Paper and Board Grades 3
Paper Composition 11
Papermaking Processes 23
Paper Structure 80
Surface Sizing and Coating 88
How to Influence on Process and Paper Quality 102
New Papermaking Developments 112
Thank You for Your Attention 129
European unofficial paper grade classification
Printing and writing papers
Mechanical printing papers
Woodfree printing and writing papers
Other tissue products
Printing paper grades
Coated & ca-
European classification of P&W paper grades
and Writing Papers
Next level classification
according to pigment coating
European mechanical paper grades
TD, Bulky etc.
RG and offset
LWC FCO MFC
Mechanical paper grades include mainly
mechanical pulp (SGW, TMP, CTMP etc.) or
deinked pulp from mechanical recovered
Amount of bleached softwood kraft pulp
(BSKP) is 0-50 % depending on paper grade.
European woodfree paper grades
like A4, A3
Folio or Rolls
Folio or Rolls
in Sheets and Rolls
Woodfree paper grades are made mainly
from chemical hardwood pulp. Some
BSKP must be added to coated grades.
Coated grades can include 5-20%
Deinked pulp made of woodfree grades
can be added especially to office papers .
Classification of coated grades
Coated one side
Gloss Finish Matt Finish
Double Coated Triple Coated
Coated two sides
Paper grades and printing methods
CSWO HSWO Sheet Fed
Newsprint xxx x
MF Specialties xxx xx x x x
SC xx xxx
MFC xxx x x
LWC xxx xx x
MWC, HWC xxx x x
WFC xx xxx xx
WFU xx x xx xxx
xxx = most common usage, xx = common usage, x = some usage
Fibers and paper properties
Chemical pulp can be bleached up to brightness 90 %.
Bright mechanical pulps have brightness 75-85 %.
Mechanical pulps give opacity, bulk and stiffness to the
paper. Hardwood chemical pulp and softwood
mechanical pulp can be used up to 100 % of paper
Softwood chemical pulp and hardwood mechanical pulp
are normally additional pulps to give special properties
to printing papers and are not normally utilized without
More BCTMP from hardwoods is used for woodfree
papers and boards. Some lignin from BCTMP will be
dissolved in alkaline papermaking conditions. Dissolved
lignin and extractives increase anionic trash and make
the control of wet end chemistry more complex.
DIP, mechanical pulps and BCTMP have lower
brightness than chemical pulp. Carbonates are best
pigments to improve brightness as filler and in coating.
Wet and dry
Hardwood vs. softwood chemical pulp
Short hardwood fibers will be more available
than long softwood fibers.
Hardwood kraft gives smoothness, bulk and
optical properties. This means that printability of
final product is good.
Average length of hardwood pulp fibers is slightly
less than one millimeter.
Refined softwood fiber is about 2 mm long.
Longer fibers give better strength for coating,
finishing and printing purposes.
Filler pigments decrease paper strength at the
wet end of paper machine but also in surface
sizing and coating where water moistens base
The trend is to increase hardwood and filler and
to decrease softwood. However, where softwood
is integrated it can be used more together with
less expensive filler.
Hardwood Chemical Pulp (Birch)
Softwood Chemical Pulp (Pine)
Fiber combinations in European white papers
Thin Eucalyptus fiber
with thick fiber wall
Vessel cell of Eucalyptus
Plantation hardwood pulps
Thin and quite long fibers of Eucalyptus having thick fiber wall can be developed by
refining without loss in bulk and tear strength. However, short and thick vessels cells
must be handled to prevent picking problems. There are several usable species of
eucalyptus, which have different properties for papermaking.
Eucalyptus is well suited for all kind of paper and board grades. Acacia is the other
competitive fiber but has thinner fiber walls and is not as good for grades requiring high
bulk and stiffness.
Pulps and paper grades
Actual fiber furnishes may vary largely and can be quite different especially in small
unintegrated paper mills.
Very often the price of fiber seems to be more important than the performance of fiber in
the product; within each end-product the quality and the price of end-products may vary
It is important to understand how each furnish component contributes the quality of the
product and the performance in the paper machine, finishing, and converting.
