Two new measurements that give paper and board manufacturers visibility into minute surface craters and fine surface variations which, if left unaddressed, could jeopardise print results is now available in an 'everyday use' measuring device. Paper producers can now minimize their risk of making paper whose uneven topography leads to disappointing print results for end users. Optical topography is a measurement technique whereby light is projected from two positions, at an acute angle and the resulting stereoscopic image shows shadows cast by surface topography variations. The image is used to create a gradient image, from which a height map can be calculated. Method was invented by Innventia, a Swedish world leading pulp & paper research institute, and prototype scale instruments has been available for some years. Now Lorentzen & Wettre together with Innventia has developed a more user friendly instrument based on this method meeting industrial standards of functionality, precision and durability. Optical topography measurement lets paper and board manufacturers measure surface crater characteristics with such high precision that the device can predict the risk of missing dots leaving areas of paper uncovered. The technology can also detect surface deviations significantly smaller than achievable by more traditional air leak methods (Bendtsen, Sheffield, PPS etc.) and much faster than advanced microscopy technologies such as confocal displacement, chromatic aberration and laser triangulation. Surface variation as fine as 0.2μm can be measured by the instrument. Many years of Innventia's research and print studies proves that optical topography measuring small scale variations and craters in paper surface is better than traditional methods to predict how ink will cover the paper or board surface in flexo, gravure, offset or hybrid printing.
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