AN EXPERIMENTAL EVALUATION OF THE GOVERNING MOISTURE MOVEMENT PHENOMENA IN THE PAPER COATING PROCESS. I. THEORETICAL ASPECTS

The most important issue when coating paper is the modelling of the moisture movement in the coating process, since the water movement pattern is strongly connected to binder movement and the final structure of fibres and coating colour, which in turn affects the final printing properties of the paper. Therefore, we are now studying a novel laboratory method to determine the dynamic water movement in a hygroscopic porous media, i.e. the liquid movement in the paper coating process. The experimentally determined physical properties yield information relevant to the mass and energy balances of a real paper coating process. We have also studied the widely used Lucas-Washburn capillary suction theory in combination with the build-up of a filter-cake in the coating colour. The study shows, that the water loss from the coating colour into a hygroscopic material can be well explained by applying vapour diffusion into the base paper as the governing mass transfer mechanism.     

AN EXPERIMENTAL EVALUATION OF THE GOVERNING MOISTURE MOVEMENT PHENOMENA IN THE PAPER COATING PROCESS. II. EXPERIMENTAL

This paper investigates the moisture movement in the paper coating process experimentally and theoretically. The experimental data is obtained by coating a base paper with a laboratory coater and by scraping off some of the coating color after a certain amount of time. The moisture content of the material, which has been scraped off, is measured and the amount of liquid absorbed from the coating color by the base paper is determined. The laboratory results are similar to measurements made on a pilot-coating machine. The mathematical solution is based on the diffusion of water vapor in air and taken the vapor partial pressure in a hygroscopic material, i.e. paper. The measurements and a theory based on vapor diffusion show that the moisture content of the base paper is an important parameter when trying to determine the loss of water from the coating color to the base paper. This kind of dependency cannot be explained by theories based on water movement in the liquid phase by capillary suction, as is discussed in Berg et al., 2000, Part I: Theoretical Aspects.     

AN EXPERIMENTAL EVALUATION OF THE GOVERNING MOISTURE MOVEMENT PHENOMENA IN THE PAPER COATING PROCESS. II. EXPERIMENTAL

This paper investigates the moisture movement in the paper coating process experimentally and theoretically. The experimental data is obtained by coating a base paper with a laboratory coater and by scraping off some of the coating color after a certain amount of time. The moisture content of the material, which has been scraped off, is measured and the amount of liquid absorbed from the coating color by the base paper is determined. The laboratory results are similar to measurements made on a pilot-coating machine. The mathematical solution is based on the diffusion of water vapor in air and taken the vapor partial pressure in a hygroscopic material, i.e. paper. The measurements and a theory based on vapor diffusion show that the moisture content of the base paper is an important parameter when trying to determine the loss of water from the coating color to the base paper. This kind of dependency cannot be explained by theories based on water movement in the liquid phase by capillary suction, as is discussed in Berg et al., 2000, Part I: Theoretical Aspects.     

Three-Layer Model for Drying of Coating Applied on Silicone-Coated Paper

Upon application of water based coating onto silicone-coated paper and during the subsequent drying process, the water permeates through the silicone layer into the paper substrate. At the same time, water evaporates from both the surface of the coated layer and throughout the paper layer. Initially, the evaporation rate from the wet coating surface may be dominant, but at longer times the bulk evaporation from the paper can dominate. Here a three-layer diffusion model for such a system is developed. Solutions obtained by Galerkin's method with finite element basis functions show that the hygroscopic nature of the paper leads to low drying rates at low moisture contents. Further, the model predicts that initially the coating dries to a moderately low residual moisture concentration faster than a coating applied on an impermeable substrate. However, at longer times, the predicted residual moisture of coatings applied on silicon-coated paper is higher than for a coating applied on an impermeable substrate.     

Three-Layer Model for Drying of Coating Applied on Silicone-Coated Paper

Abstract

Upon application of water based coating onto silicone-coated paper and during the subsequent drying process, the water permeates through the silicone layer into the paper substrate. At the same time, water evaporates from both the surface of the coated layer and throughout the paper layer. Initially, the evaporation rate from the wet coating surface may be dominant, but at longer times the bulk evaporation from the paper can dominate. Here a three-layer diffusion model for such a system is developed. Solutions obtained by Galerkin's method with finite element basis functions show that the hygroscopic nature of the paper leads to low drying rates at low moisture contents. Further, the model predicts that initially the coating dries to a moderately low residual moisture concentration faster than a coating applied on an impermeable substrate. However, at longer times, the predicted residual moisture of coatings applied on silicon-coated paper is higher than for a coating applied on an impermeable substrate.     

