The Chemistry of Printing Inks and Their Electronics and Medical Applications E-Book

Johannes Karl Fink

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 378

Veröffentlichungsjahr: 2014

Beschreibung

This book focuses on the chemistry of inkjet printing inks, as well to special applications of these materials. As is well-documented, this issue has literallyexploded in the literature in particular in the patent literature. After an introductory section to the general aspects of the field, the types and uses of inkjet printing inks are summarized followed by an overview on the testing methods. Special compounds used as additives dyes, and pigments in inkjet printing inks are documented. The applications to the medical field - drug delivery systems, tissue engineering, bioprinting in particular - are detailed. The applications in the electronics industry are also documented such as flexible electronics, integrated circuits, liquid crystal displays, along a description of their special inks. The book incorporates many structures of the organic compounds used for inkjet printing inks as they may not be familiar to the polymer and organic chemists.

Leseprobe

Contents

Cover

Half Title page

Title page

Copyright page

Preface

Chapter 1: Inkjet Inks

1.1 History of Inkjet Printing

1.2 Image Forming Methods

1.3 Commercial Printing

1.4 Nozzle Design

1.5 Classification of Inks

1.6 Thermal Inkjet

1.7 Photographic Printing

1.8 Desirable Ink Properties

References

Chapter 2: Characterization of Printer Inks

2.1 Quantization of Droplets

2.2 Solubility Parameters

2.3 HLB Value

2.4 Evaluation of Water Resistance

2.5 Evaluation of Rubbing Resistance

2.6 Evaluation of Lightfastness

2.7 Evaluation of Waterfastness

2.8 Detection of the Thermal History

2.9 Security Aspects

2.10 Characterization of Pigment

References

Chapter 3: Additives for Inks

3.1 Print Density

3.2 Solvent Systems

3.3 Wetting Agents

3.4 Adhesion Improvers

3.5 Surfactants

3.6 Penetration Control

3.7 Controlled Encapsulation of Liquids

3.8 Fixing Additives

3.9 Humectants

3.10 Colorants

3.11 Primers

3.12 Antioxidants and UV Absorbers

3.13 Hindered Amine Light Stabilizers

3.14 Ozone Resistance

3.15 Chelating Agents

3.16 Corrosion Inhibitors

3.17 pH Control

3.18 Waterfastness

3.19 Monomers and Polymers

3.20 Initiators

3.21 Gloss Unevenness

3.22 Lightfastness

3.23 Prevention of Curling

3.24 Smearing

3.25 Smudge Resistance

3.26 Slipping Agents for Cured Inks

3.27 Scratch Resistance

3.28 Bronzing

3.29 Biocides

3.30 Dispersants

3.31 Aggregation and Color Bleeding

3.32 Other Additives

References

Chapter 4: Dyes and Pigments

4.1 Dyes

4.2 Pigment Particles

4.3 Metallic Pigments

References

Chapter 5: Ink Types

5.1 Oil-Based White Ink

5.2 Nonaqueous Ink Composition

5.3 Lightfast Inkjet Inks

5.4 Flame-Retardant Inkjet Inks

5.5 Fragrant Inkjet Ink

5.6 Radiation Curable Ink

5.7 Printing of Functional and Structural Materials

5.8 Coating Compositions for Paper

5.9 Photograph-like Gloss

5.10 Printing on Plastic Films

5.11 Printing on Glass and Metal

5.12 Printing on Ceramic Surfaces

5.13 Phase Change Inks

5.14 Compositions for Textile Use

5.15 Color Filter

5.16 Ingestible or Nutritional Liquid Ink Compositions

5.17 Etched Metal Plates

5.18 High Electrical Resistivity Inkjet Ink Composition

5.19 Curable Ink with Wax

5.20 Outdoor Applications

References

Chapter 6: Electronic Applications

6.1 Radio-Frequency Identification

6.2 Inkjet Printing of Conductive Materials

6.3 Selective Surface Modification

6.4 Printing on Integrated Circuits

6.5 Special Inks

6.6 Special Applications

References

Chapter 7: Medical Applications

7.1 Bioprinting

7.2 Tissue Engineering

7.3 Drug Delivery Systems

7.4 Polymeric Materials for Surface Modification

7.5 Nanomaterials

7.6 Other Fabrication Methods

References

Chapter 8: 3D Printing

8.1 Basic Principles

8.2 Uses and Applications

8.3 Rapid Prototyping

8.4 Medical Applications

References

Chapter 9: Special Aspects

9.1 Photographic Printing

9.2 Interaction between Ink and Printed Surface

9.3 Jetting-Out Performance

9.4 Microlens Arrays

9.5 Micro-Optical Devices

9.6 Nanostructured Surfaces

9.7 Electrohydrodynamic Jet Printing

9.8 Planographic Printing Plate

9.9 Environmental Aspects and Recycling

References

Index

Tradenames

Acronyms

Chemicals

General Index

The Chemistry of Printing Inks and Their Electronics and Medical Applications

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Library of Congress Cataloging-in-Publication Data:

