Web Tension Research Articles

Roll-to-roll thin film coating on fluoropolymer webs – Status, challenges and applications

Thin film deposition on fluoropolymer webs – both in vacuum and at atmospheric pressure – faces several critical challenges such as poor mechanical and thermo-mechanical properties – especially low dimensional stability and low elastic modulus, high and textured surface roughness and low adhesion of thin films.This paper discusses critical process parameters in roll-to-roll processing for both vacuum processes and wet coating processes with respect to the unique properties of fluoropolymer webs. Reactively sputtered oxide layers as well as wet coated ORMOCER® layers are deposited on ETFE, PVDF and ECTFE webs to form single- and multi-layer permeation barrier systems. The influence of relevant process parameters on the layer adhesion and permeation barrier performance is reviewed. Permeation barrier coatings have been selected as main application for this study, because they are very sensitive to substrate surface irregularities and mechanical damage due to low adhesion, high strain or roll-to-roll processing issues and therefore are a good measure for the quality of the coating on the substrate.Both the wet coated ORMOCER® layers and reactively sputtered zinc-tin oxide (ZTO) layers show surprisingly good adhesion on both ETFE and PVDF surfaces. Both ZTO and – with adhesion promotion treatment – also aluminum oxide (Al2O3) layers have the potential for low water transmission rates (WVTR) below 5·10−2g/(m2d) at 38°C/90% r.h. on these substrates. Further reduction of the WVTR is demonstrated with a combination of wet coated ORMOCER® layers and sputtered ZTO layers yielding a WVTR of 1·10−3g/(m2d) at 38°C/90% r.h. These values were achieved using adapted process parameters and layer stack designs such as reduced web tension and lower layer thicknesses. The results shown in this paper demonstrate the potential of coated fluoropolymer webs for functionalization of membrane roofs and façades with flexible thin film solar cells; thermal insulation and solar control functionality; flexible thin film electroluminescent and OLED lighting panels as well as electrochromic devices.

The influence of strain rate and pulp properties on the stress relaxation of wet paper — modeling of relaxation

The time-dependent stress (tension) relaxation behavior of wet paper plays a key role in web transfer from the press to the dryer section of a paper machine. In this study, three linear viscoelastic models were used to predict the short time range tension relaxation of wet paper. Over longer time periods, all three models gave relaxation moduli that were apparently linear on a logarithmic timeline. However, the results showed that the tension relaxation of wet paper had more than one characteristic time constant, meaning that the initial tension relaxation phase had a different constant than the later phase or phases. In practical applications, the most relevant time range for runnability of the wet paper web is from milliseconds to a few seconds. The obtained results suggest that the strain rate and initial tension of the relaxation dictate the shape of the tension relaxation curve of wet paper: the higher the strain rate, the greater the tension loss during the first second of relaxation. The tension relaxation behavior of wet paper did not generally depend on pulp type, refining level of pulp, or solids content. However, there can be significant differences between furnishes and solids content in the amount of draw that leads to a sufficient web tension. The results indicated that the tension relaxation behavior of wet paper may be based on a general viscoelastic mechanism that is independent of fiber network properties but depends on the fiber wall material. The findings suggest that the redistribution mechanism of stresses in the wet fiber network has a high level of regularity. The Prony series was capable of predicting tension relaxation behavior of wet paper over a wide time range. Therefore, it can be a very useful simulation tool not only for wet webs, but for any viscoelastic material that shows stress (tension) relaxation.

Tuning the instrument: sonic properties in the spider's web.

Spider orb webs are multifunctional, acting to absorb prey impact energy and transmit vibratory information to the spider. This paper explores the links between silk material properties, propagation of vibrations within webs and the ability of the spider to control and balance web function. Combining experimental and modelling approaches, we contrast transverse and longitudinal wave propagation in the web. It emerged that both transverse and longitudinal wave amplitude in the web can be adjusted through changes in web tension and dragline silk stiffness, i.e. properties that can be controlled by the spider. In particular, we propose that dragline silk supercontraction may have evolved as a control mechanism for these multifunctional fibres. The various degrees of active influence on web engineering reveals the extraordinary ability of spiders to shape the physical properties of their self-made materials and architectures to affect biological functionality, balancing trade-offs between structural and sensory functions.

