Effect of electrostatic assist and gravure process parameters on voids and dot skips reduction in shrink PVC film

Gravure is the most popular process used to print on shrink films for larger volume runs and high-quality reproduction. Polyvinyl chloride (PVC) holds the major share in shrink application. However, print defects such as voids and dot skips are the major concern while printing on shrink PVC film. The presence of these defects degrades the print quality and causes print rejections. The electrostatic assist (ESA) in gravure is designed to eliminate dot skips; however, the effect of ESA parameters such as air gap and voltage on print defects needs to be explored in depth. Thus, this study aims to minimize print defects by optimization of gravure process parameters. The study investigates the effect of process parameters such as line screen, air gap (distance between charge bar and impression roller), viscosity, voltage and speed on voids and dot skips. A general full factorial was designed and statistical model was developed to determine the influence of each process parameter on defect minimization. The results showed the significance of all the process parameters in reduction of dot skips and void area. The improved ink transfer with ESA resulted in elimination of dot skips and minimization of void area by 96%.     

Regression modeling of solid mottle in coated papers

The print industry has observed an exponential growth over the last decade. A shift from plastics to paper has been observed in the packaging industry due to its sustainability. The gravure process dominates the packaging industry because of long runs and high print precision. This work focuses on the effect of gravure process parameters on print mottle for 50 GSM (gram/square meters) and 65 GSM (gram/square meters) C1S (coated-one-side) paper. Solid mottle refers to unevenness in print density and occurs due to variations in substrate, ink, and process parameters degrading the print quality, thereby resulting in printed wastage and loss to an organization. The intricate mechanism of ink transfer in the gravure process needs to be studied in depth so as to deliver higher yield and lower print waste. The Stochastic Frequency Distribution Analysis (SFDA) algorithm was used to measure the print mottle. The design of experiments (DOE) was run for gravure process parameters such as line screen, viscosity, press speed, electrostatic assist (ESA) voltage, and air gap (distance between impression roller and charge bar) at varying levels. The experimental data were analyzed through analysis of variance (ANOVA), main plot, and interaction plot. The analysis revealed significance of all process parameters for minimization of solid mottle. The optimized settings showed reduction in solid mottle by 64.68% and 67.78% for 50 GSM and 65 GSM, respectively. A stepwise regression model was developed to predict the print mottle that showed correlation coefficient of 0.912 and 0.938 for 50 GSM and 65 GSM C1S papers. This work could serve as a framework to maintain operating levels of gravure process for minimization of solid mottle.     

Effect of gravure process variables on void area in shrink film

The gravure print quality on shrink film depends on process parameters and is fairly gaged by minimum print defects such as voids. The visibility of these defects is visually disturbing and could result in product rejection. This article investigates the effect of process parameters such as viscosity, speed, hardness, and line screen frequency on ink transfer from recess gravure cells and hence on print voids in an attempt to minimize them. A general full factorial design with the abovementioned four independent variables was analyzed by variance, main, and interaction effects. The results revealed line screen, hardness, and ink viscosity as the most influential factors in minimizing the defect. A regression model was developed to predict void area. The model was validated by conducting an additional 11 runs on the press. The predicted values from the model were in close agreement with the press results. The results showed a commendable decrease in the void area by 65%.     

A comparative study on roll-to-roll gravure printing on PET and BOPP webs with aqueous ink

Ink transfer and printing characteristics in high-speed gravure printing were investigated on poly(ethylene terephthalate) (PET) and biaxial-oriented polypropylene (BOPP) substrates employing a pilot-scale gravure printing machine (maximum speed: 500 m min⁻¹). The flexible substrates were printed in an aqueous ink diluted with ethanol under various machine factors such as printing speed, nip force, and groove size.     

Gravure offset printing of polymer inks for conductors

A gravure offset printing process has been developed for Ag-filled polymer conductor ink. Pad printing and roller type printing have been used. Curing and electrical properties have been studied. A roller type of gravure offset printing has been used to evaluate the printing process and pad printing to print on the non-planar substrates. Based on differential scanning calorimetry (DSC) and resistivity measurements during ink curing, it was found that the ink had an optimum curing temperature of 140 °C. Square resistance of 300 and 150 μm wide lines can be as low as 20 and 28 mΩ/sq., respectively, for 7–8.5 μm thick line. The minimum line width was 70 μm. This minimum line width can be reduced with different ink solvents, but in this case the line thickness suffers and the square resistance increases, respectively.     

