Change search
ReferencesLink to record
Permanent link

Direct link
Finger Friction Measurements on Coated and Uncoated Printing Papers
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
Institute for Surface Chemistry (YTK), Stockholm, Sweden.
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.ORCID iD: 0000-0003-2489-0688
Oy Keskuslaboratorio - Centrallaboratorium Ab (KCL), Espoo, Finland.
Show others and affiliations
2010 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 37, no 2, 389-399 p.Article in journal (Refereed) Published
Abstract [en]

A macroscopic finger friction device consisting of a piezoelectric force sensor was evaluated on 21 printing papers of different paper grades and grammage. Friction between a human finger and the 21 papers was measured and showed that measurements with the device can be used to discriminate a set of similar surfaces in terms of finger friction. When comparing the friction coefficients, the papers group according to paper grade and the emerging trend is that the rougher papers have a lower friction coefficient than smoother papers. This is interpreted in terms of a larger contact area in the latter case. Furthermore, a decrease in friction coefficient is noted for all papers on repeated stroking (15 cycles back and forth with the finger). Complementary experiments indicate that both mechanical and chemical modifications of the surface are responsible for this decrease: (1) X-ray photoelectron spectroscopy measurements show that lipid material is transferred from the finger to the paper surface, (2) repeated finger friction measurements on the same paper sample reveal that only partial recovery of the frictional behaviour occurs and (3) profilometry measurements before and after stroking indicate small topographical changes associated with repeated frictional contacts.

Place, publisher, year, edition, pages
2010. Vol. 37, no 2, 389-399 p.
Keyword [en]
Biotribology, Coated paper, Finger friction, Friction test methods, Paper friction, Perception, Skin friction, Surface roughness, Tactile feel, Uncoated paper
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-11930DOI: 10.1007/s11249-009-9538-zISI: 000274222300031ScopusID: 2-s2.0-77649237221OAI: diva2:290449
Swedish Research CouncilKnut and Alice Wallenberg Foundation

QC 20110126

Available from: 2010-01-27 Created: 2010-01-26 Last updated: 2012-10-26Bibliographically approved
In thesis
1. Tactile Perception - Role of Physical Properties
Open this publication in new window or tab >>Tactile Perception - Role of Physical Properties
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis is to interconnect human tactile perception with various physical properties of materials. Tactile perception necessitates contact and relative motion between the skin and the surfaces of interest. This implies that properties such as friction and surface roughness ought to be important physical properties for tactile sensing. In this work, a method to measure friction between human fingers and surfaces is presented. This method is believed to best represent friction in tactile perception.

This study is focused on the tactile perception of printing papers. However, the methodology of finger friction measurements, as well as the methodology to link physical properties with human perception data, can be applied to almost whichever material or surfaces.


This thesis is based on three articles.


In Article I, one participant performed finger friction measurements, using a piezoelectric force sensor, on 21 printing papers of different paper grades and grammage (weight of the papers). Friction coefficients were calculated as the ratio of the frictional force and the normal force, shown to have a linear relationship. The values were recorded while stroking the index finger over the surface. The results show that measurements with the device can be used to discriminate a set of similar surfaces in terms of finger friction. When comparing the friction coefficients, the papers group according to paper surface treatment and an emerging trend is that the rougher (uncoated) papers have a lower friction coefficient than the smoother (coated) papers. In the latter case, this is interpreted in terms of a larger contact between the finger and paper surface.


In addition, a decrease in friction coefficient is noted for all papers on repeated stroking, where the coated papers display a larger decrease. XPS (X-ray Photoelectron Spectroscopy) reveals that skin lipids are transferred from the finger to the paper surface, acting as a lubricant and hence decrease friction. Nevertheless, there is evidence that mechanical changes of the surface cannot be completely ruled out.


The reproducibility of the finger friction measurements is elaborated in Article II, by using many participants on a selection of eight printing papers out of the 21. The trends in friction are the same; once again, the coated papers display the highest friction. There are notably large variations in the exact value of the friction coefficient, which are tentatively attributed to different skin hydration and stroking modes.