Effect of some printing nip variables on web tension

Good runnability of paper web is an important factor for improving performance of printing process. Printing nips cause web tension variations which are known to affect web runnability. However, ra ...

Spider web and silk performance landscapes across nutrient space.

Predators have been shown to alter their foraging as a regulatory response to recent feeding history, but it remains unknown whether trap building predators modulate their traps similarly as a regulatory strategy. Here we fed the orb web spider Nephila pilipes either live crickets, dead crickets with webs stimulated by flies, or dead crickets without web stimulation, over 21 days to enforce spiders to differentially extract nutrients from a single prey source. In addition to the nutrients extracted we measured web architectures, silk tensile properties, silk amino acid compositions, and web tension after each feeding round. We then plotted web and silk “performance landscapes” across nutrient space. The landscapes had multiple peaks and troughs for each web and silk performance parameter. The findings suggest that N. pilipes plastically adjusts the chemical and physical properties of their web and silk in accordance with its nutritional history. Our study expands the application of the geometric framework foraging model to include a type of predatory trap. Whether it can be applied to other predatory traps requires further testing.

Model-based feedforward register control of roll-to-roll web printing systems

Roll-to-roll (R2R) printing press provides a continuous printing process to print the multi-color patterns onto a web. To correctly print patterns on webs without the register error, it is necessary to regulate the web tension and transport velocity. In this paper, a mathematical model is built for R2R web printing system, and a model-based feedforward PD (MFPD) control method is proposed to reduce the effects of interaction in adjacent print units whose print cylinders are driven by electrical line shafts and is compared with other control methods. The proposed control method is applied to an industrial 7-color gravure printing register system. The register error can be controlled in the range of ±0.1mm at a steady high speed, which meets the requirement of modern industrial application.

Roll-to-roll infrared and hot-air sintering of gravure-printed Ag layer based on in situ tension measuring and analysis

The sintering energy was quantified and evaluated based on theoretical and experimental calculations. Moreover, the effect of the sintering energy on the web tension was simultaneously considered.

유연 기판을 이용한 PLC소자 제작을 위한 롤투롤 공정 연구

Demand for a low-cost, high-throughput, and high-resolution patterning method for fabricating devices continues to increase. The roll-to-roll (R2R) imprint lithography technique has received a great deal of attention as a means of fabricating next-generation devices. In this paper, we propose a fabrication method for polymeric planar lightwave circuit (PLC) devices that uses R2R imprint lithography. The proposed technique uses an elastomeric polydimethylsiloxane (PDMS) mold. A Si wafer with micro patterns is used as the Si master. The PDMS mold is then replicated from the Si master. By applying a precise web tension and at a given web speed, we fabricated a micro-patterned PLC device. The insertion losses were 4.0 dB for a optical splitter. As such, the proposed method of fabricating a PLC device by the R2R process was shown to be an effective solution.

Fast stabilization of web tension in drying process of roll-to-roll printing equipment for printed electronics

In roll-to-roll printing for the fabrication of flexible printed electronic devices, it is important to minimize the tension variation of the web because the tension variation strongly affects register errors and the quality of the printed devices. Moreover, the high drying temperature required to sinter functional inks causes shrinkage of the plastic web, which yields severe register errors. After the drying process, the web tension should increase, elongating the web, which contracts because of the drying process. Once the shrunken web recovers its original length by elongation, the tension stabilizes at a higher value. This steady-state stabilization of the web tension requires a long time, corresponding to the time constant between two printing units, which could increase the production time. In this study, a faststabilization method for web tension in the drying process is proposed to reduce the time required for the stabilization of the tension. For the fast stabilization, a dancer system is introduced, and the variation in the tension is used as a reference value for the tension stabilization. The proposed method is verified by simulations and experiments using actual roll-to-roll printing equipment.

Scalability of carbon-nanotube-based thin film transistors for flexible electronic devices manufactured using an all roll-to-roll gravure printing system.

