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The leveling of coating defects with shear thinning rheology

CHEMICAL engineering science 1996年第20期51卷 4611-4617页

作者： Iyer, RR Bousfield, DW Paper Surface Science Program Department of Chemical Engineering University of Maine Orono ME 04469-5737 U.S.A.

A one-dimensional model is proposed to predict the leveling of coating defects or irregularities on a planar surface. Though shear thinning rheology is the focus of this paper, any viscous non-Newtonian rheology can be included in the model. Surface tension, gravity and viscous forces are accounted for in the model. A novel numerical technique is presented to obtain solutions of the model. Results agree with a full two-dimensional solution of the flow held obtained with a spectral element method. A new dimensionless group is identified which indicates the significance of shear-thinning theology. Defects are made with a notched blade used to coat pigmented liquids on polymer films. The defect shapes are obtained at different times by drying under infrared. The dried surface is characterized with a stylus profilometer. The surface profiles and the final amount of leveling compare well with the model predictions. Copyright (C) 1996 Elsevier science Ltd

关键词： coating defects rheology modeling shear thinning leveling surface tension

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Colloidal interactions to generate novel coatings

Colloidal interactions to generate novel coatings

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TAPPICon Virtual 2021

作者： Rao, Pradnya Tripp, Carl Bousfield, Doug Department of Chemical and Biomedical Engineering Paper Surface Science Program University of Maine

Latex is a high cost component • Need to use it effectively Prevent or reduce binder migration by attaching latex to the pigment Novel coating structures may be possible that "retain" binder with coating pig... 详细信息

ISBN: (纸本)9781713829683

关键词： Coatings

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Tagging starch and latex in paper coatings

Tagging starch and latex in paper coatings

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paper Conference and Trade Show, paperCon 2015

作者： Golebiowska, Emilia Blakeley, Amy Bousfield, Douglas Gramlich, William Department of Chemical and Biological Engineering Paper Surface Science Program University of Maine United States Sappi Fine Paper North America Paper Surface Science Program University of Mainey United States Department of Chemistry Paper Surface Science Program University of Mainey United States

•Post coating staining is unsuccessful •Successful tagging method for starch and latex •Tagged starch and latex coatings can be imaged with the CLSM •Intensity data can be obtained from the CLSM analysis. © Copyr... 详细信息

ISBN: (纸本)9781510818873

关键词： Latexes

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Characterization of paper coating penetration by laser scanning microscopy

Characterization of paper coating penetration by laser scann...

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2006 TAPPI Advanced Coating Fundamentals Symposium

作者： Hirai, Kenji Bousfield, Douglas W. Paper Surface Science Program Department of Chemical and Biological Engineering University of Maine Orono ME 04469 Nippon Paper Ltd.

The quality of a coating layer, and the efficiency of the coating, depends to a large part on the penetration of the coating into the paper. Methods to characterize this penetration are limited. A new technique is proposed that combines Confocal Laser Scanning Microscopy (CLSM) and image analysis to characterize the coating layer and coating penetration into the substrate. With this technique, it is possible to obtain the information of coating layer thickness variation without any sample destruction and little sample preparation. In this paper, two methods are proposed to obtain quantitative analysis of coating layer thickness and penetration into the paper. The results are compared to scanning electron microscope (SEM) cross sections. Coatings applied onto plastic calibrate the method and demonstrate the limitations. Both methods give results that are consistent with the SEM results. In addition, a technique is shown that can characterize the penetration of the coating liquid phase into the paper by staining the coating suspension before coating. These steps allow a comparison between the penetration of the liquid phase and the coating pigments. A double staining method is demonstrated where the paper is stained with one dye and the coating layer a second dye. By detecting fluorescence at two different wavelengths, paper and coating locations can be characterized.

关键词： paper coating

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Pressure pulse measurements for coating and printing

Pressure pulse measurements for coating and printing

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paper Conference and Trade Show, paperCon 2015

作者： Gates, Harrison Bousfield, Douglas Paper Surface Science Program Department of Chemical and Biological Engineering University of Maine United States

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The correlation between coating penetration aAnd Coating Properties

The correlation between coating penetration aAnd Coating Pro...

