1. Pele Oy
Effects of Friction in
Papermaking
1

2. Pele Oy
Preface
Papermaking is a long sequential process, where all process sections
should work to get best possible overall efficiency and product quality.
It is very important to have top knowledge of all parts of the process to get
maximum possible total efficiency and good product quality.
As an example in the following, I will present how paper friction depends
on the total papermaking process and also affects to it and finally to roll
winding and product quality. This really needs more competence than only
winding expertise.
Helsinki, 9 December, 2015
Pekka Komulainen
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3. Pele Oy
FRICTION IN PAPERMAKING

4. Pele Oy
Total efficiency of papermaking process
 Papermaking is a long sequential process where all process sections should
work to get saleable production.
 If we assume five separate processes (different colors) and very good 99%
material efficiency in each, the total efficiency is 95%. When the efficiency of
each process is as good as 95% then the total efficiency is only 77%.
4
Stock
prep
Paper slitting
and winding
Packaging
Headbox et
drainage
Wet
pressing
Paper
drying
Coating /
sizing
Calen-
dering
Reeling
Sheeting
Coat
drying

5. Pele Oy
Paper friction
 The development of the tangential force F as a function of time required to
initiate and to maintain relative movement between two solid bodies, where Fs
is the static friction force and Fk is the kinetic friction force.
 Coefficient of friction µ is the measured force divided by the normal force.
5
The Friction between Paper Surfaces
Garoff, Niklas, Doctoral thesis, 2002

6. Pele Oy
Possible difficulties of COF variation
High COF
 Roll bouncing, vibration and throw-
out in winding
 High roll hardness
 Dusting, low surface strength
 Wear of web contacting machine
parts (wires, felts, rolls, dewatering
elements, knives)
 Problems in web converting
 High power consumption
Low COF
 Web spreading difficulties and crepe
wrinkles in roll winding. Low roll
hardness.
 Slipping between driven rolls and
paper.
 Sliding of sheets and packages in
treatment, storage and transport.
 Sheet grip problems in printing houses,
copier machines and automatic teller
machines.
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Coefficient of friction (COF) should be constant in every process. The level
of COF is also important. In papermaking there are mechanical and
chemical reasons which affect on friction.
More about friction:
www.fpirc.kth.se/Documents/PDF/Friction.pdf

7. Pele Oy
Measurement speed and COF
 Copy paper friction force as a function of time. Measuring speeds were 0.2
and 5 mm/s. A strong stick-slip motion is visible at the lower speed.
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ANNA JOHANSSON et al.
Paper friction—influence of measurement conditions
VOL. 81 NO. 5 TAPPI JOURNAL

8. Pele Oy
Surface roughness structure and COF
 Normally surface roughness has no effect on friction. However, paper is
sometimes a different material.
 Fibers rising from paper surface can originally be orientated or will be
orientated after first measurement. It is important to measure paper-to-paper
friction in same direction (also meaning flow from the headbox).
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Higher COF Lower COF
The Friction between Paper Surfaces
Garoff, Niklas, Doctoral thesis, 2002

9. Pele Oy
Friction sample contamination
 Contact-free handling of the test sheets is important. This is demonstrated by
comparing results for contact-free test surfaces with surfaces that had been
touched with the thumb and the hand.
 These results show that the friction decreased considerably when the surfaces
were touched before measurement.
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Paper friction—influence of measurement conditions
ANNA JOHANSSON, CHRISTER FELLERS, DENNIS GUNDERSON, AND URBAN HAUGEN
VOL. 81 NO. 5 TAPPI JOURNAL

10. Pele Oy
PAPER CHEMISTRY EFFECTS ON FRICTION
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11. Pele Oy
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Effects of low paper COF in papermaking
 Fatty chemicals reducing friction even in small amounts are mixed in the pulp. These can
be fatty acids from wood, deinking chemicals, defoamers, neutral sizes etc. In addition,
lubricants are used in coatings. With coated broke lubricants are returned to the wet end.
 These chemicals reduce paper friction and also surface tension thus lowering wet web
strength and having effect on paper winding.
Fatty acids
soaps etc.
More
broke
Bursts
Wrinkles
Winder
breaks
Low winder
capacity
Low winder
capacity
Winder
breaks
Low winder
capacity
More
broke
Winder
breaks
Low winder
capacity
Higher web
tension
Higher
speed
More
splices
Wet end
breaks
Low fiber
friction
Low paper
friction
Low surface
tension
Low wet
web strength

