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Quelle/Publication: Ausgabe/Issue: Seite/Page: European Coatings Journal 01-02/2005 36 Scratch-proofing Towards a standard scratch resistance test for parquet coatings. Rico Emmler, Rolf Nothhelfer-Richter. Scratch resistance is one of the key performance parameters on wood coatings systems, particularly in parquet coatings. However, as yet no convincing standard method exists that at the same time allows to differentiate between different coatings systems, correlates well with scratch resistance performance in real life, is easily applicable and not too costly. The study presented here aims at developing such a test. In order to reduce emissions from solvents, many environmentally friendly surface coatings on wooden flooring have been established. On multi-layer parquet, systems of 100% UV lacquers are dominant. Another common approach is to apply oiled or waxed surfaces. With sealing systems being applied on site, water-based lacquer systems have come to be widely adopted. These systems, however, require more care during application, and the place of application has a decisive influence on the selection of the appropriate system in order to prevent subsequent complaints. The useability of wooden floor lacquers is determined by complex parameters and should not be judged by single properties, such as abrasion resistance, alone. Thus, further to basic properties, such as adhesive strength and surface appearance, wooden floor coatings must also be resistant towards staining caused by domestic chemicals, rock particles and dirt. They must also show sufficient elasticity to the highest degree possible to follow dimensional changes of the hygroscopic wood substrates, or deformations caused by impact, e.g. by high-heeled shoes. In this context, the Institute for Wood Research Dresden (ihd) has developed a requirement profile for wooden floor coatings which aims to provide a complex assessment of hardness and elasticity properties [1]. The use of environmentally friendly systems, particularly of water-based coatings as well as oils and waxes, has been delayed partly due to negative experiences of users, because considerably differing qualities are available on the market. For instance, when products were chosen that are not compatible with the place of application, this often resulted in negative experiences, e.g. with respect to scratch resistance performance. Partial aspects of the usability evaluation, namely the scratch resistance, have been addressed in a joint project of the ihd and the Research Institute for Pigments and Coatings Stuttgart (FPL), with an enphasis on the methodology of testing the scratch resistance. This paper reports intermediate results of these investigations, focusing on multiple scratching test methods. Single scratch tests - too unpredictive or too costly Generally, test methods for scratch resistance of coatings can be divided into single and multiple scratch tests. The most frequently applied single scratch test of floor coatings is DIN 68861 p.4/EN 438 p.2, producing scratches by applying a constant force. However, although an orientating statement for the scratch resistance is possible with this test, the prognoses with the EN 438 parameters only rarely coincide with assessments of floor surfaces in practical use [2]. Scratch procedures using an increasing nominal force (nano-scratch procedures) permit plastic deformation processes and brittle fracture events to be registered more simply and can be correlated with viscoelastic phenomena [3]. In this procedure, however, the extensive effort in constructing application apparatuses and the requirement of a surface to be even on a micrometer scale are regarded to be disadvantageous. Comparing multiple scratch tests For multiple scratch tests the Martindale procedure, the linear abrasion procedure [4] and the Rota Hub Scratch Tester [3] can be considered the most important test methods. Felts, Scotch Brite pads, special papers and sanding papers are used as scratching media in these procedures. The principles of the methods are explained in the following: The Martindale Procedure Various defined abrasive materials are applied on an area of 80 mm diameter. The applied force is variable. The scratch material is pressed evenly onto the substrate and a so-called Lissajous pattern combining linear, circular and elliptical motions in all directions is generated. The test device has its origin in the textile industry (Figure 1). Linear Scratch Procedure In this scrub procedure, which is standardised for interior wall paint according to DIN EN ISO 11998, a scratch body is moved linearly in lift and push intervals across the coated surface. Variable scratch materials that have an impact on the surface area can be applied with defined weights. Rota Hub Scratch Test In this procedure, a rotating disk with variable scratch materials attached to it is brought onto the surface, applying defined weights. The test surface is placed on a table, across which the disk can be moved in the x and y axes [3]. For the evaluation gloss measuring and optical assessment are used. Additionally, simple test procedures accompanying product development in the lacquer industry are in use, e.g. 800 g hammers covered in Scotch Brite pads and moved linearly fifty times across a surface area. In this case, too, the loss in gloss is used for evaluation. Coatings and scrub materials The types of coatings used in this study so far, and some of their key performance data, are listed in Table 1. Table 2 provides details of the scrub materials used. The following procedure was applied in the research project, aiming at an improved standard for the evaluation of scratch resistance of parquet coatings: 1. Analysis of the surface structure of parquet surfaces used in practice 2. Selection of representative coating systems and surfaces 3. Laying of various types of floor covering and their systematic monitoring 4. Analysis of scrub materials 5. Development of test methods for determining the scratch resistance 6. Testing of various evaluation methods 7. Draft of coordinated test standards Testing methods and parameters A linear scrub tester, a Martindale device and a Rota Hub tester were used as test devices. Apart from the normal requirements on test procedures, such as differentiability, reproducibility and repeatability, the following fringe Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000

