Methods for Analyzing the Structure of Creases in Heat Sealed Paperboard Packages

Press-forming of paperboard has been previously studied by several authors. A point of interest regarding gas tight heat sealing of the packages are the creases in the package. The objective of this article was to study and compare different microscopic imaging methods to research an optimal imaging method for the formation of creases in the press-forming process of polymer coated paperboard trays. The studied methods were: Scanning electrode microscopy (SEM), X-ray Microtomography, Optical light microscopy and Polarized light microscopy. All four tested methods delivered clear images. Casting of the samples in an acrylic resin and light microscope imaging was found to be the most suitable method for the analysis of heat sealed creases and leakage detection

Convertability and Oil Resistance of Paperboard with Hydroxypropyl-Cellulose-Based Dispersion Barrier Coatings

The convertability and barrier properties of paperboard coated with hydroxypropyl-cellulose (HPC) based dispersions were studied via tray pressing trials, oil resistance measurements and microscopic analyses. To improve the oil resistance of the HPC-based coatings and to maximize their convertability, talc, gelatin and latex were used as additives in coating formulations. The oil resistance of the coatings improved to some extent with these additives, but scanning electron micrographs revealed the existence of pinholes particularly in coatings with a high HPC content. The coated paperboard samples were pressed into rectangular trays and the convertability of the paperboards was evaluated with a microscope. Thereafter, the oil resistance of the trays was determined in order to clarify how the tray pressing process affected the oil resistance. Pure HPC coating did not provide appreciable oil resistance to the paperboard, but the composite coatings resisted oil up to 11 minutes at the tray corners, which were considered the most demanding regions in the tray. The pure HPC coating was sticky and tended to stick to the converting tools in the press forming. Adding talc to the coating dispersion reduced this problem. By applying a thin pre-coating layer, it was possible to raise the blank holding force in the pressing process from 1.16 kN to 1.55 kN without causing rupture in the tray corner areas or compromising the quality of the creases. With commercial polyethylene-terephthalate-coated reference paperboard, the use of such a high force resulted in long rupture and opened creases, which confirms the excellent applicability of the developed dispersion-coating recipes for the tray-pressing process. These observations suggest that convertibility is not necessarily a major problem with bio-based dispersion barrier coatings and that more attention should be paid to their barrier properties and particularly to the prevention of pinholes being formed during the coating process

Adding a Polymer Film Barrier Layer in the Press Forming Process of Paperboard Trays

The aim of this paper was to investigate the possibility to add a barrier layer in the press forming phase of paperboard trays by sealing a polymer film to a paperboard substrate. Plastic coating is often an important part of packages manufactured for food packaging. Traditionally the paperboards for food packaging are coated in the paper mill before the actual forming of the package. Experiments with coated and uncoated boards were made and the bonding and adhesion of materials was observed. The results indicate that adhesion between the board and the film can be achieved in the forming process. However there are challenges, such as lack of adhesion, air bubble formation and deformation of formed products. It is still shown that it is possible to achieve a bond between the paperboard and a barrier film, and to subsequently add a barrier layer from a separate film to paperboard trays in the forming process

Suitability of Paper-Based Substrates for Printed Electronics

Flexible plastic substrates are widely used in printed electronics; however, they cause major climate impacts and pose sustainability challenges. In recent years, paper-based electronics has been studied to increase the recyclability and sustainability of printed electronics. The aim of this paper is to analyze the printability and performance of metal conductor layers on different paper-based substrates using both flexography and screen printing and to compare the achieved performance with that of plastic foils. In addition, the re-pulpability potential of the used paper-based substrates is evaluated. As compared to the common polyethylene terephthalate (PET) substrate, the layer conductivity on paper-based substrates was found to be improved with both the printing methods without having a large influence on the detail rendering. This means that a certain surface roughness and porosity is needed for the improved ink transfer and optimum ink behavior on the surface of the substrate. In the case of uncoated paper-based substrates, the conductivity and print quality decreased by preventing the formation of the proper and intimate ink-substrate contact during the ink transfer. Finally, the re-pulpability trials together with layer quality analysis detected very good, coated substrate candidates for paper-based printed electronics competing with or even outperforming the print quality on the reference PET foil

Effect of Blank Moisture Content on Forming Behaviour and Mechanical Properties of Paperboard Tray Packages

Tray blanks were moisturised to study the effect of different blank moisture content levels on forming behaviour and mechanical properties of paperboard tray packages. The blank moisturisation was done by spraying water to the blanks before their three-dimensional (3D) forming. The trays were 3D formed by press forming or deep drawing. Visual quality and punch force values were used as indicators to evaluate the forming behaviour of the trays. The mechanical properties of the trays were investigated with compression, torsion, and storing tests. A high blank moisture content reduced the punch force, and the elevated blank moisture was connected to a possible blistering effect in the 3D forming of coated paperboard. The compression test results indicated that the blank moisture content had only a minor effect on compression strength of the trays. The torsion test results linked a high blank moisture content to increased torsional stiffness in the trays. The storing tests yielded measurement uncertainties with the deep drawn trays while the trays press formed with a low blank moisture content showed improved dimensional stability. The blank moisturisation was concluded to enhance the torsional stiffness of 3D formed paperboard tray packages. A sufficient moisture escape during the 3D forming of coated paperboard was deemed necessary to mitigate a possible blistering effect to the coating