ISBN 978-1-119-04130-6

Preface

This book focuses on the chemistry of inkjet printing inks, as well as special applications of these materials. As is well-documented, this issue has literally exploded in the literature, particularly in patent literature.

After an introductory section on the general aspects of the field, the types and uses of inkjet printing inks are summarized, followed by an overview of some testing methods. Then, special compounds used as additives in inkjet printing inks are documented. In passing, since it turns out that in the literature for inkjet printing inks a lot of special organic compounds are used which the ordinary organic and polymer chemist are not really familiar with the structures of these organic compounds are reproduced in a lot of the figures.

The text focuses on the literature of the past decade. Beyond education, this book will serve the needs of industry engineers and specialists who have only a passing knowledge of inkjet printing inks, but need to know more.

How to Use this Book

Utmost care has been taken to present reliable data. Because of the vast variety of material presented here, however, the text cannot be complete in all aspects, and it is recommended that the reader study the original literature for more complete information.

The reader should be aware that mostly US patents have been cited where available, but not the corresponding equivalent patents of other countries. In particular, in this field of science, most of the original patents are of Japanese origin.

For this reason, the author cannot assume responsibility for the completeness, validity or consequences of the use of the material presented here. Every attempt has been made to identify trademarks; however, there were some that the author was unable to locate.

Index

There are four indices: an index of tradenames, an index of acronyms, an index of chemicals, and a general index. In the index of chemicals, compounds that occur extensively, e.g., acetone, are not included at every occurrence, but rather when they appear in an important context. When a compound is found in a figure, the entry is marked in boldface letters in the chemical index.

Acknowledgements

I am indebted to our university librarians, Dr. Christian Hasenhüttl, Dr. Johann Delanoy, Franz Jurek, Margit Keshmiri, Dolores Knabl, Friedrich Scheer, Christian Slamenik, Renate Tschabuschnig, and Elisabeth Groß for their support in literature acquisition. In addition, many thanks to the head of my department, Professor Wolfgang Kern, for his interest and permission to prepare this text.

I also want to express my gratitude to all the scientists who have carefully published their results concerning the topics dealt with herein. This book could not have been otherwise compiled.

Last, but not least, I want to thank the publisher, Martin Scrivener, for his abiding interest and help in the preparation of the text. In addition, my thanks go to Jean Markovic, who made the final copyedit with utmost care.

Johannes FinkLeoben, 20th August 2014

Chapter 1

Inkjet Inks

Inkjet recording has many advantages; for example, recording can be carried out at high speed, there is little noise, coloring is easy, high resolution can be achieved and recording on plain paper can be carried out (1).

As a result of these advantages, equipment and facilities employing this recording method have become remarkably widespread. Regarding the ink used in this recording method, an aqueous ink is the most commonly used in terms of safety and odor. In the inkjet recording method, images are formed by ejecting thousands of droplets of ink per second.

Inkjet inks are well known and are typically liquid compositions comprised of a carrier liquid, colorants such as dyes or pigments, and optional additives such as thickeners and preservatives to obtain the desired properties (2). Different types of colorants may be used for inks, for example, simple color pigments and water-soluble dyes. There are monographs on the chemistry of inkjet inks (3).

Further, the state of the art in high precision traditional printing methods as well as recently emerging techniques have been reviewed (4). Micro- and nanoprinting techniques have found a number of applications in electronics, biotechnology, and material synthesis or patterning.

1.1 History of Inkjet Printing

Concise comments on the history of inkjet printing have been given (5, 6). Actually, the idea of inkjet printing traces back to the 19th century. In 1878 Lord Rayleigh studied the breakup of droplets when a pressure wave was applied (7). However, it was only in 1960 that Richard G. Sweet fabricated printed equipment based on these previous discovered principles (8). In addition, it was found that the droplets could be charged when passing a nozzle connected with an electrode.

