Basics of wood, pulp and paper november 2012

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Wood, pulp and paper

Summary

From Tree to Pulp

From Pulp to Paper

Different kinds of paper

Paper characteristics

Summary

From Tree to Pulp

From Pulp to Paper

Wood is use for ……..

World production by area - source FAO 2009

http://www.twosides.info/#page=Latest-5

More info about the sustainability of the paper industry:

14%17%

Europe Asia & Pacific Afrique Latin America &

Caribbean

North America Western & Central Asia

woodfuel sawnwood

wood based panels industrial roundwood

pulp, paper & paperboard

Wood is used for….by continent

Production by area by

continent - source FAO 2009

Which part of a tree does the paper industry use ?

Construction wood :

for carpentry,

furniture or

construction

Wood left-overs,

wood shavings :

for pulp and

panelling

Bark :

for energy

or compost

Sawdust :

for panelling or energy

Hardwood and Softwood…

hardwood

softwood

Hardwood and Softwood…

hardwood

softwood

Chemical composition of wood

Pulp making : practically : Debarking

Cutting logs with

rotating saws

Logs rotated in

drum with water

Debarked logs

Pulp making : practically : Chipping

Chipper

Chip Screen

Chips Chips Chips!

From Tree to Pulp : Mechanical Pulp

The wood is only mechanically

treated (grounded)

The yield is about 98%, rests

products (barks) are used as

fertilizer or for heating

1 ton of wood produces 980kg

mechanical pulp

All the lignin remains in the pulp

2 Major processes :

Mechanical pulp

Stonegroundwood process

Grinding

Debarking

Bark is used to produce energy Pine

(bleaching) Washing

exit of the fibres

rotating stone

From Tree to Pulp : Chemical Pulp

The wood is treated :

• mechanically (grounded),

• thermally (heated up in boiling water)

• chemically

All the lignin is removed from the

The yield is about 50%:

With 1 ton of wood, we

produce about 500kg chemical pulp

Chemical pulp

Chemical pulp process

pine/birch

debarking

cooking

sorting

bleaching

washing

production of electricity

Cooking liquor

evaporation

Causticising

Chemical recovery

Liqueur de cuisson fraiche

Chemical pulp mill

Cooking vessel

Different types of pulp…..

Debarking

Steaming

Grinding

Thermo-

Mechanical

Debarking

Chemical pre-

softening

Grinding

Chemi -

Thermo -

Mechanical

Debarking

Chemical

cooking

Chemical

Secondary fibre

Deinking

Washing

Recycled

Debarking

Grinding

Mechanical

Between Mechanical process & Chemical process, we have intermediate processes :

TMP and CTMP. These processes only remove part of the lignin, up to the level desired.

Wood Containing Papers

Light Wood Containing Papers

Wood Free

Papers

Recycled

Papers

Under the microscope…

Pine Birch

Chemical pulp Mechanical pulp Recycled pulp

Different pulp for different kinds of paper

100 % chemical pulp 100% mechanical pulp

Strength is higher

Less stiffness

Less bulk

Easy to bleach

Lower opacity

Smooth surface

Brightness stable with time

Less strength

Higher stiffness

High bulk

Lower brightness

High opacity

Rougher surface

Trend to yellowing

Bleaching of the pulp Without bleaching, the pulp is brown

Therefore, depending on the level of brightness we want to achieve, we need to « bleach »

the pulp with chemicals. We can make it step by step with different chemicals :

2nd step 3rd step 4th step

Bleaching of the pulp

Chlorine

No Elemental

Chlorine

Free (Cl2)

(ClO2)

Summary

From Tree to Pulp

From Pulp to Paper

Integrated or not integrated…… Papermills do not always make their own pulp

they are so called “non integrated mills” (those who produce their own pulp are … integrated

mills); they received the pulp in units with a dryness of around 90%....

PULP PRODUCTION within SFPE

ALFELD

EHINGEN

GRATKORN

KIRKNIEMI

LANAKEN

STOCKSTADT

Just before the paper machine

Dyes/Filler

Hardwood pulp

Hydrapulper Refining Cleaning & Screening

Waste Filter System

Recycled Water

Softwood pulp

Pulper

Refining

Drawing of a refiner

Admission of the pulp

Outflow of the pulp

Refiner discs

Feeding screw

Refining chamber

Fibres are cut, frayed and hydrated

Refining

Fibres before refining fibers after refining

Cleaning and screening

Rejected material

Pulp entry

Cleaned pulp

Pulp entry

Rejected

material

Screened pulp

Just before the paper machine Before the pulp is sent to the papermaking machine various additives are included.

Papermaking uses a lot of water and this is why mills are built next to rivers.

A kilo of paper will use 100 litres of water.

The water systems are virtually closed where excess water is continuously recycled.

Colouring

Optical Brightening Agents are added that react with ultra violet light and give the paper a

blue whiteness.

Dyers are also added.

Binders

Both latex and starch are used to keep the fillers bound with the pulp. Starch also adds

stiffness.

