In this work, systematic studies were carried out on SLS (selective laser sintering) printed samples, with two different geometries, standard test samples dumb-bells (dog bones) and tubes (Ø 30 mm and 150 mm long), consisting of two different materials, viz. PA12 (polyamide) with and without the addition of carbon fibres (CFs). These samples were tested according to their respective ISO standards. The standard test samples exhibited relatively small differences with regards to printing directions when PA12 was used alone. Their tensile strengths (σm) were approx. 75%–80% of the injection-moulded sample. The addition of carbon fibres significantly enhanced the tensile strengths, namely 50% greater for the vertically printed test sample and more than 100% greater for the horizontally printed samples, compared to the respective objects consisting of PA12 alone. The strong difference in printing directions can be attributed to the orientation of the carbon fibres. Mechanical tests on the SLS printed tubes confirmed the trends that were found in the standard test samples. Porosity and pore structure inside the SLS printed tubes were studied by combining optical microscopy and X-ray microtomography with image analysis. It was found that porosity was a general phenomenon inside the SLS printed samples. Nevertheless, there were significant differences in porosity, which probably depended on the properties of the materials used, both with and without carbon fibres, thus causing significant differences in light absorption and heat conductivity. The printed samples made of PA12 alone possessed quite a high level of porosity (4.7%), of which the size of the biggest pore was hundreds of microns. The twenty biggest pores with an average size of 75*104 ÎŒ m3 accounted for 43% of the total porosity. However, the porosity of the printed samples made from PA12 + CF was only 0.68%, with the biggest pore being only tens of microns. The corresponding average pore size of the 20 biggest pores was 72*103 ÎŒ m3, which was one order of magnitude smaller than the printed samples made from PA12 alone. Pores inside the SLS printed samples were probably responsible for a spread in the mechanical properties measured, e.g. tensile strengths, tensile (Young’s) modulus, strain at break, etc. The ratios of their standard deviations to their corresponding mean values in the standard test samples could probably be used as an indicator of porosity, i.e. the bigger the ratio, the higher the porosity.

The outset of realistic rendering is a desire to reproduce the appearance of the real world. Rendering techniques therefore operate at a scale corresponding to the size of objects that we observe with our naked eyes. At the same time, rendering techniques must be able to deal with objects of nearly arbitrary shapes and materials. These requirements lead to techniques that oftentimes leave the task of setting the optical properties of the materials to the user. Matching the appearance of real objects by manual adjustment of optical properties is however nearly impossible. We can render objects with a plausible appearance in this way but cannot compare the appearance of a manufactured item to that of its digital twin. This is especially true in the case of translucent objects, where we need more than a goniometric measurement of the optical properties. In this survey, we provide an overview of forward and inverse models for acquiring the optical properties of translucent materials. We map out the efforts in graphics research in this area and describe techniques available in related fields. Our objective is to provide a better understanding of the tools currently available for appearance specification when it comes to digital representations of real translucent objects.

First, the study chooses ten kinds of offset paper. By using a dynamic penetration analyzer (HVL-PDA) and water as test fluid, the dynamic absorption characteristics of the ten kinds of offset paper are measured. At the same time, proofs of offset printing patterns of these ten kinds of offset paper are made by using a printability tester. Then the depths of ink penetration in ten kinds of offset paper are measured by the Three-dimensional video microscopy system and the study analyzes the effect of paper dynamic absorption property on penetration depth of ink. The results of the analyses show that the penetration depth of ink is closely related to dynamic liquid absorption, thus the permeability of ink in offset paper can be predicted from the dynamic liquid absorption of offset paper.

