Fundamentals of Inkjet Printing

The Science of Inkjet and Droplets

Stephen D. Hoath

• Publisher: Wiley-VCH
• Year: 2015
• Print ISBN:
  9783527337859
• Edition: 1
• eBook ISBN:
  9783527684830
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

From droplet formation to final applications, this practical book presents the subject in a comprehensive and clear form, using only content derived from the latest published results.

Starting at the very beginning, the topic of fluid mechanics is explained, allowing for a suitable regime for printing inks to subsequently be selected. There then follows a discussion on different print-head types and how to form droplets, covering the behavior of droplets in flight and upon impact with the substrate, as well as the droplet's wetting and drying behavior at the substrate. Commonly observed effects, such as the coffee ring effect, are included as well as printing in the third dimension. The book concludes with a look at what the future holds. As a unique feature, worked examples both at the practical and simulation level, as well as case studies are included.

As a result, students and engineers in R&D will come to fully understand the complete process of inkjet printing.

Chapter 1
Introductory Remarks

Ian M. Hutchings, Graham D. Martin and Stephen D. Hoath

1.1 Introduction

From newspapers to food packaging, from magazines to junk mail and roadside advertising, we live in a world of printed materials. The process of printing involves the reproduction of a pattern on a substrate, usually in order to represent text or images or, in many cases, both. Conventional printing methods, including, for example, lithography, flexography, gravure, and screen printing, have evolved over several centuries and can now achieve remarkable levels of quality at very low cost. All these processes share a common feature: the pattern to be printed is embodied in a physical form such as on a roll, plate, or screen and transferred from this template during the act of printing through direct or indirect contact with the substrate. The pattern of ink that forms the printed text or image on the substrate thus originates in a pattern that is defined before the printing machine starts to run. Changes to the printed product can be achieved only by changing the master pattern, which involves making physical changes to the template within the printing machine.

Inkjet printing, in contrast, employs a fundamentally different principle. Rather than the printed pattern being created by transfer of ink from a pre-existing master pattern, it is progressively built up directly on to the substrate by the deposition of a large number of individual, tiny drops of ink. Each small droplet, typically 10–100 µm in diameter, is created and deposited under digital control, so that each pattern printed in a sequence by the same machine can just as readily be different from all the others as it can be the same.

Today's printing industry represents a major area of economic activity, currently accounting for some US $900 billion per annum globally and likely to exceed US $1000 billion by 2020. Over the past 20 years, a small but increasing fraction of this activity has been based on inkjet technology, and this proportion is forecast to grow significantly. There are several reasons for this. Because the patterns to be printed by inkjet are defined digitally and thus represented by digital data files and never as physical master templates, they can very easily be changed, and the setup costs and times for inkjet printing are, therefore, low. As a digital printing process, inkjet is thus ideally suited for short print runs for which profit margins can be high, and as the process has increased in reliability and robustness, the run lengths at which inkjet competes with more conventional processes in terms of cost have also increased. High resolution and image quality, once the sole preserve of conventional printing, can be more readily attained by inkjet methods. Inkjet printing is very well established for printing variable information such as use-by dates and batch codes on to products in a manufacturing environment, and as inkjet print quality increases, more opportunities become available for printing bespoke, personalized products. Table 1.1 summarizes the very wide range of applications in which printing is used and shows how inkjet technology is progressively encroaching into major areas. Already ubiquitous in the small office and home environment, inkjet printing is likely to take an increasingly important share of the commercial printing market soon and to become more widely used for decorative products, packaging, general industrial applications, and textile printing as well [1].

Table 1.1 Range of applications for which printing is currently used, showing market penetration of inkjet-based processes

	Small office and home	Commercial print	Decorative products	Packaging	General industrial	Textiles
Already widely used	Home printers, local office printers/copiers	Billing and ticketing, graphic displays, point-of-purchase	Signage, banners, stickers, ceramic tiles		Coding and marking	T-shirts
Starting to be used		Books, brochures, flyers, newspapers, magazines	Wallpaper	Labels: self-adhesive, shrink, and so on	Displays, dashboards, plastic cards, 3D printing	“Designer” fabrics, ties, scarves
Medium-term target			Flooring, décor (e.g., melamine)	Corrugated board, cartons, cans, glass bottles	Printed circuit boards, electronic devices	Soft furnishings, other clothing
Not a current target		Banknotes, security printing		Flexible packaging, molded tubs, bottles	Toys, other durables	Carpets, rugs

The principles of inkjet printing were first developed commercially during the 1970s and 1980s and first applied practically to marking products with dates and codes and addressing mail. As indicated in Figure 1.1, the technology used for these purposes, which demand high operating speeds but can tolerate quite low resolution in the printed text, is now fully mature. These printers, which use “continuous inkjet” (CIJ) technology, are widely used as standard equipment in factories worldwide. The next development, from the 1990s onward, involved “drop-on-demand” (DOD) printing, which is capable of achieving much higher resolution than these early coders and achieving digital reproduction of text and images at low cost in the domestic and small office environment. More recently, applications of inkjet printing in the commercial world, and for other uses listed in Table 1.1, have been developing rapidly, and these applications also predominantly use the DOD technology. The principles by which small drops of ink are formed and manipula...

Table of contents

• Cover
• Title Page
• Copyright
• Table of Contents
• List of Contributors
• Preface
• Chapter 1: Introductory Remarks
• Chapter 2: Fluid Mechanics for Inkjet Printing
• Chapter 3: Inkjet Printheads
• Chapter 4: Drop Formation in Inkjet Printing
• Chapter 5: Polymers in Inkjet Printing
• Chapter 6: Colloid Particles in Ink Formulations
• Chapter 7: Jetting Simulations
• Chapter 8: Drops on Substrates
• Chapter 9: Coalescence and Line Formation
• Chapter 10: Droplets Drying on Surfaces
• Chapter 11: Simulation of Drops on Surfaces
• Chapter 12: Visualization and Measurement
• Chapter 13: Inkjet Fluid Characterization
• Chapter 14: Surface Characterization
• Chapter 15: Applications in Inkjet Printing
• Chapter 16: Inkjet Technology: What Next?
• Index
• End User License Agreement