DWR Application note: Paper & Packaging

Starch penetration in test liner

Problem
We produce and deliver recycled based test liner for a highly competitive bulky market, where production costs need to be low, but quality needs to be high and stable. Starch is a key chemical component in our process and is mainly responsible for the strength development. It is applied at the wet end, but also to the surface via the size press. Time to time we have issues to reach our strengths targets and according to our lab measurements the fluctuations are high. We anticipate that the reason is related to surface starch penetration, which is probably influenced by the porosity of the base paper as well as the solids content, type of starch and size press conditions. Presently we do not have any measuring equipment to determine the penetration of the starch and the instability of the strength properties.

Solution
ACA DWR penetration tester is a lab analyser that evaluates the liquid flow in dynamic conditions. Its main benefit is the fact that you can measure the liquid penetration using your own base paper or board and adjust the time and pressure to reflect real process conditions. The analyser has shown for example the influence of base board porosity (Figure 1) and starch solids content (Figure 2) on penetration rate. This information helps us to optimize the operating window and produce better quality. Also we use the DWR penetration rate as a standard quality control tool since the measurement is easy and fast to perform.

Learning
Starch is a key component to provide strengths in test liners or other recycled based board. When starch is applied on the surface of a board its strength enhancing properties are very much dependent on the penetration degree. High speed size press application is very dynamic process and the penetration degree is dependent on porosity of the substrate as well as the flow properties of the starch solution and machine conditions such as nip pressure. With ACA DWR penetration tester all these parameters can be simulated in lab conditions with very easy and
fast procedure. In this application note we have shown for example that the starch penetration is significantly reduced as a function of base board porosity and starch solids content.

Comment from the mill

“ACA DWR penetration tester is giving us important insights from our production and we cannot work anymore without it”

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