Some additions to the older version

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Modern Papermaking
Pekka Komulainen
Pekka.Komulainen@clarinet.fi
February, 2018

2. Pele Oy
Modern Papermaking
Contents Page
 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
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PAPER AND BOARD GRADES
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European unofficial paper grade classification
 Printing and writing papers
 Mechanical printing papers
 Woodfree printing and writing papers
 Paperboards
 Cartonboards
 Containerboards
 Special boards
 Tissue
 Hygiene products
 Other tissue products
 Air-laid paper
 Specialty papers

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Printing paper grades
News
print
MF
Spesial.
SC-A+ SC-A
SC-B SC-C
MFC
LWC
FCO
HWC
MWC
WF
Unctd
WF
Coated
Relative
Value
Relative Quality

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Uncoated
woodfree
Coated
surface
Coated & ca-
lendered
European classification of P&W paper grades
Uncoated
Woodfrees
Coated
Woodfrees
Woodfree Printing
and Writing Papers
Uncoated
Mechanicals
Coated
Mechanicals
Mechanical
Printing Papers
Next level classification
according to pigment coating
(surface quality)
Pulping Method
(Brightness)

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European mechanical paper grades
Newsprint
TD, Bulky etc.
SC-papers
RG and offset
Uncoated
Mechanicals
LWC FCO MFC
Single Coated
MWC HWC
2-3 coatings
Coated
Mechanicals
Mechanical
Paper Grades
Mechanical paper grades include mainly
mechanical pulp (SGW, TMP, CTMP etc.) or
deinked pulp from mechanical recovered
papers.
Amount of bleached softwood kraft pulp
(BSKP) is 0-50 % depending on paper grade.

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European woodfree paper grades
Office Papers
Cut Size
like A4, A3
Printing Papers
Folio Sheets
and Rolls
Uncoated
Woodfree
Single Coated
Gloss/Matt
Folio or Rolls
Multi Coated
Gloss/Matt
Folio or Rolls
Coated
Woodfree
Woodfree Papers
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%
hardwood BCTMP.
Deinked pulp made of woodfree grades
can be added especially to office papers .

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Classification of coated grades
Coated one side
C1S
Single Coated
Rolls Sheets
Gloss Finish Matt Finish
Double Coated Triple Coated
Coated two sides
C2S
Coated
Woodfree
Coated
Mechanical
Coated
Board
Coated Grades

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Paper grades and printing methods
Printing
Method
Paper Grade
CSWO HSWO Sheet Fed
Offset
Roto-
gravure
Flexo Elektrogr.
& Inkjet
Newsprint xxx x
MF Specialties xxx xx x x x
SC xx xxx
MFC xxx x x
FCO xxx
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

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PAPER COMPOSITION
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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
furnish.
 Softwood chemical pulp and hardwood mechanical pulp
are normally additional pulps to give special properties
to printing papers and are not normally utilized without
other pulps.
 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.
12
Hardwood,
Short fibers
Softwood,
Long fibers
Chemical
Pulp,
Flexible
Mechanical
Pulp, Stiff
Fiber/Pulp
Type
Wet and dry
strength
Stiffness,
opacity
Formation,
brightness
Printability,
runnability

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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
paper.
 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)
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Fiber combinations in European white papers
Hardwood
100 %
News
SC
White
Kraft
Uncoated
Woodfree
LWC
Opacity
Bulk
Brightness
Coated
Woodfree
Softwood
100 %
StrengthFormation
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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.
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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
largely.
 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.
16
Paper Grades
Short fibers
for printability
Long fibers
for runnability
Mechanical grades GW, PGW, TMP, BCTMP, DIP
Long fiber:
softwood (BSKP)Woodfree grades BHKP, DIP
Non-wood grades
Several non-woods
(bagasse, wheat straw etc.)
Bamboo, kenaf etc.

