The Association of European Producers of Laminate Flooring (EPLF) has successfully concluded a research project during which the IHD (Institute for Wood Technology, Dresden) developed new, objective and differentiating procedures for testing abrasion resistance, impact resistance and polishing behaviour of laminate flooring with deeply- structured and matt surface textures that are new to the market.
What do a discotheque in Sweden, a production facility in Belgium and a company canteen in Germany all have in common? All three (plus a number of other highly-trafficked areas) were used as locations for practical field tests on the latest generation of laminate flooring. The enduring success of laminate is based on continuous innovation, and almost one billion square metres of this type of flooring are installed each year in homes and public buildings around the world. Consumer tastes and preferences are ever-changing and technical capability continues to evolve, so it is not surprising that the laminate floorings of 2016 demonstrate different characteristics from those of its predecessors 10 or 20 years ago, plus the fact that quality standards must also keep pace.
Over the past few years, innovative surfaces have continued to create new themes. A large proportion of wood surfaces reproduce the original wood grain as true to nature as possible. This applies not only to the decorative printed layer but also to tactile textured surfaces. Some woods have well-defined pores. A deep in register embossing and simultaneous decorative print mark the ultimate in current laminate production. Other types of wood finishes are silky-smooth with a matt appearance and these satisfy the current trend for an elegant, close-to-nature style of living. Matt surfaces work perfectly in daily use and are enjoying increasing popularity on the market. The technical challenges have been overcome, but it has become apparent that the test procedures complying with the laminate flooring standard cannot cater for these new surfaces.
The quality of laminate flooring hinges around EN 13329, and the updated version EN 13329:2016, which was recently published, provides specifications, requirements and test procedures for laminate flooring for the EU, Iceland, Macedonia, Norway, Switzerland and Turkey. Although standardised testing for abrasion resistance using sandpaper in line with the Taber abraser method produces significantly lower results for the popular deep textures than for flat ones, this does not relate in any way to the positive experiences that these floors create in real-life applications. In comparison, selected matt textures trafficked heavily on a daily basis literally display “pathways” worn as a result of foot traffic. To date, the standard does not include a procedure for forecasting this polishing effect. In addition, the procedure laid down in the standard for investigating the impact resistance using a “small ball” repeatedly shows inconsistency of reproducibility due to the design of the testing device and this is something else that needs to be addressed. The sum of these issues suggested the need to develop new test procedures or modify existing tests through a combination of laboratory research and an empirical approach. That is why the EPLF proposed a research project to be publicly funded by the German Federal Ministry of Economic Affairs and Energy. The project was carried out between June 2013 and November 2015 by the IHD Institute of Wood Technology in Dresden, under the leadership of Dr Rico Emmler. An ad-hoc group from within the EPLF’s Technical Working Group was actively involved in the research and the technical report is now available.
Abrasion: Practice wins over theory
According to EN 13329:2016, establishing the abrasion resistance of laminate flooring is one of the core criteria for determining quality. Evaluation of abrasion resistance is achieved by friction on the visible surface of the test specimens with a defined grade of abrasive paper mounted on two weighted wheels. The sample material is held horizontally in the testing device and rotated, and the abrading wheels rotate vertically over the sample. The device naturally includes a counting mechanism for the number of rotations effected. If signs of abrasion appear, these run in a circular band covering a surface area of up to 30 cm². The criterion for evaluation is the point at which visible wear on the decorative printed surface occurs. The test specimen is divided into four quadrants and the IP (Initial Point of abrasion is the point at which the visible wear is detected to the extent defined in the standard in a minimum of three quadrants. The mean IP values of three test specimens measured in revolutions during the test process are defined in abrasion class ratings AC 1 to AC 6.
A comparison of laboratory and field tests conducted on “deep textures” indicated that when using the test procedure as defined in the standard, these structures achieved significantly lower abrasion classes than their “cousins” with smoother structures with an identical overlay, i.e. the transparent wear layer on the surface. On the other hand, the experience gained from the several million square metres of flooring already installed is that this does not apply in real life. The aim of the first part of the project was therefore to suitably modify the test method in order to attain corresponding results in both field and laboratory conditions. This necessitated a systematic examination of the wear processes for deep-textured flooring in both locations. The ad-hoc group from the EPLF Working Group, which was involved in the project, selected suitable materials, discussed the results, conducted round robin tests to validate the test procedure, and designated areas of flooring fitted with people counting devices for the purpose of conducting field trials: a discotheque in Lund, Sweden, where the entrance area is passed through 70,000 times per year, plus the bar area at 60,000 times per year, and dance floor (probably the most interesting test surface of all). Other test sites included a company canteen with a count of 400,000 per year; a flight of stairs at the Egger premises; a narrow office corridor at Kaindl with 60,000 passing through annually; a walkway in a production hall at Unilin with 100,000; two narrow walkways at the Classen premises each with 250,000 and, lastly, a corridor at the IHD with a footfall of 40,000.
