Gravure Roll Research Articles

Tailoring threshold voltage of R2R printed SWCNT thin film transistors for realizing 4 bit ALU

Despite the roll-to-roll (R2R) gravure printing method emerging as an alternative sustainable technology for fabricating logic circuits based on p- and n-types of single-walled carbon nanotube thin film transistors (p,n-SWCNT-TFTs), the wide variation of large threshold voltage (Vth > ~8) in the R2R printed p,n-SWCNT-TFTs prevents the integration of complementary logic circuit. Here, the Vth variation of the p,n-SWCNT-TFTs was narrowed down by developing a method of using the first gravure roll with the minimized superposition error (< ±40 µm) of engraved registration marks and implementing the R2R doping process for tailoring the Vth using polymer-based p- and n-doping inks. Through those two methods, the R2R printed the p,n-SWCNT-TFTs was tailored to shift Vth to near ±2.7 V and reduce Vth variation to ±1.6 V while the noise margin was improved by 24% so that a large number of R2R printed logic gates could be integrated with clear logic levels at ±10 V of operation voltage. Based on the tailored p,n-SWCNT-TFTs, a fully R2R printed 4-bit arithmetic and logic unit was successfully demonstrated by integrating 156 p,n-SWCNT-TFTs.

Antimicrobial-coated films as food packaging: A review.

Antimicrobial food packaging involves packaging the foods with antimicrobials to protect them from harmful microorganisms. In general, antimicrobials can be integrated with packaging materials via direct incorporation of antimicrobial agents into polymers or application of antimicrobial coating onto polymer surfaces. The former option is generally achieved through thermal film-making technology such as compression molding or film extrusion, which is primarily suitable for heat-stable antimicrobials. As a nonthermal technology, surface coating is more promising compared to molding or extrusion for manufacturing food packaging containing heat-sensitive antimicrobials. In addition, it also has advantages over direct incorporation to preserve the packaging materials' bulk properties (e.g., mechanical and physical properties) and minimize the amount of antimicrobials to reach sufficient efficacy. Herein, antimicrobial food packaging films achieved through surface coating is explored and discussed. The two components (i.e., film substrate and antimicrobials) consisting of the antimicrobial-coated films are reviewed as plastic/biopolymer films; and synthetic/naturally occurring antimicrobials. Furthermore, special emphasis is given to different coating technologies to deposit antimicrobials onto film substrate. Laboratory coating techniques (e.g., knife coating, bar coating, and spray coating) commonly applied in academic research are introduced briefly, and scalable coating methods (i.e., electrospinning/spraying, gravure roll coating, flexography coating) that have the potential to bring laboratory-developed antimicrobial-coated films to an industrial level are explained in detail. The migration profile, advantages/drawbacks of antimicrobial-coated films for food applications, and quantitative analyses of the reviewed antimicrobial-coated films from different aspects are also covered in this review. A conclusion is made with a discussion of the challenges that remain in bringing the production of antimicrobial-coated films to an industrial level.

Gravure printed Ag/conductive polymer electrodes and simulation of their electrical properties

In this paper, some practical issues related to the manufacturing, and design criteria related to the application in devices of a hybrid silver grid/poly (3,4-ethylenedioxythiophene) semi-transparent electrode are discussed. The electrodes are fabricated by gravure printing and screen printing. Experiments showed that defects in the printed grid due to imperfect ink transfer from the gravure roll to the substrate are detrimental to electrode performance. Various parameters like gravure cell design, printing speed, or particle size of the ink were investigated to minimize the fraction of defects and to obtain highly conductive grids. It will be demonstrated that overprinting of the lines is a feasible strategy to minimize the number of defects without noticeably broadening the lines. While a defect-free grid is prerequisite for such a hybrid device, for applications even stronger design criteria hold. That is addressed in the second part of the paper, where the electrical properties of the printed grids are simulated. With two exemplary device architectures, namely an organic light-emitting diode (OLED) and an organic photovoltaic cell, artificial load layers are integrated into the device structure, and potential maps are calculated. The examples show how simulations can be deployed to design and optimize grid electrodes for a specific application.

