Studies in offset ink setting

The offset printing process is complex and involves the meeting of two essentially complex materials, printing ink and paper, upon which the final product is formed. It can therefore be expected that a multitude of chemical and physical interactions and mechanisms take place at the ink-paper interface. Interactions between ink and paper are of interest to both the papermakers and ink producers, as they wish to achieve better quality in the final product. The objective of this work is to clarify the combined influence of paper coating structure, printing ink and fountain solution on ink setting and the problems related to ink setting. A further aim is to identify the mechanisms that influence ink setting problems, and to be able to counteract them by changing properties of the coating layer or by changing the properties of the ink. The work carried out for this thesis included use of many techniques ranging from standard paper and printability tests to advanced optical techniques for detection of ink filaments during ink levelling. Modern imaging methods were applied for assessment of ink filament remain sizes and distribution of ink components inside pigment coating layers. Gravimetric filtration method and assessment of print rub using Ink-Surface-Interaction-Tester (ISIT) were utilized to study the influence of ink properties on ink setting. The chemical interactions were observed with the help of modified thin layer chromatography and contact angle measurements using both conventional and high speed imaging. The results of the papers in this thesis link the press operational parameters to filament sizes and show the influence of these parameters to filament size distribution. The relative importance between the press operation parameters was shown to vary. The size distribution of filaments is important in predicting the ink setting behaviour, which was highlighted by the dynamic gloss and ink setting studies. Prediction of ink setting behaviour was also further improved by use of separate permeability factors for different ink types in connection to filtration equations. The roles of ink components were studied in connection to ink absorption and mechanism of print rub. Total solids content and ratio of linseed oil to mineral oil were found to determine the degree of print rub on coated papers. Wax addition improved print rub resistance, but would not decrease print rub as much as lowering the total solids content in the ink. Linseed oil was shown to absorb into pigment coating pores by mechanism of adsorption to pore walls, which highlights the need for sufficient pore surface area for improved chromatographic separation of ink components. These results should help press operators, suppliers of printing presses, papermakers and suppliers to papermakers, to better understand the material and operating conditions of the press as it relates to various print quality issues. Even though paper is in competition with electronic media, high quality printed products are still in demand. The results should provide useful information for this segment of the industry.

Application of cerium oxide thin films grown by atomic layer deposition for soot removal

The objective of the thesis is to study cerium oxide thin films grown by the atomic layer deposition (ALD) for soot removal. Cerium oxide is one of the most important heterogeneous catalysts and can be used in particulate filters and sensors in a diesel exhaust pipe. Its redox/oxidation properties are a key factor in soot oxidation. Thus, the cerium oxide coating can help to keep particulate filters and sensors clean permanently. The literature part of the thesis focuses on the soot removal, introducing the origin and structure of soot, reviewing emissions standards for diesel particulate matter, and presenting methods and catalysts for soot removal. In the experimental part the optimal ALD conditions for cerium oxide were found, the structural properties of cerium oxide thin films were analyzed, and the catalytic activity of the cerium oxide for soot oxidation was investigated. Studying ALD growth conditions of cerium oxide films and determining their critical thickness range are important to maximize the catalytic performance operating at comparatively low temperature. It was found that the cerium oxide film deposited at 300 °C with 2000 ALD cycles had the highest catalytic activity. Although the activity was still moderate and did not decrease the soot oxidation temperature enough for a real-life application. The cerium oxide thin film deposited at 300 °C has a different crystal structure, surface morphology and elemental composition with a higher Ce3+ concentration compared to the films deposited at lower temperatures. The different properties of the cerium oxide thin film deposited at 300 °C increase the catalytic activity most likely due to higher surface area and addition of the oxygen vacancies.

Suitability of foam coating on application of thin liquid films

This work aimed to find out the suitability of foam as medium in application of thin liquid films. This consists of research over phenomena related to foam physics and behaviour. Solutions and mixtures to be foamed, foaming agents, foam generation and application methods were evaluated. Over the evaluated solutions and mixtures coating paste and CMC did not foam well. Latex and PVA solutions were foamable and the best solution for foam use was starch. PVA and casein can be used as foaming agents, but the best results were achieved with sodium dodecyl sulphate (SDS). SDS works well with starch solutions producing fine and stable foam. Foaming was done with simple mixers where pressurized air was fed to the solution. The foaming works fine when enough shear force is used together with sufficient foaming agent concentration. Foam application with curtain, rod and cylinder methods with a gap between the application device and paper were not usable because of high coating amount. Coating amounts were smallest with the blade method which achieved 0.9 g/m2 starch layer. Although some strength decrease was expected because of the foaming agent, it dit not have significant effect. The targeted coating amount of 0.5 g/m2 was not achieved due to the limitations with the methods. More precise foam application methods are needed. Continuous foam generation and feed to the paper surface with controllable device such as application teeth could improve the results.