12. Pele Oy
12
COF and paper chemicals
Higher COF with the following chemicals (order of effectiveness):
 Silica (retention system), calcined clay and titanium dioxide
 Ground calcium carbonate and PCC
 Clean chemical pulp and starch
 More rosin acids than fatty acids from wood (more softwood)
 Generally hydrophilic/oleophobic substances with high surface energy
Lower COF with the following chemicals (order of effectiveness):
 Silicones/defoamers (several), lubricants and fatty acids from wood
 Fatty acid surfactants which are used in the deinking process
 Talc and kaolin clay (platy pigments)
 Latexes, gums, waxes especially in deinked pulp
 Generally hydrophobic/oleophilic (lipophilic) substances with low surface
energy i.e. substances having low surface tension such as surfactants

13. Pele Oy
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Fatty acids
 Fatty acids are organic acids with a
long carbon chain. Some saturated
fatty acids are:
 Butyric: CH3(CH2)2COOH
 Lauric (dodecanoic acid):
CH3(CH2)10COOH
 Myristic (tetradecanoic acid):
CH3(CH2)12COOH
 Palmitic (hexadecanoic acid):
CH3(CH2)14COOH
 Stearic (octadecanoic acid):
CH3(CH2)16COOH
 Arachidic (eicosanoic acid):
CH3(CH2)18COOH

14. Pele Oy
Paper COF and type of fatty acids
 The coefficient of friction of cellulose surfaces impregnated with different
fatty acids plotted against the number of carbon atoms in the fatty acid.
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The Friction between Paper Surfaces, Garoff, Niklas, Doctoral thesis, 2002

15. Pele Oy
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Disadvantages of fatty acids
 Increasing amount of fatty acids reduces friction and surface tension. This
might in some cases be good for winder vibration but not good for wet and dry
paper strength.
Fatty acids
Seika Tay: TAPPI Journal, August 2001

16. Pele Oy
Surface energy and hydrophobicity
 Materials with lower surface energy are more hydrophobic. More
hydrophobic surfaces have lower coefficient of friction.
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Picture: Leslie Webb

17. Pele Oy
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Extractive content of American wood species
% of dry wood
 Balsam Fir 1.0 - 1.8
 Douglas Fir 0.3 - 2.6
 Western Hemlock 0.3 - 1.3
 Eastern Hemlock 0.2 - 1.2
 Western Larch 0.7 - 0.9
 White Spruce 0.4 - 2.1
 Jack Pine 1.9 - 4.3
 Longleaf Pine 2.1 - 9.2
 Silver Maple 0.2 - 0.9
 White Birch 1.5 - 3.5
 Trembling Aspen 1.0 - 2.7
Extractives content has effect on COF. If there is variation in
wood species there is variation in COF.

18. Pele Oy
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Surface-active agents or surfactants
 Surfactants are molecules having a dual character.
Part of each molecule is hydrophilic and part is
hydrophobic.
 The dual affinity means that surfactant molecules
have a tendency to accumulate at interfaces
between polar and nonpolar phases.
 Surfactants can help in dispersing suspension
particles, spread various liquids onto solids, and
stabilize desirable foams.
 Surfactants can be a nuisance to papermakers
when they stabilize undesirable foams, hurt dry
strength of paper, or hurt fine-particle retention.
 Surfactants are added in deinking and intentionally
to retention aid formulations, biocides, and various
sizing agents to keep such products stable during
storage.

19. Pele Oy
19
Initial wet web strength
 Friction forces in the wet web form initial
wet web strength. However, there must
be pressure force between the fibers to
get friction force.
 This pressure force is formed of surface
tension forces together with fiber stiffness.
 There are several chemicals which
reduce surface tension, fiber-to-fiber
friction and paper-to-paper friction. This
would help in winder vibration and
bouncing but at the same time these
chemicals reduce paper strength and
runnability.
Friction force = μN
N

20. Pele Oy
Influence of wood extractives on COF
 S1 and S2 in the picture are static COF:s and K3 is kinetic COF. It can be noted that
clean reference has highest COF.
 The same is valid for virgin and recycled pulps: well washed pulp has higher COF.
20
THE INFLUENCE OF WOOD EXTRACTIVES ON
PAPER-TO-PAPER FRICTION, 1999 International Paper
Physics Conference Proceedings

21. Pele Oy
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Effects of wood extractives
 For winder vibration and roll
bouncing lower friction is good. For
crepe wrinkles higher friction is
better.
 Lower sheet strength especially wet
web strength has effect on paper
machine runnability.
 Best friction level is always
compromise between paper
machine runnability and winder
runnability as well as final paper
quality.
Some softwood extractives especially in the mechanical pulp
have the following effects:
Components Effects
Triglycerides,
fatty acids
Lower strength
and friction
All hydrophobic
components
Foaming, low
retention
All hydrophobic
components
Lower water
absorbance