Effects on print quality of varying acrylic binder types in water-based flexographic ink formulations

The ink industry is one of the world's largest markets due to the increasing demand for printing inks for the packaging industry. Flexography printing is a well-known promising technology for large-area printing due to its high printing speed and roll-to-roll capability to print economically on a variety of surfaces and is used in nearly in all areas of packaging printing. Water-based inks are considered non-toxic, odourless, and more environmentally friendly options compared to solvent-based inks. Therefore, in this article, the goal was to develop new water-based ink formulation with different acrylic binders for flexographic printing on commercial solid bleached sulphate (SBS) board. Five inks were formulated with four different acrylic binders and compared to a commercially available ink to study their performance. The developed inks were investigated with regard to their print qualities and print characteristics. It was found that the binder type influenced some print quality while the effect was not significant for others. Using flexography printed cyan inks, the ink formulated with the highest molecular weight had the lowest print density and the largest tonal value increase (TVI) observed between 40 and 60 tone values. The same ink had the largest mottle values and variation in topography. For values of print contrast and delta gloss at 75°, although differences were observed between average values, data had inconclusive variation and spread around averages, where no conclusive trends or effects of acrylic binder type on these response factors were observed. Print chroma and dot roundness results were equally close for all printed samples.     

Methods for the evaluation of fine-line offset gravure printing inks for ceramics

The printing of ceramic substrates by offset gravure is well established industrially and is a potentially viable method for printing circuitry. Modified inks are required to be able to print fine lines at high resolution with minimal displacement and distortion. In the present study a statistical assessment of the role of the components of the ink binder has been undertaken, the inks being evaluated by printing tests and in terms of their rheology and cohesion. The results have been examined using a factor design program and the best-fit multivariate model established in order to describe the response to each factor. Based on the models, it was possible to increase the internal cohesion of the inks which gave a decrease in the rheological phase angle and an increase in print mass. It was found practicable to print lines as fine as 9 mm wide and dots as small as 20 mm diameter on ceramic substrates.     

Visualization and simulation of the transfer process of index‐matched silica microparticle inks for gravure printing

A combined experimental and computational study of the transfer of transparent index‐matched silica‐particle inks between two flat plates is presented for gravure printing applications. The influence of printing speed and initial ink droplet size on the ability to accurately transfer ink during the printing process is explored systematically. Smooth interface volume of fluid simulations show the same trends as the ink transfer observed in experiments over a wide range of printing speeds and for inks having different silica particle loadings. Our calculations indicate that for ink droplets with characteristic dimensions in the vicinity of 10 μm, which are of particular interest for gravure printing applications, ink transfer improves significantly due to the diminishing effect of gravity, and the increased importance of capillary forces at small length scales. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1419–1429, 2017     

Optimizing inkjet printing process to fabricate thick ceramic coatings

This article describes the use of Taguchi optimization and ANOVA techniques on inkjet printing process to determine optimal parameters for fabrication of thick ceramic coatings over glass substrates. Stable nanoparticle suspensions are synthesized through high energy milling of precursor powders with adequate quantities of binder and suspending solvent. Most often, inkjet printing process is being used for developing fine and thin layers (<10 µm). However, an attempt is made to fabricate thick ceramic films by varying only IJP process parameters and without multiple layer deposition, thereby reducing efforts in ink synthesis and processing time of coated substrates. Three parameters of IJP were varied for developing a model that was used for precisely predicting the printed layer thickness under varying process parameters. ANOVA technique showed that open time interval in combination with nano particle concentration in the ink could potentially lead to thick coatings. The higher volume % of solvent in the diluted suspension ink under the influence of substrate heating contributed significantly to coffee stain effect with irregular surface coatings. However, increasing the concentration of nanoparticles in the diluted ink resulted in substantial improvement in thickness of the layer with simultaneous control of coating defects.     

Comparative study of different methods for the assessment of print mottle

Print mottle is a print defect that occurs more or less on prints and has a negative influence on the evenness in print. Several methods to assess print mottle have been proposed. In this article, we analyzed three methods for print mottle evaluation: Histogram Mottle Macro, Gray level co‐occurrence matrix (GLCM) and M‐score. The aim was to compare them and to determine their relation to perceived non‐uniformity obtained by visual assessment. In the experimental part, we printed four different substrates with different optical properties with digital printing machine based on electrophotographic process. The surface of papers was characterized by measuring optical paper properties. The results obtained in this study suggest that GLCM method should be used for print mottle assessment. This method has the strongest correlation with the visual experience of print mottle. © 2015 Wiley Periodicals, Inc. Col Res Appl, 41, 493–499, 2016     

A comparative study of the interaction between the dried ink layer and PLA film used for packaging purposes

This research aims at comparing the interactions between the water-based printing ink and polylactide (PLA) printing base. As a reference base, a polyethylene terephthalate (PET) film was chosen. The wettability of both films was investigated. The Owens–Wendt method was applied to calculate the surface free energy (SFE). The values of SFE and its polar and dispersive components were compared with the surface tension (ST) of the ink and the polar and dispersive components of ST. The wetting envelopes of the investigated PLA and PET films are presented. Finally, the bonding strength between the dried ink layer and the printing base was analyzed. The PET film exhibited higher values of SFE. However, the bonding strength between the dried ink layer and the printing base was higher for PLA films. Our results reveal that PLA films can be an excellent choice as packaging materials, with comparable or even better print quality than conventional fossil-based plastics.     

