<p>Flexographic printing is a process that employs a flexible printing form and low viscous ink, often water-based. The flexible printing form is favourable for printing on rough surfaces, but the high surface tension of the ink may cause printability problems.</p><p>This work has focused on the interaction between paper/paperboard coating and water-based flexographic ink, aimed at increasing the knowledge about the printing process in form of physical/chemical parameters that are important for ink setting. The effects of printing conditions on print quality, such as printing pressure and temperature, have also been in focus.</p><p>The work has shown that fluids of different polarities, i.e. different dipole moments, behave differently when being absorbed by a coating layer. Due to their chemical compatibility to the coating layer, fluids with large dipole moment fill the pore matrix of the coating to a lesser extent but penetrate further into the coating than fluids with small dipole moments. On the other hand, polarity of the coating layer also affects the print. When printing on coatings with different polarities, higher print densities was obtained on the more polar substrates. As a tentative explanation, it is proposed that the ink builds different layer structures during drying depending on the coating polarity.</p><p>Print gloss is related to the ink setting which, in turn, is affected by the solvent retaining capacity of the ink. Large water holding capacity allows the ink components to smoothen out before the structure is set, resulting in a higher print gloss. The rheology of inks is affected by temperature; at a higher temperature the viscosity is reduced. The reduction in ink viscosity at higher temperature has been shown to affect the print quality, e.g., print density and dot gain. It is suggested that a thicker layer is immobilised during impression due to the lower viscosity and that it is an explanation of the higher print density at a higher printing temperature.</p><p>The influence of impression pressure on dot gain has been experimentally evaluated and mathematically modelled with good agreement. The dot gain is shown to respond non-linearly to the applied printing pressure.</p><p>Studies based on pilot coated and printed paperboards is also reported, and it is shown that the print quality, e.g. print density, print gloss and dot gain, is largely dependent on the type of ink chosen and on the coating characteristics. Higher clay content in the coating resulted in increased dot gain and a decreased mottling.</p>

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Includes bibliographical references.

The influence of particle shape of coating pigments on theirpacking ability and on the flow properties of coating colourshas been investigated. The particle shapes considered werespherical, flaky and acicular (needle-shaped). In the case ofsuspensions containing monodisperse spherical polystyreneparticles, a concentration gradient appeared in the filter cakeforming during filtration under static conditions. Such agradient, monitoredby non-destructive magnetic resonanceimaging (MRI), is not accounted for in the traditionalfiltration theory used in coating technology. Good agreementwas found between a literature model describing filtrationthrough a compressible filter cake and the concentrationgradients measured by MRI. According to this model, the scaledconcentration gradient was the same at all times. For flaky (mainly kaolin) and acicular (aragonite)particles, a rapid method was evaluated to estimate a shapefactor of the pigment particle. Generalised mathematical modelsof oblate and prolate spheroids were applied to reduce thethree geometrical dimensions of the particle to two, the majoraxis and the minor axis. The shape factor, which is mass-based,was derived from a comparison between the results obtained bytwo different size-assessment instruments, viz. the Sedigraphand an instrument using light scattering. This yields a shapefactor distribution as a function of equivalent sphericalparticle size, but the results are uncertain for small particlediameters, below 0.2 µm. Good agreement was obtainedbetween the shape factor and a mass-based aspect ratio obtainedby image analysis, but the rapid method is generally moreaccurate for flaky than for acicular particles. Results obtained by capillary viscometry showed that therewas a relationship between the viscosity at high shear rates(&gt;105s-1) and the shape factor, but that it was notsufficient to use the median value of the shape factor toachieve proper information. A more complete evaluation requiresknowledge of the shape factor distribution, which is also givenin part by the method mentioned above. However, a large medianshape factor was related to a high high-shear viscosity.Non-Newtonian entrance pressure losses were sometimessignificant in capillary viscometry, indicating that it wasinappropriate to measure the shear viscosity with only onecapillary. Such effects were however relatively much morepronounced in slit die viscometry, especially in the case ofacicular particles, where the aspect ratio was a crucialparameter. The influence of the shape factor of kaolinparticles on the non-Newtonian entrance pressure losses over aslit die was surprisingly small. The high-shear viscosity ofcoating suspensions based on different pigments correlated withthe median pore size of the corresponding coating layer ratherthan with the porosity. <b>Keywords</b>: Aspect ratio, capillary viscometry, coatingcolour, filtration, particle packing, pigment, pore structure,rheology, shape factor, slit die viscometry, spheroid.