By mounting a drop generator on a movable carriage that can scan across the paper the horizontal positioning of the drops can be achieved. Such an embodiment was fabricated by the A.B. Dick Company as the world’s first inkjet printer (5).

The early products were known as continuous inkjet printers because they relied on a steady stream of droplets. Only a small fraction of these drops are needed for printing and the rest of the drops are deflected away from the paper into a gutter, where the ink is collected and possibly recirculated back to a reservoir.

The later developed thermal inkjet technology has the advantage of being able to position a drop on demand. Ink drops are not emitted continuously but only when needed for printing. This property eliminates the need for additional systems to capture and recirculate the wasted ink (5).

Early patents on modern printing technology were awarded in the 1980th (9,10), and patents are still being awarded today (11). The leading companies in this technology were and still are Canon and Hewlett-Packard (12–14). Concomitantly, literature dealing with compositions for printing inks also appeared (15–18).

In 1990, a piezoelectric inkjet printing principle was introduced by Epson (5,6,19). However, earlier patents with regard to piezoelectric elements can be found (20):

An ink jet print head for projecting droplets of ink on demand includes a pressurization chamber including at least one wall defining a vibratory plate. A nozzle is open to the pressurization chamber and defines a fluid passage through which ink is ejected. A piezoelectric element is operatively coupled to the vibratory plate which is selectively energized to vibrate the wall thereby changing the volume of the pressurization chamber to eject ink through the nozzle. A vibratory system is defined by the piezoelectric element and the vibratory plate.

Actually, until now, there is a remarkably large and still growing number of patents in the field of printers and printing inks.

1.2 Image Forming Methods

Various methods are known for forming an image on a recording medium such as paper based on an image data signal (21):

Electrophotographic methods,

Sublimation-type thermal transfer methods,

Melt-type thermal transfer method, and

Inkjet recording methods.

The electrophotographic method requires a process of forming an electrostatic latent image on a photoreceptor drum by charging and light exposure. Therefore, the system becomes complicated, resulting in increased costs of production (21).

The thermal transfer method can be conducted by an inexpensive apparatus, but requires the use of ink ribbons, which causes an increase in running costs and the generation of waste.

In the inkjet recording method, an image is directly formed by ejecting ink only to the regions of a support, e.g., paper, which should become the regions of the image. Therefore the ink is used efficiently, which results in reduced costs. Moreover, inkjet recording apparatuses are not noisy (21).

1.3 Commercial Printing

The inkjet technique is applied to both office printers and household printers. Furthermore it is increasingly being applied in the field of commercial printing (22).

In the commercial printing field, printed sheets are required to have an appearance similar to that of printed sheets obtained by using general printing paper, rather than paper that has a surface that completely blocks penetration of ink solvent into the base paper, e.g., a photograph.

However, when a solvent absorption layer of a recording medium has a thickness of 20–30 μm the surface gloss, texture and stiffness are limited.

Therefore, the application of inkjet techniques to commercial printing has been limited to posters and forms for which the restrictions on surface gloss, texture, and stiffness are tolerable.

1.4 Nozzle Design

The stability of liquid jets and the influence of nozzle design have been assessed (23). A major task of a nozzle is the efficient conversion of potential energy to kinetic energy. This is best achieved by a sudden, smooth contraction of the flow area from the supply line to the desired nozzle diameter.

The best angle of convergence seems to be uncertain. The aspect ratio of the nozzle is highly dependent on the initial jet velocity profile and the subsequent jet surface shape. Rounding and polishing of the internal surfaces of the nozzle seem to be of importance for optimal performance (23).

1.5 Classification of Inks

The inks used in the various inkjet printers can be classified as either dye-based or pigment-based (24). A dye is a colorant which is dissolved or dispersed in the carrier medium. A pigment is a colorant that is insoluble in the carrier medium, but is dispersed or suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents.

1.6 Thermal Inkjet

Thermal inkjet printheads produce ink droplets from the thermal vaporization of the ink solvent (25). In the inkjet process, a resistor is rapidly heated to produce a vapor bubble, which subsequently ejects a droplet from the orifice.

This process is extremely efficient and reproducible. Modern thermal inkjet printheads for industrial graphics applications are capable of generating uniform drops of 4 p l or smaller in volume at frequencies of 36 k Hz or greater. Typical commercial thermal inkjet devices are specifically designed to vaporize water or solvents that have physical properties close to those of water, i.e., high boiling point, large heat capacity, and low molecular weight.