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Recovered paper usage
Container
Board
Special Office Papers
Mixed to Office
PapersDeinked fibers
Hygienic Products
Mixed to Tissue
Papers
News, SC, LWC
Printing
Papers
Deinked fibers
Corrugating
Medium
OCC,
Kraft Paper
Testliner
Board
Office
Waste
ONP
OMG
Mixed
Waste
Recycled fibers
Recycled fibers
Deinked fibers
Cartonboards
White Lined
Chipboard
ONP = Old Newspapers OMG = Old Magazines

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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.
Functional
chemicals
0 - 1 0 - 2
Internal sizes, dyes etc.
(effect on paper properties)
Performance
chemicals for
process
<1 <1
Retention aids, defoamers, biocides etc.
(effect on process performance)
Water 5 - 10 4 - 7 To be in balance with ambient air

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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.
Uncoated WF
Newsprint
Kraft Papers (Bleached
or Unbleached)
LWC Magazine
SC Magazine
Coated WF
Long fibers,
BSKP
Short fibers,
BHKP or
Mechanical
pulp
0 % 100 %
0 %100 %

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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)
Broke
 10 - 30% of the primary fiber furnish
 Uncoated and coated broke (separately dosed)
Filler pigments
 Normally 4 -10 % of base paper (25 -100 % of this amount
returned back as coated broke)
 Kaolin clay, talc, calcium carbonate, titanium dioxide.
Functional Chemicals
 Cationic starch, slight hydrophobic sizing, dyes

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Effect of long fiber addition on paper properties
Positive
 Wet and dry runnability Improve
 Strength properties Increase (also tear)
 Folding endurance Increases
Negative
 Printability Decreases
 Formation Less uniform
 Smoothness Decreases
 Porosity Increases
 Ink holdout Lower
 Bulk and stiffness Decrease
 Dimensional stability Decreases
 Energy consumption Increases
 Costs Increase

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Sizing alternatives
 Internal size is pumped to the pipe before headbox.
 Surface size is added with size press (film sizer today)
Type of Size
Internal
Sizing
Surface
Sizing
Dry strength
improvement
(starch, CMC etc.)
WF papers,
mechanical printing
papers, paperboards
WF papers,
WFC not always,
paperboards
Wet strength
improvement
(resins)
Tissue,
packaging papers,
specialties
Can be added
to surface size
Hydrophobic
sizes (water repellent)
WF papers, paperboards
(coated WF not always)
Can be added
to surface size

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PAPERMAKING PROCESSES
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Cardboard recycling process
24
www.millenniumrecycling.com/process/

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Pulper
Screw
press
Disperging
Post flotation
Thickening 2
Pulp
storage
Thickening 1
Slot
screens
Pulp
storage Cleaners
Flotation CleanersHole
screens
Consistencies
= Small = Average = Very high= High
Conventional deinking process
 The filtrate from thickening 1 and 2 is flotated and reused in the process again.

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Papermaking process
Slushing Refining Forming Pressing Drying
PrecalenderCoatingFinishingConverting
Steam
Coating colour
Pulp bales
Fresh water
...or pulp
Additives
Calender

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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.
27
The amount of suspension
per ton of dry material in
different positions:
Pulp
MixThick stock
fiber
recovery
Fresh
water
Forming
Excess water for
reuse or to effluent
Long circulation
Short
circulation
Additives
White
water
tank
Wire
pit
White
water
tower
Dilutions at
web breaks
HB
Stock
prep
Position Consistency
%
m3 / ton
of dry mat.
Stock 4.0 25
To Headbox 0.5 200
After wire 20.0 5

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Simplified stock preparation in papermaking
Source: Valmet

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Conventional approach flow
Source: KnowPap
Old - holes
New - slots
29
Screening

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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.
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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.
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Headbox recirculation control
32
 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

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Octopus-type approach flow
 The pipes to headbox have same length. There is no need to recirculation (10%
smaller flow).
 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.
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Picture: GLV