To demonstrate that roll-to-roll (R2R) gravure printing is a suitable advanced manufacturing method for flexible thin film transistor (TFT)-based electronic circuits, three different nanomaterial-based inks (silver nanoparticles, BaTiO3 nanoparticles and single-walled carbon nanotubes (SWNTs)) were selected and optimized to enable the realization of fully printed SWNT-based TFTs (SWNT-TFTs) on 150-m-long rolls of 0.25-m-wide poly(ethylene terephthalate) (PET). SWNT-TFTs with 5 different channel lengths, namely, 30, 80, 130, 180, and 230 μm, were fabricated using a printing speed of 8 m/min. These SWNT-TFTs were characterized, and the obtained electrical parameters were related to major mechanical factors such as web tension, registration accuracy, impression roll pressure and printing speed to determine whether these mechanical factors were the sources of the observed device-to-device variations. By utilizing the electrical parameters from the SWNT-TFTs, a Monte Carlo simulation for a 1-bit adder circuit, as a reference, was conducted to demonstrate that functional circuits with reasonable complexity can indeed be manufactured using R2R gravure printing. The simulation results suggest that circuits with complexity, similar to the full adder circuit, can be printed with a 76% circuit yield if threshold voltage (Vth) variations of less than 30% can be maintained.

A semi-continuous Roll-to-Roll (R2R) electrohydrodynamic jet printing system

This article presents the initial integration of a new and novel additive manufacturing process with a web-based transport of a flexible substrate. The manufacturing process is the Electro-hydrodynamic Jet (E-Jet) printing process and the transport is a Roll-to-Roll (R2R) system. E-Jet printing affords a wide array of materials to be deposited at very fine resolutions, on the order of microns. The combination of E-Jet printing and R2R enables fabrication of flexible electronics and other novel flexible systems such as bio-sensors and optics. The design of a custom R2R system is presented, including the mechatronic integration of hardware and software architectures. A Norm-Optimal Iterative Learning Controller is coupled with a Linear Quadratic controller to control web motion and tension, both of which are important for accurate E-Jet printing. Results are presented demonstrating the ability to accurately position the web for printing. Subsequently, printing results are demonstrated for both conductive and non-conductive inks. The results demonstrate the clear feasibility for fine scale printing, suitable for flexible electronics, on a continuous R2R process.

Forces generated by web peeling for printing and coating applications

The tensile forces that act on a web in printing and coating applications are important in situations where the web may delaminate or break. A model is proposed that uses lubrication expressions to describe the fluid flow in the thin fluid layer combined with a force balance on the web to describe the peeling event. A novel experimental method is described that measures the forces to separate a tensioned web from a surface with a viscous fluid between them. Forces are measured for various parameters such as viscosity, web tension, separation velocity, fluid volume, and fluid geometry. Dimensionless expressions are developed to correlate experimental results. Web deformation and forces are found to be influenced by a thin air film between web and bottom plate. These initial forces are found to be larger than later peeling forces unless something is done to allow air to flow between the web and the lower plate. Low web tension and stiffness are found to reduce the maximum force. The model predicts the measured forces within the expected accuracies. However, the model overpredicts the forces for large patch areas and thin films; this is likely caused by a cavitation mechanism or be three-dimensional flows for these large patch areas. Simplified expressions are generated to correlate the peeling forces for a wide range of experimental parameters.

Output Regulation of Nonlinear Systems With Application to Roll-to-Roll Manufacturing Systems

This paper deals with the problem of synthesizing feedforward control to aid the regulation of output of a nonlinear system in the presence of partially known exogenous inputs. The problem appears in many engineering applications including Roll-to-Roll (R2R) manufacturing systems. Currently known methods for this problem either require the solution of a constrained partial differential equation or the preview information of the signal to be tracked. The novelty of this paper lies in synthesizing feedforward control as the solution of a system of differential-algebraic equations, which is considerably less complex and suitable for practical implementation. In this paper, we consider the problem of regulating the output while rejecting the disturbances and apply it to R2R manufacturing systems. The problem of tracking reference signals can also be handled with the suggested technique. We assume that the disturbance signal is the output of a known exogenous system with unknown initial conditions. A parameter identification scheme to estimate the unknown initial conditions is developed. The proposed technique is successfully applied to control of web tension in a large R2R machine which mimics most of the features of industrial R2R machines and contains real-time hardware and software that is used in industrial practice. Extensive experiments were conducted to evaluate the proposed scheme for web tension control under various experimental conditions, including different web speeds and materials. We will present and discuss the representative experimental results with the proposed technique and provide a comparison with an industrial PI control scheme to highlight the benefits of using the proposed scheme.