Mechanical grades GW, PGW, TMP, BCTMP, DIP
softwood (BSKP)Woodfree grades BHKP, DIP
(bagasse, wheat straw etc.)
Bamboo, kenaf etc.
Recovered paper usage
Special Office Papers
Mixed to Office
Mixed to Tissue
News, SC, LWC
ONP = Old Newspapers OMG = Old Magazines
Uncoated paper raw materials
Material Mech. % WF % Comment
Fibers 60 - 100 70 - 100 Wood or non-wood fibers
Fillers 40 - 0 30 - 0 Mineral or synthetic pigments
Surface sizes - 0 - 5
Starch, CMC, PVA, synthetic size,
optical brighteners etc.
0 - 1 0 - 2
Internal sizes, dyes etc.
(effect on paper properties)
Retention aids, defoamers, biocides etc.
(effect on process performance)
Water 5 - 10 4 - 7 To be in balance with ambient air
Long and short fibers in paper
Most papers contain long fibers (BSKP) to give runnability and short fibers (BHKP or
mechanical pulp) to give printability or other end use properties.
Kraft Papers (Bleached
0 % 100 %
0 %100 %
Conventional LWC base paper raw materials
Chemical pulp 30 - 50%
Bleached softwood kraft, hardwood is not used
Mechanical pulp 70 - 50%
Stone groundwood (SGW), pressure groundwood (PGW),
thermomechanical pulp (TMP) or chemithermomechanical
pulp (CTMP, BCTMP)
10 - 30% of the primary fiber furnish
Uncoated and coated broke (separately dosed)
Normally 4 -10 % of base paper (25 -100 % of this amount
returned back as coated broke)
Kaolin clay, talc, calcium carbonate, titanium dioxide.
Cationic starch, slight hydrophobic sizing, dyes
Effect of long fiber addition on paper properties
Wet and dry runnability Improve
Strength properties Increase (also tear)
Folding endurance Increases
Formation Less uniform
Ink holdout Lower
Bulk and stiffness Decrease
Dimensional stability Decreases
Energy consumption Increases
Internal size is pumped to the pipe before headbox.
Surface size is added with size press (film sizer today)
Type of Size
(starch, CMC etc.)
WFC not always,
Can be added
to surface size
sizes (water repellent)
WF papers, paperboards
(coated WF not always)
Can be added
to surface size
Cardboard recycling process
= Small = Average = Very high= High
Conventional deinking process
The filtrate from thickening 1 and 2 is flotated and reused in the process again.
Slushing Refining Forming Pressing Drying
Paper machine white water system
The objective of the white water system is to reduce water consumption and to minimize
fiber losses by recirculating water.
The amount of suspension
per ton of dry material in
Excess water for
reuse or to effluent
m3 / ton
of dry mat.
Stock 4.0 25
To Headbox 0.5 200
After wire 20.0 5
Simplified stock preparation in papermaking
Conventional approach flow
Old - holes
New - slots
Example of injection flash mixing (www.wetend.com)
Injection flash mixing of chemicals with correct order and late addition after pressure
screens can save chemicals as well as improve formation, retention and drainage.
Typical inlet header to headbox
Standard headboxes are fed from one end only. It is very difficult to get an equal jet
speed to the wire. The correct form of the header is most suitable for only one total flow.
Recirculation must be controlled for each flow to get balance for both ends. Good basis
weight CD profile is demanding. Consistency variation affects first to the inlet side.
Headbox recirculation control
Headbox recirculation valve is often in wrong position. CD profiles are not symmetric
but one edge is down and the other edge up.
There should be a pressure difference meter to be able to set the correct position from
control room. Sight glass is difficult to see and would require several new settings
during a shift.
Recirculation valve closed Recirculation valve open
Octopus-type approach flow
The pipes to headbox have same length. There is no need to recirculation (10%
If there is consistency variation it only affects MD variation, and simultaneously in
every CD position. CD variation is smaller than with conventional inlet header.
Octopus is suitable for smaller machines. Dilution control is also possible.
