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 mm Diameter 10 ~ 35 Micron Pores between Fibers : 10 ~ 100 Micron.
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Paper & Board Coating
Coating the paper surface with Fine Pigments (Diameter 1~2 Micron)
to cover the fibers and fill the pores.
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.
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.
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.
Interest : paper & ink gloss, rotogravure printability, stiffness.
Draw back : lack of brightness, closed coating.
Interest : brightness, low viscosity, high solid, ink porosity.
Draw back : gloss, low water retention, fiber coverage.
Interest : opacity, brightness, whiteness
Draw back : cost, latex demanding.
Interest : high gloss, brightness, low specific gravity.
Draw back : price, more latex demand.
Interest : brightness, viscosity, low abrasivity.
Draw back : cost, more latex demand.
Interest : brightness, high specific area, opacity.
Draw back : cost, need higher cohesion binder.
Interest : smoothness, non abrasive, best for gravure.
Draw back : gloss.
Interest : high gloss.
Draw back : work ability.
Brightness : 84 ~ 96 % ISO
Particle Size Distribution : 0.22 ~ 2.00 Micron
Surface Area :
Fine Clay 20 ~ 25 m2/gram
Standard Clay 18 ~ 20 m2/gram
Calcined Clay 13 ~ 17 m2/gram
GCC 8 ~ 13 m2/gram
Refractive Index :
R.I. is amount of lights refracted by the pigments.
High R.I. = High Opacity.
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.
Interest : Stiffness, price.
Draw Back : Mottling, low binding power, rheology at high speed.
Interest : Water retention, rheology, binding power.
Draw Back : Handling.
Interest : Excellent binding power, gloss, brightness.
Draw Back : Price, rheology at high level.
Interest : Water retention, binding power, bulkier coating layer.
Draw Back : Handling, rheology at high level, microbiology control.
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.
Poly - Acrylates Alco Gum
Urethane Modified Acrylates Poly Phobe
Cellulosic Carboxyl Methyl Cellulose (CMC),
Hydroxyl Ethyl Cellulose (HEC)