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Page 1: Scratch-proofing - European Coatings Journal · Scratch-proofing Towards a standard scratch resistance test for parquet coatings. Rico Emmler, Rolf Nothhelfer-Richter. Scratch resistance

Quelle/Publication:

Ausgabe/Issue:

Seite/Page:

European Coatings Journal

01-02/2005

36

Scratch-proofing

Towards a standard scratch resistance test for parquetcoatings.Rico Emmler, Rolf Nothhelfer-Richter.Scratch resistance is one of the key performanceparameters on wood coatings systems, particularly inparquet coatings. However, as yet no convincing standardmethod exists that at the same time allows to differentiatebetween different coatings systems, correlates well withscratch resistance performance in real life, is easilyapplicable and not too costly. The study presented hereaims at developing such a test.In order to reduce emissions from solvents, manyenvironmentally friendly surface coatings on wooden flooringhave been established. On multi-layer parquet, systems of100% UV lacquers are dominant. Another commonapproach is to apply oiled or waxed surfaces. With sealingsystems being applied on site, water-based lacquer systemshave come to be widely adopted. These systems, however,require more care during application, and the place ofapplication has a decisive influence on the selection of theappropriate system in order to prevent subsequentcomplaints.The useability of wooden floor lacquers is determined bycomplex parameters and should not be judged by singleproperties, such as abrasion resistance, alone. Thus, furtherto basic properties, such as adhesive strength and surfaceappearance, wooden floor coatings must also be resistanttowards staining caused by domestic chemicals, rockparticles and dirt. They must also show sufficient elasticity tothe highest degree possible to follow dimensional changesof the hygroscopic wood substrates, or deformations causedby impact, e.g. by high-heeled shoes. In this context, theInstitute for Wood Research Dresden (ihd) has developed arequirement profile for wooden floor coatings which aims toprovide a complex assessment of hardness and elasticityproperties [1].The use of environmentally friendly systems, particularly ofwater-based coatings as well as oils and waxes, has beendelayed partly due to negative experiences of users,because considerably differing qualities are available on themarket. For instance, when products were chosen that arenot compatible with the place of application, this oftenresulted in negative experiences, e.g. with respect to scratchresistance performance.Partial aspects of the usability evaluation, namely thescratch resistance, have been addressed in a joint project ofthe ihd and the Research Institute for Pigments andCoatings Stuttgart (FPL), with an enphasis on themethodology of testing the scratch resistance. This paperreports intermediate results of these investigations, focusingon multiple scratching test methods.

Single scratch tests - too unpredictive or too costlyGenerally, test methods for scratch resistance of coatingscan be divided into single and multiple scratch tests.The most frequently applied single scratch test of floorcoatings is DIN 68861 p.4/EN 438 p.2, producing scratchesby applying a constant force. However, although anorientating statement for the scratch resistance is possiblewith this test, the prognoses with the EN 438 parametersonly rarely coincide with assessments of floor surfaces inpractical use [2].Scratch procedures using an increasing nominal force(nano-scratch procedures) permit plastic deformationprocesses and brittle fracture events to be registered more

simply and can be correlated with viscoelastic phenomena[3]. In this procedure, however, the extensive effort inconstructing application apparatuses and the requirement ofa surface to be even on a micrometer scale are regarded tobe disadvantageous.

Comparing multiple scratch testsFor multiple scratch tests the Martindale procedure, thelinear abrasion procedure [4] and the Rota Hub ScratchTester [3] can be considered the most important testmethods. Felts, Scotch Brite pads, special papers andsanding papers are used as scratching media in theseprocedures. The principles of the methods are explained inthe following:

The Martindale ProcedureVarious defined abrasive materials are applied on an area of80 mm diameter. The applied force is variable. The scratchmaterial is pressed evenly onto the substrate and aso-called Lissajous pattern combining linear, circular andelliptical motions in all directions is generated. The testdevice has its origin in the textile industry (Figure 1).

