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Paper & Board Coating

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

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  1. Atrak Pulp & Paper Industries Ltd. Paper & Board Coating

  2. 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.

  3. Why is Paper Coated ?? • Printability • Smoothness • Uniformity • Ink Receptivity • Visual Properties • Brightness • Opacity • Gloss • Functionality • Reduce Ink Consumption • Glueability

  4. 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.

  5. Photo of Un-coated Paper Magnification 200x

  6. Photo of Coated Paper Magnification 2000x

  7. Cross Section of Coated Paper Magnification 2000x

  8. 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.

  9. Coating Ingredients, Dry Weight %

  10. 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.

  11. 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.

  12. 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.

  13. Pigments Interest : smoothness, non abrasive, best for gravure. Talc Draw back : gloss. Satin White Interest : high gloss. Draw back : work ability.

  14. Pigment Structure Magnification 5000x

  15. Pigments Properties 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

  16. 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.

  17. Pigments Properties

  18. 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.

  19. 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.

  20. What Does Binder Do ? • To hold the pigments on the base paper. • To help give good printability. • To give special characteristic. Pigment Binder Pigment

  21. Latex Structure Latex Particles Pigments Particles

  22. Main Binder Types • Styrene Butadiene. • Styrene Acrylic. • Styrene Butadiene Acrylic. • Vinyl Acetate.

  23. The Influence of Binder • Dry and Wet Pick Strength. • Sheet and Ink Gloss. • Printability. • Blister Resistance. • Ink Drying. • Yellowing.

  24. The Influence of Binder Sheet Gloss Ink Gloss Pigment Coat Weight Binder Solid Content

  25. 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.

  26. Rheology Modifiers Starch Protein Poly - Acrylates  Alco Gum Sodium Alginate Urethane Modified Acrylates  Poly Phobe Cellulosic  Carboxyl Methyl Cellulose (CMC), Hydroxyl Ethyl Cellulose (HEC)

  27. Atrak Pulp & Paper Industries Ltd. Thanks

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