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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.
34
Random or
Residual
Variation
Cross Machine
Direction
Variation
Machine
Direction
Variation
Picture: Valmet

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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
(position dependent).
 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).
35
Picture: Valmet

36. Pele Oy
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
pulsation
HB screen
pulsation
Vibrations
of rolls and
motors
HB pressure
variation
Fast MD
BW variation
f >1.0 Hz
Thick stock
flow variation
Poor mixing
of thick stock
and WW
HB consistency
variation
Slow MD
BW variation
f<1.0 Hz
HB = Headbox, WW = White Water
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MD variation frequencies
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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
not constant.
 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
control changes.
 In addition, web travel time from basis
weight valve to reel is 1-3 min.
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Thick stock mixing point
 Thick stock should be joined to the white
water as close to the mixing pump as
possible.
 The picture shows a very bad
arrangement.
 In this case speed difference of flows in
the mixing point is so small that there is
practically no turbulence. The real mixer is
next pump.
39
Current mixing point is on operating
floor, far from mixing pump
Thick stock White water
Mixing with no
turbulence
Picture: Wet End Technologies

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Principle of coaxial mixing
 The thick stock pipe connection of
the previous slide has two principle
faults.
 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.
Recommended
solution
Thick
stock
40

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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.
41
Picture: Valmet

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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.
42
Picture: Voith Paper

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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.
Temporary Unwind
Scanner
Pope
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44. Pele Oy
Effect of entrained air on papermaking
 Online measurement of entrained air
is a good solution to control foam and
chemical usage.
 Pipe and channel constructions and
design very often enhance air
entrainment.
 Some of the general air caused
problems are the following:
 Poor formation
 High paper porosity
 Pumping problems causing basis
weight and tensile variation.
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Papermaking principle (= water removal)
Headbox & wire
 Formation
 Orientation
 Strength
 Smoothness
 Two-sidedness
>99% 50% 3% 20% 8% 7%80%
Drying
 Strength
 Smoothness
 Two-sidedness
 CD profiles
Indicative
water content
Wet Pressing
 Porosity, bulk
 Strength
 Smoothness
 Two-sidedness
Surface Sizing/Coating
 Porosity, ink abs.
 Surface strength
 Smoothness
 Brightness, gloss
 Two-sidedness
Calendering
 Porosity, ink abs.
 Smoothness, gloss
 Brightness, opacity
 Bulk, stiffness
 Two-sidedness

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Attention! – 182 m long machine will appear!
Wet end of copy paper machine
Picture: Voith Paper
Wire SectionPress section
Headbox & Former
 Formation
 Orientation
 Strength
 Smoothness
 Two-sidedness
Wet Pressing
 Porosity
 Bulk
 Strength
 Smoothness
 Two-sidedness

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Predrying and surface sizing
Surface sizing or
coating Predrying
cylinders
Drying
 Moisture (MD, CD)
 Two-sidedness
 Curl
Sizing/Coating
 Porosity
 Ink absorption
 Strength
 Smoothness, Gloss
 Brightness, opacity
 Two-sidedness
Picture: Voith Paper

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Afterdrying, calendering and reeling
Reeling
Calendering
Afterdrying
Calendering
 Caliper and porosity
 Ink absorption
 Smoothness & gloss
 Brightness & opacity
 Two-sidedness
 Bulk and stiffness Picture: Voith Paper

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Forming
Drying
DryingPressing
Coating Reeling WindingCalendering
Surface
sizing
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.

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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.