Continuous roll-to-roll fabrication of transparent cellulose nanocrystal (CNC) coatings with controlled anisotropy

Cellulose nanocrystals (CNCs) can impart desirable barrier properties in film packaging applications; however, commercial production of these materials is inhibited by the absence of a large-scale manufacturing process for producing CNC coatings. To fill this knowledge gap, a potential large-scale manufacturing process, roll-to-roll gravure printing, for cellulose nanocrystal coating on a flexible polyethylene terephthalate substrate has been described in this work. Processing parameters which control the coating structure and properties were examined. For a given gravure roll, gravure speed, substrate speed, and ink viscosity were determined to be the most important parameters that control the liquid transfer from the ink bath to the substrate, which determined the coating thickness (2–6 µm). After successful fabrication, CNC coating adhesion was investigated with a crosshatch adhesion test. The adhesive strength of the CNC coating was correlated with coating thickness, and the maximum coating strength was observed for the lowest coating thickness. Coatings were characterized using atomic force microscopy and UV–Vis spectroscopy. Finally, the crystalline domain arrangement of coatings was determined for coatings made from three different CNC concentrations, and the effect of viscosity on CNC alignment was explained by variation of shear rate, which was controlled by the micro-gravure rotation.

A predictive model for discrete cell gravure roll coating

A heterogeneous multiscale model for discrete cell gravure roll coating is presented along with experimental results for the purpose of model validation. The cell volume, generalized cell shape, and the gravure patterning are considered in the model which is based on a multiscale description of the flow in the coating bead. The inclusion of a web-to-roll contact term accounts for the special gravure case when the web-roll separation tends to zero. The results show how the coating bead responds to changes in operating conditions. These are presented as profile plots of the fluid properties and coating bead shape.

Moisture resistance coating of packaging paper from biobased silylated soybean oil

• A one component cure system derived from reactive silylated soybean oil provided good moisture resistant coatings to Kraft papers. • Successful coating of Kraft papers in the lab was followed by a pilot scale-up coating using industrial gravure roll coaters. • The effects of catalyst concentration and water content on the cure rate of the oil have been studied. • Critical properties including Cobb values, WVTR and contact angle were evaluated as well as the morphology of the coated surfaces using SEM. The moisture resistance of Kraft paper was greatly improved when it was coated with silylated soybean oil that was cured via silanol condensation. This moisture barrier coating was prepared from LowSat ® Soybean oil that was grafted with vinyltrimethoxysilane (VTMS) using a relatively simple process based on the “Ene reaction”. The viscosity of the resulting oil was unaffected by the silylation reaction and remained low (32 cPs). Thus, the paper coating process required no solvent, additional diluent or the need to emulsify the oil which provided a convenient one-component cure system. Dibutyltin dilaurate (DBTDL) was found to be an effective condensation catalyst and under optimal conditions complete cure was achieved in a short period of time. The cure rate was a function of the catalyst concentration, available water and the temperature. Initially, Kraft papers were coated with the silylated soybean oil in the lab and this process was followed by a pilot scale-up using a commercial gravure roll coater. Cobb values and water vapor transmission rate indicated the cured coating provided a good barrier coating. Scanning electron microscopy (SEM) images of the coated paper confirmed a uniform coating with good adhesion of the coating material to the paper.