It is said that CD-profile and especially edges are even and stable.
Components of basis weight variation
Systematic variation in MD and CD are mathematically separated and the rest of
the variation is called random or residual variation.
MD variation reflects pressure pulsations, CD variation control of slice and residual
variation stability of the process and headbox.
Scanning mixes MD and CD variations
If scanning speed is 1 m/s and PM speed 20 m/s, it means that single scanning time of a
10 m wide machine is 10 s and the length of measured paper is 200 m.
Main MD variation frequencies are 1-100 Hz. This is 10-1000 MD peaks during one scan.
This means that almost all of the measured CD variation can be MD variation.
Several scans are needed to eliminate MD variation (time dependent) from CD variation
Fixed point measurement is needed to get fast MD variation. Fast CD variation must be
measured in lab (Valmet has a system after press section, but it is very expensive).
Machine direction BW variation
Pressure variation is fast, consistency variation slow. Pressure variation can be
measured with vibration measurement instruments from the pipe after pressure screen.
HB feed pump
of rolls and
f >1.0 Hz
of thick stock
HB = Headbox, WW = White Water
Basis weight variability by period
It is important to study the MD
variability by period, not by meters.
Pulsations or vibrations are easy to
trace to some rotating equipment.
Variation of thick stock mixing is
normally 10-100 s. Headbox pressure
variation is shorter with wave length
from 5 to 10 s. If the basic reason is
thick stock mixing, the wave length is
Final basis weight control can only
have effect on quite long variations.
Scanning time is 10-30 s and with
filtering 3-5 scans are needed to get
In addition, web travel time from basis
weight valve to reel is 1-3 min.
Thick stock mixing point
Thick stock should be joined to the white
water as close to the mixing pump as
The picture shows a very bad
In this case speed difference of flows in
the mixing point is so small that there is
practically no turbulence. The real mixer is
Current mixing point is on operating
floor, far from mixing pump
Thick stock White water
Mixing with no
Picture: Wet End Technologies
Principle of coaxial mixing
The thick stock pipe connection of
the previous slide has two principle
First fault is that the thick stock
flow comes sideways in 90 degree
angle to the flow direction. It
should always come parallel to the
flow direction i.e. coaxially.
Second thing is that the incoming
pipe should go in to the white water
pipe center, not sideways.
Wet end barring
Wet end barring is a fast pressure pulsation which is magnified on the Fourdrinier wire.
The difference between consistency variation and pressure variation is that pressure
peaks travel fast with speed of sound (343 m/s), and consistency peaks travel with flow
speed (about 3 m/s).
Consistency peaks will be on the wire very much diagonal while pressure peaks are
almost perpendicular to MD.
Wet end data collection system
Example of a comprehensive wet end data collection system. This requires very much
additional measurements and is seldom done in practice.
Picture: Voith Paper
How to analyse MD variation of basis weight
For slow vatiation: Take single point measurements with the scanner.
For fast variation: When machine is stopped unwind about 40 cm wide roll with
crawl speed through the scanner and collect data for spectral analysis.
If there is periodic variation the reason is easy to find. Spectral analysis of collected
data gives the periodic variations.
Effect of entrained air on papermaking
Online measurement of entrained air
is a good solution to control foam and
Pipe and channel constructions and
design very often enhance air
Some of the general air caused
problems are the following:
High paper porosity
Pumping problems causing basis
weight and tensile variation.
Afterdrying, calendering and reeling
Caliper and porosity
Smoothness & gloss
Brightness & opacity
Bulk and stiffness Picture: Voith Paper
Coating Reeling WindingCalendering
Coated woodfree papermaking line
About 10 m wide and 10 mm thick stock flows from the headbox to the wire. The final
paper caliper is less than 0.1 mm.
About 50% of the paper volume is air.
Formers and speed
Picture: Valmet Paper
Hybrid formers are suitable for non-wood and specialty papers where speed must
be slow due to the very difficult dewatering.
High dilution forming
There are several paper grades which require high dilution forming to get the required
paper formation uniformity. This is due to long special fibers, synthetic or natural.
