Web Material Properties: Easy Paths Through the Swamp (but beware of alligators!)

Presented by Dilwyn Jones, Emral Ltd.

The properties of webs are needed for diverse “web handling” activities such as machine specifications, design and upgrade, new and existing product development and manufacture, and troubleshooting breaks and defects – especially using formulae and models. Unfortunately, there is considerable variability hidden behind generic material names, such as BOPP and paper.  Suppliers provide some data, but often important properties, such as Young’s Modulus, are missing.   It is easy to get lost in a quagmire of suppliers, grade variants, and test methods. Fortunately, most calculations only require a few properties at an accuracy of 10% or worse. Examples will be given where a textbook value is adequate, and where it is not so new measurements should be made.

Furthermore, no web is perfect, and the ability to produce good product will depend on the level of pre-existing defects (as well as introducing no new ones). Particular issues come from thickness profile, bagginess and edge problems. Properties of multi-layer webs such as laminates must often be estimated from those of the layers, but there are dangers lurking when they are put together.