Development of the High Heat Resistance CCS Using Waterborne New Binder

Introduction: As the demands for higher power density and higher energy density lithium ion batteries continue to grow, the accompanying safety concerns are issued as a critical challenge. The separators play a significant role in the thermal safety of lithium ion cells, which is critically important in applications such as electric vehicles, ESS (energy storage system), power tool. Commonly lithium ion battery separators are made from polyolefins, either polypropylene or polyethylene. These materials undergo catastrophic shrinkage above 120℃, which leads to shorting in cells that can cause the sparks that will ignite the electrolyte and flammable gasses. Recently, a variety of approaches for overcoming these technical drawbacks of polyolefin-based separators have been investigated. Among the many alternatives, the ceramic coat separator (CCS) has drawn a great attention because of their superiority in suppressing the heat shrinkage of separators. To improve the thermal stability of CCS, coating layer should be designed to ceramic rich and thermal resistance binder. And also, from the view point of environmental friendliness and cost-effectiveness, adopting the waterborne system is preferable. We will report the high heat resistance CCS using a new waterborne binder which was synthesized based on PAA. Experimental： 1) materials Bohemite (APYRAL AOH60(D50=0.9μm) and ACTILOX 200SM(D50=0.35μm), Nabaltech AG), PVP(Poly-vinyl pyrrolidone, K-90L , DKS Co., LTD.), PNVA (Poly-N-vinyl acetoamide, GE191-103, Showa denko K.K.) were used as received. Deionized (DI) water from a PURELITE-PRB-DV25 system (ORGANO Co., >15.0 MΩcm-1) was used. Developed binder (Poly-Acrylic acid based co-polymer, SRJ2 and SRJ3) were synthesized in-house. Micro-porous polyethylene separator (PE, 612SH, SK Innovation Co. Ltd., thickness = 12mm, gurley = 120〜125 sec/100ml) was used. 2) Preparation of ceramic coat separator(CCS) The coating slurry was prepared by mixing bohemite and binder (Any one of PVP, PNVA, SRJ2 and SRJ3) at a constant ratio in DI water (AOH60/200SM/Binder/water = 83/12/5/200 by weight). After ultrasonically dispersed for 5 min, the slurry was further subjected to vigorous mixing by passing through the shaft bead-mill machine (DYNO-MILL RESEACH LAB, Shinmaru Enterprises Co.) with a speed of 2000 rpm for 4 times. The coating slurry was applied onto one side of the pristine PE separator by automatic gravure roll coating machine (THANK METAL CO., LTD.). After the coating process, the prepared separator was dried under vacuum oven at 80℃ for 12h to remove the residual water in the coating layer. The coating layer thickness of each CCS were controlled in 3 μm respectively. 3) Characterization of the ceramic coating separators The heat shrinkage of the separators (original size: 5.0×5.0cm) was investigated by measuring their length changes of MD and TD direction using Eq.(1) after heat exposure in an oven at 150℃ for 60 min, where A1 indicate the MD or TD direction length of the samples after oven storage: Thermal shrinkage ratio (%) = (5.0-A1)/5.0×100 ・・・・・(1) The 180° peel test (as described in standard No. ISO 29862:2007 (JIS Z 0237:2009)) was used to measure the adhesive force between PE separator and coating layer. CCS fixed to a stainless steel plate was adhered the pressure-sensitive adhesive tape of width 2.4 cm (Nichiban Co. SellotapeTM No.405). Then, the 180° peel strength was measured by using peel tester (SHIMAZU EZ-S, Shimadzu Corp.). The air permeability (Gurley number) of CCS was determined by measuring the time for transmission of a 100cc air using a densometer (Inner cylinder weight (pressure) 567gf, transmitting surface hole diameter 28.6mm, permeation area 6.45 cm2, Toyo Seiki Co., Ltd.) 4) Result and discussion： The heat shrinkage, adhesion and permeability were investigated, and these data are summarized in Table 1. In first, the heat shrinkage of the CCS was evaluated. The developed CCS (SRJ2 and SRJ3 were used) were showed very low length change of MD and TD each directions compare to the reference CCS (PNVA and PVP were used). Next, the adhesion between the PE surface and ceramic coating layer was measured by 180° peel test. The peel strength of the developed CCS were higher than the references. From these results, the heat shrinkage was presumed to be improved when the coating layer was securely binding. The air permeability was also determined. There was no difference in gurley number compared to the reference CCS, so developed CCS were found to have a good air permeability. In poster session, the relationship of adhesion to the heat-shrinkage and the evaluation results of the battery performance of the cells which were used developed CCS will be discussed. Figure 1

Direct thickness measurement of doctor-bladed liquid film on gravure roll surface

We provide experimental evidence that the liquid film remaining on a doctor-bladed gravure roll surface significantly influences the liquid transfer from the engraved roll surface to a moving substrate. The local free surface profiles of doctor-bladed liquid films were directly measured on both tri-helical grooves and lands (the nongrooved areas between grooves) at different roll speeds and blade thicknesses. The liquid film covered the roll surface with a finite thickness on the lands below the critical capillary number. An increase in the capillary number led to a transition from a fully filled to a starved configuration, in which the liquid barely remained on the lands and partly filled the grooves with a concave surface profile. The liquid transfer ratio monotonically decreased with a decrease in the liquid thickness on the gravure roll surface, obeying a single curve for different blade thicknesses. Furthermore, the decrease in liquid thickness promoted a flow instability transition from unstable dripping though a stable state with a uniform surface to a cascade.

