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In this work we present a systematic methodology for realizing desired sheet impedances of printable metasurfaces. This methodology allows independent control of the sheet reactance (capacitance and series inductance) and its resistance, even if the conductor properties as well as the dielectric substrate thickness and permittivity are fixed due to manufacturing process restrictions. The derived analytical formulas allow us to easily find the physical dimensions of conductive patterns which implement the required surface impedance. Numerical verification of the method shows excellent agreement with the analytical predictions, allowing the design of an arbitrary impedance without any optimization process. The method can be applied for designing lossy and low-loss metasurfaces which can be used for absorption and wavefront manipulation of electromagnetic waves. As a representative example, the design of thin perfect absorbers has been approached using the developed method. The results demonstrate that the methodology adapts various material sheet resistivity, opening new possibilities for the design of printable metasurfaces where the sheet resistivity of conductor strongly depends on the specific printing method. Finally, an experimental validation of absorbers designed for millimeter waves and printed using reverse-offset techniques is presented. To the best of authors’ knowledge, this is the first time when reverse-offset printing has been used to provide well-working devices for short millimeter waves.

This paper presents the results from evaluation of suitable materials and ink properties for printing millimeter wave components. Dielectric parameters (relative permittivity and loss tangent) of various potential substrate materials are extracted from S-parameter measurements and simulations. Test samples have been printed over Polyethylene Terephthalate (PET) and Polyethylene Naphthalate (PEN) substrates and the measurement of the ink properties have been carried out.

Several standard or material specific methods for grease barrier testing are being used. Results are expressed either as the time in which a test liquid has penetrated through a packaging material or as the amount of liquid which has penetrated through the material during a certain time period. However, such tests are not accurate, and there was a need for a new and more quantitative test method. A new test method developed by integrating two previous standard methods will be presented. Dyed oil or grease is placed on the food contact side of the sample under a specific weight. The reverse side is then scanned after pre-selected time intervals. This method combines visual data with a numerical result obtained by image analyses. Likewise, there are several methods for testing mineral oil hydrocarbon (MOH) barrier of packaging materials. Such mineral oil residues in food have raised concern as potential genotoxic carcinogens during the recent years, especially in Europe. These contaminants may originate from printing ink residues from recycled paperboard, certain additives, processing aids, and lubricants. A test method for MOH barrier will be presented in which the mineral oils are introduced to the test system in the gas phase. The amount of MOH diffused through a packaging material and absorbed into a food simulant is determined by gas chromatography. Focus was on compounds of relevant molecular weight, and using equipment and materials which are commercially available.

Possibility to control the adhesion properties is important in various industrial applications. Since the topmost surface layers have the greatest role in adhesion thus making surface-controlled atomic layer deposition (ALD) reactions appealing method for tailoring surface adhesion properties. In this presentation we show that ALD and molecular-layer-deposition (MLD) can be used to adjust wetting characteristics of polymers and metals. Recently we have been modifying surface properties for various applica-tions including ink-jet printed films, adhesion promoting layers for extrusion coatings and anti-ice coatings. In addition to conventional inorganic metal oxides, such as Al2O3, we have tested also inorganic-organic hybrid MLD materials. Various tools, such as XPS, FT-IR and TOF-ERDA, were used to characterize these films, and wetting behavior was determined using contact angles measurements with the sessile drop method

Several standards for grease barrier testing of packaging materials are being used. These include TAPPI, ASTM and ISO standards. Results are expressed either as the time in which grease has penetrated through the structure or as the amount of grease which has penetrated through the test structure in certain time. The amount of penetrated grease is evaluated either visually or by measuring the diameter and calculating the area of the grease stain. Such tests are not accurate but provide mere approximations. There is thus a need for a more accurate and exact method. A method recently developed at VTT integrates two standard methods and combines visual data with a numerical result obtained by image analysis. Dyed oil or grease is applied automatically onto the test specimen having the test side upwards. A weight is placed onto each specimen. The whole test system is then transferred to the scanner. Scanning can be performed after pre-selected time intervals, and an image analysis script is used to analyse the area fraction of penetrated grease/oil. Both visual and numerical results are obtained after each time interval. Test temperature, test grease and test duration can be selected according to the end-use of the packaging material. Benefits of this test method include automated and operator independent application of test oil, pre-selected scanning intervals, more realistic test durations and temperatures approaching actual packaging applications, and availability of both visual and numerical data. In addition, there is no need to touch the test samples during the testing.