Nearly all of the commercial inks available for thermal inkjet systems are water-based, so they contain more than 50% water. Such aqueous inks have one or more drawbacks such as long ink dry times or poor adhesion to semiporous or nonporous substrates.

Inks with attractive performance characteristics, such as short dry times, long decap times and good adhesion when using a thermal inkjet system, have been developed (25).

These compositions contain volatile organic solvents, humectants, binder resins, and dyes. The solvents are low molecular alcohols, e.g., ethanol or methanol, and ketones, e.g., methyl ethyl ketone.

A thermal inkjet ink composition has one or more attractive features, such as short unassisted dry times of printed alphanumeric or graphic images, long decap times, good adhesion to semiporous and nonporous substrates, and safety or material compatibility with one or more components of a thermal inkjet printer (25). The decap time is the time that printer nozzles can be uncovered and idle before they will become ineffective and need to be cleaned.

1.7 Photographic Printing

The recording media used in photographic printing are (26):

Glossy plain paper obtained by laminating an ink receiving layer and then a glossy layer on base paper as a substrate,

A photo-like paper obtained by laminating a recording layer laminated with an ink receiving layer and a glossy layer,

A recording layer serving as a glossy layer ink receiving layer on a resin film or resin-coated paper as a substrate.

As the demand for a recording medium having high gloss and high-quality texture has increased in recent years, photo-like paper using a substrate having enhanced smoothness has become mainstream.

A glossy layer is normally formed by coating an aqueous dispersion solution containing inorganic microparticles such as colloidal silica or alumina sol, and a hydrophilic resin serving as a binder of the inorganic microparticles onto a substrate to impart the recording layer with a function of a void forming agent capable of penetrating and absorbing an ink, and photo-like gloss. As hydrophilic resin, poly(vinyl alcohol) is mainly used.

In a glossy plain paper, moisture in the ink is rapidly absorbed in base paper as a substrate through the glossy layer and then the ink receiving layer. Accordingly, water resistance is not significantly important, because there is no likelihood that the glossy layer may hold the moisture for a long time.

On the other hand, in a photo-like paper, the substrate does not have water absorbability, and the amount of ink per unit area is increased, if multicolor printing is performed to obtain a fine image. As a result, the glossy layer may contain a large amount of moisture immediately after printing. Thus, high water resistance is required for the recording layer.

A poly(vinyl alcohol)-based resin becomes tacky by absorbing moisture. Accordingly, in such a case the recording media are likely to adhere to each other (26).

The tack can be measured by the Instron Peel Strength Test or the Tel-Tak test (27–29). Using a poly (vinyl alcohol) with an 1,2-diol as side chain with a specified saponification degree yields a coating solution with less gelation (26).

It is believed that the stability is obtained by a phenomenon in which the crosslinking reaction is inhibited by a steric hindrance of the 1,2-diol unit on the poly(vinyl alcohol) side chain. Such poly (vinyl alcohol) can be synthesized by (26):

Saponifying a copolymer of a vinyl ester monomer,

Saponifying and decarboxylating a copolymer of a vinyl ester monomer and vinyl ethylene carbonate,

Saponifying and deketalizing a copolymer of vinyl ester monomer and 2,2-dialkyl-4-vinyl-1,3-dioxolane, or

Saponifying a copolymer of vinyl ester monomer and glycerol monoallylether.

The monomer reactivity ratios for monomer pairs of interest are shown in Table 1.1.

Table 1.1 Monomer reactivity ratios.

From Table 1.1, it can be seen that the pair vinyl acetate 3,4-diacetoxy-1-butene is superior.

A boron compound is added as a crosslinking agent. Examples of the boron compound that can be used are boric acids and borates. The kind of boric acid is not specifically limited, but orthoboric acid, metaboric acid, and paraboric acid may be used. Examples of borates are sodium salts, potassium salts, and ammonium salts (26).

1.8 Desirable Ink Properties

The drop velocity, separation length of the droplets, drop size and stream stability are greatly affected by the surface tension and the viscosity of the ink (2). Inkjet inks typically have a surface tension in the range of about 20–70 dyn cm−1 at 25°C. The viscosity can be as high as 30 cP at 25°C, but is typically somewhat lower. The ink has physical properties which must be adjusted to the ejecting conditions and printhead design.

