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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.

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Paper & Board Coating

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Paper board coating

Atrak Pulp & Paper Industries Ltd.

Paper & Board Coating


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.

  • 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.


Paper board coating

Why is Paper Coated ??

  • Printability

  • Smoothness

  • Uniformity

  • Ink Receptivity

  • Visual Properties

  • Brightness

  • Opacity

  • Gloss

  • Functionality

  • Reduce Ink Consumption

  • Glueability


Paper board coating

Coatings Purposes

The whole purpose of a coating is to attach uniform layer of pigment to the base sheet.

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.


Paper board coating

Photo of Un-coated Paper

Magnification 200x


Paper board coating

Photo of Coated Paper

Magnification 2000x


Paper board coating

Cross Section of Coated Paper

Magnification 2000x


Paper board coating

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.


Paper board coating

Coating Ingredients, Dry Weight %


Paper board coating

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.


Paper board coating

Pigments

Interest : paper & ink gloss, rotogravure printability, stiffness.

Clay

Draw back : lack of brightness, closed coating.

Interest : brightness, low viscosity, high solid, ink porosity.

GCC

Draw back : gloss, low water retention, fiber coverage.

Interest : opacity, brightness, whiteness

TiO2

Draw back : cost, latex demanding.


Paper board coating

Pigments

Plastic Pigment

Interest : high gloss, brightness, low specific gravity.

Draw back : price, more latex demand.

Interest : brightness, viscosity, low abrasivity.

PCC

Draw back : cost, more latex demand.

Interest : brightness, high specific area, opacity.

Silica

Draw back : cost, need higher cohesion binder.


Paper board coating

Pigments

Interest : smoothness, non abrasive, best for gravure.

Talc

Draw back : gloss.

Satin White

Interest : high gloss.

Draw back : work ability.


Paper board coating

Pigment Structure

Magnification 5000x


Paper board coating

Pigments Properties

Brightness : 84 ~ 96 % ISO

Particle Size Distribution : 0.22 ~ 2.00 Micron

Surface Area :

Fine Clay20 ~ 25m2/gram

Standard Clay18 ~ 20 m2/gram

Calcined Clay13 ~ 17 m2/gram

GCC 8 ~ 13 m2/gram


Paper board coating

Pigments Properties

Refractive Index :

Light Comes

Angle I

Interface

Substrate

Light Refracted

R.I. is amount of lights refracted by the pigments.

Angle R

High R.I. = High Opacity.


Paper board coating

Pigments Properties


Paper board coating

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.


Paper board coating

Binders

CMC

Interest: Water retention, rheology, binding power.

Draw Back: Handling.

PVA

Interest: Excellent binding power, gloss, brightness.

Draw Back: Price, rheology at high level.

Protein

Interest: Water retention, binding power, bulkier coating layer.

Draw Back: Handling, rheology at high level, microbiology control.


Paper board coating

What Does Binder Do ?

  • To hold the pigments on the base paper.

  • To help give good printability.

  • To give special characteristic.

Pigment

Binder

Pigment


Paper board coating

Latex Structure

Latex Particles

Pigments Particles


Paper board coating

Main Binder Types

  • Styrene Butadiene.

  • Styrene Acrylic.

  • Styrene Butadiene Acrylic.

  • Vinyl Acetate.


Paper board coating

The Influence of Binder

  • Dry and Wet Pick Strength.

  • Sheet and Ink Gloss.

  • Printability.

  • Blister Resistance.

  • Ink Drying.

  • Yellowing.


Paper board coating

The Influence of Binder

Sheet Gloss

Ink Gloss

Pigment

Coat Weight

Binder

Solid Content


Paper board coating

Rheology Modifier (Thickener)

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.


Paper board coating

Rheology Modifiers

Starch

Protein

Poly - Acrylates  Alco Gum

Sodium Alginate

Urethane Modified Acrylates  Poly Phobe

Cellulosic  Carboxyl Methyl Cellulose (CMC),

Hydroxyl Ethyl Cellulose (HEC)


Paper board coating

Atrak Pulp & Paper Industries Ltd.

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