Investigation of the effect of molar mass on coating properties of self-crosslinking latexes based on acrylic microgels

The effect of reducing the molar mass of the shell layer of core–shell latex particles on film-forming and final coating properties of self-crosslinking latexes was investigated. Latex particles were prepared by the semi-continuous non-seeded emulsion polymerization of methyl methacrylate, butyl acrylate and methacrylic acid as main monomers. The particle core was slightly cross-linked (using a constant amount of allyl methacrylate as a comonomer) to prevent the copolymers forming the core phase from migration into the shell phase. For interfacial cross-linking, diacetone acrylamide was copolymerized into the shell layer of latex particles to provide sites for subsequent reaction with adipic acid dihydrazide. The molar mass of copolymers forming the shell layer was systematically varied by isooctyl 3-mercaptopropionate chain transfer agent included in the synthesis of each of the shell layers and the molar mass distribution was determined using size exclusion chromatography coupled with a multi-angle light scattering detection. Fundamental properties of latexes and cast films were systematically compared. These properties included minimum film-forming temperature, pendulum hardness, adhesion, impact resistance, stress–strain properties as well as the characterization of water absorption. The results confirmed theoretical predictions and described empirically the effects of reducing the molar mass of the shell layer copolymer on final properties of coating films.     

Characterisation of moisture diffusion and strength degradation in an epoxy-based structural adhesive considering a post-curing process

Adhesive bonding techniques have been widely used in many industrial fields, such as aerospace, vehicle and civil engineering, etc., while the bonded structures are designed to perform satisfactorily under complex service conditions. This paper presented an experimental insight into the moisture diffusion process in Araldite 2015 adhesive considering the effect of post-curing process under elevated temperature. Polytetrafluoroethylene mould was adopted for the curing process of dumbbell adhesive specimens and both distilled and salt water were introduced to simulate a severe immersion environment. Quasi-static testing was conducted on both unaged and aged bulk adhesive after certain period of immersion to reveal the mechanical properties variation. Measurements on specimen weight and thickness were performed with different time intervals during the immersion process. It is shown that the strengths of bulk adhesive were significantly degraded due to the presence of water in both immersion conditions, where higher moisture content led to greater strength degradation regardless of the curing and ageing conditions applied. In addition, distilled water environment led to notably higher saturation content and hygroscopic swelling compared to salt water. However, the rates of water diffusion and hygroscopic swelling processes in salt water were detected to be far above the ones in distilled water. It is worth noting that slight increase was observed in moisture saturation content and swelling expansion for post-cured adhesive, while the coefficients of hygroscopic swelling showed no difference for all sample groups studied. Scanning Electron Microscopy observation further revealed the transition in microscopic topography from unaged to saturated samples.     

Effect of Yellowing Inhibitors on the Brightness Stability,Rheological Properties and Water Retention of Paper Coating

Paper coating colours exhibit complex interfacial and rheological properties resulting from the interaction between paper coating colors and yellowing inhibitors, which are added to coating colors to increase the stability of paper brightness. The zeta potential of ground calcium carbonate and kaolinite particles was measured. It was found that the zeta potential increased with the percentage of added inhibitor. Moreover, the measurements revealed the influence of adsorption of inhibitors on ground calcium carbonate and kaolinite. Rheological properties of inhibitors were measured and their effect on the rheological properties of coating formulations was investigated. The elastic character of the colour containing inhibitors was more pronounced than the viscous character. The elastic modulus and viscosity were strongly influenced by the inhibitor used. Measurements of water retention of coating suspensions showed that the inhibitor (radical scavenger) reduced the water retention of coating colors.     

All starch nanocomposite coating for barrier material

Starch nanocrystals (SNC) are nanofillers of growing interest for barrier and mechanical improvement of bio‐based polymers. However, their potential use as fillers for organic coating material of industrial packaging has never been investigated. In this study, SNC processability in coating is assessed and the final properties of coated papers are measured. Coating colors composed of plasticized starch show higher Brookfield viscosity when filled with SNC even with the addition of water but rod‐coating is still possible. These diluted water‐based coatings induce paper wetting and surface crackling issues during drying as proved by drying process analysis. However no gelatinization of the SNC is observed whichever the type of drying. SNC compensate some of the water induced loss of mechanical properties of the base paper and decrease the water vapor permeability (WVP) up to 40% compared with the base paper. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39826.     