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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.
51
0
200
400
600
800
1000
1200
1400
0 0.2 0.4 0.6 0.8 1 1.2
Headbox consistency, %
Sliceopening,mm

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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
52
Picture: Glens Falls Interweb

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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.
Picture: Voith
Headbox
Yankee dryer
+ hot air hood
Pope reel
PressGap former

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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.
54
Pictures: Voith

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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
openings.
 Common practice is to flocculate
fine material to larger aggregates.
However, this can flocculate also
fibers and impair paper formation.
55

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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-
sidedness.
 Twin wire sections are used to avoid two-
sidedness and to get easier dewatering with
high speed.
 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
wire section.
Wire fabric
Filtered
web
Free
fibers
in water
Removed water
Picture: Knowpap

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Filtration in gap former
Picture: Knowpap
Wire
Wire
 Two separate fiber mats are formed
on the wires.
 Middle part of the paper web has
lower fines content and lower
bonding strength.
 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
low.

58. Pele Oy
Laboratory sheet former
Fourdrinier
Gapformer with high jet/wire speed ratio
Counterflow cylinder mold
top
wire
Filtration method and z-directional orientation
top
wire
top
wire
wire
wire
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Orientation distribution on top and wire sides
Top
side
Random
distribution
circle
MD
CD
Wire
side
59
 Fibers from a Fourdrinier machine are more
oriented on the wire side.
 Axis of sheet curl cylinder is to the machine
direction, MD.
 Fibers shrink and expand mostly in cross
direction, CD.
 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
orientation.
 Some balancing can be made with topwire
but the complete solution is a gapformer.

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Paper machine clothing
Press felt
Wire fabric
Dryer fabric
Batt fiber needled
to form fine surface
Laminate fabric

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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
steam consumption.
Felt
Web
Picture: Knowpap

62. Pele Oy
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.
Picture: Valmet
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Dryness and porosity with shoe and roll presses
KnowPap 4.0 (2002)
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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
200
400
600
800
0 1 2 3 4 5
Porosity,Bendtsen,ml/min
Press Draw, %
Picture modified from: Valmet
64

65. Pele Oy
65
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.
Picture: M.A.MacGregor
Roll side
Felt side
Smooth and open
Rough but dense


66. Pele Oy
66
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
nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
nnnnnnnnnnnnnnnnnnnnnnnnnnmnnnnnnn
nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
Rigid plate like press roll

67. Pele Oy
67
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
= area
Impulse = pressure x time =
speed
Σ linear load
Nip
pressure

68. Pele Oy
68
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
drying sections.
 After press section solids content (and water content) is about 50%.
Picture: Knowpap
Pick-up
felt
H2O
50%
H2O
80%
Press section of a slow machine:
open draw after 2nd nip

69. Pele Oy
69
 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
through press
No rewetting
after 2nd nip
Quick start-up
with new fabrics
Picture: Voith Paper

70. Pele Oy
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.
70
Picture: Voith

71. Pele Oy
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).
71
Pictures: Voith

72. Pele Oy
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.
72

73. Pele Oy
73
Principle of drying
 In dryer section about one ton water must
be evaporated per one ton of final
product.
 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
process.
 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.
Picture: Knowpap
Exhaust air

74. Pele Oy
74
Hydrogen bond formation
Hydroxyl
group

75. Pele Oy
75
Inter-fiber hydrogen bond formation 1
 Initial weak bonds via
several water molecule
layers in the beginning
of dryer section.
H
O
H
O
H
O
O
H
fiber wall surface
H O
H
OH
OH
HO
H
HO
H
HO
H
H O
H
H O
H
H
O
H O
H
H O
H
H O
H
fiber wall surface
Smook’s Handbook, 1982, adapted

76. Pele Oy
76
Inter-fiber hydrogen bond formation 2
 Stronger bonds via
monolayer of water
O
H H O
H
OH
OH
H O
H
H O
H
H
O
H
O
H
O
H
O
fiber wall surface
fiber wall surface
Smook’s Handbook, 1982, adapted

77. Pele Oy
77
Smook’s Handbook, 1982, adapted
H
O
H
O
O
H
OH
OH
H
O
H
O
fiber wall surface
fiber wall surface
Inter-fiber hydrogen bond formation 3
 Direct hydrogen
bonding between
fibers

78. Pele Oy
78
Remoistening of paper and fiber swelling
OH
OH
OH H
O
fiber wall surface
H
O
H
O
H
O
H O
HHO
H
HO
H
HO
H
H O
H
H O
H
H O
H
H O
H
H O
H
fiber wall surface
HO
H
Water molecule
This is why paper
can be recycled!