Visualization study of liquid surface stability for full reverse 3-roll coater with rigid gravure roll

Roll coating systems are widely used to coat a thin liquid layer on a moving substrate, and many publications discussing forward roll coating systems and reverse gap control coating systems are available. Recently, thinner and more uniform layers are required for use with the high-performance solutions involved. Moreover, high line speed coating is also required in order to reduce manufacturing costs. A reverse gravure roll system can coat a thin layer film at high line speed more easily than a flat roll coating system because only the liquid that enters the gravure cell is transferred to the next roll or substrate. However, the existence of the gravure cell complicates the flow between the rolls. To our knowledge, no systematic study in the literature has explored this condition in depth. In the present study, the flow between a reverse deformable roll and a solid stainless steel gravure roll is visualized in order to determine how the uniformity of coating in the high roll speed region is affected by operating parameters, that is, the speed ratio between the rolls and the properties of the coating liquid. The range for coating uniformity is compared with the case of a gap control system. The results show that the stable region can be extended by using the reverse gravure roll system.

은 잉크를 이용한 그라비아 오프셋의 전극인쇄에서 닥터링 공정의 영향

In this paper, we analyzed the effects of doctoring process on the patterns of Ag ink in gravure off-set printing. The parameters of doctoring process were the angle and the pressure, which was represented by the depth of blade movement to the gravure roll, of doctor blade to the surface of gravure roll, and the angle of patterns engraved on the gravure roll to the doctor blade moving direction. The proper parameters were extracted for the fine patterns and they were 15 mm for the pressure, <TEX>$60^{\circ}$</TEX> for the blade angle. And the angle of patterns with respect to the blade movement should be less than <TEX>$40^{\circ}$</TEX> for the best results. The gravure off-set printing with the above parameters was carried out to print gate electrodes and scan bus lines of OTFT-backplane for e-paper. The line width of <TEX>$50{\mu}m$</TEX> was successfully obtained. The thickness of electrodes was <TEX>$2.5{\mu}m$</TEX> and the surface roughness was <TEX>$0.65{\mu}m$</TEX> and the sheet resistance was <TEX>$15.8{\Omega}/{\Box}$</TEX>.

A two-scale model for discrete cell gravure roll coating

A two-dimensional model for predicting the fluid pickout and coated film thickness characteristics of a discrete cell direct gravure roll coater operating in reverse mode is derived. A novel multiscale approach is adopted for this purpose and the resulting equations solved numerically for inertia-less flow conditions. A system of stiff ordinary differential equations is found to be sufficient to capture the major gross flow features, while at the cell level the analysis is based on a finite element solution of the momentum and continuity equations. It represents the first such predictive model of its kind, with particular interest placed on the nature of both the pressure distribution and web-to-roll gap profile spanning the coating bead. The effect of key operating parameters, web-to-roll speed ratio, web-tension, wrap-angle, capillary number and cell-geometry, on the degree of fluid pickout from gravure cells and the coated film thickness is explored. Although an idealised model, the trends observed show qualitative agreement with existing experimental data collected on a small-scale gravure coating rig and point the way forward to the eventual formulation of a full three-dimensional predictive model of the process.

Tri-helical gravure roll coating

A mathematical model is presented and solved for the fluid flow within the coating bead of a tri-helical gravure roll coater, operating in reverse mode. A variety of rolls etched circumferentially with grooves of different cross-sectional shape and aligned at non-zero angles of pitch are investigated. Predictions of fluid pick-out from the grooves are compared with complementary experimental data. Quantitative agreement between the two is found to be very good, showing a linear increase in pickout as a function of web-to-roll speed ratio and groove depths up to the point at which streaking, as observed experimentally, occurs and beyond which the model is no longer valid. In regions of parameter space for which there is no experimental data available for comparison purposes the model predicts that: (i) fluid pick-out decreases with increasing groove depth while the film thickness tends to increase and (ii) an increase in groove aspect ratio leads to a reduction in both pick-out and film thickness for a given land width and groove cross-sectional shape.