Other additives

Anti bacterial, retention aids, pH buffers, …etc

Fillers

Titane dioxyde Talc

Gypsum

Calcium carbonate

Paper machine

Up to 80 km/hour

Up to 10 meters wide,

430 meters long

Cost: a few hundreds

millions €

18 months to be built

Paper machine

The function of the paper machine is mainly to remove water

Wire section

Moisture

content

Moisture

content

Wire section

Forming the web

Fourdrinier former

Twin wire

hybrid former

Duo former

Twin wire

Press section

Press felts

paperweb

about 50% of the water is removed

in the press section

The water is removed

by pressure of the sheet in the nip

Press section

Pre - drying section

The water is removed by

evaporation

The moisture content of the

paper is around 5-8%

The basis paper is ready to be

coated (for coated papers) or

sized (for uncoated papers)

Pre drying section

content

Fibrous support Fibrous support + sizing = uncoated paper

Fibrous support + (sizing) + coating = coated paper

~ 0.1 mm

Size press

A few g/m²/face is applied;

the layer is mainly made of starch

Absorption

Hydrodynamic pressure

Mechanical pressure

Split of the starch layer

Post - drying section

The water is removed by

evaporation

The moisture content of the

paper is around 5-8%

The basis paper is ready to be

coated (for coated papers) or

calendered/rewinded for

uncoated papers

Why coating papers ?

Uncoated Coated

uncoated paper light weight coated high weight coated

Print quality improves

base paper

More and more coating

light weight coated high weight coated

BRIGHTNESS

SMOOTHNESS

PRINTING QUALITY

Le couchage Coating is made of

Mineral pigments

Binders

Additives

Water (35-45%)

+ or – coating will lead to different kind of papers :

LWC, MWC, modern, classic

On-line or Off-line coating

Single, double, triple coated

What is coating ? What is the coating colour made of ?

Coating

Base paper

Coating tank

How do we coat ? Blade coating

Infra red dryers Scanner Hot air dryer Scanner Hot air dryer

Blade coating heads

How do we coat ? Blade coating

Blade coater

Cross section of a coated paper

coating fillers

fibres

Surface of the coated paper

Satin?

Satimat? Demi-mat?

Gloss?

Satin or Mat ?

Satin Mat

Classification of paper surfaces

Gloss > 70 % 30 - 40 % <15% Smoothness 1500 - 3000 sec 300 - 900 sec 50 - 200 sec

Satin / Silk

Marketing evaluation, no strict rule/norm

How do me make the surface ? Calendering

MAT, BRILLANT, DEMI MAT, SILK, ...

Pressure

Temperature

Moisture

Hardness of the rolls

Number of rolls

Supercalendering

Bottom

driver roll

The soft

rolls can

be of a

cotton,

paper or

synthetic

covering

Bottom

driver roll

Reversing nip

Blow rolls to

cool sheet and

prevent

wrinkling in nip

Uncalendered

Calendered

The soft rolls

are usually

made of

synthetic

covering

Rewinding

Slitting

Drop 3

Drop 2

Drop 1

Mother Reel

Pos. 1/A Pos. 2/B Pos. 3/C Pos. 4/D Pos. 5/E Pos. 1/A

Reels for

delivery or

sheeting

Reels packaging

Sheeting

Sheeting - slitting

Sheeting - cutting

Sheets packaging

Summary

From Tree to Pulp

From Pulp to Paper

Publication papers & end-uses

Summary

From Tree to Pulp

From Pulp to Paper

Grammage (g/m²), Thickness (µm), Bulk (cm³/g)

Substance or basis weight :

weight in grams of 1 m² paper

Thickness or Caliper :

Distance between one face of the paper

and the other

Bulk (cm³/g) = Thickness (µm) / grammage (g/m²)

ISO-brightness (%) and CIE whiteness

ISO brightness is a measurement of reflected blue light off the paper surface.

This is expressed as a percentage in comparison with an ultimate reference.

The ISO standard only measures a portion of the reflected light.

The CIE whiteness measures the reflected light of the whole spectrum.

For both measures, the higher the value, the brighter or whiter the paper is.

Opacity (%)

Opacity is related to the ability of light to

pass through paper.

The higher the percentage, the more

opaque the paper is.

Opacity isn't always determined by thickness or weight; a thinner paper may have more opacity than a thicker paper if opacifying agents are used.

High opacity

Low opacity

Opacity (ISO 2471) can be defined as the ratio of reflectance

from a paper sheet backed by a perfect black and from a

sufficiently thick stack of identical sheets of paper.

Gloss (%)

Gloss is an optical phenomenon caused when evaluating the appearance of a surface.

The evaluation of gloss describes the capacity of a

surface to reflect directed light.

The measure can be made on the paper itself (paper gloss) or on a printed area (print

gloss). Gloss papers are generally the most calendered

and thus the thinnest.

Please note we cannot compare gloss measures made

according to different norms (Tappi T480 & DIN 54502

are the most common).

Mat paper Gloss paper => smooth => high gloss

Matt paper => rough => low gloss

Smoothness Bekk. (sec)

This method measures how long it takes for a certain amount of air to escape from

between the paper surface and a smooth metal disc.

The smoother the paper, the less openings there are between paper surface and metal

disc, so the longer it will take for the air to escape.

The higher the figure is, the rougher the surface is.

Known also as “roughness”

Mat paper Silk paper

Fiber orientation

The paper fibers naturally take up

alignment roughly parallel to the

direction of travel of the web on

the PM :

this becomes the grain direction or

the Machine Direction (MD).

the other direction is called Cross Direction (CD).

This influences the strength characteristics of the finished paper.

Grain direction

Jumbo-reel 45

• Long Grain: fibres // long side (LG) : 45 X 64

• Short Grain: fibres // short side (SG) : 64 x 45

The first dimension is by convention always the dimension cross the web

64 x 45

45 x 64

Questions ?

Will be happy to answer your technical questions :

Françoise Accou

+32 492.582.287

francoise.accou@sappi.com

Basics of wood, pulp and paper november 2012

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