79. Pele Oy
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
79

80. Pele Oy
PAPER STRUCTURE
Picture: Prof Claire Davies
80

81. Pele Oy
81
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
µm.
 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
paper sheet.
 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

82. Pele Oy
82
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
 Steel 4-5
 Aluminum 3-4
 Graphite 35-40
Breaking length is the theoretical length of a material strip where it breaks
due to its own weight.

83. Pele Oy
83
Moisture sorption isotherms for paper
 Paper is hygroscopic and in
balance with the air temperature
and humidity.
 Moisture content (m) also depends
on the direction of the change
(hysteresis).

84. Pele Oy
84
Evenness of paper
Formation
 Flocculation (long fibers)
Basis Weight Variation
 Machine direction (MD)
 Cross machine direction (CD)
 Residual variation (all directions)
 From lot to lot
Two-sidedness
 Smoothness, gloss
 Absorption, density
 Color, brightness
 Curl, orientation
Orientation
 Fibers more in MD
 Orientation angle to MD ± 0 - 5º
 Tensile strength ratio MD/CD = 2...4
MD
CD
Bad formation

85. Pele Oy
85
MD and CD properties of paper
 Compared to cross-machine direction
paper in machine direction:
 has more fiber orientation
 has higher gloss
 is stiffer
 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).

86. Pele Oy
86
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)

87. Pele Oy
87
Basic printing paper properties
Importance depends on final usage
 information, packaging or hygienic
General properties
 basis weight, moisture, caliper
Strength properties
 tensile, tear, burst, folding
 surface, bond, dusting
Optical properties
 brightness, opacity, color
Surface properties
 roughness, gloss
Absorption properties
 water, oil, ink
Structural properties
 formation, orientation, two-sidedness, curl
 density/bulk, stiffness
 porosity, air permeability
Picture: Knowpap
Bulk / Density

88. Pele Oy
SURFACE SIZING AND COATING
88

89. Pele Oy
Main paper coating principles
89
Picture: Katarina Dimic-Misic

90. Pele Oy
90
Film sizer with air turn
www.mhibeloit.com

91. Pele Oy
91
Main phases in conventional pigment coating
Drying of wet coating
color with IR, hot air
and drying cylinders
Application of
coating color
Leveling of
coating color

92. Pele Oy
Main coating methods
 Blade coating produces smooth surface but uneven coating. Curtain coating produces
even coating layer but rough surface.
92Picture: Voith Paper

93. Pele Oy
Film coating layout
Typical coating processes for LWC
Blade coating layout
Picture: Valmet
93

94. Pele Oy
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.
94
Picture: Voith

95. Pele Oy
95
Effects of coating on paper
 Coating fills the cavities and covers the base paper surface
increasing smoothness.
 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.
Triple Coated
Uncoated

96. Pele Oy
96
10,000 X
Surface of Coated Paper
Fine kaolin clay
Ground Calcium Carbonate
Pictures: SMI
Precipitated Calcium Carbonate

97. Pele Oy
97
Fillers and coatings in paper
 Mineral pigments can be added as a filler before headbox or to the
surface as a coating with binders.
Paper Grades
Filler
Pigment
%
Surface size
per side
g/m2
Coating
per side
g/m2
Woodcontaining
Newsprint, TMP/GW
Newsprint, DIP
0 - 5
5 - 15
0
0 - 1.5
0
0
Unctd Mechanical, TD, Bulky
SC
5 - 15
15 - 35
0
0
0 - 5
0
Ctd Mechanical, LWC
MWC, HWC
5 - 15
8 - 18
0
0 - 2
5 - 15
20 - 40
Woodfree
Uncoated Woodfree, Copy
Printing
15 - 30
10 - 25
1 - 2
1 - 2
0
0 - 5
Coated Woodfree, standard
Premium Art
10 - 15
12 - 18
0 - 2
0 - 2
10 - 15
20 - 35

