Time-dependent rheology3.2 ....................................................................................................322
Viscosity of suspensions3.3 ......................................................................................................323
Viscoelasticity4 ....................................................................................................................325
Measurement of viscoelasticity4.1 ............................................................................................326
Stress-relaxation experiments4.2 ..............................................................................................329
Creep experiments4.3 ...............................................................................................................329
Normal forces4.4 ......................................................................................................................330
Viscoelasticity4.5 of paper coatings ..........................................................................................331
Extensional viscosity5 .........................................................................................................331
Measurement of viscosity6 .................................................................................................332
Controlled-strain versus controlled-stress measurement6.1 ......................................................332
Measuring devices for rotational rheometers6.2 ........................................................................333
Capillary rheometers6.3 ............................................................................................................336
Correction for inertial effects6.3.1 ....................................................................................336
Correction for non-Newtonian fluids6.3.2 .........................................................................337
Correction for end effects6.3.3 .........................................................................................337
Correction for wall-slip effects6.3.4 .................................................................................338
Using a capillary rheometer to characterise paper coatings6.3.5 ......................................339
Rheology of paper coatings7 ...............................................................................................339
Shear-rate ranges important to paper coatings7.1 ....................................................................339
Examples of paper coating rheograms7.2 .................................................................................340
317
Rheology of pigment slurries and coating formulations
Effect of coating-formulation components on rheology8 ..................................................342
Pigment-slurry rheology8.1 .......................................................................................................342
Effect of latex on paper coating rheology8.2 ..............................................................................345
Effect of rheology modifiers on paper coating rheology8.3 ........................................................346
Natural thickeners8.3.1 ....................................................................................................347
Synthetic thickeners8.3.2 .................................................................................................348
Using rheological measurements to predict paper coating behaviour9 ...........................349
References ..........................................................................................................................352
355
CHAPTER 11 Coating layer consolidation and formation of the coating layer structure
Introduction1 ........................................................................................................................356
Wet coating structure1.1 ...........................................................................................................357
Association between pigments and latex1.2 ..............................................................................358
Association between pigment, latex and starch1.3 ....................................................................359
Association between pigment, latex and CMC1.4 ......................................................................361
Coating-base paper interaction1.5 ............................................................................................364
Coating consolidation2 ........................................................................................................367
Introduction2.1 .........................................................................................................................367
Water flow from coating to base paper, water retention and 2.2 immobilisation..........................367
Coating coverage and immobilisation2.3 ...................................................................................371
Coating consolidation mechanisms2.4 ......................................................................................372
Coating consolidation in blade coating2.5 .................................................................................375
Dry coating structure3 .........................................................................................................376
Packing and volume fraction of pigment3.1 ...............................................................................376
Openness of the coating layer3.2 ..............................................................................................376
Surface properties3.3 ...............................................................................................................377
Structure of coating layer and its thermal properties3.4 ............................................................378
Modelling of coating consolidation and coating structure4 ..............................................380
Consolidation, dewatering and immobilisation4.1 ......................................................................380
Pore structure simulation4.2 .....................................................................................................385
References ..........................................................................................................................390
398
CHAPTER 12 Coating layer measurement and analysis techniques
Introduction1 ........................................................................................................................400
Surface structure2 ...............................................................................................................400
Topographical mapping2.1 ........................................................................................................400
Stylus profilometry2.1.1 ...................................................................................................401
Optical profilometry2.1.2 ..................................................................................................401
Confocal microscopy2.1.3 ................................................................................................402
Scanning probe microscopy2.1.4 .....................................................................................402
Optical interferometry2.1.5 ..............................................................................................403
Stereoscopy2.1.6 .............................................................................................................403
Air flow roughness2.1.7 ...................................................................................................403
Coefficient of friction2.2 ............................................................................................................404
Optical imagery2.3 ....................................................................................................................404
Contact angle analysis2.4 .........................................................................................................404
Fluid droplets2.4.8 ...........................................................................................................404
Immersion and extraction2.4.9 .........................................................................................405
Optical properties2.5 .................................................................................................................405
Gloss2.5.10 ........................................................................................................................405
Dynamic print gloss2.5.11 .................................................................................................405
Goniophotometry2.5.12 ......................................................................................................406
Specular reflectance2.5.13 uniformity ................................................................................407
Chemical distribution and chemical composition of coating3 ..........................................407
Bulk structure4 ....................................................................................................................408
Mercury porosimetry4.1 ............................................................................................................408
Fluid imbibition4.2 ....................................................................................................................412
Air permeability4.3 ....................................................................................................................413
Staining4.4 ...............................................................................................................................413
399
Coating layer measurement and analysis techniques
Brightness, colour and opacity4.5 .............................................................................................413
Transmitted light imaging4.6 .....................................................................................................414