DISCONTINUOUS VACUUM DRYING OF OAK WOOD: MODELLING AND EXPERIMENTAL INVESTIGATIONS

Abstract

Vacuum drying and especially discontinuous vacuum drying is a very attractive process for such a wood as oak, because of a reduced drying time and a high quality of the final product. In this paper, a model describing heat, mass and momentum transfer in a capillary porous and hygroscopic medium under vacuum drying with no external heating agent (the material is pre-heated during a convective phase), is presented. The choice of the following three independent unknowns, moisture content, enthalpy and dry air density, leads to a fully well described problem where the effect of gaseous pressure inside the material is taken into account. A new formulation of the boundary conditions and its numerical resolution are validated by experimental results.     

我国多彩涂料的现状与发展趋势

本文论述了多彩涂料的发展历程、现状及目前生产中存在的问题，并指出我国多彩涂料的发展方向是开发水包水型多彩涂料。     

Numerical Spray Model of the Fluidized Bed Coating Process

In this study, a new model for the batch top-spray fluidized bed coating process is presented. The model is based on the one-dimensional (axial) discretization of the bed volume into different control volumes, in which the dynamic heat and mass balances for air, water vapor, droplets, core particles, and coating material were established. The coupling of the droplet phase's mass and heat transfer terms with the gas and solid phases was established by means of a droplet submodel in which droplet trajectories were individually simulated.

The model calculation method combines a Monte Carlo technique for the simulation of the particle exchange with the first-order Euler's method for solving the heat and mass balances, enabling the prediction of both the dynamic coating mass distribution and the one-dimensional (axial) thermodynamic behavior of the fluidized bed during batch operation. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions, which were measured in a fluidized bed pilot reactor using a scanning probe.

Sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidization air and atomization air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on these sensitivity studies it was concluded that nozzle parameters, such as air pressure and positioning with respect to the bed, are as important as the fluidization air properties (humidity, temperature, and flow rate) for the coating growth rate uniformity and process yield.     

Numerical Spray Model of the Fluidized Bed Coating Process

In this study, a new model for the batch top-spray fluidized bed coating process is presented. The model is based on the one-dimensional (axial) discretization of the bed volume into different control volumes, in which the dynamic heat and mass balances for air, water vapor, droplets, core particles, and coating material were established. The coupling of the droplet phase's mass and heat transfer terms with the gas and solid phases was established by means of a droplet submodel in which droplet trajectories were individually simulated.

The model calculation method combines a Monte Carlo technique for the simulation of the particle exchange with the first-order Euler's method for solving the heat and mass balances, enabling the prediction of both the dynamic coating mass distribution and the one-dimensional (axial) thermodynamic behavior of the fluidized bed during batch operation. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions, which were measured in a fluidized bed pilot reactor using a scanning probe.

Sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidization air and atomization air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on these sensitivity studies it was concluded that nozzle parameters, such as air pressure and positioning with respect to the bed, are as important as the fluidization air properties (humidity, temperature, and flow rate) for the coating growth rate uniformity and process yield.     

凹凸棒制作中空玻璃干燥剂的研究

由于凹凸棒晶内存在庞大的微细孔道网络,比表面积极大,表面活性非常高,吸附性能特别优异,而且由于其晶内大量孔道的存在,具有不小的空气容积,因而可以考虑用作干燥剂。主要通过加入吸湿剂来提高凹凸棒石粘土的吸附性能,加入黏合剂提高样品抗压碎力。根据国家标准来选择颗粒大小和烧结工艺。自制仪器测量样品的静态水吸附量、吸湿速率和抗压碎力。研究结果表明:通过XRD衍射图可以得知,样品中含有蒙脱石和坡缕石,这些杂质严重影响了凹凸棒吸湿后的颗粒结构和抗压碎力,使其在吸湿后膨胀开裂。加入CaCl_2比加入MgCl_2和CuSO_4的吸湿效果好,加入适量的Na_2SiO_3可以提高吸湿后的颗粒强度,提纯凹土与未提纯的吸湿效果相差不明显。烧结温度为350℃,时间为1 h,粒径为2.5~3.0 mm。最合适的配比是质量比为81%凹凸棒,15%CaCl_2,4%Na_2SiO_3,静态水吸附量为32.9%,吸湿速率1.06%。     

