Paper & Board Coating
description
Transcript of Paper & Board Coating
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Paper & Board Coating
Atrak Pulp & Paper Industries Ltd.
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Why is Paper Coated ??
Cellulose Fiber Size :
• Soft Wood : Length 3 ~ 4 mm Diameter 25 ~ 50 Micron• Hard Wood : Length 0.8 ~ 1.5 mm Diameter 10 ~ 35 Micron
Pores between Fibers : 10 ~ 100 Micron.
Printing Dot Diameter : 25 ~ 50 Micron.
Coating the paper surface with Fine Pigments (Diameter 1~2 Micron) to cover the fibers and fill the pores.
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Functionality
Reduce Ink Consumption
Glueability
Why is Paper Coated ??
Printability
Smoothness Uniformity Ink Receptivity
Visual Properties
Brightness Opacity Gloss
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The whole purpose of a coating is to attach uniform layer of pigment to the base sheet.
Coatings Purposes
A Binder is used to adhere the pigment to the fibers.
There are additional additives in the coating formula to help in processing or enhance final sheet properties.
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Photo of Un-coated Paper
Magnification 200x
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Photo of Coated Paper
Magnification 2000x
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Cross Section of Coated Paper
Magnification 2000x
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Coating Ingredients
Natural Pigment: Clay, Calcium Carbonate, Talc.
Synthetic Pigment: PCC, Plastic Pigment, TiO2, Silica, Satin White.
Synthetic Binder: Latex.
Hydrosolubles Binder: Starch, CMC, PVA, Casein.
Additives: Dispersant, Thickener, Cross Linker, OBA, Lubricant, De-Foamer, etc.
Water.
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Coating Ingredients, Dry Weight %
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Function of Coating Ingredients
Pigment : Govern optical & printing properties of the paper.
Binders : Give the cohesion of the coating & adhesion of pigments to the base paper without affecting the properties brought by pigments.
Dispersant : To disperse the pigments.
Cross Linker : Provide wet pick resistant.
OBA : To increase brightness.
Lubricant : Improves flow properties, prevent coating adhesion on to calendar.
Thickener : Modifies the rheology and/or the water retention of the colour.
De-Foamer : Reduces foam.
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Pigments
ClayInterest : paper & ink gloss, rotogravure printability, stiffness.
Draw back : lack of brightness, closed coating.
GCCInterest : brightness, low viscosity, high solid, ink porosity.
Draw back : gloss, low water retention, fiber coverage.
TiO2
Interest : opacity, brightness, whiteness
Draw back : cost, latex demanding.
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Pigments
Plastic Pigment
Interest : high gloss, brightness, low specific gravity.
Draw back : price, more latex demand.
PCCInterest : brightness, viscosity, low abrasivity.
Draw back : cost, more latex demand.
SilicaInterest : brightness, high specific area, opacity.
Draw back : cost, need higher cohesion binder.
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Pigments
TalcInterest : smoothness, non abrasive, best for gravure.
Draw back : gloss.
Satin White
Interest : high gloss.
Draw back : work ability.
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Pigment Structure
Magnification 5000x
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Pigments Properties
Brightness : 84 ~ 96 % ISO
Particle Size Distribution : 0.22 ~ 2.00 Micron
Surface Area :
Fine Clay 20 ~ 25 m2/gramStandard Clay 18 ~ 20 m2/gramCalcined Clay 13 ~ 17 m2/gramGCC 8 ~ 13 m2/gram
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Pigments Properties
Refractive Index :
Interface
Substrate
Angle I
Angle R
R.I. is amount of lights refracted by the pigments.
High R.I. = High Opacity.
Light Comes
Light Refracted
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Pigments Properties
Pigments Composition Particle Size Shape R.I. Brightness
Clay Al2O3.2SiO2.2H2O 0.3 ~ 5.0 Hexagonal Platy 1.56 80 ~ 90
GCC CaCO3.MgCO3 0.7 ~ 2.0 Cubic Prismatic Platy 1.65 87 ~ 97
Talc MgO.4SiO2.H2O 0.3 ~ 5.0 Platy 1.57 85 ~ 90
Gypsum CaSO4.2H2O 0.2 ~ 2.0 Roundish 1.52 92 ~ 94
Titanium TiO2 0.2 ~ 0.5 Rod Like 2.55 98 ~ 99
Titanium TiO2 0.2 ~ 0.5 Roundish 2.70 97 ~ 98
PCC CaCO3 0.1 ~ 1.0 Variable Rod Like 1.59 96 ~ 99
Calcined C. Al2O3.2SiO2 0.7 Aggregated Platy 1.56 93
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Binders
Latex
Hard Latex : Higher gloss, low binding power, mainly for top coat.Web Offset Latex : Blistering resistance, low binding power.Soft Latex : Lower cost, high binding power, best for pre coat.
Starch
Interest : Stiffness, price.Draw Back : Mottling, low binding power, rheology at high speed.
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Binders
CMCInterest : Water retention, rheology, binding power.Draw Back : Handling.
PVAInterest : Excellent binding power, gloss, brightness.Draw Back : Price, rheology at high level.
ProteinInterest : Water retention, binding power, bulkier coating layer.Draw Back : Handling, rheology at high level, microbiology control.
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What Does Binder Do ?
1. To hold the pigments on the base paper.2. To help give good printability.3. To give special characteristic.
Pigment
Pigment
Binder
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Latex Structure
Latex Particles
Pigments Particles
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Main Binder Types
1. Styrene Butadiene.2. Styrene Acrylic.3. Styrene Butadiene Acrylic.4. Vinyl Acetate.
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The Influence of Binder
1. Dry and Wet Pick Strength.2. Sheet and Ink Gloss.3. Printability.4. Blister Resistance.5. Ink Drying.6. Yellowing.
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The Influence of Binder
Sheet Gloss Ink Gloss
Pigment
Binder
Coat Weight
Solid Content
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Increase low shear viscosity to allow proper application.
Adjust high shear viscosity to provide coat weight control and run-ability.
Increase water retention.
Can enhance optical and printing properties of the finished sheet.
Rheology Modifier (Thickener)
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Rheology Modifiers
Starch Protein Poly - Acrylates Alco Gum Sodium Alginate Urethane Modified Acrylates Poly Phobe Cellulosic Carboxyl Methyl Cellulose (CMC),
Hydroxyl Ethyl Cellulose (HEC)
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Atrak Pulp & Paper Industries Ltd.
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