Master\'s Thesis Ilkka Herrala


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The Function of Lubricants in Pigment Coating:

Effects of Lubricants
Classification of Lubricants
Potential Lubricants
Principals of Tribology
Principals of Rheology
Lubricants and Viscoelasticity
Lubricants and Blade Runnability

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Master\'s Thesis Ilkka Herrala

  1. 1. The Function of Lubricants in Pigment Coating Ilkka Herrala Laboratory of Paper Technology HUT 28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  2. 2. The Goals of the Thesis <ul><li>to describe and illustrate the function of lubricants in pigment coating . </li></ul><ul><li>to show that lubricants may contribute to up-speeding of the pigment coating process . </li></ul><ul><li>based on this information develop new lubricant products for the pigment coating market . </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  3. 3. Topics of Discussion <ul><li>E ffects of Lubricants </li></ul><ul><li>Classification of Lubricants </li></ul><ul><li>Potential Lubricants </li></ul><ul><li>Principals of Tribology </li></ul><ul><li>Principals of Rheology </li></ul><ul><li>Lubricants and Viscoelasticity </li></ul><ul><li>Lubricants and Blade Runnability </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  4. 4. Effects of Lubricants <ul><li>Lubrication of the wet coating and improvement of flow characteristics (rheology). </li></ul><ul><li>Better application and metering of the wet coating color. </li></ul><ul><li>Improved leveling. </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  5. 5. … Effects of Lubricants <ul><li>Reduction or elimination of whiskering and scratches. </li></ul><ul><li>Reduced or eliminated film split patterning. </li></ul><ul><li>Increased coating smoothness. </li></ul><ul><li>Improvement of finish (gloss). </li></ul><ul><li>Increased resistance to cracking and peeling when paper is folded. </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  6. 6. … Effects of Lubricants <ul><li>Elimination or reduction of pigment dusting, blocking, scaling and linting during finishing, slitting, sheeting, and printing operations. </li></ul><ul><li>Easier calendering making possible an acceptable machine calender finish for some grades. </li></ul><ul><li>Enhancement of printability. </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  7. 7. Classification of Lubricants <ul><li>Aqueous dispersions of metallic soaps (soluble / insoluble) </li></ul><ul><li>Wax emulsions (polyethylenes) </li></ul><ul><li>High-solids, lubricant blends containing calcium stearate </li></ul><ul><li>Diglycerides (lecithin blends) </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  8. 8. … Classification of Lubricants <ul><li>Triglycerides (fats) and other fatty acid esters </li></ul><ul><li>Polyglycols and polyglycol ethers/esters (e.g. PEG) </li></ul><ul><li>Sulfated and/or sulfonated oils </li></ul><ul><li>Fatty amines and fatty amides (synthetic waxes) </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  9. 9. Potential Lubricants <ul><li>should be attracted either chemically or physically to the surface and thus decrease the real area of contact, and therefore the adhesion, of the two rubbing surfaces (acid > amine groups) . </li></ul><ul><li>strong cohesion energy between the molecules (CH 2 - groups > CF 2 - groups). </li></ul><ul><li>optimal chain length of the fatty acid chain (low viscosity, water insolubility). </li></ul><ul><li>optimal level of the melting point . </li></ul><ul><li>org. Cl- and S-compounds as additives . </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  10. 10. Principals of Tribology <ul><li>The word tribology is derived from the Greek word tribos meaning rubbing. </li></ul><ul><li>It is the science and technology of interacting surfaces in motion and of related practices and subjects. </li></ul><ul><li>Tribology deals with friction and wear. </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  11. 11. Types of Friction <ul><li>Boundary friction </li></ul><ul><li>Hydrodynamic friction </li></ul><ul><li>Elastohydro-dynamic friction </li></ul><ul><li>pigment-pigment </li></ul><ul><li>pigment-lubricant-pigment </li></ul><ul><li>dry coating-elastomeric SC rolls </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  12. 12. Problems Affected by Paper Friction <ul><li>Roll winding and rewind problems </li></ul><ul><li>Crepe wrinkles within the roll </li></ul><ul><li>Roll telescoping during transit </li></ul><ul><li>Stack and pallet instability </li></ul><ul><li>Problems with web tracking and print registration </li></ul><ul><li> No feed or multipe feed during sheet feeding </li></ul><ul><li> Registration errors in die cutting or converting </li></ul><ul><li> Corrugator’s runnability problems of several kind </li></ul><ul><li> Friction buildup and dusting during converting operations, especially at SC and printing </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  13. 13. Dusting and Linting of Coated Paper <ul><li>Insufficient binder in the coating or at the surface of the dry coating. </li></ul><ul><li>Excessive penetration of binder into raw stock. </li></ul><ul><li>Improper coating penetration, insufficient screening, or failure to optimize dispersant requirements . </li></ul><ul><li>Overdrying the sheet (moisture content). </li></ul><ul><li>Slight variations in paper machine or coater speed, coating profile, or drying rate causing nonuniformaties in paper. </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  14. 14. Principals of Rheology <ul><li>Rheology describes the deformation of a body under the influence of stresses. </li></ul><ul><li>Rheology plays an important role in coating color processability , coater runnability and coated paper properties . </li></ul><ul><li>It still remains unclear which rheological parameters of paper coatings correlate with coater runnability and coating structure . </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  15. 15. Viscoelasticity <ul><li>The majority of fluids of technical importance lie somewhere between liquids and solids in their rheological behavior. </li></ul><ul><li>They are in varying extent both elastic and viscous and are therefore called viscoelastic materials. </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  16. 16. Viscoelasticity Affecting the Quality of Coating <ul><li>dominant in high-speed blade coating </li></ul><ul><li>formulations with high solids content </li></ul><ul><li>where relatively large blade loadings are required to obtain a target coat weight </li></ul><ul><li>depends to a great extent on the coating formulation used (type and amount of pigment and soluble additives) </li></ul><ul><li>wet bleeding and scratches </li></ul><ul><li>stalagmites at the blade (back side) </li></ul><ul><li>change in the spreading response of coatings during application </li></ul><ul><li>may promote coverage of the substrate </li></ul><ul><li>leveling-out of blade-induced streaks </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab
  17. 17. New Hypotheses of Lubricant Function <ul><li>Lubricants may turn the balance of a viscoelastic coating color from the elastic side to a slightly viscous side and thus enable the flow of a coating color still in very high coating solids. Together with higher coating solids, higher coating speeds may also be achieved. </li></ul><ul><li>They may have ability to reduce friction and increase slip at the blade boundary thus preventing bleeding and dry stalagmite formation from occurring. </li></ul>28/01/11 Ilkka Herrala / AWL Scandinavia Ab