Viscosity measurement is a reasonable and useful routine characterization and quality control measurement for fibril cellulose production. The method is based on vane geometry, which is widely accepted as a convenient way of testing viscous, polydisperse materials. The method is particularly advantageous for testing samples that are significantly heterogeneous or that could slip when tested with conventional, smooth spindle geometries such as plate or coaxial cylinder. Viscosity describes a suspension's internal resistance to flow. The higher the fibrillation degree of the fibril cellulose, the more internal friction is formed. In fibrillated celluloses, the size, the aspect ratio and the amount of fibrils are known to affect the viscosity. The routine viscosity procedure includes specified rotational speeds of a spindle from 0.5rpm to 100rpm. The apparent yield stress can also be measured during the same measurement. The measuring is performed for a sample volume of 250ml at a controlled temperature of 20°C ± 1°C. The repeatability of the Brookfield method is fairly good and the method has been found to be suitable for charactetization of various types of fibril cellulose samples. Because of different nature of unmodified and chemically modified fibril cellulose samples, the method has been fine-tuned for these two sample categories. The viscosity measurement described here has been unified within several laboratories and the same measurement procedure is now in routine use for characterization and quality control of fibril cellulose. In the future, commensurable characterization methods are needed in order to compare results between different laboratories worldwide. Based on these experiences we endeavour to get this method for standardization.

In offset printing unit the interaction between ink, blanket and paper surface defines adhesion of the web on the blanket surface. After ink transfer paper web follows the blanket surface at the nip exit until it is released due web tension. The adhesion of the web depends on the surface properties of paper, printing material combinations, the layout and press settings. In general, shorter follow-up of the web on blanket surface predicts easier release thus longer follow-up can lead to higher release angle. The purpose of this study was to clarify the factors (material and process parameters) controlling paper web's release from the blanket. The release of six various paper grades was followed. Other studied variables were the release property of blankets and the influence of ink tack on web release. Furthermore, during printing the effect of fountain solution feed and nip pressure on web release was examined. The release force between printing materials was first studied in laboratory and the verification was carried out in full-scale heatset printings. On printing press the release of the web was measured using release angle measurement arrangements. Furthermore, an acoustic signal was gathered from ink film splitting to describe the web release. According to results, paper grade determines the level of web release angle. The results indicate that the smooth paper surface induces strong adhesion on the blanket which leads to higher release angle. Furthermore, the surface structure of the paper and the speed of ink absorption affect web release. In addition, it was noted that small amount of accumulated material on blanket surface easies the web release. According to studies, the release angle of the web can be lowered by selecting easy release blanket, lower ink tack, higher fountain solution feed and lower nip pressure.

We endeavour to clarify the effect of electric field on speed and height of ink lifting from differently engraved gravure cells. The main emphasis is directed to the shape of the cell, whether it has sloped or vertical walls. Furthermore, the influence of ink and substrate properties as well as patterns and defects in the substrate on electric field assisted ink lifting was studied. An extensive set of numerical simulations was carried out and the results were verified by experimental studies. A model was developed to illustrate ink movements in a cell approaching the nip. Laboratory arrangements were set up to image electric field assisted ink lifting from the side using scaled-up V- and U-shaped grooves. Transparent impression roller arrangements were used to monitor ink lifting and formation of ink-substrate contact using electromechanically engraved and laser etched gravure cylinders. According to our simulations and experiments, ink first moves towards the front edge of the cell where the effect of the electric field is the strongest. As the influence of the electric field at the trailing edge of the cell increases the ink is also lifted from that side and an ink meniscus is formed inside the cell. The transparent impression roller images proved the forming of an ink meniscus inside the cell thus predicting printed doughnut dots. Based on the simulations, a void on the substrate has an influence on ink lifting depending on position of the void relative to the front edge of the cell. This could be one explanation to missing dots. The model provides excellent possibilities to study the influence of the process parameters on ink lifting and, in general, liquid movements in electric field. The laboratory arrangements can be utilized in different gravure applications especially when compatibility of materials or the influence of electric field is studied.

A novel fractionation method was developed to characterize nanocellulose in terms of particle size. The fractionation device ues screens or membranes with known size. The scale is in the range of micro to nano, so that NFCs can be size- or shape-fractionated accordingly. The procedure is somewhat analogous to the Bauer-McNett fiber classifier. The reproducibility of the obtained size profile was very good. The device can also produce size specific nano-celluloses, which could be applied for scientific research purposes, e.g. nano risk assessment. Fractionation with membrane filters was able to screen out almost all particles. However, the membrane permeate contained significant amounts of dissolved substances.