The inks should have excellent storage stability for long periods so as not to clog to a significant extent in an Inkjet apparatus. Further, the ink should not corrode parts of the inkjet printing device it comes in contact with, and it should be essentially odorless and nontoxic.

Tradenames appearing in the references are shown in Table 1.2.

Table 1.2 Tradenames in references.

Tradename Description

Supplier

Aerosol® (Series)

Cytec

Sulfosuccinates (2)

Cognis Versamid® 756

Cognis GmbH

Polyamide resin (25)

Dispersybyk

TM

BYK-Chemie, USA

Polymeric surfactant (25)

Dowanol® DPM

Dow Chemical Comp.

Di(propyleneglycol) methyl ether (24)

Efka® 4340

Ciba Specialty Chemicals Inc.

AB-diblock acrylate copolymeric dispersing agent (25)

Mowital® (Series)

Kuraray Co., Ltd.

Poly(vinyl butyral) (25)

Neodol® (Series)

Shell

Alkyl alkoxylated surfactants (2)

NOBEL

TM

(Series)

Nobel Enterprises

cellulose nitrate resin (25)

Pioloform® (Series)

Wacker Chemie AG

Poly(vinyl butyral) resins (25)

Proxel®

Zeneca

Biocides (24)

Silwet®

O Si Specialities, Inc.

Organo silicone surfactants (2)

Solsperse® (Series)

Lubrizol Limited Corp.

Dispersant (25)

Staybelite

TM

Ester 10

Chem Central Corp

Wood rosin ester (25)

Surfynol® (Series)

Air Products

Ethoxylated acetylene diols (2)

Tergitol® (Series)

Union Carbide Corp.

Ethoxylated C11-15-secondary alcohols, surfactant (2)

Unirez® (Series)

Arizona Chemical

polyesteramide resins (25)

Zonyl® (Series)

DuPont

Fluorinated nonionic surfactants (2)

References

1. N. Wachi, Ink composition for ink jet recording and ink jet recording method using the same, US Patent 8613510, assigned to Fujifilm Corporation (Tokyo, JP), December 24, 2013.

2. P. Frese, R.D. Bauer, M. Egen, K. Taennert, M. Wulf, and R. Zentel, Ink jet ink composition, US Patent 7122078, assigned to E. I. Du Pont de Nemours and Company (Wilmington, DE), October 17, 2006.

3. S. Magdassi, ed., The Chemistry of Inkjet Inks, World Scientific Pub. Co, Singapore Hackensack, N.J, 2010.

4. C. Ru, J. Luo, S. Xie, and Y. Sun, Journal of Micromechanics and Micro-engineering, Vol. 24, p. 053001, 2014.

5. T. A. Cleland, Printed Electronics: The Next Inkjet Revolution. Ph.D thesis, Massachusetts Institute of Technology, Cleveveland (OH), 2003.

6. A. Bourne, A history of printing innovation, Internet, 2014.

7. B. Vogt, Stability Issues and Test Methods for Ink Jet Materials. Ph.D thesis, University of Applied Science, Cologne, DE, 2001, Section 3.2.1.

8. R.G. Sweet, Review of Scientific Instruments, Vol. 36, p. 131, 1965.

9. K.A. Neel, Method and apparatus for printing composite designs on fabric, US Patent 4423676, assigned to Cannon Mills Company (Kannapolis, NC), January 3, 1984.

10. K. Terasawa, Nozzle-restoring suction device for ink jet printer, US Patent 4506277, assigned to Canon Kabushiki Kaisha (Tokyo, JP), March 19, 1985.

11. Y. Fujimoto and M. Akahira, Printing apparatus and printing method, US Patent 7472977, assigned to Cannon Kabushiki Kaisha (Tokyo, JP), January 6, 2009.

12. R.N. Low, F.L. Cloutier, and G. Siewell, Ink reservoir with essentially constant negative back pressure, US Patent 4509062, assigned to Hewlett-Packard Company (Palo Alto, CA), April 2, 1985.

13. J.P. Baker, D.T. La, and R.A. Coverstone, Thermal ink jet pen body construction having improved ink storage and feed capability, US Patent 4771295, assigned to Hewlett-Packard Company (Palo Alto, CA), September 13, 1988.

14. J.-F. Plante, Printing, US Patent 8727496, assigned to Hewlett-Packard Development Company, L.P. (Houston, TX), May 20, 2014.