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2006 TAPPI papermakers Conference and 2006 TAPPI Coating and Graphic Arts Conference

作者： Hirai, Kenji Bousfield, Douglas W. Paper Surface Science Program Department of Chemical and Biological Engineering University of Maine Orono ME 04469 Nippon Paper Ltd.

ISBN: (纸本)1595101225

The quality of a coating layer, and the efficiency of the coating, depends to a large part on the penetration of the coating into the paper. Rheology and coating solids are known to influence the final product quality, but the mechanisms are not clear. Coating rheology has been correlated with final coating void fraction, but its influence on coating penetration has not been reported. The influence of pigment shape on coating penetration has not been well documented because an economical method to measure coating penetration has not been presented. The relationship between coating color rheology, pigment type, and coating penetration is reported here. Coatings that contain different pigments and additives are characterized in terms of viscous and elastic properties and applied to paper. Coating penetration is characterized using a confocal laser scanning microscopy (CLSM) in conjunction with image analysis. The results indicate that both elasticity and viscosity prevent the coating penetration for pigments with a moderate shape factor. This relationship must be related to the flow rate into a pore. Kaolin pigments with a high shape factor have less penetration than the low shape factor pigment and do not depend on coating rheology. The results suggest that high shape factor pigments can block pores preventing pigment penetration.

关键词： paper coating

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The influence of roughness and elastic modulus on gravure print quality: A new test method and model

The influence of roughness and elastic modulus on gravure pr...

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2004 TAPPI Coating and Graphic Arts Conference and Exhibit

作者： Kai, Hidehiko Bousfield, Douglas W. Unertl, William N. Paper Surface Science Program Dept. of Chemical Engineering University of Maine Orono ME 04469-5737 Nippon Paper Tokyo Japan

Roughness and compressibility of paper surfaces are known to be important factors for minimizing the occurrence of missing dots during gravure printing. However, in most cases, only smoothness is measured for these grades. In this research, an ultra low load indenter is used to evaluate the near surface modulus of small contact points on the sample surface. The indenter is able to measure the modulus of the paper surface at different loading rates and loading forces with a contact dimension less than 0.1 mm. Coating layers with a range of binder types and pigments are applied to a woodfree base, a wood containing base, and sized basepapers. The samples are characterized in terms of compressibility and roughness. Roughness is measured with both air leak methods and a mechanical stylus. A supercalendered (SC) grade is also tested. Samples are printed with the Heliotest in the laboratory to evaluate missing dots. A model is proposed, that describes both roughness and compression and may be able to predict rotogravure print quality. The results show some correlation between roughness and missing dots, but compressibility of the surface can be just as important. The rough but compressible SC paper had the best performance in terms of missing dots. Air-leak roughness tests tend to group samples according to the base, but the mechanical stylus tends to give a good result for a range of bases. A large reduced modulus of the surface is found to promote missing dots. This result shows that poor compressibility is a factor in the missing dot issue. Model parameters are correlated with the indenter tests. The model predicts the occurrence of contact between the paper and the inside plane of a gravure cell in the printing event.

关键词： Elastic moduli

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Prediction of forces on paper during half tone dot printing

Prediction of forces on paper during half tone dot printing

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12th TAPPI Advanced Coating Fundamentals Symposium, Co-located with the 16th International Coating science and Technology Symposium, ISCST 2012

作者： Gates, Harrison Bousfield, Douglas W. Paper Surface Science Program Dept. of Chemical and Biological Engineering University of Maine United States