22. Pele Oy
22
COF and fillers
 Platy fillers decrease COF (kaolin, talc).
 Synthetic silicate and calcined clay increase COF.
Michael C. Withiam, The effect of fillers on paper friction properties
April 1991 Tappi Journal

23. Pele Oy
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Synthetic silicate and COF
 Synthetic silicate is very efficient in increasing kinetic COF. Small
amounts up to 2% have the greatest effect.
Michael C. Withiam, The effect of fillers on paper friction properties
April 1991 Tappi Journal

24. Pele Oy
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Retention control and silica
 Polyacrylamide and silica
microparticles are often used to keep
tray water consistency constant.
 Small additions of silica can increase
paper COF considerably. There can
be high variation in silica content in the
paper - more silica means higher
friction.
 Bentonite retention system might be
more slippery – bentonite is a special
type of clay.

25. Pele Oy
25
Foam control and paper COF
 Foam is controlled by varying defoamer
content according to air content measurement.
 The most universal characteristic of any
defoamer is the fact that it is surface active, but
highly insoluble in water. It has to be
formulated so that it will be dispersed as tiny
droplets, i.e. as an emulsion.
 Foam control agents in surface size or coating
stay on the paper surface and have very big
effect on paper COF.
 Defoamers normally reduce friction. Variation
of defoamer content makes variation in paper
COF.

26. Pele Oy
26
Example of water circulation system
 Let us suppose that fresh water consumption is high (30 m3/t paper) and
there is no water lock between the pulp mill and the paper machine.
Pulp Mills
Paper-
making
Fresh Water 30 m3/t paper
To effluent treatment
From PM 11 m3/t paper
Pulp consistency 10%,
water 9 m3/t pulp,
lot of dissolved &colloidal
materials to paper machine
To effluent
treatment
10 m3/t paper 20 m3/t paper
1 m3/t paper
17 m3/t paper12 m3/t paper

27. Pele Oy
27
Water lock after pulp mill
 Let us suppose that there is a double wire press between pulp mill and
paper machine and the solids after double wire press is 33%. Only 2 m3
water/t pulp is then transported to the paper machine.
Pulp
Mills
Paper-
making
Fresh 10 m3/t paper
From PM 11 m3/t paper
If consistency is 33%, water
content is 2 m3/t pulp, less
anionic trash to paper machine
Main flow to effluent from
DIP Plant  anionic trash out
0 m3/t paper 10 m3/t paper
1 m3/t paper
0 m3/t paper
9 m3/t paper

28. Pele Oy
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DCS, fresh water and water lock
 Practical fresh water usage is 10-20 m3/t. This range has very little effect on
dissolved and colloidal solids concentration. However, moving from integrated
system to interstate washing (water lock) has a big effect on DCS carry-over to
paper machine.

29. Pele Oy
29
Base paper porosity and coating coverage
 Coating coverage has effect on
smoothness after calendering.
Coating can have lower friction than
base paper.
 The final paper friction depends
more on the friction difference
between coating and base paper
than on the final paper roughness.
 Variations in fiber components and
in their shares in the furnish have
effect on paper porosity and coating
coverage.
Porous baseDense base
TING HUANG AND PIERRE LEPOUTRE: Effect of basestock surface structure and chemistry on coating holdout and coated paper properties, VOL. 81: NO. 8 TAPPI JOURNAL

30. Pele Oy
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Coating lubricants and COF
 The most effective lubricant is wax. Also stearates reduce friction.
Toshiharu Enomae · Naoya Yamaguchi - Fumihiko Onabe
Influence of coating properties on paper-to-paper friction
of coated paper

31. Pele Oy
FRICTION IN WINDING
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32. Pele Oy
TNTs and two-drum winder
 With a two-drum winder the nip force at the end of winding can be too high. If this is
compensated by tapering web tension and torque difference, the combination of heavy
nip load and low tension can create crepe wrinkles.
0
2
4
6
8
10
12
100 300 500 700 900 1100 1300 1500 1700
Roll diameter, mm
Nipload,kN/m
Nip load
Compensation with rider roll
Nip due to roll’s own weight
Tapering web tension or
torque can
be dangerous
32

33. Pele Oy
Winder types for thin printing papers
 Winders have been developed to reduce the load between winder drum and
paper roll (too heavy load breaks a thin paper). Glossy coated paper has
high density and paper is thin. This requires better winder than standard two-
drum winder (e.g. Soft drum winder, WinBelt or single drum winder).
Thinner paper or larger roll diameter
Two-drum
Winder
Belt supported
Winder
Multi-station
Winder
Multi-station
belt supported
Belt
Belt
Recommended with
soft drum cover(s)
33

