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Coating

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Getting acquainted with coating as a paper finishing technique

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Coating

  1. 1. Coating1 | Streichmaschine |
  2. 2. Contents 1. Introduction 3 1.1. Coating in the production process 4 1.2. Refinement types 5 1.3. Coated paper types 6 1.4. Coated paper classification 7 2. Coating process 8 2.1. Coating ingredients 9 2.2. Coating preparation 10 2.3. Coating application 11 2.3.1. Example – SDTA 12 2.3.2. Example - Film coater 13 2.4. Application types 14 2.5. Example with LDTA 16 2.6. Illustration 17 3. Drying phases 18 3.1. IR drying 19 4. Overview 202 | Streichmaschine |
  3. 3. 1. Introduction • Course objective: – Getting acquainted with coating as a paper finishing technique • Coating: – Covering a base paper with a watery solution – The coating layer consists of pigments, binding agents and additives – Coating must adhere to the paper surface without being dissolvable • Coating is not part of the actual process of paper production. It is a refinement technique.3 | Streichmaschine |
  4. 4. 1.1. Coating in the production process Finishing – Making the paper ready for the customer Coating machine (+ calender) – Paper refinement Paper machine – Production of paper *(sheet formation) Stock preparation – Bringing together raw materials, fillers and additives Sourcing raw materials4 | Streichmaschine |
  5. 5. 1.2. Refinement types • Coating: – Covering the paper surface with a pigment layer • Laminating: – Preparing bonded material from multiple components • Coating: – Applying a fluid mass to the paper surface • Varnishing: – Applying a film of watery or solvents-containing substance • Impregnating: – Creating fibre-supported bonding by filling the cavities in the paper • Vapourizing: – Applying a closed layer by vapour (cigarette inner liner)5 | Streichmaschine |
  6. 6. 1.3. Coated paper types • Two-sides and one-side coated papers – Matt coated papers o Magno Matt Classic, Hanno Art Bulk, Furioso, Algro Fin – Demi-matt (silk) coated papers o Magno Satin, Hanno Art Silk, Quatro Silk, Allegro demimatt, Algro Card, Algro design – Gloss coated papers o Magno Star, Hanno Art Gloss, Quatro Gloss, Algro Finess, Algro Primess – Gussgestrichene Papiere o Not produced by Sappi • Coating is possible on both woodfree and mechanical papers – Woodfree o Magno range, Allegro range – Mechanical o Royal Print range, RP 400 range, Galerie range6 | Streichmaschine |
  7. 7. 1.4. Coated paper classification Application Name Abbr. layer 05 – 06 g/m² Ultra light weight coated ULWC 07 – 12 g/m² Light weight coated LWC 13 – 15 g/m² Medium weight coated MWC 16 – 20 g/m² Heavy weight coated HWC 15 – 30 g/m² Folding boxboard 20 – 30 g/m² Art paper7 | Streichmaschine |
  8. 8. 2. Coating process • Purpose: – Creating a product with enhanced visual appeal – Preventing microporosity  Ink savings (ink does not penetrate into the paper) – Creating a smooth, closed surface  Uniform ink absorption • Basic rules: – No coated paper is better than its base paper – Both sides are equally important  Whatever is done on one side, must also be possible on the other side o Backside moistening to prevent curling (water or coating) • Quality criteria – Whiteness, opacity, smoothness, gloss, rub resistance – Printability, runnability8 | Streichmaschine |
  9. 9. 2.1. Coating ingredients • Water • Pigments: – Calcium carbonate, kaolin, titan dioxide, blancfixe, satin white • Binding agents: – Synthetic fixatives (latex) ensure that ink adheres to the paper surface • Additives: – White pigments, optical brighteners, de-foaming agents, biocide9 | Streichmaschine |
  10. 10. 2.2. Coating preparation • The coating is prepared in coating dissolvers and transported to the coating machines Coating dissolver10 | Streichmaschine |
  11. 11. 2.3. Coating application • Long Dwell Time Applicator (LDTA) – Coating colour is applied by coating rolls • Short Dwell Time Applicator (SDTA) – e.g. spray coater, curtain coater – Coating colour is sprayed unto the paper surface by jets – Short application run, no rolls • Film coater – Advanced type of size press – Applies not only starch, but coating pigments as well – Pre-dosed by metering rod  Only the actually used starch or starch mix is transferred.11 | Streichmaschine |
  12. 12. 2.3.1. Example - STDA • Curtain coater: – Spray jet makes no contact with the paper web – The coating, after leaving the jet, spreads out in an even layer – like a curtain – on the paper moving beneath the jet – The non-contact application creates a more even and, depending on viscosity, much thinner coating layer12 | Streichmaschine |
  13. 13. 2.3.2. Example - Film coater Sizing slit Roll blade Sizing jets13 | Streichmaschine |
  14. 14. 2.4. Application types • Single coating: – The paper passes through the coating machine one time • Double coating: – The paper passes through the coating machine two times  Pre-coating: coarse pigments (less expensive)  Finishing: finer pigments (more expensive) • Triple coating – In-line pre-coating (on the paper machine) – e.g. film coating – Pre-coating and finishing in the coating machine14 | Streichmaschine |
  15. 15. 2.4. Coating types • Contour coating – Coating follows the paper surface – Good coverage: even coating layer  Application by applicator rolls, spray coater, curtain coater • Level coating – Blade coating  Redundant coating is raked off with a knife (blade)  Stiff Blade: blade angle 180° (water-aided)  Bent Blade: blade angle 70 – 90°15 | Streichmaschine |
  16. 16. 2.5. Example – Coating with LDTA Paper web Coater roll Bent blade Applicator roll Coater pan16 | Streichmaschine |
  17. 17. 2.7. Illustration LDTA coater STDA coater Paper web Doctor blade Applicator roll Coater roll Spray jet17 | Streichmaschine |
  18. 18. 3. Post-coating dryingh phases • Premisse: – After drying, the paper must be fit for (re-)coating or rolling • IR drying – approx. 1000 degrees Celsius • Convection drying (airfoil dryer) – Hot air drying – approx. 300 degrees Celsius • Contact drying – Drying cylinders – approx. 120 degrees Celsius18 | Streichmaschine |
  19. 19. 3.1. IR drying • First drying section on the paper machine19 | Streichmaschine |
  20. 20. 4. Overview Coating machine20 | Streichmaschine |
  21. 21. Thank you for your attention Jörg Abelmann21 | Streichmaschine |

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