The picture below is a calculation of headbox opening of 100 gsm paper and 80%
retention as a function of consistency.
It is impossible to use slice opening over one meter with a conventional headbox. This is
one of the reasons to use inclined wire for long fibers.
0 0.2 0.4 0.6 0.8 1 1.2
Headbox consistency, %
Inclined wire technology (Deltaformer)
Inclined wire former with angle of 15° to 35°, consistencies from 0.01 to 0.2%.
Higher stock dilution is needed to keep long fibers from entangling.
Fiber lengths from 5 up to 38 mm.
Water removal capacity up to 600 l/min/cm, width up to 5 m, speed up to 600 m/min
Picture: Glens Falls Interweb
Crescent Former for tissue paper
Wire speed is about 20% higher than reeler speed
due to the shortening in creping.
Release chemicals can be sprayed on the dryer
surface to help creping.
+ hot air hood
ATMOS tissue technology
According to Voith the big advantage of this technology
is that for premium tissue production it consumes 35%
less energy than TAD and the investment costs are
much lower. While through-air drying uses only air
pressure, ATMOS uses also vacuum.
Depending on application, it also enables fiber savings
and the use of 100% recovered paper furnish.
Retention of fibers, fillers and fines
Fibers are long compared to wire
fabric openings. Retention of long
fibers is good against the wire, but
fillers and fiber fines are smaller
than wire openings.
Mechanical retention of fillers and
fiber fines is possible when the fiber
mat is thick enough with smaller
voids between fibers than in wire
Common practice is to flocculate
fine material to larger aggregates.
However, this can flocculate also
fibers and impair paper formation.
Principle of paper formation
Originally there is over100 times as much
water as fibers. Low concentration is needed
to be able to avoid flocculation and to control
basis weight (thickness).
Suction or pressure against the fabric is
needed for dewatering.
Fourdrinier wire is pressing a pattern called
wire mark to the paper. This causes two-
Twin wire sections are used to avoid two-
sidedness and to get easier dewatering with
Solids content after wire is 18-22 %.
Wire section removes about 98% of the total
water. However, very expensive equipment
and most of the energy are needed for press-
and dryer sections.
To get the final dryness dewatering by
pressing and by evaporation is needed after
Filtration in gap former
Two separate fiber mats are formed
on the wires.
Middle part of the paper web has
lower fines content and lower
Water removal capacity is more than
double compared to Fourdrinier.
Both surfaces have very little dusting
and linting material (fiber fines and
fillers). This kind of paper is very
suitable for offset printing. In
addition, it is possible to use more
filler without linting.
Fiber orientation is similar on both
surfaces. Curling tendency is very
Laboratory sheet former
Gapformer with high jet/wire speed ratio
Counterflow cylinder mold
Filtration method and z-directional orientation
Orientation distribution on top and wire sides
Fibers from a Fourdrinier machine are more
oriented on the wire side.
Axis of sheet curl cylinder is to the machine
Fibers shrink and expand mostly in cross
In moistening wire side expands more and
sheet edges will be up from the wire side.
This is a good method to check wire side.
Fourdrinier paper is always two-sided, not
only concerning fines but also fiber
Some balancing can be made with topwire
but the complete solution is a gapformer.
Paper machine clothing
Batt fiber needled
to form fine surface
Pressing of wet web
There are 1...4 nips in the press section. Earlier nips had only one felt (picture). Today
double felted nips are increasingly used. Solids content after press section is 45 - 55%.
Web will be rough but compacted against the felt side and smooth but open on the roll side.
Paper is bulkier if less wet pressing and more drying is used. This, however, increases
Wet pressing theory
Wet pressing has a strong effect on the properties of paper. The press geometry, rolls
and their covers, felts and linear pressure combinations must be selected to conform to
the running speed and the paper grade to be produced.
Dryness and porosity with shoe and roll presses
KnowPap 4.0 (2002)
Press draw and porosity
A high press draw is not only question of runnability but also paper quality is lower
when low porosity is needed.