Admittedly, it was clearly not possible to determine the number of people using the dance floor, but the twisting pressure and sequence of multi-directional motions represented interesting usage characteristics and, in the final analysis, this was the only test surface where wear became visible. However, there were no differences in abrasion behaviour between the six deep textures and the smooth reference structure installed. The same situation was evident in the heavily-trafficked staff canteen. To summarise, it was established that, depending on the structure, the two-year field tests did not mirror the clear differences (depending on texture) in the results of abrasion tests carried out according to the current standard.
To explore the cause of the differences, microscopic examinations were conducted and profile measurements carried out. The latter method is used in material technology for measuring surface roughness either mechanically or by contactless technology and results can be verifiably displayed. These specific measurements showed that in the standard-compliant laboratory procedures, the initial wear points regularly start at the steep shoulders of the elevation, i.e. the places where the friction wheels exert the highest pressure. And it is likely that this pressure at point locations is significantly higher than the more areal loading from the soles of shoes. This indicated the need to get the laboratory results closer to those of the field trial by varying the test parameters (contact pressure, duration of use and abrasion hardness of the test wheels).
Several inter-laboratory tests and continuous comparisons between field and laboratory showed, however, that variations in evaluation parameters achieve the goal more readily (dividing up the specimen, size of area abraded). The test specimens are no longer divided into quadrants, but into octants (eight sections). Presently, the IP (Initial abrasion Point) is defined as being the point at which the underlying layer clearly becomes exposed in six out of eight octants in different-sized areas (in five octants minimum 1 mm² and in the sixth exactly 1 mm²). The IHD in Dresden briefly describes a suitable modification to the standardised procedure in its works standard IHD W-479 “Determination of the Abrasion Resistance for laminate floor coverings”.
Impact resistance: relying on gravitational force
Ascertaining the resistance of laminate flooring to impact stress is a way of identifying the elasticity of a flooring surface. According to EN 13329:2016, there are test procedures using a “small ball” and a “large ball”. The test procedure used to date using a small ball involves a testing device with an integral spring that strikes via an impact bolt. But this piece of equipment shows design deficiencies for reproducibility and is repeatedly causing much discussion between laboratories.
Within the scope of the research project, an alternative solution for evaluating the impact resistance of laminate flooring with deep surface textures was developed and put to the test: following the principle of a falling mass, tests were carried out with 14 types of laminate across all impact classes and product types (DPL, EPL, PDL and HPL). Using this new design of device, the best correlation between results for the impact classes to date were produced by using a ram weight of 150 g and a ball diameter of 10 mm. Accordingly, it was possible to derive a 4-class categorisation comparable with the current system. In contrast with the procedure to date, the testing device is simpler in mechanical terms and the balls themselves can be exchanged, so as to be able to react to wear processes on the contact surface. The results of the process developed by the IHD in Dresden were successfully verified in the inter-laboratory tests involving members of the ad-hoc group. The IHD summarised the newly-developed procedure in its works standard IHD-W-425 “Determination of the small ball impact resistance of laminate floor coverings”.
Polishing effect: Trafficked pathways undesirable
It was necessary to devise a new laboratory procedure for matt surfaces to forecast the polishing processes resulting from foot traffic, thus helping to avoid complaints in this area in practical use. In the field trial, nine laminate floor surfaces installed in a corridor at the IHD were visually assessed by test persons who assigned them to a five-level rating scale, starting from 0 = “no change” up to 5 = “major change”. In parallel with this, the surfaces were examined with a reflectometer to measure the change in gloss level.
In association with this work, the nine different laminate floors were subject to technical laboratory tests using a Martindale abrasion tester. It became apparent that by using this device, changes in gloss level can be produced and evaluated more easily and with clearer differentiation than with the device used for testing sliding wear caused by furniture feet (in accordance with EN 423). The table shown in the gallery gives the results from the series of tests using the Martindale device after varying numbers of cycles, which demonstrated a very good correlation between the visual and technical measurement evaluations. The optimal test parameters (no. of cycles 320, 6N loading, polishing material SB 7448+) were subsequently validated in an round robin test involving seven EPLF members. The IHD Dresden has transposed the research results into its works standard IHD-W-475 “Determination of the polishing resistance of laminate floor coverings”.
On this basis, a proposal is being put forward with a view to developing a classification system for the test results similar to micro-scratch resistance according to EN 16094 and the intention is also to incorporate into EN 16094 a third procedure, namely the test procedure on polishing behaviour that was developed during the project.
Eberhard Herrmann (Egger), Chairman of the EPLF’s Technical Working Group, commented on the results in the technical report on the joint research project between the EPLF and the IHD: “Some years ago, our Association adopted the slogan ‘Quality and Innovation made in Europe’ and this project indicates clearly how quality and innovation work in tandem. For us, it’s not about riding on the crest of every wave of fashion that comes along – our customers can rest assured that they are getting products that are just as reliable as they are up-to-date, with an application potential that is not only transparent but also tried-and-tested. The commitment of our members in the ad-hoc group and the round robin tests confirm the consensus of the leading European laminate flooring producers.”