Pore Structure Of Coatings Research Articles

Study on characterization technology of porosity and fractal dimension of micro-arc oxidation coating

Abstract The porosity of the micro-arc oxidation coating of pure titanium was assessed through the utilization of Mercury intrusion porosimetry (MIP). The porosity values were subsequently adjusted by accounting for the proportion of coating volume, resulting in a more precise determination of the coating’s porosity. Additionally, the fractal dimension of the pore structure was determined through the application of a linear regression equation utilizing the Mercury intrusion data. The findings indicate that the observed numerical dispersion from image metohd is substantial, with a range of 34.9% between the minimum and maximum values. This suggests that the precision and validity of the porosity outcomes derived from this approach are inadequate; The MIP is capable of determining both the porosity, average pore size and pore size distribution of the sample, while also mitigating the impact of the matrix through test result correction, thereby yielding precise porosity values. Additionally, the results of the verification experiment demonstrate a positive correlation between the porosity alteration of the MIP and oxidation duration, thereby affirming the reliability of the test outcomes; Through the analysis of pressure, pore size, cumulative Mercury intrude volume, and incremental Mercury intrude volume data obtained from MIP, the fractal dimension of the coating’s pore structure then be determined. Research showed that as the oxidation time increases, the pore fractal dimension of the MAO coating gradually expands within a narrow range, from 2.57 and finally stabilized at 2.77, indicating a gradual increase in pore structure complexity.

Characterizing the hydraulic properties of paper coating layer using FIB-SEM tomography and 3D pore-scale modeling

Paper used in the printing industry generally contains a relatively thin porous coating covering a thicker fibrous base layer. The three-dimensional pore structure of coatings has a major effect on fluid flow patterns inside the paper medium. Understanding and quantifying the flow properties of thin coating layers is hence crucial. Pore spaces within the coating have an average size of about 180nm. We used scanning electron microscopy combined with focused ion beam (FIB-SEM) to visualize the nano-scale pore structure of the paper coating layer. Post-processing of the FIB-SEM images allowed us to reconstruct the three-dimensional pore space of the coating. The 3D FIB-SEM images were analyzed in detail to obtain pore size distribution and porosity value. The permeability was estimated using the GeoDict software, based on solutions of the Stokes equation. By determining the porosity and permeability of increasingly larger domain sizes, we estimated the size of a representative elementary volume (REV) for the coating layer to be 60µm3, which is well within the volume analyzed using FIB-SEM. The estimated porosity and permeability of the REV domain were 0.34 and 0.09 mDarcy, respectively. Using the pore morphology method, capillary pressure-saturation (Pc-S) and relative permeability curves of the REV domain could be constructed next. The Pc-S curves showed that the coating had a high air entry suction, which is very favorable for printing in that ink will invade the coating as soon as it is applied to the coating. Our results are essential for macroscale modelling of ink penetration into a coating layer during inkjet printing. Macroscopic models can be valuable tools for optimization of the penetration depth and the spreading of ink on and within paper substrates.

Influence of the Solution Ionic Mobility on the Impedance Response of Organic Coatings

PVC (polyvinylchloride) Plastisol films immersed in electrolyte were studied by Electrochemical Impedance Spectroscopy (EIS) and the data were fitted using one-time constant and two time constant equivalent circuits. Very often the electrical behavior of these films is better represented by the second circuit. The first time constant can be associated with the film capacitance and is independent of the immersion solution ionic mobility, whereas the second one could be related with charge separation inside the film pores and depends on cation mobility. Since the physical meaning of the two time constants is acknowledged their presence in EIS measurements should be taken into account when the results are analyzed. Electrochemical Impedance Spectroscopy (EIS) can be used to evaluate coatings. The results obtained can be interpreted with an equivalent circuit composed by a resistor (solution resistance) followed by a capacitor (coating capacitance) in parallel with a resistor (poreresistance).FrequentlytheEISresultsforanintactcoating show a second time constant in the high frequency region. Several interpretations of these results are possible, namely, water-polymer composite response, coating pore structure, charge separation occurring at the film, coating relaxation given by the water entrance, high heterogeneity of the coating and transient instability (early water uptake), interaction between adsorbed electrolyte and the polymer (dipole relaxation) and difference between the coating outer and inner parts