Linear Scratch ProcedureIn this scrub procedure, which is standardised for interiorwall paint according to DIN EN ISO 11998, a scratch body ismoved linearly in lift and push intervals across the coatedsurface. Variable scratch materials that have an impact onthe surface area can be applied with defined weights.

Rota Hub Scratch TestIn this procedure, a rotating disk with variable scratchmaterials attached to it is brought onto the surface, applyingdefined weights. The test surface is placed on a table,across which the disk can be moved in the x and y axes [3].For the evaluation gloss measuring and optical assessmentare used.Additionally, simple test procedures accompanying productdevelopment in the lacquer industry are in use, e.g. 800 ghammers covered in Scotch Brite pads and moved linearlyfifty times across a surface area. In this case, too, the loss ingloss is used for evaluation.

Coatings and scrub materialsThe types of coatings used in this study so far, and some oftheir key performance data, are listed in Table 1. Table 2provides details of the scrub materials used.The following procedure was applied in the research project,aiming at an improved standard for the evaluation of scratchresistance of parquet coatings:1. Analysis of the surface structure of parquet surfaces usedin practice2. Selection of representative coating systems and surfaces3. Laying of various types of floor covering and theirsystematic monitoring4. Analysis of scrub materials5. Development of test methods for determining the scratchresistance6. Testing of various evaluation methods7. Draft of coordinated test standards

Testing methods and parametersA linear scrub tester, a Martindale device and a Rota Hubtester were used as test devices. Apart from the normalrequirements on test procedures, such as differentiability,reproducibility and repeatability, the following fringe

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conditions were agreed upon with the project-accompanyingcommittee:- Practice-relevant scratch patterns shall be produced- Scratches deeper than 5 µm had to be simulated (up tothis depth, preserving agents can compensate scratchtraces)The following influential parameters had to be investigatedas varying test parameters:- type of scrub agent- applied pressure- velocity of movement- number of cycles requiredThe determination of gloss and mass, as well as roughnessmeasurements and optical assessments were used to judgethe applicability of the evaluation procedures.

Surface structures on used parquet coatingsAn example of a parquet surface that was in use for fiveyears is shown in Figure 2. The scratch pattern iscompletely haphazard and inhomogeneous. An underlyingsystem cannot be recognised. Size and shape of scratchesvary to a high degree. Scratch traces are partly linear, butalso irregularly curved. There are frequent changes indirection and crossovers. Ragged, splintered marginal areasof scratches are visible, as are clear-cut and sharp-edgedfringes.

Martindale scrub agents differ in effectivenessWhen applying the Martindale procedure, the followingconclusions were reached regarding the application of thescrub agent (Table 2).- The fabric of the abrasive agent produces no utilisablescratches but only features of wear.- The steel chips could not be utilised, since they renderedimpossible to produce a homogeneously sanded surface.- Of the four scrub fleeces investigated only fleeces SB 7440(medium) and SB 7447 (very fine) proved to be suitable toproduce scratch traces of the desired depth and intensity.Scrub agent SB 7448 (ultra fine) did not result in any visualchange of the test surface. Product SB 7446 (medium)attacked the surfaces too much.

Applied force needs to be calibrated to the scrubmaterialIn its standard version, the abrasion plate exerts a force of 4N, distributed on the scrub material dispersed across 80 mmin diameter, onto the sample. The force was varied up to 8 Nby adding mass pieces.With the very fine scrub material SB 7447, at 6 N load, theeffect of making scratches very clearly visible occurred anddifferentiability improved. Therefore, this level of loadexertion with this scrub material was to be selected. Withsomewhat rougher scrub material an increase in force to 6 Nresulted in undesired abrasive effects. For that reason aforce of 4 N was maintained.

Scrub velocity does not matter - the number of cyclesdoesVelocity was varied within the range of device parameters(half, normal and double velocity factor). Significantdependence of changes in gloss and scratch patterns onvelocity could not be detected.The number of cycles applied varied between 16 (= 1Lissajous movement (LM)) up to 1120 (= 70 LM). With theselected scrub materials SB 7440 and SB 7447, bestdifferentiability was established in the range of 1 LM to 5 LM(Figure 3). As a preliminary result, the number of cycles hastherefore been determinded at 5 LM.