These same participants also took part in a tactile study of perceived paper coarseness (“strävhet” in Swedish). The results reveal that the participants can distinguish a set of printing papers in terms of perceived coarseness. Not unexpectedly, surface roughness appears to be an important property related to perceived coarseness, where group data display that perceived coarseness increases with increasing surface roughness. Interestingly, friction also appears to be a discriminatory property for some subjects. A few participants showed opposite trends, which is evidence for that what is considered coarse is subjective and that different participants “weigh” the importance of the properties differently. This is a good example of a challenge when measuring one-dimensional perceptions in psychophysics.


In Article III, a multidimensional approach was used to explore the tactile perception of printing papers. To do this, the participants scaled similarity among all possible pairs of the papers, and this similarity data are best presented by a three-dimensional space solution. This means that there are three underlying dimensions or properties that the participants use to discriminate the surface feel. Also, there is a distinct perceptual difference between the rougher (uncoated) and smoother (coated) papers. The surface roughness appears to be the dominant physical property when discriminating between a real rough paper and a smooth paper, whereas friction, thermal conductivity and grammage are more important when discriminating among the smooth coated papers.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. xiii, 56 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2010:2
Finger Friction, Skin Friction, Paper Friction, Friction Coefficient, Piezoelectric Force Sensor, Skin Tribology, Biotribology, Soft Tribology, Surface Roughness, Profilometry, Coated Paper, Uncoated Paper, Printing Paper, Magazine Paper, Tactile Perception, Psychophysics, Multidimensional Scaling, Magnitude Estimation, Paper Coarseness, Thermal Conductivity, X-ray Photoelectron Spectroscopy.
National Category
Other Basic Medicine
urn:nbn:se:kth:diva-11891 (URN)978-91-7415-533-4 (ISBN)
2010-02-12, Sal E3, Osquarsbacke 14, KTH, Stockholm, 13:00 (English)
Available from: 2010-01-26 Created: 2010-01-19 Last updated: 2011-03-24Bibliographically approved
2. Tactile Perception: Role of Friction and Texture
Open this publication in new window or tab >>Tactile Perception: Role of Friction and Texture
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Tactile perception is considered an important contributor to the overall consumer experience of a product. However, what physical properties that create the specifics of tactile perception, are still not completely understood. This thesis has researched how many dimensions that are required to differentiate the surfaces perceptually, and then tried to explain these dimensions in terms of physical properties, by interconnecting human perception measurements with various physical measurements. The tactile perception was assessed by multidimensional scaling or magnitude estimation, in which methods human participants assign numbers to how similar pairs of surfaces are perceived or to the relative quantity of a specified perceptual attribute, such as softness, smoothness, coarseness and coolness. The role of friction and surface texture in tactile perception was investigated in particular detail, because typically tactile exploration involves moving (at least) one finger over a textured surface. A tactile approach for measuring friction was developed by means of moving a finger over the surfaces, mounted on a force sensor. The contribution of finger friction to tactile perception was investigated for surfaces of printing papers and tissue papers, as well as for model surfaces with controlled topography. The overarching research goal of this thesis was to study, systematically, the role of texture in tactile perception of surfaces.

The model surfaces displayed a sinusoidal texture with a characteristic wavelength and amplitude, fabricated by surface wrinkling and replica molding techniques. A library of surfaces was manufactured, ranging in wavelengths from 270 nm up to 100 µm and in amplitudes from 7 nm up to 6 µm. These surfaces were rigid and cleanable and could therefore be reused among the participants. To my knowledge, this is the first time in a psychophysical experiment, that the surface texture has been controlled over several orders of magnitude in length scale, without simultaneously changing other material properties of the stimuli.

The finger friction coefficient was found to decrease with increasing aspect ratio (amplitude/wavelength) of the model surfaces and also with increasing average surface roughness of the printing papers. Analytical modeling of the finger’s interaction with the model surfaces shows how the friction coefficient increases with the real contact area, and that the friction mechanism is the same on both the nanoscale and microscale. The same interaction mechanism also explains the friction characteristics of tissue paper. Furthermore, it was found that the perceptions of smoothness, coarseness, coolness and dryness are satisfactorily related to the real contact area at the finger-surface interface. 