Modelling the discrete-cell gravure roll coating process

New results for the process of discrete-cell, reverse mode gravure coating are presented, with the model considering a single cell and taking account of web thickness (stiffness) – an important feature neglected in previous analyses. Key results are: (i) confirmation that web tension, over the range encountered industrially, has negligible influence on web deformation; (ii) that web tension plays a secondary role to that of web stiffness. For parameters characteristic of those encountered in a typical coating operation the level of web deformation is found to be small, alluding to the importance of the two different length scales in the overall process – that at the cell (small) and coating bead (large) level.

A theoretical and experimental investigation of tri-helical gravure roll coating

Tri-helical, gravure roll coating, operated in reverse mode, is investigated via a complementary experimental and theoretical approach. Flow visualisation reveals the underlying flow structure within the roll-to-web transfer region and highlights when loss of stability, that is a propensity to streaking, occurs. The latter is found to be influenced in turn by the depth of the tri-helical grooves and the capillary number. Experiments show that as the web-to-roll speed ratio is increased, so too is fluid pick-out from the grooves, although the coated film thickness may decrease. Extensive data are provided for coated film thickness, pick-out and meniscus location as a function of speed ratio, for different operating parameters. A key feature of the present investigation is the formulation of a novel complementary mathematical model for the process. The base flow within the grooves is modelled as a Poisson equation in conjunction with simplified approximations for the attendant free-surface boundary conditions. The resultant equation set is written in terms of finite Fourier sine transforms and unique solutions obtained by varying the flux until a consistent pressure distribution throughout the coating bead is obtained. Results from the model are found to be in generally good agreement with their experimental counter-parts, and are seen to predict and capture all the major features of the process over the operating range explored.

A Parametric Study of Offset Gravure Coating

A combined theoretical and experimental investigation of an offset gravure coater with a subsequent roll-to-web fluid transfer (operated at web-to-roll speed ratio, S, greater than one) is presented. Under typical operating conditions at the offset nip (applicator and gravure roll contra-rotating with the same peripheral speed) the magnitude of the speed has little effect on the metered film thickness. The fractional pick-out of fluid from different gravure cell patterns, on the other hand, is shown to be dependent on a complex set of parameters, one of which is the cell volume. An experimental study of the roll-to-web transfer region confirms that the whole of the metered film is transferred from the applicator roll to the web at S > 1 and that at high S the transfer of fluid becomes unstable with a resultant loss of coat quality, leading to a corresponding lower limit of the film thickness for the production of uniform coatings. Lubrication theory is employed to (i) model the associated equilibrium flow and (ii) to perform a stability analysis and map out operability plots. In particular, it is found that as the speed of the applicator roll is increased, the critical speed ratio for the onset of instability decreases.

Quantitation of Ink Transferred During Pharmaceutical Printing Operations Using Inductively Coupled Plasma Atomic Emission Spectroscopy

AbstractThe identification of solid dosage forms is often achieved through printing with a non-toxic ink. Due to product purity requirements, a method to quantify the amount of ink applied to tablets and capsules is of interest to the pharmaceutical industry.The following presentation investigated the use of inductively coupled plasma atomic emission spectroscopy (ICP-AES) as a direct method of quantifying the amount of ink on a tablet. Because the ink used contained an iron oxide pigment of known composition, quantitation of the iron content could be used to measure the amount of ink transferred to the tablet.The quantitative results obtained using ICP-AES were in agreement with calculated values for the volume of ink in the gravure roll. Tablets exposed to “double printing” were easily detected by the ICP-AES method.

Direct gravure roll coating

Direct gravure roll coating has been studied experimentally over a wide range of operating conditions using an infrared gauge to measure the thickness of film transferred onto a substrate. For the three gravure geometries used, the dimensionless film thickness (film thickness/cell volume/cell wetted area) first increases with increasing Reynolds number (substrate speed × descriptive cell size × density/viscosity) but reaches rapidly a constant value of about 1/3. Changes in the speed ratio (substrate/roller) from 0.5 to 2.0 do not affect this limiting value. The results also show the ability of trihelical and pyramidal cell configurations to empty better at low Reynolds number than quadrangular geometries. This work provides a comprehensive set of experimental data describing this important coating operation, usually carried out at large speeds ( > 2 m/s) and with low-viscosity liquids, i.e. large Re.