15. M. Sugiyama, A. Ogawa, and S. Imai, Aqueous ink composition, US Patent 4388115, assigned to Fuji Photo Film Co., Ltd. (Kanagawa, JP), June 14, 1983.

16. I. Tabayashi, H. Soma, and H. Fukutomi, Ink for use in ink-jet printer, US Patent 4409040, assigned to Dainippon Ink and Chemicals Inc. (Tokyo, JP), October 11, 1983.

17. S. Miyamoto and T. Yamasaki, Ink-jet recording medium, US Patent 4613525, assigned to Mitsubishi Paper Mills Ltd. (Tokyo, JP), September 23, 1986.

18. G.C. Causley and M.J. Peterson, Ink jet printer ink composition and process for producing same, US Patent 4818285, assigned to Tektronix, Inc. (Beaverton, OR), April 4, 1989.

19. S. Miyashita, M. Shinozuka, K. Sumi, M. Murai, and T. Takahashi, Piezoelectric thin film, method for producing the same, and ink jet recording head using the thin film, US Patent 6140746, assigned to Seiko Epson Corporation (Shinjuku-Ku, JP), October 31, 2000.

20. H. Koto, Ink jet print head, US Patent 4443807, assigned to Epson Corporation (Nagano, JP) Kabushiki Kaisha Suwa Seikosha (Tokyo, JP), April 17, 1984.

21. I. Nakamura and Y. Hayata, Ink composition, ink jet recording method, method for producing planographic printing plate, and planographic printing plate, US Patent 8128746, assigned to Fujifilm Corporation (Tokyo, JP), March 6, 2012.

22. K. Tojo, Y. Ooishi, K. Mochizuki, and K. Irita, Ink composition for ink-jet recording, and ink-jet recording method, US Patent 8450394, assigned to Fujifilm Corporation (Tokyo, JP), May 28, 2013.

23. M. McCarthy and N. Molloy, The Chemical Engineering Journal, Vol. 7, p. 1, 1974.

24. J.-S. Wang and H. Chen, Ink jet ink composition, US Patent 6713530, assigned to Eastman Kodak Company (Rochester, NY), March 30, 2004.

25. C. Robertson, A. Selmeczy, and J.P. Folkers, Thermal ink jet ink composition, US Patent 8 414 695, assigned to Videojet Technologies Inc. (, April 9, 2013.

26. K. Takahashi and M. Shibutani, Aqueous composition for recording medium, and ink-jet recording medium using the same, US Patent 8 314175, assigned to The Nippon Synthetic Chemical (Osaka, JP), November 20, 2012.

27. J. Tang, S. Cai, B. Katkade, W.c. Schumacher, and K.j. Miller, Transdermal drug delivery device, US Patent Application 20 140 083 878, assigned to Mylan Inc., Morgantown (WV), March 27, 2014.

28. Touch and close fasteners. determination of peel strength, DIN EN 12242:1999, Deutsches Institut für Normung, Berlin, 1999.

29. Standard test methods for rubber-viscosity, stress relaxation, and pre-vulcanization characteristics, ASTM Standard ASTM D1646-07, ASTM International, West Conshohocken, PA, 2012.

Chapter 2

Characterization of Printer Inks

Stability issues and test methods for ink jet materials have been investigated (1). Inkjet prints have been tested under various conditions to show their complex fading behavior and to illustrate the difficulties in providing reliable tests.

In conventional photography, there are a number of standardized accelerated aging tests to compare and predict life expectancy of both the image and the support. The ISO Standard 10977, now ISO 18909:2006 (2), deals with measuring the image stability of color photographic materials and is divided into a dark-stability test and a light-stability test.

2.1 Quantization of Droplets

A liquid jet is naturally unstable and will breakup into droplets (3). The mode of disintegration is strongly related to the jet geometry and to the difference of the velocity Δv of the liquid vl and the surrounding gas vg:

(2.1)

In a large number of applications, the ability to accurately and repeatedly deposit nanogram quantities of a given substance is critical (4). This is largely driven by the usage of micro- and nanoscale products that require extremely accurate processing steps. Many applications require repeatable deposition of nl or pl quantities of solutions to precise locations on a target.

This is particularly true in the manufacturing of many medical devices, where the amount and location of drug loading must be controlled to very precise specifications. In such cases, drop-on-demand inkjet technology is an attractive choice, as it addresses the needs for both accurate targeting and repeatable droplet ejection.