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Coating

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Contents1. Introduction 3

1.1. Coating in the production process 41.2. Refinement types 51.3. Coated paper types 61.4. Coated paper classification 7

2. Coating process 82.1. Coating ingredients 92.2. Coating preparation 102.3. Coating application 11

2.3.1. Example – SDTA 122.3.2. Example - Film coater 13

2.4. Application types 142.5. Example with LDTA 162.6. Illustration 17

3. Drying phases 183.1. IR drying 19

4. Overview 20

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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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1.1. Coating in the production process

Sourcingraw materials

Stock preparation – Bringing togetherraw materials, fillers and additives

Paper machine – Production ofpaper *(sheet formation)

Coating machine (+ calender) –Paper refinement

Finishing – Makingthe paper ready forthe customer

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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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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 paperso Magno Satin, Hanno Art Silk, Quatro Silk, Allegro demimatt, Algro Card, Algro design

– Gloss coated paperso Magno Star, Hanno Art Gloss, Quatro Gloss, Algro Finess, Algro Primess

– Gussgestrichene Papiereo Not produced by Sappi

• Coating is possible on both woodfree and mechanical papers– Woodfree

o Magno range, Allegro range

– Mechanicalo Royal Print range, RP 400 range, Galerie range

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1.4. Coated paper classification

Applicationlayer

Name Abbr.

05 – 06 g/m² Ultra light weight coated ULWC07 – 12 g/m² Light weight coated LWC13 – 15 g/m² Medium weight coated MWC16 – 20 g/m² Heavy weight coated HWC

15 – 30 g/m² Folding boxboard20 – 30 g/m² Art paper

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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 sideo Backside moistening to prevent curling (water or coating)

• Quality criteria– Whiteness, opacity, smoothness, gloss, rub resistance– Printability, runnability

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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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2.2. Coating preparation

• The coating is prepared in coating dissolvers and transported to thecoating machines

Coatingdissolver

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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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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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2.3.2. Example - Film coater

Roll blade

Sizing jets

Sizing slit

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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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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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2.5. Example – Coating with LDTA

Applicator rollCoater pan

Coater roll

Paper web

Bent blade

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2.7. Illustration

Paper web

Applicator roll

LDTA coater

Coater roll

Spray jet

STDA coater

Doctor blade

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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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3.1. IR drying

• First drying section on the paper machine

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4. OverviewCoating machine

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Thank youfor your attention

Jörg Abelmann