Porosity measurement is also a good tool for evaluating what is a too high press draw
0 1 2 3 4 5
Press Draw, %
Picture modified from: Valmet
Effect of press nip on paper
Felt and roll patterns are copied to the paper surface (felt is rough and roll is smooth).
Paper web close to the felt is compressed due to the lower water pressure but higher
mechanical pressure. Paper becomes dense but rough on the felt side.
Smooth and open
Rough but dense
One-sided felt and water removal – rough
and compacted felt side surface.
Two-sided felt and water
removal – symmetric web, both
surfaces rough and compacted.
Effect of felt on paper surface
Rigid plate like press roll
Impulse in pressing and calendering
Paper is viscoelastic. This means that not only the pressure, but also the time under the
pressure has effect in pressing and calendering.
Total effect of pressure forces is related to the sum of pressure impulse in all nips.
If speed is doubled it would require double linear load or double number of nips. Shoe
press and belt calender are very effective.
Impulse = pressure x time
Pressure = linear load / nip length
Time = nip length / speed
Impulse = linear load / speed time
Impulse = pressure x time =
Σ linear load
Water content of the web
After wire section there is about 80% water in the web, even if more than 97% of the
original water is removed. Removal of the final 2% is very expensive in the press and
After press section solids content (and water content) is about 50%.
Press section of a slow machine:
open draw after 2nd nip
Basic concept for woodfree coated and uncoated: two shoe presses with
transferbelt. This gives good runnability and CD profiles, but more two-
sidedness than double-felted last press.
Modern press section
Better web run
after 2nd nip
with new fabrics
Picture: Voith Paper
Single nip shoe press
Single nip press gives best bulk but also rough paper. However it is possible to
calender paper more to get the required smoothness and printability.
Paperboard machine press sections
On the right press section of a
cartonboard machine has a
separate smoothing press after
double felted shoe press.
Kraftliner machine can have last
press double felted because
smoothness requirements are
not critical (picture below).
Typical cartonboard machine
Cartonboard machines can have higher speeds when there are more wires. Drainage of
each wire is similar to papermaking drainage of grammage less than 100 gsm.
Development of double shoe presses with totally supported web run increases web
dryness to dryers 4-5 %-unit. Increased dryness allows 20 % higher speed, when drying
capacity is limited or 20 % lower energy consumption with same speed.
Higher dryness means that web is stronger when transferred to dryers and there are less
web breaks and sticking to dryer surfaces.
The paper machine in the picture below is Bohui PM1 cartonboard machine in China
supplied by Voith. Smoothing press after double felted shoe presses is without felt.
Principle of drying
In dryer section about one ton water must
be evaporated per one ton of final
For paper drying and water evaporation,
heat must be transferred to the wet web.
This is normally done by steam heated
cylinder dryers (30 - 60 pieces).
Evaporated water must be transferred
from the paper machine hood and fresh
dry air blown back. Heat from the
exhaust air is returned back to the
Paper moisture before coating or surface
sizing is 2 - 5%. Final paper moisture is
about double (4 - 10%) mainly depending
on the mineral content and paper grade.
Hydrogen bond formation
Inter-fiber hydrogen bond formation 1
Initial weak bonds via
several water molecule
layers in the beginning
of dryer section.
fiber wall surface
fiber wall surface
Smook’s Handbook, 1982, adapted
Inter-fiber hydrogen bond formation 2
Stronger bonds via
monolayer of water
H H O
fiber wall surface
fiber wall surface
Smook’s Handbook, 1982, adapted
Smook’s Handbook, 1982, adapted
fiber wall surface
fiber wall surface
Inter-fiber hydrogen bond formation 3
Remoistening of paper and fiber swelling
fiber wall surface
fiber wall surface
This is why paper
can be recycled!
Shrinkage profile of conventional paper machine
Edges compared to center have:
• higher weight
• higher caliper
• higher roughness
• higher porosity
• lower dimension stability
• long and slack web to the rolls
Picture: Prof Claire Davies
Structure of paper
Paper structure is porous and there is lot of
air between fibers and inside the fiber lumens.