Three-dimensional Forming of Multi-layered Materials: Material Heat Response and Quality Aspects

The micro- and macrostructural changes occurring in multi-layered substrates during three-dimensional forming were studied by atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical analyses. Particular attention was paid to heat-induced deformations at the interface between of polymeric coating layer and the paperboard. With excessive heat transfer, occasional delamination of polyethylene terephthalate (PET) coating from the paperboard was observed. The mechanism behind delamination was studied in detail in-situ with an AFM at temperatures relevant to the converting process. Based on the analysis, the delamination could partially be linked to the widening of the initially-existing nano-scale cracks at the coating-paperboard interface due to the high temperature, rigid and less adhesive PET crystallites close to the paperboard layer, and the emergence of fissures and tensile stresses in the coating. SEM images also revealed severe macro-scale delamination in the paperboard matrix after forming. However, the results were somewhat conflicting, since optical and machine vision analyses showed indisputably that both the visual quality and the dimensional accuracy of formed trays were better at the higher forming temperature

Wear reliability and failure mechanism of inkjet-printed conductors on paperboard substrate

In this research, we conducted a wear test on inkjet-printed silver conductors using different loads and counter materials (two paperboards, brushed steel sheet, and sandpaper) with similar surface roughness values. The conductor’s reliability was characterized by resistance measurement, the failures and tested counter materials were analyzed using an optical microscope, profilometer, scanning electron microscope, and energy dispersive spectrometer. It was found that the counter material has a dominant impact on a conductor’s reliability and failure mechanism compared with load. The conductors were exceptionally reliable but subject to adhesive wear when tested by paperboards. They were also highly reliable when tested by brushed steel sheet although the silver became severely detached, and the conductivity was lost suddenly when a major scratch was caused by two-body and three-body abrasive wear mechanisms. Sandpaper rubbing caused the most severe silver detachment and quick loss of conductivity, as a large amount of small-size (5-15 µm) silicon carbide particles with sharp edges and corners caused a dense cutting effect via two-body abrasive wear (by cutting) mechanism. Additionally, the failures in almost all samples occurred in the areas in contact with the counter edges, suggesting that failure was accelerated by the edge effect. This study proves that inkjet-printed electronics on the investigated paperboard is exceptionally durable when rubbed by paperboards and steel sheets, and thus provides a reliable solution to intelligent packaging. To promote intelligent packaging, more paperboards, as well as approaches for reducing the edge effect can be investigated.publishedVersionPeer reviewe

Leakproof Heat Sealing of Paperboard Trays - Effect of Sealing Pressure and Crease Geometry

The leakproof sealing of paperboard trays depends on factors such as the quality of the sealed tray and the parameters of the sealing process. Leakproof sealing is critical when food products are packed, as poor sealing can result in leakage and cause a reduction in the microbiological quality and sensory shelf life of packed food products. In this paper, factors affecting the leakproof sealing of paperboard trays, such as sealing pressure and the geometry of creases in the trays, were investigated. Trays were sealed with varied sealing pressure and temperature, and the sealed trays were inspected using a coloring solution test, oxygen content measurements, and microscopic analysis. The results show that the sealing pressure is a critical parameter in the sealing process. The minimum sealing pressure that resulted in leakproof within the materials investigated was 1.8 N/mm2. The depth of crease that can be sealed in a leakproof manner was found to be up to 150 µm

Effect of Process Parameter Variation on the Dimensions of Press-Formed Paperboard Trays

The dimensional accuracy of packages has a great effect on operation of the production and supply chain. In this research, the dimensional accuracy of trays made of polymer-coated paperboard and the effect of all essential press forming process parameters on outer dimensions of the trays were studied to obtain data for the press forming and lid sealing process optimization and for the forming tool design. Paperboard trays were analysed and measured with a quality monitoring system that includes a smart camera and a backlit table. Trays with varying dimensions were sealed to investigate the effect of the package size and the product weight to the residual oxygen in the package’s headspace gas. Results showed that all heat related parameters, i.e., mould temperatures, dwell time, and pressing speed can be used to adjust the outer dimensions of the paperboard tray. Lid sealing process was found to reduce size of the trays and even out size differences substantially. All produced trays were measured to be bigger both in length and in width compared to the design values of the mould set. Therefore the mould set has to be designed undersized to obtain trays with certain outer dimensions