98. Pele Oy
98
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).
Picture:
R. Klein, U. Schulze

99. Pele Oy
99
Effect of calendering
 It is difficult to make matt but smooth paper which would be ideal for reading.
Glossy Paper
Gloss 50-80
PPS <1
Silk or semimatt
Gloss 20-40
PPS 1-2
Matt
Gloss 10-20
PPS >2
Pictures: Jouni Marttila

100. Pele Oy
100
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
sheeted grades)

101. Pele Oy
101
Offset paper runnability vs. paper properties
Pressroom runnability
 Low amount of breaks
 Low blistering tendency (heat set)
 Low fiber roughening
 Good folding
 Good register control
 Small amount of debris on blanket
Paper properties
 Profiles (moisture, basis weight,
caliper, orientation etc.)
 Tear- and tensile strength
 Mechanical faults
 Linting and dusting
 Blistering resistance (heat set)
 Ply-bond
 Porosity
 Moisture
 Number of shives
 Stiffness
 Density, stretch
dampening
unit
ink unit
plate
blanket
backing
cylinder
Paper with dust

102. Pele Oy
How to Influence on Papermaking
Process and Paper Quality

103. Pele Oy
103
Effect of chemical pulp refining on paper
Positive effects
 Wet web strength 
 Tensile, surface etc. strengths 
 Better formation
 Coating coverage 
 Porosity and ink demand 
 Smoothness and gloss 
Negative effects
 Water removal and solids content 
 Bulk and stiffness 
 Compressibility 
 Opacity and brightness 
 Drying shrinkage  dimension stability 
 Tear strength 
 Energy consumption 
Pictures: E.Gruber
Internal fibrillation External fibrillation Fiber bonding
+ =

104. Pele Oy
104
Woodfree paper process adjustments
Command Variables
Process Parameters
BHKP %

Refining

Filler %

Grammage

Drainage -- --- + ---
Retention - ± -- +++
Formation ++ + +++ --
Wet strength -- ++ --- ±
Dry paper runnability -- + -- +
Specific energy cons. + -- +++ ±
+ = positive effect, - = negative effect

105. Pele Oy
105
Effect of command variables on paper properties
Paper Properties
BHKP %

Refining

Filler %

Grammage

Optical properties ++ -- +++ +
Tear strength - + - - - +++
Other strength properties - ++ --- +++
Better bulk ± -- ± ±
Better smoothness + ++ +++ +
Dimension stability + -- ++ +
Lower porosity + ++ ± +++
Better printability + + +++ +
Total costs/ton + -- +++ ---
+ = positive effect, - = negative effect

106. Pele Oy
106
Effects of selected parameters on paper properties
Increasing the right
variables have the effects of
arrows in paper properties
Longfibers
(BSKP)
Refining
Wetendstarch
Filler
Moreorientation
inMD
Wetpressing
Finalmoisture
Calendering
Press dryness     
Initial wet web strength, MD      
Tear strength, CD        
Tensile strength, MD        
Dimension stability, CD       
Internal bond strength       
Smoothness, gloss MD       
Porosity       
Stiffness, CD        
Opacity       
Brightness       
Costs        
Red =
negative
Green =
positive
MD =
Machine
Direction
CD =
Cross direction
= main
reason to
increase

107. Pele Oy
107
Advantages of good runnability
More
- filler
- coating
Higher
- speed
- efficiency
Good
Runnability
Decreased
- basis weight
- long fibre content
Less
- energy
- water
Less
- chemicals
- wires/felts
More
- short fibres
- mech. pulp/DIP
Quality
- better
- more even
Lower
- labor cost
- supplies cost

