Far-Infrared Testing of Dielectric Sheet Materials

Abstract

Quality control in fibre based dielectric sheet materials like paper and non woven fabric is hampered by complex manufacturing processes and usually very high production rates. Far-infrared (FIR) waves are interesting for non destructive characterization of such materials: their low scattering and moderate penetration allow accurate high resolution measurement of basis weight, fibre orientation anisotropy and dominant alignment angle¹. In most applications, sheet materials need to have uniform mechanical properties in order to achieve dimensional stability and problem free handling by end users’ equipment^2,3. In the case of newsprint paper for instance, small scale variations in basis weight will affect readability⁴. Similar scale variations in fibre orientation anisotropy or angle of alignment will result in cockling, bagging, waving or curling of the sheet during the printing process⁵. This, in turn, causes local loss of register and poor quality colour rendering, due to the multiple superimposed prints required. The herein described technique should alleviate this problem by giving the producers a way of testing their product before shipment.