Coating burnout imaging4.7 ......................................................................................................414
Transmitted electron imaging4.8 ...............................................................................................414
Applicability of the Kubelka-Munk theory4.9 .............................................................................414
Physical cross sectioning and imaging4.10 .................................................................................414
Neutron scattering4.11 ...............................................................................................................416
X-ray diffraction4.12 ...................................................................................................................416
Effects of coating structure on measurements and analysis5 ..........................................417
Brightness, opacity, and colour5.1 .............................................................................................417
Sheet gloss5.2 ..........................................................................................................................417
Print gloss5.3 ............................................................................................................................417
Print mottle5.4 ..........................................................................................................................418
Offset halftone dot fidelity5.5 ....................................................................................................419
Blister resistance5.6 .................................................................................................................419
Glueability and surface strength5.7 ...........................................................................................420
Rotogravure printability5.8 ........................................................................................................420
Inkjet printability5.9 ..................................................................................................................421
Conclusions6 ........................................................................................................................421
References ..........................................................................................................................422
431
CHAPTER 13 Coating colour preparation and handling
Introduction1 ........................................................................................................................432
Coating colour chemicals – their share of material flows and logistics2 .........................433
Basic design data of coating colour plants3 ......................................................................433
Delivery and 4 storage of coating chemicals ......................................................................434
Handling of pigments5 ........................................................................................................434
Pigment make-down5.1 ............................................................................................................434
Industrial batch-type dispersers5.2 ...........................................................................................438
Commercial pigment slurries5.3 ...............................................................................................441
Processing of binders6 ........................................................................................................442
Latexes6.1 ................................................................................................................................442
Starch processing in coating colour plants6.2 ...........................................................................443
Batch cooking of starch6.2.1 ............................................................................................444
Continuous cooking and conversion of starch6.2.2 ...........................................................445
Polyvinyl alcohol6.3 ..................................................................................................................446
Protein6.4 .................................................................................................................................447
Preparation of additives6.5 .......................................................................................................447
Coating colour preparation process7 .................................................................................449
Batch preparation of coating colours7.1 ....................................................................................449
Continuous coating colour preparation7.2 .................................................................................451
Coating colour supply systems for coaters8 ......................................................................452
Ultrafiltration9 process ........................................................................................................455
References ..........................................................................................................................459
460
CHAPTER 14 Coating and surface sizing technologies
Introduction1 ........................................................................................................................462Coating machine2 ................................................................................................................462General2.1 ................................................................................................................................462Future of coating machines2.2 ..................................................................................................465Coating machine components2.3 ..............................................................................................465
Flying splice unwind2.3.1 .................................................................................................465Off-machine tail threading2.3.2 ........................................................................................466On-machine tail threading2.3.3 ........................................................................................466
Coating section web run2.4 ......................................................................................................468Multiple coating of paper and board2.5 .....................................................................................469Blade coating techniques3 ..................................................................................................472Coating station types3.1 ...........................................................................................................472
Applicator roll coating station3.1.1 ...................................................................................472Short dwell coating station3.1.2 .......................................................................................474Jet applicator coating station3.1.3 ...................................................................................475
Metering systems3.2 ................................................................................................................477Blade metering3.2.1 .........................................................................................................477Forces acting on the blade3.2.2 .......................................................................................478
Blade loading systems3.3 .........................................................................................................483Tube loading3.3.1 ............................................................................................................483Constant tip angle loading3.3.2 ........................................................................................485Bent blade loading3.3.3 ...................................................................................................487CD control of coat weight3.3.4 .........................................................................................488
Surface sizing and film coating4 ........................................................................................491Introduction4.1 .........................................................................................................................491Surface sizing and coating techniques4.2 .................................................................................492
Pond size press4.2.1 ........................................................................................................495Film size press4.2.2 .........................................................................................................495Sizing and coating process layouts4.2.3 ...........................................................................497
Size amount and coat weight development4.3 ..........................................................................498Film metering process4.3.1 ..............................................................................................498Film transfer process4.3.2 ...............................................................................................505
461
Coating and surface sizing technologies
Effect of running parameters on starch penetration and consequent paper and board quality4.4 ......514Starch penetration analysis4.4.1 method .........................................................................514Effect of linear load and nip dwell time on starch penetration4.4.2 ...................................515
Size press technology for different paper and board grades4.5 .................................................518Printing and writing paper grades 4.5.1 ............................................................................518Paperboard grades4.5.2 ...................................................................................................523Specialty paper grades 4.5.3 ............................................................................................525
