Magnus Lestelius

Y-peel characterization of adhesively-bonded carton board: an objective method

Carton board packages are often closed with an adhesive. The adhesive joint thus formed has to meet the demands during the entire product life from converting to end-use. The adhesive joint has to be characterized if it is good or bad for the actual application. Today such characterization is done by manually peeling the joint, immediately after the adhesive application in the gluing machine. The manual peel test is a subjective test that is operator dependent. An operator needs long experience to be able to perform a manual peel test. Therefore, the packaging industry is interested in a test method that can objectively predict good or bad adhesive joints. The adhesive joints have been tested in the so-called Y-peel test arrangement. An advantage of the Y-peel test is that it gives an objective result from the force–elongation curve. Testing has been performed with carton boards of two different thicknesses. Hotmelt adhesive was used and the open time was varied in the glue applicator. It was found that the Y-peel test gives results in qualitative agreement with the manual peel test. Moreover, by evaluating the energy consumption (dissipative energy) during the Y-peel test it was possible to obtain not only a qualitative but also a quantitative assessment of the adhesive joint.

Influence of kaolin addition on the dynamics of oxygen mass transport in polyvinyl alcohol dispersion coatings

The permeability of dispersion barriers produced from polyvinyl alcohol (PVOH) and kaolin clay blends coated onto polymeric supports has been studied by employing two different measurement methods: ...

Flexographic ink-coating interactions - Effects of porous structure variations of coated paperboard

Calendering of coated and uncoated paper is widely used to enhance optical properties such as gloss and print quality. The aim of this thesis is to characterize coatings and prints, and to validate models using experimental results from optical measurements of physical samples. Calendering of coated paper often leads to a brightness decrease. The mechanism for this is not altogether clear. One common explanation is that the porosity of the coating layer decreases and hence the scattering decreases. By comparing simulated and measured results it was shown that modifications of the surface properties account for the brightness decrease of ground calcium carbonate coated substrates with calendering. Monte Carlo light scattering simulations, taking into account the measured decrease of surface microroughness and increased effective refractive index, showed that surface modifications accounted for most of the observed brightness decrease of the ground calcium carbonate coated substrate, whereas the bulk scattering and absorption coefficients were not affected by calendering. It was also shown that the scattering coefficient is significantly dependent on the coat weight whereas the physical absorption coefficient is not. The penetration of ink in the z-direction of a substrate influences the quality of the print. The ink penetration affects print density, mottling and dot gain, common print effects that influence the preference of consumers. The pressure in the printing nip and the porosity of the substrate both affect the amount of ink that is pressed into the porous structure of a coating layer during printing. By printing pilot coated paperboard with different coating porosity and measuring the resulting optical properties of the prints, a basis for simulations of the different layers, that is to say the coating, the print and the mixed layer in between, was created. Results show that ink distribution is strongly affected by the roughness of the substrate. Fibres and fibre flocks underneath the two coating layers created an unevenly distributed coating thickness that affected the print quality. Differences in pore size and pore size distribution also affected the behaviour of the ink. A coating layer of broad pigment particle size distribution resulted in a relatively low print density, in comparison to coatings of narrowly distributed particle sizes. Comparison of dot gain showed that the coating layer of a narrow particle size distribution had a relatively low dot gain compared to others. In this work, these results are explained by the differences in ink distributions on and in the coating layers.

The influence of moisture content on the polymer structure of polyvinyl alcohol in dispersion barrier coatings and its effect on the mass transport of oxygen

This paper presents a study of the effect of moisture on the gas permeability of polyvinyl alcohol (PVOH) and PVOH–kaolin dispersion barrier coatings. The oxygen permeability was measured at different humidity levels, and the material properties were characterized under the same conditions: polymer crystallinity, kaolin concentration, and kaolin orientation were all evaluated. The experimental results revealed that the water plasticizes the PVOH material of the coatings, and the presence of kaolin filler is unable to affect such behavior significantly. The PVOH crystallinity was affected drastically by the humidity, as water melts polymer crystallites, which is a reversible process under removal of water. The permeability data were analyzed using a thermodynamic-based model able to account for the water effect on both the solubility of the gas and the diffusivity coefficients in the polymer and composite. The results showed good agreement between the model’s predictions and the experimental data in terms of the overall permeability of the material.

Dynamic measurements of nip force variations during post-printing of corrugated board

A method has been developed in order to measure nip force variations during flexographic post-printing of corrugated board. This method can be used to study the influence of the nip mechanics on th ...