Kelvin Probe Force Microscopy (KPFM) characterization of lanthanum lutetium oxide high-k dielectric thin films

Lanthanum lutetium oxide (LaLuO3) thin films were investigated considering their perspective application for industrial microelectronics. Scanning probe microscopy (SPM) techniques permitted to visualize the surface topography and study the electric properties. This work compared both the material properties (charge behavior for samples of 6 nm and 25 nm width) and the applied SPM modes. Particularly, Kelvin probe force microscopy (KPFM) was applied to characterize local potential difference with high lateral resolution. Measurements showed the difference in morphology, chargeability and charge dissipation time for both samples. The polarity effect was detected for this material for the first time. Lateral spreading of the charged spots indicate the diffusive mechanism to be predominant in charge dissipation. This allowed to estimate the diffusion coefficient and mobility. Using simple electrostatic model it was found that charge is partly leaking into the interface oxide layer.

Roll-to-roll atomic layer deposition process for flexible electronics applications

Atomic Layer Deposition (ALD) is the technology of choice where very thin and highquality films are required. Its advantage is its ability to deposit dense and pinhole-free coatings in a controllable manner. It has already shown promising results in a range of applications, e.g. diffusion barrier coatings for OLED displays, surface passivation layers for solar panels. Spatial Atomic Layer Deposition (SALD) is a concept that allows a dramatic increase in ALD throughput. During the SALD process, the substrate moves between spatially separated zones filled with the respective precursor gases and reagents in such a manner that the exposure sequence replicates the conventional ALD cycle. The present work describes the development of a high-throughput ALD process. Preliminary process studies were made using an SALD reactor designed especially for this purpose. The basic properties of the ALD process were demonstrated using the wellstudied Al2O3 trimethyl aluminium (TMA)+H2O process. It was shown that the SALD reactor is able to deposit uniform films in true ALD mode. The ALD nature of the process was proven by demonstrating self-limiting behaviour and linear film growth. The process behaviour and properties of synthesized films were in good agreement with previous ALD studies. Issues related to anomalous deposition at low temperatures were addressed as well. The quality of the coatings was demonstrated by applying 20 nm of the Al2O3 on to polymer substrate and measuring its moisture barrier properties. The results of tests confirmed the superior properties of the coatings and their suitability for flexible electronics encapsulation. Successful results led to the development of a pilot scale roll-to-roll coating system. It was demonstrated that the system is able to deposit superior quality films with a water transmission rate of 5x10-6 g/m2day at a web speed of 0.25 m/min. That is equivalent to a production rate of 180 m2/day and can be potentially increased by using wider webs. State-of-art film quality, high production rates and repeatable results make SALD the technology of choice for manufacturing ultra-high barrier coatings for flexible electronics.

Titanium dioxide based nanomaterials for photocatalytic water treatment

Water treatment using photocatalysis has gained extensive attention in recent years. Photocatalysis is promising technology from green chemistry point of view. The most widely studied and used photocatalyst for decomposition of pollutants in water under ultraviolet irradiation is TiO2 because it is not toxic, relatively cheap and highly active in various reactions. Within this thesis unmodified and modified TiO2 materials (powders and thin films) were prepared. Physico-chemical properties of photocatalytic materials were characterized with UV-visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES), ellipsometry, time-of-flight secondary ion mass spectrometry (ToF-SIMS), Raman spectroscopy, goniometry, diffuse reflectance measurements, thermogravimetric analysis (TGA) and nitrogen adsorption/desorption. Photocatalytic activity of prepared samples in aqueous environment was tested using model compounds such as phenol, formic acid and metazachlor. Also purification of real pulp and paper wastewater effluent was studied. Concentration of chosen pollutants was measured with high pressure liquid chromatography (HPLC). Mineralization and oxidation of organic contaminants were monitored with total organic carbon (TOC) and chemical oxygen demand (COD) analysis. Titanium dioxide powders prepared via sol-gel method and doped with dysprosium and praseodymium were photocatalytically active for decomposition of metazachlor. The highest degradation rate of metazachlor was observed when Pr-TiO2 treated at 450ºC (8h) was used. The photocatalytic LED-based treatment of wastewater effluent from plywood mill using commercially available TiO2 was demonstrated to be promising post-treatment method (72% of COD and 60% of TOC was decreased after 60 min of irradiation). The TiO2 coatings prepared by atomic layer deposition technique on aluminium foam were photocatalytically active for degradation of formic and phenol, however suppression of activity was observed. Photocatalytic activity of TiO2/SiO2 films doped with gold bipyramid-like nanoparticles was about two times higher than reference, which was not the case when gold nanospheres were used.