Additive manufacturing (3D printing) enables the designing and producing of complex geometries in a layer-by-layer approach. The layered structure leads to anisotropic behaviour in the material. To accommodate anisotropic behaviour, geometrical optimization is needed so that the 3D printed object meets the pre-set strength and quality requirements. In this article a material description for polymer powder bed fused also or selective laser sintered (SLS) PA12 (Nylon-12), which is a common 3D printing plastic, was investigated, using the Finite Element Method (FEM). The Material Model parameters were obtained by matching them to the test results of multipurpose test specimens (dumb-bells or dog bones) and the model was then used to simulate/predict the mechanical performance of the SLS printed lower-leg prosthesis components, pylon and support. For verification purposes, two FEM designs for a support were SLS printed together with additional test specimens in order to validate the used Material Model. The SLS printed prosthesis pieces were tested according to ISO 10328 Standard. The FEM simulations, together with the Material Model, was found to give good estimations for the location of a failure and its load. It was also noted that there were significant variations among individual SLS printed test specimens, which impacted on the material parameters and the FEM simulations. Hence, to enable reliable FEM simulations for the designing of 3D printed products, better control of the SLS process with regards to porosity, pore morphology and pore distribution is needed.

Highly conductive ink with low sintering temperature is important for printed electronics on paper substrate. Silver nanoparticles (Ag NPs) of different average radii ranging from 48 to 176 nm were synthesized by adjusting the Ag+ concentration in the reaction process. The electric resistivity of the Ag NP-based ink film in relation to Ag NP size, sintering temperature, amount of PVP capping agent on Ag NP surface, and morphology evolution of the film during heating process was investigated. It was found that the resistivity of the films reduced very rapidly with increasing particle size due above all to reduced amount of protective agent capping on the Ag NPs. A semi-empirical relationship between the resistivity and the particle size was proposed. With the help of this mathematical expression, one gains both systematic and detailed insight to the resistivity evaluation with regard to the Ag particle size. The optimal electric resistivity of 4.6 μΩ cm was achieved at 140 °C for 10 min which was very close to the resistivity value of bulk Ag (1.58 μΩ cm). Mechanical flexibility of the printed electronics with the Ag NP-based ink on paper substrates was investigated. The prints on the art coated paper exhibited better flexibility compared to that on the photopaper. This might be attributed to the surface coating composition, surface morphology of the paper, and their corresponding ink absorption property. © 2019, The Author(s).

Printed electronics on flexible substrates has attracted tremendous research interest research thanks its low cost, large area production capability and environmentally friendly advantages. Optimal characteristics of silver nanoparticles (Ag NPs) based inks are crucial for ink rheology, printing, post-print treatment, and performance of the printed electronics devices. In this review, the methods and mechanisms for obtaining Ag NPs based inks that are highly conductive under moderate sintering conditions are summarized. These characteristics are particularly important when printed on temperature sensitive substrates that cannot withstand sintering of high temperature. Strategies to tailor the protective agents capping on the surface of Ag NPs, in order to optimize the sizes and shapes of Ag NPs as well as to modify the substrate surface, are presented. Different (emerging) sintering technologies are also discussed, including photonic sintering, electrical sintering, plasma sintering, microwave sintering, etc. Finally, applications of the Ag NPs based ink in transparent conductive film (TCF), thin film transistor (TFT), biosensor, radio frequency identification (RFID) antenna, stretchable electronics and their perspectives on flexible and printed electronics are presented.

A high-performance ITO-free transparent conductive film (TCF) has been made by combining high resolution Ag grids with a carbon nanotube (CNT) coating. Ag grids printed with flexography have a 20 ÎŒm line width at a grid interval of 400 ÎŒm. The Ag grid/CNT hybrid film exhibits excellent overall performance, with a typical sheet resistance of 14.8 Ω/□ and 82.6% light transmittance at room temperature. This means a 23.98% reduction in sheet resistance and only 2.52% loss in transmittance compared to a pure Ag grid film. Analysis indicates that filling areas between the Ag grids and interconnecting the silver nanoparticles with the CNT coating are the primary reasons for the significantly improved conductivity of the hybrid film that also exhibits excellent flexibility and mechanical strength compared to an ITO film. The hybrid film may fully satisfy the requirements of different applications, e.g. use as the anode of polymer solar cells (PSCs). The J-V curve shows that the power conversion efficiency (PCE) of the PSCs using the Ag grid/CNT hybrid anode is 0.61%, which is 24.5% higher than that of the pure Ag grids with a PCE of 0.49%. Further investigations to improve the performance of the solar cells based on the printed hybrid TCFs are ongoing.