Gloss measurement distinguishes most clearlyThe registration of change in mass proved to be of too littleconfidence, also in terms of its reproducibility, due to thesmall change in mass.With the roughness measurements it also proved impossibleto differentiate conclusively the surface profile of theunstressed surface from that of the "scratched" sample.However, a differentiation could be made between"scratching" and polishing of the surface.Gloss seemed to be most suitable measurement. It wascarried out using a template positioned in the direction offibres (four measurements in the sample centre). The opticalassessment of the samples from all angles and perspectivesusing a light box also proved to be suitable to assess thesurfaces in a differentiated way (6 classes, from 0 = novisible scratches to 5 = very many scratches).

Two drafted test procedures yield good differentiationPre-trials for determining the scrub materials and the testand evaluation parameters were carried out on a number ofsurfaces with different properties. The stipulations derivedfrom that resulted in the specification of two test procedures,A and B (Table 3). The test obtained so far are shown inTable 4. Both procedures will be tested further on a largernumber of coating systems.It becomes obvious that after 5 LM, the results ofprocedures A und B accord very well in their sequencing ofthe materials and a clear differentiation of the surfaces ispossible. The results of procedure A after 1 LM, however,partly showed a different sequence than the one establishedin procedure B. Based on the monitoring of the products inpractical use, it remains to be determined which number ofcycles finally is to be adopted.Further tests are planned with other parquet lacquersystems. Investigations into the calibratability of scrubagents will also be carried out.Analogous tests are soon going to take off at the FPL usingthe Rota Hub procedure. The results of both procedures willthen be compared with the results from practical use.

AcknowledgementThe investigations have been carried out within the AiFProject "Development of Objective Test Methods for theDetermination of Wear Resistance of the Top Layer ofWooden Flooring and Furniture Surfaces" (AiF No.13891BG/1). This research project was supported by budgetaryfunds of the German Federal Ministry for Economics andTechnology (BMWi) via the Arbeitsgemeinschaft industriellerForschungsvereinigungen "Otto von Guericke" e.V. (AiF)and by the Deutsche Forschungsgesellschaft fürOberflächenbehandlung (DFO). The final report can beobtained from the DFO after completion of the project.

References[1] Anforderungsprofil für Holzfußbodenlackierungen,Version 01/2003, Institut für Holztechnologie DresdengGmbH.[2] R. Emmler, Verschleißfestigkeitsprüfungen nacheuropäischen Vornormen und nach ihd Prüfmethoden.Tagungsband des 2. ihd Holzfußbodenkolloquiums am29.02.2000 in Dresden.[3] E. Klinke et al., Kratzer- und der Glanz verblasstKratzbeständigkeit von Klarlacken durch eine neueVielfachverkratzungsmethode praxisnah charakterisieren.Farbe & Lack, 108. Jahrgang 2/2002 S. 52 - 61.[4] M. Metha et al., Durability of Laminate Flooring. 1.European Laminates Conference 2002, Wien.

Results at a glance

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- Intermediate results of a research project aiming to workout a reliable multiple scratch test method, for thedetermination of the scratch resistance of wood coatings, animportant aspect of their practical usability.- Initially, wear traces on used parquet surfaces wereanalysed to determine genuine scratches and scratchpatterns for test-technological purposes. Representativesurface materials for corridors were then selected and theirbehaviour was monitored.- Using a modified Martindale device, investigations on thetest material as well as on the relevant test and evaluationparameters were carried out.- With these, an initial work standard was drafted, which wastested on a series of lacquer systems. Sound differentiabilityof the coatings systems could be proved.

The authors:-> Dr.-Ing. Rico Emmler is researcher at the Institute forWood Technology, Dresden (ihd), Germany, and head ofthe ihd working group on physical surface testing.-> Dr. rer. nat. Rolf Nothhelfer-Richter is head of the physicsdepartment at the Research Institute for Pigments andCoatings, Stuttgart, Germany.

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Figure 1: The Martindale device(a) and an example of the Lissajous pattern producedby it (b) .

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Figure 2: Scratches on a parquet surface after intensive use in practice.

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Figure 3: Changes in gloss of selected lacquer systems with scrub agent SB 7440.

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