34. Pele Oy
Winder problems and COF
 There is an optimum COF especially for two-drum winders
 Papermaking variables have a great influence on the COF level
 COF is an important papermaking variable and should be monitored
34
Papercoefficientoffriction
0.5
1.0
Vibrating and bouncing range
(uncoated & matt coated grades)
Wrinkling range
(thin and smooth grades)

35. Pele Oy
Two-drum winder and uneven caliper
 The purpose of shaftless winding is to rotate the rolls with same surface speed. In
practice this is difficult. Due to axial forces the rolls try to attach to each other and try to
have the same rotational speed.
 The edge roll can be smaller in diameter. The situation is more difficult, when there is a
smaller roll in the middle of the set. Caliper profile should be all the way slightly thinner to
the edges to get better winding.
 When paper friction is high, touching rolls have big effect resulting in disturbing forces =
core misalignment, out-of-roundness, roll bouncing and throw-out.
 One remedy is to run some supporting paper layers on the cores slitters still open.
35
CD caliper profile
Winder drum
Axial force
Problem
Picture: Voith Paper

36. Pele Oy
Roll bouncing
 General unstable behavior of the roll,
i.e., roll rocking back and forth from
drum to drum caused by roll diameter
differences and high friction paper.
 Appears on shaftless two-drum type of
winders or belt supported winders.
 Can be seen as blinking in the roll
gaps or shaking of the core locks after
certain roll diameter .
Picture: Metso Paper
36

37. Pele Oy
Effect of paper COF on coated fine paper winding
 When COF is ≥0.5 there is a risk for vibration. This is very common situation
when mostly carbonate is used in coating.
 When COF is low, roll dishing can be a problem.
37
0,35 0,55
Paper Coefficient of Friction
Riskforwindingproblems
No problems

38. Pele Oy
Effect of paper COF on newsprint winding
 When COF is ≥0.5 there is a risk for vibration and bouncing. This is very
common situation when DIP quality is good (no stickies or fatty acids).
 For low grammage coated paper wrinkles and burst are a common problem.
38
0,3 0,5
Paper Coefficient of Friction
Riskforwindingproblems
No problems

39. Pele Oy
Vibration, friction and roll hardness
 When newsprint is made of mechanical pulp or lower quality DIP, coefficient
of friction (COF) is low and there are no vibration problems in winding.
 Nowadays, with better DIP processes and higher amount of carbonate fillers,
newsprint tends to have high friction and severe vibration problems (like bond
paper in the picture).
39

40. Pele Oy
Example of winder vibration and bouncing
 Due to vibration, speed of the winder must be increased stepwise. With
normal speed there are more web breaks (example in the picture) and to
avoid these, the speed must be reduced. Reduced speed, stepwise
acceleration and web breaks all reduce winder capacity.
Time, s
Speed,m/min
1000
500
1500
2000
Break
40
Roll bouncing
ALEXIS OLSHANSKY
TAPPI Journal, Feb 1997

41. Pele Oy
Roll deformations and vibration
 If paper friction is high and/or paper compressibility is high all impacts to the
roll give a permanent deformation. These tend to have a certain wavelength.
If this wavelength matches roll periphery, vibration will be heavier.
41
Roll bouncing
ALEXIS OLSHANSKY
TAPPI Journal, Feb 1997

42. Pele Oy
Vibration harmonics vs. drum’s natural frequency
Winder drum
natural frequency
Paper roll frequencies vary due
to growing roll diameter
= Heavy
Vibration
42

43. Pele Oy
J-line and crepe wrinkles
 Internal slipping of paper layers under the roll surface is
measured with J-line measurement.
 Shooting a radial line on roll end and then winding layers on
top of that will move the marked layers first to the tightening
direction and then slowly towards the winding direction (=
loosening the original maximum web tension under some top
layers).
 If the maximum tension is low and slippage high there will be
a negative tension in the machine direction resulting in a
buckle of the layers (= crepe wrinkle).
 Very bad combination is a high nip load, a low web tension
and a low COF. This is most common at the machine reel
edge, where caliper can be high and web length long (=loose
edges). In addition edges can be dry and thus COF is low.
 It is best to have curved CD profile = slightly lower caliper at
edges to avoid crepe wrinkles and other problems.
43