Softwood chemical pulp fibers are mainly
collapsed in dry paper sheet (picture).
Paper structure is layered. Main part of fiber
area is bonded to the other fibers.
Paper thickness (caliper) is from 40 to 120
Original thickness of softwood fibers is about
30 µm and hardwood fibers about 20 µm.
There are 5 to 20 fiber layers in a printing
Fibers must be collapsed or broken down to
thinner particles to be able to make a smooth
and even paper sheet.
Paper structure is oriented,
porous and layered
Breaking lengths of various materials
Breaking length km
Single softwood fiber 100-150
Pine Wood 20-25
Printing papers 2-6
Softwood kraft paper 8-10
Breaking length is the theoretical length of a material strip where it breaks
due to its own weight.
Moisture sorption isotherms for paper
Paper is hygroscopic and in
balance with the air temperature
Moisture content (m) also depends
on the direction of the change
Evenness of paper
Flocculation (long fibers)
Basis Weight Variation
Machine direction (MD)
Cross machine direction (CD)
Residual variation (all directions)
From lot to lot
Fibers more in MD
Orientation angle to MD ± 0 - 5º
Tensile strength ratio MD/CD = 2...4
MD and CD properties of paper
Compared to cross-machine direction
paper in machine direction:
has more fiber orientation
has higher gloss
has higher tensile strength
has lower tear strength
has lower elongation
has better dimensional stability i.e. shrinking
in drying is bigger in CMD
Fibers are more in machine
direction. The upper sheet in the
picture is stiffer (MD = longer
side of copy paper).
Curl directions in sheet moistening
Fibers swell and shrink more in the direction of thickness and paper in the cross
machine direction (due to fiber orientation).
MD/CD tensile ratio for roll paper can be 3 - 4 but for sheeted paper it should be 1.5 - 2
to reduce curl and to improve CD stiffness.
Wire side - more oriented in MD
(not valid if gap former paper)
Basic printing paper properties
Importance depends on final usage
information, packaging or hygienic
basis weight, moisture, caliper
tensile, tear, burst, folding
surface, bond, dusting
brightness, opacity, color
water, oil, ink
formation, orientation, two-sidedness, curl
porosity, air permeability
Bulk / Density
Main paper coating principles
Picture: Katarina Dimic-Misic
Film sizer with air turn
Main phases in conventional pigment coating
Drying of wet coating
color with IR, hot air
and drying cylinders
Main coating methods
Blade coating produces smooth surface but uneven coating. Curtain coating produces
even coating layer but rough surface.
92Picture: Voith Paper
Film coating layout
Typical coating processes for LWC
Blade coating layout
Coating section of a cartonboard machine
There can be several coating stations in a coated paperboard machine (2-5 pcs).
The picture below shows a coating sequence top-top-back-top.
Effects of coating on paper
Coating fills the cavities and covers the base paper surface
Ink absorption decreases.
Surface strength increases and dusting decreases.
Gloss increases, with the objective often being the increase
of print gloss.
Opacity increases, and hopefully also brightness.
Mechanical strength of paper decreases, when coated and
uncoated papers are compared at the same basis weight.
Stiffness decreases when papers are compared at the
same basis weight.
Surface of Coated Paper
Fine kaolin clay
Ground Calcium Carbonate
Precipitated Calcium Carbonate
Fillers and coatings in paper
Mineral pigments can be added as a filler before headbox or to the
surface as a coating with binders.
0 - 5
5 - 15
0 - 1.5
Unctd Mechanical, TD, Bulky
5 - 15
15 - 35
0 - 5
Ctd Mechanical, LWC
5 - 15
8 - 18
0 - 2
5 - 15
20 - 40
Uncoated Woodfree, Copy
15 - 30
10 - 25
1 - 2
1 - 2
0 - 5
Coated Woodfree, standard
10 - 15
12 - 18
0 - 2
0 - 2
10 - 15
20 - 35
Structure of coated paper
Coating thickness is relatively smaller than grammage of coating. Density of coating
layer is about double (2000 kg/m3) compared to the base paper density (1000 kg/m3).