Artificial neural network approach to predict the lightfastness of gravure prints on the plastic film

The lightfastness of prints is an important property for assessing their print stability. The objective of this study is to determine the lightfastness rate of printed films due to long-time exposure by applying artificial neural network (ANN). Package printing is gradually becoming extremely important because its color and quality increase the marketability of the product. Sometimes it has been observed that the initial print quality is bright and attractive. However, with time, it degrades the exposure of light, water, or other external parameters. Thus, it reduces the marketability if its color degrades before its expiration. Therefore, the lightfastness of prints may be considered for the authenticity or validity of the product. The plastic film substrate is chosen because it has extensive usage in food and other packaging industries. The samples printed in the gravure process are exposed in artificial lightfastness tester BGD 865/A Bench Xenon Test Chamber (B-SUN) for assessing the lightfastness of prints. The ocean optics spectroradiometer (DH2000BAL) is used to measure the spectrophotometric properties of prints before and after exposure. The obtained reflectance spectra are modeled by applying an ANN technique that is proposed to predict the fading rate of the printed film. The optimal model gives excellent prediction with the minimum mean square error for each color and a correlation coefficient of 0.80 to 0.99. ANN model and a Regression model (assuming first-order kinetic equation) are compared for predicting the lightfastness properties of prints. The results show that the ANN has better prediction capability than the regression model.     

Analysis of Gravure Ink: Its Adhesion Strength and Thermo-elastic Behavior

In the packaging industry, the use of gravure ink has a major influence on the product contained in the package in terms of protection and communication. Another purpose of the film of gravure ink is to prevent heat transfer either from outside or from inside of the container or pack. However, the adherent film is not always long lasting. In this work, the mechanical and thermal properties of gravure ink films were measured. The mechanical properties measured, included the density, modulus of elasticity and the Poisson's ratio. The thermal measurements were confined to thermal conductivity, specific heat, heat diffusivity and the coefficient of linear expansion. If taken into account, these findings may be helpful in applying these films for the better protection of packaged products and in improving the adhesion of the films to different metallic and non-metallic substrates.     

Ink-lift-off during offset printing: a novel mechanism behind ink–paper coating adhesion failure

This paper reports on a special pilot coating and industrial printing trial designed to gain fundamental knowledge on ink adhesion failure on coated papers. We found that ink adhesion failure resulted in white spots without ink on the paper, referred to as uncovered areas and these spots gave print mottle problems. The white spots were due to two fundamentally different types of ink adhesion failure. One is the well-known ink rejection, which simply means that ink is not transferred to the surface. The other is a new type of ink adhesion failure, confirming a previous hypothesis suggested from laboratory observations. We refer to this as ink-lift-off adhesion failure, meaning that ink initially deposited on the paper surface becomes lifted off from the surface in a subsequent print unit. Adhesion failure by this mechanism was seen to occur more frequently than failure due to the well-known ink rejection.     

Solvent-Cast 3D Printing of Biodegradable Polymer Scaffolds

3D printing is a popular fabrication technique because of its ability to produce complex architectures. Melt-based 3D printing is widely used for thermoplastic polymers like poly(caprolactone) (PCL), poly(lactic acid) (PLA), and poly(lactic-co-glycolic acid) (PLGA) because of their low processing temperatures. However, traditional melt-based techniques require processing temperatures and pressures high enough to achieve continuous flow, limiting the type of polymer that can be printed. Solvent-cast printing (SCP) offers an alternative approach to print a wider range of polymers. Polymers are dissolved in a volatile solvent that evaporates during deposition to produce a solid polymer filament. SCP, therefore, requires optimizing polymer concentration in the ink, print pressure, and print speed to achieve desired print fidelity. Here, capillary flow analysis shows how print pressure affects the process-apparent viscosity of PCL, PLA, and PLGA inks. Ink viscosity is also measured using rheology, which is used to link a specific ink viscosity to a predicted set of print pressure and print speed for all three polymers. These results demonstrate how this approach can be used to accelerate optimization by significantly reducing the number of parameter combinations. This strategy can be applied to other polymers to expand the library of polymers printable with SCP.     