Modeling and control of a rotating turret winder used in roll-to-roll manufacturing

In this paper, winding issues in an industrial R2R printing press using a rotating turret winder are investigated by utilizing a new mathematical model and data are collected during production runs. Production data and simulation results from the developed model are analyzed to identify the causes for tension disturbances that affect winding quality. Model simulations are conducted by incorporating production data as inputs to the model to gather insights into the effect of dynamic behavior of the rotating turret winder on winding web tension. The developed model captures the various dynamic events associated with the roll change operation with a rotating turret winder. Measured data are provided to support the results of this work in improving winding tension regulation during the roll change operation. The new model together with the analysis and recommendations provides a good framework for the development of model-based tension control schemes that can further improve winding tension regulation performance, and thereby improves wound roll quality.

ESTIMASI PARAMETER MODEL FUNGSI ALIH ORDE 4 PADA ROL PENGUMPAN SISTEM TRANSPORTASI WEB MATERIAL BERBASIS FORGETTING FACTOR DENGAN MATLAB 7.04

Web Materials Transport system appears in variety of industrial applications such as paper and plastics industries. The main part of web transport system is unwind roll section. The dynamic model for unwind roll section is derived from the Newton’s laws, the Hooke’s law and conservations of mass principle. This model gives a relationship between web tension output and torque input. Futhermore this relationship is expressed in transfer function form. This transfer function contains a phisical time-varying parameter namely the radius of the unwind roll. Usually before designing control system, a model parameter estimation is needed. This on-line estimation problem is investigated in this paper using RLS (recursive least square) method with forgetting factor. The estimation needs data in the form of discrete and the initial value covariance matrix diagonal (P). This research uses discrete ZOH method with sampling period T = 0.4 sec; 0.35 sec; 0.3 sec; 0.25 sec; 0.2 sec for convert transfer function from s-domain to z-domain. Parameters estimation with mean square error (MSE) in the range 2x10-5 ≤ MSE ≤ 3x10-5 are obtained using initial value covariance matrix diagonal P in the range 102 ≤ P ≤ 108 using forgetting factor 0.95.

Positional accuracy of micropatterns in the roll-to-roll imprinting process using a wrapped roll mold

Various micropatterns in flexible devices can be fabricated using the roll-to-roll (R2R) imprinting process, wherein a raw flexible plastic film is released from a roller and subjected to several patterning processes such as imprint lithography. In case a thin-film-transistor liquid-crystal display (TFT-LCD) is formed on the flexible film, overlay accuracy becomes the most important factor in the patterning process. To achieve positional accuracy, the process parameters that affect dimensional changes should be analyzed. In our system, the roll mold was fabricated by wrapping a thin film sheet to the roller. During the process, the substrate was deformed by web tension and bent by overall system architecture. Thus, web tension, misalignment angle, mold thickness, and substrate bending effects were regarded as the main parameters, which were analyzed and modeled into mathematical formulas. Positional errors and their tolerances were estimated using the formulas, and process parameters were designed to compensate for each error. Finally, the color filters in the flexible TFT-LCD display were manufactured using R2R imprinting and ink-jet printing. Dimensional error can be minimized to approximately ±15 μm for the entire area of 200 mm × 150 mm.