108. Pele Oy
108
Improved
runnability
Lower raw
material costs
Longer
wire life
Increased
machine speed
Less steam &
energy/ton
Lower
furnish
cost
Cleaner
system
Steam & el
used only once
Less starch etc.
needed
Better CD-
profiles
Less shade &
caliper variation
Stronger
paper
Better bulk
& stiffness
Better
printability
Constant
filler content
Productivity
Cost Efficiency
Easy wet end
chemistry
Advantages of low break frequency
Product
Quality
Low Break
Frequency
Less effluent
and fresh
water/ton
Better and less variable
raw materials
Less Dry
Broke
Stable and better
paper quality
More Net
Tons
Lower Chemical
Consumption
Lower losses of
fillers & chemicals Higher
press solids

109. Pele Oy
109
Example of paper quality control system
Picture: Valmet

110. Pele Oy
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.
110
Picture: ABB

111. Pele Oy
111
Source: Valmet
Consumption values for papermaking
News-
print
LWC
Fine
paper
Opti
Concept
News
Opti
Concept
LWC
Electricity
kWh/t of paper
470-570 550-700 500-650 530-630 600-750
Drying steam,
t/t of paper
1,7 - 1,8 1,7 - 1,8 1,8 - 1,9 1,1 - 1,3 1,1 - 1,3
Drying gas,
kg/t of paper
0 0,08 - 0,1 0 25 - 27 30 - 40
Fresh water
m3/t of paper
total for the mill
10 - 15 10 - 15 13 - 18 8 - 13 8 -13
Shower water
m3/t of paper
total for the PM
3 - 5 3 - 5 3 - 5 3 - 5 3 - 5

112. Pele Oy
New Papermaking Developments

113. Pele Oy
113
Basic process principle is old
Combined forming/pressing or pressing/drying ?
Do we need water in forming and coating – dry processes?

114. Pele Oy
114
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.
Flocculated:
• Bad formation
• Low strength
• Low opacity
• High porosity
• Good drainage
• Good fiber retention
Good formation
• High strength
• Good opacity
• Low porosity
• Slow drainage
• Low fiber retention
Better quality
Picture: E.Gruber

115. Pele Oy
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.
115
Fibers occupy a sphere
in the headbox
Stiff fibers form flocs
with friction forces
Flocculation results in
bad paper formation

116. Pele Oy
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.
116
Picture: Voith

117. Pele Oy
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
consistency forming.
 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.
117
SliceOpening,mm
Grammage, gsm
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
0 50 100 150 200 250 300 350
HB cons. 1 %
HB cons. 3%
HB cons. 2 %

118. Pele Oy
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
publication papers.
 This old picture on the right shows what
is the difference between filtering
(normal paper) and thickening (high
consistency paper).
118

119. Pele Oy
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
dewatering box.
119
Consistency Total mass
% tons/dry ton
0,5 200
1 100
2 50
3 33
4 25
5 20

120. Pele Oy
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
120
Bulk [cm3/g]
Picture: VTT

121. Pele Oy
Pilot foam forming machine at VTT Finland 2013
 Foam forming gives possibilities to save water, energy and material in papermaking.
121
Picture: VTT

122. Pele Oy
Microfibrillated cellulose
 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.
122

123. Pele Oy
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.
123
Picture: Valmet

124. Pele Oy
Multilayer headbox with water layering technology
 Valmet had a presentation in PaperCon2015. The following conclusion
is from this presentation:
124

125. Pele Oy
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.
125
Picture: Valmet

126. Pele Oy
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.
126

127. Pele Oy
127
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.
Picture: Valmet

128. Pele Oy
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.
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Picture: Valmet

129. Pele Oy
THANK YOU FOR YOUR ATTENTION
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