Gravure printing for thin film ceramics manufacturing from nanoparticles

Printing technologies can offer high potential for the thin film deposition of functional materials. Among the printing techniques, the gravure is considered one of the most promising, although to date it is still little employed, especially for the inorganic functional materials. In this work, the study of the gravure printing process for the metal oxides thin film production on flexible polymer substrate is reported. For this purpose, zinc oxide (ZnO) was chosen due to its versatile properties and nanosize effects, which make it suitable for many high technology areas. The gravure printing was made using low viscosity inks of ZnO nanoparticles. The characteristics of the printed thin films were examined and discussed. Thanks to the understanding of the physics underlying the film forming during the printing process combined to the knowledge on such specific material, uniform, compact, very transparent and smooth films were obtained in different nanometric thicknesses. Moreover, the possibility of fabricating ceramic nanocomposite films directly through this printing technique is also presented. Thanks to its scientific approach, this work makes available to the world of ceramics an industrial versatile and low-cost production technique which can allow to study and develop high-quality thin film ceramics with technologically interesting properties as well as nanoparticles behavior and their treatments in order to develop and use their fascinating nanosize properties.     

Polyvinyl chloride film local isometric heat treatment for hidden 3D printing on polymer packaging

A method of 3D embossed printing is proposed where both point and line images can be printed on rigid polyvinyl chloride (PVC) shrink films without any consumables, such as paints, primers, dampening solutions, or washes. Embossed lettering and symbols on packaging are intended for people with poor vision, but capable of tactile marking recognition and reading Braille. This 3D printing is based on reversible deformation and stress relaxation in anisotropic glassy polymers by local isometric heat treatment of thermoplastic films under pressure. Films can be protected from counterfeiting by hidden markings due to time separation of information recording onto the film and displaying this information for visual or tactile reading. The results quantify the rate of internal stress relaxation in PVC shrink films at various stages of 3D printing, including tactile sign formation conditions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43046.     

System Analysis of a DoD Print Head for Direct Writing of Conductive Circuits

The inkjet-printing principle is becoming more and more important for new applications besides conventional graphic printing. The target at our institute is to print conductive silver lines and areas of different widths and thicknesses. Based on a drop-on-demand (DoD) micro feeding system, a colloidal ink printer was developed to print conductive circuits. The printer has a stationary piezo-driven print head with a nozzle diameter of 100 μm. With such a nozzle, conductive paths with a width between 110 and 250 μm can be realized. A waveform generator is used to actuate the print head's piezo actuator. The most common control signal is a nearly rectangular voltage pulse. Shape, duration, and amplitude of the piezo control signal influence the stability of the printing process and thus the quality of the printed electrical structures significantly. Different rise and dwell times or pulse shapes can be considered to optimize the printing process. In this article, the piezo control signal's shape is analyzed, varied and the print head's system behavior is characterized. In a performance and signal analysis, the influence of the piezo input signal's shape on the transient behavior of the piezo output energy signal is identified. An optimized piezo control signal shall be achieved. In conclusion, a method is presented to measure droplet parameters such as radius, speed, and volume.     

Study of the lightfastness properties of prints on blister foils by spectral reflectance

This study describes the lightfastness properties of printed foil samples due to long-time exposure. Lightfastness is an important property for any kind of print products to assess their print stability. The fastness properties of prints can be described in terms of print durability and image stability. It may also be used for verification of printed expiry date and authenticity or validity of the product. Moreover, any kind of deterioration in package print quality will affect the product's sale adversely. Little work has been conducted to study the fastness properties of printed films and foils. In this work, blister foils printed in the gravure printing process have been taken as the sample as they have extensive usage in food and medicine packaging. An artificial lightfastness tester BGD 865/A Bench Xenon Test Chamber (B-SUN) is used to study the light fastness of Cyan, Magenta, Yellow, and Black inks on the foil. The spectral curves and colorimetric values are measured using an Ocean Optics Spectroradiometer (DH2000BAL) before and after exposure. A kinetic model is proposed to predict the fading rate of the printed foil. The optimal model has given excellent prediction with a correlation coefficient of 0.90 to 0.93 for Cyan, Magenta, Yellow, and Black prints, respectively. The largest color difference ΔE₀₀ is achieved for Yellow print followed by Magenta. Cyan and Black prints have shown small changes with time when the gravure prints are exposed to the artificial aging chamber.     

塑料用凹印防伪油墨的研制

塑料凹印防伪油墨在日光下不显印刷痕迹，但在紫外光照射下，即显示出闪光标志，而达到防伪目的。笔者介绍了所研制的塑料用凹印防伪油墨的工艺过程、技术指标及产品的主要特点