Spray coating 5 ....................................................................................................................527Spray coating process5.1 ..........................................................................................................527Integrated coating colour management for spray coating5.2 .....................................................527Industrial applications/installations5.3 ......................................................................................528Curtain coating6 ..................................................................................................................529Introduction6.1 .........................................................................................................................529Application and metering in curtain coating6.2 ..........................................................................529
Principle6.2.1 ...................................................................................................................529Types of curtain coater6.2.2 .............................................................................................529Curtain generation6.2.3 ...................................................................................................530Curtain 6.2.4 impingement and elongation ........................................................................532
Coating colour considerations in curtain coating6.3 ..................................................................532Rheology6.3.1 ..................................................................................................................533Curtain stability6.3.2 ........................................................................................................533Deaeration6.3.3 ...............................................................................................................534
Coating layer development and structure6.4 .............................................................................535Curtain coating process layouts6.5 ...........................................................................................535
Specialty papers6.5.1 ......................................................................................................535Commodity grades6.5.2 ...................................................................................................536
New technologies7 ..............................................................................................................537Introduction7.1 .........................................................................................................................537Modified coating techniques7.2 ................................................................................................537
Spot/pattern coating — coating specific areas7.2.1 .........................................................537Transfer and cast coating — forming the coating layer separately7.2.2 ...........................537
Methods with reduced water and energy consumption7.3 .........................................................538Foam coatings — from special additives to pigment coatings7.3.1 ..................................538Wet end coatings — making use of paper drying7.3.2 .....................................................538
Waterless coating methods7.4 ..................................................................................................539Powder coating7.4.1 ........................................................................................................539Thin surface treatments — also used to improve printability7.4.2 ....................................543Radiation curable coatings7.4.3 .......................................................................................543Hot melt and lamination methods7.4.4 .............................................................................544
Summary8 ............................................................................................................................545
References ..........................................................................................................................547
557
CHAPTER 15 Drying of paper coatings and drying equipment
Introduction1 ........................................................................................................................558
Heat and mass transfer in the drying of a coated web2 ....................................................558
Infrared drying3 ...................................................................................................................560
Introduction3.1 .........................................................................................................................560
Principles of radiation drying3.2 ................................................................................................561
Electrical IR dryers3.3 ...............................................................................................................562
Gas IR dryers3.4 .......................................................................................................................564
Air drying4 ...........................................................................................................................565
Air dryer types4.1 .....................................................................................................................565
Operating parameters4.2 ..........................................................................................................566
Construction of an air flotation dryer4.3 ....................................................................................567
Air flotation dryer retraction system4.4 .....................................................................................568
Air circulation system4.5 ...........................................................................................................568
Air dryer nozzles4.6 ..................................................................................................................570
Heat transfer4.7 and drying rate ...............................................................................................571
Energy consumption4.8 ............................................................................................................572
Cylinder drying5 ...................................................................................................................574
Felting geometry5.1 ..................................................................................................................575
Drying rate5.2 ...........................................................................................................................576
Hood enclosure5.3 ....................................................................................................................576
Correct 6 drying strategy .....................................................................................................577
Mottling6.1 ...............................................................................................................................577
Heating period and initial drying6.2 ...........................................................................................578
Consolidation, constant-rate drying6.3 ......................................................................................579
Final drying, falling-rate drying6.4 ............................................................................................582
Summary7 ............................................................................................................................582
References ..........................................................................................................................585
587
CHAPTER 16 Process control and automation in coating machine
Introduction1 ........................................................................................................................588
On-line coat weight measurement2 methods ....................................................................588
Oven-dry weight difference measurement2.1 ............................................................................589
Ash difference measurement method2.2 ...................................................................................590
Direct coat weight measurement method2.3 .............................................................................591
Machine-direction coat weight control3 ............................................................................592
Start-up control3.1 ....................................................................................................................593
Cross-direction coat weight profile control4 ......................................................................594
Machine-direction moisture control5 .................................................................................595
Drying optimisation5.1 ..............................................................................................................596
Cross-direction moisture control6 ......................................................................................596
597
CHAPTER 17 Development trends and future outlook
Pigments1 ............................................................................................................................598
Binders2 ...............................................................................................................................600
Co-binders and thickeners3 ................................................................................................601
Coating and sizing methods and technology4 ...................................................................602
Drying technology5 ..............................................................................................................603
Measurement and automation technology6 .......................................................................603
Analysis techniques, modelling and simulation methods7 ...............................................604