paper & board coating
DESCRIPTION
Atrak Pulp & Paper Industries Ltd. Paper & Board Coating. Why is Paper Coated ??. Cellulose Fiber Size : Soft Wood : Length 3 ~ 4 mm Diameter 25 ~ 50 Micron Hard Wood: Length 0.8 ~ 1.5 mmDiameter 10 ~ 35 Micron Pores between Fibers : 10 ~ 100 Micron. - PowerPoint PPT PresentationTRANSCRIPT
Paper & Board Coating
Atrak Pulp & Paper Industries Ltd.
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.
Functionality
Reduce Ink Consumption
Glueability
Why is Paper Coated ??
Printability
Smoothness Uniformity Ink Receptivity
Visual Properties
Brightness Opacity Gloss
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.
Photo of Un-coated Paper
Magnification 200x
Photo of Coated Paper
Magnification 2000x
Cross Section of Coated Paper
Magnification 2000x
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.
Coating Ingredients, Dry Weight %
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.
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.
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.
Pigments
TalcInterest : smoothness, non abrasive, best for gravure.
Draw back : gloss.
Satin White
Interest : high gloss.
Draw back : work ability.
Pigment Structure
Magnification 5000x
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
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
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
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.
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.
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
Latex Structure
Latex Particles
Pigments Particles
Main Binder Types
1. Styrene Butadiene.2. Styrene Acrylic.3. Styrene Butadiene Acrylic.4. Vinyl Acetate.
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.
The Influence of Binder
Sheet Gloss Ink Gloss
Pigment
Binder
Coat Weight
Solid Content
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)
Rheology Modifiers
Starch Protein Poly - Acrylates Alco Gum Sodium Alginate Urethane Modified Acrylates Poly Phobe Cellulosic Carboxyl Methyl Cellulose (CMC),
Hydroxyl Ethyl Cellulose (HEC)
Atrak Pulp & Paper Industries Ltd.
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