It is shown that it is possible to discern perceptually among both printing papers and tissue papers, and this differentiation is based on either two or three underlying dimensions. Rough/smooth and thin/thick were the two main dimensions of surface feel found for the printing papers, whereas friction and wavelength were strongly related to the perceptual cues employed in scaling the model surfaces. These experimental results support the duplex theory of texture perception, which holds that both a “spatial sense”; used to discriminate the roughest textures from the others, and a “vibration sense”; used to discriminate among the smoother textures, are involved. The perception of what is considered rough and smooth depends on the experimental stimulus context. It is concluded that friction is important for human differentiation of surface textures below about 10 µm in surface roughness, and for larger surface textures, friction is less important or can even be neglected.

The finger friction experiments also allowed the following conclusions to be drawn: (i) The interindividual variation in friction coefficients is too large to allow direct comparison; however, the trends in relative friction coefficients for a group of participants are the same. (ii) Lipids are transferred to the test surface of study, and this lowers the friction. (iii) Many of the studies point to a characteristic frequency during sliding of about 30 Hz, which is both characteristic of the resonance frequency of skin and the expected frequency associated with the fingerprints. (iv) The applied load in surface interrogation is in fact regulated in response to the friction force.

The limits in tactile perception were indirectly researched by similarity scaling experiments on the model surfaces. Wrinkle wavelengths of 760 nm and 870 nm could be discriminated from untextured reference surfaces, whereas 270 nm could not. The amplitude of the wrinkles so discriminated was approximately 10 nm, suggesting that nanotechnology may well have a role to play in haptics and tactile perception.

Abstract [sv]

Taktil perception bidrar starkt till den sammantagna upplevelsen av en produkt, men hur materials olika ytegenskaper påverkar och styr perceptionen är ännu inte helt klart. Den här avhandlingen undersöker hur många och vilka egenskaper som är viktiga när känslan mellan två ytor jämförs. Tillvägagångssättet är tvärvetenskapligt där fysikaliska mätningar kopplas ihop med perceptions mätningar där människor används som instrument. Två typer av perceptionsförsök har utförts, multidimensionell skalning där försökspersoner sätter siffror på hur lika två ytor känns, samt magnitud estimation där i stället intensiteten på specifika perceptuella storheter som t.ex. upplevt lenhet, upplevd mjukhet och upplevd strävhet bedömdes. Eftersom taktil perception innebär kontakt samt relativ rörelse mellan hud och ytor, har fokus i avhandlingen varit att undersöka hur friktion och ytans struktur (ytråhet) påverkar och bidrar till den taktila perceptionen. Förutom fysikaliska mätningar på friktion och ytstruktur har värmekonduktivitet, mjukhet samt olika standard mätningar inom pappersindustrin mätts. En metod för att mäta friktion mellan ett finger och olika ytor har utvecklats för att i möjligaste mån återspegla friktionskomponenten i upplevt taktil perception. Friktionskoefficienter beräknades och jämfördes mellan alla ytor. De stimuli som har studerats är tryckpapper och mjukpapper samt modellytor, gjorda för att systematiskt undersöka hur ytstruktur påverkar perceptionen.

Tillverkningsmetoden för modellytorna valdes så att ytorna var tåliga och kunde tvättas och därmed återanvändas. Strukturen på ytorna bestod av ett vågformat mönster där våglängden varierade mellan 270 nm och 100 µm och amplituden mellan 7 nm och 6 µm. Enligt vår vetskap är det första gången som strukturer i de här skalorna har gjorts utan att samtidigt ändra andra material egenskaper.

Friktionskoefficienten minskade med ökad kvot mellan amplituden och våglängden på modellytorna samt med ytråheten på tryckpappren. En analytisk modell tillämpades på kontakten mellan ett finger och ytorna som visade att friktionskoefficienten beror av den verkliga kontaktarean. För de mycket grövre mjukpappren uppmättes inga stora skillnader i friktion förmodligen för att kontakarean mellan de olika mjukpapprena var lika. Den faktiska kontakarean visade sig också vara viktig för perceptionen av lenhet, strävhet, torrhet och svalhet.