Influence on Pore Structure of Micro/Nanofibrillar Cellulose in Pigmented Coating Formulations

Nano and microfibrillated cellulose (NFC and MFC, respectively, collectively termed MNFC) is known to interact strongly with water, related to its high polarity and surface area. The swelling behaviour acts to form a gel with high water retention properties. The observation that nanocellulose could possibly be used in paper or other coating formulations, as a co-binder, for example, raises a question about the possible effects it could have on coating pore structure. In this study, we analyse the pore structure of pigmented coatings, liquid absorption and permeability, in respect to the influence of partially substituting traditional co-binder carboxymethyl cellulose with MNFC. The contrast between polar water and non-polar liquid, such as alkane, is used to probe the water interactive and extractable in-coating (internal) gel-formation properties of the nanocellulosic materials. These contrasting liquids are important in many processes, such as offset printing, but also in respect to exposure of coatings in general to environmental factors in application. Results show that permeability to liquid water is dramatically reduced when nanocellulosic material is present, though water can permeate by diffusion through the nanocellulose gel network. Long timescale exposure to water during absorption leads to extraction of any soluble salts remaining after the chemical treatment of the fibrillar material during production. Inert alkane, on the other hand, can absorb and permeate freely without interactive hindrance from the nanocellulose, with no extractive effect. Such a construct could in principle be considered for use as an oil-water differential membrane or for slow release concepts in aqueous systems by loading soluble deliverable materials within the nanocellulosic gel.

PAPER INK INTERACTIONS. The effect of coating pore structure and geometry on the drying efficiency of heatset web-offset ink solvent

Abstract This work examines the effect of coating pore structure on the evaporation behaviour of mineral oil, as a typical heatset web-offset ink solvent. Two different kinds of coating pigments are compared, a standard ground calcium carbonate (GCC) and a highly porous modified calcium carbonate (MCC) with fine intraparticle pores. The aim is to identify relevant pore structure parameters and their effect on the drying rate. Two internal stages of drying were identified for both structures : a rising drying rate period and a falling rate period. In the rising rate period, the effect of film tlow was of particular relevance for the case of GCC based structures : binder, filling the pore structure decreases the detail of geometry and thus reduces the film flow tendency, progressively depressing the drying rate. At the onset of the falling rate period the liquid phase is in the form of disconnected liquid clusters. Therefore, the diffusion resistance becomes a dominant factor. Because of the high permeability of MCC systems the evaporation rate proofed to be largely unsusceptible to the binder concentration. However, the GCC pigment systems exhibited an extended peak of the drying rate as a result of the increasing diffusion resistance with increasing binder content.

Analysis of Coating Pore Structure and its Effect on Printability of Low Gloss Coated Paper

Coating pore structure of low gloss coated paper based on different pigment blends was analyzed using mercury intrusion method in this paper. The results show that pore size of coating layer structure of low gloss coated paper ranges from 20nm-500nm, and the range from 500nm-5000nm is mainly from base paper and interactions between coating color and base paper. Printability of coated paper can be well related with coating pore structure. Print gloss is strongly influenced by pore size and pore volume. Large pore diameters and small pore volume of coating layer structure can improve print gloss. Ink density increases with the increasing of pore diameter while the pore volume is kept constant. The increasing of pore volume of coat layer structure will improve capillary absorption and then improve ink absorption. The control of coating pore structure is very important for producing low gloss coated paper.