In the last few years, especially in the developed countries, an increment in demand for fresh-cut fruit by the consumers of all ages has occurred. This increase is mainly due to the importance that people are giving to the consumption of fresh, healthy, and low-calorie food products. Fresh-cut pineapple (Ananas comosus) is one of the fruits that consumers can eat quickly and still enjoy its benefits; however, its shelf-life is very short (7 days). A means to preserve all the natural and beneficial components of fresh-cut pineapple is coating the fruit with an edible material, a coating. This coating acts as a barrier against moisture loss and gas exchanges and can be a carrier of other components like antimicrobials, which can help to extend the shelf-life of the fresh-cut fruit. The main objective of this study was to develop an edible coating with an antimicrobial agent for fresh-cut pineapple and to determine its effectiveness in extending shelf-life and preserving fruit quality attributes. Different treatments consisted of several concentrations of sodium alginate (0.5%, 1%, and 2%); beta-cyclodextrin, trans-cinnamaldehyde (antimicrobial), pectin, and calcium chloride were tested for formulation of the edible coating. The layer-by-layer technique with a dipping method was used to coat the fruits. Pineapples were properly cleaned with a chlorine solution (300 ppm) and triangular prisms (3.6 cm per side) were cut using a triangular cutter. The length of the triangular prisms was adjusted to 2.54 cm using a small knife measured with a ruler. Color, texture, pH, degrees Brix (total soluble solids), acidity, vitamin C, moisture content, and weight loss, were monitored every 3 to 4 days for 15 days. Microbiological tests (aerobic plate counts, psychrotrophic counts, and yeast and molds counts) were performed to determine the effectiveness of the antimicrobial compound. In terms of microbiological and physicochemical quality attributes, the coating improved the shelf-life of the fresh-cut pineapple up to 12 days compared to the control (fresh-cut pineapple without the coating) which only lasted 7 days at 4 degrees C. Color, texture and pH, were better preserved in the treated (coated) fruit compared to controls (uncoated). Different concentrations of the solutions in the formation of the coating had different results in terms of the preservation of the quality attributes of the fruit. Antimicrobial coatings with a concentration of alginate of 1% and 2% (w/w), pectin 2% (w/w) and calcium chloride 2% (w/w) presented a satisfactory formulation to preserve fruit quality attributes like moisture content, help to control juice leakage, and avoid microbial growth. Antimicrobial coating with 1% of alginate (w/w), 2% of pectin (w/w), 2% of calcium chloride (w/w) and 2% of antimicrobial compound (w/w) was the best formulation. This research demonstrates the feasibility of an alginate-based antimicrobial edible coating, which acts as a carrier of antimicrobial compounds for fresh-cut pineapple.

