Getting acquainted with coating as a paper finishing technique

1. Coating
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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 20
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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.
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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 materials
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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)
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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 range
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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 paper
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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, runnability
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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, biocide
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10. 2.2. Coating preparation
• The coating is prepared in coating dissolvers and transported to the
coating machines
Coating
dissolver
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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.
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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 layer
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13. 2.3.2. Example - Film coater
Sizing slit
Roll blade
Sizing jets
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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 machine
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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°
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16. 2.5. Example – Coating with LDTA
Paper web
Coater roll
Bent blade
Applicator roll
Coater pan
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17. 2.7. Illustration
LDTA coater STDA coater
Paper web
Doctor blade
Applicator roll
Coater roll
Spray jet
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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 Celsius
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19. 3.1. IR drying
• First drying section on the paper machine
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20. 4. Overview
Coating machine
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21. Thank you
for your attention
Jörg Abelmann
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