Calendering Effects on Coating Pore Structure and Ink Setting Behavior

Coating layer pore structure significantly affects surface appearance, optical properties, and print-ability performance of multiply coated papers. Generally, fast ink setting can be realized by use of fine pigments, or pigments with steep particle size distribution. Ink-paper interaction of coated papers also changes significantly in calendering. The objective of this study was to better understand the influence of calendering on the pore structure of multilayered coated papers and to highlight the effect of this pore structure change on ink setting behavior. Laboratory calendering trials demonstrated that the pore structure of calendered paper is reduced with increased calendering temperatures. Mercury porosimetry and image analysis of scanning electron microscope images of calendered papers highlighted the gradual reduction of total pore volume, which, in combination with the reduced surface porosity, resulted in slower ink setting. If ink setting speed is to be preserved, calendering at low surface temperatures and a higher number of nip passes is preferred to reach a desired paper gloss level. Results also were compared to common theoretical models for liquid penetration into porous structures. These models can also be used to describe the influence of calendering-induced pore structure changes on ink setting. This work demonstrates optimization of calendering parameters to reach a balance for paper gloss and ink setting. The optimum depends on the machine equipment available and has to be checked separately for each concept of multiply coated paper and calender conditions.

Russia: Alchemie — colour pigment pastes for paints & inks

The dynamics of wet ink gloss on model pigmented latex coatings is recorded immediately after printing, every 0.1 s, and followed for 60 s. Two distinct types of latices are used with three spherical polystyrene pigment sizes, at five pigment volume concentrations (PVCs). A novel gloss-meter device is used for the first time to investigate the influence of the latex type and the latex level on the ink gloss dynamics.The type of latex in the coating has a dramatic influence on the print gloss dynamics at low PVC: the high interactivity latex retards print gloss development at short times and results in low print gloss. As PVC increases, the print gloss reaches a maximum. As PVC becomes large, both latex types show a decrease in print gloss. The pigment size influences the results at high PVC. Two different mechanisms seem to be responsible for the gloss results: (1) the leveling of the ink film defects is slowed by penetration of the mobile phase into the coating pore structure by capillary pressure effects, and (2) the leveling is stopped when the mobile phase diffuses into the latex matrix.

The influence of latex type and concentration on ink gloss dynamics

The dynamics of wet ink gloss on model pigmented latex coatings is recorded immediately after printing, every 0.1 s, and followed for 60 s. Two distinct types of latices are used with three spherical polystyrene pigment sizes, at five pigment volume concentrations (PVCs). A novel gloss-meter device is used for the first time to investigate the influence of the latex type and the latex level on the ink gloss dynamics. The type of latex in the coating has a dramatic influence on the print gloss dynamics at low PVC: the high interactivity latex retards print gloss development at short times and results in low print gloss. As PVC increases, the print gloss reaches a maximum. As PVC becomes large, both latex types show a decrease in print gloss. The pigment size influences the results at high PVC. Two different mechanisms seem to be responsible for the gloss results: (1) the leveling of the ink film defects is slowed by penetration of the mobile phase into the coating pore structure by capillary pressure effects, and (2) the leveling is stopped when the mobile phase diffuses into the latex matrix.

紙の液体浸透特性について 第２報 顔料組成及びカレンダー掛けがコート紙への液体浸透に与える影響

Pore structure of coatings is closely related to ink absorption in printing process. In the previous paper drying conditions and latex content were discussed as regulating factors of coating structure.In the present paper influence of pigment composition and calendering on the liquid absorbency of coated paper were examined by Bristow's method and ultrasonic attenuation method.Pigment compositions of coated paper samples prepared were altered by changing clay and calcium carbonate ratio with different particle shapes and sizes.Conclusions obtained are as follows;1.Absorbed water volume increased with the ratio of calcium carbonate which has largerparticle size than clay.2. Total pore volume in coatings occupied with water could be calculated from Bristow's curve for the coated paper samples with the same smoothness as that of their base paper.3. Calendering decreased the transferred liquid volume.The reason for this finding may be that calendering leads to the smoothness improvement and compression of coatings that in turn made the pore volume smaller. However, that did not influence the absorption rate when water penetrated through the base paper layer.