44. Pele Oy
Sensitivity to crepe wrinkles
 There will be slippage and possibility to get crepe wrinkles, when
- F > µ • p • A + S
- F = buckling force from nip action = f (N and nip width)
- A = area of possible sliding
- S = paper stiffness force
 To avoid wrinkles paper static COF must be high as well as roll hardness, but nip load
should be low. Low paper stiffness and caliper increase possibilities to get wrinkles.
 With a soft drum cover the buckling force and J-lines are smaller than with a hard
winder drum. Possibility to get crepe wrinkles is very small.
Picture: Metso Paper 44

45. Pele Oy
Reasons for crepe wrinkles
 Low web-to-web coefficient of friction
 Slipping of web layers due to nip effect inside the roll surface
 When roll weight is high (close to center if center support, close to
surface if surface support)
 Combination of low web tension and high/increasing nip load
 Combination of loose web and high caliper/roll diameter
 Low basis weight or thin paper and low MD stiffness
 Hard winding on top of soft winding
 Variation in CD profiles, loose edges, uneven rider roll contact
Winding direction
45

46. Pele Oy
No-problem channel in winding
 It is important to find the correct web tension for every paper grade. If tension
is too high web breaks and internal bursts are problems.
 If tension is too low crepe wrinkles are problems.
Increasing nip load with roll diameter
No problem area
Too low web tension
 wrinkles
Too high web tension 
bursts and breaks
46

47. Pele Oy
Core burst of single drum winders
 Due to core and roll bottom bending
shear and compression forces have
most effect at roll edges against the
core chuck area.
 The situation is worst when roll
weight is highest.
 COF has effect on the slippage
between layers. Gearing is easier
with low COF.
47

48. Pele Oy
Pressure from spool to paper
 There is more pressure at reel edge when the spool is thin, reel is wide,
diameter is large and paper density is high.
 Thin groundwood papers are more sensitive.
 Reel hardness, air between layers and machine speed have influence.
The problem: Wrinkles and bursts on reel bottom.
Bottom broke up to 2% = 2000 m of 100000 m.
Problem areas
48

49. Pele Oy
Effect of COF on roll traction
 Tension change depends on
COF.
 Air cushion can reduce the real
COF depending on speed, web
porosity, capstan wrap angle
and web tension.
 With very high speeds and
dense webs there can be a
floating situation. Then the
paper-roll COF has no effect
anymore.
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Picture: Getting and Losing Traction
by Jerry Brown

50. Pele Oy
Traction between web and roller
 There are two distinct ways to improve the
traction potential between web and roller:
topography and chemistry.
 Topography is using surface roughness to
increase traction. Rough rollers will have a
higher traction with rough webs and with all
webs where air entrainment is significant.
 However, smooth rollers might have more
traction with a smooth web at speeds less
than 50 mpm or where grooving is present to
handle the air.
 The most common roller roughening
techniques are grooving and spraying with
tungsten carbide.
50

51. Pele Oy
Chemistry and roll traction
 Chemistry also affects traction. Metal surfaced rollers tend to have a
somewhat similar friction against many webs; a COF of 0.3 is typical.
However, those same webs against common resilient cover materials, such
as polyurethane have considerably higher COF.
 The effect of chemistry on COF is very efficient. Basically only molecular
layer on the surface has big effect on COF.
 Adding some lubricant or high friction chemicals to the surface size or coating
has more influence than chemicals in base paper. Similarly, contamination of
rollers can have great effect on COF between roller and paper. For example
washing of winder drums is very important to keep good traction.
 The only issue here is that higher COF topography or chemistry tend to be
expensive to achieve and expensive to maintain.
51

52. Pele Oy
Paper grades and COF
 Good deinking removes all fatty acids from the pulp. Fatty acids are lubricants
decreasing paper friction. Good deinked pulp = high paper-to-paper COF =
vibration in winding.
Newsprint
earlierImproved
deinking
52

53. Pele Oy
Loosening of fibers
 After wire section there are several kind of forces trying to loose fibers from the
paper web.
 Fiber detachment depends on the balance between binding forces and
detachment forces. To solve the dust problems it is important to increase binding
forces and reduce detachment forces. With high friction papers the detachment
forces are often higher and paper is more dusty.
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Potential dust fiber
Paper web

54. Pele Oy
Conclusion
 Be aware that COF is important to the runnability of the paper you
work with and the performance of your product.
 Be aware that COF is sensitive to changes you cannot see or feel.
 Include COF as one of the paper properties routinely measured and
controlled.
 Relate COF to the operating parameters of your equipment. Keep
records so that you can compensate for changes in paper properties.
 Work out a reasonable specification for COF - and hold to it.
54