The aim of this work was to clarify the mechanisms of accumulation build-up on heatset web offset press. The influence of press settings on accumulation tendency was also studied. On-line microscopic imaging system was used to monitor the state of the printing plate and blanket during printing. Images were taken from non-image, halftone and image areas. Press performance was followed during three different full-scale printings. According to results accumulation on blanket starts from plate conditions. Small ink particles detected on the non-image areas of the plate are transferred on the blanket surface causing accumulation build-up. Filamentation of ink emulsion at the nip exit gathers ink at the trailing edges of the image areas or even slightly over the edges. This leads to enrichment of the inked material at the trailing edges of the image areas and around the halftone dots on blanket surface. Nip pressure further enforces ink towards the edges of the image areas. The accumulated layer could be up to ten micrometres thick containing elements both from ink and paper. This can be especially harmful around the halftone dots as it can reduce the size of the printed dot during long print runs. Based on these findings mechanisms of heatset accumulation on ink transfer unit was clarified. On-line microscopic images from printing plate and blanket show that press settings have clear effect on accumulation tendency on blanket. Furthermore, the on-line imaging provides means to solve problematic accumulation related runnability issues of on-going offset process.

Nowadays the manufacturing of cellulose micro- and nanofibrils has been significantly developed and products with tailored properties can now be introduced. Different fibrillation methods and chemical treatments generate cellulose fibrils with varied dimensions, branching degree and chemical properties. It would be beneficial to classify the different kind of cellulose fibrils according to their properties with consensual agreement. We present here a classification based on the morphological and chemical properties of cellulose fibrils. We discuss the applicability of classification and different characterization methods for certain grades (from nanowhiskers and nanofibres to nano fibrillated materials with branched or ribbon-like structures) and for different applications. Characterization of cellulose fibrils is challenging not only because of the wide size distribution and high aspect ratio but also due to the wide variety of morphological properties and the complex structure of single fibrils. This paper introduces a set of simple methods which gives the basic characteristics of nanocelluloses. Five commercially available cellulose nano/microfibrils and three self-made samples produced by and birch pulp ground to various levels using supermasscolloider equipment were analysed in detail. Different rheo- and viscometers were tested and a viscosity measurement sensitive towards high aspect ratio fibrils is introduced. The transmittance measurement gives an estimation of the amount of large particles and the optical microscopy effectively detects the amount of unfibrillated material. SEM measurements can be used to analyze the fine structure nanofibers. The aspect ratio, degree of fibrillation, fibril size and the amount of unfibrillated material can be evaluated with a combination of these indirect measurements, which provide a basic set for quality assurance.

The cytotoxic and genotoxic properties of two nanomaterials with different characteristics were studied in well-characterized in vitro model systems commonly applied in toxicity testing protocols The overall analysis indicated absence of cytotoxic and genotoxic properties of the nanomaterials, whereas consistently, effects were seen with the positive control agents

In this study on-line measurement devices were utilized to clarify how the changes in fountain solution properties affect formation of non-image area piling during printing. On-line measurements of pH, conductivity, redox potential, temperature, and calcium content were installed to measure fountain solution quality. Chemical impurities in the fountain solution cycle are mainly due to dissolution of ink. The dissolution increases concentration of dissolved cations such as aluminum and calcium, which increases hardness and conductivity. This has implications both to the press runnability and product quality. Non-image area piling on blanket originates from the plate. Ink spreads to the non-image area of the plate and ends up on the non-image area of the blanket. A part of it continues further to the paper. On-line measurements of water, ink pigment, and ink binder were used to follow the interactions of ink and fountain solution on plate and blanket. The findings were verified by visually observing the press with triggered micro-imaging. When fountain solution feed level is correctly adjusted, the main reason for the non-image area piling is poor ink stability on the plate. High amounts of cations in fountain solution may separate ink pigment particles from the ink binder. The phenomenon is seen as ink pigment particles on the non-image area of the plate, and it is significant especially when the same fountain solution has been utilized for a long period of time.

Electrostatic assistance (ESA) lifts gravure ink from the engraved cells before actual nip contact. This improves ink transfer. In this work the influence of ESA on ink lifting speed and height was examined with both electromechanically engraved and laser etched cells using numerical simulation and experimental studies. Ink lifting occurs quite similarly from both cell types: without ESA ink stays in the cells until the physical ink-substrate contact in the nip is formed. With ESA ring shaped ink lifting near the cell edges is noted before the nip contact. This leads to a doughnut shape contact area in the nip. Higher ESA levels lead to faster ink lifting and stronger ring shaped ink lifting in the cells. Ink lifting occurs faster from U cells than from V cells when the cells are having the same diameter and depth. This however means different ink volume in the cells. The cell geometry affects the shape of the printed dots: even and round dots are printed with cells having flat bottom. This nearly constant depth of the cell provides equally distributed ink in the cell offering also more even ink transfer.