低密度泡沫玻璃的研究与应用

低密度泡沫玻璃是利用碎玻璃制造的一种气孔率大于90%的隔热保温材料,它具有强度高、导热系数小、吸水率低、不吸湿、耐腐蚀等特性,在潮湿环境下抗冻性能好,是一种优良的低温、超低温隔热保温材料。该产品用途广泛,所用的原材料简单易得,但生产工艺过程比较复杂,生产过程控制精度要求较高,容易产生各种缺陷而影响产品的质量。本文对低密度泡沫玻璃的生产工艺过程进行详细的分析研究,提出相应的措施,确保产品的低密度和高成品率,提高产品的性能,扩大产品的使用范围。     

STUDY AND MODELLING OF COATED CAR PAINTING FILM BY INFRARED OR CONVECTIVE DRYING

Abstract

In this study, we described and modelled some coupled material transformations with heat and mass transfer phenomena which occur during the convective or the infrared drying of coated films of model car paintings. For these very complex reactive systems -highly shrinking, hygroscopic, semi-transparent (infrared)- the vaporization process is coupled with the polymerization reaction itself which determines significantly the material properties of the dry paint coating. Three model systems (paint + support) were successively defined and investigated by association of five supports of different radiative or adhesive properties -polish aluminium, blackened aluminium, glass, galvanized iron and composite plastic (SMC)- with three model paintings : epoxy-amine system, polyurethane system and polyvinylalcohol (PVA). Two laboratory combined dryers (convective or infrared) were set up in order to control and regulate precisely the main process parameters: aerothermic conditions (temperature and velocity), spectrum (NIR or MIR) and flux density of infrared radiation.

Firstly, the kinetics of the polymerization were followed all along the process by three different techniques : DSC (Differential Scanning Calorimetry), SEC (Size Exclusion Chromatography), FT-ERS (FOURIER Transform Infrared Spectroscopy). The glass transition temperature of the material during the drying process was deduced from DSC data with the fractional conversion of the monomer. These two parameters were well correlated by the DI BENEDETTO'S relationship, thus defining some characteristic curve of the painting system. Drying curves -temperature profiles and drying rates- were determined for PVA systems for many operating conditions, principally infrared flux density, spectra type or air velocity. The two main coating properties necessary for the modeling were deduced from drying experiments 1: the mean radiative absorptivity as a function of the mean moisture content, 2: the water apparent mass diffusivity as a function of the temperature and of the local moisture content. A diffusive model - written with a mobile frame of coordinates (lagrangian coordinates)- associated with an overall heat balance of the support + coating system, has proved capable of predecting very well the drying curves and the temperatures profiles So, this whole set of results -associated with other material properties (rheological, adhesive, color, etc ?)- will be useful to rationally optimize the industrial dryers operating in the car manufactories.     

Preparation and characterisation of α-methylstyrene–butadiene latexes for paper coating applications

The purpose of this work is to demonstrate how α-methylstyrene (AMS) can replace styrene in preparing styrene–butadiene (SB) type latexes and to compare the properties of the paper coating of the prepared α-methylstyrene–butadiene emulsion with the commercial styrene–butadiene latex reference sample. A lot of work is nowadays being conducted on different biorefinery concepts replacing fossil oil with biomass based raw materials due to the expected rise of the fossil oil cost. Aromatics can in principle be produced from renewable raw materials, such as lignin, sugars and terpenes for example. The potential methods include thermochemical conversions, catalytic fast pyrolysis, metabolic engineering, catalytic aromatisation and dehydrogenation among others. Terpenes, such as α-limonene and pinene, are possible sources of aromatics, and they can indeed be catalytically converted to p-cymene. Industrial hydrodealkylation and disproportionation processes developed by major petrochemical companies can further convert p-cymene to BTX aromatics or simultaneously dehydrogenate the alkyl chain of p-cymene to styrenic monomers such as α-methylstyrene. Based on the measured paper properties for uncalendered and calendered coated samples, AMS proved to be adequate to replace the oil based styrene in commercial reference SB latexes. Even though the emulsion polymerisation for the α-methylstyrene–butadiene latex was not optimised, almost all tested properties were at least equally good as in the commercial reference sample. α-Methylstyrene containing coating colours had slightly higher viscosity than the other coating colours. Coating colours containing α-methylstyrene seems to have an improved water retention compared to the commercial reference styrene–butadiene latex coating colour and the laboratory prepared styrene–butadiene coating colour. The paper coated with the commercial reference latex containing coating colour was less porous than the other coated papers. Despite of that, both dry and wet surface strength were at least equally good as in the case of the commercial reference latex. The results are promising when thinking of the future development of the bio-based latexes.     

