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Functional Inks: Formulation, Characterization and Printing Techniques

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced Composites".

Deadline for manuscript submissions: closed (10 March 2023) | Viewed by 11203

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Dr. Francisco Galindo Rosales

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Department of Chemical Engineering, Transport Phenomena Research Center (CEFT), Faculty of Engineering of the University of Porto, Rua Dr. Roberto Frias s/n, CP 4200-465 Porto, Portugal
Interests: complex fluids; rheology; printing techniques
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Dear Colleagues,

Printed electronics are being used nowadays in many commercial applications, such as photovoltaic solar bus bars, glucose test strips, force sensors, touch screen electrodes, membrane circuits, and heating elements. These devices have been dominated by metal and metal-oxide-semiconductors, which present difficulties regarding the design of transparent and flexible electronics, heat management, and rapid device customization. Because of their unique structural features and outstanding properties, i.e., electronic properties combined with enormous mechanical flexibility and optical transparency, 2D nanomaterials have become a key class of materials in the development of the next generation of functional inks for printed electronics. Very recently, new water-based and high-concentration inks formulated with 2D materials, including conductors, semiconductors, and insulators, have been reported in the literature. As their morphology differs from the usually applied particles, their behaviour in suspensions also differs, thus affecting the printability, which is a crucial parameter to be understood in order to scale-up for industrialization. Their current limitation comes from the use of solvents to formulate stable dispersions with adequate fluidic properties. The current situation is paradoxical—the rheological properties are improved by adding chemicals that are to the detriment of the electro/mechanic/optical properties required by printed electronics. Thus, the right combination of formulation for the inks, the rheological behaviour, and the selected printing technique is of paramount importance in order to ensure printability and functionality.

This Special Issue is expected to gather contributions that describe the recent results on the formulation, rheological characterization, and printing techniques of functional inks that can provide any kind of improvement towards the printability and final properties of printed electronics.

Dr. Francisco José Galindo-Rosales
Guest Editor

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Keywords

functional inks
formulation
rheology
printing techniques

Published Papers (6 papers)

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Research

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16 pages, 2969 KiB

Open AccessArticle

Understanding the Role of Paper-Ink Interactions on the Lightfastness of Thermochromic Prints

by Rahela Kulčar, Marina Vukoje, Katarina Itrić Ivanda, Tomislav Cigula and Sonja Jamnicki Hanzer

Materials 2023, 16(8), 3225; https://doi.org/10.3390/ma16083225 - 19 Apr 2023

Viewed by 1436

Abstract

Thermochromic inks (TC) have received increasing attention in recent years, particularly in the design and packaging industries. Their stability and durability are crucial for their application. This study highlights the detrimental effects of UV radiation on the lightfastness and reversibility of thermochromic prints. Three commercially available TC inks with different activation temperatures and in different shades were printed on two different substrates, cellulose and polypropylene-based paper. Used inks were vegetable oil-based, mineral oil-based and UV-curable. The degradation of the TC prints was monitored using FTIR and fluorescence spectroscopy. Colorimetric properties were measured before and after exposure to UV radiation. The substrate with a phorus structure exhibited better colour stability, suggesting that the chemical composition and surface properties of the substrate play a crucial role in the overall stability of thermochromic prints. This can be explained by the ink penetration into the printing substrate. The penetration of the ink into the structure (cellulose fibres) protects the ink pigments from the negative effect of the UV radiation. Obtained results suggest that although the initial substrate may appear suitable for printing, its performance after ageing may not be optimal. In addition, the UV curable prints show better light stability than those made of mineral- and vegetable-based inks. In the field of printing technology, understanding the interplay between different printing substrates and inks is critical to achieve high-quality, long-lasting prints. Full article

(This article belongs to the Special Issue Functional Inks: Formulation, Characterization and Printing Techniques)

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13 pages, 4449 KiB

Open AccessArticle

Enhancing Applicability of Reversible UV Thermochromic Offset Inks: Edge Quality Parameters and Thermochromic Printing System Modulation Transfer Function

by Zrinka Jakopčević, Katarina Itrić Ivanda, Rahela Kulčar, Suzana Pasanec Preprotić and Marina Vukoje

Materials 2023, 16(8), 3125; https://doi.org/10.3390/ma16083125 - 15 Apr 2023

Viewed by 1224

Abstract

Modern logo design is characterized by its ability to convey information through the use of various images and text compositions. These designs often use simple elements such as lines to capture the essence of a product. When using thermochromic inks in logo design, it is important to consider their composition and behavior, as they differ significantly from conventional printing inks. This study aimed to determine the resolution capabilities of the dry offset printing technique when using thermochromic ink, with the ultimate goal of optimizing the thermochromic ink printing process. Horizontal and vertical lines were printed using both thermochromic and conventional inks to compare the edge reproduction characteristics of the two ink types. Moreover, the impact of the type of applied ink on the share of mechanical dot gain of the print was investigated. Additionally, modulation transfer function (MTF) reproduction curves were generated for each print. Moreover, scanning electron microscopy (SEM) was conducted to investigate the surface of the substrate and prints. It was found that the quality of the printed edge produced by thermochromic inks can rival that of conventional inks. Thermochromic edges showed lower raggedness and blurriness values for horizontal lines, whereas line orientation proved to be insignificant in the case of vertical lines. MTF reproduction curves confirmed higher spatial resolution for vertical lines in the case of conventional inks, whereas they were identical for horizontal lines. The share of mechanical dot gain is not highly influenced by the ink type. SEM micrographs confirmed that the conventional ink smooths out the micro-roughness of the substrate. However, on the surface, the microcapsules of thermochromic ink (measuring 0.5–2 µm) are observable. Full article

