Surface Treatments PPT 110 Chapter 18

Why Surface Treatments Provide Resistance to Penetration Enhance Surface Characteristics Improve some physical properties Precoating

Surface vs. Internal size Advantages  Optimum control  Less sensitive to changes in wet end  100% retention  Reduction in wet end deposits  Increased press clothing  Improve paper quality Disadvantages  Capital investment for sizing and drying equipment  Energy for drying  Size press problems shut down machine

Size Press Configurations Horizontal Vertical Incline Metering

Inclined Size Press

Puddle Size Press

Metering Blade Size Press

Principle Effects Absorption –Low solution viscosity –High temperature - ? About rolls –High sheet moisture – wet sponge –Porous sheet –Low internal sizing –Basis weight –Machine speed

Principle Effects cont. Pickup/Nip Rejection –Amount of solution –Nip pressure/width/hardness –High sheet roughness – greater film –Separation of sheet/roll –Solids content –Steam usage

Size Press Variables

Pickup – Effect of Hydraulic vs. Absorption

Film Splitting

Other Applicators Waterbox – board Tub Sizing - specialty

Coating Kitchen

Starch Corn, Tapioca, Potato et al –Amylose – linear –Amylopectin – branched Cooked –Batch or continuous –Thick boiling (cooled-setback) –Thin boiling Chemically modified Thermally modified

Coating Provide –Gloss –Slickness –Color –Printing detail –Brilliance Fill Void Areas No compensation for poor base

Pigment / Binder Pigments –Fine fillers –Plastics Binders –Water soluble –Polymer emulsions Additives

Coat – How? On Machine –Massey Print Roll –Air Knife –Metering Bar –Blade Off Machine –Brush –Cast

Comparison of Coaters

Cast Coater

Advantages On Machine Eliminate transport – reduce handling and damage Eliminate intermediate storage of rolls Reduce space requirements Reduce labor requirements Encourages early identification of coating stock quality issues Off Machine Provides greater flexibility Eliminates dependence between other operations Provides superior coating quality

Coating Cross Section

Factors Affecting Coated Sheets Surface Properties Composition of Coating Method of Coating Method of Drying Extent of Supercalendering

Coating ‘Pick’

SUPERCALENDERING Alternating Rolls  Filled  Steel High Gloss Amount of Pressure  Hard rolls – smoothness/thinness  Soft rolls – less holes Delicate Nip

Supercalender