STUDY AND MODELLING OF COATED CAR PAINTING FILM BY INFRARED OR CONVECTIVE DRYING

In this study, we described and modelled some coupled material transformations with heat and mass transfer phenomena which occur during the convective or the infrared drying of coated films of model car paintings. For these very complex reactive systems -highly shrinking, hygroscopic, semi-transparent (infrared)- the vaporization process is coupled with the polymerization reaction itself which determines significantly the material properties of the dry paint coating. Three model systems (paint + support) were successively defined and investigated by association of five supports of different radiative or adhesive properties -polish aluminium, blackened aluminium, glass, galvanized iron and composite plastic (SMC)- with three model paintings : epoxy-amine system, polyurethane system and polyvinylalcohol (PVA). Two laboratory combined dryers (convective or infrared) were set up in order to control and regulate precisely the main process parameters: aerothermic conditions (temperature and velocity), spectrum (NIR or MIR) and flux density of infrared radiation.

Firstly, the kinetics of the polymerization were followed all along the process by three different techniques : DSC (Differential Scanning Calorimetry), SEC (Size Exclusion Chromatography), FT-ERS (FOURIER Transform Infrared Spectroscopy). The glass transition temperature of the material during the drying process was deduced from DSC data with the fractional conversion of the monomer. These two parameters were well correlated by the DI BENEDETTO'S relationship, thus defining some characteristic curve of the painting system. Drying curves -temperature profiles and drying rates- were determined for PVA systems for many operating conditions, principally infrared flux density, spectra type or air velocity. The two main coating properties necessary for the modeling were deduced from drying experiments 1: the mean radiative absorptivity as a function of the mean moisture content, 2: the water apparent mass diffusivity as a function of the temperature and of the local moisture content. A diffusive model - written with a mobile frame of coordinates (lagrangian coordinates)- associated with an overall heat balance of the support + coating system, has proved capable of predecting very well the drying curves and the temperatures profiles So, this whole set of results -associated with other material properties (rheological, adhesive, color, etc ⃛)- will be useful to rationally optimize the industrial dryers operating in the car manufactories.     

Mass transport and modeling of emulsion phase-inversion coating of hydrogel beads

A new coating method named emulsion phase-inversion coating for preparing microcapsules containing hydrogel beads was reported in our previous work. In this paper, we suggest a numerical model for predicting the coating process. By defining suitable dimensionless parameters, the governing equation and its associated initial and boundary conditions are discretized using Euler's differential equation and the system of resulting differential equations is simultaneously solved using MATLAB for the dimensionless coating thickness and water content in beads. Parametric studies show that the dimensionless coating thickness depends on the dimensionless critical concentration, an internal property of the hydrogel beads, which can be calculated using the dimensionless final coating thickness. In addition, the apparent diffusion coefficient of water in coating layers can be easily obtained by fitting our experimental data to the simulated results. The comparison experiments show that there is a good agreement between the predicted and experimental coating thickness with the fitted apparent diffusion coefficient. The model also reveals that the apparent diffusion coefficient when using Polyacrylnitrile (PAN) is far smaller than that when using Polysulphone (PSf) as the coating polymer, resulting in a relatively thinner and more hydrophilic coating layer, which suggested that we could modulate the physiochemical properties of the coating layers by changing the coating polymer.     

二氧化硅凝胶在彩色喷墨打印纸涂层的应用实验

用凝胶颜料与其他辅料组成的涂料,对原纸进行涂布制成彩色喷墨打印纸。该彩喷纸经打印测试。结果表明,在颜料与胶粘剂的配比比值为70︰30时,不管是用Espson打印机打印还是用Hp打印机打印,都可获得较好的打印效果。