(This article belongs to the Special Issue Functional Inks: Formulation, Characterization and Printing Techniques)

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10 pages, 2898 KiB

Open AccessArticle

The Influence of the Matrix Selection and the Unification Process on the Key Parameters of the Conductive Graphene Layers on a Flexible Substrate

by Sandra Lepak-Kuc, Łukasz Nowicki, Daniel Janczak and Małgorzata Jakubowska

Materials 2023, 16(3), 1238; https://doi.org/10.3390/ma16031238 - 31 Jan 2023

Cited by 2 | Viewed by 1088

Abstract

Screen-printed graphene layers on flexible substrates are one of the most advanced printed electronics developments of recent years. Obtaining thin, flexible, highly conductive components, whose applications are increasingly directed towards biomedical engineering and even medicine, requires an in-depth understanding of the correct choice of materials and procedures. Our work was aimed at investigating the influence of homogenisation in the triple rolling process over pastes dedicated to the screen printing technology, on their rheological parameters and the properties of the prints. The effect of selecting a suitable polymer matrix and different packing of graphene flakes was evaluated. Several studies were carried out, which can provide an excellent knowledge base in the context of graphene screen-printing pastes. Paste rheology, printability, path thickness, sheet resistance and adhesion to the substrate were investigated. Selected layers were also subjected to SEM imaging. Full article

(This article belongs to the Special Issue Functional Inks: Formulation, Characterization and Printing Techniques)

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20 pages, 4971 KiB

Open AccessArticle

Mapping the Volume Transfer of Graphene-Based Inks with the Gravure Printing Process: Influence of Rheology and Printing Parameters

by Ahmad Fakhari, Célio Fernandes and Francisco José Galindo-Rosales

Materials 2022, 15(7), 2580; https://doi.org/10.3390/ma15072580 - 31 Mar 2022

Cited by 9 | Viewed by 1850

Abstract

It is a common practice to add rheology modifiers to functional inks, such as graphene inks, to optimize the rheological properties so that they can be printed with a certain printing technique. This practice may lead to inks formulations with poorer electrical, optical, and mechanical performance upon its application, which are of paramount importance in printed electronics. In this study, we demonstrate for three different commercial graphene-based inks that it is possible to control the amount of ink transferred to the flat surface by tweaking printing parameters, such as the velocity and the length scale of the gravure cell, without modifying the rheology of the ink. Finally, the results are summarized in printing maps based on dimensionless numbers, namely, the capillary and Reynolds numbers. Full article

(This article belongs to the Special Issue Functional Inks: Formulation, Characterization and Printing Techniques)

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14 pages, 2344 KiB

Open AccessArticle

Rheologically Assisted Design of Conductive Adhesives for Stencil Printing on PCB

by Ângelo D. M. Silva, Mariana M. Silva, Hugo Figueiredo, Isabel Delgado, Paulo E. Lopes, Maria C. Paiva and Loic Hilliou

Materials 2021, 14(24), 7734; https://doi.org/10.3390/ma14247734 - 15 Dec 2021

Cited by 5 | Viewed by 2185

Abstract

Driven by the need to deliver new, lead-free, eco-friendly solder pastes for soldering electronic components to Printed Circuit Boards (PCB), electrically conductive adhesives (ECAs) based on epoxy, carbon nanotubes (CNT), and exfoliated graphite (EG) were designed. The rheology of the adhesives prepared is paramount for the success of the deposition process, which is based on stencil printing. Thus, a rheological analysis of the process was first performed. Then, an experimental protocol was defined to assess the relevant viscoelastic characteristics of the adhesives for stencil printing application. Different composite formulations of epoxy/CNT/EG were produced. Their rheological characteristics were established following the designed protocol and benchmarked with a commercial solder paste. The thermal and electrical properties of the composite formulations were also characterized. As a result, a new, electrically conductive adhesive was delivered with potential to be an eco-friendly alternative to the solder paste currently used in stencil printing of PCB. Full article

(This article belongs to the Special Issue Functional Inks: Formulation, Characterization and Printing Techniques)

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Review

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39 pages, 7778 KiB

Open AccessReview

Functional Materials for Fabrication of Carbon-Based Perovskite Solar Cells: Ink Formulation and Its Effect on Solar Cell Performance

by Dena Pourjafari, Nidia G. García-Peña, Wendy Y. Padrón-Hernández, Diecenia Peralta-Domínguez, Alejandra María Castro-Chong, Mahmoud Nabil, Roberto C. Avilés-Betanzos and Gerko Oskam

Materials 2023, 16(11), 3917; https://doi.org/10.3390/ma16113917 - 23 May 2023

Cited by 4 | Viewed by 2201

Abstract

Perovskite solar cells (PSCs) have rapidly developed into one of the most attractive photovoltaic technologies, exceeding power conversion efficiencies of 25% and as the most promising technology to complement silicon-based solar cells. Among different types of PSCs, carbon-based, hole-conductor-free PSCs (C-PSCs), in particular, are seen as a viable candidate for commercialization due to the high stability, ease of fabrication, and low cost. This review examines strategies to increase charge separation, extraction, and transport properties in C-PSCs to improve the power conversion efficiency. These strategies include the use of new or modified electron transport materials, hole transport layers, and carbon electrodes. Additionally, the working principles of various printing techniques for the fabrication of C-PSCs are presented, as well as the most remarkable results obtained from each technique for small-scale devices. Finally, the manufacture of perovskite solar modules using scalable deposition techniques is discussed. Full article

(This article belongs to the Special Issue Functional Inks: Formulation, Characterization and Printing Techniques)

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