R. Klein, U. Schulze
Effect of calendering
It is difficult to make matt but smooth paper which would be ideal for reading.
Silk or semimatt
Pictures: Jouni Marttila
Important properties of coated paper
Good CD profiles (basis weight, caliper, moisture,
gloss, roughness, porosity, roll hardness)
Free of faults and holes (for coating), no impurities
Low fiber roughening potential (web offset grades)
High strength (MD tensile, CD tear, internal bond)
Good smoothness and minimum two-sidedness
Good formation (no mottling)
High compressibility (especially for rotogravure)
Optimal porosity and pore distribution
No blistering in heat set offset oven (high temperature)
No cracking (when folding) of higher weights
High brightness and opacity (low grammages)
Good CD stiffness, no curl (web offset grades and
Offset paper runnability vs. paper properties
Low amount of breaks
Low blistering tendency (heat set)
Low fiber roughening
Good register control
Small amount of debris on blanket
Profiles (moisture, basis weight,
caliper, orientation etc.)
Tear- and tensile strength
Linting and dusting
Blistering resistance (heat set)
Number of shives
Paper with dust
How to Influence on Papermaking
Process and Paper Quality
Effect of chemical pulp refining on paper
Wet web strength
Tensile, surface etc. strengths
Porosity and ink demand
Smoothness and gloss
Water removal and solids content
Bulk and stiffness
Opacity and brightness
Drying shrinkage dimension stability
Internal fibrillation External fibrillation Fiber bonding
Woodfree paper process adjustments
Drainage -- --- + ---
Retention - ± -- +++
Formation ++ + +++ --
Wet strength -- ++ --- ±
Dry paper runnability -- + -- +
Specific energy cons. + -- +++ ±
+ = positive effect, - = negative effect
Effects of selected parameters on paper properties
Increasing the right
variables have the effects of
arrows in paper properties
Initial wet web strength, MD
Tear strength, CD
Tensile strength, MD
Dimension stability, CD
Internal bond strength
Smoothness, gloss MD
Advantages of good runnability
- basis weight
- long fibre content
- short fibres
- mech. pulp/DIP
- more even
- labor cost
- supplies cost
Less steam &
Steam & el
used only once
Less starch etc.
Less shade &
Easy wet end
Advantages of low break frequency
Better and less variable
Stable and better
Lower losses of
fillers & chemicals Higher
Example of paper quality control system
CD profile controls
Standard scanning measurements of cross direction profiles are before all surface
sizings/coatings and before final reeler. In addition, there can be measurement after
press section and before calender.
To make a control loop there must be some adjustable profilers. Scanner
measurement – profiler pairs can be:
Basis weight: reel frame to slice screws/dilution.
Moisture: Reel to water spray, size press to steambox/press nip profiler.
Caliper: Reel to calender induction/nip profiler.
Consumption values for papermaking
kWh/t of paper
470-570 550-700 500-650 530-630 600-750
t/t of paper
1,7 - 1,8 1,7 - 1,8 1,8 - 1,9 1,1 - 1,3 1,1 - 1,3
kg/t of paper
0 0,08 - 0,1 0 25 - 27 30 - 40
m3/t of paper
total for the mill
10 - 15 10 - 15 13 - 18 8 - 13 8 -13
m3/t of paper
total for the PM
3 - 5 3 - 5 3 - 5 3 - 5 3 - 5
Basic process principle is old
Combined forming/pressing or pressing/drying ?
Do we need water in forming and coating – dry processes?
Flocculation, retention and drainage
The basic problem of papermaking is that it is difficult to get good formation,
drainage and retention at the same time. On the other hand, to avoid flocculation too
much water is needed, especially for long fibers.
• Bad formation
• Low strength
• Low opacity
• High porosity
• Good drainage
• Good fiber retention
• High strength
• Good opacity
• Low porosity
• Slow drainage
• Low fiber retention
Headbox dilution in papermaking
The biggest problem of industrial papermaking is fiber flocculation. Flocculation tendency
is the basic reason that there must be 100-1000 times water dilution in the headbox.