Det visade sig vara en stor perceptuell skillnad mellan olika typer av tryckpapper och mjukpapper utifrån hur stimuli placerade sig på en taktil karta. För de tre materialen användes enbart två alternativt tre egenskaper hos materialet för att särskilja mellan alla olika par. För tryckpapper verkade en viktig dimension kunna beskrivas av alla de perceptuella och fysikaliska egenskaper som har med kontaktarean att göra, d.v.s. lenhet, svalhet, torrhet, ytråhet, värmekonduktivitet samt friktion. För att taktilt särskilja mellan olika ytor där bara strukturen är varierade, kunde friktion och våglängden relateras till spridningen i kartan. Båda studierna stödjer duplex theory of texture perception, där ett spatialt sinne används för att särskilja en av de grövre ytorna från en slät, och ett vibrationssinne för att särskilja mellan olika släta strukturer. Friktionen visade sig alltså vara en viktig fysikalisk egenskap för strukturer under åtminstone 10 µm i ytråhet.

Från fingerfriktions mätningar kunde även följande slutsatser dras: (i) Stora skillnader i friktionskoefficient mellan olika personer uppmättes, men trenderna mellan olika individer var samma, vilket gör att relativa skillnader i friktion från en individ är representativa. (ii) Lipider (fingerfett) som överförs från fingret till ytan vid kontakt sänker friktionen. (iii) Frekvensinnehållet i friktionskraften varierar mellan olika ytor och den frekvenstopp som ses vid 30 Hz kan möjligtvis bero på fingrets struktur eller resonansfrekvensen på huden. (iv) Den pålagda kraften under en friktionsmätning visar sig omedvetet regleras av den friktionskraft som fingret möter under rörelse. 

Hur små strukturer som kan diskrimineras har indirekt undersökts genom likhetsförsöket på modellytorna där försökspersoner skulle bedöma hur lika alla par av ytor kändes. Resultaten visade att ytorna med våglängder på 760 nm och 870 nm upplevdes olika jämfört med referens ytor utan något systematiskt mönster, medan ytan med 270 nm i våglängd inte kunde särskiljas. Amplituden på ytan som kunde diskrimineras var endast ca 10 nm, vilket indikerar att nanoteknologi mycket väl kan bidra inom haptiken och för att i framtiden kontrollera den taktila perceptionen.  

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 78 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2012:48
human skin, tactile friction, finger friction, skin friction, skin tribology, biotribology, tactile perception, haptic perception, psychophysics, haptics, surface roughness, surface texture, contact area, nanostructure, model surfaces, surface wrinkling, printing paper, tissue paper, magnitude estimation, multidimensional scaling, tactile threshold, psychophysical relations, smoothness, coolness, coarseness, softness, force sensor, skin lipids, topical formulations, skin creams, taktil friktion, fingerfriktion, hudfriktion, hudtribologi, biotribologi, taktil perception, psykofysik, haptik, ytråhet, ytstruktur, ytveckning, nanostruktur, kontaktarea, modellytor, friktionskoefficient, kraftmätare, bestruket papper, obestruket papper, tryckpapper, mjukpapper, multidimensionell skalning, magnitud estimation, taktilt tröskelvärde, lenhet, mjukhet, svalhet, strävhet, hudlipider, topikala beredningar, hudkräm
National Category
Tribology Physical Chemistry Psychology (excluding Applied Psychology) Materials Chemistry Other Chemistry Topics
urn:nbn:se:kth:diva-103916 (URN)978-91-7501-499-9 (ISBN)
Public defence
2012-11-16, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20121026

Available from: 2012-10-26 Created: 2012-10-24 Last updated: 2012-11-13Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Skedung, LisaDanerlöv, KatrinOlofsson, UlfRutland, Mark W.
By organisation
Surface and Corrosion ScienceTribologi
In the same journal
Tribology letters
Chemical Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 419 hits
ReferencesLink to record
Permanent link

Direct link