The temperature dependency and reversibility of the sheet resistance of silver nanoparticles covered by 3-mercaptopropionic acid (Ag-MPA) molecules, used in the printed temperature sensor, has been investigated. The microstructural evaluation, the FTIR spectra and thermal property analyses of the Ag-MPA films suggest co-existence of both weakly adsorbed as well as firmly adsorbed MPA molecules on the surface of Ag nanoparticles. The weakly adsorbed MPA molecules was to a great extent be desorbed and removed from the surfaces of silver nanoparticles when heated up to 180 °C for the first time. While the firmly adsorbed MPA molecules remain on the surfaces of silver nanoparticles even at higher temperature. Yet the firmly adsorbed MPA molecules are likely having gone through a transformation circle from/to the gauche and trans conformations in correspondence to a heating and cooling cycle, which results in temperature dependent and reversible sheet resistance. The MPA molecules in the gauche conformation are more densely packed on the surface of silver nanoparticles and can hinder the electron’s movability within the Ag-MPA film. While in the trans conformation with lower ‘surface space’ coverage by the MPA molecules, electrons move more freely within the film. Based on the temperature dependent nature, the fully printed temperature sensor using the Ag-MPA nanoparticles as the functional layer was made, of which the highest sensitivity is 5.12% °C−1 at 200 °C.

Accurate and traceable measurements of transmittance haze are required for quality control in various different industries, such as optoelectronics, automobiles, and agriculture. Transmittance haze is defined as the fraction of light transmitted through a material that deviates from the incident beam by more than 2.5∘. Various documentary standards specify the use of an integrating sphere with a prescribed geometry for the measurement of transmittance haze. This paper uses goniometric measurements of the bidirectional transmittance distribution function (BTDF) to calculate transmittance haze according to the definition and demonstrates that the sphere-based realisation of transmittance haze specified in the documentary standards does not agree with the definition, with the difference being up to 20% for some samples. The BTDF measurements are also used to simulate the integrating sphere haze, allowing the sensitivity of the sphere haze to errors in the integrating sphere geometry to be calculated. 

 For the first time in the Bioeconomy research program at RISE, corrugatedboard has an own research area. Research is building around the main driving forcesin the corrugated board value chain like e-commerce, improved box performance anddigital printing. The main weakness of corrugated board, its moisture sensitivity, isalso addressed.These main driving forces and weaknesses of corrugated board are mirrored in thethemes of this large research program area:Fibre sorption and deformation mechanismsFundamental knowledge on the mechanisms behind moisture sorption and deformation on fibre level is developed to increase moisture and creep resistance throughmodification of paper materials. State of the art methods for characterization ofthe fibre ultra- and nano-structure such as Fourier transform infra-red spectroscopy(FTIR), small angle X-ray scattering (SAXS), and wide angle X-ray scattering (WAXS)give new insights on mechanisms and clarify effects of moisture as well as chemicalmodifications.Papermaking for improved base sheetsConcepts that are explored are fibre-based strength additives produced with novelrefining techniques, and modified ZD-profiles in the sheet for better mechanical properties.Box mechanicsMechanical performance of structures such as corrugated board boxes can be predicted through physically based mathematical modelling by taking the behaviour ofthe constituent materials as well as the geometry into account. Appropriate materialmodels for the corrugated board are identified and finite element models for simulation of corrugated board packaging performance are developed.Tool for inkjet printability on corrugatedThere is a genuine need for improved inkjet printability on corrugated materials thanksto rapid development in e-commerce as well as digitalization along the corrugatedvalue chain. Effective measurement methods and knowledge around ink-substrateinteractions are developed to enable board producers and converters to have effective product development and predictable printability on not only liners but also oncorrugated materials.

