Sample abstracts (abbreviated):
Creasing coated carton board or folding coated magazine paper, result in large strains in the surface layer of the paper product and might result in surface cracks, which decrease the quality of the products. A better understanding of the mechanical properties of coated layers increases the knowledge needed to reduce crack formation in coated fiber based materials.
A micromechanical model was used to estimate the in-plane and out-of-plane mechanical properties of clay based- and GCC based- coating layers. The clay-based coatings showed an anisotropic material behavior with considerably lower stiffness and strength during out-of-plane compared to in-plane. GCC based coatings, on the other hand, showed an isotropic material behavior with similar in-plane and out-of-plane properties. The calculated material behavior of coating layers, together with the data from the literature was used to explain the difference in cracking behavior between Clay- and GCC- based coatings during creasing of thick coated board and folding of thin coated copy paper.
Cellulose based products such as papers and boards are exceptionally versatile and attractive materials notably from the point of view of sustainability. Compared to their plastic film competitors, their application potential is however hampered by their lack of barrier resistance to water, grease and gases. Composite multilayer structures have then to be elaborated with an obvious, strong negative impact on sustainability. Chromatografting (or chromatogeny) has been shown to be able to provide a partial answer to this problem. It involves the molecular grafting of long chain natural fatty acids upon the external OH groups of cellulosic fibres. The resulting hydrophobic effect provides excellent barrier properties to liquid water while being fully compatible with paper sustainability. In this publication, we show that the application potential of chromatografting may be extended to grease and gases barrier thanks to the prior coating of specific PVOH layers. We further show that the barrier properties of chromatografted PVOH layers may be enhanced through the addition of PVOH coated particles coined “smart reacto-chromatogenic particles”.
Foam coating technique has shown to be a promising method for applying a thin pigment layer of nanoparticles on a paper web. The interest in applying a low coat weight coating layer is to create new functional surfaces using small amounts of new, typically expensive nanoparticles. The characterisation of thin pigment layer properties is more demanding than analysing traditional pigment coatings layers because of the low layer thickness of 1 µm or less with a coat weight of between 0.3 and 2 g/m2. This characterisation requires surface sensitive measuring techniques and a combination of different microscopic and spectroscopic surface analyses. In this study, the pigment layer structure and chemical properties of nanosilica-coated paper were analysed. The results were utilised in the development of the foam coating process.
“The Effects of Nano-Fibrillated Cellulose as a Coating Agent for Screen Printing” - Hitomi Hamada, Kenji Tahara and Asuka Uchida - Research Institute, National Printing Bureau of Japan
This paper reports on the printability characteristics achieved with a method involving screen printing on paper coated with nano-fibrillated cellulose (NFC). In the study, ink pigment deposition and vehicle penetration were elucidated using a scanning electron microscope (SEM) with a focused ion beam system (FIB) and a confocal laser scanning microscope (CLSM), and two types of inks (the penetration-type and the non-penetration-type) were compared.
The SEM images obtained showed that most pigment in penetration-type ink was deposited on the surface and that vehicles penetrated the sheets. Plate-shaped pearl luster pigments were oriented in the ink layer, which led to better color shifting properties and other optical variation effects. Although penetration-type ink offers superior properties of optical variation, it is also characterized by problems with strike-through, durability and other considerations due to excessive vehicle penetration with especially porous and highly absorbent sheets. However, these problems can be solved by applying NFC to control vehicle penetration rates. CLSM images clearly showed that NFC coating prevents vehicles from penetrating and spreading excessively into the substrate. The results in this report suggest that NFC can capture not only small particles of ink pigment but also even liquids such as ink vehicles. Accordingly, NFC is seen as a promising environmentally friendly surface treatment for use with low-viscosity inks for screen printing because it can capture vehicles near the surface and prevent them from penetrating the sheet excessively.
