Thermal conductivity is the material property describing the ability to conduct heat: a material with low conductivity is a good thermal insulator.

The thermal properties of paper are relevant for those products that are used for insulation purposes. Yet, converting steps involving heating or cooling of the paper substrate are common in many processing lines: plastic lamination, printing and gluing are some examples.

A complex property

The structure, the dimensions, the surface roughness, the compressibility and the hygroscopic behaviour of paper are all factors that complicate the measurement of thermal properties. Therefore, thermal conductivity is an uncommon property to characterize, even in the cases in which it is a key performance parameter for a paper product.

Innventia has developed a laboratory technique to measure the steady-state thermal conductivity of paper products. Although no absolute calibration is available at the moment, the method is remarkably repeatable. Therefore we can perform accurate comparative studies of the thermal properties of different paper samples or of paper with other materials. Measurements are performed using the uniaxial MTS press at Innventia; thereby we can replicate the loading conditions that are characteristic for a specific process operation.