Under specular reflection, non-isotropic halftones such as line halftones printed on an ink-receiving plastic layer superposed with a metallic layer change their colors upon in-plane rotation of the print. This color change is due to the orientation-dependent optical dot gain of the halftone. A strong dot gain occurs when the incident light is perpendicular to the halftone line structure. A color prediction model is proposed which predicts under specular reflection the color of cyan, magenta and yellow line halftones as a function of the azimuthal rotation angle, the incident angle and the line frequency. The model is calibrated by measuring 17 reflectances at the (25 : 25) measurement geometry, with the incident light parallel to the halftone lines. The model has been tested for several azimuthal rotation and incident viewing angles, each time for 125 different cyan, magenta and yellow ink surface coverages.

A custom-made prosthetic product is unique for each patient. Fossil-based thermoplastics are the dominant raw materials in both prosthetic and industrial applications; there is a general demand for reducing their use and replacing them with renewable, biobased materials. A transtibial prosthesis sets strict demands on mechanical strength, durability, reliability, etc., which depend on the biocomposite used and also the additive manufacturing (AM) process. The aim of this project was to develop systematic solutions for prosthetic products and services by combining biocomposites using forestry-based derivatives with AM techniques. Composite materials made of polypropylene (PP) reinforced with microfibrillated cellulose (MFC) were developed. The MFC contents (20, 30 and 40 wt%) were uniformly dispersed in the polymer PP matrix, and the MFC addition significantly enhanced the mechanical performance of the materials. With 30 wt% MFC, the tensile strength and Young´s modulus was about twice that of the PP when injection molding was performed. The composite material was successfully applied with an AM process, i.e., fused deposition modeling (FDM), and a transtibial prosthesis was created based on the end-user’s data. A clinical trial of the prosthesis was conducted with successful outcomes in terms of wearing experience, appearance (color), and acceptance towards the materials and the technique. Given the layer-by-layer nature of AM processes, structural and process optimizations are needed to maximize the reinforcement effects of MFC to eliminate variations in the binding area between adjacent layers and to improve the adhesion between layers. © 2020 by the authors.

Patterning technology on the paper based on wettability difference for paper-based devices has attracted significant attention for its low cost, easy degradability, and high flexibility. Here, conductive lines are rapidly prepared by patterned wettability-assisted bar-coating for low cost paper-based circuits. It is found that 7 s plasma treatment time for acquiring wettability difference is optimal, which resulted in not only effective splitting of the liquid film but also highly consistent line width with mask. Moreover, low retention force of hydrophobic surface is imperative for self-confinement of the ink into hydrophilic areas, especially for ink with high solid content. The sheet resistance of patterns can reach 5 Ω ◻ −1 after 980 nm laser sintering when using 50 wt% solid content ink with 110 cP viscosity. The geometries of line patterns, i.e., line width and spacing, can be readily tuned by varying the designed size of mask patterns. As-prepared conductive patterns show good conductivity even after 500 bending cycles at 2 mm bending radius. It is believed that this study will provide deeper understanding of wettability difference-assisted patterning process and represents a general strategy for selective wetting, especially for high viscosity ink.

We demonstrated patterning method for silver nanoparticle ink by wire-wound rod coating on commercial paper substrate. The hydrophobic and hydrophilic zones (patterns) on the paper surface were created by combining coating of hydrophobic dispersion with selective plasma treatment using a mask. Thanks to the surface energy difference in different zones, the silver nanoparticle ink self-aligned to form desired patterns, e.g. a matrix of lines of 0.5 mm wide with 0.3 mm spacing.