Design and implementation of adaptive PI control schemes for web tension control in roll-to-roll (R2R) manufacturing

In this paper, two adaptive Proportional-Integral (PI) control schemes are designed and discussed for control of web tension in Roll-to-Roll (R2R) manufacturing systems. R2R systems are used to transport continuous materials (called webs) on rollers from the unwind roll to the rewind roll. Maintaining web tension at the desired value is critical to many R2R processes such as printing, coating, lamination, etc. Existing fixed gain PI tension control schemes currently used in industrial practice require extensive tuning and do not provide the desired performance for changing operating conditions and material properties. The first adaptive PI scheme utilizes the model reference approach where the controller gains are estimated based on matching of the actual closed-loop tension control systems with an appropriately chosen reference model. The second adaptive PI scheme utilizes the indirect adaptive control approach together with relay feedback technique to automatically initialize the adaptive PI gains. These adaptive tension control schemes can be implemented on any R2R manufacturing system. The key features of the two adaptive schemes is that their designs are simple for practicing engineers, easy to implement in real-time, and automate the tuning process. Extensive experiments are conducted on a large experimental R2R machine which mimics many features of an industrial R2R machine. These experiments include trials with two different polymer webs and a variety of operating conditions. Implementation guidelines are provided for both adaptive schemes. Experimental results comparing the two adaptive schemes and a fixed gain PI tension control scheme used in industrial practice are provided and discussed.

System for Automatic Web Guiding for Roll-to-Roll Machine Working in a Start-Stop Mode

Web guiding used in roll-to-roll material processing machinery is connected with a number of issues including the maintenance of the web tension, the precision of the lateral web displacement, the accuracy of transport positioning of the web, and the selection of web transport velocity. The article presents the precision of the lateral web displacement issue during the start-stop work mode of the web transport. A model of a system for automatic web guiding is shown. The requirements of the lateral web guiding for transporting material over rollers in a processing machine working in a start-stop mode are presented. The control system is discussed, particularly its hardware structure and behaviour. The obtained functionality of the control system enables its application in roll-to-roll material processing machines, working either in the start-stop mode or continuously.

Modeling of Temperature Distribution in Moving Webs in Roll-to-Roll Manufacturing

A heat transfer model that can predict the temperature distribution in moving flexible composite materials (webs) for various heating/cooling conditions is developed in this paper. Heat transfer processes are widely employed in roll-to-roll (R2R) machines that are used to perform processing operations, such as printing, coating, embossing, and lamination, on a moving flexible material. The goal is to efficiently transport the webs over heating/cooling rollers and ovens within such processes. One of the key controlled variables in R2R transport is web tension. When webs are heated or cooled during transport, the temperature distribution in the web causes changes in the mechanical and physical material properties and induces thermal strain. Tension behavior is affected by these changes and thermal strain. To determine thermal strain and material property changes, one requires the distribution of temperature in moving webs. A multilayer heat transfer model for composite webs is developed in this paper. Based on this model, temperature distribution in the moving web is obtained for the web transported on a heat transfer roller and in a web span between two adjacent rollers. Boundary conditions that reflect many types of heating/cooling of webs are considered and discussed. Thermal contact resistance between the moving web and heat transfer roller surfaces is considered in the derivation of the heat transfer model. Model simulations are conducted for a section of a production R2R coating and fusion process line, and temperature data from these simulations are compared with measured data obtained at key locations within the process line. In addition to determining thermal strain in moving webs, the model is valuable in the design of heating/cooling sources required to obtain a certain desired temperature at a specific location within the process line. Further, the model can be used in determining temperature dependent parameters and the selection of operating conditions such as web speed.

Effect of static electricity on static friction force between plastic film and steel roller

To establish the new technology named Roll-to-Roll Printed Electronics, which can be applied to manufacture the high functional thin film based devices such as flexible displays, batteries, and electric skins, it is needed to combine the roll-to-roll transportation system and coating technology effectively. For that purpose, one of important factors to be considered is the effect of electrostatic force on the friction characteristics between the film and roller surface. In this paper, the static friction between the plastic film (polyethylene terephthalate film) and steel roller was measured to clarify the effect of electrostatic force on the friction characteristics. The static friction was measured by pulley method while changing the film thickness, web tension, and relative humidity of ambient air. In the process it was found that both the decrease in the film thickness and increase in relative humidity of the air have an effect of an increase in the static friction coefficient in the system. Moreover, the tendency can be pronounced with the decrease in the web tension.