This study describes the mechanical response of thermoset polymers under high compressive loads. The study is divided into two parts. The first part focuses on the behaviour of a powder coating when used in a clamping force joint and how the properties vary when the chemical and physical structure of the coating is changed. The second part discusses the fundamental understanding of the behaviour of thermoset polymers with small thickness-to-width ratio subjected to compressive stresses, the aim being to develop mathematical material models for viscoelastic materials under high compressive loads. In the first part polyester powder coatings were used with variations in molecular weight, number of functional groups of the resin, amount and type of filler and thickness of the coating. The coatings were subjected to conventional tests for coatings and polymers and also to specially designed tests developed to study the behaviour of powder coatings in clamping force joints. The high compressive loads in a clamping force joint put high demands on the relaxation and creep resistance of the coating and the study shows the importance of crosslink density, filler content, and also coating thickness in order to achieve the desired mechanical properties of a coating. A high reactivity of the resin, facilitating a high crosslink density and hence a high Tg, is the most important property of the coating. A film with high crosslink density shows increase in relaxation time and in apparent yield strength under compression, and also an increase in relaxation modulus and storage modulus in tension at temperatures above Tg. Addition of fillers reduces the deformation during compression and tension, but also induces a lower strain at break and hence a more brittle coating. The reinforcing effect of the fillers is pronounced when increasing the crosslink density of the coating, especially in the compression tests. The effect is evident in compression even at low amounts of fillers, where the relaxation time and resistance to deformation are strongly increased. The combination of high crosslink density and addition of fillers is therefore desirable since fillers then can be used moderately in order to achieve a reinforcing effect in compression while minimising embrittlement. The study also showed that increased coating thickness will give rise to defects in the coating, especially voids and blisters due to evaporation of water formed during the curing of the polyester powder coating. These defects will give rise to stress concentrations and increased plastic deformations in the coating, impairing the properties of the clamping force joint. The results from relaxation tests in tension were used to create a micromechanical model. This model was used in finite element modelling to estimate the loss of clamping force in a screw joint and to correlate with the experimental results of the powder coatings. In the second part of the study a well-defined free radically cured vinyl ester resin was used and studied in six different geometries in order to determine the dependence of apparent mechanical properties on the particular size and shape of a sample when it is subjected to high compressive loads. Variation of the specimen thickness, boundary conditions and loading conditions reveals that the geometry of the sample has a significant effect on the mechanical performance of the polymer. The apparent modulus and the yield strength increase dramatically when the thickness-to-width ratio of the sample is reduced, whereas they decrease when the friction between the sample and the compression plate is reduced. The creep strain rate decreases when the thickness of the material is reduced and it decreases even more when the amount of material surrounding the compressed part of the sample is increased. Creep and strain recovery tests on large specimens were used to develop a mathematical model including non-linear viscoelastic and viscoplastic response of a thermoset vinyl ester. The model was used in FEM calculations where the experimental results were compared with the calculated results in order to model the trends of the material response when varying the sample geometry. / QC 20100921

Ti2AlC coatings have been fabricated by cold-spray deposition. The microstructure evolution as a function of basic spray parameters temperature and pressure onto AA6060 aluminium alloy and 1.0037 steel substrates has been studied. Adherent and dense 50–80 μm thick Ti2AlC coatings were deposited on soft AA6060 substrates under gas temperature and pressure of 600 °C and 3.4 MPa, respectively, whilst comparable results were obtained on harder 1.0037 steel by using higher temperature (800 °C) and pressure (3.9 MPa).

Multilayered iron electrodeposits composed of alternating layers of coarse-grained iron (grain size: 1.87 μm; (110) texture; hardness: 177 VHN) and fine-grained iron (grain size: 132 nm; (211) texture; hardness: 502 VHN), with layer thicknesses ranging from ~0.2-7 μm were successfully synthesized. The average hardness of the multilayered electrodeposits increased from 234 VHN to 408 VHN with decreasing layer thickness, consistent with a Hall-Petch type behaviour. In three-point bending tests, they failed in a macroscopically brittle manner although local ductility was observed in certain layers. Fractography analysis has shown that strain incompatibility between alternating layers contributes to the brittle nature of these materials. This study has demonstrated the possibility of applying a multilayered structure design to tailor the microstructure and mechanical properties of electrodeposited iron.

Multilayered iron electrodeposits composed of alternating layers of coarse-grained iron (grain size: 1.87 μm; (110) texture; hardness: 177 VHN) and fine-grained iron (grain size: 132 nm; (211) texture; hardness: 502 VHN), with layer thicknesses ranging from ~0.2-7 μm were successfully synthesized. The average hardness of the multilayered electrodeposits increased from 234 VHN to 408 VHN with decreasing layer thickness, consistent with a Hall-Petch type behaviour. In three-point bending tests, they failed in a macroscopically brittle manner although local ductility was observed in certain layers. Fractography analysis has shown that strain incompatibility between alternating layers contributes to the brittle nature of these materials. This study has demonstrated the possibility of applying a multilayered structure design to tailor the microstructure and mechanical properties of electrodeposited iron.

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No description available.