Many commercial materials (papers and boards) contain optical brightening agents also known as fluorescent whitening agents. Adequate adjustment of the UV content of a measurement device (e.g., spectrophotometers) is essential for accurate color measurement. As specified in the ISO standards, the UV content is adjusted against an assigned value of an international reference transfer standard, for example, CIE whiteness (D65/10°) for the CIE illuminant D65 or ISO brightness for the C illuminant. Because of the simplicity, these approaches have gained great popularity in papermaking industry. Yet, there has been little evidence indicating how accurate the total spectral radiance factor corresponding to the single assigned value is reproduced. Hence, we present a method that quantitatively evaluates the accuracy of the UV-adjustment technique, through comparing the total spectral radiance factors obtained from UV adjustment with the assigned ones. This method has been applied to three second-level international reference transfer standard illuminated by three standard illuminants, D65, C, and D50. We found that the major differences between the assigned spectra and those obtained from the UV adjustments occur in the blue band where fluorescence is strong. At a few wavelengths, the differences may be up to 4-5%. Nevertheless, their color differences corresponding to the assigned spectra and those obtained from the UV adjustments are still smaller than unity (1 ΔE*) for all of the illumination conditions. Two instruments using the representative UV adjusting techniques, for example, the conventional UV-adjusting with an adjustable (GG395) UV filter and the numerical UV-filtering, have been studied.

ZD-tester is a measurement technique for rapid compression in Z-direction. The strain rate of compression of this device is far beyond the ordinary mechanical testing methods applied in papermaking industries. Thus, it provides insights to the material responses which are relevant to industrial applications, e. g. calendaring, printing, etc where the strain rate ranges from hundreds to thousands per second. A physics model that describes the dynamic process of the probe has been developed, where a linear Maxwell model is used to account for the viscoelasticity of paperboard. The simulation has successfully reproduced both the general features and quantitative details of the experiment. The model reveals that the ratio of the elastic modulus to the viscosity modulus of the material governs the amplitude attenuation while the angular frequency of the striking-rebounding cycle depends mainly on the elastic modulus. The dropping height determines the initial striking velocity but has no direct impact on either attenuation or angular frequency. The model and simulation provided interpretations of both experimental observations and dynamic behaviours of the material. With help of simulation, the impacts of the individual parameters, e. g. the Young's modulus, E, the viscosity modulus, η, and the drop height, H, were also explored. 

Spectral reflectance, radiance factors, gloss etc of paper and textile are often regarded as intrinsic properties of the materials alone. But in practice, instrumental readings of these properties depend even on the instruments setups, for instance, illumination/detection geometries, UV contents of the illumination, measurement areas etc. Comparative studies with four commercial spectrophotometers of three illumination/detection geometries, Diffuse/0-deg, Diffuse/8-deg and 45-deg/0-deg, have been conducted. These geometries are used in paper, textile and graphic industries, respectively. The materials analysed in this study include white and colour papers and textiles. The white papers contain fluorescent whitening agents (FWAs) whose excitation energies are only in UV wavelength bands. On the contrary, the colour papers have fluorescent agents whose excitation energies are in the visible wavelength bands, according to our measurements. Textile reference standards of different whiteness values are also included in order to study the influences from surface texture. The study confirms the strong influences of instruments setups, e.g. illumination/detection geometries, UV contents of the light sources etc, on the measured results. The study also reveals the significant influences from the combination of instrumental setups with the structural and surface characteristics of the measured samples.

A theoretical framework of nip dynamics of conventional printing, including dynamic models deducted from nip geometry,printing speed, and physics laws, is proposed. Different from previous works, the present work focuses at obtaining the nippressure from a given nip geometric setting, the common way in full-scale printing. The effects of viscoelastic characteristicsof paper substrate and print form (rubber and/or polymer) on the nip pressure, which become pronounced in a full-scale printingprocess due to high speed, are accounted and illustrated by three physical models, e.g., Maxwell model, Kelvin–Voigtmodel, and Burgers model. Details of the nip dynamic features, shape, amplitude, duration, and effective nip width, etc.,have been worked out. The viscoelastic nature of the materials was found to be responsible for the so-called speed-hardening,asymmetric nip profile, variations in the nip amplitude and effective nip width, etc. It was also found that how the viscoelasticproperties of the materials affect the nip dynamics depend on the how the elastic components and the viscos count parts areconnected with each other. The framework is applicable to calendaring, gravure, offset, and flexography.