ISBN: (纸本)9781595102201

During offset printing, delamination of the paper or paper coating can occur leading to serious print defects and press operation issues. A number of publications have reported "tack" forces that are measured during the printing of a solid region. However, there are limited reports on forces during halftone dot printing and limited theoretical work. The forces generated as a fluid cylinder is squeezed and extended as it passes through a nip are predicted based on lubrication analysis and a commercial finite element code. A set of dimensionless parameters are established for this printing event. The influence of process variables such as ink rheology, printing speeds, ink dot dimensions, roughness, and non-Newtonian behavior are predicted. Extensional properties of the ink are neglected. For the base case with no compression, roughness or non-Newtonian effects, a simple expression is found that predicts the peak force as a function of the other parameters. This expression should help understand the basic trends of the parameters. The influence of the roughness wave length is found to be negligible, but the amplitude can be significant if it scales with the dot thickness. Deformation of the substrate and rubber backing acts to reduce forces for a fixed gap. The behavior of non-Newtonian inks can cause the maximum force to be much different than the Newtonian case. Algebraic expressions are developed and correlate well with the numerical predictions.

关键词： Non Newtonian flow

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9.1 - Distribution of latex during drying in confined geometries

9.1 - Distribution of latex during drying in confined geomet...

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作者： Black, Nathan D. Unertl, W.N. Bousfield, Douglas W. Paper Surface Science Program Department of Physics and Astronomy University of Maine United States Paper Surface Science Program Department of Chemical and Biological Engineering University of Maine United States

ISBN: (纸本)1595102035

Latex is the most expensive component in a coating formulation. Therefore, the efficient use of latex is critical to reduce costs, improve the "green" aspects of paper production, and reduce cost fluctuations. Dilute model latex suspensions with up to 7.5 weight percent latex were placed in confined geometries and dried by evaporation. The geometries were comprised of spherical or cylindrical glass lenses placed on a glass cover slip forming a point or line contact. Drops of latex suspension were placed in the contact region. Images during drying and after drying were obtained with an optical microscope and video camera. The influence of latex type, surface contact angles, latex concentration, and glycerin additives were characterized. A mechanism is proposed to explain the characteristic patterns that form after drying. Instead of latex being pulled into the contact as the meniscus retreats, most of the latex is left behind in distinct "finger" patterns, far from the contact point. Little or no latex reaches the contact even for the highest concentrations studied. Some images of the fingers during evaporation reveal that they are wet, possibly increasing the local evaporation rate, thus increasing latex transport to the growing fingers. Increasing contact angles of the glass surfaces inhibited finger formation and resulted in more latex transport to the contact point. High contact angles cause reduced evaporation near the three phase contact line and reduce transport of latex to the contact line. Addition of small amounts of glycerin initially improved ordering of the fingers but, at higher concentrations, ultimately stopped their formation, possibly by accumulating in the fingers, stopping the enhanced evaporation. Implications for real paper coatings are discussed.

关键词： Geometry

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Analysis of microscope images of coating layers that contain tagged starch and latex

Analysis of microscope images of coating layers that contain...

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paper Conference and Trade Show, paperCon 2016

作者： Golebiowska, Emilia Bousfield, Douglas Gramlich, William Department of Chemical and Biological Engineering Paper Surface Science Program University of Maine OronoME04473 United States Department of Chemistry Paper Surface Science Program University of Maine OronoME04473 United States

ISBN: (纸本)9781510831193

Binders like starch and latex are known to migrate during coating and drying which can affect coating properties. A better understanding of binder migration can help determine the parameters that affect migration and can help design better coatings. A three dimensional analysis can be obtained by confocal laser scanning microscopy (CLSM) of fluorescently active samples. By individually tagging starch and latex with fluorescent molecules each component can be analyzed simultaneously. Rhodamine B was used to tag latex while fluorescein isothiocyanate (FITC) was used for starch. The tagged components were made into coatings and imaged by CLSM. Intensity profiles were created from the CLSM data and used to quantify the relative amount of each component. Fluorescence intensity plots were created of simple systems made up of dual layer coatings as well as more complex mixed systems. Mixed systems included mixtures of tagged starch and tagged latex as well as mixtures of tagged starch, tagged latex and pigments. For all coating types, intensity plots could describe the relative abundance of starch and the latex within the coating layers as a function of position. Starch and latex rich regions were observed in initially well mixed binder systems with this technique.

关键词： Starch

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