The other reason to the high dilution is cross-direction profile control. Final paper is less
than 0.1 mm thick and it should have thickness accuracy about ±1%. This is ±0.001 mm
or ±1 µm. With a 100-fold dilution this accuracy requirement is already ±0.1 mm which is
easier to achieve for a 10 m wide web.
Fibers occupy a sphere
in the headbox
Stiff fibers form flocs
with friction forces
Flocculation results in
bad paper formation
Current headbox technology
The principal construction of current hydraulic headbox technology is quite expensive due
to the very large area of highly finished surface.
For operator this kind of headbox is also demanding. Principally there is only one
optimum very narrow flow window for papermaker and outside this window the turbulence
is too high or too low.
The optimum jet-to-wire speed ratio is different for best formation and best fiber
orientation in most cases.
The most demanding flow range might be the filler ply in a multilayer board.
High consistency forming
The main improvement of papermaking should be reduction of water usage of the
internal circulations. Conventional solution to this is high consistency forming (1-3%).
In addition to the flocculation tendency the CD accuracy is demanding in high
It is easy to calculate what would be the slice opening for different headbox
consistencies. When basis weight is low slice opening is just some millimeters, which is
demanding for CD accuracy. The calculation below is for 100% retention. In practice
lower retention increases slice opening.
0 50 100 150 200 250 300 350
HB cons. 1 %
HB cons. 3%
HB cons. 2 %
High consistency forming and paper quality
The fibers from high consistency forming
are randomly oriented in all directions
rather than in the plane of the web
making this forming process unsuitable
for formation of printing papers.
The random grain orientation is believed
to be due to collision during drainage of
the densely packed fibers. In addition,
the formed web has high bulk, high
porosity, grainy formation, increased z-
direction strength (out of the plane of the
web) and reduced in-plane strength.
While this web is suitable for some
board grades it is not suitable for thin
This old picture on the right shows what
is the difference between filtering
(normal paper) and thickening (high
High consistency forming headbox
There is a very interesting patent idea (WO 2013024205 A1) of Matti Luukkanen on High
Consistency (HC) forming (2-5%). This could be very suitable for pulp drying machines and
several board grades, especially for the filler ply of three-layer board.
The picture below shows how rotating drum inside a curved chamber produces turbulence,
pressure and flow to the water removal gap between a solid apron and a moving wire on a
Consistency Total mass
% tons/dry ton
Foam forming to solve flocculation problems
New possibilities with increased headbox consistency by foam forming:
New paper properties by using special long fibers with good formation
High bulk products with good strength by combination with nanofibrillated
cellulose for insulation materials, filters and tissue products
High bulk with good z-strength for e.g. middle ply of cartonboard
Pilot foam forming machine at VTT Finland 2013
Foam forming gives possibilities to save water, energy and material in papermaking.
Microfibrillated cellulose is a potential but still today expensive development for papermaking.
MFC can be made by grinding or refining fibers to small pieces called microfibrils.
Principle of Valmet water layering technology
With multilayer headbox it is possible to get separation of fiber layers and prevention of
flocculation through the layers by using a water layer between the two fiber layers.
It is possible to put different chemicals and filler between the fiber layers with water
layering. One example is cationic starch.
Multilayer headbox with water layering technology
Valmet had a presentation in PaperCon2015. The following conclusion
is from this presentation:
Alternatives for containerboard machines
Board making is developed closer to papermaking and relative speed and production
development has been faster than in papermaking. Today there are also gapformers
in board machines.
Wet end rebuild of testliner machine.
This Valmet example is interesting how to get four layers of conventional two-layer
testliner machine by using layering headbox.
Multigrade cartonboard machine
There are five headboxes and two shoe presses with totally four felts. Five coating
stations allow different kind of products.
First calender has hot roll on top side and second calender on bottom side. It is
possible to make symmetrical graphical board.
Impingement drying possibilities
High-speed machines require good dryness after press section to get runnability.
One possibility to save bulk or add filler content is to use impingement drying in
the beginning of dryer section.