Print through is an often encountered defect of printed maters, especially on paper grades of low and medium grammages. Print through phenomena have two contributing components, show through and strike through, resulting from insufficient paper opacity and ink penetration, respectively. The existing measurement method of print through and its components are calculated from a set of spectral reflectance values of printed and non-printed paper samples. These reflectance values are from rather big areas that equal to the opening of the employed spectrophotometer (say 33 mm in diameter). Thus, the calculated print through, show through and strike through, are only average values of the measured areas. This method has intrinsic weaknesses as paper is an inhomogeneous medium whose structure and materials compositions vary from one position to another, leading to inhomogeneous show through and strike through (opacity and ink penetration) across the measured areas, especially for papers of low and medium grammages.In this report we present a new method that enables one to take into account of variations in print through across the measured areas. The method employs a scanner that scans the printed and unprinted samples into RGB images of desired spatial resolutions. With the help of calibration patches that are simultaneously scanned as the measured samples, the RGB image signals can be converted into reflectance values. These reflectance values are then used to compute the print through, show through and strike through. Moreover, by means of Kubelka-Munk model, the depth of ink penetration at each spatial position can also be obtained. The developed method has been implemented in Matlab and successfully been applied to printed samples of newsprint and office papers. Comparative studies between instrumental measurements and perceptual evaluations confirm that the print through variations across the printed areas have strong influences on the print quality assessments. It is also found that using internal size agents in paper making is helpful for reducing ink-penetration.

An effective method is proposed that enables one to simultaneously analyze details of numerous holographic grating patterns over a large area. Unlike the conventional approaches relying on sophisticated lighting and optical systems and dark environment, only a flatbed scanner is needed. Thanks to the “rotate-scan” measurement strategy, details of the holographic grating patterns can be obtained, e.g., spatial distribution of the grating patterns, interval and orientation of the grating grooves within each grating pattern, and defects of the holographic patterns. The method has been verified by applications to two holographic papers of different grating intervals and orientations. The measured values agree well with those obtained with a light optical microscope (LOM). The proposed method is applicable to both transparent and reflective holographic materials of broad grating periodicity.

A model of inkjet printing dynamics has been developed that enables a comprehensive view to be obtained of the relationships between the characteristics of the ink droplet (volume, striking speed, viscosity and surface tension), substrate properties and interactions between the ink and the substrate. Simulations based on the three equations that are the major results of the model have provided an understanding of the basics of inkjet printing. Pressure profiles resulting from ink-striking by ink droplets of different volumes and jetting speeds have been obtained. The time duration of the striking process was in the order of microsecond and the peaks of the striking pressure were solely dependent on the jetting velocities, while the duration time of the striking processes was dependent only on the droplets volumes. The penetration length (depth) was heavily dependent on the contact angle. For a coated surface of small pores, the initial penetration depth was 0.26 micron when the striking speed was 30m/s. For a larger pore, the corresponding depth was 1.30 micron.

A series of anthracene-based derivatives, namely, 9-(4-phenyl)anthracene(1), 9-(4-phenylethynyl)-anthracene(2) and 9, 10-bis(phenylethynyl)anthracene(3), was synthesized by the Suzuki/Sonogashira cross-coupling reactions in good yields. These compounds were fully characterized by X-ray crystallography, thermogravimetric analysis(TGA), differential scanning calorimetry(DSC), UV-Vis absorption and fluorescence(FL) spectroscopy, as well as density functional theory(DFT) calculations. Single-crystal X-ray analysis revealed that the packing structures were influenced by the terminal substitutions. All the compounds exhibited high thermal stability(Td=221—484 °C) and blue emission with a high quantum yield(Ωf =0.20—0.75). As the number of substituents increased, the decomposition temperatures(Td) of these compounds increased in the following order: 1<2<3. Experiments on the photophysical properties revealed that different substituents strongly affected the optical properties. In particular, compound 1b with the electron-withdrawing group(—CHO) exhibited a larger Stokes shift(113 nm) than the other compounds. Investigation of the electrochemical properties of these compounds showed that the HOMO-LUMO energy gaps(Egap) decreased obviously as the degree of conjugation increased.